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

Abstract 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 x Si 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%.