JP2018095529A - Lithium-manganese composite oxide powder and method for producing the same, and positive electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide spinel type lithium-manganese composite oxide powder for a nonaqueous electrolyte secondary battery, a production method of the same, and a positive electrode using the spinel type lithium-manganese composite oxide powder.SOLUTION: In spinel type lithium-manganese composite oxide powder, the spinel type lithium-manganese composite oxide is represented by general formula LiMMnO(M is one, two or more kinds of metal elements selected from Al, Mg, and Co, x is in the range of 0≤x≤0.33 and y is in the range of 0≤y≤0.2), in which particle size distribution measured by the laser diffractive scattering method has two frequency peaks, the first frequency peak has an apex between 4.0 to 7.0 μm, the second frequency peak has an apex between 10.0 to 17.0 μm, the height of the second peak is in the range of 2.5 to 5.0 times higher than that of the first peak, and the entire powder is in the range of size of 2.0 to 45.0 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium manganese composite oxide powder having excellent filling properties and high density used for a positive electrode for a non-aqueous electrolyte secondary battery, a method for producing the same, and a positive electrode for a non-aqueous electrolyte secondary battery.

  Lithium-ion rechargeable batteries are superior in terms of electromotive force and energy density. They can be used for power sources for portable devices such as small video cameras, mobile phones, and laptop computers, for mobile devices such as bicycles, electric bikes, and electric vehicles, and for storage Widely used for power supplies.

There are several types of positive electrode materials used in lithium ion secondary batteries, such as lithium cobaltate LiCoO ₂ and nickel cobalt lithium manganate LiNi _1/3 Co _1/3 Mn _1/3 O _2. Spinel type lithium manganese composite oxide is used.

The spinel type lithium manganese composite oxide has the advantage that the raw material Mn is inexpensive, but the true density is 4.1 to 4.3 g / cm ³ and the lithium cobalt oxide is 5.0 to 5.1 g / cm ^3. Since nickel cobalt lithium manganate is low compared with 4.6 to 4.8 g / cm ³ , the energy density per unit volume is inferior compared with other positive electrode materials.

  In patent document 1, after performing the 1st baking of 1000 to 1100 degrees C or less for the mixture of manganese oxide and lithium carbonate, the second baking is again performed at 600 degrees C, and primary particles are 3 micrometers-5 micrometers. A method for increasing the electrode density by growing the electrode is disclosed.

  In Patent Document 2, a lithium compound, a manganese compound, a substituted metal compound, a metal compound having a melting point of 800 ° C. or less, and a fluorine compound are mixed with an aqueous suspension to prepare a slurry, dried using a spray dryer, and then 850. It is disclosed that a lithium manganese composite oxide having a high packing density and a high discharge capacity per volume can be obtained by firing at 0 ° C.

  Patent Document 3 proposes that boric acid is added as a sintering aid and the filling property is improved by firing.

Patent Document 4 proposes a method for producing a high-density spinel-type LiMn ₂ O ₄ by using a roller compactor to sinter the spinel-type LiMn ₂ O ₄ powder after performing compaction and agglomeration treatment. ing.

  Patent Document 5 proposes a method of increasing the press density of lithium nickel manganese cobalt oxide with a particle ratio of 10 μm or less in the range of 26 to 60% by volume.

  In Patent Document 6, the lithium nickel composite oxide has a fine secondary particle having an average particle diameter of 2 to 4 μm and an average particle diameter of 6 to 15 μm, and the mixing ratio of the fine secondary particles is 1 to 1 in volume ratio. A method of 10% is disclosed.

In Patent Document 7, in the frequency particle size distribution obtained by compressing lithium nickel manganese cobalt oxide at 3 ton / cm ² , the frequency has two local maximum values, with respect to the local maximum frequency value (P1 (%)) on the large particle side. It has been proposed that the ratio (P2 / P1) of local maximum frequency values (P2 (%)) on the small particle side is 0 <P2 / P1 ≦ 0.4.

JP 2001-155728 A JP 2001-48547 A Japanese Patent No. 3881111 Japanese Patent No. 4086931 JP 2012-121805 A WO2011-99494 JP2012-253009A

  As described above, although studies have been made so far, a spinel type lithium manganese oxide having excellent filling properties and high density is desired. More specifically, there is a need for a spinel-type lithium manganese composite oxide that can increase the electrode density of the positive electrode without impairing battery characteristics such as charge / discharge capacity, cycle characteristics, and storage characteristics.

  The electrode density is not determined only by the positive electrode material, but also varies depending on the conductive auxiliary agent, the type and blending ratio of the binder, and the pressing pressure.

  In the lithium manganese oxide disclosed in Patent Document 1, the battery characteristics in the examples are only the discharge capacity when the current density is changed, there is no description about the life such as the cycle characteristics and the storage characteristics, and the battery characteristics are There is no description that the electrode density was improved without damage.

  The lithium manganese composite oxide of Patent Document 2 shows cycle characteristics and the like in Examples 1 to 11. Even in the best example 1, the discharge capacity is as low as 90 mAh / g, and the capacity retention rate after 30 times is high. Only 97%. In an example in which the discharge capacity per volume is high, the capacity retention rate and the recovery rate are lowered, and it can be confirmed that the life characteristics are lowered as the discharge capacity per volume is improved.

The compression density of spinel-type LiMn ₂ O _{4 in} Patent Document 3 is 2.63 g / cm ³ with the active material alone, and the electrode density remains low. Moreover, there is no description about the electrode density after positive electrode preparation.

