JP2017152295A - Positive electrode active material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium ion secondary battery having good cycle characteristics, a positive electrode, and a lithium ion secondary battery.SOLUTION: A positive electrode active material 24 for a lithium ion secondary battery contains a first compound represented by formula (1): LiwNix(M1)y(M2)O[where, M1 represents Co or the like, M2 represents Al or the like, and 1.0<w<1.1, 2.0<(w+x+y+z)≤2.1, 0.3<x<0.95, 0.01<y<0.4, and 0.001<z0.2 are satisfied], and at least one second compound represented by formula (2): Liw(M3)xVyOz[where, M3 represents at least one of Ni or the like, and 1≤w≤3, 0≤x≤2, 1≤y≤6 and 1≤z≤13 are satisfied] or represented by formula (3): Liw(M3)xPyOz[where, M3 represents Ni or the like, and 1≤w≤3, 0≤x≤3, 1≤y≤6, and 0≤z≤10 are satisfied].SELECTED DRAWING: Figure 1

Description

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

In recent years, with the spread of portable information electronic devices such as mobile phones, video cameras, and notebook computers, the performance, size, and weight of the devices are rapidly developing.
For power supplies used in these devices, demand for secondary batteries, particularly lithium ion secondary batteries, is growing due to a good balance of economy, high performance, small size and light weight. Furthermore, lithium ion secondary batteries are used in some hybrid cars and electric cars. These electronic devices are being further improved in performance and size, and lithium ion secondary batteries are also required to have high-density energy requirements, long life, and improved safety and reliability.

Many positive electrode active materials suitable for lithium ion secondary battery applications have been proposed. Generally, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ , Li (Ni _x Co _y Al) are used. _{z) O 2, Li (Co} x Ni y Mn z) O 2), there is a polyanionic compound such as represented by olivine structure _{(LiFePO 4,} LiVOPO 4). Among them, lithium nickel oxide has a high capacity and a high lithium discharge voltage of about 3.8 V, but the structural stability accompanying charge / discharge is low, and transition metals are easily eluted, so it adheres to the separator and negative electrode surfaces. It is said that there are problems such as deterioration of cycle characteristics due to precipitation.

  Recently, as disclosed in Patent Document 1, by covering the active material with lithium vanadium phosphate, the elution of oxygen and transition metals can be suppressed, and the stability of the crystal structure and the discharge energy can be improved even at high temperatures. Substances have been proposed. In addition, as in Patent Document 2, the carbon is coated and mixed with lithium vanadium phosphate and lithium nickel composite oxide, and the cycle characteristics are improved by defining the relationship between the initial charge and discharge amounts of the positive electrode and the negative electrode. There is also a proposed method.

  However, the demands of the world are not known to remain, and further improvement of cycle characteristics is required.

JP 2008-277152 A JP2013-084566A

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

In order to achieve the above object, a positive electrode active material for a lithium ion secondary battery according to the present invention comprises a composition formula (1) Liw ₁ Nix ₁ (M1) y ₁ (M2) z ₁ O ₂ [M1 is Co, Mn At least one selected, M2 is at least one element selected from Al, Fe, Cr, Ba, Mn and Mg, and 1.0 <w ₁ <1.1, 2.0 <(w ₁ + x ₁ + Y ₁ + z ₁ ) ≦ 2.1, 0.3 <x ₁ <0.95, 0.01 <y ₁ <0.4, 0.001 <z ₁ <0.2] When,
Composition formula (2) Liw ₂ (M3) x ₂ Vy ₂ Oz ₂ [M3 is at least one selected from Ni, Co, and Mn, 1 ≦ w ₂ ≦ 3, 0 ≦ x ₂ ≦ 2, 1 ≦ y ₂ ≦ 6, 1 ≦ z ₂ ≦ 13], or composition formula (3) Liw ₃ (M3) x ₃ Py ₃ Oz ₃ [M3 is at least one selected from Ni, Co, and Mn, and 1 ≦ w ₃ ≦ 3 , 0 ≦ x ₃ ≦ 3, 1 ≦ y ₃ ≦ 6, 0 ≦ z ₃ ≦ 10] and at least one second compound.

