The pressure I cc of LN2 encapsulated at -196dC will rise to on warming to ambient T is c3,000bar. About half experienced in a gun barrel.
If 10cc of LN2 the capsule could be made of SS and not be bulky.
But what materials could best be used to make a 50 Kg tank, burst strength 125%. Titanium, PEEK, CCTs, Graphene, Kevlar, 'spiders web' some or all laminated???