A battery is a device consisting of one or more electrochemical cells that converts chemical energy into electrical energy. Its reactions supply current through an external circuit to power equipment. Primary batteries are designed for single use; secondary batteries can be recharged by an external electrical supply. Batteries range from miniature cells in watches to large installations supporting electricity networks. Their performance depends on their chemistry, construction, and operating conditions. (openstax.org)
Operating principle
Battery operation is an application of electrochemistry. Each cell contains two electrodes in contact with an electrolyte, which conducts ions. During discharge, a spontaneous oxidation–reduction reaction releases useful electrical energy: oxidation at the negative electrode supplies electrons, while reduction at the positive electrode consumes them. Electrons travel through the external circuit, and ionic movement inside the cell maintains charge balance. A separator prevents direct electrode contact while permitting ionic transport. (openstax.org)
During discharge, the negative electrode is the anode and the positive electrode is the cathode. Strictly, these terms identify oxidation and reduction, respectively, so their electrochemical roles reverse during charging. Battery engineering nevertheless commonly retains the discharge-based names for the physical electrodes. Charging drives the overall chemical reaction in the reverse direction, restoring much of the cell’s chemical energy; unwanted reactions prevent perfect reversibility and eventually degrade performance. (openstax.org)
Historical development
Alessandro Volta introduced the voltaic pile in 1800. Stacked dissimilar metal plates separated by electrolyte-soaked material provided a sustained current, establishing a practical source for electrical experiments. Unlike earlier devices that accumulated static charge, the pile continuously converted chemical energy into electrical output. (aps.org)
The lead–acid battery, invented in 1859, established rechargeable storage as a practical technology. Later developments included nickel–cadmium batteries and improved portable cells. Commercial lithium-ion batteries entered the market in 1991, enabling lightweight rechargeable power sources for electronics and vehicles. The development of lithium-ion technology was recognized by the 2019 Nobel Prize in Chemistry, awarded jointly to John B. Goodenough, M. Stanley Whittingham, and Akira Yoshino. (nobelprize.org)
Types and chemistries
Primary batteries are not designed for repeated electrical recharging. Examples include zinc–carbon, alkaline, silver-oxide, and lithium-metal cells. An alkaline battery commonly uses zinc and manganese dioxide with an alkaline electrolyte. Primary batteries serve applications ranging from remote controls to watches and smoke detectors. “Lithium battery” does not necessarily mean rechargeable: lithium-metal primary cells differ from conventional lithium-ion secondary cells. (openstax.org)
Secondary batteries use reactions that can be reversed sufficiently for repeated charging. Lead–acid batteries employ lead-based electrodes and sulfuric acid and are widely used for vehicle starting and backup power. Nickel–cadmium and nickel–metal hydride are other rechargeable families. Lithium-ion cells move lithium ions between host materials; many use graphite negative electrodes and lithium-containing positive electrodes. Chemistry selection involves trade-offs among energy storage, power, durability, cost, and safety rather than a universally superior design. (openstax.org)
A flow battery stores active substances in external electrolyte tanks and circulates them through a cell stack. Tank size and stack size can therefore influence energy capacity and power separately. A solid-state battery uses a solid electrolyte instead of a conventional liquid electrolyte; this changes material requirements and may offer performance or safety advantages, depending on the complete design. (energy.gov)
Construction and performance
Cells may have cylindrical, prismatic, or pouch packaging. Multiple cells form modules and packs, with series connections increasing voltage and parallel connections increasing available capacity. Packaging, current collectors, separators, and other inactive components contribute weight and volume, so a complete pack differs from its active materials alone. (epa.gov)
Important specifications include:
- Voltage: the potential difference between terminals; nominal voltage is a reference value rather than a constant operating voltage.
- Capacity: deliverable electric charge, commonly expressed in ampere-hours.
- Energy capacity: electrical energy available under specified conditions, usually expressed in watt-hours.
- Specific energy and energy density: energy per unit mass and per unit volume.
- C-rate: current normalized to rated capacity; 1C corresponds nominally to a one-hour discharge.
- Cycle life: the number of charge–discharge cycles completed before a specified performance threshold is reached.
These quantities depend on test conditions, including current, cutoff voltage, depth of discharge, and temperature. Capacity in ampere-hours alone cannot establish energy content without voltage information. (mit.edu)
Applications, degradation, and safety
Batteries power portable electronics, tools, vehicles, and emergency systems. Stationary installations support the electrical grid and shift electricity from renewable sources between generation and consumption periods. Batteries store energy rather than create it, and storage inevitably involves losses. (energy.gov)
Repeated operation changes electrode structures and electrolyte chemistry, reducing capacity or increasing resistance. A battery management system monitors quantities such as voltage, current, and temperature and controls operation within specified limits. Some failures can cause thermal runaway, an escalating event that may produce intense heat, gas, smoke, or fire. Monitoring and protective controls reduce certain risks but cannot eliminate every internal cell failure. (energy.gov)
End-of-life management depends on chemistry. Recycling can recover valuable materials and reduce demand for newly extracted resources. Lithium-ion processing generally involves collection, identification, sorting, and specialized treatment; damaged or improperly handled batteries can also create fire hazards in waste-management systems. (epa.gov)