Plasma-engineered LiF/Al₂O₃ hybrid CEI for high-rate and stable LiFePO₄ cathodes

Despite the inherent advantages of LiFePO₄ (LFP) cathodes, including exceptional cycling stability and remarkable rate capability, significant challenges persist regarding sluggish Li⁺ transport kinetics through the cathode-electrolyte interphase (CEI) and excessive interfacial parasitic reactions. These limitations compromise cycling stability and accelerate voltage decay, critically constraining electrochemical performance. In this study, a dielectric barrier discharge (DBD) plasma-assisted interface engineering strategy was employed to construct a hybrid LiF + Al₂O₃-rich CEI on LFP electrodes within 4 min in situ. The engineered CEI simultaneously delivered high Li⁺ conductivity and structural stability without conventional fluorinating and aluminising agents. LiF facilitates rapid Li⁺ transport along grain boundaries, significantly enhancing transport kinetics at the LFP-electrolyte interface. Furthermore, the low solubility and high mechanical strength of LiF + Al₂O₃ synergistically suppress Fe²⁺ dissolution and structural degradation. Consequently, the LiF + Al₂O₃-rich CEI endowed the cathode with superior high-rate performance (105 mAh g^-1 at 20C) and excellent cycling stability (94 % capacity retention after 1000 cycles) and mitigated voltage decay (268 mV polarisation after 1000 cycles). This engineered interphase further enabled remarkable ultrahigh-rate performance, delivering 103 mAh g^-1 even at 40C. Moreover, when configured in full cells with hard carbon anodes, the cell achieved a reversible capacity of 112 mAh g^-1 at 5C. This research provides valuable insights into the efficient modification and regulation of CEI composition by DBD plasma at the electrode interface and offers a new approach for the in situ construction of CEI in LFP cathodes.