JP2017139168A - Positive electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode for a nonaqueous electrolyte secondary battery, high in capacity and excellent in high-temperature storage characteristics at temperatures of 80°C or more.SOLUTION: A positive electrode for a nonaqueous electrolyte secondary battery of the present invention includes a positive electrode mixture containing: a positive electrode active material which is represented by general composition formula LiNiMO(where, M contains at least one or more elements selected from among Co, Mn, Al, Mg, Zr, Mo, Ti, Si, Fe, P, F, and Cl, and 0≤x≤0.1 and 0≤y≤0.5 are satisfied) and which has a specific surface area (BET value) of 0.01-1.0 m/g; and carbon. The content of the carbon in the positive electrode mixture is 2.5 wt.% or more and 10.0 wt.% or less, and the porosity of the positive electrode mixture is 1-10%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery.

  In recent years, as the performance of electronic devices has increased, various sensors and cameras have been miniaturized, and various applications have been planned. Lithium ion batteries are expected to be developed especially for in-vehicle equipment applications and infrastructure applications, but high temperature durability is required to be applied to these applications.

  However, in lithium secondary batteries, the side reaction between the lithium-containing transition metal oxide, which is the positive electrode active material, and the electrolyte is accelerated at a high temperature, and the transition metal is eluted from the surface of the positive electrode or the side reaction product is deposited. The resistance increases, and the shelf life at high temperatures decreases rapidly. Moreover, the binder contained in the positive electrode mixture is swollen by the electrolytic solution, and the volume is expanded. As a result, there is a problem that the electron conduction path in the positive electrode is reduced to increase the resistance, and the shelf life at high temperature is drastically reduced.

For example, Patent Document 1 discloses that excellent high-temperature storage characteristics can be exhibited by adding lithium carbonate to a positive electrode containing a positive electrode active material based on LiMn ₂ O ₄ and optimizing the amount of carbon black. It is shown to be possible.

In Patent Document 2, a polyanionic material is used as the positive electrode active material, and Li ₄ Ti ₅ O ₁₂ , SiO _X or SnO _x , or a composite material thereof is used as the negative electrode active material, thereby charging and discharging at 120 ° C. The technology of a lithium ion battery that enables this is shown.

JP 2001-167767 A JP2013-84521A

However, the addition of the positive electrode active material _Li 2 CO ₃ as described in Patent Document 1, although the Mn elution is suppressed by reaction _Li 2 CO ₃ and HF, since the CO ₂ is generated, in particular 80 ° C. Cell swelling may occur due to the above high-temperature storage.

  Moreover, although the lithium ion battery described in Patent Document 2 has high temperature storage characteristics, there is a problem that the energy density of the battery becomes small because the average voltage is as low as about 3 V or less.

  The present invention has been made in view of the above points. The object of the present invention is to suppress the increase in resistance by focusing on the phenomenon that the resistance increases due to a decrease in the electron conduction path in the positive electrode. It is providing the positive electrode for nonaqueous electrolyte secondary batteries which improved the high temperature storage characteristic.

The positive electrode for a non-aqueous electrolyte secondary battery of the present invention that solves the above problems is
General composition formula Li _{1 + x} Ni _{1- y My} O ₂ (Formula 1)
(Wherein M includes at least one element of Co, Mn, Al, Mg, Zr, Mo, Ti, and Ba, 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.5)
Has in a positive electrode active material consisting of the specific surface area (BET ^value) 0.01m ^{2 /g~1.0m} 2 / g lithium-containing nickel layered oxide, a positive electrode mixture containing carbon,
The content of the carbon in the positive electrode mixture is 2.5 wt% or more and 10.0 wt% or less, and the porosity of the positive electrode mixture is 1 to 10%.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode for nonaqueous electrolyte secondary batteries which is high capacity | capacitance and excellent in the high temperature storage characteristic of 80 degreeC or more can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

The schematic of the lithium ion secondary battery in an Example.

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery using a lithium composite oxide as a positive electrode active material, and specifically relates to a mixture composition as a positive electrode for improving high-temperature storage characteristics. In particular, the positive electrode according to the present invention can exhibit excellent high-temperature storage characteristics in a non-aqueous electrolyte secondary battery that should operate at a high temperature of 80 ° C. or higher, such as a small camera or sensor for in-vehicle or infrastructure applications.

  Hereinafter, a positive electrode active material, a method for producing a positive electrode mixture, and a nonaqueous electrolyte battery using the positive electrode mixture according to the present invention will be described. In addition, the manufacturing method of the positive electrode mixture in this invention and the nonaqueous electrolyte battery using the positive electrode mixture are not limited to those shown below, and can be implemented with appropriate modifications within the scope not changing the gist thereof. It is.

