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Solid composite electrolytes (SCEs) that combine the advantages of solid polymer electrolytes (SPEs) and inorganic ceramic electrolytes (ICEs) present acceptable ionic conductivity, high mechanical strength, and favorable interfacial contact with electrodes, which greatly improve the electrochemical performance of all‐solid‐state batteries compared to single SPEs and ICEs. However, there are many challenges to overcome before the practical application of SCEs, including the low ionic conductivity less than 10−3 S cm−1 at ambient temperature, poor interfacial stability, and high interfacial resistance, which greatly restrict the room temperature performance. Herein, the advances of SCEs applied in all‐solid‐state lithium batteries are presented, including the Li ion migration mechanism of SCEs, the strategies to enhance the ionic conductivity of SCEs by various morphologies of ICEs, and construction methods of the low resistance and stable interfaces of SCEs with both cathode and anode. Finally, some typical applications of SCEs in lithium batteries are summarized and future development directions are prospected. This work presents how it is quite significant to further enhance the ionic conductivity of SCEs by developing the novel SPEs with the special morphology of ICEs for advanced all‐solid‐state lithium batteries. Herein, the advantages and ionic transport mechanisms of solid composite electrolyte (SCE) as well as the relationship between morphology of ceramic fillers and ionic conductivity of SCE are reviewed. Recent progress and strategies to settle interfacial issues for high‐performance all‐solid‐state lithium metal batteries with SCE are also concluded and future research directions of SCEs are proposed.

Ether based electrolytes have surfaced as alternatives to conventional carbonates allowing for enhanced electrochemical performance of sodium-ion batteries; however, the primary source of the improvement remains poorly understood. Here we show that coupling titanium dioxide and other anode materials with diglyme does enable higher efficiency and reversible capacity than those for the combination involving ester electrolytes. Importantly, the electrolyte dependent performance is revealed to be the result of the different structural evolution induced by a varied sodiation depth. A suit of characterizations show that the energy barrier to charge transfer at the interface between electrolyte and electrode is the factor that dominates the interfacial electrochemical characteristics and therefore the energy storage properties. Our study proposes a reliable parameter to assess the intricate sodiation dynamics in sodium-ion batteries and could guide the design of aprotic electrolytes for next generation rechargeable batteries. Sodium ion batteries are known to benefit from the use of ether electrolytes. Here the authors reveal the origin showing that the energy barrier of charge transfer at the electrolyte/electrode interface dominates the interfacial electrochemical characteristics and is favorably small.

The replacement of liquid organic electrolytes with solid‐state electrolytes (SSEs) is a feasible way to solve the safety issues and improve the energy density of lithium batteries. Developing SSEs materials that can well match with high‐voltage cathodes and lithium metal anode is quite significant to develop high‐energy‐density lithium batteries. Li1 + xAlxTi2 ‐ x(PO4)3 (LATP) SSE with NASICON structure exhibits high ionic conductivity, low cost and superior air stability, which enable it as one of the most hopeful candidates for all‐solid‐state batteries (ASSBs). However, the high interfacial impedance between LATP and electrodes, and the severe interfacial side reactions with the lithium metal greatly limit its applications in ASSBs. This review introduces the crystal structure and ion transport mechanisms of LATP and summarizes the key factors affecting the ionic conductivity. The side reaction mechanisms of LATP with Li metal and the promising strategies for optimizing interfacial compatibility are reviewed. We also summarize the applications of LATP including as surface coatings of cathode particles, ion transport network additives and inorganic fillers of composite polymer electrolytes. At last, this review proposes the challenges and the future development directions of LATP in SSBs. Schematic of the structure in this review.

Sodium metal batteries have potentially high energy densities, but severe sodium-dendrite growth and side reactions prevent their practical applications, especially at high temperatures. Herein, we design an inorganic ionic conductor/gel polymer electrolyte composite, where uniformly cross-linked beta alumina nanowires are compactly coated by a poly(vinylidene fluoride-co-hexafluoropropylene)-based gel polymer electrolyte through their strong molecular interactions. These  beta alumina nanowires combined with the gel polymer layer create dense and homogeneous solid-liquid hybrid sodium-ion transportation channels through and along the nanowires, which promote uniform sodium deposition and formation of a stable and flat solid electrolyte interface on the sodium metal anode. Side reactions between the sodium metal and liquid electrolyte, as well as sodium dendrite formation, are successfully suppressed, especially at 60 °C. The sodium vanadium phosphate/sodium full cells with composite electrolyte exhibit 95.3% and 78.8% capacity retention after 1000 cycles at 1 C at 25 °C and 60 °C, respectively. Here the authors show a beta alumina nanowires/gel polymer composite electrolyte design. The dense and homogeneous solid-liquid hybrid sodium-ion transportation channels promote uniform sodium deposition and stripping and significantly improve the performance of a Na metal battery.

