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MoS 2 has attracted tremendous attention as an anode for Na-ion batteries (NIBs) owing to its high specific capacity and layered graphite-like structure. Herein, MoS 2 is converted to a ternary MoS 2−x Se x alloy through the selenizing process in order to boost the electrochemical performance for Na-ion batteries. Conversion of MoS 2 to MoS 2−x Se x expands interlayer spacing, improves electronic conductivity, and creates more defects. The expanded interlayer spacing decreases Na + diffusion resistance and facilitates Na + fast transfer. The integrated graphene as a conductive network offers effective pathway for electron migration and maintains structural stability of electrodes during cycles. The ternary MoS 1.2 Se 0.8 /graphene (MoS 1.2 Se 0.8 /G) electrode demonstrates an extremely high reversible capacity of 509 mA h g −1 after 200 cycles at 0.1 A g −1 (capacity retention of 109%) as an anode for sodium-ion batteries. Even at 2 A g −1 and after 700 cycles, the MoS 1.2 Se 0.8 /G electrode also displays a relatively high reversible capacity of 178 mA h g −1 . Full cells assembled with Na 3 V 2 (PO 4 ) 2 F 3 cathodes and MoS 1.2 Se 0.8 /G anodes reveal high charge/discharge capacities. This work demonstrates that the ternary MoS 2−x Se x alloy could be a potential anode material for Na-ion storage. KEYWORDS: sodium ion batteries, anode, MoS 2 , MoS 2−x Se x , selenizing

Developing a high-performance anode with high reversible capacity, rate performance, and great cycling stability is highly important for sodium-ion batteries (SIBs). MoS has attracted extensive interest as the anode for SIBs. Herein, the vertically oxygen-incorporated MoS nanosheets/carbon fibers are constructed via a facile hydrothermal method and then by simple calcination in air. Oxygen incorporation into MoS can increase the defect degree and expand the interlayer spacing. Vertical MoS nanosheet array coated on carbon fibers not only can expose rich active sites and reduce the diffusion distance of Na, but also improve the electronic conductivity and enhance structural stability. Meanwhile, interlayer-expanded MoS can decrease Na diffusion resistance and increase accessible active sites for Na. In this work, the electrode combining the oxygen-incorporated strategy with vertical MoS nanosheet-integrated carbon fibers displays high specific capacities of 330 mAh g over 100 cycles at a current density of 0.1 A g together with excellent rate behavior as the anode for SIBs. This strategy offers a helpful way for improving the electrochemical performance.

Carbon materials with high initial Coulombic efficiency (ICE) and specific capacity in lithium-ion batteries are highly attractive. Herein, P-doped carbon has been prepared, and as an anode for lithium-ion batteries, it exhibits remarkably improved ICE and reversible capacity. P atoms are apt for the formation of the P-O bond in carbon with oxygen-containing groups. The doped P content strongly depends on the O content in carbon. The high-doped P content of 5.79 at. % can be obtained through changing the O content in carbon. Carbon with high contents of P and O displays high ICE and capacity as an anode for lithium-ion batteries. The P-O bond in carbon changes the morphology and composition of the solid electrolyte interface (SEI) layer and is beneficial to the formation of a thin and dense SEI layer. The P-O bond in carbon prevents the permeation and decomposition of solvated PF in the interior of the electrode during cycling, resulting in the improved ICE, reversible capacity, and rate capability. As an anode for lithium-ion batteries, the ICE can be improved to 70.9% for carbon with the P-O bond from 36.9% for carbon without the P-O bond. Carbon with the P-O bond displays high specific capacities of 566 mA h g after 100 cycles at 0.1 A g and 432 mA h g after 1000 cycles at 1 A g. This design offers a simple and efficient method to improve the ICE and reversible capacity of hard carbon.

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