JP5788062B1 - Negative electrode current collector for all solid state battery and all solid state battery - Google Patents

Abstract

An object of the present invention is to provide a negative electrode current collector for an all solid state battery and an all solid state, which suppresses the formation of copper sulfide and is excellent in conductivity by applying nickel plating to a copper foil used as a negative electrode current collector. Provide batteries. A negative electrode current collector for an all-solid-state battery in which a nickel film is formed on both surfaces of an electrolytic copper foil, a rolled copper foil or a copper alloy foil, wherein the thickness of one surface of the nickel film is converted to mass per unit area. And 4.5 g / m2 to 18 g / m2, and the electrolytic copper foil, the rolled copper foil and the alloy foil have a residual stress of −40 MPa or more. [Selection figure] None

Description

  The present invention relates to a negative electrode current collector for an all solid state battery and an all solid state battery, and more particularly, to use a negative electrode current collector for an all solid state battery and its negative electrode current collector capable of suppressing deterioration of battery characteristics during charge and discharge. It relates to an all-solid-state battery.

In recent years, lithium ion batteries have been put into practical use as batteries having high voltage and high energy density. Due to the widespread use of lithium ion batteries in a wide range of fields and the demand for higher performance, research has been conducted on lithium ion batteries from various viewpoints.
Among them, compared to the conventionally used non-aqueous electrolyte type lithium ion batteries, practical application of an all-solid battery that does not use an electrolyte is expected. The all-solid-state battery can simplify a system necessary for improving safety, and can manufacture a battery having a structure in which electrodes and an electrolyte are directly arranged in series. In current lithium ion battery modules, battery cells composed of a negative electrode, an electrolyte, and a positive electrode are connected in series using a copper wire, a bus bar, or the like. On the other hand, in an all-solid battery, these can be realized in one battery cell. Therefore, since the metal package for sealing the battery cell, the copper wire and the bus bar for connecting the battery cell can be omitted, the energy density of the battery can be greatly increased.

Patent Document 1 describes a sulfide solid electrolyte glass containing an ion conductor composed of Li ₄ P ₂ S ₆ and LiI. Among them, there is a description that copper, carbon, nickel, stainless steel (SUS) can be used for the negative electrode current collector of the lithium solid state battery, and SUS is particularly preferable.

  In Patent Document 2, in order to improve the characteristics of an all-solid-state battery, a conductive layer that is more easily deformed (more easily dented) than a current collector when a compressive force is applied, and a first active material layer and a current collector Between the two. According to this configuration, the contact area between the first active material layer and the conductive layer can be made larger than the contact area between the first active material layer and the current collector when no conductive layer is interposed. By adopting such a configuration, it becomes easier to increase the current collection efficiency, increase the discharge capacity, and reduce the battery resistance as compared with the case where no conductive layer is interposed. It is described that the performance of the all-solid battery can be improved thereby.

JP 2014-35865 A JP 2014-35888 A

In a conventional lithium ion secondary battery, a nonaqueous organic electrolyte such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), or the like is used as the electrolyte.
Since these organic electrolytes are flammable, there is a risk that the battery will ignite and burn if a short circuit or the like occurs in the battery. Therefore, a battery using a solid electrolyte has been developed without using the above electrolytic solution. In addition, a battery using this solid electrolyte is expected to be able to simplify the control system, for example, by putting a plurality of single cells in series in one case, and to realize a battery pack with a high energy density.
However, sulfides are used for this solid electrolyte. Therefore, when a conventional copper foil used as a negative electrode current collector in a lithium ion secondary battery is used, a sulfide in the electrolyte reacts with copper in the current collector to produce a copper sulfide by-product. As a result, there is a problem that battery characteristics such as discharge capacity and initial capacity deteriorate.

Moreover, when stainless steel (SUS) is used for the negative electrode current collector disclosed in Patent Document 1, there are problems in workability such as difficulty in thinning because SUS is hard. In addition, since the conductivity is as low as 1/10 or less that of copper, there is a problem in the high rate (large current) characteristics of the battery. Further, when carbon is used as an electrode current collector, there is a disadvantage that lithium reacts with carbon and irreversible capacity increases. When copper is used as a current collector, a reaction between copper and sulfide occurs, resulting in an increase in resistance and a decrease in cycle characteristics. When nickel is used as the current collector, although the conductivity is lower than that of the copper foil, the characteristics as sulfidation resistance are suitable. However, there is a drawback that the price of nickel is high.
Further, when the current collector disclosed in Patent Document 2 has a residual stress, the current collector is deformed such as curl, and the above performance improvement effect becomes insufficient.

