JP2013137947A - Lithium ion secondary battery and method of manufacturing cathode active material for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve capacity, cycle characteristic and rate characteristic of a battery and also suppress gas generation when cycled in a lithium ion secondary battery charged/discharged at a high charging voltage.SOLUTION: A lithium ion secondary battery includes: a positive electrode collector; and a cathode active material layer formed on the surface of the positive electrode collector. A cathode active material is comprised of secondary particles composed of primary particles. A part of the surface of the primary particles is covered with a lithium metal oxide layer, and the rest of the surface of the primary particles is a positive electrode for the lithium ion secondary battery that is covered with a metal oxide layer of a cubic crystal.

Description

The present invention relates to a lithium ion secondary battery and a method for producing a positive electrode active material for a lithium ion secondary battery.

  Lithium ion secondary batteries have high capacity, high energy density, and are easy to reduce in size and weight, and are therefore widely used as power sources for portable small electronic devices, for example. Examples of portable small electronic devices include mobile phones, personal digital assistants (PDAs), notebook personal computers, video cameras, and portable game machines.

  A typical lithium ion secondary battery includes a positive electrode containing a lithium cobalt composite oxide as a positive electrode active material, a negative electrode containing a carbon material as a negative electrode active material, and a polyolefin porous membrane (separator). As devices become smaller and lighter, demand for further increases in energy density of lithium ion secondary batteries is increasing. With conventional battery designs, the capacity is approaching the limit. Researches for long life, high output, and high charging voltage are widely conducted.

  Patent Document 1 discloses a positive electrode active material having a boron compound or a boron compound decomposition product layer on at least a part of the surface of a lithium nickel composite oxide for the purpose of reducing carbonate radicals on the surface of the positive electrode active material. Yes.

  For the purpose of improving thermal stability, Patent Document 2 discloses a positive electrode active material lithium ion secondary battery in which at least double surface treatment layers are provided.

  In addition, for the purpose of providing a lithium ion secondary battery with high high voltage resistance, Patent Document 3 employs a positive electrode active material in which a part of oxygen in a lithium nickel composite oxide is substituted with boron or fluorine for the positive electrode. A lithium ion secondary battery is disclosed.

JP 2010-40382 A JP 2002-164053 A JP 2007-66745 A

  When the surface of the positive electrode active material is coated with a lithium metal oxide in order to increase the charging voltage of the lithium ion secondary battery, there is a problem that the lithium ion conductivity is lowered and the rate characteristics are lowered. In addition, there is a problem that residual lithium is localized on the surface of the positive electrode active material and the amount of gas such as carbon dioxide is increased when cycling at a high charge voltage.

  An object of the present invention is to improve the capacity, cycle characteristics, and rate characteristics of a lithium ion secondary battery charged and discharged at a high charge voltage, and to suppress gas generation when the battery is cycled.

  Therefore, as a result of intensive studies, the present inventors have coated a part of the surface of at least one primary particle of the positive electrode active material with a lithium metal oxide and the remaining surface with a metal oxide whose crystal structure is cubic. When a lithium ion secondary battery using a coated positive electrode material is cycled at a high charge voltage, side reactions with the electrolyte in the lithium metal oxide layer are suppressed, and lithium ion conductivity is ensured in the metal oxide layer. As a result, it was found that the high voltage resistance and the rate characteristics are improved.

  Furthermore, by optimizing the coating ratio of the lithium metal oxide coating layer to the metal oxide layer and the thickness of the coating layer, the metal oxide layer lithium having a small volume expansion and contraction can be obtained when cycled at a high charge voltage. It has been found that the structure of the positive electrode active material can be stabilized by physically suppressing the volume expansion and contraction of the positive electrode active material, and as a result, the cycle characteristics are improved.

