JP2016186933A - Positive electrode active material, positive electrode using the same, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material having a high cycle characteristic, and to provide a positive electrode and a lithium ion battery using the same.SOLUTION: A positive electrode active material contains: a lithium composite oxide; and a high thermal conductive compound whose thermal conductivity is equal to or more than 10 W/m K.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material, a positive electrode using the positive electrode active material, and a lithium ion secondary battery.

  Conventionally, lithium cobaltate, lithium nickelate, lithium manganate, and the like as a positive electrode active material for a lithium ion secondary battery have been widely studied since an electromotive force exceeding 4 V can be obtained.

The positive electrode active material for a lithium ion secondary battery tends to increase the charging voltage for the purpose of improving the discharge capacity. However, when the charge voltage is increased to improve the discharge capacity, the amount of heat generated by the battery increases accordingly, and the cycle characteristics of the battery are reduced due to heat generation.

In particular, battery systems using lithium cobaltate, lithium nickelate, lithium manganate, etc. as the positive electrode active material have not obtained sufficient cycle characteristics due to heat generated when the charging voltage is raised, especially in high temperature environments. It is remarkable.

As a prior document on the cycle characteristics of lithium cobalt oxide, for example, as disclosed in Patent Document 1, it is reported that the cobalt characteristics of lithium cobalt oxide and / or a part of lithium are replaced with other metal elements to improve the cycle characteristics. However, the improvement is not sufficient, and further improvement in cycle characteristics is required. Hereinafter, in some cases, a lithium ion secondary battery is referred to as a “battery”.

JP 2006-164758 A

The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a positive electrode active material, a positive electrode, and a lithium ion secondary battery having high cycle characteristics.

In order to achieve the above goal, a positive electrode active material according to the present invention includes a lithium composite oxide represented by the following chemical formula (1):
A high thermal conductivity compound having a thermal conductivity of 10 W / m · K or more;
It is characterized by including.
Li _x M1 _y M2 _1-y O ₂ (1)
[In the above chemical formula 1, M1 is at least one metal selected from Ni, Co, and Mn, and M2 is Al, Fe, Ti, Cr, Mg, Cu, Ga, Zn, Sn, B, V, Ca, and Sr. And at least one metal selected from the group consisting of 0.05 ≦ x ≦ 1.2 and 0.3 ≦ y ≦ 1]

  According to such a configuration, since the heat generated during charging can be efficiently released by including a high thermal conductive compound of 10 W / m · K or more, the positive electrode active material is deteriorated in order to suppress the heat storage of the positive electrode. And cycle characteristics are improved. In particular, when the charging voltage is increased to around 4.2 V, crystal transition of the positive electrode active material or decomposition of the positive electrode active material occurs, and large heat generation occurs accordingly. With such a configuration, it is possible to suppress a decrease in thermal stability of the positive electrode active material.

In the positive electrode active material according to the present invention, the high thermal conductive compound is AlN, BN, Si ₃ N ₄ , TiN, ZrN, VN, Cr ₂ N, SiC, WC, TiC, TaC, ZrC, NbC, Mo ₂ C, Cr It is preferably at least one selected from ₃ C ₂ , TiB ₂ , ZrB ₂ , VB ₂ and NbB ₂ .

  According to such a configuration, by including a compound having particularly high thermal conductivity, heat generated during charging can be efficiently released, and deterioration of the positive electrode active material is prevented in order to suppress heat storage of the positive electrode, Cycle characteristics are improved.

In the positive electrode active material according to the present invention, the high thermal conductive compound is preferably at least one selected from AlN, BN, Si ₃ N ₄ , TiN, ZrN, VN, NbN, and Cr ₂ N.

Since nitride is very stable and reaction between the lithium composite oxide and the nitride hardly occurs, cycle characteristics are improved.

The lithium composite oxide used for the positive electrode active material according to the present invention is preferably represented by the following chemical formula (2).
Li _a Ni _1-b M3 _b O ₂ (2)
[In the above chemical formula 1, M3 is at least one metal selected from the group consisting of Co, Fe, Ti, Cr, Mg, Al, Cu, Ga, Mn, Zn, Sn, B, V, Ca and Sr. 0.05 ≦ a ≦ 1.2 and 0 ≦ b ≦ 0.5]

  By including the lithium composite oxide having a high Ni ratio, the discharge capacity is improved.

  The high thermal conductive compound used in the positive electrode active material according to the present invention is preferably contained in an amount of 0.05 to 10% by weight with respect to the lithium composite oxide.

  When the weight of the high thermal conductive compound is greater than 0.05% by weight, the heat generated during charging can be released more efficiently, so that the cycle characteristics are improved. Moreover, if it is 10 weight% or less, the fall of an energy density can be prevented.

  The high thermal conductive compound used for the positive electrode active material according to the present invention preferably covers at least a part of the lithium composite oxide.

  By covering at least a part of the lithium composite oxide with the high thermal conductive compound, the heat from the heat source can be conducted and released more efficiently, and the positive electrode active material can be prevented from being deteriorated by suppressing the heat storage of the positive electrode. , Cycle characteristics are improved.

