Method for producing boron-containing transition metal carbonate and method for producing positive electrode active material

Abstract

To provide a method for producing a precursor for a positive electrode active material that does not require heat treatment at a high temperature for introducing boron and that, when used as a positive electrode active material, is highly effective in increasing the capacity of lithium-ion secondary batteries and suppressing gas generation during storage.SOLUTION: A method for producing a boron-containing transition metal carbonate includes: a step of preparing an initial aqueous solution containing an ammonium ion donor and a borate ion donor in a reaction tank; and a step of forming a reaction solution to perform recrystallization by adding to the initial aqueous solution a raw aqueous solution containing transition metals, a boron-source aqueous solution containing an ammonium donor and a borate ion donor, and a pH adjustment solution. The pH of the initial aqueous solution (25°C) is 5.5-7.0. The oxygen concentration in the reaction tank is equal to or less than 5 vol%. The transition metals include Ni. The pH of the boron-source aqueous solution (25°C) is 7.5 to 9.5. The pH adjustment solution contains carbonate. The pH of the reaction solution (25°C) is 5.5-7.0.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a boron-containing transition metal carbonate. The present invention also relates to a method for producing a positive electrode active material using the boron-containing transition metal carbonate.

Background Art

[0002] In recent years, secondary batteries such as lithium-ion secondary batteries have been suitably used for portable power sources such as personal computers and mobile terminals, and power sources for vehicle drive such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] As a positive electrode active material of a lithium-ion secondary battery, lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxide are known. Techniques for introducing boron (B) into a lithium transition metal composite oxide are known (see, for example, Patent Documents 1 to 3). Patent Document 1 describes that the introduction of boron can increase the capacity of a lithium-ion secondary battery. Patent Document 2 describes that the introduction of boron can suppress gas generation during storage of a lithium-ion secondary battery. In Patent Documents 1 and 2, boron is introduced into the positive electrode active material by mixing a lithium transition metal composite oxide and a boron source and performing heat treatment at a high temperature (specifically, several hundred °C). In Patent Document 3, boron is introduced into the hydroxide of the precursor of the positive electrode active material produced by the coprecipitation method.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, introducing boron into the lithium transition metal composite oxide by heat treatment at a high temperature causes a decrease in productivity. Further, since heat treatment at a high temperature consumes a large amount of energy, it causes an increase in carbon dioxide emissions. On the other hand, when boron is introduced into the precursor hydroxide by the coprecipitation method, almost no boron is introduced, and it is difficult to obtain a high effect of improving the characteristics of the lithium ion secondary battery by boron.

[0006] Therefore, an object of the present invention is to provide a method for producing a precursor of a positive electrode active material, which does not require heat treatment at a high temperature for introducing boron, and exhibits a high effect of increasing the capacity of a lithium ion secondary battery and suppressing gas generation during storage when used as the positive electrode active material.

Means for Solving the Problems

[0007] The method for producing a boron-containing transition metal carbonate disclosed herein includes a step of preparing an initial aqueous solution containing an ammonium ion donor and a borate ion donor in a reaction vessel, and adding to the initial aqueous solution a raw material aqueous solution containing a transition metal, a boron source aqueous solution containing an ammonium donor and a borate ion donor, and a pH adjusting solution to form a reaction solution and perform a crystallization reaction. The pH of the initial aqueous solution at 25°C is in the range of 5.5 to 7.0. The oxygen concentration in the reaction vessel is 5% by volume or less. The transition metal contains at least Ni. The pH of the boron source aqueous solution at 25°C is in the range of 7.5 to 9.5. The pH adjusting solution contains a carbonate. The pH of the reaction solution at 25°C is in the range of 5.5 to 7.0.

[0008] According to such a configuration, it is possible to provide a method for producing a precursor of a positive electrode active material, which does not require heat treatment at a high temperature for introducing boron, and exhibits a high effect of increasing the capacity of a lithium ion secondary battery and suppressing gas generation during storage when used as the positive electrode active material.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that matters not mentioned in this specification but necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the relevant field. Also, in the following drawings, members and parts having the same function are denoted by the same reference numerals for explanation. Further, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships. Note that the numerical range expressed as "A to B" in this specification includes A and B.

[0011] Note that in this specification, the "secondary battery" refers to a power storage device that can be repeatedly charged and discharged. Also, in this specification, the "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and realizes charge and discharge by the movement of charges associated with lithium ions between the positive and negative electrodes.

[0012] As shown in Fig. 1, the method for producing a boron-containing transition metal carbonate according to this embodiment includes a step of preparing an initial aqueous solution containing an ammonium ion donor and a borate ion donor in a reaction tank (hereinafter, also referred to as the "initial aqueous solution preparation step") S101, and adding a raw material aqueous solution containing a transition metal, a boron source aqueous solution containing an ammonium donor and a borate ion donor, and a pH adjustment solution to the initial aqueous solution to form a reaction solution and perform a crystallization reaction (hereinafter, also referred to as the "crystallization reaction step") S102. Here, the pH of the initial aqueous solution at 25°C is in the range of 5.5 to 7.0. The oxygen concentration in the reaction tank is 5% by volume or less. The transition metal contains at least Ni. The pH of the boron source aqueous solution at 25°C is in the range of 7.5 to 9.5. The pH adjustment solution contains a carbonate. The pH of the reaction solution at 25°C is in the range of 5.5 to 7.0.

