JP2014143008A - Anode collector copper foil for lithium ion secondary battery, manufacturing method of anode for lithium ion secondary battery and evaluation method of anode collector copper foil for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anode collector copper foil for a lithium ion secondary battery of which the workability is improved by making cracking unlikely to occur when manufacturing an anode, in particular, during a roll press step, a manufacturing method of an anode for the lithium ion secondary battery and an evaluation method of the anode collector copper foil for the lithium ion secondary battery.SOLUTION: An anode collector copper foil is characterized in that, when the anode collector copper foil which is segmented for a fixed length in a length direction and of which the thickness is shorter than 26 μm is cut in a short strip shape to form a plurality of copper foil pieces, an extension percentage which is a ratio of "a difference between a length of a longest copper foil piece and a length of a shortest copper foil piece" with respect to "the length of the shortest copper foil piece" is less than 220 ppm and when at least three copper foils which are positioned in a central portion and both end portions in a width direction of the anode collector copper foil are heated to a predetermined temperature of 120°C or higher and then cooled to a room temperature again, a difference between a maximum value and a minimum value of length variations before and after heating each of the copper foil pieces is equal to or less than 593 ppm.

Description

  The present invention relates to a copper foil for a negative electrode current collector of a lithium ion secondary battery, a method for producing a negative electrode of a lithium ion secondary battery, and a method for evaluating a copper foil for a negative electrode current collector of a lithium ion secondary battery. is there.

  Lithium-ion rechargeable batteries (LIBs) are used for communication devices such as mobile phones, notebook computers, electric tools, hybrid cars, batteries for electric vehicles, and the like.

  The lithium ion secondary battery includes a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an outer can and an Al laminate film that accommodate these.

  Among these, the negative electrode includes a negative electrode current collector and an active material layer formed on the surface of the negative electrode current collector. The negative electrode current collector is generally composed of a copper foil for a negative electrode current collector having a thickness of 8 μm or more and less than 26 μm. The active material layer includes an active material such as carbon or graphite, a conductive aid such as acetylene black, and a binder (binder) such as polyvinylidene fluoride (PVDF) or styrene butadiene rubber (SBR).

  When manufacturing the negative electrode, an active material, a conductive additive, a binder, water, and a solvent such as N-methylpyrrolidone (NMP) are kneaded to form a slurry-like material. Then, this slurry-like substance is coated on the surface of the copper foil for the negative electrode current collector in a coil-to-coil manner.

  At this time, since it is necessary to make a part of the surface of the copper foil for the negative electrode current collector to be welded to the current collecting tab in a later process, the coating portion and the surface of the copper foil for the negative electrode current collector In many cases, intermittent coating is performed in such a way that uncoated portions are mixed.

  Then, after removing the solvent contained in the slurry-like material coated on the surface of the copper foil for negative electrode current collector in the drying step, the copper foil for negative electrode current collector after drying is wound up. This drying step is generally performed at a drying temperature of 120 ° C. or higher and 200 ° C. or lower.

  Similarly, the slurry-like substance is coated and dried on the back surface of the copper foil for the negative electrode current collector. Some recent coating / drying apparatuses can coat both sides of a copper foil for a negative electrode current collector in one pass.

  After the drying process, after unwinding the wound copper foil for the negative electrode current collector, in the roll press process, roll press is performed to increase the density of the active material layer and increase the charge / discharge capacity per unit volume. When performed, a negative electrode is obtained. The conditions of this roll press vary depending on the equipment, electrode configuration and size, etc., but generally the linear pressure is often 1000 N / cm to 5000 N / cm and the winding tension is 10 MPa to 50 MPa in many cases.

  After the roll press process, a heat treatment process for dehydration or the like may be performed.

  Similarly, a positive electrode using lithium cobaltate or the like as an active material is manufactured, and a negative electrode and a positive electrode welded with a current collecting tab are wound or laminated via a separator, and these are inserted into an outer can, or an Al laminate film A lithium ion secondary battery can be manufactured by pouching.

International Publication No. 2008/132987 JP 2009-245788 A

  By the way, at the time of manufacture of a negative electrode, a crack may generate | occur | produce in the copper foil for negative electrode collectors especially at a roll press process, and workability | operativity may deteriorate. Causes of the occurrence of cracks include improper alignment of the apparatus and scratches during handling of the negative electrode current collector copper foil.

