Method for producing positive electrode active material

Abstract

A method for producing a positive electrode active material according to one embodiment of the present disclosure is characterized by comprising: a firing step in which an Ni-containing metal compound and an Li compound are mixed and fired; a cooling step in which the fired product is cooled; a water washing step in which a lithium transition metal composite oxide obtained in the cooling step is washed with water; a solid-liquid separation step; a drying step; and an addition step in which a sulfonic acid compound in a liquid or powder state is added to a wet powder or dry powder. The method for producing a positive electrode active material is also characterized in that: in the cooling step, the fired product is cooled at a cooling rate of 60°C / hr or more in an atmosphere having an oxygen concentration of 30% or less; and in the water washing step, with respect to a water washing degree W that is defined by a value obtained by dividing the content of the lithium transition metal composite oxide by the water washing time, if m (mol%) is the ratio of Ni to the total number of moles of metal elements excluding Li, the water washing degree W satisfies W ≥ 400 / (100 - m).

Description

Method for manufacturing positive electrode active material

[0001] This disclosure relates to a method for producing a positive electrode active material.

[0002] Patent Document 1 contains Li ４ Ti ５ O １２ An active material has been proposed in which a surface layer containing a lithium sulfonate salt compound is formed on the surface of lithium titanate particles, which are mainly composed of [a specific component]. Patent Document 1 states that by using this active material as the negative electrode active material, changes in resistance before and after charging and storing the battery can be suppressed.

[0003] Japanese Patent Publication No. 2018-6164

[0004] Lithium transition metal composite oxides used as positive electrode active materials for non-aqueous electrolyte secondary batteries preferably contain Ni, for example, from the viewpoint of increasing the battery capacity. However, when lithium transition metal composite oxides containing Ni are used as positive electrode active materials, the reaction resistance of the positive electrode at low temperatures may increase, for example, and the DC resistance of the battery may increase. The technology described in Patent Document 1 does not take into consideration the reaction resistance of the positive electrode, and there is still much room for improvement.

[0005] A method for producing a positive electrode active material according to one aspect of the present disclosure includes: a firing step of mixing a metal compound containing Ni and a Li compound and firing them in an atmosphere with an oxygen concentration of 90% or more; a cooling step of cooling the fired product obtained in the firing step; a washing step of stirring and washing the slurry obtained by mixing the lithium transition metal composite oxide obtained in the cooling step with water or an aqueous solution; a solid-liquid separation step of separating the slurry into solid and liquid to obtain wet powder; a drying step of drying the wet powder to obtain dry powder; and a liquid or powdery sulfonic acid represented by the following formula (I) to the wet powder or dry powder. The apparatus comprises an addition step of adding a compound, a cooling step in which the mixture is cooled at a cooling rate of 60°C / hr or more in an atmosphere with an oxygen concentration of 30% or less, and a washing step in which the degree of washing W is defined by the value obtained by dividing the content of lithium transition metal composite oxide (g / L) by the washing time (min) (g / (L・min)), and when m [mol%] is the ratio of Ni to the total number of moles of metal elements excluding Li among the metal elements contained in the lithium transition metal composite oxide in a mol% or more, the degree of washing W satisfies W ≥ 400 / (100-m). (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0006] According to a method for producing a positive electrode active material, which is one aspect of this disclosure, a positive electrode active material can be obtained that can increase capacity while reducing the reaction resistance of the positive electrode at low temperatures.

[0007] The present disclosure's method for producing a positive electrode active material comprises: a firing step of mixing a metal compound containing Ni and a Li compound and firing them; a cooling step of cooling the fired product to obtain a lithium transition metal composite oxide; a washing step of washing the lithium transition metal composite oxide with water to obtain a slurry; a solid-liquid separation step of separating the slurry into solid and liquid to obtain a wet powder; a drying step of drying the wet powder to obtain a dry powder; and an addition step of adding a liquid or powdery sulfonic acid compound represented by the following formula (I) to the wet powder or the dry powder. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0008] As will be described in detail later, in the positive electrode active material produced by the method for producing a positive electrode active material of the present disclosure, oxygen deficiency is formed on the surface of a lithium transition metal composite oxide containing Ni. As a result of the study by the present inventors, it has been clarified that when a sulfonic acid compound is added to a lithium transition metal composite oxide in which oxygen deficiency is formed on the surface, the sulfonic acid compound is efficiently adsorbed on the surface of the lithium transition metal composite oxide. Thereby, for example, even when a small amount of a sulfonic acid compound is added, the sulfonic acid compound is likely to be uniformly formed on the surface of the lithium transition metal composite oxide. When the sulfonic acid compound is uniformly formed on the surface of the lithium transition metal composite oxide, the reaction resistance of the positive electrode can be reduced particularly at low temperatures due to the functions of the oxygen deficiency and the sulfonic acid compound present on the surface. Hereinafter, the method for producing a positive electrode active material of the present disclosure will be described in detail for each step.

[0009] [Firing step] In the firing step, a metal compound containing Ni and a Li compound are mixed to obtain a mixture, and the mixture is fired. The metal compound is obtained, for example, by dropping an alkaline solution such as sodium hydroxide while stirring a solution of a metal salt containing Ni and an arbitrary metal element (Co, Mn, Al, etc.), and adjusting the pH to the alkaline side (for example, 8.5 or more and 12.5 or less) to precipitate (co-precipitate) a composite hydroxide containing Ni and an arbitrary metal element, and heat-treating the composite hydroxide. The heat treatment temperature is not particularly limited, but is, for example, in the range of 250°C or higher and 700°C or lower.

[0010] Examples of the Li compound include Li ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２Examples include O, LiH, and LiF. The mixing ratio of the metal compound and the Li compound is preferably such that the molar ratio of the total amount of metal elements in the metal compound to Li is in the range of 1:0.8 to 1:1.2, and is particularly preferably 1:1.0 to 1:1.1.

[0011] Furthermore, when mixing a metal compound containing Ni with a Li compound, a compound containing at least one phosphate, sulfate, oxide, hydroxide, or chloride containing at least one element selected from the group consisting of Mg, Ca, Sr, Nb, B, Mo, Ti, Si, Zr, and Al may be mixed at the same time. Examples of such compounds include MgO and MgCl. ２ CaO, CaCl ２ Ca(OH) ２ SrO, SrCl ２ , Sr(OH) ２ Nb ２ O ５ , Nb(OH) ５ , B ２ O ３ , B(OH) ３ MoO ３ , TiO ２ SiO ２ , ZrSO ４ , ZrO ２ Al ２ O ３ Al(OH) ３ NaAl(OH) ４ AlPO ４ These are some examples. The compounds may be used individually or in combination of two or more. Furthermore, these compounds may be added in the addition step described later.

[0012] Next, the resulting mixture is calcined in an atmosphere with an oxygen concentration of 90% or higher. Calcination in an atmosphere with an oxygen concentration of 90% or higher efficiently promotes the crystal growth of the lithium transition metal composite oxide. As a result, the crystallinity inside the lithium transition metal composite oxide improves, making it easier to achieve higher capacity. The flow rate of the oxygen stream during calcination is, for example, 20 mL / min or more per liter of calcination furnace or 0.3 L or more per 1 kg of mixture.

