Manufacturing method for lithium-ion secondary batteries

Abstract

To provide a method for manufacturing lithium-ion secondary batteries that can produce lithium-ion secondary batteries in which oxidative decomposition of ester-based solvents is suppressed. [Solution] The present invention provides a method for manufacturing a lithium-ion secondary battery, comprising: an electrode body manufacturing step of manufacturing an electrode body comprising a positive electrode and a negative electrode, wherein the positive electrode has a positive electrode composite material containing a positive electrode active material and lithium phosphate; a battery cell manufacturing step of manufacturing a battery cell by sealing the electrode body and a first non-aqueous electrolyte containing an organic solvent other than an ester-based solvent in an outer casing; an activation step of activating the battery cell by applying a predetermined voltage; and a liquid replacement step of replacing the non-aqueous electrolyte by discharging the first non-aqueous electrolyte from the activated battery cell and injecting a second non-aqueous electrolyte containing an ester-based solvent.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a lithium ion secondary battery. Background Art

[0002] Patent Document 1 discloses a lithium ion secondary battery comprising: a positive electrode having a positive electrode mixture containing a positive electrode active material and lithium phosphate; and a non-aqueous electrolyte containing a carbonate-based solvent. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Patent Laid-Open No. 2019-50155 Summary of the Invention Problems to be Solved by the Invention

[0004] In lithium ion secondary batteries, a non-aqueous electrolyte containing a low-viscosity ester-based solvent may be used in place of a non-aqueous electrolyte containing a carbonate-based solvent. However, since the oxidation-reduction potential of the ester-based solvent is lower than that of the carbonate-based solvent, the ester-based solvent is prone to oxidative decomposition when the lithium ion secondary battery is activated. As a result, a lithium ion secondary battery having an inferior residual capacity retention rate compared to the case of using a non-aqueous electrolyte containing a carbonate-based solvent is produced.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a lithium ion secondary battery, which can manufacture a lithium ion secondary battery in which oxidative decomposition of the ester-based solvent is suppressed. Means for Solving the Problems

[0006] To solve the above-mentioned problems and achieve the objective, the present invention provides a method for manufacturing a lithium-ion secondary battery, comprising: an electrode body manufacturing step of manufacturing an electrode body comprising a positive electrode and a negative electrode, wherein the positive electrode has a positive electrode composite material containing a positive electrode active material and lithium phosphate; a battery cell manufacturing step of manufacturing a battery cell by sealing the electrode body and a first non-aqueous electrolyte containing an organic solvent other than an ester-based solvent in an outer casing; an activation step of activating the battery cell by applying a predetermined voltage; and a liquid replacement step of replacing the non-aqueous electrolyte by discharging the first non-aqueous electrolyte from the activated battery cell and injecting a second non-aqueous electrolyte containing an ester-based solvent.

[0007] In the lithium-ion secondary battery manufacturing method according to the present invention, after activation, the non-aqueous electrolyte of the battery cell is replaced from a first non-aqueous electrolyte to a second non-aqueous electrolyte, thereby enabling the production of a lithium-ion secondary battery in which the oxidative decomposition of the ester-based solvent is suppressed.

[0008] Furthermore, in the above, the second non-aqueous electrolyte contains the ester solvent in an amount of 10 [vol%] to 90 [vol%].

[0009] Furthermore, in the above, the organic solvent other than the ester-based solvent contained in the first non-aqueous electrolyte is a carbonate-based solvent. [Effects of the Invention]

[0010] The lithium-ion secondary battery manufacturing method according to the present invention has the effect of being able to manufacture lithium-ion secondary batteries in which the oxidative decomposition of ester-based solvents is suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the relationship between the ester solvent ratio and the residual volume retention rate for Examples A1 to A6, Comparative Examples B1 to B7, Comparative Examples B12 to B17, Comparative Examples B23 to B29, and Comparative Example B34. [Figure 2] Figure 2 shows the relationship between the ester solvent ratio and the amount of gas generated for Examples A1 to A6, Comparative Examples B1 to B7, Comparative Examples B12 to B17, Comparative Examples B23 to B29, and Comparative Example B34. [Modes for carrying out the invention]

[0012] The following describes an embodiment of the method for manufacturing a lithium-ion secondary battery according to the present invention. However, the present invention is not limited to this embodiment.

