JP2020009756A - Positive electrode active material for lithium ion secondary battery and manufacturing method thereof, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material remarkably reduced in positive electrode resistance and having a high output characteristic, and a method for manufacturing the positive electrode active material.SOLUTION: A positive electrode active material comprises: a first lithium metal composite oxide configured of secondary particles resulting from agglomeration of primary particles; and first particles having a lithium ion conductivity. The positive electrode active material contains lithium (Li), nickel (Ni), cobalt (Co) and an element M, and the ratio of quantities (mole) of the elements is represented by Li:Ni:Co:M=d1:(1-a-b):a:b. The first particles contain lithium, oxygen, lithium and an element other than oxygen. In the first particles, the quantity of the lithium and the element other than oxygen is 0.02 mass% or more and 5.2 mass% or less to a total quantity of the positive electrode active material. At least part of the first particles is present in the form of binding to the surface of the first lithium metal composite oxide.SELECTED DRAWING: Figure 1

Description

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

  2. Description of the Related Art In recent years, with the spread of portable electronic devices such as smartphones, tablet terminals, and notebook personal computers, development of small and lightweight secondary batteries having high energy density has been strongly desired. Further, there is a strong demand for the development of a secondary battery having excellent output characteristics and charge / discharge cycle characteristics as a battery for an electric vehicle such as a hybrid car.

  As a secondary battery satisfying such a demand, there is a lithium ion secondary battery. This lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of removing and inserting lithium is used as an active material of the negative electrode and the positive electrode. As the electrolyte, a non-aqueous electrolyte such as a non-aqueous electrolyte obtained by dissolving a lithium salt as a supporting salt in an organic solvent, or a non-flammable and ion-conductive solid electrolyte is used.

  Such lithium ion secondary batteries are currently being actively researched and developed.Among them, lithium using a layered rock salt type or spinel type lithium transition metal-containing composite oxide as a positive electrode active material is particularly preferred. Since an ion secondary battery can obtain a high voltage of 4V class, it is being put to practical use as a battery having a high energy density.

Lithium transition metal-containing composite oxides that have been mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize and lithium-nickel composite oxide using nickel which is cheaper than cobalt ( LiNiO ₂ ), lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), and the like.

Among the positive electrode active materials, in recent years, lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having excellent thermal stability and high capacity has been receiving attention. The lithium-nickel-cobalt-manganese composite oxide is a layered compound like the lithium-cobalt composite oxide and the lithium-nickel composite oxide, and basically has a composition ratio of nickel, cobalt and manganese of 1: 1: Included in the ratio of 1.

  On the other hand, for the purpose of obtaining a positive electrode having high performance (high cycle characteristics, high capacity, high output) as a lithium ion secondary battery, lithium having lithium ion conductivity is formed on the surface of the lithium metal composite oxide. Techniques for compounding a composite oxide containing niobium by various methods have been proposed.

For example, Patent Literature 1 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery including a lithium nickel manganese composite oxide composed of secondary particles in which a plurality of primary particles are aggregated, wherein the lithium nickel manganese composite oxide the general formula _{(1): Li d Ni 1} -a-b-c Mn a M b Nb c O 2 + γ ( the general formula (1), M is, Co, W, Mo, V , Mg, Ca, At least one element selected from the group consisting of Al, Ti, Cr, Zr and Ta, wherein 0.05 ≦ a ≦ 0.60, 0 ≦ b ≦ 0.60, 0.0003 ≦ c ≦ 0.03, 0 .95 ≦ d ≦ 1.20 and 0 ≦ γ ≦ 0.5), wherein at least a part of niobium in the lithium nickel manganese composite oxide is solid-dissolved in the primary particles. Active materials for electrolyte secondary batteries have been proposed. Further, it is described that in the positive electrode active material, a compound containing lithium and niobium may be present on at least a part of the primary particle surface. According to Patent Literature 1, the lithium niobium compound formed on the primary particle surface reduces the positive electrode resistance of the obtained secondary battery and improves the output characteristics.

  For example, in Patent Document 2, a second composite oxide composed of a composite oxide of Li and Al or Nb is formed on the particle surface of a first composite oxide containing Li, Ni, Co, Mn and W. A positive electrode active material for a lithium ion battery in which a substance exists is proposed, and a composite oxidation of Li and Al or Nb is formed on the surface of a particle of a first composite oxide containing Li, Ni, Co, Mn and W. It has been shown that the presence of the second composite oxide made of a material provides excellent battery characteristics.

International Publication No. WO2018 / 043669 JP 2017-084674 A

  However, the output characteristics of a secondary battery only include the composite oxide containing lithium and niobium on the surface of the composite oxide containing Li, Ni, Co, and Mn as shown in Patent Documents 1 and 2. Not enough to improve.

  In view of the above problems, an object of the present invention is to provide a positive electrode active material that has a significantly reduced positive electrode resistance (reaction resistance) and can have higher output characteristics when used as a positive electrode active material for a lithium ion secondary battery. It is intended to provide a substance and a method for producing the substance.

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, as a result of the existence of a specific amount of the first particles having lithium ion conductivity on the surface of the lithium metal composite oxide, the positive electrode resistance was extremely reduced. The present inventors have found that the present invention can be reduced to the above, and completed the present invention.

  According to the first aspect of the present invention, a positive electrode including: a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated; and a first particle having lithium ion conductivity. An active material, the positive electrode active material includes lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the amount (mol) ratio of these elements is Li: Ni: Co. : M = d1: (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d1 ≦ 1.5 , M is at least one element selected from Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta), and the first particles are lithium. , Oxygen, and an element other than lithium and oxygen, wherein the first particles have a content other than lithium and oxygen. The amount of element is 0.01% by mass or more and 4% by mass or less based on the whole positive electrode active material, and at least a part of the first particles is bonded to the surface of the first lithium metal composite oxide. And a positive electrode active material for a lithium ion secondary battery.

Further, it is preferable that at least a part of the first particles is present separately from the first lithium metal composite oxide. Further, it is preferable that the first particles include at least one selected from the group consisting of a lithium niobium composite oxide, a lithium tungsten composite oxide, a lithium phosphorus composite oxide, and a lithium silicon composite oxide. Further, it is preferable that the first particles include at least one of LiNbO ₃ and Li ₃ NbO ₄ . Further, it is preferable that at least a part of the first particles has a longest diameter of 0.5 μm or more.

  According to a second aspect of the present invention, a positive electrode including: a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated; and a first particle having lithium ion conductivity. A method for producing an active material, comprising: mixing a second lithium metal composite oxide with a second particle capable of forming a first particle by reacting with lithium; and Heat-treating the obtained mixture at a temperature of 400 ° C. or more and 900 ° C. or less, wherein the second lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and an element. M, and the substance amount (molar) ratio of these elements is Li: Ni: Co: M = d1: (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d2 ≦ 1.5, Is represented by at least one element selected from Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta), and the first particles include lithium, Oxygen and an element other than lithium and oxygen, and the second particles include the element other than lithium and oxygen, and the amount of the element other than lithium and oxygen in the mixture is based on the entire positive electrode active material. Not less than 0.01% by mass and not more than 4% by mass, and at least a part of the first particles is bonded to the surface of the first lithium metal composite oxide to produce a positive electrode active material for a lithium ion secondary battery. A method is provided.