  The high thermal conductive compound used for the positive electrode active material according to the present invention preferably has an average primary particle size of 10 to 500 nm.

  If the average primary particle diameter of the high heat conductive compound is 10 nm or more, it becomes easy to form a heat conduction network path, and heat can be efficiently released. Moreover, if it is 500 nm or less, since the contact point between particle | grains can be increased, a heat | fever is efficiently released and cycling characteristics improve.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material which has high cycling characteristics, a positive electrode, and a lithium ion secondary battery using the same can be provided.

It is a schematic cross section of the lithium ion secondary battery of this embodiment. It is a schematic cross section of the positive electrode active material of this embodiment. It is a schematic cross section which shows the state of the coating layer of the positive electrode active material of this embodiment.

  An example of a preferred embodiment of a lithium ion secondary battery according to the present invention will be described in detail with reference to the drawings. However, the lithium ion secondary battery of the present invention is not limited to the following embodiments. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

(Lithium ion secondary battery)
An electrode and a lithium ion secondary battery according to this embodiment will be briefly described with reference to FIG. The lithium ion secondary battery 100 mainly includes a laminate 40, a case 50 that accommodates the laminate 40 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 40. Although not shown, the electrolytic solution is housed in the case 50 together with the laminate 40.

  The laminated body 40 is configured such that the positive electrode 20 and the negative electrode 30 are disposed to face each other with the separator 10 containing a non-aqueous electrolyte interposed therebetween. The positive electrode 20 is obtained by providing a positive electrode active material layer 24 on a plate-like (film-like) positive electrode current collector 22. The negative electrode 30 is obtained by providing a negative electrode active material layer 34 on a plate-like (film-like) negative electrode current collector 32. The positive electrode active material layer 24 and the negative electrode active material layer 34 are in contact with both sides of the separator 10. Leads 62 and 60 are connected to the ends of the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the ends of the leads 60 and 62 extend to the outside of the case 50.

  Hereinafter, the positive electrode 20 and the negative electrode 30 are collectively referred to as electrodes 20 and 30, and the positive electrode current collector 22 and the negative electrode current collector 32 are collectively referred to as current collectors 22 and 32. The positive electrode active material layer 24 and the negative electrode active material The material layer 34 is collectively referred to as the active material layers 24 and 34.

  The positive electrode active material layer according to this embodiment includes a positive electrode active material, a positive electrode binder, and a conductive material.

(Positive electrode active material)
The positive electrode active material according to the present embodiment includes a lithium composite oxide represented by the following chemical formula (1) and a high thermal conductive compound having a thermal conductivity of 10 W / m · K or more.
Li _x M1 _y M2 _1-y O ₂ (1)
[In the above chemical formula 1, M1 is at least one metal selected from Ni, Co, and Mn, and M2 is Al, Fe, Ti, Cr, Mg, Cu, Ga, Zn, Sn, B, V, Ca, and Sr. And at least one metal selected from the group consisting of 0.05 ≦ x ≦ 1.2 and 0.3 ≦ y ≦ 1]

  According to such a configuration, since the heat generated during charging can be efficiently released by including a high thermal conductive compound of 10 W / m · K or more, the positive electrode active material is deteriorated in order to suppress the heat storage of the positive electrode. And cycle characteristics are improved.

The high thermal conductive compound preferably has higher thermal conductivity than at least the lithium composite oxide contained in the positive electrode active material, and AlN, BN, Si ₃ N ₄ , TiN, ZrN, VN, TaN, Cr ₂ N, SiC, More preferably, it is at least one selected from WC, TiC, TaC, ZrC, NbC, Mo ₂ C, Cr ₃ C ₂ , TiB ₂ , ZrB ₂ , VB ₂ , and NbB ₂ . By including a compound having a particularly high thermal conductivity, the heat generated during charging can be efficiently released, and the positive electrode active material is prevented from deteriorating because heat storage of the positive electrode is suppressed, and the cycle characteristics are improved.

The high thermal conductive compound is more preferably at least one selected from AlN, BN, Si ₃ N ₄ , TiN, ZrN, VN, NbN, and Cr ₂ N. Since nitride is very stable and reaction between the lithium composite oxide and the nitride hardly occurs, cycle characteristics are improved.

The lithium composite oxide is preferably represented by the following chemical formula (2).
Li _a Ni _1-b M3 _b O ₂ (2)
[In the above chemical formula 1, M3 is at least one metal selected from the group consisting of Co, Fe, Ti, Cr, Mg, Al, Cu, Ga, Mn, Zn, Sn, B, V, Ca and Sr. 0.05 ≦ a ≦ 1.2 and 0 ≦ b ≦ 0.5]
By including the lithium composite oxide having a high Ni ratio, the discharge capacity is improved.

  The weight of the high thermal conductive compound is preferably 0.05 to 10% by weight with respect to the lithium composite oxide. When the weight of the high thermal conductive compound is larger than 0.05% by weight, the heat generated during charging can be released more efficiently, so that the cycle characteristics are improved. Moreover, if it is 10 weight% or less, the fall of an energy density can be prevented.

Further, the weight of the high thermal conductive compound is more preferably 0.1 to 5% by weight. When the weight of the high thermal conductive compound is 0.1 to 5% by weight, the above-described effect can be further enhanced.

