Recent Developments and Challenges in Battery Safety with Solid State Technology

<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.

Development of lithium‐ion batteries (LIBs) with high energy density has brought a promising future for the next generation of electric vehicles (EV). In order to make EVs more competitive with combustion engine vehicles, development of an effective fast charging technique is inevitable. However, improper employment of fast charging can damage the battery and bring safety hazards. Herein, industry based along with our proposed internal resistance (IR) based fast charging techniques were performed on commercial Panasonic NCR 18650B cylindrical batteries. To further investigate the fast charging impact and electrode degradation mechanisms, electrochemical analysis and material characterization techniques including EIS (electrochemical impedance spectroscopy), GITT (galvanostatic intermittent titration technique), SEM (scanning electron microscopy), and XRD (X‐ray diffraction) were implemented. Batteries that were cycled under industry based fast charging showed 78% increase in internal resistance after 120 cycles along with rapid capacity fading. Mechanical distortion of the battery case occurred around the 60th cycle for industry based fast charging. In contrast, IR based fast charged batteries showed 29.4% increase in internal resistance over 120 cycles. In addition, mechanical distortion was not observed and the relative capacity fading was on a moderate level. Furthermore, this work could pave the way for the optimization of fast charging techniques to secure the lifespan and safety of various types of lithium‐ion batteries.

Solid-state batteries utilizing lithium metal anodes have the potential to enable batteries with a specific energy of >500 Wh/kg and an energy density of >1,500 Wh/L for thousands of cycles. When optimized they will improve the energy efficiency, operating temperature range, sustainability, and safety at a lower cost compared to projections for advanced Li-ion batteries. This improved performance is critical for the widespread adoption of electric vehicles and may enable future applications such as electric aviation. Expectations for solid-state batteries are high, there are significant materials and processing challenges that need to be overcome. Some of these challenges are well known; others are more subtle and are just becoming known. The challenges and their solutions must be clearly identified to realize high-energy solid-state Li metal batteries. In the United States, the U.S. Department of Energy (DOE) funds the majority of energy storage research and development, including solid state battery research. Web of Science publication analysis shows that worldwide DOE is second largest funder. Work on solid state batteries is distributed across different arms of DOE and is coordinated at headquarters to ensure a broad national portfolio for advanced batteries, including lithium batteries and solid-state battery devices. We note that university and national laboratory researchers in the US with a long-standing interest in solid state batteries is a small, integrated community with recognized impact for publications, patents and startup companies. The opportunity for this group to engage for research with international colleagues is growing, fostered by periodic bilateral meetings supported by DOE and by the recent joint US German research program for lithium battery interface studies. These are valuable opportunities to speed solid-state battery development. The ORNL led virtual workshop, overviewed here, confirms the community’s shared vision of the exciting advances, opportunities, and challenges. Further, we are seeing that this workshop has spawned several new informal collaborations and draft proposals. This encourages us to propose future discussion. On May 11, 2020, Oak Ridge National Laboratory (ORNL) hosted a 6-hour, on-line national workshop to discuss recent advances and most the prominent obstacles to realizing solid-state Li metal batteries. The workshop included more than 30+ experts from national laboratories, universities, and companies, all of whom have worked on solid-state batteries for multiple years. The participants shared recent advances, many not yet in print, illustrating that the community has gained significant new insights for solid-state Li battery materials over the last 5 years. In this report, the major outcomes of the workshop are organized to identify the gaps in our scientific knowledge for four core materials science areas: (1) Li metal anodes, (2) the solid electrolyte in contact with Li metal, (3) active cathode materials and solid-state composite cathodes, and (4) solid electrolytes. Illustrative examples and discussions are reported with the more comprehensive issues in the report. Discussion of additional challenges related to processing of solid-state battery materials and to the designs and architectures for mechanically robust, long-lived batteries received less attention due to time constraints. These are good themes for deeper discussion at a follow-on workshop, where a complete list of critical research topics can be identified.

