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

Abstract

This positive electrode (11) for a nonaqueous electrolyte secondary battery has a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core, and is characterized in that the positive electrode mixture layer contains a positive electrode active material and an additive, and the positive electrode active material contains a lithium-containing transition metal composite oxide having a layered structure. The lithium-containing transition metal composite oxide is a secondary particle formed by aggregating primary particles, a sulfonic acid compound represented by formula (I) is present on the surface of the secondary particle, and the additive contains a compound containing at least one element selected from the group consisting of P, Ca, Sr, B, Zr, Er, Ti, and Al. (In the formula, A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2. )

Description

Technical Field

[0001] This disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery. Background Technology

[0002] In recent years, the applications of non-aqueous electrolyte secondary batteries have expanded to include power sources for electric vehicles and / or energy storage devices for the efficient utilization of natural energy. The positive electrode has a significant impact on battery characteristics, including capacity, output characteristics, and cycle performance; therefore, extensive research has been conducted on positive electrodes. For example, Patent Document 1 discloses a positive electrode for non-aqueous electrolyte secondary batteries, aiming to improve cycle performance. As the positive electrode active material, it uses a lithium-containing transition metal composite oxide containing compounds of elements such as zirconium (Zr), titanium (Ti), and aluminum (Al) at the particle interface. Furthermore, Patent Document 2 discloses a positive electrode for non-aqueous electrolyte secondary batteries, aiming to reduce reaction resistance during high-temperature storage. As the positive electrode active material, it uses a lithium-containing transition metal composite oxide with a low-solubility Li salt deposited on its surface.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-113728

[0006] Patent Document 2: Japanese Patent Application Publication No. 2019-169286 Summary of the Invention

[0007] In recent years, lithium-containing transition metal composite oxides with high Ni content have attracted attention as positive electrode active materials for achieving high battery capacity. However, when using lithium-containing transition metal composite oxides with high Ni content as positive electrode active materials, a large amount of highly reactive Ni exists on the particle surface of the composite oxide at high state of charge (SOC). 4+ Therefore, side reactions between lithium-containing transition metal complex oxides and the electrolyte are prone to occur. Furthermore, the hydrogen fluoride produced through these side reactions reacts with the lithium-containing transition metal complex oxides, with the products depositing on the surface of the oxides or the transition metal dissolving from them. As a result, the battery's reactive resistance increases, leading to a decrease in charge-discharge cycle characteristics.

[0008] As one aspect of this disclosure, the positive electrode for a non-aqueous electrolyte secondary battery is characterized by having a positive electrode core and a positive electrode additive layer formed on the surface of the positive electrode core. The positive electrode additive layer contains a positive electrode active material and additives. The positive electrode active material contains a lithium-containing transition metal composite oxide with a layered structure. The lithium-containing transition metal composite oxide is formed from a material of the general formula Li... x Nia Co b Mn c M d O 2-y (where 0.8 < x < 1.2, 0.75 ≤ a ≤ 0.95, 0 ≤ b ≤ 0.15, 0 ≤ c ≤ 0.25, 0 ≤ d ≤ 0.10, 0 ≤ y < 0.05, a + b + c + d = 1, and M is at least one element selected from the group consisting of W, Mg, Mo, Nb, Ti, Si, Al, and Zr), and secondary particles formed by aggregation of primary particles, on the surface of the secondary particles, there is a sulfonic acid compound represented by the formula (I), and the additive contains a compound containing at least one element selected from the group consisting of P, Ca, Sr, B, Zr, Er, Ti, and Al).

[0009]

[0010] (where A is an element of Group 1 or Group 2, R is a hydrocarbon group, and n is 1 or 2.)

[0011] A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure is characterized by including the above positive electrode, negative electrode, and non-aqueous electrolyte.

[0012] According to the positive electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure, a non-aqueous electrolyte secondary battery capable of reducing the reaction resistance of the battery and improving the cycle characteristics can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery as an example of an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] As described above, a lithium-containing transition metal composite oxide having a large Ni content is likely to undergo a side reaction with an electrolyte, particularly in a state where the state of charge (SOC) is high. Therefore, when this composite oxide is used as a positive electrode active material, hydrogen fluoride generated by the side reaction reacts with the lithium-containing transition metal composite oxide, and the product is deposited on the surface of the lithium-containing transition metal composite oxide, or the transition metal dissolves out from the lithium-containing transition metal composite oxide. As a result, the reaction resistance of the battery increases.

