Novel Impact of Short Term Aging on the Electrochemistry of CO[sub 2] Treated Synthetic Graphite

Takeuchi, Kenneth J.; Marschilok, Amy C.; Davis, Stephen K.; Leising, Randolph A.; Takeuchi, Esther S.

doi:10.1149/1.1765773

Cited by 4 publications

(4 citation statements)

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“…This is consistent with our previous observation of a higher irreversible capacity for larger particles of aged CO 2 treated LK-702 graphite. 41 This is also consistent with a previous report of a decrease in irreversible capacity with decreasing graphite particle size. 11 Wilson Greatbatch Limited assisted in meeting the publication costs of this article.…”

Section: Resultssupporting

confidence: 93%

“…This is consistent with our previous observation of a higher irreversible capacity for larger particles of aged CO 2 treated LK-702 graphite. 41 Aurbach and co-workers note that when an intact, nonporous SEI layer can form quickly, reaction within carbon crevices can be minimized and may not be the major contributor to irreversible capacity. 11 Therefore, they propose that this mechanism is most likely to be significant in PC based electrolytes, as SEI formation is kinetically slower for PC than for EC, and the reduction products of PC adhere more poorly to the carbon surface than those of EC.…”

Section: Journal Of the Electrochemical Societymentioning

confidence: 99%

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Heat-Treatment of Synthetic Graphite under Argon and Effect on Li-Ion Electrochemistry

Takeuchi

Marschilok

Davis

et al. 2005

J. Electrochem. Soc.

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The novel use of heat-treatment in flowing Ar to systematically affect particle and crystallite dimensions of synthetic graphite LK-702 is reported. Samples were characterized by percent mass loss, X-ray powder diffraction, scanning electron microscopy, Brunauer-Emmett-Teller ͑BET͒ surface area, and methylene blue adsorption surface area measurements. The treated graphites were studied as possible electrode materials for Li-ion cells. The BET and methylene blue surface areas increased for treatment times up to 48 h, then remained constant. For times up to 48 h, Ar treatment was demonstrated to break apart larger graphite particles, narrowing the particle size distribution. The irreversible capacity of the graphite decreased substantially with increased Ar treatment time, while the reversible capacity remained unchanged.The chemistry of lithium ion ͑Li-ion͒ cells has been a subject of much recent research interest. 1,2 While graphites are widely used in commercial Li-ion cells, fully understanding their complex electrochemistry has remained a continuing challenge. 3-8 Graphite particle size 9,10 and shape [11][12][13][14][15][16] have been shown to have important impact on Li-ion electrochemistry, and have been studied by several authors. The relationship between graphite crystallite characteristics and Liion electrochemistry has also been investigated. [17][18][19][20][21][22] While the studies above have demonstrated the potential electrochemical significance of graphite particle size and shape, they either focus on physical methods of particle size separation such as mechanical sieving, or rely on the use of starting graphites with inherently different sizes and shapes. We present here an investigation of heat-treatment in flowing Ar as an alternative method for affecting graphite particle and crystallite size and shape. While heat-treatment under Ar has been previously used as a means of graphite surface cleaning, 23-26 to our knowledge this is the first use of Ar heattreatment to systematically affect graphite particle and crystallite characteristics. Small samples of synthetic graphite LK-702 were heat-treated under Ar for gradually increasing times at 1000°C. Using this Ar treatment, a series of LK-702 samples with varying particle size, particle shape, surface area, and crystallite size characteristics was systematically generated. Treated samples were then characterized using scanning electron microscopy ͑SEM͒, BrunauerEmmett-Teller ͑BET͒ surface area, methylene blue adsorption surface area, differential thermal ͑DT͒ analysis and X-ray powder diffraction ͑XRD͒ measurements. Finally, coin-sized cells were used to study the treated graphite electrochemistries vs. lithium metal. ExperimentalGraphite treatment.-Before all treatments, the synthetic flake graphite LK-702 ͑Nippon Carbon Company͒ was dried at 150°C under vacuum for at least 24 h. All samples were heat-treated in a Lindberg Blue M TF55035A tube furnace. For each treatment, ϳ2.5 g of graphite was added to a ceramic boat, which was then placed in ce...

