JP2019160576A - Positive electrode active material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material for a lithium ion secondary battery, high in capacity and excellent in storage characteristics and output characteristics under a high temperature environment.SOLUTION: A positive electrode active material for a lithium ion secondary battery contains a lithium-containing transition metal oxide containing at least one transition metal element selected from Ni and Co; a high lithium-containing phosphate compound represented by the following composition formula (1), and a phosphate compound containing a low amount of lithium, represented by the following composition formula (2): Li(M1)(PO)(1), where M1 represents at least one selected from Mn, Co, Ni, Fe, and V, and 2.7≤x≤3.3, 0.9≤y≤2.2 and 0.9≤z≤3.3 are satisfied; and Li(M2)(PO)(2), where M2 represents at least one selected from Mn, Co, Ni, Fe, V, and VO, and 0<u≤1.3, 0.9≤v≤2.2, and 0.9≤w≤3.3 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, various electric vehicles are expected to be widely used for solving environmental and energy problems. As an in-vehicle power source such as a motor driving power source that holds the key to practical application of these electric vehicles, lithium ion secondary batteries have been intensively developed. In order to widely spread batteries as in-vehicle power supplies, it is very important to have high thermal stability. At present, many positive electrode active materials for lithium ion secondary batteries have been proposed, but the most commonly known ones are lithium-containing cobalt oxide (LiCoO ₂ ) and lithium having a layered structure. containing nickel oxide is (LiNiO ₂₎ lithium-containing transition metal oxides such as. Lithium-containing cobalt oxide (LiCoO ₂ ) and lithium-containing nickel oxide (LiNiO ₂ ) have a high capacity and a high lithium discharge voltage of about 3.8 V, but when they are in a high temperature state or a high potential state May readily react with the electrolyte solution to release oxygen in the crystal structure, and thus may not have sufficient thermal stability particularly in a high charge state.

As a positive electrode active material for a lithium ion secondary battery excellent in stability at high temperatures, Patent Document 1 covers core particles containing a lithium-containing transition metal oxide and at least a part of the surface of the core particles. A positive electrode active material provided with a coating portion containing LiVOPO ₄ is disclosed. According to this patent document 1, since the direct contact between the core particles and the electrolyte is suppressed by covering the surface of the core particles with the covering portion containing LiVOPO ₄ having excellent structural stability at high temperatures, It is said that the crystal structure of the contained transition metal oxide at a high temperature is stabilized.

JP 2008-277152 A

  The positive electrode active material disclosed in Patent Document 1 exhibits excellent thermal stability under a high temperature environment. However, the positive electrode active material disclosed in Patent Document 1 is likely to have a low output characteristic because the output during large current discharge tends to be low, and an improvement in the output characteristic is desired.

  The present invention has been made in view of the above circumstances, and the object thereof is a positive electrode active material having a high capacity and excellent storage characteristics and output characteristics in a high temperature environment, a positive electrode for a lithium ion secondary battery, and The object is to provide a lithium ion secondary battery.

As a result of intensive studies, the inventor has obtained a lithium-containing transition metal oxide having at least one transition metal element selected from Ni and Co, and a predetermined lithium-rich phosphate compound containing relatively high lithium And a positive active material containing a relatively low lithium-containing phosphate compound that contains lithium at a relatively low concentration has a high capacity and a good balance between storage characteristics and output characteristics in a high-temperature environment. As a result, the present invention has been completed.
That is, in order to solve the above problems, the following means are provided.

(1) A positive electrode active material for a lithium ion secondary battery according to a first aspect includes a lithium-containing transition metal oxide containing at least one transition metal element selected from Ni and Co, and a composition formula (1 ) And a lithium low-containing phosphate compound represented by the following composition formula (2).

Li _x (M1) _y (PO ₄ ) _z (1)
However, in the composition formula (1), M1 is at least one selected from Mn, Co, Ni, Fe, and V, and 2.7 ≦ x ≦ 3.3, 0.9 ≦ y ≦ 2.2, It is 0.9 <= z <= 3.3.

Li _u (M2) _v (PO ₄ ) _w (2)
However, in the composition formula (2), M2 is at least one selected from Mn, Co, Ni, Fe, V, and VO, and 0 <u ≦ 1.3, 0.9 ≦ v ≦ 2.2, It is 0.9 <= w <= 3.3.

(2) In the positive electrode active material for a lithium ion secondary battery according to the first aspect, the lithium relative to the total mass (a + b) of the mass a of the lithium-rich phosphate compound and the mass b of the lithium-rich phosphate compound The ratio c / (a + b) of the mass c of the contained transition metal oxide may be 1.5 ≦ c / (a + b) ≦ 99.

(3) In the positive electrode active material for a lithium ion secondary battery according to the first aspect, the lithium-containing transition metal oxide may be an oxide represented by the following composition formula (3).

