JP2005327644A - Manufacturing method for positive electrode material for lithium secondary battery, the positive electrode material, and the lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for positive electrode material with homogeneous crystal structure for a lithium secondary battery, which enables the lithium secondary battery to output high power, even in a low temperature environment. <P>SOLUTION: Lithium hydroxide is added to mixed water solution, containing nickel sulfate, manganese sulfate, cobalt sulfate and magnesium sulfate which are mixed as raw materials, in order to coprecipitate manganese, cobalt and magnesium. Obtained coprecipitation deposit and lithium carbonate are mixed and baked at the temperature of 900°C for 8 hours, and thereby composite oxide containing lithium with lamellar crystal structure is obtained. The composite oxide containing lithium is represented by the chemical formula LiNi<SB>a</SB>Mn<SB>b</SB>Co<SB>c</SB>Mg<SB>d</SB>O<SB>2</SB>, wherein at least some nickel, some manganese or some cobalt is replaced by magnesium, valence a>b≥c, and 0.001≤d≤0.02. Contraction of the lamellar crystal in low temperature environment is suppressed by containing of magnesium in the crystal structure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a positive electrode material for a lithium secondary battery, a positive electrode material, and a lithium secondary battery, and in particular, a lithium-containing composite oxide having a layered crystal structure and containing elements of lithium, nickel, manganese, and cobalt. The present invention relates to a method for producing a positive electrode material for a lithium secondary battery, a positive electrode material produced by the production method, and a lithium secondary battery using the positive electrode material.

  Conventionally, in the field of rechargeable secondary batteries, aqueous batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries have been mainstream. In recent years, electric vehicles (EVs) and hybrid vehicles (HEVs) that assist a part of driving with electric motors have attracted attention due to problems of global warming and fuel depletion, and batteries serving as power sources have high capacity and high output. It has come to be required. As a battery that meets such requirements, a lithium secondary battery having a high voltage has attracted attention.

  A lithium-containing composite oxide is used for the positive electrode material of a lithium secondary battery. Among them, lithium cobaltate is used because of the balance of capacity and cycle characteristics, but the cost of the raw material cobalt is small and the cost is low. Therefore, lithium-containing composite oxides containing manganese such as lithium manganate are promising as positive electrode materials for EVs and HEVs, and are being developed. When this lithium-containing composite oxide has a spinel crystal structure, since the spinel crystal structure has thermal stability, a lithium secondary battery excellent in safety can be obtained. On the other hand, in lithium-containing composite oxides with a layered crystal structure, lithium ions move two-dimensionally, so the lithium ion mobility is higher at room temperature than the spinel crystal structure that moves three-dimensionally and the output characteristics are excellent. A lithium secondary battery can be obtained. However, since the layered crystal shrinks in a low temperature environment, the mobility of lithium ions is reduced, leading to a reduction in output.

  On the other hand, the negative electrode material is generally an amorphous carbon material obtained by firing natural graphite, artificial graphite such as flakes or lumps, graphite carbon material such as mesophase pitch graphite, or furan resin such as furfuryl alcohol. It is used. Since the amorphous carbon material has a theoretical capacity value higher than that of the graphite-based carbon material, a lithium secondary battery excellent in capacity and cycle characteristics can be obtained. In addition, since the voltage characteristics during charging and discharging have an inclination, it is possible to easily and accurately estimate the state of the battery by voltage measurement. However, since the irreversible capacity of the amorphous carbon material is larger than that of the graphite-based carbon material, it is difficult to increase the capacity in the battery, and the electronic conductivity between the negative electrode particles is inferior to that of the graphite-based carbon material. There is. On the other hand, the graphite-based carbon material has a low irreversible capacity and flat voltage characteristics, so that a high-capacity, high-power lithium secondary battery can be obtained, but the volume change of the crystal accompanying charge / discharge is large. Therefore, there is a problem that the electron conductivity between the negative electrode material particles cannot be maintained for a long period of time and the life is reached early, and the charge acceptability at a large current density is inferior to that of the amorphous carbon material.

  The above-described batteries for EV and HEV have a large current density in charge / discharge, and require a long life and high output characteristics. Therefore, a plurality of single cells are connected and used. Since the variation in the characteristics of the single cells greatly affects the life and safety, usually, the variation is suppressed by monitoring and controlling the voltage of the single cells in combination with a control system. However, since the voltage characteristics of the graphite-based carbon material are flat, it is difficult to accurately monitor the state of the battery with the voltage, and in order to do this, a highly accurate control system is required. Therefore, as a negative electrode material of a lithium secondary battery used for a power source for EV or HEV, it is desirable to mainly use an amorphous carbon material, and a positive electrode material using a lithium-containing composite oxide having a layered crystal structure, It is promising to improve the output.

  In order to improve the performance of lithium secondary batteries, in the cathode material, by modifying the particle surface and substituting some of the constituent elements with different elements, the crystal structure change due to charge and discharge is reduced and the bonding with oxygen Various studies have been conducted to strengthen the power. In addition, in order to increase the output of the lithium secondary battery, it is necessary to improve the electronic conductivity in the positive and negative electrode mixture layer, and a conductive agent is added to the positive and negative electrode mixture, and the positive and negative electrode mixture density is increased. For example, the resistance is reduced by securing a conductive network.

  As described above, lithium cobaltate, lithium nickelate, and spinel structure lithium manganate, which are mainly used as positive electrode materials, each have their own advantages and disadvantages. For this reason, for example, a technique for improving cycle characteristics and safety by mixing and using a layered rock salt structure lithium nickelate and a spinel structure lithium manganate is disclosed (see Patent Document 1). Further, lithium-containing composite oxides in which two or three components of cobalt, manganese, and nickel are combined have been developed (see, for example, Patent Document 2). Among them, the three-component lithium-containing composite oxides of cobalt, nickel, and manganese are excellent in thermal stability, and therefore have safety slightly lower than that of the spinel structure lithium manganate. A lithium secondary battery having an equivalent capacity can be obtained.

