JP5998368B2 - Method for manufacturing electrochemical device - Google Patents

Description

  The present invention relates to an electrochemical device, particularly a lithium secondary battery or a lithium ion capacitor.

  In recent years, electrochemical devices typified by lithium secondary batteries and lithium ion capacitors are being developed for in-vehicle applications, and it is an issue to extend the life of the devices. As countermeasures, various solutions such as (a) improvement of positive / negative electrode materials, (b) improvement of current collector foil, and (c) improvement of separator have been proposed (Patent Documents 1 to 3).

However, even if the measures (a), (b) and (c) are taken, there is a problem in extending the lifetime of the electrochemical device.
For example, in a lithium secondary battery having an electrode winding group or a stacked electrode group consisting of a positive and negative electrode and a separator inserted between the electrodes in a battery case, a predetermined constant pressure is applied to the electrode group. Otherwise, the adhesion between the separator and the positive or negative electrode will be hindered, creating a space at the interface with the separator, or even if it is in contact, the electrolyte solution will not be easy to move. In addition, there is a problem that the resistance of the battery is increased, and further, its adverse effect is increased during charging / discharging, resulting in an early life.

For this reason, the pressurization to the electrode group in a lithium battery is examined. For example, in the case of a cylindrical battery or a metal case of a rectangular battery, when the total thickness of the electrode group and the electrode group diameter are larger than the distance between the surfaces of the battery case and the inner diameter, the pressure is greatly increased. In the case of a pouch-type cell using a laminate film as a battery case, it is pressurized by reducing the pressure to a vacuum.
By applying pressure to these electrodes, pressure is applied to the electrodes, and the expansion and contraction of the electrodes can be controlled, thereby extending the life.
However, when a film separator is used as the separator, it cannot be inserted into the battery case during assembly, or if excessive pressure is applied, the film may be damaged, resulting in a short circuit, which may impair safety in some cases. There's a problem.

Conventionally, it has a power generation element in which a positive electrode and a negative electrode are laminated via a separator, and the power generation element is sealed by joining the peripheral edge of the power generation element by thermal fusion using a laminate film as a battery exterior material. A laminated laminate type battery, a battery case for storing the laminated type battery alone or in a stacked state, and a single laminated type battery or a laminated type laminated battery by a fluid sealed inside. A battery pack including a pressure bag that pressurizes inside a battery case is known (Patent Document 4).
However, there is a problem that it becomes difficult to reduce the thickness of the battery by inserting the pressure bag. In addition, there is a problem that a pressure bag must be prepared and the manufacturing process becomes complicated.

Japanese Patent No. 3867030 International Publication No. WO2011 / 049153 JP 2009-81048 A JP 2012-129209 A

  The present invention was made to cope with the above problems, and by applying an appropriate pressure to the positive and negative electrode groups in the case of an electrochemical device such as a lithium secondary battery or a lithium ion capacitor, The purpose is to provide a long-life electrochemical device.

The present invention is an electric device in which lithium ions are repeatedly occluded and released by infiltrating or immersing an organic electrolyte in a group of electrodes wound or laminated through a separator between a positive electrode and a negative electrode. In the chemical device, the separator is a woven or non-woven separator, and a pressure of 0.3 to 1.1 kgf / cm ² is applied to a main surface of the electrode group.

In the electrochemical device of the present invention, the total thickness or group diameter at the time of manufacturing the electrode group before housing the case is L ₁ , and the length between the opposing inner wall surfaces of the case is L ₀ . Is designed so that L ₁ ≧ L _0, and is accommodated in the case by using the compressible buffering action of the separator, and then the main surface of the electrode group is 0.3 by the restoring force of the separator. A pressure of ˜1.1 kgf / cm ² is applied.
Here, the group diameter at the time of manufacturing the electrode group refers to the maximum diameter of the wound electrode group.
Further, a pressure of 0.3 to 1.1 kgf / cm ² is applied to the main surface of the electrode group by fastening the entire electrode group with a tape.

  The electrochemical device of the present invention is a lithium secondary battery or a lithium ion capacitor.

Since the separator used in the electrochemical device of the present invention is a woven or non-woven separator, the contact with the electrode surface is less affected by the expansion and contraction of the electrode during charging / discharging than the synthetic resin film separator. It becomes easy to act as a buffer so as to follow. Moreover, the movement of electrolyte solution becomes easier because the pressure of 0.3-1.1 kgf / cm < ² > is applied via the said separator with respect to the positive and negative electrode surfaces which respectively oppose. As a result, the lifetime of the electrochemical device can be increased.

