Revealing the Role of Active Fillers in Li-ion Conduction of Composite Solid Electrolytes.

Composite solid electrolytes (CSEs) consisting of polyethylene oxide (PEO) matrix and active inorganic fillers have shown great potential for practical applications. However, mechanisms of how different active fillers enhance ion transport in CSEs still remain inconclusive. In this work, the component dependencies of ionic conductivity of PEO-based CSEs are investigated by comparing two widely investigated active fillers: NASICON-type (LATP) and garnet-type (LLZTO). In terms of ionic conductivity, the optimum ratios are strikingly different for LLZTO (10 wt%) and LATP (50 wt%). Through experimental and computational studies, it is demonstrated that the high affinity between LATP and PEO facilitates unhindered interfacial Li+ transfer so that LATP functions as a bulk-active filler to provide additional inorganic ion pathways. By contrast, Li+ transfer between LLZTO and PEO is found to be sluggish. Instead, LLZTO mainly improves ionic conductivity by dissociating lithium salt, making it a surface-active filler. Through categorizing active fillers based on their Li+ conductive mechanisms, this work provides new understanding and guidelines for componential design and optimization of solid composite electrolytes.

Bio-Inspired Binder Design for a Robust Conductive Network in Silicon-Based Anodes.

Due to the severe volume variations during electrochemical processes, Si-based anodes suffer from poor cycling performance as the result of a collapsed conductive network. In this regard, a key strategy for fully exploiting the capacity potential of Si-based anodes is to construct a robust conductive network through rational binder design. In this work, a bio-inspired conductive binder (PFPQDA) is designed by introducing dopamine-functionalized fluorene structure units (DA) into a conductivity enhanced polyfluorene-typed copolymer (PFPQ) to enhance its mechanical properties. Through constructing hierarchical binding networks and resilient electron transportations within both nano-sized Si and micro-sized SiOx electrodes via interweaved interactions, the PFPQDA successfully suppresses the electrode expansion and maintains the integrity of conductive pathways. Consequently, owing to the favorable properties of PFPQDA, Si-based anodes exhibit improved cycling performance and rate capability with an areal capacity over 2.5 mAh cm-2 .

Constructing a Resilient Hierarchical Conductive Network to Promote Cycling Stability of SiOx Anode via Binder Design.

Despite exhibiting high specific capacities, Si-based anode materials suffer from poor cycle life as their volume change leads to the collapse of conductive network within the electrode. For this reason, the challenge lies in retaining the conductive network during electrochemical processes. Herein, to address this prominent issue, a cross-linked conductive binder (CCB) is designed for commercially available silicon oxides (SiOx ) anode to construct a resilient hierarchical conductive network from two aspects: on the one hand, exhibiting high electronic conductivity, CCB serves as an adaptive secondary conductive network in addition to the stiff primary conductive network (e.g., conductive carbon), facilitating faster interfacial charge transfer processes for SiOx in molecular level; on the other hand, the cross-linked structure of CCB shows resilient mechanical properties, which maintains the integrity of the primary conductive network by preventing electrode deformation during prolonged cycling. With the aid of CCB, untreated micro-sized SiOx anode material delivers an areal capacity of 2.1 mAh cm-2 after 250 cycles at 0.8 A g-1 . The binder design strategy, as well as, the relevant concepts proposed herein, provide a new perspective toward promoting the cycling stability of high-capacity Si-based anodes.