TW201943133A - Rolled copper foil for lithium ion battery collectors and lithium ion battery wherein the rolled copper foil for lithium ion battery collectors has good ultrasonic weldability with a copper foil or a tab terminal and less metal powder is generated during ultrasonic welding - Google Patents

Abstract

An object of the present invention is to provide a rolled copper foil for lithium ion battery collectors which has good ultrasonic weldability with a copper foil or a tab terminal and produces less metal powder during ultrasonic welding. The solution of the present invention is to provide a rolled copper foil for lithium ion battery collectors, which satisfies an arithmetic mean roughness Ra [[mu]m] × 10 + residual oil content [mg/m2 ] ≤ 3.8, 0.01 ≤ arithmetic mean roughness Ra [mu] [m] ≤ 0.25, and residual oil content [mg/m2 ] ≥ 0.1. Preferably, the rolled copper foil for a lithium ion battery collector satisfies an arithmetic mean roughness Ra [[mu]m] × 10 + residual oil content [mg/m2] ≤ 2.8, and 0.01 ≤ arithmetic mean roughness Ra [[mu]m] ≤ 0.2. In addition, the present invention also provides a lithium ion battery using a rolled copper foil for a lithium ion battery collector as a current collector, and a negative electrode is constituted by an active material layer formed thereon. The lithium ion battery includes a lithium ion primary battery and lithium ion secondary battery, wherein the lithium ion in an electrolyte bears electrical conduction. The material of the rolled copper foil can be one selected from a group consisting of high-purity copper (oxygen-free copper, tough pitch copper, etc.), Sn containing copper, Ag containing copper, Cu-Ni-Si-based copper alloy with addition of Ni, Si, etc., and Cu-Cr-Zr copper alloy with addition of Cr, Zr, etc.. The thickness of the rolled copper foil can be 1~100 micrometers when using it as a current collector of a lithium secondary battery anode. Under the condition of the thinning of the rolled copper foil, the battery with high capacity can be obtained. From this point of view, it is typically from 2 to 50 [mu]m, more typically from 5 to 20 [mu]m.

Description

Rolled copper foil for lithium ion battery current collector and lithium ion battery

The present invention relates to a rolled copper foil for a lithium ion battery current collector and a lithium ion battery.

Lithium-ion batteries have the characteristics of high energy density and relatively high voltage, and are often used for small electronic devices such as notebook computers, video cameras, digital cameras, and mobile phones. In the future, it is also expected to be used as a power source for a large-scale device such as an electric vehicle or a distributed power source for a general household.

FIG. 1 is a schematic diagram of a stacked structure of a lithium ion battery. The electrode body of a lithium ion battery generally has a stacked structure in which the positive electrode 11, the separator 12, and the negative electrode 13 are wound or laminated dozens of times. Typically, the positive electrode is composed of a positive electrode active material, which uses a positive electrode current collector made of aluminum foil and a lithium composite oxide such as LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ provided on the surface thereof, The negative electrode is composed of a negative electrode active material, which uses a negative electrode current collector made of aluminum foil and carbon or the like provided on a surface thereof as materials. The lead plates (14, 15) are welded between the positive electrode and the negative electrode, respectively. The positive and negative electrodes are connected to lead terminals made of aluminum or nickel, but this is also performed by welding. Welding is usually performed by ultrasonic welding.

Examples of characteristics required for a copper foil used as a current collector of a negative electrode include adhesion to a negative electrode active material and low generation of metal powder during ultrasonic welding.

Regarding ultrasonic weldability, conventionally, welding energy corresponding to the weldability of a material is not a big problem. However, when a large amount of welding energy is imparted, the consumption of consumables used for welding is large. Therefore, in recent years, cost reductions have been sought for a copper foil that is excellent in welding energy even if the welding energy is reduced. As a copper foil having such a structure, in Japanese Patent Application Laid-Open No. 2009-68042, it is described that a coating amount of a chromium hydrated oxide layer on the surface of the copper foil is specified to be 0.5 to 70 μg-Cr / dm ² , and chromium is hydrated and oxidized. A method in which the Rz (10-point average roughness specified in JIS B0601-1994) of the surface covered by the physical layer is 2.0 μm or less. In the examples, it is described that such a surface roughness is formed by electrolytic copper foil.

In addition, a copper foil used as a current collector of a lithium ion battery may be peeled into a powder form during the ultrasonic welding, and there is a concern that metal powder may be generated. Such metal powders are generated in large quantities, and when they remain in the electrode body, internal short circuits may be caused, and the performance of the lithium ion battery may be reduced. As a method for suppressing the generation of metal powder, for example, Japanese Patent Application Laid-Open No. 2007-305322 describes a method of removing internal strain of a negative electrode current collector by annealing and softening it, thereby, during ultrasonic welding, A part of the current collector is suppressed from being peeled into a powder form, and the residual metal powder of 50 μm or more is reduced.

