Facile fabrication of solution-processed solid-electrolytes for high-energy-density all-solid-state-batteries by enhanced interfacial contact

Lithium-ion batteries (LIBs) using organic liquid electrolytes have been applied in portable devices such as laptops and cellular phones owing to its wide electrochemical stability, high voltages, and excellent energy density. LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode have attracted significant interest as the cathode materials for LIBs owing to their high capacity, excellent rate capability and low cost. NCM523 cathode materials have a disadvantage of structural instability, which caused by the reduction of Ni ions releases oxygen from the crystal structure at the high temeprature or high charged state, which can lead thermal runaway by reacting with the flammable electrolyte. The use of organic liquid electrolytes in LIBs raises safety issues due to its flammable character and the impact on the explosion is greater in particular for relatively large systems such as electrical vehicles and grid storage. To overcome the safety issues, solid state batteries (SSBs) using a non-combustible solid state Li-ion conductor are regarded as the realistic alternative to prohibit the leakage of liquid electrolytes and the resultant fire hazards. However, due to the large resistance in the electrode-electrolyte interface, the capacity retention and cycle effieciency of the SSBs become worse. Previous studies on SSBs have been mainly focused on developing solid state electrolytes with high ion conductivity. Despite growing interest in stability, the systematic studies of safety of SSBs depending on the type of electrolyte has never been evaluated so far. It is necessary for understanding structural deformations on the cathode material in the effects of the reactions beween the electrode and various types of electrolytes, which is essential for ensuring the safety of the batteries. In this study, we investigate the structural degradation and thermal stability on NCM523 cathode materials by taking an advantage of in situ transmission electron microscopy (TEM) in various electrolyte conditions, including conventional liquid electrolyte, poly(ethylene oxide) (PEO) complexes with LiClO4 (PEO-based solid electrolyte), and PEO/LiClO4/Li1.3Al0.3Ti1.7(PO4)3 (LATP) composite electrolyte (PEO-inorganic composite electrolyte). Since the LATP oxide electrolyte has brittleness and the PEO has flexibility, it adopts a composite electrolyte having inorganic and organic phases with good interface contact with the cell electrode. A cell composed of each electrolyte was prepared and charged with cut-off voltages of 3.9 V and 4.3 V at a rate of 0.05 C after the second formation process for stabilzing the cell. The capacity at the same cut-off voltage decreases in the order of conventional liquid electrolyte, PEO-based solid electrolyte, and PEO-inorganic composite electrolytes. To understand the thermal stability and the degradation mechanism, modifications in selected-area electron diffraction (SAED) and electron energy-loss (EEL) spectra of oxygen K-edge and transition metal (Ni, Co, Mn) L-edges of each of charged NCM523 cathode materials are monitored in real time at the range from room temperature to 300°C. Our work demonstrated that contact resistance at the interface between the electrode and electrolyte is important factor. This work provides important information on the relationship with structural deformation and thermal stability of the cathode materials, which is an essential part of the rational design to develope for high engergy densities and safe SSBs. All the details will be available at the meeting. Acknowledgement This work was supported by the Korea Institute of Science and Technology (KIST) Institutional Program (Project 2E28142). This work was also supported by the National Research Foundation of Korea (NRF) grant (No. 2018R1A2B2005205).

