Solid-state Li Metal Batteries Research Articles

Polymer solid electrolytes with ultra-stable cycles and high-capacity retention for all-solid-state Li-metal battery

Polymer electrolytes have become widely popular on account of their low expenses, reduced weight, simple processing, and excellent safety features. However, polymer electrolytes have yet to find use in commercial batteries because of their limited mechanical durability and poor ionic conductivity. In this paper, an ultra-stable cycles and interfaces blending polymer electrolyte (BPE) suitable for all solid-state Li metal batteries was prepared by blending three polymers: polymethyl methacrylate (PMMA), polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), and polyethylene oxide (PEO). Microstructure characterization showed numerous amorphous areas with strong interfacial strength of the BPE. The BPE3 exhibited a maximum of 15.65 MPa in tensile strength. BPE2 have excellent electrochemical performance, such as wide electrochemical windows (up to 4.7 V vs Li/Li+), high lithium ion transference numbers (up to 0.75), high ion conductivity (up to 1.87 × 10-4 S cm−1 at 60 °C), and excellent interface stability. By assembling all state-solid LiFePO4/BPE2/Li batteries for electrochemical testing, BPE2 exhibit high electrochemical characteristics. BPE2 discharge specific capacity is as high as 154.7 mAh g−1 at 1C. The BPE2 underwent 200 cycles at 0.5C and 400 cycles at 1C, with capacity retention rates of 95.7 % and 96.6 %, respectively. BPE is a promising electrolyte candidate for flexible lithium metal batteries.

Ultrathin, Mechanically Durable, and Scalable Polymer-in-Salt Solid Electrolyte for High-Rate Lithium Metal Batteries.

Polymer-in-salt solid-state electrolytes (PIS SSEs) are emerging for high room-temperature ionic conductivity and facile handling, but suffer from poor mechanical durability and large thickness. Here, Al2O3-coated PE (PE/AO) separators are proposed as robust and large-scale substrates to trim the thickness of PIS SSEs without compromising mechanical durability. Various characterizations unravel that introducing Al2O3 coating on PE separators efficiently improves the wettability, thermal stability, and Li-dendrite resistance of PIS SSEs. The resulting PE/AO@PIS demonstrates ultra-small thickness (25µm), exceptional mechanical durability (55.1MPa), high decomposition temperature (330°C), and favorable ionic conductivity (0.12 mS cm-1 at 25°C). Consequently, the symmetrical Li cells remain stable at 0.1mA cm-2 for 3000 h, without Li dendrite formation. Besides, the LiFePO4|Li full cells showcase excellent rate capability (131.0 mAh g-1 at 10C) and cyclability (93.6% capacity retention at 2C after 400 cycles), and high-mass-loading performance (7.5mg cm-2). Moreover, the PE/AO@PIS can also pair with nickel-rich layered oxides (NCM811 and NCM9055), showing a remarkable specific capacity of 165.3 and 175.4 mAh g-1 at 0.2C after 100 cycles, respectively. This work presents an effective large-scale preparation approach for mechanically durable and ultrathin PIS SSEs, driving their practical applications for next-generation solid-state Li-metal batteries.

Li Stripping Behavior of Anode‐Free Solid‐State Batteries Under Intermittent‐Current Discharge Conditions

AbstractAnode‐free manufacturing holds promise to enable high energy densities and lower Lithium (Li)‐metal solid‐state batteries (LMSSBs). Nevertheless, in contrast to thick Li foil (>50 µm), the stripping capacity of in situ‐formed Li (10–30 µm) is limited due to diminished creep flow, resulting in reduced accessible capacity. This study explores the correlation between stripping capacity and surface roughness of garnet Li7La3Zr2O12 (LLZO) solid electrolyte. The results reveal that stripping capacity can be enhanced through the surface modification of solid electrolytes. Additionally, this study scrutinizes the stripping behavior of in situ Li under intermittent‐current discharge conditions, which are more relevant to the operational conditions of electric vehicles (EVs). It is demonstrated that, when compared to constant‐current stripping, intermittent‐current stripping effectively suppresses void formation and enhances the stripping capacity of in situ Li by 40%. It is considered that the intermittent current inhibits the accumulation of Li vacancies, thereby delaying the void formation. These findings provide valuable insights into the development of high‐performance anode‐free LMSSBs for EVs.

