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PRIMARY BATTERIES – NONAQUEOUS SYSTEMS | Lithium–Manganese Dioxide
Lithium–Manganese Dioxide K Nishio, Kyoto University, Kyoto, Japan & 2009 Elsevier B.V. All rights reserved.
Introduction Lithium primary batteries are currently one of the most widely used batteries, although they are newly developed battery systems compared to many other primary battery systems with aqueous electrolytes. Research and development of a cell using lithium as negative electrode started in the United States in the 1960s mainly for space applications, and later, development of batteries for consumer use became active also in Europe and Japan. An electrochemical cell using lithium and a nonaqueous electrolyte was a totally new system, and both a new positive electrode material with good discharge performance in a nonaqueous electrolyte and materials for the electrolyte had to be developed. Many new positive electrode materials such as metal oxides, metal sulfides, halogenide compounds, and organic compounds were developed and tested, and lithium cells using iodine complex, polycarbon monofluoride (CFn), and manganese dioxide were commercialized in the 1970s. The lithium–manganese dioxide (Li–MnO2) system was first commercialized in Japan as a coin-type and later it became available as cylindrical cells with a high power or a high energy density.
Principles of a Li–MnO2 Battery The following reaction mechanisms were proposed for a Li–MnO2 cell: Positive electrode reaction: MnðIVÞ O2 þ Liþ þ e -MnðIIIÞ O2 ðLiþ Þ Negative electrode reaction: Li-Liþ þ e Overall battery reaction: MnðIVÞ O2 þ Li-MnðIIIÞ O2 ðLiþ Þ
The reaction at the positive electrode is insertion of lithium into the crystal lattice of manganese dioxide, which accompanies reduction of Mn(IV) to Mn(III), and the reaction at the negative electrode is dissolution of lithium into the electrolyte solution. The X-ray diffraction patterns after discharge showed a peak shift to a lower angle, demonstrating an expansion of the crystal lattice. Another simple cell reaction for lithium and manganese dioxide was proposed as follows: 2Li þ 2MnO2 -Mn2 O3 þ Li2 O
This reaction, however, does not seem to take place, because neither Mn2O3 nor Li2O was found in the reaction products.
Materials Positive Electrode Manganese dioxide is a very common material in the battery field, which has been used for a long time as the positive electrode active material in zinc–carbon dry cells and alkaline manganese dioxide cells. It was also regarded as one of the most promising positive electrode materials for lithium cells, because it was a strong oxidant and less expensive than many other materials. It became clear, however, that manganese dioxide materials used in aqueous electrolyte batteries did not show good discharge performance in a nonaqueous electrolyte. The two major requirements for the manganese dioxide active material in Li–MnO2 cells are as follows: (i) it must be anhydrous; and (ii) it must have a structure suitable for the diffusion of Li þ ions into the manganese dioxide crystal lattice. Manganese dioxide is classified as natural manganese dioxide (NMD) and synthetic manganese dioxide the latter can be chemically prepared manganese dioxide (CMD) or electrolytic manganese dioxide (EMD) according to the preparation method. EMD after heat treatment is used as a positive electrode material in a commercial lithium battery. There have been many studies by many researchers on the discharge performances of manganese dioxide. In early works in Japan, relationships between heat treatment temperatures, crystal structures, chemical composition, and discharge characteristics were studied. Their findings of a manganese dioxide material with a desirable crystal structure for lithium diffusion became the basis for the first commercial Li–MnO2 battery in the late 1970s. Heat treatment has a significant influence on the crystal structure of EMD. It is basically understood as shown in Figure 1, although it should be noted that there have been some disputes about the crystal structure change. The crystal structure of as-prepared EMD is known as g-MnO2 and it consists of major ramsdellite domain with pyrolusite domain as impurity. Pure ramsdellite has one-dimensional 1 2 tunnels formed by chains of edge-sharing MnO6 octahedra. Crystal structures of EMD gradually change as the heat treatment
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Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
(a)
using lithium offer the possibility of a high voltage and a high energy density. In a real cell, lithium is mostly used as a foil having a thickness of several tens of micrometers and cut in a proper size. It is not difficult to cut and change the shape of lithium because it is a very soft and flexible metal. It is, however, necessary to pay special attention to the handling of lithium metal. Lithium readily reacts with water to form hydrogen gas. It even reacts with moisture in the atmosphere to form lithium hydroxide on its surface. Therefore, the presence of water should be avoided in all production processes. Electrolyte An electrolyte for a Li–MnO2 cell should possess the following properties:
(b)
(c)
Figure 1 The crystal structures of electrolytic MnO2 (EMD) heat treated at different temperatures (a) 250 1C, (b) 375 1C, and (c) 450 1C.
temperature increases. By heat treatment of EMD below 250 1C, the crystal structure remains as g-MnO2. By heat treatment from about 270 to 400 1C, g-b-MnO2, which has both 1 1 and 1 2 tunnels, is formed. When the heat treatment temperature is higher than 420 1C, bMnO2 (pyrolusite) with 1 1 tunnels is obtained. Among these materials, EMD heat treated from 370 to 400 1C, which exhibits both the highest discharge capacity and best storage characteristics, is used for the commercial Li–MnO2 batteries. Negative Electrode Lithium metal is used in a lithium primary cell. The electrode potential of lithium is 3.04 V versus standard hydrogen electrode (SHE), which is the lowest value among all metal electrodes. Lithium has the lowest density (0.53 g cm3) and the lowest electrochemical equivalent (0.259 g Ah1) of all solids. As a result of these physical properties, nonaqueous electrolyte batteries
(i) high ionic conductivity in a wide range of temperature; (ii) chemical and electrochemical stability for a long period; (iii) no harmful effects on the positive and negative electrode reactions. In a Li–MnO2 cell, polar aprotic solvents have to be used, as lithium metal reacts with protic solvents such as water and alcohols. The ionic conductivity of an organic electrolyte is generally 1–2 orders of magnitude lower than that of an aqueous electrolyte. Therefore, the composition of electrolytes for higher ionic conductivity is a major research target in nonaqueous systems. In order to dissolve sufficient amounts of solutes in an electrolyte solution, it is desirable that the organic solvent has a high dielectric constant. A high dielectric constant solvent, however, usually has a high viscosity, which is an undesirable property for a solvent. In practical Li–MnO2 cells, mixed solvents consisting of a highdielectric-constant–high-viscosity solvent and a low-dielectric-constant–low-viscosity solvent are usually employed. A typical mixed solvent is a mixture (50:50 or 70:30, v/v) of propylene carbonate (PC) and 1,2-dimethoxyethane (1,2DME). It is also important that the organic solvents and solutes do not contain water. It is essential for the good long-term discharge and storage performances of a cell that the electrolyte is stable under the strong oxidizing and reducing environment at the positive and negative electrodes, respectively. An organic solvent that has a low reduction potential and a high oxidation potential, that is, with a wide potential window, should be chosen. Separator The main functions of a separator in a cell are protection against short circuit caused by direct contact of the positive and negative electrodes and retention of
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electrolyte solution. A suitable separator should be used for each cell considering the characteristics of the battery. For a Li–MnO2 cell, the separator should have the following properties: (i) (ii) (iii) (iv)
low electric resistance in an electrolyte; retention of a large amount of electrolyte solution; chemical stability in an organic solvent; and durability against both oxidation by manganese dioxide and reduction by lithium.
Separators made from polyethylene or polypropylene, which can meet the above-mentioned requirements, are mainly used for lithium batteries. They are used in the form of a nonwoven cloth or a thin film with micropores, considering the property and cost requirement of each type of battery.
