Method for manufacturing non-aqueous electrolyte secondary battery and method for testing voltage

Abstract

The present invention aims to shorten the manufacturing time in a method for manufacturing a non-aqueous electrolyte secondary battery. In a method for manufacturing a non-aqueous electrolyte secondary battery in one embodiment of the present invention, a negative electrode including a negative electrode active material and a battery having a general formula of Li a Ni x M (1‑x) A non-aqueous electrolyte secondary battery having a positive electrode with a Li-Ni composite oxide represented by O2 (wherein 0<a≤1.2, 0.6≤x<1, and M is at least one element selected from Co, Mn, and Al) as a positive electrode active material and a non-aqueous electrolyte, is charged in the first charge and discharge in such a way that the positive electrode potential based on lithium in the open circuit state after charging becomes 4.1 to 4.25 V.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a nonaqueous electrolyte secondary battery and a method for testing voltage. Background Art

[0002] In the case of manufacturing a non-aqueous electrolyte secondary battery, the first charge and discharge is sometimes performed after assembly and before shipment. By checking the voltage of the secondary battery after the first charge and discharge, only the secondary battery whose voltage change is judged to be good is shipped, and the voltage in the product after shipment can be prevented from being poor. Patent document 1 records that in the first charge in the first charge and discharge, the charging voltage is set to (open circuit voltage (OCV) when fully charged -2000mV) or more and (open circuit voltage when fully charged -25mV) or less.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-17209 Summary of the invention

[0006] Problems to be solved by the invention

[0007] It is desirable to shorten the charging time in the first charge and discharge to shorten the manufacturing time of the secondary battery. However, if the charging capacity is reduced to shorten the charging time, the expansion amount of the electrode body in the secondary battery during charging becomes smaller, so the secondary battery may not be fully activated in the first charge and discharge.

[0008] Furthermore, when voltage inspection is performed after the first charge and discharge of a secondary battery, the secondary battery is once fully charged in order to reliably exclude defective products. This makes it difficult to reliably exclude defective products while shortening the time required for voltage inspection.

[0009] The object of the present invention is to shorten the manufacturing time in a method for manufacturing a non-aqueous electrolyte secondary battery. In addition, the object of the present invention is to shorten the time required for voltage inspection after assembly in a method for inspecting the voltage of a non-aqueous electrolyte secondary battery and to reliably exclude defective products.

[0010] Means for solving problems

[0011] In the method for manufacturing a non-aqueous electrolyte secondary battery of the present invention, a negative electrode including a negative electrode active material and a battery having a general formula of Li a Ni x M (1-x)In a non-aqueous electrolyte secondary battery having a positive electrode with a Li-Ni composite oxide represented by O2 (wherein 0<a≤1.2, 0.6≤x<1, and M is at least one element selected from Co, Mn, and Al) as a positive electrode active material, and a non-aqueous electrolyte, charging is carried out in such a way that the positive electrode potential based on lithium in the open circuit state after charging becomes 4.1 to 4.25 V during the first charge and discharge.

[0012] In the voltage inspection method of the non-aqueous electrolyte secondary battery of the present invention, the non-aqueous electrolyte secondary battery comprises a negative electrode including a negative electrode active material, and a a Ni x M (l-x) A positive electrode of a Li-Ni composite oxide represented by O2 (wherein 0<a≤1.2, 0.6≤x<1, and M is at least one element selected from Co, Mn, and Al) is used as a positive electrode active material, and a non-aqueous electrolyte. For a non-aqueous electrolyte secondary battery, charging is carried out in such a way that the positive electrode potential based on lithium in an open circuit state after charging becomes 4.1 to 4.25 V, and the voltage of the non-aqueous electrolyte secondary battery is measured.

