JP2005050679A - Nonaqueous solvent-based secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous solvent-based secondary battery with foil cutting curtailed at manufacturing process, having a good cycle property, excellent in safety even when overcharged or left in an atmosphere of high temperature. <P>SOLUTION: The nonaqueous solvent system secondary battery comprises an electrode body composed of a positive electrode, a negative electrode, and a separator interposed between the electrodes, and nonaqueous solvent system electrolyte. An aluminum core body contacting N-methylpyrrolidone with an contact angle of 45 degrees or less is used as a current collector of the positive electrode. The aluminum core body using rolling oil having good wettability with N-methylpyrrolidone at the process of rolling into an aluminum foil; or the same of which rolling oil component is volatilized by heat treatment after rolling into aluminum foil at the manufacturing process; or the same of which rolling oil is volatilized by storing in a condition of low moisture; or the same to which a degreasing treatment is applied; or the same of which the surface is made coarse; or the same of which the surface is reformed by plasma treatment; or the like is used for the battery. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous solvent-based secondary battery, more specifically, reducing the occurrence of foil breakage during production, good cycle characteristics, overcharge, even if left in a high temperature atmosphere, The present invention relates to a non-aqueous solvent type secondary battery excellent in safety with few ruptures.

  With the rapid spread of portable electronic devices, the required specifications for the batteries used for them are becoming stricter year by year, and in particular, small and thin, high capacity, excellent cycle characteristics, stable performance are required Yes. In the field of secondary batteries, lithium non-aqueous solvent secondary batteries, which have a higher energy density than other batteries, are attracting attention. The proportion of lithium non-aqueous solvent secondary batteries accounts for a significant increase in the secondary battery market. Is shown.

  This lithium non-aqueous solvent type secondary battery includes a negative electrode in which a negative electrode active material mixture is applied in a film form on both sides of a negative electrode core (current collector) made of an elongated sheet-like copper foil and the like, and an elongated sheet-like battery A separator made of a microporous polypropylene film or the like is placed between both sides of a positive electrode core made of aluminum foil or the like and coated with a positive electrode active material mixture in the form of a film, and the negative electrode and the positive electrode are insulated from each other by the separator. In the case of a rectangular battery, the wound electrode body is further crushed to form a flat shape, and a negative electrode lead and a positive electrode lead are respectively attached to predetermined portions of the negative electrode and the positive electrode. It has the structure which connected and accommodated in the exterior of a predetermined shape.

  Although lithium non-aqueous solvent type secondary batteries have high energy density, the current battery performance is still insufficient to meet market demands, and further higher energy density is required. For this purpose, attempts have been made to increase the amount of active material mixture to be filled in the battery exterior, and the electrode plate after application of the active material mixture is pressed and compressed to make the active material mixture dense and to reduce voids. It has been broken.

  When manufacturing such an electrode plate for a battery, an active material mixture for a positive electrode or a negative electrode is usually applied to both surfaces of a metal core (current collector), and then the mixture layer is pressed with a roller press. Although it is cut out to the required dimensions after compression, the thickness of the mixture layer on both sides is larger than the thickness of the metal core, and the porosity of the mixture layer is usually about 10% to 30% after compression compression Is controlled.

  However, when a positive electrode active material mixture is applied to both surfaces of a conventional positive electrode core made of an elongated sheet-like aluminum foil, and then this mixture layer is pressurized and compressed by a roller press, the positive electrode made of an aluminum foil The inconvenience of cutting the core was likely to occur. Such a phenomenon is a phenomenon hardly observed in the case of manufacturing a negative electrode using a negative electrode core made of copper foil. In addition, non-aqueous solvent type secondary batteries using a positive electrode core made of aluminum foil are tests that put the battery in a state different from the normal operating environment, such as overcharging or leaving it at high temperatures for a long time. A battery that emits smoke was generated.

  On the other hand, in the following Patent Document 1, in a non-aqueous solvent secondary battery, when the volume change of the negative electrode active material mixture layer accompanying charging / discharging is large, when the battery is accidentally overcharged, In order to solve the problem that cracks, cuts, etc. occur in the body and the deterioration of the subsequent cycle characteristics becomes large, the current collector of the negative electrode has a breaking elongation of 5% or more, specifically copper. A non-aqueous solvent secondary battery using a current collector and using a negative electrode current collector having a contact angle of less than 40 ° is disclosed.

