JP5605867B2 - Positive electrode for secondary battery and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a positive electrode for a positive electrode of a secondary battery and a lithium secondary battery using the same, and more particularly to a lithium secondary battery having a long life and little deterioration in capacity even when rapid charging is performed.

  Lithium secondary batteries have the feature of being small and have a large capacity, and are widely used as power sources for mobile phones, notebook computers and the like. The lithium secondary battery described here is a battery in which a positive electrode and a negative electrode are each made of a material capable of occluding and releasing lithium or a material that forms an alloy with lithium for the positive electrode and the negative electrode.

As a positive electrode active material of a lithium secondary battery, a material using a layered structure such as lithium cobalt composite oxide, lithium nickel oxide, lithium nickel cobalt manganese composite oxide or the like is known. These materials have been widely used as batteries for small portable devices because the energy density of the battery can be increased. However, since the crystal stability of the active material in a charged state is poor, a safety measure for the battery is necessary. Further, when a large battery is used, further safety measures are required.
On the other hand, a lithium manganese composite oxide having a spinel structure typified by lithium manganate LiMn ₂ O ₄ is known. This compound can provide a battery having higher thermal stability during charging and higher safety than the material having the layered structure described above, and is composed of elements that are abundant in resources, such as energy density. Has the problem of small.
In view of this, it has been proposed to introduce various metal elements into a spinel-structure lithium manganese composite oxide typified by lithium manganate to increase the average charge / discharge voltage, energy density, and the like.

Also, depending on the mode of use, batteries such as mobile phones, notebook computers, electric cars, electric bicycles, electric bikes, uninterruptible power supplies, electric tools, digital cameras, and portable music equipment are required to shorten the charging time. It was. However, although the convenience of the battery can be improved by the rapid charging, the battery is likely to deteriorate, and the battery capacity may be significantly reduced by the rapid charging.
In order to solve these problems, it has been proposed to improve the life by mixing lithium manganate and lithium nickelate (see, for example, Patent Document 1 and Patent Document 2). It has also been proposed to improve cycle characteristics by mixing a compound in which manganese in lithium manganate is substituted with another metal element. (For example, refer to Patent Document 3).

Japanese Patent No. 2996234 Japanese Patent No. 3120789 Japanese Patent No. 3573899

  It is an object of the present invention to provide a positive electrode for a lithium battery that has a large capacity density, has little deterioration in discharge capacity even after rapid charging, and can be used for a long period of time, and a lithium secondary battery using the positive electrode.

In the present invention, 10 to 70 parts by mass of a first positive electrode active material , which is an oxide of two types of spinel structures having lithium and manganese as essential components and different types of constituent elements, A positive electrode comprising 10 to 60 parts by mass of a substance and 20 to 40 parts by mass of a third positive electrode active material containing lithium and nickel and having a layered structure; The second positive electrode active material has a chemical formula 1: Li _a1 Mn _2-x1 Ml _x1 O ₄ (Ml is at least one of Li, B, Mg, Al, Fe, Co, Ni, and 0 <a1 ≦ 1, 0 <x1 <0.3) When the M1 of the first positive electrode active material is M11, the M11 includes aluminum, and the second positive electrode active material is represented by the following formula: When M1 of the positive electrode active material is M12, the M1 Wherein boron, magnesium, iron, cobalt, at least one of nickel, the third cathode active material, chemical formula _{3: Li a3 Ni 1-x3} M3 x3 O 2 (M3 is Li, Co, Mn, Mg And a positive electrode which is a lithium nickel composite oxide which is at least one of Al and represented by 0 <a3 ≦ 1, 0 <x3 <0.7).
The composition ratio of Al contained in M11 is 0.015 or more and 0.25 or less, and the composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel contained in M12 is 0.015 or more, 0 The positive electrode is 15 or less.
The M11 further contains Li, the composition ratio of Li contained in the M11 is 0.05 or more and 0.1 or less, the M12 further contains Li, and the composition ratio of Li contained in the M12 is 0.02 or more. The positive electrode is 0.1 or less.
In the positive electrode, the composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel included in M12 is 0.02 or more and 0.12 or less.