All-solid-state lithium-ion batteries (ASSLIBs) have been considered suitable alternatives to commercial lithium-ion batteries (LIBs) in the aspect of safety issues that come from the use of inflammable solid electrolytes to replace organic flammable electrolytes. Nevertheless, there apparently remains much room for a better understanding of their properties and behaviors in order to upgrade their performance to reach the practical application level. Ni-rich layered oxides, LiNi1-x-yCoxMnyO2 (NCM), are promising cathodes for high-energy ASSLIBs because of their high capacities and redox potentials, and low material cost when compared with conventional LiCoO2. However, certain challenges associated with their use in ASSLIBs must be addressed for their effective use and industrialization. In particular, the structural integrity of the NCM electrodes during the long-term charge/discharge process suffers from the formation of an intergranular and/or intragranular cracking behavior. These microcracks are initiated at the grain boundaries from the anisotropic chemical strain of the randomly oriented polycrystal (PC) primary cathode particles. Solid evidence behind the electrochem-mechanical breakdown of an NCM cathode with liquid electrolytes has been well discussed and reported in the literature. However, the breakdown in ASSLIBs may not obey as same as in the liquid-electrolyte LIBs and display exclusive mechanics-oriented material damage in the presence of rigid solid-state electrolytes (SSEs). The primary objective of this research is to gain a deeper understanding of various cracking modes in ASSLIBs, which we believe is instrumental to improving the lifespan and cell performance as a whole. ForASSLIBs, stacking pressures greater than 100 MPa under battery operation are currently commonly used. The use of high stacking pressure increases manufacturing and usage difficulties and overall cost. Lowering the battery-operation stacking pressure, for example to the level of the liquid-electrolyte batteries, will certainly facilitate the wider applications of ASSLIBs. In this context, composite cathodes consisting of a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and brittle Li3InCl6 (LIC) SSE have been assessed for ASSLIB applications under low operation stacking pressure (coin-cell configuration; ~2.0 MPa). The study reveals the effects of material and structural characteristics of the composite cathode, including the NCM particle size and size distribution, active-material spatial distribution, particle crystallinity (polycrystal or single-crystal), and electrochemical operation parameters (voltage range, current rates) on the cycle stability of the ASSLIBs as a result of the electrochem-mechanical behaviors of the oxide cathode. Meanwhile, a novel solvent-based synthesis process of LIC for achieving high-density cathodes is introduced.

Since the electrochemical potential of lithium metal was systematically elaborated and measured in the early 19th century, lithium-ion batteries with liquid organic electrolyte have been a key energy storage device and successfully commercialized at the end of the 20th century. Although lithium-ion battery technology has progressed enormously in recent years, it still suffers from two core issues, intrinsic safety hazard and low energy density. Within approaches to address the core challenges, the development of all-solid-state lithium-ion batteries (ASSLBs) based on halide solid-state electrolytes (SSEs) has displayed potential for application in stationary energy storage devices and may eventually become an essential component of a future smart grid. In this Review, we categorize and summarize the current research status of halide SSEs based on different halogen anions from the perspective of halogen chemistry, upon which we summarize the different synthetic routes of halide SSEs possessing high room-temperature ionic conductivity, and compare in detail the performance of halide SSEs based on different halogen anions in terms of ionic conductivity, activation energy, electronic conductivity, interfacial contact stability, and electrochemical window and summarize the corresponding optimization strategies for each of the above-mentioned electrochemical indicators. Finally, we provide an outlook on the unresolved challenges and future opportunities of ASSLBs.

All-solid-state lithium-ion batteries (ASSBs) are expected to represent a future alternative compared to conventional lithium-ion batteries with liquid electrolytes (LIBs). The excellent performance of today’s LIBs relies to a large extent on the development of liquid electrolytes that form stable, or at least slowly degrading, interfaces (interphases) with both anodes and cathodes. This has not yet been achieved in ASSBs, and degradation of anode and cathode interfaces of solid electrolytes (SE) is one of the key issues to be solved. Unlike investigations of liquid/solid interfaces, the degradation of interfaces between the solid electrodes and the SE is challenging since (i) solid/solid interfaces are less easily accessed analytically, (ii) interface compounds may contribute only in very low concentrations to spectroscopic or spectrometric data, and (iii) a high spatial resolution is required to determine the local component distribution. Typically, solid/solid interface investigations are primarily based on electrochemical experiments, diffraction studies, electron microscopy, or on theoretical calculations to obtain sufficient information. Interestingly, the prospects of recent advanced analytical tools such as time-of-flight secondary-ion mass spectrometry (ToF-SIMS) are not fully exploited yet; therefore, we demonstrate in this paper that ToF-SIMS can provide valuable insights into the interphase composition and microstructure of ASSBs. For this purpose, we combine local compositional information from ToF-SIMS and complementary X-ray photoelectron spectroscopy measurements to characterize and visualize the degradation mechanism in the LiNi0.6Co0.2Mn0.2O2/Li6PS5Cl-composite cathode of an ASSB. Our results indicate that sulfates and phosphates play an important role in the formation of a solid electrolyte interface (SEI), whereas transition-metal chlorides, phosphides, and sulfides can be neglected. Furthermore, to the best of our knowledge, we show for the first time the local structure and morphology of the SEI layer on the basis of information about the chemical composition using ToF-SIMS analysis.

