Positive electrode active material for secondary battery with non-aqueous electrolyte, secondary battery with non-aqueous electrolyte, and method for producing positive electrode active material for secondary battery with non-aqueous electrolyte

Abstract

A positive electrode active material for a secondary battery with a non-aqueous electrolyte that is one example of embodiment of the present invention includes: a lithium transition metal composite oxide; a first compound that includes at least one from the group consisting of calcium and strontium and at least one from the group consisting of tungsten, molybdenum, niobium, titanium, silicon, and zirconium; and a second compound that contains phosphorus. The lithium transition metal composite oxide has a layered structure, has a nickel content ratio of at least 65 mol%, and is in the form of secondary particles formed by the aggregation of primary particles. The first compound is present at interfaces of the primary particles within the secondary particles, the second compound is present at surfaces of the second particles or at interfaces of the primary particles, and the Gini coefficient of PO3− in the interior of the secondary particles is 0.6 or less.

Description

Positive electrode active material for non-aqueous electrolyte secondary batteries, non-aqueous electrolyte secondary battery, and method for manufacturing positive electrode active material for non-aqueous electrolyte secondary batteries

[0001] This disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, and more particularly to a positive electrode active material for a non-aqueous electrolyte secondary battery with a high Ni content, a non-aqueous electrolyte secondary battery containing this active material, and a method for producing this active material.

[0002] Lithium transition metal composite oxides with a high Ni content are known as positive electrode active materials for high-capacity non-aqueous electrolyte secondary batteries. However, lithium transition metal composite oxides with a Ni content of 65% or more have highly reactive Ni on the surface when the charge level is high. ４＋ Because of the large amount of these substances present, side reactions with non-aqueous electrolytes are likely to occur. The decomposition products generated by these side reactions accumulate on the surface of the positive electrode, increasing the initial reaction resistance of the battery. Patent document 1 discloses a technique for suppressing the reaction between the positive electrode active material and the non-aqueous electrolyte by presenting a compound containing Ca, Sr, etc., at the interface between primary particles inside the secondary particles of a lithium transition metal composite oxide.

[0003] International Publication No. 2023 / 054041

[0004] Incidentally, since secondary batteries are used through repeated charging and discharging, it is important not only to suppress the initial reaction resistance but also to suppress the increase in reaction resistance due to the charge-discharge cycle. Patent Document 1 does not consider suppressing the increase in reaction resistance due to the charge-discharge cycle, and the technology described in Patent Document 1 still has room for improvement.

[0005] The purpose of this disclosure is to reduce the initial reaction resistance and suppress the increase in reaction resistance due to repeated charging and discharging in a positive electrode active material containing a lithium transition metal composite oxide with a high Ni content.

[0006] The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present disclosure includes a lithium transition metal composite oxide, at least one of Ca and Sr, and a first compound containing at least one of W, Mo, Nb, Ti, Si, and Zr, and a second compound containing P. The lithium transition metal composite oxide has a layered structure and has the general formula Li ｘ Ni ａ Co ｂ Mn ｃ Al ｄ M1 ｅ M2 ｆ O ２－ｙ (where 0.95 ≤ x ≤ 1.15, 0.65 ≤ a ≤ 0.95, 0 ≤ b ≤ 0.15, 0 ≤ c ≤ 0.30, 0 ≤ d ≤ 0.10, 0 < e ≤ 0.03, 0 ≤ f ≤ 0.03, 0 ≤ y < 0.05, a + b + c + d + e + f = 1, M1 is at least one element selected from the group consisting of W, Mo, Nb, Ti, Si, and Zr, and M2 is at least one element of Ca and Sr), and is a secondary particle formed by aggregation of primary particles. The first compound is present at the interface between primary particles inside the secondary particle, and the second compound is present on the surface of the secondary particle or at the interface between primary particles. In the elemental concentration distribution of the cross-section of the secondary particle using time-of-flight secondary ion mass spectrometry, the din coefficient of PO ３－ inside the secondary particle is 0.6 or less.

[0007] The non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode containing the above positive electrode active material, a negative electrode, and a non-aqueous electrolyte.

[0008] The method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present disclosure includes a mixing step of mixing a Ni metal compound containing 65 mol% or more of Ni with respect to the total molar amount of metal elements, a Li compound, an M1 compound, and an M2 compound to obtain a mixture, a firing step of firing the mixture to obtain a fired product, and a water washing step of washing and drying the fired product. During the water washing step, an aqueous solution containing a P compound in terms of P element of 0.0004 mass% or more and 2 mass% or less with respect to the mass of the lithium transition metal composite oxide is added.

[0009] The positive electrode active material for non-aqueous electrolyte secondary batteries according to this disclosure makes it possible to reduce the initial reaction resistance while suppressing the increase in reaction resistance due to repeated discharge.

[0010] This is a longitudinal cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment.

[0011] Lithium transition metal composite oxides with a high Ni content are particularly prone to side reactions with non-aqueous electrolytes when the charge level is high. Patent Document 1 discloses a technique for fixing a first compound containing M1 (at least one of Ca and Sr) and M2 (at least one element selected from the group consisting of W, Mo, Nb, Ti, Si, and Zr) to the interface between primary particles inside the secondary particles of a high-capacity lithium transition metal composite oxide with a high Ni content, from the viewpoint of suppressing initial reaction resistance. Our own investigations have revealed that the technique in Patent Document 1 may result in a high rate of increase in reaction resistance due to charge-discharge cycles.

[0012] The inventors have conducted extensive research and have found that the positive electrode active material contains a high-capacity lithium transition metal composite oxide with a high Ni content, a first compound containing M1 (at least one of Ca and Sr) and M2 (at least one element selected from the group consisting of W, Mo, Nb, Ti, Si, and Zr) present at the interface between primary particles within the secondary particles of the composite oxide, and a second compound containing P present on the surface of the secondary particles of the composite oxide or at the interface between primary particles, while PO inside the secondary particles ３－ We found that having a Gini coefficient of 0.6 or less reduces the initial reaction resistance and suppresses the increase in reaction resistance due to repeated charging and discharging. It is thought that the relatively uniform presence of the second compound within the secondary particles further suppresses the side reaction between the lithium transition metal composite oxide and the non-aqueous electrolyte, thereby suppressing the increase in reaction resistance due to repeated discharge.

[0013] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail. In the following, a cylindrical battery in which a wound electrode body is housed in a cylindrical outer casing will be given as an example, but the electrode body is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are stacked alternately one by one with separators in between. Furthermore, the outer casing is not limited to a cylindrical shape and may be, for example, rectangular, coin-shaped, etc., or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0014] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10, which is an example of an embodiment. As shown in Figure 1, the secondary battery 10 comprises a wound electrode body 14, an electrolyte, and an outer casing 16 that houses the electrode body 14 and the electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening of the outer casing 16 is closed by a sealing body 17. In the following, for convenience of explanation, the side of the battery with the sealing body 17 will be referred to as the top, and the bottom side of the outer casing 16 as the bottom.

