CA2138360A1 - Pre-graphitic carbonaceous insertion compounds and use as anodes in rechargeable batteries - Google Patents

Abstract

Carbonaceous insertion compounds and methods for preparation are described wherein the compounds comprise a highly disordered, impurity free, hard pre-graphitic carbonaceous host. A carbonaceous insertion compound with large reversible capacity for lithium (up to 650 mAh/g) can be prepared. Such insertion compounds can be prepared by simple pyrolysis of suitable epoxy precursors at an appropriate temperature. These insertion compounds may be suitable for use as high capacity anodes in lithium ion batteries.

Description

PRE-GRAPHITIC CARBONACEOUS INSERTION COMPOUNDS
AND USE AS ANODES IN REC~Rq~RT~ BATTERIES

FIELD OF THE lNV~NLlON

The invention pertains to the field of carbonaceous materials and, in particular, to pre-graphitic carbonaceous insertion materials. Additionally, the invention pertains to the field of rechargeable batteries and, in particular, to rechargeable batteries comprising carbonaceous anode materials.

R~KGROUND OF THE lNV~NllON

The group of pre-graphitic compounds includes carbonaceous materials that are generally prepared at low temperatures (eg: less than about 2000C) from various organic sources and that tend to graphitize when annealed at higher temperatures. There are however both hard and soft pre-graphitic carbon compounds, the former being difficult to graphitize substantially even at temperatures of order of 3000C, and the latter, on the other hand, being virtually completely graphitized around 3000C.
The aforementioned set of compounds has been of great interest for use as anode materials in rechargeable lithium-ion or rocking chair type batteries. These batteries represent the state of the art in small rechargeable power sources for consumer electronics applications. These batteries have the greatest energy density (Wh/L) of conventional rechargeable systems (ie.
NiCd, NiMH, or lead acid batteries). Additionally, lithium ion batteries operate around 3~ volts which is often sufficiently high that a single cell can suffice for many electronics applications.
Lithium ion batteries use two different insertion compounds for the active cathode and anode materials.
Insertion compounds are those that act as a host solid for the reversible insertion of guest atoms (in this case, lithium atoms). The structure of the insertion compound 213836~

host is not significantly altered by the insertion. In a lithium ion battery, lithium is extracted from the anode material while lithium is concurrently inserted into the cathode on discharge of the battery. The reverse processes occur on recharge of the battery. Lithium atoms travel or "rock" from one electrode to the other as ions dissolved in a non-aqueous electrolyte with the associated electrons travelling in the circuit external to the battery.
The two electrode materials for lithium ion batteries are chosen such that the chemical potential of the inserted lithium within each material differs by about 3 to 4 electron volts thus leading to a 3 to 4 volt battery. It is also important to select insertion compounds that reversibly insert lithium over a wide stoichiometry range thus leading to a high capacity battery.
A 3.6 V lithium ion battery based on a LiCoO2 / pre-graphitic carbon electrochemistry is commercially available (produced by Sony Energy Tec.) wherein the carbonaceous anode can reversibly insert about 0.65 Li per six carbon atoms. (The pre-graphitic carbon employed is a disordered form of carbon which appears to be similar to coke.) However, the reversible capacity of lithium ion battery anodes can be increased by using a variety of alternatives mentioned in the literature. For example, the crystal structure of the carbonaceous material affects its ability to reversibly insert lithium (as described in J.R. Dahn et al., "Lithium Batteries, New Materials and New Perspectives", edited by G. Pistoia, Elsevier North-Holland, pl-47, (1993)). Graphite, for instance, can reversibly incorporate one lithium per six carbon atoms which corresponds electrochemically to 372 mAh/g. This electrochemical capacity per unit weight of material is denoted as the specific capacity for that material.
Graphitized carbons and/or graphite itself can be employed under certain conditions (as for example in the presentation by Matsushita, 6th International Lithium Battery Conference, Muenster, Germany, May 13, 1992, or in 21~8~50 U.S. Patent No. 5,130,211).
Other alternatives for increasing the specific capacity of carbonaceous anode materials have included the addition of other elements to the carbonaceous compound.
For example, Canadian Patent Application Serial No.

2,098,248, Jeffrey R. Dahn, "Electron Acceptor Substituted Carbons for Use as Anodes in Rechargeable Lithium Batteries", filed June 11, 1993, discloses a means for enhancing anode capacity by substituting electron acceptors (such as boron, aluminum, and the like) for carbon atoms in the structure of the carbonaceous compound. Therein, reversible specific capacities as high as 440 mAh/g were obtained with boron substituted carbons. Canadian Patent Application Serial No. 2,122,770, Alfred M. Wilson, "Carbonaceous Compounds and Use as Anodes in Rechargeable Batteries", filed May 3, 1994, discloses pre-graphitic carbonaceous insertion compounds comprising nanodispersed silicon atoms wherein specific capacities of 550 mAh/g were obtained. Similarly, specific capacities of about 600 mAh/g could be obtained by pyrolyzing siloxane precursors to make pre-graphitic carbonaceous compounds containing silicon as disclosed in Canadian Patent Application Serial No. 2,127,621, Alfred M. Wilson, "Carbonaceous Insertion Compounds and Use as Anodes in Rechargeable Batteries", filed July 8, 1994.
Most recently, practitioners in the art have prepared carbonaceous materials with very high reversible capacity by pyrolysis of suitable starting materials. At the Seventh International Meeting on Lithium Batteries, Extended Abstracts Page 212, Boston, Mass. (1994), A.
Mabuchi et al. demonstrated that pyrolyzed coal tar pitch can have specific capacities as high as 750 mAh/g at pyrolysis temperatures about 700C. K. Sato et al. in Science 264, 556, (1994) disclosed a similar carbonaceous material prepared by heating polyparaphenylene at 700C
which material has a reversible capacity of 680 mAh/g. S.
Yata et al, Synthetic Metals 62, 153 (1994) also disclose 213~360 a similar material made in a similar way. These values are much greater than that of pure graphite. The aforementioned materials can have a very large irreversible capacity as evidenced by first discharge capacities that can exceed 1000 mAh/g. Additionally, the voltage versus lithium of all the aforementioned materials has a significant hysteresis (ie. about 1 volt) between discharge and charge (or between insertion and extraction of lithium). In a lithium ion battery using such a carbonaceous material as an anode, this would result in a similar significant hysteresis in battery voltage between discharge and charge with a resulting undesirable energy inefficiency.
It is not understood why the aforementioned carbonaceous materials have very high specific capacity.
All were prepared at temperatures of about 700C and are sufficiently crystalline to exhibit x-ray patterns from which the parameters doo2l Lc, a, and La can be determined.
(The definition and determination of these parameters can be found in K. Kinoshita, "Carbon - Electrochemical and Physicochemical Properties", John Wiley & Sons 1988.) Also, all have substantial amounts of incorporated hydrogen as evidenced by H/C atomic ratios that are greater than 0.1, and often near 0.2. Finally, it appears that pyrolyzing at higher temperature degrades the specific capacity substantially with a concurrent reduction in the hydrogen content. (In the aforementioned reference by Mabuchi et al, pyrolyzing the pitch above about 800C
results in a specific capacity decrease to under 450 mAh/g with a large reduction in H/C. Similar results were found in the aforementioned reference by Yata et al.) The prior art also discloses carbonaceous compounds with specific capacities higher than that of pure graphite made from precursors that form hard carbons on pyrolysis.
However, the anticipated very high specific capacities of the aforementioned materials pyrolyzed at about 700C were apparently not attained. A. Omaru et al, Paper #25, 213~36û

