JP2002075361A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery whose positive electrode active material chiefly consists of lithium manganate of spinell structure excellent in the high-temperature cyclic characteristic and high-temperature storing performance while the charge-discharge capacity is well secured. SOLUTION: The amount of positive electrode active material per unit amount of negative electrode active material can be reduced by mixing a material having a higher charge-discharge capacity than the main component of the positive electrode active material as the residue, and accordingly the contraction at charging of the positive electrode active material can be as a whole suppressed, so that there is less risk that the negative electrode active material (carbon material) expands and slackens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery which can be used as a battery for electric vehicles and portable electronic devices.

[0002]

2. Description of the Related Art In recent years, cordless electronic devices such as video cameras and portable telephones have been remarkably developed, and lithium secondary batteries having a high battery voltage (4V class) and a high energy density have attracted attention as power supplies for these devices. ing. Also, electric vehicles and hybrid vehicles are being developed in the field of automobiles due to environmental problems and the like, and lithium-ion secondary batteries are attracting attention as power sources for mounting.

As for the positive electrode active material used in this battery, LiCoO ₂ , LiNi
Lithium transition metal composite oxides such as O ₂ and LiMn ₂ O ₄ have been studied. As for LiCoO ₂ and LiNiO _2, there is a problem that the raw materials are high. On the other hand, lithium manganate LiMn ₂ O ₄ has attracted attention because it is easy to synthesize, has abundant resources and is very inexpensive.

With respect to the negative electrode active material, a carbon material has been mainly studied as a material which does not accompany the growth of Li dendrite accompanying charge / discharge and the deterioration of capacity due to powdering of Li.

However, when LiMn ₂ O ₄ is used as a positive electrode active material, the crystal structure of the positive electrode becomes unstable in a charged state where Li ions are released (deintercalated), and the composition of the positive electrode active material is reduced. There was a problem that trivalent Mn was disproportionated to tetravalent Mn and divalent Mn, and the charge / discharge capacity was significantly reduced at room temperature (the cycle characteristics at room temperature were poor).

In order to solve such a problem, LiMn is used.
A part of Mn in ₂ O ₄ is replaced with another element (Fe, Co, Ni,
Al, etc.) (JP-A-4-282560,
JP-A-4-160969, JP-A-5-28991, JP-A-9-213333, JP-A-9-270259, etc., and a method of substitution with Li (JP-A-2-270268, JP-A-4-123969, JP-A-7-282798) Etc.) have been attempted to strengthen the crystal structure of the positive electrode.
The charge-discharge characteristics at room temperature and the like were improved to some extent if the replacement amount was increased by this method.

[0007]

However, the compositions disclosed in the above publications are significantly deteriorated (even at about 60 ° C. necessary for practical use) in a high-temperature environment, and are still associated with charge / discharge cycles. This leads to a remarkable decrease in capacity and a decrease in storage or storage characteristics (remaining capacity after high-temperature storage and recovery capacity when charged and discharged after storage). When the replacement amount is increased, the charge / discharge capacity is greatly reduced, which will be described separately.

In a system in which a carbon material is combined as a Mn-based positive electrode active material and a negative electrode active material, a side reaction between the carbon material into which Li has been inserted (intercalated) and the electrolytic solution occurs under a high temperature environment. In the vicinity of the carbon negative electrode surface, an inactive Li compound is generated with respect to the battery reaction, resulting in large capacity deterioration (the Li compound is present as a film on the carbon surface). Although various research institutes are conducting various researches to solve such problems,
How to control it has not yet been resolved.

Therefore, the present invention provides a lithium ion secondary battery using lithium manganate having a spinel structure as a main positive electrode active material, which is excellent in high-temperature cycle characteristics and high-temperature storage properties while securing charge / discharge capacity. Is a problem to be solved.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a side reaction between a carbon material into which Li is inserted and a non-aqueous electrolyte during charging when Li is inserted into the carbon material. It has been found that the side reaction easily occurs when the highly reactive carbon surface is exposed. Therefore, once the inactive Li compound generated by the side reaction on the carbon surface always covers the carbon surface as a film, it is considered that the further side reaction is reduced.

