Solid Electrolyte Research Articles

Tailoring Practical Solid Electrolyte Composites Containing Ferroelectric Ceramic Nanofibers and All-Trans Block Copolymers for All-Solid-State Lithium Metal Batteries.

Ion transport efficiency, the key to determining the cycling stability and rate capability of all-solid-state lithium metal batteries (ASSLMBs), is constrained by ionic conductivity and Li+-migration ability across the multicomponent phases and interfaces in ASSLMBs. Here, we report a robust strategy for the large-scale fabrication of a practical solid electrolyte composite with high-throughput linear Li+-transport channels by compositing an all-trans block copolymer PVDF-b-PTFE matrix with ferroelectric BaTiO3-TiO2 nanofiber films. The electrolyte shows a sustainable electromechanical-coupled deformability that enables the rapid dissociation of anions with Li+ to create more movable Li+ ions and spontaneously transform the battery internal strain into Li+-ion migration kinetic energy. The ceramic framework homogenizes the interfacial potential with electrodes, endowing the electrolyte with a high conductivity of 0.782 mS·cm-1 and stable ion transport ability in ASSLMBs at room temperature. The batteries of LiFePO4/Li can stably cycle 1000 times at 0.5 C with a high capacity retention of 96.1%, and Ah-grade pouch or high-voltage Li(Ni0.8Mn0.1Co0.1)O2/Li batteries also exhibit excellent rate capability and cycling performance.

Thickness Variation of Conductive Polymer Coatings on Si Anodes for the Improved Cycling Stability in Full Pouch Cells.

Si-dominant anodes for Li-ion batteries provide very high gravimetric and volumetric capacity but suffer from low cycling stability due to an unstable solid electrolyte interphase (SEI). In this work, we improved the cycling performance of Si/NCM pouch cells by coating the Si anodes with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) prior to cell assembly via an electropolymerization process. The thicknesses of the PEDOT coatings could be adjusted by a facile process parameter variation. Glow-discharge optical emission spectroscopy was used to determine the coating thicknesses on the electrodes prior to the cell assembly. During electrochemical testing, improvements were observed closely linked to the PEDOT coating thickness. Specifically, thinner PEDOT coatings exhibited a higher capacity retention and lower internal resistance in the corresponding pouch cells. For the thinnest coatings, the cell lifetime was 18% higher compared to that of uncoated Si anodes. Postmortem analyses via X-ray photoelectron spectroscopy and cross-sectional scanning electron microscopy revealed a better-maintained microstructure and a chemically different SEI for the PEDOT-coated anodes.

Enhancing ionic conductivity and controlling lithium dendrite growth via ferroelectric ceramic Bi4Ti3O12

BackgroundSolid polymer electrolytes (SPEs) have gained numerous research interest in the field of lithium metal batteries. Solid polymer electrolytes have improved safety compared to liquid electrolytes. Despite this, their low ionic conductivity remains a major barrier to practical applications. To overcome the challenge of low ionic conductivity in SPEs, our study introduces a novel approach that integrates ferroelectric ceramics with polymer solid electrolytes. MethodsWe used a one-step molten salt method to synthesize Bi4Ti3O12 (BIT), combined with a poly (vinylidene difluoride) matrix to form the composite solid-state electrolyte. Through various electrochemical characterizations and COMSOL Multiphysics simulations, we discovered that the ferroelectric properties of BIT significantly increase the dissociation of lithium salts, leading to a greater concentration of mobile lithium ions and more efficient ion transport. Significant findingsThis electrolyte showed a remarkable improvement in lithium-ion conductivity, reaching a value of 8.5 × 10−4 S cm−1 at room temperature. Batteries made with these composite electrolytes demonstrate superior cycling stability, the capacity retention rates for LFP/SPEs/Li cells remain high, reaching 95 % even after 1,000 cycles at room temperature (25 °C). These findings highlight the promising applications of ferroelectric ceramics in solid-state batteries.

Building Flame-Retardant Polymer Electrolytes via Microcapsule Technology for Stable Lithium Batteries.

