CA2138334C

CA2138334C - Lithium secondary battery employing a non-aqueous media

Info

Publication number: CA2138334C
Application number: CA002138334A
Authority: CA
Inventors: Yuzuru Takahashi; Masatoshi Yoshimura; Hideo Yamada
Original assignee: Mitsubishi Gas Chemical Co Inc
Current assignee: Mitsubishi Gas Chemical Co Inc
Priority date: 1993-12-17
Filing date: 1994-12-16
Publication date: 1997-11-25
Anticipated expiration: 2014-12-16
Also published as: CA2138334A1; DE665602T1; EP0665602B1; US5536597A; DE69425365D1; EP0665602A1

Abstract

A lithium secondary battery employing a non-aqueous electrolyte in which the anode material is prepared by calcining a precursor organic compound obtained from the reaction of at least one polycyclic organic compound with a compound containing nitrogen and sulphur.

Description

IMPROVED LITHIUM SECONDARY BATTERY EMPLOYING A NON-AQUEOUS ELECTROLYTE

The present invention relates to an improved lithium secondary battery employing a non-aqueous electrolyte and exhibiting suPerior capacitY and charge-discharge characteristics.
In response to the trend toward miniaturization of electronic devices, it is necessarY to imProve the extent to which it is possible to realize higher capacities and greater safety and reliabili-ty, and various lithium secondarY batteries using carbonaceous materials as the anode have been proposed. For example, methods of using graphite as anode material are disclosed bY United States Patent Number 4,304,825, Japanese Laid Open Patent Application Number 1982-208079, United States Patent Number 4,423,125, Japanese Laid Open Patent Application Number 1983-102464 or JaPanese Laid Open Patent APplication Number 1992-190555. Howev-er, since graphite contains crYstallites, the intercalation and deintercalation of lithium ions damage these crystallites and impair reversibilitY.
Additionally, the high reactivitY of the lithium-intercalated anode material causes the decomposi-tion of the electrolYte, and that, in turn, causes considerable internal short circuiting. These defects make the resulting batteries inconvenient and difficult to use.
On the other hand, carbon materials having a high surface area, such as activated carbon, are dis-closed by United States Patent Number 4,497,883.
Batteries made in accordance therewith make use of electric double layer formation based on the high surface area of the activated carbon. However, ~ 2- CA2 138334 such defects as low charge-discharge efficiency and a low battery voltage are observed when secondary batteries are made using such materials as the anode.
To overcome these obstacles, the use of carbona-ceous materials differing from graphite with its crystallites and carbonaceous materials such as activated carbon with their large surface area as anodes has been ProPosed. More concretely, it has been proPosed that materials be categorized by the temperature of calcination used to produce them.
and methods using calcinated organic compounds obtained by subjecting the said organic compounds to calcination temPeratures of 1500~C or less as anode materials have been disclosed in Japanese l,aid Open Patent APPI ication Number 1983-93176 and Japanese Laid OPen Patent APPI ication Number 1985-235372. Moreover, the use of carbon fibres ob-tained by calcination at temPeratures around 2000~C
as the anode is disclosed in Japanese Laid Open Patent Application Number 1985-64181, and the use of carbonaceous material having graPhite structure that has been calcined at from 1000~C to 2500~C as anode material has been disclosed in Japanese Laid Open Patent Application Number 1985-221973. On the other hand, a carbonaceous material having a pseu-do-graphite structure in which, according to x-ray diffraction spectroscopy, the inter layer separa-tion distance (doo2) is 3.37 ~ or more and the size of the crystallite c-axis (Lc002) is 150 ~ or less is disclosed in Japanese Laid OPen Patent APPI ication Number 1987-122066. Moreover, the use as anode material of carbonaceous material falling within the scope of a relative surface area A (m2/g) repre-sented by 0.1 < A < 100, and Lcoo~ and true density,o. the values for which satisfy the relations 1.70 < p < 2.18 and 10 ~ Lc002 ~ 1200 - 189 are disclosed ~ 3- CA2 1 38334 in Japanese Laid Open Patent Application Number 1987-90863. AdditionallY, Japanese Laid Open Patent Application Number 1990-66856 discloses a (doo~ of 3.70 ~ or less, and a p value of less than 1.70 (g/cm) that moreover does not exhibit an ex-othermic differential thermal analYsis peak at 700~C or above. Among these carbon materials, various improvements have been made and some of them have been PUt into practical use: however, none of them as yet exhibit adequate capacity.
Then, it was proposed that high capacity be achieved bY adjusting the content of elements other than carbon present in the material to optimum levels. For examPle, Japanese Laid Open Patent Application Numbers 1991-137010 and 1993-74457 dis-close carbonaceous materials containing the element phosphorus, and Japanese Laid Open Patent Applica-tion Number 1991-245458 discloses a carbonaceous material containing boron. Additionally, Canadian Patent Application Serial No 2083001 discloses as an anode material having a high capacitY, a car-bonaceous material containing nitrogen made by the calcination of an organic Precursor compound ob-tained by reacting a coniugated polycyclic compound with a nitrocomPound or a nitrating agent. Ja-panese Laid Open Patent Application Number 1992-278751 discloses a sulphur containing carbonaceous anode material. However, adequate realization of a battery possessing a capacity that could suitably meet the demands of long term use in portable devices even by the use of carbonaceous materials listed above, was not possible, and it became necessary to find a carbonaceous material having a higher caPacity.
As stated above, lithium secondarY batteries made using the anode materials composed of the carbona-ceous materials of the prior art do not exhibit ~~ -4_ ~A2138334 adequate capacity. The objective of the present invention is to solve the problems of the prior art and by so doing to offer a high performance lithium secondary battery that has greater capacity, im-S proved charge - discharge cycle characteristics and superior stability and safetY.
The inventors of the Present invention, to achieve the objectives stated above, conducted their investigation based upon various existing exPeriments and investigations and prepared a carbonaceous material that included nitrogen in accordance with Japanese Patent Application Number 1992-278479, preparing it so that it had a particu-Iar type of bonding between the carbon atoms and nitrogen atoms and so that it was usable as a superior anode material. AdditionallY, theY under-stood that if in accordance with what was written in Japanese Patent Application 1992-278751, a certain amount of sulphur was included in the carbonaceous material, that material would be a superior anode material. Because of the presence of nitrogen or sulfur contained as an impurity in the raw materials used to make these carbon materi-als, a carbonaceous material was obtained by the inventors that simultaneouslY satisfied the condi-tions of both of the aforementioned patent applica-tions and a striking, greater than exPected in-crease in function was observed.
