JP2003197271A - Evaluation method of lithium secondary battery and lithium secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method of a lithium secondary battery in which evaluation of large electric current characteristic of the lithium secondary battery is possible simply and precisely in a short time, and provide the lithium secondary battery which is superior in large electric current characteristics especially in low temperature conditions and which is using the evaluation method of the lithium secondary battery. <P>SOLUTION: This is the evaluation method of the lithium secondary battery which has the inner electrode body comprised that the positive electrode plate formed by using the positive electrode active substance and the negative electrode plate formed by using the negative electrode active substance are wound or laminated via a separator, and which uses a nonaqueous electrolytic solution. The large electric current characteristic of the lithium secondary battery is evaluated by the electric current dependency of the voltage depression measured at a prescribed time after flowing an evaluating current. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an evaluation method of a lithium secondary battery and a lithium secondary battery using the evaluation method.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as small-sized and high-energy-chargeable secondary batteries that serve as a power source for electronic devices such as portable communication devices and notebook personal computers. Is becoming. In addition, as interest in resource saving and energy saving is increasing against the backdrop of the international protection of the global environment, lithium secondary batteries are being considered for active market introduction in the automobile industry, such as electric vehicles (EVs) and hybrids. It is also expected to be used as a motor drive battery for electric vehicles (HEVs) or as a means for effectively utilizing electric power by storing electric power at night, and the commercialization of large-capacity lithium secondary batteries suitable for these applications is urgently needed. .

In a lithium secondary battery, a lithium transition metal composite oxide or the like is generally used as a positive electrode active material, and a carbonaceous material such as hard carbon or graphite is used as a negative electrode active material. Since the reaction potential of the lithium secondary battery is as high as about 4.1 V, it is not possible to use a conventional aqueous electrolyte solution as an electrolyte solution. Therefore, a non-aqueous electrolyte prepared by dissolving a lithium compound, which is an electrolyte, in an organic solvent is used. A liquid is used. Then, the charging reaction causes Li ⁺ in the positive electrode active material to
It occurs by passing through the non-aqueous electrolyte to the negative electrode active material and being captured, and the reverse battery reaction occurs during discharge.

Among these, in a lithium secondary battery having a relatively large capacity, which is preferably used for EV, HEV, etc., a current collecting tab (positive electrode) that functions as a lead wire as an internal electrode body as shown in FIG. Electrode plate (positive electrode plate 2, negative electrode plate 3) to which current collecting tab 5 and negative electrode current collecting tab 6) are attached
The wound electrode body 1 is preferably used, which is wound around the outer circumference of the winding core 7 with the separator 4 interposed therebetween so as not to contact each other.

The positive electrode plate 2 and the negative electrode plate 3 are formed by forming a layer of an electrode active material (referring to both the positive electrode active material and the negative electrode active material) on both surfaces of a current collector substrate such as a metal foil. The current collecting tab 5 and the negative electrode current collecting tab 6 are provided during the work of winding the positive electrode plate 2, the negative electrode plate 3, and the separator 4 around the outer circumference of the winding core 13.
By using means such as ultrasonic welding, the positive electrode plate 2 and the negative electrode plate 3 can be joined at predetermined intervals to the exposed portions of the metal foil bodies.

Further, as shown in the perspective view of FIG. 2, the laminated electrode body 7 has a structure in which a positive electrode plate 8 and a negative electrode plate 9 each having a predetermined shape and having a certain area are alternately laminated while sandwiching a separator 10. Therefore, at least one current collecting tab (positive electrode current collecting tab 11, negative electrode tab 12) is attached to each electrode plate. The materials for forming the positive electrode plate 8 and the negative electrode plate 9 and the manufacturing method thereof are the same as those of the wound electrode body 1 shown in FIG.
The same as the positive electrode plate 8 and the negative electrode plate 9 in.

Batteries used for EV, HEV, etc.,
In addition to having a large capacity, instantaneous large current discharge may be required when starting the engine or climbing slopes.
Characteristics that meet these requirements (hereinafter referred to as "large current characteristics"
Is written. Is expected to be developed. In particular, regarding batteries that are expected to be used under low temperature conditions such as in-vehicle batteries, -30 to -2
It is required to have a characteristic that a large current of about 20 C flows even under a temperature condition such as 0 ° C.

[0008]

To determine whether or not the battery has the above-mentioned large current characteristics, the internal resistance is measured by actually flowing a large current through the battery to be evaluated, and this value is used as an index. It is possible to evaluate. However,
When such an evaluation method is carried out, the battery is likely to remain damaged, and it may be difficult or impossible to carry out subsequent evaluations of the battery characteristics, and expensive equipment is required. Had.

Further, even if the same members and parts are selected and the lithium secondary battery is manufactured through the same manufacturing process, the large current characteristics given to the obtained battery are It is difficult to prevent the occurrence of variations. In addition, when a plurality of batteries having such variations in battery characteristics are connected and used, it may be assumed that the individual battery characteristics are not sufficiently exhibited.
If the battery is manufactured through strict selection of members / parts and manufacturing process in order to solve such a problem, the manufacturing cost may increase.

The present invention has been made in view of the above problems of the conventional technique, and an object of the present invention is extremely simple and accurate in a short time with high current characteristics of a lithium secondary battery. A method for evaluating a lithium secondary battery capable of evaluating, and a lithium secondary battery using the method for evaluating a lithium secondary battery, which has excellent large current characteristics particularly under low temperature conditions. .