The positive electrode for a non-aqueous electrolyte secondary battery according to the present invention is
General composition formula Li _{1 + x} Ni _{1- y My} O ₂ (Formula 1)
(Wherein M includes at least one element of Co, Mn, Al, Mg, Zr, Mo, Ti, and Ba, 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.5)
Has in a positive electrode active material consisting of the specific surface area (BET ^value) 0.01m ^{2 /g~1.0m} 2 / g lithium-containing nickel layered oxide, a positive electrode mixture containing carbon,
The content of the carbon in the positive electrode mixture is 2.5 wt% or more and 10.0 wt% or less, and the porosity of the positive electrode mixture is 1 to 10%.

  By using the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, a non-aqueous electrolyte secondary battery having a high capacity and excellent high-temperature storage characteristics can be obtained.

  The positive electrode active material described above is in the form of particles, and is composed of secondary particles in which primary particles are aggregated or primary particles, and each shape is substantially spherical. The above shape can be confirmed by observing particles present in a predetermined region with a scanning electron microscope.

  Particles with a size distribution having a single peak may be used, and there are two size distributions consisting of a relatively large particle and a relatively small particle that fills between large particles. You may use what has a peak. For example, the particle diameter is preferably in the range of 5 μm to 50 μm, and more preferably distributed so as to have peaks in the range of 5 μm to 15 μm and in the range of 20 μm to 50 μm. . Thus, by mixing particles having a particle size distribution having two large and small particles, the small particles can be inserted between the large particles, and the porosity is 1 to 10%. It is possible to prevent the large-diameter particles from breaking during high compression. The particle size distribution can be measured by a laser diffraction / scattering particle size distribution measuring apparatus.

The positive electrode active material described above needs to reduce the interface with the non-aqueous electrolyte from the viewpoint of suppressing metal elution. Therefore, it is advantageous that the BET specific surface area is small. However, if the BET specific surface area of the particles is too small, the density at the time of lamination is small, so that the battery capacity becomes small or the discharge characteristics at high load deteriorate. Problem arises. For this reason, it is preferable that the BET specific surface area S is 0.01 <= S <= 1.0 [m < ² > / g]. The BET specific surface area can be obtained by measuring the surface area using the BET formula, which is a theoretical formula for multimolecular layer adsorption. Specifically, the BET specific surface area was determined using a specific surface area measuring device by a nitrogen adsorption method.

  In the general composition formula (1), x relating to Li is preferably 0 ≦ x ≦ 0.1, and more preferably 0 ≦ x ≦ 0.03. When x is less than 0, sufficient battery capacity cannot be obtained. Further, since the grain growth is suppressed and the surface area is increased, metal elution is likely to occur. On the other hand, when x exceeds 0.1, a large amount of oxygen deficiency occurs. The lack of oxygen makes the structure easy to collapse and the cycle life is shortened. Furthermore, since there is a lot of lithium on the surface of the positive electrode active material particles, the positive electrode mixture slurry prepared using such a positive electrode active material becomes a gel, and the resistance of the formed positive electrode mixture layer is increased or the battery reaction is increased. There is a risk that gas will be generated during this process. The value of x for Li can be quantified by inductively coupled plasma emission spectrometry.

  In the above general composition formula (1), y regarding M (Co, Mn, Al, Mg, Zr, Mo, Ti, Ba) is preferably 0 ≦ y ≦ 0.5. Regarding Co, Mn, Al, Mg, Zr, Mo, Ti, and Ba, various battery characteristics can be improved by replacing part of Ni. Moreover, Si, Fe, P, F, Cl, etc. may inevitably be contained as impurities.

  Addition of Co and Mn as M has a great effect of improving charge / discharge characteristics and cycle characteristics. The addition of Mg as M has the effect of stabilizing the structure of the lithium-containing nickel layered oxide and improving the heat resistance. However, if it is added excessively, the crystal lattice of the lithium-containing cobalt oxide is distorted, which may cause a decrease in battery capacity and a decrease in load characteristics due to a decrease in Li mobility. In addition, when Mg is excessively contained, there is a problem that Mg may elute with a charge / discharge cycle and the life of the battery may be reduced. Therefore, the addition amount y of Al and Mg is 0 <y. ≦ 0.1 is preferable, and 0.005 ≦ y ≦ 0.01 is more preferable.

