Technology Review has an article on "Nanowire anodes [which] could let lithium-ion batteries run twice as long" - More Energy in Batteries.
A start-up based in Menlo Park, CA, plans to sell a new type of anode for lithium-ion batteries that, the company says, will let electric vehicles travel farther and mobile devices last longer without a recharge. Amprius' lithium-ion anodes are made of silicon nanowires, which can store 10 times more charge than graphite, the material used for today's lithium-ion battery anodes. According to the company, electric vehicles that run 200 miles between charges could go 380 miles on its batteries, and laptops that have four hours of run time could last for seven hours between charges.
While other advanced battery companies are focused on power, which makes for fast charging and zippy acceleration, Amprius is trying to improve energy density, which enables longer run times. The more total energy a battery can store, the longer it can power a car or a phone between charges. As vehicle manufacturers look toward electric cars, and as mobile devices like iPhones run more energy-intensive applications, a battery's energy density, and thus the time it can go without a recharge, becomes a more pressing issue.