  In view of the above circumstances, the object of the present invention is to provide a copper foil used as a negative electrode current collector with nickel plating that has a low residual stress of copper, thereby suppressing the formation of copper sulfide and providing excellent conductivity. An object of the present invention is to provide a negative electrode current collector for a solid battery and an all solid state battery.

The above object of the present invention is achieved by the following means.
(1) A negative electrode current collector for an all-solid-state battery in which a nickel film is formed on both surfaces of an electrolytic copper foil, a rolled copper foil or a copper alloy foil, wherein the thickness on one side of the nickel film is in terms of mass per unit area. was ^{4.5g / m 2 ~18g / m 2} , the electrolytic copper foil, rolled copper foil and the negative electrode current collector for the all-solid-state battery residual stress is characterized in that at least -40MPa copper alloy foil.
(2) The negative electrode current collector for an all-solid-state battery according to (1), wherein each of the electrolytic copper foil, the rolled copper foil, and the copper alloy foil has a thickness of 5 to 12 μm.
(3) The ten-point average roughness Rz on both sides of the negative electrode current collector for an all-solid battery is 3.5 μm or less, and the difference between the ten-point average roughness Rz on both sides of the negative electrode current collector for an all-solid battery The negative electrode current collector for an all-solid-state battery according to (1) or (2), characterized in that is within 1.5 μm.
(4) The 10-point average roughness Rz of both surfaces of the negative electrode current collector for an all-solid battery is 3.5 μm or less, and the difference between the 10-point average roughness Rz of both surfaces of the negative electrode current collector for the all-solid battery The negative electrode current collector for an all-solid-state battery according to any one of (1) to (3), characterized in that is within 1.0 μm.
(5) The all-solid-state battery according to any one of (1) to (4), wherein the electrolytic copper foil, the rolled copper foil or the copper alloy foil has a 0.2% proof stress of 250 MPa or more. Negative electrode current collector.
(6) A solid electrolyte containing sulfur, wherein the negative electrode current collector according to any one of (1) to (5) is used as a negative electrode current collector. Solid battery.

  In the present invention, the negative electrode current collector of the all-solid-state battery is subjected to nickel plating with low copper residual stress, so that the reaction between the all-solid electrolyte containing sulfide and the current collector can be suppressed, and the electrical resistance of the current collector It is possible to improve the conductivity by reducing the above.

It is typical sectional drawing which showed preferable one Embodiment concerning the said solid battery of this invention. It is the X-ray diffraction pattern figure which showed an example of the diffraction pattern obtained by performing the residual stress measurement of copper using the X-ray analyzer with respect to the copper foil which gave the nickel membrane | film | coat.

A preferred embodiment of an all-solid battery according to the present invention will be described below with reference to FIG.
As shown in FIG. 1, the all-solid battery 10 includes an all-solid electrolyte layer 11, a positive electrode active material layer 12 and a positive electrode current collector layer 13 that are sequentially connected to one surface of the all-solid electrolyte layer 11, and The negative electrode active material layer 14 and the negative electrode current collector layer 15 are sequentially connected to a surface opposite to the one surface.
The all solid electrolyte layer 11 is made of, for example, Li ₁₀ GeP ₂ S ₁₂ , Li ₆ PS ₅ Cl, or Li ₇ P ₃ S ₁₁ .
The positive electrode active material layer 12 is made of, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ or the like.
The positive electrode current collector layer 13 is made of, for example, aluminum.
The negative electrode active material layer 14 is made of, for example, natural graphite, artificial graphite, lithium titanate, or the like.
The negative electrode current collector layer 15 is formed after a nickel film having nickel as a main component is formed on both surfaces of an electrolytic copper foil and a rolled copper foil (hereinafter sometimes collectively referred to as a copper foil). The residual stress of copper in the negative electrode current collector layer 15 is -40 MPa or more.

