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Electrochemical studies on mixtures of LiNi0.8Co0.17Al0.03O2 and LiCoO2 cathode materials for lithium ion batteries
Solid State Communications 133 (2005) 687–690 www.elsevier.com/locate/ssc
Electrochemical studies on mixtures of LiNi0.8Co0.17Al0.03O2 and LiCoO2 cathode materials for lithium ion batteries C.H. Lina, C.H. Shena, A.A.M. Princeb, S.M. Huanga, R.S. Liub,* a
SYNergy Scien Tech Corporation, Science-based Industrial Park, Hsinchu 300, Taiwan, ROC b Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, ROC Received 8 November 2004; accepted 29 November 2004 by C.N.R. Rao Available online 6 January 2005
Abstract Detailed electrochemical investigations have been carried out on LiNi0.8Co0.17Al0.03O2 as cathode materials for lithium ion batteries in the potential range of 2.8–4.3 V. This sample showed an initial discharge capacity of 186 mAh/g which corresponds to 67% of its theoretical capacity. The effect of addition of LiCoO2 to LiNi0.8Co0.17Al0.03O2 in the ratio 10:90, 30:70, 50:50 has been studied. The results showed that the addition of LiCoO2 has improved the working voltage of the cell. In addition, the percentage retention (95%) of the cell is significantly increased in the composition ratio 50:50. q 2004 Elsevier Ltd. All rights reserved. PACS: 82.47.Aa; 52.80.Ks Keywords: B. Lithium ion batteries; C. Cathode material; E. Electric charge and discharge
1. Introduction In the recent years, lithium-ion batteries has become alternative power sources for various portable electronic devices such as mobile phones, laptop computers, electric vehicles etc. The reason behind the versatile usage of lithium ion batteries is due to its high energy density compared with other rechargeable batteries. There are many lithium compounds such as LiCoO2, LiNiO2, LiMn2O4, LiFePO4 etc. have been investigated as cathode material in the lithium ion batteries [1,2]. Among these compounds LiCoO2 a layered structured compound has been used currently as cathode material in the commercially available lithium ion batteries [3]. However, only 50% of its theoretical capacity (140 mAh/g) could be utilized effectively in the voltage range 3–4.25 V. In order to obtain, a
* Corresponding author. Tel.: C886 2 23690152x148; fax: C886 2 23636359. E-mail address: [email protected] (R.S. Liu). 0038-1098/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2004.11.052
capacity higher than 140 mAh/g in LiCoO2, the cell should be charged higher than 4.2 V [4]. However, charging at higher voltage normally causes capacity fade due to structural changes. During charging, LiCoO2 experiences a lattice expansion in its c-axis and oxygen is expelled out from the lattice due to the interaction of the electrode surface with electrolyte [5]. This results in the decomposition of electrolyte and causing safety problem in the cell. Many authors have investigated the chemical instability of LiCoO2 structure and its reactivity towards the electrolyte. Based on their study, the increase capacity and decrease in capacity fade of LiCoO2 cathodes is achieved by doping of metal ions for cobalt or surface modification with chemically more stable or inert materials [6,7]. For example, 65% of its theoretical capacity is achieved when nickel is doped for Co in LiCoO2. The surface modification of LiCoO2 with metal oxides such Al2O3, TiO2 and ZrO2 has been studied by Cho et al. [8]. The electrochemical study on the metal oxide coated LiCoO2 resulted in good capacity retention than uncoated LiCoO2 when the cell is cycled above 4.2 V.