  When the negative electrode current collector copper foil is set in the apparatus and tension is applied, when a phenomenon occurs in which a part of the negative electrode current collector copper foil is greatly bent or pinched, the negative electrode current collector Tensile stress concentrates on a part of the copper foil in the width direction, and cracks are easily generated from the part. At this time, if there is a scratch on the end of the copper foil for the negative electrode current collector, tensile stress concentrates on that portion, and cracks are more likely to occur.

  In the case of a copper foil for a negative electrode current collector made of rolled copper foil, the shape changes depending on the rolling speed, roll crown shape, rolling force, contact condition of the coolant, etc. In order to obtain a flat shape, advanced techniques such as AFC (Auto Flatness Control) have been introduced.

  On the other hand, in the case of a copper foil for a negative electrode current collector made of an electrolytic copper foil, its shape is affected by the current density distribution, the blending of the additive into the electrolytic solution, the temperature distribution, and the like.

  Even if the copper foil for the negative electrode current collector having an appropriate shape obtained by controlling these factors is used and the alignment of the device is optimized, the negative electrode current collector is prone to cracking during the production of the negative electrode. There are copper foils for electric conductors and copper foils for negative electrode current collectors that are less prone to crack.

  Accordingly, an object of the present invention is to provide a copper foil for a negative electrode current collector of a lithium ion secondary battery, which is excellent in workability and hardly causes cracks during the production of the negative electrode, particularly in a roll press process, and a negative electrode of a lithium ion secondary battery And a method for evaluating a copper foil for a negative electrode current collector of a lithium ion secondary battery.

  The present invention, which has been created to achieve this object, is a method of cutting a copper foil for a negative electrode current collector having a thickness of less than 26 μm cut into a certain length in the length direction into strips in the width direction. When the copper foil piece is formed, the elongation, which is the ratio of “the difference between the length of the longest copper foil piece and the length of the shortest copper foil piece” to “the length of the shortest copper foil piece”, is less than 220 ppm. When the copper foil for negative electrode current collector is heated to a predetermined temperature of 120 ° C. or higher and returned to room temperature after at least three copper foil pieces located at the center and both ends in the width direction of the copper foil for individual current collector, This is a copper foil for a negative electrode current collector of a lithium ion secondary battery in which the difference between the maximum value and the minimum value of the length change rate before and after heating the piece is 593 ppm or less.

  The length change rate before and after the heating of the copper foil piece located in the center part in the width direction of the copper foil for the negative electrode current collector is a copper foil piece located at both ends in the width direction of the copper foil for the negative electrode current collector It is good that it is more than the rate of change in length before and after heating.

  The 1% yield strength after heating for 30 minutes or more at a temperature of 120 ° C. or more and 200 ° C. or less is preferably 250 MPa or more.

  The 1% yield strength after heating for 30 minutes or more at a temperature of 120 ° C. or higher and 400 ° C. or lower is preferably 250 MPa or higher.

  Zr is preferably contained in an amount of 0.01 mass% to 0.2 mass%.

  Moreover, this invention is a manufacturing method of the negative electrode of the lithium ion secondary battery which roll-presses, after coating and drying an active material to the copper foil for negative electrode collectors of these lithium ion secondary batteries.

  Further, the present invention provides a negative electrode current collector copper foil cut out by a certain length in the length direction and cut into strips in the width direction to form a plurality of copper foil pieces. The elongation ratio, which is a ratio of “the difference between the length of the longest copper foil piece and the length of the shortest copper foil piece” with respect to the “length”, is determined, and the center portion and both end portions in the width direction of the copper foil for the negative electrode current collector After heating at least three copper foil pieces located at a predetermined temperature of 120 ° C. or more and returning to room temperature, the difference between the maximum value and the minimum value of the length change rate before and after heating of each copper foil piece is obtained. The evaluation method of the copper foil for a negative electrode current collector of a lithium ion secondary battery for evaluating the crack resistance performance of the copper foil for a negative electrode current collector at the time of production of the negative electrode based on these values.

