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Since the late 1800s, the primary impediment to the adoption of electric vehicles has been battery technology.  And while the technology has advanced by leaps and bounds in the last decade or two (compare your cell phone with one from the early 90s), with a threefold improvement in energy density and more than an order of magnitude improvement in power density, it still lags behind gasoline.  

Some have argued that current technology is sufficient -- that the ability to drive 1 1/2 hours to 3 hours nonstop is good enough for the overwhelming majority of trips, and that paired with a range extender, rapid chargers, or battery swapping, you have a viable means of replacing the gasoline car.  However, there still is a great deal of pressure to get electric vehicle range up to that of gasoline.

Enter Yi Cui.  Again.

For those who remember the original research, Dr. Cui's team discovered that by using crystalline silicon nanowires in place of the conventional graphite anode, the anode could hold ten times more lithium than it normally could.  Silicon also offers the advantage of having almost no side-reactions with the electrolyte, which are what limit shelf life in li-ion batteries.  For his research, Dr. Cui received a Global Research Partnership (GRP) grant from King Abdullah University of Science and Technology (KAUST).

Silicon's ability to absorb huge amounts of lithium has long been known, but it's always had a fundamental problem: it absorbs so much that it swells, cracks, and pulverizes itself, becoming useless in short order.  While the nanowires proved more resistant, they still went down to 8x capacity after just the first charge cycle.  

While the original technology had promise, and research continues to be ongoing, the cycle life of the nanowires has led to research into alternate nanowire chemistries.  One that was recently published was that of "core shell" nanowires, wherein there's a crystalline nanowire core to conduct the electrons and an amorphous surface, which has better stability.  This comes at the cost of only a 3x improvement in energy density over graphite.  At this point in the research, they're already up to 90% capacity retention after 100 cycles.

While this may not sound like much, factor in the fact that the rate of capacity loss drops off dramaticly over time and the fact that increased capacity greatly offsets capacity loss.  The larger the capacity, the fewer cycles the pack needs to perform to go the same distance, and at the same time, the less of the cell's maximum capacity is drawn in a given amount of time to provide the needed amount of power.  The net result is that for a gain this large, you don't need a very long cycle life.  The same applies to price; if it costs the same to produce but yields three times the energy density, the cost per watt-hour is 1/3rd as great.

The paper also mentions that this is with a very fast cycle of about seven minutes, which obviously invites comparisons to AltairNano's "Nano-titanate" cells.  However, that's about where the comparison ends, for while AltairNano's cells achieve 70Wh/kg energy density, and normal graphite cells achieve up to 180Wh/kg, the core shell anodes achieve about three times better than those of even graphite cells.  

Note that to achieve such a density gain in total, you also need to advance the energy density for the cathode.  Technologies for this include Argonne Laboratories' composite Li2MnO3/LiMO2 or LiM2O4 cathodes, nanocomposite metal fluoride cathodes, various cathodes from Actacell, one from GM, and a LiMn2O4 nanorod cathode.  Other competitors on the anode side include graphite-encased tin nanoparticles (tin is nearly as good of a lithium absorber as silicon), LVO, silicon monoxide with silicon nanoparticles, carbon nanotubes with silicon nanoparticles, carbon nanowires coated with silicon carbide, GM's MgH metal hydride anode, and a porous silicon nanostructure anode.

With so many techs promising 2 to 10-fold increases in density for their respective battery component, it seems increasingly unlikely that lithium-ion battery technology will be stagnating any time soon.  Quite to the contrary, the pace seems to be picking up.  When it comes to range, gasoline may soon get a run for its money.

Originally posted to Rei on Wed Jan 21, 2009 at 08:16 AM PST.

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Comment Preferences

    •  Our Next Car Will Be An EV (5+ / 0-)
      Recommended by:
      GeckoBlue, KenBee, Rei, 1BQ, p gorden lippy

      We've got two Prius cars now.

      Not ever going back.


