All-Solid-state Lithium Battery with Sulfide Electrolyte: From Interface Design to Full Cell

All-solid-state lithium batteries (ASSLBs) have gained substantial attention because of their intrinsic safety and high energy density.1 However, the commercialization of ASSLBs has been stymied by insufficient ionic conductivity of solid-state electrolytes, significant interfacial challenges, as well as the large gap between fundamental research and practical engineering. Over the past several years, we have been dedicated to developing ASSLBs from solid electrolyte synthesis to interface design to engineering practical solid-state pouch cells. First, a wet-chemistry method with a low cost was proposed to produce solid-state electrolytes at the kilogram level with a high room-temperature ionic conductivity (> 1 mS.cm-1).2 Second, the interfacial challenges of ASSLBs have been well addressed via increasing the ionic conductivity of interfacial buffer layers,3 manipulating interfacial nanostructures,4, 5 using single-crystal cathodes,6 deciphering interfacial reaction mechanisms,7 and constructing artificial solid electrolyte interphases (SEI),8 which successfully boosted interfacial ion and electron transport kinetics.9 Resultantly, ASSLBs demonstrated superior electrochemical performance. Third, practical solid-state pouch cells with high energy density have been engineered. Recently, a solvent-free process was proposed to fabricate freestanding and ultrathin inorganic solid electrolyte membranes.10 Furthermore, a feasible solid-liquid transformable interface was devised to improve the solid-solid ionic contact and accommodate the significant volume change of solid-state pouch cells.11, 12 The resultant solid-state pouch cells successfully demonstrated high energy density and unparalleled safety. In summary, our research not only provides an in-depth understanding of solid electrolyte synthesis and rational interface design but also offers feasible strategies to commercialize ASSLBs with high energy density, low cost, and excellent safety. References C. Wang, J. Liang, Y. Zhao, M. Zheng, X. Li and X. Sun, Energy Environ. Sci., 2021, 14, 2577-2619.C. Wang, J. Liang, J. Luo, J. Liu, X. Li, F. Zhao, R. Li, H. Huang, S. Zhao, L. Zhang, J. Wang and X. Sun, Sci. Adv., 2021, 7, eabh1896.C. Wang, J. Liang, S. Hwang, X. Li, Y. Zhao, K. Adair, C. Zhao, X. Li, S. Deng, X. Lin, X. Yang, R. Li, H. Huang, L. Zhang, S. Lu, D. Su and X. Sun, Nano Energy, 2020, 72, 104686.C. Wang, X. Li, Y. Zhao, M. N. Banis, J. Liang, X. Li, Y. Sun, K. R. Adair, Q. Sun, Y. Liu, F. Zhao, S. Deng, X. Lin, R. Li, Y. Hu, T.-K. Sham, H. Huang, L. Zhang, R. Yang, S. Lu and X. Sun, Small Methods, 2019, 3, 1900261.C. Wang, J. Liang, M. Jiang, X. Li, S. Mukherjee, K. Adair, M. Zheng, Y. Zhao, F. Zhao, S. Zhang, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, C. V. Singh and X. Sun, Nano Energy, 2020, 76, 105015.C. Wang, R. Yu, S. Hwang, J. Liang, X. Li, C. Zhao, Y. Sun, J. Wang, N. Holmes, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, D. Su and X. Sun, Energy Storage Mater., 2020, 30, 98-103.C. Wang, S. Hwang, M. Jiang, J. Liang, Y. Sun, K. Adair, M. Zheng, S. Mukherjee, X. Li, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, J. Wang, C. V. Singh, D. Su and X. Sun, Adv. Energy Mater., 2021, 11, 2100210.C. Wang, Y. Zhao, Q. Sun, X. Li, Y. Liu, J. Liang, X. Li, X. Lin, R. Li, K. R. Adair, L. Zhang, R. Yang, S. Lu and X. Sun, Nano Energy, 2018, 53, 168-174.C. Wang, K. Adair and X. Sun, Acc. Mater. Res., 2022, 3, 21-32.C. Wang, R. Yu, H. Duan, Q. Lu, Q. Li, K. R. Adair, D. Bao, Y. Liu, R. Yang, J. Wang, S. Zhao, H. Huang and X. Sun, ACS Energy Lett., 2022, DOI: 10.1021/acsenergylett.1c02261, 410-416.C. Wang, Q. Sun, Y. Liu, Y. Zhao, X. Li, X. Lin, M. N. Banis, M. Li, W. Li, K. R. Adair, D. Wang, J. Liang, R. Li, L. Zhang, R. Yang, S. Lu and X. Sun, Nano Energy, 2018, 48, 35-43.C. Wang, K. R. Adair, J. Liang, X. Li, Y. Sun, X. Li, J. Wang, Q. Sun, F. Zhao, X. Lin, R. Li, H. Huang, L. Zhang, R. Yang, S. Lu and X. Sun, Adv. Funct. Mater., 2019, 29, 1900392.