JP 2000-251892 A JP 2002-231246 A

  However, the lithium-containing composite oxide having the above-described layered crystal structure is excellent in capacity and output characteristics in a normal temperature environment, but the output is lowered in a low temperature environment because the movement of lithium ions is hindered due to crystal shrinkage. There is a problem. In addition, in producing the above-described three-component lithium-containing composite oxide, highly precise condition management is important because of the large amount of components. For example, in order to obtain a lithium-containing composite oxide having a uniform composition, it is necessary to uniformly mix the raw materials. Furthermore, since the degree of crystal growth of the lithium-containing composite oxide differs depending on the temperature and time during firing, variations in temperature and time become variations in particle size distribution and particle density. If there is variation in the particle size distribution or particle density, the distribution of the conductive agent, binder, and non-aqueous electrolyte will be biased, resulting in variations in the electrode reaction. To do. In order to avoid these problems, if the crystal of the lithium-containing composite oxide grows greatly by baking at a high temperature for a long time, composition deviation occurs, and coarse particles and strong aggregates are generated. However, it cannot be dispersed, and defects are formed on the particle surface.

  In view of the above circumstances, the present invention uses a method for producing a positive electrode material for a lithium secondary battery having a homogeneous crystal structure and capable of increasing the output even in a low temperature environment, the positive electrode material produced by the production method, and the positive electrode material. It is an object of the present invention to provide a lithium secondary battery.

  In order to solve the above problems, a first aspect of the present invention is a positive electrode for a lithium secondary battery using a lithium-containing composite oxide having a layered crystal structure and containing elements of lithium, nickel, manganese, cobalt, and magnesium. A method for producing a material comprising preparing a mixed solution by mixing each of compounds containing at least nickel, manganese, cobalt, and magnesium in a solvent, and at least the nickel, manganese, cobalt, and magnesium in the prepared mixed solution And a compound containing lithium is selectively mixed to prepare a composite oxide precursor. The prepared composite oxide precursor is calcined and represented by the following chemical formula (1), and the valence is a. A step of producing a lithium-containing composite oxide satisfying a relationship of> b ≧ c and 0.001 ≦ d ≦ 0.02.

  In the production method of the first aspect, the compound in the prepared mixed solution is co-precipitated by mixing a compound containing at least nickel, manganese, cobalt, and magnesium with a solvent, and the lithium is not mixed into the co-precipitate. By mixing a compound containing lithium, each element is almost evenly distributed in the prepared composite oxide precursor, and by firing the composite oxide precursor in which each element is almost evenly distributed, the firing temperature Since the crystal grows almost uniformly even under low temperature conditions, a lithium-containing composite oxide represented by the chemical formula (1) and satisfying the relationships of valences a> b ≧ c and 0.001 ≦ d ≦ 0.02 is obtained. It can be produced without causing compositional deviation.

  In the first aspect, in the preparing step, each of the compounds each including nickel, manganese, cobalt, and magnesium is one selected from at least an oxide, a hydroxide, a nitrate, a sulfate, and a carbonate. In this step, the compound containing lithium may be at least one selected from oxides, hydroxides, nitrates, sulfates and carbonates. Further, in the preparing step or the preparing step, lithium, nickel, manganese, cobalt, and magnesium contained in each of the compounds containing lithium, nickel, manganese, cobalt, and magnesium correspond to the valence of chemical formula (1). It is preferable to mix at a molar ratio.

  According to a second aspect of the present invention, in the positive electrode material for a lithium secondary battery using a lithium-containing composite oxide having a layered crystal structure and containing elements of lithium, nickel, manganese, and cobalt, the lithium-containing composite oxide is , Represented by the following chemical formula (1), at least part of the elements of nickel, manganese and cobalt are substituted with magnesium element, and the valences are a> b ≧ c and 0.001 ≦ d ≦ 0. It satisfies the relationship of 02.

  In the positive electrode material of the second aspect, the lithium-containing composite oxide is represented by the chemical formula (1), at least a part of nickel, manganese, and cobalt elements are substituted with magnesium elements, and the valence is a. > B ≧ c and 0.001 ≦ d ≦ 0.02, satisfying the relationship of nickel, manganese, and magnesium larger than cobalt in the crystal, so the layered crystal shrinks even in a low temperature environment Therefore, in the lithium secondary battery using the lithium-containing composite oxide, movement of lithium ions can be ensured even in a low temperature environment.

  A third aspect of the present invention is a positive electrode plate having a layered crystal structure and using a lithium-containing composite oxide containing lithium, nickel, manganese, and cobalt elements and a conductive agent, and occlusion of lithium ions. In the lithium secondary battery including a negative electrode plate including a releasable negative electrode material, the lithium-containing composite oxide is represented by the following chemical formula (1), and at least some of the elements of nickel, manganese, and cobalt are magnesium. It is substituted with an element, and the valence satisfies the relationship of a> b ≧ c and 0.001 ≦ d ≦ 0.02.

  In the lithium secondary battery of the third aspect, the lithium-containing composite oxide is represented by the chemical formula (1), and at least a part of nickel, manganese, and cobalt elements are substituted with magnesium elements, and the valence Satisfies the relationship of a> b ≧ c and 0.001 ≦ d ≦ 0.02, and the element radius is nickel, manganese, and magnesium larger than cobalt is contained in the crystal. Therefore, the movement of lithium ions can be secured and high output can be exhibited.