[0013] First, the initial aqueous solution preparation step S101 will be described. As the reaction tank, a known reaction tank used for the crystallization reaction for the synthesis of the precursor of the positive electrode active material can be used. The reaction tank serves as a container for the crystallization reaction and may be equipped with a stirrer such as a stirring blade, a thermometer, a pH meter, a gas introduction pipe, a dropping funnel, etc.

[0014] The type of the ammonium donor is not particularly limited as long as it can supply ammonium ions. Examples of the ammonium donor include ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc. These can be used alone or in combination of two or more.

[0015] The type of the borate ion donor is not particularly limited as long as it can supply borate ions. Examples of the borate ion donor include boric acid, ammonium borate, boron oxide, etc. These can be used alone or in combination of two or more.

[0016] The ammonium donor and the borate ion donor may each be used as they are for the preparation of the initial aqueous solution, or may be used in the form of an aqueous solution for the preparation of the initial reaction solution. The ammonium donor is preferably ammonia, and it is preferably used in the form of aqueous ammonia.

[0017] The preparation of the initial aqueous solution can be carried out according to a known method. For example, water is supplied to a reaction tank, and the ammonium donor and the borate ion donor are added thereto, and the ammonium donor and the borate ion donor are dissolved in water. Alternatively, for example, it can be carried out by adding an aqueous solution of the ammonium donor and an aqueous solution of the borate ion donor to a reaction tank with or without water supplied.

[0018] The preparation of the initial aqueous solution is carried out so that the pH at 25°C thereof is 5.5 to 7.0. The pH can be adjusted by adjusting the amounts of the ammonium donor and the borate ion donor. Also, an acid (e.g., sulfuric acid, nitric acid, etc.) may be used for the adjustment of the pH. The anion of the acid is preferably the same as the anion of the water-soluble salt of the transition metal described later. In the present specification, the pH at 25°C of a liquid can be measured using a pH meter.

[0019] Here, an aqueous boron source solution containing an ammonium donor and a borate ion donor used in the subsequent crystallization reaction step S102 may be prepared in advance and used for the preparation of the initial aqueous solution. In this case, the implementation of the production method of the present embodiment becomes simple. Here, the pH at 25°C of the aqueous boron source solution is 7.5 to 9.5. Therefore, for example, the aqueous boron source solution is supplied to a reaction tank with or without water supplied, and an acid is used to adjust the pH of the initial aqueous solution to be within the range of 5.5 to 7.0.

[0020] On the one hand, in the initial aqueous solution preparation step S101, the oxygen concentration in the reaction tank is adjusted to 5% by volume or less. The adjustment of the oxygen concentration can be carried out according to a known method. The oxygen concentration can be adjusted, for example, by introducing an inert gas such as nitrogen or argon into the reaction tank. The oxygen concentration in the reaction tank is preferably 4.5% by volume or less.

[0021] In the above manner, the initial aqueous solution preparation step S101 can be carried out. Subsequently, the crystallization reaction step S102 will be described.

[0022] The raw material aqueous solution containing a transition metal used in the crystallization reaction step S102 can be prepared according to a known method. For example, it can be prepared by dissolving a water-soluble salt of a transition metal (e.g., sulfate, nitrate, halide, etc. of the transition metal) in water.

[0023] Here, the boron-containing transition metal carbonate is a precursor of a lithium transition metal composite oxide which is a positive electrode active material (especially a lithium transition metal composite oxide having a layered structure). Here, when the lithium transition metal composite oxide contains Ni, the high-capacity effect of the lithium-ion secondary battery and the gas generation suppression effect during storage are highly exhibited. Therefore, in the present embodiment, the transition metal contains at least Ni.

[0024] In addition, the transition metal may contain a transition metal other than Ni (especially a transition metal used in a lithium transition metal composite oxide known as a positive electrode active material). Since the lithium transition metal composite oxide can impart excellent characteristics to the lithium-ion secondary battery, it is preferably a lithium nickel cobalt manganese composite oxide. Therefore, the transition metal preferably contains at least Ni, Co, and Mn. At this time, the transition metal may further contain a transition metal element other than Ni, Co, and Mn.

[0025] Alternatively, the lithium transition metal composite oxide may be a lithium nickel cobalt aluminum-based composite oxide. Thus, the transition metal may contain at least Ni, Co, and Al. At this time, the transition metal may further contain transition metal elements other than Ni, Co, and Al.

[0026] When there are two or more transition metals, the raw material aqueous solution may be prepared for each type of transition metal, or may be prepared as a single raw material aqueous solution containing two or more transition metals.

[0027] The boron source aqueous solution containing an ammonium donor and a borate ion donor can be prepared by dissolving the aforementioned ammonium donor and the aforementioned borate ion donor in water so that the pH at 25 °C is 7.5 to 9.5. One or both of the ammonium donor and the borate ion donor may be prepared in the form of an aqueous solution and mixed. Since the pH of the boron source aqueous solution at 25 °C is within this range, the boron source can be sufficiently supplied to the reaction solution in an ionic state (that is, as borate ions). Since the high-capacity effect of the lithium-ion secondary battery and the gas generation suppression effect during storage are higher, the pH of the boron source aqueous solution at 25 °C is preferably 7.5 to 8.5.

