A larger work function in hybrid hard carbon-graphite negative electrodes produces a thermally stable solid electrolyte interphase for lithium-ion batteries at 65 °C floating charge conditions

The electrochemical stability of lithium-ion batteries strongly depends on the thickness of the solid electrolyte interphase (SEI) formed on graphite anodes. Nevertheless, electrolyte decomposition at the anode surface, especially at 65 °C, leads to uncontrolled SEI growth. We have designed a hybrid negative electrode by incorporating hard carbon (HC) into graphite to increase the surface work function, which effectively hinders electron escape, thereby reducing electrolyte reduction and inhibiting thick SEI formation at 65 °C. The disordered structure of HC faciitates lithium-ion diffusion and prevents lithium plating on the electrode surface. As a result, a hybrid negative electrode containing 50% HC has an especially high capacity (98 mAh/g) at 8 C and long cycle life at 0.5 C at room temperature. Furthermore, in a full battery it has an excellent capacity (128.54 mAh/g) and stable floating charge for 144 h at 65 °C. The electrode achieves a balance between high energy density and high-power density for lithium-ion batteries, thus maintaining stability even during a floating charge at a temperature of 65 °C. This is attributed to the formation of a thinner and more robust SEI. This study provides a mechanistic understanding of how the electrode work function governs electrolyte decomposition and SEI evolution, offering a practical strategy for slowing the degradation of lithium-ion batteries at 65 °C.