JP5157253B2 - Cathode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same - Google Patents

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery and a non-aqueous electrolyte secondary battery using the same.

  In recent years, alloys and carbon materials that can absorb and release lithium ions are used as the negative electrode active material, and lithium transition metal composite oxides such as lithium cobaltate, lithium nickelate, and lithium manganate are used as the positive electrode active material. In addition, non-aqueous electrolyte secondary batteries having a high energy density have been put into practical use. These nonaqueous electrolyte secondary batteries are often used as power sources for electronic devices such as mobile phones, notebook computers, digital cameras, and electric tools.

Generally, in the case of a battery using lithium cobaltate as a positive electrode active material and a carbon material as a negative electrode active material, the charge end voltage of the battery is used at 4.1 V to 4.2 V. The potential of the positive electrode active material at the end-of-charge voltage is 4.2 V to 4.3 V on the basis of lithium. However, nowadays, with higher functionality of electronic devices, further increase in battery capacity is required. Therefore, an attempt has been made to increase the capacity of the positive electrode and improve the energy density of the battery by increasing the end-of-charge voltage of the battery, for example, higher than 4.5 V with respect to lithium. However, in the case of a battery using LiCoO ₂ to which a metal element other than cobalt and lithium is not added as a positive electrode, there is a problem that cycle characteristics and thermal stability at room temperature are remarkably lowered. Therefore, in order to solve the above-described problem, Patent Document 1 uses, as a positive electrode active material, a lithium cobalt-based composite oxide containing at least one selected from Ge, Ti, Zr, Y, and Si. Is disclosed. In Patent Document 2, LiCoO ₂ containing Zr and Mg is a positive electrode active material that is excellent in thermal stability and cycle characteristics at room temperature even when the end-of-charge voltage is 4.4 V or more on the basis of lithium. It is disclosed.

JP 2001-68168 A JP 2006-147191 A

In addition to remarkably worsening the cycle characteristics and safety at room temperature due to the increase in the end-of-charge voltage, there were also problems with the cycle characteristics at high temperatures and the storage characteristics at high temperatures. For example, in the case of a battery using LiCoO ₂ to which a third component other than lithium and cobalt is not added as a positive electrode, the battery is exposed to a high temperature for a long time with a high end-of-charge voltage. When it is done, the voltage at the time of discharge will fall and it will say that an energy density will fall by that. Furthermore, the thermal stability is greatly reduced as the end-of-charge voltage is increased. Then, although the test was performed using LiCoO ₂ containing Zr and Mg of Patent Document 2 as the positive electrode active material, although the thermal stability was improved, improving the cycle characteristics at high temperature and the high temperature storage characteristics could not. Accordingly, an object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte battery and a non-aqueous electrolyte battery that are excellent in cycle characteristics at high temperatures and high-temperature storage characteristics while maintaining thermal stability.

  The present invention relates to a positive electrode active material used in a non-aqueous electrolyte secondary battery, wherein the positive electrode active material is lithium cobalt oxide, and the lithium cobalt oxide is at least three metals of zirconium, titanium, magnesium, and manganese. The present invention relates to a positive electrode active material containing an element.

  The lithium transition metal composite oxide preferably further contains an aluminum element.

Further, the lithium transition metal composite oxide has a chemical formula: Li _a Co _1-wxyz M _w Mg _x Mn _y Al _z O ₂ (wherein M is Zr or Ti, a, w, x, y, and z are 0.9 ≦ a ≦ 1.2, 0 <w ≦ 0.01, 0 <x ≦ 0.03, 0 <y ≦ 0.04, and 0 ≦ z ≦ 0, respectively. 0.02, 0.01 ≦ w + x + y + z ≦ 0.06).

  The present invention also relates to a non-aqueous electrolyte secondary battery using a positive electrode having the positive electrode active material, wherein the positive electrode active material has a potential of 4.4 V to 4.6 V on the basis of lithium.

