A sandwich-type composite polymer electrolyte for all-solid-state lithium metal batteries with high areal capacity and cycling stability

Composite Solid-State Electrolyte with Vertical Ion Transport Channels for All-Solid-State Lithium Metal Batteries

Composite solid electrolytes (CSEs) consisting of polymers and fast ionic conductors are considered a promising strategy for realizing safe rechargeable batteries with high energy density. However, randomly distributed fast ionic conductor fillers in the polymer matrix result in tortuous and discontinuous ion channels, which severely constrains the ion transport capacity and restricts its practical application. Here, CSEs with highly loaded vertical ion transport channels are fabricated by magnetically manipulating the alignment of Li0.35La0.55TiO3 nanowires. The construction of densely packed, vertically aligned ion transport channels can effectively enhance the ion transport capacity of the electrolyte, thereby significantly increasing ionic conductivity. At room temperature (RT), the presented CSE exhibits a remarkable ionic conductivity of up to 2.5 × 10-4 S cm-1. The assembled LiFePO4/Li cell delivers high capacities of 118 mAh g-1 at 5 C at 60 °C and a RT capacity of 115 mAh g-1 can be achieved at a charging rate of 0.5 C. This work paves an encouraging avenue for further development of advanced CSEs that favor lithium metal batteries with high energy density and electrochemical performance.

High-Performance Pure Polymer Electrolytes with Enhanced Ionic Conductivity for Room-Temperature Applications

All-solid-state lithium metal batteries (ASSLMBs) are renowned for their high energy density and safety, positioning them as leading candidates for next-generation energy storage solutions. In this study, pure polymer solid-state electrolytes are developed using the solution casting method, optimized for room temperature operation. The base material, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), is enhanced with succinonitrile (SN) and polyacrylonitrile (PAN) to improve its electrochemical performance at room temperature. The optimized electrolyte, PSP-0.05, demonstrated superior characteristics, including an ionic conductivity (σ) of 3.2 × 10-4 S cm-1 and a wide voltage window of up to 5 V. When integrated into full batteries, PSP-0.05 exhibited exceptional performance in multiplicative cycling tests at room temperature, achieving discharge specific capacities of 132 and 113 mAh g-1 at 3 and 5 C rates, respectively. Additionally, long-term cycling at 1 C rate resulted in an initial discharge-specific capacity of 145.2 mAh g-1 with over 94.9% capacity retention after 1000 cycles. Given the simplicity of the preparation process and its impressive electrochemical properties, the PSP-0.05 electrolyte holds significant potential for practical applications in safer ASSLMBs.

Wide-Temperature and High-Rate Operation of Lithium Metal Batteries Enabled by an Ionic Liquid Functionalized Quasi-Solid-State Electrolyte

The development of high-energy-density solid-state lithium metal battery has been hindered by the unstable cycling of Ni-rich cathodes at high rate and limited wide-temperatures adoptability. In this study, an ionic liquid functionalized quasi-solid-state electrolyte (FQSE) is prepared to address these challenges. The FQSE features a semi-immobilized ionic liquid capable of anchoring solvent molecules through electrostatic interactions, which facilitates Li+ desolvation and reduces deleterious solvent-cathode reactions. The FQSE exhibits impressive electrochemical characteristics, including high ionic conductivity (1.9 mS cm-1 at 30 °C and 0.2 mS cm-1 at -30 °C) and a Li+ transfer number of 0.7. Consequently, Li/NCM811 cells incorporating FQSE demonstrate exceptional stability during high-rate cycling, enduring 700 cycles at 1 C. Notably, the Li/LFP cells with FQSE maintain high capacity across a wide temperature range, from -30 to 60 °C. This research provides a new way to promote the practical application of high-energy lithium metal batteries.

