| All-solid-state thin film lithium battery has attracted much attention recently because of its wide application in portable electronics and mobile devices.TFB has achieved commercial application because of its good safety,high specific energy and long cycle life.Since the excellent performance of TFB is greatly affected by its solid electrolyte,the solid electrolyte is a key element of sustainability efforts focused on power sources in TFB.Among the promising materials with high ionic conductivity,perovskite compound lithium lanthanum titanate?LLTO?is a promising solid electrolyte based on its extremely high bulk ionic conductivity(10-3 S·cm-1 at room temperature),owing to its crystallographic structure and low activation energy?about 0.3-0.4eV?.Up to now,many methods have been used to prepare the LLTO thin films solid electrolyte.Among those methods,RF magnetron sputtering deposition technology is a well establish technology in industrial processing owing to its advantages on preparing large-scale and dense films with high performances.In order to prepare high quality LLTO by RF magnetron sputtering,the key issue is to control the process parameters,especially the oxygen partial pressure,substrate and annealing temperature,because they strongly influence the structure,composition and electrochemical properties of the films.The aim of this study is to grow films with high ionic conductivity by controlling the oxygen partial pressure,substrate and annealing temperature.And then,the LLTO thin film coated LiCoO2 electrode was prepared by RF magnetron sputtering to be used as the cathode.The main results and conclusions are shown as follows.?1?The LLTO thin films are dense amorphous structure with uniform and smooth surface,without pinholes and cracks.With the increasing of oxygen partial pressure,the deposition rate of LLTO thin films obviously decreases and then the thickness of LLTO thin film reduces from 306nm to 185nm accordingly.Meanwhile,the surface roughness mean square?RMS?of the prepared LLTO film increases from 1.76 nm to 2.84 nm following the enhancement of the oxygen partial pressure in a certain range.Furthermore,the ionic conductivity of the prepared LLTO films firstly increases and then decreases with the increasing oxygen partial pressure.At room temperature,the thin films prepared in the atmosphere of O2:Ar=3:7 exhibits the highest ionic conductivity of 1.81×10-5 S·cm-1.?2?The LLTO thin films prepared at different substrate temperatures are amorphous films.With the increasing of the substrate temperature,it is obvious that the grains are aggregate and getting larger;When the substrate is heated from 25?to 100?,the thickness of thin film rapidly decreases from 266 nm to 186 nm.As the substrate temperature continues to rise,the film thickness is modestly reduced,respectively 200?is 171 nm and 300?is 166 nm.There is no significant difference in ionic conductivity of LLTO thin films prepared under different substrate temperatures.The film ion conductivity at room temperature is 1.81×10-5 S·cm-1.And when the substrate temperature increases from 100?to 300?,the ionic conductivity increases from 1.55×10-5 S·cm-1 to 1.79×10-5 S·cm-1.?3?For different annealing temperature,the XRD and SEM analyses indicate that the prepared LLTO thin films are amorphous when annealed at 25?600?.While the LLTO films start crystallization when annealed above 700?.Furthermore,the surface roughness of prepared LLTO thin films increases from about 3 nm to 13.9 nm once the annealing temperature is 700?.Meanwhile,the ionic conductivities of prepared amorphous LLTO thin films are one order of magnitude higher than those of crystal films.By controlling the annealing temperature,the optimized ionic conductivity reaches5.32×10-5 S·cm-1,when the annealing temperature is 300?.While the annealing temperature is 800?,the ionic conductivity of crystalline LLTO thin film is 7.7×10-6S·cm-1.?4?The composite electrode show high discharge capacity and better cycling performance.Meanwhile,it improves the electrode-electrolyte interfacial charge transfer efficiency. |
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