Positive electrode active material for lithium-ion secondary battery, method for producing the same, and lithium-ion secondary battery

Abstract

To obtain a good positive electrode mixture slurry capable of suppressing gelation of a slurry at the time of coating of a mixture, to provide a positive electrode active material for a lithium ion secondary battery having high charge and discharge capacity, good charge and discharge cycle characteristics, and excellent productivity, and a lithium ion secondary battery using the same. A positive electrode active material for a lithium ion secondary battery, the positive electrode active material for a lithium ion secondary battery being a lithium transition metal composite oxide containing the following composition formula (1): Li 1+a Ni b Co c M d X e O 2+α (1) [wherein, in the composition formula (1), M represents at least one selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, a, b, c, d, e, and a are numbers satisfying the following: -0.04 ≤ a ≤ 0.04, 0.80 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.15, 0 ≤ d ≤ 0.20, 0 ≤ e ≤ 0.05, b + c + d + e = 1, and -0.2 < a < 0.2] represented, the residual lithium hydroxide amount (L1) of the positive electrode active material calculated by neutralization titration is 0.8 mass% or less, and the ratio L2 / L1 of the residual lithium hydroxide amount (L2) calculated by neutralization titration after compression of the positive electrode active material at a pressure of 160 MPa to the L1 is 1.10 or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a positive electrode active material for a lithium ion secondary battery and a manufacturing method thereof, and a lithium ion secondary battery using the same. BACKGROUND

[0002] A lithium ion secondary battery is widely popular as a lightweight secondary battery having a high energy density. With respect to a positive electrode active material which greatly influences the battery characteristics, in addition to establishment of high capacity and mass productivity, discussions are made on reduction of lithium ion resistance, stabilization of crystal structure, and the like. As a positive electrode active material for a lithium ion secondary battery, a lithium transition metal composite oxide having an α-NaFe02-type crystal structure (hereinafter referred to as a layered structure) is well known. In the lithium transition metal composite oxide having a layered structure, nickel is constituted of inexpensive nickel, and is expected to be applied to various uses since it shows a relatively high capacity as compared with cobalt or the like. In particular, as a positive electrode active material for a lithium ion secondary battery in which the proportion of nickel among lithium and other metals (Ni, Co, Mn, and the like) is high, it is expected more and more.

[0003] However, if a lithium transition metal composite oxide in which the proportion of nickel is high is used, the slurry for positive electrode coating is easily gelled. If gelling occurs, there is a problem that the viscosity of the positive electrode mixture slurry increases and it is difficult to coat the electrode. In general, the lithium transition metal composite oxide in which the proportion of nickel is high has more residual alkali components remaining on the surface of the oxide particles than the lithium transition metal composite oxide in which the proportion of nickel is low, and the residual alkali components contain lithium such as lithium hydroxide and lithium carbonate. In a mixture coating process for producing a positive electrode, a positive electrode mixture slurry is produced by mixing a binder or the like. At this time, the binder is easily deteriorated due to the residual alkali components, and the positive electrode mixture slurry has a property that it is easily gelled.

[0004] As a method for reducing the residual alkali components, a method for reducing the amount of residual lithium in positive electrode active material particles is disclosed in Patent Literature 1, and the method includes at least the following steps: in positive electrode active material particles composed of a lithium composite oxide, the sintering temperature is set to 850°C or higher, and after maintaining the set sintering temperature and a prescribed time in an atmospheric atmosphere, the atmosphere during cooling of the set sintering temperature is switched from the atmospheric atmosphere to a low carbon dioxide atmosphere in which the carbon dioxide concentration is 1 / 60 or less of the carbon dioxide concentration of the atmospheric atmosphere, and a mixture of a precursor compound containing Ni, Co, and Mn and a lithium compound is sintered to produce a lithium composite oxide.

[0005] A manufacturing method of a positive electrode active material for a nonaqueous electrolyte secondary battery is disclosed in Patent Literature 2, and the method includes the following steps: water is added to a mixture of a lithium compound and a transition metal compound represented by General Formula (A): Li z Ni 1-x-y Co x M yA slurry of 500 g / L to 2000 g / L is formed from a powder of a lithium-nickel composite oxide represented by O2 (where 0.10≤x≤0.20, 0≤y≤0.10, 0.97≤z≤1.20, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al), water washing is performed by stirring the slurry, and after filtration, heat treatment is performed at a temperature of 120°C or higher and 550°C or lower in an oxygen atmosphere in which the oxygen concentration is 80% by volume or higher.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-067524

[0009] Patent Document 2: WO 2014 / 189108 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] In Patent Document 1, after maintaining a prescribed sintering temperature for a prescribed period of time in an atmospheric atmosphere, the atmosphere is changed from the atmospheric atmosphere to a low carbon dioxide atmosphere and the temperature is lowered, thereby reducing the amount of residual lithium carbonate generated during the low temperature process. However, in the case of a high nickel type in which the proportion of nickel content is 80% or more, even the degree of carbon dioxide contained in the atmospheric atmosphere performs a reaction of generating lithium carbonate from the lithium-nickel composite oxide during the period of maintaining the sintering temperature for the prescribed period of time (about 3 to 10 hours). Therefore, it is difficult to sufficiently reduce the residual alkali component.

[0012] In Patent Document 2, the residual alkali component is reduced by water washing the lithium-nickel composite oxide. At this time, by prescribing the amount of lithium-nickel composite oxide and water, and the like, the release of lithium from the lithium-nickel composite oxide particles is suppressed. However, if water washing is performed, the release of lithium from the vicinity of the surface layer of the particles occurs in large amounts, and thus capacity reduction and an increase in the positive electrode resistance caused by lithium deficiency easily occur. Further, water washing itself increases the number of processes, and is not preferable in terms of production efficiency.

[0013] Therefore, the present application aims to provide a positive electrode active material having a high nickel content ratio of 80% or more, a good positive electrode material slurry in which the gelation of the slurry during coating of the mixture is suppressed, a lithium ion secondary battery positive electrode active material having high discharge capacity and good charge-discharge cycle characteristics, a manufacturing method that is excellent in productivity, and a lithium ion secondary battery using the positive electrode active material.

[0014] MEANS FOR SOLVING THE PROBLEMS

[0015] A positive electrode active material for a lithium ion secondary battery, characterized by comprising a lithium transition metal complex oxide represented by the following composition formula (1),

[0016] Li 1+a Ni b Co c M d X e O 2+α (1)

[0017] [wherein, in the composition formula (1), M represents at least one selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, a, b, c, d, e, and α are numbers satisfying -0.04 ≤ a ≤ 0.04, 0.80 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.15, 0 ≤ d ≤ 0.20, 0 ≤ e ≤ 0.05, b + c + d + e = 1, and -0.2 < α < 0.2, respectively], the residual lithium hydroxide amount (L1) of the positive electrode active material calculated by neutralization titration is 0.8 mass% or less, and the ratio L2 / L1 of the residual lithium hydroxide amount (L2) calculated by neutralization titration after compressing the positive electrode active material with a pressure of 160 MPa to the L1 is 1.10 or less.

[0018] A method for manufacturing a positive electrode active material for a lithium ion secondary battery, characterized by comprising a method for manufacturing a positive electrode active material for a lithium ion secondary battery containing a lithium transition metal complex oxide represented by the following composition formula (1),

[0019] Li 1+a Ni b Co c M d X e O 2+α (1)

[0020] [wherein, in the composition formula (1), M represents at least one selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, a, b, c, d, e, and a are numbers satisfying -0.04 ≤ a ≤ 0.04, 0.80 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.15, 0 ≤ d ≤ 0.20, 0 ≤ e ≤ 0.05, b + c + d + e = 1, and -0.2 < a < 0.2, respectively], the method for producing the positive electrode active material for a lithium ion secondary battery has: a mixing step of mixing compounds containing Li, Ni, Co, M, and X metal elements in the composition formula (1); a granulation step of obtaining granulated bodies from a raw material slurry obtained through the mixing step; a sintering step of sintering the granulated bodies to obtain a lithium transition metal composite oxide represented by the composition formula (1), and thereafter has an annealing treatment step of cooling from the maximum temperature and holding at a temperature band of 700°C or higher and 800°C or lower for 1.5 hours or more; and the sintering step is a multi-stage heat treatment step including at least a first heat treatment step of holding a heat treatment temperature at 600°C or higher and less than 750°C, and a second heat treatment step of holding a heat treatment temperature at 750°C or higher and 900°C or lower.

[0021] Further, the present application is a lithium ion secondary battery having a positive electrode including the above-described positive electrode active material for a lithium ion secondary battery.

[0022] As described in the present application, in a high-Ni ratio positive electrode active material for a lithium ion secondary battery (hereinafter also simply referred to as "positive electrode active material") in which the content ratio of nickel is increased to 80% or more, most of Ni changes from stable +2 valence to unstable +3 valence during sintering. Therefore, the crystal structure is unstable, a part of Li is not incorporated into the positive electrode active material, or Li near the surface of the positive electrode active material after sintering is removed, and a residual alkali component exists on the surface of the positive electrode active material. The present application is characterized in that it is found that the residual alkali component generated by the high-Ni ratio remains also inside the secondary particles, and not only the residual alkali component on the surface of the positive electrode active material is reduced, but also the residual alkali component inside the secondary particles is reduced. Specifically, in the sintering step, an annealing treatment of cooling in a prescribed time is applied in a temperature band of 700°C or higher and 800°C or lower after the main sintering. By performing the annealing treatment, the residual alkali component on the surface of the primary particles is caused to react and incorporated into the primary particles, and as a result, the residual alkali component inside the secondary particles can be reduced. Thus, even if the secondary particles are broken by compressing the positive electrode active material at the time of slurry coating, the residual alkali component does not increase in the case where the secondary particles are exposed inside. Therefore, it is possible to provide a positive electrode active material satisfying both the inhibition of gelation of the positive electrode slurry and high capacity and high cycle characteristics.

[0023] Advantageous Effects

[0024] According to the present application, in a high Ni ratio positive electrode active material in which the nickel content ratio is increased to 80% or more, a good positive electrode mixture slurry in which gelation at the time of mixture coating is suppressed can be obtained. In addition, a positive electrode active material for a lithium ion secondary battery having a high discharge capacity and good charge / discharge cycle characteristics can be provided by a productionally excellent manufacturing method. Furthermore, a lithium ion secondary battery using the positive electrode active material can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1A is a flowchart showing one example of the manufacturing method of the positive electrode active material of the present application.

[0026] Figure 1B is a flowchart showing another example of the manufacturing method of the positive electrode active material of the present application.

[0027] Figure 2 is a partial cross-sectional view schematically showing one example of a lithium ion secondary battery.

[0028] Figure 3 is a graph showing an example of the annealing process step in the manufacturing method of the positive electrode active material of the present application.

[0029] Figure 4 is a graph showing the particle size distribution before and after compression in Example 1 of the present application.

[0030] Figure 5 is a graph showing the relationship between the amount of residual lithium hydroxide and the number of days of gelation.

[0031] Figure 6 is a graph showing the relationship between the amount of residual lithium hydroxide and the capacity maintenance rate.

[0032] Figure 7 is a graph showing the relationship between L2 / L1 and the number of days of gelation.

