More on Boston Power’s lithium ion battery

After reading Lithium-ion batteries prepare to take a giant leap forward, a helpful reader (thanks, Rich!) pointed out the excellent article that ran in the March IEEE Spectrum on battery entrepreneur and Boston Power founder Christina Lampe-Onnerud, The Lady and the li-ion. The article has a good explanation of Boston Power’s Sonata serial battery pack architecture:

“[Laptop battery packs] consist of six cylindrical cells, arranged as pairs wired in parallel, with three sets of parallel cells wired in series. Lampe-Onnerud sketched out a design with three rectangular cells instead, each filling the space of two cylindrical cells, all wired in a series. … In the [traditional] parallel laptop battery, current is supposed to flow through the parallel paths at exactly the same rate. But slight temperature differences or tiny chemical imbalances between the two paths force more current into one of them. Over time, the current imbalance between the cells can go to an extreme that forces bits of lithium metal to adhere to the anode. When this happens, the battery is able to store less energy than it is designed to store, meaning a shorter computer run time per charge. And because lithium metal is highly reactive, those scattered bits of metal can fuel a fire if a short crops up and suddenly raises the temperature of the system.”

Lampe-Onnerud also went into detail in our conversation about the importance of controlling side chemical reactions in the cells. Unfortunately, I was able to use her description in the short 500-word EDN article, so here it is for further background on the Boston Power battery’s “secret sauce”:

"[The Sonata’s superior performance and increased cycle life] is because we have changed the cathode and fine-tuned the anode and the electrolyte. In a battery you have about 50 chemicals, and those chemicals are either inert or active. So if you can fine-tune the electrochemical reactions happening in parallel with [the purely] chemical reactions to only be useful reactions, you basically win. It sounds easy, but it’s proved to be very difficult. What we have done is fine-tune cobalt and manganese on the cathode with graphite on the anode. And we have carefully picked the inert chemical because the truth is there are really no inert chemicals — They are all somewhat reactive. But in the voltage window where we are, they have very, very limited activity, and that’s why we get the high cycle life."

Note that Lampe-Onnerud doesn’t claim any incredible chemical breakthrough, just grinding-it-out, careful tweaking of the already-known lithium ion formulation. Which gives you pause about all the attention placed on lithium ion batteries in plug-in hybrid autos: lithium ion batteries are no silver bullet. However, careful design and matching of battery cell characteristics to the application power-use curves can get us farther down the path. Take note, if you’re going after McCain’s $300M prize.