JP4514484B2 - Non-aqueous electrolyte battery manufacturing method and non-aqueous electrolyte battery - Google Patents

Description

  The present invention relates to a method for producing an electrode used in a non-aqueous electrolyte battery such as a lithium ion secondary battery.

  Currently, lithium ion secondary batteries that are lightweight and have a high capacity are generally used in portable small electronic devices.

  An electrode used for a lithium ion secondary battery is generally manufactured by applying a slurry containing an electrode active material on a current collector such as an aluminum foil or a copper foil to form an active material layer, and then rolling it. Yes. After manufacturing the positive electrode and the negative electrode by such a method, a battery is manufactured by forming a battery structure in which a separator is disposed between the positive electrode and the negative electrode.

In the lithium ion secondary battery having the above-described structure, as a method for further increasing the volume capacity density, a method of forming an active material layer by applying a slurry containing an electrode active material on a separator can be considered. In Patent Document 1, a method of forming an active material layer by applying a slurry containing an active material to a separator has been studied. However, no consideration has been given as to under what conditions the rolling is performed after the active material layer is formed.
JP-A-6-140077

  The objective of this invention is providing the manufacturing method of the electrode for nonaqueous electrolyte batteries which can obtain high charge / discharge capacity in the electrode for nonaqueous electrolyte batteries which formed the active material layer on the porous body. .

The present invention is for a nonaqueous electrolyte battery in which an active material layer is formed by applying a slurry containing an electrode active material on a porous body having no electronic conductivity, and then rolling the active material layer together with the porous body. This is a method for manufacturing an electrode, wherein rolling is performed so that the packing density d satisfies the following formula, where x is the number of rolling cycles and d is the packing density of the active material layer.
0.5515Ln (x) + 1.90959 ≦ d ≦ 0.5515Ln (x) +2.5859
(Here, x is a natural number satisfying 2 ≦ x ≦ 11.)

  According to the present invention, an electrode exhibiting a high charge / discharge capacity can be obtained by rolling under the rolling conditions satisfying the above formula. For example, in the case of roll rolling in which rolling is performed by passing between a pair of rolls, rolling is performed at a number of rollings within a range of 2 to 11 so as to satisfy the above formula while adjusting rolling conditions such as a gap between the rolls. . In addition, x in said formula means the total number of rolling. Therefore, it is sufficient that the packing density d is reached after the final rolling step. For example, when the rolling conditions are controlled by the gap between the rolls, the rolling conditions may be set each time so that the gap between the rolls gradually decreases, that is, the rolling conditions become stricter. You may roll by a roll gap. However, it is preferable to gradually narrow the roll gap.

  The packing density d in the present invention can be calculated as follows. That is, first, the electrode weight per unit area is measured, and the weight of the porous material per unit area is subtracted from this value to calculate the weight of the active material layer per unit area. The packing density d of the active material layer can be calculated by dividing the weight of the active material layer per unit area by the thickness of the active material layer. The thickness of the active material layer can be calculated by subtracting the thickness of the porous body from the thickness of the electrode after rolling.

  As the porous body in the present invention, those used as a separator in a nonaqueous electrolyte battery can be used. Examples of the material include polyamide, polyolefin, polyethylene terephthalate, polyacrylonitrile and the like. Among these, polyolefins such as polyethylene and polypropylene are preferably used because they are chemically stable, particularly very stable with respect to the electrolytic solution. The thickness of the separator is preferably thinner than the thickness of the current collector. From such a viewpoint, the thickness is preferably in the range of 1 to 30 μm, and more preferably in the range of 5 to 25 μm. Further, the pore diameter of the separator is preferably smaller than the particle diameter of the active material particles, since short-circuiting easily occurs when the active material particles are filled in the pores of the separator. Since the particle diameter of the active material is generally about 3 to 100 μm, the pore diameter of the separator is preferably 3 μm or less.

LiCoO ₂ can be used as an electrode active material used for the electrode of the present invention .

  The non-aqueous electrolyte battery of the present invention is characterized by using the electrode manufactured by the method of the present invention.