[0015] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all rectangular elongated bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape in the longitudinal direction. The separator 13 separates the positive electrode 11 and the negative electrode 12 from each other. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in both the longitudinal and transverse directions than the positive electrode 11. The two separators 13 are formed to be at least slightly larger in dimensions than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the transverse direction of the positive electrode 11 and the negative electrode 12 is the axial direction. In other words, the end faces in the short direction of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode body 14.

[0016] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends outside the insulating plate 19 towards the bottom of the outer casing 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the bottom inner surface of the outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0017] A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery. The outer casing 16 has a grooved portion 22 formed on its side surface, which protrudes inward to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0018] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side, and functions as a safety valve. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0019] The following describes in detail the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte that constitute the secondary battery 10, with particular emphasis on the positive electrode 11.

[0020] [Positive Electrode] The positive electrode 11 includes, for example, a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. Preferably, the positive electrode mixture layer is formed on both sides of the positive electrode current collector. The positive electrode current collector can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The thickness of the positive electrode current collector is, for example, 10 μm or more and 30 μm or less.

[0021] The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode active material is the main component of the positive electrode mixture layer. Here, the main component means the component with the highest mass ratio among the constituent components of the positive electrode mixture layer. The positive electrode mixture layer preferably contains 80% by mass or more of the positive electrode active material, and more preferably 90% by mass or more of the positive electrode active material, relative to the total mass of the positive electrode mixture layer.

[0022] The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode current collector. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, etc., to the surface of the positive electrode current collector, drying the coating film, and then rolling it to form a positive electrode mixture layer on both sides of the positive electrode current collector.

[0023] Examples of conductive agents included in the positive electrode mixture layer include acetylene black (AB), carbon black (CB) such as Ketjenblack, carbon nanotubes (CNT), graphene, and carbon-based particles such as graphite. These may be used individually or in combination of two or more types. The content of the conductive agent in the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less, relative to the total mass of the positive electrode mixture layer.

[0024] Examples of binders included in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These may be used individually or in combination of two or more. The binder content in the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less, relative to the total mass of the positive electrode mixture layer.

[0025] The positive electrode active material comprises a lithium transition metal composite oxide, a first compound containing at least one of Ca and Sr, and at least one of W, Mo, Nb, Ti, Si, and Zr, and a second compound containing P. The synergistic effect of the first and second compounds specifically reduces the initial reaction resistance while suppressing the increase in reaction resistance due to repeated discharge.

[0026] Lithium transition metal composite oxides have a layered structure and have the general formula Li ｘ Ni ａ Co ｂ Mn ｃ Al ｄ M1 ｅ M2 ｆ O ２－ｙ (In the formula, 0.95≦x≦1.15, 0.65≦a≦0.95, 0≦b≦0.15, 0≦c≦0.30, 0≦d≦0.10, 0<e≦0.03, 0≦f≦0.03, 0≦y<0.05, a+b+c+d+e+f=1, M1 is at least one element selected from the group consisting of W, Mo, Nb, Ti, Si, and Zr, and M2 is at least one element of Ca and Sr). Specific examples of layered structures include layered structures belonging to space group R-3m, or layered crystalline structures belonging to space group C2 / m.

[0027] As described above, lithium transition metal composite oxides contain 65 mol% or more of Ni relative to the total number of moles of metal elements excluding Li. By setting the Ni content (a in the general formula above) to 65 mol% or more, high-capacity batteries can be obtained. The upper limit of the Ni content is 95 mol%. If the Ni content exceeds 95 mol%, it becomes difficult to ensure the stability of the layered structure of the lithium transition metal composite oxide, and battery performance such as cycle characteristics may deteriorate. Examples of a suitable range for the Ni content are 75 mol% to 95 mol%, 80 mol% to 95 mol%, or 85 mol% to 95 mol%.

[0028] The value of x, which represents the proportion of Li in the lithium transition metal composite oxide, is preferably 0.95 ≤ x ≤ 1.15, and more preferably 0.97 ≤ x ≤ 1.03. If x is less than 0.95, the capacity may decrease compared to when x satisfies the above range. If x is greater than 1.15, more Li compounds will need to be added compared to when x satisfies the above range, which may not be economical from a manufacturing cost standpoint.

[0029] When Co is contained in a lithium transition metal composite oxide, the Co content (b in the general formula above) is 15 mol% or less relative to the total number of moles of metal elements excluding Li. Since Co is an expensive element, it is preferable to keep the Co content low when considering manufacturing costs.

[0030] When Mn is contained in a lithium transition metal composite oxide, the Mn content (c in the general formula above) is 30 mol% or less relative to the total number of moles of metal elements excluding Li. If the Mn content exceeds 25 mol%, the battery capacity and high-temperature cycle characteristics may decrease. An example of a suitable range for Mn content is 5 mol% to 20 mol%.

[0031] When Al is included in a lithium transition metal composite oxide, the Al content (d in the general formula above) is 10 mol% or less relative to the total number of moles of metal elements excluding Li. Since Al does not undergo oxidation state changes during charging and discharging, its inclusion in the transition metal layer is thought to stabilize the structure of the transition metal layer. On the other hand, if the Al content is too high, it will lead to a decrease in capacity. One example of a suitable range for Al content is 5 mol% or less.

[0032] The lithium transition metal composite oxide contains M1 (where M1 is at least one element selected from the group consisting of W, Mo, Nb, Ti, Si, and Zr), and the content of M1 (e in the general formula above) is 3 mol% or less relative to the total number of moles of metal elements excluding Li. The lower limit of the content of M1 is, for example, 0.01 mol%.

[0033] The lithium transition metal composite oxide may contain M2 (where M2 is at least one of Ca and Sr), and the content of M2 (f in the general formula above) is 3 mol% or less relative to the total number of moles of the metal elements excluding Li. The lower limit of the M2 content is, for example, 0.01 mol%.

[0034] Lithium transition metal composite oxides are secondary particles formed by the aggregation of multiple primary particles. The particle size of the primary particles is, for example, between 0.05 μm and 1 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM). The volume-based median diameter (D50) of the secondary particles is, for example, between 3 μm and 30 μm, preferably between 5 μm and 25 μm. D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of the composite oxide (Z) can be measured using a laser diffraction particle size distribution analyzer (for example, Microtrac-Bell MT3000II) with water as the dispersion medium.

[0035] The first compound exists at the interface between primary particles within the secondary particles. This is thought to effectively suppress side reactions between the lithium transition metal composite oxide and the non-aqueous electrolyte, thereby keeping the reaction resistance of the positive electrode 11 low. The form of the first compound is not particularly limited as long as it exists at the interface between primary particles; it may be fixed to the surface of the primary particles or exist away from the surface of the primary particles. The presence of the first compound can be confirmed by measuring the cross-section of the secondary particles using TEM-EDX (transmission microscope-energy dispersive X-ray spectroscopy). The first compound may, for example, be scattered near the surface of the primary particles, or it may exist in a layered manner so as to broadly cover the surface of the primary particles. The first compound may also be present on the surface of the secondary particles. The secondary particles of the lithium transition metal composite oxide are formed, for example, by the aggregation of five or more primary particles, and the surface area of ​​the primary particles is larger inside the secondary particles than on the surface. The first compound is present in greater quantities inside the secondary particles than on the surface.

