Comparison of “Natural” Li Diffusion Behavior on Different Li-Ion Battery Materials

Abstract

Lithium atoms exhibit “natural” diffusion and intercalation properties on certain materials at room temperature. This effect is used as a screening method of potential anode materials for higher energy and power density for Li-ion batteries as well as quality control tests for fabricated anode. This method requires an ultra-high vacuum system environment with an evaporation source to deposit Lithium thin film on the substrates being tested.Auger electron spectroscopy (AES) is used for measuring the Li-KVV line (peak) at 52 eV on anode materials such as Graphite, Si-Graphite, LTO, and Niobium Oxides. Low energy electron diffraction (LEED) is used for monitoring surface crystallographic variation upon Li deposition and diffusion on some single crystal materials such as HOPG, Si, SiC, CVD Diamond, and LiNbO3. The data analysis indicates that three categories of materials can be distinguished based on their properties. The first is “graphite-like” which has rapid Li diffusion and no changes in crystalline structure. The second is “silicon-like” with no Li diffusion and drastic changes in crystalline structure. The third is “silicon-carbide-like” with some Li “natural” diffusion and no changes in crystalline structure. This testing method is simplifying complexity of the electrochemical system as the cathode and electrolyte are not required for these tests and deliver unique test results of nanoscale Li diffusion characteristics in the fabricated battery anodes before cell assembly not possible with other methods.In addition, the Li Auger peak energy shift indicates ionic and metallic bonding of Li atoms which suggests capabilities of early detection of Li dendrite growth. This method can be used to develop interface materials quicker, reduce dendrite growth, and provide failure analysis of disassembled battery electrodes with degraded performance.