Quasi-Solid-State Electrolyte Synthesized Using a Thiol-Ene Click Chemistry for Rechargeable Lithium Metal Batteries with Enhanced Safety

Gel Polymer Electrolytes for Lithium Batteries: Advantages, Challenges, and Perspectives

The increasing demand for high-energy-density and safe lithium batteries has driven significant advancements in electrolyte technology. Among the various options, gel polymer electrolytes (GPEs) have emerged as a promising solution, combining the high ionic conductivity of liquid electrolytes with the structural integrity of solid-state (polymer) electrolytes. GPEs possess a hybrid structure composed of a polymer matrix, lithium salts, one or more solvents or plasticizers, and often functional additives, offering exceptional flexibility, adaptability, and performance for advanced energy storage systems. This review provides a comprehensive analysis of GPE technology for lithium batteries, covering fabrication methods, advantages, and challenges, while emphasizing potential application scenarios and the underlying mechanisms. Finally, future research directions are outlined to provide valuable insights and guidelines for advancing GPE technology.

Residual Monomer-Induced Side Reactions in Gel Polymer Electrolytes: Unveiled High-Ni Cathode Failure in Lithium Batteries

Coupling gel polymer electrolytes (GPEs) with high-Ni cathodes (NCM) has emerged as a compelling approach for high-energy lithium-ion batteries, capable of circumventing NCM failure modes in liquid electrolytes. However, a detailed origin of capacity decay caused by residual monomers from an uncontrollable curing process has been largely ignored. Here, we report an in-depth investigation into the side reactions of unreacted monomers within typical GPEs at the NCM cathode interfaces by utilizing multiscale spectroscopy combined with theoretical calculations. We evaluate conversion rate-interphase structure correlation, revealing that interfacial evolution is highly dependent on residual monomer content. Specifically, the degradation chemistry in NCM cathodes with thermally cured gel polymer electrolytes (TC-GPEs) is governed by monomer-initiated interphase reconstruction, leading to an imbalanced interphase growth mode with organic-rich species and retarded diffusion kinetics through the electrode. We further reveal that organic ether/ester-based byproducts, caused by the oxidative decomposition of unreacted monomers during the initial charging step, are the key factor in the acceleration of NCM failure modes. This study elucidates the multiscale fading mechanism in the NCM||GPE system, providing improved insights into interphase issues in typical GPEs and facilitating the further development of long-life NCM||GPE prototypes for commercial applications.

Polymeric Electrolytes for Solid-state Lithium Ion Batteries: Structure Design, Electrochemical Properties and Cell Performances

Solid-state electrolytes are key to achieving high energy density, safety, and stability for lithium-ion batteries. In this Review, core indicators of solid polymer electrolytes are discussed in detail including ionic conductivity, interface compatibility, mechanical integrity, and cycling stability. Besides, we also summarize how above properties can be improved by design strategies of functional monomers, groups, and assembly of batteries. Structures and properties of polymers are investigated here to provide a basis for all-solid-state electrolyte design strategies of multi-component polymers. In addition, adjustment strategies of quasi-solid-state polymer electrolytes such as adding functional additives and carrying out structural design are also investigated, aiming at solving problems caused by simply adding liquids or small molecular plasticizer. We hope that fresh and established researchers can achieve a general perspective of solid polymer electrolytes via this Review and spur more extensive interests for exploration of high-performance lithium-ion batteries.

Click Chemistry in Lithium-Metal Batteries

Lithium-metal batteries (LMBs) are considered the "holy grail" of the next-generation energy storage systems, and solid-state electrolytes (SSEs) are a kind of critical component assembled in LMBs. However, as one of the most important branches of SSEs, polymer-based electrolytes (PEs) possess several native drawbacks including insufficient ionic conductivity and so on. Click chemistry is a simple, efficient, regioselective, and stereoselective synthesis method, which can be used not only for preparing PEs with outstanding physical and chemical performances, but also for optimizing the stability of solid electrolyte interphase (SEI) layer and elevate the cycling properties of LMBs effectively. Here it is primarily focused on evaluating the merits of click chemistry, summarizing its existing challenges and outlining its increasing role for the designing and fabrication of advanced PEs. The fundamental requirements for reconstructing artificial SEI layer through click chemistry are also summarized, with the aim to offer a thorough comprehension and provide a strategic guidance for exploring the potentials of click chemistry in the field of LMBs.

