Hüseyin Göktepe

A Novel Method to Improve the Electrochemical Performance of LiMn2O4 Cathode Active Material by CaCO3 Surface Coating

Spinel LiMn2O4 was synthesized by glycine-nitrate method and coated with CaCO3 in order to enhance the electrochemical performance at room temperature (25°C) and 55°C. The uncoated and CaCO3-coated LiMn2O4 materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. XRD and SEM results indicated that CaCO3 particles encapsulated the surface of the LiMn2O4 without causing any structural change. The charge-discharge tests showed that the specific discharge capacity fade of pristine electrode at 25 and 55°C were 25.5% and 52%, respectively. However, surface modified cathode shows 7.4% and 29.5% loss compared to initial specific discharge capacity at 70th cycle for 25 and 55°C, respectively. The improvement of electrochemical performance is attributed to suppression of Mn2+ dissolution into electrolyte via CaCO3 layer.

Synthesis and cycling performance of double metal doped LiMn2O4 cathode materials for rechargeable lithium ion batteries

In order to improve the cycling performance of LiMn2O4, the spinel phases LiCo0.15Mn1.85O4 and LiCo0.05M0.1Mn1.85O4 (M = Ni, Zn, Cu) were prepared by the sol-gel method. Their structures have been investigated by x-ray diffraction. Electrochemical studies were carried out using the Li | LixMn2O4 (x = 1.05, 1.1), LiCo0.15Mn1.85O4, and LiCo0.05M0.1Mn1.85O4 (M = Ni, Zn, Cu) cells. The capacity loss of Li | LixMn2O4 (x = 1.05, 1.1) cells is about 21.7 and 6.4% after 30 cycles, whereas that for Co, Co-Ni, Co-Zn, and Co-Cu doped spinel materials is about 4.0, 2.0, 1.0, and 1.9%, respectively. The good capacity retention of LiCo0.05M0.1Mn1.85O4 (M = Ni, Zn, Cu) electrodes is attributed to stabilization of spinel structure by double metal doping for Mn ion sites. Double substituted spinels display better performance in terms of cycle-life compared with LiMn2O4.

Synthesis and Electrochemical Properties of Carbon-Mixed LiEr0.02Fe0.98PO4 Cathode Material for Lithium- ion Batteries

LiEr 0.02 Fe 0.98 PO 4 /C composite cathode was synthesized by a simple solution method with polyethylene glycol (PEG) as the reductive agent and carbon source. The effect of erbium doping on the electrochemical behavior of LiFePO 4 was studied in this paper. The samples were characterized by X-ray powder diffraction and scanning electron microscopy and the electrochemical properties were investigated by the charge-discharge test. An initial discharge capacity of 149 mAh·g −1 was achieved for the LiEr 0.02 Fe 0.98 PO 4 /C composite cathode with a rate of 0.1 C. The electronic conductivity of Er doped LiFePO 4 /C was measured as 10 −2 S·cm −1 . The results indicated that erbium doping did not destroy the lattice structure of LiFePO 4 and enlarge the lattice volume. These changes are beneficial to the improvement of the electrochemical performance of the LiFePO 4 cathode.

Influence of succinic acid and polyethylene glycol (PEG) additives on electrochemical performance of lithium-ion batteries

In this study, we report results of succinic acid and polyethylene glycol (PEG) additives at different rates in mass (the rates of %0 - %200.) The structure and electrochemical properties of the LiFePO4/C were characterized by XRD, SEM, and galvanostatic charge-discharge measurements. Among the materials studied, the sample (A) which contains %100 succinic acid and %200 PEG (w/w), exhibits a 150mAhg−1 discharge capacity and it is corresponding to 88% of the theoretical capacity. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by carbon.In this study, we report results of succinic acid and polyethylene glycol (PEG) additives at different rates in mass (the rates of %0 - %200.) The structure and electrochemical properties of the LiFePO4/C were characterized by XRD, SEM, and galvanostatic charge-discharge measurements. Among the materials studied, the sample (A) which contains %100 succinic acid and %200 PEG (w/w), exhibits a 150mAhg−1 discharge capacity and it is corresponding to 88% of the theoretical capacity. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by carbon.