  When Al is added as M, the ionic radii of 6-coordinate Ni ions and Al ions are almost the same, so the structure of the lithium-containing nickel layered oxide is stabilized by replacing the Ni radii, and metal elution is performed. There is an inhibitory effect. Moreover, there exists an effect which improves heat resistance. However, if it is added excessively as in the case of Mg, the crystal lattice of the lithium-containing cobalt oxide is distorted, and there is a possibility that the load characteristics are lowered due to the lowered mobility of Li as well as the capacity of the battery. The addition amount y of Al is preferably 0 <y ≦ 0.1, and more preferably 0 <y ≦ 0.01.

  The addition of Zr has the effect of improving the charge / discharge cycle life in addition to the effect of increasing the potential of the low charge state and improving the output. The amount y of Zr is preferably 0 <y ≦ 0.1, and more preferably 0.001 ≦ y ≦ 0.005. When it exceeds 0.1, the growth of particles of the positive electrode active material is suppressed and becomes small. When the layer of the positive electrode active material is formed using such small particles, the density is small, and thus a sufficient battery capacity cannot be obtained. Moreover, since the surface area becomes large, Co elution is likely to occur. Mo, Ti, Ba and the like can exhibit the same effect as Zr.

  The positive electrode active material described above is an oxide or fluoride containing at least one element selected from the group consisting of Li, Zr, Ti, Al, Mg, Ni, Mn, Zn, and P on the surface thereof. It may be coated. In this case, in addition to improving the deterioration suppressing effect due to the charge / discharge cycle, the Co elution suppressing effect is also improved. The coating can absorb hydrofluoric acid generated at a high temperature and suppress damage to the positive electrode active material, and can suppress an increase in resistance and improve a power recovery rate after high-temperature storage. However, if the amount of the oxide or fluoride to be coated is too large, the resistance increases and the battery capacity decreases. Therefore, the number of atoms of the element contained in the oxide or fluoride to be coated is preferably 10 mol% or less of the number of molecules of the positive electrode active material having the general composition formula (1).

<Preparation of positive electrode for nonaqueous electrolyte secondary battery>
A positive electrode for a non-aqueous electrolyte secondary battery according to the present invention is prepared by preparing a positive electrode mixture slurry in which a positive electrode active material, a binder, and carbon as a conductive additive are dispersed in a solvent. The slurry is applied to the surface of the positive electrode current collector to form a positive electrode mixture layer, and is produced by pressing after drying.

  The above-described positive electrode active material can be produced by firing a mixture powder in which Li compound, Ni compound, M compound, etc. are mixed at an appropriate ratio, but is not particularly limited, and Li can be formed by a coprecipitation method or the like. It is also possible to prepare by excluding precursor hydroxide mixed with Li compound and baking.

As the Li compound, LiOH, Li ₂ CO ₃ , or LiCl can be used. In addition, as Ni compounds and M compounds, hydroxides or oxides of these elements are used. The temperature during synthesis is 800 to 1000 ° C., the temperature holding time is 5 to 48 hours, the heating / cooling rate r is 1 ≦ r ≦ 5 ° C./min, and the atmosphere during synthesis is air, more preferably oxygen atmosphere. .

  In the general composition formula (1), when the oxygen concentration is low, oxygen desorption tends to occur when the amount of added Li is large. It was found that some Ni was likely to transition to the Li site. The oxygen concentration is preferably 80% or more. By adjusting the firing atmosphere in this manner, oxygen deficiency and Ni transition are suppressed, and from the spectrum in the powder XRD, it is a layered rock salt structure belonging to the space group R3-m and belonging to the (104) plane. The ratio of the diffraction intensity attributed to the (003) plane to the diffraction intensity is 1.5 or more. By the above production method, a lithium-containing nickel layered oxide having a high capacity and high temperature storage characteristics can be obtained.

  The surface of the positive electrode active material is covered with an oxide or fluoride containing at least one element selected from the group consisting of Li, Zr, Ti, Al, Mg, Ni, Mn, Zn, and P. For example, the following procedure is used.

  When coating with Zr, Ti, Al, Mg, Ni, Mn, and Zn oxide, in a sodium hydroxide or lithium hydroxide aqueous solution adjusted to a pH value of 9 to 11 and a temperature of 60 to 80 ° C. The positive electrode active material powder is put into and stirred and dispersed, and then the nitrate or sulfate of the covering element is dropped. At this time, a coprecipitate is generated by simultaneously dropping ammonia water so that the pH value does not change. Thereafter, the coprecipitate and the positive electrode active material powder are continuously stirred for 5 hours or longer, and adjusted so that the pH value does not fluctuate with sodium hydroxide or lithium hydroxide as needed. In particular, when obtaining a coprecipitate such as Ni and Mn, it is more preferable to replace the dissolved oxygen in the aqueous solution with nitrogen. Next, the positive electrode active material powder and the aqueous solution to which the coprecipitate is adhered are separated by suction filtration, washed with ultrapure water, and dried. By firing the powder of the positive electrode active material, particles having a coating layer formed of Zr, Ti, Al, Mg, Ni, Mn, and Zn oxide are obtained.

