Effect of Liquid Electrolyte Soaking on the Interfacial Resistance of Li7La3Zr2O12 for All-Solid-State Lithium Batteries

Progress of Polymer Electrolytes Worked in Solid-State Lithium Batteries for Wide-Temperature Application

Solid-state Li-ion batteries have emerged as the most promising next-generation energy storage systems, offering theoretical advantages such as superior safety and higher energy density. However, polymer-based solid-state Li-ion batteries face challenges across wide temperature ranges. The primary issue lies in the fact that most polymer electrolytes exhibit relatively low ionic conductivity at or below room temperature. This sensitivity to temperature variations poses challenges in operating solid-state lithium batteries at sub-zero temperatures. Moreover, elevated working temperatures lead to polymer shrinkage and deformation, ultimately resulting in battery failure. To address this challenge of polymer-based solid-state batteries, this review presents an overview of various promising polymer electrolyte systems. The review provides insights into the temperature-dependent physical and electrochemical properties of polymers, aiming to expand the temperature range of operation. The review also further summarizes modification strategies for polymer electrolytes suited to diverse temperatures. The final section summarizes the performance of various polymer-based solid-state batteries at different temperatures. Valuable insights and potential future research directions for designing wide-temperature polymer electrolytes are presented based on the differences in battery performance. This information is intended to inspire practical applications of wide-temperature polymer-based solid-state batteries.

LiPF6 Induces Phosphorization of Garnet-Type Solid-State Electrolyte for Stable Lithium Metal Batteries

Garnet solid electrolyte Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) is an excellent inorganic ceramic-type solid electrolyte; however, the presence of Li2 CO3 impurities on its surface hinders Li-ion transport and increases the interface impedance. In contrast to traditional methods of mechanical polishing, acid corrosion, and high-temperature reduction for removing Li2 CO3 , herein, a straightforward "waste-to-treasure" strategy is proposed to transform Li2 CO3 into Li3 PO4 and LiF in LiPF6 solution under 60 °C. It is found that the formation of Li3 PO4 during LLZTO pretreatment facilitates rapid Li-ion transport and enhances ionic conductivity, and the LLZTO/PAN composite polymer electrolyte shows the highest Li-ion transference number of 0.63. Additionally, the dense LiF layer serves to safeguard the internal garnet solid electrolyte against solvent decomposition-induced chemical adsorption. Symmetric Li/Li cells assembled with treated LLZTO/PAN composite electrolyte exhibit a critical current density of 1.1 mA cm-2 and a long lifespan of up to 700 h at a current density of 0.2 mA cm-2 . The Li/LiFePO4 solid-state cells demonstrate stable cycling performances for 141 mAh g-1 at 0.5 C, with capacity retention of 93.6% after 190 cycles. This work presents a novel approach to converting waste into valuable resources, offering the advantages of simple processes, and minimal side reactions.

Recent advances in in situ and operando characterization techniques for Li7La3Zr2O12-based solid-state lithium batteries

Li₇La₃Zr₂O₁₂ (LLZO)-based solid-state Li batteries (SSLBs) have emerged as one of the most promising energy storage systems due to the potential advantages of solid-state electrolytes (SSEs), such as ionic conductivity, mechanical strength, chemical stability and electrochemical stability. However, there remain several scientific and technical obstacles that need to be tackled before they can be commercialised. The main issues include the degradation and deterioration of SSEs and electrode materials, ambiguity in the Li⁺ migration routes in SSEs, and interface compatibility between SSEs and electrodes during the charging and discharging processes. Using conventional ex situ characterization techniques to unravel the reasons that lead to these adverse results often requires disassembly of the battery after operation. The sample may be contaminated during the disassembly process, resulting in changes in the material properties within the battery. In contrast, in situ/operando characterization techniques can capture dynamic information during cycling, enabling real-time monitoring of batteries. Therefore, in this review, we briefly illustrate the key challenges currently faced by LLZO-based SSLBs, review recent efforts to study LLZO-based SSLBs using various in situ/operando microscopy and spectroscopy techniques, and elaborate on the capabilities and limitations of these in situ/operando techniques. This review paper not only presents the current challenges but also outlines future developmental prospects for the practical implementation of LLZO-based SSLBs. By identifying and addressing the remaining challenges, this review aims to enhance the comprehensive understanding of LLZO-based SSLBs. Additionally, in situ/operando characterization techniques are highlighted as a promising avenue for future research. The findings presented here can serve as a reference for battery research and provide valuable insights for the development of different types of solid-state batteries.

