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

Abstract

Provided is a positive electrode active material capable of improving the durability of a non-aqueous electrolyte secondary battery. The positive electrode active material contained in the non-aqueous electrolyte secondary battery contains a lithium transition metal composite oxide, the lithium transition metal composite oxide contains Ni, Ca, and Sr, and contains secondary particles formed by aggregating primary particles, and in the element concentration distribution in the cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry, the element concentration distribution in the cross section of the lithium transition metal composite oxide is greater than the element concentration distribution in the cross section of the lithium transition metal composite oxide. The ratio of the normalized intensity of Sr, ISrOUT, on the surface of the secondary particles to the normalized intensity of Sr, ISrIN, in the interior of the secondary particles, ISrOUT / ISrIN, is greater than the ratio of the normalized intensity of Ca, ICaOUT, on the surface of the secondary particles to the normalized intensity of Ca, ICaIN, ICaOUT / ICaIN, in the interior of the secondary particles.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a positive electrode active material for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery. BACKGROUND

[0002] Conventionally, lithium nickelate (LiNiO2) is known to have a high energy density, and by substituting a part of Ni with Co, Al, Mn, or the like, battery characteristics such as durability can be improved.

[0003] Patent Document 1 discloses a technology for improving charge-discharge cycle characteristics and safety of a secondary battery using a positive electrode active material in which Sr is solid-solved in a prescribed ratio in a lithium transition metal composite oxide of an NCM system containing Ni, Co, and Mn.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent No. 6226430 SUMMARY

[0007] However, lithium transition metal composite oxides in which the content ratio of Ni is 70% or more are likely to undergo side reactions with nonaqueous electrolytes, and thus the battery capacity can easily decrease due to repeated charge-discharge, and durability can become a problem. The technology described in Patent Document 1 does not study improvement of battery characteristics using lithium transition metal composite oxides in which the content ratio of Ni is high, and there is room for improvement.

[0008] An object of the present disclosure is to provide a positive electrode active material capable of improving the durability of a nonaqueous electrolyte secondary battery.

[0009] The positive electrode active material for a nonaqueous electrolyte secondary battery of one embodiment of the present disclosure is characterized by including a lithium transition metal composite oxide containing Ni, Ca, and Sr, and including secondary particles formed by aggregation of primary particles, in an element concentration distribution in a cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry, the ratio I Sr_OUT of the normalized intensity I Sr_IN of Sr on the surface of the secondary particle to the normalized intensity I Sr_OUT of Sr inside the secondary particle Sr_IN is greater than the ratio I Ca_OUT of the normalized intensity I Ca_IN of Ca on the surface of the secondary particle to the normalized intensity I Ca_OUT of Ca inside the secondary particle Ca_IN .

[0010] As one aspect of this disclosure, the non-aqueous electrolyte secondary battery is characterized by comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, which include the aforementioned positive electrode active material for a non-aqueous electrolyte secondary battery.

[0011] According to the positive electrode active material for a non-aqueous electrolyte secondary battery, which is one aspect of this disclosure, the durability of the non-aqueous electrolyte secondary battery can be improved. Attached Figure Description

[0012] Figure 1 This is a longitudinal cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method. Detailed Implementation

[0013] Lithium transition metal composite oxides with 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 more than 70% are prone to side reactions with non-aqueous electrolytes, which may cause durability problems.

[0014] Patent Document 1 discloses a technique for improving the charge-discharge cycle characteristics and safety of secondary batteries by using a positive electrode active material in which Sr is dissolved in a specified proportion in an NCM-based lithium transition metal composite oxide containing Ni, Co, and Mn. However, the inventors conducted research and determined that even when Sr is dissolved in a lithium transition metal composite oxide with a Ni content of 70% or more, the durability of the secondary battery is sometimes not sufficiently improved.

[0015] The inventors conducted further in-depth research and found that by including Ca and Sr within the secondary particles constituting the lithium transition metal composite oxide, Sr is more dispersed on the surface of the secondary particles, and Ca is more uniformly dispersed within and on the surface of the secondary particles compared to Sr, thereby improving durability. This is attributed to improved retention of the non-aqueous electrolyte and suppression of side reactions.

[0016] The following is a detailed description of an example of an embodiment of the non-aqueous electrolyte secondary battery disclosed herein. Hereinafter, a cylindrical battery in which a wound electrode body is housed within a cylindrical outer casing is illustrated. However, the electrode body is not limited to a wound type; it can also be a laminated type formed by alternately stacking multiple positive and multiple negative electrodes separated by separators. Furthermore, the outer casing is not limited to a cylindrical shape; for example, it can be square, coin-shaped, or a battery casing made of laminated sheets including metal and resin layers. Additionally, the design of the non-aqueous electrolyte secondary battery disclosed herein is not limited to the illustrated non-aqueous electrolyte secondary battery design; known non-aqueous electrolyte secondary battery designs can also be applied.

[0017] Figure 1This is an axial cross-sectional view of a cylindrical secondary battery 10 as an example of an implementation method. (See attached image.) Figure 1 As shown, the secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer casing 16 for housing the electrode body 14 and the non-aqueous 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 into a spiral shape with the separator 13 sandwiched between them. The outer casing 16 is a bottomed cylindrical metal container with an opening on one axial side, and the opening of the outer casing 16 is sealed by a sealing body 17. Hereinafter, for ease of explanation, the sealing body 17 side of the battery is referred to as the upper side, and the bottom side of the outer casing 16 is referred to as the lower side.

[0018] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all rectangular strips, which are alternately stacked radially in the electrode body 14 by being wound into a spiral shape in the length direction. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. To prevent lithium deposition, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the length and width directions. The two separators 13 are formed to be at least one size larger than the positive electrode 11, for example, by sandwiching 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 length direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the end faces of the positive electrode 11 and the negative electrode 12 in the width direction form the axial end faces of the electrode body 14.

[0019] Insulating plates 18 and 19 are respectively disposed above and below the electrode body 14. Figure 1 In the example shown, the positive lead 20 extends to the sealing body 17 through the through hole in the insulating plate 18, and the negative lead 21 extends to the bottom side of the outer casing 16 through the outer side of the insulating plate 19. The positive 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 top plate, i.e., the cover 27, of the sealing body 17, which is electrically connected to the internal terminal plate 23, becomes the positive terminal. The negative 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 terminal.