  By using the positive electrode active material for a lithium ion secondary battery according to the present invention, when charging and discharging at a high potential, repeated charging and discharging is performed due to the presence of a stable compound having a crystal structure including V and P. In this case, the deterioration of the active material can be suppressed, and further, the transition metal eluted from the positive electrode active material for the lithium ion secondary battery is captured, and the adhesion and precipitation to the separator and the negative electrode surface are also suppressed. It is considered that the cycle characteristics can be improved.

  It is preferable that the second compound of the positive electrode active material for a lithium ion secondary battery according to the present invention covers the surface of at least a part of the particles made of the first compound.

  Thereby, the transition metal eluted from the positive electrode active material for the lithium ion secondary battery can be easily captured, and the cycle characteristics can be improved by suppressing adhesion and precipitation to the separator and the negative electrode surface.

  The second compound of the positive electrode active material for a lithium ion secondary battery according to the present invention preferably contains the compound of the composition formula (2) and the compound of the composition formula (3).

  As a result, since there is a compound having a stable crystal structure including V and P, the transition metal eluted from the positive electrode active material for the lithium ion secondary battery is captured, and adhesion and precipitation on the separator and the negative electrode surface are also performed. By suppressing it, the cycle characteristics can be further improved.

  Content of V in the compound of the composition formula (2) of the positive electrode active material for a lithium ion secondary battery according to the present invention is 0.1 to 10 at% or less with respect to the whole positive electrode active material for the lithium ion secondary battery. It is preferable that the P content in the compound represented by the composition formula (3) is 0.1 to 5 at% or less with respect to the whole positive electrode active material for a lithium ion secondary battery.

  Thereby, while protecting a positive electrode active material, cycle characteristics can be improved by improving the structural stability of the active material at the time of charging / discharging, without preventing the movement of lithium ion at the time of raising a charging voltage. .

The positive electrode active material for a lithium ion secondary battery according to the present invention has a composition formula (4) Li (M4) PO ₄ [M4 is at least one selected from the group consisting of Fe, Cu, Zn, Mg and VO]. It is preferable that the third compound to be further mixed.

  Thereby, more excellent cycle characteristics can be obtained and the capacity can be increased. This is considered to be due to the fact that the third compound has little change in structure accompanying charge / discharge.

  The positive electrode active material for a lithium ion secondary battery according to the present invention has a mass ratio of the first compound represented by the composition formula (1) and the third compound composed of the composition formula (4) of 60:40 to 95: It is preferable to be within the range of 5.

  As a result, the charge / discharge capacity of the positive electrode active material for a lithium ion secondary battery can be obtained more efficiently, and a reduction in capacity due to mixing with a phosphoric acid-based polyanion compound can be suppressed and both can be achieved at a high level. Can do.

  The positive electrode for a lithium ion secondary battery according to the present invention includes the positive electrode active material for a lithium ion secondary battery.

  A lithium ion secondary battery according to the present invention includes the above positive electrode for a lithium ion secondary battery, a negative electrode having a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution. It is characterized by becoming.

  According to the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery that have better cycle characteristics than conventional ones.

It is a schematic cross section of a lithium ion secondary battery.

  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. Furthermore, the constituent elements described below can be appropriately combined.

<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 stacked body 40, a case 50 that accommodates the stacked body 40 in a sealed state, and a pair of leads 60 and 62 connected to the stacked body 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 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.

<Positive electrode active material layer>
The positive electrode active material layer 14 contains at least the positive electrode active material for a lithium ion secondary battery according to this embodiment and a conductive additive. The positive electrode active material layer 14 may include a binder that binds the positive electrode active material and the conductive additive.

<Conductive aid>
Examples of the conductive assistant include carbon powders such as carbon blacks, carbon nanotubes, carbon materials, metal fine powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO. Can be mentioned.

<Binder>
A binder will not be specifically limited if the positive electrode active material for lithium ion secondary batteries and a conductive support agent can be bound to the positive electrode electrical power collector 12, A well-known binder can be used. The binder may be made of any material as long as the above-described binding is possible. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoro Ethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride A fluororesin such as (PVF) is used.

