JP2011198548A - Electrode plate for battery and battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery of high quality excellent in charge discharge cycle characteristics and low-temperature characteristic through maintenance of adhesion between active materials themselves and restraint of coating of an electrode mixture layer by a binding agent.SOLUTION: For an electrode plate for a battery forming an electrode plate mixture layer 3 by applying electrode mixture paint structured of at least an anode active material 2, a binder 1 and a solvent on the surface of an anode collector 4, and drying and pressing it, the binder 1 with a particle size not crushed even by being pressed is utilized.

Description

  The present invention relates to a battery electrode plate in which an electrode mixture layer containing an active material and a binder is supported on a current collector, and a battery using the same.

  Conventionally, in a non-aqueous electrolyte secondary battery such as a lithium ion battery or an alkaline storage battery such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery, a positive electrode plate or a negative electrode in which an electrode mixture made of an active material is supported on a current collector A plate is used. Then, a separator as a porous insulator is interposed between the positive electrode plate and the negative electrode plate so as to face each other to form an electrode group, and this electrode group is housed in the battery outer package together with the electrolyte solution, The battery is configured by hermetically sealing the body.

  The positive electrode plate or negative electrode plate described above is a powdered active material with a binder and a conductive agent added and mixed to form an electrode mixture paint, and after applying this electrode mixture paint to the current collector, it is dried. Compressed and manufactured to a predetermined packing density after drying. In this case, as the binder mixed in the electrode mixture layer, a polymer having a chain structure (including a network structure) is generally used. By using such a high molecular binder, the active materials are bound to each other via the binder, and the active material is bound to the current collector.

  However, when a polymer having a chain structure (including a network structure) is used as a binder, the active material is peeled off from the current collector in the electrode plate manufacturing process when the active material used is bulky. There has been a problem that the yield of this type of electrode plate tends to decrease. In addition, when an active material that expands and contracts during charge and discharge is used, there is a problem in that sudden capacity reduction occurs due to expansion and contraction during charge and discharge, and active material peeling occurs. It was.

  Therefore, in order to deal with such problems, it has been proposed to use a particulate polymer (granular polymer) as a binder instead of a polymer having a chain structure (for example, Patent Document 1). , See Patent Document 2).

  However, when the binders proposed in these are used, although the above-described bulky active material and an active material that expands and contracts during charge and discharge are used, a slight improvement in adhesion is observed, Since the binder to be used is composed only of the particulate polymer, the contact area between the binder and the active material is reduced, and the adhesion strength is insufficient in practical use.

  Therefore, in order to increase the contact area between the binder and the active material, the binders having different particle sizes are polydispersed (“polydisperse” is a state in which the binder particles have a particle size distribution. ) By increasing the contact area between the binder and the active material, the active materials are brought into close contact with each other and the adhesion between the active material and the current collector is improved, so that an electrode plate having excellent adhesion strength can be provided. (For example, refer to Patent Document 3).

JP 11-297329 A JP 2009-206079 A JP 2003-109598 A

  However, when the binders having different particle diameters are polydispersed, the adhesion strength increases, but the binder having a large particle diameter as the electrode mixture layer 23 formed on the surface of the current collector 20 as shown in FIG. Since No. 21 is crushed during pressurization and covers the surface of the active material particles 22, it has a problem that the characteristics are deteriorated by charge / discharge at a low temperature and a low temperature cycle.

  The present invention has been made to solve such problems, and provides a battery electrode plate that does not completely cover the surface of the electrode mixture layer with a binder, and has excellent adhesion strength. The object is to provide an electrode plate.

  In order to achieve the above object, the battery electrode plate of the present invention is formed by applying an electrode mixture paint composed of at least an active material, a binder and a solvent to the surface of a current collector, drying and pressurizing the electrode assembly. In the battery electrode plate in which the agent layer is formed, a binder having a particle size that does not collapse even when pressed is used as the binder.

  According to the present invention, since the binder having a particle size that does not collapse even when pressed is used, the surface of the electrode mixture layer is completely covered with the binder while maintaining the adhesion between the active materials. Therefore, when binding an active material capable of inserting and extracting lithium ions, which has the property of expanding and contracting due to charge and discharge, the active material can be removed when the battery electrode plate of the present invention is used. The charge / discharge characteristics at low temperature can be improved.

