Manufacturing method of non-aqueous electrolyte secondary battery

Abstract

To provide a manufacturing method of a non-aqueous electrolyte secondary battery that can improve rapid charge / discharge performance, maintain volumetric energy density, and improve impregnation of the non-aqueous electrolyte.SOLUTION: A manufacturing method of a non-aqueous electrolyte secondary battery includes the steps of mixing a substance with a melting point of 30°C or higher into at least one of the positive and negative electrodes in an amount of 3 mass% to 6 mass% relative to the electrode composite, and injecting a non-aqueous electrolyte solution with a viscosity of 2 mPa s or lower.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Patent Document 1 describes a method of improving the impregnation of an electrode for a non-aqueous electrolyte secondary battery with an electrolyte solution by transferring a pattern of protrusions and recesses onto the electrode using a roll mold, forming vertical and horizontal grooves, and allowing the electrolyte solution to spread through the grooves. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7301083 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the nonaqueous electrolyte secondary battery disclosed in Patent Document 1, the grooves are formed by pressing a roll mold, which results in locally high density in the grooves. This reduces the diffusibility of Li ions in the grooves, which may lead to deterioration of rapid charge / discharge performance and concerns about Li deposition in the grooves. Forming grooves by methods other than the roll mold, such as scraping or pattern coating, also reduces the amount of active material in the grooves and reduces Li ion acceptance, raising concerns about Li deposition. Therefore, an object of one embodiment of the present disclosure is to provide a method for manufacturing a nonaqueous electrolyte secondary battery that can improve rapid charge / discharge performance, maintain volumetric energy density, and improve impregnation of the nonaqueous electrolyte. [Means for solving the problem]

[0005] The present disclosure encompasses the following: <1> a step of mixing a substance having a melting point of 30°C or higher into at least one of the positive electrode and the negative electrode in an amount of 3% by mass to 6% by mass based on the mass of the electrode composite; injecting a non-aqueous electrolyte with a viscosity of 2 mPa·s or less; A method for manufacturing a non-aqueous electrolyte secondary battery, comprising: <2> The substance having a melting point of 30°C or higher is at least one of ethylene carbonate and an alkali metal salt. <1> 10. A method for producing the nonaqueous electrolyte secondary battery according to claim 9. <3> the electrode is a positive electrode, and the battery further includes a step of initiating initial charging before all of the alkali metal salt has dissolved in the non-aqueous electrolyte. <2> 10. A method for producing the nonaqueous electrolyte secondary battery according to claim 9. [Effects of the Invention]

[0006] According to one embodiment of the present disclosure, it is possible to provide a method for manufacturing a nonaqueous electrolyte secondary battery that can improve rapid charge / discharge performance, maintain volumetric energy density, and improve impregnation of the nonaqueous electrolyte. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a graph showing a Nyquist plot for explaining the impregnation completion time in Examples. [Figure 2] 1 is a graph illustrating how to determine the impregnation completion time in an example. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described. The following description is for illustrative purposes only and does not limit the scope of the present disclosure.

[0009] The method for manufacturing a nonaqueous electrolyte secondary battery according to the present disclosure includes the steps of mixing a substance having a melting point of 30°C or higher into at least one of the positive electrode and the negative electrode in an amount of 3% by mass or more and 6% by mass or less, based on the mass of the electrode composite, and injecting a nonaqueous electrolyte having a viscosity of 2 mPa s or less. Hereinafter, the "positive electrode and negative electrode" will be collectively referred to as "electrodes." "Substances with a melting point of 30°C or higher" will also be referred to as "solid substances."

[0010] In the manufacturing method of the present disclosure, mixing a solid substance into the electrode increases the wettability of the electrode with the electrolyte solution, improving the impregnation of the electrode with the nonaqueous electrolyte solution. Furthermore, injecting a nonaqueous electrolyte solution with a low viscosity of 2 mPa s or less into a battery cell equipped with this electrode further improves the impregnation of the electrode with the nonaqueous electrolyte solution.

[0011] When a non-aqueous electrolyte is injected into a battery cell equipped with electrodes containing solid materials, the solid materials in the electrodes dissolve in the non-aqueous electrolyte, leaving voids where the solid materials were previously present in the electrodes. The presence of these voids improves ion diffusion during charge and discharge, improving rapid charge and discharge performance. Furthermore, by keeping the amount of solid material mixed at 6 mass % or less, the amount of voids formed is reduced, and therefore a significant decrease in volumetric energy density is prevented.

[0012] The solid substance is preferably a substance commonly added to non-aqueous electrolytes, such as electrolyte salts, non-aqueous solvents, and other additives. Examples of non-aqueous solvents include ethylene carbonate (EC). Non-aqueous electrolytes generally contain high concentrations of dissolved electrolyte salts, and because highly viscous EC is used, the viscosity of the non-aqueous electrolyte tends to be high. Therefore, by premixing at least one of the electrolyte salt and EC with the electrode, the amounts of electrolyte salt and EC contained in the non-aqueous electrolyte can be reduced, thereby lowering the viscosity of the non-aqueous electrolyte. Examples of electrolyte salts include alkali metal salts. In other words, the non-aqueous electrolyte secondary battery according to the present disclosure may be a lithium-ion battery, a sodium-ion battery, or a potassium-ion battery. It should be noted that the solid substance is not limited to electrolyte salt and EC, since mixing a solid substance into the electrode increases the wettability of the electrode with the non-aqueous electrolyte.

