Manufacturing method for lithium-ion secondary batteries

Abstract

To provide a lithium-ion secondary battery with excellent output characteristics, regardless of the use of electrolyte additives. [Solution] The method for manufacturing a lithium-ion secondary battery comprises a negative electrode current collector foil made of copper or a copper alloy foil, a negative electrode plate having a negative electrode composite layer containing a negative electrode active material, and a positive electrode plate having a positive electrode composite layer containing a positive electrode active material, and includes an oxidation step (S102) in which the uncoated region of the negative electrode current collector foil is oxidized after the coating step (S101) of the negative electrode current collector foil of the negative electrode plate and before the reduction step (S105) of the lithium-ion secondary battery.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing lithium-ion secondary batteries, and more particularly to a method for manufacturing lithium-ion secondary batteries that exhibit excellent low-temperature power output characteristics. [Background technology]

[0002] Secondary batteries such as lithium-ion batteries, which have excellent input / output characteristics, are used in battery packs for the drive systems of hybrid vehicles (HV, PHV) and electric vehicles (BEV). In this case, it is important to ensure output in the low state of charge (SOC) region in order to maintain fuel efficiency.

[0003] To achieve this, conductive additives are sometimes added to the positive electrode composite material to reduce the positive electrode resistance R and ensure a low SOC output. However, adding conductive additives increases the amount of conductive additive, which relatively decreases the ratio of positive electrode active material. This leads to a problem of reduced capacity.

[0004] Furthermore, for example, Patent Document 1 proposes a lithium-ion secondary battery in which lithium fluorosulfonate is added to a non-aqueous electrolyte as described below. Such a lithium-ion secondary battery can be made to have excellent output characteristics. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-77477 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, while inventions like the one described in Patent Document 1 can improve output in the low SOC region, they have the problem of requiring electrolyte additives. The problem that the present invention's method for manufacturing a lithium-ion secondary battery aims to solve is to produce a lithium-ion secondary battery with excellent output characteristics without relying on electrolyte additives. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides a method for manufacturing a lithium-ion secondary battery, comprising a negative electrode current collector foil made of copper or a copper alloy foil, a negative electrode plate having a negative electrode composite layer containing a negative electrode active material, and a positive electrode plate having a positive electrode composite layer containing a positive electrode active material, characterized in that the method includes an oxidation step of oxidizing the uncoated region of the negative electrode current collector foil after the coating step of the negative electrode composite layer onto the negative electrode current collector foil and before the initial charging of the lithium-ion secondary battery.

[0008] The oxidation step may be performed in a drying step of the negative electrode composite layer after the coating step of the negative electrode composite layer, in which the uncoated area is oxidized in a set temperature environment. The oxidation process involves reducing the amount of reduced electricity [μAh / mm²] in the uncoated region of the negative electrode current collector foil. 2 ] is 0.10~0.468 [μAh / mm 2 ] can be done as follows.

[0009] The amount of reduction electricity in the oxidation process can be calculated from LSV measurement. In the oxidation process, the oxidation state of the uncoated region of the negative electrode current collector foil is defined as the brightness L according to the CIE (1976) brightness scale. * This can be determined by [the method described].

[0010] During the initial charge, the oxide in the uncoated region of the negative electrode current collector foil that was oxidized in the oxidation process can be reduced and eliminated. In the initial charge, the amount of change in the capacitance of the negative electrode plate after the initial charge, compared to before the initial charge, due to oxidation of the uncoated area of ​​the negative electrode current collector foil, can be set to 99.57 to 99.91%.

[0011] The negative electrode active material can be a graphite-based material. The positive electrode active material may contain Co, Ni, and Mn. [Effects of the Invention]

[0012] According to the lithium-ion secondary battery manufacturing method of the present invention, a lithium-ion secondary battery with excellent output characteristics can be obtained without the use of electrolyte additives. [Brief explanation of the drawing]

[0013] [Figure 1] This graph shows the positive and negative electrode potentials of a lithium-ion secondary battery. [Figure 2] This is a perspective view showing a schematic representation of the external configuration of the lithium-ion secondary battery of this embodiment. [Figure 3] This is a schematic diagram showing a configuration in which a portion of the wound electrode body is added. [Figure 4] This is a flowchart of the procedure for oxidizing and reducing the negative electrode current collector foil in this embodiment. [Figure 5] This flowchart shows an example of a manufacturing method for the lithium-ion secondary battery of this embodiment. [Figure 6] This graph shows an example of LSV measurement results. [Figure 7] This experimental result shows the relationship between the brightness L* of the negative electrode current collector foil, the amount of reduced electricity per unit [μAh / mm2], the amount of reduced electricity converted to the uncoated area [mAh], and the amount of negative electrode displacement [%] during the oxidation process. [Figure 8] This experimental result shows the relationship between the amount of reduced electricity [μAh / mm2], the amount of deviation in the charging curve [%], and the output [%] at -30[°C] and SOC=27[%]. [Figure 9] This graph shows the change in negative electrode potential before and after the initial charge using conventional technology. [Figure 10] This graph shows the change in negative electrode potential before and after the initial charge in this embodiment. [Figure 11] This graph shows the relationship between drying time [s] under different temperature conditions and brightness L*.

Mode for Carrying Out the Invention

[0014] Hereinafter, an example of a method for manufacturing a lithium-ion secondary battery of the present invention will be described according to an embodiment with reference to FIGS. 1 to 11. <Principle of the Present Embodiment> FIG. 1 is a graph showing the positive electrode potential [V] and the negative electrode potential [V] of the lithium-ion secondary battery 1. It is a so-called charge-discharge curve. The horizontal axis represents the SOC (State Of Charge · charge rate) [%] of the lithium-ion secondary battery 1. In the present embodiment, the left side is SOC = 0 [%], and for example, 40 [%] or less is referred to as a low SOC region. The high SOC region is near SOC = 100 [%] on the right side. The vertical axis represents the positive electrode potential [V] and the negative electrode potential [V] at that time. "Graph G N1 " is a graph showing the negative electrode potential [V] after the first charge of the prior art. "Graph G N2 " is a graph showing the negative electrode potential [V] after the first charge of the present embodiment. "Graph G P " is a graph showing the positive electrode potential [V]. First, as can be seen at a glance, for the positive electrode graph G P , the negative electrode graph G N1 , and graph G N2 , in all cases, the potential changes greatly in the low SOC region on the left side.

