JP2017045651A - Positive electrode active material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a positive electrode active material for a lithium ion secondary battery, capable of achieving an improvement in cycle durability under high voltages such as 4.35 V while maintaining a high energy density; a positive electrode for a lithium ion secondary battery using the same; and a lithium ion secondary battery.SOLUTION: A positive electrode active material for a lithium ion secondary battery is represented by the following composition formula (1): LiNCoMnXO...(1) (in the composition formula (1), X represents at least one selected from the group consisting of Ti, Zr, Sn and Al, z represents an oxygen number satisfying a valence, and x, 1-a-b-c, a, b, c, and X/(Mn+X) satisfy the relationships of 0.9≤x≤1.1, 0.75≤1-a-b-c≤0.90, 0<a≤0.10, 0.05≤b≤0.20, 0.01≤c≤0.10, and 0.1≤X/(Mn+X)≤0.8, respectively.).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery using the same, and a lithium ion secondary battery.

  In recent years, in order to cope with global warming, it has been eagerly desired to reduce carbon dioxide emissions. In the automobile industry, there are high expectations for reducing carbon dioxide emissions by introducing electric vehicles (EV), hybrid electric vehicles (HEV), fuel cell vehicles (FCV), and the like. The development of secondary batteries applied to these power supply devices has been actively conducted. As such a secondary battery, a lithium ion secondary battery having high theoretical energy has attracted attention, and is currently being developed rapidly. Generally, a lithium ion secondary battery has a positive electrode formed by applying a positive electrode slurry containing a positive electrode active material to the surface of the positive electrode current collector, and a negative electrode slurry containing a negative electrode active material on the surface of the negative electrode current collector. The negative electrode formed by coating the electrode and the electrolyte positioned therebetween are housed in a battery case. Lithium ion secondary batteries applied to power supply devices for electric vehicles are required to have high output and high capacity, and selection of positive electrode active materials is extremely important for these improvements. is there.

  As a positive electrode active material used for a positive electrode of a lithium ion secondary battery for an electric vehicle, a solid solution positive electrode active material containing a transition metal such as lithium and manganese is known. In particular, since manganese is relatively abundant as a resource, the raw material is inexpensive, easily available, and has a low environmental burden, and thus is suitably used as a positive electrode active material. It has been found that such a solid solution positive electrode active material has a problem that the transition metal elutes in the electrolyte liquid while charging and discharging of the lithium ion secondary battery are repeated. This is because the elution of the transition metal changes the crystal structure of the positive electrode active material, causing a reduction in the capacity of the lithium ion secondary battery.

Conventionally, as a positive electrode active material used to prevent elution of transition metals, a composition formula: xLiMO ₂ · (1-x) Li ₂ M′O ₃ (where M is V, Mn, Fe, Co, or Ni , M ′ represents Mn, Ti, Zr, Ru, Re, or Pt, and x satisfies the relationship 0 <x <1) (see Patent Document 1). ).

US Patent Application Publication No. 2004/0081888

  However, even the lithium ion secondary battery using the positive electrode active material described in Patent Document 1 has a problem that the effect of preventing the elution of the transition metal is not sufficient.

  The present invention has been made in view of such problems of the prior art. In order to realize a lithium ion secondary battery having a high energy density and a high cycle durability, the present invention maintains a high energy density and performs a cycle durability under a high voltage such as 4.35V. It is an object of the present invention to provide a positive electrode active material for a lithium ion secondary battery that can improve the property, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same.

  The present inventor has intensively studied to achieve the above object. As a result, the inventors have found that the above object can be achieved by setting the positive electrode active material to a configuration represented by a specific composition formula, and have completed the present invention.

That is, the positive electrode active material for a lithium ion secondary battery of the present invention has the following composition formula (1):
Li _x N _1-abc Co _a Mn _b X _c O _z (1)
(In the composition formula (1), X is at least one selected from the group consisting of Ti, Zr, Sn and Al, z is the number of oxygens satisfying the valence, and x is 0.9 ≦ x1. 1, 1-abc is 0.75 ≦ 1-abc ≦ 0.90, a is 0 <a ≦ 0.10, and b is 0.05 ≦ b ≦ 0. 20, c is 0.01 ≦ c ≦ 0.10, and X / (Mn + X) satisfies the relationship 0.1 ≦ X / (Mn + X) ≦ 0.8.

  Moreover, the positive electrode for lithium ion secondary batteries of this invention contains the said positive electrode active material of this invention.

  Furthermore, the lithium ion secondary battery of the present invention includes a positive electrode for a lithium ion secondary battery of the present invention, a negative electrode for a lithium ion secondary battery including a negative electrode active material capable of occluding and releasing lithium ions, and the lithium ion secondary battery. A non-aqueous electrolyte layer disposed between a positive electrode for a secondary battery and the negative electrode for a lithium ion secondary battery is provided.

According to the present invention, the composition formula (1)
Li _x N _1-abc Co _a Mn _b X _c O _z (1)
(In the composition formula (1), X is at least one selected from the group consisting of Ti, Zr, Sn and Al, z is the number of oxygens satisfying the valence, and x is 0.9 ≦ x1. 1, 1-abc is 0.75 ≦ 1-abc ≦ 0.90, a is 0 <a ≦ 0.10, and b is 0.05 ≦ b ≦ 0. 20, c is 0.01 ≦ c ≦ 0.10, and X / (Mn + X) satisfies the relationship 0.1 ≦ X / (Mn + X) ≦ 0.8. Therefore, a positive electrode active material for a lithium ion secondary battery capable of improving cycle durability under a high voltage such as 4.35 V while maintaining a high energy density, and a positive electrode for a lithium ion secondary battery using the same In addition, a lithium ion secondary battery can be provided. That is, a lithium ion secondary battery having high energy density and high cycle durability can be provided.

FIG. 1 is a chart showing X-ray diffraction patterns of positive electrode active materials for lithium ion secondary batteries obtained in some test examples. 2A to 2D are charts showing an enlarged region including each diffraction peak appearing in the X-ray diffraction pattern shown in FIG. FIG. 3 is a perspective view showing an external appearance of a flat (stacked) lithium ion secondary battery, which is a lithium ion secondary battery according to an embodiment of the present invention. 4 is a schematic cross-sectional view taken along line III-III of a non-bipolar lithium ion secondary battery which is an embodiment of the flat (stacked) lithium ion secondary battery shown in FIG. is there. FIG. 5 is a graph showing average voltages in lithium ion secondary batteries obtained in some test examples.

  Hereinafter, a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery according to an embodiment of the present invention will be described in detail.

First, a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention will be described in detail. The positive electrode active material for a lithium ion secondary battery of this embodiment has the following composition formula (1):
Li _x N _1-abc Co _a Mn _b X _c O _z (1)
(In the composition formula (1), X is at least one selected from the group consisting of Ti, Zr, Sn and Al, z is the number of oxygens satisfying the valence, and x is 0.9 ≦ x ≦ 1.1, 1-abc is 0.75 ≦ 1-abc ≦ 0.90, a is 0 <a ≦ 0.10, b is 0.05 ≦ b ≦ 0.20, c is 0.01 ≦ c ≦ 0.10, and X / (Mn + X) satisfies the relationship 0.1 ≦ X / (Mn + X) ≦ 0.8.) is there.

  In such a positive electrode active material, the effect of suppressing elution of manganese is increased. Therefore, when such a positive electrode active material is used for a lithium ion secondary battery, high cycle durability can be achieved while maintaining a high energy density.

  Here, in the composition formula (1), when x is 0.9 or more and 1.1 or less, the structure can be stabilized and a high energy density can be maintained when applied to a lithium ion secondary battery. However, high cycle durability can be achieved. On the other hand, when x is not 0.9 or more and 1.1 or less, the structure cannot be stabilized or the structure can be stabilized, but when applied to a lithium ion secondary battery, a high energy density is obtained. High cycle durability cannot be achieved while maintaining.

  In the composition formula (1), when 1-abc is 0.75 or more and 0.90 or less, the structure can be stabilized, and high when applied to a lithium ion secondary battery. High cycle durability can be achieved while maintaining the energy density. On the other hand, when 1-a-b-c is not 0.75 or more and 0.90 or less, the structure cannot be stabilized or the structure can be stabilized, but applied to a lithium ion secondary battery. In addition, high cycle durability cannot be achieved while maintaining high energy density.

