Cellulose-based high-loading flexible electrode for lithium-ion battery with high volumetric energy density

Thick electrodes with high loading are attractive for high-energy storage devices, but they face major challenges of slow ion transfer and poor mechanical stability. Carbon templates such as reduced graphene oxide and carbon nanotube can promote the electrons transfer of thick electrodes and enhance their strength, but they still exhibit a complex producing process, slow Li+ transfer and high cost. Herein, a nanofiber network with double fast Li+ and electrons transfer pathways by the self-assembly of carbon nanoparticles on the negatively charged natural cellulose fibers was designed. The abundant oxygen-containing functional groups from the cellulose fibers enabled the electrode with abundant negative charge which can adsorb the neutral particles with strong electrostatic interaction. And the Density Functional Theory calculation demonstrates that oxygen-containing functional groups also has stronger adsorption energy for PF6− anions in electrolyte which can promote the desolvation of the solvated Li salts, thus promote Li+ transfer. After integration with lithium iron phosphate, this network achieves a robust high-loaded electrode with good electrical conductivity and shortened ion transfer pathways without traditional current collector and binder. Based on the robust electrode structure and fast transfer kinetics of electrons and Li+, the batteries exhibit excellent cycle stability with capacity retention of 98 % after long 400 cycles and high volumetric energy density of 740 Wh/L, which greatly surpass the conventional batteries with coating LiFePO4 (LFP) cathode. Given the low-cost raw materials and convenient operation, the design of self-standing flexible electrodes with high loading will offer a promising and effective strategy for other storage devices with high energy.