In recent years, with the emerging of the problems such as the depletion of natural resources and the warming of the global weather, the green and low carbon life style is becoming popular. Replacing some of internal combustion engine vehicles consuming fossil fuel by electric vehicles and hybrid electric vehicles is one of the main solutions dealing with the energy crisis and environmental deterioration. The driving source is a key component affecting the promotion and use of an electric vehicle. The driving sources widely used at present include lead acid batteries, nickel-cadmium batteries (NiCd), lithium ion batteries, nickel-zinc batteries and the like. In various driving sources, nickel-zinc batteries are widely researched due to the advantages of high power, sufficient energy, free of environmental pollution, high reliability and safety, low cost, and long service life.
In nickel-zinc batteries, due to the problems of tendency to deformation, dendritic crystal, corrosion, and passivation present in zinc electrodes, a nickel-zinc battery suffers from the disadvantages of short cycling life, high self-discharging, and rapid capacity fading during cycling use. Continuous researches were made by relevant researchers on the membrane separator of the nickel-zinc battery in order to overcome the above defects existing in the nickel-zinc battery. For example, Andre H. Bull. Soc. Fr. Electrians published in 1941 reported a membrane separator, which is unstable and tends to degrade in 30% KOH solution; and U.S. Pat. No. 4,279,978 reported a membrane separator consisted of polyamide, hydrophilic polymer, and some auxiliary materials.
However, the common disadvantage present in both of the above reported membrane separators lies in that the micro-pores in the membrane separator are straight pores, as shown in FIG. 1. Since ions, which have the characteristic of moving along a line, preferably choose micro-pores having smaller resistance, zinc ions are preferably reduced and repeatedly accumulated at the straight pores during charging, so that zinc material is gradually increased at straight pores to form an elevated point higher than the electrode plane, that is, zinc dendrite. Dense and hard zinc dendrite will continue to grow, and penetrate the membrane separator from the micro-pores of the membrane separator, leading to short circuit between the electrodes of the nickel-zinc battery and in turn failure of the battery.
Therefore, the present inventor proposes a method for preparing a battery membrane separator that can be prevented from being penetrated by dendrites.