[0028] Also, a pH adjuster containing a carbonate is used. By using a pH adjuster containing a carbonate, the precursor of the positive electrode active material can be precipitated as a carbonate. The pH adjuster is typically an aqueous solution of a carbonate. Examples of carbonates include sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, etc. Among them, sodium carbonate is preferred.

[0029] An aqueous raw material solution containing a transition metal, an aqueous boron source solution, and a pH adjustment solution are added to an initial aqueous solution to form a reaction solution. At this time, the pH of the reaction solution at 25°C is controlled within the same range of 5.5 to 7.0 as that of the initial aqueous solution. When the pH of the reaction solution is within this range, boron can be efficiently introduced into the precipitated transition metal carbonate, and the high-capacity effect of the lithium-ion secondary battery and the gas generation suppression effect during storage can be highly exerted. The pH of the reaction solution at 25°C is preferably 5.7 to 6.7. Incidentally, the pH of the reaction solution at 25°C can be adjusted by controlling the addition rates of the aqueous raw material solution containing a transition metal, the aqueous boron source solution, and the pH adjustment solution, etc.

[0030] Incidentally, at this time, when it is desired to introduce a metal other than the transition metal (e.g., an alkaline earth metal, etc.) into the boron-containing lithium transition metal composite oxide, an aqueous solution containing a metal other than the transition metal may be added. The metal other than the transition metal may be added to the aqueous raw material solution containing the transition metal.

[0031] The temperature of the reaction solution is not particularly limited as long as the crystallization reaction can be carried out, and the reaction solution may or may not be heated. It is preferable not to heat the reaction solution. The temperature of the reaction solution is, for example, above 0°C and 45°C or lower, preferably 15°C to 40°C, and more preferably 25°C to 40°C.

[0032] The crystallization reaction time may be appropriately determined according to the reaction scale, the desired particle size of the boron-containing transition metal carbonate, etc. The crystallization reaction time is, for example, 0.5 hour to 24 hours, preferably 5 hours to 20 hours.

[0033] Incidentally, also in the crystallization reaction step S102, the oxygen concentration in the reaction tank is 5% by volume or less.

[0034] By performing the crystallization reaction in this way, boron-containing transition metal carbonate can be precipitated. The precipitated boron-containing transition metal carbonate can be recovered according to a known method. For example, the precipitated boron-containing transition metal carbonate can be recovered by a solid-liquid separation method such as filtration, and washing and drying may be performed at this time.

[0035] The boron-containing transition metal carbonate is typically obtained in the form of secondary particles in which primary particles are aggregated. In the obtained boron-containing transition metal carbonate, boron exists not only on the surface of the secondary particles but also inside the secondary particles. Also, the amount of boron present inside the secondary particles can be higher than that on the surface of the secondary particles.

[0036] The boron-containing transition metal carbonate preferably has a composition represented by the following formula (I). Ni (1-x-y-z-a) Co x Mn y B z A a CO 3 ··· (I)

[0037] In the formula, x, y, z, and a each satisfy 0 ≦ x < 0.5, 0 ≦ y < 0.5, 0 < z < 0.1, and 0 ≦ a ≦ 0.05. A is at least one selected from the group consisting of Mg, Ca, V, Cr, Al, Ti, Zr, Nb, Mo, and W. x preferably satisfies 0.05 ≦ x ≦ 0.35, and y preferably satisfies 0.05 ≦ y ≦ 0.35.

[0038] Using the obtained boron-containing transition metal carbonate, a boron-containing lithium transition metal composite oxide can be produced according to a known method. By using the boron-containing lithium transition metal composite oxide as a positive electrode active material in a lithium ion secondary battery, the capacity of the lithium ion secondary battery can be increased and gas generation during storage can be suppressed.

[0039] Therefore, from another aspect, the method for manufacturing a positive electrode active material disclosed herein includes a step of synthesizing a boron-containing transition metal carbonate by the above method (hereinafter, also referred to as "carbonate synthesis step"), a step of mixing the boron-containing transition metal carbonate and a lithium compound to obtain a raw material mixture (hereinafter, also referred to as "mixing step"), and a step of firing the raw material mixture at 650°C to 1000°C for 3 hours to 8 hours (hereinafter, also referred to as "firing step").

[0040] The carbonate synthesis step can be carried out by implementing the method for manufacturing a boron-containing transition metal carbonate according to the above-described embodiment.

[0041] Here, before the mixing step, a step of heat-treating the boron-containing transition metal carbonate at 100°C to 500°C may be carried out. By this heat treatment, moisture contained in the boron-containing transition metal carbonate can be removed, thereby suppressing the occurrence of variations in the composition of the obtained positive electrode active material.

[0042] The lithium compound used in the mixing step serves as the Li source for the positive electrode active material. As the lithium compound, for example, compounds that are converted into oxides by firing, such as lithium carbonate, lithium nitrate, and lithium hydroxide, can be used.

