Massachusetts Institute of Technology (MIT) battery wizard and A123 System co-founder Yet-Ming Chiang recently helped create another spin-out, 24M Technologies, that uses a semi-solid electrolyte in a flow battery.
Yet-Ming presented on the technology at the recent Yale Climate and Energy Institute annual conference, and this week MIT announced the publication of a paper on 24M's technology. The firm uses concentrated nanoparticle suspensions of common lithium-ion (Li-ion) battery cathode materials such as lithium cobalt oxide (LCO) and lithium iron phosphate (LFP) in an electrolyte to create an energy-dense liquid that can slowly flow over a membrane like the separators used in conventional Li-ion batteries; a similar suspension of an anode material like graphite or lithium titanate (LTO) flows over the membrane on the other side.
The basic electrochemistry, and thus the power densities and voltages, are like those of Li-ion batteries, but now, as in a flow battery, the energy capacity is a product of the volume of the electrolyte suspension. The paper calculates, based on the lab cells created so far, that energy densities of 300 Wh/L to 500 Wh/L and specific energies of 130 Wh/kg and 250 Wh/kg should be possible – the top ends of those ranges would beat out current Li-ion battery technology.
Just as critically, the authors project that the suspensions will contribute some $40/kWh to $80/kWh to the cost of the battery, potentially meaning that system-level costs could hit the widely cited targets of $250/kWh for electric vehicle batteries or $100/kWh for stationary (grid storage) batteries.
In this respect, the technology looks more promising than the analogous approach based on vanadium redox chemistry developed by the Fraunhofer Institute for Chemical Technology, where the electrolyte solutions alone are projected to run to over $200/kWh. However, it's clearly far from certain at this early date if those projections will pan out.