      The Bushiter's Iraq 2004 - 1268 Dead, about 25K Medivacs and 9000 Maimed... It's the Bushiter Way, wasting other people's money and lives. And it's worse now.

      by RedMeatDem on Wed Jan 21, 2009 at 08:33:48 AM PST

      [ Parent ]

      •  In case you're curious... (7+ / 0-)

        Here's a list of upcoming EVs.  I'm on the waiting list for an Aptera 2e.

        •  I've Been Looking at the Aptera 2e Myself! (1+ / 0-)
          Recommended by:

          I have not put down the $500 bucks because I want to see one before I do.

          About once a month I pester them about being able to see one.

          The other thing I've been asking them is whether the car will be 'Better Place' battery exchange program compatible.

          In the Bay Area they propose to put in 3-minute battery exchange stations. That's faster than filling up a car with gas!


          The Bushiter's Iraq 2004 - 1268 Dead, about 25K Medivacs and 9000 Maimed... It's the Bushiter Way, wasting other people's money and lives. And it's worse now.

          by RedMeatDem on Wed Jan 21, 2009 at 09:33:12 AM PST

          [ Parent ]

          •  And don't forget about fast charging :) (2+ / 0-)
            Recommended by:
            KenBee, Bule Betawi

            I prefer it because it doesn't require stocking big, expensive surplus batteries and it doesn't require different vehicles with completely different needs and rapidly evolving battery technology to be locked into a single solution.  Titanate cells can charge in 5-10 minutes, while phosphates and spinels are in the 10-20 minute range.

            I assume you're not going to the TED conference in early February; Aptera will be offering test drives there, although all of the slots are already booked (you could still show up as a spectator  ;)  ).  Also, there's been an an as-of-yet unconfirmed report that it'll be showcased at the Carlsbad Chamber of Commerce's big event on February 20th at the Four Seasons.  According to the report, "The 2e be showcased along with famed environmental artist, Wyland. The tickets are on a first come basis at $125. and it will be a sold out event."  

            Aptera's announced plans, as of their last interview with EVCast, is to begin touring all over the state in February and offering test drives.  So, sooner or later, you should be able to catch them.  :)

  •  Very interesting. Battery technology also (5+ / 0-)

    is needed to make wind and photovoltaic generation more practical.

    Batteries don't answer the question of where energy will come from, but they certainly have something to say about where energy will go.

    •  Battery tech is pretty expensive for (4+ / 0-)

      bulk power storage.  Pumped hydro or other physical shoving about tends to be cheaper on the utility scale, flywheel for large buildings or neigborhoods.  Batteries are better with mobile applications.

      •  Yes it is now, maybe getting cheaper? (0+ / 0-)

        On the other hand, the methods you mention also have drawbacks and inefficiencies.  It is good that people understand that wind and solar need augmentation to provide base load.

        Personally, I like the idea of using the wind and solar generation to make hydrogen gas, and burning that for base load.

        •  I must disagree (2+ / 0-)
          Recommended by:
          KenBee, Mother Shipper

          It's incredibly energy-wasteful to do so (you'll get about a third of your energy back), and hydrogen is very expensive to store due to its volatility, low density, and corrosive nature.

          IMHO, for now, our main issue is HVDC.  Our new energy secretary is a big advocate for it, which earns him brownie points in my book  ;)  HVDC lets you share power from where the wind is blowing to where it's not.  It even lets you link, for example, the Pacific Northwest's huge amount of hydro capacity with the midwest's wind, thus letting the dams flow at full capacity when the wind isn't blowing and letting them store up water when it's not.

          Now, that's not enough to get the US up to 100% renewables (you do need batteries or renewable baseload, such as high altitude wind or enhanced geothermal, for that), but it can get you up to half or so.

        •  Not that much cheaper (2+ / 0-)
          Recommended by:
          KenBee, Mother Shipper

          the advantage of things like pumped storage is you have one expensive piece, the dam/pump/generator, and a cheap big piece, the lake/reservoir that in theory you can make bigger cheaply.  With batteries, if you want more capacity you buy more batteries so each watt-hour costs about the same.  Flow batteries are an exception, being a bit like pumped storage but needing plastic tanks and somewhat expensive electrolyte instead of plain water.

