Ion exchange to construct a high-performance core–shell MnFe-PB@CuFe-PB cathode material for sodium ion batteries

Abstract

Sodium manganese hexacyanoferrate (MnFe-PB) is a promising cathode material for sodium-ion batteries because of its advantages of high operating voltage and high theoretical capacity. However, the structural phase transition of MnFe-PB during the working process will cause the Jahn–Teller effect, which destroys the stability of the interface and the structure of the material. Considering these factors, it is necessary to build a stable interface on the surface of MnFe-PB to keep the structure stable by using low-cost materials in a simple way for commercial applications. In this work, an ion exchange method is used to form a uniform coating layer of sodium copper hexacyanoferrate (CuFe-PB) on the surface of MnFe-PB. The existence of the coating layer effectively prevents Mn from dissolving into the electrolyte, inhibits the Jahn–Teller effect, and alleviates structural collapse. In 200 cycles at 0.1C, MnFe-PB@CuFe-PB maintains a capacity of 119.3 mA h g⁻¹, 87.3% more than that of MnFe-PB. This simple and cheap ion exchange method for constructing a stable coating on MnFe-PB can well meet the actual demand of large-scale industrial production.