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LiNi0.5Mn1.5O4 cathode material by low-temperature solid-state method with excellent cycleability in lithium ion battery
Materials Letters 64 (2010) 2328–2330
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
LiNi0.5Mn1.5O4 cathode material by low-temperature solid-state method with excellent cycleability in lithium ion battery Chih-Yuan Lin a, Jenq-Gong Duh a,⁎, Chia-Haw Hsu b, Jin-Ming Chen b a b
Department of Materials Science and Engineering National Tsing-Hua University, Hsinchu, Taiwan Material and Chemical Research Laboratories, Industrial Technology Research Institute, Chutung, Taiwan
a r t i c l e
i n f o
Article history: Received 15 May 2010 Accepted 6 July 2010 Available online 17 July 2010 Keywords: Lithium ion battery Cathode material LiNi0.5Mn1.5O4
a b s t r a c t LiNi0.5Mn1.5O4 cathode material was synthesized from a mixture of LiCl, NiCl2 6H2O and MnCl2 4H2O with 70 wt.% oxalic acid by a low-temperature solid-state method. The calcination temperature was adjusted to form disorder Fd3m structure at 700–800 °C for 10 h. XRD patterns and FTIR spectroscopy showed that the LiNi0.5Mn1.5O4 cathode material exhibited an impurityfree spinel Fd3m structure. Electrochemical property results revealed that the LiNi0.5Mn1.5O4 cathode material charged at 1C rate to 4.9 V and discharged at 2 and 3 C to 3.5 V delivered initial capacity of 120 mAh/g and maintained a capacity retention over 80% at room temperature after 1000 charge/discharge cycles. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The increasing demands on high energy and high power Li-ion batteries for hybrid electric vehicle and power tools lead the researcher to investigate the high-voltage material [1]. Various developments have achieved potential ranges of 5 V in comparison with Li/Li+. Spinel LiMn2O4 is a possible alternative to replace the standard layered oxides (LiCoO2) because of its abundance, low cost, and environmental friendliness, yet several drawbacks have restricted its application to commercial batteries. The major defects of LiMn2O4 are the dissolution of Mn2+ in the electrolyte and Jahn–Teller distortion [2]. A common way to overcome the degradation of LiMn2O4 is to replace Mn with another transition metal. LiMxMn2xO4 is high-voltage cathode material, exhibiting plateaus at voltages above 4 V. Among these cathode materials, LiNi0.5Mn1.5O4 has received great attention owing to its good electrochemical performance and high operating voltage around 4.7 V [3–5]. However, its electrochemical performance dramatically degraded during prolonged charge/discharge cycling at a high C rate or cycling at an elevated temperature [6–10]. Since the manufacturing method for LiNi0.5Mn1.5O4 powder strongly influences its rateability performance and capacity retention, many synthesis methods have been developed, such as the sol–gel [11,12], ultrasonic spray pyrolysis [13], and molten salt [14]. However, they are too complicated and it is difficult to use these methods in practical manufacturing applications. For conventional solid-state reactions, calcinations have to proceed under high temperatures, usually N800 °C, and over a long period of
⁎ Corresponding author. E-mail address: [email protected] (J.-G. Duh). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.07.017