Developing highly active and durable electrocatalysts for acidic oxygen evolution reaction remains a great challenge due to the sluggish kinetics of the four-electron transfer reaction and severe catalyst dissolution. Here we report an electrochemical lithium intercalation method to improve both the activity and stability of RuO 2 for acidic oxygen evolution reaction. The lithium intercalates into the lattice interstices of RuO 2 , donates electrons and distorts the local structure. Therefore, the Ru valence state is lowered with formation of stable Li-O-Ru local structure, and the Ru–O covalency is weakened, which suppresses the dissolution of Ru, resulting in greatly enhanced durability. Meanwhile, the inherent lattice strain results in the surface structural distortion of Li x RuO 2 and activates the dangling O atom near the Ru active site as a proton acceptor, which stabilizes the OOH* and dramatically enhances the activity. This work provides an effective strategy to develop highly efficient catalyst towards water splitting. While water splitting in acid offers higher operational performances than in alkaline conditions, there are few high-activity, acid-stable oxygen evolution electrocatalysts. Here, authors examine electrochemical Li intercalation to improve the activity and stability of RuO 2 for acidic water oxidation.

High-voltage lithium metal batteries suffer from poor cycling stability caused by the detrimental effect on the cathode of the water moisture present in the non-aqueous liquid electrolyte solution, especially at high operating temperatures (e.g., ≥60 °C). To circumvent this issue, here we report lithium hexamethyldisilazide (LiHMDS) as an electrolyte additive. We demonstrate that the addition of a 0.6 wt% of LiHMDS in a typical fluorine-containing carbonate-based non-aqueous electrolyte solution enables a stable Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) coin cell operation up to 1000 or 500 cycles applying a high cut-off cell voltage of 4.5 V in the 25 °C−60 °C temperature range. The LiHMDS acts as a scavenger for hydrofluoric acid and water and facilitates the formation of an (electro)chemical robust cathode|electrolyte interphase (CEI). The LiHMDS-derived CEI prevents the Ni dissolution of NCM811, mitigates the irreversible phase transformation from layered structure to rock-salt phase and suppresses the side reactions with the electrolyte solution. High-voltage non-aqueous lithium metal batteries suffer from poor cycling stability due to the presence of impurities in the electrolyte solution. Here, the authors report lithium hexamethyldisilazide to scavenge HF and H 2 O, prevent the Ni dissolution and suppress side reactions during cycling.

Security risks of flammability and explosion represent major problems with the use of conventional lithium rechargeable batteries using a liquid electrolyte. The application of solid‐state electrolytes could effectively help to avoid these safety concerns. However, integrating the solid‐state electrolytes into the all‐solid‐state lithium batteries is still a huge challenge mainly due to the high interfacial resistance present in the entire battery, especially at the interface between the cathode and the solid‐state electrolyte pellet and the interfaces inside the cathode. Herein, recent progress made from investigations of cathode/solid‐state electrolyte interfacial behaviors including the contact problem, the interlayer diffusion issue, the space‐charge layer effect, and electrochemical compatibility is presented according to the classification of oxide‐, sulfide‐, and polymer‐based solid‐state electrolytes. We also propose strategies for the construction of ideal next‐generation cathode/solid‐state electrolyte interfaces with high room‐temperature ionic conductivity, stable interfacial contact during long cycling, free formation of the space‐charge region, and good compatibility with high‐voltage cathodes. In this review, we present the state‐of‐the‐art development in terms of the cathode/solid‐state electrolyte interfacial issues and the corresponding solutions both at the cathode/solid‐state electrolyte pellet interface and inside the cathode. We summarize the major problems affecting the cathode/solid‐state electrolyte interfacial property (poor point‐to‐point solid–solid contact and harmful interfacial reactions) along with progressive solution strategies in terms of different solid‐state electrolyte types (oxide, sulfide, and polymer solid‐state electrolyte). We also outline the investigations of the mechanism underlying the cathode/solid‐state electrolyte interfacial behavior through modeling and advanced characterization methods.

