Cation-ordered Ni-rich positive electrode material with superior chemical and structural stability enabled by atomic substitution for lithium-ion batteries

Abstract

Ni-rich layered oxides are considered as the most promising cathode materials for lithium-ion batteries (LIBs) due to their high specific capacity and low cost. However, the disordered Li/Ni mixing greatly affects their structural stability and electrochemical performance, thus hindering their wide application in commercial LIBs. Aiming to inhibit the premature death of Ni-rich layered oxides originated from the disordered Li/Ni mixing, atomic substitution of transition metal ions in LiNi0.83Co0.11Mn0.06O2 with high-valence metal molybdenum ions (denoted as Mo-NCM) is proposed in this work. The structure evolution of the as-prepared Mo-NCM caused by molybdenum substitution and the stability of Mo-NCM cathodes are comprehensively studied. Integrating experimental characterization with calculation results, it is found that the partial substitution of transition metal ions with Mo6+ ions can induce cation ordering and promote Li+ diffusion dynamics. Moreover, Mo6+ cations can act as the pillar to prevent local collapse and structural distortion, thus maintaining structural stability of the material. Furthermore, the formation of strong Mo-O bond between molybdenum and oxygen element can stabilize lattice oxygen and enhance the chemical stability of Ni-rich cathode. In addition, molybdenum modification can effectively reduce the exchange energy of Li+/Ni2+ and increase oxygen vacancy formation energy, further enhancing structural stability and promoting the kinetics of Li+ diffusion, and eventually enhancing the electrochemical performance of Mo-NCM based Li-ion batteries. The capacity retention of LIBs with 1 mol% Mo-NCM cathode can reach 98.67% after 200 cycles at 1C. This study provides a new insight into enhancing the chemical and structural robustness of Ni-rich cathode electrode materials.