Study On High Current Discharge Impact Factors Of Lithium-ion Batteries

Lithium secondary batteries are the new types of cleanliness and recyclable energy source. They have high voltage and high energy density. Recently they are widely used in digital products, e.g, mobile phone, notebook, Bluetooth headset, MP3, digital camera, et al. but its low rate of discharge ability makes it can not compete with Ni-MH and Ni-Cd batteries at the little-capacity high power battery market.In order to improve the lithium-ion batteries high current discharge capacity, the article took 18650 cylindrical lithium-ion batteries for the study from the battery materials, battery design in areas such as research. The electrochemical properties of lithium-ion batteries were tested by the electrochemical impedance spectra (EIS), etc. Scanning electron microscopy (SEM) was used to characterize the separators.Low diffusion coefficient and conductivity of cathode material will impact the high discharge ability of the battery. And the smaller grainess of the material has more excellent high discharge ability. By comparing different separators fabricated battery discharge rate be found: the structure and parameters such as porosity under the same conditions, only the thickness different has little effect on the discharge current. And the same thickness, same porosity but different structure of separator, the high current discharge performance were difference.Through a simulation circuit of electrode analysis: When electrode can not ignore the resistance, the current density distribution will be concentrated in area where near the electrode collections. When the electrode collections were design reasonable, its high current discharge performance has improved significantly.Through the AC impedance testing, the results indicate that: the charge transfer impedance of cathode and anode has little difference. According to the relationship of cathode and anode low-frequency impedance Zre andω-1/2, fitting linear of the data collected, and calculated the cathode material and anode material diffusion coefficient are 8.84×10-10cm2/s,6.24×10-10cm2/s respectively. AC impedance results show that: Anode surface in the formation process of forming a stable SEI film. With the increase in the number cycle, the anode charge transfer impedance also growing, cathode charge transfer impedance has little change.