An In Situ Prepared Comb-like Polycaprolactone-Based Gel Electrolyte for High-Performance Lithium Metal Batteries

Herein, we present the synthesis and electrochemical performance of a comb-like polycaprolactone-based gel electrolyte from acrylate terminated polycaprolactone oligomers and liquid electrolyte for high-voltage lithium metal batteries. The ionic conductivity of this gel electrolyte at room temperature was measured to be 8.8 × 10^-3 S cm^-1, which is an exceptionally high value that is more than sufficient for the stable cycling of solid-state lithium metal batteries. The Li⁺ transference number was detected to be 0.45, facilitating the prohibition of concentration gradients and polarization, thereby prohibiting lithium dendrite formation. In addition, the gel electrolyte exhibits high oxidation voltage up to 5.0 V vs. Li⁺/Li and perfect compatibility against metallic lithium electrodes. The superior electrochemical properties provide the LiFePO₄-based solid-state lithium metal batteries with excellent cycling stability, displaying a high initial discharge capacity of 141 mAh g^-1 and an extraordinary capacity retention exceeding 74% of its initial specific capacity after being cycled for 280 cycles at 0.5C at room temperature. This paper presents a simple and effective in situ preparation process yielding an excellent gel electrolyte for high-performance lithium metal battery applications.

Organosulfur Materials for Rechargeable Batteries: Structure, Mechanism, and Application

Lithium-ion batteries have received significant attention over the last decades due to the wide application of portable electronics and increasing deployment of electric vehicles. In order to further enhance the performance of the batteries and overcome the capacity limitations of inorganic electrode materials, it is imperative to explore new cathode and functional materials for rechargeable lithium batteries. Organosulfur materials containing sulfur-sulfur bonds as a kind of promising organic electrode materials have the advantages of high capacities, abundant resources, tunable structures, and environmental benignity. In addition, organosulfur materials have been widely used in almost every aspect of rechargeable batteries because of their multiple functionalities. This review aims to provide a comprehensive overview on the development of organosulfur materials including the synthesis and application as cathode materials, electrolyte additives, electrolytes, binders, active materials in lithium redox flow batteries, and other metal battery systems. We also give an in-depth analysis of structure-property-performance relationship of organosulfur materials, and guidance for the future development of organosulfur materials for next generation rechargeable lithium batteries and beyond.

Ceramic-in-Polymer Hybrid Electrolytes with Enhanced Electrochemical Performance

Polymer electrolytes are attractive candidates to boost the application of rechargeable lithium metal batteries. Single-ion conducting polymers may reduce polarization and lithium dendrite growth, though these materials could be mechanically overly rigid, thus requiring ion mobilizers such as organic solvents to foster transport of Li ions. An inhomogeneous mobilizer distribution and occurrence of preferential Li transport pathways eventually yield favored spots for Li plating, thereby imposing additional mechanical stress and even premature cell short circuits. In this work, we explored ceramic-in-polymer hybrid electrolytes consisting of polymer blends of single-ion conducting polymer and PVdF-HFP, including EC/PC as swelling agents and silane-functionalized LATP particles. The hybrid electrolyte features an oxide-rich layer that notably stabilizes the interphase toward Li metal, enabling single-side lithium deposition for over 700 h at a current density of 0.1 mA cm^-2. The incorporated oxide particles significantly reduce the natural solvent uptake from 140 to 38 wt % despite maintaining reasonably high ionic conductivities. Its electrochemical performance was evaluated in LiNi_0.6Co_0.2Mn_0.2O₂ (NMC622)||Li metal cells, exhibiting impressive capacity retention over 300 cycles. Notably, very thin LiNbO₃ coating of the cathode material further boosts the cycling stability, resulting in an overall capacity retention of 78% over more than 600 cycles, clearly highlighting the potential of hybrid electrolyte concepts.