[0015] Here, the negative electrode graphs G N1 and graph G N2 are at positions shifted along the horizontal axis. The charge-discharge curve of the negative electrode shifts left and right according to the increase and decrease of the negative electrode capacity [Ah]. In the present application, "shift [%]" refers to the shift of the use regions of the positive electrode and the negative electrode, and means the ratio of the charge-discharge efficiency when using an electrode that does not oxidize the copper foil as 100 [%] (charge-discharge efficiency of the oxidized copper foil / charge-discharge efficiency of the non-oxidized copper foil).

[0016] In the graph G P showing the positive electrode potential [V], the higher the SOC [%], the less lithium ions Li + , and the lower the SOC [%], the more lithium ions Li +A large amount is absorbed. Therefore, graph G P Therefore, in the low SOC region, the resistance R at the positive electrode becomes large. This resistance R is shown in Graph G P The increase becomes particularly noticeable in the region where the decrease occurs.

[0017] On the other hand, graph G shows the negative electrode potential [V]. N1 or graph G N2 So, the higher the SOC[%], the more lithium ion Li + A large amount is absorbed, and the lower the SOC[%], the more lithium ions Li + The amount released is small.

[0018] Generally, the negative electrode capacity is set with a margin greater than the positive electrode capacity, a so-called positive electrode regulation. However, if the negative electrode capacity is excessively large compared to the positive electrode capacity during discharge, the lithium ion Li of the positive electrode... + When the amount of lithium absorbed reaches its limit, the resistance R of the positive electrode becomes large. Therefore, the positive electrode has an excessive amount of lithium ions. + In this way, the attempt to absorb the data resulted in a deterioration of input / output characteristics. P In the region where the potential [V] decreases, the input / output characteristics of the lithium-ion secondary battery 1 deteriorate, but in order to ensure fuel efficiency, it is important to secure output in this low SOC region.

[0019] The OCV (Open Circuit Voltage) [V] of lithium-ion secondary battery 1 is the potential difference between the positive and negative electrodes (OCP 正 -OCP 負 This is determined by [the following]. Here, graph G shows the conventional negative electrode potential [V]. N1 Graph G shows the negative electrode potential at V0[V] and the positive electrode potential[V]. P The potential difference between the two points is defined as "potential difference ΔV1[V]". Graph G shows the negative electrode potential [V] in this embodiment. N2 Graph G shows the negative electrode potential at V0[V] and the positive electrode potential[V]. P Let the potential difference between these points be "potential difference ΔV²[V]".

[0020] Conventional negative electrode graph G N1 and graph G of the positive electrode P The potential difference ΔV1[V] and the negative electrode graph G showing the negative electrode potential in this embodiment. N2 and graph G of the positive electrode P We compare the potential difference ΔV2[V] with that of the conventional battery. We find that the potential difference ΔV2[V] in this embodiment is greater than the conventional potential difference ΔV1[V] by ΔV1-ΔV2[V]. In other words, the positive electrode OCP[V] of lithium-ion secondary battery 1 in this embodiment is greater than that of the conventional lithium-ion secondary battery.

[0021] That is, the graph G of the positive electrode at that time. P It faces the negative electrode in the portion with a higher SOC[%] than before. In other words, the graph G of the positive electrode P In this embodiment, the portion with a potential difference of ΔV2[V] is greater than the portion with a potential difference of ΔV1[V] in the conventional embodiment, as it contains more lithium ions (Li) absorbed by the positive electrode. + Because the amount of resistance is small and the resistance R at the positive terminal is small, it can be seen that the input / output characteristics are good.

[0022] Since the lithium-ion secondary battery 1 of this embodiment is manufactured using this manufacturing method, it can maintain a high output even in the low SOC region. <Summary of this embodiment> Conventional negative electrode graph G N1 and graph G of the negative electrode of this embodiment N2 So, graph G N2 Graph G N1 Although it is shifted to the right of the above, in this embodiment, graph G is used in the following manner. N2 Graph G N1 It's shifted to the right.

[0023] First, graph G shown in Figure 1. N1 Graph G N2 It needs to be shifted like this. Graph G N1 Graph G N2 To shift in this way, the negative electrode capacity [Ah] during the initial charge needs to be increased. The discharge capacity during the initial discharge is lithium-ion Li+ Because it is regulated by the desorption reaction, increasing the negative electrode capacity [Ah] during the initial charge allows lithium ions Li to be released at the negative electrode in the low SOC region of lithium-ion secondary battery 1. + This will lead to early depletion, and at higher SOC[%], graph G N2 It will be sloping upwards to the left.

[0024] Figure 9 is a graph showing the change in negative electrode potential [V] before and after the initial charge of the conventional technology. In lithium-ion secondary battery 1, after the assembly process (Figure 5: S5), cell drying process (S6), and liquid injection / sealing process (S7), an activation process (S8) is performed. In the activation process, the lithium ions absorbed into the positive electrode are activated by the initial charge, which is the first charge performed after battery assembly. + By moving the material to the negative electrode and allowing it to be absorbed there, the lithium-ion secondary battery 1 is activated as a battery.

[0025] Lithium-ion secondary battery 1 has lithium ions Li as the positive electrode active material. + By inserting it into the negative electrode, it is charged, and the lithium ion Li that has detached from the negative electrode + Discharge occurs when the battery is reinserted into the positive electrode. In such lithium-ion secondary batteries 1, a negative electrode active material using graphite is widely used, as in this embodiment. However, when the negative electrode is graphite, the negative electrode potential at the time of initial charging is approximately 0.1V, so reductive decomposition of the carbonate-based organic solvent in contact with the interface occurs. At this time, a film of SEI (Solid Electrolyte Interphase) with a thickness of several to tens of nanometers is formed at the interface between the negative electrode active material and the non-aqueous electrolyte 13, consisting of organic materials such as lithium alkyl carbonate and inorganic materials such as lithium salts. The formation of SEI decomposes the non-aqueous electrolyte 13 and lithium ions Li + This is consumed. The difference between the charged capacity [Ah] and the dischargeable capacity [Ah] at this time is called the "irreversible capacity [Ah]". Since SEI is necessary for the protection of the negative electrode during subsequent charging and discharging, the occurrence of such irreversible capacity [Ah] is an unavoidable phenomenon. For this reason, the initial discharge capacity decreases to about 80-95% of the initial charge capacity.