  •  How about the... (4+ / 0-)
    Recommended by:
    KenBee, Rei, Randtntx, p gorden lippy

    ...Vanadium Flow Battery which is currently being used in Japan, Canada, and Australia?  It has a recharge rate of 10,000+ and is capable of MW storage capacity.

    The optimist thinks this is the best of all possible worlds. The pessimist fears it is true. J. Robert Oppenheimer {-8.25 / -5.64}

    by carver on Wed Jan 21, 2009 at 08:44:37 AM PST

  •  Tubes! (1+ / 0-)
    Recommended by:

    It's amazing what smart people, given time and support, can do that is of significance to the rest of us. For me, this was the best part of Obama's speech yesterday: specifically calling science out as in need of support.

    Thank, Prez (no longer elect)


  •  Ok, when can I buy some? (1+ / 0-)
    Recommended by:

    Just kiddin'...

    _Float like a manhole cover, sting like a sash weight!_ Joe Lieberman=Momzer!

    by JeffW on Wed Jan 21, 2009 at 09:15:22 AM PST

    •  Probably three to five years (3+ / 0-)
      Recommended by:
      Phoenix Woman, JeffW, Bule Betawi

      That seems to be about how long it takes to commercialize new battery techs these days.  Look at all of the lithium phosphate manufacturers, spinel manufacturers, and the couple titanate manufacturers for examples of techs developed in the late 90s/early 00s that came onto the market in the early/mid 00s.

      Not every new tech makes it.  Most don't.  But there are such a huge number of new li-ion techs that the odds of none of them making it are near zero.  

  •  great post (1+ / 0-)
    Recommended by:
    Lefty Mama

    what happens with an litium battery when it is used up, can it go into conventional landfills or does it have to be reprocessed?

    •  Batteries and landfills (3+ / 0-)
      Recommended by:
      KenBee, EthrDemon, Vladislaw

      That's a great question.  First off, there are different degrees of toxicity.

      Lead-acid and nickel-cadmium batteries are highly toxic, and should never be disposed of in a landfill.  You should always reclaim the lead and cadmium before disposal.

      Nickel-metal-hydride batteries are somewhat toxic, although not incredibly so.  It's best to recycle the nickel, but if you can't, they can be disposed of safely in controlled circumstances.

      Conventional li-ion batteries, like the Tesla uses but unlike what most others do, have a cobalt-based ceramic cathode.  This cathode is mildly toxic -- no moreso than many metals and plastics that we regularly dispose of, however.  The rest of the battery is nontoxic.  The biggest risk of disposal of conventional li-ion cells is fire.  Even still, mostly for PR, battery manufacturers often recycle them.  Here's how Tesla recycles theirs.

      One other type of li-ion in use in some EVs that has a cobalt cathode is the titanate cells.  Most manufacturers don't use them because they're very pricey, but they have outstanding performance specs.  They are not at risk of fire upon disposal, and because of their extreme longevity, are rarely disposed of.

      The other advanced li-ion variants, which are the most common type in upcoming EVs, don't use a cobalt cathode at all.  They are essentially completely nontoxic; the worst aspect of them is that their electrolyte is corrosive.  Combined with their fire resistance, you can literally just throw them in normal garbage streams, legally (at the very least, I know you can in Canada; not sure from state to state in the US).  You can try to recycle components from them, but it's not usually worth the effort -- especially due to their long life.  

      •  the reason i asked was (1+ / 0-)
        Recommended by:
        Bule Betawi

        "Lead-acid and nickel-cadmium batteries are highly toxic, "

        it is my understanding that is the type they use in china for the millions of electric scooters they build and they are going to be running into a disposal problem very soon.

        •  lead-acid batteries are fair easy to recyle (0+ / 0-)

          drain the acid for reclaiming, shred the rest and toss it in the smelter.  The problem comes about when people don't turn in the old batteries for recycling, this is likely to be less of a problem with the large amounts of batteries in BEVs as replacing the arrays is less like a DIY task and more of taking it to a service center.  Scooters use small enough packs that DIY is likely, including a deposit charge on those batteries will likely be needed to encourage recycling.

