Nano silicon reinforced carbon anodes for high-capacity lithium ion battery: State of charge (SOC) and battery life time testing

The importance of active materials for anodes has gained significant attention in recent times. Carbonaceous materials are typically used as anode candidates in lithium-ion batteries (LIBs), but their low theoretical capacity of 372mAh/g restricts their applications in advanced LIBs. Therefore, Silicon (Si) is considered a prominent alternative anode material for LIBs to replace graphite. Since the theoretical capacity of Si is ten times higher than graphite; however, it suffers from massive mechanical deformations induced during cycling. For this purpose, composites of Si-graphite are proposed for better cycling performance and increased specific capacity. Herein, nano Si powder (<100nm) containing mesocarbon microbeads (MCMB) composites are prepared, and their rate capabilities as anode material for LIBs have been investigated at different current densities. Diverse compositions of the active anode materials (Si and MCMB), carbon black (CB), a binder sodium carboxymethylcellulose (CMC-Na), and distilled water as a solvent have been utilized for the fabrication of anodes, and the fabricated anodes have been morphologically and electrochemically characterized. Moreover, the state-of-charge (SOC) analysis has been evaluated by setting three different upper and lower cut-off voltages. Our analysis revealed that a composite comprising the lowest Si content (5wt%) exhibited better rate performance and retained a capacity of 455mAh/g after 60 cycles. 15wt% Si showed the worst rate capability performance. Similarly, in theSOCanalysis,a moderate voltage window between 1-0.05V was found optimalon the basis of rate capability results. Voltage window between 1-0.07V lead to quick capacity loss and large surface cracks confirmed in FESEM images. Additionally, in the SOC analysis, 5wt% Si showed the best cycling performance and lost only 10% of its capacity at 1C and 13% at C/2 after 200 cycles between 1-0.05V.