High Capacity and Superior Cyclic Performances of All-Solid-State Lithium-Sulfur Batteries Enabled by a High-Conductivity Li10SnP2S12 Solid Electrolyte

Synergistic Interfacial Optimization for High-Sulfur-Content All-Solid-State Lithium-Sulfur Batteries

Improving the sulfur content in the cathode is essential for achieving high-energy-density all-solid-state lithium-sulfur batteries (ASSLSBs). However, the complex multiinterfaces, akin to the short wooden planks that consist of the cask, severely limit the performance of ASSLSBs with high sulfur content. Since singular approaches fail to optimize these interfaces simultaneously, we propose a synergistic approach using a dual-doped sulfide solid electrolyte (Y2S3 and LiI) and an SbSn alloy sulfur host in this work. The incorporation of Y2S3 in the solid electrolyte serves to improve the electrolyte-electrolyte interfaces and enhance the ionic conductivity, while the inclusion of LiI helps stabilize the electrolyte-anode interface and suppress dendrite formation. Meanwhile, the SbSn alloy sulfur host facilitates the transfer of Li+ at the electrolyte-cathode interfaces. Consequently, the solid-solid interfaces are significantly improved, leading to impressive specific capacities in ASSLSBs with high sulfur content (>44% in the cathode composite) at room temperature (1163.5 mAh g-1) and at 60 °C (1408.7 mAh g-1) during the 50th cycle at 0.05C. This work presents a promising strategy for achieving practical high-performance ASSLSBs.

LLZTO Nanoparticle- and Cellulose Mesh-Coreinforced Flexible Composite Electrolyte for Stable Li Metal Batteries

Composite electrolytes have been regarded as the most prospective electrolytes for commercial application because they acquire the advantages of both polymer and inorganic electrolytes, commonly exhibiting appreciated flexibility and suitable ionic conductivity. Nevertheless, the conventional solution-casting method with toxic solvent and poor interfacial contact still hamper their commercialization process. Moreover, electrolytes with higher ionic conductivity and transference number are urgently needed for satisfying fast-charging batteries. Herein, a novel composite electrolyte (LZEC) reinforced by mechanically robust LLZTO nanoparticles and flexible cellulose mesh was fabricated by a simple and advanced in situ thermal polymerization method, with adding of highly ion-conductive liquid plasticizer. Consequently, the rationally designed LZEC composite electrolyte exhibits superior flexibility and remarkable electrochemical properties in the form of high ionic conductivity, wide electrochemical stability window, and high Li+ transference number. Importantly, the in situ synthesis method is expected to help construct an enhanced electrolyte/electrode interface inside the battery, and the LZEC composite electrolyte is capable of suppressing Li dendrite growth effectively, as evidenced by the prolonged stable cycling of the Li/Li symmetric cell. Therefore, the LFP/LZEC/Li full cell exhibits superior rate performance and long cyclic life. These attractive properties make LZEC a potential composite electrolyte for boosting the practical application of safe and long-life Li metal batteries.

Multiscale Structural Engineering of Sulfur/Carbon Cathodes Enables High Performance All-Solid-State LiS Batteries

Constructing all-solid-state lithium-sulfur batteries (ASSLSBs) cathodes with efficient charge transport and mechanical flexibility is challenging but critical for the practical applications of ASSLSBs. Herein, a multiscale structural engineering of sulfur/carbon composites is reported, where ultrasmall sulfur nanocrystals are homogeneously anchored on the two sides of graphene layers with strong SC bonds (denoted as S@EG) in chunky expanded graphite particles via vapor deposition method. After mixing with Li_9.54 Si_1.74 P_1.44 S_11.7 Cl_0.3 (LSPSCL) solid electrolytes (SEs), the fabricated S@EG-LSPSCL cathode with interconnected "Bacon and cheese sandwich" feature can simultaneously enhance electrochemical reactivity, charge transport, and chemomechanical stability due to the synergistic atomic, nanoscopic and microscopic structural engineering. The assembled InLi/LSPSCL/S@EG-LSPSCL ASSLSBs demonstrate ultralong cycling stability over 2400 cycles with 100% capacity retention at 1 C, and a record-high areal capacity of 14.0 mAh cm^-2 at a record-breaking sulfur loading of 8.9 mg cm^-2 at room temperature as well as high capacities with capacity retentions of ≈100% after 600 cycles at 0 and 60 °C. Multiscale structural engineered sulfur/carbon cathode has great potential to enable high-performance ASSLSBs for energy storage applications.

