Limiting anode utilization: A strategy to increase Si content and useable capacity in Si/C composite anode without compromising cycle life

Despite having a high theoretical capacity, silicon-based anodes fall short in providing practical and cycle-stable specific capacity close to the theoretical potential. The main challenge, namely particle pulverization and loss of mechanical integrity due to a large volume expansion, is commonly addressed by nano-structuring and blending with graphite in a Si/C composite anode. However, a maximum Si content of 15% in Si/C composite anodes has been realized, leaving scope for much improvement. Herein we discuss and theoretically benchmark a new strategy to increase Si content and achievable specific capacity by limiting anode utilization to minimize degradation. Through careful consideration to differential rates of lithiation of Si and C, particle fracture, and electrode swelling limit, our physical analysis suggests that this strategy could provide specific capacities of greater than 1100 Ah/Kg while eliminating degradation. These benchmarks are arrived at though a comprehensive analysis of lithiation of Si and C on an individual component level and the associated propensity for Si particle fracture as well as reduction in electrode porosity due to volume expansion and arriving at safe lithiation limits for a given set of electrode parameters under consideration. Since this safe range of operation is dependent on particle size, we show that we can optimize the Si% in Si/C to achieve maximum utilizable specific capacity for a given particle size.