CHAPTER 3: CARBON ANODES FOR LITHIUM-ION BATTERIES

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Louise Allen
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1 CHAPTER 3: CARBON ANODES FOR LITHIUM-ION BATTERIES

2 Chapter 3: Subject Overview Currently, lithium-ion and lithium-ion polymer cells use graphitic carbons as the active material of the negative electrode. The phenomenal rate of growth of the lithium-ion battery chemistry has resulted in a steadily increasing demand for anode grade carbons. Thus, for reference, the actual worldwide sales volumes of graphitic carbon powders into this market amounted to approximately 3,000 tons in 2001, propelled up to 6,000 tons in 2003, and well exceeded 11,000 tons in Due to fierce competition among carbon manufacturers and also the lithium-ion battery becoming commodity chemistry, the prices for anode grade carbons declined from the levels of $50/kg to approximate levels of $20/kg within the same time frame. Still, one may estimate that as of the end of 2004, the market of anode materials for lithium-ion batteries amounted to a minimum of USD 220 million per year. A collection of 11 papers in this chapter seeks to address latest issues associated with development, synthesis, characterization and use of new advanced carbonaceous materials for the rapidly growing segment of electrochemical energy storage market in question. This chapter begins with an overview paper by T. Takamura and R. Brodd. The authors broadly discuss various uses of carbon materials in the main types of power sources. Besides heavy focus on carbon materials for lithium-ion batteries, authors also review a recent work by U.S. manufacturers aimed at incorporation of expanded graphite into the cathodes of alkaline primary batteries. The role of irreversible capacity loss in the design of lithium-ion grade carbons was also discussed. Placing surface coatings and control of morphology of the graphite assists in minimizing the irreversible capacity loss. In addition, the editors wish to comment that spherodizing of lithium-ion grade graphite is a necessary, but not sufficient step, when designing a carbon with low irreversible capacity loss. The second paper by H.J. Santner et al. is a derivative of an overview presentation given during the NATO-CARWC by Professor M. Winter of Graz Technical University, Austria. This interesting work summarizes over 10 years of research and development investigations by the University in the search for the most efficient electrolyte additives and solvents, which are the working environments for graphite anodes when in lithium-ion batteries. This fundamental paper could be quite useful, in particular, to those battery developers, who seek to understand the phenomena of formation of protective layers on graphite. The authors clearly differentiate between the types of layers, which are being created on graphite during the process of formation of lithium-ion batteries. In the third paper, M. Walkowiak et al. report on findings of Central laboratory of batteries and Cells (CLAiO) in Poland, as related to the electrochemical performance of spherodized purified natural graphite and boron-doped carbons in lithium-ion batteries. While it is noteworthy that 153

3 154 these authors are still working on debugging of their electrochemical devices, the fact that full cells are being used to qualify new materials at CLAiO deserves a complement, as it is less common that full cells are used for such purposes, with most academia scientists doing individual electrode studies, often being unaware of the real requirements of the battery industry. The article by Professor D. Aurbach et al. offers a comprehensive analysis of the reasons for why the synthetic and natural graphite, and mesocarbon microbeads fail in PC-containing organic electrolytes (PC is a highly attractive solvent for lithium-ion battery technology due to its low cost and inherent ability to work at temperatures below 40 C). These authors (from the Bar-Ilan University in Israel) suggest that the failure mechanism of graphite/carbon electrodes in PC-based solutions is due to particle cracking, followed by their electrical isolation by surface films, rather than due to complete graphite exfoliation due to co-intercalation of PC molecules with Li + into graphite lattices. Though not widely accepted by the scientific community, the concept appears to be very innovative. Authors report to have collected lots of evidence, proving the above theory to be valid. Among other advanced analytical methods used in their work, readers are encouraged to review the presented data utilizing atomic force microscopy (AFM). One of the obvious values of paper by F. Henry et al. is the fact that it comes from a U.S. commercial manufacturer of the industrial carbon and graphite. The reader will get an unusual insight into the evolution in understanding of what were the properties, which needed to be tailored in order to create a graphite line suitable for lithium-ion battery application. It is noteworthy that reversible and irreversible capacities, which are being usually looked at in the academia as key qualifying properties, carry a secondary role, when compared to the practical needs of having excellent adhesion to the copper substrates, increased packing densities and acceptable abuse tolerance in various lithium-ion battery environments. A fundamental work by Professor F. Beguin et al. addresses the mechanisms of reversible and irreversible intercalation and BET adsorption in lithium-ion grade carbons. The authors discuss, among other phenomena, an interesting concept that values of the active surface area (ASA) on carbon correlate with irreversible capacity loss. This is a departure from traditionally accepted belief that regular BET single point values of carbon are in proportional relationship with the irreversible capacity loss. It is noteworthy that editors also have seen the later theory to be highly inaccurate, and thus, consider the approach taken by authors as valuable. Readers should be aware that the method of determining the ASA currently is being actively promoted by Micromeritics. So far, it has received limited acceptance in the electrochemical labs dealing with fuel cell research, but the method remains relatively unknown to the battery research community.

