Ultrathin polymer-in-ceramic and ceramic-in-polymer bilayer composite solid electrolyte membrane for high-voltage lithium metal batteries

Research Progress and Challenges of High-Performance Solid-State Lithium Sulfur Batteries: Cathodes, Electrolytes, and Anodes

The development of energy storage and vehicle industries has promoted the development of batteries with high specific capacity and high safety performance. When compared with liquid batteries, solid-state batteries avoid the use of liquid electrolyte, effectively reducing electrolyte leakage and fire hazards. Solid-state lithium sulfur battery (SSLSBs) has abundant sulfur cathode, high capacity metal lithium anode, and noncombustible solid-state electrolytes (SSEs). Despite these attractive advantages, some challenges such as slow sulfur redox kinetics, lithium metal failure, and difficulties in manufacturing and storage of SSEs have hindered their practical application. In order to promote the development of SSLSBs, a detailed generalization and summarization are provided of the research progresses of high-performance SSLSBs over the past three years. In this review, the problems faced are deeply explored by the cell cathodes, SSEs, and lithium anodes in the application process, and put forward plentiful feasible solutions according to the corresponding issues. Finally, the latest achievements of SSLSBs are summarized, and the views on the future development are put forward. The review presents a comprehensive and systematic analysis of the application and mechanism of action of cell cathodes, anodes, and SSEs in SSLSBs, providing a novel viewpoint for scholars to explore high-performance SSLSBs.

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.

Regulating Metal Centers of MOF-74 Promotes PEO-Based Electrolytes for All-Solid-State Lithium-Metal Batteries

Poly(ethylene oxide) (PEO)-based electrolytes have been extensively studied for all-solid-state lithium-metal batteries due to their excellent film-forming capabilities and low cost. However, the limited ionic conductivity and poor mechanical strength of the PEO-based electrolytes cannot prevent the growth of undesirable lithium dendrites, leading to the failure of batteries. Metal-organic frameworks (MOFs) are functional materials with a periodic porous structure that can improve the electrochemical performance of PEO-based electrolytes. However, the enhancement effect of MOFs with different metal centers and the interaction mechanism with PEO remain unclear. Herein, MOF-74s with Cu or Ni centers are prepared and used as fillers of PEO-based electrolytes. Adding 15 wt % of Cu-MOF-74 to the PEO-based electrolyte (15%Cu-MOF/P-Li) effectively improves the ionic conductivity, lithium transference number, and mechanical strength of the PEO-based electrolyte simultaneously. Furthermore, the ordered pore channels of Cu-MOF-74 provide uniform Li-ion transport pathways, facilitating homogeneous Li+ deposition. As a result, the lithium symmetric cell with 15%Cu-MOF/P-Li shows stable cycles for 1080 h at 0.1 mA cm-2 and 0.1 mAh cm-2, and the Li | 15% Cu-MOF/P-Li | LFP full cell exhibits a long cycle life up to 200 cycles at 60 °C and 0.5 C, with a capacity retention rate of 89.7%.

Tunneling Interpenetrative Lithium Ion Conduction Channels in Polymer-in-Ceramic Composite Solid Electrolytes

Polymer-in-ceramic composite solid electrolytes (PIC-CSEs) provide important advantages over individual organic or inorganic solid electrolytes. In conventional PIC-CSEs, the ion conduction pathway is primarily confined to the ceramics, while the faster routes associated with the ceramic-polymer interface remain blocked. This challenge is associated with two key factors: (i) the difficulty in establishing extensive and uninterrupted ceramic-polymer interfaces due to ceramic aggregation; (ii) the ceramic-polymer interfaces are unresponsive to conducting ions because of their inherent incompatibility. Here, we propose a strategy by introducing polymer-compatible ionic liquids (PCILs) to mediate between ceramics and the polymer matrix. This mediation involves the polar groups of PCILs interacting with Li+ ions on the ceramic surfaces as well as the interactions between the polar components of PCILs and the polymer chains. This strategy addresses the ceramic aggregation issue, resulting in uniform PIC-CSEs. Simultaneously, it activates the ceramic-polymer interfaces by establishing interpenetrating channels that promote the efficient transport of Li+ ions across the ceramic phase, the ceramic-polymer interfaces, and the intervening pathways. Consequently, the obtained PIC-CSEs exhibit high ionic conductivity, exceptional flexibility, and robust mechanical strength. A PIC-CSE comprising poly(vinylidene fluoride) (PVDF) and 60 wt % PCIL-coated Li3Zr2Si2PO12 (LZSP) fillers showcasing an ionic conductivity of 0.83 mS cm-1, a superior Li+ ion transference number of 0.81, and an elongation of ∼300% at 25 °C could be produced on meter-scale. Its lithium metal pouch cells show high energy densities of 424.9 Wh kg-1 (excluding packing films) and puncture safety. This work paves the way for designing PIC-CSEs with commercial viability.

