Strain Sensitivity of Li -ion Conductivity in β - Li 3 PS 4 Solid Electrolyte
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An interfacial study is performed using ab initio molecular dynamics (AIMD) simulations to elucidate the electrochemical interfacial stability of an ionic liquid (IL) as component of an electrolyte in contact with a Li-metal anode when an additive, vinylene carbonate (VC), is added to the electrolyte. The IL electrolyte is composed of 1-butyl-1-methylpyrrolidinium bis(fluoro-sulfonyl)-imide (PYR14 + FSI − ) with lithium bis(trifluoromethane-sulfonyl)imide salt (Li + TFSI − ) in a 8:2 concentration ratio. Reactions observed at the interface electrolyte/Li-metal during the AIMD simulations are verified by electronic structure calculations using density functional theory calculations considering a continuum solvent model. We found that the addition of VC to the IL prevents further reduction of the counter-ion TFSI − and retards reduction of FSI − in comparison to the case when the additive VC is absent. The PYR14 + reduction is never observed with or without the additive. The 1st, 2nd, and 3rd electron affinities of the PYR14 + are −0.08, −0.36 and −3.65 eV, indicating little to large repulsive behavior against electrons. The opposite is observed for the two negative ions, FSI − and TFSI − , which yield 1st electron affinities of 1.73 and 1.83 eV, respectively. Reactions obtained under open circuit conditions. Dissociation mechanisms are presented for all IL components reduced at the IL/Li-metal interface.
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The fundamental understanding of the coupled mechanical/chemical degradation of the SEI layer during lithium cycling will enable the project to identify the desirable mechanical properties on SEI/lithium as a system and the specific transport properties that enable the homogenous lithium stripping/plating while avoiding the mossy structure. Furthermore, it will allow the project to develop a highly impactful strategy to protect lithium metal and achieve dendrite free high cycle efficiency, which can dramatically increase the energy density of lithium batteries for EV applications. During past three years, four coherent steps have been taken to solve the coupled mechanical and electrochemical degradation: (1) Developed a comprehensive set of in-situ diagnostic techniques to investigate the coupled mechanical/chemical properties of SEI layer and its impact on lithium striping/plating. (2) Identified failure mechanisms of SEI/Li as a whole electrode system using in-situ electrochemical tools. (3) Established a design strategy of protective coatings on Li metal to extend the cycle life Li meal electrode. (4) Developed novel surface coatings as the artificial SEI layer to protect Li metal and significantly extend cycle life. During past 3-year budget period, we have published over 16 peer-reviewed paper, filed 7 patents, and given over 30 invited talks. 5 graduated students and 2 postdocs were supported by this project.
As the world have witnessed the tremendous development in portable electronic devices as well as electric vehicles, the current generation lithium-ion battery is unlikely to satisfy the bourgeon of market and the demand of the customers. A next generation battery, with cell energy density higher than 500 Wh kg -1 , needs to be developed to meet the growth of the industry. With its high theoretical capacity (3,860 mAh g -1 , or 2,061 mAh cm -3 ) and low electrochemical potential (–3.04 V versus the standard hydrogen electrode), lithium metal has been regarded as the ideal candidate for the next generation battery anode. In fact, Lithium metal anode is irreplaceable for Lithium-Sulfur chemistry. However, the continuous formation of inactive Li, which eventually leads the loss of reversible capacity of the cell, has prevented lithium metal to be used as anode in commercial rechargeable cells. The ultimate goal of the project is to propose a pathway to enable Li metal battery for stable cycling at 99.9% of Coulombic efficiency with energy density higher than 500 Wh kg -1 . A variety of advanced characterization tools, electrolyte systems, 3D current collectors and failure analysis methodologies have been developed throughout the project during the past 5 years. The UCSD effort is carried out by the groups of Ping Liu and Shirley Meng.
The goal off this EERE-BMR-Battery 500 consortium project was to provide the supporting science and to lead the Keystone 1 project. Key findings include: identification of 1st cycle loss of high nickel NMC materials as a major opportunity to increase the capacity of these cathode materials. The selective use of substituents and surface coatings was identified as a potential way of decreasing the 1st cycle loss and in increasing capacity retention. Niobium at around the 1% level was found to be optimum. In addition, operando DSC was utilized to scope out the stability range of electrolytes developed by the Battery 500 team.
In Phase 1, the University of Texas at Austin explored many methods of cathode design, synthesis, and modification, while also developing an understanding of the relationships among the cathode, anode, and electrolyte. Some of the major accomplishments are highlighted in this report.
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Glow discharge electrolysis of fused electrolytes
Striped thick-film platinum electrodes help insure lower overall cell resistance by permitting free flow of gases in gaps between stripes. Thickfilm stripes are also easier to fabricate than porous thin-film electrodes that cover entire surface. Possible applications for improved cells include oxygen production from carbon dioxide, extraction of oxygen from air, small fluidic pumping, sewage treatment, and fuel cells.
The alkali metal thermoelectric converter (AMTEC) is a device for the direct conversion of heat to electrical energy. The sodium ion conductor beta-double prime-alumina is used to form a high-temperature regenerative concentration cell for elemental sodium. An AMTEC of mature design should have an efficiency of 20 to 40 percent, a power density of 0.5 kilowatt per kilogram or more, no moving parts, low maintenance requirements, high durability, and efficiency independent of size. It should be usable with high-temperature combustion, nuclear, or solar heat sources. Experiments have demonstrated the feasibility of the AMTEC and confirmed the theoretical analysis of the device. A wide range of applications from aerospace power to utility power plants appears possible.