Some Studies on the Materials of Li–MnO2 Batteries As mentioned in the previous sections, performances of a Li–MnO2 cell are strongly dependent on the materials, especially electrodes and electrolyte materials. Some studies on Li–MnO2 cells are presented here for better understanding of this system, although the results are not directly connected with the materials used in currently available batteries. Positive Electrode It is essential that no water exists in the positive electrode materials, but EMD before heat treatment contains about 5% of water. Heat treatment at 750 1C is required to completely remove the water. By a heat treatment at 350– 450 1C, EMD still contains about 1–2% water, but it is believed that this water is strongly combined in the crystal and does not affect the storage characteristics of a battery. This presumption was supported by a storage test. A test cell using manganese dioxide heat treated at 375 1C showed more than 90% of its initial capacity after an 11-month storage at 60 1C. Commercialization of Li–MnO2 batteries started with low-power coin-type cells, but the cells soon came to be used in some applications with higher power consumptions. For high-rate as well as low-temperature uses, a large surface area is required for the manganese dioxide material. Figure 2 shows the influence of specific surface area of manganese dioxide on the operating voltage of the test cells at low-temperature pulse discharge. The operating voltage of test cells using manganese dioxide with a high specific surface area was higher than that of test cells using manganese dioxide with a low surface area.
Pulse discharge voltage at 10th cycle (V)
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
1.9
1.8
1.7
1.6
0 0
20
30
40
50
Specific surface area (m2 g−1)
Figure 2 The influence of specific surface area of electrolytic MnO2 on the operating voltage of the test cells at lowtemperature pulse discharge. Reproduced from Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417–456. Amsterdam: Elsevier.
Negative Electrode Lithium is known to form alloys with some metals and the properties of lithium metal are modified by the alloying process. For a secondary cell using metallic lithium as the negative electrode, lithium alloy has been extensively studied to improve the cycling capability. Also in a primary cell, the discharge performance of a lithium electrode is influenced by the addition of a small amount of aluminum. Figure 3 shows the capacity retention of test cells using Li–Al alloys in which the content of aluminum ranged from 0.05% to 2%. Lithium with 0.5–2% aluminum showed good storage characteristics. However, the operating voltage after storage became lower when aluminum content was high, as shown in Figure 4. It was considered that good storage performance was achieved with a proper amount of aluminum in lithium. Electrolytes Discharge characteristics of a Li–MnO2 cell are greatly influenced by the properties of the electrolyte. Figure 5 shows the relationship between discharge capacity and conductivity of electrolyte of test cells using some twocomponent solvent systems. The test cells were discharged at a high rate of 560 O. In this test, mixed solvents consisting of PC and some ethers were used. The conductivities of the electrolytes varied from 4.6 to 13.3 mS cm1. At a high-rate condition, the conductivity of the electrolyte had a strong influence on the discharge performance. The properties of an electrolyte solution are also dependent on the solutes. Table 1 shows the physical properties of organic electrolytes using lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium hexafluoroarsenide (LiAsF6) as
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Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide 100
Capacity retention (%)
80
60
40
20
0
0.01
0.05
0.1
0.5
1
2
Al content of Li−Al alloy (wt.%)
Discharge capacity (mA h)
Pulse discharge voltage at 1st cycle (V)
Figure 3 Capacity retention of test cells (CR15400 size) using Li and Li–Al alloys after a 40-day storage at 60 1C. Reproduced with permission from Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417–456. Amsterdam: Elsevier.
solutes. The solvent is a PC–DME mixture. Conductivities of these electrolytes are around 102 S cm1, which is about 2 orders of magnitude lower than that of aqueous electrolytes. Discharge curves of test cells at 25 and 20 1C are shown in Figure 6. The LiClO4/PC–DME electrolyte, which shows a high conductivity and low viscosity at both 25 and 20 1C, is one of the most typical electrolytes. Only the LiCF3SO3/PC–DME electrolyte has a high solubility of solute at 20 1C and shows excellent low-temperature characteristics. Therefore, LiCF3SO3 is widely used in commercial batteries in spite of its comparatively low conductivity. LiAsF6/PC–DME has good properties as an electrolyte, but it is not used in consumer batteries because of the toxicity of arsenic. Storage characteristics of Li–MnO2 test cells were studied using mixed solvents of PC and 1,2-DME and some solutes. After a 40-day storage at 60 1C, which corresponds to about a 2-year storage at room temperature, test cells using LiClO4, LiCF3SO3, and LiAsF6
2.2
2.0
1.8
PC−1, 2-DME
100
PC−EME
80 60
PC−1, 2-DEE
40
PC−DMM
20
PC−1, 1-DME
1.6 0 0
0.05
0.01
0.1
0.5
1
2
Al content of Li−Al alloy (wt.%)
Figure 4 Pulse discharge voltage of test cells (CR15400 size) using Li and Li–Al. : initial, J: after a 40-day storage at 60 1C. Reproduced with permission from Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417–456. Amsterdam: Elsevier.
Table 1
0
5 10 Specific conductivity (10−3 S cm−1)
15
Figure 5 High-rate discharge capacity versus conductivity of electrolyte solution. Solvent: mixture of diether and propylene carbonate (1:1 volume ratio); solute: 1 mol dm3 LiClO4. Discharge conditions: temperature ¼ 25 1C, and load ¼ 560 O. DME, dimethoxyethane; PC, proylene carbonate. Reproduced with permission from Nishio K, Yoshimura S, and Saito T (1995). Discharge characteristics of manganese dioxide/lithium cells in various electrolyte solutions. Journal of Power Sources 55: 115–117.
Physical properties of some organic electrolytes 20 1C
25 1C
LiClO4 LiCF3SO3 LiBF4 LiPF6 LiAsF6
PC−DEM
Specific conductivity (mS cm1)
Viscosity (mPa s)
Specific conductivity (mS cm1)
Viscosity (mPa s)
Solubility (mol dm3)
12.3 5.9 8.2 17.0 16.3
1.3 1.2 1.0 1.6 1.3
7.1 3.5 5.2 7.6 7.3
3.2 2.4 2.0 3.1 2.7
1.2 46.0 2.4 1.2 1.0
Source: Reproduced with permission from Takahashi M, Yoshimura S, Nakane I, et al. (1993) A study on electrolytes for manganese dioxide–lithium cells. Journal of Power Sources 43–44: 253–258.
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide Negative electrode can
4
87
Negative electrode (Li)
Cell voltage (V)
Separator 3
LiAsF6 LiPF6 LiClO4 LiCF3SO3 LiBF4
2 1
Gasket
Positive electrode (MnO2) Positive electrode can
0
0
30
(a)
60
90
120
150
Discharge capacity (mAh)
Figure 7 Structure of a coin-type cell. Courtesy of Sanyo Electric Co., Ltd.
Cell voltage (V)
4
1
Gasket Laser seal
2
0 (b)
Terminal (−)
3
LiPF6 LiClO4 LiAsF6 LiBF4 0
30
Current collector
LiCF3SO3
60
90
120
150
Discharge capacity (mAh)
Figure 6 Discharge characteristics of a coin-type test cell using various electrolytes. Solvent: mixture of propylene carbonate (PC) and 1,2-dimethoxyethane (1,2-DME) (1:1 volume ratio); discharge conditions: (a) 25 1C, 0.5 mA cm2; (b) 20 1C, 0.5 mA cm2. Reproduced with permission from Takahashi M, Yoshimura S, Nakane I, et al. (1993) A study on electrolytes for manganese dioxide–lithium cells. Journal of Power Sources 43–44: 253–258.
showed good storage characteristics with 93% capacity retention. A cell using LiPF6 showed a large decrease in the discharge capacity, and diglyme, triglyme, and tetraglyme were detected in the electrolyte after the test. These glymes were considered to be produced by the reaction of two to four molecules of DME, which was initiated by the presence of PF5. The deterioration of discharge capacity was inferred to be the result of reaction between decomposition products and the lithium electrode. The storage characteristics of a test cell using LiBF4 were found to be worst among all solutes. In this case, manganese was observed on the surface of the negative electrode by an elemental analysis after the storage test. It was considered that decomposition of manganese dioxide had occurred in the electrolyte system using LiBF4.
