The low initial Coulombic efficiency (ICE) of SiO_x anode caused by the irreversible generation of Li_ySiO_z and Li₂O during lithiation process limits its application for high energy-density lithium-ion batteries. Herein, we report a molten-salt-induced thermochemical prelithiation strategy for regulating the electrochemically active Si/O ratio of SiO_x and thus enhancing ICE through thermal treatment of pre-synthesized LiNH₂-coated SiO_x in molten LiCl at 700 ℃. Bulk SiO_x micro-particle was transformed into pomegranate- like prelithiated micro-cluster composite (M-Li-SiO_x) with SiO_x core and outer nano-sized agglomerates consisting of Li₂Si₂O₅, SiO₂, and Si. Through the analysis of the reaction intermediates, molten-LiCl could initiate reactions and promote mass transfer by the continuous extraction of oxygen component from SiO_x particle inner in the form of inert Li₂Si₂O₅ and SiO₂ nanotubes to realize the prelithiation. The degree of prelithiation can be regulated by adjusting the coating amount of LiNH₂ layer, and the resulted M-Li- SiO_x displays a prominent improvement of ICE from 58.73% to 88.2%. The graphite/M-Li-SiO_x (8:2) composite electrode delivers a discharge capacity of 497.29 mAh·g⁻¹ with an ICE of 91.79%. By pairing graphite/M-Li-SiO_x anode and LiFePO₄ cathode in a full-cell, an enhancement of energy density of 37.25% is realized compared with the full-cell containing graphite/SiO_x anode. Furthermore, ex-situ X-ray photoelectron spectroscopy (XPS)/Raman/X-ray diffraction (XRD) and related electrochemical measurements reveal the SiO_x core and Si of M-Li-SiO_x participate in the lithiation, and pre-generated Li₂Si₂O₅ with Li⁺ diffusivity and pomegranate-like structure reduces the reaction resistance and interface impedance of the solid electrolyte interphase (SEI) film.

Herein, a two-dimensional (2D) interspace-confined synthetic strategy is developed for producing MoS₂-intercalated graphite (G-MoS₂) hetero-layers composite through sulfuring the pre-synthesized stage-1 MoCl₅-graphite intercalation compound (MoCl₅-GIC). The in situ grown MoS₂ nanosheets (3-7 layers) are evenly encapsulated in graphite layers with intimate interface thus forming layer-by-layer MoS₂-intercalated graphite composite. In this structure, the unique merits of MoS₂ and graphite components are integrated, such as high capacity contribution of MoS₂ and the flexibility of graphite layers. Besides, the tight interfacial interaction between hetero-layers optimizes the potential of conductive graphite layers as matrix for MoS₂. As a result, the G-MoS₂ exhibits a high reversible Li⁺ storage of 344 mAh·g⁻¹ even at 10 A·g⁻¹ and a capacity of 539.9 mAh·g⁻¹ after 1,500 cycles at 5 A·g⁻¹. As for potassium ion battery, G-MoS₂ delivers a reversible capacity of 377.0 mAh·g⁻¹ at 0.1 A·g⁻¹ and 141.2 mAh·g⁻¹ even at 2 A·g⁻¹. Detailed experiments and density functional theory calculation demonstrate the existence of hetero-layers enhances the diffusion rates of Li⁺ and K⁺. This graphite interspace-confined synthetic methodology would provide new ideas for preparing function-integrated materials in energy storage and conversion, catalysis or other fields.

Crystalline Ge is a highly active anode material for Li storage but inactive for Na storage because of high diffusion barrier. By in-situ Raman spectrum, we explore that the Na could reversibly alloy/dealloy with the amorphous Ge, but does not with the crystalline Ge. Herein, the amorphous Ge is fabricated by an acid-etching Zintl phase Mg₂Ge route at room temperature, which shows a mesoporous architecture with a Brunauer-Emmett-Teller (BET) surface area of 29.9 m²·g^-1 and a Barrett-Joyner-Halenda (BJH) average pore diameter of 7.6 nm. This mesoporous architecture would enhance the Na-ion/electron diffusion rate and buffer the volume expansion. As a result, the as-prepared amorphous Ge shows superior Na-ion storage performance including high reversible capacity over 550 mA·h·g^-1 at 0.2 C after 50 cycles, good rate capability with a capacity of 273 mA·h·g^-1 maintained at 5.0 C, and long-term cycling stability with capacities of 450 mA·h·g^-1 at 0.4 C after 200 cycles. For the K-ion storage, the amorphous Ge is also more active than the crystalline counter and maintains a capacity of 210 mA·h·g^-1 after 100 cycles at 0.2 C.

Two-dimensional (2D) materials have attracted enormous attention due to their functional applications in energy storage. In this work, a low-temperature molten-salt chemical exfoliation methodology is developed for producing free-standing 2D mesoporous Si through deintercalation of CaSi₂ in excess molten AlCl₃ at 195 ℃. The average dimension of these sheets is 1.5 μm, and the thickness of a single sheet is approximately 10 nm. The as-prepared 2D Si has a Brunauer–Emmett–Teller surface area of 154 m²·g^-1 and an average pore size of 5.87 nm. With this unique structure, the 2D Si exhibits superior Li-storage performance, including a reversible capacity of 2, 974 mA·h·g^-1 at 0.2 C, reversible capacities of 2, 162, 1, 947, and 1, 527 mA·h·g^-1 at 0.8, 2, and 5 C after 200 cycles, and a capacity retention of 357 mA·h·g^-1 even at 30 C (90 A·g^-1).