[0033] Figure 8 is a graph showing the relationship between L2 / L1 and the capacity maintenance rate. DETAILED DESCRIPTION

[0034] A positive electrode active material for a lithium ion secondary battery and a manufacturing method thereof, and a positive electrode mixture slurry and a lithium ion secondary battery using the same according to one embodiment of the present application will be described in detail below.

[0035] <POSITIVE ELECTRODE ACTIVE MATERIAL>

[0036] The positive electrode active material described in the present embodiment has an α-NaFeO2-type crystal structure having a layered structure, and includes a lithium transition metal composite oxide composed of lithium and a transition metal. The positive electrode active material mainly includes secondary particles composed of primary particles of the lithium transition metal composite oxide and a plurality of the primary particles. In addition, the lithium transition metal composite oxide has a layered structure in which lithium ions can be intercalated and deintercalated as a main phase.

[0037] In addition to the lithium transition metal composite oxide as the main component, the positive electrode active material described in the present embodiment can also include other components mixed with the lithium transition metal composite oxide particles and the like, such as a boron component, a phosphorus component, a sulfur component, a fluorine component, an organic substance, and the like, which are derived from impurities that are inevitable in raw materials and manufacturing processes, and which coat the lithium transition metal composite oxide particles.

[0038] The lithium transition metal composite oxide described in the present embodiment is represented by the following composition formula (1):

[0039] Li 1+a Ni b Co c M d X e O 2+α (1)

[0040] [wherein, in the composition formula (1), M represents at least one selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, a, b, c, d, e, and α are numbers that satisfy the following: -0.04 ≤ a ≤ 0.04, 0.80 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.15, 0 ≤ d ≤ 0.20, 0 ≤ e ≤ 0.05, b + c + d + e = 1, and -0.2 < α < 0.2, respectively].

[0041] The proportion of nickel among the metals other than lithium in the lithium transition metal composite oxide represented by the composition formula (1) is 80% or more. That is, the proportion of Ni is 80% or more with respect to the atomic fraction proportion of the total of Ni, Co, M, and X. Since the content of nickel is high, it is a nickel-based oxide that can achieve a high discharge capacity. In addition, since the content of nickel is high, the cost of raw materials is inexpensive compared to LiCoO2or the like, and it is also excellent in terms of productivity including the cost of raw materials.

[0042] (Chemical composition)

[0043] Here, the meaning of the chemical composition represented by the composition formula (1) is described.

[0044] The a in the composition formula (1) is set to be -0.04 or more and 0.04 or less. The a indicates excess or deficiency of lithium with respect to the stoichiometric ratio of Li(Ni, Co, M, X)02. The a is not a value at the time of raw material synthesis, but a value in the lithium transition metal composite oxide after sintering. When the excess or deficiency of lithium in the composition formula (1) is too large, that is, with respect to the total of Ni, Co, M, and X, if it is a composition with too little lithium or a composition with too much lithium, the synthesis reaction at the time of sintering cannot be properly performed, a residual alkali component remains on the surface of the positive electrode active material, cation disorder in which nickel is mixed in at lithium sites is easily generated, and crystallinity easily decreases. In particular, when the proportion of nickel increases to 80% or more, such a residual alkali component and generation of cation disorder and decrease in crystallinity easily become significant, the positive electrode mixture slurry gels, and the discharge capacity and charge / discharge cycle characteristics easily deteriorate. In contrast to this, if the a is in the above numerical range, the residual alkali component and cation disorder are reduced, and various battery performances can be improved. Therefore, even in a composition with a high nickel content, it is possible to suppress gelation of the positive electrode mixture slurry, and it is possible to obtain a high discharge capacity and good charge / discharge cycle characteristics.

[0045] The a is preferably 0.00 or more and 0.04 or less. When the a is 0.00 or more, lithium does not become deficient with respect to the stoichiometric ratio, and thus the synthesis reaction at the time of sintering is properly performed, and cation disorder is less likely to be generated. Therefore, a layered structure with few defects is formed, and a high discharge capacity and good charge / discharge cycle characteristics can be obtained. Furthermore, when the a is 0.04 or less, the excess lithium is less with respect to the stoichiometric ratio, the residual alkali component on the surface of the positive electrode active material is less, and the positive electrode mixture slurry is less likely to gel. In addition, with respect to the positive electrode active material in which the lithium transition metal composite oxide represented by the composition formula (1) is the main component, the ratio of the lithium atom concentration (mole number) included in the positive electrode active material to the total atom concentration (mole number) of the metal elements other than lithium is preferably 0.96 or more and 1.04 or less, and more preferably 1.00 or more and 1.04 or less. The sintered precursor that is sintered by heat treatment can mix other components, and there is a possibility that the reaction ratio at the time of sintering deviates from the stoichiometric ratio. However, if the atom concentration ratio is such, at the time of sintering, it is highly likely that the gelation of the positive electrode mixture slurry and the generation of cation disorder and decrease in crystallinity are suppressed based on the chemical composition represented by the composition formula (1). Therefore, a positive electrode active material with improved various battery performances can be obtained.

[0046] The above describes the preferable range of a in the powder state as a positive electrode active material, but in the case where the positive electrode active material represented by the composition formula (1) is assembled into a lithium ion secondary battery positive electrode, since charge / discharge accompanied by insertion and deinsertion of Li is performed, the a is preferably in the range from -0.9 to 0.04.

[0047] The coefficient b of nickel in the composition formula (1) is 0.80 or more and 1.00 or less. When b is 0.80 or more, the content of nickel is low, and a higher discharge capacity can be obtained compared with other nickel-based oxides and ternary oxides represented by Li(Ni, Co, M)02, etc. In addition, since the amount of transition metals other than nickel can be reduced, the cost of raw materials can be reduced.

[0048] The coefficient b of nickel can be 0.85 or more, 0.90 or more, or 0.92 or more. The larger b is, the more a tendency to obtain a high discharge capacity is obtained. In addition, the coefficient b of nickel can be 0.95 or less, 0.90 or less, or 0.85 or less. The smaller b is, the smaller the lattice deformation and the crystal structure change accompanying the intercalation and deintercalation of lithium ions are, and during sintering, cationic disordering due to the mixing of nickel into lithium sites and the decrease in crystallinity are less likely to occur, and thus a tendency to have good charge and discharge cycle characteristics is obtained.

[0049] The coefficient c of cobalt in the composition formula (1) is 0 or more and 0.15 or less. Cobalt can be added actively, or can have a composition ratio comparable to inevitable impurities. If cobalt is within the above range, the crystal structure becomes more stable, and effects such as suppression of cationic disordering due to the mixing of nickel into lithium sites can be obtained. Thus, a high discharge capacity and good charge and discharge cycle characteristics can be obtained. On the other hand, if cobalt is excessive, the cost of raw materials for the positive electrode active material becomes high. In addition, there is a possibility that the proportion of other transition metals such as nickel decreases, the discharge capacity decreases, and the effects of the metal element represented by M decrease. In contrast to this, if c is within the above numerical range, the cost of raw materials for the lithium transition metal complex oxide that exhibits a high discharge capacity, good rate characteristics, and good charge and discharge cycle characteristics can be reduced.

[0050] From the viewpoint of reducing the cost of raw materials and saving resources, the coefficient c of cobalt is preferably 0.01 or more and 0.10 or less. More preferably, it is 0.02 or more and 0.07 or less. The smaller c is, the more the cost of raw materials can be reduced.

[0051] M in the composition formula (1) is at least one or more metal elements selected from Al and Mn. These elements can be substituted in the Ni site, and considering that Al is a main group element (typical element) and thus does not change in valence state during charge and discharge and stably exists, and Mn, although it is a transition metal, also remains in the +4 valence state during charge and discharge and stably exists. Thus, the use of these metal elements can obtain the effect of stabilizing the crystal structure during charge and discharge.

[0052] The coefficient d of M in the composition formula (1) is 0 or more and 0.20 or less. If the metal element represented by M is excessive, the proportion of other transition metals such as nickel decreases, and there is a possibility that the discharge capacity of the positive electrode active material decreases. On the other hand, if d is within the above numerical range, there is a tendency to obtain a higher discharge capacity, good rate characteristics, and charge / discharge cycle characteristics.

[0053] X in the composition formula (1) is one or more metal elements other than Li, Ni, Co, Al, and Mn (hereinafter, also referred to as X element or element X). X is an element capable of forming an α-NaFe02-type crystal structure exhibiting a layered structure, and can be selected according to the desired characteristics. For example, in the case where a metal element forms a concentration layer by reacting with Li after Li and Ni form an α-NaFe02-type crystal structure exhibiting a layered structure, the X element exists on the surface of primary particles of the positive electrode active material during a sintering process at a relatively low temperature at which the reaction of Li and Ni begins, and the X element easily forms a concentration layer on the surface of the primary particles during a subsequent high-temperature sintering process. In particular, by using a solid phase method to preliminarily mix all elements including the X element, and by performing pulverization, the X element can be distributed on the surface of the primary particles inside the secondary particles. As the X element capable of forming such a concentration layer, at least one or more elements selected from the group consisting of Ti, Ga, Mg, Zr, and Zn are preferable. Of these, at least Ti is more preferable. Since Ti can take a valence of 4, the bonding with O is strong, and the effect of stabilizing the crystal structure is large. Furthermore, since the atomic weight is relatively small, the theoretical capacity of the positive electrode active material decreases less when Ti is added. By using these metal elements X, an effect of suppressing the deterioration of the crystal structure from the vicinity of the surface of the positive electrode active material during charge / discharge can be obtained.

[0054] The coefficient e of X in the composition formula (1) is 0 or more and 0.05 or less. When X is added, as described above, the crystal structure in the vicinity of the surface of the positive electrode active material becomes more stable, and good charge / discharge cycle characteristics can be obtained. On the other hand, if X is excessive, the proportion of other transition metals such as nickel decreases, the discharge capacity decreases, and there is a possibility that the effect of the metal element represented by M decreases. On the other hand, if e is within the above numerical range, a lithium transition metal composite oxide exhibiting a high discharge capacity, good charge / discharge cycle characteristics is obtained.

[0055] The coefficient e of X is preferably 0.01 or more and 0.03 or less. When e is 0.01 or more and 0.03 or less, the proportion of Ni on the surface of the primary particles decreases, and the change in the crystal structure in the vicinity of the surface of the primary particles decreases. As a result, a layered structure with fewer defects is formed, and a high discharge capacity, good charge / discharge cycle characteristics can be obtained.

[0056] α in the composition formula (1) is greater than -0.2 and less than 0.2. α indicates excess or deficiency of oxygen with respect to the stoichiometric ratio Li(Ni, Co, M, X)O2. If α is within the above numerical range, defects in the crystal structure are in a small state, and by a suitable crystal structure, high discharge capacity, good rate characteristics, and charge / discharge cycle characteristics can be obtained. In addition, the value of α can be measured by a non-active gas fusion-infrared absorption method.

[0057] (Secondary particles)

[0058] The average particle diameter of the primary particles of the positive electrode active material is preferably 0.05 μm or more and 2 μm or less. By making the average particle diameter of the primary particles of the positive electrode active material 2 μm or less, the reaction field of lithium ion intercalation and deintercalation of the positive electrode active material can be ensured, and high discharge capacity, good charge / discharge cycle characteristics can be obtained. More preferably, it is 1.5 μm or less, and further preferably, it is 1.0 μm or less. In addition, the average particle diameter of the secondary particles of the positive electrode active material is, for example, preferably 3 μm or more and 50 μm or less.