[0013] The maximum temperature during firing of lithium transition metal composite oxides is preferably between 700°C and 900°C, and more preferably between 720°C and 880°C. In this case, the crystallinity of the lithium transition metal composite oxide is further improved. As a result, it becomes easier to achieve higher battery capacity.

[0014] The heating rate during firing is, for example, 0.2°C / min or more and 4.5°C / min or less, and may be 0.3°C / min or more and 4.0°C / min or less. The holding time at the maximum temperature is preferably 1 hour or more and 10 hours or less, and more preferably 2 hours or more and 8 hours or less. Here, the holding time at the maximum temperature is the time after the maximum temperature is reached and the maximum temperature is maintained.

[0015] The firing conditions in the firing process may be a multi-stage firing process that includes, for example, a first firing process in which the product is fired at a temperature of 300°C or higher and 680°C or lower, and a second firing process in which the product obtained in the first firing process is fired at a maximum temperature exceeding 680°C. In the first firing process, for example, the temperature is raised to a first set temperature of 680°C or lower at a first heating rate of 0.2°C / min or higher and 4.5°C / min or lower. In the second firing process, for example, the temperature is raised to a second set temperature (maximum temperature) of 900°C or lower at a rate of 0.5°C / min or higher and 3.5°C / min or lower. The first heating rate and the second heating rate may be set multiple times for each temperature range, as long as they are within the ranges specified above, and there may be one or more uniform heating zones within each temperature range.

[0016] The holding time at the first set temperature in the first firing process is preferably 5 hours or less, and more preferably 3 hours or less. The holding time at the second set temperature (maximum temperature) in the second firing process is preferably 1 hour or more and 10 hours or less, and more preferably 1 hour or more and 8 hours or less.

[0017] [Cooling Process] In the cooling process, the calcined product (lithium transition metal composite oxide) obtained in the calcination process is cooled at a cooling rate of 60°C / hr or higher in an atmosphere with an oxygen concentration of 30% or less. By cooling at a cooling rate of 60°C / hr or higher in an atmosphere with an oxygen concentration of 30% or less, oxygen vacancies are formed on the surface of the lithium transition metal composite oxide. By forming oxygen vacancies on the surface of the lithium transition metal composite oxide, the electrical conductivity of the particle surface is increased, and in the addition process described later, sulfonic acid compounds are efficiently adsorbed on the surface of the lithium transition metal composite oxide. As a result, sulfonic acid compounds are more easily formed uniformly on the surface of the lithium transition metal composite oxide. The cooling process is generally carried out in the calcination furnace used for calcination, but at least a part of the cooling process may be carried out outside the calcination furnace.

[0018] In the cooling process, it is preferable to cool at a cooling rate of 60°C / hr or higher in an atmosphere with an oxygen concentration of 30% or less, at least in the temperature range from the highest temperature during firing up to 400°C. The temperature range from the highest temperature during firing up to 400°C is a temperature range that greatly affects the formation of oxygen vacancies. Therefore, by cooling at a cooling rate of 60°C / hr or higher in an atmosphere with an oxygen concentration of 30% or less in this temperature range, oxygen vacancies can be formed on the surface of the lithium transition metal composite oxide.

[0019] The oxygen concentration during cooling from 400°C to the final cooling temperature may be 30% or less, or it may be more than 30%. The cooling rate during cooling from 400°C to the final cooling temperature may be 60°C / hr or more, or it may be less than 60°C / hr. Here, the final cooling temperature refers to any temperature below 300°C. The final cooling temperature is not necessarily the temperature at which cooling is completely finished (stopped); it can be any temperature below 300°C. For example, when firing is performed in a firing furnace, the final cooling temperature may be the same as the temperature outside the firing furnace.

[0020] The cooling rate should be 60°C / hr or higher, but may also be 70°C / hr or higher, or 80°C / hr or higher. Increasing the cooling rate makes it easier for oxygen vacancies to form on the surface of the lithium transition metal composite oxide. The cooling rate may also be 300°C / hr or lower, 250°C / hr or lower, or 200°C / hr or lower. If the cooling rate is too high, excessive oxygen vacancies may form in the lithium transition metal composite oxide, reducing its crystallinity and potentially decreasing the battery capacity. Therefore, the cooling rate may be, for example, 60°C / hr or higher and 300°C / hr or lower, 70°C / hr or higher and 250°C / hr or lower, or 80°C / hr or higher and 200°C / hr or lower.

[0021] The oxygen concentration during cooling should be 30% or less, but preferably 25% or less, and more preferably 21% or less. Lowering the oxygen concentration makes it easier for oxygen vacancies to form on the surface of the lithium transition metal composite oxide. Alternatively, the oxygen concentration during cooling may be substantially 0%.

[0022] [Water Washing Process] In the water washing process, the slurry obtained by mixing the lithium transition metal composite oxide obtained in the cooling process with water or an aqueous solution is stirred and washed with water. Before the water washing process, unreacted Li compounds (e.g., lithium carbonate, etc.) used during mixing may remain on the particle surface of the lithium transition metal composite oxide. By performing the water washing process, unreacted Li compounds remaining on the particle surface of the lithium transition metal composite oxide can be removed. As a result, the surface area of ​​the lithium transition metal composite oxide particles increases, which promotes the adhesion of sulfonic acid compounds to the particle surface of the lithium transition metal composite oxide in the addition process in which sulfonic acid compounds are added, as described later.

[0023] Washing is carried out by known methods. For example, lithium transition metal composite oxide and water or aqueous solution are placed in a reaction vessel equipped with a stirring device and stirred.

[0024] Here, the degree of washing W is defined as the value obtained by dividing the content of lithium transition metal composite oxide (g / L) by the washing time (min) (g / (L・min)). The content of lithium transition metal composite oxide refers to the mass (g) of lithium transition metal composite oxide mixed with 1 L of water or aqueous solution. When m [mol%] is the ratio of Ni to the total number of moles of metal elements excluding Li among the metal elements contained in 1 mol% or more of lithium transition metal composite oxide, the washing process is performed so that the degree of washing W satisfies W ≥ 400 / (100-m). By controlling the degree of washing W to be 400 / (100-m) or higher, it is possible to suppress the elution of metal ions in the lithium transition metal composite oxide while maintaining the oxygen vacancies formed on the surface of the lithium transition metal composite oxide. As a result, the sulfonic acid compound is efficiently adsorbed on the surface of the lithium transition metal composite oxide in the addition process described later.

[0025] The content (g / L) of lithium transition metal composite oxide is preferably 500 g / L or more, and more preferably 500 g / L or more and 2000 g / L or less. If the content (g / L) of lithium transition metal composite oxide is less than 500 g / L, there is a risk that metal ions may be excessively washed away from the lithium transition metal composite oxide, which may affect the battery characteristics.