time. However, the grain size increases with the temperature, and the lithium ion diffusion path increases, leading to electrochemical fading and the presence of undesirable impurities, such as NiO or LixNi1 − xO in the final product. Ye et al. [15] developed one-step solid-state reactions at ambient temperatures, in which these reactions essentially involved self-propagating solid-state metathesis of hydrated transition metal salts and NaOH, Na2S⋅9H2O, H2C2O4⋅2H2O, and Na2CO3. In order to decrease the calcination temperature, LiNi0.5Mn1.5O4 cathode material powder was synthesized by adding oxalic acid (H2C2O4˙2H2O) in this study. The electrochemical performance, including prolonged cycling and rate-ability of the LiNi0.5Mn1.5O4 cathode material during charge/discharge was also investigated. The cells were cycled within the potential range of 3.5 to 4.9 V at 1 C charge rate and 2 and 3 C discharge rates for up to 1000 charge/discharge cycles. 2. Experiment Appropriate amounts of LiCl, NiCl2⋅6H2O, MnCl2⋅4H2O (cation ratio of Li Ni Mn = 1.04:0.5:1.5), and 70 wt.% oxalic acid were thoroughly ball-mixed, and then ground for 0.5 h to ensure a complete reaction. The precursor was heated and stirred at 150 °C for 0.5 h on a hot plate. Finally, it was sintered at 400 °C for 3 h and then calcined at 700–800 °C for 10 h in air. The crystal structure of the fresh LiNi0.5Mn1.5O4 cathode material was identified by powder XRD (Rigaku, D/MAX-B, Japan) using Cu Kα radiation at 30 KV and 20 mA. An FE-SEM (7600F, JEOL, Japan) equipped with a liquid nitrogen-free SDD EDX (Oxford, Britain) were used for the electrode morphology observation and quantitative analysis, respectively. Fourier transform infrared spectrophotometer (FTIR) was also employed on a Perkin-Elmer using KBr pellet technique.
C.-Y. Lin et al. / Materials Letters 64 (2010) 2328–2330
The LiNi0.5Mn1.5O4 electrode sheets employed for electrochemical examinations were fabricated by mixing LiNi 0.5 Mn 1.5 O 4 powder with conductive carbon (super P) and binder (PVDF) at a weight ratio of 80:13:7 in N-methyl-2-pyrrolidinone (NMP). The cathode sheet was prepared by casting the slurry in Al foil and drying at 120 °C for 24 h in a vacuum. A Li metal disk was used as an anode and reference in the cell. A 2032 type cell was fabricated by combining the LiNi0.5Mn1.5O4 cathode and Li metal anode in a stainless steel button cell containing electrolyte, which was 1 M LiPF6 dissolved in a 1:1 mixture by volume of ethylene carbonate (EC) and dimethyl carbonate (DMC). The cells were assembled in an argon-protected glove box and were then cycled within the potential range of 3.5 to 4.9 V at different C rates for 1000 cycles at room temperature. 3. Results and discussion In this study, using a low-temperature solid-state method and adding 70 wt.% oxalic acid enabled the synthesis of an impurity-free LiNi0.5Mn1.5O4 cathode material powder. In the first step, the starting materials of LiCl, NiCl2·6H2O, MnCl2·4H2O, and 70 wt.% oxalic acid were mixed with a stirring rod and heated at 150 °C for 0.5 h on a hot plate. During heating at 150 °C, a slurry-like precursor was gradually formed, and an acid mist of HCl and H2O was emitted during the process on account of the metathesis reactions between the metal chlorides and oxalic acid. For the crystal water was released, the precursor formed solution gradually and the disadvantage of inhomogeneity for traditional solid-state method could be eliminated significantly. Oxalic acid formed a mixed precursor, which acts as substrate for the homogeneous distribution of the metal oxide phase. During calcination in air, the carbonaceous substrate was oxidized to CO2, leaving behind a divided oxide phase [16]. In the second step, the precursor was sintered at 400 °C for 3 h to destroy the organic framework and form a
Fig. 1. Element analysis of LiNi0.5Mn1.5O4 cathode material measured by EDX.
