It seems only yesterday we launched the Joint Center for Energy Storage Research (JCESR), but in reality, it was nearly four years ago. Our vision was bold: high-performance, low-cost electricity storage that would lead to widespread deployment of electric vehicles and transformation of the electricity grid with renewable generation and distributed energy resources.
With that vision in mind, we set as our five-year mission the attainment of three legacies:
- A library of fundamental knowledge of the materials and phenomena of electrical energy storage at atomic and molecular levels
- Two prototypes—one for transportation and one for the electricity grid—that, when scaled to commercial production, are capable of delivering five times the energy density at one-fifth the cost of commercial batteries available in 2011
- A new paradigm for battery R&D, integrating discovery science, battery design, research prototyping, and manufacturing collaboration in a single highly interactive organization
With only a little more than a year left in our five-year charter, it is worth taking stock of our progress in achieving these legacies and the ongoing research directions that will fulfill our five-year mission. We can be proud of the tremendous amount we have accomplished in four short years. The foundation we have laid and the timetable we are pursuing are on track to complete our legacies in our final year.
Library of Knowledge
With more than 250 published scientific journal articles, we are well on our way to attaining our first legacy, a library of fundamental knowledge for beyond-lithium-ion batteries. Of these articles, 18 are designated by the ISI Web of Science as “Highly Cited Papers” and the ten most cited have collected 994 citations in other scientific papers. In addition to journal publications, JCESR has filed 52 invention disclosures and 27 patent applications.
Another important component of our library of knowledge is a database of simulated materials properties open to all interested researchers. As a part of the Electrolyte Genome/Materials Project, two sets of data were released in May 2016: 1,500 compounds investigated for multivalent intercalation electrodes and 21,000 organic molecules relevant for liquid electrolytes as well as a host of other research applications.
In all, more than 24,000 Electrolyte Genome/Materials Project calculations have been released to the public, along with apps to enable their use. These unique apps and data sets reveal otherwise invisible systematic trends in electrochemical behavior, allow innovative hypotheses to be validated or refuted, and enable rational selection of the most promising materials for a given application. Since its release, this open source database has been accessed by the community more than 18,500 times.
The five techno-economic models created by JCESR for designing virtual batteries on the computer are another important contribution to our first legacy. These models are being used to evaluate the best pathways for beyond-lithium-ion systems to reach 400 watt hours per kilogram (400 Wh/kg) and $100 per kilowatt hour ($100/kWh), key targets for batteries used in electric vehicles and on the grid.
In pursuit of the important second legacy, JCESR took a major step forward in January 2016 when it selected designs for proof-of-principle prototypes for the grid and transportation. These designs are built on the fundamental understanding of the materials and phenomena of energy storage developed in our first legacy.
Grid: The grid prototype is an organic “redox flow” battery, which consists of two energy-dense liquids that store and release charge as they flow through the battery and undergo reduction and oxidation (“redox”) reactions.
JCESR is pursuing two innovations in flow batteries. The first innovation involves the use of inexpensive, recyclable and versatile organic molecules as energy storing active ingredients, and linking these organic molecules together in oligomers of up to 10 molecules, polymers of up to 1000 molecules and colloidal particles of a million to a billion molecules. These linked “macromolecules” are large enough to be blocked by JCESR’s second innovation, a special porous polymer membrane, providing a simple solution to prevent crossover of the active materials between the anode and cathode liquids.
Transportation: The selected transportation prototype contains a lithium metal anode protected from degradation by a graphene oxide membrane, a polymer-composite sulfur cathode, and an electrolyte that is sparingly soluble for the polysulfides that form during charge and discharge.
This battery system is attractive because of its high theoretical energy density and the low cost of sulfur. Key to success will be achieving a very low ratio of electrolyte to sulfur content. Full cell testing of each of these concepts is now underway, and proof-of-principle prototypes will soon be evaluated.
JCESR maintains continued development of other promising prototype options (see Primary Research Directions below), but believes that the target of $100/kWh at the pack level will be achieved with these two systems by the end of JCESR’s five-year charter.
New R&D Paradigm
We have already achieved our third legacy. Our new paradigm for battery R&D integrates talent from 20 organizations comprising more than 180 researchers – including students, postdocs, early career researchers, senior scientists, and engineers from five national laboratories, ten universities, and five private sector partners. Key features of the new paradigm are frequent in-person interactions that build strong personal relationships, and continuous evaluation of our strategies for achieving our science and prototype legacies.
Our new paradigm embraces the larger battery R&D community – JCESR’s collaborative papers engage 60 institutions and more than 300 researchers outside our 20 partner organizations. In addition, JCESR has assembled a network of more than 100 affiliates in 25 states. We continue to grow JCESR’s momentum with its “dream team” of battery scientists and continual refinement of our new paradigm.
Primary Research Directions
Grid and Transportation Prototypes: For the remaining year, JCESR’s research will be directed primarily at improving the prototypes for the redox flow battery for the grid and lithium-sulfur battery for transportation.
With regard to flow batteries for the grid, JCESR scientists are developing our new concept of redox-active organic macromolecules comprising oligomers, polymers, and colloidal particles. These macromolecules introduce versatile new design parameters for exceeding existing limits on energy density, lifetime, and efficiency. These redox-active molecules (RAM), redox-active oligomers (RAO), redox-active polymers (RAP), and redox-active colloids (RAC) are especially impactful when used with another JCESR innovation, polymer membranes with adjustable pore sizes. The combination of macromolecular organic active materials and adjustable porous polymer membranes enables multiple pathways to higher performance and lower cost.
For the lithium-sulfur battery, we are concentrating our efforts on three design features. One is electrolytes that limit undesirable reactions of the polysulfides that form during charge and discharge. Another is binders in the sulfur cathode that trap polysulfides before they dissolve in the electrolyte and ensure mechanical integrity of the cathode during cycling. The third is special membranes that prevent movement of polysulfides from the cathode to the anode and maintain a smooth anode surface during cycling.
We believe that the final embodiment of the lithium-sulfur prototype will require a combination of these features to meet the JCESR cost and performance targets.
Air-Breathing Aqueous Sulfur Flow Batteries: JCESR researchers have developed a new approach for a flow battery for the grid that combines an aqueous sulfur anode and oxygen cathode. This concept takes advantage of the low cost of sulfur and water and eliminates the need for a lithium metal anode and its associated challenges. The extremely low cost of this concept holds promise for novel grid applications such as seasonal storage.
Oxygen was chosen as a catholyte system based on its past use in fuel cells, which convert chemical into electrical energy by reaction of oxygen and hydrogen. This battery concept represents a revolutionary approach to long duration energy storage for the grid.
Multivalent Batteries: In multivalent batteries, scientists replace the singly charged lithium ions with ions having two or three positive charges (“multivalent”) to increase the battery energy storage capacity by a factor of two or three. Cathodes for multivalent batteries are a major challenge. Only a few operate at sufficient voltage, capacity, and working ion mobility to meet JCESR’s performance targets.
We developed a materials genome approach to survey 1500 combinations of working ions with cathodes and identify the most promising candidates. Magnesium and calcium paired with oxides of chromium and manganese were found to have the highest voltage and capacity.
These genomic studies revealed the most promising cathodes and previously unrecognized general trends in battery research. Efforts continue in the area of magnesium anodes and electrolytes, complementing our focus on the cathode area.
In its first four years, JCESR cast a wide net of possible next-generation battery technologies, then narrowed its focus to the most promising opportunities. We are now exploiting these opportunities to develop and refine proof-of-principle prototypes for the remainder of our five-year charter.