Non-aqueous electrolyte battery with carbon electrode

Abstract: The present invention is directed to a non-aqueous electrolyte battery comprising an anode, a cathode using a carbon material, and a non-aqueous electrolytic solution, wherein the carbon material obtained by coating a core composed of graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.35 to 3.39 Å and the length (Lc) of a crystallite in the direction of the c axis is not less than 1000 Å with coating graphitized carbon in which spacing (d 002 ) of lattice planes (002) is more than that in the graphitizing carbon and is in the range of 3.36 to 3.48 Å, the carbon material obtained by coating a core composed of graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.35 to 3.39 Å with a calcined product of an organic substance composed of carbon containing sulfur atoms, or the carbon material composed multi-phase graphitized carbon having two or more crystals respectively different crystallinities in one particle, the length (Lc) of a crystallite in the direction of the c axis in each of the crystals being not less than 10 Å, are used for the cathode.

Description: Field of the Invention The present invention relates generally to a non-aqueous electrolyte battery comprising an anode, a cathode using a carbon material, and a non-aqueous electrolytic solution, and more particularly, to a non-aqueous electrolyte battery whose preservation characteristics and cycle characteristics are improved upon improvement of the cathode using the carbon material. Description of the Prior Art In recent years, as one of new-type batteries having high power and high energy density, a high electromotive-force non-aqueous electrolyte battery using a non-aqueous electrolytic solution as an electrolyte and utilizing oxidation and reduction of lithium has been utilized. In such a non-aqueous electrolyte battery, a carbon material capable of occluding and discharging lithium ions has been conventionally utilized widely as its cathode material. In the case of the non-aqueous electrolyte battery using the carbon material for the cathode, lithium contained in the carbon material used for the cathode reacts with a solvent or the like in the non-aqueous electrolytic solution at the time of preservation, so that self-discharge is induced, and the non-aqueous electrolytic solution is decomposed. As a result, the battery capacity is gradually decreased, and the cycle characteristics are degraded. As the carbon material used for the cathode as described above, carbon which is not graphitized and graphitized carbon have been conventionally generally used. When a carbon material having low crystallinity such as carbon which is not graphitized is used, a discharge capacity per unit weight is small, whereby a battery having a sufficient discharge capacity is not obtained. Further, a potential at a cathode is gradually increased as discharge is induced, whereby the voltage of the battery is reduced, not to obtain a stable voltage. On the other hand, when a carbon material having high crystallinity such as graphitized carbon is used, a discharge capacity per unit weight is increased. However, a potential at a cathode is gradually increased at the end of discharge, whereby a non-aqueous electrolytic solution is decomposed upon reaction on the surface of the carbon material used for the cathode, resulting in degraded cycle characteristics. In the prior art, a non-aqueous electrolyte battery whose cycle characteristics are improved by adding a non-fluorine polymer mainly composed of butadiene and a fluorine polymer as binders to graphite powder, to hold binding power in a depolarizing mix for cell as well as increase binding properties to a copper foil which is a collector has been proposed, as disclosed in Japanese Patent Laid-Open No. 215761/1994. Even when the non-fluorine polymer mainly composed of butadiene and the fluorine polymer are thus used as binders, however, a non-aqueous electrolytic solution is still decomposed upon reaction on the surface of graphite, so that the cycle characteristics cannot be sufficiently improved. Furthermore, in the prior art, an aqueous electrolyte battery whose cycle characteristics and preservation characteristics are improved by mixing a whisker such as a silicon carbide whisker, a silicon nitride whisker, or a potassium titanate whisker with powder of an active material such as a carbon material, as disclosed in Japanese Patent Laid-Open No. 302315/1994, and an aqueous electrolyte battery whose collection efficiency is improved using a carbon material obtained by mixing graphite and coke for a cathode, as disclosed in Japanese Patent Laid-Open No. 84515/1994, for example, have been also developed. Also in each of the aqueous electrolyte batteries disclosed in the gazettes, it is impossible to sufficiently prevent self-discharge from being induced upon reaction of lithium in the carbon material used for the cathode with a solvent or the like in the non-aqueous electrolytic solution as described above and sufficiently prevent the non-aqueous electrolytic solution from being decomposed, whereby the battery capacity is still reduced at the time of preservation, and the cycle characteristics are still degraded. SUMMARY OF THE INVENTION A first object