  According to the present invention, a compound containing at least nickel, manganese, cobalt and magnesium constituting a lithium-containing composite oxide is mixed and at least nickel, manganese, cobalt and magnesium are co-precipitated, and a compound containing lithium selectively. Since the crystals grow almost uniformly even when the firing temperature is set to a low temperature condition, the valence is expressed by the chemical formula (1), and the valences are a> b ≧ c and 0.001 ≦ d ≦ 0. Lithium-containing composite oxide satisfying the relationship of 02 can be produced uniformly without causing composition deviation. In the produced lithium-containing composite oxide, magnesium having an element radius greater than nickel, manganese, and cobalt is present in the crystal. Therefore, the shrinkage of the layered crystal can be suppressed even in a low temperature environment, and the lithium-containing composite oxide is used. The Um secondary battery, it is possible to obtain an effect that can exert a high output to ensure the movement of lithium ions even in a low temperature environment.

  Embodiments in which the present invention is applied to a cylindrical lithium ion secondary battery will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, the cylindrical lithium ion secondary battery 20 of the present embodiment is made of nickel-plated steel battery-bottomed battery can 7 and a polypropylene resin hollow cylinder as shown in FIG. Around the winding core 1, there is an electrode plate group 6 in which a strip-like positive electrode plate and a negative electrode plate are wound in a spiral shape with a separator interposed therebetween.

  On the upper side of the electrode plate group 6, a ring-shaped positive electrode current collecting ring 4 for collecting the electric potential from the positive electrode plate is disposed. The positive electrode current collecting ring 4 is fixed to the upper end portion of the winding core 1 via a positive electrode current collecting ring support that supports the positive electrode current collecting ring 4. The edge of the positive electrode lead piece 2 extended from the positive electrode plate is ultrasonically welded to the periphery of the positive electrode current collecting ring 4. Above the positive electrode current collecting ring 4, a disk-shaped battery lid 13 having a central portion formed in a convex shape is disposed. One end of a ribbon-like positive electrode lead plate 9 made of aluminum is fixed to the upper part of the positive electrode current collecting ring 4. The other end of the positive electrode lead plate 9 is joined to the lower portion of the battery lid 13 by welding via the lid lead plate.

  On the other hand, a ring-shaped negative electrode current collecting ring 5 for collecting a potential from the negative electrode plate is disposed below the electrode plate group 6, and the negative electrode current collecting ring 5 supports the negative electrode current collecting ring 5. It is fixed to the lower end portion of the winding core 1 via a negative electrode current collecting ring support. The edge of the negative electrode lead piece 3 extending from the negative electrode plate is welded to the periphery of the negative electrode current collecting ring 5. A negative electrode lead plate 8 is welded to the lower part of the negative electrode current collecting ring 5, and the negative electrode lead plate 8 is welded to the inner bottom portion of the battery can 7. The battery can 7 has an outer diameter of 40 mm and an inner diameter of 39 mm.

The battery cover 13 is crimped and fixed to the upper part of the battery can 7 through an insulating and heat resistant EPDM resin gasket. For this reason, the inside of the lithium ion secondary battery 20 is sealed. Further, a predetermined amount of non-aqueous electrolyte (not shown) is injected into the battery can 7. For the non-aqueous electrolyte, for example, 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) can be used by dissolving in a mixed solvent of ethylene carbonate and dimethyl carbonate. The battery lid 13 is provided with a cleavage valve (internal pressure release mechanism) that cleaves when the internal pressure of the lithium ion secondary battery 20 increases, and the cleavage pressure is set to about 9 × 10 ⁵ Pa. Further, the lithium ion secondary battery 20 is electrically operated in response to an increase in battery temperature, for example, a PTC element, or a current interruption in which a positive or negative electrical lead is disconnected in response to an increase in battery internal pressure. The mechanism is not arranged.

  In the electrode plate group 6, the positive electrode plate and the negative electrode plate are wound around the core 1 through a polyethylene separator having a width of 90 mm and a thickness of 40 μm so that the two electrode plates do not directly contact each other. The positive electrode lead piece 2 and the negative electrode lead piece 3 are respectively disposed on opposite end surfaces of the electrode plate group 6. An insulating coating is applied to the entire outer peripheral surfaces of the electrode plate group 6 and the positive electrode current collecting ring 4. For the insulation coating, an adhesive tape in which a hexamethacrylate adhesive is applied to one side of a polyimide base material is used. The diameter of the electrode plate group 6 is set to 38 ± 0.1 mm by adjusting the lengths of the positive electrode plate, the negative electrode plate, and the separator.

The negative electrode plate constituting the electrode plate group 6 has a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. On both surfaces of the rolled copper foil, a negative electrode mixture containing amorphous carbon powder having an average particle diameter of 5 to 20 μm capable of occluding and releasing lithium ions as a negative electrode active material is applied almost uniformly and uniformly. In the negative electrode mixture, acetylene black as a conductive agent and polyvinylidene fluoride (PVDF) as a binder (binder) are blended, and the blend ratio of the negative electrode active material, the conductive agent, and the binder is 100: 5: 10 is set. When applying the negative electrode mixture to the rolled copper foil, N-methylpyrrolidone (NMP) is used as a dispersion solvent, and is applied by transfer by roll-to-roll. An uncoated portion of a negative electrode mixture having a width of 30 mm is formed on the side edge on one side in the longitudinal direction of the rolled copper foil. The uncoated part is notched in a comb shape, and the negative electrode lead piece 3 is formed in the notch remaining part. The negative electrode plate is pressed by a heatable roll press so that the negative electrode mixture density is 1.0 g / cm ³ and is cut into a width of 85 mm.

