High Li-ion Conductivity Research Articles

Potential Solid-State Electrolytes with Good Balance between Ionic Conductivity and Electrochemical Stability: Li5-xM1-xMx'O4 (M = Al and Ga and M' = Si and Ge).

Exploring new solid-state electrolyte (SSE) materials with good electrochemical stability and high Li-ion conductivity for all-solid-state Li-ion batteries is vital for the development of technologies. Herein, we employ two lithium aluminates, α- and β-Li5AlO4 (α- and β-LAO), as the model framework, which have an orthorhombic crystal structure and isolated AlO4 tetrahedron units connected in lithium atoms, exhibiting large band gaps, low migration barriers (0.30-0.40 eV), fast Li-ion conductivity (LIC, in a magnitude of 10-4 S/cm), and a good electrochemical stability window (ESW, [0.01-3.20 V] vs Li+/Li). We tabulate the expected decomposition products at the interface, while considering cathodes in combination with the LAO electrolyte to discuss their compatibility. We also examine the electrochemical stability, H2O/CO2 stability, and Li-ion mobility of Li4.6Al0.6Si0.4O4 (LASO), Li5GaO4 (LGaO), and Li4.6Ga0.6Ge0.4O4 (LGaGeO) compounds. In general, there is usually a trade-off between the LIC and the ESW; however, LAO features a good balance between an outstanding LIC and a wide ESW, making the compound a promising candidate for next-generation SSE materials.

Fe3N@N-doped graphene as a lithiophilic interlayer for highly stable lithium metal batteries

Lithium (Li) metal anode is of great importance for high-energy rechargeable batteries owing to its ultrahigh theoretical capacity. However, the Li dendrite growth during the repetitive charge/discharge process will impale the separator resulting in short-circuiting and serious safety issues. To effectively suppress Li dendrite growth, for the first time we present a novel lithiophilic interlayer on commercial PP separator, which is constructed by Fe3N nanoparticles embedded and wrapped in N-doped graphene nanosheets (Fe3N@NG). The Fe3N@NG functionalized separator displays excellent electrolyte wettability, high Li ionic conductivity and ion transference number, which function synergistically to suppress Li dendrite growth. Meanwhile, the DFT calculation demonstrates that there exists a stronger interaction between Li atoms and Fe3N@NG, which can provide the deposition sites, resulting in uniform and compact Li plating. Above ameliorating merits accompany an ultra-long-life of 2300 h at 5 mA cm−2 for the Li//Li symmetric cells with Fe3N@NG functionalized separators. Moreover, the Li//LFePO4 full cell delivers superior long-term cyclic stability and ultralow capacity decay rate of 0.08%/cycle even at 2C. This work provides an innovative strategy to rationally design and new insights towards functional lithiophilic interlayer to efficiently suppress Li dendrite growth for Li metal batteries.

Influence of Powder Milling and Annealing Parameters on the Formation of Cubic Li7La3Zr2O12 Compound.

Li-ion batteries are widely used as energy storage devices due to their excellent electrochemical performance. The cubic Li7La3Zr2O12 (c-LLZO) compound is regarded as a promising candidate as a solid-state electrolyte for lithium-ion batteries due to its high bulk Li-ion conductivity, excellent thermal performance, and chemical stability. The standard manufacturing procedure involves the high-temperature and lengthy annealing of powders. However, the formation of the tetragonal modification of LLZO and other undesired side phases results in the deterioration of electrochemical properties. The mechanical milling of precursor powders can enhance the powders’ reactivity and can result in an easier formation of c-LLZO. The aim of this work was to study the influence of selected milling and annealing parameters on c-LLZO compound formation. The starting powders of La(OH)3, Li2CO3, and ZrO2 were subjected to milling in various ball mills, under different milling conditions. The powders were then annealed at various temperatures for different lengths of times. These studies showed that the phase transformation processes of the powders were not very sensitive to the milling parameters. On the other hand, the final phase composition and microstructure strongly depended on heat treatment conditions. Low temperature annealing (750 °C) for 3 h produced 90% of c-LLZO in the powder structure.

