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Abstract The low ionic conductivity of composite solid-state electrolytes due to the lack of free Li-ions and Li dendrite growth induced by the low transference number seriously hinder their application. Herein, we find that the giant dielectric ceramic of Li0.3Ti0.02Ni0.68O (LTNO) with ultra-high dielectric constant can greatly promote the dissociation of Li salt to generate abundant movable Li-ions and realize a high room-temperature ionic conductivity (4.09 × 10–4 S cm−1) as well as a low activation energy (0.16 eV). The oxygen vacancies on the surface of LTNO can effectively immobilize the anions to achieve a high Li transference number (0.61). Furthermore, the enhanced dielectric properties of the composite electrolyte induce homogenous Li plating/stripping to suppress the growth of Li dendrites. As a result, the Li||Li symmetric cells exhibit long lifespan of 2400 h and 1150 h at 0.1 mA cm−2 and 0.2 mA cm−2, respectively. The Li||LiNi0.8Co0.1Mn0.1O2 solid-state full cells show a high capacity retention of 83% after 430 cycles at 2C. This work highlights the critical role of high dielectric property and oxygen defects of fillers in composite solid-state electrolytes, and provides a demonstration for the application of giant dielectric materials in solid-state Li metal batteries.

The low ionic conductivity of composite solid-state electrolytes due to the lack of free Li-ions and Li dendrite growth induced by the low transference number seriously hinder their application. Herein, we find that the giant dielectric ceramic of Li0.3Ti0.02Ni0.68O (LTNO) with ultra-high dielectric constant can greatly promote the dissociation of Li salt to generate abundant movable Li-ions and realize a high room-temperature ionic conductivity (4.09 × 10–4 S cm−1) as well as a low activation energy (0.16 eV). The oxygen vacancies on the surface of LTNO can effectively immobilize the anions to achieve a high Li transference number (0.61). Furthermore, the enhanced dielectric properties of the composite electrolyte induce homogenous Li plating/stripping to suppress the growth of Li dendrites. As a result, the Li||Li symmetric cells exhibit long lifespan of 2400 h and 1150 h at 0.1 mA cm−2 and 0.2 mA cm−2, respectively. The Li||LiNi0.8Co0.1Mn0.1O2 solid-state full cells show a high capacity retention of 83% after 430 cycles at 2C. This work highlights the critical role of high dielectric property and oxygen defects of fillers in composite solid-state electrolytes, and provides a demonstration for the application of giant dielectric materials in solid-state Li metal batteries. [ABSTRACT FROM AUTHOR]

Highlights Ultra-thin asymmetric composite solid-state electrolytes with ultralight areal density were designed for solid-state lithium metal batteries, achieving interfacial stability to Li metal and high-voltage cathode. The improved mechanical properties of the electrolyte contribute to the inhibition of Li dendrite growth was demonstrated by both experimental and theoretical simulations. The assembled pouch cell exhibited a high gravimetric/volume energy density of 344.0 Wh kg−1/773.1 Wh L−1.

Highlights: Ultra-thin asymmetric composite solid-state electrolytes with ultralight areal density were designed for solid-state lithium metal batteries, achieving interfacial stability to Li metal and high-voltage cathode. The improved mechanical properties of the electrolyte contribute to the inhibition of Li dendrite growth was demonstrated by both experimental and theoretical simulations. The assembled pouch cell exhibited a high gravimetric/volume energy density of 344.0 Wh kg−1/773.1 Wh L−1. Solid-state lithium metal batteries (SSLMBs) show great promise in terms of high-energy–density and high-safety performance. However, there is an urgent need to address the compatibility of electrolytes with high-voltage cathodes/Li anodes, and to minimize the electrolyte thickness to achieve high-energy–density of SSLMBs. Herein, we develop an ultrathin (12.6 µm) asymmetric composite solid-state electrolyte with ultralight areal density (1.69 mg cm−2) for SSLMBs. The electrolyte combining a garnet (LLZO) layer and a metal organic framework (MOF) layer, which are fabricated on both sides of the polyethylene (PE) separator separately by tape casting. The PE separator endows the electrolyte with flexibility and excellent mechanical properties. The LLZO layer on the cathode side ensures high chemical stability at high voltage. The MOF layer on the anode side achieves a stable electric field and uniform Li flux, thus promoting uniform Li+ deposition. Thanks to the well-designed structure, the Li symmetric battery exhibits an ultralong cycle life (5000 h), and high-voltage SSLMBs achieve stable cycle performance. The assembled pouch cells provided a gravimetric/volume energy density of 344.0 Wh kg−1/773.1 Wh L−1. This simple operation allows for large-scale preparation, and the design concept of ultrathin asymmetric structure also reveals the future development direction of SSLMBs. [ABSTRACT FROM AUTHOR]

