Lithium-ion secondary battery and lithium-ion secondary battery module

Abstract

This lithium-ion secondary battery includes a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, and an electrolyte solution. A negative electrode active material included in the negative electrode active material layer includes graphite particles and Si-C composite particles including silicon and a carbon material, the electrolyte solution includes fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and a ratio according to the following formula (1a) is 0.150-1.000.　(1a): Ratio [volume% / mass%] = ((content [volume%] of the fluoroethylene carbonate in the electrolyte solution) + (content [volume%] of the sulfo-based compound in the electrolyte solution)) / (content [mass%] of the Si-C composite particles in the negative electrode active material)

Description

Lithium-ion secondary batteries and lithium-ion secondary battery modules

[0001] This invention relates to lithium-ion secondary batteries and lithium-ion secondary battery modules.

[0002] Lithium-ion secondary batteries include a positive electrode, a negative electrode, and an electrolyte. Technologies related to lithium-ion secondary batteries include those described in Patent Documents 1 and 2.

[0003] Patent Document 1 discloses that lithium secondary batteries have various problems, some of which are related to the manufacturing and operating characteristics of the negative electrode. It describes a secondary battery characterized by comprising: a positive electrode in which a positive electrode mixture containing a positive electrode active material is coated onto a current collector; a negative electrode in which a negative electrode mixture containing a negative electrode active material is coated onto a current collector, and the negative electrode contains a carbon-based material and a silicon-based compound; and an electrolyte containing a lithium salt and a non-aqueous solvent, wherein the electrolyte contains a cyclic carbonate and / or a linear solvent; and exhibits excellent lifespan characteristics and safety.

[0004] Patent Document 2 addresses the objective of providing a lithium-ion secondary battery with high capacity and excellent charge-discharge cycle characteristics, and describes a general composition formula Li ａ Ni （１－ｂ－ｃ） Co ｂ McO ２ A lithium-ion secondary battery is disclosed comprising: a positive electrode containing a lithium-containing composite oxide represented by (M being at least one element from Mn and Al, with 0.9 ≤ a ≤ 1.3, 0 < b, 0 < c, b + c ≤ 0.5); a negative electrode containing a composite of a material containing Si and O as constituent elements (where the atomic ratio x of O to Si is 0.5 ≤ x ≤ 1.5) and a conductive material, and a carbon material other than the conductive material contained in the composite as a negative electrode active material; and a non-aqueous electrolyte containing a cyclic carbonate having a C=C double bond and a halogen-substituted cyclic carbonate, wherein the relationship between the proportion of the composite in the negative electrode active material and the content of each cyclic carbonate in the non-aqueous electrolyte before and after the first charge-discharge is specified.

[0005] Japanese Patent Publication No. 2018-88419 Japanese Patent Publication No. 2011-233368

[0006] This invention provides a lithium-ion secondary battery with improved cycle characteristics.

[0007] The inventors diligently conducted research to achieve the above objectives. As a result, they discovered that cycle characteristics can be improved in a lithium-ion secondary battery containing graphite particles and Si-C composite particles as negative electrode active materials by: the electrolyte containing fluoroethylene carbonate and a sulfo-based compound, and setting the ratio calculated from the content of Si-C composite particles, fluoroethylene carbonate, and sulfo-based compound to a specific numerical range; the electrolyte containing fluoroethylene carbonate and a sulfo-based compound, and setting the ratio calculated from the specific surface area of ​​Si-C composite particles by the nitrogen adsorption BET method, and the content of fluoroethylene carbonate and sulfo-based compound to a specific numerical range; the electrolyte containing fluoroethylene carbonate and lithium fluorosulfate, and setting the content of fluoroethylene carbonate in the electrolyte to a specific numerical range; or the electrolyte containing fluoroethylene carbonate and a sulfo-based compound, and setting the volume ratio of the content of fluoroethylene carbonate to the content of sulfo-based compound to a specific numerical range. Based on these findings, the inventors completed the present invention.

[0008] According to the present invention, the following lithium-ion secondary battery and lithium-ion secondary battery module are provided.