[0043] The mixing ratio of the lithium source compound and the boron-containing transition metal carbonate may be appropriately determined according to the composition of the desired positive electrode active material. For example, in the positive electrode active material, the ratio of Li to metals other than Li is preferably 0.95 to 1.15. Therefore, preferably, the molar ratio of Li contained in the lithium source compound to the metals contained in the boron-containing transition metal carbonate is mixed so as to be 0.95 to 1.15.

[0044] The mixing step can be carried out according to a known method. For example, it can be carried out by mixing the boron-containing transition metal carbonate and the lithium compound using a mixing device such as a shaker mixer, V blender, ribbon mixer, Julia mixer, or Lodige mixer.

[0045] When it is desired to introduce a metal other than Li (also referred to as other metals) that is not contained in the boron-containing transition metal carbonate into the positive electrode active material, in the mixing step, other metal sources may be mixed according to a known method.

[0046] The firing step can be carried out according to a known method. For example, the firing of the mixture can be carried out using, for example, a batch-type electric furnace, a continuous-type electric furnace, etc. As the firing atmosphere, an oxidizing atmosphere is preferable from the viewpoint of suppressing oxygen defects in the positive electrode active material. Preferably, the oxidizing atmosphere is an atmosphere having an oxygen concentration of 10% by volume or more, and may be an air atmosphere or an oxygen atmosphere (that is, an atmosphere in which the oxygen concentration is increased compared to air). The firing temperature is 650°C to 1000°C, preferably 700°C to 900°C. The firing time is 3 hours to 8 hours, preferably 3.5 hours to 7.5 hours.

[0047] In the above manner, a boron-containing lithium transition metal composite oxide as a positive electrode active material can be obtained. The boron-containing lithium transition metal composite oxide is typically obtained in the form of secondary particles in which primary particles are aggregated. In the obtained boron-containing lithium transition metal composite oxide, boron exists not only on the surface of the secondary particles but also inside the secondary particles. Also, the amount of boron present inside the secondary particles can be higher than that on the surface of the secondary particles.

[0048] The positive electrode active material preferably has a composition represented by the following formula (II). Li d Ni (1-x-y-z-a) Co x Mn y B z A a O 2 ··· (II)

[0049] In the formula, d, x, y, z, and a satisfy 0.95 ≦ d ≦ 1.15, 0 ≦ x < 0.5, 0 ≦ y < 0.5, 0 < z < 0.1, and 0 ≦ a ≦ 0.05, respectively. A is at least one selected from the group consisting of Mg, Ca, V, Cr, Al, Ti, Zr, Nb, Mo, and W. x preferably satisfies 0.05 ≦ x ≦ 0.40, and y preferably satisfies 0.05 ≦ y ≦ 0.40.

[0050] The average particle diameter of the positive electrode active material is not particularly limited. For example, it is 0.05 μm or more and 25 μm or less, preferably 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 15 μm or less. Therefore, after the firing step, a step of adjusting the particle diameter of the boron-containing lithium transition metal composite oxide may be further performed. The adjustment of the particle diameter can be performed by a known method (e.g., crushing, classification, etc.). In this specification, the "average particle diameter" refers to the median diameter (D50). Therefore, in the volume-based particle size distribution based on the laser diffraction / scattering method, it means the particle diameter corresponding to 50 volume% of the cumulative frequency from the side of fine particles with a small particle diameter.

[0051] According to the positive electrode active material obtained by the above manufacturing method, a high capacity and high gas generation suppression performance during storage can be imparted to the lithium ion secondary battery. Therefore, the positive electrode active material obtained by the above manufacturing method is preferably a positive electrode active material of a lithium ion secondary battery. The lithium ion secondary battery can be configured according to a known method using the positive electrode active material obtained by the above manufacturing method.

[0052] Hereinafter, a configuration example of a lithium ion secondary battery using the positive electrode active material obtained by the above manufacturing method will be described with reference to FIGS. 2 and 3.

[0053] The lithium-ion secondary battery 100 shown in FIG. 2 is a sealed battery constructed by housing a flat wound electrode body 20 and a non-aqueous electrolyte 80 in a flat rectangular battery case (i.e., an exterior container) 30. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin safety valve 36 configured to release the internal pressure of the battery case 30 when the internal pressure rises above a predetermined level. Further, the battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte 80. The positive electrode terminal 42 is electrically connected to a positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector plate 44a. As the material of the battery case 30, for example, a lightweight and highly thermally conductive metal material such as aluminum is used. Note that FIG. 2 does not accurately represent the amount of the non-aqueous electrolyte 80.

[0054] As shown in FIGS. 2 and 3, the wound electrode body 20 has a configuration in which a positive electrode sheet 50 and a negative electrode sheet 60 are overlapped via two long separator sheets 70 and wound in the longitudinal direction. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (here, both sides) of a long positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (here, both sides) of a long negative electrode current collector 62.

[0055] The positive electrode 50 has a non-positive electrode active material layer formation portion 52a where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed. The negative electrode 60 has a non-negative electrode active material layer formation portion 62a where the negative electrode current collector 62 is exposed without the negative electrode active material layer 64 being formed. The non-positive electrode active material layer formation portion 52a and the non-negative electrode active material layer formation portion 62a are formed so as to protrude outward from both ends in the winding axis direction (i.e., the sheet width direction orthogonal to the longitudinal direction) of the wound electrode body 20. A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are joined to the non-positive electrode active material layer formation portion 52a and the non-negative electrode active material layer formation portion 62a, respectively.