Lithium and manganese as essential components, a first positive electrode active material 70 parts by mass 10 parts by mass of an oxide of different types two kinds of spinel structure of elements constituting the second 10 mass a positive electrode active material and 60 parts by mass parts, a positive electrode containing a from the third cathode active material 20 parts by weight of an oxide of a layered structure containing lithium and nickel 40 parts by mass, the first, second positive electrode The active material is represented by the chemical formula 1: Li _a1 Mn _2-x1 M1 _x1 O ₄ (M1 is at least one of Li, B, Mg, Al, Fe, Co, Ni, and 0 <a1 ≦ 1, 0 < x1 <0.3) is a lithium manganese-containing composite oxide, and when M1 of the first positive electrode active material is M11, M11 contains aluminum, and M1 of the second positive electrode active material Is M12, M12 is boron, Magnesium, including iron, cobalt, at least one of nickel, the third cathode active material, chemical formula _{3: Li a3 Ni 1-x3} M3 x3 O 2 (M3 is Li, Co, Mn, Mg, the Al A lithium secondary battery having at least one of them, a positive electrode that is a lithium nickel composite oxide represented by 0 <a3 ≦ 1, 0 <x3 <0.7), and a negative electrode that occludes and releases lithium. is there.
The composition ratio of Al contained in M11 is 0.015 or more and 0.25 or less, and the composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel contained in M12 is 0.015 or more, 0 The lithium secondary battery is 15 or less.
The M11 further contains Li, the composition ratio of Li contained in the M11 is 0.05 or more and 0.1 or less, the M12 further contains Li, and the composition ratio of Li contained in the M12 is 0.02 or more. The lithium secondary battery is 0.1 or less.
In the lithium secondary battery, the composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel included in the M12 is 0.02 or more and 0.12 or less.

  The lithium secondary battery using the positive electrode active material of the present invention can prolong the life of the battery, has good quick charge characteristics, and has quick charge characteristics even in batteries after long-term use. It is possible to provide a lithium secondary battery that is excellent in.

FIG. 1 is a cross-sectional view illustrating an embodiment of the lithium secondary battery of the present invention. FIG. 2 is a diagram illustrating an X-ray diffraction pattern of a spinel structure sample and lithium manganate according to an example. FIG. 3 is a diagram for explaining an X-ray diffraction pattern of a layered structure sample and lithium cobalt oxide of an example.

  The present invention includes lithium and manganese as essential constituents, first and second positive electrode active materials that are oxides of two types of spinel structures having different constituent types, and a layered structure containing lithium and nickel It has been found that it is possible to produce a lithium secondary battery having good quick charge characteristics and a long life by blending each of the third positive electrode active materials, which are oxides of the above, at a specific ratio. .

The first positive electrode active material and the second positive electrode active material preferably contain 5 to 75 parts by mass, and the third positive electrode active material which is an oxide having a layered structure containing lithium and nickel is used. What contains 45 mass parts from a mass part is preferable, and it is more preferable that the 1st positive electrode active material and the 2nd positive electrode active material are the range of 10 mass parts to 70 mass parts.
When the first positive electrode active material and the second positive electrode active material are less than 5 parts by mass, the life is shortened, which is not preferable. When the amount is more than 75 parts by mass, the life is shortened, which is not preferable. The first positive electrode active material and the second positive electrode active material are more preferably in the range of 10 parts by mass to 70 parts by mass.

  The third positive electrode active material preferably contains 15 to 45 parts by mass, more preferably 20 to 40 parts by mass. When the amount is less than 15 parts by mass, the life is shortened, which is not preferable. When the amount is more than 45 parts by mass, the life is shortened, which is not preferable.

As the first and second positive electrode active materials, chemical formula 1: Li _a1 Mn _2-x1 M1 _x1 O ₄ (M1 is at least one of Li, B, Mg, Al, Fe, Co, Ni, It is a lithium manganese-containing composite oxide represented by 0 <a1 ≦ 1, 0 <x1 <0.3), and each constituent element is different.
In the positive electrode active materials having the first and second spinel structures, a1 varies depending on the insertion and release of lithium due to charge / discharge of the battery, but is preferably a value of 1 or less.
Further, x1 is preferably 0.01 or more and 0.3 or less, more preferably 0.015 or more and 0.25 or less, and if it is less than 0.01, there is no effect, and it is more than 0.3 If it is large, the capacity decreases, which is not preferable.

When M1 is Al, x1 is preferably 0.01 or more and 0.3 or less, more preferably 0.015 or more and 0.25 or less. When the amount is less than 0.01, the effect of addition is not obtained, and when the amount is more than 0.3, the capacity decreases, which is not preferable.
When M1 is Mg, x1 is preferably 0.01 or more and 0.2 or less, more preferably 0.015 or more and 0.15 or less. When the amount is less than 0.01, the effect of addition is not obtained, and when the amount is more than 0.2, the capacity decreases, which is not preferable.
When M1 is B, Fe, Ni, or Co, x1 is preferably 0.01 or more and 0.2 or less, respectively. More preferably, it is 0.015 or more and 0.18 or less. When the amount is less than 0.01, the effect of addition is not obtained, and when the amount is more than 0.2, the capacity decreases, which is not preferable.

