JP2001313027A - Adjustment method of electrode slurry for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating equal mixture and dispersion of carbon material or the like in an electrode slurry for a lithium secondary battery as well as a lithium secondary battery made with the use of an electrode slurry for a lithium secondary battery adjusted in accordance with the above method. SOLUTION: Dispersibility of carbon material is evaluated and adjusted by an SVI value in adjustment method of an electrode slurry for a lithium secondary battery mixing carbon material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for preparing an electrode slurry for a lithium secondary battery, and more particularly, to a method for preparing an electrode slurry.
The present invention relates to a method for preparing an electrode slurry for a lithium secondary battery based on an I value, and a lithium secondary battery produced using the electrode slurry prepared by the method.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as power batteries for portable electronic devices such as mobile phones, VTRs, and notebook computers. In addition, the lithium secondary battery has a unit cell voltage of about 4 V, which is higher than that of a conventional secondary battery such as a lead storage battery, and has a higher energy density. Against this background, electric vehicles (E
V) or a motor drive power source for a hybrid electric vehicle (HEV).

In general, a lithium secondary battery includes a lithium transition metal composite oxide as a positive electrode active material, a carbonaceous material as a negative electrode active material, and an organic electrolyte obtained by dissolving a Li ion electrolyte in an organic solvent as an electrolyte. There are various types of electrode bodies that are used and perform a battery reaction, such as a sandwich type, a wound type, and a laminated type.

[0004]

Regarding the positive electrode active material used in the lithium secondary battery, regardless of the type, the resistance (electron conduction resistance) of the positive electrode active material is reduced in order to reduce the internal resistance of the battery. In other words, improving the electron conductivity of the positive electrode active material is the most important issue from the viewpoint of improving battery characteristics. In particular, EV and HE
In a large-capacity lithium secondary battery used as a power supply for driving a V motor, reducing the internal resistance of the battery enables discharge of a large current required for acceleration, climbing a hill, etc. It is extremely important to enhance.

[0005] As one means for solving this problem,
Conventionally, attempts have been made to improve the electronic conductivity by adding a conductive aid such as acetylene black or carbon black to the positive electrode and the negative electrode active material to reduce the internal resistance of the battery. . This is because the above-mentioned lithium transition element composite oxide is a mixed conductor having both lithium ion conductivity and electron conductivity, but the electron conductivity is not necessarily large.

However, the addition of acetylene black, which is an example of a conductive additive, causes a problem that the battery capacity is reduced due to a decrease in the active material filling amount. In addition, acetylene black is a kind of carbon material and is a semiconductor, and thus it is considered that there is a limit in improving electron conductivity. In addition, a conductive auxiliary such as a carbon material is generally bulky, and there are also problems in the production process such as difficulty in manufacturing an electrode plate and handling. Therefore, the addition amount is appropriately set in consideration of the positive effect of reducing the internal resistance, the negative effect of lowering the battery capacity, the ease of manufacturing, and the like.

Further, it is difficult to uniformly mix and disperse a carbon material or the like in a lithium secondary battery electrode slurry because of its bulkiness. Furthermore, when an electrode slurry for a lithium secondary battery in which the carbon material is not uniformly mixed and dispersed is applied on the electrode plate, the carbon material partially aggregates on the electrode plate and is easily peeled off. There is. In addition, due to partial aggregation on the electrode plate, a resistance distribution is generated on the electrode plate, and when used as a battery, current is concentrated, and problems such as partial heat generation and deterioration are promoted. .

In order to reduce the internal resistance of the battery, it is necessary to uniformly mix and disperse a conductive additive such as a carbon material in the electrode slurry. Japanese Patent No. 2750077 discloses a method of uniformly mixing an electrode slurry for a lithium secondary battery by adjusting the proportion of a solvent which is a composition of the electrode slurry. However, according to the method disclosed in the publication, the composition other than the solvent, for example, a positive electrode active material, a conductive auxiliary agent, a problem that when the blending amount of the binder or the like is changed, uniform mixing cannot be performed. Have.