Flame retardants could improve the safety properties of lithium batteries (LBs) with the sacrifice of electrochemical performance due to parasitic reactions. To concur with this, we designed thermal-response clothes for hexachlorophosphazene (HCP) additives by the microcapsule technique with urea-formaldehyde (UF) resin as the shell. HCP@UF combines with polyacrylonitrile (PAN) by hydrogen bonds successfully to form PAN-HCP@UF as the flame-retardant solid polymer electrolyte. The hydrogen bonds ensure excellent mechanical properties of the polymer electrolyte. The multiscale free radical-annihilating agent HCP effectively eliminates hydrogen free radicals of electrolytes under high temperature, showing excellent flame retardation. During the operation of the battery, functional groups on the UF resin act as active sites to promote the migration of lithium ions, while the internal HCP is protected from electrochemical reaction. With 25% HCP@UF addition, the limiting oxygen index of the PAN-HCP@UF increases to 28% and the Li+ transfer number up to 0.80. By UF protection, the initial capacity retention rate of the Li||LFP battery that assembles with PAN-HCP@UF is 88.8% after 500 cycles at 0.5 C. Thus, the microcapsule-encapsulated approach is deemed to provide an innovative strategy to prepare high-safety solid-state LB with a stable long cycle life.

Diversifying Ion-Transport Pathways of Composite Solid Electrolytes for High-Performance Solid-State Lithium-Metal Batteries.

The application of composite solid electrolytes (CSEs) in solid-state lithium-metal batteries is limited by the unsatisfactory ionic conductivity underpinned by the low concentration of free lithium ions. Herein, we propose an interface design strategy where an amine silane linker is employed as a coupling agent to graft the Li7La3Zr2O12 (LLZO) ceramic nanofibers to the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer matrix to enhance their interaction. The hydrogen bonding between amino-functionalized LLZO (NH2@LLZO) and PVDF-HFP not only effectively induces a uniform incorporation of high-content nanofibers (50 wt %) into the polymer matrix but also furnishes sufficient continuous surfaces to weaken the complexation between PVDF-HFP and Li-ion carriers. Additionally, introduction of the hydrogen bond and Lewis acid-base interplay strengthens the interfacial interactions between NH2@LLZO and lithium salts that release more free lithium ions for efficient interfacial transport. The impact of the linker's structure on the dissociation capacity of lithium salts is systematically studied from the steric effect perspective, which affords insights into interface design. Conclusively, the composite solid electrolyte achieves a high ionic conductivity (5.8 × 10-4 S cm-1) by synergy of multiple transport channels at ceramic, polymer, and their interface, which effectively regulates the lithium deposition behavior in symmetric cells. The excellent compatibility of the electrolyte with both LiFePO4 and LiNi0.8Co0.1Mn0.1O2 cathodes also results in a long lifetime and a high rate capability for full cells.

Correction to: Room temperature manufacture of dense NaSICON solid electrolyte films for all-solid-state-sodium batteries

Correction to: Room temperature manufacture of dense NaSICON solid electrolyte films for all-solid-state-sodium batteries

Structure and particle surface analysis of Li2S–P2S5–LiI-type solid electrolytes synthesized by liquid-phase shaking

AbstractLi2S–P2S5–LiI-type solid electrolytes, such as Li4PS4I, Li7P2S8I, and Li10P3S12I, are promising candidates for anode layers in all-solid-state batteries because of their high ionic conductivity and stability toward Li anodes. However, few studies have been conducted on their detailed local structure and particle surface state. In this study, Li7P2S8I (Li2S: P2S5:LiI = 3:1:1) solid electrolytes as the chemical composition were synthesized by mechanical milling and liquid-phase shaking, and their local structures were analyzed by transmission electron microscopy. The particle surface states were analyzed by X-ray photoelectron spectroscopy, high-energy X-ray scattering measurements, and neutron total scattering experiments. The results showed that Li7P2S8I solid electrolytes are composed of nanocrystals, such as Li4PS4I, LiI, Li10P3S12I and an amorphous area as the main region, indicating that the crystalline components alone do not form ionic conductive pathways, with both the amorphous and crystalline regions contributing to the high ionic conductivity. Moreover, the ionic conductivity of the crystalline/amorphous interface of the glass-ceramic was higher than that of the Li2S–P2S5–LiI glass. Finally, an organic-solvent-derived stable surface layer, which was detected in the liquid-phase shaking sample, served as one of the factors that contributed to its high stability (which surpassed that of the mechanically milled sample) toward lithium anodes. We expect these findings to enable the effective harnessing of particle surface states to develop enhanced sulfide solid electrolytes.