  As the copper foil before forming the nickel film, an electrolytic copper foil or a rolled copper foil can be used, and of course, a copper alloy foil made of a copper alloy may be used. The foil thickness is preferably 5 to 12 μm, and more preferably 6 to 10 μm. If the foil thickness is too thin, handling of the copper foil may be difficult. In addition, when the battery is configured, the internal resistance of the battery may increase. Even if the foil thickness is too thick, there is no problem in the characteristics as a battery. However, if the foil thickness is too thick, the volume energy density and mass energy density may decrease.

The 0.2% proof stress of the copper foil is preferably 250 MPa or more, more preferably 400 MPa or more, and further preferably 450 MPa or more. When copper foil with 0.2% proof stress is too low, the current collector layer is likely to be plastically deformed due to the stress generated during charge / discharge of the battery, and the current collector layer is deformed during the charge / discharge cycle. There is a possibility of short circuit.
In the case of a rolled copper foil, the mechanical properties are anisotropic, and the tensile strength and 0.2% yield strength in the direction of 45 degrees with respect to the rolling direction (MD direction) are the lowest. In the present invention, the 0.2% proof stress means a value in a direction forming 45 degrees with respect to the rolling direction in the case of a rolled copper foil.
The 0.2% proof stress is 250 MPa or more in the case of an electrolytic copper foil by adjusting the electrolysis conditions, additives, and the like during foil production. In the case of a rolled copper foil, this can be achieved by adjusting the components.
The electrolytic copper foil having a 0.2% proof stress of 250 MPa or more can be obtained by a known method, for example, a sulfate-copper sulfate electrolyte, a thiourea-based organic additive, a polymeric polysaccharide such as glue or gelatin, and chloride ion. It can obtain by adding in combination.

The thickness of the nickel coating is preferably 4.5g ^{/ m 2} ~18g ^/ m 2 in terms of the weight per unit area of the nickel, more preferably 6.0~16.0g / ^{m 2,} 9.0~ 13.0 g / m ² is more preferable. If the thickness is too small, pinholes and the like are generated in the nickel film, and the film cannot be formed on the copper foil with a uniform thickness, so that the formation of copper sulfide cannot be suppressed, leading to deterioration in battery characteristics. If the thickness is too thick, the nickel film can prevent the formation of copper sulfide, but problems such as decrease in conductivity and weldability of the foil occur, and the residual stress of copper in the negative electrode current collector layer 15 increases. Naturally, increasing the thickness of the nickel coating leads to an increase in material costs and processing costs, which is not desirable. Therefore, as described above, the thickness of the nickel coating is to 4.5g ^{/ m 2} ~18g ^/ m 2 in terms of the weight per unit area.

  The thickness of the nickel film can be measured by atomic absorption, high frequency inductively coupled plasma (ICP) emission spectroscopy, fluorescent X-ray analysis, gravimetry, or the like.

  The residual stress of the copper (Cu) foil in the negative electrode current collector of the present invention is preferably −40 MPa or more, more preferably −30 MPa or more, and further preferably −20 MPa or more. Here, the residual stress of the Cu foil refers to an internal stress generated by introducing strain into the crystal lattice of the Cu foil due to an external influence. The sign of the residual stress value indicates a tensile stress when positive and a compressive stress when negative. If the residual stress of the Cu foil is −40 MPa or more (that is, an absolute value of 40 MPa or less), it is possible to prevent deterioration of battery characteristics due to curving of the current collector.

  In order to adjust the residual stress of copper, it is effective to control the thickness of a nickel film (for example, nickel plating film).

  There is no restriction | limiting in particular about the ten-point average roughness (Rz) after forming a nickel membrane | film | coat. It is preferably 3.5 μm or less on each surface, and the difference in 10-point average roughness (Rz) of both surfaces is preferably 1.5 μm or less, and more preferably 1.0 μm or less. If the ten-point average roughness is too large, it becomes difficult for the active material to uniformly enter the uneven portions of the current collector, and an active material layer that cannot contribute to the reaction may be generated. Moreover, if the difference in ten-point average roughness on both sides is large, it may be difficult to uniformly apply the same amount of active material on both sides of the current collector.

  Below, based on an Example, this invention is demonstrated further in detail. The present invention is not limited to this.

  As a method of forming the nickel film, for example, there is a method of forming by nickel plating, and examples of preferable nickel bath and plating conditions are shown below.