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nanocrystals products [17]. Finally, the LiNi0.5Mn1.5O4 cathode material powder was synthesized at 700–800 °C for 10 h. The presence of Cl as a residual element in the final product could possibly deteriorate the performance of the powder. To confirm the absence of any Cl element in the obtained powders, pristine LiNi0.5Mn1.5O4 powder was measured by EDX. Fig. 1 indicates that no Cl remaining in the powder. This apparently shows that the three-step heat treatment is an appropriate method for removing all of the Cl element in the final products to produce pure LiNi0.5Mn1.5O4 powder. With raising calcination temperature, there are some disadvantages, such as increasing a diffusion pathway of lithium ion and forming LixNi1 − xO as second phase. The formation of LixNi1 − xO deteriorates the electrochemical performance of the spinel LiNi0.5Mn1.5O4 material [18]. Fig. 2(a) shows an X-ray diffraction diagram for the LiNi0.5Mn1.5O4 pristine powder. No undesirable impurities, such as NiO or LixNi1 − xO, could be observed in the LiNi0.5Mn1.5O4 prepared by a low-temperature solid-state method. The corresponding XRD peaks for these impurities are usually close to the lines (222), (400), and (440). LiNi0.5Mn1.5O4 spinel has two different space groups, i.e. transition metal disorder Fd3m and the cation ordered P4332. LiNi0.5Mn1.5O4 with disordered Fd3m exhibits better rate-ability than that of ordered P4332 spinels due to the higher electronic and ionic conductivities [19]. However, the structure difference between these two space groups can hardly be observed by XRD due to the similar scattering factors of Ni and Mn. Fig. 2(b) shows FTIR spectra of LiNi0.5Mn1.5O4 cathode material at different calcinations temperature, and the space structure changed to Fd3m above 730 °C. In the consideration of particle size, this study adopts the calcination temperature of 730 °C.
Fig. 2. (a) X-ray diffraction pattern (b) FTIR spectra of LiNi0.5Mn1.5O4 pristine powder obtained by low-temperature solid-state method at different calcination temperature.
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C.-Y. Lin et al. / Materials Letters 64 (2010) 2328–2330
4. Conclusion Mixtures of LiCl, NiCl2 6H2O, and MnCl2 4H2O with 70 wt.% oxalic acid were employed by a low-temperature solid-state method to successfully synthesize impurity-free spinel-phase LiNi0.5Mn1.5O4 cathode material, exhibiting outstanding electrochemical properties. The initial capacity was 120 mAh/g and capacity retention maintained at 80% at RT after 1000 cycles. The XRD, FTIR spectra, and electrochemical property data for impurity-free LiNi0.5Mn1.5O4 with Fd3m structure revealed excellent electrochemical properties and stable cycleability.
References Fig. 3. Extended cyclability performance of LiNi0.5Mn1.5O4 with 70 wt.% oxalic acid at a charge rate of 1 C and discharge rate of 2 and 3 C (Morphology of the powders was also shown).
The cycle life is of great importance in lithium ion batteries. The discharge curves of the LiNi0.5Mn1.5O4 cathode materials at a charge rate of 1 C and discharge rate of 2 and 3 C, where 1 C = 146.5 mAhg− 1 at RT from 3.5 V to 4.9 V are presented Fig. 3. The morphology of LiNi0.5Mn1.5O4 was also indicated in Fig. 3 and the spherical-like morphology was about 300 nm. The theoretical capacity of LiNi0.5Mn1.5O4 cathode materials is 146.5 mAh/g and these cells deliver a discharge capacity about 120 mAh/g at RT. After 500 and 1000 charge/ discharge cycles, the loss of capacity is 8% and 20%, respectively. The excellent electrochemical properties are acceptable with regard to the commercial specifications, which prescribe that the loss of capacity should be less than 20% for 500 cycles under normal use [20]. The results demonstrated that forming impurity-free LiNi0.5Mn1.5O4 with Fd3m structure and nanometer-sized primary particle size synthesized by a low-temperature solid-state method was beneficial for enhancing the reversibility of the lithium ion insertion/extraction process and improving the electronic conductivity.