  However, the invention disclosed in Patent Document 1 below is effective in solving the problems that occur in the negative electrode of a nonaqueous solvent secondary battery, but is applied to the positive electrode targeted by the present invention. Is not possible because the active material and the current collector material are completely different between the positive electrode and the negative electrode.

JP-A-11-288722 (Claims [0004] to [0012])

  In a nonaqueous solvent secondary battery typified by a lithium ion battery, measures to break the positive electrode core portion made of an aluminum foil in the positive electrode mixture compression step are an urgent manufacturing task. As a result of various investigations of the causes of the above problems, the present inventors have used N-methylpyrrolidone (hereinafter referred to as “NMP”) as a solvent on a positive electrode core made of aluminum foil. When the mixture is applied in the form of a film, as shown in FIG. 1, both the application end points of the application start point and the application end point rise, but the larger the rise, the more when this mixture layer is compressed with a roller press. Many inconveniences that the positive electrode core body made of aluminum foil is cut, and this upsurge, the rolling oil at the time of rolling remains on the surface of the positive electrode core body made of conventional aluminum foil, and this rolling oil and This is due to the poor wettability with NMP, and in order to suppress the swell of the coating end, NMP and aluminum used as a solvent at the time of manufacturing the positive electrode mixture are used. Possible to improve the wetting between the arm foil, found that it is sufficient to reduce the contact angle between the other words NMP and aluminum foil, it was accomplished the present invention.

  That is, the present invention reduces the occurrence of foil breakage during production, has good cycle characteristics, and is a non-aqueous solvent excellent in safety and reliability even when overcharged or left in a high temperature atmosphere. An object of the present invention is to provide a secondary battery.

  The above object of the present invention can be achieved by the following configurations. That is, the invention according to claim 1 of the present application is the non-aqueous solvent secondary battery including an electrode body including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and a non-aqueous solvent electrolyte. As the current collector, an aluminum core having a contact angle with NMP of 45 ° or less is used.

  The invention according to claim 2 of the present application is the non-aqueous solvent secondary battery according to claim 1, wherein the aluminum core is a rolling oil having good wettability with NMP when an aluminum foil is produced by rolling. It is characterized by using the one used.

  The invention according to claim 3 of the present application is the nonaqueous solvent secondary battery according to claim 1, wherein the aluminum core is heat-treated after the production of the aluminum foil by rolling and the rolling oil component is volatilized. It is characterized by the use of a dish.

  The invention according to claim 4 of the present application is the nonaqueous solvent secondary battery according to claim 1, wherein the aluminum core is stored under low humidity conditions after aluminum foil is produced by rolling. The rolling oil component is volatilized.

  The invention according to claim 5 of the present application uses the non-aqueous solvent secondary battery according to claim 1 that has been degreased after the production of an aluminum foil by rolling as the aluminum core. It is characterized by.

  The invention according to claim 6 of the present application is the nonaqueous solvent secondary battery according to claim 1, wherein the aluminum core has a surface roughened after the production of aluminum foil by rolling. It is used.

  Further, the invention according to claim 7 of the present application is the nonaqueous solvent secondary battery according to claim 1, wherein the aluminum core is surface-modified by plasma treatment after manufacturing an aluminum foil by rolling. It is characterized by using.

  The present invention has the following excellent effects by having the above-described configuration. That is, according to the nonaqueous solvent secondary battery according to claim 1, since the wettability between the core body made of aluminum foil and NMP as a solvent contained in the positive electrode mixture is good, Even if the positive electrode mixture is applied onto the core body, the bulge at the coating end is smaller than that of the conventional one, so the positive electrode mixture applied on the core body made of aluminum foil is pressed with a roller press. Since the positive electrode core made of aluminum foil is not cut even when compressed, the production efficiency is improved. In addition, the cycle characteristics are good, even if it is overcharged or left in a high temperature atmosphere. However, a non-aqueous solvent secondary battery having excellent safety and reliability can be obtained.