  As described above, the positive electrode active material according to the present embodiment includes a specific lithium composite oxide and a high thermal conductive compound having a thermal conductivity of 10 W / m · K or more. The form is not particularly limited as long as the high thermal conductive compound is in contact with the surface of the lithium composite oxide particles. That is, the lithium composite oxide and the high thermal conductive compound may be mixed in the positive electrode active material layer 24. Further, the mixed state at this time may be uniformly dispersed in the positive electrode active material layer 24, or the lithium composite oxide and the high thermal conductive compound may aggregate to form secondary particles. .

  For the purpose of improving cycle characteristics, the high thermal conductive compound preferably covers at least a part of the lithium composite oxide. Thereby, since heat from the heat source can be more efficiently conducted and released, deterioration is prevented and cycle characteristics are improved. An example of this form is shown in FIG. As shown in FIG. 2, a layer 120 containing the high thermal conductive compound may be formed on the lithium composite oxide 110. Of course, the structure is not limited to this, but the high thermal conductive compound 120 may be coated to such an extent that the effect of the present invention is produced. Needless to say, the lithium composite oxide 110 may not be completely covered with the coating layer 120 containing the high thermal conductive compound. Specifically, for example, the coverage of the high thermal conductive compound is 50% or more. Is preferred. The coverage is calculated as a percentage of how much the surface of the lithium composite oxide is covered with the high thermal conductive compound from the cross section of the positive electrode active material as shown in FIG. 2, for example, 50 positive electrode active materials The average value of

Further, the lithium composite oxide 110 preferably constitutes secondary particles. It is preferable that the high thermal conductivity compound 120 is coated on at least a part of the surface of the secondary particles. FIG. 3 is a schematic cross-sectional view showing the state of the coating layer of the positive electrode active material of this embodiment.
FIG. 3 shows a state in which the lithium composite oxide 110 constitutes secondary particles, and the surface of the secondary particles is covered with the particles of the high thermal conductive compound 120. In particular, the one located on the surface of the secondary particle of the lithium composite oxide 110 is shown as 120S, and the high thermal conductive compound filled between the primary particles near the secondary particle surface of the lithium composite oxide 110 is 120G. As shown.
Thus, it is preferable that the high thermal conductive compound 120 is filled between primary particles of the lithium composite oxide existing in the vicinity of the surface of the secondary particles of the lithium composite oxide 110. Moreover, the average particle diameter of the primary particles of the high thermal conductive compound is filled between the primary particles of the lithium composite oxide rather than the particles (120S) existing on the surface of the secondary particles of the lithium composite oxide. The thing (120G) is preferably smaller. According to such a configuration, it is possible to obtain denser composite particles.

The average primary particle size of the high thermal conductive compound is preferably 10 to 500 nm. If the average primary particle diameter of the high heat conductive compound is 10 nm or more, it becomes easy to form a heat conduction network path, and heat can be efficiently released. Moreover, if it is 500 nm or less, since the contact point between particle | grains can be increased, a heat | fever is efficiently released and cycling characteristics improve. In addition, what is necessary is just to calculate the average value of the average primary particle diameter at this time, for example, the particle | grains which sampled 50 pieces with the scanning electron microscope (SEM) from the cross section of the positive electrode active material layer.

Specifically, as the lithium composite oxide according to the present embodiment, Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 , Li _1.0 Ni _0.8 Co _0.15 Al Nickel-cobalt-aluminum ternary material (NCA) such as _0.05 O _2.0 , Li _1.0 Ni _0.8 Co _0.1 Mn _0.1 O _2.0 , Li _1.0 Ni _{0 .5} Co _0.2 Mn _0.3 O _2.0 , Li _1.0 Ni _0.6 Co _0.2 Mn _0.2 O _2.0 , Li _1.0 Ni _0.333 Co _0.333 Mn _{0 Examples} include nickel, cobalt and manganese ternary materials (NCM) such as _.333 O _2.0 , and lithium cobalt oxide (LCO) such as LiCoO _2. Among them, NCA is preferable because of its high energy density.

  Moreover, the lithium composite oxide according to the present embodiment may be composed of a mixture of two or more of the above.

  The type of the lithium composite oxide and the type of the high thermal conductive compound contained in the positive electrode active material according to the present embodiment can be identified by analysis of X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, and the like. Among these, X-ray diffraction is preferable. The mixing ratio can be identified by inductively coupled plasma emission spectroscopy.

  In order to observe the coating state of the high thermal conductive compound on the surface of the lithium composite oxide particles according to the present embodiment, the surface of the positive electrode cut and the cross section polished by a cross section polisher or an ion milling device is used as a scanning electron. Observation and measurement can be performed using a microscope, a transmission electron microscope, or the like.

(Positive electrode current collector)
The positive electrode current collector 22 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

(Conductive material)
Examples of the conductive material include carbon powder such as carbon black, carbon nanotube, carbon material, fine metal powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and fine metal powder, and conductive oxide such as ITO. It is done.

(Positive electrode binder)
The binder binds the active materials to each other and binds the active material to the current collector 22. The binder is not particularly limited as long as the above-described bonding is possible. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) ) And the like.

