The essential demand for functional materials enabling the realization of new energy technologies has triggered tremendous efforts in scientific and industrial research in recent years. Recently, high-entropy materials, with their...

Transition metal sulfides are appealing electrode materials for lithium and sodium batteries owing to their high theoretical capacity. However, they are commonly characterized by rather poor cycling stability and low rate capability. Herein, we investigate CoS, serving as a model compound. We synthesized a porous CoS/C micro-polyhedron composite entangled in a carbon-nanotube-based network (CoS-C/CNT), starting from zeolitic imidazolate frameworks-67 as a single precursor. Following an efficient two-step synthesis strategy, the obtained CoS nanoparticles are uniformly embedded in porous carbonaceous micro-polyhedrons, interwoven with CNTs to ensure high electronic conductivity. The CoS-C/CNT nanocomposite provides excellent bifunctional energy storage performance, delivering 1030 mAh g after 120 cycles and 403 mAh g after 200 cycles (at 100 mA g) as electrode for lithium-ion (LIBs) and sodium-ion batteries (SIBs), respectively. In addition to these high capacities, the electrodes show outstanding rate capability and excellent long-term cycling stability with a capacity retention of 80% after 500 cycles for LIBs and 90% after 200 cycles for SIBs. In situ X-ray diffraction reveals a significant contribution of the partially graphitized carbon to the lithium and at least in part also for the sodium storage and the report of a two-step conversion reaction mechanism of CoS, eventually forming metallic Co and LiS/NaS. Particularly the lithium storage capability at elevated (dis-)charge rates, however, appears to be substantially pseudocapacitive, thus benefiting from the highly porous nature of the nanocomposite.

Prussian blue analogues (PBAs) are reported to be efficient sodium storage materials because of the unique advantages of their metal–organic framework structure. However, the issues of low specific capacity and poor reversibility, caused by phase transitions during charge/discharge cycling, have thus far limited the applicability of these materials. Herein, a new approach is presented to substantially improve the electrochemical properties of PBAs by introducing high entropy into the crystal structure. To achieve this, five different metal species are introduced, sharing the same nitrogen‐coordinated site, thereby increasing the configurational entropy of the system beyond 1.5R. By careful selection of the elements, high‐entropy PBA (HE‐PBA) presents a quasi‐zero‐strain reaction mechanism, resulting in increased cycling stability and rate capability. The key to such improvement lies in the high entropy and associated effects as well as the presence of several active redox centers. The gassing behavior of PBAs is also reported. Evolution of dimeric cyanogen due to oxidation of the cyanide ligands is detected, which can be attributed to the structural degradation of HE‐PBA during battery operation. By optimizing the electrochemical window, a Coulombic efficiency of nearly 100% is retained after cycling for more than 3000 cycles.

