An Adjustable‐Porosity Plastic Crystal Electrolyte Enables High‐Performance All‐Solid‐State Lithium‐Oxygen Batteries

Electrospinning-assisted porous skeleton electrolytes for semi-solid Li-O2 batteries

Solid-state lithium-oxygen batteries offer great promise in meeting the practical demand for high-energy-density and safe energy storage. We have developed fibrous gel polymer electrolytes (GPEs) using a polyacrylonitrile (PAN) matrix via electrospinning. The 3D structure of GPEs enhances electrolyte absorption, while the interconnected design promotes strong interactions between Li+ and polar groups within the PAN matrix, thereby improving ion transport efficiency. In practical tests, both lithium symmetric cells and Li-O2 batteries demonstrated the ability to operate at high current densities over long cycles.

Light Enables the Cathodic Interface Reaction Reversibility in Solid-State Lithium-Oxygen Batteries

Limited triple-phase boundaries arising from the accumulation of solid discharge product(s) in solid-state cathodes (SSCs) pose a challenge to high-property solid-state lithium-oxygen batteries (SSLOBs). Light-assisted SSLOBs have been gradually explored as an ingenious system; however, the fundamental mechanisms of the SSCs interface behavior remain unclear. Here, we discovered that light assistance can enhance the fast inner-sphere charge transfer in SSCs and regulate the discharge products with spherical particles generated via the surface growth model. Moreover, the high photoelectron excitation and transportation capabilities of SSCs can retard cathodic catalytic decay by avoiding structural degradation of the cathode with a reduced charge voltage. The light-induced SSLOBs exhibited excellent stability (170 cycles) with a low discharge-charge polarization overpotential (0.27 V). Furthermore, transparent SSLOBs with exceptional flexibility, mechanical stability, and multiform shapes were fabricated for theory-to-practical applications in sunlight-induced batteries. Our study opens new opportunities for the introduction of solar energy into energy storage systems.

Recent advances and interfacial challenges in solid-state electrolytes for rechargeable Li-air batteries

Among the promising batteries for electric vehicles, rechargeable Li-air (O2) batteries (LABs) have risen keen interest due to their high energy density. However, safety issues of conventional nonaqueous electrolytes remain the bottleneck of practical implementation of LABs. Solid-state electrolytes (SSEs) with non-flammable and eco-friendly properties are expected to alleviate their safety concerns, which have become a research focus in the research field of LABs. Herein, we present a systematic review on the progress of SSEs for rechargeable LABs, mainly focusing on the interfacial issues existing between the SSEs and electrodes. The discussion highlights the challenges and feasible strategies for designing suitable SSEs for LABs.

In Situ Thermal Polymerization of a Succinonitrile-Based Gel Polymer Electrolyte for Lithium-Oxygen Batteries

For lithium-oxygen batteries (LOBs), the leakage and volatilization of a liquid electrolyte and its poor electrochemical performance are the main reasons for the slow industrial advancement. Searching for more stable electrolyte substrates and reducing the use of liquid solvents are crucial to the development of LOBs. In this work, a well-designed succinonitrile-based (SN) gel polymer electrolyte (GPE-SLFE) is prepared by in situ thermal cross-linking of an ethoxylate trimethylolpropane triacrylate (ETPTA) monomer. The continuous Li⁺ transfer channel, formed by the synergistic effect of an SN-based plastic crystal electrolyte and an ETPTA polymer network, endows the GPE-SLFE with a high room-temperature ionic conductivity (1.61 mS cm^-1 at 25 °C), a high lithium-ion transference number (t_Li+ = 0.489), and excellent long-term stability of the Li/GPE-SLFE/Li symmetric cell at a current density of 0.1 mA cm^-2 for over 220 h. Furthermore, cells with the GPE-SLFE exhibit a high discharge specific capacity of 4629.7 mAh g^-1 and achieve 40 cycles.

