Whether or not the ancestors who made this clay bottle knew about static electricity, what is certain is that the ancient Greeks definitely knew it. They knew that if they rubbed a piece of amber, it would attract light objects. Aristotle also knew of a magnet, an ore with a strong magnetic force that attracts iron and metals.
One day in 1780, when the Italian anatomist Galvani was dissecting a frog, he held different metal instruments in both hands and accidentally touched the frog's thigh at the same time. The muscles of the frog's leg immediately It twitched, as if it was stimulated by electric current, but only touching the frog with a metal instrument had no such reaction. Galvani believed that this phenomenon occurred because of a kind of electricity generated inside the animal's body, which he called "bioelectricity." Galvani wrote a paper on this experimental result in 1791 and published it in the academic world.
Gavani’s discovery aroused great interest among physicists. They rushed to repeat Galvani’s experiment in an attempt to find a way to generate electric current. After many experiments, Italian physicist Volta It is believed that Galvani's theory of "bioelectricity" is not correct. The reason why frog muscles can generate electric current is probably due to the action of some kind of liquid in the muscles. To prove his point, Volta tested two different metal pieces by immersing them in various solutions. It was found that as long as one of the two metal pieces reacts chemically with the solution, an electric current can be generated between the metal pieces.
In 1799, Volta immersed a zinc plate and a silver plate in salt water and found that there was an electric current flowing through the wires connecting the two metals. So he put flannel or paper soaked in salt water between many zinc and silver sheets and stacked them flat. When you touch both ends with your hands, you will feel strong current stimulation. Volta used this method to successfully create the world's first battery - the "Volt stack". This "volt stack" is actually a battery pack connected in series. It became the source of power for early electrical experiments and the telegraph machine.
The Italian physicist Volta repeated Galvani's experiment many times. As a physicist, his attention was mainly focused on the two metals, not on the frog's nerves. Regarding the twitching phenomenon of frog legs discovered by Galvani, he thought it might be related to electricity, but he believed that electricity did not exist in the muscles and nerves of frogs. He speculated that the flow of electricity might be caused by the contact of two different metals. occurs regardless of whether the metal comes into contact with live or dead animals. Experiments have shown that as long as the two metal pieces are separated by cardboard, linen, leather or other sponge-like things soaked in salt or alkaline water (even as long as they are wet) (he believes that this is necessary to make the experiment successful) ), and connect the two metal pieces with a metal wire. Regardless of whether there are frog muscles or not, current will flow through. This shows that electricity is not generated from the frog's tissues, and that the frog's legs function only as a very sensitive electroscope.
In 1836, Daniel of England improved the "voltaic pile". He used dilute sulfuric acid as the electrolyte to solve the battery polarization problem and created the first zinc-copper battery that was non-polarized and could maintain a balanced current, also known as the "Daniel battery." Since then, "Bunsen batteries" and "Grove batteries" with better depolarization effects have been introduced. However, these batteries have the problem that their voltage drops over time.
In 1860, Planté of France invented a battery using lead as the electrode. The unique feature of this kind of battery is that when the battery voltage drops after being used for a period of time, a reverse current can be passed through it to make the battery voltage rise again. Because this kind of battery can be recharged and can be used repeatedly, it is called a "storage battery".
However, no matter what kind of battery, a liquid needs to be filled between two metal plates, so it is very inconvenient to transport. Especially the liquid used in the battery is sulfuric acid, which is very dangerous when moving.
In 1887, Englishman Helleson invented the earliest dry battery. The electrolyte of dry batteries is in the form of paste, does not leak, and is easy to carry, so it is widely used.
A device that directly converts chemical energy, light energy, thermal energy, nuclear energy, etc. into electrical energy.
There are chemical batteries, solar cells, thermoelectric batteries, nuclear batteries, etc. The battery usually refers to a chemical battery.
The performance parameters of the battery mainly include electromotive force, capacity, specific energy and resistance. The electromotive force is equal to the work done by the non-electrostatic force (chemical force) of the battery when a unit positive charge moves from the negative electrode to the positive electrode through the interior of the battery. The electromotive force depends on the chemistry of the electrode material and has nothing to do with the size of the battery. The total amount of charge that a battery can output is the battery's capacity, usually measured in ampere hours. In a battery reaction, the electrical energy produced by 1 kilogram of reaction material is called the theoretical specific energy of the battery. The actual specific energy of the battery is smaller than the theoretical specific energy. Because the reactants in the battery do not all proceed according to the battery reaction, and the internal resistance of the battery also causes electromotive force drop, therefore batteries with high specific energy are often called high-energy batteries. The larger the battery area, the smaller its internal resistance.