  Further, the present invention provides a negative electrode current collector copper foil cut out by a certain length in the length direction and cut into strips in the width direction to form a plurality of copper foil pieces. The elongation ratio, which is a ratio of “the difference between the length of the longest copper foil piece and the length of the shortest copper foil piece” with respect to the “length”, is determined, and the center portion and both end portions in the width direction of the copper foil for the negative electrode current collector After heating at least three copper foil pieces located at a predetermined temperature of 120 ° C. or more and returning to room temperature, the difference between the maximum value and the minimum value of the length change rate before and after heating of each copper foil piece is obtained. And the length change rate before and after the heating of the copper foil piece located in the center part in the width direction of the copper foil for the negative electrode current collector and the copper located at both ends in the width direction of the copper foil for the negative electrode current collector The length change rate before and after heating of the foil piece is obtained, and the crack resistance performance of the copper foil for the negative electrode current collector during the production of the negative electrode is evaluated based on these values. Ion is an evaluation method of the negative electrode current collector copper foil of the secondary battery.

  The predetermined temperature may be a temperature determined according to a heat load exposed in a manufacturing process of the lithium ion secondary battery.

  According to the present invention, a copper foil for a negative electrode current collector of a lithium ion secondary battery, which is less prone to cracking and particularly excellent in workability during the production of a negative electrode, particularly in a roll press process, and the negative electrode of a lithium ion secondary battery are produced. The method and the evaluation method of the copper foil for negative electrode collectors of a lithium ion secondary battery can be provided.

It is a figure explaining the copper foil for negative electrode collectors of the lithium ion secondary battery which concerns on embodiment of this invention. It is a figure which shows the result of having measured thermal expansion about the copper foil for negative electrode collectors of the sample number 1 in an Example, (a) is a figure which shows the relationship between the temperature in one end part, and (b) is in the center part. The figure which shows the relationship between temperature and elongation, (c) is a figure which shows the relationship between the temperature and elongation in the other end part. It is a figure which shows the result of having measured thermal expansion about the copper foil for negative electrode collectors of the sample number 2 in a comparative example, (a) is a figure which shows the relationship between the temperature in one end part, and (b) is in a center part. The figure which shows the relationship between temperature and elongation, (c) is a figure which shows the relationship between the temperature and elongation in the other end part. It is a figure which shows the result of having measured thermal expansion about the copper foil for negative electrode collectors of the sample number 5 in an Example, (a) is a figure which shows the relationship between the temperature in one end part, and (b) is in a center part. The figure which shows the relationship between temperature and elongation, (c) is a figure which shows the relationship between the temperature and elongation in the other end part. It is a figure which shows the result of having measured thermal expansion about the copper foil for negative electrode collectors of the sample number 3 in an Example, (a) is a figure which shows the relationship between the temperature in one end part, and (b) is in a center part. The figure which shows the relationship between temperature and elongation, (c) is a figure which shows the relationship between the temperature and elongation in the other end part.

  Hereinafter, preferred embodiments of the present invention will be described.

  Upon creating the present invention, as a result of intensive studies, it has been found that the shape of the copper foil for negative electrode current collector after being heated in the drying step is not necessarily equivalent to that before heating.

  In the case of a copper foil for a negative electrode current collector made of a rolled copper foil, since the processing strain at the time of rolling remains, the remaining processing strain (residual strain) during the process of recovery and recrystallization by heating in the drying process ) Is opened, and the dimensions of the negative electrode current collector copper foil change. In particular, a copper foil for a negative electrode current collector made of a rolled copper foil is generally rolled at a high workability of 80% or more and has a large residual strain. The change in dimensions of the copper foil for negative electrode current collector after being opened is also large.

  As long as these residual strains are uniformly distributed in the width direction of the copper foil for the negative electrode current collector, the entire copper foil for the negative electrode current collector may stretch or shrink evenly even if it is released by heating in the drying process. It will not be a problem because it only does.

  However, if the distribution of residual strain is biased in the width direction of the copper foil for the negative electrode current collector, the amount of elongation changes depending on the size of the residual strain, so for the negative electrode current collector after being heated in the drying process The length of the copper foil varies in the width direction.

  That is, the shape of the copper foil for a negative electrode current collector, which was appropriate before being heated in the drying process, becomes an inappropriate shape by releasing the residual strain by heating in the drying process.

  In other words, the bias of the residual strain that has been included until then becomes apparent as a change in the length of the copper foil for the negative electrode current collector due to heating in the drying process.

  When the copper foil for the negative electrode current collector that is in an inappropriate shape is set in a roll press or other device and tension is applied, a part that bends or pinches appears, and this part is wound around the roll. Cracks are likely to occur.

  Therefore, during roll press, when a change in press pressure occurs in the boundary region between the coated part and the non-coated part of the slurry-like substance, and a sudden change in tension is induced, the negative electrode starts from the tensioned part. The current collector copper foil cracks.

