CA2146426A1 - Phenolic resin precursor pre-graphitic carbonaceous insertion compounds and use as anodes in rechargeable batteries - Google Patents

Abstract

Carbonaceous insertion compounds and methods f or preparation are described wherein the compounds comprise a highly disordered, impurity free, hard pre-graphitic carbonaceous host. Carbonaceous insertion compounds can be prepared which have large reversible capacity for lithium yet low irreversible capacity and voltage hysteresis. Such insertion compounds can be prepared by simple pyrolysis of suitable phenolic resin precursors at an appropriate temperature. These insertion compounds may be suitable for use as high capacity anodes in lithium ion batteries.

Description

~ ~4~42~
~ .TC RESIN PREC~RSOR PRE-GRAPHITIC
RO~ T~OUs lN~ . COMPOUNDS AND
USE AS ANODES IN RT!t'TTl~R~:R~RT.T~ BATTERIES
S FIE~D OF TRl~ T~vl3NTIoN
The invention pertaine to the f ield of carbonaceou3 materialA and, in particular, to phenolic reein precureor pre-graphitic carbonaceous ineertion materials.
Additionally, the invention pertains to the field of rechargeable batterieA and, in particular, to rechargeable batteriee comprieing ~ ArhonAceoue anode materiale .
BACK~RO~ D OF T~ INVENTION
The group of pre-graphitic compounds includeA
carbonaceous materiale that are generally prepared at low temperaturee (eg: leAe than about 2000C) from various organic eourceA and that tend to graphitize when annealed at higher temperatures. There are however both hard and eoft pre-graphitic carbon compounde, the former being difficult to graphitize Aubetantially even at temperature_ of order of 3000C, and the latter, on the other hand, being virtually completely graphitized around 3000C.
The af~,L~ n~d _et of compounds has been of great intereAt for use ae anode materialA in lithium-ion or rocking chair type batteriee. These batteries repreAent the Atate of the art in Amall rechargeable power AourceA
for coneumer electronicA applications. These batterieA
have the greatest energy denAity (wh/r~) of conv~n~ nAl rechargeable syeteme (ie. NiCd, NiMH, or lead acid batterieA). Additionally, lithium ion batterieA operate around 33~ volts which is often sufficiently high such that a eingle cell can suffice for many electronice applicatiOn-A.
Lithium ion batteriee uee two different insertion compound_ f or the active cathode and anode materials .
InAertion compounds are thoAe that act as a ho3t solid for the reverAible insertion of gueet atoms (in thie caee, . _ . . .. . . . .. . . . . . . _ _ _ _ _ _ _ _ _ . . . _ ~ 21~42~

lithium atoms). The structure of the insertion compound 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 S 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 ~t,orn;~l 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 I,iCoO2 / pre-graphitic carbon electrochemistry is commercially available (produced by Sony Energy Tec. ) wherein the carbonaceous anode can reversibly insert about 0 . 65 ~i 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 ~T.R. Dahn et al., ~.ithium ~3atteries, New Materials and New Perspectives", edited by G. Pigtoia, 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 a8 the specific capacity for that material.
Graphitized carbon8 and/or graphite itself can be employed under certain conditions (as for example in the presentation by Matsushita, 6th Inter~ational Lithium ~` 2146~2~

Battery Conference, Muenster, Germany, May 13, 1992, or in U.S. Patent No. 5,130,211) .
Other alternatives for increasing the specific capacity of carbonaceous anode materials have included the 5 addition of other Pl PnlPn~ to the carbonaceous compound.
For example, t~nA~11 An Patent Application Serial No .

