4 ms·
Post of the actual paper; https://news.ycombinator.com/item?id=20908726 https://news.ycombinator.com/item?id=20908726 For those commenting that the discharge
by zaroth 7y ago
Post of the actual paper;
https://news.ycombinator.com/item?id=20908726 https://news.ycombinator.com/item?id=20908726
For those commenting that the discharge rate is too slow in the test, or the depth of discharge was fudged... the tests were run with a high discharge rate combined with 100% charge at storage.
> Figure 23 shows the projected fractional capacity of these NMC532/graphite cells as a function of time in years in a scenario where the cells are cycled once per day (100% DOD to 4.3 V) in a cycling event that takes 6 hours. It is also assumed that during the remaining time, cells are stored at full state of charge. It is clear from Figure 23 that these cells would provide an exceptionally long total driving range in an EV if the cells were maintained at an average tem- perature of 20°C. Even if the cells were continually at 40°C, 10 years of lifetime to 70% capacity and a total driven distance of 1,200,000 km is projected. It is worth noting that only 3650 cycles would be required for this total driven distance and 3700 cycles have been demonstrated in Figure 16.
> Most important to realize is that Figure 23 assumes 100% DOD cycling on every cycle and storage at full state of charge. If the reader reviews the literature data in Figures 1 and 2, the reader will realize that the lifetime will be much better in situations where the DOD is limited and in situations where cells are stored at lower states of charge. Admittedly, the projections in Figure 23 use the incredibly simple model described by equation 1. It is our opinion that more sophisticated models will lead to even longer lifetime projections.
- falcolas 7y agoNothing here indicates a discharge rate. I'm having trouble finding the actual wattage produced by these cells over the 6 hour discharge time. Also, 6 hours is a longer than the current Tesla will run full charge at highway speeds (350 mile range, 75 mph ~= 4.5 hours). Plus, the current tesla can be re-charged and continue to operate, conditions I don't see mentioned. If it is similar to existing batteries though... great!
- Reason077 7y ago"Nothing here indicates a discharge rate." In battery terminology, and this paper, charge/discharge rate is referred to as "C". Charging or discharging at 1C means a battery would be fully charged/discharged in 1 hour. A 100 Wh cell discharging at 1C would produce 100 W. Likewise, at 3C it would take 20 minutes and produce 300 W. At C/3, it would take 3 hours.
- rat9988 7y agoAre charge and discharge rate usually equal?
- hwillis 7y agoNo, but it is common to treat them as if they were. It depends on the chemistry as some are worse, but charging is slightly rougher than discharging. During charge the lithium ions need to intercalate into the graphite anode, which is slower than the reverse.
- falcolas 7y agoThat doesn’t give us any information on the capacity of the cells. Once we know the MAh of the cells, that gives us the output amperage, but without the capacity (or an amperage/watt value to derive the capacity), it’s a useless value.
- Reason077 7y agoThis information is given in the paper. Look for terms like capacity (mAh), specific energy (Wh/kg), and energy density (Wh/L).
- Osiris30 7y agoWould this be a correct summary of the paper? 1) eliminates Cobalt 2) improves energy density (more range) 3) faster charge rate 4) less SOC (state of charge) swing, meaning less cost & weight 4) 5x longer lifespan
- alanh 7y agowhat is 'state of charge swing'?
- hwillis 7y agoI think it is referring to the fact that it is ubiquitous to leave some amount of reserve so that the battery is never fully charged (100% SoC) or discharged (0% SoC). This formulation is capable of going the full 0-100%, while most formulations will last significantly longer if they don't do that.[1] In that graph, charging to 75% and discharging to 25% gives you about 3x more life than from 25%-100%. NB that most li-ion cells are rated for 300-1000 cycles at 100% Depth of Discharge. Reducing the DoD to 90% or 80% will get you thousands or tens of thousands of cycles, although it is abnormal to actually measure that long. A charge-discharge cycle at .1 C (the former standard) takes 20 hours. [1]: https://batteryuniversity.com/_img/content/DST-cycles-web2.jpg https://batteryuniversity.com/_img/content/DST-cycles-web2.j...
- FooHentai 7y ago24kw leaf battery is an example of this with user stats seemingly bearing it out. Charge it to 80% each time, you can expect 3000 cycles before it's spent (drops below 85% of original capacity). If you charge to 100% each time, you'll only get 1000 cycles. 3-4 years versus 8-10 years use makes a big difference.
- taneq 7y agoThe 85% capacity benchmark seems pretty arbitrary to me. I'd imagine most owners very rarely use more than 85% of their range (or at least, could avoid doing so easily) at which point 85% isn't "needs expensive battery replacement", it's just "slightly less range buffer". I imagine in 20 years' time we'll see plenty of old beaters, student cars etc. with 50% or less range that are still quite happily driving around.