Electric battery is a device that converts chemical energy into electric. All batteries are made up of an electrolyte (which can be liquid, solid or pasty), a positive and a negative electrode. The electrolyte is an ionic conductor; while one electrode generates electrons and the other accepts them. When connecting the electrodes to the circuit to be powered, an electric current is produced. The batteries are divided into primary or voltaic, in which the chemical reaction cannot be reversed (not rechargeable) and secondary or accumulators, in which the reaction is reversible and can be brought to its original state (rechargeable), passing a current through the circuit in the opposite direction to the normal flow of electrons in the cell.
In recent years, solar cells have been developed that produce electricity through a photoelectric conversion process. The source of electricity is a photosensitive semiconductor substance, like a silicon crystal to which impurities have been added. When light strikes the crystal, the electrons on the surface are released, targeting the opposite surface where they are distributed. Solar batteries have a very long life and are mainly used in aircraft and space vehicles as a source of electricity.
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- 1 Mechanism of reactions in a pile
- 2 types of battery
- 3 Composition of the most common batteries
- 1 Voltaic battery
- 2 Homemade pile or Daniell pile
- 4 Source
Reaction mechanism in a pile
By introducing a metal more active than hydrogen in an acidic solution, a redox reaction will occur: the metal will oxidize, passing its ions into the solution and the hydrogen ions will be reduced on the surface of the metal, releasing hydrogen gas. If another less active metal is introduced into said solution and both are connected by means of a metallic conductor, part of the electrons, produced by the oxidation of the more active metal, will circulate through the conductor towards the less active metal and on its surface will be reduced good part of the hydrogen ions. The flow of electrons through the conductor constitutes an electric current and can be used to perform work such as lighting a light bulb; feed a resistance; carry out an electrolysis.
- The most common primarycell is the Leclanché or dry cell, invented by the French chemist Georges Leclanché in the 1860s . The dry cell used today is very similar to the original invention. The electrolyte is a paste consisting of a mixture of ammonium chloride and zinc chloride . The negative electrode is zinc, just like the battery container, and the positive electrode is a carbon rod surrounded by a mixture of carbon and manganese dioxide . This battery produces an electromotive force of about 1.5 volts.
Another widely used primary battery is the zinc – mercury oxide battery , commonly known as the mercury battery. It can be in the form of a small disk and is used in hearing aids, photoelectric cells, and electric wristwatches. The negative electrode is zinc, the positive electrode is mercury oxide, and the electrolyte is a solution of potassium hydroxide. The mercury battery produces approximately 1.34V.
The fuel cell is another type of primary cell. It differs from the others in that the chemicals are not inside the stack, but are supplied from outside.
- Secondarybattery or accumulator, which can be recharged by reversing the chemical reaction, was invented in 1859 by the French physicist Gastón Planté. Planté’s battery was a lead-acid battery, and is the most widely used today. Containing three to six series-connected batteries, this battery is used in cars, trucks, planes, and other vehicles. Its main advantage is that it can produce enough electric current to start an engine; however, it runs out quickly.
The electrolyte is a dilute solution of sulfuric acid, the negative electrode is lead, and the positive electrode is lead dioxide. In operation, the negative lead electrode dissociates into free electrons and positive lead ions. The electrons move through the external electrical circuit, and the positive lead ions react with the sulfate ions in the electrolyte to form lead sulfate.
When electrons re-enter the cell through the positive lead dioxide electrode, another chemical reaction occurs. Lead dioxide reacts with the hydrogen ions in the electrolyte and with the electrons to form water and lead ions; the latter will be released into the electrolyte again producing lead sulfate.
A lead and acid accumulator is depleted because sulfuric acid gradually turns into water and lead sulfate. By recharging the battery, the chemical reactions described above are reversed until the chemicals return to their original condition. A lead-acid battery has a lifespan of about four years. Produces about 2 V per battery. Recently, lead acid batteries have been developed for special applications with a useful life of 50 to 70 years.
Another widely used secondary battery is the alkaline battery or nickel-iron battery, devised by the American inventor Thomas Edison around 1900. The working principle is the same as in the acid-lead cell, but here the negative electrode is iron, the positive electrode is nickel oxide, and the electrolyte is a solution of potassium hydroxide. The nickel-iron battery has the disadvantage of giving off hydrogen gas during charging. This battery is mainly used in heavy industry. Edison’s battery has a life of about ten years and produces approximately 1.15 V.
Another alkaline battery similar to Edison’s battery is the nickel -cadmium battery or cadmium battery, in which the iron electrode is replaced by a cadmium one. It also produces 1.15 V and its useful life is about 25 years.
- Solar batteriesproduce electricity by a photoelectric conversion process. The source of electricity is a photosensitive semiconductor substance, like a silicon crystal to which impurities have been added. When light strikes the glass, the electrons are released from the glass surface and are directed to the opposite surface. There they are collected as electric current .
Solar batteries have a very long life and are mainly used in aircraft as a source of electricity for on-board equipment.
- Leclanché, or Zinc / Carbon (ZN / C), or “dry cells” type batteries Based on the oxidation of zinc in a slightly acidic medium, they are composed of metallic zinc, ammonium chloride and manganese dioxide. They are the so-called common batteries. They are used for simple and low-consumption devices.
- Alkalineor DE batteries Zinc / Manganese Dioxide (ZN / MNO2) The difference with the dry cell is the electrolyte used, in this case, potassium hydroxide, instead of ammonium chloride, and zinc is in powder. They are long-lasting. Almost all of them are armored, making it difficult for the constituents to spill. However, this armor has a very long life but its duration is not unlimited.