Enabling high-performance all-solid-state lithium batteries with high ionic conductive sulfide-based composite solid electrolyte and ex-situ artificial SEI film

All-solid-state lithium batteries (ASSLBs) have attracted increasing attention due to their high safety and energy density. Among all corresponding solid electrolytes, sulfide electrolytes are considered to be the most promising ion conductors due to high ionic conductivities. Despite this, many challenges remain in the application of ASSLBs, including the stability of sulfide electrolytes, complex interfacial issues between sulfide electrolytes and oxide electrodes as well as unstable anodic interfaces. Although oxide cathodes remain the most viable electrode materials due to high stability and industrialization degrees, the matching of sulfide electrolytes with oxide cathodes is challenging for commercial use in ASSLBs. Based on this, this review will present an overview of emerging ASSLBs based on sulfide electrolytes and oxide cathodes and highlight critical properties such as compatible electrolyte/electrode interfaces. And by considering the current challenges and opportunities of sulfide electrolyte-based ASSLBs, possible research directions and perspectives are discussed.

Manipulating interfacial stability of LiNi0.5Co0.3Mn0.2O2 cathode with sulfide electrolyte by nanosized LLTO coating to achieve high-performance all-solid-state lithium batterie

Interface engineering of sulfide electrolytes for all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLBs) are attracting tremendous attention due to their improved safety and higher energy density. However, the use of a metallic lithium anode poses a major challenge due to its low stability and processability. Instead, the graphite anode exhibits high reversibility for the insertion/deinsertion of lithium ions, giving ASSLBs excellent cyclic stability but a lower energy density. To increase the energy density of ASSLBs with the graphite anode, it is necessary to lower the negative/positive (N/P) capacity ratio and to increase the charging voltage. These strategies bring new challenges to lithium metal plating and dendrite growth. Here, a nano-Ag-modified graphite composite electrode (Ag@Gr) is developed to overcome these shortcomings for Li5.5PS4.5Cl1.5-based ASSLBs. The Ag@Gr composite exhibits a strong ability to inhibit lithium metal plating and fast lithium-ion transport kinetics. Ag nanoparticles can accommodate excess Li, and the as-obtained Li-Ag alloy enhances the kinetics of the composite electrode. The ASSLB with the Li(Ni0.8Co0.1Mn0.1)O2 cathode and Ag@Gr anode achieves an energy density of 349 W h kg-1. The full cell using Ag@Gr with an N/P ratio of 0.6 also highlights the rate performance. This work provides a simple and effective method to regulate the charge transport kinetics of graphite anodes and improve the cyclic performance and energy density of ASSLBs.

