Solvent-Mediated Synthesis and Characterization of Li3InCl6 Electrolytes for All-Solid-State Li-Ion Battery Applications.

Superionic halides have attracted widespread attention as solid electrolytes due to their excellent ionic conductivity, soft texture, and stability toward high-voltage electrode materials. Among them, Li3InCl6 has aroused interest since it can be easily synthesized in water or ethanol. However, investigations into the influence of solvents on both the crystal structure and properties remain unexplored. In this work, Li3InCl6 is synthesized by three different solvents: water, ethanol, and water-ethanol mixture, and the difference in properties has been studied. The results show that the product obtained by the ethanol solvent demonstrates the largest unit cell parameters with more vacancies, which tend to crystallize on the (131) plane and provide the 3D isotropic network migration for lithium-ions. Thus, it exhibits the highest ionic conductivity (1.06 mS cm-1) at room temperature and the lowest binding energy (0.272 eV). The assembled all-solid-state lithium metal batteries (ASSLMBs) employing Li3InCl6 electrolytes demonstrate a high initial discharge capacity of 153.9 mA h g-1 at 0.1 C (1 C = 170 mA h g-1) and the reversible capacity retention rate can reach 82.83% after 50 cycles. This work studies the difference in ionic conductivity between Li3InCl6 electrolytes synthesized by different solvents, which can provide a reference for the future synthesis of halide electrolytes and enable their practical application in halide-based ASSLMBs with a high energy density.

A Localized High-Concentration Water/Organic Hybrid Electrolyte for 2.5 V Li4Ti5O12/LiMn2O4 Batteries.

The "solvent-in-salt" electrolytes for an aqueous system, including "water-in-salt" electrolytes and "bisolvent-in-salt" electrolytes, have shown significantly improved electrochemical stability toward low-voltage anodes and high-voltage cathodes. However, the heavy use of salt raises concerns of high cost, high viscosity, inferior wettability, and poor low-temperature performance. Herein, a "localized bisolvent-in-salt electrolyte" is proposed by introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as the diluent to the high-concentration water/sulfolane hybrid (BSiS-SL) electrolytes, forming a ternary solvent-based electrolyte, Li(H2O)0.9SL1.3·TTE1.3 (HS-TTE). The introduction of TTE dilutes the compact ionic clusters, while the original primary Li+ solvation structure remains, and in the meantime, boosts the formation of a robust solid electrolyte interphase. As a result, a wide electrochemically stable window of 4.4 V is achieved. In comparison with the bisolvent BSiS-SL system, the trisolvent HS-TTE electrolyte exhibits a low salt concentration of 2.1 mol kg-1, resulting in drastically reduced viscosity, superb separator wettability, and largely improved low-temperature performance. The constructed 2.5 V Li4Ti5O12/LiMn2O4 cell shows an excellent capacity retention of 80.7% after 800 cycles, and the cell can even work at -30 °C. With these extraordinary advantages, the fundamental designing strategy of the HS-TTE electrolyte developed in this work can promote the practical applications of solvent-in-salt electrolytes.

Tuning the Electrolyte Solvation Structure via a Nonaqueous Co-Solvent to Enable High-Voltage Aqueous Lithium-Ion Batteries.

"Water-in-salt" electrolytes have significantly expanded the electrochemical stability window of the aqueous electrolytes from 1.23 to 3 V, making highly safe 3.0 V aqueous Li-ion batteries possible. However, the awkward cathodic limit located at 1.9 V (versus Li+/Li) and the high cost of the expensive salts hinder the practical applications. In this work, an ideal "bisolvent-in-salt" electrolyte is reported to tune the electrolyte solvation structure via introducing sulfolane as the co-solvent, which significantly enhances the cathodic limit of water to 1.0 V (versus Li+/Li) at a significantly reduced salt concentration of 5.7 mol kg-1. Due to the competitive coordination of sulfolane, water molecules that should be in the primary solvation sheath of Li+ are partly substituted by the electrochemically stable sulfolane, significantly decreasing the hydrogen evolution. Meanwhile, the unique electrolyte structures enable the formation and stabilization of a robust solid electrolyte interphase. As a result, a 2.4 V LiMn2O4/Li4Ti5O12 full cell with a high energy density of 128 Wh kg-1 is realized. The hybrid water/sulfolane electrolytes provide a brand new strategy for designing aqueous electrolytes with an expanded electrochemical stability window at a low salt concentration.

