WO2012073747A1 - Positive electrode for nonaqueous electrolyte secondary batteries, method for producing same, and nonaqueous electrolyte secondary battery - Google Patents

Positive electrode for nonaqueous electrolyte secondary batteries, method for producing same, and nonaqueous electrolyte secondary battery Download PDF

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Publication number
WO2012073747A1
WO2012073747A1 PCT/JP2011/076850 JP2011076850W WO2012073747A1 WO 2012073747 A1 WO2012073747 A1 WO 2012073747A1 JP 2011076850 W JP2011076850 W JP 2011076850W WO 2012073747 A1 WO2012073747 A1 WO 2012073747A1
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positive electrode
electrolyte secondary
secondary battery
inorganic particle
nonaqueous electrolyte
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PCT/JP2011/076850
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French (fr)
Japanese (ja)
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山本　諭
伸宏 鉾谷
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三洋電機株式会社
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Priority to JP2012546787A priority Critical patent/JP5888512B2/en
Publication of WO2012073747A1 publication Critical patent/WO2012073747A1/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
    • 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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • 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

Definitions

  • the present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery, and particularly for a non-aqueous electrolyte secondary battery capable of improving storage characteristics and cycle characteristics in a high temperature and high voltage state.
  • the present invention relates to a positive electrode, a manufacturing method thereof, and a nonaqueous electrolyte secondary battery including the positive electrode.
  • non-aqueous electrolyte secondary batteries represented by high-capacity lithium ion secondary batteries are widely used.
  • the positive electrode active material of these nonaqueous electrolyte secondary batteries is represented by LiMO 2 (where M is at least one of Co, Ni, and Mn) capable of reversibly occluding and releasing lithium ions.
  • a carbon material such as graphite or a material alloyed with lithium such as Si or Sn is used as the negative electrode active material.
  • lithium-cobalt composite oxides and heterogeneous metal element-added lithium-cobalt composite oxides are often used because various battery characteristics are superior to others.
  • cobalt is expensive and has a small abundance as a resource. Therefore, in order to continue using these lithium cobalt composite oxides and lithium cobalt composite oxides containing different metal elements as positive electrode active materials for non-aqueous electrolyte secondary batteries, further enhancement of the performance of non-aqueous electrolyte secondary batteries is desired. ing.
  • non-aqueous electrolyte secondary batteries are required to have higher capacities due to demands for increased power consumption and long-term driving of HEVs and EVs with enhancement of entertainment functions such as video playback and game functions in recent mobile information terminals.
  • the end-of-charge voltage is 4.
  • a method of raising the voltage from 3V to about 4.6V is known.
  • the above side reaction is likely to occur, and battery performance such as cycle characteristics and storage characteristics is greatly impaired.
  • the oxidization reaction (dehydrogenation reaction) of the separator reduces the piercing strength and tensile strength of the separator, impairing the insulating function and shutdown function that the separator should originally perform, and lowering the reliability of the battery.
  • Patent Document 1 and Patent Document 2 below disclose a technique for suppressing these side reactions by forming a porous inorganic particle layer on the surface of the positive electrode mixture layer.
  • Patent Document 3 listed below discloses an invention of a lithium ion secondary battery in which high-temperature storage characteristics and cycle characteristics are improved by including an alkali metal phosphate in the positive electrode mixture layer. .
  • the porous inorganic particle layer is formed on the surface of the positive electrode mixture layer, so that the storage characteristics and cycle characteristics in a high voltage state are improved. Although improvement is achieved to some extent, the effect is still insufficient particularly in a high temperature environment, and there is room for further improvement.
  • no porous inorganic particle layer is formed on the surface of the positive electrode mixture layer.
  • An object of the present invention is to provide a positive electrode for a nonaqueous electrolyte secondary battery with improved capacity and charge / discharge cycle characteristics, a method for producing the same, and a nonaqueous electrolyte secondary battery including the positive electrode.
  • a positive electrode for a non-aqueous electrolyte secondary battery is formed on a surface of a positive electrode mixture layer including a positive electrode active material formed on the surface of a positive electrode core and the positive electrode mixture layer.
  • the porous inorganic particle layer is selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate It contains at least one sodium phosphate salt.
  • an inorganic particle layer is formed on the surface of the positive electrode mixture layer. Therefore, the oxidative decomposition product of the non-aqueous electrolyte on the positive electrode surface is trapped by this inorganic particle layer. Therefore, deposition on the negative electrode can be suppressed.
  • At least one sodium phosphate selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate in the inorganic particle layer. Contains salt.
  • the nonaqueous electrolyte secondary battery is inevitably mixed with a trace amount of water from the manufacturing process. Moreover, under high charging voltage, moisture is generated by the decomposition of the non-aqueous electrolyte.
  • the inorganic particle layer contains sodium phosphate salt, the reaction rate between these sodium phosphate salt and moisture is faster than the reaction rate between lithium salt as electrolyte and moisture.
  • the decomposition reaction of the lithium salt as the electrolyte can be suppressed.
  • the sodium phosphate salt is included in the inorganic particle layer, the sodium phosphate salt and the non-aqueous electrolyte solution are more contained in the positive electrode active material mixture layer than in the case of including the sodium phosphate salt as in the conventional example. It becomes easy to come into contact with moisture.
  • the charge end voltage is set to a high level of 4.4 V or more and 4.6 V or less on a lithium basis, and a high temperature environment. Even when placed underneath, both the storage characteristics and the cycle characteristics are much better than when the positive electrode for a nonaqueous electrolyte secondary battery of the conventional example is used.
  • the content of sodium phosphate contained in the porous inorganic particle layer is set to 0.03% by mass or more to 1% by mass of the positive electrode active material mixture. It is preferable to make it 0.0 mass% or less.
  • the content of sodium phosphate salt is less than 0.03% by mass, the above effect is hardly achieved, and when it exceeds 1.0% by mass, the positive electrode active material mixture that can be filled in the battery outer can by that much Since the amount decreases, the charge capacity per unit volume decreases, which is not preferable.
  • the inorganic particles contained in the porous inorganic particle layer are at least selected from titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), silicon oxide (SiO 2 ), and zirconium oxide (ZrO 2 ).
  • TiO 2 titanium oxide
  • Al 2 O 3 aluminum oxide
  • SiO 2 silicon oxide
  • ZrO 2 zirconium oxide
  • One kind can be used, and aluminum oxide and rutile type titanium oxide are particularly preferable in consideration of stability in the battery, reactivity with lithium, and cost.
  • the average particle diameter of the inorganic particles is preferably 1 ⁇ m or less, and more preferably in the range of 0.1 to 0.8 ⁇ m. Moreover, it is preferable that an average particle diameter is larger than the average hole diameter of the separator used for a nonaqueous electrolyte secondary battery.
  • the method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to the present invention includes a step of forming a positive electrode mixture layer on the surface of the positive electrode core, and a porous material on the surface of the positive electrode mixture layer.
  • porous inorganic particle layer in the method for producing a positive electrode for a non-aqueous electrolyte secondary battery having a step of forming a porous inorganic particle layer, and the step of forming the porous inorganic particle layer includes: inorganic particles, sodium hexametaphosphate, sodium pyrophosphate, phosphoric acid A slurry containing at least one sodium phosphate selected from trisodium and disodium hydrogen phosphate is applied by a gravure coating method and then dried.
  • the surface of the positive electrode mixture layer contains inorganic particles and sodium phosphate salt.
  • the slurry is applied by a gravure coating method and then dried. When such a method is employed, a slurry containing inorganic particles and sodium phosphate salt is thinly formed on the surface of the positive electrode mixture layer, and can be continuously formed with a uniform thickness.
  • a positive electrode for a non-aqueous electrolyte secondary battery of the present invention it becomes possible to continuously manufacture a positive electrode for a non-aqueous electrolyte secondary battery having a uniform quality, and the end-of-charge voltage is 4 based on lithium.
  • the production efficiency of a nonaqueous electrolyte secondary battery having excellent storage characteristics and cycle characteristics is improved even when placed in a high temperature environment of .4 V or more and 4.6 V or less.
  • phosphorous comprising at least one selected from inorganic particles and sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate.
  • a solvent it is preferable to select a solvent according to the type of the binder contained in the positive electrode active material mixture layer.
  • the binder contained in the positive electrode mixture layer is a hydrophobic substance
  • the binder to be used is a hydrophilic substance
  • the above lithium cobaltate powder was mixed to 96 parts by mass, carbon powder as a conductive material to 2 parts by mass, and polyvinylidene fluoride (PVdF) powder as a binder to 2 parts by mass, and this was mixed with N-methylpyrrolidone.
  • a positive electrode active material mixture slurry was prepared by mixing with (NMP) solution. This slurry was applied to both surfaces of a positive electrode core made of aluminum having a thickness of 15 ⁇ m by a doctor blade method.
  • the coated portion on one surface of the positive electrode core was 277 mm, the uncoated portion was 57 mm, the coated portion on the other surface was 208 mm, After coating so that the coated portion was 126 mm, NMP was removed by drying by passing through a dryer.
  • the positive electrode mixture layer was formed on both surfaces of the positive electrode core body by compressing using a compression roller so that the thickness of the double-side coated portion was 132 ⁇ m.
  • inorganic particle slurry 30% by mass of aluminum oxide (Al 2 O 3 ) as inorganic particles, 0.15% by mass of carboxymethylcellulose (CMC), and 69.85% by mass of pure water are mixed, and a kneader (TK High-Pixics manufactured by PRIMIX) After kneading, the obtained slurry was dispersed with a bead mill (Nanomill dispersing device manufactured by Asada Tekko) to obtain an inorganic particle slurry containing no phosphate.
  • TK High-Pixics manufactured by PRIMIX a kneader
  • the dispersion conditions were as follows: internal volume: 0.3 L, bead diameter: 0.5 ⁇ , slit: 0.15 mm, bead filling amount: 90%, peripheral speed 40 Hz, treatment flow rate: 1.0 kg / min.
  • aluminum oxide AK3000 (trade name: manufactured by Sumitomo Chemical Co., Ltd.) was used.
  • CMC Daicel Chemical Industries 1380 was used.
  • binder (acrylic rubber-type binder) is added with respect to aluminum oxide to an inorganic particle slurry. Furthermore, sodium hexametaphosphate as a phosphate is added so that it may become 33 mass% of slurry solid content whole quantity. It was. Thereafter, by adding pure water so that the ratio of aluminum oxide to the total amount of the slurry is finally 30% by mass, and kneading again with the above kneader, the phosphate-containing inorganic particle slurry used in each example is obtained. Prepared.
  • the positive electrode mixture layer formed on both surfaces of the positive electrode core is coated and coated on the surface of the positive electrode mixture layer with the phosphate-containing inorganic particle slurry obtained as described above by the gravure coating method.
  • a porous inorganic particle layer was formed to obtain a positive electrode plate used in Example 1.
  • the coating amount of the phosphate-containing inorganic particle slurry was 1% by mass in terms of solid content of the phosphate-containing inorganic particle slurry with respect to the positive electrode active material mixture (solid content).
