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Film packed lithium–ion battery with polymer stabilizer
Electrochimica Acta 50 (2004) 561–564
Film packed lithium–ion battery with polymer stabilizer Masaharu Satoh∗ , Kentaro Nakahara Environment and Material Research Laboratories, NEC Corporation, 1-1 Miyazaki 4-chome, Miyamae-ku, Kawasaki, Kanagawa 216-8555, Japan Received 2 June 2003; received in revised form 14 December 2003; accepted 30 January 2004 Available online 5 October 2004
Abstract The 1600 mAh class of film packed lithium–ion battery has been fabricated with the polymer stabilizer. The adhesive polymer covered with fluorinated polymer beads enables to penetrate into the prismatically wounded jerry-roll layers and connects the electrode layers and separator film. The battery demonstrates the improved properties after repeating the charge and discharge processes and should be useful for the various electronics equipment such as notebook type computer. © 2004 Elsevier Ltd. All rights reserved. Keywords: Polymer stabilizer; Poly(1,2-butadiene); Lithium–ion battery; Film packed cell
1. Introduction Polymer battery using a polymer electrolyte [1–6] has attracted much attention since it has been considered to achieve a lightweight and thin cell with improved stability and high energy density. So far, many attempts have been carried out to develop the polymer solid/gel [4–6] electrolytes with ionic conductivity sufficiently large for battery applications. However, the conductivity of these polymer electrolytes was found to be several times lower than that of the liquid electrolyte. The lower conductivity brings to an extremely small capacity at high rate discharge process. On the other hand, the film packed cell [7] based on the lithium–ion system with liquid electrolyte has been confirmed to have satisfactorily high capacity at low temperature and high discharge rate. In case of the laminated film packed cell, deformation with the charge and discharge processes are considered to be the critical characteristics. The electrochemical reaction of the battery system induces charge and discharge process accompanying a volume change of the cathode and anode layers. The inner stress of the electrode layer should cause the swelling or twisting in the jerry-roll. For the film packed cell ∗
Corresponding author. E-mail address: [email protected] (M. Satoh).
0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2004.01.129
these deformation brings about the detachment of cathode and anode layers, leading to the rapid decrease of the capacity. To improve the stability of the film packed cell we have investigated the polymer stabilizer located between anode and cathode layers. The stabilizer consists of reactive polymer covered with fluorinated polymer beads. Here we describe the fabrication and fundamental properties of the battery.
2. Experimental The batteries used in this study were prepared by using the lithium–ion electrodes with spinel LiMn2 O4 cathode and graphite anode. These electrodes were prismatically wound with separator film in a jelly roll configuration. The Mn-spinel is unique as cathode active material, and presents cost and environmental advantages over the cobalt-based lithium–ion system. Fig. 1 shows a schematic illustration of a liquid electrolyte cell packed with laminated film. The polymer stabilizer consists of the reactive polymer of poly(1,2-butadiene) and fluorinated polyolefin. Poly(1,2butadiene) dissolved in cyclohexane were precipitated in fluorinated polyolefin micro-beads by adding a methanol to phase separation. Fig. 2 shows the surface structure of the polymer stabilizer. The dispersed solution of polymer stabilizer was penetrated into the electrode layers and then
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M. Satoh, K. Nakahara / Electrochimica Acta 50 (2004) 561–564
Fig. 1. Schematic representation of the film packed cell.
dried at 60 ◦ C under high vacuum. Next, the jerry-roll was annealed at 80 ◦ C under pressure with an additive of radical initiator. In this process the cross-linking of the reactive poly(1,2-butadiene) changes the polymer particle from plastic to infusible and enables to bind the electrode layers. The jerry-rolls were packed with the electrolyte solution (diethylcarbonate/ethylcarbonate/1 M LiPF6 ) which was identical to the lithium–ion battery. That implies the major properties of the cell, i.e., impedance, power density and working temperature, are the same as the conventional lithium–ion battery. The thickness of the laminated film is 0.12 mm, which provides a lightweight and flexible package of the battery. It was shaped by pressing out according to the form of the jerry-rolls before use. Due to the simple process in packaging, the battery is easily prepared. It should be noted that the major properties, i.e., capacitance, impedance and power density are the same as these of the conventional lithium–ion battery. Applying the film package to the lithium–ion system should make a lightweight and high energy density battery practicable. The charge and discharge properties were measured with a KIKUSUI Battery Tester PFX20W-12 at a constant current
Fig. 2. SEM photographs of reactive polymer particles (20 m)covered with fluorinated polymer micro-beads (0.1–0.2 m).