[0015] The inventors' research indicates that the presence of the sulfonic acid compound shown in formula (I) on the surface of secondary particles of the lithium-containing transition metal complex oxide used as the positive electrode active material can reduce the battery's reaction resistance. This is believed to be because the sulfonic acid compound reduces the reaction resistance in the positive electrode. However, the presence of the sulfonic acid compound introduces a new problem: reduced cycle characteristics at high voltages. This is presumably because the positive electrode potential increases, and the reactivity in the positive electrode becomes higher, thereby increasing the amount of hydrogen fluoride produced during repeated charge-discharge cycles due to side reactions between the lithium-containing transition metal complex oxide and the electrolyte.

[0016] The inventors further conducted in-depth research and discovered that by including a compound containing at least one element selected from the group consisting of P, Ca, Sr, B, Zr, Er, Ti, and Al as an additive in the positive electrode additive layer constituting the positive electrode, the reaction resistance of the battery is reduced and the cycle characteristics are improved. It is speculated that this is because by utilizing sulfonic acid compounds to reduce the reaction resistance in the positive electrode and preferentially reacting the hydrogen fluoride generated through side reactions with the additives, the lithium-containing transition metal complex oxide can be protected from the effects of hydrogen fluoride.

[0017] The following is a reference to the appendix. Figure 1 The following is a detailed description of one embodiment of the non-aqueous electrolyte secondary battery disclosed herein. It should be noted that configurations formed by selectively combining the constituent elements of the various embodiments and modifications described below are included within the scope of this disclosure. It should also be noted that in this specification, "~" refers to the range including both the upper and lower limits before and after "~".

[0018] Hereinafter, as a non-aqueous electrolyte secondary battery, an example is a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer casing 16. However, the outer casing of the battery is not limited to a cylindrical outer casing. The non-aqueous electrolyte secondary battery of this disclosure can be, for example, a square battery with a square outer casing, a coin-shaped battery with a coin-shaped outer casing, or a pouch-shaped battery with an outer casing composed of a laminate containing a metal layer and a resin layer. In addition, the electrode body is not limited to a wound type, but can also be a stacked type electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators. Furthermore, the design of the non-aqueous electrolyte secondary battery of this disclosure is not limited to the illustrated non-aqueous electrolyte secondary battery design, and can also use known non-aqueous electrolyte secondary battery designs.

[0019] Figure 1 This is an axial cross-sectional view of a cylindrical non-aqueous electrolyte secondary battery 10, as an example of an implementation method. (See attached image.) Figure 1As shown, the non-aqueous electrolyte 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.

[0020] 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 along their length. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. Two separators 13 are arranged, for example, to sandwich the positive electrode 11. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode body 14, the 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 short side direction form the axial end faces of the electrode body 14.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The following is a detailed description of the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte constituting the non-aqueous electrolyte secondary battery 10, especially the positive electrode 11.

[0025] [positive electrode]

[0026] 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 to 30 μm.

[0027] The positive electrode mixture layer comprises a positive electrode active material and additives, wherein the additives are composed of compounds containing at least one element selected from the group consisting of P, Ca, Sr, B, Zr, Er, Ti, and Al. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode core.

[0028] The positive electrode active material comprises a lithium-containing transition metal composite oxide with a layered structure. This lithium-containing transition metal composite oxide comprises secondary particles formed by the aggregation of primary particles. The particle size of the primary particles constituting the secondary particles of the lithium-containing transition metal composite oxide is, for example, 0.02 μm to 2 μm. 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 of the lithium-containing transition metal composite oxide is, for example, 2 μm to 30 μm. Here, the average particle size refers to the median particle size (D50) on a volume basis. D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution reaches 50% from the smallest end, also known as the median diameter. The particle size distribution of the secondary particles of the lithium-containing transition metal composite oxide can be measured using a laser diffraction-type particle size distribution measuring device (e.g., MicrotracBEL Co., Ltd., MT3000II) with water as the dispersion medium.

[0029] As the layered structure of the lithium-containing transition metal composite oxide, for example, a layered structure belonging to the space group R-3m, a layered structure belonging to the space group C2 / m, etc. can be cited. From the viewpoints of high capacity and stabilization of the crystal structure, the lithium-containing transition metal composite oxide preferably has a layered structure belonging to the space group R-3m. The layered structure of the lithium-containing transition metal composite oxide may include a transition metal layer and a Li layer.

