Stabilizing voltage and prolonged cycling life of Li-rich Mn-based oxides through spinel “lithium ion pump” heteroepitaxial coating strategy

The practical application of Li-rich layered oxides is impeded by its cycle instability, poor rate capability and serious voltage decay. Here, nano-sized spinel Li₄Ti₅O₁₂ (LTO) is constructed on Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ (LLNCMO). The distinctly heteroepitaxial structure of LTO nanocoating on LLNCMO is corroborated by HAADF-STEM. The LTO coating with fast lithium ion diffusion kinetics acts as “lithium ion pump” when Li⁺-ions cross over it. The integrated structure can effectively retard oxygen evolution and phase transformation engendering higher capacity and voltage retention. LTO heteroepitaxially coated LLNCMO (LTO@LLNCMO) shows an improvement of initial coulombic efficiency to 74.3% and more stable life with a high capacity retention up to 96.9% at 2C after 500 cycles (40.5% for LLNCMO). LTO@LLNCMO demonstrates minimal voltage fading of 1.33 mV per cycle suggesting suppression of phase conversion to spinel-like structure. The epitaxial spinel modification strategy can be applied to control the surface stability of cathodes.