• Journal of Electrochemical Science and Technology
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• v.2 no.2
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• pp.116-123
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• 2011

Herein, a novel preparation method of highly homogeneous carbon-silicon composite materials was presented. In contrast to conventional solvent evaporation method, a milled silicon-graphite or its oxidized material were directly reacted with petroleum-derived pitch precursor. After thermal reaction under high pressure, pitch-graphite-silicon composite was prepared. Carbon-graphite-silicon composite were prepared by an air-oxidization and following carbonization. From energy dispersive spectroscopy, it was observed that small Si particles were highly embedded within carbon, which was confirmed by disappearance of Si peaks in Raman spectra. Furthermore, X-ray diffraction and Raman spectra revealed that carbon crystallinity decreased when the strongly oxidized silicon-graphite was added, which was probably due to oxygen-induced cross-linking. From the anode application in lithium ion batteries, carbon-graphite-silicon composite anode displayed a high capacity ($565\;mAh\;g^{-1}$), a good initial efficiency (68%) and an good cyclability (88% retention at 50 cycles), which were attributed to the high dispersion of Si particles within cabon. In case of the strongly oxidized silicongraphite addtion, a decrease of reversible capacity was observed due to its low crystallinity.

• Korean Chemical Engineering Research
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• v.59 no.4
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• pp.487-492
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• 2021

In this study, the electrochemical properties of pitch coated silicon sheets/graphite anode materials were investigated. Using NaCl as a template, silicon sheets were prepared through the stöber method and the magnesiothermic reduction methode. In order to synthesize the anode composite, the silicon sheets and graphite were combined with SDBS. The pitch coated silicon sheets/graphite was synthesized using THF as a solvent for the anode material composite. The physical properties of the prepared anode composites were analysed by XRD, SEM, EDS and TGA. The electrochemical performances of the prepared anode composites were performed by the current charge/discharge, rate performance, cyclic voltammetry and EIS tests in the electrolyte LiPF₆ dissolved solvents (EC:DMC:EMC=1:1:1 vol%). As the silicon composition of silicon sheets/graphite composite material increased, the discharge capacity also increased, but the cycle stability tended to decrease. The anode material of pitch coated silicon sheets/graphite composite (silicon sheets:graphite=3:7 weight ratio) showed the initial discharge capacity of 1228.8 mAh/g and the capacity retention ratio of 77% after 50 cycles. From these results, it was found that the cycle stability of pitch coated silicon sheets/graphite was improved.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.118-123
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• 2019

In this study, the electrochemical characteristics of Graphite/Silicon/Pitch anode composites were analyzed to improve the low theoretical capacity of graphite as a lithium ion battery. The Graphite/Silica composites were synthesized by bonding silica onto polyvinylpyrrolidone coated graphite. The surface of used silica was treated with (3-Aminopropyl)triethoxysilane(APTES). Graphite/Silicon/Pitch composites were prepared by carbonization of petroleum pitch, the fabrication processes including the magnesiothermic reduction of nano silica to obtain silicon and varying the mass ratio of silica. The Graphite/Silicon/Pitch composites were analysed by XRD, SEM and XRD. Also the electrochemical performances of Graphite/Silicon/Pitch composite as the anode of lithium ion battery were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance tests in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC:DMC:EMC=1:1:1 vol%). The Graphite/Silicon/Pitch anode composite (silica 28.5 in weight) has better capacity (537 mAh/g). The cycle performance has an excellent capacity retention to 30th cycle of 95% and the retention rate capability of 98% in 0.1 C/0.2 C.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.142-149
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• 2020

In this study, the electrochemical performance of Graphite/Silicon/Pitch composites as anode material was investigated to improve the low theoretical capacity of artificial graphite. Spherical artificial graphite surface was coated with polyvinylpyrrolidone (PVP) amphiphiles material to synthesize Graphite/Silica material by silica islands growth. The Graphite/Silicon/Pitch composites were prepared by petroleum pitch coating and magnesiothermic reduction. The Graphite/Silicon/Pitch composite electrodes manufactured using poly(vinylidene fluoride) (PVDF), carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) binders. The coin type half cell was assembled using various electrolytes and additives. The Graphite/Silicon/Pitch composites were analysed by X-ray diffraction (XRD), scanning electron microscope (SEM) and a thermogravimetric analyzer (TGA). The electrochemical characteristics of Graphite/Silicon/Pitch composite were investigated by constant current charge/discharge, rate performance, cyclic voltammetry and electrochemical impedance spectroscopy. The Graphite/Silicon/Pitch composites showed high cycle stability at a graphite/silica/pitch ratio (1:4:8 wt%). When the electrode is prepared using PAA binder, the high capacity and stability is obtained. The coin type half cell assembled using EC: DMC: EMC electrolyte showed high initial capacity (719 mAh/g) and excellent cycle stability. The rate performance has an capacity retention (77%) at 2 C/0.1 C and an capacity recovery (88%) at 0.1 C / 0.1 C when the vinylene carbonate (VC) was added.

• Carbon letters
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• v.8 no.4
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• pp.335-339
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• 2007

Carbon/silicon composites were synthesized by mixing silicon powders with petroleum pitch and subsequent heat-treatment. The resultant composites were composed of carbon and nano-size crystalline silicon identified by XRD and EDX. FIB images and SEM images were taken respectively to detect the existence of silicon impregnated in carbon and the distribution of silicon on the carbon surface. The obtained carbon/silicon materials were assembled as half cell anodes for lithium ion secondary battery and their electrochemical properties were tested. The pitch/silicon composite (3 : 1 wt. ratio) heat treated at $1000^{\circ}C$ and mixed with 55.5 wt.% of graphite showed relatively good electrochemical properties such as the initial efficiency of 78%, the initial discharge capacity of 605 mAh/g, and the discharge capacity of 500 mAh/g after 20 cycles.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1435-1440
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• 2013

To investigate the influence of the carbon matrix on the electrochemical performance of Si/C composites, four types of Si/C composites were prepared using graphite, petroleum coke, pitch and sucrose as carbon precursors. A ball mill was used to prepare Si/C blends from graphite and petroleum coke, whereas a dispersion technique was used to fabricate Si/C composites where Si was embedded in disordered carbon matrix derived from pitch or sucrose. The Si/pitch-based carbon composite showed superior Si utilization (96% in the first cycle) and excellent cycle retention (70% after 40 cycles), which was attributed to the effective encapsulation of Si and the buffering effect of the surrounding carbon matrix on the silicon particles.

• Journal of Electrochemical Science and Technology
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• v.12 no.1
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• pp.74-81
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• 2021

Silicon (Si) is recognized as a promising anode material for high-energy-density lithium-ion batteries. However, under a condition of electrode comparable to commercial graphite anodes with low binder content and a high electrode density, the practical use of Si is limited due to the huge volume change associated with Si-Li alloying/de-alloying. Here, we report a novel core-shell composite, having a reversible capacity of ~ 500 mAh g-1, by forming a shell composed of a mixture of nano-Si, graphite nanosheets and a pitch carbon on a spherical natural graphite particle. The electrochemical measurements are performed using electrodes with 2 wt % styrene butadiene rubber (SBR) and 2 wt.% carboxymethyl cellulose (CMC) binder in an electrode density of ~ 1.6 g cm-3. The core-shell composites having the reversible capacity of 478 mAh g-1 shows the outstanding capacity retention of 99% after 100 cycles with the initial coulombic efficiency of 90%. The heterostructure of core-shell composites appears to be very effective in buffering the volume change of Si during cycling.