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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. 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]

The development of high-performance solid-state electrolyte (SSE) films is critical to the practical application of all-solid-state Li metal batteries (ASSLMBs). However, developing high-performance free-standing electrolyte films remains a challenging task. In this work, we demonstrate a novel scalable solvent-free process for fabricating high ceramic content composite solid-state electrolyte (HCCSE) films. Specifically speaking, a mixture of ceramic and polymer is dry mixed, fibered, and calendered into a free-standing porous ceramic film, on which polymer precursor is coated and polymerized to bridge the inorganic ceramic particles, resulting in a flexible HCCSE film with a ceramic content of up to 80 wt.%. High ceramic content not only leads to high ionic conductivity but also brings good mechanical properties; while the organic phase enables electrode electrolyte interfacial stability. When Li10GeP2S12 (LGPS) and polymeric ionic liquid-based solid polymer electrolytes (PIL-SPEs) were used as the inorganic and organic phases, respectively, the room temperature ionic conductivity of the resulted HCCSE reaches 0.91 mS·cm−1. Based on this HCCSE, Li∥Li symmetric battery cycled stably for more than 2,400 h with ultra-low overpotential, and ASSLMBs with different cathodes (LiFePO4 and sulfurized polyacrylonitrile (PAN-S)) present small polarization and decent cyclability at room temperature. This work provides a novel scalable solvent-free strategy for preparing high-performance freestanding composite solid-state electrolyte (CSE) film for room temperature ASSLMBs. [ABSTRACT FROM AUTHOR]

Solid-state Li metal batteries with solid electrolytes have built a potential way to solve the safety and low energy density problems of current commercial Li-ion batteries with liquid electrolyte. As a key component of solid-state Li metal batteries, solid electrolytes require high ionic conductivities and good mechanical properties. We have designed a composite solid electrolyte (CSE) consisting of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-Li6.5La3Zr1.5Ta0.5O12 (LLZTO)-succinonitrile (SN) and Li bis(trifluoromethylsulphonyl)imide (LiTFSI). The PVDF-HFP-based porous matrix made by electrospinning ensures good mechanical properties of the electrolyte membrane, and the large proportion of SN filling material makes the electrolyte membrane have an ionic conductivity of 1.11 mS·cm−1 without the addition of liquid electrolyte. The symmetric battery assembled with CSE can be cycled stably for more than 600 h, and the LiFePO4∣CSE∣Li full battery can also be cycled stably for more than 200 cycles. In addition to Li metal batteries, Li-O2 and Li-CO2 batteries that use CSE as electrolytes also have good performances, reflecting the universality of CSE. CSE does not only guarantee good mechanical properties but also obtain a high ionic conductivity. This design provides a new idea for the commercial application of polymer-based solid batteries. [ABSTRACT FROM AUTHOR]

The solid-state electrolyte (SSE) has promising applications in next-generation lithium (Li) metal batteries (LMBs) because of its significantly enhanced safety and more compatible interface characteristics than flammable traditional liquid electrolytes. However, only a few attempts have achieved high-performance high-voltage LMBs, which is attributed to the fact that both high ionic conductivity and good compatibility with electrodes can hardly be achieved simultaneously. Herein, a composite solid-state electrolyte (CSE) based on star-shaped siloxane-based polymer electrolyte coupled with Li6.75La3Zr1.75Ta0.25O12 (LLZTO) ceramic fillers is designed and prepared through a facile in-situ polymerization method. The obtained CSE exhibits high ionic conductivity (i.e., 1.68 × 10−4 S cm−1 at a temperature of 60 °C), superior anodic stability, and high Li-ion transference number (i.e., 0.53) because of the multifunctional synergistic effect of the polymer electrolyte with LLZTO ceramic fillers. Moreover, the as-developed CSE shows excellent compatibility with Li anodes. As a result, the as-developed CSE enables the development of long-life 4.4-V-class solid-state LMBs with a LiCoO2 cathode, with 79.7% capacity retention and 99.74% average Coulombic efficiency after 500 cycles at a 0.5 C rate. Postmortem analysis of cycled batteries confirms that such superior battery performance can be mainly ascribed to the formation of a compatible electrode/electrolyte interface. Furthermore, excellent safety features can be observed in LiCoO2/Li pouch batteries. This work provides an important guide for the rational design of SSEs for high-voltage LMBs. [ABSTRACT FROM AUTHOR]