Surface-intensive doping of Na via pH-dependent polymer for Co-free Ni-rich cathodes in Li-ion batteries

Abstract

Ongoing research is actively being undertaken to identify alternatives to Co for high-capacity Ni-rich NCM cathode materials, driven by concerns related to cost and ethics. In this context, Na was proposed as a suitable replacement for Co. In addition, a process utilizing a pH-dependent polymer was introduced for the controlled doping of the material to ensure uniformity, and Co-free Ni-rich cathode materials with a form where Na is intensively doped in the surface region. The resulting material exhibits superior rate capabilities (20C, 121 mAh/g) and high-voltage, fast-rate cycle performance (100 cycles, 2.5–4.5 V (vs. Li/Li+), 2C) compared to the pristine LiNi0.8Mn0.2O2. Notably, surface-intensive doping with Na during high-voltage, fast-rate cycles suppressed the formation of oxygen vacancies in Ni-rich materials. This study introduces a novel approach to improving the performance of Co-free Ni-rich materials.