Over 110 years ago, the legendary inventor Thomas Edison was granted a patent for the nickel-zinc (NiZn) battery, but a multitude of technical problems blocked the commercial success of this type of battery, and it vanished into distant memory. However, the situation started to change around 2000, when nickel-zinc battery technology again became a focus of intensive research due certain advantages over nickel-cadmium (NiCd) and nickel metal hydride (NiMH) batteries – in particular a higher cell voltage, which simplifies the use of primary batteries as direct power sources. The EU is also campaigning to prohibit the use of NiCd batteries due to their cadmium content. The first generation of NiZn rechargeable batteries is now available in AAA and AA formats from suppliers such as Conrad and Volkner (in Germany).
The nominal cell voltage of NiZn batteries (1.55 V) is not their only difference from NiCd and NiMH batteries. The voltage across the terminals of a fully charged cell is 1.8 V, dropping to around 1.2 V when fully discharged, depending on the current level. NiZn batteries have very low internal resistance, which allows them to be charged quickly at 0.5 to 1C. However, the manufacturers are currently keeping mum on the allowable number of charge cycles. In the medium term NiZn batteries could be more economical than NiCd or NiMH batteries because zinc is relatively cheap.
With the currently available types, the energy capacity is specified in mWh instead of the usual mAh. A typical figure for an AA-format NiZn cell is 2,500 mWh, corresponding to roughly 1,400 to 1,500 mAh with a 1C discharge curve. NiZn batteries require suitable chargers. The charging method is simple and similar to the method for lead-acid or LiPo batteries: the cells are charged at a constant current of 0.5 to 1C (700 to 1,500 mA with an AA cell) until the cell voltage reaches 1.9 V. The cell is fully charged when the charging current drops below 0.05C (75 mA).
The main advantage of NiZn cells is that they are easier to use as replacements for primary cells with a nominal voltage of 1.5 V, since the voltage at the end of the discharge cycle is significantly higher than that of commonly used NiMH cells. This means that battery-powered devices in daily use, such as wireless keyboards and mice, do not need to be recharged as often.
Image: Shenzhen BetterPower Battery Co., Ltd