[0020] A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure the airtightness of the battery interior. A groove 22 is formed in the outer casing 16, a portion of which protrudes inward and supports the sealing body 17. The groove 22 is preferably formed in a ring 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 groove 22 and the open end of the outer casing 16 that fits relative to the sealing body 17.

[0021] 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 cover 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected through their respective central portions, and the insulating member 25 is located between the peripheral portions. When the internal pressure of the battery rises due to abnormal heating, the lower valve body 24 deforms and breaks by pushing the upper valve body 26 upwards towards the cover 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cover 27.

[0022] The following is a detailed description of the positive electrode 11, negative electrode 12, separator 13 and non-aqueous electrolyte constituting the secondary battery 10, especially the positive electrode 11.

[0023] The positive electrode 11, for example, has a positive electrode core and a positive electrode flux layer formed on the surface of the positive electrode core. The positive electrode flux layer is preferably formed on both sides of the positive electrode core. For the positive electrode core, a metal foil stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a thin film formed by depositing this metal on the surface, can be used. The thickness of the positive electrode core is, for example, 10 μm or more and 30 μm or less.

[0024] The positive electrode binder layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode binder layer is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode core. The positive electrode 11 can be manufactured, for example, by coating the surface of the positive electrode core with a positive electrode binder slurry containing a positive electrode active material, a conductive agent, etc., allowing the coating to dry, and then calendering it to form positive electrode binder layers on both sides of the positive electrode core.

[0025] Examples of conductive agents included in the positive electrode mixture layer include acetylene black (AB), carbon black (CB) such as Ketjen black, carbon nanotubes (CNTs), graphene, graphite, and other carbon-based particles. These can be used individually or in combination of two or more. The content of the conductive agent in the positive electrode mixture layer relative to the total mass of the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less.

[0026] Examples of binders included in the positive electrode binder layer include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These can be used individually or in combination of two or more. The binder content in the positive electrode binder 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 binder layer.

[0027] The positive electrode active material contained in the positive electrode binder layer includes lithium transition metal complex oxide. This lithium transition metal complex oxide contains Ni, Ca, and Sr.

[0028] The Ni content in the lithium transition metal composite oxide is 70 mol% or more relative to the total molar percentage of metal elements other than Li. This improves battery capacity. The Ni content is preferably 85 mol% or more, more preferably 90 mol% or more. Furthermore, from the viewpoint of structural stabilization, the Ni content is preferably 98 mol% or less.

[0029] The content of Ca in the lithium transition metal composite oxide is preferably 0.01 mol% or more and 1 mol% or less relative to the total number of moles of metal elements other than Li, more preferably 0.1 mol% or more and 0.5 mol% or less, and even more preferably 0.2 mol% or more and 0.4 mol% or less.

[0030] The content of Sr in the lithium transition metal composite oxide is preferably 0.01 mol% or more and 1 mol% or less relative to the total moles of metal elements other than Li, more preferably 0.02 mol% or more and 0.5 mol% or less, and even more preferably 0.05 mol% or more and 0.2 mol% or less.

[0031] The lithium transition metal complex oxide may also contain one or more elements selected from the group consisting of Co, Al, and Mn. The content of Co, Al, and Mn in the lithium transition metal complex oxide, relative to the total moles of metal elements other than Li, is, for example, 0 mol% or more and 30 mol% or less, respectively. Furthermore, the combined content of Co, Al, and Mn is, for example, 0 mol% or more and 30 mol% or less.

[0032] The lithium transition metal composite oxide may further contain one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo. The content of Nb, Ti, Zr, W, Si, and Mo in the lithium transition metal composite oxide, relative to the total moles of metal elements other than Li, is, for example, 0 mol% or more and 1 mol% or less. Furthermore, the combined content of Nb, Ti, Zr, W, Si, and Mo is, for example, 0 mol% or more and 5 mol% or less.

[0033] Lithium transition metal composite oxides, for example, are of the general formula Li a Ni x M1 y M2 z Ca s Sr t O 2-b(Where, 0.8≤a≤1.2, 0.70≤x≤0.98, 0≤y≤0.30, 0≤z≤0.05, 0.0001≤s≤0.01, 0.0001≤t≤0.01, 0≤b≤0.05, x+y+z+s+t=1, M1 is one or more elements selected from the group consisting of Co, Al, and Mn, and M2 is one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo) shows the composite oxide. The proportion of metal elements contained in the lithium transition metal composite oxide can be determined, for example, by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0034] Lithium transition metal composite oxides contain secondary particles formed by the 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 determined as the diameter of the circumcircle in a particle image observed by 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 median particle size (D50) on a volumetric basis. D50 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution reaches 50% from the smallest end, also known as the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction-type particle size distribution measuring device (e.g., Microtrac BEL Co., Ltd., MT3000II) with water as the dispersion medium.

[0035] Ca and Sr exist on the surface and inside of secondary particles. Ca and Sr inside secondary particles, for example, exist on the surface of primary particles but are not dissolved within the primary particles. This significantly reduces the side reactions between non-aqueous electrolytes and lithium transition metal oxides. Ca can also exist as a Ca-containing compound on the surface and inside secondary particles. Examples of Ca-containing compounds include CaO, Ca(OH)₂, and CaCO₃. Sr can also exist as a Sr-containing compound on the surface and inside secondary particles. Examples of Sr-containing compounds include SrO, Sr(OH)₂, and SrCO₃. The presence of Ca and Sr on the surface and inside secondary particles can be confirmed, for example, by energy-dispersive X-ray spectroscopy (TEM-EDX), in addition to the time-of-flight secondary ion mass spectrometry described later.

[0036] In the elemental concentration distribution of lithium transition metal composite oxide cross sections using time-of-flight secondary ion mass spectrometry (TOF-SIMS), the normalized intensity I of Sr on the surface of the aforementioned secondary particles is... Sr_OUT The normalized strength I relative to Sr inside the secondary particles Sr_IN The ratio of I Sr_OUT / I Sr_INThe normalized intensity I of Ca greater than that of secondary particle surface Ca_OUT The normalized strength I relative to Ca inside the secondary particles Ca_IN The ratio of I Ca_OUT / I Ca_IN (The following will be I) Ca_OUT / I Ca_IN The normalized strength ratio, called Ca, is used to determine the strength ratio of I. Sr_OUT / I Sr_IN (This is referred to as the normalized strength ratio of Sr). As a result, the durability of the secondary battery is improved. It is speculated that this is because the surface of the primary particles, including the surface of the secondary particles, is appropriately protected both on and inside the secondary particles.