[0056] As the positive electrode current collector 52, a known positive electrode current collector used in a lithium ion secondary battery may be used. Examples thereof include a sheet or foil made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.). As the positive electrode current collector 52, an aluminum foil is preferable.

[0057] The dimensions of the positive electrode current collector 52 are not particularly limited and may be appropriately determined according to the battery design. When an aluminum foil is used as the positive electrode current collector 52, its thickness is not particularly limited, but is, for example, 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0058] The positive electrode active material layer 54 contains a positive electrode active material. As the positive electrode active material, the positive electrode active material obtained by the production method according to the above-described embodiment is used. The positive electrode active material layer 54 may contain other positive electrode active materials in addition to the positive electrode active material obtained by the production method according to the above-described embodiment, as long as the effects of the present invention are not inhibited.

[0059] The positive electrode active material layer 54 may contain components other than the positive electrode active material, such as trilithium phosphate, a conductive material, a binder, etc. As the conductive material, for example, carbon black such as acetylene black (AB) and other carbon materials (e.g., graphite, carbon nanotubes, etc.) can be preferably used. As the binder, for example, polyvinylidene fluoride (PVDF) etc. can be used.

[0060] The content of the positive electrode active material in the positive electrode active material layer 54 (that is, the content of the positive electrode active material with respect to the total mass of the positive electrode active material layer 54) is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more and 99% by mass or less, and still more preferably 85% by mass or more and 98% by mass or less. The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less. The content of the binder in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 0.8% by mass or more and 10% by mass or less.

[0061] The thickness of the positive electrode active material layer 54 is not particularly limited, but for example, it is 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less.

[0062] In the non-forming portion 52a of the positive electrode active material layer of the positive electrode sheet 50, an insulating protective layer (not shown) containing insulating particles may be provided at a position adjacent to the positive electrode active material layer 54. This protective layer can prevent a short circuit between the non-forming portion 52a of the positive electrode active material layer and the negative electrode active material layer 64.

[0063] As the negative electrode current collector 62, a known negative electrode current collector used in a lithium ion secondary battery may be used. Examples thereof include a sheet or foil made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.). As the negative electrode current collector 62, a copper foil is preferable.

[0064] The dimensions of the negative electrode current collector 62 are not particularly limited and may be appropriately determined according to the battery design. When a copper foil is used as the negative electrode current collector 62, its thickness is not particularly limited, but for example, it is 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0065] The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, for example, carbon materials such as graphite, hard carbon, and soft carbon can be used. The graphite may be natural graphite or artificial graphite, or may be amorphous carbon-coated graphite in a form in which the graphite is coated with an amorphous carbon material.

[0066] The average particle diameter (median diameter: D50) of the negative electrode active material is not particularly limited, but for example, it is 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 25 μm or less, and more preferably 5 μm or more and 20 μm or less. The average particle diameter (D50) of the negative electrode active material can be obtained, for example, by the laser diffraction scattering method.

[0067] The negative electrode active material layer 64 may contain components other than the active material, such as a binder, a thickener, etc. As the binder, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), etc. may be used. As the thickener, for example, carboxymethyl cellulose (CMC), etc. may be used.

[0068] The content of the negative electrode active material in the negative electrode active material layer 64 is preferably 90% by mass or more, more preferably 95% by mass or more and 99% by mass or less. The content of the binder in the negative electrode active material layer 64 is preferably 0.1% by mass or more and 8% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less. The content of the thickener in the negative electrode active material layer 64 is preferably 0.3% by mass or more and 3% by mass or less, more preferably 0.5% by mass or more and 2% by mass or less.

[0069] The thickness of the negative electrode active material layer 64 is not particularly limited, but for example, it is 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less.

[0070] Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0071] The thickness of the separator 70 is not particularly limited, but for example, it is 5 μm or more and 50 μm or less, preferably 10 μm or more and 30 μm or less.

[0072] The non-aqueous electrolyte 80 typically contains a non-aqueous solvent and a supporting salt (electrolyte salt). As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, lactones, etc. used in the electrolytes of general lithium-ion secondary batteries can be used without particular limitation. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), etc. Such non-aqueous solvents can be used alone or in appropriate combinations of two or more kinds.

[0073] As the supporting salt, for example, lithium salts such as LiPF 6 , LiBF 4 , lithium bis(fluorosulfonyl)imide (LiFSI), etc. (preferably LiPF 6 ) can be preferably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0074] In addition, as long as the effects of the present invention are not significantly impaired, the non-aqueous electrolyte 80 may contain components other than the above-described components, for example, film-forming agents such as vinylene carbonate (VC) and oxalato complex; gas generators such as biphenyl (BP) and cyclohexylbenzene (CHB); thickeners; and various other additives.

[0075] The lithium-ion secondary battery 100 configured as described above has a high capacity and suppresses gas generation during storage. The lithium-ion secondary battery 100 can be used for various applications. Specific applications include portable power sources such as personal computers, portable electronic devices, and mobile terminals; vehicle drive power sources such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); and storage batteries for small power storage devices. Among them, a vehicle drive power source is preferred. The lithium-ion secondary battery 100 can typically be used in the form of a battery pack formed by connecting a plurality of batteries in series and / or in parallel.