In addition, although a rolled copper foil used as a current collector of a lithium-ion battery is manufactured by a rolling process, rolling oil used during rolling is adhered to the surface of the copper foil. The rolling oil is washed and removed in the degreasing step after rolling, but it is not completely removed. If a large amount of rolling oil remains on the surface of the copper foil, the adhesion between the copper foils during ultrasonic welding is deteriorated, which is not preferable. For example, in Japanese Patent Application Laid-Open No. 10-212562, a method is described in which a laminated copper foil is not adhered to each other in a wound product (coil) obtained by winding a copper foil obtained by cold rolling. The copper foil surface before the winding is cleaned, and the fine copper powder and the like adhered to the surface are removed, and the residual oil content such as rolling oil remaining on the surface is set to a predetermined value or less. Final annealing method.

Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent Application Laid-Open No. 2009-68042 Patent Literature 2: Japanese Patent Application Laid-Open No. 2007-305322 Patent Literature 3: Japanese Patent Application Laid-Open No. 10-212562

Problems to be solved by invention

In this way, although technical developments have been made to improve the characteristics of copper foils used as current collectors for lithium-ion batteries, there are still technologies for simultaneously improving the ultrasonic weldability and suppressing the generation of metal powder during ultrasonic welding. Room for development.

Therefore, an object of the present invention is to provide a rolled copper foil for a lithium ion battery current collector that has excellent ultrasonic weldability with copper foil or lead terminal and has less metal powder generation during ultrasonic welding.
Solution to Problem

The present inventors have repeatedly studied in order to solve the above problems, and found that by controlling the relationship between the residual oil content of the rolled copper foil and the residual oil content of the rolled copper foil and the surface roughness, the numerical range of the arithmetic mean roughness Ra is further controlled. Therefore, it is possible to provide a rolled copper foil for a lithium ion battery current collector which improves ultrasonic weldability and has less metal powder generation during ultrasonic welding.

An embodiment of the present invention completed based on the above findings is, on the one hand, a rolled copper foil for a lithium-ion battery current collector that satisfies an arithmetic average roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≤ 3.8; 0.01 ≤ arithmetic mean roughness Ra [μm] ≤ 0.25; and residual oil content [mg / m ² ] ≥ 0.1.

Regarding the rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention, in one embodiment, the arithmetic mean roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≦ 2.8 is satisfied.

Regarding the rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention, in another embodiment, 0.01 ≦ arithmetic average roughness Ra [μm] ≦ 0.2 is satisfied.

Another aspect of the present invention is a lithium ion battery using a rolled copper foil for a lithium ion battery current collector according to an embodiment of the present invention as a current collector.
Invention effect

According to the present invention, it is possible to provide a rolled copper foil for a lithium-ion battery current collector, which has good ultrasonic weldability with a copper foil or a lead terminal, and has less metal powder generated during ultrasonic welding.

(Rolled copper foil for lithium ion battery current collector)

The copper foil base material of the rolled copper foil for lithium ion battery current collectors which concerns on embodiment of this invention uses rolled copper foil. The rolled copper foil also includes a rolled copper alloy foil. There is no particular limitation on the material of the rolled copper foil, and it may be appropriately selected according to the application and required characteristics. For example, without limitation, in addition to high-purity copper (oxygen-free copper, tough copper, etc.), Cu-Ni-Si-based copper alloys containing Sn-containing copper, Ag-containing copper, Ni, Si, etc., and Copper alloys such as Cu-Cr-Zr based copper alloys such as Cr and Zr.

The thickness of the rolled copper foil is not particularly limited, and may be appropriately selected according to the required characteristics. Generally, it is 1 to 100 μm. However, when used as a current collector for a negative electrode of a lithium secondary battery, a battery with a higher capacity can be obtained when the rolled copper foil is thinned. From such a viewpoint, it is typically 2 to 50 μm, and more typically 5 to 20 μm.

The rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention satisfies the arithmetic mean roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≦ 3.8. By controlling the relationship between the residual oil content of the rolled copper foil and the arithmetic average roughness Ra in this way, lithium having good ultrasonic weldability with copper foil or lead terminal and less metal powder generated during ultrasonic welding can be obtained. Rolled copper foil for an ion battery current collector. The rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention preferably satisfies the arithmetic mean roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≤ 3.3, and more preferably satisfies the arithmetic mean roughness Ra [ μm] × 10 ＋ Residual oil content [mg / m ² ] ≤2.8.

The rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention further satisfies 0.01 ≦ arithmetic average roughness Ra [μm] ≦ 0.25. When the arithmetic average roughness Ra is less than 0.01 μm, the anchoring effect may be reduced, and the adhesion with the negative electrode active material may be deteriorated. In addition, when the arithmetic average roughness Ra is larger than 0.25 μm, the contact between the overlapped copper foil and the copper foil during ultrasonic welding becomes smaller, so that ultrasonic weldability deteriorates, and the amount of metal powder generated during ultrasonic welding significantly increases. . The rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention preferably satisfies 0.01 ≤ arithmetic mean roughness Ra [μm] ≤ 0.2, and more preferably 0.01 ≤ arithmetic mean roughness Ra [μm] ≤ 0.15.

The rolled copper foil for a lithium ion battery current collector according to the embodiment of the present case also satisfies the residual oil content [mg / m ² ] ≥ 0.1 after degreasing. When the residual oil content is less than 0.1 mg / m ² , the surface becomes active, and the surface deteriorates due to some chemical reactions, and the ultrasonic weldability becomes poor. When the residual oil content on the surface of the copper foil is excessive, ultrasonic welding may be hindered. Therefore, in order to obtain better ultrasonic weldability, it is preferable to set the residual oil content after degreasing to 3.7 mg / m ² or less.

The rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention that controls the residual oil content of the rolled copper foil, the relationship between the residual oil content, and the arithmetic average roughness Ra, and the arithmetic average roughness Ra as described above. Instead of performing a roughening treatment such as polishing treatment or plating of electrodeposited particles, it is possible to construct by controlling the uneven state of the surface caused by oil pits. Oil pits are fine depressions locally generated on the surface of the material being rolled by the rolling oil enclosed in the roll gap by the rolling roll and the material being rolled. Since the roughening process step is omitted, there is an advantage that economic efficiency and productivity are improved.

The shape of the oil pits of the rolled copper foil, that is, the surface properties, can be adjusted by adjusting the surface roughness of the rolling rolls, the rolling speed, the viscosity of the rolling oil, and the average rolling reduction per pass (especially the final rolling pass Down rate) and so on. For example, if a roll having a large surface roughness is used, the surface roughness of the obtained rolled copper foil also becomes large. Conversely, if a roll having a small surface roughness is used, the surface of the obtained rolled copper foil is increased. The roughness is also easily reduced. In addition, by increasing the rolling speed, increasing the viscosity of the rolling oil, or reducing the average rolling reduction per pass, the amount of oil pits is also easily increased. On the contrary, by slowing the rolling speed, reducing the viscosity of the rolling oil, or increasing the rolling reduction per pass, the amount of oil pits easily decreases.
(Lithium Ion Battery)

A lithium ion battery can be produced by a common method using a negative electrode composed of a current collector using the rolled copper foil according to the embodiment of the present invention as a material and an active material layer formed thereon. Lithium-ion batteries include lithium-ion primary batteries and lithium-ion secondary batteries that use lithium ions in the electrolyte as a conductive material. The negative electrode active material is not limited, but examples include carbon, silicon, tin, germanium, lead, antimony, aluminum, indium, lithium, tin oxide, lithium titanate, lithium nitride, indium tin oxide, and indium- Tin alloy, lithium-aluminum alloy, lithium-indium alloy, etc.
(Production method)

The rolled copper foil for a lithium ion battery current collector according to the embodiment of the present invention can be produced by, for example, the following production method.

First, an ingot as a raw material is manufactured and rolled by hot rolling. Next, annealing and cold rolling are repeated. In the final cold rolling, the work roll diameter is set to 50 to 100 mm, the work roll surface roughness Ra is set to 0.03 to 0.1 μm, and the rolling speed of the final pass is set to 300 to 500m / min, finishing to a thickness of 1 ~ 100μm. The viscosity of the rolling oil can be set to 3.0 to 5.0 cSt (25 ° C). After the final cold rolling, oil components such as rolling oil used in the final cold rolling are attached to the copper foil. Therefore, the copper foil was washed with a solution containing a petroleum-based solvent and an anionic surfactant, and the copper The powder, rolling oil, etc. are removed and then air-dried.

It should be noted that, as a method for removing rolling oil and the like from the surface of a copper foil, a conventionally known degreasing treatment or cleaning treatment may be adopted. As a further organic solvent (degreasing solvent), for example, normal paraffin, isopropyl Alcohols such as alcohols, acetone, dimethylacetamide, tetrahydrofuran, ethylene glycol.

