Pressurized vs. unpressurized LiFePO₄ batteries: A comparative study on interfacial stability and electrochemical performance

The lithium-ion batteries are always under a certain mechanical pressure when they are being used. This pressure has a tremendous influence on the extent to which the electrodes expand and shrink, as well as affecting the interface stabilities of electrodes. Nevertheless, we do not have a complete realization of the effect of mechanical pressure on battery performance and failure. The chemical and mechanical nature of the solid electrolyte interphase (SEI) under applied pressure is still not thoroughly understood. This further affects the performances of positive and negative electrodes. In this study, we investigated the pivotal role of mechanical pressure on LiFePO₄/graphite full battery by testing LiFePO₄/graphite full battery with and without external pressure. We discovered that the battery exhibits superior high-rate performance with an appropriate level of pressure. It was demonstrated that pressure assists in developing a robust and LiF-enriched SEI onto the graphite anode. This superior SEI film not only effectively preserves the graphite crystal structure but also prevents the movement of damaging substances of the cathode in the battery. Furthermore, on the cathode side, the corrosion of aluminium current collector is minimized, and the reversible phase transition of LiFePO₄ is accelerated by pressure. This work systematically elucidates the effect of mechanical pressure in slowing down the degradation of the batteries, which is associated with the coupling of chemical and mechanical effects at the interface and the interaction between the anode and cathode. These results provide novel theoretical and practical insights for designing of superior and prolonged lithium-ion batteries based on mechanical control.