The third positive electrode active material is represented by the chemical formula 3: Li _a3 Ni _1-x3 M3 _x3 O ₂ (M3 is at least one of Li, Co, Mn, Mg, Al, and 0 <a3 ≦ 1, It is a lithium nickel composite oxide represented by 0 <x3 <0.7).
a3 varies depending on the insertion and removal of lithium due to charging and discharging of the battery, but is preferably smaller than 1.
Further, x3 is preferably 0.01 or more and 0.68 or less, more preferably 0.01 or more and 0.5 or less, and when it is less than 0.1, there is no effect, and more than 0.68. If it is large, the charge / discharge rate characteristics may be inferior.

A method for manufacturing a positive electrode active material of an oxide having a spinel structure as the first and second positive electrode active materials will be described.
As a raw material for preparation, lithium carbonate, lithium hydroxide, lithium oxide, lithium nitrate, lithium sulfate, or the like can be used as the lithium raw material.
Among these, lithium salts such as lithium carbonate and lithium hydroxide are highly reactive with the transition metal raw material, and the carbonate group and hydroxyl group are volatilized in the form of carbon dioxide, water, etc. during firing to the active material produced. It is preferable because it does not have an adverse effect.
As the manganese raw material, various manganese oxides such as electrolytic manganese dioxide, manganese trioxide, and manganese trioxide, manganese carbonate, manganese sulfate, and the like can be used.
Moreover, magnesium hydroxide etc. can be used as a magnesium raw material. Aluminum hydroxide, aluminum oxide, etc. can be used as the aluminum raw material. Boron oxide or the like can be used as the boron raw material. As the cobalt raw material, cobalt sesquioxide, cobalt tetroxide, cobalt hydroxide, cobalt carbonate, cobalt sulfate and the like can be used. Moreover, iron hydroxide, iron sesquioxide, etc. can be used as an iron raw material. As the nickel raw material, nickel oxide, nickel hydroxide, nickel sulfate, nickel nitrate or the like can be used.

  These raw materials are weighed so as to have a desired metal element composition ratio, and pulverized and mixed by a ball mill or the like. An active material is obtained by baking the mixed powder at a temperature of 500 ° C. to 1200 ° C. in air or oxygen. The firing temperature is preferably a high temperature for diffusing each element, but if the firing temperature is too high, oxygen vacancies are generated, or when used as a battery active material, it adversely affects the characteristics. There is a case. For these reasons, the firing temperature is desirably about 500 ° C. to 900 ° C. Further, it is preferable to perform firing in an oxygen atmosphere so as not to cause oxygen deficiency.

The specific surface area of the obtained active material is desirably 0.01 m ² / g or more and 10 m ² / g or less, preferably 0.1 m ² / g or more and 3 m ² / g or less. The larger the specific surface area, the more binders are required, which is disadvantageous in terms of the capacity density of the electrode. If the specific surface area is too small, the ionic conductivity between the electrolytic solution and the active material may be reduced. . The average particle size of the active material is preferably 0.1 μm or more and 70 μm or less, and more preferably 1 μm or more and 30 μm or less. If the particle diameter is larger than 70 μm, uneven portions such as irregularities may occur in the electrode layer during electrode deposition. When it is smaller than 0.1 μm, the binding property of the electrode formed on the current collector may be lowered.

A method for producing a positive electrode active material having a layered structure as the third positive electrode active material will be described. As a raw material for preparation, lithium carbonate, lithium hydroxide, lithium oxide, lithium nitrate, lithium sulfate, or the like can be used as the lithium raw material.
As the nickel raw material, nickel oxide, nickel hydroxide, nickel sulfate, nickel nitrate or the like can be used. As the cobalt raw material, cobalt hydroxide, cobalt sesquioxide, cobalt tetroxide, cobalt sulfate and the like can be used. Aluminum hydroxide or the like can be used as the aluminum raw material. As the manganese raw material, various manganese oxides such as electrolytic manganese dioxide, manganese trioxide, and manganese trioxide, manganese carbonate, manganese sulfate, and the like can be used. Magnesium hydroxide can be used as the magnesium raw material.

  These raw materials are weighed so as to have a desired metal element composition ratio, and pulverized and mixed by a ball mill or the like. An active material is obtained by baking the mixed powder at a temperature of 500 ° C. to 1200 ° C. in air or oxygen. The firing temperature is preferably a high temperature for diffusing each element, but since the powder may be aggregated, there is a practical problem even if the firing temperature is too high. Therefore, the firing temperature is preferably about 500 ° C to 1000 ° C.

