JP5512332B2 - Method for designing negative electrode for secondary battery, method for producing negative electrode for secondary battery, negative electrode for secondary battery, and negative electrode copper foil for secondary battery - Google Patents

Description

  The present invention relates to a method for producing a negative electrode for a secondary battery, a negative electrode for a secondary battery, and a negative electrode copper foil for a secondary battery. In particular, the present invention relates to a method for producing a negative electrode for a lithium ion secondary battery, a negative electrode for a secondary battery, and a negative electrode copper foil for a secondary battery.

  Lithium ion secondary batteries used for communication devices such as mobile phones, notebook computers, power tools, hybrid cars, electric vehicles, large-scale power storage, etc. include current collectors and active materials such as carbon and graphite A negative electrode for a lithium ion secondary battery comprising a conductive auxiliary such as acetylene black, a layer having a binder such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and polyimide (PI). It is used.

  And as above-mentioned, the carbon-type material is mainly used for the active material of the negative electrode of a lithium ion secondary battery. However, the charge / discharge capacity of a lithium ion secondary battery using an active material made of a carbon-based material almost reaches the theoretical value of 372 mAh / g. Therefore, for the purpose of further increasing the capacity, practical application of an active material for a negative electrode mainly composed of Sn having a charge / discharge capacity of 990 mAh / g or Si having 4200 mAh / g has been studied.

  Conventionally, as a negative electrode for a lithium ion secondary battery, a current collector and a layer made of carbon or graphite material, including an active material provided on the current collector and a binder made of a thermoplastic resin, the active material is Sn There is known a negative electrode for a lithium ion secondary battery, which is made of an alloy powder containing bismuth and the binder is made of a resin having an elastic modulus of 3.0 GPa or more (for example, see Patent Document 1).

  Since the negative electrode for lithium ion secondary batteries described in Patent Document 1 uses an alloy powder containing Sn as an active material, a lithium ion secondary battery that can exhibit good charge / discharge cycle characteristics can be provided.

JP 2007-149604 A

  However, the negative electrode for a lithium ion secondary battery described in Patent Document 1 has a large volume change due to charge / discharge compared to the case where a carbon-based material is used as the active material. Peeling and falling off of materials are likely to occur. As a result, in the negative electrode for a lithium ion secondary battery described in Patent Document 1, the battery capacity decreases due to the reduction in the electrical connection between the current collector and the active material due to the peeling and dropping of the active material. In addition, the life of the lithium ion secondary battery may be shortened.

  Therefore, the objective of this invention is providing the manufacturing method of the negative electrode for secondary batteries excellent in charging / discharging cycling characteristics, the negative electrode for secondary batteries, and the negative electrode copper foil for secondary batteries.

In order to achieve the above object, the present invention includes a copper foil preparation step of preparing a copper foil and an active material layer formation step of forming an active material layer on the surface of the copper foil, and t _AM × σ _AM ≦ 0. 5 × t _Cu × σ _Cu (where t _AM is the thickness of the active material layer, σ _AM is the stress generated in the active material layer during charging, t _Cu is the thickness of the copper foil, and σ _Cu is the thickness of the copper foil. A method for producing a negative electrode for a secondary battery satisfying (2% yield strength) is provided.

  Moreover, in the manufacturing method of the said negative electrode for secondary batteries, it is preferable that copper foil has 0.2% yield strength of 350 Mpa or more, after giving a heating for 30 minutes at 200 degreeC.

  In the method for producing a secondary battery negative electrode, the active material layer is preferably formed mainly from Sn or Si.

In order to achieve the above object, the present invention includes a copper foil and an active material layer provided on the surface of the copper foil, and includes t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu (where t _AM Is the thickness of the active material layer, σ _AM is the stress generated in the active material layer during charging, t _Cu is the thickness of the copper foil, and σ _Cu is the 0.2% proof stress of the copper foil) Provided.

  In the secondary battery negative electrode, the active material layer is preferably formed mainly from Sn or Si.