Then, the inventors of the present invention searched for a method of obtaining a carbonaceous material satisfying simultaneously the conditions stated in the above two patent applications bY
altering the composition of various organic com-pounds through the addition of compounds containing nitrogen and sulphur. As a result, and to their surprise, the carbonaceous material obtained by calcining precursor organic compounds obtained from CA21 3'8334 the reaction of a conjugated polycyclic compound such as pitch with a nitrogen containing compound and a sulphur containing compound was considerably superior to those of the Prior art. By using this material as an anode material, they were able to prepare a superior lithium secondary battery and in so doing achieved their objective.
The anode material used in the lithium secondary battery of the present invention is a carbonaceous material PrePared by calcining a precursor organic compound obtained by reacting at least one conju-gated polycyclic comPound with a compound contain-ing nitrogen and sulphur.
The conjugated polycyclic comPound maY be a conjugated,polycyclic hydrocarbon such as naphtha-lene, anthracene, pyrene, coronene or the like or their derivatives; a conjugated heteropolycyclic compound such as benzofuran, quinoline, thio-naphthalene, silanaphthalene or their derivatives, compounds derived bY linking any of the foregoing compounds together; or, additionallY, tars, sYn-thetic pitch, coal tar Pitch, petrdleum pitch, cokes. petroleum or related heavy oils that are composed Partially or completelY of or contain the foregoing comPounds or mixtures thereof. Pitch or tar having a softening point of 170~C or less are preferred as the conjugated polycyclic compound.
Optimization of conditions and pretreatment depend-ing upon the kind of conjugated polycyclic compound are also desirable. For example, where naphthalene is used, it is desirable to synthesize pitch or tar having a softening point of 170~C or less from naphthalene using HF and BF3 as a catalyst.
The compound containing nitrogen and sulphur contains both elements in the same molecule.
As the comPound containing nitrogen and sulphur of the present invention, ammonium sulphate, ammonium persulphate, acid ammonium sulphate and the like may be used, however, from the standpoint of cost and safety, ammonium sulphate is preferred. The amount of the included nitrogen and sulphur should be optimized with respect to the amount of polycyclic compound used. For example, in the case of ammonium sulPhate and pitch, a ratio by weight of ammonium sulPhate to pitch of on the order of 0.1:1 to 3:1 is preferred, and, in the case of ammonium sulphate to tar, a ratio by weight of ammonium sulPhate to tar of 0.05 to 2 is Preferred. The temperature of reaction for the ammonium sulphate and the coniugated polycyclic compound should be the optimum reac-tion temperature for the particular reactants concerned.
These oPtimum values generally fall within the range of 200~C to 600~C.
The method of reacting the coniugated polycylic compound with the nitrogen and sulPhur containing comPound is the optimum method for reaction depending uPOn the particular reactants. For example, where naphthalene is used, after reacting it to form pitch as described above, the pitch obtained may be reacted with ammonium sulphate and it is also possible to add dinitronaphthalene in addition to the ammonium sulphate. In addition, nitrocompound, a nitrating agent, ammonium sulfate, sulfur, sulfuric acid or a mixture of sulfuric and fuming sulfuric acid and various hardeners may be added. The nitration reaction bY a nitrating agent of the Present invention should be the optimum nitration reaction for the particular organic compound used. In addition, a lithium salt maY be added in accordance with Japanese Patent APPI ication No. 1993-184066 to the organic precursor compound PrePared as described herein for the purpose of reducin~ capacity loss when the anode material is used in the preParation of a batterY to obtain a more suPe-rior anode material.
The carbonaceous material for anode use of the Present invention is obtained bY calcination of the lithium contain-ing compound under an atmosphere of inert gas or a vacuum.
lhe calcination temperature is between 800~C to 1800~C, and preferably 1000~C to 1300~C. The calcination period is from 0.1 hour to 50 hours, and more preferably from 1 hour to 5 hours optimally determined based upon the characteristics of the precursor organic comPound and other reactants. Addi-tionally, a Precalcination at a temPerature of 800~C or lessmay be conducted. The inert gas is preferably nitrosen and is supplied in a continuous flow that, upon exiting, carries away the waste gas of calcination. Reaction under vacuum results in stronger removal of the reaction product gases allowing their disposal as waste gas, but calcination con-ducted where the Partial vapor pressure of the gas generated is maintained at 30 mm Hg or less is preferred.
The carbonaceous material thus obtained contains nitrogen and sulphur in appropriate amounts. Nitrogen is usually present within the range of from 0.1 wt% to 6 wt% and pre-ferably within the range of from 0.3 wt% to 4 wt%. Addi-tionally, most of this nitrogen, when observed using x-raY
photoelectron spectroscopy, occurs in certain specific forms, the bonding of which generates 2 peaks apPearing in the vicinity of 399 eV (more precisely within the range of 398.8 + 0.4 eV) and 401 eV (more Precisely within the range of 401;2 +0.2 eV), due to carbon-nitrogen bonding. Of all of the bonding involving nitrogen in the anode material of the present invention, 80% or more is represented by the 2 peaks appearing in the vicinity of binding energies corre-sponding to 399 eV and 401 eV respectivelY. The amount of sulphur present is PreferablY within the range of from 0.1 wt% to 6 wt%, and 2 peaks at binding energies of 164.1 +0.2 eV and 165.3 +0.2 are observed for sulphur using x-raY
photoelectron spectroscopy.
The parameters of crYstallinity of the carbonaceous mate-rial of the Present invention depend upon the structural conditions of the material. However, usually, the inter layer spacing (doo2) is 3.4 ~ or more and the size of the crystallites Lcoo~ is 70 ~ or less. The true density is in the range of from 1.4 g/cm3 to 2.0 g/cm.

