Understanding the Role of Nano-Aluminum Oxide in All-Solid-State Lithium-Sulfur Batteries

Opportunities of Flexible and Portable Electrochemical Devices for Energy Storage: Expanding the Spotlight onto Semi-solid/Solid Electrolytes

The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

Mixed Ionically/Electronically Conductive Double-Phase Interface Enhanced Solid-State Charge Transfer for a High-Performance All-Solid-State Li-S Battery

An all-solid-state lithium-sulfur battery (ASSLSB) is a promising candidate for post-Li-ion battery technologies with high energy densities and good safety performance. However, the intrinsic insulating nature of sulfur requires triple-phase contact with an ionic conductor and an electronic conductor for electrochemical reactions, which decreases the amount of active surface and lowers the charge-transfer efficiency. In this work, a double-phase interface constructed from a mixed ionic/electronic conductor is proposed to enhance the solid-state electrochemical reaction of sulfur. By employing lithium lanthanum titanium oxide/carbon (LLTO/C) nanofibers with mixed ionic/electronic conductivity, enhanced charge-transfer behavior is realized at the sulfur-LLTO/C double-phase interface, compared to the traditional triple-phase interface. As a result, high sulfur utilization and excellent rate performance are achieved. And the facilitated charge transfer shows great potential to lower the operating temperature and improve the sulfur content for practical applications of ASSLSBs. Cycle performance is also enhanced due to the suppressed shuttle effect of polysulfides by the incorporation of the LLTO/C nanofibers.

Lithium-Ion-Engineered Interlayers of V2C MXene as Advanced Host for Flexible Sulfur Cathode with Enhanced Rate Performance

A flexible free-standing S@lithium-ion-intercalated V₂C MXene/rGO-CNT (S@V₂C-Li/C) electrode was rationally prepared to address the neglected issue of Li-ion transport for high-rate lithium-sulfur batteries. In this unique nanoarchitecture, rGO and CNTs serve as a flexible skeleton with high conductivity, whereas V₂C-Li MXene plays a vital role in both the chemical absorption of polysulfides and the enhanced transport of lithium ions due to its high polarity and enlarged interlayer distance. Benefiting from the synergistic effect of strong chemical absorption capability and fast lithium-ion migration and exchange, the as-prepared S@V₂C-Li/C electrode demonstrates long-term cycling stability with small capacity decay rates of 0.053 and 0.051% per cycle over 500 cycles at 1 and 2 C, respectively.

Solid/Solid Interfacial Architecturing of Solid Polymer Electrolyte-Based All-Solid-State Lithium-Sulfur Batteries by Atomic Layer Deposition

Solid polymer electrolytes (SPEs)-based all-solid-state lithium-sulfur batteries (ASSLSBs) have attracted extensive research attention due to their high energy density and safe operation, which provide potential solutions to the increasing need for harnessing higher energy densities. There is little progress made, however, in the development of ASSLSBs to improve simultaneously energy density and long-term cycling life, mostly due to the "shuttle effect" of lithium polysulfide intermediates in the SPEs and the low interfacial compatibility between the metal lithium anode and the SPE. In this work, the issues of solid/solid interfacial architecturing through atomic layer deposition of Al₂ O₃ on poly(ethylene oxide)-lithium bis(trifluoromethanesulfonyl)imide SPE surface are effectively addressed. The Al₂ O₃ coating promotes the suppression of lithium dendrite formation for over 500 h. ASSLSBs fabricated with two layers of Al₂ O₃ -coated SPE deliver high gravimetric/areal capacity and Coulombic efficiency, as well as excellent cycling stability and extremely low self-discharge rate. This work provides not only a simple and effective approach to boost the electrochemical performances of SPE-based ASSLSBs, but also enriches the fundamental understanding regarding the underlying mechanism responsible for their performance.