JP5124933B2 - Positive electrode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery - 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 (hereinafter also simply referred to as “positive electrode active material”) and a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries are characterized by higher operating voltage and higher energy density compared to conventional nickel cadmium secondary batteries, etc. Mobile electronics such as mobile phones, notebook computers, digital cameras, etc. Widely used as a power source for equipment. Examples of the positive electrode active material of the non-aqueous electrolyte secondary battery include lithium transition metal composite oxides typified by LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and among them, LiCoO ₂ is used for mobile electronic devices. Conventionally used, sufficient battery characteristics have been obtained.

However, at present, the use environment of mobile devices has become even more severe due to high functionality such as various functions added and use at high and low temperatures. In addition, application to power sources such as batteries for electric vehicles is expected, and conventional non-aqueous electrolyte secondary batteries using LiCoO ₂ cannot obtain sufficient battery characteristics, and further improvements are required. Yes.

  By the way, in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a protection circuit is conventionally incorporated in the battery in order to prevent overdischarge. However, if this protection circuit can be eliminated, the space is reduced. The capacity can be increased by adding an active material to the. Further, the manufacturing cost can be reduced by omitting the work of installing the protection circuit. Therefore, means for eliminating the protection circuit have been studied.

  In order to eliminate the protection circuit, it is necessary to prevent various problems from occurring even when overdischarge occurs. In general, when overdischarge occurs, the potential of the negative electrode rises, and a metal (for example, copper (Cu)) used as a negative electrode current collector is eluted, so that battery characteristics are significantly deteriorated. Hereinafter, the reason for elution will be specifically described by taking Cu as an example of the metal.

  FIG. 2 is a graph schematically showing a change in potential of the positive electrode and the negative electrode during a charge / discharge cycle of the lithium ion secondary battery. As shown in FIG. 2, in the conventional example, when the battery is charged, the potential of the positive electrode rises along the path indicated by arrow a and the potential of the negative electrode falls along the path indicated by arrow b.

  When the battery is discharged after charging, the potential of the negative electrode increases, but retention (a phenomenon in which lithium ions are not released) occurs in the negative electrode, and the path is as indicated by an arrow c. On the other hand, the potential of the positive electrode falls along the path indicated by the arrow d. Therefore, at point A, the potentials of the positive electrode and the negative electrode are equal. Here, since the potential at point A is higher than the potential at which Cu used as the negative electrode current collector is eluted, Cu is eluted.

On the other hand, as a technique for preventing Cu from eluting even when overdischarged, Patent Document 1 discloses a main active material composed of a first lithium compound having a potential nobler than the oxidation potential of the negative electrode current collector, and a negative electrode. A positive electrode active material including a secondary active material composed of a second lithium compound having a potential lower than the oxidation potential of the current collector is described. Specifically, LiCoO ₂ is used as a main active material, and Li _x A positive electrode active material having MoO ₃ (x: 1 to 2) as a secondary active material is described.

  However, in the positive electrode active material described in Patent Document 1, although improvement in overdischarge characteristics is observed, improvement in cycle characteristics, thermal stability, and the like currently required for mobile electronic devices can be realized. There wasn't.

JP-A-2-265167

  Accordingly, an object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that have excellent battery characteristics even in a more severe use environment. That is, it is an object to provide a positive electrode active material for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery that are excellent in excellent battery characteristics, particularly overdischarge characteristics, cycle characteristics, and thermal stability.

  As a result of earnest research to achieve the above object, the present inventors have found that the overdischarge characteristics can be improved by using a lithium transition metal composite oxide having at least a layered structure and a spinel structure as the positive electrode active material. The headline and the present invention were completed.

That is, the present invention provides the following (1) to ( 4 ).

(1) A positive electrode active material for a non-aqueous electrolyte secondary battery having a main active material having a first lithium transition metal composite oxide and a secondary active material having a second lithium transition metal composite oxide,
The first lithium transition metal composite oxide has only a layered structure, and has a lithium transition having only a peak due to the layered structure between 2θ = 18.4 and 19.6 ° obtained by an X-ray diffraction method. A metal complex oxide,
The second lithium transition metal composite oxide is obtained by firing a raw material containing lithium and cobalt at 800 ° C. or lower, has at least a layered structure and a spinel structure, and 2θ = obtained by an X-ray diffraction method. A lithium transition metal composite oxide having two or more independent peaks between 18.4 and 19.6 °;
The amount of the secondary active material is 1 to 30% by weight based on the amount of the positive electrode active material, the positive electrode active material for a non-aqueous electrolyte secondary battery.

( 2 ) a positive electrode having the positive electrode active material for a nonaqueous electrolyte secondary battery according to (1) above,
A negative electrode having a negative electrode active material and a negative electrode current collector made of metallic lithium, a lithium alloy, a carbon material capable of occluding and releasing lithium ions, or a compound capable of occluding and releasing lithium ions, and sandwiched between the positive electrode and the negative electrode A non-aqueous electrolyte secondary battery comprising a separator containing an electrolyte.

( 3 ) The nonaqueous electrolyte secondary battery according to ( 2 ), wherein the ratio of the initial discharge capacity to the initial charge capacity is 90% or less.

( 4 ) The nonaqueous electrolyte secondary battery according to ( 2 ) or ( 3 ), wherein a discharge curve at the time of initial discharge has a blister portion or a flat portion in a range of 3.0 to 3.5V.

  As described below, the use of the positive electrode active material of the present invention can improve the overdischarge characteristics, cycle characteristics, thermal stability, and the like of the nonaqueous electrolyte secondary battery. As a result, a non-aqueous electrolyte secondary battery having excellent battery characteristics that could not be achieved in the past can be put into practical use, and can be applied to various fields.

  Hereinafter, the positive electrode active material for a nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery according to the present invention will be specifically described. First, the positive electrode active material of the present invention will be described.

  The positive electrode active material according to the first aspect of the present invention has a lithium transition metal composite oxide having at least a layered structure and a spinel structure (spinel-type crystal structure).

“Layered structure” means that the crystal structure of the lithium transition metal composite oxide is layered. The layered structure is called an α-NaFeO ₂ type structure and is a structure in which lithium ions and transition metal ions regularly occupy half of each of the six coordination sites in a solid matrix having a cubically packed oxygen array.