High Li-ionic conductivity of Li29Zr9Nb3O40 ceramic sintered in oxygen-deficient atmosphere

Lithium ion batteries (LIBs) based on solid state electrolytes have attracted much attention for their high safety and energy density. Li29Zr9Nb3O40 powders as Li-ionic conductors were prepared using a sol-gel method in this work, and the related ceramics were sintered in air or in an oxygen-deficient atmosphere in which sample was covered with corundum crucible. All the sintered ceramics are consisted of orthorhombic phase. Li29Zr9Nb3O40 ceramic sintered in oxygen-deficient atmosphere has conductivity of 1.03 × 10−3 S cm−1 at room temperature and has ionic transference number of 0.9996, while the ceramic sintered in air has conductivity of 4.41 × 10−5 S cm−1. The influence of oxygen vacancy on the migration path of Li-ion was discussed. The migration paths of Li-ions between two kinds of Li29Zr9Nb3O40 ceramics were simulated and visualized by method of bond valence site energy with VESTA software.

Structural origin of low Li-ion conductivity in perovskite solid-state electrolyte

Perovskite solid-state electrolyte, Lithium Lanthanum Titanium Oxide, has long been considered as a promising candidate enabling all-solid-state Li batteries due to its high bulk Li-ion conductivity and wide electrochemical window. However, the Li-ion conductivity at so called “grain boundaries” (GBs) off LLTO pellets is much lower than that of its bulk phase. Thus, understanding the structural origin of the low Li-ion conductivity of LLTO is critical yet remains largely elusive. Here, we identify two types of GBs at different length scales, namely “macro” and “micro” GBs in LLTO pellets and originate them to the processing of LLTO. We also find a nanosized Li-poor orthogonal phase at micro-GBs, which largely deteriorate the Li conduction. Corroborated by electrochemical measurements, we revealed the phase transformation from tetragonal Li0.33La0.56TiO3 to orthogonal Li0.18La0.6TiO3 during the heat-treatment process is responsible for this deterioration. During phase transformation process, La atoms move to the original Li-rich layer and block the diffusion path of Li-ions in LLTO. These results reveal the structural origin of low Li-ion conductivity in LLTO pellets and provide insights to prevent Li-loss induced phase transformation for commercial application of LLTO.

Research and Development of Thermally Durable Electrolyte for Lithium Ion Battery

For ensuring safety of lithium ion batteries (LIBs), we have extensively investigated the quasi-solid electrolyte where lithium ion conducive liquid is quasi-solidified at silica surfaces as thermally durable electrolyte, and applied it to high capacity and high energy density LIB. For the liquid phase, a solvate ionic liquid, which is an equimolar complex of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraethylene glycol dimethyl ether (G4), Li(G4)TFSA, was used. For enhancing discharge capability at a higher rate, Li(G4)TFSA was diluted by low viscos solvent such as propylene carbonate (PC). The developed electrolyte possessed a favorable volatilization temperature higher than 373 K. A 100-Wh-class laminated LIB with energy density of 363 Wh L−1 was fabricated by employing the electrolyte to graphite-LiNixCoyMnzO2 chemistry, and it generated neither fire nor smoke in a nail-penetration test. The result suggest that the developed LIB has high safety compared to a LIB comprised of a conventional organic liquid electrolyte. In addition, to enhance the cycle life of the LIB, the formation and growth mechanism of a solid-electrolyte interphase on a graphite-based negative electrode was investigated. Nuclear magnetic resonance and hard x-ray photoelectron spectroscopy revealed that the decompositions of LiTFSA, PC, and G4 contributed to the SEI formation at the initial charge, and that continuous decompositions of G4 and PC were a major reason for the SEI growth during charge-discharge cycles. Based on these analysis, we have substituted a highly concentrated sulfolane based liquid which exhibits a high Li ion conductivity with less amount of the low viscos solvent, for the G4 based liquid. The modification effectively improved the electrochemical durability of the electrolyte, leading to a higher capacity retention after charge-discharge cycle test.