In general, as a method of evaluating the dispersibility of a substance in a slurry by stirring and mixing, a method of measuring the viscosity at a certain shear rate and comparing the viscosity before and after stirring and mixing as a dispersibility index is used. Can be mentioned.
However, there is a problem in that the method for evaluating the dispersibility of a powder that easily aggregates, such as a carbon material, lacks accuracy.

The present invention has been made in view of the above-mentioned problems of the related art, and an object of the present invention is to uniformly mix a carbon material or the like into an electrode slurry for a lithium secondary battery. An object of the present invention is to provide a lithium secondary battery manufactured by using a method for evaluating dispersion and an electrode slurry for a lithium secondary battery prepared based on the evaluation method.

[0011]

Means for Solving the Problems According to the present invention, in a method for preparing an electrode slurry for a lithium secondary battery in which a carbon material is mixed, the carbon material is prepared by evaluating the dispersibility of the carbon material by an SVI value. A method for preparing an electrode slurry for a lithium secondary battery is provided.

In the present invention, the SVI value of the electrode slurry for a lithium secondary battery is preferably 4.3 or less.

In the present invention, the carbon material is:
Acetylene black and / or carbon black
Preferably, the electrode is a positive electrode.
The positive electrode active material contained in the positive electrode is
Titanium (LiMn _TwoO_FourIs more preferable.

Further, in the present invention, the electrode is preferably a negative electrode, and it is preferable to use two or more carbon materials for the negative electrode.

In the present invention, the produced lithium secondary battery has a battery capacity of 2 Ah or more, and the lithium secondary battery is suitably used as a vehicle-mounted battery.

The manufactured lithium secondary battery is suitably used for an electric vehicle or a hybrid electric vehicle, and is preferably used for starting an engine.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on embodiments, but the present invention is not limited to these embodiments.

The present invention relates to a method for preparing an electrode slurry for a lithium secondary battery, which focuses on the SVI value of a slurry as a method for evaluating the dispersibility of a carbon material, and prepares a slurry based on the SVI value. The SVI value used herein is a value expressed by a ratio of apparent viscosities at two different shear rates, and the viscosity at the lower shear rate is η ₁ , and the viscosity at the higher shear rate is η ₂ Then, the SVI value (S) is represented by S = η ₁ / η ₂ . At this time, the ratio of the shear rates, that is, the ratio of the number of rotations is 1:10
So that The method of measuring the apparent viscosity is described in J
ISK 7117 (1987, viscosity test method of liquid resin by rotational viscometer) and JIS Z 8803 (1
991, viscosity of liquid-measurement method).

In general, when the dispersion state of the particles in the slurry is not uniform and aggregated particles are present, the apparent viscosity η tends to increase on the low shear rate side, and the SVI value tends to increase. By applying this tendency and measuring the SVI value, which is the ratio of the apparent viscosities at two different shear rates, to use as an index for evaluating the dispersibility of the carbon material in the electrode slurry for lithium secondary batteries. Can be.

In general, the apparent viscosity of a slurry changes each time depending on its composition, so that it can be used as an index for evaluating the dispersibility of particles only in the case of a fixed material / mixing ratio. However, the SVI value is different from the absolute value such as the apparent viscosity, and the dispersibility of the particles can be evaluated even when the type of the slurry composition and the mixing ratio are different. Therefore, the method for preparing an electrode slurry for a lithium secondary battery according to the present invention is a preparation method that can evaluate the dispersibility of a carbon material in various materials and mixing ratios, that is, has a wide range of application.

