Structures, issues, and optimization strategies of Ni-rich and Co-low cathode materials for lithium-ion battery

Ni-rich and Co-low ternary layered materials are considered as desirable cathode materials for construction of next-generation lithium-ion batteries (LIBs) because of their high energy density, sufficient resources, and environmental friendliness. However, the increase of nickel content in these ternary layered cathode materials causes problems concerning structural stability, cycling stability, and thermal safety. To date, researchers have explored various strategies to solve the stability problems of Ni-rich and Co-low cathode materials in order to develop sustainable electric vehicles and portable electronic devices. In this review, we introduce the structural characteristics of Ni-rich and Co-low cathode materials and comprehensively analyze the issues that causing capacity degradation and structural instability of these materials. We also review the four effective strategies to improve the electrochemical performance of Ni-rich and Co-low layered cathode materials. Besides, we point out that, for single crystal materials or polycrystalline materials, a combination of modification strategies should be adopted to optimize their structure and thus improve the performance. At last, we discuss the challenges of these layered cathode materials by describing their advantages/disadvantages, and then put forward our views on the future development trend of LIBs cathode materials.