  According to the present invention, by using a lithium transition metal composite oxide in which at least three metal elements of zirconium, titanium, magnesium, and manganese are contained in lithium cobaltate as a positive electrode active material, thermal stability, high temperature cycle It can be set as the nonaqueous electrolyte battery excellent in a characteristic and a high temperature storage characteristic.

Hereinafter, the present invention will be described in more detail. However, the present invention is not limited to this embodiment and examples.
[Lithium transition metal composite oxide]
The lithium transition metal composite oxide used in the present invention (hereinafter sometimes referred to as a positive electrode active material) has a chemical formula: Li _a Co _1-wxyz M _w Mg _x Mn _y Al _z O ₂ (In the formula, M is Zr or Ti, and a, w, x, y, and z are 0.9 ≦ a ≦ 1.2, 0 <w ≦ 0.01, and 0 <x ≦ 0. 03, 0 <y ≦ 0.04, 0 ≦ z ≦ 0.02, 0.01 ≦ w + x + y + z ≦ 0.06).

  Here, the composition formula will be described. In general, in the notation method shown in the above composition formula, it means that an additive element such as zirconium or magnesium is substituted or dissolved in the main component cobalt. However, in the present invention, the above composition formula is applied for the sake of convenience in order to express the content of the additive element, which means that the additive element only needs to be contained in the positive electrode active material.

  The average voltage during discharge varies greatly depending on whether zirconium or titanium is added. Even if the average voltage is a difference of 0.1 V, since it is greatly reduced when converted to energy density, it is important to make the potential of the positive electrode active material itself as high as possible. The addition amount of zirconium or titanium may be greater than 0 mol% and 1.0 mol% or less. If the amount of zirconium or titanium added is 0.01 mol% or more, the average voltage is improved, and if it is 0.1 mol% or more, the effect is constant. Therefore, the amount of zirconium or titanium added is preferably 1.0 mol% or less. This is because the discharge capacity decreases as the amount of zirconium or titanium added increases.

  The addition of magnesium affects the calorific value measured by DSC (differential scanning calorimeter). This calorific value is sometimes used as an indicator of battery safety, and if the calorific value is small, it is considered that the battery is unlikely to run away in safety tests such as a nail penetration test. If the amount of magnesium added is less than 0.1 mol%, the calorific value is unlikely to decrease. Further, as magnesium increases, the amount of heat generation also decreases, but the discharge capacity also decreases, and as a result, the energy density also decreases. Therefore, the amount of magnesium added is preferably 0.1 mol% or more and 3.0 mol% or less.

  By adding manganese, a drop in discharge voltage after high temperature storage is suppressed. Furthermore, the cycle characteristics at high temperatures are improved. Although the detailed mechanism of action for improving these properties is unclear, it is thought that the added manganese is strengthening the crystal structure by partially replacing cobalt sites. Further, a part of manganese is present on the particle surface as a composite oxide of lithium and manganese, and is considered to have a film-like action. Actually, by adding manganese, the amount of cobalt present on the negative electrode side after high-temperature storage is reduced. That is, it is considered that the elution of cobalt is reduced and the voltage drop is suppressed by the stabilization of the crystal structure and the coating effect by addition of manganese. Moreover, it is thought that the cycle characteristics at high temperature are improved by the same effect. If the amount of manganese added is less than 0.1 mol%, the effect of suppressing the elution of cobalt is small, and the voltage drop is not suppressed. Moreover, since it is thought that a part of added manganese produces | generates the compound which contributes to charging / discharging, the grade of the fall of the discharge capacity by the increase in addition amount is small compared with zirconium or magnesium. However, excessive addition of manganese rather promotes elution of manganese into the electrolyte, resulting in voltage drop and deterioration of cycle characteristics. Therefore, the addition amount of manganese is preferably 0.1 mol% or more and 4.0 mol% or less.