Rational Design of High-Performance PEO/Ceramic Composite Solid Electrolytes for Lithium Metal Batteries

Composite solid electrolytes (CSEs) with poly(ethylene oxide) (PEO) have become fairly prevalent for fabricating high-performance solid-state lithium metal batteries due to their high Li+ solvating capability, flexible processability and low cost. However, unsatisfactory room-temperature ionic conductivity, weak interfacial compatibility and uncontrollable Li dendrite growth seriously hinder their progress. Enormous efforts have been devoted to combining PEO with ceramics either as fillers or major matrix with the rational design of two-phase architecture, spatial distribution and content, which is anticipated to hold the key to increasing ionic conductivity and resolving interfacial compatibility within CSEs and between CSEs/electrodes. Unfortunately, a comprehensive review exclusively discussing the design, preparation and application of PEO/ceramic-based CSEs is largely lacking, in spite of tremendous reviews dealing with a broad spectrum of polymers and ceramics. Consequently, this review targets recent advances in PEO/ceramic-based CSEs, starting with a brief introduction, followed by their ionic conduction mechanism, preparation methods, and then an emphasis on resolving ionic conductivity and interfacial compatibility. Afterward, their applications in solid-state lithium metal batteries with transition metal oxides and sulfur cathodes are summarized. Finally, a summary and outlook on existing challenges and future research directions are proposed.

Sulfide-Based All-Solid-State Lithium-Sulfur Batteries: Challenges and Perspectives

Lithium-sulfur batteries with liquid electrolytes have been obstructed by severe shuttle effects and intrinsic safety concerns. Introducing inorganic solid-state electrolytes into lithium-sulfur systems is believed as an effective approach to eliminate these issues without sacrificing the high-energy density, which determines sulfide-based all-solid-state lithium-sulfur batteries. However, the lack of design principles for high-performance composite sulfur cathodes limits their further application. The sulfur cathode regulation should take several factors including the intrinsic insulation of sulfur, well-designed conductive networks, integrated sulfur-electrolyte interfaces, and porous structure for volume expansion, and the correlation between these factors into account. Here, we summarize the challenges of regulating composite sulfur cathodes with respect to ionic/electronic diffusions and put forward the corresponding solutions for obtaining stable positive electrodes. In the last section, we also outlook the future research pathways of architecture sulfur cathode to guide the develop high-performance all-solid-state lithium-sulfur batteries.

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

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

Solid/Quasi-Solid Phase Conversion of Sulfur in Lithium-Sulfur Battery

The lithium-sulfur (Li-S) battery is considered as one of the most promising options because the redox couple has almost the highest theoretical specific energy (2600 Wh kg^-1 ) among all solid anode-cathode candidates for rechargeable batteries. The "solid-liquid-solid" mechanism has become a dominating phase transformation process since it was first reported, although this cathode mode suffers from a tough "shuttle" phenomenon due to the dissolution of the soluble intermediate polysulfides generated during the charging-discharging process, which causes rapid loss of energy-bearing material and shortened lifespan. For decades, tremendous efforts have been made to restrict the shuttle effect. Changing sulfur conversion to "solid-solid" mode or "quasi-solid" mode, which successfully exceed the limit of the dissolution of the intermediates, and may address the root of the problem. In this review, the main focus is on the fundamental chemistry of the "solid-solid" and "quasi-solid" phase transformation of the sulfur cathode. First, the strategies of sulfur immobilization in "solid-liquid-solid" multi-phase conversions as well as the pivotal influence factors for the electrochemical conversion process are briefly introduced. Then, the different routes are summarized to realize the "solid-solid" and "quasi-solid" redox mechanisms. Finally, a perspectives on building high-energy-density Li-S batteries are provided.