  • the sodium hexametaphosphate content of the positive electrode is 0.33% by mass with respect to the positive electrode active material mixture (solid content).
  • the coating amount of the negative electrode active material mixture was the mass per unit area after drying, and the coating mass on one side was 11.3 mg / cm 2 . Then, the negative electrode active material layer was formed on both surfaces of the negative electrode core by passing through a dryer and drying. Subsequently, it was set as the negative electrode plate used by each Example and a comparative example by compressing so that the thickness of a double-sided application part might be 155 micrometers using a compression roller.
  • the potential of graphite at the time of charging is about 0.1 V with respect to Li.
  • the positive electrode and negative electrode active material filling amount is such that the charge capacity ratio of the positive electrode to the negative electrode (negative electrode charge capacity / positive electrode charge capacity) is 1.0 to 1.1 at the potential of the positive electrode active material as a design standard. Adjusted.
  • Lithium hexafluorophosphate LiPF 6
  • MEC methyl ethyl carbonate
  • VC vinylene carbonate
  • Electrode body An aluminum lead wire is welded and fixed to the obtained positive electrode plate, and a nickel lead wire is welded and fixed to the obtained negative electrode plate, and then the positive electrode plate and the negative electrode plate are made of a polyethylene microporous film.
  • a spiral electrode body was produced by winding it in a flat shape through a separator.
  • the obtained electrode body was sealed in a laminate container, and the obtained nonaqueous electrolytic solution was injected in a glove box filled with Ar. Thereafter, the injection hole was closed to produce a laminate battery, and a nonaqueous electrolyte secondary battery according to Example 1 was obtained.
  • the design capacity of the obtained non-aqueous electrolyte secondary battery is 800 mAh.
  • Example 2 and 3 A non-aqueous electrolyte secondary battery according to Examples 2 and 3 was prepared by producing a laminated battery in the same manner as in Example 1 except that the amount of sodium hexametaphosphate added to the inorganic particle slurry was changed in the inorganic particle slurry preparation step. It was.
  • a phosphate-containing inorganic particle slurry in which the content of sodium hexametaphosphate is 3.3% by mass (Example 2) and 50% by mass (Example 3) with respect to the total amount of slurry solids is mixed with the positive electrode mixture.
  • the nonaqueous electrolyte secondary battery which concerns on Example 2 and 3 was produced using the positive electrode plate obtained by apply
  • the sodium hexametaphosphate content of the positive electrode is 0.03% by mass (Example 2) and 0.5% by mass (Example 3) with respect to the positive electrode active material mixture (solid content).
  • Example 4 to 6 A non-aqueous electrolyte secondary battery according to Examples 4 to 6 was prepared in the same manner as in Example 1 except that the kind of phosphate contained in the inorganic particle slurry was changed in the preparation process of the inorganic particle slurry. did.
  • the positive electrode plates obtained by applying the slurry to the surface of the positive electrode mixture layer non-aqueous electrolyte secondary batteries according to Examples 4 to 6 were produced.
  • content of the phosphate in an inorganic particle slurry shall be 33 mass% similarly to Example 1, and the phosphate content in a positive electrode is 0.33 mass with respect to positive electrode active material mixture (solid content). %.
  • Example 1 A laminated battery was produced in the same manner as in Example 1 except that phosphate was not added to the inorganic particle slurry, and a nonaqueous electrolyte secondary battery according to Comparative Example 1 was obtained. That is, a comparative example using a positive electrode plate obtained by applying a slurry obtained by kneading after adding only a binder to an inorganic particle slurry not containing phosphate, on the surface of the positive electrode mixture layer A non-aqueous electrolyte secondary battery according to No. 1 was produced.
  • Example 2 A laminated battery was produced in the same manner as in Example 1 except that the porous inorganic particle layer was not formed on the positive electrode plate, and a nonaqueous electrolyte secondary battery according to Comparative Example 2 was obtained. That is, a non-aqueous electrolyte secondary battery according to Comparative Example 2 was manufactured using only a positive electrode mixture layer formed on the positive electrode core as a positive electrode plate.
  • the positive electrode plates in Comparative Examples 3 to 5 were obtained by adding sodium hexametaphosphate to the positive electrode active material mixture slurry in Example 1 and kneading them (phosphate-containing positive electrode active material mixture). Slurry) is applied to both surfaces of the positive electrode core to form a positive electrode mixture layer, and then the slurry obtained by kneading after adding only a binder to the inorganic particle slurry containing no phosphate is mixed with the positive electrode mixture.
  • a positive electrode plate used in Comparative Examples 3 to 5 was further produced using a positive electrode plate obtained by forming an inorganic particle layer by coating on the surface of the layer. The amount of sodium hexametaphosphate added was 0.05% by mass (Comparative Example 3), 0.5% by mass (Comparative Example 4), and 1.0% by mass (comparative) with respect to the positive electrode active material mixture (solid content). Example 5).
  • Remaining capacity ratio (%) (Remaining capacity after high temperature storage / Charging capacity before high temperature storage) x 100
  • Capacity maintenance rate (%) (Discharge capacity at 500th cycle / discharge capacity at the first cycle) x 100
  • Comparative Example 1 has improved high-temperature storage characteristics and high-temperature cycle characteristics as compared with Comparative Example 2.
  • Comparative Example 2 By forming an inorganic particle layer on the surface of the positive electrode mixture layer, high-temperature storage characteristics and high-temperature cycle characteristics are to some extent. It can be confirmed that there is an improvement. This indicates that the oxidation reaction of the separator is suppressed by the trap effect of the inorganic particle layer formed on the surface of the positive electrode mixture layer.
  • Example 1 the high-temperature storage characteristics and the high-temperature cycle characteristics are more significantly improved as compared with Comparative Example 1, and sodium hexametaphosphate is added to the inorganic particle layer formed on the surface of the positive electrode mixture layer.
  • a non-aqueous electrolyte secondary battery having significantly improved high-temperature storage characteristics and high-temperature cycle characteristics can be obtained.
  • the effect of improving the high-temperature storage characteristics and the high-temperature cycle characteristics by containing sodium hexametaphosphate in the inorganic particle layer is that the sodium hexametaphosphate content is positive electrode active material mixture (solid It can be seen that even a very small amount of 0.03% by mass with respect to (min) is sufficiently exerted.
  • the presence of moisture in the battery causes hydrolysis of a lithium salt such as LiPF 6 that is an electrolyte salt, and accordingly, hydrofluoric acid is generated. Since the positive electrode active material is corroded by this hydrofluoric acid and the original charge / discharge function cannot be exhibited, it is considered that the storage characteristics and the cycle characteristics particularly in a high temperature and high voltage state are deteriorated.
  • a lithium salt such as LiPF 6 that is an electrolyte salt
  • an inorganic particle layer is formed on the surface of the positive electrode mixture layer, and sodium hexametaphosphate, sodium pyrophosphate, and trisodium phosphate are further formed in the inorganic particle layer. Because it contains any phosphate of disodium hydrogen phosphate, hydrolysis of lithium salt due to moisture and oxidation of the separator are suppressed, improving storage characteristics and cycle characteristics at high temperature and high voltage it is conceivable that. This is because decomposition of the lithium salt can be suppressed because the reactivity of the phosphate with moisture is higher than that of the lithium salt.
  • Example 3 and Comparative Example 4 are compared, the amount of phosphate present in the battery is the same, but the effect is greatly different. This is thought to be because the contact efficiency between the phosphate and the electrolyte is high by mixing only the positive electrode inorganic particle layer rather than simply mixing the phosphate with the positive electrode mixture layer. In order to increase the filling of the positive electrode material for the purpose, it is necessary to contain only the positive electrode inorganic particle layer with the phosphate.
  • an inorganic particle layer is formed on the surface of the positive electrode mixture layer, and the phosphate is selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate in the inorganic particle layer.
  • the phosphate is selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate in the inorganic particle layer.
  • lithium cobaltate was used as the positive electrode active material.
  • the present invention is not limited to this, and lithium ions can be reversibly occluded / released.
  • graphite was used as the negative electrode active material.
  • carbonaceous materials such as natural graphite, artificial graphite, and coke capable of reversibly occluding and releasing lithium ions, silicon, tin, etc.
  • An alloy, an oxide, a mixture thereof, or the like can be used.
  • nonaqueous solvent organic solvent
  • carbonates lactones, ethers, esters and the like
  • two or more of these solvents can be used in combination.
  • carbonates are preferable.
  • EC EC
  • MEC propylene carbonate
  • BC butylene carbonate
  • FEC fluoroethylene carbonate
  • sulfolane 3-methylsulfolane, 2,4.
  • -Dimethylsulfolane 3-methyl-1,3-oxazolidine-2-one, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, ⁇ -Butyrolactone, ⁇ -valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dioxane, etc. be able to.
  • DMC dimethyl carbonate
  • DEC diethyl carbonate
  • methyl propyl carbonate methyl butyl carbonate
  • ethyl propyl carbonate ethyl butyl carbonate
  • dipropyl carbonate ⁇ -Butyrolactone, ⁇
  • a lithium salt generally used as a solute in the nonaqueous electrolyte secondary battery can be used.
  • a lithium salt in addition to LiPF 6 used in the examples, LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Li 2 B 10 Cl 10, Li 2 B 12 Examples include Cl 12 and mixtures thereof.
  • the amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.
  • an organic solvent such as N-methyl-pyrrolidone (NMP) as the slurry solvent when preparing the inorganic particle slurry, in which case the dispersion stability of the slurry is good.
  • NMP N-methyl-pyrrolidone
  • organic solvents such as MNP are easy to vaporize, the water content in the porous inorganic particle layer can be easily reduced by drying, so that the amount of water in the porous inorganic particle layer can be made extremely low.
  • a non-aqueous electrolyte secondary battery having excellent storage characteristics and cycle characteristics can be produced.
  • the solvent from which a binder is hard to elute to an inorganic particle layer can be selected.
  • a highly hydrophobic binder is used in preparing the positive electrode active material mixture slurry, such as PVdF used in the above examples, the binder (PVdF) is eluted into the inorganic particle layer.
  • PVdF highly hydrophobic binder
  • an inorganic particle slurry is used using a non-aqueous solvent. Is preferably prepared.
  • Examples of the method of applying the inorganic particle slurry on the surface of the positive electrode mixture layer include a die coating method, a gravure coating method, a dip coating method, a curtain coating method, and a spray coating method.
  • the inorganic particle slurry can be continuously formed in a thin and uniform thickness, so that a positive electrode for a non-aqueous electrolyte secondary battery of uniform quality can be continuously manufactured. Become.
  • the charging voltage of the battery is 4.4 V on the basis of lithium
  • the charging voltage of the positive electrode is 4.5 V on the basis of lithium
  • the charging voltage of the positive electrode is 4.4 V on the basis of lithium. If it is above, the same effect is produced. However, if the charging voltage of the positive electrode exceeds 4.6 V on the basis of lithium, the oxidative decomposition of the nonaqueous electrolyte becomes severe and the positive electrode active material tends to deteriorate, so the charging voltage is 4.4 V or more on the basis of lithium. It is preferable that it is 6V or less.

