Cathode materials with higher energy density than layered oxide materials are required for future demands of vehicle electrification. Disordered rock-salt Li-excess structures, such as Li3NbO4, have been demonstrated to achieve capacities of greater than 300 mAh/g reversible capacities at elevated temperatures. The high capacity is believed to be due to reversible redox chemistry of the oxide anions. This new class of high energy cathode materials provides an opportunity for a step change increase in cell level energy density. However, improvements are still required in material conductivity and stability. In this presentation, we demonstrate material improvements which enable high specific capacity at room temperature and extended cycle life.
Development of a practical, low cost high voltage electrolyte to enable lithium ion battery (LIB) operation above 4.5V will enable high energy density cells for vehicle applications. Towards that end, Dow Energy Materials is investing in programs to develop safe, cost-effective, high voltage electrolyte solutions. This effort leverages core capabilities of Dow's large R&D organization, such as fundamental modeling, low cost synthesis methods, and combinatorial formulation development. A practical solution to a high voltage electrolyte formulation requires all of these elements for success. This multi-faceted approach was utilized by Dow to determine the viability of ethylmethoxyethyl sulfone (EMES) as a high voltage electrolyte in full lithium ion cells.
Over the last decade, many governments have implemented more stringent regulations on vehicle fuel economy and CO2 emissions. For example, European targets for new passenger cars reduce emissions to 130g CO2 per kilometer by 2015, with further reduction to 95g by 2021. Start-stop vehicle engines, which shut off during stops for traffic or at a light, play an important role in achieving these targets. These vehicles require a battery with sufficient power to re-start the engine over a wide range of conditions and sufficient energy to run the lights, air conditioning, etc. on the vehicle when stopped. Lithium ion batteries are promising candidates to replace currently used lead acid batteries due to their high energy density as well as longer cycle life. However, the power performance of lithium ion batteries is limited at low temperatures required for automotive applications due to low conductivities of the electrolyte and the solid electrolyte interphase (SEI). Solutions to the low temperature problem generally consist of adding solvents with very low melting points and/or low viscosity to the formulation which keep the formulation from freezing or reduce the viscosity at low temperature. However, these solvents tend to be detrimental to high temperature stability, required to meet the lifetime requirements of the vehicle batteries. Wildcat has developed electrolyte formulations that improve the power performance at low temperature, but improve or maintain the high temperature stability relative to baseline electrolyte formulation. Wide temperature range formulations were developed for both NMC//graphite and NMC//LTO electrode chemistries.
Solid state batteries offer significant advantages over today’s cells containing liquid electrolytes. In large format cells required for automotive applications, replacement of volatile, flammable organic solvents with a solid phase electrolyte eliminates safety concerns. Other benefits include lower costs due to elimination of the costly separator and the potential to improve energy density by enabling safe lithium metal anodes. Solid state cells also offer opportunities for novel cell formats, shapes, and packaging. While significant improvements in ionic conductivity of materials have been demonstrated, few examples of solid state batteries with practical electrode thicknesses are reported. A primary challenge in an all solid state battery is the difficulty of rapidly moving charge across solid/solid interfaces within the electrodes and across the electrode/electrolyte interface. Demonstrated progress in improving the ionic conductivity of solid electrolytes does not necessarily result in improved cell performance due to these interfacial impedances within the cathode and/or between the electrodes and the electrolyte. Research in solid state batteries primarily centers on maximizing bulk ionic conductivity of the solid electrolyte or adding coating/interface layers to reduce impedance. However, all solid cells can be enabled through formulation optimization using known materials by reducing the dominant interfacial impedances. In this presentation, we present results showing the marked improvement in all solid cell performance through formulation optimization and the novel use of solid electrolyte additives. In liquid electrolyte cells, significant optimization of electrode composition and processing conditions are required to achieve desired porosity, connectivity, etc. for optimal performance. Similar logic is required to optimize ionic conductivity, electronic conductivity, and electrode density in solid state composite electrodes. Electrode additives are shown to reduce interfacial impedance both within the electrode and across the electrode/electrolyte interfaces. Composite electrolytes based on ceramic particles embedded in an ionically conductive polymer can also benefit from formulation optimization. The inclusion of the ceramic particles into a polymer membrane can 1) improve ionic conductivity by altering the total crystallinity of the polymer and 2) improve the mechanical properties of the membrane. However, use of a composite membrane provides additional interfaces between the particles and the polymer, and can also alter the interfacial impedance between the solid electrolyte and the electrodes. Again, formulation with additives can affect both ionic conductivity and interfacial impedance. A further aspect in formulation designs for solid state batteries are interactions between components. Similar to observations in liquid electrolyte cell where, for example, components in the cathode can have negative effects on other cell components, interactions can also be observed in solid state batteries. Thus, substantial opportunities will be shown for improvement in solid state cell performance by proper formulation of the cathode and electrolyte without the need for new ionic conductor material development.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.