[0026] The washing temperature is, for example, 10°C to 40°C. The washing time is, for example, 5 minutes to 60 minutes. The water or aqueous solution used is not particularly limited, but from the viewpoint of removing unreacted Li compounds remaining on the particle surface of the lithium transition metal composite oxide, for example, water with an electrical conductivity of less than 10 μS / cm is preferred, and water with an electrical conductivity of 1 μS / cm or less is preferred. If an aqueous solution other than water is used for washing, further washing with water may be performed afterward to reduce the amount of impurities contained in the aqueous solution.

[0027] [Solid-Liquid Separation Process] In the solid-liquid separation process, the slurry prepared in the washing process is separated into solid and liquid components to obtain a cake-like wet powder. The method of solid-liquid separation is not particularly limited and is carried out using commonly used equipment and methods. For example, suction filters, centrifuges, filter presses, etc., are used.

[0028] The moisture content of the wet powder obtained by solid-liquid separation is, for example, 3.0% by mass or more. When the moisture content of the wet powder is 3.0% by mass or more, and a sulfonic acid compound is added to the wet powder, the sulfonic acid compound penetrates into the moisture in the wet powder, diffuses throughout the wet powder, and easily adheres to the surface of the lithium transition metal composite oxide. Furthermore, it is preferable that the moisture content of the wet powder obtained by solid-liquid separation is 10% by mass or less. The wet powder is generally transported by belt conveyor to the next process. Therefore, if the moisture content of the wet powder exceeds 10% by mass, the wet powder may adhere to the belt conveyor, reducing its transportability by belt conveyor.

[0029] [Addition Process] In the addition process, a sulfonic acid compound represented by the following formula (I), either in solution or powder form, is added to the wet powder after the solid-liquid separation process, thereby creating a sulfonic acid compound on the surface of the lithium transition metal composite oxide. 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.

[0030] Specific examples of sulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, sodium ethanesulfonate, magnesium methanesulfonate, calcium methanesulfonate, calcium ethanesulfonate, and lithium fluoromethanesulfonate. Among these, at least one selected from the group consisting of lithium methanesulfonate, lithium ethanesulfonate, calcium methanesulfonate, and sodium methanesulfonate is preferred, with lithium methanesulfonate being particularly preferred.

[0031] The solution containing the sulfonic acid compound is not particularly limited as long as it contains the sulfonic acid compound, but it is preferable to dissolve the sulfonic acid compound in an alkaline aqueous solution such as lithium hydroxide or sodium hydroxide. The concentration of the sulfonic acid compound in the solution is, for example, 0.5 mol / L or more and 15 mol / L or less. The pH of the solution containing the sulfonic acid compound may be in the range of 1 or more and 13 or less, and is preferably in the range of 7 or more and 12 or less.

[0032] In the addition step, the amount of sulfonic acid compound added is preferably 0.01% by mass or more and 0.8% by mass or less, more preferably 0.05% by mass or more and 0.7% by mass or less, and even more preferably 0.1% by mass or more and 0.6% by mass or less, relative to the mass of the lithium transition metal composite oxide, from the viewpoint of reducing reaction resistance. As described above, the positive electrode active material of this disclosure has oxygen vacancies formed on the surface of the lithium transition metal composite oxide. As a result, even when the amount of sulfonic acid compound added is small, the sulfonic acid compound is uniformly formed on the surface of the lithium transition metal composite oxide. This makes it possible to reduce the reaction resistance of the positive electrode.

[0033] In the addition step, a sulfonic acid compound in solution or powder form is added to the wet powder and mixed. The mixing method is not particularly limited; for example, the wet powder and the sulfonic acid compound can be mixed by stirring, vibrating, or agitating. A general mixer can be used when mixing the wet powder with the solution containing the sulfonic acid compound. Examples include shaker mixers, Redigge mixers, Julia mixers, V-blenders, rotary drum mixers, container blenders, and Nauta mixers. Mixing suppresses the uneven distribution of the sulfonic acid compound on a portion of the surface of the lithium transition metal composite oxide.

[0034] The above mixing may be performed either after adding the sulfonic acid compound to the wet powder or during the addition. For example, the wet powder may be fed into the mixer, and the solution containing the sulfonic acid compound may be added while mixing in the mixer. Alternatively, for example, the solution containing the sulfonic acid compound may be added to the cake while it is being transported by a conveying device such as a belt conveyor or screw conveyor, and then the cake and the solution containing the sulfonic acid compound may be mixed in a mixer.

[0035] [Drying Process] In the drying process, the wet powder is dried to obtain dry powder (positive electrode active material). In the drying process, for example, from the viewpoint of suppressing deterioration of battery characteristics when used as a positive electrode active material, it is preferable to dry until the moisture content is 1.0% by mass or less. The drying conditions are preferably such that the drying is performed at a temperature of 100°C or higher and 300°C or lower. The drying time is preferably 0.5 hours or more.

[0036] In the above example, the addition step was described as adding a solution or powdered sulfonic acid compound to the wet powder after the solid-liquid separation step. However, the solution or powdered sulfonic acid compound may also be added to the dry powder after the drying step. In that case, a heat treatment may be performed after adding the sulfonic acid compound. Heat treatment facilitates the formation of the sulfonic acid compound on the surface of the lithium transition metal composite oxide. The heating temperature is, for example, 100°C or higher and 300°C or lower.

[0037] The positive electrode active material obtained by this manufacturing method is preferably subjected to a sieving process to remove coarse particles, if necessary. This results in positive electrode active material adjusted to a predetermined particle size. Examples of equipment used for the sieving process include vibrating screens and centrifugal classifiers. Furthermore, the positive electrode active material before the sieving process may be crushed using a jet mill, roll mill, muscoloider, or the like, if necessary.

[0038] A non-aqueous electrolyte secondary battery to which the positive electrode active material produced by the above manufacturing method is applied can be obtained, for example, by housing an electrode body, in which electrodes (positive electrode, negative electrode) and a separator are stacked or wound together, with a non-aqueous electrolyte in a container such as an outer casing or laminate. The positive electrode, negative electrode, separator, and non-aqueous electrolyte will be described below.

[0039] [Positive Electrode] The positive electrode comprises, for example, a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core. Preferably, the positive electrode mixture layer is formed on both sides of the positive electrode core. The positive electrode core can be made of a metal foil that is stable in the positive electrode potential range, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The thickness of the positive electrode core is, for example, 10 μm or more and 30 μm or less.

[0040] The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode core. The positive electrode can be manufactured, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, conductive agent, etc., to the surface of the positive electrode core, drying the coating film, and then rolling it to form the positive electrode mixture layer on both sides of the positive electrode core.

[0041] Examples of conductive agents included in the positive electrode mixture layer include acetylene black (AB), carbon black (CB) such as Ketjenblack, carbon nanotubes (CNT), graphene, and carbon-based particles such as graphite. These may be used individually or in combination of two or more types.

[0042] Examples of binders included in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These may be used individually or in combination of two or more types.