_{Li n M3 p M4 q O 2} ··· (3)
However, in the composition formula (3), M3 is at least one selected from Ni and Co, and M4 is Mn, Fe, Ti, Cr, Mg, Al, Cu, Si, Zr, Nb, Ga, Zn , Sn, B, V, Ca, Sr, Ba, 0.5 ≦ n ≦ 1.2, 0.5 ≦ p + q ≦ 1.2, and 0 ≦ q ≦ 0.5. .

(4) In the positive electrode active material for a lithium ion secondary battery according to the first aspect, the lithium-containing transition metal oxide is a lithium-containing nickel composite metal oxide represented by the following composition formula (4): Also good.

Li _r Ni _1-st Co _s Al _t O ₂ (4)
However, in the composition formula (4), 0.5 ≦ r ≦ 1.2, 0 <s ≦ 0.5, 0 <t ≦ 0.5, and 0 <s + t ≦ 0.5.

(5) The positive electrode concerning a 2nd aspect has any one positive electrode active material of said (1)-(4).

(6) The lithium ion secondary battery according to the third aspect includes the positive electrode, the negative electrode, the separator, and the electrolyte solution of (5).

  According to the present invention, it is possible to provide a positive electrode active material, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery that have a high capacity and excellent storage characteristics and output characteristics in a high temperature environment. .

It is a cross-sectional schematic diagram of the lithium ion secondary battery concerning this embodiment.

  Hereinafter, the present embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented without departing from the scope of the invention.

[Lithium ion secondary battery]
FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery according to this embodiment. A lithium ion secondary battery 100 shown in FIG. 1 mainly includes a laminated body 40, a case 50 that accommodates the laminated body 40 in a sealed state, and a pair of leads 60 and 62 connected to the laminated body 40. Although not shown, the nonaqueous electrolyte solution is accommodated in the case 50 together with the laminate 40.

  The stacked 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. In FIG. 1, the case 50 has one laminated body 40 in the case 50, but a plurality of laminated bodies 40 may be laminated.

"Positive electrode"
The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24 provided on the positive electrode current collector 22.

(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 layer)
The positive electrode active material layer 24 includes a positive electrode active material and a positive electrode binder, and includes a positive electrode conductive material as necessary.

  The positive electrode active material contains a lithium-containing transition metal oxide, a lithium-rich phosphate compound represented by the following composition formula (1) containing relatively high lithium, and a relatively low concentration of lithium. And a lithium-containing phosphoric acid compound represented by the following composition formula (2).

Li _x (M1) _y (PO ₄ ) _z (1)
However, in the composition formula (1), M1 is at least one selected from Mn, Co, Ni, Fe, and V, and 2.7 ≦ x ≦ 3.3, 0.9 ≦ y ≦ 2.2, It is 0.9 <= z <= 3.3.

Li _u (M2) _v (PO ₄ ) _w (2)
However, in the composition formula (2), M2 is at least one selected from Mn, Co, Ni, Fe, V, and VO, and 0 <u ≦ 1.3, 0.9 ≦ v ≦ 2.2, It is 0.9 <= w <= 3.3.

  When the positive electrode active material contains the above three compounds, the high-temperature storage characteristics and the output characteristics are improved. Although the details of this reason are not clear, it is thought to be due to the following effects.

  The metal element other than lithium (M1 in composition formula (1)) contained in the high lithium phosphate compound and the metal element other than lithium (M2 in composition formula (2)) contained in the low lithium phosphate compound are respectively The number is different. The metal element other than lithium contained in the high lithium-containing phosphate compound has a relatively small valence compared to the metal element other than lithium contained in the low lithium-containing phosphate compound. For this reason, the lithium-rich phosphate compound has a relatively weak bond between a metal element other than lithium and oxygen, and can keep a wide space for the insertion and removal of lithium ions in the crystal structure. It becomes easy to insert. Fine potential gradient between lithium-rich phosphate compound and other compounds (lithium-containing transition metal oxide, lithium-rich phosphate compound) by lithium ion desorption / insertion into this lithium-rich phosphate compound Occurs. Then, with this small potential gradient as a driving force, lithium ions move between the lithium-rich phosphate compound and other compounds, or are desorbed into other compounds, so that lithium ions can move within the positive electrode active material. Becomes easier to diffuse. Therefore, the output characteristics of the positive electrode active material are improved by including this lithium-rich phosphate compound.

  On the other hand, the metal element other than lithium contained in the low lithium phosphate compound has a relatively large valence compared to the metal element other than lithium contained in the high lithium phosphate compound. For this reason, the low lithium-containing phosphate compound has a strong bond between a metal element other than lithium and oxygen, and is excellent in stability under a high temperature environment. And when this lithium low content phosphoric acid compound contacts other compounds (lithium content transition metal oxide, lithium high content phosphoric acid compound), the surface is protected also about other compounds, and under high temperature environment Stability is improved. Therefore, the high temperature storage stability of the positive electrode active material is improved by including this low lithium-containing phosphate compound.