Advanced Nonflammable Organic Electrolyte Promises Safer Li-Metal Batteries: From Solvation Structure Perspectives

Batteries with a Li-metal anode have recently attracted extensive attention from the battery communities owing to their high energy density. However, severe dendrite growth hinders their practical applications. More seriously, when Li dendrites pierce the separators and trigger short circuit in a highly flammable organic electrolyte, the results would be catastrophic. Although the issues of growth of Li dendrites have been almost addressed by various methods, the highly flammable nature of conventional organic liquid electrolytes is still a lingering fear facing high-energy-density Li-metal batteries given the possibility of thermal runaway of the high-voltage cathode. Recently, various kinds of nonflammable liquid- or solid-state electrolytes have shown great potential toward safer Li-metal batteries with minimal detrimental effect on the battery performance or even enhanced electrochemical performance. In this review, recent advances in developing nonflammable electrolyte for high-energy-density Li-metal batteries including high-concentration electrolyte, localized high-concentration electrolyte, fluorinated electrolyte, ionic liquid electrolyte, and polymer electrolyte are summarized. Then, the solvation structure of different kinds of nonflammable liquid and polymer electrolytes are analyzed to provide insight into the mechanism for dendrite suppression and fire extinguishing. Finally, guidelines for future design of nonflammable electrolyte for safer Li-metal batteries are provided.

Filler-Integrated Composite Polymer Electrolyte for Solid-State Lithium Batteries

Composite polymer electrolytes (CPEs) utilizing fillers as the promoting component bridge the gap between solid polymer electrolytes and inorganic solid electrolytes. The integration of fillers into the polymer matrices is demonstrated as a prevailing strategy to enhance Li-ion transport and assist in constructing Li⁺ -conducting electrode-electrolyte interface layer, which addresses the two key barriers of solid-state lithium batteries (SSLBs): low ionic conductivity of electrolyte and high interfacial impedance. Recent review articles have largely focused on the performance of a broad spectrum of CPEs and the general effects of fillers on SSLBs device. Recognizing this, in this review, after briefly presenting the categories of fillers (traditional and emerged) and the promoted ionic conducting mechanisms in CPEs, the progress in the interfacial structure design principle, with the emphasis on the crucial influence of filler size, concentration, and hybridization strategies on filler-polymer interface that is the most critical to Li-ion transport is assessed. The latest exciting advances on filler-enabled in situ generation of a Li⁺ -conductive layer at the electrode-electrolyte interface to greatly reduce the interfacial impedance are further elaborated. Finally, this review discusses the challenges to be addressed, outlines research directions, and provides a future vision for developing advanced CPEs for high-performing SSLBs.

Light-Assisted Metal-Air Batteries: Progress, Challenges, and Perspectives

Metal-air batteries are considered one of the most promising next-generation energy storage devices owing to their ultrahigh theoretical specific energy. However, sluggish cathode kinetics (O₂ and CO₂ reduction/evolution) result in large overpotentials and low round-trip efficiencies which seriously hinder their practical applications. Utilizing light to drive slow cathode processes has increasingly becoming a promising solution to this issue. Considering the rapid development and emerging issues of this field, this Review summarizes the current understanding of light-assisted metal-air batteries in terms of configurations and mechanisms, provides general design strategies and specific examples of photocathodes, systematically discusses the influence of light on batteries, and finally identifies existing gaps and future priorities for the development of practical light-assisted metal-air batteries.

Metal-air batteries: progress and perspective

The metal-air batteries with the largest theoretical energy densities have been paid much more attention. However, metal-air batteries including Li-air/O₂, Li-CO₂, Na-air/O_2, and Zn-air/O₂ batteries, are complex systems that have their respective scientific problems, such as metal dendrite forming/deforming, the kinetics of redox mediators for oxygen reduction/evolution reactions, high overpotentials, desolution of CO₂, H₂O, etc. from the air and related side reactions on both anode and cathode. It should be the main direction to address these shortages to improve performance. Here, we summarized recently research progress in these metal-air/O₂ batteries. Some perspectives are also provided for these research fields.

