WO2012147647A1 - Lithium ion secondary cell - Google Patents

Lithium ion secondary cell Download PDF

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Publication number
WO2012147647A1
WO2012147647A1 PCT/JP2012/060710 JP2012060710W WO2012147647A1 WO 2012147647 A1 WO2012147647 A1 WO 2012147647A1 JP 2012060710 W JP2012060710 W JP 2012060710W WO 2012147647 A1 WO2012147647 A1 WO 2012147647A1
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negative electrode
ion secondary
lithium ion
battery
active material
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PCT/JP2012/060710
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French (fr)
Japanese (ja)
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洋生 西山
愛知　且英
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新神戸電機株式会社
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Priority to JP2013512326A priority Critical patent/JPWO2012147647A1/en
Publication of WO2012147647A1 publication Critical patent/WO2012147647A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery that has a high capacity and a long life by devising a negative electrode active material.
  • a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to the surface of the current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to the surface of the current collector using a binder. It is connected via an electrolyte layer containing an electrolyte and has a configuration of being housed in a battery case.
  • a negative electrode active material constituting the negative electrode of such a lithium ion secondary battery a carbon / graphite negative electrode material or an alloy negative electrode material such as silicon (Si) or tin (Sn) that can be alloyed with lithium is used. .
  • a conductive material is used to provide an electron supply path to the negative electrode active material.
  • a carbon-based conductive material is used.
  • Known carbon-based conductive materials include, for example, acetylene black, ketjen black, carbon fiber, and carbon nanotube.
  • graphite is a layered material, and lithium ions are taken in between the layers to generate a lithium graphite intercalation compound of composition formula LiC 6 . Since the potential at this time is only about +0.06 V away from the potential of lithium metal, a high electromotive force can be maintained when combined with the positive electrode reaction. In addition, the charge / discharge potential is almost constant, and the graphite itself has high conductivity, so the internal resistance loss is small, and the charge / discharge efficiency (ratio of charge to discharge). ) Exceeds 90%, and stable operation can be expected. For this reason, graphite materials are mostly used for lithium ion secondary batteries used in current cellular phones and the like.
  • alloy-based negative electrode materials are expected as candidates for vehicle batteries because they can achieve higher energy density than carbon / graphite-based negative electrode materials.
  • the negative electrode material has a large expansion / contraction associated with insertion / extraction of lithium ions.
  • the volume expansion when lithium ions are occluded is about 1.2 times for graphite and about 4 times for silicon-based negative electrode materials.
  • the active material greatly expands, the contact between the active materials or the adhesion between the active material layer and the current collector decreases while charging and discharging are repeated. As a result, it has been pointed out that the active material is cracked, pulverized, or peeled off from the current collector, and desired cycle characteristics cannot be obtained.
  • Patent Document 1 The invention described in Patent Document 1 has been proposed as an invention for solving the above problems.
  • a countermeasure for extending the service life is achieved by functioning as a buffer material against expansion and swelling of the electrode.
  • Patent Document 1 adds carbon nanohorn as a conductive material to a graphite negative electrode, and improves the high-rate discharge characteristics by improving the life characteristics and reducing the electrode resistance.
  • carbon nanohorn which is a conductive material with a large specific surface area, increases the contact area between the negative electrode mixture and the electrolyte compared to the case where other conductive materials are added.
  • SEI is insulative, when it is produced in large quantities, it increases the internal resistance of the battery and leads to a decrease in battery capacity.
  • an object of the present invention is to provide a lithium-ion secondary battery having a long life as well as reducing electrode resistance and irreversible capacity.
  • a lithium ion secondary battery in which the weight of the carbon nanotube is 0.5 wt% or more and 1.5 wt% or less with respect to the active material weight of the negative electrode plate.
  • the lithium ion secondary battery BET specific surface area of the carbon nanotubes is less than 200 meters 2 / g or more 300m 2 / g.
  • a lithium ion secondary battery in which the primary particle length of the carbon nanotube is 5 to 20 ⁇ m.
  • the lithium ion secondary battery of the present invention by adding carbon nanotubes having excellent conductivity as a conductive material to the negative electrode mixture, it is possible to reduce the electronic resistance of the electrode and improve the high rate discharge characteristics.
  • the contact area between the current collector and the mixture layer increases, and the fibrous CNTs act as an anchor material to improve the adhesion and cycle characteristics. Can be improved.
  • the addition amount is suppressed to a small amount, the irreversible capacity of the battery can be reduced and excessive SEI generation can be suppressed, and the battery capacity is not greatly reduced.
  • FIG. 2 is an external view of a lithium ion secondary battery according to an embodiment to which the present invention is applicable. It is a figure which shows the relationship between the length of the primary particle of the carbon nanotube of embodiment which can apply this invention, and a battery characteristic. It is a figure which shows the relationship between the cycling characteristics of the lithium ion secondary battery of embodiment which can apply this invention, and high rate discharge capacity.
  • FIG. 1 (A) is a schematic view showing the inside of a lithium ion secondary battery which is an embodiment of the nonaqueous electrolyte battery of the present invention in a transparent state
  • FIG. 1 (B) is FIG. 1 (A).
  • FIG. 1C is an external view of a lithium ion secondary battery which is an embodiment of the non-aqueous electrolyte battery of the present invention.
  • the lithium ion secondary battery (laminated battery 1) includes a positive electrode plate 2 including a positive electrode lead terminal 2a, a negative electrode plate 3 including a negative electrode lead terminal 3a, and a separator disposed between the positive electrode plate 2 and the negative electrode plate 3. 4 and a nonaqueous electrolytic solution 5 in which a lithium salt is dissolved in an organic solvent.
  • the positive electrode plate 2, the negative electrode plate 3, and the separator 4 constitute an electrode plate group 6 that is a laminate.
  • the electrode plate group 6 is housed in the case 7 with the positive electrode lead terminal 2a and the negative electrode lead terminal 3a being connectable to the outside.
  • the inside of the case 7 is evacuated with the nonaqueous electrolyte 5 filled.
  • such a lithium ion secondary battery 1 was produced as follows.
  • the lithium ion secondary battery of this embodiment is characterized in that carbon nanotubes are used as the carbon-based conductive material of the negative electrode active material.
  • a negative electrode current collector coated with a negative electrode active material and a positive electrode current collector coated with a positive electrode active material are stacked with a separator interposed therebetween and impregnated with an electrolytic solution.
  • carbon nanotubes as a conductive material are dispersed almost uniformly between the particles of the negative electrode active material.
  • the BET specific surface area of the carbon nanotubes is desirably 200 m 2 / g or more and 300 m 2 / g or less.
  • the BET specific surface area of the carbon nanotube is less than 200 m 2 / g, the effect of reducing the electronic resistance by adding a small amount of the carbon nanotube is small.
  • the BET specific surface area of the carbon nanotubes exceeds 300 m 2 / g, a large amount of binder is required when preparing the negative electrode slurry, and thus a large amount of binder is required, making it difficult to prepare the slurry. .
  • the carbon nanotube used for the negative electrode conductive material has higher electronic conductivity than known conductive materials such as acetylene black, the addition of the carbon nanotube can reduce the electronic resistance of the electrode.
  • the contact area between the current collector and the mixture layer increases when added, and the fibrous carbon nanotubes work as an anchor material, improving adhesion. Cycle characteristics can be improved.
  • the addition amount is 0.5% by weight or more and 1.5% by weight or less with respect to the weight of the negative electrode active material, the high rate discharge characteristics / cycle characteristics are improved, and the battery capacity is greatly reduced.
  • the inventor found that there was no.
  • the addition amount is less than 0.5% by weight, the effect as an anchor material is small and the influence on the cycle characteristics is small.
  • the addition amount exceeds 1.5% by weight the battery capacity is greatly reduced due to an increase in the amount of SEI produced, and due to aggregation of primary particles, the dispersibility in the mixture is reduced, leading to an increase in electrode resistance.
  • the primary particle length of the carbon nanotube is 5 to 20 ⁇ m. If the length of the primary particles is less than 5 ⁇ m, the formation of a conductive path due to the addition of a small amount is insufficient, and if it exceeds 20 ⁇ m, the effect on the electronic resistance of the electrode is reduced due to aggregation of the conductive material.
  • the amount of carbon nanotubes added to the negative electrode active material is 0.5% by weight or more. It is desirable that it is 1.5% by weight or less, and the primary particle length is in the range of 5 to 20 ⁇ m.
  • the porosity of the negative electrode mixture is preferably 25 to 40% from the viewpoint of maintaining discharge characteristics such as high discharge capacity and large current discharge.
  • the porosity is less than 25%, the ion permeability or ion conductivity is lowered, so that the discharge characteristics are lowered.
  • the porosity exceeds 40%, the adhesion between the negative electrode mixture layer and the negative electrode current collector is lowered, so that the electron transfer resistance is increased and the discharge characteristics are lowered.
  • the positive electrode active material is not particularly limited as long as it absorbs positive ions or discharges negative ions during discharge, and a metal oxide such as LiMnO 2 , LiMn 2 O 4 , LiCoO 2 , LiNiO 2 can be used. .
  • An aluminum foil or the like can be used as the positive electrode current collector.
  • the negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing cations.
  • Crystalline carbon such as graphitized carbon obtained by heat treatment of natural graphite, coal, petroleum pitch, etc., coal, petroleum Amorphous carbon obtained by heat-treating pitch coke, acetylene pitch coke or the like can be used.
  • a copper foil or the like can be used as the negative electrode current collector.
  • the current collector a known material such as a metal foil such as copper or nickel can be appropriately used.
