JP2016100064A - Positive electrode active material and method for manufacturing the same, and positive electrode, nonaqueous secondary battery and secondary battery module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material which enables the achievement of both of satisfactory cycle and high-capacity characteristics in a nonaqueous secondary battery.SOLUTION: A positive an electrode active material for a nonaqueous secondary battery comprises: active material particles of a layered structure, each having a core portion and a surface layer portion which differ in composition from each other. The active material particles have a composition expressed by the following formula (1), of which the a zeta potential isoelectric point is 5-7: LiNiMnCoMO(1). In the formula (1), M is at least one element selected from a group consisting of Mg, Al, Ti, Mo and Nb; "a", "b", "c", "d" and "e" are numbers satisfying: -0.1≤a≤0.3, 0.5≤b≤0.95, 0<c≤0.95, 0≤d≤0.6, 0≤e≤0.1, and b+c+d+e=1.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to a positive electrode active material used in a non-aqueous secondary battery, a method for producing the same, and a positive electrode, a non-aqueous secondary battery, and a secondary battery module using the positive electrode active material.

  One type of non-aqueous secondary battery in which a non-aqueous electrolyte mediates electrical conduction between electrodes is a lithium ion secondary battery. A lithium ion secondary battery is a secondary battery in which lithium ions are responsible for electrical conduction between electrodes in charge and discharge reactions. Compared to other secondary batteries such as nickel-hydrogen storage batteries and nickel-cadmium storage batteries, the energy density Is high and the memory effect is small. Therefore, lithium ion secondary batteries can be used for small power sources such as portable electronic devices and household electric appliances, stationary power sources such as power storage devices, uninterruptible power supply devices, power leveling devices, ships, railways, hybrid vehicles, Applications are expanding to medium and large power sources such as drive power sources for electric vehicles. Lithium ion secondary batteries used in such a wide range of fields are required to further improve battery performance. For example, in in-vehicle applications such as hybrid vehicles and electric vehicles, the cruising distance must be increased. Realization of higher energy density is required.

For example, in view of the need for a cathode material with high stability, high capacity, and high energy, a core including a layered lithium metal oxide having an O3 crystal structure, an O3 crystal structure surrounding the core, and an oxygen deficiency A composite particle including a shell layer including a layered lithium metal oxide having a surface area has been developed (see Patent Document 1 below). In Patent Document 1, the core includes 30 to 85 mole percent composite particles based on the total moles of atoms of the composite particles. The core also has a layered lithium metal oxide when the layered lithium metal oxide is incorporated into the cathode of a lithium ion battery and discharged after being charged to at least 4.6 volts relative to the lithium ion battery Li / Li ⁺ . The oxide shows no dQ / dV peak below 3.5 volts.

  In addition, the metal composition has a continuous concentration gradient with the objective of improving the thermal stability, high capacity characteristics, low temperature characteristics, energy density, life characteristics, conductivity, discharge capacity, and high rate characteristics of the active material. Providing a positive electrode active material for a lithium battery has been studied (see Patent Document 2 below). Patent Document 2 discloses a positive electrode active material that includes an inner bulk portion and an outer bulk portion surrounding the inner bulk portion, and a metal composition exists in a continuous concentration gradient from the boundary surface between the outer bulk portion and the inner bulk portion to the active material surface. Is described. In Patent Document 2, the positive electrode active material has a metal component having a continuous concentration distribution depending on the position, and is excellent in electrochemical characteristics such as life and capacity, and thermal stability.

Special table 2014-505992 gazette Special table 2009-525578

In the composite particle described in Patent Document 1, a layered lithium metal oxide having an oxygen vacancy constituting a shell layer is represented by Li [Li _0.2 Mn _0.54 Ni _0.13 Co _0.13 ] O ₂ . Li-rich positive electrode material. When such a Li-excess positive electrode material is used for a positive electrode of a lithium ion secondary battery, the battery plate voltage has a potential plateau region of 4.5 V (vs Li / Li ⁺ ) upon initial charging of the lithium ion secondary battery. It has a solid solution. When the shell layer is a solid solution having a plateau at 4.5 V at the first charge, the battery voltage is 4.3 V (vs. Li ^/ Li ⁺ ) or lower, and the positive electrode is 4.4 V (vs. Li / Li ⁺ ) or less) is not considered. Further, although a high capacity can be obtained at 50 ° C., there is a problem that the capacity is low at room temperature. Therefore, it is difficult to achieve both high cycle characteristics and high capacity.

The positive electrode active material for lithium battery described in Patent Document 2, the internal bulk _{material, Li a Ni 1-x-} y-z Co x Mn y M z O 2-δ X δ (0.95 ≦ a ≦ 1.2, 0.01 ≦ x ≦ 0.4, 0.01 ≦ y ≦ 0.5, 0.005 ≦ z ≦ 0.3, 0.05 ≦ x + y + z ≦ 0.4, M Is at least one element selected from the group consisting of Mg, Al, Cr, V, Ti, Cr, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W and combinations thereof, X is composed of a halogen element such as F, Cl, Br, or I, 0 ≦ δ ≦ 0.1), and includes a high Ni layered material having a Ni composition ratio of 0.6 or more. About the positive electrode active material described in patent document 2, in order to suppress cycle deterioration, it is necessary to enlarge the ratio of an external bulk material. However, since the external bulk material has a Ni composition ratio of less than 0.6, a high capacity cannot be obtained if the proportion of the external bulk material is increased.

  The present invention has been made in view of the above problems, and a positive electrode active material capable of achieving both good cycle characteristics and high capacity characteristics of a non-aqueous secondary battery, a manufacturing method thereof, and a positive electrode using the same, An object is to provide a non-aqueous secondary battery and a secondary battery module.

  In order to achieve the above object, the positive electrode active material of the present invention is a positive electrode active material for a non-aqueous secondary battery comprising active material particles having a layered structure having a core portion and a surface layer portion having different compositions. The substance particles have a composition represented by the following formula (1) and have an isoelectric point of zeta potential of 5 or more and 7 or less.

_{Li 1 + a Ni b Mn c} Co d M e O 2 ... (1)

  In the above formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Mo, and Nb, and a, b, c, d, and e are −0. 0.1 ≦ a ≦ 0.3, 0.5 ≦ b ≦ 0.95, 0 <c ≦ 0.95, 0 ≦ d ≦ 0.6, 0 ≦ e ≦ 0.1, and b + c + d + e = 1 Is a number.

  According to the positive electrode active material and the positive electrode, non-aqueous secondary battery, and secondary battery module using the positive electrode active material of the present invention, both good cycle characteristics and high capacity characteristics of the non-aqueous secondary battery can be achieved.

The schematic cross section of the active material particle which concerns on Embodiment 1 of the positive electrode active material of this invention. The schematic external view of the active material particle shown to FIG. 1A. The schematic cross section of the active material particle which concerns on Embodiment 2 of the positive electrode active material of this invention. The schematic cross section of the active material particle which concerns on Embodiment 3 of the positive electrode active material of this invention. The schematic cross section of the active material particle which concerns on Embodiment 4 of the positive electrode active material of this invention. 4B is a schematic external view of the active material particles shown in FIG. 4A. FIG. The schematic cross section of the active material particle which concerns on Embodiment 5 of the positive electrode active material of this invention. The schematic cross section of the active material particle which concerns on Embodiment 6 of the positive electrode active material of this invention. The flowchart which shows embodiment of the positive electrode active material manufacturing method of this invention. The typical fragmentary sectional view which shows embodiment of the non-aqueous secondary battery of this invention. The schematic block diagram which shows the secondary battery module of this invention. The TEM image which shows an example of the measurement position of TEM-EDX of the active material particle which concerns on the Example of the positive electrode active material of this invention. The graph which shows the TEM-EDX measurement result of the active material particle which concerns on Example 1 of the positive electrode active material of this invention. The graph which shows the TEM-EDX measurement result of the active material particle which concerns on Example 2 of the positive electrode active material of this invention. The graph which shows the TEM-EDX measurement result of the active material particle which concerns on Example 3 of the positive electrode active material of this invention.

  Hereinafter, embodiments of a positive electrode active material and a method for producing the same, and a positive electrode, a non-aqueous secondary battery, and a secondary battery module will be described with reference to the drawings.

(Positive electrode active material: Embodiment 1)
FIG. 1A is a schematic cross-sectional view of an active material particle 1A constituting a positive electrode active material 10A according to Embodiment 1 of the present invention. FIG. 1B is a schematic external view of the active material particle 1A shown in FIG. 1A.

  10 A of positive electrode active materials of this embodiment are positive electrode active materials for non-aqueous secondary batteries which consist of the active material particle 1A of the layered structure which has the core part 11 and the surface layer part 12 from which a composition differs. The active material particle 1A has a composition represented by the following formula (1), and has an isoelectric point of zeta potential of 5 or more and 7 or less.

_{Li 1 + a Ni b Mn c} Co d M e O 2 ... (1)

  In the above formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Mo, and Nb, and a, b, c, d, and e are −0. 0.1 ≦ a ≦ 0.3, 0.5 ≦ b ≦ 0.95, 0 <c ≦ 0.95, 0 ≦ d ≦ 0.6, 0 ≦ e ≦ 0.1, and b + c + d + e = 1 Is a number.

That is, the core portion 11 and the surface layer portion 12 of the active material particle 1A are both represented by the above formula (1) and have different compositions including at least Li, Ni, and Mn. (Α-NaFeO ₂ type) structure.

  Note that b in the composition formula (1) is preferably in the range of 0.6 ≦ b ≦ 0.9 from the viewpoint of increasing the capacity of the non-aqueous secondary battery. Further, c in the composition formula (1) is preferably 0.05 ≦ c ≦ 0.3. When c is 0.05 or more, cycle deterioration of the non-aqueous secondary battery can be further suppressed, and when c is 0.3 or less, the capacity of the non-aqueous secondary battery can be increased. Further, d in the composition formula (1) is preferably 0.05 ≦ d ≦ 0.2. When d is 0.05 or more, cation mixing can be suppressed, and the capacity of the non-aqueous secondary battery can be increased. If d is larger than 0.2, the amount of expensive Co becomes excessive and the cost increases.

  Moreover, oxygen in the composition formula (1) may be lost as long as the layered structure in the core portion 11 and the surface layer portion 12 of the active material particle 1A is maintained.

  The atomic concentration of Ni in the core portion 11 is preferably higher than the atomic concentration of Ni in the surface layer portion 12. That is, it is preferable that the relationship Cs <Cc is established, where the atomic concentration of Ni in the core portion 11 is Cc and the atomic concentration of Ni in the surface layer portion 12 is Cs. Thereby, when the positive electrode active material 10A is used for the positive electrode of the non-aqueous secondary battery, the capacity of the non-aqueous secondary battery is increased by the core portion 11 of the active material particles 1A having a relatively high atomic concentration of Ni. Can be realized. In addition, the surface layer portion 12 of the active material particles 1A having a relatively low atomic concentration of Ni can suppress cycle deterioration of the non-aqueous secondary battery and improve the cycle characteristics of the non-aqueous secondary battery. The atomic concentration of Ni is the atomic concentration of Ni in a metal element other than Li in the composition formula (1).

