1, Department of Chemical Engineering, School of Chemistry, Nazarbayev University, Astana, , Kazakhstan
Rechagrable Li-ion batteries (LIBs) are very promising candidates for electrochemical energy storage in electrical vechiles. Electrical conduction propeties in these systems are strongly affected by thermal transport properties during electrochemical cycling. Therefore, thermal management in these systems is very crucial for the control of electrical properties of these storage devices . Si-based anode is a very attractive material because of potentially large achievable capacity of 3700 mAhg-1  that is ten times more than that for graphitic carbon, which is mainly used as an anode material in LIBs. However it is well known that Si electrodes suffer from volumetric change during the electrochemical cycling/recycling processes, which in turn leads to change in mechanical and electrical properties. But little research has been done on thermal conductivity variation in Si films during the lithiation. In this work we aim to study nanoscale thermal transport in this nanoscale-thick material using ex situ picosecond time-domain thermoreflectance (TDTR) approach . RF magnetron sputtering was used to deposit a ~300 nm thick Si films on glass subatrate. A 50 nm thick Al was deposited on top of Si serving as an optical absorber and efficient heat transducer in TDTR experiments. The lithiation of films has been performed in the beaker cell with lithium hexafluorophosphate (LPF) in the solution of ethylene, diethyl carbonate and ethyl methyl carbonates (EC:DC:EMC = 1:1:1, v/v) using a constant current of 25 µA up to 0.05 V. Thermal transport measurements were done for non-lithiated and lithiated samples. The results show that for non-lithiated amorphous Si films the thermal conductivity value is ~ 1.4 W/m*K, which is very close to literature value . After electrochemical lithation process, the thermal conductivity of lithiated amorphous Si was in the range between 1.3 to 2.2 W/m*K. This sizeable thermal transport fluctuation was likely due to inhomogeneous lateral Li ion distribution on the near-surface region. We also have done measurements on Young’s elastic modulus of these thin film materials using nanosecond laser pulse-induced surface acoustic waves. The results showed the decrease in Young’s modulus after lithiation as it is expected because of volumetric expansion of Si crystal.
Funding from MES RK state-targeted programs BR05236454, BR05236524 and grant AP05130446 is acknowledged.
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