  That is, the present invention employs, as a positive electrode, a positive electrode active material in which at least one primary particle surface is coated with a lithium metal oxide and the remaining surface is coated with a metal oxide layer having a cubic crystal structure. A lithium ion secondary battery that can suppress side reactions with an electrolyte in a lithium metal oxide layer, and that physically suppresses volume expansion and contraction of a positive electrode active material when cycled at a high voltage. be able to. In addition, the lithium oxide conductivity can be ensured by the metal oxide layer. As a result, even when the battery is charged at a high voltage, the lithium ion secondary having excellent battery capacity, cycle characteristics and rate characteristics. A battery can be obtained.

  According to the present invention, in a lithium ion secondary battery charged at a high voltage, side reactions with the non-aqueous electrolyte during charging and discharging can be suppressed, and the capacity, cycle characteristics, and rate characteristics of the battery can be improved. it can.

Schematic cross-sectional view of a positive electrode material in one embodiment of the present invention Schematic cross-sectional view of a lithium ion secondary battery in one embodiment of the present invention

  First, the positive electrode for a lithium ion secondary battery used in the present invention will be described.

  The positive electrode for a lithium ion secondary battery includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector, and the positive electrode active material 10 is composed of secondary particles composed of primary particles. A part of the surface of the primary particles is covered with a lithium metal oxide layer 11 and the surface of the remaining primary particles is covered with a cubic metal oxide layer 12.

The lithium metal oxide is at least one selected from the group consisting of lithium metaborate, lithium niobate, lithium titanate, lithium tungstate, and lithium molybdate.
If the thickness of the lithium metal oxide layer 11 is 0.5 nm or less, side reactions with the electrolytic solution cannot be suppressed, and if it is 5 nm or more, the excess lithium metal oxide layer becomes a resistance layer and the rate characteristics are deteriorated. Since there is a tendency to make it, it is preferable that it is 0.5 nm or more and 5 nm or less. The cubic metal oxide is nickel oxide.
When the thickness of the cubic metal oxide layer 12 is 0.5 nm or less, side reactions with the electrolytic solution cannot be suppressed, and when the thickness is 10 nm or more, the capacity tends to decrease. It is preferably 0.5 nm or more and 10 nm or less.
When the average coverage x of the lithium metal oxide layer 11 is less than 0.8, side reactions with the electrolytic solution cannot be suppressed, and when it is 1.0, the rate characteristics tend to decrease. 0.8 or more and less than 1.0.
When the average coverage y of the metal oxide layer 12 is 0.2 or more, there is a tendency that a side reaction with the electrolytic solution cannot be suppressed, and therefore it is preferably less than 0.2.
The average primary particle size of the positive electrode active material 10 tends to decrease the mixture density when it is less than 30 nm, and tends to decrease the rate characteristics when it is 300 nm or more.
It is preferably 30 nm or more and 300 nm or less.

  Next, the nonaqueous electrolytic solution used in the present invention will be described.

  As the non-aqueous electrolyte, a non-aqueous electrolyte containing a fluorinated solvent excellent in high voltage resistance was used.

  The fluorinated solvent is at least one selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate.

  Next, the covering process of the lithium metal oxide layer 11 and the metal oxide layer will be described.

  The coating step includes a step of depositing a lithium metal oxide on the surface of the active material, a heat treatment step for improving the coating strength of the coated lithium metal oxide, and a part of the layer of the coated lithium metal oxide. It comprises a water washing treatment step for removing and a drying step for providing a metal oxide layer on the portion where the lithium metal oxide has been removed.

  The step of depositing comprises preparing a solution containing a different element by dissolving or dispersing lithium metal oxide in water or an organic solvent, and then dispersing lithium nickel composite oxide in the solution containing lithium metal oxide. The solvent was completely removed by heating, and a lithium metal oxide was deposited on the surface of the lithium nickel composite oxide.

  The condition of the above-mentioned heat treatment is that the coating strength of the lithium metal oxide tends to be insufficient when the temperature is 210 ° C. or lower, and when the temperature is 700 ° C. or higher, the primary particles re-sinter, Since there exists a tendency to fall, it is preferable that it is 210 degreeC or more and 700 degrees C or less.