  FIG. 3 is a schematic view showing a crystal structure of a lithium transition metal composite oxide having a layered structure. In FIG. 3, lithium occupies 3b site 3, oxygen occupies 6c site 2, and transition metal occupies 3a site 1.

  The layered structure is not particularly limited, and examples thereof include a layered rock salt structure and a zigzag layered rock salt structure. Among these, a layered rock salt structure is preferable.

  The lithium transition metal composite oxide having a layered structure is not particularly limited. Examples thereof include lithium cobaltate, lithium nickelate, lithium chromate, lithium vanadate, lithium manganate, lithium nickel cobaltate, nickel cobalt lithium manganate, and nickel cobalt lithium aluminate. Preferable examples include lithium cobaltate, lithium nickel cobaltate, nickel cobalt lithium aluminate and nickel cobalt lithium manganate.

  The lithium transition metal composite oxide can have at least one element selected from the group consisting of aluminum, titanium, zirconium, magnesium, calcium, and sodium. In this case, the reactivity of the raw materials is improved, the degree of synthesis is increased, and the Li elution amount is decreased. Thereby, a coating characteristic and a slurry characteristic improve.

The “spinel structure” is one of the typical crystal structure types found in double oxide AB ₂ O ₄ type compounds (A and B are metal elements).

  FIG. 4 is a schematic diagram showing a crystal structure of a spinel-structure lithium transition metal composite oxide. In FIG. 4, the lithium atom occupies the tetrahedral site of the 8a site 1 'and the 16c site 4', the oxygen atom occupies the 32e site 2 ', and the transition metal atom (and possibly the excess lithium atom) is 16d. Occupies the octahedral site of site 3 '.

  As described above, the lithium transition metal composite oxide used in the positive electrode active material according to the first aspect of the present invention has at least a layered structure and a spinel structure.

  The structure of the lithium transition metal composite oxide can be confirmed by, for example, X-ray diffraction (XRD).

  In addition, the lithium transition metal composite oxide used in the present invention has two or more independent peaks between 2θ = 18.4 ° and 19.6 ° obtained by the X-ray diffraction method. That is, at least the peak attributed to the layered structure and the peak attributed to the spinel structure are in the above range.

  In the present invention, “having a peak” means that the primary differential value dI / dt has a negative value when the X-ray diffraction intensity is I and the diffraction angle 2θ is t degrees.

  Among two or more independent peaks, the ratio of the peak attributed to the layered structure to the peak attributed to the spinel structure (peak attributed to the layered structure / peak attributed to the spinel structure) was 0.1 to 3.5. Preferably there is. When it is in the above range, the overdischarge characteristics are more excellent.

  The (104) crystallinity of R3m of the lithium transition metal composite oxide is preferably 450Å or less. Within the above range, the thermal stability becomes more excellent.

  The (104) crystallinity of R3m is an index indicating the degree of regularity of the unit cell arrangement.

  In the present application, the notation “R3m” means “R3 bar m”.

  The (104) crystallinity of R3m of the lithium transition metal composite oxide can be determined by, for example, an X-ray diffraction method. The X-ray diffraction method can be performed, for example, under conditions of a tube current of 40 mA and a tube voltage of 40 kV. From the diffraction peak due to the (104) plane determined by the X-ray diffraction method, the crystallinity is calculated by the Scherrer formula represented by the following formula (1).

D = Kα / (βcosθ) (1)
In the above formula, D represents (104) crystallinity (Å), K represents Scherrer constant (K is sintered Si for optical system adjustment (manufactured by Rigaku Corporation), and diffraction is caused by the (104) plane. Λ represents the wavelength of the X-ray source (1.540562 場合 in the case of CuKα1), β is β = By (B means the width of the observation profile, and y is calculated by y = 0.9991-0.019505b−2.8205b ² + 2.878b ³ −1.0366b ⁴ where b means the width of the device constant profile. Represents a diffraction angle (degree).

  The form of the lithium transition metal composite oxide is not particularly limited. Examples of the form of the lithium transition metal composite oxide include particles and films.

  In the present invention, the lithium transition metal composite oxide is preferably in the form of particles. The particles may be primary particles, secondary particles, or a mixture of these.

In the case where the lithium transition metal composite oxide is a particle, it is preferable that the intermediate position (D ₅₀ ) is ₅ to 20 μm. It is excellent in slurry application | coating characteristic and slurry settling property as it is the said range.

If the lithium transition metal composite oxide is particles, BET specific surface area is preferably from 0.2~5m ² / g, and more preferably 0.5-3 m ² / g. Within the above range, not only battery characteristics are excellent, but also slurry application characteristics and application characteristics are excellent.

  The specific surface area can be measured by a constant pressure BET adsorption method using nitrogen gas.

  The positive electrode active material of the present invention preferably has a Li elution amount of 20000 ppm or less, more preferably 10,000 ppm or less, still more preferably 8000 ppm or less, still more preferably 5000 ppm or less, and 3000 ppm or less. More preferably, it is 1000 ppm or less, more preferably 500 ppm or less. Within the above range, not only battery characteristics are excellent, but also slurry application characteristics and application characteristics are excellent.

  The amount of Li elution was determined by adding pure water to the positive electrode active material at a weight ratio such that the positive electrode active material / pure water = 1/5 and stirring the supernatant for 1 hour with a membrane filter. It can be measured by a method of suction filtration, analyzing the filtrate by ICP spectroscopy, and calculating the Li elution amount (weight of Li element with respect to the weight of pure water).

  In general, when a nonaqueous electrolyte secondary battery does not have a protection circuit for preventing overdischarge, when the battery voltage decreases to near 0 V due to overdischarge, the potential of the negative electrode rises and is used as a negative electrode current collector. Since Cu and the like are eluted, the battery characteristics are remarkably deteriorated.

  In contrast, in the present invention, a lithium transition metal composite oxide having at least a layered structure and a spinel structure is used as the positive electrode active material, and the lithium transition metal composite oxide is obtained by 2θ obtained by an X-ray diffraction method. Since it has two or more independent peaks between 18.4 and 19.6 °, it has the effect of supplementing the retention at the positive electrode, and as a result, the difference between the retention at the positive electrode and the retention at the negative electrode is reduced. Thereby, even when the battery is in an overdischarged state, the battery voltage when the potentials of the positive electrode and the negative electrode are equal at the time of discharging is lowered, and the battery characteristics can be maintained even in the overdischarged state. That is, the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention is excellent in overdischarge characteristics.

