All Solid-state Thick Film Lithium Battery

In recent years,all solid-state lithium batteries have attracted wide attention because of their high safety and high energy density.Among them,all solid-state thin film lithium battery is the only one type of all solid-state batteries which is commercialized presently.Due to high-cost cathode preparation process and low cell capacity,its application is limited in the field of microelectronic devices.Alternatively,all solid-state thick film lithium battery can be developed via replacing the thin-film cathode with a thick-film cathode prepared by economical and efficient coating method.And the thin-film electrolyte and anode are fabricated by physical vapor deposition method,which are same as all solid-state thin film lithium battery.This methodology is not only cost effective,but also improves the cell capacity greatly,which can significantly broaden the application range of all solid-state thin film lithium battery.In this thesis,the effect of adding interface buffer layer between the electrolyte and the anode is also discussed.The main research contents are listed as follows:（1）The influence of cold-pressing pressure on thick-film cathode,working temperature and anode thickness is studied.In the process of cathode preparation,the cold-pressing technique can effectively reduce the surface roughness of the cathode and the impedance of the assembled thick-film battery.The pressure of 40 MPa leads to better electrochemical performance with respect to 10 MPa.Increasing the working temperature can obviously improve the discharge capacity of thick film battery.Compared with 25℃,the discharge capacity at 60℃is increased by 62.1 m Ah/g,which is attributed to the higher ionic conductivity of composite cathode and electrolyte film at elevated temperature.At 60℃,the anode structure in the thick film battery is more seriously damaged,resulting in rapid capacity attenuation.By increasing the thickness of the anode,its structure stability and cycle stability can be improved.（2）According to post-mortem analysis on the morphology evolution of the failed thick film battery,the failure mechanism of thick film battery is mainly ascribed to the destructed anode film and the blurred anode-electrolyte interface.To increase the anode thickness can effectively prolongate the cycling lifetime.（3）In order to enhance the cycle stability of the thick film battery,an aluminum interface layer is introduced between the anode and the electrolyte by DC magnetron sputtering,which the interface structure is well reserved after multiple cycles.Consequently,the initial discharge capacity is as high as 144.4 m Ah/g（0.3 m Ah/cm~2）at60℃and 0.2 C,and the capacity retention rate is increased from 21.1%to 76.2%after100 cycles in comparison to the unmodified one.Meanwhile,the cell impedance is down to 850Ωprior to the cycling and 592Ωafter 50 cycles,which is much lower than 4000Ωand 5800 of the unmodified one,separately.Furthermore,the rate performance is excellent with the capacity retention rate of 45.4%at 5 C.Finally,a preliminary attempt is made to prepare thick film Li anode via a molten lithium technique,and the as-assembled thick-film battery releases 86%of its theoretical specific capacity.Unfortunately,the processing of molten lithium may destroy the integrity of the electrolyte film,which causes a sudden failure of the battery.It is necessary to develop a more stable interface layer or a more compatible anode fabrication technique.