[0013] The method for manufacturing a lithium-ion secondary battery according to the embodiment includes an electrode body manufacturing step, a battery cell manufacturing step, an activation step, and a electrolyte replacement step.

[0014] The electrode fabrication process is a process for fabricating an electrode body comprising a positive electrode and a negative electrode, wherein the positive electrode has a positive electrode active material and a positive electrode composite material containing lithium phosphate (Li3PO4). The positive electrode active material has a positive electrode potential of approximately 4.3 [V] (vs. metallic Li), for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 can be used.

[0015] The battery cell manufacturing process involves enclosing an electrode body and a first non-aqueous electrolyte containing an organic solvent other than an ester-based solvent in an outer casing to produce a battery cell. The organic solvent other than the ester-based solvent contained in the first non-aqueous electrolyte is, for example, a carbonate-based solvent. Examples of carbonate-based solvents that can be used include ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0016] The activation step is a step of activating a battery cell by applying a predetermined voltage thereto. The ultimate voltage in the activation step is 4.5 V (vs. metallic Li) or higher. In the activation step included in the method for manufacturing a lithium ion secondary battery according to the embodiment, Li₃PO₄ in the positive electrode mixture of the positive electrode forms a protective film, thereby achieving the effect of suppressing oxidative decomposition on the surface of the positive electrode.

[0017] The liquid replacement step is a step of, after activation, discharging the first non-aqueous electrolyte from the battery cell, injecting a second non-aqueous electrolyte containing an ester-based solvent, and replacing the non-aqueous electrolyte. It is preferable that the second non-aqueous electrolyte contains the ester-based solvent in a range of 10 vol% or more and 90 vol% or less. As the ester-based solvent, for example, methyl propionate (MP) or methyl acetate (MA) can be used.

[0018] In the method for manufacturing a lithium ion secondary battery according to the embodiment, by using the first non-aqueous electrolyte containing an organic solvent other than an ester-based solvent as the non-aqueous electrolyte in the activation step, it is possible to facilitate formation of a protective film on lithium phosphate (Li₃PO₄) in the positive electrode mixture. Further, since the non-aqueous electrolyte in the battery cell is replaced from the first non-aqueous electrolyte to the second non-aqueous electrolyte after activation, decomposition of the ester-based solvent caused by activation is suppressed. Thereby, the method for manufacturing a lithium ion secondary battery according to the embodiment can manufacture a lithium ion secondary battery in which oxidative decomposition of the ester-based solvent is suppressed.

Examples

[0019] Hereinafter, the technology of the present disclosure will be described in further detail with reference to Examples A1 to A10 and Comparative Examples B1 to B34, but the technology of the present disclosure is not limited to the following examples.

[0020] [Preparation of Positive Electrode] As the positive electrode active material for each of Examples A1 to A10 and Comparative Examples B1 to B34, LiNi 1 / 3 Co 1 / 3 Mn1 / 3 O₂ was used. The electrode was produced by preparing a slurry at a ratio (wt%) of active material:conductive auxiliary agent:PVdF = 87:10:3, and applying the slurry onto an Al foil. For the levels mixed with Li₃PO₄ (Examples A1 to A6 and Comparative Examples 23B to 34B), electrodes were produced by replacing 5 wt% of the active material content.

[0021] [Preparation of Negative Electrode] For each negative electrode of Examples A1 to A10 and Comparative Examples B1 to B34, a natural graphite-based material with an average particle diameter of 20 μm was used. A carbon material, a styrene-butadiene copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed at a ratio (wt%) of carbon material:SBR:CMC = 98:1:1 using water as a dispersion solvent, and the mixture was applied onto a copper foil to obtain an electrode. The weight of the negative electrode mixture was adjusted to achieve a capacity ratio of approximately 1.1 relative to the capacity of the positive electrode.

[0022] [Confirmation of Areal Weight, Film Thickness and Density of Electrodes] The electrodes produced respectively for Examples A1 to A10 and Comparative Examples B1 to B34 were punched out using a punch with a diameter of Φ12. The weight and film thickness of the punched Φ12 electrodes were measured, after subtracting the weight and thickness of the conductive foil used, the areal weight and density were calculated.

[0023] [Electrode Assembly Production Step] For each of Examples A1 to A10 and Comparative Examples B1 to B34, an electrode assembly was produced by arranging a positive electrode and a negative electrode to face each other with a polypropylene / polyethylene / polypropylene three-layer porous membrane having an air permeability of 300 seconds obtained by the Gurley test method interposed therebetween.

