JP2015197978A - Positive electrode active material for nonaqueous electrolyte secondary battery and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material that can exhibit sufficient cycle characteristics, in a nonaqueous electrolyte secondary battery.SOLUTION: A positive electrode active material for nonaqueous electrolyte secondary battery is represented by a compositional formula (1):Li[NiMnCo[Li]Sn]O(in the formula, 0.01≤e≤0.15, a+b+c+d+e=1.5, 0.1≤d≤0.4, 1.1≤[a+b+c+e]≤1.4, where z represents the number of oxygen satisfying the valency). In the X-ray diffraction measurement, there are diffraction peaks indicating a rock-salt layer structure at 20-23°, 35-40°(101), 42-45°(104) and 64-65(108)/65-66(110).

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same.

  In recent years, hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles have been manufactured and sold from the viewpoint of environment and fuel consumption, and new developments are continuing. In these so-called electric vehicles, it is essential to use a power supply device that can be charged and discharged. As the power supply device, a secondary battery such as a lithium ion battery or a nickel metal hydride battery, an electric double layer capacitor, or the like is used. In particular, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are considered suitable for electric vehicles because of their high energy density and high durability against repeated charge and discharge, and various developments are underway. .

  Non-aqueous electrolyte secondary batteries intended for application to electric vehicles are required to have high output and high capacity. As a positive electrode active material used for the positive electrode of such a nonaqueous electrolyte secondary battery, 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 and easily available, and has a low environmental load, and thus is suitably used as a positive electrode active material.

  It is known that such a solid solution positive electrode active material elutes a transition metal (for example, Ni, Mn) in the positive electrode active material into the electrolytic solution while the battery is repeatedly charged and discharged. When the transition metal is eluted, the crystal structure of the positive electrode active material changes, and sufficient lithium ions cannot be occluded, which may cause a problem that the capacity of the battery decreases.

In order to prevent elution of transition metals, in Patent Document 1, the composition formula: xLiMO ₂ · (1-x) Li ₂ M′O ₃ (where 0 <x <1, M is V, Mn, Fe, Co Or, Ni and M ′ are Mn, Ti, Zr, Ru, Re, or Pt). Furthermore, the Examples of the document describe that a positive electrode active material having the above composition is produced using a molten salt method and a coprecipitation method.

US Patent Application Publication No. 2004/0081888

  However, even with the technique described in Patent Document 1, elution of the transition metal from the positive electrode active material is not sufficiently prevented, and the desired cycle characteristics cannot be achieved.

  Then, an object of this invention is to provide the positive electrode active material which can exhibit sufficient cycling characteristics, and its manufacturing method in a nonaqueous electrolyte secondary battery.

  As a result of intensive studies by the present inventors, it has been found that the above-mentioned problems can be solved by dissolving Sn as a substitution element in a solid solution positive electrode active material containing Ni, Mn or Co as a transition element. It came to complete.

That is, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a composition formula (1): Li _1.5 [Ni _a Mn _b Co _c [Li] _d Sn _e ] O _z (in the formula, 0.01 ≦ e ≦ 0.15, a + b + c + d + e = 1.5, 0.1 ≦ d ≦ 0.4, 1.1 ≦ [a + b + c + e] ≦ 1.4, and z represents the number of oxygen satisfying the valence) It is represented by And in X-ray diffraction measurement, rock salt type layered structures are shown at 20-23 °, 35-40 ° (101), 42-45 ° (104) and 64-65 (108) / 65-66 (110). It has a diffraction peak.

  According to the positive electrode active material of the present invention, elution of transition metal (especially Mn) in the positive electrode active material is suppressed by using Sn as a substitution element. Therefore, sufficient cycle characteristics can be obtained in a nonaqueous electrolyte secondary battery. It becomes possible to demonstrate.

2 is a chart showing an X-ray diffraction pattern of a positive electrode active material C1 obtained in Example 1. FIG. 6 is a chart showing an X-ray diffraction pattern of a positive electrode active material C3 obtained in Example 3. 6 is a chart showing an X-ray diffraction pattern of a positive electrode active material D1 obtained in Comparative Example 1. 2 is a transmission electron microscope (SEM) photograph of the positive electrode active material C1 obtained in Example 1. FIG. 2 is a transmission electron microscope (SEM) photograph of a positive electrode active material D1 obtained in Comparative Example 1. 1 is a schematic cross-sectional view schematically showing the overall structure of lithium ion secondary batteries stacked in parallel according to an embodiment of the present invention.

<Positive electrode active material>
Embodiments of the present invention will be described below. In this specification, “positive electrode active material for non-aqueous electrolyte secondary battery” is simply “positive electrode active material”, “positive electrode for non-aqueous electrolyte secondary battery” is simply “positive electrode”, and “non-aqueous electrolyte secondary battery”. The “secondary battery” is also simply referred to as “secondary battery” or “battery”.

A positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a composition formula (1): Li _1.5 [Ni _a Mn _b Co _c [Li] _d Sn _e ] O _z (where 0 .01 ≦ e ≦ 0.15, a + b + c + d + e = 1.5, 0.1 ≦ d ≦ 0.4, 1.1 ≦ [a + b + c + e] ≦ 1.4, and z represents the number of oxygen satisfying the valence. Represented). And in X-ray diffraction measurement, rock salt type layered structures are shown at 20-23 °, 35-40 ° (101), 42-45 ° (104) and 64-65 (108) / 65-66 (110). It has a diffraction peak.

  In the positive electrode active material of this embodiment, the crystal structure is stabilized when Sn is dissolved as a substitution element in the transition metal (Ni, Mn, Co) layer. It is considered that elution of transition metal is suppressed. In general, when a substitutional element is dissolved in a solid solution positive electrode active material, the crystal structure can be stabilized, but the charge transfer resistance is increased and the conductivity is lowered. However, in the positive electrode active material of this embodiment, since the substitution element Sn can form a conductive oxide, the charge transfer resistance is suppressed as compared to the case where other substitution elements are used, and Ni is charged and discharged. It is considered that the oxidation-reduction reaction of Co and Co proceeds rapidly. As a result, even if charging / discharging is repeated, the capacity reduction of the battery can be prevented, excellent cycle characteristics can be realized, and excellent charge / discharge characteristics can be realized even at high rates. However, the present invention is not limited by the mechanism described above.

  In the composition formula (1), a + b + c + e satisfies 1.1 ≦ [a + b + c + e] ≦ 1.4. Generally, nickel (Ni), manganese (Mn), and cobalt (Co) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of the material and improving the electronic conductivity. Tin (Sn) is a substitution element that substitutes a part of Mn in the crystal lattice. More preferably, when 1.1 ≦ [a + b + c + e] ≦ 1.2, the content of each element can be optimized, and the capacity and output characteristics can be further improved. Therefore, when a positive electrode active material that satisfies this relationship is used in a lithium ion secondary battery, it is possible to exhibit excellent initial charge / discharge efficiency while maintaining high capacity by maintaining high reversible capacity. Become.