However, during charging, the crystal lattice of the spinel-type lithium manganese composite oxide on the positive electrode side largely shrinks with the release of Li ions, and the carbon material on the negative electrode side expands with the insertion of Li ions. for that reason,
During charging, the carbon material on the negative electrode side is likely to be loosened, and it is assumed that the loosened carbon material causes macroscopic movement of the carbon material. Due to this movement of the carbon material, the film of the Li compound existing on the surface of the carbon material is mechanically partially removed to expose the surface of the highly reactive carbon material, or the adjacent carbon material particles move to remove the Li material. The part where the compound film is not adsorbed is exposed, or the carbon material particles are split
It is considered that a side surface is promoted by generating a new surface on which the compound film is not adsorbed. Therefore, in order to suppress such side reactions, it is only necessary to reduce the looseness of the carbon material.

That is, a lithium ion secondary battery according to the present invention which solves the above-mentioned problems comprises a positive electrode having a positive electrode active material capable of doping and undoping lithium ions, and a negative electrode comprising a carbon material capable of doping and undoping lithium ions. In a lithium ion secondary battery having a negative electrode having an active material and a non-aqueous electrolyte, the positive electrode active material is mainly composed of a spinel-type lithium manganese-containing composite oxide and the spinel-type lithium manganese-containing composite oxide And a residual component composed of a lithium-containing composite oxide having a larger charge / discharge capacity per unit mass than that of a lithium-containing composite oxide.

That is, if a material having a higher charge / discharge capacity than the main component of the positive electrode active material is mixed as a residual component, the amount of the positive electrode active material per unit amount of the negative electrode active material can be reduced. Since the shrinkage of the material during charging can be suppressed, there is less room for expansion and loosening of the negative electrode active material (carbon material).

Further, it is preferable that the charge / discharge capacity per unit mass of the residual component is 1.3 times or more higher than that of the main component, because the effect becomes more remarkable.

Further, a lithium ion secondary battery according to the present invention for solving the above-mentioned problems comprises a positive electrode having a positive electrode active material capable of doping and undoping lithium ions, and a negative electrode comprising a carbon material capable of doping and undoping lithium ions. In a lithium ion secondary battery having a negative electrode having an active material, a separator, and a non-aqueous electrolyte, the positive electrode active material contains a main component composed of a spinel-type lithium manganese-containing composite oxide, and a layered structure containing lithium. And a residual component comprising a composite oxide.

That is, since the lithium-containing composite oxide having a layered structure has a layered structure of transition metal-oxygen-lithium-oxygen-transition metal, when Li is released in a charged state, strong static electricity is generated between oxygen layers. Electrostatic repulsion acts, the crystal structure expands in the direction of the interlayer, and the shrinkage during charging becomes smaller than that of the spinel-type lithium manganese composite oxide. This is because the shrinkage of the positive electrode active material during charging can be suppressed, and the room for expansion and loosening of the negative electrode active material (carbon material) is reduced.

Further, in order to more reliably exert the effect, it is preferable that the mass ratio of the residual component to the entire positive electrode active material is 5/100 or more.

By the way, in a battery using LiMn ₂ O ₄ as a positive electrode, an ideal positive electrode charging reaction at a 4V class battery voltage is represented by the following equation.

LiMn ₂ O ₄ → Li _1-x Mn ₂ O ₄ + X
Li ⁺ + Xe ⁻ → Mn ₂ O ₄ + Li ⁺ + e ^{− In} other words, when LiMn ₂ O ₄ is charged, Li ions (Li ⁺ ) in the crystal are extracted, and ideally Mn ₂ O ₄ (λ−M
nO ₂ ). At that time, the valence of Mn in the crystal is trivalent or tetravalent, and the average oxidation valence of Mn changes from 3.5 (discharged state) to tetravalent (charged state). It should be noted that the reverse process occurs during discharging.

Therefore, the theoretical capacity of LiMn ₂ O ₄ (L
The i-ion extraction amount is 148 mAh / g (actually, when X is large, the ion conductivity inside the crystal is reduced, so that it is not completely extracted).