  The positive electrode active material of the first aspect of the present invention is not particularly limited in its production method. For example, when the lithium transition metal composite oxide has lithium and cobalt, the raw material containing lithium and cobalt is 800 ° C. or lower. A method obtained by firing is preferable.

  Hereinafter, an example of the manufacturing method of the positive electrode active material of the 1st aspect of this invention is demonstrated.

(1) Preparation of raw material mixture The compounds described later are mixed so that each constituent element has a predetermined composition ratio to obtain a raw material mixture. The compound used for the raw material mixture is selected according to the elements constituting the target composition.

  The mixing method is not particularly limited, for example, a method of mixing powdery compounds as they are to obtain a raw material mixture; mixing in a slurry form using water and / or an organic solvent, and then drying to obtain a raw material mixture Method: A method in which an aqueous solution of the above-mentioned compound is mixed and precipitated, and the resulting precipitate is dried to obtain a raw material mixture; a method in which these are used in combination.

  Below, the compound used for a raw material mixture is illustrated.

Lithium compound is not particularly limited, for _{example, Li 2 CO 3, LiOH,} LiOH · H 2 O, Li 2 O, LiCl, LiNO 3, Li 2 SO 4, LiHCO 3, Li (CH 3 COO), LiF, Examples include LiBr, LiI, and Li ₂ O ₂ . Among these, Li ₂ CO ₃ , LiOH, LiOH.H ₂ O, Li ₂ O, LiCl, LiNO ₃ , Li ₂ SO ₄ , LiHCO ₃ , and Li (CH ₃ COO) are preferable, and Li ₂ CO ₃ is more preferable.

The cobalt compound is not particularly limited. For example, cobalt oxide (Co ₃ O ₄ , CoO, Co ₂ O ₃ ), cobalt carbonate, cobalt chloride (CoCl ₂ , CoCl ₃ ), cobalt iodide, cobalt sulfate, cobalt bromate And cobalt nitrate. Of these, Co ₃ O ₄ is preferable.

The nickel compound is not particularly limited, and examples thereof include nickel oxide, nickel hydroxide, nickel carbonate, nickel chloride, nickel bromide, nickel iodide, nickel sulfate, and nickel nitrate. Among these, NiSO ₄ · 6H ₂ O and Ni (NO ₃ ) ₂ · 6H ₂ O are preferable.

The chromium compound is not particularly limited, and examples thereof include chromium oxide, chromium chloride, chromium carbonate, and chromium sulfate. Among these, CrO and Cr ₂ O ₃ are preferable.

The vanadium compound is not particularly limited, and examples thereof include vanadium oxide, vanadium hydroxide, and vanadium sulfate. Among these, V ₂ O ₅ and VCl ₂ are preferable.

The manganese compound is not particularly limited. For example, manganese metal, oxide (for example, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ ), hydroxide, nitrate, carbonate (MnCO ₃ ), chloride salt ( Examples thereof include MnCl ₂ ), manganese iodide, manganese sulfate, and manganese nitrate (for example, MnSO ₄ ). Among these, manganese metal, MnCO ₃ , MnSO ₄ , and MnCl ₂ are preferable.

Aluminum compound is not particularly limited, for _{example, Al 2 O 3, Al (} NO 3) 3, Al 2 (SO 4) 3, Al 2 (CO 3) 3, is _Al (CH _{3 COO)} 3 and the like.

The titanium compound is not particularly limited, and examples thereof include titanium fluoride, titanium chloride, titanium bromide, titanium iodide, titanium oxide, titanium sulfide, and titanium sulfate. Of these, TiO, TiO ₂ , Ti ₂ O ₃ , TiCl ₂ , and Ti (SO ₄ ) ₂ are preferable.

The zirconium compound is not particularly limited, and examples thereof include zirconium fluoride, zirconium chloride, zirconium bromide, zirconium iodide, zirconium oxide, zirconium sulfide, and zirconium carbonate. Of these, ZrF ₂ , ZrCl, ZrCl ₂ , ZrBr ₂ , ZrI ₂ , ZrO, ZrO ₂ , ZrS ₂ , Zr (OH) _{3 and the} like are preferable.

The magnesium compound is not particularly limited. For example, MgO, MgCO ₃ , Mg (OH) ₂ , MgCl ₂ , MgSO ₄ , Mg (NO ₃ ) ₂ , Mg (CH ₃ COO) ₂ , magnesium iodide, perchloric acid Examples include magnesium. Among these, MgSO ₄ and Mg (NO ₃ ) ₂ are preferable.

Calcium compound is not particularly limited, for _{example, CaO, CaCO 3, Ca (} OH) 2, CaCl 2, CaSO 4, Ca (NO 3) 2, Ca (CH 3 COO) 2 and the like.

Sodium compound is not particularly limited, for _{example, Na 2 CO 3, NaOH,} Na 2 O, NaC1, NaNO 3, Na 2 SO 4, NaHCO 3, CH 3 COONa and the like.

  You may use the compound containing 2 or more types of each element mentioned above.

  When elements other than lithium and cobalt (third element) are included, compounds containing such elements (namely, nickel compounds, chromium compounds, vanadium compounds, manganese compounds, aluminum compounds, titanium compounds, zirconium compounds, magnesium) It is preferable to mix the compound, calcium compound, sodium compound, etc.) with the cobalt compound and perform the firing described above.

  The mixing method is not particularly limited, and is a method in which a powdered compound is mixed as it is to obtain a raw material mixture; a method of mixing in a slurry form using water and / or an organic solvent, and then drying to obtain a raw material mixture; Examples include a method in which an aqueous solution of the above-described compound is mixed and precipitated, and the resulting precipitate is dried to obtain a raw material mixture; a method in which these are used in combination.

  The lithium compound described above and a cobalt compound (preferably a cobalt compound and a third element compound when a third element is contained) are mixed to obtain a raw material mixture. At this time, a raw material mixture may be further mixed with a compound of another element (third element) that is arbitrarily used.

(2) Firing and grinding of raw material mixture Next, the raw material mixture is fired.