  The conditions of the water washing treatment described above tend to cause excessive dissolution of the lithium metal oxide when the weight of the active material per liter of water is 750 g or less. Therefore, the weight of the active material per liter of water is preferably 750 g or more and 1500 g or less.

  When the drying conditions are lower than 120 ° C., the metal oxide layer 12 tends not to be sufficiently formed. When the temperature is higher than 200 ° C., internal lithium tends to migrate to the active material surface. Therefore, it is preferably 120 ° C. or higher and 200 ° C. or lower.

  As the positive electrode current collector, a current collector used for a positive electrode of a lithium ion secondary battery is not particularly limited. Specifically, aluminum, an aluminum alloy, or the like can be used in the form of a foil, a film, a film, a sheet, or the like. The thickness of the positive electrode current collector is usually 1 to 500 μm, and can be appropriately set according to the capacity and size of the lithium ion secondary battery.

The positive electrode active material layer is obtained, for example, by mixing a lithium nickel composite oxide, a binder, a dispersion medium, and an additive such as a conductive agent as necessary to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry can be applied to the surface of the positive electrode current collector, dried and rolled.

  As a binder, the binder used for a lithium ion secondary battery can be mentioned without particular limitation. Specifically, polytetrafluoroethylene, polyvinylidene fluoride and modified products thereof, fluorine-containing polymers such as tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene rubber, etc. And polyolefin resins such as polyethylene, polypropylene, and the like. These can be used individually by 1 type and can also be used in combination of 2 or more type. As the conductive agent, a conductive agent used for a lithium ion secondary battery can be mentioned without particular limitation. Specifically, carbon blacks such as graphites, acetylene black, ketjen black, furnace black, lamp black and thermal black, carbon fibers, metal fibers and the like can be mentioned.

  The lithium metal oxide includes at least one lithium metal selected from the group consisting of lithium metaborate, lithium niobate, lithium titanate, lithium tungstate, lithium molybdate, lithium europate, lithium erbate, and lithium samarate. It is an oxide.

  As the raw material mixture of the lithium nickel composite oxide, various raw materials conventionally used for producing lithium nickel composite oxide can be used without any particular limitation. Specifically, examples of the lithium compound include lithium hydroxide and lithium carbonate, and examples of the nickel compound include nickel hydroxide and nickel oxide. Examples of the different element compound include various oxides, carbonates, nitrates, hydroxides and the like.

  The mixing of the raw material mixture and the different element compound described above may be either dry mixing or wet mixing, but dry mixing is preferred from the standpoint of simplicity. Examples of the mixing device include a ball mill.

  By firing the obtained raw material mixture and the mixture with the different element compound in an air atmosphere, a lithium nickel composite oxide in which the different element is internally added can be obtained. As baking conditions at this time, 600 to 900 degreeC and 12 to 24 hours are preferable.

  Next, the negative electrode for a lithium ion secondary battery used in the present invention will be described.

  A negative electrode for a lithium ion secondary battery includes a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector.

  As the negative electrode current collector, a current collector used for a negative electrode of a lithium ion secondary battery is not particularly limited. Specifically, stainless steel, nickel, copper, or the like can be used in the form of a foil, a film, a film, a sheet, or the like. The thickness of the negative electrode current collector can be appropriately set in the range of 1 μm to 500 μm according to the capacity, size, etc. of the lithium ion secondary battery.

As the carbon material, a carbon material capable of inserting and extracting lithium used in a lithium ion secondary battery is not particularly limited. Specific examples include carbon materials such as graphite and amorphous carbon. As a binder, what is used for the negative electrode of a lithium ion secondary battery is used without limitation. Specific examples include polyolefins such as polyethylene and polypropylene; styrene-butadiene rubber (SBR) and modified products thereof. These can be used individually by 1 type and can also be used in combination of 2 or more type. Examples of the conductive agent include those exemplified as the conductive agent used for the positive electrode active material layer.

  In addition, if the nonaqueous electrolyte contains at least one fluorinated solvent selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate, the surface of the negative electrode is good. It is preferable from the point that a thick film can be formed.