[0076] Note that, as an example, a rectangular lithium-ion secondary battery 100 including a flat wound electrode body 20 has been described. However, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a lithium-ion secondary battery including a laminated electrode body (i.e., an electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated). The laminated electrode body may include a plurality of separators such that one separator is interposed between each of the positive electrode and the negative electrode, and the positive electrode and the negative electrode may be alternately laminated while one separator is folded.

[0077] Also, the lithium-ion secondary battery 100 can be configured as a coin-type lithium-ion secondary battery, a button-type lithium-ion secondary battery, a cylindrical lithium-ion secondary battery, or a laminated case-type lithium-ion secondary battery.

[0078] On the other hand, a all-solid-state lithium-ion secondary battery can also be constructed using the positive electrode active material obtained by the manufacturing method according to the present embodiment and using a solid electrolyte instead of the non-aqueous electrolyte 80 according to a known method.

[0079] Hereinafter, examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such examples. In the following description, "pH" is a value based on a liquid temperature of 25°C.

[0080] [Example 1] <Preparation of Boron-Containing Transition Metal Carbonate> As an ammonium donor, aqueous ammonia with a concentration of 1% by mass was prepared. As a boric acid ion donor, an aqueous boric acid solution with a concentration of 0.3 mol% was prepared. This aqueous ammonia and the aqueous boric acid solution were mixed so that the pH became 8.2 to prepare a boron source aqueous solution.

[0081] The boron source aqueous solution was supplied into a 5 L reaction tank and stirred at 600 rpm. Also, nitrogen was introduced into the reaction tank to adjust the oxygen concentration in the reaction tank to 3% by volume. Subsequently, using sulfuric acid with a concentration of 1 mol%, the pH of the boron source aqueous solution was adjusted to 6.5 to obtain an initial aqueous solution.

[0082] Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water at a molar ratio of 1:1:1 to prepare a raw material metal aqueous solution with a concentration of 1 mol / L. As a pH adjusting solution, an aqueous sodium carbonate solution with a concentration of 0.5 mol / L was prepared.

[0083] Into the reaction tank, the above-prepared raw material metal aqueous solution, the pH adjusting solution, and the boron source aqueous solution were supplied in a volume ratio of 1:1:1 at appropriate times, and a crystallization reaction was carried out for 10 hours under the condition that the pH was 6.5. The obtained product was washed with water, filtered, and dried to obtain a powdery boron-containing transition metal carbonate (that is, boron-containing nickel cobalt manganese composite carbonate).

[0084] <Preparation of Cathode Active Material> The above-prepared boron-containing nickel cobalt manganese composite carbonate and a lithium compound were mixed so that the total number of moles of nickel, cobalt, and manganese and the number of moles of lithium were 1:1.1. The obtained mixture was calcined in a firing furnace at 780 °C for 6 hours in an oxidizing atmosphere. Thereby, a boron-containing lithium nickel cobalt manganese composite oxide, which is a cathode active material, was obtained.

[0085] [Example 2] An initial aqueous solution was obtained in the same manner as in Example 1, except that the stirring speed was changed to 700 rpm and the pH of the boron source aqueous solution was changed to the value shown in Table 2. A crystallization reaction was carried out in the same manner as in Example 1, except that the obtained initial aqueous solution was used, to obtain a powdery boron-containing transition metal carbonate.

[0086] Using the obtained boron-containing transition metal carbonate, a boron-containing lithium nickel cobalt manganese composite oxide, which is a positive electrode active material, was obtained in the same manner as in Example 1, except that the firing temperature and firing time were changed to the temperature and time shown in Table 2.

[0087] [Example 3] An initial aqueous solution was obtained in the same manner as in Example 1, except that the stirring speed was changed to 700 rpm and the pH of the boron source aqueous solution, the oxygen concentration in the reaction layer, and the pH of the initial aqueous solution were changed to the values shown in Table 2. Using the obtained initial aqueous solution, a crystallization reaction was carried out in the same manner as in Example 1, except that the pH of the reaction solution during the crystallization reaction was changed to the value shown in Table 2 and the reaction time was changed to 11 hours, to obtain a powdery boron-containing transition metal carbonate.

[0088] The prepared boron-containing nickel cobalt manganese composite carbonate and a lithium compound were mixed so that the total molar number of nickel, cobalt, and manganese and the molar number of lithium were 1:1.2. A boron-containing lithium nickel cobalt manganese composite oxide, which is a positive electrode active material, was obtained by firing in the same manner as in Example 1, except that the firing temperature and firing time were changed to the temperature and time shown in Table 2.

[0089] [Example 4] An initial aqueous solution was obtained in the same manner as in Example 1, except that the stirring speed was changed to 700 rpm and the pH of the boron source aqueous solution was changed to the value shown in Table 2.

[0090] Nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were dissolved in water at a molar ratio of 55.9:19.9:19.9:0.3 to prepare a raw material metal aqueous solution with a concentration of 1 mol / L. A crystallization reaction was carried out in the same manner as in Example 1 except that this raw material metal aqueous solution and the obtained initial aqueous solution were used, and a powdery boron-containing transition metal carbonate was obtained.