On the other hand, the positive electrode plate has an aluminum foil having a thickness of 20 μm as a positive electrode current collector. A positive electrode mixture containing a lithium-containing composite oxide powder having a layered crystal structure as a positive electrode active material is applied to both surfaces of the aluminum foil almost uniformly and uniformly. In the positive electrode mixture, flaky graphite as a conductive agent and PVDF as a binder are blended. The compounding ratio of the positive electrode active material, the conductive agent, and the binder is set to a mass ratio of 100: 10: 5. When the positive electrode mixture is applied to the aluminum foil, NMP is used as a dispersion solvent and is applied by transfer by roll-to-roll. An uncoated portion of the positive electrode mixture is formed on the side edge on one side in the longitudinal direction of the aluminum foil in the same manner as the negative electrode plate, and the positive electrode lead piece 2 is formed. The positive electrode plate is pressed in the same manner as the negative electrode plate so as to have a positive electrode mixture density of 2.70 g / cm ³ and cut into a width of 80 mm.

(Preparation of positive electrode material)
The lithium-containing composite oxide described above is represented by the following chemical formula (1), and the valence satisfies the relationship of a> b ≧ c and 0.001 ≦ d ≦ 0.02, and lithium, nickel, manganese, cobalt It is prepared by mixing and firing raw materials containing magnesium. When the valence b (manganese ratio) increases, it becomes difficult to synthesize a single-phase lithium-containing composite oxide, and when the valence c (cobalt ratio) increases, the cost increases and the battery capacity significantly decreases. Note that the valence of lithium in the chemical formula (1) is not limited to 1, but may be slightly deficient or excessive, and the valence of oxygen is not limited to 2, but is slightly deficient in oxygen. May occur.

  As raw materials, oxides, hydroxides, nitrates, sulfates, carbonates and the like of each element can be used. For example, examples of the lithium source include lithium carbonate, lithium nitrate, and lithium hydroxide. Examples of the nickel source include nickel carbonate, nickel sulfate, nickel hydroxide, nickel oxide, nickel peroxide and the like. Examples of manganese sources include manganese dioxide, nimanganese trioxide, trimanganese tetroxide, manganese carbonate, manganese nitrate, and manganese sulfate. Examples of the cobalt source include cobalt oxide, niobium trioxide, tricobalt tetroxide, cobalt hydroxide, cobalt nitrate, and cobalt sulfate. Examples of the magnesium source include magnesium carbonate, magnesium sulfate, magnesium hydroxide, magnesium nitrate and the like.

  These nickel source, manganese source, cobalt source, and magnesium source are wet mixed, then co-precipitated, dried and pulverized, and then the lithium source is mixed in a dry method (dry mixing method) as a firing raw material (composite oxide precursor) Body). Alternatively, a lithium source, a nickel source, a manganese source, a cobalt source, and a magnesium source can all be wet mixed and then coprecipitated (wet mixing method) to obtain a fired raw material. Hereinafter, in this embodiment, a dry mixing method will be described. However, the wet mixing method can be performed in the same manner as the dry mixing method except that the lithium source is mixed in the mixed solution preparation step.

  First, in the mixed solution preparation step, nickel, manganese, cobalt, and magnesium contained in each compound of a nickel source, a manganese source, a cobalt source, and a magnesium source are converted into moles corresponding to the valence represented by the above chemical formula (1). Prepare a mixed solution by mixing at a ratio. At this time, water or an organic solvent can be used as a solvent for wet mixing of the raw materials, but water is preferably used. Representative examples of the mixer and the disperser include a bead mill, a ball mill, and a jet mill.

  Next, in the precursor preparation step, nickel, manganese, cobalt, and magnesium in the mixed solution are coprecipitated by adding a coprecipitation solution to the mixed solution prepared in the preparation step. After the obtained coprecipitate is dried and pulverized to have various average particle sizes, the lithium contained in the compound of the lithium source is converted into a molar ratio corresponding to the valence represented by the above chemical formula (1). To prepare a firing raw material. The method for drying the coprecipitate is not particularly limited, and a spray drying method that can be easily dried at an appropriate drying temperature and spray amount can be employed. Air or an inert gas can be used as the atomizing gas, but air is usually used. When the drying temperature is low, it may cause poor drying or dew condensation in the furnace.

  In the next firing step, the obtained firing material is left standing in an electric furnace and fired. Firing is performed at a temperature of 700 to 1100 ° C. for 8 to 24 hours. The rate of temperature increase is not particularly limited, but it is necessary to keep the firing temperature at least 4 hours in order to form a single crystal phase. When the firing temperature is low, the firing time becomes long and the crystal growth is insufficient, so that the packing density of the primary particles in the secondary particles of the obtained lithium-containing composite oxide is also reduced. On the other hand, when the firing temperature is high, another crystal phase is formed or defects are increased. Further, the lithium source may sublimate and compositional deviation may occur. Even in the cooling after firing, in order to suppress the formation of another crystal phase and the generation of a lithium-containing composite oxide having many defects, it is desirable to slowly cool by limiting the cooling rate, for example, 300 ° C./h or less It is desirable to carry out at a cooling rate. As a baking apparatus, a gas furnace, a tunnel furnace, a rotary kiln, etc. can be used besides an electric furnace.

  The composition of the calcined lithium-containing composite oxide was analyzed by ICP (inductively coupled plasma) emission spectroscopic analysis, represented by the above chemical formula (1), and the valences were a> b ≧ c and 0.001 ≦ d ≦ 0. .02 satisfying the relationship. The layered crystal structure was confirmed by powder X-ray diffraction measurement.

