High Lithium Ion Conductivity Research Articles

Borophosphate glass based electrolyte composite for high lithium ionic conductivity

The application requirements of solid-state lithium (Li) metal batteries are satisfied by the ionic conductivity of composite solid-state electrolytes, attributed to their minimal interfacial resistance. Herein, composite solid electrolytes were obtained by mixing a crystalline Li0.5La0.5TiO3 (LLTO) perovskite with different amount of 47Li2O-30B2O3-23P2O5 (LBP) glass phase. The results show that the crystal phase of the composite samples exhibit a tetragonal perovskite structure with a P4/mmm space group. Frequency dependent AC conductivity shows that composite containing 1 % LBP glass avoids the phenomenon of charge carrier blocking at low frequency and low temperature at the same time. The room temperature maximum total ionic conductivity was obtained for sample with 0.5 % LBP glass presenting a conductivity that is almost three times higher than that of pure LLTO. The factors influencing ionic conductivity are not only grain morphology and size, and activation energy, but also lithium content, and entropic effects contribute to the facility or difficulty with which Li+ can migrate into the LLTO solid electrolyte.

Dual optimization of LiFePO4 cathode performance using manganese substitution and a hybrid lithiated Nafion-modified PEDOT:PSS coating layer for lithium-ion batteries

The energy storage market necessitates an increase in the specific capacity of battery materials, particularly cathodes, to meet growing demands. Manganese (Mn) substitution of lithium iron phosphate (LFP) cathodes presents a promising avenue, offering high specific capacity and operability at elevated voltages. However, during cycling, the dissolution of Fe/Mn ions into the electrolyte leads to capacity fading. In this study, we enhance the specific capacity of LFP by Mn substitution in the iron position at various ratios (0.1, 0.2, 0.3, and 0.4). LiFe0.6Mn0.4PO4 exhibits the highest capacity of 159.1 mAh g-1 at 0.1C with an initial Coulombic efficiency of 97.9 %. This improvement stems from an enhanced lithium diffusion coefficient, increasing from 1.86 × 10–14 cm2 s-1 for pristine LFP to 2.46 × 10–12 cm2 s-1 for LiFe0.6Mn0.4PO4. However, LiFe0.6Mn0.4PO4 demonstrates the poorest capacity retention among the substituted samples, reaching 78.4 % over 100 cycles due to severe Fe/Mn ion dissolution. To address this issue, we coat Mn-substituted LFP with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and lithiated Nafion (LN) polymer, which offer high electronic and lithium-ion conductivity, respectively. This coating layer enhances the capacity retention of LiFe0.6Mn0.4PO4 to 90.1 % at 0.2C after 100 cycles, effectively mitigating active material loss during charge-discharge processes. This study demonstrates that PEDOT:PSS-LN can improve the electronic and ionic conductivity of cathode materials and maintain high capacity retention during cycling.

Homogeneous Fluorine Doping toward Highly Conductive and Stable Li10GeP2S12 Solid Electrolyte for All-Solid-State Lithium Batteries.

The unique structure and exceptionally high lithium ion conductivity over 10mScm-1 of Li10GeP2S12 have gained extensive attention in all-solid-state lithium batteries. However, its poor resistivity to moisture and chemical/electrochemical incompatibility with lithium metal severely impede its practical application. Herein, a fluorine functionalized Li10GeP2S12 is synthesized by stannous fluoride doping and employed as a monolayer solid electrolyte to realize stable all-solid-state lithium batteries. The atomic-scale mechanism underlying the impact of fluorine doping on both moisture and electrochemical stability of Li10GeP2S12 is revealed by density functional theory calculations. Fluorine surface doping significantly reduces surface hydrophilicity by electronic regulation, thereby retarding the hydrolysis reaction of Li10GeP2S12. After exposed to a relative humidity of 35%-40% for 20min, the ionic conductivity of Li9.98Ge0.99Sn0.01P2S11.98F0.02 maintains as high as 2.21mScm-1, nearly one order of magnitude higher than that of Li10GeP2S12 with 0.31mScm-1. Meanwhile, bulk doping of highly electronegative fluorine promotes the formation of lithium vacancies in the Li10GeP2S12 system, thus allowing stable lithium plating/stripping in Li | Li symmetric batteries, boosting a critical current density reaching 2.1mAcm-2. The LiCoO2 | lithium all-solid-state batteries display improved cycling stability and rate capability, showing 80.1% retention after 600 cycles at 1C.