[0091] Using the obtained boron-containing transition metal carbonate, a boron-containing lithium nickel cobalt manganese composite oxide, which is a positive electrode active material, was obtained in the same manner as in Example 1 except that the firing temperature was changed to the temperature and time shown in Table 2.

[0092] [Comparative Example 1] An initial aqueous solution was obtained in the same manner as in Example 1 except that the stirring speed was changed to 700 rpm and the pH of the boron source aqueous solution, the oxygen concentration in the reaction layer, and the pH of the initial aqueous solution were changed to the values shown in Table 2. Using the obtained initial aqueous solution, a crystallization reaction was carried out in the same manner as in Example 1 except that the pH of the reaction solution during the crystallization reaction was changed to the value shown in Table 2 and the reaction time was changed to 11 hours, and a powdery boron-containing transition metal carbonate was obtained.

[0093] Using the obtained boron-containing transition metal carbonate, a boron-containing lithium nickel cobalt manganese composite oxide, which is a positive electrode active material, was obtained in the same manner as in Example 1.

[0094] [Comparative Examples 2 to 5] An initial aqueous solution was obtained in the same manner as in Example 1 except that the stirring speed was changed to 700 rpm and the pH of the boron source aqueous solution, the oxygen concentration in the reaction layer, and the pH of the initial aqueous solution were set to the values shown in Table 2. Using the obtained initial aqueous solution, a crystallization reaction was carried out in the same manner as in Example 1 except that the pH of the reaction solution during the crystallization reaction was set to the value shown in Table 2, and a powdery boron-containing transition metal carbonate was obtained.

[0095] Using the obtained boron-containing transition metal carbonate, a boron-containing lithium nickel cobalt manganese composite oxide, which is a positive electrode active material, was obtained in the same manner as in Example 1, except that the firing temperature and firing time were set to the temperature and time shown in Table 2.

[0096] <ICP Analysis of Boron-Containing Transition Metal Carbonate> The compositions of the boron-containing transition metal carbonates obtained in Examples 1 to 4 and Comparative Example 1 were analyzed using a commercially available ICP emission spectrometer. As a result, the atomic ratios of Ni, Co, Mn, and B were as shown in Table 1 below. In Example 4, the atomic ratio of Zr was also determined.

[0097]

Table 1

[0098] <Fabrication of Lithium-Ion Secondary Battery for Evaluation> The prepared positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed with N-methylpyrrolidone (NMP) at a mass ratio of active material:AB:PVdF = 100:1:1 to prepare a positive electrode slurry. This positive electrode slurry was applied to both sides of an aluminum foil with a thickness of 15 μm. At this time, an uncoated portion of the positive electrode slurry was provided on the aluminum foil as a lead connection portion. The applied slurry was dried to form a positive electrode active material layer. After roll pressing the positive electrode active material layer, the obtained sheet was processed into a predetermined size to obtain a positive electrode sheet.

[0099] Graphite (C) as a negative electrode active material, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) were mixed with water at a mass ratio of C:CMC:SBR = 98:1:1 to prepare a negative electrode slurry. This negative electrode slurry was applied to both sides of a copper foil. At this time, an uncoated portion of the negative electrode slurry was provided on the copper foil as a lead connection portion. The applied slurry was dried to form a negative electrode active material layer. After roll pressing the negative electrode active material layer, the obtained sheet was processed into a predetermined size to obtain a negative electrode sheet.

[0100] Leads were attached to each of the above-prepared positive and negative electrodes. A single-layer separator made of polypropylene was prepared. The positive electrode and the negative electrode were laminated via the separator to fabricate an electrode body.

[0101] A mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:40:30 was prepared. Vinylene carbonate was dissolved in this mixed solvent at a concentration of 2% by mass, and lithium bis(oxalate) borate was dissolved at a concentration of 0.8% by mass. LiPF 6 was dissolved at a concentration of 1.15 mol / L. Thereby, a non-aqueous electrolyte was obtained.

[0102] The above-prepared electrode body and the non-aqueous electrolyte were housed in a battery case made of a laminate film and sealed to obtain a lithium-ion secondary battery for evaluation.

[0103] <Discharge Capacity Evaluation> Each of the above-prepared lithium-ion secondary batteries for evaluation was placed in an environment at 25°C. Each lithium-ion secondary battery for evaluation was subjected to constant-current charging up to 4.2 V at a current value of 1 / 3C, and then constant-voltage charging was performed until the current value reached 0.01C. Subsequently, each lithium-ion secondary battery for evaluation was discharged at a constant current of 1 / 3C down to 3.0 V. The discharge capacity at this time was measured. The results are shown in Table 2.

[0104] <Gas Generation Amount Evaluation> The volume of each lithium-ion secondary battery for evaluation was determined by the Archimedes method using Florinate as a solvent. This volume was taken as the initial volume. Next, in an environment at 25°C, each lithium-ion secondary battery for evaluation was subjected to constant current charging up to 4.4 V at a current value of 0.3 C, and then constant voltage charging was performed until the current value reached 0.01 C. Each charged lithium-ion secondary battery for evaluation was placed in a thermostat at 60°C and stored for 24 hours. Thereafter, each lithium-ion secondary battery for evaluation was allowed to cool in an environment at 25°C. Again, the volume of each lithium-ion secondary battery for evaluation was determined by the Archimedes method using Florinate as a solvent. The difference (mL) between the volume after storage and the initial volume was determined, and this was taken as the gas generation amount. The results are shown in Table 2.