  Next, in accordance with this embodiment, a lithium ion secondary battery using a lithium-containing composite oxide produced by changing the molar ratio of nickel, manganese, cobalt, and magnesium and firing conditions with different firing temperatures and temperature variations in the electric furnace. Twenty examples will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

(Example 1)
As shown in Table 1 below, in Example 1, a wet mixing method was used for mixing raw materials, and the molar ratio of each element was Li: Ni: Mn: Co: Mg = 1: 0.34: 0.33: 0. .33: 0.001 A lithium-containing composite oxide having a rhombohedral layered crystal structure was synthesized and used. As raw materials, 89.4 g of nickel sulfate hexahydrate having an average particle diameter of 1 μm, 92.8 g of cobalt sulfate heptahydrate having an average particle diameter of 1 μm, and manganese sulfate hexahydrate having an average particle diameter of 1 μm 79.6 g, 0.25 g of magnesium sulfate heptahydrate, and 74 g of lithium carbonate were dissolved and dispersed in 1 liter of ion exchange water, and then aggregates were removed through a 400-mesh filter. A 0.5 mol / liter aqueous lithium hydroxide solution was gradually added to the resulting solution to coprecipitate a lithium / nickel / cobalt / manganese / magnesium mixed hydroxide. The coprecipitate was filtered with an accordion type filter press, dried with stirring at 120 ° C. for 1 hour, and then pulverized with a jet mill to have various average particle diameters to obtain a calcined raw material. The firing raw material placed in a zirconia container was left in an electric furnace, heated to a firing temperature of 900 ° C. at a heating rate of 5 ° C./min, and held for 8 hours. At this time, the temperature variation in the electric furnace was 5 ° C. After firing, it was gradually cooled at a cooling rate of 5 ° C / min. Next, the obtained lithium-containing composite oxide was pulverized by an airflow collision type pulverizer and classified to obtain a positive electrode material having an average particle diameter of 5 μm. In Table 1, the amounts (moles) of magnesium, nickel, manganese, and cobalt indicate amounts when the amount of lithium is 1 mol. In addition, wet mixing of raw materials is a wet mixing method in which all of lithium, nickel, cobalt, manganese and magnesium are co-precipitated, and dry is a co-precipitate in which nickel, cobalt, manganese and magnesium are co-precipitated. A dry mixing method in which lithium is mixed by a dry method is shown.

(Example 2)
As shown in Table 1, Example 2 was the same as Example 1 except that the amount of magnesium was 0.005 mol.

(Example 3)
As shown in Table 1, Example 3 was the same as Example 1 except that the amount of magnesium was 0.01 mol and the firing temperature was 750 ° C. The temperature variation was 2 ° C.

Example 4
As shown in Table 1, Example 4 was the same as Example 1 except that the amount of magnesium was 0.01 mol.

(Example 5)
As shown in Table 1, Example 5 was the same as Example 3 except that the firing temperature was 1050 ° C. The temperature variation was 10 ° C.

(Example 6)
As shown in Table 1, Example 6 was the same as Example 1 except that the amount of magnesium was 0.02 mol.

(Comparative Examples 1 to 3)
As shown in Table 1, in Comparative Examples 1 to 3, lithium-containing composite oxides were produced without mixing magnesium. Except for not mixing magnesium, Comparative Example 1 was the same as Example 3, Comparative Example 2 was the same as Example 4, and Comparative Example 3 was the same as Example 5.

(Comparative Example 4 to Comparative Example 5)
As shown in Table 1, Comparative Example 4 was the same as Example 1 except that the amount of magnesium was 0.03 mol. In Comparative Example 5, the amount of nickel was 0.4 mol and the amount of manganese was 0.4 mol. The same procedure as in Comparative Example 2 was conducted except that the amount of cobalt was 0.2 mol.

(Example 7 to Example 9)
As shown in Table 1, Examples 7 to 9 were the same as Example 4 except that the molar ratio of nickel, manganese, and cobalt was changed. In Example 7, the amount of nickel was 0.4 mol, the amount of manganese was 0.4 mol, and the amount of cobalt was 0.2 mol. In Example 8, the amount of nickel was 0.45 mol, the amount of manganese was 0.4 mol, cobalt In Example 9, the amount of nickel was 0.6 mol, the amount of manganese was 0.3 mol, and the amount of cobalt was 0.1 mol.

(Comparative Example 6 to Comparative Example 7)
As shown in Table 1, Comparative Example 6 to Comparative Example 7 were the same as Example 4 except that the molar ratio of nickel, manganese, and cobalt was changed. In Comparative Example 6, the amount of nickel was 0.3 mol, the amount of manganese was 0.5 mol, and the amount of cobalt was 0.2 mol. In Comparative Example 7, the amount of nickel was 0.3 mol, the amount of manganese was 0.3 mol, cobalt The amount was 0.4 mol.

(Example 10)
As shown in Table 1, in Example 10, a dry mixing method was used for mixing raw materials, and the molar ratio of each element was Li: Ni: Mn: Co: Mg = 1: 0.34: 0.33: 0. A lithium-containing composite oxide having a rhombohedral layered crystal structure at 33: 0.01 was synthesized and used. As raw materials, 89.4 g of nickel sulfate hexahydrate having an average particle diameter of 1 μm, 92.8 g of cobalt sulfate heptahydrate having an average particle diameter of 1 μm, and manganese sulfate hexahydrate having an average particle diameter of 1 μm 79.6 g and 2.5 g of magnesium sulfate heptahydrate were dissolved and dispersed in 1 liter of ion-exchanged water, and then aggregates were removed through a 400-mesh filter. A 0.5 mol / liter aqueous lithium hydroxide solution was gradually added to the resulting solution to coprecipitate a nickel / cobalt / manganese / magnesium mixed hydroxide. The coprecipitate is filtered with an accordion-type filter press, dried at 120 ° C for 1 hour with stirring, and then mixed with nickel, cobalt, manganese, and magnesium that are pulverized to various average particle sizes with a jet mill. 74 g of lithium carbonate was added to the hydroxide in a dry manner and mixed with a jet mill to obtain a calcined raw material. The firing raw material placed in a zirconia container was left in an electric furnace, heated to a firing temperature of 900 ° C. at a heating rate of 5 ° C./min, and held for 8 hours. At this time, the temperature variation in the electric furnace was 5 ° C. After firing, it was gradually cooled at a cooling rate of 5 ° C / min. Next, the obtained lithium-containing composite oxide was pulverized by an airflow collision type pulverizer and classified to obtain a positive electrode material having an average particle diameter of 5 μm.

