Mitigating magnetic frustration to improve single-crystalline nonstoichiometric Li1.06Ni0.90Mn0.04O2 for lithium-ion batteries

Abstract

Single-crystalline Co-free layered nickel-rich oxide LiNi_1−xMn_xO₂ (x ≤ 0.1) is an appealing cathode material but suffers from significant structural degradation that correlates with the Li⁺/Ni²⁺ cation mixing induced by the magnetic frustration. In this study, we propose a molten salt-assisted synthesis and a Li-refeeding strategy to prepare a single-crystalline slightly Li-rich Li_1.06Ni_0.90Mn_0.04O₂ cathode material. A small amount of lithium doping into the transition metal layer increases the average valence of Ni and Mn, and reduces the magnetic frustration, as evidenced by electron energy loss spectroscopy and superconducting quantum interference device. Benefiting from mitigated magnetic frustration, the single-crystalline slightly Li-rich Li_1.06Ni_0.90Mn_0.04O₂ delivers a high specific capacity of 214.8 mA h g⁻¹ at 0.1 C, and a remarkable capacity retention of 93.4% after 100 cycles at 5C in a coin cell, and achieves a superior long-term stability of 400 cycles with 79.4% capacity retention at 2C in a 362.9 mA h pouch full cell. The results validate the mitigation of magnetic frustration by tuning the Li stoichiometry to reinforce the structural stability for the design of better Co-free nickel-rich oxide cathode materials.