| Lithium-ion battery shell is one of the important components of battery structure,and the quality of battery shell has a great impact on the battery life,cycle performance and safety performance.If the shell rusts or breaks,it will cause a fire or even an explosion.Taking the cylindrical lithium-ion battery as an example,the shell material of the cylindrical lithium-ion battery is mainly nickel-plated steel strip,and the coating of the existing market products is mainly composed of two or more layers of nickel coating,because the stress distribution between the multi-layer nickel coating is more uniform and the coating is closer.The nickel-plated steel strip has better corrosion resistance.Due to the increasing demand for corrosion resistance of battery steel strip,the design of coating materials with more excellent performance has become an urgent technical problem to be solved.The results show that the addition of phosphorus or molybdenum to the metal coating can effectively improve the corrosion resistance of the coating.Therefore,a kind of Ni/Ni-P/Ni-Mo-P multilayer material is designed in this paper to further improve the corrosion resistance of battery steel strip.The research contents of this thesis are as follows:(1)The cold-rolled steel(BDCK)for battery shell of Baosteel was selected as the substrate,and the nickel coating was prepared on the substrate by DC plating and the properties of the coating were tested.Then,the Ni-P coating was prepared on the substrate by adjusting the current density and bath temperature.The data show that the corrosion resistance of Ni-P coating is better under the condition of 3 A/dm~2and60°C.According to the optimal process parameters,Ni/Ni-P bilayer films were prepared on the substrate,and the hardness and corrosion resistance were tested.Compared with Ni-P coating,the microhardness of Ni/Ni-P coating decreased by5.9%,the porosity decreased by 31.8%,the impedance increased by 20.3%,the protection grade of neutral salt spray test increased by 1 grade,and Ni/Ni-P coating showed better corrosion resistance.(2)Based on the preparation process in the previous chapter,the Ni-P coating was prepared on the substrate by adding molybdenum to the Ni-Mo-P alloy and adjusting the current density and bath temperature.The data show that the corrosion resistance of Ni-Mo-P coating is better under the condition of 10 A/dm~2and 30°C.On the basis of Ni/Ni-P,Ni/Ni-P/Ni-Mo-P multilayer films were prepared on the substrate,and their hardness and corrosion resistance were tested.Compared with Ni/Ni-P coating,the porosity of multilayer film decreased by 73.3%,the roughness decreased by 2.7%,the microhardness increased by 1.7%,the impedance value increased by 61.6%,and the protection grade of neutral salt spray test increased by 1grade.The performance of the multilayer film is compared with that of the market product,in which the neutral salt spray test protection grade of the Ni/Ni-P/Ni-Mo-P multilayer film is 1 grade higher than that of the market product,while the hardness of the multilayer film is slightly higher than that of the market product.(3)On the basis of the preparation of multilayer films in the laboratory,the rack plating process was improved,the process parameters were optimized,and the rack plating experimental equipment was designed.The device can realize the small batch preparation of multilayer films on the surface of BDCK and other substrates,such as the coating structure of Ni/Ni-P/Ni-Mo-P multilayer films,and the multilayer films of other electroplating systems can be prepared by changing the plating solution.In the course of the test,the difficulties in disassembly and disassembly of plating parts,uneven coating and excessive impurities in the bath were analyzed and solved one by one,and the preparation efficiency and coating quality were improved. |
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