Battery of galvanic cells. Galvanic cells

A galvanic cell is a chemical source of electric current in which direct conversion occurs chemical energy to electric. Therefore he is. Appearance The most common batteries are shown in Figure 1.

Figure 1. Appearance of finger-type galvanic cells

There are salt (dry), alkaline and lithium cells. Galvanic cells are often called batteries, but this name is incorrect because... A battery is a connection of several identical devices. For example, connecting three galvanic cells in series produces the widely used 4.5 volt battery.

The principle of operation of a galvanic cell is based on the interaction of two metals through an electrolyte, leading to the generation of electric current in a closed circuit. The voltage depends on the metals used. Some of these chemical current sources are listed in Table 1.

Type of current sources	Cathode	Electrolyte	Anode	Voltage, IN
Manganese-zinc	MnO2	KOH	Zn	1,56
Manganese-tin	MnO2	KOH	Sn	1,65
Manganese-magnesium	MnO2	MgBr 2	Mg	2,00
Lead-zinc	PbO2	H2SO4	Zn	2,55
Lead-cadmium	PbO2	H2SO4	Cd	2,42
Lead-chlorine	PbO2	HClO4	Pb	1,92
Mercury-zinc	HgO	KOH	Zn	1,36
Mercury-cadmium	HgO2	KOH	Cd	1,92
Mercury-tin oxide	HgO2	KOH	Sn	1,30
Chrome-zinc	K2Cr2O7	H2SO4	Zn	1,8-1,9

The main products on sale are manganese-zinc elements, which are called salt elements. Battery manufacturers usually do not indicate their chemical composition. These are the cheapest galvanic cells that can only be used in devices with low consumption such as watches, electronic thermometers or remote controls remote control. Figure 2 shows the appearance and internal structure of a salt battery.

Figure 2. Appearance and structure of a “dry” galvanic cell

Alkaline manganese batteries are an equally common battery. On sale they are called alkaline, without bothering to translate the name into Russian. Internal organization alkaline galvanic cell is shown in Figure 2.

Figure 3. Internals and structure of an alkaline voltaic cell

These chemical sources current have larger capacity(2...3 A/h) and they can provide higher current for a long time. Higher current became possible because... zinc is used not in the form of a glass, but in the form of a powder, which has a larger area of ​​​​contact with the electrolyte. Potassium hydroxide is used as an electrolyte. It is precisely due to the ability of this type of galvanic cells to deliver significant current (up to 1 A) for a long time that it is most common today.

Another fairly common type of galvanic cells are lithium batteries. Thanks to the use of alkali metal, they have a high potential difference. The voltage of lithium cells is 3 V. However, 1.5 V are also available on the market lithium batteries. These batteries have the highest capacity per unit weight and a long shelf life. Mainly used to power clocks motherboards computers and photographic equipment. As a disadvantage we can name high cost. The appearance of lithium batteries is shown in Figure 4.

Figure 4. Appearance of lithium batteries

It should be noted that almost all galvanic cells can be recharged from network sources nutrition. The exception is lithium batteries, which may explode if you try to recharge them.

For use in various devices batteries were standardized. The most common types of galvanic cell housings are shown in Table 2.

Ready-made battery compartments are currently available for mounting batteries inside the housing of radio-electronic devices. Their use can significantly simplify the development of the case radio-electronic device and reduce the cost of its production. The appearance of some of them is shown in Figure 5.

Figure 5. Appearance of compartments for fastening galvanic batteries

The first question that worries battery buyers is their operating time. It depends on the production technology of the galvanic cell. A graph of the typical dependence of output voltage on battery production technology is shown in Figure 5.

Figure 6. Graph of battery operating time depending on production technology at a discharge current of 1 A

The results of tests of batteries from various companies conducted on the website http://www.batteryshowdown.com/ are shown in Figure 7.

Figure 7. Chart of operating time of batteries from various companies at a discharge current of 1 A

And finally, let's draw conclusions where it makes sense to use which type of batteries, since when purchasing batteries we always try to get the maximum useful effect at the minimum cost.

