High-performance silicon diphosphide/nanocarbon composite anode for Li-ion batteries: Role of chemical bonding and interfaces in the establishment of cycling stability

Silicon diphosphide (SiP₂), a next-generation anode material for lithium ion batteries, exhibits a high theoretical specific capacity (2900 mAh g⁻¹), however, its capacity is rapidly faded due to its large volume change. An effective way to improve the electrochemical performances of SiP₂ is to composite with carbon buffer. In the composite, chemical bonds of SiP₂ and carbon are expected to maintain SiP₂ to carbon connections during cycling, thereby, provide electron conduction pathways even under the volume change of SiP₂. However, effect of the chemical bonds is not clearly understood. Thus, it is very important to distinguish contributions of the carbon buffer and chemical bonds to the electrochemical properties of SiP₂. Herein, SiP₂ composites with nanocarbon are prepared with and without chemical bonds between SiP₂ and carbon by controlling ball milling parameter with an aim to investigate respective contribution of the carbon buffer and chemical bonds to the electrochemical properties of SiP₂. The SiP₂/nanocarbon composite with P–O–C and Si–O–C chemical bonds shows great improvement of electrode performances over the composite without the chemical bonds. Furthermore, the SiP₂–nanocarbon interface is found to facilitate fast ion conduction, overcoming the issues associated with the ionically insulative LiP.