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.