Is Microporous Carbon Confined Nano Si Composite the Best Anode Choice for High-Energy-Density Lithium-Ion Batteries?

Microporous carbon confined nano silicon composites (Si/m-C) are considered to be the best anode materials for high-energy-density lithium-ion batteries compared with the other Si-based materials such as SiO, due to high initial Coulombic efficiency (ICE) and capacity, as well as good cycling stability. However, there is a lack of multilevel comprehensive evaluation of Si/m-C, which poses potential risks to the commercial application. Herein, combined with quantitative titration, mechanical characterization, and bulk/interface evolution analysis, a systematic evolution of commercialized Si/m-C from the particle level to the cylindrical cell level is conducted, revealing the decay mechanism and proposing corresponding solutions. Among them, it is well demonstrated that the Si/m-C still withstands huge volume expansion of over 200% with poor mechanical strength, causing the electrical contact loss of active Li_xSi and severe interfacial side reactions. Moreover, even blending more than 90% graphite cannot completely suppress its volumetric strain, and the combination of highly flexible single-walled carbon nanotubes (SWCNT) is necessary. In response to this, the 32700-type cylindrical cell with a designed capacity of 9.5 Ah is assembled by mixing Si/m-C with 90% graphite and SWCNT as anode, achieving a long-term cycling stability over 300 cycles at 0.5 C with a capacity retention of 94.8%.