In the method for producing a high-density spinel type LiMn ₂ O ₄ of Patent Document 4, the density is compared only with the tap density of LiMn ₂ O ₄ , and there is no description regarding the electrode density after the positive electrode is manufactured.

  The lithium nickel manganese cobalt oxide of Patent Document 5 is a method for improving the press density of only powder, and there is no description regarding the density at the time of producing a positive electrode containing a conductive material and a binder.

  In the lithium nickel composite oxide of Patent Document 6, the volume ratio of fine secondary particles is specified, but the purpose is to improve safety, by controlling the two peaks of the particle size distribution, There is no disclosure about excellent fillability and high electrode density without impairing battery characteristics such as charge / discharge capacity and cycle characteristics.

In the lithium nickel manganese cobalt oxide of Patent Document 7, the particle size distribution after the compression treatment of 3 ton / cm ² is specified, and the particle size distribution before the compression treatment, that is, after the oxide synthesis is shown in the figure. As shown in 1 and 3, it is a particle size distribution having one maximum frequency value, and by controlling two peaks of the particle size distribution, it has excellent filling properties without impairing battery characteristics such as charge / discharge capacity and cycle characteristics, There is no disclosure that the electrode density can be increased.

  Therefore, in view of these circumstances, the present invention is a spinel type lithium manganese for non-aqueous electrolyte secondary batteries that has excellent filling properties and high electrode density without impairing battery characteristics such as charge / discharge capacity, cycle characteristics, and storage characteristics. It aims at providing the positive electrode using composite oxide powder, its manufacturing method, and the said spinel type lithium manganese composite oxide powder.

  In order to solve the above problems, the present inventors have intensively studied and, as a result, controlled the shape of the particle size distribution of spinel type lithium manganese composite oxide powder (hereinafter sometimes simply referred to as lithium manganese composite oxide powder). As a result, it has been found that the powder has a high filling property, and that when the electrode is manufactured, the density is high and the energy density per volume can be increased.

  The present invention has been completed based on these findings, and the gist of the invention is as follows.

(1) General _formula: Li ₁ + _{x M y Mn} is _{2-x-y O 4 (} M is one or more metal elements selected Al, Mg, and from Co, x is 0 ≦ x ≦ 0 .33, and y takes the range of 0 ≦ y ≦ 0.2.) The spinel-type lithium-manganese composite oxide represented by the following formula, and the particle size distribution measured by the laser diffraction / scattering method is Has two frequency peaks, the first frequency peak has a peak between 4.0 and 7.0 μm, the second frequency peak has a peak between 10.0 and 17.0 μm, The height of the second peak is in the range of 2.5 to 5.0 times the height of the first peak, and all of the powder is in the range of 2.0 to 45.0 μm Spinel type lithium manganese oxide powder.

(2) The spinel-type lithium manganese composite oxide powder as described above, wherein the secondary particle surface and the inside thereof contain 0.1 mass% to 2.0 mass% of phosphate as PO ₄ in total ( Spinel type lithium manganese composite oxide powder according to 1).

  (3) The spinel type lithium manganese composite as described in (2) above, wherein the phosphate is any one of aluminum phosphate, magnesium phosphate, lithium phosphate, ammonium dihydrogen phosphate, or a combination thereof. Oxide powder.

  (4) Lithium compound, manganese compound, other metal M compound (metal M is one or more metal elements selected from Al, Mg and Co), borate and phosphate, The method for producing a spinel-type lithium-manganese composite oxide powder according to any one of the above (1) to (3), which is calcined at 600 to 900 ° C., crushed and sized.

(5) The spinel-type lithium manganese composite oxide according to any one of (1) to (3) above, a conductive additive and a binder, and the proportion of the conductive material is 6% by mass or less, and the proportion of the binder. Is a positive electrode for a lithium secondary battery of 4% by mass or less, and the mixture density of the positive electrode at a press load of 4 MPa is 2.75 g / cm ³ or more and 2.87 g / cm ³ or less. Secondary battery positive electrode.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the lithium manganese complex oxide powder for nonaqueous electrolyte secondary batteries which can manufacture the positive electrode for lithium secondary batteries with a high density and a high energy density per volume. .

It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 1 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 2 of this invention measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 3 of this invention measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 4 of this invention measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 5 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 6 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 7 of this invention measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 8 of this invention measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 9 of this invention measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 10 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 11 of this invention measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 12 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 13 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 14 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 15 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of Example 16 of this invention measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of the comparative example 1 measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of the comparative example 2 measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of the comparative example 3 measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of the comparative example 4 measured using the particle size distribution measuring apparatus of a laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of the comparative example 5 measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method. It is a figure which shows the particle size distribution of the lithium manganese complex oxide powder of the comparative example 6 measured using the particle size distribution measuring apparatus of the laser diffraction / scattering method.

  Hereinafter, the present invention will be described in detail.

The lithium manganese composite oxide powder of the present invention has a chemical composition of the general formula: Li _{1 + x} M _y Mn _2−xy O ₄ (M is one or more metals selected from Al, Mg, and Co) X is in the range of 0 ≦ x ≦ 0.33, and y is in the range of 0 ≦ y ≦ 0.2.) The particle size distribution measured by the laser diffraction / scattering method is Has two frequency peaks, the first frequency peak has a peak between 4.0 and 7.0 μm, the second frequency peak has a peak between 10.0 and 17.0 μm, The height of the second peak is in the range of 2.5 to 5.0 times the height of the first peak, and all of the powder is in the range of 2.0 μm to 45.0 μm .