Fig. 3. Thermogravimetric curves of electrolyte solution containing the fluorinated polymer.
with voltage from 3.0 to 4.2 V. The inner resistance of the battery was estimated by extrapolation in the cole–cole plots of the ac impedance measured with CH Instruments model 604 Electrochemical Analyzer.
3. Results and discussion The polymer stabilizer is selected an adhesive polymer particle with functionalized polyolefin derivatives. The dispersed solution of polymer particle with average diameter of 20 m is capable to penetrate the wounded jerry-roll. The reacted polymer stabilizer on the electrode surface binds the cathode and anode layers to the separator film. The cured polymer remains infusible up to 200 ◦ C and stable to the electrolyte solution with the modulus of 10 MPa at room temperature. The polymer beads (vinylidene-fluoride/hexafuluoroethylene copolymer) on polymer particle dispersed in electrolyte solution are effective in flame-proof by melting at elevated temperature. Fig. 3 shows the thermogravimetric curves of electrolyte solutions. It is shown that the curves shift to the higher temperature for the solution containing the fluorinated polymer beads. Fig. 4 shows the discharge profiles of the film packed cells fabricated with (open circle) and without (full circle) the polymer stabilizer. Apparently, the capacity of the cell using the stabilizer is larger than that of the simple film packed cell. The estimated capacity is agreed with the inherent capacity of the jerry-roll used. It suggests that the polymer stabilizer exist without stoppering the micropores in separator films and overcome the inner stress during the charge and discharge process. Contrary, both of the charge capacity and charge efficiency of the film packed cell prepared without polymer stabilizer are smaller than the design values. Fig. 5 shows the plots of the capacities versus chargedischarge cycle number. The significant decrease should be due to the residual water in additive free type electrolyte
M. Satoh, K. Nakahara / Electrochimica Acta 50 (2004) 561–564
Fig. 4. Discharge profiles of the film packed cell prepared with (a) and without (b) polymer stabilizer. Discharge rate: 1650 mA, 3.0 V cut off, at 20 ◦ C.
solution. Nonetheless, the capacity of the cell with polymer stabilizer after is larger than that of the simple film packed cell for all cycle number examined. Furthermore, the deviation between the curves becomes notable with increasing the cycling. The residual capacity after cycling should not be necessarily the upper limit of the capacity, and enabled to increase by the optimization of the liquid electrolytes and the preparation conditions. For the film packed cell prepared without polymer stabilizer the thickness increases with charge and discharge cycle number up to 30% of the initial. The decreased capacity of these swelled cells is somewhat recovered by pressing. It is also indicates that the detachment of electrodes is responsible for the capacity loss. At this stage of the experiment, the contact strengths of the adhesive polymer to the electrode materials and the separator film have not been estimated. However, the scanning electron micrograph of the peeled layers (Fig. 6) display the polymer in the form of elongated fibriler structure contact to the electrode materials and separator film. It implies that the
563
Fig. 6. SEM photographs of polymer stabilizer between electrode layer.
contact strengths are larger than that of the tensile strength of the adhesive polymer particle. The storage energy of film packed cell with polymer stabilizer is estimated as 6.27 Wh. With increasing the cycle number, the thickness of the cell increased from 8.6 to 9.2 mm, however, the swelling is smaller than that of the cell prepared without the polymer stabilizer. The sufficiently high capacity in the work temperature range from −10 to 60 ◦ C is also confirmed. With the abuse tests of short circuit, hot-box (150 ◦ C), overcharge and nail penetration, combustion and fuming of the cell are not observed. Swelling or deformation of the film package should reduce the pressure generated the abuse tests by isolating the cathode and anode layers. The polymer stabilizer presented here should be applicable to a variety of battery system. Replacing the metal canned case to the laminated film, it is possible to obtain the battery with the thickness smaller than that of a lower limit (4 mm) of the conventional prismatic cell. Additionally, owing to the lightweight package, the improved energy density is expected. Because of the simple process in packaging, the battery with polymer stabilizer is favorable to produce with short turn around time for the notebook type computer, the energy consumed increases significantly with the progress in high-speed and high-density technologies. The higher energy density of the film packed battery is favorable for this use.