Gradual gradient distribution composite solid electrolyte for solid-state lithium metal batteries with ameliorated electrochemical performance

Composite solid electrolytes (CSEs) have emerged as promising contenders for tackling the safety concerns associated with lithium metal batteries and attaining elevated energy densities. Nonetheless, augmenting ion conductivity and curtailing the growth of lithium dendrites within the electrolyte remain pressing challenges. We have developed CSEs featuring a unique structure, in which Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is distributed in a gradient decline from the center to both sides (GCSE). This distinctive arrangement encompasses heightened polymer content at the edges, thereby enhancing the compatibility between CSEs and electrode materials. Concurrently, the escalated LLZTO content at the center functions to impede the proliferation of lithium dendrites. The uniform gradient distribution state facilitates the consistent and rapid transport of lithium ions. At room temperature, GCSE exhibits an ionic conductivity of 1.5 × 10-4 S cm-1, with stable constant current cycling of lithium for over 1200 h. Furthermore, CR2032 coin batteries with a LiFePO4 (LFP)|GCSE|Li configuration demonstrate excellent rate performance and cycling stability, yielding a discharge capacity of 120 mA h g-1 at 0.5C and retaining 90 % capacity after 200 cycles at 60 °C. Flexible solid electrolytes with gradient structures offer substantial advantages in dealing with ion conductivity and inhibition of lithium dendrites, thereby expected to propel the practical application of lithium metal batteries.

Flexible Composite Electrolyte Membranes with Fast Ion Transport Channels for Solid-State Lithium Batteries

Numerous endeavors have been dedicated to the development of composite polymer electrolyte (CPE) membranes for all-solid-state batteries (SSBs). However, insufficient ionic conductivity and mechanical properties still pose great challenges in practical applications. In this study, a flexible composite electrolyte membrane (FCPE) with fast ion transport channels was prepared using a phase conversion process combined with in situ polymerization. The polyvinylidene fluoride-hexafluoro propylene (PVDF-HFP) polymer matrix incorporated with lithium lanthanum zirconate (LLZTO) formed a 3D net-like structure, and the in situ polymerized polyvinyl ethylene carbonate (PVEC) enhanced the interface connection. This 3D network, with multiple rapid pathways for Li+ that effectively control Li+ flux, led to uniform lithium deposition. Moreover, the symmetrical lithium cells that used FCPE exhibited high stability after 1200 h of cycling at 0.1 mA cm-2. Specifically, all-solid-state lithium batteries coupled with LiFePO4 cathodes can stably cycle for over 100 cycles at room temperature with high Coulombic efficiencies. Furthermore, after 100 cycles, the infrared spectrum shows that the structure of FCPE remains stable. This work demonstrates a novel insight for designing a flexible composite electrolyte for highly safe SSBs.

Progress and Perspectives on the Development of Pouch-Type Lithium Metal Batteries

Lithium (Li) metal batteries (LMBs) are the "holy grail" in the energy storage field due to their high energy density (theoretically >500 Wh kg-1 ). Recently, tremendous efforts have been made to promote the research & development (R&D) of pouch-type LMBs toward practical application. This article aims to provide a comprehensive and in-depth review of recent progress on pouch-type LMBs from full cell aspect, and to offer insights to guide its future development. It will review pouch-type LMBs using both liquid and solid-state electrolytes, and cover topics related to both Li and cathode (including LiNix Coy Mn1-x-y O2 , S and O2 ) as both electrodes impact the battery performance. The key performance criteria of pouch-type LMBs and their relationship in between are introduced first, then the major challenges facing the development of pouch-type LMBs are discussed in detail, especially those severely aggravated in pouch cells compared with coin cells. Subsequently, the recent progress on mechanistic understandings of the degradation of pouch-type LMBs is summarized, followed with the practical strategies that have been utilized to address these issues and to improve the key performance criteria of pouch-type LMBs. In the end, it provides perspectives on advancing the R&Ds of pouch-type LMBs towards their application in practice.