[0059] The secondary particles (granules) of the positive electrode active material can be obtained by granulating the primary particles manufactured according to the manufacturing method of the positive electrode active material described later by dry granulation or wet granulation. As a granulation means, for example, a granulator such as a spray dryer and a rotary fluidized bed device can be used.

[0060] The BET specific surface area of the lithium transition metal complex oxide represented by the composition formula (1) is preferably 0.2 m 2 / g or more, more preferably 0.4 m 2 / g or more, further preferably 0.6 m 2 / g or more. In addition, the BET specific surface area is preferably 1.5 m 2 / g or less, more preferably 1.2 m 2 / g or less. If the BET specific surface area is 0.2 m 2 / g or more, a positive electrode in which the molding density and the positive electrode active material filling rate are very high can be obtained. In addition, if the BET specific surface area is 1.5 m 2 / g or less, damage, deformation, particle shedding, and the like are less likely to occur at the time of press molding of the lithium transition metal complex oxide and at the time of volume change accompanying charge / discharge, and at the same time, the adsorption of the binder caused by fine pores can be suppressed. Therefore, the coating property and the adhesion property of the positive electrode active material are good, and high discharge capacity and good charge / discharge cycle characteristics can be obtained.

[0061] (Positive electrode mixture slurry and residual lithium hydroxide amount)

[0062] The positive electrode active material of the embodiment of the present application contains a residual alkali component. The residual alkali component contains lithium, and at least contains lithium hydroxide and lithium carbonate other than a compound that makes Li reversibly intercalate and deintercalate. In the residual alkali component, the residual lithium hydroxide amount (L1) is 0.8 mass% or less with respect to the positive electrode active material, and the ratio (L2 / L1) of the residual lithium hydroxide amount (L2) after compression of the positive electrode active material at a pressure of 160 MPa (≈16,327 N / cm 2 ) is 1.10 or less. Here, the residual alkali component can be confirmed by neutralization titration.

[0063] In the neutralization titration, the following reactions are performed by using hydrochloric acid (HCl).

[0064] LiOH + HCl → LiCl + H2O

[0065] Li2CO3 + HCl → LiHCO3 + LiCl

[0066] LiHCO3 + HCl → LiCl + H2O + CO2

[0067] Thus, the residual lithium hydroxide amount and the residual lithium carbonate amount can be calculated from the titration amount of hydrochloric acid. The residual lithium hydroxide amount can be 0.8 mass% or less, preferably 0.77 mass% or less, and more preferably 0.6 mass% or less with respect to the positive electrode active material. If the residual lithium hydroxide amount is 0.8 mass% or less, even in the case where polyvinylidene fluoride (PVDF) having high versatility is used as a binder, the unstable PVDF defluorination reaction of the basic compound does not occur, and the gelation of the positive electrode mixture slurry can be suppressed.

[0068] The residual lithium hydroxide amount measured by the neutralization titration is limited to the surface of the secondary particles of the positive electrode active material that is in contact with water, and the surface of the voids inside the secondary particles that can be immersed in water. However, when the positive electrode mixture slurry is produced, it is necessary to uniformly mix the positive electrode active material, the conductive material, the binder, and the like, and thus a part of the secondary particles can be collapsed due to the mixing performed with application of high shear. Therefore, the residual lithium hydroxide amount inside the secondary particles is small, and the suppression of the gelation of the positive electrode mixture slurry is also effective. The ratio L2 / L1 of the residual lithium hydroxide amount L1 to L2 after compression is preferably 1.10 or less. If L2 / L1 is 1.10 or less, even in the state where a part of the secondary particles is collapsed, the state where the residual lithium hydroxide amount is sufficiently small can be maintained, and the gelation of the positive electrode mixture slurry can be suppressed. Here, the pressure at the time of compression can be used in the following manner.

[0069] (Viscosity of the positive electrode mixture slurry)

[0070] To coat the positive electrode mixture slurry containing the conductive material, the binder, the solvent, and the positive electrode active material on the surface of the positive electrode current collector (for example, an Al foil) appropriately, it is required to suppress gelation of the positive electrode mixture slurry, and more specifically, it is required to stabilize the viscosity of the positive electrode mixture slurry. That is, it is preferable that the slurry viscosity η0immediately after the positive electrode mixture slurry is prepared is the same as the slurry viscosity η5measured after the slurry is left to stand for 5 days from the above production date, and the ratio of the slurry viscosities (η5 / η0) is 0.80 or more and 1.2 or less, and the slurry can be coated appropriately.

[0071] (Compression of the positive electrode active material)

[0072] For the positive electrode active material in the positive electrode mixture slurry, a part of the secondary particles is broken during adjustment in the mixture coating process by high shear force. Therefore, to simulate the state of the positive electrode active material in the positive electrode mixture slurry, the positive electrode active material is compressed to break a part of the secondary particles.

[0073] Specifically, after 1 g of the positive electrode powder is put into a mold (die) having an area of 0.49 cm 2 , the positive electrode active material is recovered after compression using an autograph device "AGS-1kNX" (manufactured by Shimadzu Corporation) with a load of 8 kN (that is, a pressure per unit area of 16,327 N / cm 2 (160 MPa in the SI unit system)). Note that, although the compression force is 16,327 N / cm 2 in calculation, it is set to 16.0 kN / cm 2 for convenience here, and further converted to a pressure expression of 160 MPa.

[0074] (Crystallinity)

[0075] The positive electrode active material has residual alkali components on the surface, and lithium near the surface is likely to be deficient in the manufacturing process, and thus the crystallinity is likely to be reduced as compared with the inside of the positive electrode active material. The crystallinity near the surface of the positive electrode active material can be analyzed by Raman spectroscopy. In the Raman spectroscopy of the positive electrode active material, the positive electrode active material of the embodiment of the present application preferably has a half-width of the E g vibration of 68 cm -1 or more, and a half-width of the A 1g vibration of 50 cm -1 or more. The E g vibration originates from the variable angle vibration of Ni-O, and has a peak at a wave number of 472 to 482 cm -1 . The A 1g vibration originates from the stretching vibration of Ni-O, and has a peak at a wave number of about 545 to 555 cm -1 . If the half-width of the E g vibration is 68 cm -1The following, the crystallinity near the surface of the positive electrode active material is sufficiently high, and high discharge capacity and good charge-discharge cycle characteristics can be obtained. In addition, if A 1g The half-width of the vibration is 50 cm -1 The following, the crystallinity is sufficiently high, and high discharge capacity and good charge-discharge cycle characteristics can be obtained.

[0076] <Measurement method of positive electrode active material>

[0077] The average composition of the particles of the positive electrode active material can be confirmed by high-frequency inductively coupled plasma (ICP), atomic absorption spectrometry (AAS), or the like. For the average particle diameter of the primary particles of the positive electrode active material, a scanning electron microscope (SEM) is used, the particle diameter of the primary particles is calculated by dividing the length of the cross line when a straight line is drawn in a prescribed direction of the cross-sectional observation image of the secondary particles by the number of primary particles contained in the cross line, and the average value of ten secondary particles is used as the average particle diameter of the primary particles. In addition, the straight line in the prescribed direction is noted as the cross line as a straight line until the primary particles are connected and disconnected, taking into account the case where the cross section of the secondary particles has a gap or the like. For example, the average particle diameter of the particles in the raw material slurry and the secondary particles of the positive electrode active material can be measured by a laser diffraction type particle size distribution measuring instrument or the like. The BET specific surface area can be calculated by a gas adsorption method using an automatic specific surface area measuring device. The residual alkali component of the positive electrode active material can be calculated by neutralization titration. The compression of the positive electrode active material can be performed by a punch press and an autograph or the like as described above.

[0078] <Manufacturing method of positive electrode active material>

[0079] The positive electrode active material described in the present embodiment can be manufactured by causing the synthesis reaction of lithium with nickel, cobalt, or the like to proceed substantially by using raw material ratios having a chemical composition represented by the composition formula (1) and appropriate sintering conditions. As the manufacturing method of the positive electrode active material described in the present embodiment, a solid phase method described below is used.

[0080] FIG. 1 is a flowchart of the manufacturing method of the positive electrode active material for lithium ion secondary batteries described in one embodiment of the present application.

[0081] As Figure 1AAs shown, the method for manufacturing the positive electrode active material for lithium-ion secondary batteries described in this embodiment includes, in sequence, a mixing step S10, a granulation step S20, and a sintering step S30. Here, the granulation step also includes granulation drying via a sprayer and chemical synthesis via co-precipitation. Alternatively, steps other than these can be added. For example, if the granulated powder obtained through the granulation step S20 has a high residual moisture content, since a large amount of water vapor is generated in the sintering step S30, a dehydration step by heating can be added to the granulation step S20 to reduce the moisture content of the granulated powder. Furthermore, as... Figure 1B As shown, the following manufacturing method is also feasible: in the mixing process S10 and the granulation process S20, after treating the compound containing metals other than Li, a Li compound is added, mixed in the second mixing process S11, and then sintered in the sintering process S30.

[0082] exist Figure 1A In the mixing process S10 shown, a compound containing the metallic elements Li, Ni, Co, M, and X from formula (1) is mixed. For example, by weighing, pulverizing, and mixing these raw materials separately, a powdery mixture with uniformly mixed raw materials can be obtained. For example, a general precision pulverizer, such as a ball mill, jet mill, rod mill, or sand mill, can be used as the pulverizer for pulverizing the raw materials. The pulverization of the raw materials can be either dry pulverization or wet pulverization. After dry pulverization, a solvent such as water can be added to form a slurry composed of the raw materials and the solvent, or the raw materials can be slurried by adding a solvent such as water to them before wet pulverization. From the viewpoint of obtaining a uniform and fine powder with an average particle size of less than 0.3 μm, it is preferable to use a medium such as water for wet pulverization.

[0083] In this embodiment, in order to concentrate the X element near the surface of the primary particle inside the secondary particle, a solid phase is used, which is simultaneously pulverized with other raw materials in the process of mixing raw materials. It is important to mix them into a uniform and fine powder with an average particle size of less than 0.3 μm.

[0084] Examples of lithium-containing compounds include lithium carbonate, lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride, and lithium sulfate. However, lithium carbonate has better supply stability and is cheaper than other lithium-containing compounds, making it readily available. Furthermore, because lithium carbonate is weakly alkaline, it causes less damage to manufacturing equipment, resulting in excellent industrial applicability and practicality.

[0085] As compounds containing metal elements other than Li, compounds containing nickel, cobalt, metal elements represented by M, and metal elements represented by X are mixed according to the composition of lithium transition metal complex oxides. Compounds containing metal elements other than Li are preferably compounds composed of C, H, O, and N, such as carbonates, hydroxides, hydroxy oxides, sulfates, acetates, citrates, and oxides. From the viewpoint of ease of pulverization and the amount of gas released during thermal decomposition, carbonates, hydroxides, or oxides are particularly preferred.

