In-situ modification of ultrathin and uniform layer on LiCoO2 particles for 4.2 V poly(ethylene oxide) based solid-state lithium batteries with excellent cycle performance

Poly(ethylene oxide) based polymer electrolytes(PEO-SPEs) suffer from a narrow electrochemical window and deliver poor electrochemical performance when coupling with 4.2 V cathode. This severely limits the scope of its application. Here, a combination of physical stirring and electrochemistry is used to form an ultrathin and uniform cladding layer on the LiCoO 2 particles. The results show that in addition to the decomposition of LiPO 2 F 2 during the charge/discharge cycling, decomposition reactions occur during the stirring and drying process by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). This novel method effectively improves the electrochemical performance of 4.2 V PEO based solid-state lithium batteries . In particular, the cell shows excellent and stable electrochemical performance, exhibiting a discharge capacity of 112.0 mAh g −1 after 200 cycles, a capacity retention rate of 79.4% and a capacity decay rate of approximately 0.1% per cycle when the surface of LiCoO 2 is coated with 2 wt% LiPO 2 F 2 . In comparison, the discharge capacity of the unmodified LiCoO 2 cathode is found to be only 75.6 mAh g −1 after 100 cycles, with a poor capacity retention rate of 56.8%. Based on the basis of the above research, a new process was explored and also shows excellent interfacial stability by dispersing LiPO 2 F 2 directly inside the binder which with a discharge capacity of 109.2 mAh g −1 and a capacity retention rate of 84.5% after 145 cycles. This novel approach opens up a new pathway for solving the problem of interfacial stability between PEO based polymer electrolytes and high-voltage cathode.