The block diagram which shows typically the state of the active material particle and binder particle | grains after rolling in this invention Sectional drawing which shows the structure of the principal part of the electrode group using the battery electrode plate of this invention. Sectional drawing which shows the battery comprised using the electrode plate for batteries of this invention Configuration diagram schematically showing the state of active material particles and binder particles after conventional rolling

  The first invention of the present invention is for a battery in which an electrode mixture coating composed of at least an active material, a binder and a solvent is applied to the surface of a current collector, and dried and pressed to form an electrode mixture layer In the electrode plate, a battery electrode plate having a particle size that does not collapse even when pressed is used as the binder.

  According to the present invention, the surface of the electrode mixture layer is not completely covered with the binder because it uses a binder having a particle size that does not collapse even when pressed, and expands and contracts due to charge and discharge. When the battery electrode plate of the present invention is used when binding an active material capable of inserting and extracting a certain lithium ion, dropping of the active material can be reduced and charge / discharge characteristics at a low temperature are improved.

  In the second invention of the present invention, it is preferable to use a binder having an average particle diameter of 0.01 to 10 μm. This is because, when the average particle size is smaller than 0.01 μm, the adhesion between the active materials is extremely lowered, and the active materials fall off. Moreover, when it is larger than 10 μm, the binder is crushed during pressurization and the surface of the electrode mixture layer is covered with the binder.

In the third aspect of the present invention, the amount of the binder added is preferably 0.4 to 3.0 parts by weight with respect to 100 parts by weight of the active material. This is because when the addition amount is less than 0.4 parts by weight, the electrode mixture paint does not sufficiently thicken and does not have a viscosity suitable for coating. On the other hand, when the amount is more than 3.0 parts by weight, the energy density of the negative electrode is lowered, which adversely affects battery characteristics such as high load discharge and low temperature discharge.

  In the fourth aspect of the present invention, it is preferable to use a negative electrode active material as the active material. This is because improvement in adhesion of the negative electrode mixture layer and improvement in low temperature characteristics are required.

  According to a fifth aspect of the present invention, there is provided an electrode group comprising a positive electrode plate having an electrode mixture layer formed on the surface of a current collector and a negative electrode plate stacked or wound via a porous insulator as a battery electrode plate. A battery comprising a battery case and an electrolyte solution, wherein the battery electrode plate according to any one of the first to fourth inventions is used for at least one of the positive electrode plate and the negative electrode plate. is there. When the battery electrode plate of the present invention is used, the surface of the electrode mixture layer is not completely covered with the binder, and can absorb and release lithium ions that have the property of expanding and contracting due to charge and discharge. When binding a possible active material, dropping of the active material can be reduced, and charge / discharge characteristics at a low temperature can be improved.

  Hereinafter, an example in which the battery electrode plate of the present invention is applied to a negative electrode plate will be described in detail as an embodiment.

  The negative electrode plate of the present invention will be described with reference to FIG. First, the negative electrode active material 2, water, and a thickener are mixed. Thereafter, an aqueous binder 1 is mixed with the obtained mixture to prepare a negative electrode mixture paint. The addition of the thickener is to give the negative electrode mixture paint a certain viscosity. Then, as shown in FIG. 1, the obtained negative electrode mixture paint is applied to the negative electrode current collector 4 and dried to form the negative electrode mixture layer 3, whereby a negative electrode plate is obtained. The method for applying the negative electrode mixture paint to the negative electrode current collector 4 is not particularly limited. For example, the negative electrode mixture paint is applied in a predetermined pattern to the raw material of the negative electrode current collector 4 using a die coat. The drying temperature of the coating film is not particularly limited. The coating film after drying is rolled to a predetermined thickness by a rolling roll. By the rolling process, the adhesive strength between the negative electrode mixture layer 3 and the negative electrode current collector 4 and the adhesive strength between the active material particles are increased. The negative electrode mixture layer 3 thus obtained is cut into a predetermined shape together with the negative electrode current collector 4 to complete a negative electrode plate.

