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Cathode material Li [Li0.2Ni0.2Co0.08Mn0.52−xCux]O2 (x = 0, 0.01, 0.03, 0.05, 0.07) has been synthesized via carbonate coprecipitation method and modified by Cu2+ which was introduced at different stages. The crystal structure features, morphology, and electrochemical properties of the powders are studied in detail using X-ray diffraction spectroscopy, scanning electron microscopy, EDS spectroscopy, and electrochemical measurements. The experimental results show that the electrochemical properties of Li [Li0.2Ni0.2Co0.08Mn0.52−xCux]O2 (x = 0, 0.01, 0.03, 0.05, 0.07) oxides are improved. This is because an appropriate amount of Cu2+ doping increases the lattice spacing of the layered material, reduces the agglomeration of the particles, and improves the uniformity of the particles. Especially in the coprecipitation stage, Cu2+ was introduced and x = 3% showed better rate and cycle performance. The specific discharge capacity at 1C and 2C was 197.28 mAhg−1 and 124.92 mAhg−1, respectively, and cycle returned to 0.1C capacity after 45 cycles, the discharge specific capacity is still up to 261.5 mAhg−1. [ABSTRACT FROM AUTHOR]

Abstract In this paper, Li 2 Fe 0.98 × 0.02 SiO 4 /C (X = Ag, Zn, Ti, Cu, Pb, Al, W, Mo, Ga, Cs, V, Mn) was synthesized for lithium ion battery as cathode material by solid-state method and modified by doping metal ion on the Fe-site. The constant current charge-discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were chosen to investigate the electrochemical performance of Li 2 Fe 0.98 × 0.02 SiO 4 /C. The results shows that the materials doped with Ag, Zn, Ti and Cu on the Fe-site have good electrochemical properties. Then Li 2 Fe 1−y X y SiO 4 /C (X = Ag, Zn, Ti, Cu; y = 0.01, 0.02, 0.03, 0.05) were synthesized by solid-state method. After their electrochemical properties were compared, we found Li 2 Fe 0.98 Ag 0.02 SiO 4 /C, Li 2 Fe 0.98 Zn 0.02 SiO 4 /C, Li 2 Fe 0.97 Ti 0.03 SiO 4 /C and Li 2 Fe 0.98 Cu 0.02 SiO 4 /C have excellent electrochemical performance. The first discharge capacity of Li 2 Fe 0.98 Zn 0.02 SiO 4 /C and Li 2 Fe 0.98 Cu 0.02 SiO 4 /C were 201 mAh/g, which is equivalent to 1.2 Li+ deintercalation. The initial discharge capacity of Li 2 Fe 0.97 Ti 0.03 SiO 4 /C is 104 mAh/g, which is higher than that of other materials doped with Ti. Li 2 Fe 0.98 Ag 0.02 SiO 4 /C has good cyclic stability, the first discharge capacity is 143.4 mAh/g, the diffusion coefficient of lithium ion is two orders of magnitude higher than that of pure phase, and the electrochemical properties are stable. XRD and SEM tests were conducted on Li 2 Fe 0.98 Ag 0.02 SiO 4 /C, Li 2 Fe 0.98 Zn 0.02 SiO 4 /C, Li 2 Fe 0.97 Ti 0.03 SiO 4 /C and Li 2 Fe 0.98 Cu 0.02 SiO 4 /C. It can be seen from the XRD patterns that there are no characteristic peaks of Fe or Li 2 SiO 3 impurities in the materials mentioned above. The impurity peak of Li 2 Fe 3 O 4 was not found in the Li 2 Fe 0.98 Ag 0.02 SiO 4 /C material, which indicated that the purity of the material was high. It can be seen from the SEM diagram that the particle size of Li 2 Fe 0.98 Ag 0.02 SiO 4 /C is more uniform and there is no obvious agglomeration. Then, Li 2 Fe 0.98 Ag 0.02 SiO 4 /C with better performance was