  The atomic concentration of Li in the surface layer portion 12 of the active material particle 1 </ b> A is preferably higher than the atomic concentration of Li in the core portion 11. In the active material particles 1A of the positive electrode active material 10A constituting the positive electrode of the non-aqueous secondary battery, when the atomic concentration of Li increases, cycle deterioration at a high potential of the non-aqueous secondary battery is suppressed. The rate characteristics of the secondary battery deteriorate.

  Therefore, by making the Li atom concentration in the surface layer portion 12 of the active material particle 1 </ b> A higher than the Li atom concentration in the core portion 11, the surface layer portion 12 having a relatively high Li atom concentration allows the non-aqueous secondary battery. Of the non-aqueous secondary battery can be maintained by the core 11 having a relatively low atomic concentration of Li. That is, by using the positive electrode material composed of the active material particles 1A in which the atomic concentration of Li in the surface layer portion 12 is higher than the atomic concentration of Li in the core portion 11, while maintaining the rate characteristics of the non-aqueous secondary battery, Cycle degradation at a high potential of the water-based secondary battery can be suppressed.

  Moreover, it is preferable that the surface layer part 12 has a composition represented by following formula (2).

_{Li 1 + a Ni b Mn c} Co d M e O 2 ... (2)

  In the above formula (2), M is at least one element selected from the group consisting of Mg, Al, Ti, Mo, and Nb, and a, b, c, d, and e are 0 < It is a number that satisfies a ≦ 0.3, 0.2 ≦ b ≦ 0.95, 0 <c ≦ 0.95, 0 ≦ d ≦ 0.6, 0 ≦ e ≦ 0.1, and b + c + d + e = 1. .

  By making a in Formula (2) larger than 0, the surface layer portion 12 of the active material particle 1 </ b> A has a Li excess composition in which the Li composition ratio is larger than 1. Thereby, in the non-aqueous secondary battery using the positive electrode active material 10 </ b> A made of the active material particles 1 </ b> A, cycle deterioration at a high potential can be suppressed and cycle characteristics can be improved.

  In the present embodiment, the zeta potential (hereinafter referred to as ζ potential) means an electrokinetic potential. Specifically, when the active material particles 1A are dispersed in a liquid, a diffusion electric double layer is formed in the vicinity of the surface of the active material particles 1A, and a potential difference is generated. When the active material particles 1A move in the liquid, a part of the diffusion layer in which ions are gradually diffused moves together with the fixed layer in which ions are strongly attracted and fixed to the surface of the active material particles 1A. The surface where the movement of the diffusion layer occurs is defined as a sliding surface, the potential of an electrically neutral region sufficiently separated from the active material particle 1A is set to zero, and the potential of the sliding surface measured with reference to this zero point is It can be defined as ζ potential.

  Further, when the pH value of the liquid in which the active material particles 1A are dispersed is changed, the ζ potential fluctuates, the surface potential of the active material particles 1A becomes zero at a certain specific pH value, and the active material particles 1A undergo electrophoresis or the like. No electrokinetic phenomenon is exhibited. The pH value at this time is referred to as an isoelectric point of the ζ potential of the active material particle 1A. The isoelectric point of the ζ potential of the active material particle 1A can be measured as follows using, for example, a ζ potential measuring device.

  First, 1 part by mass of positive electrode active material 10A is added to 1000 parts by mass of pure water and stirred to disperse active material particles 1A using pure water as a dispersion medium. Next, by adjusting the pH value of the dispersion medium using sodium hydroxide and hydrochloric acid, the pH value is sequentially decreased to 11, 10, 9, 7, 5, 4, 3, and ζ at each pH value. Measure the potential. The obtained ζ potential for each pH value is plotted on a graph in which the ordinate is ζ potential and the abscissa is pH, and the ζ potential is negative and the absolute value is the smallest, and the ζ potential is positive and the absolute value is the most. The small points are connected by a straight line, and the pH value at which the ζ potential is 0 is obtained. This determined pH value is taken as the isoelectric point of the ζ potential.

The active material particles 1A thus measured have a zeta potential isoelectric point of 5 or more and 7 or less, and the active material particles 1A have different compositions represented by the above formula (1). It has been found that the following effects can be obtained when a layered structure having That is, the non-aqueous secondary battery using the positive electrode active material 10A made of the active material particles 1A as the positive electrode not only improves cycle characteristics by suppressing cycle deterioration from a low potential to a high potential, but is also high at room temperature. Capacity can be obtained. Here, the low potential is, for example, a battery voltage of 4.3 V (vs Li / Li ⁺ ) or less, a positive electrode single electrode of 4.4 V (vs Li / Li ⁺ ) or less, and the high potential is, for example, The battery voltage is 4.5 V (vs Li / Li ⁺ ) or less, and the positive electrode single electrode is 4.6 V (vs Li / Li ⁺ ) or less.

  That is, the positive electrode active material 10A of the present embodiment has a layered structure in which the active material particle 1A has the core portion 11 and the surface layer portion 12 having different compositions represented by the formula (1), and the active material particle 1A The solid solution condition and the solid solution state of the surface layer portion 12 are adjusted by adjusting the isoelectric point of the ζ potential to a pH value in the range of 5 to 7. It is known that there is a correlation between the isoelectric point of the ζ potential and the electronegativity of the particle surface, and the isoelectric point of the ζ potential can grasp the state of the particle surface. By adjusting the isoelectric point of the ζ potential of the active material particle 1A to a pH value in the range of 5 or more and 7 or less, the surface property and the solid solution state of the surface layer portion 12 can be adjusted, and cycle deterioration from a low potential to a high potential can be achieved. It is suppressed and the cycle characteristics are improved, and a high capacity can be obtained even at room temperature. The method for preparing the isoelectric point of the ζ potential of the active material particle 1A will be described in detail in a positive electrode active material manufacturing method, examples and comparative examples described later.

  The composite particle described in Patent Document 1 is a solid solution that is a low Ni layered material. In the solid solution which is a low Ni layered material, the isoelectric point of ζ potential is higher than 7 in pH value. Therefore, it is difficult to suppress cycle deterioration from a low potential to a high potential. There is also a problem that a high capacity can be obtained at 50 ° C., but a low capacity at room temperature.

  Further, the positive electrode active material for a lithium battery described in Patent Document 2 is a low Ni layered material in which the external bulk material has a Ni composition ratio of less than 0.6, and unlike a solid solution that is a low Ni layered material, ζ The isoelectric point of the potential is lower than 5 at the pH value. Therefore, it is difficult to achieve both suppression of cycle deterioration and increase in capacity.

  On the other hand, the active material particle 1A constituting the positive electrode active material 10A of the present embodiment has a layered structure including the core portion 11 and the surface layer portion 12 having different compositions represented by the formula (1), The isoelectric point of the ζ potential of the substance particle 1A is adjusted to a range of 5 to 7 in terms of pH value. Thereby, the surface layer part 12 of 1 A of active material particles can be made into the solid solution state of these different from the said solid solution and the said high Ni layered material. Therefore, by using the positive electrode active material 10A of the present embodiment as the positive electrode material of the non-aqueous secondary battery, it is possible to achieve both good cycle characteristics and high capacity characteristics of the non-aqueous secondary battery.

  In addition, it is preferable that the thickness of the surface layer part 12 of 1 A of active material particles is 20 nm or more and 200 nm or less, for example. By setting the thickness of the surface layer portion 20 to 20 nm or more, cycle deterioration can be more effectively suppressed. On the other hand, by setting the thickness of the surface portion to 200 nm or less, the ratio of the core portion 11 of the active material particles 1A responsible for increasing the capacity of the non-aqueous secondary battery can be increased, and the non-aqueous secondary battery can be made more The capacity can be increased.

  Further, the core portion 11 of the active material particle 1A may be completely covered by the surface layer portion 12 as shown in FIG. 1A, but the core portion 11 is completely covered by the surface layer portion 12 as shown in FIG. 1B. The core portion 11 may be partly exposed from the surface layer portion 12 without being covered. That is, the surface layer portion 12 may be formed on the entire periphery of the core portion 11 or may be formed on a part of the periphery of the core portion 11. In addition, the coverage of the core part 11 by the surface layer part 12, ie, the ratio in which the surface layer part 12 is formed on the surface of the material to be the core part 11, is 80 from the viewpoint of suppressing cycle deterioration of the non-aqueous secondary battery. % Or more is preferable. Moreover, it is preferable that the ratio of 1 A of active material particles which have the core part 11 and the surface layer part 12 in 10A of positive electrode active materials is 50% or more from a viewpoint of suppressing the cycle deterioration of a non-aqueous secondary battery.

(Positive electrode active material: Embodiment 2)
FIG. 2 is a schematic cross-sectional view of the active material particles 1B constituting the positive electrode active material 10B according to Embodiment 2 of the present invention.

  The positive electrode active material 10B of the present embodiment is different from the positive electrode active material 10A described in the first embodiment in that the positive electrode active material 10B is a composite particle obtained by sintering a plurality of particles having the core portion 11 and the surface layer portion 12. Yes. Since the other points of the positive electrode active material 10B of this embodiment are the same as those of the positive electrode active material 10A described in the first embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.

  The particles constituting the active material particles 1B of the present embodiment are particles corresponding to the active material particles 1A described in the first embodiment. That is, the positive electrode active material 10B of the present embodiment, like the positive electrode active material 10A of the first embodiment, is a non-aqueous secondary material composed of active material particles 1B having a layered structure having a core portion 11 and a surface layer portion 12 having different compositions. It is a positive electrode active material for batteries. The active material particle 1B has a composition represented by the formula (1), and has an isoelectric point of zeta potential of 5 or more and 7 or less. Therefore, according to the positive electrode active material 10B of the present embodiment, the same effect as that of the positive electrode active material 10A of the first embodiment can be obtained. Note that the active material particles 1B constituting the positive electrode active material 10B of the present embodiment may include particles different from the particles corresponding to the active material particles 1A of the first embodiment in a part near the surface.

  The active material particles 1B (secondary particles) may be composed of a plurality of particles (primary particles) having a core portion 11 and a surface layer portion 12 by physical force, but constitute the active material particles 1B. It is preferable that the particles to be sintered are sintered. Since the particles constituting the active material particles 1B are sintered, the strength of the active material particles 1B is increased, the allowable shear force during the production of the positive electrode is increased, and the production of the positive electrode is facilitated.

(Positive electrode active material: Embodiment 3)
FIG. 3 is a schematic cross-sectional view of the active material particles 1C constituting the positive electrode active material 10C according to Embodiment 3 of the present invention.

  In the active material particle 1C constituting the positive electrode active material 10C of the present embodiment, the core portion 11 is a sintered body obtained by sintering a plurality of particles, and the surface layer portion 12 is formed on the surface of the sintered body. Thus, it is different from the positive electrode active material 10A described in the first embodiment. Since the other points of the positive electrode active material 10C of the present embodiment are the same as those of the positive electrode active material 10A described in the first embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.