[0013] Effects of the Invention

[0014] According to the manufacturing method of the nonaqueous electrolyte secondary battery of the present invention, the manufacturing time can be shortened. In addition, according to the voltage inspection method of the nonaqueous electrolyte secondary battery of the present invention, the time required for voltage inspection can be shortened and defective products can be reliably eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flowchart showing a method for manufacturing a nonaqueous electrolyte secondary battery and a method for testing voltage according to an example of an embodiment.

[0016] Figure 2 This is a graph showing the relationship between the change ratio of the volume of the active material in the electrode body of the non-aqueous electrolyte secondary battery and the depth of charge (SOC).

[0017] Figure 3 This is a graph showing the measurement results of the charging time of the non-aqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Example 1. DETAILED DESCRIPTION

[0018] The present inventors have found that when a nonaqueous electrolyte secondary battery including the Li—Ni composite oxide as a positive electrode active material is charged, the electrode body expands to the maximum at a predetermined positive electrode potential before full charge, and based on this finding, the above-mentioned problems have been solved.

[0019] The "first charge and discharge" in the present invention refers to the charge and discharge accompanied by the first discharge after assembling the nonaqueous electrolyte secondary battery. Before the charge and discharge, partial charging for exhaust in the secondary battery or aging of the partially charged battery may be performed. That is, the charging in the first charge and discharge may start from a state where the secondary battery has a predetermined depth of charge (SOC) due to partial charging before the first charge and discharge.

[0020] The "positive electrode potential based on lithium in an open circuit state after charging" in the present invention is calculated, for example, by measuring the open circuit voltage (OCV) of the secondary battery 30 minutes after the end of charging.

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific materials, numerical values, etc. are used for easy understanding of the present invention, and can be appropriately changed to match the specifications of the secondary battery manufactured by the embodiment. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical shell is described, but the battery is not limited to a cylindrical shape and can also be a square shape. In addition, the electrode body can also be a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked with a separator.

[0022] [Non-aqueous electrolyte secondary battery]

[0023] The non-aqueous electrolyte secondary battery has a wound electrode body, a non-aqueous electrolyte, and a shell for accommodating the electrode body and the non-aqueous electrolyte. Hereinafter, the non-aqueous electrolyte secondary battery is recorded as a secondary battery. The electrode body has a positive electrode, a negative electrode, and a separator, and the positive electrode and the negative electrode are wound into a spiral shape with the separator between them. The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0024] The positive electrode has a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector. For example, the positive electrode active material layer is formed on both sides of the positive electrode collector. In the positive electrode collector, a foil of a metal such as aluminum, a film of the metal disposed on the surface, etc. is used. The preferred positive electrode collector is a foil of a metal with aluminum or an aluminum alloy as the main component. The thickness of the positive electrode collector is, for example, 10 μm to 30 μm. The positive electrode active material layer preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode is made, for example, by coating a positive electrode composite material slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) on both sides of the positive electrode collector, and then drying and rolling.

[0025] As the positive electrode active material, Li a Ni x M (1-x)Li-Ni composite oxide represented by O2 (wherein 0<a≤1.2, 0.6≤x<1, M is at least one element selected from Co, Mn, and Al). It is preferred to use a Li-Ni composite oxide represented by the general formula Li a Ni x Co y Al z O2 (wherein, 0<a≤1.2, 0.8≤x<1, 0<y<0.1, 0<z<0.1, x+y+z=1). In the above general formula, "a" representing the amount of Li is set to 0<a≤1.2 because the amount of Li changes during charge and discharge. However, if the positive electrode active material is just made, a preferably satisfies 0.95≤a≤1.2.

[0026] As the example of the above-mentioned conductive agent, carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, graphite, etc. can be enumerated. As the example of the above-mentioned binding agent, fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resin, polyolefin resin, etc. can be enumerated. In addition, these resins can also be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. These can be used alone or in combination with more than two kinds.

