N-Doped Graphene-Modified Li-Rich Layered Li_1.2Mn_0.6Ni_0.2O₂ Cathode for High-Performance Li-Ion Batteries

Abstract

Lithium-rich layered oxides (LLOs) due to their delivered capacity of over 250 mA h g–1 are regarded as the most attractive cathode for lithium-ion batteries (LIBs) with higher energy density. However, the unstable cycling performance, poor rate capability, and large voltage decay in LLOs hinder their commercial application. Here, we construct a highly conductive electrode where Li1.2Mn0.6Ni0.2O2 (LMN) is wrapped in a N-doped graphene carbon matrix (LMN-NG) to address the fast capacity fading and suppress the voltage decay. The LMN-NG electrode can deliver a capacity of 286.4 mA h g–1 at 0.2 C and maintain a capacity retention of 86% after 200 cycles, which is much higher than the LMN control electrode with values of 268 mA h g–1 and 75%, respectively. The theoretical calculation and differential electrochemical mass spectrometry (DEMS) analysis investigation suggest that the functional group in NG can effectively trap active oxygen species and mitigate the successive electrolyte decomposition, thus protecting LLOs. Transmission electron microscopy and Raman spectroscopy results reveal that the LMN-NG electrode maintains better layered structural stability after long-term cycling and exhibits a less spinel-like disordered phase of 18% compared to 40% of the LMN electrode. The superior electrochemical performance of LMN-NG indicates that enwrapping LLOs in NG has a potential application in LIBs.