[0043] The positive electrode mixture layer contains a positive electrode active material produced by the manufacturing method described above. This positive electrode active material contains a lithium transition metal composite oxide containing Ni, and a sulfonic acid compound is present on the surface of the lithium transition metal composite oxide.

[0044] Lithium transition metal composite oxides are composed of secondary particles formed by the aggregation of primary particles. The particle size of the primary particles constituting the secondary particles of lithium transition metal composite oxides is, for example, between 0.02 μm and 2 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM). The average particle diameter of the secondary particles of lithium transition metal composite oxides is, for example, between 2 μm and 30 μm. Here, the average particle diameter refers to the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of the secondary particles of lithium transition metal composite oxides can be measured using a laser diffraction particle size distribution analyzer (for example, Microtrac-Bell MT3000II) with water as the dispersion medium.

[0045] Lithium transition metal composite oxides have, for example, a layered structure. Examples of layered structures of lithium transition metal composite oxides include a layered structure belonging to space group R-3m and a layered structure belonging to space group C2 / m. From the viewpoint of increasing capacity and stabilizing the crystal structure, it is preferable that lithium transition metal composite oxides have a layered structure belonging to space group R-3m. The layered structure of lithium transition metal composite oxides may include a transition metal layer and a Li layer.

[0046] Lithium transition metal composite oxides include, for example, those with the general formula Li ｘ Ni ａ Co ｂ Mn ｃ M ｄ O ２－ｙ(In the formula, 0.8 ≤ x ≤ 1.2, 0.80 ≤ a ≤ 0.95, 0 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.2, 0 ≤ d ≤ 0.20, 0 ≤ y ≤ 0.05, a + b + c + d = 1, and M is at least one element selected from the group consisting of Mg, Ca, Sr, Nb, B, Mo, Ti, Si, Al, and Zr). The content of the elements constituting the lithium transition metal composite oxide can be measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron beam microanalyzer (EPMA), or an energy dispersive X-ray spectrometer (EDX), etc.

[0047] The Ni content in the lithium transition metal composite oxide is, for example, 80 mol% or more, and preferably 80 mol% to 95 mol%. By setting the Ni content in the lithium transition metal composite oxide to 80 mol% or more, the battery capacity can be increased. Furthermore, the higher the Ni content, the higher the reaction resistance of the positive electrode at low temperatures tends to be, so the effects of this disclosure are exhibited more significantly.

[0048] The Co content in lithium transition metal composite oxides is between 0 mol% and 20 mol%, and Co is an optional component. In other words, lithium transition metal composite oxides do not need to contain Co. By containing Co, lithium transition metal composite oxides can improve the heat resistance of batteries.

[0049] The Mn content in lithium transition metal composite oxides is between 0 mol% and 20 mol%, and Mn is an optional component. In other words, lithium transition metal composite oxides do not need to contain Mn. The presence of Mn in lithium transition metal composite oxides can stabilize their crystal structure.

[0050] The content of M (where M is at least one element selected from the group consisting of Mg, Ca, Sr, Nb, B, Mo, Ti, Si, Al, and Zr) in lithium transition metal composite oxides is between 0 mol% and 20 mol%, and M is an optional component. In other words, lithium transition metal composite oxides do not need to contain M.

[0051] A sulfonic acid compound represented by the following formula (I) is present on the surface of secondary particles of lithium transition metal composite oxides. 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. Among these, Li or Na is more preferred, and Li is particularly preferred. In addition to Li and Na, A may be an element added during the production of the positive electrode active material (for example, Mg or Ca). The sulfonic acid compound may be scattered so as to cover at least a part of the surface of the secondary particles of the lithium transition metal composite oxide, or it may be present so as to cover the entire surface of the secondary particles. It is preferable that the sulfonic acid compound is directly fixed to the surface of the secondary particles. The sulfonic acid compound may also be present on the surface of the primary particles of the lithium transition metal composite oxide.

[0052] In formula (I), R is preferably an alkyl group. The alkyl group has 5 or fewer carbon atoms, and more preferably 3 or fewer. From the viewpoint of reducing reaction resistance, a suitable example of R is an alkyl group with 3 or fewer carbon atoms, and among these, a methyl group is preferred. In addition, some of the hydrogen atoms bonded to carbon in R may be substituted with fluorine. Furthermore, n in formula (I) is preferably 1.

[0053] Specific examples of sulfonic acid compounds include, as mentioned above, lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, sodium ethanesulfonate, magnesium methanesulfonate, calcium methanesulfonate, calcium ethanesulfonate, and lithium fluoromethanesulfonate. Among these, at least one selected from the group consisting of lithium methanesulfonate, lithium ethanesulfonate, calcium methanesulfonate, and sodium methanesulfonate is preferred, with lithium methanesulfonate being particularly preferred.

[0054] Sulfonic acid compounds reduce the reaction resistance at the positive electrode. This allows for improvements in initial charge-discharge efficiency and increased capacity of the battery, for example. Although sulfonic acid compounds exert this effect even in very small amounts, it is preferable to have them present on the particle surface of the lithium transition metal composite oxide in an amount of 0.01% by mass or more relative to the mass of the composite oxide. Furthermore, from the viewpoint of ensuring battery capacity, the content of the sulfonic acid compound is preferably 0.8% by mass or less relative to the mass of the lithium transition metal composite oxide. Therefore, an example of a suitable range for the amount of sulfonic acid compound is 0.01% by mass or more and 0.8% by mass or less relative to the mass of the lithium transition metal composite oxide.

[0055] The presence of sulfonic acid compounds on the secondary particle surface of lithium transition metal composite oxides can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectrum obtained by FT-IR, the cathode active material containing lithium methanesulfonate shows, for example, 1238 cm⁻¹. －１ , 1175cm －１ , 1065cm －１ 785cm －１ There is an absorption peak in the vicinity. 1238 cm －１ , 1175cm －１ , 1065cm －１ The nearby peak is due to SO stretching vibrations originating from lithium methanesulfonate. 785 cm －１ The nearby peaks are due to CS stretching vibrations originating from lithium methanesulfonate. Furthermore, the presence of cathode active materials containing sulfonic acid compounds other than lithium methanesulfonate can also be confirmed from the absorption peaks originating from sulfonic acid compounds in the infrared absorption spectrum.

[0056] Furthermore, the presence of sulfonic acid compounds can also be confirmed by X-ray photoelectron spectroscopy (XPS). In spectra obtained by XPS, cathode active materials containing lithium methanesulfonate show peaks with binding energies of 165 eV and above, and 170 eV and intensities (c / s) of 200 and above, and between 1000. The presence of sulfonic acid compounds on the secondary particle surface of lithium transition metal composite oxides can also be confirmed by ICP, atomic absorption spectrometry, synchrotron XRD measurements, TOF-SIMS, etc.