Tremendous effort has been dedicated to the research on all-solid-state lithium-ion batteries (ASSLIBs) using oxide-type solid electrolytes instead of flammable organic liquid electrolytes. ASSLIBs using oxide-based solid electrolytes are expected to be used for a wide range of applications because of their excellent safety, lifetime, and reliability. Despite those advantages, oxide-type ASSLIBs still have challenges before achieving widespread use. In conventional liquid-type lithium-ion batteries, electrolyte/electrode interfaces can be spontaneously formed by injecting electrolyte solution. However, co-sintering of solid electrolytes and electrode materials at high temperatures are required to form highly ion conducting interfaces with maintaining their intrinsic crystal structures and physicochemical properties [1, 2]. However, they often react with each other, resulting in the formation of highly resistive interlayers and/or decomposition of substances [1]. Therefore, it is very important to understand and control the reaction of solid electrolytes and electrode materials for developing a rational process to form a highly ion conducting interfaces from a variety of materials with suppressing the undesired side reactions.In the present study, Li1.3Al0.3Ti1.7(PO4)3 (LATP), which is one of the oxide-based solid electrolytes with a relatively high ionic conductivity at room temperature, is co-sintered with positive electrode materials, LiFePO4 (LFP) and LiNiPO4 (LNP) at various temperatures and atmospheres, and the reaction products were quantitatively analyzed by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), energy-dispersive X-ray spectroscopy (EDS), and thermogravimetry-differential thermal analysis (TG-DTA).When LFP/LATP composites were co-sintered in air, LFP started to decompose at a relatively low temperature; FePO4 at 300°C and Li3Fe2(PO4)3 in the temperature range of 500 – 700°C are the major products and Fe2O3 is the minor product existing in the temperature range of 300 – 800°C. Although LATP was remained unchanged up to 700°C, it reacted with Li3Fe2(PO4)3 to form a Fe-doped LATP, Lix(Al,Ti,Fe)2(PO4)3. In an Ar/H2 atmosphere, LFP and LATP retained their crystal structures up to 650°C, and they started to react with each other at 700°C to form Fe2P2O7 and Fe-doped Liy(Al,Ti,Fe)2(PO4)3. In contrast to LFP/LATP, both LNP and LATP retained their crystal structures throughout the temperature range when LNP/LATP composites were co-sintered in air. In an Ar/H2 atmosphere, however, various products such as Ni12P5 and Li4P2O7 at 500°C, Ni2P at 600°C were formed as well as Li-rich Liz(Al,Ti)2(PO4)3 at 800°C. Those reaction products were compared with the prediction based on thermodynamic calculations, and their consistence and contradiction were discussed based on the validity of thermodynamic parameters of reference materials in database, diffusion of metal ions and releasing oxygen and water during co-sintering.Reference list[1] F. Ichihara, S. Miyoshi, T. Masuda, Phys. Chem. Chem. Phys., 24, 25878 (2022)[2] F. Ichihara, K. Niitsu, Y. Tanaka, Y. Niwa, K. Mitsuishi, S. Miyoshi, T. Ohno, T. Masuda, J. Phys. Chem. C, 127, 15043 (2023)