  Next, the lithium ion secondary battery according to the present invention will be described.

  The lithium ion secondary battery according to the present invention is a lithium ion battery in which a part of the surface of at least one primary particle is covered with a lithium metal oxide and the remaining surface is covered with a metal oxide layer having a crystal structure of a cubic structure. A positive electrode employing a nickel composite oxide, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte are provided.

  As shown in FIG. 2, in the lithium ion secondary battery 20, a positive electrode 21, a negative electrode 22, and a microporous separator 23 interposed between the positive electrode 21 and the negative electrode 22 are wound in a spiral shape. An electrode group 24 is provided. The electrode group 24 includes a positive-side insulating plate 25 at one end in the winding axis direction, and a negative-side insulating plate 26 at the other end. The electrode group 24 is housed together with a non-aqueous electrolyte in a battery case 27 that also serves as a negative electrode terminal. The battery case 27 is sealed with a sealing plate 28. The battery case 27 is electrically connected to the negative electrode 22 via the negative electrode lead 29, and the positive terminal 30 of the sealing plate 28 is electrically connected to the positive electrode 21 via the positive electrode lead 31.

  Hereinafter, although components other than the positive electrode 21 and the negative electrode 22 will be described, the components other than the positive electrode 21 and the negative electrode 22 are not particularly limited in the lithium ion secondary battery, and a known configuration is appropriately used as the lithium ion secondary battery. be able to.

  The separator 23 is interposed between the positive electrode and the negative electrode. Examples of the separator 23 include microporous thin films, woven fabrics, and non-woven fabrics that have high ion permeability and sufficient mechanical strength. The material of the separator 23 is preferably a polyolefin such as polypropylene or polyethylene from the viewpoint that it has excellent durability and can exhibit a shutdown function when overheated. The thickness of the separator is generally 10 μm to 300 μm, preferably 10 μm to 40 μm. The separator may be a single layer film made of one kind of material, or a composite film or a multilayer film made of two or more kinds of materials. The porosity of the separator is preferably 30% to 70%, more preferably 35% to 60%. The porosity indicates the ratio of the volume of the hole portion to the total volume of the separator.

  The nonaqueous electrolytic solution includes a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent.

As the non-aqueous solvent, various non-aqueous solvents used for the non-aqueous electrolyte of the lithium ion secondary battery can be used. Specifically, cyclic carbonate solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, chain carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane Cyclic ether solvents such as 1, 2-dimethoxyethane, chain ether solvents such as 1,2-diethoxyethane, cyclic ester solvents such as γ-butyrolactone, chain ester solvents such as methyl acetate, fluoroethylene carbonate, fluoro A fluorinated solvent that is at least one selected from the group consisting of methyl propionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate can be used. Moreover, these can be used individually by 1 type and can also be used in combination of 2 or more type.

Examples of the lithium salt include various lithium salts used as a solute in the non-aqueous electrolyte of a lithium ion secondary battery. _{Specifically, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiSO 3 CF 3, LiN (SO 2 CF 3) 2, LiN (SO 2 C 2 F 5) 2, LiN (SO 2 CF 3) ( SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) _{3 and the} like. These can be used individually by 1 type and can also be used in combination of 2 or more type. The concentration of the lithium salt is preferably 0.5 mol / L to 2 mol / L.

  In the above description, a wound cylindrical battery is illustrated as a specific embodiment of the lithium ion secondary battery, but the shape of the lithium ion secondary battery is not limited thereto. The lithium ion secondary battery can be appropriately selected not only in a cylindrical shape but also in a shape such as a coin shape, a square shape, a sheet shape, a button shape, a flat shape, and a stacked shape, depending on the application.

