The most popular rechargeable batteries in the world today are lithium ion. In 2007, the independent market research company Frost & Sullivan predicted revenues from these batteries would amount to $10.4 billion worldwide by 2012. A new report released in 2013 from the same company stated that the actual number was even higher: $11.7 billion. In addition, this report predicts that sales of lithium ion batteries will double by 2016.[i]The primary cathode material used in lithium ion batteries is lithium cobalt oxide (LiCoO2 – to make this easier, we’ll call these “cobalt”), which is popular because of its high energy density (i.e., the amount of energy stored) by both weight and volume. However, this material has some safety concerns, and is expensive.
Other cathode materials are available, most notably lithium manganese oxide (LiMn2O4 – again, to make it easy, let’s call this “manganese”). Although cell voltages and energy performance is slightly less than the cobalt cathodes, the manganese version has a similarly low recharge time and favorably compares to cobalt in terms of specific energy and cost.
|Comparing LiCoO2 with LiMn2O4 cathodes |
without our nanoparticle coating; adding
our coating improves cycle life.
In fact, in terms of material costs, reports have stated that the cobalt based cathode material costs an average of about $30 to $35/kg, while the manganese version was significantly less, at anywhere between $2 to $15/kg, depending on what study one believes.[ii] And, major thermal stability studies have shown that the manganese cathode is much less prone to thermal runaway issues suffered by the cobalt cathode, which makes cobalt cathodes less safe.[iii]The main reason manganese cathodes are not more widely used has to do with more pronounced “capacity fade” (especially at higher temperatures) than cobalt. This is a decrease in the energy content of the battery, especially after repeated charging and discharging (capacity fade is seen by the consumer when a battery can no longer power a laptop on an entire cross country flight or when a cell phone battery drains more quickly than it used to).
So, manganese cathodes are a much safer and less expensive alternative to cobalt.
So, manganese cathodes are a much safer and less expensive alternative to cobalt.
Were it not for capacity fade, the manganese cathode might well be the chemistry of choice for lithium ion cells. Consider what others have stated about manganese (LiMn2O4):
· In a white paper, General Electronics Battery Co., Ltd., stated: “The chemistry of lithium manganese oxide LiMn2O4 is not a good option . . . because of its poor cycle life, especially at elevated temperature.”[iv]
· S.C. Park, et al, stated: “In order to use LiMn2O4 [i.e., what we called “manganese”] as a cathode material of lithium-secondary battery for an electric vehicle (EV), its rate capability should be improved.”[v]
· And, Schwartz summed up the main reason LiMn2O4 is not widely used as a cathode, despite greater safety and lower cost: “LiMn2O4 that has been investigated extensively over the years has been plagued by severe capacity fade, particularly at elevated temperatures.”[vi]
Our subsidiary, SolRayo, has found a solution to the capacity fade issue. Using nanoparticles, deposited onto manganese cathodes in specific ways, we have seen a significant improvement in cycle life.
|Scanning electron microscope (SEM) images of LiMn2O4 material |
without and without our nanoparticle coating. For perspective,
consider that the actual width of the material in each picture
is about 13/1000th the width of an average human hair.
We submitted a proposal to the National Science Foundation (NSF), under their STTR program, to commercialize this process. The program has two phases (called, appropriately enough, Phase I and Phase II). We completed a proof of concept under Phase I and, out of over 1000 initial proposals -- all of
which were subject to extensive peer reviews by experts in both industry and
academia -- SolRayo's was one of only 3% chosen by the NSF to be awarded a Phase II grant.
|The above tests were conducted at elevated |
temperatures (55C / 131F). With our nanoparticle coating,
batteries last longer.
Now, the pathway to continued, full commercialization of this concept is not as straight-forward as one might think. Some chemistries and some nanoparticles don't always behave the same way when stepped-up into larger packages. So, during meetings with cathode manufacturers, as well as some consultation with experts from a local national lab and our partners at the University of Wisconsin, we concluded that the best path to full commercialization will include stepping up our process to prove its performance and reliability in increasingly larger cells.
We have started by using coin-sized cells: CR2032-sized packages (i.e., about the diameter of a nickel and the thickness of, say, 20 or 30 sheets of paper). The research involves varying the concentrations of the nanoparticles, cathodes materials, method of coating, firing processes, cathode preparation processes – initially in half cells, then in full cells – and many, many other steps to determine the steps that give us the best and most reliable performance, as well as the most economical process. The process needs to be repeated until desirable results are consistent over a couple hundred cells. Only when this is achieved can we say that the "nanoparticle recipe" – for that particular size and chemistry composition – is well-established.
|One of our coin cells, next to a nickel for size comparison.|
Our Phase II work has gained the attention of potential commercial partners and may open up certain markets to us sooner rather than later. The results to date have culminated in meetings with Global 75 companies, and some anticipate new patent filings. The Phase II effort is scheduled to be completed in March 2014.
The next step is to prepare larger cells (not to say that there isn't a market for coin-sized cells utilizing our nanoparticle solution); in our case, 1Ah cells which would be assembled in pouches. Following this, the process would be stepped-up further to 3Ah cells, and eventually 20Ah cells. Once this is done, we would consider the process fully commercialized, and we would better understand the specific fields of use in which the process would apply.This is not as easy as it sounds and requires a level of expertise that isn't easily found. In our case, it requires certain commercial, academic and/or gov't-funded laboratory partners with experience in this area and a depth of knowledge that is really rather unique.
And, yes, these resources are available to us.We may find that our nanoparticle process might work out well for smaller consumer applications or for larger industrial uses. The process may end up as renewable energy storage for residential or utility scale applications, or it might end up being used in the battery bank of an electric or hybrid vehicle.
Or, it may apply to all these, in one way or another.
[i] Frost & Sullivan, World Secondary Lithium-Ion Battery Markets, 2007, p 2-7 and “Despite Recent Issues, Global Lithium-Ion Battery Market To Double”, RenewGrid, 22 Feb 2013, retrieved from http://www.renewgridmag.com/e107_plugins/content/content.php?content.9612#.Uef6vfPn-Uk
[ii] J. Amirault, et. al. The Electric Vehicle Landscape: Opportunities and Challenges,2009, p 12; Dr. Wolfgang Bernhart, Power Train 2020: The Li-Ion Battery Value Chain – Trends and Implications, Roland Berger Strategy Consultants, Aug 2011 (presentation), slide 11; and Comparison of Different Battery Technologies, Trade Korea, 26 May 2006, retrieved from http://www.tradekorea.com/product/file/download.mvc?prodId=P00233231&fileSysNm=/upload_file2/product/231/P00233231/cbe9caa6_bc17a819_5d6e_4664_b546_3e4384d1c8a6.pdf
[iii] J. Dahn, et. al., Thermal Stability of LixCoO2, LixNiO2 and LiMnO2 and Consequences for the Safety of Li-ion Cells. Solid State Ionics, Vol 69, 1994, p. 265
[iv] Comparison of Different Battery Technologies, General Electronics Battery Co., white paper, 2006, p.4, retrieved from http://www.tradevv.com/chinasuppliers/angelgeb/pdf/LiFePO4-battery-75ee.pdf
[v] S.C. Park, et. al., Improvement of the rate capability of LiMn2O4 by surface coating with LiCoO2, Journal of Power Sources, 103:86, 2001
[vi] Mel Schwartz, Smart Materials, CRC Press, 2009, p. 8-5