[0086] In the mixing step S10, it is preferable to mix the raw materials so that the sintering precursor supplied to the sintering step S30 has a chemical composition represented by the composition formula (1). Specifically, it is preferable to adjust the atomic concentration ratio (molar ratio) of lithium contained in the sintering precursor to the total atomic concentration (molar ratio) of metal elements other than lithium contained in the sintering precursor to be 0.96 or more and 1.04 or less. However, as Figure 1B As shown, in the case of mixing a compound containing metal elements other than Li in the mixing step S10, the atomic concentration ratio (molar ratio) of the total amount of lithium and metal elements other than lithium is adjusted in the second mixing step S11. If the atomic concentration ratio (molar ratio) is less than 0.96, it is likely that a suitable main phase with fewer heterogeneous phases cannot be sintered due to insufficient lithium. On the other hand, if the atomic concentration ratio exceeds 1.04, there is a possibility that the synthesis reaction will not proceed properly and the crystallinity of the layered structure will decrease. Therefore, the mixing step of mixing a compound containing metal elements of Li, Ni, Co, M, and X in formula (1) includes Figure 1A The mixing process S10 and Figure 1B The second mixing process S11 is shown.

[0087] To obtain lithium transition metal composite oxides that reduce lattice distortion and crystal structure changes caused by lithium-ion insertion and extraction, it is necessary to sufficiently suppress cation mixing that is prone to occur with divalent nickel. During sintering, from the viewpoint of sufficiently suppressing cation mixing, it is necessary to ensure the reliable synthesis reaction of lithium and nickel, etc. Therefore, it is desirable for lithium and nickel to react in approximately a stoichiometric ratio of 1:1.

[0088] Therefore, it is preferable to adjust these atomic concentration ratios in advance at the mixing step S10 stage at which precise pulverization mixing can be performed. If adjusted in advance, the atomic concentration ratio (mole ratio) of the atomic concentration (moles) of lithium included in the sintering precursor to the atomic concentration (moles) of the metal elements other than lithium in total is more preferably 1.00 or greater and 1.04 or less. However, at the time of sintering, lithium contained in the sintering precursor can react with or evaporate from the sintering container. In consideration of the fact that a portion of lithium disappears due to the reaction of the container used for sintering and lithium and the evaporation of lithium at the time of sintering, it is also not problematic to excessively add lithium at the time of addition.

[0089] Further, in order to obtain a lithium transition metal composite oxide in which the lattice distortion and crystal structure change accompanying lithium ion intercalation and deintercalation are reduced, after the mixing step S10 and before the sintering step S30, it is preferable that metal elements other than lithium, such as unavoidable impurities from the manufacturing process, other components that coat the lithium transition metal composite oxide particles, other components that are mixed with the lithium transition metal composite oxide particles, and the like, are not mixed in.

[0090] In the granulation step S20, the mixture obtained in the mixing step S10 is granulated to obtain secondary particles (granules) in which the particles are agglomerated. The granulation of the mixture can be performed using any one of a dry granulation and a wet granulation. For example, for the granulation of the mixture, an appropriate granulation method such as a tumbling granulation method, a fluidized bed granulation method, a compression granulation method, a spray granulation method, and the like can be used. Further, a chemical particle synthesis such as a coprecipitation method can also be implemented.

[0091] As the granulation method for granulating the mixture, a spray granulation method is particularly preferable. As a spray granulator, various types such as a two-fluid nozzle type, a four-fluid nozzle type, a disk type, and the like can be used. If a spray granulation method is used, the mixture (raw material slurry) that has been precisely mixed and pulverized by wet pulverization can be granulated while being dried. Further, by adjusting the concentration of the raw material slurry, the spray pressure, the disk rotation speed, and the like, the particle diameter of the secondary particles can be accurately controlled within a prescribed range, and granules that are close to true spheres and have a uniform chemical composition can be effectively obtained. In the granulation step S20, it is preferable to granulate the mixture obtained in the mixing step S10 to have an average particle diameter (D 50 ) of 3 μm or greater and 50 μm or less.

[0092] In the sintering step S30, the granulated body granulated in the granulation step S20 is heat-treated, and the lithium transition metal composite oxide represented by the composition formula (1) is sintered. The sintering step S30 is simply a step of sintering the lithium transition metal composite oxide to obtain the positive electrode active material, but is preferably performed by a multi-stage heat treatment in which the heat treatment temperature is controlled in ranges different from each other. From the viewpoint of obtaining a lithium transition metal composite oxide that exhibits high crystalline purity, high discharge capacity, good rate characteristics, and charge / discharge cycle characteristics, as shown in FIG. 1, the sintering step S30 has at least a multi-stage heat treatment step including a first heat treatment step S31, a second heat treatment step S32, and an annealing step S33, and prescribed conditions can be satisfied respectively.

[0093] (First heat treatment step)

[0094] In the first heat treatment step S31, the heat treatment temperature is controlled to be 600°C or higher and less than 750°C, and the granulated body obtained by the granulation step S20 is heat-treated to obtain a first precursor. The main purpose of the first heat treatment step S31 is to remove carbonic and hydroxide components by the reaction of lithium compounds and nickel compounds and the like, and to generate crystals of the lithium transition metal composite oxide at the same time. Nickel in the sintered precursor is sufficiently oxidized, and cationic disordering of nickel mixed into lithium sites is suppressed, and cubic crystal domains of nickel are suppressed from being generated. In addition, in order to reduce lattice distortion and crystal structure changes caused by lithium ion intercalation and deintercalation, the metal element represented by M can be sufficiently oxidized, and thus the composition uniformity of the layer composed of MeO2 is improved. For example, the time of the first heat treatment step S31 can be 2 hours or more and 50 hours or less.

[0095] In the case where the lithium compound is lithium carbonate, carbon dioxide gas (CO2 gas) generated as a reaction by-product can hinder the progress of the sintering reaction. In order to avoid this, multistage heat treatment that can gradually discharge the CO2 gas is preferable. In the first heat treatment step S31, the unreacted lithium carbonate remaining in the first precursor is preferably reduced to 0.3% by mass or more and 3% by mass or less, and more preferably to 0.5% by mass or more and 2% by mass or less, with respect to the total mass of the granulated body charged. If the amount of the lithium carbonate remaining in the first precursor is too large, in the second heat treatment step S32, the lithium carbonate can melt to form a liquid phase. If the lithium transition metal complex oxide is sintered in the liquid phase, the primary particles having a layered structure can become in an excessively oriented state or have a reduced specific surface area due to over-sintering, which can result in deterioration of the discharge capacity, charge-discharge cycle characteristics, and the like. In addition, if the amount of the lithium carbonate remaining in the first precursor is too small, the specific surface area of the sintered lithium transition metal complex oxide is too large, and thus the charge-discharge cycle characteristics can deteriorate due to an increased contact area with the electrolyte. In contrast, if the amount of the unreacted lithium carbonate is within the above range, a lithium transition metal complex oxide having a high crystalline purity can be obtained, and a high discharge capacity and good charge-discharge cycle characteristics can be obtained.

[0096] In addition, in the first heat treatment step S31, if the reaction of the lithium carbonate is insufficient and a large amount of lithium carbonate remains at the end of the first heat treatment step S31, the oxygen can not be distributed throughout the first precursor. In the second heat treatment step S32, if the oxygen is not distributed throughout the first precursor, nickel is not sufficiently oxidized, and thus divalent nickel that easily causes cationic disordering is likely to remain. In contrast, if the reaction of the lithium carbonate is caused to proceed in the first heat treatment step S31, the oxygen is likely to be distributed throughout the first precursor in a powder form. Thus, while the manganese and the like are sufficiently oxidized, the excessive remaining of the divalent nickel that easily causes cationic disordering can be suppressed.

[0097] In the first heat treatment step S31, if the heat treatment temperature is 600°C or higher, the generation of crystals is promoted by the reaction of the lithium carbonate and the nickel compound and the like, and thus the excessive remaining of the unreacted lithium carbonate can be avoided. Thus, in the subsequent heat treatment, the lithium carbonate is less likely to form a liquid phase, the coarsening of the crystal grains is suppressed, good output characteristics and the like can be obtained, the oxygen is likely to be distributed throughout the first precursor, and cationic disordering is likely to be suppressed. In addition, if the heat treatment temperature is less than 750°C, in the first heat treatment step S31, the grain growth does not excessively proceed, and thus the manganese and the like can be sufficiently oxidized, and the composition uniformity of the layer composed of MeO2 can be improved.

[0098] The heat treatment temperature in the first heat treatment step S31 is preferably 620°C or higher, more preferably 650°C or higher, and further preferably 680°C or higher. The higher the heat treatment temperature, the more the synthesis reaction is promoted, and the more the remaining of the lithium carbonate can be prevented.

[0099] The heat treatment temperature in the first heat treatment step S31 is preferably less than 750°C. If the heat treatment temperature is 750°C or more, unreacted lithium carbonate forms a liquid phase, and the crystal grains become coarse.

[0100] The heat treatment time in the first heat treatment step S31 means that the temperature is maintained at the prescribed temperature for 4 hours or more. Further, the heat treatment time is preferably 15 hours or less. If the heat treatment time is within this range, the reaction of lithium carbonate proceeds sufficiently, and thus the carbonic acid component can be removed practically. Further, the time required for the heat treatment is shortened, and the productivity of the lithium transition metal complex oxide is improved.

[0101] The first heat treatment step S31 is preferably performed in an oxidizing atmosphere. The oxygen concentration in the atmosphere is preferably 50% or more, more preferably 60% or more, and further preferably 80% or more. Further, the carbon dioxide (CO2) concentration in the atmosphere is preferably 5% or less, and more preferably 2% or less. Further, the first heat treatment step S31 is preferably performed under a stream of oxidizing gas. By performing the heat treatment under a stream of oxidizing gas, nickel can be oxidized practically, and carbon dioxide released into the atmosphere can be eliminated practically.

[0102] (Second heat treatment step)

[0103] In the second heat treatment step S32, the heat treatment temperature is maintained at 750°C or more and 900°C or less, and the first precursor obtained by the first heat treatment step S31 is heat-treated to obtain a second precursor. The main purpose of the second heat treatment step S32 is to grow the crystal grains of the lithium transition metal complex oxide having a layered structure to an appropriate particle diameter and specific surface area. For example, the time of the second heat treatment step S32 means that the temperature is maintained at the prescribed temperature for 0.5 hours or more and 15 hours or less, similarly to the heat treatment time of the first heat treatment step S31.

[0104] In the second heat treatment step S32, if the heat treatment temperature is 750°C or more, nickel can be oxidized sufficiently to suppress cation mixing, and at the same time, the crystal grains of the lithium transition metal complex oxide can be grown to an appropriate particle diameter and specific surface area. Further, since the main phase in which lattice distortion and crystal structure change accompanying lithium ion intercalation and deintercalation are reduced is formed, a lithium transition metal complex oxide having a high discharge capacity and good charge / discharge cycle characteristics can be obtained. Further, if the heat treatment temperature is 900°C or less, lithium is difficult to volatilize, and the purity of the crystal is high, and thus a lithium transition metal complex oxide having a good discharge capacity, charge / discharge cycle characteristics, and the like can be obtained.

[0105] The heat treatment temperature in the second heat treatment step S32 is preferably 760°C or higher, more preferably 780°C or higher, and further preferably 800°C or higher. The higher the heat treatment temperature, the more the metal elements represented by nickel and M are oxidized, thereby promoting the growth of the lithium transition metal composite oxide.