High Performance Carbon Fiber Structural Batteries Using Cellulose Nanocrystal Reinforced Polymer Electrolyte

In recent years, structural batteries have received great attention for future automotive application in which a load-bearing car panel is used as an energy storage. However, based on the current advances, achieving both high ionic conductivity and mechanical performance has remained a challenge. To address this challenge, this study introduces a cellulose nanocrystal (CNC) reinforced structural battery electrolyte (CSBE) consisting of CNC, triethylene glycol dimethyl ether (TriG) electrolyte containing a quasi-solid additive, e.g., cyclohexanedimethanol (CHDM), in a vinyl ester polymer. This green and renewable CSBE electrolyte system was in situ polymerized via reaction induced phase transition to form a high performance multidimensional channel electrolyte to be used in structural carbon fiber-based battery fabrication. The effect of various concentrations of CNC on the electrolyte ionic conductivity and mechanical properties was obtained in their relation to intermolecular interactions, interpreted by FTIR, Raman, Li NMR results. Compared to the neat SBE system, the optimized CSBE nanocomposite containing 2 wt % CNC shows a remarkable ionic conductivity of 1.1 × 10^-3 S cm^-1 at 30 °C, which reveals ∼300% improvement, alongside higher thermal stability. Based on the FTIR, Raman, Li NMR results, the content of CNC in the CSBE structure plays a crucial role not only in the formation of cellulose network skeleton but also in physical interaction with polymer matrix, providing an efficient Li⁺ pathway through the electrolyte matrix. The carbon fiber composite was fabricated by 2 wt % CNC reinforced SBE electrolyte to evaluate as a battery half-cell. The results demonstrated that by addition of 2 wt % CNC into SBE system, 7.6% and 33.9% improvements were achieved in specific capacity at 0.33 C and tensile strength, respectively, implying outstanding potential of ion conduction and mechanical load transfer between the carbon fibers and the electrolyte.

Lithium Salt-Induced In-Situ Polymerizations Enable Double Network Polymer Electrolytes

Structural design is an intriguing strategy to improve the physical and electrochemical performance of polymer electrolytes (PEs) for lithium-ion batteries. However, the complex synthetic process and introduction of non-electrolyte composition severely limit the development and practical application of PEs. Here we report a facile method for the fabrication of a double network polymer electrolyte (DN-PE) through combining the lithium salt-accelerated thiol-Michael addition and lithium salt-catalyzed radical polymerization. By adjusting the reaction temperature, the double network with the crosslinking structure could be in-situ formed step by step at room temperature and 80 °C. Notably, using lithium salt as the accelerator and catalyst avoids the addition of extra species and the related side reactions in the electrolyte system. Compared with single network polymer electrolyte (SN-PE), DN-PE has a distinctly improved mechanical strength and a better interfacial compatibility with the electrode, which leads to a stable cycling of the symmetric Li|DN-PE|Li cell over 1000 h at a current density of 0.05 mA cm^-2 . In addition, the Li|DN-PE|LiFePO₄ cell shows a high discharge specific capacity of 150.3 mAh g^-1 at 0.1 C and coulomb efficiency of 99%. This article is protected by copyright. All rights reserved.

Electrolyte Design for Lithium Metal Anode-Based Batteries Toward Extreme Temperature Application

Lithium anode-based batteries (LBs) are highly demanded in society owing to the high theoretical capacity and low reduction potential of metallic lithium. They are expected to see increasing deployment in performance critical areas including electric vehicles, grid storage, space, and sea vehicle operations. Unfortunately, competitive performance cannot be achieved when LBs operating under extreme temperature conditions where the lithium-ion chemistry fail to perform optimally. In this review, a brief overview of the challenges in developing LBs for low temperature (<0 °C) and high temperature (>60 °C) operation are provided followed by electrolyte design strategies involving Li salt modification, solvation structure optimization, additive introduction, and solid-state electrolyte utilization for LBs are introduced. Specifically, the prospects of using lithium metal batteries (LMBs), lithium sulfur (Li-S) batteries, and lithium oxygen (Li-O2 ) batteries for performance under low and high temperature applications are evaluated. These three chemistries are presented as prototypical examples of how the conventional low temperature charge transfer resistances and high temperature side reactions can be overcome. This review also points out the research direction of extreme temperature electrolyte design toward practical applications.