  In addition to the above, as binders, for example, polyethylene, polypropylene, polyethylene terephthalate, polyamide (PA), polyimide (PI), polyamideimide (PAI), aromatic polyamide, cellulose, styrene-butadiene rubber (SBR), isoprene Rubber, butadiene rubber, ethylene / propylene rubber, polyacrylic acid and its salt, alginic acid and its salt and the like may be used. Also, thermoplastic elastomeric polymers such as styrene / butadiene / styrene block copolymers, hydrogenated products thereof, styrene / ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers, and hydrogenated products thereof. May be used. Further, syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (carbon number 2 to 12) copolymer may be used.

  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.

  The ratio of the positive electrode active material for the lithium ion secondary battery, the conductive additive and the binder in the positive electrode active material layer 14 is not particularly limited. However, if the ratio of the positive electrode active material is small, the electrode density tends to decrease. The ratio is preferably 80% by mass or more.

<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.
<Positive electrode active material>

The positive electrode active material for a lithium ion secondary battery according to this embodiment has a composition formula (1): Liw ₁ Nix ₁ (M1) y ₁ (M2) z ₁ O ₂ [M1 is at least one selected from Co and Mn The seed, M2, is at least one element selected from Al, Fe, Cr, Ba, Mn and Mg, and 1.0 <w ₁ <1.1, 2.0 <(w ₁ + x ₁ + y ₁ + z ₁ ) ≦ 2.1, 0.3 <x ₁ <0.95, 0.01 <y ₁ <0.4, 0.001 <z ₁ <0.2]
Composition formula (2): Liw ₂ (M3) x ₂ Vy ₂ Oz ₂ [M3 is at least one kind of Ni, Co, and Mn, 1 ≦ w ₂ ≦ 3, 0 ≦ x ₂ ≦ 2, 1 ≦ y ₂ ≦ 6, 1 ≦ z ₂ ≦ 13],
Or composition formula (3): Liw ₃ (M3) x ₃ Py ₃ Oz ₃ [M3 is at least one kind of Ni, Co, and Mn, 1 ≦ w ₃ ≦ 3, 0 ≦ x ₃ ≦ 3, 1 ≦ y ₃ ≦ 6, 0 ≦ z ₃ ≦ 10] and at least one second compound selected from the group consisting of 2 ≦ z and ₃ ≦ 10].

The first compound is
Composition formula (1): Liw ₁ Nix ₁ (M1) y ₁ (M2) z ₁ O ₂ [M1 is at least one selected from Co and Mn, M2 is from Al, Fe, Cr, Ba, Mn and Mg At least one element selected, 1.0 <w ₁ <1.1, 2.0 <(w ₁ + x ₁ + y ₁ + z ₁ ) ≦ 2.1, 0.3 <x ₁ <0. 95, 0.01 <y ₁ <0.4, 0.001 <z ₁ <0.2], specifically, Li _1.0 Ni _0.8 Co _0.15 Al _0.05 O ₂ , Li _1.0 Ni _0.87 Co _0.10 Al _0.03 O ₂ , Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O ₂ , Li _1.0 Ni _{0 .78} Co _0.19 Al _0.03 O _{2 and, Li 1.0 Ni 0.8 Co 0.1 Mn} 0.1 O 2 _{Li 1.0 Ni 0.5 Co 0.2 Mn 0.3} O 2, Li 1.0 Ni 0.6 Co 0.2 Mn 0.2 O 2, Li 1.0 Ni 0.3 Co 0.3 such as Mn _0.3 O _2, and the like. Among them, it is preferable to use Li _1.0 Ni _0.8 Co _0.15 Al _0.05 O ₂ . Thereby, a high capacity can be obtained.

The first compound preferably has an average primary particle size of 0.3 to 5 μm. When the average primary particle diameter is in the range of 0.3 to 5 μm, the second compound is sufficiently coated and the first compound has high crystallinity, so that the cycle characteristics are particularly improved.

