Fundamentals, page-26

They have been working on commercialising sodium batteries since the '80's. They are about 20% cheaper to produce that a Li battery, but have much lower capacity and discharge rates than Li. They will probably be suitable for fixed installations in the pretty near future, but not suitable for any mobile use with our current knowledge... the price of lithium will start falling I believe in the early '30's, that is why we should be investing in technologies further up the chain, maybe even making batteries. but I think you can forget about sodium batteries for cars in the foreseeable future, unless you have information not readily available ...