Positive electrode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

Provided is a positive electrode active material which contributes to an improvement of safety of secondary batteries. A positive electrode active material included in a nonaqueous electrolyte secondary battery contains a lithium transition metal composite oxide containing Ni, P, and at least one of Ca and Sr at prescribed content ratios and containing secondary particles formed with aggregated primary particles. The ratio m / n of the half width m of the diffraction peak of the (003) plane to the half width n of the diffraction peak of the (110) plane of the X-ray diffraction pattern by X-ray diffraction satisfies 0.75≤m / n≤0.85, and in the elemental concentration distribution of the cross-section of the lithium transition metal composite oxide according to the time-of-flight secondary ion mass spectrometry, the ratio IP_OUT / IP_IN of the normalized intensity IP_OUT of P of the secondary particle surface to the normalized intensity IP_IN of P inside the secondary particles satisfies 1≤IP_OUT / IP_IN≤150.

Description

Positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery, and in particular to a positive electrode active material for a non-aqueous electrolyte secondary battery containing Ni at a high concentration, and a non-aqueous electrolyte secondary battery using this positive electrode active material for a non-aqueous electrolyte secondary battery.

[0002] Previously, lithium nickel oxide (LiNiO ２ ) is known to have a high energy density, and by substituting a part of Ni with Co, Al, Mn, etc., it is possible to improve battery characteristics such as reliability.

[0003] Patent Document 1 describes a method for forming a lithium transition metal composite oxide containing Ni, Mn, Co, and Sr on the surface thereof. ３ P.O. ４ Patent Document 1 discloses a positive electrode active material having an oxide coating layer formed thereon, the oxide coating layer containing the compound. Patent Document 1 describes that the use of this positive electrode active material improves the charge-discharge cycle characteristics of a secondary battery.

[0004] Patent No. 6749973

[0005] However, lithium transition metal composite oxides with a Ni content of 75% or more are prone to side reactions with non-aqueous electrolytes, and furthermore, due to the large amount of Li extracted during charging, their layered crystal structure is easily destroyed. Therefore, in non-aqueous electrolyte secondary batteries containing such lithium transition metal composite oxides in the positive electrode, if the temperature inside the battery rises due to overcharging, short circuit, or the like, the temperature rise can lead to further heat-generating chemical reactions (self-heating reactions) within the battery, potentially triggering the battery's safety valve. The technology described in Patent Document 1 does not address the issue of improving battery safety, and there is still room for improvement.

[0006] An object of the present disclosure is to provide a positive electrode active material that contributes to improving the safety of non-aqueous electrolyte secondary batteries.

[0007] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a lithium transition metal composite oxide. The lithium transition metal composite oxide contains Ni, P, and at least one of Ca and Sr, and includes secondary particles formed by aggregation of primary particles. The Ni content in the lithium transition metal composite oxide is 75 mol%≦Ni content≦95 mol% with respect to the total number of moles of elements excluding Li and O, and the P content in the lithium transition metal composite oxide is 0 mol%<P content with respect to the total number of moles of elements excluding Li and O. ≦2 mol%, the sum of the Ca content and the Sr content in the lithium transition metal composite oxide is 0 mol%<Ca content + Sr content ≦2 mol% with respect to the total number of moles of elements excluding Li and O, the ratio m / n of the half width m of the diffraction peak of the (003) plane to the half width n of the diffraction peak of the (110) plane in the X-ray diffraction pattern by X-ray diffraction satisfies 0.75≦m / n≦0.85, and in the element concentration distribution of the cross section of the lithium transition metal composite oxide obtained by time-of-flight secondary ion mass spectrometry, the normalized intensity I of P inside the secondary particles is Ｐ＿ＩＮ Normalized intensity I of P on the secondary particle surface Ｐ＿ＯＵＴ Ratio I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ However, 1≦I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ≦150.

[0008] A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure is characterized by including a positive electrode containing the above-described positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

[0009] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure improves the safety of the secondary battery, particularly at high temperatures. Furthermore, the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure can be produced by a method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery.

[0010] 1 is a longitudinal cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention, and FIG. 2 is an X-ray diffraction pattern obtained when X-ray diffraction measurement is performed on the positive electrode active material according to Example 1-1.

[0011] The layered structure of lithium transition metal composite oxides includes a transition metal layer (e.g., Ni) and a Li layer. The reversible movement of Li ions in the Li layer promotes the charge / discharge reaction of the battery. Generally, lithium transition metal composite oxides containing Ni as the main component are known as high-capacity positive electrode active materials. However, lithium transition metal composite oxides with a Ni content of 75% or more are prone to side reactions with non-aqueous electrolytes. Furthermore, the amount of Li extracted during charging is large, making the layered crystal structure susceptible to breakdown. Therefore, if the temperature inside the battery rises due to overcharging, short circuiting, or the like, the temperature rise can lead to further heat-generating chemical reactions (self-heating reactions) within the battery, potentially triggering the battery's safety valve (described later).

[0012] In Patent Document 1, from the viewpoint of improving charge-discharge cycle characteristics, Li is attached to the surface of a lithium transition metal composite oxide containing Ni, Mn, Co, and Sr. ３ P.O. ４ However, Patent Document 1 does not consider improving the safety of the battery.

[0013] As a result of intensive research to solve the above-mentioned problems, the present inventors have found a lithium transition metal composite oxide having a Ni content of 75% or more, which contains P and at least one of Ca and Sr at a predetermined content, and in which the ratio m / n of the half width m of the diffraction peak of the (003) plane to the half width n of the diffraction peak of the (110) plane in an X-ray diffraction pattern by X-ray diffraction satisfies 0.75≦m / n≦0.85, and further in which the normalized intensity I of P inside the secondary particles is 0.75≦m / n≦0.85 in an element concentration distribution of a cross section of the lithium transition metal composite oxide obtained by time-of-flight secondary ion mass spectrometry. Ｐ＿ＩＮ Normalized intensity I of P on the secondary particle surface Ｐ＿ＯＵＴ Ratio I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ However, 1≦I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ It was found that the safety of the battery is improved by satisfying the condition I≦150. Ｐ＿ＯＵＴ / I Ｐ＿ＩＮBy satisfying the above range, P is distributed in a balanced manner not only on the surface but also inside the secondary particles. The coexistence of P distributed on the surface and inside the secondary particles, and at least one of Ca and Sr, can effectively suppress side reactions with the non-aqueous electrolyte. Furthermore, by keeping the half-width ratio within the specified range, the crystal structure can be stabilized, and it is presumed that the synergistic effect of these factors suppresses the self-heating reaction of the battery and improves the safety of the battery.