  Moreover, according to the nonaqueous solvent type secondary battery of Claims 2-7, the positive electrode core body which consists of aluminum whose contact angle with NMP is 45 degrees or less comes to be obtained easily. That is, in the nonaqueous solvent secondary battery according to claim 2, by using a positive electrode core made of an aluminum foil using a rolling oil that has good solubility with NMP when producing an aluminum foil by rolling, In the non-aqueous solvent secondary battery according to Item 3, the non-aqueous solvent secondary battery according to Claim 4 is obtained by using a heat-treated aluminum foil produced after rolling to volatilize the rolling oil component. The non-aqueous solvent secondary battery according to claim 5 is degreased after the production of the aluminum foil by rolling by using the one in which the rolling oil component has been volatilized by being stored under low humidity conditions after the production of the aluminum foil by rolling. By using the treated one, the nonaqueous solvent secondary battery according to claim 6 uses the one whose surface is roughened after the production of the aluminum foil by rolling. Furthermore, in the non-aqueous solvent secondary battery according to claim 7, since the surface modified by plasma treatment after the production of the aluminum foil by rolling was used, the contact angle with NMP was easily 45 °. A positive electrode core made of the following aluminum can be obtained.

Hereinafter, the best mode for carrying out the present invention will be described in detail using Examples and Comparative Examples.
[Production of various aluminum foils with improved wettability to NMP]
Both the rolling oil used when rolling conventional aluminum foil and the material name of rolling oil with good wettability with custom-made NMP are both unknown to the general user as trade secrets, but provided by the aluminum foil manufacturer. The data is as follows. First, the rolling oil conventionally used in the production of aluminum foil is the rolling oil X, the rolling oil having good wettability with NMP is the rolling oil Y, and each rolling oil and NMP are in a volume ratio of 1: The sample was placed in a test tube so as to be 1 and stirred vigorously for several minutes, and then allowed to stand to measure the separation. The following results were obtained.
Rolling oil X: NMP = 4.8: 5.2
Rolling oil Y: NMP = 4.2: 5.8
This data shows that the rolling oil Y is more easily dissolved in NMP than the rolling oil X, and thus shows that the rolling oil Y has better wettability with respect to NMP.

Next, six types of aluminum foils of Samples A to F were prepared under the following conditions.
(Samples A and B)
An aluminum foil rolled using the rolling oil X is referred to as sample A, and an aluminum foil rolled using the rolling oil Y is referred to as sample B.
(Sample C)
Sample C is an aluminum foil in which the aluminum foil of sample B is left as it is at room temperature with a relative humidity of 60% or less for one month.
(Sample D)
Sample D is an aluminum foil obtained by degreasing the aluminum foil of sample A with an acetone solvent.
(Sample E)
The aluminum foil of sample A is directly brought into contact with a roll that rotates in the direction opposite to the traveling direction of the foil, and the aluminum foil having a fine scratch on the surface of the aluminum foil is referred to as sample E.
(Sample F)
Sample F is an aluminum foil obtained by subjecting the aluminum foil of sample A to plasma discharge treatment as it is.

  1 μL of NMP was dropped onto the aluminum foil surfaces of the above samples A to F, the contact state between NMP and the aluminum foil was imaged, and the contact angle was calculated by image analysis of the image. Also, using the aluminum foils of Samples A to F, a slurry made of lithium cobaltate, acetylene black and NMP was applied and dried by a die coating method to prepare a positive electrode plate. Then, at the application start point and the application end point of the coating electrode plate, it rises as shown in FIG. The values of a and b were measured with a micro gauge at the coating start point and the coating end point, and the value of ab was determined as an average value. Furthermore, the number of occurrences of foil breakage when each positive electrode plate in which the positive electrode mixture is intermittently applied on both sides for each predetermined length is continuously compressed by 1000 m with a constant pressure compression device having a compression linear pressure of 2000 kg / cm is obtained. It was measured. The results are summarized in Table 1.