Effects of H2O on Improving the Performance of a Solid Composite Electrolyte Fabricated via an Air-Processable Technique.

Inert atmosphere is normally necessary for fabrication of solid composite electrolytes (SCEs) as a crucial part of solid-state Li-metal batteries in order to avoid undesirable reactions induced by ambient moisture. Herein, we developed an air-processable technique to fabricate SCEs by employing LiCF3SO3 (LiOTf) as the Li salt, which was combined with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) as the fast Li-conductor and polyvinylidene difluoroethylene/polyvinyl acetate (PVDF/PVAC) as the polymer matrix. With the assistance of trace H2O dissolved in electrolyte solution, the room-temperature Li+ conductivity of the obtained aSCE reached as high as 5.09 × 10-4 S cm-1, which was over 3 orders of magnitude higher than that of the one (iSCE, 1.93 × 10-7 S cm-1) cast by the electrolyte solution prepared in an inert atmosphere. The theoretical calculation results reveal that the oxygen atom of H2O exhibits a high propensity to interact with the Li atom in LiOTf (Li···O), thereby establishing a hydrogen bond with the oxygen atom (H···O) in N,N-dimethylformamide (solvent). Such interactions promoted the dissociation of LiOTf and led to the formation of uniform Li+ transportation channels. Simultaneously, the composition distribution was also altered, resulting in a smoother surface of aSCE and lowered crystallinity of PVDF. On this basis, the LiOTf/LLZTO/PVDF/PVAC solution at 60 °C was directly coated onto the surface of the LiFePO4 (LFP) cathode to fabricate the LFP-aSCE film after drying in an oven. The assembled LFP-aSCE/Li battery wetted by trace sulfolane exhibited an initial Coulombic efficiency of 94.7% and a capacity retention rate of up to 96% at 0.2 C (137 mAh g-1) after 180 cycles and a high capacity of 143.7 mAh g-1 at 0.5 C (150 cycles). Overall, this work could pave the way for the facile fabrication of solid electrolytes.

Rationally coordinating polymer enabling effective Li-ion percolation network in composite electrolyte for solid-state Li-metal batteries

The sluggish lithium-ion mobility and inferior electrolyte/electrode interfacial compatibility of composite solid electrolytes greatly hinder the practical application of solid-state lithium-metal batteries. Here, a novel composite polymer electrolyte (CPE) with effective Li+ percolation network is synthesized based on single-ion conductive polymer lithiated polyvinyl formal (LiPVFM) and garnet Li6.4La3Zr2Ga0.2O12 (LLZGO) nanoparticles. The supramolecular interaction between the branched hydroxyl in LiPVFM and the lattice oxygen in LLZGO fillers endows CPE with a continuous percolation structure and improved toughness. Meanwhile, the rational O-Li+ coordination in the LiPVFM random polymer significantly enhances Li+ transfer within the percolation network. Therefore, this as-prepared CPE presents a lithium-ion transference number of 0.75 and an ionic conductivity of 0.527 mS cm−1 at 30 °C, alongside an electrochemical stability window of 4.6 V and a substantial suppression of Li dendrite growth. In addition, ultra-stable interfaces between this CPE and high-voltage LiNi0.6Mn0.2Co0.2O2 (NMC) cathode during cycling can be determined by in-situ electrochemical impedance spectroscopy and in-situ differential electrochemical mass spectrometry characterization. This work is a new exploration for the structural design of CPEs and highlights the importance of “rational coordination” of alkali cation in solid batteries.

A Stable Matrix Assisting Highly Compatible and Maintainable Lithium-Garnet Interface for Solid-State Batteries.