<p indent="0mm">Since the commercialization of lithium-ion batteries in the 1990s, lithium-ion batteries have been successfully applied in portable electronics, electric vehicles, and grid energy storage. Although current organic liquid electrolytes have high ionic conductivities, they are inherently flammable, volatile, and prone to leakage. Moreover, severe side reactions and dendrite growth on the surface of the lithium anode during the charge-discharge process can cause safety hazards, which greatly impede their applications in lithium metal batteries. Solid electrolytes, including inorganic solid electrolytes and polymer electrolytes, are regarded as effective alternatives to organic liquid electrolytes for the construction of lithium metal batteries with high energy density and safety. Among them, solid polymer electrolytes offer excellent flexibility, processability, and interfacial compatibility over inorganic solid electrolytes, and they are extraordinarily promising for lithium metal batteries with high energy density and safety. Ideal solid polymer electrolytes should have following features: (1) High ionic conductivity (&gt; <sc>10 ^–4 S cm ^–1) </sc> at room temperature; (2) high lithium ion transference number (~1) to reduce the concentration polarization and improve the rate performance of batteries; (3) intimate contact at the electrode/electrolyte interfaces; (4) wide electrochemical window <sc>(&gt;4.5 V</sc> vs. Li/Li ⁺) to match high-voltage cathodes and improve the energy density of batteries; (5) good mechanical stability to resist processing, buffer electrode volume change and inhibit dendrite growth; (6) good thermal stability to withstand environmental changes. Generally, the ionic conductivity of pure solid polymer electrolytes at room temperature is low <sc>(~10 ^–6 S cm ^–1). </sc> Researchers have tried to improve the ionic conductivities by adjusting the lithium salt concentration, such as developing “polymer-in-salt” solid electrolytes. However, increasing the concentration of lithium salt leads to the deterioration of the mechanical strength. Strategies such as developing novel lithium salts, modifying polymer matrix, and incorporating inorganic fillers into solid polymer electrolytes are proposed to promote ionic conductivities of solid polymer electrolytes. In particular, composite polymer electrolytes, fabricated by dispersing a certain amount of inorganic fillers into solid polymer electrolytes, have improved ionic conductivities without sacrificing their mechanical performances. Poor interfacial property between electrodes and electrolytes is also a critical issue for solid polymer electrolytes. On one hand, poor and uneven solid/solid contacts at the electrode/electrolyte interfaces lead to high resistance and sluggish ionic transport kinetics. Furthermore, the volume change of the positive and negative electrodes in the charge/discharge process deteriorates the interfacial contacts, blocks the ion and electron transport through the interfaces, and greatly reduces the electrochemical reaction kinetics. On the other hand, the electrochemical windows of solid polymer electrolytes are usually narrow <sc>(＜4.5 V).</sc> During cycling, redox reactions are prone to occur at the electrode/electrolyte interfaces, causing battery failure. Solid polymer electrolytes have also poor thermal and mechanical stabilities. Therefore, design and synthesis of polymer-based solid electrolytes with excellent comprehensive performances and construction of fast and stable ion transport channels at the electrolyte/electrode interfaces are of great significance for the successful development of solid-state lithium metal batteries. This paper presents a brief review of the research progress in solid polymer electrolytes from two aspects: Improving the ionic conductivities of solid polymer electrolytes and enhancing the interfacial performance at electrolyte/electrode interfaces. First, targeted optimization strategies on ionic conductivities of solid polymer electrolytes, including constructing continuously aligned ionic transport paths and shortening the ionic transport distance, are summarized. Second, interface optimization strategies, including constructing wetting interfaces and synthesizing asymmetric electrolytes, are presented to reduce the interface resistance and improve the interfacial contact. Finally, perspectives on the development of solid polymer electrolytes and high-performance solid-state lithium metal batteries are discussed, and key research directions and advanced test methods are proposed. This review may provide a comprehensive understanding and further guidance for not only the material design of solid polymer electrolytes, but also the structural design of lithium metal batteries with favorable electrochemical and interfacial performances.

All-solid-state lithium-ion batteries (ASSLIBs) without organic liquid electrolytes have attracted considerable attention as a solution to existing safety issues. Si is the most promising anode active material for increasing the energy density of such batteries owing to its high theoretical capacity. However, the stress relaxation of Si with large structural fluctuations is a major challenge to its practical use. In the present study, nanoporous Si particles and a sulfide-based solid electrolyte are composited to accommodate the volumetric expansion. To the best of our knowledge, this is a novel approach in the case of ASSLIBs. We find that the capacity retention of highly dispersed Si composite anodes is 80% up to 150 cycles. Such excellent cyclability is explained by our results, which suggest the following microstructural behavior. The pores in the Si particles act as buffer regions for large volume changes. In addition, the strains arising from the slightly expanded Si particles are relieved by the elasticity of the surrounding sulfide-based solid electrolyte. In summary, this study is a significant step toward the development of high-performance ASSLIBs for various applications.