  • the thickness of the metal foil at this time may generally be about 10 ⁇ m.
  • the material for the current collector include metals selected from copper, nickel, iron, aluminum, zinc, gold, platinum, and the like.
  • the positive electrode current collector is preferably aluminum from the viewpoint of high oxidation resistance.
  • the binder plays a role of bonding the particles of the active material, the active material and the conductive material, and the active material and the current collector.
  • the binder for example, polyvinylidene fluoride, polyvinyl pyridine, polytetrafluoroethylene, styrene butadiene rubber, or the like can be used.
  • electrolytic solution examples include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ⁇ -butyrolactone, N, N′-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and m-cresol.
  • Examples of highly polar solvents that can be used as electrolytes for secondary batteries include alkali metal cations such as Li, K, and Na, ClO 4 ⁇ , BF 4 ⁇ , PF 6 ⁇ , CF 3 SO 3 ⁇ , and (CF 3 SO 2 ) 2 N -, (C 2 F 5 SO 2) 2 N -, (CF 3 SO 2) 3 C -, (C 2 F 5 SO 2) 3 C - a salt composed of anions of a compound containing halogen such as It can be dissolved.
  • the solvent and electrolyte salt which consist of these basic solvents can also be used individually or in combination.
  • a lithium ion secondary battery using the carbon nanotube of the present invention as a conductive material for a negative electrode as a constituent member such as a positive electrode material and an electrolyte solution (electrolyte, solvent), etc.
  • a constituent member such as a positive electrode material and an electrolyte solution (electrolyte, solvent), etc.
  • electrolyte solution electrolyte, solvent
  • Example 1 (Preparation of positive electrode plate) A lithium cobalt composite oxide (LiCoO 2 ) is prepared as a positive electrode active material for the positive electrode plate.
  • This lithium cobalt composite oxide, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are mixed at a mass ratio of 90: 5: 5 and dispersed in a solvent of N-methylpyrrolidone.
  • a slurry was prepared. This slurry was applied to an aluminum foil as a positive electrode current collector and dried, followed by press working to produce a positive electrode sheet.
  • the positive electrode sheet on which such a coating layer was formed was cut out to 10 cm ⁇ 20 cm, and a current collecting tab of aluminum foil was welded to prepare a positive electrode plate 2.
  • a positive electrode active material layer is formed on the surface of the positive electrode plate 2
  • a flame retardant layer is further formed on the surface of the positive electrode active material layer.
  • Artificial graphite is prepared as a negative electrode active material. This artificial graphite, a conductive agent, and polyvinylidene fluoride as a binder were mixed at a mass ratio of 92: 1: 7 and dispersed in a solvent of N-methylpyrrolidone to prepare a slurry.
  • the slurry was applied on a copper foil as a negative electrode current collector and dried, and then subjected to press working to produce a negative electrode sheet.
  • the negative electrode sheet was cut to 10 cm ⁇ 20 cm, and a nickel current collecting tab was welded to the cut sheet to prepare the negative electrode plate 3.
  • the positive electrode plate 2, the negative electrode plate 3, and the separator 4 are laminated with the separator sheet (separator 4) made of polyethylene sandwiched between the positive electrode plate 2 and the negative electrode plate 3 thus manufactured, and the battery capacity becomes 1 Ah.
  • the electrode group 6 was produced.
  • a mixed solvent consisting of 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate was prepared.
  • LiPF 6 was dissolved in this mixed solvent so as to have a concentration of 1 mol / L to prepare an electrolyte solution.
  • the prepared electrode plate group 6 is inserted into an outer packaging material (which will later be a case 7) made of a heat-sealing film (aluminum laminate film), and the prepared non-aqueous electrolyte 4 is further contained in the outer packaging material. Injected into. Then, the inside of the exterior material was evacuated, and the opening of the exterior material was quickly heat-sealed to produce a non-aqueous electrolyte battery (lithium ion secondary battery) having the structure of the flat laminate battery 1. (Evaluation of battery characteristics) The battery characteristics of the non-aqueous electrolyte battery thus produced were evaluated by the methods shown below.
  • the battery characteristics of the produced nonaqueous electrolyte battery were evaluated. Specifically, the discharge characteristics of the battery in which the type of the negative electrode conductive material was changed were evaluated. Note that the addition amount of the conductive material was 1.0 wt% with respect to the negative electrode active material.
  • the evaluation results of the discharge characteristics are as shown in Table 1.
  • the charge / discharge efficiency in Table 1 means a 0.2C discharge capacity with respect to the initial charge capacity.
  • the battery characteristics were evaluated by a high rate discharge test.
  • a charge / discharge cycle with a current value of 0.2 C was repeated twice in a voltage range of 4.2 to 3.0 V in an environment of 25 ° C. Further, after charging the battery to 4.2 V, charging / discharging was performed by constant current discharge with a final voltage of 3.0 V at current values of 0.2 C, 1 C, and 3 C.
  • the carbon nanotube is a fibrous material with very small primary particles of about 10 nm, it is considered that the addition of carbon nanotubes enters between the negative electrode active materials and electrically connects the negative electrode active materials.
  • Example 2 In preparation of the negative electrode 2, lithium was sputtered on a part of the negative electrode active material coating portion. A lithium film having a length of 200 mm and a width of 60 mm was formed at intervals of 200 mm from the end in the longitudinal direction of the negative electrode active material coating portion.
  • the lithium film was formed by forming a lithium film at 15 locations with a negative electrode having a length of 3000 mm.
  • the total area of the formed lithium film was 50% of the total area of the negative electrode active material coating part.
  • the average was 13.8 ⁇ m (minimum thickness 12.3 ⁇ m, maximum thickness 14.7 ⁇ m).
  • Others were the same as in Example 1, and cells 2a and 2b were produced. (Characteristic evaluation of cells 2a and 2b) Similarly to Example 1, the cell capacity and internal resistance of the cell 2a were evaluated.
  • Example 2 the capacity
  • FIG. (Examples 2 to 6)
  • the charging pattern each lithium battery was subjected to constant current charging at 0.2 C up to an upper limit voltage of 4.2 V, followed by constant voltage charging at 4.2 V.
  • the discharge was performed at a constant current of 3C up to 3.0V. Note that the addition amount of the conductive material was 1.0 wt% with respect to the negative electrode active material.
  • carbon nanotubes which are carbon-based conductive materials, have superior performance in charge / discharge efficiency and discharge characteristics as compared with acetylene black and carbon nanohorns.
  • the carbon nanotubes themselves exhibit excellent characteristics, and in particular, batteries with carbon nanotubes having a specific surface area of 200 to 300 m 2 / g exhibit good high rate discharge characteristics.
  • the specific surface area is less than 200 m 2 / g, the influence on the discharge characteristics with the same addition amount is reduced due to the reduction of the contact area with the active material.
  • the specific surface area exceeds 300 m 2 / g, uniform dispersion becomes difficult due to aggregation of the conductive material, and the effect for reducing the resistance becomes somewhat insufficient.
  • the specific surface area of the carbon nanotube to be added is preferably in the range of 200 to 300 m 2 / g. (Example 7) Next, in the laminated battery 1, the relationship between the type of the negative electrode conductive material and the life characteristics was confirmed.
  • each lithium battery was subjected to constant current charging at 0.2 C up to an upper limit voltage of 4.2 V, followed by constant voltage charging at 4.2 V.
  • the discharge was performed at a constant current of 1 C up to 3.0 V. Note that the addition amount of the conductive material was 1.0 wt% with respect to the negative electrode active material.
  • Table 3 shows the test results.
  • the capacity maintenance rate in Table 3 represents the discharge capacity ratio at the 50th cycle with respect to the initial discharge capacity.
  • a battery having a primary particle length of carbon nanotube of 5 to 20 ⁇ m exhibits good high rate discharge characteristics. If the length of the primary particles is less than 5 ⁇ m, the primary particles are too small and the particles are aggregated, making it difficult to enter between the active materials. For this reason, a favorable conductive path cannot be formed, and the effect of reducing the electronic resistance of the electrode becomes insufficient.
  • the length of the primary particles exceeds 20 ⁇ m, the molecular chains are entangled with each other and only adhere to the surface. For this reason, the negative electrode active materials cannot be electrically connected to each other and function as a resistance component, so that the high rate discharge characteristics are deteriorated.
  • the primary particle length of the carbon nanotube to be added is preferably in the range of 5 to 20 ⁇ m, particularly preferably in the range of 10 to 15 ⁇ m.
  • Examples 12 to 14 Next, in the laminated battery 1, the relationship between the amount of carbon nanotube added and the battery characteristics was confirmed. Specifically, the high rate discharge capacity and cycle characteristics were confirmed for the batteries in which the amount of carbon nanotube added was changed. The fiber length of the carbon nanotube was 10 ⁇ m.
  • the test results are shown in Table 5 and FIG.
  • the initial capacity in FIG. 3 means a 0.2C discharge capacity ratio in each cycle with respect to the initial discharge capacity.
  • the high rate discharge characteristics tended to increase by increasing the amount of carbon nanotube added. However, an increase in irreversible capacity was observed with the addition. For this reason, when the addition amount exceeds 1.5 wt%, the internal resistance due to the generated SEI increases, and the effect of improving the high rate discharge characteristics becomes small. If the addition amount is less than 0.5 wt%, the effect of reducing the electronic resistance due to the addition is insufficient, and if it exceeds 1.5 wt%, the high rate discharge characteristics may be caused by a decrease in battery capacity due to an increase in SEI or an increase in internal resistance. descend.