Solid-state Li metal batteries (SSLMBs) are attractive due to their capability to simultaneously offer high energy density and high-level safety when combining Li metal anodes, solid-state electrolytes (SSEs), and high-voltage cathodes together. However, SSLMBs may well incur short circuits caused by Li dendrites penetrations, which mainly originate from the instability and poor contact between Li metal and SSEs. Herein, by taking full advantage of the reaction products of Li and Li1.3Al0.3Ti1.7(PO4)3 (LATP), a lithium-LATP composite anode (Li-LATP) is obtained, in which a stable matrix is formed to enhance the contact between Li and the garnet-type SSEs, alleviating the volume change and preserving an intact interface during the charge/discharge process. Consequently, the Li-LATP/garnet/Li-LATP symmetric cell displays a fairly low interfacial resistance of 6Ωcm2 and stable cycling performance for over 2500h with a low overpotential. Furthermore, the LiCoO2/garnet/Li-LATP full cell also shows a high discharge capacity of 159mAhg-1 and great cycling performance.

Polyethylene oxide-Based solid electrolytes with fast Li-ion transport channels constructed from 2D montmorillonite for solid-state lithium-metal batteries

Polyethylene oxide (PEO)-based solid-state electrolytes (SSEs) typically struggle with poor ionic conductivity, low lithium (Li)-ion transference number, and narrow electrochemical window. For overcoming these drawbacks, we designed a promising composite SSE (CSSE), i.e., a Li-containing ionic liquid (LiIL) was inserted into the Li-montmorillonite (LiMNT) layered structure to form an active filler (LiIL@LiMNT), involving two-dimensional (2D) fast transport channels of Li-ion inside PEO electrolyte. Benefitting from an enhancement of the 2D Li-ion transport channels, the obtained CSSE exhibited an excellent ion conductivity of 1.38 × 10−4 S cm−1 at 30 °C as well as a satisfactory Li-ion transference number (0.38). A Li symmetric battery with the CSSE exhibited a steady cycle for 3000 h with 0.2 mA cm−2 at 60 °C. Under the rate of 0.5C at 60 °C, the solid-state Li-metal batteries (SSLMBs) assembled with LiFePO4 and LiNi0.33Co0.33Mn0.33O2 cathodes maintained a considerable reversible capacity after 400 and 100 cycles, respectively. The assembled SSLMB also achieved a satisfactory performance at 40 °C. The 2D active filler prepared in this work forms efficient 2D Li-ion transport channels inside the CSSE while maintaining a tight interfacial contact with electrodes, which is crucial to achieve a superior performance for CSSEs. This strategy of constructing 2D ion transport channels in polymer electrolytes also provides another way for the design of other CSSEs.

Understanding the complexities of Li metal for solid-state Li-metal batteries

Understanding the complexities of Li metal for solid-state Li-metal batteries

Ferroelectric BaTiO3 Regulating the Local Electric Field for Interfacial Stability in Solid-State Lithium Metal Batteries.

Solid-state Li metal batteries (SSLMBs) are widely investigated since they possess promising energy density and high safety. However, the poor interfacial compatibility between the electrolyte and electrodes limits their promising development. Herein, a robust composite electrolyte (poly(vinyl ethylene carbonate) electrolyte with 3 wt % of BaTiO3, PVEC-3BTO) with excellent interfacial performance is rationally designed by incorporating ferroelectric BaTiO3 (BTO) nanoparticles into the poly(vinyl ethylene carbonate) (PVEC) electrolyte matrix. Benefiting from the high dielectric constant and ferroelectric properties of BTO, the interfacial compatibility between electrolytes and electrodes was significantly improved. The enhanced Li+ transference number (0.64) of solid electrolyte and in situ generated BaF2 inorganic interphase contribute to the enhanced cycling stability of PVEC-3BTO based Li//Li symmetrical batteries. Furthermore, the antioxidation ability of PVEC-3BTO has also been enhanced by modulating the local electric field for good pairing with high-voltage LiCoO2 material. Therefore, in this work, the mechanism of BTO for improving interfacial compatibility is revealed, and also useful methods for addressing the interface issues of SSLMBs have been provided.

