Study Of Mechanical Properties Of Sn Anode Materials Under Different Lithiation States For Lithium-ion Battery

With the development of human society and technology, the drying up of the nonrenewable resources makes the novel lithium ion batteries(LIBs) which have the advantages of a high energy density, long cycle life, low cost, high security, pollutionfree and etc, become the new darling. Up to now, graphite is the most widely used negative electrode material in LIBs, but its theoretical capacity is relatively low(372 mAh·g-1), which cannot meet the increasing demand for energy. In contrast, Sn exhibits an extraordinarily large theoretical capacity of 994 mAh·g-1, which is about two and a half times of graphite anodes. As an anode material, however, Sn experiences a massive volume change(~300%) during lithiation-delithiation processes, which results in their capacity loss and poor cycling performance and severely restrict the widely application of the tin anode materials in lithium ion batteries, especially in power battery. To make full use of Sn anode materials, it is necessary to make a deeply research to its failure mechanism.In this paper, we have mainly conducted the preparation of the Sn anode material by using the electrodeposition method, as well as its electrochemical performance analysis and mechanical properties characterization. In the experiment, we have used X-ray diffraction, atomic force microscope, scanning electron microscope, Electrochemical Workstation,, methods of nano indentation and etc to test and analyz the chemical compositions, surface morphology, electrochemical properties, as well as the mechanical properties.of the prepared electrode materials. The mainly research works are as follows:(1) The ? theorem was used to the dimensional analysis of nano indentation, which obtains the dimensionless function relationship between the basic mechanical properties of metallic materials and the correlation parameters of indentation tests, which provides theoretical guidance for the establishment of their specific dimensionaless function relationship by numerical approach.(2) The electrodeposition method was used for the preparation of Sn anode materials of lithium ion battery with copper strip of 0.4 mm. The obtained electrode material was assembled to a battery and we have also made a characteristic to its, electrochemical performance. The first discharging and charging specific capacities of tin anode materials are as high as 755 mAh·g-1 and 697 mAh·g-1, respectively. In addition, it also shows good charging-discharging voltage platform. But its actual specific capacity decays very quickly in the charge and discharge processes with constant current, its 10 th discharge specific capacity is already close to zero, showing poor cycle performance. In order to study the failure mechanism of Sn anode materials, in the experiment, we have quantitatively obtained the Sn anode materials under different lithiation condition(3) We have conducted indentation test to Sn anode material with different degrees of lithiation using dimensionless function relationship. By using Matlab software, we have calculate their elastic moduli, yield strengths, strain hardening exponents and have drawed their stress-strain relations. We obtain that the elastic modulus, yield strength, strain hardening exponent of the electrode materials after first lithiation process are 60.3 GPa, 32.6 MPa and 0.3, respestively. At the same time, we have also drawing the relation curves between these parameters and SOC. The curves quantitatively give a explaination the poor cycle performance of Sn anode material, which provides theoretical basises to the design and application of Sn anode material in lithium ion batteries.