  Further, the lithium-containing transition metal oxide has a higher capacity than the high lithium-containing phosphate compound and the low lithium-containing phosphate compound. Therefore, the capacity | capacitance of a positive electrode active material improves by including this lithium containing transition metal oxide.

  Due to the action and effect of each compound as described above, the positive electrode active material obtained by combining the above three kinds of compounds has a high capacity and is excellent in high-temperature storage characteristics and output characteristics.

  In the above composition formula (1) representing a lithium-rich phosphate compound, z is preferably any one of 1, 2, and 3. When z is 1, x is preferably 2.7 ≦ x ≦ 3.3, and y is preferably 0.9 ≦ y ≦ 1.2. When z is 2, x is preferably 2.7 ≦ x ≦ 3.3, and y is preferably 0.9 ≦ y ≦ 1.2. When z is 3, x is preferably 2.7 ≦ x ≦ 3.3, and y is preferably 1.9 ≦ y ≦ 2.2. The lithium-rich phosphate compound need not have a stoichiometric composition. Moreover, it is preferable that x, y, and z satisfy 1 ≦ (3 × z−1 × x) / y ≦ 3. In this case, since the valence of the metal element other than lithium (M1 in the composition formula (1)) contained in the lithium-rich phosphate compound is 3 or less, lithium ions can be more easily inserted and removed.

Examples of the lithium-rich phosphate compound include Li ₂ Mn (PO ₄ ) ₂ , Li ₂ Co (PO ₄ ) ₂ , Li ₂ Ni (PO ₄ ) ₂ , Li ₂ Fe (PO ₄ ) ₂ , Li ₂ V (PO ₄ ) ₂ , Li ₃ Mn ₂ (PO ₄ ) ₃ , Li ₃ Co ₂ (PO ₄ ) ₃ , Li ₃ Ni ₂ (PO ₄ ) ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , Li ₃ V ₂ (PO ₄ ) ₃ can be mentioned. One of these lithium-rich phosphate compounds may be used alone, or two or more thereof may be used in combination. Among the above lithium-rich phosphoric acid compounds, Li ₃ Fe ₂ (PO ₄ ) ₃ and Li ₃ V ₂ (PO ₄ ) ₃ are preferable.

  In the above composition formula (2) representing the low lithium phosphate compound, w is preferably any one of 1, 2, and 3. When w is 1, u is preferably 0 <u ≦ 1.3 and v is preferably 0.9 ≦ v ≦ 1.2. When w is 2, u is preferably 0 <u ≦ 1.3 and v is preferably 0.9 ≦ v ≦ 1.2. When w is 3, u is preferably 0 <u ≦ 1.3, and v is preferably 1.9 ≦ v ≦ 2.2. Note that the low lithium phosphate compound need not have a stoichiometric composition. U, v, and w preferably satisfy 4 ≦ (3 × w−1 × u) / v ≦ 5. In this case, since the valence of the metal element other than lithium (M1 in the composition formula (1)) contained in the low lithium phosphate compound is 4 or more, the stability in a high temperature environment is further improved.

Examples of the low lithium phosphate compound include Li ₁ Mn ₂ (PO ₄ ) ₃ , Li ₁ Co ₂ (PO ₄ ) ₃ , Li ₁ Ni ₂ (PO ₄ ) ₃ , and Li ₁ Fe ₂ (PO ₄ ) _3. , Li ₁ V ₂ (PO ₄ ) ₃ , and LiVOPO ₄ . One of these low lithium phosphate compounds may be used alone, or two or more thereof may be used in combination. Among the above-described low lithium phosphate compounds, Li ₁ Fe ₂ (PO ₄ ) ₃ and LiVOPO ₄ are preferable.

The lithium-containing transition metal oxide has at least one transition metal element selected from Ni and Co.
The lithium-containing transition metal oxide is preferably an oxide represented by the following composition formula (3). By using this lithium-containing transition metal oxide, a high capacity can be obtained.

_{Li n M3 p M4 q O 2} ··· (3)
However, in the composition formula (3), M3 is at least one selected from Ni and Co. When M3 contains Ni and Co, the atomic number ratio of Ni and Co is preferably in the range of 1: 9 to 9: 1 (Ni: Co). M4 is at least one selected from Mn, Fe, Ti, Cr, Mg, Al, Cu, Si, Zr, Nb, Ga, Zn, Sn, B, V, Ca, Sr, Ba, and 0.5 ≦ n ≦ 1.2, 0.5 ≦ p + q ≦ 1.2, and 0 ≦ q ≦ 0.5. Note that the lithium-containing transition metal oxide need not have a stoichiometric composition.

  The lithium-containing transition metal oxide is preferably a lithium-containing nickel composite metal oxide represented by the following composition formula (4). By using this lithium-containing transition metal oxide, a higher capacity can be obtained.

Li _r Ni _1-st Co _s Al _t O ₂ (4)
However, in the composition formula (4), 0.5 ≦ r ≦ 1.2, 0 <s ≦ 0.5, 0 <t ≦ 0.5, and 0 <s + t ≦ 0.5.