Imidazolium-Type Poly(ionic liquid) Endows the Composite Polymer Electrolyte Membrane with Excellent Interface Compatibility for All-Solid-State Lithium Metal Batteries

Developing a poly(ethylene oxide) (PEO)-based polymer electrolyte with high ionic conductivity and robust mechanical property is beneficial for real applications of all-solid-state lithium metal batteries (ASSLMBs). Herein, an excellent organic/inorganic interface compatibility of all-solid-state composite polymer electrolytes (CPEs) is achieved using a novel imidazolium-type poly(ionic liquid) with strong electrostatic interactions, providing insights into the achievement of highly stable CPEs. The key properties such as micromorphologies, thermal behavior, crystallinity, t_Li⁺, mechanical property, lithium anode surficial morphology, and electrochemical performance are systematically investigated. The combined experimental and density functional theory (DFT) simulation results exhibit that the strong electrostatic interaction and ion-dipole interaction cooperated to improve the compatibility of the CPE, with a high ionic conductivity of 1.46 × 10^-4 S cm^-1 at 40 °C and an incredible mechanical strain of 2000% for dendrite-free and highly stable all-solid-state LMBs. This work affords a promising strategy to accelerate the development of PEO-based polymer electrolytes for real applications in ASSLMBs.

Advanced Material Engineering to Tailor Nucleation and Growth towards Uniform Deposition for Anode-Less Lithium Metal Batteries

Anode-less lithium metal batteries (ALMBs), whether employing liquid or solid electrolytes, have significant advantages such as lowered costs and increased energy density over lithium metal batteries (LMBs). Among many issues, dendrite growth and non-uniform plating which results in poor coulombic efficiency are the key issues that viciously decrease the longevity of the ALMBs. As a result, lowering the nucleation barrier and facilitating lithium growth towards uniform plating is even more critical in ALMBs. While extensive reviews have focused to describe strategies to achieve high performance in LMBs and ALMBs, this review focuses on strategies designed to directly facilitate nucleation and growth of dendrite-free ALMBs. The review begins with a discussion of the primary components of ALMBs, followed by a brief theoretical analysis of the nucleation and growth mechanism for ALMBs. The review then emphasizes key examples for each strategy in order to highlight the mechanisms and rationale that facilitate lithium plating. By comparing the structure and mechanisms of key materials, the review discusses their benefits and drawbacks. Finally, major trends and key findings are summarized, as well as an outlook on the scientific and economic gaps in ALMBs.

Recent Developments and Research Avenues for Polymers in Electric Vehicles

Plastics have been an indispensable material of choice in automobiles with wide range of applications such as interior, exterior, under the hood, and lighting/wiring applications. The prime motive of inclusion of these materials is increase in fuel efficiency and reduction in carbon footprint by replacing the energy intensive metallic counterparts. The current decade i. e., the 2020s has seen a recent surge in the sales of electronic vehicles. Although these numbers are promising, the growth in the rest of the parts of the world is not encouraging. It is primarily due to the skepticism involving battery life and efficiency, profitability, and environmental footprint when compared to conventional and hybrid vehicles. Also, a more concerted effort is needed in the lagging areas in order to install the required infrastructure. The emergence of plastics in the development and acceptance of e-vehicles is going to be pivotal especially when the efficiency and profitability are considered as they give the required freedom to the engineers for the design and development of various parts and sizes by replacing the bulkier and more dense materials. Also, the research on bionanocomposites has received great interest from the research community due to their versatility in application along with their eco-friendly nature throughout the lifecycle starting from feedstock up to end-of-life treatment. This review paper will be one of its kind to present a critical review of the recent developments of polymers suitable for use in e-vehicles. Also, a comprehensive discussion comprising of newer research areas for polymers in their use for e-vehicles will be presented.

