Sol-gel Preparation Of NMC811 Cathode Thin Film And Macro-micro Characterization Of Electrochemical Properties

The development of micro-electromechanical systems(MEMS)and intelligent wearable electronic devices has accelerated the miniaturization of power supplies,the thin-film lithium micro-batteries have great application potential.Among its main components,the cathode film occupies an important position,which largely determines the cycle life,specific energy,and safety of the battery.Among many cathode materials,Li Ni_0.8Co_0.1Mn_0.1O₂(NCM811)nickel-rich layered cathode has good market prospect due to its high specific capacity(200 m Ah/g)and low cost.However,current researches and reports on NMC811 thin film are rare,and most of the conventional testing techniques about it are also carried out at the macro and device level,and there is a lack of understanding the factors of the cathode material structure and lithium ion transport mechanism at the micro-nano scale.In this paper,NMC811 film is selected as the research object.Through the optimization of the Sol-Gel and spin coating process parameters,and controls formation and growth process of the film,the NMC811 film with better structure and performance is obtained,then it is assembled into three electrodes,and study the influence of different parameters on its macro-electrochemical performance.Finally,we use the electrochemical strain atomic force microscope(ESM),conductive atomic force microscope(C-AFM)and Kelvin probe atomic force microscope(KPFM)to systematically observe the surface volume deformation,lithium ion diffusion,phase transition process,electrical conductivity and Electro-mechanism properties such as potential distribution.The main contents are as follows:(1).We use the sol-gel and spin coating method,combined with different parameters to prepare NMC811 thin film with different structures and properties.The results show that:the cation mixing degree of film is the smallest,the crystal structure and surface morphology is the best,when the current driver concentration is 0.3 M,the molar concentration of M⁺:PVP is 1.3,and the annealing temperature is 700?,(2).We use the NMC811 thin film as working electrode,and select lithium sheets for the counter electrode and the reference electrode to form a three-electrode system.The experimental results show that the current drive body concentration is 0.3 M,the molar concentration of M⁺:PVP is 1.3,and the annealing temperature is 700?,the charge-discharge specific capacity of the film is highest,its crystallinity is good,and its reversibility is the highest.The charge transfer resistance and Warburg impedance of the thin film is smallest.(3).The NMC811 film that prepared by sol-gel and spin methods has polycrystalline structure.Using ESM,C-AFM and KPFM technologies,we found that as the applied voltage and temperature increase,the lithium ion concentration,conductivity,potential and quality factor on the surface of the film increase to a certain extent.However,when the voltage increased to 4 V or the temperature increased to200?,the surface of the film occurred irreversible deformation,the phase angle changes,and the surface electrochemical activity decreases,which in turn leads to a decrease in conductivity,electric potential and charge storage capacity.This may be caused by the phase transition of the material from layered order to spinel-like disorder.