(Example 11)
As shown in Table 1, Example 11 was the same as Example 10 except that the amount of magnesium was 0.005 mol.

(Example 12)
As shown in Table 1, Example 12 was the same as Example 10 except that the firing temperature was 750 ° C. The temperature variation was 2 ° C.

<Evaluation, test>
For the lithium-containing composite oxides produced in the examples and comparative examples, the tap density representing the apparent density after applying vibration (tapping) to the lithium-containing composite oxide placed in a measurement container is measured with a powder characteristic measuring device (Hosokawa Micron Corporation) It was measured with a powder tester PT-R type manufactured by company. In the measurement, a 100 cc tapping cell was used, the tapping height was 3 mm, and the tapping frequency was set to 180 times for 5 minutes. The specific surface area was measured by a nitrogen gas adsorption method (BET method). The measurement results of tap density and specific surface area are shown in Table 2 below.

As shown in Table 2, the lithium-containing composite oxides of Examples 1 to 12 having a layered crystal structure represented by the above-described chemical formula (1) and at least a part of nickel, manganese, and cobalt substituted with magnesium. The product had a tap density of 1.7 to 2.2 g / cm ³ and a specific surface area of 0.7 to 1.0 m ² / g. For this reason, primary particles are sufficiently grown even under low-temperature conditions (Example 3) and temperature variations in the electric furnace (Example 5) under firing conditions, and the primary particle packing density in the secondary particles is also large. There was found. Further, since it can be fired at a low temperature, it has been found that there are few generations and defects of another crystal phase and a small compositional deviation. The obtained lithium-containing composite oxide was pulverized and classified in a low-pressure air stream, and the workability was excellent.

  Next, the following tests were performed on the batteries of the examples and comparative examples. First, a constant-current / constant-voltage charge (set voltage 4.1 V) is performed for 5 hours at a 3-hour rate (0.33 C) in a room temperature (25 ° C.) atmosphere, and then a discharge end voltage is set at a 1-hour rate (1 C). The battery was discharged to 2.7 V and charged again under the same conditions. Next, in accordance with Japanese Industrial Standard (JIS C 8711), discharge was performed at each current value of discharge current 1, 3, 6A, the voltage at the 5th second was measured, and the initial output was obtained from this current-voltage characteristic. The battery whose initial output was measured was left in a low temperature (−25 ° C.) constant temperature bath for 24 hours to cool the entire battery to −25 ° C., and the initial output was measured in the room temperature atmosphere described above. The output in a low temperature atmosphere was measured under the same conditions. Furthermore, in order to measure the decrease in output due to the charge / discharge cycle, the sample was allowed to stand at room temperature for 24 hours and then charged at a constant current and constant voltage (set voltage 4.1 V) at a rate of 3 hours (0.33 C) in an atmosphere of 25 ° C. ) Was performed for 5 hours, and charging and discharging were repeated at a rate of 1 hour (1C) until the discharge final voltage reached 2.7V. After 100 cycles, the output of the battery was measured in the same manner as the measurement of the initial output, and the ratio of the output after 100 cycles to the initial output was obtained as a percentage to obtain the maintenance rate. Table 3 below shows the measurement results of the output and the maintenance factor in a room temperature and low temperature atmosphere.

  As shown in Table 3, Examples 1 to 12 using a lithium-containing composite oxide represented by the chemical formula (1) and having at least a part of nickel, manganese, or cobalt elements substituted with magnesium elements were used as positive electrode materials. In the lithium ion secondary battery 20, it was found that an output of 330 W or more in a low temperature environment was secured, and an output of 85% or more of the initial output was maintained even after 100 charge / discharge cycles were repeated. did. On the other hand, in the lithium ion secondary battery of Comparative Example 1 in which the lithium-containing composite oxide fired at a low temperature without replacing the constituent element of the lithium-containing composite oxide with the magnesium element as the positive electrode material, the room temperature environment The output decreased significantly in both low and low temperature environments. From this, the lithium-containing composite oxide used in each comparative example has insufficient crystal growth of the primary particles, so that it is impossible to form a conductive network up to the inside of the secondary particles, and charge / discharge is repeated. It is considered that the secondary particle structure gradually collapses due to the volume change accompanying the decrease in the electron conductivity and the nonuniformity of the electrode reaction.

  In addition, in the lithium ion secondary batteries of Comparative Example 6 and Comparative Example 7 in which the lithium-containing composite oxide in which the ratio of manganese or cobalt was increased was used as the positive electrode material, the output was remarkably reduced in both the room temperature environment and the low temperature environment. When the proportion of manganese increases, it becomes difficult to obtain a single-phase lithium-containing composite oxide, and the physical properties of powder particles (coarse particles and aggregates) caused by temperature variations during firing deteriorate battery performance. Inferred.