  10 C of positive electrode active materials of this embodiment are the same as the positive electrode active material 10A of Embodiment 1, For non-aqueous secondary batteries which consist of the active material particle 1C of the layer structure which has the core part 11 and the surface layer part 12 from which a composition differs. The positive electrode active material. In the present embodiment, the core portion 11 of the active material particle 1 </ b> C is a sintered body in which a plurality of particles are sintered. In the active material particle 1C, the composition of the core portion 11 and the surface layer portion 12 is represented by the above formula (1), and the isoelectric point of the zeta potential is 5 or more and 7 or less, as in the positive electrode active material 10A of Embodiment 1. is there. Therefore, according to the positive electrode active material 10C of the present embodiment, the same effects as those of the positive electrode active material 10A of the first embodiment can be obtained.

  In the active material particle 1C (secondary particle), a plurality of particles (primary particles) constituting the core part 11 may be aggregated by physical force, but the particles constituting the core part 11 are sintered. It is preferable. Since the particles constituting the core portion 11 are sintered, the strength of the active material particles 1C is increased, the allowable shear force during the production of the positive electrode is increased, and the production of the positive electrode is facilitated.

(Positive electrode active material: Embodiment 4)
FIG. 4A is a schematic cross-sectional view of active material particles 1D constituting a positive electrode active material 10D according to Embodiment 4 of the present invention. FIG. 4B is a schematic external view of the active material particle 1D shown in FIG. 4A.

  The active material particle 1D constituting the positive electrode active material 10D of the present embodiment is different from the positive electrode active material 10A described in the first embodiment described above in that the intermediate portion 13 is provided between the core portion 11 and the surface layer portion 12. ing. Since the other points of the positive electrode active material 10D of this embodiment are the same as those of the positive electrode active material 10A described in the first embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.

  The active material particle 1 </ b> D constituting the positive electrode active material 10 </ b> D of the present embodiment has an intermediate portion 13 between the core portion 11 and the surface layer portion 12. The atomic concentration of Ni in the intermediate portion 13 is preferably lower than the atomic concentration of Ni in the core portion 11 and higher than the atomic concentration of Ni in the surface layer portion 12. That is, if the atomic concentration of Ni in the surface layer portion 12 is Cs, the atomic concentration of Ni in the intermediate portion 13 is Cm, and the atomic concentration of Ni in the core portion 11 is Cc, the relationship Cs <Cm <Cc is established. Is preferred. When the active material particle 1D has a core part 11 and a surface layer part 12 having a layered structure with different compositions represented by the formula (1), and the isoelectric point of the zeta potential is 5 or more and 7 or less, This is because when the relationship of Cs <Cm <Cc is established, cycle deterioration of the nonaqueous secondary battery using the positive electrode active material 10D made of the active material particles 1D can be more effectively suppressed.

  Moreover, it is preferable that the concentration gradient of Ni atom concentration in the surface layer portion 12 is smaller than the concentration gradient of Ni atom concentration in the intermediate portion 13. That is, if the Ni concentration gradient in the surface layer portion 12 is Gs and the Ni concentration gradient in the intermediate portion 13 is Gm, the relationship of Gs <Gm is preferably established. By interposing an intermediate portion 13 having a concentration gradient larger than that of the surface layer portion 12 between the surface layer portion 12 and the core portion 11, while smooth movement of Li ions from the surface of the active material particle 1D toward the center, The thickness of the surface layer portion 12 and the intermediate portion 13 can be reduced. Therefore, relatively increasing the volume of the core 11 that contributes to increasing the capacity of the non-aqueous secondary battery and increasing the capacity of the non-aqueous secondary battery using the positive electrode active material 10D made of the active material particles 1D. Can do.

  The surface layer part 12, the intermediate part 13, and the core part 11 of the active material particle 1D can be defined as follows, for example. When the Ni atom concentration has a gradient of −0.01 mol% / nm or more at a distance within 200 nm from the surface of the active material particle 1D toward the center, the Ni atom concentration gradually decreases until the end of the gradient. Is defined as the surface layer portion 12. Further, the core portion 11 is defined as a portion where the difference between the center of the active material particle 1D and the Ni atom concentration is 2 mol% or less. Further, a portion between the surface layer portion 12 and the core portion 11 of the active material particle 1 </ b> D is defined as an intermediate portion 13. Here, the center of the active material particle 1D can be, for example, the center of gravity of the active material particle 1D or the center of gravity of the cross-sectional shape of the active material particle 1D.

  When the Ni atom concentration does not have a slope of −0.01 mol% / nm or more at a distance within 200 nm from the surface of the active material particle 1D toward the center, the surface of the active material particle 1D and the Ni atom concentration Can be defined as the surface layer portion 12, and the portion where the difference between the center of the active material particle 1 </ b> D and the Ni atom concentration is within 2 mol% can be defined as the core portion 11.

  The thickness of the intermediate portion 13 of the active material particle 1D is preferably 10 nm or more and 100 nm or less. By making the thickness of the intermediate part 13 10 nm or more, the movement of Li ions in the active material particles 1D becomes smoother. On the other hand, by setting the thickness of the intermediate part 13 to 100 nm or less, the volume of the core part 11 contributing to the increase in capacity of the non-aqueous secondary battery is increased, and the non-aqueous secondary using the positive electrode active material 10D as the positive electrode. The capacity of the battery can be increased.

  The thickness of the surface layer part 12 or the intermediate part 13 of the active material particle 1D and the concentration gradient Gs or Gm of the atomic concentration of Ni in the surface layer part 12 or the intermediate part 13 of the active material particle 1D are, for example, transmission electron microscope-energy It can be measured by dispersive X-ray spectroscopy (TEM-EDX), transmission electron microscope-electron energy loss spectroscopy (TEM-EELS). .

  Specifically, the thickness of the surface layer portion 12 or the intermediate portion 13 of the active material particle 1D is determined by, for example, TEM-EDX line analysis in the active material particle 1D randomly selected in the transmission electron microscope image. It can be measured by performing point analysis at intervals of several nm to 50 nm. In addition, the concentration gradient Gs or Gm of the Ni atomic concentration in the surface layer portion 12 or the intermediate portion 13 of the active material particle 1D is determined by TEM-EDX in the active material particle 1D randomly selected in the transmission electron microscope image. It can be measured by performing line analysis or point analysis at intervals of several nm to 10 nm.

  4A, the core part 11 of the active material particle 1D may be completely covered by the surface layer part 12 and the intermediate part 13, but the core part 11 is formed by the surface layer part as shown in FIG. 4B. 12 and the intermediate part 13 may not be completely covered, and a part of the core part 11 and the intermediate part 13 may be exposed from the surface layer part 12. That is, the surface layer portion 12 and the intermediate portion 13 may be formed on the entire periphery of the core portion 11 or may be formed on a part of the periphery of the core portion 11. Further, the intermediate portion 13 may not be formed between the core portion 11 and the surface layer portion 12, and there may be a region where the core portion 11 and the surface layer portion 12 are in contact with each other.

(Positive electrode active material: Embodiment 5)
FIG. 5 is a schematic cross-sectional view of active material particles 1E constituting the positive electrode active material 10E according to Embodiment 5 of the present invention.

  The positive electrode active material 10E of the present embodiment is a composite particle obtained by sintering a plurality of particles having a core part 11, an intermediate part 13, and a surface layer part 12, and has been described in the fourth embodiment. It is different from 10D. Since the other points of the positive electrode active material 10E of the present embodiment are the same as those of the positive electrode active material 10D described in the fourth embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.

  The particles constituting the active material particles 1E of the present embodiment are particles corresponding to the active material particles 1D described in the fourth embodiment. That is, the positive electrode active material 10E of the present embodiment is composed of layered structure active material particles 1E having a core part 11, an intermediate part 13, and a surface layer part 12 having different compositions, like the positive electrode active material 10D of the fourth embodiment. It is a positive electrode active material for non-aqueous secondary batteries. The active material particle 1E has a composition represented by the formula (1), and has an isoelectric point of zeta potential of 5 or more and 7 or less. Therefore, according to the positive electrode active material 10E of this embodiment, the same effect as the positive electrode active material 10D of Embodiment 4 can be obtained. The active material particles 1E constituting the positive electrode active material 10E of the present embodiment may include particles different from the particles corresponding to the active material particles 1D of the fourth embodiment in a part near the surface.

(Positive electrode active material: Embodiment 6)
FIG. 6 is a schematic cross-sectional view of active material particles 1F constituting positive electrode active material 10F according to Embodiment 6 of the present invention.

  In the active material particle 1F constituting the positive electrode active material 10F of the present embodiment, the core portion 11 is a sintered body obtained by sintering a plurality of particles, and the intermediate portion 13 and the surface layer portion 12 are formed on the surface of the sintered body. This is different from the positive electrode active material 10D described in the fourth embodiment. Since the other points of the positive electrode active material 10F of this embodiment are the same as those of the positive electrode active material 10D described in the above-described fourth embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.

  Similarly to the positive electrode active material 10D of the fourth embodiment, the positive electrode active material 10F of the present embodiment is a non-aqueous system composed of active material particles 1F having a layered structure having a core part 11, an intermediate part 13, and a surface layer part 12 having different compositions. It is a positive electrode active material for a secondary battery. In the present embodiment, the core portion 11 of the active material particle 1F is a sintered body in which a plurality of particles are sintered. In the active material particle 1F, the composition of the core portion 11 and the surface layer portion 12 is expressed by the above formula (1), and the isoelectric point of the zeta potential is 5 or more and 7 or less, as in the positive electrode active material 10D of Embodiment 4. is there. Therefore, according to the positive electrode active material 10F of this embodiment, the same effect as the positive electrode active material 10D of Embodiment 4 can be obtained.

(Positive electrode active material manufacturing method)
Hereinafter, an embodiment of the positive electrode active material manufacturing method of the present invention will be described. FIG. 7 is a flowchart showing the steps of the positive electrode active material manufacturing method of the present embodiment.

  In general, a positive electrode active material for a non-aqueous secondary battery can be produced by, for example, a solid phase method, a coprecipitation method, a sol-gel method, a hydrothermal method, or the like. These methods can also be employed in the positive electrode active material manufacturing method of the present embodiment.

  The positive electrode active material manufacturing method of the present embodiment is a precursor particle manufacturing step S1 for manufacturing the precursor particles of the core part 11 and the surface layer part 12 having different compositions of the active material particles 1A-1F represented by the formula (1). And a mixing step S2 for mixing the produced precursor particles, and a heat treatment step S3 for heat-treating the mixed mixture.

  In the precursor particle manufacturing step S1, the transition metal compound and the Li compound are mixed and fired to manufacture the core part precursor particles and the surface layer part precursor particles. More specifically, first, raw material Li compound, Ni compound, Mn compound, transition metal M compound included in the above-described composition formula (1), and the like are weighed at a ratio of a predetermined element composition, pulverized and mixed. Prepare raw material powder.

