Enhancing the depressed initial Coulombic efficiency of regenerated graphite anodes via the surface modification of a TiNb2O7 nanolayer

Abstract

Spent graphite (SG) anodes are extensively overlooked despite being a potential anode material on account of their relatively low cost when compared to the valuable metal elements of cathode materials. However, the cracked surface structure and unstable solid electrolyte interphase (SEI) of SG will lead to depressed initial Coulombic efficiency (ICE), which hampers the application of graphite recovery techniques. Here, a uniform layer of TiNb2O7 nanoparticles is successfully constructed on a damaged SG surface. Benefiting from the stable structure, the TiNb2O7 coating can effectively protect the cracked sites and enhance Li+ diffusion. In addition, this layer can provide a high Li+ insertion potential and effectively suppress the unfavorable formation of an unstable SEI. The TiNb2O7 coating can also provide extra capacity, compensating for the capacity fade of SG. After modification, the regenerated graphite not only exhibits enhanced rate performance by means of reconstructed Li+ transfer channels but also demonstrates a prolonged cycle life due to the stabilized bulk structure. A full cell containing LiFePO4 and a regenerated graphite anode shows a high capacity retention, namely, 89.0% after 500 cycles at 1C. This study obtains regenerated graphite with a high ICE, thereby promoting the reutilization of spent graphite anodes.