As the negative electrode active material 2, a material having conductivity, a carbon material capable of inserting and extracting lithium ions, a silicon oxide such as SiO _{2, and the} like can be used. In particular, carbon materials are preferable, and carbon materials are conductive, and inactive material carbon that can occlude and release lithium ions, coke, natural active material, artificial active material, active material mesophase carbon Particles can be used. The particle diameter of these carbon materials is not particularly limited.

Although it does not specifically limit as a thickener, A cellulose, polyvinyl alcohol, polyvinylpyrrolidone, these derivatives, etc. are mentioned. Of these, cellulose, cellulose derivatives and the like are particularly preferable. As the cellulose derivative, methyl cellulose, carboxymethyl cellulose, Na salt of carboxymethyl cellulose and the like are preferable.
The binder 1 contained in the negative electrode mixture layer needs to have a particle size that does not collapse even when pressed. This is to avoid covering the surface of the electrode mixture layer 3 with the binder 1 due to the binder 1 being crushed by pressurization.

  The binder 1 preferably has an average particle size of 0.01 to 10 μm, more preferably 0.05 to 1 μm, and particularly preferably 0.05 to 0.1 μm. This is because, when the average particle size is smaller than 0.01 μm, the adhesion between the active materials is extremely lowered, and the active materials fall off. Moreover, when it is larger than 10 μm, the binder is crushed during pressurization and the surface of the electrode mixture layer is covered with the binder.

The amount of the binder 1 contained in the negative electrode mixture layer 3 is 0.4 to 3.0 per 100 parts by weight of the active material.
Parts by weight are preferred, 0.4 to 1.0 parts by weight are more preferred, and 0.4 to 0.7 parts by weight are particularly preferred. This is because when the addition amount is less than 0.4 parts by weight, the electrode mixture paint does not sufficiently thicken and does not have a viscosity suitable for coating. On the other hand, when the amount is more than 3.0 parts by weight, the energy density of the negative electrode is lowered, which adversely affects battery characteristics such as high load discharge and low temperature discharge.

  As the negative electrode current collector 4, a metal foil or the like is used. When producing a negative electrode plate of a lithium ion secondary battery, a copper foil, a copper alloy foil or the like is generally used as the negative electrode current collector 4. Of these, copper foil (which may contain components other than copper of 0.2 mol% or less) is preferable, and electrolytic copper foil is particularly preferable.

  As shown in FIG. 3, the battery of the present invention has a negative electrode plate 5, a positive electrode plate 6 capable of electrochemically inserting and extracting Li, and a porous material interposed between the negative electrode plate 5 and the positive electrode plate 6. The electrode group 8 is configured by stacking or winding the separator 7 as an insulator, and the electrode group 8 is combined with a non-aqueous electrolyte and a battery case 9 as a battery outer package together with the insulator 12 as shown in FIG. The battery 11 is configured by being housed and sealing the sealing plate 10 in the opening of the battery case 9. The battery of the present invention can be applied to batteries having various shapes such as a cylindrical shape, a flat shape, a coin shape, and a square shape, and the shape of the battery is not particularly limited.

  For example, the positive electrode plate 6 is formed by applying a positive electrode mixture paint containing a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride to a positive electrode current collector such as an aluminum foil, and drying. It is obtained by forming a positive electrode mixture layer formed by rolling. The binder used for the negative electrode plate 5 may also be used for the positive electrode plate 6.

  As a solvent for the electrolytic solution, a solvent composed of a high dielectric constant solvent and a low viscosity solvent is preferable. Preferred examples of the high dielectric constant solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate. These high dielectric constant solvents may be used alone or in combination of two or more.

  Low-viscosity solvents include symmetric chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and methyl-i-propyl carbonate. Asymmetric chain carbonates such as ethyl-i-propyl carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, chain esters such as methyl acetate and methyl propionate, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydro Examples include cyclic ethers such as pyran, chain ethers such as dimethoxyethane and dimethoxymethane, and amides such as dimethylformamide. These low-viscosity solvents can be used alone or in combination of two or more. The high dielectric constant solvent and the low viscosity solvent can be arbitrarily selected and used in combination.