  The solvent used in the battery of the present invention is not particularly limited as long as it can be used in a non-aqueous electrolyte battery. For example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3 -Cyclic carbonates such as butylene carbonate, cyclic esters such as propane sultone, chain carbonates such as methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, Examples include chain ethers such as ethyl methyl ether, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, acetonitrile, and the like. .

The solute used in the battery of the present invention is not particularly limited as long as it can be used in a nonaqueous electrolyte battery. For example, LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (C ₁ F _{2l + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) (l and m are integers of 1 or more), LiC (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) ( C _r F _{2r + 1} SO ₂ ) (p, q, r are integers of 1 or more), Li [(C ₂ O ₄ ) ₂ B], LiBF ₂ (C ₂ O ₄ ), LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ or the like, and a plurality of these may be used in combination. The solute is preferably dissolved in the non-aqueous electrolyte at a concentration of 0.1 to 1.5 M (mol / liter), preferably 0.5 to 1.5 M (mol / liter).

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte battery which can obtain a high charging / discharging capacity | capacitance can be manufactured in the electrode for nonaqueous electrolyte batteries which formed the active material layer on the porous body.

  Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications without departing from the scope of the present invention. It is.

FIG. 1 is a diagram showing the relationship between the number of rolling operations and the packing density of the active material layer. In FIG. 1, the solid line indicates the relationship between the number of rollings and the packing density in the examples described later, and is a line represented by the following equation.
y = 0.5515Ln (x) +2.28859

In FIG. 1, the lower dotted line is a line represented by the following formula obtained by subtracting 0.3 from the formula of the solid line.
y = 0.5515Ln (x) +1.9859

  That is, the lower dotted line indicates the lower limit value in the present invention.

In FIG. 1, the upper dotted line is a line represented by the following formula obtained by adding 0.3 to the formula of the solid line.
y = 0.5515Ln (x) +2.5859

  That is, it is a line indicating the upper limit in the present invention.

  Therefore, in the present invention, the rolling conditions are set so that the packing density of the active material layer is located in the region between the upper dotted line and the lower dotted line shown in FIG. Rolling is done.

  Table 1 shows the lower limit value and the upper limit value of the packing density of the active material layer in the rolling times 2 to 11.

(Example)
Lithium cobalt oxide (LiCoO ₂ ) was used as the positive electrode active material, carbon material (AB and acetylene black “SP300”) was used as the conductive agent, and polyvinylidene fluoride (PVdF) was used as the binder. Lithium cobaltate has a layered rock salt structure and its true density is 5 g / ml.

  Lithium cobaltate, carbon material, and polyvinylidene fluoride were mixed so that the mass ratio of lithium cobaltate: AB: SP300: polyvinylidene fluoride was 92.5: 3: 1.5: 3. This mixture was added and mixed with N-methyl-pyrrolidone to prepare a positive electrode mixture slurry.

  A positive electrode mixture slurry is applied on a polypropylene separator (pore diameter 2 μm) having a thickness of 22 μm and dried. Then, the separator and the positive electrode active material layer are cut into 2.5 cm squares, and a central part 2 × 2 cm square part The active material layer in the surrounding area was peeled off and removed. Five separator samples in which the positive electrode active material layer was formed in this way were prepared, and each was subjected to a rolling treatment as follows.

  About the said sample, the rolling processing of rolling frequency x = 2, 3, 5, 9, and 11 was given, respectively. Specifically, the sample was sandwiched between a pair of stainless steel plates having a thickness of 100 μm, and rolling was performed with the gap (slit width) between the rolls of the rolling roll set to the values shown in Table 2. As shown in Table 2, rolling was performed with a narrow slit width each time the rolling was repeated. Note that the thickness of the sample before rolling is 53 μm.

A test cell as shown in FIG. 2 was produced using each sample after rolling as a positive electrode.
As shown in FIG. 2, the active material layer 4 is formed on the back surface of the separator 3 in the sample. On the surface of the separator 3 opposite to the side on which the active material layer 4 is formed, a lithium metal plate 2 as a counter electrode is stacked. A nickel tab 1 is attached to the lithium metal plate 2. On the side of the separator 3 where the active material layer 4 is formed, an aluminum foil 5 as a current collector is disposed. A lithium metal plate 6 as a reference electrode is disposed under the aluminum foil 5 via a separator 9. A nickel tab 7 is connected to the lithium metal plate 6.