          On the other hand, recycling lead means less processing of lead ores, and those ores are sources of indium, so indium production declines.

        •  Lead-acid is really a very poor solution (1+ / 0-)
          Recommended by:

          for EVs.  Low quality EVs use it because it's dirt cheap, but in nearly every regard, it's pretty awful.  It's toxic, as you mentioned.  They have very poor energy density.  Their power density isn't that much better (esp. compared to the advanced li-ions, which can output several kW/kg -- over an order of magnitude better).  They suffer badly from something called Peukert's Law, which basically means the harder you use them, the less the energy you can get out of them.  They only last 2-5 years.  They're inefficient.  They outgas hydrogen.  And on and on down the line.

          There are some improvements to the tech, such as Firefly's carbon foam-backed cells, but from the stats I've seen disclosed from them, it's too little, too late, at too high of a price premium.

          •  Firefly is interesting (1+ / 0-)
            Recommended by:

            the second generation batteries look to give densities of 110-150 Wh/kg at roughly 1/3 the cost of Li-ion.  Theory gives around 180 Wh/kg as a limit.

            But Firefly had already backed off manufacturing batteries early this summer and was looking for partnerships with existing producers.  With the economic situation as it is, continuing development of their concept seems less probably especially for the second generation type.

            •  Firefly (2+ / 0-)
              Recommended by:
              KenBee, Bule Betawi

              As of last January, they were reporting only 38Wh/kg on the 3D cells; I can't imagine the 3D2 cells are that much better (their website states "Significantly lower volumes and weights (by up to ~50%) relative to comparable lead-acid products in terms of energy output" -- which doesn't even make sense, as by definition you don't output energy -- you output power).  Sure you're not thinking of W/kg?  All of the stats I've seen for firefly batteries show significantly better power density (although still nothing like the advanced li-ions), and better cycle life (again, still nothing like the advanced li-ions), but the energy density was only marginally better and not even up to NiMH standards.  And it's still PbA, so it still suffers from Peukert's and charge efficiency issues, plus the prices I've seen suggested are way too high for viability.

              Yes, theory for PbA is a max of around 180Wh/kg.  Practice in batteries is generally nowhere even close to the theoretical max.  LiS batteries, for example, have a theoretical max of 2.6kW/kg, but in practice, they're only a little better than traditional li-ion.  Each li-ion chemistry has a theoretical max that's way above what's actually achievable.

              •  Their original battery product (2+ / 0-)
                Recommended by:
                KenBee, Bule Betawi

                was targeted at starter applications, particularly for cold weather.  They weren't optimizing for EV apps, although they talked about it.  And their product was also targeted at fast payback of startup costs as momma was looking at cutting the strings or at least reducing cash flow as they saw to downturn coming - you don't sell construction equipment when no one is constructing.

                Supposed numbers for cells late last spring were 35 to 45 Wh/kg.  Second hand I've been told the 3D2 has done 2 to 3 times better in the lab, the same place as most new Li development reports are.

                The battery is fairly low tech, and shouldn't bee too expensive to make.  Besides recovering development costs the pricing reflected fairly small scale production on a new line.

                Pricing I saw was a bit less than 2X conventional PbA for more that 2X Wh/kg.  For the 3D the pricing was expected to drop to around 1.2 X conventional PbA batteries.

                There's a form of Peukert's for most battery chemistries. It relates to the resistance between electrode and electrolyte, the intrinsic resistance of the plates, the intrinsic resistance of the electrolyte, and the electrolyte's bulk resistance.  

                In chemistries where gases can be generated during operation the bulk resistance is increased by bubbles, some chemistries have no bulk effects like that.

                PbA has problems with the el-ectrode-electrolyte interface because of the low conductivity of PbSO4. It also runs into electrolyte resistance changes caused by depletion of H2SO4 and bulk diffusion rates under high current conditions.  The 3D plates greatly reduce electrolyte resistance problems, and they have a much higher area-to-volume ration for the anode, they don't loses efficiency until much higher currents than conventional PbA.  They also have a slightly lower resistance of the anode mix, as less additional materials - BaSO4, aromatic sulphonates - are needed.

