Battery is a device, which consists of one or more electrochemical cells, which converts stored chemical energy into electrical energy. Batteries are used everywhere in our daily life. We use them in technology, like mobile phones, computers, music players and etc. We use them for medical reasons, like wheelchairs, defibrillator, pace makers, hearing aids and many others. Batteries have solver an enormous amount of problems. For instance, without batteries there wouldn’t be mobile phones and computers.
Batteries work by reduction and oxidation reaction. Battery is a device, which consists of one or more cells. Each cell consists of at least two half-cells: a reduction cell and an oxidation cell. Chemical reactions in the two half-cells provide the energy for the battery. (Wikipedia) The reason why chemical reactions happen is that one element is more reactive than the other. Oxidation is a loss of electrons and reduction is a gain of electrons. Each cell consists of two metal electrodes (cathode (-) and anode (+)) and at least one electrolyte solution (solution which can conduct electricity).
Oxidation occurs at the anode and reduction occurs at the cathode. (Gary L. Bernard) Oxidation either removes negative ions or produces positive ions to the solution at the anode. Reduction does the opposite; it either removes positive ions or produces negative ions in the solution at the cathode. (Bryant, Charles W) In order for electrons to move freely through the wire, there must be a path for electrons. Putting the two solutions together could make this path, but that makes the energy run out too quickly. (Science)
The first battery was invented in 1800 by a scientist- Alessandro Volta. In 1780, Volta saw his friend Luigi Galvani dissecting a frog affixed to a brass hook. When he touched its leg with an iron scalpel, the leg twitched. Galvani thought that the energy came from the leg of the frog, but Volta proved that he was wrong. Alessandro Volta proved that two different metals joined together caused the leg twitching. (Wikipedia) In 1800, Volta invented the first battery called the “voltaic pile”. The voltaic pile was made of alternating discs of zinc and copper with pieces of cardboard soaked in brine between the metals, which produced electrical current. Voltaic pile was the first “wet cell battery” that produced a reliable, steady current of electricity. (Marry Bellis)
There are three main types of batteries: primary cells, secondary cell and fuel cell batteries. The primary cell batteries are non-rechargeable batteries. These are usually used in toys, flashlights, TV-remote, watches, clocks, hearing aids, radios and etc. The primary cell batteries are good, because they have a low cost and high energy density. (Wikipedia) The secondary cell batteries are the rechargeable batteries. These are usually used in traction, power tools, laptops, mobile phones, cameras, toys and etc.
The advantage of a secondary cell battery is that you can reuse it. (Battery and Energy technologies) Fuel cell battery is a battery, which uses oxygen and hydrogen chemicals to convert them into water, and in the process it produces electricity. The advantage of it is that as long as it has water and oxygen coming in, it will always produce electricity, and you don’t have to change it or recharge it. These batteries are usually used in airplanes, cars, motorcycles, boats, submarines, buses and etc. (Wikipedia)
Wheelchair is a very important device, because without it people who are immobilized wouldn’t be able to move around. Mobilization is a very important factor of life. Being able to move around brings people satisfaction and joy. There are many people in the world, which cannot move around, either because they have been born like that, or after an accident. Years ago, back when there were no wheelchairs, people who were immobilized would have to just deal with it and stay at home. This problem, which affects so many people, was solved with time. First wheelchair was invented in 16th century by an unknown inventor. Later on there were few other wheelchairs made, but only in the18th century, the comfort of the disabled people was considered. That’s when the “seating” wheelchair was invented.
It differed from the other wheelchairs by the rear push wheels and small front casters. The wheels were made out of rubber, like the bicycle wheels. (History Of The Wheelchair) However, these wheelchairs weren’t solving the problem very well. They still left disabled people being dependent from someone else, because they couldn’t control the wheelchair. The first powered wheelchair was made in 1916 by George J. Klein in order to assist injured veterans after the World War II. (Wikipedia) This wheelchair only had two speeds: high and low. It wasn’t very good. To change between the speeds you first had to stop the wheelchair and then you could change it. But science improves all the time and there have been invented all sorts of electrical wheelchairs, because the batteries of it were improved.