Example 1
(1) Production of lithium nickel composite oxide 1 g of lithium metaborate was dissolved in water. In the obtained solution, 100 g of lithium nickel composite oxide (LiNi _0.8 Co _0.16 Al _0.04 O ₂ : NCA) was dispersed. Next, the solvent was completely removed by heating with stirring. The obtained mixture was heat-treated at 250 ° C. for 12 hours in a vacuum atmosphere to obtain a lithium nickel composite oxide coated with lithium metaborate. The obtained lithium nickel composite oxide coated with lithium metaborate was dispersed in water and the water was removed by suction filtration to obtain a lithium nickel composite oxide in which the lithium metaborate layer was partially dissolved. Furthermore, the lithium nickel composite oxide in which the obtained lithium metaborate layer is partially dissolved is heated in vacuum at 150 ° C. for 5 hours to oxidize the surface not covered with lithium metaborate, thereby at least one primary A lithium nickel composite oxide in which part of the particle surface was coated with a lithium metaborate layer and the remaining surface was coated with a nickel oxide layer was obtained. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

(2) Production of positive electrode 90 parts by mass of positive electrode active material particles, 3 parts by mass of a conductive agent, 87.5 parts by mass of a 2-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) (concentration of 8 parts by mass of PVDF, The positive electrode mixture slurry was obtained by mixing the solid content of PVDF (7 parts by mass). The obtained positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 10 μm, dried and rolled to obtain a positive electrode having a total thickness of 140 μm provided with a positive electrode active material layer.

(3) Production of negative electrode 93.5 parts by mass of artificial graphite (C) powder and 12.5 parts by mass of modified styrene-butadiene rubber (solid content 40 parts by mass)) 1.5 parts by mass of sodium carboxymethylcellulose Thus, an artificial graphite mixture slurry was obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm.

(4) Preparation of non-aqueous electrolyte Fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1: 6 to obtain a non-aqueous solvent. It was. A non-aqueous electrolyte (F / E / E) was prepared by dissolving LiPF ₆ in the non-aqueous solvent thus obtained to a concentration of 1.0 mol / L.

(5) Fabrication of lithium ion secondary battery Microporous separator (Polyethylene and polypropylene composite film, product number “2300” manufactured by Celgard Co., Ltd.), thickness inserted between the positive electrode, the negative electrode, the positive electrode, and the negative electrode An electrode group was obtained by winding a laminate of 25 μm in a spiral shape. Then, an aluminum positive electrode lead was welded to a part of the positive electrode current collector, and a nickel negative electrode lead was welded to a part of the negative electrode current collector. Such an electrode group was accommodated in a battery case having a bottomed substantially cylindrical shape having a diameter of 18 mm and a height of 65 mm. And 5.2 mL of nonaqueous electrolyte solution was inject | poured in the battery case.

(6) Evaluation of battery The cycle characteristics of the obtained lithium ion secondary battery were evaluated according to the following methods.

<Initial discharge capacity>
After charging the lithium ion secondary battery with a charge end voltage of 4.4V and charging at a rate of 1C, the discharge end voltage is set to 2.5V and at a rate of 0.2C, 1C and 2C. Discharged. The discharge capacity at 0.2 C obtained at this time was defined as the initial discharge capacity.

<Cycle characteristics>
The charge / discharge cycle under the following conditions was repeated for the lithium ion secondary battery. The environmental temperature at the time of charging / discharging was set to 25 degreeC. Initially, the maximum current value was set to 2.5 A, and constant current charging was performed until the voltage reached 4.4 V, and then constant voltage charging was performed at 4.4 V until the current value decreased to 50 mA. Next, the discharge end voltage was set to 2.5 V, and constant current discharge was performed at a rate of 0.2 C. The pause time between charging and discharging was 30 minutes. This charging / discharging cycle was made into 1 cycle, and charging / discharging was repeated 100 cycles. The discharge capacity at the 100th cycle in the charge / discharge cycle was regarded as 100%, and the cycle characteristics were evaluated by expressing the discharge capacity when 100 cycles passed as a percentage as the capacity retention rate. The results are shown in Table 1.
(Example 2)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the heat treatment was 500 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

(Example 3)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the heat treatment was 700 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

Example 4
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the weight of the active material per liter of water was set to 1000 g under the conditions of the water washing treatment. At this time, the lithium metaborate layer had a thickness of 3 nm, and the nickel oxide layer had a thickness of 5 nm. Moreover, the average coverage of the lithium metaborate layer at this time was 0.85, and the average coverage of the nickel oxide layer was 0.15.