[0036] The total amount of Ca and Sr contained in the positive electrode active material is preferably 1 mol% or less relative to the total molar amount of metal elements excluding Li in the lithium transition metal composite oxide. When the total amount of Ca and Sr is 1 mol% or less, the effect of suppressing reaction resistance becomes more pronounced. The first compound may contain both Ca and Sr, but the effect of suppressing reaction resistance can be obtained if either one of the elements is included.

[0037] The first compound is, for example, an oxide. An example of a suitable composition of this oxide is the general formula M2 α M1 β O γ (wherein the formula, 1 ≤ α ≤ 2, 1 ≤ β ≤ 4, 3 ≤ γ ≤ 9, M2 is at least one selected from Ca and Sr, and M1 is at least one selected from W, Mo, Nb, Ti, Si, and Zr). When the first compound is an oxide with the composition represented by the general formula, the effect of suppressing reaction resistance becomes more pronounced.

[0038] M2 α M1 β O γ A concrete example is CaWO ４ CaMoO ３ CaMoO ４ , CaNbO ３ CaTiO ３ CaSiO ３ Ca ２ SiO ４ CaZrO ３ CaZr ４ O ９ , SrWO ４ , SrMoO ３ , SrMoO ４ , SrNbO ３ SrTiO ３ , Sr ２ TiO ４ , SrSiO ３ , Sr ２ SiO ４ , SrZrO ３ , SrZr ４ O ９ These are some examples.

[0039] M2 α M1 β Oγ The content of element M1 inside is lithium transition metal composite oxide and M2 α M1 β It is preferable that the amount of metal elements excluding Li be 3 mol% or less relative to the total molar amount of the metal elements. M2 α M1 β Similarly, regarding the content of element M2 within, lithium transition metal composite oxide and M2 α M1 β It is preferable that the amount of metal excluding Li is 3 mol% or less relative to the total molar amount of the metal. α M1 β The content of elements M1 and M2 in the mixture is preferably 0.1 mol% or more, for each element.

[0040] The second compound is present on the surface of the secondary particles or at the interface between primary particles. Furthermore, in the elemental concentration distribution of the cross-section of the secondary particles using time-of-flight secondary ion mass spectrometry, PO is present inside the secondary particles. ３－ The Gini coefficient is 0.6 or less. This more significantly suppresses the side reaction between the lithium transition metal composite oxide and the non-aqueous electrolyte, and keeps the rate of increase in reaction resistance due to charge-discharge cycles low.

[0041] The second compound is not particularly limited in its form, as long as it is present on the surface of the secondary particles or at the interface between primary particles. The second compound may be fixed to the surface of the secondary particles, fixed to the surface of the primary particles, or present away from the surface of the primary particles. The presence of the second compound can be confirmed by measuring the cross-section of the secondary particles using TEM-EDX (transmission microscope-energy dispersive X-ray spectroscopy). The second compound may be scattered near the surface of the primary particles, including the surface of the secondary particles, or it may exist in a layered manner so as to broadly cover the surface of the primary particles.

[0042] Since P is detected due to the second compound, PO inside the secondary particle ３－ A smaller Gini coefficient indicates that the second compound is uniformly dispersed within the secondary particles. ３－ The Gini coefficient is, for example, 0.1 or greater.

[0043] PO inside secondary particles３－ The Gini coefficient is the PO inside the secondary particle. ３－ Normalized strength I ＰＯ３－＿ＩＮ The Gini coefficient is the value obtained by doubling the area enclosed by the diagonal and the Lorenz curve when the cumulative rate is expressed in order of intensity. The Gini coefficient is 0 when the environment is perfectly uniform, and its value increases as the uniformity decreases.

[0044] Normalized strength I of P ＰＯ３－ This is obtained by measurement using a time-of-flight secondary ion mass spectrometer (TOF-SIMS5, IONTOF Corporation) under the following conditions: Primary ion: Bi ３ ＋ Ion voltage: 30 kV; Ion current: 0.03 pA @ 100 us; Observation range: 50 μm × 50 μm; Mass range: 60 us (~310 amu); Detection: 4 frames / scan, 150 scans

[0045] The image showing the concentration distribution of Ni and P obtained from the above measurements is divided into 256 x 256 pixels, and the detection intensity of Ni and P is calculated for each pixel. Furthermore, the ratio of the detection intensity of P to the detection intensity of Ni is used to determine the normalized intensity of P. ＰＯ３－ It is calculated as follows.

[0046] The surface of the secondary particle is defined as the area from the surface of the secondary particle recognized in the image above up to 0.5 μm inward. The area inside this secondary particle surface is defined as the interior of the secondary particle, and the pixels contained within the interior of the secondary particle (hereinafter referred to as interior pixels) are defined. I corresponding to each interior pixel Ｐ The set is I ＰＯ３－＿ＩＮ And so, I ＰＯ３－＿ＩＮ Therefore, PO inside secondary particles ３－ The Gini coefficient is calculated. The sample to be observed in cross-section may be a sample in which the positive electrode active material is embedded in resin or the like, or a positive electrode mixture layer containing the positive electrode active material. Note that in this specification, the PO inside the secondary particles ３－ The Gini coefficient is calculated by arbitrarily selecting 50 secondary particles and determining the PO inside the secondary particles. ３－ This refers to the value obtained by measuring the Gini coefficient using the method described below and taking the arithmetic mean of those measurements.

[0047] The total amount of the second compound contained in the positive electrode active material is, for example, 0.001% by mass or more and 1% by mass or less based on the mass of the lithium transition metal composite oxide. Also, the total amount of P contained in the positive electrode active material is 0.001 mol% or more and 0.5 mol% or less based on the total molar amount of the metal elements excluding Li in the lithium transition metal composite oxide.

[0048] The second compound includes, for example, at least one of Li-P compounds, Ca-P compounds, and Sr-P compounds. The Li-P compounds, Ca-P compounds, and Sr-P compounds are, for example, oxides. The Li-P compound is a compound containing Li and P, and for example, Li ３ PO ４ etc. can be mentioned. The Ca-P compound is a compound containing Ca and P, and for example, Ca(H ２ PO ４ ), Ca(H ２ PO ２ ), Ca(H ４ ), Ca(H ２ ), Ca(H ２ ), CaHPO ４ ), CaHPO ４ ), Ca(H ２ O), Ca ３ ), Ca(PO ４ ), Ca ２ etc. can be mentioned. The Sr-P compound is a compound containing Sr and P, and for example, Sr(H ２ PO ４ ), SrHPO ２ ), Sr ４ ), Sr ３ ), Sr(PO ４ ), Sr ２ etc. can be mentioned.