It is a perspective view which shows the structure of a square lithium secondary battery. It is sectional drawing of the direction where the applied pressure to an electrode group is applied.

As an example of the present invention, an example of a prismatic lithium secondary battery will be described with reference to FIG. FIG. 1 is a perspective view showing a configuration of a lithium secondary battery.
As shown in FIG. 1, a lithium secondary battery 1 includes an electrode group 3 having a total thickness L accommodated in a case 2 having a distance length L ₀ between opposing inner wall surfaces. A positive / negative electrode tab 4 that is electrically connected to 3 is pulled out of the case body from the upper portion 2a of the case body. The lithium secondary battery 1 is obtained by housing the electrode group 3 in the case 2 and sealing it with the case body upper part 2a. The organic electrolyte is permeated or immersed in the electrode group 3 to repeatedly occlude and release lithium ions. The present invention is also applied to a lithium ion capacitor.

In the present invention, the separator used for the electrode group 3 is a woven or non-woven separator, and the pressure F applied to the main surface 3a of the electrode group 3 is 0.3 to 1.1 kgf / cm ² , preferably 0. .8 to 1.0 kgf / cm ² .
If the applied pressure F is less than 0.3 kgf / cm ² , the internal resistance of the battery may increase and the discharge capacity may be lost, and if it exceeds 1.1 kgf / cm ² , a short circuit is likely to occur between the electrodes.

A preferred method for generating the pressure applied to the main surface 3a of the electrode group 3 will be described with reference to FIG. 2 is a cross-sectional view in the direction in which the pressing force F is applied to the electrode group 3, FIG. 2 (a) is a diagram showing the total thickness when the electrode group is manufactured, and FIG. 2 (b) is housed in a case. FIG. 2C is a diagram showing the thickness of the electrode group after being accommodated in the case.
The electrode group 3 is laminated between the positive electrode 5 and the negative electrode 6 with a separator 7 interposed therebetween. When the electrode group 3, L ₁ the total thickness of the front of the electrode group 3 during manufacture to accommodate the case 2, the distance length between the between inner wall surface facing the case 2 shown in FIG. 1 and L _0, L ₁ ≧ L ₀ is designed (FIG. 2A).

As shown in FIG. 2 (a), cross-sectional thickness L _5a of the positive electrode 5, cross-sectional thickness L _6a of the negative electrode 6, when the cross-sectional thickness L _7a of the separator 7, the electrode group in that they are laminated to each other The thickness of 3 is L ₁ . Here, since L _5a and L _6a are electrodes made of a metal foil and a solid active material, the ratio of thickness reduction is small even when pressure is applied to the main surface 3a of the electrode group. On the other hand, L _7a is a cross section of a woven or non-woven fabric separator, and therefore is more likely to be compressed by the buffering action of the woven or non-woven fabric when pressure F is applied as compared to a film separator. That is, even when the pressure F is applied, the length of L _5a is approximately L _5b and the length of L _6a is approximately L _6b , whereas when the pressure F is applied, L _7b is L _7a Shorter than.
Therefore, even if the thickness of the electrode group 3 is L ₁ , the pressure F is applied in the thickness direction of the main surface 3 a of the electrode group, so that the cross-sectional thickness of the separator 7 is reduced, and the thickness of the electrode group 3 is reduced. Becomes L ₂ (FIG. 2B). The electrode group 3 can be accommodated in the case 2 by compressing so that L ₂ <L ₀ . Even if L ₂ is the same as L ₀ , the electrode group 3 can be accommodated by slightly deforming the case 2.

As a method of applying the pressure F in the thickness direction of the main surface 3a of the electrode group, any method that can satisfy L ₂ <L ₀ may be used. For example, a method of winding the electrode group with tapes, case 2 There is a method of using the clearance between the inner walls.
The method of winding the electrode group with tapes is a method in which L ₂ <L ₀ by tightening the periphery of the electrode group with an adhesive tape or the like so that the pressure F can be applied to the electrode group. In this case, the electrode group after tightening the tape is accommodated in the case as it is.

