Mo Doping and Dual-Conductive Layer Coatings to Mitigate Structural Degradation and Extend Service Life for Ni-Rich Layered Cathode Oxides

Bulk-phase Mo doping as well as multiple coatings of ion-conducting LiAlO2/Al2O3 and electron-conducting PPy polymers were applied to modify layered Ni-rich cathode materials. Mo ions effectively stabilized the crystal lattice, suppressing anisotropic lattice changes and reducing the generation of microscopic cracks and dislocations, thus stabilizing the crystal and phase structures. The LiAlO2/Al2O3 coating reduced the lithium residue on the surface, which in turn greatly inhibited the generation of the inert layer during charging and discharging. At the same time, the diffusion rate of Li+ was improved. The thin and uniform PPy coating layer effectively avoided direct contact between the cathode material and electrolyte, blocking harmful side reactions while increasing the electron-transfer rate at the interface. The elastic PPy shell resisted internal pressure, reducing macrocracks and electrolyte penetration. The structural stability as well as the ionic and electronic conductivities of the modified Ni-rich cathode material was improved. This resulted in a 13.1 mAh·g–1 increase in the first discharge specific capacity of the modified Ni-rich oxide over the pristine NM75 at a 1C rate within 2.8–4.4 V at room temperature and a 12.8% increase in capacity retention after 100 cycles. Capacity retention after 100 cycles was improved by 8.1% at a 1C rate (2.8–4.3 V, 55 °C). The analysis results showed that the modified Ni-rich cathode material had a more stable crystal structure and a smaller degree of deformation. This design can be extended to other high-capacity cathode materials, which is expected to promote the development of high-performance cathode materials and improve the viability of lithium-ion batteries.