[0049] The positive electrode binder layer may contain a positive electrode active material other than the positive electrode active material containing the above-mentioned lithium transition metal composite oxide, the first compound, and the second compound. For example, the positive electrode binder layer may contain a positive electrode active material that does not contain the first compound or the second compound. The proportion of the positive electrode active material containing the above-mentioned lithium transition metal composite oxide, the first compound, and the second compound in the positive electrode active material is preferably 70% by mass or more, and may be substantially 100% by mass.

[0050] Hereinafter, an example of the method for producing the above-mentioned positive electrode active material will be described.

[0051] The manufacturing process for the positive electrode active material includes, for example, a mixing step of mixing a Ni metal compound containing 65 mol% or more Ni, a Li compound, an M1 compound, and an M2 compound to obtain a mixture; a firing step of firing the mixture; and a washing step of washing and drying the fired product. By adding a compound containing element M1 (M1 compound) and a compound containing element M2 (M2 compound) in the mixing step, a first compound can be made to exist at the interface between primary particles inside the secondary particles of the lithium transition metal composite oxide.

[0052] In the mixing step, for example, a Ni metal compound containing 65 mol% or more Ni, a Li compound, an M1 compound, and an M2 compound are mixed. Examples of Ni metal compounds include Ni-containing metal hydroxides, Ni-containing metal oxides, and Ni-containing metal carbonate compounds. Ni metal compounds can be obtained, for example, by adding an alkaline solution such as sodium hydroxide dropwise to a solution of a metal salt containing Ni and an arbitrary metal element (Co, Mn, etc.) while stirring, adjusting the pH to the alkaline side (for example, 8.5 or higher and 12.5 or lower), thereby precipitating (coprecipitation) a composite hydroxide containing Ni and an arbitrary metal element, and then heat-treating the composite hydroxide. The heat treatment temperature is not particularly limited, but for example, it is in the range of 250°C or higher and 600°C or lower. An example of a Li compound is Li ２ CO ３ LiOH, Li ２ O ２ Li ２ O, LiNO ３ LiNO ２ Li ２ SO ４ LiOH H ２ Examples include O, LiH, and LiF. The Ni metal compound and the Li compound are preferably mixed in a ratio such that the molar ratio of the total amount of metal elements excluding Li to Li is 1:0.98 to 1:1.12.

[0053] Examples of M1 compounds include hydroxides, oxides, carbonates, sulfates, and nitrates of element M1. An example of the above M1 compound is Nb ２ O５ , Nb ２ O ５ nH ２ O, WO ３ Li ２ WO ４ ,TiO ２ ,Ti(OH) ４ , ZrO ２ , Zr(OH) ４ MoO ３ Li ２ MoO ４ SiO,SiO ２ Examples include Ca(OH) ２ CaO, CaCO ３ CaSO ４ Ca(NO ３ ) ２ , Sr(OH) ２ , Sr(OH) ２ 8H ２ O, Sr(OH) ２ ・H ２ O, SrO, SrCO ３ , SrSO ４ , Sr(NO ３ ) ２ These are some examples. Compounds M1 and M2 may be dried and dehydrated before use to reduce the amount of moisture generated during calcination. Compounds M1 and M2 may also be crushed or otherwise processed to reduce the particle size to 0.1 to 20 μm before use.

[0054] The Ni metal compound and the M1 compound are preferably mixed in a ratio such that the molar ratio of the total amount of metal elements in the Ni metal compound (excluding Li) to element M1 is 1:0.0005 to 1:0.03. When multiple types of M1 compounds are used, they are mixed so that the total amount of element M1 contained in the M1 compounds satisfies this ratio. The preferred mixing ratio with the Ni metal compound is the same for the M2 compound. Furthermore, elements M1 and M2 are M2 α M1 β O γ It is preferable to mix them in accordance with the stoichiometric ratio.

[0055] The firing step is a multi-stage firing process that includes, for example, a first firing step in which the product is fired at a temperature of 450°C to 680°C under an oxygen stream, and a second firing step in which the product obtained in the first firing step is fired at a temperature exceeding 680°C under an oxygen stream. In the first firing step, the temperature is raised to a first set temperature of 680°C or less at a first heating rate of 0.2°C / min to 5.5°C / min. In the second firing step, the temperature is raised to a second set temperature of 900°C or less at a second heating rate of 0.1°C / min to 3.5°C / min, and slower than the first heating rate. Note that the first and second heating rates may be set to multiple values ​​for each predetermined temperature range within the above ranges.

[0056] The holding time at the first set temperature in the first firing process is preferably 5 hours or less, and more preferably 3 hours or less. The holding time at the first set temperature is the time after the first set temperature is reached and maintained at that temperature; however, the holding time may be zero. The holding time at the second set temperature in the second firing process is preferably 1 hour or more and 10 hours or less, and more preferably 1 hour or more and 5 hours or less. The holding time at the second set temperature is the time after the second set temperature is reached and maintained at that temperature. The firing of the mixture is carried out, for example, in an oxygen stream with an oxygen concentration of 60% or more, and the flow rate of the oxygen stream is set to 10 cm in the firing furnace. ３ The amount per unit is 0.2 mL / min to 4 mL / min, and the amount per 1 kg of mixture is 0.3 L / min or more.

[0057] Furthermore, in order to have the first compound present at the interface between primary particles within the secondary particles of the lithium transition metal composite oxide, it is necessary to add both the M1 compound and the M2 compound. In other words, even if a compound containing both elements M1 and M2 is used, it is not possible to have the first compound present on the surface of the primary particles inside the secondary particles. Moreover, it is thought that the first compound is formed when element M2 melts and incorporates element M1, and unless heat treatment is performed at a temperature of at least 600°C in the presence of the M1 and M2 compounds, it is not possible to have the first compound present on the surface of the primary particles inside the secondary particles. In addition, some of the elements M1 and M2 contained in the added M1 and M2 compounds may be dissolved in the lithium transition metal composite oxide.

[0058] In the washing step, the calcined material obtained in the calcination step is washed with water to remove impurities, while a P compound is added. The washed calcined material is then heated and dried to obtain the positive electrode active material. In the washing step, the washed calcined material may be dehydrated before heating and drying. If necessary, the positive electrode active material is crushed, classified, etc., to adjust its D50 to the desired range. Drying of the washed calcined material may be carried out at a temperature below 100°C. An example of a suitable drying temperature is 150°C to 400°C. The drying process may be carried out under vacuum or air. An example of a drying time is 1 hour to 5 hours.

[0059] By adding the P compound during the water washing before drying or before heat drying after dehydration, P can be dispersed relatively uniformly inside the secondary particles of the lithium transition metal composite oxide, thus reducing the amount of P inside the secondary particles. ３－ The Gini coefficient can be reduced to 0.6 or less. Examples of P compounds include H ３ PO ４ , P ２ O ５ Li ３－ｘ H ｘ PO ４ (0<x<3), Ca(H ２ PO ４ ) ２ Ca(H ２ PO ４ ) ２ ・H ２ O, CaHPO ４ CaHPO ４ ・2(H ２ O), Ca ３ (PO ４ ) ２、 Sr(H ２ PO ４ ) ２ SrHPO ４ , Sr ３ (PO ４ ) ２ These are some examples. From the viewpoint of being able to more uniformly disperse P inside the secondary particles of lithium transition metal composite oxide, it is preferable to add the P raw material during the water washing before drying.

