Product Code Database
An alkaline battery is a type of Primary cell where the electrolyte (most commonly potassium hydroxide) has a pH value above 7. Typically, these batteries derive energy from the reaction between Zinc and manganese dioxide.
Compared with zinc–carbon batteries of the Leclanché cell or zinc chloride types, alkaline batteries have a higher energy density and longer shelf life yet provide the same voltage.
The alkaline battery gets its name because it has an electrolyte of potassium hydroxide (KOH) instead of the acidic ammonium chloride (NH4Cl) or zinc chloride (ZnCl2) electrolyte of the zinc–carbon batteries. Other battery systems also use alkaline electrolytes, but they use different active materials for the electrodes.
alkaline batteries accounted for 80% of manufactured batteries in the US and over 10 billion individual units produced worldwide. In Japan, alkaline batteries accounted for 46% of all primary battery sales. In Switzerland, alkaline batteries accounted for 68%, in the UK 60% and in the EU 47% of all battery sales including secondary types.
Alkaline batteries contain zinc (Zn) and manganese dioxide (MnO2), which is a cumulative neurotoxin and can be toxic in higher concentrations. However, compared to other battery types, the toxicity of alkaline batteries is moderate.
Alkaline batteries are used in many household items such as portable media players, , toys, , and radio receiver.
When alkaline batteries were introduced in the late 1960s, their zinc electrodes (in common with the then ubiquitous carbon-zinc cells) had a surface film of mercury amalgam. Its purpose was to control electrolytic action on impurities in the zinc; that unwanted electrolytic action would reduce shelf life and promote Battery leakage. When reductions in mercury content were mandated by various legislatures, it became necessary to greatly improve the purity and consistency of the zinc.
The two half-reactions are:
The overall reaction (sum of the anodic and cathodic reactions) is:
In comparison, Lithium-ion and Ni-MH batteries can handle with ease on the standard AA size.
A cylindrical cell is contained in a drawn stainless steel can, which is the cathode connection. The positive electrode mixture is a compressed paste of manganese dioxide with carbon powder added for increased conductivity. The paste may be pressed into the can or deposited as pre-molded rings. The hollow center of the cathode is lined with a separator, which prevents contact of the electrode materials and short-circuiting of the cell. The separator is made of a non-woven layer of cellulose or a synthetic polymer. The separator must conduct ions and remain stable in the highly alkaline electrolyte solution.
The negative electrode is composed of a dispersion of zinc powder in a gel containing the potassium hydroxide electrolyte. The zinc powder provides more surface area for chemical reactions to take place, compared to a metal can. This lowers the internal resistance of the cell. To prevent gassing of the cell at the end of its life, more manganese dioxide is used than required to react with all the zinc. Also, a plastic-made gasket is usually added to increase leakage resistance.
The cell is then wrapped in aluminium foil, a plastic film, or rarely, cardboard, which acts as a final layer of leak protection as well as providing a surface on which logos and labels can be printed.
When describing AAA, AA, C, sub-C and D size cells, the negative electrode is connected to the flat end, and the positive terminal is the end with the raised button. This is usually reversed in button cells, with the flat-ended cylindrical can being the positive terminal.
In 2017 Gautam G. Yadav published papers reporting that alkaline batteries made by interleaving the interlayers with copper ions could be recharged for over 6,000 cycles due to the theoretical second electron capacity of manganese dioxide. The energy density of these rechargeable batteries with copper intercalated manganese dioxide is reported to be over , the best among the aqueous-based chemistries. It could be capable of energy densities comparable to lithium-ion (at least ) if zinc utilization in the batteries were improved.
All batteries gradually self-discharge (whether installed in a device or not) and dead batteries eventually leak. Extremely high temperatures can also cause batteries to rupture and leak (such as in a car during summer) as well as decrease the shelf life of the battery.
The reason for leaks is that as batteries dischargeeither through usage or gradual self-dischargethe 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.
Once a leak has formed due to corrosion of the outer steel shell, potassium hydroxide absorbs carbon dioxide from the air to form a feathery crystalline structure of potassium carbonate that grows and spreads out from the battery over time, following along metal electrodes to circuit boards where it commences oxidation of copper tracks and other components, leading to permanent circuitry damage.
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 varies by jurisdiction. For example, the state of California considers all batteries as hazardous waste when discarded, and has banned the disposal of batteries in 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.
/ref> In 2006, the EU committed to recycling 45% of all batteries by 2016. In 2023, a new regulation set a target of 63% by 2027 and 73% by 2036.
In the US, only one state, California, requires all alkaline batteries to be recycled. Vermont also has a statewide alkaline battery collection program. In other US states, individuals can purchase battery recycling kits used to ship batteries to recyclers. Some stores such as IKEA also collect alkaline batteries for recycling. However, some chain stores that advertise battery recycling (such as Best Buy) accept rechargeable batteries only, and generally do not accept alkaline batteries.
For recycling, the metals from crushed alkaline batteries are mechanically separated, and the waste black mass is treated chemically to separate zinc, manganese dioxide and potassium hydroxide.
|
|