  In other words, the shape of the copper foil for the negative electrode current collector after rolling is also important, but the shape of the copper foil for the negative electrode current collector after heating at 120 ° C. or higher is great for preventing cracks. Influence.

Therefore, the copper foil for a negative electrode current collector of the lithium ion secondary battery according to the present embodiment is a negative electrode having a thickness of less than 26 μm cut out by a certain length L _{st in} the length direction, as shown in FIG. The current collector copper foil 11 was cut into strips in the width direction (direction W in FIG. 1), and a plurality of pieces (m (pieces), m: integer of 3 or more, m = 10 in FIG. 1) of copper foil pieces. (in FIG. 1, 12a-12j) when forming the length L _max of the "longest copper foil piece to the" shortest copper foil piece length L ₀ of (in FIG. 1 12j) "(in FIG. 1 12f) And elongation ratio ε (= ΔL / L ₀ = (L _max −L) defined as a ratio of difference ΔL = L _max −L ₀ ”between the length L ₀ of the copper foil piece and the shortest copper foil piece (12j in FIG. 1) ₀₎ / L ₀₎ is less than 220 ppm, copper least three located in the central portion and both end portions in the width direction of the negative electrode current collector foil 11 (in FIG. 1, four) When the pieces (12a, 12e, 12f, and 12j in FIG. 1) are heated to a predetermined temperature of 120 ° C. or higher and then returned to room temperature, the individual copper foil pieces (12a, 12e, 12f, and 12j) are heated. length variation rate before and after (i.e., (length after heating l _m - before cutting into strips the length L _st) / strip into cut length before L _st) a d _a, d _e, d _f , D _j , these maximum values d _max (in FIG. 1, the rate of change of the length related to the copper foil piece 12e) and minimum values d _min (in FIG. 1, the length related to the copper foil piece 12j) Change rate) (hereinafter referred to as the maximum change rate difference Δd) is 593 ppm or less, preferably 430 ppm or less.

Further, Dohakuhen 12e (or 12f) length before and after heating changing rate d _e (or d _f) of the negative electrode current collector foil located at the center in the width direction of the negative electrode current collector foil 11 The length change rates d _a and d _j before and after the heating of the copper foil pieces 12a and 12j located at both ends in the width direction of 11 are good.

  The negative electrode current collector copper foil 11 having a thickness of less than 26 μm is targeted because the possibility of cracking is low in the negative electrode current collector copper foil 11 having a thickness of 26 μm or more. This is because it is not necessary to pay attention.

  When the elongation ε is less than 220 ppm, it means that the copper foil 11 for negative electrode current collector having excellent flatness before heating is used. This is because the copper foil 11 for negative electrode current collector, which already has poor flatness before heating, naturally has poor flatness even after heating.

  The maximum change rate difference Δd is set to 593 ppm or less, preferably 430 ppm or less. The negative electrode current collector is excellent in flatness by suppressing variations in the width direction of the length of the copper foil 11 for a negative electrode current collector after heating. This is to obtain the body copper foil 11.

  In order to suppress a change in the size of the negative electrode current collector copper foil 11 before and after heating, it is important to equalize the rolling load applied to both ends of the work roll in each pass of rolling after the final annealing. That is, by making the difference in rolling load applied to both ends of the work roll relative to the sum of the rolling loads applied to both ends of the work roll to be 1% or less, the negative electrode current collector copper having the desired maximum change rate difference Δd as described above The foil 11 can be obtained.

  In addition, when obtaining the maximum change rate difference Δd, heating to 120 ° C. or higher is performed at a drying temperature of 120 ° C. or higher and 200 ° C. or lower because a typical heat load in the drying step after active material coating is performed. It is because it is necessary to heat more than the minimum heat load of a drying process.

  As for the temperature for this heat treatment, it is desirable to carry out at the temperature if the heat treatment conditions such as the drying step after the application of the active material are known. This is to simulate the thermal load that the copper foil 11 for the negative electrode current collector actually receives.