[0030] The lithium-containing transition metal composite oxide is represented by the general formula Li x Ni a Co b Mn c M d O 2-y (where 0.8 < x < 1.2, 0.75 ≤ a ≤ 0.95, 0 ≤ b ≤ 0.15, 0 ≤ c ≤ 0.25, 0 ≤ d ≤ 0.10, 0 ≤ y < 0.05, a + b + c + d = 1, and M is at least one element selected from the group consisting of W, Mg, Mo, Nb, Ti, Si, Al, and Zr). The content ratios of the elements constituting the lithium-containing transition metal composite oxide can be measured by an inductively coupled plasma emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0031] By setting the content ratio of Ni in the lithium-containing transition metal composite oxide to 75 mol% to 95 mol%, a high-capacity battery can be obtained. The higher the Ni content ratio, the higher the capacity of the battery that can be obtained.

[0032] The content ratio of Co in the lithium-containing transition metal composite oxide is 0 mol% to 15 mol%, and Co is an optional component. In other words, the lithium-containing transition metal composite oxide may also contain no Co. By containing Co in the lithium-containing transition metal composite oxide, the heat resistance of the battery can be improved.

[0033] The content ratio of Mn in the lithium-containing transition metal composite oxide is 0 mol% to 25 mol%, and Mn is an optional component. In other words, the lithium-containing transition metal composite oxide may also contain no Mn. By containing Mn in the lithium-containing transition metal composite oxide, the crystal structure can be stabilized.

[0034] The content ratio of M (M is at least one element selected from the group consisting of W, Mg, Mo, Nb, Ti, Si, Al, and Zr) in the lithium-containing transition metal composite oxide is 0 mol% to 10 mol%, and M is an optional component. In other words, the lithium-containing transition metal composite oxide may also contain no M.

[0035] A sulfonic acid compound represented by the formula (I) is present on the surface of the secondary particles of the lithium-containing transition metal composite oxide.

[0036]

[0037] In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2. A is preferably a Group 1 element. More preferably, it is Li or Na, and particularly preferably Li. The sulfonic acid compound may be present in the form of dots covering at least a portion of the surface of the secondary particles containing lithium transition metal composite oxides, or it may be present covering the entire surface of the secondary particles. In addition, the sulfonic acid compound may also be present on the surface of the primary particles containing lithium transition metal composite oxides.

[0038] In formula (I), R is preferably an alkyl group. The alkyl group preferably has 5 or fewer carbon atoms, more preferably 3 or fewer. From the viewpoint of reducing reaction resistance, an example of preferred R is an alkyl group with 3 or fewer carbon atoms, wherein methyl is preferred. It should be noted that in R, a portion of the hydrogen atoms bonded to the carbon atoms can be replaced by fluorine. Furthermore, n in formula (I) is preferably 1.

[0039] Specific examples of sulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, sodium ethanesulfonate, magnesium methanesulfonate, and lithium fluoromethanesulfonate. Preferably, at least one compound is selected from the group consisting of lithium methanesulfonate, lithium ethanesulfonate, and sodium methanesulfonate, and lithium methanesulfonate is particularly preferred.

[0040] The sulfonic acid compound reduces the reaction resistance in the positive electrode 11, thus reducing the overall reaction resistance of the battery. This effect is achieved even in very small amounts of the sulfonic acid compound, but it is preferable that it exists at least 0.05% by mass on the surface of the secondary particles of the lithium transition metal composite oxide, and more preferably at least 0.1% by mass. There is no particular upper limit to the content of the sulfonic acid compound, but from the viewpoint of cycle characteristics, it is preferably 1.5% by mass relative to the mass of the lithium transition metal composite oxide. Therefore, an example of a preferred range for the amount of the sulfonic acid compound is 0.05% to 1.5% by mass relative to the mass of the lithium transition metal composite oxide.

[0041] The presence of sulfonic acid compounds on the surface of secondary particles containing lithium transition metal composite oxides can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectra obtained by FT-IR, positive electrode active materials containing lithium methanesulfonate, for example, show an absorption rate of 1238 cm⁻¹. -1 1175cm -1 1065cm -1 785cm -1 There is an absorption peak nearby. 1238cm -1 1175cm -1 1065cm -1The nearby peak originates from the SO stretching vibration of lithium methanesulfonate. 785 cm⁻¹ -1 The nearby peaks are caused by the CS stretching vibration of lithium methanesulfonate. It should be noted that for positive electrode active materials containing sulfonic acid compounds other than lithium methanesulfonate, their presence can also be confirmed by the absorption peaks originating from sulfonic acid compounds in the infrared absorption spectrum.

