基于原位参比的氧化亚硅-石墨复合负极循环衰减机制

In this study, a capacity calibration method at low current was introduced during cycling to eliminate the influence of polarization voltage and to better understand the degradation mechanisms of the composites containing silicon oxide and graphite. The electrochemical characteristics of the cathode and the anode at different cycles were compared by pre-embedding a reference electrode in the pouch battery. The evolution process and attenuation degree of silicon oxide and graphite were analyzed using the negative differential curves. In addition, AC impedance spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, and plasma emission spectroscopy were discussed. The results demonstrate that capacity attenuation was caused due to the loss of active lithium and the decay of silicon oxide, and the resultant capacity loss was 0.45 Ah and 0.36 Ah, respectively. Moreover, the degradation rate of the anode was found to be faster than that of the cathode, while the attenuation of the graphite and the silicon oxide in the negative electrode was 2.2% and 30.3%, respectively, after 600 cycles. During cycling, a new interface impedance was generated, and all kinetic impedance parameters increased gradually. Serious volume expansion and side reactions occurred in the aged anode on disassembling the cycled battery, leading to lithium inactivation in the anode, thickening of the solid electrolyte interphase layer, and capacity degradation. The quantitative evaluation of the decay degree of silicon oxide and graphite during cycling is helpful for engineering applications of silicon-graphite composite electrode.