  In the composition formula (1), the values of a, b and c are not particularly limited as long as the relationship of a + b + c + d + e = 1.5 and 1.1 ≦ [a + b + c + e] ≦ 1.4 is satisfied. However, a is preferably 0 <a <1.4, and more preferably 0.1 ≦ a ≦ 0.75. When the value a is in the above range, the capacity retention rate can be further improved in the secondary battery. Here, the positive electrode active material contains nickel in the positive electrode active material within the range of d on the condition that nickel (Ni) is divalent. Therefore, in the positive electrode active material, the crystal structure may not be stabilized depending on the composition ratio. However, if a ≦ 0.75, the crystal structure of the positive electrode active material tends to be a rock salt type layered structure.

  In the composition formula (1), b is preferably 0 <b <1.4, and more preferably 0.2 ≦ b ≦ 0.9. When b is in the above range, the capacity retention rate can be further improved in the secondary battery. Here, the positive electrode active material contains manganese in the positive electrode active material within the range of d on the condition that manganese is tetravalent, and further contains nickel (Ni) in the positive electrode active material. Therefore, in the positive electrode active material, the crystal structure may not be stabilized depending on the composition ratio, but by setting b ≦ 0.9, the crystal structure of the positive electrode active material is likely to be a rock salt type layered structure.

  In the composition formula (1), c is preferably 0 ≦ c <1.4, and more preferably 0 ≦ c ≦ 0.6. When c is in the above range, high charge / discharge characteristics can be obtained in the secondary battery. Here, the positive electrode active material contains nickel and manganese in the positive electrode active material within the range of d on condition that cobalt is trivalent. Further, cobalt (Co) is contained in the positive electrode active material within the above range d on condition that nickel (Ni) is divalent and manganese (Mn) is tetravalent. Therefore, in the positive electrode active material, the crystal structure may not be stabilized depending on the composition ratio, but when c ≦ 0.6, the crystal structure of the positive electrode active material tends to be a rock salt type layered structure.

  In the composition formula (1), a + b + c + d + e = 1.5. By satisfying this formula, the crystal structure of the positive electrode active material can be stabilized.

In the composition formula (1), d is 0.1 ≦ d ≦ 0.4. When the value of d is in this range, the positive electrode active material tends to have a rock salt type layered structure. In particular, when d is 0.1 or more, the composition is unlikely to be close to Li ₂ MnO ₃ , and charging / discharging becomes easy. Conversely, when the value of d is outside the range, the crystal structure of the positive electrode active material may not be stabilized. d is more preferably 0.15 ≦ d ≦ 0.35.

In the composition formula (1), e is 0.01 ≦ e ≦ 0.15. When the value of e is within the above range, Mn ⁴⁺ can be sufficiently substituted with Sn as a substitution element so that elution is suppressed. On the other hand, if the value of e is outside the range, the substitution element may not be uniformly dissolved in the crystal structure and the crystal structure may not be stabilized. e is preferably 0.02 ≦ e ≦ 0.12.

The ion radius of each element is Ni ²⁺ 0.69Å, Mn ⁴⁺ 0.54Å, Co ³⁺ 0.61Å, and Sn ⁴⁺ 0.69Å, and Sn ⁴⁺ is larger than Mn ⁴⁺ . Therefore, as Mn ⁴⁺ in the positive electrode active material is replaced with Sn, the crystal lattice expands, and the diffraction peak indicating the rock salt type layered structure shifts to the lower angle side. Conversely, if the diffraction peak is shifted to a lower angle side, the substitution amount of Mn ⁴⁺ by Sn is larger, and the crystal structure is likely to be stabilized. That is, elution of Mn at the time of charging / discharging is further suppressed, and the capacity reduction in the secondary battery can be more effectively prevented.

  In the X-ray diffraction (XRD) measurement, the positive electrode active material represented by the above composition formula (1) is 20-23 °, 35-40 ° (101), 42-45 ° (104), and 64-65 ( 108) / 65-66 (110) has a diffraction peak indicating a rock salt type layered structure. At this time, those having substantially no peak attributed to other than the diffraction peak of the rock salt type layered structure are preferable. More preferably, one having three diffraction peaks at 35-40 ° (101) and one diffraction peak at 42-45 ° (104) is suitable. However, as long as it belongs to a diffraction peak of a rock salt type layered structure, it does not necessarily have to be counted as three and one peak, respectively. The X-ray diffraction measurement shall employ the measurement method described in the examples described later. In addition, the notation of 64-65 (108) / 65-66 (110) has two peaks close to 64-65 and 65-66. It is meant to include.

The positive electrode active material represented by the composition formula (1) has a plurality of specific diffraction peaks in the X-ray diffraction (XRD) measurement. The positive electrode active material having the above composition formula is a solid solution system of Li ₂ MnO ₃ and LiMnO ₂ , and among the plurality of diffraction peaks specified above, the diffraction peak at 20-23 ° is characteristic of Li ₂ MnO _3. It is a superlattice diffraction peak. In addition, the diffraction peaks at 36.5-37.5 ° (101), 44-45 ° (104) and 64-65 (108) / 65-66 (110) are characteristic of the rock salt type layered structure of LiMnO _2. It is a thing.

  The positive electrode active material of this embodiment preferably has three diffraction peaks at 35-40 ° (101) and one diffraction peak at 42-45 ° (104) as part of a diffraction peak showing a rock salt type layered structure. Moreover, it is preferable that the positive electrode active material of this embodiment does not include a material having a peak other than a diffraction peak showing a rock salt type layered structure, for example, another peak derived from impurities or the like in these angular ranges. When such other peaks exist, it means that a structure other than the rock salt type layered structure is included in the positive electrode active material. If the structure other than the rock salt type layered structure is not included, the effect of improving the cycle characteristics can be surely obtained in the secondary battery.

In the positive electrode active material of this embodiment, Sn is considered to be solid-solved by substituting Mn ⁴⁺ in the transition metal layer to form a rock salt type layered structure. It is considered that elution of transition metals including Mn is suppressed during charge and discharge because the crystal structure is stabilized by solid solution of Sn. Furthermore, since Sn can form a conductive oxide, when Sn dissolves, the charge transfer resistance in the active material surface layer and / or in the bulk decreases, and the redox reaction of Ni or Co during charge / discharge Is expected to proceed quickly. As a result, even if charging / discharging is repeated, the capacity reduction of the battery can be prevented, excellent cycle characteristics can be realized, and excellent charge / discharge characteristics can be realized even at high rates. In addition, battery performance itself and durability can be improved. When the rock salt type layered structure is changed by elution of Mn, a spinel phase is usually formed, and the diffraction peak in the X-ray diffraction (XRD) measurement of the positive electrode active material represents the spinel phase. In the spinel phase, diffraction peaks appear at 35-36 ° (101) and 42.5-43.5 ° (104). In the positive electrode active material of this embodiment, it is considered that a spinel phase is not formed even after repeated charge and discharge, and a rock salt type layered structure is maintained. However, the present invention is not limited to the above consideration.