Tuning Site Energy by XO6 Units in LiX2(PO4)3 Enables High Li Ion Conductivity and Improved Stability.

Solid-state electrolytes (SSEs) with high ion conductivity are necessary for all-solid-sate lithium ion batteries. Here, a less studied NASICON-type LiZr2(PO4)3 (LZP) is screened out from seven LXP compounds (LiX2(PO4)3, X = Si, Ge, Sn, Ti, Zr, Hf, and Mo), which combines the electrochemical stability with high Li conductivity. The bond valence site energy (BVSE), climbing image nudged elastic band (Cl-NEB) method, and electrochemical phase diagram prove LZP has a lower Li migration barrier and the largest electrochemical stability window. The underlying reason for high Li conductivity is analyzed from the structural features to the electronic structures. Furthermore, the XO6 unit mixed frameworks Li1.667Ca0.333Zr1.667(PO4)3 (LCZP) and Li1.667Mg0.333Zr1.667(PO4)3 (LMZP) exhibit high Li ion conductivity associated with a very low Li migration barrier (∼0.20 eV). This work opens a new avenue of broad compositional spaces in LXP for SSEs.

Fast Li-ion Conductor of Li3HoBr6 for Stable All-Solid-State Lithium–Sulfur Battery

Rare-earth (RE) solid-state halide electrolytes have been extensively studied recently in the field of lithium (Li) ion all-solid-state batteries (ASSBs) due to their excellent electrochemical performances. Herein, a new RE-based solid halide electrolyte Li3HoBr6 (LHB) has been synthesized and exhibits high Li ion conductivity up to mS cm-1 at room temperature. Theoretical calculations have identified four different Li ion migration pathways, in which the out-of-plane pathways are much more favorable than the direct in-plane pathways. In addition, LHB has a wider electrochemical window in comparison to a sulfide solid electrolyte and good deformability. The LHB-based Li-sulfur ASSB assembled by cold pressing can exhibit good cycling stability with high Coulombic efficiency, which shows that LHB has potential application in ASSBs.

Fast Charging of High Energy Density Li-Ion Batteries with High Li Ion Transport Electrolyte

Enabling fast charging capability of high energy density Li-ion cells could dramatically increase the widespread adoption of battery electric vehicles. However, fast charging is limited by Li ion depletion in the electrolyte and the accompanying Li plating over graphite anodes. This phenomenon was pointed out as a major reason for cell performance degradation and failure. One of the solutions for enabling extreme fast charging while retaining most of the battery energy can be achieved through the significant enhancement of the Li-ion mass-transport in electrolytes such that enough Li ions are available for intercalation in graphite.Researchers at ORNL have developed high performance electrolytes with optimized Li salt, solvents, and additives. The electrolytes have both higher Li ion conductivity and Li ion transference number, compared to state-of-the-art electrolyte. The electrolyte development is ideal for higher Li ion transport and has been identified as a significant step towards realizing cells with XFC capabilities.The electrolytes were filled into NMC622||graphite Li-ion cells (1.5 Ah pouch cells) and the cells were tested under 6C (10 minutes) XFC protocol in Figure 1. The cell with ORNL V2 electrolyte has 89% capacity retained after 500 XFC cycles, which is better than the targeted goal (80% after 500 cycles), and much better than the 64% retention for the Gen2 baseline electrolyte (1.2 M LiPF6 in EC:EMC 30:70 wt%). Continued cycling of the cells show 80% capacity retention after 1000 cycles. The cell can have an energy density of ~180 Wh/Kg (when scaled up to 50 Ah), which has met the targeted goal for energy density. After 1000 XFC cycles, the cell still has 141 Wh/kg energy density. When the cell was charged/discharged at C/3 after 1000 XFC cycles, it can still deliver 193 Wh/kg. This demonstrates the excellent performance of Li-ion cell using ORNL V2 electrolyte formulation for XFC capability.