  In addition to the above, as the binder, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFPPTFE-based) Fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride Ride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber It may be used vinylidene fluoride-based fluorine rubbers such as rubber (VDF-CTFE-based fluorine rubber).

  Alternatively, an electron conductive conductive polymer or an ion conductive conductive polymer may be used as the binder. Examples of the electron conductive conductive polymer include polyacetylene. In this case, since the binder also functions as a conductive material, it is not necessary to add a conductive material. Examples of the ion conductive conductive polymer include those obtained by combining a polymer compound such as polyethylene oxide and polypropylene oxide with a lithium salt or an alkali metal salt mainly composed of lithium.

(Negative electrode active material layer)
The negative electrode active material layer according to this embodiment includes a negative electrode active material, a negative electrode binder, and a conductive material.

(Negative electrode active material)
The negative electrode active material should just be a compound which can occlude / release lithium ion, and can use the well-known negative electrode active material for lithium ion batteries. Examples of the negative electrode active material include carbon materials that can occlude and release lithium ions (natural graphite, artificial graphite), carbon nanotubes, non-graphitizable carbon, graphitizable carbon, low-temperature calcined carbon, and the like, aluminum, silicon And particles containing a metal that can be combined with lithium such as tin, an amorphous compound mainly composed of an oxide such as silicon dioxide and tin dioxide, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). . It is preferable to use graphite having a high capacity per unit weight and relatively stable.

(Negative electrode current collector)
The negative electrode current collector 32 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

(Negative electrode conductive material)
Examples of the conductive material include carbon powder such as carbon black, carbon nanotube, carbon material, fine metal powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and fine metal powder, and conductive oxide such as ITO. It is done.

(Negative electrode binder)
The binder used for a negative electrode can use the same thing as a positive electrode.

(Separator)
The separator 10 only needs to be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene, or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose, polyester, and Examples thereof include a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polypropylene.

(Nonaqueous electrolyte)
The nonaqueous electrolytic solution has an electrolyte dissolved in a nonaqueous solvent, and may contain a cyclic carbonate and a chain carbonate as a nonaqueous solvent.

  The cyclic carbonate is not particularly limited as long as it can solvate the electrolyte, and a known cyclic carbonate can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, and the like can be used.

  The chain carbonate is not particularly limited as long as the viscosity of the cyclic carbonate can be reduced, and a known chain carbonate can be used. Examples thereof include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. In addition, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like may be mixed and used.

  The ratio of the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 by volume.

Examples of the electrolyte include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ , CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ Lithium salts such as CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , LiBOB can be used. In addition, these lithium salts may be used individually by 1 type, and may use 2 or more types together. In particular, LiPF ₆ is preferably included from the viewpoint of conductivity.

When LiPF ₆ is dissolved in a non-aqueous solvent, the concentration of the electrolyte in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L. When the concentration of the electrolyte is 0.5 mol / L or more, the conductivity of the nonaqueous electrolytic solution can be sufficiently secured, and a sufficient capacity can be easily obtained during charging and discharging. Moreover, by suppressing the electrolyte concentration to within 2.0 mol / L, it is possible to suppress an increase in the viscosity of the non-aqueous electrolyte, to sufficiently secure the mobility of lithium ions, and to obtain a sufficient capacity during charging and discharging. It becomes easy.

Even when LiPF ₆ is mixed with another electrolyte, the lithium ion concentration in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L, and the lithium ion concentration from LiPF ₆ is 50 mol%. More preferably, it is contained.

(Method for producing positive electrode active material)
The positive electrode active material according to this embodiment can be manufactured by the following mixing process and coating process.

(Mixing process)
In the mixing step, the positive electrode active material can be obtained by mixing the lithium composite oxide and the high thermal conductive compound. The mixing method is not particularly limited, and can be performed using an existing apparatus such as a Turbuler mixer or a Henschel mixer.

(Coating process)
In the coating step, the surface of the lithium composite oxide can be coated with a high thermal conductive compound to form a coating layer. The method for forming the coating layer is not particularly limited, but an existing method for forming the coating layer on the particle surface, such as a mechanochemical method using mechanical energy such as friction or compression, or a spray drying method in which a coating liquid is sprayed on the particle is used. be able to. Among these, the mechanochemical method is preferable because it can form a coating layer that is uniform and has good adhesion.

(Method for manufacturing electrodes 20 and 30)
Next, a method for manufacturing the electrodes 20 and 30 according to the present embodiment will be described.

  The active material, binder and solvent are mixed. A conductive material may be further added as necessary. As the solvent, for example, water, N-methyl-2-pyrrolidone or the like can be used. The mixing method of the components constituting the paint is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the current collectors 22 and 32. There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method.

  Subsequently, the solvent in the paint applied on the current collectors 22 and 32 is removed. The removal method is not particularly limited, and the current collectors 22 and 32 to which the paint is applied may be dried, for example, in an atmosphere of 80 ° C. to 150 ° C.

  Then, the electrode on which the positive electrode active material layer 24 and the negative electrode active material layer 34 are formed in this way is subjected to a press treatment by a roll press device or the like as necessary. The linear pressure of the roll press can be, for example, 100 to 2500 kgf / cm.