[0009] [1] A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1a) is 0.150 or more and 1.000 or less. Ratio [volume % / mass %] = ((Content of the above fluoroethylene carbonate in the above electrolyte [volume %]) + (Content of the above sulfo-based compound in the above electrolyte [volume %])) / (Content of the above Si-C composite particles in the above negative electrode active material [mass %]) ... (1a) Here, the content of the above fluoroethylene carbonate and the content of the above sulfo-based compound in the above electrolyte are values ​​when the content of the above organic solvent (S) contained in the above electrolyte is taken as 100 volume %, and the content of the above Si-C composite particles in the above negative electrode active material is value when the total amount of the above negative electrode active material contained in the above negative electrode active material layer is taken as 100 mass %. [2] A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1b) is 0.50 or more and 2.00 or less. Ratio [volume %・g / m³] ２ ] = ((Content of the above fluoroethylene carbonate in the above electrolyte [volume %]) + (Content of the above sulfo-based compound in the above electrolyte [volume %])) / (Specific surface area of ​​the above Si-C composite particles by nitrogen adsorption BET method [m²] ２ / g]) ... (1b) Here, the content of fluoroethylene carbonate and the content of sulfo compounds in the electrolyte are values ​​when the content of the organic solvent (S) contained in the electrolyte is taken as 100 volume%. [3] A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, the electrolyte comprises fluoroethylene carbonate, a sulfo compound, and an organic solvent (S), and the volume ratio of the content of fluoroethylene carbonate to the content of the sulfo compound in the electrolyte is 1.05 or more and 5.00 or less. [4] A lithium-ion secondary battery according to any one of [1] to [3] above, wherein the content of the fluoroethylene carbonate in the electrolyte is 1.00% by volume or more and 10.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume. [5] A lithium-ion secondary battery according to any one of [1] to [4] above, wherein the sulfo-based compound comprises one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone, methylene methanedisulfonate, and ethylene sulfate. [6] A lithium-ion secondary battery according to any one of [1] to [5] above, wherein the content of the sulfo-based compound in the electrolyte is 1.00% by volume or more and 5.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume. [7] The lithium-ion secondary battery according to any one of [1] to [6], wherein the content of the electrolyte in the lithium-ion secondary battery is 15 parts by mass or more and 60 parts by mass or less when the sum of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass. [8] Median diameter D in the volume frequency particle size distribution of the graphite particles by laser diffraction scattering method. ５０is 1.0 µm or more and 30.0 µm or less, the lithium ion secondary battery according to any one of [1] to [7] above. [9] The content of the graphite particles in the negative electrode active material is 10 parts by mass or more and 99 parts by mass or less, where the total content of the graphite particles and the Si-C composite particles is 100 parts by mass, the lithium ion secondary battery according to any one of [1] to [8] above.

[10] The carbon material in the Si-C composite particles comprises a porous carbon material, and the silicon is present in at least a part of the pores of the porous carbon material, the lithium ion secondary battery according to any one of [1] to [9] above.

[11] The specific surface area of the Si-C composite particles measured by nitrogen adsorption BET method is 1 m ２ / g or more and 20 m ２ / g or less, the lithium ion secondary battery according to any one of [1] to

[10] above.

[12] The median diameter D in the volume frequency particle size distribution of the Si-C composite particles measured by laser diffraction scattering method ５０ is 1.0 µm or more and 20.0 µm or less, the lithium ion secondary battery according to any one of [1] to

[11] above.

[13] The content of the Si-C composite particles in the negative electrode active material is 1 part by mass or more and 90 parts by mass or less, where the total content of the graphite particles and the Si-C composite particles is 100 parts by mass, the lithium ion secondary battery according to any one of [1] to

[12] above.

[14] The organic solvent (S) comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and γ-butyrolactone, the lithium ion secondary battery according to any one of [1] to

[13] above.

[15] A capacity retention ratio R at 45°C determined by the following (Method 1) ４５However, the lithium-ion secondary battery described in any of [1] to

[14] above has a capacity retention rate of 79.0% or higher. (Method 1) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the first time is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times have been performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the 500th time is measured. After that, the capacity retention rate R is calculated from the following formula (2). ４５ The following is calculated: Equation (2): The above capacity retention rate R ４５= (Discharge capacity at the 500th time) / (Discharge capacity at the 1st time) × 100 (Charge-discharge cycle) Charge the lithium-ion secondary battery at 30 mA until the upper limit voltage of 4.25 V is reached. After the upper limit voltage of 4.25 V is reached, charge the lithium-ion secondary battery at a constant voltage until 2.5 hours have elapsed since the start of charging, and then discharge the lithium-ion secondary battery at a constant current of 30 mA until the lower limit voltage of 2.5 V is reached.