Cl-Doped Li10SnP2S12 with Enhanced Ionic Conductivity and Lower Li-Ion Migration Barrier

All-solid-state lithium batteries based on sulfide solid electrolytes have attracted much attention because of their high ionic conductivity. Li₁₀SnP₂S₁₂ (LSPS) has the same structure as Li₁₀GeP₂S₁₂, and there is little difference in ionic conductivity between them, but the preparation cost of LSPS is lower. Here, Cl doping is used to improve the electrochemical stability of the LSPS to the anode and the Li-ion transport performance. Among them, Li_9.9SnP₂S_11.9Cl_0.1 had a high ion conductivity of 2.62 mS cm^-1 after cold pressure. On the crystal structure, X-ray diffraction Rietveld refinement indicated that the Cl-substituted portion S is successfully incorporated into the lattice of the LSPS, increasing Li-ion vacancies and reducing the distance between adjacent Li-ion distributed along the c-axis, these are conducive to Li-ion transmission. The temperature-dependent AC impedance experiment and density functional theory calculation show that doping with Cl makes Li_9.9SnP₂S_11.9Cl_0.1 have a lower activation energy. The assembled lithium symmetric batteries show that the doping of Cl promotes the stability of the interface between LSPS and the lithium metal anode. The charge-discharge tests of all-solid-state batteries using Li_9.9SnP₂S_11.9Cl_0.1 as electrolyte have confirmed that Cl doping can improve the electrochemical performance of LSPS, which have a higher specific capacity and cycle life.

Super Mg2+ Conductivity around 10-3 S cm-1 Observed in a Porous Metal-Organic Framework

We first report a solid-state crystalline “Mg²⁺ conductor” showing a superionic conductivity of around 10^–3 S cm^–1 at ambient temperature, which was obtained using the pores of a metal–organic framework (MOF), MIL-101, as ion-conducting pathways. The MOF, MIL-101⊃{Mg(TFSI)₂}_1.6 (TFSI^– = bis(trifluoromethanesulfonyl)imide), containing Mg²⁺ inside its pores, showed a superionic conductivity of 1.9 × 10^–3 S cm^–1 at room temperature (RT) (25 °C) under the optimal guest vapor (MeCN), which is the highest value among all Mg²⁺-containing crystalline compounds. The Mg²⁺ conductivity in the MOF was estimated to be 0.8 × 10^–3 S cm^–1 at RT, by determining the transport number of Mg²⁺ (t_Mg²⁺ = 0.41), which is the level as high as practical use for secondary battery. Measurements of adsorption isotherms, pressure dependence of ionic conductivity, and in situ Fourier transform infrared measurements revealed that the “super Mg²⁺ conductivity” is caused by the efficient migration of the Mg²⁺ carrier with the help of adsorbed guest molecules.

Highly Stable Halide-Electrolyte-Based All-Solid-State Li-Se Batteries

Solid-state Li-S and Li-Se batteries are promising devices that can address the safety and electrochemical stability issues that arise from liquid-based systems. However, solid-state Li-Se/S batteries usually present poor cycling stability due to the high resistance interfaces and decomposition of solid electrolytes caused by their narrow electrochemical stability windows. Here, an integrated solid-state Li-Se battery based on a halide Li₃ HoCl₆ solid electrolyte with high ionic conductivity is presented. The intrinsic wide electrochemical stability window of the Li₃ HoCl₆ and its stability toward Se and the lithiated species effectively inhibit degeneration of the electrolyte and the Se cathode by suppressing side reactions. The inherent thermodynamic mechanism of the lithiation/delithiation process of the Se cathode in solid is also revealed and confirmed by theoretical calculations. The battery achieves a reversible capacity of 402 mAh g^-1 after 750 cycles. The electrochemical performance, thermodynamic lithiation/delithiation mechanism, and stability of metal-halide-based Li-Se batteries confer theoretical study and practical applicability that extends to other energy-storage systems.

Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal-Sulfur and Selenium Batteries

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal-sulfur batteries remain challenged by several factors, including polysulfides' (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li-S and the emerging Na-S and K-S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li-S are relatively mature, less progress has been made with Na-S and K-S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal-selenium and the metal-selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal-sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li-S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure-battery electrochemical performance interrelations. Throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.

Hf-based UiO-66-type solid electrolytes for all-solid-state lithium batteries

Solid electrolytes composed of Hf-based metal–organic frameworks (MOFs) were synthesized with excellent cycling stabilities. Their ionic conductivities were up to 2.82 × 10−3 S cm−1 at room temperature.

Single-Crystal-Layered Ni-Rich Oxide Modified by Phosphate Coating Boosting Interfacial Stability of Li10 SnP2 S12 -Based All-Solid-State Li Batteries

All-solid-state lithium batteries (ASSLBs) adopting sulfide electrolytes and high-voltage layered oxide cathodes have moved into the mainstream owing to their superior safety and immense potential in high energy density. However, the poor electrochemical compatibility between oxide cathodes and sulfide electrolytes remains a challenge for high-performance ASSLBs. In this study, a nanoscale Li_1.4 Al_0.4 Ti_1.6 (PO₄ )₃ (LATP) phosphate coating is reasonably constructed on the surface of single-crystal LiNi_0.6 Co_0.2 Mn_0.2 O₂ particles to achieve cathode/electrolyte interfacial stability. The conformal LATP layer with inherent high-voltage stability can effectively suppress the oxidation decomposition of the electrolyte and demonstrate chemical inertness to both the oxide cathode and Li₁₀ SnP₂ S₁₂ electrolyte. ASSLBs with an LATP-modified cathode exhibited a high initial discharge capacity (152.1 mAh g^-1 ), acceptable rate capability, and superior cycling performance with a capacity retention of 87.6% after 100 cycles at 0.1 C. Interfacial modification is an effective approach for achieving high-performance sulfide-based ASSLBs with superior interfacial stability.

Congener Substitution Reinforced Li7P2.9Sb0.1S10.75O0.25 Glass-Ceramic Electrolytes for All-Solid-State Lithium-Sulfur Batteries

Glass-ceramic sulfide solid electrolytes like Li₇P₃S₁₁ are practicable propellants for safe and high-performance all-solid-state lithium-sulfur batteries (ASSLSBs); however, the stability and conductivity issues remain unsatisfactory. Herein, we propose a congener substitution strategy to optimize Li₇P₃S₁₁ as Li₇P_2.9Sb_0.1S_10.75O_0.25 via chemical bond and structure regulation. Specifically, Li₇P_2.9Sb_0.1S_10.75O_0.25 is obtained by a Sb₂O₅ dopant to achieve partial Sb/P and O/S substitution. Benefiting from the strengthened oxysulfide structural unit of POS₃^3- and P₂OS₆^4- with bridging oxygen atoms and a distorted lattice configuration of the Sb-S tetrahedron, the Li₇P_2.9Sb_0.1S_10.75O_0.25 electrolyte exhibits prominent chemical stability and high ionic conductivity. Besides the improved air stability, the ionic conductivity of Li₇P_2.9Sb_0.1S_10.75O_0.25 could reach 1.61 × 10^-3 S cm^-1 at room temperature with a wide electrochemical window of up to 5 V (vs Li/Li⁺), as well as good stability against Li and Li-In alloy anodes. Consequently, the ASSLSB with the Li₇P_2.9Sb_0.1S_10.75O_0.25 electrolyte shows high discharge capacities of 1374.4 mAh g^-1 (0.05C, 50th cycle) at room temperature and 1365.4 mAh g^-1 (0.1C, 100th cycle) at 60 °C. The battery also presents remarkable rate performance (1158.3 mAh g^-1 at 1C) and high Coulombic efficiency (>99.8%). This work provides a feasible technical route for fabricating ASSLSBs.