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stability, power density, and safety. [1,3,4] Among the alternative electrode materials, transition metal sulfides (TMSs) are quite appealing due to their improved safety and high theoretical capacity (e.g., CuS: 560 mAh g −1 ; CoS 2 : 870 mAh g −1 ; and FeS 2 : 894 mAh g −1 , as calculated for the full conversion reaction). [4] Important, compared to other conversion materials, e.g., oxides, TMSs usually show improved electronic conductivity as well as faster reaction kinetics due to the weaker metal-sulfur bond (compared to the metal-oxygen bond), making the conversion reaction easier. [4] In addition, the voltage hysteresis of sulfides (≈0.7 V) is distinctly lower than that of oxides (≈0.9 V), thus promising better energy efficiencies. [5] Manganese sulfide (α-MnS) is particularly appealing as anode material for LIBs, as it possesses a large theoretical capacity (616 mAh g −1 ) and a lower redox potential compared to other TMSs, such as copper, cobalt, and iron sulfides-besides being highly abundant, ecofriendly, and less expensive. [3,6,7] Despite these advantages, the application of α-MnS as anode material in LIBs has been hampered due to common problems of TMSs such as: (i) serious volume variation during repeated (dis)charge processes leading to poor cycling stability, and (ii) low rate capability arising from low electronic conductivity and Li-ion mobility. [3,7] In order to improve the lithium-ion storage performance of TMSs, many approaches have been proposed. One of the most efficient strategies, so far, is to fabricate nano/microstructured composite materials, Herein, a Mn-based metal-organic framework is used as a precursor to obtain well-defined α-MnS/S-doped C microrod composites. Ultrasmall α-MnS nanoparticles (3-5 nm) uniformly embedded in S-doped carbonaceous mesoporous frameworks (α-MnS/SCMFs) are obtained in a simple sulfidation reaction. As-obtained α-MnS/SCMFsshows outstanding lithium storage performance, with a specific capacity of 1383 mAh g −1 in the 300th cycle or 1500 mAh g −1 in the 120th cycle (at 200 mA g −1 ) using copper or nickel foil as the current collector, respectively. The significant (pseudo)capacitive contribution and the stable composite structure of the electrodes result in impressive rate capabilities and outstanding long-term cycling stability. Importantly, in situ X-ray diffraction measurements studies on electrodes employing various metal foils/disks as current collector reveal the occurrence of the conversion reaction of CuS at (de)lithiation process when using copper foil as the current collector. This constitutes the first report of the reaction mechanism for α-MnS, eventually forming metallic Mn and Li 2 S. In situ dilatometry measurements demonstrate that the peculiar structure of α-MnS/SCMFs effectively restrains the electrode volume variation upon repeated (dis)charge processes. Finally, α-MnS/SCMFs electrodes present an impressive performance when coupled in a full cell with commercial LiMn 1/3 Co 1/3 Ni 1/3 O 2 cathodes.

Carefully selecting the transition metal dopant in consideration of its redox potential allows for further increased energy and power densities.

Improving the interfacial stability between cathode active material (CAM) and solid electrolyte (SE) is a vital step toward the development of high‐performance solid‐state batteries (SSBs). One of the challenges plaguing this field is an economical and scalable approach to fabricate high‐quality protective coatings on the CAM particles. A new wet‐coating strategy based on preformed nanoparticles is presented herein. Nonagglomerated nanoparticles of the coating material (≤5 nm, exemplified for ZrO2) are prepared by solvothermal synthesis, and after surface functionalization, applied to a layered Ni‐rich oxide CAM, LiNi0.85Co0.10Mn0.05O2 (NCM85), producing a uniform surface layer with a unique structure. Remarkably, when used in pelletized SSBs with argyrodite Li6PS5Cl as SE, the coated NCM85 is found to exhibit superior lithium‐storage properties (qdis ≈ 204 mAh gNCM85−1 at 0.1 C rate and 45 °C) and good rate capability. The key to the observed improvement lies in the homogeneity of coating, suppressing interfacial side reactions while simultaneously limiting gas evolution during operation. Moreover, this strategy is proven to have a similar effect in liquid electrolyte‐based Li‐ion batteries and can potentially be used for the application of other, even more favorable, nanoparticle coatings.

Solid-state batteries (SSBs) have been touted as the next major milestone for electrochemical energy storage, improving safety and enabling higher energy densities. LiNiO 2 (LNO) has long been considered a promising cathode material; however, its commercial implementation is complicated by stability issues, including reactivity toward the electrolyte components. To address this, a detailed study probing the electrochemical behavior of LNO in pellet-stack SSB cells, in combination with argyrodite Li 6 PS 5 Cl solid electrolyte (SE) and Li 4 Ti 5 O 12 anode, is for the first time presented herein. In this configuration, LNO delivers a specific capacity of 105 mAh/g LNO after 60 cycles (0.2C, 45 °C), which was improved considerably to 153 mAh/g LNO by applying a LiNbO 3 coating to the material. Using complementary operando and ex situ characterization techniques, contributions to the initial capacity loss and capacity fading could be resolved and attributed to decomposition of the argyrodite SE and to volume changes and gas evolution in LNO.