[0026] Therefore, due to SEI generation during the initial charge, lithium ion Li + As it is consumed, irreversible capacity is generated, so as shown in Figure 9, the graph of the negative electrode before the initial charge G N0 The graph shifts to the right due to the initial charge. N1 This is the result.

[0027] Figure 10 is a graph showing the change in negative electrode potential [V] before and after the initial charge in this embodiment. The negative electrode plate 2 has an "uncoated region" where the copper foil is exposed and the negative electrode composite layer 22 is not coated on the negative electrode current collector foil 21. In this embodiment, the negative electrode current collector 23 corresponds to this uncoated region. This embodiment includes an oxidation step (Figure 4: S102) to oxidize this uncoated region. In this oxidation step (S102), copper oxide (CuO, Cu2O) is formed in the uncoated region of the negative electrode current collector foil 21. The copper oxide is reduced to copper by electrons during the initial charge. At this time, electrons are consumed. Since the reduction reaction of copper oxide to copper is an irreversible reaction, electrons are fixed and the capacity of the negative electrode decreases.

[0028] As a result, as shown in Figure 10, graph G before the initial charge N0 The capacity decreases due to SEI formation and increases due to the reduction of copper oxide. The discharge capacity is lithium ion Li + Because it is constant due to the desorption reaction, if the capacity reduction is only due to SEI formation, the discharge curve is G N1 It shifts to this. In addition to this, electrons are consumed in the reduction reaction of copper oxide (CuO, Cu2O) formed in the uncoated region of the negative electrode current collector foil 21, and the charging capacity increases, as shown in graph G N2 Shift to the position.

[0029] As a result, as shown in Figure 1, graph G of this embodiment N2 This is a conventional graph G N1 It is shifted significantly to the right. <Formation of copper oxide> Figure 4 is a flowchart of the procedure for oxidation and reduction of the negative electrode current collector foil 21 in this embodiment. As described above, this embodiment includes an oxidation step (S102) for oxidizing the negative electrode current collector portion 23, which corresponds to the uncoated area of ​​the negative electrode current collector foil 21. In this embodiment, the oxidation step (Figure 4: S102) is performed in the drying step of the negative electrode composite layer 22.

[0030] In the oxidation and reduction procedure of the negative electrode current collector foil 21 in this embodiment, first, a negative electrode plate coating process (S101) is performed. As shown in Figure 3, a negative electrode composite paste is coated onto the negative electrode current collector foil 21, which is made of a long strip of copper foil, except for one end in the width direction W (right side in Figure 3), to form a negative electrode composite layer 22. This coated negative electrode composite layer 22 is dried in the oxidation process (S102), which is also a drying process, and the solvent in the negative electrode composite paste evaporates and solidifies, forming the negative electrode composite layer 22. The binder contained in the negative electrode composite layer 22 fixes the negative electrode composite layer 22 to adhere closely to the negative electrode current collector foil 21.

[0031] Meanwhile, in the oxidation process (S102), hot air is blown on for drying. This hot air is usually around 130-160°C. However, in the oxidation process (S102) of this embodiment, the purpose is not only to solidify the negative electrode composite layer 22, but also to oxidize the negative electrode current collector portion 23, which corresponds to the uncoated area of ​​the negative electrode current collector foil 21. This hot air is atmospheric and contains moisture and oxygen. Furthermore, since this hot air is used not only to promote drying but also to promote oxidation, it is at a higher temperature than in a normal drying process (for example, 175-180°C). As a result, the Cu constituting the negative electrode current collector portion 23 undergoes oxidation over time.

[0032] Furthermore, the portion of the negative electrode current collector foil 21 where the negative electrode composite layer 22 is formed does not come into direct contact with the atmosphere containing moisture and oxygen, and its temperature does not rise significantly. Therefore, even when drying is performed at high temperatures, oxidation in this portion hardly progresses.

[0033] Figure 11 shows the drying time [s] and brightness L under different temperature conditions. *This graph shows the relationship between the two. Copper oxides include the red "Cu2O (copper(I) oxide (cuprous oxide))" and the black "CuO copper(II) oxide (cupric oxide)". When copper comes into contact with dissolved oxygen in moisture, cuprous oxide is formed on the surface of the copper. This cuprous oxide is what is known as "copper rust," and it mainly appears reddish-brown. If this cuprous oxide is placed in a highly oxidizing environment, it gradually darkens, and cupric oxide, which appears blackish-brown, is formed. In the oxidation process (S102) of this embodiment, the color changes over time [s].

[0034] Here, "Brightness L" * " refers to CIE(1976)L as defined in JIS Z 8105. * a * b * L refers to brightness in a color space. * a * b * Color spaces, used to represent the colors of objects, were standardized by the International Commission on Illumination (CIE) in 1976 and are also adopted in Japan in JIS Z 8781-4. * a * b * In the color space, brightness is L * , hue a * , saturation b * This is shown. Brightness L * This is an index independent of hue and saturation, and can be measured continuously for different hues. In the oxidation process (S102) of this embodiment, as shown in Figure 11, the lightness L is measured according to the drying time [s]. * The brightness decreases. In other words, it gradually becomes darker. In this embodiment, "brightness L * " is brightness L * If the value is close to 100 (higher), the color will be closer to white, and the brightness L * If the value is close to 0 (low), the color will be close to black. Line L1 in Figure 11 shows the change when the drying temperature is 175 [°C]. Line L2 shows the change when the drying temperature is 180 [°C]. The lines were derived from multiple measured values ​​using the least squares method. Thus, even with different temperatures, the relationship between drying time [s] and lightness L is significant. *Since there is a strong correlation, a linear relationship is derived. Also, depending on the drying temperature [°C], the change is different, and the higher the drying temperature [°C], the lower the brightness L * decreased more rapidly. That is, from the straight line L1, the straight line L2 with a higher temperature has a steeper gradient in the graph.

