Multifunctional Composite Binder for Thick High-Voltage Cathodes in Lithium-Ion Batteries

High-voltage LiNi0.5Mn1.5O4 (LNMO) spinel offers high specific energy and good rate capability with relatively low raw-material cost due to cobalt-free and manganese-rich chemical compositions. Also, increasing mass loading (mg/cm2) by thickening cathodes has been one of the focused areas to greatly improve the energy density of lithium-ion batteries (LIBs) at the cell level. The LNMO cathode made with a polyvinylidene fluoride (PVdF) binder, however, suffers from an oxidative decomposition of liquid electrolytes and cathode delamination from a current collector. This problem is exacerbated with an increase in thickness. In this study, we developed a lithium polyacrylate (LiPAA)-sodium alginate (Na-Alg) composite binder series that offer positive multifunctions such as enhancing cathode adhesion and cohesion, improving cycle life, creating an effective passivating layer at the cathode-electrolyte interface (CEI), and lowering cell impedance. Comprehensive design of systematic experiments revealed a close chemo-mechano-electrochemical relationship in the thick high-voltage cathodes. Among the various binder compositions, the LiPAA (30 wt %)-Na-Alg (70 wt %) binder offered a strong adhesion property and positive multifunctions at the CEI layer, which consequently stabilized the solid-electrolyte interfacial (SEI) layer on the graphite anode and improved LIB performances. This novel composite binder will be applicable to various types of thick cathodes in future studies.