In situ transmission electron microscopy for understanding materials and interfaces challenges in all-solid-state lithium batteries

The all-solid-state lithium battery (ASSLB) is widely regarded as one of the most promising battery systems for the future owing to its high energy density and enhanced safety. However, the spontaneous reaction between the lithium metal and solid-state electrolytes (SSEs) results in the formation of lithium dendrites, which impedes further progress in the use of lithium metal anodes in ASSLBs. Li-In-based anodes have been widely used to address Li anode/SSE interfacial challenges; however, their synthesis and cell fabrication compromise the applicability of ASSLBs. Herein, we explore aluminum as an anode in ASSLBs by dry mixing and investigate its compatibility with two typical types of SSEs: halide-based Li3InCl6 and sulfide-based Li5.4PS4.4Cl1.6, which show distinguished electrochemical behaviors. In halide-based ASSLBs, the continuous decomposition and reduction of Li3InCl6 cause the accumulation of indium metal at the interface between the Li3InCl6 SSE and the aluminum anode, which blocks Li-ion transport, causing cell impedance increase and rapid cell failure. By sharp contrast, a redox-active interphase is formed between the sulfide SSE and aluminum anode during the electrochemical lithiation/delithiation process. The interphase consisting of highly reversible redox intermediates addresses the limiting factor of the poor reversibility of Li-Al alloying, which accounts for the conventionally low Coulombic efficiency of Al anodes. This work aims to develop Al anodes for ASSLBs and sheds light on the significance of redox-active interphase in enabling highly reversible anodes in ASSLBs.

Oxide-ceramic based all-solid-state lithium batteries (ASSLB) can provide high intrinsic safety, extended operational temperature range, and high energy density. As the first two are intrinsic to the materials system, one prerequisite to obtain high energy densities with such ASSLBs is the manufacturing of composite cathodes. Preferably, cathode active material (CAM) and electrolyte should form an intertwined 3D-network with an intimate extended contact between two phases. The interface between the CAM and the electrolyte should feature high total surface area with a low impedance to enable an efficient charge transfer and transport and minimize the resistance losses in a battery.Composite solid cathode microstructures can be formed via a co-sintering of solid electrolyte and CAM powders. However, many CAMs such as Li[Ni1-x-yCoxMny]O2 (NMC), Li[Ni1-x-yCoxAly]O2 (NCA) or Li2NiMn3O8 (LMO) cannot withstand sintering temperatures required, for oxide class solid electrolytes as Li7La3Zr2O12 (LLZ) or Li1+xAlxTi2-x(PO4)3, to obtain sintered composite cathodes. Furthermore, the thermodynamic stability of CAMs significantly decreases in the presence of solid electrolytes. Still, several groups have demonstrated that thermodynamic limitations can be significantly lessened via a kinetic control of the process such as reduction of reaction times and a careful control of powder morphology during ceramic sintering process.Following this work, we now demonstrate that FAST/SPS enables fabrication of different solid-state battery components within minutes such as a dense LLZ separator layer with a high ionic conductivity, a dense dual LiCoCO2 (LCO)/LLZ composite cathode without any interfacial reactions, and an integrated cathode half-cell consisting of a composite cathode and a LLZ separator layer at temperatures as low as 675 – 800 °C. Analyzing the structure, morphology, and electrochemical performance of the obtained components, we conclude that the impurities (carbonates) on the surface of LLZ powder play a decisive role in the formation of high-quality interfaces and the minimization of porosity. Furthermore, these impurities decrease the ionic conductivity at low sintering temperature and deteriorate the cycling stability of an ASSLB. High areal capacity of up to 4.0 mA h/cm2 at 80 °C with a constant current of 50 µA/cm2 and a good utilization of LCO was achieved for ASSLB with LLZ powders free of surface impurities. FAST/SPS can therefore open new processing windows for ceramic-based ASSLBs to alleviate the problem of interphase formation.