The battery used in an electrical wheelchair is a rechargeable battery; therefore it’s a secondary cell, specifically- lead acid battery. Lead Acid battery is one of the best rechargeable batteries in terms of self-discharge. It has a low self-discharge, considering the amount of energy wheelchairs need to use. (Battery University) Each cell of a Lead Acid battery consists of a negative plate- lead (Pb), a positive plate- lead oxide (PbO2) and an electrolyte solution- sulfuric acid (H2SO4) when charged. Lead Acid battery’s charging process in the positive plate, made out of lead oxide (PbO2) by a reversible charging and discharging reaction (redox) which is shown below:
“PbSO4(s)+2H2O(l) → PbO2(s)+HSO4(aq)+3H+(aq)+2e”
In this charging process, the positive plate is called the anode, because it’s being reduced. (Lead-Acid Battery Half-Cell Reactions) The discharging process is the exact same process but in reverse, because it’s a reversible reaction. So the Lead Acid battery’s discharging process in the positive plate would happen this way:
During this process the positive plate is called the cathode, because it’s being oxidized. (Lead-Acid Battery Half-Cell Reactions) In the negative plate, made out of lead (Pb) the reactions for charging process are next:
“PbSO4(s) + H+(aq) + 2e- → Pb(s) + HSO4-(aq)”
In this process the negative plate is called the cathode, because now the plate material is being reduced. The discharging process of the negative plate would be the reverse of the above:
“Pb(s) + HSO4(aq) → PbSO4(s) + H+(aq) + 2e-“
In this process the negative plate is called the anode, because the material is being oxidized. (Lead-Acid Battery Half-Cell Reactions) Combining the negative and positive plates’ charging reaction we can get one full equation, which would be the reverse of the combined negative and positive plates’ discharging reaction:
“2PbSO4(s) + 2H2O(l) → Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4-(aq)” (charge)
(Lead Storage Battery)
“Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4-(aq) → 2PbSO4(s) + 2H2O(l)” (discharge)
(Lead Storage Battery)
There are many types of lead acid batteries, but the one, which is used in wheelchairs, is the deep-cycle battery. This battery is usually used for golf cars, scooters and wheelchairs and is built for maximum capacity and high cycle count. Lead Acid batteries have many advantages. For instance they are not very expensive, comparing to some other rechargeable batteries, considering the energy they require.
However many advantages the lead acid battery has, it is not perfect and has much more limitations than advantages. These limitations are the reasons, which stop the batteries from changing the way we live. In the past there were many limitations too, which were successfully solved by science. For instance when the first sealed lead acid battery has been invented in the mid-1970s, the engineers argued that the term “sealed lead acid” wasn’t very right because no lead acid battery can be completely sealed. That’s because there is a valve in the battery to control venting of gases, because during stressful recharge and rapid discharge, hydrogen gets formed in the acid and this might cause an explosion of the battery. So if the battery isn’t completely sealed it might cause a leakage. Scientists came up with a solution for that too: rather than sinking the plates in the acid liquid, the electrolyte is deeped into a moistened separator.
This enables to operate the battery in any physical orientation without leakage. (Lead-based Batteries)There are though many limitations still existing. One of the main limitations of a deep-cycle lead acid battery is the limited cycle life. Repeated deep cycling reduces the battery life and repeated deep cycling is commonly used in a wheelchair, because disabled people need to move around a lot, just like us. Another huge limitation of a lead acid battery is that it must always be stored in a charged condition. If the battery is not stored is stored in a discharged condition, then a chemical reaction called sulfation happens to it. Lead and lead dioxide, the materials on the batteries’ plates react with sulfuric acid in the electrolyte and form lead sulfate. At first the lead sulfate form in an amorphous state, and then easily goes back to lead, lead dioxide and sulfuric acid, but after a few discharges and charges it no longer reverts back, but slowly converts into crystalline.
Therefore, the lead doesn’t return to the plates anymore, leaving the battery damaged. (Lead-Acid Battery) Users of electrical wheelchairs usually don’t not charge the battery long enough. They usually charge it for about 8 hours over the night when they are not using the chair. This is not enough time for a lead acid battery to get fully charged. Lead acid batteries must be periodically charged from 14-16 hours to reach full saturation (this is the only way to prevent sulfation). This is usually the reason why wheelchair batteries only last for about two years, whereas golf car batteries, which are the exact same type of batteries, last for twice as long. (Battery University) Another limitation is that the lead acid battery is really heavy. Its heaviness limits the capabilities of a wheelchair. For instance making the speed of it slower, because it has to carry the heavy battery, apart from the person.