Compositional formula (2) and compositional formula (3) can be used as the second compound.
First, composition formula (2) is Liw ₂ (M3) x ₂ Vy ₂ Oz ₂ [M3 is at least one kind of Ni, Co, and Mn, and 1 ≦ w ₂ ≦ 3, 0 ≦ x ₂ ≦ 2, 1 ≦ y ₂ ≦ 6, 1 ≦ z ₂ ≦ 13],
_{Specifically,} LiNiVO _4, LiMniVO 4 and LiCoiVO ₄ is used, preferably, LiNiVO ₄ and the like. In addition, a part of the transition metal element may be substituted with one or more elements selected from other transition metals.

Further, as the second compound, composition formula _{(3): Liw 3 (M3} ) x 3 Py 3 Oz 3 [M3 is at least one consisting Ni, Co, from _{Mn, 1 ≦ w 3 ≦ 3,0} ≦ x ₃ ≦ 3, 1 ≦ y ₃ ≦ 6, 0 ≦ z ₃ ≦ 10], specifically, Li ₂ Ni ₃ P ₆ O ₁₉ , LiCo ₂ P ₃ O ₁₀ and LiMnP ₂ O ₇ Preferred is Li ₂ Ni ₃ P ₆ O ₁₉ . In addition, a part of the transition metal element may be substituted with one or more elements selected from other transition metals.

  In the positive electrode active material for a lithium ion secondary battery according to the present embodiment, it is preferable that the second compound covers at least a part of the surface of the particles made of the first compound.

  By providing the coating portion, the effect of capturing the elution of transition metal ions into the electrolyte solution without reducing the capacity in the positive electrode active material and the effect of preventing electron transfer at the interface with the electrolyte solution are provided. It can be obtained efficiently and high cycle characteristics can be obtained. The second compound is preferably coated so as to partially cover the first compound with a thickness of 0.1 to 10 μm, but the thickness may be unevenly coated.

  The state of the covering portion is not particularly limited, and the surface of the first compound may be covered in an island shape or a lattice shape.

  The second compound may be attached to the surface of the first compound or the surface of the secondary particle of the second compound, and together with the conductive auxiliary agent, is in the vicinity of the surface of the first compound or the surface of the secondary particle of the second compound. Also good.

  The covering portion preferably covers 20% or more of the surface of the first compound. This further improves the cycle characteristics.

  It is preferable that the thickness of a coating | coated part is 0.1-5 micrometers. Within this range, the above-described effect of the covering portion can be obtained efficiently without increasing the resistance component of the covering portion, so that high cycle characteristics can be obtained.

  As for the 2nd compound to coat | cover, since the direction mentioned above can obtain the above-mentioned effect more efficiently, it is preferable that both the composition formula (2) and the composition formula (3) are coated, but only one of them is mixed and coated. Also good.

  In the positive electrode active material for a lithium ion secondary battery according to this embodiment, the second compound preferably contains the compound represented by the composition formula (2) and the compound represented by the composition formula (3).

  Since the second compound contains both the composition formula (2) and the composition formula (3), the compound of V and P having a stable crystal structure is used. Therefore, the positive electrode active material for a lithium ion secondary battery can be used. More eluting transition metals can be captured and adhesion / precipitation on the separator and negative electrode surfaces can be suppressed, thereby further improving cycle characteristics.

By setting the compound ratio of V and P to 2: 1, it is considered that the transition metal in the positive electrode active material can be efficiently captured, and the movement of the transition metal to the electrolytic solution is hindered. That is, it is preferable because elution of the transition metal into the electrolytic solution is suppressed.

  In the positive electrode active material for a lithium ion secondary battery according to this embodiment, the content of V in the compound of the composition formula (2) is 0.1 to 10 at% or less with respect to the entire positive electrode active material for the lithium ion secondary battery. It is preferable that the content of P in the compound of the composition formula (3) is 0.1 to 5 at% or less with respect to the whole positive electrode active material for a lithium ion secondary battery.

