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Make a details description of the way electricity is stored

Customer Question

make a details description of the way electricity is stored in
1. A lead acid cell (car battery)
2. A nickel-cadmium (NI CAD) battery
Submitted: 3 years ago.
Category: Engineering
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Expert:  Plumbers_Mate replied 3 years ago.
Lead acid battery;
A 12-volt motorcycle battery is made up of a plastic case containing six cells. Each cell is made up of a set of positive and negative plates immersed in a dilute sulfuric acid solution known as electrolyte, and each cell has a voltage of around 2.1 volts when fully charged. The six cells are connected together to produce a fully charged battery of about 12.6 volts.
That's great, but how does sticking lead plates into sulfuric acid produce electricity? A battery uses an electrochemical reaction to convert chemical energy into electrical energy. Let's have a look. Each cell contains plates resembling tiny square tennis rackets made either of lead antimony or lead calcium. A paste of what's referred to as "active material" is then bonded to the plates; sponge lead for the negative plates, and lead dioxide for the positive. This active material is where the chemical reaction with the sulfuric acid takes place when an electrical load is placed across the battery terminals.
How It Works
Let me give you the big picture first for those who aren't very detail oriented. Basically, when a battery is being discharged, the sulfuric acid in the electrolyte is being depleted so that the electrolyte more closely resembles water. At the same time, sulfate from the acid is coating the plates and reducing the surface area over which the chemical reaction can take place. Charging reverses the process, driving the sulfate back into the acid. That's it in a nutshell, but read on for a better understanding. If you've already run from the room screaming and pulling your hair, don't worry.
The electrolyte (sulfuric acid and water) contains charged ions of sulfate and hydrogen. The sulfate ions are negatively charged, and the hydrogen ions have a positive charge. Here's what happens when you turn on a load (headlight, starter, etc). The sulfate ions move to the negative plates and give up their negative charge. The remaining sulfate combines with the active material on the plates to form lead sulfate. This reduces the strength of the electrolyte, and the sulfate on the plates acts as an electrical insulator. The excess electrons flow out the negative side of the battery, through the electrical device, and back to the positive side of the battery. At the positive battery terminal, the electrons rush back in and are accepted by the positive plates. The oxygen in the active material (lead dioxide) reacts with the hydrogen ions to form water, and the lead reacts with the sulfuric acid to form lead sulfate.
The ions moving around in the electrolyte are what create the current flow, but as the cell becomes discharged, the number of ions in the electrolyte decreases and the area of active material available to accept them also decreases because it's becoming coated with sulfate. Remember, the chemical reaction takes place in the pores on the active material that's bonded to the plates.
Odyssey Automotive BatteryMany of you may have noticed that a battery used to crank a bike that just won't start will quickly reach the point that it won't even turn the engine over. However, if that battery is left to rest for a while, it seems to come back to life. On the other hand, if you leave the switch in the "park" position overnight (only a couple of small lamps are lit), the battery will be totally useless in the morning, and no amount of rest will cause it to recover. Why is this? Since the current is produced by the chemical reaction at the surface of the plates, a heavy current flow will quickly reduce the electrolyte on the surface of the plates to water. The voltage and current will be reduced to a level insufficient to operate the starter. It takes time for more acid to diffuse through the electrolyte and get to the plates' surface. A short rest period accomplishes this. The acid isn't depleted as quickly when the current flow is small (like to power a tail light bulb), and the diffusion rate is sufficient to maintain the voltage and current. That's good, but when the voltage does eventually drop off, there's no more acid hiding in the outer reaches of the cell to migrate over to the plates. The electrolyte is mostly water, and the plates are covered with an insulating layer of lead sulfate. Charging is now required.
NiCd batteries;
‘NiCd’ is the chemical abbreviation for the composition of Nickel-Cadmium batteries, which are a type of secondary (rechargeable) batteries. Nickel-Cadmium batteries contain the chemicals Nickel (Ni) and Cadmium (Cd), in various forms and compositions. Typically the positive electrode is made of Nickel hydroxide (Ni (OH) 2) and the negative electrode is composed of Cadmium hydroxide (Cd (OH) 2), with the electrolyte itself being Potassium hydroxide (KOH).
How NiCd Batteries are Unique
NiCad batteries are different from typical alkaline batteries or lead-acid batteries in several key ways. One of the main key differences is in cell voltage. A typical alkaline or lead-acid battery has a cell voltage of approximately 2V, which then steadily drops off as it is depleted. NiCad batteries are unique in that they will maintain a steady voltage of 1.2v per cell up until it is almost completely depleted. This causes the NiCad batteries to have the ability to deliver full power output up until the end of its discharge cycle. So, while they have a lower voltage per cell, they have a more powerful delivery throughout the entirety of the application. Some manufacturers make up the voltage difference by adding an extra cell to the battery pack. This allows for the voltage to be the same as the traditional type batteries, while still retaining the constant voltage that is so unique of NiCads. Another reason the NiCad batteries can deliver such high power output, is they have very low internal resistance. Because their internal resistance is so low, they are capable of discharging a lot of power very quickly, as well as accepting a lot of power very quickly. Having such a low internal resistance keeps the internal temperature low as well, allowing for quick charge and discharge times. This feature, combined with the constant voltage of the cells, allows them to put out a high amount of amperage, at a consistently higher voltage than comparable alkaline batteries.
