Minimizing Undesired Side Reactions Induced by Nanoscale Conductive Carbon Enables Stable Cycling of Semi‐Solid Li‐Ion Full Batteries

Abstract Semi‐solid lithium‐ion batteries (SSLIBs) based on “slurry‐like” electrodes hold great promise to enable low‐cost and sustainable energy storage. However, the development of the SSLIBs has long been hindered by the lack of high‐performance anodes. Here the origin of low initial Coulombic efficiency (iCE, typically <60%) is elucidated in the graphite‐based semi‐solid anodes (in the non‐flowing mode) and develop rational strategies to minimize the irreversible capacity loss. It is discovered that Ketjen black (KB), a nanoscale conductive additive widely used in SSLIB research, induces severe electrolyte decomposition during battery charge due to its large surface area and abundant surface defects. High iCEs up to 92% are achieved for the semi‐solid graphite anodes by replacing KB with other low surface‐area, low‐defect conductive additives. A semi‐solid full battery (LiFePO₄ vs graphite, in the non‐flowing mode) is further demonstrated with stable cycle performance over 100 cycles at a large areal capacity of 6 mAh cm⁻² and a pouch‐type semi‐solid full cell that remains functional even when it is mechanically abused. This work demystifies the SSLIBs and provides useful physical insights to further improve their performance and durability.