  The content of V in the compound of the composition formula (2), which becomes the covering portion, is preferably 0.1 to 3.5 at% or less with respect to the whole positive electrode active material for a lithium ion secondary battery. The content of P in the compound of 3) is preferably 0.1 to 1.8 at% or less with respect to the whole positive electrode active material for a lithium ion secondary battery. This is preferable because it can efficiently obtain the effect of trapping the elution and the effect of preventing the electron transfer at the interface with the electrolytic solution, and can obtain high cycle characteristics.

<Method for producing positive electrode active material>
The positive electrode active material for a lithium ion secondary battery of the present embodiment has a composition formula (1) Liw ₁ Nix ₁ (M1) y ₁ (M2) z ₁ O ₂ [M1 is at least one selected from Co and Mn, M2 is at least one element selected from Al, Fe, Cr, Ba, Mn, and Mg, and 1.0 <w ₁ <1.1, 2.0 <(w ₁ + x ₁ + y ₁ + z ₁ ) ≦ 2.1, 0.3 <x ₁ <0.95, 0.01 <y ₁ <0.4, 0.001 <z ₁ <0.2], and at least one of the above compounds Composition formula (2): Liw ₂ (M3) x ₂ Vy ₂ Oz ₂ [M3 is at least one kind of Ni, Co, Mn, and 1 ≦ w ₂ ≦ 3, 0 ≦ x ₂ ≦ _{2,1 ≦ y 2 ≦ 6,1 ≦ z} 2 ≦ 13 ], or composition formula _{(3): Liw 3 (M3} ) x Py ₃ Oz ₃ [M3 is at least one consisting Ni, Co, from _{Mn, 1 ≦ w 3 ≦ 3,0} ≦ x 3 ≦ 3,1 ≦ y 3 ≦ 6,0 ≦ z 3 ≦ 10 ] complex consisting of The positive electrode active material is manufactured by a method including a coating step of coating with a layer.

  The production step can be produced by various production methods such as known solid phase synthesis, hydrothermal synthesis, carbothermal reduction method, coprecipitation method, sol-gel process, and the like, and is not limited to a specific method.

  If the composite layer can be coated on the surface of the compound particles to be coated, a known surface coating method, that is, a sputtering method, a CVD (Chemical Vapor Deposition) method, a dipping method such as dip coating, may be used. It can be manufactured by a general-purpose coating method such as a method. The simplest of these coating methods is simply by adding compound particles to the coating solution to produce a mixture (mixing step), removing the solvent (solvent removing step), and drying by drying. Although it is a law, it is not limited to a specific method.

The positive electrode active material for a lithium ion secondary battery according to the present embodiment has a composition formula (4): Li (M4) PO ₄ [M4 is at least one selected from the group consisting of Fe, Cu, Zn, Mg and VO] It is preferable that the 3rd compound which consists of is further mixed.

Specific examples of the third compound include LiVOPO _{4. The} crystal form is not particularly limited and may be partially amorphous. In particular, LiVOPO ₄ that is orthorhombic is mixed with the first compound. This is preferable because an increase in resistance due to charging and discharging is suppressed and a decrease in capacity can be suppressed.

  The primary particle size of the third compound is preferably 0.05 to 1 μm, and preferably 5% or more in the weight of the positive electrode active material.

  In the positive electrode active material for a lithium ion secondary battery according to this embodiment, the mass ratio of the first compound represented by the composition formula (1) and the third compound composed of the composition formula (4) is 60:40 to 95: 5. It is preferable to be within the range.

  When the mass ratio with the positive electrode active material is within the above range, the charge / discharge capacity of the positive electrode active material can be obtained more efficiently, and the decrease in capacity due to mixing with the phosphate polyanion compound is suppressed. However, both can be achieved at a high level. The range of 90:10 is more preferable because the above effect can be efficiently exhibited.

  Although the manufacturing method of a 3rd compound is not specifically limited, At least a raw material preparation process and a baking process are provided. In the raw material preparation step, a lithium source, a transition metal source, a phosphorus source, and water are stirred and mixed to prepare a mixture (mixed solution). You may implement the drying process which dries the mixture obtained by the raw material preparation process before a baking process. You may implement a hydrothermal synthesis process before a drying process and a baking process as needed.

