Reducing Side Reactions Using PF 6 -based Electrolytes in Multivalent Hybrid Cells
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Reducing Side Reactions Using PF6-based Electrolytes in Multivalent Hybrid Cells Danielle L. Proffit1,2, Albert L. Lipson1,2, Baofei Pan1,2, Sang-Don Han1,2, Timothy T. Fister1,2, Zhenxing Feng1,2, Brian J. Ingram1,2, Anthony K. Burrell1,2, and John T. Vaughey1,2 1
Joint Center for Energy Storage Research, Argonne National Laboratory, Argonne, IL 60439, U.S.A. 2 Electrochemical Energy Storage Department, Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439, U.S.A. ABSTRACT The need for higher energy density batteries has spawned recent renewed interest in alternatives to lithium ion batteries, including multivalent chemistries that theoretically can provide twice the volumetric capacity if two electrons can be transferred per intercalating ion. Initial investigations of these chemistries have been limited to date by the lack of understanding of the compatibility between intercalation electrode materials, electrolytes, and current collectors. This work describes the utilization of hybrid cells to evaluate multivalent cathodes, consisting of high surface area carbon anodes and multivalent nonaqueous electrolytes that are compatible with oxide intercalation electrodes. In particular, electrolyte and current collector compatibility was investigated, and it was found that the carbon and active material play an important role in determining the compatibility of PF6-based multivalent electrolytes with carbon-based current collectors. Through the exploration of electrolytes that are compatible with the cathode, new cell chemistries and configurations can be developed, including a magnesiumion battery with two intercalation host electrodes, which may expand the known Mg-based systems beyond the present state of the art sulfide-based cathodes with organohalide-magnesium based electrolytes. INTRODUCTION With the spread of renewable energy production and the electrification of transportation, the role of and requirements for batteries will expand in future years. An important technical requirement for batteries, especially those with commercial goals, is that their energy density as a function of mass and/or volume must be high. One approach for achieving energy densities beyond that offered by lithium ion technology is to replace the monovalent Li1+ ion with a multivalent ion, such as Mg2+. If the cathode material can accommodate the charge transfer from such a multivalent ion, this technology could ideally double the capacity from the cathode, given the same volume, as compared to lithium ions. While research on magnesium batteries has historically focused on sulfide based cathodes combined with highly corrosive electrolytes [1], many scientific challenges remain as the field moves towards enabling oxide cathodes that may provide higher voltage and power. One of those scientific challenges is the ability to identify the intercalation of the ion of interest, as opposed to side reactions that do not correspond to reversible energy storage. For example, Figure 1a shows electrochemical behav
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