Composite solid-state electrolytes are viewed as promising materials for solid-state lithium-ion batteries due to their combined advantages of inorganic solid-state electrolytes and solid-state polymer electrolytes. In this study, the solid electrolytes Li6.7−xLa3Zr1.7−xSb0.3NbxO12 (LLZSNO) with Sb and Nb co-doping were prepared by a high-temperature solid-phase method. Results indicate that Sb/Nb co-doping causes lattice deformation in LLZO and increases the lithium vacancy concentration and conductivity of LLZO. Then, with the co-doped LLZSNO as an inorganic filler, a composite solid electrolyte of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was prepared with a casting method. The obtained composite solid electrolyte exhibits a high ionic conductivity of 1.76 × 10−4 S/cm at room temperature, a wide electrochemical stable window of 5.2 V, and a lithium-ion transfer number of 0.32. The Li|LiFePO4 coin battery with the composite solid electrolyte shows a high specific capacity of 161.2 mAh/g and a Coulombic efficiency close to 100% at 1 C. In addition, the symmetrical lithium battery Li|Li with the composite electrolyte could cycle stably for about 1500 h without failure at room temperature. [ABSTRACT FROM AUTHOR]

Composite solid-state electrolytes are viewed as promising materials for solid-state lithium-ion batteries due to their combined advantages of inorganic solid-state electrolytes and solid-state polymer electrolytes. In this study, the solid electrolytes Li6.7−xLa3Zr1.7−xSb0.3NbxO12 (LLZSNO) with Sb and Nb co-doping were prepared by a high-temperature solid-phase method. Results indicate that Sb/Nb co-doping causes lattice deformation in LLZO and increases the lithium vacancy concentration and conductivity of LLZO. Then, with the co-doped LLZSNO as an inorganic filler, a composite solid electrolyte of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was prepared with a casting method. The obtained composite solid electrolyte exhibits a high ionic conductivity of 1.76 × 10−4 S/cm at room temperature, a wide electrochemical stable window of 5.2 V, and a lithium-ion transfer number of 0.32. The Li|LiFePO4 coin battery with the composite solid electrolyte shows a high specific capacity of 161.2 mAh/g and a Coulombic efficiency close to 100% at 1 C. In addition, the symmetrical lithium battery Li|Li with the composite electrolyte could cycle stably for about 1500 h without failure at room temperature.

[Display omitted] • Aminopropyl triethoxysilane is introduced to tailor the organic/inorganic interfaces in the CSSE based on the –NH 2 effect. • The hydrogen bond interaction between –NH 2 and PEO can enhance the interface interaction. • Lone pair electrons on N can react with electron-deficient -CN in solvent ACN and promote the uniform dispersion of LLZAO. • Lone pair electrons on N can complex with Li+ and promote the dissociation of Li salts and uniform Li+ diffusion. Composite solid-state electrolyte (CSSE) with integrated strengths avoids the weaknesses of organic and inorganic electrolytes, and thus become a better choice for all-solid-state lithium battery (ASSLB). However, the poor dispersion of inorganic fillers and the organic/inorganic nature difference leads to their interface incompatibility, which greatly destroys the performance of CSSE and ASSLB. Herein, silane coupling agent (SCA) aminopropyl triethoxysilane (ATS) is introduced to tailor the organic/inorganic interfaces in CSSE by the common chemical bridging effect of SCA and the special amino effect (hydrogen bond and lone pair electron effects). It is found that the hydrogen bond interaction between –NH 2 and polyethylene oxide (PEO) enhances their interface interaction. And the lone pair electrons on nitrogen atom allow it to react with solvent acetonitrile and promote the uniform dispersion of ceramic fillers. Moreover, the lone pair electrons can complex with Li+, which promotes the dissociation of Li salts, uniforms Li+ diffusion and inhibits the Li dendrite. Thanks to the above merits, the interface compatibility and stability of organic/inorganic CSSE are much enhanced by innovatively introducing ATS, showing high ionic conductivity and superior mechanical/thermal stability. The ASSLB with this modified CSSE exhibits excellent electrochemical performance with a reversible capacity of 140.9 mAh g−1 and a capacity retention of 94.4% after 280 cycles. These achievements offer a new insight into improving the stability of organic/inorganic CSSE interface and promoting their applicability into ASSLB. [ABSTRACT FROM AUTHOR]

