Most P2-type layered oxides suffer from multiple voltage plateaus, due to Na+/vacancy-order superstructures caused by strong interplay between Na–Na electrostatic interactions and charge ordering in the transition metal layers. Here, Mg ions are successfully introduced into Na sites in addition to the conventional transition metal sites in P2-type Na0.7[Mn0.6Ni0.4]­O2 as new cathode materials for sodium-ion batteries. Mg ions in the Na layer serve as “pillars” to stabilize the layered structure, especially for high-voltage charging, meanwhile Mg ions in the transition metal layer can destroy charge ordering. More importantly, Mg ion occupation in both sodium and transition metal layers will be able to create “Na–O–Mg” and “Mg–O–Mg” configurations in layered structures, resulting in ionic O 2p character, which allocates these O 2p states on top of those interacting with transition metals in the O-valence band, thus promoting reversible oxygen redox. This innovative design contributes smooth voltage profiles and high structural stability. Na0.7Mg0.05[Mn0.6Ni0.2Mg0.15]­O2 exhibits superior electrochemical performance, especially good capacity retention at high current rate under a high cutoff voltage (4.2 V). A new P2 phase is formed after charge, rather than an O2 phase for the unsubstituted material. Besides, multiple intermediate phases are observed during high-rate charging. Na-ion transport kinetics are mainly affected by elemental-related redox couples and structural reorganization. These findings will open new opportunities for designing and optimizing layer-structured cathodes for sodium-ion batteries.

Sponge-like composites assembled by cobalt sulfides quantum dots (Co 9 S 8 QD), mesoporous hollow carbon polyhedral (HCP) matrix, and a reduced graphene oxide (rGO) wrapping sheets are synthesized by a simultaneous thermal reduction, carbonization, and sulfidation of zeolitic imidazolate frameworks@GO precursors. Specifically, Co 9 S 8 QD with size less than 4 nm are homogenously embedded within HCP matrix, which is encapsulated in macroporous rGO, thereby leading to the double carbon-confined hierarchical composites with strong coupling effect. Experimental data combined with density functional theory calculations reveal that the presence of coupled rGO not only prevents the aggregation and excessive growth of particles, but also expands the lattice parameters of Co 9 S 8 crystals, enhancing the reactivity for sodium storage. Benefiting from the hierarchical porosity, conductive network, structural integrity, and a synergistic effect of the components, the sponge-like composites used as binder-free anodes manifest outstanding sodium-storage performance in terms of excellent stable capacity (628 mAh g −1 after 500 cycles at 300 mA g −1 ) and exceptional rate capability (529, 448, and 330 mAh g −1 at 1600, 3200, and 6400 mA g −1 ). More importantly, the synthetic method is very versatile and can be easily extended to fabricate other transition-metal-sulfides-based sponge-like composites with excellent electrochemical performances.

Potassium‐ion hybrid capacitors (PIHCs), elaborately integrate the advantages of high output power as well as long lifespan of supercapacitors and the high energy density of batteries, and exhibit great possibilities for the future generations of energy storage devices. The critical next step for future implementation lies in exploring a high‐rate battery‐type anode with an ultra‐stable structure to match the capacitor‐type cathode. Herein, a “dual‐carbon” is constructed, in which a three‐dimensional nitrogen‐doped microporous carbon polyhedron (NMCP) derived from metal‐organic frameworks is tightly wrapped by two‐dimensional reduced graphene oxide (NMCP@rGO). Benefiting from the synergistic effect of the inner NMCP and outer rGO, the NMCP@rGO exhibits a superior K‐ion storage capability with a high reversible capacity of 386 mAh g−1 at 0.05 A g−1 and ultra‐long cycle stability with a capacity of 151.4 mAh g−1 after 6000 cycles at 5.0 A g−1. As expected, the as‐assembled PIHCs with a working voltage as high as 4.2 V present a high energy/power density (63.6 Wh kg−1 at 19 091 W kg−1) and excellent capacity retention of 84.7% after 12 000 cycles. This rational construction of advanced PIHCs with excellent performance opens a new avenue for further application and development.