[0057] Furthermore, compounds other than sulfonic acid compounds may be present on the surface of the lithium transition metal composite oxide. Examples of compounds other than sulfonic acid compounds include compounds containing at least one of phosphates, sulfates, oxides, hydroxides, and chlorides, which contain at least one element selected from the group consisting of Mg, Ca, Sr, Nb, B, Mo, Ti, Si, Zr, and Al. An example of such a compound is Li ３ PO ４ , CaO, MgO, MgCl ２ CaCl ２ Ca(OH) ２ SrO, SrCl ２ , Sr(OH) ２ Nb ２ O ５ , Nb(OH) ５ , B ２ O ３ , B(OH) ３ MoO ３ , TiO ２ SiO ２ , ZrSO ４ , ZrO ２ Er ２ (SO ４ ) ３ Al ２ O ３ Al(OH) ３ NaAl(OH) ４ AlPO ４ Examples include the above. Furthermore, the compound may exist as a single compound or as two or more compounds.

[0058] Here, the positive electrode active material of this disclosure preferably has a volume resistivity of 20 Ω·cm or less, and more preferably 15 Ω·cm or less, when the positive electrode active material is compacted at 100 MPa. The volume resistivity of the positive electrode active material is thought to correlate with oxygen vacancies, and it is estimated that it will be 20 Ω·cm or less when sufficient oxygen vacancies are formed on the surface of the lithium transition metal composite oxide. This makes it easier for sulfonic acid compounds to be uniformly formed on the surface even with a small amount of lithium transition metal composite oxide. In other words, when the volume resistivity of the positive electrode active material is 20 Ω·cm or less, it becomes easier to achieve both high capacity and low battery resistance at low temperatures. The volume resistivity of the positive electrode active material is measured using a powder resistivity measuring device, with a powder probe unit (four probes) measuring the volume resistivity (Ω·cm) of the sample under a pressure of 100 MPa.

[0059] As described above, the volume resistivity of the positive electrode active material when it is compacted at 100 MPa is an indicator of the amount of oxygen vacancies on the surface of the lithium transition metal composite oxide. Therefore, the volume resistivity of the positive electrode active material can be adjusted by the cooling conditions of the cooling process and the degree of water washing W in the water washing process. Specifically, the volume resistivity of the positive electrode active material can be reduced by decreasing the oxygen concentration during cooling and increasing the cooling rate. In addition, by increasing the degree of water washing W, the oxygen vacancies on the formed active material surface are less likely to be damaged, and the volume resistivity of the positive electrode active material can be reduced.

[0060] [Negative Electrode] The negative electrode may have, for example, a negative electrode core and a negative electrode mixture layer formed on the surface of the negative electrode core, or a metallic Li foil may be used as the negative electrode. Alternatively, the negative electrode may have a negative electrode core, and lithium metal may be deposited on the surface of the negative electrode core by charging. When the negative electrode has a negative electrode mixture layer, it is preferable that the negative electrode mixture layer is formed on both sides of the negative electrode core. The negative electrode core can be made of a metal foil that is stable in the negative electrode potential range, such as copper or a copper alloy, or a film with the metal arranged on its surface. The thickness of the negative electrode core is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode core. The negative electrode can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc., to the surface of the negative electrode core, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0061] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly intercept and release lithium ions, and generally carbon materials such as graphite are used. The graphite may be any of the following: natural graphite such as flake graphite, lump graphite, or clay graphite; lump artificial graphite; or artificial graphite such as graphitized mesophase carbon microbeads. In addition, metals that alloy with Li such as Si and Sn, metal compounds containing Si and Sn, or lithium titanium composite oxides may be used as the negative electrode active material. Furthermore, materials with a carbon coating may also be used. For example, SiO ｘ Si-containing compounds represented by (0.5 ≤ x ≤ 1.6), or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine Si particles are dispersed in a lithium silicate phase represented by (0 < y < 2) may be used in combination with graphite.

[0062] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0063] [Separator] A porous sheet having ion permeability and insulating properties is used as the separator. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator include polyethylene, polyolefins such as polypropylene, and cellulose. The separator may have a single-layer structure or a multi-layer structure. In addition, a heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator.

[0064] A filler layer containing an inorganic filler may be formed at the interface between the separator and at least one of the positive electrode and the negative electrode. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphoric acid compounds. The filler layer can be formed by coating the surface of the positive electrode, the negative electrode, or the separator with a slurry containing the filler.

[0065] [Non-aqueous electrolytes] Non-aqueous electrolytes are ionic conductive (for example, lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0066] A liquid electrolyte (electrolyte solution) includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted solvents include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0067] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0068] Examples of the above ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, etc., and chain ethers such as 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, 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, etc.

[0069] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lithium lower aliphatic carboxylate, LiCl, LiBr, LiI, phosphate, borate, imide salt. Examples of the phosphate include lithium difluorophosphate (LiPO ２ F ２), lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium tetrafluoro(oxalato)phosphate, and the like. Examples of borate salts include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), and the like. Examples of imide salts include lithium bisfluorosulfonyl imide (LiN(FSO ２ ), ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ )), ２ ), lithium trifluoromethanesulfonyl nonafluorobutanesulfonyl imide (LiN(CF ３ SO ２ )(C ４ F ９ SO ２ ​​​​​​​​​​​​​​​​Examples of unsaturated cyclic carbonate esters include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. Unsaturated cyclic carbonate esters may be used individually or in combination of two or more. Some hydrogen atoms in the unsaturated cyclic carbonate esters may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, but it is preferable that it be an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0072] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0073] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanate methylcyclohexane (BIMCH). Examples of sultone compounds include propanesultone and propensultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethylborate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethylphosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethylphosphite and tris(trimethylsilyl)phosphite.

[0074] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0075] The present disclosure will be further illustrated below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0076] <Example 1> [Preparation of positive electrode active material] [Ni obtained by coprecipitation method ０．８５ Co ０．１０ Al ０．０５ ] (OH) ２The composite hydroxide represented by was calcined at 500°C for 8 hours to obtain a metal oxide (metal compound) containing Ni, Co, and Al. Next, lithium hydroxide (LiOH) as a Li compound was mixed in such a way that the molar ratio of Li to the total amount of Ni, Co, and Al was 1:1.03 to obtain a mixture. Then, this mixture was heated from room temperature to 650°C at a heating rate of 2.5°C / min under an oxygen stream with an oxygen concentration of 94%, and then heated from 650°C to 760°C at a heating rate of 1°C / min, and held at 760°C (maximum temperature) for 5 hours to calcinate (calcination process).

[0077] Subsequently, the mixture was cooled from the maximum temperature to 400°C in a nitrogen atmosphere with 0% oxygen concentration at a cooling rate of 60°C / hr (cooling step). Then, the slurry obtained in the cooling step, mixed with pure water, was stirred and a water washing step was performed (water washing step). Here, the lithium transition metal composite oxide content was set to 900 g / L and the water washing time was set to 30 min. The degree of water washing W under these conditions was 30 g / (L·min). The slurry after water washing was subjected to solid-liquid separation using a filter press to obtain wet powder containing lithium transition metal composite oxide (solid-liquid separation step). The moisture content of the obtained wet powder was 4.5% by mass.