  Further, in the composition formula (1), when a is greater than 0 and less than or equal to 0.10, the structure can be stabilized, and when applied to a lithium ion secondary battery, while maintaining a high energy density, High cycle durability can be realized. On the other hand, if a is greater than 0 and not less than 0.10, the structure cannot be stabilized or the structure can be stabilized, but a high energy density is maintained when applied to a lithium ion secondary battery. However, high cycle durability cannot be realized.

  Furthermore, in the composition formula (1), when b is 0.05 or more and 0.20 or less, the structure can be stabilized, and when applied to a lithium ion secondary battery, a high energy density is maintained. High cycle durability can be realized. On the other hand, when b is not 0.05 or more and 0.20 or less, the structure cannot be stabilized or the structure can be stabilized, but when applied to a lithium ion secondary battery, a high energy density is obtained. High cycle durability cannot be achieved while maintaining.

  Further, in the composition formula (1), when c is 0.01 or more and 0.10 or less, manganese elution is suppressed by at least one selected from the group consisting of Ti, Zr, Sn, and Al. The structure can be sufficiently replaced, the structure can be stabilized, and when applied to a lithium ion secondary battery, high cycle durability can be achieved while maintaining high energy density. On the other hand, when c is not 0.01 or more and 0.10 or less, at least one selected from the group consisting of Ti, Zr, Sn, and Al is hardly uniformly contained in the positive electrode active material, and the structure is stable. Even if it cannot be achieved or the structure is stabilized, when applied to a lithium ion secondary battery, high cycle durability cannot be achieved while maintaining a high energy density.

  Furthermore, in the composition formula (1), when X / (Mn + X) is 0.1 or more and 0.8 or less, the structure can be stabilized, and when applied to a lithium ion secondary battery, a high energy density is obtained. High cycle durability can be achieved while maintaining the above. On the other hand, if X / (Mn + X) is not 0.1 or more and 0.8 or less, the structure cannot be stabilized or the structure can be stabilized, but when applied to a lithium ion secondary battery, While maintaining high energy density, high cycle durability cannot be achieved.

  Further, the positive electrode active material for a lithium ion secondary battery of the present embodiment is not particularly limited, but in the composition formula (1), (Mn + X) / Co is preferably greater than 1, and is 3 or more. More preferably, it is more preferably 4 or more. By making (Mn + X) / Co larger than 1, the content ratio of manganese, titanium, etc., which are relatively inexpensive compared with cobalt, can be increased, and the cost can be reduced. Also, increasing the manganese content is advantageous from the viewpoint of improving energy density. Further, although not particularly limited, (Mn + X) / Co is preferably 20 or less, and more preferably 10 or less. By setting (Mn + X) / Co to 20 or less, the content ratio of cobalt does not become extremely small, so that it is easily contained uniformly in the positive electrode active material, and productivity can be improved. Moreover, when the content rate of manganese becomes large, it may become unstable. Further, although not particularly limited, for example, in the composition formula (1), (Mn + X) / Co is preferably greater than 1 and 20 or less, more preferably 3 or more and 20 or less, and more preferably 4 or more. More preferably, it is 10 or less.

  Furthermore, in the positive electrode active material for a lithium ion secondary battery of the present embodiment, although not particularly limited, in the composition formula (1), X / Mn may be 0.05 or more and 2.0 or less. Preferably, it is 0.10 or more and 1.0 or less. By setting X / Mn to 0.05 or more, the content ratio of titanium or the like does not become extremely small, so that it is easily contained uniformly in the positive electrode active material, and productivity can be improved. In addition, by setting X / Mn to 2.0 or less, the content ratio of manganese does not become extremely small, so that it is easily contained uniformly in the positive electrode active material, and productivity can be improved. Moreover, when the content rate of manganese becomes large, it may become unstable.

Moreover, in the positive electrode active material for lithium ion secondary batteries of this embodiment, in a X-ray diffraction (XRD) measurement, it shows a layered rock salt type (α-NaFeO ₂ ) structure, 18-20 ° (003), 36- Diffraction peaks appearing at positions 37 ° (101), 37-38 ° (006), 38-39 ° (012), 44-45 ° (104) and 64-65 (108) / 65-66 (110). By including at least one selected from the group consisting of Ti, Zr, Sn, and Al, it is preferable that it appears at a position shifted to the low angle side.

  In addition, the notation of 64-65 (108) / 65-66 (110) has two peaks close to 64-65 and 65-66. Depending on the composition, one peak is broadly separated without being clearly separated. It is meant to include.

  In such a positive electrode active material, the shift of the diffraction peak to the lower angle side is such that one of Ti, Zr, Sn, and Al or two or more of any combination are substituted with manganese. Thus, the effect of suppressing elution of Mn can be further increased. Therefore, when such a positive electrode active material is applied to a lithium ion secondary battery, higher cycle durability can be realized while maintaining a high energy density.

Here, diffraction peaks in X-ray diffraction (XRD) measurement will be described in detail with reference to the drawings. FIG. 1 is a chart showing X-ray diffraction patterns of positive electrode active materials for lithium ion secondary batteries obtained in some test examples. FIGS. 2A to 2D are charts showing an enlarged region including each diffraction peak appearing in the X-ray diffraction pattern shown in FIG. Furthermore, the X-ray diffraction patterns indicated by reference signs a to e in FIGS. 1 and 2 are Test Example 1 (LiNi _0.75 Co _0.1 Mn _0.15 O ₂ ) and Test Example 2 ( LiNi _0.75 Co _0.1 Mn _0.12 Ti _0.03 O ₂ ), Test Example 3 (LiNi _0.75 Co _0.1 Mn _0.07 Ti _0.08 O ₂ ), Test Example 4 (LiNi _{0 .75} Co _0.1 Mn _0.05 Ti _0.10 O ₂ ) and Test Example 5 (LiNi _0.75 Co _0.1 Ti _0.15 O ₂ ). Test examples 2 to 4 are included in the scope of the present invention. Moreover, the positive electrode active material for lithium ion secondary batteries in each test example was prepared by the same operation as the preparation of the positive electrode active material for lithium ion secondary batteries in the examples described later. Furthermore, the X-ray diffraction (XRD) measurement of the positive electrode active material for lithium ion secondary batteries in each test example is also measured by the same operation as the measurement in the examples described later.

As shown in FIGS. 1 and 2, the diffraction peak in X-ray diffraction pattern shown by reference numeral b~d shows the X-ray diffraction (XRD) measurement, the layered rock salt-type (alpha-NaFeO ₂₎ Structure , 18-20 ° (003), 36-37 ° (101), 37-38 ° (006), 38-39 ° (012), 44-45 ° (104) and 64-65 (108) / 65- 66 (110) where the diffraction peak (here, the diffraction peak in the X-ray diffraction pattern indicated by symbol a is applied) is shifted to the lower angle side due to the inclusion of titanium. It appears in As shown in FIGS. 1 and 2, in the X-ray diffraction patterns indicated by reference numerals b to d, the reference numerals increase as the content ratio of titanium increases from b to c and from c to d. Since it approaches the X-ray diffraction pattern indicated by e, it can be seen that manganese is substituted by titanium.

As shown in FIGS. 1 and 2, when manganese is substituted with titanium, diffraction peaks indicating a layered rock salt type (α-NaFeO ₂ ) structure are 18-20 ° (003), 36-37 °. (101), 37-38 ° (006), 38-39 ° (012), 44-45 ° (104), 64-65 ° (108) and 64-65 ° (110). .

  Furthermore, in the positive electrode active material for a lithium ion secondary battery of the present embodiment, the X-ray diffraction (XRD) measurement is characterized by a solid solution, in other words, a superlattice peak indicating a solid solution structure has a 20-23. It is preferable that it does not appear at the position of °.

  Such a positive electrode active material shows that one of Ti, Zr, Sn, and Al or two or more of any combination thereof is surely substituted with manganese, and does not have a solid solution structure. Excellent stability. Therefore, when such a positive electrode active material is used for a lithium ion secondary battery, higher cycle durability can be achieved while maintaining a high energy density.

Moreover, in the positive electrode active material for lithium ion secondary batteries of this embodiment, in a X-ray diffraction (XRD) measurement, it shows a layered rock salt type (α-NaFeO ₂ ) structure, 18-20 ° (003), 36- Diffraction peaks appearing at positions 37 ° (101), 37-38 ° (006), 38-39 ° (012), 44-45 ° (104) and 64-65 (108) / 65-66 (110). By including at least one selected from the group consisting of Ti, Zr, Sn, and Al, there is substantially no other diffraction peak derived from, for example, impurities other than the diffraction peak appearing at the position shifted to the low angle side. It is preferable not to appear. When such other diffraction peaks are present, it means that a material having a structure other than the layered rock salt structure is included in the positive electrode active material. The effect of improving the cycle durability can be surely obtained if a structure other than the layered rock salt structure is not included.