2,098,248, Jeffrey R. Dahn et al., 'Electron Acceptor Substituted Carbons for Use as Anodes in Rechargeable Lithium Batteries', filed June 11, 1993, discloses a means 10 for PnhAnr; ng 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 a3 high as 440 mAh/g were obtained with boron substituted carbons.
'AnA(1;An Patent Application Serial No. 2,122,770, Alfred M.
Wilson et al., '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 r.,ntAin;nrJ gilicon as disclosed in ~nA~l;An Patent Application Serial No. 2,127,621, Alfred M. Wilson et al., ' Carbonaceous Insertion Compounds and Use as Anodes in Rechargeable Batteries', filed July 8, 1994.
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. have demonstrated that pyrolyzed coal tar pitch can have specific capacities as high as 750 mAh/g at pyrolysis temperatures about 700C. ~. Sato et al. in Science 264, 556, (1994) disclosed a similar carbonaceous material prepared by heating polyparaphenylene at 700C
which has a reversible capacity of 680 mAh/g. S. Yata et , :
`- 21~642 al, Synthetic Metals 62, 153 (1994) also discloee a similar material made in a similar way. These values are much greater than that of pure graphite. The afur~ t;oned materials can have a very large irreversible capacity as 5 evidenced by f irst di8charge 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 ~l0 lithium ion battery using such a material as an anode, this would result in a similar signlficant hysteresis in battery voltage between discharge and charge with a resulting undesirable energy inefficiency.
It is not understood why the afor~ml~nt;r~n 15 carbonaceous materials have very high specif ic capacity .
All were prepared at temperatures of about 700C and are crystalline enough to exhibit x-ray patterns from which the parameters doo2, Lc, a, and L~, can be determined. (The definition and determination of these parameters can be 20 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 25 pyrolyzing at higher temperature degrades the specific capacity substantially with a concurrent reduction in the hydrogen content. (In the aforementioned reference by ~abuchi et al, pyrolyzing the pitch above about 800C
results in a specific capacity decrease to under 450 mAh/g 30 with a large reduction in H/C. Similar results were found in the afor~m~nt; on~(l reference by Yata et al . ) The prior art also discloses carbonaceous compounds with specif ic capacitie8 higher than that of pure graphite made from precursors that form hard carbons on pyrolysis.
35 However, the very high specific capacities of the aforementioned materials pyrolyzed at about 700C were apparently not at~ained. A. Omaru et al, Paper #25, ~ 21~2~
s Extended Abetracts of Battery Division, p34, Meeting of the ~lectrochemical Society, Toronto, Canada (1992), disclose the preparation of a hard carbonaceous compound Cont;~;n;n~
phosphorus with a specific capacity of about 450 mAh/g by 5 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 discloee a hard carbonaceous compound comprising 2.4~6 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 suostantially less than o.1). These hard carbonaceous compounds neither exhibited the very high specif ic capacities nor the same serious hysteresis in voltage of the aforementioned materials pyrolyzed at about 700C.
Additionally, other high capacity carbonaceous materials have recently been prepared which show high capacity for lithium and little or no voltage hysteresiH.
In Paper 2B05 at the 35th Battery Symposium in Nagoya, Japan, Nov. 14-16, 1994, Y. T~k~h~Rh; et al. describe materials with reversible capacities of about 480 mAh/g, but do not give the details of their preparation. In paper 2BO9 at the same Symposium, N. Sonobe et al. deecribe hard carbon materials made from petroleum pitch with reversible capacites near 500 mAh/g. The synthesis procedure therein was not given.
In ~'An~ n Patent Application Serial No. 2,138,360, Y. Liu and J. Dahn, of the same title, filed Dec. 16, 1994, carbonaceous insertion compounds also having high capacity for lithium and little voltage hysteresis were disclosed.
Therein, the carbonaceous insertion compounds comprised 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 - `
-- 214642~

background level, i8 less than about 2.2; ii) the H/C
atomic ratio is less than about 0.1; and iii) the methylene blue ab60rption capacity of the pre-graphitic carbonaceous host is less than about 4 micromoles per gram of host.
These carbonaceous insertion compounds were prepared by pyrolyzing suitable organic precursors. Specifically shown in the Examples were insertion compound3 prepared from different epoxy precursors.
SI~ aRY OF T~IE LNV~ N
The instant invention pertains to phenolic resin precursors which can be employed to produce carbonaceous insertion compounds with a high capacity for lithium and little voltage hysteresis. Thus, carbonaceous insertion compounds derived from phenolic resins, methods of preparing said compounds, and the use of said compounds as electrode materials in electrochemical devices comprise the subject matter of the instant invention.
Car3~onaceous insertion compounds of the invention comprise a pre-graphitic r~rh~n~reous host prepared by pyrolyzing a phenolic resin precursor and atoms of an alkali metal inserted therein. The alkali metal inserted 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 aoout O.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 metal, R can pref erably be less than about 1. 6 .
Hydrogen can be pr~ ;ni~ntly removed from the phenolic resin precursor by pyrolysis at a temperature above about 800C. However, the pyrolysis temperature cannot be too high in order that the empirical parameter R, .