Solid polymer electrolytes (SPEs) are critical for the development of safe and high-performance solid-state lithium batteries that power the next generation of electric vehicles, drones, and robotics. To date, one of the major disadvantages of SPEs limiting their wide applications is their low ionic conductivity. The use of ionic liquids as plasticizers in SPEs has been demonstrated as a promising strategy to enhance the ionic conductivity of SPEs at room temperature while maintaining their safety features and mechanical properties. However, the optimization of plasticizers is largely intuition based without general design rules and predictive design strategies. Therefore, in this work, we developed a fast and low cost, data-driven workflow that advances the design and optimization of ionic liquid plasticizers for SPEs. Using this approach, we successfully identified a new plasticized SPE material that showed high ionic conductivity and superior cycling stability. Our data-driven model revealed that important design factors correlated to highly effective plasticizers, providing insights into the conduction mechanism of plasticized SPEs. More importantly, we found that these key factors are transferrable and applicable in other plasticized SPEs beyond our data set, highlighting the generality of the findings obtained by our data-driven approach.

1. Purpose Solid-state lithium-ion batteries (SSLIBs) have attracted extensive attentions because of their potentials to improve safety and to achieve higher power and energy densities compared with the conventional lithium-ion batteries. In composite electrodes for SSLIBs, particles of active material (AM) and solid electrolyte (SE) are three-dimensionally distributed and form complicated Li-ion and electron pathways. Then, especially during high rate charging/discharging, the inhomogeneous reaction distribution may be formed in the electrode. The reaction distribution can substantially deteriorate the battery performances of SSLIBs such as capacity, power output, rate capability, and cyclability. Therefore, understanding how the reaction distribution affects the battery performances is crucial for the development of high-performance SSLIBs. In this study, we performed operando three-dimensional (3D) observation of reaction distributions in composite electrodes for SSLIBs using CT-XAFS1 to elucidate the influence of reaction distributions on the battery performances of SSLIBs. 2. Experimental An SSLIB cell with a configuration of Li x CoO2 (LCO)-Li2.2C0.8B0.2O3 (LCBO) composite electrode|LCBO electrolyte|poly (ethylene oxide) (PEO)-based polymer electrolyte|Li metal electrode was fabricated based on the literature2. The composite electrode comprised 8 mg of LCO and 2 mg of LCBO. The SSLIB cell was charged to 4.5V and discharged to 2.0 V with a current of 240 μA (0.3 C) for 3 cycles at 100 °C. The reaction distribution in the composite electrode was observed every 40 minutes during charging and discharging using operando CT-XAFS. The CT-XAFS measurements were carried out in the energy range between 7725.5-7730 eV with an energy step of 0.1 eV under an exposure time of 20 ms per energy and projection angle from -65 to 65° with an angle step of 0.1°. The observation area was 517 × 517 × 49 μm. The spatial and time resolutions were 3.1 μm and 40 min., respectively. 3. Results and Discussion Figure 1(a) shows the charge-discharge curves of the SSLIB cell. The SSLIB cell exhibited the initial charge and discharge capacities of 84 and 46 mAh·g−1, respectively. Those degraded to 24 and 13 mAh·g−1 in the 2nd cycle, and 12 and 12 mAh·g−1 in the 3rd cycle, respectively. Figure 1(b) shows the 3D charging state (Li content) maps of the composite electrode and the representative 2D cross-sectional charging state maps in the in-plane direction at the end of 1st, 2nd, and 3rd charge. Colored/uncolored areas stand for the regions where the AMs exist or not, respectively. The red/blue areas stand for the charged (x = 0.6) /discharged (x = 1.0) AMs, respectively. After the 1st charge, the AMs generally showed a high charging state (red). However, the regions with high charging state significantly decreased after the 2nd charge, and most of the AMs showed a charging state corresponding to x = 0.7 ~ 0.8 (green). The regions with high charging state further decreased after the 3rd charge, and AMs with a low charging state were increased (blue). To more precisely investigate where the less-charged AMs existed after the 2nd and 3rd charge, we subtracted the charging state map after the 1st discharge from that after the 2nd charge, and also the charging state map after the 2nd discharge from that after the 3rd charge (Fig. 1(c)). The 2D maps in Fig. 1(c) thus indicate to what extent the charge reaction progressed during the 2nd or 3rd charge compared with the end of the 1st or 2nd discharge, respectively. The red/blue areas in Fig. 1(c) represent the AM regions where the reaction progressed (Δx = 0.4) or not (Δx = 0) from the end of the 1st or 2nd discharge, respectively. As shown in the left map in Fig. 1(c), the inner parts of the aggregated AMs were significantly less charged compared to the regions near AM/SE interfaces during the 2nd charge. Similarly to the 2nd charge, the charge reaction preferentially progressed near the AM/SE interfaces, while the reaction insufficiently progressed at the inner parts of the aggregated AMs during the 3rd charge. Such a variation in the charging state distribution during cycling could be explained by considering the microstructural change due to the expansion/shrinkage of AM particles. The above results suggest that the expansion/shrinkage of AM particles reduced the connections between AM particles but did not reduce the AM/SE interfaces. We further discuss the mechanism of the capacity degradation during cycling in the presentation.

