Editing Energy storage (section)

==== Capacitor ====
{{Main|capacitor}}
[[File:Mylar-film oil-filled low-inductance capacitor 6.5 MFD @ 5000 VDC.jpg|thumb|175px|right|This mylar-film, oil-filled capacitor has very low inductance and low resistance, to provide the high-power (70 megawatts) and the very high speed (1.2 microsecond) discharges needed to operate a [[dye laser]].]]

A [[capacitor]] (originally known as a 'condenser') is a [[passivity (engineering)|passive]] [[terminal (electronics)|two-terminal]] [[electronic component|electrical component]] used to store [[energy]] [[electrostatic]]ally. Practical capacitors vary widely, but all contain at least two [[electrical conductor]]s (plates) separated by a [[dielectric]] (i.e., [[insulator (electricity)|insulator]]). A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary [[Battery (electricity)|battery]], or like other types of [[rechargeable energy storage system]].<ref name="Miller" /> Capacitors are commonly used in electronic devices to maintain power supply while batteries change. (This prevents loss of information in volatile memory.) Conventional capacitors provide less than 360 [[joule]]s per kilogram, while a conventional [[alkaline battery]] has a density of 590 kJ/kg.

Capacitors store [[energy]] in an [[electric field|electrostatic field]] between their plates. Given a [[potential difference]] across the conductors (e.g., when a capacitor is attached across a battery), an [[electric field]] develops across the dielectric, causing positive charge (+Q) to collect on one plate and negative charge (-Q) to collect on the other plate. If a battery is attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if an accelerating or alternating voltage is applied across the leads of the capacitor, a [[displacement current]] can flow. Besides capacitor plates, charge can also be stored in a dielectric layer.<ref>{{cite journal|last1=Bezryadin|first1=A.|last2=et.|first2=al.|title=Large energy storage efficiency of the dielectric layer of graphene nanocapacitors|journal=Nanotechnology|date=2017|volume=28|issue=49|pages=495401|doi=10.1088/1361-6528/aa935c|pmid=29027908|arxiv=2011.11867|bibcode=2017Nanot..28W5401B|s2cid=44693636}}</ref>

Capacitance is greater given a narrower separation between conductors and when the conductors have a larger surface area. In practice, the dielectric between the plates emits a small amount of [[leakage (electronics)|leakage current]] and has an electric field strength limit, known as the [[breakdown voltage]]. However, the effect of recovery of a dielectric after a high-voltage breakdown holds promise for a new generation of self-healing capacitors.<ref>{{cite journal|last1=Belkin|first1=Andrey|last2=et.|first2=al.|title=Recovery of Alumina Nanocapacitors after High Voltage Breakdown|journal=Sci. Rep.|volume=7|issue=1|pages=932|date=2017|doi=10.1038/s41598-017-01007-9|pmid=28428625|pmc=5430567|bibcode=2017NatSR...7..932B}}</ref><ref>{{cite journal|last1=Chen|first1=Y.|last2=et.|first2=al.|date=2012|title=Study on self-healing and lifetime characteristics of metallized-film capacitor under high electric field.|journal=IEEE Transactions on Plasma Science|volume=40|issue=8|pages=2014–2019|doi=10.1109/TPS.2012.2200699|bibcode=2012ITPS...40.2014C|s2cid=8722419}}</ref> The conductors and [[Lead (electronics)|lead]]s introduce undesired [[Equivalent series inductance|inductance]] and [[Equivalent series resistance|resistance]].

Research is assessing the quantum effects of [[Nanoscopic scale|nanoscale]] capacitors<ref>{{cite journal|last1=Hubler|first1=A.|last2=Osuagwu|first2=O.|title=Digital quantum batteries: Energy and information storage in nanovacuum tube arrays|journal=Complexity|date=2010|volume=15|issue=5 |pages=48–55|doi=10.1002/cplx.20306|doi-access=free}}</ref> for digital quantum batteries.<ref name="TechReview-2009.12.21" /><ref name="Complexity-Vol14.Iss3" />