Abstract In this paper, [Ni 0.9 Co 0.1 ](OH) 2 precursor is used to dope H 3 BO 3 to synthesize positive electrode material when mixing lithium in wet method, and to explore the best doping by testing the microscopic morphology and electrochemical performance of the positive electrode material amount and calcination temperature. After doping with B, the microstructure of the material is improved, and the primary crystal grains are oriented and agglomerated into a needle shape. This good crystal structure can slow down the generation of grain microcracks and mechanical fracture, and improve the cycle stability of the positive electrode material. After doping B, the discharge specific capacity was slightly improved. When the calcination temperature is 750 °C and the doping amount of B is 1.0 mol%, the first discharge specific capacity reaches 223 mAh g −1 . More importantly, the capacity retention rate of the battery after 100 cycles has been greatly improved, from 74 % without doping B to 87 %.
Abstract High‐nickel cathode materials are widely used in lithium‐ion batteries because of their advantages of high energy density and high safety. High‐nickel cathode materials need to further improve cycling stability because they are prone to structural changes and capacity degradation. This paper proposes a method to improve high‐nickel cathode materials by Mg doping. XRD proves that Mg‐doped high‐nickel materials still have R‐3 m spatial structural characteristics; Rietveld refinement confirms that the c‐axis gradually increases with the increase of Mg content. Combined with DFT calculations, the presence of Mg can inhibit structural collapse during charge and discharge, reduce Li/Ni antisite defects, improve the electronic conductivity of the material, and improve the cyclic stability of the material. The 0.6 mol % Mg‐doped sample has an initial discharge capacity of 233 mAh g −1 at 0.1 C in the range of 2.7–4.3 V, a capacity retention rate of 91.0 % after 50 cycles at 1 C, still retains 79.9 % after 100 cycles. The dQ/dV curves further indicate that the presence of Mg improves the structural stability of the material.
Iron-chromium redox flow batteries (ICRFBs) have the advantages of high safety, long cycle life, flexible design, and low maintenance costs. Polyacrylonitrile-based graphite felt composite material has good temperature resistance, corrosion resistance, large surface area and excellent electrical conductivity, and is often used as the electrode material of ICRFB, but its chemical activity is poor. In order to improve the activity of the graphite felt electrode, In3+ was used for modification in this paper, and the modified graphite felt was used as the electrode material for iron-chromium batteries. The structure and surface morphology of the modified graphite felt were analyzed by the specific surface area analyzer and scanning electron microscope; the electrochemical impedance spectroscopy and cyclic voltammetry experiments were carried out on the electrochemical workstation to study the electro catalytic activity of In3+ modified graphite felt and its performance in ICRFBS. The results show that the graphite felt electrode modified with a concentration of 0.2 M In3+ was activated at 400°C for 2 h, and its surface showed a lot of grooves, and the specific surface area reached 3.889 m2/g, while the specific surface area of the untreated graphite felt was only 0.995 m2/g significantly improved. Electrochemical tests show that the electrochemical properties of graphite felt electrodes are improved after In3+ modification. Therefore, the In3+ modified graphite felt electrode can improve the performance of ICRFB battery, and also make it possible to realize the engineering application of ICRFB battery.
Abstract In this paper, cobalt oxide‐modified graphite felt electrodes were prepared by electrodepositing cobalt nitrate on graphite felt and calcined. The surface morphology of graphite felt modified by cobalt oxide was characterized in detail by scanning electron microscope X‐ray diffraction and X‐ray photoelectron spectroscopy. Shape, microstructure, etc. And using the three‐electrode system to conduct cyclic voltammetry, electrochemical impedance spectroscopy, and single‐cell constant current charge and discharge detection on the graphite felt electrodes modified with different concentrations of cobalt oxide, and study its use as an electrode for iron‐chromium redox flow battery performance. The results show that the method of calcination after electrodeposition successfully attaches cobalt oxide to the graphite felt fiber uniformly in granular form, increases a large number of oxygen‐containing functional groups, and has the highest coulombic efficiency for the first charge‐discharge cycle at a current density of 142mAcm −2 It can reach 82 %, and the charging capacity is also increased by 1.59 times compared with the original graphite felt.
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