  Through the above steps, an electrode in which the electrode active material layers 24 and 34 are formed on the current collectors 22 and 32 is obtained.

(Method for producing lithium ion secondary battery)
Then, the manufacturing method of the lithium ion secondary battery which concerns on this embodiment is demonstrated. The method for manufacturing a lithium ion secondary battery according to the present embodiment includes a positive electrode 20 including the active material, a negative electrode 30, a separator 10 interposed between the positive electrode and the negative electrode, and a nonaqueous electrolytic solution including a lithium salt. And a step of enclosing the outer body 50 in the exterior body 50.

  For example, the positive electrode 20 including the active material described above, the negative electrode 30 and the separator 10 are stacked, and the positive electrode 20 and the negative electrode 30 are heated and pressed with a press tool from a direction perpendicular to the stacking direction. 20, the separator 10 and the negative electrode 30 are brought into close contact with each other. Then, for example, a lithium ion secondary battery can be manufactured by putting the laminate 40 into a bag-shaped exterior body 50 prepared in advance and injecting a non-aqueous electrolyte containing the lithium salt. Instead of injecting the non-aqueous electrolyte containing the lithium salt into the outer package, the laminate 40 may be impregnated with the non-aqueous electrolyte containing the lithium salt in advance.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same function and effect. Are included in the technical scope.

Example 1
(Preparation of positive electrode)
Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 (hereinafter referred to as NCA) as a lithium composite oxide and AlN (manufactured by Iritech Co., Ltd.) having an average particle diameter of 50 nm are 100: 0. 1. Weighed at a mass ratio of 1 and coated the NCA surface with AlN by a mechanochemical method to obtain a positive electrode active material. A slurry was prepared by dispersing a mixture of the obtained active material, polyvinylidene fluoride (PVDF), which is a binder, and acetylene black, in N-methyl-2-pyrrolidone (NMP), which is a solvent. The slurry was prepared so that the weight ratio of the positive electrode active material, acetylene black, and PVDF was 93: 3: 4 in the slurry. This slurry was applied onto a 20 μm thick aluminum foil as a current collector, dried, and then rolled at a linear pressure of 1000 kgf / cm to obtain a positive electrode of Example 1.

(Measurement of high thermal conductivity compounds inside the positive electrode)
Observation of the state of coating with AlN on the surface of the lithium composite oxide particles includes transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), cross section polisher, ion milling device Was observed. A sample for measurement was prepared by cutting the positive electrode and polishing the cut surface with a cross section polisher and an ion milling device.

  Observation of the positive electrode surface and the positive electrode cross section by SEM, EDX, and TEM confirmed that the surface of the lithium composite oxide particles was uniformly coated with AlN.

(Preparation of negative electrode)
As a negative electrode active material, 90 wt% of natural graphite powder and 10 wt% of PVDF were dispersed in NMP to prepare a slurry. The obtained slurry was coated on a copper foil having a thickness of 15 μm, dried under reduced pressure at a temperature of 140 ° C. for 30 minutes, and then pressed using a roll press apparatus to obtain a negative electrode.

(Nonaqueous electrolyte)
A nonaqueous electrolytic solution in which LiPF ₆ was dissolved at 1.0 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was prepared. The volume ratio of EC to DEC in the mixed solvent was EC: DEC = 30: 70.

(Separator)
A polyethylene microporous membrane having a thickness of 16 μm (porosity: 40%, shutdown temperature: 134 ° C.) was prepared.

(Production of battery)
The positive electrode, the negative electrode, and the separator were laminated to constitute a power generation element, and a battery cell of Example 1 was produced using this and the non-aqueous electrolyte.

(C rate)
The current density at which the battery cell capacity is discharged at a constant current in one hour in an environment of 25 ° C. is called 1C. Hereinafter, the current density during charging or discharging is expressed using a constant multiple of the C rate (for example, 10C of 1C). (Partial current density is expressed as 0.1 C).

(Measurement of discharge capacity)
Using the produced battery cell of Example 1, constant current charging was performed until the voltage reached 4.2 V (vs. Li ^/ Li ⁺ ) at a current density of 0.1 C, and the current density was further increased to 0.05 C. Constant voltage charging was performed at 4.2 V (vs. Li ^/ Li ⁺ ) until the voltage decreased, and the charge capacity was measured. The results are shown in Table 1 as 0.1 C discharge capacity.

Subsequently, after resting for 5 minutes, constant current discharge was performed at a current density of 0.1 C until the voltage reached 2.5 V (vs. Li ^/ Li ⁺ ), and the discharge capacity was measured. The current density is calculated with 1C as 186 mAh / g with respect to the positive electrode active material amount, and the larger the discharge capacity, the better.

(Measurement of cycle characteristics)
Using the battery cell after rate measurement, 0.5C charge / 1C discharge was repeated 100 cycles according to the charge / discharge procedure. Moreover, charging / discharging was performed in a 45 degreeC thermostat. The initial discharge capacity was 100%, and the discharge capacity value after 100 cycles was the capacity retention rate. Furthermore, five battery cells prepared under the same conditions were prepared, and the average value of the capacity retention rates was calculated. The larger the capacity maintenance rate, the better. The results are shown in Table 1 as the average value of the capacity maintenance rate after 100 cycles.