Abstract

[Problem] To provide: a positive electrode for nonaqueous electrolyte secondary batteries, which is capable of improving storage characteristics and cycle characteristics in a high-temperature high-voltage state; a method for producing the positive electrode for nonaqueous electrolyte secondary batteries; and a nonaqueous electrolyte secondary battery which is provided with the positive electrode. [Solution] A positive electrode for nonaqueous electrolyte secondary batteries, which is provided with: a positive electrode mixture layer that contains a position electrode active material, a conductive agent and a binder; and a porous inorganic particle layer that is formed on the surface of the positive electrode mixture layer. The porous inorganic particle layer contains at least one substance that is selected from among sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate and disodium hydrogen phosphate.

Description

非水電解質二次電池用正極、その製造方法及び非水電解質二次電池Non-aqueous electrolyte secondary battery positive electrode, manufacturing method thereof, and non-aqueous electrolyte secondary battery
　本発明は、非水電解質二次電池用正極、その製造方法及び非水電解質二次電池に関し、特に高温高電圧状態での保存特性及びサイクル特性を向上することのできる非水電解質二次電池用正極、その製造方法及びその正極を備えた非水電解質二次電池に関する。 The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery, and particularly for a non-aqueous electrolyte secondary battery capable of improving storage characteristics and cycle characteristics in a high temperature and high voltage state. The present invention relates to a positive electrode, a manufacturing method thereof, and a nonaqueous electrolyte secondary battery including the positive electrode.
　今日の携帯電話機、携帯型パーソナルコンピューター、携帯型音楽プレイヤー等の携帯型電子機器の駆動電源として、更には、ハイブリッド電気自動車（ＨＥＶ）や電気自動車（ＥＶ）用の電源として、高エネルギー密度を有し、高容量であるリチウムイオン二次電池に代表される非水電解質二次電池が広く利用されている。 It has high energy density as a driving power source for portable electronic devices such as today's mobile phones, portable personal computers, portable music players, and also as a power source for hybrid electric vehicles (HEV) and electric vehicles (EV). However, non-aqueous electrolyte secondary batteries represented by high-capacity lithium ion secondary batteries are widely used.
　これらの非水電解質二次電池の正極活物質としては、リチウムイオンを可逆的に吸蔵・放出することが可能なＬｉＭＯ２（但し、ＭはＣｏ、Ｎｉ、Ｍｎの少なくとも１種である）で表されるリチウム遷移金属複合酸化物、すなわち、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＮｉｙＣｏ１－ｙＯ２（ｙ＝０．０１～０．９９）、ＬｉＭｎＯ２、ＬｉＣｏｘＭｎｙＮｉｚＯ２（ｘ＋ｙ＋ｚ＝１）や、ＬｉＭｎ２Ｏ４又はＬｉＦｅＰＯ４などが一種単独もしくは複数種を混合して用いられている。また、負極活物質としては、黒鉛等の炭素材料や、Ｓｉ又はＳｎ等のリチウムと合金化する材料などが用いられている。 The positive electrode active material of these nonaqueous electrolyte secondary batteries is represented by LiMO 2 (where M is at least one of Co, Ni, and Mn) capable of reversibly occluding and releasing lithium ions. Lithium transition metal composite oxides, that is, LiCoO 2 , LiNiO 2 , LiNi y Co 1-y O 2 (y = 0.01 to 0.99), LiMnO 2 , LiCo x Mn y Ni z O 2 (x + y + z) = 1) and, like LiMn 2 O 4 or LiFePO 4 is used as a mixture of one kind alone or in combination. In addition, as the negative electrode active material, a carbon material such as graphite or a material alloyed with lithium such as Si or Sn is used.
　このうち、特に各種電池特性が他のものに対して優れていることから、リチウムコバルト複合酸化物や異種金属元素添加リチウムコバルト複合酸化物が多く使用されている。しかしながら、コバルトは高価であると共に資源としての存在量が少ない。そのため、これらのリチウムコバルト複合酸化物や異種金属元素添加リチウムコバルト複合酸化物を非水電解質二次電池の正極活物質として使用し続けるには非水電解質二次電池のさらなる高性能化が望まれている。 Of these, lithium-cobalt composite oxides and heterogeneous metal element-added lithium-cobalt composite oxides are often used because various battery characteristics are superior to others. However, cobalt is expensive and has a small abundance as a resource. Therefore, in order to continue using these lithium cobalt composite oxides and lithium cobalt composite oxides containing different metal elements as positive electrode active materials for non-aqueous electrolyte secondary batteries, further enhancement of the performance of non-aqueous electrolyte secondary batteries is desired. ing.
　特に、近年の移動情報端末における動画再生、ゲーム機能といった娯楽機能の充実に伴う消費電力の増大化及びＨＥＶやＥＶの長時間駆動の要望から、非水電解質二次電池のさらなる高容量化が要求されている。このようなリチウムコバルト複合酸化物を正極活物質として用いた非水電解質二次電池の高容量化の手段の一つとして、充電終止電圧を従来の一般的に採用されていたリチウム基準で４．３Ｖから、４．６Ｖ程度まで引き上げる方法が知られている。 In particular, non-aqueous electrolyte secondary batteries are required to have higher capacities due to demands for increased power consumption and long-term driving of HEVs and EVs with enhancement of entertainment functions such as video playback and game functions in recent mobile information terminals. Has been. As one means for increasing the capacity of a non-aqueous electrolyte secondary battery using such a lithium cobalt composite oxide as a positive electrode active material, the end-of-charge voltage is 4. A method of raising the voltage from 3V to about 4.6V is known.
　しかしながら、充電終止電圧を引き上げた非水電解質二次電池では、正極活物質の酸化力が高まり、電解液の分解やリチウム塩の分解、セパレータの酸化反応が加速される現象が見られる。 However, in a nonaqueous electrolyte secondary battery in which the end-of-charge voltage is raised, the oxidizing power of the positive electrode active material is increased, and a phenomenon in which the decomposition of the electrolytic solution, the decomposition of the lithium salt, and the oxidation reaction of the separator are accelerated.
　特に高温環境下においては、上記の副反応が起こりやすく、サイクル特性や保存特性といった電池性能が大きく損なわれる。また、セパレータの酸化反応（脱水素化反応）によって、セパレータの突き刺し強度や引っ張り強度が低下し、セパレータが本来担うべき絶縁機能やシャットダウン機能が損なわれ、電池の信頼性が低下してしまう。 Especially in a high temperature environment, the above side reaction is likely to occur, and battery performance such as cycle characteristics and storage characteristics is greatly impaired. Further, the oxidization reaction (dehydrogenation reaction) of the separator reduces the piercing strength and tensile strength of the separator, impairing the insulating function and shutdown function that the separator should originally perform, and lowering the reliability of the battery.
　また、非水電解質二次電池の高容量化の方法として、充電終止電圧の引き上げとは別に、正極活物質及び負極活物質の充填密度を高くすることも考えられるが、正極活物質や負極活物質の充填密度を高くした場合には、電解液の浸透性が悪化し、電極反応が不均一となるため、部分的に正極の充電電圧が高くなり、結果的に上記の副反応が促進されて、やはり電池の性能及び信頼性の低下が生じてしまう。 Further, as a method for increasing the capacity of the nonaqueous electrolyte secondary battery, it is conceivable to increase the packing density of the positive electrode active material and the negative electrode active material separately from raising the end-of-charge voltage. When the packing density of the substance is increased, the electrolyte permeability deteriorates and the electrode reaction becomes non-uniform, so the charging voltage of the positive electrode is partially increased, resulting in the promotion of the above side reaction. As a result, the performance and reliability of the battery are deteriorated.
　このような課題に対して、例えば下記特許文献１や下記特許文献２には、正極合剤層表面に多孔質無機粒子層を形成することで、これらの副反応を抑制する技術が開示されている。また、下記特許文献３には、正極合剤層中にリン酸アルカリ金属塩を含有させることで高温状態での保存特性及びサイクル特性を向上させたリチウムイオン二次電池の発明が開示されている。 In response to such problems, for example, Patent Document 1 and Patent Document 2 below disclose a technique for suppressing these side reactions by forming a porous inorganic particle layer on the surface of the positive electrode mixture layer. Yes. Patent Document 3 listed below discloses an invention of a lithium ion secondary battery in which high-temperature storage characteristics and cycle characteristics are improved by including an alkali metal phosphate in the positive electrode mixture layer. .
特開２００７－１３４２７９号公報JP 2007-134279 A 特開２００９－３０２００９号公報JP 2009-302009 A 特開２００７－２２０３３５号公報JP 2007-220335 A
　しかしながら、上記特許文献１及び２に記載されている非水電解質二次電池では、正極合剤層の表面に多孔質無機粒子層を形成することで、高電圧状態での保存特性及びサイクル特性の向上はある程度達成されるものの、特に高温環境下においてはその効果はまだまだ不充分なものであり、さらなる改善の余地を有する。また、上記特許文献３に記載されている非水電解質二次電池では、充分な効果を達成するためにはリン酸アルカリ金属塩を正極活物質に対して少なくとも１質量％も添加する必要があるため、リン酸アルカリ金属塩を混合した分だけ電池容量が低下するという課題が存在する。なお、上記特許文献３に記載されている非水電解質二次電池の正極では、正極合剤層の表面に多孔質無機粒子層は形成されていない。 However, in the non-aqueous electrolyte secondary battery described in Patent Documents 1 and 2, the porous inorganic particle layer is formed on the surface of the positive electrode mixture layer, so that the storage characteristics and cycle characteristics in a high voltage state are improved. Although improvement is achieved to some extent, the effect is still insufficient particularly in a high temperature environment, and there is room for further improvement. In the nonaqueous electrolyte secondary battery described in Patent Document 3, it is necessary to add at least 1% by mass of an alkali metal phosphate to the positive electrode active material in order to achieve a sufficient effect. Therefore, there is a problem that the battery capacity is reduced by the amount of alkali metal phosphate mixed. In the positive electrode of the non-aqueous electrolyte secondary battery described in Patent Document 3, no porous inorganic particle layer is formed on the surface of the positive electrode mixture layer.
　本発明は、上記のような従来技術の問題点を解決すべく開発されたものであり、充電終止電圧をリチウム基準で４．３Ｖを超えるような高電圧としても、高温環境下における充電保存後の容量及び充放電サイクル特性の向上した非水電解質二次電池用正極、その製造方法及びその正極を備えた非水電解質二次電池を提供することを目的とする。 The present invention has been developed to solve the above-described problems of the prior art. Even when the charge end voltage exceeds 4.3 V on the basis of lithium, the present invention has been developed after charge storage in a high temperature environment. An object of the present invention is to provide a positive electrode for a nonaqueous electrolyte secondary battery with improved capacity and charge / discharge cycle characteristics, a method for producing the same, and a nonaqueous electrolyte secondary battery including the positive electrode.
