Hard carbon composites as high performance anode materials for alkali metal ion batteries: Advances and perspectives

The study of anode materials for batteries is one of the key directions in the field of battery technology. Hard carbon (HC) materials are rich in defects, disordered internal crystal arrangement with large interlayer spacing, abundant pore structure and high specific capacity, making them excellent anode materials for batteries, However, HC anode materials also face challenges such as low initial Coulombic efficiency (ICE), poor rate capability and poor cyclic stability. Composites can improve the energy density, rate capability, and cyclic life of batteries. This review investigates the application of HC composites as anode materials for alkali metal ion batteries, revealing their ability to enhance the electrochemical performance of HC composites. This paper summarizes the preparation and the electrochemical performance of the composite of HC and soft carbon (SC) materials, HC and non-metallic materials, HC and metal materials, HC and metal compound composite, and highlights the preparation, structural features and electrochemical performance of HC composites used in lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs). Research has found that single materials often have performance bottlenecks. Through compositing HC with other materials, in some cases other materials can improve the performance of HC, whereas in others, HC mitigates the limitations of the partner materials. The main objective of this review is to summarize the research progress and challenges of HC composites as anode for alkali metal ion batteries, which will help the development of high-performance batteries in the future.