Double-Layered Multifunctional Composite Electrolytes for High-Voltage Solid-State Lithium-Metal Batteries

The need for safe storage systems with a high energy density has increased the interest in high-voltage solid-state Li-metal batteries (LMBs). Solid-state electrolytes, as a key material for LMBs, must be stable against both high-voltage cathodes and Li anodes. However, the weak interfacial contact between the electrolytes and electrodes poses challenges in the practical applications of LMBs. In this study, a double-layered solid composite electrolyte (DLSCE) was synthesized by introducing an antioxidative poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-10 wt % Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) to the cathode interface, whereas a lithium-friendly poly(oxyethylene) (PEO)-5 wt % LATP was made to come into contact with Li metal. Owing to the heterogeneous double-layered structure of the DLSCE, a high ionic transfer number (0.43), high ionic conductivity (1.49 × 10^-4 S/cm), and a wide redox window (4.82 V) were obtained at ambient temperature. Moreover, the DLSCE showed excellent Li-metal stability, thereby enabling the Li-Li symmetric cells to stably run for over 600 h at 0.2 mA/cm² with effective lithium dendrite inhibition. When paired with a high-voltage LiNi_1/3Co_1/3Mn_1/3O₂ cathode, the Li/DLSCE/NCM111 cell exhibited excellent electrochemical performance: long-term cyclability with 85% capacity retention could be conducted at 0.2C after 100 cycles corresponding to 100% Coulombic efficiencies.

Sulfur-Embedded FeS2 as a High-Performance Cathode for Room Temperature All-Solid-State Lithium-Sulfur Batteries

All-solid-state lithium-sulfur batteries employing sulfur electrodes and a solid electrolyte at room temperature are still a great challenge owing to the low conductivities of sulfur cathodes. In this work, we report room temperature all-solid-state lithium-sulfur batteries using thin sulfur layer-embedded FeS₂ (FeS₂@S) microsphere composites as active materials in the FeS₂@S-Li₁₀GeP₂S₁₂-Super P cathode electrode. Setting the cut-off voltage between 1.5 and 2.8 V, only lithiation-delithiation reactions between L₂FeS₂ and FeS_y and direct reaction between Li₂S and S will occur, which avoids large volume change of FeS₂ caused by the conversion reaction, leading to the structure integrity of FeS₂@S. The resultant batteries exhibit excellent rate and cyclic performances, delivering specific capacities of 1120.9, 937.2, 639.7, 517.2, 361.5, and 307.0 mA h g^-1 for the FeS₂@S composite cathode, corresponding to the normalized capacities of 1645.5, 1252.9, 782.5, 700.2, 478.4, and 363.6 mA h g^-1 for sulfur at 30, 50, 100, 500, 1000, and 5000 mA g^-1, respectively. Besides, they can retain the normalized capacity of 430.7 mA h g^-1 for sulfur at 1000 mA g^-1 after 200 cycles at room temperature.

Towards high-performance solid-state Li-S batteries: from fundamental understanding to engineering design

Solid-state lithium-sulfur batteries (SSLSBs) with high energy densities and high safety have been considered among the most promising energy storage devices to meet the demanding market requirements for electric vehicles. However, critical challenges such as lithium polysulfide shuttling effects, mismatched interfaces, Li dendrite growth, and the gap between fundamental research and practical applications still hinder the commercialization of SSLSBs. This review aims to combine the fundamental and engineering perspectives to seek rational design parameters for practical SSLSBs. The working principles, constituent components, and practical challenges of SSLSBs are reviewed. Recent progress and approaches to understand the interfacial challenges via advanced characterization techniques and density functional theory (DFT) calculations are summarized and discussed. A series of design parameters including sulfur loading, electrolyte thickness, discharge capacity, discharge voltage, and cathode sulfur content are systematically analyzed to study their influence on the gravimetric and volumetric energy densities of SSLSB pouch cells. The advantages and disadvantages of recently reported SSLSBs are discussed, and potential strategies are provided to address the shortcomings. Finally, potential future directions and prospects in SSLSB engineering are examined.