Spinel-type lithium manganese complex oxide according to the present invention, the chemical composition _formula: represented by _{Li 1 + x M y Mn 2} -x-y O 4. That is, some of the basic substances spinel-type lithium manganese oxide (chemical formula: LiMn ₂ O ₄ ) in which a part of Mn is replaced with the third metal element M are included, and Li is slightly excessive with respect to Mn. Also included in This metal element M is selected as having an effect on suppressing elution of manganese components into the battery and improving high-temperature characteristics, and applies one or more elements selected from Al, Mg, and Co. be able to. The substitution amount of the metal element M is set such that y is in the range of 0 ≦ y ≦ 0.2 in the chemical formula: Li _{1 + x} M _y Mn _2−xy O ₄ . This is because if the amount of substitution is too large, the discharge capacity of secondary batteries using these as a positive electrode active material tends to decrease, and an extreme decrease in discharge capacity is not preferable, so y ≦ 0.2 is limited. . Moreover, since it is not always necessary to contain M, the lower limit of y is 0.

  In the spinel-type lithium manganese composite oxide according to the present invention, Li is set to 1 to 1.33 (x is in a range of 0 ≦ x ≦ 0.33). As the Li ratio increases, the discharge capacity as a lithium secondary battery decreases. For example, when Li: 1.33 (x = 0.33), the Mn valence is almost 4 and the charge is theoretically increased in the 4V region. Since the discharge does not occur, the upper limit of x is set to 0.33. Therefore, the range of x is set to 0 ≦ x ≦ 0.33.

In the lithium manganese composite oxide of the present invention, the amount of manganese elution is small because the surface contains and contains 0.1 mass% to 2.0 mass% of phosphate as PO ₄ on the surface and inside of the secondary particles. This is because a lithium manganese composite oxide for a non-aqueous electrolyte secondary battery having excellent characteristics is obtained. If the total amount of PO ₄ is less than 0.1% by mass, the effect of phosphate addition is not clearly seen. If it exceeds 2.0% by mass, the proportion of lithium manganese composite oxide that acts as an active material is reduced. This is not preferable because the capacity decrease due to the increase in the initial discharge capacity is reduced. In addition, since phosphate has a low true density, it is not preferable because the true density of the lithium manganese composite oxide is reduced. Therefore, it was set as the range of 0.1 mass%-2.0 mass%.

  As the phosphate, an alkali metal salt of phosphoric acid, an alkaline earth metal salt, a phosphate of M metal, etc. can be used, but any of aluminum phosphate, magnesium phosphate, lithium phosphate, ammonium dihydrogen phosphate or That combination is preferred.

  The powder in the present invention is a powder (particle) obtained by mixing, firing, crushing, and sizing raw materials such as lithium salt and manganese salt, and secondary particles (particles obtained by sintering primary particles). It is in the state of. The particle size distribution of the secondary particles of the present invention has two frequency peaks, the first frequency peak has a peak between 4.0 and 7.0 μm, and the second frequency peak is 10. It has an apex between 0 and 17.0 μm, the height of the second peak ranges from 2.5 to 5.0 times the height of the first peak, and all of the powder is 2.0 μm To 45.0 μm. This particle size distribution can be measured using a particle size distribution measuring apparatus using a laser diffraction / scattering method, for example, trade name Microtrac HRAx100 manufactured by Nikkiso Co., Ltd.

  The reason why the particle size distribution of the lithium manganese composite oxide powder in the present invention is as described above will be described below.

  (1) The reason why all the powders are in the range of 2.0 μm to 45.0 μm in the particle size distribution measurement result is as follows.

Fine particles of less than 2.0 μm cause an increase in the specific surface area of the powder, and a lithium manganese composite oxide having a large specific surface area tends to cause elution of Mn into the electrolyte, resulting in a decrease in life characteristics mainly due to Mn elution. It is not preferable because it is easy to proceed.
On the other hand, particles exceeding 45.0 μm depend on the design thickness of the positive electrode plate, but when a slurry is prepared for the production of the positive electrode and coated on an aluminum foil, it tends to cause poor coating such as stringing. Therefore, it is not preferable.

  (2) The reason why the first frequency peak has a particle size distribution having an apex between 4.0 and 7.0 μm is as follows. In the particle size distribution having an apex at 4 μm or less, a fine powder of less than 2.0 μm is physically added. As a result, the specific surface area increases as a powder. A lithium-manganese composite oxide having a large specific surface area is not preferable because it easily causes Mn elution into the electrolytic solution and deteriorates life characteristics. On the other hand, if it exceeds 7.0 μm, the particle size difference from the second peak cannot be obtained, and the effect of improving the density cannot be seen.

  (3) The reason why the second frequency peak has a particle size distribution having an apex between 10.0 and 17.0 μm is that when the frequency peak is larger than 17.0 μm, the maximum particle size is 45.0 μm or less. This is because if the particle size is less than 10.0 μm, the particle size difference from the first peak cannot be obtained, and the effect of improving the density cannot be seen.

  (4) When a particle belonging to the second peak is expressed as a large particle and a particle belonging to the first peak is expressed as a small particle, a high mixture is obtained when the positive electrode is manufactured in such a manner that the small particle fills the gap between the large particles The density is realized.

  When the particle sizes of the large particles and the small particles are close to each other, the above-described effects are not exhibited, and the positive electrode has a low mixture density, which is not preferable. Therefore, the peak of the first frequency peak and the second frequency peak is preferably a combination of 4.0 to 7.0 μm and 10.0 to 17.0 μm, respectively, more preferably 5.0 to 6.0 μm. The combination is 13.0 to 15.0 μm.

