Antioxidation Mechanism of Highly Concentrated Electrolytes at High Voltage

570 Wh kg⁻1-Grade Lithium Metal Pouch Cell with 4.9V Highly Li+ Conductive Armor-Like Cathode Electrolyte Interphase via Partially Fluorinated Electrolyte Engineering

Lithium-rich manganese-based layered oxides (LRMOs) are promisingly used in high-energy lithium metal pouch cells due to high specific capacity/working voltage. However, the interfacial stability of LRMOs remains challenging. To address this question, a novel armor-like cathode electrolyte interphase (CEI) model is proposed for stabilizing LRMO cathode at 4.9 V by exploring partially fluorinated electrolyte formulation. The fluoroethylene carbonate (FEC) and tris (trimethylsilyl) borate (TMSB) in formulated electrolyte largely contribute to the formation of 4.9 V armor-like CEI with LiBxOy and LixPOyFz outer layer and LiF- and Li3PO4-rich inner part. Such CEI effectively inhibits lattice oxygen loss and facilitates the Li+ migration smoothly for guaranteeing LRMO cathode to deliver superior cycling and rate performance. As expected, Li||LRMO batteries with such electrolyte achieve capacity retention of 85.7% with high average Coulomb efficiency (CE) of 99.64% after 300 cycles at 4.8 V/0.5 C, and even obtain capacity retention of 87.4% after 100 cycles at higher cut-off voltage of 4.9 V. Meanwhile, the 9 Ah-class Li||LRMO pouch cells with formulated electrolyte show over thirty-eight stable cycling life with high energy density of 576 Wh kg-1 at 4.8 V.

Engineering a Dynamic Solvent-Phobic Liquid Electrolyte Interphase for Long-Life Lithium Metal Batteries

The heterogeneity, species diversity, and poor mechanical stability of solid electrolyte interphases (SEIs) in conventional carbonate electrolytes result in the irreversible exhaustion of lithium (Li) and electrolytes during cycling, hindering the practical applications of Li metal batteries (LMBs). Herein, this work proposes a solvent-phobic dynamic liquid electrolyte interphase (DLEI) on a Li metal (Li-PFbTHF (perfluoro-butyltetrahydrofuran)) surface that selectively transports salt and induces salt-derived SEI formation. The solvent-phobic DLEI with C-F-rich groups dramatically reduces the side reactions between Li, carbonate solvents, and humid air, forming a LiF/Li3PO4-rich SEI. In situ electrochemical impedance spectroscopy and Ab-initio molecular dynamics demonstrate that DLEI effectively stabilizes the interface between Li metal and the carbonate electrolyte. Specifically, the LiFePO4||Li-PFbTHF cells deliver 80.4% capacity retention after 1000 cycles at 1.0 C, excellent rate capacity (108.2 mAh g-1 at 5.0 C), and 90.2% capacity retention after 550 cycles at 1.0 C in full-cells (negative/positive (N/P) ratio of 8) with high LiFePO4 loadings (15.6 mg cm-2) in carbonate electrolyte. In addition, the 0.55 Ah pouch cell of 252.0 Wh kg-1 delivers stable cycling. Hence, this study provides an effective strategy for controlling salt-derived SEI to improve the cycling performances of carbonate-based LMBs.

Interface Regulation via Electric Double Layer for Rechargeable Batteries

Interphases, especially the electrochemically formed solid electrolyte interphase (SEI), are significantly important for cycling stability, reaction kinetics and safety of rechargeable batteries. The structure and composition of the electric double layer (EDL) greatly affect the formation of the SEI and the performance of electrodes. However, as far as we know, there is no review discussing the theme specifically. Herein, the recent substantial progress for EDL and its impact on the formation of SEI in rechargeable batteries are reviewed and discussed. Firstly, the specific adsorption of electrolyte components on electrodes' surface and the ionic solvation structure are introduced. Furthermore, various methods for controlling EDL in different electrode systems are described. Finally, the potential future advancements of the SEI through the manipulation of EDL are discussed, aiming to enhance the electrochemical performance of rechargeable batteries.

Inhibition of transition-metal dissolution with an inert soluble product interface constructed by high-concentration electrolyte

The formation of a compact and stable cathode electrolyte interphase (CEI) film is a promising way to improve the high voltage resistance of lithium-ion batteries (LIBs). However, challenges arise due to the corrosion of hydrogen fluoride (HF) and the dissolution of transition metal ions (TMs) in harsh conditions. To address this issue, researchers have constructed an anion-derived CEI film enriched with LiF and LiPO₂F₂ soluble product on the surface of LiNi_0.5Mn_1.5O₄ (LNMO) cathode in highly concentrated electrolytes (HCEs). The strong binding of LiF and LiPO₂F₂ generated an inert LiPO₂F₂ soluble product interface, which inhibited HF corrosion and maintained the spinel structure of LNMO, contributing to a capacity retention of 92% after 200 cycles at 55°C in the resulting cell with a soluble LiPO₂F₂-containing CEI film. This new approach sheds light on improving the electrode/electrolyte interface for high-energy LIBs.