[0011]

Means for Solving the Problem That is, according to the present invention, a positive electrode plate made of a positive electrode active material and a negative electrode plate made of a negative electrode active material are wound or laminated with a separator interposed therebetween. A method for evaluating a lithium secondary battery using a non-aqueous electrolytic solution, which comprises an internal electrode body, wherein the current dependence of a voltage drop measured after a predetermined time by passing an evaluation current causes the lithium secondary battery to Provided is a method for evaluating a lithium secondary battery, which is characterized by evaluating a large current characteristic.

In the present invention, it is preferable to measure the voltage drop that occurs 1 second after flowing two or more different evaluation currents, and the large current characteristics are the maximum capacity Q _max (Ah) of the lithium secondary battery and the following. It is preferably represented by the value of the current I ₀ and the coefficient α at −25 ° C. calculated according to the equations (7) to (9).

[0013]

(Equation 7) ΔE = a + b × ln (I) (7) (where ΔE is a voltage drop (V), I is an evaluation current (A), and a and b are ln (I) respectively X and ΔE. Is the slope of the XY graph in which Y is plotted as Y, and the Y intercept.)

[0014]

A = R × {T / (α × F)} × ln (I ₀ ) ... (8) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

[0015]

## EQU9 ## b = R × T / (α × F) (9) (where, R is a gas constant (8.314 J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

In the present invention, when the current I ₀ (A) and the maximum capacity Q _max (Ah) satisfy the relationship of I ₀ / Q _max > 0.5 and the coefficient α is 0.02 or more. It is preferable to evaluate that the large current characteristics are excellent.

In the present invention, lithium manganate having a cubic spinel structure is preferably used as the positive electrode active material, and lithium manganate having a Li / Mn ratio of more than 0.5 is preferably used.

Further, in the present invention, as the positive electrode active material, a part of the transition element Mn in lithium manganate (LiMn ₂ O ₄ ) contains Ti, and in addition, Li, Fe,
Ni, Mg, Zn, B, Al, Co, Cr, Si, S
LiM _X Mn _2-X O ₄ (provided that at least one element selected from the group consisting of n, P, V, Sb, Nb, Ta, Mo and W is substituted with two or more elements) It is preferable to use M as a substitution element and X as a substitution amount.

In the present invention, it is preferable to use at least one selected from the group consisting of artificial graphite, natural graphite, amorphous carbon, and amorphous carbon as the negative electrode active material. It is preferable to use a mixed solvent of a cyclic carbonate and a chain carbonate as the solvent.

Further, according to the present invention, in the battery case
The positive electrode plate using the positive electrode active material and the negative electrode active material
Wound or laminated with a negative electrode plate formed by interposing a separator
With an internal electrode body made of
Is impregnated with a non-aqueous electrolyte that is dissolved in an organic solvent.
A lithium secondary battery having the following formulas (10) to (1
The lithium content at -25 ° C calculated according to 2)
Secondary battery current I ₀Of (A) and coefficient α, the current I
₀(A) is the maximum capacity Q of the lithium secondary battery _max(A
h) and I₀/ Q_maxSatisfies the relationship of> 0.5,
Richiu, wherein the coefficient α is 0.02 or more
A secondary battery is provided.

[0021]

(Equation 10) ΔE = a + b × ln (I) (10) (where ΔE is a voltage drop (V), I is an evaluation current (A), and a and b are ln (I) respectively X and ΔE. Is the slope of the XY graph in which Y is plotted as Y, and the Y intercept.)

[0022]

A = R × {T / (α × F)} × ln (I ₀ ) ... (11) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

[0023]

## EQU12 ## b = R × T / (α × F) (12) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

In the present invention, the positive electrode active material has a cubic spinel structure lithium manganate (LiMn ₂
O ₄ ), and the Li / Mn ratio in lithium manganate is preferably more than 0.5.

Further, in the present invention, the positive electrode active material contains Ti as a part of the transition element Mn in lithium manganate (LiMn ₂ O ₄ ), and in addition, Li, Fe, N
i, Mg, Zn, B, Al, Co, Cr, Si, Sn,
P, V, Sb, Nb, Ta, composed of one or more elements selected from the group consisting of Mo and _{W, LiM X Mn 2-X} O 4 obtained by replacing in two or more kinds of elements (where, M is It is preferable that X represents a substitution amount, which is a substitution element.

In the present invention, the negative electrode active material is preferably at least one selected from the group consisting of artificial graphite, natural graphite, amorphous carbon and amorphous carbon, and the organic solvent is at least a symmetrical chain. A mixed solvent containing carbonate and asymmetric chain carbonate is preferable.

INDUSTRIAL APPLICABILITY The lithium secondary battery of the present invention is suitably adopted for a large battery having a battery capacity of 2 Ah or more, and is a motor drive power source or engine for an electric vehicle or a hybrid electric vehicle that frequently discharges a large current. It is preferably used as a power source for startup.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. It should be understood that design changes, improvements, etc. can be appropriately made based on the knowledge of.

A first aspect of the present invention comprises a positive electrode plate made of a positive electrode active material and a negative electrode plate made of a negative electrode active material,
A method of evaluating a lithium secondary battery using a non-aqueous electrolytic solution, which is provided with an internal electrode body that is wound or laminated with a separator interposed between them, and is a voltage drop current measured after a predetermined time by passing an evaluation current. The feature is that the large current characteristic of the lithium secondary battery is evaluated by the dependency. The details will be described below.