Furthermore, in the positive electrode active material for a lithium ion secondary battery of the present embodiment, the BET specific surface area is preferably 0.1 m ² / g or more and 0.8 m ² / g or less, and 0.25 m ² / g or more and 0. more preferably .5m ² / g or less, and more preferably not more than 0.25 m ² / g or more 0.4 m ² / g. When the BET specific surface area is 0.1 m ² / g or more, when such a positive electrode active material is used for a lithium ion secondary battery, high output can be realized. On the other hand, when the BET specific surface area is 0.8 m ² / g or less, elution of manganese is further suppressed, and when such a positive electrode active material is used in a lithium ion secondary battery, the energy density is maintained while High cycle durability can be realized.

  The positive electrode active material for a lithium ion secondary battery of the present embodiment described above is preferably prepared by the following manufacturing method, for example. However, the positive electrode active material for a lithium ion secondary battery of the present invention is not limited to those prepared by the following manufacturing method.

  The positive electrode active material for a lithium ion secondary battery according to this embodiment described above is obtained in the first step and the first step, in which a raw material mixed solution in which a raw material is dissolved in an aqueous solvent is spray-dried to obtain a dried product. A second step of thermally decomposing at least part of the salt contained in the dried product to obtain a precursor, and a third step of firing the precursor obtained in the second step at 400 to 1000 ° C. , And can be prepared by a production method.

  In such a production method, first, a raw material mixed solution such as an organic acid salt (complex) is spray-dried to obtain a dried product (powder), so that individual components are prevented from aggregating at the time of drying. It is possible to obtain a dry product in which each element is uniformly mixed at the atomic level. Moreover, since thermal decomposition and baking are performed after spray drying, a positive electrode active material having a very uniform composition can be produced at a relatively low temperature. Furthermore, according to such a manufacturing method, since the raw material mixed solution is spray-dried, the specific surface area of the obtained positive electrode active material can be increased as compared with the molten salt method or the coprecipitation method.

  Hereinafter, each step will be described in more detail.

[First step (spray drying step)]
In the first step, a raw material mixed solution obtained by dissolving a raw material in an aqueous solvent is spray-dried (spray drying) to obtain a dried product. As raw materials, (1) at least one nitrate selected from the group consisting of Ti, Zr, Sn and Al and / or an organic acid salt having a decomposition temperature of 100 ° C. to 350 ° C., (2) Ni, Co And at least one nitrate selected from the group consisting of Mn and / or at least one organic acid salt selected from the group consisting of Ni, Co and Mn, whose decomposition temperature is 100 ° C. to 350 ° C., and (3) Lithium nitrate and / or an organic acid salt of lithium having a decomposition temperature of 100 ° C to 350 ° C is used.

(1) At least one nitrate selected from the group consisting of Ti, Zr, Sn and Al and / or an organic acid salt having a decomposition temperature of 100 ° C. to 350 ° C. In such a production method, in the positive electrode active material, As a raw material for the substitution element contained, at least one nitrate selected from the group consisting of Ti, Zr, Sn and Al and / or an organic acid salt having a decomposition temperature of 100 ° C. to 350 ° C. is used. As a typical example of the organic acid salt, for example, citrate (also referred to as citric acid complex or citric acid complex salt) can be given. Since at least one citrate selected from the group consisting of Ti, Zr, Sn and Al has a decomposition temperature of about 130 ° C., it is easily thermally decomposed in the second step described later.

  At least one citrate selected from the group consisting of Ti, Zr, Sn and Al can be prepared, for example, by the following method. However, the method for obtaining at least one citrate selected from the group consisting of Ti, Zr, Sn and Al is not particularly limited, and may be purchased or by a method other than the following. It may be prepared.

  The Ti source, Zr source, Sn source, and Al source are not particularly limited. For example, titanium tetraisopropoxide can be used as the Ti source.

  For example, Ti citrate can be easily prepared by using the following method using titanium tetraisopropoxide as a Ti source. First, citric acid monohydrate is heated and dissolved in pure water, and titanium tetraisopropoxide is added to this solution. At this time, the molar ratio of Ti and citric acid is preferably Ti / citric acid = 1/1 to 1/3.

  Next, a basic aqueous solution (for example, about 1 to 10% by volume of ammonia water) is slowly added to the obtained solution, and the pH is adjusted to 4 to 8, whereby an aqueous solution of Ti citrate (citric acid complex solution) is obtained. ) Is obtained.

(2) At least one nitrate selected from the group consisting of Ni, Co and Mn and / or at least one selected from the group consisting of Ni, Co and Mn having a decomposition temperature of 100 ° C. to 350 ° C. In addition, in such a production method, the nitrate and / or decomposition temperature of these elements is 100 ° C. to 350 ° C. as a raw material for the transition metal (Ni, Co or Mn) contained in the positive electrode active material. It is preferable to use an organic acid salt.

  Although it does not specifically limit as nitrate, For example, it is preferable to use nitrate hydrates, such as nickel nitrate hexahydrate, manganese nitrate hexahydrate, and cobalt nitrate hexahydrate. . These nitrates have relatively low decomposition temperatures (for example, nickel nitrate hexahydrate: 137 ° C, manganese nitrate hexahydrate: 129 ° C, cobalt nitrate hexahydrate: 100-105 ° C) In the second step (pyrolysis step) described later, it is easily pyrolyzed.

  The organic acid salt having a decomposition temperature of 100 ° C to 350 ° C is not particularly limited. For example, citrates such as nickel citrate, manganese citrate, and cobalt citrate, nickel acetate tetrahydrate It is preferable to use hydrates such as acetate, manganese acetate tetrahydrate, cobalt acetate tetrahydrate and the like. Among these, from the viewpoint that it can be easily thermally decomposed in the second step described later, it is preferable to use an organic acid salt having a decomposition temperature of 100 ° C. to 300 ° C., and an organic acid having a decomposition temperature of 100 ° C. to 280 ° C. It is more preferable to use a salt. In particular, the above-mentioned acetate has a relatively low decomposition temperature (for example, nickel acetate tetrahydrate: 250 ° C., manganese acetate tetrahydrate: 210 ° C., cobalt acetate tetrahydrate: 140 ° C.). It is easily pyrolyzed in the second step described later.

(3) Lithium nitrate and / or an organic acid salt of lithium having a decomposition temperature of 100 ° C. to 350 ° C. In such a production method, lithium nitrate and / or decomposition are used as a raw material of lithium contained in the positive electrode active material. It is preferable to use an organic acid salt of lithium having a temperature of 100 ° C to 350 ° C.

  Although it does not specifically limit as an organic acid salt of lithium whose decomposition temperature is 100 degreeC-350 degreeC, For example, lithium acetate, lithium citrate, lithium oxalate etc. are mentioned.

  The lithium source material preferably contains at least one organic acid salt of lithium having a decomposition temperature of 100 ° C. to 350 ° C. from the viewpoint of making the composition of the positive electrode active material uniform and obtaining a more stable crystal structure. Further, the lithium raw material preferably contains at least one organic acid salt of lithium having a decomposition temperature of 100 ° C. to 300 ° C., and particularly preferably contains lithium acetate and / or lithium citrate.

  In such a manufacturing method, productivity can be improved by using the specific nitrate and organic acid salt of said (1)-(3), without using a sulfate and a halide as a raw material. That is, when sulfate or halide is used as a raw material, a step of removing sulfuric acid or halogen becomes essential. However, as described above, when nitrate or organic acid salt is used, it is necessary to perform a step of removing sulfuric acid or halogen. Absent. As will be described later, since nitric acid and organic acid salt can sufficiently remove nitric acid and organic acid by heating (thermal decomposition), a special removal step of nitric acid and organic acid is unnecessary. In addition, by using a nitrate or an organic acid salt, it is possible to suppress contamination of impurities such as sulfuric acid and halogen, which deteriorate battery characteristics.

  In the first step, the preparation method of the raw material mixed solution in which the raw material is dissolved in the aqueous solvent is not particularly limited. In the present specification, “aqueous solvent” refers to water or a solvent containing water as a main component. More specifically, water or a mixed solvent of water and a water-soluble organic solvent such as methanol, ethanol, acetone, N, N-dimethylformamide, N, N-dimethylacetamide, tetrahydrofuran and the like can be mentioned. Is water.

