Nonuniform Ionic and Electronic Transport of Ceramic and Polymer/Ceramic Hybrid Electrolyte by Nanometer‐Scale Operando Imaging for Solid‐State Battery

Replacing the liquid electrolyte in lithium batteries with solid‐state ion conductor is promising for next‐generation energy storage that is safe and has high energy density. Here, nanometer‐resolution ionic and electronic transport imaging of Li₃PS₄ (LPS), a solid‐state electrolyte (SSE), is reported. This nm resolution is achieved by using a logarithm‐scale current amplifier that enhances the current sensitivity to the fA range. Large fluctuations of ion current—one to two orders of magnitude on the LPS and on the LPS region of a polymer/LPS bulk hybrid SSE—that must be mitigated to eliminate Li dendrite formation and growth, are found. This ion current fluctuation is understood in terms of highly anisotropic transport kinetic barriers along the different crystalline axes due to different grain orientations in the polycrystalline and glass ceramic materials. The results on the bulk hybrid SSE show a sharp transition of ionic and electronic transport at the LPS/polymer boundary and decreases in average ionic current with decreasing polyimine particle size and with extensive cycling. The results elucidate the mechanism of polyimine extension into interparticles to prevent Li dendrite growth. This work opens up novel characterization of charge transport, which relates to Li plating and stripping for solid‐state‐batteries.     

Solid‐State Prelithiation Enables High‐Performance Li‐Al‐H Anode for Solid‐State Batteries

Lithium alanates exhibit high theoretical specific capacities and appropriate lithiation/delithiation potentials, but suffer from poor reversibility, cycling stability, and rate capability due to their sluggish kinetics and extensive side reactions. Herein, a novel and facile solid‐state prelithiation approach is proposed to in situ prepare a Li₃AlH₆‐Al nanocomposite from a short‐circuited electrochemical reaction between LiAlH₄ and Li with the help of fast electron and Li‐ion conductors (C and P6₃mc LiBH₄). This nanocomposite consists of dispersive Al nanograins and an amorphous Li₃AlH₆ matrix, which enables superior electrochemical performance in solid‐state cells, as much higher specific capacity (2266 mAh g^?1), Coulombic efficiency (88%), cycling stability (71% retention in the 100th cycle), and rate capability (1429 mAh g^?1 at 1 A g^?1) are achieved. In addition, this nanocomposite works well in the solid‐state full cell with LiCoO₂ cathode, demonstrating its promising application prospects. Mechanism analysis reveals that the dispersive Al nanograins and amorphous Li₃AlH₆ matrix can dramatically enhance the lithiation and delithiation kinetics without side reactions, which is mainly responsible for the excellent overall performance. Moreover, this solid‐state prelithiation approach is general and can also be applied to other Li‐poor electrode materials for further modification of their electrochemical behavior.     

Dynamic Visualization of Cathode/Electrolyte Evolution in Quasi‐Solid‐State Lithium Batteries

Solid‐state lithium–sulfur batteries (SSLSBs) are highly appealing for electrochemical energy devices because of their promising theoretical energy density. An intensive acquaintance of SSLS interfacial behavior is of importance in gaining fundamental knowledge of working/failure mechanisms and clarifying further optimized design of advanced batteries. Herein, a direct visualization of the evolution of both component and structure is present inside a working SSLSB. In situ Raman spectroscopy clearly sheds light on the potential‐dependent evolution of sulfur speciation via subtly fabricating the electrochemical cell. Moreover, the real‐time optical microscopic views show that the irreversible structure deformation of solid‐state electrolytes (SSEs), which results from the decomposition of dissolved polysulfides (PSs) and gas generation inside the SSE, directly causes the fracture of sulfur cathode with the cycling times increasing. Furthermore, by an atomic force microscopy study, the evolving structure and dynamic behavior of SSEs are directly captured at the nano/microscale and further elucidate the PS shuttling determining the mechanism stability of electrolyte. This work provides a straightforward monitoring of the compositional and morphological evolution, which contributes one to exploring the failure mechanisms and interfacial reactions for the cell performance enhancement.     

Stable Seamless Interfaces and Rapid Ionic Conductivity of Ca–CeO2/LiTFSI/PEO Composite Electrolyte for High‐Rate and High‐Voltage All‐Solid‐State Battery

Stable and seamless interfaces among solid components in all‐solid‐state batteries (ASSBs) are crucial for high ionic conductivity and high rate performance. This can be achieved by the combination of functional inorganic material and flexible polymer solid electrolyte. In this work, a flexible all‐solid‐state composite electrolyte is synthesized based on oxygen‐vacancy‐rich Ca‐doped CeO₂ (Ca–CeO₂) nanotube, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and poly(ethylene oxide) (PEO), namely Ca–CeO₂/LiTFSI/PEO. Ca–CeO₂ nanotubes play a key role in enhancing the ionic conductivity and mechanical strength while the PEO offers flexibility and assures the stable seamless contact between the solid electrolyte and the electrodes in ASSBs. The as‐prepared electrolyte exhibits high ionic conductivity of 1.3 × 10^?4 S cm^?1 at 60 °C, a high lithium ion transference number of 0.453, and high‐voltage stability. More importantly, various electrochemical characterizations and density functional theory (DFT) calculations reveal that Ca–CeO₂ helps dissociate LiTFSI, produce free Li ions, and therefore enhance ionic conductivity. The ASSBs based on the as‐prepared Ca–CeO₂/LiTFSI/PEO composite electrolyte deliver high‐rate capability and high‐voltage stability.     