In order to maintain such a battery reaction without lowering the capacity, there is no change in the composition of the active material in the Li _1-x Mn ₂ O ₄ during each oxidation (the oxidation value of Mn due to the change in the composition). The capacity changes when the range in which the number can be changed changes),
In addition, it is necessary that the ionic conductivity and the electron conductivity do not significantly decrease in the crystal, inside the surface, etc. of the active material.

The main cause of such capacity deterioration is the disproportionation of Mn in the positive electrode active material. That is, the crystal of the active material is distorted and unstable (especially at a high temperature) in a state close to the charging state in which the crystal lattice is contracted (a state in which Li has escaped to some extent in LiMn ₂ O ₄ ), and Mn ³⁺ in the active material is 2Mn ^{3 +} → Mn ⁴⁺ +
Disproportionate like Mn ²⁺ . As a result, Mn ⁴⁺ increases (Mn ³⁺ decreases), and Mn ²⁺ which does not originally exist is newly generated and adheres to the surface of the positive electrode active material or dissolves in the electrolytic solution. As a result, the composition of the positive electrode active material itself changes (the average Mn oxidation valency increases), causing a decrease in capacity,
Mn oxides and the like caused by ²⁺ move and grow on the active material surface, grain boundaries, and defects, and become resistance to Li movement, resulting in a decrease in capacity.

It is considered that such a disproportionation of Mn occurs in the interior of the crystal.
The most frequent locations are a crystal transition portion where crystal strain tends to concentrate, a composition defect portion, an active material surface, and the like.

As a method of suppressing the disproportionation of Mn, conventionally, a part of Mn in the positive electrode active material is replaced with Li or another element (LiMn _2-x M _x O ₄ ; M is Li or other element). Element) method. That is, by replacing a part of Mn with another element, the electron orbit in the crystal is changed, and the bonding force between Mn-O forming the skeleton of the crystal is increased to strengthen the crystal structure. It is aim. Since the lattice constant becomes smaller as the substitution amount of other elements is actually increased (≒ Mn—O bond distance is shortened), the electrostatic energy between Mn—O increases and the bond strength is strengthened. You can see that.

As a result of the study, it was found that the effect of substituting another element greatly varies depending on the element type. That is,
How much electrons can be supplied between the skeleton Mn-O,
It is considered that the ionic radius affecting the lattice constant changes depending on whether it is larger or smaller than Mn. When the substitution amount is increased, Mn4 valence having an ionic radius smaller than Mn3 valence increases, and the lattice constant can be further reduced.

However, contrary to the above effects, the substitution of another element causes a reduction in capacity.

That is, depending on the valence of the element to be replaced, the average oxidation valence of Mn in the discharged state becomes larger than 3.5, so that the amount of movable Li decreases and the capacity decreases. further,
As the substitution amount of the other element increases and the valence of the substitution element decreases, the average oxidation valency of Mn increases, so that the capacity decrease is large.

Therefore, the effect of replacing other elements (structural enhancement) is more effective as the amount of substitution increases, but the capacity also decreases greatly (when the amount of substitution increases extremely, the A single composition having a structure cannot be obtained, making synthesis difficult and reducing the effect).

Considering the element type, L as a substitution element type
Although i has a very high deterioration suppressing effect as compared with other elements, i has a valence of 1, so that the oxidation valence in the discharged state is large and the capacity is significantly reduced. Al, on the other hand,
Although the effect of suppressing deterioration is slightly inferior to that of Li, the effect of suppressing deterioration is high because the ionic radius is small and the effect of reducing the lattice constant is high as compared with other element types other than Li. Further, since the valence of the substitution element (Al) is substantially trivalent, the reduction in capacity can be suppressed as compared with Li substitution, and the substitution element (Al) is the most suitable substitution element species for improving the characteristics while securing the capacity (it is also inexpensive). .

Therefore, in order to secure high-temperature cycle characteristics and high-temperature storability while securing charge / discharge capacity, the crystal structure is strengthened as much as possible by substituting part of Mn with another element by Al or the like. Further, it is necessary to suppress a side reaction between the carbon material into which Li has been inserted and the electrolytic solution.