Examples of lithium-containing transition metal oxides include LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0. Examples include ₆ Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and LiNi _0.33 Co _0.33 Mn _0.33 O ₂ . A lithium containing transition metal oxide may be used individually by 1 type, and may be used in combination of 2 or more type.

  In the positive electrode active material, the ratio c / (a + b) of the mass c of the lithium-containing transition metal oxide to the total mass (a + b) of the mass a of the lithium-rich phosphate compound and the mass b of the lithium-low phosphate compound is 1 It is preferable that 5 ≦ c / (a + b) ≦ 99. A positive electrode active material in which the ratio c / (a + b) is in this range has a higher capacity and is excellent in high-temperature storage characteristics and output characteristics. While maintaining the high capacity of the lithium-containing transition metal oxide, the effect of improving the output characteristics of the lithium-rich phosphate compound and the effect of improving the high-temperature storage stability of the lithium-containing phosphate compound This is thought to be in a balanced manner.

  In the positive electrode active material, the ratio a / b of the mass a of the lithium-rich phosphate compound to the mass b of the lithium-low phosphate compound is as follows. 0.01 ≦ a / b ≦ 0.25 is preferable. When w is 2 or 3, it is preferable that 4 ≦ a / b ≦ 99. The positive electrode active material in which the ratio a / b is in this range expresses in a well-balanced manner the effect of improving the output characteristics of the high lithium-containing phosphate compound and the effect of improving the high-temperature storage stability of the low lithium-containing phosphate compound. Therefore, the high-temperature storage characteristics and the output characteristics are more reliably improved.

  The positive electrode active material has a structure in which a lithium-containing phosphate compound having a relatively small particle size and a phosphate compound having a low lithium content are attached around a lithium-containing transition metal oxide having a relatively large particle size. Is preferred. In this case, with the lithium-containing transition metal oxide as the center, the lithium-containing transition metal oxide, the lithium-rich phosphate compound, and the lithium-low phosphate compound are in contact with each other, so that the diffusion of lithium ions due to a minute potential gradient is further improved. As a result, the output characteristics are further improved. The lithium-containing transition metal oxide preferably has an average particle size in the range of 1 μm to 50 μm. The high lithium-containing phosphate compound and the low lithium-containing phosphate compound preferably have an average particle size in the range of 50 nm to 800 nm. The average particle diameter can be measured by a laser diffraction / scattering method.

  The positive electrode active material can be produced by mixing a lithium-containing transition metal oxide, a lithium-rich phosphate compound, and a lithium-low phosphate compound. There is no restriction | limiting in particular in the mixing method, You may mix by a dry type and may mix by a wet type. Moreover, there is no restriction | limiting in particular in the order of mixing. For example, a lithium-containing transition metal oxide, a lithium-rich phosphate compound, and a lithium-low phosphate compound may be mixed at the same time, or a lithium-containing transition metal oxide and a lithium-rich phosphate compound may be mixed first. After that, the lithium-containing phosphate compound may be added and mixed, or after the lithium-containing transition metal oxide and the lithium-containing phosphate compound are mixed first, the lithium-rich phosphate compound is added and mixed. Alternatively, after mixing a lithium-rich phosphate compound and a lithium-low phosphate compound, a mixture containing a lithium-containing transition metal oxide may be added. In addition, you may granulate the obtained positive electrode active material.

  Although the manufacturing method of a lithium containing transition metal oxide is not specifically limited, At least a raw material preparation process and a baking process are provided. It can be produced by blending a predetermined lithium source and metal source so as to have a desired molar ratio, and by methods such as pulverization / mixing, thermal decomposition mixing, precipitation reaction, or hydrolysis.

Although the manufacturing method of a lithium high content phosphate compound and a lithium low content phosphate 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 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. It can be produced by blending a predetermined lithium source, metal source and phosphorus source so as to have a desired molar ratio, and drying and firing the mixture. Moreover, lithium content of the lithium-containing phosphate compound can be adjusted by electrochemically desorbing lithium from the obtained lithium-containing phosphate compound. Alternatively, a phosphorus source, a metal source and distilled water are agitated to prepare a mixture thereof, and the mixture is dried to produce a hydrate of the phosphoric acid compound, followed by further heat treatment to produce a phosphoric acid compound. May be. A lithium-containing phosphate compound can be produced by mixing and heat-treating the obtained phosphate compound and a lithium source.
The compound forms of the metal source, lithium source, metal source, and phosphorus source described above are not particularly limited, and known materials such as oxides and salts of each raw material can be selected according to the process.

(Positive electrode binder)
The positive electrode binder binds the positive electrode active materials and the positive electrode current collector 22 together with the positive electrode active materials or the positive electrode active material and the conductive material. 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-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber The containing rubbers (VDF-CTFE-based fluorine rubber) vinylidene fluoride-based fluorine rubbers such as may be used.

