Influence of Binder Coverage on Interfacial Chemistry of Thin Film LiNi_0.6Mn_0.2Co_0.2O₂ Cathodes

In this work, we explore the influence of binder coverage and chemistry on the interfacial properties of the textured Ni-rich cathode LiNi_0.6Mn_0.2Co_0.2O₂. We find that the formation of the cathode/electrolyte interphase (CEI) composition varies significantly for cathodes coated with either poly(vinylene fluoride) (PVDF), carboxymethyl cellulose (CMC), or lithium polyacrylate (LiPAA) after cycling to high upper cutoff voltages (4.5 V vs Li/Li). The PVDF-coated samples had a thinner CEI and twice the relative concentration of LiF and Li₂CO₃ to Li_xPO_yF_z species in the CEI compared to the uncoated sample. This correlated with significantly lower interfacial impedance (285 vs ∼1700 Ohm-cm²) and improved capacity retention between cycles of the PVDF-coated samples compared to the other binder compositions and the uncoated sample. CMC-coated samples performed worst, with a CEI comprised of greater amounts of Li_xPO_yF_z. In addition, we find the choice of binder results in the selective protection or promotion of electrolyte reactions at the (104) surface of the 622 cathode. This suggests that the choice of binder can impact the surface chemistry and performance of high voltage cathodes and supports an avenue for interest in multifunctional binders for stabilizing the CEI.