In the present invention, an evaluation current is passed through the lithium secondary battery to be evaluated, and the large current characteristic, which is the characteristic of the battery when a large current is passed compared to the evaluation current, is evaluated. . That is, since it is not necessary to measure the internal resistance, which is an index for evaluating the large current characteristics, by actually flowing a large current, damage to the battery is unlikely to remain, and evaluation of other battery characteristics, etc. There is no problem in using. In addition, since it is a simple evaluation method because no special evaluation equipment is required, it also shows the effect of reducing the manufacturing cost of the battery.

Specific embodiments of the method for evaluating a lithium secondary battery according to the first aspect of the present invention will be described.
As a preferred embodiment, first, the voltage drop that occurs 1 second after flowing two or more different evaluation currents is measured for the lithium secondary battery to be evaluated. By passing "two or more different evaluation currents", it is possible to obtain a plurality of data and make the evaluation contents with higher accuracy. It should be noted that in the present invention, the large current characteristic is defined as the maximum capacity Q _max (Ah) of the lithium secondary battery to be evaluated and the following formula (1)
3) to (15) and can be represented by the current I ₀ (A) at −25 ° C. and the value of the coefficient α.

[0032]

(Equation 13) ΔE = a + b × ln (I) (13) (where ΔE is the voltage drop (V), I is the evaluation current (A), and a and b are ln (I) for X and ΔE, respectively) Is the slope of the XY graph in which Y is plotted as Y, and the Y intercept.)

[0033]

A = R × {T / (α × F)} × ln (I ₀ ) ... (14) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

[0034]

B = R × T / (α × F) (15) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

Specifically, the evaluation current I having two or more different values is passed through the lithium secondary battery, and the voltage drop ΔE generated 1 second after that is measured. Next, a graph in which ln (I) is plotted on the horizontal axis (X axis) and ΔE on the vertical axis (Y axis) is created, and the slope obtained by the least squares method is represented by b and the intercept ( Y intercept) is calculated as a.
From the calculated values of a and b, the current I ₀ and the coefficient α at an arbitrary temperature (T) can be calculated according to the above equations (14) and (15). The method for measuring the maximum capacity Q _max will be described later, but it may be measured based on a standard method.

The inventors of the present invention represent the large current characteristics of the lithium secondary battery to be evaluated by the measured and calculated maximum capacity Q _max , and the current I _{0 at} −25 ° C. and the value of the coefficient α. Found that is possible. The "evaluation current" referred to in the present invention is a current passed to the lithium secondary battery to be evaluated in order to evaluate its large current characteristic, and the "large current" of the evaluated large current characteristic. "
The current is low compared to. As an example, when evaluating the large current characteristic with respect to a current value of 150 A, the evaluation current may be 5 to 30 A, and preferably 8 to 25 A.

In the present invention, the current I ₀ (A) and the maximum capacity Q _max (Ah) at −25 ° C. are I ₀ / Q _max >
When the coefficient α is 0.02 or more while satisfying the relationship of 0.5, it is preferable to evaluate that the large current characteristic of the lithium secondary battery to be evaluated is good, and I ₀
It is more preferable to evaluate that the large current characteristic is good when the relationship of / Q _max > 0.7 is satisfied and the coefficient α is 0.03 or more. A lithium secondary battery satisfying the evaluation criteria has a low internal resistance at high current under low temperature conditions such as −30 to −20 ° C., for example,
Excellent high current characteristics are given. Further, since the quality I / _O of the large current characteristic can be determined by the calculated current I ₀ and the coefficient α, the battery component members are appropriately selected, and the current I ₀ and the coefficient α of the manufactured battery are controlled to the optimum values. by doing,
It is possible to stably provide an excellent battery without variations in its characteristics.

In the present invention, when lithium manganate having a cubic spinel structure containing Li and Mn as main components (hereinafter simply referred to as “lithium manganate”) is used, another positive electrode active material is used. Compared to the case, it is preferable because the resistance of the electrode body can be reduced. The excellent effect of giving a large current characteristic in the present invention described above is preferable because it is more prominent when combined with the effect of reducing the internal resistance.

The stoichiometric composition of lithium manganate is L
Although represented by iMn ₂ O ₄ , in the present invention, it is not limited to such a stoichiometric composition, and a part of the transition element Mn contains Ti, and in addition, Li, Fe, Ni, Mg,
Zn, Co, Cr, Si, Sn, P, V, Sb, Nb,
LiM composed of one or more elements selected from the group consisting of Ta, Mo and W and substituted with two or more elements
_X Mn _2-X O ₄ (where M is a substitution element and X represents the substitution amount) is also preferably used.

When the element substitution as described above is performed, the Li / Mn ratio (molar ratio) becomes (1 + X) / (2-X) in the case of Li excess with Mn being replaced by Li, When substituted with a substitution element M other than Li, 1 /
(2-X), so L is always L in any case.
The i / Mn ratio is> 0.5.

In the present invention, as described above, Li / M
It is preferable to use lithium manganate having an n ratio of more than 0.5. This further stabilizes the crystal structure as compared with the case of using a stoichiometric composition,
A lithium secondary battery having excellent cycle characteristics can be obtained.