The specific surface area of the obtained active material is desirably 0.01 m ² / g or more and 10 m ² / g or less, preferably 0.1 m ² / g or more and 3 m ² / g or less. The larger the specific surface area, the more binder is necessary, which is disadvantageous in terms of the capacity density of the electrode. On the other hand, if the specific surface area is too small, ion conduction between the electrolytic solution and the active material may be reduced. The number average particle size of the active material is preferably 0.1 μm or more and 70 μm or less, and more preferably 1 μm or more and 30 μm or less. If the number average particle size is large, uneven portions such as irregularities may occur in the electrode layer during electrode deposition. If it is small, the binding property of the deposited electrode may be lowered.

Next, a method for manufacturing the positive electrode will be described.
The obtained active material is mixed with a conductivity-imparting material and a binder and applied onto a current collector to form an electrode. Examples of the conductivity-imparting material include carbon materials such as acetylene black, carbon black, graphite, or fibrous carbon, metal materials such as aluminum, and conductive oxide powders. As the binder, polyvinylidene fluoride, an acrylic polymer, an imide polymer, or the like is used. As the current collector, an aluminum foil or the like that is a stable metal at the operating potential of the positive electrode of the battery can be used.

The addition amount of the conductivity-imparting material to be blended in the positive electrode active material is preferably about 0.5 to 30% by mass with respect to the total amount of the active material, the conductivity-imparting material and the binder. Is preferably 1 to 10% by mass. If the ratio between the conductivity-imparting material and the binder is small, the electron conductivity may be inferior, or the problem of electrode peeling may occur.
On the other hand, since the capacity per battery mass may be small when the ratio of the conductivity-imparting material and the binder is large, the ratio of the active material to the total amount of the active material, the conductivity-imparting material and the binder is 70. To 98 mass%. More preferably, it is 85-97 mass%.
If the ratio of the active material is too small, it is disadvantageous in terms of the energy density of the battery. If the proportion of the active material is too large, the proportion per mass of the conductivity-imparting material and the binder becomes low, which is disadvantageous because it tends to be inferior in electronic conductivity or easily peeled off from the electrode.

The density of the electrode applied on the current collector is preferably 1 g / cm ³ or more and 4.5 g / cm ³ or less. If the density is too high, the electrolytic solution is difficult to enter the gaps between the electrodes, so that the amount of lithium ions transferred is small, and the rate characteristics of the battery may be small. Moreover, if the electrode density is too small, the energy density of the battery may decrease. For this reason, it is more preferably 2 g / cm ³ or more and 4 g / cm ³ or less.

  In addition to the first, second, and third positive electrode active materials, the positive electrode active material of the present invention includes spinel structure materials, layered structure materials, olivine structure materials, and other composites having other compositions. An oxide may be included.

Examples of the negative electrode active material include carbon materials such as graphite or amorphous carbon that occlude and release lithium, materials that form an alloy with lithium such as metallic lithium, silicon, tin, and aluminum, silicon oxide, and materials other than silicon and silicon. Silicon composite oxide containing other metal elements, tin oxide, silicon composite oxide containing other metal elements other than tin and tin, composite oxide containing titanium such as Li ₄ Ti ₅ O _12, etc. Can be used. The negative electrode can be manufactured by the same method as the positive electrode, but a metal foil such as copper is preferably used for the current collector.

As an electrolytic solution that can be used in the lithium secondary battery of the present invention, a solution obtained by dissolving a supporting electrolyte in an aprotic organic solvent can be used.
Examples of aprotic solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl Linear carbonates such as carbonate (DEC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2- Chain ethers such as ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethyl ether Tylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2 -Use of aprotic organic solvents such as oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylates, or a mixture of two or more it can.
The electrolytic solution may be gelled by adding a polymerizable substance or the like. An ionic liquid composed of a cyclic ammonium cation and an anion may be used. Among these, from the viewpoint of conductivity and stability at high voltage, it is suitable to use a mixture of cyclic carbonate and chain carbonate.

As the supporting electrolyte to be blended in the electrolytic solution, LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiCH ₃ SO ₃ , LiC ₂ H ₅ SO ₃ , LiC ₃ H ₇ SO ₃ , lower aliphatic carboxylic acid, lithium carboxylate, chloro Examples thereof include lithium borane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, and LiF. The electrolyte concentration is, for example, 0.5 mol / l to 1.5 mol / l. If the concentration is too high, the density and the viscosity of the electrolyte increase. If the concentration is too low, the electrical conductivity of the electrolytic solution may decrease.

  The lithium secondary battery according to the present invention includes a positive electrode and a negative electrode laminated in a dry air or inert gas atmosphere via a separator, or after being rolled up, the lithium secondary battery is accommodated in a battery can or A battery can be manufactured by sealing with a film-like exterior material composed of a laminate with a metal foil.