1. You should not buy batteries at kiosks or in the market. Usually they lie there for a long time and therefore, due to self-discharge, practically lose their capacity. This can even be dangerous for the equipment, because... When using cheap galvanic cells (batteries), electrolyte may leak from them. This will lead to equipment failure! It is better to buy in stores with a good turnover of goods.
2. Alkaline (alkaline) batteries should be used in devices that consume fairly high current, such as flashlights, players or cameras. In low-power devices, their operating life is no different from salt batteries.
3. Salt (“ordinary”, carbon-zinc galvanic cells) will work perfectly in watches, IR remote controls and other devices designed to operate on one set of batteries for a year or more. However, they cannot work in the cold.
4. The most cost-effective batteries today are AA batteries. Both the little ones (AAA) and the big ones (R20), with the same capacity, are more expensive. The capacity of modern R20 batteries is almost the same as AA batteries AA, and this is at three times the size!
5. Don't pay attention to popular brands. Galvanic cells from Duracell and Energizer cost one and a half to two times more expensive than batteries from other companies and at the same time work about the same

Galvanic elements. Galvanic cells are primary chemical current sources (CHS), which use irreversible processes converting chemical energy into electrical energy. They are widely used as DC power supplies for small-sized and portable radio equipment.

In parallel connection elements, the battery capacity is equal to the sum of the capacities of the elements included in it, and with serial connection– the smallest capacity of the element included in it.

Capacity element a is the amount of electricity given off by the element during discharge and determined in ampere-hours.

Manganese-zinc elements and mercury-zinc elements are widely used.

Batteries. Batteries, like galvanic cells, are devices for directly converting chemical energy into electrical energy. Unlike galvanic cells, batteries are capable of restoring their performance based on efficiency electrical energy receivers by charging them from an external source of electrical energy. Therefore, a battery is a reusable device that can accumulate and store electrical energy for some time. It is a secondary chemical source of current. A reserve of chemical energy is created in it during charging from an external source. When charging a battery, the materials included in its composition are transformed into a state in which they can enter into a chemical reaction with each other, releasing electrical energy. Thus, batteries accumulate electrical energy when they are charged and consume it when discharged.

Batteries are characterized by the following main parameters.

EMF of the battery E, which depends on the composition of the active mass of the plates, on the temperature and concentration (density) of the electrolyte. The battery EMF is measured with a voltmeter with a high input resistance (more than 1000 Ohm/V). Since the EMF of a charged and partially discharged battery can be the same, it is impossible to judge the degree of discharge of the battery based on the EMF value.

Battery voltage– potential difference between the positive and negative plates when the load is on. Voltage when charging U Z = E + I Z r 0, and when discharging U P = E - I P r 0,

where I З, I Р – charge and discharge currents in A; r 0 – internal resistance of the battery, Ohm (it is determined by the design of the electrodes, the density of the electrolyte, the degree of discharge of the battery, and the ambient temperature).

The nominal capacity of a battery is the amount of electricity in Ah that it can supply with a ten-hour discharge mode, constant current and electrolyte temperature of +25 o C. The current value of the 10-hour discharge mode is equal to the quotient of the nominal capacity (C 10) divided by 10 .

Batteries are capable self-discharge, i.e. reduce its capacity when the load circuit is open. The intensity of self-discharge depends on the ambient temperature, electrolyte composition and electrode material.

Depending on the composition of the electrolyte, batteries are either acidic or alkaline.

Acid batteries. The housing (made of hard rubber or plastic) houses positive and negative electrodes mounted in blocks. The active mass of the positive plate is lead dioxide (PbO 2), and the negative one is lead (Pb). The electrolyte is an aqueous solution of sulfuric acid. The nominal voltage of an acid battery is 2.0 V. When charging, the voltage is increased to 2.6 - 2.8 V. At the beginning of the discharge, the voltage quickly decreases to 2.2 V. It should be remembered that discharging acid battery lower than 1.8 V is not possible, since in this case a difficultly soluble substance is formed on the negative plates white coating(battery sulfation occurs). To protect the battery from sulfation, it is recommended to charge it every 30 days, regardless of the remaining capacity.

Disadvantages of acid batteries: they are difficult to maintain and have low strength, increased sensitivity to short circuits and overloads, they cannot be placed inside the electronic control unit (evaporations spoil the parts).

The industry produces acid batteries of the SK type with a nominal capacity of 36 to 5328 Ah, for example SK-148 (if this number 148 is multiplied by 36, you get a nominal capacity of 5328 Ah).

