In Situ Fabrication of Cuprous Selenide Electrode via Selenization of Copper Current Collector for High-Efficiency Potassium-Ion and Sodium-Ion Storage

Nitrogen-Vacancy-Rich VN Clusters Embedded in Carbon Matrix for High-Performance Zinc Ion Batteries

Vanadium nitride (VN) is a potential cathode material with high capacity and high energy density for aqueous zinc batteries (AZIBs). However, the slow kinetics resulting from the strong electrostatic interaction of the electrode materials with zinc ions is a major challenge for fast storage. Here, VN clusters with nitrogen-vacancy embedded in carbon (C) (Nv-VN/C-SS-2) are prepared for the first time to improve the slow reaction kinetics. The nitrogen vacancies can effectively accelerate the reaction kinetics, reduce the electrochemical polarization, and improve the performance. The density functional theory (DFT) calculations also prove that the rapid adsorption and desorption of zinc ions on Nv-VN/C-SS-2 can release more electrons to the delocalized electron cloud of the material, thus adding more active sites. The Nv-VN/C-SS-2 exhibits a specific capacity and outstanding cycle life. Meanwhile, the quasi-solid-state battery exhibits a high capacity of 186.5 mAh g-1, ultra-high energy density of 278.9 Wh kg-1, and a high power density of 2375.1 W kg-1 at 2.5 A g-1, showing excellent electrochemical performance. This work provides a meaningful reference value for improving the comprehensive electrochemical performance of VN through interface engineering.

Interfacial-Confined Isochronous Conversion to Biphasic Selenide Heterostructure with Enhanced Adsorption Behaviors for Robust High-Rate Na-Ion Storage

Sodium-ion batteries (SIBs) have gradually become one of the most promising energy storage techniques in the current era of post-lithium-ion batteries. For anodes, transitional metal selenides (TMSe) based materials are welcomed choices , owing to relatively higher specific capacities and enriched redox active sites. Nevertheless, current bottlenecks are blamed for their poor intrinsic electronic conductivities, and uncontrollable volume expansion during redox reactions. Given that, an interfacial-confined isochronous conversion strategy is proposed, to prepare orthorhombic/cubic biphasic TMSe heterostructure, namely CuSe/Cu3 VSe4 , through using MXene as the precursor, followed by Cu/Se dual anchorage. As-designed biphasic TMSe heterostructure endows unique hierarchical structure, which contains adequate insertion sites and diffusion spacing for Na ions, besides, the surficial pseudocapacitive storage behaviors can be also proceeded like 2D MXene. By further investigation on electronic structure, the theoretical calculations indicate that biphasic CuSe/Cu3 VSe4 anode exhibits well-enhanced properties, with smaller bandgap and thus greatly improves intrinsic poor conductivities. In addition, the dual redox centers can enhance the electrochemical Na ions storage abilities. As a result, the as-designed biphasic TMSe anode can deliver a reversible specific capacity of 576.8 mAh g-1 at 0.1 A g-1 , favorable Na affinity, and reduced diffusion barriers. This work discloses a synchronous solution toward demerits in conductivities and lifespan, which is inspiring for TMSe-based anode development in SIBs systems.

Low-Temperature and Fast-Charge Sodium Metal Batteries

Low-temperature operation of sodium metal batteries (SMBs) at the high rate faces challenges of unstable solid electrolyte interphase (SEI), Na dendrite growth, and sluggish Na+ transfer kinetics, causing a largely capacity curtailment. Herein, low-temperature and fast-charge SMBs are successfully constructed by synergetic design of the electrolyte and electrode. The optimized weak-solvation dual-salt electrolyte enables high Na plating/stripping reversibility and the formation of NaF-rich SEI layer to stabilize sodium metal. Moreover, an integrated copper sulfide electrode is in situ fabricated by directly chemical sulfuration of copper current collector with micro-sized sulfur particles, which significantly improves the electronic conductivity and Na+ diffusion, knocking down the kinetic barriers. Consequently, this SMB achieves the reversible capacity of 202.8 mAh g-1 at -20 °C and 1 C (1 C = 558 mA g-1 ). Even at -40 °C, a high capacity of 230.0 mAh g-1 can still be delivered at 0.2 C. This study is encouraging for further exploration of cryogenic alkali metal batteries, and enriches the electrode material for low-temperature energy storage.

Construction of Synchronous-Deposition K Metal Anodes Via Modulation of Ion/Electron Transport Kinetics for High-Rate and Low-Temperature K Metal Batteries

The construction of conductive scaffolds is demonstrated to be an ideal strategy to alleviate the volume expansion and dendrite growth of K metal anodes. Nevertheless, the heterogeneous top-bottom deposition behavior caused by incompatible electronic/ionic conductivity of three-dimensional (3D) skeleton severely hinders its application. Here, a K2 Se/Cu conducting layer is fabricated on the Cu foam so as to enhance ionic transport and weaken electronic conductivity of the skeleton. Then, an excellent simultaneous deposition behavior of K metal inside the host is obtained for the first time via tuning fast ionic transport and low electronic conductivity. The simultaneous deposition mode can not only utilize the entire 3D structure to accommodate the volume expansion during K deposition but also avoid the formation of K dendrites at high current and ultra-low temperature. Consequently, the symmetric cells present a long cycle lifespan over 1000 h with a low deposition overpotential of 80 mV at 1 mA cm-2 . Furthermore, the full cell matching with the perylene-tetracarboxylic dianhydride (PTCDA) cathode presents an outstanding cycle lifespan over 600 cycles at 5 C at -20°C. The proposed simultaneous deposition strategy provides a new design direction for the construction of dendrite-free K metal anodes.