Rational design of continuous and short-range lithium ion pathways based on polydopamine-anchored metal-organic frameworks for all-solid-state electrolytes

The immerging three dimensional (3D) metal-organic framework (MOF)-reinforced composite solid-state electrolytes have attracted great interest because of the enhanced ionic conductivity and mechanical properties. However, the defective spatial arrangement of MOFs restricted by fabrication methodology leads to insufficient lithium ion transport in electrolytes. Herein, a 3D interconnected MOF framework tailored for all-solid-state electrolytes is rationally designed by a universal polydopamine (PDA)-engineered “double-sided tape” strategy. The PDA serves as a double-sided tape, firmly adhering on the special single-layer Nylon grid as well as offering uniform nucleation sites to anchor the metal nodes to ensure continuous growth of well-ordered MOFs. Benefiting from the Lewis acid feature of MOFs and its cage effect toward TFSI−, a fast and homogeneous lithium ion transport can be achieved through the internal channels within neighboring MOFs and the continuous MOFs/polymer interfaces both along the short-range circumferential boundary of Nylon fiber. The resultant composite electrolytes exhibit high lithium ion conductivity and prominent mechanical properties, rendering excellent cyclic stability whether used in coin or pouch cells. This work demonstrates a widely applicable “double-sided tape” strategy for controllable spatial arrangement of MOF nanoparticles on optional substrates, which provides a scalable approach to rationally construct desired lithium ion pathways within composite electrolytes.

Separator engineering: Assisting lithium salt dissociation and constructing LiF-rich solid electrolyte interphases for high-rate lithium metal batteries

Challenges associated with lithium dendrite growth and the formation of dead lithium significantly limit the achievable energy density of lithium metal batteries (LMBs), particularly under high operating current densities. Our innovative design employs a state-of-the-art 2500 separator featuring a meticulously engineered cellulose acetate (CA) coating (CA@2500) to suppress dendrite nucleation and propagation. The CO functional groups in CA enhances charge transfer kinetics and triggering the decomposition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which leads to the formation of a more robust solid electrolyte interphase (SEI) composed primarily of LiF. Moreover, the introduction of polar functional groups in the CA enhances the separator’s hydrophilic properties, facilitating the uniform Li+ flux and creating a conductive pathway for efficient lithium migration. As a result, the CA@2500 separator exhibits a high lithium-ion transfer number (0.88) and conductivity. The lithium symmetric cell assembles with the CA@2500 separator displays a stable cycling performance over 5500 h at a current density and capacity of 10 mA cm−2 and 10 mAh cm−2, respectively. Additionally, LPF battery with CA@2500 separator shows an excellent capacity retention at 0.2 C with an average decay of 0.055 % per cycle. Moreover, a high capacity of 105 mAh g−1 is maintained after 500 cycles at 5 C with an average decay of only 0.027 % per cycle. This work achieved high stability of LMBs through simplified engineering.