  In addition, for example, cellulose, styrene butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, acrylic resin, or the like may be used as the binder.

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. As the ion-conductive conductive polymer, for example, those having ion conductivity such as lithium ion can be used. For example, polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide) , Polyphosphazene, etc.) and a lithium salt such as LiClO ₄ , LiBF ₄ , LiPF ₆ , or an alkali metal salt mainly composed of lithium, and the like. Examples of the polymerization initiator used for the combination include a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-described monomer. The binder content of the positive electrode active material layer 24 is preferably in the range of 1.0% by mass or more and 20% by mass or less.

(Positive electrode conductive material)
As the positive electrode conductive material, for example, a carbon material, metal fine powder, or conductive oxide can be used. These may be used individually by 1 type and may be used in combination of 2 or more type. Examples of the carbon material include carbon black such as acetylene black and ethylene black, and carbon nanotubes. Examples of the metal fine powder include copper, nickel, stainless steel, and iron. Examples of the conductive oxide include ITO (tin-doped indium oxide). Among these, carbon black such as acetylene black and ethylene black is particularly preferable. The content of the positive electrode conductive material in the positive electrode active material layer 24 is preferably in the range of 1.0% by mass to 20% by mass. In addition, when sufficient electroconductivity is securable only with a positive electrode active material, the positive electrode active material layer 24 does not need to contain the electrically conductive material.

"Production of positive electrode"
The positive electrode 20 can be produced as follows.
A positive electrode active material, a binder and a solvent are mixed to prepare a paint. A conductive material may be further added to the paint as necessary. As the solvent, for example, water, N-methyl-2-pyrrolidone or the like can be used. The mixing ratio of the positive electrode active material, the binder, and the conductive material is preferably 80 to 98% by mass: 1.0 to 20% by mass: 1.0 to 20% by mass. These mass ratios are adjusted to 100% by mass as a whole. The mixing method of these components constituting the paint is not particularly limited, and the mixing order is not particularly limited.

  Next, the paint is applied to the positive electrode current collector 22. 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 positive electrode current collector 22 is removed. The positive electrode active material layer 24 is formed by removing the solvent, and the positive electrode 20 is obtained. The method for removing the solvent is not particularly limited. For example, the positive electrode current collector 22 coated with the paint may be dried at a temperature of 80 to 150 ° C.

  Next, the positive electrode active material layer 24 of the positive electrode 20 obtained in this way is pressed to adjust the thickness of the positive electrode active material layer 24. A roll press can be used as the press device.

"Negative electrode"
The negative electrode 30 includes a negative electrode current collector 32 and a negative electrode active material layer 34 provided on the negative electrode current collector 32.

(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. The negative electrode current collector 32 is preferably not alloyed with lithium, and copper is particularly preferable. The thickness of the negative electrode current collector 32 is preferably 6 to 30 μm.

(Negative electrode active material layer)
The negative electrode active material layer 34 includes a negative electrode active material and a thiol compound. Moreover, the negative electrode active material layer 34 has a negative electrode binder and a negative electrode electrically conductive material as needed.

(Negative electrode active material)
As a negative electrode active material, the well-known negative electrode active material for lithium ion secondary batteries which can occlude / release lithium ion can be used. Specifically, for example, metallic lithium, a carbon material, a metal combined with lithium, a compound mainly composed of an oxide, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the like can be given.
Examples of the carbon material used as the negative electrode active material include graphite (natural graphite, artificial graphite), carbon nanotube, non-graphitizable carbon, graphitizable carbon, low-temperature calcined carbon, and the like. Examples of the metal combined with lithium include aluminum, silicon, and tin. Examples of the compound mainly composed of oxide include silicon oxide (SiO _x (0 <x <2)) and tin dioxide.

(Negative electrode binder)
As the negative electrode binder, those exemplified for the positive electrode binder can be used.

(Negative electrode conductive material)
As the negative electrode conductive material, those exemplified for the positive electrode conductive material can be used. Note that in the case where sufficient conductivity can be ensured with only the negative electrode active material, the negative electrode active material layer 34 may not contain a conductive material.

"Production of negative electrode"
The negative electrode 30 can be produced as follows.
A negative electrode active material, a conductive material, a binder and a solvent are mixed to prepare a paint.
As the solvent, for example, water, N-methyl-2-pyrrolidone and the like can be used as in the case of manufacturing the positive electrode. The constituent ratio of the negative electrode active material, the conductive material, and the binder is preferably 80 to 99% by mass: 0 to 20% by mass: 1.0 to 20% by mass. These mass ratios are adjusted to 100% by mass as a whole.

  The mixing method of these components constituting the paint is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the negative electrode current collector 32. The coating method is not particularly limited, as in the case of producing the positive electrode, and a method usually employed when producing an electrode can be used.