[0060] In the washing step, an aqueous phosphoric acid solution may be added as the P raw material. The concentration of the aqueous phosphoric acid solution is, for example, 0.1% by mass or more and 85% by mass or less, and preferably 0.3% by mass or more and 10% by mass or less from the viewpoint of dispersibility. By adding the P raw material as an aqueous phosphoric acid solution, P can be dispersed more uniformly inside the secondary particles. For example, by adding an aqueous solution containing a P compound such that it is 0.0004% by mass or more and 2% by mass or less relative to the mass of the lithium transition metal composite oxide, the mass of the P compound contained in the positive electrode active material can be made 0.00015% by mass or more and 0.35% by mass or less in terms of P element relative to the mass of the lithium transition metal composite oxide.

[0061] The amount of P compound added is, for example, 0.001% by mass or more and 1% by mass or less, and more preferably 0.01% by mass or more and 0.5% by mass or less, relative to the mass of the lithium transition metal composite oxide. In this case, an appropriate amount of phosphorus-containing compound can be present on the surface of the secondary particles of the lithium transition metal composite oxide and at the grain boundaries of the primary particles, and a significant effect of suppressing the reaction resistance of the battery is exhibited. The P contained in the P compound may react with Li, Ca, or Sr eluted from the lithium transition metal composite oxide during washing with water to produce a second compound, such as a Li-P compound, a Ca-P compound, or a Sr-P compound.

[0062] [Negative Electrode] The negative electrode 12 may, for example, have a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector, or a metallic Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode current collector, and lithium metal may be deposited on the surface of the negative electrode current collector by charging. When the negative electrode 12 has a negative electrode mixture layer, it is preferable that the negative electrode mixture layer is formed on both sides of the negative electrode current collector. For the negative electrode current collector, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on the surface layer, can be used. The thickness of the negative electrode current collector is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode current collector. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc., to the surface of a negative electrode current collector, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode current collector.

[0063] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly intercept and release lithium ions, and generally carbon materials such as graphite are used. The graphite may be any of the following: natural graphite such as flake graphite, lump graphite, or clay graphite; lump artificial graphite; or artificial graphite such as graphitized mesophase carbon microbeads. In addition, metals that alloy with Li such as Si and Sn, metal compounds containing Si and Sn, or lithium titanium composite oxides may be used as the negative electrode active material. Furthermore, materials with a carbon coating may also be used. For example, SiO ｘ Si-containing compounds represented by (0.5 ≤ x ≤ 1.6), or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine Si particles are dispersed in a lithium silicate phase represented by (0 < y < 2) may be used in combination with graphite.

[0064] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0065] [Separator] The separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. In addition, a heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13.

[0066] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphoric acid compounds. The filler layer can be formed by coating the surface of the positive electrode 11, the negative electrode 12, or the separator 13 with a slurry containing the filler.

[0067] [Non-aqueous electrolytes] Non-aqueous electrolytes, for example, have lithium ion conductivity. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0068] A liquid electrolyte (electrolyte solution) includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted solvents include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0069] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0070] Examples of the above ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methylphenyl ether. Examples include chain ethers such as ethylphenyl ether, butylphenyl ether, pentylphenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0071] The electrolyte salt is preferably a lithium salt. A suitable lithium salt is LiClO ４ LiBF ４ LiPF ６ LiAlCl ４ LiSbF ６ , LiSCN, LiCF ３ SO ３ LiCF ３ CO ２ LiAsF ６ LiB １０ Cl １０ Examples include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO4). ２ F ２Examples include lithium difluorobis(oxalato)phosphate (LiDFOBP), lithium tetrafluoro(oxalato)phosphate, etc. Examples of borates include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), etc. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO)). ２ ) ２ ), bistrifluoromethanesulfonate lithium (LiN(CF ３ SO ２ ) ２ ), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), bispentafluoroethanesulfonate lithium (LiN(C) ２ F ５ SO ２ ) ２ ) etc. are used. Of these, LiPF is used from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ It is preferable to use the following. The concentration of the lithium salt may be, for example, 4 moles or less per liter of non-aqueous solvent, or 3 moles or less, preferably 1.8 moles or less, and more preferably 0.8 moles or more and 1.8 moles or less.

[0072] Non-aqueous electrolytes may contain additives. Examples of additives include unsaturated carbonate esters, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0073] Examples of unsaturated cyclic carbonate esters include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. Unsaturated cyclic carbonate esters may be used individually or in combination of two or more. Some hydrogen atoms in the unsaturated cyclic carbonate esters may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, but it is preferable that it be an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0074] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0075] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanate methylcyclohexane (BIMCH). Examples of sultone compounds include propanesultone and propensultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethylborate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethylphosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethylphosphite and tris(trimethylsilyl)phosphite.

[0076] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0077] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0078] <Example 1-1> [Preparation of positive electrode active material] Ni obtained by coprecipitation method ０．８８ Co ０．０４ Mn ０．０８ (OH) ２The composite hydroxide represented by was calcined at 400°C for 8 hours to obtain a Ni-containing metal oxide containing Ni, Co, and Mn. Next, the above Ni-containing metal oxide and Ca(OH) were mixed so that the molar ratio of Ca to the total number of moles of Ni, Co, and Mn was 0.4 mol%, the molar ratio of Zr was 0.2 mol%, and the molar ratio of Ti was 0.5 mol%. ２ And, ZrO ２ And, TiO ２ Mix the following, and further, lithium hydroxide monohydrate (LiOH·H) is added so that the molar ratio of Li to the total number of moles of Ni, Co, Mn, Ca, Zr, and Ti is 103 mol%. ２ O) was mixed to obtain a mixture. This mixture was heated under an oxygen stream with an oxygen concentration of 95% (flow rate of 3 L / min per 1 kg of mixture) at a heating rate of 4°C / min from room temperature to 500°C, and then heated from 500°C to 650°C at a heating rate of 2°C / min. After that, the temperature was heated from 650°C to 750°C at a heating rate of 1°C / min, and held for 5 hours to obtain a calcined product. In a 3 L reaction vessel, water was added to the calcined product so that the solid-liquid ratio was 500 g / L, and then 0.05 mass% of H was added to the calcined product. ３ PO ４ A phosphoric acid aqueous solution containing [the substance] was added, and the mixture was washed with water for 10 minutes at a stirring speed of 300 rpm. The concentration of the phosphoric acid aqueous solution was 0.5% by mass. Subsequently, the cathode active material was obtained by vacuum drying at 180°C for 2 hours.