  A calcination temperature is 800 degrees C or less, Preferably it is 400-600 degreeC. By firing at such a low temperature, a lithium transition metal composite oxide having a layered structure and a spinel structure (the positive electrode active material of the first aspect of the present invention) can be obtained.

  In general, the firing time is preferably 10 to 40 hours, and more preferably 20 to 35 hours. If the firing time is too short, the reaction between the mixed raw materials does not proceed sufficiently. If the firing time is too long, firing after the diffusion reaction is almost completed is wasted, and coarse particles may be formed by sintering.

  The firing may be divided into a plurality of firing steps.

  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. Among these, an atmosphere in which the oxygen concentration is controlled is preferable.

  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. Thus, by pulverizing after firing, the particle size can be within the preferred range described above.

  The positive electrode active material of the first aspect of the present invention can be used in combination with another lithium transition metal composite oxide.

  That is, the positive electrode active material of the second aspect of the present invention is a non-aqueous material having a main active material having a first lithium transition metal composite oxide and a secondary active material having a second lithium transition metal composite oxide. A positive electrode active material for an electrolyte secondary battery, wherein the secondary active material is a positive electrode active material for a non-aqueous electrolyte secondary battery, which is the positive electrode active material according to the first aspect of the present invention described above.

  The 1st lithium transition metal complex oxide used for a main active material is not specifically limited. The first lithium transition metal composite oxide is not limited to one lithium transition metal composite oxide.

  In the positive electrode active material of the second aspect of the present invention, the first lithium transition metal composite oxide is composed of a lithium cobalt composite oxide, a lithium nickel composite oxide, a lithium manganese composite oxide, and a lithium nickel cobalt manganese composite oxide. It is preferably at least one selected from the group consisting of

  Thereby, not only the improvement of the overdischarge characteristic, the cycle characteristic and the high temperature characteristic, but also the charge / discharge capacity is increased, and a nonaqueous electrolyte secondary battery excellent in load characteristic and output characteristic can be obtained.

The lithium cobalt composite oxide is preferably a lithium cobalt composite oxide represented by the general formula Li _{1 + x} CoO ₂ (x represents a number satisfying −0.5 ≦ x ≦ 0.5). This lithium cobalt composite oxide is selected from the group consisting of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin. It may have at least one kind.

The lithium nickel composite oxide is preferably a lithium nickel composite oxide represented by the general formula Li _{1 + x} NiO ₂ (x represents a number satisfying −0.5 ≦ x ≦ 0.5). This lithium nickel composite oxide is selected from the group consisting of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin. It may have at least one kind.

The lithium manganese composite oxide represented by the general formula _{Li a Mn 3-a O 4} + f (a is a number satisfying 0.8 ≦ a ≦ 1.2, f satisfies -0.5 ≦ f ≦ 0.5 The lithium-manganese composite oxide represented by This lithium manganese composite oxide is selected from the group consisting of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin. It may have at least one kind.

As the lithium nickel cobalt manganese composite oxide, the general formula Li _k Ni _m Co _p Mn _(1-mp) O _r (k represents a number satisfying 0.95 ≦ k ≦ 1.10. 0.1 ≦ m ≦ 0.9, p represents a number satisfying 0.1 ≦ p ≦ 0.9 and m + p ≦ 1, and r represents a number satisfying 1.8 ≦ r ≦ 2.2.) The lithium nickel cobalt manganese composite oxide represented is preferable. This lithium nickel cobalt manganese composite oxide is partly composed of magnesium, aluminum, calcium, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, strontium, zirconium, niobium, molybdenum and tin. You may have at least 1 sort (s) chosen from.

  The amount of the secondary active material in the positive electrode active material according to the second aspect of the present invention is preferably 1 to 30% by weight with respect to the amount of the positive electrode active material. The amount of the secondary active material is more preferably 3% by weight or more, and more preferably 15% by weight or less. When the amount of the secondary active material is too small, elution of Cu as a negative electrode current collector occurs during overdischarge. If the amount of the secondary active material is too large, the cycle characteristics deteriorate.

  The production method of the positive electrode active material of the second aspect of the present invention is not particularly limited, but can be produced, for example, as in the following (1) to (3).

(1) Preparation of main active material A compound is mixed so that each component may become a predetermined composition ratio, and a raw material mixture is obtained. The compound used for the raw material mixture is selected according to the elements constituting the target composition.

  The mixing method is not particularly limited, for example, a method of mixing powdery compounds as they are to obtain a raw material mixture; mixing in a slurry form using water and / or an organic solvent, and then drying to obtain a raw material mixture Method: A method in which an aqueous solution of the above-mentioned compound is mixed and precipitated, and the resulting precipitate is dried to obtain a raw material mixture; a method in which these are used in combination.

  Next, the raw material mixture is fired to obtain the main active material. The humidity, time, atmosphere, etc. of the firing are not particularly limited and can be appropriately determined according to the purpose.

  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.

(2) Production of side active material A side active material can be obtained by the method for producing a positive electrode active material according to the first aspect of the present invention described above.

(3) Mixing of main active material and sub-active material The obtained main active material and sub-active material can be mixed at a predetermined weight ratio to obtain the positive electrode active material of the second aspect of the present invention.

  The method for mixing the main active material and the sub active material is not particularly limited. For example, it can be mixed with a high-speed agitator.

  The positive electrode active material of the present invention is suitably used for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and lithium ion polymer secondary batteries. The nonaqueous electrolyte secondary battery may be a conventionally known nonaqueous electrolyte secondary battery in which the positive electrode active material is the positive electrode active material of the first or second aspect of the present invention. Other configurations are not particularly limited.

  That is, the non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode having the positive electrode active material of the present invention and metallic lithium, a lithium alloy, a carbon material capable of occluding and releasing lithium ions, or a compound capable of occluding and releasing lithium ions. A non-aqueous electrolyte secondary battery comprising a negative electrode having a negative electrode active material and a negative electrode current collector. More preferably, it further comprises a separator impregnated with an electrolyte sandwiched between the positive electrode and the negative electrode.

  Examples of the negative electrode current collector include copper and nickel.

  In the nonaqueous electrolyte secondary battery of the present invention, the element of the negative electrode current collector present in the electrolyte refers to an element that is a component of the negative electrode current collector. For example, Cu and Ni are mentioned. Preferably, it is Cu.

