Wiktor Wise
A battery is a device that stores chemical energy and converts it to electricity. The system underpinning a battery is called an electrochemical cell, which consists of two electrodes separated by an electrolyte. The electrolyte is a chemical medium that allows the flow of electrical charge between the cathode and anode. When a battery is connected to an external electric load, negatively charged electrons flow through the circuit and reach the positive terminal, causing a redox reaction by attracting positively charged ions, or cations. This process continues until the electrolyte is completely transformed, and the battery is flat.
| Characteristics | Values |
|---|---|
| What is a battery? | A device that stores chemical energy and converts it to electricity. |
| How does a battery work? | When a battery is connected to an external electric load, negatively charged electrons flow through the circuit and reach the positive terminal, thus causing a redox reaction by attracting positively charged ions, or cations. |
| What are the components of a battery? | Two terminals made of different chemicals (typically metals), the anode and the cathode; and the electrolyte, which separates these terminals. |
| What is an electrolyte? | A chemical medium that allows the flow of electrical charge between the cathode and anode. |
| What is a redox reaction? | The technical chemical term for a reaction that involves the exchange of electrons. |
| What is an electrochemical cell? | A battery can be made up of one or several electrochemical cells. Each electrochemical cell consists of two electrodes separated by an electrolyte. |
| What is an electrode? | The electrodes in a battery are always made from two dissimilar materials (so never both from the same metal), which are conductors of electricity. |
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What You'll Learn
The role of chemical energy
A battery is a device that stores chemical energy and converts it to electricity. This process is known as electrochemistry, and the system that underpins a battery is called an electrochemical cell.
The electrochemical cell consists of two electrodes—the cathode and the anode—separated by an electrolyte. The cathode and anode are the positive and negative terminals of the battery, respectively. The electrolyte is a chemical material that allows the flow of charged ions to balance the flow of electrons moving through the external circuit.
The chemical reactions in a battery involve the flow of electrons from one electrode to another through the external circuit. These electrons are produced by a chemical reaction at one electrode, accumulate at the anode, and then flow to the other electrode where they are used up. This flow of electrons provides an electric current that can be used to do work.
When a battery is connected to an external electric load, the negatively charged electrons flow through the circuit and reach the positive terminal, causing a redox reaction. This reaction involves the exchange of electrons between the anode and cathode, which converts chemical potential energy to electricity and discharges the battery. During this process, the oppositely charged ions move inside the battery through the electrolyte to balance the charge of the electrons.
When the battery is recharged, the chemical reaction that occurred during discharge is reversed. The positive ions and electrons return to the anode, and the system is primed to run again.
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The electrolyte's function
The electrolyte is a critical component of a battery. It is a liquid or paste-like substance, depending on the battery type. However, regardless of the type of battery, the electrolyte serves the same purpose. It is a solution that allows electrically charged particles (ions) to pass between the two terminals (electrodes). By releasing the chemicals required for the reaction, the electrolyte comes in contact with the anode and cathode, converting stored energy into usable electricity.
The electrolyte is electronically insulating, meaning electrons cannot flow through the solution. Electrons must flow through the external circuit. If electrons flow through the solution, the battery is short-circuited. The electrolyte solution must be ionically conductive, allowing charged species to form during redox reactions. The electrolyte functions as a medium for the transfer of positively charged ions between the cathode and anode terminals.
When the battery is in use, there is a continuous flow of electrons through the external circuit and positively charged ions through the electrolyte. If the continuous flow is stopped, the flow of electrons is halted, and the chemical reactions driving the battery cease.
The electrolyte is also important in maintaining electroneutrality. Cations generated through oxidation cause a charge imbalance. The electrolyte moves around to remove the charge imbalance, and a net positive charge is present at the cathode. These cations undergo reduction via the electrons that have passed through the external circuit.
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How electrons flow
The flow of electrons in a battery is a complex process that involves multiple components and chemical reactions. At a fundamental level, the flow of electrons is what defines electricity, and batteries are designed to accept, store, and release this electrical energy.
A battery consists of two electrical terminals, the cathode and the anode, separated by a chemical material called an electrolyte. The cathode is the positive terminal, and the anode is the negative terminal. When a battery is connected to an external circuit, electrons flow from the negative terminal to the positive terminal, attracted by the positive charge. This flow of electrons is what powers the connected device.
Inside the battery, the movement of electrons is facilitated by chemical reactions. At the anode, the electrode reacts with the electrolyte, producing electrons that accumulate at the anode. These electrons then move through the external circuit to the cathode, where another chemical reaction occurs, enabling the electrode to accept the electrons. This movement of electrons increases the chemical potential energy, charging the battery.
When the battery is in use, there is a continuous flow of electrons through the external circuit. If this flow is interrupted, the charges will build up, and the chemical reactions driving the battery will stop. The movement of electrons through the circuit also facilitates the movement of ions through the electrolyte, which helps maintain charge balance within the battery.
