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Lithium peroxide
	; __ Li+ __ O−
Names
	IUPAC name Lithium peroxide
	Other names Dilithium peroxide; Lithium(I) peroxide
Identifiers
CAS Number	12031-80-0 ;
3D model (JSmol)	Interactive image;
ChemSpider	23787 ;
ECHA InfoCard	100.031.585
PubChem CID	25489;
UNII	9ANX556R5F ;
CompTox Dashboard (EPA)	DTXSID7065178 ;
	InChI InChI=1S/2Li.O2/c;;1-2/q2+1;-2 Key: HPGPEWYJWRWDTP-UHFFFAOYSA-N ; InChI=1/2Li.O2/c;;1-2/q2+1;-2 Key: HPGPEWYJWRWDTP-UHFFFAOYAV;
	SMILES [Li+].[Li+].[O-][O-];
Properties
Chemical formula	Li2O2
Molar mass	45.885 g/mol
Appearance	fine, white powder
Odor	odorless
Density	2.32 g/cm3
Melting point	Decomposes to Li2O at ~450°C but melts at 197°C
Boiling point	NA
Solubility in water	soluble[vague]
Structure
Crystal structure	hexagonal
Thermochemistry
Std enthalpy of; formation (ΔfH⦵298)	-13.83 kJ/g
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H271, H272, H314
Precautionary statements	P210, P220, P221, P260, P264, P280, P283, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P306+P360, P310, P321, P363, P370+P378, P371+P380+P375, P405, P501
NFPA 704 (fire diamond)	3 0 2 OX
Related compounds
Other cations	Sodium peroxide; Potassium peroxide; Rubidium peroxide; Caesium peroxide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Lithium peroxide is the inorganic compound with the formula Li₂ O₂. Lithium peroxide is a white solid, and unlike most other alkali metal peroxides, it is nonhygroscopic. Because of its high oxygen:mass and oxygen:volume ratios, the solid has been used to remove CO₂ from and release O₂ to the atmosphere in spacecraft.^[4]

Preparation

It is prepared by the reaction of hydrogen peroxide and lithium hydroxide. This reaction initially produces lithium hydroperoxide:^[4]^[5]

LiOH + H₂O₂ → LiOOH + H₂O

This lithium hydroperoxide may exist as lithium peroxide monoperoxohydrate trihydrate (Li₂O₂·H₂O₂·3H₂O). Dehydration of this material gives the anhydrous peroxide salt:

2 LiOOH → Li₂O₂ + H₂O₂

Li₂O₂ decomposes at about 450 °C to give lithium oxide:

2 Li₂O₂ → 2 Li₂O + O₂

The structure of solid Li₂O₂ has been determined by X-ray crystallography and density functional theory. The solid features eclipsed "ethane-like" Li₆O₂ subunits with an O-O distance of around 1.5 Å.^[6]

Uses

Air Purification

It is used in air purifiers where weight is important, e.g., spacecraft or other sealed spaces and apparatuses to absorb carbon dioxide and release oxygen in the reaction:^[4]

Li₂O₂ + CO₂ → Li₂CO₃ + 1⁄2 O₂

Similar to the reaction of lithium hydroxide with carbon dioxide to release 1 Li₂CO₃ and 1 H₂O, lithium peroxide has high absorption capacity and absorbs more CO₂ than does the same weight of lithium hydroxide and offers the bonus of releasing oxygen instead of water. ^[7]

Polymerization of Styrene

Lithium peroxide can also act as a catalyst for polymerization of styrene to polystyrene. The polymerization of styrene to polystyrene typically involves the use of radical initiators via the free radical chain mechanism but lithium peroxide can also initiate radical polymerization reactions under certain conditions, although not as widely used.

Lithium-air Battery

The reversible lithium peroxide reaction is the basis for a prototype lithium–air battery. Using oxygen from the atmosphere allows the battery to eliminate storage of oxygen for its reaction, saving battery weight and size.^[8]

References

^ "Physical Constants of Inorganic Compounds," in CRC Handbook of Chemistry and Physics, 91st Edition (Internet Version 2011), W. M. Haynes, ed., CRC Press/Taylor and Francis, Boca Raton, Florida. (pp: 4-72).
^ Speight, James G. (2005). Lange's Handbook of Chemistry (16th Edition). (pp: 1.40). McGraw-Hill. Online version available at: http://www.knovel.com/web/portal/browse/display?_EXT_KNOVEL_DISPLAY_bookid=1347&VerticalID=0
^ Phys.Chem.Chem.Phys.,2013,15, 11025. doi:10.1039/c3cp51056e
^ ^a ^b ^c Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 98. ISBN 978-0-08-022057-4.
^ E. Dönges "Lithium and Sodium Peroxides" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 979.
^ L. G. Cota and P. de la Mora "On the structure of lithium peroxide, Li₂O₂" Acta Crystallogr. 2005, vol. B61, pages 133-136. doi:10.1107/S0108768105003629
^ Ulrich Wietelmann, Richard J. Bauer "Lithium and Lithium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH: Weinheim. doi:10.1002/14356007.a15_393.pub2
^ Girishkumar, G.; B. McCloskey; AC Luntz; S. Swanson; W. Wilcke (July 2, 2010). "Lithium- air battery: Promise and challenges". The Journal of Physical Chemistry Letters. 1 (14): 2193–2203. doi:10.1021/jz1005384.