  The element of the negative electrode current collector may exist in an ionic state or may exist in a compound state. The presence of these elements increases the electrical conductivity of the active material and provides a nonaqueous electrolyte secondary battery with further improved load characteristics.

  In the non-aqueous electrolyte secondary battery of the present invention, the concentration of the element of the negative electrode current collector present in the electrolyte is preferably 0 ppm or more, more preferably 1 ppm or more, and 20 ppm or less. Preferably, it is 15 ppm or less. If the concentration of the element of the negative electrode current collector present in the electrolyte is too high, it causes an internal short circuit and a decrease in cycle characteristics, which is not preferable.

  The concentration of the element of the negative electrode current collector present in the electrolyte can be measured by various methods. For example, it can be measured by ICP spectroscopy, atomic absorption spectrometry, or fluorescent X-ray analysis.

  The nonaqueous electrolyte secondary battery of the present invention has a high electrode plate density and is extremely excellent in overdischarge characteristics.

  In the nonaqueous electrolyte secondary battery of the present invention, it is preferable that there is no protective circuit for preventing overdischarge. The positive electrode active material in the nonaqueous electrolyte secondary battery of the present invention described above can be placed in the space of the protection circuit, and not only the overdischarge characteristics, cycle characteristics and load characteristics are improved, but also a high capacity nonaqueous electrolyte secondary battery. It becomes a battery.

  Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described by taking a lithium ion secondary battery as an example.

  As the negative electrode active material, metallic lithium, a lithium alloy, a carbon material capable of occluding and releasing lithium ions, and a compound capable of occluding and releasing lithium ions can be used. Examples of the lithium alloy include a LiAl alloy, a LiSn alloy, and a LiPb alloy. Examples of the carbon material capable of occluding and releasing lithium ions include graphite and graphite. Examples of the compound capable of occluding and releasing lithium ions include oxides such as tin oxide and titanium oxide.

  The electrolyte solution is not particularly limited as long as it is a compound that does not change or decompose with the operating voltage.

  Examples of the solvent include organic solvents such as dimethoxyethane, diethoxyethane, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, γ-butyrolactone, 2-methyltetrahydrofuran, dimethyl sulfoxide, and sulfolane. Is mentioned. These can be used alone or in admixture of two or more.

  Examples of the electrolyte include lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium trifluoromethanoate.

  The above-described solvent and electrolyte 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 a hygroscopic polymer. Further, a solid electrolyte having conductivity of inorganic or organic lithium ions may be used.

  Examples of the separator include a porous film made of polyethylene or polypropylene.

  Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyamide acrylic resin, and the like.

  Using the positive electrode active material of the present invention and the above-described negative electrode active material, electrolytic solution, separator, and binder, a lithium ion secondary battery can be obtained according to a conventional method. Thereby, the outstanding battery characteristic which was not able to be achieved conventionally is realizable.

  As a preferred embodiment of the nonaqueous electrolyte secondary battery of the present invention, a positive electrode active material layer using the positive electrode active material of the first or second embodiment of the present invention is formed on at least one surface of a strip-shaped positive electrode current collector. And a negative electrode active material layer using a metal cathode, a lithium material, a carbon material capable of occluding and releasing lithium ions, or a compound capable of occluding and releasing lithium ions as a negative electrode active material. A belt-like negative electrode formed by forming on at least one side; and a belt-like separator, and the belt-like positive electrode and the belt-like negative electrode are wound a plurality of times in a state of being laminated via the belt-like separator, Examples include a non-aqueous electrolyte secondary battery that forms a spiral wound body in which the strip separator is interposed between the strip negative electrode.

  Such a non-aqueous electrolyte secondary battery has a simple manufacturing method and is less susceptible to cracking of the positive electrode active material layer and the negative electrode active material layer and separation from these strip separators. Moreover, the battery capacity is large and the energy density is high. In particular, the positive electrode active material of the present invention has excellent filling properties and is easily compatible with the binder. Therefore, since the positive electrode has a high charge / discharge capacity and excellent binding properties and surface smoothness, it is possible to prevent the positive electrode active material layer from being cracked or peeled off.

  In addition, a positive electrode active material layer using the positive electrode active material of the present invention is formed on both surfaces of the strip-shaped positive electrode current collector, and a negative electrode active material layer using the negative electrode active material is formed on both surfaces of the strip-shaped negative electrode current collector. By doing so, a nonaqueous electrolyte secondary battery having a higher charge / discharge capacity can be obtained without impairing the battery characteristics of the present invention.

  A preferred method for producing a positive electrode using the positive electrode active material of the present invention will be described below.

  A positive electrode mixture is prepared by mixing the positive electrode active material powder of the present invention with a carbon-based conductive agent such as acetylene black and graphite, a binder, and a binder solvent or dispersion medium. The obtained positive electrode mixture is made into a slurry or a kneaded product, applied to or supported on a current collector such as an aluminum foil, and press-rolled to form a positive electrode active material layer on the current collector.

  FIG. 5 is a schematic cross-sectional view of the positive electrode. As shown in FIG. 5, the positive electrode 13 is obtained by holding the positive electrode active material 6 on the current collector 12 with the binder 5.

  It is considered that the positive electrode active material of the present invention is excellent in mixing with the conductive agent powder and has a low internal resistance of the battery. Accordingly, the charge / discharge characteristics, particularly the discharge capacity, are excellent.

In addition, the positive electrode active material of the present invention is excellent in fluidity when kneaded with a binder, and is easily entangled with a polymer of the binder and has excellent binding properties.
Furthermore, since the positive electrode active material of the present invention does not contain coarse particles and is spherical, the surface of the coating film surface of the produced positive electrode has excellent smoothness. For this reason, the coating film surface of a positive electrode plate is excellent in binding property, and becomes difficult to peel off. In addition, since the surface is smooth and lithium ions are uniformly introduced and exited on the surface of the coating film accompanying charging / discharging, the cycle characteristics are remarkably improved.

  In the nonaqueous electrolyte secondary battery of the present invention, the ratio of the initial discharge capacity to the initial charge capacity is preferably 90% or less. Here, “initial discharge capacity” is a value of capacity at the time of initial discharge, and “initial charge capacity” is a value of capacity at the time of initial charge before discharge.