[0042] Furthermore, the presence of sulfonic acid compounds can also be confirmed by X-ray photoelectron spectroscopy (XPS). In the spectra obtained by XPS, peaks with binding energies around 165–170 eV and intensities (c / s) of 200–1000 can be observed for positive electrode active materials containing lithium methanesulfonate. It should be noted that the presence of sulfonic acid compounds on the surface of secondary particles containing lithium transition metal composite oxides can also be confirmed by ICP, atomic absorption spectrometry, synchrotron XRD, and TOF-SIMS.

[0043] As an example of an implementation method, the positive electrode active material can be manufactured by the following method. It should be noted that the manufacturing method described herein is an example, and the manufacturing method of the positive electrode active material is not limited to this method.

[0044] The manufacturing process of the positive electrode active material includes: a synthesis process to obtain a lithium-containing transition metal composite oxide; a cleaning process to wash and dehydrate the lithium-containing transition metal composite oxide obtained by the synthesis process to obtain a cake-like composition; an addition process to add at least one of a sulfonic acid compound and a sulfonic acid solution to the cake-like composition; and a drying process to dry the cake-like composition to obtain a powder-like composition.

[0045] In the synthesis process, for example, a metal oxide containing 75 mol% to 95 mol% Ni, 0 mol% to 15 mol% Co, 0 mol% to 25 mol% Mn and 0 mol% to 10 mol% M (M is at least one element selected from W, Mg, Mo, Nb, Ti, Si, Al and Zr) is mixed with a Li compound to obtain a mixture.

[0046] Metal oxides can be obtained, for example, by stirring a solution containing Ni and any metal element (Co, Mn, M, etc.) while adding an alkaline solution such as sodium hydroxide dropwise to adjust the pH to alkaline (e.g., 8.5~12.5), causing a composite hydroxide containing Ni and any metal element to precipitate (co-precipitate), and then subjecting the composite hydroxide to heat treatment. There are no particular limitations on the heat treatment temperature, for example, a range of 250℃~600℃.

[0047] Examples of Li compounds include Li₂CO₃, LiOH, Li₂O₂, Li₂O, LiNO₃, LiNO₂, Li₂SO₄, LiOH·H₂O, LiH, and LiF. From the viewpoint of easily adjusting the above parameters to the ranges specified above, the mixing ratio of the metal oxide and the Li compound is preferably set to a molar ratio of the total amount of metal elements in the metal oxide to Li in the range of 1:0.8 to 1:1.2, and more preferably to a ratio in the range of 1.0 to 1.1.

[0048] Next, the synthesis process includes a firing process for firing the obtained mixture. The firing process is, for example, a multi-stage firing process that includes at least a first firing process under an oxygen flow at 300°C to 680°C, and a second firing process for firing the calcined product obtained in the first firing process under an oxygen flow at a temperature exceeding 680°C. In the first firing process, the temperature is increased to a first set temperature below 680°C at a first heating rate of 0.2°C / min to 4.5°C / min. In the second firing process, the temperature is increased to a second set temperature below 900°C at a first heating rate of 0.5°C / min to 3.5°C / min. It should be noted that multiple first and second heating rates can be set in each temperature range, provided they are within the aforementioned ranges.

[0049] The holding time of the first set temperature in the first firing step is preferably 5 hours or less, more preferably 3 hours or less. The holding time of the first set temperature refers to the time during which the first set temperature is maintained after it has been reached; the holding time can be zero. The holding time of the second set temperature in the second firing step is preferably 1 hour to 10 hours, more preferably 1 hour to 5 hours. The holding time of the second set temperature refers to the time during which the second set temperature is maintained after it has been reached. The firing of the mixture is carried out, for example, in an oxygen flow with an oxygen concentration of 60% or more, with the oxygen flow rate set to 10 cm³ / s. 3 The firing rate is 0.2 mL / min to 4 mL / min or more per 1 kg of mixture.

[0050] The synthesis process is not limited to the above-described process. For example, it may also include the following known synthesis method: obtaining a precursor by co-precipitating and / or mixing a compound containing at least one of Ni, Co, Mn, and M (M is at least one element selected from W, Mg, Mo, Nb, Ti, Si, Al, and Zr) such as hydroxides, oxides, or carbonates, mixing it with a Li source, and then calcining it to obtain a lithium-containing transition metal composite oxide. If the precursor does not contain compounds such as M, these compounds such as M can be mixed and calcined when mixing the precursor with the Li source. Alternatively, these compounds may be compounds whose particle shape and / or particle size are appropriately changed by pulverization, or whose moisture content is adjusted by containing hydrates.