In order to achieve the above object, the present invention provides a negative electrode copper foil for a secondary battery that functions as a negative electrode for a secondary battery by providing an active material layer, and has a region on the surface where the active material layer is provided. Provided with copper foil, t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu (where t _AM is the thickness of the active material layer, σ _AM is the stress generated in the active material layer during charging, and t _Cu is copper A negative electrode copper foil for a secondary battery that satisfies the foil thickness (σ _Cu is 0.2% proof stress of copper foil) is provided.

  Moreover, in the said negative electrode copper foil for secondary batteries, it is preferable that copper foil has 0.2% yield strength of 350 Mpa or more, after giving a heating for 30 minutes at 200 degreeC.

  In the negative electrode copper foil for a secondary battery, the active material layer is preferably formed mainly from Sn or Si.

  According to the method for manufacturing a negative electrode for a secondary battery, the negative electrode for a secondary battery, and the negative electrode copper foil for a secondary battery according to the present invention, the method for manufacturing a negative electrode for a secondary battery excellent in charge / discharge cycle characteristics, and the secondary battery A negative electrode for a battery and a negative electrode copper foil for a secondary battery can be provided.

It is a figure which shows the manufacturing process of the negative electrode for secondary batteries which concerns on embodiment of this invention. In the negative electrode copper foil for secondary batteries which concerns on this Embodiment, it is sectional drawing of the negative electrode copper foil for secondary batteries in which curvature generate | occur | produced. In the negative electrode copper foil for secondary batteries which concerns on this Embodiment, it is a figure which shows distribution of the stress of the negative electrode copper foil for secondary batteries in which curvature generate | occur | produced. It is the figure which showed the relationship of the tensile strength with respect to the heat processing temperature of each copper alloy. The product (t _Cu × σ _Cu ) of the 0.2% proof stress of the copper foil and the thickness of the copper foil is taken on the horizontal axis, and the thickness (t _NiSn ) of the Ni—Sn alloy plating as the active material layer is _taken on the vertical axis, This is a plotted graph. It is a graph at the time of employ | adopting 897 Mpa as 0.2% yield strength at the time of charge of Ni-Sn alloy plating.

[Summary of embodiment]
In a method for producing a negative electrode for a secondary battery comprising a copper foil having an active material layer, a copper foil preparation step for preparing the copper foil, and an active material layer formation step for forming the active material layer on the surface of the copper foil, T _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu (where t _AM is the thickness of the active material layer, σ _AM is the stress generated in the active material layer during charging, and t _Cu is the above A method for producing a negative electrode for a secondary battery that satisfies the thickness of copper foil, σ _Cu is 0.2% proof stress of the copper foil) is provided.

[Embodiment]
FIG. 1 shows an example of a manufacturing process of a negative electrode for a secondary battery according to an embodiment of the present invention.

  First, it is usually difficult to calculate the stress generated in the active material layer during charging. Therefore, first, an active material layer is formed on “one side” of the copper foil, and charging / discharging is performed to examine whether the copper foil is plastically deformed or elastically deformed. At this time, it is necessary to prepare a copper foil having a changed thickness and / or 0.2% proof stress, or to change the thickness of the active material layer. Based on this result, the stress generated during charging of the active material layer to be used is calculated. Details are described below.

  The negative electrode 1 for a secondary battery according to the present embodiment includes a copper foil 10 as a negative electrode copper foil for a secondary battery, and an active material layer 12 provided on the surface of the copper foil 10. Such a negative electrode 1 for a secondary battery is manufactured as follows. First, a copper foil 10 having a predetermined thickness is prepared (copper foil preparation step, FIG. 1 (a)). Here, in a copper foil preparation process, after performing the heating for 30 minutes at 200 degreeC, the copper foil 10 which has 0.2% yield strength of 350 Mpa or more is prepared. Then, a cleaning process is performed on the surface of the copper foil 10. The cleaning process is performed by, for example, cathodic electrolytic degreasing, anodic electrolytic pickling, and / or an immersion process using an oxidizing agent.

  Next, when the active material layer 12 is formed by alloy plating, the surface of the copper foil 10 is preferably subjected to rough plating. By roughening the surface of the copper foil 10 by roughening plating, the adhesion between the copper foil 10 and the active material layer 12 can be improved (that is, the copper foil 10 and the active material layer 12 are bonded by the anchor effect). Improved adhesion). In addition, when providing the active material layer 12 on the surface of the copper foil 10 using a binder containing polyvinylidene fluoride (PVDF), polyimide (PI), etc., depending on the blending ratio of PVDF and / or PI added to the binder, The surface of the copper foil 10 need not be roughened.

