Sand-Based Anode Triples Lithium-Ion Battery Performance 60
Zothecula (1870348) writes "Conventional lithium-ion batteries rely on anodes made of graphite, but it is widely believed that the performance of this material has reached its zenith, prompting researchers to look at possible replacements. Much of the focus has been on nanoscale silicon, but it remains difficult to produce in large quantities and usually degrades quickly. Researchers at the University of California, Riverside have overcome these problems by developing a lithium-ion battery anode using sand."
Re:Correct me if I'm wrong, but... (Score:5, Informative)
1024 mAhg1 is excellent capacity even vs. brand new graphite or amorphous carbon, about 3x as much as graphite's maximum. Silicon's theoretical max is 8-10x that of graphite, but the main problem with it is durability, it tends to tear itself apart on loading. There are silicon anodes in some newer li-ion cells on the market, but the tech is in its infancy.
That said, the real papers you want to be on the lookout for are cathode improvements, there's a lot more potential for volume/mass reduction there than in the anode. But it seems to be a more difficult challenge. Getting a 3x improvement in anode density is absolutely not the same a getting a 3x improvement in battery life.
That said... (Score:5, Informative)
... the greater your capacity, the less cycle life matters. If you want an EV that battery that will run a 250Wh/mi vehicle for an average 20 miles a day for 15 years, then you want it to cycle through about 30MWh. If you use a 100 mile (25kWh) battery pack, then that's 1100 cycles. If you use a 200 mile (50kWh) battery pack, then that's 550 cycles. If you use a 400 mile (100kWh) battery pack, then that's a mere 275 cycles. Actually, the improvement is even better than that in the real world, because the greater your capacity vs. how far you're actually driving, the more you can cycle the cells through a less destructive state of charge range rather than doing deep discharges.
A lot of people picture battery packs in EVs backwards, they think that things like hybrids stress the packs the least, PHEVs moderately, and EVs the worst. But it's reversed. If you look at how big hybrid packs are vs. how much electric range they hold, you'll see that they're disproportionately large, even after you factor in any differences in Wh/kg. The reason is that because hybrid packs get cycled so much, they have to keep the cycling in a very narrow state of charge range, only allowing shallow discharges. So if you only have a narrow discharge range, you have to make your pack bigger to make up for it. EVs can discharge through much more of their pack because they need fewer total cycles and only rarely go down toward the lower end of their allowable discharge range. Some EVs also let you limit the max that your pack charges up to to further extend lifespan (it's usually destructive both to use the very top end and the bottom end of the discharge range).