The carbonaceous material of the present invention pos-sesses various excellent ProPertieS as anode material, and, in particular, it has a substantially higher caPacity than the carbonaceous materials of the prior art. In particular, in the range of 0 to 0.2 volts (V), it is 300 mAh/g or more and between 0 and 1.5 volts (V), it is Possible to obtain a capacity of 500 mAh/g or more.
The construction of the secondary battery employing a non-aqueous media of the Present invention that uses the afore-mentioned carbonaceous material as the anode is an anode using the carbonaceous material of the Present invention as an anode, and a cathode, separator, non-aqueous electrolYte and casing as described below.
The method of using the carbonaceous material of the present invention as the anode is not particularly limited.
For examPle, an electrode maY be Prepared bY mixing a binder with the powdered anode material of the present invention, using a solvent where required, and then pressing the electrode material onto a collector after it has been formed into a sheet or by coating it directly onto the collector. Moreover, as the binder, anY tyPe of pitch maY
be used, and the Plate type electrode obtained by calcining a mixture of the pitch with the powdered,anode material has been used effectively. The cathode material is not particu-larly limited. For example, such lithium containine oxidesas LiCoO2, LiNiO2, LiMnO2, LiMn2O4 and the like, such oxides as l'iO2, V2O~, MoO3, MnO2, such sulfides as TiS~, FeS, and MoS3 and such selenides as NbSe3, or such conductive polymers as polyacetylene, polYparaphenylene, polypyrrole and polyani--line or activated carbon maybe used. The method of usingthese cathode materials as the cathode is not particularlY
limited. For example, a cathodé may be prepared by mixing a binder with the Powdered cathode material of the present invention, using a solvent where required, and -then pressin~
the cathode material onto a collector after it has been formed into a sheet or by coating it directly onto the collector. The separator that may be used is not Particu-g larly limited. For example, the separator may be made ofsynthetic or glass fibre or natural fibre either unwoven or in the form of cloth, and micro porous resin and the like may also be used.
In the secondary battery employing a non-aqueous media of the present invention either an organic liquid electrolyte or solid electrolyte maY be used. A solution of a lithium salt dissolved in an organic solvent having a high dielec-tric constant maY be used. The kind of lithium salt that maY be used is not Particularly limited, and, for example, LiClO~. LiPF6 or LiSbF6 may be used either singlY or as mixtures of two or more in appropriate proportions. The organic solvent that maY be used for the electrolYte is one that is able to dissolve the applicable lithium salt or salts and preferably is non-protic and has a high dielectric content, and nitriles, carbonates, ethers, nitrocompounds, sulphur containing compounds, chlorinated compounds. ke-tones, esters and the like maY be used. More concretely, for example, aceton.itrile, Propionitrile, proPYlenecar-bonate, ethylenecarbonate, diethylcarbonate, dimethylcar-bonate, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, nitromethane, N, N-dimethylformamide, dimethylsulfoxide, sulpholane, and r -butYrolactone maY be used singly or in rlixtures of two or more as mixed electro~Ytes depending upon the requirements of the particular situation. The battery casing is usually constructed of stainless steel plate or nickel plated material but maY also be constructed of multi-layer materials constructed from synthetic resin and insu-lating inorganic membranes.
The examples of the present invention and comparative experiments are recorded below, and the results are con-cretely and specifically explained. These examPles and comparative experiments are provided for the PurPose of concrete explanation of the present invention and do not in any way limit the manner in which the Present invention maY
be practised or the scope of the Present inventi~n. Moreo-ver, the analysis methods and analysis conditions for the --1 o--anode material to be used in the present invention are recorded below.
1. Particle Size Distribution Measurement The equipment used was a Horiba, Ltd. LA-500 Laser Dif-fraction Type Powder Size Distribution Measuring Device.
The measurement was performed by adding 3 drops of surface active agent to 100 ml of pure water and then adding the sample to this mixture until it reached a predetermined concentration. After subiecting the sample to ultrasonic sound wave dispersion for 10 minutes, the measurement was taken and the median diameter obtained was used as the average particle diameter.