[0014] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below. Hereinafter, a cylindrical battery in which a wound electrode assembly is housed in a cylindrical exterior body will be exemplified. However, the electrode assembly is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are alternately stacked one by one with separators interposed therebetween. Furthermore, the exterior body is not limited to a cylindrical shape and may be, for example, prismatic or coin-shaped, or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0015] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. As shown in FIG. 1 , the secondary battery 10 includes a wound electrode assembly 14, an electrolyte, and an exterior body 16 that accommodates the electrode assembly 14 and the electrolyte. The electrode assembly 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 spirally wound with the separator 13 interposed therebetween. The exterior body 16 is a cylindrical metal container with a bottom and an opening on one axial side, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the battery will be referred to as the top, and the bottom side of the exterior body 16 will be referred to as the bottom.

[0016] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode assembly 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and alternately stacked in the radial direction of the electrode assembly 14. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal and lateral directions. The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The electrode assembly 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 assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the lateral direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the end faces in the lateral direction of the positive electrode 11 and the negative electrode 12 form the end faces in the axial direction of the electrode body 14 .

[0017] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom side of the exterior body 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the exterior body 16 by welding or the like, and the exterior body 16 serves as the negative electrode terminal.

[0018] A gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior body 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior body 16 by the grooved portion 22 and the open end of the exterior body 16 that is crimped to the sealing body 17.

[0019] The sealing body 17 has a structure in which, in order from the electrode body 14 side, 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, and functions as a safety valve. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and each component except for 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, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0020] The positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte that constitute the secondary battery 10 will be described in detail below, with the positive electrode 11 being particularly described below.

[0021] [Positive Electrode] The positive electrode 11 has, for example, a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core. The positive electrode mixture layer is preferably formed on both sides of the positive electrode core. The positive electrode core can be made of a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer. The thickness of the positive electrode core is, for example, 10 μm or more and 30 μm or less.

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

[0023] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphene, graphite, and other carbon-based particles. These may be used alone or in combination of two or more. 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 with respect to the total mass of the positive electrode mixture layer.

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

[0025] The positive electrode active material contained in the positive electrode mixture layer includes a lithium transition metal composite oxide, which contains Ni, P, and at least one of Ca and Sr.

[0026] The Ni content in the lithium transition metal composite oxide is 75 mol%≦Ni content≦95 mol% based on the total number of moles of elements excluding Li and O. The Ni content is preferably within this range from the viewpoint of achieving both high capacity and structural stability. The lower limit of the Ni content is preferably 80 mol%, more preferably 85 mol%.

[0027] The P content in the lithium transition metal composite oxide is 0 mol% < P content ≦ 2 mol% relative to the total number of moles of elements excluding Li and O. The coexistence of P at this content with Ca and Sr can improve the safety of the lithium transition metal composite oxide. The lower limit of the P content is, for example, 0.01 mol%.

[0028] The sum of the Ca content and Sr content in the lithium transition metal composite oxide is 0 mol% < Ca content + Sr content ≦ 2 mol% relative to the total number of moles of elements excluding Li and O. The safety of the lithium transition metal composite oxide can be improved by allowing at least one of Ca and Sr at this content to coexist with P. The lower limit of the sum of the Ca content and Sr content is, for example, 0.01 mol%.

[0029] The lithium transition metal composite oxide preferably contains both Ca and Sr, which can significantly improve the safety of the lithium transition metal composite oxide.

[0030] The lithium transition metal composite oxide preferably satisfies the condition of Ca content > Sr content, which can significantly improve the safety of the lithium transition metal composite oxide.

[0031] The lithium transition metal composite oxide may further contain B. The B content in the lithium transition metal composite oxide is, for example, 0 mol % < B content ≦ 3 mol % relative to the total number of moles of elements excluding Li and O. The lower limit of the B content is, for example, 0.01 mol %. It is presumed that the lithium transition metal composite oxide containing a predetermined amount of B can further suppress side reactions with the non-aqueous electrolyte.

[0032] The lithium transition metal composite oxide may further contain Sb. The Sb content in the lithium transition metal composite oxide is, for example, 0 mol % < Sb content ≦ 1 mol % relative to the total number of moles of elements excluding Li and O. The lower limit of the Sb content is, for example, 0.01 mol %. It is presumed that the lithium transition metal composite oxide containing a predetermined amount of Sb can further stabilize the crystal structure.

[0033] The lithium transition metal composite oxide is, for example, a compound represented by the general formula Li ａ Ni ｘ Me ｙ P ｚ Ca ｓ Sr ｔ O ２－ｂ(wherein 0.8≦a≦1.2, 0.75≦x≦0.95, 0.01≦y<0.25, 0<z≦0.02, 0<s+t≦0.02, 0≦b≦0.05, x+y+z+s+t=1, and Me is at least one element selected from the group consisting of Mn, Co, Al, B, Sb, Si, Ti, Fe, Zr, Nb, Mo, Sn, W, and Bi). The proportion of metal elements contained in the lithium transition metal composite oxide can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The upper limit of the Me content is, for example, 24 mol% with respect to the total number of moles of elements excluding Li and O.

[0034] The lithium transition metal composite oxide contains secondary particles formed by aggregation of primary particles. The particle size of the primary particles is, for example, 0.02 μm or more and 2 μm or less. The particle size of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM). The average particle size of the secondary particles is, for example, 2 μm or more and 30 μm or less. Here, the average particle size refers to the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0035] P is present on the surface and inside of the secondary particles. Inside the secondary particles, P is present, for example, on the surface of the primary particles or in a region of 30 nm or less from the surface of the primary particles in the inward direction. This significantly suppresses the side reaction between the non-aqueous electrolyte and the lithium transition metal composite oxide. P may be present on the surface and inside of the secondary particles as a P-containing compound. Examples of the P-containing compound include P ２ O ５ , Li ３ P.O. ４ Examples include:

[0036] Ca and Sr are present on the surface and inside of the secondary particles. Inside the secondary particles, Ca and Sr are present, for example, on the surface of the primary particles or in a region 30 nm or less inward from the surface of the primary particles. The coexistence of at least one of Ca and Sr and P on the surface of the primary particles or in a region 30 nm or less inward from the surface of the primary particles more significantly suppresses side reactions between the non-aqueous electrolyte and the lithium transition metal composite oxide.