表１より、ＮＭＰとの接触角が４５°以下の試料Ｂ〜Ｆは、塗布盛り上り量が小さく、この塗布盛り上り部分による圧縮時に過圧縮を起して箔切れしていたものが全く見られなくなった。それに対して、ＮＭＰとの接触角が４７°と大きい試料Ａは、塗布盛り上がり量も試料Ｂ〜Ｆのものに比すると非常に大きく、圧縮時の箔切れも２回生じた。

From Table 1, it can be seen that Samples B to F having a contact angle with NMP of 45 ° or less have a small coating swell amount, and the foil severed due to over-compression when compressed by this coating swelled portion. I can't. On the other hand, the sample A having a large contact angle with NMP of 47 ° has a very large coating swell amount as compared with those of samples B to F, and the foil breakage during compression occurred twice.

  From the results of Table 1 above, it was recognized that the coating swell amount significantly changed when the contact angle with NMP was around 45 °, and therefore, a plurality of contact angles with NMP in the range around 45 °. Aluminum foil was prepared, the same positive electrode mixture as that used in Samples A to F was applied, and the relationship between the contact angle and the amount of swelling was determined. The result is shown in FIG. FIG. 2 also shows the relationship between the contact angle and the swell amount of Samples A to F shown in Table 1.

  From FIG. 2, it can be seen that the swell amount of the positive electrode mixture gradually increases when the contact angle is 40 ° to 45 °, but suddenly increases when the contact angle exceeds 45 °. Therefore, the contact angle is preferably 45 ° or less. The lower limit of the contact angle is not critical, but it is difficult to produce a contact angle of less than 40 °, so that a contact angle of 40 ° or more is necessarily preferable. Therefore, it can be said that the contact angle is preferably 40 ° or more and 45 ° or less.

[Preparation of battery sample]
[Comparative Example 1]
Next, a slurry composed of lithium cobaltate, acetylene black and NMP is applied and dried on both surfaces of an aluminum core having a contact angle with NMP of 45.5 °, and then compressed with a constant pressure compression device having a compression linear pressure of 2000 kg / cm. A battery prepared by applying and sealing a negative electrode created by applying and drying graphite on a copper foil to face each other through a separator, inserted into an outer can made of iron, and sealed. Cylindrical batteries having a size of φ18 mm and a height of 65 mm were manufactured, and five batteries of Comparative Example 1 of samples a1 to a5 were manufactured. Incidentally, the electrolyte, an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate was used after dissolving LiPF ₆ at a rate of 1 mole / liter.

  Samples b1 to b1 were prepared in the same manner as in the battery of Comparative Example 1 except that the positive electrode core was prepared using an aluminum core whose surface was removed with acetone and the contact angle with NMP was 44 °. Five batteries of Example 1 of b5 were produced.

[Measurement of battery cycle characteristics]
For each sample produced as described above, charging at room temperature until the battery voltage reached 4.2V and then discharging to 2.75V at a constant current of 2000 mA was taken as one cycle, and repeated until 500 cycles were reached. The cycle characteristics were measured as a ratio of the capacity after 500 cycles to the capacity at the cycle (initial capacity). The results are shown in Table 2.

  From Table 2, the batteries b1 to b5 of Example 1 using an aluminum core having a small contact angle with NMP are cycle characteristics as compared with the batteries a1 to a5 of Comparative Example 1 using an aluminum core having a large contact angle. Was found to have improved. In addition, when the battery after measurement was disassembled, in one of the batteries a1 to a5 having a large coating swell, it was observed that lithium deposition was unevenly distributed on the negative electrode on the part facing the positive swell. On the other hand, such precipitation was not observed in the batteries b1 to b5 of Example 1.

  The cause of lithium deposition in this negative electrode is presumed to be as follows. That is, the electrode plate of a normal lithium ion battery is designed so that the lithium ion acceptance tolerance of the negative electrode is slightly larger than the lithium release amount of the positive electrode. Therefore, even if more lithium ions are supplied due to some swell at the positive electrode, the negative electrode still has the ability to accept it, but if the swell of the positive electrode becomes too large, lithium ions will exceed the margin of the negative electrode. Will be deposited, and the portion unacceptable to the negative electrode will be deposited. As can be confirmed from the description in Table 1 and FIG. 2, the threshold is “45 °” in the contact angle between the NMP and the aluminum core.