Extended Abstracts of Battery Division, p34, Meeting of the Electrochemical Society, Toronto, Canada (1992), disclose the preparation of a hard carbonaceous compound containing phosphorus with a specific capacity of about 450 mAh/g by pyrolyzing polyfurfuryl alcohol. The polyfurfuryl alcohol in turn had been prepared from the monomer polymerized in the presence of phosphoric acid. In Japanese Patent Application Laid Open number 06-132031, Mitsubishi Gas Chemical disclose a hard carbonaceous compound comprising 2.4~ sulfur with a specific capacity of about 500 mAh/g.
These hard carbonaceous compounds have additional elements incorporated therein and have all been pyrolyzed at sufficient temperature such that they contain little hydrogen (ie. the H/C atomic ratio is substantially less than 0.1). These hard carbonaceous compounds neither exhibited the very high specific capacities nor the same serious hysteresis in voltage of the aforementioned materials pyrolyzed at about 700C.

SUMMARY OF THE lN V~N'l'lON

The subject invention includes carbonaceous insertion compounds, methods of preparing said compounds, and the use of said compounds as electrode materials in electrochemical devices in general.
Carbonaceous insertion compounds of the invention comprise a pre-graphitic carbonaceous host and atoms of an alkali metal inserted therein. The inserted alkali metal can be lithium as would be the case for use in lithium ion batteries. The empirical parameter R, determined from an x-ray diffraction pattern of the host and defined as the {002} peak height divided by the background level, is less than about 2.2. The H/C atomic ratio of the host is less than about 0.1. Additionally, the host has an adsorption capacity for methylene blue that is less than about 4 micromoles per gram of host. To achieve a large stoichiometry range for reversible insertion of alkali 21~36~

metal, R is preferably less than about 2, and most preferably less than about 1.5.
The pre-graphitic carbonaceous host can be prepared by pyrolyzing an epoxy precursor at a temperature above about 700C, thereby predominantly removing hydrogen from the precursor. However, the pyrolysis temperature cannot be too high in order that the empirical parameter R, determined from an x-ray diffraction pattern of the host and defined as the {002} peak height divided by the background level, is less than about 2.2.
The epoxy precursor can be an epoxy novolac resin and can comprise a hardener in a range from zero to about 40 by weight. The hardener can be phthallic anhydride and the epoxy can be cured at about 120C before pyrolysis. The maximum pyrolysis temperature can be attained by ramping at from about 1C/min to about 20C/min. A possible embodiment of the invention can be prepared by pyrolyzing an epoxy novolac resin having the formula 0-CH2-CH-CH2 0-CHz-CH-CH2 0-C~2-CH-CHz ~ CHz ~ CH

Epoxy Novolac Resin n = l.

at a maximum temperature below about 1100C.
Alternatively, the epoxy precursor can be a bisphenol A epoxy resin. The maximum pyrolysis temperature can be attained by ramping at about 30C/min. A possible embodiment of the invention can be prepared by pyrolyzing a bisphenol A epoxy resin having the formula CH2~H--CH2--o~3C~o-CH2-CH-CH2--O~CH~O-CH2-CH-CH2 CH3 n CH., .-5 Bisphenol-A Epoxy Resin n = 12 at a temperature about 800C.
Methods of the invention include processes for preparing suitable pre-graphitic carbonaceous hosts for the aforementioned compounds. Such hosts can be prepared by pyrolyzing an epoxy precursor at a temperature above about 700C such that the empirical parameter R, determined from 15 an x-ray diffraction pattern and defined as the {002} peak height divided by the background level, is less than about 2.2.
Alkali metal atoms can be inserted into the host thereafter by conventional chemical or electrochemical means to make insertion compounds of the invention. The epoxy employed in the method of the invention can be an epoxy novolac resin having a formula O _ O _ O
2 50--CH2--CH--C~20--CH2--CH--CH2 0--CH2--Cl I--CH2 ~ CH, ~ CH2 _ --n Epoxy Novolac Resin n = 1.6 35 wherein the pyrolysis is performed at a maximum temperature below about 1100C. Alternately, the epoxy employed in the method of the invention can be a bisphenol A epoxy resin having a formula CH2~-cH2-o ~ CH3 0-CH2-CH-CH2-O ~ CH3 0-CH2-CH-CH2 Bisphenol-AEpoxyResin n = 12 wherein the pyrolysis is performed at a temperature about 800C.
Compounds of the invention can be used as a portion of an electrode in various electrochemical devices based on insertion materials (eg. supercapacitors, electrochromic devices, etc.). A preferred application for these compounds is use thereof as an electrode material in a battery, in particular a non-aqueous lithium ion battery comprising a lithium insertion compound cathode; a non-aqueous electrolyte comprising a lithium salt dissolved in a mixture of non-aqueous solvents; and an anode comprising the carbonaceous insertion compound of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate specific embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way:

Figure 1 shows the definition of R on an almost featureless x-ray diffraction pattern of a pre-graphitic carbon in the region around the {002} peak.
Figure 2 shows a cross-sectional view of a conventional lithium ion spiral-wound type battery.