[0037] Ca may be present on the surface and inside of the secondary particles as a Ca-containing compound. Examples of the Ca-containing compound include CaO and Ca(OH). ２ , CaCO ３ Sr may be present on the surface and inside of the secondary particles as a compound containing Sr. Examples of the compound containing Sr include SrO, Sr(OH), etc. ２ , SrCO ３ Ca and Sr may be present on the surface and inside of the secondary particles as a compound containing Ca or Sr and P. Examples of such compounds include CaHPO ４ , SrHPO ４ , Ca(H ２ P.O. ４ ) ２ , Ca ３ (P.O. ４ ) ２ , Sr(H ２ P.O. ４ ) ２ , and Sr ３ (P.O. ４ ) ２ The presence of Ca, Sr, and P on the surface and inside of the secondary particles can be confirmed by, for example, energy dispersive X-ray spectroscopy (TEM-EDX) in addition to time-of-flight secondary ion mass spectrometry, which will be described later.

[0038] In the element concentration distribution of the cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry (TOF-SIMS), the normalized intensity I of P inside the secondary particles Ｐ＿ＩＮ Normalized intensity I of P on the secondary particle surface Ｐ＿ＯＵＴ Ratio I Ｐ＿ＯＵＴ / IＰ＿ＩＮ However, 1≦I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ≦150 (hereinafter, I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ (This is referred to as the normalized intensity ratio of P.) This improves the safety of the battery. It is presumed that this is because P is distributed in a balanced manner on the surface and inside of the secondary particles, and the coexistence of P distributed on the surface and inside of the secondary particles with at least one of Ca and Sr effectively suppresses side reactions with the non-aqueous electrolyte.

[0039] The normalized intensity ratio of P is obtained by measurement under the following conditions using a time-of-flight secondary ion mass spectrometer (TOF-SIMS5 manufactured by IONTOF). Primary ions: Bi ３ ＋ Ion voltage: 30 kV Ion current: 0.03 pA @ 100 us Observation range: 50 μm x 50 μm Mass range: 60 us (up to 310 amu) Detection: 4 frames / scan, 150 scans

[0040] The image showing the concentration distribution of Ni and P obtained by the above measurement is divided into 256 × 256 pixels, and the detected intensities of Ni and P are calculated for each pixel. Furthermore, the ratio of the detected intensity of P to the detected intensity of Ni is defined as the normalized intensity I of P. Ｐ It is calculated as follows.

[0041] The area from the surface of the secondary particle recognized from the image to the inside by 0.5 μm is defined as the surface of the secondary particle, and the pixels included in the surface of this secondary particle (hereinafter referred to as surface pixels) are determined. Ｐ The set of Ｐ＿ＯＵＴ The area inside the secondary particle surface defined above is defined as the interior of the secondary particle, and the pixels included in the interior of this secondary particle (hereinafter referred to as "interior pixels") are defined. Ｐ The set of Ｐ＿ＩＮ From the normalized intensities of P on the surface and inside of the secondary particles thus obtained, the normalized intensity ratio of P (I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮThe sample for cross-section observation may be a sample in which a lithium transition metal composite oxide is embedded in a resin or the like, or may be a positive electrode mixture layer containing a lithium transition metal composite oxide.

[0042] In the element concentration distribution of the cross section of the lithium transition metal composite oxide using TOF-SIMS, the normalized intensity I of Ca and Sr inside the secondary particles Ｃａ＋Ｓｒ＿ＩＮ Normalized intensity I of Ca and Sr on the secondary particle surface Ｃａ＋Ｓｒ＿ＯＵＴ Ratio I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ However, 0.7≦I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ It is preferable that the ratio satisfies the following: Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ Similarly, I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ is called the normalized intensity ratio of Ca and Sr). This makes the synergistic effect with P more pronounced. The normalized intensity ratio of Ca and Sr (I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ ) is similar to P. Ｃａ＿ＯＵＴ , I Ｃａ＿ＩＮ , I Ｓｒ＿ＯＵＴ , and I Ｓｒ＿ＩＮ Calculate I Ｃａ＿ＯＵＴ and I Ｓｒ＿ＯＵＴ The sum of I Ｃａ＋Ｓｒ＿ＯＵＴ And I Ｃａ＿ＩＮ and I Ｓｒ＿ＩＮ The sum of I Ｃａ＋Ｓｒ＿ＩＮ is obtained as:

[0043] The normalized intensity ratio of P (I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ) and the normalized intensity ratio of Ca and Sr (I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ ) is, for example, the normalized intensity ratio of P (I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ) + normalized intensity ratio of Ca and Sr (I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ ) ≧2.

[0044] In the lithium transition metal composite oxide, the ratio m / n of the half-width m of the diffraction peak of the (003) plane to the half-width n of the diffraction peak of the (110) plane in the X-ray diffraction pattern satisfies 0.75≦m / n≦0.85. If m / n is less than 0.75, the distortion of the layered structure is too large, making the layered structure brittle. The upper limit of m / n is, for example, 0.85. If m / n is more than 0.85, the battery capacity may decrease.

[0045] The X-ray diffraction pattern was obtained by powder X-ray diffraction using a powder X-ray diffractometer (Rigaku Corporation, trade name "SmartLab", Cu-Kα radiation source) under the following conditions: Measurement range: 15-120° Scan speed: 4° / min Analysis range: 30-120° Background: B-spline Profile function: divided pseudo-Voigt function Constraint conditions: Li(3a) + Ni(3a) = 1 Ni(3a) + Ni(3b) = α (α is the Ni content of each element) ICSD No.: 98-009-4814

[0046] The crystallite size s of the lithium transition metal composite oxide calculated by the Scherrer formula from the half-width of the diffraction peak of the (104) plane in the X-ray diffraction pattern obtained by the above X-ray diffraction is preferably 300 Å≦s≦700 Å from the viewpoint of increasing the capacity of the battery and improving the output characteristics of the battery. The Scherrer formula is expressed by the following formula. In the formula, s is the crystallite size, λ is the wavelength of the X-ray, B is the half-width of the diffraction peak of the (104) plane, θ is the diffraction angle (rad), and K is the Scherrer constant. In this embodiment, K is set to 0.9. s=Kλ / B cos θ

[0047] In the X-ray diffraction pattern obtained by X-ray diffraction measurement of the lithium transition metal composite oxide, CaCO ３ The peak derived from may be in the range of 29.4±0.3°. In this case, the effect of suppressing the side reaction between the non-aqueous electrolyte and the lithium transition metal composite oxide can be further obtained.

