Nano-encapsulation of LiCoO₂ cathodes by a novel polymer electrolyte and its influence on thermal safeties of Li-ion batteries

A new approach enabling the target control of exothermic reaction between delithiated LiCoO₂ and liquid electrolytes has been presented, which is based on the nano-encapsulation of LiCoO₂ by cPVA (cyanoethyl polyvinylalcohol)-based gel polymer electrolytes. This novel morphology and the possible formation of coordinated complexes between the cyano (-CN) groups of cPVA and the cobalt cations of LiCoO₂ are considered as key factors to significantly suppress the exothermic reaction in the delithiated LiCoO₂. Such an improved thermal stability of the cPVA-modified LiCoO₂ has led to a noticeable achievement in the hot-oven safety behavior of cells. Meanwhile, it was observed that both the excellent ionic conductivity of cPVA-based gel polymer electrolytes and the well-preserved porous structure of modified cathodes contribute to the satisfactory C-rate capability and the cyclability of cells.