22 January 2009

Misplaced Priorities

So the Securities Exchange Commission is said to be probing Apple over accusations that they may have misled the public over the state of Steve Jobs' health.

Let's play a word association game:
Pancreatic cancer
Corporate executive
One can imagine that if Jobs had cancer in the Islets of Langerhans, the portion of the pancreas responsible for insulin regulation, that yes, he might have some diabetic-like health issues associated with that. Doesn't the SEC have something better to do? E.g. meanwhile we learn that Merrill-Lynch maneuvered to deliver $3 billion inbonuses before being bought-out by Bank of America. Merrill-Lynch lost over $20 billion in that quarter, and BoA is demanding that it be bailed out by the US taxpayer now for the same amount. This idea that financial companies need to pay out bonuses to retain "top talent" during a period when the financial sector is undergoing a severe contraction is a canard. Where are they going to go work, the construction industry?

20 January 2009

Bitumen-producer Suncor Posts Significant Loss

Via Nathan Vanderklippe at the Globe and Mail, we learn that Suncor, one of the original and bigger oil sands producers, has posted a C$215 million loss for the 4th quarter of 2008.

The price of oil has fallen since then. I don't imagine the other producers will be doing much better, although Suncor does burn the least amount of natural gas and predominately runs an open-pit mine to the best of my knowledge. As I've pointed out previously, the marginal cost-of-production for synthetic crude from bitumen is around $50/bbl. The article is claiming it's more like $36/bbl although that may not include refining. If the oil sands of Alberta shut down due to extended low prices, that's approximately $1.3 million barrels per day taken off the market.

07 January 2009

Column-like Films of Silicon for Battery Applications

About a year-ago I relayed the story of Chan's work on using silicon nanowires as a potential anode material for Lithium-ion batteries. Silicon can store some ten-times more charge than Carbon, the current industry standard, but this comes at the expense of a huge volume change. The difference in volume between charged and uncharged is 300 % for Si. Just to give you an idea, the alloy of Lithium and Silicon that's formed is Li14Si4 from metallic Si. The article from Nature Nano suggested that forming the silicon into high aspect-ratio wires would allow the silicon freedom to expand along the long-axis of the wire and hence be less likely to physically break and no longer have a physical, conductive pathway to the anode.

In general, the lifetime of a battery is determined by how great of a volume change it undergoes when cycling from the charged to uncharged state and vice versa. Volume changes imply stress and the gradual introduction of defects that can trap electrons and reduce electrical conductivity. For LiFePO4 cathodes, the volume change is around 4-7 %, but this is a crystalline material. Silicon nanowires are amorphous (i.e. poorly ordered) and the introduction of defects on cycling is not necessarily an issue.

The previous work was truly proof of principal, but unlikely for variety of reasons to be a direct path to commercialization. There's some new work out by a local group that expands on the work of Chen. Fleischeur et al. tried their specialty, glancing angle vapour deposition, to form a thin-film of Silicon composed of many, regular pillars. (Disclosure: our research group collaborates with the group that did this research. I personally do not, however.) In glancing angle deposition, the substrate (onto which the film is deposited) is at nearly right angles to the incoming vapour stream. In thin film deposition, one tends to see small clusters form first due to surface tension. As the clusters grow, they amalgamate together and form a (porous) solid thin film. When the substrate is at high angles of incidence, the first clusters to form shadow any smaller trees and grab more than their fair share of the incoming mass stream. Hence glancing-angle deposition typically forms column-like thin films.

The glancing-angle fabrication method has a number of potential advantages over Chan's technique:
  1. Chan's thin film process relied on a gold catalyst ($$$), whereas the GLAD process only requires a thin layer of chromium for adhesion on Si substrate and none at all on a stainless steel substrate.
  2. Glancing-angle deposition can easily control the spacing of pillars by patterning the substrate.
  3. The glancing-angle films were "robust" when I asked the author about it. He said hitting the batteries with a hammer had no effect on performance, so presumably the pillars were not breaking.
  4. Glancing-angle deposition requires a microscopically smooth surface for proper column formation.
Let's look at some results. The question is, how durable are these anodes compared to graphite? The charge curve is really all we are interested in.

Figure 1: Chan et al. charge capacity after 10 total cycles.
Figure 2: Fleischauer et al. charge capacity after cycling up to cycle 70. I don't recall the reason for the discontinuities but I vaguely recall it had something to do with the test electronics.

Both authors show a very large drop in charge capacity after the first recharge. This means there is some sort of irreversible change to the material occuring from film fabrication to charged and uncharged Si. Then there is a progressive loss in capacity. Evidently Chan and company are less confident in their material as they are only showing results up to ten cycles. Average capacity fade for Fleischeur's battery was found to be 0.3 % per cycle. If we extrapolate, that would imply it would take approximately 750 cycles for the charge capacity of the silicon anode to drop below that of a conventional graphite one. Obviously, that's not good enough for commercial applications.

Overall, I think that this is an important step in terms of fabrication and longevity. We are still looking at a minimum of a decade before any such silicon Li-ion batteries hit the shelves; this is progress on that path.