The US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) will award up to $30 million in funding for a new program focused on creating innovative components for the next generation of batteries, fuel cells, and other electrochemical devices.
ARPA-E’s Integration and Optimization of Novel Ion Conducting Solids (IONICS) program (DE-FOA-0001478) seeks to create transformational electrochemical cells by creating components built with solid ion conductors that have a wide range of desirable properties including low ionic area-specific resistance (ASR); high chemical and electrochemical stability; high selectivity; good mechanical properties; etc. through innovative approaches to overcome tradeoffs among coupled properties.
IONICS also seeks to develop and apply methods for processing of solid ion conductors and their integration into electrochemical devices.
Components built with solid ion conductors, especially separators, have the potential to serve as enabling platforms, as demonstrated by the wide application of Yttria-Stabilized Zirconia (YSZ) ceramics and perfluorosulfonic acid (PFSA) polymers (e.g., Nafion). The IONICS Program Categories focus on specific electrochemical cells with high impact for the energy sector whose commercial potential will be significantly enhanced with improved components built from solid ion conductors.
Program Categories include:
- Lithium (Li) ion conductors that enable the cycling of Li metal without shorting;
- Selective and low-cost separators for batteries with liquid reactants (e.g., flow batteries);
- Alkaline conductors with high chemical stability and conductivity; and
- Other approaches that could achieve the IONICS Program Objectives.
A key requirement of the IONICS program is the creation of manufacturable components with dimensions comparable to that used in a practical device, in order to ensure that technical challenges associated with large-area processing are addressed. A second key requirement is that the cost of materials and processing is sufficiently low to allow for the broad adoption necessary for significant energy impacts.
Background. Electrochemical cells can be used to both extract electrical energy from chemical bonds (e.g. in a fuel cell for combined heat and power applications) as well as to store electrical energy in chemical bonds (e.g. charging a battery). The cells can carry out these processes efficiently and across a wide range of power levels, which allows them to be used in both a distributed manner and in large centralized facilities.
These basic capabilities of electrochemical cells have two additional benefits: (1) high round-trip energy efficiency that in many cases has been realized practically (e.g., Li-ion cells can provide 90% round-trip DC-DC efficiency at relevant rates); and (2) scalability across a wide range of power levels (i.e., <1 kW to >1 MW), making them suitable for both small, distributed and large, centralized installations.
Previous ARPA-E programs have pursued advances in electrochemical devices and processes, including Batteries for Electrical Energy Storage in Transportation (BEEST); Grid-Scale Rampable Intermittent Dispatchable Storage (GRIDS); Robust Affordable Next Generation Energy Storage Systems (RANGE); Modern Electro/Thermochemical Advances in Light-metal Systems (METALS); Reliable Electricity Based on Electrochemical Systems (REBELS); and many projects within the OPEN portfolios.
These projects, however, principally focused on advances at the device or process level.
Based on the key challenges encountered in previous ARPA-E programs and in other research and development efforts, ARPA-E believes tremendous opportunities exist in developing a new generation of enabling components built with solid ion conductors.
There are many classes of ion conductors, including aqueous and nonaqueous salt solutions; solid ceramics; polymers and polymer gels; molten salts; and others. Electrochemical cells that operate near ambient temperatures typically use either a liquid electrolyte (e.g., aqueous H2SO4 in the case of lead-acid batteries, or LiPF6 in organocarbonates in the case of Li-ion batteries) or a polymer containing small molecules (e.g., hydrated PFSA in the case of fuel cells and electrolyzers).
While liquid electrolytes have benefits including high conductivity and excellent wetting of electrode surfaces, IONICS is specifically focused on electrolyte attributes unattainable with liquids, including resistance to deformation (i.e., a “solid” form), wide thermal stability, high selectivity for desired ions and neutral molecules, and other attributes detailed through this FOA.
Among the properties required of a solid ion conductor are:
The ionic area-specific resistance (ASR), which helps determine the power capability of an electrochemical device; it includes the ionic conductivity (an intrinsic property) and the thickness (an extrinsic property).
Selectivity—the ability of a material to transport ions and neutral molecules at different rates, with a goal of high selectivity for a desired species, typically a single ion.
- Electro)chemical stability—both electrochemical stability and chemical stability, the former generally referring to stability as a function of an applied potential. In the ideal case all adjacent phases in a device are thermodynamically stable against reaction; in practice, stability is frequently realized with the help of slow kinetics and the formation of passivating layers.
- he electronic ASR reflects resistance to electronic current, and includes the electronic conductivity and thickness. For a separator, the electronic ASR is ideally infinite, while for mixed conductors within electrodes a low ionic and electronic ASR is desirable.
- Thermal properties refers to the dependence of key properties such as ionic and electronic ASR, (electro)chemical stability, mechanical properties, etc. on temperature. Ideally, a component is able to conduct current, resist degradation, and remain strong and tough across a wide range of temperatures.
- Mechanical properties are critical both during both fabrication (e.g., for roll-to-roll processing the tensile strength and ability to wind around a mandrel are relevant) and during operation (e.g., a high shear modulus is theorized to prevent shorting during cycling of Li metal).
- Processing—the method used to create components built with solid ion conductors, and cost includes both the processing cost and the bill of materials.
- Device integration—the ability to integrate components built with solid ion conductors with other device components, as well as the implication of the components built with solid ion conductors on other device components (e.g., existing PFSA membranes require the use of costly Pt for the oxygen electrode catalyst).
The overall objective of the IONICS program is to enable widespread deployment of transformational electrochemical cells with energy applications through the development of separators and porous electrodes built with solid ion conductors.
To meet this objective, the IONICS program seeks to overcome difficult technical challenges associated with simultaneously achieving a wide set of property attributes noted above; cost-effective and scalable processing of solid ion conductors; and the integration of component with solid ion conductors into devices.