Abundant Hydrogen Bonds Formed in a Urea-Based Gel Polymer Electrolyte Improve Interfacial Stability in Lithium Metal Batteries

As an emerging and potential replacement system for liquid electrolytes, polymer electrolytes (PEs) exhibit unique capacity in suppressing metal dendrite formation and leakage risks. However, the most used polymer matrix, including polyether, polyester, and polysiloxane, still cannot meet the practical demands for metal electrode compatibility and long lifespan. In this study, gel polymer electrolytes consisting of a polyurea network with abundant hydrogen bonds and deep eutectic electrolyte (DEE) are designed and prepared in-situ. The hydrogen bonding between polyurea chains and polyurea-DEE provides good interfacial stability between PEs and lithium metal. As a result, the assembled Li/LiFePO₄ cells based on this electrolyte deliver a long cycle life with 90 % retention after 500 cycles and 76.5 % retention after 1000 cycles at 1 C. In addition, the flexible design characteristics of polyurea structure permit easy operation for performance optimization by modulating the composition of hard and soft segments, and enhanced ionic conductivity and self-healing efficiency are obtained. This study provides a novel method for preparing advanced polymer electrolytes for lithium metal batteries.

On the Surface Modification of LLZTO with LiF via a Gas-Phase Approach and the Characterization of the Interfaces of LiF with LLZTO as Well as PEO+LiTFSI

In this study we present gas-phase fluorination as a method to create a thin LiF layer on Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO). We compared these fluorinated films with LiF films produced by RF-magnetron sputtering, where we investigated the interface between the LLZTO and the deposited LiF showing no formation of a reaction layer. Furthermore, we investigated the ability of this LiF layer as a protection layer against Li₂CO₃ formation in ambient air. By this, we show that Li₂CO₃ formation is absent at the LLZTO surface after 24 h in ambient air, supporting the protective character of the formed LiF films, and hence potentially enhancing the handling of LLZTO in air for battery production. With respect to the use within hybrid electrolytes consisting of LLZTO and a mixture of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), we also investigated the interface between the formed LiF films and a mixture of PEO+LiTFSI by X-ray photoelectron spectroscopy (XPS), showing decomposition of the LiTFSI at the interface.

Perspective on design and technical challenges of Li-garnet solid-state batteries

Solid-state Li-ion batteries based on Li-garnet Li₇La₃Zr₂O₁₂ (LLZO) electrolyte have seen rapid advances in recent years. These solid-state systems are poised to address the urgent need for safe, non-flammable, and temperature-tolerant energy storage batteries that concomitantly possess improved energy densities and the cycle life as compared to conventional liquid-electrolyte-based counterparts. In this vision article, we review present research pursuits and discuss the limitations in the employment of LLZO solid-state electrolyte (SSE) for solid-state Li-ion batteries. Particular emphasis is given to the discussion of pros and cons of current methodologies in the fabrication of solid-state cathodes, LLZO SSE, and Li metal anode layers. Furthermore, we discuss the contributions of the LLZO thickness, cathode areal capacity, and LLZO content in the solid-state cathode on the energy density of Li-garnet solid-state batteries, summarizing their required values for matching the energy densities of conventional Li-ion systems. Finally, we highlight challenges that must be addressed in the move towards eventual commercialization of Li-garnet solid-state batteries.

Reaction Mechanisms of Ta-Substituted Cubic Li7La3Zr2O12 with Solvents During Storage

The reactivity of garnet solid electrolytes toward humid air hinders their practical application despite their attractive, superior properties such as high Li⁺ conductivity and wide electrochemical window. Sealing garnets with organic solvents can not only prevent them from reacting with humid air but also render them compatible with other processing technologies. Therefore, the chemical and structural stability of garnets in organic solvents must be studied. In this study, we selected several commonly used organic solvents with different representative functional groups to investigate their stability with garnets and reaction mechanisms. The experiments and theoretical calculations revealed that all of the solvents reacted with garnets through Li-H exchange, and solvent acidity determined the reaction strength. Furthermore, the solvent acidity was closely correlated to the functional groups connected to H atoms, which can affect charge distribution. Solvents or the tautomer of the solvents with hydroxyl groups such as alcohol, acetone, and N-methyl pyrrolidone, which are relatively more acidic, can lead to a violent reaction with changes in the lattice parameters of garnets. Ether compounds and saturated aliphatic hydrocarbons with relatively low acidity are highly stable against garnets. The proposed reaction mechanisms and rules may help in selecting appropriate solvents for different applications of garnets.