Outstanding interfacial issues exist between oxide cathodes and sulfide electrolytes in all‐solid‐state lithium batteries (ASSLBs), while high‐capacity Li‐rich sulfide cathodes are gaining attention for application. Herein, a sulfide cathode active material Li2TiS3 (LTS) that is chemically compatible with sulfide solid electrolytes, is used in high‐performance Li6PS5Cl‐based ASSLBs at room temperature. The batteries demonstrate a maximum discharge capacity of 423.2 mAh g−1 (910 Wh kg−1 based on Li2TiS3) with 95% capacity retention after 100 cycles at 0.1 C (0.33 mA cm−2). Traces of elemental sulfur on the surface of LTS are mainly responsible for the excessive Li‐intercalation and the capacity exceedance. The Li6PS5Cl is also found to offer a nonnegligible capacity (at least 27% of excess capacity) by comparing the Li6PS5Cl‐based and Li3YCl6‐based cells using Li2TiS3 as cathode active material. During long cycling, the amorphization and degradation of Li2TiS3 and Li6PS5Cl cause capacity decay. The electrochemical kinetics of Li6PS5Cl‐based cells are evaluated as a reference to further exploit the potential of Li2TiS3 material for practical applications in ASSLBs. Overall, this superior Li‐rich sulfide material is an attractive alternative to oxide cathodes for the development of high‐performance ASSLBs.

Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10-8 S cm-1 ) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li-Li symmetric cells with 30 times longer cycling life and Li-LiCoO2 full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li-LiCoO2 ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm-2 . The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity.

Benefiting from the significantly improved energy density and safety, all-solid-state lithium batteries (ASSLBs) are considered to be one of the most promising next-generation energy technologies. Their practical applications, however, are strongly impeded by Li dendrite formation. Despite this recognized challenge, a comprehensive understanding of the Li dendrite nucleation and formation mechanism remains elusive. In particular, the initial locations of Li dendrite formation are still ambiguous: do Li clusters form directly at the Li anode surface, inside the bulk solid electrolyte (SE), or within the solid-electrolyte interphase (SEI)? Here, based on the deep-potential molecular dynamics simulations combined with enhanced sampling techniques, we investigate the atomic-level mechanism of Li cluster nucleation and formation at the Li anode/SE interface. We observe that an isolated Li cluster initially forms inside the SEI between the Li6PS5Cl SE and the Li metal anode, located ∼1 nm away from the Li anode/SEI boundary. The local electronic structure of the spontaneously formed SEI is found to be a key factor enabling the Li cluster formation within the SEI, in which a significantly decreased band gap could facilitate electronic conduction through the SEI and reduce Li+ ions to metallic Li atoms therein. Our work provides atomic-level insights into Li-dendrite nucleation at anode/SE interfaces in ASSLBs and could guide future design for developing Li-dendrite-inhibiting strategies.

The demand for next generation secondary batteries with high energy density and safety has increased significantly with the rapid adoption of electric vehicles and energy storage systems. Among the various candidates, all-solid-state lithium batteries (ASSLBs) have attracted significant interest due to their potential to replace flammable organic electrolytes with solid-state electrolytes, thereby enhancing thermal stability and safety during operation.Silicon (Si), with its high theoretical capacity of 3,579 mAh g-1, is a strong candidate for high-capacity anodes in ASSLBs. However, its practical application remains challenging due to severe volume expansion during cycling, mechanical degradation, unstable interfaces, and poor intrinsic electronic conductivity. These issues become more critical in solid-state systems, where interfacial resistance can dominate overall performance. In order to address these issues, strategies for doping silicon so as to tailor its electrical properties have been proposed. In contrast to the existing range of methods for using conductive materials, the deposition method through doping has the potential to enhance the electrical conductivity of the active material itself, thus avoiding the need for additional conductive materials and improving the energy density more effectively.In this study, phosphorus-doped silicon anodes were fabricated via thin-film deposition and integrated into ASSLBs with sulfide-based solid electrolytes. A systematic analysis was conducted to investigate the impact of doping on electronic conductivity and interfacial characteristics, through rate capability and long-term cycling tests. The findings of this study are expected to provide insight into the design of doped silicon-based anodes and contribute to the development of practical ASSLBs with high capacity and durability.