As an example of the lithium secondary battery of the present invention, FIG. 1 shows a battery in which one each of a positive electrode and a negative electrode are arranged facing each other with a separator interposed therebetween and covered with a film-like exterior material.
The lithium secondary battery 1 includes a positive electrode 4 in which a positive electrode active material layer 3 is formed on a positive electrode current collector 2 and a negative electrode 7 in which a negative electrode active material layer 6 is formed on a negative electrode current collector 5 through a separator 8. The positive electrode conductive tab 9 connected to the positive electrode current collector 2 and the negative electrode tab 10 connected to the negative electrode current collector 5 were joined, and a polyethylene film and a polyester film were laminated on both surfaces of the aluminum foil. It is covered with a film-like exterior material 11 and sealed.
In the example shown in FIG. 1, an example having one positive electrode and one negative electrode has been described. However, a positive electrode and a negative electrode in which a plurality of positive electrodes and negative electrodes are stacked with a separator interposed therebetween. , A coin type, a square type, a cylindrical type, or the like, and a metal container can be used instead of the film-like exterior material.
Hereinafter, the present invention will be described with reference to examples and comparative examples of the present invention.

Example 1 and Comparative Example 1
Preparation of First Positive Electrode Active Material Sample 1-1 Lithium hydroxide, manganese dioxide, and aluminum hydroxide were weighed so as to have a predetermined metal element composition ratio, and these raw materials were pulverized and mixed in a mortar for 1 hour. The sample after mixing was fired in air at 900 ° C. for 12 hours. After firing, the sample was pulverized and mixed again, and then fired for the second time in oxygen at 700 ° C. for 12 hours. Then, coarse powder was removed with a sieve having a passing particle diameter of 50 μm to obtain a positive electrode active material of Sample 1-1 represented by LiMn _1.85 Li _0.1 Al _0.05 O ₄ . The specific surface area of the obtained powder was measured by gas adsorption measuring type specific surface area measuring apparatus (Yuasa Ionics Quantasorb), a 5 m ² / g from 0.1 m ² / g, number average particle diameter 0. The range was 5 to 40 μm. Further, measurement was performed with an X-ray diffractometer (RINT-2000 manufactured by Rigaku Corporation) using a voltage of 40 kV, a current of 50 mA, and CuKα rays, and the measurement results are shown in FIG. For comparison, FIG. 2B shows the measurement results of measuring LiMn ₂ O ₄ having a spinel structure under the same conditions. It was confirmed that the prepared sample 1-1 had a spinel structure.

Second Cathode Material Preparation of Sample 2-1 LiMn _1.85 Li _0.15 O _{4 in the same} manner as Sample 1-1, except that it was weighed so as to have a predetermined metal element composition ratio of lithium hydroxide and manganese dioxide. The positive electrode active material of sample 2-1 shown by this was prepared.

Preparation of Third Positive Electrode Active Material Sample 3-1 Lithium hydroxide, nickel hydroxide, cobalt oxide, and aluminum hydroxide were weighed so as to have a predetermined metal composition ratio. After these raw materials were pulverized and mixed in a mortar for 1 hour, the mixed sample was fired in air at 900 ° C. for 12 hours. After firing, the sample was pulverized and mixed again, and then fired for the second time in oxygen at 700 ° C. for 12 hours. Thereafter, the coarse powder was removed with a sieve having a particle diameter of 50 μm to obtain a positive electrode active material represented by LiNi _0.8 Co _0.15 Al _0.05 O ₂ .
When the specific surface area of the obtained powder was measured in the same manner as in Sample 1-1, it was 0.1 m ² / g to 5 m ² / g, and the number average particle diameter was in the range of 0.5 to 40 μm. Further, measurement was performed by X-ray diffraction measurement in the same manner as in Sample 1-1, and the result is shown in FIG. For comparison, FIG. 3B shows the measurement results of measuring LiCoO ₂ having a layered structure under the same conditions. It was confirmed that the prepared sample 3-1 had a layered structure.

Production of Positive Electrode The obtained first positive electrode active material: Sample 1-1, second positive electrode active material: Sample 2-1, third positive electrode active material: Sample 3-1, And dispersed in a solution of polyvinylidene fluoride (PVDF) dissolved in a carbon material, N-methylpyrrolidone (NMP), which is a conductivity-imparting material, to form a slurry. Conductive carbon black (Ketjen Black) was used as the conductivity imparting material. The mass ratio of the active material, the conductivity-imparting material, and the binder was 90/6/4. The slurry was applied on a current collector made of an aluminum foil having a thickness of 20 μm.
The capacity per area of the electrode was adjusted so that the initial charge capacity was 2.0 mAh / cm ² . Then, it was dried in vacuum for 12 hours to obtain an electrode material. The electrode was cut into 20 mm length and 20 mm width. Then, it pressure-molded at 3 t / cm < ² >.