(Example 5)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 2 except that the weight of the active material per liter of water was changed to 1500 g under the conditions of the water washing treatment. At this time, the lithium metaborate layer had a thickness of 2 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.95, and the average coverage of the nickel oxide layer was 0.05.

(Example 6)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the drying step was 100 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 3 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

(Example 7)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the drying step was 180 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 7 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

(Example 8)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the lithium metal oxide was changed to lithium niobate. At this time, the lithium niobate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

Example 9
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the lithium metal oxide was changed to lithium titanate. At this time, the lithium titanate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

(Example 10)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the lithium metal oxide was changed to lithium tungstate. At this time, the lithium tungstate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.
(Example 11)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the lithium metal oxide was changed to lithium molybdate. At this time, the lithium molybdate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

(Comparative Example 1)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that lithium metal oxide and NCA not coated with metal oxide were used as the positive electrode active material.

(Comparative Example 2)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the heat treatment was 200 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. Moreover, the average coverage of the lithium metaborate layer at this time was 1.0, and the average coverage of the nickel oxide layer was 0.

(Comparative Example 3)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the heat treatment was 750 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 5 nm. The average coverage of the lithium metaborate layer at this time is 0
. 9. The average coverage of the nickel oxide layer was 0.1.

(Comparative Example 4)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the weight of the active material per liter of water was 650 g under the conditions of the water washing treatment. At this time, the lithium metaborate layer had a thickness of 7 nm, and the nickel oxide layer had a thickness of 5 nm. Moreover, the average coverage of the lithium metaborate layer at this time was 0.8, and the average coverage of the nickel oxide layer was 0.2.

(Comparative Example 5)
A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the weight of the active material per liter of water was changed to 1600 g under the conditions of the water washing treatment. At this time, the lithium metaborate layer had a thickness of 1 nm, and the nickel oxide layer had a thickness of 5 nm. At this time, the average coverage of the lithium metaborate layer was 0.98, and the average coverage of the nickel oxide layer was 0.02.

(Comparative Example 6)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the drying step was 80 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 2 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

(Comparative Example 7)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the temperature of the drying step was 200 ° C. At this time, the lithium metaborate layer had a thickness of 4 nm, and the nickel oxide layer had a thickness of 7 nm. At this time, the average coverage of the lithium metaborate layer was 0.9, and the average coverage of the nickel oxide layer was 0.1.

  The battery of Example 1 had good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium metaborate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value.

  Furthermore, Example 1 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate.

  Further, the battery of Example 1 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  Further, the battery of Example 2 had a good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium metaborate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value.

  Furthermore, the battery of Example 2 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate. However, although the rate characteristic is lower than that in Example 1, it is considered that a part of the lithium metaborate layer was decomposed to become a resistance layer by increasing the temperature of the heat treatment.

  The battery of Example 2 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Example 3 had a good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium metaborate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value.

  Furthermore, the battery of Example 3 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate. However, although the rate characteristic is lower than that in Example 1, it is considered that this is because a part of the lithium metaborate layer was decomposed to become a surface resistance layer by increasing the temperature of the heat treatment. .

  Further, the battery of Example 3 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Example 4 had a good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium metaborate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value.

  Furthermore, the battery of Example 4 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate.

  Further, the battery of Example 4 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles. However, although the cycle characteristics are lower than in Example 1, the average coverage of the lithium metaborate layer is 0.85 because the weight of the active material per liter of water is 750 g. This is considered to be because the effect of physically suppressing the volume expansion and contraction of the active material when the cycle is repeated is reduced.

  In addition, the battery of Example 5 had a good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium metaborate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value.

  Furthermore, the battery of Example 5 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate. However, the rate characteristic is lower than that of Example 1, but this is because the weight ratio of the active material per liter of water is 1500 g, and the average coverage of the lithium metaborate layer is 0.95. This is considered to be due to a decrease in lithium ion conductivity.