The degreasing process controls the processing conditions in a manner that satisfies the relationship between the residual oil content on the surface of the copper foil and the arithmetic average roughness Ra (arithmetic average roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≤ 3.8). For example, the degreasing process is performed so that the residual oil content after degreasing of the copper foil whose arithmetic average roughness Ra is 0.068 micrometers may be 3.12 mg / m <^2> or less. The immersion time in the degreasing liquid is adjusted as shown in FIG. 2 in accordance with the roughness of the copper foil surface, thereby preventing discoloration of the copper foil surface and suppressing defects in ultrasonic solderability.

In the degreasing treatment, the immersion time of the copper foil in the degreasing solvent may be 1.0 s or more. On the other hand, if the immersion time is too long, productivity is poor, and discoloration due to alkali ablation on the surface of the copper foil. For copper foils with large Ra, that is, many or deep oil pits, in order to remove the rolling oil entering the oil pits and the oxide film formed in the oil pits, it is preferable to immerse for a long time. The immersion time of the copper foil in the degreasing solvent can be set to 1.0 to 8.0 s.
[Example]

Examples of the present invention are shown below, but they are provided for better understanding of the present invention and are not intended to limit the present invention.
(Examples 1 to 10, Comparative Examples 1 to 8)
[Manufacture of rolled copper foil]

An ingot of 600 mm wide toughness copper was produced and rolled by hot rolling.

Next, annealing and cold rolling were repeated. Finally, in the cold rolling, the work roll diameter was set to 60 mm, the work roll surface roughness Ra was set to 0.03 μm, and the final pass was finished at a rolling speed of 400 m / min into Table 1. The thickness described in. The viscosity of the rolling oil was 4.0 cSt (25 ° C). In this state, oil components such as rolling oil used in the final cold rolling are adhered to the copper foil. This copper foil was washed with a solution containing a petroleum-based solvent and an anionic surfactant to remove copper fine powder, rolling oil, and the like adhered to the surface of the copper foil, and then air-dried.

The rolling oil in the copper foil surface was removed by a degreasing treatment using an n-paraffin as an organic solvent (a degreasing solvent). Table 1 shows the immersion time of the copper foil subjected to the degreasing treatment in an organic solvent (degreasing solvent). It should be noted that in Examples 1 to 10, the relationship between the residual oil content on the copper foil surface and the arithmetic mean roughness Ra at this time (the arithmetic mean roughness Ra [μm] × 10 + the residual oil content [mg / m ² ] ≤3.8).
[Arithmetic average roughness Ra]

The arithmetic average roughness Ra is a value obtained by measuring in accordance with JIS B0601 2001 using a confocal microscope (manufactured by LASERTEC, model: HD100D), and measuring the surface of the sample in a rolling parallel direction with a length of 175 μm.
[Residual oil content]

The residual oil content was measured by the following method. This copper foil sample and a solvent (H-997 manufactured by HORIBA, Ltd.) were placed in a beaker, and ultrasonic cleaning was performed with an ultrasonic cleaner for 2 minutes. Then, the oil content concentration meter OCMA-555 manufactured by Horiba was placed in a dedicated area and the oil content concentration was measured. The solvent was measured using H-997 manufactured by Horiba.

In addition, in addition to the oil content concentration meter OCMA-555 manufactured by Horiba, used in this Example, the said oil content concentration can also be measured by a well-known general method. As the solvent, in addition to H-997 manufactured by HORIBA, Ltd. used in this example, a well-known general solvent such as carbon tetrachloride may be used.
[Ultrasonic weldability]

The ultrasonic weldability was evaluated in the following procedure.
(1) The copper foil was cut out to a size of 100 mm × 30 mm, and 30 sheets were overlapped.
(2) A welding head (pitch 0.8 mm, height 0.4 mm) was attached to an actuator (model: Ultraweld L20E) manufactured by Branson Corporation. Anvil uses 0.2mm pitch.
(3) The welding conditions were a pressure of 40 psi, an amplitude of 60 μm, and a vibration frequency of 20 kHz, and the welding time was set to 0.1 second.
(4) When the copper foil is peeled one by one after soldering according to the above conditions, the case where 11 or more copper foils are damaged at the soldering portion is set to "○", and 0 to 10 copper foils are When the welded part was broken, it was set to "×". In addition, before peeling the copper foil, the soldering part of the copper foil on the outermost surface which is in contact with the horn was enlarged by 20 times with a stereo microscope and observed. After peeling, no peel test was performed.
[Number of metal powder generated during ultrasonic welding]

The number of metal powders generated during ultrasonic welding was counted in the following order.
(1) The adhesive surface of a 20 mm wide tape is used as a surface, and it is mounted on both sides of the anvil of an actuator (model: Ultraweld L20E) manufactured by Branson Corporation. The size of the bonding surface is 20mm × 60mm.
(2) Cut out copper foil into a size of 100 mm x 30 mm, and overlap 30 sheets.
(3) The welding conditions were a pressure of 40 psi, an amplitude of 60 μm, and a vibration frequency of 20 kHz. The welding time was set to 0.1 second.
(4) Under the above conditions, after changing the welding position and welding 30 times with the same sample, the number of metal powders adhering to the adhesive surfaces of the tape installed on both sides of the anvil was counted.