  (5) In the case of a particle size distribution in which the height of the second frequency peak is higher than 5.0 times the height of the first frequency peak, or there is no first frequency peak, The gap cannot be sufficiently filled, and the density of the mixture decreases when the positive electrode is manufactured. Conversely, if the second frequency peak has a low particle size distribution that is less than 2.5 times the height of the first frequency peak, the proportion of small particles in the powder is too high and the bulk density of the powder itself Is not preferable. For this reason, the height of the second frequency peak is preferably 2.5 to 5.0 times the height of the first frequency peak. More preferably, it is 3.0 to 3.5 times.

For the reasons (1) to (5) above, the particle size distribution measured by the laser diffraction / scattering method has two frequency peaks, and the first frequency peak is between 4.0 and 7.0 μm. Has a peak, the second frequency peak has a peak between 10.0 and 17.0 μm, and the height of the second peak is 2.5 to 5.0 times the height of the first peak And using a spinel type lithium manganese composite oxide in which all of the powder falls within the range of 2.0 to 45.0 μm, the proportion of the conductive material is 6% by mass or less, and the proportion of the binder is When a positive electrode is produced at 4 mass% or less, the mix density of the positive electrode at a press load of 4 MPa can be 2.75 g / cm ³ or more.

  Next, a method for producing the lithium manganese composite oxide powder of the present invention will be described.

The spinel-type lithium manganese composite oxide powder of the present invention includes lithium salts such as lithium carbonate and lithium hydroxide and manganese oxides such as MnO ₂ , Mn ₂ O ₃ , and Mn ₃ O ₄ (which become oxides upon firing). Manganese carbonate and manganese hydroxide if available), one or more metal oxides or metal hydroxides selected from Al, Mg and Co (hereinafter referred to as M metal compounds), boric acid as B 0.01 mass% to 0.1 mass% as a whole, or 0.1 mass% to 2.0 mass% as a whole with phosphate as PO ₄ and 0.01 mass% as a whole with B as boric acid It is obtained by mixing, firing, crushing, and sizing with 0.1% by mass.

  Manganese oxides may be used by mixing two or more types of manganese oxides having different average particle diameters in order to obtain a particle size distribution having two frequency peaks.

  Manganese oxide and M metal compound are manganese M metal-containing hydroxides (or oxides) prepared in advance from the liquid phase by coprecipitation, and manganese M metal prepared by firing manganese oxide and M metal compounds in advance. A contained oxide may be used.

  Similarly, it is preferable to use an M metal compound having an average particle size smaller than that of the manganese oxide used as a raw material.

  As the phosphate, an alkali metal salt of phosphoric acid, an alkaline earth metal salt, a phosphate of M metal, etc. can be used, but any of aluminum phosphate, magnesium phosphate, lithium phosphate, ammonium dihydrogen phosphate or That combination is preferred.

  The mixing method and timing of the phosphate can be mixed with the lithium salt, manganese oxide, and M metal compound, but if the phosphate is an aqueous solution such as ammonium dihydrogen phosphate, it is sprayed as an aqueous solution. It doesn't matter. Although it does not specifically limit as a mixing method, It is preferable to dry-mix with a precision mixer.

By firing (heating treatment) after adding the phosphate, 0.1 mass in total is obtained as a highly crystalline phosphate on the surface and part of the secondary particles as lithium manganese composite oxide particles PO _4. % To 2.0% by mass.

  The firing temperature when firing the mixed mixture is set to a range of 600 to 900 ° C. The firing time is not necessarily the same depending on the firing temperature, but is preferably about 5 to 24 hours. The reason for controlling these heating time and firing time is that if the firing temperature is low, a spinel crystal structure is not formed or a different phase is likely to be mixed, so the lower limit of the firing temperature is 600 ° C. On the other hand, if the firing temperature is too high, oxygen vacancies occur and the cycle characteristics are significantly degraded.

  Further, it is better to add boric acid as a sintering aid at the time of firing so that the total amount is 0.01 mass% to 0.1 mass%.

  If the amount of boric acid added is less than 0.01% by mass as B, the effect as a sintering aid to which boric acid has been added is not clearly seen. If an amount exceeding 0.1% by mass is added, Although it depends on the firing conditions (firing temperature, firing time), it is not preferable because negative growth such as excessive particle growth and an increase in battery resistance is observed. The added boric acid is present on the surface and inside of the secondary particles together with the role of the sintering aid, and when added so that the total amount of B is 0.01% by mass to 0.1% by mass, the dissolution of manganese is suppressed. The effect is improved. The boric acid may be a boric acid aqueous solution, boron oxide or the like.

  By firing, a lithium manganese composite oxide is obtained. After firing, secondary particles (particles obtained by sintering primary particles) having a desired particle size distribution are obtained by, for example, crushing and sizing with a pulverizing and granulating machine or the like. Lithium manganese composite oxide powder in which phosphate or phosphate and boric acid are present on the surface and inside of the secondary particles can be obtained.

  The reason why the lithium manganese composite oxide powder of the present invention has a small amount of manganese elution and excellent cycle characteristics (durability) is not necessarily clear, but is estimated as follows.

In general, LiPF ₆ is often used as an electrolyte salt in the electrolytic solution. LiPF ₆ reacts with moisture in the battery to generate hydrofluoric acid (hydrofluoric acid) as shown in the following formulas (1) and (2). The manganese content in the lithium manganese composite oxide powder reacts with hydrofluoric acid and dissolves as shown in the following formulas (3-1) and (3-2), and generates water. Water present in the secondary battery causes manganese elution, which is one of the causes of battery deterioration during charging and discharging and when left.

