PI-LAGP Separator─Construction, Battery Application Performance, and Chemical Valence Changes of Germanium

Abstract

We successfully prepared a porous polyimide film (PIBPDA–ODA) with a three-dimensional network structure using an optimized amount of pore-forming agents and a nonsolvent-induced phase separation method. Then, the nanoparticles of an inorganic ion conductor Li1.5Al0.5Ge1.5(PO4)3 (LAGP) were filled into the pore of the PIBPDA–ODA to form a PI–LAGP composite film with an ionic conductivity of 1.42 mS·cm–1 and a lithium-ion transference number of 0.87 (at room temperature). A NCM811||Li battery assembled with the PI–LAGP separator delivered a discharge capacity of 191.7 mA h·g–1 during the first cycle at 0.2 C which retained 167.5 mA h·g–1 (87.4%) after 200 cycles, while its first discharge capacity was 151.7 mA h·g–1 at 5 C which retained 127 mA h·g–1 (83.7%) after 200 cycles. In addition, the Li||PI–LAGP||Li symmetric battery was found to run stably at a current density of 5 mA cm–2 for more than 1,000 h. The three-dimensional network structure of the composite film and the evenly filled LAGP particles improved the transport of lithium ions, promoted the uniform deposition of Li ions during battery cycling, inhibited the growth of Li dendrites, and induced the rapid formation of a stable and dense solid electrolyte interface layer on the surface of the Li anode. In addition, we also investigated the valence state changes of Ge4+ ions on the surface and inside the composite film.

Prediction of Swelling of Polypropylene Separators and Its Effect on the Lithium-Ion Battery Performance

“…Note that a recent experimental study showed that the commercial cellulose-based separators show similar swelling and weakening behavior as polyolefins; we expect our model could also apply to those materials. Furthermore, much work in recent years has been focused on developing new battery separator materials, − while only a few of them assess the new materials for swelling and softening in the presence of electrolyte solvents. Our model can help make such an assessment with minimal experimental effort.…”