Research on new Taylor flow reactor to prepare Ni-rich oxide and LLZO ceramic Li+ ion conductors

New, green technologies are better for the environment and this is increasingly important in the context of worsening global warming and climate change. With the prevalence of battery powered devices, an important part of this is improved battery technology with improved performance and enhanced energy efficiency. Professor Chun-Chen Yang, Department of Chemical Engineering, Ming Chi University of Technology, Taiwan is also a director of the Battery Research Centre of Green Energy (BRCGE), Taiwan, which is conducting R&D on new, revolutionary battery technologies. A focus for Yang and his team is lithium (Li) batteries and new versions that incorporate different elements, with a view to improving energy storage capacity and green sustainable energy practices. He recognises the need to increase the energy density and safety of these batteries in order to meet the requirements of future applications and is exploring the benefits of using a full solid-state Li metal battery (ASSLMB). The researchers are conducting studies using a Taylor flow reactor to prepare Ni-rich oxide and LLZO ceramic Li+ ion conductors and have already yielded advantages and they hope, in the future, the method can be adopted on a wide scale and lead to the development of new and improved batteries. First, the team is keen to overcome issues associated with the difficulty of controlling uniformity and quality.

Unconventional PEO-PPC quasi-solid state blend polymer electrolyte for high efficiency solid-state Li-metal batteries

Polymer electrolytes represent a safer alternative over traditional liquid electrolytes, enabling the use of higher energy density active materials as electrodes for batteries. Among the wide variety of different polymeric matrix that are currently been proposed, polyethylene oxide (PEO) is considered one of the most promising. In this work, a PEO-based quasi-solid polymer electrolyte (QSPE) was produced by easily scalable solution casting technique, optimized with addition of plasticizers and blended with polypropylene carbonate (PPC). The resulting polymer electrolyte was ultimately supported to glass fiber separator. Improvement of ionic conductivity, transfer number and electrochemical stability window of the different formulations was confirmed through electrochemical impedance spectroscopy and linear sweep voltammetry. Plating and stripping tests in symmetric LiLi cells and charge–discharge tests in half-cell configuration (Li vs LFP) were performed to evaluate the cyclability and stability of the QSPEs. The PEO-PPC polymer electrolyte showed improved efficiency and stability during charge–discharge cycles, at room temperature, suggesting the positive effect of the presence of carbonate groups in the polymer matrix. The promising results demonstrate that the as-prepared QSPE could represent a feasible and viable alternative to conventional liquid electrolytes and could accelerate the adoption of high energy density storage systems, like Li-metal batteries.

Interfacial self-healing polymer electrolytes for long-cycle solid-state lithium-sulfur batteries

Coupling high-capacity cathode and Li-anode with solid-state electrolyte has been demonstrated as an effective strategy for increasing the energy densities and safety of rechargeable batteries. However, the limited ion conductivity, the large interfacial resistance, and unconstrained Li-dendrite growth hinder the application of solid-state Li-metal batteries. Here, a poly(ether-urethane)-based solid-state polymer electrolyte with self-healing capability is designed to reduce the interfacial resistance and provides a high-performance solid-state Li-metal battery. With its dynamic covalent disulfide bonds and hydrogen bonds, the proposed solid-state polymer electrolyte exhibits excellent interfacial self-healing ability and maintains good interfacial contact. Full cells are assembled with the two integrated electrodes/electrolytes. As a result, the Li||Li symmetric cells exhibit stable long-term cycling for more than 6000 h, and the solid-state Li-S battery shows a prolonged cycling life of 700 cycles at 0.3 C. The use of ultrasound imaging technology shows that the interfacial contact of the integrated structure is much better than those of traditional laminated structure. This work provides an interesting interfacial dual-integrated strategy for designing high-performance solid-state Li-metal batteries.

Novel design of high elastic solid polymer electrolyte for stable lithium metal batteries