Examples of the electrolyte salt of the electrolytic solution include an inorganic lithium salt selected from LiClO ₄ , LiPF ₆ , and LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , Examples thereof include fluorine-containing organic lithium salts such as LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) and LiC (CF ₃ SO ₂ ) ₃ . Of these, LiPF ₆ and LiBF ₄ are preferably used. These electrolyte salts can be used alone or in combination of two or more. These electrolytes are desirably used in the above non-aqueous solvent at a concentration of usually 0.1 to 3M, preferably 0.5 to 2M.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples in any way, and can be appropriately modified and implemented without departing from the scope of the present invention. Is.

(Creation of negative electrode plate)
First, 100 parts by weight of natural graphite particles as a negative electrode active material and 1 part by weight of a thickener were mixed and stirred while controlling the temperature of the mixture at 20 ° C. Each of 0.01 μm, 0.05 μm, 0.1 μm, 1 μm, and 10 μm having rubber elasticity containing styrene units and butadiene units in 101 parts by weight of the mixture (that is, 100 parts by weight of graphite + 1 part by weight of thickener) 0.7 parts by weight of a binder having a particle size was mixed to prepare negative electrode mixture paints A1 to A5 having the ratios shown below (Table 1). In addition, 0.4 parts by weight, 0.7 parts by weight, 1 part by weight, and 3 parts by weight of a binder having a particle diameter of 0.1 μm were mixed, and the negative electrode mixture paint A6 having a ratio as shown below (Table 1). -A9 was prepared. The obtained negative electrode mixture paint was applied on both surfaces of an electrolytic copper foil (thickness 8 μm) as the negative electrode current collector 4, and the coating film was dried at 110 ° C. Thereafter, the dried coating film was rolled with a rolling roller to form a negative electrode mixture layer having a thickness of 148 μm. A negative electrode plate 5 was obtained by cutting the negative electrode mixture layer 3 together with the negative electrode current collector 4 into a predetermined shape.

(Creation of positive electrode plate)
4 parts by weight of polyvinylidene fluoride (PVDF) as a binder was added to 100 parts by weight of LiCoO _{2 as} a positive electrode active material, and mixed with an appropriate amount of NMP to prepare a positive electrode mixture paint. The obtained positive electrode mixture paint was applied to both surfaces of a 15 μm-thick aluminum foil as a positive electrode current collector, the coating film was dried, and further rolled to form a positive electrode mixture layer. A positive electrode plate 6 was obtained by cutting the positive electrode mixture layer into a predetermined shape together with the positive electrode current collector.

(Preparation of electrolyte)
LiPF ₆ was dissolved at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1: 1 to obtain an electrolyte solution. Prepared. The electrolyte contained 3% by weight of vinylene carbonate.

(Battery assembly)
A square lithium ion secondary battery as shown in FIG. 3 was produced.

  The negative electrode plate 5 and the positive electrode plate 6 were wound through a separator 7 made of a polyethylene microporous film between them to form an electrode group 8 having a substantially elliptical cross section. The electrode group 8 was accommodated in a rectangular battery case 9 made of aluminum. The battery case 9 has a bottom part and a side wall, and the upper part is opened. Thereafter, an insulator 12 for preventing a short circuit between the battery case 9 and the positive electrode lead or the negative electrode lead was disposed on the electrode group 8. Next, a rectangular sealing plate 10 having a negative electrode terminal surrounded by an insulating gasket in the center was disposed in the opening of the battery case 9. The negative electrode lead was connected to the negative electrode terminal. The positive electrode lead was connected to the lower surface of the sealing plate 10. The end of the opening and the sealing plate 10 were welded with a laser to seal the opening of the battery case 9. Thereafter, an electrolytic solution was injected into the battery case 9 from the injection hole of the sealing plate 10. Finally, the injection hole was closed by welding with a sealing plug to prepare square lithium ion secondary batteries A1 to A9. Here, the prismatic lithium ion secondary batteries A1 to A9 were prepared by changing the particle diameter and addition amount of the binder 1 as shown in (Table 1).

(Comparative Example 1)
The basic structure of the battery is the same as that of the example, and the particle system of the binder for the negative electrode plate and the amount added are shown in Table 1. Comparative batteries B1 and B2 were produced in the same manner as in the examples except that the negative electrode mixture paint containing 0.7 parts by weight of 0.008 μm and 12 μm SBR binder was prepared.

(Comparative Example 2)
Similarly, Comparative Battery B3 was prepared in the same manner as in Example except that a negative electrode mixture paint containing 4 parts by weight of SBR having a binder particle size of 0.1 μm was prepared.

(Battery evaluation)
The batteries of these examples and comparative examples were charged and discharged under the following conditions in a 20 ° C. environment, then charged at 20 ° C., then discharged at −10 ° C. under the following conditions, and the discharge capacity was measured. The ratio (capacity maintenance ratio) of the discharge capacity at −10 ° C. to the discharge capacity at 20 ° C. was obtained as a percentage.

<Cycle test conditions>
Constant current charging: Charging current value 700mA / end-of-charge voltage 4.2V
Constant voltage charging: Charging voltage value 4.2V / Charge termination current 35mA
Constant current discharge: discharge current value 700 mA / discharge end voltage 3 V
As shown below (Table 2), it can be seen that the capacity retention ratios of the batteries A1 to A5 of the present invention are superior to the batteries B1 and B2 of the comparative example. In particular, the low-temperature characteristics of A2 and A3 are very excellent, and the average particle size of the binder is preferably 0.01 to 10 μm, and particularly optimal in the range of 0.05 to 0.1 μm. .

  If the particle size is in the range of 0.01 to 10 μm, the binder is not crushed even when pressurized, and the surface of the electrode mixture layer is not covered with the binder, so even at low temperatures. This is because the acceptability of lithium ions does not decrease.

  Moreover, it turns out that it is excellent in the capacity | capacitance maintenance factor of battery A6-A9 of this invention compared with battery B3 of a comparative example. In particular, since the low temperature characteristics of A6 and A7 are very excellent, the amount of the binder added is preferably 0.4 to 3 parts by weight, particularly 0.4 to 0.7 parts by weight. Is optimal. This is because the surface of the electrode mixture layer is not completely covered with the binder in the range of 0.4 to 3 parts by weight.

  In addition, this invention is not limited to the Example described, The various combination which can be easily guessed from the meaning of invention is possible. Moreover, although the said Example is related with a lithium ion secondary battery, this invention is applied to the battery in general.

  According to the battery electrode plate of the present invention, the surface of the electrode mixture layer is completely covered with the binder because it uses a particle size that is not crushed even when the binder in the mixture layer is pressurized. In addition, in order to provide an electrode plate in which the adhesion between the active materials is maintained, even when the negative electrode mixture layer repeatedly expands and contracts in the charge / discharge cycle, the falling off of the active material particles can be reduced, and lithium ions can be received. Improves. Therefore, a highly reliable battery having excellent charge / discharge cycle characteristics and low temperature characteristics can be obtained.

DESCRIPTION OF SYMBOLS 1 Binder 2 Negative electrode active material 3 Negative electrode mixture layer 4 Negative electrode collector 5 Negative electrode plate 6 Positive electrode plate 7 Separator 8 Electrode group 9 Battery case 10 Sealing plate 11 Battery 12 Insulator 20 Current collector 21 Binder 22 Active Material particles 23 Mixture layer

Claims (5)

  In the electrode plate for a battery in which an electrode mixture coating composed of at least an active material, a binder and a solvent is applied to the surface of the current collector, and the electrode mixture layer is formed by drying and pressing. A battery electrode plate having a particle size that does not collapse even when pressed.   The battery electrode plate according to claim 1, wherein the binder has an average particle diameter of 0.01 to 10 μm.   The battery electrode plate according to claim 1, wherein 0.4 to 3.0 parts by weight of the binder is added to 100 parts by weight of the active material.   The battery electrode plate according to claim 1, wherein a negative electrode active material is used as the active material. In a battery in which an electrode group formed by laminating or winding a positive electrode plate and a negative electrode plate with an electrode mixture layer formed on the surface of a current collector through a porous insulator is enclosed in a battery outer package together with an electrolyte. ,
A battery comprising the battery electrode plate according to claim 1 as at least one of the positive electrode plate and the negative electrode plate.

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