(Digital Presentation) All-Solid-State Lithium Batteries: From Materials and Interface Design to Practical Pouch Cell Engineering

All-solid-state lithium batteries (ASSLBs) have gained intensive attention because of their intrinsic safety and high energy density.1 However, significant interfacial challenges such as detrimental interfacial reactions, poor solid-solid ionic contact, and lithium dendrite growth have stymied the development of ASSLBs. Besides that, the large gap between fundamental research and practical engineering design has slowed down ASSLBs commercialization. Over the past five years, our group has been dedicated to the research and development of ASSLBs, with the aims of overcoming the interfacial challenges and pushing ASSLBs closer to commercialization. First, we have regulated the interfacial ion and electron transport via increasing the ionic conductivity of interfacial buffer layers,2 manipulating interfacial nanostructures,3, 4 using single-crystal cathodes,5 deciphering interfacial reaction mechanisms,6 and constructing artificial solid electrolyte interphases (SEI).7 Based on these advanced and innovative strategies, the large interfacial resistance was successfully eliminated. As a result, ASSLBs with sulfide electrolytes demonstrated both ultra-long cycling stability and high-rate performance. To transfer these viable technologies into practical application and bridging the large gap between laboratory research and practical full cells, we are committed to engineering solid-state pouch cells with competitive energy density and low cost. Recently, a solvent-free and cost-effective process was developed for fabricating ultra-thin inorganic solid electrolyte membranes as well as solid-state thick electrodes. Furthermore, a solid-liquid interface and a plastic crystal electrolyte were engineered to enable practical solid-state pouch cells with high energy density and excellent safety.8, 9 These works not only provide an in-depth understanding of interfacial mass and charge transport but also offer feasible strategies to commercialize practical solid-state pouch cells. References C. Wang, J. Liang, Y. Zhao, M. Zheng, X. Li, X. Sun*, Energy Environ. Sci. , 2021, doi:10.1039/d1ee00551k.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, X. Sun*. Adv. Energy Mater., 2021, 2100210. doi:10.1002/aenm.202100210.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, 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

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

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.

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.

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.

There is a growing interest in all-solid-state lithium batteries(ASLBs) for their safety and high energy density. However, the power density for ASLBs is still far away from satisfactory on the account of high interfacial resistance at electrode / solid electrolyte interface. For example, Garnet-type solid-state electrolytes (SSEs) are considered as a good choice for solid-state batteries, yet the interfacial issues with metallic Li limit their applications. In my group, we propose an ultra-simple and effective strategy to enhance the interfacial connection between garnet SSEs and Li metal just by drawing a graphite-based soft interface with a pencil[1]. Both experimental analysis and theoretical calculations confirm that the reaction between graphite-based interfacial layer and metallic lithium forms a lithiated connection interface with good lithium-ionic and electronic conductivity. Compared to the reported interfacial materials, the graphite material provides a soft interface with better ductility and compressibility. With the improvement by this soft interface, the impedance of symmetric Li cells significantly decreases from 1350 to 105Ωcm2 and the cell can cycle for over 1000hoursat a current density of 300 μA/cm2 at room temperature. Moreover, a solid-state battery with Li-metal anode, ternary cathode NCM523 and graphite-based interface modified garnet SSEs is fabricated and displays excellent rate capability and long cycling performance. In addition, LGPS-type materials show extremely high Li+ conductivity. But when in contact to Li metal, they can be reduced to produce Li2S, Li3P and Li-M alloy and form a mixed ionic and electronic conducting layer at the interface, which hinders the application of Li metal in such solid electrolyte system. We report on a simple approach for the modification of the interface between Li and Li10SnP2S12 sulfide solid electrolyte by utilizing ionic liquid[2]. Our study shows that the addition of 1.5M LiTFSI/Pyr13TFSI ionic liquid can not only promote intimate contact but can in-situ form a stable SEI layer at the interface between Li and solid electrolyte as well. A stable SEI layer instead of mixed conducting layer can prevent sulfide solid electrolyte from further decomposition and improve the cycle performance of batteries.

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

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.

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.

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

All solid-state lithium batteries (ASSLBs) employing inorganic solid electrolytes or solid polymer electrolytes are attracting increasing interests for electrochemical energy storage devices due to their advantages of high energy density, high safety, wide operating temperature range and long cycle life. However, the large interfacial resistance originated from the insufficient solid-solid contact at electrolyte/electrode interface hinders the development of ASSLBs. In addition, the interfacial stability and compatibility also greatly affect the electrochemical performance of batteries. To realize the ASSLB’s application requires significant research in solid electrolyte materials and solid electrolyte/electrode interfaces. This review summarizes the research and development in solid electrolyte materials and the interfaces of solid electrolyte/electrode, paying special attention to the challenges and progress for the studies of interface issues in ASSLBs. Based on the overview, we attempt to propose approaches to the issue by interface engineering and prospective developments of ASSLBs.

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.

