As demand for energy and power density of lithium-ion batteries (LIBs) continues to rise with the growth of new energy storage and electric vehicles, cobalt-free spinel LiNi_0.5Mn_1.5O₄ (LNMO) has emerged as a core candidate for next-generation high-voltage cathodes. This is due to its high operating voltage of 4.7 V, high theoretical energy density of 650 Wh kg⁻¹, low cost, and environmental benefits.

However, conventional electrolytes struggle to adapt to the complex working conditions of high voltage, fast charging, and wide temperature ranges. In high-voltage environments, they are prone to oxidative decomposition, which hinders ion transport and degrades electrode interface stability, while their inherent flammability poses a risk of thermal runaway.

Although existing weakly solvating electrolytes can form contact ion pair (CIP)/aggregate (AGG)-rich solvation structures to optimize the cathode/electrolyte interface (CEI), they generally suffer from drawbacks such as low salt solubility and poor oxidation resistance (ethers < 4.6 V).

Therefore, achieving rapid Li⁺ transport while maintaining weakly solvating characteristics and anion-enriched solvation structures has become a critical challenge in designing electrolytes for high-voltage, wide-temperature, and fast-charging lithium batteries.

To address this, a research group led by Professor Wang Pengfei from the School of Electrical Engineering at Xi'an Jiaotong University (XJTU) has proposed a "salt-in-salt mediated strong-weak synergistic" design strategy.

They constructed a DFEC/FEMC/TTE perfluorinated weakly-solvating system and introduced Mg(TFSI)₂ as a mild Lewis acid inducer to promote the dissociation of poorly soluble LiDFOB, thereby forming a CIP/AGG-enriched solvation structure involving multiple anions (PF₆⁻、DFOB⁻、TFSI⁻).

Through a "dragging effect," Mg²⁺ replaces components of the primary solvation shell of Li⁺, increasing the coordination sites available to PF₆⁻. This strengthens the cation-anion coordination while maintaining high Li⁺ mobility.

The MgF₂ generated in situ at the interface dynamically captures anions, inducing the formation of a thin, dense, and inorganic CEI rich in F, B, N, and S. This strategy optimizes bulk ion transport and interfacial stability, addressing the pain points of high desolvation energy barriers and large interfacial impedance commonly found in traditional weakly-solvating electrolytes.

This electrolyte enables LNMO||Li batteries to achieve both excellent fast-charging capability and long cycling performance across a wide temperature range of -30 to 70 C. It delivers a capacity of 106 mAh g⁻¹ at a 10 C rate, retains 89.2 percent capacity after 1,200 cycles at 5 C, and pouch cells maintain 88.9 percent capacity even after 400 cycles.

Nail penetration and accelerating rate calorimetry (ARC) tests verified its outstanding safety profile, demonstrating intrinsic flame retardancy and broad compatibility with other cathodes, including 4.6 V NCM811, 4.6 V NCM92, and LFP.

This research, titled Salt-in-Salt Mediated Weak-Solvent Electrolyte Enabling Fast-Charging and Wide-Temperature Lithium-Ion Batteries, has been published in Angewandte Chemie International Edition, a top-tier international academic journal.