Halide solid electrolytes have been considered as the most promising candidates for practical high-voltage all-solid-state lithium-ion batteries (ASSLIBs) due to their moderate ionic conductivity and good interfacial compatibility with oxide cathode materials. Aliovalent ion doping is an effective strategy to increase the ionic conductivity of halide electrolytes. However, the effects of ion doping on the electrochemical stability window of halide electrolytes and carbon additive on electrochemical performance are still unclear by far. Herein, a series of Zr-doped Li3-xEr1-xZrxCl6 halide solid electrolytes (SEs) are synthesized through a mechanochemical method and the effects of Zr substitution on the ionic conductivity and electrochemical stability window are systematically investigated. Zr doping can increase the ionic conductivity, whereas it narrows the electrochemical stability window of the Li3ErCl6 electrolyte simultaneously. The optimized Li2.6Er0.6Zr0.4Cl6 electrolyte exhibits both a high ionic conductivity of 1.13 mS cm-1 and a high oxidation voltage of 4.21 V. Furthermore, carbon additives are demonstrated to be beneficial for achieving high discharge capacity and better cycling stability and rate performance for halide-based ASSLIBs, which are completely different from the case of sulfide electrolytes. ASSLIBs with uncoated LiCoO2 cathode and carbon additives exhibit a high discharge capacity of 147.5 mAh g-1 and superior cycling stability with a capacity retention of 77% after 500 cycles. This work provides an in-depth understanding of the influence of ion doping and carbon additives on halide solid electrolytes and feasible strategies to realize high-energy-density ASSLIBs.

<p indent="0mm">In order to deal with the increasingly severe global energy crisis as well as serious environmental pollution, it is urgent to develop new energy resources. Although lithium-ion batteries have only been successfully introduced into the market since 1990s, there is still an exponentially growing demand for lithium-ion batteries all over the world. As a considerable novel energy source, lithium-ion batteries have significant potential, which is widely used in electric vehicles, energy-storage systems, metallurgy, ceramic production, glass manufacturing and aviation fuel industries. Among them, the solid-state lithium-ion batteries (SSLIBs) represent a promising evolution in battery technology, offering superior safety, energy density, and longevity compared to conventional liquid electrolyte batteries. Traditional lithium-ion batteries, which use liquid electrolytes, suffer from safety issues such as leakage, flammability and thermal runaway. SSLIBs replace these liquid electrolytes with solid electrolytes, mitigating these risks and enabling higher energy densities due to the ability to accommodate lithium metal anodes. The SSLIB consists of a positive electrode, a negative electrode and a solid electrolyte. Compared with liquid electrolytes, solid electrolytes avoid the direct contact between positive electrodes and negative electrodes, fundamentally eliminating the risk of lithium dendrites piercing the separator, so as to enhance the safety of lithium batteries greatly. Furthermore, the SSLIBs are expected to be a hot spot in future lithium battery research due to the advantages of high energy density, wide operating voltage range and long cycle life. Advancements in SSLIBs technology are crucial for the next generation of electric vehicles, portable electronics, and large-scale energy storage systems, pushing the boundaries of battery performance, safety and sustainability. Solid electrolytes are regarded as the key component of SSLIBs, serving dual functions as both separators and electrolytes. The currently developed solid electrolytes can be divided into two categories: Polymer solid electrolytes and inorganic solid electrolytes, in which the oxide solid electrolytes, as the earliest developed inorganic solid electrolytes, play an indispensable role in the development of solid-state battery industry. The typical oxide solid electrolytes, including sodium super ionic conductor (NASICON), garnet (LLZO), inorganic perovskite (LLTO), and LiPON films, are reviewed in this paper. NASICON, for example, is known for its high ionic conductivity and structural stability. Garnet-type electrolytes, such as LLZO, possess high ionic conductivity and chemical stability with lithium. Inorganic perovskite (LLTO) provides a good balance between ionic conductivity and mechanical strength. LiPON films, widely used in thin-film batteries, have excellent electrochemical stability and compatibility with lithium metal. In addition, the crystal structures and ion-transport mechanism, the solutions to improve conductivity and measures to improve the compatibility between electrodes and electrolytes are introduced, along with a comparation of oxide solid electrolytes. Finally, several suggestions for future development directions are proposed. These include enhancing the ionic conductivity of solid electrolytes, improving the interface compatibility between the electrolytes and electrodes, and developing cost-effective and scalable manufacturing processes. Additionally, further research is needed to understand the degradation mechanisms and long-term stability of solid-state batteries. These recommendations aim to provide a more comprehensive reference for ongoing and future research on oxide solid electrolytes, supporting the broader goal of advancing solid-state lithium battery technology.