[0048] The lithium transition metal composite oxide may have a layered structure. Examples of the layered structure of the lithium transition metal composite oxide include a layered structure belonging to the space group R-3m and a layered structure belonging to the space group C2 / m. From the viewpoints of increasing capacity and crystalline structure stability, the lithium transition metal composite oxide preferably has a layered structure belonging to the space group R-3m. The layered structure of the lithium transition metal composite oxide may include a transition metal layer and a Li layer.

[0049] In the layered structure of the lithium transition metal composite oxide, the proportion of metal elements other than Li present in the Li layer is 8 mol% or less relative to the total number of moles of elements excluding Li and O in the lithium transition metal composite oxide. If the proportion of metal elements other than Li in the Li layer exceeds 8 mol%, the diffusibility of Li ions in the Li layer may decrease, resulting in a decrease in battery capacity. The metal elements other than Li present in the Li layer are mainly Ni, but may also contain other metal elements. The proportion of metal elements other than Li in the Li layer is, for example, 0.1 mol% or more.

[0050] The proportion of metal elements other than Li present in the Li layer of the layered structure can be obtained from the results of Rietveld analysis of the X-ray diffraction pattern obtained by the powder X-ray diffraction measurement of the lithium transition metal composite oxide. Rietveld analysis of the X-ray diffraction pattern can be performed using, for example, Rietveld analysis software SmartLab Studio II (Rigaku Corporation).

[0051] The positive electrode mixture layer may contain other positive electrode active materials in addition to the positive electrode active material of the present embodiment. Examples of other positive electrode active materials include lithium transition metal composite oxides that do not contain Ca, Sr, or P.

[0052] Next, an example of a method for producing a cathode active material according to the present embodiment will be described. The method for producing a cathode active material includes, for example, a step of mixing a metal oxide containing at least Ni, a Li raw material, a P raw material, and at least one of a Ca raw material and a Sr raw material to obtain a mixture, and a step of firing the mixture to obtain a cathode active material.

[0053] A metal oxide containing at least Ni can be produced by separately dropping a solution of a metal salt containing Ni, Co, Al, Mn, etc. and an alkaline solution such as sodium hydroxide into a reaction vessel in which a pH-adjusted solution is being stirred, adjusting the pH to the alkaline side (e.g., 8.5 to 12.5) to precipitate (co-precipitate) a composite hydroxide, and then heat-treating the metal hydroxide. The calcination temperature is not particularly limited, but is, for example, in the range of 250°C to 600°C.

[0054] Next, a mixture is obtained by mixing a metal oxide containing at least Ni, a Li raw material, a P raw material, and at least one of a Ca raw material and a Sr raw material. ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２ Examples of the phosphorus raw material include P. ２ O ５ , CaHPO ４ , Ca(H ２ P.O. ４ ) ２ , Ca ３ (P.O. ４ ) ２ Examples of Ca raw materials include Ca(OH) ２ , CaHPO ４ , Ca(H ２ P.O. ４ ) ２ , Ca ３ (P.O. ４ ) ２ , CaO, CaCO ３ , CaSO ４ , Ca(NO ３ ) ２、 CaCl ２ , CaAlO ４ The Sr raw material is Sr(OH) ２ , SrHPO ４ , Sr(H ２ P.O. ４ )２ , Sr ３ (P.O. ４ ) ２ , SrO, SrCO ３ , SrSO ４ , Sr(NO ３ ) ２、 SrCl ２ , SrAlO ４ In addition, CaHPO ４ , Ca(H ２ P.O. ４ ) ２ , and Ca ３ (P.O. ４ ) ２ is a raw material to which Ca and P can be added, and SrHPO ４ , Sr(H ２ P.O. ４ ) ２ , and Sr ３ (P.O. ４ ) ２ is a raw material to which Sr and P can be added. Furthermore, a Me raw material may be mixed during mixing. The Me raw material is ZrO ２ , Nb ２ O ５ , Nb ２ O ５ ・nH ２ O, TiO ２ , Ti(OH) ４ , SiO, SiO ２ , Li ２ MoO ４ , MoO ３ , H ２ MoO ４ , W.O. ３ , Li ２ WO ４ , Al(OH) ２ , Al ２ O ３ , Al ２ (SO ４ ) ３ , Al(NO ３ ) ３ , Fe(OH) ２ , Fe ２ O ３ , SnO ２ , Bi(OH) ３ , Bi ２ O ３ , H３ BO ３ , B ２ O ３ , Sb ２ O ３ etc.

[0055] The above mixture is calcined to obtain a lithium transition metal composite oxide as a positive electrode active material. The mixture is calcined, for example, in an oxygen stream with an oxygen concentration of 60% or higher, with the flow rate of the oxygen stream ranging from 0.1 L / min to 4 L / min per 10 cm3 of the calcination furnace, or 1 L / min or higher per 1 kg of the mixture. The calcination conditions include a first set temperature of 450°C or lower, a holding time at the first set temperature ranging from 0 to 8 hours, and a temperature rise rate at 450°C or lower ranging from more than 1.5°C / min to 6.0°C / min. The second set temperature is set at 450°C or higher and 680°C or lower, a holding time at the second set temperature ranging from 0 to 8 hours, and a temperature rise rate at 450°C or higher and 680°C or lower ranging from more than 1.0°C / min to 4.5°C / min. The maximum temperature reached is in the range of 690°C or higher and 900°C or lower. The rate of temperature rise from above 680°C to the maximum temperature may be, for example, 0.1°C / min to 3.5°C / min. Furthermore, the holding time at the maximum temperature may be 1 hour or more and 10 hours or less. Furthermore, this firing step may be a multi-stage firing, and multiple stages may be set for each temperature range as long as they are within the above-specified range. For example, by changing the first set temperature, the second set temperature, the respective heating rates until the maximum temperature is reached, and the respective holding times, the crystallinity of the lithium transition metal composite oxide can be changed, and the value of the half-width ratio m / n can be adjusted.

