Next-generation lithium-ion battery anode materials for silicon carbon composites: A review

Si/C composite materials are widely studied for use in lithium-ion batteries due to their high theoretical capacity. Nevertheless, three issues need to be addressed for Si/C to be considered practical. First, silicon swells by a factor of three in volume during charging, increasing its density from 0.12 nm -3 to 0.48 nm -3 . Such swelling leads to particle fragmentation when particle diameters exceed 150 nm and also causes irreversible lithium loss of 30-50%. Second, the SEI layer thickness increases by 2-5 nm per cycle, reaching 200 nm after 100 cycles, thereby increasing the interface resistance to 500 Ω·cm 2 from the initial 20 Ω·cm 2 . Third, low silicon conductivity is another disadvantage; a conductivity of 10 -3 S·cm -1 results in losses of about 100 mV per cycle at a current density of 2 mA·cm -2 . This literature review examines the relationships among the structure, properties, and performance of Si/C composites. The effectiveness of using multidimensional carbon structures 1D, 2D, and 3D in solving these problems is highlighted. By rationalizing carbon structuring, it is possible to obtain specific reversible capacity values exceeding 1300 mAh·g -1 , 500 cycling endurance, and a CE value exceeding 86%. Recent in-situ investigations using 7 Li NMR revealed a four-step lithiation process; TEM revealed the particle-size limit for preserving a frustration-free state ≥ 150 nm; and cryo-STEM revealed degradation processes in Si/C composites. Advances in scalable material fabrication include fluidized-bed technology, fast Joule heating >10 3 K·s -1 , and laser synthesis, resulting in CE levels exceeding 97%. In addition, AI and machine learning increase the effectiveness of the fabrication process and provide 92% capacity after 1000 cycles at a 3C rate. Nevertheless, despite these important advancements, there are still some hurdles to be overcome, such as inconsistencies in areal loading, a relatively low initial Coulombic efficiency of 70-85%, and sustainability concerns. With that said, the following is the proposed roadmap that incorporates the principles discussed above to advance future Si/C anode development.