  The blending ratio of the raw materials can be appropriately set by those skilled in the art depending on the composition of the desired positive electrode active material. Further, the order of mixing the raw materials is not particularly limited. For example, as in the examples described later, transition water (Ni, Co or Mn) is added to pure water, at least one citric acid complex aqueous solution selected from the group consisting of Ti, Zr, Sn and Al. And a method of sequentially dissolving an organic acid salt having a nitrate and / or decomposition temperature of 100 ° C. to 350 ° C., lithium nitrate and / or an organic acid salt of lithium having a decomposition temperature of 100 ° C. to 350 ° C.

  In such a production method, in addition to the above raw materials, citric anhydride may be added separately to prepare a raw material mixed solution. By adding anhydrous citric acid, it is possible to stabilize at least one citric acid complex selected from the group consisting of Ti, Zr, Sn and Al in the raw material mixed solution. Can contribute to dispersion in a stable state.

  Moreover, in such a manufacturing method, it is preferable to adjust pH of a raw material mixed solution using basic aqueous solution, such as aqueous ammonia, as needed. Specifically, the pH of the raw material mixed solution is preferably 8 or less, more preferably 4 to 8, and even more preferably 5 to 7. By setting the pH of the raw material mixed solution in the above range, it is possible to set the powder density and bulkiness of the dried product obtained after spray drying to suitable values. Furthermore, by adjusting the pH of the raw material mixed solution, it is possible to make precipitation less likely to occur in the raw material mixed solution.

  In the first step, the raw material mixed solution is spray-dried to obtain a dried product. Specifically, the raw material mixed solution is sprayed and dried with hot air using a spray drying apparatus. Thereby, the solvent in the raw material mixed solution is removed, and a powdery dried product in which the metal elements are mixed almost uniformly is obtained.

In this step, it is preferable to use an inert gas (N ₂ or the like) or a low oxygen concentration gas (oxygen concentration of 5% by volume or less) as a spray gas used for spraying the raw material mixed solution or an atmosphere during hot air drying. This is to prevent the organic acid salt (citrate, acetate, etc.) in the raw material from being thermally decomposed to generate organic substances (citric acid, acetic acid) and ignite.

  In this step, the hot air temperature at the time of drying is not particularly limited, but is preferably 200 to 350 ° C, more preferably 200 to 300 ° C. When the hot air temperature is in this range, the actual temperature of the material to be dried is approximately 150 to 300 ° C., and the solvent can be removed in a short time. In particular, when the solvent of the raw material mixture solution is water, water can be sufficiently removed by setting the temperature of the material to be dried within the above range. As a result, it is possible to prevent moisture absorption of the organic acid salt contained in the raw material mixed solution and to efficiently perform the second step that follows. Moreover, aggregation of the dried substance (powder) after spray-drying can be suppressed by preventing the organic acid salt from absorbing moisture. In addition, in the said temperature range, a part of nitrate and organic acid salt (citric acid, acetic acid, etc.) in a raw material may thermally decompose.

[Second step (pyrolysis step)]
In the second step, at least a part of the salt contained in the dried product obtained in the first step is thermally decomposed to obtain a precursor of the positive electrode active material. The temperature at the time of thermal decomposition (heat treatment temperature) varies depending on the thermal decomposition temperature of the salt as a raw material, but is preferably 150 to 400 ° C, more preferably 200 to 400 ° C, and 200 to 350 ° C. More preferably it is. Moreover, although heat processing time also changes with kinds of salt used as a raw material, 1 to 48 hours are preferable and it is more preferable that it is 4 to 12 hours. In this step, it is not necessary to thermally decompose all of the salt contained in the dried product. When lithium nitrate (decomposition temperature: about 600 ° C.) is used as a raw material, it is not thermally decomposed in this step. May remain. On the other hand, at least one citrate selected from the group consisting of Ti, Zr, Sn and Al, an nitrate of a transition element (Ni, Co or Mn) and / or an organic acid having a decomposition temperature of 100 ° C. to 350 ° C. The salt and the organic acid salt of lithium having a decomposition temperature of 100 ° C. to 350 ° C. are thermally decomposed in this step, and unnecessary nitric acid (NO ₃ ) and organic substances (citric acid, acetic acid, etc.) are removed.

In this step, it is preferable to perform thermal decomposition in an atmosphere of an inert gas (N ₂ or the like) or a low oxygen concentration gas (oxygen concentration of 5% by volume or less), as in the first step (spray drying step) described above. This is because organic substances (citric acid, acetic acid, etc.) are generated from organic acid salts (citrate, acetate, etc.) due to thermal decomposition and are prevented from igniting.

  Moreover, it is preferable to heat-process in this process, making the dried material (powder) obtained at the 1st process flow at the time of thermal decomposition. Specifically, it heat-processes, making a dry substance (powder) flow, using flow apparatuses, such as a fluid-fired furnace (rotary kiln). By performing the heat treatment in this manner, the growth of particles (primary particles, secondary particles) can be suppressed, so that the BET specific surface area of the obtained positive electrode active material can be increased.

[Third step (firing step)]
In the third step, the precursor obtained in the second step is fired, whereby the crystal structure is constructed and stabilized, and a positive electrode active material is obtained. The firing in this step is not particularly limited, but is preferably performed at a firing temperature (heat treatment temperature) of 400 to 1200 ° C. within a range of firing time of 1 to 48 hours. Further, it is preferable to perform the firing while raising the firing temperature from a low temperature to a high temperature stepwise or continuously. For example, it is preferable to perform primary firing at 700 to 1000 ° C. for 1 to 24 hours after preliminary firing at 400 to 600 ° C. for 1 to 24 hours. Through such a firing step, a positive electrode active material having a stable crystal structure can be obtained.

  Next, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the dimension ratio of drawing quoted by the following embodiment is exaggerated on account of description, and may differ from an actual ratio.

  FIG. 3 is a perspective view showing an external appearance of a flat (stacked) lithium ion secondary battery, which is a lithium ion secondary battery according to an embodiment of the present invention. FIG. 4 is a schematic cross section taken along line III-III of a non-bipolar lithium ion secondary battery which is an embodiment of the flat (stacked) lithium ion secondary battery shown in FIG. FIG.

  As shown in FIG. 3, in the lithium ion secondary battery 1 of the present embodiment, the battery element 10 to which the positive electrode tab 21 and the negative electrode tab 22 are attached is wrapped by the battery outer body 30, and the periphery of the battery outer body 30 is The battery element 10 is sealed inside the battery outer package 30 with the positive electrode 21 and the negative electrode tab 22 drawn out of the battery outer package 30. The positive electrode tab 21 and the negative electrode tab 22 are led out in opposite directions from the inside of the battery outer package 30 to the outside.

  Although not shown, the positive electrode tab and the negative electrode tab may be led out from the same side in the same direction, for example, from the inside to the outside of the battery outer package. Moreover, although not shown in figure, the positive electrode tab and the negative electrode tab may be derived | led-out from each edge | side, for example, dividing each into plurality. Further, such a positive electrode tab and a negative electrode tab can be attached to a positive electrode current collector and a negative electrode current collector, which will be described later, by, for example, ultrasonic welding or resistance welding.

  As shown in FIG. 4, the substantially rectangular battery element 10 in which the charge / discharge reaction actually proceeds includes a positive electrode 11 having a positive electrode active material layer 11B formed on both surfaces of the positive electrode current collector 11A, and an electrolyte layer. 13 and a plurality of negative electrodes 12 having a negative electrode active material layer 12B formed on both surfaces of the negative electrode current collector 12A. At this time, the positive electrode active material layer 11B formed on one surface of the positive electrode current collector 11A of one positive electrode 11 and the negative electrode current collector 12A of the negative electrode 12 adjacent to the one positive electrode 11 are formed. A plurality of layers of a positive electrode, an electrolyte layer, and a negative electrode are stacked in this order so that the negative electrode active material layer 12 </ b> B faces the electrolyte layer 13. As a result, the adjacent positive electrode active material layer 11B, electrolyte layer 13 and negative electrode active material layer 12B constitute one unit cell layer. Therefore, the lithium ion secondary battery 1 has a configuration in which a plurality of single battery layers 14 are stacked and electrically connected in parallel. In each of the outermost layer negative electrode current collectors 12 </ b> A ′ positioned in both outermost layers of the battery element 10, the negative electrode active material layer 12 </ b> B is disposed only on one side.