The substitution element M is theoretically
Li is +1, and Fe, Mn, Ni, Mg, and Zn are +2.
Valence, B, Al, Co, Cr are +3 valence, Si, Ti, Sn
Is +4 valence, P, V, Sb, Nb, Ta is +5 valence, Mo,
W becomes an ion with a valence of +6 and is an element that forms a solid solution in LiMn ₂ O ₄ , but with respect to Co and Sn, in the case of a valence of +2, F
e, Sb, and Ti are +3 valences, Mn is +3 valences, +4 valences, Cr is +4 valences, +
It may be hexavalent. Therefore, the various substitution elements M may exist in a state having mixed valences, and the amount of oxygen does not necessarily have to be 4 as represented by the theoretical chemical composition, and the crystal structure It may be deficient or excessively present within the range for maintaining.

Further, in the present invention, it is preferable to use a highly graphitized carbon material such as artificial graphite or natural graphite, or a material such as amorphous carbon as the negative electrode active material. It is preferable that an internal short circuit due to dendrite, which is seen when a metal is used as a negative electrode, is unlikely to occur, and the safety at the time of battery damage is increased. From the viewpoint of safety, it is more preferable to use a fibrous highly graphitized carbon material as the negative electrode active material.

As the separator, a Li ⁺ permeable polyolefin film is used. Specifically, a three-layer structure in which a Li ⁺ permeable polyethylene film (PE film) having micropores is sandwiched between porous Li ⁺ permeable polypropylene films (PP film) is preferably used. . This is because the PE film is softened at about 130 ° C. and the micropores are crushed when the temperature of the electrode body rises, and also serves as a safety mechanism for suppressing the movement of Li ⁺ , that is, the battery reaction. By sandwiching this PE film between PP films having a higher softening temperature, even if the PE film is softened, P
The P film retains its shape to prevent contact and short circuit between the positive electrode plate 2 and the negative electrode plate 3, and it is possible to reliably suppress battery reaction and ensure safety.

As the separator, paper made of cellulose, cellulose derivative, or a mixture thereof may be used, or a nonwoven fabric containing polyolefin as a main component may be used. Specifically, paper with appropriate size micropores, polypropylene,
It is preferable to use a nonwoven fabric made of polyethylene or the like. Since these materials are porous membranes having a large number of micropores of an appropriate size and have electrical insulation properties, they exhibit physical characteristics suitable as a separator for lithium secondary batteries. Further, since it is inexpensive and easily available, it is possible to reduce the manufacturing cost of the separator, and by extension, the lithium secondary battery manufactured using the separator.

Further, as the solvent used in the non-aqueous electrolyte in the present invention, a carbonate ester type solvent such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), or acetic acid. A single solvent or a mixed solvent such as ethyl (EA), γ-butyrolactone, tetrahydrofuran or acetonitrile is preferable. Further, in the present invention, in particular, from the viewpoint of the solubility of the lithium compound which is the electrolyte and the temperature range in which the electrode body is used, a mixed solvent of a cyclic carbonate and a chain carbonate can be preferably used, and further, a symmetric chain A mixed solvent containing a linear carbonate and an asymmetric chain carbonate can be preferably used.

Next, the second aspect of the present invention will be described. A second aspect of the present invention is an internal electrode formed by winding or stacking a positive electrode plate made of a positive electrode active material and a negative electrode plate made of a negative electrode active material in a battery case via a separator. A lithium secondary battery comprising a body and impregnated with a non-aqueous electrolytic solution in which a lithium compound is dissolved in an organic solvent, wherein the lithium secondary battery is calculated according to the following formulas (16) to (18). Secondary battery current I ₀
Among (A) and the coefficient α, the current I ₀ (A) is the maximum capacity Q _max (Ah) of the lithium secondary battery and I ₀ / Q _max > 0.5.
Is satisfied, and the coefficient α is 0.02 or more. The details will be described below.

[0048]

[Equation 16] ΔE = a + b × ln (I) (16) (where ΔE is a voltage drop (V), I is an evaluation current (A), and a and b are ln (I) respectively X and ΔE. Is the slope of the XY graph in which Y is plotted as Y, and the Y intercept.)

[0049]

A = R × {T / (α × F)} × ln (I ₀ ) ... (17) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

[0050]

B = R × T / (α × F) (18) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

As already mentioned, the first aspect of the present invention
According to the evaluation method of the lithium secondary battery, which is the side surface,
By the current dependence of the voltage drop measured by the method of
Can evaluate the large current characteristics of lithium secondary batteries
It The second aspect of the present invention is an application of this,
Current I of lithium secondary battery at -25 ° C ₀With (A)
Maximum capacity Q_max(Ah) is I₀/ Q_max> 0.5 relationship
And the coefficient α at −25 ° C. is 0.0
The lithium secondary battery according to the present invention having two or more is
In comparison with lithium secondary batteries that do not meet the requirements
It has characteristics such as excellent flow characteristics.
High current discharge is possible even under low temperature conditions. Na
Excellent in large current characteristics, suitable for use in low temperature conditions
Also from the viewpoint of providing a suitable lithium secondary battery
Is the current I at −25 ° C.₀(A) and maximum capacity Q
_max(Ah) is I₀/ Q_maxSatisfies the relation of> 0.7
At the same time, the coefficient α at −25 ° C. is 0.03 or more.
More preferably.

The current I ₀ and the coefficient α can be calculated by the calculation method described above. That is, two or more evaluation currents I having different values are passed through the target lithium secondary battery, and the voltage drop ΔE after 1 second generated at that time is measured. Next, a graph in which ln (I) is plotted on the horizontal axis (X axis) and ΔE is plotted on the vertical axis (Y axis) is created, and the above equation (1
According to 6), the slope obtained by the method of least squares is calculated as b, and the intercept (Y intercept) is calculated as a. From the calculated values of a and b, the current I ₀ and the coefficient α at an arbitrary temperature (T) can be calculated according to the above equations (17) and (18).