[0024] [Non-aqueous Electrolyte Solution] For each of Examples A1 to A10 and Comparative Examples B1 to B34, a non-aqueous solvent was prepared to have the specified solvent type and composition. Then, using 1.0 M [mol / L] of LiPF6 as the electrolyte, electrolyte A (first non-aqueous electrolyte) and electrolyte B (second non-aqueous electrolyte) were prepared for each of Examples A1 to A10 and Comparative Examples B1 to B34 by adjusting them to the specified volume ratio and molar concentration.

[0025] The electrolyte A in Examples A1 to A10 is a non-aqueous electrolyte containing a carbonate-based solvent, which is an organic solvent other than an ester-based solvent. Furthermore, the composition of the electrolyte A in Examples A1 to A10 contains 30 [vol%] EC and 70 [vol%] EMC.

[0026] Furthermore, the electrolyte B in Examples A1 to A10 is a non-aqueous electrolyte containing an ester-based solvent. The composition of electrolyte B in Examples A1 to A3 is 30 [vol%] of EC, 60, 50, and 30 [vol%] of EMC, and 10, 20, and 40 [vol%] of MP, respectively. The composition of electrolyte B in Example A4 is 30 [vol%] of EC and 70 [vol%] of MP. The composition of electrolyte B in Example A5 is 20 [vol%] of EC and 80 [vol%] of MP. The composition of electrolyte B in Example A6 is 10 [vol%] of EC and 90 [vol%] of MP. The composition of electrolyte B in Examples A7 to A9 is 30 vol% EC, 60, 50, and 30 vol% EMC, and 10, 20, and 40 vol% MA. The composition of electrolyte B in Example A10 is 30 vol% EC and 70 vol% MA.

[0027] The electrolyte A in Comparative Example B1 is a non-aqueous electrolyte containing a carbonate-based solvent, which is an organic solvent other than an ester-based solvent. The composition of the electrolyte A in Comparative Example B1 contains 30 [vol%] EC and 70 [vol%] EMC. The electrolytes A in Comparative Examples B2 to B11 are non-aqueous electrolytes containing an ester-based solvent. The composition of the electrolytes A in Comparative Examples B2 to B4 contains 30 [vol%] EC, 60, 50, and 30 [vol%] EMC, and 10, 20, and 40 [vol%] MP, respectively. The composition of the electrolyte A in Comparative Example B5 contains 30 [vol%] EC and 70 [vol%] MP. The composition of the electrolyte A in Comparative Example B6 contains 20 [vol%] EC and 80 [vol%] MP. The electrolyte A composition of Comparative Example B7 contains 10 vol% EC and 90 vol% MP. The electrolyte A compositions of Comparative Examples B8 to B10 contain 30 vol% EC, 60, 50, and 30 vol% EMC, and 10, 20, and 40 vol% MA, respectively. The electrolyte A composition of Comparative Example B11 contains 30 vol% EC and 70 vol% MA.

[0028] Furthermore, the composition of electrolyte B in Comparative Examples B1 to B11 is the same as the composition of electrolyte A in each of those examples.

[0029] The electrolyte A in Comparative Examples B12 to B22 is a non-aqueous electrolyte containing a carbonate-based solvent, which is an organic solvent other than an ester-based solvent. Furthermore, the composition of the electrolyte A in Comparative Examples B12 to B22 contains 30 [vol%] of EC and 70 [vol%] of EMC.

[0030] Furthermore, the electrolyte B in Comparative Example B12 is a non-aqueous electrolyte containing a carbonate-based solvent, which is an organic solvent other than an ester-based solvent. The composition of the electrolyte B in Comparative Example B12 contains 30 [vol%] of EC and 70 [vol%] of EMC. The electrolyte B in Comparative Examples B13 to B22 is a non-aqueous electrolyte containing an ester-based solvent. The composition of the electrolyte B in Comparative Examples B13 to B15 contains 30 [vol%] of EC, 60, 50, and 30 [vol%] of EMC, and 10, 20, and 40 [vol%] of MP, respectively. The composition of the electrolyte B in Comparative Example B16 contains 30 [vol%] of EC and 70 [vol%] of MP. The composition of the electrolyte B in Comparative Example B17 contains 20 [vol%] of EC and 80 [vol%] of MP. The electrolyte B composition of Comparative Example B18 contains 10 vol% EC and 90 vol% MP. The electrolyte B compositions of Comparative Examples B19 to B21 contain 30 vol% EC, 60, 50, and 30 vol% EMC, and 10, 20, and 40 vol% MA, respectively. The electrolyte B composition of Comparative Example B22 contains 30 vol% EC and 70 vol% MA.