  • the addition amount was 0.5 wt% or more, the capacity ratio in 3C discharge exceeded 90%, and the efficiency discharge characteristics were greatly improved.
  • the absolute value of the 3C discharge capacity is an increase rate of less than 1% in a battery in which the amount of carbon nanotubes added is 2.0 wt%. If the increase rate of the irreversible capacity is less than 1%, it is considered that the influence due to the increase of the irreversible capacity appears larger than the improvement effect of the high rate discharge characteristics by the addition of the carbon nanotubes.
  • the amount of carbon nanotubes added is preferably in the range of 0.5 wt% to 1.5 wt%.
  • the addition amount is 0.2 wt%, the effect of suppressing the volume expansion of the graphite due to the addition is small, and when 2.0 wt%, the cycle characteristics deteriorate due to the increase in internal resistance.
  • the amount of carbon nanotube added is in the range of 0.5 wt% to 1.5 wt%, the capacity retention rate after 100 cycles has exceeded 96%, confirming that good cycle characteristics can be obtained. did.
  • the addition amount of carbon nanotubes is preferably in the range of 0.5 wt% to 1.5 wt% for improving the cycle characteristics.
  • the porosity of the negative electrode mixture is preferably in the range of 25 to 40%, particularly preferably in the range of 30 to 35 ⁇ m.
  • carbon nanotubes are added as a conductive material to the negative electrode, and the added amount is 0.5 to 1.5% by weight with respect to the weight of the negative electrode active material, so that high rate charge / discharge characteristics / cycle characteristics
  • a lithium ion secondary battery that does not significantly reduce battery capacity can be provided.
  • SYMBOLS 1 Lithium ion secondary battery, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Non-aqueous electrolyte, 6 ... Electrode plate group, 7 ... Case.

Abstract

The problem to be solved by the present invention is to provide an extended-life lithium ion secondary cell in which electrode resistance and irreversible capacity are reduced. In this lithium ion secondary cell, a non-aqueous electrolyte liquid, together with an electrode plate group of a positive electrode plate of a positive electrode mixture layer containing an active substance and formed over a current collector, and a negative electrode plate of a negative electrode mixture layer containing an active substance and a carbon based conductive material and formed over a current collector, disposed alternately with a separator therebetween, are housed in a case. Carbon nanotubes make up the carbon based conductive material.

Description

リチウムイオン二次電池Lithium ion secondary battery
　本発明は、リチウムイオン二次電池に係り、特に負極活物質に工夫することで高容量かつ長寿命となるリチウムイオン二次電池に関する。 The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery that has a high capacity and a long life by devising a negative electrode active material.
　リチウムイオン二次電池は、一般に、バインダを用いて正極活物質等を集電体の表面に塗布した正極と、バインダを用いて負極活物質等を集電体の表面に塗布した負極とが、電解質を含む電解質層を介して接続され、電池ケースに収納される構成を有している。このようなリチウムイオン二次電池の負極を構成する負極活物質としては、炭素・黒鉛系負極材料や、リチウムと合金化し得るケイ素（Ｓｉ）やスズ（Ｓｎ）等の合金系負極材料が用いられる。 Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to the surface of the current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to the surface of the current collector using a binder. It is connected via an electrolyte layer containing an electrolyte and has a configuration of being housed in a battery case. As a negative electrode active material constituting the negative electrode of such a lithium ion secondary battery, a carbon / graphite negative electrode material or an alloy negative electrode material such as silicon (Si) or tin (Sn) that can be alloyed with lithium is used. .
　また、負極活物質に電子の供給パスを提供するため、導電材が用いられている。導電材としては、例えば、炭素系導電材が用いられる。炭素系導電材としては、例えば、アセチレンブラック、ケッチェンブラック、カーボンファイバー、カーボンナノチューブなどが知られている。 Also, a conductive material is used to provide an electron supply path to the negative electrode active material. As the conductive material, for example, a carbon-based conductive material is used. Known carbon-based conductive materials include, for example, acetylene black, ketjen black, carbon fiber, and carbon nanotube.
　負極活物質の中でも黒鉛は、層状物質であり、その層間にリチウムイオンを取り込んで、組成式ＬｉＣ６のリチウム黒鉛層間化合物が生成する。このときの電位はリチウム金属の電位と約＋０．０６Ｖほどしか離れていないために、正極反応と併せた時には、高い起電力が保持できる。また、その充放電電位はほぼ一定であり、黒鉛自体は導電性が高いため内部抵抗ロスが小さく、充放電効率（放電量に対する充電量の割合。すなわち、入れた電気をどれだけ取り出せるかの目安）も９０％を超えるなど、安定した動作が見込めるため、現在の携帯電話などに使用されるリチウムイオン二次電池には、ほぼ黒鉛材料が用いられている。 Among the negative electrode active materials, graphite is a layered material, and lithium ions are taken in between the layers to generate a lithium graphite intercalation compound of composition formula LiC 6 . Since the potential at this time is only about +0.06 V away from the potential of lithium metal, a high electromotive force can be maintained when combined with the positive electrode reaction. In addition, the charge / discharge potential is almost constant, and the graphite itself has high conductivity, so the internal resistance loss is small, and the charge / discharge efficiency (ratio of charge to discharge). ) Exceeds 90%, and stable operation can be expected. For this reason, graphite materials are mostly used for lithium ion secondary batteries used in current cellular phones and the like.
　また、合金系負極材料は、炭素・黒鉛系負極材料と比較して高いエネルギー密度が達成可能であることから、車両用電池の候補として期待されている。 Also, alloy-based negative electrode materials are expected as candidates for vehicle batteries because they can achieve higher energy density than carbon / graphite-based negative electrode materials.
　しかし、上記負極材料は、リチウムイオンの吸蔵・放出に伴う膨張・収縮が大きい。例えば、リチウムイオンを吸蔵した場合の体積膨張は、黒鉛では約１．２倍であり、ケイ素系負極材料では約４倍にも達する。このように、活物質が大きく膨張すると、充放電を繰り返すうちに、活物質同士の接触、または活物質層と集電体との密着性が低下する。その結果、活物質の割れや微粉化、または集電体からの剥離が起こり、所望のサイクル特性が得られないという問題が以前から指摘されていた。 However, the negative electrode material has a large expansion / contraction associated with insertion / extraction of lithium ions. For example, the volume expansion when lithium ions are occluded is about 1.2 times for graphite and about 4 times for silicon-based negative electrode materials. As described above, when the active material greatly expands, the contact between the active materials or the adhesion between the active material layer and the current collector decreases while charging and discharging are repeated. As a result, it has been pointed out that the active material is cracked, pulverized, or peeled off from the current collector, and desired cycle characteristics cannot be obtained.
　上述の問題を解決する発明として、特許文献１に記載された発明が提案されている。黒鉛負極に導電材として粒状のカーボンナノホーンを添加することにより、電極の膨張・膨潤に対する緩衝材として機能させることで長寿命化への対策が図られている。 The invention described in Patent Document 1 has been proposed as an invention for solving the above problems. By adding granular carbon nanohorn as a conductive material to the graphite negative electrode, a countermeasure for extending the service life is achieved by functioning as a buffer material against expansion and swelling of the electrode.
特開２０１０－１２３４３７号公報JP 2010-123437 A
　特許文献１に記載された発明は、黒鉛負極に導電材としてカーボンナノホーンを添加し、寿命特性の改善とともに電極抵抗の低減により高率放電特性を向上させる。しかし、比表面積の大きな導電材であるカーボンナノホーンの添加により、他の導電材を添加した場合に比べて、負極合剤と電解液との接触面積が増加し、電極表面の不導体皮膜（以下、ＳＥＩと称する）の形成量が増加する。ＳＥＩは絶縁性であるため、大量に生成されると電池の内部抵抗を上げ電池容量の低下につながる。 The invention described in Patent Document 1 adds carbon nanohorn as a conductive material to a graphite negative electrode, and improves the high-rate discharge characteristics by improving the life characteristics and reducing the electrode resistance. However, the addition of carbon nanohorn, which is a conductive material with a large specific surface area, increases the contact area between the negative electrode mixture and the electrolyte compared to the case where other conductive materials are added. , Referred to as SEI). Since SEI is insulative, when it is produced in large quantities, it increases the internal resistance of the battery and leads to a decrease in battery capacity.
　そこで、本発明の課題は、電極抵抗、不可逆容量の低減とともに、長寿命なリチウムイオン二次電池を提供することを目的の一つとする。 Therefore, an object of the present invention is to provide a lithium-ion secondary battery having a long life as well as reducing electrode resistance and irreversible capacity.
　上記課題を解決するために、次に示すような構成が有効と考えられる。 In order to solve the above problems, the following configuration is considered effective.
　活物質を含む正極合剤層が集電体上に形成されてなる正極板と、活物質および炭素系導電材を含む負極合剤層が集電体上に形成されてなる負極板と、がセパレータを介して交互に配置された極板群が、非水電解液とともにケースに収納されてなり、炭素系導電材がカーボンナノチューブであるリチウムイオン二次電池。 A positive electrode plate in which a positive electrode mixture layer containing an active material is formed on a current collector, and a negative electrode plate in which a negative electrode mixture layer containing an active material and a carbon-based conductive material is formed on the current collector. A lithium ion secondary battery in which electrode plates arranged alternately via separators are housed in a case together with a non-aqueous electrolyte, and the carbon-based conductive material is a carbon nanotube.
　その際、負極板の活物質粒子間において、カーボンナノチューブがほぼ均一に分散されているリチウムイオン二次電池。 At that time, a lithium ion secondary battery in which carbon nanotubes are almost uniformly dispersed among the active material particles of the negative electrode plate.
