Biomass-derived, 3D interconnected N-doped carbon foam as a host matrix for Li/Na/K-selenium batteries

From Solid-Solution MXene to Cr-Substituted Na3V2(PO4)3: Breaking the Symmetry of Sodium Ions for High-Voltage and Ultrahigh-Rate Cathode Performance

Stabilizing Na⁺ accessibility at high voltage and accelerating Na⁺ diffusivity are pressing issues to further enhance the energy density of the Na₃V₂(PO₄)₃ (NVP) cathode for sodium-ion batteries (SIBs). Herein, by taking a V/Cr solid-solution MXene as a precursor, a facile in-situ reactive transformation strategy to embed Cr-substituted NVP (NVCP) nanocrystals in a dual-carbon network is proposed. Particularly, the substituted Cr atom triggers the accessibility of additional Na⁺ in NVCP, which is demonstrated by an additional reversible redox plateau at 4.0 V even under extreme conditions. More importantly, the Cr atom alters the Na⁺ ordering at the Na2 sites with an additional intermediate phase formation during charging/discharging, thus reducing the energy barriers for Na⁺ migration. As a result, Na⁺ diffusivity in NVCP accelerates to 2-3 orders of magnitude higher than that of NVP. Eventually, the NVCP cathode exhibits extraordinarily high-rate capability (78 mA g^-1 at 200 C and 68975 W kg^-1), outstanding cycle stability (over 1500 cycles at 10 C), excellent low-temperature property, and full cell performance.

Reduced Graphene Oxide-Coated Separator to Activate Dead Potassium for Efficient Potassium Batteries

Potassium (K) metal batteries (KMBs) have the advantages of relatively low electric potential (-2.93 V), high specific capacity (687 mAh g^-1), and low cost, which are highly appealing to manufacturers of portable electric products and vehicles. However, the large amounts of "dead K" caused by K dendrite growth and volumetric expansion can cause severe K metal anode deactivation. Here, a thin layer of conductive reduced graphene oxide (rGO) was coated on a GF separator (rGO@GF) to activate the generated dead K. Compared with the batteries adopting an original separator, those adopting a modified separator have significantly improved specific capacity and cycling stability. The life of full-cell of KMBs combining an rGO@GF separator with synthesized K_0.51V₂O₅ is expected to exceed 400 cycles, with an initial capacity of 92 mAh g^-1 at 0.5 A g^-1 and an attenuation rate per cycle as low as 0.03%. Our work demonstrates that a composite separator of high conductivity is beneficial for high performance KMBs.

Bimetallic Selenide Decorated Nanoreactor Synergizing Confinement and Electrocatalysis of Se Species for 3D-Printed High-Loading K-Se Batteries

The potassium-selenium (K-Se) battery has been considered an appealing candidate for next-generation energy storage systems owing to the high energy and low cost. Nonetheless, its development is plagued by the tremendous volume expansion and sluggish reaction kinetics of the Se cathode. Moreover, implementing favorable areal capacity and longevous cycling of a high-loading K-Se battery remains a daunting challenge facing commercial applications. Herein, we devise a Se and CoNiSe₂ coembedded nanoreactor (Se/CoNiSe₂-NR) affording low carbon content as an advanced cathode for K-Se batteries. We systematically uncover the enhanced K₂Se₂/K₂Se adsorption and promoted K⁺ diffusion behavior with the incorporation of Co throughout theoretical simulation and electrokinetic analysis. As a result, Se/CoNiSe₂-NR harvests high cycling stability with a capacity decay rate of 0.038% per cycle over 950 cycles at 1.0 C. More encouragingly, equipped with a 3D-printed Se/CoNiSe₂-NR electrode with tunable Se loadings, K-Se full batteries enable steady cycling at an elevated Se loading of 3.8 mg cm^-2. Our endeavor ameliorates the capacity and lifetime performance of the emerging K-Se device, thereby offering a meaningful tactic in pursuing its practical application.

Toward Theoretical Capacity and Superhigh Power Density for Potassium-Selenium Batteries via Facilitating Reversible Potassiation Kinetics

Potassium-selenium (K-Se) batteries attract tremendous attention because of the two-electron transfer of the selenium cathode. Nonetheless, practical K-Se cells normally display selenium underutilization and unsatisfactory rate capability. Herein, we employ a synergistic spatial confinement and architecture engineering strategy to establish selenium cathodes for probing the effect of K⁺ diffusion kinetics on K-Se battery performance and improving the charge transfer efficiency at ultrahigh rates. By impregnating selenium into hollow and solid carbon spheres with similar diameters and porous structures, the obtained parallel Se/C composites possess nearly identical selenium loadings, molecular structures, and heterogeneous interfaces but enormously different paths for K⁺ diffusion. Remarkably, as the solid-state K⁺ diffusion distance is significantly reduced, the K-Se cell achieves 96% of 2e^- transfer capacity (647.1 mA h g^-1). Reversible capacities of 283.5 and 224.1 mA h g^-1 are obtained at 7.5 and 15C, respectively, corresponding to an unprecedented high power density of 8777.8 W kg^-1. Quantitative kinetic analysis demonstrated a twofold higher capacitive charge storage contribution and a 1 order of magnitude higher K⁺ diffusion coefficient due to the short K⁺ diffusion path. By combining the determination of potassiation products by ex situ characterization and density functional theory (DFT) calculations, it is identified that the kinetic factor is decisive for K-Se battery performances.

