Evaluating the capacity ratio and prelithiation strategies for extending cyclability in porous silicon composite anodes and lithium iron phosphate cathodes for high capacity lithium-ion batteries

Abstract

Silicon-based composites are considered a promising anode for lithium-ion batteries (LIBs) due to their high theoretical capacity of 3579 mAh/g at room temperature. However, when paired with conventional cathode materials, silicon-based full-cells perform poorly due to an unbalanced capacity ratio (N/P ratio) between the anode and the cathode. Their performance is further diminished by the irreversible Li+ losses in the silicon-based anode associated with the continuous volume expansion during cycling. To address these issues, we implement various N/P ratios and cycling strategies in a silicon-based anode and track the occurrence of lithium plating. A porous silicon-carbon (PSi-C) based composite anode is paired with a lithium-iron phosphate (LFP) cathode to investigate the effects of different N/P ratios in full-cell batteries. Based on these results, the optimal N/P ratio is tested using a three-electrode cell to monitor the anode and cathode voltages (versus reference electrode, Li) simultaneously in full-cell cycling and to detect lithium plating. Contrary to expectation, no lithium plating is observed at the optimized N/P ratio of 0.8. Finally, prelithiation strategies, such as contact treatment on the PSi-C anode with Li metal and precycling of the PSi-C anode against a lithium foil counter electrode, are performed to compensate for the initial lithium losses. When the PSi-C anode is cycled 5.5 times (5 full cycles and follow by 1 lithiation process) against lithium metal and then assembled with an oversized LFP cathode, the full-cell battery achieves 1000 mAh/(g-anode) for over 500 cycles. These results further validate the use of silicon-based anodes in full-cell LIBs by providing new assembly strategies and techniques to significantly improve stability and cycling performance.