4. Conclusion
Fig. 5. Plots of capacities of the film packed cell prepared with (a) and without (b) the polymer stabilizer vs. charge/discharge cycle number. Charge/discharge rates: 1650 mA, 3.0 V cut off, at 20 ◦ C.
The film packed battery has been fabricated with advanced polymer technologies. The electrochemical properties such as the capacity, voltage, power density, work temperature range are comparable with the conventional lithium–ion cell. The large capacity of 1650 mAh is attained utilizing the adhesive polymer stabilizer in jerry-roll with excellent stability and safety. Due to the simple process in packaging, the battery is easily prepared with short turn around time.
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M. Satoh, K. Nakahara / Electrochimica Acta 50 (2004) 561–564
References [1] M.B. Armand, J.M. Chabagno, M. Duclot, in: P. Vashishta, J.N. Mundy, G.K. Shenoy (Eds.), Fast Ion Transport in Solids, Elsevier, New York, 1979, p. 131. [2] D.E. Fenton, J.M. Parker, P.V. Wright, Polymer 14 (1973) 589. [3] P.V. Wright, Br. Polym. J. 7 (1975) 319.
[4] D.-W. Kim, J. Power Sources 87 (2000) 78. [5] J.M. Tarascon, A.S. Gozdz, C. Schmutz, F. Shokoohi, P.C. Warren, Solid State Ionics 86–88 (1996) 49. [6] J.M. Tarascon, W.R. McKinnon, F. Coowar, T.N. Bowmer, G. Amatucci, D.G. Guyomard, J. Electrochem. Soc. 141 (1994) 1421. [7] M. Satoh, N. Ohyama, M. Shirakata, R. Shimizu, H. Yageta, Y. Bannai, NEC Res. Dev. 41 (2000) 18.
Film packed lithium–ion battery with polymer stabilizer Masaharu Satoh∗ , Kentaro Nakahara Environment and Material Research Laboratories, NEC Corporation, 1-1 Miyazaki 4-chome, Miyamae-ku, Kawasaki, Kanagawa 216-8555, Japan Received 2 June 2003; received in revised form 14 December 2003; accepted 30 January 2004 Available online 5 October 2004
Abstract The 1600 mAh class of film packed lithium–ion battery has been fabricated with the polymer stabilizer. The adhesive polymer covered with fluorinated polymer beads enables to penetrate into the prismatically wounded jerry-roll layers and connects the electrode layers and separator film. The battery demonstrates the improved properties after repeating the charge and discharge processes and should be useful for the various electronics equipment such as notebook type computer. © 2004 Elsevier Ltd. All rights reserved. Keywords: Polymer stabilizer; Poly(1,2-butadiene); Lithium–ion battery; Film packed cell
1. Introduction Polymer battery using a polymer electrolyte [1–6] has attracted much attention since it has been considered to achieve a lightweight and thin cell with improved stability and high energy density. So far, many attempts have been carried out to develop the polymer solid/gel [4–6] electrolytes with ionic conductivity sufficiently large for battery applications. However, the conductivity of these polymer electrolytes was found to be several times lower than that of the liquid electrolyte. The lower conductivity brings to an extremely small capacity at high rate discharge process. On the other hand, the film packed cell [7] based on the lithium–ion system with liquid electrolyte has been confirmed to have satisfactorily high capacity at low temperature and high discharge rate. In case of the laminated film packed cell, deformation with the charge and discharge processes are considered to be the critical characteristics. The electrochemical reaction of the battery system induces charge and discharge process accompanying a volume change of the cathode and anode layers. The inner stress of the electrode layer should cause the swelling or twisting in the jerry-roll. For the film packed cell ∗
Corresponding author. E-mail address: [email protected] (M. Satoh).