[0105]

Table 2

[0106] From the results in Table 1, regarding the conditions for producing the transition metal carbonate containing nickel and boron, it can be seen that when the pH of the initial aqueous solution is within the range of 5.5 to 7.0, the pH of the boron source aqueous solution is within the range of 7.5 to 9.5, the pH of the reaction solution is within the range of 5.5 to 7.0, and the oxygen concentration in the reaction tank is 5% by volume or less, the gas generation amount during storage is small and at the same time the discharge capacity is high. Therefore, it can be seen that boron can be efficiently introduced into the transition metal carbonate, which is the precursor of the positive electrode active material, without performing heat treatment at a high temperature for boron.

[0107] Also, as the firing conditions for converting the transition metal carbonate into the positive electrode active material, it can be seen that a firing temperature in the range of 650°C to 1000°C and a firing time in the range of 3 hours to 8 hours are suitable.

[0108] Therefore, from the above results, according to the method for producing the boron-containing transition metal carbonate disclosed herein, heat treatment at a high temperature for boron introduction is unnecessary, and the high-capacity effect of the lithium-ion secondary battery when used as the positive electrode active material and the gas generation suppression effect during storage are highly exhibited, and it can be seen that the precursor of the positive electrode active material can be produced.

[0109] As described above, specific examples of the present invention have been described in detail, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

[0110] That is, the method for producing a boron-containing transition metal carbonate and the method for producing a positive electrode active material disclosed herein are as follows in items [1] to [4]. [1] A step of preparing an initial aqueous solution containing an ammonium ion donor and a borate ion donor in a reaction tank, and A step of adding a raw material aqueous solution containing a transition metal, a boron source aqueous solution containing an ammonium donor and a borate ion donor, and a pH adjusting solution to the initial aqueous solution to form a reaction solution and performing a crystallization reaction provided that the pH of the initial aqueous solution at 25°C is in the range of 5.5 to 7.0, the oxygen concentration in the reaction tank is 5% by volume or less, the transition metal contains at least Ni, the pH of the boron source aqueous solution at 25°C is in the range of 7.5 to 9.5, the pH adjusting solution contains a carbonate, the pH of the reaction solution at 25°C is in the range of 5.5 to 7.0, A method for producing a boron-containing transition metal carbonate. [2] The method for producing a boron-containing transition metal carbonate according to item [1], wherein the transition metal contains at least Ni, Co, and Mn. [3] The method for producing a boron-containing transition metal carbonate according to item [1] or [2], wherein the pH of the boron source aqueous solution at 25°C is in the range of 7.5 to 8.5. [4] A step of synthesizing a boron-containing transition metal carbonate by the method according to any one of items [1] to [3], a step of mixing the boron-containing transition metal carbonate and a lithium compound to obtain a raw material mixture, and a step of firing the raw material mixture at 650°C to 1000°C for 3 hours to 8 hours A method for manufacturing a positive electrode active material comprising the same.

Explanation of reference numerals

[0111] 20 wound electrode body 30 battery case 36 safety valve 42 positive electrode terminal 42a positive electrode current collector 44 negative electrode terminal 44a negative electrode current collector 50 positive electrode sheet (positive electrode) 52 positive electrode current collector 52a exposed portion of positive electrode current collector 54 positive electrode active material layer 60 negative electrode sheet (negative electrode) 62 negative electrode current collector 62a exposed portion of negative electrode current collector 64 negative electrode active material layer 70 separator sheet (separator) 80 non-aqueous electrolyte 100 lithium ion secondary battery

Claims

1. A step of preparing an initial aqueous solution containing an ammonium ion donor and a borate ion donor in a reaction vessel, and a step of adding a raw material aqueous solution containing a transition metal, a boron source aqueous solution containing an ammonium donor and a borate ion donor, and a pH adjusting solution to the initial aqueous solution to form a reaction solution and performing a crystallization reaction comprising the pH of the initial aqueous solution at 25 °C being in the range of 5.5 to 7.0, the oxygen concentration in the reaction vessel being 5% by volume or less, the transition metal containing at least Ni, the pH of the boron source aqueous solution at 25 °C being in the range of 7.5 to 9.5, the pH adjusting solution containing a carbonate, the pH of the reaction solution at 25 °C being in the range of 5.5 to 7.0, A method for producing a boron-containing transition metal carbonate.

2. The method for producing a boron-containing transition metal carbonate according to claim 1, wherein the transition metal contains at least Ni, Co, and Mn.

3. The method for producing a boron-containing transition metal carbonate according to claim 1, wherein the pH of the boron source aqueous solution at 25 °C is in the range of 7.5 to 8.

5.

4. A step of synthesizing a boron-containing transition metal carbonate by the method according to claim 1, a step of mixing the boron-containing transition metal carbonate and a lithium compound to obtain a raw material mixture, and a step of firing the raw material mixture at 650 °C to 1000 °C for 3 hours to 8 hours A method for producing a cathode active material comprising.

Images