Editing Lithium polymer battery (section)

== Safety and robustness ==
{{main|Lithium-ion battery#Safety}}
[[File:Expanded lithium-ion polymer battery from an Apple iPhone 3GS.jpg|thumb|Apple [[iPhone 3GS]]'s Lithium-ion battery, which has expanded due to a short-circuit failure]]
[[File:NASA Lithium Ion Polymer Battery.jpg|thumb|An experimental lithium-ion polymer battery made by Lockheed Martin for NASA]]

All Li-ion cells expand at high levels of [[state of charge]] (SOC) or overcharge due to slight vaporisation of the electrolyte. This may result in [[delamination]] and, thus, bad contact with the internal layers of the cell, which in turn diminishes the reliability and overall cycle life.<ref name="ageing"/> This is very noticeable for LiPos, which can visibly inflate due to the lack of a hard case to contain their expansion. Lithium polymer batteries' safety characteristics differ from those of [[Lithium iron phosphate battery#Safety|lithium iron phosphate batteries]].

Unlike lithium-ion cylindrical and prismatic cells, with a rigid metal case, LiPo cells have a flexible, foil-type (polymer [[laminate]]) case, so they are relatively unconstrained. Moderate pressure on the stack of layers that compose the cell results in increased capacity retention, because the contact between the components is maximised and [[delamination]] and deformation is prevented, which is associated with increase of cell impedance and degradation.<ref name="ageing">{{cite journal |journal=Journal of Power Sources |volume=147 |issue=1–2 |date=9 September 2005 |pages=269–281 |title=Ageing mechanisms in lithium-ion batteries |last1=Vetter |first1=J. |last2=Novák |first2=P. |last3=Wagner |first3=M.R. |last4=Veit |first4=C. |doi=10.1016/j.jpowsour.2005.01.006|bibcode=2005JPS...147..269V }}</ref><ref name="pressure">{{cite journal |journal=Journal of Power Sources |volume=245 |date=1 January 2014 |pages=745–751 |title=Stress evolution and capacity fade in constrained lithium-ion pouch cells |last1=Cannarella |first1=John |last2=Arnold |first2=Craig B. |doi=10.1016/j.jpowsour.2013.06.165|bibcode=2014JPS...245..745C }}</ref>