Origin of capacity rise in LiFePO4 batteries: practical implications for reliable cell design

Abstract

LiFePO₄ (LFP) batteries have been widely adopted in electric vehicles due to their low cost, safety, and durability. Many LFP cells exhibit a counterintuitive “capacity rise” phenomenon during early cycles, but its origin has remained unclear. Here, we systematically elucidate the mechanism through differential voltage analysis and three-electrode measurements. We show that the reversible capacity gain mainly stems from undischarged anode capacity, which supplies additional Li ions, coupled with activation of the LFP cathode. The extent of the capacity rise is further modulated by Li loss during cycling. Guided by this understanding, we demonstrate control over capacity rise by tuning the undischarged anode capacity and employing sacrificial cathodes, enabling flexible design trade-offs between energy density and cycle life. Finally, we validate the proposed mechanism using 79 prismatic cells representing 39 designs and develop a predictive model using mechanism-based features from early cycles (R² = 0.93) to provide a rapid protocol for practical cell optimization. This work delivers both mechanistic insight and actionable guidelines for the design of LFP-based batteries.