Solid-State Lithium-Ion Superionic Electrolytes with Reduced Moisture Sensitivity

The remarkable safety and high energy density of solid-state batteries (SSBs) created significant advantages in the development of next-generation energy storage. The properties of these batteries are highly dependent on the characteristics of solid-state electrolytes (SSEs), making them a crucial material in the development of such batteries. Following diverse principles of material design, lithium halide SSEs, particularly Li3InCl6, open new opportunities in the development of SSBs due to their unique properties including broad electrochemical stability window, high lithium-ion conductivity, and excellent deformability. Through a mechano-thermal synthesis approach, Li3InCl6 demonstrates substantial ionic conductivity at room temperature. We studied the temperature-dependent behavior of Li3InCl6 by using in-situ/operando techniques such as XRD and XPS. However, its susceptibility to moisture poses a significant challenge for practical implementation in SSBs. To overcome this limitation, this research is focused on a novel solution: hafnium doping of Li3InCl6. Integrating hafnium into the Li3InCl6 structure results in a substantial improvement in electrochemical performance. The Li2.6In0.6Hf0.4Cl6 solid-state electrolyte not only showcases heightened ionic conductivity but also demonstrates improved resistance to moisture. The achieved ionic conductivity reaches approximately 1 mS cm-1, marking a significant 3.5-fold increase compared to Li3InCl6. Noteworthy is the fact that, after 5 hours of exposure to air with 15% humidity, the observed reduction in ionic conductivity for Li2.6In0.6Hf0.4Cl6 is 37%, a notably lower decrease compared to the 57% reduction seen in Li3InCl6.The efficacy of hafnium doping provides a crucial advancement in the field of solid-state electrolytes, promising a transformative impact on next-generation energy storage systems.

Ion Conduction Mechanism and Interfacial Stability in Fluorine Containing Lithium Argyrodite Electrolytes for Solid-State Lithium-Sulfur Batteries

Solid-state lithium-sulfur batteries (SSLSBs) hold great potential as a safe and energy-dense storage technology for wide variety of applications. Among solid-state electrolytes, halogen-doped lithium argyrodites have become an attractive category. This is attributed to their notable features, including high lithium-ion conductivity (~10-3 S/cm), favorable elastic stiffness (~ 30 GPa), and low flammability, making them promising candidates for enhancing the performance of SSLSBs.Despite their potential, SSLSBs based on sulfide faces challenges due to a limited atomic-scale understanding of ion-conduction, charge transport, structural evolution, and interfacial reactions such as dendrite growth, electrolyte decomposition. Here we employ a combination of density functional theory calculations, and ab initio molecular dynamics simulations to address this challenge for fluorinated argyrodites. Specifically, using accurate materials modeling, we design fluorine-containing argyrodite electrolytes that simultaneously offer enhanced (a) Li-ion conduction facilitated by unique Li-disorder induced by fluorine and other halogen co-dopants, and (b) stability against Li-anode owing to formation of a stable solid-electrolyte interface containing conductive species (Li3P), alongside LiCl and LiF. We will discuss these results in the context of accelerating design of novel solid-state electrolytes for long-lived, stable, and high-energy density SSLSBs.

A Hybrid Solid-State Electrolyte with High Lithium-Ion Conductivity and Thermal Stability for Highly Stable Long-Cycle Lithium-Oxygen Batteries

Solid-state electrolytes in lithium-oxygen batteries have garnered attention due to their high energy density and stability. Traditional electrolytes suffer from high interfacial resistance and poor ionic conductivity. We have developed a novel hybrid solid electrolyte by optimizing the ratio of inorganic to polymer electrolytes, incorporating doped and modified PVDF-HFP-SO3 as the polymer electrolyte in lithium-air batteries for the first time. The crystallinity and performance of this hybrid electrolyte improve with increasing LATP content. Notably, the HSE-SO3-3 electrolyte with 60% LATP exhibits exceptionally high conductivity (4.76 × 10−4 S∙cm−1 at room temperature) and a stability window exceeding 5 V, with stable operation in lithium symmetric cells for over 3500 h. Thermal stability tests indicate that the material does not ignite or deform under flame exposure. In quasi-solid-state lithium-oxygen batteries, using manganese dioxide as a catalyst and HSE-SO3-3 as the electrolyte, the battery demonstrates high discharge capacity, long-term cyclability, and stable charging performance at high rates. Therefore, this novel hybrid solid electrolyte shows great potential for high-voltage solid-state lithium-oxygen batteries.