Alkaline batteries. They are easy to maintain, can be charged faster (4–7 hours instead of 10–12 hours for acid ones), and can be placed inside the REU without harm to them. The most commonly used alkaline batteries are nickel-cadmium (NC), nickel-iron (NI) and silver-zinc (SC). An aqueous solution of caustic potassium is used as an electrolyte.

For alkaline batteries, the emf is 1.5 V (in a discharged battery E = 1.3 V). The average density of the electrolyte in alkaline batteries is approximately constant during charging and discharging. Therefore, their condition is characterized mainly by the EMF value.

Alkaline batteries are produced by the factory without electrolyte. When preparing the electrolyte, special care must be taken, since mixing potassium hydroxide with water releases a large amount of heat. Solid alkali is broken into small pieces, while covering it with material so that the fragments do not get into the eyes or skin. The alkali is dipped into the water in pieces, continuously stirring the solution with a glass or steel rod.

GALVANIC BATTERIES - groups of galvanic cells electrically connected to each other that generate electricity due to chemicals. reactions occurring between the active materials of the electrodes. Galvanic batteries most often use galvanic cells, in which the positive electrode is made of a mixture of manganese dioxide and graphite, and the negative electrode is made of zinc. A solution of ammonium chloride (ammonia) and other chloride salts is usually used as an electrolyte. Such elements are called manganese-zinc.

Rice. 1. Cup-type dry cell: 1 - negative electrode (zinc), 2 - cardboard case, 3 - current leads, 4 - cap, 5 - positive electrode, 6 - electrolyte layer (paste), 7 - resin, 8 - cardboard washer, 9 - insulating gasket, 10 - glass tube(gas outlet)

Sometimes, in addition to manganese dioxide and graphite, the positive electrode contains Activated carbon, which absorbs oxygen from the surrounding atmosphere, which allows it to be used in chemicals. reactions. Such elements are called manganese-air-zinc. They have higher capacity and lower cost. For special purposes, coal-zinc and iron-carbon bulk elements are used, which have a high voltage constant. Due to the inconvenience of using bulk cells with liquid electrolyte, the latter is converted into a viscous state with the help of flour, starch, cardboard or other fillers, due to which it loses its fluidity and does not pour out of the cell in any position. Such elements are called dry.

There are two main types of dry elements: cup and biscuit. The cup element (Fig. 1) has a negative electrode (zinc pole) in the form of a cylindrical, seamless or having a longitudinal seam (brazed, welded, rolled) rectangular cup. The positive electrode is a cylinder or prism pressed onto a carbon rod that serves as a current conductor. The positive electrode is placed inside the negative one, and the space between them is filled with condensed electrolyte. In a biscuits element (Fig. 2), the electrodes have the form of plates, which are separated by a cardboard diaphragm impregnated with electrolyte. All parts are tightened with an elastic vinyl chloride rim (ring). The current conductor is a layer of electrically conductive mass, impenetrable to the electrolyte, applied to outside zinc electrode. Manganese-air-zinc elements are produced only in cup type.

Rice. 2. Dry cell of the biscuits type: 1 - negative electrode (zinc) with an electrically conductive layer, 2 - positive electrode, 3 - cardboard diaphragms impregnated with electrolyte, 4 - positive electrode wrapping paper, 5 - vinyl chloride ring

The main indicators of the element are its electromotive force (emf) and voltage, the value of which is measured by a voltmeter (see), in the first case - in the absence of load resistance, in the second - when connecting a load resistance specified by the standard. E.m.f. manganese - zinc elements range from 1.5 to 1.8 V, e. d.s. manganese-air-zinc elements is 1.4 V. The voltage value of the element is always less than e. d.s., the difference between them increases with decreasing load resistance. The most important parameters Galvanic batteries are also the amount of electricity they supply and the ability to store it for a long time (safety). The amount of energy released is measured either by the duration of operation of the element in hours, or by its electrical capacity in a - hour. Since the element voltage drops during discharge, then in tech. documentation is always specified lower limit voltage (final voltage), which determines the lower limit of its performance. At a given final voltage, the electrical capacitance of the element, and therefore the duration of its operation, also depends on the temperature and value of the load resistance (see Table 1), as well as the frequency of the discharge.