  Furthermore, it is preferable that the diffraction peak which shows the rock salt type | mold layered structure in this form is shifted to the low angle side. That is, the positive electrode active material of this embodiment has a 20-23 °, 35.5-36.5 ° (101), 43.5-44.5 ° (104), and 64− in X-ray diffraction (XRD) measurement. It is preferable to have a diffraction peak at 65 (108) / 65-66 (110). The shift of the diffraction peak to the lower angle side indicates that Sn is more dissolved in the positive electrode active material and substituted for Mn, and it is considered that the effect of suppressing Mn elution is greater.

In addition, Sn substitutes for Mn ⁴⁺ and dissolves in the transition metal layer of the positive electrode active material, so that the covalent bond between the substitution element and oxygen is strengthened, and the oxygen in the crystal lattice accompanying the oxidation of the transition metal is increased. Separation can also be reduced. Thereby, generation of oxygen gas can be suppressed, and oxygen defects in the crystal structure can be reduced.

BET specific surface area of the positive electrode active material of the present embodiment is preferably 2 to 10 m ² / g, more preferably 3~9m ² / g. When the BET specific surface area is 2 m ² / g or more, a sufficient output (rate characteristic) can be obtained in the battery. On the other hand, when the BET specific surface area is 10 m ² / g or less, elution of Ni and Mn can be further suppressed. In addition, in this specification, the value measured by the method as described in an Example shall be employ | adopted for the value of a BET specific surface area.

  The average particle size (average secondary particle size) of the positive electrode active material of this embodiment is preferably 10 to 20 μm, and more preferably 12 to 18 μm. When the average particle size is 10 μm or more, elution of Mn can be further suppressed. On the other hand, when the average particle size is 20 μm or less, foil breakage, clogging, and the like can be suppressed in the application process to the current collector during the production of the positive electrode. The average particle diameter is measured by a particle size distribution measuring apparatus using a laser diffraction / scattering method. Specifically, it can be measured using a particle size distribution analyzer (model LA-920) manufactured by Horiba.

<Method for producing positive electrode active material>
One embodiment of the present invention relates to a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. The production method includes a first step of obtaining a dried product by spray-drying a raw material mixed solution obtained by dissolving the following specific raw material in an aqueous solvent; at least a salt contained in the dried product obtained in the first step A second step in which a part is thermally decomposed to obtain a precursor; and a third step in which the precursor obtained in the second step is calcined at 400 to 1000 ° C. And, in the first step, as raw materials, at least one nitrate selected from the group consisting of Sn citrate, Ni, Mn and Co and / or a decomposition temperature of 100 ° C. to 350 ° C., Ni, At least one organic acid salt selected from the group consisting of Mn and Co, and lithium nitrate and / or an organic acid salt of lithium having a decomposition temperature (also referred to as a decomposition point) of 100 ° C. to 350 ° C. are used. It is characterized by that.

  According to the study by the present inventors, the conventional molten salt method or coprecipitation method has a problem that a stable crystal structure cannot be obtained when Sn is used as a substitution element. The molten salt method requires sintering and reaction at high temperatures, often resulting in compositional fluctuations (mosaic-like compositional fluctuations due to the ubiquity of some components) and fluctuations in physical properties. , Could affect the reproducibility. Further, even in the coprecipitation method, individual components may be aggregated separately at the time of formation of the precipitate or drying. Thus, since it is difficult to obtain a uniform composition by the conventional molten salt method or coprecipitation method, it was considered that a stable crystal structure could not be constructed even if Sn was dissolved.

  On the other hand, the production method of this embodiment is characterized in that after a raw material mixed solution such as an organic acid salt (complex) is spray-dried to obtain an original dried product (powder), thermal decomposition and firing are performed. By using an organic acid salt (such as tin citrate) as a raw material, it is possible to prevent the individual components from aggregating separately during drying, and a dried product in which each element is uniformly mixed at the atomic level. Can be obtained. By thermally decomposing and baking this, a solid solution having a very uniform composition can be produced at a relatively low temperature. As a result, even when Sn is used as a substitution element, a solid solution having a stable crystal structure can be obtained. Furthermore, according to the manufacturing method of this embodiment, since the raw material 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. However, the present invention is not limited by the mechanism described above. Hereafter, each process of the manufacturing method of this form is demonstrated in detail.

[First step (spray drying step)]
In the first step, a raw material mixed solution obtained by dissolving a specific raw material in an aqueous solvent is spray-dried to obtain a dried product. And as a raw material, the following salts (1) to (3) are essentially used. (1) Sn citrate; (2) At least one nitrate selected from the group consisting of Ni, Mn and Co and / or Ni, Mn and Co having a decomposition temperature of 100 ° C to 350 ° C At least one organic acid salt selected from the group; and (3) lithium nitrate and / or an organic acid salt of lithium having a decomposition temperature of 100C to 350C.

(1) Sn Citrate In the manufacturing method of this embodiment, Sn citrate (also referred to as a citric acid complex or a citric acid complex salt) is used as a raw material for the substitution element contained in the positive electrode active material. Features. Since the citrate of Sn has a decomposition temperature of about 130 ° C., it can be easily thermally decomposed in the second step described later.

  Sn citrate can be prepared, for example, by the following method. However, the method for obtaining Sn citrate is not particularly limited, and may be purchased or of course prepared by methods other than those described below.

  The Sn source is not particularly limited. For example, tin (II) oxalate (stannic stannate), tin organic acid salts such as tin acetate, and tin alkoxides such as tin tetra n-butoxide and tin tetra tert-butoxide. Can be used.

  For example, Sn citrate can be easily prepared by using the following method using tin (II) oxalate as the Sn source. First, citric acid monohydrate is dissolved by heating in pure water, and tin (II) oxalate is added to this solution. At this time, the molar ratio of Sn and citric acid is preferably Sn / 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 Sn citrate (citric acid complex solution). ) Is obtained.

(2) at least one nitrate selected from the group consisting of Ni, Mn and Co and / or at least one selected from the group consisting of Ni, Mn and Co, having a decomposition temperature of 100 ° C. to 350 ° C. Organic Acid Salts In the production method of the present embodiment, nitrates and / or decomposition temperatures of these elements are 100 ° C. to 350 ° C. as raw materials for transition metals (Ni, Mn, or Co) contained in the positive electrode active material. An organic acid salt is used.

  Although it does not restrict | limit especially as nitrate, For example, it is preferable to use nitrate hydrates, such as nickel nitrate hexahydrate, manganese nitrate hexahydrate, 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) It can be easily thermally decomposed in a second step (thermal decomposition step) described later.

  Although it does not restrict | limit especially as an organic acid salt whose decomposition temperature is 100 degreeC-350 degreeC, For example, citrates, such as nickel citrate, manganese citrate, cobalt citrate; Nickel acetate tetrahydrate, manganese acetate -It is preferable to use tetrahydrate and hydrates of acetate such as cobalt acetate tetrahydrate. 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 compound having a decomposition temperature of 100 ° C. to 280 ° C. It is more preferable to use an acid 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 can be easily thermally decomposed 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. Further, in the manufacturing method of this embodiment, lithium nitrate (LiNO ₃ ) is used as a raw material of lithium contained in the positive electrode active material. And / or an organic acid salt of lithium having a decomposition temperature of 100 ° C. to 350 ° C. is used.