213836() Figure 3 depicts an exploded view of the laboratory coin cell battery used in the Examples.

Figure 4 shows the H/C atomic ratio versus pyrolysis temperature for the samples of Comparative Example 2 and of Inventive Example 1.

Figure 5 shows the x-ray diffraction patterns in the vicinity of the {002} peak for some of the samples of Comparative Example 2. The patterns have been offset vertically by 2000 counts for clarity.

Figures 6a and 6b show the voltage versus capacity plots for some of the batteries of Comparative Example 2.
Figure 6a is an expanded version of Figure 6b in the region near zero volts. The points at which lithium plating and stripping occur are indicated by arrows for the battery comprising the 550C pyrolyzed sample. The plots in each Figure are offset sequentially by 0.05 volts and 0.1 volts respectively for clarity.

Figure 7 shows the x-ray diffraction patterns in the vicinity of the {002} peak for the M20E activated carbon samples of Comparative Example 3.

Figure 8 shows the second cycle voltage versus capacity plot for the battery containing M30 activated carbon pyrolyzed at 1000C of Comparative Example 3.
Figure 9 shows the first cycle voltage versus capacity plot for the battery containing M30 activated carbon pyrolyzed at 1000C of Comparative Example 3.

Figure 10 compares the second cycle voltage versus capacity plots of sample no. I of Inventive Example 1 to that of the 700C pyrolyzed sample of Comparative Example 213~360 Figure 11 shows the x-ray diffraction patterns in the vicinity of the {002} peak for samples I, II, and III of Inventive Example 1. The patterns have been offset vertically by 1600 counts for clarity.

Figures 12a and 12b show the voltage versus capacity plots of samples I, II, III, and IV of Inventive Example 1.
Figure 12a is an expanded version of Figure 12b in the region near zero volts. The points at which lithium plating and stripping occur are indicated by arrows for the battery comprising sample IV. The plots in each Figure are offset sequentially by 0.05 volts and 0.1 volts respectively for clarity.

Figures 13a and 13b show the voltage versus capacity plots of samples V, VI, VII, and IX of Inventive Example 1 and illustrates the relation between R and specific capacity for samples pyrolyzed at 1000C to 1100C. Figure 13a is an expanded version of Figure 13b in the region near zero volts. The points at which lithium plating and stripping occur are indicated by arrows for the battery comprising sample VII. The plots in each Figure are offset sequentially by 0.05 volts and 0.1 volts respectively for clarity.

Figure 14 shows the x-ray diffraction pattern in the vicinity of the {002} peak for the samples of Figures 13a and b. The patterns have been offset vertically by 3000 counts for clarity.

Figure 15 shows a summary plot of specific capacity versus R for sample nos. III to IX inclusive of Inventive Example 1.

Figure 16 shows the voltage versus capacity plot of 2138~0 the first discharge and charge of the battery comprising sample no. VII of Inventive Example 1.

Figures 17a and 17b show the voltage versus capacity plots of a battery of Inventive Example 2. Figure 17a is an expanded version of Figure 17b in the region near zero volts.