The capacity of galvanic batteries increases with increasing load resistance and increasing temperature. The lowest temperature at which the elements can operate: for manganese-zinc -20°, for manganese-air-zinc -5°. The frequency of discharge is characterized by the alternation and duration of periods of discharge and rest of the element. As a rule, manganese-zinc cells with an intermittent discharge give off a greater capacity than with a continuous discharge, and manganese-air-zinc cells, on the contrary, give less.

The safety of galvanic batteries (cells) is the period from the moment of manufacture to the start of operation, during which the product retains its functionality. The amount of remaining capacity (or operating time) is specified by the standard and is usually 60-75% of the original.

The shelf life indicated on the label is minimal and almost always the batteries are galvanic and the cells can be used for some time. Their suitability in this case is determined by voltage.

The connection of elements in galvanic batteries can be serial, parallel and mixed. In a series connection, the positive pole of one element is connected to the negative pole of the next element, etc. (Fig. 3).

Rice. 3. Diagram of serial connection of elements

Rice. 4. Diagram of parallel connection of battery elements

Rice. 5. Mixed connection of battery cells

This combination of elements is used to create more high voltage galvanic battery, which in this case is directly proportional to the number of elements connected in series. The capacity of the galvanic battery does not change and is equal to the capacity individual element. A parallel connection is carried out by connecting together, on the one hand, all the positive poles of the elements, and on the other, the negative ones (Fig. 4). At the same time, the capacity of the galvanic battery increases, and its voltage remains equal to the voltage of the individual element. For a mixed connection, both of the above methods are used: several identical groups are assembled with a series connection of elements that are connected to each other in parallel (Fig. 5). At the same time, both voltage and capacitance increase accordingly.

Depending on their purpose, galvanic batteries are divided into anode, grid, incandescent and lantern.

Galvanic anode batteries (Fig. 6) are intended to power the anode circuits of radio receivers.

Rice. 6. Battery BS-G-70

Their voltage is relatively high - from 60 to 120 V. They are used for low current - from 3 to 12 mA. Typically, these galvanic batteries have additional current leads in the form of a socket in the panel or soft wires, which allow you to use part of the galvanic battery first and connect the rest as the voltage drops. This mode is called sectional discharge and allows, within certain limits, to increase the service life of a galvanic battery.

Grid batteries galvanic are intended to create a bias voltage on the grids of radio tubes.

Rice. 7. Battery BSG-60-S-8

They use a serial connection. Voltage from 4.5 to 12.0 V. Current consumption does not exceed 3 mA. They are mounted in the same case with galvanic anode batteries (Fig. 7) and are composed of elements identical to them.

Galvanic filament batteries (Fig. 8) are designed to power the filaments of radio tubes.

Rice. 8. Battery BNS-MVD-500

For stationary battery radios (Rodina, Iskra, etc.), galvanic filament batteries, in order to create a larger capacity, are made up of four parallel-connected manganese-zinc-air elements big size. Their voltage is equal to the voltage of one element, and the current consumption is from 0.3 to 0.5 A. In filament batteries of galvanic portable battery radios, parallel and mixed connections of small elements are used. For the Tula battery radio, the industry produces a power supply kit in a special case, consisting of an anode and an incandescent galvanic battery (Fig. 9).

Rice. 9. Kit - power supply for the radio "Tula"

Galvanic lantern batteries Designed to power flashlight bulbs. They are characterized by high current consumption (from 150 to 280 A) at low voltage (3.0-4.5 V) and small dimensions. Most widespread received galvanic batteries of the KBS-L-0.50 type (Fig. 10), consisting of three series-connected elements. For lanterns round section And measuring instruments(ohmmeters, avometers, etc.) the industry produces elements cylindrical FBS type, a serial connection between which, if necessary, is carried out directly when they are inserted into the body of the flashlight (device).