[0037] The normalized intensity ratio of Ca and Sr was obtained by measurement using a time-of-flight secondary ion mass spectrometer (IONTOF-SIMS5) under the following conditions.

[0038] Primary ion: Bi3 +

[0039] Ionization voltage: 30kV

[0040] Ion current: 0.03pA@100us

[0041] Observation range: 50μm × 50μm

[0042] Quality range: 60µs (~310amu)

[0043] Detection: 4 frames / scan, 150 scans

[0044] The image representing the concentration distributions of Ni, Ca, and Sr obtained from the above measurements was segmented into 256×256 pixels, and the detection intensity of Ni, Ca, and Sr was calculated for each pixel. Furthermore, the ratio of the detection intensity of Ca to the detection intensity of Ni was set as the normalized intensity I of Ca. Ca The ratio of the detection intensity of Sr to the detection intensity of Ni is set as the normalized intensity I of Sr. Sr Calculate them separately.

[0045] The area from the surface of the secondary particle identified in the above image to within 0.5 μm is defined as the surface of the secondary particle, and the pixels contained on the surface of this secondary particle (hereinafter referred to as surface pixels) are determined. I corresponds to each surface pixel. Ca The set becomes I Ca_OUT I corresponding to each surface pixel Sr The set becomes I Sr_OUTFurthermore, the inner part of the surface of the secondary particle, as determined above, is considered the interior of the secondary particle, and the pixels contained within this interior (hereinafter referred to as internal pixels) are determined. I corresponds to each internal pixel. Ca The set becomes I Ca_IN I corresponding to each surface pixel Sr The set becomes I Sr_IN Based on the normalized intensities of Ca and Sr obtained from the surface and interior of the secondary particles, the normalized intensity ratio of Ca (I0.05) is calculated. Ca_OUT / I Ca_IN The normalized intensity ratio of Sr to Sr (I) Sr_OUT / I Sr_IN The specimens for cross-sectional observation can be specimens in which lithium transition metal composite oxides are embedded in resin or the like, or positive electrode composite layers containing lithium transition metal composite oxides.

[0046] The normalized strength ratio of Ca is preferably 1 or more. The normalized strength ratio of Ca is, for example, 1 or more and 5 or less. The normalized strength ratio of Sr is preferably 5 or more. The normalized strength ratio of Sr is, for example, 5 or more and 10 or less. The ratio of the normalized strength of Sr to the normalized strength of Ca (normalized strength of Sr / normalized strength of Ca) is, for example, 1.5 or more and 5 or less.

[0047] Metal compounds containing metallic elements such as W, Zr, Al, and rare earth elements can exist on the surface of lithium transition metal composite oxides. Examples of compounds containing W include WO3. Examples of compounds containing Al include Al2O3. Examples of compounds containing Zr include ZrO2, Zr(OH)4, Zr(CO3)2, and / or Zr(SO4)2·4H2O. Examples of compounds containing rare earth elements include rare earth oxides, hydroxides, carbonates, sulfates, nitrates, and phosphates. Furthermore, the metal compounds may contain these metallic elements and also contain Ca or Sr, as exemplified by SrAlO4 and CaAlO4. The metal compounds may further contain Li, as exemplified by lithium tungstate.

[0048] Nonmetallic compounds can also exist on the surface of lithium transition metal complex oxides. These nonmetallic compounds contain, for example, one or more nonmetallic elements selected from the group consisting of P and B. Li can be cited as an example of a compound containing P. 3- x H x PO4 (0≤x≤3). Examples of compounds containing B include H3BO3, Li3BO3, and Li2B4O7.

[0049] The pore volume of lithium transition metal complex oxides is, for example, greater than 0.1 mL / g and between 0.5 mL / g. The pore volume of lithium transition metal complex oxides can be determined by mercury porosimetry using a mercury porosimeter (e.g., Autopore IV9510, Micromeritics).

[0050] Lithium transition metal composite oxides can have a layered structure. Examples of layered structures for lithium transition metal composite oxides include those belonging to space group R-3m and those belonging to space group C2 / m. From the viewpoints of high capacity and crystal structure stability, lithium transition metal composite oxides preferably have a layered structure belonging to space group R-3m. The layered structure of lithium transition metal composite oxides can include a transition metal layer, a Li layer, and an oxygen layer.

[0051] The positive electrode active material preferably contains a sulfonic acid compound present on the surface of the lithium transition metal complex oxide. The sulfonic acid compound is represented, for example, by general formula I. By presenting the sulfonic acid compound on the surface of the lithium transition metal complex oxide, Li₂O₃ readily forms due to the coating containing the sulfonic acid compound. + The embedding / de-embedding of the material reduces the DC resistance (DCIR).

[0052]

[0053] (In the formula, A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0054] In the above general formula I, A is preferably a group 1 element, and more preferably Li. This further reduces the DC resistance. It should be noted that when A is a group 1 element, n=1.

[0055] In general formula I, R is preferably an alkyl group. R is more preferably an alkyl group with 5 or fewer carbon atoms, even more preferably an alkyl group with 3 or fewer carbon atoms, and particularly preferably methyl. Furthermore, in R, some of the hydrogen atoms bonded to the carbon atoms can be replaced by fluorine. However, in R, not all the hydrogen atoms bonded to the carbon atoms are replaced by fluorine. A smaller molecular weight of R reduces DC resistance.

[0056] Examples of sulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, magnesium methanesulfonate, and lithium fluoromethanesulfonate.

[0057] The amount of sulfonic acid compound present on the surface of the lithium transition metal complex oxide is preferably 0.1% by mass or more and 2% by mass or less relative to the mass of the lithium transition metal complex oxide, more preferably 0.25% by mass or more and 1.0% by mass or less.

[0058] The presence of sulfonic acid compounds on the surface of lithium transition metal composite oxides can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectra obtained by FT-IR, lithium transition metal composite oxides can be observed at 1238 cm⁻¹. -1 1175cm -1 1065cm -1 785cm -1 At least one nearby location has an absorption peak.