The method using the clearance between the inner walls of the case 2 is a method of applying pressure to the electrode group by the restoring force of the separator 7.
The electrode group 3 is compressed to L ₂ <L ₀ by a compressor or the like, and is accommodated in the case 2 immediately after the compression, and due to the restoring force of the separator 7, the sectional thickness L ₁ at the time of manufacture is about to be accommodated. Since the distance from the inner wall surface of the case 2 cannot be more than the distance, the thickness of the electrode group 3 becomes L ₀ (FIG. 2C). Pressure is applied to the main surface of the electrode group 3 by this restoring force.
In the present invention, a pressure of 0.3 to 1.1 kgf / cm ² , preferably 0.8 to 1.0 kgf / cm ² is applied to the main electrode group 3 by adjusting the type and thickness of the separator 7. Apply to the surface.
For example, when a separator made of cellulose fiber or the like is used, it is assembled by compressing the entire cross-sectional thickness of the electrode group 3, applying a pressure of 0.3 to 1.1 kgf / cm ² and inserting it into the case. It is done. This pressure can be controlled by a pressure sensor or by a thickness reduction rate of the electrode group when the electrode group is put in a pouch-type cell and the inside is decompressed.

The separator that can be used in the present invention electrically insulates the positive electrode and the negative electrode and retains the electrolyte solution, and is made of synthetic fiber or inorganic fiber that has resilience even if it is compressed to some extent when the electrode group is manufactured. Woven fabric and non-woven fabric.
Synthetic fibers include polyolefin fibers such as polypropylene and polyethylene, polyester fibers, polyamide fibers, vinyl chloride fibers, polyphenylene sulfide fibers, wholly aromatic polyester fibers, polyparaphenylene benzobisoxazole fibers, aromatic polyamide fibers, and semi-aromatic polyamides. Fiber, polyimide fiber, polyamideimide fiber, melamine fiber, polybenzimidazole fiber, polyketone (polyether ether ketone, etc.) fiber, polyacrylonitrile fiber, polyvinyl alcohol fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyvinylidene fluoride fiber Other examples include fluoropolymer fibers, cellulose fibers, and cellulose-modified (such as carboxymethyl cellulose) fibers.
Inorganic fibers include silica, alumina, titanium dioxide, barium titanate, alumina-silica composite oxide, silicon carbide, zirconia, glass, etc., clays such as talc and montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, Examples thereof include fibrous materials such as spinel, olivine, sericite, bentonite, and mica, or fibrous materials such as artificial products or whiskers.
Of these, preferred are cellulose fiber woven fabrics and nonwoven fabrics.

The thickness of the separator that can be used in the present invention is appropriately selected depending on the type and application of the electrochemical device, but is preferably 10 to 100 μm, and more preferably 15 to 50 μm.
The porosity is preferably 50 to 95%, more preferably 65 to 80%.
Here, the porosity is based on the basis weight M (g / cm ² ), the thickness T (μm), and the polymer density D (g / cm ³ ), and the porosity (%) = [1− (M / T) / D] × 100.

The electrochemical device of the present invention has a layered or spinel structure lithium-containing metal oxide or solid solution as a positive electrode active material, a lithium-containing metal phosphate compound or lithium-containing metal silicate having an olivine structure, and fluorides thereof. Further, a lithium-containing compound such as sulfur is used as a main material, and a composite layer composed of the material, a binder, and a conductive material is formed on an aluminum foil.
Lithium-containing metal oxides having a layered and spinel structure include LiCoO ₂ , Li (Ni / Co / Mn) O ₂ , LiMn ₂ O ₄ , and Li ₂ MnO ₃ —LiMO ₂ (M = Ni, Co, Mn) as a solid solution. Examples of the lithium-containing metal phosphate compound include LiFePO ₄ , LiCoPO ₄ , and LiMnPO _4, and examples of the siliceous oxide include LiFeSiO ₄ . Examples of the fluoride include Li ₂ FePO ₄ · F. Examples of the lithium-containing compound include LiS ₄ , LiTi ₂ (PO ₄ ) ₃ , LiFeO _{2 and the} like. In this, electrochemical characteristics, in safety and _{cost, LiCoO 2, Li (Ni x} / Co y / Mn z) O 2 (x + y + z = 1), Li (Ni x / Mn y) O ₄ (x + y = 2), LiFePO ₄ is preferably used. Examples of the conductive material include carbon black and carbon nanotubes. Then, an active material mixture layer to which a synthetic resin binder is added is formed on the aluminum foil surface.

  On the other hand, as the negative electrode active material of the counter electrode, when the electrochemical device is a lithium secondary battery, a carbon material such as graphite or amorphous, metal silicon or metal tin, or an oxide thereof alone, or A mixture layer with a carbon material and further lithium titanate are formed on a copper foil, the latter on an aluminum foil, and a composite layer is formed on the aluminum foil together with the same conductive material and binder as those used for the positive electrode. When the electrochemical device is a capacitor, a composite layer of activated carbon, a conductive material and a binder is formed on the aluminum foil.

