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Pseudocapacitive characteristics of low-carbon silicon oxycarbide for lithium-ion capacitors Martin Halim, Guicheng Liu, Ryanda Enggar Anugrah Ardhi, Chairul Hudaya, Ongky Wijaya, Sang-Hyup Lee, A-Young Kim, and Joong Kee Lee ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 30 May 2017 Downloaded from http://pubs.acs.org on June 4, 2017
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ACS Applied Materials & Interfaces
Pseudocapacitive characteristics of low-carbon silicon oxycarbide for lithium-ion capacitors
Martin Halim‡a,b, Guicheng Liu‡a, Ryanda Enggar Anugrah Ardhia,b, Chairul Hudayac, Ongky Wijayad, Sang-Hyup Leee,f, A-Young Kima,g, Joong Kee Lee*a,b
a
Center for Energy Convergence, Korea Institute of Science and Technology, Seoul
02792, Republic of Korea b
Energy and Environmental Engineering, Korea University of Science and Technology,
Daejeon 34113, Republic of Korea c
Department of Electrical Engineering, Faculty of Engineering, Universitas Indonesia,
Depok 16421, Republic of Indonesia d
Department of Chemical Engineering, Faculty of Industrial Technology, Universitas
Katolik Parahyangan, Bandung 40141, Republic of Indonesia e
Center of Water Resource Cycle Research, Korea Institute of Science and Technology,
Seoul 02792, Republic of Korea f
Green School, Korea University, Seoul 02841, Republic of Korea
g
Department of Material Science and Engineering, Korea University, Seoul 02841,
Republic of Korea
‡ These authors contributed equally to this work.
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ABSTRACT Lithium-ion capacitors (LICs) and lithium-ion batteries (LIBs) are important energy storage devices. As a material with good mechanical, thermal, and chemical properties, low-carbon silicon oxycarbide (LC-SiOC), a kind of silicone oil derived SiOC, is of interest as an anode material, and we have examined the electrochemical behavior of LCSiOC in LIB and LIC devices. We found that the lithium storage mechanism in LC-SiOC prepared by pyrolysis of phenyl-rich silicon oil depends on an oxygen-driven rather than a carbon-driven mechanism within our experimental scope. An investigation of the electrochemical performance of LC-SiOC in half- and full-cell LIBs revealed that, LCSiOC might not be suitable for full-cell LIBs because it has a lower capacity (238 mAh g−1) than graphite (290 mAh g−1) in a cut-off voltage range of 0–1 V vs. Li/Li+, as well as a substantial irreversible capacity. Surprisingly, LC-SiOC acts as a pseudocapacitive material when it is tested in a half-cell configuration within a narrow cut-off voltage range of 0–1 V vs. Li/Li+. Further investigation of a “hybrid” supercapacitor, also known as a LIC, in which LC-SiOC is coupled with an activated carbon electrode demonstrated that a power density of 156,000 W kg−1 could be achieved while maintaining an energy density of 25 Wh kg−1. In addition, the resulting capacitor had an excellent cycle life, holding ~90% of its energy density, even after 75,000 cycles. Thus, LC-SiOC is a promising active material for LICs in applications such as heavy-duty electric vehicles.
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Low-carbon silicon oxycarbide, Silicone oil derived SiOC, Pseudocapacitive characteristic, Oxygen-driven mechanism, Lithium-ion capacitor, Prelithiation
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1. INTRODUCTION The glass-ceramics materials have been proven to be a promising anode material for energy storage devices.1 Silicon oxycarbide (SiOC) is a ceramic material with a fractal network in which oxygen and carbon atoms are bonded randomly to silicon in a threedimensional covalent structure, forming SiC4, SiOC3, SiO2C2, SiO3C, and SiO4.2-4 The unique structure of SiOC results in improved mechanical, thermal, and chemical properties compared with amorphous SiO2; consequently, SiOC has attracted increasing attention for energy storage applications. In 1994, the first study of SiOC as an anode material for lithium-ion batteries (LIBs) was published.5 Since then, many effective efforts have been made to enhance the electrochemical performance of SiOC as an anode material in LIBs. Mechanism studies on lithium storage in SiOC have been previously carried out by two main groups: Fukui et al.6,7 and Liao et al.8,9 Their studies can be simply categorized as carbon- and oxygen-driven mechanism, respectively. The carbon-driven mechanism theory, which has been widely adopted in several reports, states that higher carbon content results in higher capacity. In contrast, the oxygen-driven mechanism theory states that carbon atoms do not attract lithium, and instead, lithium ion storage is strongly related to the presence of SiOC tetrahedra. In this study, we developed our own SiOC, which was obtained by pyrolysis of phenyl-rich silicone oil. We defined the resulting sample as low-carbon silicon oxycarbide (LC-SiOC), a kind of silicone oil derived SiOC, which has a very low carbon content compared with other SiOC materials
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used in previous studies, as shown in Table S1. The electrochemical performance of the resulting LC-SiOC can be explained by the oxygen-driven mechanism theory. We have carefully compiled all reports regarding the application of SiOC in LIBs (Table S2).10-27 These reports present SiOC as a potential anode material for LIB. However, this claim may be biased because all previous work focused only on half-cell studies without considering the performance of SiOC in full-cells 28. In all of the previous reports, a high discharge voltage of ≥2 V vs. Li/Li+ was applied, with more than 87% of them using a wide cut-off voltage of up to 3 V vs. Li/Li+. The issue with SiOC is its steep voltage gradient during cycling, which will greatly reduce the overall working voltage of a full cell. Thus, compared with common graphite-based LIBs, SiOC-based LIBs may have lower power or less capacity at the same working voltage. Unfortunately, to date, researchers have never attempted an objective electrochemical study of LC-SiOC in LIBs by investigating its performance in both half- and full-cell configurations. We found that SiOC might be not suitable for LIB application owing to the steep cut-off voltage in the half-cell configuration that lowers the voltage profile of the full-cell LIB when commercial LiCoO2 was used as the cathode material (LNF, Co., Republic of Korea). Hence, the capacity of a LC-SiOC-based LIB is ~50% lower than a graphite-based LIB. In contrast with most previous studies that reported SiOC as a potential anode material for LIBs, we discovered that SiOC might be more suitable as an active material in lithiumion capacitors (LICs). Moreover, our study proves that LC-SiOC possesses pseudocapacitive characteristics, which, to the best of our knowledge, has not been 5
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reported previously. Thus, we also investigated the electrochemical performance of LCSiOC in LICs, which might be good energy storage devices for specific applications, such as heavy-duty electric vehicles. The growing market for heavy-duty electric vehicles has significantly increased the demand for advanced energy storage systems that can deliver high power and energy densities and long cycle life.29-35 In practical applications, LIBs and supercapacitors represent energy storage systems with high energy and power densities, respectively. To harvest both high power and high energy, LICs have been extensively studied. Over the last decade, a combination consisting of an anode material with faradaic behavior (usually an LIB anode) or good pseudocapacitive behavior and an activated carbon (AC) cathode, as used in supercapacitors, has been studied to obtain high-performance LICs.36-51 Specifically, anode materials originally applied in LIBs, such as graphite,38,52 hard carbon,38,42 Li4Ti15O12 (LTO),43-47 Fe3O4,48 SnO2,50 and B-Si/SiO2/C,49 have been investigated as anode materials in LICs. Graphite, a widely used anode material in LIBs, provides a relatively high power density of 1,500 W kg−1 at an energy density of