[0059] In the infrared absorption spectra obtained by FT-IR, for example, lithium transition metal complex oxides containing lithium methanesulfonate show absorption at 1238 cm⁻¹. -1 1175cm -1 1065cm -1 785cm -1 There is an absorption peak nearby. 1238cm -1 1175cm -1 1065cm -1 The nearby peak originates from the SO stretching vibration of lithium methanesulfonate. (785 cm⁻¹) -1 The nearby peaks are absorption peaks caused by the CS stretching vibration of lithium methanesulfonate.

[0060] In lithium transition metal complex oxides with sulfonic acid compounds other than lithium methanesulfonate on their surface, absorption peaks originating from sulfonic acid compounds can be identified in the same way as in lithium transition metal complex oxides with lithium methanesulfonate on their surface. It should be noted that the presence of sulfonic acid compounds on the surface of lithium transition metal complex oxides can also be confirmed by ICP, atomic absorption spectrometry, X-ray photoelectron spectroscopy (XPS), synchrotron radiation XRD, and TOF-SIMS.

[0061] In addition to the positive electrode active material described in this embodiment, the positive electrode additive layer may also contain other positive electrode active materials. Examples of other positive electrode active materials include lithium transition metal composite oxides containing Ni, Ca, and Sr, where the normalized strengths of Ca and Sr do not satisfy the above-described relationship.

[0062] Next, an example of a method for manufacturing the positive electrode active material according to this embodiment will be described. It should be noted that the manufacturing method described here is an example, and the method for manufacturing the positive electrode active material is not limited to this method.

[0063] The manufacturing process of the positive electrode active material includes: a synthesis step to obtain a lithium transition metal composite oxide; a cleaning step to wash and dehydrate the lithium transition metal composite oxide obtained by the synthesis step to obtain a cake-like composition; an addition step to add at least one of a sulfonic acid compound and a sulfonic acid solution to the cake-like composition; and a drying step to dry the cake-like composition to obtain a powder-like composition. Additionally, the synthesis step may include, for example, a mixing step to obtain a mixture by mixing metal oxides, Li raw materials, Ca raw materials, Sr raw materials, etc., and a calcination step to obtain a lithium transition metal composite oxide by calcining the mixture.

[0064] In the mixing process, a mixture is obtained by mixing metal oxides, Li raw materials, Ca raw materials, and Sr raw materials. The metal oxides can be prepared by stirring a solution containing metal salts such as Ni, Co, Al, and Mn while adding an alkaline solution such as sodium hydroxide dropwise to adjust the pH to alkaline (e.g., above 8.5 and below 12.5), causing a composite hydroxide to precipitate (co-precipitate), and then heat-treating the metal hydroxide. There are no particular limitations on the firing temperature, for example, a range of 250°C to 600°C. Examples of Li raw materials include: Li₂CO₃, LiOH, Li₂O₂, Li₂O, LiNO₃, LiNO₂, Li₂SO₄, LiOH·H₂O, LiH, and LiF. Examples of Ca raw materials include Ca(OH)₂, CaHPO₄, Ca(H₂PO₄)₂, Ca₃(PO₄)₂, CaO, CaCO₃, CaSO₄, Ca(NO₃)₂, CaCl₂, and CaAlO₄. Examples of Sr raw materials include Sr(OH)₂, SrHPO₄, Sr(H₂PO₄)₂, Sr₃(PO₄)₂, SrO, SrCO₃, SrSO₄, Sr(NO₃)₂, SrCl₂, and SrAlO₄. By adjusting the average particle size (D₅₀) of the Ca and Sr raw materials, Sr can be more dispersed on the surface of the secondary particles, and Ca can be more uniformly dispersed inside and on the surface of the secondary particles compared to Sr. Therefore, the effect of adding Ca and Sr becomes more significant. Additionally, M₂ raw materials can be mixed in during mixing to add M₂, wherein M₂ is selected from one or more elements in the group consisting of Nb, Ti, Zr, W, Si, and Mo. Examples of M₂ raw materials include Nb₂O₅, TiO₂, ZrO₂, and WO₃.

[0065] Lithium transition metal composite oxides can be obtained by calcining the above mixture (calcination process). The calcination process is carried out, for example, under an oxygen flow in a calcination furnace. The calcination process includes, for example, a first calcination process, calcining at a first heating rate to a first set temperature of 300°C or higher and 600°C or lower; and a second calcination process, calcining at a second heating rate from the first set temperature to a second set temperature of more than 600°C and 800°C or lower. The first heating rate is, for example, in the range of 10°C / min or higher and 100°C / min or lower, and the second heating rate is, for example, in the range of 0.1°C / min or higher and less than 10°C / min. By increasing the first heating rate, Sr can be more dispersed on the surface of the secondary particles, thus increasing the value of the normalized strength ratio of Sr. Even with an increase in the first heating rate, the normalized strength ratio of Ca does not change as drastically as that of Sr. It should be noted that further subdivided temperature zones can be set in the first and second calcination processes to perform multi-stage calcination.

[0066] It should be noted that the synthesis process is not limited to the above-mentioned steps. A precursor obtained by co-precipitation and / or mixing of compounds such as hydroxides, oxides, and carbonates containing at least one of Ni, M1, and M2 (M1 being one or more elements selected from the group consisting of Co, Al, and Mn, and M2 being one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo) can be used instead of metal oxides. If the precursor does not contain compounds such as M1 and M2, these compounds can be added during mixing of the precursor, Li feedstock, Ca feedstock, and Sr feedstock. Furthermore, these compounds can also be compounds whose particle shape and / or particle size are appropriately modified by pulverization, or whose moisture content is adjusted by containing hydrates.

[0067] In the washing process, the lithium transition metal composite oxide is washed with water and dehydrated to obtain a cake-like composition. The lithium transition metal composite oxide can be granular lithium transition metal composite oxide obtained in the synthesis process. Washing with water removes unreacted components of the lithium compound added in the synthesis process and / or impurities other than the lithium compound. During washing, for example, 300g to 5000g of lithium transition metal composite oxide is added relative to 1L of water. It should be noted that washing can be repeated multiple times. Dehydration after washing can be carried out, for example, using a filter press.

[0068] In the drying process, the cake-like composition obtained in the cleaning process is dried to obtain a powder-like composition. The drying process can be carried out under a vacuum atmosphere. The drying conditions are, for example, 150°C or higher and 400°C or lower, and 0.5 hours or higher and 15 hours or lower.