Giant dielectric ceramic of Li0.3Ti0.02Ni0.68O with abundant oxygen vacancies enabling high lithium-ion conductivity in composite solid-state electrolyte

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.

Amorphous Boron Nitride Nanosheet‐Based Solid State Electrolytes with High Ionic Conductivity

AbstractAmorphous boron nitride nanosheets, with natural electrical insulation, outstanding chemical stability and mechanical properties, are introduced as a matrix to be incorporated with lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and polymer polyvinylidene fluoride‐hexafluoropropylene copolymer (PVDF‐HFP), for constructing a novel composite solid‐state electrolyte by a simple solution‐casting method. Amorphous boron nitride nanosheets are produced via a combination method of ball milling and pure water exfoliation. The obtained composite solid‐state electrolyte containing 40 % (mass fraction) PVDF‐HFP shows a high lithium ion conductivity (1.936×10−3 S cm−1) and lithium ion transference number (0.47), and a wide electrochemical stability window (5 V) at room temperature. The LiFePO4/Li based all solid‐state battery, consisting of the composite solid electrolyte (40 % PVDF‐HFP), delivers a capacity of 128.1 mAh g−1, a Coulombic efficiency of 99.79 % after 500 cycles and a capacity retention rate of 94.5 % at 1.0 C and 25 °C. The composite solid electrolyte (40 % PVDF‐HFP) can maintain flat and stable stripping/plating plateaus for over 800 hours in symmetrical cells. The amorphous boron nitride nanosheets with high lithium ion conductivity are employed to construct solid‐state electrolytes, which is important significant for the development of high energy density, high safety, and long cycle life all‐solid‐state lithium‐ion batteries.

Lithium-Ion Conductive Coatings for Nickel-Rich Cathodes for Lithium-Ion Batteries.

Nickel (Ni)-rich cathodes are among the most promising cathode materials of lithium batteries, ascribed to their high-power density, cost-effectiveness, and eco-friendliness, having extensive applications from portable electronics to electric vehicles and national grids. They can boost the wide implementation of renewable energies and thereby contribute to carbon neutrality and achieving sustainable prosperity in the modern society. Nevertheless, these cathodes suffer from significant technical challenges, leading to poor cycling performance and safety risks. The underlying mechanisms are residual lithium compounds, uncontrolled lithium/nickel cation mixing, severe interface reactions, irreversible phase transition, anisotropic internal stress, and microcracking. Notably, they have become more serious with increasing Ni content and have been impeding the widespread commercial applications of Ni-rich cathodes. Various strategies have been developed to tackle these issues, such as elemental doping, adding electrolyte additives, and surface coating. Surface coating has been a facile and effective route and has been investigated widely among them. Of numerous surface coating materials, have recently emerged as highly attractive options due to their high lithium-ion conductivity. In this review, a thorough and comprehensive review of lithium-ion conductive coatings (LCCs) are made, aimed at probing their underlying mechanisms for improved cell performance and stimulating new research efforts.

Structural and electrical properties of mol% (100 − x)Li2SO4:xP2O5 solid electrolyte system (0 ≤ x ≤ 20)

Abstract Extensive research has been focused on solid electrolytes exhibiting high lithium ion conductivity, with the goal of advancing their use in solid-state lithium-ion batteries. This study investigates the influence of a glass former, P2O5, on the structure and ionic conductivity of the solid electrolyte Li2SO4. Quenching of Li2SO4 in the presence of P2O5 resulted in a glass–crystal composite with significant amorphous content. The XRD analysis of the 20 mol% glass ceramics detects the presence of Li4P2O7 without altering the original crystal structure. Notably, a conductivity value of 1.11 × 10−4 S cm−1 at 563 K was observed for 20 mol%, which is around two orders higher than that of polycrystalline Li2SO4. The introduction of a small amount of glass former P2O5 appears to loosen the structure of Li2SO4 creating an easier path for Li+ ion migration in the combined SO4–PO4 network structure.

