Interfacial engineering of LiFePO₄ cathodes: Decoupling coating conformability and transport effects for enhanced cycling stability

The interfacial degradation between the electrode-electrolyte interface is one of the main drawbacks to cycling stability of lithium-ion batteries (LIBs) over the long run. This work demonstrates a comparative study, which is performed using a mechanism by using which the behavior of the LiFePO₄ (LFP) cathodes in the degradation process can be explained. The novelty of the research is that it has provided a common framework of interfacial design capable of correlating the conformability of the coating, the chemical passivation, and the transport properties with the long-term electrochemical durability, which has not been done in conventional performance comparisons. Three example surface-engineering approaches (atomic layer deposition, or ALD) of Al₂O₃, sol-gel-based TiO 2 coating and solution-based modification of graphene oxide (GO) are methodically explored to decouple the conflicting activities of chemical stability and charge-transport enhancement. Extensive structural and morphological studies prove that all coatings maintain the original olivine crystal structure of LFP and create unique interfacial structures. Electrochemical characterization indicates that surface modification greatly decomposes polarization, diminishes charge-transfer resistance and interfacial kinetics are stabilized in the case of extended cycling. Of the coatings studied, an ultrathin (~10 nm) Al 2 O 3 coating prepared by ALD, produces a chemically inert artificial cathode-electrolyte interphase, which yields better cycling stability, with 94.8% capacity retention after 300 cycles at 1 C. GO coatings are highly effective in increasing both electronic conductivity and rate capability but offer little chemical passivation whilst TiO 2 coatings are intermediate performers because of incomplete surface coverage and mixed ionic-electronic transport action. All in all, the findings prove that coating conformability and chemical inertness are more determining in long-term cycle stability compared to electronic conductivity. The suggested mechanism-driven framework offers practical principles of rational design of surface-engineered cathodes and optimization of nanoscale interfacial control strategies of the next generation durable lithium-ion batteries of electric automobiles and grid-scale energy storage.