  Subsequently, an active material layer 12 is formed on the surface of the copper foil 10 (active material layer forming step, FIG. 1B). The active material layer 12 is mainly formed from Sn or Si. For example, the active material layer 12 can be formed from a Ni—Sn plating film made of a Ni—Sn alloy. The active material layer may be formed by a method of kneading fine powder mainly composed of Si or Sn together with a binder and / or a conductive agent, or by sputtering or electron beam evaporation, in addition to the above-described plating method. It can also be formed by a film forming method.

  2 shows an outline of a cross section of the negative electrode copper foil for a secondary battery in which warpage has occurred in the negative electrode copper foil for a secondary battery according to the present embodiment, and FIG. 3 shows the secondary battery according to the present embodiment. It is a figure which shows the distribution of the stress of the negative electrode copper foil for secondary batteries in which curvature generate | occur | produced in the negative electrode copper foil for batteries.

  First, Stoney's formula (1) is known as a relationship between stress and deflection of a thin film.

σ _NiSn = Et _Cu ² / 6rt _NiSn ... Formula (1)

Here, in the case of t _NiSn << t _Cu , the neutral axis 10a is at a position 2/3 from the Ni-Sn plating layer 14 side, and the following equation (2) showing the geometric similarity condition and FIG. From this, the following equation (3) can be derived.

d / r = Δd / (2t _Cu / 3)... formula (2)

t _NiSn σ _NiSn = 0.25σ _Cu t _Cu ... (3)

Note that t _NiSn indicates the thickness of the Ni—Sn plating layer 14, and σ _NiSn indicates the magnitude of stress generated at the interface between the active material and the copper foil 10 by charging. T _Cu is the thickness of the copper foil 10, σ _Cu is the 0.2% proof stress of the copper foil 10, and E is the Young's modulus of the copper foil 10 (however, 110 × 10 ⁹ N / m ² ). Further, r is a curvature radius of warpage, d is a circumferential length on the neutral axis, and Δd is a displacement amount on the outer surface of the Ni—Sn plating layer 14.

Equation (3) indicates that plastic deformation occurs in the copper foil 10 when t _NiSn σ _NiSn > 0.25σ _Cu t _Cu , and that the copper foil 10 elastically deforms when t _NiSn σ _NiSn ≦ 0.25σ _Cu t _Cu. Show. Therefore, the 0.2% yield strength and thickness required for the copper foil 10 are determined according to the type of active material layer provided on the surface of the copper foil 10 and the thickness of the active material layer. Here, by determining the type of the active material layer, the stress generated in the active material layer when the secondary battery including the secondary battery negative electrode copper foil according to the present embodiment is charged is also determined.

  Next, in an actual lithium ion secondary battery, since an active material layer is formed on both surfaces of a copper foil, the relational expressions are different. In this case, it is considered that the limit conditions for elastic deformation are as follows.

2 * _tAM * (sigma) _AM = _tCu * (sigma) _Cu ... Formula (4)

  That is, it is considered that the copper foil does not cause plastic deformation when the following formula (5) is satisfied.

t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu ... (5)

Here, sigma _AM, a value obtained from experiments with an active material layer formed on one surface of the copper foil described above.

In the secondary battery negative electrode 1 thus manufactured, the copper foil 10 is generated in the active material layer 12 when the thickness of the active material layer 12 and the secondary battery including the secondary battery negative electrode 1 are charged. Thickness and proof stress value determined from the stress to be generated. Specifically, the copper foil 10 has t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu (where t _AM is generated in the active material layer 12 and σ _AM is generated in the active material layer 12 during charging). Stress, t _Cu is the thickness of the copper foil 10, and σ _Cu is the 0.2% proof stress of the copper foil 10). If the copper foil 10 is plastically deformed, the deformation of the copper foil 10 does not follow the volume change of the active material in the copper foil 10 after the plastic deformation has occurred. In this case, the active material layer peels from the copper foil 10 and the life of the secondary battery is reduced. However, since the negative electrode copper foil for secondary batteries according to the present embodiment satisfies t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cuu , the copper foil 10 is elastically deformed.

