Researchers at the USC Viterbi School of Engineering have developed a cheap, high-performing silicon anode and sulfur-based cathode for lithium-ion batteries.  The new anode is reported to be a cost-effective (and therefore commercially viable) silicon anode nearly three times more powerful and longer lasting than a typical commercial anode.

Using silicon for the anode is important because it increases the battery’s capacity dramatically.  The capacity of a lithium-ion battery is determined by how many lithium ions can be stored in the cathode and anode.  One silicon atom can bond up to 3.75 lithium ions, whereas today’s commercial graphite anode six carbon atoms are needed for every lithium atom.

Lithium-ion batteries are a popular type of rechargeable battery commonly found in portable electronics and electric or hybrid cars.  Traditionally, lithium-ion batteries contain a graphite anode, but silicon has recently emerged as a promising anode substitute because it is the second most abundant element on earth and has a theoretical capacity of 3600 milliamp hours per gram (mAh/g), almost 10 times the capacity of graphite.

The USC Viterbi team developed a cost-effective (and therefore commercially viable) silicon anode with a stable capacity above 1100 mAh/g working for an extended 600 cycles, making their anode nearly three times more powerful and longer lasting than a typical commercial anode.

Up until recently, the successful implementation of silicon anodes in lithium-ion batteries faced one big hurdle: the severe pulverization of the electrode due to the volume expansion and retraction that occurs with the use of silicon.  Last year, the same team led by USC Viterbi electrical engineering professor Chongwu Zhou developed a successful anode design using porous silicon nanowires that allowed the material to expand and contract without breaking, effectively solving the pulverization problem.

Silicon Reduction Steps for Battery Anode at USC Viterbi School of Engineering. Click image for the largest view.

Silicon Reduction Steps for Battery Anode at USC Viterbi School of Engineering. Click image for the largest view.

The new solution yielded a new problem.  The method of producing nanostructured silicon was prohibitively expensive for commercial adoption.

Undeterred, graduate student Mingyuan Ge and other members of Zhou’s team built on their previous work to develop a cost-efficient method of producing porous silicon particles through the simple and inexpensive methods of ball-milling and stain-etching.

Zhou explains, “Our method of producing nanoporous silicon anodes is low-cost and scalable for mass production in industrial manufacturing, which makes silicon a promising anode material for the next generation of lithium-ion batteries. We believe it is the most promising approach to applying silicon anodes in lithium-ion batteries to improve capacity and performance.”

Great, but what about the other terminal, the cathode?

Graduate student Jiepeng Rong and other team members developed a method of coating sulfur powder with graphene oxide to improve performance in lithium-sulfur batteries. Sulfur has been a promising cathode candidate for many years due to its high theoretical capacity, which is over 10 times greater than that of traditional metal oxide or phosphate cathodes. Elemental sulfur is also abundant, cheap, and has low toxicity. However, the practical application of sulfur has been greatly hindered by challenges including poor conductivity and poor cyclability, meaning the battery loses power after each charge and dies after a low number of recharges.

The USC Viterbi team has shown that a graphene oxide coating over sulfur can solve both problems. Graphene oxide has unique properties such as high surface area, chemical stability, mechanical strength and flexibility, and is therefore commonly used to coat core materials in products like sensors or solar cells to improve their performance. The team’s graphene oxide coating improved the sulfur cathode’s capacity to 800 mAh/g for 1000 cycles of charge/discharge, which is over 5 times the capacity of commercial cathodes.

Zhou and his team’s results on silicon anodes have been published in Nano Letters. The paper was a collaborative effort among Zhou, USC Viterbi graduate students Mingyuan Ge, Jiepeng Rong, and Xin Fang, as well as Matthew Mecklenburg from the Center for Electron Microscopy and Microanalysis at USC, and researchers from China’s Zhejiang University and Lawrence Berkeley National Laboratory.

Separately, Zhou, Rong, Ge, and Fang also published results in Nano Letters on their method to easily produce graphene-coated sulfur cathodes for lithium-ion batteries.

Now that their separate tests of the negative and positive electrodes have yielded excellent results, the team is now working to test them together in a complete battery. They will next integrate the silicon anode with the sulfur cathode, as well as with other traditional cathode materials, in order to maximize lithium-ion battery capacity and overall performance.

USC Viterbi graduate student Rong, said, “As far as e can tell, our technologies with both the silicon anode and sulfur cathode are among the most cost-effective solutions and therefore show promise for commercialization to make the next-generation of lithium-ion batteries to power portable electronics and electric vehicles.”

If the technology can go commercial lithium ion batteries will really be much improved.  Lets hope it takes off, your humble writer’s cell phone spends way too much time on the charger.


4 Comments so far

  1. roseland67 on April 2, 2014 11:27 AM

    Very much looking forward to Gen II of this advancement.
    Possible you could do a yearly update on ALL of the battery advancements you have reported on?
    Kolibri, Battery 500, Nasa etc.

    Stay humble and keep the faith

  2. mmarq on April 7, 2014 4:51 PM

    Another one !… for the hamsters on the treadmill…

    Silicon turns very brittle upon alloying, expands tremendously, though its potential is unsurpassed, its another “story” of the perfect is enemy of the good

    This anode cathode is tremendously better…

    Over 900mAhg⁻1 or capacity, roughly 3 times the value of today graphite, and much better than that, and of this silicon solutions, is essentially an all carbon (nanotubes) anode directly build on top of a copper current collector (can’t make it more cheap)… that doesn’t need binders or additives or doping to make it more conductive (carbon nanotubes can be much better than copper at conducting electricity)… so it could recharge incredible fast if pared with the right cathode … and if you look at the discharge chart at ACSNano ( reversible capacity x nºcycles), its a flat line… meaning it practically doesn’t lose capacity upon cycling!-> lets see if “silicon” can do that LOL…

  3. mmarq on April 7, 2014 5:20 PM

    Oh! yes, sulfur also…

    Apart from the “air cathodes”, Sulfur is also unsurpassed in its capacity as a Li-ion battery cathode, but the way they are doing that -> coating directly sulfur powder, seems more one of those “planned obsolescence” stories… what is the good to have a tremendous capacity battery, if you can never realize it, by keeping adding coatings and additives and binders to that electrode that eats heavily on the capacity, and worst your battery goes to garbage in 6 months ??

    You could add sulfur to a polymer, and make a heck of a battery that lasts much longer
    this one as a cathode, has double the capacity of the best today… and most probably would last much longer
    but if you want *real* ‘energy density’ this one has potentially more than 2000 Wh/kg ( 1500mAhg⁻1)… though the “fading” is notorious… although 85% retention capacity during the test is encouraging for a *real* battery that doesn’t fade too fast.

  4. me on July 12, 2014 7:59 AM

    I was searching for news about kolibri batteries (that batteries with which a car did 600 km on single charge).
    I found this:
    so maybe they are real after all.

    Let hope they start producing soon

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