Rice. 10. Battery for flashlight KBS-L-0.50

Element legends typically have four parts. The initial number indicates the dimensions (in mm): No. 2 - 40x40x100, No. 3-55x55x130, No. 6 - 80x80x175; letters - C - dry, L - summer, X - cold-resistant; the following numbers indicate the capacity of the element. So, 3S-L-30 means: element No. 3, dry, summer, with a capacity of 30 a-hour. Name of galvanic batteries starting with letter designations, consists of 4-5 parts, having the following meanings: B - battery, A - anode, N - incandescent, C - dry, G - biscuits, F - lantern, K - pocket. The number after the letters for galvanic anode batteries shows the voltage, for incandescent batteries - the capacity. However, sometimes in the designation of galvanic anode batteries the letter A is omitted, and at the end of the designation a second numerical indicator is added - the capacity of the galvanic battery. The names of galvanic batteries starting with numbers have the following meanings: the initial number indicates the voltage, the final number indicates the capacity, the letters: MC - zinc-manganese system, B - indicates the use of atmospheric oxygen, H - incandescent, A - anode, T - telephone, C - for hearing aids, P - panel. Galvanic batteries intended for powering radios are also given trade names. Galvanic batteries are marked by affixing a label indicating: the name or trademark of the manufacturer, symbol galvanic batteries, rated voltage, initial capacity, warranty period of storage and capacity at the end of the storage period.

The suitability of galvanic batteries and cells is determined external inspection and measuring voltage on down conductors. During inspection, you should make sure that the down conductors are intact and that there are no external defects: breakages, destruction of the casting resin (mastic), damage and wetness of the case. The voltage is checked with a voltmeter; it should not be lower than the values ​​indicated in the table. 2. Galvanic batteries are packaged in wooden boxes with a gross weight of 65-80 kg, lined inside with moisture-proof paper, and separated from their walls by a layer of dry shavings or other packaging material. Galvanic batteries must be stored in a dry and cool place. High humidity in the storage room, as well as increased temperature, sharply reduce their shelf life. Low temperatures are not dangerous for galvanic batteries: after warming up, they completely restore their properties. Galvanic batteries are manufactured by the enterprises of Glavakkumulyatorproma of the Ministry of Electrical Engineering of the USSR.

Lit.: Sochevanov V.G., Galvanic elements, M., 1951; Morozov GG. and Gantmav S.A., Chemical current sources for powering communications equipment, M., 1949; Consolidated catalog of chemical current sources, M., 1950.

Low-power sources of electrical energy

Galvanic cells and batteries are used to power portable electrical and radio equipment.

Galvanic cells- these are single action sources, batteries- reusable sources.

The simplest galvanic element

The simplest element can be made from two strips: copper and zinc, immersed in water slightly acidified with sulfuric acid. If the zinc is pure enough to be free from local reactions, no noticeable change will occur until the copper and zinc are connected by wire.

However, the strips have different potentials relative to each other, and when they are connected by a wire, a will appear in it. As this action proceeds, the zinc strip will gradually dissolve, and gas bubbles will form near the copper electrode and collect on its surface. This gas is hydrogen, formed from the electrolyte. Electric current flows from the copper strip through the wire to the zinc strip, and from it through the electrolyte back to the copper.

Gradually, the sulfuric acid of the electrolyte is replaced by zinc sulfate, formed from the dissolved part of the zinc electrode. Due to this, the voltage of the element is reduced. However, an even greater voltage drop is caused by the formation of gas bubbles on the copper. Both of these actions produce "polarization." Such elements have almost no practical significance.

Important parameters of galvanic cells

The magnitude of the voltage provided by galvanic cells depends only on their type and design, i.e., on the material of the electrodes and chemical composition electrolyte, but does not depend on the shape and size of the elements.

The current strength that can be given galvanic cell, is limited by its internal resistance.

Very important characteristic galvanic cell is . Electrical capacity means the amount of electricity that a galvanic or battery cell is capable of delivering during the entire time of its operation, i.e., until the final discharge occurs.

The capacity given by the element is determined by multiplying the strength of the discharge current, expressed in amperes, by the time in hours during which the element was discharged until the onset of complete discharge. Therefore, electrical capacity is always expressed in ampere-hours (A x h).

Based on the capacity of the element, you can also determine in advance how many hours it will work before it is completely discharged. To do this, you need to divide the capacity by the discharge current permissible for this element.

However, electrical capacitance is not a strictly constant value. It varies within fairly wide limits depending on the operating conditions (mode) of the element and the final discharge voltage.

If the element is discharged with maximum current and without interruption, then it will give off significantly less capacity. On the contrary, when the same element is discharged with a lower current and with frequent and relatively long breaks, the element will give up its full capacity.

As for the influence of the final discharge voltage on the capacitance of the element, it must be borne in mind that during the discharge of the galvanic element its operating voltage does not remain at the same level, but gradually decreases.