                The bulk resistance increase from gas formation is mostly an effect of high charge rates and associated diffusion limits.  Again the Firefly anodes aren't really hit by those effects until higher charging rates.  All these means that their Peukert's exponent is lower than most other PbA batteries.

                Note that as Peukert's impacts higher discharge rates, and related effects charging rates, avoiding those reduces Peukert's impact, for any battery chemistry.   High charging rates are desired for matching the ICE operational style, but undesirable from the standpoint of the electric power grid, which has its lowest efficiency at the local distribution level. For discharge the use of ultracapacitors, also used to handle regenerative breaking currents, reduce the load on the batteries; at the cost of additional complexity, true.

                Because the carbon foam's stabilization of the anode Pb-PbSO4 particles, some tricks to reduce electrolyte effects that don't play well with conventional PbA cells may be applicable to the 3D batteries.  There just hasn't been the level and range of research into PbA as into Ni and Li chemistries for portable applications, there could be a good deal of improvement methods to be found.

                All this came from someone who talked with a researcher from Firefly at a conference. As such it is 'forward looking' and may not come to pass, especially as Firefly seems to be scaling back.

                Li-ion still has better performance potential, in part because of the density difference between Li and Pb. But it is unlikely to get as cheap as the PbA designs, and that may be important for lower end short range vehicles.  And short range fits the needs of the majority of trips, for 2 car families 3/4 of the daily travel for one of those cars is under 35 miles.


                •  Do you have any refs? (2+ / 0-)
                  Recommended by:
                  KenBee, Bule Betawi

                  I've been told the 3D2 has done 2 to 3 times better in the lab, the same place as most new Li development reports are.

                  First off, that wouldn't put them where new Li development reports are.  That's put them at best where Li on the market today is.  And I've searched and searched for refs, and can't find any to support that claim.  Certainly not any in published literature like the li-ion techs I'm talking about (for example, the current one was published in [i]Nano Letters[/i]).  So if you had a ref, I'd greatly appreciate it.

                   High charging rates are desired for matching the ICE operational style, but undesirable from the standpoint of the electric power grid, which has its lowest efficiency at the local distribution level.

                  It depends.  The most high-powered chargers I'm aware of have their own battery banks.  The banks trickle charge off the grid and rapid discharge when you hook up a level-3 connector.  Which is actually beneficial to the grid, as the rate in which the battery banks charge can be increased or decreased according to the needs of the grid.

                  All this came from someone who talked with a researcher from Firefly at a conference. As such it is 'forward looking' and may not come to pass, especially as Firefly seems to be scaling back.

                  Ah, I see  ;)  Well, if they're not even to the point where they can publish yet, how could one possibly make any claims about pricing from that?  I too seem to recall the 2x higher than PbA pricing for their original 3D cells, but those were only, as you note, an unimpressive 35-45Wh/kg.

                  Well, I suppose we'll have to want and see what they can pull off.  For now, I'll treat those claims with the same kind of skepticism I use with EEStor.  Getting anywhere close to a chemistry's theoretical maximum is generally almost impossible to do in a practical manner.  But again, we'll just have to wait and see   :)

  •  could you explain the capacity loss a bit? (1+ / 0-)
    Recommended by:
    Bule Betawi

    I'm with you up to here:

    At this point in the research, they're already up to 90% capacity retention after 100 cycles.

    While this may not sound like much, factor in the fact that the rate of capacity loss drops off dramaticly over time and the fact that increased capacity greatly offsets capacity loss.

    Are you saying that after 200 cycles we could expect a capacity retention that's higher than 81%? And why could we expect this characteristic if we are using a new-and-different technology?
    I guess I should poke around in your links. Nice diary, though - this is something that could literally save the world.