Power Tool Applications
Dewalt, Black and Decker Cordless Power Tool Battery UpgradeOne of the most practical applications for NiCad batteries is in cordless power tools. Power tools demand a high amount of power delivery throughout the entire time of use, and do not function as well with dropping voltages as a typical battery would deliver. With NiCad technology, power tools are able to operate at full capacity for the entire time of use, not only the first few minutes of operation. With a Lithium-ion, alkaline, or even a lead-acid battery, the power tool will perform extremely well from the start, with a steady decline in power, until the power tool barely works at all. NiCads, on the other hand, will cause the power tool to stay at full power up until the very end of the charge. Not only that, but then NiCads can be safely charged in as little as 1-2 hours! We recommend PremiumGold NiCad replacement power tool batteries.
Charging NiCd batteries
Smart 1.4A, NiMH/NiCd Battery Pack Charger: 12V - 16.8V T-01004Another unique feature of NiCad batteries lies in the way they charge. Unlike a lead-acid battery which can take large variations in amperage and voltage while charging, the NiCad batteries require steady amperage and only very slight variations in voltage. The charge rate for a NiCad is right between 1.2 V and 1.45 V per cell. When charging NiCad batteries, a charge rate of c/10 (10% of capacity) is normally used, with the exceptions being speed chargers, which charge at either c/1 (100% capacity) or c/2 (50% capacity). NiCad’s have the ability to receive a much higher rate of charge up to 115% of their total capacity, with minimal reduction in life span, which makes NiCad batteries the ideal battery for power tools. If you notice the battery heating up while it is charging, cool it down, and then complete the charge. The chemical reaction in a NiCad while charging is heat absorbing, instead of heat producing, so higher power absorption is possible while charging, allowing for the quick recharge times.
Storing NiCd Batteries
When storing NiCad batteries, be sure to pick a cool, dry place. The temperature range for storing batteries is between −20 °C and 45 °C. When preparing to store NiCad batteries, be sure to discharge the batteries fairly deeply. The range in recommendations is between 40% and 0% charged when going into storage. NEVER short circuit a NiCad to drain as this causes excessive heat and can cause hydrogen gas to be released…AKA-Boom! The self-discharge rate for NiCad’s is right around 10% at 20 °C, and rising up to 20% at higher temperatures. It is recommended not to store NiCads for an extended amount of time without occasionally using the batteries. Over long periods of storage the cadmium in the NiCad can form dendrites (thin, conductive crystals), which can bridge the gap between contacts and short out the cell. Once this happens, there is really nothing that can be done to fix it long term. The best way to prevent this from happening is frequent use.
The Memory Effect
One of the most discussed topics about NiCad’s is whether or not they have a ‘memory’. The idea of a charge memory came when they started using NiCad batteries in satellites where they were typically charging for twelve hours out of twenty-four for several years.1 After several years it was noticed that the battery capacity has seemed to have declined severely, and while still operable, they would only discharge to the point that the charger would typically kick in, and then would drop off as if they were completely discharged. For the typical consumer this does not have a large effect, however, we do recommend fully discharging the NiCad you are using before recharging. Occasionally completely draining (but NEVER short circuiting) a NiCad can prevent the on setting of this mysterious battery ‘memory’. An effect with similar symptoms to the memory effect is what is called the voltage depression or lazy battery effect. This is caused by frequent overcharging of the NiCad. You can tell this is happening when the battery appears to be fully charged but discharges quickly after only a brief period use. This is not the memory­ effect, which is limited to NiCad batteries alone, but is something that can happen to any battery, and is almost always from overcharging. Occasionally this can be fixed by running the battery through a few very deep discharge cycles, but doing so can reduce the overall life of the battery. NiCad batteries are the only battery chemistry that benefit from completely discharging before recharging.
Proper Disposal
NiCad batteries contain Cadmium, a highly toxic ‘heavy’ metal. Never burn NiCads, and never throw them in the trash or break them open. Always recycle NiCad’s at an official NiCad recycle place. As long as NiCads are kept sealed, and never short circuited or severely over charged, NiCad batteries are perfectly safe to use, and do not vent toxic material. If a NiCad battery is treated well, it should last to the 1000 cycle mark. Speed charging NiCads can slightly shorten their life span, as can extended improper storage.
While limited in application, NiCad batteries are an exceptional choice for all of you cordless power tool requirements. There are other chemistry batteries coming online as technology marches on, however the best bang for your buck, insofar as Power Tool replacement batteries, still lies with this tried and tested battery type.