　また、カーボンナノチューブ重量が負極板の活物質重量に対して０．５重量％以上１．５重量％以下であるリチウムイオン二次電池。 Also, a lithium ion secondary battery in which the weight of the carbon nanotube is 0.5 wt% or more and 1.5 wt% or less with respect to the active material weight of the negative electrode plate.
　そして、カーボンナノチューブのＢＥＴ比表面積が２００ｍ２／ｇ以上３００ｍ２／ｇ以下であるリチウムイオン二次電池。 The lithium ion secondary battery BET specific surface area of the carbon nanotubes is less than 200 meters 2 / g or more 300m 2 / g.
　また、カーボンナノチューブの一次粒子の長さが５～２０μｍであるリチウムイオン二次電池。 Also, a lithium ion secondary battery in which the primary particle length of the carbon nanotube is 5 to 20 μm.
　さらに、負極合剤層の空隙率が２５～４０％であるリチウムイオン二次電池。 Furthermore, a lithium ion secondary battery in which the porosity of the negative electrode mixture layer is 25 to 40%.
　本発明のリチウムイオン二次電池は、負極合剤に導電材として導電性に優れるカーボンナノチューブを添加することで、電極の電子抵抗を低減して、高率放電特性を向上させることができる。 In the lithium ion secondary battery of the present invention, by adding carbon nanotubes having excellent conductivity as a conductive material to the negative electrode mixture, it is possible to reduce the electronic resistance of the electrode and improve the high rate discharge characteristics.
　また、比表面積の大きな繊維状の導電材を添加すれば、集電体と合剤層との接触面積が増加し、繊維状のＣＮＴがアンカー物質として働くことで密着性を向上させ、サイクル特性を向上させられる。 In addition, if a fibrous conductive material with a large specific surface area is added, the contact area between the current collector and the mixture layer increases, and the fibrous CNTs act as an anchor material to improve the adhesion and cycle characteristics. Can be improved.
　さらに、添加量を少量に抑えれば、電池の不可逆容量を低減し過剰なＳＥＩの生成を抑えることができ、電池容量を大きく低下させることがない。 Furthermore, if the addition amount is suppressed to a small amount, the irreversible capacity of the battery can be reduced and excessive SEI generation can be suppressed, and the battery capacity is not greatly reduced.
（Ａ）は本発明が適用可能な実施形態のリチウムイオン二次電池の内部を透視した状態で示す概略図であり、（Ｂ）は（Ａ）のＩＢ－ＩＢ断面図であり、（Ｃ）は本発明が適用可能な実施形態のリチウムイオン二次電池の外観図である。(A) is a schematic view showing the inside of a lithium ion secondary battery according to an embodiment to which the present invention can be applied in a transparent state, (B) is a cross-sectional view taken along the line IB-IB in (A), and (C) FIG. 2 is an external view of a lithium ion secondary battery according to an embodiment to which the present invention is applicable. 本発明が適用可能な実施形態のカーボンナノチューブの一次粒子の長さと電池特性との関係を示す図である。It is a figure which shows the relationship between the length of the primary particle of the carbon nanotube of embodiment which can apply this invention, and a battery characteristic. 本発明が適用可能な実施形態のリチウムイオン二次電池のサイクル特性と高率放電容量との関係を示す図である。It is a figure which shows the relationship between the cycling characteristics of the lithium ion secondary battery of embodiment which can apply this invention, and high rate discharge capacity.
　以下、図面を参照して、本発明の実施の形態について説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
　図１（Ａ）は、本発明の非水電解液電池の実施の形態であるリチウムイオン二次電池の内部を透視状態で示した概略図であり、図１（Ｂ）は図１（Ａ）のＩＢ－ＩＢの断面図であり、図１（Ｃ）は本発明の非水電解液電池の実施の形態であるリチウムイオン二次電池の外観図である。このリチウムイオン二次電池（ラミネート電池１）は、正極リード端子２ａを備える正極板２と、負極リード端子３ａを備える負極板３と、正極板２と負極板３との間に配置されたセパレータ４と、リチウム塩を有機溶媒に溶解させた非水電解液５とを備える。正極板２、負極板３およびセパレータ４は、積層体である極板群６を構成する。極板群６は、正極リード端子２ａおよび負極リード端子３ａが外部に接続可能な状態でケース７内に収納されている。ケース７内は、非水電解液５が充填された状態で真空になっている。本例では、このようなリチウムイオン二次電池１を、以下のように作製した。 FIG. 1 (A) is a schematic view showing the inside of a lithium ion secondary battery which is an embodiment of the nonaqueous electrolyte battery of the present invention in a transparent state, and FIG. 1 (B) is FIG. 1 (A). FIG. 1C is an external view of a lithium ion secondary battery which is an embodiment of the non-aqueous electrolyte battery of the present invention. The lithium ion secondary battery (laminated battery 1) includes a positive electrode plate 2 including a positive electrode lead terminal 2a, a negative electrode plate 3 including a negative electrode lead terminal 3a, and a separator disposed between the positive electrode plate 2 and the negative electrode plate 3. 4 and a nonaqueous electrolytic solution 5 in which a lithium salt is dissolved in an organic solvent. The positive electrode plate 2, the negative electrode plate 3, and the separator 4 constitute an electrode plate group 6 that is a laminate. The electrode plate group 6 is housed in the case 7 with the positive electrode lead terminal 2a and the negative electrode lead terminal 3a being connectable to the outside. The inside of the case 7 is evacuated with the nonaqueous electrolyte 5 filled. In this example, such a lithium ion secondary battery 1 was produced as follows.
　本実施形態のリチウムイオン二次電池は、負極活物質の炭素系導電材としてカーボンナノチューブを用いている点が特徴である。リチウムイオン二次電池は、負極活物質が塗布された負極集電体と、正極活物質が塗布された正極集電体とがセパレータを挟んで積層され、電解液に含浸されている。また、負極活物質の各粒子間には、導電材としてのカーボンナノチューブをほぼ均一に分散させている。なお、カーボンナノチューブの均一分散には、前記カーボンナノチューブのＢＥＴ比表面積が２００ｍ２／ｇ以上、３００ｍ２／ｇ以下であることが望ましい。カーボンナノチューブのＢＥＴ比表面積が２００ｍ２／ｇ未満であると、カーボンナノチューブを少量添加することによる電子抵抗の低減に対する効果が小さい。一方、前記カーボンナノチューブのＢＥＴ比表面積が３００ｍ２／ｇを超えると、負極スラリーを作製の際、カーボンナノチューブの比表面積が大きいことから、多量のバインダが必要であり、スラリーの作製が困難になる。 The lithium ion secondary battery of this embodiment is characterized in that carbon nanotubes are used as the carbon-based conductive material of the negative electrode active material. In a lithium ion secondary battery, a negative electrode current collector coated with a negative electrode active material and a positive electrode current collector coated with a positive electrode active material are stacked with a separator interposed therebetween and impregnated with an electrolytic solution. In addition, carbon nanotubes as a conductive material are dispersed almost uniformly between the particles of the negative electrode active material. For the uniform dispersion of the carbon nanotubes, the BET specific surface area of the carbon nanotubes is desirably 200 m 2 / g or more and 300 m 2 / g or less. When the BET specific surface area of the carbon nanotube is less than 200 m 2 / g, the effect of reducing the electronic resistance by adding a small amount of the carbon nanotube is small. On the other hand, if the BET specific surface area of the carbon nanotubes exceeds 300 m 2 / g, a large amount of binder is required when preparing the negative electrode slurry, and thus a large amount of binder is required, making it difficult to prepare the slurry. .
　負極の導電材に使用するカーボンナノチューブは、アセチレンブラックなど公知の導電材と比べて高い電子伝導性を持っていることから、添加することにより電極の電子抵抗を低減することができる。また比表面積の大きな繊維状の導電材であるため、添加することにより集電体と合剤層との接触面積が増加し、繊維状のカーボンナノチューブがアンカー物質として働くことで、密着性を向上させ、サイクル特性を向上させることができる。 Since the carbon nanotube used for the negative electrode conductive material has higher electronic conductivity than known conductive materials such as acetylene black, the addition of the carbon nanotube can reduce the electronic resistance of the electrode. In addition, because it is a fibrous conductive material with a large specific surface area, the contact area between the current collector and the mixture layer increases when added, and the fibrous carbon nanotubes work as an anchor material, improving adhesion. Cycle characteristics can be improved.
　一方、カーボンナノチューブは大きな比表面積を持つため、添加量を増やすことで電極界面でのＳＥＩの生成量が増加する。ＳＥＩは絶縁性であるために、大量に生成されると電池の内部抵抗を上げ、電池容量の低下につながる。 On the other hand, since carbon nanotubes have a large specific surface area, increasing the amount added increases the amount of SEI produced at the electrode interface. Since SEI is insulative, when it is produced in large quantities, it increases the internal resistance of the battery, leading to a decrease in battery capacity.
　検討の結果、添加量は負極活物質重量に対して０．５重量％以上、１．５重量％以下とすると、高率放電特性・サイクル特性を向上させ、しかも電池容量が大幅に低下することがないことを発明者は見出した。添加量が０．５重量％未満であると、アンカー物質としての効果が小さくサイクル特性に与える影響も小さい。添加量が１．５重量％を超えるとＳＥＩの生成量の増加による電池容量の低下が大きく、一次粒子同士の凝集により、合剤内での分散性が低下し電極抵抗の増加につながる。 As a result of the study, if the addition amount is 0.5% by weight or more and 1.5% by weight or less with respect to the weight of the negative electrode active material, the high rate discharge characteristics / cycle characteristics are improved, and the battery capacity is greatly reduced. The inventor found that there was no. When the addition amount is less than 0.5% by weight, the effect as an anchor material is small and the influence on the cycle characteristics is small. When the addition amount exceeds 1.5% by weight, the battery capacity is greatly reduced due to an increase in the amount of SEI produced, and due to aggregation of primary particles, the dispersibility in the mixture is reduced, leading to an increase in electrode resistance.
