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

Abstract

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 LiCoO2 particles. The results show that in addition to the decomposition of LiPO2F2 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 LiCoO2 is coated with 2 wt% LiPO2F2. In comparison, the discharge capacity of the unmodified LiCoO2 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 LiPO2F2 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.