  Further, the second particles preferably include at least one element selected from the group consisting of niobium, tungsten, phosphorus, and silicon. Further, the second particles preferably contain niobic acid. Further, the second lithium metal composite oxide is formed by firing a compound containing nickel, cobalt, and manganese obtained by crystallization and a lithium compound at a temperature of 700 ° C or higher and 1000 ° C or lower. Is preferred.

  According to a third aspect of the present invention, there is provided a positive electrode for a lithium ion secondary battery, comprising: a first lithium metal composite oxide; and first particles having lithium ion conductivity. The lithium metal composite oxide includes lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the substance amount (molar) ratio of these elements is Li: Ni: Co: M = d3. : (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d3 ≦ 1.5, M is Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and at least one element selected from the group consisting of lithium, oxygen, , Lithium and an element other than oxygen, and a part of the first particles is There was bound to the surface of the oxide, and a portion of the first particles, the first lithium metal composite oxide exists in isolation, the positive electrode is provided for a lithium ion secondary battery.

Further, it is preferable that the first particles include at least one of LiNbO ₃ and Li ₃ NbO ₄ .

  According to a fourth aspect of the present invention, there is provided a lithium ion secondary battery including a positive electrode including the above-described positive electrode active material, a negative electrode, and an electrolyte.

  The positive electrode active material of the present invention can significantly reduce the positive electrode resistance of the obtained lithium ion secondary battery by including the lithium metal composite oxide and the first particles having lithium ion conductivity. Therefore, the lithium ion secondary battery using the positive electrode active material of the present invention for the positive electrode can further improve the output characteristics. In addition, the method for producing a positive electrode active material of the present invention can easily produce the above-mentioned positive electrode active material with high productivity.

FIG. 1A is a diagram illustrating an example of a positive electrode active material according to the present embodiment, and FIG. 1B is a diagram illustrating an example of a structure of a lithium metal composite oxide. FIG. 2 is a diagram illustrating an example of a method for manufacturing a positive electrode active material according to the present embodiment. FIG. 3 is a diagram illustrating an example of a method for manufacturing a positive electrode active material according to the present embodiment. FIG. 4 is a schematic sectional view of a coin-type battery used for battery evaluation. FIG. 5 is a schematic explanatory diagram of a measurement example of impedance evaluation and an equivalent circuit used for analysis. FIG. 6 is a graph showing the relationship between the positive electrode resistance and the amount of niobium of the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 1 to 4. FIG. 7 is a graph showing the relationship between the positive electrode resistance and the amount of niobium of the positive electrode active materials obtained in Examples 7 to 9 and Comparative Examples 5 to 7. FIG. 8 is a diagram showing a reflected electron image (COMP image) of the positive electrode active material obtained in Example 1 by SEM. FIG. 9 is a diagram showing a backscattered electron image (COMP image) of the positive electrode active material obtained in Comparative Example 4 by SEM.

  Hereinafter, a positive electrode active material for a lithium ion secondary battery and a method for producing the same, a positive electrode mixture paste for a lithium ion secondary battery, and a lithium ion secondary battery according to the present embodiment will be described with reference to the drawings. In the drawings, some components are emphasized or some components are simplified for easy understanding, and actual structures, shapes, scales, and the like may be different.

1. Positive electrode active material for lithium ion secondary battery FIG. 1A is a schematic diagram showing an example of the positive electrode active material for a lithium ion secondary battery according to the present embodiment. As shown in FIG. 1A, the positive electrode active material 100 according to the embodiment includes a first lithium metal composite oxide 10 and first particles 20 having lithium ion conductivity.

(1) Composition of Positive Electrode Active Material (Whole) The positive electrode active material 100 contains lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the ratio of the amounts (moles) of these elements is large. , Li: Ni: Co: M = d1: (1-ab): a: b: c (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0 .95 ≦ d1 ≦ 1.5, M is at least one element selected from W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta). Note that, as described later, the positive electrode active material 100 also includes niobium derived from the first particles 20.

  Nickel (Ni) is an element that contributes to higher potential and higher capacity of the secondary battery. In the above molar ratio, the value of (1-ab) indicating the Ni content preferably exceeds 0.6, more preferably 0.65 or more and 0.99 or less, and even more preferably 0.8 or more and 0 or less. .95 or less. When the value of (1-ab) exceeds 0.6, a high battery capacity can be obtained.

  Cobalt (Co) is an element that contributes to improvement of charge / discharge cycle characteristics. In the above molar ratio, the value of a indicating the Co content is 0 or more and less than 0.4, preferably 0.05 or more and less than 0.4, preferably 0.05 or more and less than 0.4, more preferably 0.1 or less. 1 or more and less than 0.4. If the value of a is less than 0.05, the effect of improving the charge-discharge cycle characteristics obtained by containing Co cannot be sufficiently obtained.

  M representing the additional element is at least one element selected from Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta. In the above molar ratio, the value of b indicating the content of M is 0 ≦ b <0.35. When b is greater than 0, the thermal stability, output characteristics, cycle characteristics, and the like can be improved. it can. Further, M preferably contains Al. When M is Al, the value of b is 0.01 or more and 0.1 or less.

  In the above molar ratio, d1 indicating the lithium content is preferably 0.95 or more and 1.5 or less, more preferably 1.0 or more and 1.10. When the molar ratio (d1) of lithium is less than 0.95, other elements occupy the portion of the lithium metal composite oxide which should be occupied by lithium, and the charge / discharge capacity may decrease. On the other hand, when the molar ratio of lithium exceeds 1.5, there is a surplus lithium compound that does not contribute to charge and discharge together with the lithium nickel composite oxide, and the battery resistance increases and the charge and discharge capacity decreases. Sometimes.

In addition, the positive electrode active material 100 has a composition excluding niobium as a general formula (1): Li _d1 Ni _1-ab Co _{a Mb} O _{2 + α} (wherein M is Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and at least one element selected from Ta, 0 ≦ a ≦ 0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d1 ≦ 1.5, and 0 ≦ α ≦ 0.5). In the general formula (1), the preferable range of each element can be the same range as the above-described molar ratio.

(2) First Lithium Metal Complex Oxide FIG. 1B is a schematic diagram illustrating an example of the first lithium metal complex oxide 10. The first lithium metal composite oxide 10 is composed of secondary particles 2 formed by aggregating a plurality of primary particles 1. The shape of the secondary particles 2 is not particularly limited, and may have a structure such as a solid structure, a hollow structure, and a porous structure. Here, the solid structure refers to a structure in which the entirety of the secondary particles 2 is formed by an aggregate of a plurality of primary particles 1, and the hollow structure includes one or a plurality of spaces inside the secondary particles 2. Structure. Further, the porous structure refers to a structure in which a large number of voids exist inside the secondary particles 2. The first lithium metal composite oxide 10 may include not only the secondary particles 2 but also a small number of single primary particles 1.

  The size of the first lithium metal composite oxide 10 is not particularly limited, but its volume average particle diameter MV is preferably about 1 μm or more and 30 μm or less, more preferably 3 μm or more and 10 μm or less. The volume average particle size MV can be determined, for example, from a volume integrated value measured by a laser diffraction / scattering particle size distribution meter.