Silicon (Si)‐based solid‐state batteries (Si‐SSBs) are attracting tremendous attention because of their high energy density and unprecedented safety, making them become promising candidates for next‐generation energy storage systems. Nevertheless, the commercialization of Si‐SSBs is significantly impeded by enormous challenges including large volume variation, severe interfacial problems, elusive fundamental mechanisms, and unsatisfied electrochemical performance. Besides, some unknown electrochemical processes in Si‐based anode, solid‐state electrolytes (SSEs), and Si‐based anode/SSE interfaces are still needed to be explored, while an in‐depth understanding of solid–solid interfacial chemistry is insufficient in Si‐SSBs. This review aims to summarize the current scientific and technological advances and insights into tackling challenges to promote the deployment of Si‐SSBs. First, the differences between various conventional liquid electrolyte‐dominated Si‐based lithium‐ion batteries (LIBs) with Si‐SSBs are discussed. Subsequently, the interfacial mechanical contact model, chemical reaction properties, and charge transfer kinetics (mechanical–chemical kinetics) between Si‐based anode and three different SSEs (inorganic (oxides) SSEs, organic–inorganic composite SSEs, and inorganic (sulfides) SSEs) are systemically reviewed, respectively. Moreover, the progress for promising inorganic (sulfides) SSE‐based Si‐SSBs on the aspects of electrode constitution, three‐dimensional structured electrodes, and external stack pressure is highlighted, respectively. Finally, future research directions and prospects in the development of Si‐SSBs are proposed. This review provides a systematic overview of silicon‐based solid‐state batteries (Si‐SSBs), focusing on the different interfacial configuration characteristics and mechanisms between various types of solid‐state electrolytes and Si‐based anodes as well as the correlations between these interfacial characteristics and electrochemical performance. We envision that this review can point navigation for benefiting the future advancement of Si‐SSBs.

The application of lithium‐based batteries is challenged by the safety issues of leakage and flammability of liquid electrolytes. Polymer electrolytes (PEs) can address issues to promote the practical use of lithium metal batteries. However, the traditional preparation of PEs such as the solution‐casting method requires a complicated preparation process, especially resulting in side solvents evaporation issues. The large thickness of traditional PEs reduces the energy density of the battery and increases the transport bottlenecks of lithium‐ion. Meanwhile, it is difficult to fill the voids of electrodes to achieve good contact between electrolyte and electrode. In situ polymerization appears as a facile method to prepare PEs possessing excellent interfacial compatibility with electrodes. Thus, thin and uniform electrolytes can be obtained. The interfacial impedance can be reduced, and the lithium‐ion transport throughput at the interface can be increased. The typical in situ polymerization process is to implant a precursor solution containing monomers into the cell and then in situ solidify the precursor under specific initiating conditions, and has been widely applied for the preparation of PEs and battery assembly. In this review, we focus on the preparation and application of in situ polymerization method in gel polymer electrolytes, solid polymer electrolytes, and composite polymer electrolytes, in which different kinds of monomers and reactions for in situ polymerization are discussed. In addition, the various compositions and structures of inorganic fillers, and their effects on the electrochemical properties are summarized. Finally, challenges and perspectives for the practical application of in situ polymerization methods in solid‐state lithium‐based batteries are reviewed. In situ polymerization appears as a facile method to prepare polymer electrolytes (PEs) possessing excellent interfacial compatibility with electrodes. The kinds of PEs, monomers, fillers, and reactions for in situ polymerization are summarized. Challenges and perspectives are discussed.

Solid polymer electrolytes (SPEs) are considered as promising electrolytes for high-voltage lithium metal batteries. Whereas, the strong dipole-dipole interaction in polymer electrolytes limits the enhancement of the ionic conductivity. Here, we propose the 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropylether (TTE) diluent to significantly regulate the dipole-dipole interaction in polymer-ionic solvate electrolytes (TPISEs). The TTE encapsulates ionic solvate to reduce the dipole-dipole interaction of ionic solvate with the polymer matrix, which promotes their homogeneous distribution, creating a continuous ion percolating network among the polymer matrix. The ion conductivity of TPISEs is therefore enhanced to 1.27×10 −3 S cm −1 at 25 °C. Meanwhile, the TTE induces the ionic solvate to transform from contact ion pairs to aggregates, contributing to a stable lithium/electrolyte interface with exchange current density 190 times larger than that without TTE. The Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cells exhibit good cycling stability from −30 °C to 60 °C. The practical pouch cells consisting of a thin Li metal foil (50 μm) and a high-areal-capacity positive electrode (3.58 mAh cm −2 ) achieve a high specific energy of 354.4 Wh·kg −1 and maintain 78.1% capacity after 450 cycles at 54 mA g −1 and 25 °C. This work provides a design strategy for SPEs beyond the bottleneck of ionic conductivity for practical solid-state batteries. Solid polymer electrolytes suffer from limited ionic conductivity and poor interfacial stability for lithium batteries. Here, authors propose a fluorinated ether diluent to reduce the dipole-dipole interaction of ionic solvate with the polymer matrix and induce the formation of aggregates.