DET~TT.T~n DESCRIPTION OF THE SPECIFIC
EMBODIMENTS OF THE lNV~L.llON

Compounds of the invention comprise hard pre-graphitic carbonaceous hosts having very poorly stacked graphene layers, little hydrogen content, and a low adsorption capacity for common non-aqueous electrolyte solutions.
Said compounds can be derived from pyrolysis products of suitable epoxy precursors. Herein, epoxy precursor refers to that group of thermosetting resins based on the reactivity of the epoxide group (as per the definition in The Condensed Chemical Dictionary, Ninth Ed., Van Nostrand Reinhold, 1977). Common members of this group include bisphenol A-based epoxies and epoxy novolac resins.
Suitable epoxy precursors are those that, when pyrolyzed at temperatures above about 700C, do not graphitize to such an extent that the empirical parameter R as determined by x-ray diffraction pattern exceeds about 2.2. Herein, R is defined as the {002} graphite peak height divided by the background level. (The detailed method for this determination is described later in the specification.) R
provides a convenient empirical means of quantifying the degree of graphitization of these compounds which have almost featureless x-ray diffraction patterns. Figure 1 illustrates the definition of R on a representative, almost featureless x-ray diffraction pattern of a pre-graphitic carbon in the region around the {002} peak.
Pyrolyzing suitable epoxy precursors above 700C
provides pre-graphitic carbonaceous hosts that do not exhibit severe hysteresis in voltage upon insertion or extraction of lithium. Hosts prepared in this way are also characterized by low H/C atomic ratios. Pyrolyzing at temperatures such that R is below 2.2 provides for hosts with very high specific capacities for lithium. The specific capacity for lithium increases as R decreases.
Based on the Examples to follow, R appears to be preferably less than about 2 and most preferably less than about 1.5.
The pyrolysis should be performed under a controlled atmosphere to prevent formation of undesired oxides of carbon. A suitable reaction system could consist of a reaction tube (quartz for example) installed in a conventional tube furnace wherein the tube has sealed inlet and outlet connections for purposes of controlling the atmosphere therein. The epoxy precursor/s could thus be pyrolyzed in the reaction tube under an inert gas flow or even under reduced or elevated pressure. Additionally, controlled partial reduction or oxidation, if desired, can be achieved by admitting controlled amounts of an appropriate gas.
To ensure good product yields, ideally the epoxy precursor/s should substantially pyrolyze rather than simply evaporate. This issue must be considered in the selection of preferred precursor/s. Also, in certain cases, the extent of the curing or cross-linking may be a significant variable affecting the desired ultimate properties of the pyrolyzed epoxy. Thus, it may be advantageous to consider incorporating soaking periods at several temperatures as part of the heat treatment. For example, a low temperature soak might be used for curing the epoxy prior to a final heating to the pyrolysis temperature. Alternately, the heating rate might be varied to control the extent of the curing prior to pyrolysis.
The product of pyrolysis can have relatively large surface areas, of order of 200 m2/g, as determined by conventional nitrogen adsorption methods (eg. BET).
However, the surface area that is actually accessible to common non-aqueous electrolyte solutions is relatively small. This is especially important for application in lithium ion batteries. Electrolyte reactions that consume lithium occur at the anode surface in such batteries.
Thus, use of an anode having a large surface area accessible to electrolyte results in substantial irreversible capacity loss and electrolyte loss. These losses are avoided if the anode surface is not accessible to the electrolyte.
10The aforementioned product has no alkali metal inserted as prepared. Alkali metal atoms, in particular Li, can be inserted thereafter via conventional chemical or electrochemical means (such as in a lithium or lithium ion battery).
15Generally, powdered forms of such compounds are used in electrode applications and thus a grinding of the pyrolyzed product is usually required. A variety of embodiments, in particular various battery configurations, are possible using electrode material prepared by the method of the invention. Miniature laboratory batteries employing a lithium metal anode are described in the examples to follow. However, a preferred construction for a lithium ion type product is that depicted for a conventional spiral-wound type battery in the cross-sectional view of Figure 2. A jelly roll 4 is created byspirally winding a cathode foil (not shown), an anode foil (not shown), and two microporous polyolefin sheets (not shown) that act as separators.
Cathode foils are prepared by applying onto a thin aluminum foil a mixture of a suitable powdered (about 10 micron size typically) cathode material, such as a lithiated transition metal oxide, possibly other powdered cathode material if desired, a binder, and a conductive dilutant. Typically, the application method first involves dissolving the binder in a suitable liquid carrier. Then, a slurry is prepared using this solution plus the other powdered solid components. The slurry is then coated 2138~60 uniformly onto the substrate foil. Afterwards, the carrier solvent is evaporated away. Often, both sides of the aluminum foil substrate are coated in this manner and subsequently the cathode foil is calendered.
Anode foils are prepared in a similar manner except that a powdered (also typically about 10 micron size) carbonaceous insertion compound of the invention is used instead of the cathode material and thin copper foil is usually used instead of aluminum. Anode foils are typically slightly wider than the cathode foils in order to ensure that anode foil is always opposite cathode foil.
This feature is illustrated with the cathode upper edge 13, cathode lower edge 14, anode upper edge 12, and anode lower edge 15 depicted in Figure 2.
The jelly roll 4 is inserted into a conventional battery can 3. A header 1 and gasket 10 are used to seal the battery 16. The header may include safety devices if desired. A combination safety vent and pressure operated disconnect device may be employed. Figure 2 shows one such combination that is described in detail in Canadian Patent Application No. 2,099,657, Alexander H. Rivers-Bowerman, "Electrochemical Cell and Method of Manufacturing Same", filed June 25, 1993. Additionally, a positive thermal (PTC) coefficient device may be incorporated into the header to limit the short circuit current capability of the battery. The external surface of the header 1 is used as the positive terminal, while the external surface of the can 3 serves as the negative terminal.
Appropriate cathode tab 5 and anode tab 6 connections are made to connect the internal electrodes to the external terminals. Appropriate insulating pieces 2 and 7 may be inserted to prevent the possibility of internal shorting.
Prior to crimping the header 1 to the can 3 in order to seal the battery, electrolyte 8 is added to fill the porous spaces in the jelly roll 4.
Those skilled in the art will understand that the types of and amounts of the component materials must be chosen based on component material properties and the desired performance and safety requirements. The compounds prepared in the Examples that follow have increased irreversible capacity for lithium along with an increased reversible capacity over that of many typical commercial carbonaceous anode materials. Also, the Example compounds typically have lower density than that of typical commercial anode materials. This must be taken into account in the battery design. Generally an electrical conditioning step, involving at least the first recharge of the battery, is part of the assembly process. Again, the determination of an appropriate conditioning step along with the setting of the battery operating parameters (eg.
voltage, current, and temperature limits) would be required of someone familiar with the field.
Other configurations or components are possible for the batteries of the invention. For example, a prismatic format is considered highly desirable and possible. A
miniature embodiment, eg. coin cell, is also possible and the general construction of such cells is described in the laboratory coin cell examples to follow.
There is no known quantitative model which can explain how certain prior art carbonaceous materials can have specific capacities that significantly exceed that of graphite. (However, J. Dahn et al, Electrochimica Acta, Vol. 3, No.9, p 1179-1191, 1993 speculated on the possibility of certain unorganized carbons exceeding the capacity of graphite via lithium adsorption on single graphite layers contained within. Also, in the aforementioned reference by K. Sato et al, Li dimer formation was proposed as an explanation for the very high specific capacity of their carbonaceous material.) Without wishing to be bound by theory, adversely or otherwise, the inventors offer the following view of the prior art and of the instant invention.
The presence of substantial hydrogen in carbonaceous materials of the prior art prepared by pyrolysis at low 213836~

temperatures (between 550C and 750C) correlates with very high specific capacity. Certain hard carbonaceous materials of the prior art however have little hydrogen but still exhibit high specific capacities that exceed that of graphite. The graphene sheets in the precursors for these hard carbonaceous materials are cross-linked and this prevents the ordered stacking of layers in the graphite structure as the precursors are pyrolyzed. When poorly stacked graphene layers are present, it may be possible to adsorb lithium onto the surfaces of each side of the layers. These surfaces are found within the carbon particles, on the atomic scale. In graphite, the layers are well stacked in a parallel fashion and intercalation of lithium to a composition of LiC6 is possible (corresponding to about 370 mAh/g and one intercalated layer of lithium per graphene sheet). In materials with poorly stacked layers, unshared lithium layers might possibly be found on each side of the graphene sheets, resulting in compositions up to almost Li2C6 (corresponding to about 740 mAh/g).
Thus, the number of single layer graphene sheets in the carbonaceous material may be important vis a vis specific capacity.
X-ray diffraction can be used to learn about the average number, N, of stacked graphene sheets in a carbon in between serious stacking mistakes. This number N, multiplied by the average layer spacing is commonly given the name, Lc. It may therefore be desirable to make carbonaceous materials with N about 1 and with very small Lc (eg. less than about 5A). The {002} Bragg peak measured in a powder x-ray diffraction experiment is normally used to determine Lc and N (see for example, the aforementioned reference by K. Kinoshita). For N=1, there is no {002}
peak since there are no stacked parallel graphene layers to create interferences. (Such a carbon sample might be thought of as having single graphene sheets arranged as in a house of cards.) As N increases (beginning to stack the deck of cards), the {002} peak increases in height and 213~36~