There are many types of batteries. Commonly used batteries are mainly dry batteries, storage batteries, and small micro batteries. In addition, there are metal-air batteries, fuel cells and other energy conversion batteries such as solar cells, thermoelectric batteries, nuclear batteries, etc.
Dry cell battery is one of the most widely used chemical batteries. In 1865, the Frenchman Leclanché developed a wet battery of carbon/manganese dioxide/ammonium chloride solution/zinc system based on the voltaic battery. After development, there are more than 100 types of dry batteries. In addition to zinc-manganese dry batteries, there are also magnesium-manganese dry batteries, zinc-mercury oxide dry batteries, zinc-silver oxide dry batteries, etc. Since the reversibility of the oxidation and reduction reactions of dry batteries is very poor, charging methods generally cannot be used to restore the positive and negative active materials to their original states after use. Therefore, dry batteries are also called primary batteries. The most commonly used dry batteries are zinc-manganese dry batteries, which are available in paste type, cardboard type, alkaline type and laminated type.
Paste zinc-manganese dry battery consists of zinc cylinder, electric paste layer, manganese dioxide positive electrode, carbon rod, copper cap, etc. The outermost layer is a zinc cylinder, which is both the negative electrode of the battery and a container. It is gradually dissolved during the discharge process; in the center is a carbon rod that acts as a current collector; tightly surrounding this carbon rod is A mixture of dark brown or black manganese dioxide powder and a conductive material (graphite or acetylene black). Together with the carbon rod, it forms the positive electrode body of the battery, also called a carbon pack. To avoid evaporation of water, the upper part of the dry cell is sealed with paraffin or asphalt. The electrode reaction of the zinc-manganese dry battery when working is zinc electrode: Zn→Zn2 +2e
Carbon electrode:
The cardboard zinc-manganese dry battery is based on the paste zinc-manganese dry battery Improved. It is based on high-quality kraft paper with a thickness of 70 to 100 microns and does not contain metal impurities. The surface is coated with a prepared paste, and then dried to make cardboard to replace the paste in paste zinc-manganese dry batteries. electrolyte layer. The actual discharge capacity of cardboard zinc-manganese dry batteries is 2 to 3 times higher than that of ordinary paste zinc-manganese dry batteries. Most dry batteries labeled "high performance" are cardboard type.
The electrolyte of alkaline zinc-manganese dry battery is gelatinized from amalgamated zinc powder, 35% potassium hydroxide solution and some sodium carboxymethylcellulose. Since the potassium hydroxide solution has a low freezing point and small internal resistance, alkaline zinc-manganese dry batteries can operate at a temperature of -20°C and can discharge at high currents. Alkaline zinc-manganese dry batteries can be charged and discharged more than 40 times, but they cannot be deeply discharged before charging (retaining 60% to 70% of the capacity), and the charging current and voltage at the end of the charging period need to be strictly controlled.
Stacked zinc-manganese dry batteries are composed of several compact flat single cells stacked together. Each single cell is composed of a plastic casing, zinc skin, conductive film, separator paper, and carbon cake (positive electrode). The diaphragm paper is a pulp paper with a starch layer on the surface that absorbs the electrolyte. It is attached to the zinc skin; the top of the diaphragm paper is a carbon cake. The separator paper is like the electric paste layer of a paste dry battery, which serves to isolate the zinc skin negative electrode and the carbon cake positive electrode. The laminated zinc-manganese dry battery eliminates the trouble of series combination of cylindrical paste dry batteries. It has a compact structure, small size and large volume specific capacity. However, the storage life is short and the internal resistance is large, so the discharge current should not be too large.