4 155 The seventh paper in this chapter (R. Yazami et al.) has focused on fundamental aspects of understanding the transition between graphite intercalation stages #1 and #2. Authors note peculiar anomalies, apparently not described in the literature up until now (even though the subject of investigation of graphite staging upon its lithiation has been around for decades). The paper offers a fundamentally new look into the stage transition phenomena. In the article by the renowned Accumulator Research and Design Institute Istochnik of St. Petersburg, Russia, basic performance of various types of carbon materials in the coin and pouch-type lithium-ion cells is described. On a side note, detailed descriptions of various component suppliers furnished by the authors, suggest that Russia is slowly but surely establishing an internal supply chain of anode, cathode, separator, current collector materials and components for the needs of the lithium-ion technology, which is being actively developed internally as well. Authors reported performance of the following carbon materials: pyrolytic carbon; a version of nanotubes; expanded graphite; spectrally pure graphite; special RIECP graphite (derived from natural flake) all are Russian-made grades. Authors also tested thermally purified spherodized flake graphite SLA1020 and surface coated spheroidal flake graphite SLC1115 from Superior Graphite (USA). According to conclusions by the authors, the best for Li + intercalation are: SLA, SLC and Spectral Pure carbon materials. Editors, however, have no doubts, that many inquiries will be made to Istochnik after publishing their comments from testing of Russia s Astrin Co. nanotubes. What could not be effectively achieved by other classic nanotube developers thus far, apparently could be achieved with a particular grade of Russia-made nanotubes. The authors report observing good stability of these nanomaterials under conditions of prolonged cycling in lithium-ion cells. The editors wish to comment that the authors did not discuss the nature of these nanotubes, but it may be speculated that such nanotubes might be rather coarse, and partially-to-well-graphitized nanoparticles of untraditional nature. In the next paper by R. Yazami, I. Goncharova and N. Plakhotnik, a joint work between the U.S./France and Ukraine researchers is presented. Authors investigate mechanisms of BF 4 - and PF 6 - anion intercalation into the single walled carbon nanotubes (SWCNT), produced by pulsed laser ablation technique. Authors conclude that BF 4 - and PF 6 - anions can intercalate into SWCNT structures, and that this process has some reversibility. It is noteworthy that the only electrochemical method used by the authors to arrive with the above conclusion was a method of cyclic voltametry (CV). It is known that CV is a highly sensitive method when it comes to studying the surface processes occurring on working electrodes, while the limitation of the method is its inability to detect what is happening in the bulk electrode. In the mean time, intercalation is a process, which is happening in the bulk

5 156 of carbon. Intercalation processes are also well studied by the technique of galvanostatic cycling, a constant current technique that was not used in the present paper. A fundamental review paper by Professor A. Churikov et al. of Saratov State University, Russia focuses on cons and pros of lithium intercalation into hard and soft carbons, as related to application of these materials as lithium-ion battery anodes. Besides offering what the editors consider a good tutorial on various forms of carbon used for intercalation, the authors arrive with the conclusion that an optimum carbon for lithiumion battery should be a physical blend of soft and hard carbons. While being an interesting concept, editors wish to note that North American and Pacific Rim lithium-ion battery industries already use an enhanced version of this concept, e.g. soft or hard carbon coated graphitic carbons. Authors also report observing a synergistic capacity increase effect from combining two types of carbons. As shown by Figure 2 in the subject paper, the resultant capacity, surprisingly goes above 372 mah/g, which is the theoretical limit for graphite formulated as LiC 6. A paper by Dr. J. Liu et al. of Argonne National Laboratory in the U.S. describes some of the analytical procedures used to qualify candidate carbon materials for their use as anodes of emerging high power lithium-ion batteries for hybrid electric vehicle (HEV) application. This work in the United States is being supported by the U.S. Department of Energy s FreedomCar program, which, besides conducting the development work, enables cooperation between all members of the battery production chain with three major car manufacturers. The particular paper describes performance of thermally purified, spheroidal natural graphite, SL-20, and also, that of surface coated by amorphous carbon, thermally purified, spherodized natural graphite SLC1015 (both grades are the products of Superior Graphite Co., a Chicago, IL, USA graphite/carbon manufacturer). Carbon coating and reduction of particle size were seen to improve high rate, pulse performance and abuse tolerance of natural graphite to the extent of making it a suitable candidate material for the HEV battery application. We hope you will find these papers interesting and useful in your work.

2014 GCEP Report - External

2014 GCEP Report - External Project title: High-Energy-Density Lithium Ion Battery using Self-Healing Polymers Investigators Zhenan Bao, Professor, Chemical Engineering Yi Cui, Professor, Material Sciences