  Although not shown, negative electrode active material layers may be provided on both surfaces of the outermost negative electrode current collector located in both outermost layers of the battery element. In other words, the negative electrode current collector having the negative electrode active material layer on both sides is not used as the negative electrode current collector for the outermost layer provided with the negative electrode active material layer only on one side. Also good. Further, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 2 so that the outermost positive electrode current collector is positioned in both outermost layers of the power generation element, and the positive electrode is disposed on one or both surfaces of the outermost layer positive electrode current collector. An active material layer may be arranged.

  FIG. 4 shows a lithium ion secondary battery that is not a flat type (stacked type) bipolar type. However, the positive electrode active material layer disposed on one surface of the current collector is opposite to the current collector. A flat type (stacked type) bipolar bipolar battery having a negative electrode active material layer disposed on the side surface may be used. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

  Furthermore, the laminated lithium ion secondary battery is more suitable than the lithium ion secondary battery, which is expected to have an effect of suppressing swelling, by applying an appropriate pressure to the positive electrode such as a wound lithium ion secondary battery. There is an advantage that it is difficult to apply pressure to the positive electrode.

  Hereinafter, each configuration will be described in more detail.

[Positive electrode]
The positive electrode 11 has a positive electrode current collector 11A and a positive electrode active material layer 11B formed on the surface of the positive electrode current collector 11A.

(Positive electrode current collector)
The positive electrode current collector is not particularly limited. For example, a conductive resin in which a conductive filler is added to a metal, a conductive polymer, or a nonconductive polymer material can be applied. .

  Examples of the metal include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. In addition to these, preferred examples include a clad material of nickel and aluminum, a clad material of copper and aluminum, and a plated material of a combination of these metals. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel (SUS), and copper are preferably used from the viewpoint of conductivity and battery operating potential.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the positive electrode current collector.

  Further, as the non-conductive polymer material, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), Polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) ), Polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polystyrene (PS), and the like. Such a non-conductive polymer material has excellent potential resistance or solvent resistance.

  A conductive filler can be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin that is the base material of the positive electrode current collector is made of only a nonconductive polymer, a conductive filler is essential to impart conductivity to the resin. The conductive filler is not particularly limited as long as it is a substance having conductivity, and examples thereof include metals, conductive carbon, and the like as materials excellent in conductivity, potential resistance, or lithium ion blocking properties. It is done. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these It is preferable to contain an alloy or metal oxide containing any of these metals. The conductive carbon is not particularly limited, but is selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It is preferable that at least one kind is included. The addition amount of the conductive filler is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the positive electrode current collector, and is generally about 5 to 35% by mass.

  The size of the positive electrode current collector is appropriately determined according to the intended use of the battery. For example, if it is used for a large battery requiring high energy density, a positive electrode current collector having a large area is used. The thickness of the positive electrode current collector is not particularly limited. The thickness of the positive electrode current collector is usually about 1 to 100 μm.

(Positive electrode active material layer)
The positive electrode active material layer includes the positive electrode active material represented by the composition formula (1) described above as an essential component, and may include a conductive additive, a binder, and the like as necessary. Since the positive electrode active material represented by the composition formula (1) has been described above, the description thereof is omitted.

(Conductive aid)
The conductive auxiliary agent is not particularly limited. For example, carbon black such as acetylene black, channel black, thermal black and ketjen black, carbon powder such as graphite, and carbon fiber such as vapor grown carbon fiber. And carbon materials. When the positive electrode active material layer contains a conductive additive, an electronic network inside the positive electrode active material layer is effectively formed, and the output characteristics of the battery can be improved.

(Binder)
Examples of the binder include polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide. However, the present invention is not limited to these, and conventionally known ones used for lithium ion secondary batteries can be applied. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more type.

[Negative electrode]
The negative electrode 12 has a negative electrode current collector 12A and a negative electrode active material layer 12B formed on the surface of the negative electrode current collector 12A. Note that the negative electrode current collector can be appropriately selected and used as described for the positive electrode, and thus the description thereof is omitted.

(Negative electrode active material layer)
The negative electrode active material layer includes a negative electrode active material as an essential component, and may include a conductive additive, a binder, and the like as necessary. Note that the conductive auxiliary agent and binder can be appropriately selected and used as those described for the positive electrode, and thus description thereof is omitted.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can release lithium ions during discharge and occlude lithium ions during charging. For example, a metal such as Si or Sn, or a metal oxide such as TiO, Ti ₂ O ₃ , TiO ₂ , SiO ₂ , SiO, SnO ₂ , Li _4/3 Ti _5/3 O _4, or Li ₇ MnN ₄ Complex oxide of lithium and transition metal, Li-Pb alloy, Li-Al alloy, Li, or carbon powder, natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, or hard Examples thereof include carbon materials such as carbon. Such a negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more types as appropriate. In addition, by using an element that forms an alloy with lithium among these negative electrode active materials, a battery having a high energy density, a high capacity, and excellent output characteristics as compared with a conventional carbon-based material can be obtained. Is possible. In addition, the element that forms an alloy with lithium is not particularly limited. For example, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl can be mentioned.

  In addition, the negative electrode active material preferably includes a carbon material and / or at least one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn. It is more preferable to include an element of Sn, and it is particularly preferable to use a carbon material.

  As the carbon material, carbonaceous particles having a low discharge potential relative to lithium are preferable. For example, natural graphite, artificial graphite, a blend of natural graphite and artificial graphite, natural graphite coated material, soft carbon, hard carbon Etc. can be mentioned as a suitable example. The shape of the carbonaceous particles is not particularly limited. For example, the shape may be any shape such as a lump shape, a sphere shape, and a fiber shape, but is preferably not a scale shape, and may be a sphere shape or a lump shape. preferable. What is not scale-like is preferable from a viewpoint of performance and durability.

  The carbonaceous particles are preferably those whose surfaces are coated with amorphous carbon. At that time, it is more preferable that the amorphous carbon covers the entire surface of the carbonaceous particles, but it may be a coating of only a part of the surface. By covering the surfaces of the carbonaceous particles with amorphous carbon, it is possible to prevent the graphite and the electrolytic solution from reacting during charging and discharging of the battery. The method for coating the surface of the graphite particles with amorphous carbon is not particularly limited. For example, carbonaceous particles (cores) in a mixed solution in which amorphous carbon is dissolved or dispersed in a solvent are used. There is a wet method in which the solvent is removed after the powder is dispersed and mixed. Other examples include a dry method in which carbonaceous particles and amorphous carbon are mixed with each other, and mechanical energy is added to the mixture to cover the amorphous carbon, and a vapor phase method such as a CVD method. Whether the carbonaceous particles are coated with amorphous carbon can be confirmed by a method such as laser spectroscopy.

[Nonaqueous electrolyte layer]
The nonaqueous electrolyte layer 13 functions as a spatial partition (spacer) between the positive electrode 11 and the negative electrode 12. In addition, it also has a function of holding an electrolyte that is a lithium ion transfer medium between the positive and negative electrodes during charging and discharging. There is no restriction | limiting in particular in the electrolyte which comprises a nonaqueous electrolyte layer, Polymer electrolytes, such as a liquid electrolyte, a polymer gel electrolyte, and a polymer solid electrolyte, can be used suitably. In the present embodiment, it is preferable to apply a liquid electrolyte.

  The liquid electrolyte has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), fluorine-containing cyclic carbonate (fluoroethylene carbonate (FEC), etc.), fluorine-containing chain carbonate, fluorine-containing chain ether, and fluorine-containing chain ester. it can. These may be used alone or in combination of two or more.

Moreover, it is preferable to use at least LiPF ₆ as the lithium salt. In addition, LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiSO ₃ CF _3, or the like can be used. The lithium salt concentration is preferably 0.1 to 5 mol / L, more preferably 0.1 to 2 mol / L.

  Furthermore, in the case of liquid electrolytes, organic sulfone compounds, organic disulfone compounds, vinylene carbonate derivatives, ethylene carbonate derivatives, ester derivatives, divalent phenol derivatives, terphenyl derivatives, phosphate derivatives, and lithium fluorophosphate derivatives as additives Preferably, at least one selected from the group consisting of: Of these, lithium fluorophosphate derivatives such as lithium monofluorophosphate and lithium difluorophosphate are more preferable. Use of these additives is preferable from the viewpoint of performance and life characteristics. It is preferable that 0.1-5 mass% of additives are contained in electrolyte solution, and it is more preferable that 0.5-3.5 mass% is contained.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and a polymer solid electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer having lithium ion conductivity. Examples of the matrix polymer having lithium ion conductivity include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. Such a matrix polymer easily dissolves an electrolyte salt such as a lithium salt.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include a microporous film made of a polyolefin such as polyethylene or polypropylene, a hydrocarbon such as polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, or the like.

