JPH09115523A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic secondary battery on which an occupying rate of current collectors is reduced and which has high energy density by manufacturing the current collecting bodies on which rolling rupture is not caused and which has a high yield by forming a positive electrode current collector and a negative electrode current collector by using specific metal and specific metallic alloy whose tensile strengths have respectively a specific value. SOLUTION: A nonaqueous electrolytic secondary battery is provided with a chargeable-dischargeable positive electrode, nonaqueous electrolyte and a chargeable- dischargeable negative electrode. A positive electrode current collector of this positive electrode is formed of Al alloy whose tensile strength is not less than 100N/mm<2> . On the other hand, a negative electrode current collector is formed of Cu or Cu alloy whose tensile strength is not less than 250N/mm<2> or Ni alloy whose tensile strength is not less than 350N/mm<2> . Then, since tensile strength is large, at manufacturing time, the current collectors can be manufactured with a high yield without causing rolling rupture, and when these current collectors are used, since tensile strength is large, the nonaqueous electrolyte secondary battery on which an occupying rate of the current collectors is reduced and which has high energy density can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement in the current collector of its electrode.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using an alkali metal as a negative electrode have high electromotive force and are expected to have a higher energy density than conventional nickel-cadmium storage batteries and lead storage batteries, and have been actively researched. There is. Of these, lithium secondary batteries have received the most attention, and many studies have been made.
Until now, LiMn has been used as a positive electrode active material for lithium secondary batteries.
₂ O ₄ , LiCoO ₂ , LiNiO ₂ , V ₂ O ₅ , Cr ₂ O ₅ ,
Oxides of transition metals such as MnO ₂ , TiS ₂ and MoS ₂ and chalcogen compounds are known. These have a layered or tunnel structure, and have a crystal structure through which lithium ions can enter and exit. On the other hand, as the negative electrode active material,
Many studies have been conducted on metal Li or Al that can be alloyed with Li.

However, when theoretically the highest capacity metal Li (theoretical capacity of 3860 mAh / g) is used for the negative electrode, dendrites are generated during charging, short circuit is likely to occur, and the battery becomes low in reliability. Therefore, it has not been put to practical use yet. Further, the LiAl alloy can also have a higher capacity next to the metal Li, but if charge and discharge are repeated at a capacity close to the theoretical value, it is pulverized severely and there is a problem in cycleability. In order to solve this problem, theoretically metallic Li,
A carbon material that has a smaller capacity than LiAl alloy but has excellent cycleability, does not easily generate dendrites, and is capable of reversibly taking Li in and out between layers (theoretical capacity 37
A lithium secondary battery using 2 mAh / g) as a negative electrode is currently in practical use.

[0004]

When a carbon material is used for the negative electrode, the theoretical capacity is smaller than that of metallic Li, so that the high energy density expected in lithium secondary batteries has not been reached. . In addition, the main lithium secondary batteries that have been put into practical use at present are of a cylindrical type in which the electrode plate group has a spiral structure as shown in FIG. Generally, a battery is roughly composed of a positive electrode mixture, a negative electrode mixture, a collector thereof, and a separator for separating the positive electrode and the negative electrode. The occupancy of the positive and negative electrode current collectors that do not contribute to the improvement of the energy density of the battery within the limited battery volume is large. In the conventional battery construction, in particular, when an electrode mixture containing a binder is applied to a sheet-shaped current collector and rolled to produce an electrode, workability at the time of rolling is considered to be at least 2.
An electrode current collector having a thickness of 0 to 30 μm had to be used. This is because the mechanical strength of the current collector is weak, the edge portion is broken during rolling, and the yield is reduced.

It is an object of the present invention to solve the above problems and to provide a current collector which gives an electrode with high yield without breakage during rolling. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high energy density by reducing the occupation ratio of the electrode current collector.