[0056] The prepared lithium transition metal composite oxide may then be subjected to a water washing and drying step and a heat treatment step. The water washing and drying step can be carried out by a known method and under known conditions. The Me raw material may be added to the cake-like composition after water washing or during the heat treatment step. The heat treatment step is carried out, for example, in a vacuum, in an oxygen stream, or in the atmosphere at a temperature of 150°C to 600°C. The Me raw material added after water washing or during the heat treatment step may be, for example, tungsten oxide (WO ３ ), lithium tungstate (Li ２ WO ４ , Li ４ WO５ , Li ６ W ２ O ９ ), boric acid (H ３ BO ３ ), lithium borate (Li ２ B ４ O ７ , Li ３ BO ３ , LiB ３ O ５ , LiBO ２ ), aluminum oxide (Al ２ O ３ ), aluminum sulfate (Al ２ (SO ４ ) ３ ), calcium sulfate (CaSO ４ ), sodium sulfate (Na ２ SO ４ ), magnesium sulfate (MgSO ４ ), calcium phosphate (Ca ３ (P.O. ４ ) ２ ), calcium hydrogen phosphate (CaHPO ４ ) etc.

[0057] [Negative Electrode] The negative electrode 12 may have, for example, a negative electrode core and a negative electrode mixture layer formed on the surface of the negative electrode core, or a metal Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode core, and lithium metal may be deposited on the surface of the negative electrode core upon charging. When the negative electrode 12 has a negative electrode mixture layer, the negative electrode mixture layer is preferably formed on both sides of the negative electrode core. The negative electrode core may be a foil of a metal stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with such a metal disposed on the surface. The thickness of the negative electrode core 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 core. The negative electrode 12 can be produced, 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 core, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0058] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, carbon materials such as graphite are used. Graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, metals that alloy with Li, such as Si and Sn, metal compounds containing Si, Sn, and lithium-titanium composite oxides may also be used as the negative electrode active material. Furthermore, those provided with a carbon coating may also be used. For example, SiO ｘ (0.5≦x≦1.6) or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2) may be used in combination with graphite.

[0059] Examples of binders contained in the negative electrode mixture layer include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0060] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0061] 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 and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0062] [Non-aqueous electrolyte] The non-aqueous electrolyte has, for example, lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0063] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0064] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates 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 chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0065] Examples of the 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 methyl phenyl ether. and chain ethers such as ethyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl 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.

[0066] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include 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 , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less, per 1 L of the non-aqueous solvent.

[0067] The non-aqueous electrolyte may contain an additive such as an unsaturated carbonate ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, a sulfate compound, a borate ester compound, a phosphate ester compound, or a phosphite ester compound.

[0068] Examples of unsaturated cyclic carbonates 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. One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. Some of the hydrogen atoms in the unsaturated cyclic carbonate may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by intermolecular condensation of multiple carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0069] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0070] 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 bisisocyanatomethylcyclohexane (BIMCH). Examples of sultone compounds include propane sultone and propene sultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethyl phosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethyl phosphite and tris(trimethylsilyl)phosphite.

[0071] 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, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, 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 the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0072] Hereinafter, the present disclosure will be further described with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0073] Example 1-1 [Preparation of Positive Electrode Active Material] [Ni ０．９０ Co ０．０６ Mn ０．０４ ](OH) ２The composite hydroxide represented by the formula (1) was calcined at 400°C for 8 hours to obtain a metal oxide containing Ni, Co, and Mn. Next, the metal oxide and CaHPO were mixed together so that the molar ratios of Ca and P to the total amount of metal elements were each 0.25 mol%. ４ and further, lithium hydroxide monohydrate (LiOH·H ) was added so that the molar ratio of Li to the total amount of Ni, Co, Mn, Ca, and P was 103 mol %. ２ O) were mixed to obtain a mixture. This mixture was heated from room temperature to 400°C at a temperature increase rate of 4°C / min under an oxygen stream with an oxygen concentration of 95% (flow rate of 3 L / min per 1 kg of the mixture), and then heated from 400°C to 650°C at a temperature increase rate of 2°C / min. Thereafter, the temperature was increased from 650°C to 740°C at a temperature increase rate of 1°C / min, and then maintained for 6 hours to obtain a lithium transition metal composite oxide. This lithium transition metal composite oxide was washed with water and dried to obtain the positive electrode active material of Example 1-1.

[0074] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (iCAP6300, manufactured by Thermo Fisher Scientific). As a result, the elements shown in Table 1 below were confirmed as elements other than Li and O. The element concentration distribution in the cross section of the positive electrode active material was measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS). As a result, the normalized intensity ratio of P (I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ) is 70.0, and the normalized intensity ratio of Ca and Sr (I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ ) was 2.5. X-ray diffraction measurement results showed that the half-width ratio m / n of this positive electrode active material was 0.79. The proportion of metal elements other than Li present in the Li layer was 1.8 mol % relative to the total number of moles of elements excluding Li and O in the lithium transition metal composite oxide serving as the positive electrode active material, and the crystallite size s of the lithium transition metal composite oxide was 543 Å.

[0075] [Preparation of Positive Electrode] 95 parts by mass of the above positive electrode active material, 3 parts by mass of acetylene black (AB), and 2 parts by mass of polyvinylidene fluoride (PVDF) were mixed, 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 core made of aluminum foil, and after drying the coating, the coating was rolled with a rolling roller and cut to a predetermined electrode size to prepare a positive electrode. In addition, an exposed portion in which the surface of the positive electrode core was exposed was provided in a part of the positive electrode.

[0076] [Preparation of Negative Electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, carboxymethyl cellulose sodium (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution at a solids 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 core made of copper foil, and after drying the coating, the coating was rolled with a rolling roller and cut to a predetermined electrode size to prepare a negative electrode. Note that an exposed portion was provided in part of the negative electrode, exposing the surface of the negative electrode core.