[0035] Figure 6 is a graph showing an example of the results of LSV measurement. The horizontal axis is the swept potential [V vs Li / Li + , and the vertical axis is the reduction current [A / cm + which is the reaction current at that swept potential [V vs Li / Li 2 . "[V vs Li / Li + " is the unit of the average reaction potential based on the potential at which the oxidation-reduction reaction of lithium occurs. It is a concept representing the electrical potential energy at which the intercalation reaction of lithium occurs.

[0036] Here, "LSV measurement (Linear Sweep Voltammetry)" is an electrochemical measurement method that measures current by sweeping voltage. By extrapolating the slope of the solution resistance from the current-voltage curve to obtain the decomposition voltage and finding the overvoltage which is the difference from the theoretical decomposition voltage, it is used for the evaluation of batteries, capacitors, etc. In the present application, the reduction potential [V vs Li / Li + indicating the electron-accepting tendency of a chemical substance for investigating the reduction behavior of copper ions becomes specific to the substance under certain conditions. Therefore, in electrochemical measurement, a potential is applied to cause a chemical reaction, and the reaction amount etc. is quantified by measuring the reduction current [A / cm 2 . In this embodiment, graphs G1 to G3 which are voltammograms were obtained by continuously sweeping at a potential of 3.0 to 0 [V vs Li / Li + . <晓少

[0037] The measurement was performed using the three-electrode method to obtain the accurate reduction current [A / cm 2 at the negative electrode. The swept potential [V] when this reduction current [A / cm 2 occurs can be used to estimate the substance reduced at that time from the specific potential at which the substance decomposes.

[0038] In Figure 6, graph G1 shows the case with the highest degree of oxidation, graph G2 shows the case with a moderate degree of oxidation, and graph G3 shows the case where almost no copper oxide is produced. From these graphs G1 to G3, it can be seen that the reduction current [A / cm] is high in graphs G1 and G2. 2 [VvsLi / Li] is the potential at which the ] occurs. + From this, it could be inferred that CuO and Cu2O were present. This suggests that the copper foil of the negative electrode current collector 23, which corresponds to the uncoated area of ​​the negative electrode current collector foil 21 where the oxidation process (S102) was carried out, was oxidized.

[0039] (Details of the configuration of this embodiment) The configuration for implementing the embodiment described above will be explained in detail below. <Configuration of Lithium-ion secondary battery 1> Figure 2 is a perspective view showing a schematic of the external configuration of the lithium-ion secondary battery 1 of this embodiment. First, the configuration of the lithium-ion secondary battery 1 of this embodiment will be described.

[0040] As shown in Figure 2, the lithium-ion secondary battery 1 is configured as a cell battery. The lithium-ion secondary battery 1 includes a plate-shaped rectangular parallelepiped battery case 11 with an opening on the top. An electrode body 12 is housed inside the battery case 11. The battery case 11 is filled with a non-aqueous electrolyte 13 from a filling port. The battery case 11 is made of a metal such as an aluminum alloy and forms a sealed battery case with a lid. The lithium-ion secondary battery 1 also includes a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging power. The positive electrode external terminal 14 is electrically connected to a positive electrode current collector terminal 16 inside the battery case 11 via the lid. The negative electrode external terminal 15 is electrically connected to a negative electrode current collector terminal 17 inside the battery case 11 via the lid. The positive electrode current collector terminal 16 is electrically connected to the positive electrode current collector portion 33 (see Figure 3) of the electrode body 12. Furthermore, the negative electrode current collector terminal 17 is electrically connected to the negative electrode current collector section 23 (see Figure 3) of the electrode body 12.

[0041] <Electrode body 12> Figure 3 is a schematic diagram showing the configuration of the wound electrode body 12. The electrode body 12 is made up of a number of stacked negative electrode plates 2, positive electrode plates 3, and separators 4 placed between them. The stacked negative electrode plates 2, positive electrode plates 3, and separators 4 are wound together to form a flat shape. The negative electrode plate 2 has a negative electrode composite layer 22 formed on a negative electrode current collector foil 21 made of copper foil, which serves as the base material. A negative electrode current collector portion 23 is provided on one end in the width direction W (winding axis direction) perpendicular to the winding direction (winding direction L).

[0042] This negative electrode current collector section 23 is the part of the negative electrode current collector foil 21 in which the negative electrode composite layer 22 is not formed and the copper foil of the negative electrode current collector foil 21 is exposed, corresponding to the "uncoated region" of the present invention. The positive electrode plate 3 has a positive electrode composite layer 32 formed on a positive electrode current collector foil 31 made of aluminum foil, which serves as the base material. As shown in Figure 3, the positive electrode current collector portion 33 is provided on the other end (opposite side from the negative electrode current collector portion 23) in the width direction W (winding axis direction) perpendicular to the winding direction (winding direction L) of the positive electrode current collector foil 31. The positive electrode composite layer 32 is not formed on the positive electrode current collector portion 33, and the metal of the positive electrode current collector foil 31 is exposed.

[0043] <Laminated structure of electrode body 12> As shown in Figure 3, the basic configuration of the electrode body 12 of the lithium-ion secondary battery 1 includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4.

[0044] The negative electrode plate 2 has a negative electrode composite material layer 22 on both sides of the negative electrode current collector foil 21, which serves as the negative electrode base material. One end of the negative electrode current collector foil 21 is a negative electrode current collector portion 23 where metal is exposed. The positive electrode plate 3 has a positive electrode composite material layer 32 on both sides of the positive electrode current collector foil 31, which serves as the positive electrode base material. The other end of the positive electrode current collector foil 31 is a positive electrode current collector portion 33 where metal is exposed.

[0045] The negative electrode plate 2 and the positive electrode plate 3 are stacked on top of each other via a separator 4 to form a laminate. As shown in Figure 3, this laminate is wound longitudinally around a winding axis to form a wound electrode body 12 that is flattened as shown in Figure 2.