(3) First Particle The first particle 20 is not particularly limited as long as it has lithium ion conductivity and contains lithium, oxygen, and an element other than lithium and oxygen. Elements other than lithium and oxygen are not particularly limited, and may be, for example, at least one element from the group consisting of Nb, W, P, and Si. Note that the first particles may be of one type or a plurality of types.

It is preferable that the first particles 20 include, for example, at least one selected from the group consisting of a lithium niobium composite oxide, a lithium tungsten composite oxide, a lithium phosphorus composite oxide, and a lithium silicon composite oxide. For example, the first particles 20 include lithium niobium composite oxides such as Li ₃ NbO ₄ and LiNbO ₃ , lithium tungsten composite oxides such as Li ₂ WO ₄ , Li ₂ W ₂ O ₇ , Li ₄ WO ₅ , and Li Examples thereof include lithium phosphorus composite oxides such as ₃ PO ₄ and lithium silicon composite oxides such as Li ₄ SiO ₄ . Among these, from the viewpoint of increasing the lithium ion conductivity, it is more preferable to include at least one of LiNbO ₃ and Li ₃ NbO ₄ , and it is more preferable to include LiNbO ₃ . When the first particles 20 include LiNbO ₃ , the first particles 20 can have higher lithium ion conductivity.

  The composition and compound type of the compound of the first particles 20 can be evaluated and identified by analysis by ICP emission spectroscopy and X-ray diffraction (XRD) described later. Note that the first particles 20 may include an amorphous phase. The amorphous phase has excellent lithium ion conductivity and may further improve battery characteristics.

  The amount of the element other than lithium and oxygen in the first particles 20 is 0.02% by mass or more and 5.2% by mass or less, preferably 0.1% by mass or more and 5% by mass with respect to the whole positive electrode active material 100. Or less, more preferably 0.15% by mass or more and 4.5% by mass or less. When the amounts of the elements other than lithium and oxygen are in the above ranges, the reaction resistance (positive electrode resistance) of the secondary battery can be reduced, and the output characteristics can be improved.

  When the first particles 20 are a lithium-niobium composite oxide, the amount of niobium in the lithium-niobium composite oxide is, for example, 2% by mass or more and 4% by mass or less based on the whole positive electrode active material. Is also good. When the amount of niobium is in the above range, the positive electrode resistance (reaction resistance) of the secondary battery can be further reduced, and the output characteristics can be further improved.

  In the positive electrode active material 100, at least a part of the first particles 20 is bonded (or adhered) to the surface of the first lithium metal composite oxide 10 (see 20a in FIG. 1A). . The first particles 20 may be present as long as they are bonded to at least a part of the surface of the first lithium metal composite oxide 10 and may cover the entire surface. 10 may be bonded to a part of the surface. The first particles 20 can be bonded (adhered) to the surface of the first lithium metal composite oxide 10 by a heat treatment (step S20) described later.

  Further, in the positive electrode active material 100, it is preferable that at least a part of the first particles 20 exists separately from the first lithium metal composite oxide 10 (see 20b in FIG. 1A). Due to the presence of the first particles 20a which are present in combination with the first lithium metal composite oxide 10 and the first particles 20b which are present separately, when the positive electrode of the secondary battery is formed, It is presumed that a lithium ion conduction path is formed between the particles of the first lithium metal composite oxide 10 to improve the ion conductivity between the particles of the first lithium metal composite oxide 10.

  The first particles 20b which are present separately from the first lithium metal composite oxide 10 contain the same elements as the first particles 20a which are present on the surface of the first lithium metal composite oxide 10. It is preferable that they have the same composition, and it is more preferable that they have the same composition.

  Further, the size of the first particles 20 is not particularly limited, but at least a part of the first particles 20 preferably has a longest diameter of 0.5 μm or more, and may be 1 μm or more. Further, the average particle size of the first particles 20 may be 0.5 μm or more. When the first particles 20 are irregular or the like, the average particle diameter may be an average longest diameter when a plurality of first particles 20 are observed with a scanning electron microscope (SEM).

2. 2. Method for Producing Positive Electrode Active Material FIG. 2 is a diagram illustrating an example of a method for producing a positive electrode active material according to the present embodiment. The method for producing a positive electrode active material includes mixing a second lithium metal composite oxide with a second particle capable of forming a first particle by reacting with lithium (step S10); Heat treating the obtained mixture (step S20). According to the method for manufacturing a positive electrode active material, the above-described positive electrode active material 100 can be easily manufactured with high productivity.

  As shown in FIG. 3, the second lithium metal composite oxide obtains a compound containing nickel, cobalt, and optionally an element M (hereinafter, also simply referred to as “nickel compound”) by crystallization. It may be manufactured by a process including (Step S1), mixing the obtained nickel compound and lithium compound (Step S2), and firing the obtained mixture (Step S3). When a nickel compound obtained by crystallization is used as a precursor of a positive electrode active material, a positive electrode active material having a more uniform composition can be obtained. The nickel compound includes one or both of a hydroxide and an oxide. Hereinafter, an example of the method for manufacturing the positive electrode active material according to the present embodiment will be described.

[Crystallization Step (Step S1)]
The nickel-containing compound (precursor of the positive electrode active material) can be obtained by a known production method, but is preferably obtained by crystallization. In the case of crystallization, two steps of a nucleation step and a particle growth step are performed. It is more preferable to perform the steps separately. By separating crystallization into the above two steps, a nickel compound having a more uniform particle size and a narrow particle size distribution can be obtained. Since the form of the nickel compound (precursor of the positive electrode active material) is inherited by the form of the second lithium metal composite oxide after firing, the finally obtained positive electrode active material must have a uniform particle size. Thus, battery characteristics such as cycle characteristics can be improved. Hereinafter, as an example of the crystallization step, a case where the separation is performed into a nucleation stage and a particle growth stage will be described.

(Nucleation process)
First, a compound containing nickel, cobalt and optionally an element M is dissolved in water at a predetermined ratio to prepare a raw material aqueous solution. When the element M is aluminum, an aluminum supply liquid is separately prepared using sodium aluminate or the like. Further, an alkaline aqueous solution and an aqueous solution containing an ammonium ion supplier are supplied and mixed into the reaction tank, and the pH value measured at a liquid temperature of 25 ° C. is 12.0 to 14.0 and the ammonium ion concentration is 3 g. A pre-reaction aqueous solution of not less than / L and not more than 25 g / L is prepared. The pH value of the aqueous solution before the reaction can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

  Next, the raw material aqueous solution is supplied while stirring the aqueous solution before the reaction. When the element M is aluminum, an aluminum supply liquid is separately supplied. Thereby, an aqueous solution for nucleation, which is a reaction aqueous solution in the nucleation step, is formed in the reaction tank. Since the pH value of the aqueous solution for nucleation is in the above-described range, nuclei hardly grow in the nucleation step, and nucleation occurs preferentially. In the nucleation step, the pH value of the aqueous solution for nucleation and the concentration of ammonium ions change with the nucleation, so that an alkaline aqueous solution and an aqueous ammonia solution are supplied at appropriate times, and the pH value of the solution in the reaction tank is adjusted to a liquid temperature of 25%. Control is performed so that the pH is maintained in the range of 12.0 to 14.0 and the concentration of ammonium ion is maintained in the range of 3 g / L to 25 g / L on the basis of ° C.

