Composite solid electrolyte comprising poly(propylene carbonate) and Li1.5Al0.5Ge1.5(PO4)3 for long-life all-solid-state Li-ion batteries

Research Advances in Rare-Earth-Based Solid Electrolytes for All-Solid-State Batteries

All-solid-state batteries (ASSBs) and solid-state electrolytes (SSE) have emerged as promising alternative energy storage devices for traditional lithium-ion batteries, drawing significant attention from researchers. Notably, SSE materials incorporating rare earth elements have demonstrated remarkable advancements in terms of ionic conductivity, electrochemical stability, and cycle-reversible performance. The unique electron layer structures of rare earth elements facilitate diverse energy level transitions. Meanwhile, their relatively large ionic radius contributes to excellent ionic conductivity, mechanical strength, and electrochemical properties in the electrolyte. This paper offers a comprehensive review of rare-earth-based oxide solid electrolytes, rare-earth-based sulfide solid electrolytes, rare-earth-based halide solid electrolytes, and composite polymer electrolytes enriched with rare earth elements. The characteristics, applications, modification methods, and underlying mechanisms of these SSE materials are investigated, offering valuable insights and inspiration for the design of future SSE materials. Additionally, this paper systematically presents solutions for improving the performance of ASSBs and explores the ion transmission in these batteries. Finally, the research direction, optimization methods, and development prospects of rare-earth-based solid electrolytes are analyzed and forecasted.

An interactive organic-inorganic composite interface enables fast ion-transport, low self-discharge and stable storage of lithium battery

Lithium batteries have been widely used in various fields, however, further research needs to be conducted to improve their stability and long-term storage performance for the highly active lithium metal anode. Herein, an organic-inorganic composite film composed of polypropylene carbonate (PPC), lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) and Li6.5La3Zr1.5Nb0.5O12 (LLZNO) is fabricated on the lithium foil surface by spin-coating technique to passivate the lithium anode and regulate the ion transport behavior. The Li/CFx battery with the optimized composite film coated lithium anode exhibits excellent discharge capacity (1006.6 mAh/g, 0.1C) and high-rate capability (639.4 mAh/g, 5C), much higher than those of the uncoated Li/CFx battery. The discharge specific capacity remains 521.7 mAh/g at 0.1C after stored at 55 °C for 60 days, corresponding to a monthly self-discharge of 1.87 %, while the battery without coating film has almost failed. Theoretical calculation, Raman mapping and Kelvin probe force microscopy (KPFM) measurements demonstrate that the stable and ion-conductive composite film effectively increases ion channels, regulates ion migration and passivates the Li anode from the corrosion of liquid electrolyte during discharge and storage. Constructing a rational organic-inorganic composite film with high mechanical stability and ionic conductivity on the Li anode surface is a facile and cost-effective strategy to enhance the high-rate and long-term storage performance of Li/CFx battery.

Construction of SnO2 buffer layer and analysis of its interface modification for Li and Li1.5Al0.5Ge1.5(PO4)3 in solid-state batteries

SnO2 layer between Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and lithium anode was prepared through simple scratch-coating process to improve interface properties. The physical phase, morphology, and electrochemical properties of Li/SnO2/LAGP structure were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical analytical methods. It was found that SnO2 layer effectively improved the interface stability of LAGP and lithium anode. The prepared Li/SnO2/LAGP/SnO2/Li symmetric cell exhibited a large critical current density of 1.8 mA cm-2 and demonstrated excellent cycling characteristics. The polarization voltages of symmetric cell were 0.1 V and 0.8 V after 1000 h of cycling at current densities of 0.04 mA cm-2 and 0.5 mA cm-2, respectively. Li/SnO2@LAGP/LiFePO4 solid-state full cells were also assembled, exhibiting a discharge specific capacity of 150 mAh g-1 after 200 cycles at 0.1C with capacity retention rate of 96 %. The good interface properties of Li/SnO2/LAGP structure are attributed to the transformation of SnO2 layer into a buffer layer containing Li2O, Sn0, and LixSny alloy during cycling process, which effectively inhibits the reduction reaction between LAGP and lithium anode.

Construction of a High-Performance Composite Solid Electrolyte Through In-Situ Polymerization within a Self-Supported Porous Garnet Framework

Composite solid electrolytes (CSEs) have emerged as promising candidates for safe and high-energy-density solid-state lithium metal batteries (SSLMBs). However, concurrently achieving exceptional ionic conductivity and interface compatibility between the electrolyte and electrode presents a significant challenge in the development of high-performance CSEs for SSLMBs. To overcome these challenges, we present a method involving the in-situ polymerization of a monomer within a self-supported porous Li6.4La3Zr1.4Ta0.6O12 (LLZT) to produce the CSE. The synergy of the continuous conductive LLZT network, well-organized polymer, and their interface can enhance the ionic conductivity of the CSE at room temperature. Furthermore, the in-situ polymerization process can also construct the integration and compatibility of the solid electrolyte-solid electrode interface. The synthesized CSE exhibited a high ionic conductivity of 1.117 mS cm-1, a significant lithium transference number of 0.627, and exhibited electrochemical stability up to 5.06 V vs. Li/Li+ at 30 °C. Moreover, the Li|CSE|LiNi0.8Co0.1Mn0.1O2 cell delivered a discharge capacity of 105.1 mAh g-1 after 400 cycles at 0.5 C and 30 °C, corresponding to a capacity retention of 61%. This methodology could be extended to a variety of ceramic, polymer electrolytes, or battery systems, thereby offering a viable strategy to improve the electrochemical properties of CSEs for high-energy-density SSLMBs.