[0046] <Nonaqueous electrolyte 13> The non-aqueous electrolyte 13 of the lithium-ion secondary battery 1 of this embodiment, shown in Figure 2, is held by the separator 4 shown in Figure 3. The non-aqueous electrolyte 13 is a composition obtained by dissolving a lithium salt in an organic solvent. Examples of lithium salts that can be used include LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butanesultone; or phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One or more of these can be mixed and used as the non-aqueous electrolyte 13. However, the composition of the non-aqueous electrolyte 13 is not limited to these.

[0047] <Components of electrode body 12> Next, we will describe the components that make up the electrode body 12: the negative electrode plate 2, the positive electrode plate 3, and the separator 4.

[0048] <Negative electrode plate 2> As shown in Figure 3, the negative electrode plate 2 is constructed by forming a negative electrode composite material layer 22 on both sides of the negative electrode current collector foil 21, which is the negative electrode substrate. The negative electrode composite material layer 22 is formed in the source process (Figure 5: S1) by coating the negative electrode current collector foil 21 with negative electrode composite material paste. The negative electrode plate 2 is then completed through a drying process, a pressing process, and a cutting process.

[0049] <Negative electrode current collector foil 21> The negative electrode current collector foil 21 is a metal foil made of Cu or a Cu alloy, and in this embodiment, it is made of Cu foil. The negative electrode current collector foil 21 serves as a base as aggregate for the negative electrode composite layer 22 and also functions as a current collector that collects electricity from the negative electrode composite layer 22. One end of the negative electrode current collector foil 21 is a negative electrode current collector section 23 where the metal surface is exposed and the negative electrode composite layer 22 is not formed thereon. In other words, the negative electrode active material particles are electrically connected to the negative electrode external terminal 15 via the negative electrode current collector foil 21, the negative electrode current collector section 23, and the negative electrode current collector terminal 17.

[0050] <Negative electrode composite layer 22> The negative electrode composite layer 22 consists of a negative electrode active material as a raw material, and a binder (binding agent) and additives as auxiliary materials. The raw material and auxiliary materials are mixed with an organic solvent to produce a negative electrode composite paste. This negative electrode composite paste is coated onto the negative electrode current collector foil 21. The coated negative electrode composite paste is dried and adheres tightly to the negative electrode current collector foil 21 by the binder. Therefore, the coated area of ​​this negative electrode composite paste is less susceptible to oxidation. On the other hand, the negative electrode current collector foil 21 that is not coated with this negative electrode composite paste is the negative electrode current collector section 23 where the copper foil is exposed for electrical connection with the negative electrode current collector terminal 17, and this is the "uncoated area" in this embodiment. In this embodiment, the problem is solved by oxidizing and reducing the copper foil in this "uncoated area".

[0051] <Negative electrode active material> In this embodiment, the negative electrode active material is powdered graphite particles made of graphite having a layered structure, and lithium ions Li + It is a material capable of absorbing and releasing substances.

[0052] <Positive plate 3> As shown in Figure 3, the positive electrode plate 3 consists of a positive electrode current collector foil 31, which is the positive electrode base material, and a positive electrode composite layer 32 coated thereon. The positive electrode composite layer 32 is formed in the source process (Figure 5: S1) when the positive electrode composite paste is coated onto the positive electrode current collector foil 31. After that, the positive electrode plate 3 is completed through a drying process, a pressing process and a cutting process.

[0053] <Positive current collector foil 31> A positive electrode plate 3 is formed by forming a positive electrode mixture layer 32 on both sides of a positive electrode current collector foil 31 which is a positive electrode base material. In the embodiment, the positive electrode current collector foil 31 is made of an Al foil. The positive electrode current collector foil 31 serves as a base as an aggregate of the positive electrode mixture layer 32 and has a function of a current collecting member that collects electricity from the positive electrode mixture layer 32.

[0054] First, although the positive electrode base material constituting the positive electrode current collector foil 31 is exemplified by an Al foil, for example, it may be constituted by a conductive material made of a metal having good conductivity. As a material having good conductivity, for example, in addition to an AL foil, a material containing an Al alloy can be used. The configuration of the positive electrode current collector foil 31 is not limited to this.

[0055] <Positive electrode mixture layer 32> The positive electrode mixture layer 32 is formed by applying and drying a positive electrode mixture paste on the positive electrode current collector foil 31. The positive electrode mixture layer 32 contains, in addition to positive electrode active material particles, additives such as a conductive auxiliary material, a binder, and a dispersant.

[0056] <Composition of positive electrode active material> The positive electrode active material particles contain a lithium transition metal oxide having a layered crystal structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn. The positive electrode active material of this embodiment has a so-called NCM ternary system having a lithium transition metal oxide containing all of Ni, Co, and Mn, for example, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2 can be exemplified.

[0057] Note that the positive electrode active material of this embodiment is not limited to those having a lithium transition metal oxide containing all of Ni, Co, and Mn. Also, a composition containing, for example, Al may be used in addition to these.

[0058] <Separator 4> The separator 4 is a highly insulating nonwoven fabric, such as polypropylene, which is a porous resin, for holding the non-aqueous electrolyte 13 between the negative electrode plate 2 and the positive electrode plate 3. Alternatively, the separator 4 can be a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or an ion-conductive polymer electrolyte membrane, either alone or in combination.

[0059] <Manufacturing method for lithium-ion secondary battery 1> Figure 5 is a flowchart showing an example of a manufacturing method for the lithium-ion secondary battery 1 of this embodiment. The manufacturing method for the lithium-ion secondary battery 1 of this embodiment will be described below. The lithium-ion secondary battery 1, which is a cell battery, first has its power generation elements, the negative electrode plate 2, positive electrode plate 3, and separator 4, created in the source process (S1).

[0060] In the source process (S1), the manufacturing process of the negative electrode plate 2 involves the negative electrode plate coating process (S101) and the oxidation process (S102), as shown in Figure 4, as described above. In the oxidation process (S102) of this embodiment, the drying process of this embodiment is also carried out.

[0061] In the source process (S1), the negative electrode plate 2, positive electrode plate 3, and separator 4 are created. Then, in the lamination process (S2), the negative electrode plate 2 and positive electrode plate 3 are stacked and integrated via the separator 4. The laminate thus created is then wound in the winding process (S3) in the winding direction L, as shown in Figure 3. The laminate wound in the winding process (S3) is generally in the shape of a plate. In the wound body pressing process (S4), this wound body is pressed from the thickness direction T by the press surface of an opposing press machine. In the wound body pressing process (S4), the electrode body 12 is pressed until it reaches a specified thickness [mm] so that it fits snugly into the battery case 11 shown in Figure 2.