　また、導電材をほぼ均一に分散させ、少量を添加することで効果を得るためには、カーボンナノチューブの一次粒子の長さが、５～２０μｍであることが望ましい。一次粒子の長さが５μｍ未満であると、少量の添加による導電パスの形成が不十分であり、２０μｍを超えると、導電材の凝集により電極の電子抵抗への効果が小さくなる。 Also, in order to obtain an effect by dispersing the conductive material almost uniformly and adding a small amount, it is desirable that the primary particle length of the carbon nanotube is 5 to 20 μm. If the length of the primary particles is less than 5 μm, the formation of a conductive path due to the addition of a small amount is insufficient, and if it exceeds 20 μm, the effect on the electronic resistance of the electrode is reduced due to aggregation of the conductive material.
　以上の点から、リチウムイオン二次電池の高率放電特性、サイクル特性を確保して、しかも電池容量を維持するためには、負極活物質に対するカーボンナノチューブの添加量は、０．５重量％以上１．５重量％以下であり、一次粒子の長さが５～２０μｍの範囲にあることが望ましい。 From the above points, in order to ensure the high rate discharge characteristics and cycle characteristics of the lithium ion secondary battery and to maintain the battery capacity, the amount of carbon nanotubes added to the negative electrode active material is 0.5% by weight or more. It is desirable that it is 1.5% by weight or less, and the primary particle length is in the range of 5 to 20 μm.
　また、非水電解液電池では、高放電容量、大電流放電性などの放電特性を維持したいという観点から、負極合剤の空隙率は２５～４０％とするのが好ましい。空隙率（Ｐ）は、多孔質層の体積Ｖ１に占めるに細孔の体積Ｖ２を百分率で表したもの（Ｐ＝Ｖ２／Ｖ１×１００）として定義することができる。また空隙率（Ｐ）は、難燃性材料の比重（真比重）をｄ１とし、多孔質層の比重（見かけ比重）をｄ２とした場合に、Ｐ＝〔１－ｄ２／ｄ１〕×１００の式から演算したものを用いることもできる。 Further, in the non-aqueous electrolyte battery, the porosity of the negative electrode mixture is preferably 25 to 40% from the viewpoint of maintaining discharge characteristics such as high discharge capacity and large current discharge. The porosity (P) can be defined as a percentage (P = V2 / V1 × 100) representing the volume V2 of the pores in the volume V1 of the porous layer. The porosity (P) is P = [1-d2 / d1] × 100, where d1 is the specific gravity (true specific gravity) of the flame retardant material and d2 is the specific gravity (apparent specific gravity) of the porous layer. What was computed from the formula can also be used.
　なお、空隙率が２５％未満であると、イオン透過性またはイオン伝導性が低下するため、放電特性が低下する。一方、空隙率が４０％を超えると、負極合剤層と負極集電体との間の密着性が低下するため、電子移動抵抗が増大し、放電特性が低下する。 Note that if the porosity is less than 25%, the ion permeability or ion conductivity is lowered, so that the discharge characteristics are lowered. On the other hand, when the porosity exceeds 40%, the adhesion between the negative electrode mixture layer and the negative electrode current collector is lowered, so that the electron transfer resistance is increased and the discharge characteristics are lowered.
　正極活物質としては、放電時に正イオンを吸収するもの又は負イオンを放出するものであれば特に限定されず、ＬｉＭｎＯ２、ＬｉＭｎ２Ｏ４、ＬｉＣｏＯ２、ＬｉＮｉＯ２等の金属酸化物を使用できる。正極集電体としてはアルミニウム箔などを使用できる。 The positive electrode active material is not particularly limited as long as it absorbs positive ions or discharges negative ions during discharge, and a metal oxide such as LiMnO 2 , LiMn 2 O 4 , LiCoO 2 , LiNiO 2 can be used. . An aluminum foil or the like can be used as the positive electrode current collector.
　負極活物質としては、カチオンを吸蔵・放出可能な材料であれば特に限定されず、天然黒鉛、石炭・石油ピッチ等を高温で熱処理して得られる黒鉛化炭素等の結晶質カーボン、石炭、石油ピッチコークス、アセチレンピッチコークス等を熱処理して得られる非晶質カーボンなどを使用できる。負極集電体としては銅箔等を使用できる。 The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing cations. Crystalline carbon such as graphitized carbon obtained by heat treatment of natural graphite, coal, petroleum pitch, etc., coal, petroleum Amorphous carbon obtained by heat-treating pitch coke, acetylene pitch coke or the like can be used. A copper foil or the like can be used as the negative electrode current collector.
　集電体としては、銅、ニッケル等の金属箔など、周知のものを適宜用いることができる。この時の金属箔の厚みは、一般的に１０μｍ程度で良い。集電体の材質として、銅、ニッケル、鉄、アルミニウム、亜鉛、金、白金等から選択される金属を挙げられる。この内、正極集電体には、耐酸化性が高いという観点からアルミニウムが好ましい。 As the current collector, a known material such as a metal foil such as copper or nickel can be appropriately used. The thickness of the metal foil at this time may generally be about 10 μm. Examples of the material for the current collector include metals selected from copper, nickel, iron, aluminum, zinc, gold, platinum, and the like. Among these, the positive electrode current collector is preferably aluminum from the viewpoint of high oxidation resistance.
　結着材（バインダ）は、活物質の粒子同士、活物質と導電材、さらに活物質と集電体とを接着する役割を担っている。結着剤としては、例えば、ポリフッ化ビニリデン、ポリビニルピリジン、ポリテトラフルオロエチレンやスチレンブタジエンゴム等を用いることができる。 The binder (binder) plays a role of bonding the particles of the active material, the active material and the conductive material, and the active material and the current collector. As the binder, for example, polyvinylidene fluoride, polyvinyl pyridine, polytetrafluoroethylene, styrene butadiene rubber, or the like can be used.
　電解液としては、例えば、エチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、γ―ブチロラクトン、Ｎ，Ｎ’－ジメチルホルムアミド、ジメチルスルホキシド、Ｎ－メチルピロリドン、ｍ－クレゾール等の、二次電池の電解液として利用可能な極性の高い溶媒に、ＬｉやＫ、Ｎａ等のアルカリ金属のカチオンとＣｌＯ４ －、ＢＦ４ －、ＰＦ６ －、ＣＦ３ＳＯ３ －、（ＣＦ３ＳＯ２）２Ｎ－、（Ｃ２Ｆ５ＳＯ２）２Ｎ－、（ＣＦ３ＳＯ２）３Ｃ－、（Ｃ２Ｆ５ＳＯ２）３Ｃ－等のハロゲンを含む化合物のアニオンからなる塩を溶解したものを挙げられる。また、これらの塩基性溶媒からなる溶剤や電解質塩を単独、あるいは複数組み合わせて用いることもできる。 Examples of the electrolytic solution include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, N, N′-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and m-cresol. Examples of highly polar solvents that can be used as electrolytes for secondary batteries include alkali metal cations such as Li, K, and Na, ClO 4 − , BF 4 − , PF 6 − , CF 3 SO 3 − , and (CF 3 SO 2 ) 2 N -, (C 2 F 5 SO 2) 2 N -, (CF 3 SO 2) 3 C -, (C 2 F 5 SO 2) 3 C - a salt composed of anions of a compound containing halogen such as It can be dissolved. Moreover, the solvent and electrolyte salt which consist of these basic solvents can also be used individually or in combination.
　また、本発明では電解液の添加剤による影響が無く、全ての添加剤において適用することができる。 Further, in the present invention, there is no influence by the additive of the electrolytic solution, and it can be applied to all the additives.
　本発明のカーボンナノチューブを負極の導電材として利用したリチウムイオン二次電池において、正極材料、電解液（電解質、溶媒）等の構成部材としては、炭素系材料を負極とするこの種のリチウムイオン二次電池において使用されるものがそのまま適用できる。 In a lithium ion secondary battery using the carbon nanotube of the present invention as a conductive material for a negative electrode, as a constituent member such as a positive electrode material and an electrolyte solution (electrolyte, solvent), etc. Those used in the secondary battery can be applied as they are.
（実施例１）
（正極板の作製）
　正極板の正極活物質として、リチウムコバルト複合酸化物（ＬｉＣｏＯ２）を用意する。このリチウムコバルト複合酸化物と、導電剤であるアセチレンブラックと、結着剤であるポリフッ化ビニリデンとを、質量比９０：５：５で混合し、これをＮ－メチルピロリドンの溶媒に分散させてスラリーを調製した。このスラリーを、正極集電体としてアルミニウム箔に塗布して乾燥した後、プレス加工を施して、正極シートを作製した。 Example 1
(Preparation of positive electrode plate)
A lithium cobalt composite oxide (LiCoO 2 ) is prepared as a positive electrode active material for the positive electrode plate. This lithium cobalt composite oxide, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are mixed at a mass ratio of 90: 5: 5 and dispersed in a solvent of N-methylpyrrolidone. A slurry was prepared. This slurry was applied to an aluminum foil as a positive electrode current collector and dried, followed by press working to produce a positive electrode sheet.
