Preparation of lithium iron phosphate composites by electrodeposition with a tunnel structure on aluminium foil surface

2020 
Abstract In this paper, aluminium foil with a tunnel structure was used as a cathode to prepare a lithium iron phosphate composite by electrochemical deposition using propylene carbonate as the electrolyte solvent, and lithium nitrate, ferric nitrate and phosphoric acid as raw materials. The results show that the positive electrode composite is composed of a mixture of an olivine structured LiFePO4 and polyanion Li9Al3P8O29. The chemical composition of the mixture is related to the voltage of the electrochemical deposition and the acidity of the electrolyte solution. For a voltage of 1.8 V and pH of 1.0, the composite material deposited in the tunnel of the aluminium foil takes the form of a one-dimensional nanotube, with a particle size ranging from 80 nm to100 nm. The composite material is closely combined with the aluminium foil. The aluminium foil can be directly used as a positive current collector, with a lithium sheet as the negative electrode. After mounting into a battery, an electrochemical performance test is performed. The battery test results show an initial discharge capacity of 95 mAh/g, 79 mAh/g and 59 mAh/g at 0.1 C, 0.2 C and 0.5 C, respectively. After the material is doped with magnesium and cobalt, the initial discharge capacity of the battery is 100 mAh/g and 130 mAh/g, respectively, at a rate of 0.1 C. The cyclic voltammetry analysis of the battery show that after electrochemical deposition of the element, the symmetry between the oxidation and reduction peaks is increased, and the difference between the oxidation and reduction peak potentials is reduced. Element doping improves battery cycle performance. The AC impedance analysis show that the embedding impedance for lithium ions at the SEI interface is reduced from 300 Ω to 250 Ω, 100 Ω after doping with magnesium, and cobalt. And the reaction mechanism of electrochemical deposition is discussed.
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