Preparation of negative electrode Using graphite as an active material, a binder solution in which PVDF is dissolved in NMP, and carbon black as a conductivity-imparting material are mixed to form a slurry, and then a positive electrode using a 10 μm thick copper foil as a current collector It applied similarly to the slurry. The capacity per area of the electrode was adjusted so that the initial charge capacity was 2.4 mAh / cm ² . Then, it was dried in vacuum for 12 hours to obtain an electrode material. It was used. The negative electrode was cut into a length of 22 mm and a width of 22 mm. Then, it pressure-molded at 1 t / cm < ² >.

Preparation of Sample Battery A positive electrode and a negative electrode were placed opposite to each other with a polypropylene separator interposed therebetween, an aluminum tab was bonded to the positive electrode current collector, and a nickel tab was bonded to the negative electrode current collector.
After both sides of the aluminum foil are heat-sealed with a film-like exterior material in which polyethylene film and polypropylene film are laminated, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at 30:70 (volume%). An electrolytic solution containing LiPF ₆ having a concentration of 1 mol / l as a supporting electrolyte was poured into the solvent and sealed to obtain a sample battery 1 to a sample battery 7 and a comparative sample battery 1 to a comparative sample battery 8.

Charging / Discharging Characteristic Evaluation After charging each sample battery and comparative sample battery with constant voltage charging at 4.2 V and a current of 8 mA, charging at 4.2 V for 1.5 hours, The lower limit voltage was set to 3 V and the battery was discharged at a constant current to obtain an initial capacity.
The initial charge capacity was 8 mAh. The charge rate was set based on the initial charge / discharge capacity.
After being fully charged under the same conditions as the first charge, the battery was stored at 60 ° C. for 90 days.
After storage, after discharging to a lower limit voltage of 3V at a current value of 1C in a temperature atmosphere of 20 ° C, the upper limit voltage was set to 4.2V at a current value of 10C, and after charging for 15 minutes by the constant current constant voltage method, Discharge the battery with a lower limit voltage of 3V, compare the initial discharge capacity before storage with the discharge capacity after quick charge after storage, evaluate the quick charge characteristics after life, and show the results in Table 1. Show.

Example 2 and Comparative Example 2
In the same manner as in Example 1, Sample 1-2: LiMn _1.85 Li _0.1 Al _0.05 O ₄ as the first positive electrode active material, Sample 2-2: LiMn _1.85 Li _0.1 Ni _0.05 O ₄ as the second positive electrode material, As the third positive electrode active material, materials represented by Sample 3-2: LiNi _0.8 Co _0.2 O ₂ were prepared.
Next, sample battery 8-sample battery 14 and comparative sample battery 9-comparative sample battery 14 were prepared in the same manner as in Example 1 and evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Example 3 and Comparative Example 3
In the same manner as in Example 1, Sample 1-3: LiMn _1.87 Li _0.03 Al _0.1 O ₄ as the first positive electrode active material, Sample 2-3: LiMn _1.85 Li _0.1 Co _0.05 O ₄ as the second positive electrode material, Substances represented by Sample 3-3: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ were prepared as the three positive electrode active materials.

  Next, in the same manner as in Example 1, a sample battery 15 was prepared from the sample battery 21, and a comparative sample battery 15 was prepared from the comparative sample battery 15, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

Example 4 and Comparative Example 4
In the same manner as in Example 1, as the third positive electrode active material, Sample 3-4: LiNi _0.8 Co _0.15 Mn _0.05 O ₂ , Sample 3-5: LiNi _0.8 Co _0.15 Mg _0.05 O ₂ , Sample 3-6: LiNi _{0 . 5} Mn _0.5 O _2, and sample 3-7 was prepared: substances represented respectively by LiCoO _2.

Next, 40 parts by mass of the sample 1-1 as the first positive electrode active material used in Example 1, 40 parts by mass of the sample 2-1 as the second positive electrode active material, and the third positive electrode active material Sample batteries 22, 23, 24, and 25 were prepared in the same manner as in Example 1, except that 20 parts by mass of Sample 3-4, Sample 3-5, Sample 3-6, and Sample 3-3 were blended. Then, the capacity after storage was measured in the same manner as in Example 1, and the results are shown in Table 4. Further, as a third positive electrode active material, a comparative sample battery 23 was prepared in the same manner as the sample battery 22 except that 20 parts by mass of the sample 3-7 was blended, and the capacity after storage was measured in the same manner. Table 4 shows. For comparison, the sample battery 3 is also shown.
As shown in Table 4, when the third positive electrode active material contains nickel, an excellent effect is obtained.

