Negative electrode plate and method for manufacturing the negative electrode plate, as well as lithium ion secondary battery and method for manufacturing the lithium ion secondary battery

Abstract

To reduce a diffusion resistance of a negative electrode plate of a lithium ion secondary battery.SOLUTION: A negative electrode plate of a lithium ion secondary battery comprises a collector 11, and a mixture layer 12 laminated on the collector 11. In an embodiment hereof, the mixture layer 12 contains, as a negative electrode active material, carbon particles 14 of 80 wt.% or more. The mixture layer 12 further contains lactone of 0.2 pt.wt. or less per 98.8 pts.wt. of the carbon particles 14. In the embodiment, the mixture layer 12 contains lactone of 0.005 pt.wt. or more per 98.8 pts.wt. of the carbon particles 14. In another embodiment, the mixture layer contains a negative electrode active material and coumarin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode plate for a lithium ion secondary battery. [Background technology]

[0002] Patent Documents 1 to 4 disclose lithium ion secondary batteries using an electrolyte solution containing lactone. Patent Document 5 discloses a binder for a negative electrode containing γ-butyrolactone. Patent Document 6 discloses a negative electrode containing γ-butyrolactone. Patent Document 7 discloses a negative electrode containing an acid dianhydride having a coumarin ring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-019274 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-020702 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-89457 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-078799 [Patent Document 5] Patent No. 6052529 [Patent Document 6] Japanese Patent Application Laid-Open No. 2011-044310 [Patent Document 7] International Publication No. 2014 / 119377 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention reduces the diffusion resistance of the negative electrode plate of a lithium ion secondary battery. [Means for solving the problem]

[0005] [1] A battery comprising a current collector and a mixture layer laminated on the current collector, the mixture layer contains 80% by weight or more of a carbon material as a negative electrode active material, the mixture layer further contains 0.2 parts by weight or less of a lactone per 98.8 parts by weight of carbon material; Negative electrode plate of a lithium-ion secondary battery. [2] The mixture layer contains 0.005 parts by weight or more of lactone per 98.8 parts by weight of carbon material. [1] The negative electrode plate according to [1]. [3] The lactone is one or more compounds selected from the following: α-lactones, such as α-acetolactone; β-lactones, such as β-propiolactone; γ-lactones, such as γ-butyrolactone, γ-nonalactone, γ-decalactone and γ-octalactone; δ-lactones, such as δ-valerolactone, coumarin and gluconolactone; Cyclopentadecanolide; and cyclohexadecanolide, The negative electrode plate according to [1] or [2]. [4] A current collector and a mixture layer laminated on the current collector, the mixture layer contains a negative electrode active material and a lactone, The lactone is a coumarin. Negative electrode plate of a lithium-ion secondary battery. [5] The negative electrode active material is graphite. The negative electrode plate according to any one of [1] to [4]. [6] A battery comprising a positive electrode plate, the negative electrode plate according to any one of [1] to [5], and an electrolyte solution. Lithium-ion secondary battery. [7] A battery is fabricated by combining a positive electrode plate, the negative electrode plate according to any one of claims 1 to 5, and an electrolyte solution, wherein the electrolyte solution does not contain the same lactone as the lactone contained in the mixture layer; Conditioning is performed by energizing the battery. A method for manufacturing lithium-ion secondary batteries. [8] A paste is prepared by mixing more than 80% by weight of a carbon material as a negative electrode active material, a binder, a lactone, and a dispersion medium; the paste is applied onto a current collector, and the dispersion medium is removed to laminate a mixture containing the carbon material, the binder, and the lactone on the current collector. Method for manufacturing negative electrode plates. [Effects of the Invention]

[0006] The present invention reduces the diffusion resistance of the negative electrode plate of a lithium ion secondary battery. [Brief explanation of the drawings]

[0007] [Figure 1] Cross section of negative electrode plate [Figure 2] Schematic diagram of paste preparation [Figure 3] Change in diffusion resistance [Figure 4] Change in IV resistance DETAILED DESCRIPTION OF THE INVENTION

[0008] <Negative electrode>

[0009] FIG. 1 shows a cross section of a negative electrode plate 10 of a lithium-ion secondary battery. The negative electrode plate 10 includes a current collector 11 and a mixture layer 12. The current collector 11 is made of, for example, copper foil. The mixture layer 12 is laminated on the current collector 11. The mixture layer 12 contains carbon particles 14, which are negative electrode active materials, and lactone. The carbon particles 14 are made of a carbon material used as a negative electrode active material, such as synthetic graphite or natural graphite. The mixture layer 12 shown in FIG. 1 contains 80% by weight or more of the carbon particles 14. Dispersion media such as non-aqueous solvents for lithium salts and water are excluded from the 100% by weight of the entire mixture layer 12. The coating 15 that covers the carbon particles 14 will be described later.