As the organic acid salt of lithium decomposition temperature of 100 ° C. to 350 ° C., in particular but not limited, for example, lithium acetate, lithium citrate _{(C 6 H 5 Li 3 O} 7, C 6 H 5 Li 3 O 7 · 4H ₂ O), lithium oxalate, and the like.

  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 the manufacturing method of this embodiment, productivity can be improved by using the specific nitrate or organic acid salt of the above (1) to (3) without using sulfate or 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 is essential, but when nitrate or organic acid salt is used as in this embodiment, it is necessary to perform such a removal step. 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 method for preparing 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, pure water, an aqueous solution of Sn citrate complex, an organic compound having a transition metal (Ni, Mn or Co) nitrate and / or a decomposition temperature of 100 ° C. to 350 ° C. Examples thereof include a method of sequentially dissolving an acid salt, lithium nitrate and / or an organic acid salt of lithium having a decomposition temperature of 100 ° C to 350 ° C.

  In the manufacturing method of this embodiment, 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, the Sn citric acid complex in the raw material mixed solution can be stabilized, and this can contribute to the uniform dispersion of the citric acid complex.

  Moreover, in the manufacturing method of this form, it is preferable to adjust pH of a raw material mixed solution using basic aqueous solution, such as ammonia water, 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 can be thermally decomposed.

[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. 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. It can remain. On the other hand, Sn citrate, transition element (Ni, Mn or Co) nitrate and / or organic acid salt having a decomposition temperature of 100 ° C to 350 ° C, lithium organic acid having a decomposition temperature of 100 ° C to 350 ° C The salt is thermally decomposed by 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) 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 stepwise or continuously from a low temperature to a high temperature. 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.

<Nonaqueous electrolyte secondary battery>
By applying the positive electrode active material described above to a non-aqueous electrolyte secondary battery, the cycle characteristics of the battery can be improved. Therefore, according to another embodiment of the present invention, there is provided a positive electrode for a non-aqueous electrolyte secondary battery in which a positive electrode active material layer containing the above-described positive electrode active material is formed on the surface of a current collector. Furthermore, according to another embodiment of the present invention, the power generation element includes the positive electrode, the electrolyte layer, and a negative electrode in which a negative electrode active material layer including a negative electrode active material is formed on the surface of the current collector. A non-aqueous electrolyte secondary battery is provided.

  Hereinafter, a non-aqueous electrolyte secondary battery to which the positive electrode active material of the present embodiment can be applied will be described taking a lithium ion secondary battery as an example with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

  FIG. 6 is a schematic cross-sectional view schematically showing the overall structure of a lithium ion secondary battery (hereinafter simply referred to as “parallel stacked battery”) stacked in parallel according to an embodiment of the present invention. As shown in FIG. 6, the parallel stacked battery 10 a of this embodiment has a structure in which a substantially rectangular power generation element 17 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 22 that is a battery exterior material. Have. Specifically, the power generation element 17 is housed and sealed by using a polymer-metal composite laminate film as a battery exterior material and joining all of its peripheral parts by thermal fusion.

  The power generation element 17 includes a negative electrode in which the negative electrode active material layer 12 is disposed on both sides of the negative electrode current collector 11 (only one side for the lowermost layer and the uppermost layer of the power generation element), an electrolyte layer 13, and a positive electrode current collector 14. And a positive electrode in which the positive electrode active material layer 15 is disposed on both sides. Specifically, the negative electrode, the electrolyte layer 13 and the positive electrode are laminated in this order so that one negative electrode active material layer 12 and the positive electrode active material layer 15 adjacent to the negative electrode active material layer 15 face each other with the electrolyte layer 13 therebetween. Yes. For the positive electrode active material layer, the positive electrode active material having the specific composition and structure described above is used.

  Thus, the adjacent negative electrode, electrolyte layer 13 and positive electrode constitute one single cell layer 16. Therefore, it can be said that the parallel laminated battery 10 of this embodiment has a configuration in which a plurality of the single battery layers 16 are laminated so that they are electrically connected in parallel. Further, a seal portion (insulating layer) (not shown) for insulating between the adjacent negative electrode current collector 11 and the positive electrode current collector 14 may be provided on the outer periphery of the unit cell layer 16. . The negative electrode active material layer 12 is disposed only on one side of the outermost layer negative electrode current collector 11 a located in both outermost layers of the power generation element 17. Note that the arrangement of the negative electrode and the positive electrode is reversed from that in FIG. 6 so that the outermost positive electrode current collector is positioned in both outermost layers of the power generation element 17, and the positive electrode is provided only on one side of the outermost positive electrode current collector. An active material layer may be arranged.

  The negative electrode current collector 11 and the positive electrode current collector 14 are attached with a negative electrode current collector plate 18 and a positive electrode current collector plate 19 that are electrically connected to the respective electrodes (negative electrode and positive electrode), and are sandwiched between ends of the laminate film 22. Thus, it has a structure led out of the laminate film 22. The negative electrode current collector 18 and the positive electrode current collector 19 are connected to the negative electrode current collector 11 and the positive electrode current collector 14 of each electrode by ultrasonic welding or resistance via a negative electrode terminal lead 20 and a positive electrode terminal lead 21 as necessary. It may be attached by welding or the like (this form is shown in FIG. 6). However, the negative electrode current collector 11 may be extended to form the negative electrode current collector plate 18 and may be led out from the laminate film 22. Similarly, the positive electrode current collector 14 may be extended to form a positive electrode current collector plate 19, which may be similarly derived from the battery exterior material 22.

  Here, the parallel stacked battery has been described as an example, but the type of the non-aqueous electrolyte secondary battery to which the positive electrode active material of the present embodiment can be applied is not particularly limited, and the single battery layers are connected in series in the power generation element. The present invention is also applicable to any conventionally known non-aqueous electrolyte secondary battery such as a so-called bipolar battery that is connected. Hereinafter, main components of the parallel stacked battery will be described in detail.

[Positive electrode]
A positive electrode according to one embodiment of the present invention includes a positive electrode active material layer including the positive electrode active material. The positive electrode has a function of generating electrical energy by transferring lithium ions together with the negative electrode. The positive electrode essentially includes a current collector and a positive electrode active material layer, and the positive electrode active material layer is formed on the surface of the current collector.

(Current collector)
The current collector is made of a conductive material, and a positive electrode active material layer is disposed on one side or both sides thereof. There is no particular limitation on the material constituting the current collector, and for example, a conductive resin in which a conductive filler is added to a metal or a conductive polymer material or a non-conductive polymer material may be employed.

  Examples of the metal include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, or copper is 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 current collector.

  Examples of non-conductive polymer materials include 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), Examples include polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. 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 metals. It is preferable to include an alloy or metal oxide. In addition, the conductive carbon is not particularly limited, but is acetylene black, Vulcan (registered trademark), black pearl (registered trademark), carbon nanofiber, ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon. And at least one selected from the group consisting of fullerenes. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. Although there is no restriction | limiting in particular also about the thickness of a collector, Usually, it is about 1-100 micrometers.