Enabling fast-charging capability for all-solid-state lithium-ion batteries

Development of lithium-ion batteries for automotive applications such as electric vehicles (EVs) has been focused on enhancement of energy density, power, safety, and life. In particular, all-solid-state batteries have been extensively studied in order to respond to these demands. However, the solid electrolytes such as sulfide or oxide materials have important subjects for practical uses. Sulfide solid electrolytes have low chemical stability in air and low mechanical strength for thin separator. Oxide solid electrolytes have low ionic conductivity and large resistance at interfaces between active material and solid electrolyte. We proposed a thin hybrid electrolyte system instead of solid electrolytes [1]. The thin hybrid electrolyte consisting of lithium-ion conducting solid particles of a cubic garnet-type Li7La3Zr2O12 (LLZ) and a gel polymer electrolyte exhibits smaller activation energy for ionic conductivity than a gel polymer electrolyte without LLZ. The fabricated cells using the hybrid electrolyte show high-rate charge-discharge performance [1, 2]. We have also investigated electrochemical properties of other hybrid electrolytes consisting of NASICON-type Li-Al-Ti-P-O (LATP) particles wetted with liquid electrolytes of LiPF6-PC/DEC. Figure 1 shows fast-charge performance of 1 Ah TiNb2O7/LiNi0.5Co0.2Mn0.3O2 cells using the hybrid and the liquid electrolyte at 10 C rate. The charge performance of the cell using the hybrid electrolyte was significantly superior to that of the cell using the liquid electrolyte, which indicates the existence of LATP particles contributing to enhancement of migration of lithium ions in the hybrid electrolyte. Figure 2 shows high-rate discharge properties of the cells using the hybrid and the liquid electrolytes containing different LiPF6 concentration. The voltage decline of the cells using the hybrid electrolytes were more gradual than that of the cell using the liquid electrolytes with LiPF6 concentration of 0.5 M and 1 M. The difference between hybrid electrolytes and liquid electrolytes was clearly observed in the cell with LiPF6 concentration of 0.5 M. In the case of a high LiPF6 concentration of 2 M, the voltage decline of the cells using the hybrid and the liquid electrolytes showed almost no difference. Electrochemical kinetics on the discharge were more effectively enhanced by the existence of LATP particles wetted with the liquid electrolyte containing smaller amount of LiPF6. From these results, we considered that lithium-ionic conducting solid particles in hybrid electrolyte have effects to enhance lithium-ion conductivity by promoting lithium-ion migration on the surface of the solid particles and the amount of lithium-ions for charge transfer on the electrodes. However the detail of this mechanism for effects has not been cleared yet. In order to understand the phenomenon, it is determined that properties of lithium-ion conducting and electrochemical performances of hybrid electrolytes with different ratio of solid particles and liquid electrolyte and so on. In this presentation, we will discuss the role of lithium-ion conducting solid particles in hybrid electrolytes.