[0051] In the washing process, the lithium-containing transition metal composite oxide is washed with water and dehydrated to obtain a cake-like composition. The lithium-containing transition metal composite oxide can be the granular lithium-containing transition metal composite oxide obtained in the synthesis process. Water washing removes unreacted components of the lithium compound added in the synthesis process and / or impurities other than the lithium compound. During water washing, for example, 300g to 5000g of the lithium-containing transition metal composite oxide is added relative to 1L of water. It should be noted that water washing can be repeated multiple times. Dehydration after water washing can be carried out, for example, using a filter press.

[0052] 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. This allows the sulfonic acid compound to adhere to the surface of the lithium-containing transition metal complex oxide. The sulfonic acid compound can be in powder or solution form. The sulfonic acid solution is, for example, a methanesulfonic acid solution obtained by dissolving methanesulfonic acid in water. Li compounds remain in the cake-like composition, and these residual Li compounds dissolve in the water contained in the cake-like composition; therefore, even with the addition of the sulfonic acid solution, a sulfonic acid compound containing Li is formed. From the viewpoint of more easily obtaining the effects of this application, the Li compound or Li compound solution can be added to the cake-like composition together with the sulfonic acid solution, 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. 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 is preferably 0.05% to 1.5% by mass relative to the mass of the lithium transition metal complex oxide, more preferably 0.1% to 1.0% by mass. The concentrations of the sulfonic acid solution and the sulfonic acid compound solution are, for example, 0.5% to 40% by mass.

[0053] 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 to 400°C for 0.5 to 15 hours.

[0054] The additives contained in the positive electrode composite layer include compounds containing at least one element selected from the group consisting of P, Ca, Sr, B, Zr, Er, Ti, and Al. The additives exist, for example, in particulate form between the positive electrode active materials. The additives readily react with hydrogen fluoride, and therefore preferentially react with hydrogen fluoride produced through the decomposition of non-aqueous electrolytes. As a result, lithium-containing transition metal composite oxides are protected from the effects of hydrogen fluoride.

[0055] Additives may be, for example, compounds containing at least one element selected from the group consisting of phosphates, sulfates, oxides, hydroxides, and chlorides. Examples of additives include: Li3PO4, CaO, CaCl2, Ca(OH)2, SrO, SrCl2, Sr(OH)2, B2O3, B(OH)3, ZrSO4, ZrO2, ZrF4, Er2(SO4)3, TiO2, Ti(OH)4, Al2O3, Al(OH)3, AlPO4, AlF3, etc. It should be noted that additives may be used alone or in combination of two or more. Furthermore, these compounds may also be used by pulverizing to appropriately change the particle shape and / or particle size, or by containing hydrates to adjust the moisture content.

[0056] The amounts of P, Ca, Sr, B, Zr, Er, Ti, and Al contained in the additives in the positive electrode mixture layer are preferably 0.001% to 1% by mass, more preferably 0.01% to 1% by mass, relative to the total mass of the positive electrode active material. In this case, the effects of this disclosure can be more significantly achieved. It should be noted that when using multiple additives, it is preferable that the total amount of P, Ca, Sr, B, Zr, Er, Ti, and Al contained in all additives is included within the above range. Furthermore, the content of the additives may vary along the thickness direction of the positive electrode mixture layer, but it is preferable that it is approximately the same along the thickness direction of the positive electrode mixture layer.

[0057] The presence of additives can be confirmed by synchrotron radiation XRD, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), etc.

[0058] In addition to the positive electrode active material and additives, the positive electrode binder layer also includes, for example, conductive agents and binders. Examples of conductive agents included in the positive electrode binder layer include acetylene black (AB), carbon black (CB) such as Ketjen black, carbon nanotubes (CNTs), graphene, and carbon-based particles such as graphite. These can be used individually or in combination of two or more.

[0059] Examples of binders used 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.

[0060] As an example of an implementation, the positive electrode 11 can be manufactured through the following steps: a manufacturing step of producing a positive electrode active material, a manufacturing step of preparing a positive electrode slurry containing the positive electrode active material, a conductive agent, and a binder, a coating step of coating the positive electrode slurry onto the surface of the positive electrode core and drying it, and a calendering step of calendering the coating film produced in the coating step. Here, an additive is added in the manufacturing step. This allows the additive to be dispersed in the positive electrode binder layer.