[16] A lithium-ion secondary battery according to any of [1] to

[15] above, wherein the amount of gas generated by (Method 2) below is 0.40 cc / Ah or less. (Method 2) Place the lithium-ion secondary battery in a constant temperature bath at 45°C, and then charge and discharge the lithium-ion secondary battery according to the following (charge-discharge cycle) and measure the discharge capacity at the first time. Then, repeat the charging and discharging of the lithium-ion secondary battery according to the following (charge-discharge cycle) until a total of 499 times are performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge / discharge cycle), the discharge capacity after the 500th time is measured, and then the volume of the lithium-ion secondary battery after the 500th charge / discharge is measured. After that, the amount of gas generated (cc / Ah) is calculated from the following formula (3). Formula (3): Amount of gas generated = {(Volume of the lithium-ion secondary battery after the 500th charge / discharge) - (Volume of the lithium-ion secondary battery before the first charge / discharge)} / [{(Discharge capacity after the first time) + (Discharge capacity after the 500th time)} / 2] (Charge / discharge cycle) The lithium-ion secondary battery is charged at 30 mA until the upper limit voltage of 4.25 V is reached. After the upper limit voltage of 4.25 V is reached, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V is reached.

[17] A lithium-ion secondary battery module comprising a lithium-ion secondary battery as described in any of [1] to

[16] above.

[0010] Furthermore, according to the first embodiment of the present invention, the following lithium-ion secondary battery and lithium-ion secondary battery module are provided.

[0011] [1a] A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1a) is 0.150 or more and 1.000 or less. Ratio [volume % / mass %] = ((Content of the above fluoroethylene carbonate in the above electrolyte [volume %]) + (Content of the above sulfo-based compound in the above electrolyte [volume %])) / (Content of the above Si-C composite particles in the above negative electrode active material [mass %]) ... (1a) Here, the content of the above fluoroethylene carbonate and the content of the above sulfo-based compound in the above electrolyte are values ​​when the content of the above organic solvent (S) contained in the above electrolyte is taken as 100 volume%, and the content of the above Si-C composite particles in the above negative electrode active material is value when the total amount of the above negative electrode active material contained in the above negative electrode active material layer is taken as 100 mass%. [2a] The lithium-ion secondary battery according to [1a] above, wherein the content of the above fluoroethylene carbonate in the above electrolyte is 1.00 volume% or more and 10.00 volume% or less when the content of the above organic solvent (S) contained in the above electrolyte is taken as 100 volume%, [3a] The lithium-ion secondary battery according to [1a] or [2a], wherein the sulfo-based compound comprises one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone, methylene methanedisulfonate, and ethylene sulfate. [4a] The lithium-ion secondary battery according to any one of [1a] to [3a], wherein the content of the sulfo-based compound in the electrolyte is 1.00% by volume or more and 5.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is 100% by volume. [5a] The lithium-ion secondary battery according to any one of [1a] to [4a], wherein the content of the electrolyte in the lithium-ion secondary battery is 15 parts by mass or more and 60 parts by mass or less, when the sum of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass.[6a] Median diameter D in the volume frequency particle size distribution of the above graphite particles obtained by laser diffraction scattering. ５０ A lithium-ion secondary battery according to any one of [1a] to [5a] above, wherein the particle size is 1.0 μm or more and 30.0 μm or less. [7a] A lithium-ion secondary battery according to any one of [1a] to [6a] above, wherein the content of the graphite particles in the negative electrode active material is 10 parts by mass or more and 99 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [8a] A lithium-ion secondary battery according to any one of [1a] to [7a] above, wherein the carbon material in the Si-C composite particles includes a porous carbon material, and the silicon is present in at least a part of the pores of the porous carbon material. [9a] The specific surface area of ​​the Si-C composite particles by nitrogen adsorption BET method is 1 m ２ / g or more 20m ２ A lithium-ion secondary battery according to any one of [1a] to [8a] above, wherein the amount is less than or equal to / g. [10a] Median diameter D in the volume frequency particle size distribution of the Si-C composite particles by laser diffraction scattering method. ５０ A lithium-ion secondary battery according to any one of [1a] to [9a] above, wherein the particle size is 1.0 μm or more and 20.0 μm or less. [11a] A lithium-ion secondary battery according to any one of [1a] to [10a] above, wherein the content of the Si-C composite particles in the negative electrode active material is 1 part by mass or more and 90 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [12a] A lithium-ion secondary battery according to any one of [1a] to [11a] above, wherein the organic solvent (S) contains one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone. [13a] The capacity retention rate R at 45°C according to the following (Method 1) ４５However, the lithium-ion secondary battery described in any of [1a] to [12a] above has a capacity retention rate of 79.0% or more. (Method 1a) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the first time is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times are performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the 500th time is measured. After that, the capacity retention rate R is calculated from the following formula (2a). ４５ The following is calculated: Equation (2a): The above capacity retention rate R ４５= (Discharge capacity at the 500th time) / (Discharge capacity at the 1st time) × 100 (Charge-discharge cycle) Charge the lithium-ion secondary battery at 30 mA until the upper limit voltage of 4.25 V is reached. After the upper limit voltage of 4.25 V is reached, charge the lithium-ion secondary battery at a constant voltage until 2.5 hours have elapsed since the start of charging, and then discharge the lithium-ion secondary battery at a constant current of 30 mA until the lower limit voltage of 2.5 V is reached. [14a] A lithium-ion secondary battery according to any of [1a] to [13a] above, wherein the amount of gas generated by (Method 2a) below is 0.40 cc / Ah or less. (Method 2a) Place the lithium-ion secondary battery in a constant temperature bath at 45°C, and then charge and discharge the lithium-ion secondary battery according to the following (charge-discharge cycle) and measure the discharge capacity at the first time. Then, repeat the charging and discharging of the lithium-ion secondary battery according to the following (charge-discharge cycle) until a total of 499 times are performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge / discharge cycle), the discharge capacity after the 500th time is measured, and then the volume of the lithium-ion secondary battery after the 500th charge / discharge is measured. After that, the amount of gas generated (cc / Ah) is calculated from the following formula (3a). Formula (3a): Amount of gas generated = {(Volume of the lithium-ion secondary battery after the 500th charge / discharge) - (Volume of the lithium-ion secondary battery before the first charge / discharge)} / [{(Discharge capacity after the first time) + (Discharge capacity after the 500th time)} / 2] (Charge / discharge cycle) The lithium-ion secondary battery is charged at 30 mA until the upper limit voltage of 4.25 V is reached. After the upper limit voltage of 4.25 V is reached, the lithium-ion secondary battery is charged at a constant voltage until the elapsed time since the start of charging is 2.5 hours, and then the lithium-ion secondary battery is discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V is reached. [15a] A lithium-ion secondary battery module comprising the lithium-ion secondary battery described in any of [1a] to [14a] above.