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C.H. Lin et al. / Solid State Communications 133 (2005) 687–690
Table 1 Discharge capacity values for LiNi0.8Co0.17Al0.03O2, mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2 under different discharge rates Cathode material LiNi0.8Co0.17Al0.03O2 LiNi0.8Co0.17Al0.03O2C10% LiCoO2 LiNi0.8Co0.17Al0.03O2C30% LiCoO2 LiNi0.8Co0.17Al0.03O2C50% LiCoO2
Capacity (mAh/g) 0.1 C
0.2 C
0.5 C
1C
183.9 175.8 171.5 160.1
175.3 170.2 167.8 156.6
165.4 163.7 162.3 151.8
158.5 156.1 157.3 148.1
In the present study, we have investigated a detailed electrochemical performance of LiNi0.8Co0.17Al0.03O2 under various conditions. Besides, the electrochemical performance of a mixture containing various amount of LiNi0.8Co0.17Al0.03O2 and LiCoO2 has been studied. The results are discussed in this paper.
(dimethyl carbonate) in a 1:1 volume ratio. A polymer membrane was used as separator. The coin-cells were assembled in an argon filled glove box. The cells were galvanostatically cycled at room temperature (MACCOR 4000) in the range 2.8–4.3 V [9]. The same procedure has been followed for the cathode film consisting of mixture of LiNi0.8Co0.17Al0.03O2 and LiCoO2 in the ratio 90:10, 70:20, 50:50 wt%.
2. Experimental The LiNi0.8Co0.17Al0.03O2 sample was obtained from Lithium Ion Business Unit, Rechargeable Battery Company, Matsushita Battery Industrial Co., Ltd., Japan. Electrochemical studies were performed, by assembling coin cells using Li metal as anode. Cathode films were prepared by mixing 94 wt% active material, 3 wt% conducting carbon, 3 wt% binder (consists of N-methyl-2-pyrrolidone (NMP) and polyvinylidene difluoride (PVDF) in the ratio of 9:1). All ingredients were thoroughly mixed in a mechanical stirrer at w3000 rpm for 1 h. The resultant slurry was coated uniformly onto an aluminum foil (used as current collector), which was dried at 75 8C for 1 h in a vacuum oven and further dried at 110 8C for 1 h. The cathode film was subjected to roll press and discs of size 1.3 cm diameter were punched out. The average active material present in each disc was ca. 23 mg/cm2. The electrolyte consists of 1 M LiPF6 (Merck) in EC (ethylene carbonate) and DMC
Fig. 1. First charge/discharge curve for the pure LiNi0.8Co0.17Al0.03O2 coin-cells cycled between 3.0 and 4.3 V at room temperature using 0.05 C rate.
3. Results and discussion Electrochemical performance on pristine LiNi0.8Co0.17Al0.03O2 sample is evaluated by cycling the cells from 2.8 to 4.3 V. The cells exhibited an open circuit potential of around 3.4 V vs. Li metal. The first charge and discharge values at 0.05 C rate are 203 and 186 mAh/g as shown in Fig. 1. A comparison of the first discharge capacity with its theoretical capacity (277 mAh/g) confirmed that the cell delivered about 67% of its theoretical capacity [9]. This value is higher than LiCoO2 where only 50% theoretical capacity is achieved. For the first cycle the percentage irreversibility is calculated using Eq. (1). % irreversibility Z
ðcharge capacity discharge capacityÞ !100 charge capacity
(1)
Fig. 2. First charge discharge curve for 90 wt% LiNi0.8Co0.17Al0.03O2 and LiCoO2 10 wt% coin-cells cycled between 3.0 and 4.3 V at room temperature using 0.05 C rate.
C.H. Lin et al. / Solid State Communications 133 (2005) 687–690
Fig. 3. The working voltage vs. discharge rate for pristine LiNi0.8Co0.17Al0.03O2, LiCoO2 and the mixture of these two samples.
