Enhancing the High-Voltage Cycling Performance and Rate Capability of LiNi0.8Co0.1Mn0.1O2 Cathode Material by Codoping with Na and Br

Ni-rich cathode materials have been increasingly studied due to their satisfactory capacity. However, the rapid attenuation in capacity and poor rate capability of Ni-rich cathodes, especially at a high voltage, limit their practical use. We propose a new strategy for codoping LiNi0.8Co0.1Mn0.1O2 with Na and Br. Various morphological and structural characterizations show that Na doped at Li sites act as pillar ions that expand the lithium-layer spacing, and Br doped at O sites form stronger covalent bonds. Codoping inhibits Li+/Ni2+ mixing, decreases residual lithium on the surface, and stabilizes the crystal structure. Electrochemical tests show that codoping 0.02 mol of Na and Br provides the best cycling performance and rate capability. The capacity retention rate after 100 cycles reaches 87.68% at 0.2C and 94.41% at 1C at high voltages of 3.0-4.5 V; in contrast, pristine LiNi0.8Co0.1Mn0.1O2 provides a capacity retention rate of only 69.02% at 0.2C. Cyclic voltammetry and electrochemical impedance show that the Li+ diffusion coefficient increases and the charge-transfer resistance decreases, while the capacity versus voltage curves demonstrate the inhibition of phase transitions. These results indicate that codoping Na and Br is a simple and effective strategy for developing high-performance Ni-rich cathode materials.