  As another method for coating Zr, Ti, Al, Mg, Ni, Mn, and Zn oxide, an alkoxide of a desired element is dissolved in an alcohol solvent, and stirred and dried at a temperature of 60 ° C. to 80 ° C. There is also a method of adhering to the particle surface of the positive electrode active material and firing.

When covering the particle surface with Zr, Ti, Al, Mg, Ni, Mn, Zn, or P oxide containing Li, the precursor of the coating element is attached to the particle surface of the positive electrode active material by any of the above methods. Then, LiOH or Li ₂ CO ₃ may be mixed and fired.

For example, when a fluoride such as AlF ₃ is coated, the positive electrode active material powder in an aqueous solution of sodium hydroxide or lithium hydroxide adjusted to a pH value of 9 to 11 and a temperature of 60 to 80 ° C. After stirring and dispersing, aluminum nitride hydrate is added. The ammonium fluoride aqueous solution is gradually dropped into the solution, stirred for 5 hours or longer, filtered, dried, and fired in an inert gas atmosphere.

  The firing temperature at the time of coating is preferably 400 to 600 ° C., and the firing time is preferably 5 to 24 hours. The firing atmosphere is preferably an oxidizing atmosphere such as air or oxygen when obtaining an oxide, and an inert atmosphere such as nitrogen when obtaining a fluoride.

  As the binder, a thermoplastic resin that is chemically stable in a non-aqueous electrolyte secondary battery and has a swelling degree of 1 to 1.2 when immersed in an electrolytic solution at 100 ° C. for 1 week, thermosetting Any of the resins may be used. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotri Fluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECT E), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its Na + ion crosslinked product, ethylene- Methacrylic acid copolymer or its Na + ion crosslinked body, ethylene-methyl acrylate copolymer or its Na + ion crosslinked body, ethylene-methyl methacrylate copolymer or its Na + ion crosslinked body, polyimide amide, etc. can be used. . These may be used alone or in combination of two or more. Among these, considering the stability in the nonaqueous electrolyte secondary battery and the influence on the characteristics, PVDF, acrylic materials, and polyimideamide materials are preferable. The mass of the binder in the positive electrode mixture is preferably 0.2 to 5%.

  Carbon as a conductive aid includes, for example, graphite such as natural graphite and artificial graphite, single-walled or multi-walled carbon nanotubes, graphene, fullerene, VGCF, acetylene black, ketjen black (trade name), channel black, furnace black, Carbon black such as lamp black and thermal black, carbon fiber, and the like can be used. These may be used alone or in combination of two or more. For example, in the case of particles, those having a form of aggregate such as secondary particles and chain structures are not limited to primary particles.

The carbon content in the positive electrode mixture is 2.5 wt% or more and 10.0 wt% or less.
If it is less than 2.5% by weight, there will be a problem that the electron conduction path after high-temperature storage is insufficient and the battery characteristics vary. On the other hand, if the content exceeds 10.0% by weight, the high-temperature storage characteristics deteriorate due to a decrease in electrode density.

  Carbon DBP oil supply (value of how much oil is retained in the voids of the structure) is 100 (ml / 100g) or more, so it can be stored at high temperature with a small addition of 2.5 to 10.0% by weight. It becomes possible to secure sufficient electron conductivity later. In particular, it is preferable to add carbon of 150 (ml / 100 g) or more and 500 (ml / 100 g) or less to 2.5 wt% or more and 10.0 wt% or less. It is more preferably 0% by weight or less, and the disappearance of the electron conduction path due to the swelling of the binder can be suppressed.

  The mass of the positive electrode active material in the positive electrode mixture layer is preferably 85 to 95%. When the content ratio of the positive electrode active material is less than 85%, the battery capacity becomes small. Conversely, when the content ratio is more than 95%, the amount of the conductive auxiliary agent becomes relatively small, and the electron conduction path after high temperature storage decreases. The resistance of the positive electrode becomes extremely high. The porosity of the positive electrode mixture layer is 1 to 10%, preferably 5 to 10%. By setting the porosity to 1 to 10%, not only the contact area with the electrolytic solution is reduced, but also the high temperature storage characteristics are improved because it is less susceptible to swelling after high temperature storage.