Therefore, the main component is preferably further
A lithium manganese composite oxide having an Al element is more preferable.
Preferably, the main component is of the general formula Li_{1 + x}Mn_2-xyzAl_y
M_zO _Four, 0.05 ≧ x ≧ 0, 0.35 ≧ y ≧ 0.2,
0.15 ≧ z ≧ 0, M: small amount other than Li, Mn and Al
Lithium man represented by at least one metal element)
Gunn composite oxides are desirable.

Further, it is preferable that the residual component is a layered lithium metal-containing composite oxide containing at least one of manganese, cobalt and nickel.

Furthermore, it is preferable that the residual component is a lithium nickel cobalt-containing composite oxide having a layered structure.

Further, it is preferable that the residual component is a lithium nickel cobalt aluminum-containing composite oxide having a layered structure.

Preferably, the remaining component is a layered lithium iron-containing composite oxide.

As described above, the main parts where Mn disproportionation is likely to occur are the surface of the positive electrode active material and the crystal dislocations.
This is a portion where crystallinity is reduced, such as a defect due to a composition deviation. Therefore, the specific surface area of the main component is 0.9 m ²
/ G or less, it is possible to further suppress the disproportionation of Mn and secure more excellent high-temperature cycle and high-temperature storage characteristics while securing the charge / discharge capacity.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The lithium ion secondary battery of the present invention will be described below based on embodiments. Note that the present invention is not limited by the following embodiments.

The lithium ion secondary battery of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and other necessary elements. The shape of the lithium secondary battery of the present embodiment is not particularly limited, and can be used as batteries of various shapes such as a coin shape, a cylindrical shape, and a square shape. In the present embodiment, description will be given based on a cylindrical lithium secondary battery.

In the lithium secondary battery of the present embodiment, the positive electrode and the negative electrode are formed in a sheet shape, both of which are laminated via a separator, and wound in a spiral shape many times. It is housed in a cylindrical case. The positive electrode and the positive electrode terminal are electrically connected to each other, and the negative electrode and the negative electrode terminal are electrically connected to each other. The method of combining the components of the lithium secondary battery is not particularly limited, and for example, a known method can be used.

The positive electrode has a lithium-metal composite oxide capable of releasing (undoping) lithium ions during charging and occluding (doping) during discharging, as a positive electrode active material. The lithium-metal composite oxide has excellent performance of the active material, such as excellent diffusion performance of electrons and lithium ions. Therefore, when such a composite oxide of lithium and transition metal is used for the positive electrode active material, high charge / discharge efficiency and good cycle characteristics can be obtained. Further, the positive electrode is a positive electrode active material,
It is preferable to use a material obtained by applying a positive electrode mixture obtained by mixing a conductive material and a binder to a current collector. The method for producing the positive electrode is not particularly limited, and for example, a known method can be used.

The positive electrode active material contains a main component and a residual component.
As for the mixing ratio of the main component and the residual component, it is desirable that the mass ratio of the residual component to the whole positive electrode active material is 5/100 or more, more preferably 10/100 or more.

The main component is a spinel-type lithium manganese-containing composite oxide. The main component may further include an Al element, for example, a general formula Li _{1 + x} Mn
_{2-xyz Al y M z O} 4, 0.05 ≧ x ≧ 0,0.35 ≧ y
≧ 0.2, 0.15 ≧ z ≧ 0, M: Li, Mn and A
at least one or more metal elements other than 1).
The main component may be a mixture of a plurality of compounds or a compound having a specific composition as long as it is a spinel-type lithium manganese-containing composite oxide.

The specific surface area of the main component is 0.9 m ² / g
The following is preferred. The specific surface area is a value measured by a BET method using nitrogen adsorption.

Although the method for controlling the specific surface area is not particularly limited, it is preferable to control the raw material by pulverizing and / or classifying the raw material. The specific surface area is greatly affected by the specific surface area of the manganese compound as a raw material. Then, the positive electrode active material may be pulverized and / or classified after firing and production.

Whether the crystal structure of the positive electrode active material for a lithium secondary battery has a spinel structure can be confirmed by an X-ray diffraction pattern or the like in powder X-ray diffraction.

As the remaining component, a lithium-containing composite oxide or a layered lithium-containing composite oxide having a larger charge / discharge capacity per unit mass than the main component can be used. The remaining component may be not only a pure compound but also a mixture of a plurality of compounds.

