Flexible hybrid solid electrolyte incorporating ligament-shaped Li6.25Al0.25La3Zr2O12 filler for all-solid-state lithium-metal batteries

The Structural Effect of a Composite Solid Electrolyte on Electrochemical Performance and Fire Safety

In this study, we investigated the structural effect of composite solid electrolytes of Al-doped LLZO and PVDF-HFP (0D_Al-LLZO@PVDF-HFP and 1D_Al-LLZO@PVDF-HFP) on electrochemical (EC) performance and fire safety through a systematic evaluation and comparative tests. The unique structure and advantageous features of composite solid electrolytes (1D_Al-LLZO@PVDF-HFP) were highlighted by comparing controls (PVDF-HFP and 0D_Al-LLZO@PVDF-HFP) with physicochemical and electrochemical analyses and fire safety tests The structure and morphology of Al-doped LLZO/PVDF-HFP composites were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM), while their chemical functionalities and free ion clusters were examined with Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, respectively. The 1D_Al-LLZO@PVDF-HFP composite with a 1D structured Al-LLZO filler network in the PVDF-HFP matrix could effectively regulate the crystallinity of PVDF-HFP and facilitated lithium salt dissociation, resulting in a high lithium-ion transference number and ionic conductivity. As a result, the 1D_Al-LLZO@PVDF-HFP composite electrolyte with an optimized structure and low Al-LLZO content (~5.1 wt%) exhibited enhanced ionic conductivity (σ: 1.40 × 10-4 S/cm) with low interfacial resistance, broadened EC stability (voltage window: 4.75 V vs. Li/Li+), and a high lithium-ion transference number (0.75) superior to that of 0D_Al-LLZO@PVDF-HFP. In electrochemical characterizations, the 1D_Al-LLZO@PVDF-HFP-based EC cell demonstrated enhanced performance in a lithium symmetric cell (>2000 h) and full cell (LiFePO4|electrolyte|Li) of a reversible capacity of 102.7 mAh/g at 2C with a capacity retention of 85.7% over 200 cycles, better than that of a 0D_ Al-LLZO@PVDF-HFP-based EC cell. In flammability tests, Al-LLZO@PVDF-HFP demonstrated enhanced fire safety (nonflammability) compared with that of a PVDF-HFP-based electrolyte regardless of the composite structure, suggesting the importance of inorganic filler rather than their structural morphology in the composite.

Hopping-Phase Ion Bridge Enables Fast Li+ Transport in Functional Garnet-Type Solid-State Battery at Room Temperature

Composite polymer electrolytes (CPEs) containing Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is widely regarded as leading candidate for high energy density solid-state lithium-metal batteries due to its exceptional ionic conductivity and environmental stability. However, Li2CO3 and LiOH layers at LLZTO surface greatly hinder Li+ transport between LLZTO-polymer and the electrode-electrolyte interface. Herein, the surface of LLZTO is boronized to obtain functionalized LLZTO, and its conversion mechanism is clarified. By dissolving the crystal structure of cellulose to obtain hopping-phase ion bridge (HPIB), which release the Li+ transport activity of its oxygen-containing polar functional group (─OH, ─O─). Therefore, a high-throughput ion transporter (HTIT-37) with high ion transfer number (0.86) is prepared by introducing the HPIB into functionalized LLZTO and polyvinylidene fluoride interface by intermolecular hydrogen bond interaction, and it is demonstrated that the HPIB acts as a "highway" for the Li+ across this heterogeneous interface. Moreover, the HPIB is found to self-adsorb on the SEI surface, leading to fast Li+ transport kinetics at anode-CPE interface. Thus, the lifespan of Li|HTIT-37|Li is over 8000 h, and the critical current density exceeds 2.3 mA cm-2. The LiNi0.5Co0.2Mn0.3O2|Li and Li1.2Ni0.13Co0.13Mn0.54O2|Li battery remains stable with the HPIB-enhanced electrode process, proving the application potential of LLZTO-based CPE in high energy density SSLMB.

