/kloc-one day in 0/780, when Italian anatomist Gavagni dissected a frog, he accidentally touched the frog's thigh with different metal instruments in his hand, and the muscles of the frog's leg twitched immediately, as if stimulated by current, but only one metal instrument was used to touch the frog, but there was no such reversal. Galvani believes that this phenomenon is due to a kind of electricity generated in animals, which he calls "bioelectricity". 179 1 year, Gavagni wrote a paper about the experimental results, which was published in academic circles.
Galvani's discovery aroused great interest of physicists, who competed to repeat the experiment of flail Vanni, trying to find a way to generate current. After many experiments, Italian physicist Volt thinks that Galvani's bioelectricity theory is incorrect. The reason why frog muscle can generate current is probably that some liquid in the muscle is working. To prove his point, Volt immersed two different kinds of metal sheets in different solutions for experiments. It is found that as long as one of the two kinds of metal sheets reacts with the solution, an electric current can be generated between the metal sheets.
1799, Volt immersed a zinc plate and a silver plate in salt water, and found that a current passed through the wire connecting the two metals. So he put many pieces of flannel or paper soaked in salt water between zinc and silver, and then folded them flat. When you touch both ends with your hands, you will feel a strong current stimulus. Volt successfully manufactured the world's first battery-"Volt reactor" in this way. This "volt stack" is actually a series battery pack. It became the power supply for early electrical experiments and telegrams.
Italian physicist Volta repeated galvani's experiment many times. As a physicist, his attention is mainly focused on those two metals, not on the frog's nerves. For the frog leg twitching phenomenon discovered by Gavagni, he thought it might be related to electricity, but he thought that the frog's muscles and nerves had no electricity. He speculated that the current may be caused by the contact between two different metals, whether they are in contact with living or dead animals. Experiments have proved that as long as hard paper, linen, leather or other spongy things soaked in salt water or alkaline water are separated between two metal sheets (which he thinks is a necessary condition for the success of the experiment), and the two metal sheets are connected with metal wires, whether there is frog muscle or not, there will be current passing through them. This shows that electricity is not generated from the frog's tissue, and the frog's leg is only equivalent to a very sensitive electroscope.
1836, Daniel of Britain improved the "Walter reactor". He used dilute sulfuric acid as electrolyte to solve the problem of battery polarization and made the first unpolarized zinc-copper battery, also known as "Daniel battery". Since then, "Bunsen battery" and "Grove battery" with better depolarization effect have appeared one after another. However, these batteries all have the problem that the voltage decreases with the extension of service time.
1860, Plante of France invented a battery with lead as the electrode. This kind of battery is unique in that when the battery is used for a period of time to reduce the voltage, it can be energized with reverse current to increase the battery voltage. Because this kind of battery can be used repeatedly, it is called "storage battery".
However, no matter what kind of battery needs to be filled with liquid between two metal plates, it is very inconvenient to carry, especially the liquid used by the battery is sulfuric acid, which is very dangerous when moving.
1887, Englishman Hellesen invented the earliest dry battery. The electrolyte of dry battery is paste-like, does not leak and is easy to carry, so it has been widely used.
A device that directly converts chemical energy, light energy, heat energy and nuclear energy into electrical energy. There are chemical batteries, solar batteries, thermoelectric batteries and nuclear batteries. Batteries usually refer to chemical batteries.
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 the unit positive charge moves from the negative electrode to the positive electrode through the battery. The electromotive force depends on the chemical properties 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 capacity of the battery, usually in ampere hours. In the battery reaction, the electric energy generated by 1 kg reactant is called the theoretical specific energy of the battery. The actual specific energy of the battery is less than the theoretical specific energy. Because the reactants in the battery are not all carried out according to the battery reaction, and the internal resistance of the battery will also cause the electromotive force to drop, the battery with high specific energy is often called high-energy battery. The larger the area of the battery, the smaller its internal resistance.
There are many kinds of batteries, and the commonly used ones 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 cells and nuclear cells.
Dry battery is one of the most widely used chemical batteries. 1865, Leclanche of France developed a carbon/manganese dioxide/ammonium chloride solution/zinc wet battery based on the voltaic battery. After development, the types of dry batteries have exceeded 100. In addition to zinc-manganese dry batteries, there are magnesium-manganese dry batteries, zinc-mercury oxide dry batteries and zinc-silver oxide dry batteries. Because of the poor reversibility of redox reaction of dry battery, it is generally impossible to restore the positive and negative active materials to their original state by charging after use, so dry battery is also called primary battery. The most commonly used dry batteries are zinc-manganese dry batteries, including paste type, cardboard type, alkaline type and laminated type.
Paste zinc-manganese dry battery consists of zinc tube, paste layer, manganese dioxide anode, carbon rod and copper cap. The outermost layer is a zinc tube, which is not only the negative electrode of the battery, but also the container of the battery, and will gradually dissolve during discharge; In the middle is a carbon rod, which has the function of collecting current; Tightly surrounding this carbon rod is a mixture of dark brown or black manganese dioxide powder and conductive material (graphite or acetylene black), which together with the carbon rod constitutes the positive electrode body of the battery, also known as carbon pack. In order to avoid water evaporation, the upper part of the dry battery is sealed with paraffin or asphalt. The electrode reaction of zinc-manganese dry battery is zinc electrode: Zn→ Zn2++2e.
