No abstract

The FeF3·0.33H2O cathode material can exhibit a high capacity and high energy density through transfer of multiple electrons in the conversion reaction and has attracted great attention from researchers. However, the low conductivity of FeF3·0.33H2O greatly restricts its application. Generally, carbon nanotubes (CNTs) and graphene can be used as conductive networks to improve the conductivities of active materials. In this work, the FeF3·0.33H2O cathode material was synthesized via a liquid-phase method, and the FeF3·0.33H2O/CNT + graphene nanocomposite was successfully fabricated by introduction of CNTs and graphene conductive networks. The electrochemical results illustrate that FeF3·0.33H2O/CNT + graphene nanocomposite delivers a high discharge capacity of 234.2 mAh g−1 in the voltage range of 1.8–4.5 V (vs. Li+/Li) at 0.1 C rate, exhibits a prominent cycling performance (193.1 mAh g−1 after 50 cycles at 0.2 C rate), and rate capability (140.4 mAh g−1 at 5 C rate). Therefore, the electronic conductivity and electrochemical performance of the FeF3·0.33H2O cathode material modified with CNTs and graphene composite conductive network can be effectively improved.

A Cr3+ and F− composite-doped LiNi0.5Mn1.5O4 cathode material was synthesized by the solid-state method, and the influence of the doping amount on the material’s physical and electrochemical properties was investigated. The structure and morphology of the cathode material were characterized by XRD, SEM, TEM, and HRTEM, and the results revealed that the sample exhibited clear spinel features. No Cr3+ and F− impurity phases were found, and the spinel structure became more stable. The results of the charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) test results suggested that LiCr0.05Ni0.475Mn1.475O3.95F0.05 in which the Cr3+ and F− doping amounts were both 0.05, had the optimal electrochemical properties, with discharge rates of 0.1, 0.5, 2, 5, and 10 C and specific capacities of 134.18, 128.70, 123.62, 119.63, and 97.68 mAh g−1 , respectively. After 50 cycles at a rate of 2 C, LiCr0.05Ni0.475Mn1.475O3.95F0.05 showed extremely good cycling performance, with a discharge specific capacity of 121.02 mAh g−1 and a capacity retention rate of 97.9%. EIS test revealed that the doping clearly decreased the charge-transfer resistance.

A sol-gel method was adopted to obtain LiNi0.5-xGaxMn1.5O4 (x = 0, 0.04, 0.06, 0.08, 0.1) samples. The effect of Ga doping on LiNi0.5Mn1.5O4 and its optimum content were investigated, and the electrochemical properties at room temperature and at a high temperature were discussed. The structural, morphological, and vibrational features of LiNi0.5-xGaxMn1.5O4 (x = 0, 0.04, 0.06, 0.08, 0.1) compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The XRD results demonstrate that all samples have a disordered spinel structure with a space group of Fd3m, and Ga doping restrains the formation of the LixNi1-xO secondary phase. FT-IR analysis reveals that Ga doping increases the degree of cation disorder. The SEM results reveal that all samples possess a fine spinel octahedron crystal. The electrochemical performance of the samples was investigated by galvanostatic charge/discharge tests, dQ/dV plots, and electrochemical impedance spectroscopy (EIS). The LiNi0.44Ga0.06Mn1.5O4 sample with the optimum content shows a superior rate performance and cycle stability after Ga doping, especially at a high discharge rate and high temperature. In addition, the LiNi0.44Ga0.06Mn1.5O4 sample retained 98.3% of its initial capacity of 115.7 mAhg−1 at the 3 C discharge rate after 100 cycles, whereas the pristine sample delivered a discharge capacity of 87.3 mAhg−1 at 3 C with a capacity retention of 80% at the 100th cycle. Compared with the pristine material, the LiNi0.44Ga0.06Mn1.5O4 sample showed a high capacity retention from 74 to 98.4% after 50 cycles at a 1 C discharge rate and 55 °C.

No abstract