In the electrochemical device of the present invention, it is preferable to use a nonaqueous electrolytic solution containing lithium electrolyte salt, an ion conductive polymer, or the like as the electrolytic solution in which the electrode group described above is immersed.
The binder that can be used together with the positive and negative electrode active materials includes polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), styrene butadiene copolymer emulsion (SBR), polyvinyl alcohol (PVA), polyacryl emulsion, and silicon emulsion. Etc. can be used.

Examples of the non-aqueous solvent in the non-aqueous electrolyte containing a lithium salt include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC).
Examples of lithium salts that can be dissolved in the non-aqueous solvent include lithium hexafluorophosphate (LiPF ₆ ), lithium borotetrafluoride (LiBF ₄ ), and lithium trifluoromethanesulfonate (LiSO ₃ CF ₄ ). .

  The case of the electrochemical device of the present invention is not particularly limited as long as it is appropriately selected depending on the type, application, and shape of the electrochemical device and is a material and shape having a strength capable of applying pressure to the electrode group. Examples include cases using metals such as steel and aluminum, laminates of metals and plastic films, and synthetic resins such as polycarbonate.

  The electrochemical device of the present invention includes a lithium ion secondary battery, a lithium ion capacitor, an electric double layer capacitor, an electrolytic capacitor, etc., and these electrochemical devices are for mobile phones, personal computers, electric vehicles and hybrid vehicles. Can be used for

Example 1 and Comparative Example 1
A positive electrode of a lithium secondary battery was produced by the following method.
An olivine type lithium iron phosphate coated with conductive carbon having a secondary particle diameter of 2 to 3 μm on the surface is used as a positive electrode active material, and 10 parts by mass of conductive carbon and conductive as a conductive agent are added to 84 parts by mass of the active material. The carbon fiber mixture and 6 parts by mass of polyvinylidene fluoride as a binder were added. To this, N-methylpyrrolidone was added as a dispersion solvent and kneaded to prepare a positive electrode mixture (positive electrode slurry).
An aluminum foil having a thickness of 20 μm and a width of 150 mm is prepared. The positive electrode slurry was applied to both sides of the aluminum foil and dried. Then, the positive electrode for lithium secondary batteries was obtained by pressing and cutting. The total thickness of the positive electrode when pressed after applying and drying the positive electrode slurry on both sides of the aluminum foil was 160 μm.

A negative electrode serving as a counter electrode of the positive electrode was produced by the following method.
1 part by mass of a carbon nanotube conductive material was added to the graphite material, and 5 parts by mass of a polyvinylidene fluoride (PVdF) solution of a binder was added to prepare a slurry. Next, the slurry was applied to a copper foil having a thickness of 10 μm and dried. Thereafter, press treatment was performed to obtain a negative electrode for a lithium secondary battery. The total negative electrode thickness when pressed was 124 μm.

In order to produce a 3.4 V-500 mAh prismatic lithium ion battery using the negative electrode and the positive electrode, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) solvent were mixed in the electrolyte. lithium hexafluorophosphate in the solution (LiPF ₆₎ was prepared by dissolving 1 mol / l. As the prismatic lithium ion battery, a battery case in which the distance between the inner surfaces in the surface direction in which pressure is applied to the vertical × horizontal × thickness × electrode group was about 10 cm × 8 cm × 0.3 cm × 0.22 cm was used.
A cellulose nonwoven fabric with a thickness of 25 μm was used for the separator. On the other hand, the film separator of the same thickness made from a polyethylene film was used as a comparative example.

Using the positive electrode and the negative electrode described above, the electrode plates were laminated via separators, and after pouring the electrolyte solution, a laminate film was thermally welded to produce a square cell. In Example 1, the electrode group was clamped with an adhesive tape so that a pressure of 0.9 kgf / cm ² was applied to the electrode group and the cellulose nonwoven fabric separator.
As a comparative example, a polyethylene film separator was used, and the same pressure as in Example 1 was applied. This battery was referred to as Comparative Example 1.

Example 2 and Comparative Example 2
Except that the pressure applied to the electrode group and 0.4 kgf / cm ² is carried out to produce a battery in the same manner as in Example 1 the same electrode group configuration and Example 1 and using the cellulose nonwoven fabric separator Example 2 It was.
Similarly, a battery was produced in the same manner as in Example 1 and in the same manner as in Example 1 except that the pressure was 0.2 kgf / cm ² , and used as Comparative Example 2.