0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2004.01.129
these deformation brings about the detachment of cathode and anode layers, leading to the rapid decrease of the capacity. To improve the stability of the film packed cell we have investigated the polymer stabilizer located between anode and cathode layers. The stabilizer consists of reactive polymer covered with fluorinated polymer beads. Here we describe the fabrication and fundamental properties of the battery.
2. Experimental The batteries used in this study were prepared by using the lithium–ion electrodes with spinel LiMn2 O4 cathode and graphite anode. These electrodes were prismatically wound with separator film in a jelly roll configuration. The Mn-spinel is unique as cathode active material, and presents cost and environmental advantages over the cobalt-based lithium–ion system. Fig. 1 shows a schematic illustration of a liquid electrolyte cell packed with laminated film. The polymer stabilizer consists of the reactive polymer of poly(1,2-butadiene) and fluorinated polyolefin. Poly(1,2butadiene) dissolved in cyclohexane were precipitated in fluorinated polyolefin micro-beads by adding a methanol to phase separation. Fig. 2 shows the surface structure of the polymer stabilizer. The dispersed solution of polymer stabilizer was penetrated into the electrode layers and then
562
M. Satoh, K. Nakahara / Electrochimica Acta 50 (2004) 561–564
Fig. 1. Schematic representation of the film packed cell.
dried at 60 ◦ C under high vacuum. Next, the jerry-roll was annealed at 80 ◦ C under pressure with an additive of radical initiator. In this process the cross-linking of the reactive poly(1,2-butadiene) changes the polymer particle from plastic to infusible and enables to bind the electrode layers. The jerry-rolls were packed with the electrolyte solution (diethylcarbonate/ethylcarbonate/1 M LiPF6 ) which was identical to the lithium–ion battery. That implies the major properties of the cell, i.e., impedance, power density and working temperature, are the same as the conventional lithium–ion battery. The thickness of the laminated film is 0.12 mm, which provides a lightweight and flexible package of the battery. It was shaped by pressing out according to the form of the jerry-rolls before use. Due to the simple process in packaging, the battery is easily prepared. It should be noted that the major properties, i.e., capacitance, impedance and power density are the same as these of the conventional lithium–ion battery. Applying the film package to the lithium–ion system should make a lightweight and high energy density battery practicable. The charge and discharge properties were measured with a KIKUSUI Battery Tester PFX20W-12 at a constant current
Fig. 2. SEM photographs of reactive polymer particles (20 m)covered with fluorinated polymer micro-beads (0.1–0.2 m).
Fig. 3. Thermogravimetric curves of electrolyte solution containing the fluorinated polymer.
with voltage from 3.0 to 4.2 V. The inner resistance of the battery was estimated by extrapolation in the cole–cole plots of the ac impedance measured with CH Instruments model 604 Electrochemical Analyzer.
3. Results and discussion The polymer stabilizer is selected an adhesive polymer particle with functionalized polyolefin derivatives. The dispersed solution of polymer particle with average diameter of 20 m is capable to penetrate the wounded jerry-roll. The reacted polymer stabilizer on the electrode surface binds the cathode and anode layers to the separator film. The cured polymer remains infusible up to 200 ◦ C and stable to the electrolyte solution with the modulus of 10 MPa at room temperature. The polymer beads (vinylidene-fluoride/hexafuluoroethylene copolymer) on polymer particle dispersed in electrolyte solution are effective in flame-proof by melting at elevated temperature. Fig. 3 shows the thermogravimetric curves of electrolyte solutions. It is shown that the curves shift to the higher temperature for the solution containing the fluorinated polymer beads. Fig. 4 shows the discharge profiles of the film packed cells fabricated with (open circle) and without (full circle) the polymer stabilizer. Apparently, the capacity of the cell using the stabilizer is larger than that of the simple film packed cell. The estimated capacity is agreed with the inherent capacity of the jerry-roll used. It suggests that the polymer stabilizer exist without stoppering the micropores in separator films and overcome the inner stress during the charge and discharge process. Contrary, both of the charge capacity and charge efficiency of the film packed cell prepared without polymer stabilizer are smaller than the design values. Fig. 5 shows the plots of the capacities versus chargedischarge cycle number. The significant decrease should be due to the residual water in additive free type electrolyte
M. Satoh, K. Nakahara / Electrochimica Acta 50 (2004) 561–564
Fig. 4. Discharge profiles of the film packed cell prepared with (a) and without (b) polymer stabilizer. Discharge rate: 1650 mA, 3.0 V cut off, at 20 ◦ C.