　上記目的を達成するため、本発明の非水電解質二次電池用正極は、正極芯体の表面に形成された正極活物質を含む正極合剤層と、前記正極合剤層の表面に形成された多孔質無機粒子層とを備えた非水電解質二次電池用正極において、前記多孔質無機粒子層は、ヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムから選択される少なくとも１種からなるリン酸ナトリウム塩を含有することを特徴とする。 In order to achieve the above object, a positive electrode for a non-aqueous electrolyte secondary battery according to the present invention is formed on a surface of a positive electrode mixture layer including a positive electrode active material formed on the surface of a positive electrode core and the positive electrode mixture layer. In the positive electrode for a non-aqueous electrolyte secondary battery provided with a porous inorganic particle layer, the porous inorganic particle layer is selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate It contains at least one sodium phosphate salt.
　本発明に係る非水電解質二次電池用正極においては、正極合剤層の表面に無機粒子層が形成されているため、正極表面における非水電解質の酸化分解物は、この無機粒子層によってトラップされるので、負極での堆積を抑制することができる。 In the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, an inorganic particle layer is formed on the surface of the positive electrode mixture layer. Therefore, the oxidative decomposition product of the non-aqueous electrolyte on the positive electrode surface is trapped by this inorganic particle layer. Therefore, deposition on the negative electrode can be suppressed.
　さらに、本発明に係る非水電解質二次電池用正極では、無機粒子層中にヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムより選択される少なくとも１種のリン酸ナトリウム塩が含まれている。非水電解質二次電池は、製造工程中からの微量の水分の混入はどうしても避けられないものである。また、高充電電圧下では、非水電解液の分解によって水分が生じる。微量水分が電池内に存在すると、電解質としての例えばＬｉＰＦ６等のリチウム塩の加水分解反応が生じ、それに伴ってフッ酸が発生し、このフッ酸によって正極活物質が腐食されるため、本来の充放電機能を発揮することができなくなる。 Furthermore, in the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, at least one sodium phosphate selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate in the inorganic particle layer. Contains salt. The nonaqueous electrolyte secondary battery is inevitably mixed with a trace amount of water from the manufacturing process. Moreover, under high charging voltage, moisture is generated by the decomposition of the non-aqueous electrolyte. When a minute amount of moisture is present in the battery, a hydrolysis reaction of a lithium salt such as LiPF 6 as an electrolyte occurs, and hydrofluoric acid is generated along with it, and the positive electrode active material is corroded by this hydrofluoric acid. The charge / discharge function cannot be exhibited.
　しかしながら、無機粒子層中にリン酸ナトリウム塩が含まれていると、これらのリン酸ナトリウム塩と水分との間の反応速度が電解質としてのリチウム塩と水分との間の反応速度よりも早いので、電解質としてのリチウム塩の分解反応を抑制することができる。しかも、無機粒子層中にリン酸ナトリウム塩を含有させると、従来例のように正極活物質合剤層中にリン酸ナトリウム塩を含有させた場合よりもリン酸ナトリウム塩と非水電解質溶液中の水分とが接触しやすくなる。そのため、本発明の非水電解質二次電池用正極を用いて非水電解質二次電池を作製すれば、充電終止電圧をリチウム基準で４．４Ｖ以上４．６Ｖ以下と高くした状態でかつ高温環境下におかれた場合でも、従来例の非水電解質二次電池用正極を用いた場合よりも、保存特性及びサイクル特性共に非常に優れたものとなる。 However, if the inorganic particle layer contains sodium phosphate salt, the reaction rate between these sodium phosphate salt and moisture is faster than the reaction rate between lithium salt as electrolyte and moisture. The decomposition reaction of the lithium salt as the electrolyte can be suppressed. Moreover, when the sodium phosphate salt is included in the inorganic particle layer, the sodium phosphate salt and the non-aqueous electrolyte solution are more contained in the positive electrode active material mixture layer than in the case of including the sodium phosphate salt as in the conventional example. It becomes easy to come into contact with moisture. Therefore, if a nonaqueous electrolyte secondary battery is produced using the positive electrode for a nonaqueous electrolyte secondary battery according to the present invention, the charge end voltage is set to a high level of 4.4 V or more and 4.6 V or less on a lithium basis, and a high temperature environment. Even when placed underneath, both the storage characteristics and the cycle characteristics are much better than when the positive electrode for a nonaqueous electrolyte secondary battery of the conventional example is used.
　なお、本発明の非水電解質二次電池用正極においては、多孔質無機粒子層中に含まれるリン酸ナトリウム塩の含有量を、正極活物質合剤量に対して０．０３質量％以上１．０質量％以下とすることが好ましい。リン酸ナトリウム塩の含有が０．０３質量％未満であると上記効果が奏され難くなり、１．０質量％を越えるとその分だけ電池外装缶内に充填することができる正極活物質合剤量が減少するため、単位体積当たり充電容量が減少するために好ましくない。 In the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, the content of sodium phosphate contained in the porous inorganic particle layer is set to 0.03% by mass or more to 1% by mass of the positive electrode active material mixture. It is preferable to make it 0.0 mass% or less. When the content of sodium phosphate salt is less than 0.03% by mass, the above effect is hardly achieved, and when it exceeds 1.0% by mass, the positive electrode active material mixture that can be filled in the battery outer can by that much Since the amount decreases, the charge capacity per unit volume decreases, which is not preferable.
　また、前記多孔質無機粒子層に含まれる無機粒子としては、酸化チタン（ＴｉＯ２）、酸化アルミニウム（Ａｌ２Ｏ３）、酸化ケイ素（ＳｉＯ２）、酸化ジルコニウム（ＺｒＯ２）より選択される少なくとも１種を用いることができ、電池内での安定性、リチウムとの反応性やコストを考慮すれば、酸化アルミニウム及びルチル型の酸化チタンが特に好ましい。 The inorganic particles contained in the porous inorganic particle layer are at least selected from titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), silicon oxide (SiO 2 ), and zirconium oxide (ZrO 2 ). One kind can be used, and aluminum oxide and rutile type titanium oxide are particularly preferable in consideration of stability in the battery, reactivity with lithium, and cost.
　なお、前記無機粒子の平均粒子径としては、１μｍ以下のものが好ましく、さらに好ましくは０．１～０．８μｍの範囲内のものである。また、平均粒子径は、非水電解質二次電池に用いられるセパレータの平均孔径よりも大きいことが好ましい。セパレータの平均孔径よりも無機粒子の平均粒子径を大きくすることにより、より効果的にセパレータへのダメージを軽減し、セパレータの微多孔内に無機粒子が侵入するのを抑制することができる。 The average particle diameter of the inorganic particles is preferably 1 μm or less, and more preferably in the range of 0.1 to 0.8 μm. Moreover, it is preferable that an average particle diameter is larger than the average hole diameter of the separator used for a nonaqueous electrolyte secondary battery. By making the average particle diameter of the inorganic particles larger than the average pore diameter of the separator, it is possible to more effectively reduce damage to the separator and to prevent the inorganic particles from entering the micropores of the separator.
　さらに、上記目的を達成するため、本発明の非水電解質二次電池用正極の製造方法は、正極芯体の表面に正極合剤層を形成する工程と、前記正極合剤層の表面に多孔質無機粒子層を形成する工程と、を有する非水電解質二次電池用正極の製造方法において、前記多孔質無機粒子層を形成する工程を、無機粒子とヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムから選択される少なくとも１種からなるリン酸ナトリウム塩とを含有するスラリーをグラビアコート法によって塗布した後、乾燥することによって行うことを特徴とする。 Furthermore, in order to achieve the above object, the method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to the present invention includes a step of forming a positive electrode mixture layer on the surface of the positive electrode core, and a porous material on the surface of the positive electrode mixture layer. And forming the porous inorganic particle layer in the method for producing a positive electrode for a non-aqueous electrolyte secondary battery having a step of forming a porous inorganic particle layer, and the step of forming the porous inorganic particle layer includes: inorganic particles, sodium hexametaphosphate, sodium pyrophosphate, phosphoric acid A slurry containing at least one sodium phosphate selected from trisodium and disodium hydrogen phosphate is applied by a gravure coating method and then dried.
　本発明の非水電解質二次電池用正極の製造方法では、正極芯体の表面に正極合剤層を形成した後に、この正極合剤層の表面に無機粒子とリン酸ナトリウム塩とを含有するスラリーをグラビアコート法で塗布した後、乾燥することによって形成している。このような方法を採用すると、正極合剤層の表面に無機粒子とリン酸ナトリウム塩とを含有するスラリーを薄く、均一の厚さで連続的に形成できるようになる。そのため、本発明の非水電解質二次電池用正極の製造方法によれば、均一な品質の非水電解質二次電池用正極を連続的に製造できるようになり、充電終止電圧をリチウム基準で４．４Ｖ以上４．６Ｖ以下と高くした状態でかつ高温環境下におかれた場合でも保存特性及びサイクル特性が優れた非水電解質二次電池の製造効率が向上する。 In the method for producing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention, after forming a positive electrode mixture layer on the surface of the positive electrode core body, the surface of the positive electrode mixture layer contains inorganic particles and sodium phosphate salt. The slurry is applied by a gravure coating method and then dried. When such a method is employed, a slurry containing inorganic particles and sodium phosphate salt is thinly formed on the surface of the positive electrode mixture layer, and can be continuously formed with a uniform thickness. Therefore, according to the method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention, it becomes possible to continuously manufacture a positive electrode for a non-aqueous electrolyte secondary battery having a uniform quality, and the end-of-charge voltage is 4 based on lithium. The production efficiency of a nonaqueous electrolyte secondary battery having excellent storage characteristics and cycle characteristics is improved even when placed in a high temperature environment of .4 V or more and 4.6 V or less.
　なお、本発明の非水電解質二次電池用正極の製造方法においては、無機粒子とヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムから選択される少なくとも１種からなるリン酸ナトリウム塩とを含有する無機粒子スラリーを調整する際には、正極活物質合剤層に含まれる結着剤の種類に応じて、溶媒を選択することが好ましい。 In the method for producing a positive electrode for a non-aqueous electrolyte secondary battery of the present invention, phosphorous comprising at least one selected from inorganic particles and sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate. When adjusting the inorganic particle slurry containing an acid sodium salt, it is preferable to select a solvent according to the type of the binder contained in the positive electrode active material mixture layer.
　例えば、正極合剤層に含まれる結着剤が疎水性物質である場合は、無機粒子スラリーを調製する際に用いる溶媒としては、水系溶媒を用いることが好ましく、また、正極合剤層に含まれる結着剤が親水性物質である場合は、非水系溶媒を用いることが好ましい。このように溶媒を選択することで、正極活物質合剤層に含まれる結着剤が無機粒子層中へ溶出することを抑制することが可能となる。 For example, when the binder contained in the positive electrode mixture layer is a hydrophobic substance, it is preferable to use an aqueous solvent as the solvent used when preparing the inorganic particle slurry, and also included in the positive electrode mixture layer. When the binder to be used is a hydrophilic substance, it is preferable to use a non-aqueous solvent. Thus, by selecting a solvent, it becomes possible to suppress that the binder contained in a positive electrode active material mixture layer elutes into an inorganic particle layer.