  Examples of the Li compound include lithium acetate, lithium nitrate, lithium carbonate, lithium hydroxide, lithium chloride, and lithium sulfate. Examples of the Ni compound include nickel acetate, nickel nitrate, nickel carbonate, nickel sulfate, and nickel hydroxide. As the Mn compound, for example, nickel acetate, manganese nitrate, manganese carbonate, manganese sulfate, manganese oxide, manganese hydroxide, or the like can be used. In addition, when an element of Co or transition metal M is contained, these acetates, nitrates, carbonates, sulfates, hydroxides, oxides, and the like can be used.

  For the pulverization and mixing for preparing the raw material powder, any of dry pulverization and wet pulverization methods can be used. As the pulverizing means, for example, a pulverizer such as a ball mill, a bead mill, a planetary ball mill, an attritor, or a jet mill can be used.

  The raw material powders prepared with different materials or different ratios are fired, respectively, and core part precursor particles that are precursors of the core part 11 of the active material particles 1A-1F and the surface layer part 12 of the active material particles 1A-1F. It becomes the surface layer part precursor particle | grains which are the precursor of this. It is preferable to sinter the raw material powder by subjecting the raw material compound to thermal decomposition by calcination in an inert gas atmosphere or an oxidizing gas atmosphere, and appropriately pulverizing and classifying the material compound, followed by main calcination. The heating temperature in the pre-baking can be, for example, in a range of approximately 300 ° C. to 700 ° C., and the heating temperature in the main baking can be, for example, in a range of approximately 700 ° C. to 1100 ° C., for example.

  In order to produce the active material particles 1A, 1B, 1D, and 1E of Embodiments 1, 2, 4, and 5 shown in FIG. 1A and FIG. 1B, FIG. 2, FIG. 4A, and FIG. Crushing is performed to separate the core part precursor particles, which are sintered bodies (secondary particles) in a sintered state, into individual particles (primary particles). Moreover, in order to produce the active material particles 1C and 1F of Embodiments 3 and 6 shown in FIGS. 3 and 6, the core part precursor particles, which are sintered bodies in which a plurality of particles are sintered, are used as they are. Can do. Further, it is preferable that the surface layer precursor particles are pulverized into individual particles of a sintered body in which a plurality of particles are sintered, or the pulverized individual particles are further finely pulverized.

  In the precursor particle manufacturing step S1, the median diameter of the core part precursor particles can be, for example, not less than 2 times and not more than 100 times the median diameter of the surface layer part precursor particles. That is, when the median diameter of the core part precursor particles is D50A and the median diameter of the surface layer part precursor particles is D50B, it is preferable that the relationship 2 ≦ D50A / D50B ≦ 100 is satisfied. If D50A / D50B is 2 or more, the surface layer part precursor particles can be arranged on the surface of the core part precursor particles. On the other hand, when D50A / D50B is 100 or more, the surface layer precursor particles become too small, and the production becomes difficult.

  Next, a mixing step S2 for mixing the core part precursor particles and the surface layer part precursor particles manufactured in the precursor particle manufacturing step S1 is performed. In the mixing step S2, the core part precursor particles and the surface layer part precursor particles are mixed, or the surface part part precursor particles are supported on the surface of the core part precursor particles. The mixing step S2 can be performed using, for example, a levester, a Henschel mixer, a ball mill, a bead mill, a planetary ball mill, an attritor, a surface modification device, a compounding device, or the like.

  In the mixing step S2, it is preferable to mix the surface layer precursor particles at a ratio of 0.1 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the core part precursor particles. By mixing the core part precursor particles and the surface layer part precursor particles at such a mass ratio, the thickness of the surface layer part 12 of the active material particles 1A-1F or the thicknesses of the surface layer part 12 and the intermediate part 13 can be reduced. Can be adjusted.

  Next, a heat treatment step S3 is performed in which the mixture obtained in the mixing step S2 is heat-treated so as to become active material particles 1A-1F having an isoelectric point of zeta potential of 5 or more and 7 or less. The heating temperature in the heat treatment step S3 can be, for example, 300 ° C. or higher and 1100 ° C. or lower. The heating temperature of the heat treatment in the heat treatment step S3 is not less than a temperature that is 200 ° C. lower than the firing temperature of main firing of the core part precursor particles in the precursor particle manufacturing step S1, and not more than 50 ° C. higher than the firing temperature. It is preferable that Thereby, the formation rate and the formation particle rate of the active material particles 1A-1F are improved.

  Here, the formation rate and the formation particle rate of the active material particles 1A-1F can be calculated by measuring the composition of a plurality of locations of the active material particles 1A-1F. Specifically, for example, the atomic concentration of Ni at the center of the active material particles 1A-1F is measured in the cross section of the randomly selected active material particles 1A-1F. Further, for example, the atomic concentration of Ni at a position of 10 nm from the surface to the center side is measured at four locations on the top, bottom, left and right of the cross section of the active material particles 1A-1F. Then, the value obtained by dividing the number of measurement points where the atomic concentration of Ni higher than the atomic concentration of Ni in the central portion is divided by the total number of all measurement points and multiplying by 100 is the active material particle 1A- The formation rate can be 1F. The composition of the active material particles 1A-1F such as the atomic concentration of Ni can be measured by, for example, TEM-EDX, TEM-EELS, or the like.

  Moreover, in order to calculate the formation particle ratio of the active material particles 1A-1F, as in the case of calculating the formation ratio, in the cross section of the randomly selected active material particles 1A-1F, The atomic concentration of Ni in the center is measured. In addition, in the same cross section, for example, the atomic concentration of Ni at a position of 10 nm from the surface to the center side is measured at four positions on the surface of the active material particles 1A-1F. And the number of particles in which the Ni atom concentration higher than the Ni atom concentration at the center of the active material particle 1A-1F is measured at one or more locations at a distance of 10 nm from the surface of the active material particle 1A-1F. The value obtained by dividing by the number of all measured particles and multiplying by 100 can be defined as the percentage of particles formed of the active material particles 1A-1F.

  Furthermore, the heating temperature of the heat treatment in the heat treatment step S3 is more preferably at least 50 ° C. lower than the firing temperature of the main firing in the precursor particle manufacturing step S1. Thereby, the formation rate and the formation particle rate of active material particle 1A-1F improve more.

  The heating time of the heat treatment in the heat treatment step S3 is preferably equal to or shorter than the firing time of the main firing of the core part precursor particles in the precursor particle manufacturing step S1. Thereby, the formation rate and the formation particle rate of active material particle 1A-1F improve more. More specifically, in the heat treatment in the heat treatment step S3, the holding time for keeping the precursor particles at the above-described constant heating temperature is preferably less than 3 hours. Thereby, the formation rate and the formation particle rate of active material particle 1A-1F improve more. Depending on the heating temperature profile, there may be no holding time for maintaining the heating temperature constant. The heat treatment in the heat treatment step S3 may be performed in an inert gas atmosphere, but it is preferable to perform the heat treatment in an oxidizing gas atmosphere because oxygen deficiency can be prevented even if the atomic concentration of Ni is high.

  According to the positive electrode active material manufacturing method of the present embodiment, the active material particles 1A-1F have a layered structure having a core part 11 and a surface layer part 12 having different compositions, and the composition is represented by the formula (1), A positive electrode active material 10A-10F for a non-aqueous secondary battery comprising active material particles 1A-1F having an isoelectric point of zeta potential of 5 or more and 7 or less can be produced.

(Positive electrode and non-aqueous secondary battery)
Hereinafter, embodiments of the positive electrode and the non-aqueous secondary battery of the present invention will be described. FIG. 8 is a schematic partial cross-sectional view of the positive electrode 111 of the present embodiment and the nonaqueous secondary battery 100 including the positive electrode 111.

  The non-aqueous secondary battery 100 of the present embodiment is, for example, a cylindrical lithium ion secondary battery, and is housed in a bottomed cylindrical battery can 101 that contains a non-aqueous electrolyte, and the battery can 101. A wound electrode group 110 and a disk-shaped battery lid 102 that seals the upper opening of the battery can 101 are provided. The battery can 101 and the battery lid 102 are made of, for example, a metal material such as aluminum, and the battery lid 102 is fixed to the battery can 101 by caulking or the like via a sealing material 106 made of an insulating resin material. The battery cans 101 are sealed by the battery lid 102 and are electrically insulated from each other. The shape of the non-aqueous secondary battery 100 is not limited to a cylindrical shape, and other arbitrary shapes such as a square shape, a button shape, and a laminate sheet shape can be adopted.

  The wound electrode group 110 is manufactured by winding a long strip-like positive electrode 111 and a negative electrode 112 facing each other with a long strip-like separator 113 around a winding center axis. In the wound electrode group 110, the positive electrode current collector 111 a is electrically connected to the battery lid 102 via the positive electrode lead piece 103, and the negative electrode current collector 112 a is electrically connected to the bottom of the battery can 101 via the negative electrode lead piece 104. Connected. An insulating plate 105 is disposed between the wound electrode group 110 and the battery lid 102 and between the wound electrode group 110 and the bottom of the battery can 101 to prevent a short circuit. The positive electrode lead piece 103 and the negative electrode lead piece 104 are members for current extraction made of the same material as the positive electrode current collector 111a and the negative electrode current collector 112a, respectively, and the positive electrode current collector 111a and the negative electrode current collector, respectively. 112a is joined by spot welding or ultrasonic pressure welding.

  The positive electrode 111 of this embodiment includes a positive electrode current collector 111a and a positive electrode mixture layer 111b formed on the surface of the positive electrode current collector 111a. As the positive electrode current collector 111a, for example, a metal foil such as aluminum or an aluminum alloy, an expanded metal, a punching metal, or the like can be used. The metal foil can have a thickness of, for example, about 8 μm to 30 μm. The positive electrode mixture layer 111b includes positive electrode active materials 10A-10F made of the active material particles 1A-1F shown in FIGS. 1A to 6. Further, the positive electrode mixture layer 111b may contain a conductive material, a binder, and the like.

The positive electrode mixture layer 111b is, for example, a solid solution positive electrode active material expressed as Li ₂ MnO ₃ —LiM ₁ O ₂ (M 1 represents a transition metal element such as Co, Ni, or Mn), LiM ₂ O ₂ . It may include a layered oxide-based positive electrode active material represented, a polyanion-based positive electrode active material represented as LiM3A _p O _q , and the like. Here, M2 and M3 are at least one transition metal element selected from the group consisting of Mn, Ni, Co, and Fe, and A is bonded to oxygen to form PO ₄ , SiO ₄ , BO _3, etc. It is a typical element that forms an anion, and p and q are numbers satisfying 1 ≦ p ≦ 2, 3 ≦ q ≦ 7. A part of the transition metal elements of M2 and M3 may be substituted with elements such as Ti, Zr, Al, Mg, Cr, V, Nb, Ta, W, and Mo.