  By adding lithium phosphate to the electrolyte, the generation of hydrofluoric acid is suppressed as shown in the following formulas (4-1) to (5-3), and it is also possible to simply add lithium phosphate at the time of making the battery positive electrode. Manganese elution is reduced.

  The chemical reaction formula can be estimated as follows.

LiPF ₆ used as an electrolyte salt reacts with water to generate hydrofluoric acid HF according to the following formulas (1) and (2).

LiPF ₆ + H ₂ O → LiF + 2HF + POF ₃ (1)
POF ₃ + 3H ₂ O → 3HF + H ₃ PO ₄ (2)
The manganese content in the lithium manganese composite oxide powder reacts with hydrofluoric acid according to the following formulas (3-1) and (3-2) to dissolve, and generates water.

Mn oxide + 2HF → MnF ₂ (dissolved) + H ₂ O (3-1)
When the Mn oxide is represented by LiMn ₂ O ₄ , 4LiMn ₂ O ₄ + 8HF → 3Mn ₂ O ₄ + 4LiF + 2MnF ₂ + 4H ₂ O. (3-2)
That is, water present in the secondary battery is a major cause of manganese elution.

  The phosphate first captures water in the following formulas (4-1) to (4-3) or hydrofluoric acid in the following formulas (5-1) to (5-3). Since the generated phosphoric acid content itself has a small function of decomposing and eluting manganese in the lithium manganese composite oxide powder, elution of manganese can be suppressed. Water is not regenerated.

Li ₃ PO ₄ + H ₂ O → Li ₂ HPO ₄ + LiOH (4-1)
Li ₃ PO ₄ + 2H ₂ O → LiH ₂ PO ₄ + 2LiOH (4-2)
Li ₃ PO ₄ + 3H ₂ O → H ₃ PO ₄ + 3LiOH (4-3)
Li ₃ PO ₄ + HF → Li ₂ HPO ₄ + LiF (5-1)
Li ₃ PO ₄ + 2HF → LiH ₂ PO ₄ + 2LiF (5-2)
Li ₃ PO ₄ + 3HF → H ₃ PO ₄ + 3LiF (5-3)
Even when lithium phosphate is simply added, the PO ₄ concentration in the electrolyte solution becomes high, so that the reaction formula (2) becomes difficult to proceed, the decomposition of LiPF ₆ is suppressed, and the hydrofluoric acid concentration in the battery decreases. However, in the secondary battery, the potential at the particle interface changes due to charge / discharge, and the influence of the state of the interface is large. Therefore, as in the present invention, phosphate exists on the surface and inside of the secondary particle of the lithium manganese composite oxide powder. The effect is greater. It can be estimated that the presence of phosphate on the surface and inside of the secondary particles of the lithium manganese composite oxide powder decreases the reactivity with the electrolyte and the electrolyte and further improves the durability.
Subsequently, the manufacturing method of the positive electrode using the lithium manganese complex oxide powder of this invention is demonstrated.

  (1) As a constituent material of the positive electrode, lithium manganese composite oxide powder is used as a positive electrode active material, two types of graphite and amorphous carbon are used as a conductive additive, and polyvinylidene fluoride (PVdF) is used as a binder. be able to.

(2) About the conductive assistant, the energy density of the positive electrode becomes higher when the proportion is made as small as possible and the proportion of the active material is made as high as possible. Therefore, the conductive auxiliary agent may have a particle size as small as possible, and a minimum ratio that can sufficiently bring out the battery performance of the active material. Although it depends on the particle size of the positive electrode active material and the conductive auxiliary agent, in the case of the lithium manganese composite oxide, the ratio of the conductive auxiliary agent is 4 to 6% by mass, and sufficient battery performance can be obtained. Even if the proportion of the conductive auxiliary exceeds 6% by mass, the energy density is rarely increased, but rather, the mixture density is lowered by increasing the proportion of the conductive auxiliary having a true density of about 2.2 g / cm ^3. In addition, the energy density per volume is reduced.

  (3) It is necessary to add the binder at such a rate that the active material does not peel from the aluminum current collector even when the lithium ion secondary battery is repeatedly charged and discharged. Further, the binder PVdF is a resin that does not have electrical conductivity, and increasing the ratio also causes an increase in resistance. The ratio of the binder depends on the particle size of the positive electrode active material and the conductive additive, but in the case of the lithium manganese composite oxide, it is sufficient to set the ratio of the binder to 3 to 4% by mass. Wearability is obtained. On the other hand, if the proportion of the binder exceeds 4% by mass, the increase in resistance causes a decrease in energy density.

  For the reasons (1) to (3), the proportion of the conductive auxiliary agent constituting the positive electrode using the lithium manganese composite oxide was set to 6% by mass or less, and the ratio of the binder was set to 4% by mass or less.

  Hereinafter, effects of the present invention will be described in detail based on examples (invention examples) and comparative examples. However, the present invention is not limited to these examples.

Example 1
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content to add 0.025% by mass of boron after calcination, and mixed again. Here, the manganese oxide was electrolytic manganese dioxide (MnO ₂ ), which was prepared by premixing manganese oxide having an average particle size of 5 μm and 15 μm manganese oxide in a mass ratio of 3 to 7.

  The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder. The obtained powder was measured with a particle size distribution measuring device by a laser diffraction / scattering method, a trade name of Microtrac HRAx100 of Nikkiso Co., Ltd. The result is shown in FIG. As shown in the particle size distribution of the spinel type lithium manganese composite oxide powder in FIG. 1, the particle size distribution of the spinel type lithium manganese composite oxide powder has two frequency peaks, and the first frequency peak is at the top of 5.5 μm. The second frequency peak is at the top of 14.3 μm, the height of the second peak is 3.4 times the height of the first peak, and all of the powder is 2.0 μm to 45.0 μm Confirmed to be in the range.

