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Study on High Current Discharge Impact Factors of Lithium-ion Batteries

Author: ZuoYuXia
Tutor: LiQi
School: Hunan University
Course: Materials Science
Keywords: Lithium ion battery High-current discharge Battery design AC impedance
CLC: TM912.9
Type: Master's thesis
Year: 2008
Downloads: 756
Quote: 6
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Abstract


Lithium-ion batteries as a new clean, renewable sources of secondary energy, high voltage, high energy density, light weight, etc., have been widely used in the field of mobile phones, laptops, Bluetooth headsets, MP3, digital camera, etc. . However, due to the lithium-ion battery high rate discharge performance is poor, limiting its application in the field of small high-power battery, this area is mainly occupied by nickel cadmium and nickel metal hydride batteries. Large current discharge capacity, in order to improve the lithium-ion battery to 18650 cylindrical lithium-ion battery for the study, the study from the battery materials, battery design. Using constant current - constant voltage charge and discharge, electrochemical impedance spectroscopy test the electrochemical performance of the battery large current discharge performance and cycle performance electrode impedance analysis. Using a scanning electron microscope (SEM) to characterize the diaphragm. The type of positive electrode material due to the crystal structure, the diffusion coefficient, the electronic conductivity type, the impact of large-current discharge performance of the battery type. Diffusion coefficient and low electronic conductivity of LiFePO4 cathode material for large current discharge performance than other cathode materials. The small particle size of the cathode material is more conducive to lithium-ion embedded in them. The large current discharge performance than the relatively large particle size of the material is better. Rate discharge performance of the battery by the type of diaphragm assembly that: under the same conditions as in the structure and porosity parameters, the thickness of the diaphragm large-current discharge of lithium-ion battery. While the thickness of the same type structure and porosity of the diaphragm, the relatively large difference in the large current discharge performance. The porosity of the separator for lithium ion migration hindered, polarization is easy to cause a large current discharge, resulting in a more obvious polarization peak. Large current discharge performance of lithium-ion battery high rate discharge temperature diaphragm will have an impact. Analyzed: analog circuit through the pole pieces when the collector resistance can not be ignored, the current density will be relatively concentrated in the positive and negative electrode current collector on the surface of the fluid the lead line near the electrode. Reasonably designed to lead the way, the battery very ears large current discharge performance has improved significantly. AC impedance test: the battery into positive and negative charge transfer impedance little difference. 1/2 of the relationship according to the positive electrode and the negative electrode low frequency impedance Zre and omega-linear fit of the data obtained, the ion diffusion coefficient of the obtained positive electrode active material and the negative electrode active material, respectively, 8.84 x 10-10cm2 / s, 6.24 × 10 -10cm2 / s. AC impedance analysis results show that the stability of the SEI film is formed, the negative electrode surface in the chemical conversion process. With the increase of the cycle, the negative charge transfer resistance and the increasing positive charge transfer impedance changes. The battery capacity is reduced with increasing number of cycles.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery > A variety of materials, battery
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