A value of 9.0% is obtained which shows a good cyclability of LiNi0.8Co0.17Al0.03O2 sample. The Table 1 compares discharge capacity of LiNi0.8Co0.17Al0.03O2 under different discharge rates the capacity. Based on the Table 1 it is understood that as the discharge rate increases the specific capacity value decreases. Fig. 2 shows the first charge and discharge curve of the cathode material containing 90% LiNi0.8Co0.17Al0.03O2 and 10% LiCoO2 at 0.05 C rate. The first charge and discharge capacities are 197.7 and 177.7 mAh/g. This value is slightly lower than pure LiNi0.8Co0.17Al0.03O2; however, the irreversible capacity is increased from 9.0 to 9.7% when 10% LiCoO2 is added. More investigations are performed by varying LiNi0.8Co0.17Al0.03O2:LiCoO2 in the ratio of 70:30 and 50:50 in terms of %wt. The first charge/discharge for the ration 70:30 are 189.2 and 172.2 mAh/g. The values are 177.5 and 161.4 mAh/g for the ratio 50:50. Based on the experimental values it is inferred that as the amount of LiCoO2 is increased there is a noticeable decrease in the
689
capacity value. However, it is interesting to observe that the irreversible capacity value is not altered significantly with varying the ratio of LiNi0.8Co0.17Al0.03O2 and LiCoO2. The capacity values under different discharge rates for mixture containing 10–50 wt% of LiCoO2 is given in Table 1. In all experiments, the working voltages of the cells are measured at different discharge rates and the values are shown in Fig. 3. There is a significant increase in the working voltage from 3.79 to 3.88 V on varying the amount of LiCoO2. Nevertheless, the pure LiCoO2 showed a higher working voltage (3.96 V) than the mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2. The cycling behavior of the cathode mixture consists of LiNi0.8Co0.17Al0.03O2 and LiCoO2 were evaluated in the voltage range 3–4.3 V. The percentage retention was calculated by taking the ratio of the capacity at a particular cycle number with the initial capacity. The capacity retention vs. cycle number is plotted in Fig. 4 for the pristine samples and the mixture containing these two materials up to 20 cycles. The result looks very interesting for the mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2 in the ratio of 50:50 wt%, which showed a much higher retention value of 93.6% after 20 cycles. This value could be due to the synergistic effect of LiCoO2 on LiNi0.8Co0.17Al0.03O2 samples.
4. Conclusions The electrochemical study on the pristine LiNi0.8Co0.17Al0.03O2 sample showed that about 67% of its theoretical capacity. This sample showed a good irreversibility upon cycling the cells in the potential range of 2.8–4.3 V. The electrochemical performance of LiNi0.8Co0.17Al0.03O2 is increased by the addition of LiCoO2. An excellent cycle life is observed on the composition of 50:50 wt%.
Acknowledgements Two of the authors (AAMP and RSL) thank National Science Council (NSC) for the financial support under grant number NSC 93-2113-M-002-006.
References
Fig. 4. The % retention vs. cycle no for pristine LiNi0.8Co0.17Al0.03O2 and the mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2.
[1] J.M. Tarascon, M. Armand, Nature 143 (2001) 359. [2] M. Thackeray, Nature Mater. 1 (2002) 81. [3] D. Carlier, I. Saadoune, M. Menetrier, C. Delmas, J. Electrochem. Soc. 149 (2002) 1310. [4] M. Zou, M. Yoshio, S. Gopukumar, J. Yamaki, Chem. Mater. 15 (2003) 4699. [5] S. Venkataraman, Y. Shin, A. Manthiram, Electrochem. SolidState Lett. 6 (2003) 9.
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C.H. Lin et al. / Solid State Communications 133 (2005) 687–690
[6] Z. Chen, J.R. Dahn, Electrochem. Solid-State Lett. 6 (2003) 221. [7] A.M. Kannan, L. Rabenberg, A. Manthiram, Electrochem. Solid-State Lett. 6 (2003) 16.
[8] J. Cho, C. Kim, B. Park, J. Electrochem. Soc. 148 (2001) 1110. [9] A.A.M. Prince, S. Mylswamy, C.Y. Wang, S.C. Chang, R.S. Liu, C.H. Lin, Y.K. Lin, C.H. Shen, S.M. Huang, J.F. Lee, Solid State Commun. 132 (2004) 273.