　以下、本願発明を実施するための形態を実施例及び比較例を用いて詳細に説明する。但し、以下に示す実施例は、本発明の技術思想を具体化するための非水電解質二次電池用正極の一例を示すものであって、本発明をこの実施例に限定することを意図するものではなく、本発明は特許請求の範囲に示した技術思想を逸脱することなく種々の変更を行ったものにも均しく適用し得るものである。 Hereinafter, modes for carrying out the present invention will be described in detail using examples and comparative examples. However, the following examples show one example of a positive electrode for a non-aqueous electrolyte secondary battery for embodying the technical idea of the present invention, and are intended to limit the present invention to this example. Instead, the present invention can be equally applied to various changes made without departing from the technical idea shown in the claims.
　最初に、実施例１～６及び比較例１～５の非水電解質二次電池の具体的製造方法について説明する。
［正極極板の作製］
　［正極活物質の作製］
　出発原料としてのリチウム源には炭酸リチウム（Ｌｉ２ＣＯ３）を用いた。コバルト源には、炭酸コバルトを５５０℃で焼成し、熱分解反応によって得られた四酸化三コバルト（Ｃｏ３Ｏ４）を用いた。これらをリチウムとコバルトのモル比が１：１になるように秤量した。その後乳鉢で混合し、これを空気雰囲気下において８５０℃で２０時間焼成し、コバルト酸リチウムを得た。これを乳鉢で平均粒径１５μｍまで粉砕して、各実施例及び比較例で用いる正極活物質としてのコバルト酸リチウム粉末を得た。 First, specific manufacturing methods of the nonaqueous electrolyte secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 5 will be described.
[Preparation of positive electrode plate]
[Preparation of positive electrode active material]
Lithium carbonate (Li 2 CO 3 ) was used as a lithium source as a starting material. As the cobalt source, tricobalt tetroxide (Co 3 O 4 ) obtained by calcining cobalt carbonate at 550 ° C. and thermal decomposition reaction was used. These were weighed so that the molar ratio of lithium to cobalt was 1: 1. Then, it mixed with the mortar, this was baked at 850 degreeC for 20 hours in air atmosphere, and lithium cobaltate was obtained. This was ground to an average particle size of 15 μm with a mortar to obtain lithium cobaltate powder as a positive electrode active material used in each example and comparative example.
　［正極合剤層の形成］
　上記のコバルト酸リチウム粉末が９６質量部、導電材としての炭素粉末が２質量部、結着剤としてのポリフッ化ビニリデン（ＰＶｄＦ）粉末が２質量部となるよう混合し，これをＮ－メチルピロリドン（ＮＭＰ）溶液と混合して正極活物質合剤スラリーを調製した。このスラリーを厚さ１５μｍのアルミニウム製の正極芯体の両面にドクターブレード法により、正極芯体の一方の面の塗布部分が２７７ｍｍ、未塗布部分が５７ｍｍ、他方の面の塗布部分が２０８ｍｍ、未塗布部分が１２６ｍｍとなるように塗布した後、乾燥機中を通過させることによりＮＭＰを乾燥除去した。なお、正極活物質合剤の塗布量は乾燥後の単位面積当たりの質量で、片面塗布部で２１．２ｍｇ／ｃｍ２、両面塗布部で４２．４ｍｇ／ｃｍ２とした。次いで、圧縮ローラーを用いて両面塗布部分の厚みが１３２μｍになるように圧縮することで、正極芯体の両面に正極合剤層を形成した。 [Formation of positive electrode mixture layer]
The above lithium cobaltate powder was mixed to 96 parts by mass, carbon powder as a conductive material to 2 parts by mass, and polyvinylidene fluoride (PVdF) powder as a binder to 2 parts by mass, and this was mixed with N-methylpyrrolidone. A positive electrode active material mixture slurry was prepared by mixing with (NMP) solution. This slurry was applied to both surfaces of a positive electrode core made of aluminum having a thickness of 15 μm by a doctor blade method. The coated portion on one surface of the positive electrode core was 277 mm, the uncoated portion was 57 mm, the coated portion on the other surface was 208 mm, After coating so that the coated portion was 126 mm, NMP was removed by drying by passing through a dryer. The coating amount of the positive electrode active material mixture in mass per unit area after drying, 21.2 mg / cm 2 in the single-side coating unit, was 42.4 mg / cm 2 in both the coating portion. Subsequently, the positive electrode mixture layer was formed on both surfaces of the positive electrode core body by compressing using a compression roller so that the thickness of the double-side coated portion was 132 μm.
　［無機粒子スラリーの調製］
　無機粒子としての酸化アルミニウム（Ａｌ２Ｏ３）３０質量％と、カルボキシメチルセルロース（ＣＭＣ）０．１５質量％と、純水６９．８５質量％とを混合し、混練機（ＰＲＩＭＩＸ社製ＴＫハイピスミクス）にて混練した後、得られたスラリーをビーズミル（浅田鉄工製ナノミル分散装置）にて分散させて、リン酸塩を含まない無機粒子スラリーを得た。分散条件は、内容積：０．３Ｌ、ビーズ径：０．５φ、スリット：０．１５ｍｍ、ビーズ充填量：９０％、周速４０Ｈｚ、処理流量：１．０ｋｇ／ｍｉｎとした。なお、酸化アルミニウムとしては、ＡＫ３０００（商品名：住友化学株式会社製）を用いた。また、ＣＭＣについては、ダイセル化学工業株式会社製１３８０を用いた。 [Preparation of inorganic particle slurry]
30% by mass of aluminum oxide (Al 2 O 3 ) as inorganic particles, 0.15% by mass of carboxymethylcellulose (CMC), and 69.85% by mass of pure water are mixed, and a kneader (TK High-Pixics manufactured by PRIMIX) After kneading, the obtained slurry was dispersed with a bead mill (Nanomill dispersing device manufactured by Asada Tekko) to obtain an inorganic particle slurry containing no phosphate. The dispersion conditions were as follows: internal volume: 0.3 L, bead diameter: 0.5φ, slit: 0.15 mm, bead filling amount: 90%, peripheral speed 40 Hz, treatment flow rate: 1.0 kg / min. As aluminum oxide, AK3000 (trade name: manufactured by Sumitomo Chemical Co., Ltd.) was used. Moreover, about CMC, Daicel Chemical Industries 1380 was used.
　次いで、無機粒子スラリーに酸化アルミニウムに対して３．７５質量％のバインダー（アクリルゴム系バインダー）を加え、更にリン酸塩としてのヘキサメタリン酸ナトリウムをスラリー固形分全量の３３質量％となるように加えた。その後、最終的にスラリー総量に対する酸化アルミニウムの割合が３０質量％となるように純水を加え、再度上述の混練機にて混練することにより、各実施例で用いるリン酸塩含有無機粒子スラリーを調製した。 Subsequently, 3.75 mass% binder (acrylic rubber-type binder) is added with respect to aluminum oxide to an inorganic particle slurry, Furthermore, sodium hexametaphosphate as a phosphate is added so that it may become 33 mass% of slurry solid content whole quantity. It was. Thereafter, by adding pure water so that the ratio of aluminum oxide to the total amount of the slurry is finally 30% by mass, and kneading again with the above kneader, the phosphate-containing inorganic particle slurry used in each example is obtained. Prepared.
　［多孔質無機粒子層の形成］
　正極芯体の両面に形成された正極合剤層を、上述のようにして得られたリン酸塩含有無機粒子スラリーでグラビアコート法により塗布して被覆することで、正極合剤層の表面に多孔質無機粒子層を形成して、実施例１で用いる正極極板とした。なお、リン酸塩含有無機粒子スラリーの塗布量は、正極活物質合剤（固形分）に対してリン酸塩含有無機粒子スラリーの固形分換算で1質量％とした。この場合、正極のヘキサメタリン酸ナトリウム含有量は、正極活物質合剤（固形分）に対して０．３３質量％となる。 [Formation of porous inorganic particle layer]
The positive electrode mixture layer formed on both surfaces of the positive electrode core is coated and coated on the surface of the positive electrode mixture layer with the phosphate-containing inorganic particle slurry obtained as described above by the gravure coating method. A porous inorganic particle layer was formed to obtain a positive electrode plate used in Example 1. The coating amount of the phosphate-containing inorganic particle slurry was 1% by mass in terms of solid content of the phosphate-containing inorganic particle slurry with respect to the positive electrode active material mixture (solid content). In this case, the sodium hexametaphosphate content of the positive electrode is 0.33% by mass with respect to the positive electrode active material mixture (solid content).
［負極極板の作製］
　負極活物質としての黒鉛９７．５質量部と、増粘剤としてのＣＭＣ１．０質量部と、結着剤としてのスチレンブタジエンゴム（ＳＢＲ）１．５質量部と、適量の水とを混合して負極活物質合剤スラリーとした。このスラリーを厚さ１０μｍの銅製の負極芯体の両面にドクターブレード法により、一方の面の塗布部分が２８４ｍｍ、未塗布部分が１８ｍｍ、他方の面の塗布部分が２２６ｍｍ、未塗布部分が７３ｍｍとなるように塗布した。負極活物質合剤の塗布量は、乾燥後の単位面積当たり質量で、片面の塗布質量で１１．３ｍｇ／ｃｍ２とした。その後、乾燥機中を通過させて乾燥することにより、負極芯体の両面に負極活物質層を形成した。次いで圧縮ローラーを用いて両面塗布部分の厚みが１５５μｍとなるように圧縮することで、各実施例及び比較例で用いる負極極板とした。 [Production of negative electrode plate]
Mix 97.5 parts by mass of graphite as a negative electrode active material, 1.0 part by mass of CMC as a thickener, 1.5 parts by mass of styrene butadiene rubber (SBR) as a binder, and an appropriate amount of water. Thus, a negative electrode active material mixture slurry was obtained. This slurry was applied to both surfaces of a copper negative electrode core having a thickness of 10 μm by a doctor blade method. The coated portion on one surface was 284 mm, the uncoated portion was 18 mm, the coated portion on the other surface was 226 mm, and the uncoated portion was 73 mm. It applied so that it might become. The coating amount of the negative electrode active material mixture was the mass per unit area after drying, and the coating mass on one side was 11.3 mg / cm 2 . Then, the negative electrode active material layer was formed on both surfaces of the negative electrode core by passing through a dryer and drying. Subsequently, it was set as the negative electrode plate used by each Example and a comparative example by compressing so that the thickness of a double-sided application part might be 155 micrometers using a compression roller.
　なお、充電時の黒鉛の電位はＬｉ基準で約０．１Ｖである。また、正極及び負極の活物質充填量は、設計基準となる正極活物質の電位において、正極と負極の充電容量比（負極充電容量／正極充電容量）が１．０～１．１となるように調整した。 Note that the potential of graphite at the time of charging is about 0.1 V with respect to Li. The positive electrode and negative electrode active material filling amount is such that the charge capacity ratio of the positive electrode to the negative electrode (negative electrode charge capacity / positive electrode charge capacity) is 1.0 to 1.1 at the potential of the positive electrode active material as a design standard. Adjusted.
