Development of Quasi-solid-state Na-ion Battery Based on DPEPA-derived Gel Polymer Electrolyte

Compared to Li-ion batteries, Na-ion batteries hold significant advantages and market value for achieving low-cost and large-scale energy storage, thanks to the utilization of cheap and abundant Na resources. However, the use of highly flammable liquid electrolytes with leaky risk raises safety concerns for conventional Na-ion batteries under abuse conditions such as mechanical damage, short-circuiting, and thermal runaway. Limited electrochemical stability of liquid electrolytes also hinders further enhancement of the performance of Na-ion batteries for practical use. This study reports a facile way for the preparation of high-performance gel polymer electrolyte (GPE) by thermal-driven radical in-situ polymerization of dipentaerythritol penta-/hexa-acrylat (DPEPA). This GPE exhibits an ionic conductivity of 1.97 mS<middle dot>cm(-1), a Na+ transference number of 0.66, and a broad electrochemical stability window. The DPEPA displays a lower lowest unoccupied molecular orbit (LUMO) energy level than that of ethylene carbonate (EC) and diethyl carbonate (DEC) solvents, allowing for its preferential decomposition alongside NaPF6 on the anode surface. This leads to a stable organic-inorganic composite film of solid-state electrolyte interphase, inhibiting the decomposition of electrolyte solvents on the anode surface. The quasi-solid-state Na-ion battery employing Na(Ni 1/3Fe1/3Mn (1/3))O-2 (NFM) cathode and hard carbon (HC) anode in this GPE exhibits a high capacity retention rate of 92% after 300 stable cycles at a current density of 120 mA<middle dot>g(-1), while achieving the specific capacities of 99-120 mAh<middle dot>g(-1) within a wide temperature range of 20-80 degrees C. In-situ X-ray diffractometer analysis reveals the highly reversible structural evolution of the NFM cathode during Na storage and the "adsorption-pore-filling" mechanism of Na+ storage in the HC anode. All data in this research demonstrates that introducing polymers with low LUMO energy levels proves an effective approach to enhance the electrochemical stability of solid-state Na-ion batteries while improving cell safety.