A novel surface modification strategy for Li-rich Mn-based layered oxide cathodes of high-capacity and high-cyclic stability by an additive of LiBH4 to the electrolyte

Abstract

Li-rich Mn-based layered oxide (LMLO) cathode materials have high-capacity and high-energy density, which are highly potential for next generation Li-ion batteries; however, their disadvantages of low initial coulombic efficiency, poor cyclic stability, large voltage fading during cycling and poor rate capability hinder their practical applications. In this work, a novel surface modification strategy to improve the electrochemical properties of LMLO cathodes is developed, where a highly reductive compound of LiBH4 is adopted as an additive to a conventional electrolyte. Examined by a conventional LMLO material of Li[Formula: see text]Ni[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2- (L[Formula: see text]M[Formula: see text]LO), the cyclic stability and rate capability of the cathode are significantly improved when 0.3 wt.% LiBH4 is added. The cathode has an initial reversible discharge capacity of 280 mAh g[Formula: see text] at 20 mA g[Formula: see text], showing the capacity retention of 94.3% after 100 cycles. A capacity of 193 mAh g[Formula: see text] maintains after 300 cycles at 200 mA g[Formula: see text], corresponding to the capacity retention of 86.2%, and the capacity reaches as high as 138 mAh g[Formula: see text] at 2000 mA g[Formula: see text]. It is found that partial transition metals (TMs) at the surface of the L[Formula: see text]M[Formula: see text]LO particles are reduced by LiBH4 during the initial several cycles of activation, resulting in an in situ formation of a stable and lithium-diffusion feasible spinel structure surface coating in thickness of several nanometers with atomic match to the bulk particle. The surface coating not only retards the dissolution of the TMs from L[Formula: see text]M[Formula: see text]LO to the electrolyte, stabilizing the crystal structure during cycling, but also facilitates the lithium diffusion. As a result, the cyclic stability and rate capability of the cathode are evidently improved. The method is facile, scalable, and low cost, which has potential for commercial utilization.