(Positive electrode active material layer)
The positive electrode active material layer essentially includes the positive electrode active material described above, and may further include other positive electrode active materials, conductive additives, binders, and other additives.

  A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. When the positive electrode active material layer contains a conductive material, an electronic network inside the positive electrode active material layer is effectively formed, and the output characteristics of the battery can be improved.

  Although it does not restrict | limit especially as a conductive support agent, Carbon powder, such as acetylene black, carbon black, channel black, thermal black, Ketjen black (registered trademark), graphite, vapor growth carbon fiber (VGCF; registered trademark), etc. And various carbon fibers and expanded graphite.

  Content of the conductive support agent with respect to the whole quantity of a positive electrode active material layer is 0-30 mass% normally, Preferably it is 1-10 mass%, More preferably, it is 3-7 mass%.

  The binder is added for the purpose of maintaining the electrode structure by binding the constituent members in the active material layer or the active material layer and the current collector.

  The binder is not particularly limited, but polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyvinyl acetate, acrylic resin, polyimide, epoxy resin, polyurethane resin, urea resin, styrene- Examples thereof include a synthetic rubber binder such as butadiene rubber (SBR).

  The content of the binder with respect to the total amount of the positive electrode active material layer is usually 0 to 50% by mass, preferably 5 to 45% by mass, more preferably 10 to 25% by mass, and particularly preferably 15 to 20%. % By mass.

[Negative electrode]
The negative electrode has a function of generating electrical energy by transferring lithium ions together with the positive electrode. The negative electrode essentially includes a current collector and a negative electrode active material layer, and the negative electrode active material layer is formed on the surface of the current collector.

(Current collector)
Since the current collector that can be used for the negative electrode is the same as the current collector that can be used for the positive electrode, description thereof is omitted here.

(Negative electrode active material layer)
The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer may further include additives such as a conductive additive and a binder.

The negative electrode active material has a composition capable of releasing lithium ions during discharging and occluding lithium ions during charging. The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium. Examples of the negative electrode active material include metals such as Si and Sn, TiO, Ti ₂ O ₃ , TiO ₂ , or Metal oxides such as SiO ₂ , SiO, SnO ₂ , complex oxides of lithium and transition metals such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN, Li—Pb alloys, Li—Al alloys , Li, or carbon powder, natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, or carbon material such as hard carbon is preferably exemplified. Among these, by using an element that forms an alloy with lithium, it becomes possible to obtain a battery having a high capacity and an excellent output characteristic having a higher energy density than that of a conventional carbon-based material. The negative electrode active material may be used alone or in the form of a mixture of two or more. The element alloying with lithium is not limited to the following, but specifically, 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, and the like.

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

  The carbon material is preferably a carbonaceous particle having a low lithium relative discharge potential, such as natural graphite, artificial graphite, a blend of natural graphite and artificial graphite, a material obtained by coating natural graphite with amorphous, soft carbon, hard Carbon or the like can be used. The shape of the carbonaceous particles is not particularly limited and may be any shape such as a lump shape, a sphere shape, and a fiber shape, but is preferably not a scale shape, and preferably a sphere shape and a lump shape. Those that are not scaly are preferred from the viewpoints 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, there is a wet method in which carbonaceous particles (powder) serving as nuclei are dispersed and mixed in a mixed solution in which amorphous carbon is dissolved or dispersed in a solvent, and then the solvent is removed. 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 coat 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.

The BET specific surface area of the negative electrode active material is preferably 0.8 to 1.5 m ² / g. If the specific surface area is in the above range, the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved. Moreover, it is preferable that the tap density of a negative electrode active material is 0.9-1.2 g / cm < ³ >. It is preferable from the viewpoint of energy density that the tap density is in the above range.

  The average particle diameter of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm and more preferably 1 to 20 μm from the viewpoint of increasing the capacity, reactivity, and cycle durability of the negative electrode active material. preferable.

  In addition, since the conductive support agent and binder which can be used for a negative electrode are the same as that which can be used for a positive electrode, description is abbreviate | omitted here.

[Electrolyte layer]
The electrolyte layer functions as a spatial partition (spacer) between the positive electrode and the negative electrode. 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 an electrolyte layer, Polymer electrolytes, such as a liquid electrolyte and a polymer gel electrolyte and a polymer solid electrolyte, can be used suitably. In this embodiment, a liquid electrolyte is preferable.

  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. Can be mentioned.

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, as additives, 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 It is preferable that at least one of these is included. Of these, lithium fluorophosphate derivatives such as lithium monofluorophosphate and lithium difluorophosphate are more preferable. Use of these additives is preferable from the viewpoints of performance and life characteristics. The additive is preferably contained in the electrolyte at 0.1 to 5% by mass, and more preferably 0.5 to 3.5% by mass.

  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. In such a matrix polymer, an electrolyte salt such as a lithium salt can be well dissolved.

  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.

  A matrix polymer of a polymer gel electrolyte or a 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.

[Current collector (tab)]
In a lithium ion secondary battery, a current collector plate (tab) electrically connected to a current collector is taken out of a laminate film as an exterior material for the purpose of taking out current outside the battery.

  The material which comprises a current collector plate is not specifically limited, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, 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. Note that the same material may be used for the positive electrode current collector plate (positive electrode tab) and the negative electrode current collector plate (negative electrode tab), or different materials may be used.

[Positive terminal lead and negative terminal lead]
As a material for the negative electrode and the positive electrode terminal lead, a lead used in a known laminated secondary battery can be used. In addition, the parts removed from the battery exterior material should be heat-insulating so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

[Exterior material; Laminate film]
A conventionally known metal can case can be used as the exterior material. In addition, the power generation element 17 may be packed using a laminate film 22 as shown in FIG. The laminate film can be configured as a three-layer structure in which, for example, polypropylene, aluminum, and nylon are laminated in this order. By using such a laminate film, it is possible to easily open the exterior material, add the capacity recovery material, and reseal the exterior material.

  Since the nonaqueous electrolyte secondary battery such as the lithium ion secondary battery described above uses the positive electrode active material of this embodiment, it can exhibit excellent cycle characteristics. The battery is also excellent in terms of discharge capacity and / or discharge characteristics (particularly at high rates). Therefore, the nonaqueous electrolyte secondary battery to which the positive electrode active material of this embodiment is applied is suitable as a power supply device for an electric vehicle.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to a following example.

[Example 1]
< _{Preparation of Positive Electrode Active} Material C1 (Li _1.5 [Ni _0.375 Mn _0.825 [Li] _0.25 Sn _0.05 ] O _z )>
(Preparation of tin citrate complex aqueous solution)
21 g (0.1 mol) of citric acid monohydrate (molecular weight 210.14 g / mol) was added to 1000 ml of pure water and dissolved. Next, 10.5 g (0.05 mol) of tin (II) oxalate (molecular weight 206.73 g / mol, purity 98%) was added and stirred for about 10 minutes. To this, 5.6 vol% aqueous ammonia (about 100 ml) was slowly added to adjust pH = 6 and solubilize. This solution was filtered with a filter paper to remove insoluble matters, thereby obtaining an aqueous tin citrate complex solution. In addition, the density | concentration of Sn contained in the said tin-citrate complex aqueous solution was 0.05 mol / L as Sn.