    In a democracy, everyone is a politician. ~ Ehren Watada

    by Lefty Mama on Wed Jan 21, 2009 at 09:24:50 AM PST

    •  capacity is lost with use through (3+ / 0-)
      Recommended by:
      KenBee, Rei, Bule Betawi

      changes in the electrodes.  Depending on the exact chemistry in use the electrodes may become less permeable to lithium, trapping some; the fine structure may erode, with bits of nanowires dropped off or several wires fusing together - both of which reduce electrode surface area. Lithium can react in unwanted ways with electrodes or electrolyte, becoming unavailable to the useful battery chemistry.  All this reduces the amount of charge that can be retained; eventually the charge retention drops too low, or electrode degradation shorts out cells in the battery dropping the pack voltage as well as charge retention.

      In lead-acid batteries the lead sulfate tends to form larger crystals with repeated charge-discharge cycles. These crystal as less reactive, decreasing capacity, and also fall off the electrode which also decreases capacity. One company has used carbon foam to contain the lead sulfate in nanosized pockets in the foam, that greatly reduces the rate of crystal growth which extends the battery lifespan. It also brings about better contact between active electrolyte and lead sulfate, giving better performance.  This pushed the capacity retention from 90% at about 100 cycles to 90% at 1,000 cycles.

    •  Yes, you can. (3+ / 0-)
      Recommended by:
      Lefty Mama, KenBee, Bule Betawi

      Virtually every li-ion battery chemistry, and most rechargable battery chemistries in general, have a curve along the lines of this.  Here's another for a different chemistry. The best way to describe it is that the nanoscale-level parts of the anode, cathode, separator, or whatever that are more likely to fail, fail first.  I.e., the risk of a given part of the cathode or anode being pulverized is not constant across its surface; it varies from place to place depending on the atomic structure there.  As the more vulnerable parts fail, you're increasingly left with less and less vulnerable parts remaining.

      Now, it's possible that for some reason this is different, but that's highly unlikely.

      It's important to remember that if you have a chemistry that is 3x as dense and gets down to 90% capacity after 100 cycles, and let's just say 80% capacity at 500, 70% capacity at 2500, and 60% capacity at 10000... it's still 1.8 times higher capacity than a new normal battery at 0 cycles.  And the other point, which I tried to make in the article, is that the bigger the battery pack, the less stress on the cells.  The testing here revolved on some extremely stressful tests -- discharging and charging the cells in 7 minutes.  A hybrid vehicle may charge/discharge that fast because it has a tiny pack.  A plug-in hybrid will take half an hour to 45 minutes to discharge its pack, and a long-range EV may take many hours.  So, the bigger your pack, the less you stress the individual cells.  And there's yet another benefit in that the bigger the pack, the less energy a given cell has to contribute per mile.  In EV that has a range of 100 miles, if you go 100 miles, each cell goes through a complete cycle.  In an EV that has a range of 200 miles, if you go 100 miles, each cell only goes through a half cycle.  I.e., it's the same distance but half the cycles.  Combine this with each cell being less stressed in the process, and combine that still with the much greater capacity even after capacity loss, and you can see how critical increasing energy density is to longevity.

    •  I should add (2+ / 0-)
      Recommended by:
      Lefty Mama, KenBee

      .. that this doesn't apply to every kind of degradation.  For example, conventional li-ion suffer shelf-life degradation due to the electrolyte reacting with the graphite.  This doesn't occur at a per-cycle rate, but simply happens over time (it is affected by temperature, however).  To solve this, advanced li-ion manufacturers either use nanoscale amorphous carbon particles instead of graphite (such as A123) or a carbon/titanate structure (such as AltairNano).  Silicon is immune to this reaction, so it's not an issue for this anode.

      Also, just because the charge capacity decrease drops off quickly doesn't mean that useful capacity will follow the exact same curve; it depends on how you're using the cell.   For example, if you use an alkaline battery in a digital camera, you'll get almost no life in it, but if you use camera batteries, which are designed to keep the voltage just high enough for longer, you'll get many times the life.  But if you use those same cells in a flashlight, the camera batteries won't last much longer at all.

      So, there's a lot of implementation-specific stuff involved.  But, in general, capacity drops for EVs are much faster in the beginning than later on.