(Effect of embodiment)
The negative electrode copper foil for a secondary battery according to the present embodiment includes a copper foil 10 and an active material layer 12, and the copper foil 10 is t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu (where, t _AM is the thickness of the active material layer 12, σ _AM is the stress generated in the active material layer 12 during charging, t _Cu is the thickness of the copper foil 10, and σ _Cu is the 0.2% proof stress of the copper foil 10. Therefore, the charging / discharging characteristics can be improved.

  The negative electrode copper foil for secondary batteries was produced by giving Ni-Sn alloy plating as an active material layer to one side of each copper foil shown in Table 1. In each of the copper foils, the Ni—Sn alloy plating has a thickness of 0.1 μm secondary battery negative electrode copper foil, 1.0 μm secondary battery negative electrode copper foil, and 3.0 μm secondary copper. A negative electrode copper foil for a secondary battery was prepared. That is, three types of negative electrode copper foils for secondary batteries were prepared for each of the copper foils shown in Table 1.

In Table 1, TPC represents tough pitch copper. TPC is a copper having a purity of about 99.5% and an oxygen concentration of 0.01 wt% to 0.06 wt%, and softens when a temperature of about 200 ° C. is applied for about 30 minutes, resulting in a 0.2% proof stress value. Reduce to about 70 N / mm ² . HCL02Z is a Cu—Zr alloy, and Zr is a solid solution type alloy in which Cu is dissolved. As a result, the 0.2% yield strength is slightly higher than that of TPC. HCL64T is a Cu-Cr-Sn-Zn alloy, which is a precipitation type alloy in which Cr particles are precipitated in Cu. HCL305 is a Cu—Ni—Si alloy, which is a precipitation type alloy in which NiSi particles are precipitated in Cu.

An example is shown above, but in the case of the same solid solution type copper alloy, the value of 0.2% proof stress also changes if the composition of the material is different. For example, in the case of an HCL01Z-based copper alloy, when the total of Cu and Zr is 99.96% by mass or more and Zr is 0.015% by mass or more and 0.03% by mass or less, about 70 N / mm ² 0.2% yield strength value is shown. In the case of an HCL305-based copper alloy, Ni is 2.2 mass% or more and 2.8 mass% or less, Si is 0.3 mass% or more and 0.7 mass% or less, and Zn is 1.5 mass% or more. When 0 mass% or less, P is 0.015 mass% or more and 0.06 mass% or less, and the balance is Cu, a 0.2% proof stress value of about 70 N / mm ² is shown. Further, in the case of a copper alloy of HCL64T, Cr is 0.20% by mass to 0.30% by mass, Sn is 0.23% by mass to 0.27% by mass, and Zn is 0.18% by mass to 0.26% by mass. When the content is less than mass% and the balance is Cu, a 0.2% proof stress value of about 70 N / mm ² is shown. If the active material to be used is determined, even if it is Cu foil other than the above composition, the 0.2% proof stress can be measured, and the minimum value of the thickness of the copper foil can be determined as will be described later. Therefore, the copper foil of Table 1 is an illustration to the last, and the copper foil which can be used in this Embodiment is not limited to these materials.

  FIG. 4 is a diagram showing the relationship between the tensile strength and the heat treatment temperature of each copper alloy.

  As can be seen in FIG. 4, HCL02Z, HCL64T, and HCL305 have high heat resistance and do not soften with a thermal history of about 200 ° C. × 30 minutes. All are copper alloys manufactured by Hitachi Cable, Ltd.

  Table 2 shows the Ni—Sn alloy plating conditions.

  As shown in Table 2, the Ni—Sn alloy plating is cathodic electrolytic degreasing (first step), anodic electrolytic pickling (second step), copper roughening plating 1 (third step), and copper roughening. It produced by implementing each process of the plating 2 (4th process) and NiSn plating (5th process) in this order. In Table 2, electrolytic pickling was employed in the second step. In addition, the washing | cleaning in a 2nd process can also employ | adopt the immersion treatment using oxidizing agents, such as hydrogen peroxide solution or potassium persulfate.