2. Elemental Analysis The analytical equipment used was a PERKIN-ELMER 2400 CHN
type elemental analysis device. The measurement was per-formed by placing 1.5 + 0.2 mg of the test anode material in a small tin cup in the instrument, calcining the sample at a temperature of 975~C for 5 minutes. The measurement was performed by TCD using helium as the carrier gas. To estab-lish correspondence between sample measurements and standardtest values, the device was calibrated for the sample using acetanilide (2.0 + 0.1 mg) as the standard.
AnalYsis for sulphur content was conducted using a 3270 type fluorescent x-ray diffraction device. Measurement was conducted using a sample of anode material having 0.66 grams after sufficiently mixing it with dilutant cellulose weighed at 1.34 grams (Whatman CF11 made by W&R Balston). The sample was formed by the addition of pressure at 24tf and was then placed in the measuring device and analysis was conducted. The measurement was conducted using a Toshiba Cr lamp as the x-ray lamP and using a Germanium diffraction crYstal having an output of 50kV-50mA. Moreover, with respect to the specified qUantitY of sulphur test sample, at first, a standard samPle containing a known quantitY of added sulphur was analyzed 3. Elemental AnalYsis (Lithium) Analysis of lithium content was conducted by means of inductively coupled plasma analysis (ICP analysis). The equipment was an SPS-1200 VR type manufactured by Seiko Electronics Industries. Preparation of the samPle consisted of reducing the anode material to ash at 900~C in a muffle furnace, dissolving the residue in 1 N aqueous hydrochloric acid, and then conducting the measurement. An absolute calibration curve was prepared using standard solutions prepared using determined amounts of lithium.