This report briefly reviews the characteristics of solid-state batteries (SSBs) and the life-cycle analysis (LCA) studies that have been completed for SSBs. Compared with conventional lithium-ion batteries (LIBs), SSBs offer improved safety and potentially higher energy density — both enabled by replacing liquid electrolytes with solid electrolytes and using lithium metal anodes. Several challenges impede the commercialization of SSBs, primarily related to the stability of the interface between the solid electrolyte and the electrodes. Several options are under consideration for SSB electrolyte and cathode chemistries. As a result, the production processes for these components and the corresponding battery packs are still under development and can differ significantly from those used for conventional LIB pack production. A robust comparison of SSBs with LIBs through LCA is important to analyze the environmental benefits and challenges associated with this alternative battery system. While the literature provides only a few LCA studies focused on SSBs, with significant uncertainty in their life-cycle inventories (LCIs), those studies collectively suggest that solid electrolyte manufacturing is the major environmental hotspot, followed by cathode and anode production.

Due to the hidden benefits such as the possibilities to make energy density high, safety improved, and lifespan extended, solid-state batteries are a focal point in battery technology research. Current liquid electrolyte-based lithium-ion batteries, despite their maturity, have inherent issues like safety risks and limited energy density. While the advancement in solid-state battery technology can potentially overcome certain challenges, it also encounters its own issues including high contact interface impedance and ion transmission efficiency. For solid-state batteries to supplant traditional lithium-ion batteries in the future, these challenges must be addressed. The research provides an in-depth analysis of the three major types of solid-state electrolytes currently prevalent in the market, including oxide, sulfide, and polymer electrolytes. This is especially true for the electrochemical analysis of batteries after the electrolyte has been used. Each has its unique properties, synthesis methods, and limitations. Oxide electrolytes excel in high-temperature ionic conductivity but underperform at room temperature. Moreover, the synthesis of oxide solid electrolytes requires fine control over temperature and atmosphere, thus demanding high technical expertise. The sulfide category shows promise in room temperature conductivity, albeit with stability issues. Polymer electrolytes, however, are flexible and processable but have generally lower ionic conductivity. To enable large-scale applications, future research needs to focus on improving these electrolytes’ performance and developing cost-effective and efficient synthesis methods. The importance of research into solid-state lithium-ion batteries is tied to their capacity to transform the energy storage sector.