[0069] In the addition step, at least one of a sulfonic acid compound and a sulfonic acid solution is added to the cake-like composition obtained in the cleaning step or the powder-like composition obtained in the drying step. This allows the sulfonic acid compound to adhere to the surface of the lithium-containing composite oxide. Preferably, at least one of a sulfonic acid compound and a sulfonic acid solution is added to the cake-like composition. The sulfonic acid compound can be in either powder or solution form. The sulfonic acid solution is, for example, a methanesulfonic acid solution obtained by dissolving methanesulfonic acid in water. Since a Li compound remains in the cake-like composition, and this residual Li compound dissolves in the water contained in the cake-like composition, a Li-containing sulfonic acid compound is formed even when a sulfonic acid solution is added. From the viewpoint of more easily obtaining the effects of this application, the Li compound or Li compound solution can be added together with the sulfonic acid solution to the cake-like composition or the powder-like composition, or a mixed solution obtained by pre-mixing the sulfonic acid solution with the Li compound or Li compound solution can be added to the cake-like composition or the powder-like composition. The Li compound is, for example, LiOH, and the Li compound solution is, for example, a LiOH solution obtained by dissolving LiOH in water. The amounts of Li compound and sulfonic acid solution added to the cake-like composition preferably satisfy a molar ratio of 0 ≤ Li compound / sulfonic acid ≤ 1.3. The amount of sulfonic acid compound or sulfonic acid added relative to the mass of the lithium-containing composite oxide is preferably 0.1% by mass or more and 2% by mass or less. The concentrations of the sulfonic acid solution and the sulfonic acid compound solution are, for example, 0.5% by mass or more and 40% by mass or less. The addition process can be carried out at any time during the cleaning process, after the cleaning process, during the drying process, or after the drying process, and the timing can be appropriately varied.

[0070] By adding raw materials containing metal or non-metal compounds at any of the following stages—such as during, after, during, or after a synthesis process, a cleaning process, a drying process, a drying process, or an addition process—metal compounds containing one or more metal elements selected from the group consisting of W, Zr, Al, and rare earth elements, and non-metal compounds containing one or more non-metal elements selected from the group consisting of P and B, can be attached to the surface of lithium-containing composite oxides. Examples of Zr raw materials include Zr(OH)4, ZrO2, Zr(CO3)2, and Zr(SO4)2·4H2O. These metal compounds can also be pulverized, with appropriate changes in particle size, and the water content, including hydrates, can be adjusted. Examples of rare earth raw materials include rare earth oxides, hydroxides, and carbonates. Examples of W raw materials include tungsten oxide (WO3) and lithium tungstate (Li2WO4, Li4WO5, Li6W2O9). It should be noted that solutions containing W can also be used as W raw materials. In addition, Al₂O₃, Al(OH)₃, Al₂(SO₄)₃, etc., can be used as raw materials for Al, or Al derived from lithium-containing complex oxides can be used. Li₂ can be used as a raw material for P.3-x H x PO4 (0 ≤ x ≤ 3), etc. As the B raw material, H3BO3, Li3BO3, Li2B4O 7、 LiBO2, etc. It should be noted that when adding liquid raw materials after the drying process, heat treatment can also be performed to evaporate moisture.

[0071] [Negative electrode]

[0072] The negative electrode 12 can, for example, have a negative electrode core body and a negative electrode mixture layer formed on the surface of the negative electrode core body, and a metal Li foil can also be used as the negative electrode 12. In addition, the negative electrode 12 can also have a negative electrode core body, and lithium metal is deposited on the surface of the negative electrode core body by 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 body. The negative electrode core body can use a foil of a metal such as copper or copper alloy that is stable within the potential range of the negative electrode 12, a thin film having such a metal disposed on the surface layer, etc. The thickness of the negative electrode core body is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer, for example, contains 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 body. The negative electrode 12 can be produced, for example, by the following method: Coating a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. on the surface of the negative electrode core body, drying the coating film, and then performing rolling to form a negative electrode mixture layer on both sides of the negative electrode core body.

[0073] As the negative electrode active material contained in the negative electrode mixture layer, there is no particular limitation as long as it can reversibly absorb and release lithium ions, and carbon materials such as graphite are usually used. The graphite can be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, massive artificial graphite, graphitized mesophase carbon microspheres, etc. artificial graphite. In addition, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si and Sn, lithium titanium composite oxides, etc. can also be used. In addition, materials provided with a carbon coating film for these can also be used. For example, a Si-containing compound represented by SiO x (0.5 ≤ x ≤ 1.6), or a Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by Li 2y SiO (2+y) (0 < y < 2) can be used in combination with graphite.

[0074] As the binder contained in the negative electrode mixture layer, for example, styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salt, polyacrylic acid (PAA) or its salt (which can be PAA-Na, PAA-K, etc., and in addition, partially neutralized salts), polyvinyl alcohol (PVA), etc. can be cited. These can be used alone or in combination of two or more.

[0075] [Separator]

[0076] The separator 13 can be a porous sheet with ion permeability and insulation. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably a polyolefin such as polyethylene or polypropylene, or cellulose. The separator 13 can be a single-layer structure or a multi-layer structure. In addition, a resin layer with high heat resistance, such as an aromatic polyamide resin, can be formed on the surface of the separator 13.

[0077] A filler layer containing inorganic filler can 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 a slurry containing the filler onto the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0078] [Non-aqueous electrolytes]

[0079] Non-aqueous electrolytes, for example, have lithium-ion conductivity. Non-aqueous electrolytes can be liquid electrolytes (electrolytes) or solid electrolytes.

[0080] Liquid electrolytes (electrolytes) may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent may be, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these solvents. The non-aqueous solvent may contain a halogen-substituted form, in which at least a portion of the hydrogen atoms of the solvent are replaced by halogen atoms such as fluorine. Examples of halogen-substituted forms include fluorocyclic carbonates such as fluoroethylene carbonate (FEC), fluorochain carbonates, and fluorochain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0081] Examples of the aforementioned esters include: cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl 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).

[0082] Examples of the aforementioned ethers include: 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eucalyptol, crown ethers and other cyclic ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and dihexyl ether. Ethyl vinyl ether, butyl vinyl ether, methyl 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, tetraethylene glycol dimethyl ether, and other chain ethers.

