Super‐Ionic Conductor Soft Filler Promotes Li+ Transport in Integrated Cathode‐Electrolyte for Solid‐State Battery at Room Temperature

Composite polymer solid electrolytes (CPEs), possessing good rigid-flexible, are expected to be used in solid-state lithium metal batteries. The integration of fillers into polymer matrices emerges as a dominant strategy to improve Li+ transport and form a Li+-conducting electrode-electrolyte interface. However, challenges arise as traditional fillers: (1) inorganic fillers, characterized by high interfacial energy, induce agglomeration; (2) organic fillers, with elevated crystallinity, impede intrinsic ionic conductivity, both severely hindering Li+ migration. Here, we introduce a concept of super-ionic conductor soft filler, utilizing a Li+ conductivity nano-cellulose (Li-NC) as a model, which exhibits super-ionic conductivity. Li-NC anchors anions, and enhance Li+ transport speed, and assists in the integration of cathode-electrolyte electrodes for room temperature solid-state batteries. The tough dual-channel Li+ transport electrolyte (TDCT) with Li-NC and polyvinylidene fluoride (PVDF) demonstrates a high Li+ transfer number (0.79) due to the synergistic coordination mechanism in Li+ transport. Integrated electrodes design enable stable performance in LiNi0.5Co0.2Mn0.3O2|Li cells, with 720 cycles at 0.5 C, and 88.8% capacity retention. Furthermore, the lifespan of Li|TDCT|Li cells over 4000 h, and Li-rich Li1.2Ni0.13Co0.13Mn0.54O2|Li cells exhibit excellent performance, proving the practical application potential of soft filler for high energy density solid-state lithium metal batteries at room temperature. This article is protected by copyright. All rights reserved.