[0027] The negative electrode has a negative electrode collector and a negative electrode active material layer formed on the negative electrode collector. For example, the negative electrode active material layer is formed on both sides of the negative electrode collector. The negative electrode collector includes, for example, a metal foil such as copper. The thickness of the negative electrode collector is, for example, 5 μm to 30 μm. The negative electrode active material layer preferably includes a negative electrode active material and a binder. The negative electrode is made, for example, by applying a negative electrode mixture slurry including a negative electrode active material, a binder and water to both sides of the negative electrode collector, followed by drying and rolling.

[0028] As the negative electrode active material, there is no particular limitation as long as it is a material that can reversibly absorb and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals such as Si and Sn alloyed with lithium, or alloys and composite oxides containing them can be used. Preferably, the negative electrode contains a mixture of graphite and 0 to 10 mass % of Si-containing materials relative to the total mass of the negative electrode active material as the negative electrode active material. The binder contained in the negative electrode active material layer uses, for example, the same resin as in the case of the positive electrode. When preparing the negative electrode mixture slurry with an aqueous solvent, styrene-butadiene rubber (SBR), CMC or its salt, polyacrylic acid or its salt, polyvinyl alcohol, etc. can be used. These can be used alone or in combination of two or more.

[0029] A porous sheet having ion permeability and insulation can be used as the separator. Specific examples of the porous sheet include microporous films, woven fabrics, nonwoven fabrics, etc. As the material of the separator, olefin resins such as polyethylene and polypropylene are preferred. The thickness of the separator is, for example, 10 μm to 50 μm.

[0030] [Secondary battery manufacturing method and voltage inspection method]

[0031] Next, a method for manufacturing a secondary battery and a method for checking the voltage will be described. Figure 1 1 is a flowchart of a method for manufacturing a non-aqueous electrolyte secondary battery and a method for checking voltage, showing an example of an embodiment. The method for manufacturing a secondary battery includes a battery assembly step (S10) and a first charge and discharge step (S12, S14). The method for checking voltage of a secondary battery includes a first charge and discharge step (S12, S14) and a voltage measurement step (S16) for checking the voltage of the secondary battery.

[0032] In step S10, the secondary battery is assembled. For example, in the case of a cylindrical battery, an electrode body wound with the positive electrode and the negative electrode facing each other with a separator interposed therebetween is inserted into a bottomed cylindrical case body, and then an electrolyte is injected and the opening of the case body is sealed with a sealing body, thereby assembling the battery.

[0033] Next, in step S12, the battery is connected to the charging circuit to perform charging in the first charge and discharge process. At this time, charging is performed in such a way that the positive electrode potential based on the lithium reference in the open circuit state after charging becomes 4.1 to 4.25V. The positive electrode potential based on the lithium reference of 4.1 to 4.25V corresponds to a depth of charge (SOC) of 75 to 95% in the secondary battery. Thus, in step S12, the secondary battery can be charged in such a way that the depth of charge becomes 75 to 95%. More preferably, in step S12, charging is performed in such a way that the positive electrode potential based on the lithium reference in the open circuit state after charging becomes 4.208 to 4.218V. The positive electrode potential based on the lithium reference of 4.208 to 4.218V corresponds to a depth of charge (SOC) of 90 to 92% in the secondary battery. It should be noted that the positive electrode potential based on the lithium reference in the open circuit state after charging can be controlled based on the voltage of the secondary battery.

[0034] In step S12, only constant current charging (CC charging) may be performed, or constant current constant voltage charging (CCCV charging) may be performed. In step S12, multi-step CC charging in which the current value of CC charging is switched stepwise may be performed.

[0035] In step S12, as described later, the electrode body of the secondary battery can be expanded to the maximum extent. Thus, the assembled secondary battery can be fully activated. In addition, since the secondary battery is not charged to the positive electrode potential of the lithium reference corresponding to the full charge, the time of step S12 can be shortened. Thus, the manufacturing time of the secondary battery can be shortened.