［非水電解液の調製］
　エチレンカーボネート（ＥＣ）３０体積％とメチルエチルカーボネート（ＭＥＣ）７０体積％との混合溶媒にヘキサフルオロリン酸リチウム（ＬｉＰＦ６）を１ｍｏｌ／Ｌになるように溶解、その後ビニレンカーボネート（ＶＣ）を１質量％添加することで、各実施例及び比較例で用いる非水電解液を調製した。 [Preparation of non-aqueous electrolyte]
Lithium hexafluorophosphate (LiPF 6 ) is dissolved in a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of methyl ethyl carbonate (MEC) to 1 mol / L, and then vinylene carbonate (VC) is 1 The non-aqueous electrolyte solution used by each Example and a comparative example was prepared by adding the mass%.
［電極体の作製］
　上記得られた正極極板にはアルミニウム製のリード線を、上記得られた負極極板にはニッケル製のリード線を溶接固定した後、正極極板及び負極極板をポリエチレン製微多孔膜から成るセパレータを介して扁平型に巻回して渦巻状の電極体を作製した。 [Production of electrode body]
An aluminum lead wire is welded and fixed to the obtained positive electrode plate, and a nickel lead wire is welded and fixed to the obtained negative electrode plate, and then the positive electrode plate and the negative electrode plate are made of a polyethylene microporous film. A spiral electrode body was produced by winding it in a flat shape through a separator.
［電池の作製］
　上記得られた電極体をラミネート容器に封入し、Ａｒを満たしたグローブボックス内で上記得られた非水電解液を注液した。その後、注液口を塞いでラミネート電池を作製し、実施例１に係る非水電解質二次電池とした。なお、得られた非水電解質二次電池の設計容量は８００ｍＡｈである。 [Production of battery]
The obtained electrode body was sealed in a laminate container, and the obtained nonaqueous electrolytic solution was injected in a glove box filled with Ar. Thereafter, the injection hole was closed to produce a laminate battery, and a nonaqueous electrolyte secondary battery according to Example 1 was obtained. The design capacity of the obtained non-aqueous electrolyte secondary battery is 800 mAh.
［実施例２及び３］
　無機粒子スラリーの調製工程において、無機粒子スラリーへのヘキサメタリン酸ナトリウムの添加量を変更した以外は、実施例１と同様にラミネート電池を作製して実施例２及び３に係る非水電解質二次電池とした。 [Examples 2 and 3]
A non-aqueous electrolyte secondary battery according to Examples 2 and 3 was prepared by producing a laminated battery in the same manner as in Example 1 except that the amount of sodium hexametaphosphate added to the inorganic particle slurry was changed in the inorganic particle slurry preparation step. It was.
　すなわち、ヘキサメタリン酸ナトリウムの含有量が、スラリー固形分全量に対して３．３質量％（実施例２）及び５０質量％（実施例３）であるリン酸塩含有無機粒子スラリーを、正極合剤層の表面に塗布することで得られる正極極板をそれぞれ用いて実施例２及び３に係る非水電解質二次電池を作製した。正極のヘキサメタリン酸ナトリウム含有量は、正極活物質合剤（固形分）に対して、０．０３質量％（実施例２）及び０．５質量％（実施例３）である。 That is, a phosphate-containing inorganic particle slurry in which the content of sodium hexametaphosphate is 3.3% by mass (Example 2) and 50% by mass (Example 3) with respect to the total amount of slurry solids is mixed with the positive electrode mixture. The nonaqueous electrolyte secondary battery which concerns on Example 2 and 3 was produced using the positive electrode plate obtained by apply | coating to the surface of a layer, respectively. The sodium hexametaphosphate content of the positive electrode is 0.03% by mass (Example 2) and 0.5% by mass (Example 3) with respect to the positive electrode active material mixture (solid content).
［実施例４～６］
　無機粒子スラリーの調製工程において、無機粒子スラリーに含有させるリン酸塩の種類を変更した以外は、実施例１と同様にラミネート電池を作製し実施例４～６に係る非水電解質二次電池とした。 [Examples 4 to 6]
A non-aqueous electrolyte secondary battery according to Examples 4 to 6 was prepared in the same manner as in Example 1 except that the kind of phosphate contained in the inorganic particle slurry was changed in the preparation process of the inorganic particle slurry. did.
　すなわち、無機粒子スラリーに添加するリン酸塩を、ピロリン酸ナトリウム（実施例４）、リン酸三ナトリウム（実施例５）ないしリン酸水素二ナトリウム（実施例６）としたリン酸塩含有無機粒子スラリーを、正極合剤層の表面に塗布することで得られる正極極板をそれぞれ用いて、実施例４～６に係る非水電解質二次電池を作製した。なお、無機粒子スラリー中のリン酸塩の含有量は実施例１と同様に３３質量％とし、正極中のリン酸塩含有量は正極活物質合剤（固形分）に対して０．３３質量％である。 That is, phosphate-containing inorganic particles in which the phosphate added to the inorganic particle slurry was sodium pyrophosphate (Example 4), trisodium phosphate (Example 5) or disodium hydrogen phosphate (Example 6). Using the positive electrode plates obtained by applying the slurry to the surface of the positive electrode mixture layer, non-aqueous electrolyte secondary batteries according to Examples 4 to 6 were produced. In addition, content of the phosphate in an inorganic particle slurry shall be 33 mass% similarly to Example 1, and the phosphate content in a positive electrode is 0.33 mass with respect to positive electrode active material mixture (solid content). %.
［比較例１］
　無機粒子スラリーにリン酸塩を加えない点以外は実施例１と同様にしてラミネート電池を作製し、比較例１に係る非水電解質二次電池とした。すなわち、リン酸塩を含まない無機粒子スラリーに、バインダーのみを加えてから混練することで得られるスラリーを、正極合剤層の表面に塗布することで得られる正極極板を用いて、比較例１に係る非水電解質二次電池を作製した。 [Comparative Example 1]
A laminated battery was produced in the same manner as in Example 1 except that phosphate was not added to the inorganic particle slurry, and a nonaqueous electrolyte secondary battery according to Comparative Example 1 was obtained. That is, a comparative example using a positive electrode plate obtained by applying a slurry obtained by kneading after adding only a binder to an inorganic particle slurry not containing phosphate, on the surface of the positive electrode mixture layer A non-aqueous electrolyte secondary battery according to No. 1 was produced.
［比較例２］
　正極極板に多孔質無機粒子層を形成しない点以外は、実施例１と同様にしてラミネート電池を作製し、比較例２に係る非水電解質二次電池とした。すなわち、正極芯体に正極合剤層を形成しただけのものを、正極極板として用いて、比較例２に係る非水電解質二次電池を作製した。 [Comparative Example 2]
A laminated battery was produced in the same manner as in Example 1 except that the porous inorganic particle layer was not formed on the positive electrode plate, and a nonaqueous electrolyte secondary battery according to Comparative Example 2 was obtained. That is, a non-aqueous electrolyte secondary battery according to Comparative Example 2 was manufactured using only a positive electrode mixture layer formed on the positive electrode core as a positive electrode plate.
［比較例３～５］
　実施例１においてヘキサメタリン酸ナトリウムを無機粒子層に含有させた正極極板を用いるのに替えて、ヘキサメタリン酸ナトリウムを正極合剤層に含有させた正極極板を用いて、ラミネート電池を作製して比較例３～５に係る非水電解質二次電池とした。 [Comparative Examples 3 to 5]
Instead of using the positive electrode plate containing sodium hexametaphosphate in the inorganic particle layer in Example 1, a positive electrode plate containing sodium hexametaphosphate in the positive electrode mixture layer was used to produce a laminated battery. Non-aqueous electrolyte secondary batteries according to Comparative Examples 3 to 5 were obtained.
　すなわち、比較例３～５における正極極板は、実施例１における正極活物質合剤スラリーに対して、さらにヘキサメタリン酸ナトリウムを添加し混練して得られるスラリー（リン酸塩含有正極活物質合剤スラリー）を、正極芯体の両面に塗布して正極合剤層を形成した後、リン酸塩を含まない無機粒子スラリーにバインダーのみを加えてから混練することで得られるスラリーを、正極合剤層の表面に塗布することで、無機粒子層を形成して得られる正極極板を用いて、さらに、比較例３～５で用いる正極極板を作製した。ヘキサメタリン酸ナトリウムの添加量は、正極活物質合剤（固形分）に対して、０．０５質量％（比較例３）、０．５質量％（比較例４）及び１．０質量％（比較例５）とした。 That is, the positive electrode plates in Comparative Examples 3 to 5 were obtained by adding sodium hexametaphosphate to the positive electrode active material mixture slurry in Example 1 and kneading them (phosphate-containing positive electrode active material mixture). Slurry) is applied to both surfaces of the positive electrode core to form a positive electrode mixture layer, and then the slurry obtained by kneading after adding only a binder to the inorganic particle slurry containing no phosphate is mixed with the positive electrode mixture. A positive electrode plate used in Comparative Examples 3 to 5 was further produced using a positive electrode plate obtained by forming an inorganic particle layer by coating on the surface of the layer. The amount of sodium hexametaphosphate added was 0.05% by mass (Comparative Example 3), 0.5% by mass (Comparative Example 4), and 1.0% by mass (comparative) with respect to the positive electrode active material mixture (solid content). Example 5).
　上述のようにして作製した各実施例及び比較例の非水電解質二次電池について、それぞれ下記の試験を実施し、高温保存特性及び高温サイクル特性を求めた。結果を表１に纏めて示す。 The non-aqueous electrolyte secondary batteries of Examples and Comparative Examples produced as described above were subjected to the following tests to obtain high temperature storage characteristics and high temperature cycle characteristics. The results are summarized in Table 1.
［高温保存試験］
　高温保存試験における充放電条件は以下のとおりである。
・充電：０．５Ｉｔ（４００ｍＡ）の電流で電池電圧が４．４０Ｖとなるまで定電流充電を行い、その後４．４０Ｖの定電圧で電流が１／２０Ｉｔ（４０ｍＡ）になるまで充電した。
・放電：０．５Ｉｔの電流で電池電圧が３．００Ｖとなるまで定電流放電を行った。
・環境温度：充放電は室温（２５℃）で行った。
　上記の充放電条件で、最初に各電池を充電した後、放電してその時の放電容量を測定して、「高温保存する前の充電容量」として求め、再び充電して６０℃の恒温槽に入れて充電状態のまま１４日間保存した後、恒温層から取り出して室温まで冷却してから放電してその時の放電容量を測定することで「高温保存後の残存容量」を求め、下記の計算式から高温保存後の残存容量率を算出し、高温保存特性として求めた。
　　残存容量率（％）
　　　　＝　（高温保存後の残存容量／高温保存前の充電容量）×１００ [High temperature storage test]
The charge / discharge conditions in the high temperature storage test are as follows.
-Charging: Constant current charging was performed at a current of 0.5 It (400 mA) until the battery voltage reached 4.40 V, and then charging was performed at a constant voltage of 4.40 V until the current became 1/20 It (40 mA).
Discharge: Constant current discharge was performed until the battery voltage reached 3.00 V at a current of 0.5 It.
-Environmental temperature: Charging / discharging was performed at room temperature (25 degreeC).