  The negative electrode 112 includes a negative electrode current collector 112a and a negative electrode mixture layer 112b formed on the surface of the negative electrode current collector 112a. As the negative electrode current collector 112a, metal foil such as copper or copper alloy, nickel or nickel alloy, expanded metal, punching metal, or the like can be used. The metal foil can have a thickness of, for example, about 5 μm or more and 20 μm or less. The negative electrode mixture layer 112b contains a negative electrode active material used in a general lithium ion secondary battery. The negative electrode mixture layer 112b may include a conductive material, a binder, and the like.

  As the negative electrode active material, for example, one or more of a carbon material, a metal material, a metal oxide material, and the like can be used. As the carbon material, graphites such as natural graphite and artificial graphite, carbides such as coke and pitch, amorphous carbon, carbon fiber, and the like can be used. Further, as the metal material, lithium, silicon, tin, aluminum, indium, gallium, magnesium and alloys thereof, and as the metal oxide material, a metal oxide containing tin, silicon, lithium, titanium, or the like is used. it can.

  As the separator 113, for example, a polyolefin resin such as polyethylene, polypropylene, or a polyethylene-polypropylene copolymer, a microporous film such as a polyamide resin or an aramid resin, a nonwoven fabric, or the like can be used.

  The positive electrode 111 and the negative electrode 112 can be manufactured through, for example, a composite material adjusting process, a composite material coating process, and a shaping process. In the composite material adjusting step, for example, the positive electrode active material 10A-10F or the negative electrode active material is mixed with, for example, a conductive material and a binder using a stirring means such as a planetary mixer, a disper mixer, and a rotation / revolution mixer. Together with stirring and homogenization, a mixture slurry is prepared.

  As the conductive material, a conductive material used in a general lithium ion secondary battery can be used. Specifically, for example, carbon particles such as graphite powder, acetylene black, furnace black, thermal black, and channel black, carbon fibers, and the like can be used as the conductive material. As the conductive material, for example, an amount of about 1% by mass or more and about 10% by mass or less can be used with respect to the total mass of the composite material.

  As the binder, a binder used in a general lithium ion secondary battery can be used. Specifically, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, carboxymethylcellulose, polyacrylonitrile, modified polyacrylonitrile, and the like can be used as the binder. For example, the binder can be used in an amount of about 1% by mass to about 10% by mass, more preferably about 5% by mass with respect to the total mass of the composite material.

  As the solvent of the solution, N-methylpyrrolidone, water, N, N-dimethylformamide, N, N-dimethylacetamide, methanol, ethanol, propanol, isopropanol, ethylene glycol, diethylene glycol, glycerin depending on the type of binder. , Dimethyl sulfoxide, tetrahydrofuran and the like.

  In the composite material coating process, first, the composite material slurry containing the positive electrode active material 10A-10F adjusted in the composite material adjustment process and the composite material slurry containing the negative electrode active material, for example, a bar coater, a doctor blade, a roll transfer machine, etc. Are applied to the surfaces of the positive electrode current collector 111a and the negative electrode current collector 112a, respectively. Next, the positive electrode current collector 111a and the negative electrode current collector 112a coated with the mixture slurry are respectively heat-treated to volatilize or evaporate the solvent of the solution contained in the mixture slurry, thereby removing the positive electrode current collector. A positive electrode mixture layer 111b and a negative electrode mixture layer 112b are formed on the surfaces of 111a and the negative electrode current collector 112a, respectively.

  In the forming step, first, the positive electrode mixture layer 111b formed on the surface of the positive electrode current collector 111a and the negative electrode mixture layer 112b formed on the surface of the negative electrode current collector 112a are subjected to, for example, roll press or the like. Each is pressure-molded using a pressure means. Thereby, the positive electrode mixture layer 111b can be made to have a thickness of, for example, about 15 μm to 300 μm, and the negative electrode mixture layer 112b can be made to have a thickness of, for example, about 10 μm to 150 μm. Thereafter, the positive electrode current collector 111a and the positive electrode composite material layer 111b, and the negative electrode current collector 112a and the negative electrode composite material layer 112b are each cut into long strips, whereby the positive electrode 111 and the negative electrode 112 can be manufactured. .

  The positive electrode 111 and the negative electrode 112 manufactured as described above are wound around the winding central axis in a state of being opposed to each other with the separator 113 interposed therebetween, so that a wound electrode group 110 is formed. In the wound electrode group 110, the negative electrode current collector 112a is connected to the bottom of the battery can 101 via the negative electrode lead piece 104, and the positive electrode current collector 111a is connected to the battery lid 102 via the positive electrode lead piece 103 for insulation. A short circuit with the battery can 101 and the battery lid 102 is prevented by the plate 105 and the like, and the battery can 101 is accommodated. Thereafter, a non-aqueous secondary battery 100 is manufactured by injecting a non-aqueous electrolyte into the battery can 101, fixing the battery lid 102 to the battery can 101 via the sealing material 106, and sealing the battery can 101. Can do.

The non-aqueous electrolyte injected to the battery can _{101, LiClO 4, LiPF 6,} LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 A solution in which a lithium salt such as F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , or LiC (CF ₃ SO ₂ ) ₃ is dissolved in a non-aqueous solvent can be used. The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.7M or more and 1.5M or less.

  As the non-aqueous solvent, diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl acetate, dimethoxyethane and the like can be used. In addition, various additives should be added to the non-aqueous electrolyte for the purpose of suppressing oxidative decomposition and reductive decomposition of the electrolytic solution, preventing precipitation of metal elements, improving ion conductivity, and improving flame retardancy. Can do. Examples of such additives include 1,3-propane sultone and 1,4-butane sultone that suppress decomposition of the electrolytic solution, insoluble polyadipic anhydride that improves the storage stability of the electrolytic solution, and hexahydrophthalic anhydride. An acid or the like, or a fluorine-substituted alkyl boron that improves flame retardancy can be used.

  The non-aqueous secondary battery 100 having the above configuration uses the battery lid 102 as a positive electrode external terminal and the bottom of the battery can 101 as a negative electrode external terminal, and accumulates power supplied from the outside in the wound electrode group 110, and The electric power accumulated in the rotating electrode group 110 can be supplied to an external device or the like. As described above, the non-aqueous secondary battery 100 according to the present embodiment includes, for example, small power sources such as portable electronic devices and household electric devices, stationary power sources such as uninterruptible power sources and power leveling devices, ships, railways, and hybrids. It can be used as a drive power source for automobiles, electric cars and the like.

  Here, the positive electrode mixture layer 111b of the positive electrode 111 of the present embodiment includes the positive electrode active material 10A-10F made of the active material particles 1A-1F shown in any of FIGS. 1A to 6. Therefore, according to the positive electrode 111 of the present embodiment, it is possible to achieve both good cycle characteristics and high capacity characteristics of the nonaqueous secondary battery 100. Moreover, the non-aqueous secondary battery 100 of this embodiment includes a positive electrode 111 having a positive electrode mixture layer 111b including positive electrode active materials 10A-10F made of active material particles 1A-1F shown in any of FIGS. 1A to 6. I have. Therefore, according to the nonaqueous secondary battery 100 of the present embodiment, it is possible to achieve both good cycle characteristics and high capacity characteristics.

(Secondary battery module)
Hereinafter, embodiments of the secondary battery module of the present invention will be described. FIG. 9 is a schematic diagram of the secondary battery module 200 of the present embodiment.

  The secondary battery module 200 of the present embodiment includes the non-aqueous secondary battery 100 described above. In the secondary battery module 200 of the present embodiment, a plurality of non-aqueous secondary batteries 100 are connected in series in order to ensure a desired output, thereby forming a battery group. In addition, it can also be set as a high capacity | capacitance secondary battery module by combining several battery groups in parallel and storing in a housing | casing. Although illustration is omitted, the secondary battery module 200 may include a controller, a fuse, and a balance circuit.

  The fuse can have a protection function against overcurrent. The balance circuit can have a function of leveling the voltage between the electrodes. The controller can have a function of monitoring the interelectrode voltage, current, and temperature of the non-aqueous secondary battery 100. The controller may include a protection circuit, and may have a function of preventing overcharge, overdischarge, and the like within a charge / discharge end potential range set by the protection circuit.

  The controller may be connected to signal input / output means for performing communication with the outside. The signal input / output means may be, for example, an input of a control signal from an ECU provided in a vehicle or a battery monitoring to the ECU. It may have a function of outputting information. The secondary battery module 200 may further have a capacity monitoring, leveling function, cooling function, and the like of each non-aqueous secondary battery 100.

  The secondary battery module 200 of the present embodiment can be used for in-vehicle use. In particular, since the secondary battery module 200 of the present embodiment includes the non-aqueous secondary battery 100 that can achieve both good cycle characteristics and high capacity characteristics, for example, in an electric vehicle, a hybrid vehicle, and the like, A stable output can be made possible over a long period of time.

(Examples and Comparative Examples)
Examples of the positive electrode active material, the positive electrode, and the nonaqueous secondary battery of the present invention and comparative examples thereof will be described.

Example 1
A positive electrode active material for a non-aqueous secondary battery was produced by the following procedure.

  First, core part precursor particles having a relatively high atomic concentration of Ni, which mainly becomes the core part of the active material particles, were produced by the following procedure. Lithium carbonate, nickel carbonate, cobalt carbonate, and manganese carbonate as raw materials are weighed so that Li: Ni: Co: Mn is 1.03: 0.80: 0.10: 0.10 in molar concentration ratio, These were wet pulverized and mixed to prepare a raw material powder. The obtained raw material powder was dried with a nozzle type spray dryer, and then charged into a high-purity alumina container, and pre-baked at a pre-baking temperature of 650 ° C. for 12 hours under an oxygen stream. The obtained calcined product is taken out from the high-purity alumina container and air-cooled, and the calcined product composed of a plurality of particles is crushed into individual particles, put into the high-purity alumina container again, and 850 under an oxygen stream. The main baking was performed at a main baking temperature of 0 ° C. for 8 hours. The obtained fired body was taken out from the high-purity alumina container, air-cooled, and classified. Thereby, the core part precursor particle | grains as a sintered compact by which several particle | grains were sintered were obtained.

When the elemental analysis of the obtained core part precursor particle was performed by TEM-EDX, Li: Ni: Co: Mn was 1.00: 0.80: 0.10: 0.10. Therefore, the elemental composition is estimated to be Li _1.0 Ni _0.8 Co _0.1 Mn _0.1 O ₂ . Moreover, as a result of analyzing the crystal structure of the core portion precursor particles using CuKα rays with an X-ray diffractometer (RINTIII manufactured by Rigaku Corporation), a peak of a layered structure belonging to R3-m could be confirmed. Moreover, the median diameter (D50) obtained by measuring the particle size distribution of core part precursor particle | grains with the laser diffraction / scattering type particle size distribution measuring apparatus (LA-920 by Horiba Ltd.) was 11 micrometers.

  Next, surface layer part precursor particles having a relatively low atomic concentration of Ni and a high atomic concentration of Li were produced mainly by the following procedure. Lithium carbonate, manganese carbonate and nickel carbonate as raw materials are weighed so that Li: Ni: Mn is a molar concentration ratio of 1.20: 0.2: 0.6, and these are wet-ground and mixed. Raw material powder was prepared.

