Constructing an Inhomogeneous Surface to Suppress the Capacity Decay of Li-Rich Layered Cathode Materials

摘要

Lithium-rich layered oxides with superior capacity over 250 mA h g~(-1) have been regarded as one of the most promising cathode materials to address the problem of low endurance of electric vehicles. Unfortunately, their practical application has been blocked for decades by severe voltage decay and capacity fading, which mainly originate from structure evolution of layered to spinel-like phase and undesirable cathode-electrolyte interfacial reactions. Herein, the inhomogeneous distribution of LiMO_2 and Li_2MnO_3 components on the surface of Li_(1.2)Mn_(0.6)Ni_(0.2)O_2 (LMNO) is constructed by a facile NH_3·H_2O-assisted Mn- and Ni-treatment method, demonstrated by Raman results. As supported by dQ/dV curves and electrochemical impedance spectroscopy data, the inhomogeneous surface improves the corrosion resistance against the electrolyte and enhances the surface-interface stability. Compared with the pristine one (P-LMNO), the Mn- and Ni-treated samples (M-LMNO and N-LMNO) deliver excellent cycling stability. After 200 cycles, the discharge capacity of the M-LMNO and N-LMNO samples is still as large as 154.5 and 174.0 mA h g~(-1) at 200 mA g~(-1), respectively, which is about twice as large as that of the P-LMNO sample. This work proposes a facile and effective surface-treated strategy for Li-rich layered cathodes to alleviate structure evolution and suppress the erosion of electrolytes.