decreases in width. Simultaneously, the background on the low angle side of the peak decreases, as N increases.
Herein, the empirical parameter R is used for purposes of describing such structures and is determined by dividing 5 the {002} peak height (B in Figure 1) by an estimate of the background level at the Bragg angle corresponding to the position of the { 002 } peak (A in Figure 1). The background estimate (A in Figure 1) is that value given by the intersection of a line tangential to the background in the immediate vicinity of the {002} peak and B (the position of the { 002 } peak). R can thus be used to distinguish the stacking order in very disorganized materials. Materials having very small R values (about 1) would have N values near 1. Materials having R near 5 would have significantly 15 larger N, possibly with N about 10. Thus, increases in R
can be interpreted as increases in the average N in the sample. To quantitatively measure R reproducibly, all of the x-ray beam of the diffractometer must be confined to the carbon sample in the angular range of interest (ie.
20 from 10 to 35 when a copper target x-ray tube is used).
The following examples are provided to illustrate certain aspects of the invention but should not be construed as limiting in any way. In general, carbonaceous materials were prepared from hydrocarbon or polymer 25 precursors by pyrolysis under inert gas. Weighed amounts of the precursors were placed in alumina boats and inserted within a stainless steel or quartz furnace tube. The tube was flushed with inert gas for about 30 minutes and then it was inserted into a tube furnace. The furnace and hence 30 the sample temperature was raised to the final pyrolysis temperature and held there for one hour. The heating rate was sometimes deemed to be important, and in those cases the rate was carefully controlled using a programmable temperature controller.
Powder x-ray diffraction was used to characterize samples using a Seimens D5000 diffractometer equipped with a copper target x-ray tube and a diffracted beam 213~36~

monochromator. The diffractometer operates in the Bragg-Brentano pseudofocussing geometry. The samples were made by filling a 2mm deep well in a stainless steel block with powder and levelling the surface. The incident slits used were selected so that none of the x-ray beam missed the sample in the angular range from 10 to 35 in scattering angle. The slit width was fixed during the measurement. This ensured reproducibility in the measured values of R.
Carbon, hydrogen, and nitrogen content was determined on samples using a standard CHN analysis (gas chromatographic analysis after combustion of the samples in air). The results are reported in weight percent of the sample made up by each element and have a standard deviation of +0.3~. In every case, the carbon content was greater than 90~ of the sample weight and the hydrogen content was less than 3.3~. The H/C atomic ratio was estimated by taking the ratio of the hydrogen and carbon weight percentages and multiplying by 12 (the approximate mass ratio of carbon to hydrogen). The nitrogen content of all the samples was low and has not been reported. The oxygen content of the samples was not analyzed.
Conventional BET methods were used to determine the surface area of some samples based on the adsorption of nitrogen. The surface area of samples of the invention could not be determined reliably in this way however.
During analysis, adsorption continued slowly over long periods of time (hours). It seemed therefore that the samples had substantial surface area that was difficult, but possible, to access with nitrogen.
The sample surface area accessible to common non-aqueous electrolytes was not directly measurable. Instead, the adsorption capacity for methylene blue (commonly used for activated carbons) was determined to provide a related measurement. In the literature (see for example, Active Carbon by H. Jankowska, A. Swiatkowski, J. Choma, translated by T.J. Kemp, published by Ellis Horwood, New 213836~

York, 1991), methylene blue (MB) is considered to have an equivalent minimum linear dimension of 1.5 nm. That is, MB
is expected to penetrate into pores having diameters greater than 1.5 nm. Although certain specific non-aqueous electrolyte solutions can have equivalent linear dimensions smaller than this, generally those of interest for commercial applications might be of that order in size or greater. Thus, it was estimated that if certain areas of a sample were not accessible to MB, then these same areas would also not be accessible to electrolyte.
The adsorption capacity for MB was determined using a modification of conventional methods (as in the aforementioned reference Active Carbon). Samples were dried prior to testing at 130C. About 0.1 grams of sample was placed in a flask along with 1-2 ml of 0.2~ surfactant solution (prepared using Micro-Liquid Laboratory Cleaner (trademark), a standard laboratory detergent) plus about 5 ml of deionized water. A titration was then performed using a 1.5 g/L titrating solution of hydrated MB in discrete steps. An initial amount of solution was added followed by 5 minutes of vigorous shaking. (The initial amount was either a minimum 0.1 ml or 1.0 ml depending on the estimated adsorption capacity of the sample.) The resulting mixture was then visually compared to a 0.4 mg/L
reference solution of MB. If the mixture was clearer than the reference, another 1.0 ml of titrating solution was added and the steps repeated. If the mixture was not clearer than the reference, adsorption was allowed to continue for a maximum of 3 days. If the mixture again became clearer than the reference, the discrete titrating continued. Otherwise, the measurement was finished and the adsorption capacity was taken to be that amount of MB
titrated just before the last stepwise addition. For the samples tested, generally the titrated MB was adsorbed in the 5 minute interval periods with the exception of the last few stepwise additions. Laboratory coin cell batteries were used to determine electrochemical characteristics of the samples including specific capacity for lithium. These were assembled using conventional 2325 hardware and with assembly taking place in an argon filled glove box as described in J.R. Dahn et al, Electrochimica 5 Acta, 38, 1179 (1993). Figure 3 shows an exploded view of the coin cell type battery. For purposes of analysis, the samples were used as cathodes in these batteries opposite a lithium metal anode. A stainless steel cap 21 and special oxidation resistant case 30 comprise the container and also serve as negative and positive terminals respectively. A gasket 22 is used as a seal and also serves to separate the two terminals. Mechanical pressure is applied to the stack comprising lithium anode 25, separator 26, and sample cathode 27 by means of mild steel 15 disc spring 23 and stainless disc 24. The disc spring was selected such that a pressure of about 15 bar was applied following closure of the battery. 125 ~m thick metal foil was used as the lithium anode 25. Celgard 2502 microporous polypropylene film was used as the separator 26. The 20 electrolyte 28 was a solution of lM LiPF6 salt dissolved in a solvent mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 30/70.
Sample cathodes 27 were made using a mixture of powdered sample compound plus Super S (trademark of 25 Ensagri) carbon black conductive dilutant and polyvinylidene fluoride (PVDF) binder (both in amounts of about 5~ by weight to that of the sample) uniformly coated on thin copper foil. The powdered sample and the carbon black were initially added to a solution of 20~ PVDF in N-30 methylpyrollidinone (NMP) to form a slurry such that 5~ ofthe final electrode mass would be PVDF. Excess NMP was then added until the slurry reached a smooth syrupy viscosity. The slurry was then spread on small preweighed pieces of Cu foil (about 1. 5 cm2 in area) using a spreader, 35 and the NMP was evaporated off at about 90C in air. Once the sample cathode stock was dried, it was compressed between flat plates at about 25 bar pressure. These ~13836~