  Subsequently, the solvent in the paint applied on the negative electrode current collector 32 is removed. The negative electrode active material layer 34 is formed by removing the solvent, and the negative electrode 30 is obtained. The method for removing the solvent is not particularly limited. For example, the negative electrode current collector 32 to which the paint has been applied may be dried in an atmosphere at 80 ° C. to 150 ° C.

  And the negative electrode active material layer 34 of the negative electrode 30 obtained in this way is pressed, and the thickness of the negative electrode active material layer 34 is adjusted. A roll press can be used as the press device.

"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 solution"
The nonaqueous electrolyte solution includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent. The non-aqueous solvent preferably contains a cyclic carbonate and a chain carbonate.

As cyclic carbonate, what can solvate electrolyte can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, and the like can be used.
Since the chain carbonate has a relatively low viscosity compared to the cyclic carbonate, the viscosity of the non-aqueous solvent can be reduced. Examples thereof include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.
The ratio of the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably in the range of 1: 9 to 1: 1 by volume ratio.

  The non-aqueous solvent may contain other organic solvents other than the cyclic carbonate and the chain carbonate. Examples of other organic solvents include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, and 1,2-diethoxyethane.

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 CF _{2 SO 2) 2, LiN (} CF 3 SO 2) (C 4 F 9 SO 2), LiN (CF 3 CF 2 CO) 2, lithium salts such as 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 the degree of ionization.

When LiPF ₆ is dissolved in a non-aqueous solvent, the concentration of the electrolyte in the non-aqueous electrolyte solution 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 lithium ion concentration of the non-aqueous electrolyte solution can be sufficiently ensured, 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 solution, 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 solution 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.

"Case"
The case 50 seals the laminate 40 and the nonaqueous electrolyte solution therein. The case 50 is not particularly limited as long as it can prevent leakage of the non-aqueous 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. Then, the leads 60 and 62 are respectively welded to the positive electrode current collector 22 and the negative electrode current collector 32 by a known method, and a separator is provided between the positive electrode active material layer 24 of the positive electrode 20 and the negative electrode active material layer 34 of the negative electrode 30. 10 is inserted into the case 50 together with the nonaqueous electrolyte solution, and the entrance of the case 50 is sealed.

[Method for producing lithium ion secondary battery]
The lithium ion secondary battery 100 can be manufactured as follows.
A positive electrode 20 having a positive electrode active material layer 24, a negative electrode 30 having a negative electrode active material layer 34, a separator 10 interposed between the positive electrode 20 and the negative electrode 30, and a nonaqueous electrolyte solution are enclosed in a case 50. .

  For example, the positive electrode 20, 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, and the positive electrode 20, the separator 10, and the negative electrode 30. Adhere. For example, the laminated body 40 is put into a bag-like case 50 prepared in advance.

  Finally, a non-aqueous electrolyte solution is injected into the case 50, whereby the lithium ion secondary battery 100 is manufactured. Instead of injecting the nonaqueous electrolyte solution into the case, the laminate 40 may be impregnated with the nonaqueous electrolyte solution.

  In the lithium ion secondary battery 100 of the present embodiment, the positive electrode active material includes a predetermined lithium-rich phosphate compound that contains lithium at a relatively high concentration, and a predetermined low lithium content that contains lithium at a relatively low concentration. Since the phosphoric acid compound is contained, the storage characteristics and output characteristics in a high capacity and high temperature environment are improved in a balanced manner.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and omission of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible.

[Example 1]
(Preparation of positive electrode)
Li _1.01 Ni _0.83 Co _0.13 Al _0.03 O _2.0 having an average particle diameter of 20 μm as the lithium-containing transition metal oxide, and Li ₃ having an average particle diameter of 300 nm as the lithium-containing phosphate compound V ₂ (PO ₄ ) ₃ and Li ₁ V ₂ (PO ₄ ) ₃ having an average particle diameter of 300 nm as a low lithium-containing phosphate compound are weighed at a mass ratio of 80: 19: 1 and mixed in a mortar. This was used as the positive electrode active material. In the positive electrode active material, the ratio c / (a + b) of the mass c of the lithium-containing transition metal oxide to the total mass (a + b) of the mass a of the lithium-rich phosphate compound and the mass b of the lithium-low phosphate compound is 4. The ratio a / b of the mass a of the high lithium phosphate compound to the mass b of the low lithium phosphate compound is 19.

  90 parts by mass of the positive electrode active material, 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 paint. The obtained coating material was applied onto an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C. for 30 minutes, and then subjected to press treatment at a linear pressure of 1000 kgf / cm using a roll press device to obtain a positive electrode.

(Preparation of negative electrode)
As 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.

(Nonaqueous electrolyte solution)
A non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ at a concentration of 1.0 mol / L and LiBF ₄ at a concentration of 0.1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC). 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 cells)
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.

[Evaluation of battery cells]
The following evaluation was performed about the battery cell produced as mentioned above. The results are shown in Table 2.