The lithium secondary battery of the present invention has a characteristic that the maximum capacity thereof has a fixed relationship with the current at a predetermined temperature and a predetermined coefficient, and is excellent in large current characteristics. Therefore, there is no limitation on the material or the battery structure that constitutes the battery. Hereinafter, the main members and structure of the lithium secondary battery and the manufacturing method will be described by taking the case where the configuration of the electrode body is a wound type electrode body as an example.

FIG. 1 is a perspective view showing the structure of a wound electrode body.
It is a figure. The positive electrode plate 2 is coated with a positive electrode active material on both sides of the current collecting substrate.
It is made by working. As a collector board,
For positive electrode electrochemical reactions such as aluminum foil and titanium foil
A metal foil with good corrosion resistance is used.
You can also use punching metal or mesh
Wear. Further, as the positive electrode active material, lithium manganate is used.
(LiMn ₂O_Four) And lithium cobalt oxide (LiCo
O₂), Lithium nickel oxide (LiNiO₂) Etc.
A transition metal complex oxide is preferably used. This is
Carbon fine powder such as acetylene black was added to these positive electrode active materials.
It is preferably added as a conductive auxiliary agent. Here, the present invention
Is a cubic spinel containing Li and Mn as main components.
Lithium manganate having a structure (hereinafter simply referred to as "manga
Lithium acid salt ". ) With other positive electrode active materials
The resistance of the electrode body can be reduced compared to the case where
It is preferable because it can

In the lithium secondary battery of the present invention,
Lithium manganate is used as the positive electrode active material. Here, the stoichiometric composition of lithium manganate is LiMn ₂
Although represented by O ₄ , the present invention is not limited to such a stoichiometric composition, and a part of the transition element Mn may be represented by T
i, and in addition, Li, Fe, Ni, Mg, Zn,
Co, Cr, Si, Sn, P, V, Sb, Nb, Ta,
LiM _x Mn formed by substituting two or more kinds of elements consisting of one or more kinds of elements selected from the group consisting of Mo and W
_2-X O ₄ (However, M is a substitution element, and X represents the substitution amount.)
Is also preferably used.

When the element substitution as described above is performed, the Li / Mn ratio (molar ratio) becomes (1 + X) / (2-X) in the case of excess Li in which Mn is replaced by Li, When substituted with a substitution element M other than Li, 1 /
(2-X), so L is always L in any case.
The i / Mn ratio is> 0.5.

In the present invention, as described above, Li / M
It is preferable to use lithium manganate having an n ratio of more than 0.5. This further stabilizes the crystal structure as compared with the case of using a stoichiometric composition,
A battery having excellent cycle characteristics can be obtained.

Note that theoretically the substitution element M is
Li is +1, and Fe, Mn, Ni, Mg, and Zn are +2.
Valence, B, Al, Co, Cr are +3 valence, Si, Ti, Sn
Is +4 valence, P, V, Sb, Nb, Ta is +5 valence, Mo,
W becomes an ion with a valence of +6 and is an element that forms a solid solution in LiMn ₂ O ₄ , but with respect to Co and Sn, in the case of a valence of +2, F
e, Sb, and Ti are +3 valences, Mn is +3 valences, +4 valences, Cr is +4 valences, +
It may be hexavalent. Therefore, the various substitution elements M may exist in a state having mixed valences, and the amount of oxygen does not necessarily have to be 4 as represented by the theoretical chemical composition, and the crystal structure It may be deficient or excessively present within the range for maintaining.

The positive electrode active material is applied by coating a current collector substrate with a slurry or paste prepared by adding a solvent, a binder and the like to the positive electrode active material powder using a roll coater method or the like.
It is performed by drying, and thereafter, a pressing process or the like is performed if necessary.

The negative electrode plate 3 can be manufactured in the same manner as the positive electrode plate 2. As the current collector substrate of the negative electrode plate 3, a metal foil such as a copper foil or a nickel foil having a good corrosion resistance against a negative electrode electrochemical reaction is preferably used. As the negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon, a highly graphitized carbon material such as artificial graphite or natural graphite, or a material such as amorphous carbon is further used. A fibrous material is preferably used as the material.

As the separator 4, a Li ⁺ permeable polyolefin film is used. Specifically, a three-layer structure in which a Li ⁺ permeable polyethylene film (PE film) having micropores is sandwiched between porous Li ⁺ permeable polypropylene films (PP film) is preferably used. . This is because the PE film is softened at about 130 ° C. and the micropores are crushed when the temperature of the electrode body rises, and also serves as a safety mechanism for suppressing the movement of Li ⁺ , that is, the battery reaction. Then, by sandwiching this PE film between PP films having a higher softening temperature, even when the PE film is softened,
The PP film retains its shape to prevent contact and short circuit between the positive electrode plate 2 and the negative electrode plate 3, and it is possible to reliably suppress battery reaction and ensure safety.

As the separator, paper made of cellulose, a cellulose derivative, or a mixture thereof can be used, and a nonwoven fabric containing polyolefin as a main component can also be used. Specifically, paper with appropriate size micropores, polypropylene,
It is preferable to use a nonwoven fabric made of polyethylene or the like. Since these materials are porous membranes having a large number of micropores of an appropriate size and have electrical insulation properties, they exhibit physical characteristics suitable as a separator for lithium secondary batteries. Further, since it is inexpensive and easily available, it is possible to reduce the manufacturing cost of the separator, and by extension, the lithium secondary battery manufactured using the separator.