Solid‐State Lithium/Selenium–Sulfur Chemistry Enabled via a Robust Solid‐Electrolyte Interphase

Lithium/selenium‐sulfur batteries have recently received considerable attention due to their relatively high specific capacities and high electronic conductivity. Different from the traditional encapsulation strategy for suppressing the shuttle effect, an alternative approach to directly bypass polysulfide/polyselenide formation via rational solid‐electrolyte interphase (SEI) design is demonstrated. It is found that the robust SEI layer that in situ forms during charge/discharge via interplay between rational cathode design and optimal electrolytes could enable solid‐state (de)lithiation chemistry for selenium‐sulfur cathodes. Hence, Se‐doped S_22.2Se/Ketjenblack cathodes can attain a high reversible capacity with minimal shuttle effects during long‐term and high rate cycling. Moreover, the underlying solid‐state (de)lithiation mechanism, as evidenced by in situ ⁷Li NMR and in operando synchrotron X‐ray probes, further extends the optimal sulfur confinement pore size to large mesopores and even macropores that have been long considered as inferior sulfur or selenium host materials, which play a crucial role in developing high volumetric energy density batteries. It is expected that the findings in this study will ignite more efforts to tailor the compositional/structure characteristics of the SEI layers and the related ionic transport across the interface by electrode structure, electrolyte solvent, and electrolyte additive screening.     

Thermally Chargeable Solid‐State Supercapacitor

Ubiquitous low‐grade thermal energy, which is typically wasted without use, can be extremely valuable for continuously powering electronic devices such as sensors and wearable electronics. A popular choice for waste heat recovery has been thermoelectric energy conversion, but small output voltage without energy‐storing capability necessitates additional components such as a voltage booster and a capacitor. Here, a novel method of simultaneously generating a large voltage from a temperature gradient and storing electrical energy without losing the benefit of solid‐state no‐moving part devices like conventional thermoelectrics is reported. Thermally driven ion diffusion is used to greatly increase the output voltage (8 mV K^?1) with polystyrene sulfonic acid (PSSH) film. Polyaniline‐coated electrodes containing graphene and carbon nanotube sandwich the PSSH film where thermally induced voltage‐enabled electrochemical reactions, resulting in a charging behavior without an external power supply. With a small temperature difference (5 K) possibly created over wearable energy harvesting devices, the thermally chargeable supercapacitor produce 38 mV with a large areal capacitance (1200 F m^?2). It is anticipated that the attempt with thermally driven ion diffusion behaviors initiates a new research direction in thermal energy harvesting.     

Reversible Short‐Circuit Behaviors in Garnet‐Based Solid‐State Batteries

Garnet‐based solid‐state electrolytes (SSEs) are attractive for solid‐state lithium metal batteries due to their wide electrochemical window, high conductivity, and excellent stability against lithium metal. However, the risk of short‐circuit encumbers the cycle life and capacity of garnet‐based solid‐state batteries without clear reason or mechanism. Here, reversible short‐circuit behavior in the garnet‐based solid‐state batteries, which differs from the short‐circuit in liquid cells, is reported for the first time. In situ neutron depth profiling is adopted to quantitatively measure Li transport, which helps forecast and confirm the reversible nature of the short‐circuit in garnet‐based batteries. A real‐time Li accumulation monitoring system of NMC//CNT/garnet/Li cell is designed to reveal the Li dendrite formation mechanism. The voltage drops of the CNT monitoring electrode during the charging process indicate the formation of Li dendrites inside the garnet bulk, while the smooth voltage profile during the discharging process demonstrates the disappearance of the short‐circuit. This is the first confirmation of short‐circuit behavior that provides clarification of the Li dendrite formation mechanism in garnet‐based solid‐state batteries, which is shown to be a reversible process caused by the low ionic conductivity and non‐negligible electronic conductivity of garnet SSEs.     

All‐Solid‐State Printed Bipolar Li–S Batteries

Despite their potential advantages over currently widespread lithium‐ion batteries, lithium–sulfur (Li–S) batteries are not yet in practical use. Here, for the first time bipolar all‐solid‐state Li–S batteries (ASSLSBs) are demonstrated that exhibit exceptional safety, flexibility, and aesthetics. The bipolar ASSLSBs are fabricated through a solvent‐drying‐free, ultraviolet curing‐assisted stepwise printing process at ambient conditions, without (high‐temperature/high‐pressure) sintering steps that are required for inorganic electrolyte‐based all‐solid‐state batteries. Two thermodynamically immiscible and nonflammable gel electrolytes based on ethyl methyl sulfone (EMS) and tetraethylene glycol dimethyl ether (TEGDME) are used to address longstanding concerns regarding the grain boundary resistance of conventional inorganic solid electrolytes, as well as the polysulfide shuttle effect in Li–S batteries. The EMS gel electrolytes embedded in the sulfur cathodes facilitate sulfur utilization, while the TEGDME gel composite electrolytes serve as polysulfide‐repelling separator membranes. Benefiting from the well‐designed cell components and printing‐driven facile processability, the resulting bipolar ASSLSBs exhibit unforeseen advancements in bipolar cell configuration, safety, foldability, and form factors, which lie far beyond those achievable with conventional Li–S battery technologies.