This Small Business Innovation Research Phase I project will develop a novel secondary battery platform based on a lithium sulfide-carbon composite cathode and a silicon anode that demonstrates high energy density and long cycle life. 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. Li2S/Si configuration offers the highest theoretical specific energy (1.55 kWh/kg) based on the lithium-ion battery platform and furthermore is not subject to the safety issues related to other secondary lithium battery systems which employ metallic lithium. The development of the Li2S/Si battery has been hindered by the limited cycle life of the cathode and the anode. On the cathode side the company has developed methods of creating porous carbon hosts for sequestering sulfur and on the anode side methods of synthesizing Si nanowires to prevent pulverization, hence obtaining stable performance for both electrodes. In the Phase I Project the company will optimize performance of their electrodes and develop scalable processes for production. This research will result in continued performance improvement of the Li2S/Si platform and identify critical processing techniques and challenges for scale-up.
The broader impact/commercial potential of this project is that it is able to bring about significant changes to the rechargeable lithium battery technologies and the market because of their approximately three fold energy density advantage over the current chemistry platforms (0.2-0.6 kWh/kg). Lithium-ion batteries (LIB) currently have a market of $11-13 billion and the sales are expected to increase to at least $40 billion by 2020. LIBs are widely employed in portable electronics and are expected to be the driving force for development of the new generation of hybrid and electric vehicles. If the proposed technology can be brought to commercialization, the improved performance characteristics such as higher energy density, higher power and longer cycle life will allow manufacturers/consumers to power their devices/vehicles for longer periods of time and gain performance advantages in their respective applications.
Lithium-ion batteries are among the most promising and fastest growing technologies in the energy storage sector. They 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, various challenges associated with safety, cost, storage capacity, and reliability has limited their adoption as the electrochemical storage technology of choice. Current lithium-ion cells with oxide-based cathodes, such as LiCoO2 and LiMn2O4, have theoretical specific energies of approximately 430−570 Wh/kg, but their practical (or obtainable) specific energies are only in the range of 120−200 Wh/kg. The goal of this Phase I work was to develop a novel secondary battery platform based on a lithium sulfide-carbon composite cathode and silicon anode that demonstrates high energy density and long cycle life. Growing needs in consumer applications are driving the current battery technologies to their limits. Li2S/Si configuration offers the highest theoretical specific energy (1.55 kWh/kg) based on the lithium-ion battery platform and furthermore is not subject to the safety issues related to other secondary lithium battery systems, which employ metallic lithium. The development of the Li2S/Si battery has been hindered by the limited cycle life of the cathode and the anode. On the cathode side our team has developed methods of creating an in situ porous carbon host for sequestering lithium sulfide to improve cycle life. Specific Phase I/IB objectives were 1) developing scalable processes for production of the cathode material; 2) materials characterization; 3) Optimizing the electrolyte for best cathode and anode performance and 4) fabricating and testing of cell prototypes for high energy and long cycle life. We feel that our cathode material (Li2S@C) paired with high capacity Si anode is a potential disruptive technology in the lithium-ion battery market. In Phase I of the SBIR project we have developed functional Li2S@C cathode material with high capacity and stable cycling performance building upon the NOHMs in situ synthesis technology. Coin cell testing has shown that the composite yields a gravimetric capacity of ~450mAh/g at 0.5C charge-discharge rate and stable cycling performance. Half cell and full cell testing using a silicon anode has been performed and stable performance of up to ~300 cycles has been obtained. In Phase 1B we have developed electrolyte formulations compatible with both the anode and cathode and accomplished a full cell configuration which gives good capacity and stable cycling performance. We have also performed preliminary studies on the multi-gram scale synthesis of Li2S-based cathode materials and demonstrated their performance in pouch cell configuration. We have successfully demonstrated the feasibility of the Li2S-Si battery as a promising power source for applications requiring high specific energy, energy density, long cycle life, and safety.