　このような塗布層が形成された正極シートを１０ｃｍ×２０ｃｍに切り取り、アルミニウム箔の集電タブを溶接して正極板２を作製した。これにより正極板２の表面には、正極活物質層が形成され、さらに正極活物質層の表面には難燃化剤層が形成される。
（負極板の作製）
　負極活物質として、人造黒鉛を用意する。この人造黒鉛と、導電剤と結着剤であるポリフッ化ビニリデンとを、質量比９２：１：７で混合し、これをＮ－メチルピロリドンの溶媒に分散させてスラリーを調製した。このスラリーを、負極集電体である銅箔上に塗布して乾燥した後、プレス加工を施して、負極シートを作製した。この負極シートを１０ｃｍ×２０ｃｍに切り取り、切り取ったシートにニッケルの集電タブを溶接して負極板３を作製した。
（極板群の作製）
　このように作製した正極板２と負極板３との間に、ポリエチレンからなるセパレータシート（セパレータ４）を挟んで、正極板２、負極板３およびセパレータ４を積層して電池容量が１Ａｈになるように極板群６を作製した。
（非水電解液の調製）
　エチレンカーボネート５０体積％とジメチルカーボネート５０体積％とからなる混合溶媒を調製した。この混合溶媒に、濃度が１ｍｏｌ／ＬになるようにＬｉＰＦ６を溶解させて電解質溶液を調製した。
（電池の組立）
　熱融着フィルム（アルミラミネートフィルム）からなる一端が開口した外装材（後にケース７となる）の中に、作製した極板群６を挿入し、さらに調製した非水電解液４を外装材中に注入した。その後、外装材中を真空にして、すばやく外装材の開口部をヒートシールして、平板状のラミネート電池１の構造を有する非水電解液電池（リチウムイオン二次電池）を作製した。
（電池特性の評価）
　このように作製した非水電解液電池の電池特性を、下記に示す方法で評価した。 The positive electrode sheet on which such a coating layer was formed was cut out to 10 cm × 20 cm, and a current collecting tab of aluminum foil was welded to prepare a positive electrode plate 2. As a result, a positive electrode active material layer is formed on the surface of the positive electrode plate 2, and a flame retardant layer is further formed on the surface of the positive electrode active material layer.
(Preparation of negative electrode plate)
Artificial graphite is prepared as a negative electrode active material. This artificial graphite, a conductive agent, and polyvinylidene fluoride as a binder were mixed at a mass ratio of 92: 1: 7 and dispersed in a solvent of N-methylpyrrolidone to prepare a slurry. The slurry was applied on a copper foil as a negative electrode current collector and dried, and then subjected to press working to produce a negative electrode sheet. The negative electrode sheet was cut to 10 cm × 20 cm, and a nickel current collecting tab was welded to the cut sheet to prepare the negative electrode plate 3.
(Production of electrode group)
The positive electrode plate 2, the negative electrode plate 3, and the separator 4 are laminated with the separator sheet (separator 4) made of polyethylene sandwiched between the positive electrode plate 2 and the negative electrode plate 3 thus manufactured, and the battery capacity becomes 1 Ah. Thus, the electrode group 6 was produced.
(Preparation of non-aqueous electrolyte)
A mixed solvent consisting of 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate was prepared. LiPF 6 was dissolved in this mixed solvent so as to have a concentration of 1 mol / L to prepare an electrolyte solution.
(Battery assembly)
The prepared electrode plate group 6 is inserted into an outer packaging material (which will later be a case 7) made of a heat-sealing film (aluminum laminate film), and the prepared non-aqueous electrolyte 4 is further contained in the outer packaging material. Injected into. Then, the inside of the exterior material was evacuated, and the opening of the exterior material was quickly heat-sealed to produce a non-aqueous electrolyte battery (lithium ion secondary battery) having the structure of the flat laminate battery 1.
(Evaluation of battery characteristics)
The battery characteristics of the non-aqueous electrolyte battery thus produced were evaluated by the methods shown below.
　作製した非水電解液電池（ラミネート電池１）について、電池特性を評価した。具体的には、負極の導電材の種類を変化させた電池の放電特性を評価した。なお、導電材の添加量は、負極活物質に対して１．０重量％とした。放電特性の評価結果は表１に示すとおりである。表１における充放電効率は、初回充電容量に対する０．２Ｃ放電容量を意味する。 The battery characteristics of the produced nonaqueous electrolyte battery (laminated battery 1) were evaluated. Specifically, the discharge characteristics of the battery in which the type of the negative electrode conductive material was changed were evaluated. Note that the addition amount of the conductive material was 1.0 wt% with respect to the negative electrode active material. The evaluation results of the discharge characteristics are as shown in Table 1. The charge / discharge efficiency in Table 1 means a 0.2C discharge capacity with respect to the initial charge capacity.
　電池特性の評価は、高率放電試験により行った。高率放電試験では、まず、２５℃の環境下において４．２～３．０Ｖの電圧範囲で、０．２Ｃの電流値による充放電サイクルを２回繰り返した。さらに４．２Ｖまで電池の充電後、電流値０．２Ｃ、１Ｃ、３Ｃの各電流値で終止電圧３．０Ｖの定電流放電による充放電を行った。 The battery characteristics were evaluated by a high rate discharge test. In the high rate discharge test, first, a charge / discharge cycle with a current value of 0.2 C was repeated twice in a voltage range of 4.2 to 3.0 V in an environment of 25 ° C. Further, after charging the battery to 4.2 V, charging / discharging was performed by constant current discharge with a final voltage of 3.0 V at current values of 0.2 C, 1 C, and 3 C.
表１　同添加量での充放電高率および放電特性の比較
Figure JPOXMLDOC01-appb-I000001
Table 1 Comparison of charge / discharge high rate and discharge characteristics at the same addition amount
Figure JPOXMLDOC01-appb-I000001
　表１に示すように、不可逆容量を示す初回の充放電効率はアセチレンブラック（比較例1）では約１８%、カーボンナノホーン（比較例２）では約１６．７%の増加が見られた。一方、カーボンナノチューブを添加したものでは約１５．５%の増加となっており、他の導電材種に比べ、不可逆容量を低減できることを確認した。 As shown in Table 1, the initial charge / discharge efficiency showing irreversible capacity increased by about 18% for acetylene black (Comparative Example 1) and about 16.7% for carbon nanohorn (Comparative Example 2). On the other hand, when carbon nanotubes were added, the increase was about 15.5%, and it was confirmed that irreversible capacity could be reduced compared to other conductive material types.
　また、１．０重量%の添加では他の導電材に比べ、カーボンナノチューブを添加することで放電特性の向上に対する効果が高いことがわかった。 It was also found that the addition of 1.0% by weight has a higher effect on improving the discharge characteristics by adding carbon nanotubes than other conductive materials.
　カーボンナノチューブは一次粒子が１０ｎｍ程度と非常に小さく繊維状の材料であるため、添加することで負極活物質間に入り込み、負極活物質同士を電気的に接続する効果が現れたと考えられる。一方で、アセチレンブラックは黒鉛粒子によるストラクチャーが発達していることから負極活物質間に入り込むことが困難であり、少量の添加では導電パスを形成するのには不十分であったと考えられる。
（実施例２）
　負極２の作製において、負極活物質塗工部の一部にリチウムをスパッタリングした。負極活物質塗工部の、長手方向の端部から２００ｍｍ間隔で、長さ２００ｍｍ、幅６０ｍｍの大きさでリチウム膜を形成した。リチウム膜の形成部は、長さ３０００ｍｍの負極で１５か所にリチウム膜を形成した。形成したリチウム膜の総面積は、負極活物質塗工部全面積の５０％であった。リチウム膜の厚さを１０か所計測したところ、平均１３．８μｍ（最小厚さ１２．３μｍ、最大厚さ１４．７μｍ）であった。その他は、実施例１と同様にして、セル２ａ、２ｂを作製した。
（セル２ａ、２ｂの特性評価）
　実施例１と同様に、セル２ａのセル容量と内部抵抗を評価した。 Since the carbon nanotube is a fibrous material with very small primary particles of about 10 nm, it is considered that the addition of carbon nanotubes enters between the negative electrode active materials and electrically connects the negative electrode active materials. On the other hand, it is difficult for acetylene black to enter between the negative electrode active materials because the structure of graphite particles has developed, and it is considered that addition of a small amount was insufficient to form a conductive path.
(Example 2)
In preparation of the negative electrode 2, lithium was sputtered on a part of the negative electrode active material coating portion. A lithium film having a length of 200 mm and a width of 60 mm was formed at intervals of 200 mm from the end in the longitudinal direction of the negative electrode active material coating portion. The lithium film was formed by forming a lithium film at 15 locations with a negative electrode having a length of 3000 mm. The total area of the formed lithium film was 50% of the total area of the negative electrode active material coating part. When the thickness of the lithium film was measured at 10 locations, the average was 13.8 μm (minimum thickness 12.3 μm, maximum thickness 14.7 μm). Others were the same as in Example 1, and cells 2a and 2b were produced.
(Characteristic evaluation of cells 2a and 2b)
Similarly to Example 1, the cell capacity and internal resistance of the cell 2a were evaluated.