Inhibiting Residual Solvent induced side reactions in Vinylidene Fluoride-based Polymer Electrolytes enables ultra-stable Solid-State Lithium Metal Batteries.

Residual solvents in vinylidene fluoride (VDF)-based solid polymer electrolytes (SPEs) have been recognized as responsible for their high ionic conductivity. However, side reactions by the residual solvents with the lithium (Li) metal induce poor stability, which has been long neglected. This study proposes a strategy to achieve a delicate equilibrium between ion conduction and electrode stability for VDF-based SPEs. Specifically, 2,2,2-Trifluoro-N, N-dimethylacetamide (FDMA) is developed as the non-side reaction solvent for poly(vinylidene fluoride-co-hexafluoropropylene) (PVHF)-based SPEs, achieving both high ionic conductivity and significantly improved electrochemical stability. The developed FDMA solvent fosters the formation of a stable solid electrolyte interphase (SEI) through interface reactions with Li metal, effectively mitigating side reactions and dendrite growth on the Li metal electrode. Consequently, the Li||Li symmetric cells and Li||LiFePO4 cells demonstrate excellent cycling performance, even under limited Li (20μm thick) supply and high-loading cathodes (>10mg cm-2, capacity >1 mAh cm-2) conditions. The stable Li||LiCoO2 cells operation with a cutoff voltage of 4.48V indicates the high-voltage stability of the developed SPE. This study offers valuable insights into developing advanced VDF-based SPEs for enhanced lithium metal battery performance and longevity. This article is protected by copyright. All rights reserved.

Formulating Interfacial Impedances for Designing High-Energy and High-Power All-Solid-State Battery Cathodes.

All-solid-state batteries (ASSBs) are safe, high-energy-storage systems. However, despite the progress achieved in the development of high-ionic-conductivity solid electrolytes (SEs), the power performance of ASSBs remains low because of the high interfacial impedances in composite cathodes. Therefore, understanding the interfacial factors is crucial for obtaining high power ASSBs. This study provides a quantitative analysis of the influence of these factors using impedance spectroscopy measurements, which enables the elucidation of the interfacial impedance values of two key parameters, the grain-boundary resistance (ri,gb) and charge-transfer resistance (ri/e). Systematic investigation revealed an unexpected increase in the cathodic resistance with the decrease in the size of the cathode active material (CAM) particles, indicating that even high-reaction-surface-area CAMs yield low ri/e but high ri,gb values owing to their high porosity, resulting in a trade-off relationship. In contrast, this phenomenon is unlikely to occur in liquid-electrolyte-based batteries. Notably, we discuss how composite cathode design impacts performances of stable, high-power, and high-energy ASSBs.

Amorphous lithiophilic cobalt‐boride@rGO interlayer for dendrite‐free and highly stable lithium metal batteries

AbstractLithium metal batteries (LMBs) are recognized to be crucial for secondary battery technology targeting electric vehicles and portable electronic devices. However, the undesirable growth of lithium dendrites would result in reduced capacity, short‐circuit, and overheating, seriously hindering the practical applications of LMBs. To address this issue, a neoteric lithiophilic interlayer on a commercial polypropylene separator is presented for the first time, which is constructed by amorphous CoB nanoparticles decorated reduced graphene oxide nanosheets (CoB@rGO). Density Functional Theory calculations and experimental analysis reveal remarkable lithiophilicity features for CoB@rGO and provide multiple Li deposition sites and improved electrolyte wettability, which facilitates the formation of durable solid electrolyte interphase (SEI), reduces side reactions, and improves Li+ flux regulation for long‐term cycling stability in LMBs. Taking advantage of these merits, the symmetric Li//Li cell with CoB@rGO/PP separator exhibits stable cycling for up to 1600 h at 1 mA cm−2 with 1 mAh cm−2. Employed with CoB@rGO separator, the Li//LiFePO4 full cell with a high LiFePO4 loading of 11 mg cm−2 delivers a high initial specific capacity of 115.3 mAh g−1 and a low decay rate of 0.08% per cycle after 200 cycles even at a high rate of 2C.

