Sources of current are chemical. Kinds of chemical sources of a current and their device

Sources of current chemical (short for HIT) - devices in which the energy of the oxidation-reduction reaction is converted into electrical. Other names are an electrochemical cell, a galvanic cell , an electrochemical cell. The principle of their action is as follows: as a result of the interaction of the two reagents, a chemical reaction takes place with the release of the energy of a constant electric current. In other sources of current, the process of electricity generation takes place according to a multistage scheme. First, heat energy is released, then it turns into a mechanical one and only then into an electrical one. The advantage of HIT is a one-step process, that is, electricity is obtained immediately, bypassing the stages of obtaining thermal and mechanical energies.

History

How did the first sources of current appear? Chemical Sources Have received the name of galvanic elements in honor of the Italian scientist of the eighteenth century - Luigi Galvani. He was a doctor, anatomist, physiologist and physicist. One of the directions of his research was the study of animal reactions to various external influences. The chemical method of obtaining electricity was discovered by Galvani accidentally, during one of the experiments on frogs. He connected two metal plates to the bare nerve on the frog's foot. At the same time, a muscular contraction occurred. His own explanation of this phenomenon Galvani was incorrect. But the results of his experiments and observations helped his compatriot Alessandro Volta in subsequent studies.

Volta presented in his works the theory of the emergence of an electric current as a result of a chemical reaction between two metals upon contact with the muscle tissue of a frog. The first chemical source of current looked like a container with brine, with zinc and copper plated in it.

On an industrial scale, HIT began to be produced in the second half of the nineteenth century, thanks to the Frenchman Leclanche, who invented the primary manganese-zinc element with salt electrolyte, named after him. A few years later this electrochemical cell was improved by another scientist and was the only primary chemical source of current until 1940.

The device and principle of operation of HIT

The device of chemical sources of current includes two electrodes (conductors of the first kind) and the electrolyte located between them (a conductor of the second kind, or ionic conductor). At the boundary between them there is an electronic potential. The electrode on which the reducing agent is oxidized is called the anode, and the one on which the oxidant is reduced is cathode. Together with the electrolyte they form an electrochemical system.

A side effect of the oxidation-reduction reaction between the electrodes is the occurrence of an electric current. During this reaction, the reducing agent oxidizes and gives off the electrons to the oxidant, which takes them and thereby recovers. The presence between the cathode and the anode of the electrolyte is a necessary condition for the reaction. If you simply mix together powders from two different metals, no electricity will be released, all energy will be released as heat. Electrolyte is needed to order the process of electron transfer. Most often in its quality is a saline solution or a melt.

The electrodes look like metal plates or lattices. When they are immersed in the electrolyte, there is a difference in electrical potentials between them - the voltage of the open circuit. The anode has a tendency to recoil electrons, and the cathode - to their acceptance. On their surface, chemical reactions begin. They stop when the circuit is opened, and when one of the reagents is consumed. The circuit is opened when one of the electrodes or electrolyte is removed.

Composition of electrochemical systems

Sources of chemical current as oxidizers use oxygen-containing acids and salts, oxygen, halides, higher metal oxides, nitroorganic compounds, etc. The restorers are metals and their lower oxides, hydrogen and hydrocarbon compounds. How electrolytes are used:

1. Aqueous solutions of acids, alkalis, salt, etc.
2. Non-aqueous solutions with ionic conductivity, obtained by dissolving salts in organic or inorganic solvents.
3. Melts of salts.
4. Solid compounds with an ionic lattice in which one of the ions is mobile.
5. Matrix electrolytes. These are liquid solutions or melts that are in the pores of a solid non-conducting body, an electrical carrier.
6. Ion exchange electrolytes. These are solid compounds with fixed ionogenic groups of the same sign. The ions of another sign are mobile at the same time. This property makes the conductivity of such an electrolyte unipolar.

Galvanic batteries

Sources of chemical current consist of galvanic cells - cells. The voltage in one of these cells is small - from 0.5 to 4V. Depending on the need, the HIT uses a galvanic battery consisting of several series-connected elements. Sometimes a parallel or serial-parallel connection of several elements is used. In a sequential circuit, only the same primary cells or accumulators are always included. They should have the same parameters: electrochemical system, design, technological variant and size. For parallel connection, the use of elements of different size is acceptable.

HIT classification

Chemical sources of current differ in:

• Size;
• Construction;
• Reagents;
• Nature of the energy-forming reaction.

These parameters determine the operational properties of the HIT, suitable for a particular application.