A positive electrode mixture containing the above-described positive electrode active material, binder, conductive additive (carbon) and the like is dispersed in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) to form a slurry mixture composition (positive electrode) A mixture slurry) is prepared. After this mixture composition is applied to one or both sides of the positive electrode current collector, NMP is evaporated, and a press treatment is performed to form a positive electrode mixture layer on the current collector surface. The press treatment is for adjusting the thickness and density of the positive electrode mixture layer, and can be performed using, for example, a roll press machine or a hydraulic press machine. The density of the positive electrode mixture layer thus prepared is preferably 3.5 g / cm ³ or more and 4.5 g / cm ³ or less, and the porosity is preferably 1 to 10%. The method for manufacturing the positive electrode is not limited to the above, and other manufacturing methods may be used. The porosity can be calculated from the true density, volume, weight, and composition ratio of each material.

  The material of the positive electrode current collector is not particularly limited as long as it is a chemically stable electron conductor in the nonaqueous electrolyte secondary battery. For example, in addition to aluminum, aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., aluminum, aluminum alloy, a composite material in which a carbon layer or a titanium layer is formed on the surface of stainless steel, or the like can be used. . Among these materials, aluminum or aluminum alloy is preferable because it is lightweight and has high conductivity. As a material of the positive electrode current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like of the above materials can be used. Further, the surface of the positive electrode current collector can be roughened by surface treatment. Although the thickness of a positive electrode electrical power collector is not specifically limited, 1-500 micrometers is preferable.

  As a method for applying the positive electrode mixture composition to the surface of the current collector, various methods such as spin coating, dipping, and screen printing can be used.

  The nonaqueous electrolyte secondary battery has the positive electrode for a nonaqueous electrolyte secondary battery according to the present invention. There is no restriction | limiting in particular about a structure and structure other than a positive electrode, The well-known thing which the nonaqueous electrolyte secondary battery similar to the past has can be used.

[Example 1]
<Preparation of positive electrode>
As a positive electrode active material, 92.5 parts by mass of a lithium-containing nickel layered oxide powder having a specific surface area of 0.6 m ² / g of the general composition formula LiNi _0.8 Co _0.15 Al _0.05 O ₂ , and a conductive auxiliary agent As a binder, 5 parts by mass of carbon and 2.5 parts by mass of polyvinylidene fluoride as a binder were mixed, and NMP was added to adjust the viscosity to prepare a positive electrode mixture slurry.

  The positive electrode mixture slurry was applied to a positive electrode current collector made of aluminum foil having a thickness of 15 μm by adjusting the gap (gap) to 100 μm using a baker type applicator, and then dried at 80 ° C. for 1 hour to form a positive electrode mixture. An agent layer was formed. After processing the positive electrode current collector on which the positive electrode mixture layer is formed into a disk shape having a diameter of 15 mm, the positive electrode mixture is pressed so that the porosity of the positive electrode mixture is 10%, and then is vacuum dried at 100 ° C. for 20 hours. Dried. A positive electrode was produced by such a process.

<Production of negative electrode>
A metal lithium rolled plate having a predetermined thickness was processed into a disk shape having a diameter of 16 mm to produce a negative electrode.

<Non-aqueous electrolyte>
A non-aqueous electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a molar concentration (mol / l) in a solvent in which ethylene carbonate and diethyl carbonate having a volume ratio of 1: 2 are mixed. did.

<Battery assembly>
A flat nonaqueous electrolyte secondary battery was assembled using the positive electrode, negative electrode, and nonaqueous electrolyte described above. FIG. 1 schematically shows a cross section of the assembled nonaqueous electrolyte secondary battery 1. The assembly was performed as follows.

  After inserting the insulating ring 8 into the side surface of the stainless steel container 13, the negative electrode 4, the separator 3, and the positive electrode 2 were stacked in this order, and the nonaqueous electrolyte was impregnated in the separator 3. As the separator 3, a microporous film made of polypropylene was used. An aluminum pressing plate 5 and a leaf spring 6 are sequentially stacked on the positive electrode 2, a stainless steel lid 7 is placed on the insulating packing 9, and tightened with bolts 12 and nuts 11 on the insulating sleeve 10. A flat nonaqueous electrolyte secondary battery was constructed.

  The positive electrode 2 is electrically connected to the lid 7 via the pressing plate 5 and the leaf spring 6, and the negative electrode 4 is electrically connected to the bolt 12 via the container 13. Thereby, electrical energy can be taken out from the inside of the battery using the lid 7 and the bolt 12 as terminals.