[0077] [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 hexafluorophosphate (LiPF ６ ) was dissolved in the solution to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0078] [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 spirally wound with a polyolefin separator interposed therebetween, and then pressed radially to prepare a flat wound electrode assembly. This electrode assembly was housed in an exterior body made of an aluminum laminate sheet, and the nonaqueous electrolyte was poured into it. The opening of the exterior body was then sealed to obtain a test cell.

[0079] [Evaluation of Heat Release Rate] At an ambient temperature of 25 ° C, the test cell was charged at a constant current of 0.3 C to 4.2 V, and then charged at a constant voltage of 0.02 C at 4.2 V to enter a charged state. The test cell in the charged state was then set in a runaway reaction measurement device (Accelerated Rate Calorimeter: ARC, manufactured by Thermal Hazard Technology, Inc.), and the heat release rate (° C. / min) of the test cell was measured by observing the cell temperature using a thermocouple attached to the test cell. If a temperature rise of 0.02 ° C. / min or more was not detected when the test cell was held for 20 minutes in an environment with a measurement start temperature of 80 ° C., the ambient temperature was raised by 5 ° C. and held for 20 minutes again to measure the heat release rate. As described above, the ambient temperature was raised by 5 ° C. at a time, and measurements were performed until a temperature rise of 0.02 ° C. / min or more was detected. When a temperature rise of 0.02°C / min or more was detected, it was determined that self-heating had begun, and the heat generation rates 8 hours after the start of self-heating were compared.

[0080] Example 1-2 In the preparation of the positive electrode active material, [Ni ０．９２ Co ０．０５ Al ０．０３ ](OH) ２ In the firing step, the molar ratio of Ca to the total amount of metal elements was 0.6 mol % and the molar ratio of P was 0.4 mol %. ３ (P.O. ４ ) ２ The temperature was increased from room temperature to 300°C at a rate of 4°C / min, from 300°C to 500°C at a rate of 3°C / min, and from 500°C to 650°C at a rate of 2°C / min. Thereafter, the temperature was increased from 650°C to 700°C at a rate of 1°C / min and then held for 5 hours to obtain a lithium transition metal composite oxide. A test cell was produced and evaluated in the same manner as in Example 1-1, except that

[0081] Example 1-3 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 ０．９０ Mn ０．０８ Al ０．０２ ](OH) ２(2) In the calcination step, a metal oxide was obtained using a composite hydroxide represented by the formula: CaHPO 4 , so that the molar ratios of Ca and P were 0.5 mol %, the molar ratio of Ti was 0.5 mol %, and the molar ratio of Nb was 0.5 mol %, relative to the total amount of metal elements. ４ , TiO ２ and Nb ２ O ５ , was added. (3) The conditions of the calcination step were changed. The oxygen flow rate was changed to 5 L / min per 1 kg of the mixture. The mixture was heated from room temperature to 300°C at a heating rate of 4°C / min, then heated from 300°C to 550°C at a heating rate of 3°C / min, and held at 550°C for 4 hours. Thereafter, the mixture was heated from 550°C to 680°C at a heating rate of 3°C / min, and then heated from 680°C to 750°C at a heating rate of 0.8°C / min, and held for 6 hours to obtain a lithium transition metal composite oxide.

[0082] Example 1-4 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 ０．９０ Co ０．０２ Mn ０．０６ Al ０．０２ ](OH) ２ (2) In the calcination step, a metal oxide was obtained using a composite hydroxide represented by the formula: CaHPO 4 , so that the molar ratios of Ca and P were 1 mol %, the molar ratio of Sr was 0.5 mol %, the molar ratio of Nb was 0.4 mol %, and the molar ratio of Sb was 0.1 mol %, relative to the total amount of metal elements. ４ , Sr(OH) ２ , Nb ２ O ５ , and Sb ２ O ３ (3) The conditions for the calcination step were changed. The temperature was raised from 650°C to 750°C at a rate of 1°C / min, and then maintained for 6 hours to obtain a lithium transition metal composite oxide. (4) After washing with water and drying, the obtained lithium transition metal composite oxide was treated with H to adjust the molar ratio of B to the total amount of Ni, Co, Mn, and Al to 1 mol %. ３ BO ３ The mixture was mixed and heat-treated at 400° C. in an oxygen stream.

[0083] Example 1-5 In the preparation of the positive electrode active material, [Ni ０．９０ Co ０．０２ Mn ０．０８ ](OH) ２ In the calcination step, the molar ratios of Ca and P were 0.5 mol %, the molar ratio of Sr was 0.1 mol %, the molar ratio of Zr was 0.25 mol %, the molar ratio of Si was 0.25 mol %, and the molar ratio of Sb was 0.4 mol % relative to the total amount of metal elements. ４ , Sr(OH) ２ , ZrO ２ , SiO ２ , and Sb ２ O ３ A test cell was prepared in the same manner as in Example 1-1 except that the above was added, and evaluation was carried out.

[0084] Example 1-6 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 ０．９０ Mn ０．０８ Al ０．０２ ](OH) ２ (2) In the calcination step, a metal oxide was obtained using a composite hydroxide represented by the formula: CaHPO 4 , so that the molar ratio of Ca, P, Sr, and Nb relative to the total amount of metal elements was 0.6 mol %, 0.3 mol %, 0.1 mol %, and 0.5 mol %, respectively. ４ , Ca(OH) ２ , Sr(OH) ２ , and Nb ２ O was added. (3) The conditions of the calcination step were changed. The oxygen flow rate was changed to 5 L / min per 1 kg of mixture. The mixture was heated from room temperature to 300°C at a temperature increase rate of 4°C / min, then heated from 300°C to 550°C at a temperature increase rate of 3°C / min, and held at 550°C for 4 hours. Thereafter, the mixture was heated from 550°C to 680°C at a temperature increase rate of 3°C / min, and then heated from 680°C to 750°C at a temperature increase rate of 0.8°C / min, and held for 6 hours to obtain a lithium transition metal composite oxide. (4) The mixture was washed with water and dried, and the resulting lithium transition metal composite oxide was treated with H to adjust the molar ratio of B to the total amount of Ni, Mn, and Al to 0.5 mol%. ３ BO３ was added, and the mixture was heat-treated at 400° C. in an air stream.

