Researchers at Cambridge University demonstrated their latest version of what is being called the Lithium-Air battery. It can be more accurately referred to as a Lithium-Oxygen but Air sounds cooler.
The early estimates look pretty impressive with the energy density being 93% efficient which could be up to 10 times the energy density of Lithium-Ion and claims to be rechargeable up to 2,000 times. Recent improvements toward Lithium-Air batteries include a graphene contact and using lithium hydroxide in place of lithium peroxide which increased both stability and efficiency.
Here's the rub: Lithium-Air batteries are still years away from being ready for commercial use. There are still problems with the battery's ability to charge and discharge (kind of a deal breaker if the battery won't charge or discharge right?) There are still issues with safety, performance, efficiency, and the all too apparent need for pure oxygen.