[0010] The mixture layer 12 shown in Figure 1 contains more than 0 parts by weight and not more than 0.5 parts by weight of lactone per 98.8 parts by weight of carbon particles 14. The mixture layer 12 preferably contains 0.001 to 0.2 parts by weight, more preferably 0.002 to 0.2 parts by weight, even more preferably 0.005 to 0.2 parts by weight, even more preferably 0.01 to 0.2 parts by weight, and still more preferably 0.05 to 0.2 parts by weight of lactone per 98.8 parts by weight of carbon material. The mixture layer 12 may contain 0.1 part by weight of lactone per 98.8 parts by weight of carbon material.

[0011] Lactones are cyclic esters formed by dehydration condensation between a hydroxyl group (-OH) and a carboxyl group (-COOH) in a molecule. In one aspect, lactones are heterocyclic compounds consisting of two or more carbon atoms and one oxygen atom. The carbon atom adjacent to the oxygen atom that constitutes the ring forms a carbonyl group (>C=O).

[0012] The lactone is at least one of α-lactones such as α-acetolactone, β-lactones such as β-propiolactone, γ-lactones such as γ-butyrolactone, γ-nonalactone, γ-decalactone, and γ-octalactone, δ-lactones such as δ-valerolactone, coumarin, and gluconolactone, cyclopentadecanolide, and cyclohexadecanolide. The lactone is preferably coumarin, as shown in the following formula:

[0013] [ka]

[0014] <Preparation of negative electrode plate>

[0015] A method for producing a negative electrode plate will be described using Figure 2. Figure 2 schematically shows the production of a negative electrode mixture paste used in a negative electrode plate. The paste is produced by mixing more than 80 wt% carbon particles 14, binder 17, lactone particles 18, and a dispersion medium 19. The carbon particles 14, binder 17, and lactone particles 18 are dispersed in the dispersion medium 19. The lactone particles 18 may be dissolved in the dispersion medium 19. In one embodiment, the dispersion medium 19 does not contain lactone itself. In one embodiment, the dispersion medium 19 is water. The lactone particles 18 may be dissolved in the dispersion medium 19.

[0016] 2, the lactone constituting the lactone particles 18 is a lactone that is solid at room temperature, 20° C.±15° C., such as coumarin. The lactone particles 18 may be replaced with a lactone that is liquid at room temperature, 20° C.±15° C., such as γ-butyrolactone.

[0017] As shown in Figure 2, the prepared paste is applied to a current collector, such as copper foil. The dispersion medium is removed from the applied paste. If the lactone is dissolved in the dispersion medium, the lactone is left in the applied paste. As a result, a mixture layer 12 containing carbon particles, a binder, and a lactone is laminated on the current collector 11 as shown in Figure 1.

[0018] By adding lactone, the oxo group (=O) of the lactone decomposes and converts to a hydroxyl group (-OH). This improves the affinity between the lactone decomposition product and water. This allows the carbon particles 14 and binder 17 shown in FIG. 2 to be uniformly dispersed in the negative electrode mixture paste. This improves the condition of the mixture layer 12 shown in FIG. 1 formed by applying the paste. Furthermore, lithium ions diffuse well from the carbon particles 14.

[0019] The effect of uniformly dispersing the carbon particles and binder described above is achieved by adding lactone to the negative electrode mixture paste. In contrast, when lactone is not added to the negative electrode mixture paste but is added to the electrolyte solution as described in Patent Documents 1 to 4, this effect is not achieved. Furthermore, when lactone is added to the electrolyte solution, the effect of improving the diffusion of lithium ions from the carbon particles is not significantly achieved.

[0020] <Battery construction>

[0021] A battery is fabricated by combining a positive electrode plate, a negative electrode plate 10 shown in FIG. 1, and an electrolyte solution containing a lithium salt. In one embodiment, the electrolyte solution is non-aqueous. In one embodiment, the electrolyte solution does not contain the lactone contained in the paste shown in FIG. 1. This does not include the lactone being dissolved from the negative electrode plate after the battery is fabricated, resulting in the lactone being contained in the electrolyte solution.

[0022] The fabricated battery is conditioned by passing a current through it. During conditioning, lactone decomposes in the vicinity of the carbon particles 14 shown in FIG. 1. The decomposed lactone coordinates as a ligand to the carbon atoms on the surface of the carbon particles 14. The coordinated decomposition product forms a coating 15 on the surface of the carbon particles. The coating 15 reduces the diffusion resistance of lithium ions around the negative electrode plate 10. [Example]

[0023] Coumarin was selected as the lactone. Example C The components of the negative electrode mix were mixed as shown in C1 and C2. In these examples, coumarin was not mixed into the negative electrode mix. Furthermore, as shown in examples W1, W2, W3, and W4, coumarin and the components of the negative electrode mix were mixed. In each example, the total weight of the mix, excluding the water dispersion medium, was 100%. CMC is carboxymethyl cellulose. SBR is styrene-butadiene rubber.