[Example 2]
The nonaqueous electrolyte secondary battery according to Example 2 was subjected to the same procedure as in Example 1 except that the positive electrode active material of Example 1 was pressed so that the porosity of the positive electrode mixture was 8%. Produced.

[Example 3]
Using the positive electrode active material of Example 1, the positive electrode active material content in the positive electrode mixture was adjusted to 88 parts by mass, the carbon content was adjusted to 8 parts by mass, and 4 parts by mass of polyvinylidene fluoride. A non-aqueous electrolyte secondary battery according to Example 3 was produced in the same procedure as in Example 1.

[Example 4]
The positive electrode active material of Example 1 was replaced with LiNi _0.75 Co _0.15 Al _0.05 Mg _0.05 O ₂ having a specific surface area of 0.54 m ² / g, and the same procedure as in Example 1 was used. A non-aqueous electrolyte secondary battery according to No. 4 was produced.

[Example 5]
The positive electrode active material of Example 1 was replaced with LiNi _0.8 Co _0.1 Mn _0.1 O ₂ having a specific surface area of 0.4 m ² / g, and the same procedure as in Example 1 was followed. A water electrolyte secondary battery was produced.

[Example 6]
The positive electrode active material of Example 1 was replaced with LiNi _0.87 Co _0.1 Mn _0.01 Al _0.01 Mg _0.01 O ₂ having a specific surface area of 0.51 m ² / g, and the same as in Example 1 above. A nonaqueous electrolyte secondary battery according to Example 6 was produced according to the procedure.

[Example 7]
The positive electrode active material of Example 1 was stirred and dispersed in an aqueous lithium hydroxide solution adjusted to a pH value of 9 to 11 and a temperature of 60 to 80 ° C., and then Al (NO ₃ ) ₃ · 9H _2. O was added dropwise. At this time, Al (OH) ₃ coprecipitate was produced by simultaneously dropping ammonia water so that the pH value did not change. Thereafter, stirring was continued for 5 hours or longer, and the pH value was adjusted so as not to fluctuate with lithium hydroxide as needed. Next, the powder and aqueous solution of the positive electrode active material to which Al (OH) ₃ was adhered were separated by suction filtration, washed with ultrapure water, and vacuum-dried at 80 ° C. for 24 hours. The powder was fired at 400 ° C. for 10 hours in an air atmosphere. In the oxide film formed on the surface of the positive electrode active material by such a process, a positive electrode active material having a specific surface area of 0.72 m ² / g containing 1 mol% of Al in a molar ratio with respect to the positive electrode active material was produced. Using this positive electrode active material, a non-aqueous electrolyte secondary battery according to Example 7 was fabricated in the same procedure as in Example 1.

[Example 8]
Zirconium isopropoxide was dissolved in an isopropyl alcohol solvent, stirred with the positive electrode active material of Example 1 at a temperature of 60 ° C. for 10 hours, and dried at 80 ° C. to obtain a positive electrode active material powder. The positive electrode active material powder was fired at 400 ° C. in an air atmosphere for 10 hours. In the oxide film formed on the surface of the positive electrode active material by such a process, a positive electrode active material having a specific surface area of 0.68 m ² / g in which 1 mol% of Zr was contained in a molar ratio with respect to the positive electrode active material was produced. . Using this positive electrode active material, a non-aqueous electrolyte secondary battery according to Example 8 was produced in the same procedure as in Example 1.

[Example 9]
The positive electrode active material of Example 1 is stirred and dispersed in an aqueous lithium hydroxide solution adjusted to a pH value of 9 or more and 11 or less and a temperature of 60 ° C., and then aluminum nitride hydrate is added. Ammonium fluoride aqueous solution was dropped into the solution little by little, stirred for 10 hours or more, suction filtered, washed with ultrapure water, and then vacuum dried at 80 ° C. for 24 hours. This powder was fired in a nitrogen gas atmosphere for 10 hours. A positive electrode active material having a specific surface area of 0.66 m ² / g in which 1 mol% of AlF ₃ formed on the surface of the positive electrode active material by such a process was contained at a molar ratio to the positive electrode active material was produced. Using this positive electrode active material, a nonaqueous electrolyte secondary battery according to Example 9 was produced in the same procedure as in Example 1.

[Example 10]
Using the positive electrode active material of Example 1, the positive electrode active material content in the positive electrode mixture was 92.7 parts by mass, the carbon content was 3 parts by mass, and the polyvinylidene fluoride was 4.3 parts by mass. A nonaqueous electrolyte secondary battery according to Example 10 was produced in the same procedure as in Example 1 except that the pressing was performed so that the rate was 6%.

