Looking beyond lithium-ion, what’s next for EV batteries?
Consumer Reports News: November 07, 2011 09:08 AM
Lithium-ion batteries are considered the silver bullet to making electric cars possible. But what kind of lithium-ion batteries? Battery and automakers all tout their own proprietary varieties as superior. So which ones are best?
We interviewed Seth Fletcher, an editor with Popular Science magazine, who literally wrote the book on the subject: “Bottled Lightning, Superbatteries, electric cars, and the New Lithium Economy” to better understand the lithium landscape.
The key technology today, according to Fletcher, is the chemical makeup of the anode, or the positive electrode in lithium batteries. Here are the various battery types and how they lay out in the lithium battery landscape:
The first-generation lithium batteries are made from lithium-cobalt oxide. These are the batteries widely used in consumer electronics today, and they were used in the pioneering Tesla Roadster. These batteries have good power, but they are less stable than other kinds. On a few occasions, they have been cited as causing laptops to burst into flames. Tesla went to great lengths to design a battery pack that isolates the risk of individual cells experiencing such thermal runaway, and thus far there have been no reports of batteries in these cars suffering such a meltdown. While lithium-cobalt oxide batteries are readily available, commercial versions are not set up for cars. For example, those in the Tesla Roadster are cylindrical, Fletcher says, so they take up much more room than flat, rectangular cells. They are mainly made by Sony.
The second-generation lithium batteries, developed for the Chevrolet Volt, are made of lithium-manganese oxide. General Motors chose this chemical combination because it is more stable than lithium-cobalt oxide, limiting the company’s potential liabilities. But lithium-manganese stores less energy, which limits the range of electric cars. In partnership with GM, the lithium-manganese batteries for the Volt are made by Korean manufacturing giant LG.
The third-generation lithium-based batteries use lithium-iron phosphate chemistry. The advantage is that they’re inherently very stable, Fletcher says. But they have even less energy density than lithium-manganese. The primary manufacturer of lithium-iron phosphate batteries is an American company, A123 Systems, and this battery type is commonly used in power tools. A123 is involved in a patent dispute with Hydro Quebec and the University of Texas over the technology.
The next-generation lithium batteries, Fletcher says, builds on lithium manganese oxide, and mixes in elements of nickel and cobalt. A substance dubbed NMC (nickel manganese cobalt) is added to the basic lithium manganese oxide formula in varying concentrations to boost the energy capacity. Fletcher expects to see increasing amounts of NMC blended into lithium-manganese batteries to boost energy density and range for electric cars, and to lower prices.
Future developments, Fletcher says, may come from altering the chemistry in the cathode or the battery’s negative electrode. Fletcher says Panasonic, which is building the battery for the upcoming Tesla Model S, is now experimenting with a new silicon-alloy cathode technology that it believes may store more energy.
Ultimately, Fletcher says, the Holy Grail of lightweight, powerful, and affordable batteries is lithium air—when lithium is combined with oxygen. That’s where the development of modern lithium batteries may be leading, says Fletcher.
Other companies, including Toyota, have told us they’re working on batteries from magnesium, zinc, and other metals, which they think may eventually supercede lithium. But Fletcher cautions that it takes 20 years for new battery technology to develop. So lithium battery technology, its advantages and inherent compromises, are likely to remain relevant for a very long time.
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