The compounding ratio of the lithium source, the transition metal source, and the phosphorus source is, for example, the molar ratio of Li, transition metal element and P in the mixture, Li (M4) PO ₄ [M4 is from Fe, Cu, Zn, Mg and VO. The third compound can be produced by adjusting the stoichiometric ratio (1: 1: 1) of at least one selected from the group consisting of, and drying and firing the mixture, preferably with a high charge. It is preferable to use LiVOPO ₄ that can realize the discharge voltage.

  In addition, compound forms, such as the lithium source mentioned above, a transition metal source, and a phosphorus source, are not specifically limited, A well-known material can be selected according to a process, such as an oxide and salt of each raw material.

  In order to obtain a powder of an active material having a desired particle size, a pulverizer or a classifier may be used. For example, a mortar, a ball mill, a bead mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

<Method for producing positive electrode>
The positive electrode 10 is obtained by adding a slurry obtained by adding a known method, for example, a positive electrode active material for a lithium ion secondary battery, a conductive additive, and a binder to an organic solvent or an aqueous solvent according to the type of the positive electrode current collector 12. It can be manufactured by applying to the surface and drying. 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 of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and toluene.

The aqueous solvent may be water or a mixed solution with an organic solvent (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water.
<Negative electrode active material layer>
As the negative electrode active material layer 24, a material containing a negative electrode active material, a conductive additive, and a binder can be used.

  As the binder and the conductive additive used for the negative electrode, the same materials as those for the positive electrode can be used.

<Negative electrode active material>
The negative electrode active material of the present invention may be any compound that can occlude and release lithium ions, and known negative electrode active materials for batteries can be used. 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.

<Method for producing negative electrode>
The negative electrode 20 may be manufactured by adjusting the slurry and applying it to the negative electrode current collector 22 in the same manner as the positive electrode 10.

<Separator>
The separator 18 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.

<Case>
The case 50 seals the power generation element 40 and the electrolyte solution therein. The case 50 is not particularly limited as long as it can suppress leakage of the electrolyte solution to the outside and entry of moisture or the like into the lithium ion secondary battery 100 from the outside. For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52 and a film such as polypropylene can be used as the polymer film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point, such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). Etc. are preferred.

<Lead>
The leads 60 and 62 are made of a conductive material such as aluminum or nickel.

<Electrolyte>
The electrolytic solution of this embodiment is composed of a solute, a solvent, and an additive.

<Solute>
In the case of a lithium ion secondary battery, a lithium salt is used as the solute. Examples of the lithium salt can be used particularly limited not known material, _{specifically, LiPF 6, LiClO 4, LiBF} 4, LiAsF 6, 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 CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (SO ₂ F) ₂ , LiN (CF ₃ CF ₂ CO) _{2 and the} like. In addition, these salts may be used individually by 1 type, and may use 2 or more types together. As the solute, LiPF ₆ , LiBF ₄ , and LiN (SO ₂ F) ₂ are preferable from the viewpoint of cycle characteristics and storage characteristics, and LiPF ₆ is more preferable. The concentration of the solute is preferably 0.8 to 1.5 M regardless of whether it is one type or two or more types.

<Solvent>
The solvent is not particularly limited, and a solvent used in known electrochemical devices can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxylene, 4-methyl-1,3 -Dixylene, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, sulfolane, 2-methyl sulfolane, dimethyl sulfoxide, N, N-dimethylformamide, N-methyloxazolidinone, etc. . These solvents can be used alone or in combination. Cyclic carbonates and chain carbonates are preferable from the viewpoint of cycle characteristics and storage characteristics, and ethylene carbonate and diethyl carbonate are more preferable.

<Additives>
Moreover, you may add a well-known additive as an additive. For example, 0.01 to 5% by mass of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3,2-dioxathiolane-2,2, -dioxide, ethylene sulfite and the like may be added.

<Separator>
The separator 18 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.