  Further, the battery of Example 5 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Example 6 had a good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium metaborate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value.

  Furthermore, the battery of Example 6 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate.

  Further, the battery of Example 6 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles. However, the cycle characteristics are lower than in Example 1, but this is because the drying condition is set to 100 ° C., and the thickness of the nickel oxide layer is 3 nm, thereby suppressing the side reaction with the electrolyte. This is thought to be due to the decline.

  In addition, the battery of Example 7 had good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium metaborate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value.

  Furthermore, the battery of Example 7 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate. However, the rate characteristics are lower than in Example 1, but this is because the lithium ion conductivity was lowered because the thickness of the nickel oxide layer was 7 nm by setting the drying condition to 180 ° C. it is conceivable that.

  Further, the battery of Example 7 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Example 8 had a good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing the lithium niobate layer and the nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value. However, although the initial discharge capacity is lower than that in Example 1, it is considered that this is because the lithium metaborate layer is more effective in suppressing side reactions with the electrolyte.

  Furthermore, the battery of Example 8 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate.

  Further, the battery of Example 8 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Example 9 had a good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium titanate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value. However, although the initial discharge capacity is lower than that in Example 1, it is considered that this is because the lithium metaborate layer is more effective in suppressing side reactions with the electrolyte.

  Furthermore, the battery of Example 9 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate.

  Further, the battery of Example 9 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Example 10 had a good initial discharge capacity. This is probably because the side reaction with the electrolyte was suppressed by providing a lithium tungstate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value. However, although the initial discharge capacity is lower than that in Example 1, it is considered that this is because the lithium metaborate layer is more effective in suppressing side reactions with the electrolyte.

  Furthermore, the battery of Example 10 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate.

  Further, the battery of Example 10 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Example 11 had good initial discharge capacity. This is probably because the side reaction with the electrolytic solution was suppressed by providing a lithium molybdate layer and a nickel oxide layer on the surface of the primary particles, and the discharge capacity showed a good value. However, although the initial discharge capacity is lower than that in Example 1, it is considered that this is because the lithium metaborate layer is more effective in suppressing side reactions with the electrolyte.

  Furthermore, the battery of Example 11 had good rate characteristics. This is probably because the lithium ion conductivity was ensured by providing a nickel oxide layer on a part of the surface of the primary particles, and the discharge capacity showed a good value even at a high discharge rate.

  Further, the battery of Example 11 had good cycle characteristics. This is considered to have exhibited good cycle characteristics by physically suppressing the volume expansion / contraction of the active material caused by repeating the cycle by providing a layer of lithium metaborate on the surface of the primary particles.

  In addition, the battery of Comparative Example 1 showed lower values of initial discharge capacity and cycle characteristics than the batteries of Examples 1-11. This is presumably due to the absence of a layer on the active material surface that suppresses side reactions with the electrolyte.

  On the other hand, the battery of Comparative Example 2 showed lower initial discharge capacity and cycle characteristics than the batteries of Examples 1-11. This is presumably because the coating strength of the lithium metaborate layer was lowered due to the heat treatment condition being 200 ° C., and the side reaction inhibition effect with the electrolytic solution was lowered.

  Furthermore, the battery of Comparative Example 3 exhibited lower values for the initial discharge capacity, rate characteristics, and cycle characteristics than the batteries of Examples 1-11. This is considered to be due to the fact that the lithium metaborate was decomposed due to the heat treatment condition being 750 ° C. and became a surface resistance layer.

  In addition, the battery of Comparative Example 4 showed lower initial discharge capacity and cycle characteristics than the batteries of Examples 1-11. This is considered to be due to the fact that the weight of the active material per liter of water was 650 g under water washing conditions, so that the coverage of the lithium metaborate layer was 0.8 and the side reaction suppression effect with the electrolytic solution was reduced. .