[0012] Furthermore, according to a second embodiment of the present invention, the following lithium-ion secondary battery and lithium-ion secondary battery module are provided.

[0013] [1b] A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1b) is 0.50 or more and 2.00 or less. Ratio [volume %・g / m³] ２ ] = ((Content of the above fluoroethylene carbonate in the above electrolyte [volume %]) + (Content of the above sulfo-based compound in the above electrolyte [volume %])) / (Specific surface area of ​​the above Si-C composite particles by nitrogen adsorption BET method [m²] ２ [g]) ... (1b) Here, the content of the fluoroethylene carbonate and the content of the sulfo compound in the electrolyte are values ​​when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume. [2b] The lithium-ion secondary battery according to [1b], wherein the content of the fluoroethylene carbonate in the electrolyte is 1.00% by volume or more and 10.00% by volume or less when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume. [3b] The lithium-ion secondary battery according to [1b] or [2b], wherein the sulfo compound comprises one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone, methylene methanedisulfonic acid, and ethylene sulfate. [4b] The lithium-ion secondary battery according to any one of [1b] to [3b], wherein the content of the sulfo-based compound in the electrolyte is 1.00% by volume or more and 5.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is 100% by volume. [5b] The lithium-ion secondary battery according to any one of [1b] to [4b], wherein the content of the electrolyte in the lithium-ion secondary battery is 15 parts by mass or more and 60 parts by mass or less, when the sum of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass. [6b] Median diameter D in the volume frequency particle size distribution of the graphite particles by laser diffraction scattering method. ５０A lithium-ion secondary battery according to any one of [1b] to [5b] above, wherein the particle size is 1.0 μm or more and 30.0 μm or less. [7b] A lithium-ion secondary battery according to any one of [1b] to [6b] above, wherein the content of the graphite particles in the negative electrode active material is 10 parts by mass or more and 99 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [8] A lithium-ion secondary battery according to any one of [1b] to [7b] above, wherein the carbon material in the Si-C composite particles includes a porous carbon material, and the silicon is present in at least a part of the pores of the porous carbon material. [9b] ​​The specific surface area of ​​the Si-C composite particles by nitrogen adsorption BET method is 1 m ２ / g or more 20m ２ A lithium-ion secondary battery according to any of [1b] to [8b] above, wherein the amount is less than or equal to / g. [10b] Median diameter D in the volume frequency particle size distribution of the Si-C composite particles by laser diffraction scattering method. ５０ A lithium-ion secondary battery according to any one of [1b] to [9b] ​​above, wherein the particle size is 1.0 μm or more and 20.0 μm or less. [11b] A lithium-ion secondary battery according to any one of [1b] to [10b] above, wherein the content of the Si-C composite particles in the negative electrode active material is 1 part by mass or more and 90 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [12b] A lithium-ion secondary battery according to any one of [1b] to [11b] above, wherein the organic solvent (S) contains one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone. [13b] The capacity retention rate R at 45°C according to the following (Method 1) ４５However, the lithium-ion secondary battery described in any of [1b] to [12b] above has a capacity retention rate of 79.0% or more. (Method 1b) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the first time is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times have been performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the 500th time is measured. After that, the capacity retention rate R is calculated from the following formula (2b). ４５ The following is calculated: Equation (2b): The above capacity retention rate R ４５= (Discharge capacity at the 500th time) / (Discharge capacity at the 1st time) × 100 (Charge-discharge cycle) Charge the lithium-ion secondary battery at 30mA until it reaches the upper limit voltage of 4.25V. After reaching the upper limit voltage of 4.25V, charge the lithium-ion secondary battery at a constant voltage until 2.5 hours have elapsed since the start of charging, and then discharge the lithium-ion secondary battery at a constant current of 30mA until it reaches the lower limit voltage of 2.5V. [14b] A lithium-ion secondary battery according to any of [1b] to [13b] above, wherein the amount of gas generated by the following (Method 2b) is 0.40cc / Ah or less. (Method 2b) Place the lithium-ion secondary battery in a constant temperature bath at 45°C, and then charge and discharge the lithium-ion secondary battery according to the following (charge-discharge cycle) and measure the discharge capacity at the first time. Then, repeat the charging and discharging of the lithium-ion secondary battery according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge / discharge cycle), the discharge capacity after the 500th time is measured, and then the volume of the lithium-ion secondary battery after the 500th charge / discharge is measured. After that, the amount of gas generated (cc / Ah) is calculated from the following formula (3b). Formula (3b): Amount of gas generated = {(Volume of the lithium-ion secondary battery after the 500th charge / discharge) - (Volume of the lithium-ion secondary battery before the first charge / discharge)} / [{(Discharge capacity after the first time) + (Discharge capacity after the 500th time)} / 2] (Charge / discharge cycle) The lithium-ion secondary battery is charged at 30 mA until the upper limit voltage of 4.25 V is reached. After the upper limit voltage of 4.25 V is reached, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V is reached. [15b] A lithium-ion secondary battery module comprising a lithium-ion secondary battery as described in any of [1b] to [14b] above.

