ИСТИНА

The enhancement of volumetric energy density of the Li-ion batteries is critical to meet the requirements of electric vehicles and energy storage grids. The energy density of conventional LiFePO4 cathodes is limited by the amount of the added carbon conduit and PVdF binder which make up significant weight and volume fraction of the cathode. Using electrically conducting polymer binders is a promising approach for increasing the loading of active material in cathode to enhance its energy density. In the present study, the composite binders based on electrically conducting poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) and ionically conducting co-binding polymers – poly(ethylene oxide) (PEO) and sulfonated poly(phenylene oxide) (SPPO) – were developed. Both SPPO and PEO demonstrated good miscibility with PEDOT:PSS. The resulting composite binders exhibited film-forming properties, electronic conductivity (1–40 S cm–1), and Li+ ionic conductivity (10–5–10–4 S cm–1) as well as electrochemical stability over the potential range of 2.0–4.5 V vs. Li/Li+. The Li-ion battery cathodes with active material (95 wt.% of commercial LiFePO4/C) were fabricated using the developed binders. The cathodes were processed using “green” aqueous media in conventional fabrication procedure, avoiding toxic and expensive N-methyl-2-pyrrolidone solvent. The PEDOT:PSS/PEO binder revealed poor cyclic performance with conventional carbonate electrolytes due to the solubility of PEO in the electrolyte solution. However, that issue was resolved by using sulfolane-based electrolytes. The PEDOT:PSS/SPPO binder can be used in conventional carbonate electrolytes, showing high stability and cyclability. It was found that PEDOT:PSS increased the macroscopic electronic conductivity of cathode blends resulting in better utilization of the active material. On the other hand, co-binding polymers (PEO or SPPO) enhanced Li+ conduction and the adhesion of the cathode layer to the aluminum current collector. As a result, the specific capacity and cyclic performance of the developed cathodes were improved compared to conventional LiFePO4 cathodes. The addition of co-binding polymers to PEDOT:PSS increased the packing density of the active material. The resulting cathodes exhibited denser morphology leading to the enhanced volumetric capacity. The rate capability of the cathodes is highly influenced by the cathode porosity. The cathode containing 2.5 wt.% PEDOT:PSS, 2.5 wt.% SPPO, and 95 wt.% LiFePO4/C demonstrated the optimal porosity of 43% resulting in high volumetric energy density at discharge rates 0.1C–50C. In summary, the developed polymer binders can replace conventionally used carbon black and PVdF in the LiFePO4 cathode composition to enhance its specific capacity and volumetric energy density.