  When the ratio of the initial discharge capacity to the initial charge capacity of the positive electrode active material of the present invention falls within the above range, excellent battery characteristics can be maintained even when the battery is in an overdischarged state.

  The nonaqueous electrolyte secondary battery of the present invention preferably has a blister or flat portion in the range of 3.0 to 3.5 V in the discharge curve at the time of initial discharge (at the time of initial discharge). In this case, the overdischarge characteristics are better.

  Hereinafter, the “bulging portion” and the “flat portion” will be described.

  The blister portion is a portion in which a blister occurs like a hump on the side of the discharge curve where the capacity is large. Further, the flat portion is a portion where the slope is approaching horizontal in the discharge curve descending to the right. The blister portion and the flat portion are generated from the same cause although the appearance in the discharge curve is different.

  This will be described more specifically.

  FIG. 1 is a charge / discharge curve at the time of initial charge / discharge for each positive electrode active material obtained in Examples described later. In FIGS. 1A and 1B, the curves from the lower left to the upper right are charging curves, and the curves from the upper left to the lower right are discharge curves.

  It can be seen that the discharge curve in FIG. 1A has a flat portion in the range of 3.0 to 3.5V. Moreover, it turns out that the discharge curve of FIG. 1 (B) has a swelling part in the range of 3.0-3.5V.

  The shape of the lithium ion secondary battery is not particularly limited, and may be a cylindrical shape, a coin shape, a square shape, a laminate shape, or the like.

  FIG. 6 is a schematic cross-sectional view of a cylindrical battery. As shown in FIG. 6, in the cylindrical battery 20, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12, and the negative electrode 11 in which the negative electrode active material layer is formed on the current collector 12. Are repeatedly laminated via the separator 14.

  FIG. 7 is a schematic partial cross-sectional view of a coin-type battery. As shown in FIG. 7, in the coin-type battery 30, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12 and the negative electrode 11 are stacked via the separator 14.

  FIG. 8 is a schematic perspective view of a prismatic battery. As shown in FIG. 8, in the square battery 40, the positive electrode 13 in which the positive electrode active material layer is formed on the current collector 12, and the negative electrode 11 in which the negative electrode active material layer is formed on the current collector 12. However, they are repeatedly stacked via the separator 14.

  The use of the nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention is not particularly limited. For example, notebook computers, pen input computers, pocket computers, notebook word processors, pocket word processors, electronic book players, mobile phones, cordless phones, electronic notebooks, calculators, LCD TVs, electric shavers, electric tools, electronic translators, car phones , Portable printer, transceiver, pager, handy terminal, portable copy, voice input device, memory card, backup power supply, tape recorder, radio, headphone stereo, handy cleaner, portable compact disc (CD) player, video movie, navigation system It can be used as a power source for such devices.

  Also, lighting equipment, air conditioner, TV, stereo, water heater, refrigerator, oven microwave, dishwasher, washing machine, dryer, game machine, toy, road conditioner, medical equipment, automobile, electric car, golf cart, It can be used as a power source for electric carts, power storage systems and the like.

  Furthermore, the application is not limited to consumer use, and may be used for military use or space.

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these.
1. Preparation of positive electrode active material [ Experimental Example 1]
2020 g of powder of tribasic cobalt oxide (CO ₃ O ₄ ) and 998.3 g of lithium hydroxide monohydrate powder were mixed to obtain a powder of a raw material mixture. The obtained raw material mixture was baked in an air atmosphere at about 500 ° C. for about 24 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
[ Experimental Example 2 and Comparative Examples 1 and 2]
The experiment was conducted except that 887.6 g of lithium carbonate powder was used instead of 998.3 g of lithium hydroxide monohydrate powder, and the firing temperature and firing time of the raw material mixture were as shown in Table 1. A positive electrode active material was obtained in the same manner as in Example 1.
[ Experimental Examples 3 to 21]
Except for changing the particle size of lithium tetroxide (CO ₃ O ₄ ) and / or lithium carbonate, the raw material mixing treatment conditions, etc., and changing the firing temperature and firing period of the raw material mixture as shown in Table 1 Obtained a positive electrode active material by the same method as in Experimental Example 2.
[Example 1 ]
The positive electrode active material obtained in Experimental Example 11 and the positive electrode active material obtained in Comparative Example 1 were mixed at a mass ratio of 12/88 to obtain a positive electrode active material.
[Example 2 ] The positive electrode active material obtained in Experimental Example 12 and the positive electrode active material obtained in Comparative Example 1 were mixed at a mass ratio of 10/90 to obtain a positive electrode active material.
[ Experimental example 22 ]
2000 g of tribasic cobalt oxide (Co ₃ O ₄ ) powder and aluminum oxide (Al ₂ O ₃ ) powder were mixed so that aluminum was 10 mol% with respect to tribasic cobalt oxide, 400 g of the mixed powder and lithium carbonate Was mixed with 177.1 g of powder to obtain a powder of a raw material mixture. The obtained raw material mixed powder was fired at about 500 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
[ Experimental Example 23 ]
1500 g of cobalt tetroxide (Co ₃ O ₄ ) powder and titanium oxide (TiO ₂ ) powder are mixed so that titanium is 10 mol% with respect to cobalt tetroxide, 400 g of the mixed powder and lithium carbonate powder 169.8g was mixed and the powder of the raw material mixture was obtained. The obtained raw material mixed powder was fired at about 500 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
[ Experimental example 24 ]
1500 g of cobalt trioxide (Co ₃ O ₄ ) powder and zirconium oxide (ZrO ₂ ) powder were mixed so that zirconium was 10 mol% with respect to tribasic cobalt oxide, and 400 g of the mixed powder and lithium carbonate powder 161.1g was mixed and the powder of the raw material mixture was obtained. The obtained raw material mixed powder was fired at about 500 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
[ Experimental Example 25 ]
2000 g of cobalt tetroxide (Co ₃ O ₄ ) powder and magnesium hydroxide (Mg (OH) ₂ ) powder were mixed so that the magnesium content was 10 mol% with respect to cobalt tetroxide, and 400 g of the mixed powder was obtained. 177.1 g of lithium carbonate powder was mixed to obtain a powder of the raw material mixture. The obtained raw material mixed powder is fired at about 500 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
[ Experimental example 26 ]
2000 g of tribasic cobalt oxide (Co ₃ O ₄ ) powder and calcium hydroxide (Ca (OH) ₂ ) powder were mixed so that the calcium content was 10 mol% with respect to tribasic cobalt oxide, and 400 g of the mixed powder was obtained. 172.2 g of lithium carbonate powder was mixed to obtain a powder of the raw material mixture. The obtained raw material mixed powder was fired at about 500 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
[ Experiment 27 ]
2000 g of cobalt trioxide (Co ₃ O ₄ ) powder and sodium hydrogen carbonate (NaHCO ₃ ) powder were mixed so that sodium was 10 mol% with respect to cobalt trioxide, and 400 g of the mixed powder and lithium carbonate 176.6 g of powder was mixed to obtain a powder of a raw material mixture. The obtained raw material mixed powder was fired at about 500 ° C. for about 10 hours. The obtained fired product was pulverized to obtain a positive electrode active material.
2. Properties of positive electrode active material (1) Composition of positive electrode active material The composition of the obtained positive electrode active material was determined by inductively coupled high-frequency plasma spectroscopy (ICP spectroscopy).