When a lithium-containing composite oxide having a larger charge / discharge capacity per unit mass than the main component is used as the residual component, the charge / discharge capacity per unit mass of the residual component is 1.3 times that of the main component. Above, preferably 1.5
More preferably, it is at least twice as high.

When the layered structure lithium-containing composite oxide is used as the residual component, lithium manganese-containing composite oxide / lithium cobalt-containing composite oxide / lithium nickel-containing composite, which allows Li to enter and exit as the battery is charged and discharged, Oxide, lithium nickel cobalt-containing composite oxide
Lithium nickel cobalt aluminum-containing composite oxides and lithium iron-containing composite oxides are preferred. And a lithium metal-containing composite oxide having a layered structure containing at least one of manganese, cobalt, and nickel, or a lithium nickel cobalt-containing composite oxide having a layered structure,
More preferably, it is a lithium nickel cobalt aluminum-containing composite oxide having a layered structure, a lithium iron-containing composite oxide having a layered structure, or a mixture of at least one of these layered lithium-containing composite oxides.

The residual components are generally
Within the range where the charge / discharge capacity is higher than the component,
Mix one or more other common lithium-metal oxides
Can also be used. For example, Li_(1-X)NiO_Two,
Li_(1-X)MnO_Two, Li_{(1-X )}Mn_TwoO_Four, Li_(1-X)Co
O_TwoAnd transition metals such as Li, Al, and Cr
Materials added or replaced. Examples of this positive electrode active material
X in the following indicates a number of 0 to 1.

The method for producing such a positive electrode active material is not particularly limited, and a known method can be used.

The negative electrode is a material capable of occluding lithium ions during charging and releasing lithium ions during discharging. In particular, it is preferable to use a material obtained by applying a negative electrode mixture obtained by mixing a negative electrode active material, a conductive material and a binder to a current collector. As the negative electrode active material,
A carbon material can be used. Considering the balance between the output and the regenerative density, the carbon material is preferable because the voltage change accompanying charging and discharging is relatively large. In addition, when a carbon material is used for the negative electrode active material, high charge / discharge efficiency and good cycle characteristics can be obtained. The method for producing the negative electrode is not particularly limited,
For example, a known method can be used.

The non-aqueous electrolyte is obtained by dissolving a supporting salt in an organic solvent.

The organic solvent is not particularly limited as long as it is an organic solvent usually used for an electrolyte of a lithium secondary battery, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, and the like. Lactones,
An oxolane compound or the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-
Dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like and a mixed solvent thereof are suitable.

By using one or more non-aqueous solvents selected from the group consisting of carbonates and ethers among these organic solvents mentioned in the examples, the solubility, dielectric constant and viscosity of the supporting salt can be improved. It is preferable because it is excellent and the charge and discharge efficiency of the battery is high.

The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt,
LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ and LiN
It is preferably at least one kind of an organic salt selected from (SO ₃ CF ₃ ) ₃ and a derivative of the organic salt.

With this supporting salt, the battery performance can be further improved, and the battery performance can be maintained even higher in a temperature range other than room temperature.

The concentration of the supporting salt is not particularly limited, either, and it is preferable to appropriately select the concentration in consideration of the type of the supporting salt and the organic solvent depending on the application. The method for producing the electrolytic solution is not particularly limited, and for example, a known method can be used.

The separator serves to electrically insulate the positive electrode and the negative electrode and hold the electrolyte. For example, a microporous membrane such as polyethylene may be used.
The thickness of the separator is preferably larger than the particle diameters of the positive electrode and the negative electrode in order to ensure insulation between the positive electrode and the negative electrode. The method for producing the separator is not particularly limited, and for example, a known method can be used.

The case is not particularly limited.
It can be made of a known material and form. The method for manufacturing the case is not particularly limited, and for example, a known method can be used.

The gasket ensures electrical insulation between the case and both the positive and negative terminals and the hermeticity of the case. For example, it can be composed of a polymer such as polypropylene which is chemically and electrically stable with respect to the electrolytic solution. The method of manufacturing the gasket is not particularly limited,
For example, a known method can be used.