Under the above charging / discharging conditions, after charging each battery for the first time, discharging and measuring the discharging capacity at that time, obtaining as “charging capacity before storing at high temperature”, charging again into a constant temperature bath of 60 ° C. After charging and storing for 14 days in a charged state, taking out from the thermostatic layer, cooling to room temperature, discharging and measuring the discharge capacity at that time to obtain the “remaining capacity after high temperature storage”, the following formula From the above, the residual capacity ratio after high temperature storage was calculated and obtained as high temperature storage characteristics.
Remaining capacity ratio (%)
= (Remaining capacity after high temperature storage / Charging capacity before high temperature storage) x 100
［高温サイクル試験］
　高温サイクル試験における充放電条件は以下のとおりである。
・充電：０．５Ｉｔの電流で電池電圧が４．４０Ｖとなるまで定電流充電を行い、その後４．４０Ｖの定電圧で電流が１／２０Ｉｔになるまで充電した。
・休止：充電と放電及び放電と充電の間に、１０分間の休止間隔を設けた。
・放電：０．５Ｉｔの電流で電池電圧が３．００Ｖとなるまで定電流放電を行った。
・環境温度：充放電は４５℃の恒温槽中で行った。
　上記の充放電条件で、充放電サイクルを５００回繰り返した。１サイクル目の放電容量及び５００サイクル目の放電容量を測定して、下記の計算式から５００サイクル後の容量維持率を算出して、高温サイクル特性として求めた。
　　容量維持率（％）
　　　　＝　（５００サイクル目の放電容量／１サイクル目の放電容量）×１００ [High-temperature cycle test]
The charge / discharge conditions in the high-temperature cycle test are as follows.
-Charging: Constant current charging was performed until the battery voltage reached 4.40 V at a current of 0.5 It, and then charging was performed until the current became 1/20 It at a constant voltage of 4.40 V.
Pause: A pause of 10 minutes was provided between charging and discharging and discharging and charging.
Discharge: Constant current discharge was performed until the battery voltage reached 3.00 V at a current of 0.5 It.
-Environmental temperature: Charging / discharging was performed in a 45 degreeC thermostat.
The charge / discharge cycle was repeated 500 times under the above charge / discharge conditions. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were measured, and the capacity retention rate after 500 cycles was calculated from the following calculation formula to obtain high temperature cycle characteristics.
Capacity maintenance rate (%)
= (Discharge capacity at 500th cycle / discharge capacity at the first cycle) x 100
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に示した結果から以下のことが分かる。
　すなわち、比較例１は比較例２よりも高温保存特性及び高温サイクル特性が向上しており、正極合剤層の表面に無機粒子層を形成することで、高温保存特性及び高温サイクル特性のある程度の向上が見られることが確認できる。これは、正極合剤層表面に形成された無機粒子層のトラップ効果によりセパレータの酸化反応が抑制されていることを示す。 From the results shown in Table 1, the following can be understood.
That is, Comparative Example 1 has improved high-temperature storage characteristics and high-temperature cycle characteristics as compared with Comparative Example 2. By forming an inorganic particle layer on the surface of the positive electrode mixture layer, high-temperature storage characteristics and high-temperature cycle characteristics are to some extent. It can be confirmed that there is an improvement. This indicates that the oxidation reaction of the separator is suppressed by the trap effect of the inorganic particle layer formed on the surface of the positive electrode mixture layer.
　一方、実施例１は比較例１と比べて、高温保存特性及び高温サイクル特性がより顕著に向上しており、正極合剤層表面に形成された無機粒子層に、ヘキサメタリン酸ナトリウムを含有させることで、高温保存特性及び高温サイクル特性を顕著に向上した非水電解質二次電池が得られることがわかる。 On the other hand, in Example 1, the high-temperature storage characteristics and the high-temperature cycle characteristics are more significantly improved as compared with Comparative Example 1, and sodium hexametaphosphate is added to the inorganic particle layer formed on the surface of the positive electrode mixture layer. Thus, it can be seen that a non-aqueous electrolyte secondary battery having significantly improved high-temperature storage characteristics and high-temperature cycle characteristics can be obtained.
　また、実施例２の結果より、上記の無機粒子層にヘキサメタリン酸ナトリウムを含有させることによる、高温保存特性及び高温サイクル特性の向上効果は、ヘキサメタリン酸ナトリウム含有量が、正極活物質合剤（固形分）に対して０．０３質量％という非常に微量であっても充分に発揮されることがわかる。 Further, from the results of Example 2, the effect of improving the high-temperature storage characteristics and the high-temperature cycle characteristics by containing sodium hexametaphosphate in the inorganic particle layer is that the sodium hexametaphosphate content is positive electrode active material mixture (solid It can be seen that even a very small amount of 0.03% by mass with respect to (min) is sufficiently exerted.
　また、実施例４～６の結果より、上記の無機粒子層に含有させるリン酸塩が、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムであっても、同様に高温保存特性及び高温サイクル特性の向上効果が得られることがわかる。 Further, from the results of Examples 4 to 6, even when the phosphate contained in the inorganic particle layer is sodium pyrophosphate, trisodium phosphate, or disodium hydrogen phosphate, the high temperature storage characteristics and the high temperature It turns out that the improvement effect of cycling characteristics is acquired.
　これは、以下のようなメカニズムによるものと考えられる。すなわち、高電圧充電状態、特に高温環境下においては、有機溶媒の分解により水分が生成されることが知られており、また、電池製造工程における電池内への微量水分の混入は避けられないものでもある。 This is thought to be due to the following mechanism. That is, it is known that moisture is generated by decomposition of the organic solvent in a high voltage charged state, particularly in a high temperature environment, and a minute amount of moisture is inevitably mixed in the battery in the battery manufacturing process. But there is.
　電池内に水分が存在することによって、電解質塩であるＬｉＰＦ６等のリチウム塩の加水分解が起き、それに伴ってフッ酸が発生する。このフッ酸により正極活物質が腐食され、本来の充放電機能を発揮することが出来なくなるため、特に高温高電圧状態での保存特性やサイクル特性が低下するものと考えられる。 The presence of moisture in the battery causes hydrolysis of a lithium salt such as LiPF 6 that is an electrolyte salt, and accordingly, hydrofluoric acid is generated. Since the positive electrode active material is corroded by this hydrofluoric acid and the original charge / discharge function cannot be exhibited, it is considered that the storage characteristics and the cycle characteristics particularly in a high temperature and high voltage state are deteriorated.
　一方、実施例１～６に係る各非水電解質二次電池では、正極合剤層の表面に無機粒子層が形成され、さらに無機粒子層中にヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムのいずれかのリン酸塩を含むため、水分によるリチウム塩の加水分解及び、セパレータの酸化が抑制され、高温高電圧状態での保存特性やサイクル特性が向上しているものと考えられる。これは、上記リン酸塩の水分との反応性がリチウム塩よりも高いために、リチウム塩の分解を抑制することが出来るためである。 On the other hand, in each of the nonaqueous electrolyte secondary batteries according to Examples 1 to 6, an inorganic particle layer is formed on the surface of the positive electrode mixture layer, and sodium hexametaphosphate, sodium pyrophosphate, and trisodium phosphate are further formed in the inorganic particle layer. Because it contains any phosphate of disodium hydrogen phosphate, hydrolysis of lithium salt due to moisture and oxidation of the separator are suppressed, improving storage characteristics and cycle characteristics at high temperature and high voltage it is conceivable that. This is because decomposition of the lithium salt can be suppressed because the reactivity of the phosphate with moisture is higher than that of the lithium salt.
　また、比較例３～５の結果から、ヘキサメタリン酸ナトリウムを無機粒子層ではなく正極合剤層に含有させた場合は、実施例と比べて非常に多量のヘキサメタリン酸ナトリウムを含有させなければ、高温保存特性及び高温サイクル特性の向上効果が得られないことがわかる。 In addition, from the results of Comparative Examples 3 to 5, when sodium hexametaphosphate was contained in the positive electrode mixture layer instead of the inorganic particle layer, a very high amount of sodium hexametaphosphate was required as long as the sodium hexametaphosphate was not contained in comparison with the examples. It turns out that the improvement effect of a storage characteristic and a high temperature cycling characteristic is not acquired.
　特に実施例３と比較例４を比較すると、電池内に存在するリン酸塩は等量であるが、その効果は大きく異なる。これは、単に正極合剤層にリン酸塩を混合するよりも、正極無機粒子層のみに混合させことで、リン酸塩と電解液の接触効率が高いためであると考えられ、高容量化を目的とする正極材料の高充填化を目指すには、リン酸塩を正極無機粒子層のみ含有させる必要がある。 Especially when Example 3 and Comparative Example 4 are compared, the amount of phosphate present in the battery is the same, but the effect is greatly different. This is thought to be because the contact efficiency between the phosphate and the electrolyte is high by mixing only the positive electrode inorganic particle layer rather than simply mixing the phosphate with the positive electrode mixture layer. In order to increase the filling of the positive electrode material for the purpose, it is necessary to contain only the positive electrode inorganic particle layer with the phosphate.
　すなわち、正極合剤層の表面に無機粒子層を形成し、さらに無機粒子層中にヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムより選択されるいずれかのリン酸塩を含有させることで、高温保存特性及び高温サイクル特性の向上とともに高容量化を達成することができる。 That is, an inorganic particle layer is formed on the surface of the positive electrode mixture layer, and the phosphate is selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate in the inorganic particle layer. By containing, it is possible to achieve high capacity while improving high temperature storage characteristics and high temperature cycle characteristics.
　なお、上記実施例においては、正極活物質としてコバルト酸リチウムを用いたが、本発明の実施においては、これに限定されるものではなく、リチウムイオンを可逆的に吸蔵・放出することが可能なＬｉＭＯ２（但し、ＭはＣｏ、Ｎｉ、Ｍｎの少なくとも１種である）で表されるリチウム遷移金属複合酸化物、すなわち、ＬｉＣｏＯ２、ＬｉＮｉＯ２、ＬｉＮｉｙＣｏ１－ｙＯ２（ｙ＝０．０１～０．９９）、ＬｉＭｎＯ２、ＬｉＭｎ２Ｏ４、ＬｉＣｏｘＭｎｙＮｉｚＯ２（ｘ＋ｙ＋ｚ＝１）、又はＬｉＦｅＰＯ４などを一種単独もしくは複数種を混合して用いることが可能であり、リチウム基準での正極電位で４．４～４．６Ｖまで電池を充電したときに、良好な電池特性が得られるものであればよい。 In the above embodiment, lithium cobaltate was used as the positive electrode active material. However, the present invention is not limited to this, and lithium ions can be reversibly occluded / released. A lithium transition metal composite oxide represented by LiMO 2 (where M is at least one of Co, Ni, and Mn), that is, LiCoO 2 , LiNiO 2 , LiNi y Co 1-y O 2 (y = 0) 0.01 to 0.99), LiMnO 2 , LiMn 2 O 4 , LiCo x Mn y Ni z O 2 (x + y + z = 1), or LiFePO 4 can be used singly or in combination. Any battery may be used as long as good battery characteristics are obtained when the battery is charged to 4.4 to 4.6 V at a positive electrode potential based on lithium.