  Moreover, it is preferable that 1% yield strength after heating for 30 minutes or more at the temperature of 120 to 200 degreeC or 120 to 400 degreeC is 250 Mpa or more. The reason why the temperature is set to 120 ° C. or higher is for the same reason as that for obtaining the maximum change rate difference Δd, and the temperature is set to 200 ° C. or lower because the maximum heat load in the drying process is 200 ° C. or lower. is there. The temperature of 400 ° C. or lower is set to 300 ° C. which may be applied after the drying step or in the dehydration heat treatment step when polyimide (PI) is used as the binder for forming the active material layer. This is because it is considered to be 400 ° C. or lower. The 1% yield strength is measured in accordance with JISZ2241 “Total elongation method”. By setting the 1% proof stress to the above value, even when an active material layer having a large expansion and contraction is formed for the purpose of increasing the battery capacity, etc., when the battery is charged / discharged, the copper foil for the negative electrode current collector is cracked. Can be made difficult.

  However, when the temperature related to the heat treatment actually performed is unknown or for the purpose of simplifying the process, it may be performed at 120 ° C. or 400 ° C. as described later.

  Furthermore, it is preferable that Zr is contained in an amount of 0.01 mass% to 0.2 mass%. As a result, the heat resistance of the copper foil 11 for the negative electrode current collector can be increased, the residual strain can be prevented from being released by heating in the drying process, and the change in the dimensions of the copper foil 11 for the negative electrode current collector can be suppressed to be extremely small. become.

  The copper foil 11 for a negative electrode current collector that satisfies the conditions described so far is not easily cracked during the production of the negative electrode, particularly in the roll press process, and has excellent workability.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above-described embodiment, the negative electrode current collector copper foil 11 having a thickness of less than 26 μm cut out by a certain length in the length direction is cut into strips in the width direction to form a plurality of copper foil pieces 12a. -12j was formed, and various conditions were obtained using the plurality of copper foil pieces 12a-12j, but the negative electrode collector copper having a thickness of less than 26 μm cut out by a certain length in the length direction When the length is measured at a plurality of locations in the width direction along the surface of the foil 11, the “difference ΔL between the length of the longest location and the length of the shortest location _{” with} respect to “the length L _{0 of} the shortest location” When the elongation ε as a ratio is less than 220 ppm and the negative electrode current collector copper foil 11 is heated to a predetermined temperature of 120 ° C. or higher and then returned to room temperature, the width direction of the negative electrode current collector copper foil 11 is increased. The maximum change rate difference Δd before and after heating at the center and both ends of the steel is 593 ppm or more It is possible to obtain the same effect even negative electrode current collector foil 11 is.

  Furthermore, when the above-described heating is performed, the rate of change in length before and after heating in the central portion in the width direction of the copper foil 11 for negative electrode current collector is before and after heating at both ends in the width direction of the copper foil 11 for negative electrode current collector It is the copper foil 11 for negative electrode electrical power collectors which is more than the length change rate of this.

  At this time, the copper foil 11 for the negative electrode current collector is left on a flat plate, and the uneven state of the surface of the copper foil 11 for the negative electrode current collector is measured in the length direction and the width direction using a laser displacement sensor or an eddy current displacement sensor. And measuring the length of the copper foil 11 for the negative electrode current collector from the trace length of the unevenness.

  The negative electrode of a lithium ion secondary battery can be manufactured by performing roll press after applying and drying an active material on any one of these copper foils 11 for negative electrode current collectors.

  At this time, by using the copper foil 11 for the negative electrode current collector that satisfies the above-described conditions, the cracking probability of the copper foil 11 for the negative electrode current collector during the production of the negative electrode can be greatly reduced, and the production process of the negative electrode can be reduced. It is possible to improve the retention.

  In addition, although it may heat again at about 120 degreeC at the time of roll press, since the residual distortion has already been open | released at this time and the shape of the copper foil 11 for negative electrode collectors hardly changes, the heating at the time of roll press Has a small influence on the negative electrode current collector copper foil 11.

  In addition, according to the present invention, the negative electrode current collector copper foil 11 is evaluated, and the negative electrode current collector copper foil 11 which is not easily cracked and particularly excellent in workability during the production of the negative electrode, particularly in the roll press process, is selected. It becomes possible.

That is, in the evaluation method of the copper foil for negative electrode current collector of the lithium ion secondary battery according to the embodiment of the present invention, the copper foil 11 for negative electrode current collector cut out by a certain length in the length direction is used in the width direction. A plurality of copper foil pieces are cut into strips, and “the difference ΔL between the length of the longest copper foil piece and the length of the shortest copper foil piece relative to the length L _{0 of} the shortest copper foil piece” is formed. Is obtained, and at least three copper foil pieces located at the center and both ends in the width direction of the copper foil 11 for the negative electrode current collector are heated to a predetermined temperature of 120 ° C. or higher and then returned to room temperature. Then, the difference between the maximum value and the minimum value of the length change rate before and after heating of each copper foil piece is obtained, and the crack resistance performance of the copper foil 11 for the negative electrode current collector during the production of the negative electrode is determined based on these values. It is something to evaluate.