Li metal anodes have high specific capacity and low electrode potential, and have always been considered as one of the most promising anode materials. However, the growth of Li dendrites, unstable solid electrolyte interface layer (SEI), severe side reactions at the Li/electrolyte interface, and infinite volume expansion of the Li anode seriously hinder the practical application of solid-state Li metal batteries (LMBs). Herein, we report a polyurethane elastomer (TPU) material with high elasticity and interfacial stability as a solid polymer electrolyte (SPE) for LMBs. The synergistic effects of its designed soft chain forging (PEO) and hard chain segments (IPDI) can enhance Li ion conductivity, elastic modulus and flexibility of the SPE to settle the challenges of the Li metal anodes. Moreover, Li2S, as a solid-state electrolyte additive, is able to effectively inhibit the occurrence of side reactions at the interface between Li metal and SPE, promote the decomposition of N(CF3SO2)2− and in-situ generation of LiF with low Li+ diffusion barrier and excellent electronic insulation, achieving rapid Li ion transport and uniform Li deposition. As a result, stable cycle of up to 1400 h has been achieved for a Li||TPU-Li2S||Li battery at 0.1 mA/cm2 at 50 ℃, accompanied with a stable cycling performance of 350 h at a higher current density of 0.5 mA/cm2. Finally, the LiFePO4||TPU-Li2S||Li full battery exhibits an excellent cycling performance with a capacity retention rate of 80 % after 500 cycles at 1C. This simple and low-cost strategy provides novel design thoughts for practical application of high-performance SPEs in stable and long-life LMBs.

Interface engineering of Li6.75La3Zr1.75Ta0.25O12via in situ built LiI/ZnLix mixed buffer layer for solid-state lithium metal batteries.

Garnet-type solid-state Li metal batteries (SSLMBs) are viewed as hopeful next-generation batteries due to their high energy density and safety. However, the major obstacle to the development of garnet-type SSLMBs is the lithiophobicity of Li6.75La3Zr1.75Ta0.25O12 (LLZTO), resulting in a large interfacial impedance. Herein, a LiI/ZnLix mixed ion/electron conductive buffer layer is constructed at the interface by an in situ reaction of molten Li metal with ZnI2 film. This mixed buffer layer ensures close contact between the Li metal and garnet, significantly reducing interfacial impedance. As a result, the Li symmetrical cell with the LiI/ZnLix buffer layer shows an interface impedance of 10.3 Ω cm2, much lower than that of the cell with bare LLZTO (1173.4 Ω cm2). The critical current density (CCD) is up to 2.3 mA cm-2, and the symmetric cells present a long cycle life of 2000 h at 0.1 mA cm-2 and 800 h at 1.0 mA cm-2. In addition, the full cells assembled with the LiFePO4 cathode show a capacity of 143.9 mA h g-1 after 200 cycles at 0.5C with a low-capacity decay of 0.021% per cycle. This work reveals a simple, feasible, and practical interface modification strategy for solid-state Li metal batteries.

Co-sintering a cathode material and garnet electrolyte to develop a bulk-type solid-state Li metal battery with wide electrochemical windows

Co-sintering a cathode material and the Li7La3Zr2O12 (LLZ) electrolyte can assist in fabricating bulk-type all-solid-state batteries (ASSBs).

Dielectric Filler-Induced Hybrid Interphase Enabling Robust Solid-State Li Metal Batteries at High Areal Capacity.

The fillers in composite solid-state electrolyte are mainly responsible for the enhancement of the conduction of Li ions but barely regulate the formation of solid electrolyte interphase (SEI). Herein, a unique filler of dielectric NaNbO3 for the poly(vinylidene fluoride) (PVDF)-based polymer electrolyte, which is subjected to the exchange of Li+ and Na+ during cycling, is reported and the substituted Na+ is engaged in the construction of a fluorinated Li/Na hybrid SEI with high Young's modulus, facilitating the fast transport of Li+ at the interface at a high areal capacity and suppressing the Li dendrite growth. The dielectric NaNbO3 also induces the generation of high-dielectric β phase of PVDF to promote the dissociation of Li salt. The Li/Li symmetrical cell exhibits a long-term dendrite-free cycling over 600h at a high areal capacity of 3mA h cm-2. The LiNi0.8Mn0.1Co0.1O2/Li solid-state cells with NaNbO3 stably cycle 2200 times at 2 C and that paired with high-loading cathode (10mg cm-2) can stably cycle for 150 times and exhibit excellent performances at -20 °C. This work provides a novel design principle of fillers undertaking interfacial engineering in composite solid-state electrolytes for developing the safe and stable solid-state lithium metal battery.