Foldable nano-Li2MnO3 integrated composite polymer solid electrolyte for all-solid-state Li metal batteries with stable interface

All-solid-state lithium-ion batteries (ASSLBs) are considered as the most promising next-generation energy storage devices. In this work, a low-cost foldable nano-Li₂MnO₃ integrated Poly (ethylene oxide) (PEO) based composite polymer solid electrolyte (CPSE) is prepared by simply solid-phase method. Density functional theory calculations indicate that the LMO could provide faster ion transfer channels for the migration of lithium ions between PEO chains and segments. As such, the CPSE obtained has a high ionic conductivity of 5.1 × 10^-4 S cm^-1 at 60 °C with a high lithium ions transference number of 0.5. The CPSE remains stable even at high temperature with no heat escaping. This could improve the safety performance of the batteries. As a result, the lithium metal battery assembled with CPSE works stably after over 200 cycles at a high rate of 0.5C, and its specific capacity is as high as 125 mAh g^-1. Also, it is confirmed that this CPSE adapts to three cathode materials. The Li metal pouch battery assembled with the CPSE is foldable and has excellent mechanical properties. All these results indicate that the CPSE obtained has excellent electrochemical and outstanding safety performances, which can make it have broad commercial applications in ASSLBs.

Solid-State Lithium Metal Battery of Low Capacity Fade Enabled by a Composite Electrolyte with Sulfur-Containing Oligomers

A solid-state lithium metal battery of low capacity fade is acquired using the electrolyte membrane of a polyurethane-acrylate-thiocarbonate (PUAT) oligomer, macromolecules, lithium salt, and an oxide additive. Two types of composite electrolytes have been prepared: the free-standing electrolyte (PUAT-FS) and the electrode-coated electrolyte (PUAT-EC). Featuring a less PUAT content and a finer granular size, PUAT-FS is less ion-conductive than PUAT-EC; 0.44 mS cm^-1 in contrast to 0.51 mS cm^-1 at room temperature. Nonetheless, the lithium iron phosphate battery of PUAT-FS is far superior to that of PUAT-EC in terms of cycling stability. When cycled at 0.1C and room temperature, the PUAT-FS battery reaches a maximum discharge capacity of 169.7 mAh g^-1 at its 20th cycle and decreases to 141.0 mAh g^-1 at the 500th cycle, 83.1% retention. The capacity fading rate of the PUAT-FS battery is 0.034% per cycle at 0.1C, significantly less than that of the PUAT-EC battery, 0.138% per cycle. Other maximum capacities and fading rates of the PUAT-FS battery are 152.5 mAh g^-1 and 0.050% per cycle at 0.2C in 800 cycles and 126.1 mAh g^-1 and 0.051% per cycle at 0.5C in 1000 cycles. These features of a low fading rate and high capacity are attributed to a balanced ratio of oligomer to macromolecule (1:1 w/w) in the free-standing electrolyte and the sulfur-containing oligomer.

Bridging Li7La3Zr2O12 Nanofibers with Poly(ethylene oxide) by Coordination Bonds to Enhance the Cycling Stability of All-Solid-State Lithium Metal Batteries

A solid-state composite polymer electrolyte comprising Li₇La₃Zr₂O₁₂ nanofibers (LLZO NFs) as fillers has the advantages of flexibility, ease of processing, and being low cost, thus being considered to be a promising electrolyte material for use in the next generation of highly safe lithium metal batteries. However, poor compatibility of organic parts and inorganic materials leads to quick capacity decay after long-term charge/discharging running because of inorganic/organic interface deterioration and thus, the related ineffective lithium-ion (Li⁺) conduction. Herein, a "Boston ivy-style" method is proposed to prepare a solid ceramic/polymer hybrid electrolyte that exhibits a dense interface structure. After grafting on Dynasylan IMEO (DI), the modified LLZO NFs are used as ligands to bond with coordinatively unsaturated metal centers of Ca²⁺. Furthermore, these Ca²⁺ bridge the modified LLZO NFs with poly(ethylene oxide) (PEO) via the ether oxygen atoms they possess. The bridges built between the two phases, PEO and LLZO NFs, are effective to interface strengthening and guarantee rapid Li⁺ conduction even after 900 cycles. The PEO/LLZO NFs-DI-Ca²⁺/LiTFSI electrolyte shows a high Li⁺ transference number of 0.72 (60 °C). The Li||LiFePO₄ cell delivers excellent cycling stability (capacity retention of 70.8% after 900 cycles, 0.5 C) and rate performance. The bridge strategy is proved to be effective and probably a promotion to the application of ceramic polymer-based solid-state electrolytes.