[0079] The obtained positive electrode active material was measured using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements shown in Table 1 were identified. The amount of P was 0.05 mol% of the total molar amount of metal elements excluding Li in the positive electrode active material. Furthermore, synchrotron X-ray diffraction measurements identified compounds present in the positive electrode active material, resulting in the identification of CaTiO2. ３、 CaZrO ３ The presence of compounds containing , and P was confirmed. Furthermore, TEM-EDX confirmed the presence of Ca, Ti, and Zr at the interface between primary particles inside the secondary particles, and the presence of P on the surface of the secondary particles and at the interface between primary particles. In addition, PO inside the secondary particles ３－ The Gini coefficient was 0.3.

[0080] [Preparation of the positive electrode] The above positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 98:1:1, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil, and after the coating film was dried, the coating film was rolled out with a rolling mill and cut to a predetermined electrode size to produce the positive electrode. An exposed portion was provided on a part of the positive electrode in which the surface of the positive electrode current collector was exposed.

[0081] [Fabrication of the negative electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethylcellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution in a solid content mass ratio of 100:1:1 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and after the coating film was dried, the coating film was rolled using a rolling mill and cut to a predetermined electrode size to produce the negative electrode. An exposed portion was provided on a part of the negative electrode in which the surface of the negative electrode core body was exposed.

[0082] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluoride phosphate (LiPF) was added to this mixed solvent. ６ A non-aqueous electrolyte was prepared by dissolving the substance to a concentration of 1.2 mol / liter.

[0083] [Preparation of Test Cell] A positive electrode lead was attached to the exposed portion of the positive electrode, and a negative electrode lead was attached to the exposed portion of the negative electrode. The positive and negative electrodes were wound in a spiral shape via a polyolefin separator, and then press-molded radially to produce a flat, wound electrode body. This electrode body was housed in an outer casing made of aluminum laminate sheet, the non-aqueous electrolyte was injected, and the opening of the outer casing was sealed to obtain a test cell.

[0084] [Measurement of Initial Reaction Resistance] The test cell was charged with a constant current of 0.3 It at a temperature of 25°C until the battery voltage reached 4.2V. Operation A involved constant voltage charging until the current value was reduced to 1 / 50 It at 4.2V. Operation B involved constant current discharge with a constant current of 0.2 It until the battery voltage reached 2.5V. This process was repeated twice. Next, the test cell was charged with a constant current of 0.3 It at a temperature of 25°C until the battery voltage reached 4.2V. Operation B involved constant voltage charging until the current value was reduced to 1 / 50 It at 4.2V. After that, AC impedance measurements were performed under the conditions of a temperature of 25°C, a frequency of 0.01 Hz to 100,000 Hz, and an applied voltage of 10 mV. The initial resistance (Ω) was determined by equivalent circuit fitting of the Nyquist plot.

[0085] [Measurement of Resistance Increase Rate] The test cell, whose initial resistance was measured, was charged at a constant current of 0.3 It at 25°C until the battery voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current value was 1 / 50 It. After that, it was discharged at a constant current of 0.5 It until the battery voltage reached 2.5V. This charge-discharge cycle was considered one cycle, and 100 cycles were performed. Next, the test cell was charged at a constant current of 0.3 It at 25°C until the battery voltage reached 4.2V, and then charged at a constant voltage until the current value was 1 / 50 It at 4.2V. After that, AC impedance measurements were performed under the conditions of a temperature of 25°C, a frequency of 0.01 Hz to 100,000 Hz, and an applied voltage of 10 mV, and the reaction resistance (Ω) after the cycle was determined by equivalent circuit fitting of the Nyquist plot. The resistance increase rate of the test cell during the charge-discharge cycle was determined using the following formula. Resistance increase rate (%) = (Resistance after cycle - Initial resistance) / Initial resistance × 100

[0086] <Example 1-2> In the preparation of the positive electrode active material, Ca(OH) ２ Without mixing, the molar ratio of Sr to the total number of moles of Ni, Co, and Mn is 0.2 mol%, the molar ratio of Zr is 0.5 mol%, and the molar ratio of Ti is 0.3 mol%. ２ , ZrO ２ , and TiO ２ The fact that it was mixed with H ３ PO ４Except for changing the amount of added material to 0.1% by mass, a test cell was prepared and evaluated in the same manner as in Example 1-1. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 1. In addition, Sr was present in the positive electrode active material. ２ TiO ４ , SrZrO ３ It was confirmed that compounds containing and P exist, that Sr, Zr, and Nb are present at the interfaces between primary particles inside the secondary particles, and that P is present on the surface of the secondary particles and at the interfaces between primary particles. Furthermore, PO inside the secondary particles ３－ The Gini coefficient was 0.2.

[0087] <Comparative Example 1-1> In the preparation of the positive electrode active material, Ca(OH) ２ , ZrO ２ , and TiO ２ The fact that they were not mixed and 、 H ３ PO ４ A test cell was prepared and evaluated in the same manner as in Example 1-1, except that one element was not added. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 1.

[0088] <Comparative Example 1-2> In the preparation of the positive electrode active material, H ３ PO ４ A test cell was prepared and evaluated in the same manner as in Example 1-1, except that CaTiO was not added. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 1. In addition, the positive electrode active material contained CaTiO ３ and CaZrO ３ We confirmed that these elements exist, and that Sr, Zr, and Nb are present at the interfaces between primary particles within the secondary particles.

[0089] <Example 2-1> A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９１ Co ０．０３ Mn ０．０５ Al ０．０１ ] (OH) ２A composite hydroxide represented by was calcined to obtain a Ni-containing metal oxide. (2) The molar ratio of Ca to the total number of moles of Ni, Co, Mn, and Al was 0.2 mol%, the molar ratio of Sr was 0.1 mol%, the molar ratio of Nb was 0.4 mol%, and the molar ratio of Zr was 0.3 mol%, so that the above Ni-containing metal oxide and Ca(OH) ２ And, Sr(OH) ２ And, Nb ２ O ５ And, ZrO ２ (3) H ３ PO ４ The amount added was changed to 0.1% by mass.

[0090] The fabricated positive electrode active material was confirmed to contain the elements shown in Table 2. Furthermore, the positive electrode active material contained CaNbO ３ CaZrO ３ , SrZrO ３ It was confirmed that Ca, Sr, Zr, and Nb are present at the interfaces between primary particles within the secondary particles of the compound containing P, and that P is present on the surface of the secondary particles and at the interfaces between primary particles. Furthermore, it was confirmed that PO inside the secondary particles ３－ The Gini coefficient was 0.3.

[0091] <Example 2-2> In the preparation of the positive electrode active material, Sr(OH) ２ Without mixing, the molar ratio of Ca to the total number of moles of Ni, Co, Mn, and Al is 0.4 mol%, the molar ratio of Nb is 0.4 mol%, and the molar ratio of Zr is 0.2 mol%. ２ , Nb ２ O ５ , and ZrO ２ A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the mixture contained the elements shown in Table 2. Furthermore, the positive electrode active material contained CaNbO ３ CaZrO ３ It was confirmed that compounds containing , and P exist, and that Ca, Zr, and Nb are present at the interfaces between primary particles inside the secondary particles, and P is present on the surface of the secondary particles and at the interfaces between primary particles. Furthermore, PO inside the secondary particles ３－ The Gini coefficient was 0.2.