While the general flow of electrons is from the negative to the positive terminal, it is important to note that there is no flow of individual free electrons inside the battery. Instead, the movement of electrons occurs via charged chemicals, or ions, which can dissolve off the electrodes. These ions include electrons, so there is still a net flow of electrons within the battery.
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The cathode and anode
The anode and cathode are two of the four key components of a battery, the other two being a separator and an electrolyte. The anode and cathode are the battery's negative and positive electrodes, respectively. They are essential to creating electricity within the battery.
The anode is the negative electrode or terminal of a battery. It is usually made of an oxidizing metal, such as zinc or lithium, which loses electrons, giving it a negative charge. The anode is submerged in an electrolyte solvent, and as electrons move along a conductor to the cathode, the anode slowly erodes. Once the anode is completely eroded, the battery loses its charge.
The cathode is the positive electrode or terminal of a battery. It is an efficient oxidizing agent and is stable when in contact with an electrolyte. Metallic oxides, such as copper oxide, lithium oxide, and graphic oxide, are commonly used as cathode materials due to their helpful working voltage. The cathode receives electrons from the anode, and this flow of electrons is what creates electricity within the battery.
It is important to note that the roles of the anode and cathode switch during the discharge/charge cycle of a battery. During discharge, the positive electrode is the cathode, and the negative electrode is the anode. However, during the charging process, the positive electrode becomes the anode, and the negative electrode becomes the cathode.
The anode and cathode are essential components of a battery, facilitating the flow of electrons and enabling the battery to generate and store electrical energy.
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Charging and recharging
Batteries are a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. They use chemistry, in the form of chemical potential, to store energy. To charge a battery, a device called a battery charger, recharger, or simply charger, is used to store energy in an electric battery by running current through it. The charging protocol depends on the size and type of the battery being charged. Some battery types have high tolerance for overcharging after the battery has been fully charged and can be recharged by connection to a constant voltage source or a constant current source. Simple chargers of this type must be manually disconnected at the end of the charge cycle. Other battery types use a timer to cut off when charging should be complete.
Charging a battery is the opposite of discharging it. When a battery is supplying power, its positive terminal is the cathode and its negative terminal is the anode. The terminal marked negative is the source of electrons. When a battery is connected to an external electric load, the negatively charged electrons flow through the circuit and reach the positive terminal, thus causing a redox reaction by attracting positively charged ions, or cations. When the electrons move from the cathode to the anode, they increase the chemical potential energy, thus charging the battery. Once charged, the battery can be disconnected from the circuit to store the chemical potential energy for later use as electricity.
Different types of rechargeable batteries need charging in different ways, for different times, sometimes using several different methods in turn, which make up what's called the charging algorithm. Pulse charging involves sending intermittent pulses of high current through the battery, with rest periods in between to allow the battery chemicals to absorb the charge. NiCd chargers, for example, often use a primary method called −ΔV (also written negative delta V or NDV, which refers to the slight voltage drop that a NiCd battery shows just after it's fully charged), with a backup timer or temperature-change detector. NiMH chargers are more likely to rely on temperature changes as their primary method with a backup timer cut-off circuit.
There are two main types of chargers used for vehicles: To recharge a fuel vehicle's starter battery, a modular charger is used; typically a 3-stage charger. To recharge an electric vehicle (EV) battery pack, a charging station is used. Chargers for car batteries come in varying ratings. Chargers that are rated up to two amperes may be used to maintain charge on parked vehicle batteries or for small batteries on garden tractors or similar equipment. A motorist may keep a charger rated a few amperes to ten or fifteen amperes for maintenance of automobile batteries or to recharge a vehicle battery that has accidentally discharged. Solar chargers convert light energy into low-voltage DC current. They are generally portable, but can also be fixed mounted. Fixed mount solar chargers are also known as solar panels.
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Frequently asked questions
A battery is a device that stores chemical energy and converts it into electricity.
A battery consists of two terminals made of different chemicals, typically metals, called the anode and the cathode, and a chemical medium called the electrolyte that separates these terminals. When a device is connected to a battery, chemical reactions occur on the electrodes that create a flow of electrical energy to the device.
The chemical reactions in a battery involve the flow of electrons from one material (electrode) to another, through an external circuit. The flow of electrons provides an electric current that can be used to do work.
Primary batteries are designed to be used until they are exhausted of energy and then discarded. Their chemical reactions are generally not reversible, so they cannot be recharged. Secondary batteries, on the other hand, are rechargeable and can be restored by reversing the chemical reactions using an external source of electrical energy.
The electrolyte is a chemical medium that allows the flow of electrical charge between the cathode and anode. It puts the chemicals of the anode and cathode into contact with one another, allowing the conversion of stored chemical energy into electrical energy.