[0061] [negative electrode]

[0062] The negative electrode 12 may have a negative electrode core and a negative electrode binder layer formed on the surface of the negative electrode core, or a metallic Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode core, with lithium metal deposited on the surface of the negative electrode core during charging. When the negative electrode 12 has a negative electrode binder layer, the binder 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 thin film of the metal disposed on its surface. The thickness of the negative electrode core is, for example, 5 μm to 30 μm. The negative electrode binder layer may contain, for example, a negative electrode active material and a binder. The thickness of the negative electrode binder layer is, for example, 10 μm to 150 μm on one side of the negative electrode core. The negative electrode 12 can be made, for example, by coating the surface of the negative electrode core with a negative electrode slurry containing negative electrode active material, binder, etc., and after the coating is dried, calendering is performed to form a negative electrode slurry layer on both sides of the negative electrode core.

[0063] As the negative electrode active material contained in the negative electrode mixture layer, there is no particular limitation as long as it is a material capable of reversibly storing and releasing lithium ions. Usually, carbon materials such as graphite can be 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, Sn, etc., 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.

[0064] 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 also partially neutralized salts), polyvinyl alcohol (PVA), etc. can be cited. These can be used alone or in combination of two or more.

[0065] [Separator]

[0066] The separator 13 can use a porous sheet having ion permeability and insulation. As specific examples of the porous sheet, microporous films, woven fabrics, non-woven fabrics, etc. can be cited. As the material of the separator 13, polyolefins such as polyethylene and polypropylene, cellulose, etc. are preferred. The separator 13 can be a single-layer structure or can have a multilayer 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.

[0067] A filler layer containing an 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. As the inorganic filler, for example, oxides containing metal elements such as Ti, Al, Si, Mg, etc., phosphate compounds, etc. can be cited. The filler layer can be formed by coating a slurry containing the filler on the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0068] [Non-aqueous electrolyte]

[0069] The non-aqueous electrolyte has ionic conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte can be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0070] 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).

[0071] 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).

[0072] 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.

[0073] 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 10Examples 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, and more preferably 0.8 to 1.8 moles.

[0074] 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.

[0075] 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.

[0076] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0077] 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.

[0078] 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.

[0079] Example

[0080] 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.

[0081] <Example 1>

[0082] [Preparation of positive electrode active material]

[0083] [Ni] obtained by coprecipitation method 0.90 Co 0.05 Al 0.05 The complex hydroxide represented by [OH]2 was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. Next, lithium hydroxide monohydrate (LiOH·H2O) was mixed with Li at a molar ratio of 1:1.03 to the total amount of Ni, Co, and Al to obtain a mixture. Then, this mixture was subjected to an oxygen gas flow of 95% oxygen concentration (per 10 cm³). 3The mixture was heated from room temperature to 650°C at a rate of 2 mL / min and 5 L / min per 1 kg of mixture, and then heated from 650°C to 740°C at a rate of 0.5°C / min to obtain a lithium-containing transition metal composite oxide (synthesis process).

[0084] Water was added to the obtained lithium-containing transition metal composite oxide at a slurry concentration of 1500 g / L, stirred for 15 minutes, and filtered to obtain a cake-like composition (washing step). Then, powdered lithium methanesulfonate was added to the obtained cake-like composition (addition step). It should be noted that the amount of lithium methanesulfonate added was 0.3% by mass relative to the total mass of the lithium-containing transition metal composite oxide. The obtained cake-like composition was then dried under a vacuum atmosphere at 180°C for 2 hours to obtain the positive electrode active material of Example 1 (drying step). The prepared positive electrode active material was then measured using Fourier transform infrared spectroscopy (FT-IR), and the results confirmed the presence of lithium methanesulfonate on the surface of the secondary particles of the lithium-containing transition metal composite oxide.

[0085] [The production of the positive electrode]

[0086] The above-mentioned positive electrode active material, acetylene black (AB), and polyvinylidene fluoride were mixed in a mass ratio of 86:10:4, and TiO2 was added as an additive. N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare a positive electrode slurry. It should be noted that TiO2 was added at a mass percentage of 0.08% of the total mass of the positive electrode active material. Next, the positive electrode slurry was coated onto a positive electrode core formed from aluminum foil. After drying and compressing the coating, the positive electrode core was cut into specified electrode sizes to obtain a positive electrode with positive electrode slurry layers disposed on both sides of the positive electrode core. It should be noted that an exposed portion of the positive electrode is provided, exposing the surface of the positive electrode core.

[0087] [Preparation of non-aqueous electrolytes]

[0088] 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.