  The polymer solid electrolyte has a configuration in which a lithium salt is dissolved in the matrix polymer and does not contain an organic solvent. Therefore, when the electrolyte layer is composed of a polymer solid electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

  The matrix polymer of the polymer gel electrolyte or the polymer solid electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte, using an appropriate polymerization initiator. A polymerization treatment may be performed. In addition, the said electrolyte may be contained in the active material layer of an electrode.

(Positive electrode tab and negative electrode tab)
The material which comprises the positive electrode tab 21 and the negative electrode tab 22 is not specifically limited, The well-known highly conductive material conventionally used as a positive electrode tab and a negative electrode tab for lithium ion secondary batteries can be used. . As a constituent material of the positive electrode tab and the negative electrode tab, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. In the positive electrode tab 21 and the negative electrode tab 22, the same material may be used, or different materials may be used.

(Battery exterior)
Although it does not specifically limit as the battery exterior body 30, For example, it is suitable to use the bag-shaped case using the laminate film containing aluminum which can cover an electric power generation element. Such a form is suitable from the viewpoint of achieving weight reduction, for example. Specific examples of such a laminate film include a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order. A laminate film is preferred from the viewpoint that it is excellent in high output and cooling performance and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the electric power generation element applied from the outside can be adjusted easily and it is easy to adjust to the desired electrolyte layer thickness, the exterior body is more preferably an aluminate laminate.

(Battery)
The lithium ion secondary battery may be an assembled battery formed by connecting a plurality of lithium ion secondary batteries. In detail, it can be set as the assembled battery comprised by serialization or parallelization, or both using several lithium ion secondary batteries. Capacitance and voltage can be freely adjusted by serialization or parallelization.

  A plurality of lithium ion secondary batteries can be connected in series or in parallel to form a small assembled battery that can be attached and detached. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many lithium-ion secondary batteries are connected to produce an assembled battery, and how many stages of small assembled batteries are stacked to produce a large-capacity assembled battery depends on the mounted vehicle (electric vehicle) Depending on the battery capacity and output.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[Example 1]
<Preparation of Positive Electrode Active Material Represented by Composition Formula (1)>
(Preparation of aqueous solution of titanium citrate complex)
155 g (0.8 mol) of anhydrous citric acid (molecular weight: 192.12 g / mol) was added to 1000 ml of ethanol, and this was heated to 60 ° C. and dissolved. Next, 120 g (0.4 mol) of titanium tetraisopropoxide (molecular weight: 284.22 g / mol, purity 95%) was added to the obtained solution, and this was stirred for about 10 minutes. Further, pure water (500 ml) and 5.6% aqueous ammonia (about 100 ml) were slowly added to the obtained solution. Further, the obtained solution was boiled to remove water and ethanol / isopropanol, concentrated to 500 ml, and then cooled to room temperature. Further, 5.6% aqueous ammonia (about 50 ml) was slowly added to the obtained concentrated liquid to adjust pH = 6. Furthermore, the obtained solution was filtered with a filter paper to remove insoluble matters. Further, a part of the obtained filtrate was put in an evaporating dish and dried at 100 ° C. for 24 hours. Thereafter, the obtained dried product (powder) was calcined and decomposed at 600 ° C. for 12 hours and quantified as TiO ₂ . The Ti concentration was 6.0% by mass as TiO ₂ (molecular weight: 79.87 g / mol).

(Preparation of raw material mixed solution)
Next, 66.5 g of the titanium citrate complex aqueous solution (Ti concentration: 6.0% by mass as TiO ₂ (molecular weight: 79.87 g / mol)), nickel acetate tetrahydrate (molecular weight: molecular weight: 2500 ml of pure water. 248.84 g / mol) 186.6 g, cobalt acetate tetrahydrate (molecular weight: 249.08 g / mol) 24.9 g, manganese acetate tetrahydrate (molecular weight: 245.09 g / mol) 24.5 g, Lithium acetate dihydrate (molecular weight: 102.02 g / mol) 103.0 g was added in order and dissolved. Thereafter, 5.6% aqueous ammonia was slowly added to the resulting solution to adjust to pH = 6 to obtain a raw material mixed solution.

(First step (drying step))
The raw material mixed solution is spray-dried at a hot air temperature of 250 ° C. to 300 ° C. by a spray device using an inert gas (N ₂ ) to remove moisture, and a dried product (powder) is obtained as a raw material mixture. It was.

(Second step (pyrolysis step))
Next, the dried product (powder) is baked for 4 hours at 300 ° C. to 400 ° C. under a flow of 5% by volume-O ₂ / N ₂ in a fluidized baking furnace to thermally decompose the organic acid salt, A precursor was obtained.

(Third step (firing step))
Thereafter, the precursor was calcined at 600 ° C. for 12 hours in an oxygen atmosphere, and then calcined at 900 ° C. for 12 hours to obtain a positive electrode active material of this example.

(Quantitative analysis of composition: ICP)
The positive electrode active material sample is dissolved in an acid, and nickel (Ni), cobalt (Co), manganese (Mn), titanium (Ti), and lithium (Li) contained in the solution are analyzed by inductively coupled plasma emission spectroscopy. Quantified. For the measurement, an inductively coupled plasma emission spectrometer SPS-3520 type manufactured by SII Nanotechnology Inc. was used. As a result, the composition of the positive electrode active material of this example was as follows.

Composition formula: Li _1.01 Ni _0.75 Co _0.10 Mn _0.10 Ti _0.05 O _z

  This is because in the composition formula (1), X is Ti, x = 1.01, 1-abc = 0.75, a = 0.10, b = 0.10, c = 0. 05, Ti / (Mn + Ti) = 0.33, (Mn + Ti) /Co=1.5, Ti / Mn = 0.50.

(X-ray diffraction measurement)
The positive electrode active material was evaluated for crystal structure and crystallinity by X-ray diffraction. Cu-Kα rays were used as the X-ray source, and the measurement conditions were a tube voltage of 40 KV, a tube current of 20 mA, a scanning speed of 2 ° / min, a divergence slit width of 0.5 °, and a light receiving slit width of 0.15 °.

(BET specific surface area)
About the said positive electrode active material, the BET specific surface area was measured using the BET specific surface area measuring apparatus (Nippon Bell, BET by BELSORP-miniII). As a result, the BET specific surface area was 0.5 m ² / g.

<Preparation of Positive Electrode with Positive Electrode Active Material Layer Formed on One Side of Positive Electrode Current Collector>
First, a positive electrode slurry having the following composition was prepared.

(Composition of slurry for positive electrode)
Positive electrode active material: positive electrode active material (9.2 parts by weight)
Conductive aid: flake graphite (0.2 parts by weight), acetylene black (0.2 parts by weight)
Binder: Polyvinylidene fluoride (PVDF) (0.4 parts by weight)
Solvent: N-methyl-2-pyrrolidone (NMP) (8.2 parts by weight)

  Specifically, a positive electrode slurry having the above composition was prepared as follows. First, 0.4 parts by weight of a conductive additive, 9.2 parts by weight of a positive electrode active material, and 4.0 parts by weight of a solvent (NMP) are added to a 50 ml disposable cup, and a stirring defoamer (spinning revolution mixer: Awa It was stirred for 1 minute with Tori Rentaro AR-100). Next, 4.0 parts by weight of a 10% binder solution in which the binder was dissolved in the solvent (NMP) and 0.6 parts by weight of the solvent (NMP) were added to the obtained mixture. Thereafter, this was stirred for 3 minutes with a stirring deaerator to obtain a positive electrode slurry (solid content concentration: 55% by mass).

(Application of positive electrode slurry)
Next, a desired amount of the obtained positive electrode slurry was applied to one surface of an aluminum current collector foil having a thickness of 20 μm by an automatic coating apparatus (Doctor blade manufactured by Tester Sangyo: PI-1210 automatic coating apparatus).

(Drying positive electrode slurry)
Further, the current collector foil coated with the positive electrode slurry was dried on a hot plate (drying temperature: 100 to 110 ° C., drying time: 30 minutes), and the amount of NMP remaining in the positive electrode active material layer was 0.02 mass. % Sheet-shaped positive electrode was obtained. The weight of the positive electrode active material layer on one side was about 15.0 mg / cm ² .

(Positive electrode press)
Furthermore, the obtained sheet-like positive electrode was compression-molded by a roller press so that the density of the positive electrode active material layer on one side was 2.5 to 2.7 g / cm ^3, and cut for cell production.