~ 642~

determined from an x-ray diffraction pattern of the host and defined as the {002} peak height divided by the background level, i8 leBs than about 2 . 2 .
The phenolic resin precursor can be of the novolac or 5 the resole type. The latter can be preferably pyrolyzed at a temperature in the range from about 900C to about 1100C. Both types can be cured at about 150C before pyrolysis. The pyrolysis temperature for both types can be maintained for about one hour.
Methods of the invention include processes f or preparing suitable pre-graphitic carbonaceous hosts for the afc~ nt;oned compounds. Such hosts can be prepared by pyrolyzing a phenolic resin precursor at a temperature above about 800C such that the empirical parameter R, 15 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. The phenolic resin employed can be of either the novolac or the resole type. Alkali metal atoms can be inserted into the ho~t thereafter by convf~nt; nni~l 20 chemical or electrochemical means to make insertion compounds of the invention.
Compounds of the invention can be used as a portion of an electrode in various electrochemical devices based on insertion materials (eg. supercapacitors, electrochromic 25 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 30 a mixture of non-aqueous solvents; and an anode comprising the carbonaceous insertion compound of the iLvention.
BRIEF DES~ ~r~ , OF ~I'TTR nR~-wrl-".c Figure 1 shows a cross-sectional view of a conv~nt;nn~l lithium ion spiral-wound type battery.
.

` ~14~42~

Figure 2 depicts an exploded view of the laboratory coin cell battery used in the Examples.
Figures 3a and 3b show the voltage versus capacity 5 plots for the first and second cycles respectively for batteries comprising samples prepared from the A type precursor in Inventive Example 1. The curves have been offset sequentially for clarity. (In both Figures, the shifts are 0.0, 0.15, 0.3, 0.45, and 0.7 volts for sample A700, A800, A900, A1000, and A1100 respectively.) Figures 4a and ~b show the voltage versus capacity plots for the first and second cycles respectively for batteries comprising samples prepared from the B type 15 precursor in Inventive Example 1. The curves have been offset sequentially for clarity. (In Figure 4a, the shifts are 0.0, 0.1, 0.25, 0.3, and 0.4 volts for sample B700, B800, B900, B1000, and B1100 respectively. In Figure 4b, the shifts are 0.0, O.I, 0.3, 0.5, and 0.8 volts for sample B700, B800, B900, B1000, and B1100 respectively ) Figures 5a and 5b show the voltage versus capacity plots for the irst and second cycles respectively for 25 batteries comprising samples prepared from the C type precursor in Inventive Example 1. The curves have been offset se~]~nt;Ally for clarity. (In both Figures, the shifts are 0.0, 0.15, 0.3, and 0.45 volts for sample C800, C900, C1000, and C1100 respectively.) Figure 6 shows the capacity ver~us cycle number for the battery comprising sample B1000 of Inventive ~xample 1.
Figure 7 shows the voltage versus capacity plots for 35 the second cycle of batteries comprising samples prepared from the B type precursor in Inventive Example 2. The plots have been se~l~nt.Ally offset ~y O.lV for clarity.

` ~14~425 DET~TT.T.'TI DES' ~TV-l~JN OF TT~R SPT~'rTT~IC
~ OF TTTT~ lNV~N~ ~VN
Compounds of the invention comprise hard pre-graphitic 5 carbonaceous hoste 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 phenolic resin precursors. The pyrolysis of epoxy 10 novolac resins (eg. DEN 438, trademark of DOW) gives product yields near 30~. It is well known however that phenolic resins (or phenol-formaldehyde resins) can also be pyrolysed to give hard carbons with high yield (as for example mentioned in E. Fitzer et al., Carbon 7, 643 (1969). Since the former can cost about $5 per pound versus about $1. 00 per pound for the latter at the time of this writing, a cost advantage might be expected for phenolic resin precursors.
Suitable phenolic resin precursors are those that, 20 when pyrolyzed at temperatures above about 800C, do not graphitize to such an extent that the empirical parameter R as determined by the x-ray diffraction pattern exceeds about 2.2. R is defined as the {002} graphite peak height divided by the background level. (The detailed method for 25 this determination is described again 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 dif fraction patterns .
Pyrolyzing suitable phenolic resin precursors above 30 800C provides pre-graphitic carbonaceous hosts that do not exhibit severe hysteresis in voltage upon in~ertion 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 35 with high specific capacities for lithium. Based on the Examples to follow, R appears to be preferably less than about 1. 6 .