[0085] <Comparative Example 1-1> In the preparation of a positive electrode active material, no P raw material was added, and in the firing step, Ca(OH) was added so that the molar ratio of Ca and the molar ratio of W were 0.5 mol % relative to the total amount of metal elements. ２ , and W.O. ３ A test cell was prepared in the same manner as in Example 1-1 except that the above was added, and evaluation was carried out.

[0086] <Comparative Example 1-2> In the preparation of the positive electrode active material, no Ca source was added, and in the firing step, Nb was added so that the molar ratio of Nb was 0.1 mol % and the molar ratio of P was 2 mol % relative to the total amount of metal elements. ２ O and P ２ O ５ A test cell was prepared in the same manner as in Example 1-1 except that the above was added, and evaluation was carried out.

[0087] Comparative Example 1-3 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 ０．０５ Al ０．０３ ](OH) ２ A metal oxide was obtained using a composite hydroxide represented by the formula (1). (2) Neither a Ca source nor a P source was added in the calcination step. (3) The conditions for the calcination step were changed. The mixture was heated from room temperature to 300°C at a heating rate of 4°C / min, then from 300°C to 500°C at a heating rate of 3°C / min, and then from 500°C to 650°C at a heating rate of 2°C / min. Thereafter, the mixture was heated from 650°C to 700°C at a heating rate of 1°C / min, and then maintained for 5 hours to obtain a lithium transition metal composite oxide.

[0088] Comparative Example 1-4 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, CaHPO was added so that the molar ratios of Ca and P were 1 mol % and the molar ratio of Sr was 1 mol % relative to the total amount of metal elements. ４ , and Sr(OH) ２(2) The conditions for the calcination step were changed. The mixture was heated from room temperature to 400°C at a heating rate of 4°C / min, and then heated from 400°C to 700°C at a heating rate of 5°C / min. Thereafter, the mixture was heated from 700°C to 740°C at a heating rate of 4°C / min, and then maintained at this temperature for 2 hours to obtain a lithium transition metal composite oxide.

[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 ０．８０ Co ０．１０ Mn ０．１０ ](OH) ２ (2) In the calcination step, the molar ratio of Ca to the total amount of metal elements was 0.5 mol %, the molar ratio of Sr was 0.25 mol %, and the molar ratio of P was 1.25 mol %. ２ P.O. ４ ) ２ , and SrHPO ４ (3) The conditions for the calcination step were changed. The mixture was heated from room temperature to 400°C at a heating rate of 4°C / min, and then heated from 400°C to 650°C at a heating rate of 2°C / min. Thereafter, the mixture was heated from 650°C to 800°C at a heating rate of 1°C / min, and then maintained at this temperature for 10 hours to obtain a lithium transition metal composite oxide.

[0090] Example 2-2 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 ０．８３ Co ０．１２ Mn ０．０５ ](OH) ２ (2) In the calcination step, a composite hydroxide represented by the formula: SrHPO was used so that the molar ratio of Sr and the molar ratio of P were 0.75 mol % and 0.75 mol %, respectively, relative to the total amount of metal elements. ４(3) The conditions for the calcination step were changed. The mixture was heated from room temperature to 300°C at a heating rate of 5°C / min, then heated from 300°C to 550°C at a heating rate of 2°C / min, and held at 550°C for 3 hours. Thereafter, the mixture was heated from 550°C to 800°C at a heating rate of 1°C / min, and held for 10 hours to obtain a lithium transition metal composite oxide.

[0091] Comparative Example 2-1 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, no P raw material was added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements was 1 mol %. ２ (2) The conditions for the calcination step were changed. The mixture was heated from room temperature to 400°C at a heating rate of 4°C / min, and then heated from 400°C to 650°C at a heating rate of 2°C / min. Thereafter, the mixture was heated from 650°C to 780°C at a heating rate of 1°C / min, and then maintained at this temperature for 10 hours to obtain a lithium transition metal composite oxide.

[0092] Comparative Example 2-2 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, no P raw material was added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements was 0.5 mol %. ２ (2) The conditions of the calcination step were changed. The mixture was heated from room temperature to 400°C at a heating rate of 4°C / min, and then heated from 400°C to 650°C at a heating rate of 2°C / min. Thereafter, the mixture was heated from 650°C to 780°C at a heating rate of 1°C / min, and then maintained for 10 hours to obtain a lithium transition metal composite oxide. (3) After washing with water and drying, Li was added to the obtained lithium transition metal composite oxide so that the molar ratio of P to the total amount of Ni, Co, and Mn was 0.5 mol%. ３ P.O. ４ was added and mixed.

[0093] The evaluation results of the test cells of the examples and comparative examples are shown in Tables 1 and 2. Tables 1 and 2 also show the normalized intensity ratios of P (I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ), the normalized intensity ratio of Ca and Sr (IＣａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ The values ​​also include the half-width ratio m / n, the proportion of metal elements other than Li present in the Li layer, and the crystallite size s. In Table 1, the heat generation rates of the test cells other than Comparative Example 1-1 are expressed relative to the heat generation rate of the test cell of Comparative Example 1-1, which is set to ±0. In Table 2, the heat generation rates of the test cells other than Comparative Example 2-1 are expressed relative to the heat generation rate of the test cell of Comparative Example 2-1, which is set to ±0.

[0094]

[0095]

[0096] In Tables 1 and 2, the test cells of the examples have a lower heat generation rate than the test cells of the comparative examples. Therefore, in a lithium transition metal composite oxide having an Ni content of 75% or more, P and at least one of Ca and Sr are contained in a predetermined content, and the ratio m / n of the half width m of the diffraction peak of the (003) plane to the half width n of the diffraction peak of the (110) plane in an X-ray diffraction pattern by X-ray diffraction satisfies 0.75≦m / n≦0.85, and further, in the element concentration distribution of the cross section of the lithium transition metal composite oxide obtained by time-of-flight secondary ion mass spectrometry, the normalized intensity I of P inside the secondary particles is Ｐ＿ＩＮ Normalized intensity I of P on the secondary particle surface Ｐ＿ＯＵＴ Ratio I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ However, 1≦I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ It can be seen that the safety of the battery is improved by satisfying the condition of ≦150.