  The addition of aluminum can further improve the thermal stability as compared with the case where zirconium, titanium, magnesium, or manganese is added. The addition of aluminum affects the heat generation starting temperature measured by DSC. This heat generation start temperature is sometimes used as an indicator of battery safety. If the heat generation start temperature in DSC is on the high temperature side, it is considered that the battery is unlikely to run out of heat in safety tests such as a nail penetration test. ing. If the amount of aluminum added is less than 0.1 mol%, there is almost no shift of the heat generation start temperature to the high temperature side. Further, as the amount of aluminum increases, the heat generation start temperature sequentially shifts to the high temperature side, but the discharge capacity also decreases. Therefore, the amount of aluminum added is preferably 0.1 mol% or more and 2.0 mol% or less.

  The addition of zirconium or titanium, magnesium, manganese, and aluminum is the amount specified above, and the total amount of those added is in the range of 6 mol% or less, so that the capacity reduction can be suppressed and the thermal stability, high temperature Thus, a battery having excellent cycle characteristics and high-temperature storage characteristics can be obtained.

Additive elements such as zirconium or titanium, magnesium, manganese, and aluminum cannot achieve the above-described effects only by mixing with lithium cobalt oxide that has already been formed. Therefore, it is preferable that zirconium or titanium, magnesium, manganese and aluminum are preliminarily contained in the lithium raw material and the cobalt raw material and fired.
[Method for producing lithium transition metal composite oxide]
As the raw material of the lithium transition metal composite oxide of the present invention, oxides, hydroxides, nitrates, sulfates, carbonates and the like of each element can be used. For example, examples of the lithium source include lithium carbonate, lithium nitrate, and lithium hydroxide. Examples of the cobalt source include cobalt oxide, niobium trioxide, tricobalt tetroxide, cobalt hydroxide, cobalt nitrate, and cobalt sulfate. Examples of manganese sources include manganese dioxide, nimanganese trioxide, trimanganese tetroxide, manganese carbonate, manganese nitrate, and manganese sulfate. Examples of the zirconium source include zirconium fluoride, zirconium chloride, zirconium bromide, zirconium iodide, zirconium oxide, zirconium sulfide, and zirconium carbonate. Examples of the titanium source include titanium fluoride, titanium chloride, titanium bromide, titanium iodide, titanium oxide, titanium sulfide, and titanium sulfate. Examples of the magnesium source include magnesium oxide, magnesium carbonate, magnesium hydroxide, magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium acetate, magnesium iodide, and magnesium perchlorate. Examples of the aluminum source include aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum chloride, aluminum iodide, aluminum sulfate, and aluminum nitrate.

  When producing lithium cobaltate containing zirconium, magnesium and manganese, for example, it can be obtained by the following steps.

  An aqueous solution containing cobalt ions, zirconium ions and magnesium ions having a predetermined composition ratio prepared from the cobalt compound, zirconium compound and magnesium compound described above is dropped into the stirring pure water. The aqueous solution temperature is set to 40 to 80 ° C., and while stirring the aqueous solution, a sodium hydrogen carbonate aqueous solution is dropped so that the aqueous solution has a pH of 7 to 11, thereby forming a composite hydroxide comprising cobalt, zirconium, magnesium and manganese as a precipitate. A thing is obtained. In addition, instead of the sodium hydrogen carbonate aqueous solution, an alkali solution such as an ammonium hydrogen carbonate aqueous solution, sodium hydroxide, potassium hydroxide aqueous solution, or lithium hydroxide aqueous solution can be used.

  Next, the slurry is filtered to collect a precipitate. The collected precipitate is washed with water and heat-treated to form an oxide, and then the above-described lithium compound is mixed to obtain a raw material mixture. Here, an embodiment in which a lithium compound is mixed with a composite oxide composed of cobalt, zirconium, magnesium and manganese has been described. For example, a lithium compound and a manganese compound are mixed and fired in an oxide composed of cobalt, zirconium and magnesium. Embodiments are possible.