As the copper foil before the nickel film was applied, double-sided glossy foil NC-WS manufactured by Furukawa Electric Co., Ltd., TPC foil manufactured by Nippon Foil Co., Ltd., and alloy copper foil manufactured by Nippon Foil Co., Ltd. were used. In some examples, a copper foil heat-softened by heat treatment was used to adjust the strength.
Nickel film generation conditions Pretreatment: Meltex manufactured copper foil was subjected to electrolytic treatment at 60 ° C. and 2.5 A / dm ² for 30 seconds with a cleaner 160S (60 g / L), and then in 10 g / L sulfuric acid. Processed for 60 seconds.
Nickel plating treatment: A nickel film was applied under the following conditions. The film formation conditions of the nickel film shown below are examples, and the present invention is not limited to the following method.
(Example 1) Nickel sulfamate bath:
Nickel sulfamate 500 g / L, boric acid 30 g / L, nickel (II) chloride hexahydrate 30 g / L, pH 3.5 to 4.0, at a current density of 10 A / dm ^{2 in} a bath at 50 ° C. Form. The film thickness is controlled by the energization time.
(Example 2) Nickel sulfate bath 1:
It is formed at a current density of 10 A / dm ^{2 in} a bath of nickel sulfate hexahydrate 250 g / L, boric acid 30 g / L, pH 3.5 to 4.0, bath temperature 50 ° C. The film thickness is controlled by the energization time.
(Example 3) Nickel sulfate bath 2:
Nickel sulfate hexahydrate 250 g / L, boric acid 30 g / L, hypophosphorous acid Na 10 g / L, pH 3.5 to 4.0, formed at a current density of 10 A / dm ^{2 in} a bath temperature of 50 ° C. . The film thickness is controlled by the energization time.

The nickel coating is mainly composed of nickel. The main component of nickel preferably includes 99.0% or more of nickel, more preferably 99.5% or more of nickel, and still more preferably 99.7% or more of nickel.
Depending on the formation method and conditions of the nickel coating, phosphorus (P), sulfur (S), carbon (C), nitrogen (N), and oxygen (O) may be incorporated into the nickel coating. Acceptable as a nickel coating. Most preferably, these elements are not included, and even if included from the viewpoint of appearance after plating, corrosion resistance, stress, etc., 1.0% or less is preferable, 0.5% or less is more preferable, and 3% or less is more preferable.

  Note that the nickel film may be formed by a method other than nickel plating.

<Measurement of residual stress in copper>
The residual stress of copper was measured using a D8 DISCOVER X-ray analyzer (manufactured by Bruker Avex Co., Ltd.) on the copper foil having the nickel film described in Examples and Comparative Examples. This apparatus uses a two-dimensional detector (VANTEC-500). The distance between the sample and the detector is 200 mm, and the 2θ angle of the detector is 95 °. The diffraction pattern can be measured simultaneously. The sample inclination angle ψ was set to 15 ° and 45 °, and the sample rotation angle φ was measured every 30 ° in the range of 0 to 180 °, respectively, and the diffraction pattern of a total of 14 frames was measured.

An example of the obtained diffraction pattern is shown in FIG.
As shown in FIG. 2, peak 1 which is a diffraction peak from the Cu (311) plane, peak 3 which is a diffraction peak from the Cu (222) plane, and a peak which is a diffraction peak from the Ni (311) plane depending on the sample. 2. Peak 4 which is a diffraction peak from the Ni (222) plane is observed.
For measurement of Cu residual stress, peak 1 which is a diffraction peak from the Cu (311) plane was used. Peak 1 was equally divided into 10 in the x direction, and the sample tilt angle ψ at each point and the position 2θ where peak 1 exists were obtained. Thus, 10 points of information can be obtained from one diffraction pattern (diffraction peak map). The residual stress is obtained by integrating 140 points of information obtained from these 14 diffraction patterns. The following equation (1) is used to calculate the residual stress σ, and a total of 140 obtained (ψ, θ) is fitted by the least square method, so that the residual stress σ1 acting in the direction parallel to the incident X-ray is obtained. And the residual stress σ2 acting in the direction perpendicular to the incident X-ray. In this specification, the average value of σ1 and σ2 is shown as the residual stress of copper.