[0036] After step S12, the secondary battery is discharged in step S14. In step S14, the discharge termination voltage is preferably set to 2.5V or more and 3.5V or less. After step S14, the voltage measurement of step S16 is performed. The voltage measurement is preferably performed after the secondary battery is placed for a prescribed time after step S14. The state of the secondary battery can be checked based on the measured value. In addition, the voltage of the secondary battery immediately after step S14 can also be measured. By passing through step S12, the electrode body is fully expanded, so it is possible to reliably exclude defective products with a large voltage drop in the voltage inspection process including steps S12 to S16. Compared with the case where the secondary battery is fully charged, the charging time of step S12 is shortened. Therefore, the above-mentioned voltage inspection process can take into account both shortening the required time and reliably excluding defective products. It should be noted that aging of the secondary battery can be performed between step S14 and step S16.

[0037] According to the manufacturing method of the secondary battery, the manufacturing time can be shortened. In addition, according to the voltage inspection method of the secondary battery, it is possible to shorten the time required for the voltage inspection process and reliably eliminate defective products. The insights that formed the basis for discovering these manufacturing methods and voltage inspection methods are described. Figure 2 The present inventors have used an X-ray diffraction method using an X-ray diffraction device (XRD) to obtain a secondary battery having a structure composed of a general formula Li a Ni x M (1-x) In a secondary battery with a positive electrode active material of a Li-Ni composite oxide represented by O2, the change in the lattice constant of the positive electrode and the negative electrode accompanying the change in SOC was calculated. Then, based on the estimated volume change of the positive and negative electrodes, the inventors calculated the change ratio of the volume of the positive and negative active materials of the electrode body (the sum of the volumes of the positive and negative active materials). Figure 2 In the figure, the horizontal axis represents SOC, and the vertical axis represents the change ratio (expansion ratio) of the volume of the positive and negative electrode active materials when the expansion amount of the positive and negative electrode active materials at the maximum expansion is set to 100%, based on the volume of the positive and negative electrode active materials when the SOC is 0%.

[0038] The inventors found that Figure 2As shown, the change ratio of the volume of the positive and negative active materials reaches the maximum in the range of the depth of charge (SOC) of 75 to 95%. The reason is that if the depth of charge of the secondary battery increases from 0%, the volume of the negative active material increases roughly linearly due to the insertion of Li. On the other hand, the volume of the positive active material gradually decreases during the increase of the depth of charge due to the detachment of Li, but decreases sharply after a certain depth of charge (SOC). Based on this insight, the inventors discovered the above-mentioned manufacturing method and voltage inspection method.

[0039] [Example]

[0040] Next, in order to confirm that the charging time can be shortened when charging the secondary battery using the manufacturing method of the embodiment, the charging time under the respective charging conditions of Examples 1 to 3 and Comparative Example 1 was measured. In Examples 1 to 3 and Comparative Example 1, secondary batteries of the same structure were used, and the charging method of the first charge and discharge was changed.

[0041] [Example 1]

[0042] As the secondary battery, a cylindrical non-aqueous electrolyte secondary battery including a wound electrode body is used. In the positive electrode of the secondary battery, LiNi is used as a positive electrode active material. 0.88 Co 0.075 Al 0.045 A lithium nickel cobalt aluminum composite oxide represented by O2. A mixture of Si oxide and graphite is used as the negative electrode active material. A non-aqueous electrolyte is used.

[0043] As shown in Table 1, in Example 1, in the first charge after assembly, only constant current charging (CC charging) at 0.4C was performed under an environment of 25°C. At this time, 1C=4000mA. Charging was performed in a manner that the depth of charge (SOC) of the secondary battery became 90%. The open circuit voltage of the secondary battery after charging was 4.108V, and the positive electrode potential based on lithium at this time was 4.208V. Table 1 shows the measurement results of Examples 2 and 3 described later and Comparative Example 1 and the measurement results of Example 1.