  Next, the raw material mixture is fired. The firing temperature is preferably 800 ° C. or higher. If the firing temperature is too low, unreacted raw materials remain in the positive electrode active material, resulting in a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage. Moreover, it is preferable that a calcination temperature is 1100 degrees C or less. If the firing temperature is too high, by-products are likely to be generated, resulting in a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage. The firing time is preferably 5 hours or longer. Within the above range, the diffusion reaction between the particles of the mixture proceeds sufficiently. The firing time is preferably 30 hours or less. Within the above range, productivity is excellent.

  Examples of the firing atmosphere include air, oxygen gas, a mixed gas of these with an inert gas such as nitrogen gas and argon gas, an atmosphere in which the oxygen concentration (oxygen partial pressure) is controlled, and a weak oxidizing atmosphere.

After firing, if desired, the powder may be pulverized using a rough mortar, ball mill, vibration mill, pin mill, jet mill or the like to obtain a powder having a desired particle size.
[Positive electrode]
The positive electrode is formed by forming a positive electrode active material layer containing a lithium transition metal composite oxide, a conductive material and a binder on a current collector.

  The positive electrode active material layer is usually prepared by dispersing a positive electrode active material, a binder, and a conductive material in a liquid medium to form a slurry, which is applied to a positive electrode current collector and dried. Furthermore, the positive electrode active material layer obtained by coating and drying is pressurized by a roll press machine or the like in order to increase the packing density of the positive electrode active material.

  The material for the positive electrode current collector is preferably aluminum.

  The binder used for manufacturing the positive electrode active material layer is not particularly limited, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, and polyamide acrylic resin.

The positive electrode active material layer usually contains a conductive material in order to increase conductivity. Although there is no restriction | limiting in particular in the kind, Carbon materials, such as graphite (graphite), such as natural graphite and artificial graphite, carbon black, such as acetylene black, etc. can be mentioned. In addition, these substances may be used individually by 1 type, and may use 2 or more types together.
[Nonaqueous electrolyte battery]
The nonaqueous electrolyte battery of the present invention includes a positive electrode using the positive electrode active material of the present invention, a negative electrode capable of inserting and extracting lithium, and a nonaqueous electrolyte using a lithium salt as an electrolyte. Furthermore, a separator for holding a nonaqueous electrolyte is provided between the positive electrode and the negative electrode.

  The negative electrode is usually configured by forming a negative electrode active material layer on a negative electrode current collector, similarly to the positive electrode.

  Examples of the negative electrode active material include lithium alloys such as metallic lithium and lithium aluminum alloy, and carbon materials capable of inserting and extracting lithium. Usually, a carbon material capable of inserting and extracting lithium is used from the viewpoint of high safety. Examples thereof include graphite such as natural graphite and artificial graphite.

  In addition to the carbon material described above, a compound capable of inserting and extracting lithium can be used as the negative electrode active material. Examples thereof include metal oxides such as tin oxide and titanium oxide.

  The electrolyte is not particularly limited as long as it is a compound that is not altered or decomposed by the operating voltage. The electrolyte includes an electrolytic solution. Examples of the solvent for the electrolytic solution include dimethoxyethane, diethoxyethane, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, γ-butyrolactone, 2-methyltetrahydrofuran, dimethyl sulfoxide, sulfolane and the like. These organic solvents are mentioned. These can be used alone or in admixture of two or more.

  Examples of the lithium salt of the electrolytic solution include lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium trifluoromethanoate. The above-described solvent and lithium salt are mixed to obtain an electrolytic solution. Here, a gelling agent or the like may be added and used as a gel. Moreover, you may make it absorb and use for the polymer which has a liquid absorptivity. The lithium salt is usually contained in the electrolyte so as to be 0.5 mol / L or more and 1.5 mol / L or less.