` ~14642S

The pyrolysis should be performed under a controlled atmo3phere to prevent formation of undesired oxides of carbon. A suitable reaction system could consist of a reaction tube (quartz for example) installed in a 5 conv~nt~n:~l tube furnace wherein the tube has sealed inlet and outlet connections for purposes of controlling the atmosphere therein. The phenolic resin precursor/s could thus be pyrolyzed in the reaction tube under an inert gas flow or even under reduced or elevated pre~sure.
10 Additionally, controlled partial reduction or oxidation, if desired, can be achieved by admitting controlled amounts of an d~ L iate gas .
To ensure good product yields, ideally the phenolic resin precursor/s should substantially pyrolyze rather than 15 simply evaporate. This issue must be considered in the selection of preferred precursor/s. It can therefore be advantageous to cure, or cross-link, the precursor before pyrolysis. Such curing may be a significant variable affecting the desired ultimate properties of the pyrolyzed 20 precursor/s. It may therefore 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 precursor/s prior to a f inal heating to the pyrolysis temperature . Alternately, 25 the heating rate might be varied to control the extent of the curing prior to pyroly~3is.
The product of pyrolysis can have relatively large surface areas, of order of 200 m~/g, as determined by conventional nitrogen adsorption methods (eg. BET).
30 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 con~ume lithium occur at the anode surface in such batteries.
35 Thus, use of an anode having a large surf ace area accessible to electrolyte results in substantial irreversible capacity 1O8B and electrolyte loss. These ~ 21~642G

loeeee are avoided if the anode 3urface ie not acceseible to the electrolyte.
The aforementioned product hae no alkali metal inserted ae prepared. Alkali metal atome, in particular Li, can be ineerted thereafter via conv~n~;-)ri~l chemical or electrochemical means (such ae in a lithium or lithium ion battery) .
Generally, powdered forme of euch compounde are used in electrode applicatione and thue a grinding of the pyrolyzed product i8 ueually required. A variety of embodiments, in particular varioue battery conf iguration3, are poesible using electrode material prepared by the method of the invention. Miniature laboratory batteriee employing a lithium metal anode are deecribed in the examplee to follow. However, a preferred conetruction for a lithium ion type product ie that depicted for a conventional spiral-wound type battery in the croee-eectional view of Figure 1. A j elly roll 4 ie created by epirally winding a cathode foil (not 3hown), an anode foil (not ehown), and two microporoue polyolefin sheete (not shown) that act as eèparatore.
Cathode foils are prepared by applying a mixture of a suitable powdered (about 10 micron eize typically) cathode material, euch ae a lithiated traneition metal oxide, poeeibly other powdered cathode material if deeired, a binder, and a conductive dilutant onto a thin aluminum foil. Typically, the application method firet involvee di3solving the binder in a suitable liquid carrier. Then, a elurry i8 prepared using thie eolution plue the other powdered eolid components. The ~lurry ie then coated uniformly onto the eub3trate foil. Afterwarde, the carrier solvent ie evaporated away. Often, both eide3 of the aluminum foil substrate are coated in thie manner and eubeequently the cathode foil ie calendered.
Anode foils are prepared in a like manner except that a powdered (aleo typically about 10 micron size) carbonaceoue ineertion compound of the invention i8 ueed ` 214~2S