  The positive electrode active material for a lithium ion secondary battery of the present embodiment can also be used as an electrode material for electrochemical elements other than lithium ion secondary batteries. As such an electrochemical element, two types of batteries other than lithium ion secondary batteries such as a metal lithium secondary battery (one using the positive electrode active material of the present embodiment as the positive electrode and using metal lithium as the negative electrode) are used. Examples thereof include secondary batteries and electrochemical capacitors such as lithium capacitors.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1 <Preparation of Positive Electrode Active Material> In the positive electrode active material for a lithium ion secondary battery in the present embodiment, a lithium nickel composite oxide (Li _1.0 Ni _0.8 Co _0.15 Al as the first compound). _0.05 O ₂ ) and LiNiVO ₄ and Li ₂ Ni ₃ P ₆ O _{19 as} the second compound with respect to the lithium nickel composite oxide, LiNiVO ₄ at 10 at%, Li ₂ Ni ₃ P ₆ O ₁₉ at 5 at% And were synthesized by a known hydrothermal synthesis method.

(Measurement of the form of the second compound element)
In order to investigate the composition of the compound synthesized in this manner, a cross-sectional sample for STEM-EDS measurement was prepared by sampling from the positive electrode so as to contain the active material by the FIB method (Focus Ion Beam). The cross section sample was measured for the active material surface and the interior of the active material surface at 50 nm by the STEM-EDS method. The STEM used for measurement was JEM-2100F manufactured by JEOL, and the electron beam diameter was 1 nm, and measurement was performed with a storage time of 30 seconds per point. An amount of 10 at% of LiNiVO ₄ and 5 at% of Li ₂ Ni ₃ P ₆ O ₁₉ was confirmed.

<Preparation of positive electrode>
As the positive electrode active material for a lithium ion secondary battery, the lithium nickel composite oxide (Li _1.01 Ni _0.8 Co _0.15 Al _0.05 O ₂ ) synthesized and produced as described above, and the third compound Then, orthorhombic LiVOPO ₄ was weighed at a mass ratio of 95: 5 and mixed to use as a positive electrode active material for a lithium ion secondary battery. Then, 90 parts by mass of the positive electrode active material powder, 5 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride (PVDF) were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The obtained slurry was coated on an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C. for 30 minutes, and then pressed using a roll press apparatus at a linear pressure of 1000 kgf / cm to obtain a positive electrode.

<Production of negative electrode>
As a negative electrode active material, 90 parts by mass of natural graphite powder and 10 parts by mass 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.

<Electrolyte>
An electrolyte 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 20 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 electrolyte solution.
<Measurement of battery characteristics>
The evaluation cell of Example 1 was charged by a constant current constant voltage method at 25 ° C. up to 4.3 V at 0.1 C, and then discharged by a constant current method up to 2.8 V at 0.1 C. At this time, the discharge capacity of Example 1 was 130 mAh / g (initial discharge capacity). A cycle test was repeated for 100 cycles of this charge / discharge cycle. When the initial discharge capacity of the evaluation cell of Example 1 was 100%, the discharge capacity after 100 cycles was 92%. Hereinafter, the ratio of the discharge capacity after 100 cycles when the initial discharge capacity is 100% is referred to as cycle characteristics. A high cycle characteristic indicates that the battery is excellent in charge / discharge cycle durability.

(Examples 2 to 24)
In Examples 2 to 24, the evaluation cell was produced and the battery characteristics were evaluated in the same manner as in Example 1, except that the amounts of the second compounds LiNiVO ₄ and Li ₂ Ni ₃ P ₆ O ₁₉ were changed. Went. The results are shown in Table 1.

(Examples 25-27)
In Examples 25 to 27, the first compound was Li _1.0 Ni _0.87 Co _0.10 Al _0.03 O ₂ , Li _1.0 Ni _0.83 Co _0.14 Al _0.03 O ₂ , An evaluation cell was prepared and battery characteristics were evaluated in the same manner as in Example 1 except that the material was changed to Li _1.0 Ni _0.78 Co _0.19 Al _0.03 O ₂ . The results are shown in Table 2.