The SVI value of the electrode slurry for a lithium secondary battery according to the present invention is preferably adjusted to 4.3 or less. FIG. 1 is a flow curve of a positive electrode slurry for a lithium secondary battery prepared by a normal manufacturing method. As a positive electrode active material, 6 kg of lithium manganate (LiMn ₂ O ₄ ) was used.
0.24 kg of acetylene black as a conductive aid and 4% of an NMP (N-methyl-2-pyrrolidone) solution of 12% PVDF (polyvinylidene fluoride) as a binder.
kg (equivalent to 8% by weight), a slurry mixed with 3.3 kg of NMP and stirred and prepared (sample 1), and FIG. 2 is a flow curve of an experimental slurry prepared without a positive electrode active material. 5 is a flow curve of a slurry (sample 2) without lithium manganate (LiMn ₂ O ₄ ). In each of the figures, the peripheral speed is 20 m / s × 5 min, and the peripheral speed is 3
0m / s × 5min, + peripheral speed 30m / s × 5mi
The flow curve after n stirring is shown. Table 1 shows the measured SVI values of the respective flow curves. At this time, it is clear that the addition of acetylene black affects the viscosity characteristics of the slurry, and that the flow curve has a substantially constant shape when the SVI value is 4.3 or less.
Therefore, it can be used as an index of acetylene black dispersibility in the slurry, and as described above, the dispersibility of carbon materials in various materials and blending ratios can be evaluated based on the SVI value.

[0022]

[Table 1]

In the method for preparing an electrode slurry for a lithium secondary battery according to the present invention, it is preferable to use acetylene black and / or carbon black as a carbon material to be mixed with the electrode slurry for a lithium secondary battery. In addition, it is possible to produce an electrode plate having a uniform resistance distribution, and simultaneously reduce the internal resistance of the lithium secondary battery.

According to the present invention, a method for preparing an electrode slurry for a lithium secondary battery in which the dispersibility of a carbon material is evaluated based on an SVI value can be suitably adopted, particularly as a method for preparing a positive electrode slurry. This makes use of the feature of the present invention, that is, the accurate evaluation of the dispersibility of the carbon material in the electrode slurry for a lithium secondary battery. Generally, coating of a positive electrode active material on a current collecting substrate (metal foil) is performed by applying and drying a positive electrode slurry on a current collecting substrate of aluminum, titanium or the like using a roll coater method or the like. Therefore, in the present invention, since the positive electrode slurry in which the dispersibility of the carbon material is accurately evaluated is prepared and applied to the current collecting substrate, the lithium slurry is such that the carbon material does not partially aggregate on the current collecting substrate. It is possible to produce a positive electrode plate for a secondary battery.

When a lithium secondary battery is manufactured and used by using a positive electrode plate in which acetylene black does not partially aggregate, current is concentrated in a portion having a high acetylene black density and partial heat generation occurs. This does not easily cause adverse effects such as the occurrence of heat generation, and does not cause problems such as accelerated deterioration of the battery due to heat generation. Further, since no deterioration occurs, the cycle characteristics of the battery are also improved, and a lithium secondary battery having good charge / discharge efficiency and long-term use can be manufactured.

In general, examples of the negative electrode active material used in the lithium secondary battery include amorphous carbonaceous materials such as soft carbon and hard carbon, and carbonaceous powders such as artificial graphite and natural graphite. Regarding these carbonaceous materials and carbonaceous powders, it is often difficult to disperse them in a slurry.Therefore, the method for preparing an electrode slurry for a lithium secondary battery according to the present invention comprises forming a negative electrode of a lithium secondary battery. It can also be suitably used as a method for preparing a negative electrode slurry for performing the method. Furthermore, when preparing a negative electrode slurry for a lithium secondary battery, in addition to the amorphous carbonaceous material as the negative electrode active material, or carbonaceous powder, when simultaneously adding a conductive auxiliary such as acetylene black and carbon black, That is, even when two or more types of carbon materials are used, they can be suitably used.