[0024] The negative electrode mixture was applied to a current collector to prepare a negative electrode plate. A negative electrode plate, a positive electrode plate, and an electrolyte were combined to prepare an evaluation cell. Coumarin was added to the electrolyte solution in Example C2 at the concentration (wt%) listed in Table 1. The IV resistance, diffusion resistance, and reaction resistance of the negative electrode plate were measured using conventional methods. IV resistance is the so-called internal resistance, and its components include diffusion resistance and reaction resistance. Diffusion resistance is the resistance to lithium ion migration within the active material particles. Reaction resistance is the resistance to charge transfer at the interface between the active material and the electrolyte. The results are shown in Table 1. The measured IV resistance in Example C1 was set to 100 (%), and the measured values ​​of each resistance were converted.

[0025] [Table 1]

[0026] Figure 3 shows the change in diffusion resistance as points. One point is the measured IV resistance of Example C1 divided by 100. Comparing Examples W1 to W4 with Example C1 reveals that the addition of lactone, such as coumarin, to the composite layer reduces the diffusion resistance of the negative electrode plate. To achieve the effect of reducing diffusion resistance, the lactone content can be anywhere from 0.005 to 0.5 parts by weight per 98.8 parts by weight of graphite. Comparing Example W2 with Example C2 reveals that, at the same content ratio, adding lactone, such as coumarin, to the negative electrode composite is more effective at reducing the diffusion resistance of the negative electrode plate than adding it to the electrolyte.

[0027] Figure 4 shows the change in IV resistance at points. Comparing Examples W1 to W3 with Example C1, it can be seen that the IV resistance of the negative electrode plate also decreases when the composite layer contains 0.005 to 0.2 parts by weight of a lactone, such as coumarin, per 98.8 parts by weight of graphite. Furthermore, as shown in Example W2, the effect is strongest when 0.05 parts by weight of a lactone, such as coumarin, is added per 98.8 parts by weight of graphite.

[0028] Based on Table 1, we will examine the IV resistance in more detail. When the mixture layer contains lactone, the reaction resistance increases according to the lactone content. This contributes to an increase in the IV resistance of the negative electrode plate. However, when the mixture layer contains 0.005 to 0.2 parts by weight of lactone per 98.8 parts by weight of graphite, the contribution of the reduction in diffusion resistance exceeds this. Therefore, adding lactone in the above amount helps to reduce the IV resistance. [Explanation of symbols]

[0029] 10 negative electrode plate, 11 current collector, 12 mixture layer, 14 carbon particles, 15 coating, 17 binder, 18 lactone particles, 19 dispersion medium

Claims

1. A negative electrode plate of a lithium ion secondary battery having an electrolyte solution that does not contain lactone, a current collector and a mixture layer laminated on the current collector, the mixture layer contains 80% by weight or more of a carbon material as a negative electrode active material, the mixture layer further contains 0.2 parts by weight or less of a lactone per 98.8 parts by weight of carbon material; The lactone is a coumarin. Negative electrode plate of a lithium-ion secondary battery.

2. the mixture layer contains 0.005 parts by weight or more of lactone per 98.8 parts by weight of carbon material; The negative electrode plate according to claim 1 .

3. The negative electrode active material is graphite. The negative electrode plate according to claim 1 or 2.

4. A battery comprising a positive electrode plate, a negative electrode plate according to any one of claims 1 to 3, and the electrolyte solution. Lithium-ion secondary battery.

5. A battery is fabricated by combining a positive electrode plate, the negative electrode plate according to any one of claims 1 to 3, and the electrolytic solution, wherein the electrolytic solution does not contain the same lactone as the lactone contained in the mixture layer; Conditioning is performed by energizing the battery. A method for manufacturing lithium-ion secondary batteries.

6. A method for manufacturing a negative electrode plate of a lithium ion secondary battery having an electrolyte solution that does not contain lactone, comprising: A paste is prepared by mixing more than 80% by weight of a carbon material as a negative electrode active material, a binder, a lactone, and a dispersion medium; the paste is applied onto a current collector, and the dispersion medium is removed to form a mixture layer containing the carbon material, the binder, and the lactone on the current collector; the mixture layer contains 0.2 parts by weight or less of a lactone per 98.8 parts by weight of carbon material; The lactone is a coumarin. Method for manufacturing negative electrode plates.

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