Alkaline batteries are a type of primary battery dependent upon the reaction between zinc and manganese dioxide (Zn/MnO2).
Another type of alkaline batteries are secondary rechargeable alkaline battery, which allows reuse of specially designed cells.
Alkaline batteries have a higher energy density and longer shelf-life compared with zinc-carbon batteries with the same voltage.
Alkaline batteries account for 80% of manufactured batteries in the US and over 10 billion individual units produced worldwide.
Some alkaline batteries are designed to be recharged, but most are not. Attempts to recharge may cause rupture, or the leaking of hazardous liquids which will corrode the equipment. However, attempts at recharging alkaline cells a highly limited number of times (10 or fewer times with reduced capacity after each charge) are reported and chargers are available commercially.
Alkaline batteries are used in many household items such as MP3 players, remote controls, digital cameras, pagers, toys, lights, and radios.
Alkaline batteries constructions & properties:
- Compared to zinc-carbon batteries that produce about 1.5V per cell, alkaline batteries have higher energy density and longer shelf life.
- Compared to silver-oxide batteries, they have a lower energy density and a shorter life, but a lower cost.
- Alkaline batteries get their name from the alkaline electrolyte of potassium hydroxide, unlike the acidic electrolyte of zinc-carbon batteries, which are available in the same nominal voltages and physical size.
- Alkaline battery capacity is greater than the equal size or zinc chloride cell, because the dioxide anode material is cleaner and thicker and the space occupied by the internal components as shoe collectors is less.
- The alkaline cell can provide between three to five times longer service life.
- The capacity of the alkaline battery is highly dependent on the load. An AA size alkaline battery can have an effective capacity of 3000Mhz (lowest ampere hours) at the lowest power, but with a 1000mAh charge, which is common to digital cameras, the capacity can be at least 700mAh.
- Alkaline batteries are manufactured in standard cylindrical forms interchangeable with zinc-carbon batteries
- Some alkaline batteries are designed to recharge, but most are not. Attempting to recharge can cause a breakage or leakage of hazardous liquids that will lead to corrosion of the equipment.
- Over time, alkaline batteries are susceptible to leakage of potassium hydroxide, which can lead to breathing problems and irritation of the eyes and skin. This can be avoided by not trying to recharge the alkaline cells and mixing the different types of batteries in the same device.
- When introduced in 1960, alkaline batteries contain a small amount of mercury, amalgam, to control unwanted zinc cathode reactions. Improving the purity and consistency of the materials has enabled manufacturers to reduce the mercury content.
Alkaline batteries are prone to leaking potassium hydroxide, a caustic agent that can cause respiratory, eye and skin irritation. Risk of this can be reduced by not attempting to recharge disposable alkaline cells, not mixing different battery types in the same device, replacing all of the batteries at the same time, storing in a dry place and at room temperature, and removing batteries for storage of devices.
The reason for leaks is that as batteries discharge — either through usage or gradual self-discharge – the chemistry of the cells changes and some hydrogen gas is generated. This out-gassing increases pressure in the battery. Eventually, the excess pressure either ruptures the insulating seals at the end of the battery, or the outer metal canister, or both. In addition, as the battery ages, its steel outer canister may gradually corrode or rust, which can further contribute to containment failure.
The leaking crystalline growths can also emerge from seams around battery covers to form a furry coating outside the device, that corrodes any objects in contact with the leaking device.
Disposal & Recycling:
With the reduction in mercury in 1996, alkaline batteries are allowed to be disposed of as regular domestic waste in some locations. However, older alkaline batteries with mercury, and the remaining other heavy metals and corrosive chemicals in all batteries (new and old), still present problems for disposal—especially in landfills. There is also the issue of simplifying the disposal of batteries to exclude them all so that the most toxic will be diverted from general waste streams.
Disposal varies by jurisdiction. For example, the state of California considers all batteries as hazardous waste when discarded, and has banned the disposal of batteries with other domestic waste. In Europe, battery disposal is controlled by the WEEE Directive and Battery Directive regulations, and as such alkaline batteries must not be thrown in with domestic waste. In the EU, most stores that sell batteries are required by law to accept old batteries for recycling.
For recycling, the metals from crushed alkaline batteries are mechanically separated, and the waste black mass is treated chemically to separate zinc, manganese and potassium.