  After these electrode groups are inserted into the outer package 8 and the electrolyte is injected, the seal portion 8a is sealed. Next, this is sandwiched between glass plates 10 from above and below to form a test cell.

  In addition, as electrolyte solution, the ratio of 1 mol / liter of lithium hexafluorophosphate as a solute in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC: DEC = 50: 50) What was dissolved in was used.

  FIG. 3 is a diagram showing a charge / discharge curve in a sample with the number of rolling times x = 5. This sample had a packing density d of 3.2 g / ml and a discharge capacity of 160 mAh / g.

  FIG. 4 shows a charge / discharge curve of a sample with the number of rolling times x = 2. This sample had a packing density d of 2.57 g / ml and a discharge capacity of 154 mAh / g.

The packing density and discharge capacity of each of the rolling times x = 3, 9 and 11 were as follows.
x = 3: packing density d = 2.96 g / ml, discharge capacity 158 mAh / g
x = 9: packing density d = 3.45 g / ml, discharge capacity 152 mAh / g
x = 11: packing density d = 3.60 g / ml, discharge capacity 161 mAh / g

(Comparative Example 1)
In the above example, a sample was prepared in the same manner except that it was not rolled, and a test cell was prepared using this sample. When rolling was not performed, that is, when the number of rolling times was 0, the packing density d was 1.1 g / ml.

  FIG. 5 is a diagram showing a charge / discharge curve using this sample. As shown in FIG. 5, the discharge capacity was 8.47 mAh / g, and only a very low discharge capacity could be obtained.

(Comparative Example 2)
In the above example, a sample was prepared in the same manner as in the above example except that the slit width was fixed at 15 (× 10 μm) and rolling was performed 8 times under this condition, and a test cell was prepared using this sample. . The packing density d was 2.1 g / ml.

  FIG. 6 is a diagram showing a charge / discharge curve of a test cell using this sample. As shown in FIG. 6, it can be seen that the discharge capacity is as low as about 90 mAh / g.

(Comparative Example 3)
In the above example, a sample was prepared in the same manner as in the above example except that the slit width was 7.5 (× 10 μm) and rolling was performed four times under these conditions, and a test cell was prepared using this sample. Produced. The packing density d was 3.4 g / ml. In the test cell using this sample, the working electrode and the counter electrode were short-circuited and could not be charged / discharged.

  From the above, by rolling so that the filling density d is within the range between the upper dotted line and the lower dotted line shown in FIG. I understand that I can do it.

The figure which shows the relationship between the frequency | count of rolling and the packing density of an active material layer. The disassembled perspective view which shows the test cell produced in the Example of this invention. The figure which shows the charging / discharging curve in one Example according to this invention. The figure which shows the charging / discharging curve in the other Example according to this invention. The figure which shows the charging / discharging curve of a comparative example. The figure which shows the charging / discharging curve of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nickel tab 2 ... Lithium metal plate 3 ... Separator 4 ... Active material layer 5 ... Aluminum foil 6 ... Lithium metal plate 7 ... Nickel tab 8 ... Exterior body 8a ... Sealing part of exterior body 9 ... Separator 10 ... Glass plate

Claims (2)

An electrode for a nonaqueous electrolyte battery in which an active material layer is formed by applying a slurry containing an electrode active material on a porous body having no electron conductivity, and then rolling the active material layer together with the porous body. A manufacturing method comprising:
The porous body is a separator, and the electrode active material is LiCoO ₂ ;
A method for producing an electrode for a nonaqueous electrolyte battery, wherein the rolling is performed such that the number of rolling is x and the packing density of the active material layer is d, so that the packing density d satisfies the following formula.
0.5515Ln (x) + 1.90959 ≦ d ≦ 0.5515Ln (x) +2.5859
(Here, x is a natural number satisfying 2 ≦ x ≦ 11.) A nonaqueous electrolyte battery using the electrode manufactured by the method according to claim 1 .

Images