li-ion battery life

PR blasts about supposed innovation in battery design pour into ET’s mailbox like water into the Titanic, but a recent story about an MIT grad who founded a battery company is worth paying attention to. Qichao Hu is the CEO of SolidEnergy, a company that’s been working to improve lithium-ion energy density for the past five years.

The problem with lithium-ion is that whether you measure by energy per kilogram or energy per unit weight, Li-ion batteries aren’t very good. The graph below also illustrates why fossil fuels are so difficult to replace. It’s not just because they pack a relatively high amount of energy — though they do — but because fuels like ethanol, kerosene, gasoline, and diesel are stable at room temperature and pressure (even if you need to keep a lid on them) and don’t require specialized storage or pumping procedures. Lithium-ion batteries, meanwhile, are the tiny dot at the bottom-left side of the graph. Anything that can bump them upwards or outwards is therefore an improvement and Hu thinks he has the answer.

 Li-ion batteries

SolidEnergy’s technology works by substituting a thin lithium foil for the larger anode used in most lithium-ion batteries. This solves one problem, by shrinking the battery form factor by ~50 percent, but it creates others. As originally designed, the battery only worked above 80C, which makes it a non-starter for most commercial applications. Pang appears to have solved this problem by adding phosphorous and sulfur to the electrolyte, which forms a thin shield over the lithium metal electrode, protecting it from forming dendrites under use. According to Hu, “Combining the solid coating and new high-efficiency ionic liquid materials was the basis for SolidEnergy on the technology side.”

 Lithium-ion batteries

Will we see this technology come to market any time soon? I don’t know, but if it performs as advertised, we may. Battery capacity is the biggest single problem in many device designs; lithium-ion energy capacity has not nearly kept pace with device hunger. Removing the anode gives such a capacity boost, it could be a net positive even if the first commercial designs are below the predicted energy density.

There’s no word on how hard it is to build these structures, but they don’t appear to rely on expensive metals (another plus), and there’s nothing particularly expensive about sulfur or phosphorous. None of this proves we’ll be packing smartphones with 2x the battery life in a year or two, but there seem to be fewer barriers to commercial introduction for SolidEnergy than we’ve seen in the past.