[Display omitted] The room and low-temperature performances of solid-state lithium batteries are crucial to expand their practical application. Polyethylene oxide (PEO) has received great attention as the most representative polymer electrolyte matrix. However, most PEO-based solid-state batteries need to operate at high temperature due to low room temperature ionic conductivity. Improving the ionic conductivity by adding plasticizers or reducing the crystallinity of PEO often compromises its mechanical strength. Here, an amorphous PEO-based composite solid-state electrolyte is obtained by ultraviolet (UV) polymerizing PEO and methacryloyloxypropyltrimethoxy silane (KH570)-modified SiO 2 which demonstrates both satisfactory mechanical performance and high ionic conductivity at room (3.37 × 10−4 S cm−1) and low temperatures (1.73 × 10−4 S cm−1 at 0 °C). In this electrolyte, the crystallinity of PEO is reduced through cross-linking, and therefore provides a fast Li+ ions transfer area. Moreover, the KH570-modified SiO 2 inorganic particles promote the dissociation of lithium salts by Lewis acid centers to increase the ionic conductivity. Importantly, this kind of cross-linking networks endows the final electrolyte much higher mechanical strength than the pure PEO polymer electrolyte or PEO-inorganic filler blended systems. The solid-state LiFePO 4 /Li cell assembled with this electrolyte exhibits excellent cycling performance and high capacity at room and low temperatures. [ABSTRACT FROM AUTHOR]

A high-safety composite solid-state electrolyte (CSSE) was constructed by embedding the high ionic conductivity garnet type Li 6.5 La 3 Zr 1.5 Ta 0.1 Nb 0.4 O 12 (LLZTNO) powder into a polyvinylidene fluoride (PVDF) matrix. The ionic conductivity of the CSSE containing 10% LLZTNO could reach 1.05 × 10−4 S cm−1, and the electrochemical window was extended to 4.80 V vs Li/Li+. In addition, the evolution and composition of the SEI layer were characterized by in-situ optical microscopic observation, X-ray photoelectron spectroscopy and cryogenic electron microscopy (cryo-EM). When paired with an NCM811 cathode, the batteries showed good rate cycling performance, and the discharge capacity could be maintained at 137.1 and 91.2 mAh g−1 at 0.3C and 2C after 80 and 100 cycles. The needle penetration test further demonstrated superior safety and potential applications of the PVDF-based room-temperature CSSE batteries. • A composite solid-state electrolyte with high ionic conductivity was developed. • It demonstrates a wide electrochemical window and excellent cycling performance. • The characteristics of SEI were identified by cryogenic TEM. • The Li metal battery assembled from the composite electrolyte show excellent safety. [ABSTRACT FROM AUTHOR]

• The novel internal lithium polymeric salt interfacial phase is well constructed • The in-situ polymerization and solvent-free methods are designed and investigated. • The interfacial phase construction process is suitable for various ceramic fillers. • Enhanced ionic conductivity properties and electrochemical stability of electrolytes. • The improved long-cycle performance of Li symmetric cells and full metal batteries. The solid-state lithium metal batteries are considered a promising direction for developing lithium-based energy storage devices because of their superiority over lithium-ion batteries containing liquid electrolytes in energy density and safety performance. However, the design, preparation, and optimization of solid-state electrolytes (SSEs), especially composite solid-state electrolytes (CSEs), still face critical construction design and composite process challenges. This work proposes and designs a method to construct a highly compatible and lithium-ion conductive interfacial phase by coating the inorganic phase with polymeric lithium salt in the composite solid electrolytes. The introduction of the lithium salt interfacial phase efficiently improves the cycle performance and stability of CSEs in lithium metal batteries by synergistic optimization of the composite interfacial phase. We investigate two different modification methods (solvent-free and in-situ methods) in two different inorganic systems (Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) and LiTa 2 PO 8 (LTPO)) to demonstrate the practical value of this design. The highest ionic conductivity of the modified PEO/LTPO CSEs (50 wt%) can be improved to 9.3 × 10-4 S·cm−1 at 80℃ and 4.0 × 10-5 at RT (∼25℃, hereinafter inclusive), while those of the modified PEO/LLZTO CSEs can reach 1.4 × 10-3 S·cm−1 at 80℃ and 5.5 × 10-5 at RT. The results demonstrate that the interfacial phase also enhances the electrochemical and cycle stability of CSEs. [ABSTRACT FROM AUTHOR]