Structures and Assembly of Li–MnO2 Batteries Lithium–manganese dioxide batteries are classified according to their shapes and structures. Figure 7 shows the structure of a coin-type cell that was commercialized in the early stage. The positive electrode of coin-type cells consists of manganese dioxide with the addition of a conductive material and binder. The negative electrode
Positive electrode (MnO2) Separator
Negative electrode (Li)
Positive electrode can
Figure 8 Structure of a cylindrical cell with an inside-out structure. Courtesy of Sanyo Electric Co., Ltd.
consists of a lithium metal disk, which is pressed onto the stainless steel can. The typical separator material is a nonwoven cloth made of polypropylene, which is placed between the cloth and the anode. Cylindrical cells can be classified into two basic types: one with an inside-out structure and one with a spiral structure. The former is constructed by pressing the positive electrode mixture into a high-density cylindrical form. The latter consists of a wound, thin positive electrode and a lithium negative electrode with a separator in between. Cells with the inside-out construction are suitable for high energy density, and those with the spiral construction are suitable for high-rate drain. Figure 8 shows an inside-out structure cell with laser sealing. Figure 9 shows two types of spiral structure cells with crimp and laser sealing. The nominal voltage of a Li–MnO2 cell is 3 V, which is about double that of other primary cells. Discharge voltages of manganese dry cell, alkaline manganese cell, zinc–silver oxide cell, mercury oxide cell, and zinc–air primary cell are about 1.5 V or lower. Therefore, the
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Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Terminal (+)
PTC device
Terminal (−)
Gasket Laser seal
Gasket
Tab (+)
Tab (+)
Tab (−) Negative electrode (Li)
Separator
Positive electrode (MnO2)
Positive electrode (MnO2)
Separator Negative electrode (Li)
Insulator
Tab (−)
Insulator
Can (−)
(a)
(b)
Terminal (+)
Figure 9 Structures of spiral-type cylindrical cells: (a) crimp and (b) laser sealing. PTC, positive temperature coefficient. Courtesy of Sanyo Electric Co., Ltd.
usage of a Li–MnO2 cell in place of other primary cells may result in damages. In order to avoid such misuses, Li–MnO2 cells are usually designed in different shapes. As mentioned above, lithium metal is very sensitive to water and it must be handled in a dry atmosphere. All components have to be dried before the battery assembly, because any residual water may cause deterioration of performance and pressure rise owing to reaction of lithium and water. The cell assembly process, in which lithium and other cell components after drying are handled, is conducted in a dry air room or a glove box filled with dry argon gas.
(3)
(4)
Advantages of Li–MnO2 Batteries The general advantages of the Li–MnO2 battery system are as follows: (1) High voltage Lithium–manganese dioxide cells are capable of maintaining a stable voltage of 3 V, which is about twice that of a conventional dry cell. The discharge profile is much flatter than conventional dry cell or alkaline batteries. Because of this advantage, a single Li–MnO2 cell can replace two conventional cells. (2) High energy density Energy densities and specific energies of Li–MnO2 batteries are highest among primary batteries. This is an important merit for many applications, which enables longer usage of appliances without battery replacement. The theoretical specific energy of a Li–MnO2 cell is 856 Wh kg1, which is much higher than that of aqueous electrolyte primary cells. Energy density values of real cells vary according to the types and sizes of the cells. Cylindrical cells with an inside-out structure
(5)
(6)
(7)
have high specific energy of about 280–360 Wh kg1 and energy density of 600–740 Wh L1. Excellent discharge characteristics As Li–MnO2 cells are capable of maintaining stable voltage levels throughout long periods of discharge, a single cell can be used as the internal power source throughout the operational lifetime of a given equipment. In addition, cells using a cylindrical, spiral structure can be used to provide high current discharge for a wide variety of applications. Superior leakage resistance The use of an organic solvent rather than an alkaline aqueous solution for the electrolyte results in significantly reduced corrosion and a much lower possibility of electrolyte leakage. Superior storage characteristics Lithium–manganese dioxide cells employing manganese dioxide, lithium, and a stable electrolyte exhibit a very low tendency toward self-discharge. Average self-discharge rate exhibited by Li–MnO2 cells stored at room temperature is as follows: Crimp-sealed cells: B1% per year Laser-sealed cells: B0.5% per year A wide operating temperature range Because Li–MnO2 cells use an organic electrolyte with a very low freezing point, lithium batteries can be operated at extremely low temperatures. Moreover, they demonstrate superior characteristics over a wide range of temperature from cold to hot, as follows: Crimp-sealed cells: 20 to þ 70 1C Laser-sealed cells: 40 to þ 85 1C A high degree of stability and safety As Li–MnO2 cells do not contain toxic liquids or gases, they pose no pollution problems. They are suitable for appliances for general consumers.
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Specifications of Some Commercially Available Li–MnO2 Batteries Lithium–manganese dioxide batteries are available in a variety of sizes and specifications. In this section, some examples of specifications of Li–MnO2 batteries are shown. Table 2 shows specifications of commercially available coin-type cells; cylindrical, inside-out-type cells; cylindrical, spiral-type cells; and Li–MnO2 batteries. Specifications are not always the same among manufacturers, and they are sometimes changed by improvement.
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range between 40 and þ 20 1C, discharge profiles are flat over a long period of about 10 years, although discharge time becomes shorter at þ 60 1C, which is a severe discharge condition. The actual discharge capacity is influenced by the discharge load (discharge current) and ambient temperature, as summarized in Figure 11. This type of battery shows excellent storage characteristics, which is important for a battery used or stored for a long period. After a 50-day storage at 80 1C, which corresponds to about 10-year storage at room temperature, this cell retains more than 97% of the initial capacity. Cylindrical, Spiral-Type Cells
coin-Type Cells Coin-type cells are mostly used for low-capacity and low current drain applications. Most of the coin-type Li–MnO2 cells have a model name like ‘CR2024’ (C: International Electrotechnical Commission (IEC) code for Li–MnO2 system; R: round; 20: diameter, 20 mm; 24: height, 2.4 mm).
A cylindrical, spiral-type cell CR17450E-R can be operated in a wide range of temperature from 40 to þ 85 1C. This cell exhibits a very flat discharge profile even at 40 1C. Influences of discharge load and temperature on the discharge capacity of a CR17450E-R are summarized in Figure 12.
Cylindrical, Inside-Out-Type Cells
Li–MnO2 Cell Packs
Figure 10 shows discharge characteristics of a CR17450SE cell at a standard discharge current. This cell shows a very flat discharge profile. In a temperature
For automatic and digital cameras, Li–MnO2 cells are used as cell packs with a nominal voltage of 3 or 6 V, as shown in Table 2.
Table 2
Specifications of some commercial Li–MnO2 batteries
Structure
Coin (crimp seal)
Cylindrical, inside-out (laser seal)
Cylindrical, spiral (crimp seal)
Cylindrical, spiral (laser seal) Battery pack
a
Model
Nominal capacity (mA h)
Dimensions (mm)
Weight (g)
Diameter
Height
CR1220 CR2016 CR2430 CR2450 CR17335SE
3 3 3 3 3
36 80 280 610 1800
12.5 20.0 24.5 24.5 17.0
2.0 1.6 3.0 5.0 33.5
0.8 1.7 4.0 6.9 17
CR17450SE CR23500SE CR-1/3Na
3 3 3
2500 5000 160
17.0 23.0 11.6
45.0 50.0 10.8
22 42 3.3
CR2b CR123Ac CR17335E-R
3 3 3
850 1400 1600
15.6 17.0 17.0
27.0 34.5 33.5
11 17 17
CR17450E-R CR-V3d
3 3
2400 3300
45.0
23 38
CR-P2e
6
1400
2CR5f
6
1400
17.0 29.0(L) 14.5(W) 52.0(H) 34.8(L) 19.5(W) 35.8(H) 34(L) 17(W) 45(H)
CR11108. CR15H270. c CR17345. d CP3152. e 2CP4036. f 2CP3945. Courtesy of Sanyo Electric Co., Ltd. b
Nominal voltage (V)
37 40
90
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide 3.5 60 °C
Load: 2.7 kohm (= 1 mA) 23 °C
Cell voltage (V)
3.0
2.5
0 °C
2.0
1.5
1.0
0
10
20
30
40
50
70
60
80
90
100
110
120
Discharge time (day)
Figure 10 Discharge characteristics of a CR17450SE cell at a standard discharge current: load: 2.7 kO, temperature: 0, 23, and 60 1C. Courtesy of Sanyo Electric Co., Ltd.
