Experimental Study On Li-rich Thin Film Cathode Prepared By Pulsed Laser Deposition

Pulsed laser deposition is a process to prepare thin films by the help of laser. Forthe advantages such as high deposition speed, good stoichiometric ratio retainion, ithas been successfully used in preparing high-temperature superconducting thin films,ferroelectric thin films, piezoelectric thin films and lithium ion battery related thinfilms. However, duo to the high cost of one-time investment and the difficulty inoperating traditional self-assembly equipment, the application of the process waslimited. Lithium-rich cathode material is a solid solution between Li2MnO3andLiMO2(M=Mn, Co, Ni) which show relatively good application prospects for theadvantages as a high specific energy density (>300mAh/g) and abundant reserves ofconstituent elements. However, there is still no systematic study on lithium-richcathode thin film.In order to study related problems of lithium-rich thin film cathode prepared bypulsed laser deposition system, a new PLD system was built in this paper andlithium-rich cathode thin films were prepared by it, the films were charatorized bydifferent techniques, the influence rule of the process parameters were studied,appropriate process parameters were explored and an exploratory research on theapplication of lithium-rich thin film cathode in solid-state batteries was conducted.In view of the problems of the existing and traditional pulsed laser depositionequipment, through improving the hardware and software, vacuum gauge controllerACM1000, turbo pump controller ACT600T, heating controller SRS10A and steppermotor etc. were built into a new PLD system via serial port communication and I/Oport control with PC, the programmed automatical deposition process was achieved,the operation of PLD was simplified, visual control and multi-target layer by layerdeposition were achineved, the problems of common traditional pulsed laserdeposition systems such as complicated operation, high labor intensity and could notdeposit visually layer by layer by multi-targets etc. were solved.Based on the improved integration of the PLD system, lithium-rich cathode thinfilms were prepared using a single target method and a multi-target method. By thehelp of FESEM, XRD, XPS and electrochemical charge-discharge tester, morphology,composition, charge and discharge, lithium ion diffusion coefficient of lithium-richcathode thin films were characterized and the suitable process parameters were obtained. The charactorization results of thin films prepared by single target methodshow that the performance of lithium-rich cathode film is similar to powder lithiumrich cathode material, the discharge capacity can reach70μAh/cm2μm (~140mAh/g)which is bigger than the other reported thin film cathodes. The results also show thatspinel structure formed when the oxygen pressure is lower than200mTorr, and whenthe oxygen pressure is higher than450mTorr, lithium content in the thin film isinadequate, lithium rich thin film can not be obtained; when annealing temperature isbelow700℃, the crystallization of the film is poor, there is no significant dischargeplateau, and when the annealing temperature is higher than900℃, the film showed aspinel structure, at the same time, for a severe lithium loss during the annealingprocess, the electrochemical properties of the film is poor. A lithium ion diffusioncoefficient of lithium rich cathode material was tested to be1×10-15~1×10-13cm2/s.Based on lithium-rich cathode thin films, Li-rich/LLZO/Li, Li-rich/LAGP/TiO2and Li-rich/LICGC/Li were prepared. Through the analization of thin film electrolytesLLZO and LAGP, thin film anode TiO2and solid-state full batteries, the performanceof the solid state batteries based on lithium-rich thin films were studied. Due to thelow ionic conductivity of LLZO electrolyte thin films and the problem ofthe interface between lithium metal and LLZO films, Li-rich/LLZO/Li failed to showthe electrochemical characters of lithium-rich cathode material. Li-rich/LAGP/TiO2showed similar characteristics to Li rich cathode material and a5hour dischargeprocess at a current value of3nA/cm2. Li-rich/LICGC/Li showed similarcharge-discharge plateau to lithium-rich cathode material which caused by the valencechange of the related elements and a40minutes discharge process at a current valueof50nA/cm2.