Editing Energy storage (section)

=== Electrochemical ===

==== Rechargeable battery ====
[[File:Datacenter Backup Batteries.jpg|thumb|A rechargeable battery bank used as an [[uninterruptible power supply]] in a data center<ref>{{Cite web |title=Microsoft datacenter batteries to support growth of renewables on the power grid |url=https://news.microsoft.com/source/features/sustainability/ireland-wind-farm-datacenter-ups/ |access-date=2025-04-24 |website=Source |language=en-US}}</ref><ref>{{Cite web |title=What is an Uninterruptible Power Supply - Definition from TechTarget.com |url=https://www.techtarget.com/searchdatacenter/definition/uninterruptible-power-supply |access-date=2025-04-24 |website=Search Data Center |language=en}}</ref>]]
{{Main|Rechargeable battery|Battery storage power station}}

A rechargeable battery comprises one or more [[electrochemical cell]]s. It is known as a 'secondary cell' because its [[electrochemistry|electrochemical]] [[chemical reaction|reactions]] are electrically reversible. Rechargeable batteries come in many shapes and sizes, ranging from [[Button cell#Rechargeable variants|button cell]]s to megawatt grid systems.

Rechargeable batteries have lower total cost of use and environmental impact than non-rechargeable (disposable) batteries. Some rechargeable battery types are available in the same form factors as disposables. Rechargeable batteries have higher initial cost but can be recharged very cheaply and used many times.

Common rechargeable battery chemistries include:
* [[Lead–acid battery]]: Lead acid batteries hold the largest market share of electric storage products. A single cell produces about 2V when charged. In the charged state the metallic lead negative electrode and the [[lead sulfate]] positive electrode are immersed in a dilute [[sulfuric acid]] (H<sub>2</sub>SO<sub>4</sub>) [[electrolyte]]. In the discharge process electrons are pushed out of the cell as lead sulfate is formed at the negative electrode while the electrolyte is reduced to water.
** Lead–acid battery technology has been developed extensively. Upkeep requires minimal labor and its cost is low. The battery's available energy capacity is subject to a quick discharge resulting in a low life span and low energy density.<ref>{{cite journal |last1=Yao |first1=L. |last2=Yang |first2=B. |last3=Cui |first3=H. |last4=Zhuang |first4=J. |last5=Ye |first5=J. |last6=Xue |first6=J. |title=Challenges and progresses of energy storage technology and its application in power systems |journal=Journal of Modern Power Systems and Clean Energy |volume=4 |issue=4 |date=2016 |pages=520–521 |doi=10.1007/s40565-016-0248-x |doi-access=free }}</ref>
* [[Nickel–cadmium battery]] (NiCd): Uses [[nickel oxide hydroxide]] and metallic [[cadmium]] as [[electrode]]s. Cadmium is a toxic element, and was banned for most uses by the European Union in 2004. Nickel–cadmium batteries have been almost completely replaced by nickel–metal hydride (NiMH) batteries.
* [[Nickel–metal hydride battery]] (NiMH): First commercial types were available in 1989.<ref name="Aifantis et al" /> These are now a common consumer and industrial type. The battery has a hydrogen-absorbing [[alloy]] for the negative [[electrode]] instead of [[cadmium]].
* [[Lithium-ion battery]]: The choice in many consumer electronics and have one of the best [[specific energy|energy-to-mass ratios]] and a very slow [[self-discharge]] when not in use.
* [[Lithium-ion polymer battery]]: These batteries are light in weight and can be made in any shape desired.
* [[Aluminium]]-[[sulfur]] battery with rock salt crystals as electrolyte: aluminium and sulfur are Earth-abundant materials and are much more cheaper than traditional Lithium.<ref>{{cite web|url=https://news.mit.edu/2022/aluminum-sulfur-battery-0824|title=A new concept for low-cost batteries|date=August 24, 2022|author=David L. Chandler}}</ref>

===== Flow battery =====
{{Main|Flow battery|Vanadium redox battery}}

A [[flow battery]] works by passing a solution over a membrane where ions are exchanged to charge or discharge the cell. [[Electrode potential#Potential difference of a cell assembled of two electrodes|Cell voltage]] is chemically determined by the [[Nernst equation]] and ranges, in practical applications, from 1.0 V to 2.2 V. Storage capacity depends on the volume of solution. A flow battery is technically akin both to a [[fuel cell]] and an [[electrochemical cell|electrochemical accumulator cell]]. Commercial applications are for long half-cycle storage such as backup grid power.

==== Supercapacitor ====
[[File:Expo 2010 Electric Bus.jpg|thumb|One of a fleet of [[capa vehicle|electric capabuses]] powered by supercapacitors, at a quick-charge station-bus stop, in service during [[Expo 2010|Expo 2010 Shanghai China]]. Charging rails can be seen suspended over the bus.]]
{{main|Supercapacitor}}

[[Supercapacitor]]s, also called electric double-layer capacitors (EDLC) or ultracapacitors, are a family of [[electrochemical capacitor]]s<ref name="Conway" /> that do not have conventional solid [[dielectric]]s. [[Capacitance]] is determined by two storage principles, double-layer capacitance and [[pseudocapacitance]].<ref name="Halper" /><ref name="Frackowiak1" />

Supercapacitors bridge the gap between conventional capacitors and [[Rechargeable battery|rechargeable batteries]]. They store the most energy per unit volume or mass ([[energy density]]) among capacitors. They support up to 10,000 [[farads]]/1.2 Volt,<ref name="Elton" /> up to 10,000 times that of [[electrolytic capacitor]]s, but deliver or accept less than half as much power per unit time ([[power density]]).<ref name="Conway" />

While supercapacitors have specific energy and energy densities that are approximately 10% of batteries, their power density is generally 10 to 100 times greater. This results in much shorter charge/discharge cycles. Also, they tolerate many more charge-discharge cycles than batteries.

Supercapacitors have many applications, including:
* Low supply current for memory backup in [[static random-access memory]] (SRAM)
* Power for cars, buses, trains, cranes and elevators, including energy recovery from braking, short-term energy storage and burst-mode power delivery