When the tab structure-type wound body as shown in FIG. 1 is manufactured, the electrode plate (the positive electrode plate 2 and the negative electrode plate 3) and the separator 4 are wound at the end of the electrode plate, A plurality of current collecting tabs (a positive electrode current collecting tab 5 and a negative electrode current collecting tab 6) are attached to the exposed portions (uncoated portions) of the current collecting substrate on which the active material is not coated. As the current collection tab,
A strip-shaped foil body made of the same material as that of the collector substrate forming each electrode plate is preferably used. When the positive electrode current collecting tab 5 and the negative electrode current collecting tab 6 are attached to the positive electrode plate 2 and the negative electrode plate 3, means such as ultrasonic welding or spot welding can be used.

Next, the non-aqueous electrolyte used in the lithium secondary battery of the present invention will be described. Examples of the solvent include carbonate-based solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and propylene carbonate (PC), ethyl acetate (EA), γ-butyrolactone, tetrahydrofuran, and acetonitrile. A single solvent or a mixed solvent is preferably used. In the present invention, in particular, from the viewpoint of the solubility of the lithium compound that is the electrolyte, the operating temperature range of the battery, and the like, a mixed solvent in which a cyclic carbonate and a chain carbonate are mixed at an arbitrary ratio can be preferably used, and A mixed solvent containing a symmetric chain carbonate and an asymmetric chain carbonate can be preferably used.

Examples of the electrolyte include lithium complex fluoride compounds such as lithium hexafluorophosphate (LiPF ₆ ) and lithium borofluoride (LiBF ₄ ), or lithium halides such as lithium perchlorate (LiClO ₄ ). One kind or two or more kinds are used by dissolving in the above-mentioned organic solvent (mixed solvent). In particular, in the present invention, L, which is less likely to undergo oxidative decomposition and has high conductivity in the non-aqueous electrolyte,
It is preferable to use iPF ₆ . Note that it is possible to use a non-aqueous electrolytic solution in which the type and concentration of the lithium compound that is the electrolyte, the type and composition ratio of the organic solvent, etc. are variously changed.

Here, the obtained non-aqueous electrolytic solution may be used as it is, but it is also preferable to use a heat-treated non-aqueous electrolytic solution as the non-aqueous electrolytic solution because the internal resistance is reduced. At this time, it is preferable to heat-treat the non-aqueous electrolytic solution in an inert atmosphere, which can prevent deterioration of the non-aqueous electrolytic solution due to oxidation, absorption of moisture in the air, or the like as much as possible. The above-mentioned "inert atmosphere" means that the inside of the system for heat-treating the nonaqueous electrolytic solution is filled with, for example, a general inert gas. The general inert gas referred to here corresponds to Ar, N ₂ gas, or the like.

When assembling the lithium secondary battery,
First, while ensuring continuity between the terminal for taking out an electric current and the positive electrode current collecting tab 5 and the negative electrode current collecting tab 6, the produced wound electrode body 1 is inserted into a battery case and placed at a stable position. Hold on. Then, the lithium secondary battery is manufactured by impregnating the above-mentioned non-aqueous electrolyte and sealing the battery case.

As above, the lithium secondary battery according to the present invention has been described with reference to an embodiment mainly using a wound electrode body, but the present invention is not limited to the above embodiment. It goes without saying that it is not limited. In addition, the lithium secondary battery according to the present invention is particularly preferably used for a large battery having a battery capacity of 2 Ah or more, but it does not prevent application to a battery having such a capacity or less. Further, the lithium secondary battery of the present invention,
Large capacity, low cost, high reliability as an in-vehicle battery, further preferable as a power source for driving a motor of an electric vehicle or a hybrid electric vehicle, and especially for starting an engine that requires a high voltage. It can be preferably used.

[0069]

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. (Production of wound electrode body) Li / Mn as shown in Table 1>
A lithium manganese spinel and a lithium manganate (LiMn ₂ O ₄ ) spinel having a ratio of 0.5 were used as a positive electrode active material, and acetylene black as a conductive additive was added thereto in an external ratio of 4% by mass. The positive electrode plate 2 was prepared by coating the positive electrode agent slurry prepared by adding the above to both sides of an aluminum foil having a thickness of 20 μm so as to have a thickness of about 100 μm. Further, various carbon materials as shown in Table 1 were used as the negative electrode active material and the thickness was 10 μm.
A negative electrode plate 3 was produced by coating both sides of a copper foil having a thickness of m to a thickness of about 80 μm. Next, separators made of various materials as shown in Table 1 were prepared, and the positive electrode plate 2 and the negative electrode plate 3 were used to fabricate a wound electrode body 1 as shown in FIG. 1 to 7, Comparative Example 1,
2). In Table 1, a separator of "microporous polyolefin three layer" is a Li ⁺ permeability of PE film having micropores, like the three-layer structure by being sandwiched Li ⁺ permeable PP film having micropores It was done.

(Preparation of Non-Aqueous Electrolyte) Various organic solvents such as EC, DEC and DMC were prepared and mixed at a ratio (volume ratio) shown in Table 1 to prepare a mixed solvent.
A non-aqueous electrolytic solution was prepared by dissolving LiPF ₆ as an electrolyte so as to have a concentration of ol / l (Examples 1, 3, 4,
6, 7 and Comparative Examples 1 and 2). In addition, among the obtained non-aqueous electrolytes, in Examples 2 and 5, those subjected to heat treatment at 60 ° C. for 30 days were used as the non-aqueous electrolytes.