Integrated Design for Regulating the Interface of a Solid-State Lithium-Oxygen Battery with an Improved Electrochemical Performance

A composite solid-state electrolyte (SSE) with acceptable safety and durability is considered as a potential candidate for high-performance lithium-oxygen (Li-O₂) batteries. Herein, to address the safety issues and improve the electrochemical performance of Li-O₂ batteries, a solvent-free composite SSE is prepared based on the thermal initiation of poly(ethylene glycol) diacrylate radical polymerization, and an integrated battery is achieved by injecting an electrolyte precursor between electrodes during the assembly process through a simple heat treatment. The Li-metal symmetric cells based on this composite SSE achieve a critical current density of 0.8 mA cm^-2 and a stable cycle life of over 900 h at a current density of 0.2 mA cm^-2. This composite SSE effectively inhibits the erosion of O₂ on the Li metal anode, optimizes the interface between the electrolyte and cathode, and provides abundant reaction sites for the electrochemical reactions during cycling. The integrated solid-state Li-O₂ battery prepared in this work achieves stable long cycling (118 cycles) at a current density of 500 mA g^-1 at room temperature, showing the promising future application prospects.

Tailoring electronic-ionic local environment for solid-state Li-O2 battery by engineering crystal structure

Solid-state Li-O2 batteries (SSLOBs) have attracted considerable attention because of their high energy density and superior safety. However, their sluggish kinetics have severely impeded their practical application. Despite efforts to design highly efficient catalysts, efficient oxygen reaction evolution at gas-solid interfaces and fast transport pathways in solid-state electrodes remain challenging. Here, we develop a dual electronic-ionic microenvironment to substantially enhance oxygen electrolysis in solid-state batteries. By designing a lithium-decorative catalyst with an engineering crystal structure, the coordinatively unsaturated sites and high concentration of defects alleviate the limitations of electronic-ionic transport in solid interfaces and create a balanced gas-solid microenvironment for solid-state oxygen electrolysis. This strategy facilitates oxygen reduction reaction, mediates the transport of reaction species, and promotes the decomposition of the discharge products, contributing to a high specific capacity with a stable cycling life. Our work provides previously unknown insight into structure-property relationships in solid-state electrolysis for SSLOBs.

Soluble and Perfluorinated Polyelectrolyte for Safe and High-Performance Li-O2 Batteries

The severe performance degradation of high-capacity Li-O₂ batteries induced by Li dendrite growth and concentration polarization from the low Li⁺ transfer number of conventional electrolytes hinder their practical applications. Herein, lithiated Nafion (LN) with the sulfonic group immobilized on the perfluorinated backbone has been designed as a soluble lithium salt for preparing a less flammable polyelectrolyte solution, which not only simultaneously achieves a high Li⁺ transfer number (0.84) and conductivity (2.5 mS cm^-1 ), but also the perfluorinated anion of LN produces a LiF-rich SEI for protecting the Li anode from dendrite growth. Thus, the Li-O₂ battery with a LN-based electrolyte achieves an all-round performance improvement, like low charge overpotential (0.18 V), large discharge capacity (9508 mAh g^-1 ), and excellent cycling performance (225 cycles). Besides, the fabricated pouch-type Li-air cells exhibit promising applications to power electronic equipment with satisfactory safety.

Assessing the Importance of Cation Size in the Tetragonal-Cubic Phase Transition in Lithium-Garnet Electrolytes

Lithium garnets are promising solid-state electrolytes for next-generation lithium-ion batteries. These materials have high ionic conductivity, a wide electrochemical window and stability with Li metal. However, lithium garnets have a maximum limit of seven lithium atoms per formula unit (e.g., La₃ Zr₂ Li₇ O₁₂ ), before the system transitions from a cubic to a tetragonal phase with poor ionic mobility. This arises from full occupation of the Li sites. Hence, the most conductive lithium garnets have Li between 6-6.55 Li per formula unit, which maintains the cubic symmetry and the disordered Li sub-lattice. The tetragonal phase, however, forms the highly conducting cubic phase at higher temperatures, thought to arise from increased cell volume and entropic stabilisation permitting Li disorder. However, little work has been undertaken in understanding the controlling factors of this phase transition, which could enable enhanced dopant strategies to maintain room temperature cubic garnet at higher Li contents. Here, a series of nine tetragonal garnets were synthesised and analysed by variable temperature XRD to understand the dependence of site substitution on the phase transition temperature. Interestingly the octahedral site cation radius was identified as the key parameter for the transition temperature with larger or smaller dopants altering the transition temperature noticeably. A site substitution was, however, found to make little difference irrespective of significant changes to cell volume.