[0078] Next, a solution containing a sulfonic acid compound was added to the wet powder and mixed (addition step). The solution containing the sulfonic acid compound was a 33% by mass aqueous solution of lithium methanesulfonate prepared by adding 500 g of 98% methanesulfonic acid to 1.00 kg of pure water and dissolving 220 g of lithium hydroxide monohydrate. The solution containing the sulfonic acid compound was sprayed onto the cake so that the amount of sulfonic acid compound added was 0.5% by mass relative to the mass of the lithium transition metal composite oxide. Next, the wet powder to which the sulfonic acid compound solution had been sprayed was heated to 200°C and dried for 2 hours (drying step). The dried powder was sieved through a 45 μm mesh to remove coarse particles and obtain the positive electrode active material.

[0079] [Preparation of the positive electrode] The above positive electrode active material, acetylene black (AB), and polyvinylidene fluoride were mixed in a mass ratio of 86:10:4, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to a positive electrode core made of aluminum foil, the coating was dried and compressed, and then the positive electrode core was cut to a predetermined electrode size to obtain a positive electrode in which positive electrode slurry layers were arranged on both sides of the positive electrode core.

[0080] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluoride phosphate (LiPF) was added to this mixed solvent. ６ A non-aqueous electrolyte was prepared by dissolving the substance to a concentration of 1.2 mol / liter.

[0081] [Preparation of Test Cell] A lithium metal foil was used as the negative electrode, and the positive and negative electrodes were arranged facing each other via a separator to form an electrode body. This electrode body and the non-aqueous electrolyte were placed in a coin-shaped outer casing, and the opening of the outer casing was sealed with a gasket and a sealing body to produce a test cell (non-aqueous electrolyte secondary battery).

[0082] [Evaluation of Charge / Discharge Efficiency at Low Temperatures] The test cell was charged to 4.3V with a constant current of 0.2C under a temperature environment of -10°C, and then charged again with a constant voltage of 4.3V until the current value was equivalent to 0.01C. After a 1-hour rest period, it was discharged to 2.5V with a constant current of 0.2C. The charge and discharge capacities at this time were measured, and the charge / discharge efficiency of the test cell was calculated using the following formula: Charge / Discharge Efficiency = Discharge Capacity / Charge Capacity

[0083] [Evaluation of reaction resistance at low temperatures] For the test cells, under a temperature environment of -10°C, a Solartron 1255B (manufactured by Solartron Corporation) was used to charge the cells at a constant voltage of 4.4V with a current equivalent to 0.01C. Then, the AC impedance of each cell was measured with an applied voltage of 10mV and a measurement frequency range of 0.01 to 200kHz, and the value of the reaction resistance was determined from the Nyquist plot (circular arc of approximately 1Hz to 0.1Hz).

[0084] <Comparative Example 1> A test cell was prepared and evaluated in the same manner as in Example 1, except that the oxygen concentration conditions in the firing process, the cooling process conditions, and the degree of water washing W in the water washing process were changed in the preparation of the positive electrode active material. Specifically, the oxygen concentration in the firing process was set to 95%. In the cooling process, the material was cooled in an oxygen atmosphere with an oxygen concentration of 100% at a cooling rate of 60°C / hr. In the water washing process, the content of lithium transition metal composite oxide was set to 900 g / L, and the water washing time was set to 15 min. Under these conditions, the degree of water washing W was 60 g / (L・min).

[0085] <Comparative Example 2> A test cell was prepared and evaluated in the same manner as in Example 1, except that the conditions of the cooling process were changed in the preparation of the positive electrode active material. Specifically, in the cooling process, the material was cooled at a cooling rate of 40°C / hr in a nitrogen atmosphere with an oxygen concentration of 0%.

[0086] <Comparative Example 3> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 1, except that the conditions of the cooling process were changed and the addition process was omitted. Specifically, in the cooling process, the material was cooled at a cooling rate of 40°C / hr in a nitrogen atmosphere with an oxygen concentration of 0%.

[0087] <Comparative Example 4> A test cell was prepared and evaluated in the same manner as in Example 1, except that the degree of water washing W in the water washing step and the amount of sulfonic acid compound added in the addition step were changed in the preparation of the positive electrode active material. Specifically, in the water washing step, the content of lithium transition metal composite oxide was set to 700 g / L and the water washing time was set to 45 min. Under these conditions, the degree of water washing W was 16 g / (L·min). In addition, in the addition step, the amount of sulfonic acid compound added was set to 1.2% by mass relative to the mass of lithium transition metal composite oxide.

[0088] Table 1 shows the low-temperature charge-discharge efficiency and reaction resistance of the test cells of Example 1 and Comparative Examples 1-4. Table 1 also shows the volume resistivity of the positive electrode active material of Example 1 and Comparative Examples 1-4 when compacted at 100 MPa. In Table 1, the charge-discharge efficiency and reaction resistance are expressed relatively, with the charge-discharge efficiency and reaction resistance of the test cell of Comparative Example 1 set to 100. A higher charge-discharge efficiency value indicates better efficiency, while a lower reaction resistance value indicates lower resistance. Furthermore, a test cell with superior charge-discharge efficiency can be considered a high-capacity test cell.

[0089]

[0090] As shown in Table 1, the test cell of Example 1 exhibits improved charge-discharge efficiency and reduced reaction resistance compared to the test cells of Comparative Examples 1 to 4. On the other hand, although sulfonic acid compounds are added, the test cell of Comparative Example 1, which is cooled in an oxygen atmosphere, the test cell of Comparative Example 2, which has a low cooling rate, and the test cell of Comparative Example 4, which has a low degree of water washing W, exhibit reduced reaction resistance compared to the test cell of Comparative Example 3, which does not have a sulfonic acid compound added, but still have higher reaction resistance than the test cell of Example 1. Therefore, in order to sufficiently reduce reaction resistance, it is necessary to rapidly cool the cells in an atmosphere with an oxygen concentration of 30% or less and to set the degree of water washing W to a predetermined value or higher.

[0091] <Example 2> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 1, except that the composition of the metal oxide, the conditions of the calcination process, the conditions of the cooling process, the degree of water washing W in the water washing process, and the amount of sulfonic acid compound added in the addition process were changed. Specifically, [Ni obtained by coprecipitation method ０．９０ Co ０．０５ Al ０．０５ ] (OH) ２A composite hydroxide represented by was calcined at 500°C for 2 hours to obtain a metal oxide containing Ni, Co, and Al. During the calcination process, it was held at 750°C (maximum temperature) for 2 hours. In the cooling process, it was cooled at a cooling rate of 120°C / hr in a nitrogen atmosphere with an oxygen concentration of 0%. In the washing process, the content of the lithium transition metal composite oxide was set to 1500 g / L, and the washing time was set to 30 min. The degree of washing W under these conditions was 50 g / (L·min). In the addition process, the amount of sulfonic acid compound added was 0.8% by mass relative to the mass of the lithium transition metal composite oxide.