4. X-raY Photoelectron Spectroscopy Analysis The equipment used was a V. G. Scientific ESCALAB MK-II.
The analysis was performed using Mg-Ka as the x-ray source at 15 KV - 20 mA and using an A1 slit (2 X 5 mm). PrePara-tion for analysis consisted of Placing the samPle on double sided taPe. Measurement was conducted with the sample in this condition, or, in some cases, after argon etching of the sample surface. The analysis was performed by measuring each peak precisely within a narrow range after first meas-uring all of the peaks over a broad range and identifying individual peaks. The charge uP correction was made by setting the observed carbon 1s energy ("C-ls") at 284.4 eV
and adiusting the value for each peak accordingly.
4. True DensitY
True density was determined bY the float and sink method using a carbon tetrachloride-bromoform mixture at 25~C.
EXAMPLES
Example 1.
Thirty parts by weight of ammonium sulphate were added to 70 parts by weight of tar (manufactured by Kawasaki Steel Company) at 100~C, and the temperature was raised to 400~C
after mixing them together. This comPound was Powdered using a ball mill. The black powder thus obtained was then calcined for 2 hours at 1000~C under a stream of nitrogen gas to obtain a powdered anode material with a particle diameter of 10U. This anode material contained 93.5 wt%
carbon, l.l9 wt% of nitrogen and 1.62 wt% of sulphur. The result of XPS measurement was 2 peaks rePresenting binding energies of 401.4 eV and 398.6 eV having an intensity ratio ~- ~A21 38334 (the intensity of the 401.4 eV peak/ the intensity of the 398.6 eV peak) of 2.5 which peaks accounted for 100% of the bonding involving nitrogen observed in the anode material.
Moreover, peaks with a binding energY of 164.1 eV and 165.3 eV based on sulPhur bonding were observed.
Evaluation of the Anode Material A flexible shaped article for use as a test electrode was prepared by mixing 100 parts bY weight of the powdered anode material thus obtained with 5 parts by weight of polytetra-fluoroethylene (binder) and compressing them into a rounddisk. A half cell was prepared using this test electrode, according to the usual methods, using LiC104 dissolved in a solvent comPosed of an equal volume mixture of propylene carbonate and 1.2-dimethoxyethane (concentration of LiC104:
1.0 mol/l) prepared as an electrolyte and using a separator made from a porous polypropylene membrane with a thickness of 50 ~m. As the counter electrode, a 16 mm diameter, 0.5 mm thick disk of lithium metal was used. A small Piece of lithium metal similar to the counter electrode was used as the reference electrode.
The first cycle circuit potential of the half cell ob-tained above was 3.18 V (volts). Subsequently, the half cell was charged at a constant current densitY of 1.0 mA/cm2 until there was no change in the potential of the test electrode with respect to the reference electrode. The charge capacity was 707 mAh/g. Then, the half cell was dis-charged at a constant current density of 1.0 mA/cm2, and by the time the electrode reached 0.2 V, the observed discharge capacity was 318 mAh/g, by the time the electrode potential reached 1.5V, the observed discharge CapacitY was 529 mAh/g and finally, when discharging had proceeded sufficiently for the electrode potential to reach 3.0 V, the observed dis-charge capacity was 542 mAh/g.
Evaluation of the Secondary Battery A test electrode with a thickness of 0.3 mm, a diameter of 15 mm and a weight of 90 mg prepared by the same methods as the above test electrode was used as the anode, and using CA21 ~8334 LiC104 dissolved in a solvent composed of an equal volume mixture of propylene carbonate and 1,2-dimethoxyethane (LiCI04: 1.0 mol/l) prePared as an electrolyte and using a separator made from a Porous polyproPylene membrane with a thickness of 50 ~m, a secondary battery was prepared. The cathode was prepared by mixing 85 parts by weight of LiCoO2 with 10 parts by weight of acetylene black (conducting agent) and 5 parts by weight of polytetrafluoroethYlene (binder) and compressing the mixture into a disk (diameter 14 mm).
The circuit voltage for the initial cycle of the secondary battery thus obtained was 0.03 V. When, after charging at a constant current until the charging voltage at a current density of 1.0 mA/cm2 reached 4.10 V, the battery was then discharged at a constant current until the charging voltage at a current densitY of 1.0 mA/cm~, an initial discharge capacity of 32.4 mAh was observed.
Example 2 1 mole of naphthalene, 0.5 moles of hydrofluoric acid and 0.5 moles of boron trifluorid-e BF3 were added to an acid resistant autoclave having a capacity of 500 ml and, after the temperature was raised to 200~C at a Pressure of 25 kg/cm3 it was maintained under these conditions for 2 hours and reacted. Then, according to the usual methods the interior of the autoclave was charged with nitrogen, the HF
and BF3 were flushed out and recovered and after the low boiling point components were driven off, a pitch having a softening point of about 115~C was obtained. Then 70 parts by weight of the pitch having a softening point of 115~C
