Why are the negative electrode tab welding tips and the positive electrode welding tips of lithium b

I don't know which lithium battery you are talking about: cylindrical, aluminum cased, soft pack, polymer, etc. Each has some differences in processing technology. Generally, the positive electrode tab is made of aluminum and the negative electrode. the tab is nickel. The different welding heads you mentioned probably use different welding methods: if the positive electrode is not converted from aluminum to nickel, it is usually welded with an ultrasonic welding machine or a welding machine laser. If it was converted to nickel, by precision resistance spot welding. is used. machine, the negative electrode is usually welded by precision resistance spot welding machine, and there are also laser spot welding machines used by high-end customers. So the welding heads you mentioned are differentferent. It is estimated that two different welding machines were used for the welding.