Advanced Composite Solid Electrolyte Architecture Constructed with Amino‐Modified Cellulose and Carbon Nitride via Biosynthetic Avenue

AbstractPolyethylene oxide (PEO) solid electrolytes are regarded as a promising candidate for all‐solid‐state lithium batteries owing to their high safety and interfacial compatibility. However, PEO electrolyte is plagued by relatively weak structural strength and unsatisfactory Li+ conductivity. Herein, a mechanically strong and Li+ conductively favorable cellulosic scaffold of PEO is fabricated through amino (‐NH2) modification and g‐C3N4 (CN) incorporation of bacterial cellulose (BC) under a microbial circumstance. The biologically ‐NH2 modified BC (B‐NBC) is entangled with CN nanosheets (CN@B‐NBC) through an in situ secretion of nanocellulose followed by hydrogen bond‐induced self‐assembly. The ‐NH2 groups from B‐NBC weaken the complexation of Li+ with its counterpart, thus facilitating the release of more free Li+. CN with strong C‐N covalence and extra lone electrons of N further strengthens the BC skeleton and meanwhile offers sufficient anchors for Li+ migration. After infiltrating by LiTFSI/PEO (LP), the LP/CN@B‐NBC composite solid electrolyte (CSE) exhibits high lithium transference number and ionic conductivity. Upon coupling with LiFePO4 cathode, the full battery exhibits a remarkably high specific capacity, superior rate capability, and decent cycling stability. This work pioneers the attempts of chemical decoration and ingredient incorporation of BC architecture in CSE with the aid of a bottom‐up biosynthetic avenue.

Synthesis, Crystal structure, electronic structure, and Raman spectra of Li4Sr2SiP4

AbstractRecently, ternary lithium phosphides have been studied intensively owing to their high lithium ion conductivities. During investigations aiming for derivatives with less lithium content the new compound Li4Sr2SiP4 was obtained. It crystallizes in the monoclinic space group P21/m (N°11) with lattice parameters of a=7.2919(8) Å, b=8.3679(6) Å, c=6.9965(8) Å, and β=90.061(9)°. The crystal structure contains isolated [SiP4]8− tetrahedra that are charge balanced by two Sr2+ and four Li+ counter ions. The structure can be derived as a superstructure of the layered CaAl2Si2 structure type comprising a hexagonal closest packing of P atoms and tetrahedral voids filled with Si and Li atoms, whereas octahedral voids are filled with Sr and Li atoms. DFT calculations confirm the structure with ordered atom positions as a global minimum and predict an indirect band gap of 2.23 eV. In addition, the experimental Raman spectrum is in good agreement with the calculated one.

Garnet-type lithium sensors for the monitoring and control of Pb-Li alloys in tritium breeding modules

During the EU-DEMO conceptualization, eutectic Pb-Li was considered as the prime candidate liquid breeding material. Nonetheless, the conversion of lithium into tritium through the breeding reaction will result in a decrease in the lithium concentration within the alloy. Then, the monitoring of the lithium concentration in Pb-Li alloys is critical for the optimal Tritium Breeding Blanket (TBB) performance, as lithium affects dissolution of structural materials, tritium inventory and extraction rates. Garnet-like ceramics possess desirable properties for their use in lithium sensors, like high lithium-ion conductivity, good chemical stability, low thermal expansion coefficient, and great mechanical strength. For these reasons, electrochemical sensors based on garnet-type ceramics offer advantages for measuring lithium in molten Pb-Li alloys, such as high selectivity and fast response. This work presents the development of lithium sensors based on the garnet-type ceramic Li6BaLa2Ta2O12. The material was characterized by XRD and SEM, exhibiting good crystallinity and a homogeneous microstructure. The sensors were evaluated in a potentiometric configuration in molten Pb-Li alloys with lithium concentrations ranging from 3 to 35 at% Li. Potentiometric measurements were used to obtain correlations that allow the determination of the lithium activity in the lead–lithium alloys studied.

