Separator-Wetted, Acid- and Water-Scavenged Electrolyte with Optimized Li-Ion Solvation to Form Dual Efficient Electrode Electrolyte Interphases via Hexa-Functional Additive

Visualizing and Regulating Dynamic Evolution of Interfacial Electrolyte Configuration during De-solvation Process on Lithium-Metal Anode

Acting as a passive protective layer, solid-electrolyte interphase (SEI) plays a crucial role in maintaining the stability of the Li-metal anode. Derived from the reductive decomposition of electrolytes (e.g., anion and solvent), the SEI construction presents as an interfacial process accompanied by the dynamic de-solvation process during Li-metal plating. However, typical electrolyte engineering and related SEI modification strategies always ignore the dynamic evolution of electrolyte configuration at the Li/electrolyte interface, which essentially determines the SEI architecture. Herein, by employing advanced electrochemical in situ FT-IR and MRI technologies, we directly visualize the dynamic variations of solvation environments involving Li+-solvent/anion. Remarkably, a weakened Li+-solvent interaction and anion-lean interfacial electrolyte configuration have been synchronously revealed, which is difficult for the fabrication of anion-derived SEI layer. Moreover, as a simple electrochemical regulation strategy, pulse protocol was introduced to effectively restore the interfacial anion concentration, resulting in an enhanced LiF-rich SEI layer and improved Li-metal plating/stripping reversibility.

Research Progress of Liquid Electrolytes for Lithium Metal Batteries at High Temperatures

Lithium metal batteries (LMBs) are the most promising high energy density energy storage technologies for electric vehicles, military, and aerospace applications. LMBs require further improvement to operate efficiently when chronically or routinely exposed to high temperatures. Electrolyte engineering with high temperature tolerance and electrode compatibility has been essential to the development of LMBs. In this review, the primary obstacles to achieving high-temperature LMBs are first explored. Subsequently, electrolyte tailoring options, such as lithium salt optimization, solvation structure modification, and the addition of additives are reviewed in detail. In addition, the feasibility of utilizing LMBs at high temperatures has been investigated. In conclusion, this study provides insights and perspectives for future research on electrolyte design at high temperatures.

Dendrite inhibited and dead lithium activated dual-function additive for lithium metal batteries

In this study, 2-fluoro-5-iodopyridine (2-F-5-IPy) was used as an electrolyte additive, which can not only protect the negative electrode effectively by forming a stable SEI, but also convert dead lithium into active lithium. Benefits from this are a capacity retention of a Li‖LiFePO4 cell after 300 cycles from 36.5% to 89.4%, and the symmetrical cell can work stably for more than 800 hours. Therefore, the addition of 2-F-5-IPy can effectively improve the performance of lithium metal batteries.

Multifunctional electrolyte additive for realizing high-temperature and high-voltage lithium metal batteries

Methyl 1H-1,2,4-triazole-3-carboxylate (MTC) was added into lithium metal batteries as an electrolyte additive, and not only did this addition lead to formation of solid electrolyte interfaces to protect both the anode and cathode, but the added MTC also served as a Lewis base in removing HF from the electrolyte to prevent the electrolyte from deteriorating. Therefore, the addition of MTC, in an appropriate amount, can be very effective at improving the electrochemical performance of lithium metal batteries.

Low-temperature electrolytes based on linear carboxylic ester co-solvents for SiO x /graphite composite anodes

Silicon-based anode materials have been applied in lithium-ion batteries with high energy density. However, developing electrolytes that can meet the specific requirements of these batteries at low temperatures still remains a challenge. Herein, we report the effect of linear carboxylic ester ethyl propionate (EP), as the co-solvent in a carbonate-based electrolyte, on SiO _x /graphite (SiOC) composite anodes. Using electrolytes with EP, the anode provides better electrochemical performance at both low temperatures and ambient temperature, showing a capacity of 680.31 mA h g^-1 at -50 °C and 0.1C (63.66% retention relative to that at 25 °C), and a capacity retention of 97.02% after 100 cycles at 25 °C and 0.5C. Within the EP-containing electrolyte, SiOC‖LiCoO₂ full cells also exhibit superior cycling stability at -20 °C for 200 cycles. These substantial improvements of the EP co-solvent at low temperatures are probably due to its involvement to form a solid electrolyte interphase with high integrity and facile transport kinetics in electrochemical processes.

Lithium Hexamethyldisilazide Endows Li||NCM811 Battery with Superior Performance

The construction of stable cathode electrolyte interphase (CEI) is the key to improve the NCM811 particle structure and interfacial stability via electrolyte engineering. In He's work, lithium hexamethyldisilazide (LiHMDS) as the electrolyte additive is proposed to facilitate the generation of stable CEI on NCM811 cathode surface and eliminate H2O and HF in the electrolyte at the same time, which boosts the cycling performance of Li||NCM811 battery up to 1000 or 500 cycles with 4.5 V cut-off voltage at 25 or 60 °C.

Ionic Liquid-Type Additive for Lithium Metal Batteries Operated in LiPF6 Based-Electrolyte Containing 2500 ppm H2O

The presence of trace amounts of moisture in the electrolyte can cause hydrolysis of LiPF₆ and deteriorate the stability of lithium metal batteries. Herein, we propose a multifunctional ionic liquid-type additive constituting a 1-methyl-1-butyl pyrrolidium cation (Py₁₄⁺) and an acetate anion (CH₃COO^-) (denoted as IL-AC in this study), which can effectively adsorb the trace moisture and thus prevent the hydrolysis of LiPF₆ via intermolecular interactions. The prepared IL-AC can also remove HF to suppress the dissolution of transition metal ions from cathode materials through the reaction CH₃COO^- + HF → CH₃COOH + F^-. Compared with the baseline electrolyte, the contents of HF and transition metal ions are significantly lower in the electrolyte with 0.5% IL-AC. Upon the addition of 0.5% IL-AC additive and 2500 ppm H₂O, the Li||NCM811 battery shows a capacity of 153.7 mAh g^-1 after 300 cycles, while the Li||LNMO battery possesses stable capacity retention of 93.22% after 500 cycles at 1C and a Coulombic efficiency greater than 99%. Thus, this work provides a convenient and effective method to absorb trace amounts of water and remove HF in the electrolyte and provides a new path for the expensive and tedious process of water removal from the electrolyte in industry.