[0106] The heat treatment temperature in the second heat treatment step S32 is preferably 880°C or lower, and more preferably 860°C or lower. The lower the heat treatment temperature, the more difficult it is for lithium to volatilize, and thus the decomposition of the lithium transition metal composite oxide can be prevented, and a lithium transition metal composite oxide having good discharge capacity, charge / discharge cycle characteristics, and the like can be obtained.

[0107] The heat treatment time (holding time) in the second heat treatment step S32 is preferably 0.5 hours or longer. Furthermore, the heat treatment time is preferably 15 hours or shorter. If the heat treatment time is within this range, the nickel can be sufficiently oxidized, and a lithium transition metal composite oxide in which the lattice distortion and crystal structure change caused by the intercalation and deintercalation of lithium ions are reduced can be obtained. Furthermore, the time required for the heat treatment is shortened, and thus the productivity of the lithium transition metal composite oxide can be improved.

[0108] The second heat treatment step S32 is preferably performed in an oxidizing atmosphere. The oxygen concentration in the atmosphere is preferably 80% or higher, more preferably 90% or higher, and further preferably 95% or higher. Furthermore, the carbon dioxide concentration in the atmosphere is preferably 2% or lower, and more preferably 0.5% or lower. Furthermore, the second heat treatment step S32 is preferably performed under a stream of oxidizing gas. If the heat treatment is performed under a stream of oxidizing gas, the nickel and the like can be sufficiently oxidized, and the carbon dioxide released into the atmosphere can be sufficiently eliminated.

[0109] (Annealing Treatment Step)

[0110] After the two or more heat treatment stages in which the above-described heat treatment temperature is controlled to be 600°C or higher and less than 750°C (first heat treatment step S31) and 750°C or higher and 900°C or lower (second heat treatment step S32), the annealing treatment step S33 for obtaining a lithium transition metal composite oxide is performed in a temperature zone of 700°C or higher and 800°C or lower for 1.5 hours or longer in a cooling process starting from the highest temperature (for example, 840°C). As described below, the main purpose of the annealing treatment step S33 is to incorporate the residual alkali components remaining inside the secondary particles of the lithium transition metal composite oxide having a layered structure into the lithium transition metal composite oxide, and to obtain a positive electrode active material having a small amount of residual alkali components and high crystallinity.

[0111] In the first heat treatment step S31, the layer compound formation can be promoted without promoting the particle growth of the primary particles. Further, in the second heat treatment step S32, the crystallinity of the layer compound can be sufficiently improved together with the particle growth of the primary particles. On the other hand, since the layered structure formed at a high temperature exceeding 800°C is partially decomposed, in order to further improve the crystallinity, the annealing treatment step S33 of 1.5 hours or more is provided in a temperature zone of 700°C or higher and 800°C or lower around the melting point 723°C of lithium carbonate. If the annealing temperature is in this range, residual lithium which cannot be crystallized in the second heat treatment step is layer-compounded from the surface of the secondary particles of the positive electrode active material and the surface of the primary particles inside the secondary particles, and as a result, a lithium transition metal composite oxide with high crystallinity can be obtained.

[0112] By the above annealing treatment, while the residual alkali component inside the secondary particles of the positive electrode active material is suppressed, the main phase with reduced lattice distortion and crystal structure change accompanying lithium ion intercalation and deintercalation is formed, and thus a positive electrode mixture slurry with excellent gelation resistance and high discharge capacity, good charge / discharge cycle characteristics can be obtained. In addition, in the absence of such an annealing treatment step, the residual alkali component inside the secondary particles of the positive electrode active material is likely to increase, and after the positive electrode active material is compressed, the residual lithium hydroxide amount is likely to increase when the residual alkali component is calculated by neutralization titration.

[0113] In the annealing treatment step S33, in order to maintain the temperature of 700°C or higher and 800°C or lower for 1.5 hours or more, it is preferable to adjust the cooling rate when the temperature is decreased from the maximum temperature so that the cooling is performed in a manner that takes 1.5 hours or more in the temperature zone of 700°C or higher and 800°C or lower. Further, it is possible to maintain the temperature in a certain temperature range of 700°C or higher and 800°C or lower for a prescribed time during the cooling, and it is also possible to temporarily decrease the temperature to less than 700°C, then heat it again to the temperature zone of 700°C or higher and 800°C or lower, and maintain the temperature in a certain temperature for a prescribed time. The upper limit of the annealing temperature is preferably 790°C or lower, and further preferably 780°C or lower. The lower limit of the annealing temperature is preferably 720°C or higher, and further preferably 740°C or higher.

[0114] The heat treatment time in the annealing treatment step S33 is preferably 1.5 hours or more. When the heat treatment time is 1.5 hours or more, the residual lithium carbonate inside the secondary particles of the positive electrode active material can be sufficiently reacted with the positive electrode active material, and a lithium transition metal composite oxide with high crystallinity can be obtained. Further, even if the heat treatment time exceeds 10 hours, the effect does not change, and it is preferably 2 hours or more and 8 hours or less, and more preferably 3 hours or more and 6 hours or less. If the heat treatment time is in this range, the residual alkali component can be reduced and the productivity of the lithium transition metal composite oxide can be improved.

[0115] The annealing treatment step S33 is preferably performed in an oxidizing atmosphere. The oxygen concentration in the atmosphere is preferably 80% or more, more preferably 90% or more, and further preferably 95% or more. In addition, the carbon dioxide concentration in the atmosphere is preferably 0.5% or less, and more preferably 0.1% or less. In addition, the annealing treatment step S33 is preferably performed under a stream of oxidizing gas. When heat treatment is performed under a stream of oxidizing gas, carbon dioxide released into the atmosphere after the lithium carbonate reaction can be reliably eliminated.

[0116] (CO2 concentration)

[0117] In the sintering step S30, the maximum CO2 concentration in the atmosphere of the first heat treatment step S31 is higher than the maximum CO2 concentration in the second heat treatment step S32, and the maximum CO2 concentration in the second heat treatment step S32 is higher than the maximum CO2 concentration in the annealing treatment step S33. In the first heat treatment step S31, decarbonation is one of the objects, and the maximum CO2 concentration is higher than that in the second heat treatment step S32 and the annealing treatment step S33 due to CO2 generated by heat treatment. On the other hand, in the second heat treatment step S32 and the annealing treatment step S33, an environment in which the maximum CO2 concentration is low is preferred in order to improve the crystallinity of the positive electrode active material, and the maximum CO2 concentration is preferably lower than that in the first heat treatment step S31. In particular, in the annealing treatment step S33, an environment in which the maximum CO2 concentration is lower than that in the first heat treatment step S31 and the second heat treatment step S32 is preferred in order to reduce residual alkali components in the secondary particles of the positive electrode active material.

[0118] (Sintering furnace)

[0119] In the sintering step S30, as a means of heat treatment, a rotary furnace (rotary kiln) or the like, a continuous furnace such as a roller hearth kiln, a tunnel furnace, a pusher-type furnace, or the like, or a suitable heat treatment device such as a batch-type furnace can be used. The first heat treatment step S31, the second heat treatment step S32, and the annealing treatment step S33 can each use the same heat treatment device, or different heat treatment devices from each other. In addition, each heat treatment step can be performed intermittently by changing the atmosphere, or can be performed continuously in a case where heat treatment is performed while discharging gas in the atmosphere.

[0120] By the above mixing step S10, granulation step S20, and sintering step S30, a positive electrode active material composed of a lithium transition metal composite oxide represented by the composition formula (1) can be manufactured. In the present application, the residual lithium hydroxide amount, specific surface area can be controlled mainly by adjusting: the manufacturing method of the precursor before heat treatment; the composition ratio of metal elements such as nickel; the residual amount of unreacted lithium carbonate remaining in the first precursor; the conditions of pre-sintering, formal sintering, annealing treatment in the sintering step S30 (for example, the heat treatment temperature, heat treatment time of the first heat treatment step S31 and the second heat treatment step S32, and the annealing treatment step S33). In the chemical composition represented by the composition formula (1), if the residual lithium hydroxide amount is reduced, while sufficiently reducing the increase in the residual lithium hydroxide amount after compressing the positive electrode active material, an excellent positive electrode active material that exhibits high discharge capacity, good charge-discharge cycle characteristics, and whose gelation of the positive electrode mixture slurry is suppressed can be obtained.

[0121] Further, even after the positive electrode active material is assembled into a battery and subjected to charge-discharge, the characteristics of the present application are maintained, but for the Li amount, it is considered that Li escapes and the value of a changes to around -0.9 to 0.

[0122] In addition, for the purpose of controlling the secondary particle diameter and the like, the synthesized lithium transition metal composite oxide can have a pulverization step of pulverizing the lithium transition metal composite oxide, a classification step of classifying the lithium transition metal composite oxide into a prescribed particle size, and the like.

[0123] < Lithium ion secondary battery >

[0124] Next, a lithium ion secondary battery in which the above-described positive electrode active material (positive electrode active material for lithium ion secondary battery) including the lithium transition metal composite oxide is used for a positive electrode is described.

[0125] Figure 2 is a partial cross-sectional view schematically showing one example of a lithium ion secondary battery.

[0126] As shown in Figure 2 , a lithium ion secondary battery 100 is provided with a bottomed cylindrical battery can 101 that houses a nonaqueous electrolytic solution, a wound electrode group 110 housed inside the battery can 101, and a disc-shaped battery lid 102 that seals the upper opening of the battery can 101.

[0127] The battery can 101 and the battery lid 102 are formed of, for example, a metal material such as stainless steel, aluminum, or the like. The positive electrode 111 is provided with a positive electrode current collector 111a and a positive electrode mixture layer 111b formed on the surface of the positive electrode current collector 111a. Further, the negative electrode 112 is provided with a negative electrode current collector 112a and a negative electrode mixture layer 112b formed on the surface of the negative electrode current collector 112a.

[0128] The positive electrode current collector 111a is formed of, for example, a metal foil of aluminum, aluminum alloy, or the like; a porous metal mesh (expansion metal); punched metal (punching metal); or the like. The metal foil can have a thickness of, for example, 15 μm or more and 25 μm or less. The positive electrode mixture layer 111b is formed of a positive electrode active material containing the above-described lithium transition metal complex oxide. The positive electrode mixture layer 111b is formed of, for example, a positive electrode mixture in which the positive electrode active material and a conductive material, a binder, or the like are mixed.

[0129] The negative electrode current collector 112a is formed of, for example, a metal foil of copper, copper alloy, nickel, nickel alloy, or the like; a porous metal mesh; punched metal; or the like. The metal foil can have a thickness of, for example, 7 μm or more and 10 μm or less. The negative electrode mixture layer 112b is formed of a lithium ion secondary battery negative electrode active material. The negative electrode mixture layer 112b is formed of, for example, a negative electrode mixture in which the negative electrode active material and a conductive material, a binder, or the like are mixed.

[0130] As the negative electrode active material, a suitable kind used in general lithium ion secondary batteries can be used. As specific examples of the negative electrode active material, there are mentioned: a substance obtained by subjecting an easy graphitizable material obtained from natural graphite, petroleum coke, pitch coke, or the like to treatment at a high temperature of 2500°C or higher; a substance obtained by coating amorphous carbon on the surface of mesophase carbon, amorphous carbon, or graphite; a carbon material in which the surface of natural graphite or artificial graphite is subjected to mechanical treatment to reduce the crystallinity of the surface; a material in which an organic substance such as a polymer is coated / adsorbed on the surface of carbon; carbon fiber; lithium metal; an alloy of lithium and aluminum, tin, silicon, indium, gallium, magnesium, or the like; a material in which a metal is supported on the surface of silicon particles or carbon particles; an oxide of tin, silicon, lithium, titanium, or the like. As the supported metal, there are mentioned, for example, lithium, aluminum, tin, indium, gallium, magnesium, alloys thereof, or the like.

