Enhanced electrochemical properties of NCM811 cathode material due to synergistic modification with Sm as doping and coating agent

Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) has been considered as the most attractive cathode material for lithium-ion batteries (LIBs). However, the fast capacity decay and poor rate performance limit its practical applications. Bulk doping and surface coating have been demonstrated as the most important and effective technologies for enhancing its electrochemical performance; nevertheless, overall performance still remains unsatisfactory. In this study, simple dual-modification strategy was proposed in which samarium (Sm) was both doped into and coated on NCM811 to provide inside and outside synergistic modification. This can comprehensively improve electrochemical performance of NCM811. X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electrochemical tests were used to discuss improvement mechanism. Results indicated that parts of Sm successfully enter crystal lattice, which increases interlayer spacing, stabilizes structure, and reduces Li+/Ni2+ mixing. Simultaneously, another part of Sm coated on surfaces in the form of oxide, prevents electrolyte corrosion and inhibits side reactions. With the optimum Sm content (0.5%), obtained NCM811 displayed the highest discharge specific capacity (184.2 mA h g−1 at 1 C), capacity retention (94.19% after 100 cycles at 1 C), and rate performance (152.2 mA h g−1 at 5 C). This study provides efficient approach to improve electrochemical performance of NCM811 as cathode material.