Salt-with-Salt, a novel strategy to design the flexible solid electrolyte membrane for highly safe lithium metal batteries

Ion transport mechanisms in covalent organic frameworks: implications for technology

Covalent organic frameworks (COFs) have emerged as promising materials for ion conduction due to their highly tunable structures and excellent electrochemical stability. This review paper explores the mechanisms of ion conduction in COFs, focusing on how these materials facilitate ion transport across their ordered structures, which is crucial for applications such as solid electrolytes in batteries and fuel cells. We discuss the design strategies employed to enhance ion conductivity, including pore size optimization, functionalization with ionic groups, and the incorporation of solvent molecules and salts. Additionally, we examine the various applications of ion-conductive COFs, particularly in energy storage and conversion technologies, highlighting recent advancements and future directions in this field. This review paper aims to provide a comprehensive overview of the current state of research on ion-conductive COFs, offering insights into their potential to design highly ion-conductive COFs considering not only fundamental studies but also practical perspectives for advanced electrochemical devices.

Across Interfacial Li+ Conduction Accelerated by a Single-Ion Conducting Polymer in Ceramic-Rich Composite Electrolytes for Solid-State Batteries

Composite electrolytes have been accepted as the most promising species for solid-state batteries, exhibiting the synergistic advantages of solid polymer electrolytes (SPEs) and solid ceramic electrolytes (SCEs). Unfortunately, the interrupted Li+ conduction across the SPE and SCE interface hinders the ionic conductivity improvement of composite electrolytes. In our study on a ceramic-rich composite electrolyte (CRCE) membrane composed of borate polyanion-based lithiated poly(vinyl formal) (LiPVFM) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) particles, it is found that the strong interaction between the polyanions in LiPVFM and LATP particles results in a uniform distribution of ceramic particles at a high proportion of 50 wt % and good robustness of the electrolyte membrane with a Young's modulus of 9.20 GPa. More importantly, ab initio molecular dynamics simulation and experimental results demonstrate that Li+ conduction across the SPE and SCE interface is induced by the polyanion-based polymer due to its high lithium-ion transference number and similar Li+ diffusion coefficient with the SCE. Therefore, the unblocked Li+ conduction among ceramic particles dominates in the CRCE membrane with a high ionic conductivity of 6.60 × 10-4 S cm-1 at 25 °C, a lithium-ion transference number of 0.84, and a wide electrochemical stable window of 5.0 V (vs Li/Li+). Consequently, the high nickel ternary cathode LiNi0.8Mn0.1Co0.1O2-based batteries with CRCE deliver a high-rate capability of 135.08 mAh g-1 at 1.0 C and a prolonged cycle life of 100 cycles at 0.2 C between 3.0 and 4.3 V. The polyanion-induced Li+ conduction across the interface sheds new light on solving composite electrolyte problems for solid-state batteries.

Flexible All-in-one Quasi-Solid-State Batteries Enabled by Low-water-content Hydrogel Films

The high conductivities and good mechanical properties of hydrogel electrolyte films are critical for energy storage devices with high flexibility, fast redox kinetics, and long life. Herein, a low water content (6.63 wt%) hydrogel film is prepared, and a favorable environment is created, with an electrochemical stability window of 2.26 V and a high ionic conductivity of 2.6 mS cm-1 . The hydrogel film exhibits good folding ability, low in-plane swelling, and anti-freezing abilities. These properties are benefitted by immobilizing free water molecules on the abundant oxygenic groups of polymer fibers in the hydrogel film, offering a unique 3D channel to allow Li+ to quickly transport along the polymer network. Therefore, the hydrogel film-based all-in-one flexible cell exhibits stable cycling performance with a retention of 81.8% of the initial capacity after 500 cycles at room temperature and 66.2% of capacity retention at -30 °C. Furthermore, the full cell with high cathode loading (≈21 mg cm-2 ) exhibits a high areal capacity of 2.5 mAh cm-2 (≈119 mAh g-1 ). The overall merits of flexible all-in-one quasi-solid-state batteries demonstrate high potential to be used for power wearable electronics.

In Situ Construction Channels of Lithium-Ion Fast Transport and Uniform Deposition to Ensure Safe High-Performance Solid Batteries

Solid-state lithium-ion batteries (SLIBs) are the promising development direction for future power sources because of their high energy density and reliable safety. To optimize the ionic conductivity at room temperature (RT) and charge/discharge performance to obtain reusable polymer electrolytes (PEs), polyvinylidene fluoride (PVDF), and poly(vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)) copolymer combined with polymerized methyl methacrylate (MMA) monomers are used as substrates to prepare PE (LiTFSI/OMMT/PVDF/P(VDF-HFP)/PMMA [LOPPM]). LOPPM has interconnected lithium-ion 3D network channels. The organic-modified montmorillonite (OMMT) is rich in the Lewis acid centers, which promoted lithium salt dissociation. LOPPM PE possessed high ionic conductivity of 1.1 × 10-3 S cm-1 and a lithium-ion transference number of 0.54. The capacity retention of the battery remained 100% after 100 cycles at RT and 0.5 C. The initial capacity of one with the second-recycled LOPPM PE is 123.9 mAh g-1 . This work offered a feasible pathway for developing high-performance and reusable LIBs.