[0131] As the conductive material, a suitable kind used in general lithium ion secondary batteries can be used. As specific examples of the conductive material, there are mentioned carbon particles such as graphite, acetylene black, furnace black, thermal carbon black, and slot method carbon black; and carbon fiber such as pitch-based and polyacrylonitrile (PAN)-based. One of these conductive materials can be used alone, or a plurality of kinds can be used in combination. For example, the amount of the conductive material can be 3% by mass or more and 10% by mass or less with respect to the entire mixture.

[0132] As the binder, a suitable kind generally used for lithium ion secondary batteries can be used. As specific examples of the binder, there are mentioned PVDF, polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, polyacrylonitrile, modified polyacrylonitrile, and the like. One of these binders can be used alone, or a plurality of kinds can be used in combination. In addition, a tackifying binder such as carboxymethyl cellulose can be used simultaneously. For example, the amount of the binder can be 2% by mass or more and 10% by mass or less with respect to the entire mixture.

[0133] The positive electrode 111 and the negative electrode 112 can be manufactured in accordance with a general manufacturing method of an electrode for a lithium ion secondary battery. For example, the electrodes can be manufactured by the following processes: a slurry preparation process of mixing an active material and a conductive material, a binder, and the like in a solvent to prepare an electrode slurry; a slurry coating process of coating the prepared electrode slurry on a substrate such as a current collector and then drying to form an electrode slurry layer; and a molding process of pressure forming the electrode slurry layer.

[0134] In the slurry preparation process, as a mixing means for mixing the materials, for example, a planetary mixer, a dispersion mixer, a revolution and rotation mixer, or the like can be used. As the solvent, for example, N-methylpyrrolidone, water, N,N-dimethylformamide, N,N-dimethylacetamide, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, diethylene glycol, glycerol, dimethyl sulfoxide, tetrahydrofuran, or the like can be used.

[0135] The viscosity of the electrode slurry (positive electrode slurry) described above is, for example, in the range of 100 to 500 mPa-s, and it is important from the viewpoint of stable production that the viscosity does not change much after the slurry is prepared. The cause of the change in viscosity is mainly that the binder is polymerized and gelled by the alkali component eluted from the positive electrode active material. In determining the positive electrode active material that can suppress this gelling, it is appropriate to use the amount of change in the viscosity of the slurry as an index. That is, when the viscosity of the positive electrode slurry on the day of preparation is η0, and the viscosity of the positive electrode slurry that has been stored for 5 days from the day of preparation is η5, η5 / η0 is preferably 0.80 or more and 1.2 or less.

[0136] In the slurry coating process, as a means for coating the prepared electrode slurry in the form of a slurry, for example, a bar coater, a doctor blade, a roll transfer machine, or the like can be used. As a means for drying the coated electrode slurry, for example, a hot air heating device, a radiation heating device, or the like can be used.

[0137] In the molding process, as a means for pressure forming the electrode slurry layer, for example, a roll press or the like can be used. For the positive electrode slurry layer 111b, for example, a thickness of 100 μm or more and 300 μm or less can be used. In addition, for the negative electrode slurry layer 112b, for example, a thickness of 20 μm or more and 150 μm or less can be used. The electrode slurry layer after pressure forming can be cut together with the positive electrode current collector as needed, and an electrode for a lithium ion secondary battery in a desired shape can be manufactured.

[0138] As described above, Figure 2As shown, the wound electrode assembly 110 is formed by winding a separator 113 between a strip-shaped positive electrode 111 and a negative electrode 112. The wound electrode assembly 110 is wound onto a shaft formed of polypropylene, polyphenylene sulfide, etc., and housed inside the battery canister 101.

[0139] As the diaphragm 113, polyolefin resins such as polyethylene, polypropylene, and polyethylene-polypropylene copolymers can be used; microporous membranes such as polyamide resins and aromatic polyamide resins can be used; and membranes with heat-resistant substances such as alumina particles coated on the surface of such microporous membranes can also be used.

[0140] like Figure 2 As shown, the positive current collector 111a is electrically connected to the battery cover 102 via the positive lead 103. On the other hand, the negative current collector 112a is electrically connected to the bottom of the battery can 101 via the negative lead 104. An insulating plate 105 to prevent short circuits is disposed between the wound electrode assembly 110 and the battery cover 102, and between the wound electrode assembly 110 and the bottom of the battery can 101. The positive lead 103 and the negative lead 104 are formed of the same material as the positive current collector 111a and the negative current collector 112a, respectively, and are joined to the positive current collector 111a and the negative current collector 112a by spot welding, ultrasonic pressing, or the like.

[0141] A non-aqueous electrolyte is injected into the battery canister 101. The non-aqueous electrolyte can be injected directly with the battery cover 102 open, or injected through an injection port on the battery cover 102 with the battery cover 102 closed. The battery cover 102 is then fixed in place by riveting or similar means to seal the battery canister 101. A sealing material 106 made of insulating resin is sandwiched between the battery canister 101 and the battery cover 102, providing electrical insulation between them.

[0142] Non-aqueous electrolytes are composed of an electrolyte and a non-aqueous solvent. Examples of electrolytes include various lithium salts such as LiPF6, LiBF4, and LiClO4. Examples of non-aqueous solvents include chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, and vinylene carbonate; chain carboxylic acid esters such as methyl acetate, methyl ethyl carbonate, and methyl propyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone; and ethers. The concentration of the electrolyte can be, for example, 0.6 M or higher and 1.8 M or lower.

[0143] In order to suppress oxidative decomposition, reductive decomposition of the electrolytic solution, prevent the precipitation of metal elements, improve ion conductivity, improve flame retardancy, and the like, various additives can be added to the non-aqueous electrolytic solution. As the additives, for example, organic phosphorus compounds such as trimethyl phosphate, trimethyl phosphite, and the like; organic sulfur compounds such as 1,3-propane sultone, 1,4-butane sultone, and the like; carboxylic anhydrides such as polyadipic anhydride, hexahydrophthalic anhydride, and the like; boron compounds such as trimethyl borate, lithium bisoxalate borate, and the like are cited.

[0144] The lithium ion secondary battery 100 having the above structure is capable of storing electric power supplied from the outside into the wound electrode group 110, with the battery lid 102 as the positive external terminal and the bottom of the battery can 101 as the negative external terminal. Further, the electric power stored in the wound electrode group 110 can be supplied to an external device or the like. In addition, the lithium ion secondary battery 100 is in a cylindrical form, but the shape and the battery structure of the lithium ion secondary battery are not particularly limited, and for example, can have an appropriate shape such as a square shape, a coin shape, a laminate shape, and the like, and other battery structures.

[0145] The lithium ion secondary battery according to the present embodiment can be used for various purposes. As the purposes, for example, small-sized power sources for portable electronic devices, household appliances, and the like, stationary power sources for power storage devices, uninterruptible power supply devices, power equalization devices, and the like are cited, but are not limited to these. The lithium transition metal complex oxide described above has a high content of nickel, and in addition to exhibiting a high discharge capacity, has good charge / discharge cycle characteristics, and thus can be particularly suitable for use in small-sized power sources and vehicle-mounted power sources and the like that require high energy density and long life.

[0146] As for the chemical composition of the positive electrode active material used in the lithium ion secondary battery, the battery can be disassembled, and the positive electrode active material constituting the positive electrode can be collected to perform high-frequency inductively coupled plasma emission spectroscopy analysis, atomic absorption analysis, and the like. Further, since the composition ratio of lithium (1 + a in the composition formula (1)) depends on the state of charge, the chemical composition of the positive electrode active material can also be judged based on whether the coefficient a of lithium after charge / discharge satisfies -0.9 ≤ a ≤ 0.04.

[0147] Example

[0148] The positive electrode active material described in the present embodiment was synthesized, and the composition, the residual alkali amount, the discharge capacity, and the charge / discharge cycle characteristics (capacity retention rate) were evaluated. Further, as a control of the example, the positive electrode active material described in the comparative example in which the chemical composition was changed was synthesized, and was also evaluated.

[0149] Hereinafter, the present application will be specifically described by showing examples and comparative examples, but the technical scope of the present application is not limited thereto.

[0150] (Examples 1 to 19)

[0151] The positive electrode active material of Example 1 was manufactured. Lithium carbonate, nickel hydroxide, cobalt carbonate, and manganese carbonate were prepared as raw materials. Each raw material was weighed according to the molar ratio of metal elements:Li:Ni:Co:Mn = 1.04:0.80:0.15:0.05. Pure water was added to bring the solid component ratio to 50% by mass. Then, wet grinding (wet mixing) was performed using a pulverizer to prepare a raw material slurry (mixing step S10). The average particle size D of the raw material slurry was... 50 It is 0.15μm.

[0152] The raw material slurry obtained after the mixing process was spray-dried using a nozzle-type spray dryer (manufactured by Okawahara Chemical Machinery Co., Ltd., model ODL-20) at a spray pressure of 0.21 MPa and a spray rate of 260 g / min to obtain granules (granulation process S20). The average particle size D of the granules is... 50 The particle size was 12 μm. Then, lithium transition metal composite oxide was obtained by sintering the granules (sintering step S30). Specifically, in the sintering step, the granules were heat-treated for 6 hours at 650°C in an oxygen-filled rotary furnace to obtain the first precursor (first heat treatment step S31). The CO2 concentration in the exhaust gas from the rotary furnace was at most 8500 ppm. Then, the first precursor was heat-treated for 10 hours at 800°C in an oxygen-filled tunnel furnace to obtain the second heat treatment step S32. The CO2 concentration in the exhaust gas from the tunnel furnace was at most 200 ppm in the second heat treatment step S32. Next, the temperature was adjusted to a cooling rate of 0.5°C / min, decreasing from 800°C to 700°C, and held at the temperature range of 800°C to 700°C for 3 hours and 20 minutes (annealing) to obtain the lithium transition metal composite oxide (annealing step S33). The highest CO2 concentration in the tunnel furnace exhaust during the S33 annealing process was 40 ppm. Figure 3 (a) shows a diagram of the annealing process, with the vertical axis representing the cooling temperature zone and the horizontal axis representing the cooling time.

[0153] Then, the sintered powder obtained by sintering was classified using a sieve with a mesh size of 53 μm, and the powder that passed through the sieve was used as the positive electrode active material of the sample.

[0154] The chemical composition of the obtained positive electrode active material Li:Ni:Co:Mn was determined by high-frequency inductively coupled plasma atomic emission spectrometry and confirmed to be 1.03:0.80:0.15:0.05. Furthermore, the α value of the positive electrode active material obtained in Example 1 was also determined by inactive gas melting-infrared absorption spectrometry, confirming -0.2 < α < 0.2. This value was also confirmed in Example 2 and thereafter.

[0155] In Example 2, titanium oxide was added as a raw material in a molar ratio of Li:Ni:Co:Mn:Ti = 1.04:0.80:0.04:0.15:0.01, and the main sintering temperature was 820°C. The annealing time was 3 hours and 20 minutes at a temperature zone of 700°C or more and less than 800°C. Other than this, the positive electrode active material was obtained in the same manner as in Example 1.