(Grain growth process)
After the nucleation step, the pH value of the nucleation aqueous solution in the reaction tank is adjusted to 10.5 or more and 12.0 or less based on a liquid temperature of 25 ° C., and the aqueous solution for particle growth, which is a reaction aqueous solution in the particle growth step, Form. The pH value can be adjusted by stopping the supply of the aqueous alkali solution. However, in order to obtain a nickel compound having a narrow particle size distribution, it is necessary to temporarily stop the supply of all the aqueous solutions and adjust the pH value. Is preferred. Specifically, it is preferable to adjust the pH value by stopping the supply of all the aqueous solutions and then supplying the nucleation aqueous solution with the same kind of inorganic acid as the acid constituting the metal compound as the raw material.

  Next, the raw material aqueous solution is supplied while stirring the aqueous solution for particle growth. At this time, since the pH value of the aqueous solution for particle growth is in the above-described range, almost no new nuclei are generated, nucleus (particle) growth proceeds, and particles of the nickel compound having a predetermined particle size are formed. . In the particle growth step, the pH value and the ammonium ion concentration of the aqueous solution for particle growth change as the particles grow, so that an alkaline aqueous solution and an aqueous ammonia solution are supplied at appropriate times to maintain the pH value and the ammonium ion concentration in the above ranges. It is necessary to do.

  The reaction atmosphere in the nucleation step and the particle growth step is appropriately adjusted according to the required structure of the secondary particles 2. For example, when a nickel compound obtained when the reaction atmosphere is a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less throughout the nucleation step and the particle growth step is fired, a lithium-transition metal composite oxide having a solid structure is obtained. Is obtained.

  On the other hand, when the reaction atmosphere in the initial stage of the nucleation step and the particle growth step is an oxidizing atmosphere in which the oxygen concentration exceeds 5% by volume, and the reaction atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere in the particle growing step, The resulting nickel compound has a low-density central portion composed of fine primary particles and a high-density outer shell composed of plate-like primary particles larger than the fine primary particles. By firing such a nickel compound, the first lithium metal composite oxide 10 having a hollow structure is obtained.

  Further, the reaction atmosphere in the nucleation step is set to a non-oxidizing atmosphere, and in the particle growing step, the reaction atmosphere is switched to the oxidizing atmosphere, and then the reaction atmosphere is switched to the non-oxidizing atmosphere once or more times. Thus, a nickel compound having a laminated structure in which low-density layers and high-density layers are alternately laminated can be obtained. By firing such a nickel compound, a first lithium metal composite oxide 10 having a porous structure in which a plurality of voids are dispersed inside the particles is obtained.

  The nickel composite hydroxide (nickel compound) obtained after the crystallization (step S1) may be oxidized and roasted so that at least a part of the hydroxide may be converted to a nickel composite oxide. (Nickel compound).

[Mixing Step Before Firing (Step S2)]
Next, the obtained nickel compound and lithium compound are mixed (step S2). Although the kind of the lithium compound to be mixed before firing is not particularly limited, lithium carbonate, lithium hydroxide, lithium nitrate and the like can be suitably used. Of these, lithium carbonate or lithium hydroxide is preferably used, and lithium carbonate is more preferably used in consideration of ease of handling and stability of quality.

  In the mixing step (Step S2), the sum (Me) of the number of atoms of metal other than lithium, nickel, cobalt, and other elements M in the mixture obtained by mixing and the number of atoms of lithium (Li) (Li / Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, and further preferably 1.0 to 1.35. A nickel compound and a lithium compound are mixed so as to be 2 or less. That is, since Li / Me does not change before and after the baking step (step S3) described later, the Li / Me in the mixing step (step S2) depends on the intended cathode active material 100 (or the second lithium metal composite). An oxide) is mixed with a nickel compound and a lithium compound so that Li / Me is obtained.

  It is preferable that the nickel compound and the lithium compound are sufficiently mixed so that fine powder is not generated. Insufficient mixing may cause variations in Li / Me between the individual particles, making it impossible to obtain sufficient battery characteristics. Note that a general mixer can be used for mixing. For example, a shaker mixer, a redige mixer, a julia mixer, a V blender, and the like can be used.

[Firing Step (Step S3)]
Next, the obtained mixture is fired to obtain a second lithium metal composite oxide (Step S3). The furnace used in the firing step is not particularly limited as long as it can be heated in the air or an oxygen stream. Similarly, from the viewpoint of keeping the atmosphere in the furnace uniform, it is preferable to use a batch-type or continuous-type electric furnace that does not generate gas.

  The firing temperature in the firing step (Step S3) is preferably from 700 ° C to 1000 ° C, more preferably from 730 ° C to 950 ° C. If the firing temperature is lower than 700 ° C., the resulting second lithium metal composite oxide may have insufficient crystallinity. On the other hand, when the sintering temperature exceeds 1000 ° C., the particles of the second lithium metal composite oxide are violently sintered, causing abnormal grain growth and increasing the proportion of irregularly shaped coarse particles.

  The holding time at the firing temperature in the firing step (step S3) is preferably 1 hour or more and 10 hours or less, and more preferably 2 hours or more and 6 hours or less. If the holding time at the firing temperature in the firing step (Step S3) is less than 1 hour, the resulting second lithium metal composite oxide may have insufficient crystallinity.

  The atmosphere during the firing is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% by volume or more and 100% by volume or less, and a mixed atmosphere of oxygen having the above oxygen concentration and an inert gas. Is particularly preferred. That is, firing is preferably performed in the air or an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium metal composite oxide may be insufficient.

  The secondary particles constituting the obtained second lithium metal composite oxide may have undergone aggregation or mild sintering. In such a case, it is preferable to crush the aggregate or the sintered body of the secondary particles. Thereby, the average particle size and particle size distribution of the obtained second lithium metal composite oxide can be adjusted to a suitable range.

  In addition, crushing means that mechanical energy is applied to an aggregate composed of a plurality of secondary particles generated by sintering necking between the secondary particles during firing, and the secondary particles themselves are almost not destroyed. It means an operation of separating and loosening aggregates.

  Known means can be used for crushing, and for example, a pin mill, a hammer mill, or the like can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

  The second lithium metal composite oxide obtained after the firing step (step S3) contains lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the amount (molar) of these elements. ) Ratio: Li: Ni: Co: M = d2: (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d2 ≦ 1.5, M is at least one element selected from Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta) May be done. The preferred range of the molar ratio of each element is the same as that of the first lithium metal composite oxide described above. Note that, as described later, in the heat treatment step (step S20), part of lithium in the second lithium metal composite oxide may react with the second particles. Therefore, the molar ratio (d2) of lithium in the second lithium metal composite oxide is larger than the molar ratio (d3) of lithium in the finally obtained first lithium metal composite oxide in the second particles. It may be prepared so as to increase as much as reacts with.

[Mixing Step (Step S10)]
Next, the second lithium metal composite oxide and the second particles capable of forming the first particles 20 by reacting with lithium are mixed (Step S10). Note that the second lithium metal composite oxide may be obtained by a method other than the methods of Steps S1 to S3 described above.