Sulfide-based solid electrolyte such as Li6PS5Cl (LPSCl) is unstable in contact with Li metal electrode due to decomposing to by-product resulting in poor performance. Therefore, the introduction of an interlayer to suppress reactivity is essential. In this study, instead of an interlayer, an oxide/polymer composite electrolyte was applied to suppress side reactions, while a sulfide-based electrolyte was used at the cathode to improve interfacial control between the cathode and the electrolyte. All-solid-state lithium batteries (ASLBs) were prepared by applying sulfide-based solid electrolyte (argyrodite, Li6PS5Cl) including NCM424, polyvinylidene fluoride (PVDF), and Super-P in a composite cathode layer, and a composite solid electrolyte (CSE) layer by mixing an oxide-based solid electrolyte (garnet, Al-doped Li7La3Zr2O12 (LLZO)), polymer (PEO, polyethylene oxide) and lithium metal as the anode. In this study, NCM424 powder was coated with LiNbO3 to prevent chemical reaction with the sulfide electrolyte. As the PVDF binder was applied to the cathode of the ASLB, the discharge capacity of the cell was approximately 163 mAh g−1 at 70 °C, 0.1 C, and 4.2 V cut-off and its capacity retention was 83% after 50 cycles. The effects of the PVDF were evaluated using both pouch-type cells. The capacity and cycle retention are greatly dependent on the PVDF content of the cathode materials and the drying temperature during the fabrication of the cathode. When the cathode with PVDF binder was dried at 130 °C, initial cycling was required for activation of the pouch cell, and it was possible to overcome this by adding a plasticizer.

All-solid-state lithium batteries (ASSLB) are promising candidates for next-generation energy storage devices. Nevertheless, the large-scale commercial application of high energy density ASSLB with the polymer electrolyte still faces challenges. In this study, a thin solid polymer composite electrolyte (SPCE) is prepared through a facile and cost-effective strategy with an infiltration of thermoplastic polyurethane (TPU), lithium salt (LiTFSI or LiFSI), and halloysite nanotubes (HNTs) in a porous framework of polyethylene separator (PE) (TPU–HNTs–LiTFSI–PE or TPU–HNTs–LiFSI–PE). The composition, electrochemical performance, and especially the effect of anions (TFSI− and FSI−) on cycling performance are investigated. The results reveal that the flexible TPU–HNTs–LiTFSI–PE and TPU–HNTs–LiFSI–PE with a thickness of 34 μm exhibit wide electrochemical windows of 4.9 and 5.1 V (vs. Li+/Li) at 60 ℃, respectively. Reduction in FSI− tends to form more LiF and sulfur compounds at the interface between TPU–HNTs–LiFSI–PE and Li metal anode, thus enhancing the interfacial stability. As a result, cell composed of TPU–HNTs–LiFSI–PE exhibits a smaller increase in interfacial resistance of solid electrolyte interphase (SEI) with a distinct decrease in charge-transfer resistance during cycling. Li|Li symmetric cell with TPU–HNTs–LiFSI–PE could keep its stable overpotential profile for nearly 1300 h with a low hysteresis of approximately 39 mV at a current density of 0.1 mA cm−2, while a sudden voltage rise with internal cell impedance-surge signals was observed within 600 h for cell composed of TPU–HNTs–LiTFSI–PE. The initial capacities of NCM|TPU–HNTs–LiTFSI–PE|Li and NCM|TPU–HNTs–LiFSI–PE|Li cells were 149 and 114 mAh g−1, with capacity retention rates of 83.52% and 89.99% after 300 cycles at 0.5 C, respectively. This study provides a valuable guideline for designing flexible SPCE, which shows great application prospect in the practice of ASSLB.