[0083] The preferred electrolyte salt is a lithium salt. Examples of lithium salts include: LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB. 10 Cl 10 Examples of lithium salts include lower aliphatic carboxylic acids such as lithium Cl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO₂F₂), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium tetrafluoro(oxalate)phosphate. Examples of borates include lithium bis(oxalate)borate (LiBOB) and lithium difluoro(oxalate)borate (LiDFOB). Examples of imide salts include lithium difluorosulfonylimide (LiN(FSO₂)₂), lithium bis(trifluoromethanesulfonate)imide (LiN(CF₃SO₂)₂), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF₃SO₂)(C₄F₉SO₂)), and lithium bis(pentafluoroethanesulfonate)imide (LiN(C₂F₅SO₂)₂). Among these, LiPF₆ is preferred from the perspectives of ionic conductivity and electrochemical stability. The concentration of lithium salt can be, for example, less than 4 moles per 1 L of non-aqueous solvent, less than 3 moles, preferably less than 1.8 moles, more preferably more than 0.8 moles and less than 1.8 moles.

[0084] Non-aqueous electrolytes may contain additives. Examples of additives include unsaturated carbonates, acid anhydrides, phenolic compounds, benzene compounds, nitrile compounds, isocyanate compounds, sulpholactone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0085] 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, vinyl ethylene carbonate, divinyl ethylene carbonate, etc. Unsaturated cyclic carbonates can be used alone or in combination of two or more. A portion of the hydrogen atoms in an unsaturated cyclic carbonate can be replaced by fluorine atoms. An anhydride can be an anhydrous product formed by the intermolecular condensation of multiple carboxylic acid molecules, preferably an anhydride of a polycarboxylic acid. Examples of anhydrides of polycarboxylic acids include: succinic anhydride, maleic anhydride, phthalic anhydride, etc.

[0086] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0087] Examples of nitrile compounds include adiponitrile, heptanonitrile, propionitrile, and succinic anionyl. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and methylcyclohexane diisocyanate (BIMCH). Examples of sulcolone compounds include propane sulcolone and propenyl sulcolone. Examples of sulfuric acid compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate compounds include trimethyl phosphate and tris(trimethylsilyl) phosphate. Examples of phosphite compounds include trimethyl phosphite and tris(trimethylsilyl) phosphite.

[0088] As a solid electrolyte, examples include solid or gel-like polymer electrolytes and inorganic solid electrolytes. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Polymer electrolytes may contain, for example, lithium salts and a matrix polymer, or non-aqueous solvents, lithium salts, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing non-aqueous solvents is used. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins.

[0089] Example

[0090] The present disclosure is further illustrated below by way of examples and comparative examples, but the present disclosure is not limited to the following examples.

[0091] <Example 1-1>

[0092] [Preparation of positive electrode active material]

[0093] [Ni] obtained by coprecipitation method 0.92 Co 0.04 Al 0.04 The composite hydroxide represented by [OH]2 was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. Next, Ca(OH)2 and Sr(OH)2 were added to the above metal oxide in such a way that the molar ratio of Ca relative to the total amount of Ni, Co, and Al was 0.3 mol% and the molar ratio of Sr was 0.1 mol%. Then, lithium hydroxide monohydrate (LiOH·H2O) was mixed in such a way that the molar ratio of Li relative to the total amount of Ni, Co, Al, Ca, and Sr was 103 mol%, to obtain a mixture. The average particle size (D50) of Ca(OH)2 was 3 μm, and the D50 of Sr(OH)2 was 3 μm. This mixture was calcined under an oxygen gas flow of 95% oxygen concentration (flow rate of 5 L / min per 1 kg of mixture) from room temperature to 450°C at a first heating rate of 30°C / min, and then calcined from 450°C to 720°C at a second heating rate of 3°C / min to obtain a lithium transition metal composite oxide. The lithium transition metal composite oxide was washed with water and dried to obtain the positive electrode active material of Example 1-1.

[0094] The results of the positive electrode active material were determined using ICP-AES, and the elements other than Li and O were confirmed as shown in Table 1 (described later). The elemental concentration distribution of the positive electrode active material cross-section was determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the normalized intensity ratio (I0.05) of Ca was [determined]. Ca_OUT / I Ca_IN The normalized strength ratio of Sr is 2.6, and the normalized strength ratio (I) is 2.6. Sr_OUT / I Sr_IN The value is 8.3. In addition, the pore volume of the positive electrode active material is 0.20 mL / g.

[0095] [The production of the positive electrode]

[0096] 95 parts by weight of the above-mentioned positive electrode active material, 3 parts by weight of acetylene black (AB), and 2 parts by weight of polyvinylidene fluoride (PVDF) were mixed, and N-methyl-2-pyrrolidone (NMP) was added in appropriate amount to prepare a positive electrode slurry. Next, the positive electrode slurry was coated onto both sides of a positive electrode core made of aluminum foil. After the coating was dried, it was calendered using calendering rollers and cut into specified electrode sizes to manufacture the positive electrode. It should be noted that an exposed portion of the positive electrode is provided, protruding from the surface of the positive electrode core.

[0097] [Making the negative electrode]

[0098] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution at a solid component mass ratio of 100:1:1 to prepare a negative electrode slurry. Next, the negative electrode slurry was coated onto both sides of a negative electrode core made of copper foil. After the coating was dried, it was calendered using calendering rollers and cut into specified electrode sizes to fabricate the negative electrode. It should be noted that a portion of the negative electrode is provided that exposes the surface of the negative electrode core.

[0099] [Preparation of non-aqueous electrolytes]

[0100] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. A non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) in this mixed solvent at a concentration of 1.2 mol / L.

[0101] [Fabrication of the Experimental Battery Cell]

[0102] A positive electrode lead is installed on the exposed portion of the positive electrode, and a negative electrode lead is installed on the exposed portion of the negative electrode. The positive and negative electrodes are wound into a spiral shape, sandwiched between a polyolefin separator, and then radially pressed to form a flat, wound electrode body. This electrode body is then housed in an outer casing made of aluminum laminate, and the aforementioned non-aqueous electrolyte is injected. The opening of the outer casing is then sealed to obtain the experimental battery cell.