  The second particles contain the same elements as the elements other than lithium and oxygen contained in the target first particles 20. For example, the second particles preferably include at least one element selected from the group consisting of niobium, tungsten, phosphorus, and silicon, and more preferably a compound containing niobium (niobium compound). Further, the second particles may or may not contain lithium, but it is preferable that the second particles do not contain lithium. When the second particles do not contain lithium, they can efficiently react with surplus lithium and the like in the second lithium metal composite oxide in a heat treatment step (step S20) described later. Note that, in this specification, “not including lithium” means that substantially does not include lithium. For example, a trace amount of lithium may be included as an impurity or the like. It may contain 0.1% by mass or less of lithium.

As the niobium compound, known compounds including niobium can be used, and for example, niobate, niobium oxide, niobium nitrate, niobium pentachloride, niobium nitrate and the like can be used. Among these, niobic acid, niobium oxide, or a mixture thereof is preferable from the viewpoints of availability and avoiding contamination of the first lithium metal composite oxide with impurities, and niobate (Nb ₂ O) is preferred. ₅ · nH ₂ O) is more preferred. In addition, when impurities are mixed in the first lithium metal composite oxide, the thermal stability, battery capacity, and cycle characteristics of the obtained secondary battery may be reduced.

  The mixing amount of the second particles is such that the amount of the above elements other than lithium and oxygen in the mixture is 0.02% by mass or more and 5.2% by mass or less, preferably 0.02% by mass or less, based on the entire positive electrode active material 100 obtained. The mixing can be carried out so as to be from 05% by mass to 5% by mass, more preferably from 0.1% by mass to 4.5% by mass.

  Further, the second particles are preferably mixed in the form of particles (solid phase). The average particle size of the second particles is preferably 0.01 μm or more and 10 μm or less, more preferably 0.03 μm or more and 3.0 μm or less, and even more preferably 0.05 μm or more and 1.5 μm or less. When the average particle size is in the above range, the reactivity with the second lithium metal composite oxide becomes good. The average particle size of the second particles may be, for example, 0.1 μm or more, or may be 0.5 μm or more.

  If the average particle size of the second particles is smaller than 0.01 μm, there may be a problem that handling of the powder becomes extremely difficult. On the other hand, when the average particle diameter is larger than 10 μm, elements other than lithium and oxygen (eg, Nb) contained in the second particles are not uniformly distributed in the positive electrode active material 100, and the battery characteristics are not improved. There is. The average particle size of the second particles is a volume average particle size MV, which can be determined, for example, from a volume integrated value measured by a laser diffraction / scattering particle size distribution meter.

  The second particles may be pulverized in advance by using various types of pulverizers such as a ball mill, a planetary ball mill, a jet mill / nano jet mill, a bead mill, and a pin mill so as to have a particle size in the above range. In addition, the niobium compound may be classified by a dry classifier or a sieve if necessary. For example, sieving can be performed to obtain particles close to 0.01 μm.

  It is preferable that the second lithium metal composite oxide and the second particles are sufficiently mixed so that fine powder is not generated. If mixing is insufficient, the reactivity between the lithium derived from the second lithium metal composite oxide and the second particles varies among the individual particles, and sufficient battery characteristics cannot be obtained. There are cases. Note that a general mixer can be used for mixing. For example, a shaker mixer, a redige mixer, a julia mixer, a V blender, and the like can be used.

  Note that, in addition to the second lithium metal composite oxide and the second particles, a lithium compound may be further mixed. The second particles can react with lithium (excess lithium or lithium in crystals) in the second lithium metal composite oxide in a heat treatment step (step S20) described later. In some cases, lithium in the crystal of the lithium metal composite oxide is excessively extracted, and the battery characteristics may be degraded. When a lithium compound is further mixed in the mixing step (step S10), the lithium compound becomes a lithium source that reacts with the second particles, and excessive lithium is extracted from the crystal of the second lithium metal composite oxide. Can be suppressed. In addition, although it does not specifically limit as a lithium compound, For example, the lithium compound described in the mixing process (step S2) before baking can be used.

[Heat treatment step (Step S20)]
Next, the mixture obtained by mixing is heat-treated at a temperature of 400 ° C. or more and 900 ° C. or less (step S20). By the heat treatment (Step S20), the second particles react with the lithium derived from the second lithium metal composite oxide or the arbitrarily mixed lithium compound to form the first particles 20 described above. Can be.

  The heat treatment temperature is 400 ° C. to 900 ° C., preferably 500 ° C. to 800 ° C., more preferably 550 ° C. to 700 ° C. When the heat treatment temperature is within the above range, the lithium and the second particles react with each other, so that the first particles 20 can be easily and uniformly formed in the positive electrode active material.

  The furnace used at the time of the heat treatment is not particularly limited as long as it can be heated in the air or an oxygen stream. Similarly, from the viewpoint of keeping the atmosphere in the furnace uniform, it is preferable to use a batch-type or continuous-type electric furnace that does not generate gas.

  The holding time at the above heat treatment temperature is preferably from 1 hour to 10 hours, more preferably from 2 hours to 6 hours. If the holding time at the heat treatment temperature in this step is less than 1 hour, the resulting lithium metal composite oxide may have insufficient crystallinity.

  The atmosphere during the heat treatment (step S20) is preferably an oxidizing atmosphere, more preferably an atmosphere having an oxygen concentration of 18% to 100% by volume, and a mixed atmosphere of oxygen and an inert gas having the above oxygen concentration. It is particularly preferred that That is, firing is preferably performed in the air or an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium metal composite oxide may be reduced.

3. Positive Electrode The positive electrode according to the present embodiment includes the first lithium metal composite oxide 10 and the first particles 20 having lithium ion conductivity, and can be suitably used for a lithium ion secondary battery.

  The first lithium metal composite oxide 10 includes, for example, lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the material (molar) ratio of these elements is Li: Ni : Co: M = d3: (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d3 ≦ 1 And M may be represented by at least one element selected from W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta). The preferred range of the molar ratio of each element is the same as that of the first lithium metal composite oxide described above. Note that, as described above, in the heat treatment step (step S20), part of lithium in the second lithium metal composite oxide may react with the second particles. Therefore, the molar ratio (d3) of lithium in the finally obtained first lithium metal composite oxide is larger than the molar ratio (d2) of lithium in the first lithium metal composite oxide in the second particles. It may be reduced by the amount that has reacted with.

  Further, preferred compositions and characteristics of the first lithium metal composite oxide 10 and the first particles 20 are the same as those described in the item of the positive electrode active material.

  In the positive electrode according to the present embodiment, a part of the first particles 20 is present in combination with the surface of the first lithium metal composite oxide 10, and a part of the first particles 20 is It is preferable to exist separately from the lithium metal composite oxide 10. In the positive electrode, it is presumed that the distribution of the first particles 20 as described above forms a suitable lithium ion conduction path between the particles of the first lithium metal composite oxide 10.

  The method for manufacturing the positive electrode is not particularly limited. For example, using the positive electrode active material 100 including the first lithium metal composite oxide 10 and the first particles 20 having lithium ion conductivity, the following method is used. It is manufactured as follows.