3000 2500 Capacity (mAh)
80 °C 2000 60 °C
1500
−20 °C
23 °C
−40 °C
1000 500 End voltage: 2.0 V 0
0.1
0.3
1
3
10
30
100
Discharge load (kΩ)
Figure 11 Relationship between the discharge load and the discharge capacity of a CR17450SE cell. Courtesy of Sanyo Electric Co., Ltd.
3000
Capacity (mAh)
2500 2000 +85 °C +60 °C 1500
−20 °C
+23 °C
1000 500 −40 °C 0
5
10
50
End voltage = 2.0 V 100
500
1000
Discharge load (Ω)
Figure 12 Relationship between the discharge load and the discharge capacity of a CR17450E-R cell. Courtesy of Sanyo Electric Co., Ltd.
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Cell pack 2CR5 for automatic cameras
The 2CR5 consists of two CR15400 cells connected in series and the nominal voltage is 6 V. A Li–MnO2 cell with a spiral structure is suitable for a fully automatic camera because high output current is needed for film winding, quick charging of strobe light, etc. This battery was developed in the mid-1980s as a user-replaceable lithium battery. At that time, most cylindrical lithium cells were equipped in appliances by the manufacturers. This cell pack is designed with special safety measures. Individual cells of 2CR5 are encapsulated in a plastic container and designed in an asymmetric shape that will prevent misuse. When a 2CR5 pack is short-circuited, a positive temperature coefficient (PTC) thermistor prevents the battery from overheating by substantially increasing the resistance. When the short circuit is removed, the 2CR5 operates normally. The battery case is usually equipped with the PTC thermistor, and hence the ability of the 2CR5 to deliver high current is not impeded. Heating of a Li–MnO2 battery by unusually high current or other reasons brings it to a dangerous state. The battery becomes especially dangerous and may give rise to firing or explosion when the temperature exceeds the melting point of lithium (180 1C). However, upon usual temperature rise, the polyolefin separator melts and shuts down the current flow by closing its micropores. The battery cap is equipped with a safety vent and operates under high pressure. Cell pack CR-V3 for digital cameras
A CR-V3 cell pack, which consists of two CR14500 cells in parallel, has a nominal voltage of 3 V and is designed mainly for use in digital cameras. A CR14500 cell has the same dimensions as an AA-size cell; hence, this pack is compatible with two AA-size alkaline manganese cells in series. The average operating voltage of a Li–MnO2 cell is about double that of other primary cells, such as alkaline manganese cells and dry cells. If a lithium cell is used in place of a low-voltage cell, it might cause damages to the electronic circuit. In order to avoid this kind of misuse, dimensions of most of the Li–MnO2 cells are different from those of other cell systems. The individual cell of the CR-V3, namely CR14500 (diameter: 14 mm, height: 50 mm), however, is an exception, which has almost the same size as an AA cell. Therefore, the package of a CRV3 pack is designed so that it is not easily disassembled. A digital camera needs both a large output power and a high energy density for its power source. It is necessary to make electrodes thinner and longer to achieve high output power with a battery of the same size, but this generally causes lowering of the energy density. As a result of optimization of thicknesses of electrodes, a CR-V3 exhibits good high-rate and low-temperature discharge characteristics without sacrificing the energy density. It was reported that a CR-V3 pack is more
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advantageous in high-rate, pulse, and low-temperature characteristics than alkaline manganese cells.
Applications Lithium–manganese dioxide batteries are used in a wide variety of applications according to their size and performances. Coin-type cells are used in applications that generally need low output power. In the 1980s, they made great contributions to the popularization of electronic watches and small-sized calculators. They are used in electronic diaries, PC cards, card-type radios, lightemitting diode (LED) lights, and remote controls of many appliances. Memory backups in many personal computers and office automation equipment are also important applications. Cylindrical cells with an inside-out structure are used for high energy density, low current drain applications, such as electronic meters and memory backups. In these applications, battery life up to 10 years and superior reliability are required. Cylindrical cells with a spiral structure are used for high output power applications. They are used in an exposure meter for cameras and as power sources for fully automatic cameras and digital cameras.
Nomenclature Abbreviations and Acronyms CMD DEE DEM DME DMM EMD EME IEC LED NMD PC PTC SHE
chemically prepared manganese dioxide diethoxyethane diethoxymethane dimethoxyethane dimethoxymethane electrolytic manganese dioxide ethoxymethoxyethane International Electrotechnical Commission light-emitting diode natural manganese dioxide propylene carbonate positive temperature coefficient standard hydrogen electrode
See also: Chemistry, Electrochemistry, and Electrochemical Applications: Lithium; Electrolytes: Non-Aqueous; History: Primary Batteries; Primary Batteries – Nonaqueous Systems: Lithium Primary: Overview; Lithium–Polycarbon Monofluoride; Primary Batteries: Overview.
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Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Further Reading Bowden W, Bofinger T, Zhang F, et al. (2007) New manganese dioxides for lithium batteries. Journal of Power Sources 165: 609--615. Ikeda H (1983) Lithium–manganese dioxide cells. In: Gabano JP (ed.) Lithium Batteries, pp. 169--210. London: Academic Press. Ikeda H, Saito T, and Tamura H (1977) Lithium–manganese dioxide cell. Electrochemistry 45: 314–318 (in Japanese). Ikeda H, Ueno S, Saito T, Nakaido S, and Tamura H (1977) Lithium– manganese dioxide cell. Electrochemistry 45: 391–395 (in Japanese). Johnson CS (2007) Development and utility of manganese oxides as cathodes in lithium batteries. Journal of Power Sources 165: 559--565. Kurimoto H, Suzuoka K, and Murakami T (1995) High surface area electromigration damage for 3 V Li-cell cathodes. Journal of the Electrochemical Society 142: 2156--2162. Manev V, Ilchev N, and Nassalevska A (1989) The lithium–manganese dioxide cell. I. Oxygen and water release during the thermal treatment of MnO2. Journal of Power Sources 25: 167--175. Nagao M, Pitteloud C, Kamiyama T, et al. (2005) Further understanding of reaction processes in electrolytic manganese dioxide electrodes for lithium cells. Journal of the Electrochemical Society 152: E230--E237. Nishio K and Furukawa N (1999) Practical batteries. In: Besenhard JO (ed.) Handbook of Battery Materials, pp. 19--61. Weinheim: Wiley-VCH.
Nishio K, Yoshimura S, and Saito T (1995) Discharge characteristics of manganese dioxide/lithium cells in various electrolyte solutions. Journal of Power Sources 55: 115--117. Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417--456. Amsterdam: Elsevier. Ohzuku T, Kitagawa M, and Hirai T (1989) Electrochemistry of manganese dioxide in lithium nonaqueous cell I. X-ray diffractional study on the reduction of electrolytic manganese dioxide. Journal of the Electrochemical Society 136: 3169--3174. Pistoia G (1982) Some restatements on the nature and behavior of MnO2 for Li batteries. Journal of the Electrochemical Society 129: 1861--1865. Shao-Horn Y, Hackney SA, and Cornilsen BC (1997) Structural characterization of heat-treated electrolytic manganese dioxide and topotactic transformation of discharge products in the Li–MnO2 cells. Journal of the Electrochemical Society 144: 3147--3153. Takahashi M, Yoshimura S, Nakane I, et al. (1993) A study on electrolytes for manganese dioxide–lithium cells. Journal of Power Sources 43–44: 253--258. Thackeray MM, Rossouw MH, de Kock A, et al. (1993) The versatility of MnO2 for lithium battery applications. Journal of Power Sources 43– 44: 289--300. Urushihara K, Tanaka A, Nishitani T, Morita S, and Fujimoto M (2002) High-power primary MnO2/lithium battery CR-V3. Sanyo Technical Review 34(1): 106--110.