Self‐Supporting Solid Electrolyte Based on Supramolecular Interaction for Stable Li Metal Batteries

Li metal batteries based on solid polymer electrolytes offer the benefits of high energy density and safety, as well as extended cycling life, making them an excellent candidate for the next‐generation battery system. However, current solid polymer electrolytes still suffer from low ion conductivity and Li+ transfer number, which seriously restricts its practical application. Herein, a self‐supporting composite solid polymer electrolyte was prepared, where phenolic resin rich in hydroxyl groups (BR) and polyethylene oxide (PEO) are mixed evenly and poured onto a cellulose membrane in one step. In such an electrolyte, PEO and BR combine to form intermolecular hydrogen bonds, lowering the crystallinity of PEO and increasing the Li+ transfer number. Lastly, the obtained solid electrolytes exhibited a high ion conductivity (1.1×10‐4 S cm‐1) and Li+ transfer number (0.53), as well as improved electrochemical window. Consequently, Li || Li symmetrical cells can run stably for more than 700 h at 0.1 mA cm‐2/0.25 mAh cm‐2. And full cells with LiFePO4 cathode can also demonstrate high discharge capacity of 152.12 mAh g‐1 and rate performance. We believe that such a design based on supramolecular interaction offer a new avenue to advanced solid polymer electrolytes.

Amphoteric Supramolecular Nanofiber Separator for High‐Performance Sodium‐Ion Batteries

The separator is an essential component of sodium‐ion batteries (SIBs) to determine their electrochemical performances. However, the separator with high mechanical strength, good electrolyte wettability and excellent electrochemical performance remains an open challenge. Herein, a new separator consisting of amphoteric nanofibers with abundant functional groups was fabricated through supramolecular assembly of natural polymers for SIB. The uniform nanoporous structure, remarkable mechanical properties and abundant functional groups (e.g. −COOH, −NH2 and −OH) endow the separator with lower dissolution activation energy and higher ion migration numbers. These metrics enable the separator to lower the barrier for desolvation of Na+, accelerate the migration of Na+, and generate more stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). The battery assembled with the amphoteric nanofiber separator shows higher specific capacity and better stability than that assembled with glass fiber (GF) separator.

On the formation and properties of amorphous and crystalline Li3-yBay/2OCl electrolytes

All-solid-state batteries (ASSBs) have potential to provide higher specific energy, higher power, and longer cycle life than Li-ion batteries (LIBs) for continuously increasing demands of high-performance rechargeable batteries with intrinsic safety. However, one of the barriers for successful design and fabrication of ASSBs is the lack of solid-state electrolytes (SSEs) that can meet multi-functional requirements for ASSBs. To address this issue, the present study investigates hydrothermal synthesis of amorphous and crystalline Ba-doped Li3OCl solid electrolytes and develops the understanding of the relationships between the synthesis conditions and electrochemical properties of the products. It is shown that the formation of an amorphous/crystalline Ba-doped Li3OCl mixture with little hydroxide impurities depends strongly on the hydrothermal reaction temperature, drying temperature, Ba concentration, and rate of removing OH− and H+ ions as steam from water solvated Ba-doped Li3OCl. The key to generate amorphous Li3OCl-based electrolytes with high ionic conductivities (7.65 × 10−3 S/cm) at room temperature is to create non-equilibrium synthesis conditions such as the one identified in this study. The understanding developed in this study will offer critical guidelines for synthesizing amorphous and crystalline Li3OCl-based electrolytes with superior electrochemical properties for ASSBs reliably and reproducibly in the near future.