Example 5
In the same manner as in Example 1, Sample 1-4 as the first cathode active _{material: LiMn 1.85 Li 0.1 Mg 0.05 O4} , Sample _{1-5: LiMn 1.85 Li 0.1 Ni 0.05} O4, Sample 1-6: LiMn _1.85 Li _{0 .} 1Co _0.05 O _4, sample _{1-7: LiMn 1.85 Li 0.1 Fe 0.05} O 4, sample _{1-8: LiMn 1.76 Li 0.01 Al 0.23} O 4, sample _{1-9: LiMn 1.82 Li 0.03 Al 0.15} O 4, sample 1 -10: LiMn _1.85 Li _0.05 Al _0.1 O ₄ , Sample 1-11: LiMn _1.85 Li _0.1 Al _0.025 Co _0.025 O ₄ , Sample 1-12: LiMn _1.85 Li _0.1 Al _0.025 Ni _0.025 O ₄ , Sample 1-13: LiMn _{1.85 Li 0.1 Al 0.025 Fe 0.025 O} 4, sample _{1-14: LiMn 1.84 Li 0.05 Al 0.1} B 0.01 O 4, sample _{1-15: LiMn 1.85 Li 0.08 Al 0.03} Co 0.03 B 0.01 O 4, sample 1-16: Li _{n 1.85 Li 0.1 Mg 0.0 1Al 0.02} Co 0.02 O 4, and sample 1-17: was prepared materials respectively represented by _{LiMn 1.82 Li 0.04 Mg 0.06 Al 0.08} O 4.

  Next, 40 parts by mass of the first positive electrode active material and 40% by mass of the first positive electrode active material were obtained in the same manner as the sample battery 3 described in Example 1, except that the first positive electrode active material was changed as shown in Table 5. Each sample battery was prepared with a composition of 40 parts by mass of the positive electrode active material and 20 parts by mass of the third positive electrode active material, evaluated in the same manner as in Example 1, and the results are shown in Table 5. For comparison, the sample battery 3 is also shown. Among these, the capacity after rapid charging was large in the positive electrode active material containing aluminum.

Example 6
In the same manner as in Example 1, Sample 1-18: LiMn _1.84 Li _0.1 Al _0.03 Co _0.03 O ₄ and Sample 1-19: LiMn _1.83 Li _0.1 Al _0.03 Co _0.03 B _0.01 O ₄ were used as the first positive electrode active material. Each was prepared.
As the second positive electrode active material, Sample 2-4: LiMn _1.88 Li _0.1 Mg _0.05 O ₄ , Sample 2-5: LiMn _1.87 Li _0.1 Co _0.05 O ₄ , Sample 2-6: LiMn _1.87 Li _0.1 Ni _0.05 O ₄ , Sample 2-7: LiMn _1.87 Li _0.1 Fe _0.05 O ₄ , Sample 2-8: LiMn _1.88 Li _0.1 B _0.02 O ₄ , Sample 2-9: LiMn _1.88 Li _0.02 Mg _0.1 O ₄ , Sample 2-10: LiMn _1.86 Li _0.02 Mg _0.12 O ₄ , Sample 2-11: LiMn _1.85 Li _0.05 Mg _0.08 Al _0.02 O ₄ , Sample 2-12: LiMn _1.88 Li _0.05 Mg _0.05 Co _0.02 O ₄ , Sample 2-13: LiMn _1.88 Li _0.05 Mg _0.05 Fe _0.02 O ₄ , Sample 2-14: LiMn _1.87 Li _0.05 Mg _0.08 O ₄ , Sample 2-15: LiMn _1.82 Li _0.04 Mg _0.08 Al _0.06 O ₄ , and Sample 2-16: LiMn _1.83 Li _0.05 Mg _0.0 Substances each represented by ₈ Al _0.04 O ₄ were prepared.

  Next, in each of the sample batteries 3 described in Example 1, each sample battery was formed in the same manner as the sample battery 3 except that the first positive electrode active material and the second positive electrode active material were changed to those shown in Table 6. It was fabricated and evaluated in the same manner as in Example 1, and the results are shown in Table 6.

  As shown in the above Examples and Comparative Examples, when a spinel compound containing aluminum is included, a lithium secondary battery having a high effect of improving the retention rate of the discharge capacity after rapid charging can be obtained. Furthermore, by using a spinel compound containing magnesium in addition to lithium and manganese as the second positive electrode active material for the first positive electrode active material having a spinel structure containing aluminum, the maintenance rate of discharge capacity after rapid charging The improvement effect of was high.

