Zinc batteries. Air-zinc cells (Zinc-Air) - a possible alternative to lithium
Long time scope air-zinc batteries did not go beyond medicine. High capacity and long service life (when inactive) allowed them to easily occupy the niche of disposable hearing aid batteries. But in recent years, there has been a great increase in interest in this technology from automakers. Some believe that an alternative to lithium has been found. Is it so?
An air-zinc battery for an electric vehicle can be arranged as follows: electrodes are inserted into a container divided into compartments, on which air oxygen is adsorbed and reduced, as well as special removable cassettes filled with anode consumables, in this case zinc granules. A separator is laid between the negative and positive electrodes. An aqueous solution of potassium hydroxide or a solution of zinc chloride can be used as an electrolyte.
The air supplied from the outside with the help of catalysts forms hydroxide ions in the aqueous electrolyte solution, which oxidize the zinc electrode. During this reaction, electrons are released, forming an electric current.
Advantages
According to some estimates, world reserves of zinc are about 1.9 gigatons. If we start the world production of metallic zinc now, then in a couple of years it will be possible to assemble a billion air-zinc batteries with a capacity of 10 kWh each. For example, it would take more than 180 years to create the same amount under current lithium mining conditions. The availability of zinc will also reduce the price of batteries.
It is also very important that air-zinc cells, having a transparent recycling scheme for used zinc, are environmentally friendly products. The materials used here do not poison the environment and can be recycled. The reaction product of air-zinc batteries (zinc oxide) is also absolutely safe for humans and their environment. No wonder zinc oxide is used as the main ingredient in baby powder.
The main advantage, thanks to which electric vehicle builders look to this technology with hope, is the high energy density (2-3 times higher than that of li-ion). Already, the energy intensity of Zinc-Air reaches 450 Wh/kg, but the theoretical density can be 1350 Wh/kg!
Flaws
Since we do not drive electric cars with zinc-air batteries, then there are disadvantages. Firstly, such cells are difficult to make rechargeable with a sufficient number of discharge / charge cycles. During the operation of a zinc-air battery, the electrolyte simply dries out, or it penetrates too deeply into the pores of the air electrode. And since the deposited zinc is distributed unevenly, forming a branched structure, short circuits often occur between the electrodes.
Scientists are trying to find a way out. The American company ZAI solved this problem by simply changing the electrolyte and adding fresh zinc cartridges. Naturally, this will require a developed infrastructure of filling stations, where the oxidized active material in the anode cassette will be replaced with fresh zinc.
And although the economic component of the project has not yet been worked out, manufacturers claim that the cost of such a “charge” will be significantly lower than refueling a car with an internal combustion engine. In addition, the process of changing the active material will require no more than 10 minutes. Even ultra-fast ones can only replenish 50% of their potential in the same time. Last year, the Korean company Leo Motors already demonstrated ZAI zinc-air batteries on its electric truck.
Working on improving the Zinc-Air battery and technology firm from Switzerland ReVolt. She proposed special gel-forming and binder additives that control the moisture and shape of the zinc electrode, as well as new catalysts that significantly improve the performance of the cells.
Still, the engineers of both companies never managed to overcome the milestone of 200 discharge / charge cycles of Zinc-Air. Therefore, it is too early to talk about zinc-air cells as electric batteries.
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In the fifth issue of our magazine, we told how to make a gas accumulator ourselves, and in the sixth issue, a lead-potash accumulator. We offer readers another type of current source - an air-zinc element. This element does not require charging during operation, which is a very important advantage over batteries.
The zinc-air element is now the most advanced current source, since it has a relatively high specific energy (110-180 Wh / kg), is easy to manufacture and operate, and is the most promising in terms of increasing its specific characteristics. The theoretically calculated power density of a zinc-air element can be up to 880 Wh/kg. If even half of this power is achieved, the element will become a very serious rival to the internal combustion engine.
A very important advantage of the air-zinc element is
small change in voltage under load as it is discharged. In addition, such an element has considerable strength, since its vessel can be made of steel.
The principle of operation of air-zinc elements is based on the use of an electrochemical system: zinc - a solution of caustic potassium - activated carbon that adsorbs oxygen from the air. By selecting the compositions of the electrolyte, the active mass of the electrodes and choosing the optimal design of the element, it is possible to significantly increase its specific power.
Battery technology has improved significantly over the past 10 years, increasing the value of hearing aids and improving their performance. Ever since the digital processor dominated the CA market, the battery industry has exploded.The number of people using zinc-air batteries as a power source for hearing aids is increasing day by day. These batteries are environmentally friendly and, due to their increased capacity, last much longer than other types of batteries. However, it is difficult to name the exact service life of the element used, it depends on many factors. At certain points, users have questions and complaints.<Радуга Звуков>will try to give an exhaustive answer to a very important question: so what does the battery life depend on?