thus obtained were added to 30 parts by weight of ammonium sulphate while heating the mixture to 180~C, after which the temperature was raised to 270~C. The reaction mixture was allowed to cool and the compound thus obtained was ground to a Powder using a ball mill. Then, the black Powder thus obtained was calcined for two hours at 1000~C under a flow of nitrogen gas to obtain an anode material in powdered form. This anode material contained 94.5 wt% carbon, 1.23 CA21 3~334 wt% of nitrogen and 2.13 wt% of sulPhur. The result of XPS
measurement was 2 peaks representing binding energies of 401.4 eV and 398.6 eV having an intensitY ratio (the intens-ity of the 401.4 eV peak/ the intensity of the 398.6 eV
peak) of 2.6 which peaks accounted for 100% of the bonding involving nitrogen observed in the anode material.
Moreover, a half cell and secondarY battery were prepared according to the same procedures used in Example 1, and when constant current charge - discharge experiments were con-ducted, the results obtained were the same as those forExample 1.
ExamPle 3 20 parts by weight of acid ammonium sulphate were added to 100 parts by weight of tar at a temperature of 100~C and mixed after which the temperature was raised to 400~C. The resulting compound was cooled and ground using a ball mill.
Then, the black powder thus obtained was calcined for 2 hours at 1100~C under a flow of nitrogen gas and a Powdered anode material was obtained. This anode material contained 92.5 wt% carbon, 1.05 wt% of nitrogen and 1.23 wt% of sulphur. The result of XPS measurement was 2 peaks rePre-senting binding energies of 401.4 eV and 398.6 eV having an intensity ratio (the intensitY of the 40~.4 eV peak/ the intensity of the 398.6 eV peak) of 2.5 which peaks accounted for 100% of the bonding involving nitrogen observed in the anode material. Moreover, peaks with a binding energy of 164.1 eV and 165.3 eV based on sulPhur bonding were ob-served.
A half cell was PrePared in the same waY as in Example 1 and, when constant current charge - discharge exPeriments were conducted, the charge capacitY was 640 mAh/g. Then the capacity up to the point the electrode potential rose to 0.2 V was 320 mAh/g, the discharge capacity up to the point the electrode potential rose to 1.5 V was 510 mAh/g and the capacity up to the point the electrode potential rose to 3.0 V was 532 mAh/g. Then, a secondary battery was Prepared in the same waY as in Example 1. When constant current charge ~ - ~A21 3~334 - discharge experiments were conducted, the initial cycle voltage was 0.03 V and the initial caPaCitY was 32.8 mAh.
Example 4 A black powder obtained after grinding the comPound ob-tained in Example 1 to a powder using an impact powderer wascalcined at 1200~C for 2 hours under a vacuum of 30 mg Hg or Iess to obtain an anode material having an average Particle size of 13 ~. This anode material contained 92.1 wt%
carbon, 0.74 wt% of nitrogen and 0.93 wt% of sulphur. The result of XPS measurement was 2 Peaks representing binding energies of 401.4 eV and 398.6 eV having an intensity ratio (the intensity of the 401.4 eV peak/ the intensity of the 398.6 eV Peak) of 2.5 which peaks accounted for 100% of the bonding involving nitrogen observed in the anode material.
Moreover, Peaks with a binding energy of 164.1 eV and 165.3 eV based on sulphur bonding were observed.
Moreover. a half cell was PrePared in the same way as in Example 1 and, when constant current (2 mA/cm~ - constant Potential experiments were conducted, and when the total time had reached 20 hours, the charge capacity was 610 mAh/g. Then up until the electrode potential of the test electrode against a reference electrode where discharge was conducted at a current density of on the.order of 1.0 mA/cm~
rose to 0.2 V the caPaCitY was 320 mAh/g, the discharge capacity up to the Point the electrode potentia! rose to 1.5 V was 503 mAh/g and the capacity up to the point the elec-trode Potential rose to 3.0 V was 526 mAh/g.
Then, a secondarY battery was prepared in the same way as in Example 1. When constant current charge - discharge experiments were conducted, the initial capacitY was 33.4 mAh.
Example 5 70 parts by weight of tar (manufactured bY Kawasaki Steel Company~, 30 parts by weight of ammonium sulphate and 5 parts by weight of lithium carbonate were heated to 100~C
and mixed. and then the after the temperature was raised to 400~C a lithium containing comPound composed of 1.0% lithium CA2 1 3~334 was obtained. This comPound was ground to a powder using a ball mill. The black powder thus obtained was calcined under a stream of nitrogen gas to obtain the Powdered anode material. This anode material contained 0.9 wt% lithium, 92.6 wt% of carbon, 1.19 wt% of nitrogen and 0.9 wt% of sulphur. The result of XPS measurement was 2 peaks repre-senting binding energies of 401.4 eV and 398.6 eV having an intensity ratio (the intensity of the 401.4 eV peak/ the intensitY of the 398.6 eV peak) of 2.5 which peaks accounted for 100% of the bonding involving nitrogen observed in the anode material. Moreover, peaks with a binding energy of 164.1 eV and 165.3 eV based on sulphur bonding were ob-served.
