Mitigating Interfacial Issues in All-Solid-State Li Battery By Using a Polymer-Solid-Electrolyte-Incorporated Composite Electrode

Abstract

All-solid-state-batteries (ASSBs) provide technical solution to address the challenges of high safety and high energy density for future energy storage. However, their practical applications have been mainly hindered by the interfacial issues, since it is very challenging to construct intimate contact between the solid electrode and electrolyte due to their rigidity in conventional ASSBs, which leads to high polarization and low utilization of active materials. Herein, we demonstrate a simple but effective interfacial engineering approach to mitigate the poor interfacial contact via incorporating deformable polymer solid electrolyte (PSE) into the composite electrode. For the purpose, the poly(ethylene glycol)-based PSE was directly casted on and thermally infiltrated into the composite cathode (LiFePO4). From the various physicochemical and microstructural analyses, it was found that PSE exhibits the moderate Li+ conductivity (~ 6.6 × 10-4 S cm-1 at 65 oC) and wide electrochemical window (~ 4.5 V vs. Li/Li+), and its rheological properties are strongly dependent on the temperature. It was also observed that micro-pores in the composite electrode are completely filled without any cracking and the active components are fully covered by the deformable PSE. The cells assembled with PSE-incorporated cathode clearly exhibited the superior storage capacity, rate-capability and cyclablity in comparison with the pristine composite electrode. Moreover, 10 V-class bipolar ASSB (~10 mAh) comprising three unit cells connected in series was designed and constructed by using PSE-incorporated cathode, and its stable electrochemical performance was also demonstrated. Those results suggest that the PSE-infiltration process is considerably helpful for promoting the Li+ transport in the composite electrode by establishing intimate contacts between the solid electrolyte and active materials, and continuous ionic path through the whole composite electrode.