[0061]

EXAMPLES (Preparation of Positive Electrode Active Material) Electrolytic manganese dioxide (MnO ₂ ) was used so that the molar ratio of Li, Mn, Al, Co, Ni and Fe was as shown in Table 1 with respect to each of Examples and Comparative Examples.
And lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (Li
OH), lithium oxide (Li ₂ O), aluminum hydroxide (Al (OH) ₃ ), cobalt carbonate (CoCO ₃ ), nickel hydroxide (Ni (OH) ₂ ), and iron oxide hydroxide (Fe
O (OH)). The mixing ratio was determined so that the composition of the active material was set so that the initial charge / discharge capacity was substantially the same. For example, Mn-based (LiMn ₂ O ₄ ) mainly contains MnO
₂ and Li ₂ CO ₃ , and Co-based (LiCoO ₂ ) mainly contains C
oCO ₃ and Li ₂ CO ₃ , Ni-based (LiNiO ₂ ) mainly Ni (OH) ₂ and LiOH, Fe-based (LiFe
In O ₂ ), FeO (OH) and Li ₂ O are mainly mixed.
Thereafter, a positive electrode active material was prepared by a conventional method.

The specific surface area was realized by setting the particle size of electrolytic manganese dioxide to a predetermined size.

(Preparation of Lithium Ion Secondary Battery) [Positive Electrode] In each of Examples and Comparative Examples, the positive electrode active materials were mixed at the positive electrode active material compositions and mixing ratios shown in Table 1, and 86 parts by weight of the mixed positive electrode active materials were used. Parts, graphite as a conductive agent at 10 parts by weight, and PVDF as a binder at a ratio of 4 parts by weight in a solvent N.
-Methyl-2-pyrrolidone was mixed to prepare a paste, the paste was applied on an Al foil current collector at a predetermined weight and film thickness, dried, punched into a disk having a diameter of 14 mm, and pressed. Thereafter, the positive electrode was manufactured by vacuum drying.

[Negative electrode] A mixture of 90 parts by weight of mesophase-based carbon and 10 parts by weight of PVDF as a binder,
Mixing into methyl-2-pyrrolidone to make a paste,
This paste was applied on a Cu foil current collector at a predetermined weight and thickness, dried, punched into a disk having a diameter of 15 mm, pressed, and dried under vacuum to produce a negative electrode.

[Non-aqueous electrolyte] LiPF ₆ was dissolved at a concentration of 1 mol / l in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 to prepare a non-aqueous electrolyte. .

[Assembly of Battery] A flat battery having a diameter of 20 mm and a thickness of 3 mm was assembled using the above-described positive electrode, negative electrode and electrolyte solution. Incidentally, a polyethylene microporous membrane was used as a separator.

[0067]

[Table 1]

(Evaluation of Characteristics of Positive Electrode Active Material and Evaluation of High Temperature Characteristics of Lithium Secondary Battery) [Evaluation of Positive Electrode Active Material] The specific surface areas of the positive electrode active materials obtained in Examples and Comparative Examples were evaluated.

The specific surface area was measured using the BET method based on N ₂ adsorption. Table 1 shows the measurement results.

[Evaluation of Charge / Discharge Capacity] The charge / discharge capacity of the batteries obtained in Examples and Comparative Examples was evaluated. The conditions were as follows: charging at room temperature was performed at 4.2 V at a constant current of 1.1 mA / cm ^2.
Thereafter, the test was performed at a constant voltage of 4.2 V for a total of 4 hours. The discharge was performed at a constant current of 0.5 mA / cm ² up to 3 V, and this was repeated 5 cycles. Table 1
5 shows the discharge capacity at the fifth cycle.

[Evaluation of High-Temperature Cycle Characteristics] High-temperature cycle characteristics were evaluated using the batteries obtained in Examples and Comparative Examples (high-temperature cycle evaluations stricter than the storage test were performed). The conditions were as follows: the battery whose charge / discharge capacity was evaluated was 60 ° C.
In a constant temperature bath of 2.2 mA / cm ² ,
Charge and discharge were repeated when the voltage between the battery electrodes was between 4.2 V and 3 V. Table 1 shows the ratio of the discharge capacity at the 400th cycle to the discharge capacity at the first cycle, that is, the capacity retention rate after the cycle.