Further, the thickness of the Ni—Sn alloy plating was controlled by adjusting the plating time. The thickness of the Ni—Sn alloy plating was confirmed by a fluorescent X-ray film thickness meter (using SFT 9450 manufactured by SII Nano Technology Co., Ltd.). Furthermore, the crystal structure of the Ni—Sn alloy plating was confirmed by an X-ray diffractometer (using Rint 2000 manufactured by Rigaku). And the composition of Ni-Sn alloy plating was confirmed by performing ICP emission spectroscopic analysis (ICP-OES, using ICPS7510 made by Shimazu Co., Ltd.) for a solution in which Ni-Sn alloy plating was dissolved in nitric acid. As a result, it was confirmed that the formed Ni—Sn alloy plating was Ni ₃ Sn ₄ .

The prepared negative electrode copper foil for a secondary battery was used as a working electrode, metallic lithium as a reference electrode and a counter electrode, and a charge / discharge cycle test was performed. Measuring device with a HJ1001SM8A Hokuto Denko Co., electrolyte mixed solution of Toyama Yakuhin Kogyo Co., Ltd. LIPASTER-EDMC / PF1 (1mol / L ethylene carbonate was dissolved LiPF ₆ in a diethyl carbonate, however, mixed The ratio is 1: 1). The charge / discharge cycle test was conducted using a working electrode made of a negative electrode copper foil for a secondary battery and metallic lithium in a glove box in an atmosphere of high purity Ar gas (however, Ar gas having a purity of 99.9999%). The reference electrode and the counter electrode were held in a beaker filled with an electrolytic solution. In the charge / discharge cycle test, the potential range was set from 0.01 vs Li / Li + to 1.0 vs Li / Li +, the current density was set to 0.4 mA / cm ² , and the rest time between charge and discharge was 10 minutes. Set and implemented.

  In the charge / discharge cycle test, when charging was started, the Ni—Sn alloy plating, which was an active material layer provided on one side of the copper foil, expanded in volume. And with the volume expansion of the active material layer, all the electrodes were bent with the active material layer side outside. When subsequently discharged, the negative electrode copper foil for a secondary battery according to the example returned to a straight state before the start of charging, and repeated bending and return after the second and subsequent cycles. On the other hand, the negative electrode copper foil for the secondary battery according to the comparative example, when discharged, does not return to the initial straight state while being curved, and remains in a curved shape even if the second charge / discharge cycle is continued. It was. The results are shown in Table 3. In Table 3, the elastically deformed sample is represented by “◯”, the plastically deformed sample is represented by “Δ”, the elastically deformed sample is the negative electrode copper foil for the secondary battery according to the example, and the plastically deformed sample is It is the negative electrode copper foil for secondary batteries which concerns on a comparative example.

  In the negative electrode copper foil for the secondary battery according to the comparative example, the copper foil as the current collector copper foil is plastically deformed during charging, so that the original shape is obtained even when the active material layer contracts due to discharge and the stress disappears. It is thought that he did not return to. On the other hand, in the negative electrode copper foil for secondary batteries according to the example, the stress generated in the copper foil due to the expansion of the active material layer during charging was less than 0.2% proof stress of the copper foil, so that the curve and return It is thought that was repeated. That is, in the negative electrode copper foil for secondary batteries according to the example, since the copper foil was elastically deformed because the stress generated in the copper foil was 0.2% proof stress or less of the copper foil, the active material layer by discharge It is considered that the copper foil springs back due to the shrinkage of the resin and returns to its initial shape.

Here, first, from the results shown in FIG. 5 and Table 3, the horizontal axis represents the product (t _Cu × σ _Cu ) of the 0.2% proof stress of the copper foil and the thickness of the copper foil, and Ni—Sn as the active material layer. The thickness of the alloy plating ( _tNiSn ) was plotted on the vertical axis.

  Referring to FIG. 5, the boundary between the elastic deformation and the plastic deformation is the sample No. in the sample according to the elastically deformed example. 3 and sample No. in the sample according to the comparative example plastically deformed. 7 is considered to be between.

