Significance of Al doping for excellent electrochemical performance of LiNi0.98Co0.02O2 cathode materials

Abstract

Ni-rich layered oxides materials, such as LiNixCoyO2 (NC, x ≥ 0.8, x + y = 1), are one of the most considerable potential materials in lithium-ion batteries (LIBs). However, what with the performance degradation and structural collapse upon prolonged cycling, studies are still ongoing to enhance their performance. Among the available research methods, doping has been shown to enhance the cycle life of materials by stabilizing the layered structure. Herein, both the electrochemical properties and the structural stability of the Ni-rich (LiNi0.98Co0.02O2) materials are significantly improved via the doping of Al. This can be attributed to the Al-doped Ni-rich cathode maintaining a wider lithium layer spacing at high charge states without collapse, facilitating the de-intercalation/intercalation of Li+. In addition, the stronger Al-O bonded Al can act to stabilize the structure to retard capacity/voltage decay. Electrochemical testing results indicate that the Al-doped Ni-rich materials exhibit specific capacities of 235 mAh g−1 at 0.1 C (1 C = 180 mA g−1), 202 mAh g−1 at 1 C, and the capacity retention rate is 80.02% after 200 cycles. Moreover, the capacity of 183 mAh g−1 at a rate of 10 C illustrates its remarkable rate capability. The Al doping inhibits the phase transformation and expands the lattice spacing, which significantly improves the electrochemical performance of LiNi0.98Co0.02O2. Therefore, this paper focuses on the role of Al doping on the structure of layered cathode materials and pioneers the way for enhancing the structural stability of layered cathode materials for high energy LIBs.