In situ surface protection for enhancing stability and performance of conversion-type cathodes
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Review In situ surface protection for enhancing stability and performance of conversion-type cathodes
Feixiang Wu, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA Oleg Borodin, Electrochemistry Branch, Sensors and Electron Devices Directorate, Army Research Laboratory, Adelphi, Maryland 20783, USA Gleb Yushin, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA Address all correspondence to Gleb Yushin at [email protected] (Received 7 March 2017; accepted 13 June 2017)
ABSTRACT The use of in situ formed protective layer on conversion cathodes was introduced as a cheap and simple strategy to shield these materials from undesirable interactions with liquid electrolytes. Conversion-type cathodes have been viewed as promising candidates to replace Ni- and Co-based intercalation-type cathodes for next-generation lithium (Li) and Li-ion batteries with higher specific energy, lower cost, and potentially longer cycle life. Typically, in conversion reactions two or three Li ions may be stored per just one atom of chalcogen (e.g., S or Se) or transition metal (e.g., Fe or Cu used in halides). Unfortunately, in conversion chemistries the active materials or intermediate charge/discharge products suffer from various unfavorable interactions and dissolution in organic electrolytes. In this mini-review article, we discuss the current interfacial challenges and focus on the protective layers in situ formed on the cathode surface to effectively shield conversion materials from undesirable interactions with liquid electrolytes. We further explore the mechanisms and current progress of forming such protective layers by using various salts, solvents, and additives together with the insight from molecular modeling. Finally, we discuss future opportunities and perspectives of in situ surface protection. Keywords: Li; S; F; coating; energy storage
DISCUSSION POINTS • C onversion-type cathodes have been viewed as promising candidates for next-generation lithium (Li) and Li-ion batteries with higher specific energy, lower cost, and potentially longer cycle life. • C onversion-type cathodes or intermediate charge/discharge products suffer from various unfavorable interactions and dissolution in organic electrolytes. • T he use of in situ surface protection of conversion cathodes was introduced as a cheap and straightforward strategy to protect these materials from dissolution in organic electrolytes.
Promises of conversion cathode chemistries Lithium and lithium-ion batteries (LBs and LIBs) are the most popular battery systems for electrochemical energy storage technologies. Commercial LIBs utilize intercalation-type cathode materials, mostly nickel (Ni)-based and cobalt (Co)based cathodes, showing specific capacities of up to ∼200 mA h/g
(theoretical capacity below 300 mA h/g), which limit the specific energy of batteries, and are additionally expensive and toxic. An EPA study showed that the Ni- and Co-containing b
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