(Output characteristics)
The battery cell is charged at a constant current density of 0.5 C until the end-of-charge voltage is 4.2 V (vs. Li ^/ Li ⁺ ), and is further set to 4.2 V (vs. Li ^/ Li ⁺ ). The constant voltage charging was performed until the current value decreased to a current density of 0.05 C by voltage. Then, after resting for 10 minutes, the battery was discharged at a constant current density of 0.5 C until the discharge end voltage reached 2.8 V (vs. Li ^/ Li ⁺ ), and the discharge capacity (mAh) of the battery cell was measured. A value obtained by dividing the measured discharge capacity by the mass of the positive electrode active material was taken as 0.5 C discharge capacity (mAh / g).

The battery cell is charged at a constant current density of 0.5 C until the end-of-charge voltage is 4.2 V (vs. Li ^/ Li ⁺ ), and is further set to 4.2 V (vs. Li ^/ Li ⁺ ). The constant voltage charging was performed until the current value decreased to a current density of 0.05 C by voltage. Then, after resting for 10 minutes, the battery cell was discharged at a constant current density of 5 C until the discharge end voltage reached 2.8 V (vs. Li ^/ Li ⁺ ), and the discharge capacity (mAh) of the battery cell was measured. A value obtained by dividing the measured discharge capacity by the mass of the positive electrode active material was defined as 5C discharge capacity (mAh / g). The discharge capacity was measured in a room temperature (25 ° C.) environment.

The output characteristics were evaluated from the 5C / 0.5 discharge capacity ratio (%) calculated from the following formula from the measured 5C discharge capacity and 0.5C discharge capacity.
5C / 0.5 discharge capacity ratio (%) = (5C discharge capacity / 0.5C discharge capacity) × 100

(High temperature storage characteristics)
The battery cell whose 5 C discharge capacity was measured was charged at a constant current density of 1 C until the end-of-charge voltage was 4.2 V (vs. Li ^/ Li ⁺ ), and then 4.2 V (vs. Li / Li). ^The constant voltage charging was performed until the current value decreased to a current density of 0.05 C at a constant voltage of ⁺ ). Subsequently, the charged battery cell was preserve | saved for 10 days in a 60 degreeC thermostat. The battery cell after storage is allowed to stand for 24 hours in a room temperature (25 ° C.) environment and allowed to cool, and then the discharge end voltage becomes 2.8 V (vs. Li ^/ Li ⁺ ) at a constant current density of 1C. Until discharged.
For the discharged battery cells, the 5C (after storage) discharge capacity was measured in the same manner as the output characteristics described above.
High-temperature storage characteristics are 5C (after storage) /0.5C (before storage) discharge calculated from the following formula from 5C (after storage) discharge capacity and 0.5C discharge capacity before storage measured by the above output characteristics. Evaluation was based on the volume ratio (%).
5C (after storage) /0.5C (before storage) discharge capacity ratio (%) = (5C (after storage) discharge capacity / 0.5C discharge capacity) × 100

[Examples 2 to 5]
A battery cell was produced in the same manner as in Example 1 except that the compounds shown in Table 1 were used as the lithium-containing transition metal oxide, the lithium-rich phosphate compound, and the lithium-low phosphate compound.

[Example 6]
As in Example 1, except that the compounds shown in Table 1 were used in a mass ratio of 80: 1: 19 as lithium-containing transition metal oxide, lithium-rich phosphate compound, and lithium-low phosphate compound, respectively. Thus, a battery cell was produced.

[Comparative Examples 1 to 10]
In Comparative Examples 1, 4, 6, and 8, the lithium-containing transition metal oxide and the lithium-rich phosphate compound shown in Table 1 were weighed at a mass ratio of 80:20 without adding the low lithium phosphate compound. A battery cell was produced in the same manner as in Example 1 except that. In Comparative Examples 2, 5, 7, and 9, the mass ratio of the lithium-containing transition metal oxide and the low lithium-containing phosphate compound shown in Table 1 was 80:20 without adding the lithium-rich phosphate compound. A battery cell was produced in the same manner as in Example 1 except that it was weighed. Furthermore, in Comparative Examples 3 and 10, the lithium-containing phosphate compound and the lithium-containing phosphate compound shown in Table 1 were weighed at a mass ratio of 90:10 without adding the lithium-containing transition metal oxide. A battery cell was produced in the same manner as in Example 1 except for the above.

  About the battery cell produced in Examples 2-6 and Comparative Examples 1-10, the output characteristic and the high temperature storage characteristic were evaluated similarly to Example 1. FIG. The results are shown in Table 2.