(Preparation of raw material mixed solution)
In 2500 ml of pure water, the total amount of the tin citrate complex aqueous solution (Sn 0.05 mol / L), manganese acetate tetrahydrate (molecular weight 245.09 g / mol) 172.0 g, nickel acetate tetrahydrate (molecular weight 248) .84 g / mol) 62.0 g and lithium acetate dihydrate (molecular weight 102.02 g / mol) 153.0 g were dissolved in this order. Furthermore, 183 g of anhydrous citric acid was added. To this, 5.6 vol% aqueous ammonia was slowly added to adjust pH = 6 to obtain a raw material mixed solution.

(First step (drying step))
The raw material mixed solution was spray-dried at a hot air temperature of 250 ° C. to 350 ° C. with a spray apparatus using an inert gas (N ₂ ) to remove moisture, and a dried product (powder) that was a raw material mixture was obtained. .

(Second step (pyrolysis step))
The dried product (powder) was subjected to thermal decomposition of the organic acid salt at 300 ° C. to 400 ° C. for 4 hours using a fluidized firing furnace under the flow of 5% by volume −O ₂ / N ₂ to obtain a precursor. .

(Third step (firing step))
The precursor was fired at 900 ° C. for 12 hours in an air atmosphere to obtain a positive electrode active material C1.

A sample of the positive electrode active material C1 was dissolved in an acid, and each element contained in the solution was quantified by inductively coupled plasma emission spectrometry. In addition, the SII nanotechnology company make; inductively coupled plasma emission spectroscopic analyzer SPS-3520 type was used for the measurement. As a result, the composition of the positive electrode active material C1 was as follows.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.825 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

<Preparation of positive electrode C11>
(Preparation of slurry for positive electrode)
A positive electrode slurry having the following composition was prepared.

  First, 6.8 parts by weight of PVDF was dissolved in 30 parts by weight of NMP to prepare a binder solution. Next, 36.8 parts by weight of the binder solution is added to a mixed powder of 6.8 parts by weight of the conductive additive and 100 parts by weight of the positive electrode active material C1 (powder), and a planetary mixer (PVM100, manufactured by Asada Tekko) is used. After kneading, 40 parts by weight of NMP was added to the kneaded product to obtain a positive electrode slurry (solid content concentration: 62% by weight).

(Application and drying of positive electrode slurry)
While the 20 μm-thick aluminum foil current collector was run at a running speed of 1 m / min, the positive electrode slurry was applied to one surface of the current collector using a die coater. Subsequently, the current collector coated with the positive electrode slurry is dried in a hot air drying oven (100 ° C. to 110 ° C., 3 minutes), and the amount of NMP remaining in the positive electrode active material layer is 0.02 wt% or less. did. Furthermore, the positive electrode slurry was applied to the other surface of the current collector in the same manner as described above, and dried to prepare a sheet-like positive electrode having positive electrode active material layers on both surfaces of the current collector.

(Positive electrode press)
The sheet-like positive electrode was compression-molded by applying a roller press and cut to obtain a weight of about 11.0 mg / cm ² and a density of 2.70 g / cm ³ of the positive electrode active material layer on one side.

(Dry cathode)
Next, the pressed positive electrode was dried in a vacuum drying furnace. After the positive electrode was installed inside the drying furnace, the air in the drying furnace was removed under reduced pressure (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C., the same applies hereinafter). Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 120 ° C. at 10 ° C./min, the pressure was reduced again at 120 ° C., and nitrogen was maintained in the furnace for 12 hours. The temperature was lowered. In this way, the positive electrode C11 was completed.

<Preparation of negative electrode A1>
(Preparation of slurry for negative electrode)
A positive electrode slurry having the following composition was prepared.

First, 5.0 parts by weight of PVDF was dissolved in 50 parts by weight of NMP to prepare a binder solution. Next, 55.0 parts by weight of the binder solution is added to a mixed powder of 1.0 part by weight of a conductive additive and 100 parts by weight of natural graphite powder, and then kneaded with a planetary mixer (PVM100, manufactured by Asada Tekko). Then, 47 parts by weight of NMP was added to the kneaded product to obtain a slurry for negative electrode (solid content concentration 52% by weight). In addition, it confirmed that the shape of the negative electrode active material (natural graphite) was not scaly by a scanning electron microscope (SEM). The specific surface area of natural graphite was 1.05 m ² / g (measuring device: BELSORP-miniII manufactured by Nippon Bell), and the tap density was 1.1 g / cm ³ (measuring device: tap density measuring device manufactured by Nippon Luft).

(Application and drying of slurry for negative electrode)
While the 10 μm thick electrolytic copper foil current collector was run at a running speed of 1.5 m / min, the negative electrode slurry was applied to one surface of the current collector using a die coater. Subsequently, the current collector coated with this negative electrode slurry was dried (100 ° C. to 110 ° C., 2 minutes) in a hot air drying furnace, and the amount of NMP remaining in the negative electrode active material layer was 0.02 wt% or less. did. Further, the negative electrode slurry was applied to the other surface of the current collector in the same manner as described above, and dried to prepare a sheet-shaped negative electrode having a negative electrode active material layer on both surfaces of the current collector.

(Negative electrode press)
The sheet-like negative electrode was compression-molded by applying a roller press and cut to give a weight of about 9.50 mg / cm ² and a density of 1.45 g / cm ³ of the negative electrode active material layer on one side. In addition, when the surface of the negative electrode active material layer after pressing was observed, generation of cracks was not observed.

(Dry anode drying)
Next, the pressed negative electrode was dried in a vacuum drying furnace. After installing the negative electrode inside the drying furnace, the pressure in the room was reduced (100 mmHg (1.33 × 10 ⁴ Pa)) to remove the air in the drying furnace. Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 135 ° C. at 10 ° C./min, the pressure was reduced again at 135 ° C., and the nitrogen in the furnace was kept exhausted for 12 hours, The temperature was lowered. In this way, the negative electrode A11 was completed.

<Production of battery>
A tab was welded to the current collector portion of the positive electrode C11 (positive electrode active material layer area length: 3.6 cm × width: 5.3 cm) and negative electrode A11 (negative electrode active material layer area length: 3.8 cm × width: 5.5 cm). A porous polypropylene separator (S) (4.5 cm long × 6.0 cm wide, 25 μm thick, porosity 55%) is sandwiched between the negative electrode A11 and the positive electrode C11 welded with these tabs. A laminate (A11-S-C11-S-A11) was produced. Next, both sides of the laminate were sandwiched by an exterior body (length 5.0 cm × width 6.5 cm) made of an aluminum laminate film, and three sides of the exterior body were sealed by thermocompression bonding to accommodate the laminate.