  When these values satisfy the above-mentioned conditions, it means that the copper foil 11 for the negative electrode current collector is excellent in workability because cracks are hardly generated during the production of the negative electrode, particularly in the roll press process.

Similarly, the length is measured at a plurality of locations in the width direction along the surface of the copper foil 11 for the negative electrode current collector cut out by a certain length in the length direction, and “the length L of the shortest location is measured. _After obtaining the elongation ε, which is the ratio of “the difference ΔL between the length of the longest part and the shortest part _” to “ _0”, and heating the copper foil 11 for negative electrode current collector to a predetermined temperature of 120 ° C. or higher The temperature is returned again to room temperature, and the difference between the maximum value and the minimum value of the length change rate before and after heating of each copper foil piece is determined, and crack resistance of the copper foil 11 for the negative electrode current collector during the production of the negative electrode is determined based on these values. It is also possible to evaluate the performance.

  Next, examples of the present invention will be described.

(Experiment 1)
As the copper foil for the negative electrode current collector, a TPC-H foil having a width of 600 mm and a thickness of 10 μm, a TPC-O foil (annealing foil), and an HCL02Z foil manufactured by Hitachi Cable, Ltd. were used. Sample number 1 (Example 1) and sample number 3 were set such that the difference in rolling load applied to both ends of the work roll with respect to the sum of the rolling loads applied to both ends of the work roll in each pass of rolling was 1% or less, and the rolling conditions were changed. (Example 2), Sample No. 4 (Example 3), Sample No. 5 (Example 4), and Sample No. 6 (Example 5) were produced. Sample No. 2 (Comparative Example 1) was produced with a rolling load difference of 1.5%. Sample No. 7 (Comparative Example 2) was prepared by using a TPC-H foil and rolling it intentionally.

(Measurement of elongation)
The elongation percentage ε after rolling of these copper foils for negative electrode current collector was 70 ppm to 220 ppm for TPC-H foil, 100 ppm for TPC-O foil, and 50 ppm for HCL02Z foil, and the flatness was good.

(Measurement of maximum change rate difference Δd after heat treatment)
A test piece having a width of 5 mm and a length of 20 mm was cut out from the center and both ends in the width direction of the copper foil for the negative electrode current collector, and thermally expanded using a thermal dilatometer TMA8310 manufactured by Rigaku Corporation. Was measured. The measurement conditions are as follows. The room temperature was 25 ° C.
Effective measurement length: 15 mm
Tensile load: 2 MPa
Maximum temperature: 200 ° C
Temperature increase rate: 5 ° C / min (cooling is allowed to cool naturally)
Temperature cycle: room temperature → 200 ° C → room temperature → 200 ° C → room temperature (measurement stopped during cooling)

  The measurement results are shown in FIGS.

  Each sample has an inflection point where the amount of elongation increases during the first temperature increase, and this temperature corresponds to the softening temperature of the copper foil for the negative electrode current collector.

  The amount of elongation generated by the first temperature increase varied depending on the sample and the position in the width direction. It was also confirmed that there was a difference in elongation after heating depending on the processing history and material.

  Elongation increases even at the second temperature rise, but this elongation is thermal expansion, which is around 16 ppm / K in all samples, and the thermal expansion coefficient of copper is 16.2 ppm / K (Source: RIKEN, Iwanami Shoten) Was in good agreement.

  Thereby, it has confirmed that the residual distortion which the copper foil for negative electrode collectors included was released by passing through the application | coating and drying process of a slurry-like substance.

  Further, the length increase (μm) at three points after the heat treatment measured in the width direction of the copper foil for the negative electrode current collector and the maximum change rate difference Δd (maximum difference / effective length) at the three points were calculated. I summarized it.

  In the TPC-H foils of sample numbers 1 to 4 and 7, the maximum change rate difference Δd changed in the range of 373 ppm to 713 ppm. This depends on the difference in rolling conditions.