      •  LI batteries in my portable power tools (0+ / 0-)

        don't have anything preventing me from completely discharging them. This degrades their lifespan, correct? opposed to recharging them anytime I can and not discharging fully?
        I noticed that because B&D is selling a new cordless tool that quits when the charge gets too low. Maybe that's because they thought that would sell more, a Feature, or maybe too many warranty claims, I don't know.
         Back when cordless tools came out, I remember reading that they were to be fully discharged, and my last set of expensive batteries died quickly...and no I finally see why, heh. Why that is chemically/physically I can't could, heh.

        "Outside of a dog, a book is man's best friend. Inside of a dog it's too dark to read." - Marx

        by KenBee on Wed Jan 21, 2009 at 03:36:08 PM PST

        [ Parent ]

        •  Li-ion has no memory effect (0+ / 0-)

          So it doesn't matter how discharged they are before you start recharging them.  It's nice that way  :)  By limiting how deep you can discharge, though, you can make a single cycle less damaging, and thus last longer.

          Power tools are very stressful on batteries.  Picture how long it takes you to drain the battery pack on an EV, and then compare that to how long it takes to drain the battery pack on a power tool that's been left on.  Very high discharge currents compared to the size of the pack = very hard on longevity.

          •  Hmmm, I'll look around and see why I disagree (0+ / 0-)

            with you, I say that many places that talk about Li battery operation issues say that they must NOT be totally discharged, the point of my comment, and that software in the EV's is organized to prevent that, that there are warning lights and cutouts that won't let you discharge below a 'safe' point, which, iirc is a decision the engineers the case I was reading the engineer was building his own car and writing the battery monitoring software, and he selected 2.4v as the lowest ...I'll remember, I'll get back to you, but it wasn't the only place I saw it.
             And he was making it so he could override the cutout in an emergency, at the expense of the longevity of the battery pack.
              I'll look for that...and of course I may be allwrong :>

            "Outside of a dog, a book is man's best friend. Inside of a dog it's too dark to read." - Marx

            by KenBee on Thu Jan 22, 2009 at 12:36:08 AM PST

            [ Parent ]

            •  Discharges (1+ / 0-)
              Recommended by:

              "I say that many places that talk about Li battery operation issues say that they must NOT be totally discharged"

              First off, as I mentioned, the deeper the discharge, the more the damage, so you'll generally want a cutoff voltage (in fact, inverters have a minimum voltage anyways, so you'll need one).  However, it's not like the battery will suddenly die instantly if you put it through a deep discharge -- at least not the types we're talking about.  

              When you say "li battery", you're acting like there's only one chemistry of li-ion (which I should note is itself different from "lithium batteries").  However, there are a number of different chemistries for li-ion.  The type that you find in cell phones and laptops (LiCoO2+graphite) is a lot more vulnerable to damage from deep discharges.  In fact, it's a lot more vulnerable to damage from everything, even sitting on a shelf or being used normally.  The types found in power tools and most EVs (Tesla being a notable exception) are not.  These are the phosphate-based olivines and the various spinels, as well as those with titanate cathodes.  On RCGroups, for example, one participant did 100 cycles of discharging A123 cells all the way down to zero volts, and they only showed minimal signs of damage.  A123 cells are probably what's in your power tools; they were the first company to start providing advanced li-ions for that market.

              But again, even with the more stable forms, it is better for them not to discharge too far, and your inverter will impose a practical limit anyways.  And no forms of li-ion have a memory effect.

    •  one more graph (3+ / 0-)
      Recommended by:
      Lefty Mama, KenBee, Bule Betawi

      showing the impact of going to nanoscale electrode surfaces.  This for lead-acid, but similar results can be had in other battery chemistry systems with nanotech appropriate to that chemistry.

  •  Waiting for my EV opportunity (2+ / 0-)
    Recommended by:
    KenBee, Bule Betawi

    thanks REI!

    Find your own voice--the personal is political.

    by In her own Voice on Wed Jan 21, 2009 at 09:31:05 AM PST

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