Solid-State Electrolytes in Lithium-Sulfur Batteries: Latest Progresses and Prospects

Developing Cathode Films for Practical All-Solid-State Lithium-Sulfur Batteries

The development of all-solid-state lithium-sulfur batteries (ASSLSBs) toward large-scale electrochemical energy storage is driven by the higher specific energies and lower cost in comparison with the state-of-the-art Li-ion batteries. Yet, insufficient mechanistic understanding and quantitative parameters of the key components in sulfur-based cathode hinders the advancement of the ASSLSB technologies. This review offers a comprehensive analysis of electrode parameters, including specific capacity, voltage, S mass loading and S content toward establishing the specific energy (Wh kg-1) and energy density (Wh L-1) of the ASSLSBs. Additionally, this work critically evaluates the progress in enhancing lithium ion and electron percolation and mitigating electrochemical-mechanical degradation in sulfur-based cathodes. Last, a critical outlook on potential future research directions is provided to guide the rational design of high-performance sulfur-based cathodes toward practical ASSLSBs.

Advanced Polymers in Cathodes and Electrolytes for Lithium-Sulfur Batteries: Progress and Prospects

Lithium-sulfur (Li-S) batteries, which store energy through reversible redox reactions with multiple electron transfers, are seen as one of the promising energy storage systems of the future due to their outstanding advantages. However, the shuttle effect, volume expansion, low conductivity of sulfur cathodes, and uncontrollable dendrite phenomenon of the lithium anodes have hindered the further application of Li-S batteries. In order to solve the problems and clarify the electrochemical reaction mechanism, various types of materials, such as metal compounds and carbon materials, are used in Li-S batteries. Polymers, as a class of inexpensive, lightweight, and electrochemically stable materials, enable the construction of low-cost, high-specific capacity Li-S batteries. Moreover, polymers can be multifunctionalized by obtaining rich structures through molecular design, allowing them to be applied not only in cathodes, but also in binders and solid-state electrolytes to optimize electrochemical performance from multiple perspectives. The most widely used areas related to polymer applications in Li-S batteries, including cathodes and electrolytes, are selected for a comprehensive overview, and the relevant mechanisms of polymer action in different components are discussed. Finally, the prospects for the practical application of polymers in Li-S batteries are presented in terms of advanced characterization and mechanistic analysis.

An Advanced Gel Polymer Electrolyte for Solid-State Lithium Metal Batteries

All-solid-state lithium metal batteries (LMBs) are regarded as one of the most viable energy storage devices and their comprehensive properties are mainly controlled by solid electrolytes and interface compatibility. This work proposes an advanced poly(vinylidene fluoride-hexafluoropropylene) based gel polymer electrolyte (AP-GPEs) via functional superposition strategy, which involves incorporating butyl acrylate and polyethylene glycol diacrylate as elastic optimization framework, triethyl phosphate and fluoroethylene carbonate as flameproof liquid plasticizers, and Li7La3Zr2O12 nanowires (LLZO-w) as ion-conductive fillers, endowing the designed AP-GPEs/LLZO-w membrane with high mechanical strength, excellent flexibility, low flammability, low activation energy (0.137 eV), and improved ionic conductivity (0.42 × 10-3 S cm-1 at 20 °C) due to continuous ionic transport pathways. Additionally, the AP-GPEs/LLZO-w membrane shows good safety and chemical/electrochemical compatibility with the lithium anode, owing to the synergistic effect of LLZO-w filler, flexible frameworks, and flame retardants. Consequently, the LiFePO4/Li batteries assembled with AP-GPEs/LLZO-w electrolyte exhibit enhanced cycling performance (87.3% capacity retention after 600 cycles at 1 C) and notable high-rate capacity (93.3 mAh g-1 at 5 C). This work proposes a novel functional superposition strategy for the synthesis of high-performance comprehensive GPEs for LMBs.

An approach to enhance carbon/polymer interface compatibility for lithium-ion supercapacitors

Developing high-efficiency and easy machining components, as well as high-performance energy storage components, is a pressing issue on the road to economic and social progress. Optimizing the interface compatibility between composites and promoting the efficient utilization of the electrochemical active sites are crucial factors in improving the electrochemical performance of composite electrode materials. To address this challenge, a carbon-based flexible lithium-ion supercapacitor positive material (Polyaniline @ Carbon Foam-Supercritical carbon dioxide (P@C-SC)) is synthesized using commercial melamine foam and aniline monomer. The synthesis process utilizes supercritical fluid technology, effectively solving the interface compatibility problem between the composite materials. Consequently, the electrochemical performance of the composite electrode materials is significantly improved. The supercapacitive properties of this material are investigated in 1 mol/L sulfuric acid (H2SO4) and lithium sulfate (Li2SO4) electrolytes using a three-electrode system. In H2SO4 electrolyte, the material exhibits a working voltage of up to 2.2 V and a specific capacitance of 898F/g (at 1 A/g), resulting in a maximum energy density of 50.8 Wh kg-1. Furthermore, this electrode demonstrates superior lithium storage performance, with a specific capacity of approximately 900 mAh/g (at 1 A/g) and a retention of about 400 mAh/g after 200 cycles, along with a coulomb efficiency of 100%. This work offers insights into the integrated design of composite materials with improved electrochemical properties and interface compatibility, thus providing potential applicability of supercritical fluids in the field of lithium-ion supercapacitors.