Battery is a chemical battery that converts electrical energy into chemical energy through charging, stores it, and then converts chemical energy into electrical energy and releases it when used. The transformation process is reversible. When the battery is fully or partially discharged, new compounds are formed on the surfaces of the two electrode plates. At this time, if an appropriate reverse current is passed into the battery, the compounds formed during the discharge process can be reduced to the original active substances to provide Discharge and reuse it next time. This process is called charging, that is, electrical energy is stored in the battery in the form of chemical energy. The process of connecting the battery to the load and supplying current to the external circuit is called discharge. The charging and discharging process of the battery can be repeated many times, so the battery is also called a secondary battery. Depending on the electrolyte solution used, batteries are divided into two categories: acidic and alkaline. According to the active materials used in the positive and negative plates, there are lead batteries, cadmium-nickel, iron-nickel, silver-zinc, and cadmium-silver batteries. Lead-acid batteries are acid batteries, and the last four are alkaline batteries.
Lead-acid batteries are composed of positive plate group, negative plate group, electrolyte and container. The charged positive plate is brown lead dioxide (PbO2), and the negative plate is gray velvety lead (Pb). When the two plates are placed in a sulfuric acid (H2SO4) aqueous solution with a concentration of 27% to 37%, the polarity will The lead on the plate reacts chemically with sulfuric acid, and the divalent lead cation (Pb2) is transferred to the electrolyte, leaving two electrons (2e-) on the negative plate. Due to the attraction of positive and negative charges, lead ions gather around the negative plate, and the positive plate has a small amount of lead dioxide (PbO2) seeping into the electrolyte under the action of water molecules in the electrolyte, in which the divalent oxygen ions combine with water. , turning the lead dioxide molecule into a dissociable and unstable substance - lead hydroxide [Pb (OH4]). Lead hydroxide is composed of 4-valent lead cations (Pb4) and 4 hydroxide radicals [4(OH)-]. The tetravalent lead ions (Pb4) remain on the positive plate, making the positive plate positively charged. Since the negative plate is negatively charged, a certain potential difference is generated between the two plates, which is the electromotive force of the battery. When the external circuit is connected, current flows from the positive pole to the negative pole. During the discharge process, the electrons on the negative plate continue to flow to the positive plate through the external circuit. At this time, the sulfuric acid molecules inside the electrolyte are ionized into positive hydrogen ions (H) and negative sulfate ions (SO42-). Under the action of the ion electric field force , the two ions move toward the positive and negative electrodes respectively. After reaching the negative plate, the sulfate anions combine with the lead ions to form lead sulfate (PbSO2). On the positive plate, due to the inflow of electrons from the external circuit, they combine with the 4-valent lead cations (Pb4) to form divalent lead ions (Pb2), and immediately combine with the sulfate negative ions near the positive plate to form lead sulfate. on the positive terminal. The chemical reaction of the positive and negative plates of lead-acid batteries during the discharge process is:
As the battery discharges, both the positive and negative plates are sulfurized, and at the same time, the sulfuric acid in the electrolyte gradually decreases, while the water increases, resulting in The specific gravity of the electrolyte decreases. In actual use, the discharge degree of the battery can be determined by measuring the specific gravity of the electrolyte. Under normal use conditions, lead-acid batteries should not be over-discharged, otherwise the fine lead sulfate crystals mixed with the active material will form into larger bodies, which not only increases the resistance of the plates, but also makes it difficult to recharge during charging. Reduction directly affects the capacity and life of the storage tank. Lead-acid battery charging is the reverse process of discharging. The total chemical reaction during charging is
Lead-acid batteries have stable operating voltage, wide range of operating temperature and operating current, can charge and discharge hundreds of cycles, and have good storage performance (especially suitable for dry charge storage) , low cost, and therefore widely used. The performance of lead-acid batteries can be improved by using new lead alloys. If lead-calcium alloy is used as the grid, it can ensure the minimum floating charge current of the lead-acid battery, reduce the amount of water added, and extend its service life; using lead-lithium alloy to cast the positive grid can reduce self-discharge and meet the need for sealing. In addition, open-type lead-acid batteries should be gradually changed to sealed types, and acid-proof, explosion-proof and hydrogen-depleting lead-acid batteries should be developed.
Alkaline batteries are small in size, long in life and capable of high current discharge compared with lead batteries of the same capacity, but the cost is higher.