[0031] The electrolyte A in Comparative Examples B23 and B34 is a non-aqueous electrolyte containing a carbonate-based solvent, which is an organic solvent other than an ester-based solvent. The composition of electrolyte A in Comparative Examples B23 and B34 contains 30 [vol%] of EC and 70 [vol%] of EMC. The electrolyte A in Comparative Examples B24 to B33 is a non-aqueous electrolyte containing an ester-based solvent. The composition of electrolyte A in Comparative Examples B24 to B26 contains 30 [vol%] of EC, 60, 50, and 30 [vol%] of EMC, and 10, 20, and 40 [vol%] of MP, respectively. The composition of electrolyte A in Comparative Example B27 contains 30 [vol%] of EC and 70 [vol%] of MP. The composition of electrolyte A in Comparative Example B28 contains 20 [vol%] of EC and 80 [vol%] of MP. The electrolyte A composition of Comparative Example B29 contains 10 vol% EC and 90 vol% MP. The electrolyte A compositions of Comparative Examples B30 to B32 contain 30 vol% EC, 60, 50, and 30 vol% EMC, and 10, 20, and 40 vol% MA, respectively. The electrolyte A composition of Comparative Example B33 contains 30 vol% EC and 70 vol% MA.

[0032] Furthermore, the composition of electrolyte B in Comparative Examples B23 to B34 is the same as the composition of electrolyte A in each of those examples.

[0033] [Battery cell manufacturing process] For each of Examples A1 to A10 and Comparative Examples B1 to B34, a battery cell was fabricated by enclosing the electrode body and electrolyte A in an outer casing (sealing with lamination).

[0034] [Activation process] For each battery cell of Examples A1 to A10 and Comparative Examples B1 to B34, the initial charge was performed in a 25°C constant temperature bath using a constant current method, charging to a predetermined voltage with a current value of 0.1C. Subsequently, the battery cells were discharged to 3.0V using a constant current method with a current value of 0.3C. This process was repeated three times.

[0035] The full cell voltage reached upon activation in Examples A1 to A10 is 4.5[V]. The full cell voltage reached upon activation in Comparative Examples B1 to B11 is 4.3[V]. The full cell voltage reached upon activation in Comparative Examples B12 to B22 is 4.5[V]. The full cell voltage reached upon activation in Comparative Examples B23 to B33 is 4.3[V], and the full cell voltage reached upon activation in Comparative Example B34 is 4.5[V].

[0036] [Liquid replacement process] For each of the activated battery cells in Examples A1 to A10 and Comparative Examples B1 to B34, electrolyte A was discharged from inside the battery cell and electrolyte B was injected into the battery cell using a flow-type electrolyte injection device in an inert atmosphere or a dry air atmosphere. The electrolyte exchange process was carried out for 5 minutes to ensure that electrolyte A was completely replaced with electrolyte B.

[0037] [Initial characteristic evaluation] For each of the battery cells in Examples A1 to A10 and Comparative Examples B1 to B34 after the electrolyte replacement process, charging was performed using a constant current-constant voltage method with a current value of 0.1[C] up to 4.2[V], and then constant voltage charging was continued until the current value during constant voltage charging became 1 / 50[C], bringing the battery to a fully charged state. Subsequently, the capacity obtained when the battery was discharged using a constant current method with a current value of 0.2[C] down to 3.0[V] was defined as the initial capacity.

[0038] [Measurement of battery cell volume] For each battery cell in Examples A1 to A10 and Comparative Examples B1 to B34, the battery cell volume (total volume of the battery cell) was measured using the Archimedes method.

[0039] [Storage test (durability test)] For each battery cell of Examples A1 to A10 and Comparative Examples B1 to B34, charging was performed in a 25°C constant temperature bath using a constant current-constant voltage method with a current value of 0.1°C to 4.30V. After that, the temperature of the constant temperature bath was raised to 60°C and the cells were stored for 100 days. After the storage period, the constant temperature bath was returned to 25°C, and after temperature control for 3 hours, the cells were discharged using a constant current method with a current value of 0.2°C to 3.00V, and the remaining capacity and battery cell volume were measured. The remaining capacity was calculated as (discharge capacity after storage) / (discharge capacity before storage). The amount of gas generated during the storage test was calculated as (battery cell volume after storage test) - (battery cell volume before storage test).