Electrochemical studies on mixtures of LiNi0.8Co0.17Al0.03O2 and LiCoO2 cathode materials for lithium ion batteries C.H. Lina, C.H. Shena, A.A.M. Princeb, S.M. Huanga, R.S. Liub,* a
SYNergy Scien Tech Corporation, Science-based Industrial Park, Hsinchu 300, Taiwan, ROC b Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, ROC Received 8 November 2004; accepted 29 November 2004 by C.N.R. Rao Available online 6 January 2005
Abstract Detailed electrochemical investigations have been carried out on LiNi0.8Co0.17Al0.03O2 as cathode materials for lithium ion batteries in the potential range of 2.8–4.3 V. This sample showed an initial discharge capacity of 186 mAh/g which corresponds to 67% of its theoretical capacity. The effect of addition of LiCoO2 to LiNi0.8Co0.17Al0.03O2 in the ratio 10:90, 30:70, 50:50 has been studied. The results showed that the addition of LiCoO2 has improved the working voltage of the cell. In addition, the percentage retention (95%) of the cell is significantly increased in the composition ratio 50:50. q 2004 Elsevier Ltd. All rights reserved. PACS: 82.47.Aa; 52.80.Ks Keywords: B. Lithium ion batteries; C. Cathode material; E. Electric charge and discharge
1. Introduction In the recent years, lithium-ion batteries has become alternative power sources for various portable electronic devices such as mobile phones, laptop computers, electric vehicles etc. The reason behind the versatile usage of lithium ion batteries is due to its high energy density compared with other rechargeable batteries. There are many lithium compounds such as LiCoO2, LiNiO2, LiMn2O4, LiFePO4 etc. have been investigated as cathode material in the lithium ion batteries [1,2]. Among these compounds LiCoO2 a layered structured compound has been used currently as cathode material in the commercially available lithium ion batteries [3]. However, only 50% of its theoretical capacity (140 mAh/g) could be utilized effectively in the voltage range 3–4.25 V. In order to obtain, a
* Corresponding author. Tel.: C886 2 23690152x148; fax: C886 2 23636359. E-mail address: [email protected] (R.S. Liu). 0038-1098/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2004.11.052
capacity higher than 140 mAh/g in LiCoO2, the cell should be charged higher than 4.2 V [4]. However, charging at higher voltage normally causes capacity fade due to structural changes. During charging, LiCoO2 experiences a lattice expansion in its c-axis and oxygen is expelled out from the lattice due to the interaction of the electrode surface with electrolyte [5]. This results in the decomposition of electrolyte and causing safety problem in the cell. Many authors have investigated the chemical instability of LiCoO2 structure and its reactivity towards the electrolyte. Based on their study, the increase capacity and decrease in capacity fade of LiCoO2 cathodes is achieved by doping of metal ions for cobalt or surface modification with chemically more stable or inert materials [6,7]. For example, 65% of its theoretical capacity is achieved when nickel is doped for Co in LiCoO2. The surface modification of LiCoO2 with metal oxides such Al2O3, TiO2 and ZrO2 has been studied by Cho et al. [8]. The electrochemical study on the metal oxide coated LiCoO2 resulted in good capacity retention than uncoated LiCoO2 when the cell is cycled above 4.2 V.
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C.H. Lin et al. / Solid State Communications 133 (2005) 687–690
Table 1 Discharge capacity values for LiNi0.8Co0.17Al0.03O2, mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2 under different discharge rates Cathode material LiNi0.8Co0.17Al0.03O2 LiNi0.8Co0.17Al0.03O2C10% LiCoO2 LiNi0.8Co0.17Al0.03O2C30% LiCoO2 LiNi0.8Co0.17Al0.03O2C50% LiCoO2
Capacity (mAh/g) 0.1 C
0.2 C
0.5 C
1C
183.9 175.8 171.5 160.1
175.3 170.2 167.8 156.6
165.4 163.7 162.3 151.8
158.5 156.1 157.3 148.1
In the present study, we have investigated a detailed electrochemical performance of LiNi0.8Co0.17Al0.03O2 under various conditions. Besides, the electrochemical performance of a mixture containing various amount of LiNi0.8Co0.17Al0.03O2 and LiCoO2 has been studied. The results are discussed in this paper.