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.

Interfacial Plasticization Strategy Enabling a Long-Cycle-Life Solid-State Lithium Metal Battery

The limited ionic conductivity and unstable interface due to poor solid-solid interface pose significant challenges to the stable cycling of solid-state batteries (SSBs). Herein, an interfacial plasticization strategy is proposed by introducing a succinonitrile (SN)-based plastic curing agent into the polyacrylonitrile (PAN)-based composite polymer electrolytes (CPE) interface. The SN at the interface strongly plasticizes the PAN in the CPE, which reduces the crystallinity of the PAN drastically and enables the CPE to obtain a low modulus surface, but it still maintains a high modulus internally. The reduced crystallinity of PAN provides more amorphous regions, which are favorable for Li+ transport. The gradient modulus structure not only ensures intimate interfacial contact but also favors the suppression of Li dendrites growth. Consequently, the interfacial plasticized CPE (SF-CPE) obtains a high ionic conductivity of 4.8 × 10-4 S cm-1 as well as a high Li+ transference number of 0.61. The Li-Li symmetric cell with SF-CPE can cycle for 1000 h at 0.1 mA cm-2, the LiFeO4 (LFP)-Li full-cell demonstrates a high capacity retention of 86.1% after 1000 cycles at 1 C, and the LiCoO2 (LCO)-Li system also exhibits an excellent cycling performance. This work provides a novel strategy for long-life 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.

Preparation of Metal-Oxide-Doped Li7P2S8Br0.25I0.75 Solid Electrolytes for All-Solid-State Lithium Batteries

The all-solid-state lithium battery (ASSB) has received great attention due to its greater safety than the conventional lithium-ion battery (LIB). Sulfide-based inorganic solid electrolytes are an important component to fabricate the ASSB. But to attain a better performance, the ionic conductivity and electrochemical stability of the sulfide-based solid electrolytes need to be improved. In this work, we prepared the metal-oxide-doped/mixed Li₇P₂S₈I_0.75Br_0.25 lithium superionic conductors by a dry ball-milling process. The high ionic conductivity was achieved by a low-temperature (200 °C) heat-treatment process. The metal-oxide-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte exhibited a higher ionic conductivity value of 7.3 mS cm^-1 at room temperature than the bare Li₇P₂S₈I_0.75Br_0.25 solid electrolyte. The structural characteristics of the prepared solid electrolytes were studied by solid NMR and laser Raman analysis. The electrochemical stability of the prepared solid electrolyte was studied by cyclic voltammetry and DC charge-discharge analysis. The addition of metal oxide increased the electrochemical stability and dry-air stability of the Li₇P₂S₈I_0.75Br_0.25 solid electrolyte. The Ta₂O₅-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte was stable even after 300 charge-discharge DC cycles and also 100 h of dry-air exposure. Further, the Ta₂O₅-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte-based ASSB exhibited a high discharge capacity value of 184 mA h g^-1 at 0.1 C rate with 66% initial cycle Coulombic efficiency.

Uncoordinated chemistry enables highly conductive and stable electrolyte/filler interfaces for solid-state lithium-sulfur batteries

