Electrochemical Characteristics of a Polymer/Garnet Trilayer Composite Electrolyte for Solid-State Lithium-Metal Batteries

Flexible High Lithium-Ion Conducting PEO-Based Solid Polymer Electrolyte with Liquid Plasticizers for High Performance Solid-State Lithium Batteries

Lithium-ion secondary batteries (LIB) with high energy density have attracted much attention for electric vehicle (EV) applications. However, LIBs have a safety problem because these batteries contain a flammable organic electrolyte. As such, all-solid secondary batteries that are not flammable have been extensively reported recently. In this study, we have focused on polymer electrolytes, which is flexible and is expected to address the safety problem. However, the conventional polymer electrolytes have low electrial conductivity at room temperature. Various attempts have been made to solve this problem, such as the addition of inorganic fillers and ionic liquids; however, these composite polymer electrolytes have not yet reached a practical level of lithium-ion conductivity. In this study, high electrical conductivity and lithium dendrite formation-free PEO based composite electrolytes are developed with both a filler of Li6,4La3Zr1.4Ta0.6O12 and liquid plasticizers of tetraethylene glycol dimethyl ether and 1,2 dimethoxyethane. The proposed flexible polymer electrolyte shows a high electrical conduciviy of 6.01×10-4 S cm-1 at 25 °C.

Progress of Polymer Electrolytes Worked in Solid-State Lithium Batteries for Wide-Temperature Application

Solid-state Li-ion batteries have emerged as the most promising next-generation energy storage systems, offering theoretical advantages such as superior safety and higher energy density. However, polymer-based solid-state Li-ion batteries face challenges across wide temperature ranges. The primary issue lies in the fact that most polymer electrolytes exhibit relatively low ionic conductivity at or below room temperature. This sensitivity to temperature variations poses challenges in operating solid-state lithium batteries at sub-zero temperatures. Moreover, elevated working temperatures lead to polymer shrinkage and deformation, ultimately resulting in battery failure. To address this challenge of polymer-based solid-state batteries, this review presents an overview of various promising polymer electrolyte systems. The review provides insights into the temperature-dependent physical and electrochemical properties of polymers, aiming to expand the temperature range of operation. The review also further summarizes modification strategies for polymer electrolytes suited to diverse temperatures. The final section summarizes the performance of various polymer-based solid-state batteries at different temperatures. Valuable insights and potential future research directions for designing wide-temperature polymer electrolytes are presented based on the differences in battery performance. This information is intended to inspire practical applications of wide-temperature polymer-based solid-state batteries.

Enhanced High-Temperature Cycling Stability of Garnet-Based All Solid-State Lithium Battery Using a Multi-Functional Catholyte Buffer Layer

The pursuit of safer and high-performance lithium-ion batteries (LIBs) has triggered extensive research activities on solid-state batteries, while challenges related to the unstable electrode-electrolyte interface hinder their practical implementation. Polymer has been used extensively to improve the cathode-electrolyte interface in garnet-based all-solid-state LIBs (ASSLBs), while it introduces new concerns about thermal stability. In this study, we propose the incorporation of a multi-functional flame-retardant triphenyl phosphate additive into poly(ethylene oxide), acting as a thin buffer layer between LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and garnet electrolyte. Through electrochemical stability tests, cycling performance evaluations, interfacial thermal stability analysis and flammability tests, improved thermal stability (capacity retention of 98.5% after 100 cycles at 60 °C, and 89.6% after 50 cycles at 80 °C) and safety characteristics (safe and stable cycling up to 100 °C) are demonstrated. Based on various materials characterizations, the mechanism for the improved thermal stability of the interface is proposed. The results highlight the potential of multi-functional flame-retardant additives to address the challenges associated with the electrode-electrolyte interface in ASSLBs at high temperature. Efficient thermal modification in ASSLBs operating at elevated temperatures is also essential for enabling large-scale energy storage with safety being the primary concern.

Ultrathin and Robust Composite Electrolyte for Stable Solid-State Lithium Metal Batteries

Solid-state polymer electrolytes (SPEs) are considered as one of the most promising candidates for the next-generation lithium metal batteries (LMBs). However, the large thickness and severe interfacial side reactions with electrodes seriously restrict the application of SPEs. Herein, we developed an ultrathin and robust poly(vinylidene fluoride) (PVDF)-based composite polymer electrolyte (PPSE) by introducing polyethylene (PE) separators and SiO₂ nanoparticles with rich silicon hydroxyl (Si-OH) groups (nano-SiO₂). The thickness of the PPSE is only 20 μm but possesses a quite high mechanical strength of 64 MPa. The introduction of nano-SiO₂ fillers can tightly anchor the essential N,N-dimethylformamide (DMF) to reinforce the ion-transport ability of PVDF and suppress the side reactions of DMF with Li metal, which can significantly enhance the electrochemical stability of the PPSE. Meanwhile, the Si-OH groups on the surface of nano-SiO₂ as a Lewis acid promote the dissociation of the lithium bis(fluorosulfonyl)imide (LiFSI) and immobilize the FSI^- anions, achieving a high lithium transference number (0.59) and an ideal ionic conductivity (4.81 × 10^-4 S cm^-1) for the PPSE. The assembled Li/PPSE/Li battery can stably cycle for a record of 11,000 h, and the LiNi_0.8Co_0.1Mn_0.1O₂/PPSE/Li battery presents an initial specific capacity of 173.3 mA h g^-1 at 0.5 C, which can stably cycle 300 times. This work provides a new strategy for designing composite solid-state electrolytes with high mechanical strength and ionic conductivity by modulating their framework.