(dimethyl carbonate) in a 1:1 volume ratio. A polymer membrane was used as separator. The coin-cells were assembled in an argon filled glove box. The cells were galvanostatically cycled at room temperature (MACCOR 4000) in the range 2.8–4.3 V [9]. The same procedure has been followed for the cathode film consisting of mixture of LiNi0.8Co0.17Al0.03O2 and LiCoO2 in the ratio 90:10, 70:20, 50:50 wt%.
2. Experimental The LiNi0.8Co0.17Al0.03O2 sample was obtained from Lithium Ion Business Unit, Rechargeable Battery Company, Matsushita Battery Industrial Co., Ltd., Japan. Electrochemical studies were performed, by assembling coin cells using Li metal as anode. Cathode films were prepared by mixing 94 wt% active material, 3 wt% conducting carbon, 3 wt% binder (consists of N-methyl-2-pyrrolidone (NMP) and polyvinylidene difluoride (PVDF) in the ratio of 9:1). All ingredients were thoroughly mixed in a mechanical stirrer at w3000 rpm for 1 h. The resultant slurry was coated uniformly onto an aluminum foil (used as current collector), which was dried at 75 8C for 1 h in a vacuum oven and further dried at 110 8C for 1 h. The cathode film was subjected to roll press and discs of size 1.3 cm diameter were punched out. The average active material present in each disc was ca. 23 mg/cm2. The electrolyte consists of 1 M LiPF6 (Merck) in EC (ethylene carbonate) and DMC
Fig. 1. First charge/discharge curve for the pure LiNi0.8Co0.17Al0.03O2 coin-cells cycled between 3.0 and 4.3 V at room temperature using 0.05 C rate.
3. Results and discussion Electrochemical performance on pristine LiNi0.8Co0.17Al0.03O2 sample is evaluated by cycling the cells from 2.8 to 4.3 V. The cells exhibited an open circuit potential of around 3.4 V vs. Li metal. The first charge and discharge values at 0.05 C rate are 203 and 186 mAh/g as shown in Fig. 1. A comparison of the first discharge capacity with its theoretical capacity (277 mAh/g) confirmed that the cell delivered about 67% of its theoretical capacity [9]. This value is higher than LiCoO2 where only 50% theoretical capacity is achieved. For the first cycle the percentage irreversibility is calculated using Eq. (1). % irreversibility Z
ðcharge capacity discharge capacityÞ !100 charge capacity
(1)
Fig. 2. First charge discharge curve for 90 wt% LiNi0.8Co0.17Al0.03O2 and LiCoO2 10 wt% coin-cells cycled between 3.0 and 4.3 V at room temperature using 0.05 C rate.
C.H. Lin et al. / Solid State Communications 133 (2005) 687–690
Fig. 3. The working voltage vs. discharge rate for pristine LiNi0.8Co0.17Al0.03O2, LiCoO2 and the mixture of these two samples.