[0103] [Durability Evaluation]

[0104] At an ambient temperature of 45°C, the test battery cell was charged to 4.3V at a constant current of 0.3C, and then charged to 0.02C at a constant voltage of 4.3V. It was then discharged to 2.5V at a constant current of 0.5C. This charge-discharge cycle was counted as one cycle, and 200 cycles were performed. The durability of the test battery cell was calculated using the following formula.

[0105] Durability = (Discharge capacity at 200th cycle / Discharge capacity at 1st cycle) × 100

[0106] [Evaluation of DC Resistance]

[0107] At an ambient temperature of 25°C, the test battery cell was charged to 4.3V at a constant current of 0.3C, and then charged to 0.02C at a constant voltage of 4.3V. After being left to stand for 2 hours, the battery cell was discharged at a constant current of 0.5C for 10 seconds. The open-circuit voltage (OCV), closed-circuit voltage (CCV) after 10 seconds of discharge, and current value (I) after 10 seconds of discharge were recorded. 10s The DC resistance (DCIR) can be calculated using the following formula.

[0108] DCIR = (OCV - CCV) / I 10s

[0109] <Examples 1-2>

[0110] In the preparation of the positive electrode active material, powdered lithium methanesulfonate was added to the water-washed lithium transition metal composite oxide. Otherwise, test battery cells were prepared and evaluated in the same manner as in Examples 1-1. The amount of lithium methanesulfonate added was 0.5% by mass relative to the lithium transition metal composite oxide.

[0111] <Examples 1-3>

[0112] In the preparation of the positive electrode active material, the Ca raw material was changed to Ca(OH)2 with a D50 of 1 μm, and the test battery cells were prepared and evaluated in the same manner as in Examples 1-2.

[0113] <Examples 1-4>

[0114] In the preparation of the positive electrode active material, the Sr raw material was changed to Sr(OH)2 with a D50 of 1 μm, and the test battery cells were prepared and evaluated in the same manner as in Examples 1-2.

[0115] <Comparative Example 1-1>

[0116] In the preparation of the positive electrode active material, the first heating rate was changed to 5°C / min. Otherwise, the test battery cells were prepared and evaluated in the same manner as in Example 1-1.

[0117] <Comparative Examples 1-2>

[0118] In the preparation of the positive electrode active material, the first heating rate was changed to 5°C / min. Otherwise, the test battery cells were prepared and evaluated in the same manner as in Examples 1-2.

[0119] <Comparative Examples 1-3>

[0120] In the fabrication of the positive electrode active material, [Ni] obtained through co-precipitation is used. 0.92 Co0.04 Al 0.04 The composite hydroxide represented by (OH)2 was calcined at 500°C for 12 hours to obtain a metal oxide containing Ni, Co, and Al. The first heating rate was changed to 5°C / min, and the test cell was fabricated and evaluated in the same manner as in Examples 1-2.

[0121] <Example 2-1>

[0122] In the fabrication of the positive electrode active material, [Ni] obtained through co-precipitation is used. 0.90 Co 0.05 Mn 0.05 The composite hydroxide represented by ](OH)2 was used instead of the metal oxide, the Ca raw material was changed to Ca(OH)2 with a D50 of 1 μm, and the Sr raw material was changed to Sr(OH)2 with a D50 of 1 μm. Otherwise, the test cell was fabricated and evaluated in the same manner as in Example 1-1.

[0123] <Examples 2-2~2-5>

[0124] In the preparation of the positive electrode active material, WO3, Nb2O5, TiO2, or ZrO2 were added to prepare a mixture in the manner shown in Table 2, with the molar ratio of W, Nb, Ti, or Zr relative to the total amount of Ni, Co, and Mn. Powdered lithium methanesulfonate was added to the water-washed lithium transition metal composite oxide. Otherwise, test battery cells were prepared and evaluated in the same manner as in Example 2-1. The amount of lithium methanesulfonate added was 0.5% by mass relative to the lithium transition metal composite oxide.

[0125] <Comparative Example 2-1>

[0126] In the preparation of the positive electrode active material, the Ca raw material was changed to Ca(OH)2 with a D50 of 3μm, the Sr raw material was changed to Sr(OH)2 with a D50 of 3μm, and the first heating rate was changed to 5℃ / min. Otherwise, the test battery cell was prepared and evaluated in the same manner as in Example 2-1.

[0127] <Comparative Examples 2-2~2-5>

[0128] In the preparation of the positive electrode active material, WO3, Nb2O5, TiO2, or ZrO2 were added to prepare a mixture in such a way that the molar ratio of W, Nb, Ti, or Zr relative to the total amount of Ni, Co, and Mn was as shown in Table 2. For Comparative Examples 2-3 to 2-4, powdered lithium methanesulfonate was further added to the water-washed lithium transition metal composite oxide. Otherwise, test battery cells were prepared and evaluated in the same manner as in Comparative Example 2-1. The amount of lithium methanesulfonate added was 0.5% by mass relative to the lithium transition metal composite oxide.

[0129] <Example 3-1>

[0130] In the fabrication of the positive electrode active material, [Ni] obtained through co-precipitation is used. 0.90 Mn 0.10 The composite hydroxide represented by ](OH)2 was used instead of the metal oxide, the Ca raw material was changed to Ca(OH)2 with a D50 of 1 μm, and the Sr raw material was changed to Sr(OH)2 with a D50 of 1 μm. Otherwise, the test cell was fabricated and evaluated in the same manner as in Examples 1-2.

[0131] <Examples 3-2~3-5>

[0132] In the preparation of the positive electrode active material, WO3, Nb2O5, TiO2 or ZrO2 were added to prepare a mixture in such a way that the molar ratio of W, Nb, Ti or Zr to the total amount of Ni, Co and Mn was as shown in Table 3. Otherwise, test battery cells were prepared and evaluated in the same manner as in Example 3-1.

[0133] <Comparative Examples 3-1~3-5>

[0134] In the preparation of the positive electrode active material, except as described below, the test battery cells were prepared and evaluated in the same manner as in Example 3-1.

[0135] (1) Change the Ca raw material to Ca(OH)2 with a D50 of 3μm and change the Sr raw material to Sr(OH)2 with a D50 of 3μm.

[0136] (2) For Comparative Examples 3-1 and 3-2, lithium methanesulfonate was not added.

[0137] (3) Change the first heating rate to 5℃ / min.