Designing Polymer-in-Salt Electrolyte and Fully Infiltrated 3D Electrode for Integrated Solid-State Lithium Batteries

Solid-state lithium batteries (SSLBs) are promising owing to enhanced safety and high energy density but plagued by the relatively low ionic conductivity of solid-state electrolytes and large electrolyte-electrode interfacial resistance. Herein, we design a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer-in-salt solid electrolyte (PISSE) with high room-temperature ionic conductivity (1.24×10^-4  S cm^-1 ) and construct a model integrated TiO₂ /Li SSLB with 3D fully infiltration of solid electrolyte. With forming aggregated ion clusters, unique ionic channels are generated in the PISSE, providing much faster Li⁺ transport than common polymer electrolytes. The integrated device achieves maximized interfacial contact and electrochemical and mechanical stability, with performance close to liquid electrolyte. A pouch cell made of 2 SSLB units in series shows high voltage plateau (3.7 V) and volumetric energy density comparable to many commercial thin-film batteries.

Inorganic Fillers in Composite Gel Polymer Electrolytes for High-Performance Lithium and Non-Lithium Polymer Batteries

Among the various types of polymer electrolytes, gel polymer electrolytes have been considered as promising electrolytes for high-performance lithium and non-lithium batteries. The introduction of inorganic fillers into the polymer-salt system of gel polymer electrolytes has emerged as an effective strategy to achieve high ionic conductivity and excellent interfacial contact with the electrode. In this review, the detailed roles of inorganic fillers in composite gel polymer electrolytes are presented based on their physical and electrochemical properties in lithium and non-lithium polymer batteries. First, we summarize the historical developments of gel polymer electrolytes. Then, a list of detailed fillers applied in gel polymer electrolytes is presented. Possible mechanisms of conductivity enhancement by the addition of inorganic fillers are discussed for each inorganic filler. Subsequently, inorganic filler/polymer composite electrolytes studied for use in various battery systems, including Li-, Na-, Mg-, and Zn-ion batteries, are discussed. Finally, the future perspectives and requirements of the current composite gel polymer electrolyte technologies are highlighted.

Lithium-Air Batteries: Air-Electrochemistry and Anode Stabilization

ConspectusIt is a permanent issue for modern society to develop high-energy-density, low-cost, and safe batteries to promote technological innovation and revolutionize the human lifestyle. However, the current popular Li-ion batteries are approaching their ceiling in energy density, and thus other battery systems with more power need to be proposed and studied to guide this revolution. Lithium-air batteries are among the candidates for next-generation batteries because of their high energy density (3500 Wh/kg). The past 20 years have witnessed rapid developments of lithium-air batteries in electrochemistry and material engineering with scientists' collaboration from all over the world. Despite these advances, the investigation on Li-air batteries is still in its infancy, and many bottleneck problems, including fundamental and application difficulties, are waiting to be resolved. For the electrolyte, it is prone to be attacked by intermediates (LiO₂, O₂^-, ¹O₂, O₂^2-) and decomposed at high voltage, accompanying side reactions that will induce cathode passivation. For the lithium anode, it can be corroded severely by H₂O and the side products, thus protection methods are urgently needed. As an integrated system, the realization of high-performance Li-air batteries requires the three components to be optimized simultaneously.In this Account, we are going to summarize our progress for optimizing Li-air batteries in the past decade, including air-electrochemistry and anode optimization. Air-electrochemistry involves the interactions among electrolytes, cathodes, and air, which is a complex issue to understand. The search for stable electrolytes is first introduced because at the early age of its development, the use of incompatible Li-ion battery electrolytes leads to some misunderstandings and troubles in the advances of Li-air batteries. After finding suitable electrolytes for Li-air batteries, the fundamental research in the reaction mechanism starts to boom, and the performance has achieved great improvement. Then, air electrode engineering is introduced to give a general design principle. Examples of carbon-based cathodes and all-metal cathodes are discussed. In addition, to understand the influence of air components on Li-air batteries, the electro-activity of N₂ has been tested and the role of CO₂ in Li-O₂/CO₂ has been refreshed. Following this, the strategies for anode optimization, including constructing artificial films, introducing hydrophobic polymer electrolytes, adding electrolyte additives, and designing alloy anodes, have been discussed. Finally, we advocate researchers in this field to conduct cell level optimizations and consider their application scenarios to promote the commercialization of Li-air batteries in the near future.