  In the examples and comparative examples described below, the particle size distribution was measured in the same manner. The results are shown in FIGS. 2 to 16 for Examples 2 to 16, and FIGS. 17 to 22 for Comparative Examples 1 to 6, respectively.

(Example 2)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. After dry-mixing with a precision mixer, a 2% by mass boric acid aqueous solution is calculated from the pure Mn content so that it becomes 0.02% by mass after calcination as boron, and further a 15% by mass ammonium dihydrogen phosphate aqueous solution. Was added as phosphate (PO ₄ ) so as to be 0.6% by mass of the whole after firing and mixed again. Here, the manganese oxide was electrolytic manganese dioxide (MnO ₂ ), which was prepared by premixing manganese oxide having an average particle size of 5 μm and 15 μm manganese oxide in a mass ratio of 3 to 7. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Examples 3 to 5)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content to add 0.025% by mass of boron after calcination, and mixed again. Here, the manganese oxide was electrolytic manganese dioxide (MnO ₂ ), which was prepared by premixing manganese oxide having an average particle size of 5 μm and manganese oxide having a particle diameter of 15 μm at a mass ratio shown in Table 1. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Examples 6 and 7)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. Dry-mix with a precision mixer, and then calculate a 2% by weight boric acid aqueous solution from the pure Mn amount so that it becomes 0.020% by weight of the total after firing as boron, and further a 15% by weight ammonium dihydrogen phosphate aqueous solution. Was added as phosphate (PO ₄ ) so as to be 0.6% by mass of the whole after firing and mixed again. Here, the manganese oxide was electrolytic manganese dioxide (MnO ₂ ), which was prepared by premixing manganese oxide having an average particle size of 5 μm and manganese oxide having a particle diameter of 15 μm at a mass ratio shown in Table 1. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 8)
Lithium carbonate, manganese oxide, and aluminum hydroxide were weighed so as to have the composition shown in Table 1. After dry-mixing with a precision mixer, 2% by weight boric acid aqueous solution is calculated from the pure Mn content, so that it becomes 0.030% by weight of the total after baking as boron, and further 15% by weight ammonium dihydrogen phosphate aqueous solution. Was added as phosphate (PO ₄ ) so as to be 0.9% by mass of the whole after firing and mixed again. Here, the manganese oxide was Mn ₃ O ₄ , and a manganese oxide having an average particle diameter of 6 μm and a manganese oxide of 14 μm premixed at a mass ratio of 3 to 7 was used. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

Example 9
Lithium carbonate, manganese oxide, aluminum hydroxide, cobalt oxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. Dry-mix with a precision mixer, and then calculate a 2% by weight boric acid aqueous solution from the pure Mn amount so that it becomes 0.020% by weight of the total after firing as boron, and further a 15% by weight ammonium dihydrogen phosphate aqueous solution. Was added as phosphate (PO ₄ ) so as to be 0.9% by mass of the whole after firing and mixed again. Here, the manganese oxide was Mn ₃ O ₄ , and a manganese oxide having an average particle diameter of 6 μm and a manganese oxide of 14 μm premixed at a mass ratio of 3 to 7 was used. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 10)
Lithium carbonate, manganese oxide, aluminum hydroxide, cobalt oxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. After dry-mixing with a precision mixer, a 15% by mass aqueous solution of ammonium dihydrogen phosphate was added as phosphate (PO ₄ ) so as to be 0.6% by mass after firing and mixed again. Here, the manganese oxide was Mn ₃ O ₄ , and a manganese oxide having an average particle diameter of 6 μm and a manganese oxide of 14 μm premixed at a mass ratio of 3 to 7 was used. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 11)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium phosphate were weighed so as to have the composition shown in Table 1. Magnesium phosphate was added as a phosphate (PO ₄ ) so as to be 0.4% by mass after firing. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content, and added as boron so that it would be 0.020% by mass of the total after firing, and mixed again. Here, the manganese oxide was Mn ₃ O ₄ , and a manganese oxide having an average particle diameter of 6 μm and a manganese oxide of 14 μm premixed at a mass ratio of 3 to 7 was used. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 12)
Lithium carbonate, manganese oxide, aluminum hydroxide, magnesium oxide, and lithium phosphate were weighed so as to have the composition shown in Table 1. Lithium phosphate was added as a phosphate (PO ₄ ) so as to be 0.6% by mass after firing. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content, and added as boron so that it would be 0.020% by mass of the total after firing, and mixed again. Here, the manganese oxide was Mn ₃ O ₄ , and a manganese oxide having an average particle diameter of 6 μm and a manganese oxide of 14 μm premixed at a mass ratio of 3 to 7 was used. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 13)
Lithium carbonate, manganese oxide, aluminum hydroxide, magnesium oxide, and aluminum phosphate were weighed so as to have the composition shown in Table 1. Aluminum phosphate was added as a phosphate (PO ₄ ) so as to be 0.6% by mass after firing. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content, and added as boron so that it would be 0.020% by mass of the total after firing, and mixed again. Here, the manganese oxide was Mn ₃ O ₄ , and a manganese oxide having an average particle diameter of 6 μm and a manganese oxide of 14 μm premixed at a mass ratio of 3 to 7 was used. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 14)
Lithium carbonate, manganese oxide to which aluminum was added, and magnesium oxide were weighed so as to have the composition shown in Table 1. After dry-mixing with a precision mixer, a 2% by mass boric acid aqueous solution is calculated from the pure Mn content so that it becomes 0.025% by mass after calcination as boron, and a further 15% by mass ammonium dihydrogen phosphate aqueous solution. Was added as phosphate (PO ₄ ) so as to be 0.6% by mass of the whole after firing and mixed again. Here, the manganese oxide to which aluminum is added is a premixed mixture of electrolytic manganese dioxide (MnO ₂ ) having an average particle size of 5 μm and electrolytic manganese dioxide of 15 μm at a mass ratio of 3 to 7, and then a predetermined amount of hydroxide. A powder prepared by adding aluminum and precision mixing was subjected to a heat treatment at 870 ° C. for 8 hours to obtain Mn ₂ O ₃ . The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 15)
Lithium carbonate, manganese oxide to which aluminum was added, and magnesium oxide were weighed so as to have the composition shown in Table 1. Dry-mix with a precision mixer, and then calculate a 2% by weight boric acid aqueous solution from the pure Mn amount so that it becomes 0.020% by weight of the total after firing as boron, and further a 15% by weight ammonium dihydrogen phosphate aqueous solution. Was added as phosphate (PO ₄ ) so as to be 0.6% by mass of the whole after firing and mixed again. Here, the manganese oxide added with aluminum is prepared by premixing Mn ₃ O ₄ having an average particle diameter of 6 μm and Mn ₃ O ₄ having a particle diameter of 14 μm at a mass ratio of 3 to 7, and then adding a predetermined amount of aluminum hydroxide. In addition, the precisely mixed powder was heat treated at 870 ° C. for 8 hours to obtain Mn ₂ O ₃ . The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized to obtain a spinel type lithium manganese composite oxide powder.