  First, the above-described positive electrode active material 100, a conductive material and a binder are mixed, and if necessary, activated carbon or a solvent for viscosity adjustment or the like is added, and the mixture is kneaded to prepare a positive electrode mixture paste. . At that time, the respective mixing ratios in the positive electrode mixture paste can be appropriately adjusted according to the intended performance of the secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, and the content of the conductive material is 1 part by mass or more and 20 parts by mass or less. And the content of the binder may be 1 part by mass or more and 20 parts by mass or less.

  The conductive material is not particularly limited. For example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and Ketjen black can be used.

  The binder plays a role of retaining the active material particles and is not particularly limited. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose A system resin and polyacrylic acid can be used.

  If necessary, the positive electrode active material, the conductive material and the activated carbon may be dispersed, and a solvent for dissolving the binder may be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon may be added to the positive electrode mixture in order to increase the electric double layer capacity.

  The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, aluminum foil, dried, and the solvent is scattered. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. Thus, a sheet-shaped positive electrode can be manufactured. The sheet-shaped positive electrode can be cut to an appropriate size according to the intended battery, and used for battery production. Note that the method for manufacturing the positive electrode is not limited to the above method, and may be another method.

4. Lithium ion secondary battery A lithium ion secondary battery (hereinafter, also referred to as “secondary battery”) according to the present embodiment includes a positive electrode including the above-described positive electrode active material, a negative electrode, and an electrolyte. The lithium ion secondary battery can be configured by the same components as the conventionally known lithium ion secondary battery, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. The secondary battery may be, for example, an all-solid secondary battery including a positive electrode, a negative electrode, and a solid electrolyte. Hereinafter, each component other than the positive electrode will be described.

  The embodiment described below is merely an example, and the lithium-ion secondary battery according to the present embodiment is based on the embodiment described in the present specification and may be variously modified based on the knowledge of those skilled in the art. , Can be implemented in an improved form. Further, the use of the lithium ion secondary battery according to the present embodiment is not particularly limited.

(Negative electrode)
For the negative electrode, metallic lithium or a lithium alloy may be used. Alternatively, a negative electrode active material capable of absorbing and desorbing lithium ions is mixed with a binder, and an appropriate solvent is added to form a negative electrode composite. A material formed by applying a material to the surface of a metal foil current collector such as copper, drying the material, and compressing the material to increase the electrode density as necessary may be used.

  As the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite and a phenol resin, and a powdered carbon material such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder similarly to the positive electrode, and an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material and the binder. Solvents can be used. As the binder, an aqueous binder such as styrene butanediene rubber may be used in addition to the organic binder such as PVDF. The aqueous binder may use carboxymethyl cellulose (CMC) as a viscosity modifier. For example, in the case of an aqueous binder using styrene-butadiene latex as a main additive and CMC as a viscosity modifier in combination, the binding power in a small amount can be increased.

(Separator)
A separator is interposed between the positive electrode and the negative electrode as necessary. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and may be a thin film such as polyethylene or polypropylene having a large number of fine pores.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, a non-aqueous electrolyte can be used. As the non-aqueous electrolyte, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent may be used. Further, as the non-aqueous electrolyte, an ionic liquid in which a lithium salt is dissolved may be used. In addition, the ionic liquid refers to a salt composed of cations and anions other than lithium ions, and which is liquid even at normal temperature.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, and chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and dipropyl carbonate, and further, tetrahydrofuran and 2-hydrogen carbonate. One compound selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone or as a mixture of two or more. Can be used.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used. Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  When the lithium ion secondary battery is an all-solid secondary battery, a solid electrolyte may be used as the non-aqueous electrolyte. The solid electrolyte has a property that can withstand a high voltage. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.

  As the inorganic solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, or the like is used.

The oxide solid electrolyte is not particularly limited, and any oxide containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. The oxide-based solid electrolyte, for example, lithium phosphate _{(Li 3 PO 4), Li} 3 PO 4 N X, LiBO 2 N X, LiNbO 3, LiTaO 3, Li 2 SiO 3, Li 4 SiO 4 -Li 3 PO ₄ , Li ₄ SiO ₄ —Li ₃ VO ₄ , Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₂ O—B ₂ O ₃ —ZnO, Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), Li _{1 + X} Al _X Ge _2-X (PO ₄ ) ₃ (0 ≦ X ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2 / 3-X} TiO ₃ (0 ≦ X ≦ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ etc. I can do it.

The sulfide-based solid electrolyte is not particularly limited, and any electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. The sulfide-based solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 2 S 5, LiI-Li 2 _{S-B 2 S 3, Li} 3 PO 4 -Li 2 S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O _{5, LiI-Li 3 PO 4} -P 2 S 5 , and the like.

In addition, as the inorganic solid electrolyte, one other than the above may be used. For example, Li ₃ N, LiI, Li ₃ N—LiI—LiOH, or the like may be used.

  The organic solid electrolyte is not particularly limited as long as it is a polymer compound having ion conductivity, and for example, polyethylene oxide, polypropylene oxide, a copolymer thereof, or the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Battery shape and configuration)
The positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above, the positive electrode, the negative electrode, and the lithium ion secondary battery according to the present embodiment including the solid electrolyte include various types such as a cylindrical type and a stacked type. Can be formed.

  When a non-aqueous electrolyte is used as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with the non-aqueous electrolyte, and the positive electrode current collector and the outside are impregnated. The positive electrode terminal and the negative electrode terminal and the negative electrode terminal that communicate with the outside are connected using a current collecting lead and sealed in a battery case to complete a lithium ion secondary battery. .

  Next, the positive electrode active material according to one embodiment of the present invention will be described in more detail with reference to examples. Note that the present invention is not limited to these examples. In addition, the analysis method of the metal contained in the positive electrode active material and various evaluation methods of the positive electrode active material in Examples and Comparative Examples are as follows.

[composition]
After dissolving the positive electrode active material in acid, it was measured with an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).

[Compound species identification]
The positive electrode active material was evaluated with a powder X-ray diffractometer (X'Pert, PROMRD, manufactured by Spectris).

[Evaluation of battery characteristics of positive electrode active material]
A 2032 type coin battery CBA having a structure shown in FIG. 6 (hereinafter, also referred to as “coin type battery CBA”) was used. The method of manufacturing the 2032 type coin battery CBA is as follows.

  First, 52.5 mg of a positive electrode active material, 15 mg of acetylene black, and 7.5 mg of PTEE were mixed, and press-molded under a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm. For 12 hours to prepare a positive electrode PE.

Next, using this positive electrode PE, a 2032 type coin battery CBA was produced in a glove box in an Ar atmosphere where the dew point was controlled at -80 ° C. For the negative electrode NE of the 2032 type coin battery CBA, a lithium metal having a diameter of 17 mm and a thickness of 1 mm is used, and as an electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte are used. An equal volume mixture (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. A 25 μm-thick polyethylene porous film was used as the separator SE. Note that the 2032 type coin battery CBA has a gasket GA and is assembled into a coin-shaped battery with the positive electrode can PC and the negative electrode can NC.