ADVANTAGES...
For many years, mercury-oxide batteries have been the main source of power for hearing aids. However, in the mid 90s. it became clear that they were completely outdated. First, they contained mercury - an extremely harmful substance. Secondly, digital SA appeared and began to rapidly conquer the market, presenting fundamentally different requirements for the characteristics of batteries.
Mercury-oxide technology has been replaced by air-zinc technology. It is unique in that one of the components (cathode) of the chemical battery uses ambient air oxygen, which enters through special holes. By removing mercury or silver oxide, which until now served as the cathode, from the battery case, more space was freed up for zinc powder. Therefore, a zinc-air battery is more energy-intensive when compared to different types of batteries of the same volume. With this ingenious solution, the zinc-air battery will remain unrivaled as long as its capacity is limited by the tiny volume of today's miniature SAs.
On the positive side of the battery, there are one or more holes (depending on its size) into which air enters. The chemical reaction during which the current is generated proceeds quite quickly and is completely completed within two to three months, even without loading the battery. Therefore, during the manufacturing process, these holes are covered with a protective film.
To prepare for work, it is necessary to remove the sticker and allow time for the active substance to saturate with oxygen (from 3 to 5 minutes). If you start using the battery immediately after opening, then activation will occur only in the surface layer of the substance, which will significantly affect the service life.
The size of the battery plays an important role. The larger it is, the more reserves of the active substance in it, and, therefore, the more accumulated energy. Therefore, a 675 size battery has the largest capacity, and a size 5 battery has the smallest. The battery capacity also depends on the manufacturer. For example, for batteries of size 675, it can vary from 440 mAh to 460 mAh.
AND FEATURES
First, the voltage supplied by a battery depends on how long it has been in use, or more specifically, on the degree to which it has been discharged. A new zinc-air battery can deliver up to 1.4 volts, but only for a short time. Then the voltage drops to 1.25 V, and holds for a long time. And at the end of the battery life, the voltage drops sharply to a value of less than 1 V.
Secondly, zinc-air batteries function better the warmer it is around. In this case, of course, you should not exceed the maximum temperature set for this type of battery. This applies to all batteries. But the peculiarity of zinc-air batteries is that their performance also depends on the humidity of the air. The chemical processes occurring in it depend on the presence of a certain amount of moisture. To put it simply, the hotter and more humid the better (this only applies to CA batteries!). And the fact that humidity has a negative effect on other components of the auditory system is another matter.
Thirdly, the internal resistance of the battery depends on a number of factors: temperature, humidity, operating time and the technology used by the manufacturer. The higher the temperature and humidity, the lower the impedance, which has a beneficial effect on the functioning of the auditory system. The new 675th battery has an internal resistance of 1-2 ohms. However, at the end of the service life, this value can increase to 10 ohms, and for the 13th battery - up to 20 ohms. Depending on the manufacturer, this value can vary significantly, which creates problems when the maximum power specified in the data sheet is required.
If the critical current draw is exceeded, the final stage or the entire hearing system is switched off so that the battery can recover. If after<дыхательной паузы>the battery again begins to give current in an amount sufficient for operation, the SA is turned on again. In many hearing systems, restarting is accompanied by an audible signal, the same one that alerts you to a low battery voltage. That is, in a situation where the CA turns off due to high current consumption, an alarm sounds when it is turned on again, although the battery may be completely new. This situation usually occurs when the hearing aid is receiving a very high input SPL and the hearing aid is set to full power.
Factors affecting service life
One of the main tasks facing batteries is to provide a constant supply of current throughout the life of the battery.
Battery life is primarily determined by the type of CA you use. As a rule, analog devices consume more current than digital ones, and powerful devices consume more than low-power devices. Typical current consumption values for medium power devices are from 0.8 to 1.5 mA, and for high-power and heavy-duty devices - from 2 to 8 mA.
Digital HAs are generally more economical than analog HAs of the same power. However, they have one disadvantage - at the moment of switching programs or automatic operation of complex signal processing functions (noise suppression, speech recognition, etc.), these devices consume significantly more current than in normal mode. The energy requirement can rise and fall depending on what signal processing function the digital circuitry is currently performing, and even whether the correction of a patient's hearing loss requires different amplification for different input SPLs.