Therefore, from the results shown in Table 3 and Equation (3), the stress generated during charging in the Ni—Sn alloy plating as the active material layer was calculated. Sample No. in the sample according to the elastically deformed example. 3 (however, the thickness of the Ni—Sn alloy plating was 3 μm) was 0.25 × t _Cu × σ _Cu / t _NiSn = 897 (MPa), and the maximum value of σ _NiSn was obtained.

On the other hand, sample No. in the sample according to the comparative example plastically deformed. 7 (however, the thickness of the Ni—Sn alloy plating was 1 μm) was 0.25 × t _Cu × σ _Cu / t _NiSn = 829 (MPa), and the minimum value of σ _NiSn was obtained.

  From the above, it was shown that the stress generated during charging in the Ni—Sn alloy plating is larger than 829 MPa and 897 MPa or less. Therefore, in the examples, the stress value 897 MPa, which is a stricter value, is defined as the value of the stress generated in the Ni—Sn alloy plating during charging. (FIG. 6 shows a graph when 897 MPa is adopted as the 0.2% proof stress during charging of the Ni—Sn alloy plating.)

In other words, a value of 897 MPa was substituted into Equation (5) as the value of σ _NiSn , and the thicknesses required for various copper foils were calculated when the thickness t _NiSn of the active material layer was 3 μm. The results are shown in Table 4.

From Table 4, when using Ni—Sn alloy plating (more specifically, plating made of Ni ₃ Sn ₄ and having a thickness of 3 μm) as an active material layer, when forming a copper foil from an electrolytic copper foil, It is required to use a copper foil having a thickness of at least 20 μm. When a copper foil is formed from a Corson alloy (for example, HCL305), a copper foil having a thickness of 8 μm can be used.

Furthermore, in order to compare the charge / discharge capacity and capacity retention rate of the examples and comparative examples of the present invention, a negative electrode copper foil for a secondary battery was manufactured as a sample electrode with a constant area to be evaluated. Specifically, Ni—Sn alloy plating as an active material layer is applied to one side of each copper foil shown in Table 1, and the copper foil on which the active material layer is formed is punched into a circle having an area of 2 cm ^2. A negative electrode copper foil for a secondary battery was produced. And the test cell which makes metal lithium a counter electrode was produced, and the charge / discharge characteristic was evaluated. The measurement cell used was a modified measurement cell obtained by remodeling an HS cell manufactured by Hosen Co., Ltd., the measuring device was HJ1001SM8A manufactured by Hokuto Denko Co., Ltd., the separator was # 2400 manufactured by Cellguard Co., Ltd., and the electrolyte was Toyama. LIPASTER-EDMC / PF1 (mixed solution of ethylene carbonate and diethyl carbonate in which 1 mol / L LiPF ₆ was dissolved, but the mixing ratio was 1: 1) was used. The charge / discharge cycle test was performed with the potential range set from 0.01 vs Li / Li + to 1.0 vs Li / Li + and the current density set to 0.25 mA / cm ² .

  In the modified measurement cell, the sample electrode was held so that a gap of about 0.5 mm was formed on both sides of the sample electrode. As a result, both surfaces of the sample electrode were not firmly fixed to the cell, and the sample electrode was allowed to be deformed. A through hole having a diameter of 1 mm was provided in the sample electrode so that the electrolyte filled in the gap could move through the through hole in accordance with the deformation of the sample electrode. The test cell configured as described above is closer to the actual internal environment of the secondary battery than when a measurement cell without modification is used.

  The sample electrode was evaluated using the test cell thus prepared. The evaluation results are shown in Table 5.

  Referring to Table 5, the capacity retention rate after 20 cycles was 75% to 80% or more in the negative electrode copper foil for secondary battery according to the example. On the other hand, in the negative electrode copper foil for secondary batteries which concerns on a comparative example, it was 45 to 55%. Thereby, it was shown by using the negative electrode copper foil for secondary batteries which concerns on an Example that the charging / discharging characteristic of a secondary battery is improved. In Table 5, the sample whose discharge capacity retention rate after 20 cycles is shown in italics is the negative electrode copper foil for secondary battery according to the comparative example, and the other is the negative electrode copper for secondary battery according to the example. It is a foil.