Therefore, the SVI of the slurry according to the present invention
In the negative electrode slurry for lithium secondary batteries prepared based on the slurry preparation method focusing on the value, the carbon material as the negative electrode active material can be uniformly mixed and dispersed in the negative electrode slurry, and the conductive auxiliary agent Can be uniformly mixed and dispersed even when acetylene black or the like is added. That is, it is possible to produce a negative electrode plate in which the electron conductivity of the negative electrode active material is improved, and at the same time, there is a problem such as partial heat generation due to concentration of current when used as a battery and accelerated deterioration. Does not occur. In addition, since no deterioration occurs, the cycle characteristics of the battery are improved, and a decrease in the battery capacity over time due to repeated charging and discharging is suppressed.

Next, details of the present invention will be described with reference to an example of manufacturing a lithium secondary battery having a wound internal electrode body. The wound internal electrode body is formed by winding the positive electrode plate and the negative electrode plate such that they do not come into direct contact with each other via a separator made of a porous polymer film. Specifically, as shown in FIG. 3, the internal electrode body 1 is formed by winding a positive electrode plate 2 and a negative electrode plate 3 with a separator 4 interposed therebetween.
A tab 5 is provided for each of the electrodes 3 (hereinafter, referred to as “electrode plates 2 and 3”). The attachment of the tab 5 to the electrode plates 2 and 3 can be performed by means such as ultrasonic welding when the electrode plates 2 and 3 are wound together with the separator 4.
The opposite end of each tab 5 connected to the electrode plates 2 and 3 is attached to an output terminal (not shown) or a current extraction terminal (not shown) that is connected to the output terminal.

As the positive electrode active material used in the positive electrode slurry for a lithium secondary battery according to the present invention, lithium manganate is suitably used. Lithium manganate (LiMn
₂ O ₄ ) belongs to the space group Fd3m and has the property that diffusion of Li ions occurs three-dimensionally.
(-3) m ( "-". The showing a Kaihan) belongs to, Lithium cobaltate (LiCoO ₂₎ having a layered structure or lithium nickel oxide (LiNiO ₂₎ as the diffusion of Li ions two-dimensionally in The diffusion resistance of Li ions in the battery reaction is smaller than in the case of using
Suitable for high output purpose. In addition, since lithium manganate itself has excellent electric conductivity, it also has a remarkable effect in reducing the resistance of the positive electrode plate. Furthermore, a battery using lithium manganate has an excellent feature that the resistance is small even in a state where the discharge is advanced, that is, a state where the depth of discharge is deep, and the battery in an application where high output discharge is required. Particularly excellent as a material.

The lithium manganate is not limited to such a stoichiometric composition, but may be Mn.
Of the general formula LiMx in which a part of is replaced by one or more other elements
Lithium manganate represented by Mn _2-X O ₄ (M represents a substitution element and X represents a substitution amount) is also suitably used. In lithium manganate subjected to such element substitution,
The Li / Mn ratio exceeds 0.5.

As the substitution element M, listed below by element symbols, Li, Fe, Mn, Ni, Mg, Zn,
B, Al, Co, Cr, Si, Ti, Sn, P, V, S
b, Nb, Ta, Mo, and W can be mentioned. In theory, Li has +1 valence, and Fe, Mn, Ni, Mg, and Zn have +
Divalent, B, Al, Co, Cr are trivalent, Si, Ti, S
n is +4, P, V, Sb, Nb and Ta are +5, M
o and W are +6 valent ions, and are elements that form a solid solution in LiMn ₂ O ₄ . However, when Co and Sn are +2 valent, and when Fe, Sb and Ti are +3 valent, M
For n + 3 and +4, for Cr +
It may be tetravalent or +6 valent.

Therefore, the various substitution elements M may exist in a state having a mixed valence, and the amount of oxygen needs to be 4, as represented by the stoichiometric composition. However, it may be deficient or excessive in the range for maintaining the crystal structure.

On the other hand, as the negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon, artificial graphite such as highly graphitized carbon material, or a carbonaceous powder such as natural graphite is used. These electrode active materials are slurried, applied and fixed to a current collector, and
3 is made.