(Example 2)
In the production of the positive electrode, the battery of Example 2 was produced and evaluated in the same manner as in Example 1 except that the mass ratio of the lithium composite oxide and AlN was 100: 0.03.

Example 3
In the production of the positive electrode, a battery of Example 3 was produced and evaluated in the same manner as in Example 1 except that the mass ratio of the lithium composite oxide and AlN was 100: 0.05.

Example 4
In the production of the positive electrode, the battery of Example 4 was produced and evaluated in the same manner as in Example 1 except that the mass ratio of the lithium composite oxide and AlN was 100: 1.

(Example 5)
In the production of the positive electrode, a battery of Example 5 was produced and evaluated in the same manner as in Example 1 except that the mass ratio of the lithium composite oxide and AlN was 100: 5.

(Example 6)
In the production of the positive electrode, a battery of Example 6 was produced and evaluated in the same manner as in Example 1 except that the mass ratio of the lithium composite oxide and AlN was 100: 10.

(Example 7)
In the production of the positive electrode, a battery of Example 7 was produced and evaluated in the same manner as in Example 1 except that the mass ratio of the lithium composite oxide and AlN was 100: 11.

(Example 8)
In the production of the positive electrode, the battery of Example 8 was produced and evaluated in the same manner as in Example 1 except that BN was used instead of AlN.

Example 9
In the production of the positive electrode, a battery of Example 9 was produced and evaluated in the same manner as in Example 1 except that BN was used instead of AlN and the weight ratio of the lithium composite oxide and BN was set to 100: 5. went.

(Example 10)
In the production of the positive electrode, a battery of Example 10 was produced and evaluated in the same manner as in Example 1 except that Si ₃ N ₄ was used instead of AlN.

(Example 11)
The battery of Example 11 was made in the same manner as in Example 1 except that Si ₃ N ₄ was used instead of AlN in the production of the positive electrode and the weight ratio of the lithium composite oxide to Si ₃ N ₄ was set to 100: 5. Were prepared and evaluated.

(Example 12)
In the production of the positive electrode, the battery of Example 12 was produced and evaluated in the same manner as in Example 1 except that TiN was used instead of AlN.

(Example 13)
In the production of the positive electrode, the battery of Example 13 was produced and evaluated in the same manner as in Example 1 except that ZrN was used instead of AlN.

(Example 14)
In the production of the positive electrode, a battery of Example 14 was produced and evaluated in the same manner as in Example 1 except that VN was used instead of AlN.

(Example 15)
In the production of the positive electrode, a battery of Example 15 was produced and evaluated in the same manner as in Example 1 except that Cr ₂ N was used instead of AlN.

(Example 16)
In the production of the positive electrode, a battery of Example 16 was produced and evaluated in the same manner as in Example 1 except that SiC was used instead of AlN.

(Example 17)
In the production of the positive electrode, the battery of Example 17 was produced and evaluated in the same manner as in Example 1 except that WC was used instead of AlN.

(Example 18)
In the production of the positive electrode, a battery of Example 18 was produced and evaluated in the same manner as in Example 1 except that TiC was used instead of AlN.

(Example 19)
In the production of the positive electrode, a battery of Example 19 was produced and evaluated in the same manner as in Example 1 except that TaC was used instead of AlN.

(Example 20)
In the production of the positive electrode, a battery of Example 20 was produced and evaluated in the same manner as in Example 1 except that ZrC was used instead of AlN.

(Example 21)
In the production of the positive electrode, a battery of Example 21 was produced and evaluated in the same manner as in Example 1 except that NbC was used instead of AlN.

(Example 22)
In the production of the positive electrode, a battery of Example 22 was produced and evaluated in the same manner as in Example 1 except that Cr ₃ C ₂ was used instead of AlN.

(Example 23)
In the production of the positive electrode, a battery of Example 23 was produced and evaluated in the same manner as in Example 1 except that Mo ₂ C was used instead of AlN.

(Example 24)
In the production of the positive electrode, a battery of Example 24 was produced and evaluated in the same manner as in Example 1 except that TiB ₂ was used instead of AlN.

(Example 25)
In the production of the positive electrode, a battery of Example 25 was produced and evaluated in the same manner as in Example 1 except that ZrB ₂ was used instead of AlN.

(Example 26)
In the production of the positive electrode, a battery of Example 26 was produced and evaluated in the same manner as in Example 1 except that VB ₂ was used instead of AlN.

(Example 27)
In the production of the positive electrode, a battery of Example 27 was produced and evaluated in the same manner as in Example 1 except that NbB ₂ was used instead of AlN.

(Example 28)
The battery of Example 28 was prepared in the same manner as in Example 1 except that in the production of the positive electrode, the lithium composite oxide and AlN were mixed using a turbulent mixer without performing the step of coating AlN with the lithium composite oxide. Were prepared and evaluated. In addition, the positive electrode active material produced using the turbuler mixer in this manner was in a state where the lithium composite oxide and AlN, which is a high thermal conductive compound, were uniformly mixed.