[0092] <Example 3> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 2, except that the oxygen concentration conditions in the calcination process, the conditions in the cooling process, the degree of water washing W in the water washing process, the amount of sulfonic acid compound added in the addition process, and the timing of the addition of the sulfonic acid compound were changed. Specifically, in the calcination process, the oxygen concentration was set to 96%. In the cooling process, the material was cooled at a cooling rate of 150°C / hr in an atmosphere with an oxygen concentration of 25% and a nitrogen concentration of 75%. In the water washing process, the content of lithium transition metal composite oxide was set to 1500 g / L and the water washing time was set to 15 min. The degree of water washing W under these conditions was 100 g / (L・min). In the addition process, the amount of sulfonic acid compound added was set to 0.3% by mass relative to the mass of lithium transition metal composite oxide. The solution containing the sulfonic acid compound was added to the dry powder after the drying process, and after addition, it was heated in a dryer to 200°C for 2 hours.

[0093] <Example 4> In the preparation of the positive electrode active material, when mixing the metal oxide and the Li compound, Ca(OH) ２ Furthermore, a test cell was prepared and evaluated in the same manner as in Example 3, except that the amount of sulfonic acid compound added in the addition step was changed. Specifically, the total moles of Ni, Co, and Al were mixed to the moles of Li and Ca in a ratio of 1:1.03:0.005. In addition, the amount of sulfonic acid compound added in the addition step was 0.1% by mass relative to the mass of the lithium transition metal composite oxide.

[0094] <Comparative Example 5> A test cell was prepared and evaluated in the same manner as in Example 2, except that the oxygen concentration conditions in the calcination process, the cooling conditions, the degree of water washing W in the water washing process, and the amount of sulfonic acid compound added in the addition process were changed in the preparation of the positive electrode active material. Specifically, the oxygen concentration in the calcination process was set to 95%. In the cooling process, the cell was cooled at a cooling rate of 40°C / hr in an atmosphere with an oxygen concentration of 50% and a nitrogen concentration of 50%. In the water washing process, the content of lithium transition metal composite oxide was set to 1500 g / L and the water washing time was set to 45 min. The degree of water washing W under these conditions was 50 g / (L・min). In the addition process, the amount of sulfonic acid compound added was set to 0.1% by mass relative to the mass of lithium transition metal composite oxide.

[0095] <Comparative Example 6> A test cell was prepared and evaluated in the same manner as in Example 2, except that the oxygen concentration conditions in the firing process, the cooling process conditions, and the degree of water washing W in the water washing process were changed in the preparation of the positive electrode active material. Specifically, the oxygen concentration in the firing process was set to 82%. In the cooling process, the material was cooled at a cooling rate of 150°C / hr in an atmosphere with an oxygen concentration of 25% and a nitrogen concentration of 75%. In the water washing process, the lithium transition metal composite oxide content was set to 1500 g / L and the water washing time was set to 20 min. Under these conditions, the degree of water washing W was 33 g / (L・min).

[0096] <Comparative Example 7> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 4, except that the oxygen concentration conditions in the calcination process, the cooling process conditions, the degree of water washing W in the water washing process, and the amount of sulfonic acid compound added in the addition process were changed. Specifically, in the calcination process, the oxygen concentration was set to 95%. In the cooling process, the cell was cooled at a cooling rate of 40°C / hr in an atmosphere with an oxygen concentration of 50% and a nitrogen concentration of 50%. In the water washing process, the content of lithium transition metal composite oxide was set to 800 g / L, and the water washing time was set to 30 min. Under these conditions, the degree of water washing W was 75 g / (L・min). In the addition process, the amount of sulfonic acid compound added was 0.1% by mass relative to the mass of lithium transition metal composite oxide.

[0097] <Comparative Example 8> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 2, except that the oxygen concentration conditions in the calcination process, the conditions in the cooling process, the degree of water washing W in the water washing process, the amount of sulfonic acid compound added in the addition process, and the timing of the addition of the sulfonic acid compound were changed. Specifically, in the calcination process, the oxygen concentration was set to 95%. In the cooling process, the material was cooled at a cooling rate of 40°C / hr in an atmosphere with an oxygen concentration of 50% and a nitrogen concentration of 50%. In the water washing process, the content of lithium transition metal composite oxide was set to 800 g / L, and the water washing time was set to 20 min. Under these conditions, the degree of water washing W was 27 g / (L・min). In the addition process, the amount of sulfonic acid compound added was set to 0.3% by mass relative to the mass of lithium transition metal composite oxide. The solution containing the sulfonic acid compound was added to the dry powder after the drying process, and after addition, it was heated to 200°C in a dryer for 2 hours.

[0098] Table 2 shows the low-temperature charge-discharge efficiency and reaction resistance of the test cells of Examples 2-4 and Comparative Examples 5-8. Table 2 also shows the volume resistivity of the positive electrode active materials of Examples 2-4 and Comparative Examples 5-8 when compacted at 100 MPa. In Table 2, the charge-discharge efficiency and reaction resistance are expressed relatively, with the charge-discharge efficiency and reaction resistance of the test cell of Comparative Example 5 set to 100.

[0099]

[0100] As shown in Table 2, the test cells of Examples 2 to 4 showed improved charge-discharge efficiency and reduced reaction resistance compared to the test cells of Comparative Examples 5 to 8. This suggests that even when the Ni content is increased, the reaction resistance can be sufficiently reduced by rapidly cooling in an atmosphere with an oxygen concentration of 30% or less and by setting the degree of water washing W to a predetermined value or higher. Furthermore, the test cell of Comparative Example 6, where the oxygen concentration during firing was less than 90%, showed a significant increase in reaction resistance compared to the other test cells. Therefore, it can be said that in order to reduce the reaction resistance, the oxygen concentration during firing needs to be 90% or higher.

[0101] <Example 5> In the preparation of the positive electrode active material, a test cell was prepared and evaluated in the same manner as in Example 1, except that the composition of the metal oxide, the conditions of the calcination process, the conditions of the cooling process, the degree of water washing W in the water washing process, and the amount of sulfonic acid compound added in the addition process were changed. Specifically, [Ni obtained by coprecipitation method ０．９０ Co ０．０５ Mn ０．０５ ] (OH) ２ The composite hydroxide represented by was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Mn. In the calcination process, the mixture was held at 800°C (maximum temperature) for 2 hours to achieve an oxygen concentration of 92%. In the cooling process, the mixture was cooled at a cooling rate of 60°C / hr in a nitrogen atmosphere with an oxygen concentration of 25% and a nitrogen concentration of 75%. In the washing process, the lithium transition metal composite oxide content was set to 1200 g / L, and the washing time was 25 min. The degree of washing W under these conditions was 48 g / (L·min). In the addition process, the amount of sulfonic acid compound added was 0.3% by mass relative to the mass of the lithium transition metal composite oxide.

[0102] <Example 6> A test cell was prepared and evaluated in the same manner as in Example 5, except that the oxygen concentration conditions in the firing process, the cooling process conditions, and the degree of water washing W in the water washing process were changed in the preparation of the positive electrode active material. Specifically, the oxygen concentration in the firing process was set to 91%. In the cooling process, the material was cooled at a cooling rate of 150°C / hr in a nitrogen atmosphere with an oxygen concentration of 0%. In the water washing process, the lithium transition metal composite oxide content was set to 1350 g / L and the water washing time was set to 20 min. Under these conditions, the degree of water washing W was 68 g / (L・min).