[0156] In Example 3, titanium oxide was added as a raw material in a molar ratio of Li:Ni:Co:Mn:Ti = 1.05:0.80:0.15:0.04:0.01. Other than this, the positive electrode active material was obtained in the same manner as in Example 1.

[0157] In Example 4, titanium oxide was added as a raw material in a molar ratio of Li:Ni:Co:Mn:Ti = 0.97:0.80:0.15:0.04:0.01. Other than this, the positive electrode active material was obtained in the same manner as in Example 1.

[0158] In Example 5, titanium oxide was added as a raw material in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.85:0.03:0.10:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 820°C. Thus, the annealing time was 3 hours and 20 minutes. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. In addition, the maximum CO2 concentration at the pre-sintering was 11000 ppm, the maximum CO2 concentration at the main sintering was 160 ppm, and the maximum CO2 concentration at the annealing was 50 ppm.

[0159] In Example 6, titanium oxide was added as a raw material in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.85:0.03:0.10:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 820°C. In addition, it was adjusted so as to reach 700°C at a temperature decreasing rate of 1.0°C / minute, and the annealing time at a temperature zone of 700°C or more and less than 800°C was 1 hour and 40 minutes. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. In addition, Figure 3 (b) shows a diagram of the annealing process.

[0160] In Example 7, titanium oxide was added as a raw material in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.85:0.03:0.10:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 820°C. In addition, it was adjusted so as to reach 700°C at a temperature decreasing rate of 0.25°C / minute, and the annealing time at a temperature zone of 700°C or more and less than 800°C was 6 hours and 40 minutes. Other than this, the positive electrode active material was obtained in the same manner as in Example 1.

[0161] In Example 8, titanium oxide was added as a raw material, weighed in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.85:0.03:0.10:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 820°C. Further, the temperature was decreased to room temperature at 5°C / min, and then increased to 740°C at 5°C / min, and held at 740°C for 4 hours, and then decreased to room temperature at 5°C / min. Thus, the total annealing time in the temperature zone of 700°C or more and less than 800°C was 4 hours and 36 minutes. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. Further, Figure 3 (c) shows a diagram of the annealing process.

[0162] In Example 9, titanium oxide was added as a raw material, weighed in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.85:0.03:0.10:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 820°C. Further, the temperature was decreased to 780°C at 5°C / min, and held at 780°C for 4 hours, and then decreased to room temperature at 5°C / min. Thus, the total annealing time in the temperature zone of 700°C or more and less than 800°C was 4 hours and 20 minutes. Other than this, the positive electrode active material was obtained in the same manner as in Example 1.

[0163] In Example 10, titanium oxide was added as a raw material, and cobalt carbonate was removed, weighed in a molar ratio of Li:Ni:Mn:Ti = 1.03:0.85:0.13:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. Thus, the total annealing time in the temperature zone of 700°C or more and less than 800°C was 3 hours and 20 minutes.

[0164] In Example 11, titanium oxide was added as a raw material, weighed in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.90:0.03:0.05:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes. Further, the maximum CO2 concentration in the pre-sintering was 10,000 ppm, the maximum CO2 concentration in the main sintering was 110 ppm, and the maximum CO2 concentration in the annealing was 30 ppm.

[0165] In Example 12, as the raw material, cobalt carbonate was removed and titanium oxide was added, and was weighed in a molar ratio of Li:Ni:Mn:Ti = 1.03:0.90:0.08:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Except for this, the positive active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0166] In Example 13, as the raw material, titanium oxide was added, and was weighed in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.94:0.02:0.02:0.02, the pre-sintering temperature was 740°C, and the main sintering temperature was 860°C. Except for this, the positive active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0167] In Example 14, as the raw material, manganese carbonate was removed and aluminum oxide was added, and was weighed in a molar ratio of Li:Ni:Co:Al = 1.03:0.90:0.07:0.03, the pre-sintering temperature was 700°C, and the main sintering temperature was 820°C. Except for this, the positive active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0168] In Example 15, as the raw material, aluminum oxide was added, and was weighed in a molar ratio of Li:Ni:Co:Mn:Al = 1.03:0.90:0.03:0.02:0.05, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Except for this, the positive active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0169] In Example 16, as the raw material, gallium oxide was added, and was weighed in a molar ratio of Li:Ni:Co:Mn:Ga = 1.03:0.90:0.03:0.05:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Except for this, the positive active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0170] In Example 17, as the raw material, magnesium oxide was added, and was weighed in a molar ratio of Li:Ni:Co:Mn:Mg = 1.03:0.90:0.03:0.06:0.01, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Except for this, the positive active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0171] In Example 18, zirconium oxide was added as a raw material, weighed in a molar ratio of Li:Ni:Co:Mn:Zr = 1.03:0.90:0.03:0.05:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0172] In Example 19, zinc oxide was added as a raw material, weighed in a molar ratio of Li:Ni:Co:Mn:Zn = 1.03:0.90:0.03:0.05:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. Thus, the annealing time was 3 hours and 20 minutes.

[0173] (Comparative Examples 1 to 3)

[0174] In Comparative Example 1, there was almost no annealing treatment. After the main sintering, the temperature was decreased to room temperature at 5°C / minute. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. Thus, from the highest temperature of the main sintering, the time period for maintaining the temperature in the temperature zone of 700°C or higher and 800°C or lower was 20 minutes. Further, the highest CO2 concentration of the pre-sintering was 8600 ppm, the highest CO2 concentration of the main sintering was 210 ppm, and the highest CO2 concentration of the annealing was 20 ppm.

[0175] In Comparative Example 2, the annealing time was shortened. Titanium oxide was added as a raw material, weighed in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.85:0.03:0.10:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 820°C. After the main sintering, the temperature was decreased to room temperature at 2°C / minute. Thus, the annealing time was 50 minutes. Other than this, the positive electrode active material was obtained in the same manner as in Example 1. Further, the highest CO2 concentration of the pre-sintering was 11000 ppm, the highest CO2 concentration of the main sintering was 160 ppm, and the highest CO2 concentration of the annealing was 20 ppm.

[0176] In Comparative Example 3, there was almost no annealing time, and the sintered powder was also subjected to water washing. Titanium oxide was added as a raw material, weighed in a molar ratio of Li:Ni:Co:Mn:Ti = 1.03:0.90:0.03:0.05:0.02, the pre-sintering temperature was 700°C, and the main sintering temperature was 840°C. After the main sintering, the temperature was decreased to room temperature at 5°C / minute. Thus, the annealing time was 20 minutes. Pure water was added to the obtained sintered powder so as to obtain a mass ratio of sintered powder / pure water = 2 / 1, the mixture was stirred for 1 minute, the powder recovered by filtration was dried under vacuum at 80°C for 12 hours, and further dried at 240°C for 12 hours, to obtain the positive electrode active material.

[0177] (Measurement of chemical composition of positive electrode active material)

[0178] The chemical composition of the synthesized positive electrode active material was analyzed using an ICP-AES emission spectrometer "OPTIMA 8300" (manufactured by PerkinElmer). As a result, it was confirmed that the positive electrode active materials described in Examples 1 to 19 and the positive electrode active materials described in Comparative Examples 1 to 3 had the chemical compositions shown in Table 1-1.

[0179] (Compression of positive electrode active material)

[0180] The positive electrode active material in the positive electrode mixture slurry is subjected to shear force during adjustment in the mixture coating process, and a part of the secondary particles is broken, so a load is applied to the positive electrode active material, simulating the state of the positive electrode active material in the positive electrode mixture slurry. After 1 g of the positive electrode powder was put into a mold having an area of 0.49 cm 2 , compression was performed using an autograph device "AGS-1 kNX" (manufactured by Shimadzu Corporation) at a load of 8 kN (i.e., a pressure per unit area of 160 MPa (≈16,327 N / cm 2 ), and the positive electrode active material was recovered. Figure 4 The particle size distribution of the positive electrode active material before and after compression in Example 1 is shown in Table 1-2. Before compression, an average particle diameter of 13.5 μm was shown, and after compression, particles of less than 5 μm, which were not seen before compression, were increased, and the average particle diameter was 8.5 μm.

[0181] (Neutralization titration)

[0182] The residual alkali component of the positive electrode active material was measured using an automatic titration device "COM-1700A" (manufactured by Hiranuma Sangyo) in the following order. After 0.5 g of the positive electrode powder was put into 30 mL of pure water, the inside of the container was replaced with Ar, and the Li component was extracted by stirring for 1 hour, and the extract was obtained by suction filtration. The obtained extract of 25 mL was diluted to about 40 mL with pure water, and titrated with 0.02 M hydrochloric acid, and the amount of the lithium carbonate component and the lithium hydroxide component in the extract was analyzed. The peak of the titration curve had two stages, the amount of the lithium carbonate was taken as the amount of titration between the equivalent point of the first stage and the equivalent point of the second stage, and the amount of the lithium hydroxide was taken as the amount of titration up to the equivalent point of the first stage minus the amount of the lithium carbonate.

[0183] The residual lithium hydroxide amount Ll (mass %) of the positive electrode active material calculated from the above neutralization titration and the residual lithium hydroxide amount L2 (mass %) of the positive electrode active material calculated from the above neutralization titration after compression were measured, and the ratio L2 / Ll of L2 with respect to Ll was obtained. The results are shown in Table 1-2.

[0184] (Raman spectroscopy)

[0185] Raman micro-spectroscopy was performed using a laser Raman microscope "RAMAN force" (Nanophoton) under conditions of a wavelength of 532 nm and a diameter of 0.36 μm to obtain Raman spectra in a range of 413 x 373 μm. Using the obtained spectra, the half-height width (cm"1) of the Eg and Alg vibration peaks was calculated by fitting analysis of a Lorentz distribution function. -1 The results are shown in Tables 1-2.

[0186] (gelation resistance)

[0187] The positive electrode active material, the carbon-based conductive material, and the binder (PVdF) previously dissolved in N-methyl-2-pyrrolidone (NMP) were weighed in a mass ratio of 96:2:2, and a positive electrode mixture slurry was prepared using a kneader "Hibis Mix 2P-03" (manufactured by Primix Corporation). The viscosity of the obtained positive electrode mixture slurry was measured using a viscosity meter "TVB 10" (manufactured by Tokimec) at a rotation speed of 0.5 rpm. In addition, the positive electrode mixture slurry was placed in a plastic container and stored under an atmospheric atmosphere of 25°C, 50% RH, and the viscosity was measured every 1 day. The viscosity of the positive electrode mixture slurry having a positive electrode active material ratio of 96% or more was thus measured.

[0188] The number of days during which the ratio (ηd / η0) of the viscosity η0 of the positive electrode mixture slurry on the slurry preparation day to the viscosity ηd of the positive electrode mixture slurry after standing for d days after the slurry preparation day was maintained at 0.80 or more and 1.2 or less was taken as the gelation resistance (days). The results are shown in Tables 1-2. In addition, as representative examples of the gelation resistance, the ratio (η5 / η0) of the viscosity η0 of the positive electrode mixture slurry on the slurry preparation day to the viscosity η5 of the positive electrode mixture slurry after standing for 5 days after the slurry preparation day was also shown in Tables 1-2 for Example 1, Example 5, and Example 11.