of the present invention is to provide, in a non-aqueous electrolyte battery comprising an anode, a cathode using a carbon material, and a non-aqueous electrolytic solution, the non-aqueous electrolyte battery having good preservation characteristics in which lithium in the carbon material used for the cathode hardly reacts with a solvent or the like in the non-aqueous electrolytic solution to induce self-discharge at the time of preservation. A second object of the present invention is to provide, in the above-mentioned non-aqueous electrolyte battery, a non-aqueous electrolyte lithium battery which is superior in cycle characteristics, and has a sufficient discharge capacity, and causes a stable battery voltage to be obtained by preventing the non-aqueous electrolytic solution from being decomposed upon reaction on the surface of the carbon material due to a rapid increase in a potential at the cathode using the carbon material at the end of the discharge. There and further objects of the present invention are achieved by a battery according to claim 1. The dependent claims treat further developments of the present invention. In a non-aqueous electrolyte battery comprising an anode with anode materials which occlude and discharge lithium ions, a cathode using a carbon material, and a non-aqueous electrolytic solution, a first non-aqueous electrolyte battery according to the present invention is characterized in that the carbon material is composed of a core and a surface layer, the core is coated with the surface layer, the core is composed of graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.35 to 3.39 Å and the length (Lc) of a crystallite in the direction of the c axis is not less than 1000 A, and the surface layer is composed of coating graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.36 to 3.49 Å and is more than the spacing (d 002 ) of lattice planes (002) in the graphitized carbon to be the core. When the carbon material obtained by coating the graphitized carbon to be a core with the coating graphitized carbon is used for the cathode as in the first non-aqueous electrolyte battery according to the present invention, self-discharge is prevented from being induced upon reaction of lithium in the graphitized carbon to be a core with a solvent or the like in the non-aqueous electrolytic solution at the time of preservation by the coating graphitized carbon, whereby the battery capacity is hardly decreased at the time of the preservation, resulting in improved preservation characteristics in the non-aqueous electrolyte battery. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional illustration showing the internal construction of non-aqueous electrolyte batteries in embodiments and comparative examples of the present invention; Fig. 2 is a diagram showing the relationship between the amount of coating graphitized carbon with which graphitized carbon to be a core is coated and a discharged capacity after preservation in an experimental example 1; Fig. 3 is a diagram showing the relationship between spacing (d 002 ) of lattice planes (002) in coating graphitized carbon with which graphitized carbon to be a core is coated and a discharge capacity after preservation in an experimental example 2; PREFERRED EMBODIMENTS OF THE PRESENT INVENTION Description is now made of preferred embodiments of first to third non-aqueous electrolyte batteries in the present invention. The reason why in the first non-aqueous electrolyte battery, graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.35 to 3.39 A and the length (Lc) of a crystallite in the direction of the c axis is not less than 1000 Å is used as graphitized carbon to be a core of a carbon material used for its cathode is that such graphitized carbon is high in crystallinity and sufficiently occludes and discharges lithium ions, so that a large-capacity battery is obtained. Natural graphite is generally used as such graphitized carbon. On the other hand, graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.36 to 3.49 Å and is more than the spacing (d 002 ) of lattice planes (002) in the graphitized carbon to be a core is used as coating graphitized carbon with which the graphitized carbon to be a core is to be coated in order to sufficiently prevent lithium in the graphitized carbon to be a core from reacting with a solvent or the like in a non-aqueous electrolytic solution. Artificial graphite is generally used as such coating graphitized carbon. In coating the graphitized carbon to be a core with the coating graphitized carbon, if the amount of the coating graphitized carbon is small, the graphitized carbon to be a core cannot be sufficiently coated, so that lithium contained in the graphitized carbon to be a core cannot be sufficiently prevented from reacting with the solvent or the like in the non-aqueous electrolytic solution. On the other hand, if the amount thereof is too large, the amount of the graphitized carbon to be a core is decreased, so that the capability to occlude and discharge lithium ions at the cathode is decreased. Therefore, the amount of the coating graphitized carbon is set in the range of 0.1 to 60 % by weight, preferably in the range of 1 to 50 % by weight, and more preferably in the range of 10 to 30 % by weight