As the separator 4, one having a three-layer structure in which a lithium ion permeable polyethylene film having micropores is sandwiched between porous lithium ion permeable polypropylene films is preferably used. When the temperature of the internal electrode body 1 rises, the polyethylene film softens at about 130 ° C., crushes the micropores, and also serves as a safety mechanism for suppressing the movement of lithium ions, that is, the battery reaction. By sandwiching the polyethylene film with a polypropylene film having a higher softening temperature, contact and short circuit between the electrode plates 2 and 3 can be prevented.

As the electrolytic solution, ethylene carbonate
(EC), diethyl carbonate (DEC), dimethyl
Carbonate (DMC), propylene carbonate (P
Carbonic acid esters such as C), γ-butyrolact
Organic solvents such as ethylene, tetrahydrofuran and acetonitrile
LiP as an electrolyte in a single solvent or a mixed solvent of
F₆And LiBF_FourLithium complex fluorine compounds such as
Is LiClO _FourSuch as lithium halide compounds
Or two or more non-aqueous organic electrolytes
Is preferably used. Note that the type of electrode
And it is not limited to wound type, but sandwich
Producing an electrode body with a shape as required, such as a mold and a lamination mold
Is possible.

FIG. 4 is a sectional view showing an embodiment of the lithium secondary battery of the present invention. The electrode body 1 manufactured by the above-described process is inserted into the battery case 11 and placed in a stable position.
The battery case 11 is sealed by interposing a packing 18 therebetween and performing caulking (caulking portion 12). Next, the battery case 11 and the electrode cover 16 are impregnated with an electrolytic solution (not shown).
The lithium secondary battery 30 according to the present invention is manufactured by a manufacturing method in which the packing 18 is sandwiched therebetween, the caulking (caulking portion 12) is performed, and the battery case 11 is sealed.

As described above, the lithium secondary battery according to the present invention has been described with reference to the embodiments. However, needless to say, the present invention is not limited to the above embodiments.

The above-described lithium secondary battery according to the present invention is preferably used particularly for a large-sized battery having a battery capacity of 2 Ah or more, but does not prevent application to a battery having such a capacity or less. Absent. In addition, the lithium secondary battery of the present invention, as a vehicle-mounted battery, taking advantage of the features of large capacity, low cost, and high reliability, furthermore, has a low internal resistance and good cycle characteristics, so that an electric vehicle or It is preferably used for a hybrid electric vehicle and can be particularly suitably used for starting an engine requiring a high voltage. Therefore, when the lithium secondary battery according to the present invention is used, a predetermined acceleration performance,
An excellent effect is obtained in that traveling performance such as climbing performance is maintained, and a continuous traveling distance per charge is kept long.

[0039]

EXAMPLES Specific results of the present invention will be described below. (Preparation of positive electrode slurry and measurement of viscosity) 6 kg of lithium manganate (LiMn ₂ O ₄ ) was used as a positive electrode active material, and acetylene black powder was used as a conductive auxiliary in 0.1 kg.
As a binder, 24 kg of a 12% PVDF (polyvinylidene fluoride) in NMP (N-methyl-2-pyrrolidone) was added in an amount of 4 kg (corresponding to 8% by weight), and these were mixed with 3.3 kg of NMP to prepare Sample 1. . Further, among the above-mentioned compositions, the one without lithium manganate (LiMn ₂ O ₄ ) was designated as Sample 2.

After mixing and stirring the two kinds of samples prepared according to the above composition, JIS K 7117 (1
987, viscosity test method using a rotational viscometer for liquid resin) and JIS Z 8803 (1991, viscosity of liquid-measurement method), apparent viscosity η at each shear rate.
Was measured to create a flow curve. The stirring conditions are as follows:
. A peripheral speed of 20 m / s × 5 min,. + 30m / peripheral speed
s × 5 min,. + 3 of peripheral speed 30m / s x 5min
Cone-flat disk (φ60m
m, the angle between the circular plate and the flat disk 2 °) was used.

The flow curve of Sample 1 is shown in FIG. 1, and the flow curve of Sample 2 is shown in FIG. Further, the SVI value (S) in each flow curve was calculated and is shown in Table 1.