analyzed by EDS, XPS and FT-IR spectra. From the EDS analysis, it can be seen that the theoretical value of each element's scale were close to each other. By the data got from XPS spectrum the existences of the characteristic peaks of Li, Fe, Si and O in the sample were confirmed, which proves Ag+ has succeeded in replacing Fe2+ in the crystal structure of Li 2 FeSiO 4. The positions of the absorption peaks of Li 2 Fe 0.98 Ag 0.02 SiO 4 /C in FT-IR spectra are consistent with those of Li 2 FeSiO 4 , indicating that stable Li 2 Fe 0.98 Ag 0.02 SiO 4 /C materials have been synthesized. Highlights • Li 2 Fe 0.98 X 0.02 SiO 4 /C were synthesized which modified by doping metal ion on the site of Fe. • The materials were synthesized by solid state method which is suitable for industrial production. • The first discharge capacity of Li 2 Fe 0.98 Ag 0.02 SiO 4 /C is 143.4mAh/g and the diffusion coefficient of Li+ is extremely high. [ABSTRACT FROM AUTHOR]

Abstract In this paper, Li 2 Fe 1−x Ni x SiO 4 /C, Li 2 FeSi 1−x Ni x O 4 /C, Li 2 Fe 1−x Pb x SiO 4 /C and Li 2 FeSi 1−x Pb x O 4 /C(x = 0.01, 0.02, 0.03, 0.05) were synthesized as cathode materials via the high temperature solid-phase method. After synthesizing, a comparative study of the electrochemical properties was conducted on these materials of which Fe site and Si site were doped with Ni or Pb respectively through a range of methods including constant current charge-discharge test, cyclic voltammetry and electrochemical impedance analysis. The study shows that the materials with doping Ni or Pb at Fe site present more stable electrochemical attribute. The initial discharge capacity of Li 2 Fe 0.97 Ni 0.03 SiO 4 /C is 146.0 mAh/g, and the capacity retention rate is 93.3% after 10 cycles at 0.1 C. The electrochemical performance of Li 2 Fe 0.97 Pb 0.03 SiO 4 /C is more stable than that of other materials doped with Pb in different doping ratio. Its capacity is 162.2 mAh/g after 10 cycles at 0.1 C, and the capacity retention rate is 95.2%. The initial discharge capacity of the material is improved by Ni or Pb doped at Si site. The initial discharge capacity of Li 2 FeSi 0.98 Ni 0.02 O 4 /C and Li 2 FeSi 0.97 Pb 0.03 O 4 /C is equivalent to 1.06 and 1.08 Li+ deintercalation respectively. Furthermore, Li 2 Fe 0.97 Ni 0.03 SiO 4 /C, Li 2 FeSi 0.98 Ni 0.02 O 4 /C, Li 2 Fe 0.97 Pb 0.03 SiO 4 /C and Li 2 FeSi 0.97 Pb 0.03 O 4 /C were selected for SEM and XRD tests. The graph of SEM shows that the particle size of Li 2 Fe 0.97 Ni 0.03 SiO 4 /C and Li 2 Fe 0.97 Pb 0.03 SiO 4 /C are uniform and no obvious agglomeration phenomenon could be observed. The XRD shows that there is no the peak characteristic of Fe, Li 2 SiO 3 and Li 2 Fe 3 O 4. The cell volume of Li 2 Fe 0.97 Ni 0.03 SiO 4 /C and Li 2 Fe 0.97 Pb 0.03 SiO 4 /C is increased and the electrochemical property of them is stable. Highlights • The initial discharge capacity of Li 2 Fe 0.97 Ni 0.03 SiO 4 /C is 146.0 mAh/g. • The capacity of Li 2 Fe 0.97 Pb 0.03 SiO 4 /C is 162.2 mAh/g after 10 cycles under 0.1 C. • Li 2 FeSi 0.98 Ni 0.02 O 4 /C is equal to the material in which the deintercalation of 1.06 Li+ is happened. • The first discharge capacity of Li 2 FeSi 0.97 Pb 0.03 O 4 /C is equal to 1.08 Li+ deintercalation. [ABSTRACT FROM AUTHOR]