Double-Layer Solid Composite Electrolytes Enabling Improved Room-Temperature Cycling Performance for High-Voltage Lithium Metal Batteries

The development of solid-state electrolytes (SSEs) for high energy density lithium metal batteries (LMBs) usually needs to take into account of the interfacial compatibility against lithium metal and the electrolyte stability suitable for a high-potential cathode. In this study, through a facile two-step coating process, novel double-layer solid composite electrolytes (SCEs) with Janus characteristics are customized for the high-voltage LMBs with improved room-temperature cycling performance. Among which, high-voltage resistant poly(vinylidene fluoride) (PVDF) is adopted here for the construction of an electrolyte layer facing the cathode, while the other layer against the lithium anode is composed of the polymer matrix of poly(ethylene oxide) (PEO) blended with PVDF to obtain a lithium metal-friendly interface. With the further incorporation of Laponite clay, the PVDF/(PEO+PVDF)-L SCEs not only exhibit improved mechanical properties, but also achieve a highly increased ionic conductivity (5.2 × 10^-4 S cm^-1) and lithium ion migration number (0.471) at room temperature. The assembled NCM523|PVDF/(PEO+PVDF)-L SCEs|Li cells thus are able to deliver the initial discharge capacity of 153.9 mAh g^-1 with 80.8% capacity retention after 200 cycles at 0.3 C. Such easily manufactured double-layer SCEs capable of operating steadily at room temperature provide a competitive electrolyte option for high-voltage solid-state LMBs.

Effect of nanostructured Al2O3 on poly(ethylene oxide)-based solid polymer electrolytes

In this study, we investigated the effect of nanostructured Al2O3 particles on Li ion conducting, poly(ethylene oxide) (PEO)-based membranes prepared by electrospinning, solution casting and hot pressing. Pure PEO:LiBF4 solid polymer electrolytes (SPEs) and also plasticizer containing membranes were investigated with various amounts of Al2O3. In a first step, the best-performing composition of pure PEO:LiBF4 concerning the resulting ionic conductivity was identified and used as a standard for further experiments. In the following, the influence of the preparation method, the nature of the Al2O3, and the type of the plasticizer additives on the thermal and electrochemical properties for this standard composition were investigated. The Al2O3 composition was varied between 1 and 5 wt%. The ionic conductivity of bare electrospun PEO:LiBF4 SPE standard material has been improved by a factor ten to 1.9 × 10−6 S cm−1 at T = 293 K when 5 wt% of Al2O3 is added. For solution-casted PEO:LiBF4 standard compositions 18:1 with an initial ionic conductivity of 6.7 × 10−8 S cm−1, the addition of 2 wt% Al2O3 increased the performance to 1.4 × 10−7 S cm−1, both at T = 293 K. If succinonitrile and Al2O3 was admixed to the solution casted standard material, the ionic conductivity was further increased to reach 5.5 × 10−5 S cm−1 at T = 293 K. This material with a composition of 18:3:1 + 2 wt% Al2O3, outperforms the standard material by three orders of magnitude.

Metal-Air Batteries—A Review

Metal–air batteries are a promising technology that could be used in several applications, from portable devices to large-scale energy storage applications. This work is a comprehensive review of the recent progress made in metal-air batteries MABs. It covers the theoretical considerations and mechanisms of MABs, electrochemical performance, and the progress made in the development of different structures of MABs. The operational concepts and recent developments in MABs are thoroughly discussed, with a particular focus on innovative materials design and cell structures. The classical research on traditional MABs was chosen and contrasted with metal–air flow systems, demonstrating the merits associated with the latter in terms of achieving higher energy density and efficiency, along with stability. Furthermore, the recent applications of MABs were discussed. Finally, a broad overview of challenges/opportunities and potential directions for commercializing this technology is carefully discussed. The primary focus of this investigation is to present a concise summary and to establish future directions in the development of MABs from traditional static to advanced flow technologies. A systematic analysis of this subject from a material and chemistry standpoint is presented as well.