The coin battery CBA was left for about 24 hours after being manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was set to 0.1 mA / cm ² , and the cutoff voltage was set to 4.3 V. Until the cut-off voltage reached 3.0 V. Thereafter, the coin-type battery CBA is charged to a potential corresponding to SOC of 20%, and measured by an AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) to obtain a Nyquist plot shown in FIG. Can be Since this Nyquist plot is represented as the sum of characteristic curves indicating solution resistance, negative electrode resistance and its capacity, and positive electrode resistance and its capacity, fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and positive electrode resistance is calculated. (Reaction resistance) was calculated.

(Example 1)
(A) Crystallization step [Nucleation step]
First, the temperature inside the reaction vessel was set to 40 ° C. while water was added and stirred. At this time, nitrogen gas was passed through the reaction tank for about 30 minutes, and the reaction atmosphere was a non-oxidizing atmosphere having an oxygen concentration of 2% by volume or less. Subsequently, an appropriate amount of a 25% by mass aqueous solution of sodium hydroxide and 25% by mass of aqueous ammonia are supplied into the reaction tank, and the pH value is adjusted to 12.8 and the ammonium ion concentration to 10 g / L. An aqueous solution was formed.

Next, nickel sulfate and cobalt sulfate were dissolved in water to prepare a 2 mol / L raw material aqueous solution. Separately, after the element M is aluminum and sodium aluminate as a raw material is dissolved in water, a 25% aqueous sodium hydroxide solution is added to the solution so that the molar ratio of sodium to aluminum is 1.7, and 2 mol of sodium hydroxide is added. / L of an aluminum supply liquid was prepared. Furthermore, sodium hydroxide, sodium ^{_{carbonate, [CO 3 2-] / [}} OH -] to become 0.025 to prepare an alkaline aqueous solution dissolved in water.

  A raw material aqueous solution, an aluminum supply solution, an alkaline aqueous solution, and 25% by mass aqueous ammonia are added at a constant rate to the aqueous solution before the reaction to form an aqueous solution for the nucleation step, and the ammonium ion concentration is maintained at 10 g / L. Was controlled to 12.8 (nucleation step pH) to perform nucleation. The addition rates of the raw material aqueous solution and the aluminum supplier were adjusted so that the metal element molar ratio of the slurry was Ni: Co: Al = 82: 15: 3.

[Grain growth step]
After the nucleation was completed, the supply of all the aqueous solutions was temporarily stopped, and sulfuric acid was added to adjust the pH value to 11.6, thereby forming an aqueous solution for particle growth. After confirming that the pH value reached a predetermined value, supply of all the aqueous solutions was restarted, crystallization was continued while controlling the pH at 11.6, and nuclei (particles) generated in the nucleation step. Grew.

  Thereafter, the obtained product was washed with water, filtered, and dried to obtain powdery nickel composite hydroxide (nickel compound) particles. When aluminum is used as the element M, it is preferable to use a solution containing sodium aluminate and sodium hydroxide as the aluminum supply liquid used in the crystallization step. Other compounds, for example, when aluminum sulfate is used, aluminum hydroxide precipitates at a lower pH than nickel hydroxide or cobalt hydroxide, so aluminum hydroxide is easily precipitated alone, and the particle size is small. A nickel composite hydroxide (nickel compound) having a narrow distribution and a uniform particle size cannot be obtained.

(B) Mixing and Firing Step The nickel compound obtained as described above is subjected to a heat treatment at 700 ° C. for 6 hours in a stream of air (oxygen: 21% by volume) to form a nickel composite oxide (nickel compound). Collected. Further, lithium hydroxide as a lithium compound was weighed such that Li / Me = 1.025, and mixed with the recovered nickel composite oxide to prepare a lithium mixture. The mixing operation was performed using a shaker mixer (TURBULA-TypeT2C manufactured by Willie & Bacoffen (WAB)).

  Next, the produced lithium mixture is calcined at 500 ° C. for 4 hours in an oxygen (oxygen: 100% by volume) stream, further calcined at 730 ° C. for 24 hours, crushed after cooling, and lithium metal composite oxidation. I got something.

  Agglomeration or slight sintering occurred in the lithium metal composite oxide thus obtained. For this reason, this lithium metal composite oxide was crushed using a continuous mill (manufactured by IKA, MF10 basic).

(C) Mixing Step of Second Particles (Niobium Compound) The obtained lithium metal composite oxide powder and niobate powder (D50 particle size: 1.0 μm) are mixed, and the mixture is mixed with an electric furnace (Toyo Seisakusho, Using a muffle furnace), the positive electrode active material was manufactured by maintaining the film at a temperature of 650 ° C. for 3 hours in a stream of air (oxygen concentration: 21% by volume).

(D) Evaluation of positive electrode active material [Composition]
According to the analysis using an ICP emission spectrometer, this positive electrode active material has a metal element molar ratio of Li: Ni: Co: Al = 1.1: 0.82: 0.15: 0.03. Nb was found to be contained at 5.2 wt%.
[Crystal structure]
The obtained positive electrode active material was evaluated by powder X-ray diffraction. As a result, a peak derived from the layered rock salt type of LiNi _0.82 Co _0.15 Al _0.03 O ₂ and a peak derived from LiNbO ₃ and Li ₃ NbO ₄ were confirmed. Table 1 shows the evaluation results of the obtained positive electrode active materials.
[Shape observation]
When the obtained positive electrode active material was confirmed by observation of a reflected electron image (COMPO image) by SEM, as shown in FIG. 8, the surface of the first lithium metal composite oxide 10 and the first lithium metal High-brightness particles were observed in a state separated from the composite oxide 10. In the backscattered electron image, an element having a higher atomic number is observed with a higher luminance contrast. Therefore, when combined with the result of the powder X-ray diffraction, particles observed with a higher luminance contrast are LiNbO ₃ and And / or Li ₃ NbO ₄ (first particles 20).

(Example 2)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the amount of the niobium compound added was 2.70 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. It is observed, and it is considered that LiNbO ₃ and / or Li ₃ NbO ₄ (first particles) exist as in Example 1.

(Example 3)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the addition amount of the niobium compound was 1.00 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. The obtained positive electrode active material was evaluated by powder X-ray diffraction. As a result, a peak derived from the layered rock salt type of LiNi _0.82 Co _0.15 Al _0.03 O ₂ and a peak derived from LiNbO ₃ were confirmed. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. It is considered that LiNbO ₃ (first particles) is present.

(Example 4)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the addition amount of the niobium compound was 0.60 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed, it is considered that LiNbO ₃ (first particles) is present as in Example 3.

(Example 5)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the amount of the niobium compound added was 0.10 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed, it is considered that LiNbO ₃ (first particles) is present as in Example 3.

(Example 6)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the addition amount of the niobium compound was 0.02 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed, it is considered that LiNbO ₃ (first particles) is present as in Example 3.

(Example 7)
A positive electrode was prepared in the same manner as in Example 1 except that the addition rates of the raw material aqueous solution and the aluminum supplier were adjusted so that the metal element molar ratio of the slurry was Ni: Co: Al = 92.5: 2: 5.5. Active materials were prepared and evaluated. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. It is observed, and it is considered that LiNbO ₃ and / or Li ₃ NbO ₄ (first particles) exist as in Example 1.