[0006]

The present invention provides a non-aqueous electrolyte secondary battery comprising a chargeable / dischargeable positive electrode, a non-aqueous electrolyte, and a chargeable / dischargeable negative electrode, which is used as a current collector for the positive electrode and / or the negative electrode. It uses a metal having a specific tensile strength. That is, the positive electrode current collector has a tensile strength of 100 N.
/ Al ² or more is used. In addition, the negative electrode current collector has a tensile strength of 250 N / mm ² or more of Cu or Cu.
Alloy or N with a tensile strength of 350 N / mm ² or more
It is characterized by using an i alloy.

As a result of detailed investigations on various metal materials as the positive electrode and negative electrode current collectors of non-aqueous electrolyte secondary batteries, the present inventors have found that the above-mentioned Al alloy and negative electrode current collector are used as the positive electrode current collector. It was found that by using the above-mentioned Cu, Cu alloy, or Ni alloy for the above, it is possible to reduce the thickness of the current collector as compared with the conventional one, while suppressing the reduction in yield due to the breakage of the edge portion during rolling in the electrode manufacturing process. According to the present invention, it becomes possible to lower the occupancy of the positive electrode current collector and the negative electrode current collector in the battery volume as compared with the conventional one, and it is possible to increase the filling amount of the positive electrode active material and the negative electrode active material. High energy density is possible with the same battery volume.

The tensile strength of the Al alloy of the positive electrode current collector is preferably 100 N / mm ² or more, and 200 N / mm ²
The above is more preferable, and 300 N / mm ² or more is particularly preferable. As the Al alloy having such tensile strength, Al containing 0.7 to 5 wt% of the total weight of at least one element of Si, Fe, Cu, Mn, Zn, and Ti.
An alloy is used. The tensile strength of Cu or Cu alloy of the negative electrode current collector is preferably 250 N / mm ² or more, more preferably 350 N / mm ² or more, 450 N
/ Mm ² or more is particularly preferable. As the Cu or Cu alloy having such tensile strength, cold-worked electrolytic copper or a Cu alloy containing 1 to 2% of Ti is used. Further, the tensile strength of the Ni alloy of the negative electrode current collector is preferably 350 N / mm ² or more, 450
N / mm ² or more is more preferable, and 550 N / mm ² or more is particularly preferable. As a Ni alloy having such tensile strength, cold-worked or hot-worked Co is used.
A Ni alloy with a content of 0.05 wt% is used.

The reason why the negative electrode current collector needs a higher tensile strength than that of the positive electrode current collector is that the negative electrode current collector and the negative electrode active material are different in consideration of cycle characteristics. This is because it is necessary to maintain strong adhesion. This is because the volume change due to charge and discharge of the carbon material normally used for the negative electrode material is larger than that of the composite oxide such as LiCoO ₂ used for the positive electrode active material. Furthermore, the Cu alloy or Ni alloy of the negative electrode current collector is harder than the Al alloy of the positive electrode current collector, and for this reason, a stronger rolling process is required to improve the adhesion between the active material and the current collector. This is necessary. The tensile strength of the Ni alloy current collector is higher than that of the Cu or Cu alloy current collector because Ni is harder than copper.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to embodiments. Example 1 In this example, a positive electrode current collector will be described. As the current collector, Al foil or Al alloy foil shown in Table 1 having various tensile strengths of 10 μm and 15 μm was used. The Al foil has a purity of 99.9% and a tensile strength of 50 N / mm ² . In addition, Al alloy foil,
1 wt% of each of Si, Fe, Cu, Mn, Zn, and Ti
%, And an Al alloy (tensile strength 100 to 350 N / mm ² ) containing 0.7 to 5 wt% in total weight was used. The positive electrode plate was manufactured as follows. To 100 g of positive electrode active material LiMn ₂ O ₄ having reversibility for charge and discharge, 10 g of carbon powder as a conductive agent and 5 g of polyvinylidene fluoride as a binder were added, and dimethylformamide was added thereto to form a paste. It was applied on various aluminum foils or aluminum alloy foils shown in 1 and dried. The positive electrode plate thus obtained had a thickness of 275 μm. A positive electrode plate using a current collector having the same tensile strength was cut into 5 cm square pieces, passed through a rolling roller 5 to 7 times, respectively, and rolled so that the positive electrode plate thickness after rolling was 170 μm. Then, the presence or absence of breakage of the edge portion of the current collector in the rolled electrode was checked. The number of samples was 100 each. Table 1 shows the yields of each of the current collectors, in which the edge portion of the current collector did not break. The yield is a value obtained by dividing the number of non-defective products by 100 samples.