A half cell was prepared in the same way as in Example 1 and, when constant current charge - discharge experiments were conducted, the charge capacity was 620 mAh/g. Then the capacity up to the point the electrode potential rose to 0.2 V was 312 mAh/g, the discharge capacity up to the Point the electrode potential rose to 1.5 V was 519 mAh/g and the capacitY up to the point the electrode potential rose to 3.0 V was 535 mAh/g. Charge discharge cycle loss was 85 mAh/g.
Then, a secondary battery was Prepared in the same way as in Example 1. When constant current charge - discharge experi-ments were conducted, the initial cycle voltage was 0.03 V
and the initial capacity was 34.2 mAh.
Comparative Experiment 1 Thirty parts by weight of dinitronaPhthalene were added to 70 parts by weight of tar (manufactured by Kawasaki Steel Company) at 150~C and the temperature was raised to 500~C
after mixing them together. This compound was powdered using a ball mill. The black powder thus obtained was then calcined for 2 hours at 1150~C under a stream of nitrogen gas to obtain a powdered anode material with a particle diameter of 10~. This anode material contained 95.73 wt%
carbon, 0.13 wt% hydrogen 0.91 wt% nitrogen and 0.42 wt%
sulphur.
Subsequently, when a half cell was prepared as in Example .
1 and charge-discharge experiments were conducted at con-stant current and the initial charge discharge caPaCity was 610 mAh/g. By the time the electrode potential of the test electrode against a reference electrode reached 0.2 V, the observed discharge caPaCitY was 312 mAh/g. By the time the electrode potential reached 1.5 V, the observed discharge capacity was 486 mAh/g and by the time it had reached 3.0 V, the discharge capacitY was 498 mAh/g. Next, a secondary battery was prepared using the same methods as in ExamPle 1, except for the use of the anode material obtained above.
When charge-discharge experiments were conducted at constant voltage, the initial Period circuit voltage was 0.03 V and the initial Period discharge capacity was 29.7 mAh. The carbonaceous material of the present invention was obtained by the calcination of only a precursor organic compound obtained by reacting a conjugated polycyclic compound with a nitrogen containing compound (an aromatic nitrate under the conditions described in Japanese Patent Application No.
1992-258479) and because the amount of sulphur present in the material present was onlY at the level of an impuritY
and was therefore too small, an initial period discharge capacity of onlY 498 mAh/g was obtained.
Comparative Experiment 2 One hundred fifty parts bY weight of 97% sulphuric acid and 150 parts fuming sulPhuric acid were added to 100 parts by weight of tar ~manufactured by Kawasaki Steel Company) at 80~C at which they were maintained for one hour, after which the temperature was raised to 150~C and the mixture reacted for one hour. The resulting reaction mixture was filtered, washed with water and dried to obtain a sulphonated pitch.
The sulphonated pitch thus obtained was then calcined for 2 hours at 1000~C under a stream of nitrogen gas to obt~in a black calcined mass. This calcined mass was powdered USillg a ball mill and then calcined again for 2 hours at 1000~C
under a stream of nitrogen gas and a powdered anode material with a particle diameter of 10~ was obtained. This anode material contained 94.10 wt% carbon, 0.03 wt% hYdrogen, 0.2 2~3g334 wt% of nitrogen and 2.41 wt% of sulphur. The result of XPS
measurement was 2 S-ls peaks representing binding energies of 164.1 eV and 165.3 eV based on sulfur bonding were ob-served.
Subsequently, when a half cell was prepared as in Example 1 and charge-discharge exPeriments were conducted at con-stant current, the charge - discharge capacity was 615 mAh/g. By the time the electrode potential of the test electrode against a reference electrode reached 0.2 V, the observed discharge capacity was 304 mAh/g. BY the time the electrode potential reached 1.5 V, the observed discharge capacity was 473 mAh/g and bY the time it had reached 3.0 V, the discharge capacitY was 485 mAh/g. Next, a secondary battery was prepared using the same methods as in Example 1, except for the use of the anode material obtained above.
When charge-discharge experiments were conducted at constant voltage, the initial Period circuit voltage was 0.03 V and the initial Period discharge capacitY was 28.9 mAh. The carbonaceous material of this comparative examPle was ob-tained bY the calcination of onlY a precursor organic com-pound obtained bY reacting a coniugated Polycyclic compound with a sulphur containing compound and because the amount of nitrogen present in the material is at the level of an impurity (and was therefore too small), an initial period discharge caPaCitY of onlY 485 was obtained.
Effects of the Present Invention The secondarY batterY of the present invention, compared with those of the prior art, is less prone to exPerience a deterioration of performance over time, and the secondarY
battery of the present invention shows excellent safety and has excellent charge - discharge characteristics in addition to its large capacity.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A lithium secondary battery comprising a non-aqueous electrolyte and an anode of a carbonaceous material prepared by calcining a precursor organic compound obtained from the reaction of at least one polycyclic organic compound with a compound containing nitrogen and sulphur.