electrodes were then weighed and the weight of the foil, the PVDF, and the carbon black were subtracted to obtain the active electrode mass. Typical electrodes were 100 micrometers thick and had an active mass of 15 mg.
After construction, the coin cell batteries were removed from the glove box, thermostatted at 30 + 1C, and then charged and discharged using constant current cyclers with + 1~ current stability. Data was logged whenever the cell voltage changed by more than 0.005 V. Currents were adjusted to be either 7.4 mA/g, 18.5 mA/g, or 37mA/g of active material, depending on the desired test. Much of the discharge capacity of the example carbons is very close to the potential of lithium metal. Thus, special testing methods were required to determine the full reversible capacity. Coin cell batteries were therefore discharged at constant current for a fixed time, the time being chosen such that the battery voltage would fall below zero volts (versus Li) and such that lithium plating on the carbon electrode would occur. It should be noted that the plating of lithium does not occur immediately after the battery voltage goes below zero volts due to the overvoltage caused by the finite constant current used. However, plating does begin shortly thereafter (usually around -0.02V) and is characterized by a region where the voltage of the battery rises slightly once plating is initiated followed by a constant or nearly constant voltage region. The onset of lithium plating is clearly and easily determined as shown in the following examples. The plating of lithium on the carbon electrode was continued for a few hours and then the current was reversed. First, the plated lithium is stripped, and then inserted lithium is removed from the carbon. The two processes are easily distinguished provided that the charge rates are small (ie. less than 37 mA/g of active material). The reversible capacity was calculated as being the average of the second discharge and second charge capacities of the battery, excluding lithium plating and stripping. The first discharge capacity was 213~36~

not used for this calculation because irreversible processes occur on the first discharge.

Comparative Example 1.

Several samples were made by preparing a thermoset polymer from furfuryl alcohol in the presence of either phosphoric, oxalic, or boric acid followed by pyrolysis at various temperatures up to 1100C according to the methods of the aforementioned A. Omaru reference. R values for all these samples were determined as mentioned above and the results are listed in Table 1.

Table 1 Data for the samples of Comparative Example 1.

P~c~;ul~olPolylllcli~hlg Acid Pyrolysis R
Lt;~ dLul~i (C) Polyrulrulyl Alcohol Pho~ph~rir 600 2.30 Polyrulrulyl Alcohol Phosphoric 1100 2.45 Polyrulrulyl Alcohol Oxalic 900 2.56 2 o POlyrulrulyl Alcohol Phosphoric 1000 2.74 Polyfurfuryl Alcohol Boric 900 4.9 The high capacity, hard carbon samples of the prior art appear to have R values that exceed 2.2.
Comparative Example 2 KSRAW grade (trademark) petroleum pitch was obtained from Kureha Company of Japan in order to replicate the prior art material of Mabuchi et al. A series of soft carbon samples was made by pyrolysing said pitch at 213836~

temperatures between 550C and 950C. The H/C atomic ratios for this series was determined as mentioned above and are shown in Figure 4 (also shown are H/C ratios for samples of Inventive Example 1 to follow). The x-ray diffraction pattern in the vicinity of the {002} peak is shown in Figure 5 for some of these samples along with the pattern of the precursor itself. (Note that the patterns have been offset vertically by 2000 counts for clarity.) R values and H/C data for this series are presented in Table 2. None of the samples have both Rc2.2 and H/C~0.1.

Table 2 Data for the samples of Comparative Example 2.

Pyrolysis T~ ldtul~ H/C R
(C) 550 0.382.67 600 0.2352.14 700 0.1832.33 900 0.0803.33 Laboratory coin cell batteries were prepared using some of these samples as described previously. Figure 6b shows the voltage versus capacity plot for the second cycle of these batteries. (The plots have been shifted upwards sequentially by 0.05 V for clarity in Figure 6b.) Figure 6a shows an expanded version of Figure 6b near 0 volts to better indicate the onset of lithium plating and completion of lithium stripping (indicated by arrows for the 550C
data) during cycling. (The data have been shifted upwards sequentially by 0.1 V for clarity in Figure 6a.) Each of the samples pyrolyzed at 700C or less show a maximum specific capacity (calculated as described previously) of about 650 mAh/g. Samples pyrolyzed above 700C had significantly less capacity (down to about 400 213836~

mAh/g for the sample pyrolyzed at 900C). Substantial hysteresis in the voltage plots can be seen, especially for samples pyrolyzed at the lower temperatures.
The very high capacity carbon samples of the prior art appear to lose their very high capacity characteristics when pyrolyzed at temperatures above about 700C. There seems to be a correlation between larger specific capacity and larger H/C ratio for these samples.

