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Conversion Reaction of Nanoporous ZnO for Stable Electrochemical Cycling of Binderless Si Microparticle Composite Anode Donghyuk Kim, Minkyu Park, Sang-Min Kim, Hyungcheoul Shim, Seungmin Hyun, and Seung Min Han ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b03951 • Publication Date (Web): 04 Sep 2018 Downloaded from http://pubs.acs.org on September 5, 2018
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ACS Nano
Conversion Reaction of Nanoporous ZnO for Stable Electrochemical Cycling of Binderless Si Microparticle Composite Anode Donghyuk Kim†,§, Minkyu Park†, Sang-Min Kim†, §, Hyungcheoul Shim§, Seungmin Hyun§ and Seung Min Han*†,‡
† Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Republic of Korea ‡ Graduate School of EEWS, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Republic of Korea § Department of Applied Nano Mechanics, Korea Institute of Machinery & Materials, Daejeon, 305343, Republic of Korea
Donghyuk Kim and Minkyu Park contributed equally to this work.
Corresponding author e-mail:
[email protected] Keywords: silicon microparticles, binderless electrode, lithium-ion battery, combustion reaction, composite electrode
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Abstract Binderless, additive-less Si electrode design is developed where a nanoporous ZnO matrix is coated on a Si microparticle electrode to accommodate extreme Si volume expansion and facilitate stable electrochemical cycling. The conversion reaction of nanoporous ZnO forms an ionically and electrically conductive matrix of metallic Zn embedded in Li2O that surrounds the Si microparticles. Upon lithiation, the porous Li2O/Zn matrix expands with Si preventing extensive pulverization while Zn serves as active material to form LixZn to further enhance capacity. Electrodes with Si mass loading of 1.5 mg/cm2 was fabricated and high initial capacity of ~3,900 mAh/g was achieved with excellent reversible capacity of ~1,500 mAh/g (areal capacity ~1.7 mAh/cm2) beyond 200 cycles. A high first cycle coulombic efficiency was obtained owing to the conversion reaction of nanoporous ZnO, which is a notable feature in comparison to conventional Si anodes. Ex situ analyses confirmed that the nanoporous ZnO coating maintained the coalescence of SiMPs throughout extended cycling. Therefore, the Li2O/Zn matrix derived from conversion reacted nanoporous ZnO acted as an effective buffer to lithiation induced stresses from volume expansion and served as a binder-like matrix that contribute to the overall electrode capacity and stability.
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Demand for next generation energy storage devices for wearable electronics and electric vehicles has dramatically increased, culminating in the need for energy storage devices with higher energy density. However, conventional electrode materials such as graphite (375 mAh/g) demonstrate limited specific capacity and insufficient energy and power densities. In this context, Si is a promising candidate due to its unparalleled theoretical capacity (3,578 mAh/g), relatively low discharge potential (~0.5V versus Li0/Li+) while being one of the most abundant and inert material on earth. 1-4 Significant challenges still exist that limit the commercialization of Si most serious of which is the extreme volume expansion (~400%) during lithiation that results in large lithiation induced stresses that cause pulverization/delamination. 2, 5-7 Performance degradation due to pulverization over extended cycles is caused by the exposure of fresh Si surfaces that form thicker, unstable solid-electrolyte interphases (SEI) responsible for low initial coulombic efficiency (CE,