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). In this, 1.8% by weight of lithium difluorophosphate (LiPO ₂ F ₂ ) and 1.0% by weight of lithium monofluorophosphate (Li ₂ PO ₃ F) were dissolved as lithium fluorophosphate acting as an additive. An electrolytic solution was obtained. After injecting this electrolyte solution 0.6 cm ³ / cell into a bag-shaped exterior body containing the laminate, the remaining one side was temporarily sealed by thermocompression bonding to produce a laminate type cell. In order to sufficiently permeate the electrolytic solution into the electrode pores, the battery was completed by holding at room temperature for 24 hours while applying a surface pressure of 0.5 MPa.

[Example 2]
A positive electrode active material C2 and a battery were produced in the same manner as in Example 1 except that the amount of the raw materials was changed in “(Preparation of raw material mixed solution)”. It was as follows when the composition of the said positive electrode active material C2 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.845 [Li] _0.25 Sn _0.03 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.03).

[Example 3]
A positive electrode active material C3 and a battery were produced in the same manner as in Example 1 except that the amount of raw materials was changed in the above-mentioned “(Preparation of raw material mixed solution)”. It was as follows when the composition of the said positive electrode active material C3 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.795 [Li] _0.25 Sn _0.10 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.10).

[Example 4]
A positive electrode active material C4 and a battery were produced in the same manner as in Example 1 except that anhydrous citric acid was not added in “(Preparation of raw material mixed solution)”. It was as follows when the composition of the said positive electrode active material C4 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.825 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

[Example 5]
A positive electrode active material C5 and a battery were produced in the same manner as in Example 2 except that anhydrous citric acid was not added in “(Preparation of raw material mixed solution)”. It was as follows when the composition of the said positive electrode active material C5 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.845 [Li] _0.25 Sn _0.03 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.03).

[Example 6]
A positive electrode active material C5 and a battery were produced in the same manner as in Example 3 except that in the above “(Preparation of raw material mixed solution)”, anhydrous citric acid was not added. It was as follows when the composition of the said positive electrode active material C5 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.795 [Li] _0.25 Sn _0.10 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.10).

[Example 7]
In the above “(preparation of tin citrate complex aqueous solution)” and “(preparation of raw material mixed solution)”, except that the tin citrate complex aqueous solution and raw material mixed solution were adjusted to pH = 4, the same method as in Example 1 was used. A positive electrode active material C7 and a battery were produced. It was as follows when the composition of the said positive electrode active material C7 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.825 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

[Example 8]
In the above “(preparation of tin citrate complex aqueous solution)” and “(preparation of raw material mixed solution)”, the same procedure as in Example 1 was performed, except that the tin citrate complex aqueous solution and the raw material mixed solution were adjusted to pH = 8. A positive electrode active material C8 and a battery were produced. It was as follows when the composition of the said positive electrode active material C8 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.825 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

[Example 9]
Other than using 141.0 g of lithium citrate tetrahydrate (molecular weight 281.98 g / mol) in place of lithium acetate dihydrate as the raw material in the above “(Preparation of raw material mixed solution)” Produced a positive electrode active material C9 and a battery in the same manner as in Example 1. It was as follows when the composition of the said positive electrode active material C9 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.825 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

[Example 10]
A positive electrode active material C10 and a battery were produced in the same manner as in Example 9 except that anhydrous citric acid was not added in “(Preparation of raw material mixed solution)”. It was as follows when the composition of the said positive electrode active material C10 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.825 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

[Example 11]
In the above-mentioned “(Preparation of raw material mixed solution)”, the total amount of the tin citrate complex aqueous solution (Sn 0.05 mol / L), manganese nitrate hexahydrate (molecular weight 287.04 g / mol) 126. 6 g, nickel nitrate hexahydrate (molecular weight 290.79 g / mol) 33.8 g, cobalt nitrate hexahydrate (molecular weight 291.03) 34.2 g, lithium nitrate (molecular weight 68.945 g / mol) 74. 5 g was dissolved in order. Furthermore, 126 g of anhydrous citric acid was added. To this, 5.6 vol% aqueous ammonia was slowly added to adjust pH = 6 to obtain a raw material mixed solution. Other than this, a positive electrode active material C11 and a battery were produced in the same manner as in Example 1. It was as follows when the composition of the said positive electrode active material C11 was confirmed.
Composition formula: Li _1.5 [Ni _0.225 Mn _0.750 Co _0.225 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

[Example 12]
A positive electrode active material C12 and a battery were produced in the same manner as in Example 11 except that anhydrous citric acid was not added in “(Preparation of raw material mixed solution)”. It was as follows when the composition of the said positive electrode active material C12 was confirmed.
Composition formula: Li _1.5 [Ni _0.225 Mn _0.750 Co _0.225 [Li] _0.25 Sn _0.05 ] O _z
(In composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25, e = 0.05).

[Comparative Example 1]
<Preparation of _{Positive Electrode Active} Material D1 Using Coprecipitation Method (Li _1.5 [Ni _0.375 Mn _0.875 [Li] _0.25 ] O _z )>
A 2 mol / L aqueous solution of nickel sulfate and manganese sulfate was prepared. Next, a predetermined amount of these were weighed to prepare a mixed solution. Further, while stirring the mixed solution, aqueous ammonia was added dropwise until the pH reached 7. Further, a 2 mol / L sodium carbonate aqueous solution was added dropwise to precipitate a nickel-manganese composite carbonate. The obtained precipitate was subjected to suction filtration, washed with water, and dried at 120 ° C. for 12 hours. Lithium hydroxide was added to this dry powder at a predetermined molar ratio (Li / [Ni + Mn] = 1.5) and mixed for about 2 hours in an automatic mortar. Subsequently, after 6-hour temporary baking at 500 degreeC, main baking was performed at 900 degreeC for 12 hours, and the positive electrode active material D1 and the battery were produced.

It was as follows when the composition of the said positive electrode active material D1 was confirmed.
Composition formula: Li _1.5 [Ni _0.375 Mn _0.875 [Li] _0.25 ] O _z (in composition formula (1), a + b + c + d + e = 1.5, d = 0.25, a + b + c + e = 1.25) E = 0).

<Measurement of BET specific surface area of positive electrode active material>
The specific surface areas of the positive electrode active materials C1 to C12 and D1 obtained in Examples 1 to 12 and Comparative Example 1 were measured by the nitrogen adsorption BET single point method. In addition, the specific surface area measuring apparatus (MacLab1208) made from Mountec was used for the measurement.

<X-ray diffraction (XRD) measurement of positive electrode active material>
The crystal structures and crystallinity of the positive electrode active materials C1, C3, and D1 obtained in Examples 1 and 3 and Comparative Example 1 were evaluated by X-ray diffraction measurement. For measurement, an Rigaku X-ray diffractometer (SmartLab 9 kW) was used, Cu-Kα rays were used as the X-ray source, measurement conditions were tube voltage 45 KV, tube current 200 mA, scanning speed 2 ° / min, The diverging slit width was 0.5 ° and the light receiving slit width was 0.15 °. Each X-ray diffraction pattern is shown in FIGS.