  Furthermore, in the lithium ion secondary battery of Comparative Example 3 in which the lithium-containing composite oxide in which the primary temperature crystal is excessively grown by increasing the firing temperature is used as the positive electrode material, the output drop under a low temperature environment is significantly reduced. In the overcharge test, it was confirmed that the battery ruptured and the safety was significantly impaired. This is because the non-aqueous electrolyte distribution in the positive electrode mixture is non-uniform, so the electrode reaction is concentrated on the portion where the non-aqueous electrolyte is present, and that portion has reached an overcharged state from an early stage. Conceivable. In addition, the pulverization of the lithium-containing composite oxide after firing is extremely difficult and requires a long time for classification. Therefore, the surface of the particle is damaged, the particle size distribution, and the primary particle density in the secondary particles vary. It can be considered that the life performance and safety are significantly reduced while the output is significantly reduced.

  As described above, at least part of nickel, manganese, and cobalt elements represented by the chemical formula (1), which is prepared from the firing raw material prepared using the coprecipitation method (dry mixing method, wet mixing method), is a magnesium element. And lithium-containing composite oxides having a layered crystal structure satisfying the relationship of valence a> b ≧ c and 0.001 ≦ d ≦ 0.02 promotes crystal growth of particles even at low temperatures In addition, it has been found that variations in the particle size distribution and the primary particle density in the secondary particles can be reduced. In the lithium ion secondary battery 20 using this lithium-containing composite oxide as the positive electrode material, it has been found that it is possible to improve the life performance and safety by increasing the output, particularly at a low temperature.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the ternary lithium-containing composite oxide of cobalt, nickel, and manganese obtained by firing a firing raw material, secondary particles in which primary particles are aggregated are formed, and in order to obtain a positive electrode material having a uniform composition It is necessary to mix the raw materials more uniformly. In addition, since the degree of crystal growth of the primary particles varies depending on the drying conditions, firing temperature and time of the firing raw material, the variation in these conditions varies in the particle size distribution and the primary particle density in the secondary particles (secondary particle voids). It becomes. In addition, if the primary particle crystals grow significantly, coarse secondary particles and very strong aggregates of secondary particles are generated, and the aggregates cannot be released even if pulverized after firing. A deficiency will be formed. The firing temperature is 700 to 1100 ° C. However, in order to suppress temperature variation during firing, it is necessary to slow the temperature increase rate or to maintain at a constant temperature for each step, which is necessary for firing. Time is significantly increased. In a lithium ion secondary battery using a positive electrode material with particle size distribution of secondary particles and variation in voids, the distribution of conductive agent, binder and non-aqueous electrolyte is biased, so a dense conductive network in the positive electrode mixture And the capacity and output are significantly reduced. In addition, the electrode reaction in the secondary particles varies and concentrates partially, so the lithium-containing composite oxide deteriorates and the service life decreases, and the concentrated part reaches an overcharged state early and safety Damage. In particular, since the layered crystal of the lithium-containing composite oxide shrinks under a low temperature environment, the lithium ion diffusibility is lowered and the variation in electrode reaction becomes remarkable.

  In the lithium ion secondary battery 20 of the present embodiment, the lithium-containing composite oxide of the positive electrode material is manufactured and used as follows. That is, a compound containing lithium element is mixed in a coprecipitate obtained by coprecipitation of nickel, manganese, cobalt, and magnesium in a mixed solution in which compounds containing elements of nickel, manganese, cobalt, and magnesium are mixed, or A compound containing each of lithium, nickel, manganese, cobalt, and magnesium elements is mixed to co-precipitate lithium, nickel, manganese, cobalt, and magnesium. For this reason, the baking raw material in which each element was distributed substantially uniformly can be prepared. By firing this firing material, the crystals grow almost uniformly even if the firing temperature is low or the firing conditions with large temperature fluctuations in the electric furnace, so the primary particle packing density in the secondary particles is large and non-aqueous electrolysis. It is possible to appropriately form voids through which the liquid can permeate. In addition, since it can be fired at a low temperature, it is represented by the chemical formula (1) without generation of another crystal phase and defects, and without compositional deviation, and the valences are a> b ≧ c and 0.001 ≦ d. A lithium-containing composite oxide satisfying the relationship of ≦ 0.02 can be manufactured. The crystal of the lithium-containing composite oxide contains magnesium whose element radius is greater than nickel, manganese, and cobalt, and therefore, the shrinkage of the layered crystal can be suppressed even in a low temperature environment. Furthermore, since coarse secondary particles and very strong aggregates of secondary particles are not generated, the resulting lithium-containing composite oxide can be pulverized and classified in a low-pressure air stream, improving workability. be able to.

  In the lithium ion secondary battery 20 of the present embodiment using this lithium-containing composite oxide, the lithium-containing composite oxide can suppress the shrinkage of the layered crystal even in a low temperature environment, Since the voids into which the non-aqueous electrolyte can permeate are formed in the particles, variations in the electrode reaction between the lithium-containing composite oxide and the non-aqueous electrolyte can be suppressed even in a low temperature environment. Therefore, since the electrode reaction proceeds almost uniformly, it is possible to suppress the reduction of the life without concentrating the electrode reaction and ensure safety, and the lithium ions in the lithium-containing composite oxide can be maintained even in a low temperature environment. A high output can be demonstrated while securing the movement.

  In this embodiment, a nickel source, a manganese source, a cobalt source, and a magnesium source are wet-mixed and then co-precipitated, and the co-precipitate and the lithium source are dry-mixed to prepare a calcined raw material, and The lithium source, the nickel source, the manganese source, the cobalt source, and the magnesium source are mixed in a wet manner and then co-precipitated to prepare a fired raw material, but the lithium-containing secondary battery 20 can be used. The method for producing the composite oxide is not limited to this. For example, it is possible to obtain a calcined raw material by a method in which each raw material is mixed and pulverized, or by a method in which each raw material is mixed in a wet manner and granulated and dried. The method is preferably used.

