中国物理B ›› 2021, Vol. 30 ›› Issue (7): 73101-073101.doi: 10.1088/1674-1056/abeeeb

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A strategy to improve the electrochemical performance of Ni-rich positive electrodes: Na/F-co-doped LiNi0.6Mn0.2Co0.2O2

Hui Wan(万惠)1, Zhixiao Liu(刘智骁)1, Guangdong Liu(刘广东)2, Shuaiyu Yi(易帅玉)2, Fei Gao(高飞)3, Huiqiu Deng(邓辉球)2, Dingwang Yuan(袁定旺)1, and Wangyu Hu(胡望宇)1,†   

  1. 1 College of Materials Science and Engineering, Hunan University, Changsha 410082, China;
    2 School of Physics and Electronics, Hunan University, Changsha 410082, China;
    3 Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109, USA
  • 收稿日期:2021-01-06 修回日期:2021-02-20 接受日期:2021-03-16 出版日期:2021-06-22 发布日期:2021-06-26
  • 通讯作者: Wangyu Hu E-mail:wyuhu@hnu.edu.cn
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 51802092 and 51771073) and the Fundamental Research Funds for the Central Universities, China.

A strategy to improve the electrochemical performance of Ni-rich positive electrodes: Na/F-co-doped LiNi0.6Mn0.2Co0.2O2

Hui Wan(万惠)1, Zhixiao Liu(刘智骁)1, Guangdong Liu(刘广东)2, Shuaiyu Yi(易帅玉)2, Fei Gao(高飞)3, Huiqiu Deng(邓辉球)2, Dingwang Yuan(袁定旺)1, and Wangyu Hu(胡望宇)1,†   

  1. 1 College of Materials Science and Engineering, Hunan University, Changsha 410082, China;
    2 School of Physics and Electronics, Hunan University, Changsha 410082, China;
    3 Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109, USA
  • Received:2021-01-06 Revised:2021-02-20 Accepted:2021-03-16 Online:2021-06-22 Published:2021-06-26
  • Contact: Wangyu Hu E-mail:wyuhu@hnu.edu.cn
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 51802092 and 51771073) and the Fundamental Research Funds for the Central Universities, China.

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摘要： Ni-rich layered lithium transition metal oxides LiNixMnyCozO2 (1 - y-z ≥ 0.6) are promising candidates for cathode materials, but their practical applications are hindered by high-voltage instability and fast capacity fading. Using density functional theory calculations, we demonstrate that Na-, F-doping, and Na/F-co-doping can stabilize the structure and result into a higher open circuit voltage than pristine LiNi0.6Mn0.2Co0.2O2 (NMC622) during the charging process, which may attain greater discharge capacity. F doping may inhibit the diffusion of Li ions at the beginning and end of charging; Na doping may improve Li ion diffusion due to the increase in Li layer spacing, consistent with prior experiments. Na/F-co-doping into NMC622 promotes rate performance and reduces irreversible phase transitions for two reasons: (i) a synergistic effect between Na and F can effectively restrain the Ni/Li mixing and then enhances the mobility of Li ions and (ii) Ni/Li mixing hinders the Ni ions to migrate into Li layers and thus, stabilizes the structure. This study proposes that a layer cathode material with high electrochemical performance can be achieved via rational dopant modification, which is a promising strategy for designing efficient Li ion batteries.

关键词: Li ion batteries, ion diffusion, Na/F-co-doping, first-principles calculations

Abstract: Ni-rich layered lithium transition metal oxides LiNixMnyCozO2 (1 - y-z ≥ 0.6) are promising candidates for cathode materials, but their practical applications are hindered by high-voltage instability and fast capacity fading. Using density functional theory calculations, we demonstrate that Na-, F-doping, and Na/F-co-doping can stabilize the structure and result into a higher open circuit voltage than pristine LiNi0.6Mn0.2Co0.2O2 (NMC622) during the charging process, which may attain greater discharge capacity. F doping may inhibit the diffusion of Li ions at the beginning and end of charging; Na doping may improve Li ion diffusion due to the increase in Li layer spacing, consistent with prior experiments. Na/F-co-doping into NMC622 promotes rate performance and reduces irreversible phase transitions for two reasons: (i) a synergistic effect between Na and F can effectively restrain the Ni/Li mixing and then enhances the mobility of Li ions and (ii) Ni/Li mixing hinders the Ni ions to migrate into Li layers and thus, stabilizes the structure. This study proposes that a layer cathode material with high electrochemical performance can be achieved via rational dopant modification, which is a promising strategy for designing efficient Li ion batteries.

Key words: Li ion batteries, ion diffusion, Na/F-co-doping, first-principles calculations

中图分类号:  (Ab initio calculations)

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