(Examples 28 to 35)
In Examples 28-35, LiNiVO ₄ of the second compound type was changed to LiMnVO ₄ and LiCoVO ₄ , and Li ₂ Ni ₃ P ₆ O ₁₉ was changed to LiMnP ₂ O ₇ and LiCo ₂ P ₃ O ₁₀ , and each combination was changed. A cell for evaluation and battery characteristic evaluation were performed in the same manner as in Example 1 except that the above was confirmed. The results are shown in Table 3.

(Examples 36 to 39)
In Examples 36 to 39, the type of the first compound is Li _1.0 Ni _0.8 Co _0.1 Mn _0.1 O ₂ , Li _1.0 Ni _0.5 Co _0.2 Mn _0.3 O. ₂ , Li _1.0 Ni _0.6 Co _0.2 Mn _0.2 O ₂ , Li _1.0 Ni _0.3 Co _0.3 Mn _0.3 O ₂ In this way, an evaluation cell was prepared and battery characteristics were evaluated. The results are shown in Table 4.

(Examples 40 to 44, Comparative Example 1)
In Examples 40 to 44 and Comparative Example 1, production of evaluation cells and evaluation of battery characteristics were performed in the same manner as in Example 1 except that the type and ratio of the third compound were changed. The results are shown in Table 4.

  As shown in Tables 1 to 4, the examples have improved cycle characteristics. As described above, according to the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery with better cycle characteristics, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the positive electrode active material.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  By using the positive electrode active material for a lithium ion secondary battery of the present invention, higher cycle characteristics can be obtained. Therefore, the present invention is a useful technique in the field of secondary batteries.

(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 ... case, 52 ... metal foil, 54 ... polymer film, 60, 62 ... lead, 100 ... lithium ion secondary battery

Claims (8)

Composition formula (1): Liw ₁ Nix ₁ (M1) y ₁ (M2) _z1 O ₂ [M1 is at least one selected from Co and Mn, M2 is selected from Al, Fe, Cr, Ba, Mn and Mg 1.0 <w ₁ <1.1, 2.0 <(w ₁ + x ₁ + y ₁ + z ₁ ) ≦ 2.1, 0.3 <x ₁ <0.95 A first compound represented by 0.01 <y ₁ <0.4, 0.001 <z ₁ <0.2],
Composition formula (2): Liw ₂ (M3) x ₂ Vy ₂ Oz ₂ [M3 is at least one kind of Ni, Co, and Mn, 1 ≦ w ₂ ≦ 3, 0 ≦ x ₂ ≦ 2, 1 ≦ y ₂ ≦ 6, 1 ≦ z ₂ ≦ 13],
Or composition formula (3): Liw ₃ (M3) x ₃ Py ₃ Oz ₃ [M3 is at least one kind of Ni, Co, and Mn, 1 ≦ w ₃ ≦ 3, 0 ≦ x ₃ ≦ 3, 1 ≦ y ₃ ≦ 6, 0 ≦ z ₃ ≦ 10] and at least one second compound selected from the group consisting of:
Positive electrode active material for lithium ion secondary batteries.   2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the second compound covers a surface of at least a part of particles made of the first compound.   The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the second compound contains the compound of the composition formula (2) and the compound of the composition formula (3).   The amount of V in the compound of the composition formula (2) is 0.1 to 10 at% or less with respect to the whole positive electrode active material for the lithium ion secondary battery, and the amount of P in the compound of the composition formula (3). 4. The positive electrode active material for a lithium ion secondary battery according to claim 3, wherein is present at 0.1 to 5 at% or less with respect to the whole positive electrode active material for the lithium ion secondary battery. The positive electrode active material for a lithium ion secondary battery includes a third compound having the composition formula (4): Li (M4) PO ₄ [M4 is at least one selected from the group consisting of Fe, Cu, Zn, Mg, and VO]. The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein is further mixed.   6. The mass ratio of the first compound represented by the composition formula (1) and the third compound composed of the composition formula (4) is in the range of 60:40 to 95: 5. The positive electrode active material for lithium ion secondary batteries as described in 2.   The positive electrode for lithium ion secondary batteries using the positive electrode active material for lithium ion secondary batteries as described in any one of Claim 1 to 6. A lithium ion secondary battery comprising: the positive electrode according to claim 7; a negative electrode having a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolytic solution.

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