  On the other hand, the battery of the comparative example 5 showed a value with a low rate characteristic compared with the battery of Examples 1-11. This is thought to be due to the fact that the weight of the active material per liter of water was 1600 g, and the lithium metaborate layer coverage was 0.98 and the lithium ion conductivity was reduced.

  Furthermore, the battery of Comparative Example 6 showed a lower cycle characteristic than the batteries of Examples 1-11. This is presumably because the thickness of the nickel oxide layer was 2 nm because the drying condition was 80 ° C., and the side reaction suppression effect with the electrolytic solution was reduced.

  In addition, the battery of Comparative Example 7 showed a lower rate characteristic than the batteries of Examples 1-11. This is presumably because the surface resistance increased because the thickness of the nickel oxide layer became 7 nm because the drying condition was 200 ° C.

The lithium ion secondary battery of the present invention has a large discharge capacity even when charged at a high voltage, shows a high rate characteristic, and can further suppress the decomposition of the non-aqueous electrolyte during the charge / discharge cycle. Good characteristics. Therefore, the lithium ion secondary battery of the present invention is useful as a power source for various portable electronic devices such as mobile phones, PDAs, personal computers, digital cameras, and portable game machines. Further, it can be applied to the use of a driving power source for an electric vehicle, a hybrid vehicle and the like.

DESCRIPTION OF SYMBOLS 10 Positive electrode active material 11 Lithium metal oxide layer 12 Metal oxide layer 20 Lithium ion secondary battery 21 Positive electrode 22 Negative electrode 23 Separator 24 Electrode group 25 Positive electrode side insulating plate 26 Negative electrode side insulating plate 27 Battery case 28 Sealing plate 29 Negative electrode Lead 30 Positive terminal 31 Positive lead

Claims (7)

A lithium ion secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte.
The positive electrode active material consists of secondary particles composed of primary particles,
A lithium nickel composite oxide in which a part of the surface of the primary particle is coated with a layer of lithium metal oxide and the surface of the remaining primary particle is coated with a layer of cubic metal oxide,
The lithium metal oxide is at least one selected from the group consisting of lithium metaborate, lithium niobate, lithium titanate, lithium tungstate, and lithium molybdate,
The lithium metal oxide layer has a thickness of 0.5 nm or more and 5 nm or less,
The cubic metal oxide is nickel oxide;
The cubic metal oxide layer has a thickness of 0.5 nm or more and 10 nm or less,
The average coverage x of the lithium metal oxide layer is 0.85 or more and less than 0.95,
The lithium ion secondary battery, wherein the metal oxide layer has a coverage y of 0.05 or more and less than 0.15 (x + y = 1).   The lithium ion secondary battery according to claim 1, wherein the lithium nickel composite oxide has an average primary particle diameter of 30 nm or more and 300 nm or less.   The non-aqueous electrolyte includes a fluorinated solvent that is at least one selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. Item 3. The lithium ion secondary battery according to Item 1 or 2. A method for producing a positive electrode active material for a lithium ion secondary battery, comprising:
The positive electrode active material consists of secondary particles composed of primary particles,
A lithium nickel composite oxide in which a part of the surface of the primary particle is coated with a layer of lithium metal oxide and the surface of the remaining primary particle is coated with a layer of cubic metal oxide,
Depositing the lithium metal oxide on the surface of the lithium nickel composite oxide using water or an organic solvent;
A heating step of heat-treating lithium nickel composite oxide lithium to which the lithium metal oxide is deposited;
A step of washing the heat-treated lithium nickel composite oxide with water;
A drying step of drying the lithium nickel composite oxide washed with water;
The manufacturing method of the positive electrode active material for lithium ion secondary batteries which has this.   5. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 4, wherein the temperature of the heat treatment is 200 ° C. or more and 500 ° C. or less.   6. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 4, wherein the amount of the active material for the water washing treatment is 750 g to 1500 g per liter of water.   The temperature of the said drying process is 120 to 200 degreeC, The manufacturing method of the positive electrode active material for lithium ion secondary batteries in any one of Claims 4-6 characterized by the above-mentioned.