To meet the demands of high-voltage lithium-ion batteries (LIBs), we develop a novel electrolyte through theoretical calculations and electrochemical characterization. Triphenylphosphine oxide (TPPO) is introduced as a film-forming additive into a sulfone-based electrolyte containing 1 mol L⁻¹ lithium difluoro(oxalate)borate. Density functional theory calculations show that TPPO has a lower reduction potential than the sulfone-based solvent. Hence, TPPO should be oxidized before the sulfone-based solvent and form a cathode electrolyte interphase layer on the Li-rich cathode. Our research findings demonstrate that adding 2 wt% TPPO to the sulfone-based electrolyte considerably enhances the ionic conductivity within a range of 20–60 ℃. In addition, it increases the discharge capacity of LIBs in a range of 2–4.8 V while maintaining excellent rate performance and cycling stability. Flammability tests and thermal gravimetric analysis results indicate excellent nonflammability and thermal stability of the electrolyte.

It is of great significance to design and innovate electrode materials with unique structures to effectively optimize the electrochemical properties of the secondary battery. Herein, inspired by neuron networks, an ingenious synthesis is proposed to fabricate NiSe with multidimensional micro-nano structures, followed by in situ construction of NiSe/NiO heterostructures via a temporary calcination. The major structure of bulk NiSe synthesized by the solvothermal method is 3-dimensional micron cluster spherical particles interwoven by uniform one-dimensional nanofibers. Such structures possess the synergistic advantages of nano and micro materials. After a temporary calcination in air, NiSe/NiO heterostructures should be formed in the bulk NiSe, which provides a built-in electric field to enhance diffusion kinetics of sodium ions. This special neural-like network and heterojunction structures ensure the excellent structural stability combined with rapid kinetics of the electrode, releasing 310.9 mAh g⁻¹ reversible capacity after 2,000 cycles at 10 A g⁻¹. Furthermore, the electrochemical storage and ion transport mechanisms are elaborated by electrochemical analysis and theoretical calculation in more detail.