- Nickel / Cadmium batteries(NI / CD) They are based on a system consisting of nickel hydroxide, potassium hydroxide and metallic cadmium. They have multiple life cycles, presenting the disadvantage of their relatively low voltage. They can be recharged up to 1000 times and can last tens of years. They do not contain mercury, but cadmium is a metal with toxic characteristics.
- Buttoncells These are so-called, small cells, flat and round. The electronic goods market requires more and more of them. They are essential for hearing aids, pacemakers, watches, calculators and precision medical devices. Its composition is varied.
- Mercúrio Oxide BatteriesThey are the most toxic, they contain 30% approx. of mercury. They should be handled with caution in homes, since their accidental ingestion, which is feasible due to their shape and size, can be fatal.
- Zinc-Air stacksThey are distinguished by having a large number of tiny holes in their surface. They have a lot of capacity and once in operation their electricity production is continuous. They contain more than 1% mercury, so they have serious residual problems.
- Nickel / Metal Hydride(NI / MH) batteries These are secondary batteries such as nickel / cadmium, but where cadmium has been replaced by a metal alloy capable of storing hydrogen, which fulfills the role of anode. The cathode is nickel oxide and the electrolyte is potassium hydroxide.
The energy density produced by Ni / MH batteries is double that produced by Ni / DC, at similar operating voltages, so they represent the new generation of rechargeable batteries that will replace the latter.
- Silver Oxide BatteriesThey are small in size, usually button type. They contain approximately 1% mercury so they have toxic effects on the environment.
- Fuel cellElectrochemical mechanism in which the energy of a chemical reaction is converted directly into electricity. Unlike an electric cell or battery, a fuel cell does not run out or need to be recharged; It works as long as the fuel and oxidant are supplied from outside the battery.
A fuel cell consists of an anode into which the fuel is injected – commonly hydrogen, ammonia or hydrazine – and a cathode into which an oxidant is introduced – usually air or oxygen. The two electrodes of a fuel cell are separated by a conductive ionic electrolyte. In the case of a hydrogen-oxygen fuel cell with an alkali metal hydroxide electrolyte, the anode reaction is 2H2 + 4OH- + 4H2O + 4e- and the cathode reaction is O2 + 2H2O + 4e- + 4OH- .
The electrons generated at the anode move through an external circuit that contains the charge and pass to the cathode. The OH- ions generated at the cathode are led by the electrolyte to the anode, where they combine with hydrogen and form water. The fuel cell voltage in this case is about 1.2V but decreases as the load increases. The water produced in the anode must be continuously extracted to avoid flooding the battery. Hydrogen-oxygen fuel cells using ion exchange membranes or phosphoric acid electrolytes were used in the Gemini and Apollo space programs respectively. Those with phosphoric acid have limited use in electrical power generating installations.
Composition of the most common batteries
- Zinc / Carbon : theseare the common or special batteries for flashlight, they contain very little Mercury, less than 0.01%. It is made up of Carbon, Zinc, Manganese Dioxide and Ammonia Chloride. It can contaminate 3,000 liters of water per unit.
- Alkalines ( Manganese ): theyare more recent than the previous ones. Its active ingredient is an alkaline compound (Potassium Hydroxide). Its duration is 6 times longer than Zinc / Carbon. It is composed of Manganese Dioxide, Potassium Hydroxide, Zinc paste amalgamated with Mercury (total 1%), Carbon or Graphite. A single alkaline battery can pollute 175,000 liters of water (more than a man can consume in his entire life).
- Mercury:It was the first battery that was built of the micropile or button type. Externally they are made of steel and consists of a Mercury Oxide electrode with Graphite powder, the electrolyte is composed of Potassium Hydroxide embedded in a spongy absorbent material and Zinc paste dissolved in Mercury. It contains between 25 and 30% of Mercury. This micropile can contaminate 600,000 liters of water.
- Nickel / Cadmium:This battery is shaped like the classic or alkaline battery, but it has the advantage that it can be recharged many times. It is made of rolled Nickel and Cadmium separated by nylon or polypropylene, all wound in a spiral. Does not contain Mercury. Its residues are dangerous for the environment, mainly due to the presence of Cadmium.
A voltaic cell uses electricity from a spontaneous chemical reaction to light a light bulb (bulb). The zinc and copper strips, within dilute sulfuric acid and copper sulfate solutions respectively, act as electrodes. The salt bridge (in this case potassium chloride) allows the electrons to flow between the cuvettes without mixing the solutions. When the circuit between the two systems is complete (as shown on the right), the reaction generates an electric current. Note that the metal in the zinc strip is consumed (oxidation) and the strip disappears. The copper strip grows by reacting the electrons with the copper sulfate solution to produce additional metal (reduction). If the bulb is replaced by a battery the reaction will be reversed,
Homemade Stack or Daniell Stack
You need a wide-mouth glass jar, a clean piece of copper tubing, a strip of zinc or a metal sharpener, two electrical wires, a glass of vinegar, an LED (light-emitting diode), which is like a very small light bulb, similar to those illuminated by some Christmas trees, an alarm clock or any other device that runs on batteries.
Then the experiment is prepared:
- Fill the glass jar with vinegar.
- The copper pencil sharpener or strip is connected to one end of one of the cables, and the copper pipe is connected to one end of the other cable. Both elements are placed in the jar with vinegar.
- The free ends of the two cables connect either to each LED terminal or to the two poles of the device’s battery holder. Connect the polarity, in the case of the watch, correctly. The positive pole with the copper pipe and the negative pole with the pencil sharpener or zinc strip.
- What happens to the LED?
Explanation: The batteries have two electrodes that are usually two metals (in our case the zinc or magnesium strip of the sharpener and the copper of the pipe) and an electrolyte, which is the substance that allows the electric current to be conducted (in our case is vinegar). The battery we are manufacturing has a very low current intensity, so we can only operate something that requires very little power, such as the LED