[0011]

[Table 1]

As shown in Table 1, the higher the tensile strength, the less the fracture of the edge portion after rolling and the higher the yield. Tensile strength is 100N /
The yield reaches 70% when a current collector plate having a size of mm ² or more is used. In order to improve the yield by using a current collector having a tensile strength of less than 100 N / mm ² , use a current collector having a thickness of 15 μm or more, or use a positive electrode having a thickness of 170 μm after rolling.
Need to be bigger. Then, the filling amount of the positive electrode active material is reduced, and the battery capacity is reduced. From the above results, it is preferable to use an Al alloy having a tensile strength of 100 N / mm ² or more for the positive electrode current collector.

[Example 2] In this example, a battery was constructed using the positive electrode plate prepared in Example 1 and its characteristics were evaluated. The positive electrode plate has the tensile strength of 300 N / mm ² shown in Example 1 and the thickness of the positive electrode current collector is 10 μm and 15 μm.
Was used. The negative electrode plate was prepared by adding 5 g of polyvinylidene fluoride as a binder to 100 g of artificial graphite, which is a negative electrode active material having reversibility for charging and discharging, and made a paste using dimethylformamide, and had a current collector thickness of 20 μm. After being coated on the Cu foil, dried, and rolled, it was manufactured. A vertical cross-sectional view of the battery used in this example is shown in FIG. Positive plate 1
And a negative electrode plate 2 and a band-shaped porous polypropylene separator 3 wider than the electrode plate interposed between the negative electrode plate 2 and the both electrode plates are spirally wound to form an electrode group. 7 is placed and inserted in the battery case 8, a step is formed on the upper part of the battery case 8, a non-aqueous electrolyte is injected, and the battery is sealed with a synthetic resin sealing plate 9 provided with a positive electrode terminal 10. And The non-aqueous electrolyte used was a mixed solution of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 in which 1 mol / l lithium hexafluorophosphate (LiPF ₆ ) was dissolved. Further, leads 4 and 5 made of the same material as the current collector are connected to the positive electrode plate and the negative electrode plate by spot welding, respectively.

As a comparative example, a similar battery was manufactured by using a conventionally used positive electrode current collector having a thickness of 25 μm. In these batteries, the electric capacity of the negative electrode is larger than that of the positive electrode, and the capacity of the battery is determined by the capacity of the positive electrode.
These batteries were operated at 4.3 V at a constant current of 0.5 mA / cm ^2.
Was repeatedly charged and discharged up to 3.0 V. Table 2 shows the discharge capacity at the 10th cycle and the capacity retention rate at the 100th cycle. Regarding the discharge capacity, the discharge capacity of the battery having a thickness of the positive electrode current collector of 25 μm shown as the comparative example was 10
Shown as 0. The discharge capacity retention rate was calculated by the following formula. Capacity retention rate (%) = 100 × (100th cycle discharge capacity) / (10th cycle discharge capacity)

[0015]

[Table 2]

As shown in Table 2, it can be seen that the thinner the positive electrode current collector, the larger the discharge capacity. This is because the positive electrode active material filling amount was increased by making the thickness of the current collector thinner. Further, all the batteries had a capacity retention ratio at the 100th cycle of 96% or more, and showed excellent cycle characteristics.