(Example 16)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content to add 0.025% by mass of boron after calcination, and mixed again. Here, Mn ₃ O ₄ having an average particle size of 14 μm was used as the manganese oxide. The partially granulated mixed powder is fired in air at 800 ° C. for 20 hours, pulverized using a jet mill, resized in air at 680 ° C. for 20 hours, and then sized to spinel lithium manganese composite An oxide powder was obtained.

(Comparative Example 1)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 2. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content to add 0.025% by mass of boron after calcination, and mixed again. Here, electrolytic manganese dioxide (MnO ₂ ) having an average particle size of 15 μm was used as the manganese oxide. The partially granulated mixed powder was fired in the air at 800 ° C. for 20 hours, crushed and sized, and a spinel type lithium manganese composite oxide powder was synthesized as Comparative Example 1.

(Comparative Examples 2 to 5)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 2. Dry-mix with a precision mixer, and then calculate a 2% by weight boric acid aqueous solution from the pure Mn amount so that it becomes 0.020% by weight of the total after firing as boron, and further a 15% by weight ammonium dihydrogen phosphate aqueous solution. Was added as phosphate (PO ₄ ) so as to be 0.6% by mass of the whole after firing and mixed again. Here, the manganese oxide is Mn ₃ O ₄ listed in Table 2, electrolytic manganese dioxide (MnO ₂ ), or manganese oxide to which aluminum is added. In Comparative Example 2, Mn ₃ O ₄ having an average particle size of 14 μm is used. In Comparative Example 3, MnO ₂ having an average particle diameter of 5 μm and MnO ₂ having an average particle diameter of 15 μm were premixed at a mass ratio of 4 to 6, and MnO ₂ having an average particle diameter of 15 μm was used in Comparative Example 4. after preliminarily mixed at a ratio of 15: 85 at the Mn ₂ O ₃ and 14μm of Mn ₂ O ₃ of Comparative example 5 in average particle size 6μm mass ratio, the powder was refined mixture by adding a predetermined amount of aluminum hydroxide, 870 A heat treatment was performed at 8 ° C. for 8 hours to obtain Mn ₂ O ₃ . The partially granulated mixed powder was baked at 800 ° C. for 20 hours in the air, pulverized and sized to synthesize comparative examples 2 to 5 of spinel type lithium manganese composite oxide powder.

(Comparative Example 6)
Lithium carbonate, manganese oxide, aluminum hydroxide, and magnesium oxide were weighed so as to have the composition shown in Table 1. After dry mixing with a precision mixer, a 2% by mass boric acid aqueous solution was calculated from the pure Mn content, and added as boron so that it would be 0.020% by mass of the total after firing, and mixed again. Here, Mn ₃ O ₄ having an average particle size of 14 μm was used as the manganese oxide. The partially granulated mixed powder is fired at 800 ° C. for 20 hours in the air, pulverized using a jet mill, re-fired at 400 ° C. for 10 hours in the air, and then sized and spinel type lithium manganese composite A comparative example 6 of oxide powder was synthesized.

(Preparation of positive electrode)
A positive electrode was produced using the lithium manganese composite oxide powder synthesized in the above Examples and Comparative Examples as the positive electrode active material. Timcal's trade name KS6 and Super-P were used as the conductive assistant, and Kureha's trade name KF polymer (a solution in which PVdF was dissolved in N-methylpyrrolidone) was used as the binder. In a weight ratio, “positive electrode active material: KS6: Super-P: binder” was weighed at a ratio of “90: 5: 1: 4”, NMP was added, and a slurry was prepared using a homogenizer. The obtained slurry was applied to an aluminum current collector having a thickness of 20 μm, dried, punched out to a diameter of 11 mm, pressurized with a hand press using a load of 4 MPa, and dried at 120 ° C. under reduced pressure to produce a positive electrode. .