As a result, the composition of the positive electrode active material was LiCoO ₂ in any of Experimental Examples 1 to 21 and Comparative Examples 1 and 2.
(2) Measurement of peak of positive electrode active material by X-ray diffraction method The obtained positive electrode active material was subjected to an X-ray diffraction method. The X-ray diffraction method was performed using an X-ray diffractometer (Ultimate, manufactured by Rigaku Corporation), using CuKα1 as an X-ray source, and a tube current of 40 mA and a tube voltage of 40 kV.

As a result, between 2θ = 18.4 and 19.6 °, in Experimental Examples 1 to 27 , a peak due to a layered structure near 18.9 ° and a peak due to a spinel structure near 19.2 ° In Comparative Examples 1 and 2, a peak due to a layered structure around 18.9 ° was measured. Tables 1 and 2 show ratios (peak ratios) of measured peak values and peak values attributed to the lamellar structure near 18.9 ° and peak values attributed to the spinel structure near 19.2 °. Shown in

9A to 9C show the X-ray diffraction patterns of Experimental Examples 1 , 7 and 12, and FIGS. 10A to 10C show the X-ray diffraction patterns of Experimental Example 20 and Comparative Examples 1 and 2. FIGS. 11A to 11C show X-ray diffraction patterns of Experimental Examples 22 to 24, and FIGS. 12A to 12C show X-ray diffraction patterns of Experimental Examples 25 to 2, respectively.
(3) R104 of the positive electrode active material (104) crystallinity Based on the X-ray diffraction pattern obtained by the X-ray diffraction method, from the Scherrer equation represented by the above formula (1), R3m of the positive electrode active material The (104) crystallinity was determined. The results are shown in Table 1.
(4) Median diameter of positive electrode active material (D ₅₀ )
The particle size distribution of the obtained positive electrode active material was measured by a laser diffraction scattering method to determine the median diameter. The results are shown in Table 1.
3. Evaluation of positive electrode active material (1) Preparation of secondary battery for testing
For each positive electrode active material obtained in Experimental Examples 1-27, Examples 1 and 2, and Comparative Examples 1 and 2, test secondary batteries were prepared and evaluated as follows.

A paste was prepared by kneading 60 parts by weight of the positive electrode active material powder, 20 parts by weight of carbon powder as a conductive agent, and a normal methylpyrrolidone solution of polyvinylidene fluoride (20 parts by weight as the amount of polyvinylidene fluoride). The obtained paste was applied to a positive electrode current collector to obtain a test secondary battery in which the negative electrode was lithium metal.
(2) Initial characteristics Charging / discharging of the test secondary battery was performed at 25 ° C. under the following conditions.

That is, constant current constant voltage charging was performed at a constant current value of 0.2 mA / cm ² , a constant voltage value of 4.3 V, and a charge termination condition of 0.02 mA, and then a discharge current value of 0.2 mA / cm ² and a discharge termination condition of 2 A constant current was discharged at .75V.

  The charge capacity of the 1st cycle obtained at this time was defined as the initial charge capacity, and the discharge capacity was defined as the initial discharge capacity.

The initial efficiency was determined by dividing the obtained initial discharge capacity value by the initial charge capacity value. In addition, the difference between the obtained initial charge capacity value and the initial discharge capacity value was determined to obtain an irreversible capacity. The results for each positive electrode active material obtained in Experimental Examples 1 to 27 and Comparative Examples 1 and 2 are shown in Tables 1 and 2. In addition, it is excellent in an overdischarge characteristic, so that an irreversible capacity | capacitance is large.
(3) Swelling portion or flat portion of discharge curve at initial discharge The test secondary battery was discharged under the conditions of a charging potential of 4.3 V, a discharging potential of 2.75 V, and a discharging current value of 0.2 mA / cm ² . In the discharge curve, it was examined whether or not it has a blister or flat portion in the range of 3.0 to 3.5V.

As a result, when each positive electrode active material obtained in Experimental Examples 1 to 27 was used, a blistered portion or a flat portion was observed. Among these, the charge / discharge curves for the respective positive electrode active materials obtained in Experimental Examples 3 and 12 are shown in FIG. 1A is a charge / discharge curve of Experimental Example 3, and FIG. 1B is a charge / discharge curve of Experimental Example 12. FIG. In FIGS. 1A and 1B, the curves from the lower left to the upper right are charging curves, and the curves from the upper left to the lower right are discharge curves.
(4) Thermal stability Charging / discharging with a constant current was performed using a secondary battery for testing, and it was made to adapt. Thereafter, constant current and constant voltage charging was performed at a constant current value of 0.2 mA / cm ² , a constant voltage value of 4.3 V, and a charge termination condition of 0.02 mA. After the charging was completed, the positive electrode was taken out from the test secondary battery, washed with one component solution contained in the electrolytic solution used in the test secondary battery, and dried, and the positive electrode mixture was scraped off from the positive electrode. In an aluminum cell, ethylene carbonate used for the electrolyte and the positive electrode mixture scraped from the positive electrode were put in a weight ratio of 0.40: 1.00, and the differential scanning calorific value was measured at a heating rate of 5.0 ° C./min. .