(Invited) Grain Boundary and Surface Atomic Structures and Diffusion in Li-Ion Battery Related Crystals

The properties of lithium ion battery cathodes strongly depend on the diffusion of lithium ions during charge/discharge process. Then, direct visualization of lithium site is required to understand the mechanism of the diffusion of lithium ions. In this study, aberration (Cs) corrected STEM were applied to directly observe the {010} surface, which corresponded to perpendicular to the 1-D diffusion orientation, of the olivine LixFePO4. The morphology of the interface between Li-rich and Li-poor phases of LixFePO4 after chemical delithiation were observed with atomic resolution at fit intervals during half a year. It was found that orientation of boundary layers at the FePO4/Li2/3FePO4 interface gradually changed from lower index planes to higher index planes. This indicates that intermediate phase plays an important role in healing crystal cracking by allowing the interface to remain coherent so that Li ions can diffuse back into regions depleted during delithiation. The mechanism of the lithiation/delithiation from and to the surface will be discussed based on the observation results.Lithium lanthanum titanate (LLTO) is expected to apply for an electrolyte in the all-solid-state Li-ion battery because of its high Li-ion conductivity in the bulk. However, it has been reported that Li-ion conductivity is strongly suppressed at the grain boundaries (GBs) in polycrystalline materials. It is therefore needed to understand the atomistic mechanism of the reduction of Li-ion conductivity at individual GBs in order to design suitable LLTO polycrystals. In this study, two different GBs, Σ5 and Σ13, were prepared by fabricating the bicrystals, and their structures were observed by Cs corrected STEM and atomic force microscopy (AFM). Then, the charge states, Li-ion conductivities, atomic and electronic structures at the respective Σ5 and Σ13 GBs of LLTO were systematically and quantitatively investigated. It was found that the Σ5 GB has no significant influence on Li-ion conductivity, but the Σ13 GB shows the significant reduction of the Li-ion conductivity. We further found that Σ13 GB is positively charged by the formation of large amount of oxygen vacancies at the GB. Li-ion depletion layers is considered to be formed at the Σ13 GB, which causes the significant reduction of Li-ion conductivity, to compensate such positive charge at the GB.References Kobayashi, C.A.J.Fisher, T.Kato,Y.Ukyo,T.Hirayama and Y.Ikuhara, Nano Lett. 16, 5409 (2016).Kobayashi, A. Kuwabara, C. A.J. Fisher, Y. Ukyo and Y. Ikuhara,Nat. Commun., 9, 2863 (2018)Sasano, R. Ishikawa, I. Sugiyama, T. Higashi, T. Kimura, Y. H. Ikuhara, N. Shibata and Y. Ikuhara, Applied Physics Express, 10, 061102 (2017)Sasano, R. Ishikawa, K. Kawahara, T. Kimura, Y. H. Ikuhara, N. Shibata and Y. Ikuhara, Applied Physics Letters, 116, 043901 (2020)

Ultrathin Coating of Metal Nitride as a Robust and Efficient Artificial Solid Electrolyte Interphase Using Atomic Layer Deposition

The lithium metal anode (LiMA) is considered promising that can achieve high specific energy > 500 Wh kg-1 for future electric vehicles. Despite attractive features, Li-metal-based anode integration still faces barriers such as lithium dendrite growth, unstable solid electrolyte interphase (SEI) formation, and continuous side reactions, limiting its use in the practical application. Here, metal nitride-based artificial SEI is designed to enhance the stability of LiMA under the synergic effect guidance provided by the SEI. During the ALD coating of MNx (where M=metal), the metal nitride reacts with Li to form Li-metal alloy and lithium nitride (Li3N). The Li-metal alloy and Li3N provide high Li-ion conductivity, lithiophilicity, and a physical barrier between the liquid electrolyte and LiMA, stabilizing the interface and suppressing the Li dendrite growth. As a result, metal nitride deposited Li, compared to bare Li, demonstrates significantly improved electrochemical cell performance with longer cycling stability and lower overpotential. This work will provide an insight on stabilizing SEI for dendrite-free Li deposition to develop long-term cycling stability and safer lithium metal batteries.