A value of 9.0% is obtained which shows a good cyclability of LiNi0.8Co0.17Al0.03O2 sample. The Table 1 compares discharge capacity of LiNi0.8Co0.17Al0.03O2 under different discharge rates the capacity. Based on the Table 1 it is understood that as the discharge rate increases the specific capacity value decreases. Fig. 2 shows the first charge and discharge curve of the cathode material containing 90% LiNi0.8Co0.17Al0.03O2 and 10% LiCoO2 at 0.05 C rate. The first charge and discharge capacities are 197.7 and 177.7 mAh/g. This value is slightly lower than pure LiNi0.8Co0.17Al0.03O2; however, the irreversible capacity is increased from 9.0 to 9.7% when 10% LiCoO2 is added. More investigations are performed by varying LiNi0.8Co0.17Al0.03O2:LiCoO2 in the ratio of 70:30 and 50:50 in terms of %wt. The first charge/discharge for the ration 70:30 are 189.2 and 172.2 mAh/g. The values are 177.5 and 161.4 mAh/g for the ratio 50:50. Based on the experimental values it is inferred that as the amount of LiCoO2 is increased there is a noticeable decrease in the
689
capacity value. However, it is interesting to observe that the irreversible capacity value is not altered significantly with varying the ratio of LiNi0.8Co0.17Al0.03O2 and LiCoO2. The capacity values under different discharge rates for mixture containing 10–50 wt% of LiCoO2 is given in Table 1. In all experiments, the working voltages of the cells are measured at different discharge rates and the values are shown in Fig. 3. There is a significant increase in the working voltage from 3.79 to 3.88 V on varying the amount of LiCoO2. Nevertheless, the pure LiCoO2 showed a higher working voltage (3.96 V) than the mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2. The cycling behavior of the cathode mixture consists of LiNi0.8Co0.17Al0.03O2 and LiCoO2 were evaluated in the voltage range 3–4.3 V. The percentage retention was calculated by taking the ratio of the capacity at a particular cycle number with the initial capacity. The capacity retention vs. cycle number is plotted in Fig. 4 for the pristine samples and the mixture containing these two materials up to 20 cycles. The result looks very interesting for the mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2 in the ratio of 50:50 wt%, which showed a much higher retention value of 93.6% after 20 cycles. This value could be due to the synergistic effect of LiCoO2 on LiNi0.8Co0.17Al0.03O2 samples.
4. Conclusions The electrochemical study on the pristine LiNi0.8Co0.17Al0.03O2 sample showed that about 67% of its theoretical capacity. This sample showed a good irreversibility upon cycling the cells in the potential range of 2.8–4.3 V. The electrochemical performance of LiNi0.8Co0.17Al0.03O2 is increased by the addition of LiCoO2. An excellent cycle life is observed on the composition of 50:50 wt%.
Acknowledgements Two of the authors (AAMP and RSL) thank National Science Council (NSC) for the financial support under grant number NSC 93-2113-M-002-006.
References
Fig. 4. The % retention vs. cycle no for pristine LiNi0.8Co0.17Al0.03O2 and the mixture containing LiNi0.8Co0.17Al0.03O2 and LiCoO2.
[1] J.M. Tarascon, M. Armand, Nature 143 (2001) 359. [2] M. Thackeray, Nature Mater. 1 (2002) 81. [3] D. Carlier, I. Saadoune, M. Menetrier, C. Delmas, J. Electrochem. Soc. 149 (2002) 1310. [4] M. Zou, M. Yoshio, S. Gopukumar, J. Yamaki, Chem. Mater. 15 (2003) 4699. [5] S. Venkataraman, Y. Shin, A. Manthiram, Electrochem. SolidState Lett. 6 (2003) 9.
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C.H. Lin et al. / Solid State Communications 133 (2005) 687–690
[6] Z. Chen, J.R. Dahn, Electrochem. Solid-State Lett. 6 (2003) 221. [7] A.M. Kannan, L. Rabenberg, A. Manthiram, Electrochem. Solid-State Lett. 6 (2003) 16.
[8] J. Cho, C. Kim, B. Park, J. Electrochem. Soc. 148 (2001) 1110. [9] A.A.M. Prince, S. Mylswamy, C.Y. Wang, S.C. Chang, R.S. Liu, C.H. Lin, Y.K. Lin, C.H. Shen, S.M. Huang, J.F. Lee, Solid State Commun. 132 (2004) 273.