The evaluation conditions and evaluation results are shown in Table 1.
[Table 1]

In Examples 1 to 10, the arithmetic mean roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≤ 3.8, and 0.01 ≤ arithmetic mean roughness Ra ≤ 0.25, and the residual oil content [mg / m ² ] ≥ 0.1, therefore, the ultrasonic weldability is good, and the number of metal powders generated is small.

In Comparative Example 1, the arithmetic average roughness Ra [μm] × 10 + the residual oil content [mg / m ² ] was greater than 3.8, and the arithmetic average roughness Ra was greater than 0.25 μm. Therefore, the ultrasonic weldability was poor and metal powder was generated. The number is significantly more than copper foils satisfying 0.01 ≦ arithmetic mean roughness Ra [μm] ≦ 0.25.

In Comparative Examples 2 and 3, since the arithmetic average roughness Ra [μm] × 10 + the residual oil content [mg / m ² ] was greater than 3.8, the ultrasonic weldability was poor. More specifically, in Comparative Examples 2 and 3, the residual oil content is larger than the arithmetic average roughness Ra. When the copper foils are recombined and welded in ultrasonic welding, the oil content prevents the copper foils from adhering to each other. . As a result, the ultrasonic weldability deteriorates compared with a copper foil satisfying the arithmetic mean roughness Ra [μm] × 10 + the residual oil content [mg / m ² ] ≦ 3.8.

In Comparative Examples 4 to 6, since the arithmetic average roughness Ra was larger than 0.25 μm, the number of metal powders produced was significantly larger than that of copper foils satisfying 0.01 ≦ arithmetic average roughness Ra [μm] ≦ 0.25.

In Comparative Example 7, since the immersion time was longer than 8 s, the residual oil content was small and the surface was active. Therefore, the surface was deteriorated by some chemical reaction, and thus the ultrasonic weldability was poor.

In Comparative Example 8, since the arithmetic average roughness Ra was less than 0.01, there was little rolling oil attached to the surface of the copper foil before degreasing. Therefore, even if the immersion time is short, the copper foil surface may be caused by alkali ablation. The discoloration of the ultrasonic welding is poor.

FIG. 3 is a graph showing the relationship between the residual oil content and the arithmetic average roughness Ra of Examples 1 to 10. Example 1 which satisfies the relationship between the arithmetic mean roughness Ra [μm] × 10 + the residual oil content [mg / m ² ] ≤ 3.8 and the residual oil content [mg / m ² ] ≥ 0.1 within a range surrounded by a dotted line. In 10, the ultrasonic weldability was good, and the number of metal powders produced was small.

11‧‧‧Positive

12‧‧‧ diaphragm

13‧‧‧ negative

14, 15‧‧‧ guide plate

FIG. 1 is a schematic diagram of a stacked structure of a lithium ion battery according to an embodiment of the present invention.

Fig. 2 is a graph showing the relationship between the surface roughness Ra of the copper foil of the example and the immersion time in the degreasing solution.

FIG. 3 is a graph showing the relationship between the residual oil content and the arithmetic mean roughness Ra in the examples and comparative examples.

Claims (4)

A rolled copper foil for a lithium ion battery current collector, wherein the following conditions are satisfied: arithmetic average roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≤ 3.8; 0.01 ≤ arithmetic average roughness Ra [μm] ≤0.25; and the residual oil content [mg / m ² ] ≥0.1. The rolled copper foil for a lithium ion battery current collector according to item 1 of the scope of the patent application, wherein the following conditions are satisfied: Arithmetic average roughness Ra [μm] × 10 + residual oil content [mg / m ² ] ≦ 2.8. The rolled copper foil for a lithium-ion battery current collector according to item 1 or item 2 of the scope of patent application, wherein: The following conditions: 0.01 ≤ arithmetic mean roughness Ra [μm] ≤ 0.2. A lithium-ion battery uses a rolled copper foil for a lithium-ion battery current collector as described in any one of claims 1 to 3 of the scope of patent application.