An Asymmetric Cross-Linked Ionic Copolymer Hybrid Solid Electrolyte with Super Stretchability for Lithium-Ion Batteries

Composite solid electrolytes are recommended to be the most promissing strategy for solid-state batteries because they combine the advantages of inorganic ceramics and polymers. However, the huge interfacial resistance between the inorganic ceramic and polymer results in low ionic conductivity, which is still the major impediment that limits their applications. Herein, a novel highly elastic and weakly coordinated ionic copolymer hybrid electrolyte with asymmetric structure based on surface-modified Li_1.5 Al_0.5 Ge_1.5 (PO₄ )₃ by "in situ" polymerization is proposed to improve ionic conductivity and mechanical properties simultaneously. The all-solid hybrids electrolytes exhibit room-temperature ionic conductivity up to 2.61 × 10^-4 S cm^-1 and lithium-ion transference number of 0.41. The hybrids electrolytes can be repeatedly stretching-releasing-stretching, showing a super stretchability with the elongation at break up to 496%. The Li symmetrical cells assembled with the hybrid electrolytes can continuously operate for 800 h at 0.1 mA cm^-2 without discernable dendrites, indicating good interfacial compatibility between the hybrid electrolytes and lithium electrodes. The Li|LiFePO₄ batteries assembled with the hybrid electrolytes deliver an initial discharge specific capacity of 165.5 mAh g^-1 with an initial coulombic efficiency of 94.8% and 154 mAh g^-1 after 100 cycles at 0.1 C, and maintain 95.4% capacity retention after 100 cycles at 0.5 C.

Improving Cyclability of All-Solid-State Batteries via Stabilized Electrolyte-Electrode Interface with Additive in Poly(propylene carbonate) Based Solid Electrolyte

In this study, tetraethylene glycol dimethyl ether (TEGDME) is demonstrated as an effective additive in poly(propylene carbonate) (PPC) polymers for the enhancement of ionic conductivity and interfacial stability and a tissue membrane is used as a backbone to maintain the mechanical strength of the solid polymer electrolytes (SPEs). TEGDME in the PPC allows the uniform distribution of conductive LiF species throughout the cathode electrolyte interface (CEI) layer which plays a critically important role in the formation of a stable and efficient CEI. In addition, the high modulus of SPEs suppresses the formation of a protrusion-type CEI on the cathode. The SPE with the optimized TEGDME content exhibits a high ionic conductivity of 0.89 mS cm^-1 , an adequate potential stability of up to 4.89 V, and a high Li-ion transference number of 0.81 at 60 °C. Moreover, the Li/SPE/Li cell demonstrates excellent cycling stability for 1650 h, and the Li/SPE/LFP full cell exhibits an initial reversible capacity of 103 mAh g^-1 and improved stability over 500 cycles at a rate of 1 C. The TEGDME additive improves the electrochemical properties of the SPEs and promotes the creation of a stable interface, which is crucial for ASSLIBs.

Thermal Decomposition Characteristics of PEO/LiBF4/LAGP Composite Electrolytes

Lithium-based batteries with improved safety performance are highly desired. At present, most safety hazard is the consequence of the ignition and flammability of organic liquid electrolytes. Dry ceramic-polymer composite electrolytes are attractive for their merits of non-flammability, reduced gas release, and thermal stability, in addition to their mechanical strength and flexibility. We recently fabricated free-standing solid composite electrolytes made up of polyethylene oxide (PEO), LiBF4 salt, and Li1+xAlxGe2−x(PO4)3 (LAGP). This study is focused on analyzing the impacts of LAGP on the thermal decomposition characteristics in the series of PEO/LiBF4/LAGP composite membranes. It is found that the appropriate amount of LAGP can (1) significantly reduce the organic solvent trapped in the polymer network and (2) increase the peak temperature corresponding to the thermal degradation of the PEO/LiBF4 complex. In the presence of LAGP, although the peak temperature related to the degradation of free PEO is reduced, the portion of free PEO, as well as its decomposition rate, is effectively reduced, resulting in slower gas release.

Development on Solid Polymer Electrolytes for Electrochemical Devices

Electrochemical devices, especially energy storage, have been around for many decades. Liquid electrolytes (LEs), which are known for their volatility and flammability, are mostly used in the fabrication of the devices. Dye-sensitized solar cells (DSSCs) and quantum dot sensitized solar cells (QDSSCs) are also using electrochemical reaction to operate. Following the demand for green and safer energy sources to replace fossil energy, this has raised the research interest in solid-state electrochemical devices. Solid polymer electrolytes (SPEs) are among the candidates to replace the LEs. Hence, understanding the mechanism of ions' transport in SPEs is crucial to achieve similar, if not better, performance to that of LEs. In this paper, the development of SPE from basic construction to electrolyte optimization, which includes polymer blending and adding various types of additives, such as plasticizers and fillers, is discussed.