The obtained raw material powder was dried by a nozzle type spray drying apparatus, and then charged into a high-purity alumina container, followed by calcination for 12 hours at a calcination temperature of 700 ° C. in an air atmosphere. And the sintered compact in which the some particle | grains sintered was air-cooled, the sintered compact was grind | pulverized so that it might become finer than the particle | grains which comprise a sintered compact, and surface layer part precursor particle | grains were obtained. When the elemental analysis of the obtained surface layer part precursor particle was conducted, Li: Ni: Mn was 1.16: 0.20: 0.60. Therefore, the elemental composition is estimated to be Li _1.16 Ni _0.2 Mn _0.6 O ₂ . Moreover, the median diameter (D50) obtained by measuring the particle size distribution of the surface layer precursor particles with a laser diffraction / scattering particle size distribution measuring apparatus (LA-920 manufactured by Horiba Ltd.) was 0.17 μm. .

  Next, 100 parts by mass of core part precursor particles and 5 parts by mass of surface layer part precursor particles were mixed using a mortar. The obtained mixture was put into a high-purity alumina container and subjected to heat treatment for 1 hour at a heating temperature of 800 ° C. in an oxygen atmosphere to produce a positive electrode active material composed of active material particles. Thereafter, the active material particles were taken out from the high-purity alumina container and air-cooled to obtain the positive electrode active material of Example 1 composed of the active material particles having the structure shown in FIG. When the particle size distribution of the positive electrode active material was measured with a laser diffraction / scattering particle size distribution analyzer (LA-920 manufactured by Horiba Ltd.), the median diameter (D50) of the active material particles constituting the positive electrode active material of Example 1 was 9 μm.

Moreover, when the elemental analysis of the active material particle which comprises the positive electrode active material of Example 1 was performed by TEM-EDX, Li: Ni: Mn: Co was 1.02: 0.77: 0.13: 0. 10. Therefore, the elemental composition of the active material particles of Example 1 is estimated to be Li _1.02 Ni _0.77 Mn _0.13 Co _0.10 O ₂ . In addition, the ratio of oxygen in the elemental composition of the active material particles of Example 1 may vary within a range of about 1.9 to 2.1 where the layered structure can be maintained.

  FIG. 10 is an electron microscopic image showing measurement positions of active material particles constituting the positive electrode active material of Example 1 by TEM-EDX. FIG. 11 is a graph showing a measurement result by TEM-EDX of the active material particles constituting the positive electrode active material of Example 1. Table 1 is a table | surface which shows the measurement result by TEM-EDX of the active material particle which comprises the positive electrode active material of Example 1. FIG.

  Among the active material particles randomly selected from the positive electrode active material of Example 1, the particle 1-1 has, for example, the active position of the center of gravity of the cross-sectional shape in the cross section passing through the two-dimensional outline of the active material particle in the electron microscope image. The center (C) of the substance particle was used, and the composition of the center (C) was measured by TEM-EDX. In addition, the composition by TEM-EDX at the position (T / 10, B / 10, L / 10, R / 10) where the distance from the surface of the active material particle is 10 nm at the top, bottom, left and right of the cross section of the active material particle. Was measured. Further, on the right side of the cross section of the active material particles, the TEM− is at positions (R / 20, R / 50, R / 75, R / 100) at distances of 20 nm, 50 nm, 75 nm, and 100 nm from the surface of the active material particles. The composition was measured by EDX. Similarly, among the active material particles randomly selected from the positive electrode active material, in the particles 1-2 to 1-4, the center (C) of the cross section of the active material particles and the four surfaces on the top, bottom, left, and right are provided. The composition was measured by TEM-EDX at a position of 10 nm (T / 10, B / 10, L / 10, R / 10).

  From the measurement results shown in Table 1 and FIG. 11, the active material particles constituting the positive electrode active material of Example 1 have a surface layer portion with a thickness of 50 nm, and the atomic concentration of Ni in the surface layer portion is 71 mol%, It was confirmed that the gradient of the Ni atomic concentration in the surface layer portion was 0.028 mol% / nm. The active material particles constituting the positive electrode active material of Example 1 have an intermediate part with a thickness of 50 nm, the atomic concentration of Ni in the intermediate part is 75 mol%, and the gradient of the atomic concentration of Ni in the intermediate part Was confirmed to be 0.18 mol% / nm. Further, it was confirmed that the core part of the active material particles constituting the positive electrode active material of Example 1 had an Ni atomic concentration of 80 mol% and a Ni atomic concentration gradient of 0.012 mol% / nm. .

  Moreover, it was confirmed that the surface layer portion of the active material particles constituting the positive electrode active material of Example 1 had an Mn atomic concentration of 21 mol% and an Mn atomic concentration gradient of 0.028 mol% / nm. . Moreover, it has confirmed that the intermediate part of the active material particle which comprises the positive electrode active material of Example 1 was 15 mol% of atomic concentration of Mn, and the gradient of the atomic concentration of Mn was 0.22 mol% / nm. . Moreover, the core part of the active material particle which comprises the positive electrode active material of Example 1 has confirmed that the atomic concentration of Mn was 10 mol%, and the gradient of the atomic concentration of Mn was 0.022 mol% / nm. .

  Moreover, the formation rate of the positive electrode active material of Example 1 was 88%, and the formation particle rate was 50%. Moreover, the electron diffraction pattern of a surface layer part and a core part was measured by TEM, and the pattern of the layered structure which all belonged to R3-m has been confirmed. Furthermore, when the isoelectric point of the ζ potential of the positive electrode active material of Example 1 was measured, it was 6.0.

(Example 2)
The positive electrode active material of Example 2 was manufactured by the following procedure. First, 100 parts by mass of the core part precursor particles produced in Example 1 and 2.5 parts by mass of the surface layer part precursor produced in Example 1 were mixed using a composite apparatus. Here, the compounding device is a high energy mill capable of compounding particles without performing heat treatment. The obtained mixture was put into a high-purity alumina container and heat-treated at a heating temperature of 800 ° C. for 1 hour in an oxygen atmosphere to produce the positive electrode active material of Example 2. After taking out the positive electrode active material of Example 2 from a high-purity alumina container and air-cooling, the particle size distribution was measured with a laser diffraction / scattering particle size distribution analyzer (LA-920 manufactured by Horiba Ltd.). The median diameter (D50) of the active material particles constituting the active material was 10 μm.

Moreover, when the elemental analysis of the active material particle which comprises the positive electrode active material of Example 2 was performed by TEM-EDX, Li: Ni: Mn: Co was 1.02: 0.79: 0.11: 0. 10. Therefore, the elemental composition of the active material particles constituting the positive electrode active material of Example 2 is estimated to be Li _1.02 Ni _0.79 Mn _0.11 Co _0.10 O ₂ . In addition, the ratio of oxygen in the elemental composition of the active material particles of Example 2 may vary within a range of about 1.9 to 2.1 where the layered structure can be maintained.

  FIG. 12 is a graph showing a measurement result by TEM-EDX of the active material particles constituting the positive electrode active material of Example 2. Table 2 is a table | surface which shows the measurement result by TEM-EDX of the active material particle which comprises the positive electrode active material of Example 2.

  Of the active material particles randomly selected from the positive electrode active material of Example 2, Particle 2-1, Particle 2-3, Particle 2-6 to Particle 2-10 are particles from Particle 1-2 of Example 1 Similarly to 1-4, the position (T / 10, B / 10, L / 10) where the distance from the surface of the active material particles is 10 nm at the center (C) of the cross section of the active material particles and at the four positions on the top, bottom, left and right. , R / 10) and the composition was measured by TEM-EDX. In the particle 2-2 and the particle 2-5, the center and upper and lower two places (T / 10, B / 10) were measured. In the particle 2-4, the distance from the surface of the active material particle (T / 10, B / 10, L / 10, 4C) at the center (C) of the cross section of the active material particle and the four positions on the top, bottom, left, and right The composition is measured by TEM-EDX at R / 10), and on the right side of the cross section, the composition is measured by TEM-EDX at intervals of 10 nm (R / 20-R / 140) until the distance from the active material particle surface is 140 nm. Was measured.

  From the measurement results shown in Table 2 and FIG. 12, the active material particles constituting the positive electrode active material of Example 2 have a surface layer portion with a thickness of 100 nm, and the atomic concentration of Ni in the surface layer portion is 72 mol%, It was confirmed that the gradient of the Ni atom concentration in the surface layer portion was 0.12 mol% / nm. Moreover, the active material particles constituting the positive electrode active material of Example 2 have an intermediate part with a thickness of 20 nm, the atomic concentration of Ni in the intermediate part is 73 mol%, and the gradient of the atomic concentration of Ni in the intermediate part Was confirmed to be 0.80 mol% / nm. Further, it was confirmed that the core part of the active material particles constituting the positive electrode active material of Example 2 had an Ni atomic concentration of 79 mol% and a Ni atomic concentration gradient of 0.0086 mol% / nm. .

  Further, it was confirmed that the surface layer portion of the active material particles constituting the positive electrode active material of Example 2 had an Mn atomic concentration of 19 mol% and a Mn atomic concentration gradient of 0.132 mol% / nm. . Further, it was confirmed that the intermediate part of the active material particles of Example 2 had an Mn atomic concentration of 18 mol% and a Mn atomic concentration gradient of 0.9 mol% / nm. Further, it was confirmed that the core part of the active material particles constituting the positive electrode active material of Example 2 had an Mn atomic concentration of 10 mol% and an Mn atomic concentration gradient of 0.006 mol% / nm. .

  Moreover, the formation rate of the positive electrode active material of Example 2 was 86%, and the formation particle rate was 70%. Moreover, the electron diffraction pattern of a surface layer part and a core part was measured by TEM, and the pattern of the layered structure which all belonged to R3-m has been confirmed. Furthermore, the isoelectric point of the zeta potential of the positive electrode active material of Example 2 was measured and found to be 5.8.

(Example 3)
In the same manner as the surface layer portion precursor manufactured in Example 1, the surface layer portion precursor particles of Example 3 were manufactured by the following procedure. First, raw material lithium carbonate and manganese carbonate were weighed so that the molar ratio of Li: Mn was 2.02: 1.0, and these were wet pulverized and mixed to prepare a raw material powder.

The obtained raw material powder was dried by a nozzle type spray drying apparatus and then put into a high-purity alumina container and pre-baked at 700 ° C. for 12 hours in the air. And the sintered compact in which the several particle | grains sintered was air-cooled, the sintered compact was grind | pulverized so that it might become finer than the particle | grains which comprise a sintered compact, and the surface layer part precursor particle | grain of Example 3 was obtained. When the elemental analysis of the obtained surface layer part precursor particle was performed, Li: Mn was 2.0: 1.0. Therefore, the elemental composition is estimated to be Li ₂ MnO ₃ . The median diameter (D50) obtained by measuring the particle size distribution of the surface layer precursor particles of Example 3 with a laser diffraction / scattering particle size distribution measuring apparatus (LA-920 manufactured by Horiba, Ltd.) is 0. 18 μm.