(Example 8)
A positive electrode active material was prepared and evaluated in the same manner as in Example 7, except that niobic acid was mixed so that the amount of the niobium compound added was 2.70 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. It is observed, and it is considered that LiNbO ₃ and / or Li ₃ NbO ₄ (first particles) exist as in Example 1.

(Example 9)
A positive electrode active material was prepared and evaluated in the same manner as in Example 7, except that niobic acid was mixed so that the addition amount of the niobium compound was 0.02 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. It is observed, and it is considered that LiNbO ₃ and / or Li ₃ NbO ₄ (first particles) exist as in Example 1.

(Comparative Example 1)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that niobic acid was mixed so that the amount of the niobium compound added was 6.4 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed.

(Comparative Example 2)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1 except that niobic acid was mixed so that the addition amount of the niobium compound was 5.5 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed.

(Comparative Example 3)
A positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that niobic acid was mixed so that the addition amount of the niobium compound was 0.01 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed.

(Comparative Example 4)
In Example 1, a positive electrode active material was prepared and evaluated in the same manner as in Example 1, except that the firing step was performed, and the mixing and heat treatment of the niobium compound were not performed. Table 1 shows the evaluation results of the obtained positive electrode active materials. Further, as confirmed by observing the reflected electron image (COMPO image) by SEM, as shown in FIG. 9, no high-luminance particles were observed.

(Comparative Example 5)
A positive electrode active material was prepared and evaluated in the same manner as in Example 7, except that niobic acid was mixed so that the amount of the niobium compound added was 6.4 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed.

(Comparative Example 6)
A positive electrode active material was prepared and evaluated in the same manner as in Example 7, except that niobic acid was mixed so that the addition amount of the niobium compound was 0.01 wt%. Table 1 shows the evaluation results of the obtained positive electrode active materials. In addition, it was confirmed by observation of a backscattered electron image (COMPO image) by SEM that high-luminance particles were formed on the surface of the lithium metal composite oxide and in a state separated from the lithium metal composite oxide as in Example 1. Observed.

(Comparative Example 7)
In Example 7, a positive electrode active material was prepared and evaluated in the same manner as in Example 7, except that the firing step was performed, and the mixing and heat treatment of the niobium compound were not performed. Table 1 shows the evaluation results of the obtained positive electrode active materials. Further, as a result of observing the reflected electron image (COMPO image) by SEM, no high-luminance particles were observed.

[Evaluation results]
6 and 7 show graphs in which the reaction resistances of the examples and comparative examples shown in Table 1 are plotted against the amount of niobium.

  As shown in the graphs of FIGS. 6 and 7, the examples in which a specific amount of the niobium compound is added are effective in reducing the reaction resistance and improving the output characteristics of the secondary battery. Further, as in Comparative Example 4, in the positive electrode active material in which the niobium compound was mixed before firing, high-brightness particles (first particles) having a clear particle shape were not observed, and the reaction was higher than that in Example. Resistance was high. In Comparative Example 4, niobium is presumed to be mainly present inside the secondary particles. From this, the reaction resistance is reduced because the particles of the niobium compound having lithium ion conductivity (first particles) are present in the form of distinct particles on the surface of the lithium metal composite oxide. it is conceivable that.

100 Positive electrode active material 10 First lithium metal composite oxide 1 Primary particle 2 Secondary particle 20 First particle 20a First particle (present on the surface of first lithium metal composite oxide)
20b: first particles (present separately from the first lithium metal composite oxide)
CBA: coin-type battery PE: positive electrode NE: negative electrode GA: gasket PE: positive electrode NE: negative electrode SE: separator

Claims (12)

A positive electrode active material including: a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated; and a first particle having lithium ion conductivity,
The positive electrode active material contains lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the ratio (mol) of these elements is Li: Ni: Co: M = d1: (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d1 ≦ 1.5, M is Mn , W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and at least one element selected from Ta)
The first particles include lithium, oxygen, and an element other than lithium and oxygen,
The amount of elements other than lithium and oxygen in the first particles is 0.02% by mass or more and 5.2% by mass or less based on the whole positive electrode active material;
At least a part of the first particles is present by bonding to the surface of the first lithium metal composite oxide,
A positive electrode active material for lithium ion secondary batteries.   The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein at least a part of the first particles is present separately from the first lithium metal composite oxide.   2. The method according to claim 1, wherein the first particles include at least one selected from the group consisting of a lithium niobium composite oxide, a lithium tungsten composite oxide, a lithium phosphorus composite oxide, and a lithium silicon composite oxide. 3. Item 3. The positive electrode active material for a lithium ion secondary battery according to Item 2. 4. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the first particles include at least one of LiNbO ₃ and Li ₃ NbO _{4. 5} .   5. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein at least a part of the first particles has a longest diameter of 0.5 μm or more. A method for producing a positive electrode active material, comprising: a first lithium metal composite oxide composed of secondary particles in which a plurality of primary particles are aggregated; and a first particle having lithium ion conductivity,
Mixing a second lithium metal composite oxide and second particles capable of forming the first particles by reacting with lithium;
Heat-treating the mixture obtained by mixing at a temperature of 400 ° C. or more and 900 ° C. or less,
The second lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the substance (molar) ratio of these elements is Li: Ni: Co. : M = d1: (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d2 ≦ 1.5 , M is at least one element selected from Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta),
The first particles include lithium, oxygen, and an element other than lithium and oxygen,
The second particles include the element other than lithium and oxygen,
The amount of the element other than lithium and oxygen in the mixture is 0.02% by mass or more and 5.2% by mass or less based on the whole positive electrode active material;
At least a part of the first particles is present by binding to a surface of the first lithium metal composite oxide.
A method for producing a positive electrode active material for a lithium ion secondary battery.   The method of claim 6, wherein the second particles include at least one element selected from the group consisting of niobium, tungsten, phosphorus, and silicon.   The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 6, wherein the second particles include niobic acid.   The second lithium metal composite oxide is formed by firing a compound containing nickel, cobalt, and manganese obtained by crystallization, and a lithium compound at a temperature of 700 ° C to 1000 ° C, A method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 6 to 8. A positive electrode for a lithium ion secondary battery, comprising: a first lithium metal composite oxide; and first particles having lithium ion conductivity,
The first lithium metal composite oxide contains lithium (Li), nickel (Ni), cobalt (Co), and the element M, and the substance (molar) ratio of these elements is Li: Ni: Co. : M = d3: (1-ab): a: b (where 0 ≦ a <0.40, 0 ≦ b <0.35, a + b <0.40, 0.95 ≦ d2 ≦ 1.5 , M is at least one element selected from Mn, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, La, and Ta),
The first particles include lithium, oxygen, and an element other than lithium and oxygen,
A part of the first particles is present in combination with a surface of the first lithium metal composite oxide, and a part of the first particles is a part of the first lithium metal composite oxide. Is a positive electrode for a lithium ion secondary battery that exists separately. It said first particles comprise at least one of LiNbO ₃ and _Li 3 NbO _4, the positive electrode for a lithium ion secondary battery according to claim 10.   A lithium ion secondary battery comprising a positive electrode containing the positive electrode active material according to claim 1, a negative electrode, and an electrolyte.