  Further, a solid electrolyte having conductivity of inorganic or organic lithium ions may be used.

  Examples of the separator include porous films such as polyethylene and polypropylene.

  The nonaqueous electrolyte battery of the present invention is manufactured by assembling a positive electrode using the positive electrode active material of the present invention, a negative electrode, an electrolyte, and a separator used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary.

Examples of the present invention will be specifically described below, but the present invention is not limited to them.
(1) Production of positive electrode active material <Example 1 to Example 10>
An aqueous solution containing cobalt ions, zirconium ions, magnesium ions, and manganese ions prepared from cobalt sulfate, zirconium oxychloride, magnesium sulfate, and manganese sulfate is prepared in a reaction vessel. Cobalt sulfate, zirconium oxychloride, magnesium sulfate, and manganese sulfate dropped into the reaction vessel are appropriately adjusted so that the molar ratio of zirconium, magnesium, and manganese in the positive electrode active material finally obtained is as shown in Tables 1 to 3. The aqueous solution temperature is set to 65 ° C., and while stirring the aqueous solution, a certain amount of aqueous sodium hydrogen carbonate solution is added dropwise to adjust the pH of the reaction vessel to 7-8. Thereby, cobalt, zirconium, magnesium and manganese are precipitated, and a precipitate composed of a cobalt-zirconium-magnesium-manganese composite hydroxide is obtained. The obtained precipitate is filtered, washed with water, and heat-treated to convert the hydroxide into an oxide. Lithium carbonate is mixed with the heat-treated product to obtain a raw material mixture. Lithium carbonate is adjusted so that the molar ratio of lithium is 1.01 with respect to the total molar amount of cobalt, zirconium, magnesium, and manganese. The raw material mixture is fired at 1050 ° C. for 15 hours in the air. After firing, pulverization is performed to obtain a positive electrode active material.

<Comparative Examples 1 to 6>
In preparation of the positive electrode active material of Examples 1-10, it compares with the manufacturing method similar to Examples 1-10 except changing the molar ratio of zirconium, magnesium, and manganese as shown in Table 1-Table 3. The positive electrode active materials of Examples 1 to 6 are obtained. However, for elements having zero content in the table, an aqueous solution containing the ions is not used in the process in the reaction vessel.

<Examples 11 to 14 and Comparative Example 7>
The reaction vessel is further charged with aluminum sulfate to obtain a precipitate composed of a cobalt-zirconium-magnesium-arnium composite hydroxide, and the positive electrode active material so that the molar ratio of zirconium, magnesium, manganese, and aluminum is as shown in Table 4. Except for producing, the positive electrode active materials of Examples 11 to 14 and Comparative Example 7 are obtained by the same production method as in Examples 1 to 10.

The contents of lithium, zirconium, magnesium, aluminum, and manganese in the positive electrode active materials obtained from the above examples and comparative examples are determined by ICP (inductively coupled plasma) emission spectrometry. The content of cobalt is obtained by a droplet method using an EDTA (ethylene tetraacetic acid) solution after dissolving the positive electrode active material with hydrochloric acid, adding murexide powder and aqueous ammonia.
(2) Production of battery (production of positive electrode)
90 parts by weight of the obtained positive electrode active material, 5.0 parts by weight of acetylene black, and 5.0 parts by weight of polyvinylidene fluoride (PVDF) as a binder were added to N-methyl-2-pyrrolidone (NMP). Disperse to prepare slurry. The obtained slurry is applied to one side of an aluminum foil, dried and then compression molded with a press. Cut to a size of 15 cm ² . The weight of the applied positive electrode active material layer is about 0.35 g.
(Preparation of negative electrode)
A slurry is prepared by dispersing 1.5 parts by weight of carboxymethyl cellulose (CMC) and 1.0 parts by weight of styrene butadiene rubber (SBR) as a binder in 97.5 parts by weight of natural graphite. The obtained slurry is applied to a copper foil, dried, compression-molded with a press, and cut to be 16.64 cm ² to obtain a negative electrode. The weight of the applied negative electrode active material layer is about 3.3 g.
(Nonaqueous electrolyte adjustment)
Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are mixed at a volume ratio of 3: 7. A nonaqueous electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) in the obtained mixed solvent so that its concentration becomes 1 mol / L.
(Battery assembly)
After attaching a lead electrode to the current collector of the positive electrode and the negative electrode, respectively, a separator is arranged between the positive electrode and the negative electrode, and they are stored in a bag-like laminate pack.