　また、上記各実施例では、負極活物質として黒鉛を用いたが、リチウムイオンを可逆的に吸蔵・放出することが可能な天然黒鉛、人造黒鉛、コークスなどの炭素質物質、ケイ素、スズなどを含む合金や酸化物、これらの混合物などを用いることができる。 In each of the above examples, graphite was used as the negative electrode active material. However, carbonaceous materials such as natural graphite, artificial graphite, and coke capable of reversibly occluding and releasing lithium ions, silicon, tin, etc. An alloy, an oxide, a mixture thereof, or the like can be used.
　また、非水電解質を構成する非水溶媒（有機溶媒）としては、カーボネート類、ラクトン類、エーテル類、エステル類などを使用することができ、これら溶媒の２種類以上を混合して用いることができるが、中でもカーボネート類が好ましい。 Further, as the nonaqueous solvent (organic solvent) constituting the nonaqueous electrolyte, carbonates, lactones, ethers, esters and the like can be used, and two or more of these solvents can be used in combination. Among them, carbonates are preferable.
　具体例としては、実施例で用いたＥＣ、ＭＥＣ、ＶＣの他、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、フルオロエチレンカーボネート（ＦＥＣ）シクロペンタノン、スルホラン、３－メチルスルホラン、２，４－ジメチルスルホラン、３－メチル－１，３オキサゾリジン－２－オン、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、メチルプロピルカーボネート、メチルブチルカーボネート、エチルプロピルカーボネート、エチルブチルカーボネート、ジプロピルカーボネート、γ－ブチロラクトン、γ－バレロラクトン、１，２－ジメトキシエタン、テトラヒドロフラン、２－メチルテトラヒドロフラン、１，３－ジオキソラン、酢酸メチル、酢酸エチル、１，４－ジオキサンなどを挙げることができる。 Specific examples include EC, MEC, VC used in the examples, propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC) cyclopentanone, sulfolane, 3-methylsulfolane, 2,4. -Dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, γ -Butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dioxane, etc. be able to.
　また、本発明の非水電解質二次電池で使用する非水電解質の溶質としては、非水電解質二次電池において一般に溶質として用いられるリチウム塩を用いることができる。このようなリチウム塩としては、実施例で用いたＬｉＰＦ６の他に、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）（Ｃ４Ｆ９ＳＯ２）、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣ（Ｃ２Ｆ５ＳＯ２）３、ＬｉＡｓＦ６、ＬｉＣｌＯ４、Ｌｉ２Ｂ１０Ｃｌ１０、Ｌｉ２Ｂ１２Ｃｌ１２など及びそれらの混合物が例示される。前記非水溶媒に対する溶質の溶解量は、０．５～２．０ｍｏｌ／Ｌとするのが好ましい。 Moreover, as a solute of the nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery of the present invention, a lithium salt generally used as a solute in the nonaqueous electrolyte secondary battery can be used. As such a lithium salt, in addition to LiPF 6 used in the examples, LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Li 2 B 10 Cl 10, Li 2 B 12 Examples include Cl 12 and mixtures thereof. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.
　また、本発明においては、無機粒子スラリーの調製の際に、スラリーの溶媒としてＮ－メチル－ピロリドン（ＮＭＰ）等の有機溶媒を用いることも可能であり、その場合スラリーの分散安定性は良好となる。しかも、ＭＮＰ等の有機溶媒は気化し易いため、乾燥することにより容易に多孔質無機粒子層中の水分量を極めて低い状態とすることができるので、溶媒として水を用いて作製した場合よりも保存特性及びサイクル特性共に非常に優れた非水電解質二次電池を作製することができるようになる。 In the present invention, it is also possible to use an organic solvent such as N-methyl-pyrrolidone (NMP) as the slurry solvent when preparing the inorganic particle slurry, in which case the dispersion stability of the slurry is good. Become. Moreover, since organic solvents such as MNP are easy to vaporize, the water content in the porous inorganic particle layer can be easily reduced by drying, so that the amount of water in the porous inorganic particle layer can be made extremely low. A non-aqueous electrolyte secondary battery having excellent storage characteristics and cycle characteristics can be produced.
　なお、無機粒子スラリーを調整する際に用いる溶媒については、正極活物質合剤層に含まれる結着剤の種類に応じて、結着剤が無機粒子層に溶出しにくい溶媒を選択することが好ましい。すなわち、上記実施例で用いたＰＶｄＦのように、疎水性の高い結着剤を正極活物質合剤スラリーを調製する際に用いた場合は、無機粒子層への結着剤（ＰＶｄＦ）の溶出を防ぐために、水系溶媒を用いて無機粒子スラリーを調製することが好ましく、有機溶媒に溶解しにくい（親水性の高い）結着剤を用いた場合には、非水系溶媒を用いて無機粒子スラリーを調製することが好ましい。 In addition, about the solvent used when adjusting an inorganic particle slurry, according to the kind of binder contained in a positive electrode active material mixture layer, the solvent from which a binder is hard to elute to an inorganic particle layer can be selected. preferable. That is, when a highly hydrophobic binder is used in preparing the positive electrode active material mixture slurry, such as PVdF used in the above examples, the binder (PVdF) is eluted into the inorganic particle layer. In order to prevent this, it is preferable to prepare an inorganic particle slurry using an aqueous solvent. When a binder that is difficult to dissolve in an organic solvent (highly hydrophilic) is used, an inorganic particle slurry is used using a non-aqueous solvent. Is preferably prepared.
　また、正極合剤層表面の上に無機粒子スラリーを塗布する方法としては、ダイコート法、グラビアコート法、ディップコート法、カーテンコート法、スプレーコート法等が挙げられるが、特に、上記実施例で採用したグラビアコート法を用いると、無機粒子スラリーを薄く、均一の厚さで連続的に形成できるようになるので、均一な品質の非水電解質二次電池用正極を連続的に製造できるようになる。 Examples of the method of applying the inorganic particle slurry on the surface of the positive electrode mixture layer include a die coating method, a gravure coating method, a dip coating method, a curtain coating method, and a spray coating method. Using the adopted gravure coating method, the inorganic particle slurry can be continuously formed in a thin and uniform thickness, so that a positive electrode for a non-aqueous electrolyte secondary battery of uniform quality can be continuously manufactured. Become.
　さらに、上記実施例では、電池の充電電圧をリチウム基準で４．４Ｖ、すなわち正極の充電電圧をリチウム基準で４．５Ｖとした例を示したが、正極の充電電圧がリチウム基準で４．４Ｖ以上であれば同様の効果を奏する。しかし、正極の充電電圧がリチウム基準で４．６Ｖを越えると、非水電解質の酸化分解が激しくなると共に正極活物質も劣化しやすくなるため、充電電圧はリチウム基準で４．４Ｖ以上、４．６Ｖ以下であることが好ましい。 Further, in the above embodiment, an example in which the charging voltage of the battery is 4.4 V on the basis of lithium, that is, the charging voltage of the positive electrode is 4.5 V on the basis of lithium, but the charging voltage of the positive electrode is 4.4 V on the basis of lithium. If it is above, the same effect is produced. However, if the charging voltage of the positive electrode exceeds 4.6 V on the basis of lithium, the oxidative decomposition of the nonaqueous electrolyte becomes severe and the positive electrode active material tends to deteriorate, so the charging voltage is 4.4 V or more on the basis of lithium. It is preferable that it is 6V or less.

Claims (7)

  1. 　正極芯体の表面に形成された正極活物質を含む正極合剤層と、前記正極合剤層の表面に形成された多孔質無機粒子層とを備えた非水電解質二次電池用正極において、　前記多孔質無機粒子層は、ヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムから選択される少なくとも１種からなるリン酸ナトリウム塩を含有することを特徴とする非水電解質二次電池用正極。 In a positive electrode for a nonaqueous electrolyte secondary battery comprising a positive electrode mixture layer containing a positive electrode active material formed on the surface of a positive electrode core, and a porous inorganic particle layer formed on the surface of the positive electrode mixture layer, The porous inorganic particle layer contains a sodium phosphate salt composed of at least one selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate. Secondary battery positive electrode.
  2. 　前記リン酸ナトリウム塩の含有量は、前記正極活物質合剤量に対して０．０３質量％以上、１．０質量％以下であることを特徴とする、請求項１に記載の非水電解質二次電池用正極。 2. The nonaqueous electrolyte according to claim 1, wherein the content of the sodium phosphate salt is 0.03% by mass or more and 1.0% by mass or less with respect to the amount of the positive electrode active material mixture. Secondary battery positive electrode.
  3. 　前記多孔質無機粒子層は、ＴｉＯ２、Ａｌ２Ｏ３、ＳｉＯ２、ＺｒＯ２より選択される少なくとも１種を無機粒子として含有することを特徴とする、請求項１に記載の非水電解質二次電池用正極。 2. The non-aqueous electrolyte according to claim 1, wherein the porous inorganic particle layer contains at least one selected from TiO 2 , Al 2 O 3 , SiO 2 , and ZrO 2 as inorganic particles. Positive electrode for secondary battery.
  4. 　正極芯体の表面に正極合剤層を形成する工程と、　前記正極合剤層の表面に多孔質無機粒子層を形成する工程と、を有する非水電解質二次電池用正極の製造方法において、
    　前記多孔質無機粒子層を形成する工程を、無機粒子とヘキサメタリン酸ナトリウム、ピロリン酸ナトリウム、リン酸三ナトリウム、リン酸水素二ナトリウムから選択される少なくとも１種からなるリン酸ナトリウム塩とを含有するスラリーをグラビアコート法によって塗布した後、乾燥することによって行うことを特徴とする、非水電解質二次電池用正極の製造方法。     In a method for producing a positive electrode for a non-aqueous electrolyte secondary battery, comprising: forming a positive electrode mixture layer on the surface of the positive electrode core; and forming a porous inorganic particle layer on the surface of the positive electrode mixture layer.
    The step of forming the porous inorganic particle layer includes inorganic particles and at least one sodium phosphate salt selected from sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, and disodium hydrogen phosphate. A method for producing a positive electrode for a non-aqueous electrolyte secondary battery, wherein the slurry is applied by a gravure coating method and then dried.
  5. 　前記正極合剤層は親水性の結着剤を含有し、
    　前記スラリーとして非水系スラリーを用いることを特徴とする、請求項４に記載の非水電解質二次電池用正極の製造方法。     The positive electrode mixture layer contains a hydrophilic binder,
    The method for producing a positive electrode for a nonaqueous electrolyte secondary battery according to claim 4, wherein a nonaqueous slurry is used as the slurry.
  6. 　前記正極合剤層は疎水性の結着剤を含有し、
    　前記スラリーとして水系スラリーを用いることを特徴とする、請求項４に記載の非水電解質二次電池用正極の製造方法。     The positive electrode mixture layer contains a hydrophobic binder,
    The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein an aqueous slurry is used as the slurry.
  7. 　請求項１～３のいずれかに記載の非水電解質二次電池用正極と、負極と、セパレータと、非水電解質とを備え、前記正極活物質の電位が、リチウム基準で４．４Ｖ以上４．６Ｖ以下であることを特徴とする、非水電解質二次電池。 A positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode active material has a potential of 4.4 V or more based on lithium. A non-aqueous electrolyte secondary battery characterized by having a voltage of 6 V or less.
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