Insights into the Ionic Conduction Mechanism of Quasi-Solid Polymer Electrolytes through Multispectral Characterization

Quasi-solid polymer electrolytes (QPE) composed of Li salts, polymer matrix, and solvent, are beneficial for improving the security and energy density of batteries. However, the ionic conduction mechanism, existential form of solvent molecules, and interactions between different components of QPE remain unclear. Here we develop a multispectral characterization strategy combined with first-principles calculations to unravel aforesaid mysteries. The results indicate that the existential state of solvent in QPE is quite different from that in liquid electrolyte. The Li cations in gel polymer electrolyte are fully solvated by partial solvent molecules to form a local high concentration of Li⁺ , while the other solvent molecules are fastened by polymer matrix in QPE. As a result, the solvation structure and conduction mechanism of Li⁺ are similar to those in high-concentrated liquid electrolyte. This work provides a new insight into the ionic conduction mechanism of QPE and will promote its application for safe and high-energy batteries.

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.

Solid Polymer Electrolytes with Flexible Framework of SiO2 Nanofibers for Highly Safe Solid Lithium Batteries

Composite electrolytes consisting of polymers and three-dimensional (3D) fillers are considered to be promising electrolytes for solid lithium batteries owing to their virtues of continuous lithium-ion pathways and good mechanical properties. In the present study, an electrolyte with polyethylene oxide-lithium (bis trifluoromethyl) sulfate-succinonitrile (PLS) and frameworks of three-dimensional SiO₂ nanofibers (3D SiO₂ NFs) was prepared. Taking advantage of the highly conductive interfaces between 3D SiO₂ NFs and PLS, the total conductivity of the electrolyte at 30 °C was approximately 9.32 × 10^-5 S cm^-1. With a thickness of 27 μm and a tensile strength of 7.4 MPa, the electrolyte achieved an area specific resistance of 29.0 Ω cm². Moreover, such a 3D configuration could homogenize the electrical field, which was beneficial for suppressing dendrite growth. Consequently, Li/LiFePO₄ cells assembled with PLS and 3D SiO₂ NFs (PLS/3D SiO₂ NFs), which delivered an original specific capacity of 167.9 mAh g^-1, only suffered 3.28% capacity degradation after 100 cycles. In particular, these cells automatically shut down when PLS was decomposed above 400 °C, and the electrodes were separated by the solid framework of 3D SiO₂ NFs. Therefore, the solid lithium batteries based on composite electrolytes reported here offer high safety at elevated temperatures.

Nickel phosphate nanorod-enhanced polyethylene oxide-based composite polymer electrolytes for solid-state lithium batteries

Solid-state electrolytes with high ionic conductivity, large electrochemical window, and excellent stability with lithium electrode are needed for high-energy solid-state lithium batteries. In this work, a novel polyethylene oxide (PEO)-Lithium bis(trifluoromethylsulphonyl)imide (LiTFSI)-nanocomposite-based polymer electrolyte was prepared by using nickel phosphate (VSB-5) nanorods as the filler. The ionic conductivity of the obtained PEO-LiTFSI-3%VSB-5 solid polymer electrolyte was found to be as high as 4.83 × 10^-5 S·cm^-1 at 30 °C and electrochemically stable up to about 4.13 V versus Li/Li⁺. The enhanced ionic conductivity was attributed to the reduced crystallinity of the PEO and the interaction between VSB and 5 and PEO-LiTFSI. In addition, the solid polymer electrolyte exhibited improved compatibility to the lithium metal anode with excellent suppression of lithium dendrites. The assembled LiFePO₄/Li battery with the PEO-LiTFSI-3%VSB-5 solid polymer electrolyte showed better rate performance and higher cyclic stability than the PEO-LiTFSI electrolyte. It is demonstrated that this new solid polymer hybrid should be a promising electrolyte applied in solid state batteries with lithium metal electrode.