Metal phosphides have shown great application potential as anode for sodium-ion batteries (NIBs) owing to high theoretical capacity, suitable operation voltage and abundant resource. Unfortunately, the application of NiP₂ anode is severely impeded by low practical capacity and fast capacity decay due to the huge volume variation and low reactivity of internal phosphorus (P) component towards Na⁺. Herein, electronic structure modulation of NiP₂ via heteroatoms doping and introducing vacancies defects to enhance Na⁺ adsorption sites and diffusion kinetics is successfully attempted. The as-synthesized three-dimensional (3D) bicontinuous carbon matrix decorated with well-dispersed fluorine (F)-doped NiP₂ nanoparticles (F-NiP₂@carbon nanosheets) delivers a high reversible capacity (585 mAh·g⁻¹ at 0.1 A·g⁻¹) and excellent long cycling stability (244 mAh·g⁻¹ over 1,000 cycles at 2 A·g⁻¹) when tested as anode in NIBs. Density functional theory (DFT) calculations reveal that F doping in NiP₂ induces the formation of P vacancies with increased Na⁺ adsorption energy and accelerates the alloying of internal P component. The F-NiP₂@carbon nanosheets//Na₃V₂(PO₄)₃ full cell is evaluated showing stable long cycling life. The heteroatoms doping-induced dual defects strategy opens up a new way of metal phosphides for sodium storage.

The use of TiO₂ as an anode in rechargeable sodium-ion batteries (NIBs) is hampered by intrinsic low electronic conductivity of TiO₂ and inferior electrode kinetics. Here, a high-performance TiO₂ electrode for NIBs is presented by designing a multichannel porous TiO₂ nanofibers with well-dispersed Cu nanodots and Cu²⁺-doping derived oxygen vacancies (Cu-MPTO). The in-situ grown well-dispersed copper nanodots of about 3 nm on TiO₂ surface could significantly enhance electronic conductivity of the TiO₂ fibers. The one-dimensional multichannel porous structure could facilitate the electrolyte to soak in, leading to short transport path of Na⁺ through carbon toward the TiO₂ nanoparticle. The Cu²⁺-doping induced oxygen vacancies could decrease the bandgap of TiO₂, resulting in easy electron trapping. With this strategy, the Cu-MPTO electrodes render an outstanding rate performance for NIBs (120 mAh·g^-1 at 20 C) and a superior cycling stability for ultralong cycle life (120 mAh·g^-1 at 20 C and 96.5% retention over 2, 000 cycles). Density functional theory (DFT) calculations also suggest that Cu²⁺ doping can enhance the conductivity and electron transfer of TiO₂ and lower the sodiation energy barrier. This strategy is confirmed to be a general process and could be extended to improve the performance of other materials with low electronic conductivity applied in energy storage systems.

Germanium-based oxide has been found to be a promising high-capacity anode material for lithium-ion batteries (LIBs). However, it exhibits poor electrochemical performance because of the drastic volume change during cycling. Herein, we designed porous Ge-Fe bimetal oxide nanowires (Ge-Fe-O_x-700 NWs) by a large-scale and facile solvothermal reaction. When used as the anode material for LIBs, these Ge-Fe-O_x-700 NWs exhibited superior electrochemical performance (~ 1, 120 mAh·g^-1 at a current density of 100 mA·g^-1) and good cycling performance (~ 750 mAh·g^-1 after 50 cycles at a current density of 100 mA·g^-1). The improved performance is due to the small NW diameter, which allows for better accommodation of the drastic volume changes and zero-dimensional nanoparticles, which shorten the diffusion length of ions and electrons.

As a typical two-dimensional transition metal dichalcogenide, molybdenum disulfide (MoS₂) is considered a potential anode material for sodium-ion batteries (NIBs), due to its relatively high theoretical capacity (~ 670 mAh·g^–1). However, the low electrical conductivity of MoS₂ and its dramatic volume change during charge/discharge lead to severe capacity degradation and poor cycling stability. In this work, we developed a facile, scalable, and effective synthesis method to embed nanosized MoS₂ into a thin film of three-dimensional (3D)-interconnected carbon nanofibers (CNFs), producing a MoS₂/CNFs film. The free-standing MoS₂/CNFs thin film can be used as anode for NIBs without additional binders or carbon black. The MoS₂/CNFs electrode exhibits a high reversible capacity of 260 mAh·g^–1, with an extremely low capacity loss of 0.05 mAh·g^–1 per cycle after 2, 600 cycles at a current density of 1 A·g^–1. This enhanced sodium storage performance is attributed to the synergistic effect and structural advantages achieved by embedding MoS₂ in the 3D-interconnected carbon matrix.

A flexible and free-standing multichannel carbon nanofiber (MCNF) film electrode was fabricated through electrospinning and carbonization. After high-temperature treatment of MCNFs in vacuum, the obtained fibers (MCNFs-V) had a dilated interlayer spacing of graphene sheets (0.398 nm) and an ultra-low specific surface area (15.3 m²/g). When used as an anode for sodium-ion batteries, the MCNFs-V showed a discharge plateau below 0.1 V, and sodium was intercalated into the stacked graphene sheets layers during the sodiation process. The MCNFs-V exhibited a reversible and high specific capacity of 222 mAh/g at a current density of 0.1 A/g after 100 cycles and excellent long-term cycling stability, which was superior to that of MCNFs. The improved sodium storage performance was attributed to the unique microstructure of the MCNFs-V with an enlarged interlayer spacing of graphene sheets for sodium intercalation. The MCNFs-V electrode holds great promise as an anode material for commercial sodium-ion batteries.

Sb is considered a promising anode material for high-performance sodium-ion batteries (NIBs) owing to its high theoretical specific capacity (660 mAh·g⁻¹). However, Sb shows a very large volume change (~200%) during sodiation and desodiation, leading to poor electrochemical performance. Here, we designed and tested a sandwich-like graphene-supported Sb nanocomposite (denoted Sb@RGO@Sb), in which ultrafine Sb nanoparticles are uniformly anchored on a reduced graphene oxide (RGO) surface. The ultrafine Sb nanocrystals anchored on the RGO surface minimize the aggregation of Sb and inhibit restacking of the RGO sheets, leading to a minimum transport length for both ions and electrons. The graphene layer not only accommodates the large volume variation of Sb during cycling but also promotes the electron conductivity of the whole electrode. Owing to its unique structure, this sandwich-like composite exhibits superior sodium storage properties.

Activated graphene (AG) with various specific surface areas, pore volumes, and average pore sizes is fabricated and applied as a matrix for sulfur. The impacts of the AG pore structure parameters and sulfur loadings on the electrochemical performance of lithium-sulfur batteries are systematically investigated. The results show that specific capacity, cycling performance, and Coulombic efficiency of the batteries are closely linked to the pore structure and sulfur loading. An AG3/S composite electrode with a high sulfur loading of 72 wt.% exhibited an excellent long-term cycling stability (50% capacity retention over 1, 000 cycles) and extra-low capacity fade rate (0.05% per cycle). In addition, when LiNO₃ was used as an electrolyte additive, the AG3/S electrode exhibited a similar capacity retention and high Coulombic efficiency (~98%) over 1, 000 cycles. The excellent electrochemical performance of the series of AG3/S electrodes is attributed to the mixed micro/mesoporous structure, high surface area, and good electrical conductivity of the AG matrices and the well-distributed sulfur within the micro/mesopores, which is beneficial for electrical and ionic transfer during cycling.