Shaping Li Deposits from Wild Dendrites to Regular Crystals via the Ferroelectric Effect.

Manipulating the Li plating behavior remains a challenging task toward Li-based high-energy batteries. Generally, the Li plating process is kinetically controlled by ion transport, concentration gradient, local electric field, etc. A myriad of strategies have been developed for homogenizing the kinetics; however, such kinetics-controlled Li plating nature is barely changed. Herein, a ferroelectric substrate comprised of homogeneously distributed BaTiO3 was deployed and the Li plating behavior was transferred from a kinetic-controlled to a thermodynamic-preferred mode via ferroelectric effect. Such Li deposits with uniform hexagonal and cubic shapes are highly in accord with the thermodynamic principle where the body-centered cubic Li is apt to expose more (110) facets as possible to maximally minimize its surface energy. The mechanism was later confirmed due to the spontaneous polarization of BTO particles trigged by an applied electric field. The instantly generated reverse polarized field and charged ends not only neutralized the electric field but also leveled the ion distribution at the interface.

Wrapping Sb2Te3 with a Graphite Layer toward High Volumetric Energy and Long Cycle Li-Ion Batteries.

Many recent efforts on the electrode design for advanced Li-ion batteries (LIBs) are often devoted to increasing the gravimetric capacity, but little attention is paid to the volumetric capacity which is more critical for practical application. Though the alloying-type anode materials are quite attractive, the challenge is that they must be composited with a large amount of carbon materials (e.g., GO, rGO, CNT) to buffer their large volume change, which would undoubtedly sacrifice the volumetric energy density of the whole electrode due to the carbon's low tap density (∼0.05 g/cm3). Herein, we propose the unique layered Sb2Te3, which possesses high conductivity and a large volumetric capacity (3419 mAh/cm3), to be served as the alternative anode for LIBs. Furthermore, we introduce natural graphite, which is low price and with high density (2.25 g/cm3), into Sb2Te3 to successfully build a novel Sb2Te3@Gra composite in which the Sb2Te3 particles are wrapped by graphite layers. Interestingly, this modified Sb2Te3@Gra exhibits much more superior cycle stability (570 mAh/g after 200 cycles, 96% retention) than pure Sb2Te3 (130 mAh/g after 200 cycles, 22% retention), while keeping its original large volumetric capacity output (∼3200 mAh/cm3) at the same time. More specially, it enables a reversible structure recovery of Sb2Te3, guaranteeing the electrode integrity and cyclability. These extraordinary phenomena are investigated in detail, whose results display that the outer graphite layer plays an important role by facilitating the intimate contact with Sb2Te3 particles and protecting them from pulverization. Besides, such graphite layer greatly promotes the electron-transfer during lithiation, helping to improve the rate capability (372 mAh/g at 2000 mA/g, 60% retention). Consequently, the assembled Sb2Te3//LiCoO2 full cell delivers a large capacity of 500 mAh/g, with stable discharge plateau and cycle stability, revealing its high potential for practical application.

Investigation of the temperature-dependent behaviours of Li metal anode.

Effects of temperature on Li nucleation/deposition behaviours and electrochemical performances are thoroughly investigated. Higher temperature leads to lower nucleation density with larger deposit sizes due to the reduced surface migration barrier and accelerated ion diffusion, plus better lifespans and coulombic efficiency owing to the relatively conducive morphology characteristics and a favorable SEI layer.