  Sample No. 5 is an HCL02Z foil having improved heat resistance by containing 0.02 mass% of Zr. Since the HCL02Z foil has a semi-softening temperature of about 400 ° C., it does not soften at 200 ° C. in this experiment and does not release residual strain. Therefore, the dimensional change was also extremely small.

  Sample No. 6 is a TPC-O foil obtained by annealing the TPC foil. The TPC-O foil is heat-treated at 150 ° C. for 4 hours in a nitrogen atmosphere. Since the residual strain was released in the annealing process, the amount of newly released residual strain in this experiment was small.

(Experiment 2)
And the active material layer was formed on both surfaces of these copper foils for negative electrode collectors. The active material is artificial graphite MAG (average particle size 21 μm) manufactured by Hitachi Chemical Co., Ltd., the binder is SBR aqueous solution manufactured by Nippon Zeon Co., Ltd., and the thickener is Daiichi Kogyo Seiyaku Co., Ltd. ) CMC manufactured by the company was used. The composition was a non-volatile component ratio, and active material: binder: thickening material = 99: 0.5: 0.5.

  After kneading these, intermittent coating with 600 mm coating and 30 mm non-coating was carried out with a coating machine, followed by drying at a maximum temperature of 180 ° C. The active material layer thickness after drying was approximately 150 μm.

  Next, an active material layer was similarly provided on the opposite surface of the copper foil for the negative electrode current collector. At this time, the positions of the coated part / non-coated part were matched on both sides.

The negative electrode in which the active material layer was intermittently coated on both surfaces of the copper foil for the negative electrode current collector was placed on a roll press. The roll press was a constant pressure and the rolling force was 4 × 10 ³ N / cm.

  Under this condition, the above-mentioned negative electrode was rolled 1000 m at a time, and the number of cracks generated during this operation (number of cracks) was determined and summarized in Table 1.

(Result of Experiment 2)
Sample No. 2 having the largest maximum change rate difference Δd of 713 ppm cracked twice, whereas Sample Nos. 1, 3, 4, 5, and 6 having a maximum change rate of 593 ppm or less never cracked.

  From this result, in order to prevent the occurrence of cracks in the copper foil for the negative electrode current collector, at least three points were sampled at the positions in the center and both ends in the width direction of the copper foil for the negative electrode current collector. It was found that it is important that the maximum change rate difference Δd at the three points when the length change rate in the length direction before and after heating is 593 ppm or less.

  Moreover, it was difficult to carry the sample number 7, and the result that the crack had arisen was obtained. It has been found that when the elongation ε before heat treatment is 220 ppm or more, the copper foil for the negative electrode current collector does not pass straight through the transfer line but is shifted to one side, making it difficult to transfer and causing cracks to occur easily.

  From the results of Experiment 2, it was found that the elongation ε needs to be suppressed to less than 220 ppm.

  In addition, as above-mentioned, when the drying process after active material coating has become clear, it is desirable to perform the temperature which concerns on heat processing at that temperature. This is to simulate the thermal load that the copper foil for the negative electrode current collector actually receives. However, it may be performed at 120 ° C. or 400 ° C. when the temperature related to the heat treatment actually performed is unknown or for the purpose of simplifying the process. The reason for this will be described below.

  When the copper foil 11 for a negative electrode current collector having a low semi-softening temperature (about 100 ° C. or more and about 120 ° C. or less) used in Examples and the like is subjected to a heat treatment of 120 ° C. or more, the strain is released. For this reason, the theoretical maximum change rate difference Δd when the heat treatment temperature is changed to 120 ° C. and 400 ° C. is zero. When the inventors investigated the copper foil 11 for a negative current collector having a low semi-softening temperature according to Examples and the like, the difference when the experiment was performed at 120 ° C. and 400 ° C. was negligible. . For this reason, regarding the copper foil 11 for negative electrode collectors with such a low semi-softening temperature, it is thought that heat processing may be performed at 120 degreeC.

  Next, regarding the copper foil 11 for negative electrode current collector having a high semi-softening temperature used in Examples etc. (for example, copper foil for negative electrode current collector based on 02Z, etc.), 120 ° C., 180 ° C., Even when heat treatment was performed at 350 ° C. and 400 ° C., the maximum change rate difference Δd was almost unchanged from the state after rolling (the state before heat treatment). For this reason, regarding the copper foil 11 for negative electrode collectors with such high heat resistance, it is thought that heat processing may be performed at 120 degreeC.