Introduction Lithium primary batteries are currently one of the most widely used batteries, although they are newly developed battery systems compared to many other primary battery systems with aqueous electrolytes. Research and development of a cell using lithium as negative electrode started in the United States in the 1960s mainly for space applications, and later, development of batteries for consumer use became active also in Europe and Japan. An electrochemical cell using lithium and a nonaqueous electrolyte was a totally new system, and both a new positive electrode material with good discharge performance in a nonaqueous electrolyte and materials for the electrolyte had to be developed. Many new positive electrode materials such as metal oxides, metal sulfides, halogenide compounds, and organic compounds were developed and tested, and lithium cells using iodine complex, polycarbon monofluoride (CFn), and manganese dioxide were commercialized in the 1970s. The lithium–manganese dioxide (Li–MnO2) system was first commercialized in Japan as a coin-type and later it became available as cylindrical cells with a high power or a high energy density.
Principles of a Li–MnO2 Battery The following reaction mechanisms were proposed for a Li–MnO2 cell: Positive electrode reaction: MnðIVÞ O2 þ Liþ þ e -MnðIIIÞ O2 ðLiþ Þ Negative electrode reaction: Li-Liþ þ e Overall battery reaction: MnðIVÞ O2 þ Li-MnðIIIÞ O2 ðLiþ Þ
The reaction at the positive electrode is insertion of lithium into the crystal lattice of manganese dioxide, which accompanies reduction of Mn(IV) to Mn(III), and the reaction at the negative electrode is dissolution of lithium into the electrolyte solution. The X-ray diffraction patterns after discharge showed a peak shift to a lower angle, demonstrating an expansion of the crystal lattice. Another simple cell reaction for lithium and manganese dioxide was proposed as follows: 2Li þ 2MnO2 -Mn2 O3 þ Li2 O
This reaction, however, does not seem to take place, because neither Mn2O3 nor Li2O was found in the reaction products.
Materials Positive Electrode Manganese dioxide is a very common material in the battery field, which has been used for a long time as the positive electrode active material in zinc–carbon dry cells and alkaline manganese dioxide cells. It was also regarded as one of the most promising positive electrode materials for lithium cells, because it was a strong oxidant and less expensive than many other materials. It became clear, however, that manganese dioxide materials used in aqueous electrolyte batteries did not show good discharge performance in a nonaqueous electrolyte. The two major requirements for the manganese dioxide active material in Li–MnO2 cells are as follows: (i) it must be anhydrous; and (ii) it must have a structure suitable for the diffusion of Li þ ions into the manganese dioxide crystal lattice. Manganese dioxide is classified as natural manganese dioxide (NMD) and synthetic manganese dioxide the latter can be chemically prepared manganese dioxide (CMD) or electrolytic manganese dioxide (EMD) according to the preparation method. EMD after heat treatment is used as a positive electrode material in a commercial lithium battery. There have been many studies by many researchers on the discharge performances of manganese dioxide. In early works in Japan, relationships between heat treatment temperatures, crystal structures, chemical composition, and discharge characteristics were studied. Their findings of a manganese dioxide material with a desirable crystal structure for lithium diffusion became the basis for the first commercial Li–MnO2 battery in the late 1970s. Heat treatment has a significant influence on the crystal structure of EMD. It is basically understood as shown in Figure 1, although it should be noted that there have been some disputes about the crystal structure change. The crystal structure of as-prepared EMD is known as g-MnO2 and it consists of major ramsdellite domain with pyrolusite domain as impurity. Pure ramsdellite has one-dimensional 1 2 tunnels formed by chains of edge-sharing MnO6 octahedra. Crystal structures of EMD gradually change as the heat treatment
83
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Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
(a)
using lithium offer the possibility of a high voltage and a high energy density. In a real cell, lithium is mostly used as a foil having a thickness of several tens of micrometers and cut in a proper size. It is not difficult to cut and change the shape of lithium because it is a very soft and flexible metal. It is, however, necessary to pay special attention to the handling of lithium metal. Lithium readily reacts with water to form hydrogen gas. It even reacts with moisture in the atmosphere to form lithium hydroxide on its surface. Therefore, the presence of water should be avoided in all production processes. Electrolyte An electrolyte for a Li–MnO2 cell should possess the following properties:
(b)
(c)
Figure 1 The crystal structures of electrolytic MnO2 (EMD) heat treated at different temperatures (a) 250 1C, (b) 375 1C, and (c) 450 1C.
temperature increases. By heat treatment of EMD below 250 1C, the crystal structure remains as g-MnO2. By heat treatment from about 270 to 400 1C, g-b-MnO2, which has both 1 1 and 1 2 tunnels, is formed. When the heat treatment temperature is higher than 420 1C, bMnO2 (pyrolusite) with 1 1 tunnels is obtained. Among these materials, EMD heat treated from 370 to 400 1C, which exhibits both the highest discharge capacity and best storage characteristics, is used for the commercial Li–MnO2 batteries. Negative Electrode Lithium metal is used in a lithium primary cell. The electrode potential of lithium is 3.04 V versus standard hydrogen electrode (SHE), which is the lowest value among all metal electrodes. Lithium has the lowest density (0.53 g cm3) and the lowest electrochemical equivalent (0.259 g Ah1) of all solids. As a result of these physical properties, nonaqueous electrolyte batteries
(i) high ionic conductivity in a wide range of temperature; (ii) chemical and electrochemical stability for a long period; (iii) no harmful effects on the positive and negative electrode reactions. In a Li–MnO2 cell, polar aprotic solvents have to be used, as lithium metal reacts with protic solvents such as water and alcohols. The ionic conductivity of an organic electrolyte is generally 1–2 orders of magnitude lower than that of an aqueous electrolyte. Therefore, the composition of electrolytes for higher ionic conductivity is a major research target in nonaqueous systems. In order to dissolve sufficient amounts of solutes in an electrolyte solution, it is desirable that the organic solvent has a high dielectric constant. A high dielectric constant solvent, however, usually has a high viscosity, which is an undesirable property for a solvent. In practical Li–MnO2 cells, mixed solvents consisting of a highdielectric-constant–high-viscosity solvent and a low-dielectric-constant–low-viscosity solvent are usually employed. A typical mixed solvent is a mixture (50:50 or 70:30, v/v) of propylene carbonate (PC) and 1,2-dimethoxyethane (1,2DME). It is also important that the organic solvents and solutes do not contain water. It is essential for the good long-term discharge and storage performances of a cell that the electrolyte is stable under the strong oxidizing and reducing environment at the positive and negative electrodes, respectively. An organic solvent that has a low reduction potential and a high oxidation potential, that is, with a wide potential window, should be chosen. Separator The main functions of a separator in a cell are protection against short circuit caused by direct contact of the positive and negative electrodes and retention of
85
electrolyte solution. A suitable separator should be used for each cell considering the characteristics of the battery. For a Li–MnO2 cell, the separator should have the following properties: (i) (ii) (iii) (iv)
low electric resistance in an electrolyte; retention of a large amount of electrolyte solution; chemical stability in an organic solvent; and durability against both oxidation by manganese dioxide and reduction by lithium.
Separators made from polyethylene or polypropylene, which can meet the above-mentioned requirements, are mainly used for lithium batteries. They are used in the form of a nonwoven cloth or a thin film with micropores, considering the property and cost requirement of each type of battery.
Some Studies on the Materials of Li–MnO2 Batteries As mentioned in the previous sections, performances of a Li–MnO2 cell are strongly dependent on the materials, especially electrodes and electrolyte materials. Some studies on Li–MnO2 cells are presented here for better understanding of this system, although the results are not directly connected with the materials used in currently available batteries. Positive Electrode It is essential that no water exists in the positive electrode materials, but EMD before heat treatment contains about 5% of water. Heat treatment at 750 1C is required to completely remove the water. By a heat treatment at 350– 450 1C, EMD still contains about 1–2% water, but it is believed that this water is strongly combined in the crystal and does not affect the storage characteristics of a battery. This presumption was supported by a storage test. A test cell using manganese dioxide heat treated at 375 1C showed more than 90% of its initial capacity after an 11-month storage at 60 1C. Commercialization of Li–MnO2 batteries started with low-power coin-type cells, but the cells soon came to be used in some applications with higher power consumptions. For high-rate as well as low-temperature uses, a large surface area is required for the manganese dioxide material. Figure 2 shows the influence of specific surface area of manganese dioxide on the operating voltage of the test cells at low-temperature pulse discharge. The operating voltage of test cells using manganese dioxide with a high specific surface area was higher than that of test cells using manganese dioxide with a low surface area.