Comparative Example 3 M20E and M30 (trademarks) grade activated carbons were obtained from Spectracorp, MA, U.S.A.. Some of each activated carbon sample was analyzed as is and some was pyrolyzed at 1000C prior to analysis. Additionally, polyvinylidene fluoride (PVDF, obtained from Aldrich Chemical company, U.S.A.) was pyrolyzed at 1000C. R, H/C, CHN, and specific capacity values were obtained as described in the preceding discussion for each of these samples. For each activated carbon sample, R was about 1.1 and the H/C atomic ratio was very small (~0.03). Figure 7 shows the x-ray diffraction pattern in the vicinity of the {002} peak for the M20E sample as received and after pyrolysis to 1000C. For the pyrolyzed PVDF sample, R was about 1.3 and the H/C atomic ratio was 0.053.
The BET surface areas for all these samples are relatively high (~100 m2/g). Also, the adsorption capacity for MB is also relatively high. For M20E and M30 activated carbons as supplied, the MB adsorption capacity exceeded 400 micromoles/g. (It was deemed to be unnecessary to continue the titration.) The pyrolyzed PVDF carbon sample adsorbed about 200 micromoles of MB per gram.
All samples exhibited high specific capacities but also substantial hysteresis in the voltage plot and substantial irreversible capacity on the first discharge.
For instance, Figure 8 shows the second cycle voltage versus capacity plot for the battery containing M30 213836~

activated carbon pyrolyzed at 1000C. The specific capacity is about 550 mAh/g and there is substantial hysteresis. Figure 9 shows the first cycle voltage versus capacity plot for the same battery containing M30 activated carbon pyrolyzed at 1000C. The first discharge capacity is enormous at about 2000 mAh/g and thus there is substantial irreversible capacity.
This example shows that some hard carbons, derived from precursors other than epoxies, when pyrolyzed at temperatures above 700C can have R<2.2 and H/C<0.1 and yet not provide the low hysteresis and irreversible capacity advantages of the invention. Such hard carbons have high BET surface areas and also have relatively high adsorption capacities for MB ( ~>4 micromoles/g carbon).
Inventive Example 1 A series of samples was prepared using Dow 438 (trademark of Dow Chemical Co., U.S.A.) epoxy novolac resin as a precursor. The resin was usually mixed with different amounts of phthallic anhydride hardener which was cured at about 120C to a hard plastic state prior to pyrolysis. Pyrolysis was performed at temperatures varying from 700C to 1100C. Afterwards, R, H/C, CHN, and specific capacity values were obtained for most samples in the series as described in the preceding discussion. BET
and MB adsorption capacities were also obtained for some representative samples in the series. A summary of samples prepared with these corresponding values is shown in Table 3.

t; ~ ~ O O O ~ ~
~ ` ~ Z ~ ~^ ~ ô ~

~ ~ l-- a~ o ~ ~ o G~
V Z ~ V ~ V V

m ~ Z Z Z Z ~ Z A Z Z c~

C~ V ~ ~ ~ ~
C -- ~ ~ o o o o o o o X ~ o o o o o o o ~
o D
~ ~ O O O
c 3 ~ v v v '~
o C '~ ~ ~ ~D ~ ~ '~
ce 3 ~ -- O O O O O O O O ~
c O -0~ v O ~ ~ ~ ~ ~ ~ ~ ~ ~_ a ~ ~ ~ ~ ~ ~ O ~ 00 ~ ~

~ o o o o P~ ~
, E-o o o o _ _ o X o z ~ ,~ 5 5 ;~ ~

213836~

The voltage versus capacity plots for sample no. I
pyrolyzed at 700C is compared to that of the pitch sample of Comparative Example 2 pyrolyzed at the same temperature in Figure 10. These two plots show almost identical behaviour (although the battery using sample no. I was allowed to plate more lithium). Figure 4 indicates that the two samples in Figure 10 have almost the same H/C
ratio. Figure 11 shows the x-ray diffraction patterns of samples no. I, II, and III (offset by 1600 counts).
Therein, it can be seen that sample no. I has a substantially smaller R than the corresponding pitch sample in Figure 5. There are very few stacked graphene layers in sample no. I as evidenced by the {002} peak amounting to only a shoulder on the low angle background. Figures 11 and 5 also show that these structural differences persist at higher pyrolysis temperatures.
Figures 12a and b show the voltage versus capacity plots for samples no. I, II, III, and V (plots are offset by 0.05 and 0.1 volts in Figures a and b respectively).
These samples all have R~2.2. Sample I shows considerable hysteresis in the voltage plot. At higher pyrolysis temperatures, the capacity available near 1.0 V during the charge of sample no. I is shifted down near 0 V, so that around 900C to 1000C reversible cycling with little hysteresis is obtained. Furthermore, high specific capacity is maintained in samples no. III and V at pyrolysis temperatures of 900C to 1000C, unlike that of the pyrolyzed pitch of Comparative Example 2.
Figures 13a and b show the voltage versus capacity plots for samples no. V, VI, VII, and IX (plots are offset by 0.05 and 0.1 volts in Figures a and b respectively).
These Figures also illustrate the relation between R and specific capacity for samples pyrolyzed at 1000C to 1100C. As R increases, the specific capacity decreases.
Figure 14 shows the x-ray diffraction patterns in the vicinity of the {002} peak for the samples of Figures 13a - 21383~

and b. (The patterns have been offset upwards sequentially by 3000 counts for clarity.) Figure 15 is provided to show a summary plot of specific capacity versus R for samples III to IX inclusive which were all pyrolyzed between 900C
and 1100C. The samples therein all exhibited voltage curves with little hysteresis and all had H/CcO.1. Again, as R increases, the specific capacity decreases.
Figure 16 shows the first discharge and charge of the laboratory coin cell battery employing sample no. VII. The battery shows a first discharge capacity of about 625 mAh/g and a first recharge capacity of about 465 mAh/g. The irreversible capacity of sample VII is therefore only about 160 mAh/g, which is considered to be in an acceptable range for practical lithium ion batteries. The surface area measured by the BET method for sample VII was 217 m2/g. If this area were all accessible to electrolyte, such low values for the irreversible capacity would not be expected (for example, based on the disclosure of U.S. Patent No.
5,028,500). However, the MB adsorption capacity is relatively low (<5 micromoles/g) for this and all the other inventive samples tested.
Insertion compounds of the invention can therefore have very high specific capacity coupled with acceptable associated hysteresis in voltage and acceptable associated irreversible capacity.

