Nickel–zinc battery

A nickel–zinc battery, abbreviated NiZn, is a type of rechargeable battery similar to NiMH batteries, but with a higher voltage of 1.6 V. Larger nickel–zinc battery systems have been known for over 100 years. Since 2000, development of a stabilized zinc electrode system has made this technology viable and competitive with other commercially available rechargeable battery systems. Unlike some other technologies, trickle charging is not recommended. In 1901 Thomas Alva Edison was awarded U.S. Patent 684,204 for a rechargeable nickel–zinc battery system. The battery was later developed by the Irish chemist Dr. James J. Drumm (1897–1974), and installed in four two-car Drumm railcar sets between 1932 and 1949 for use on the Dublin–Bray railway line. Although successful, they were withdrawn when the batteries wore out. Early nickel–zinc batteries provided only a small number of discharge/recharge cycles. In the 1960s nickel–zinc batteries were investigated as an alternative to silver–zinc batteries for military applications, and in the 1970s were again of interest for electric vehicles. Evercel Inc. developed and patented several improvements in nickel–zinc batteries, but withdrew from that area in 2004. Nickel–zinc batteries have a charge/discharge curve similar to 1.2 V NiCd or NiMH cells, but with a higher 1.6 V nominal voltage. Nickel–zinc batteries perform well in high-drain applications, and may have the potential to replace lead–acid batteries because of their higher energy-to-mass ratio and higher power-to-mass ratio — as little as 25% of the mass for the same power. NiZn are cheaper than nickel-cadmium batteries, and are expected to be priced somewhere between NiCd and lead–acid types. NiZn may be used as a substitute for nickel–cadmium. The European Parliament has supported bans on cadmium-based batteries; nickel–zinc is a good alternative for power tools and other applications. A disadvantage is increased self-discharge rate after about 30 cycles, so that batteries do not hold their charge as long as when new. Where this is not a problem NiZn is a good battery choice for applications requiring high-power and high-voltage. If used properly NiZn batteries can last for hundreds of cycles. Compared with cadmium hydroxide, the tendency of the soluble zinc hydroxide ion (zincate) to dissolve into solution and not fully migrate back to the cathode during recharging has, in the past, presented challenges for the commercial viability of the NiZn battery. Another common issue with zinc rechargeable batteries is electrode shape change and dendrites (or 'whiskers'), which may reduce the cell discharging performance or, eventually, short out the cell, resulting in a low cycle life.