Li+ conductivity in the system Li2O-Nb2O5-P2O5-LiCl as solid electrolyte based on synthesized glasses and sintered glass ceramics

All solid-state batteries (ASSB) employing solid Li-ion conductors instead of liquid electrolytes are considered promising candidates for future energy storage solutions with increased energy density and improved safety properties. For oxidic electrolytes, this is enabled by proper densification of the mixed powder compacts made of oxidic solid electrolyte and active material, e. g. by sintering at high temperatures. For this purpose, oxide glasses with lower softening temperatures (< 1000 °C) are discussed as Li-conductive electrolyte. Herein, the synthesis of Li-ion conductive glasses in the system Li2O-Nb2O5-P2O5-LiCl by means of melting and quenching, powder preparation by milling and sintering of powder compacts in air are investigated. The highest Li-ion conductivity of 5.5 × 10−6 S/cm was obtained for the optimized composition of 40Li2O-10Nb2O5-30P2O5-20LiCl in glassy state as well as for glass ceramics obtained after sintering at 700 °C. The high Li-ion conductivity of the glasses is retained in the glass-ceramic microstructure after sintering, although crystallization, grain size and porosity significantly influence the resulting overall properties.

Coupling a Three-Dimensional Nanopillar and Robust Film to Guide Li-Ion Flux for Dendrite-Free Lithium Metal Anodes.

Lithium metal batteries with high theoretical capacity critically suffer from low cycling stability and safety issues mostly due to lithium dendrites. Regulating the Li-ion conduction and Li deposition is essential to achieve dendritic-free Li metal anodes. Herein, a synergistic strategy that combines a 3D nanocopper layer and a robust polymer protective layer is proposed. The 3D nanocopper layer in situ formed on the Li surface could achieve a uniform electric field distribution and contribute to reducing the nucleation barrier for Li deposition and refining the grain size of Li crystallites. Meanwhile, the Li-Nafion film with high Li-ion conductivity and good flexibility was used as a protective layer to provide homogeneous ion distribution and adapt to the volume change during the Li deposition. Consequently, the NCuLi∥LiCoO2 full cells exhibited outstanding cycling stability (a capacity retention of 90% over 500 cycles). Our results indicate that the synergistic control of Li-ion conduction and Li deposition is a promising method to achieve dendritic-free Li metal anodes.

Ionic Liquid Functionalized Gel Polymer Electrolytes for Stable Lithium Metal Batteries

AbstractMetallic lithium (Li) is regarded as the ideal anode material in lithium‐ion batteries due to its low electrochemical potential, highest theoretical energy density and low density. There are, however, still significant challenges to be addressed such as Li‐dendrite growth and low interfacial stability, which impede the practical application of Li metal anodes. In order to circumvent these shortcomings, herein, we present a gel polymer electrolyte containing imidazolium ionic liquid end groups with a perfluorinated alkyl chain (F‐IL) to achieve both high ionic conductivity and Li ion transference number by fundamentally altering the solubility of salt within the gel electrolyte through Lewis‐acidic segments in the polymer backbone. Moreover, the presence of F‐IL moieties decreased the binding affinity of Li cation towards the glycol chains, enabling a rapid transfer of Li cation within the gel network. These structural features enabled the immobilization of anions on the ionic liquid segments to alleviate the space‐charge effect while promoting stronger anion coordination and weaker cation coordination in the Lewis‐acidic polymers. Accordingly, we realized a high Li ion conductivity (9.16×10−3 S cm−1) and high Li ion transference number of 0.69 simultaneously, along with a good electrochemical stability up to 4.55 V, while effectively suppressing Li dendrite growth. Moreover, the gel polymer electrolyte exhibited stable cycling performance of the Li|Li symmetric cell of 9 mAh cm−2 for more than 1800 hours and retained 86.7 % of the original capacity after 250 cycles for lithium‐sulfur (Li‐S) full cell.