Micro Area Interface Wetting Structure with Tailored Li+-Solvation and Fast Transport Properties in Composite Polymer Electrolytes for Enhanced Performance in Solid-State Lithium Batteries

To satisfy the demand for high safety and energy density in energy storage devices, all-solid-state lithium metal batteries with solid polymer electrolytes (SPE) replacing traditional liquid electrolytes and separators have been proposed and are increasingly regarded as one of the most promising candidates as next-generation energy storage systems. In this study, poly(vinylidene fluoride)-hexafluoropropylene/lignosulfonic acid (PVDF-HFP/LSA) composite polymer electrolyte (CPE) membranes with a micro area interface wetting structure were successfully prepared by incorporating LSA into the PVDF-HFP polymer matrix. The enhanced interaction between the polar functional group in LSA and the C═O in N-methylpyrrolidone (NMP) hinders the evaporation of solvent NMP, thus creating a micro area wetting structure, which offers a flexible region for the chain segment movement and enlarging the area of the amorphous zone in PVDF-HFP. From the results of IR and Raman spectroscopy, it was found that the presence of LSA induced unique ion transport channels created by the massive aggregated ion pair (AGG) and contact ion pair (CIP) of ion cluster structures composed of Li+ and multiple TFSI- and, at the same time, effectively reduced the crystallinity of the polymer electrolyte, hence further contributing to the Li+ diffusion. As a result, at a rate of 2 C, the Li|CPE-15|LiFePO4 solid-state battery delivers an initial discharge-specific capacity of 134.9 mAh g-1 and maintains stability with a retention of 84% during 400 charge-discharge cycles while the Li|CPE-0|LiFePO4 battery fails after only a few cycles at the same rate.

Recent progress and strategic perspectives of inorganic solid electrolytes: fundamentals, modifications, and applications in sodium metal batteries

Solid-state electrolytes (SEs) have attracted overwhelming attention as a promising alternative to traditional organic liquid electrolytes (OLEs) for high-energy-density sodium-metal batteries (SMBs), owing to their intrinsic incombustibility, wider electrochemical stability window (ESW), and better thermal stability. Among various kinds of SEs, inorganic solid-state electrolytes (ISEs) stand out because of their high ionic conductivity, excellent oxidative stability, and good mechanical strength, rendering potential utilization in safe and dendrite-free SMBs at room temperature. However, the development of Na-ion ISEs still remains challenging, that a perfect solution has yet to be achieved. Herein, we provide a comprehensive and in-depth inspection of the state-of-the-art ISEs, aiming at revealing the underlying Na⁺ conduction mechanisms at different length scales, and interpreting their compatibility with the Na metal anode from multiple aspects. A thorough material screening will include nearly all ISEs developed to date, i.e., oxides, chalcogenides, halides, antiperovskites, and borohydrides, followed by an overview of the modification strategies for enhancing their ionic conductivity and interfacial compatibility with Na metal, including synthesis, doping and interfacial engineering. By discussing the remaining challenges in ISE research, we propose rational and strategic perspectives that can serve as guidelines for future development of desirable ISEs and practical implementation of high-performance SMBs.