  From the results in Table 2, all of the battery cells of Examples 1 to 6 prepared using a positive electrode active material containing a lithium-containing transition metal oxide, a lithium-rich phosphate compound, and a lithium-low phosphate compound are stored. The previous 0.5C discharge capacity is large, and the 5C / 0.5C discharge capacity ratio and the 5C (after storage) /0.5C (before storage) discharge capacity ratio are high, and the output characteristics and storage characteristics are excellent. I understand that. On the other hand, the battery cells of Comparative Examples 1, 4, 6, and 8 prepared using the lithium-containing transition metal oxide and the lithium-rich phosphate compound all have 5C (after storage) /0.5C ( Before storage) The discharge capacity ratio was greatly reduced, and the storage characteristics were inferior. In addition, the battery cells of Comparative Examples 2, 5, 7, and 9 prepared using the lithium-containing transition metal oxide and the low lithium-containing phosphate compound all have a reduced 5C / 0.5C discharge capacity ratio, and output. The characteristics were inferior. Furthermore, the battery cells of Comparative Examples 3 and 10 prepared using a lithium-rich phosphate compound and a lithium-low phosphate compound all had 0.5C discharge capacity before storage.

[Examples 7 to 15]
A battery cell was produced in the same manner as in Example 1 except that the positive electrode active material prepared as described below was used in the production of the positive electrode.
Lithium-rich phosphate compounds _{(Li 3 V 2 (PO 4} ) 3) and lithium low-containing phosphate compound _{(Li 1 V 2 (PO 4} ) 3) and 95: 5 weight ratio (Li Low-containing phosphate compound The ratio a / b of the mass a of the lithium-rich phosphate compound to the mass b of 19 was mixed at 19) to obtain a phosphate compound mixture. Next, lithium-containing transition metal oxide (Li _1.01 Ni _0.83 Co _0.13 Al _0.03 O ₂ ) and the phosphoric acid compound mixture described above are contained in lithium with respect to the mass (a + b) of the phosphoric acid compound mixture. A positive electrode active material was prepared by weighing and mixing in a mortar so that the ratio c / (a + b) of the mass c of the transition metal oxide was the value shown in Table 3 below.
About the produced battery cell, the output characteristic and the high temperature storage characteristic were evaluated similarly to Example 1. The results are shown in Table 4 together with the results of Example 1.

  From the results of Table 4, the output characteristics and the high-temperature storage characteristics indicate that the mass c of the lithium-containing transition metal oxide with respect to the total mass (a + b) of the mass a of the lithium-rich phosphate compound and the mass b of the lithium-low phosphate compound. It can be seen that it varies depending on the ratio c / (a + b). In particular, it can be seen that the battery cells of Examples 1 and 9 to 14 in which the ratio c / (a + b) is 1.5 ≦ c / (a + b) ≦ 99 have excellent balance between output characteristics and high-temperature storage characteristics. .

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 ... Laminate, 50 ... Case, 52 ... Metal foil, 54 ... Polymer film, 60, 62 ... Lead, 100 ... Lithium ion secondary battery

Claims (6)

A lithium-containing transition metal oxide containing at least one transition metal element selected from Ni and Co, a lithium-rich phosphate compound represented by the following composition formula (1), and the following composition formula (2) A positive electrode active material for a lithium ion secondary battery, comprising: a low lithium-containing phosphate compound represented by:
Li _x (M1) _y (PO ₄ ) _z (1)
However, in the composition formula (1), M1 is at least one selected from Mn, Co, Ni, Fe, and V, and 2.7 ≦ x ≦ 3.3, 0.9 ≦ y ≦ 2.2, It is 0.9 <= z <= 3.3.
Li _u (M2) _v (PO ₄ ) _w (2)
However, in the composition formula (2), M2 is at least one selected from Mn, Co, Ni, Fe, V, and VO, and 0 <u ≦ 1.3, 0.9 ≦ v ≦ 2.2, It is 0.9 <= w <= 3.3.   The ratio c / (a + b) of the mass c of the lithium-containing transition metal oxide to the total mass (a + b) of the mass a of the high lithium phosphate compound and the mass b of the low lithium phosphate compound is 1.5. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein ≦ c / (a + b) ≦ 99. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the lithium-containing transition metal oxide is an oxide represented by the following composition formula (3).
_{Li n M3 p M4 q O 2} ··· (3)
However, M3 is at least one selected from Ni and Co, and M4 is Mn, Fe, Ti, Cr, Mg, Al, Cu, Si, Zr, Nb, Ga, Zn, Sn, B, V, At least one selected from Ca, Sr, and Ba, and 0.5 ≦ n ≦ 1.2, 0.5 ≦ p + q ≦ 1.2, and 0 ≦ q ≦ 0.5. The lithium ion transition metal oxide according to any one of claims 1 to 3, wherein the lithium-containing transition metal oxide is a lithium-containing nickel composite metal oxide represented by the following composition formula (4). Positive electrode active material for secondary battery.
Li _r Ni _1-st Co _s Al _t O ₂ (4)
However, in the composition formula (3), 0.5 ≦ r ≦ 1.2, 0 <s ≦ 0.5, 0 <t ≦ 0.5, and 0 <s + t ≦ 0.5.   The positive electrode for lithium ion secondary batteries which has a positive electrode active material of any one of Claims 1-4.   A lithium ion secondary battery comprising the positive electrode according to claim 5, a negative electrode, a separator, and an electrolyte solution.

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