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.
S 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 1.
The j elly roll 4 is inserted into a conventional battery can 3. A header 1 and gasket 10 are used to seal 10 the battery 16. The header may include safety devices if desired. A combination safety vent and pressure operated disconnect device may be employed. Figure 1 shows one such combination that is described in detail in t~;3nA~ n Patent Application No. 2,099,657, Alexander H. Rivers-Bowerman, 15 'Electrochemical Cell and Method of Manufacturing Same', filed June 25, 1993. Additionally, a positive thermal coefficient device (PTC) may be incorporated into the header to limit the short circuit current capability of the battery. The extf~rnill surface of the header 1 is used as 20 the positive terminal, while the external surface of the can 3 serves as the negative ter~inal.
Appropriate cathode tab 5 and anode tab 6 connections are made to connect the ;ntGrni~l electrodes to the ex~rn~l terminals. Appropriate insulating pieces 2 and 7 may be 25 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 30 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 to follow can have somewhat increased irreversible capacity for lithium along with an 35 increased reversible capacity over that of many typical commercial carbonaceous anode materials. Also, Example compounds typically have somewhat lower density than that ` 21~6425 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, i3 part of the assembly process.
5 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 10 the batteries of the invention (eg. prismatic format). 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.
Without wishing to be bound by theory, adversely or otherwise, the inventor3 offer the following view of the prior art and of the instant invention to explain how certain prior art carbonaceous materials can have specific capacities that significantly exceed that of graphite.
The presence of substantial hydrogen in carbonaceous materials of the prior art prepared by pyrolysis at low 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 ~urface~ oE each side of the layers. These surfaces are found within the carbon particlec, on the atomic ~cale. In graphite, the layers are well stacked in a parallel fashion and intercalation of lithium to a composition of ~iC6 is pos~ible (corresponding to about 370 mAh/g and one intercalated layer of lithium per graphene sheet). In materials with poorly stacked .

.-- 214642~

layers, unshared lithium layer3 might possibly be found on each side of the graphene ~heets, resulting in compositions up to almost Li~C6 (corresponding to about 740 mAh/g).
Thus, the number of single layer graphene ~heets in the 5 carbonaceous material may be important vi~ a vis specific capacity .
X-ray diffraction can be used to learn about the average number, N, of 3tacked graphene sheets in a carbon in between serious stacking mistakes. Thi3 number N, lO 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 15 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 20 a house of cards. ) A8 N increases (beginning to stack the deck of cards), the {002} peak increases in height and 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 25 describing such structures and is determined by dividing the {002} peak height by an estimate of the background level at the Bragg angle corresponding to the position of the {002} peak. The background e~timate is that value given by the intersection of a line tangential to the 30 background in the immediate vicinity of the {002} peak and a line positioned at 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 35 would have significantly 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 ~` ~146~2~

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. 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. Carbonaceous materials were prepared from cured 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 for pyrolysis.
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 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 80 that none o~ the x-ray beam missed the sample in the angular range from 10 to 35 in scattering angle. The slit width was ~ixed during the mea~UL. t. This ensured reproducibility in the measured values of R.
Carbon, 1IYdL~JY~ and nitrogen content was determined on samples using a standard CHN analysis (gas chromatographic analysis after combustion of the samples in air) . The weight percents 80 determined had a standard deviation of ::0.39~. In every case, the carbon content was greater than 90~ of the sample weight and the hydrogen content was less than 29~. The H/C atomic ratio was estimated by taking the ratio of the hydrogen and carbon weight percentages and multiplying by 12 (the mass ratio o~
carbon to hydrogen). The oxygen content oE the samples was not analyzed.
The sample surface area accessible to common non-` 214~2~