Pulse discharge voltage at 10th cycle (V)
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
1.9
1.8
1.7
1.6
0 0
20
30
40
50
Specific surface area (m2 g−1)
Figure 2 The influence of specific surface area of electrolytic MnO2 on the operating voltage of the test cells at lowtemperature pulse discharge. Reproduced from Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417–456. Amsterdam: Elsevier.
Negative Electrode Lithium is known to form alloys with some metals and the properties of lithium metal are modified by the alloying process. For a secondary cell using metallic lithium as the negative electrode, lithium alloy has been extensively studied to improve the cycling capability. Also in a primary cell, the discharge performance of a lithium electrode is influenced by the addition of a small amount of aluminum. Figure 3 shows the capacity retention of test cells using Li–Al alloys in which the content of aluminum ranged from 0.05% to 2%. Lithium with 0.5–2% aluminum showed good storage characteristics. However, the operating voltage after storage became lower when aluminum content was high, as shown in Figure 4. It was considered that good storage performance was achieved with a proper amount of aluminum in lithium. Electrolytes Discharge characteristics of a Li–MnO2 cell are greatly influenced by the properties of the electrolyte. Figure 5 shows the relationship between discharge capacity and conductivity of electrolyte of test cells using some twocomponent solvent systems. The test cells were discharged at a high rate of 560 O. In this test, mixed solvents consisting of PC and some ethers were used. The conductivities of the electrolytes varied from 4.6 to 13.3 mS cm1. At a high-rate condition, the conductivity of the electrolyte had a strong influence on the discharge performance. The properties of an electrolyte solution are also dependent on the solutes. Table 1 shows the physical properties of organic electrolytes using lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium hexafluoroarsenide (LiAsF6) as
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Capacity retention (%)
80
60
40
20
0
0.01
0.05
0.1
0.5
1
2
Al content of Li−Al alloy (wt.%)
Discharge capacity (mA h)
Pulse discharge voltage at 1st cycle (V)
Figure 3 Capacity retention of test cells (CR15400 size) using Li and Li–Al alloys after a 40-day storage at 60 1C. Reproduced with permission from Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417–456. Amsterdam: Elsevier.
solutes. The solvent is a PC–DME mixture. Conductivities of these electrolytes are around 102 S cm1, which is about 2 orders of magnitude lower than that of aqueous electrolytes. Discharge curves of test cells at 25 and 20 1C are shown in Figure 6. The LiClO4/PC–DME electrolyte, which shows a high conductivity and low viscosity at both 25 and 20 1C, is one of the most typical electrolytes. Only the LiCF3SO3/PC–DME electrolyte has a high solubility of solute at 20 1C and shows excellent low-temperature characteristics. Therefore, LiCF3SO3 is widely used in commercial batteries in spite of its comparatively low conductivity. LiAsF6/PC–DME has good properties as an electrolyte, but it is not used in consumer batteries because of the toxicity of arsenic. Storage characteristics of Li–MnO2 test cells were studied using mixed solvents of PC and 1,2-DME and some solutes. After a 40-day storage at 60 1C, which corresponds to about a 2-year storage at room temperature, test cells using LiClO4, LiCF3SO3, and LiAsF6
2.2
2.0
1.8
PC−1, 2-DME
100
PC−EME
80 60
PC−1, 2-DEE
40
PC−DMM
20
PC−1, 1-DME
1.6 0 0
0.05
0.01
0.1
0.5
1
2
Al content of Li−Al alloy (wt.%)
Figure 4 Pulse discharge voltage of test cells (CR15400 size) using Li and Li–Al. : initial, J: after a 40-day storage at 60 1C. Reproduced with permission from Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417–456. Amsterdam: Elsevier.
Table 1
0
5 10 Specific conductivity (10−3 S cm−1)
15
Figure 5 High-rate discharge capacity versus conductivity of electrolyte solution. Solvent: mixture of diether and propylene carbonate (1:1 volume ratio); solute: 1 mol dm3 LiClO4. Discharge conditions: temperature ¼ 25 1C, and load ¼ 560 O. DME, dimethoxyethane; PC, proylene carbonate. Reproduced with permission from Nishio K, Yoshimura S, and Saito T (1995). Discharge characteristics of manganese dioxide/lithium cells in various electrolyte solutions. Journal of Power Sources 55: 115–117.
Physical properties of some organic electrolytes 20 1C
25 1C
LiClO4 LiCF3SO3 LiBF4 LiPF6 LiAsF6
PC−DEM
Specific conductivity (mS cm1)
Viscosity (mPa s)
Specific conductivity (mS cm1)
Viscosity (mPa s)
Solubility (mol dm3)
12.3 5.9 8.2 17.0 16.3
1.3 1.2 1.0 1.6 1.3
7.1 3.5 5.2 7.6 7.3
3.2 2.4 2.0 3.1 2.7
1.2 46.0 2.4 1.2 1.0
Source: Reproduced with permission from Takahashi M, Yoshimura S, Nakane I, et al. (1993) A study on electrolytes for manganese dioxide–lithium cells. Journal of Power Sources 43–44: 253–258.
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide Negative electrode can
4
87
Negative electrode (Li)
Cell voltage (V)
Separator 3
LiAsF6 LiPF6 LiClO4 LiCF3SO3 LiBF4
2 1
Gasket
Positive electrode (MnO2) Positive electrode can
0
0
30
(a)
60
90
120
150
Discharge capacity (mAh)
Figure 7 Structure of a coin-type cell. Courtesy of Sanyo Electric Co., Ltd.
Cell voltage (V)
4
1
Gasket Laser seal
2
0 (b)
Terminal (−)
3
LiPF6 LiClO4 LiAsF6 LiBF4 0
30
Current collector
LiCF3SO3
60
90
120
150
Discharge capacity (mAh)
Figure 6 Discharge characteristics of a coin-type test cell using various electrolytes. Solvent: mixture of propylene carbonate (PC) and 1,2-dimethoxyethane (1,2-DME) (1:1 volume ratio); discharge conditions: (a) 25 1C, 0.5 mA cm2; (b) 20 1C, 0.5 mA cm2. Reproduced with permission from Takahashi M, Yoshimura S, Nakane I, et al. (1993) A study on electrolytes for manganese dioxide–lithium cells. Journal of Power Sources 43–44: 253–258.
showed good storage characteristics with 93% capacity retention. A cell using LiPF6 showed a large decrease in the discharge capacity, and diglyme, triglyme, and tetraglyme were detected in the electrolyte after the test. These glymes were considered to be produced by the reaction of two to four molecules of DME, which was initiated by the presence of PF5. The deterioration of discharge capacity was inferred to be the result of reaction between decomposition products and the lithium electrode. The storage characteristics of a test cell using LiBF4 were found to be worst among all solutes. In this case, manganese was observed on the surface of the negative electrode by an elemental analysis after the storage test. It was considered that decomposition of manganese dioxide had occurred in the electrolyte system using LiBF4.