per the total amount of the graphitized carbon and the coating graphitized carbon. The reason why in an further non-aqueous electrolyte battery, graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.35 to 3.39 Å is used as a carbon material used for its cathode is that such graphitized carbon is high in crystallinity and sufficiently occludes and discharges lithium ions, so that a large-capacity battery is obtained, as in the case of the above-mentioned first non-aqueous electrolyte battery. Natural graphite is generally used. Furthermore, in each of the non-aqueous electrolyte batteries in the present invention, it is possible to use, as an anode material used for its anode, a known anode material capable of occluding and discharging lithium ions which has been conventionally used. For example, a lithium transition metal composite oxide containing at least one of manganese, cobalt, nickel, iron, vanadium, and niobium can be used. Specifically, a known material such as LiCoO 2 , LiNiO 2 , LiMnO 2 , or LiFeO 2 can be used. Furthermore, it is possible to use, as the non-aqueous electrolytic solution used in each of the non-aqueous electrolyte batteries, a known non-aqueous electrolytic solution which has been conventionally used. As the solvent in the non-aqueous electrolytic solution, organic solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, dimethylsulfolane, 3-methyl-1, 3-oxazolidine-2-on, γ-buthyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, and ethyl acetate can be used independently or in combination. Furthermore, in the non-aqueous electrolytic solution, lithium compounds such as LiPF 6 , LiBF 4 , LiClO 4 , LiCF 3 SO 3 , LiAsF 6 , LiN(CF 3 SO 2 ) 2 , LiOSO 2 and (CF 2 ) 3 CF 3 can be used as a solute dissolved in the above-mentioned solvent. The above-mentioned non-aqueous electrolyte batteries will be described by taking more specific embodiments, and it will be made apparent that the non-aqueous electrolyte batteries according to the embodiment are superior in preservation characteristics, cycle characteristics and the like by taking comparative examples. (Embodiment 1) In the present embodiment, an anode and a cathode produced in the following manner were used, and a non-aqueous electrolytic solution prepared in the following manner was used, to fabricate a cylindrical-type non-aqueous electrolyte secondary battery as shown in Fig. 1. [Production of Anode] In producing an anode, lithium-containing cobalt dioxide LiCoO 2 heat-treated at a temperature of 800°C was used as an anode material. The heat treatment can be carried out at temperatures in the range of 700 to 900°C. The anode material LiCoO 2 , carbon powder which is a conductive agent, fluorocarbon polymer powder which is a binding agent were mixed in the weight ratio of 85 : 10 : 5. A mixture obtained was applied to an aluminum foil composing an anode-side collector, after which the mixture was heat-treated at a temperature of 150°C, to produce the anode. The heat treatment can be carried out at temperatures in the range of 100 to 200°C. [Production of Cathode] In producing a cathode, a material obtained by coating graphitized carbon to be a core in which spacing (d 002 ) of lattice planes (002) is 3.36 Å and the length (Lc) of a crystallite in the direction of the c axis is 2100 Å with coating graphitized carbon in which spacing (d 002 ) of lattice planes (002) is 3.40 Å so that the amount of the coating graphitized carbon is 20 % by weight per the total amount of the graphitized carbon and the coating graphitized carbon was used as a cathode material. The cathode material and polyvinylidene fluoride which is a binding agent were mixed in the weight ratio of 95 : 5, and a mixture obtained was applied to a cathode-side collector composed of a copper foil, after which the mixture was heat-treated at a temperature of 200°C, to produce the cathode. The heat treatment can be carried out at temperatures in the range of 150 to 250°C. [Preparation of Non-aqueous Electrolytic Solution] In preparing a non-aqueous electrolytic solution, a mixed solvent obtained by mixing ethylene carbonate and 1, 2-dimethoxyethane in the volume ratio of 1 : 1 was used, and lithium hexafluorophosphate LiPF 6 was dissolved as a solute in the mixed solvent in the ratio of 1 mol/1, to prepare the non-aqueous electrolytic solution. [Production of Battery] In fabricating the non-aqueous electrolyte secondary battery according to the present embodiment, a microporous film made of polypropylene having permeability to lithium ions was interposed as a separator 3 between an anode 1 and a cathode 2 produced in the above-mentioned manner, and they were contained upon being wound in a spiral shape in a battery can 4, after which the non-aqueous electrolytic solution was poured in the battery can 4 and the battery can 4 was sealed, and the anode 1 was connected to an anode outer terminal 6 through an anode lead 5 and the cathode 2 was connected to the battery can 4 through a cathode lead 7, to electrically separate the battery can 4 and the anode outer terminal 6 from each other by an insulating packing 8. (Comparative Examples 1 to 4) In the comparative examples, non-aqueous electrolyte secondary batteries were fabricated in the same manner as that in the embodiment 