Lithiophilic hollow Co3[Co(CN)6]2 embedded carbon nanotube film for dendrite-free lithium metal anodes

Lithium metal is considered to be an ideal anode material due to its ultra-high theoretical capacity and extremely low electric potential. Unfortunately, the infinite volume expansion and unregulated formation of lithium dendrites in the plating/stripping process restrict its practical utilization. Herein, we designed a hollow Co₃[Co(CN)₆]₂ (CoCoPBA) embedded high-conductivity carbon film as a three-dimensional (3D) lithiophilic current collector (h-CoCoPBAs@SWCNT). The interwoven carbon nanotubes with hollow nanoparticles can effectively promote electron transfer and reduce local current density, adapting to the huge volume expansion in long-term electrochemical cycling. At the same time, lithiophilic hollow CoCoPBA nanoparticles provide abundant active sites due to their large surface area, efficiently reducing nucleation overpotential and making lithium deposition easier and more uniform, both confirmed by theoretical calculation and experiment. Accordingly, compared with bare Cu electrodes, h-CoCoPBAs@SWCNT electrodes have a flat and uniform Li deposition morphology, which is beneficial to enhance the cycle life of lithium metal anodes. And the symmetrical cell assembled by h-CoCoPBAs@SWCNT shows stable cycling performance of more than 500 h at 2 mA cm^-2 with 1 mAh cm^-2. Besides, the assembled lithium-sulfur full cell also has higher cycle stability and rate performance.

Electrolyte Engineering for High-Voltage Lithium Metal Batteries

High-voltage lithium metal batteries (HVLMBs) have been arguably regarded as the most prospective solution to ultrahigh-density energy storage devices beyond the reach of current technologies. Electrolyte, the only component inside the HVLMBs in contact with both aggressive cathode and Li anode, is expected to maintain stable electrode/electrolyte interfaces (EEIs) and facilitate reversible Li⁺ transference. Unfortunately, traditional electrolytes with narrow electrochemical windows fail to compromise the catalysis of high-voltage cathodes and infamous reactivity of the Li metal anode, which serves as a major contributor to detrimental electrochemical performance fading and thus impedes their practical applications. Developing stable electrolytes is vital for the further development of HVLMBs. However, optimization principles, design strategies, and future perspectives for the electrolytes of the HVLMBs have not been summarized in detail. This review first gives a systematical overview of recent progress in the improvement of traditional electrolytes and the design of novel electrolytes for the HVLMBs. Different strategies of conventional electrolyte modification, including high concentration electrolytes and CEI and SEI formation with additives, are covered. Novel electrolytes including fluorinated, ionic-liquid, sulfone, nitrile, and solid-state electrolytes are also outlined. In addition, theoretical studies and advanced characterization methods based on the electrolytes of the HVLMBs are probed to study the internal mechanism for ultrahigh stability at an extreme potential. It also foresees future research directions and perspectives for further development of electrolytes in the HVLMBs.

Study on Control of Polymeric Architecture of Sulfonated Hydrocarbon-Based Polymers for High-Performance Polymer Electrolyte Membranes in Fuel Cell Applications

Polymer electrolyte membrane fuel cell (PEMFC) is an eco-friendly energy conversion device that can convert chemical energy into electrical energy without emission of harmful oxidants such as nitrogen oxides (NOx) and/or sulfur oxides (SOx) during operation. Nafion®, a representative perfluorinated sulfonic acid (PFSA) ionomer-based membrane, is generally incorporated in fuel cell systems as a polymer electrolyte membrane (PEM). Since the PFSA ionomers are composed of flexible hydrophobic main backbones and hydrophilic side chains with proton-conducting groups, the resulting membranes are found to have high proton conductivity due to the distinct phase-separated structure between hydrophilic and hydrophobic domains. However, PFSA ionomer-based membranes have some drawbacks, including high cost, low glass transition temperatures and emission of environmental pollutants (e.g., HF) during degradation. Hydrocarbon-based PEMs composed of aromatic backbones with proton-conducting hydrophilic groups have been actively studied as substitutes. However, the main problem with the hydrocarbon-based PEMs is the relatively low proton-conducting behavior compared to the PFSA ionomer-based membranes due to the difficulties associated with the formation of well-defined phase-separated structures between the hydrophilic and hydrophobic domains. This study focused on the structural engineering of sulfonated hydrocarbon polymers to develop hydrocarbon-based PEMs that exhibit outstanding proton conductivity for practical fuel cell applications.