[Embodiment 3] In this embodiment, a negative electrode current collector will be described. The thickness of the current collector is 10 μm and 12 μm
The Cu or Cu alloy foils shown in Table 3 having various tensile strengths were used. The Cu foil contains electrolytic copper (tensile strength 200 to 350 N / mm ² ) having different cold working ratios, and the Cu alloy foil contains Cu alloy containing 1 to 2 wt% of Ti (tensile strength 400 ~500N / mm ²⁾ were used, respectively. The negative electrode plate was prepared by adding 5 g of polyvinylidene fluoride as a binder to 100 g of artificial graphite, which is a negative electrode active material having reversibility for charge and discharge, and made a paste using dimethylformamide, and applied on various Cu foils. Then, it was dried. The thickness of the negative electrode plate thus obtained was 200 μm. A negative electrode plate using a current collector having the same tensile strength was cut into 5 cm squares, and the rolling roller was cut 9 times to 10 times, respectively.
It was passed through each time and rolled so that the negative electrode thickness after rolling was 150 μm. Then, the presence or absence of breakage of the edge portion of the current collector in the rolled electrode was checked. Table 3 shows the yields obtained in the same manner as in Example 1.

[0018]

[Table 3]

As shown in Table 3, it can be seen that the higher the tensile strength, the less the fracture of the edge portion after rolling and the higher the yield. Tensile strength is 250 N /
The yield reaches 74% when a current collector plate of mm ² or more is used. In order to improve the yield by using a current collector having a tensile strength of less than 250 N / mm ² , the thickness is 12 μm.
Use a collector plate of m or more, or set the thickness of the negative electrode plate after rolling to 1
It is necessary to set the thickness to 50 μm or more, so that the filling amount of the negative electrode active material is reduced and the battery capacity is reduced. From the above results, the negative electrode current collector has a tensile strength of 250 N / containing Cu.
It is preferable to use a metal of mm ² or more.

Example 4 In this example, a battery was constructed using the negative electrode plate prepared in Example 3 and its characteristics were evaluated. The negative electrode plate has the tensile strength of 350 N / mm ² shown in Example 3 and the thickness of the negative electrode current collector is 10 μm and 12 μm.
Was used. The positive electrode plate is made of positive electrode active material LiMn ₂ O ₄
To 100 g, 10 g of carbon powder as a conductive agent and 5 g of polyvinylidene fluoride as a binder were added and made into a paste using dimethylformamide, and the thickness of the current collector was 25 μm.
It was prepared by coating on 1-foil, drying and rolling. The battery manufacturing conditions are the same as in Example 2. Further, as a comparative example, a similar battery was manufactured using a conventionally used negative electrode current collector having a thickness of 20 μm. In these batteries, the electric capacity of the positive electrode is larger than that of the negative electrode, and the capacity of the battery is determined by the capacity of the negative electrode. These batteries are 0.5mA /
The battery was charged to 4.3 V with a constant current of cm ² and discharged to 3.0 V for charging and discharging. Table 4 shows the discharge capacity at the 10th cycle and the capacity retention rate at the 100th cycle. Regarding the discharge capacity, the discharge capacity of a battery having a negative electrode current collector thickness of 20 μm shown as a comparative example is shown as 100.

[0021]

[Table 4]

As shown in Table 4, the thinner the negative electrode current collector, the larger the discharge capacity. This is because the negative electrode active material filling amount was increased by reducing the thickness of the current collector. Further, all the batteries had a capacity retention ratio at the 100th cycle of 96% or more, and showed excellent cycle characteristics.

[Embodiment 5] In this embodiment, a negative electrode current collector will be described. Table 5 shows Ni alloy foils having various tensile strengths of 10 μm and 12 μm in thickness. The Ni alloy foil was obtained by hot rolling a Ni alloy containing 0.05 wt% Co (tensile strength: 300 to 400 N / m).
m ² ) or cold-rolled (tensile strength 400
˜600 N / mm ² ) was used. The negative electrode plate was prepared by adding 5 g of polyvinylidene fluoride as a binder to 100 g of artificial graphite, which is a negative electrode active material having reversibility for charge and discharge, and made a paste using dimethylformamide.
It was prepared by coating on an alloy foil and drying. The negative electrode plate thus obtained had a thickness of 220 μm. A negative electrode plate using a current collector having the same tensile strength was cut into 5 cm square pieces, passed through a rolling roller 10 times to 12 times each, and rolled to have a negative electrode thickness of 170 μm after rolling. Then, the presence or absence of breakage of the edge portion of the current collector in the rolled electrode was checked. The yield obtained in the same manner as in Example 1 is shown in Table 4.