All‐solid‐state lithium batteries (ASSLBs) are considered as an alternative solution to lithium‐ion batteries, because of their safety and high theoretical energy density. Argyrodite‐based solid‐electrolytes (SEs), Li6PS5X (X = Cl, Cl0.5Br0.5 or Br), are promising candidates for ASSLBs. Most of the previous reports have used Li6PS5Cl as the default SE composition. Here, the electrochemical behavior of three different argyrodites with Cl− or Br−, or both, as the halogen is systematically studied. Using LiNi0.6Co0.2Mn0.2O2 as a model cathode, the behavior of these SEs in ASSLB cells is also studied. SEs containing Br show higher near‐room‐temperature ionic conductivity (>2 mS cm−1) and the critical current density (≥1 mA cm−2) during Li plating/stripping, and are stable up to 5 V versus Li/Li+. Li6PS5Br gives the best electrochemical performance in terms of C‐rate and long‐term cycling among the three samples. Specifically, the cathode delivers an initial reversible capacity of 156 mAh g−1, with ≈27% irreversible capacity loss and 90% capacity retention over 100 cycles, and >99% Coulombic efficiency. It delivers ≈56 mAh g−1 at 10C, 36% of its initial capacity at 0.2C, whereas Li6PS5Cl and Li6PS5Cl0.5Br0.5 deliver only 20 and 46 mAh g−1 at 10C.

All-solid-state lithium batteries (ASSBs) are considered like the next generation of electrochemical energy storage devices because of their safety and their high energy density up to 400Wh/kg. The all-solid-state battery is composed of a positive electrode (e.g., NMC (Li(Ni1∕3Mn1∕3Co1∕3)O2)), a negative one (Li), and a solid electrolyte, which is the critical component, composed of inorganic compound and/or solid polymer electrolyte (SPE) [1]. On the one hand, SPE have the advantage of an easy shaping with the technique already used in the manufacture of batteries and their flexibility allows obtaining a good interface with the electrode materials [2]. On the other hand, inorganic compounds generally have high ionic conductivity (10-3S/cm), they are stable electrochemically vs Li/Li+ and their transport number is close to 1 to promote the diffusion/migration of Li+ ions only. In order to combine the advantages of both types of materials, hybrid materials have been designed [3].First, a new adaptable polymer matrix based on PEO derivatives has been developed. A solvent-free synthesis has been designed from liquid and commercial precursors Poly(ethylene glycol) methyl methacrylate (PEGM) and Poly(ethylene glycol) dimethacrylate (PEGDM). These latter were copolymerized with Lithium 3-[(trifluoromethane)sulfonamidosulfonyl] propyl methacrylate (MTFSLi). The anion TFSI- is thus grafted to the PEO network, allowing exclusively the diffusion of the Li+ ion. This polymer matrix can be thus classified as single-ion conductor. In addition, the proportions between PEGM and PEGDM, acting as crosslinker, can be easily tuned. The PEGDM proportion controls the cross-linking density which modifies not only the glass transition temperature (Tg), but also the storage modulus (E’) and the free volume, and consequently the ionic conductivity of the polymer matrix which is the main property required for SPE. Finally, a ratio of PEGM:PEGDM (80:20) allows obtaining homogeneous SPE, self-standing and soft at room temperature, amorphous with a Tg of -41°C. The EO/Li ratio was then modulated in single-ion networks with the MTFSLi proportion, and an optimum in ionic conductivity of 2.10-7 S/cm @25°C has been measured for EO/Li ratio of about 20. The transport number measured by the Bruce and Vincent method [4] was t+=1,0 for the single ion conductor, demonstrating the effective grafting of the counter anion. This value has been validated by measuring the diffusion coefficients of 7Li and 19F in NMR. To our knowledge, this is the first time a real unity transport number is reported in the literature for a polymer electrolyte. Moreover, the electrochemical stability of this single ion system extends from 0 to 6V vs Li+/Li. These experiments suggest the interest of using the single-ion polymer in the formulation of composite positive electrode with high potential cathode materials, due to its stability in potential. Li metal is considered the ultimate anode for Li-batteries. The long-term electrochemical stability has been evaluated in symmetric Li/polymer electrolyte/Li cell. The cell is cycled at a constant current density of 0.2 mA/cm2. After 200 h of cycling the voltage reaches solely 2V. Accordingly, the grafting of the anion to the network limits an overpotential in the cell, allowing a more stable system over time.Second, the garnet Li6.4La3Zr2Al0.2O12 (LLZO) of the oxide family was associated to the previous polymer matrix. This garnet presents a high conductivity (10-4 S/cm @ 25°C), a good chemical stability not only against lithium metal but also against air and humidity, which is not the case of sulphides homologues. A 3D-fibrous network obtained by the electrospinning method was carried out with a solution containing the inorganic precursors, a polymer and an appropriate solvent [5]. Then this membrane is calcined at 850°C to obtain the 3D fibrous network of LLZO. The resulting self-standing porous inorganic material (~80% of porosity) exhibits a conductivity of the order of 10-6 S/cm @25°C. It was then impregnated with the polymer matrix precursors by capillarity and following by a polymerization. A self-standing membrane as thin as 80 µm containing 9%vol of LLZO was obtained. The conductivity of this hybrid membrane is comparable to that of the polymer (10-7S/cm @ 25°C). The resulting hybrid is mainly polymeric where the ionic conduction was realized by the polymeric matrix and the inorganic acts as a mechanical reinforcement. Preliminary results on high content of LLZO hybrid will also be presented, where a synergy of the both components is observed.[1] Janek. Nature Energy. 2016. Vol 1(9)p.16141. [2] Yue. Energy Storage Materials. 2016. Vol 5p.139-164. [3] Zheng. Chem Soc Rev. 2020. Vol 49p.8790-8839. [4] Bruce. Solid State Ion. 1988. Vol 28–30p.918–922. [5] A. La Monaca. Electrochemistry Communications. 2019. Vol 104p.106483. Figure 1