Impact of Newly Developed Styrene–Butadiene–Rubber Binder on the Electrode Performance of High-Voltage LiNi_0.5Mn_1.5O₄ Electrode

Chemically modified styrene–butadiene–rubber (SBR) with sodium carboxymethyl cellulose (CMC) was investigated as a water-dispersible binder for a high-voltage spinel electrode, LiNi0.5Mn1.5O4 (LNMO). Decreasing the cross-link density and introducing cyano (−CN) groups into SBR increased the battery-solvent uptake of the SBR, but the solubility of the polymers in the solvent remained negligibly low. The LNMO particles were successfully dispersed into the SBR/CMC-based aqueous slurry. The adhesive strength of the composite electrode layer on the Al foil increased at a higher rate with acrylonitrile-substituted SBR than it did with PVdF and other SBR electrodes due to the interaction between the introduced cyano group and LNMO particles. Surface analysis revealed that a relatively thick passivation layer formed on the cycled LNMO surface in the case of acrylonitrile-substituted SBR and CMC, suppressing surface degradation and manganese dissolution from LNMO. This passivation layer enabled higher retention capacity for both LNMO//Li half cells and LNMO//graphite full cells, as well as suppressed self-discharge even at an elevated temperature of 45 °C. The enhanced solvent uptake in the acrylonitrile-substituted SBRs also results in improved rate capability compared to that of standard SBR- and PVdF-based electrodes. The increased affinity of acrylonitrile-substituted SBRs to LNMO particles contributes to the formation of a relatively thick passivation layer, resulting in superior cycling performance in the LiNi0.5Mn1.5O4//graphite full cell.