(Example 29)
In the production of the positive electrode, the same procedure as in Example 1 was performed except that BN was used instead of AlN, and the lithium composite oxide and BN were mixed using a turbuler mixer without performing the coating step on the lithium composite oxide. Thus, a battery of Example 29 was produced and evaluated.

(Example 30)
In the production of the positive electrode, except that Si ₃ N ₄ was used instead of AlN and the lithium composite oxide and Si ₃ N ₄ were mixed using a turbuler mixer without performing the coating step on the lithium composite oxide, In the same manner as in Example 1, the battery of Example 30 was produced and evaluated.

(Example 31)
In the production of the positive electrode, the battery of Example 31 was produced and evaluated in the same manner as in Example 1 except that AlN having an average primary particle diameter of 10 nm was used instead of AlN having an average primary particle diameter of 50 nm. It was.

(Example 32)
In the production of the positive electrode, a battery of Example 32 was produced and evaluated in the same manner as in Example 1 except that AlN having an average primary particle diameter of 100 nm was used instead of AlN having an average primary particle diameter of 50 nm. It was.

(Example 33)
In the production of the positive electrode, a battery of Example 33 was produced and evaluated in the same manner as in Example 1 except that AlN having an average primary particle diameter of 500 nm was used instead of AlN having an average primary particle diameter of 50 nm. It was.

(Example 34)
In the preparation of the positive _{electrode, Li 1.0 Ni 0.83 Co 0.14 Al} Li 1.0 instead of _0.03 lithium composite oxide _{O 2.0 Ni 0.8 Co 0.1 Al 0.1} O A battery of Example 34 was made and evaluated in the same manner as Example 1 except that _2.0 lithium composite oxide was used.

(Example 35)
In the preparation of the positive _{electrode, Li 1.0 Ni 0.83 Co 0.14 Al} Li 1.0 instead of _0.03 lithium composite oxide _{O 2.0 Ni 0.8 Co 0.1 Mn 0.1} O Example 35 was conducted in the same manner as in Example 1 except that a lithium composite oxide of _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material when measuring the discharge capacity. A battery was prepared and evaluated.

(Example 36)
In the preparation of the positive _{electrode, Li 1.0 Ni 0.83 Co 0.14 Al} Li 1.0 instead of _0.03 lithium composite oxide _{O 2.0 Ni 0.5 Co 0.2 Mn 0.3} O Example 36 was conducted in the same manner as in Example 1 except that a lithium composite oxide of _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material when measuring the discharge capacity. A battery was prepared and evaluated.

(Example 37)
In the preparation of the positive _{electrode, Li 1.0} Ni _0.83 Co Li _1.0 instead of _{0.14 Al 0.03} lithium composite oxide _{O 2.0 Ni 0.34 Co 0.33 Mn 0.33} O Example 37 was performed in the same manner as in Example 1 except that a lithium composite oxide of _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the positive electrode active material amount when measuring the discharge capacity. A battery was prepared and evaluated.

(Example 38)
In the preparation of the positive _{electrode, Li 1.0 Ni 0.83 Co 0.14 Al} Li 1.0 instead of _0.03 lithium composite oxide _{O 2.0 Ni 0.6 Co 0.2 Mn 0.2} O Example 38 was carried out in the same manner as Example 1 except that a lithium composite oxide of _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material when measuring the discharge capacity. A battery was prepared and evaluated.

(Example 39)
In the production of the positive electrode, LiCoO ₂ lithium composite oxide was used instead of Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 lithium composite oxide, and the current density was measured when measuring the discharge capacity. A battery of Example 39 was produced and evaluated in the same manner as in Example 1 except that 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material.

(Example 40)
Li _1.0 Ni _{0.9 in the} form of spherical secondary particles instead of Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 lithium composite oxide in the production of the positive electrode A battery of Example 40 was produced and evaluated in the same manner as Example 1 except that a lithium composite oxide of Co _0.07 Al _0.03 O _2.0 was used. In addition, when the cross section of this positive electrode was confirmed by TEM, it was confirmed that AlN was coated on the surface and grain boundary of the secondary particles as shown in FIG.

(Example 41)
Li _1.0 Ni _{0.7 in the} form of spherical secondary particles instead of Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 lithium composite oxide in the production of the positive electrode A battery of Example 41 was made and evaluated in the same manner as Example 1 except that a lithium composite oxide of Co _0.27 Al _0.03 O _2.0 was used. In addition, when the cross section of this positive electrode was confirmed by TEM, it was confirmed that it had the structure as shown in FIG.

(Comparative Example 1)
In the production of the positive electrode, a battery of Comparative Example 1 was produced and evaluated in the same manner as in Example 1 except that AlN was not used.

(Comparative Example 2)
In the production of the positive electrode, Li _1.0 Ni _0.8 Co _0.1 was used instead of Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 lithium composite oxide without using AlN. A battery of Comparative Example 2 was produced and evaluated in the same manner as in Example 1 except that a lithium composite oxide of Al _0.1 O _2.0 was used.

