Investigation of the Direct Contact Prelithiation of Silicon-Graphite Composite Anodes for Lithium-Ion Batteries

Silicon is a promising anode material for lithium-ion batteries due to its high theoretical capacity. However, current lithium-ion batteries with high silicon shares in the anodes suffer from rapid capacity fading. The continuous reformation of the solid electrolyte interphase due to particle volume changes during lithiation consumes cyclable lithium. Direct contact prelithiation is a method to counteract lithium losses during the formation and operation of lithium-ion batteries. By providing excess lithium to the anodes during battery cell production, the cycle life of lithium-ion batteries can be increased. Within this work, the process characteristics of direct contact prelithiation and its effect on battery performance are investigated experimentally. Therefore, silicon-graphite composite anodes were mechanically prelithiated using lithium foil and incorporated in lithium-ion battery pouch cells. The prelithiation time and the cell pressure were systematically varied to obtain insights in to the process behavior. Additionally, the lithium quantity was controlled by lithium foil thickness and sample geometry. The prelithiation state of the anodes was examined by optical analysis and measurements of the cells’ open circuit voltage. The effect of anode prelithiation on the battery cell cycling behavior showed a cycle life increase of up to 150% compared to reference cells with non-prelithiated anodes.