The classification of electrochemical cells is based on the difference in the principle of operation of the device. Depending on these characteristics, distinguish:

1. Primary chemical sources of current are elements of a single action. In them there is a definite stock of reagents, which is consumed during the reaction. After a full discharge, this cell loses its operability. In another way, primary HITs are called galvanic cells. It will be right to call them simply - an element. The simplest examples of a primary power source are a "battery" AA.
2. Rechargeable chemical sources of current - accumulators (also called secondary, reversible HITs) are reusable elements. By passing current from the external circuit in the reverse direction through the battery after a full discharge, the consumed reagents are regenerated, re-accumulating chemical energy (charging). Due to the possibility of recharging from an external constant current source, this device is used for a long time, with interruptions to recharging. The process of generating electricity is called a battery discharge. To such HIT it is possible to carry power elements of many electronic devices (laptops, mobile phones, etc.).
3. Thermal chemical sources of current are devices of continuous action. In the course of their work, new portions of reagents are continuously supplied and the products of the reaction are removed.
4. In the combined (semi-fuel) galvanic cells there is a reserve of one of the reagents. The second is fed into the device from the outside. The life of the device depends on the reserve of the first reagent. Combined chemical sources of electric current are used as accumulators if it is possible to restore their charge by passing current from an external source.
5. HIT renewables are recharged mechanically or chemically. For them, it is possible to replace the consumed reagents with new portions after a full discharge. That is, they are not continuous devices, but, like accumulators, periodically recharge.

Characteristics of HIT

The main characteristics of chemical sources of current are:

1. Open circuit voltage (NDC or discharge voltage). This indicator, first of all, depends on the chosen electrochemical system (a combination of a reducing agent, an oxidizer and an electrolyte). Also, the concentration of electrolyte, the degree of discharge, temperature and other influence the NRC. The NDC depends on the value of the current flowing through the HIT.
2. Power.
3. The discharge current depends on the resistance of the external circuit.
4. Capacity - the maximum amount of electricity that HIT gives when it is completely discharged.
5. Energy storage is the maximum energy received when the device is completely discharged.
6. Energy characteristics. For batteries, this is, first of all, a guaranteed number of charge-discharge cycles without decreasing the capacitance or charge voltage (resource).
7. Temperature range of efficiency.
8. The shelf life is the maximum allowable time between manufacture and the first digit of the device.
9. Service life is the maximum permissible total shelf life and work. For fuel cells, the service life is important with continuous and intermittent operation.
10. Total energy given for the whole lifetime.
11. Mechanical strength in relation to vibration, shock, etc.
12. Ability to work in any position.
13. Reliability.
14. Easy to maintain.

Requirements for HIT

The design of electrochemical cells must provide the conditions that contribute to the most effective course of the reaction. These conditions include:

• Prevention of leakage current;
• Uniform work;
• Mechanical strength (including tightness);
• Separation of reagents;
• Good contact between electrodes and electrolyte;
• The current is removed from the reaction zone to the external terminal with minimal losses.

Sources of current chemical should meet the following general requirements:

• The highest values of specific parameters;
• Maximum temperature range of operability;
• The greatest stress;
• The minimum cost of a unit of energy;
• Stability of voltage;
• Safety of charge;
• security;
• Simplicity of service, and, ideally, no need for it;
• Long service life.

Operation of HIT

The main advantage of primary galvanic cells is that there is no need for any maintenance. Before you start using them, you just need to check the appearance, expiration date. When connecting, it is important to observe the polarity and check the integrity of the contacts of the device. More complex chemical sources of current - batteries, require more serious care. The purpose of their service is to maximize the service life. Care of the battery is:

• Maintaining cleanliness;
• Monitoring of open circuit voltage;
• Maintenance of the electrolyte level (only distilled water can be used for refilling);
• Control of the electrolyte concentration (using a hydrometer - a simple device for measuring the density of liquids).

When operating galvanic cells, it is necessary to comply with all requirements relating to the safe use of electrical appliances.

HIT classification by electrochemical systems

Types of chemical sources of current, depending on the system:

• Lead (acid);
• Nickel-cadmium, nickel-iron, nickel-zinc;
• Manganese-zinc, copper-zinc, mercury-zinc, chlorine-zinc;
• Silver-zinc, silver-cadmium;
• Air-metal;
• Nickel-hydrogen and silver-hydrogen;
• Manganese-magnesium;
• Lithium, etc.

Modern application of HIT

Sources of current, chemical Currently applied in:

• Vehicles;
• Portable devices;
• Military and space technology;
• Scientific equipment;
• Medicine (pacemakers).

Familiar examples of HIT in everyday life:

• Batteries (dry batteries);
• Batteries of portable household appliances and electronics;
• Uninterruptible power supplies;
• Car batteries.

Lithium chemical sources of current were especially widely used. This is due to the fact that lithium (Li) has the highest specific energy. The fact is that it has the most negative electrode potential among all other metals. Lithium-ion batteries (LIA) outperform all other HIT in terms of specific energy and operating voltage. Now they are gradually mastering a new field - automobile transport. In the future, the development of scientists associated with the improvement of lithium batteries will move in the direction of ultra-thin structures and large-capacity supercharged batteries.