　また、実施例１と同様に、セル２ｂの負極の活物質単位重量当たりの容量を測定した。
（実施例２～６）
　次に、ラミネート電池１において、カーボンナノチューブの比表面積と電池特性との関係を確認した。電池特性は充放電試験にて評価した。充電パターンは、それぞれのリチウム電池を０．２Ｃの定電流充電を上限電圧４．２Ｖまで行い、続いて４．２Ｖで定電圧充電を行った。放電は、３Ｃで定電流放電を３．０Ｖまで行うものとした。なお、導電材の添加量は、負極活物質に対して１．０重量％とした。 Moreover, the capacity | capacitance per active material unit weight of the negative electrode of the cell 2b was measured similarly to Example 1. FIG.
(Examples 2 to 6)
Next, in the laminated battery 1, the relationship between the specific surface area of the carbon nanotube and the battery characteristics was confirmed. The battery characteristics were evaluated by a charge / discharge test. As for the charging pattern, each lithium battery was subjected to constant current charging at 0.2 C up to an upper limit voltage of 4.2 V, followed by constant voltage charging at 4.2 V. The discharge was performed at a constant current of 3C up to 3.0V. Note that the addition amount of the conductive material was 1.0 wt% with respect to the negative electrode active material.
　試験結果を表２に示す。 Table 2 shows the test results.
　　　表２　カーボンナノチューブの比表面積を変更した電池の電池特性
Figure JPOXMLDOC01-appb-I000002
Table 2 Battery characteristics of batteries with specific surface area of carbon nanotubes changed
Figure JPOXMLDOC01-appb-I000002
　表１に示すように、炭素系導電材であるカーボンナノチューブは、アセチレンブラックやカーボンナノホーンと比較し、充放電効率や放電特性において優れた性能を有していることがわかった。 As shown in Table 1, it was found that carbon nanotubes, which are carbon-based conductive materials, have superior performance in charge / discharge efficiency and discharge characteristics as compared with acetylene black and carbon nanohorns.
　一方、表２に示すように、カーボンナノチューブ自体が優れた特性を示す中、特に、比表面積が２００～３００ｍ２／ｇのカーボンナノチューブを添加した電池で良好な高率放電特性を示すことがわかる。比表面積が２００ｍ２／ｇ未満であると、活物質との接触面積の減少により、同添加量での放電特性に与える影響が小さくなる。一方、比表面積が３００ｍ２／ｇを超えると、導電材の凝集により均一分散が困難となり、抵抗低減に対する効果が幾分不十分となる。 On the other hand, as shown in Table 2, it can be seen that the carbon nanotubes themselves exhibit excellent characteristics, and in particular, batteries with carbon nanotubes having a specific surface area of 200 to 300 m 2 / g exhibit good high rate discharge characteristics. . When the specific surface area is less than 200 m 2 / g, the influence on the discharge characteristics with the same addition amount is reduced due to the reduction of the contact area with the active material. On the other hand, when the specific surface area exceeds 300 m 2 / g, uniform dispersion becomes difficult due to aggregation of the conductive material, and the effect for reducing the resistance becomes somewhat insufficient.
　以上の点から、添加するカーボンナノチューブの比表面積は２００～３００ｍ２／ｇの範囲が好ましいことがわかる。
（実施例７）
　次に、ラミネート電池１において、負極の導電材の種類と寿命特性との関係を確認した。 From the above points, it can be seen that the specific surface area of the carbon nanotube to be added is preferably in the range of 200 to 300 m 2 / g.
(Example 7)
Next, in the laminated battery 1, the relationship between the type of the negative electrode conductive material and the life characteristics was confirmed.
　寿命特性は充放電を繰り返すサイクル試験にて評価した。充電パターンは、それぞれのリチウム電池を０．２Ｃの定電流充電を上限電圧４．２Ｖまで行い、続いて４．２Ｖで定電圧充電を行った。放電は、１Ｃで定電流放電を３．０Ｖまで行うものとした。なお、導電材の添加量は、負極活物質に対して１．０重量％とした。 The life characteristics were evaluated by a cycle test with repeated charge and discharge. As for the charging pattern, each lithium battery was subjected to constant current charging at 0.2 C up to an upper limit voltage of 4.2 V, followed by constant voltage charging at 4.2 V. The discharge was performed at a constant current of 1 C up to 3.0 V. Note that the addition amount of the conductive material was 1.0 wt% with respect to the negative electrode active material.
　試験結果を表３に示す。なお、表３における容量維持率は初回の放電容量に対する５０サイクル目の放電容量比を表している。 Table 3 shows the test results. In addition, the capacity maintenance rate in Table 3 represents the discharge capacity ratio at the 50th cycle with respect to the initial discharge capacity.
　　　　表３　導電材を変更した負極のサイクル特性
Figure JPOXMLDOC01-appb-I000003
Table 3 Cycle characteristics of negative electrode with different conductive materials
Figure JPOXMLDOC01-appb-I000003
　表３に示すように、カーボンナノチューブを添加した電池においてサイクル試験開始時の容量に対する容量維持率は９６%を大きく超えて、他の導電材を添加した電池に比べてサイクル特性が同等以上であった。この結果、同じ添加量での比較ではカーボンナノチューブによる効果が高いことがわかった。カーボンナノチューブは他の導電材に比べて強靭な機械的強度を持つため、負極活物質間および活物質周辺に存在することで、充放電による黒鉛の膨張・収縮を抑制する効果が現れたと考えられる。
（実施例８～１１）
　次にラミネート電池１において、カーボンナノチューブの一次粒子の長さと電池特性との関係を確認した。具体的には、カーボンナノチューブの繊維長を変化させた実施例および比較例について、高率放電容量を確認した。なお、カーボンナノチューブの添加量は負極活物質に対して１．０重量％とした。試験結果を表４、図２に示す。 As shown in Table 3, the capacity retention rate with respect to the capacity at the start of the cycle test in the battery added with the carbon nanotubes greatly exceeded 96%, and the cycle characteristics were equivalent or better than the battery added with other conductive materials. It was. As a result, it was found that the effect of carbon nanotubes was high in comparison with the same addition amount. Since carbon nanotubes have tougher mechanical strength than other conductive materials, the presence of carbon nanotubes between and around the negative electrode active material is thought to have an effect of suppressing the expansion and contraction of graphite due to charge and discharge. .
(Examples 8 to 11)
Next, in the laminated battery 1, the relationship between the length of the primary particle of the carbon nanotube and the battery characteristics was confirmed. Specifically, high-rate discharge capacity was confirmed for Examples and Comparative Examples in which the fiber length of the carbon nanotube was changed. The amount of carbon nanotube added was 1.0% by weight with respect to the negative electrode active material. The test results are shown in Table 4 and FIG.
　　表４　カーボンナノチューブの一次粒子の長さを変えた電池の電池特性
Figure JPOXMLDOC01-appb-I000004
Table 4 Battery characteristics of carbon nanotubes with different primary particle lengths
Figure JPOXMLDOC01-appb-I000004
　表４、図２に示すように、カーボンナノチューブの一次粒子の長さが５～２０μmの電池で良好な高率放電特性を示すことがわかる。また、一次粒子の長さが５μm未満であると、一次粒子が小さすぎることから粒子同士が凝集してしまい、活物質間に入り込むことが困難になる。このため、良好な導電パスを形成することができず、電極の電子抵抗を低減する効果が不十分になる。 As shown in Table 4 and FIG. 2, it can be seen that a battery having a primary particle length of carbon nanotube of 5 to 20 μm exhibits good high rate discharge characteristics. If the length of the primary particles is less than 5 μm, the primary particles are too small and the particles are aggregated, making it difficult to enter between the active materials. For this reason, a favorable conductive path cannot be formed, and the effect of reducing the electronic resistance of the electrode becomes insufficient.
　一方で、一次粒子の長さが２０μmを超えると、分子鎖同士で絡み合い表面に付着するだけになる。このため、負極活物質同士を電気的に接続することはできず、抵抗成分として働くため高率放電特性が低下する。 On the other hand, when the length of the primary particles exceeds 20 μm, the molecular chains are entangled with each other and only adhere to the surface. For this reason, the negative electrode active materials cannot be electrically connected to each other and function as a resistance component, so that the high rate discharge characteristics are deteriorated.
　上記の結果から、添加するカーボンナノチューブの一次粒子の長さは５～２０μmの範囲が好ましく、特に１０～１５μmの範囲が好ましいことがわかる。
（実施例１２～１４）
　次にラミネート電池１において、カーボンナノチューブの添加量と電池特性との関係を確認した。具体的には、カーボンナノチューブの添加量を変化させた電池について、高率放電容量およびサイクル特性を確認した。なお、カーボンナノチューブの繊維長さは１０μmとした。試験結果を表５、図３に示す。図３における対初期容量は、初回放電容量に対する各サイクルでの０．２Ｃ放電容量比を意味する。 From the above results, it is understood that the primary particle length of the carbon nanotube to be added is preferably in the range of 5 to 20 μm, particularly preferably in the range of 10 to 15 μm.
(Examples 12 to 14)
Next, in the laminated battery 1, the relationship between the amount of carbon nanotube added and the battery characteristics was confirmed. Specifically, the high rate discharge capacity and cycle characteristics were confirmed for the batteries in which the amount of carbon nanotube added was changed. The fiber length of the carbon nanotube was 10 μm. The test results are shown in Table 5 and FIG. The initial capacity in FIG. 3 means a 0.2C discharge capacity ratio in each cycle with respect to the initial discharge capacity.