[0138] The evaluation results of the test battery cells of the Examples and Comparative Examples are shown in Tables 1 to 3, respectively. Additionally, the pore volume of the positive electrode active material is also shown in Tables 1 to 3. In Table 1, the durability and DC resistance of the test battery cells other than Comparative Example 1-1 are expressed relative to the durability and DC resistance of the test battery cell of Comparative Example 1-1, which are each set to 100. In Table 2, the durability and DC resistance of the test battery cells other than Comparative Examples 2-4 are expressed relative to the durability and DC resistance of the test battery cells of Comparative Examples 2-4, which are each set to 100. In Table 3, the durability and DC resistance of the test battery cells other than Comparative Examples 3-5 are expressed relative to the durability and DC resistance of the test battery cells of Comparative Examples 3-5, which are each set to 100.

[0139] [Table 1]

[0140]

[0141] [Table 2]

[0142]

[0143] [Table 3]

[0144]

[0145] In Tables 1-3, the test battery cells of the embodiments show improved durability compared to the test battery cells of the comparative examples. Therefore, it can be seen that by including Sr in the positive electrode active material, the normalized strength ratio (I0.05) is improved. Sr_OUT / I Sr_IN The normalized strength ratio (I) is greater than that of Ca. Ca_OUT / I Ca_IN The durability of lithium transition metal composite oxides is improved. Furthermore, by incorporating sulfonic acid compounds on the surface of the lithium transition metal composite oxides into the positive electrode active material, DC resistance can be reduced.

[0146] This disclosure is further illustrated by the following embodiments.

[0147] Option 1:

[0148] A positive electrode active material for non-aqueous electrolyte secondary batteries, comprising lithium transition metal composite oxide.

[0149] The lithium transition metal composite oxide contains Ni, Ca, and Sr, and includes secondary particles formed by the aggregation of primary particles.

[0150] In the elemental concentration distribution of the lithium transition metal composite oxide cross section obtained using time-of-flight secondary ion mass spectrometry.

[0151] The normalized strength I of Sr on the surface of the secondary particles Sr_OUT The normalized intensity I relative to Sr inside the secondary particles Sr_IN The ratio of I Sr_OUT / I Sr_IN The normalized intensity I of Ca on the surface of the secondary particles is greater than that of the secondary particles. Ca_OUT The normalized strength I relative to Ca inside the secondary particles Ca_IN The ratio of I Ca_OUT / I Ca_IN .

[0152] Option 2:

[0153] According to the positive electrode active material for non-aqueous electrolyte secondary batteries described in Scheme 1, the content of Ni in the lithium transition metal composite oxide is more than 70 mol% relative to the total molar number of metal elements other than Li in the lithium transition metal composite oxide.

[0154] Option 3:

[0155] According to Scheme 1 or 2, the positive electrode active material for a non-aqueous electrolyte secondary battery further comprises one or more elements selected from the group consisting of Co, Al and Mn.

[0156] Option 4:

[0157] The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Schemes 1 to 3, wherein the lithium transition metal composite oxide further comprises one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si and Mo.

[0158] Option 5:

[0159] The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Schemes 1 to 4, wherein the I Ca_OUT / I Ca_IN It is 1 or higher.

[0160] Option 6:

[0161] According to any one of Schemes 1 to 5, the positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the pore volume of the lithium transition metal composite oxide is 0.1 mL / g or more and 0.5 mL / g.

[0162] Option 7:

[0163] The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Schemes 1 to 6 comprises a sulfonic acid compound present on the surface of the lithium transition metal composite oxide.

[0164] The sulfonic acid compound is represented by general formula I.

[0165]

[0166] (In the formula, A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0167] Option 8:

[0168] According to the positive electrode active material for non-aqueous electrolyte secondary batteries described in Scheme 7, wherein A is a group 1 element.

[0169] Option 9:

[0170] According to the positive electrode active material for non-aqueous electrolyte secondary batteries described in Scheme 7, wherein A is Li.

[0171] Option 10:

[0172] The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Schemes 7 to 9, wherein R is an alkyl group.

[0173] Option 11:

[0174] The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Schemes 7 to 9, wherein R is methyl.

[0175] Option 12:

[0176] According to any one of Schemes 7 to 11, the amount of the sulfonic acid compound present on the surface of the lithium transition metal composite oxide is 0.1% by mass or more and 2% by mass or less relative to the mass of the lithium transition metal composite oxide.

[0177] Option 13:

[0178] A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte, including any one of claims 1 to 12, a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0179] Explanation of reference numerals in the attached figures

[0180] 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 lead, 21 Negative lead, 22 Groove section, 23 Internal terminal block, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium transition metal composite oxide. The lithium transition metal composite oxide contains Ni, Ca, and Sr, and includes secondary particles formed by the aggregation of primary particles. In the elemental concentration distribution of the lithium transition metal composite oxide cross section obtained using time-of-flight secondary ion mass spectrometry. The normalized strength I of Sr on the surface of the secondary particles Sr_OUT The normalized intensity I relative to Sr inside the secondary particles Sr_IN The ratio of I Sr_OUT / I Sr_IN The normalized intensity I of Ca on the surface of the secondary particles is greater than that of the secondary particles. Ca_OUT The normalized strength I relative to Ca inside the secondary particles Ca_IN The ratio of I Ca_OUT / I Ca_IN .

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The content of Ni in the lithium transition metal composite oxide is more than 70 mol% relative to the total molar number of metal elements other than 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 lithium transition metal composite oxide also contains one or more elements selected from the group consisting of Co, Al and Mn.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The lithium transition metal composite oxide further comprises one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The I Ca_OUT / I Ca_IN It is 1 or higher.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The pore volume of the lithium transition metal composite oxide is greater than 0.1 mL / g and less than 0.5 mL / g.

7. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, comprising a sulfonic acid compound present on the surface of the lithium transition metal composite oxide. The sulfonic acid compound is represented by general formula I. In the formula, A is a group 1 element or a group 2 element, R is a hydrocarbon group, and n is 1 or 2.

8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein, A is a group 1 element.

9. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein, A is Li.

10. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein, R is an alkyl group.

11. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein, R is a methyl group.

12. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein, The amount of the sulfonic acid compound present on the surface of the lithium transition metal composite oxide is more than 0.1% by mass and less than 2% by mass relative to the mass of the lithium transition metal composite oxide.

13. A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte, all comprising the positive electrode active material for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 12.

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