The development of solid-state batteries (SSBs) is crucial for advancing next-generation battery technology. Compared to conventional lithium-ion batteries using organic liquid electrolytes, SSBs offer higher energy density, improved safety, and wide operating temperature range. Nonetheless, constructing a practical SSB with lithium-metal anode (LMA) and optimal inorganic solid electrolyte (SE) presents significant challenges. In this presentation, we introduce our findings addressing the two primary obstacles impeding the remarkable advancement of SSBs.The electrochemical instability at the interface between LMA and SE is the first persistent issue to overcome. Solid materials constituting SSBs exhibit distinct physical and chemical properties. When these materials, in the form of electrodes or electrolytes, are assembled into an electrochemical cell configuration, they establish solid–solid interfaces within the energy storage system. Achieving electrochemically stable SSBs requires non-reactive interfaces between LMA and SE with conformal contact. Previous studies have predominantly focused on developing interface modification methods to enhance the long-term cycling stability of SSBs. However, such approaches often offer phenomenological solutions without a thorough understanding of the interface dynamics. Additionally, the role of charges within an electric field in the operation of lithium-ion batteries is often overlooked. The LMA-SE interface of SSBs experiences an in situ electric field during the charging process, where the SEs exhibit semiconducting properties distinct from liquid electrolytes. Consequently, identifying the governing mechanism of interface stabilization cannot rely solely on conventional electrochemical techniques or a materials science perspective alone.Interface modeling by tailoring energy band alignment is a fundamental approach to achieving the cycling stability of SSBs. In this study, we used Li1.3Al0.3Ti1.7(PO4)3 (LATP), a representative NASICON-type SE, alongside a Li-metal foil. Although LATP possesses excellent electrochemical stability with a high anodic limit (4.31 V) and small decomposition energy (- 65 meV per atom at 5 V), its direct contact with LMA leads to the formation of a reactive interface having mixed ionic-electronic conducting interphases (MCI). The presence of MCI expedites the reduction of LATP’s metallic constituents by enabling electron transfer across the interface. Given the heightened risk of interfacial instability in the electrochemical cell, controlling interfacial reactions is imperative for constructing SSBs. Herein, we deposited titanium (45 nm) onto the surface of LATP to stabilize the inherently reactive LMA-LATP interface. The pure transition metal interlayer transformed into an ion-conducting crystal structure through electrochemical interactions with Li-metal. This titanium compound self-induced interlayer (TSI) served as a stable Li-ion conductor and electron buffer between LMA and LATP. Lithium symmetric cells having TSI maintained constant overpotential over 1000 cycles and exhibited significantly reduced impedance.Another critical obstacle to realizing practical SSBs is the intrinsic structural instability of SEs. This physical instability shortens the lifespan of SSBs and severely diminishes their electrochemical performance at the typical ambient temperatures of electric vehicle power batteries (25-50 °C). Over the past decade, various solid-state Li-ion conductors have been developed such as Li7La3Zr2O12 (garnet-type oxide SE) and Li6PS5Cl (argyrodite-type sulfide SE). By associating lattice dynamics and ionic transport in these materials, previous studies could improve the ionic conductivity of SE through major substitution with large cations like tantalum or partial substitution with large anions. Recently, antiperovskite-type SEs with the anion-centered unit of Li3AB, where A represents hydroxyl and B represents halogen groups, have attracted attention. The representative composition Li2OHCl is renowned for its facile fabrication process through solid-state reaction, high ionic conductivity (10-3 S cm-1), and excellent compatibility with LMA. Still, significant limitations exist in its use for constructing practical SSBs, as is common with most other types of SEs.We found that substituting trace amounts of aliovalent cations to modify atomic interactions in SEs can significantly enhance the electrochemical reliability of SSBs. This strategy effectively resolves the intrinsically unstable structure of SEs and simultaneously enhances the LMA-SE interfaces. As a proof-of-concept, we substituted lithium in Li2OHCl with metal elements that do not experience crystal field stabilization energy. The resulting modified electrolytes led to prolonged lifespan and superior rate performance in lithium symmetric cells at room temperature. The cells with the modified SEs exhibited a remarkable critical current density exceeding 10.5 mA cm-2 and maintained a stable voltage profile for 3000 hours at 10.0 mA cm-2, whereas the pristine cells achieved a relatively low critical current density of 2.0 mA cm-2 and a short lifespan of 1000 hours at 1.0 mA cm-2. These findings underscore a strong correlation between the physical properties of inorganic materials and the electrochemical stability of SSBs. Finally, we anticipate that the revealing results will contribute to the advancement of high-power SSBs employing solid electrolytes and metallic electrodes.

Multi-strategies interface and structure design of Li- and Mn-rich layered oxide for all-solid-state lithium batteries

Reversible thixotropic gel electrolytes for safer and shape-versatile lithium-ion batteries

All-solid-state lithium-ion batteries (ASSLIBs) are emerging as promising alternatives to conventional batteries with liquid electrolytes due to their enhanced safety, increased energy density, and longer lifespan. However, their widespread adoption is hampered by challenges in developing effective solid electrolytes. Phosphate glassy electrolytes have attracted attention as a viable solution, offering high lithium-ion conductivity, robust chemical stability, and excellent compatibility with lithium metal anodes. This review summarizes our earlier work on phosphate glassy electrolytes for ASSLIBs, focusing on strategies to overcome critical industrial hurdles. It discusses various elements such as synthesis methods, structural properties, and electrochemical performance, with particular emphasis on enhancing ionic conductivity, mechanical resilience, and interface stability. The review also explores how these electrolytes are integrated into ASSLIB designs and interact with diverse cathode materials, and it outlines future research directions that could enable the next generation of lithium-ion battery systems to overcome existing limitations and achieve safer, more efficient energy storage.