Ionic Liquid Functionalized Gel Polymer Electrolytes for Stable Lithium Metal Batteries.

Metallic lithium (Li) is regarded as the ideal anode material in lithium‐ion batteries due to its low electrochemical potential, highest theoretical energy density and low density. There are, however, still significant challenges to be addressed such as Li‐dendrite growth and low interfacial stability, which impede the practical application of Li metal anodes. In order to circumvent these shortcomings, herein, we present a gel polymer electrolyte containing imidazolium ionic liquid end groups with a perfluorinated alkyl chain (F‐IL) to achieve both high ionic conductivity and Li ion transference number by fundamentally altering the solubility of salt within the gel electrolyte through Lewis‐acidic segments in the polymer backbone. Moreover, the presence of F‐IL moieties decreased the binding affinity of Li cation towards the glycol chains, enabling a rapid transfer of Li cation within the gel network. These structural features enabled the immobilization of anions on the ionic liquid segments to alleviate the space‐charge effect while promoting stronger anion coordination and weaker cation coordination in the Lewis‐acidic polymers. Accordingly, we realized a high Li ion conductivity (9.16×10−3 S cm−1) and high Li ion transference number of 0.69 simultaneously, along with a good electrochemical stability up to 4.55 V, while effectively suppressing Li dendrite growth. Moreover, the gel polymer electrolyte exhibited stable cycling performance of the Li|Li symmetric cell of 9 mAh cm−2 for more than 1800 hours and retained 86.7 % of the original capacity after 250 cycles for lithium‐sulfur (Li‐S) full cell.

Effects of Li ion-solvent interaction on ionic transport and electrochemical properties in highly concentrated cyclic carbonate electrolytes

In recent research, the importance of electrolytes with high Li + transference number ( t Li ) and ionic conductivity ( σ ion ) has been emphasized to realize rapid charge for Li secondary batteries. Simultaneously fulfilling high t Li and σ ion is still unsolved in liquid electrolytes; however, highly concentrated electrolytes (HCEs) of weakly coordinating solvents and Li salts will be promising for addressing this challenge. This idea is inspired by a recent study by Angell et al. on superprotonic ionic liquids comprising a weak Brønsted base and a superacid; highly labile and exchangeable H + can be formed between significantly weak proton accepting sites. Here, we studied weakly coordinating fluoroethylene carbonate (FEC)-based electrolytes with lithium bis(fluorosulfonyl)amide (Li[FSA]) and compared with ethylene carbonate (EC)-based electrolytes. Experimental and computational studies indicated that solvent and ion exchange is more pronounced in the FEC-based HCE, resulting in higher t Li PP (0.73) and ionic conductivity (1.02 mS cm −1 ) compared to those of the EC-based HCE ( t Li PP = 0.53 and σ ion = 0.84 mS cm −1 ). However, the FEC-based HCE exhibited lower electrochemical stability due to the intrinsically lower reductive stability of FEC and the oxidative decomposition of the liberated solvent in the HCE. Despite the superior transport properties, the Li/LiCoO 2 cell with the FEC-based electrolyte showed lower discharge capacities and lower Coulombic efficiencies at higher current densities due to side reactions of the electrolyte. This study demonstrates that weak Li-solvent interactions can simultaneously enhance t Li and σ ion of HCEs, but they have the potential to sacrifice the electrochemical stability. • An electrolyte design approach to high Li ion conductivity is proposed. • A weakly coordinating solvent/Li salt combination shows high Li ion conductivity. • Solvent/ion exchange is more pronounced in weakly coordinating system. • Weak solvent-Li interaction compromises electrochemical stability.