2. A lithium secondary battery according to claim 1 wherein the compound containing nitrogen and sulphur is selected from the group consisting of ammonium sulphate, acid ammonium sulphate and ammonium persulphate.

3. A lithium secondary battery according to claim 1 wherein the compound containing nitrogen and sulphur is ammonium sulphate.

4. A lithium secondary battery according to claims 1, 2, or 3 wherein the polycyclic organic compound is tar or pitch having a softening point of 170°C or less.

5. A lithium secondary battery employing a non-aqueous electrolyte according to claims 1, 2 or 3 wherein the anode material is prepared by calcining the precursor organic compound at from 800°C to 1800°C under an atmosphere of non-reactive gas.

6. A lithium secondary battery employing a non-aqueous electrolyte according to claim 1, 2 or 3 in which the d002 inter layer spacing of the anode material is 3.4 ~ or more and the size of the crystallites Lc002 is 70 ~ or less.

7. A lithium secondary battery employing a non-aqueous electrolyte according to claim 6 wherein true density of the anode material is in the range of from 1.4 g/cm3 to 2 g/cm3.

8. A lithium secondary battery employing a non-aqueous electrolyte according to claim 1, 2 or 3 wherein the anode material contains 0.1 % to 6% by weight of nitrogen, 80% or more of which is bonded by C-N or C=N bonds, and in which the x-ray photoelectron spectroscopy binding energy peaks observed for nitrogen atoms are present at 401.2 ~ 0.2 eV and 398.8 ~
0.4 eV in an intensity ratio of the former to the latter of 1.0 or more, and containing between 0.1 % and 6% by weight of sulphur and in which the x-ray photoelectron spectroscopy binding energy peaks observed for sulphur atoms are present at 164.1 ~ 0.2 eV and 165.3 ~ 0.2 eV.

9. A lithium secondary battery according to claim 1, 2 or 3 which further comprises a casing, a cathode and a separator.

10. An anode for a lithium secondary battery, the anode being made of a carbonaceous material which consists essentially of carbon, oxygen, hydrogen, 0 or 0.1 to 6 wt% of nitrogen and 0 or 0.1 to 6 wt% of sulphur and is prepared by calcining a precursor organic compound obtained by reacting at least one polycyclic organic compound with a compound containing nitrogen and sulphur.

11. An anode for a lithium secondary battery according to claim 10 wherein the compound containing nitrogen and sulphur is ammonium sulphate.

12. An anode material for a lithium secondary battery according to claim 10 wherein the polycyclic organic compound is tar or pitch having a softening point of 170°C or less.

13. An anode according to claim 10, 11 or 12 wherein at least 80% of the nitrogen is bonded by C-N or C=N bonds, and in which the X-ray photoelectron spectroscopy binding energy peaks observed for nitrogen atoms are present at 401.2 ~ 0.2 eV and 398.8 ~ 0.4 eV in an intensity ratio of the former to the latter of 1.0 or more, and which contains between 0.1 % and 6% by weight of sulphur and in which the x-ray photoelectron spectroscopy binding energy peaks observed for sulphur atoms are present at 164.1 ~ 0.2 eV and 165.3 ~ 0.2 eV.

14. An anode according to claim 10, 11 or 12 wherein the d002 inter layer spacing of the anode material is 3.4 ~ or more, the size of the crystallites Lc002 is 70 ~ or less and the true density is in the range of from 1.4 g/cm3 to 2 g/cm3.

15. A process for producing the anode as defined in any one of claims 10. 11 and 12 which comprises calcining the precursor organic compound at a temperature of from 800°C to 1800°C under an atmosphere of inert gas or under vacuum.

16. A process according to claim 15 wherein the precursor organic compound is prepared by reacting at least one member selected from the group consisting of organic polymers, conjugated polycyclic compounds or reaction products of conjugated polycyclic compounds with nitro compounds or nitrating agents with a compound containing nitrogen and sulphur.

17. A process according to claim 16 wherein the compound containing nitrogen and sulphur is ammonium sulphate.

18. A process according to claim 16 wherein the precursor organic compound is produced by reacting pitch or tar having a softening point of 170°C or less as the conjugated polycyclic compound with ammonium sulphate as the compound containing nitrogen and sulphur at a temperature of 100°C to 500°C.