  Further, in this embodiment, an example is shown in which sulfates of each element are used for the nickel source, manganese source, cobalt source, and magnesium source, and lithium hydroxide is used for the coprecipitation solution. However, the present invention is limited to this. Is not to be done. For example, oxides, hydroxides, nitrates, and carbonates of each element may be used. The coprecipitation solution may be selected depending on the properties of the mixed solution in which the respective compounds are mixed. For example, when the solution is basic, an acidic solution may be used.

Further, in the present embodiment, specific numerical values, for example, LiNi _0.34 Mn _0.33 Co _0.33 Mg _0.01 O ₂ are exemplified in the composition of the lithium-containing composite oxide, but the present invention is not limited thereto. The ratio of the valence of nickel, manganese and cobalt satisfying the relationship of a> b ≧ c and the valence of magnesium element 0.001 ≦ d ≦ 0.02, and having a layered crystal structure. I just need it.

  Furthermore, in the present embodiment, the cylindrical lithium ion secondary battery 20 is illustrated in which the positive and negative electrode plates are wound and accommodated in a bottomed cylindrical battery can, but the present invention is limited to the shape and structure of the battery. For example, the present invention can be applied to a rectangular or other polygonal battery or a stacked type battery in which positive and negative electrode plates are stacked. Moreover, as a battery structure to which the present invention can be applied, for example, a battery having a structure in which positive and negative external terminals pass through a battery lid and are pressed through a winding core in a battery container can be exemplified.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, an example in which amorphous carbon is used as the negative electrode active material has been shown, but the present invention is not limited to this. For example, graphite-based carbon materials such as natural graphite, various artificial graphite materials, and coke may be used, and the particle shape is not particularly limited, such as scaly, spherical, fibrous, or massive.

  Moreover, in the lithium ion secondary battery 20 of this embodiment, although the example which uses PVDF for a binder was shown, this invention is not limited to this, For example, polytetrafluoroethylene (PTFE), polyethylene, polystyrene , Polymers such as polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride and the like Mixtures may be used.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, scaly graphite is exemplified as the positive electrode conductive agent, but the present invention is not limited to this, and any graphite-based carbon material may be used. Examples of the positive electrode conductive agent that can be used other than in the present embodiment include natural graphite, various artificial graphite materials, coke, and the like. Also in the particle shape, scaly, spherical, fibrous, massive, etc. It is not limited. Moreover, there is no restriction | limiting in particular also in the electrically conductive agent of a negative electrode, For example, amorphous carbon, such as ketjen black, can be used.

Furthermore, in the lithium ion secondary battery 20 of the present embodiment, a lithium hexafluorophosphate dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate is exemplified in a nonaqueous electrolyte solution. However, the present invention is not limited thereto, and a general lithium salt can be used as an electrolyte, which is dissolved in an organic solvent. There are no particular limitations on the lithium salt or organic solvent used. For example, as the electrolyte, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, or a mixture thereof may be used. Examples of the organic solvent include propylene carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3- Dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, or a mixed solvent of two or more of these may be used. The mixing ratio is not limited.

  The present invention relates to a method for producing a positive electrode material for a lithium secondary battery having a homogeneous crystal structure and capable of increasing the output even in a low temperature environment, a positive electrode material produced by the production method, and a lithium secondary material using the positive electrode material It provides batteries, contributes to manufacturing and sales, and can be used industrially.

It is sectional drawing which shows the cylindrical lithium ion secondary battery of embodiment which can apply this invention.

Explanation of symbols

6 electrode plate group 20 cylindrical lithium ion secondary battery (lithium secondary battery)

Claims (5)

A method for producing a positive electrode material for a lithium secondary battery using a lithium-containing composite oxide having a layered crystal structure and containing elements of lithium, nickel, manganese, cobalt, and magnesium,
Prepare a mixed solution by mixing each of compounds containing at least nickel, manganese, cobalt, and magnesium in a solvent,
Co-precipitating the at least nickel, manganese, cobalt and magnesium in the prepared mixed solution, and selectively mixing a compound containing lithium to prepare a composite oxide precursor;
The prepared composite oxide precursor is fired to produce a lithium-containing composite oxide represented by the following chemical formula (1) and satisfying the relationship of valence a> b ≧ c and 0.001 ≦ d ≦ 0.02. To
The manufacturing method characterized by including a step.
  In the preparing step, each of the compounds each including nickel, manganese, cobalt, and magnesium is at least one selected from an oxide, a hydroxide, a nitrate, a sulfate, and a carbonate, and the preparing step Then, the compound containing lithium is at least one selected from oxides, hydroxides, nitrates, sulfates and carbonates.   In the preparing step or the preparing step, lithium, nickel, manganese, cobalt, and magnesium contained in each of the compounds each containing lithium, nickel, manganese, cobalt, and magnesium correspond to the valence of the chemical formula (1). The manufacturing method according to claim 1, wherein the mixture is mixed in a molar ratio. In the positive electrode material for a lithium secondary battery using a lithium-containing composite oxide having a layered crystal structure and including elements of lithium, nickel, manganese, and cobalt, the lithium-containing composite oxide is represented by the following chemical formula (1). , At least a part of the elements of nickel, manganese and cobalt is substituted with magnesium element, and the valence satisfies the relationship of a> b ≧ c and 0.001 ≦ d ≦ 0.02. Positive electrode material.
A positive electrode plate having a layered crystal structure and using a lithium-containing composite oxide containing lithium, nickel, manganese, and cobalt elements, a positive electrode plate containing a conductive agent, and a negative electrode plate containing a negative electrode material capable of inserting and extracting lithium ions And the lithium-containing composite oxide is represented by the following chemical formula (1), and at least a part of the nickel, manganese and cobalt elements are substituted with a magnesium element, and A lithium secondary battery having a valence satisfying a relationship of a> b ≧ c and 0.001 ≦ d ≦ 0.02.