  Subsequently, the moisture adsorbed on each member is removed by vacuum drying at 60 ° C.

A laminate-type battery is assembled by injecting and sealing the non-aqueous electrolyte in a laminate pack under an argon atmosphere.
(3) Evaluation of battery characteristics (high temperature storage characteristics)
The laminate type battery is placed in a constant temperature bath at 25 ° C., and aged with a weak current, so that the electrolyte is sufficiently applied to the positive electrode and the negative electrode. Fully charged with charging potential set to 4.4V-charging current 0.2C (1C is a current load that completes discharging in 1 hour) and charging time 12 hours with 25 ° C constant temperature bath I do. After 12 hours, the battery is connected to a thermostat set at 60 ° C., and stored for 15 hours while trickle charging at a charging potential of 4.4 V and a charging current of 0.2 C. Again, after returning to a 25 degreeC thermostat and fully cooling, it discharges with discharge potential 2.75V-discharge current 1.0C. Tables 1 to 4 show the average voltage and discharge capacity at that time, and the energy density that is the integrated value thereof. FIG. 1 shows the relationship between the zirconium content in the positive electrode active material and the energy density, and FIG. 3 shows the relationship between the manganese content in the positive electrode active material and the energy density.

Table 5 shows the results of high-temperature storage characteristics in Example 2 and Comparative Example 5 when the charging potential is changed to 4.2 V and 4.3 V (carbon reference). In Table 5, the charging potential is shown on a lithium basis.
(High temperature cycle characteristics)
A positive electrode active material obtained in Example 2 and Comparative Example 5 is used for the positive electrode, and natural graphite is used for the negative electrode, and a laminate type battery similar to the above is fabricated and evaluated. The battery is placed in a constant temperature bath at 25 ° C., and aged with a weak current, so that the electrolyte is sufficiently applied to the positive electrode and the negative electrode. After switching to a constant temperature bath set at 45 ° C. and charging with a constant current at a charging potential of 4.4 V and a charging current of 1.0 C, the battery is discharged at a discharging potential of 2.75 and a discharging current of 1.0 C. This charge / discharge is defined as one cycle, and 200 cycles are performed. Table 6 shows the discharge capacity at 1 cycle, 100 cycles, and 200 cycles, the average voltage, and the energy density as an integrated value thereof.
(Initial characteristics)
The same thing as the above is used for a positive electrode and a nonaqueous electrolyte, and lithium metal is used for a negative electrode, and a laminate type battery is produced.

  The test is performed in a thermostat set at 25 ° C. After charging at a constant current and a constant voltage at a charging potential of 4.5 V and a charging current of 0.2 C, the battery is discharged at a discharging potential of 2.75 V and a discharging current of 1.5 C. Tables 1 to 4 show the discharge capacity and the average voltage at that time, and the energy density as an integrated value thereof. 1 to 4 show the relationship between the content of additive elements in the positive electrode active material and energy.