3D space-confined Co0.85Se architecture with effective interfacial stress relaxation as anode material reveals robust and highly loading potassium-ion batteries

Conversion-type transition metal chalcogenide anodes could bring relatively high specific capacity in potassium ion storage due to multiple electron transport reactions, but often accompanying huge volume changes and resulting in low cycle life and rapid capacity fading.While electrode materials are closely packed, the contact at the interface during potassiation/depotassiation is similar to point-to-point contact, generating strong stress to make self-aggregation occur. In this work, we constructed a 3D carbon framework to confine Co_0.85Se nanocrystals in three-dimensional space, both fulfilling the requirements of the material's size in the nano-scale and providing the largest contact area for releasing stress. With this optimization, nitrogen-doped carbon confined Co_0.85Se nanocrystals (Co_0.85Se@NC) reach an ultra-stable cycle life over 4000 times with a specific capacity of 190.9 mA h g^-1 at 500 mA g^-1 and provide 155.6 mA h g^-1 at 10 A g^-1 in the rate capability test. It also renders the areal capacity up to 1.03 mA h cm^-2 at 500 mA g^-1 in the high-mass loading test. Furthermore, based on the finite element analysis, the 3D confinement strategy has the lowest interfacial stress, ensuring Co_0.85Se nanocrystals with high structural integrity. This strategy can relieve the stress issue in the conversion-type anode and demonstrate superior electrochemical performance even at high-loading mass electrodes.

CuSe2 Nanocubes Enabling Efficient Sodium Storage

As the most promising candidate for lithium-ion batteries (LIBs), the electrochemical performance of sodium-ion batteries (SIBs) is highly dependent on the electrode materials. Copper selenides have established themselves as potential anode materials for SIBs due to their high theoretical capacity and good conductivity. However, the poor rate performance and fast capacity fading are the major challenges to their practical application in SIBs. Herein, single-crystalline CuSe₂ nanocubes (CuSe₂ NCs) are successfully synthesized via a solvothermal method. As an anode of SIBs, the CuSe₂ NCs render an almost 100% initial Coulombic efficiency, an outstanding long cycle life, e.g., 380 mA h g^-1 after 1700 cycles at 10 A g^-1, and an unprecedented rate performance of 344 mA h g^-1 at 50 A g^-1. Ex situ X-ray diffraction (XRD) patterns reveal the crystalline transformation of energy-storage materials, and the density functional theory (DFT) conclusion suggests that fast and stable ion diffusion kinetics enhances their electrochemical performance upon sodiation/desodiaton. The investigation into the mechanism provides a theoretical basis for subsequent practical applications.

Ni3 S2 -Ni Hybrid Nanospheres with Intra-Core Void Structure Encapsulated in N-Doped Carbon Shells for Efficient and Stable K-ion Storage

Iron group metals chalcogenides, especially NiS, are promising candidates for K-ion battery anodes due to their high theoretical specific capacity and abundant reserves. However, the practical application of NiS-based anodes is hindered by slow electrochemical kinetics and unstable structure. Herein, a novel structure of Ni₃ S₂ -Ni hybrid nanosphere with intra-core voids encapsulated by N-doped carbon shells (Ni₃ S₂ -Ni@NC-AE) is constructed, based on the first electrodeposited NiS nanosphere particles, dopamine coating outer layer, oxygen-free annealing treatment to form Ni₃ S₂ -Ni core and N-doped carbon shell, and selective etching of the Ni phase to form intra-core void. The electron/K⁺ transport and K⁺ storage reaction kinetics are enhanced due to shortened diffusion pathways, increased active sites, generation of built-in electric field, high K⁺ adsorption energies, and large electronic density of states at Fermi energy level, resulting from the multi-structures synergistic effect of Ni₃ S₂ -Ni@NC-AE. Simultaneously, the volume expansion is alleviated due to the sufficient buffer space and strong chemical bonding provided by intra-core void and yolk-shell structure. Consequently, the Ni₃ S₂ -Ni@NC-AE exhibits excellent specific capacity (438 mAh g^-1 at 0.1 A g^-1 up to 150 cycles), outstanding rate performances, and ultra-stable long-cycle performance (176.4 mAh g^-1 at 1 A g^-1 up to 5000 cycles) for K-ion storage.

Doping-Induced Electronic/Ionic Engineering to Optimize the Redox Kinetics for Potassium Storage: A Case Study of Ni-Doped CoSe2

Heteroatom doping effectively tunes the electronic conductivity of transition metal selenides (TMSs) with rapid K⁺ accessibility in potassium ion batteries (PIBs). Although considerable efforts are dedicated to investigating the relationship between the doping strategy and the resulting electrochemistry, the doping mechanisms, especially in view of the ion and electronic diffusion kinetics upon cycling, are seldom elucidated systematically. Herein, the crystal structure stability, charge/ion state, and bandgap of the active materials are found to be precisely modulated by favorable heteroatom doping, resulting in intrinsically fast kinetics of the electrode materials. Based on the combined mechanisms of intercalation and conversion reactions, electron and K⁺ ion transfer in Ni-doped CoSe₂ embedded in carbon nanocomposites (Ni-CoSe₂ @NC) can be significantly enhanced via electronic engineering. Benefiting from the synthetic controlled Ni grains, the heterointerface formed by the intermediate products of electrochemical reactions in Ni-CoSe₂ @NC strengthens the conversion kinetics and interdiffusion process, developing a low-barrier mesophase with optimized potassium storage. Overall, an electronic tuning strategy can offer deeper atomic insights into the conversion reaction of TMSs in PIBs.