[0097] The present 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, wherein the lithium transition metal composite oxide comprises Ni, P, and at least one of Ca and Sr, and comprises secondary particles formed by aggregation of primary particles, wherein the Ni content in the lithium transition metal composite oxide is 75 mol%≦Ni content≦95 mol% relative to the total number of moles of elements excluding Li and O, wherein the P content in the lithium transition metal composite oxide is 0 mol%<P content≦2 mol% relative to the total number of moles of elements excluding Li and O, wherein the sum of the Ca content and the Sr content in the lithium transition metal composite oxide is 0 mol%<Ca content+Sr content≦2 mol% relative to the total number of moles of elements excluding Li and O, and wherein the ratio m / n of the half width m of the diffraction peak of the (003) plane to the half width n of the diffraction peak of the (110) plane in an X-ray diffraction pattern satisfies 0.75≦m / n≦0.85, In the element concentration distribution of the cross section of the lithium transition metal composite oxide obtained by time-of-flight secondary ion mass spectrometry, the normalized intensity I of P inside the secondary particle Ｐ＿ＩＮ The normalized intensity I of P on the secondary particle surface relative to Ｐ＿ＯＵＴ Ratio I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ However, 1≦I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ≦150. Configuration 2: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein Ca and Sr are present on the surface of the primary particles or in a region 30 nm or less inward from the surface of the primary particles. Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein P is present on the surface of the primary particles or in a region 30 nm or less inward from the surface of the primary particles. Configuration 4: In an element concentration distribution of a cross section of the lithium transition metal composite oxide obtained by time-of-flight secondary ion mass spectrometry, the normalized intensity I of Ca and Sr inside the secondary particles is Ｃａ＋Ｓｒ＿ＩＮ Normalized intensity I of Ca and Sr on the secondary particle surface relative to Ｃａ＋Ｓｒ＿ＯＵＴ Ratio I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ However, 0.7≦I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 3, wherein the positive electrode active material satisfies the condition of ≦20. Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ and the above I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ But, I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ +I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ ≧2. Configuration 6: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the lithium transition metal composite oxide further contains B, and the B content in the lithium transition metal composite oxide is 0 mol %<B content≦3 mol %, based on the total number of moles of elements excluding Li and O. Configuration 7: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the lithium transition metal composite oxide further contains Sb, and the Sb content in the lithium transition metal composite oxide is 0 mol %<Sb content≦1 mol %, based on the total number of moles of elements excluding Li and O. Configuration 8: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the lithium transition metal composite oxide contains both Ca and Sr. Configuration 9: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 8, wherein the Ca content is greater than the Sr content. Aspect 10: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Aspects 1 to 9, wherein the lithium transition metal composite oxide has a layered structure, and a ratio of metal elements other than Li present in the Li layer of the layered structure is 8 mol % or less relative to the total number of moles of elements excluding Li and O in the lithium transition metal composite oxide. Aspect 11: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Aspects 1 to 10, wherein the crystallite size s of the lithium transition metal composite oxide calculated from the half width of the diffraction peak of the (104) plane in an X-ray diffraction pattern by X-ray diffraction measurement is 300 Å≦s≦700 Å. Aspect 12: A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Aspects 1 to 10, wherein the X-ray diffraction pattern by X-ray diffraction measurement does not contain CaCO ３12. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 11, wherein a peak derived from the peak is in the range of 29.4±0.3°. 13. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 12, a negative electrode, and a non-aqueous electrolyte.

[0098] REFERENCE SIGNS LIST 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Exterior body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 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, wherein the lithium transition metal composite oxide comprises Ni, P, and at least one of Ca and Sr, and comprises secondary particles formed by aggregation of primary particles, the Ni content in the lithium transition metal composite oxide is 75 mol%≦Ni content≦95 mol% based on the total number of moles of elements excluding Li and O, the P content in the lithium transition metal composite oxide is 0 mol%<P content≦2 mol% based on the total number of moles of elements excluding Li and O, the sum of the Ca content and Sr content in the lithium transition metal composite oxide is 0 mol%<Ca content+Sr content≦2 mol% based on the total number of moles of elements excluding Li and O, and the ratio m / n of the half width m of the diffraction peak of the (003) plane to the half width n of the diffraction peak of the (110) plane in an X-ray diffraction pattern by X-ray diffraction satisfies 0.75≦m / n≦0.85, In the element concentration distribution of the cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry, the normalized intensity I of P inside the secondary particle is Ｐ＿ＩＮ The normalized intensity I of P on the secondary particle surface Ｐ＿ＯＵＴ Ratio I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ However, 1≦I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ ≦150.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein Ca and Sr are present on the surface of the primary particles or in a region 30 nm or less inward from the surface of the primary particles.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein P is present on the surface of the primary particles or in a region 30 nm or less inward from the surface of the primary particles.

4. In the element concentration distribution of the cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry, the normalized intensity I of Ca and Sr inside the secondary particles Ｃａ＋Ｓｒ＿ＩＮ Normalized intensity I of Ca and Sr on the secondary particle surface Ｃａ＋Ｓｒ＿ＯＵＴ Ratio I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ However, 0.7≦I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material satisfies the following:

5. Section I above Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ And the above I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ But, I Ｐ＿ＯＵＴ / I Ｐ＿ＩＮ +I Ｃａ＋Ｓｒ＿ＯＵＴ / I Ｃａ＋Ｓｒ＿ＩＮ 5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein 6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide further contains B, and the B content in the lithium transition metal composite oxide is 0 mol %<B content≦3 mol % with respect to the total number of moles of elements excluding Li and O.

7. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide further contains Sb, and the Sb content in the lithium transition metal composite oxide is 0 mol %<Sb content≦1 mol % with respect to the total number of moles of elements excluding Li and O.

8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide contains both Ca and Sr.

9. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the Ca content is greater than the Sr content.

10. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a layered structure, and a ratio of metal elements other than Li present in the Li layer of the layered structure is 8 mol % or less relative to the total number of moles of elements other than Li and O in the lithium transition metal composite oxide.

11. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein the crystallite size s of the lithium transition metal composite oxide calculated from the half-width of the diffraction peak of the (104) plane in an X-ray diffraction pattern by X-ray diffraction using the Scherrer formula is 300 Å≦s≦700 Å.

12. X-ray diffraction measurement: CaCO ３ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the peak derived from is in the range of 29.4±0.3°.

13. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 12, a negative electrode, and a non-aqueous electrolyte.

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