(Dry cathode)
Thereafter, the cut sheet-like positive electrode was dried in a vacuum drying furnace. Specifically, the sheet-like positive electrode was dried as follows. First, the cut sheet-like positive electrode was placed inside the drying furnace with the sheet-like positive electrode sandwiched between glass plates. Subsequently, the pressure was reduced (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.) to remove air inside the drying furnace. Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 120 ° C. at 10 ° C./min, and the pressure was reduced again at 120 ° C., and the inside of the drying furnace was evacuated and held for 12 hours. Thereafter, the temperature was lowered to room temperature, moisture on the surface of the positive electrode was removed, and the positive electrode of this example was obtained.

<Preparation of Negative Electrode with Negative Electrode Active Material Layer Formed on One Side of Negative Electrode Current Collector>
First, a negative electrode slurry having the following composition was prepared.

(Composition of slurry for negative electrode)
Negative electrode active material: natural graphite (9.3 parts by weight)
Conductive aid: acetylene black (0.1 parts by weight)
Binder: Polyvinylidene fluoride (PVDF) (0.6 parts by weight)
Solvent: N-methyl-2-pyrrolidone (NMP) (10.0 parts by weight)

  Specifically, a negative electrode slurry having the above composition was prepared as follows. First. To a 50 ml disposable cup, 0.1 part by weight of a conductive additive, 9.3 parts by weight of a negative electrode active material, and 4.0 parts by weight of a solvent (NMP) are added, and a stirring defoaming machine (spinning revolution mixer: Awatori smelting) Taro AR-100) was stirred for 1 minute. Next, 6.0 parts by weight of a 10% binder solution in which the binder was dissolved in the solvent (NMP) and 0.6 parts by weight of the solvent (NMP) were added to the obtained mixture. Thereafter, this was stirred for 3 minutes with a stirring deaerator to obtain a negative electrode slurry (solid content concentration: 50% by mass).

(Slurry coating for negative electrode)
Next, a desired amount of the obtained negative electrode slurry was applied to one side of a 10 μm thick copper current collector foil using an automatic coating apparatus (Doctor blade manufactured by Tester Sangyo Co., Ltd .: PI-1210 automatic coating apparatus).

(Slurry drying for negative electrode)
Further, the current collector foil coated with the negative electrode slurry was dried on a hot plate (drying temperature: 100 to 110 ° C., drying time: 30 minutes), and the amount of NMP remaining in the negative electrode active material layer was 0.02 mass. % Sheet-shaped negative electrode was obtained. The weight of the negative electrode active material layer on one side was about 9.0 mg / cm ² .

(Negative electrode press)
Furthermore, the obtained sheet-like negative electrode was compression-molded with a roller press so that the density of the negative electrode active material layer on one side was 1.4 to 1.6 g / cm ^3, and cut for cell production.

(Dry anode drying)
Thereafter, the cut sheet-like negative electrode was dried in a vacuum drying furnace. Specifically, the sheet-like negative electrode was dried as follows. First, the cut sheet-like negative electrode was placed inside the drying furnace with the sheet-like negative electrode sandwiched between glass plates. Subsequently, the pressure was reduced (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.) to remove air inside the drying furnace. Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 130 ° C. at 10 ° C./min, and the pressure was reduced again at 130 ° C., and the nitrogen inside the drying furnace was evacuated and held for 12 hours. Thereafter, the temperature was lowered to room temperature, the moisture on the negative electrode surface was removed, and the negative electrode of this example was obtained.

<Production of pouch cell>
The positive electrode (coated portion area 2.4 cm × 4.0 cm) ultrasonically welded with an aluminum tab to the positive electrode current collector portion and the negative electrode (coated portion area) ultrasonically welded with a nickel tab to the negative electrode current collector portion 2.6 cm × 4.4 cm) through a separator (3.5 cm × 5.0 cm, Celgard Corp., Cellguard 2400), and then an exterior body made of an aluminum laminate film (5.0 cm × 6.5 cm) ) Sandwiched both sides of the laminate, and thermocompression sealed the three sides of the outer package to store the laminate. After injecting 0.3 cm ³ / cell of an electrolyte solution in which 1.0 mol / L LiPF ₆ (electrolyte) was dissolved in a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC), the rest Was sealed by thermocompression bonding to produce a battery (pouch cell). In order to sufficiently permeate the electrolyte into the electrode pores, the battery of this example was completed by holding at room temperature for 24 hours while applying a surface pressure of 0.5 MPa.

[Examples 2 to 4]
In the preparation of the positive electrode active material represented by the composition formula (1), the same operation as in Example 1 was repeated except that the content ratios of two of cobalt, manganese, and titanium were changed. A positive electrode active material, a positive electrode, and a battery were obtained.

[Example 5]
Instead of 66.6 g of the titanium citrate complex aqueous solution (Ti concentration: TiO ₂ (molecular weight: 79.87 g / mol), 66.6 g), zirconium oxynitrate dihydrate (molecular weight: 267.26 g / mol) Except for using 13.3 g, the same operation as in Example 1 was repeated to obtain a positive electrode active material, a positive electrode, and a battery of this example. In addition, the composition of the positive electrode active material of this example was as follows.

Composition formula: Li _1.01 Ni _0.75 Co _0.10 Mn _0.10 Zr _0.05 O _z

  In the composition formula (1), X is Zr, x = 1.01, 1-abc = 0.75, a = 0.10, b = 0.10, c = 0. 05, Zr / (Mn + Zr) = 0.33, (Mn + Zr) /Co=1.5, Zr / Mn = 0.50.

[Example 6]
Instead of the above-mentioned titanium citrate complex aqueous solution (Ti concentration: TiO ₂ (molecular weight: 79.87 g / mol) 6.0 mass%) 66.6 g, tin citrate complex aqueous solution (Sn concentration: SnO (molecular weight: 134.71 g) The same operation as in Example 1 was repeated except that 6.0 wt%) and 112.2 g were used as / mol), to obtain a positive electrode active material, a positive electrode, and a battery of this example. In addition, the composition of the positive electrode active material of this example was as follows.

Composition formula: Li _1.01 Ni _0.75 Co _0.10 Mn _0.10 Sn _0.05 O _z

  In the composition formula (1), X is Sn, x = 1.01, 1-abc = 0.75, a = 0.10, b = 0.10, c = 0. 05, Sn / (Mn + Sn) = 0.33, (Mn + Sn) /Co=1.5, Sn / Mn = 0.50.

[Example 7]
In place of 66.6 g of the titanium citrate complex aqueous solution (Ti concentration: TiO ₂ (molecular weight: 79.87 g / mol) 66.6 g), aluminum nitrate.9 hydrate (molecular weight 375.13 g / mol) Except having used 18.7g, the same operation as Example 1 was repeated and the positive electrode active material of this example, the positive electrode, and the battery were obtained. In addition, the composition of the positive electrode active material of this example was as follows.

Composition formula: Li _1.01 Ni _0.75 Co _0.10 Mn _0.10 Al _0.05 O _z

  This is because in the composition formula (1), X is Al, x = 1.01, 1-abc = 0.75, a = 0.10, b = 0.10, c = 0. 05, Al / (Mn + Al) = 0.33, (Mn + Al) /Co=1.5, Al / Mn = 0.50.

[Examples 8 to 13]
In the preparation of the positive electrode active material, the same operation as in Example 1 was repeated except that the content ratios of lithium, nickel, cobalt, manganese, and titanium were changed to obtain the positive electrode active material, the positive electrode, and the battery of this example. .

[Comparative Example 1]
In preparation of the positive electrode active material represented by the composition formula (1), nickel acetate tetrahydrate (molecular weight: 248.84 g / mol) 186.6 g, cobalt acetate tetrahydrate (molecular weight: 249.08 g / mol) 24.9 g, manganese acetate tetrahydrate (molecular weight: 245.09 g / mol) 36.8 g, lithium acetate dihydrate (molecular weight: 102.02 g / mol) 103.0 g only. Except for the above, the same operation as in Example 1 was repeated to obtain a positive electrode active material, a positive electrode, and a battery of this example.

[Comparative Examples 2 to 4]
In the preparation of the positive electrode active material, the same operation as in Example 1 was repeated except that the content ratios of lithium, nickel, cobalt, and manganese were changed to obtain the positive electrode active material, the positive electrode, and the battery of this example.

