Sodium-ion batteries (SIBs) are regarded as the ideal low-cost choice for next-generation large-scale energy storage system. Carbonyl-based organic salt-disodium rhodizonate (Na₂C₆O₆) with high theoretical specific capacity (501 mAh·g⁻¹) is considered as a promising cathode material for SIBs. However, the dissolution of active material in electrolyte and low electronic conductivity lead to rapidly capacity decay and poor rate performance. Herein, a simple method is designed to construct free-standing and flexible Ti₃C₂T_x Na₂C₆O₆/MXene paper via vacuum-assisted filtration and antisolvent approach. The MXene can form an electronic conductive network, adsorb the active materials, and offer additional active sites for Na storage. The binder-free Na₂C₆O₆/MXene paper delivers excellent electrochemical property with a high rate performance of 231 mAh·g⁻¹ at 1,000 mA·g⁻¹ and a high capacity of 215 mAh·g⁻¹ after 100 cycles. This work provides an attractive strategy for designing high-performance organic electrode materials of SIBs.

Lithium metal (Li) is believed to be the ultimate anode for lithium-ion batteries (LIBs) owing to the advantages of high theoretical capacity, the lowest electrochemical potential, and light weight. Nevertheless, issues such as uncontrollable growth of Li dendrites, large volume changes, high chemical reactivity, and unstable solid electrolyte interphase (SEI) hinder its rapid development and practical application. Herein a stable and dendrite-free Li-metal anode is obtained by designing a flexible and freestanding MXene/COF framework for metallic Li. COF-LZU1 microspheres are distributed among the MXene film framework. Lithiophilic COF-LZU1 microspheres as nucleation seeds can promote uniform Li nucleation by homogenizing the Li⁺ flux and lowering the nucleation barrier, finally resulting in dense and dendrite-free Li deposition. Under the regulation of the COF-LZU1 seeds, the Coulombic efficiency of the MXene/COF-LZU1 framework and electrochemical stability of corresponding symmetric cells are obviously enhanced. Li-S full cells with the modified Li-metal anode and sulfurized polyacrylonitrile (S@PAN) cathode also exhibited a superior electrochemical performance.

Silicon is considered an exceptionally promising alternative to the most commonly used material, graphite, as an anode for next-generation lithium-ion batteries, as it has high energy density owing to its high theoretical capacity and abundant storage. Here, microsized walnut-like porous silicon/reduced graphene oxide (P-Si/rGO) core–shell composites are successfully prepared via in situ reduction followed by a dealloying process. The composites show specific capacities of more than 2, 100 mAh·g^-1 at a current density of 1, 000 mA·g^-1, 1, 600 mAh·g^-1 at 2, 000 mA·g^-1, 1, 500 mAh·g^-1 at 3, 000 mA·g^-1, 1, 200 mAh·g^-1 at 4, 000 mA·g^-1, and 950 mAh·g^-1 at 5, 000 mA·g^-1, and maintain a value of 1, 258 mAh·g^-1 after 300 cycles at a current density of 1, 000 mA·g^-1. Their excellent rate performance and cycling stability can be attributed to the unique structural design: 1) The graphene shell dramatically improves the conductivity and stabilizes the solid– electrolyte interface layers; 2) the inner porous structure supplies sufficient space for silicon expansion; 3) the nanostructure of silicon can prevent the pulverization resulting from volume expansion stress. Notably, this in situ reduction method can be applied as a universal formula to coat graphene on almost all types of metals and alloys of various sizes, shapes, and compositions without adding any reagents to afford energy storage materials, graphene-based catalytic materials, graphene-enhanced composites, etc.