[0040] Table 1 shows the composition of the positive electrode mixture, electrolyte A, the voltage reached at full cell upon activation, the composition of electrolyte B, the residual capacity retention rate, and the amount of gas generated for Examples 1 to 10. Table 2 shows the composition of the positive electrode mixture, electrolyte A, the voltage reached at full cell upon activation, the composition of electrolyte B, the residual capacity retention rate, and the amount of gas generated for Comparative Examples B1 to B11. Table 3 shows the composition of the positive electrode mixture, electrolyte A, the voltage reached at full cell upon activation, the composition of electrolyte B, the residual capacity retention rate, and the amount of gas generated for Comparative Examples B12 to B22. Table 4 shows the composition of the positive electrode mixture, electrolyte A, the voltage reached at full cell upon activation, the composition of electrolyte B, the residual capacity retention rate, and the amount of gas generated for Comparative Examples B23 to B34. In Tables 1 to 4, non-aqueous solvents are indicated by the abbreviations EC (ethylene carbonate), EMC (ethyl methyl carbonate), MP (methyl propionate), and MA (methyl acetate).

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3]

[0044] [Table 4]

[0045] Figure 1 shows the relationship between the ester solvent ratio and the remaining volume retention rate for Examples A1 to A6, Comparative Examples B1 to B7, Comparative Examples B12 to B17, Comparative Examples B23 to B29, and Comparative Example B34. Figure 2 shows the relationship between the ester solvent ratio and the gas generation amount for Examples A1 to A6, Comparative Examples B1 to B7, Comparative Examples B12 to B17, Comparative Examples B23 to B29, and Comparative Example B34. In both Figure 1 and Figure 2, the ester solvent ratio is the ratio of ester solvent contained in electrolyte B.

[0046] As is clear from Tables 1 to 4 and Figures 1 and 2, Examples A1 to A10 achieve a higher residual capacity retention rate and lower gas generation compared to Comparative Examples B1 to B34. Specifically, in Examples A1 to A10, by using electrolyte A (first non-aqueous electrolyte) containing an organic solvent other than an ester-based solvent in the activation process, a protective film is formed on the lithium phosphate (Li3PO4) in the positive electrode composite, thereby reducing the amount of gas that may be generated when a lithium-ion secondary battery (battery cell) is discharged after long-term storage. Furthermore, in Examples A1 to A10, after activation, the non-aqueous electrolyte of the battery cell is replaced from electrolyte A (first non-aqueous electrolyte) to electrolyte B (second non-aqueous electrolyte) containing an ester-based solvent, which suppresses the decomposition of the ester-based solvent by activation and allows for a high residual capacity retention rate.

[0047] In Examples A1 to A10, the ester solvent content in electrolyte B ranges from 10 vol% to 90 vol%, but according to the principles, similar effects can be obtained even if the ester solvent content in electrolyte B is 100 vol%.

Claims

1. An electrode body comprising a positive electrode and a negative electrode, wherein the positive electrode has a positive electrode composite material containing a positive electrode active material and lithium phosphate, and an electrode body manufacturing step for manufacturing the electrode body, A battery cell manufacturing step involves enclosing the electrode body and a first non-aqueous electrolyte containing an organic solvent other than an ester-based solvent in an outer casing to produce a battery cell, An activation step in which the battery cell is activated by applying a predetermined voltage, A liquid replacement step is performed in which the first non-aqueous electrolyte is discharged from the activated battery cell and a second non-aqueous electrolyte containing an ester-based solvent is injected, thereby replacing the non-aqueous electrolyte. Having A method for manufacturing a lithium-ion secondary battery, characterized by the following features.

2. The second non-aqueous electrolyte contains the ester solvent in an amount of 10 [vol%] to 90 [vol%]. A method for manufacturing a lithium-ion secondary battery according to claim 1.

3. The organic solvent other than the ester-based solvent contained in the first non-aqueous electrolyte is a carbonate-based solvent. A method for manufacturing a lithium-ion secondary battery according to claim 1 or 2, characterized by the above.

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