High-voltage LiNi₀.₅Mn₁.₅O₄ (LNMO) cobalt-free cathode material is considered a promising cathode for sustainable energy storage, mainly when fabricated into electrodes with water-soluble binders. Here, the influence of different binder types, including conventional polyvinylidene fluoride, water-soluble carboxymethyl cellulose (CMC) and conductive poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) with CMC on the electrochemical performance of commercial LiNi0.5Mn1.5O4-based cathode materials was evaluated through galvanostatic charge/discharge cycling (GCD) and cyclic voltammetry (CV). Applying a conductive binder with a low content enabled the highest capacity value of 137 mAh∙g−1 for LNMO at a current density of 0.1 C. The use of the composite water-soluble conductive binder CMC/PEDOT:PSS improved the electrochemical properties of the cathode compared to the cathode based on CMC alone. The results achieved with the CMC/PEDOT:PSS binder are comparable to those of PVDF, which suggests that water-soluble and eco-friendly binders may be a promising alternative for high-voltage cathodes. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry were utilized to estimate the diffusion coefficients of lithium.