<Measurement of 0.2% yield strength>
It measured according to international standard IPC-TM-650.
<Measurement method of initial capacity>
Initial conditions Charging: Constant current charging at a current equivalent to 0.1 C. After reaching 0.02 V (vs. Li / Li +), charging at a constant potential was completed when the charging current was equivalent to 0.05 C.
Discharge: A constant current was discharged at a current equivalent to 0.1 C, and the discharge was terminated when the voltage reached 1.5V.
<Cycle characteristics>
Cycle characteristics indicate the ratio of battery capacity in% after repeating the discharge to the end-of-discharge voltage and the charge to the end-of-charge voltage 100 times at a rate of 0.5 C, assuming the initial capacity as 100%. Value.
<High rate characteristics>
The high rate characteristic is a value indicating the ratio of the battery capacity in% after repeating the discharge to the end-of-discharge voltage and the charge to the end-of-charge voltage 100 times at an initial capacity of 100% and charging to the end-of-charge voltage. is there.

<Experimental conditions>
Positive electrode active material: LiCoO ₂
Negative electrode active material: natural graphite All solid electrolyte: Li ₁₀ GeP ₂ S ₁₂
A stack type battery was manufactured using the above and tested with a rate characteristic of 0.5 C (high rate test 5 C) and a cycle number of 100 cycles. C is the C rate, and the amount of current that discharges the entire capacity of the battery in one hour is referred to as the 1C rate.
<Evaluation criteria for initial capacity>
The initial capacity when natural graphite is used is 372 mA / g. The initial capacity of 350 mA / g or more is indicated as “A”, 340 mA / g or more and less than 350 mA / g is indicated as “B”, and less than 340 mA / g is indicated as “C”.
<Evaluation criteria for cycle characteristics and high-rate characteristics>
Regarding the cycle characteristics and the high rate characteristics (evaluated at 5C rate), the capacity after 100 cycles is “A”, assuming that 80% or more of the initial capacity is excellent, and “B”, where 70% or more and less than 80% are good. Less than 70% was expressed as “C” as inferior.
The evaluation results are shown in Table 1.

As is clear from Examples 1 to 7, if the Ni mass per unit area on one side is 4.5 g / m ² or more and 18 g / m ² or less and the residual stress of copper is −40 MPa or more, the initial capacity is An evaluation “A” of 350 mA / g or higher, an evaluation “A” of 80% or higher of the cycle characteristics, an evaluation “A” of 80% or higher of the high rate characteristics, or an evaluation “B” of 70% or higher is obtained. It was. Moreover, the 0.2% yield strength of the copper foil was 250 MPa or more. For this reason, the current collector layer is less likely to be deformed due to the stress generated during charging / discharging of the battery. Therefore, the current collector layer is deformed during the charge / discharge cycle, and short circuit is less likely to occur. Therefore, the area of the current collector layer can be increased, and the charge / discharge capacity can be increased.
In contrast, Comparative Example 1 had an initial capacity of 348 mA / g and an evaluation “B”. However, the Ni mass per unit area on one side exceeded the upper limit of 18 g / m ² of the present invention and was 21 g / m ² , and the residual stress of copper was −43 MPa lower than the lower limit of −40 MPa of the present invention. Therefore, the evaluation was “C” with a cycle characteristic of less than 70% and a high rate characteristic of less than 70%, resulting in inferior results.
Comparative Example 2 was evaluated “A” with an initial capacity of 350 mA / g or more. However, the Ni mass per unit area on one side exceeded the upper limit of 18 g / m ² of the present invention and was 36 g / m ² , and the residual stress of copper was −70 MPa lower than the lower limit of −40 MPa of the present invention. Therefore, the evaluation was “C” with a cycle characteristic of less than 70% and a high rate characteristic of less than 60%, resulting in inferior results.
In Comparative Example 3, the Ni mass per unit area on one side was ² g / m ² which is 4.5 g / m ² or less, which is the lower limit of the present invention. For this reason, the initial capacity was 350 mA / g or less, the cycle characteristics were less than 70%, and the high rate characteristics were less than 60%.
Comparative Examples 4 and 5 were excellent with an evaluation “A” having an initial capacity of 350 mA / g or more. However, the residual stress of copper was −50 MPa and −45 MPa which are lower than the lower limit value of −40 MPa of the present invention. Therefore, the cycle characteristics were less than 70% and the high rate characteristics were less than 60%, both of which were evaluated as “C”, resulting in inferior results. Moreover, the 0.2% yield strength of the copper foil was as low as 200 MPa.