Composite-polymer-electrolytes (CPEs) embedded with advanced filler materials offer great promise for fast and preferential Li+ conduction. The filler surface chemistry determines the interaction with electrolyte molecules and thus critically regulates the Li+ behaviors at the interfaces. Herein, we probe into the role of electrolyte/filler interfaces (EFI) in CPEs and promote Li+ conduction by introducing an unsaturated coordination Prussian blue analog (UCPBA) filler. Combining scanning transmission X-ray microscope stack imaging studies and first-principle calculations, fast Li+ conduction is revealed only achievable at a chemically stable EFI, which can be established by the unsaturated Co-O coordination in UCPBA to circumvent the side reactions. Moreover, the as-exposed Lewis-acid metal centers in UCPBA efficiently attract the Lewis-base anions of Li salts, which facilitates the Li+ disassociation and enhances its transference number (tLi+). Attributed to these superiorities, the obtained CPEs realize high room-temperature ionic conductivity up to 0.36 mS cm-1 and tLi+ of 0.6, enabling an excellent cyclability of lithium metal electrodes over 4,000 h as well as remarkable capacity retention of 97.6% over 180 cycles at 0.5 C for solid-state lithium-sulfur batteries. This work highlights the crucial role of EFI chemistry in developing highly conductive CPEs and high-performance solid-state batteries.

Al and Ta co-doped LLZO as active filler with enhanced Li+conductivity for PVDF-HFP composite solid-state electrolyte

Battery safety calls for solid state batteries and how to prepare solid electrolytes with excellent performance are of significant importance. In this study, hybrid solid electrolytes combined with organic PVDF-HFP and inorganic active fillers are studied. The modified active fillers of Li_7-x-3yAl_yLa₃Zr_2-xTa_xO₁₂are obtained by co-element doping with Al and Ta when LLZO is synthesized by calcination. And an high room temperature ionic conductivity of 5.357 × 10^-4S cm^-1is exhibited by ATLLZO ceramic sheet. The composite solid electrolyte PVDF-HFP/LiTFSI/ATLLZO (PHL-ATLLZO) is prepared by solution casting method, and its electrochemical properties are investigated. The results show that when the contents of lithium salt LiTFSI and active filler ATLLZO are controlled at 40 wt% and 10%, respectively, the ionic conductivity of the resulting composite solid electrolyte is as high as 2.686 × 10^-4S cm^-1at room temperature, and a wide electrochemical window of 4.75 V is exhibited. The LiFePO₄/PHL-ATLLZO/Li all-solid-state battery assembled based on the composite solid-state electrolyte exhibits excellent cycling stability at room temperature. The cell assembled by casting the composite solid-state electrolyte on the cathode surface shows a discharge specific capacity of 134.3 mAh g^-1and 96.2% capacity retention after 100 cycles at 0.2 C. The prepared composite solid-state electrolyte demonstrates excellent electrochemical performance.

High-Performance Poly(vinylidene fluoride-hexafluoropropylene)-Based Composite Electrolytes with Excellent Interfacial Compatibility for Room-Temperature All-Solid-State Lithium Metal Batteries

Composite solid-state electrolytes (CSEs) have been developed rapidly in recent years owing to their high electrochemical stability, low cost, and easy processing characteristics. Most CSEs, however, require high temperatures or flammable liquid solvents to exhibit their acceptable electrochemical performance. Room-temperature all-solid-state batteries without liquid electrolytes are still unsatisfactory and under development. Herein, we have prepared a composite solid electrolyte with excellent performance using a polymer electrolyte poly(vinylidene fluoride-hexafluoropropylene) and an inorganic electrolyte Li_6.4La₃Zr_1.4Ta_0.6O₁₂. With the assistance of lithium salts and plasticizers, the prepared CSE achieves a high ionic conductivity of 4.05 × 10^-4 S·cm^-1 at room temperature. The Li/CSE/Li symmetric cell can be stably cycled for more than 1000 h at 0.1 mA/cm² without short circuits. The all-solid-state lithium metal battery using a LiFePO₄ cathode displays a high discharge capacity of 148.1 mAh·g^-1 and a capacity retention of 90.21% after 100 cycles. Moreover, the high electrochemical window up to 4.7 V of the CSE makes it suitable for high-voltage service environments. The all-solid-state battery using a lithium nickel-manganate cathode shows a high discharge specific capacity of 197.85 mAh·g^-1 with good cycle performance. This work might guide the improvement of future CSEs and the exploration of flexible all-solid-state lithium metal batteries.

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.