All‐solid‐state Li‐metal batteries (ASLMBs) represent a significant breakthrough in the quest to overcome limitations associated with traditional Li‐ion batteries, particularly in energy density and safety aspects. However, widespread implementation is stymied due to a lack of profound understanding of the complex mechano‐electro‐chemical behavior of Li metal in the ASLMBs. Herein, operando neutron imaging and X‐ray computed tomography (XCT) are leveraged to nondestructively visualize Li behaviors within ASLMBs. This approach offers real‐time observations of Li evolutions, both pre‐ and post‐ occurrence of a “soft short”. The coordination of 2D neutron radiography and 3D neutron tomography enables charting of the terrain of Li metal deformation operando. Concurrently, XCT offers a 3D insight into the internal structure of the battery following a “soft short”. Despite the manifestation of a “soft short”, the persistence of Faradaic processes is observed. To study the elusive “soft short” , phase field modeling is coupled with electrochemistry and solid mechanics theory. The research unravels how external pressure curbs dendrite growth, potentially leading to dendrite fractures and thus uncovering the origins of both “soft” and “hard” shorts in ASLMBs. Furthermore, by harnessing finite element modeling, it dive deeper into the mechanical deformation and the fluidity of Li metal.

The surge in electric vehicle demand has propagated the extensive application of lithium-ion batteries (LIBs) in recent years. Gaining significant traction due to their promising high-energy density and elevated safety over traditional LIBs, all-solid-state Li batteries (ASLBs) have nonetheless been faced with hurdles relating to battery performance. These include concerns with interfacial compatibility, structural stability, Li dendrite inhibition, and large-scale manufacturing. To tackle these issues, it is necessary to employ advanced characterization methods to comprehend the intrinsic mechanisms within ASLBs. In this article, we advocate for the use of neutron imaging as a nondestructive approach for the operando visualization of ASLBs. We draw comparisons with other operando visualization strategies, underline the benefits of neutron imaging, and discuss its potential applicability in the scrutiny of all-solid-state Li metal batteries and all-solid-state Li-sulfur batteries. Neutron imaging provides valuable insights into the dynamics of Li concentration, reaction mechanisms, and transport constraints in ASLBs. These insights are pivotal in contributing to the evolution of high-performance all-solid-state batteries. Graphical abstract This article discusses the application of neutron imaging for operando characterization of all-solid-state batteries. It compares neutron imaging to other techniques and highlights its advantages in visualizing light elements such as lithium. It also covers recent progress in using neutron imaging to investigate reaction mechanisms, lithium dynamics, and failure modes in all-solid-state lithium metal and lithium sulfur batteries. It also analyzes the future outlook for neutron imaging as a powerful nondestructive tool to gain insights into interfacial phenomena in all-solid-state batteries.

Li-sulfur (Li-S) batteries are promising as the next-generation energy storage technology but face challenges due to sluggish sulfur redox reaction (SRR) kinetics and a sulfur shuttling effect. While many studies have explored polycaprolactone (PCL)-based gel polymer electrolytes (GPEs) to address these issues, the influence of solvent properties, including dielectric constant (ϵ) and donor and acceptor numbers (DN and AN), remain unexplored despite their critical impact on performance and full-scale implementation. This study systematically compares three distinct electrolytes, dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and tetraethylene glycol dimethyl ether (TEGDME)-paired with PCL, to correlate the varied solvent properties and their effects on the physical properties of the GPE, in terms of Li⁺ transport and solvation, and polysulfide's confinement. Among them, the DME-based GPE, with an intermediate DN, exhibited the lowest crystallinity (2.31%), highest ionic conductivity (7.49 mS/cm), and high Li⁺ transference number (0.77). As a result, it achieved a specific capacity of 795 mAh/g sulfur and an average Coulombic efficiency of 97.5% after 120 cycles at C/5, outperforming its competitors. Operando Raman and UV-vis spectroscopy confirmed that PCL effectively confines long-chain polysulfides within its network, mitigating the shuttle effect and facilitating reversible polysulfide conversion. These findings demonstrate that GPEs with moderate DN values and balanced ϵ significantly enhance stability, extend cycle life, and improve rate performance for Li-S batteries. This work provides valuable insights into the design of advanced electrolyte systems for practical energy storage applications.

Solid electrolytes are critical to enabling safe and high-energy-density batteries; yet, their practical deployment is impeded by poor electrochemical stability, inadequate interfacial contact, and challenging manufacturing processes. Here, we introduce a novel "solid-in-solid" electrolyte architecture comprising a porous Li zeolite electrolyte (LiX) infiltrated with a melt-processable plastic crystal electrolyte (PCE). This LiX-PCE electrolyte achieves an ionic conductivity of 0.55 mS/cm at 20 °C, alongside improved electrochemical stability over pure PCE. Solid-state nuclear magnetic resonance reveals three Li⁺ transport pathways: through LiX, through PCE, and via ion exchange at phase boundaries. Leveraging the melt-processability of the PCE, we proposed a roll-to-roll-compatible melt infiltration strategy for scalable solid-state battery (SSB) fabrication with the LiX-PCE electrolyte. The SSBs demonstrate excellent rate performance (up to 10 C), 93% capacity retention after 200 cycles at 2C, and 4.5 V compatibility. This work elucidates critical design principles for high-performance solid-state electrolytes and presents a viable path toward practical, fast-charging, high-power SSBs.

All-solid-state lithium-sulfur batteries (ASLSBs) have been considered a promising next-generation energy storage technology due to their remarkable safety and high energy density. In ASLSBs, the electrochemical pathways are intrinsically different from conventional Li-S batteries using liquid electrolytes. However, the mechanism still lacks clear identification and deep understanding. Herein, for the first time, we investigated the chemistries and explored the electrochemical reaction mechanism and kinetic in ASLSBs through coupling operando Raman spectroscopy and ex-situ X-ray absorption spectroscopy. We proved no long-chain lithium polysulfides (Li2Sn, 4≤n≤8) were formed during the redox reactions, but a short-chain polysulfide (Li2S2) intermediate phase formation was identified in the conversion between active material S8 and reduction product Li2S. The existence of intermediate phase Li2S2 results in low sulfur utilization and poor battery performance. In comparison to liquid cells, ASLSBs exhibit sluggish reaction kinetics due to the higher conversion barrier and slower charger transfer in solid-solid reactions. This study revealed the generation of Li2S2 intermediates in ASLSBs, inspiring future research to further improve the performance of ASLSBs through completing the conversions and promoting reaction kinetics in ASLSBs.