Zwitterion grafted polyimide separator for improving lithium-ion transport and its application in LiCoO2 batteries

To improve the lithium-ion transport ability and cycle life of lithium-ion batteries, a high-performance polyimide-based lithium-ion battery separator (PI-SO3) was prepared by chemically grafting zwitterion onto the surface of heat-resistant polyimide nanofiber matrix with the assistance of amino-rich polyethyleneimine (PEI). The PI-SO3 not only maintains good dimensional stability (over 200 °C) and flame retardancy, but also ensures the safety of the battery under extreme conditions. Electrochemical experimental results show that PI-SO3 has high ion conductivity (1.99 mS·cm−1), Li+ transference number (0.632), and excellent oxidation potential (5.28 V), which are all higher than those of pure PI separator (1.14 mS·cm−1, 0.444, and 4.56 V, respectively). Meanwhile, LiCoO2/PI-SO3/Li batteries exhibit excellent high-rate performance (139.5 mAh·g−1 at 5C current) and long-term cycle stability (138.9 mAh·g−1 after 100 cycles at 1C current, and 127.9 mAh·g−1 after 100 cycles at 2C current). In addition, the symmetrical battery, Li/PI-SO3/Li, shows stable more than 360 cycles. Compared with batteries using commercial separators, such as Celgard 2325 and pure polyimide matrix, the assembled coin cells with PI-SO3 separators have higher lithium-ion conductivity, Li+ transference number, and diffusion coefficient after grafting zwitterion, showing better rate ability and capacity retention. In this paper, the modification strategy of thermal-resistant separator by grafting zwitterions provides an efficient way to prepare next generation high-performance lithium-ion batteries with good safety.

In Situ/Operando Techniques for Unraveling Mechanisms of Ionic Transport in Solid-State Lithium Indium Halide Electrolyte

Over the past years, lithium-ion solid-state batteries have demonstrated significant advancements regarding such properties as safety, long-term endurance, and energy density. Solid-state electrolytes based on lithium halides offer new opportunities due to their unique features such as a broad electrochemical stability window, high lithium-ion conductivity, and elasticity at close to melting point temperatures that could enhance lithium-ion transport at interfaces. A comparative study of lithium indium halide (Li3InCl6) electrolytes synthesized through a mechano-thermal method with varying optimization parameters revealed a significant effect of temperature and pressure on lithium-ion transport. An analysis of Electrochemical Impedance Spectroscopy (EIS) data within the temperature range of 25–100 °C revealed that the optimized Li3InCl6 electrolyte reveals high ionic conductivity, reaching 1.0 mS cm−1 at room temperature. Herein, we present the utilization of in situ/operando X-ray Photoelectron Spectroscopy (XPS) and in situ X-ray powder diffraction (XRD) to investigate the temperature-dependent behavior of the Li3InCl6 electrolyte. Confirmed by these methods, significant changes in the Li3InCl6 ionic conductivity at 70 °C were observed due to phase transformation. The observed behavior provides critical information for practical applications of the Li3InCl6 solid-state electrolyte in a broad temperature range, contributing to the enhancement of lithium-ion solid-state batteries through their improved morphology, chemical interactions, and structural integrity.

