The National Aeronautics and Space Administration has selected two research proposals—one focused on silicon-anode lithium batteries, and the other on lithium-sulfide energy cells—for additional funding under its space technology development program. As part of the administration’s Game Changing Development initiative, the funding is being put toward the construction of high-density, low-mass energy storage devices.
The development of high-density batteries will reduce the mass required to store electrical power in future human and robotic space missions. Specifically, the proposals are targeting energy storage systems that are highly reliable, can survive harsh space environments, and are more than 50% lighter than existing systems. According to Steve Jurczyk, associate administrator for NASA’s Technology Mission Directorate, this field of research is critical for future missions to Mars, the edges of the solar system, and into deep space.
Both research projects are focused on technology that could propel lithium-ion batteries into the next stage of their evolution. The first was submitted by Amprius Inc., an energy storage company based in Sunnyvale, Calif.. The company proposed a Li-ion battery system using silicon as the anode material. As opposed to most Li-ion batteries, which are designed with graphite anodes, a silicon-anode battery has the potential to deliver up to 10 times more energy per unit. Amprius has made some progress with these devices, using a nanostructured silicon material that creates four times the energy density of graphite-based Li-ion batteries.
The problem with silicon-anode batteries, however, has always been the nature of the silicon itself. In contrast to graphite, the silicon anode expands up to 400% of its volume upon lithium-ion insertion. While this allows the anode material to store a larger amount of electrical energy, it also forms cracks in the silicon, resulting in significant loss of charge and eventually battery failure. As a result, the charge-discharge cycle life is generally very short. Amprius has apparently overcome these problems using silicon nanowires that can expand and contract without breaking.
The University of Maryland Energy Research Center (UMERC) submitted the proposal for the second project. It focuses on a garnet electrolyte-based lithium-sulfur battery system. Unlike liquid-electrolyte batteries, the lithium-sulfur device uses a solid-state ceramic electrolyte, which not only has an extremely low resistance, but also protects against battery fires. According to Chunsheng Wang, an associate professor of chemical and biomolecular engineering at the university, the high stability of the garnet-ceramic electrolytes has enabled the use of metallic lithium anodes, which have the highest theoretical energy density among anode materials, and sulfur cathodes.
Both projects will be awarded up to $1 million in funding over the next 12 months, as part of second phase of the GCD program. Phase I projects were awarded about $250,000. This gave the research teams an opportunity to conduct an eight-month component test and analysis phase. Phase II is the engineering hardware phase, while Phase III will consist of prototype development.