1 except that only the cathode material used was changed in the production of the cathode in the non-aqueous electrolyte secondary battery in the embodiment 1. In the comparative example 1, only the graphitized carbon to be a core used in the embodiment 1 was used as the cathode material. In the comparative example 2, a material obtained by coating the graphitized carbon to be a core with 20 % by weight of a silicon nitride whisker was used as the cathode material. In the comparative example 3, a material obtained by coating the graphitized carbon to be a core with 20 % by weight of coke in which spacing (d 002 ) of lattice planes (002) is 3.46 to 3.48 Å and the length (Lc) of a crystallite in the direction of the c axis is 15 to 20 Å was used as the cathode material. In the comparative example 4, a material obtained by coating the graphitized carbon to be a core with 20 % by weight of amorphous carbon composed of a carbide of 3, 5-dimethyl phenol formaldehyde resin was used as the cathode material. Each of the non-aqueous electrolyte secondary batteries in the embodiment 1 and the comparative examples 1 to 4 fabricated in the above-mentioned manner was discharged to a final discharge voltage of 2.75 V at a discharge current of 200 mA before preservation and after preservation for two months at a temperatures of 60 °C, respectively, to measure discharge capacities before the preservation and after the preservation, to find the self-discharge rate (%) of the non-aqueous electrolyte secondary battery after the preservation for two months in the above-mentioned manner. The results are shown in the following Table 1. embodiment 1 comparative example 1 2 3 4 self-discharge rate (%) 7.1 12.4 12.1 11.3 11.1 As a result, the non-aqueous electrolyte secondary battery in the embodiment 1 in which the graphitized carbon to be a core is coated with the coating graphitized carbon was lower in the self-discharge rate than the non-aqueous electrolyte secondary battery in the comparative example 1 in which the graphitized carbon to be a core is not coated and the non-aqueous electrolyte secondary batteries in the comparative examples 2 to 4 in which the graphitized carbon to be a core is coated with the silicon nitride whisker, the coke and the carbide of 3, 5-dimethyl phenol formaldehyde resin. (Embodiment 2) In the embodiment, a non-aqueous electrolyte secondary battery was fabricated in the same manner as that in the above-mentioned embodiment 1 except that a mixed solvent obtained by mixing propylene carbonate and 1, 2-dimethoxyethane in the volume ratio of 1 : 1 was used as a solvent in the preparation of the non-aqueous electrolytic solution in the non-aqueous electrolyte secondary battery in the embodiment 1. (Comparative Examples 5 to 8) In the comparative examples, non-aqueous electrolyte secondary batteries were fabricated in the same manner as that in the above-mentioned embodiment 1 except that a mixed solvent obtained by mixing propylene carbonate and 1, 2-dimethoxyethane in the volume ratio of 1 : 1 was used as in the above-mentioned embodiment 2 as a solvent in a non-aqueous electrolytic solution, and only graphitized carbon to be a core as in the above-mentioned comparative example 1, a material obtained by coating graphitized carbon to be a core with a silicon nitride whisker as in the above-mentioned comparative example 2, a material obtained by coating graphitized carbon to be a core with coke as in the above-mentioned comparative example 3, and a material obtained by coating graphitized carbon to be a core with a carbide of 3, 5-dimethyl phenol formaldehyde resin as in the above-mentioned comparative example 4 were respectively used as cathode materials in the comparative example 5, the comparative example 6, the comparative example 7, and the comparative example 8. With respect to each of the non-aqueous electrolyte secondary batteries in the embodiment 2 and the comparative examples 5 to 8 fabricated in the above-mentioned manner, discharge capacities before preservation and after preservation for two months at a temperature of 60°C were also measured in the same manner as the foregoing, to find the self-discharge rate (%) of the non-aqueous electrolyte secondary battery after the preservation for two months. The results are shown in the following Table 2. embodiment 2 comparative example 5 6 7 8 self-discharge rate (%) 7.3 12.6 12.4 11.6 11.3 As a result, even when the type of the solvent used in the non-aqueous electrolytic solution was changed, the non-aqueous electrolyte secondary battery in the embodiment 2 in which the graphitized carbon to be a core is coated with the coating graphitized carbon was lower in the self-discharge rate than the non-aqueous electrolyte secondary batteries in the comparative examples 5 to 8, as in the case of the embodiment 1 and the comparative examples 1 to 4. (Experimental Example 1) In the experimental example, in coating the graphitized carbon to be a core with the coating graphitized carbon in the production of the cathode in the non-aqueous electrolyte secondary battery in the embodiment 1, the amount of the coating graphitized carbon was changed in the range of 0 to 70 % by weight as shown in the following Table 3 per the total amount of the graphitized carbon