[0062] In the winding press process (S4), once the thickness of the electrode body 12 is adjusted, the assembly process (S5) is performed. This assembly process is the same as the assembly process (S104) of this embodiment shown in Figure 5. In the assembly process (S5), as shown in Figure 2, the negative electrode current collector terminal 17 and the positive electrode current collector terminal 16 are attached to the electrode body 12, and then the negative electrode external terminal 15 and the positive electrode external terminal 14 are attached via the cover. The electrode body 12 is then housed in the battery case 11. The opening is sealed by welding the cover to the battery case 11. At this stage, the liquid injection port of the cover is open, so the cell is heated in the cell drying process (S6) to dry the inside of the cell. Once the inside of the cell is dry in the cell drying process (S6), the non-aqueous electrolyte 13 is injected in the liquid injection and sealing process (S7), and the liquid injection port is sealed to create a tight seal. This completes the assembly of the lithium-ion secondary battery 1.

[0063] Subsequently, an SEI coating is formed during the initial charge in the activation step (S8). This initial charge in the activation step (S8) is the same as the initial charge in the reduction step (S105) of this embodiment. In addition, during the activation step (S8), minute short circuits are eliminated by storing the device at a high temperature for a long period of time during the aging step.

[0064] Once this activation process (S8) is complete, the battery capacity, internal resistance, self-discharge, OCV, etc. are checked in the inspection process (S9), and only those that pass are shipped as products. (An embodiment of this invention) The following describes an example of this embodiment.

[0065] As a premise, the lithium-ion secondary battery 1 used in the experiment uses copper foil as the negative electrode current collector foil 21. A graphite-based negative electrode active material is used as the negative electrode active material. Furthermore, the positive electrode active material is a so-called ternary system containing Co, Ni, and Mn, for example, lithium nickel cobalt manganese oxide (LiNi 1 / 3 C o1 / 3 Mn 1 / 3 It is a lithium transition metal oxide such as O2.

[0066] <Oxidation process (S102)> The oxidation process is a drying process for the negative electrode composite layer 22 after the negative electrode plate coating process (S101), in which the uncoated negative electrode current collector 23 is oxidized in a set temperature environment.

[0067] As shown in Figure 6, the reduction current required for reduction [μAh / mm²] varies depending on the degree of oxidation. 2 ] is different. For this reason, as mentioned above, the amount of reduced electricity [μAh / mm 2 This is calculated from LSV measurement.

[0068] This is the amount of reduced electricity [μAh / mm²] used in the reduction process (S105) to reduce and eliminate the oxides in the uncoated region of the negative electrode current collector foil 21 that were oxidized in the oxidation process. 2 This corresponds to ].

[0069] Furthermore, what is the amount of reduced electricity [μAh / mm²]? 2 Whether ] is necessary depends on how much capacity reduction is required and how much capacity deviation is needed. In this embodiment, the amount of capacity deviation of the negative electrode plate 2 after the initial charge compared to before the initial charge due to oxidation of the uncoated area of ​​the negative electrode current collector foil 21 is set to 99.57 to 99.91 [%]. As shown in Figure 1, by setting it to this range, the graph G of the positive electrode charge / discharge curve P Graph G of the charge / discharge curves of the negative electrode N2 It was found that this relationship results in the avoidance of using a range where the positive electrode resistance R is large in the low SOC region.

[0070] As a result, the oxidation in the oxidation process (S102) reduces the amount of reduced electricity [μAh / mm²] in the uncoated region of the negative electrode current collector foil 21. 2 ] is 0.10~0.468 [μAh / mm 2 It was found that ] was the appropriate choice.

[0071] Next, such reduction charge [μAh / mm 2 The degree of oxidation of the uncoated area of ​​the negative electrode current collector 23 is calculated from LSV measurement. In other words, the amount of reduced electricity [μAh / mm²] is calculated. 2 ] is 0.10~0.468 [μAh / mm2 We will find the degree of oxidation of graph G such that ].

[0072] <Experimental Results> Figure 7 shows the brightness L of the negative electrode current collector foil 21 during the oxidation process (S102). * and the amount of reduced electricity per unit [μAh / mm²] 2 This is an experimental result showing the relationship between the amount of reduced charge [mAh] converted to the uncoated region and the amount of displacement [%] of the negative electrode. According to the experimental results shown in Figure 7, the amount of reduced charge [μAh / mm 2 ] is 0.10~0.468 [μAh / mm 2 The amount of reducing electricity in the uncoated region [mAh] was converted to the amount of reducing electricity [mAh] in such an oxidation state. Furthermore, the brightness L corresponding to such oxidation state was calculated. * The range was found to be between 70 and 42.

[0073] First, looking at Comparative Example 1 of the conventional technology where the shift in the negative electrode charge / discharge curve is 100%, that is, there is no shift, the brightness L * The unoxidized Cu with a value of 85 has a bright metallic color. The amount of reducing charge at this time is -0.041 [μAh / mm²]. 2 The reduced electric charge [mAh] converted to the uncoated area is -3.163 [mAh].

[0074] In contrast, looking at experimental example 1, the brightness L * =81.6 and brightness L * As the value decreases, the amount of reduced electricity is -0.053 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -4.089 [mAh]. The deviation was 99.96 [%].

[0075] Looking at experimental example 2, the brightness L * The color becomes even darker at =80, and the amount of reduced electricity also decreases to -0.06 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -4.629 [mAh]. The displacement was 99.95 [%].

[0076] Looking at experimental example 3, the brightness L* The color becomes even darker at =75, and the amount of reduced electricity also decreases to -0.08 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -6.172 [mAh]. The displacement was 99.93 [%].

[0077] Looking at experimental example 4, the brightness L * The color becomes even darker at =70, and the amount of reduced electricity also decreases to -0.1 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -7.715 [mAh]. The deviation was 99.91 [%].