Alkaline batteries are divided into iron-nickel, cadmium-nickel, zinc-silver battery series according to plate active materials. Taking the nickel-cadmium battery as an example, the working principle of the alkaline battery is: after the active material of the battery plate is charged, the positive plate is nickel hydroxide [Ni(OH)3], the negative plate is metal cadmium (Cd); and the discharge When it terminates, the positive plate changes to nickel hydroxide [Ni(OH2)], the negative plate changes to cadmium hydroxide [Cd (OH) 2], and potassium hydroxide (KOH) solution is mostly used as the electrolyte. During the charge and discharge process, the total chemical reaction
It can be seen from the chemical reaction during the charge and discharge process that the electrolyte only serves as a carrier of current and the concentration does not change, so it can only be judged based on the change in voltage
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The degree of charge and discharge. During the charging process of the cadmium-nickel sealed battery, oxygen is released from the positive electrode and hydrogen is released from the negative electrode. Since the negative electrode material of the cadmium-nickel sealed battery is manufactured, the occurrence of hydrogen is avoided; and the oxygen generated on the positive electrode is absorbed by the negative electrode due to electrochemical action, thus preventing gas from accumulating inside the battery, thereby ensuring The battery works normally under sealed conditions. Cadmium-nickel batteries have a history of decades. They were originally used as traction, starting, lighting and signal power supplies, and are now used as starting and ignition power supplies for diesel locomotives and aircraft. Sealed batteries made in the 1960s are used as power sources for satellites, portable power tools, and emergency equipment. One of the directions for improving nickel-cadmium batteries is to adopt a bipolar structure. This structure has a small internal resistance and is suitable for pulsed high-current discharge, which can meet the power supply needs of high-power equipment. In addition, the electrodes are pressed or sintered. and foil style.
Metal-air battery is a high-energy battery that uses oxygen in the air as the positive active material and metal as the negative active material. The metals used are generally magnesium, aluminum, zinc, cadmium, iron, etc.; the electrolyte is an aqueous solution. Among them, zinc-air batteries have become mature products.
Metal-air batteries have a higher specific energy because the air is not counted in the weight of the battery. The specific energy of the zinc-air battery is the highest among currently produced batteries, reaching 400 watt·hour/kg (Wh/kg). It is a high-performance medium-power battery and is developing towards a high-power battery. The metal-air batteries currently produced are mainly primary batteries; the secondary metal-air batteries under development are mechanical rechargeable batteries that use replacement metal electrodes. Because metal-air batteries require a constant supply of air when working, they cannot work in a sealed state or in an environment lacking air. In addition, the electrolyte solution in the battery is easily affected by air humidity, which degrades battery performance; oxygen in the air will penetrate the air electrode and diffuse to the metal electrode, causing corrosion of the battery and causing self-discharge.
Fuel cells are electrolyte batteries that can undergo chemical reactions as long as they are continuously supplied with chemical raw materials and convert chemical energy into electrical energy. When these chemical raw materials react inside the battery (one raw material is at the positive electrode and the other is at the negative electrode), they must be prevented from reacting directly, otherwise a chemical short circuit will occur and electrical energy cannot be obtained from the reaction. The chemical reactions suitable for fuel cells are mainly combustion reactions, and only hydrogen-oxygen fuel cells have entered the practical stage. Since hydrogen-oxygen fuel cells use the precious metal platinum as electrode material, the cost is too high, so this type of battery is now only used as a power source for spacecraft. The fuel cell has high conversion efficiency, high specific energy, no noise and pollution during operation, and a simple structure.
Other energy conversion batteries mainly include: ① Solar cells. A device that converts sunlight energy into light energy, made of semiconductors. When sunlight hits the cell surface, a potential difference forms on both sides of the semiconductor PN junction. Its efficiency is above 10%. ② Thermoelectric battery. When two metals are connected into a closed loop and different temperatures are maintained at the two joints, a thermoelectric electromotive force will be generated in the loop. This device is called a thermocouple. When thermocouples are connected in series to form a thermoelectric stack, a thermoelectric battery is formed. Thermoelectric batteries can also be made of semiconductor materials, which have a strong temperature difference effect. ③Nuclear battery. A device that converts nuclear energy directly into electrical energy is called a nuclear battery.
It usually consists of 3 parts: a radioactive source that emits beta rays (high-speed electron flow), a current collector that collects these electrons, and an insulator. One end of the radioactive source becomes a positive electrode due to loss of negative charge, and one end of the collector gains negative charge and becomes a negative electrode. A potential difference is formed between the two electrodes. This kind of nuclear battery has high voltage but low current