[0089] [Fabrication of the Experimental Battery Cell]

[0090] A positive electrode lead is installed on the exposed portion of the positive electrode, and a negative electrode lead is installed on the lithium metal foil serving as the negative electrode. A polyolefin separator is sandwiched between them to create a spiral-shaped electrode body in which the positive and negative electrodes are wound together. This electrode body is then housed in an outer casing made of aluminum laminate, and after injecting the aforementioned non-aqueous electrolyte, the opening of the outer casing is sealed to obtain the experimental battery cell.

[0091] [Evaluation of reactive resistance]

[0092] For the test battery cells, at a temperature of 25°C, they were charged with a constant current at 0.2C until the battery voltage reached 4.4V (vsLi), and then charged with a constant voltage at 4.4V until the current value reached 0.02C. After a 1-hour pause, they were discharged with a constant current of 0.2C until the voltage reached 2.5V, which was taken as the initial charge-discharge. Then, after a 2-hour pause at a temperature of 10°C, they were charged with a constant voltage of 4.4V at a current equivalent to 0.01C using a Solartron 1255B (manufactured by Solartron). The AC impedance of each battery cell was measured with an applied voltage of 10mV and a measurement frequency range of 0.01~200kHz. The reactive resistance was determined from the Nyquist plot (an arc approximately 1Hz~0.1Hz).

[0093] [Evaluation of Cyclic Characteristics]

[0094] For the test battery cells, at a temperature of 25°C, they were charged at a constant current of 0.2C until reaching 4.4V (vsLi), then charged at a constant voltage of 4.4V until the current value was equivalent to 0.01C. After a 1-hour pause, they were discharged to 2.5V at a constant current of 0.2C, which was considered one cycle. The discharge capacity at 0.2C was measured after 30 cycles. The capacity retention rate was calculated using the following formula.

[0095] Capacity retention = Discharge capacity after 30 cycles / Discharge capacity in the first cycle

[0096] <Examples 2-9>

[0097] In the fabrication of the positive electrode, the composition of the additives was changed as described in Table 1. Otherwise, the test battery cells were fabricated and evaluated in the same manner as in Example 1. It should be noted that the additives were added in the manner described in Table 1, with the mass of the elements listed in Table 1 relative to the total mass of the positive electrode active material.

[0098] <Comparative Example 1>

[0099] In the process of adding positive electrode active material, lithium methanesulfonate was not added, and no additives were added in the preparation of the positive electrode. Otherwise, the test battery cell was prepared and evaluated in the same manner as in Example 1.

[0100] <Comparative Example 2>

[0101] In the fabrication of the positive electrode, no additives were added. Otherwise, the test battery cells were fabricated and evaluated in the same manner as in Example 1.

[0102] <Comparative Example 3>

[0103] In the process of adding positive electrode active material, lithium methanesulfonate was not added. Otherwise, the test battery cells were prepared and evaluated in the same manner as in Example 1.

[0104] <Comparative Example 4>

[0105] In the process of adding positive electrode active material, 10% by mass of lithium succinate solution was added instead of lithium methanesulfonate. The amount of lithium succinate added was set to 0.5% by mass relative to the total mass of lithium transition metal composite oxide. Otherwise, the test battery cell was prepared and evaluated in the same manner as in Example 1.

[0106] The reaction resistance and capacity retention of the test battery cells of the Examples and Comparative Examples are shown in Table 1. Additionally, Table 1 also shows the composition of the lithium transition metal composite oxide, the composition of the added sulfonic acid compound and the additives, and the amounts added. The reaction resistance and capacity retention of the test battery cells of Examples 1-9 and Comparative Examples 1-4 shown in Table 1 are expressed relative to the reaction resistance and capacity retention of the test battery cell of Comparative Example 1, which are set to 100. A smaller reaction resistance value indicates a lower reaction resistance, and a larger capacity retention value indicates better cycle characteristics.

[0107] [Table 1]

[0108]

[0109] As shown in Table 1, the test battery cells of the embodiments showed lower reaction resistance and improved cycle characteristics compared to the test battery cells of the comparative examples. On the other hand, the test battery cell of Comparative Example 2, which had sulfonic acid compounds on the surface of the secondary particles and no additives added, showed lower reaction resistance but worse cycle characteristics compared to the test battery cell of Comparative Example 1. Furthermore, the test battery cell of Comparative Example 3, which had no sulfonic acid compounds on the surface of the secondary particles and had additives added, showed improved cycle characteristics but increased reaction resistance compared to the test battery cell of Comparative Example 1. Additionally, the test battery cell of Comparative Example 4, which had lithium succinate on the surface of the secondary particles instead of sulfonic acid compounds, showed increased reaction resistance compared to the test battery cell of Comparative Example 1. In other words, even if compounds other than sulfonic acid compounds are present on the surface of the secondary particles, the effects of this disclosure cannot be obtained.