and the coating graphitized carbon, to fabricate respective non-aqueous electrolyte secondary batteries. Each of the non-aqueous electrolyte secondary batteries was preserved for two months at a temperature of 60°C, and was then discharged to a final discharge voltage of 2.75 V at a discharge current of 200 mA as described above, to examine a discharge capacity in the non-aqueous electrolyte secondary battery after the preservation. The results are shown in the following Table 3 and Fig. 2. A discharge capacity before the preservation in the non-aqueous electrolyte secondary battery was 600 mAh. coating amount (% by weight) 0 0.05 0.1 0.5 1 3 5 discharge capacity (mAh) 526 536 540 542 544 546 548 coating amount (% by weight) 10 20 30 40 50 60 70 discharge capacity (mAh) 551 557 551 548 544 540 536 As a result, the non-aqueous electrolyte secondary battery in which the graphitized carbon to be a core is coated with the coating graphitized carbon was significantly improved in the discharge capacity after the preservation, as compared with the non-aqueous electrolyte secondary battery in which the graphitized carbon to be a core is not coated. When the graphitized carbon to be a core was coated with the coating graphitized carbon, the decrease in the discharge capacity after the preservation was reduced when the amount of the coating graphitized carbon was in the range of 0.1 to 60 % by weight, preferably in the range of 1 to 50 % by weight, and more preferably in the range of 10 to 30 % by weight per the total amount of the graphitized carbon and the coating graphitized carbon, whereby a non-aqueous electrolyte secondary battery superior in preservation characteristics was obtained. (Experimental Example 2) In the experimental example, in coating the graphitized carbon to be a core with the coating graphitized carbon in the production of the cathode in the non-aqueous electrolyte secondary battery in the embodiment 1, coating graphitized carbons in which spacing (d 002 ) of lattice planes (002) is in the range of 3.36 to 3.49 Å as shown in the following Table 4 were used as the coating graphitized carbon, to fabricate respective non-aqueous electrolyte secondary batteries. With respect to each of the non-aqueous electrolyte secondary batteries, a discharge capacity after preservation for two months at a temperature of 60°C in the non-aqueous electrolyte battery was also examined in the same manner as that in the above-mentioned experimental example 1. The results are shown in the following Table 4 and Fig. 3. A discharge capacity before the preservation in the non-aqueous electrolyte secondary battery was 600 mAh. d 002 (Å) in coating graphitized carbon 3.36 3.37 3.38 3.39 3.40 3.41 3.42 discharge capacity (mAh) 540 543 548 551 553 552 551 d 002 (Å) in coating graphitized carbon 3.43 3.44 3.45 3.46 3.46 3.48 3.49 discharge capacity (mAh) 550 549 548 547 546 545 544 As a result, in coating the graphitized carbon to be a core in which spacing (d 002 ) of lattice planes (002) is 3.36 with the coating graphitized carbon as described above, when the graphitized carbon to be a core was coated with the coating graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.36 to 3.49 Å and is not less than the spacing (d 002 ) of lattice planes (002) in the graphitized carbon to be a core, the discharge capacity after the preservation was significantly improved, as compared with that in a case where the graphitized carbon to be a core is not coated. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A non-aqueous electrolyte battery comprising an anode (1) with anode materials which occlude and discharge lithium ions, a cathode (2) using a carbon material, and a non-aqueous electrolytic solution, wherein the carbon material is composed of a core and a surface layer, the core is coated with the surface layer, the core is composed of graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.35 to 3.39 Å and the length (Lc) of a crystallite in the direction of the c axis is not less than 1000 Å, and the surface layer is composed of coating graphitized carbon in which spacing (d 002 ) of lattice planes (002) is in the range of 3.36 to 3.49 Å and is more than the spacing (d 002 ) of lattice planes (002) in the graphitized carbon to be the core. The non-aqueous electrolyte battery according to claim 1, wherein the amount of the coating graphitized carbon is in the range of 0.1 to 60% by weight per the total amount of the graphitized carbon and the coating graphitized carbon. The non-aqueous electrolyte battery according to claim 1, wherein the amount of the coating graphitized carbon is in the range of 1 to 50 % by weight per the total amount of the graphitized carbon and the coating graphitized carbon. The non-aqueous electrolyte battery according to claim 1, wherein the amount of the coating graphitized carbon is in the range of 10 to 30 % by weight per the total amount of the graphitized carbon and the coating graphitized carbon.

Inventors: KOJI NISHIO, MIKIYA YAMASAKI, TOSHIYUKI NOHMA, YASUYUKI KUSUMOTO, YOSHIHIRO SHOJI, KOJI, NISHIO, MIKIYA, YAMASAKI, TOSHIYUKI, NOHMA, YASUYUKI, KUSUMOTO, YOSHIHIRO, SHOJI
Applicants: SANYO ELECTRIC CO, SANYO ELECTRIC CO., LTD.
Application year: 1997
Main classification: H01M4
IPC codes: H01M4