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Two-dimensional (2D) hydroxide nanosheets can exhibit exceptional electrochemical performance owing to their shortened ion diffusion distances, abundant active sites, and various valence states. Herein, we report ZnCo(OH)Cl·0.45HO nanosheets (thickness ∼30 nm) which crystallize in a layered structure and exhibit a high specific capacitance of 3946.5 F g at 3 A g for an electrochemical pseudocapacitor. ZnCo(OH)Cl·0.45HO was synthesized by a homogeneous precipitation method and spontaneously crystallized into 2D nanosheets in well-defined hexagonal morphology with crystal structure revealed by synchrotron X-ray powder diffraction data analysis. In situ growth of ZnCo(OH)Cl·0.45HO nanosheet arrays on conductive Ni foam substrate was successfully realized. Asymmetric supercapacitors based on ZnCo(OH)Cl·0.45HO nanosheets @Ni foam// PVA, KOH//reduced graphene oxide exhibits a high energy density of 114.8 Wh kg at an average power density of 643.8 W kg, which surpasses most of the reported all-solid-state supercapacitors based on carbonaceous materials, transition metal oxides/hydroxides, and MXenes. Furthermore, a supercapacitor constructed from ZnCo(OH)Cl·0.45HO nanosheets@PET substrate shows excellent flexibility and mechanical stability. This study provides layered bimetallic hydroxide nanosheets as promising electroactive materials for flexible, solid-state energy storage devices, presenting the best reported performance to date.

All‐solid‐state lithium metal batteries (ASSLMBs) stand out for the next generation of energy storage system. However, the further realization is severely hampered by the lithium dendrite formation in solid state electrolytes (SSEs), by mechanisms that remain controversial. Herein, with the aid of experimental and theoretical approaches, the origin of dendrite formation in representative LiBH4 SSE, which is thermodynamically stable with the Li metal, suppressing the side reaction between Li and SSE is elucidated. It is demonstrated that upon diffusion, Li+ encounters an electron, and is subsequently reduced to Li0 within the grain boundary/pore of SSE, eventually leading to short circuit. Thus, introducing LiF with the ability of interstitial filling and low electronic conductivity into SSE is the effective countermeasure, and as expected, with the addition of LiF, the critical current density (CCD) increases by 235% compared to the value of pure LiBH4. The TiS2|LiBH4–LiF|Li ASSLMBs manifest a reversible capacity of 137 mAh g−1 at 0.4 C upon 60 cycles. These findings not only unravel critical issues in Li dendrite formation in SSE, but also propose the countermeasure.

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Two-dimensional LDH nanosheets recently have generated considerable interest in various promising applications because of their intriguing properties. Herein, we report a facile in situ nucleation strategy toward in situ decorating monodispersed Ni-Fe LDH ultrafine nanosheets (UNs) on graphene oxide template based on the precise control and manipulation of LDH UNs anchored, nucleated, grown, and crystallized. Anion-exchange behavior was observed in this Ni-Fe LDH UNs@rGO composite. The Ni-Fe LDH UNs@rGO electrodes displayed a significantly enhanced specific capacitance (2715F g at 3 A g) and energy density (82.3 Wh kg at 661 W kg), which exceeds the energy densities of most previously reported nickel iron oxide/hydroxides. Moreover, the asymmetric supercapacitor, with the Ni-Fe LDH UNs @rGO composite as the positive electrode material and reduced graphene oxide (rGO) as the negative electrode material, exhibited a high energy density (120 Wh kg ) at an average power density of 1.3 kW kg. A charge transfer from LDH layer to graphene layer, which means a built in electric field directed from LDH to graphene can be established by DFT calculations, which can significantly accelerate reaction kinetics and effectively optimize the capacitive energy storage performance.