• Li 0.35 La 0.55 TiO 3 (LLTO) are synthesized by sol-gel method and two-step calcination. • LLTO-(PEO-FEC) possess high Li+ conductivity vs low electronic conductivity at 25 °C. • LLTO-(PEO-FEC) show a wide electrochemical window of 5.2 V (vs. Li+/Li). • FEC-Li+ coordination enables interface self-healing and dendrite-free Li deposition. Solid-state Li-metal batteries have attracted much attention owing to the high energy density and safety afforded by Li-metal anode and solid-state electrolytes. However, Li-dendrite penetration and unstable interface between solid-state electrolyte and Li-metal incumber their application. Herein, fluoroethylene carbonate (FEC) added Li 0.35 La 0.55 TiO 3 -Poly (ethylene oxide) (LLTO-(PEO-FEC)) composite solid-state electrolytes (CSSEs) are fabricated to address the bottlenecks. The CSSE possesses high Li+ conductivity of 1.13 × 10−4 S·cm−1 vs low electronic conductivity of 1.68 × 10−9 S·cm−1 at 25 °C, presents a wide electrochemical window of 5.2 V (vs. Li+/Li), and shows much more stable lithium deposition at current density of 0.2 mA·cm−2 for 800 h. FEC is driven by Li+ to the damaged interface to form new LiF-rich interface layer, which enables the self-healing of Li-metal and CSSE interface and enhances the electrochemical stability of CSSEs against Li-metal. Li| (LLTO-(PEO-FEC)) |LiFePO 4 cell presents discharge capability of about 115 mAh·g−1 after 100 cycles at 50 °C. This work reveals the mechanism of dendrite-free Li deposition via interface self-healing process under the effect of FEC–Li+ coordination and provides a promising way to prepare the high performances composite solid-state electrolytes and to fabricate the dendrite-free all-solid-state lithium battery. [ABSTRACT FROM AUTHOR]

Sulfide-based composite solid-state electrolyte has been deemed as "Holy Grail" for unlocking solid-state lithium metal batteries (SSLMBs) with high-energy density, combining the extremely high ionic conductivity of sulfide and machinability of organic polymer. However, this appealing system is hitherto stymied by two hindrances, difficult to synthesize due to the chemical incompatibility of sulfide with moisture and polar solvents, moreover, interfacial instability with lithium (Li) anode inducing severe Li dendrite grown. Herein, by utilizing perfluoropolyethers as bifunctional adjuvant, we initiatively fabricate sulfide-based composite electrolyte, Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/Li 10 GeP 2 S 12 and assemble SSLMBs. Perfluoropolyethers with low molecular weight facilitate the stable dispersion of Li 10 GeP 2 S 12 in casting solution, ascribed to their strong electronegativity of C–F bonds. In addition, high molecular weight perfluoropolyethers function as interfacial stabilizer, dramatically improving the interfacial compatibility with Li anode by in-situ forming a LiF-rich solid electrolyte interphase layer. This composite electrolyte exhibits high room temperature ionic conductivity (0.18 mS cm−1), outstanding lithium ion transfer number (0.68), good mechanical strength and nonflammability. The solid-state LiFePO 4 ǁLi battery presents superior long-term cycling stability and rate capability. Our study paves a new way for fabricating the sulfide-based composite electrolyte, provides an effective strategy for constructing compatible solid-state electrolyteǁLi interface. Image 1 • PVDF-HFP/Li 10 GeP 2 S 12 electrolyte is prepared by binary solution casting method. • PFPE 500 as dispersing solvents exhibit good chemical compatibility with Li 10 GeP 2 S 12. • A high ion conductivity (σ RT = 10−4 S cm−1) and Li+ transfer number (0.68) are obtained. • PFPEs as interfacial stabilizers enhance the compatibility of Li 10 GeP 2 S 12 with Li. • LiFePO 4 ‖Li battery shows good cycling stability and rate capability. [ABSTRACT FROM AUTHOR]