Sterling Baird and Dr. Robert Davis, Department of Physics and Astronomy
Batteries have applications in medical, defense, communication, transportation, and a host of other technologies. In the last several years of conducting experimental energy storage research, I began noticing gaps between what literature research was reporting and the criteria industry uses to assess the commercial potential of a new technology (i.e. determine commercial viability). For example, many articles report seemingly fantastic values of how much energy is stored per unit mass (specific energy), a critical performance metric for energy storage systems (think cars, planes, sending things to space). However, they often fail to include critical information such as mass of the electrolyte (sometimes up to 95% of the total mass for these experimental devices). Another example is reports of being able to charge and then discharge a battery many times (high cycle life). Yet, they often fail to include the actual amount of energy storing material within the battery, rendering the results of low practical value (several hundred cycles may correspond to a very low cumulative energy).
Several resources exist already to help bridge the gap between science and industry. Researchers have conducted reviews that compare articles based on small component-level performance without including enough information to determine overall performance. In addition, other reviews exist where researchers extrapolate what the performance might be like if less electrolyte or excess materials were used, demonstrate a few articles that do include enough information, or discuss the need for more information to be included in studies. Other articles provide cost-estimate models for new battery chemistries or use visual charts to represent trends. My project has two goals. First is to help researchers understand what must be reported and why through establishing performance criteria and rankings for specific applications (e.g. renewable energy, electric vehicles). Second is to help industry assess and compare experimental literature by delivering a visual battery database tool.
Every battery has requirements and limitations. Requirements are imposed by the application: energy, time, safety, and ambient conditions. Limitations result from the battery itself: mass, volume, and cost. These result in essential criteria for evaluating a battery’s performance (e.g. specific energy comes from energy divided by mass). I chose specific metrics based on datasheets, a go-to document that helps assess performance of a battery, usually already commercialized.
In this project, I accomplished several things. This included: assigning criteria rankings for battery applications, conducting a literature review, and creating a visual database tool. When I speak of criteria rankings, I mean “what are the most important features of a battery for a given application?” For example, reducing mass and volume is very important in many medical applications (e.g. heart pump). In other examples, a high number of cycles and long lifetime might be necessary (e.g. 20-year lifetime solar farm). I identified high-impact battery applications and then assigned these criteria rankings for battery applications (i.e. how do battery needs differ based on where its used?) based on preliminary assumptions and common sense. Then, I identified commercial technologies from a variety of applications (electric vehicle, cell phone, drone, etc.). I then used the available data to then validate and refine those rankings. This was important for putting the next step, current research, into context of commercial technologies.
In the literature review process, I identified several hundred articles, and categorized them according to whether they included enough information to determine commercial viability, and if their results were competitive with the performance of already commercialized batteries. I found that only 2-3% of articles included sufficient information to calculate the kind of information commonly included in battery datasheets. Using the information available in that subset of articles, I found that 20% of those articles demonstrated results competitive with commercial technology. So, which of the 98% of other articles demonstrate that same sort of performance? Without the information, it’s impossible to tell. For those that do include enough information, I made assessments and comparisons using a visual database tool.
This database tool uses a graphic called a radar chart (see figure 1) to assess whether a particular device meets the necessary requirements for an application, or to compare the relative performance of several devices. In order to establish “high marks” for a given criterion, I identified first-in-class commercial technologies and organized performance data. For example, I found a battery chemistry called Lithium Titanate (LTO) that can last for more than 25,000 cycles (appealing for renewable energy applications).
This data was then processed using a simple filter format in Excel that allowed me to see the best-in-class for a particular category. I discovered that drone batteries can deliver the highest power of almost any battery. Electric vehicle batteries were by far the most affordable. Medical and defense technologies had the highest specific energy. Using this tool, industry can make a one-to-one comparison between various researches, and science can identify directions with high commercial potential. This is a tool that helps strengthen the tie between science and industry in the energy storage sector.
I re-emphasize that because certain criteria are essential to know for practical commercial batteries, researchers help the scientific community and industry by including enough information to make those evaluations. Paying attention to both component-level and cell-level metrics enhances scientific understanding, delivers better performance, and frees up time and money for further research and opportunities. I am currently working on developing this tool into a user-experience oriented application tailored towards energy storage professionals.