[0014] Furthermore, according to a third embodiment of the present invention, the following lithium-ion secondary battery and lithium-ion secondary battery module are provided.

[0015] [1c] A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, lithium fluorosulfate, and an organic solvent (S), wherein the content of fluoroethylene carbonate in the electrolyte is 1.50% by volume or more and 10.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is 100.0% by volume. [2c] The lithium-ion secondary battery according to [1c], wherein the content of lithium fluorosulfate in the electrolyte is 0.10% by volume or more and 1.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is 100.0% by volume. [3c] The lithium-ion secondary battery according to [1c] or [2c], wherein the volume ratio of the content of fluoroethylene carbonate to the content of lithium fluorosulfate in the electrolyte is 2.0 or more and 15.0 or less. [4c] The lithium-ion secondary battery according to any one of [1c] to [3c], wherein the electrolyte further contains a sulfo-based compound other than lithium fluorosulfate. [5c] The lithium-ion secondary battery according to [4c], wherein the sulfo-based compound other than lithium fluorosulfate contains one or more selected from the group consisting of 1,3-propanesultone, methylene methanedisulfonate, and ethylene sulfate. [6c] The lithium-ion secondary battery according to [4c] or [5c], wherein the content of the sulfo-based compound other than lithium fluorosulfate in the electrolyte is 0.10% by volume or more and 5.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is 100.0% by volume. [7c] The lithium-ion secondary battery according to any one of [1c] to [6c], wherein the content of the electrolyte in the lithium-ion secondary battery is 15 parts by mass or more and 60 parts by mass or less when the sum of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass. [8c] Median diameter D in the volume frequency particle size distribution of the graphite particles by laser diffraction scattering method. ５０A lithium-ion secondary battery according to any one of [1c] to [7c] above, wherein the particle size is 1.0 μm or more and 30.0 μm or less. [9c] A lithium-ion secondary battery according to any one of [1c] to [8c] above, wherein the content of the graphite particles in the negative electrode active material is 10 parts by mass or more and 99 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [10c] A lithium-ion secondary battery according to any one of [1c] to [9c] above, wherein the carbon material in the Si-C composite particles includes a porous carbon material, and the silicon is present in at least a part of the pores of the porous carbon material. [11c] The specific surface area of ​​the Si-C composite particles by nitrogen adsorption BET method is 1 m ２ / g or more 20m ２ A lithium-ion secondary battery according to any of [1c] to [10c] above, wherein the amount is less than or equal to / g. [12c] Median diameter D in the volume frequency particle size distribution of the above Si-C composite particles by laser diffraction scattering method. ５０ A lithium-ion secondary battery according to any one of [1c] to [11c] above, wherein the particle size is 1.0 μm or more and 20.0 μm or less. [13c] A lithium-ion secondary battery according to any one of [1c] to [12c] above, wherein the content of the Si-C composite particles in the negative electrode active material is 1 part by mass or more and 90 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [14c] A lithium-ion secondary battery according to any one of [1c] to [13c] above, wherein the organic solvent (S) contains one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone. [15c] The capacity retention rate R at 45°C according to the following (Method 1) ４５However, the lithium-ion secondary battery described in any of [1c] to [14c] above has a capacity retention rate of 79.0% or higher. (Method 1c) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the first time is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times have been performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the 500th time is measured. After that, the capacity retention rate R is calculated from the following formula (2c). ４５ The following is calculated: Equation (2c): The above capacity retention rate R ４５= (Discharge capacity at the 500th time) / (Discharge capacity at the 1st time) × 100 (Charge-discharge cycle) Charge the lithium-ion secondary battery at 30mA until the upper limit voltage of 4.25V is reached. After the upper limit voltage of 4.25V is reached, charge the lithium-ion secondary battery at a constant voltage until 2.5 hours have elapsed since the start of charging, and then discharge the lithium-ion secondary battery at a constant current of 30mA until the lower limit voltage of 2.5V is reached. [16c] A lithium-ion secondary battery according to any of [1c] to [15c] above, wherein the amount of gas generated by (Method 2c) below is 0.40cc / Ah or less. (Method 2c) Place the lithium-ion secondary battery in a constant temperature bath at 45°C, and then charge and discharge the lithium-ion secondary battery according to the following (charge-discharge cycle) and measure the discharge capacity at the first time. Then, repeat the charging and discharging of the lithium-ion secondary battery according to the following (charge-discharge cycle) until a total of 499 times are performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge / discharge cycle), the discharge capacity after the 500th time is measured, and then the volume of the lithium-ion secondary battery after the 500th charge / discharge is measured. After that, the amount of gas generated (cc / Ah) is calculated from the following formula (3c). Formula (3c): Amount of gas generated = {(Volume of the lithium-ion secondary battery after the 500th charge / discharge) - (Volume of the lithium-ion secondary battery before the first charge / discharge)} / [{(Discharge capacity after the first time) + (Discharge capacity after the 500th time)} / 2] (Charge / discharge cycle) The lithium-ion secondary battery is charged at 30 mA until the upper limit voltage of 4.25 V is reached. After the upper limit voltage of 4.25 V is reached, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V is reached. [17c] A lithium-ion secondary battery module comprising a lithium-ion secondary battery as described in any of [1c] to [16c] above.

[0016] Furthermore, according to a fourth embodiment of the present invention, the following lithium-ion secondary battery and lithium-ion secondary battery module are provided.