Carbon pole:
Paperboard zinc-manganese dry battery is improved on the basis of paste zinc-manganese dry battery. High-quality kraft paper with a thickness of 70 ~ 100 micron is used as the base material and contains no metal impurities. The prepared paste was coated on the surface of kraft paper, and then dried to make cardboard to replace the paste electrolyte layer in paste zinc-manganese dry battery. The actual discharge capacity of cardboard zinc-manganese dry battery is 2 ~ 3 times higher than that of ordinary paste zinc-manganese dry battery. Most dry batteries labeled "high performance" are cardboard.
The electrolyte of alkaline Zn-Mn dry battery is gelatinized by amalgam zinc powder, 35% potassium hydroxide solution and part of sodium carboxymethyl cellulose. Because of the low freezing point and low internal resistance of potassium hydroxide solution, alkaline zinc-manganese dry battery can work at -20℃ and discharge with high current. The alkaline Zn-Mn dry battery can be charged and discharged for more than 40 times, but it cannot be discharged deeply before charging (60% ~ 70% capacity is reserved), and the charging current and the voltage at the end of charging should be strictly controlled.
The laminated zinc-manganese dry battery is composed of several compact flat single cells stacked together. Each unit cell consists of plastic shell, zinc skin, conductive film, separator paper and carbon cake (positive electrode). Diaphragm paper is a kind of pulp paper with starch layer on its surface, which absorbs electrolyte and adheres to zinc skin. The isolation paper is covered with charcoal cakes. The separator paper, like the paste layer of paste dry battery, plays the role of isolating the zinc-coated negative electrode and the carbon cake positive electrode. The laminated Zn-Mn dry battery eliminates the trouble of series combination of cylindrical paste dry batteries. It has compact structure, small volume and large specific volume, but it has short storage life and large internal resistance, so the discharge current should not be too large.
Battery is a kind of chemical battery, which converts electrical energy into chemical energy by charging and stores it, and then converts chemical energy into electrical energy and releases it when it is used. The transformation process is reversible. When the battery is fully or partially discharged, new compounds will be formed on the surfaces of the two electrode plates. At this time, if an appropriate reverse current flows into the battery, the compounds formed in the discharge process can be reduced to the original active substances for reuse in the next discharge. This process is called charging, that is, electric energy is stored in the battery in the form of chemical energy. The process of connecting a battery to a load to supply current to an external circuit is called discharge. The charging and discharging process of a battery can be repeated many times, so the battery is also called a secondary battery. According to the different electrolytes used, batteries can be divided into two categories: acidic and alkaline. According to the positive and negative plates, there are several active material materials, such as lead battery, cadmium nickel, iron nickel, silver zinc, cadmium silver battery and so on. Lead batteries are acidic batteries, and the last four are alkaline batteries.
Lead-acid battery consists of positive plate group, negative plate group, electrolyte and container. After charging, the positive plate is brown lead dioxide (PbO2) and the negative plate is gray velvet lead (Pb). When the two plates are put into sulfuric acid (H2SO4) solution with a concentration of 27% ~ 37%, lead on the plates reacts with sulfuric acid, and divalent lead positive ions (Pb2+) are transferred to the electrolyte, leaving two electrons (2e-) on the negative plate. Due to the attraction of positive and negative charges, lead positive ions gather around the negative plate, and a small amount of lead dioxide (PbO2 _ 2) penetrates into the positive plate under the action of water molecules in the electrolyte, in which divalent oxygen ions combine with water, making lead dioxide molecules become dissociable and unstable substances-lead hydroxide (Pb (OH _ 4)). Lead hydroxide is composed of tetravalent lead cation (Pb4+) and four hydroxyl groups [4 (OH)-]. Tetravalent lead positive ions (Pb4+) remain on the positive plate, making the positive plate positively charged. Because the negative plate is negatively charged, there is a certain potential difference between the two plates, which is the electromotive force of the battery. When an external circuit is connected, current flows from the positive electrode to the negative electrode. During the discharge process, the electrons on the negative plate continuously flow to the positive plate through the external circuit. At this time, sulfuric acid molecules are ionized into hydrogen ions (H+) and sulfate anions (SO42-) in the electrolyte. Under the action of ionic electric field force, the two ions move to the positive and negative electrodes respectively, and the sulfate negative ions reach the negative plate and combine with the lead positive ions to form lead sulfate (PbSO2). On the positive plate, due to the inflow of external circuit electrons, it reacts with tetravalent lead positive ions (Pb4+) to generate divalent lead positive ions (Pb2+), and immediately combines with sulfate negative ions near the positive plate to generate lead sulfate, which is attached to the positive electrode. The chemical reactions of the positive and negative plates of lead-acid batteries during discharge are as follows
With the discharge of the battery, both the positive and negative plates are vulcanized, and at the same time, the sulfuric acid in the electrolyte gradually decreases, while the water content increases, resulting in a decrease in the specific gravity of the electrolyte. In practical use, the discharge degree of the battery can be determined by measuring the specific gravity of the electrolyte. Under normal use, lead-acid batteries should not be overdischarged, otherwise tiny lead sulfate crystals mixed with active substances will form larger bodies, which will not only increase the plate resistance, but also be difficult to reduce when charging, which will directly affect the capacity and life of the batteries. The charging of lead-acid battery is the reverse process of discharging. The total chemical reaction during charging is
Lead-acid batteries are widely used because of their stable working voltage, wide range of temperature and current, good storage performance (especially suitable for dry charge storage) and low cost. The performance of lead storage battery can be improved by using new lead alloy. If lead-calcium alloy is used as grid, the minimum floating current of lead-acid battery can be ensured, the water addition can be reduced and the service life can be prolonged. Casting positive plate grid with lead-lithium alloy can reduce self-discharge and meet the needs of sealing. In addition, open lead-acid batteries should be gradually changed to sealed ones, and acid-proof, explosion-proof and hydrogen-eliminating lead-acid batteries should be developed.