A multifunctional energy storage composite (MESC) combines the high energy density of lithium-ion batteries with the structural benefits of carbon fiber composites, resulting in a lightweight structural battery with excellent mechanical strength and enhanced safety for electric vehicles (EVs). This paper presents the design-tofabrication development of new MESC, with a specific focus on the design, fabrication, and testing of an electronic skateboard (e-skateboard) as a representative system-level study for the EVs. A finite element analysis (FEA) is employed to design the MESC eskateboard. The FEA of the MESC e-skateboard is validated through mechanical testing, demonstrating a significant 24% reduction in weight, leading to an impressive 31.6% improvement in energy density compared to a conventional e-skateboard. As a part of the MESC technology, an embedded smart sensor network is also developed for the e-skateboard, showcasing the capability for real-time battery monitoring, and estimating its state of charge during in-service operation. The promising outcomes of the new MESC technology position it as a novel solution for enabling multifunctional structural battery composites in future electronic vehicles and aircraft applications.

The Data Time Flow Simulator (DTF) has been developed at the AIT Austrian Institute of Technology in the course of the EU ARTEMIS Project POLLUX which is related to the design of electronic control systems for the next generation of electric vehicles. In previous work, we have introduced a generic approach for performance analysis of vehicle electronic control systems using the DTF. The main issue of this paper is to demonstrate the practicability of this design methodology by means of a specific use case, namely the performance analysis of a vehicle control system for an electric city car, designed using inputs from different POLLUX project partners from the automotive industry.

The shift from internal combustion (IC) engines to electric vehicles (EVs) marks a significant transformation in the automotive industry, prompting a comprehensive reassessment of various engineering considerations. Among these, tribological factors play a critical role in ensuring the performance, reliability, and longevity of vehicle components. This review examines the tribological challenges and opportunities posed by the transition to EVs, focusing on key components such as bearings, gears, and braking systems, which face unique operating conditions in electric powertrains compared to their IC counterparts. The paper addresses how electric vehicles encounter distinct tribological scenarios, such as lower operating temperatures but higher torque loads, which demand new materials and lubrication strategies. It also explores how the near absence of internal combustion in EVs affects component wear and the mechanisms of friction reduction. Additionally, the tribological challenges in IC engines are revisited to provide a comparative understanding of how they differ from those in EVs, particularly regarding energy efficiency and frictional losses. This review emphasizes the importance of minimizing wear and friction to maximize energy efficiency, which is crucial for extending vehicle range and improving performance in EVs. By synthesizing the latest research findings and industry advancements, the review offers valuable insights for researchers and engineers involved in the design and optimization of tribological systems for the next generation of electric vehicles.

Alleviating range anxiety: Solid-state batteries and extreme fast charging

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.