[0013] Preferably, the electrode into which the solid substance is mixed is a positive electrode, and the method further includes a step of initiating initial charging before all of the alkali metal salt dissolves in the non-aqueous electrolyte. Since the dissolution rate of the alkali metal salt in the non-aqueous electrolyte increases as the concentration of the alkali metal salt decreases, charging is initiated before all of the alkali metal salt dissolves in the non-aqueous electrolyte to reduce the concentration of the alkali metal salt in the positive electrode mixture. This accelerates the dissolution rate of the alkali metal salt, further shortening the time required for battery production.

[0014] The electrodes according to the present disclosure can be made of general electrode active materials, materials such as binders, current collectors, etc. In addition, general components such as separators can be used as components other than electrodes. [Example]

[0015] The present disclosure will be described in more detail below using examples, but the technical scope of the present disclosure is not limited to the following examples.

[0016] [Example 1] As shown in Table 1, in Examples 1 to 3 and Comparative Examples 2 to 7, LiPF6 and EC were mixed in the amounts (X mass %) shown in Table 1 relative to the electrode mixture in at least one of the positive electrode and the negative electrode. 0.8 Co 0.1 Mn 0.1 A slurry of graphite, acetylene black, polyvinylidene fluoride, and a solid material mixed in N-methyl-2-pyrrolidone at a mass ratio of 96:2:2:100X / (100-X) was applied to aluminum foil. The negative electrode was prepared by applying a slurry of graphite, styrene-butadiene rubber, carboxymethyl cellulose, and a solid material mixed in pure water at a mass ratio of 97:2:1:100X / (100-X) to copper foil. A 2032-type coin cell was fabricated using the positive electrode, the negative electrode, and a polypropylene separator. The non-aqueous electrolyte to be injected into the electrode was prepared so that when the EC and LiPF6 in the electrode were dissolved, the concentration of LiPF6 was 1.0 mol / L and the ratio of EC:DMC (dimethyl carbonate) was 3:7 (by volume).

[0017] (Measurement of impregnation completion time) The non-aqueous electrolyte was poured into the battery, and the time required for the impregnation to be completed was measured. The impregnation completion time can be measured by impedance (see, for example, JP 2004-311343 A). Immediately after injecting the nonaqueous electrolyte, the coin cell was placed in an impedance measuring device, and measurements were performed for 12 hours under the following conditions. If the time for one impedance measurement was less than 12 hours, the impedance measurement was repeated until the cumulative time reached 12 hours. As shown in Figure 1, the Nyquist plot shifts to the left as the impregnation progresses, and stabilizes at a constant value once impregnation is complete. This value is defined as the convergence value. As shown in Figure 2, the time at which the value at the intersection of the Nyquist plot and the x-axis (solution resistance) first falls within +1% of the convergence value was defined as the "impregnation completion time." -Impedance measurement conditions- Potential amplitude: 10 mV Frequency range: 100,000Hz to 0.01Hz

[0018] (Evaluation of rapid charge / discharge performance) The battery cells were charged by passing a constant current equivalent to 0.1C until they reached 4.2V, and then maintaining the voltage at 4.2V until the current value decreased to 1 / 50C. The cells charged in this manner were discharged at a constant current, and the capacity up to 2.5V was defined as the discharge capacity at that rate. The ratio of the 1C discharge capacity to the 0.1C discharge capacity (1C discharge capacity / 0.1C discharge capacity) was calculated as an index of rapid charge / discharge performance.

[0019] (Measurement of relative volumetric energy density) The volumetric energy density was calculated by multiplying the discharge capacity measured under the above conditions by the average voltage during discharge and dividing the product by the volume of the battery container. The relative energy density of each battery was calculated when the volumetric energy density of the battery of Comparative Example 1 was set to 1.

[0020] [Table 1]

[0021] As shown in Table 1, Examples 1 to 3, in which a solid substance was mixed in an amount of 3 mass % or more and 6 mass % or less with respect to the mass of the electrode composite and a nonaqueous electrolyte solution with a viscosity of 2 mPa s or less was injected, had a significantly shorter impregnation completion time and were also excellent in rapid charge / discharge performance and relative volumetric energy density compared to Comparative Example 1, in which no solid substance was mixed. In Comparative Examples 2 to 4, in which the amount of solid substance mixed was less than 3 mass %, the impregnation completion time was shorter than in Comparative Example 1, but the effect was small and limited. Furthermore, even when the amount of solid substance mixed was increased to more than 6 mass % as in Comparative Examples 5 and 6, the impregnation completion time did not change significantly compared to the Examples, but the relative volumetric energy density decreased significantly. In Comparative Example 7, the impregnation completion time was shortened, but the relative volumetric energy density decreased significantly.

Claims

[Claim 1] a step of mixing a substance having a melting point of 30°C or higher into at least one of the positive electrode and the negative electrode in an amount of 3% by mass to 6% by mass based on the mass of the electrode composite; injecting a non-aqueous electrolyte solution having a viscosity of 2 mPa·s or less; A method for manufacturing a non-aqueous electrolyte secondary battery, comprising:

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