Atomistic Origin of Li-Ion Conductivity Reduction at (Li3xLa2/3-x)TiO3 Grain Boundary.

Lithium lanthanum titanate (LLTO) is one of the excellent candidates for an electrolyte in the all-solid-state Li-ion battery, owing to the high Li-ion conductivity in the bulk. However, the Li-ion conductivity at the grain boundary (GB) is largely reduced, and it is therefore important to reveal the origin of Li-ion conductivity reduction at the GB. Here, by using atomic-resolution scanning transmission electron microscopy combined with atomic force microscopy, we investigate the charge states, Li-ion conductivities, atomic and electronic structures at the LLTO Σ5 and Σ13 GBs. Although the Σ5 GB has no significant influence on Li-ion conductivity, the Σ13 GB shows the evident reduction of Li-ion conductivity. We further elucidate that the Σ13 GB is positively charged by the formation of oxygen vacancies at the GB. Such a positive charge would form the Li-ion depletion layers adjacent to the GB, which causes the significant reduction of Li-ion conductivity.

Development of Novel High Li-Ion Conductivity Hybrid Electrolytes of Li10GeP2S12 (LGPS) and Li6.6La3Zr1.6Sb0.4O12 (LLZSO) for Advanced All-Solid-State Batteries

A lithium superionic conductor of Li10GeP2S12 that exhibits the highest lithium ionic conductivity among the sulfide electrolytes and the most promising oxide electrolytes, namely, Li6.6La3Sr0.06Zr1.6Sb0.4O12 and Li6.6La3Zr1.6Sb0.4O12, are successfully synthesized. Novel hybrid electrolytes with a weight ratio of Li6.6La3Zr1.6Sb0.4O12 to Li10GeP2S12 from 1/1 to 1/3 with the higher Li-ion conductivity than that of the pure Li10GeP2S12 electrolyte are developed for the fabrication of the advanced all-solid-state Li batteries.

Enhanced Electrochemical Performance of Poly(ethylene oxide) Composite Polymer Electrolyte via Incorporating Lithiated Covalent Organic Framework

The lithiated covalent organic framework (named TpPa-SO3Li), which was prepared by a mild chemical lithiation strategy, was introduced in poly(ethylene oxide) (PEO) to produce the composite polymer electrolytes (CPEs). Li-ion can transfer along the PEO chain or across the layer of TpPa-SO3Li within the nanochannels, resulting in a high Li-ion conductivity of 3.01 × 10−4 S/cm at 60 °C. When the CPE with 0.75 wt.% TpPa-SO3Li was used in the LiFePO4||Li solid-state battery, the cell delivered a stable capacity of 125 mA·h/g after 250 cycles at 0.5 C, 60 °C. In comparison, the cell using the CPE without TpPa-SO3Li exhibited a capacity of only 118 mA·h/g.

Influence of synthesis parameters on crystallization behavior and ionic conductivity of the Li4PS4I solid electrolyte

Superionic solid electrolytes are key to the development of advanced solid-state Li batteries. In recent years, various materials have been discovered, with ionic conductivities approaching or even exceeding those of carbonate-based liquid electrolytes used in high-performance Li-ion batteries. Among the different classes of inorganic solid electrolytes under study, lithium thiophosphates are one of the most promising due to their high Li-ion conductivity at room temperature and mechanical softness. Here, we report about the effect of synthesis parameters on the crystallization behavior and charge-transport properties of Li4PS4I. We show that thermally induced crystallization of Li4PS4I (P4/nmm), starting from the glassy phase 1.5Li2S–0.5P2S5–LiI, adversely affects the material’s conductivity. However, both conductivity and crystallization temperature can be significantly increased by applying pressure during the preparation.