This Small Business Innovation Research Phase I project will address issues related to the development of high-energy lithium-ion batteries. Today, mobile devices require faster performance and smaller sizes for greater portability. However, the faster processors in these devices impose energy density requirements that push today's lithium battery technologies to their limits. State-of-the-art lithium-ion electrode materials used in mobile devices produce a maximum energy density of 0.28-0.6 kWh/kg. Our team is developing a commercial secondary/rechargeable Li-S battery with a theoretical energy density of 2.3 kWh/kg, which could dramatically alter the electrical energy storage landscape for all portable devices. Development of this Li-S battery has been limited by poor cycle life. This project will remedy this by developing an optimal porous carbon host for sequestering sulfur in the battery cathode. The host will limit polysulfide dissolution in order to increase cycle life of our current sulfur-infused carbon nanostructure (S@C) composite cathode materials from 650 cycles to 1000 (or more) cycles. In addition, by utilizing low-cost, commercially available carbon feedstocks (carbon aerogels, graphene, and high-sulfur coal), the results of this research will likely reduce the direct costs of manufacturing carbon-sulfur composite cathodes.
The broader impact/commercial potential of this project is significant. Li-ion batteries currently have a $11-13 billion market and the market size is expected to reach $44 billion by 2020. Li-ion batteries account for close to 75% of all secondary (rechargeable) batteries used in portable electronics. Secondary lithium-sulfur batteries employing sulfur as the cathode and metallic lithium as the anode offer the highest energy storage potential of any battery based on two solid elements. These devices offer more than twice the energy capacity of the currently deployed lithium-ion battery technology with half the weight. If this potential can be brought to commercialization, it has the potential to displace lithium-ion cell technology because of the higher energy density, low cost, and widespread availability of sulfur. This could have significant impacts on mobile devices, electric vehicles market, and the broader energy storage market, enabling greater efficiency and performance in all those sectors.
Li-ion batteries currently have a $14 billion market and are expected to reach $44 billion by 2020. They account for close to 75% of all secondary (rechargeable) batteries used in portable electronics. However, state-of-the-art lithium-ion electrode materials are limited to a maximum power density of 0.28-0.6 kWh/kg while lithium-sulfur batteries have the highest theoretical specific energy of the secondary solid-state lithium battery chemistries. However, the most significant barrier to commercialization of this ultra high energy battery chemistry is polysulfide dissolution in the electrolyte - that is, the dissolving of soluble electrochemical discharge products during cell cycling. NOHMs Technologies has developed a sulfur-carbon composite electrode that ensures sulfur is tightly bound to the carbon, effectively arresting dissolution in the battery. This Phase I project investigated a number of porous carbon hosts for sequestering sulfur for use in a Li-S secondary battery. The carbon host plays an important role in encapsulating the sulfur and providing a conductive substrate for electron transfer increasing the life of the battery. We have tested low-cost commercially available carbon feedstocks: carbon aerogels, graphene, and high-sulfur coal (lignite, flame coal), and have shown high specific capacities and long cycle life. Our approach using our optimum carbon cathode to sequester sulfur (S@C) has demonstrated superior specific energy density and increased columbic efficiency. In addition to an optimum carbon we have also developed a novel method of infusing sulfur into porous carbon host, this has been shown to ensure long-term sequestration. The objectives of this Phase I work was to: 1. Evaluate different carbon matrices, as hosts for sequestering sulfur for Li-S batteries. 2. Conduct detailed physical and electrochemical characterization of the carbon matrices to determine how activation and thermal treatment conditions affect their physical properties. 3. Conduct experiments to enhance the sulfur loadings in the most promising carbon frameworks. 4. Assemble coin cells with lithium metal as the anode and S@C cathodes and demonstrate high specific energy and high specific capacity at various C rates. We have identified necessary characteristics needed in a carbon for sulfur support in a Li-S battery and we are working with a promising carbon blend that we are now testing on larger scale pouch cells with the aim to make prototype consumer electronics batteries.