Improvement of Ionic Conductivity in Li7La3Zr2O12 (LLZO) Solid Electrolyte By Doping with Aluminum/Tungsten

Recently, there has been increasing interest in solid electrolytes, which are the most important materials in all-solid-state lithium-ion batteries. Among all solid electrolytes, garnet-type Li7La3Zr2O12 (LLZO) has been proven to be one of the most promising electrolytes due to its high Li+ conductivity, wide potential window, and electrochemical stability towards metallic lithium anode. In particular, cubic garnet-type LLZO solid electrolytes have received a lot of attention for the development of high-performance all-solid-state batteries with safety, energy density, and long cycle life. In this study, we synthesized LLZO solid electrolyte powders with garnet structure and determined the optimal composition and sintering temperature by adding Al/W to form a stable cubic phase.In this study, Al or W-doped LLZO were prepared by a post-doping method. In this process, LLZO powder was first prepared, and then mixed with Al2O3 or WO3 powders to produce doped LLZO ceramic electrolytes, respectively. During this process, the doped ions entered the LLZO lattice, increasing the lithium ion transport channels and promoting lithium ion conductivity. The sintering time, crucible, and sintering temperature were adjusted to investigate the optimal process conditions of the post-doping method. As a result, the doped solid electrolyte exhibited high lithium ion conductivity and low activation energy. Using the high lithium ion conductivity and broad electrochemical stability window of the Al or W doped LLZO SSE, the (NCM622)/(Al or W doped-LLZO) cell delivered a steady cycle for 100 cycles at 0.1C. The Al or W doped-LLZO prepared in this study showed advantages of high conductivity, simple preparation process, high reproducibility, and low cost, which provides technical support and reference for further application of garnet-type SSEs in solid-state batteries with high energy density.

Solid Electrolyte Coated NCM523 for Composite Cathode in All-Solid-State Batteries

All-solid-state battery using sulfide solid electrolyte has advantages such as high lithium ionic conductivity and wide electrochemical stability window. Although it is attracting great attention in that it is capable of high power and high energy density, there are problems to be improved.Organic liquid electrolytes in conventional lithium ion batteries have excellent wettability and can form uniform lithium ion transfer channels in electrodes. However, in the case of all-solid-state battery, the formation of a solid-solid interface is limited due to the solid characteristics. In addition, the degradation of the interfacial contact between the active material and solid electrolyte in the composite electrode due to the volume change of the active material with (de)-intercalation of lithium ion during cycling causes loss of the lithium ionic pathway and deterioration of cell performance. This study focuses on improving battery performance by coating the surface of active material with solid electrolyte to maintain an even lithium ion transfer path in the composite electrode. The solid electrolyte coating of the active material has a decisive effect on the electrochemical behavior of the cell because it affects the formation of smooth lithium ionic pathway and suppression of voids in the composite electrode. Therefore, the focus of this study is to confirm the formation of uniform solid electrolyte coating layer according to the size of the solid electrolyte.Therefore, the particle size of the solid electrolyte was diversified using a liquid-phase process and a dispersant, and the solid electrolyte coating was performed using a dispersion process. It was confirmed that an even solid electrolyte coating layer was formed as the particles size of the solid electrolyte decreased, and the electrochemical performance was improved due to the solid electrolyte coating layer. In addition, it was confirmed that the lithium ionic pathway was maintained even after long cycling with the solid electrolyte coating layer, and also the side reactions occurred less according to the homogeneous electrochemical reaction.

Firefighting Gel Polymer Electrolyte for Non-Flammable Li-Ion Batteries Based on Extremely Low Amount of a Cross-Linkable Polymer