A Critical Review for an Accurate Electrochemical Stability Window Measurement of Solid Polymer and Composite Electrolytes

All-solid-state lithium batteries (ASSLB) are very promising for the future development of next generation lithium battery systems due to their increased energy density and improved safety. ASSLB employing Solid Polymer Electrolytes (SPE) and Solid Composite Electrolytes (SCE) in particular have attracted significant attention. Among the several expected requirements for a battery system (high ionic conductivity, safety, mechanical stability), increasing the energy density and the cycle life relies on the electrochemical stability window of the SPE or SCE. Most published works target the importance of ionic conductivity (undoubtedly a crucial parameter) and often identify the Electrochemical Stability Window (ESW) of the electrolyte as a secondary parameter. In this review, we first present a summary of recent publications on SPE and SCE with a particular focus on the analysis of their electrochemical stability. The goal of the second part is to propose a review of optimized and improved electrochemical methods, leading to a better understanding and a better evaluation of the ESW of the SPE and the SCE which is, once again, a critical parameter for high stability and high performance ASSLB applications.

Thermal Stability Analysis of Lithium-Ion Battery Electrolytes Based on Lithium Bis(trifluoromethanesulfonyl)imide-Lithium Difluoro(oxalato)Borate Dual-Salt

Lithium-ion batteries with conventional LiPF₆ carbonate electrolytes are prone to failure at high temperature. In this work, the thermal stability of a dual-salt electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiODFB) in carbonate solvents was analyzed by accelerated rate calorimetry (ARC) and differential scanning calorimetry (DSC). LiTFSI-LiODFB dual-salt carbonate electrolyte decomposed when the temperature exceeded 138.5 °C in the DSC test and decomposed at 271.0 °C in the ARC test. The former is the onset decomposition temperature of the solvents in the electrolyte, and the latter is the LiTFSI-LiODFB dual salts. Flynn-Wall-Ozawa, Starink, and autocatalytic models were applied to determine pyrolysis kinetic parameters. The average apparent activation energy of the dual-salt electrolyte was 53.25 kJ/mol. According to the various model fitting, the thermal decomposition process of the dual-salt electrolyte followed the autocatalytic model. The results showed that the LiTFSI-LiODFB dual-salt electrolyte is significantly better than the LiPF₆ electrolyte in terms of thermal stability.

Macromolecular Design of Lithium Conductive Polymer as Electrolyte for Solid-State Lithium Batteries

In the development of solid-state lithium batteries, solid polymer electrolyte (SPE) has drawn extensive concerns for its thermal and chemical stability, low density, and good processability. Especially SPE efficiently suppresses the formation of lithium dendrite and promotes battery safety. However, most of SPE is derived from the matrix with simple functional group, which suffers from low ionic conductivity, reduced mechanical properties after conductivity modification, bad electrochemical stability, and low lithium-ion transference number. Appling macromolecular design with multiple functional groups to polymer matrix is accepted as a strategy to solve the problems of SPE fundamentally. In this review, macromolecular design based on lithium conducting groups is summarized including copolymerization, network construction, and grafting. Meanwhile, the construction of single-ion conductor polymer is also focused herein. Moreover, synergistic effects between the designed matrix, lithium salt, and fillers are reviewed with the objective to further improve the performance of SPE. At last, future studies on macromolecular design are proposed in the development of SPE for solid-state batteries with high energy density and durability.

A 3D composite lithium metal anode with pre-fabricated LiZn via reactive wetting

Lithium metal anodes (LMAs) have been suffering from challenging problems of solid electrolyte interface (SEI) formation and lithium morphological instability (LMI), which lead to a poor cycling life and notorious safety concerns. Herein, we prepared a 3D composite anode (Li@NFZO) by heat treatment and reactive wetting where nickel foam serves as the framework and LiZn/Li fills in the holes. Interestingly, it is found that such a nickel foam + LiZn combination can largely reinforce the electrode/electrolyte interface stability and thus slows down the electrolyte consumption. Furthermore, uniformly distributed and lithiophilic LiZn contributes to the homogenous Li plating so that dendrites can be geometrically disturbed. Therefore, stable cycling for 185 h at 5 mA h cm-2/5 mA cm-2 in symmetrical cells, 2.8× bare Li, was achieved. The cycling life of the LiFePO4//Li@NFZO full-cell at ≈6.6 g A h-1 electrolyte addition was prolonged to 120 cycles (80% capacity retention), compared to 66 cycles for the LiFePO4//Li full-cell.