Structures and Assembly of Li–MnO2 Batteries Lithium–manganese dioxide batteries are classified according to their shapes and structures. Figure 7 shows the structure of a coin-type cell that was commercialized in the early stage. The positive electrode of coin-type cells consists of manganese dioxide with the addition of a conductive material and binder. The negative electrode
Positive electrode (MnO2) Separator
Negative electrode (Li)
Positive electrode can
Figure 8 Structure of a cylindrical cell with an inside-out structure. Courtesy of Sanyo Electric Co., Ltd.
consists of a lithium metal disk, which is pressed onto the stainless steel can. The typical separator material is a nonwoven cloth made of polypropylene, which is placed between the cloth and the anode. Cylindrical cells can be classified into two basic types: one with an inside-out structure and one with a spiral structure. The former is constructed by pressing the positive electrode mixture into a high-density cylindrical form. The latter consists of a wound, thin positive electrode and a lithium negative electrode with a separator in between. Cells with the inside-out construction are suitable for high energy density, and those with the spiral construction are suitable for high-rate drain. Figure 8 shows an inside-out structure cell with laser sealing. Figure 9 shows two types of spiral structure cells with crimp and laser sealing. The nominal voltage of a Li–MnO2 cell is 3 V, which is about double that of other primary cells. Discharge voltages of manganese dry cell, alkaline manganese cell, zinc–silver oxide cell, mercury oxide cell, and zinc–air primary cell are about 1.5 V or lower. Therefore, the
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Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Terminal (+)
PTC device
Terminal (−)
Gasket Laser seal
Gasket
Tab (+)
Tab (+)
Tab (−) Negative electrode (Li)
Separator
Positive electrode (MnO2)
Positive electrode (MnO2)
Separator Negative electrode (Li)
Insulator
Tab (−)
Insulator
Can (−)
(a)
(b)
Terminal (+)
Figure 9 Structures of spiral-type cylindrical cells: (a) crimp and (b) laser sealing. PTC, positive temperature coefficient. Courtesy of Sanyo Electric Co., Ltd.
usage of a Li–MnO2 cell in place of other primary cells may result in damages. In order to avoid such misuses, Li–MnO2 cells are usually designed in different shapes. As mentioned above, lithium metal is very sensitive to water and it must be handled in a dry atmosphere. All components have to be dried before the battery assembly, because any residual water may cause deterioration of performance and pressure rise owing to reaction of lithium and water. The cell assembly process, in which lithium and other cell components after drying are handled, is conducted in a dry air room or a glove box filled with dry argon gas.
(3)
(4)
Advantages of Li–MnO2 Batteries The general advantages of the Li–MnO2 battery system are as follows: (1) High voltage Lithium–manganese dioxide cells are capable of maintaining a stable voltage of 3 V, which is about twice that of a conventional dry cell. The discharge profile is much flatter than conventional dry cell or alkaline batteries. Because of this advantage, a single Li–MnO2 cell can replace two conventional cells. (2) High energy density Energy densities and specific energies of Li–MnO2 batteries are highest among primary batteries. This is an important merit for many applications, which enables longer usage of appliances without battery replacement. The theoretical specific energy of a Li–MnO2 cell is 856 Wh kg1, which is much higher than that of aqueous electrolyte primary cells. Energy density values of real cells vary according to the types and sizes of the cells. Cylindrical cells with an inside-out structure
(5)
(6)
(7)
have high specific energy of about 280–360 Wh kg1 and energy density of 600–740 Wh L1. Excellent discharge characteristics As Li–MnO2 cells are capable of maintaining stable voltage levels throughout long periods of discharge, a single cell can be used as the internal power source throughout the operational lifetime of a given equipment. In addition, cells using a cylindrical, spiral structure can be used to provide high current discharge for a wide variety of applications. Superior leakage resistance The use of an organic solvent rather than an alkaline aqueous solution for the electrolyte results in significantly reduced corrosion and a much lower possibility of electrolyte leakage. Superior storage characteristics Lithium–manganese dioxide cells employing manganese dioxide, lithium, and a stable electrolyte exhibit a very low tendency toward self-discharge. Average self-discharge rate exhibited by Li–MnO2 cells stored at room temperature is as follows: Crimp-sealed cells: B1% per year Laser-sealed cells: B0.5% per year A wide operating temperature range Because Li–MnO2 cells use an organic electrolyte with a very low freezing point, lithium batteries can be operated at extremely low temperatures. Moreover, they demonstrate superior characteristics over a wide range of temperature from cold to hot, as follows: Crimp-sealed cells: 20 to þ 70 1C Laser-sealed cells: 40 to þ 85 1C A high degree of stability and safety As Li–MnO2 cells do not contain toxic liquids or gases, they pose no pollution problems. They are suitable for appliances for general consumers.
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Specifications of Some Commercially Available Li–MnO2 Batteries Lithium–manganese dioxide batteries are available in a variety of sizes and specifications. In this section, some examples of specifications of Li–MnO2 batteries are shown. Table 2 shows specifications of commercially available coin-type cells; cylindrical, inside-out-type cells; cylindrical, spiral-type cells; and Li–MnO2 batteries. Specifications are not always the same among manufacturers, and they are sometimes changed by improvement.
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range between 40 and þ 20 1C, discharge profiles are flat over a long period of about 10 years, although discharge time becomes shorter at þ 60 1C, which is a severe discharge condition. The actual discharge capacity is influenced by the discharge load (discharge current) and ambient temperature, as summarized in Figure 11. This type of battery shows excellent storage characteristics, which is important for a battery used or stored for a long period. After a 50-day storage at 80 1C, which corresponds to about 10-year storage at room temperature, this cell retains more than 97% of the initial capacity. Cylindrical, Spiral-Type Cells
coin-Type Cells Coin-type cells are mostly used for low-capacity and low current drain applications. Most of the coin-type Li–MnO2 cells have a model name like ‘CR2024’ (C: International Electrotechnical Commission (IEC) code for Li–MnO2 system; R: round; 20: diameter, 20 mm; 24: height, 2.4 mm).
A cylindrical, spiral-type cell CR17450E-R can be operated in a wide range of temperature from 40 to þ 85 1C. This cell exhibits a very flat discharge profile even at 40 1C. Influences of discharge load and temperature on the discharge capacity of a CR17450E-R are summarized in Figure 12.
Cylindrical, Inside-Out-Type Cells
Li–MnO2 Cell Packs
Figure 10 shows discharge characteristics of a CR17450SE cell at a standard discharge current. This cell shows a very flat discharge profile. In a temperature
For automatic and digital cameras, Li–MnO2 cells are used as cell packs with a nominal voltage of 3 or 6 V, as shown in Table 2.
Table 2
Specifications of some commercial Li–MnO2 batteries
Structure
Coin (crimp seal)
Cylindrical, inside-out (laser seal)
Cylindrical, spiral (crimp seal)
Cylindrical, spiral (laser seal) Battery pack
a
Model
Nominal capacity (mA h)
Dimensions (mm)
Weight (g)
Diameter
Height
CR1220 CR2016 CR2430 CR2450 CR17335SE
3 3 3 3 3
36 80 280 610 1800
12.5 20.0 24.5 24.5 17.0
2.0 1.6 3.0 5.0 33.5
0.8 1.7 4.0 6.9 17
CR17450SE CR23500SE CR-1/3Na
3 3 3
2500 5000 160
17.0 23.0 11.6
45.0 50.0 10.8
22 42 3.3
CR2b CR123Ac CR17335E-R
3 3 3
850 1400 1600
15.6 17.0 17.0
27.0 34.5 33.5
11 17 17
CR17450E-R CR-V3d
3 3
2400 3300
45.0
23 38
CR-P2e
6
1400
2CR5f
6
1400
17.0 29.0(L) 14.5(W) 52.0(H) 34.8(L) 19.5(W) 35.8(H) 34(L) 17(W) 45(H)
CR11108. CR15H270. c CR17345. d CP3152. e 2CP4036. f 2CP3945. Courtesy of Sanyo Electric Co., Ltd. b
Nominal voltage (V)
37 40
90
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide 3.5 60 °C
Load: 2.7 kohm (= 1 mA) 23 °C
Cell voltage (V)
3.0
2.5
0 °C
2.0
1.5
1.0
0
10
20
30
40
50
70
60
80
90
100
110
120
Discharge time (day)
Figure 10 Discharge characteristics of a CR17450SE cell at a standard discharge current: load: 2.7 kO, temperature: 0, 23, and 60 1C. Courtesy of Sanyo Electric Co., Ltd.