[1] Xianfa Zhang, Jing Liu, Haiying Yu, Guiling Yang, Jiawei Wang, Zijia Yu, et al. Electrochim Acta 2010;55:2414. [2] Arrebola JC, Caballero A, Hernan L, Morales J. J Power Sources 2008;180:852. [3] Fang HS, Wang ZX, Li XH, Guo HJ, Peng WJ. J Power Sources 2006;153:174. [4] Wu X, Kim SB. J Power Sources 2002;109:53. [5] Myung ST, Komaba S, Kumagai N, Yashiro H, Chung HT, Cho TH. Electrochim Acta 2002;47:2543. [6] Fan Y, Wang J, Tang Z, He W, Zhang. J Electrochim Acta 2007;52:3870. [7] Sun YK, Hong KJ, Prakash J, Amine K. Electrochem Commun 2002;4:344. [8] Sun YK, Yoon CS, Oh IH. Electrochim Acta 2003;48:503. [9] Arrebola J, Caballero A, Hernán L, Morales J, Castellón ER, Barrado JR. J Electrochem Soc 2007;154:A178. [10] Talyosef Y, Markovsky B, Salitra G, Aurbach D, Kim HJ, Choi S. J Power Sources 2005;146:664. [11] Xu HY, Xie S, Ding N, Liu BL, Shang Y, Chen CH. Electrochim Acta 2006;51:4352. [12] Alcantara R, Jaraba M, Lavela P, Tirado JL. Electrochim Acta 2002;47:1829. [13] Oh SW, Park SH, Kim JH, Bae YC, Sun YK. J Power Sources 2006;157:464. [14] Kim JH, Myung ST, Sun YK. Electrochim Acta 2004;49:219. [15] Ye XR, Jia DZ, Yu JQ, Xin XQ, Xue Z. Adv Mater 1999;11:941. [16] Patil AJ, Shinde MH, Potdar HS. Mater Chem Phys 2001;68:7. [17] Patil AJ, Shinde MH, Potdar HS. Mater Chem Phys 2001;68:7. [18] Santhanam R, Rambabu B. J Power Sources 2010;195:5442. [19] Kunduraci M, Amatucci GG. Electrochim Acta 2008;53:4193. [20] Patoux S, Sanniera L, Lignier H, Reynier Y, Bourbon C, Jouanneau S, et al. Electrochim Acta 2008;53:4137.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
LiNi0.5Mn1.5O4 cathode material by low-temperature solid-state method with excellent cycleability in lithium ion battery Chih-Yuan Lin a, Jenq-Gong Duh a,⁎, Chia-Haw Hsu b, Jin-Ming Chen b a b
Department of Materials Science and Engineering National Tsing-Hua University, Hsinchu, Taiwan Material and Chemical Research Laboratories, Industrial Technology Research Institute, Chutung, Taiwan
a r t i c l e
i n f o
Article history: Received 15 May 2010 Accepted 6 July 2010 Available online 17 July 2010 Keywords: Lithium ion battery Cathode material LiNi0.5Mn1.5O4
a b s t r a c t LiNi0.5Mn1.5O4 cathode material was synthesized from a mixture of LiCl, NiCl2 6H2O and MnCl2 4H2O with 70 wt.% oxalic acid by a low-temperature solid-state method. The calcination temperature was adjusted to form disorder Fd3m structure at 700–800 °C for 10 h. XRD patterns and FTIR spectroscopy showed that the LiNi0.5Mn1.5O4 cathode material exhibited an impurityfree spinel Fd3m structure. Electrochemical property results revealed that the LiNi0.5Mn1.5O4 cathode material charged at 1C rate to 4.9 V and discharged at 2 and 3 C to 3.5 V delivered initial capacity of 120 mAh/g and maintained a capacity retention over 80% at room temperature after 1000 charge/discharge cycles. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The increasing demands on high energy and high power Li-ion batteries for hybrid electric vehicle and power tools lead the researcher to investigate the high-voltage material [1]. Various developments have achieved potential ranges of 5 V in comparison with Li/Li+. Spinel LiMn2O4 is a possible alternative to replace the standard layered oxides (LiCoO2) because of its abundance, low cost, and environmental friendliness, yet several drawbacks have restricted its application to commercial batteries. The major defects of LiMn2O4 are the dissolution of Mn2+ in the electrolyte and Jahn–Teller distortion [2]. A common way to overcome the degradation of LiMn2O4 is to replace Mn with another transition metal. LiMxMn2xO4 is high-voltage cathode material, exhibiting plateaus at voltages above 4 V. Among these cathode materials, LiNi0.5Mn1.5O4 has received great attention owing to its good electrochemical performance and high operating voltage around 4.7 V [3–5]. However, its electrochemical performance dramatically degraded during prolonged charge/discharge cycling at a high C rate or cycling at an elevated temperature [6–10]. Since the manufacturing method for LiNi0.5Mn1.5O4 powder strongly influences its rateability performance and capacity retention, many synthesis methods have been developed, such as the sol–gel [11,12], ultrasonic spray pyrolysis [13], and molten salt [14]. However, they are too complicated and it is difficult to use these methods in practical manufacturing applications. For conventional solid-state reactions, calcinations have to proceed under high temperatures, usually N800 °C, and over a long period of
⁎ Corresponding author. E-mail address: [email protected] (J.-G. Duh). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.07.017
time. However, the grain size increases with the temperature, and the lithium ion diffusion path increases, leading to electrochemical fading and the presence of undesirable impurities, such as NiO or LixNi1 − xO in the final product. Ye et al. [15] developed one-step solid-state reactions at ambient temperatures, in which these reactions essentially involved self-propagating solid-state metathesis of hydrated transition metal salts and NaOH, Na2S⋅9H2O, H2C2O4⋅2H2O, and Na2CO3. In order to decrease the calcination temperature, LiNi0.5Mn1.5O4 cathode material powder was synthesized by adding oxalic acid (H2C2O4˙2H2O) in this study. The electrochemical performance, including prolonged cycling and rate-ability of the LiNi0.5Mn1.5O4 cathode material during charge/discharge was also investigated. The cells were cycled within the potential range of 3.5 to 4.9 V at 1 C charge rate and 2 and 3 C discharge rates for up to 1000 charge/discharge cycles. 2. Experiment Appropriate amounts of LiCl, NiCl2⋅6H2O, MnCl2⋅4H2O (cation ratio of Li Ni Mn = 1.04:0.5:1.5), and 70 wt.% oxalic acid were thoroughly ball-mixed, and then ground for 0.5 h to ensure a complete reaction. The precursor was heated and stirred at 150 °C for 0.5 h on a hot plate. Finally, it was sintered at 400 °C for 3 h and then calcined at 700–800 °C for 10 h in air. The crystal structure of the fresh LiNi0.5Mn1.5O4 cathode material was identified by powder XRD (Rigaku, D/MAX-B, Japan) using Cu Kα radiation at 30 KV and 20 mA. An FE-SEM (7600F, JEOL, Japan) equipped with a liquid nitrogen-free SDD EDX (Oxford, Britain) were used for the electrode morphology observation and quantitative analysis, respectively. Fourier transform infrared spectrophotometer (FTIR) was also employed on a Perkin-Elmer using KBr pellet technique.