[0110] This disclosure is further illustrated by the following embodiments.

[0111] Scheme 1: A positive electrode for a non-aqueous electrolyte secondary battery, which has a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core. The positive electrode mixture layer contains a positive electrode active material and an additive. The positive electrode active material contains a layered lithium-containing transition metal composite oxide. The lithium-containing transition metal composite oxide is represented by the general formula Li x Ni a Co b Mn c M d O 2-y (where 0.8 < x < 1.2, 0.75 ≤ a ≤ 0.95, 0 ≤ b ≤ 0.15, 0 ≤ c ≤ 0.25, 0 ≤ d ≤ 0.10, 0 ≤ y < 0.05, a + b + c + d = 1, and M is at least one element selected from the group consisting of W, Mg, Mo, Nb, Ti, Si, Al, and Zr), and secondary particles formed by aggregation of primary particles, on the surface of the secondary particles, there is a sulfonic acid compound represented by formula (I). The additive contains a compound containing at least one element selected from the group consisting of P, Ca, Sr, B, Zr, Er, Ti, and Al).

[0112]

[0113] (where A is an element of Group 1 or Group 2, R is a hydrocarbon group, and n is 1 or 2).

[0114] Scheme 2: The positive electrode for a non-aqueous electrolyte secondary battery according to Scheme 1, wherein A is an element of Group 1.

[0115] Scheme 3: The positive electrode for a non-aqueous electrolyte secondary battery according to Scheme 1 or 2, wherein A is Li.

[0116] Scheme 4: The positive electrode for a non-aqueous electrolyte secondary battery according to any one of Schemes 1 to 3, wherein R is an alkyl group.

[0117] Scheme 5: The positive electrode for a non-aqueous electrolyte secondary battery according to any one of Schemes 1 to 4, wherein R is a methyl group.

[0118] Scheme 6: The positive electrode for a non-aqueous electrolyte secondary battery according to any one of Schemes 1 to 5, wherein in the positive electrode active material, the amount of the sulfonic acid compound present on the surface of the lithium-containing transition metal composite oxide is 0.05% by mass or more and 1.5% by mass or less relative to the mass of the lithium-containing transition metal composite oxide.

[0119] Option 7: A positive electrode for a non-aqueous electrolyte secondary battery according to any one of Options 1 to 6, wherein, in the positive electrode additive layer, the amount of P, Ca, Sr, B, Zr, Er, Ti and Al contained in the additive is 0.001% by mass and less than 1% by mass relative to the total mass of the positive electrode active material.

[0120] Option 8: A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte as described in any one of Options 1 to 7.

[0121] Explanation of reference numerals in the attached figures

[0122] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive lead, 21 Negative lead, 22 Groove section, 23 Internal terminal board, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket.

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery, comprising a positive electrode core and a positive electrode flux layer formed on the surface of the positive electrode core. The positive electrode mixture layer contains positive electrode active materials and additives. The positive electrode active material comprises a lithium-containing transition metal composite oxide with a layered structure. The lithium-containing transition metal composite oxide is represented by the general formula Li x Ni a Co b Mn c M d O 2-y and is a secondary particle formed by aggregation of primary particles. In the formula, 0.8 < x < 1.2, 0.75 ≤ a ≤ 0.95, 0 ≤ b ≤ 0.15, 0 ≤ c ≤ 0.25, 0 ≤ d ≤ 0.10, 0 ≤ y < 0.05, a + b + c + d = 1, and M is at least one element selected from the group consisting of W, Mg, Mo, Nb, Ti, Si, Al, and Zr. A sulfonic acid compound of formula (I) is present on the surface of the secondary particles. The additive comprises a compound containing at least one element selected from the group consisting of P, Ca, Sr, B, Zr, Er, Ti, and Al. In the formula, A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.

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

3. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein, A is Li.

4. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein, R is an alkyl group.

5. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein, R is a methyl group.

6. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein, In the positive electrode active material, the amount of the sulfonic acid compound present on the surface of the lithium-containing transition metal composite oxide is more than 0.05% by mass and less than 1.5% by mass relative to the mass of the lithium-containing transition metal composite oxide.

7. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein, In the positive electrode compound layer, the amount of P, Ca, Sr, B, Zr, Er, Ti and Al contained in the additive is more than 0.001% by mass and less than 1% by mass relative to the total mass of the positive electrode active material.

8. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 7.

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