Antioxidant Interfaces Enabled by Self‐Deoxidizing and Self‐Dehydrogenating Redox Couple for Reversible Zinc Metal Batteries

AbstractParasitic electrolyte reactions and dendrite growth make Zn metal anodes with high Zn utilization rates (ZURs) more inaccessible, holding back the advance of aqueous zinc metal batteries (AZMBs). Here, sodium isoascorbate (SIA) is introduced to aqueous electrolytes as a self‐deoxidizing and self‐dehydrogenating additive. Coexisting C6H7O6−/C6H5O6− couple spontaneously captures dissolved oxygen and eliminates generated hydrogen by acting as a redox buffer, which leads to the creation of antioxidant Interfaces due to an in situ formed ZnCO3‐dominated solid electrolyte interphase (SEI). This SEI enables the (100) faceted electrode with dendrite‐free and non‐corrosive Zn plating/stripping, thus yielding a Coulombic efficiency of 99.7% up to 1100 h at 5 mAh cm−2, as well as a stable cycle sustaining for over 335 h under a high ZUR of 85.5%. Full‐cell properties are demonstrated by matching a poly(3,4‐ethylenedioxythiophene) intercalated vanadium oxide (PEDOT‐V2O5) cathode, which harvests a high capacity of 302 mAh g−1 (at 0.01 A g−1) and holds 94.2% capacity retention over 600 cycles (at 1 A g−1) under practical conditions (N/P = 4.2 and E/C = 7.6 µL mg−1). These findings provide a new solution for electrolyte design for industrializing AZMBs.

A Physics-based Model Assisted by Machine-Learning for Sodium-ion Batteries with both Liquid and Solid Electrolytes

Abstract In the absence of experimental data of a fully developed hierarchical 3D sodium solid state batteries, we developed an improved continuum model by relying on Machine Learning-assisted parameter fitting to uncover the intrinsic material properties that can be transferred into different battery models. The electrochemical system simulated has sodium metal P2-type Na2/3[Ni1/3Fe1/12Mn7/12]O2 (NNFMO) as the cathode, paired with two types of electrolytes have been modeled viz, the organic liquid electrolyte and a solid polymer electrolyte. We implemented a 1D continuum model in COMSOL to suit both liquid and solid electrolytes, then used a Gaussian Process Regressor to fit and evaluate the electrochemical parameters in both battery systems. To enhance the generalizability of our model, the liquid cell and solid cell models share the same OCV input for the cathode materials. The resulting parameters are well aligned with their physical meaning and literature values. The continuum model is then used to understand the effect of increasing the thickness of the cathode and current density by analysing the cathode utilization, and the overpotentials arising from transport and charge transfer. This 1D model and the parameter set are ready to be used in a 3D battery architecture design.

Reviving Cost-Effective Organic Cathodes in Halide-Based All-Solid-State Lithium Batteries.

The evolution of inorganic solid electrolytes has revolutionized the field of sustainable organic cathode materials, particularly addressing the dissolution problems in traditional liquid electrolytes. However, current sulfide-based all-solid-state lithium-organic batteries still face challenges such as high working temperatures, high costs, and low voltage. Here, we design an all-solid-state lithium battery based on a cost-effective organic cathode material phenanthrenequinone (PQ) and a halide solid electrolyte Li2ZrCl6. Thanks to the good compatibility between PQ and Li2ZrCl6, the PQ cathode achieved a high specific capacity of 248 mAh g-1 (96% of the theoretical capacity), a high average discharge voltage of 2.74 V (vs. Li+/Li), and a good capacity retention of 95% after 100 cycles at room temperature (25 °C). Furthermore, the interaction between the high-voltage carbonyl PQ cathode and both sulfide and halide solid electrolytes, as well as the redox mechanism of PQ cathode in all-solid-state batteries, were carefully studied by a variety of advanced characterizations. We believe such a design and the corresponding investigations for the underlying chemistry give insights into the further development of practical all-solid-state lithium-organic batteries.

Porous Organic Framework Materials (MOF, COF, and HOF) as the Multifunctional Separator for Rechargeable Lithium Metal Batteries.