[0078] Looking at experimental example 5, the brightness L * The color becomes even darker at =65, and the amount of reduced electricity also increases to -0.14 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -10.802 [mAh]. The displacement was 99.80 [%].

[0079] Looking at experimental example 6, the brightness L * The color becomes even darker at =57, and the amount of reduced electricity also increases to -0.232 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -17.900 [mAh]. The amount of displacement was 99.79 [%].

[0080] Looking at experimental example 7, the brightness L * The color becomes even darker at =50, and the amount of reduced electricity also increases to -0.308 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -23.763 [mAh]. The displacement was 99.72 [%].

[0081] Looking at experimental example 8, the brightness L * The color becomes even darker at =42, and the amount of reduced electricity also increases to -0.468 [μAh / mm²]. 2 The amount of reduced electricity [mAh] converted to the uncoated area increased to -36.108 [mAh]. The deviation was 99.57 [%].

[0082] Therefore, in this embodiment, in the oxidation step (S102) in which the uncoated region of the negative electrode current collector foil 21 in Figure 4 is oxidized, the brightness L * The threshold was set to be in the range of 70 to 42 for the determination (S103). Brightness L * The value decreases as oxidation progresses. Therefore, the threshold is set to an arbitrary value between 70 and 42. If the value exceeds this threshold (S103: NO), the oxidation process continues; if it falls below this threshold (S103: YES), the oxidation process is terminated.

[0083] As a simpler method, this oxidation process (S102) may be performed by measuring the time required to reach a predetermined degree of oxidation at a pre-set temperature, and then determining whether or not the process is complete based on the elapsed time.

[0084] <Restoration Process> In the initial charging process (S105), which is a reduction process, charging is performed starting from a state of charge (SOC) of 0%. Through this initial charging, the copper oxide in the uncoated region of the negative electrode current collector foil 21 is reduced to copper without excess or deficiency.

[0085] <Inspection Process> The initial charge takes place inside a sealed cell, so the brightness L * Since monitoring is not possible, it is impossible to know whether the reduction of copper oxide has been carried out completely or completely. Therefore, in the inspection process (Figure 5: S9), the charge-discharge curve of lithium-ion secondary battery 1 is measured to confirm whether it is within the design value in the low SOC region.

[0086] <Confirming the effect> Figure 8 shows the amount of reduced electricity [μAh / mm³] at -30°C and SOC=27%. 2 This is an experimental result showing the relationship between the shift amount [%] in the charge / discharge curve and the output [%]. In this embodiment, a low SOC region is defined as a SOC of approximately 30 [%] or less. In this experimental example, the output of lithium-ion secondary battery 1 was tested under harsh conditions of extremely low temperature and extremely low SOC, at -30 [°C] and SOC = 27 [%].

[0087] First, in Comparative Example 1 in Figure 7, which serves as the basis for comparison in Figure 8, in the case of the conventional technology where the shift in the charge / discharge curve is 100%, there is almost no copper oxide formation, so the amount of reduced electricity is -0.05 [μAh / mm²]. 2 ] and its output [A] is set to 100[%].

[0088] On the other hand, in experimental example 4 shown in Figure 8, the amount of reduced electricity was -0.10 [μAh / mm²]. 2 When the deviation of the charge / discharge curve reached 99.91%, the output [A] improved to 102%.

[0089] Furthermore, in experimental example 8 shown in Figure 8, the amount of reduced electricity was -0.47 [μAh / mm²]. 2 When the deviation of the charge-discharge curve reached 99.57%, the output [A] clearly improved to 105%.

[0090] As described above, by generating a sufficient amount of copper oxide in the uncoated region of the negative electrode current collector foil 21, the charge-discharge curve of the negative electrode is shifted, and as a result, it was confirmed that the output of the lithium-ion secondary battery 1 is improved even under harsh conditions of extremely low temperature and extremely low SOC, such as -30°C and SOC=27%.

[0091] (Operation of this embodiment) In the manufacturing method of the lithium-ion secondary battery 1 of this embodiment, copper oxide is generated by oxidizing the uncoated region of the negative electrode current collector foil 21 in the oxidation step (S102). The copper oxide generated here is reduced by initial charging in the reduction step (S105). At this time, electrons are consumed during the initial charging, increasing the charging capacity of the negative electrode, resulting in the negative electrode charge / discharge curve graph G shown in Figure 1. N2 Shift it to the right. Graph G of the charge / discharge curve. N2 Shifting to the right yields graph G, which represents the charge / discharge curve of the positive electrode. P Avoid using the low SOC region where the resistance R is large. As a result, this improves the input / output characteristics in the low SOC region.

[0092] (Effects of this embodiment) (1) The problem that the manufacturing method of the lithium-ion secondary battery 1 of this embodiment aims to solve is that it is possible to produce a lithium-ion secondary battery 1 with excellent output characteristics without using electrolyte additives.

[0093] (2) After the coating process of the negative electrode plate 2 with the negative electrode composite layer 22 onto the negative electrode current collector foil 21, and before the initial charge, an oxidation process (S102) is provided in which the uncoated area of ​​the negative electrode current collector foil 21 is oxidized. Therefore, it has the effect of being easily implemented within the normal process by simply controlling the temperature and time, without the need for electrolyte additives or separate equipment.

[0094] (3) The oxidation process (S102) is performed in the source process (S1) after the anode plate coating process (S101) of the anode composite layer 22, and oxidizes the uncoated area in a set temperature environment. Therefore, it has the effect of being easily carried out within the normal process by simply controlling the temperature and time, without the need for electrolyte additives or separate equipment.

[0095] (4) Oxidation process (S102) is performed to reduce the amount of reduced electricity [μAh / mm²] in the uncoated region of the negative electrode current collector foil 21. 2 ] is 0.10~0.468 [μAh / mm 2 This is the result of controlling it in this way, which has the effect of effectively shifting the charge / discharge curve of the negative electrode.

[0096] (5) Amount of reduction charge in the oxidation process (S102) [μAh / mm 2 This is calculated from the LSV measurement. Therefore, in the reduction process (S105), there is an effect that copper oxide can be reduced without excess or deficiency.