  Next, 100 parts by mass of the core part precursor particles produced in Example 1 and 5 parts by mass of the surface part precursor particles produced in Example 3 were mixed using a mortar. The obtained mixture was put into a high-purity alumina container, and heat-treated for 1 hour at a heating temperature of 800 ° C. in an oxygen atmosphere to produce a positive electrode active material of Example 3 made of active material particles. Thereafter, the active material particles of Example 3 were taken out from the high-purity alumina container and air-cooled to obtain a positive electrode active material composed of active material particles having the structure shown in FIG. When the particle size distribution of the positive electrode active material was measured with a laser diffraction / scattering particle size distribution analyzer (LA-920 manufactured by Horiba Ltd.), the median diameter (D50) of the active material particles constituting the positive electrode active material of Example 3 was 9 μm.

Moreover, when the elemental analysis of the active material particle which comprises the positive electrode active material of Example 3 was performed by TEM-EDX, Li: Ni: Mn: Co was 1.05: 0.76: 0.14: 0. 10. Therefore, the elemental composition of the active material particles of Example 1 is estimated to be Li _1.05 Ni _0.76 Mn _0.14 Co _0.10 O ₂ . In addition, the ratio of oxygen in the elemental composition of the active material particles constituting the positive electrode active material of Example 3 may vary within a range of about 1.9 to 2.1 where the layered structure can be maintained. is there.

  FIG. 13 is a graph showing a measurement result by TEM-EDX of the active material particles constituting the positive electrode active material of Example 3. Table 3 is a table | surface which shows the measurement result by TEM-EDX of the active material particle which comprises the positive electrode active material of Example 3. FIG.

  Of the active material particles randomly selected from the positive electrode active material of Example 3, the particles 3-1 and 3-2 are the active material particles in the same manner as the particles 1-2 to 1-4 of Example 1. The composition was measured by TEM-EDX at a position where the distance from the surface of the active material particles was 10 nm at the center (C) of the cross-section of and the four positions on the top, bottom, left and right. In the particle 3-3, the distance from the surface of the active material particle (T / 10, B / 10, L / 10, 4) at the center (C) of the cross section of the active material particle and the four positions on the top, bottom, left, and right R / 10) and the composition is measured by TEM-EDX, and on the right side of the cross section, the distance from the surface of the active material particles is 30 nm to 200 nm, 20 nm, 30 nm, 30 nm, 35 nm, 5 nm, 5 nm, 15 nm, The composition was measured by TEM-EDX at intervals of 15 nm and 50 nm (R / 30-R / 200).

  From the measurement results shown in Table 3 and FIG. 13, the active material particles constituting the positive electrode active material of Example 3 have a surface layer portion with a thickness of 115 nm, and the atomic concentration of Ni in the surface layer portion is 75 mol%, It was confirmed that the gradient of Ni atom concentration in the surface layer portion was 0.0095 mol% / nm. Moreover, the active material particles constituting the positive electrode active material of Example 3 have an intermediate part with a thickness of 15 nm, the atomic concentration of Ni in the intermediate part is 78 mol%, and the gradient of the atomic concentration of Ni in the intermediate part Was confirmed to be 0.30 mol% / nm. Further, it was confirmed that the core part of the active material particles constituting the positive electrode active material of Example 3 had an Ni atomic concentration of 81 mol% and a Ni atomic concentration gradient of 0.028 mol% / nm. .

  Moreover, it was confirmed that the surface layer portion of the active material particles constituting the positive electrode active material of Example 3 had an Mn atomic concentration of 17 mol% and an Mn atomic concentration gradient of 0.149 mol% / nm. . Further, it was confirmed that the intermediate part of the active material particles of Example 3 had an Mn atomic concentration of 13 mol% and a Mn atomic concentration gradient of 0.4 mol% / nm. Further, it was confirmed that the core part of the active material particles constituting the positive electrode active material of Example 2 had an Mn atomic concentration of 10 mol% and a Mn atomic concentration gradient of 0.018 mol% / nm. .

  Moreover, the formation rate of the positive electrode active material of Example 3 was 88%, and the formation particle rate was 66%. Moreover, the electron diffraction pattern of a surface layer part and a core part was measured by TEM, and the pattern of the layered structure which all belonged to R3-m has been confirmed. Furthermore, when the isoelectric point of the zeta potential of the positive electrode active material of Example 3 was measured, it was 6.3.

Example 4
The positive electrode active material of Example 4 was manufactured by the following procedure. First, in the same manner as in Example 2, 100 parts by mass of the core part precursor particles manufactured in Example 1 and 2.5 parts by mass of the surface layer part precursor particles manufactured in Example 1 were combined. Used and mixed. Next, the obtained mixture is put into a high-purity alumina container, heated to a heating temperature of 850 ° C. in an oxygen atmosphere, and then subjected to heat treatment with a heating temperature holding time of 0 hour so that the temperature is immediately lowered. The positive electrode active material of Example 4 was manufactured. After taking out the positive electrode active material of Example 4 from a high-purity alumina container and air-cooling, the particle size distribution was measured with a laser diffraction / scattering type particle size distribution analyzer (LA-920 manufactured by Horiba, Ltd.). The median diameter (D50) of the active material particles constituting the active material was 11 μm.

  Moreover, the electron diffraction pattern of a surface layer part and a core part was measured by TEM, and the pattern of the layered structure which all belonged to R3-m has been confirmed. Furthermore, the isoelectric point of the ζ potential of the positive electrode active material of Example 4 was measured and found to be 5.4. This is because the composition of the core particle precursor particles and the composition of the surface layer precursor particles are appropriately interdiffused by performing a heat treatment at a heating temperature of 850 ° C. in an oxygen atmosphere at a heating temperature holding time of 0 hour. This is considered to be because a surface layer portion having a relatively higher Li concentration and higher Mn than the core portion was formed.

(Example 5)
The positive electrode active material of Example 5 was manufactured by the following procedure. First, 100 parts by mass of the core part precursor particles produced in Example 1 and 2.5 parts by mass of the surface layer part precursor particles produced in Example 1 were used in the same manner as in Example 2 using a composite device. And mixed. Next, the obtained mixture was put into a high-purity alumina container and subjected to a heat treatment for 1 hour at a heating temperature of 850 ° C. in an oxygen atmosphere to produce the positive electrode active material of Example 5. After taking out the positive electrode active material of Example 5 from a high purity alumina container and air-cooling, when the particle size distribution was measured with the laser diffraction / scattering type particle size distribution measuring apparatus (LA-920 by Horiba Ltd.), the positive electrode of Example 5 was obtained. The median diameter (D50) of the active material particles constituting the active material was 11 μm.

  Moreover, the electron diffraction pattern of a surface layer part and a core part was measured by TEM, and the pattern of the layered structure which all belonged to R3-m has been confirmed. Furthermore, when the isoelectric point of the zeta potential of the positive electrode active material of Example 5 was measured, it was 6.4. This is because the composition of the core particle precursor particles and the composition of the surface layer precursor particles are appropriately interdiffused by performing a heat treatment for 1 hour at a heating temperature of 850 ° C. in an oxygen atmosphere. This is probably because a surface layer portion having a relatively high Li concentration and a high Mn was formed.

(Comparative Example 1)
The positive electrode active material of Comparative Example 1 was manufactured according to the following procedure. In the same manner as in Example 5, 100 parts by mass of the core part precursor particles produced in Example 1 and 2.5 parts by mass of the surface layer part precursor particles produced in Example 1 were combined using a composite device. Mixed. Next, the obtained mixture was put into a high-purity alumina container and subjected to a heat treatment for 3 hours at a heating temperature of 850 ° C. in an oxygen atmosphere to produce a positive electrode active material of Comparative Example 1. After taking out the positive electrode active material of Comparative Example 1 from the high-purity alumina container and air-cooling, the particle size distribution was measured with a laser diffraction / scattering particle size distribution measuring device (LA-920 manufactured by Horiba, Ltd.). The median diameter (D50) of the active material particles constituting the active material was 11 μm.

  When the isoelectric point of the ζ potential of the positive electrode active material of Comparative Example 1 was measured, it was 4.6. This is because the heat treatment at 850 ° C. for 3 hours in an oxygen atmosphere causes the mutual diffusion of the composition of the core particle precursor particles and the composition of the surface layer precursor particles to be excessive, and the ζ potential, etc. It is thought that the electric point decreased.

(Comparative Example 2)
The positive electrode active material of Comparative Example 2 was manufactured by the following procedure. In the same manner as in Example 5, 100 parts by mass of the core part precursor particles produced in Example 1 and 2.5 parts by mass of the surface layer part precursor particles produced in Example 1 were combined using a composite device. Mixed. Next, the obtained mixture was put into a high-purity alumina container and subjected to a heat treatment at a heating temperature of 850 ° C. for 6 hours in an oxygen atmosphere to produce a positive electrode active material of Comparative Example 2. After taking out the positive electrode active material of Comparative Example 2 from the high-purity alumina container and air-cooling, the particle size distribution was measured with a laser diffraction / scattering particle size distribution analyzer (LA-920 manufactured by Horiba Ltd.). The median diameter (D50) of the active material particles constituting the active material was 11 μm.

  When the isoelectric point of the ζ potential of the positive electrode active material of Comparative Example 2 was measured, it was 4.5. This is because heat treatment at 850 ° C. for 6 hours in an oxygen atmosphere results in excessive interdiffusion between the composition of the core particle precursor particles and the composition of the surface layer precursor particles, and the like of the ζ potential. It is thought that the electric point decreased.

(Comparative Example 3)
The positive electrode active material of Comparative Example 3 was produced by the following procedure. In the same manner as in Example 5, 100 parts by mass of the core part precursor particles produced in Example 1 and 2.5 parts by mass of the surface layer part precursor particles produced in Example 1 were combined using a composite device. Mixed. And the obtained mixture was made into the positive electrode active material of the comparative example 3 without performing heat processing.

  The isoelectric point of the zeta potential of the positive electrode active material of Comparative Example 3 was measured and found to be 9.2. Since the positive electrode active material of Comparative Example 3 was not heat-treated, the composition of the core precursor particles and the composition of the surface layer precursor particles were not appropriately interdiffused, and the isoelectric point of the ζ potential remained high. It is believed that there is.

(Comparative Example 4)
The core part precursor particles produced in Example 1 were used as the positive electrode active material of Comparative Example 4 as it was. When the isoelectric point of the ζ potential of the positive electrode active material of Comparative Example 4 was measured, it was 4.1.

  Using the positive electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 4 obtained as described above, the positive electrodes and non-aqueous systems of Examples 1 to 5 and Comparative Examples 1 to 4 were used. A secondary battery was manufactured.