Multimodal Characterization of Nucleation and Progression of Interfacial Degradation in All Solid-State Batteries

We face an immediate need for more energy-dense batteries that are stable over long-term cycling, to address the increased electrification of the transportation sector. All-solid state batteries (ASSBs) that combine a solid-state electrolyte with a Li metal anode offer the potential to achieve this objective by replacing intercalation anodes such as graphite with Li metal. However, interfacial degradation at the Li | solid electrolyte interface currently compromises the safety and cycling stability of ASSBs [1]. This interfacial degradation is usually a combination of instabilities of mechanical, chemical or electrochemical origin. This in turn compromises the structural and morphological stability of ASSBs over cycling, causing them to fail in fewer cycles than required for implementation as next-generation batteries in automobiles [2]. Thus, in order to improve their cycling stability, the understanding of the origin and nature of these interfacial instabilities needs to be multimodal, to understand the interplay between the different degradation mechanisms. Argyrodite (Li6PS5Cl) is a particularly attractive solid-state electrolyte (SSE) due to a high ionic conductivity (comparable to liquid electrolytes), as well as potential for batch processing [3]. However, its brittle nature and chemical composition makes it susceptible to cracking and deleterious side reactions, which hamper its stability. This work will focus on elucidating the effect of (1) current density and (2) processing conditions on the cycling stability of Li | LPSCl | Li ASSBs.We use 4-D XRD-CT (X-ray diffraction computed tomography) combined with phase contrast micro-computed tomography (μCT) to conduct the multimodal investigation of interfacial degradation, under pseudo operando conditions. The methodology is to obtain a 3-D XRDCT scan around the interface in a particular cycled condition, followed by a higher-resolution 3D μCT scan on the same region. This sequence is repeated after every stripping/plating cycle, starting from the pristine cell up to cell failure. These experiments are conducted at a synchrotron source, to enable the acquisition at high spatial resolution (~5 μm) over large volumes (~mm3), in a reasonable amount of time. A standard swagelok-style cell is used for repeatability of results and optimal geometry for conducting tomography. XRD-CT can furnish quantitative phase maps of all phases (argyrodite and reaction by-products), as well as the elastic strain in the sample. The μCT on the other hand gives information on the evolution of morphology around the interface with cycling (cracks/voids). Thus, by correlating the two datasets together over cycling, we are able to connect mechanical instabilities to the chemical/electrochemical instabilities.Here, we focus on varying two specific processing parameters for argyrodite: the sintering temperature and pressure, and studying their effect on nucleation and propagation of interfacial instabilities over repeated cycling. Through cycling, we track the evolution of cracks/voids, chemical by-products such as LiCl, Li3P and Li2S using XRD-CT and μCT. Finally, we track the filling of metallic Li into certain cracks in dendritic form, which leads to shorting and failure of the cell. We find that both of these parameters heavily influence the behavior of the interface, with cells failing between 4-20 cycles, and a marked difference in how the degradation initiates and propagates. Finally, for the processing condition that shows the best cycling behavior, we do a C-rate study, by increasing the current density for plating/stripping with each cycle up to failure. This discusses the utility of a parameter such as critical current density for a cell, where the local current densities are very heterogeneous and different from the global current reading while cycling.We envisage these results being used as inputs into modeling studies to optimize strategies for interfacial stabilization in ASSBs going forward.[1] Paul, P. P. et al. Interfaces in all solid state Li-metal batteries: a review on instabilities, stabilization strategies, and scalability. Energy Storage Materials 2022, 45, 969-1001.[2] Hao, S. et al. Tracking lithium penetration in solid electrolytes in 3D by in-situ synchrotron X-ray computed tomography. Nano Energy 2021, 82, 105744.[3] Chen, Y-T. et al., Investigating dry room compatibility of sulfide solid-state electrolytes for scalable manufacturing, Journal of Materials Chemistry A 2022, 10, 7155-7164.