[0092] <Comparative Example 2-1> In the preparation of the positive electrode active material, Ca(OH) ２ , Sr(OH) ２ , Nb ２ O ５ , and ZrO ２ The fact that they were not mixed, and H ３ PO ４ A test cell was prepared and evaluated in the same manner as in Example 2-1, except that one element was not added. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 2.

[0093] <Comparative Example 2-2> In the preparation of the positive electrode active material, Ca(OH) ２ , Sr(OH) ２ , Nb ２ O ５ , and ZrO ２ A test cell was prepared and evaluated in the same manner as in Example 2-1, except that the element was not mixed. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 2. Furthermore, it was confirmed that a compound containing P was present in the positive electrode active material, and that P was present on the surface of the secondary particles and at the interfaces between primary particles. In addition, PO was found inside the secondary particles. ３－ The Gini coefficient was 0.3.

[0094] <Comparative Example 2-3> In the preparation of the positive electrode active material, Sr(OH) ２ Without mixing, the molar ratio of Ca to the total number of moles of Ni, Co, Mn, and Al is 0.4 mol%, the molar ratio of Nb is 0.4 mol%, and the molar ratio of Zr is 0.2 mol%. ２ , Nb ２ O ５ , and ZrO ２ The fact that it was mixed with H ３ PO ４ Except for the absence of the additive, a test cell was prepared and evaluated in the same manner as in Example 2-1. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 2. In addition, the positive electrode active material contained CaNbO ３ , and CaZrO ３ It was confirmed that these elements exist, and that Ca, Zr, and Nb are present at the interfaces between primary particles within the secondary particles.

[0095] <Comparative Example 2-4> In the preparation of the positive electrode active material, Sr(OH) ２ Without mixing, the molar ratio of Ca to the total number of moles of Ni, Co, Mn, and Al is 0.45 mol%, the molar ratio of Nb is 0.4 mol%, the molar ratio of Zr is 0.2 mol%, and the molar ratio of P is 0.05 mol%. ２ , Nb ２ O ５ , ZrO ２ , and P ２ O ５ The mixture and the P ２ O ５ Except for the absence of the additive, a test cell was prepared and evaluated in the same manner as in Example 2-1. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 2. In addition, the positive electrode active material contained CaNbO ３ CaZrO ３ It was confirmed that compounds containing , and P exist, and that Ca, Zr, and Nb are present at the interfaces between primary particles inside the secondary particles, and P is present on the surface of the secondary particles and at the interfaces between primary particles. Furthermore, PO inside the secondary particles ３－ The Gini coefficient was 0.8.

[0096] <Example 3-1> A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．９２ Co ０．０２ Mn ０．０４ Al ０．０２ ] (OH) ２ A composite hydroxide represented by was calcined to obtain a Ni-containing metal oxide. (2) The molar ratio of Ca to the total number of moles of Ni, Co, Mn, and Al was 0.4 mol%, the molar ratio of Nb was 0.3 mol%, and the molar ratio of Zr was 0.2 mol%, so that the above Ni-containing metal oxide and Ca(OH) ２ And, Nb ２ O ５ And, ZrO ２ They were mixed together.

[0097] The fabricated positive electrode active material was confirmed to contain the elements shown in Table 3. Furthermore, the positive electrode active material contained CaNbO３ CaZrO ３ It was confirmed that compounds containing , and P exist, and that Ca, Zr, and Nb are present at the interfaces between primary particles inside the secondary particles, and P is present on the surface of the secondary particles and at the interfaces between primary particles. Furthermore, PO inside the secondary particles ３－ The Gini coefficient was 0.4.

[0098] <Example 3-2> In the preparation of the positive electrode active material, Ca(OH) ２ and Nb ２ O ５ Without mixing, the molar ratio of Sr to the total number of moles of Ni, Co, Mn, and Al is 0.1 mol%, the molar ratio of Zr is 0.2 mol%, and the molar ratio of Ti is 0.3 mol%. ２ , ZrO ２ , and TiO ２ A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the mixture contained the elements shown in Table 3. In addition, the positive electrode active material contained SrZrO ３ SrTiO ３ It was confirmed that compounds containing P are present, Sr, Zr, and Ti are present at the interfaces between primary particles inside the secondary particles, and P is present on the surface of the secondary particles and at the interfaces between primary particles. Furthermore, PO inside the secondary particles ３－ The Gini coefficient was 0.4.

[0099] <Comparative Example 3-1> In the preparation of the positive electrode active material, Ca(OH) ２ , Nb ２ O ５ , and ZrO ２ The fact that they were not mixed, and H ３ PO ４ A test cell was prepared and evaluated in the same manner as in Example 3-1, except that one element was not added. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 3.

[0100] <Comparative Example 3-2> In the preparation of the positive electrode active material, H ３ PO ４A test cell was prepared and evaluated in the same manner as in Example 3-1, except that one element was not added. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 3.

[0101] <Example 4-1> A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows: (1) [Ni ０．７９ Co ０．０５ Mn ０．１５ Al ０．０１ ] (OH) ２ A composite hydroxide represented by was calcined to obtain a Ni-containing metal oxide. (2) The molar ratio of Ca to the total number of moles of Ni, Co, Mn, and Al was 0.3 mol%, the molar ratio of Nb was 0.5 mol%, and the molar ratio of W was 0.4 mol%, so that the above Ni-containing metal oxide and Ca(OH) ２ And, Nb ２ O ５ And, WO ３ They were mixed together.

[0102] The fabricated positive electrode active material was confirmed to contain the elements shown in Table 4. Furthermore, the positive electrode active material contained CaNbO ３ CaWO ４ It was confirmed that compounds containing , and P exist, and that Ca, Nb, and W are present at the interfaces between primary particles inside the secondary particles, and P is present on the surface of the secondary particles and at the interfaces between primary particles. Furthermore, PO inside the secondary particles ３－ The Gini coefficient was 0.3.

[0103] <Comparative Example 4-1> In the preparation of the positive electrode active material, Ca(OH) ２ , Nb ２ O ５ , and WO ３ The fact that they were not mixed, and H ３ PO ４ A test cell was prepared and evaluated in the same manner as in Example 4-1, except that one element was not added. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 4.

[0104] <Comparative Example 4-2> In the preparation of the positive electrode active material, H ３ PO ４A test cell was prepared and evaluated in the same manner as in Example 4-1, except that one element was not added. It was confirmed that the prepared positive electrode active material contained the elements shown in Table 4.