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1 Negative electrode for secondary batteries 10 Copper foil 10a Neutral axis 12 Active material layer 14 Ni-Sn plating layer

Claims (9)

0.2% proof stress sigma _Cu, respectively both sides of a copper foil having a thickness of _{t Cu,} the active material layer made of Ni-Sn alloy layer having a thickness of _{t AM} (but _{a t} AM << t _Cu.) a Bei negative electrode design method for a secondary battery with painting,
Of the 0.2% proof stress σ _Cu of the copper foil, the thickness t _{Cu of the} copper foil, and the thickness t _NiSn of the Ni—Sn alloy layer (where t _NiSn << t _Cu ). A step of preparing a plurality of samples in which at least one is different and the Ni-Sn alloy layer is formed on one side of the copper foil;
A charge / discharge cycle test is performed on each of the samples, and after the charge / discharge cycle test, an elastic deformation sample that has returned to an initial straight state is selected, and
A graph in which the product t _Cu × σ _Cu of the thickness of the copper foil and the 0.2% proof stress of the copper foil is taken on the horizontal axis and the thickness t _NiSn of the Ni—Sn alloy layer is taken on the vertical axis _{shows the} elasticity Plotting each condition of the deformed sample;
Selecting a plot in which the slope of the straight line passing through the origin of the graph is the largest among the plots;
Substituting into the equation (6) the condition of the plot in which the slope of the straight line passing through the origin is the largest, and calculating the maximum value σ _AM of the stress generated in the Ni-Sn alloy layer during charging ;
σ _AM = 0.25 × t _Cu × σ _Cu / t _NiSn formula (6)
Substituting the σ _AM into the equation (7) and satisfying the equation (7), the thickness t _AM of the Ni—Sn alloy layer, the thickness t _Cu of the copper foil, and 0.2% of the copper foil Determining the combination of yield strength σ _Cu ;
t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu formula (7)
A method for designing a negative electrode for a secondary battery comprising: The thickness t _AM of the Ni-Sn alloy layer, the thickness t _Cu of the copper foil, and the 0.2% yield strength σ _{Cu of the} copper foil determined by the method for designing a negative electrode for a secondary battery according to claim 1. Use
0.2% proof stress sigma _Cu, the thickness _t on both surfaces of the copper foil of _Cu, the negative electrode manufacturing method for a secondary battery to form an active material layer made of the Ni-Sn alloy layer having a thickness of _{t AM.} The method for producing a negative electrode for a secondary battery according to claim 2 , wherein the copper foil has a 0.2% proof stress of 350 MPa or more after being heated at 200 ° C for 30 minutes. Copper foil,
Provided on both surfaces of the copper foil, comprising an active material layer made of Ni-Sn alloy layer,
t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu
(Where t _AM is the thickness of the active material layer, σ _AM is the stress generated in the active material layer during charging, t _Cu is the thickness of the copper foil, and σ _Cu is the 0.2% proof stress of the copper foil. And t _AM << t _Cu )
A negative electrode for a secondary battery satisfying the requirements. The negative electrode for a secondary battery according to claim 4, wherein the copper foil has a 0.2% proof stress of 350 MPa or more after being heated at 200 ° C. for 30 minutes . The Ni-Sn alloy layer is made of Ni-Sn alloy plating,
Σ _AM The negative electrode for a secondary battery according to claim 4 or 5, wherein is 897 MPa. A negative electrode copper foil for a secondary battery that functions as a negative electrode for a secondary battery by providing an active material layer made of a Ni-Sn alloy layer ,
Comprising a copper foil having a region where the active material layer is provided on both sides,
t _AM × σ _AM ≦ 0.5 × t _Cu × σ _Cu
(Where tAM is the thickness of the active material layer, σ _AM is the stress generated in the active material layer during charging, t _Cu is the thickness of the copper foil, σ _Cu is the 0.2% proof stress of the copper foil , And a negative electrode copper foil for a secondary battery satisfying t _AM << t _Cu ). The negative electrode copper foil for secondary batteries according to claim 7 , wherein the copper foil has a 0.2% proof stress of 350 MPa or more after being heated at 200 ° C. for 30 minutes. The Ni-Sn alloy layer is made of Ni-Sn alloy plating,
Σ _AM The negative electrode copper foil for a secondary battery according to claim 7 or 8, wherein is 897 MPa.

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