Garnet-type solid electrolytes have been extensively investigated in recent times as potential candidates for solid-state batteries. Among them, garnets with nominal composition Li7La3Zr2O12(LLZO) have received particular attention due to their high Li-ion conductivity (10-3 Scm-1) at room temperature and chemical stability against metallic lithium besides possessing a large electrochemical window >5V.[1] Despite of striking properties, LLZO suffers from several challenges such as interfacial instability with cathodes, e.g., LCO, during high temperature processing, resulting in a huge interface resistance, which is one of the fundamental reasons for the failure of solid-state batteries based on LLZO.[2-4] So far, the high interfacial impedance has been related to LLZO|LCO interface decomposition occurring due to diffusion of Co across the cathode-electrolyte interface. Herein, we investigated the hypothesis that interfacial degradation originate from the incorporation of Co into the LLZO lattice. The solubility limit of Co is determined to be 0.16 per formula unit, whilst the concentrations beyond promote phase transition (cubic LLZO-to-tetragonal LLZO). We investigated in detail the temperature-dependent Co diffusion into LLZO and concluded that detrimental cross diffusion could take place at any relevant process condition. Besides, the optimal protective Al2O3 coating thickness for relevant temperatures was studied, which allowed to create a process diagram to provide mitigation strategies towards enabling stable LCO|LLZO interface in all-solid-state batteries. Keywords: Solid-state batteries, Interfaces, cross diffusion, interfacial degradation AcknowledgementsD.R. acknowledges financial support by the Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development and the Christian Doppler Research Association (Christian Doppler Laboratory for Solid-State Batteries). D.R. and J. F. acknowledges financial support by the Austrian Science Fund (FWF) in the frame of the project InterBatt (P 31437). D.K. acknowledges funding by the European Union’s Horizon 2020 Research and Innovation Programme (Grant No. 823717, project “ESTEEM3”) and by the Zukunftsfond Steiermark.Reference[1] Murugan, R., Thangadurai, V. and Weppner, W., 2007. Fast Lithium Ion Conduction in Garnet‐type Li7La3Zr2O12. Angew. Chemie. Int. Edt., 46(41), 7778-7781.[2] Chen, X., Xie, J., Zhao, X., & Zhu, T., 2021. Electrochemical Compatibility of Solid‐State Electrolytes with Cathodes and Anodes for All‐Solid‐State Lithium Batteries: A Review. Adv. Energy Sustain. Res., 2(5), 2000101.[3] Sakuda, A., Hayashi, A., Tatsumisago, M., 2010. Interfacial Observation Between LiCoO2 Electrode and Li2S-P2S5 Solid Electrolytes of All-Solid-State Lithium Secondary Batteries Using Transmission Electron Microscopy. Chem. Mater., 22(3), 949–956.[4] Ihrig, M., Kuo, L.Y., Lobe, S., Laptev, A.M., Lin, C.A., Tu, C.H., Ye, R., Kaghazchi, P., Cressa, L., Eswara, S. and Lin, S.K., 2023. Thermal Recovery of the Electrochemically Degraded LiCoO2/Li7La3Zr2O12: Al, Ta Interface in an All-Solid-State Lithium Battery. ACS Appl. Mater. Interfaces.

Solid-state batteries have been widely studied due to their unique advantages such as high mechanical strength, good temperature adaptability, and long cycle life. However, the coupling effect of external pressures and ambient temperatures on the cycle performance of solid-state batteries has not been systematically evaluated. Based on the finite element simulation, this work establishes a temperature-pressure-electrochemical coupling model to assess the coupling effect of temperature and pressure on the cycle capacity decay of solid-state batteries. Taking an NMC811-Li6PS5Cl-Li/In solid-state battery as an example, the results show that the optimal pressure range of the battery is 127.38 MPa-254.76 MPa. Applying external stress to a solid-state battery can significantly reduce its capacity decay rate, 191.07 MPa was selected in the optimal stress interval, ten cycles of charge-discharge cycle experiment were carried out on NMC811-Li6PS5Cl-Li/In battery at an ambient temperature of 60°C, the tenth turn capacity of this battery only decays to 97.78% of the initial capacity, while the tenth turn capacity of the non-pressure battery decays to 96.57%. The model established in this study provides an effective approach for finding the optimal external pressure range for solid state batteries, which will contribute to the development of batteries with longer cycle life.

Self-standing carbon fiber electrodes hold promise for solid-state battery technology owing to their networked structures improving interparticle connectivity, robustness contributing to mechanical integrity, and surface sites confining Li dendrites. We here evaluate carbonized 3D electrospun fibers filled with polymer electrolytes as anodes in solid-state lithium half cells. Microscopic analysis of the cells demonstrates the high wettability of carbon fibers with electrolytes, promoting an intimate contact between electrolytes and fibers. Solid-state cells delivered high initial capacities up to ∼300 mAh g−1, although the latter cycles were characterized by gradual capacity fade (∼100 mAh g−1 in the 100th cycle with nearly 100% coulombic efficiency), attributed to the onset of parasitic reactions increasing the cell resistance and polarization. When these were benchmarked against similar cells but with the liquid electrolyte, it was found that Li storage in these fiber electrodes is intermediate between graphite and hard carbon in terms of lithiation voltage (vs Li/Li+), corroborating with the nature of carbon assessed by XRD and Raman analysis. These observations can contribute to further development and optimization of solid-state batteries with 3D electrospun carbon fiber electrodes.