[0024]

[Table 5]

As shown in Table 5, it can be seen that the higher the tensile strength, the less the fracture of the edge portion after rolling and the higher the yield. Tensile strength is 350 N /
The yield reaches 77% when a current collector plate of mm ² or more is used. In order to improve the yield by using a current collector having a tensile strength of less than 350 N / mm ² , use a current collector having a thickness of 12 μm or more, or use a negative electrode plate having a thickness of 170 μm after rolling.
Since it is necessary to make it m or more, the filling amount of the negative electrode active material is reduced, and the battery capacity is reduced. From the above results, the negative electrode current collector has a tensile strength including Ni of 350 N / mm ²
It is preferable to use the above metals.

Example 6 In this example, a battery was constructed using the negative electrode plate prepared in Example 5 and its characteristics were evaluated. The negative electrode plate has the tensile strength of 450 N / mm ² shown in Example 5, and the thickness of the negative electrode current collector is 10 μm and 12 μm.
Was used. The positive electrode plate is made of positive electrode active material LiMn ₂ O ₄
To 100 g, 10 g of carbon powder as a conductive agent and 5 g of polyvinylidene fluoride as a binder were added to form a paste using dimethylformamide, and the paste was applied on an Al foil having a thickness of 25 μm and dried. It was rolled and produced. The battery manufacturing conditions are the same as in Example 2. In addition, as a comparative example, the thickness of the negative electrode current collector that has been conventionally used is 20 μm.
A similar battery was produced by using m. In these batteries, the electric capacity of the positive electrode is larger than that of the negative electrode, and the capacity of the battery is determined by the capacity of the negative electrode. 0.5m for these batteries
The battery was charged up to 4.3 V with a constant current of A / cm ² and discharged up to 3.0 V, which was repeated. Table 6 shows the discharge capacity at the 10th cycle and the capacity retention rate at the 100th cycle.
The discharge capacity is shown by setting the discharge capacity of the battery having a negative electrode current collector thickness of 20 μm shown as a comparative example to 100.

[0027]

[Table 6]

As shown in Table 6, the thinner the negative electrode current collector, the larger the discharge capacity. This is because the negative electrode active material filling amount was increased by making the thickness of the current collector thinner. Further, all the batteries had a capacity retention ratio at the 100th cycle of 96% or more, and showed excellent cycle characteristics. In addition, in the above-mentioned embodiment, the cylindrical battery has been described, but it goes without saying that the same effect can be obtained even with a rectangular battery using an electrode plate having a rolling process.

[0029]

According to the present invention, it is possible to provide a high energy density non-aqueous electrolyte secondary battery.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view of a secondary battery used in an example of the present invention.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode lead 5 Negative electrode lead 6 and 7 Insulating plate 8 Battery case 9 Sealing plate 10 Positive electrode terminal

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yasuhiko Mito 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Inside the corporation

Claims (3)

[Claims] 1. A chargeable / dischargeable positive electrode, a non-aqueous electrolyte, and a chargeable / dischargeable negative electrode, wherein the positive electrode current collector is 100.
A non-aqueous electrolyte secondary battery, which is an Al alloy having a tensile strength of N / mm ² or more. 2. A chargeable / dischargeable positive electrode, a nonaqueous electrolyte, and a chargeable / dischargeable negative electrode, wherein the negative electrode current collector is 250.
A non-aqueous electrolyte secondary battery, which is Cu or a Cu alloy having a tensile strength of N / mm ² or more. 3. A chargeable / dischargeable positive electrode, a nonaqueous electrolyte, and a chargeable / dischargeable negative electrode, wherein the negative electrode current collector is 350.
A non-aqueous electrolyte secondary battery, which is a Ni alloy having a tensile strength of N / mm ² or more.