how-does-a-cordless-power-tool-battery-work

How does a cordless power tool battery work?

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Electricity is stored in a battery for use in cordless electric devices eg power tools. Batteries work by storing energy and releasing it when an electrical circuit is completed. The energy can be harnessed and put to work to create light, heat or movement. This energy is more commonly called electricity.
Motor circuit shows how power travels through the wires to the drill and is used. When you press the ‘on’ switch of a cordless power tool you complete the electrical circuit which allows the power to flow from the battery into the tool and causes, for instance, the drill bit to turn.
Recharging a battery requires electricity input from the charger. The battery can only store a limited amount of power and when it runs out it needs to be recharged using a charger. The charger uses electricity from the mains to refill the battery with energy and it’s ready to go again.
Chemistry of a battery. If you are interested in the chemistry that makes all this work, read on!

Battery chemistry

Cells of a battery including a normal AA single celled battery and a multiple celled rechargeable cordless power tool battery. A rechargeable battery designed for cordless power tools is made up of multiple battery ‘cells’ and is known as a battery pack. The more cells, the more work the battery can do before running down.
Anode and cathode (electrodes) and electrolyte in battery cell. Inside each cell there is an anode, a cathode and an electrolyte. An anode and cathode, known collectively as the ‘electrodes’, are made from materials that react if they are put together. The electrolyte is a liquid or moist paste that separates the electrodes from each other.
Positive, negative and neutral charges of atoms, molecules, materials in a rechargeable battery. Everything in the world is made up of tiny molecules which interact based on their electrical charge (positive, negative or neutral). In order to understand the battery, we need to look at how the molecules in the electrodes interact with each other.
A molecule is made up of atoms attached together by bonds. A molecule is made up of one or more atoms which are the smallest building blocks.
An atom with electron, protons and neutrons dictate charge of parts of bettery cell. Each atom has a ‘nucleus’ at its centre which contains neutrons and protons. Whizzing around the nucleus are electrons. Neutrons have a neutral charge, protons have a positive charge and electrons have a negative charge. The balance between the charges dictates the overall charge of the atom and the balance between the atoms in a molecule dictates the overall charge of the molecule.
Molecule ion behaviour in the presences of electrons depending on if it is positive or negative. Each molecule wants to become neutral. The only way they can do this is by losing or gaining electrons. If they have an overall positive charge they attract electrons, if they have an overall negative charge, they lose electrons.
Anode molecules react with the electrolyte to produce positive ions and electrons. The anode molecules have a neutral charge until they react with the electrolyte which causes electrons to be released (known as an ‘oxidation reaction’) and positive ions (charged molecules) to form.
Negative electrons build up in anode creating a negatively charged environment. These ‘free’ electrons build up in the anode, turning the anode negative.
Cathode reductions reaction with electrolyte causes the free electrons to be used up to make negative ions but a positive cathode. The cathode molecules also have a neutral charge until they start reacting with the electrolyte which uses up free electrons and forms negative ions (known as a reduction reaction).
Anode is now negative and cathode is positive. The consumption of free electrons causes the cathode to become increasingly positive until there are no electrons to use up.
Electrons can't travel through the electrolyte to the cathode where they are needed. The anode is now repelling electrons and the cathode is demanding them but, if the circuit is incomplete, the free electrons in the anode cannot cross over to the cathode because they cannot pass through the electrolyte.
Electrons travel round the circuit and are put to work in the motor of the tool. When the circuit it completed, the free electrons can flow through the conductive wire away from the anode and towards the cathode. As they pass through the tool, the energy they are carrying can be used to perform ‘work’ such as turning a drill bit in a cordless power drill.
Lots of electrons enter the cathode and pair up with cathode material molecules. When they reach the cathode they supply the electrons to continue the reduction reaction, producing even more negative ions as electrons are added.
Positive ions from the anode move across the electrolyte and mix with the negative ions in the cathode. Meanwhile, in the anode, the loss of electrons is producing even more positive ions which are being attracted to the negative ions in the cathode, so the positive ions start moving through the electrolyte and mixing in with the negative ions in the cathode.
When the battery stops working properly it needs to be recharged using a charger. Once all of the positive ions have moved across to the cathode and there are no more free electrons left, the battery stops working properly and needs to be recharged.
Charger voltage is higher than battery voltage so current flows into battery. Chargers pass a voltage that is higher than the battery voltage through the discharged battery. This causes the reactions in the battery to reverse.
Electrons and ions are forced back by an input of energy from the charger so that the battery is recharged and can start again. The input of electricity from the charger forces the electrons in the cathode back along the circuit towards the anode. As the anode becomes increasingly negative due to all the electrons, the positive anode ions start leaving the cathode and moving through the electrolyte back to the anode where they join to the free electrons and become neutral again.
Battery is charged with a charger and is ready to complete another cycle. The battery cell is now ready to go again!