(Comparative Example 3)
In the production of the positive electrode, Li _1.0 Ni _0.8 Co _0.1 was used instead of Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 lithium composite oxide without using AlN. The same as Example 1 except that a lithium composite oxide of Mn _0.1 O _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material when measuring the discharge capacity. Thus, a battery of Comparative Example 3 was produced and evaluated.

(Comparative Example 4)
In the production of the positive electrode, Li _1.0 Ni _0.5 Co _0.2 was used instead of Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 lithium composite oxide without using AlN. The same as Example 1 except that a lithium composite oxide of Mn _0.3 O _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material when measuring the discharge capacity. Thus, a battery of Comparative Example 4 was produced and evaluated.

(Comparative Example 5)
In the preparation of the positive electrode, without using _{AlN, Li} 1.0 _Ni 0.34 _{Co 0.33} instead of the lithium composite oxide of _{Li 1.0 Ni 0.83 Co 0.14 Al 0.03} O 2.0 The same as Example 1 except that a lithium composite oxide of Mn _0.33 O _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material when measuring the discharge capacity. Thus, a battery of Comparative Example 5 was produced and evaluated.

(Comparative Example 6)
In the preparation of the positive electrode, without using _{AlN, Li} 1.0 _Ni 0.6 _{Co 0.2} instead of the lithium composite oxide of _{Li 1.0 Ni 0.83 Co 0.14 Al 0.03} O 2.0 Except that a lithium composite oxide of Mn _0.2 O _2.0 was used and the current density of 1C was calculated as 160 mAh / g with respect to the amount of the positive electrode active material when measuring the discharge capacity, the same as in Example 1. Then, a battery of Comparative Example 6 was produced and evaluated.

(Comparative Example 7)
In the production of the positive electrode, without using AlN, LiCoO ₂ lithium composite oxide was used instead of Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O _2.0 lithium composite oxide, and the discharge capacity A battery of Comparative Example 7 was produced and evaluated in the same manner as in Example 1 except that 1 C of current density was calculated as 160 mAh / g with respect to the amount of the positive electrode active material at the time of measurement.

(Comparative Example 8)
In the production of the positive electrode, a battery of Comparative Example 8 was produced and evaluated in the same manner as in Example 1 except that SiO ₂ was used instead of AlN.

  As can be seen from the results of Table 1, the capacity retention rate after 100 cycles is increased and the cycle characteristics are improved by including the lithium composite oxide and the high thermal conductive compound.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 10 ... Separator, 20 ... Positive electrode, 22 ... Positive electrode collector, 24 ... Positive electrode active material layer, 30 ... Negative electrode, 32 ... Negative electrode collector, 34 ... Negative electrode Active material layer, 40 ... power generation element, 50 ... exterior body, 52 ... metal foil, 54 ... polymer film, 60, 62 ... lead, 100 ... lithium ion secondary battery 110 ... lithium composite oxide, 120 ... high thermal conductive compound-containing coating layer

Claims (9)

A lithium composite oxide represented by the following chemical formula (1);
A high thermal conductivity compound having a thermal conductivity of 10 W / m · K or more;
A positive electrode active material comprising:
Li _x M1 _y M2 _1-y O ₂ (1)
[In the above chemical formula 1, M1 is at least one metal selected from Ni, Co, and Mn, and M2 is Al, Fe, Ti, Cr, Mg, Cu, Ga, Zn, Sn, B, V, Ca, and Sr. And at least one metal selected from the group consisting of 0.05 ≦ x ≦ 1.2 and 0.3 ≦ y ≦ 1] The high thermal conductive compounds are AlN, BN, Si ₃ N ₄ , TiN, ZrN, VN, Cr ₂ N, SiC, WC, TiC, TaC, ZrC, NbC, Mo ₂ C, Cr ₃ C ₂ , TiB ₂ , ZrB _2. The positive electrode active material according to claim 1, which is at least one selected from VB ₂ and NbB ₂ . _3. The positive electrode active material according to claim 1, wherein the high thermal conductive compound is at least one selected from AlN, BN, Si ₃ N ₄ , TiN, ZrN, VN, NbN, and Cr ₂ N. ₄ . The positive electrode active material according to claim 1, wherein the lithium composite oxide is represented by the following chemical formula (2).
Li _a Ni _1-b M3 _b O ₂ (2)
[In the above chemical formula 1, M3 is at least one metal selected from the group consisting of Co, Fe, Ti, Cr, Mg, Al, Cu, Ga, Mn, Zn, Sn, B, V, Ca and Sr. 0.05 ≦ x ≦ 1.2 and 0 ≦ y ≦ 0.5]   5. The positive electrode active material according to claim 1, wherein the high thermal conductive compound is contained in an amount of 0.05 to 10 wt% with respect to the lithium nickel composite oxide.   The positive active material according to claim 1, wherein the high thermal conductive compound covers at least a part of the lithium nickel composite oxide.   7. The positive electrode active material according to claim 1, wherein an average primary particle diameter of the high thermal conductive compound is 10 to 500 nm.   The positive electrode using the positive electrode active material as described in any one of Claims 1-7.   A lithium ion secondary battery comprising the positive electrode according to claim 8, a negative electrode, and an electrolyte.

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