An Overview on Polymer-Based Electrolytes with High Ionic Mobility for Safe Operation of Solid-State Batteries

Liquid electrolytes used in commercial Li-ion batteries are generally based on toxic volatile and flammable organic carbonate solvents, thus raising safety concerns in case of thermal runaway. The most striking solution at present is to switch on all solid-state designs exploiting polymer materials, films, ceramics, low-volatile, green additives, etc. The replacement of liquids component with low-flammable solids is expected to improve the safety level of the device intrinsically. Moreover, a solid-state configuration is expected to guarantee improved energy density systems. However, low ionic conductivity, low cation transport properties and issues in cell manufacturing processes must be overcome [1].Electrochemical performance in lab-scale devices can be readily improved using different RTILs or specific low-volatile additives. Here, an overview is offered of the recent developments in our labs on innovative polymer-based electrolytes allowing high ionic mobility, particularly attractive for safe, high-performing, solid-state Li-metal batteries, and obtained by different techniques, including solvent-free UV-induced photopolymerization. Cyclic voltammetry and galvanostatic charge/discharge cycling coupled with electrochemical impedance spectroscopy exploiting different electrode materials (e.g., LFP, Li-rich NMC, LNMO, Si/C) demonstrate specific capacities approaching theoretical values even at high C-rates and stable operation for hundreds of cycles at ambient temperature [2,3]. Direct polymerization procedures on top of the electrode films are also used to obtain an intimate electrode/electrolyte interface and full active material utilization in both half and full-cell architectures. In addition, results of composite hybrid polymer electrolytes [4] and new single-ion conducting polymers [5] are shown, specifically developed to attain improved ion transport and high oxidation stability for safe operation with high voltage electrodes even at ambient conditions.

Polyoxometalate Li3 PW12 O40 and Li3 PMo12 O40 Electrolytes for High-energy All-solid-state Lithium Batteries.

Solid-state lithium (Li) batteries promise both high energy density and safety while existing solid-state electrolytes (SSEs) fail to satisfy the rigorous requirements of battery operations. Herein, novel polyoxometalate SSEs, Li3 PW12 O40 and Li3 PMo12 O40 , are synthesized, which exhibit excellent interfacial compatibility with electrodes and chemical stability, overcoming the limitations of conventional SSEs. A high ionic conductivity of 0.89 mS cm-1 and a low activation energy of 0.23 eV are obtained due to the optimized three-dimensional Li+ migration network of Li3 PW12 O40 . Li3 PW12 O40 exhibits a wide window of electrochemical stability that can both accommodate the Li anode and high-voltage cathodes. As a result, all-solid-state Li metal batteries fabricated with Li/Li3 PW12 O40 /LiNi0.5 Co0.2 Mn0.3 O2 display a stable cycling up to 100 cycles with a cutoff voltage of 4.35 V and an areal capacity of more than 4 mAh cm-2 , as well as a cost-competitive SSEs price of $5.68 kg-1 . Moreover, Li3 PMo12 O40 homologous to Li3 PW12 O40 was obtained via isomorphous substitution, which formed a low-resistance interface with Li3 PW12 O40 . Applications of Li3 PW12 O40 and Li3 PMo12 O40 in Li-air batteries further demonstrate that long cycle life (650 cycles) can be achieved. This strategy provides a facile, low-cost strategy to construct efficient and scalable solid polyoxometalate electrolytes for high-energy solid-state Li metal batteries.

Surface modification strategies for an improved interfacial compatibility between LLZO and a polymer substrate for applications in high-performance solid-state Li-metal batteries

The interfacial compatibility between inorganic powder and polymeric matrix is one of the most important key factors for the applications of polymer ceramic composite electrolytes (PCCEs). In the present study, a surface modification strategy has been proposed by using three different terminating groups of silane coupling agents in the modification of the interfacial compatibility between LLZO and PEO in PEO/LLZO composite electrolyte. Experiments and density functional theory (DFT) calculations have been performed in studying the effect of different silane coupling agents on interfacial properties. Especially, the interface compatibility is found to be improved when using amino-terminated silane coupling agent KH550, which is due to hydrogen bond interactions between amino groups and PEO. In addition, the mechanical strength and conductivity are significantly increased by increasing the interaction energy and by decreasing the crystallinity, and the values of 1.39 MPa and 0.22 mS cm−1 at 30 °C are then successfully achieved. As a result, the solid-state LiFePO4|PCCE|Li battery demonstrates a high discharge specific capacity of 157 mAh g−1 at 60 °C and 1C. And it has a cycle capacity decay rate of only 0.034 % for 380 cycles. These results pave the way for future developments of high-performance PCCEs.