[0103] <Comparative Example 9> A test cell was prepared and evaluated in the same manner as in Example 5, except that the oxygen concentration conditions in the firing process, the cooling process conditions, and the degree of water washing W in the water washing process were changed in the preparation of the positive electrode active material. Specifically, the oxygen concentration in the firing process was set to 93%. In the cooling process, the material was cooled in an oxygen atmosphere with an oxygen concentration of 100% at a cooling rate of 60°C / hr. In the water washing process, the lithium transition metal composite oxide content was set to 800 g / L and the water washing time was set to 30 min. Under these conditions, the degree of water washing W was 27 g / (L・min).

[0104] <Comparative Example 10> A test cell was prepared and evaluated in the same manner as in Example 5, except that the oxygen concentration conditions in the firing process, the cooling process conditions, and the degree of water washing W in the water washing process were changed in the preparation of the positive electrode active material. Specifically, the oxygen concentration in the firing process was set to 82%. In the cooling process, the material was cooled in an oxygen atmosphere with an oxygen concentration of 100% at a cooling rate of 60°C / hr. In the water washing process, the content of lithium transition metal composite oxide was set to 1200 g / L, and the water washing time was set to 25 min. Under these conditions, the degree of water washing W was 48 g / (L・min).

[0105] Table 3 shows the low-temperature charge-discharge efficiency and reaction resistance of the test cells for Examples 5 and 6 and Comparative Examples 9 and 10. Table 3 also shows the volume resistivity of the positive electrode active materials for Examples 5 and 6 and Comparative Examples 9 and 10 when compacted at 100 MPa. In Table 3, the charge-discharge efficiency and reaction resistance are expressed relatively, with the charge-discharge efficiency and reaction resistance of the test cell for Comparative Example 9 set to 100.

[0106]

[0107] As shown in Table 3, the test cells of Examples 5 and 6 exhibit improved charge-discharge efficiency and reduced reaction resistance compared to the test cells of Comparative Examples 9 and 10. Therefore, even when the lithium transition metal composite oxide contains Mn instead of Al, the reaction resistance can be sufficiently reduced by rapidly cooling in an atmosphere with an oxygen concentration of 30% or less and by setting the degree of water washing W to a predetermined value or higher.

[0108] This disclosure is further illustrated by the following embodiments. Configuration 1: A firing step of mixing a metal compound containing Ni and a Li compound and firing them in an atmosphere with an oxygen concentration of 90% or more; a cooling step of cooling the fired product obtained in the firing step; a washing step of stirring and washing the slurry obtained by mixing the lithium transition metal composite oxide obtained in the cooling step with water or an aqueous solution; a solid-liquid separation step of separating the slurry into solid and liquid to obtain wet powder; a drying step of drying the wet powder to obtain dry powder; and an additive step of adding a liquid or powdery sulfonic acid compound represented by the following formula (I) to the wet powder or the dry powder. A method for producing a positive electrode active material, comprising: a cooling step, cooling at a cooling rate of 60°C / hr or more in an atmosphere with an oxygen concentration of 30% or less; and a washing step, wherein the degree of washing W is defined by the value obtained by dividing the content (g / L) of the lithium transition metal composite oxide by the washing time (min) (g / (L・min)), and when m [mol%] is the ratio of Ni to the total number of moles of metal elements excluding Li among the metal elements contained in the lithium transition metal composite oxide in a quantity of 1 mol% or more, the degree of washing W satisfies W ≥ 400 / (100-m). (In the formula, A is a group 1 or group 2 element, R is a hydrocarbon group, and n is 1 or 2.) Configuration 2: A method for producing a positive electrode active material according to Configuration 1, wherein in the cooling step, the material is cooled at a cooling rate of 60°C / hr or more in an atmosphere with an oxygen concentration of 30% or less, in a temperature range of at least from the maximum temperature during firing up to 400°C. Configuration 3: A method for producing a positive electrode active material according to Configuration 1 or 2, wherein in the firing step, the maximum temperature during firing is 700°C or higher and 900°C or lower. Configuration 4: A method for producing a positive electrode active material according to any one of Configurations 1 to 3, wherein the Ni content in the lithium transition metal composite oxide is 80 mol% or more with respect to the total number of moles of metal elements excluding Li. Configuration 5: A method for producing a positive electrode active material according to any one of Configurations 1 to 4, wherein in the addition step, the amount of the sulfonic acid compound added is 0.01% by mass or more and 0.8% by mass or less with respect to the mass of the lithium transition metal composite oxide. Configuration 6: A method for producing a positive electrode active material according to any one of Configurations 1 to 5, wherein the volume resistivity of the final obtained positive electrode active material when compacted at 100 MPa is adjusted to be 20 Ω·cm or less.

Claims

1. A firing step comprising: mixing a metal compound containing Ni and a Li compound and firing them in an atmosphere with an oxygen concentration of 90% or more; a cooling step of cooling the fired product obtained in the firing step; a washing step of stirring and washing the slurry obtained by mixing the lithium transition metal composite oxide obtained in the cooling step with water or an aqueous solution; a solid-liquid separation step of separating the slurry into solid and liquid to obtain wet powder; a drying step of drying the wet powder to obtain dry powder; and an addition step of adding a liquid or powdery sulfonic acid compound represented by the following formula (I) to the wet powder or the dry powder, wherein in the cooling step, the mixture is cooled in an atmosphere with an oxygen concentration of 30% or less at a cooling rate of 60°C / hr or more. A method for producing a positive electrode active material, wherein, in the washing step, the degree of washing W is defined by the value obtained by dividing the content (g / L) of the lithium transition metal composite oxide by the washing time (min) (g / (L・min)), and when m [mol%] is the ratio of Ni to the total number of moles of metal elements excluding Li among the metal elements contained in the lithium transition metal composite oxide in a mol% or more, the degree of washing W satisfies W ≥ 400 / (100-m). (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 method for producing a positive electrode active material according to claim 1, wherein in the cooling step, the material is cooled at a cooling rate of 60°C / hr or more in an atmosphere with an oxygen concentration of 30% or less, in a temperature range from the highest temperature during firing up to 400°C.

3. The method for producing a positive electrode active material according to claim 1, wherein the maximum temperature during firing is 700°C or higher and 900°C or lower in the firing step.

4. The method for producing a positive electrode active material according to claim 1, wherein the Ni content in the lithium transition metal composite oxide is 80 mol% or more relative to the total number of moles of metal elements excluding Li.

5. The method for producing a positive electrode active material according to claim 1, wherein in the addition step, the amount of the sulfonic acid compound added is 0.01% by mass or more and 0.8% by mass or less, relative to the mass of the lithium transition metal composite oxide.

6. The method for producing a positive electrode active material according to claim 1, wherein the volume resistivity of the final positive electrode active material when it is compacted at 100 MPa is adjusted to be 20 Ω·cm or less.

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