  As a method for confirming whether the copper foil 11 for a negative electrode current collector according to the present invention is used by utilizing these characteristics, for example, when manufacturing conditions from a raw material to a copper foil are established, a desired active material coating is performed. It is conceivable to confirm that it falls within the scope of the present invention under the conditions of the subsequent heat treatment, and then periodically sample and perform the same confirmation at 120 ° C. or 400 ° C.

11 Copper foil 12a-12j for negative electrode collectors Copper foil piece

Claims (9)

When a copper foil for a negative electrode current collector having a thickness of less than 26 μm cut into a certain length in the length direction is cut into strips in the width direction to form a plurality of copper foil pieces, the “shortest copper foil piece The elongation, which is a ratio of “the difference between the length of the longest copper foil piece and the length of the shortest copper foil piece” to “the length of the length of,” is less than 220 ppm,
When at least three copper foil pieces positioned at the center and both ends in the width direction of the copper foil for negative electrode current collector are heated to a predetermined temperature of 120 ° C. or higher and then returned to room temperature, individual copper foil pieces A copper foil for a negative electrode current collector of a lithium ion secondary battery, wherein a difference between a maximum value and a minimum value of a length change rate before and after heating is 593 ppm or less.   The length change rate before and after the heating of the copper foil piece located in the center part in the width direction of the copper foil for the negative electrode current collector is a copper foil piece located at both ends in the width direction of the copper foil for the negative electrode current collector The copper foil for a negative electrode current collector of a lithium ion secondary battery according to claim 1, wherein the copper foil for the negative electrode current collector of the lithium ion secondary battery is equal to or greater than a rate of change in length before and after heating.   3. The copper foil for a negative electrode current collector of a lithium ion secondary battery according to claim 1, wherein the 1% yield strength after heating at a temperature of 120 ° C. or more and 200 ° C. or less for 30 minutes or more is 250 MPa or more.   4. The copper foil for a negative electrode current collector of a lithium ion secondary battery according to claim 1, wherein a 1% yield strength after heating at a temperature of 120 ° C. or more and 400 ° C. or less for 30 minutes or more is 250 MPa or more. .   The copper foil for a negative electrode current collector of a lithium ion secondary battery according to any one of claims 1 to 4, wherein Zr is contained in an amount of 0.01 mass% to 0.2 mass%.   A lithium ion secondary battery comprising: a roll press after applying and drying an active material on the copper foil for a negative electrode current collector of the lithium ion secondary battery according to any one of claims 1 to 5. Manufacturing method of negative electrode. The negative electrode current collector copper foil cut out by a certain length in the length direction is cut into strips in the width direction to form a plurality of copper foil pieces. Find the elongation, which is the ratio of the difference between the length of the long copper foil piece and the length of the shortest copper foil piece,
At least three copper foil pieces positioned at the center and both ends in the width direction of the copper foil for negative electrode current collector are heated to a predetermined temperature of 120 ° C. or more and then returned to room temperature, and heating of each copper foil piece is performed. Find the difference between the maximum and minimum length change rate before and after,
The evaluation method of a copper foil for a negative electrode current collector of a lithium ion secondary battery, wherein the crack resistance performance of the copper foil for a negative electrode current collector at the time of production of the negative electrode is evaluated based on these values. The negative electrode current collector copper foil cut out by a certain length in the length direction is cut into strips in the width direction to form a plurality of copper foil pieces. Find the elongation, which is the ratio of the difference between the length of the long copper foil piece and the length of the shortest copper foil piece,
At least three copper foil pieces positioned at the center and both ends in the width direction of the copper foil for negative electrode current collector are heated to a predetermined temperature of 120 ° C. or more and then returned to room temperature, and heating of each copper foil piece is performed. Find the difference between the maximum and minimum length change rate before and after, and
The length change rate before and after heating of the copper foil piece located in the center part in the width direction of the copper foil for the negative electrode current collector and the copper foil piece located at both ends in the width direction of the copper foil for the negative electrode current collector Find the rate of change in length before and after heating,
The evaluation method of a copper foil for a negative electrode current collector of a lithium ion secondary battery, wherein the crack resistance performance of the copper foil for a negative electrode current collector at the time of production of the negative electrode is evaluated based on these values.   The negative electrode collection of a lithium ion secondary battery according to claim 7 or 8, wherein the predetermined temperature is a temperature determined according to a thermal load exposed in a manufacturing process of the lithium ion secondary battery. Evaluation method of copper foil for electric conductors.