High-Voltage Lithium Batteries Enabled by Facile In Situ Fabrication of Monophasic Cellulose-Based Single-Ion Conductors

The growing demand for high-energy-density, safe, and sustainable lithium-ion batteries (LIBs) necessitates the development of innovative electrolytes. Herein, we present a facile in situ preparation strategy for fabricating a high-performance single-ion conductor (SC). This SC is based on hydroxypropyl cellulose (HPC) integrated with polyethylene glycol diacrylate cross-linker, in combination with sodium styrene sulfonate (NaSS) as a functional monomer. The introduction of NaSS is crucial, as it introduces sulfonate groups that are immobilized within the polymer network, enabling selective lithium-ion transport. This approach offers a significant advancement over conventional polyether-based gel polymer electrolytes (GPEs), which usually suffer from limited oxidative stability and require the use of separators, particularly in high-voltage battery applications. The in situ polymerization method presented here eliminates the need for a separator and offers several key advantages: rapid processability, excellent scalability, and the formation of a stable solid electrolyte interface. The result is a robust, separator-free GPE. Our HPC-based single-ion conductor (MHPC SC) exhibits a high lithium transference number of 0.89 and an ionic conductivity of 2.4 mS cm^-1 at room temperature. These properties are attributed to efficient lithium-ion transport through its synergistic effect of the polyanionic conductor and HPC matrix. The mechanically robust and highly conformal polymer network effectively suppresses detrimental interfacial reactions and mitigates dendrite growth, resulting in an enhanced cycling stability. Notably, the MHPC SC enables stable operation with high-voltage cathodes up to 4.3 V, achieving 94% capacity retention over 100 cycles. These findings highlight the potential of cellulose-based GPEs as a sustainable and high-performance electrolyte that significantly enhances both the safety and performance of advanced LIBs.