SI NANOSTRUCTURED COMPOSITE AS HIGH PERFORMANCE ANODE MATERIAL FOR NEXT GENERATION LITHIUM-ION BATTERIES

Silicon has attracted huge attention in the last decade as the anode material for Li-ion batteries because it has a theoretical capacity ∼10 times that of graphite. However, the practical application of Si is hindered by three major challenges: large volume expansion during cycling (∼300%), low electrical conductivity, and instability of the SEI layer caused by repeated volume changes of the Si material. Our study focused on novel design and synthesis of Si anodes that can solve all the key problems of Si anodes simultaneously. The Si micro-reactors we designed and synthesized contain well-designed internal structures, including (i) nanoscale Si building blocks, (ii) the engineered void space, and (iii) a conductive carbon shell. Because of these internal structures and nitrogen doped carbon shell, these sub micrometer-sized Si particles are termed as Si micro-reactors and denoted as Si@void@C(N). According to our electrochemical results, the as-synthesized Si micro-reactors could live up to 1000 charge/discharge cycles at high current densities (up to 8 A/g) while still providing a higher specific capacity than the state-of-the-art carbonaceous anodes. Our investigation shows that the unique design of Si@void@C(N) has a relatively low specific surface area (SSA) which significantly reduces the undesired surface side reactions and increases ICE to 91%, while the engineered voids with nano-channel shape inside the structure can accommodate Si volume expansion and keep the structure and SEI layer stable. Furthermore, the porous N-doped carbon shell along with nano-channeled voids allows rapid lithiation of the Si micro-reactor without Li plating during ultrafast charging. As a result, Si@void@C(N) exhibits ultrafast charging capability with high ICE, superior specific capacity and long cycle life