  Differential scanning calorimetry (DSC) is a method of measuring the difference in energy input between a substance and a reference substance as a function of temperature while changing the temperature of the substance and the reference substance according to a program. Although the differential scanning calorific value did not change even when the temperature rose in the low temperature part, the differential scanning calorific value greatly increased above a certain temperature. The temperature at this time was defined as the heat generation start temperature. The higher the heat generation start temperature, the better the thermal stability.

Table 5 shows the heat generation start temperatures of the positive electrode active materials obtained in Experimental Example 11, Example 1, and Comparative Example 1. The heat generation start temperature was measured at n = 2.
(5) Production of Laminate Battery For each positive electrode active material obtained in Examples 1 and 2 and Comparative Examples 1 and 2, a laminate battery was produced and evaluated as follows.

A positive electrode plate was obtained in the same manner as in the case of the test secondary battery. Also, graphite was used as the negative electrode active material, and applied to a negative electrode current collector made of copper and dried to obtain a negative electrode plate. A porous polypropylene film was used as the separator. As the electrolytic solution, a solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate = 3/7 (volume ratio) to a concentration of 1 mo1 / L was used. The positive electrode plate, the negative electrode plate, and the separator were formed into a thin sheet, laminated, and stored in a battery case of a laminated film, and an electrolyte solution was injected into the battery case to obtain a laminated battery.
(6) Overdischarge characteristics Under conditions of a charge potential of 4.2 V and a discharge load of 0.2 C (where 1 C is a current load that completes the discharge in one hour), a bipolar voltage (a positive potential and a negative potential) The laminate battery was discharged until the difference was 0V. Table 3 shows the negative electrode potential after discharge for each positive electrode active material obtained in Example 2 and Comparative Example 1. In addition, the negative electrode potential at this time was measured using the potential of the Li metal inserted into the laminated battery as a reference electrode as a reference potential.

Thereafter, charge and discharge were repeated under the conditions of a charge potential of 4.2 V, a discharge potential of 2.75 V, and a discharge load of 0.2 C, and capacity retention rates (discharge capacity / charge capacity) at the 100th cycle and the 200th cycle were calculated. Table 3 shows capacity retention rates at the 100th cycle and the 200th cycle for each positive electrode active material obtained in Example 2 and Comparative Example 1.
(7) Capacity recovery rate The laminate battery was discharged until the bipolar voltage became 0 V under the conditions of a charging potential of 4.2 V and a discharge load of 0.2 C, and further held at 0 V voltage for 15 hours. At this time, the value of the charge capacity before discharge was defined as the capacity before overdischarge.

  Next, the discharged laminate battery was charged to a charging potential of 4.2V. The value of the charge capacity at this time was defined as the capacity after overdischarge.

The obtained capacity value after overdischarge was divided by the capacity value before overdischarge to obtain the capacity recovery rate. Table 4 shows the results of the capacity before overdischarge, the capacity after overdischarge, and the capacity recovery rate of each positive electrode active material obtained in Example 2 and Comparative Example 1. In Tables 1 and 2, items that are not measured are indicated by “−”.

As is apparent from Tables 1 to 5, the non-permanent electrolyte secondary batteries (Examples 1 and 2 ) of the present invention using the positive electrode active material of the present invention have only a layered structure and a spinel structure. When a positive electrode active material which does not have two or more independent peaks between 2θ = 18.4 and 19.6 °, which is obtained by X-ray diffractometry, is used. Compared with (Comparative Examples 1 and 2), it has excellent overdischarge characteristics and thermal stability.

2 is a charge / discharge curve for each positive electrode active material obtained in Examples 3 and 12. FIG. It is a graph which shows typically the change of the electric potential of the positive electrode and negative electrode at the time of charging / discharging cycle of a lithium ion secondary battery. It is a schematic diagram which shows the crystal structure of the lithium transition metal complex oxide of a layered structure. It is a schematic diagram which shows the crystal structure of lithium transition metal complex oxide of a spinel structure. It is typical sectional drawing of a positive electrode. It is typical sectional drawing of a cylindrical battery. It is a typical fragmentary sectional view of a coin type battery. It is a typical perspective view of a square battery. It is an X-ray diffraction pattern of Experimental Examples 1, 7, and 12. It is an X-ray diffraction pattern of Experimental Example 20 and Comparative Examples 1 and 2. It is an X-ray diffraction pattern of Experimental Examples 22-24 . It is an X-ray-diffraction pattern of Experimental example 25-27 .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 3a site 1 '8a site 2 6c site 2' 32e site 3 3b site 3 '16d site 4' 16c site 5 Binder 6 Positive electrode active material 11 Negative electrode 12 Current collector 13 Positive electrode 14 Separator 20 Cylindrical battery 30 Coin type Battery 40 Square battery

Claims (4)

A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a main active material having a first lithium transition metal composite oxide and a secondary active material having a second lithium transition metal composite oxide,
The first lithium transition metal composite oxide has only a layered structure, and has a lithium transition having only a peak due to the layered structure between 2θ = 18.4 and 19.6 ° obtained by an X-ray diffraction method. A metal complex oxide,
The second lithium transition metal composite oxide is obtained by firing a raw material containing lithium and cobalt at 800 ° C. or lower, has at least a layered structure and a spinel structure, and 2θ = 18 obtained by an X-ray diffraction method. A lithium transition metal composite oxide having two or more independent peaks between .4 and 19.6 °;
The amount of the secondary active material is 1 to 30% by weight with respect to the amount of the positive active material. The positive active material for a non-aqueous electrolyte secondary battery (provided that the surface of the primary active material is made of the secondary active material ). Excluding those covered with a surface treatment layer) . A positive electrode comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1;
A negative electrode having a negative electrode active material and a negative electrode current collector made of metallic lithium, a lithium alloy, a carbon material capable of occluding and releasing lithium ions, or a compound capable of occluding and releasing lithium ions;
A nonaqueous electrolyte secondary battery comprising a separator containing an electrolyte sandwiched between the positive electrode and the negative electrode.   The nonaqueous electrolyte secondary battery according to claim 2, wherein a ratio of the initial discharge capacity to the initial charge capacity is 90% or less.   The non-aqueous electrolyte secondary battery according to claim 1, wherein a discharge curve at the time of initial discharge has a blister portion or a flat portion in a range of 3.0 to 3.5V.

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