aqueous electrolytes wa3 not directly measurable. In3tead, the adsorption capacity for methylene blue (MB) was u3ed to provide a related mea~uL~ -n~. [In the literature (see for example, Active Carbon by H. Jankowska, A. Swiatkowski, J.
5 Choma, tran31ated by T.J. Kemp, publi3hed by Elli3 Horwood, New York, 1991), methylene blue (MB) i3 con3idered to have an equivalent minimum linear dimen3ion of 1.5 nm. That i3, MB is expected to penetrate into pores having diameters greater than 1.5 nm. Although certain specific non-aqueou3 lO electrolyte 301utions can have equivalent linear dimension3 3maller than this, generally tho3e of interest for commercial application3 might be of that order in 3ize or greater. Thus, it wa3 e3timated that if certain area3 of a 3ample were not acce33ible to MB, then the3e 3ame area3 15 would al30 not be acce33ible to electrolyte. ]
The method for det~orm;nln~ ad30rption capacity for MB
i3 a modif ication of conventional method3 . A 3ample wa3 dried prior to te3ting at 130C. About 0.1 grams of sample wa3 placed in a fla3k along with 1-2 ml of 0.296 3urfactant 20 301ution (prepared u3ing Micro-Liquid Laboratory Cleaner (trademark), a 3tandard laboratory detergent) plu3 about 5 ml of deionized water. A titration wa3 then performed u3ing a 1. 5 g/~ titrating solution of hydrated MB in discrete step3. An initial 0.1 ml amount of 301ution wa3 25 added followed by 5 minute3 of vigorou3 3haking. (The initial amount wa3 either a minimum O .1 ml or 1. 0 ml depending on the e3timated ad30rption capacity of the 3ample. ) The re3ulting mixture wa3 then visually compared to a 0.4 mg/~ reference solution of MB. If the mixture wa3 30 clearer than the reference, another 1. 0 ml of titrating 301ution would be added and the 3tep3 repeated. If the mixture wa3 not clearer than the reference, ad30rption wa3 allowed to ~ nt;nll~ for a maximum of 3 day3. If the mixture again became clearer than the reference, the 35 di3crete titrating would be c~n~;n~ l. Otherwi3e, the mea3urement wa3 f ini3hed and the ad30rption capacity wa3 taken to be that amount of MB titrated ju3t before the la3t ` ~14~426 stepwise addition.
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 Acta, 38, 1179 (1993) . Figure 2 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 cr~nt~;npr and also serve as negative and positive t~rm;n;~l~ 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 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 mic~ us polypropylene film was used as the separator 26. The 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 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 f oil . The powdered sample and the carbon black were initially added to a solution of 2096 PVDF in N-methylpyrol 1; 1; n~n~ (NMP) to form a slurry such that 5~ of the f inal 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 cm~ in area) using a spreader, and the NMP was evaporated of f at about 9 0C in air . Once 14~426 the sample cathode stock was dried, it was compressed between flat plates at about 25 bar pressure. These electrodes were then weighed and the weight of the foil, the PVDF, and the carbon black were subtracted to obtain 5 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 i 1C, and then charged and discharged using constant current cyclers 10 with i 19~i current stability. Data was logged whenever the battery voltage changed by more than 0 . 005 V. Currents were adjusted to be 18.5 m~/g of active material for the initial two cycles of the battery and 37mA/g of active ~aterial thereafter for ~tPn~lP~l cycle testing. Much of lS 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 20 such that the battery voltage would fall below zero volts (versus I.i) and such that lithium plating on the carbon electrode would occur. Note that the plating of lithium does not occur immediately after the battery voltage goes below zero volts due to the overvoltage caused by the 25 f inite constant current used. ~owever, plating does begin shortly thereaf ter (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 30 lithium plating is clearly and easily ~tF~rm; nf~d 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 35 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 ` 2146~2~

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 not used for this calculation because irreversible processes occur on the f irst discharge .
Inveative Example 1 A series of samples was prepared using three different phenolic resins as a precursor. Two are base-catalysed or resole types and one is an acid catalyzed or novolac type.
The three dif f erent precursors used were:
A) resole type, product # 11760 of Plenco, Plastics Engineering Company, Sheboygan, WI, 53082-0758 U.S.A.;
B) resole type, product # 29217 of Oxychem, of ~ nt~l Chemical Corp, Durez Engineering Materials, 5005 LBJ
freeway, Dallas, Texas 75244, U.S.A.; and C) novolac type, product # 12116 of Plenco, supra.
The phenolic resin precursors were all supplied in powder form. In each case, the powder was cured at from about 150C to 160C for 30 minutes prior to pyrolysis. At the end of the curing step, a solid lump was obtained. The lump was next reduced to powder in an autogrinder. The powdered cured resin was then pyrolyzed in a tube furnace under f lowing argon . The samples were ramped f rom room temperature to the desired pyrolysis temperature over 3 hours and held there for 1 hour. The furnace power was then turned of f and the samples were cooled to near room temperature within the furnace tube under flowing argon.
Cooling took several hours.
Pyrolysis was performed at temperatures varying from 700C to 1100C. Afterwards, the samples were ground into a powder. R, H/C (by CH~analysis), and specific capacity value~ (by coin cell battery tests) were obtained for most samples in the series as described in the preceding. The MB adsorption capacity was also obtained ~or sample B1000 ~` 2146~2~