[Comparative Example 5]
In preparation of the positive electrode active material, instead of 36.8 g of manganese acetate tetrahydrate (molecular weight: 245.09 g / mol), an aqueous solution of titanium citrate complex (Ti concentration: TiO ₂ (molecular weight: 79.87 g / mol)) The same procedure as in Comparative Example 1 was repeated except that 199.7 g was used, and a positive electrode active material, a positive electrode, and a battery of this example were obtained. A part of the specification of each example is shown in Table 1.

[Performance evaluation]
Using the pouch cell of each of the above examples, the following various performances were evaluated at room temperature (25 ° C.).

[0.1C capacity evaluation]
The battery was charged by a constant current charging method until the maximum voltage reached 4.35 V at a 0.1 C rate. Then, it was kept (rested) for about 0.5 hours. Thereafter, the battery was discharged by a constant current discharge method at a 0.1 C rate until the minimum voltage of the battery reached 2.5V. The discharge capacity at the 0.1 C rate at this time was defined as “0.1 C discharge capacity (mAh / g)”. The obtained results are also shown in Table 1.

[Rate characteristics evaluation]
The battery was charged by a constant current constant voltage charging method until the maximum voltage reached 4.35 V at a 1.0 C rate. Then, it was kept (rested) for about 0.5 hours. Thereafter, the battery was discharged by a constant current discharge method at a 0.2 C rate until the minimum voltage of the battery became 2.5V. The discharge capacity at the 0.2 C rate at this time was defined as “0.2 C discharge capacity (mAh / g)”.

  Moreover, it charged by the constant current constant voltage charging method until the maximum voltage became 4.35V at 1.0C rate. Then, it was kept (rested) for about 0.5 hours. Thereafter, the battery was discharged by a constant current discharge method at a 2.0 C rate until the minimum voltage of the battery became 2.5V. The discharge capacity at the 2.0 C rate at this time was defined as “2.0 C discharge capacity (mAh / g)”.

  The ratio of the 2.0 C discharge capacity to the 0.2 C discharge capacity was defined as “2.0 C / 0.2 C capacity retention rate (%)” (see Formula (1)). The obtained results are also shown in Table 1.

[Cycle durability evaluation]
In the cycle durability test of the battery, constant current charge / discharge at 1.0 C was repeated 100 cycles at 25 ° C. The battery performance evaluation in the cycle endurance test is a constant current charging method in which charging is controlled so that the charging capacity per active material weight is 180 mAh / g, and discharging is performed with a minimum battery voltage of 2.0V. Up to 1.0 C rate. The ratio of the discharge capacity after 100 cycles to the discharge capacity after 1 cycle was defined as “capacity maintenance rate after 100 cycles (%)” (see formula (2)). The obtained results are also shown in Table 1.

  From Table 1, in Examples 1 to 13 belonging to the scope of the present invention, compared with Comparative Examples 1 to 5 outside the present invention, discharge capacity and rate characteristics can be maintained, and cycle durability is improved. It turns out that it is excellent. This is presumably because the positive electrode active material represented by the composition formula (1) was used.

In the X-ray diffraction (XRD) measurement of the positive electrode active materials of Examples 1 to 13, 18-20 ° (003), 36-37 ° (101) indicating a layered rock salt type (α-NaFeO ₂ ) structure. , 37-38 ° (006), 38-39 ° (012), 44-45 ° (104) and 64-65 (108) / 65-66 (110) at diffraction peaks observed at Ti, By including Zr, Sn, or Al, it was observed at a position shifted to the low angle side. Further, in this X-ray diffraction (XRD) measurement, for example, other diffraction peaks derived from impurities or the like were not substantially observed. From these results, it is considered that the high cycle durability can be realized while maintaining the discharge capacity and the rate characteristics in Examples 1 to 13 because of the diffraction pattern as described above.

In the composition formula (1), for example, when 1-abc is 0.75 or more and less than 0.80, X / (Mn + X) is preferably 0.50 or more, and X / Mn is preferably 1.0 or more.
In the composition formula (1), for example, when 1-abc is 0.80 or more and less than 0.85, X / (Mn + X) is preferably 0.33 or less, and X / Mn is preferably 0.5 or less.
Furthermore, in the composition formula (1), for example, when 1-abc is 0.85 or more and 0.90 or less, c is preferably 0.03 to 0.08, and X / ( Mn + X) is preferably 0.23 or more, and X / Mn is preferably 0.3 or more.

  Moreover, in Examples 1 to 13, a high average voltage of about 3.5 V was shown, but when Ti was applied as X, a particularly high average voltage was shown (Test Examples 7 and 8 below). reference.).

FIG. 5 is a graph showing average voltages in lithium ion secondary batteries obtained in some test examples. In Test Example 6 to Test Example 10 in the figure, LiNi _0.75 Co _0.1 Mn _0.15 O ₂ prepared by the same operation as the preparation of the positive electrode active material for a lithium ion secondary battery in the above-described example, respectively. LiNi _0.75 Co _0.1 Mn _0.10 Ti _0.05 O ₂ , LiNi _0.75 Co _0.1 Mn _0.05 Ti _0.10 O ₂ , LiNi _0.75 Co _0.1 Ti _{0. A} predetermined battery is manufactured using ₁₅ O ₂ and LiNi _0.8 Co _0.05 Mn _0.15 O ₂ . Note that Test Example 7 and Test Example 8 are included in the scope of the present invention. The batteries of Test Example 6 to Test Example 10 were charged by the constant current constant voltage charging method until the maximum voltage reached 4.35 V at a 1.0 C rate, and held (rested) for about 0.5 hours. The battery was discharged by a constant current discharge method at a rate of 0.2C, 0.5C, 1.0C, and 2.0C until the voltage reached 2.5 V, and an average discharge voltage (V) was calculated (see Formula (3)). .

  As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.

  In the above-described embodiments and examples, as a lithium ion secondary battery, a laminated type (laminated type battery) in which a laminated type battery element (however, in the examples is a single layer) is sealed with an outer package made of a laminated film. However, the present invention is not limited to this. That is, it can also be applied to a lithium ion secondary battery having a conventionally known form or structure, for example, a lithium ion in which a laminated or wound battery element is sealed with an outer package made of a rectangular metal can. Examples thereof include a secondary battery and a lithium ion secondary battery in which a wound battery element is sealed with an outer package made of a cylindrical metal can. Note that in a lithium ion secondary battery in which a wound battery element is sealed with an outer package made of a cylindrical metal can, a terminal may be formed using a metal can, for example, instead of a tab.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Battery element 11 Positive electrode 11A Positive electrode collector 11B Positive electrode active material layer 12 Negative electrode 12A Negative electrode collector 12A 'Outermost layer negative electrode collector 12B Negative electrode active material layer 13 Nonaqueous electrolyte layer 14 Single battery layer 21 Positive electrode tab 22 Negative electrode tab 30 Exterior body

Claims (6)

The following composition formula (1)
Li _x N _1-abc Co _a Mn _b X _c O _z (1)
(In the composition formula (1), X is at least one selected from the group consisting of Ti, Zr, Sn and Al, z is the number of oxygens satisfying the valence, and x is 0.9 ≦ x ≦ 1.1, 1-abc is 0.75 ≦ 1-abc ≦ 0.90, a is 0 <a ≦ 0.10, b is 0.05 ≦ b ≦ 0.20, c is 0.01 ≦ c ≦ 0.10, and X / (Mn + X) satisfies the relationship 0.1 ≦ X / (Mn + X) ≦ 0.8). A positive electrode active material for a lithium ion secondary battery. In X-ray diffraction (XRD) measurement, it shows a layered rock salt type (α-NaFeO ₂ ) structure, 18-20 ° (003), 36-37 ° (101), 37-38 ° (006), 38-39 °. The diffraction peaks appearing at positions (012), 44-45 ° (104) and 64-65 (108) / 65-66 (110) appear at positions shifted to the lower angle side due to the inclusion of X. The positive electrode active material for a lithium ion secondary battery according to claim 1.   3. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein in the composition formula (1), (Mn + X) / Co satisfies a relationship of 1.0 <(Mn + X) / Co. material.   The lithium ion according to any one of claims 1 to 3, wherein in the composition formula (1), X / Mn satisfies a relationship of 0.05 ≦ X / Mn ≦ 2.0. Positive electrode active material for secondary battery.   A positive electrode for a lithium ion secondary battery comprising the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4.   The positive electrode for a lithium ion secondary battery according to claim 5, a negative electrode for a lithium ion secondary battery containing a negative electrode active material capable of inserting and extracting lithium ions, the positive electrode for a lithium ion secondary battery, and the lithium ion secondary And a nonaqueous electrolyte layer disposed between the negative electrode for the battery.

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