Safety issues of lithium-ion batteries(LIBs) have caught a priority of concerns as the electric vehicle(EV) market expands dramatically and requires higher energy densities. To be free from a variety of unpredictable situations and environments triggering such a safety issue, materials that provide a mechanism to control the factors causing fire and explosion are required to be involved in LIB cells.In this work, we present a gel polymer electrolyte(GPE) characterized by nonflammability and fire-extinguishing capability by radical scavenging(Rs). This GPE was realized within battery cells by in situ crosslinking a small amount of a cross-linkable fluoro-functionalized cyanoethyl polyvinyl alcohol(F7) in conventional carbonate electrolytes having LiPF6. The cyanoethyl functional groups(-CN) is responsible for gelation by cross-linking while the fluorine-containing moiety terminated radical chain reactions triggering thermal runaway by Rs. The strong interaction between the polymer and solvent molecules restricted solvent volatility. The tiny solid content at 2 wt. % in GPE guaranteed a liquid-level ionic conductivity at 9 mS/cm, disallowing battery performances to be sacrificed. Formation of the LiF-dominant solid-electrolyte-interphase(SEI) layer on anodes was encouraged by the fluoro-moiety of F7.In previous research of our group, PVA-CN was used as cross-linkable polymer for enhancement of mechanical property with additional metal-chelating functional group. Hydroxy group of PVA-CN is useful to modify the functional group by DCC coupling mechanism. Herein, as same as previous modification, the Heptafluorobutyric acid(HFB) was used for non-flammability and battery performance. F7 was expected to not only increase thermal stability but also scavenge the radicals. In addition, LiF-rich SEI layers would be made by fluorine groups.First, GPE increase its thermal stability by strong interaction between cross-linked polymer matrix and organic solvents. The binding energy of ethylene carbonate (EC) and hydrogen of cyanoethyl side chain was 0.4 eV which is stronger compared with general hydrogen bond(0.2 eV). Therefore, the flammable gas generation was suppressed by strong interaction between solvents and polymer matrix.In addition, the flash point demonstrated the strong interaction in GPE. The flash point of GPE which contained different polymer contents was decreased as the ratio of polymer content was increased. The composition of the atmosphere in the devices changed into more flammable because of the higher ratio of EMC gas in the atmosphere within enough time to equilibrate. In other words, EC forms a greater number of strong interactions with the polymer matrix while the polymer contents increased. The SET test of 2 wt.% PVA-CN-based GPE(G2)(3.36 s/g) and 5 wt.% PVA-CN-based GPE(G5)(0 s/g) proved that higher contents of PVA-CN in GPE ensure the non-flammability.Second, to overcome the poor electrochemical ability of G5, Rs functionalized F7 was used instead of PVA-CN. Unlike G2, only with 2 wt. % of F7 guaranteed the 0 s/g of SET. Non-flammability of 2 wt.% F7-based GPE(FG2) is due to the fluorine moiety scavenge the O• or H•. In the nail penetration test, only the FG2 was not exploded and maintained charged voltage while the nail penetrates the whole pouch cell vertically because of its elasticity.The Rs capability was demonstrated by cyclic voltammetry(CV) with 2,2’-azobisisobutyronitrile(AIBN) and alpha-tocopherol(α-TOH). After α-TOH react with AIBN radicals at the 70 ℃, the oxidation current decreased because of consumption of α-TOH. The Rs capability was calculated by ratio of current retention of α-TOH oxidation current with a same amount of among scavenger additives. The Rs capability of F7 was 214%.Lastly, our findings suggest sufficient non-flammability without battery performances degradation. The capacity retention of FG2 was higher than LE at the 300th Cycles. This is because the fluorine moiety contributed to make LiF-rich SEI layers. The rigid SEI layers and GPE suppressed volume expansion of graphite. Also, the capacity fade was not observed in FG2 with higher current density. The reason for great rate capability is higher lithium-ion conductivity which is a multiplication of ionic conductivity and lithium-ion transference number(tLi+). FG2has 4.82 of lithium-ion conductivity, while 3.63 in LE. Therefore, the mass transfer resistance was not large on the electrode surface due to the higher lithium-ion mobility in FG2.In this work, the non-flammability and battery performance were successfully demonstrated by thermal stability and Rs capability without any battery performances degradation. The thermal stability was enhanced by strong intermolecular forces between polymer chain and polar organic solvents. The radical chain reaction was terminated by fluorine moiety of GPEs matrix. The capacity retention of FG2 was outstanding compared with LE. Therefore, due to the FG2, the battery will be able to ensure non-flammability without degradation of performance. Figure 1