(Preparation of Battery) After the wound electrode body was housed in a battery case, each non-aqueous electrolyte was filled, and then the battery case was sealed to prepare batteries (Examples 1 to 7, Comparative Example) Example 1,
2). The other members and the test environment were the same for all the samples, and the battery members were thoroughly dried until just before the battery was assembled, and the effects of water infiltration from the outside of the battery due to defective sealing of the battery were also eliminated. . These battery capacity after the first charge of the battery (maximum capacity: Q _{ma x)} are all 8A
It was h. The method for measuring the battery capacity (maximum capacity) is as follows.

(Battery Capacity Measuring Method) The lithium secondary battery thus prepared was fully charged at room temperature (25 ° C.), 1C constant current and 4.1V constant voltage, and then 10 A (1C) at room temperature.
(Equivalent current) A 1C discharge capacity at room temperature was measured by discharging at a constant current until the terminal voltage became 2.5 V, and this was defined as the maximum capacity Q _max (Ah).

[0073]

[Table 1]

(Large Current Characteristic Evaluation Test) Prepared Example 1
~ 7, about each lithium secondary battery of Comparative Examples 1 and 2,
The voltage drop ΔE after 1 second which occurred when two different evaluation currents I of 25 A and 20 A were applied was measured. Then, a graph in which ln (I) is plotted on the horizontal axis (X axis) and ΔE is plotted on the vertical axis (Y axis) is prepared, and the slope obtained by the least squares method is represented by b and the intercept (Y (Intercept) is calculated as a, and using these values, the current I _{0 at} −25 ° C. is calculated according to the following equations (20) and (21).
And the coefficient α was calculated. In addition, 150 at -25 ℃ of each battery
The internal resistance R (mΩ) when the current of A was passed was actually measured, and its expected value was calculated. The results are shown in Table 2.
The actual measurement value of the internal resistance R is R = ΔE / I, where ΔE is the voltage drop after 1 second when the current I flows.
The estimated value of the internal resistance R is calculated by using the relational expression of Eq. (19), and ΔE when I = 150 is obtained by using Eq. (19). It was calculated by

[0075]

(Equation 19) ΔE = a + b × ln (I) (19) (where ΔE is a voltage drop (V), I is an evaluation current (A), and a and b are ln (I) respectively X and ΔE. Is the slope of the XY graph in which Y is plotted as Y, and the Y intercept.)

[0076]

A = R × {T / (α × F)} × ln (I ₀ ) ... (20) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

[0077]

B = R × T / (α × F) (21) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). )

[0078]

[Table 2]

(Discussion) From the results shown in Table 2, the internal resistance R
It is clear that the expected value of (mΩ) is close to the measured value. Therefore, according to the lithium secondary battery evaluation method of the present invention, the internal resistance of the battery when a large current is applied under low temperature conditions is accurately calculated by applying a lower current evaluation current, It was found that it is possible to evaluate the large current characteristics of. Further, the current I ₀ (A) and the maximum capacity Q _max (Ah) at −25 ° C. are I ₀ / Q _max
A lithium secondary battery satisfying the condition of> 0.5 and satisfying the condition that the coefficient α at −25 ° C. is 0.02 or more is a lithium secondary battery that does not satisfy the above condition (Comparative Examples 1, 2). It was found that the internal resistance of the battery was small and a large current characteristic was excellent when a large current was applied under low temperature conditions. Therefore, the superiority of the lithium secondary battery of the present invention satisfying the above conditions could be confirmed.

[0080]

As described above, according to the evaluation method of the lithium secondary battery of the present invention, the lithium secondary battery has a large capacity due to the current dependency of the voltage drop measured after a predetermined time after passing the evaluation current. Since the current characteristics are evaluated, the large current characteristics of the lithium secondary battery can be evaluated very easily and accurately in a short time. Further, the lithium secondary battery of the present invention has a current I ₀ (A) and a maximum capacity Q _max (Ah) which are physical properties peculiar to the battery under a predetermined low temperature condition.
And the coefficient α satisfy the predetermined relations and numerical values, the internal resistance is low, the large current characteristics are excellent especially under low temperature conditions, and it can be provided very easily. Consideration has also been given to cost.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a wound electrode body.

FIG. 2 is a perspective view showing a structure of a laminated electrode body.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wound type electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Positive electrode current collecting tab, 6 ... Negative electrode current collecting tab, 7 ... Laminated electrode body, 8 ... Positive electrode plate, 9 ... Negative electrode plate, 10 ... Separator, 11 ... Positive electrode current collecting tab, 12 ... Negative electrode current collecting tab, 13 ...
Winding core.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5H029 AJ14 AK03 AL06 AM03 BJ12                       BJ14 HJ02 HJ16                 5H030 AS08 FF41 FF52                 5H050 AA06 BA17 CA09 CB07 FA02                       FA05 GA27 GA28 HA02 HA16                       HA20

Claims (19)