C.-Y. Lin et al. / Materials Letters 64 (2010) 2328–2330
The LiNi0.5Mn1.5O4 electrode sheets employed for electrochemical examinations were fabricated by mixing LiNi 0.5 Mn 1.5 O 4 powder with conductive carbon (super P) and binder (PVDF) at a weight ratio of 80:13:7 in N-methyl-2-pyrrolidinone (NMP). The cathode sheet was prepared by casting the slurry in Al foil and drying at 120 °C for 24 h in a vacuum. A Li metal disk was used as an anode and reference in the cell. A 2032 type cell was fabricated by combining the LiNi0.5Mn1.5O4 cathode and Li metal anode in a stainless steel button cell containing electrolyte, which was 1 M LiPF6 dissolved in a 1:1 mixture by volume of ethylene carbonate (EC) and dimethyl carbonate (DMC). The cells were assembled in an argon-protected glove box and were then cycled within the potential range of 3.5 to 4.9 V at different C rates for 1000 cycles at room temperature. 3. Results and discussion In this study, using a low-temperature solid-state method and adding 70 wt.% oxalic acid enabled the synthesis of an impurity-free LiNi0.5Mn1.5O4 cathode material powder. In the first step, the starting materials of LiCl, NiCl2·6H2O, MnCl2·4H2O, and 70 wt.% oxalic acid were mixed with a stirring rod and heated at 150 °C for 0.5 h on a hot plate. During heating at 150 °C, a slurry-like precursor was gradually formed, and an acid mist of HCl and H2O was emitted during the process on account of the metathesis reactions between the metal chlorides and oxalic acid. For the crystal water was released, the precursor formed solution gradually and the disadvantage of inhomogeneity for traditional solid-state method could be eliminated significantly. Oxalic acid formed a mixed precursor, which acts as substrate for the homogeneous distribution of the metal oxide phase. During calcination in air, the carbonaceous substrate was oxidized to CO2, leaving behind a divided oxide phase [16]. In the second step, the precursor was sintered at 400 °C for 3 h to destroy the organic framework and form a
Fig. 1. Element analysis of LiNi0.5Mn1.5O4 cathode material measured by EDX.
2329
nanocrystals products [17]. Finally, the LiNi0.5Mn1.5O4 cathode material powder was synthesized at 700–800 °C for 10 h. The presence of Cl as a residual element in the final product could possibly deteriorate the performance of the powder. To confirm the absence of any Cl element in the obtained powders, pristine LiNi0.5Mn1.5O4 powder was measured by EDX. Fig. 1 indicates that no Cl remaining in the powder. This apparently shows that the three-step heat treatment is an appropriate method for removing all of the Cl element in the final products to produce pure LiNi0.5Mn1.5O4 powder. With raising calcination temperature, there are some disadvantages, such as increasing a diffusion pathway of lithium ion and forming LixNi1 − xO as second phase. The formation of LixNi1 − xO deteriorates the electrochemical performance of the spinel LiNi0.5Mn1.5O4 material [18]. Fig. 2(a) shows an X-ray diffraction diagram for the LiNi0.5Mn1.5O4 pristine powder. No undesirable impurities, such as NiO or LixNi1 − xO, could be observed in the LiNi0.5Mn1.5O4 prepared by a low-temperature solid-state method. The corresponding XRD peaks for these impurities are usually close to the lines (222), (400), and (440). LiNi0.5Mn1.5O4 spinel has two different space groups, i.e. transition metal disorder Fd3m and the cation ordered P4332. LiNi0.5Mn1.5O4 with disordered Fd3m exhibits better rate-ability than that of ordered P4332 spinels due to the higher electronic and ionic conductivities [19]. However, the structure difference between these two space groups can hardly be observed by XRD due to the similar scattering factors of Ni and Mn. Fig. 2(b) shows FTIR spectra of LiNi0.5Mn1.5O4 cathode material at different calcinations temperature, and the space structure changed to Fd3m above 730 °C. In the consideration of particle size, this study adopts the calcination temperature of 730 °C.
Fig. 2. (a) X-ray diffraction pattern (b) FTIR spectra of LiNi0.5Mn1.5O4 pristine powder obtained by low-temperature solid-state method at different calcination temperature.
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C.-Y. Lin et al. / Materials Letters 64 (2010) 2328–2330
4. Conclusion Mixtures of LiCl, NiCl2 6H2O, and MnCl2 4H2O with 70 wt.% oxalic acid were employed by a low-temperature solid-state method to successfully synthesize impurity-free spinel-phase LiNi0.5Mn1.5O4 cathode material, exhibiting outstanding electrochemical properties. The initial capacity was 120 mAh/g and capacity retention maintained at 80% at RT after 1000 cycles. The XRD, FTIR spectra, and electrochemical property data for impurity-free LiNi0.5Mn1.5O4 with Fd3m structure revealed excellent electrochemical properties and stable cycleability.