<Scanning Electron Microscope (SEM) Observation of Positive Electrode Active Material>
The positive electrode active materials C1 and D1 obtained in Example 1 and Comparative Example 1 were observed with a scanning electron microscope (SEM). As a pretreatment, the powder was fixed to a conductive tape and then subjected to a conductive treatment. At this time, a field emission scanning electron microscope (S-4700, manufactured by Hitachi, Ltd.) was used, and the acceleration voltage was set to 3 kV. The results are shown in FIGS.

<Evaluation of battery performance>
Each battery obtained in Examples 1 to 12 and Comparative Example 1 was set in an evaluation cell attachment jig, and a positive electrode lead and a negative electrode lead were attached to each tab end portion of the battery for testing. The initial charge process and activation process were performed under the following conditions, and the battery performance was evaluated.

(First charging process)
The initial charging process of the battery was performed as follows. At room temperature, the battery was charged at a constant current of 0.05 C for 4 hours (SOC approximately 20%). Next, the charging was stopped, and the battery was kept in that state (SOC about 20%) for about 1 day (24 hours).

(Activation process)
After the initial charging process was completed, the battery was charged at room temperature by a constant current charging method at 0.1 C until the voltage reached 4.75 V, and then discharged once at a temperature of 0.1 C to 2.0 V.

(Gas removal treatment)
One side temporarily sealed by thermocompression bonding was opened, gas was removed at 10 ± 3 hPa for 5 minutes, and then the one piece was thermocompression bonded again and temporarily sealed. Furthermore, it pressure-molded with the roller (surface pressure 0.5 ± 0.1 MPa), and the electrode and the separator were sufficiently adhered.

(Performance evaluation)
The battery performance was evaluated at room temperature as follows. First, the battery is charged at a 1.0 C rate until the maximum voltage reaches 4.45 V (constant current constant voltage charging method), and then held for about 0.5 hours to 1.0 hour. The battery was discharged at a 0.2 C rate until reaching 0 V (constant current discharge method). The discharge capacity at the 0.2 C rate at this time was defined as “0.2 C discharge capacity (mAh / g)”.

  Next, the battery is charged at a 1.0 C rate until the maximum voltage reaches 4.45 V (constant current constant voltage charging method), and then held for about 0.5 hour to 1.0 hour. The battery was discharged at a 1.0 C rate until reaching 0 V (constant current discharge method). The discharge capacity at the 1.0 C rate at this time was defined as “1.0 C discharge capacity (mAh / g)”.

  Further, the battery is charged at a 1.0 C rate until the maximum voltage becomes 4.45 V (constant current constant voltage charging method), and then held for about 0.5 to 1.0 hour, and the minimum voltage of the battery is 2. The battery was discharged at a 2.0 C rate until reaching 0 V (constant current discharge method). The discharge capacity at the 2.0 C rate at this time was defined as “2.0 C discharge capacity (mAh / g)”.

  Then, “capacity maintenance ratio (%)” was calculated by the following formula, and the rate characteristics were evaluated. The results are shown in Table 1.

(Cycle characteristic evaluation)
The cycle characteristic test of the battery was performed by repeating the above charge / discharge at 1.0 C for 300 cycles at room temperature. And the battery performance after 1 cycle and after 300 cycles was evaluated on condition of the following. Charge the battery at a 1.0C rate until the maximum voltage reaches 4.45V (constant-current constant-voltage charging method), and then hold for about 0.5 hours to 1.0 hour. The minimum battery voltage is 2.0V. The battery was discharged at a rate of 0.2 C until constant (constant current discharge method). All were performed at room temperature.

  Then, “capacity maintenance ratio (%)” was calculated by the following formula, and cycle characteristics were evaluated. The results are shown in Table 1.

  As shown in Table 1, according to the positive electrode active materials of Examples 1 to 12 obtained by the production method of the present invention, excellent cycle characteristics were exhibited in the battery. Moreover, the battery using the positive electrode active material of Examples 1-12 showed sufficient performance also in terms of discharge capacity and rate characteristics. Furthermore, the positive electrode active materials of Examples 1 to 12 had a BET specific surface area larger than that of Comparative Example 1.

10a Parallel stacked battery,
11 negative electrode current collector,
11a outermost layer negative electrode current collector,
12 negative electrode active material layer,
13 electrolyte layer,
14 positive electrode current collector,
15 positive electrode active material layer,
16 cell layer,
17 Power generation elements,
18 negative electrode current collector plate,
19 positive current collector,
20 Negative terminal lead,
21 positive terminal lead,
22 Laminated film.

Claims (9)

Composition formula (1): Li _1.5 [Ni _a Mn _b Co _c [Li] _d Sn _e ] O _z
(Wherein 0.01 ≦ e ≦ 0.15, a + b + c + d + e = 1.5, 0.1 ≦ d ≦ 0.4, 1.1 ≦ [a + b + c + e] ≦ 1.4, and z represents the valence. (Represents the satisfactory oxygen number)
Represented by
In X-ray diffraction measurement, diffraction peaks showing rock salt type layered structures at 20-23 °, 35-40 ° (101), 42-45 ° (104) and 64-65 (108) / 65-66 (110) A positive electrode active material for a non-aqueous electrolyte secondary battery.   2. The non-aqueous electrolyte secondary battery according to claim 1, which has three diffraction peaks at 35-40 ° (101) and one diffraction peak at 42-45 ° (104) in X-ray diffraction measurement. Positive electrode active material.   Diffraction to 20-23 °, 35.5-36.5 ° (101), 43.5-44.5 ° (104) and 64-65 (108) / 65-66 (110) in X-ray diffraction measurement The positive electrode active material for nonaqueous electrolyte secondary batteries according to claim 1 or 2, which has a peak.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein 0.02 ≦ e ≦ 0.12 in the composition formula (1). BET specific surface area is 2 to 10 m ² / g, the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4. Sn citrate,
At least one nitrate selected from the group consisting of Ni, Mn and Co and / or at least one organic acid salt selected from the group consisting of Ni, Mn and Co having a decomposition temperature of 100 ° C. to 350 ° C. And lithium nitrate and / or an organic acid salt of lithium having a decomposition temperature of 100 ° C. to 350 ° C.,
A first step of obtaining a dried product by spray-drying a raw material mixed solution in which is dissolved in an aqueous solvent;
A second step of thermally decomposing at least a part of the salt contained in the dried product obtained in the first step to obtain a precursor;
A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, comprising: a third step of firing the precursor obtained in the second step at 400 to 1000 ° C.   The manufacturing method of Claim 6 which further includes the process of obtaining the said citrate of Sn by mixing aqueous solution containing a citric acid and tin oxalate (II), and aqueous ammonia, and setting it as pH 4-8.   A positive electrode active material layer containing the positive electrode active material according to any one of claims 1 to 5 or the positive electrode active material produced by the production method according to claim 6 or 7 is formed on a surface of a current collector. A positive electrode for a non-aqueous electrolyte secondary battery. A positive electrode according to claim 8;
An electrolyte layer;
A negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of the current collector;
A non-aqueous electrolyte secondary battery having a power generation element comprising: