JP5994467B2 - Method for producing lithium ion secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing a lithium ion secondary battery. In particular, the present invention relates to a method for manufacturing a lithium ion secondary battery in which a mixture layer including an active material and a binder is formed on a separator.

A lithium ion secondary battery is manufactured by inserting an electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator between them into a case, and injecting and sealing an electrolyte.
In the production of lithium ion secondary battery electrodes, a paste prepared by kneading an active material and a binder into a solvent on a surface of a current collector such as an aluminum foil or a copper foil in a solvent is applied in a thin film, and then A coated electrode manufactured by drying and pressing is generally known.
However, in the case of the conventional coated electrode, the migration is such that the active material and the binder are separated inside the paste applied in a thin film due to the thermal convection of the solvent in the drying process, and the binder segregates upward in the film thickness. Tend to occur. When the active material and the binder are separated and segregated, the active material expands and contracts during charge and discharge, and the active material and the active material and the current collector are easily separated, and the battery performance. There was a problem of deterioration.
Therefore, a method for producing an electrode by powder molding that does not cause segregation of the binder has been developed, and is disclosed in Patent Document 1, for example.
In the technique of Patent Document 1, powdered granulated particles made of an electrode material such as an active material and a binder are supplied onto one or both opposing pressure rollers by a powder supply device, and the space between the pressure rollers is In this method, a mixture layer is formed by pressure molding the supplied granulated particles on the surface of the current collector that passes.

JP 2009-212113 A

However, since the technique of Patent Document 1 is a method of pressure-molding powdered granulated particles on the current collector surface, if the binder is not sufficiently supplied between the current collector surface and the active material, The required adhesion could not be obtained. In that case, since the current collector and the mixture layer are easily peeled off, there is a problem that the electrodes are peeled off on the production line.
Further, when the electrode plate is repeatedly charged and discharged, the mixture layer repeats expansion and contraction, but the stretchability of the current collector made of metal foil is smaller than the expansion and contraction amount (about 10%) of the mixture layer. For this reason, there is a problem that expansion and contraction between the mixture layer and the current collector is generated, the mixture layer is cracked and peeled, resulting in a decrease in capacity.

  The present invention has been made to solve the above-described problems, and its purpose is to produce a lithium ion secondary battery that can increase the peel strength of the mixture layer on the electrode plate and prevent a decrease in battery capacity retention rate. Is to provide a method.

  In order to solve the above-mentioned problems, the present inventors changed the conventional idea of forming a mixture layer on a current collector, and embodied a new idea of forming a mixture layer on a separator. The manufacturing method of the lithium ion secondary battery of this invention has the following structures.

(1) Powdered granulated particles containing at least an active material and a binder are supplied onto a separator made of polyolefin resin or PET or PEN to form a deposited layer, and the deposited layer is pressure-molded. The manufacturing method of the lithium ion secondary battery which forms a mixture layer on the said separator .

In the present invention, since thereby a mixture layer formed on a separator made of a polyolefin resin or PET or PEN, to follow the expansion and shrinkage of the active material during charge and discharge, even separator made of a polyolefin resin or PET or PEN Can expand and contract. The separator made of polyolefin resin or PET or PEN can be expanded and contracted following the expansion and contraction of the active material, so that the active material and the separator made of polyolefin resin or PET or PEN are hardly misaligned. Therefore, the mixture layer is not easily cracked or peeled off.
Therefore, the durability of the electrode plate is improved as compared with the method of forming the mixture layer on the current collector of the metal foil having low elasticity.

Further, in the present invention, powdered granulated particles containing at least an active material and a binder are supplied onto a separator made of polyolefin resin or PET or PEN to form a deposited layer, and the deposited layer is Since the mixture layer is formed on the separator by pressure molding, unlike the case where a paste-like coating liquid is applied, migration in which the binder segregates upward in the film thickness does not occur. Therefore, the active material and the separator can be bound by the binding material. Therefore, the peel strength of the mixture layer to the separator is increased. Further, as in the case of applying a paste-like coating liquid, the binder dissolved in the solvent is not clogged with the pores provided in the separator , and the resistance does not increase.
Therefore, according to this invention, the peeling strength of the mixture layer in an electrode plate can be improved, and the capacity | capacitance maintenance factor fall of a battery can be prevented.

(2) In the method for producing a lithium ion secondary battery described in (1),
The separator is charged positively or negatively.

In the present invention, the separator, since the positively or negatively charged, powdered granulated particles are attracted to charged positive or negative charge to the separator, is electrostatically attracted to the separator. For this reason, the powdered granulated particles are in close contact with the surface of the separator and are less likely to fall down during the transport of the separator.
In addition, since the binder (for example, styrene butadiene rubber (SBR)) is generally an organic substance and is easily dielectrically polarized, it is easily attracted and collected on the charged separator . Therefore, when the binder enters between the separator and the active material, and the deposited layer of granulated particles is pressure-molded, the binder can effectively bind the separator and the active material, and the mixture layer The peel strength can be further increased.
The separator can be easily charged by simply rewinding it from the coil, so that it can be charged while the separator is being transported.

(3) In the method for producing a lithium ion secondary battery described in (1) or (2),
The separator is controlled to be charged positively or negatively by corona discharge treatment.

In the present invention, since the separator is controlled to be positively or negatively charged by corona discharge treatment, the adhesion with the mixture layer can be further enhanced. For example, when the separator is made of a polyolefin-based film, it has been proved by experiments that the charging control may be performed by a corona discharge treatment of about 40 to 300 W · min / m ² . In addition, in the process of less than 40 W · min / m ² , charging is insufficient, and when the process exceeds 300 W · min / m ² , the pores of the polyolefin-based separator are dissolved and closed by heat during corona discharge. Because there is.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the lithium ion secondary battery which can raise the peeling strength of the mixture layer in an electrode plate and can prevent the capacity | capacitance maintenance factor fall of a battery can be provided.

It is sectional drawing of the lithium ion secondary battery which concerns on this embodiment. FIG. 2 is a detailed electrode diagram (enlarged cross-sectional view of part B) of the lithium ion secondary battery shown in FIG. 1. It is a part of manufacturing apparatus of the lithium ion secondary battery which concerns on this embodiment. It is typical sectional drawing of the state by which the granulated particle of the mixture was adsorbed on the separator in this embodiment. It is a graph which shows the 90 degree peeling strength of the mixture layer in the electrode plate manufactured by this embodiment. It is a graph which shows the capacity | capacitance maintenance factor after the endurance test in the electrode plate manufactured by this embodiment.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. First, after briefly explaining the structure of a lithium ion secondary battery, an embodiment in which a mixture layer is formed on a separator will be described. Next, as the operational effects of this embodiment, the peel strength and capacity retention rate of the manufactured electrode plate will be described.

<Structure of lithium ion secondary battery>
First, the structure of the lithium ion secondary battery according to this embodiment will be described. FIG. 1 shows a cross-sectional view of a lithium ion secondary battery according to this embodiment. FIG. 2 shows a detailed electrode diagram (enlarged sectional view of part B) of the lithium ion secondary battery shown in FIG.

As shown in FIGS. 1 and 2, the lithium ion secondary battery 100 includes an electrode body 101, an electrolytic solution 103, and a battery case 104 that accommodates these. The battery case 104 includes a battery case main body 1041 and a sealing plate 1042. The sealing plate 1042 includes an insulating member 1043 and a safety valve 1044.
In the electrode body 101, a positive electrode active material, a binder, and a positive electrode mixture layer S containing a thickener are formed on one surface of a polyolefin-based separator Z, and a negative electrode active material, a binder, and a thickener are formed on the other surface. A negative electrode mixture layer F containing an agent is formed, wound between the positive electrode plate 1011 and the negative electrode plate 1012, and then formed into a flat shape.

As shown in FIG. 1, the external terminal T1 of the positive electrode plate 1011 protrudes from the sealing plate 1042 on the right hand side of the drawing, and the external terminal T2 of the negative electrode plate 1012 protrudes from the sealing plate 1042 on the left hand side of the drawing. The electrolyte solution 103 is stored under the battery case body 1041, and the polyolefin separator Z, the positive electrode plate 1011, and the negative electrode 1012 are immersed in the electrolyte solution 103.
As shown in FIG. 2, from the left side of the drawing, the positive electrode plate 1011, the positive electrode mixture layer S, the polyolefin separator Z, the negative electrode mixture layer F, the negative electrode plate 1012, the negative electrode mixture layer F, the polyolefin separator Z, the positive electrode mixture layer. S and the positive electrode plate 1011 are arranged in this order. Here, since the positive electrode plate 1011 and the positive electrode mixture layer S, and the negative electrode plate 1012 and the negative electrode mixture layer F are in close contact with each other, the positive electrode plate 1011 and the positive electrode mixture layer S, and the negative electrode plate 1012 and Conductive paths are formed between the negative electrode mixture layer F and each of them.

<Method for producing lithium ion secondary battery>
Next, a method for forming a mixture layer on a separator, which is a technical feature, in the method for manufacturing a lithium ion secondary battery according to the present embodiment will be described. FIG. 3 shows a part of a lithium ion secondary battery manufacturing apparatus according to the present embodiment.

As shown in FIG. 3, the lithium ion secondary battery manufacturing apparatus 10 according to the present embodiment includes a separator coil rewinding machine ZC, feed rollers 1 and 2, a corona discharge device 3, a powder feeder 4, and a pressurization. Rollers 5 and 6 are provided.
The coil rewinding machine ZC is a device that rewinds the polyolefin separator Z wound in a coil shape while applying a predetermined tension.
The polyolefin separator Z has a width of about 200 to 300 mm and a thickness of about 10 to 40 μm. In addition to the polyolefin resin, for example, PET, PEN or the like is suitable for the separator Z, and it may be a film or a non-woven fabric. The polyolefin-based separator Z is formed with a plurality of pores through which the electrolytic solution can pass. Small irregularities may be formed on the surface of the polyolefin separator Z. Due to the anchor effect due to minute irregularities, the adhesion of the mixture layer formed thereon can be enhanced.

The feed rollers 1 and 2 are devices that convey the polyolefin separator Z at a predetermined feed speed by rotating with the polyolefin separator Z sandwiched between both rollers. Via the arc of the feed roller 2, the polyolefin separator Z has its feed direction converted from a vertical direction to a horizontal direction.
The corona discharge device 3 is disposed above the polyolefin separator Z conveyed from the feed rollers 1 and 2 and generates a corona discharge 31 for charging the polyolefin separator Z. The polyolefin separator Z is subjected to a corona discharge treatment of about 40 to 300 W · min / m ² . The charging voltage is 1.2 kV or higher.

The powder feeder 4 is disposed adjacent to the corona discharge device 3 and behind the polyolefin separator Z in the transport direction. The powder feeder 4 is an apparatus that continuously supplies granulated particles 41 of powder containing an active material, a binder, and the like on a charged polyolefin separator Z with a predetermined thickness. The granulated particles 41 are produced by using powders for the active material and the binder, and mixing them together. For the active material, for example, amorphous coated graphite can be used as the negative electrode active material. Moreover, SBR and polytetrafluoroethylene (PTFE) can be used for a binder, for example. The granulated particles 41 are a mixture of an active material and a binder at a ratio (wt%) of about 98: 2.
The granulated particles 41 may be produced by a method in which an active material, a binder and a thickener are dissolved in a solvent, kneaded, dried and granulated. In this case, the mixing ratio (wt%) of the active material, the binder, and the thickener is approximately 97.3: 2.0: 0.7. For example, carboxymethylcellulose (CMC) can be used as the thickener.
Here, the deposition amount of the granulated particles 41 is about 10 mg / cm ² , and the thickness of the deposition layer 42 is about 100 to 120 μm.

The polyolefin-based separator Z that has passed through the powder feeder 4 and on which the deposited layer 42 of the granulated particles 41 has been formed passes between the pressure rollers 5 and 6. The pressure rollers 5 and 6 are devices that press the deposited layer 42 of the granulated particles 41 to form a mixture layer 43 having a predetermined density. By pressure molding, the mixture layer 43 can increase the peel strength by bringing the binder material between the polyolefin separator Z and the active material into close contact. The thickness of the mixture layer 43 after pressurization is about 80 μm.
As mentioned above, according to the manufacturing method of the lithium ion secondary battery which concerns on this embodiment, the mixture layer 43 can be formed in the single side | surface of the polyolefin-type separator Z in an electrode plate. In addition, when forming the mixture layer 43 on both surfaces of the polyolefin-type separator Z in an electrode plate, the said manufacturing method will be repeated twice.

<Mechanism for improving peel strength of mixture layer and its effect>
Next, in the electrode plate of the lithium ion secondary battery manufactured by the manufacturing method according to the present embodiment, a mechanism for improving the peel strength of the mixture layer and the effect thereof will be described. The mechanism for improving the peel strength of the mixture layer has three characteristics. FIG. 4 is a schematic cross-sectional view showing a state in which the granulated particles of the mixture are adsorbed on the separator in the present embodiment.

The first feature is that the polyolefin separator Z expands and contracts following the active material K that expands and contracts during charge and discharge.
The active material K is bound on the polyolefin separator Z. When lithium ions enter and exit the crystal of the active material K by charging and discharging, the volume of the active material K expands and contracts by about 10%. When the active material K is bound to the separator during the expansion and contraction and the movement is restricted, the crystal of the active material K is divided or peeled off from the separator.
However, the polyolefin-based separator Z is highly stretchable compared to a positive electrode plate or a negative electrode plate that is a metal foil. When the active material K expands and contracts, the polyolefin separator Z can expand and contract following the active material K. That is, since the polyolefin-based separator Z can be expanded and contracted with the expansion and contraction of the active material K, there is hardly any deviation between the active material K and the polyolefin-based separator Z.
Therefore, the mixture layer is not easily cracked or peeled off against the active material K that expands and contracts during charge and discharge.

The second feature is that the active material K of the granulated particles and the binder BD are dispersed in a substantially uniform manner.
As shown in FIG. 4, on the surface of the polyolefin-based separator Z, the active material K of the granulated particles and the binder BD are deposited in a substantially uniform manner at a predetermined ratio. Therefore, the binding material BD does not segregate above the deposition layer G as in the case of a conventional coating electrode, and an appropriate amount of the binding material BD is dispersed between the active materials K.
Therefore, when the deposited layer G is pressurized and powder-molded, the active materials are bound substantially uniformly by the binding material BD dispersed substantially uniformly, and the peel strength is improved. Since the binder BD is not segregated above the deposited layer G, a conductive path can also be reliably formed.

The third feature is that the binder BD is preferentially sucked onto the charged polyolefin separator Z.
The polyolefin-based separator Z is charged while being rewound and conveyed by the coil rewinder ZC. Therefore, as shown in FIG. 4, the organic binder BD is dielectrically polarized and sucked onto the polyolefin separator Z preferentially over the inorganic active material K.
Therefore, when a large amount of the binder BD gathers between the active material K and the polyolefin-based separator Z, and the deposited layer G is pressed and powder-molded, the active material K and the polyolefin-based material are bound by the binder BD. The separator Z is securely bound. A corona discharge treatment is more effective.

In FIG. 5, the graph of the 90 degree | times peeling strength of the mixture layer in the electrode plate manufactured by this embodiment is shown. FIG. 5 shows the peel strength of a conventional coated electrode, an electrode powder-molded on a carbon-coated foil, and an electrode powder-molded on a polyolefin-based separator Z (this embodiment) by a 90-degree peel test (according to JIS K6854). It is the graph which compared.
As shown in FIG. 5, the peel strength of the electrode (this embodiment) molded on the polyolefin separator Z is the highest, which is about 65% higher than the conventional coated electrode, and is powder molded on the carbon coated foil. That is about 130% higher.
As described above, the electrode plate of the lithium ion secondary battery manufactured by the manufacturing method according to the present embodiment can greatly improve the peel strength of the mixture layer.

<Capacity retention after endurance test>
Next, in the electrode plate of the lithium ion secondary battery manufactured by the manufacturing method according to the present embodiment, the capacity maintenance rate after the durability test will be described. In FIG. 6, the graph of the capacity | capacitance maintenance factor after the endurance test in the electrode plate manufactured by this embodiment is shown.
FIG. 6 shows a conventional coated electrode, an electrode powder-molded on a carbon-coated foil, and an electrode powder-molded on a polyolefin-based separator Z (this embodiment) at a current 2C rate in a 60 ° C. environment. It is the graph which performed the durability test of 400 cycles and compared the capacity retention rate after that.
As shown in FIG. 6, the capacity retention rate of the electrode (this embodiment) molded on the polyolefin separator Z is the highest, rising about 2.4% from the conventional coated electrode, and the powder is applied to the carbon coated foil. It is about 4.5% higher than the molded electrode.
As described above, the electrode plate of the lithium ion secondary battery manufactured by the manufacturing method according to the present embodiment can improve the capacity retention rate after the durability test.

<Modification>
Next, the manufacturing method of the lithium ion secondary battery which can be implemented without changing the gist of the present invention will be described.
Although this embodiment is a method of forming a mixture layer containing an active material, a binder and the like on each side of the separator, the mixture layer can also be formed simultaneously on both sides of the separator.
Specifically, the left and right pressure rollers are arranged at positions facing each other with the polyolefin-based separator Z narrowed. With the first powder feeder and the second powder feeder arranged on the left and right pressure rollers, the granulated particles of the powder containing the active material and the binder are laminated on the left and right pressure rollers, The laminated deposition layer is rotated while being pressed against the polyolefin separator, and a mixture layer is simultaneously formed on both surfaces of the polyolefin separator.

  The present invention can be used as a method of manufacturing a lithium ion secondary battery mounted on an electric vehicle, a hybrid vehicle, or the like.

DESCRIPTION OF SYMBOLS 1, 2 Feed roller 3 Corona discharge apparatus 4 Powder feeder 5, 6 Pressure roller 10 Lithium ion secondary battery manufacturing apparatus 31 Corona discharge 41 Granulated particle 42 Deposited layer 43 Mixture layer 100 Lithium ion secondary battery 101 Electrode body

Claims (3)

Powdered granulated particles containing at least an active material and a binder are supplied onto a separator made of polyolefin resin or PET or PEN to form a deposited layer, and the deposited layer is formed by pressure molding on the separator . A method for producing a lithium ion secondary battery in which a mixture layer is formed. In the manufacturing method of the lithium ion secondary battery described in claim 1,
A method for producing a lithium ion secondary battery, wherein the separator is charged positively or negatively. In the manufacturing method of the lithium ion secondary battery described in claim 1 or claim 2,
The separator is controlled to be positively or negatively charged by corona discharge treatment, and the method for producing a lithium ion secondary battery.

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