Table 5 shows the results of the initial characteristics in Example 2 and Comparative Example 5 when the charging potential is changed to 4.3 V and 4.4 V (lithium reference).
(4) Characteristic evaluation of positive electrode active material (cobalt elution amount after high temperature storage)
Use a battery that has been evaluated for its high-temperature storage characteristics. Remove the negative electrode from the battery. The negative electrode taken out is put into pure water, whereby the negative electrode active material layer composed of the negative electrode active material, the binder and the dispersant is peeled off from the copper foil. After adding hydrochloric acid to the aqueous solution containing the negative electrode active material layer, the content of cobalt in the aqueous solution is measured by an ICP emission spectroscopic analyzer, and the value is defined as the cobalt elution amount. The results are shown in Tables 1 to 4. Further, FIG. 3 shows a change in cobalt elution amount depending on the manganese content in the positive electrode active material.

Table 5 shows the results of cobalt elution amounts in Example 2 and Comparative Example 5 when the charging potential is changed to 4.2 V and 4.3 V (carbon reference). In Table 5, the charging potential is shown on a lithium basis.
(Thermal stability)
A Shimadzu DSC6200 (differential scanning calorimeter) is used as the measuring device. As a measurement sample, a positive electrode of a battery in which the counter electrode used in the measurement of initial characteristics is metallic lithium is used. In a constant temperature bath at 25 ° C., the battery is charged at a constant potential and a constant voltage of a charging potential of 4.4 V and a charging current of 0.2 C, and then decomposed in an argon box. Under an argon atmosphere, about 5 mg of the active material layer and about 2.0 mg of ethylene carbonate scraped from the positive electrode are sealed in an aluminum cell. The aluminum cell is set in the DSC and heated from 100 ° C. to 240 ° C. at a temperature rising rate of 4.5 ° C./min, and the heat generation start temperature and the heat generation amount are measured. The exothermic start temperature is a temperature at which the compound in the cell starts self-heating, which means a temperature at the time when a peak starts to be formed in the differential thermal analysis chart, and can be determined by a tangent method. The calorific value means the height from the peak of the maximum peak to the baseline in the differential thermal analysis chart. The results are shown in Tables 1 to 4. Further, FIG. 2 shows changes in the magnesium content and the heat generation amount in the positive electrode active material, and FIG. 4 shows changes in the aluminum content in the positive electrode active material and the heat generation start temperature.

It is a graph which shows the relationship between the zirconium content in a positive electrode active material, and an energy density. It is a graph which shows the relationship between magnesium content in a positive electrode active material, energy density, and calorific value. It is a graph which shows the relationship between manganese content in a positive electrode active material, energy density, and cobalt elution amount. It is a graph which shows the relationship between aluminum content in a positive electrode active material, an energy density, and heat generation start temperature.

  The positive electrode active material for a nonaqueous electrolyte secondary battery of the present invention can be used for a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery of the present invention can be used as a power source for mobile devices such as mobile phones, notebook computers, digital cameras, and batteries for electric vehicles.

Claims (6)

In the positive electrode active material used for the nonaqueous electrolyte secondary battery,
The positive electrode active material is a lithium transition metal composite oxide ,
The lithium transition metal composite oxide has a chemical formula: Li _a Co _1-wx-yz M _w Mg _x Mn _y Al _z O ₂ (wherein M is Zr or Ti, a, w, x, y, and z are 0.9 ≦ a ≦ 1.2, 0 <w ≦ 0.01, 0 <x ≦ 0.03, 0 <y ≦ 0.04, and 0 ≦ z ≦ 0.02, respectively. 0.01 ≦ w + x + y + z ≦ 0.06)) . The positive electrode active material according to claim 1, wherein w is 0.0001 ≦ w ≦ 0.01. The positive electrode active material according to claim 1, wherein x is 0.001 ≦ x ≦ 0.03. The positive electrode active material according to claim 1, wherein y is 0.001 ≦ y ≦ 0.04. The positive electrode active material according to claim 1, wherein the z is 0.001 ≦ z ≦ 0.02. In the positive electrode active material a non-aqueous electrolyte secondary battery using a positive electrode having a according to claims 1 to 5,
The non-aqueous electrolyte secondary battery, wherein the positive electrode active material has a potential of 4.4 V to 4.6 V based on lithium.

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