[Comparative Example 1]
The non-aqueous solution according to Comparative Example 1 was prepared in the same manner as in Example 1 except that LiCoO ₂ was used instead of the positive electrode active material of Example 1 and the positive electrode material mixture was pressed so that the porosity was 13%. An electrolyte secondary battery was produced.

[Comparative Example 2]
The same procedure as in Example 1 was applied to Comparative Example 2 except that Li ₂ MnO ₄ was used instead of the positive electrode active material of Example 1 and the positive electrode mixture was pressed so that the porosity of the positive electrode mixture was 18%. A non-aqueous electrolyte secondary battery was produced.

[Comparative Example 3]
Example 1 except that LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used instead of the positive electrode active material of Example 1 and the positive electrode mixture was pressed so that the porosity of the positive electrode mixture was 20%. A non-aqueous electrolyte secondary battery according to Comparative Example 3 was produced in the same procedure as described above.

[Comparative Example 4]
A non-aqueous electrolyte secondary battery according to Comparative Example 4 was prepared in the same procedure as in Example 1 except that the positive electrode active material of Example 1 was pressed so that the porosity of the positive electrode mixture was 15%. Produced.

[Comparative Example 5]
Using the positive electrode active material of Example 1, the positive electrode active material content in the positive electrode mixture was 92.8 parts by mass, the carbon content was 2 parts by mass, and polyvinylidene fluoride was 5.2 parts by mass. A non-aqueous electrolyte secondary battery according to Comparative Example 5 was produced in the same procedure as in Example 1 except that pressing was performed so that the rate was 12%.

  Table 1 shows the compositions of the positive electrode active materials of Examples 1 to 10, the elements covering the surface of the positive electrode active material, the contents of the positive electrode active material, the carbon content, and the porosity. Table 1 shows the compositions of the positive electrode active materials of Comparative Examples 1 to 5, the positive electrode active material content, the carbon content, and the porosity.

<Battery evaluation>
About the nonaqueous electrolyte secondary battery of Examples 1-10 and Comparative Examples 1-5, the electrochemical characteristic and the high temperature storage characteristic, and the metal elution amount of the positive electrode were evaluated in the following manner.

<Evaluation of electrochemical characteristics>
At room temperature (25 ° C.), the battery is charged with a constant current until the battery voltage becomes 4.2 V vs Li / Li ⁺ at a load factor of 0.1 C, and then a constant voltage of 4.2 V vs Li / Li ⁺ The battery was charged until the current reached a load factor of 0.01C. Thereafter, the battery was left for 1 hour and discharged at a constant current until the battery voltage reached 2.5 V at a current of 0.1 C load factor. This process was repeated 2 cycles, and the initial electric energy (Wh) was evaluated from the last discharge curve. The amount of electric power was calculated by the product of the voltage and the capacity at which the discharge capacity at 2.5V discharge becomes 1/2.

<Evaluation of high-temperature storage characteristics>
After the evaluation of the electrochemical characteristics at room temperature, the battery is left for 1 hour and charged at a constant current until the battery voltage becomes 4.2 V vs Li / Li ⁺ with a current with a load factor of 0.1 C, and then 4.2 V The battery was charged at a constant voltage of vs Li / Li ⁺ until the current reached a load factor of 0.01C.

Thereafter, the positive electrode was taken out, and lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a solvent in which ethylene carbonate and diethyl carbonate having a volume ratio of 1: 2 were mixed so as to have a molar concentration (mol / l). It was stored at 100 ° C. for 48 hours in a sealed container together with 2 mL of non-aqueous electrolyte.

  Next, the positive electrode is taken out from the sealed container, and the non-aqueous electrolyte secondary battery is reassembled again by the method described in the examples, and the battery voltage is set to 2. at a current of a load factor of 0.1 C at room temperature (25 ° C.). Discharge was performed at a constant current until 5V was reached.

Furthermore, the battery is charged at a constant current until the battery voltage becomes 4.2 V vs Li / Li ⁺ with a current of 0.1 C load factor, and then the current becomes a load factor of 0 with a constant voltage of 4.2 V vs Li / Li ^+. The battery was charged until .01C was reached. Thereafter, the battery was left for 1 hour and discharged at a constant current until the battery voltage reached 2.5 V at a current of 0.05 C load factor. The amount of electric power (Wh) after the storage test was evaluated from the last discharge curve. The evaluation results are shown in Table 2.