and was found to be about 1. 6 micromoles per gram of host .
Yield was determined from the weights of the samples before and after pyrolysis. The results of these mea~uL~ t~ is given in Table 1. (Two batteries of each sample were made 5 and the results from each experiment were within 20 mAh/g.
The values given in Table 1 represent the average values ~.hti~; n~rl . ) 2146~2~

T~ble 1. Data ïor the samples oS Inventive Example 1 Sample Pyrolysis Weight Weight Weight H/C Yield R Reversible h~versible IDTemp. % C % H % N (%) Capacity Capacity (C) (mAhlg) (mAh/g) (i20) (i20) A700 700 91.2 1.5 1.2 0.19 57 1.37 500 440 A800 800 93.1 1.0 1.3 0.13 55 1.56 510 280 A900 900 92.3 0.6 1.2 0.07 55 1.63 510 210 A10001000 94.2 0.4 1.9 0.05 54 1.68 450 160 AllO01100 96.7 0.3 0.8 0.04 52 1.79 330 70 B700 700 94.7 1.8 0.4 o.n 58 1.33 630 260 B800 800 95.8 0.9 0.7 0.11 57 1.39 540 210 B900 900 94.8 0.5 0.5 0.06 57 1.32 410 300 B10001000 95.6 0.3 0.6 0.04 56 1.34 560 200 BllO01100 97.4 0.4 1.4 0.05 56 1.64 340 110 C800 800 95.7 0.9 0.6 0.11 64 1.53 530 210 C900 900 95.1 0.4 0.7 0.05 57 1.63 450 180 C10001000 96.5 0.3 0.8 0.04 58 1.54 450 130 CllO01100 97.0 0.3 1.3 0.03 56 1.64 330 120 2~642~

Figure 3a shows the first discharge-charge cycle for the series of pyrolyzed A type precursors. The samples heated at 700C and 800C show significant hysteresis in the voltage prof ile (Li is inserted near OV but is removed 5 near 1. OV) . Thi3 has been ascribed to the large hydrogen content in the samples. Upon heating to 900C, the hysteresis is prP~~;n~ntly eliminated and the samples show substantial capacity at low voltage. Figure 3b shows the second cycle of the same series. The vertical lines 10 indicate the onset of lithium plating during discharge and the t~rTn;n~t;on of lithium stripping during charge. The batteries prepared from material heated to 900C and 1000C appear most promising for this series. Their reversible capacities are about 510 and 450 mAh/g 15 respectively.
Figures 4a and 4b show the first and second cycle voltage prof iles for the series of pyrolyzed B type precursors. The sample made at 1000C gives a reversible capacity of about 560 mAh/g and an irreversible capcity of 20 only about 200 mAh/g. This is a very attractive material for use as a lithium ion battery anode . Figures 5a and 5b show the f irst and second cycle voltage prof iles for the series of pyrolyzed C type precursors. The samples made at 900C and 1000C give reversible capacities near 450 25 mAh/g. The latter has an irrever3ible capacity of only 130 mAh/g .
Exterlded cycling was carried out on a battery comprising sample B1000. Figure 6 shows the capacity versus cycle number for this battery. There is little 30 capacity loss upon cycling.
Insertion compounds of the invention can theref ore have high reversible specif ic capacity coupled with acceptable associated hysteresis in voltage and acceptable associated irreversible capacity.