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Section: Resultssupporting

confidence: 93%

Section: Journal Of the Electrochemical Societymentioning

confidence: 99%

Heat-Treatment of Synthetic Graphite under Argon and Effect on Li-Ion Electrochemistry

Takeuchi

Marschilok

Davis

et al. 2005

J. Electrochem. Soc.

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“…The other method is surface modification of graphite by mild burn-off treatment to reduce the concentration of oxygen functional groups that are directly bonded to the graphite edge plane. [5][6][7][8][9][10][11][12] The effects of the two methods are investigated using graphite half-cells and graphite/LiCoO 2 cells.…”

mentioning

confidence: 99%

Suppression of an Alkyl Dicarbonate Formation in Li-Ion Cells

Sasaki

Abe

Iriyama

et al. 2005

J. Electrochem. Soc.

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Two methods were developed to suppress the formation of alkyl dicarbonate in Li-ion cells. One is the addition of vinylene carbonate ͑VC͒, which is vulnerable to nucleophilic attack, into the electrolyte to trap alkoxide anions that promote an alkyl dicarbonate formation. The addition of VC into the electrolyte of practical graphite/LiCoO 2 prismatic cells effectively suppressed an alkyl dicarbonate formation and gave better cycle and power performance. The other method is a surface treatment of graphite to reduce the concentration of phenolic groups that were directly bonded to the graphite edge plane. The mild burn-off treatment successfully decreased the oxygen concentration on graphite surface and effectively suppressed an alkyl dicarbonate formation in the electrolyte. However, the irreversible capacity increased significantly, which was considered to be due to a change in the surface morphology of graphite by the burn-off treatment.

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“…21 As mentioned above, if the graphite surface is changed, then a different electrochemical performance will be obtained. This has been clearly shown by changing the surface structure, [1][2][3][4][5][6][7][8][9][10][11][12]22,23 and here we tried to modify the graphite surface by depositing metals. Figure 2 shows the high-resolution electron micrographs ͑HREMs͒ of our prepared composites A and B from the modification of graphite LS17 by depositing with copper and silver.…”

Section: Resultsmentioning

confidence: 99%

Surface Active Sites: An Important Factor Affecting the Sensitivity of Carbon Anode Material toward Humidity

Zhang

et al. 2005

Electrochem. Solid-State Lett.

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We report that various kinds of active sites on graphite surface including active hydrophilic sites markedly affect the electrochemical performance of graphite anodes for lithium-ion batteries under different humidity conditions. After depositing metals such as Ag and Cu by immersion and heat-treating, these active sites on the graphite surface were removed or covered and its electrochemical performance under the high humidity conditions was markedly improved. This suggests that lithium-ion batteries can be assembled under less strict conditions and provides a valuable direction toward lowering the manufacturing cost for lithium-ion batteries.To date, many kinds of anode materials for lithium-ion batteries have been studied. 1,2 However, graphitic carbons are still primarily available on the market, and this shows the importance of carbonaceous materials. A current research focus on the carbonaceous anode materials for lithium-ion batteries is the modification of graphite by, e.g., mild oxidation, deposition of metals or their oxides, coating with polymers, and other kinds of carbons on the graphite surface. 1-12 Nevertheless, few studies are devoted to investigate the sensitivity of anode materials towards humidity. 13,14 It has long been realized that the electrochemical performance of carbon anode materials is more sensitive to humidity than that of cathodic ones. When the humidity is high, anode materials easily absorb water resulting in rapid fading of the reversible capacity. Unfortunately, the water content in a manufacturing facility is very difficult to maintain at a desirably low level of essentially 0 ppm. If sensitivity of anode materials to humidity can be decreased, the requirements for controlling the atmosphere in the manufacturing unit will be lowered and lithium-ion batteries can be produced under less demanding conditions.In this paper, the sensitivity of graphitic carbon with hydrophilic active sites to humidity was studied, then the graphite surface was modified by covering or removing the surface active sites with deposited metals and the electrochemical performance of the composites prepared under high humidity condition was investigated. ExperimentalA natural graphite from mild oxidation ͑designated as LS17, d 002 3.351 Å, L c 120 Å and average particle size 17 m͒ as described in Ref. 8 was used for this study. Capacity measurements were performed as follows. A mixture of graphitic material and 5 wt % ͑based on the graphite͒ polyvinylidene fluoride ͑binder͒ was pressed into pellets with a diameter of ca. 1 cm. After drying under vacuum at 120°C overnight, the pellets were kept in an argon glove box at different humidities ͑Ͻ100 ppm and about 1000 ppm͒ for 1 h; later they were assembled into model cells under the same humidity conditions as the working electrode. Lithium foil was used as the counter and reference electrode, a solution of 1 M LiClO 4 in EC/ DEC ͑v/v = 3:7͒ as the electrolyte and a homemade porous polypropylene film as the separator. Electrochemical performance was measured g...

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Novel Impact of Short Term Aging on the Electrochemistry of CO[sub 2] Treated Synthetic Graphite

Cited by 4 publications

References 44 publications

Heat-Treatment of Synthetic Graphite under Argon and Effect on Li-Ion Electrochemistry

Heat-Treatment of Synthetic Graphite under Argon and Effect on Li-Ion Electrochemistry

Suppression of an Alkyl Dicarbonate Formation in Li-Ion Cells

Surface Active Sites: An Important Factor Affecting the Sensitivity of Carbon Anode Material toward Humidity

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