References Fig. 3. Extended cyclability performance of LiNi0.5Mn1.5O4 with 70 wt.% oxalic acid at a charge rate of 1 C and discharge rate of 2 and 3 C (Morphology of the powders was also shown).
The cycle life is of great importance in lithium ion batteries. The discharge curves of the LiNi0.5Mn1.5O4 cathode materials at a charge rate of 1 C and discharge rate of 2 and 3 C, where 1 C = 146.5 mAhg− 1 at RT from 3.5 V to 4.9 V are presented Fig. 3. The morphology of LiNi0.5Mn1.5O4 was also indicated in Fig. 3 and the spherical-like morphology was about 300 nm. The theoretical capacity of LiNi0.5Mn1.5O4 cathode materials is 146.5 mAh/g and these cells deliver a discharge capacity about 120 mAh/g at RT. After 500 and 1000 charge/ discharge cycles, the loss of capacity is 8% and 20%, respectively. The excellent electrochemical properties are acceptable with regard to the commercial specifications, which prescribe that the loss of capacity should be less than 20% for 500 cycles under normal use [20]. The results demonstrated that forming impurity-free LiNi0.5Mn1.5O4 with Fd3m structure and nanometer-sized primary particle size synthesized by a low-temperature solid-state method was beneficial for enhancing the reversibility of the lithium ion insertion/extraction process and improving the electronic conductivity.
[1] Xianfa Zhang, Jing Liu, Haiying Yu, Guiling Yang, Jiawei Wang, Zijia Yu, et al. Electrochim Acta 2010;55:2414. [2] Arrebola JC, Caballero A, Hernan L, Morales J. J Power Sources 2008;180:852. [3] Fang HS, Wang ZX, Li XH, Guo HJ, Peng WJ. J Power Sources 2006;153:174. [4] Wu X, Kim SB. J Power Sources 2002;109:53. [5] Myung ST, Komaba S, Kumagai N, Yashiro H, Chung HT, Cho TH. Electrochim Acta 2002;47:2543. [6] Fan Y, Wang J, Tang Z, He W, Zhang. J Electrochim Acta 2007;52:3870. [7] Sun YK, Hong KJ, Prakash J, Amine K. Electrochem Commun 2002;4:344. [8] Sun YK, Yoon CS, Oh IH. Electrochim Acta 2003;48:503. [9] Arrebola J, Caballero A, Hernán L, Morales J, Castellón ER, Barrado JR. J Electrochem Soc 2007;154:A178. [10] Talyosef Y, Markovsky B, Salitra G, Aurbach D, Kim HJ, Choi S. J Power Sources 2005;146:664. [11] Xu HY, Xie S, Ding N, Liu BL, Shang Y, Chen CH. Electrochim Acta 2006;51:4352. [12] Alcantara R, Jaraba M, Lavela P, Tirado JL. Electrochim Acta 2002;47:1829. [13] Oh SW, Park SH, Kim JH, Bae YC, Sun YK. J Power Sources 2006;157:464. [14] Kim JH, Myung ST, Sun YK. Electrochim Acta 2004;49:219. [15] Ye XR, Jia DZ, Yu JQ, Xin XQ, Xue Z. Adv Mater 1999;11:941. [16] Patil AJ, Shinde MH, Potdar HS. Mater Chem Phys 2001;68:7. [17] Patil AJ, Shinde MH, Potdar HS. Mater Chem Phys 2001;68:7. [18] Santhanam R, Rambabu B. J Power Sources 2010;195:5442. [19] Kunduraci M, Amatucci GG. Electrochim Acta 2008;53:4193. [20] Patoux S, Sanniera L, Lignier H, Reynier Y, Bourbon C, Jouanneau S, et al. Electrochim Acta 2008;53:4137.