[Claims] 1. An internal electrode body formed by winding or stacking a positive electrode plate made of a positive electrode active material and a negative electrode plate made of a negative electrode active material with a separator interposed between the inner electrode body and the nonaqueous electrolytic solution. A method for evaluating a used lithium secondary battery, characterized in that a large current characteristic of the lithium secondary battery is evaluated by a current dependency of a voltage drop measured after a predetermined time by passing an evaluation current. Evaluation method of secondary battery. 2. The method for evaluating a lithium secondary battery according to claim 1, wherein the voltage drop that occurs 1 second after flowing the two or more different evaluation currents is measured. 3. The large current characteristics are the maximum capacity Q _max (Ah) of the lithium secondary battery and the current I ₀ (A) at −25 ° C. calculated according to the following formulas (1) to (3). The method for evaluating a lithium secondary battery according to claim 1, which is represented by a value of a coefficient α. ## EQU1 ## ΔE = a + b × ln (I) (1) (where ΔE is a voltage drop (V), I is an evaluation current (A), and a and b are ln (I) respectively X and ΔE. Is the slope of the XY graph in which is plotted as Y, and the Y intercept.) ## EQU2 ## a = R × {T / (α × F)} × ln (I ₀ ) ... (2) (where R Is the gas constant (8.314J / (K ・ mo
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). ) [Expression 3] b = R × T / (α × F) (3) (where, R is a gas constant (8.314 J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). ) 4. The current I ₀ (A) and the _maximum capacity Q _max (A
4. The lithium according to claim 3, wherein h) satisfies the relationship of I ₀ / Q _max > 0.5 and the large current characteristic is evaluated as good when the coefficient α is 0.02 or more. Evaluation method of secondary battery. 5. The method for evaluating a lithium secondary battery according to claim 1, wherein lithium manganate having a cubic spinel structure is used as the positive electrode active material. 6. The method for evaluating a lithium secondary battery according to claim 5, wherein the lithium manganate having a Li / Mn ratio of more than 0.5 is used. 7. The positive electrode active material contains a part of transition element Mn in lithium manganate (LiMn ₂ O ₄ ) containing Ti, and further contains Li, Fe, Ni, Mg, Zn, B,
Al, Co, Cr, Si, Sn, P, V, Sb, Nb,
LiM composed of one or more elements selected from the group consisting of Ta, Mo and W and substituted with two or more elements
_The method for evaluating a lithium secondary battery according to any one of claims 1 to 4, wherein _X Mn _2-X O ₄ (where M is a substitution element and X represents a substitution amount) is used. 8. The lithium secondary battery according to claim 1, wherein at least one selected from the group consisting of artificial graphite, natural graphite, and amorphous carbon is used as the negative electrode active material. Evaluation methods. 9. The method for evaluating a lithium secondary battery according to claim 1, wherein a mixed solvent of a cyclic carbonate and a chain carbonate is used as an organic solvent that constitutes the non-aqueous electrolytic solution. 10. A battery case is provided with an internal electrode body formed by winding or stacking a positive electrode plate made of a positive electrode active material and a negative electrode plate made of a negative electrode active material with a separator interposed therebetween. A lithium secondary battery impregnated with a non-aqueous electrolytic solution in which a lithium compound is dissolved in an organic solvent, the lithium secondary battery at −25 ° C. calculated according to the following formulas (4) to (6): Of the current I ₀ (A) and the coefficient α, the current I ₀ (A) is the maximum capacity Q of the lithium secondary battery.
_max (Ah) and with satisfying the relation of _{I 0 / Q m ax> 0.5} , a lithium secondary battery engaging several α is equal to or is 0.02 or more. ΔE = a + b × ln (I) (4) (where ΔE is a voltage drop (V), I is an evaluation current (A), and a and b are ln (I) respectively X and ΔE). Is a slope of an XY graph in which Y is plotted as Y, and a Y intercept.) A = R × {T / (α × F)} × ln (I ₀ ) ... (5) (where R Is the gas constant (8.314J / (K ・ mo
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). ) (6) b = R × T / (α × F) (6) (where, R is a gas constant (8.314J / (K · mo)
l)), T is the absolute temperature (K), and F is the Faraday constant (96500 C / mol). ) 11. The lithium secondary battery according to claim 10, wherein the positive electrode active material is lithium manganate (LiMn ₂ O ₄ ) having a cubic spinel structure. 12. Li / in the lithium manganate
The lithium secondary battery according to claim 11, wherein the Mn ratio is more than 0.5. 13. The positive electrode active material contains Ti as a part of a transition element Mn in lithium manganate (LiMn ₂ O ₄ ), and in addition, Li, Fe, Ni, Mg, Zn, B, A.
l, Co, Cr, Si, Sn, P, V, Sb, Nb, T
LiM _{x formed} by substituting two or more elements consisting of one or more elements selected from the group consisting of a, Mo and W
The lithium secondary battery according to claim 10, which is Mn _2-X O ₄ (where M is a substitution element and X represents a substitution amount). 14. The negative electrode active material is artificial graphite, natural graphite,
The lithium secondary battery according to any one of claims 10 to 13, which is at least one selected from the group consisting of: and amorphous carbon. 15. The lithium secondary battery according to claim 10, wherein the organic solvent is a mixed solvent containing at least a symmetric chain carbonate and an asymmetric chain carbonate. 16. The battery capacity is 2 Ah or more.
The lithium secondary battery according to any one of 0 to 15. 17. The lithium secondary battery according to claim 10, which is an on-vehicle battery. 18. The lithium secondary battery according to claim 17, which is used in an electric vehicle or a hybrid electric vehicle. 19. The method according to claim 1, which is used for starting an engine.
The lithium secondary battery according to 7 or 18.