solution. Nonetheless, the capacity of the cell with polymer stabilizer after is larger than that of the simple film packed cell for all cycle number examined. Furthermore, the deviation between the curves becomes notable with increasing the cycling. The residual capacity after cycling should not be necessarily the upper limit of the capacity, and enabled to increase by the optimization of the liquid electrolytes and the preparation conditions. For the film packed cell prepared without polymer stabilizer the thickness increases with charge and discharge cycle number up to 30% of the initial. The decreased capacity of these swelled cells is somewhat recovered by pressing. It is also indicates that the detachment of electrodes is responsible for the capacity loss. At this stage of the experiment, the contact strengths of the adhesive polymer to the electrode materials and the separator film have not been estimated. However, the scanning electron micrograph of the peeled layers (Fig. 6) display the polymer in the form of elongated fibriler structure contact to the electrode materials and separator film. It implies that the
563
Fig. 6. SEM photographs of polymer stabilizer between electrode layer.
contact strengths are larger than that of the tensile strength of the adhesive polymer particle. The storage energy of film packed cell with polymer stabilizer is estimated as 6.27 Wh. With increasing the cycle number, the thickness of the cell increased from 8.6 to 9.2 mm, however, the swelling is smaller than that of the cell prepared without the polymer stabilizer. The sufficiently high capacity in the work temperature range from −10 to 60 ◦ C is also confirmed. With the abuse tests of short circuit, hot-box (150 ◦ C), overcharge and nail penetration, combustion and fuming of the cell are not observed. Swelling or deformation of the film package should reduce the pressure generated the abuse tests by isolating the cathode and anode layers. The polymer stabilizer presented here should be applicable to a variety of battery system. Replacing the metal canned case to the laminated film, it is possible to obtain the battery with the thickness smaller than that of a lower limit (4 mm) of the conventional prismatic cell. Additionally, owing to the lightweight package, the improved energy density is expected. Because of the simple process in packaging, the battery with polymer stabilizer is favorable to produce with short turn around time for the notebook type computer, the energy consumed increases significantly with the progress in high-speed and high-density technologies. The higher energy density of the film packed battery is favorable for this use.
4. Conclusion
Fig. 5. Plots of capacities of the film packed cell prepared with (a) and without (b) the polymer stabilizer vs. charge/discharge cycle number. Charge/discharge rates: 1650 mA, 3.0 V cut off, at 20 ◦ C.
The film packed battery has been fabricated with advanced polymer technologies. The electrochemical properties such as the capacity, voltage, power density, work temperature range are comparable with the conventional lithium–ion cell. The large capacity of 1650 mAh is attained utilizing the adhesive polymer stabilizer in jerry-roll with excellent stability and safety. Due to the simple process in packaging, the battery is easily prepared with short turn around time.
564
M. Satoh, K. Nakahara / Electrochimica Acta 50 (2004) 561–564
References [1] M.B. Armand, J.M. Chabagno, M. Duclot, in: P. Vashishta, J.N. Mundy, G.K. Shenoy (Eds.), Fast Ion Transport in Solids, Elsevier, New York, 1979, p. 131. [2] D.E. Fenton, J.M. Parker, P.V. Wright, Polymer 14 (1973) 589. [3] P.V. Wright, Br. Polym. J. 7 (1975) 319.
[4] D.-W. Kim, J. Power Sources 87 (2000) 78. [5] J.M. Tarascon, A.S. Gozdz, C. Schmutz, F. Shokoohi, P.C. Warren, Solid State Ionics 86–88 (1996) 49. [6] J.M. Tarascon, W.R. McKinnon, F. Coowar, T.N. Bowmer, G. Amatucci, D.G. Guyomard, J. Electrochem. Soc. 141 (1994) 1421. [7] M. Satoh, N. Ohyama, M. Shirakata, R. Shimizu, H. Yageta, Y. Bannai, NEC Res. Dev. 41 (2000) 18.