Compared with lead-acid batteries with the same capacity, alkaline batteries have the advantages of small size, long life and high current discharge, but the cost is higher. Alkaline batteries are divided into Fe-Ni batteries, Cd-Ni batteries and Zn-Ag batteries according to the active substances of the plates. Taking a nickel-cadmium battery as an example, the working principle of an alkaline battery is as follows: after the active material of the battery plate is charged, the positive plate is nickel hydroxide [Ni (OH) 3] and the negative plate is metal cadmium (CD); ; After the discharge, the positive electrode sheet becomes nickel hydroxide [Ni (OH2)], the negative electrode sheet becomes cadmium hydroxide [[CD (OH) 2]], and the electrolyte is mostly potassium hydroxide (KOH). In the process of charging and discharging, the total
According to the chemical reaction in the process of charging and discharging, electrolyte is only used as the carrier of current, and its concentration is constant, so it can only be judged according to the change of voltage.
Degree of charge and discharge. In the process of charging, the positive electrode releases oxygen and the negative electrode releases hydrogen. Because the negative electrode material of cadmium-nickel sealed storage battery is excessive in the manufacturing process, hydrogen is avoided; Oxygen generated on the positive electrode is absorbed by the negative electrode due to electrochemical action, thus preventing gas from accumulating inside the battery, thus ensuring the normal operation of the battery under sealed conditions. Cadmium-nickel battery has a history of several decades. Originally used as traction, starting, lighting and signal power supply, it is now used as starting and ignition power supply for diesel locomotives and aircraft. Sealed batteries made in 1960s are used as power sources for satellites, portable power tools and emergency equipment. One of the improvement directions of Cd-Ni battery is to adopt bipolar structure, which has low internal resistance, is suitable for pulsed high current discharge, and can meet the power supply requirements of high-power equipment. In addition, the electrodes are pressed, sintered and foil-pasted.
Metal-air battery is a kind of high-energy battery with 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. What kind of zinc? Air battery has become a mature product.
Metal-air battery has a high specific energy because air is not included in the weight of the battery. Zinc? The specific energy of air batteries is the highest among the batteries currently produced, reaching 400 watt-hours per kilogram (Wh/kg). It is a high-performance medium-power battery, which is developing towards high-power batteries. At present, the metal-air batteries produced are mainly primary batteries; The secondary metal-air battery being developed is a mechanical rechargeable battery with metal electrodes. Because the metal-air battery is constantly supplied with air when it works, it 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 reduces the performance of the battery; Oxygen in the air will penetrate the air electrode, diffuse to the metal electrode, corrode the battery and cause self-discharge.
Fuel cell is an electrolyte battery. As long as chemical raw materials are continuously supplied, chemical reactions can occur and chemical energy can be converted 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 directly reacting, otherwise, chemical short circuit will occur and electric energy cannot be obtained from the reaction. The chemical reaction suitable for fuel cells is mainly combustion reaction, and only hydrogen-oxygen fuel cells have entered the practical stage. Hydrogen-oxygen fuel cell is only used as the power supply of spacecraft because of the high cost of using precious metal platinum as electrode material. The fuel cell has high conversion efficiency, high specific energy, no noise and no pollution when working, and simple structure.
Other energy conversion batteries mainly include: ① solar cells. A device that converts the energy of sunlight into light energy, which is made of semiconductor. When the sun shines on the surface of the battery, a potential difference is formed 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 two joints, thermoelectric electromotive force will be generated in the loop. This device is called a thermocouple. When thermocouples are connected in series to form a thermopile, a thermoelectric battery is formed. It can also be made of semiconductor materials, with strong temperature difference effect. ③ Nuclear battery. The device that directly converts nuclear energy into electric energy is called a nuclear battery. It usually consists of three parts: a radioactive source that radiates 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 the loss of negative electricity, and one end of the current collector becomes a negative electrode, and a potential difference is formed between the two electrodes. This kind of nuclear battery has high voltage and low current.