Preparation And Lithium Storage Mechanism Of Silicon Based Multilayer Thin Film

Silicon has a lithium storage capacity of about 4200 m Ah g^-1,which is much higher than that of commercial graphite(372 m Ah g^-1),so it has received great attention.However,the volume expansion is very severe(about 280%)during charging and discharging,which greatly limits its application.In this paper,a kind of Si/SiCO/Si"sandwich"structure multilayer film system is proposed in order to use the carbon net structure of Si CO to restrain the expansion of silicon system on both sides,so as to improve the capacity retention and rate performance.The experimental results show that when the thickness ratio of Si to Si CO layer is 1:1,the capacity retention rate of the film system is 91%after 100 cycles,and the reversible capacity is as high as 1946 m Ah g^-1,which is significantly higher than the range of 643.8 m Ah g^-1 to 1271 m Ah g^-1 of the existing silicon-based anode.Its capacity is higher than that of most silicon-based anodes.At high current density(3 C),the reversible capacity of the electrode is still as high as 1675 m Ah g^-1 after 20 cycles.By changing the sputtering power of carbon target,the results show that when the sputtering power is 40 W,the capacity retention rate of carbon target is as high as 97%compared with the second cycle,which reflects its great cycle performance.On the basis of experiments,the effects of thickness ratio and free carbon size on the electrochemical properties of Si/Si CO/Si system were studied by first principles calculation.The results show that with the increase of the thickness of carbon layer,the volume expansion rates of lithium intercalation saturated system are 205%,162%and 140%,respectively,which confirmed that the Si CO layer plays an important role in improving the cycling performance of the electrode system.The theoretical capacities predicted by the formation energy are 3510 m Ah g^-1,2900 m Ah g^-1and 2800 m Ah g^-1 respectively,which are close to the experimental initial discharge capacities of 3080 m Ah g^-1,2600 m Ah g^-1and 2558 m Ah g^-1.The results show that the first principle calculation can accurately reveal the mechanism of experimental phenomena,and provide a theoretical basis for subsequent experiments.Based on the analysis of the atomic structure,it is proposed that the formation of short Li-Si and Li-O bonds is the main source of irreversible capacity.According to the prediction,the reversible capacity of silicon-based multilayer system is 2146 m Ah g^-1,which is correspond to the experimental value of 2140 m Ah g^-1.Therefore,the first principles analysis method proposed in this paper can accurately predict the key performance of the electrode system,which provides a theoretical basis for the material design of further experiments.The experimental and computational analysis methods proposed in this work lay an important foundation for the design and development of silicon-based thin film lithium batteries.