  When the lithium secondary battery using the positive electrode active material of the present invention is used as the positive electrode active material, the retention rate of the discharge capacity after rapid charging is high. Therefore, the mobile phone, notebook computer, electric vehicle, electric bicycle The convenience of an electric motorcycle, an uninterruptible power supply, an electric tool, or a portable device such as a digital camera or a portable music device can be greatly improved.

  DESCRIPTION OF SYMBOLS 1 ... Lithium secondary battery, 2 ... Positive electrode collector, 3 ... Positive electrode active material layer, 4 ... Positive electrode, 5 ... Negative electrode collector, negative electrode active material layer, 7 ... Negative electrode, 8 ... Separator, 9 ... Conductivity for positive electrodes Tab, 10 ... Electrode tab for negative electrode, 11 ... Film-like exterior material

Claims (8)

Lithium and manganese as essential components, a first positive electrode active material 70 parts by mass 10 parts by mass of an oxide of different types two kinds of spinel structure of elements constituting the second cathode active material, 10 and 60 parts by mass parts by mass, a positive electrode containing a from the third cathode active material 20 parts by weight of an oxide of a layered structure containing lithium and nickel 40 parts by weight,
The first and second positive electrode active materials are represented by chemical formula 1: Li _a1 Mn _2-x1 Ml _x1 O ₄ (Ml is at least one of Li, B, Mg, Al, Fe, Co, Ni, A lithium manganese-containing composite oxide represented by 0 <a1 ≦ 1, 0 <x1 <0.3),
When M1 of the first positive electrode active material is M11, the M11 includes aluminum,
When M1 of the second positive electrode active material is M12, the M12 includes at least one of boron, magnesium, iron, cobalt, and nickel,
The third positive electrode active material has a chemical formula 3: Li _a3 Ni _1-x3 M3 _x3 O ₂ (M3 is at least one of Li, Co, Mn, Mg, and Al, and 0 <a3 ≦ 1, 0 A positive electrode characterized by being a lithium nickel composite oxide represented by <x3 <0.7).   The composition ratio of Al contained in M11 is 0.015 or more and 0.25 or less, and the composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel contained in M12 is 0.015 or more, 0 The positive electrode according to claim 1, wherein the positive electrode is 15 or less.   The M11 further contains Li, the composition ratio of Li contained in the M11 is 0.05 or more and 0.1 or less, the M12 further contains Li, and the composition ratio of Li contained in the M12 is 0.02 or more. The positive electrode according to claim 1, wherein the positive electrode is 0.1 or less.   4. The positive electrode according to claim 1, wherein a composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel included in M12 is 0.02 or more and 0.12 or less. Lithium and manganese as essential components, a first positive electrode active material 70 parts by mass 10 parts by mass of an oxide of different types two kinds of spinel structure of elements constituting the second 10 mass a positive electrode active material and 60 parts by mass parts, a positive electrode containing a from the third cathode active material 20 parts by weight of an oxide of a layered structure containing lithium and nickel 40 parts by weight,
The first and second positive electrode active materials are represented by chemical formula 1: Li _a1 Mn _2-x1 M1 _x1 O ₄ (M1 is at least one of Li, B, Mg, Al, Fe, Co, Ni, A lithium manganese-containing composite oxide represented by 0 <a1 ≦ 1, 0 <x1 <0.3),
When M1 of the first positive electrode active material is M11, the M11 includes aluminum, and when M1 of the second positive electrode active material is M12, the M12 is made of boron, magnesium, iron, cobalt, nickel. Including at least one of them,
The third positive electrode active material has a chemical formula 3: Li _a3 Ni _1-x3 M3 _x3 O ₂ (M3 is at least one of Li, Co, Mn, Mg, Al, and 0 <a3 ≦ 1, A lithium secondary battery comprising: a positive electrode that is a lithium nickel composite oxide represented by 0 <x3 <0.7); and a negative electrode that absorbs and releases lithium.   The composition ratio of Al contained in M11 is 0.015 or more and 0.25 or less, and the composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel contained in M12 is 0.015 or more, 0 The lithium secondary battery according to claim 5, wherein the lithium secondary battery is .15 or less.   The M11 further contains Li, the composition ratio of Li contained in the M11 is 0.05 or more and 0.1 or less, the M12 further contains Li, and the composition ratio of Li contained in the M12 is 0.02 or more. The lithium secondary battery according to claim 5, which is 0.1 or less.   8. The lithium secondary battery according to claim 5, wherein a composition ratio of at least one of boron, magnesium, iron, cobalt, and nickel included in M12 is 0.02 or more and 0.12 or less. Next battery.

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