  The 3.4 V-500 mAh battery obtained in each example and each comparative example was evaluated by the following method. After the initial charge and capacity check of each battery, discharge was performed up to 2.0 V at a constant current of each ItA in the table below, and the ratio of each ItA discharge capacity to 0.2 ItA discharge was calculated to examine each rate discharge performance. . In addition, the discharge DC resistance at 50% SOC of each battery was measured. Further, in each battery, charging and discharging at 3 ItA at 25 ° C. were repeated, and the capacity transition was measured to summarize the capacity maintenance rate after 1000 cycles. . Table 1 shows the results.

From Table 1, it was found that in Examples 1 and 2 of the cellulose nonwoven fabric separator and Comparative Example 1 of the polyethylene film separator, the discharge was possible although the capacity decreased rapidly with 30 ItA discharge. On the other hand, in Comparative Example 2, it became impossible to discharge at the time of 10 ItA. From the result of the discharge DC resistance, it is considered that when the pressure applied to the electrode group is less than 0.3 kgf / cm ² , the internal resistance of the battery is extremely increased and the discharge capability is lost. At a low pressure, it is considered that each electrode surface cannot be sufficiently in contact with the separator surface in the electrode group, and that the ionic conduction is impaired due to a part of the space.
Moreover, when the comparative example 1 of a polyethylene separator and Example 1 of a cellulose nonwoven fabric separator were compared, even if the same pressure could be applied, it turned out that direct current | flow resistance is low and a discharge capability becomes high. This is because even if pressure is applied through the separator to the electrode surface, it is difficult for a thin film to stick on all the electrode surfaces without gaps, and because polyethylene film is water repellent with respect to the polar solvent of the electrolyte. It is thought that this is because it is difficult to hold the electrolytic solution.

  From the results of the capacity maintenance ratio shown in Table 1, the comparative example 2 where the pressure applied by the electrode group was low caused rapid capacity deterioration, and in Example 2, although the capacity was lowered, the battery was in operation. On the other hand, in Example 1, it turned out that a battery operation | movement is possible, without almost a capacity | capacitance fall. Moreover, in the comparative example 1 of the polyethylene film, the performance that was not much different from that in Example 1 was shown at the beginning of the battery life, but in the cycle life test, the result was worse than that in the case where the pressure in Example 2 was lowered. As described above, even when sufficient pressure is applied to the separator and the electrode plate, the wettability of the separator with respect to the polar solvent is poor and the holding ability is lowered. It is considered that the capacity decreased due to the decrease in the lithium ion conductivity, as the liquid moved and decreased.

The above results were obtained even in a system in which the pressure was increased as the distance between the inner wall of the battery case of the rectangular battery or the cylindrical battery and the electrode group thickness and group diameter including the separator decreased.
Specifically, using the same battery case as in Example 1, the same electrode group as in Example 1 was compressed to a thickness of 0.19 cm with a compressor, and was immediately accommodated in the battery case after compression. In this case, the results of the rate discharge performance, the discharge DC resistance, and the capacity retention rate substantially the same as in Example 1 were obtained. In addition, the same effect was obtained with other positive / negative electrode materials and lithium ion capacitors regardless of the positive / negative electrode materials of this example.

  Electrochemical devices such as the lithium secondary battery and lithium ion capacitor of the present invention become a long-life battery and can be developed into industrial batteries such as in-vehicle use.

DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 2 Case 3 Electrode group 4 Tab for positive / negative electrodes 5 Positive electrode 6 Negative electrode 7 Separator

Claims (3)

Manufacture of electrochemical devices that are housed in a case and in which lithium electrolyte is repeatedly occluded / desorbed by infiltrating or immersing the organic electrolyte in a wound or laminated electrode group through a separator between the positive and negative electrodes A method,
The separator is a woven or non-woven separator;
A pressure of 0.3 to 1.1 kgf / cm ² is applied to the main surface of the electrode group,
When the total thickness or group diameter at the time of manufacturing the electrode group before housing the case is L ₁ and the length between the opposing inner wall surfaces of the case is L ₀ , the electrode group has L ₁ > L ₀ It is designed to be accommodated in the case after being compressed using the compressible buffering action of the separator, and the pressure is applied to the main surface of the electrode group by the restoring force of the separator ,
The method for producing an electrochemical device, wherein the compression is performed by fastening the periphery of the electrode group with a tape .   The method for producing an electrochemical device according to claim 1, wherein the electrochemical device is a lithium secondary battery.   The method of manufacturing an electrochemical device according to claim 1, wherein the electrochemical device is a lithium ion capacitor.

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