[0017] [1d] A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the volume ratio of the fluoroethylene carbonate content to the sulfo-based compound content in the electrolyte is 1.05 or more and 5.00 or less. [2d] The lithium-ion secondary battery according to [1d], wherein the fluoroethylene carbonate content in the electrolyte is 1.00% by volume or more and 10.00% by volume or less, when the organic solvent (S) content in the electrolyte is taken as 100% by volume. [3d] The lithium-ion secondary battery according to [1d] or [2d], wherein the sulfo-based compound comprises one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone, methylene methanedisulfonic acid, and ethylene sulfate. [4d] The lithium-ion secondary battery according to any one of [1d] to [3d], wherein the content of the sulfo-based compound in the electrolyte is 1.00% by volume or more and 5.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is 100% by volume. [5d] The lithium-ion secondary battery according to any one of [1d] to [4d], wherein the content of the electrolyte in the lithium-ion secondary battery is 15 parts by mass or more and 60 parts by mass or less, when the sum of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass. [6d] Median diameter D in the volume frequency particle size distribution of the graphite particles by laser diffraction scattering method. ５０A lithium-ion secondary battery according to any one of [1d] to [5d] above, wherein the particle size is 1.0 μm or more and 30.0 μm or less. [7d] A lithium-ion secondary battery according to any one of [1d] to [6d] above, wherein the content of the graphite particles in the negative electrode active material is 10 parts by mass or more and 99 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [8d] A lithium-ion secondary battery according to any one of [1d] to [7d] above, wherein the carbon material in the Si-C composite particles includes a porous carbon material, and the silicon is present in at least a part of the pores of the porous carbon material. [9d] The specific surface area of ​​the Si-C composite particles by nitrogen adsorption BET method is 1 m ２ / g or more 20m ２ A lithium-ion secondary battery according to any of [1d] to [8d] above, wherein the amount is less than or equal to / g. [10d] Median diameter D in the volume frequency particle size distribution of the Si-C composite particles by laser diffraction scattering method. ５０ A lithium-ion secondary battery according to any one of [1d] to [9d] above, wherein the particle size is 1.0 μm or more and 20.0 μm or less. [11d] A lithium-ion secondary battery according to any one of [1d] to [10d] above, wherein the content of the Si-C composite particles in the negative electrode active material is 1 part by mass or more and 90 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass. [12d] A lithium-ion secondary battery according to any one of [1d] to [11d] above, wherein the organic solvent (S) contains one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone. [13d] The capacity retention rate R at 45°C according to the following (Method 1) ４５However, the lithium-ion secondary battery described in any of [1d] to [12d] above has a capacity retention rate of 79.0% or more. (Method 1d) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the first time is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times have been performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the 500th time is measured. After that, the capacity retention rate R is calculated from the following formula (2d). ４５ The following is calculated: Equation (2d): The above capacity retention rate R ４５= (Discharge capacity at the 500th time) / (Discharge capacity at the 1st time) × 100 (Charge-discharge cycle) Charge the lithium-ion secondary battery at 30mA until the upper limit voltage of 4.25V is reached. After the upper limit voltage of 4.25V is reached, charge the lithium-ion secondary battery at a constant voltage until 2.5 hours have elapsed since the start of charging, and then discharge the lithium-ion secondary battery at a constant current of 30mA until the lower limit voltage of 2.5V is reached. [14d] A lithium-ion secondary battery according to any of [1d] to [13d] above, wherein the amount of gas generated by the following (Method 2d) is 0.40cc / Ah or less. (Method 2d) Place the lithium-ion secondary battery in a constant temperature bath at 45°C, and then charge and discharge the lithium-ion secondary battery according to the following (charge-discharge cycle) and measure the discharge capacity at the first time. Then, repeat the charging and discharging of the lithium-ion secondary battery according to the following (charge-discharge cycle) until a total of 499 times are performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge / discharge cycle), the discharge capacity after the 500th time is measured, and then the volume of the lithium-ion secondary battery after the 500th charge / discharge is measured. After that, the amount of gas generated (cc / Ah) is calculated from the following formula (3d). Formula (3d): Amount of gas generated = {(Volume of the lithium-ion secondary battery after the 500th charge / discharge) - (Volume of the lithium-ion secondary battery before the first charge / discharge)} / [{(Discharge capacity after the first time) + (Discharge capacity after the 500th time)} / 2] (Charge / discharge cycle) The lithium-ion secondary battery is charged at 30 mA until the upper limit voltage of 4.25 V is reached. After the upper limit voltage of 4.25 V is reached, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V is reached. [15d] A lithium-ion secondary battery module comprising a lithium-ion secondary battery as described in any of [1d] to [14d] above.

[0018] According to the present invention, a lithium-ion secondary battery with improved cycle characteristics can be provided.

[0019] This is a schematic cross-sectional view illustrating an example of a lithium-ion secondary battery according to this embodiment.

[0020] The embodiments of the present invention will be described in detail below with reference to the drawings. To avoid complexity, if there are multiple identical components in the same drawing, only one will be given a reference numeral, and not all of them may be given reference numerals. The drawings are for illustrative purposes only. The shapes and dimensional ratios of each component in the drawings do not necessarily correspond to actual articles. In these embodiments, "A to B" indicating a numerical range means A or greater and B or less unless otherwise specified. In this specification, the first to fourth embodiments will also be collectively referred to as "this embodiment."

[0021] [First Embodiment] <Lithium-ion secondary battery> The lithium-ion secondary battery of the first embodiment is a lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1a) is 0.150 or more and 1.000 or less. Ratio [volume % / mass %] = ((Content of the above fluoroethylene carbonate in the above electrolyte [volume %]) + (Content of the above sulfo-based compound in the above electrolyte [volume %])) / (Content of the above Si-C composite particles in the above negative electrode active material [mass %]) ... (1a) Here, the content of the above fluoroethylene carbonate and the content of the above sulfo-based compound in the above electrolyte are values ​​when the content of the organic solvent (S) contained in the above electrolyte is taken as 100 volume %, and the content of the above Si-C composite particles in the above negative electrode active material is value when the total amount of the above negative electrode active material contained in the above negative electrode active material layer is taken as 100 mass %.