Inventive Example 2 A sample was prepared using Dow D.E.R. 667 (trademark of Dow Chemical Co., U.S.A.) bisphenol A type epoxy resin as a precursor. No hardener was used in this preparation.
Pyrolysis was performed by heating first at 250C for 2 hours followed by ramping at 30C/min to 800C and thereafter holding for 2 hours. R for this sample was about 1.52. Laboratory coin cell batteries were then prepared and specific capacity values were obtained.
The voltage versus capacity plot for one of these batteries is shown in Figures 17a and b (plots are offset by 0.05 and 0.1 volts in Figures a and b respectively).
Therein, the specific capacity was 410mAh/g. The irreversible capacity is only about 160 mAh/g and the hysteresis in the voltage is considered acceptable.
It thus appears possible to make insertion compounds of the invention using bisphenol A type epoxy resin.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example, mixtures of more than one precursor may be used to prepare compounds. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Claims (27)

WHAT IS CLAIMED IS:

1. A carbonaceous insertion compound comprising:
a pre-graphitic carbonaceous host wherein i) the empirical parameter R, determined from an x-ray diffraction pattern and defined as the {002} peak height divided by the background level, is less than about 2.2, ii) the H/C atomic ratio is less than about 0.1, and iii) the methylene blue absorption capacity is less than about 4 micromoles per gram of host; and atoms of an alkali metal inserted into the carbonaceous host.

2. A carbonaceous insertion compound as claimed in claim 1 wherein R is less than about 2.

3. A carbonaceous insertion compound as claimed in claim 1 wherein R is less than about 1.5.

4. A carbonaceous insertion compound as claimed in claim 1 wherein the alkali metal is lithium.

5. A carbonaceous insertion compound comprising:
a pre-graphitic carbonaceous host prepared by pyrolyzing an epoxy precursor at a temperature above about 700°C wherein the empirical parameter R, determined from an x-ray diffraction pattern and defined as the {002} peak height divided by the background level, is less than about 2.2; and atoms of an alkali metal inserted into the carbonaceous host.

6. A carbonaceous insertion compound as claimed in claim 5 wherein the epoxy precursor comprises an epoxy novolac resin.

7. A carbonaceous insertion compound as claimed in claim 6 wherein the epoxy precursor comprises a hardener in a range from zero to about 40% by weight.

8. A carbonaceous insertion compound as claimed in claim 7 wherein the hardener is phthallic anhydride.

9. A carbonaceous insertion compound as claimed in claim 8 wherein the epoxy precursor is cured at about 120°C
before pyrolysis.

10. A carbonaceous insertion compound as claimed in claim 6 wherein the pyrolysis temperature is attained by ramping at from about 1°C/min to about 20°C/min.

11. A carbonaceous insertion compound comprising:
a pre-graphitic carbonaceous host prepared by pyrolyzing an epoxy novolac resin having the formula Epoxy Novolac Resin n = 1.6 at a temperature above about 700°C and below about 1100°C; and lithium atoms inserted into the carbonaceous host.

12. A carbonaceous insertion compound as claimed in claim 5 wherein the epoxy precursor comprises a bisphenol A epoxy resin.

13. A carbonaceous insertion compound as claimed in claim 12 wherein the pyrolysis temperature is attained by ramping at about 30°C/min.

14. A carbonaceous insertion compound comprising:
a pre-graphitic carbonaceous host prepared by pyrolyzing a bisphenol A epoxy resin having the formula Bisphenol-A Epoxy Resin n = 12 at a temperature about 800°C, and lithium atoms inserted into the carbonaceous host.

15. A process for preparing a pre-graphitic carbonaceous host for a carbonaceous insertion compound comprising pyrolyzing an epoxy precursor at a temperature above about 700°C such that the empirical parameter R, determined from an x-ray diffraction pattern and defined as the {002} peak height divided by the background level, is less than about 2.2.

16. A process as claimed in claim 15 wherein the epoxy precursor is an epoxy novolac resin with formula Epoxy Novolac Resin n = 1.6 and the pyrolysis is performed at a maximum temperature below about 1100°C.

17. A process as claimed in claim 15 wherein the epoxy precursor is a bisphenol A epoxy resin with formula Bisphenol-A Epoxy Resin n = 12 and the pyrolysis is performed at a temperature about 800°C.

18. An electrochemical device comprising an electrode wherein at least a portion of the electrode comprises the carbonaceous insertion compound as claimed in claim 1, 4, 5, 6, 11, 12, or 14.

19. A battery comprising an electrode wherein at least a portion of the electrode comprises the carbonaceous insertion compound as claimed in claim 1, 4, 5, 6, 12, or 14.

20. A non-aqueous battery comprising:
a cathode comprising a lithium insertion compound;
a non-aqueous electrolyte comprising a lithium salt dissolved in a mixture of non-aqueous solvents; and an anode comprising the carbonaceous insertion compound as claimed in claim 1, 5, 6, 12, or 14 wherein the alkali metal is Li.

21. The use of a carbonaceous insertion compound in an electrochemical device comprising an electrode, said carbonaceous insertion compound comprising:
a pre-graphitic carbonation host prepared by pyrolizing an epoxy precursor at a temperature above about 700°C wherein the empirical parameter R, determined from an X-ray diffraction pattern, and defined as the {002} peak height divided by the background level, is less than about 2.2; and atoms of an alkali metal inserted into the carbonaceous host.

22. The use of the carbonaceous insertion compound as claimed in claim 21 wherein the epoxy precursor is a novolac epoxy resin.

23. The use of the carbonaceous insertion compound as claimed in claim 21 wherein the epoxy precursor is a bisphenol A epoxy resin.

24. The use of a carbonaceous insertion compound in a rechargeable battery comprising an electrode, said carbonaceous insertion compound comprising:
a pre-graphitic carbonation host prepared by pyrolizing an epoxy precursor at a temperature above about 700°C wherein the empirical parameter R, determined from an X-ray diffraction pattern, and defined as the {002} peak height divided by the background level, is less than about 2.2; and atoms of an alkali metal inserted into the carbonaceous host.

25. The use of the carbonaceous insertion compound as claimed in claim 24 wherein the epoxy precursor is a novolac epoxy resin.

26. The use of the carbonaceous insertion compound as claimed in claim 24 wherein the epoxy precursor is a bisphenol A epoxy resin.

27. The use of the carbonaceous insertion compound as claimed in claims 21, 22, 23, 24, 25 or 26 wherein the alkaline metal is lithium.