3000 2500 Capacity (mAh)
80 °C 2000 60 °C
1500
−20 °C
23 °C
−40 °C
1000 500 End voltage: 2.0 V 0
0.1
0.3
1
3
10
30
100
Discharge load (kΩ)
Figure 11 Relationship between the discharge load and the discharge capacity of a CR17450SE cell. Courtesy of Sanyo Electric Co., Ltd.
3000
Capacity (mAh)
2500 2000 +85 °C +60 °C 1500
−20 °C
+23 °C
1000 500 −40 °C 0
5
10
50
End voltage = 2.0 V 100
500
1000
Discharge load (Ω)
Figure 12 Relationship between the discharge load and the discharge capacity of a CR17450E-R cell. Courtesy of Sanyo Electric Co., Ltd.
Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Cell pack 2CR5 for automatic cameras
The 2CR5 consists of two CR15400 cells connected in series and the nominal voltage is 6 V. A Li–MnO2 cell with a spiral structure is suitable for a fully automatic camera because high output current is needed for film winding, quick charging of strobe light, etc. This battery was developed in the mid-1980s as a user-replaceable lithium battery. At that time, most cylindrical lithium cells were equipped in appliances by the manufacturers. This cell pack is designed with special safety measures. Individual cells of 2CR5 are encapsulated in a plastic container and designed in an asymmetric shape that will prevent misuse. When a 2CR5 pack is short-circuited, a positive temperature coefficient (PTC) thermistor prevents the battery from overheating by substantially increasing the resistance. When the short circuit is removed, the 2CR5 operates normally. The battery case is usually equipped with the PTC thermistor, and hence the ability of the 2CR5 to deliver high current is not impeded. Heating of a Li–MnO2 battery by unusually high current or other reasons brings it to a dangerous state. The battery becomes especially dangerous and may give rise to firing or explosion when the temperature exceeds the melting point of lithium (180 1C). However, upon usual temperature rise, the polyolefin separator melts and shuts down the current flow by closing its micropores. The battery cap is equipped with a safety vent and operates under high pressure. Cell pack CR-V3 for digital cameras
A CR-V3 cell pack, which consists of two CR14500 cells in parallel, has a nominal voltage of 3 V and is designed mainly for use in digital cameras. A CR14500 cell has the same dimensions as an AA-size cell; hence, this pack is compatible with two AA-size alkaline manganese cells in series. The average operating voltage of a Li–MnO2 cell is about double that of other primary cells, such as alkaline manganese cells and dry cells. If a lithium cell is used in place of a low-voltage cell, it might cause damages to the electronic circuit. In order to avoid this kind of misuse, dimensions of most of the Li–MnO2 cells are different from those of other cell systems. The individual cell of the CR-V3, namely CR14500 (diameter: 14 mm, height: 50 mm), however, is an exception, which has almost the same size as an AA cell. Therefore, the package of a CRV3 pack is designed so that it is not easily disassembled. A digital camera needs both a large output power and a high energy density for its power source. It is necessary to make electrodes thinner and longer to achieve high output power with a battery of the same size, but this generally causes lowering of the energy density. As a result of optimization of thicknesses of electrodes, a CR-V3 exhibits good high-rate and low-temperature discharge characteristics without sacrificing the energy density. It was reported that a CR-V3 pack is more
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advantageous in high-rate, pulse, and low-temperature characteristics than alkaline manganese cells.
Applications Lithium–manganese dioxide batteries are used in a wide variety of applications according to their size and performances. Coin-type cells are used in applications that generally need low output power. In the 1980s, they made great contributions to the popularization of electronic watches and small-sized calculators. They are used in electronic diaries, PC cards, card-type radios, lightemitting diode (LED) lights, and remote controls of many appliances. Memory backups in many personal computers and office automation equipment are also important applications. Cylindrical cells with an inside-out structure are used for high energy density, low current drain applications, such as electronic meters and memory backups. In these applications, battery life up to 10 years and superior reliability are required. Cylindrical cells with a spiral structure are used for high output power applications. They are used in an exposure meter for cameras and as power sources for fully automatic cameras and digital cameras.
Nomenclature Abbreviations and Acronyms CMD DEE DEM DME DMM EMD EME IEC LED NMD PC PTC SHE
chemically prepared manganese dioxide diethoxyethane diethoxymethane dimethoxyethane dimethoxymethane electrolytic manganese dioxide ethoxymethoxyethane International Electrotechnical Commission light-emitting diode natural manganese dioxide propylene carbonate positive temperature coefficient standard hydrogen electrode
See also: Chemistry, Electrochemistry, and Electrochemical Applications: Lithium; Electrolytes: Non-Aqueous; History: Primary Batteries; Primary Batteries – Nonaqueous Systems: Lithium Primary: Overview; Lithium–Polycarbon Monofluoride; Primary Batteries: Overview.
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Primary Batteries – Nonaqueous Systems | Lithium–Manganese Dioxide
Further Reading Bowden W, Bofinger T, Zhang F, et al. (2007) New manganese dioxides for lithium batteries. Journal of Power Sources 165: 609--615. Ikeda H (1983) Lithium–manganese dioxide cells. In: Gabano JP (ed.) Lithium Batteries, pp. 169--210. London: Academic Press. Ikeda H, Saito T, and Tamura H (1977) Lithium–manganese dioxide cell. Electrochemistry 45: 314–318 (in Japanese). Ikeda H, Ueno S, Saito T, Nakaido S, and Tamura H (1977) Lithium– manganese dioxide cell. Electrochemistry 45: 391–395 (in Japanese). Johnson CS (2007) Development and utility of manganese oxides as cathodes in lithium batteries. Journal of Power Sources 165: 559--565. Kurimoto H, Suzuoka K, and Murakami T (1995) High surface area electromigration damage for 3 V Li-cell cathodes. Journal of the Electrochemical Society 142: 2156--2162. Manev V, Ilchev N, and Nassalevska A (1989) The lithium–manganese dioxide cell. I. Oxygen and water release during the thermal treatment of MnO2. Journal of Power Sources 25: 167--175. Nagao M, Pitteloud C, Kamiyama T, et al. (2005) Further understanding of reaction processes in electrolytic manganese dioxide electrodes for lithium cells. Journal of the Electrochemical Society 152: E230--E237. Nishio K and Furukawa N (1999) Practical batteries. In: Besenhard JO (ed.) Handbook of Battery Materials, pp. 19--61. Weinheim: Wiley-VCH.
Nishio K, Yoshimura S, and Saito T (1995) Discharge characteristics of manganese dioxide/lithium cells in various electrolyte solutions. Journal of Power Sources 55: 115--117. Nohma T, Yoshimura S, Nishio K, and Saito T (1994) Commercial cells based on MnO2 and MnO2-related cathodes. In: Pistoia G (ed.) Lithium Batteries, pp. 417--456. Amsterdam: Elsevier. Ohzuku T, Kitagawa M, and Hirai T (1989) Electrochemistry of manganese dioxide in lithium nonaqueous cell I. X-ray diffractional study on the reduction of electrolytic manganese dioxide. Journal of the Electrochemical Society 136: 3169--3174. Pistoia G (1982) Some restatements on the nature and behavior of MnO2 for Li batteries. Journal of the Electrochemical Society 129: 1861--1865. Shao-Horn Y, Hackney SA, and Cornilsen BC (1997) Structural characterization of heat-treated electrolytic manganese dioxide and topotactic transformation of discharge products in the Li–MnO2 cells. Journal of the Electrochemical Society 144: 3147--3153. Takahashi M, Yoshimura S, Nakane I, et al. (1993) A study on electrolytes for manganese dioxide–lithium cells. Journal of Power Sources 43–44: 253--258. Thackeray MM, Rossouw MH, de Kock A, et al. (1993) The versatility of MnO2 for lithium battery applications. Journal of Power Sources 43– 44: 289--300. Urushihara K, Tanaka A, Nishitani T, Morita S, and Fujimoto M (2002) High-power primary MnO2/lithium battery CR-V3. Sanyo Technical Review 34(1): 106--110.