(Characteristic Evaluation Results of Positive Electrode Active Material and High-Temperature Characteristic Evaluation Results of Lithium Secondary Battery) The results of initial capacity evaluation and high-temperature cycle evaluation are shown in Table 1. As for the initial capacity, a capacity of 90 mAh / g or more was secured for all levels.

When only the main component was used (Comparative Examples 1 and 2), the performance was improved by substituting other elements, but it was confirmed that the deterioration was still large.

In the case where the main component was lithium manganese oxide having a spinel structure in which no other element was substituted (Comparative Examples 3 to 8), no significant improvement in characteristics was confirmed even when the remaining components were mixed.

When the spinel-type lithium manganese oxide was mixed (Comparative Examples 9 to 12, Examples 1 and 2), the charge / discharge capacity ratio of the main component to the residual component (residual component / main component) was 1.
It was confirmed that the performance was greatly improved when the mixing weight ratio (residual component to be mixed / (main component + residual component)) was 3/100 or more and 5/100 or more.

Further, by mixing a compound having a layered structure as a residual component with a main component substituted with another element (Al substitution), the mixture weight ratio (residual component / (main component + residual component)) is 5/100 or more. In this case, it was confirmed that the performance could be greatly improved. When the mixing weight ratio (residual component / (main component + residual component)) was 10/100 or more, it was confirmed that the effect of mixing increased and the performance was greatly improved.

[0077]

Accordingly, the present invention provides a lithium ion secondary battery using lithium manganate having a spinel structure as a main positive electrode active material having excellent high-temperature cycle characteristics and high-temperature storability while securing charge / discharge capacity. It has the effect that it can be done.

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Claims (11)

[Claims] 1. A lithium battery comprising: a positive electrode having a positive electrode active material capable of doping and undoping lithium ions; a negative electrode having a carbon material capable of doping and undoping lithium ions as a negative electrode active material; and a nonaqueous electrolyte. In the ion secondary battery, the positive electrode active material is mainly composed of a spinel-type lithium manganese-containing composite oxide and a lithium-containing composite oxide having a larger charge / discharge capacity per unit mass than the spinel-type lithium manganese-containing composite oxide. A lithium ion secondary battery having a residual component composed of a material. 2. The charge / discharge capacity per unit mass of the residual component is 1.3 times or more higher than that of the main component.
4. The lithium ion secondary battery according to 1. 3. A positive electrode having a positive electrode active material capable of doping and undoping lithium ions; a negative electrode having a carbon material capable of doping and undoping lithium ions as a negative electrode active material; a separator; Wherein the positive electrode active material has a main component comprising a spinel-type lithium manganese-containing composite oxide and a residual component comprising a layered structure lithium-containing composite oxide. Lithium ion secondary battery. 4. The lithium ion secondary battery according to claim 1, wherein a mass ratio of the residual component to the entire positive electrode active material is 5/100 or more. 5. The lithium ion secondary battery according to claim 1, wherein said main component further has an Al element. 6. The method according to claim 1, wherein the main component is a general formula Li _{1 + x} Mn _{2-xyz
Al y M z O 4, 0.05} ≧ x ≧ 0,0.35 ≧ y ≧ 0.
2, 0.15 ≧ z ≧ 0, M: at least one or more metal elements other than Li, Mn and Al).
6. The lithium ion secondary battery according to any one of claims 1 to 5. 7. The specific surface area of the main component is 0.9 m ² / g.
The lithium ion secondary battery according to claim 1, wherein: 8. The method according to claim 1, wherein the residual component is manganese-cobalt.
The lithium ion secondary battery according to any one of claims 1 to 7, which is a lithium metal-containing composite oxide having a layered structure containing at least one of nickel. 9. The lithium ion secondary battery according to claim 1, wherein the remaining component is a lithium nickel cobalt-containing composite oxide having a layered structure. 10. The composite oxide according to claim 1, wherein the residual component is a lithium nickel cobalt aluminum-containing composite oxide having a layered structure.
8. The lithium ion secondary battery according to any one of items 1 to 7. 11. The lithium ion secondary battery according to claim 1, wherein the residual component is a lithium iron-containing composite oxide having a layered structure.