Lengthy, but without apologies
Quote:
Originally Posted by wdb
This isn't a chemistry breakthrough, it's a mechanical breakthrough...
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This is exactly the point. The advances apparently come from the rectilinear three dimensional matrix structure of the anode, itself a major advancement. (Thinking about the manufacturing process, I have to wonder just how they do it.)
One year ago I purchased what was essentially a deeply factory discounted Think City EV. -- $22.5K vs.~$32.5K. Before I did so I spent a great deal of time doing research on the cars lithium titanate battery which was said to be the most advanced and safest EV battery then on the market. I wondered, Why? I was also motivated by the fact that both ThinkUSA and the organizational element of EnerDel that was formed specifically to build the Think EV battery had declared bankruptcy!
Below is a summary of the info I found at that time. It comes from multiple sites on the Inter-web. Clearly, I am not an expert, just an interested, educated to the best of my limited abilities lithium-ion battery user.
Lithium-ion battery charge/discharge rates have to do with the lithium-ion chemistry and cathode/anode materials and structure... and heat whether from environmental conditions -- think LEAFs in Arizona -- or heat generated in discharging the battery. IIRC, there are 4 or 5 different lithium-ion battery (anode) chemistries.
There are different electrolyte chemistries, and for the most part it is difficult to determine what they are. It may not matter much though because once there is electrolyte breakdown, due to "overheating" which can occur at ~120 degF, the battery is ruined. The electrolyte is typically a jell contained in the thin plastic film separating the anodes and cathodes.
The different lithium-ion battery types typically refer to the anode material. In all cases the anode and cathode are not made from the same material. As I understand it, of the two the anode is the more critical. The issue is getting electrons into and out of the anode quickly and with minimum heat generated.
Carbon/graphite anodes are way old school and greatly out of favor. But they graphically ;-) illustrate the essential problem. Under high discharge and charge rates electrons are forced into the spaces between the layers of the graphite. In a short time, the graphite is irreversibly deformed, it swells in size and pieces fall off or cells short out .
Leading edge anodes are porous, sort of like a sponge, but they are actually made of compressed rods; lots of area surface area -- IIRC, about 20 times that of graphite -- with lots of openings for the electrons to get deep into the material without causing physical damage. The rod shaped pieces are sometimes referred to as 'spinels.' As I understand it, the rods are tapered somewhat on the ends. As to their size, IIRC they are something like 1 mm in length.
Well, enough about anodes, and electrons, and cathodes, Oh my!
There is a vast difference between an EV manufacturer's "100 mile" lithium-ion battery and an EV owner/driver's daily experience.
Never mind charging times, there are physical/chemical considerations that strongly suggest that the manufacturer's "100 miles" is for the owner/driver an every day 60 to 75 miles if he/she is concerned about maintaining battery capacity over time.
While the EV manufacturers don't say it clearly, if you dig really deeply, slowly you come to the understanding that researchers and folks who use lithium-ion batteries a whole lot say that you should stay away from charging to 100% State of Charge, SOC, and discharging below 20% SOC on a frequent basis if long term battery capacity is a concern. If it is, 80% charge to 20% discharge is better and can be done repeatedly.
These folks go further. It would be best to keep SOC around 50%, charging above that number and discharging below it equally as needed for next days mileage needs. In this scenario, frequent small chargeings are necessary. Enter the desirability, if not need, for many conveniently placed public L2 chargers.
EV manufacturers don't always tell you what your SOC meter measures. Is it full range from actual 0-100% or some reduced range with buffers at top and bottom. Like the Prius that allows driver discretionary use only between ~40-80% actual battery capacity.
Finally, FWIW:
* a good place to begin to get info on lithium-ion batteries is:
Types of Lithium-ion Batteries
*
Eurostar Auto Gallery in Randallstown, MD has the last 10 new (MY2011) Thinks for sale. They routinely ship cars by truck all over the lower 48 states.
* I am pleased, and greatly relieved, to say that both the larger EnerDel and ThinkUSA are still in business and actively support the 400 or so ThinkCity EVs in the USA.