The ambient acoustic situation also affects battery life. In a quiet environment, the acoustic signal level is usually low - about 30-40 dB. In this case, the signal entering the SA is also small. In a noisy environment, such as in the subway, train, at work or in a noisy street, the acoustic signal level can reach 90 dB or more (a jackhammer is about 110 dB). This leads to an increase in the level of the output signal of the SA and, accordingly, an increased current of its consumption. At the same time, the settings of the device also begin to affect - with a greater gain, the current consumption is also greater. Typically, ambient noise is concentrated in the low-frequency range, therefore, with greater suppression of the low-frequency range by the tone control, the current consumption also decreases.
The current consumption of medium-power devices does not depend too much on the level of the incoming signal, but for high-power and super-power SA the difference is quite large. For example, with an incoming signal with an intensity of 60 dB (at which the current consumption of the SA is normalized), the current strength is 2-3 mA. With an input signal of 90 dB (and the same SA settings), the current increases to 15-20 mA.
Battery Life Estimation Method
Typically, the battery life is estimated taking into account its nominal capacity and the estimated current consumption of the device, specified in the technical data (passport) for the device. Let's take a typical case: a 675 zinc-air battery with a typical capacity of 460 mAh.
When used in a medium power device with a current consumption of 1.4mA, the theoretical service life will be 460/1.4=328 hours. When wearing the device for 10 hours a day, this means more than a month of device operation (328/10=32.8).
When powering a powerful device in a quiet environment (current consumption 2 mA), the service life will be 230 hours, that is, about three weeks with a 10-hour wear. But, if the environment is noisy, then the current consumption can reach 15-20 mA (depending on the type of device). In this mode, the service life will be 460/20=23 hours, i.e. less than 3 days. Of course, no one walks in such an environment for 10 hours, and the real mode will be mixed in terms of current consumption. So this example is just illustrating the calculation methodology by giving extreme life values. Usually the battery life in a powerful device is in the range of two to three weeks.
Use hearing aid batteries (labeled or labeled) from well-known power supply manufacturers (GP, Renata, Energizer, Varta, Panasonic, Duracell Activair, Rayovac).
Do not break the protective film of the battery (do not open) until it is installed in the hearing aid.
Store batteries in blisters at room temperature and normal humidity. A wish<сберечь>a longer battery in the refrigerator can lead to the exact opposite result - the CA with a new battery will not work at all.
Before installing the battery in the device, keep it without film for 3-5 minutes.
Turn off the SA when not in use. Remove the power sources from the device at night and leave the battery compartment open.
The novelty promises to surpass lithium-ion batteries in terms of energy consumption by three times and at the same time cost half as much.
Note that now zinc-air batteries are produced only in the form of disposable cells or "rechargeable" manually, that is, by changing the cartridge. By the way, this type of battery is safer than lithium-ion, as it does not contain volatile substances and, accordingly, cannot ignite.
The main obstacle to creating rechargeable options from the network - that is, batteries - is the rapid degradation of the device: the electrolyte is deactivated, the oxidation-reduction reactions slow down and stop altogether after just a few recharge cycles.
To understand why this happens, we must first describe the principle of operation of air-zinc elements. The battery consists of air and zinc electrodes and electrolyte. During discharge, the air coming from outside, not without the help of catalysts, forms hydroxyl ions (OH -) in an aqueous electrolyte solution.
They oxidize the zinc electrode. During this reaction, electrons are released, forming a current. During battery charging, the process goes in the opposite direction: oxygen is produced at the air electrode.
Previously, during the operation of a rechargeable battery, the aqueous electrolyte solution often simply dried out or penetrated too deeply into the pores of the air electrode. In addition, the deposited zinc was unevenly distributed, forming a branched structure, due to which short circuits began to occur between the electrodes.
The novelty is devoid of these shortcomings. Special gelling and astringent additives control the moisture and shape of the zinc electrode. In addition, scientists have proposed new catalysts, which also significantly improved the performance of the elements.
So far, the best performance of prototypes does not exceed hundreds of recharge cycles (photo by ReVolt).
ReVolt CEO James McDougall believes that the first products, unlike current prototypes, will be recharged up to 200 times, and will soon be able to reach the mark of 300-500 cycles. This indicator will allow the element to be used, for example, in cell phones or laptops.
The prototype of the new battery was developed at the Norwegian research foundation SINTEF, while ReVolt is commercializing the product (ReVolt illustration).
ReVolt is also developing zinc air batteries for electric vehicles. Such products resemble fuel cells. The zinc suspension in them plays the role of a liquid electrode, while the air electrode consists of a system of tubes.
Electricity is generated by pumping the suspension through the tubes. The resulting zinc oxide is then stored in another compartment. When recharged, it goes through the same path, and the oxide turns back into zinc.
Such batteries can produce more electricity, since the volume of the liquid electrode can be much larger than the volume of the air electrode. McDougall believes this type of cell could be recharged between two and ten thousand times.