[0044] [Table 1]

[0045]

[0046] [Example 2]

[0047] In Example 2, constant current constant voltage charging (CCCV charging) was performed in the first charge after assembly. In CC charging, multi-stage CC charging with a stepwise reduction in current value was performed. The cutoff voltage (termination voltage) in the multi-stage CC charging was set to 4.164V. Then, CV charging was performed with the cutoff current (termination current) set to 0.2C. The open circuit voltage of the secondary battery after charging was 4.106V, and the lithium reference positive electrode potential at this time was 4.206V. The SOC of the secondary battery was 89%.

[0048] [Example 3]

[0049] In Example 3, only the same multi-stage CC charging as in Example 2 was performed in the first charge after assembly. The cutoff voltage (termination voltage) in the multi-stage CC charging was 4.2 V. The open circuit voltage of the secondary battery after charging was 4.108 V, and the lithium reference positive electrode potential at this time was 4.208 V. The SOC of the secondary battery was 90%.

[0050] [Comparative Example 1]

[0051] In Comparative Example 1, constant current constant voltage charging (CCCV charging) was performed in the first charge after assembly. In CC charging, multi-stage CC charging was not performed, but only 0.4C CC charging was performed. The cutoff voltage (termination voltage) in CC charging was set to 4.2V. Then, CV charging was performed with the cutoff current set to 0.02C. The open circuit voltage of the secondary battery after charging was 4.184, and the lithium reference positive electrode potential at this time was 4.284V. The SOC of the secondary battery was 100%.

[0052] Figure 3 The measurement results of the charging time of Examples 1 to 3 and Comparative Example 1 are shown in a graph. Figure 3 In the figure, the shaded area indicates CC charging, and the sand dot area indicates CV charging. Figure 3 The results shown show that the charging time is significantly shortened in Examples 1 to 3 compared to Comparative Example 1. In particular, it is found that when multi-stage CC charging is performed as in Examples 2 and 3, charging can be performed in a charging time that is less than half of the charging time in the charging method of Comparative Example 1, and the charging time can be further shortened.

Claims

1. A method for manufacturing a non-aqueous electrolyte secondary battery, wherein: A negative electrode including a negative electrode active material, including a general formula Li a Ni x M (1-x) A non-aqueous electrolyte secondary battery having a positive electrode with a Li-Ni composite oxide represented by O2 as a positive electrode active material and a non-aqueous electrolyte is charged in the first charge and discharge in such a way that the positive electrode potential based on lithium in the open circuit state after charging becomes 4.1V~4.25V, the charging depth is 75~95%, and the volume expansion of the positive and negative electrode active materials is 100%. In the above general formula, 0<a≤1.2, 0.6≤x<1, and M is at least one element selected from Co, Mn, and Al.

2. The method for manufacturing a nonaqueous electrolyte secondary battery according to claim 1, wherein: The negative electrode active material comprises graphite and a silicon compound, The content of the silicon compound is more than 0 mass % and less than 20 mass % relative to the total mass of the negative electrode active material.

3. The method for producing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein: The Li-Ni composite oxide is composed of the general formula Li a Ni x Co y Al z O2 represents, in the general formula, 0<a≤1.2, 0.8≤x<1, 0<y<0.1, 0<z<0.1, x+y+z=1.

4. A method for checking the voltage of a non-aqueous electrolyte secondary battery, wherein: The non-aqueous electrolyte secondary battery comprises a negative electrode including a negative electrode active material, and a a Ni x M (1-x) A positive electrode having a Li-Ni composite oxide represented by O2 as a positive electrode active material, and a non-aqueous electrolyte, wherein 0<a≤1.2, 0.6≤x<1, M is at least one element selected from Co, Mn, and Al, The non-aqueous electrolyte secondary battery is charged in such a manner that the lithium-based positive electrode potential in the open circuit state after charging becomes 4.1V to 4.25V, the charging depth is 75 to 95%, and the volume expansion of the positive and negative electrode active materials is 100%. After discharging in such a manner that the discharge termination voltage is greater than 2.5V and less than 3.5V, the voltage of the non-aqueous electrolyte secondary battery is measured.

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