表５　カーボンナノチューブの添加量を変更した電池の電池特性
Figure JPOXMLDOC01-appb-I000005
Table 5 Battery characteristics of batteries with different carbon nanotube additions
Figure JPOXMLDOC01-appb-I000005
　表５に示すように、カーボンナノチューブの添加量を増加することで高率放電特性が増加する傾向であった。しかし、添加により不可逆容量の増加が見られた。このため、添加量１．５ｗｔ％を超えると生成したＳＥＩによる内部抵抗が増加し、高率放電特性改善の効果が小さくなる。添加量が０．５ｗｔ％未満であると添加による電子抵抗の低減効果が不十分であり、１．５ｗｔ％を超えるとＳＥＩの増加による電池容量の低下もしくは内部抵抗の増加により高率放電特性が低下する。 As shown in Table 5, the high rate discharge characteristics tended to increase by increasing the amount of carbon nanotube added. However, an increase in irreversible capacity was observed with the addition. For this reason, when the addition amount exceeds 1.5 wt%, the internal resistance due to the generated SEI increases, and the effect of improving the high rate discharge characteristics becomes small. If the addition amount is less than 0.5 wt%, the effect of reducing the electronic resistance due to the addition is insufficient, and if it exceeds 1.5 wt%, the high rate discharge characteristics may be caused by a decrease in battery capacity due to an increase in SEI or an increase in internal resistance. descend.
　カーボンナノチューブの添加効果としては、添加量が０．５ｗｔ％以上となると３Ｃ放電での容量比が９０％を超えて、効率放電特性が大きく向上することを確認した。しかしカーボンナノチューブを添加すると不可逆容量も増加するため、３Ｃ放電容量の絶対値では、カーボンナノチューブの添加量が２．０ｗｔ％の電池で１％未満の増加率となる。不可逆容量の増加率が１％未満では、カーボンナノチューブの添加による高率放電特性の向上効果に比べて、不可逆容量の増加による影響の方が大きく現れていることが理由だと考えられる。 As an effect of adding carbon nanotubes, it was confirmed that when the addition amount was 0.5 wt% or more, the capacity ratio in 3C discharge exceeded 90%, and the efficiency discharge characteristics were greatly improved. However, since the irreversible capacity increases when carbon nanotubes are added, the absolute value of the 3C discharge capacity is an increase rate of less than 1% in a battery in which the amount of carbon nanotubes added is 2.0 wt%. If the increase rate of the irreversible capacity is less than 1%, it is considered that the influence due to the increase of the irreversible capacity appears larger than the improvement effect of the high rate discharge characteristics by the addition of the carbon nanotubes.
　効率放電特性、効率放電容量の向上のためには、カーボンナノチューブの添加量が０．５ｗｔ％ないし１．５ｗｔ％の範囲であることが好ましい。 In order to improve efficiency discharge characteristics and efficiency discharge capacity, the amount of carbon nanotubes added is preferably in the range of 0.5 wt% to 1.5 wt%.
　また、図３に示すサイクル試験の結果から、添加量が０．２ｗｔ％では添加による黒鉛の体積膨張を抑制する効果が小さく、２．０ｗｔ％では内部抵抗の増加によりサイクル特性が低下する。一方、カーボンナノチューブの添加量が０．５ｗｔ％ないし１．５ｗｔ％の範囲にある電池では、１００サイクル経過後の容量維持率が９６％を超えており、良好なサイクル特性が得られることを確認した。結果として、サイクル特性の向上に向けては、カーボンナノチューブの添加量が０．５ｗｔ％ないし１．５ｗｔ％の範囲が好ましいことがわかった。 Further, from the results of the cycle test shown in FIG. 3, when the addition amount is 0.2 wt%, the effect of suppressing the volume expansion of the graphite due to the addition is small, and when 2.0 wt%, the cycle characteristics deteriorate due to the increase in internal resistance. On the other hand, in the case of a battery in which the amount of carbon nanotube added is in the range of 0.5 wt% to 1.5 wt%, the capacity retention rate after 100 cycles has exceeded 96%, confirming that good cycle characteristics can be obtained. did. As a result, it was found that the addition amount of carbon nanotubes is preferably in the range of 0.5 wt% to 1.5 wt% for improving the cycle characteristics.
　以上のことから、高率放電特性と寿命特性の向上を両立させるには、０．５～１．５ｗｔ％のカーボンナノチューブを添加することが好ましいことがわかる。
（実施例１５～１８）
　次にラミネート電池１において、負極合剤の空隙率と電池特性との関係を確認した。具体的には、負極合剤の空隙率を変化させた実施例および比較例について、高率放電容量を確認した。なお、カーボンナノチューブの添加量は負極活物質に対して１．０重量％とした。試験結果を表６に示す。 From the above, it can be seen that it is preferable to add 0.5 to 1.5 wt% of carbon nanotubes in order to achieve both high rate discharge characteristics and improved life characteristics.
(Examples 15 to 18)
Next, in the laminated battery 1, the relationship between the porosity of the negative electrode mixture and the battery characteristics was confirmed. Specifically, the high rate discharge capacity was confirmed about the Example and comparative example which changed the porosity of the negative mix. The amount of carbon nanotube added was 1.0% by weight with respect to the negative electrode active material. The test results are shown in Table 6.
　表６　負極合剤の空隙率と電池特性との関係
Figure JPOXMLDOC01-appb-I000006
Table 6 Relationship between porosity of negative electrode mixture and battery characteristics
Figure JPOXMLDOC01-appb-I000006
　表６に示すように、負極合剤の空隙率が２５～４０％の電池で良好な高率放電特性を示すことがわかる。また、負極合剤の空隙率が２５%未満であると、空隙率の減少によりイオン拡散が阻害され高率放電特性が低下する。一方で、空隙率が４０%を超えると負極合剤と集電体との密着性が低下し、電子移動抵抗が増加する。このため、高率放電特性が低下する。 As shown in Table 6, it can be seen that a battery having a negative electrode mixture with a porosity of 25 to 40% exhibits good high rate discharge characteristics. On the other hand, when the porosity of the negative electrode mixture is less than 25%, ion diffusion is inhibited due to the decrease in the porosity, and the high rate discharge characteristics are deteriorated. On the other hand, when the porosity exceeds 40%, the adhesion between the negative electrode mixture and the current collector decreases, and the electron transfer resistance increases. For this reason, a high rate discharge characteristic falls.
　上記の結果から、負極合剤の空隙率は２５～４０%の範囲が好ましく、特に３０～３５μmの範囲が好ましいことがわかる。 From the above results, it can be seen that the porosity of the negative electrode mixture is preferably in the range of 25 to 40%, particularly preferably in the range of 30 to 35 μm.
　以上の実施例から、負極に導電材としてカーボンナノチューブを添加し、その添加量を負極活物質重量に対して０．５～１．５重量％とすることで、高率充放電特性・サイクル特性が向上し、しかも電池容量を大幅に低下させることのないリチウムイオン二次電池を提供することができる。 From the above examples, carbon nanotubes are added as a conductive material to the negative electrode, and the added amount is 0.5 to 1.5% by weight with respect to the weight of the negative electrode active material, so that high rate charge / discharge characteristics / cycle characteristics In addition, a lithium ion secondary battery that does not significantly reduce battery capacity can be provided.
　１…リチウムイオン二次電池、２…正極板、３…負極板、４…セパレータ、５…非水電解液、６…極板群、７…ケース。 DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Non-aqueous electrolyte, 6 ... Electrode plate group, 7 ... Case.

Claims (6)

  1. 　活物質を含む正極合剤層が集電体上に形成されてなる正極板と、
    　活物質および炭素系導電材を含む負極合剤層が集電体上に形成されてなる負極板と、
    がセパレータを介して交互に配置された極板群が、非水電解液とともにケースに収納されてなるリチウムイオン二次電池であって、
    　前記炭素系導電材が、カーボンナノチューブであることを特徴とするリチウムイオン二次電池。     A positive electrode plate in which a positive electrode mixture layer containing an active material is formed on a current collector;
    A negative electrode plate in which a negative electrode mixture layer containing an active material and a carbon-based conductive material is formed on a current collector;
    Is a lithium ion secondary battery in which electrode plates arranged alternately through separators are housed in a case together with a non-aqueous electrolyte,
    The lithium ion secondary battery, wherein the carbon-based conductive material is a carbon nanotube.
  2. 　前記負極板の活物質粒子間において、前記カーボンナノチューブがほぼ均一に分散されていることを特徴とする請求項１に記載のリチウムイオン二次電池。 2. The lithium ion secondary battery according to claim 1, wherein the carbon nanotubes are dispersed substantially uniformly between the active material particles of the negative electrode plate.
  3. 　前記カーボンナノチューブ重量が、前記負極板の活物質重量に対して、０．５重量％以上１．５重量％以下であることを特徴とする請求項１または請求項２に記載のリチウムイオン二次電池。 3. The lithium ion secondary according to claim 1, wherein a weight of the carbon nanotube is 0.5 wt% or more and 1.5 wt% or less with respect to an active material weight of the negative electrode plate. battery.
  4. 　前記カーボンナノチューブのＢＥＴ比表面積が、２００ｍ２／ｇ以上３００ｍ２／ｇ以下であることを特徴とする請求項１ないし請求項３のいずれかに記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 3, wherein the carbon nanotube has a BET specific surface area of 200 m 2 / g or more and 300 m 2 / g or less.
  5. 　前記カーボンナノチューブの一次粒子の長さが、５～２０μｍであることを特徴とする請求項１ないし請求項４のいずれかに記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 4, wherein a primary particle length of the carbon nanotube is 5 to 20 µm.
  6. 　前記負極合剤層の空隙率が、２５～４０％であることを特徴とする請求項１ないし請求項５のいずれかに記載のリチウムイオン二次電池。 6. The lithium ion secondary battery according to claim 1, wherein a porosity of the negative electrode mixture layer is 25 to 40%.
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