An Study On Preparation And Corrosion Resistance Of Ni-Co/Ni/Ni-Co Multilayer Films

Nickel-plated deeply-draw steel strip, developed by the material and devices group of xiangtan university, is prepared by continues electroplating nickel film up to 2-3μm on the surface of low-carbon steel. The manufacturing costs can be reduced by controlling the grain size of film and simplifying the finishing or/and heat treatment process. The deep drawing steel strip made by this method has excellent elongation and corrosion resistance, can satisfy the high-performance condition of mercury-free alkaline battery. With the increasing in the performance requirement of alkali battery, the deficiency in good coating material has become the long-term and urgent bottleneck problem for the development of battery shell.Recent years, with the rapid development of electric vehicles, technical problems such as the life issues and security performance of batteries have restricted the development of electric cars. Cylindrical lithium ion battery is the most important part of Lithium-ion battery at present, and the main technics of shell preparation are Barrel Plating, Pre-plating and Pre-coated firstly then Barrel plating. However, Barrel Plating and pre-plating can not meet the performance requirements of the shells of dynamical lithium-ion batteries. The manufacturing processes of steel shells produced by Pre-coated firstly then Barrel plating are complexly and costly. Therefore, the problem that how to design and optimize plating coating on the batterys,shells to improve the storage performance and corrosion resistance of the battery, are pivotal in preparation of cylindrical lithium ion battery shells to be solved.This paper focuses on enhancing the corrosion resistance and storage performance of the alkaline battery and the Lithium-ion battery, so the Ni-Co/Ni/Ni-Co multilayer film was designed. First of all, Multilayer coatings consisting of different Ni–Co and Ni layers were prepared by combining electrodeposition with pulse electrodeposition. and the microstructure, surface morphology, cross-section morphology of Ni-Co/Ni/Ni-Co multilayer film was studied. and the salt spray test, The corrosion electrochemical environment constituted of acid or alkaline, and the evaluation techniques employed included tafel curve, linear anode polarization, the salt spray test , and electrochemical impedance spectroscopy(EIS) was studied in detail. Specific tasks and the results summarized as follows: First, Ni-Co/Ni/Ni-Co multilayer coatings consisting of different Ni–Co and Ni layers were prepared by combining electrodeposition with pulse electrodeposition. The semi-bright bath additives was added to the Watt system, semi-bright Ni-Co alloy film were prepared by pulse electrodeposition; the middle layer of microcrystalline nickel film by DC electrodeposition; The bright bath additives was added into the Watts bath system, the bright Ni-Co alloy film was prepared by pulse electrodeposition.Second, The microstructure of the coatings was analyzed by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The EDS showed that the cobalt content of the bright Ni-Co alloy coating and the semi-bright Ni-Co alloy coatings were about 5%. XRD results show that nickel and cobalt formed a solid solution, the lattice structure is fcc. SEM results show that the entire surface of bright nickel-cobalt alloy plating fine grain size, coating density. Section shows the surface morphology of multilayer films of nickel and cobalt alloy coatings effectively filling the empty micro crystalline nickel and the pinhole. Multilayer surface AFM results show that the surface roughness of multilayers is lowest.Third, the salt spray test, Tafel extrapolation and electrochemical impedance means were employed to study the corrosion rersistance of the Ni-Co/Ni/Ni-Co multilayer film. Tafel curves showed, the surface passivation effect of Ni-Co/Ni/Ni-Co multilayer film was strongest. The EIS results showed that the charge transfer resistance of the Ni-Co/Ni/Ni-Co multilayer film was largest. Salt spray test results show that after 8 hours salt spray, the red rust were least on the surface of the Ni-Co/Ni/Ni-Co multilayer .In short, the grain size and thickness of each layer in Ni-Co/Ni/Ni-Co multilayer film are specifically designed for integration of all the advantages of monolayers. By different coatings with different grain sizes alternating deposition, coating structure was compact, the pitting corrosion of steel plating were reduced, and the corrosion resistance of the battery shell was improved. In summary, the performance of the Ni-Co/Ni/Ni-Co multilayer films is better than the Nickel-plated deeply-draw steel strips.