[0097] (6) In the oxidation process (S102), the oxidation state of the uncoated area of ​​the negative electrode current collector foil 21 is defined as the brightness L according to the CIE (1976) brightness scale. * This is used to determine the degree of oxidation. Therefore, it has the advantage of allowing for accurate and easy determination of the degree of oxidation.

[0098] (7) In the reduction step (S105), the oxides in the uncoated region of the negative electrode current collector foil 21 that were oxidized in the oxidation step (S102) are reduced and eliminated. As a result, the copper oxide of the negative electrode has the effect of becoming metallic copper with low resistance when the lithium-ion secondary battery 1 is completed as a product.

[0099] (8) In the reduction process (S105), the amount of shift in the negative electrode capacity after the initial charge compared to before the initial charge due to oxidation of the uncoated region of the negative electrode current collector foil 21 was set to 99.57 to 99.91 [%]. As a result, especially in the low SOC region, the correspondence between the charge / discharge curve of the positive electrode and the charge / discharge curve of the negative electrode does not use the region where the resistance R is large in the positive electrode, which has the effect of improving the input / output characteristics.

[0100] (9) Since the negative electrode active material is graphite-based, this embodiment can be particularly favorably implemented. (10) Since the positive electrode active material is a ternary system containing Co, Ni, and Mn, this embodiment can be particularly favorably implemented.

[0101] (Another example) ○In this embodiment, the lithium-ion secondary battery 1 is exemplified as a cell battery constituting a battery pack for vehicle propulsion, but the lithium-ion secondary battery 1 of the present invention is not limited in terms of its structure, composition, shape, etc.

[0102] ○In this embodiment, copper oxide is formed by changing the temperature conditions in the oxidation process (S102) during the drying process after the coating process of the negative electrode plate 2. This improves the efficiency of the procedure. However, the oxidation process (S102) may be carried out in a separate process from the drying process.

[0103] ○In this embodiment, the oxidation process (S102) is controlled by temperature and time, but it may also be carried out by adjusting humidity, for example. ○ Oxidation process (S102) is lightness L * The degree of oxidation is determined by this method, but hue and other factors may also be referenced.

[0104] ○The amount of reduced electricity is measured by LSV measurement, but other methods may also be used, such as preparing a half-cell using oxidized copper foil and metallic lithium and measuring the capacitance at the reduction reaction potential of copper.

[0105] ○In this embodiment, copper foil is used as an example for the negative electrode current collector foil 21, but a copper alloy that generates copper oxide may also be used. ○In this embodiment, graphite is used as the negative electrode active material, but the negative electrode active material of the present invention is not limited to graphite, and various negative electrode active materials can be used within the scope in which the present invention can be implemented.

[0106] Furthermore, although a ternary active material is used as the positive electrode active material in this embodiment, the positive electrode active material of the present invention is not limited to this, and various positive electrode active materials can be used within the scope in which the present invention can be implemented, such as LiMn2O4 and LiCoO2, which have an inflection point in the low SOC region.

[0107] The drawings are for reference to help understand the invention, but do not limit the invention. ○The numerical values, numerical ranges, compositions, etc., in this embodiment are illustrative and do not limit the present invention. They can be appropriately optimized and implemented by those skilled in the art.

[0108] The flowcharts shown in Figures 4 and 5 are examples of implementation, and the steps may be added, deleted, rearranged, or modified. ○The present invention can be implemented by those skilled in the art with additions, deletions, and modifications, without departing from the scope of the claims. [Explanation of Symbols]

[0109] 1…Lithium-ion rechargeable battery 11…Battery case 12...Electrode body 13...Nonaqueous electrolyte 14…Positive external terminal 15…Negative external terminal 16…Positive current collection terminal 17... Negative current collection terminal 2… Negative plate 21... Negative electrode current collector foil 22...Negative electrode composite material layer 23…Negative electrode current collector (unpainted area) 3…Positive plate 31...Positive current collector foil 32…Positive electrode composite layer 33…Positive electrode current collector 4... Separator

Claims

1. In a lithium-ion secondary battery comprising a negative electrode current collector foil made of copper or a copper alloy foil, a negative electrode plate having a negative electrode composite layer containing a negative electrode active material, and a positive electrode plate having a positive electrode composite layer containing a positive electrode active material, After the coating process of the negative electrode plate with the negative electrode current collector foil, Before the initial charging of the aforementioned lithium-ion secondary battery, A method for manufacturing a lithium-ion secondary battery, characterized by comprising an oxidation step for oxidizing the uncoated region of the negative electrode current collector foil.

2. The oxidation step is, A method for manufacturing a lithium-ion secondary battery according to claim 1, characterized in that, in the drying step of the negative electrode composite layer after the coating step of the negative electrode composite layer, the uncoated region is oxidized in a set temperature environment.

3. The oxidation step is, The amount of reduced electricity [μAh / mm²] in the uncoated region of the negative electrode current collector foil. ２ ] is 0.10 to 0.468 [μAh / mm ２ A method for manufacturing a lithium-ion secondary battery according to claim 1, characterized by the following:

4. The method for manufacturing a lithium-ion secondary battery according to claim 3, characterized in that the amount of reduced electricity in the oxidation step is calculated from LSV measurement.

5. In the oxidation process, The oxidation state of the uncoated region of the negative electrode current collector foil is determined by the lightness L according to the CIE (1976) lightness scale. ＊ A method for manufacturing a lithium-ion secondary battery according to claim 1, characterized by determining by the above.

6. During the initial charge, The method for manufacturing a lithium-ion secondary battery according to claim 1, characterized in that the oxide in the uncoated region of the negative electrode current collector foil that has been oxidized in the oxidation step is reduced and eliminated.

7. During the initial charge, The method for manufacturing a lithium-ion secondary battery according to claim 1, characterized in that the amount of deviation in the capacity of the negative electrode plate after the initial charge compared to before the initial charge due to oxidation of the uncoated region of the negative electrode current collector foil is 99.57 to 99.91%.

8. The method for manufacturing a lithium-ion secondary battery according to claim 1, characterized in that the negative electrode active material is graphite-based.

9. The method for manufacturing a lithium-ion secondary battery according to claim 1, characterized in that the positive electrode active material contains Co, Ni, and Mn.

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