  First, 90 parts by mass of a positive electrode active material, 6 parts by mass of a conductive material, and 4 parts by mass of a binder are mixed with a solvent N-methylpyrrolidone and homogenized to prepare a slurry-like positive electrode mixture. did. As the conductive material, acetylene black “DENKA BLACK (registered trademark)” (manufactured by Denki Kagaku Kogyo Co., Ltd.) was used. In addition, polyvinylidene fluoride was used as the binder.

  Next, the prepared positive electrode mixture was applied to a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried at 120 ° C., pressed twice at 60 MPa, and compression molded to obtain an electrode plate. Then, the electrode plate was punched into a disk shape having a diameter of 15 mm, and positive electrodes for non-aqueous secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 4 were manufactured.

Next, the positive electrode for the non-aqueous secondary battery of Examples 1 to 5 and Comparative Example 1 to Comparative Example 4 and the negative electrode for the non-aqueous secondary battery made of metallic lithium were used, respectively. Nonaqueous secondary batteries of 1 to Example 5 and Comparative Examples 1 to 4 were manufactured. In addition, as a non-aqueous electrolyte of the non-aqueous secondary battery, LiPF ₆ was dissolved in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 2 so as to have a concentration of 1.0 mol / l. A thing was used.

  Next, the non-aqueous secondary batteries according to Examples 1 to 5 and Comparative Examples 1 to 4 manufactured were subjected to the following charge / discharge test, and the discharge capacity was measured. The charge / discharge test was conducted at an environmental temperature of 25 ° C.

  First, each non-aqueous secondary battery is charged with a constant current and a constant voltage up to an upper limit voltage of 4.3 V at a current equivalent to 0.2 C, and after resting for 30 minutes, a lower limit voltage of 3 with a constant current equivalent to 0.2 C. The battery was discharged to 3 V and charged / discharged for 30 minutes, followed by two cycles to initialize the non-aqueous secondary battery. The discharge capacity of each non-aqueous secondary battery was the value at the first cycle. Thereafter, each non-aqueous secondary battery is charged with a constant current and a constant voltage up to an upper limit voltage of 4.4 V at a current equivalent to 1 C. After resting for 5 minutes, it is discharged to a lower limit voltage of 3.3 V with a constant current equivalent to 1 C. Then, 50 cycles of charging / discharging for 5 minutes were performed. The discharge capacity at the 50th cycle of constant current discharge equivalent to 1C is divided by the discharge capacity at the first cycle of constant current discharge equivalent to 1C, and multiplied by 100, the capacity maintenance rate of each non-aqueous secondary battery It was. The results are shown in Table 4 below.

  Next, the following charge / discharge test was performed on the nonaqueous secondary batteries of Example 1 and Comparative Example 4 to measure the discharge capacity. The charge / discharge test was conducted at an environmental temperature of 25 ° C.

  First, each non-aqueous secondary battery is charged with a constant current and a constant voltage up to an upper limit voltage of 4.6 V at a current equivalent to 0.2 C. After resting for 30 minutes, the lower limit voltage 3 is supplied with a constant current equivalent to 0.2 C. The battery was discharged to 3 V and charged / discharged for 30 minutes, followed by two cycles to initialize the non-aqueous secondary battery. Thereafter, each non-aqueous secondary battery is charged with a constant current and a constant voltage up to an upper limit voltage of 4.6 V at a current equivalent to 1 C. After resting for 5 minutes, it is discharged to a lower limit voltage of 3.3 V with a constant current equivalent to 1 C. Then, 50 cycles of charging / discharging for 5 minutes were performed. The value obtained by dividing the discharge capacity at the 50th cycle of the constant current discharge equivalent to 1C by the discharge capacity at the first cycle of the constant current discharge equivalent to 1C and multiplying by 100 is 4.6 V for each non-aqueous secondary battery. The capacity maintenance rate was used. The results are shown in Table 4 below.

  The positive electrode active material contained in the positive electrodes of the non-aqueous secondary batteries of Example 1 to Example 5 is the firing temperature of the core part precursor particles after mixing the core part precursor particles and the surface layer part precursor particles 850. The heat treatment is performed at 800 ° C., which is 50 ° C. lower than the temperature C, or at a heating temperature of 850 ° C., which is the same as the firing temperature of the core part precursor particles. As a result, as shown in Table 4, it was confirmed that the positive electrode active material contained in the positive electrodes of the non-aqueous secondary batteries of Examples 1 to 5 had an isoelectric point of ζ potential of 5 or more and 7 or less. It was. Moreover, as shown in Example 4 and Example 5 and Comparative Example 1 and Comparative Example 2, when the heating temperature of the heat treatment after mixing the core part precursor particles and the surface layer part precursor particles is 850 ° C., the heat treatment It was confirmed that the isoelectric point of the ζ potential was 5 or more and 7 or less by setting the time to less than 3 hours, more preferably 1 hour or less.

In the non-aqueous secondary batteries of Examples 1 to 5 in which the isoelectric point of ζ potential is 5 or more and 7 or less, Comparative Example 1, Comparative Example 2, and Comparative Example 4 in which the isoelectric point of ζ potential is less than 5. In addition, compared with the non-aqueous secondary battery of Comparative Example 3 in which the isoelectric point of the ζ potential is larger than 7, the battery voltage is 4.3 V (vs Li / Li ⁺ ) or less, and the positive electrode single electrode is 4.4 V (vs. The value of the capacity retention rate at a low potential of (Li / Li ⁺ ) or lower became high. That is, it was confirmed that cycle deterioration is suppressed when the isoelectric point of the ζ potential is 5 or more and 7 or less.

In addition, compared with Example 1 in which the isoelectric point of ζ potential is 5 or more and 7 or less and Comparative Example 4 in which the isoelectric point of ζ potential is less than 5, the battery voltage is 4.5 V (vs Li / Li ⁺ ), The capacity retention ratio at a high potential of 4.6 V (vs Li / Li ⁺ ) was high for the single positive electrode. That is, it was confirmed that cycle deterioration is suppressed when the isoelectric point of the ζ potential is 5 or more.

As described above, when the isoelectric point of the ζ potential is 5 or more and 7 or less, the non-aqueous secondary battery has a battery voltage of 4.5 V (vs Li / Li ⁺ ) and a positive electrode single electrode of 4.6 V (vs Li / Li). ⁺ ) In addition to suppressing cycle deterioration when used up to a high potential, a non-aqueous secondary battery is not more than 4.3 V (vs Li / Li ⁺ ) in terms of battery voltage and 4.4 V (vs Li / in) with a single positive electrode. It was confirmed that the cycle deterioration when using a low potential of Li ⁺ ) or less can also be suppressed.

  The embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

1A-1F active material particles, 10A-10F positive electrode active material, 11 core part, 12 surface layer part, 13 intermediate part, 100 nonaqueous secondary battery, 111 positive electrode, 111a positive electrode current collector, 111b positive electrode mixture layer, 200 2 Secondary battery module, S1 precursor particle manufacturing process, S2 mixing process, S3 heat treatment process

Claims (16)

A positive electrode active material for a non-aqueous secondary battery comprising active material particles having a layered structure having a core portion and a surface layer portion having different compositions,
The positive electrode active material, wherein the active material particles have a composition represented by the following formula (1) and an isoelectric point of zeta potential is 5 or more and 7 or less.
_{Li 1 + a Ni b Mn c} Co d M e O 2 ... (1)
In the above formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Mo, and Nb, and a, b, c, d, and e are −0. 0.1 ≦ a ≦ 0.3, 0.5 ≦ b ≦ 0.95, 0 <c ≦ 0.95, 0 ≦ d ≦ 0.6, 0 ≦ e ≦ 0.1, and b + c + d + e = 1. It is a number that satisfies.   The positive electrode active material according to claim 1, wherein the active material particles are composite particles obtained by sintering a plurality of particles having the core portion and the surface layer portion. The core part is a sintered body in which a plurality of particles are sintered,
The positive electrode active material according to claim 1, wherein the surface layer portion is formed on a surface of the sintered body.   4. The positive electrode active material according to claim 1, wherein an atomic concentration of Ni in the core portion is higher than an atomic concentration of Ni in the surface layer portion. 5.   The positive electrode active material according to claim 4, wherein an atomic concentration of Li in the surface layer portion is higher than an atomic concentration of Li in the core portion. Having an intermediate part between the core part and the surface part,
The atomic concentration of Ni in the intermediate portion is lower than the atomic concentration of Ni in the core portion, and higher than the atomic concentration of Ni in the surface layer portion,
The positive electrode active material according to claim 5, wherein a concentration gradient of Ni concentration in the surface layer portion is smaller than a concentration gradient of Ni concentration in the intermediate portion. The positive electrode active material according to claim 5, wherein the surface layer portion has a composition represented by the following formula (2).
_{Li 1 + a Ni b Mn c} Co d M e O 2 ... (2)
In the above formula (2), M is at least one element selected from the group consisting of Mg, Al, Ti, Mo, and Nb, and a, b, c, d, and e are 0 < A number satisfying a ≦ 0.3, 0.2 ≦ b ≦ 0.95, 0 <c ≦ 0.95, 0 ≦ d ≦ 0.6, 0 ≦ e ≦ 0.1, and b + c + d + e = 1. is there.   The positive electrode active material according to claim 5 or 6, wherein a thickness of the surface layer portion is 20 nm or more and 200 nm or less.   The positive electrode active material according to claim 6, wherein a thickness of the intermediate portion is 10 nm or more and 100 nm or less. A method for producing a positive electrode active material according to any one of claims 1 to 9,
A precursor particle production process for producing a core part precursor particle and a surface layer part precursor particle having different compositions by mixing and firing a transition metal compound and a Li compound,
A mixing step of mixing the core part precursor particles and the surface layer part precursor particles;
A heat treatment step of heat-treating the mixture obtained in the mixing step so that the active material particles have an isoelectric point of zeta potential represented by the formula (1) of 5 or more and 7 or less;
The positive electrode active material manufacturing method characterized by including. In the precursor particle production step, the median diameter of the core part precursor particles is set to be 2 to 100 times the median diameter of the surface layer part precursor particles,
The said mixing process WHEREIN: The said surface part precursor particle | grain is mixed in the ratio of 0.1 to 15 mass parts with respect to 100 mass parts of said core part precursor particles, The Claim 10 characterized by the above-mentioned. A method for producing a positive electrode active material.   The method for producing a positive electrode active material according to claim 10 or 11, wherein a heating time of the heat treatment in the heat treatment step is equal to or shorter than a firing time of the core part precursor particles in the precursor particle production step. .   The heating temperature of the heat treatment in the heat treatment step is not less than a temperature 200 ° C. lower than the firing temperature of the core part precursor particles in the precursor particle manufacturing step and not more than 50 ° C. higher than the firing temperature. The method for producing a positive electrode active material according to claim 12. A positive electrode for a non-aqueous secondary battery comprising a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector,
The positive electrode mixture layer includes the positive electrode active material according to any one of claims 1 to 9.   A non-aqueous secondary battery comprising the positive electrode according to claim 14.   A secondary battery module comprising the nonaqueous secondary battery according to claim 15.

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