Reduced Silicon Fragmentation in Lithium Ion Battery Anodes Using Electronic Doping Strategies

Although Si anodes have the potential to achieve gravimetric capacities >3000 mA g–1 for Li ion batteries, their utility has been limited by their large volumetric expansion on lithiation and electrode fragmentation. We show that n-type doping reduces the lithiation potential of (100) Si and conclude that the Li ion insertion energy into crystalline Si increases with n-type dopant density. This allows tuning of the n-type dopant density in Si electrodes to reduce surface fragmentation and increase electrode cycle life. Using a combination of n-type doping, prelithiation at a low current density of 0.05 mA cm–2 and an areal capacity capping at 2 mAh cm–2, we show that stable cycling can be achieved at a current density of 1 mA cm–2 within the potential range of 0.01–1.5 V for at least 140 cycles using an organic electrolyte without additives. Further improvements in cyclability can be achieved by using alternative electrolytes with greater electrochemical stability at low potentials. Because of the massively reduced cost of Si wafers, heavily doped wafer-based current collectors may present an alternative to Si thin film anodes with improved adhesion between the current collector and electroactive Si surface provided that the wafers can be sufficiently thin to reduce electrode mass and volume. Alternatively, n-type doping of Si can be used to reduce fragmentation in particle-based electrodes permitting more controllable lithiation and a longer cycle life.