Weakened functional group activity enables the uniform distribution of the gel electrolyte to achieve the high-performance of Li-ion batteries

Abstract

Electrolyte gelation is considered to be one of the main routes to solve the safety problem of liquid electrolytes. However, the distribution of gel polymer electrolyte (GPE) on the surface of electrodes and the mechanism of their effect on the performance of battery are still unknown. Here, methyl methacrylate (MMA) containing methyl (-CH₃) and methyl-2-cyanoacrylate (MCA) containing cyanide (-CN) are employed as representative monomers to explore the relationship between gel distribution and battery performance. Due to the stronger electron-withdrawing properties, PMCA gel has shorter chain length and greater shrinkage, showing many cracks on the electrode surface, while PMMA gel can evenly cover the surfaces of electrodes. As a result, the capacity retention rate of 1.4 Ah NCM811/Gr pouch cells with PMMA is 93.5% for 500 cycles at 25 °C and 91.5% for 600 cycles at 60 °C, which these of the cells with PMCA are 58.8% for 266 cycles at 25 °C and 69.1% for 327 cycles at 60 °C. XPS analysis of the electrode sheets before and after cycling reveal that the PMCA-electrode has a large number of rzero valent lithium element precipitation, whereas the PMMA-electrode has the more stable interface film. This study indicates that the uniform distribution of gel electrolyte with -CH₃ functional group on the electrode surface can improve the electrochemical performance of NCM811/Gr battery, which has the guiding significance.