~14~ 42S

IAveAtive Example 2 The serie3 of 3ample3 made from the B type precur30r were 3hown to have the highe3t rever3ible capacitie3 in the 5 preceding Example. In order to determine how the rever3ible and irrever3ible capacities varied in the narrower temperature range between 900C and 1100C, an additional 3erie3 of 3amples using thi3 precur30r wa3 prepared. The 3ample3 were te3ted in coin cell batteries 10 a3 de3cribed earlier and voltage profile3, irrever3ible capacitie3, and rever3ible capacities were mea3ured. Two batteries of each were made and the result3 from each experiment were within 2 0 mAh/g .
Table 2 summarize3 the average ~pecific capacity 15 re3ults for all the 3amples prepared from the B type precur30r. Figure 7 show3 representative second cycle voltage prof iles for the batterie3 made with the3e sample3 .
2 0 Table 2. Data for the ssrnples of InYentive Example I
Sample ID F~eversible Capacity Irreve~sible Capacity (mAh/g) (~t20) (mAh/g) (~ 20) s900 4 l0 300 s1000 560 200 slO30 540 140 Bl100 340 llO

` ' 214642~

Appropriate selection of the pyrolysis temperature appears to be important in order to optimize the properties of these insertion compounds.
As will be apparent to those skilled in the art in the 5 light of the foregoing disclosure, rnany alteration~ and modif ications are possible in the practice of this invention without departing from the spirit or scope thereof. For example, mixture8 of more than one precursor may be used to prepare compounds. Accordingly, the scope 10 of ~he invention is to be construed in accordance with the substance defined by the following claims.

Claims (21)

WHAT IS CLAIMED IS:

1. A phenolic resin precursor carbonaceous insertion compound comprising:
a pre-graphitic carbonaceous host prepared by pyrolyzing a phenolic resin precursor at a temperature above 800°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.

2. A carbonaceous insertion compound as claimed in claim 1 wherein the H/C atomic ratio of the pre-graphitic carbonaceous host is less than about 0.1.

3. A carbonaceous insertion compound as claimed in claim 1 wherein the methylene blue absorption capacity of the pre-graphitic carbonaceous host is less than about 4 micromoles per gram of host.

4. A carbonaceous insertion compound as claimed in claim 1 wherein R is less than about 1.6.

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

6. A carbonaceous insertion compound as claimed in claim 1 wherein the phenolic resin precursor is cured at about 150°C before pyrolysis.

7. A carbonaceous insertion compound as claimed in claim 1 wherein the pyrolysis temperature is maintained for about an hour.

8. A carbonaceous insertion compound as claimed in claim 1 wherein the phenolic resin precursor is of the novolac type.

9. A carbonaceous insertion compound as claimed in claim 1 wherein the phenolic resin precursor is of the resole type.

10. A carbonaceous insertion compound as claimed in claim 9 wherein the phenolic resin precursor is pyrolyzed at a temperature in the range from about 900°C to about 1100°C.

11. A process for preparing a phenolic resin precursor pre-graphitic carbonaceous host for a carbonaceous insertion compound comprising pyrolyzing a phenolic resin precursor at a temperature above 800°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.

12. A process as claimed in claim 11 wherein the phenolic resin precursor is of the novolac type.

13. A process as claimed in claim 11 wherein the phenolic resin precursor is of the resole type

14. A process as claimed in claim 13 wherein the pyrolysis is performed at a temperature in the range from about 900°C
to about 1100°C.

15. An electrochemical device comprising an electrode wherein a portion of the electrode comprises the carbonaceous insertion compound as claimed in claim 1, 5, 8, or 9.

16. A battery comprising an electrode wherein a portion of the electrode comprises the carbonaceous insertion compound as claimed in claim 1, 5, 8, or 9.

17. 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, 8, or 9 wherein the alkali metal is Li.

18. The use of a carbonaceous insertion compound in an electrode of an electrochemical device, said carbonaceous insertion compound comprising:
a pre-graphitic carbonaceous host prepared by pyrolyzing a phenolic resin precursor at a temperature above 800°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.

!9. The use of the carbonaceous insertion compound as claimed in claim 18 wherein the phenolic resin precursor is of the novolac type.

20. The use of the carbonaceous insertion compound as claimed in claim 18 wherein the phenolic resin precursor is of the resole type.

21. The use of the carbonaceous insertion compound as claimed in claim 18, 19, or 20 wherein the alkali metal is lithium and the electrochemical device is a non-aqueous battery, the 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 said carbonaceous insertion compound.