Nitrogen/oxygen codoped hierarchical porous Carbons/Selenium cathode with excellent lithium and sodium storage behavior

A nitrogen/oxygen codoped carbon derived from sweet potato (SPC) with interconnected micro-mesopores is applied to encapsulate selenium composite (SPC/Se) with a high Se loading (74.3%). As a cathode for advanced Li-Se and Na-Se batteries, the SPC/Se exhibits superior electrochemical behavior in low-cost carbonate electrolyte. Including the hierarchically porous structure of SPC and the chemical bonding between Se and carbon, the strong binding energy between SPC and Li₂Se/Na₂Se is also proved by DFT method, which results in the effective mitigation of shuttle reaction and volume change for SPC/Se cathode. For Li-Se batteries, the SPC/Se composite shows the initial specific charge capacity of 668 mAh g^-1 with a high initial coulombic efficiency of 78%, and maintains a stable reversible capacity of 587 mAh g^-1 after 1000 cycles with a weak capacity decay of 0.082% at 0.2C. It still retains a reversible specific capacity of 375 mAh g^-1 even at 20C. For Na-Se battery, the SPC/Se composite displays the initial specific charge capacity of 671 mAh g^-1 at 0.2C and maintains a reversible specific capacity of 412 mAh g^-1 after 500 cycles with a capacity retention of 61.4%. When the current density increases to 20C, it still delivers a high reversible specific capacity of 420 mAh g^-1. Finally, the transformation mechanism of Se molecule is illustrated detailedly in (de)lithi/sodiation process.

Ultra-small Fe3O4 nanodots encapsulated in layered carbon nanosheets with fast kinetics for lithium/potassium-ion battery anodes

Iron oxides are regarded as promising anodes for both lithium-ion batteries (LIBs) and potassium-ion batteries (KIBs) due to their high theoretical capacity, abundant reserves, and low cost, but they are also facing great challenges due to the sluggish reaction kinetics, low electronic conductivity, huge volume change, and unstable electrode interphases. Moreover, iron oxides are normally prepared at high temperature, forming large particles because of Ostwald ripening, and exhibiting low electronic/ionic conductivity and unfavorable mechanical stability. To address those issues, herein, we have synthesized ultra-small Fe₃O₄ nanodots encapsulated in layered carbon nanosheets (Fe₃O₄@LCS), using the coordination interaction between catechol and Fe³⁺, demonstrating fast reaction kinetics, high capacity, and typical capacitive-controlled electrochemical behaviors. Such Fe₃O₄@LCS nanocomposites were derived from coordination compounds with layered structures via van der Waals's force. Fe₃O₄@LCS-500 (annealed at 500 °C) nanocomposites have displayed attractive features of ultra-small particle size (∼5 nm), high surface area, mesoporous and layered feature. When used as anodes, Fe₃O₄@LCS-500 nanocomposites delivered exceptional electrochemical performances of high reversible capacity, excellent cycle stability and rate performance for both LIBs and KIBs. Such exceptional performances are highly associated with features of Fe₃O₄@LCS-500 nanocomposites in shortening Li/K ion diffusion length, fast reaction kinetics, high electronic/ionic conductivity, and robust electrode interphase stability.

Ultra-small Fe₃O₄ nanodots encapsulated in layered carbon nanosheet nanocomposites were synthesized, showing fast reaction kinetics, high conductivity, and robust stability.

Nanocavity-enriched Co3O4@ZnCo2O4@NC porous nanowires derived from 1D metal coordination polymers for fast Li+ diffusion kinetics and super Li+ storage

Nanocavity-enriched Co3O4@ZnCo2O4@NC porous nanowires have been successfully prepared by a two-step annealing process of one-dimensional (1D) coordination polymer precursors. Such unique nanowires with nanocavity-based porous channels can provide a large specific surface area, which allows fast electron/ion transfer and alleviates the volume expansion caused by strain during the charge/discharge processes. While used as the anode material of lithium-ion batteries (LIBs), Co3O4@ZnCo2O4@NC electrodes exhibit outstanding rate capacity and cycling stability, such as a high reversible capacity of 931 mA h g-1 after 50 cycles at a current density of 0.1 A g-1 and a long-term cycling efficiency of 649 mA h g-1 after 600 cycles at 1 A g-1. This coordination polymer template method lays a solid foundation for the design and preparation of bimetal oxide materials with outstanding electrochemical performance for LIBs.

Pseudocapacitance-dominated high-performance and stable lithium-ion batteries from MOF-derived spinel ZnCo2O4/ZnO/C heterostructure anode

Spinel ZnCo₂O₄/ZnO/C hierarchically porous structures were successfully synthesized by two-step annealing of cyanide-bridged coordination polymer precursors.

Binary zinc–cobalt metal–organic framework derived mesoporous ZnCo2O4@NC polyhedron as a high-performance lithium-ion battery anode

Ternary transition metal oxides have attracted increasing attention due to their many merits, and will enhance electrochemical performance via the synergistic effects of the different single metal oxides.