Next, Table 2 shows the relationship between the ten-point average roughness (Rz) and the cycle characteristics as an influence of the surface roughness.
Ten-point average roughness (Rz) shown in Table 2 was measured according to JIS B 0601-1994.
For the 10-point average roughness, the copper foil thickness was 10 μm, the Ni weight on one side was 9 g / dm ² , the Cu residual stress was −20 MPa ± 10 MPa, and an electrode in which only the 10-point average roughness of the copper foil was changed was prepared. evaluated.
Regarding the cycle characteristics, the capacity after 100 cycles was evaluated as “A” when 80% or more of the initial capacity was evaluated and “B” when 70% or more and less than 80%.

As is clear from Example 11 (Example 1 in Table 1) to Table 16 in Table 2, the 10-point average roughness on both sides of the copper foil is 3.5 μm or less, and the difference in 10-point average roughness on both sides is 1. When the thickness was 0.5 μm or less, good results were obtained that the cycle characteristics after 100 cycles were 78% or more. That is, good results were obtained in which the cycle characteristics were evaluated as “A” or “B”. In particular, Examples 11 to 15 in which the 10-point average roughness on both sides of the copper foil is 3.5 μm or less and the difference in the 10-point average roughness on both sides is 1.0 μm or less have a cycle characteristic of 82% after 100 cycles. An extremely excellent evaluation result as described above was obtained.
In Examples 18 to 22, the 10-point average roughness of one side of the copper foil is rougher than the specified 3.5 μm, or the difference between the 10-point average roughness of both sides is larger than the specified 1.5 μm. However, the Ni mass per unit area on one side is within the specified range of 4.5 to 18 g / m ² , and the residual stress of copper is within the specified range of −40 MPa or more. In Examples 18 to 22, it was found that the cycle characteristics after 100 cycles were good evaluation “B” of 70% or more.
Thus, it can be seen that the cycle characteristics are particularly good by using a current collector having a small 10-point average roughness on each surface and a small difference in the 10-point average roughness on both surfaces.

DESCRIPTION OF SYMBOLS 10 All-solid-state battery 11 All-solid-state electrolyte layer 12 Positive electrode active material layer 13 Positive electrode collector layer 14 Negative electrode active material layer 15 Negative electrode collector layer

Claims (6)

A negative electrode current collector for an all solid state battery in which a nickel film is formed on both surfaces of an electrolytic copper foil, a rolled copper foil or a copper alloy foil,
Wherein a 4.5g ^{/ m 2} ~18g ^/ m 2 by weight in terms of per a unit area thickness at one side of the nickel coating,
The negative electrode current collector for an all-solid-state battery, wherein the residual stress of the electrolytic copper foil, the rolled copper foil and the alloy foil is -40 MPa or more.   2. The all-solid-state battery negative electrode current collector according to claim 1, wherein each of the electrolytic copper foil, the rolled copper foil, and the copper alloy foil has a thickness of 5 to 12 μm.   The 10-point average roughness Rz on both sides of the all-solid battery negative electrode current collector is 3.5 μm or less, and the difference between the 10-point average roughness Rz on both sides of the all-solid battery negative electrode current collector is 1. The negative electrode current collector for an all-solid battery according to claim 1 or 2, wherein the current collector is within 5 µm.   The 10-point average roughness Rz on both sides of the all-solid battery negative electrode current collector is 3.5 μm or less, and the difference between the 10-point average roughness Rz on both sides of the all-solid battery negative electrode current collector is 1. The anode current collector for an all solid state battery according to any one of claims 1 to 3, wherein the anode current collector is within 0 µm.   The negative electrode current collector for an all-solid-state battery according to any one of claims 1 to 4, wherein the electrolytic copper foil, the rolled copper foil, or the copper alloy foil has a 0.2% proof stress of 250 MPa or more. An all-solid battery comprising a solid electrolyte containing sulfur and using the negative electrode current collector for an all-solid battery according to claim 1 as the negative electrode current collector.