<Evaluation of metal elution amount>
An acid was added to 2 mL of the non-aqueous electrolyte used in the evaluation of the above high-temperature storage characteristics and heated to remove organic substances. Then, it diluted with water, the amount of metals contained in the positive electrode active material was quantified by inductively coupled plasma emission spectrometry, and the amount of metal elution was calculated. The evaluation results are shown in Table 2.

From the results shown in Table 2, the following can be understood.
In Examples 1 to 10, the metal elution amount was less than 1 atomic weight%, whereas in Comparative Examples 1 to 5, the metal elution amount was higher than 1 atomic weight%.

  This is considered as follows. In Examples 1 to 10, a layered oxide containing Ni is used as the positive electrode active material, and this positive electrode active material suppresses metal elution by forming NiO having a high binding force with oxygen on the surface. doing. On the other hand, since Comparative Examples 1 to 3 did not contain or contained Ni in the positive electrode active material, metal elution was increased. On the surfaces of the positive electrode active materials of Comparative Examples 1 and 2, disproportionation reaction and reduction easily occur, and Co and Mn are eluted in large amounts. In Comparative Example 3, Ni, Co, and Mn were eluted at almost the same ratio because Ni was less in the positive electrode active material. In Comparative Examples 4 and 5, since the porosity of the positive electrode mixture was higher than 10%, the reaction area with the nonaqueous electrolytic solution was increased, and the metal elution amount was increased.

  In the above experiment, the storage temperature was 100 ° C. However, when the storage temperature is 80 ° C., the metal elution amount becomes small, so the difference between the example and the comparative example becomes small. When the temperature is less than 80 ° C., for example, 60 ° C., the difference in the amount of metal elution due to the positive electrode active material and the porosity is further reduced, and the effect of the present invention becomes extremely small.

  Moreover, in Examples 1-10, while the electric energy recovery rate exceeded 80%, in Comparative Examples 1-5, it turns out that the electric energy recovery rate is less than 80%. This is due to the fact that the metal content of the positive electrode active material of Examples 1 to 10 is small, the content of carbon as the conductive additive is large, and the porosity of the positive electrode mixture is small.

  When the carbon content was 5 parts by mass or more, the disappearance of the electron conduction path due to the swelling of the binder during high temperature storage was reduced. Further, since the porosity of the positive electrode mixture was reduced to 10% or less, not only the side reaction with the electrolytic solution during high temperature storage but also the collapse of the electrode structure due to the swelling of the binder could be suppressed.

  Due to the above effects, the electrical contact of the positive electrode active material was maintained, and the amount of power did not decrease. On the other hand, Comparative Examples 1 to 5 have a low carbon content and a high porosity, so the electrical contact of the positive electrode active material was lost, the resistance was increased, and the amount of power was greatly reduced.

  As described above, various embodiments and modifications have been described, but the present invention is not limited to these contents. Other embodiments conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Positive electrode 3 Separator 4 Negative electrode 5 Holding plate 6 Leaf spring 7 Lid 8 Insulating ring 9 Insulating packing 10 Insulating sleeve 11 Nut 12 Bolt 13 Container

Claims (5)

General composition formula Li _{1 + x} Ni _{1- y My} O ₂ (Formula 1)
(Wherein M includes at least one element of Co, Mn, Al, Mg, Zr, Mo, Ti, and Ba, 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.5)
Has in a positive electrode active material consisting of the specific surface area (BET ^value) 0.01m ^{2 /g~1.0m} 2 / g lithium-containing nickel layered oxide, a positive electrode mixture containing carbon,
The nonaqueous electrolyte secondary battery, wherein the carbon content in the positive electrode mixture is 2.5 wt% or more and 10.0 wt% or less, and the porosity of the positive electrode mixture is 1 to 10%. Positive electrode.   The particle surface of the positive electrode active material is coated with an oxide or fluoride containing at least one element selected from the group consisting of Li, Zr, Ti, Al, Mg, Ni, Mn, Zn, and P. 2. The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the number of atoms of the element contained in the oxide or fluoride to be coated is 10 mol% or less of the number of molecules of the positive electrode active material. .   The positive electrode active material has a substantially spherical particle shape, and the particle size distribution has peaks in a particle diameter range of 5 μm to 15 μm and a range of 20 μm to 50 μm, respectively. The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1 or 2.   The said positive electrode mixture contains the binder whose swelling degree is 1-1.2 when immersed in electrolyte solution at 100 degreeC for 1 week, It is any one of Claims 1-3 characterized by the above-mentioned. Positive electrode for non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery which has a positive electrode for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-4.

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