Investigation on the Anode Surface of High Specific Energy Li-Ion Batteries

Lithium-ion batteries have become the most popular secondary battery of electric cars, electronic products and power grids with high specific energy and cycle life. Currently, the specific energy density of commercial lithium-ion battery is less than 250Wh / kg, with the continuous development of lithium-ion batteries, the indicator of the next generation of lithium-ion batteries energy density have reached 300Wh / kg. Lithium-ion batteries show good electrical performance advantages, are also facing a number of security issues and challenges, including the thermal decomposition of cathode electrodes , the decomposition reaction of the electrolyte, the surface of the anode electrode and aggregation effect, etc. which have become main factors affecting the security and stability of the cycle. At present, the carbon materials dominate the anode materials of lithium ion batteries, and high specific energy Li-ion batteries mainly use graphite as the anode material, which enhances the specific energy density due to the high-capacity, long cycle life and high press density. However, this material tends to form lithium deposition in conditions of high C rate, charging at low temperature and higher polarization, and the deposited lithium becomes thicker to form the dendrite, which may penetrate through the separator, causing internal short circuit, even the safety issue. In this paper, we investigate the mechanism of lithium deposited on the anode surface of high specific energy li-ion batteries(with NCA as the cathode，graphite as the anode) by the  electrochemical method combined with the physical characteristics analysis. From the potential of the battery, measured by three-electrodes and electrochemical analysis tools, the results show that, the lithium deposited on the anode electrode surface is mainly owing to the polarization of cathode and anode. For the charging process, if the polarization is higher enough, the potential of the anode electrode constantly is reduced, even to 0V or less, i.e., the lithium will be deposited on the anode surface. The investigation also shows that, using the method of pre-charge can maintain the anode potential above 0V, and it can effectively suppress the deposition of metal lithium on the anode electrode surface. Figure 1