Common types of galvanic cells

The most common galvanic cells are manganese-zinc, manganese-air, air-zinc and mercury-zinc systems with salt and alkaline electrolytes. Dry manganese-zinc cells with a salt electrolyte have an initial voltage of 1.4 to 1.55 V, operating time at temperature environment from -20 to -60 o C from 7 hours to 340 hours.

Dry manganese-zinc and zinc-air cells with an alkaline electrolyte have a voltage from 0.75 to 0.9 V and an operating time from 6 hours to 45 hours.

Dry mercury-zinc cells have an initial voltage of 1.22 to 1.25 V and a run time of 24 hours to 55 hours.

Largest guarantee period dry mercury-zinc elements have a storage life of up to 30 months.

These are secondary galvanic cells.Unlike galvanic cells, no chemical processes occur in the battery immediately after assembly.

So that chemical reactions associated with movement begin in the battery electric charges, you need to change the chemical composition of its electrodes (and partly the electrolyte) accordingly. This change in the chemical composition of the electrodes occurs under the influence of electric current passed through the battery.

Therefore, in order for the battery to produce electric current, it must first be “charged” with a constant electric shock from some external current source.

Batteries also differ favorably from conventional galvanic cells in that after discharge they can be charged again. At good care behind them and under normal operating conditions, batteries can withstand up to several thousand charges and discharges.
Battery device

Currently, lead and cadmium-nickel batteries are most often used in practice. For the former, the electrolyte is a solution of sulfuric acid, and for the latter, a solution of alkalis in water. Lead batteries are also called acid batteries, and nickel-cadmium batteries are called alkaline batteries.

The principle of operation of batteries is based on the polarization of electrodes. The simplest acid battery is designed as follows: these are two lead plates dipped into an electrolyte. As a result of the chemical substitution reaction, the plates are covered with a slight coating of lead sulfate PbSO4, as follows from the formula Pb + H 2 SO 4 = PbSO 4 + H 2.

Acid battery device

This state of the plates corresponds to a discharged battery. If you now turn on the battery for charging, i.e. connect it to the generator direct current, then polarization of the plates will begin in it due to electrolysis. As a result of charging the battery, its plates are polarized, that is, they change the substance of their surface, and from homogeneous (PbSO 4) turn into dissimilar (Pb and Pb O 2).

The battery becomes a source of current, and its positive electrode is a plate coated with lead dioxide, and the negative electrode is a clean lead plate.

Towards the end of the charge, the electrolyte concentration increases due to the appearance of additional sulfuric acid molecules in it.

This is one of the features lead battery: its electrolyte does not remain neutral and itself participates in chemical reactions when the battery is running.

Towards the end of the discharge, both battery plates are again covered with lead sulfate, as a result of which the battery ceases to be a source of current. The battery is never brought to this state. Due to the formation of lead sulfate on the plates, the electrolyte concentration at the end of the discharge decreases. If you put the battery on charge, you can again cause polarization in order to put it on discharge again, etc.

How to charge the battery

There are several ways to charge batteries. The simplest is normal battery charging, which occurs as follows. Initially, for 5 - 6 hours, the charge is carried out with double normal current until the voltage on each battery bank reaches 2.4 V.

Normal charging current is determined by the formula I charge = Q/16

Where Q - nominal battery capacity, Ah.

After this, the charging current is reduced to a normal value and the charge and flow continue for 15 - 18 hours, until signs of the end of the charge appear.

Modern batteries

Cadmium-nickel, or alkaline batteries, appeared much later than lead batteries and, in comparison with them, are more advanced chemical current sources. The main advantage of alkaline batteries over lead batteries is the chemical neutrality of their electrolyte with respect to the active masses of the plates. Due to this, the self-discharge of alkaline batteries is much less than that of lead batteries. The operating principle of alkaline batteries is also based on the polarization of the electrodes during electrolysis.

To power radio equipment, sealed cadmium-nickel batteries are produced, which are operational at temperatures from -30 to +50 o C and can withstand 400 - 600 charge-discharge cycles. These batteries are made in the form of compact parallelepipeds and disks with a mass of several grams to kilograms.

They produce nickel-hydrogen batteries for power supply to autonomous facilities. Specific energy nickel-hydrogen battery is 50 - 60 Wh kg -1.