Status Quo on Graphene Electrode Catalysts for Improved Oxygen Reduction and Evolution Reactions in Li-Air Batteries

Reduced global warming is the goal of carbon neutrality. Therefore, batteries are considered to be the best alternatives to current fossil fuels and an icon of the emerging energy industry. Voltaic cells are one of the power sources more frequently employed than photovoltaic cells in vehicles, consumer electronics, energy storage systems, and medical equipment. The most adaptable voltaic cells are lithium-ion batteries, which have the potential to meet the eagerly anticipated demands of the power sector. Working to increase their power generating and storage capability is therefore a challenging area of scientific focus. Apart from typical Li-ion batteries, Li-Air (Li-O₂) batteries are expected to produce high theoretical power densities (3505 W h kg^-1), which are ten times greater than that of Li-ion batteries (387 W h kg^-1). On the other hand, there are many challenges to reaching their maximum power capacity. Due to the oxygen reduction reaction (ORR) and oxygen evolution reaction (OES), the cathode usually faces many problems. Designing robust structured catalytic electrode materials and optimizing the electrolytes to improve their ability is highly challenging. Graphene is a 2D material with a stable hexagonal carbon network with high surface area, electrical, thermal conductivity, and flexibility with excellent chemical stability that could be a robust electrode material for Li-O₂ batteries. In this review, we covered graphene-based Li-O₂ batteries along with their existing problems and updated advantages, with conclusions and future perspectives.

Lithium Nafion-Modified Li6.05Ga0.25La3Zr2O11.8F0.2 Trilayer Hybrid Solid Electrolyte for High-Voltage Cathodes in All-Solid-State Lithium-Metal Batteries

All-solid-state batteries containing ceramic-polymer solid electrolytes are possible alternatives to lithium-metal batteries containing liquid electrolytes in terms of their safety, energy storage, and stability at elevated temperatures. In this study we prepared a garnet-type Li_6.05Ga_0.25La₃Zr₂O_11.8F_0.2 (LGLZOF) solid electrolyte modified with lithium Nafion (LiNf) and incorporated it into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrixes. We used a solution-casting method to obtain bilayer (Bi-HSE) and trilayer (Tri-HSE) hybrid solid electrolytes. A layer of functionalized multiwalled carbon nanotubes (f-MWCNTs) coated with LiNf (LiNf@f-MWCNT) in the Tri-HSE led to good compatibility with the polymer slurry and adhered well to the Li anode, thereby improving the interfacial contact at the electrode-solid electrolyte interface and suppressing dendrite growth. The Tri-HSE membrane displayed high ionic conductivity (5.6 × 10^-4 S cm^-1 at 30 °C), a superior Li⁺ transference number (0.87), and a wide electrochemical window (0-5.0 V vs Li/Li⁺). In addition, Li symmetrical cells incorporating this hybrid electrolyte possessed excellent interfacial stability over 600 h at 0.1 mA cm^-2 and a high critical current density (1.5 mA cm^-2). Solid-state lithium batteries having the structure LiNf@LiNi_0.8Co_0.1Mn_0.1O₂/Tri-HSE/Li delivered excellent room-temperature stable cycling performance at 0.5C, with a capacity retention of 85.1% after 450 cycles.

Designing Versatile Polymers for Lithium-Ion Battery Applications: A Review

Solid-state electrolytes are a promising family of materials for the next generation of high-energy rechargeable lithium batteries. Polymer electrolytes (PEs) have been widely investigated due to their main advantages, which include easy processability, high safety, good mechanical flexibility, and low weight. This review presents recent scientific advances in the design of versatile polymer-based electrolytes and composite electrolytes, underlining the current limitations and remaining challenges while highlighting their technical accomplishments. The recent advances in PEs as a promising application in structural batteries are also emphasized.

Flexible, Mechanically Robust, Solid-State Electrolyte Membrane with Conducting Oxide-Enhanced 3D Nanofiber Networks for Lithium Batteries

Using a three-dimensional (3D) Li-ion conducting ceramic network, such as Li₇La₃Zr₂O₁₂ (LLZO) garnet-type oxide conductor, has proved to be a promising strategy to form continuous Li ion transfer paths in a polymer-based composite. However, the 3D network produced by brittle ceramic conductor nanofibers fails to provide sufficient mechanical adaptability. In this manuscript, we reported a new 3D ion-conducting network, which is synthesized from highly loaded LLZO nanoparticles reinforced conducting polymer nanofibers, by creating a lightweight continuous and interconnected LLZO-enhanced 3D network to outperform conducting heavy and brittle ceramic nanofibers to offer a new design principle of composite electrolyte membrane featuring all-round properties in mechanical robustness, structural flexibility, high ionic conductivity, lightweight, and high surface area. This composite-nanofiber design overcomes the issues of using ceramic-only nanoparticles, nanowires, or nanofibers in polymer composite electrolyte, and our work can be considered as a new generation of composite electrolyte membrane in composite electrolyte development.