Hua-Chao Tao

Synthesis and electrochemical performance of Na-modified Li2Fe0.5Mn0.5SiO4 cathode material for Li-ion batteries

A series of Li2−xNaxFe0.5Mn0.5SiO4/C (x = 0.00, 0.01, 0.03 and 0.05) composites have been synthesized via a refluxing-assisted solid-state reaction, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), galvanostatic charge–discharge measurements, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests. XRD results show that Li2−xNaxFe0.5Mn0.5SiO4/C can be well indexed as the structure of two mixed polymorphs with space group P21 and Pmn21. XPS results confirms that Na not only exists on the surface of Li2Fe0.5Mn0.5SiO4 particles, but also has been successfully doped into the crystal lattice of Li2Fe0.5Mn0.5SiO4. Na-doping can significantly improve the discharge capacity and the rate capability of Li2Fe0.5Mn0.5SiO4/C. The enhanced electrochemical performance can be attributed to the increased electronic conductivity, the decreased charge transfer impedance, and the improved Li-ion diffusion coefficient.

Synthesis and electrochemical performance of Li2FeSiO4/C cathode material using ascorbic acid as an additive

Carbon-coated Li2FeSiO4 composite (LFS/C-AA) was synthesized via a refluxing-assisted solid-state reaction by using ascorbic acid as additive and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, galvanostatic charge/discharge measurements, and electrochemical impedance spectra (EIS) tests. The results show that ascorbic acid can to some extent prohibit the oxidation of Fe2+ during the synthesis process, and the pyrolytic carbon from ascorbic acid shows higher electronic conductivity and improves the degree of graphitization of residual carbon in the LFS/C-AA composite. Compared with LFS/C prepared without ascorbic acid, LFS/C-AA displays better electrochemical performance. The desirable property is attributed to the reduced particle size, the enhanced electronic conductivity, and the improved diffusion coefficient of lithium ions.

Achieving a High-Performance Carbon Anode through the P–O Bond for Lithium-Ion Batteries

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 PF6- 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-1 after 100 cycles at 0.1 A g-1 and 432 mA h g-1 after 1000 cycles at 1 A g-1. This design offers a simple and efficient method to improve the ICE and reversible capacity of hard carbon.

Vertically Oxygen-Incorporated MoS2 Nanosheets Coated on Carbon Fibers for Sodium-Ion Batteries

Developing a high-performance anode with high reversible capacity, rate performance, and great cycling stability is highly important for sodium-ion batteries (SIBs). MoS2 has attracted extensive interest as the anode for SIBs. Herein, the vertically oxygen-incorporated MoS2 nanosheets/carbon fibers are constructed via a facile hydrothermal method and then by simple calcination in air. Oxygen incorporation into MoS2 can increase the defect degree and expand the interlayer spacing. Vertical MoS2 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 MoS2 can decrease Na+ diffusion resistance and increase accessible active sites for Na+. In this work, the electrode combining the oxygen-incorporated strategy with vertical MoS2 nanosheet-integrated carbon fibers displays high specific capacities of 330 mAh g-1 over 100 cycles at a current density of 0.1 A g-1 together with excellent rate behavior as the anode for SIBs. This strategy offers a helpful way for improving the electrochemical performance.