[0105] The evaluation results of the test cells for the examples and comparative examples are shown in Tables 1 to 4. In Table 1, the initial reaction resistance and the rate of increase in reaction resistance of the test cells for Examples and Comparative Examples 1-2 are expressed relatively, with the initial reaction resistance and the rate of increase in reaction resistance of the test cell for Comparative Example 1-1 each set to 100. In Table 2, the initial reaction resistance and the rate of increase in reaction resistance of the test cells for Examples and Comparative Examples 2-2 to 2-4 are expressed relatively, with the initial reaction resistance and the rate of increase in reaction resistance of the test cell for Comparative Example 2-1 each set to 100. In Table 3, the initial reaction resistance and the rate of increase in reaction resistance of the test cells for Examples and Comparative Example 3-2 are expressed relatively, with the initial reaction resistance and the rate of increase in reaction resistance of the test cell for Comparative Example 3-1 each set to 100. In Table 4, the initial reaction resistance and the rate of increase in reaction resistance of the test cells for Examples and Comparative Example 4-2 are expressed relatively, with the initial reaction resistance and the rate of increase in reaction resistance of the test cell for Comparative Example 4-1 each set to 100.

[0106]

[0107]

[0108]

[0109]

[0110] As shown in Tables 1 to 4, in all of the example test cells, both the initial reaction resistance and the rate of increase in reaction resistance were kept low compared to the test cells of the corresponding comparative examples. The positive electrode active material of the comparative examples, excluding Comparative Examples 2-4, lacked at least one of the first or second compound. This indicates that the presence of both the first and second compounds is necessary to reduce the initial reaction resistance while suppressing the increase in reaction resistance due to repeated discharge. Furthermore, in Comparative Examples 2-4, by adding the P compound during calcination rather than during washing, the distribution of P inside the secondary particles became uneven, and PO ３－The increase in reaction resistance is thought to be due to the Gini coefficient exceeding 0.6.

[0111] This disclosure is further illustrated by the following embodiments. Configuration 1: A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal composite oxide, a first compound comprising at least one of Ca and Sr and at least one of W, Mo, Nb, Ti, Si, and Zr, and a second compound comprising P, wherein the lithium transition metal composite oxide has a layered structure and the general formula is Li ｘ Ni ａ Co ｂ Mn ｃ Al ｄ M1 ｅ M2 ｆ O ２－ｙ (wherein the formula, 0.95≦x≦1.15, 0.65≦a≦0.95, 0≦b≦0.15, 0≦c≦0.30, 0≦d≦0.10, 0<e≦0.03, 0≦f≦0.03, 0≦y<0.05, a+b+c+d+e+f=1, M1 is at least one element selected from the group consisting of W, Mo, Nb, Ti, Si and Zr, and M2 is at least one element of Ca and Sr), and is a secondary particle formed by the aggregation of primary particles, the first compound exists at the interface between the primary particles inside the secondary particle, the second compound exists on the surface of the secondary particle or at the interface between the primary particles, and in the elemental concentration distribution of the cross-section of the secondary particle using time-of-flight secondary ion mass spectrometry, PO inside the secondary particle ３－ A positive electrode active material for a non-aqueous electrolyte secondary battery having a Gini coefficient of 0.6 or less. Configuration 2: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein the total amount of Ca and Sr is 1 mol% or less relative to the total molar amount of metal elements excluding Li in the lithium transition metal composite oxide. Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the total amount of P is 0.001 mol% or more and 0.5 mol% or less relative to the total molar amount of metal elements excluding Li in the lithium transition metal composite oxide. Configuration 4: The first compound is of general formula M2 α M1 β O γA positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 3, comprising a compound represented by the formula (wherein 1 ≤ α ≤ 2, 1 ≤ β ≤ 4, 3 ≤ γ ≤ 9). Configuration 5: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 4, wherein the total amount of the second compound is 0.00015% by mass or more and 0.35% by mass or less in terms of element P relative to the mass of the lithium transition metal composite oxide. Configuration 6: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 5, wherein the second compound comprises at least one of Li-P compounds, Ca-P compounds, and Sr-P compounds. Configuration 7: A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material according to any one of configurations 1 to 6, a negative electrode, and a non-aqueous electrolyte. Configuration 8: A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a mixing step of mixing a Ni metal compound containing 65 mol% or more Ni relative to the total molar amount of metal elements, a Li compound, an M1 compound, and an M2 compound to obtain a mixture; a firing step of firing the mixture to obtain a fired product; and a washing step of washing and drying the fired product with water, wherein an aqueous solution containing a P compound in an amount of 0.0004% by mass or more and 2% by mass or less in terms of P element relative to the mass of the lithium transition metal composite oxide is added to the washing step.

[0112] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium transition metal composite oxide, a first compound containing at least one of Ca and Sr and at least one of W, Mo, Nb, Ti, Si, and Zr, and a second compound containing P, wherein the lithium transition metal composite oxide has a layered structure and has the general formula Li ｘ Ni ａ Co ｂ Mn ｃ Al ｄ M1 ｅ M2 ｆ O ２－ｙ (where 0.95 ≦ x ≦ 1.15, 0.65 ≦ a ≦ 0.95, 0 ≦ b ≦ 0.15, 0 ≦ c ≦ 0.30, 0 ≦ d ≦ 0.10, 0 < e ≦ 0.03, 0 ≦ f ≦ 0.03, 0 ≦ y < 0.05, a + b + c + d + e + f = 1, M1 is at least one element selected from the group consisting of W, Mo, Nb, Ti, Si and Zr, M2 is at least one element of Ca and Sr), and is a secondary particle formed by aggregation of primary particles, the first compound is present at the interface between the primary particles inside the secondary particles, the second compound is present on the surface of the secondary particles or at the interface between the primary particles, and in the element concentration distribution of the cross section of the secondary particles using time-of-flight secondary ion mass spectrometry, the din coefficient of PO ３－ inside the secondary particles is 0.6 or less. A positive electrode active material for a non-aqueous electrolyte secondary battery.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the total amount of Ca and Sr is 1 mol% or less relative to the total molar amount of metal elements excluding Li in the lithium transition metal composite oxide.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the total amount of P is 0.001 mol% or more and 0.5 mol% or less relative to the total molar amount of metal elements excluding Li in the lithium transition metal composite oxide.

4. The first compound has the general formula M2 α M1 β O γ A positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, comprising a compound represented by the formula (wherein 1 ≤ α ≤ 2, 1 ≤ β ≤ 4, 3 ≤ γ ≤ 9).

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the total amount of the second compound is 0.00015% by mass or more and 0.35% by mass or less in terms of element P relative to the mass of the lithium transition metal composite oxide.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the second compound comprises at least one of a Li-P compound, a Ca-P compound, and a Sr-P compound.

7. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material described in any one of claims 1 to 6, a negative electrode, and a non-aqueous electrolyte.

8. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a mixing step of mixing a Ni metal compound containing 65 mol% or more Ni relative to the total molar amount of metal elements, a Li compound, an M1 compound, and an M2 compound to obtain a mixture; a firing step of firing the mixture to obtain a fired product; and a washing step of washing and drying the fired product with water, wherein an aqueous solution containing a P compound in an amount of 0.0004% by mass or more and 2% by mass or less in terms of P element relative to the mass of the lithium transition metal composite oxide is added to the washing step.

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