The separator is an important component in batteries, with the primary function of separating the positive and negative electrodes and allowing the free passage of ions. Porous organic framework materials have a stable connection structure, large specific surface area, and ordered pores, which are natural places to store electrolytes. And these materials with specific functions can be designed according to the needs of researchers. The performance of porous organic framework-based separators used in rechargeable lithium metal batteries is much better than that of polyethylene/propylene separators. In this paper, thethree most classic organic framework materials (MOF, COF, and HOF) are analyzed and summarized. The applications of MOF, COF, and HOF separators in lithium-sulfur batteries, lithium metal anode, and solid electrolytes are reviewed. Meanwhile, the research progress of these three materials in different fields is discussed based on time. Finally, in the conclusion, the problems encountered by MOF, COF, and HOF in different fields as well as their future research priorities are presented. This review will provide theoretical guidance for the design of porous framework materials with specific functions and further stimulate researchers to conduct research on porous framework materials.

Reviving Cost‐Effective Organic Cathodes in Halide‐Based All‐Solid‐State Lithium Batteries

The evolution of inorganic solid electrolytes has revolutionized the field of sustainable organic cathode materials, particularly addressing the dissolution problems in traditional liquid electrolytes. However, current sulfide‐based all‐solid‐state lithium‐organic batteries still face challenges such as high working temperatures, high costs, and low voltage. Here, we design an all‐solid‐state lithium battery based on a cost‐effective organic cathode material phenanthrenequinone (PQ) and a halide solid electrolyte Li2ZrCl6. Thanks to the good compatibility between PQ and Li2ZrCl6, the PQ cathode achieved a high specific capacity of 248 mAh g‐1 (96% of the theoretical capacity), a high average discharge voltage of 2.74 V (vs. Li+/Li), and a good capacity retention of 95% after 100 cycles at room temperature (25 °C). Furthermore, the interaction between the high‐voltage carbonyl PQ cathode and both sulfide and halide solid electrolytes, as well as the redox mechanism of PQ cathode in all‐solid‐state batteries, were carefully studied by a variety of advanced characterizations. We believe such a design and the corresponding investigations for the underlying chemistry give insights into the further development of practical all‐solid‐state lithium‐organic batteries.

Novel binary regulated silicon-carbon materials as high-performance anodes for lithium-ion batteries.

The massive volume dilation, unsteady solid electrolyte interphase, and weak conductivity about Si have failed to bring it to practical applications, although its potential capacity is up to 4200 mAh g-1. For solving these problems, novel binary regulated silicon-carbon materials (Si/BPC) were done by a sol-gel procedure combined with single carbonization. Analytical techniques were systematically utilized to examine the effects of element doping at several gradients on morphology, structure and electrochemical properties of composites, thus the optimal content was identified. Si/BPC preserves a discharge specific capacity of 1021.6 mAh g-1with a coulomb efficiency of 99.27% after 180 cycles at 1000 mA g-1, within the upgrade than single-doped and undoped. In rate test, it has a specific capacity of 1003.2 mAh g-1at a high current density of 5000 mA g-1, quickly back towards 2838.6 mAh g-1at 200 mA g-1. The inclusion of B and P elements is linked to the electrochemical characteristics. In the co-doped carbon layers, the synergistic impact of doping B and P accelerates the diffusion kinetics of lithium ions, boosts diffusion rate of Li+, offers low electrochemical impedance (45.75 Ω). This brings more defects to provide transport carriers and induces a substantial amount of electrochemically active sites, which fosters the storage of Li+, thus making silicon material electrochemically more active and potential.

Cation-polymerized artificial SEI layer modified Li metal applied in soft-matter polymer electrolyte.

Li metal batteries with polymer electrolyte are of great interest for next-generation batteries for high safety and high energy density. However, uneven deposition on the lithium metal surface can greatly affect battery life. Therefore, surface modification on the Li metal become necessary to achieve good performance. Herein, an artificial solid electrolyte interface (SEI) modified lithium metal anode is prepared using cation-polymerization process, as triggered by PF5 generated from CsPF6. As a result, the polarization voltage of Li||Li symmetric battery assembled with artificial SEI-modified Li metal anode was stable with a small over-potential of 25 mV after 3000 h at current density of 1.5 mA cm-2. Electrochemical performance of Li||NCM 622 (LiNi0.6Co0.2Mn0.2O2) full cell with soft-matter polymer electrolyte is significantly improved than bare Li-metal, the capacity retention is 75% after 120 cycles with N/P=3:1 at a cut-off voltage of 4.3 V. Our work has shed lights on the commercialization of Li metal battery with polymer electrolyte.