[0189] (discharge capacity, capacity retention rate)

[0190] A lithium ion secondary battery was produced using the synthesized positive electrode active material as a positive electrode material. Thereafter, the discharge capacity and the capacity retention rate of the lithium ion secondary battery were calculated.

[0191] First, the uniformly mixed positive electrode mixture slurry was applied to a positive electrode current collector of an aluminum foil having a thickness of 20 μm at an application amount of 10 mg / cm 2 . Subsequently, the positive electrode mixture slurry applied to the positive electrode current collector was subjected to heat treatment at 120°C to distill and remove the solvent, thereby forming a positive electrode mixture layer. Then, the positive electrode mixture layer was press-formed by hot pressing and punched into a circular shape having a diameter of 15 mm as a positive electrode.

[0192] Next, a lithium ion secondary battery was produced using the produced positive electrode, negative electrode, and separator. As the negative electrode, metal lithium punched into a circular shape having a diameter of 16 mm was used. As the separator, a porous separator made of polypropylene having a thickness of 30 μm was used. The positive electrode and the negative electrode were opposed to each other in a nonaqueous electrolyte solution through the separator, and a lithium ion secondary battery was assembled. As the nonaqueous electrolyte solution, a solution in which LiPF6 was dissolved in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3:7 so as to be 1.0 mol / L was used.

[0193] The produced lithium ion secondary battery was charged at a constant current / constant voltage of 40 A / kg based on the mass of the positive electrode mixture at an upper limit potential of 4.3 V in an environment at 25°C. Then, the discharge capacity (initial capacity) was measured by discharging at a constant current of 40 A / kg based on the mass of the positive electrode mixture to a lower limit potential of 2.5 V. Next, the lithium secondary battery in which the initial capacity was measured was charged at a constant current / constant voltage of 100 A / kg based on the mass of the positive electrode mixture at an upper limit potential of 4.3 V in an environment at 25°C. Then, the discharge to a lower limit potential of 2.5 V at a constant current of 100 A / kg based on the mass of the positive electrode mixture was repeated 100 times, and the discharge capacity after 100 cycles was measured. As the capacity retention rate, the percentage of the discharge capacity after 100 cycles with respect to the initial capacity was calculated.

[0194] The discharge capacity (Ah / Kg) and the capacity retention rate (%) after 100 cycles measured above are shown in Table 1-2.

[0195] [Table 1-1]

[0196]

[0197] [Table 1-2]

[0198]

[0199] Hereinafter, the results shown in Table 1 were investigated.

[0200] First, Examples 1 to 19 satisfied the chemical composition represented by the composition formula (1), the residual lithium hydroxide amount L1 before compression was 0.8 mass% or less, and the ratio L2 / L1 of the residual lithium hydroxide amount L2 after compression by Autograph to L1 was 1.10 or less. As a result, the positive electrode mixture slurry was maintained for at least 5 days or more before gelling, and there was even a case where it was maintained for 10 days or more. Therefore, it was confirmed that the gelling resistance was excellent. Furthermore, with respect to the electrode characteristics, the discharge capacity also showed a high value of substantially 190 Ah / kg or more, and a high capacity retention rate of 90% or more was obtained.

[0201] On the other hand, in Comparative Example 1, since there is almost no annealing treatment, the residual lithium hydroxide amount Ll is large, and L2 / Ll is also high. As a result, the positive electrode mixture slurry gels in less than one day, and is an unqualified product.

[0202] Further, in Comparative Example 2, the annealing treatment is shortened to one hour or less, and both the residual lithium hydroxide amount Ll and L2 / Ll are slightly larger than in the examples. The positive electrode mixture slurry gels after three days. Although there is a tolerance in the manufacturing process, generally, the gelation resistance is required to be five days or more, and the result is unqualified.

[0203] Further, in Comparative Example 3, although there is no annealing treatment, the residual alkali component is removed by water washing. Therefore, the residual lithium hydroxide amount Ll is very small, and L2 / Ll is larger than in the examples. Also, the positive electrode mixture slurry gels in 30 days, and is a good product. However, the capacity maintenance rate is as low as 79%. It is considered that this is because, after water washing, Li in the surface layer of the positive electrode active material is partially eluted in addition to the residual alkali component. Further, since the water washing process and the subsequent drying process are added, it is considered that this is also poor in productivity.

[0204] Next, Figure 5 shows the relationship between the residual lithium hydroxide amount and the gelation days, Figure 6 shows the relationship between the residual lithium hydroxide amount and the capacity maintenance rate. As Figures 5-6 shown, it can be said that the residual lithium hydroxide amount and the gelation days and the residual lithium hydroxide amount and the capacity maintenance rate have a correlation, respectively. That is, if the residual lithium hydroxide amount is 0.8 mass% or less, the gelation days are shown to be five days or more, and if the residual lithium hydroxide amount is 0.6 mass% or less, the gelation days are about 10 days or more. However, as shown in Comparative Example 2, even if the residual lithium hydroxide amount is 0.8 mass% or less, there is a product in which the gelation days are less than five days. It is considered that this is because, in the process of handling the positive electrode active material in the atmosphere, a part of the residual lithium hydroxide reacts with CO2 gas in the atmosphere and deteriorates to lithium carbonate. In this case, if the residual lithium hydroxide ratio L2 / Ll before and after compression is measured, the result exceeds 1.10. In order to evaluate the gelation resistance, not only the residual lithium hydroxide but also the management of L2 / Ll is important. Further, if the residual lithium hydroxide amount is 0.8 mass% or less, and the capacity maintenance rate is 90% or more. In addition, the discharge capacity at this time also shows a characteristic of about 190 Ah / Kg or more.

[0205] In summary, it is believed that if the residual lithium hydroxide content is below 0.8% by mass, the gelation of the binder is suppressed, resulting in a highly crystalline positive electrode active material and preventing a decrease in capacity retention. Furthermore, although the residual lithium hydroxide content in Comparative Example 3 was below 0.8% by mass, the capacity retention was low. This is believed to be due to the lithium removal near the surface of the positive electrode active material along with the residual lithium hydroxide during water washing, as described above, which reduces crystallinity and the structural stability of the crystal, thus decreasing the capacity retention.

[0206] also, Figure 7 The relationship between L2 / L1 and gelation days is shown in the figure. Figure 8 The relationship between L2 / L1 and capacity maintenance is shown in the figure. Figures 7-8 As shown, it can be said that L2 / L1 is correlated with the number of days of gelation and with the capacity retention rate. That is, if L2 / L1 is below 1.10, it can be said that the number of days of gelation is more than 5 days and the capacity retention rate is more than 90%. Furthermore, it is believed that if L2 / L1 is below 1.10, even if some of the secondary particles of the positive electrode active material break down and the interface inside the secondary particles is re-exposed during the binder coating process, the increase in residual lithium hydroxide and the decrease in crystallinity are less, which can suppress the gelation of the binder and the decrease in capacity.

[0207] Symbol Explanation

[0208] 100 Lithium-ion Secondary Battery

[0209] 101 Battery Cans

[0210] 102 Battery Cover

[0211] 103 Positive Lead Sheet

[0212] 104 negative electrode lead

[0213] 105 Insulation Board

[0214] 106 Sealing Material

[0215] 110 Winded Electrode Assembly

[0216] 111 Positive electrode

[0217] 111a Positive Current Collector

[0218] 111b Positive electrode mixture layer

[0219] 112 Negative electrode

[0220] 112a Negative Current Collector

[0221] 112b Negative Electrode Mixture Layer

[0222] 113 septum

Claims

1. A positive electrode active material for a lithium ion secondary battery, the positive electrode active material for a lithium ion secondary battery being a positive electrode active material for a lithium ion secondary battery containing a lithium transition metal composite oxide represented by the following composition formula (1), a residual lithium hydroxide amount L1 of the positive electrode active material calculated by neutralization titration being 0.8 mass% or less, and a ratio L2 / L1 of a residual lithium hydroxide amount L2 calculated by neutralization titration after the positive electrode active material is compressed at a pressure of 160 MPa to the L1 being 1.10 or less. Li 1+a Ni b Co c M d X e O 2+α (1) wherein In the composition formula (1), M represents at least one selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, a, b, c, d, e, and a are numbers satisfying -0.04 ≤ a ≤ 0.04, 0.80 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.15, 0 ≤ d ≤ 0.20, 0 ≤ e ≤ 0.05, b + c + d + e = 1, and -0.2 < a < 0.2, respectively; the positive electrode active material has secondary particles containing residual lithium hydroxide inside, the secondary particles having a plurality of primary particles containing the lithium transition metal composite oxide; the positive electrode active material has an a-NaFe02-type crystal structure having a layered structure.

2. The positive electrode active material for a lithium ion secondary battery according to claim 1, the residual lithium hydroxide amount L1 of the positive electrode active material calculated by the neutralization titration being 0.6 mass% or less.

3. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, the X being selected from at least one or more elements of a group consisting of Ti, Ga, Mg, Zr, and Zn.

4. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, when a positive electrode mixture slurry containing the positive electrode active material for a lithium ion secondary battery is left to stand for 5 days after a production day, a ratio η5 / η0 of a positive electrode mixture slurry viscosity η0 on the production day to a positive electrode mixture paste viscosity η5 after the left standing for 5 days after the production day is 0.80 or more and 1.2 or less.

5. A method for manufacturing a positive electrode active material for a lithium ion secondary battery, the method for manufacturing a positive electrode active material for a lithium ion secondary battery being a method for manufacturing a positive electrode active material for a lithium ion secondary battery containing a lithium transition metal composite oxide represented by the following composition formula (1), the positive electrode active material including a plurality of secondary particles aggregated from a plurality of primary particles, the secondary particles containing residual lithium hydroxide inside, Li 1+a Ni b Co c M d X e O 2+α (1) wherein In the composition formula (1), M represents at least one selected from Al and Mn, X represents one or more metal elements other than Li, Ni, Co, Al, and Mn, a, b, c, d, e, and a are numbers satisfying -0.04 ≤ a ≤ 0.04, 0.80 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.15, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.05, b + c + d + e = 1, and -0.2 < a < 0.2, respectively; the method for manufacturing a positive electrode active material for a lithium ion secondary battery has: a mixing step of mixing a compound containing Li, Ni, Co, M, and X in the composition formula (1); a granulation step of obtaining a granulated body from a raw material slurry obtained through the mixing step; a sintering step of sintering the granulated body to obtain the positive electrode active material having an α-NaFeO2-type crystal structure in a layered structure, the positive electrode active material containing a plurality of secondary particles formed of a plurality of primary particles containing a lithium transition metal composite oxide represented by the composition formula (1), a subsequent annealing treatment step of cooling from the highest temperature and maintaining at a temperature zone of 700°C or higher and 800°C or lower for 1.5 hours or longer, the sintering step being a multistage heat treatment step including at least a first heat treatment step of maintaining a heat treatment temperature at 600°C or higher and less than 750°C and a second heat treatment step of maintaining a heat treatment temperature at 750°C or higher and 900°C or lower.

6. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 5, in the sintering step, the highest CO2 concentration of the atmosphere of the second heat treatment step is lower than the highest CO2 concentration of the first heat treatment step, and the highest CO2 concentration of the annealing treatment step is lower than the highest CO2 concentration of the second heat treatment step.

7. A lithium ion secondary battery having a positive electrode containing the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4.

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