(Positive electrode mixture density)
About the positive electrode using the lithium manganese complex oxide powder synthesize | combined in the said each Example and comparative example, the mixture density was measured. The measurement results are shown in Table 3.

As shown in the examples of the present invention, the mixture density of the electrode is 2 when the height of the second peak is in the range of 2.5 to 5.0 times the height of the first peak and the press load is 4 MPa. It was 0.75 g / cm ³ or more, and a high mixture density was shown relative to the comparative example.

(Coin cell assembly)
In the positive electrode, negative electrode, electrolyte solution, and separator of the examples and comparative examples, metal lithium was cut out in a disc shape, and ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7. Using a solution of 1 mol / l of solute LiPF ₆ in a solvent and a microporous membrane made of polypropylene, a coin type battery CR2032 type (diameter 20 mm, height 3.2 mm) was assembled, and battery evaluation measurement was performed.

(Battery evaluation)
The initial capacity was measured in a constant temperature bath at 25 ° C. by charging and discharging the current density to 10 mAh / g, 4.3 V to a constant current, and then to a constant current to 3.0 V. The energy density per volume was calculated by multiplying the discharge capacity, average discharge voltage, and 94% of the positive electrode mixture density. The cycle characteristics were repeated in a constant temperature bath of 60 ° C. with a charge / discharge current density of 50 mAh / g and a voltage range of 3.0 to 4.3 V, and the capacity maintained from the discharge capacity after 100 times the initial discharge capacity. The rate was calculated. The results are shown in Table 4.

(Dissolution test)
About the spinel type lithium manganese complex oxide powder obtained in Examples 1-16 and Comparative Examples 1-6, the elution test was done as follows.

  5.00 g of each spinel-type lithium manganese composite oxide powder was weighed individually in a sealable fluororesin container having an internal volume of 100 ml, which had been washed and dried in advance, and used in the above (coin cell assembly, evaluation) 25 ml of the same electrolyte solution and 0.03% by mass of water were intentionally added, and after sealing, stored in a 60 ° C. constant temperature bath for 7 days. Thereafter, the analysis of the Mn concentration eluted in the electrolytic solution was performed by ICP emission spectroscopy. The measurement results are shown in Table 4.

As shown in Table 4, in the embodiment of the present invention shows a value energy density exceeding 1080mWh / cm ³ per unit volume, and 1050mWh / cm less than ³ Comparative Example than at least 3% or more, up to eight. 7% (Comparison between Example 1 and Comparative Example 2) The energy density was high. The particle size distribution measured by the laser diffraction / scattering method has two frequency peaks, the first frequency peak has a peak between 4.0 and 7.0 μm, and the second frequency peak is 10 The peak has a peak between 0.0 and 17.0 μm, the height of the second peak is in the range of 2.5 to 5.0 times the height of the first peak, and all of the powder is 2. By making it fall within the range of 0 μm to 45.0 μm, the energy density per volume of the lithium manganese composite oxide can be increased.

In the examples of the present invention, the total amount of phosphate in the range of 0.4% to 0.9% by mass with PO ₄ as PO ₄ was used. It was confirmed that a lithium manganese composite oxide in which the Mn elution amount was lower than 5, the energy density per volume was high, and the manganese elution amount was small was obtained. In Example 10 in which no boron was added, the cycle characteristics (capacity retention rate) were inferior. Furthermore, in Comparative Example 6 in which a powder of 2.0 μm or less remained, the Mn elution amount was large.

  From the above examples, according to the present invention, a positive electrode having a high energy density per volume can be obtained, the manganese elution amount is small, and the spinel type for non-aqueous electrolyte secondary batteries excellent in cycle characteristics (durability) is obtained. It was confirmed that lithium manganese composite oxide powder was obtained.

Claims (5)

General formula: Li _{1 + x} M _y Mn _2-xy O ₄ (M is one or more metal elements selected from Al, Mg and Co, and x is in the range of 0 ≦ x ≦ 0.33. Y takes a range of 0 ≦ y ≦ 0.2.) The spinel-type lithium-manganese composite oxide represented by (2), and the particle size distribution measured by the laser diffraction / scattering method has two frequency peaks. The first frequency peak has an apex between 4.0 and 7.0 μm, the second frequency peak has an apex between 10.0 and 17.0 μm, and the second peak Spinel type lithium manganese, characterized in that the height of the powder ranges from 2.5 to 5.0 times the height of the first peak, and all of the powder falls within the range of 2.0 to 45.0 μm Composite oxide powder. The spinel-type lithium-manganese composite oxide powder, wherein the secondary particle surface and inside the phosphate to claim 1, characterized in that in total containing 0.1 wt% to 2.0 wt% as PO ₄ Spinel type lithium manganese composite oxide powder.   The spinel-type lithium-manganese composite oxide powder according to claim 2, wherein the phosphate is any one of aluminum phosphate, magnesium phosphate, lithium phosphate, ammonium dihydrogen phosphate, or a combination thereof.   Lithium compound, manganese compound, other metal M compound (metal M is one or more metal elements selected from Al, Mg and Co), boric acid and phosphate are mixed, at 600 to 900 ° C. The method for producing a spinel-type lithium manganese composite oxide powder according to any one of claims 1 to 3, which is fired, crushed and sized. It consists of the spinel type lithium manganese complex oxide powder according to any one of claims 1 to 3, a conductive additive and a binder, the proportion of the conductive material is 6 mass% or less, and the proportion of the binder is 4 mass. % Lithium secondary battery, wherein the mixture density of the positive electrode at a press load of 4 MPa is 2.75 g / cm ³ or more and 2.87 g / cm ³ or less. Positive electrode.

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