(Consideration) From FIGS. 1 and 2 and Table 1, it is clear that the viscosity characteristics of the slurry are influenced by the addition of acetylene black, and the SVI value is 4.
It can be seen that the flow curve has a substantially constant shape when it is 3 or less. Therefore, it can be used as an index of the dispersibility of carbon materials such as acetylene black in the slurry, and, as described above, the dispersion of carbon materials in various materials and blending ratios based on the SVI value as described above. Sex can be evaluated.

[0043]

As described above, according to the method for preparing the electrode slurry for a lithium secondary battery of the present invention, the dispersibility of the carbon material in the electrode slurry for a lithium secondary battery is evaluated by the SVI value. By doing so, the dispersibility of the carbon material in the electrode slurry for a lithium secondary battery can be accurately evaluated. Accordingly, it is possible to obtain an electrode slurry for a lithium secondary battery in which a carbon material or the like is uniformly mixed and dispersed, and by using the electrode slurry for a lithium secondary battery, a lithium having a low internal resistance and excellent cycle characteristics is obtained. It is possible to provide a secondary battery.

[Brief description of the drawings]

FIG. 1 is a flow curve of a positive electrode slurry for a lithium secondary battery prepared by an ordinary manufacturing method.

FIG. 2 is a flow curve of an experimental slurry prepared without a positive electrode active material.

FIG. 3 is a perspective view showing a structure of a wound internal electrode body.

FIG. 4 is a cross-sectional view showing one embodiment of the lithium secondary battery of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Tab, 11 ... Battery case, 12 ... Caulking part, 15 ... Output terminal, 16 ... Electrode lid, 17 ... Pressure release hole , 1
8 ... packing, 19 ... constricted part, 26 ... insulating film, 30 ...
Lithium secondary battery.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 10/40 H01M 10/40 Z F-term (Reference) 5H029 AJ05 AJ06 AJ14 AK03 AL07 AL08 AM03 AM04 AM05 AM07 BJ02 BJ14 CJ08 DJ08 DJ16 EJ04 HJ00 5H050 AA07 AA12 AA19 BA17 CA09 CB08 CB09 DA02 DA03 DA10 EA10 EA24 FA17 GA10 HA00

Claims (11)

[Claims] 1. A method of preparing an electrode slurry for a lithium secondary battery in which a carbon material is mixed, wherein the dispersibility of the carbon material is evaluated by an SVI value to prepare the slurry. Method. 2. The electrode slurry for a lithium secondary battery according to claim 2, wherein
2. The VI value is 4.3 or less.
A method for preparing the electrode slurry for a lithium secondary battery according to the above. 3. The method according to claim 1, wherein the carbon material is acetylene black and / or
Or carbon black.
A method for preparing the electrode slurry for a lithium secondary battery according to the above. 4. The method for preparing an electrode slurry for a lithium secondary battery according to claim 1, wherein the electrode is a positive electrode. 5. The method for preparing an electrode slurry for a lithium secondary battery according to claim 4, wherein the positive electrode active material contained in the positive electrode is lithium manganate. 6. The method for preparing an electrode slurry for a lithium secondary battery according to claim 1, wherein the electrode is a negative electrode. 7. The method for preparing an electrode slurry for a lithium secondary battery according to claim 6, wherein two or more kinds of carbon materials are used for the negative electrode. 8. The method for preparing an electrode slurry for a lithium secondary battery according to claim 1, wherein the battery capacity of the lithium secondary battery is 2 Ah or more. 9. The method for preparing an electrode slurry for a lithium secondary battery according to claim 1, wherein the lithium secondary battery is an on-vehicle battery. 10. The method for preparing an electrode slurry for a lithium secondary battery according to claim 1, wherein the lithium secondary battery is used for an electric vehicle or a hybrid electric vehicle. 11. The method for preparing an electrode slurry for a lithium secondary battery according to claim 1, wherein the lithium secondary battery is used for starting an engine.