[Safety test] (Stability test under abnormal conditions)
[Comparative Example 2]
As Comparative Example 2, 100 batteries were manufactured in the same manner as in Comparative Example 1, 50 of which were overcharged and the remaining 50 were subjected to thermal testing. In the overcharge test, charging was performed at a constant current of 1.5 It until the battery voltage reached 12 V, and the state of the battery was observed. In the thermal test, the battery charged at 1.5 It until the battery voltage became 4.3 V was left in a constant temperature bath at 150 ° C. for 1 hour to observe the smoke generation state of the battery. In manufacturing the battery, in order to clarify the difference in safety between the comparative example and the example, a safety device such as a safety valve attached to the battery shipped as a product was not added. The results are shown in Table 3 (the same applies to the following examples).

  As Example 2, 100 batteries were manufactured in the same manner as in Example 1, overcharge test was performed on 50 of them, and thermal test was performed on the remaining 50 batteries. The overcharge test and thermal test conditions were the same as in Comparative Example 2. The results are shown in Table 3 together with the results of Comparative Example 2.

  From Table 3, in the battery of Comparative Example 2 using an aluminum core having a contact angle with NMP exceeding 45 °, the majority of the batteries smoked in both the overcharge test and the thermal test, but the contact angle with NMP was In the battery of Example 2 using an aluminum core of less than 45 °, none of the batteries emitted smoke in this safety test, and it was found that the battery safety was improved.

  In preparation of various aluminum foils with improved wettability to NMP, the degreasing method using acetone (sample D) is performed as a degreasing method, and the foil is rotated in the reverse direction to the surface roughening method. Although the method of contacting with the roll (sample E) has been shown, the present invention is not limited to these methods, and other methods can be used. For example, as a degreasing method, a method using a solvent other than acetone or a well-known electrolytic degreasing method other than acetone can be used, and a sandblasting method or a sanding method is also used as a surface roughening method. be able to.

  In the present invention, if the rolling oil remaining on the aluminum foil surface is removed and the contact angle with NMP is 45 ° or less, a predetermined effect is obtained. A method of volatilizing or decomposing the rolling oil remaining on the surface of the aluminum foil by plasma treatment or the like can be employed. In this case, the heat treatment temperature and the heat treatment time are not critical, and the temperature range is preferably 150 ° C. to 300 ° C., for example, about 250 ° C. × 2 days in the coil state of aluminum foil. Moreover, the preservation | save process under low-humidity conditions is not a critical condition, Specifically, what is necessary is just to use what was preserve | saved at normal temperature and 50% of humidity for 7 days or more. Further, with respect to the plasma treatment, an aluminum foil having a contact angle with NMP of 45 ° or less can be easily obtained by using a known metal surface treatment plasma treatment apparatus under mild conditions.

It is a figure explaining the shape in the application start point at the time of apply | coating positive mix to an aluminum core, and an application end point. It is a figure which shows the relationship between the contact angle with NMP of an aluminum core, and the amount of swelling of a positive electrode mixture.

Claims (7)

  In a non-aqueous solvent secondary battery comprising a positive electrode and a negative electrode and a separator interposed between the two and a non-aqueous solvent electrolyte, the contact angle with N-methylpyrrolidone as a current collector of the positive electrode A non-aqueous solvent type secondary battery using an aluminum core having an angle of 45 ° or less.   2. The non-aqueous solvent secondary battery according to claim 1, wherein the aluminum core is made of a rolling oil that has good wettability with N-methylpyrrolidone when producing an aluminum foil by rolling.   2. The nonaqueous solvent secondary battery according to claim 1, wherein the aluminum core is a heat-treated aluminum foil produced by rolling and the rolling oil component is volatilized. 3.   2. The non-aqueous solvent secondary battery according to claim 1, wherein the aluminum core is made by volatilizing a rolling oil component by storing under low humidity conditions after producing an aluminum foil by rolling.   2. The nonaqueous solvent secondary battery according to claim 1, wherein the aluminum core is degreased after producing an aluminum foil by rolling.   2. The non-aqueous solvent secondary battery according to claim 1, wherein the aluminum core is made of a roughened surface after producing an aluminum foil by rolling.   2. The nonaqueous solvent secondary battery according to claim 1, wherein the aluminum core is a surface modified by plasma treatment after aluminum foil is produced by rolling.

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