[0022] The lithium-ion secondary battery of the first embodiment can improve cycle characteristics by having the above configuration. The reason why the lithium-ion secondary battery of the first embodiment can improve cycle characteristics is not clear, but it is thought that when an electrolyte in which the ratio according to formula (1a) is within the above range is used, an SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode active material contained in the negative electrode active material layer, which can maintain its structure stably even after repeated charging and discharging.

[0023] In the lithium-ion secondary battery of the first embodiment, the ratio according to formula (1a) above is preferably 0.155 to 0.950, more preferably 0.160 to 0.900, even more preferably 0.165 to 0.850, even more preferably 0.170 to 0.800, even more preferably 0.175 to 0.750, even more preferably 0.180 to 0.700, even more preferably 0.190 to 0.650, even more preferably 0.200 to 0.600, even more preferably 0.210 to 0.550, and even more preferably 0.220 to 0.500, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and its cycle characteristics.

[0024] The configuration of the lithium-ion secondary battery of the first embodiment will be explained with reference to the figures. Figure 1 is a schematic cross-sectional view showing an example of the lithium-ion secondary battery of this embodiment. Note that Figure 1 is a common figure in all four embodiments from the first to the fourth. In the first embodiment, the lithium-ion secondary battery 10 includes a positive electrode containing a positive electrode active material layer 1, a negative electrode containing a negative electrode active material layer 2, and an electrolyte. A separator 5 can be provided between the positive electrode and the negative electrode. Multiple pairs of positive and negative electrodes can be provided.

[0025] The lithium-ion secondary battery 10 has a positive electrode comprising a positive electrode current collector 3 and a positive electrode active material layer 1 containing a positive electrode active material provided thereon. The lithium-ion secondary battery 10 also has a negative electrode comprising a negative electrode current collector 4 and a negative electrode active material layer 2 containing a negative electrode active material provided thereon. The positive electrode and the negative electrode are stacked via a separator 5, for example, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. The electrode pair consisting of the positive electrode and the negative electrode is housed in a container formed by an outer casing 6 and an outer casing 7. A positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4. The positive electrode tab 9 and the negative electrode tab 8 are drawn out of the container. The injected electrolyte is sealed inside the container. The container may contain an electrode group in which multiple electrode pairs are stacked.

[0026] <Method for Manufacturing a Lithium-Ion Secondary Battery> In the first embodiment, a lithium-ion secondary battery can be manufactured according to a known method. For electrodes, for example, laminates or wound bodies can be used. For the outer casing, a metal casing or an aluminum laminate casing can be used as appropriate. The shape of the battery may be any shape such as laminate type, coin type, button type, sheet type, cylindrical type, prismatic type, or flat type, but a laminate type battery is preferred.

[0027] Next, we will explain lithium-ion secondary batteries by their constituent components.

[0028] [Electrolyte] In the lithium-ion secondary battery of the first embodiment, the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S).

[0029] In the lithium-ion secondary battery of the first embodiment, the content of fluoroethylene carbonate in the electrolyte is preferably 1.00% to 10.00% by volume, more preferably 1.10% to 9.50% by volume, even more preferably 1.20% to 9.00% by volume, even more preferably 1.30% to 8.50% by volume, even more preferably 1.40% to 8.00% by volume, even more preferably 1.50% to 7.50% by volume, even more preferably 1.60% to 7.00% by volume, even more preferably 1.70% to 6.50% by volume, and even more preferably 1.80% to 6.00% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume.

[0030] From the viewpoint of further improving the performance balance between reducing the amount of gas generated in lithium-ion secondary batteries and their cycle characteristics, the sulfo compounds preferably include one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone (PS), 1,3-propanesultone derivatives, methylene methanedisulfonic acid ester (MMDS), ethylene sulfate (DTD), ethylene disulfonic acid ester, propylene methanedisulfonic acid ester, vinyl sulfonic acid ester, sulfonic acid amide, methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, and biphenyldisulfonic acid, and more preferably include one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone (PS), methylene methanedisulfonic acid (MMDS), and ethylene sulfate (DTD). In the first embodiment, a sulfo-based compound is defined as a compound containing a functional group selected from the group consisting of a sulfo group, a sulfonic acid ester group, and a sulfonyl group (except for compounds containing lithium).

[0031] In the lithium-ion secondary battery of the first embodiment, the content of sulfo-based compounds in the electrolyte is preferably 1.00% to 5.00% by volume, more preferably 1.05% to 4.50% by volume, even more preferably 1.10% to 4.00% by volume, even more preferably 1.15% to 3.50% by volume, even more preferably 1.20% to 3.00% by volume, and even more preferably 1.30% to 2.50% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and the cycle characteristics.

[0032] The organic solvent (S) preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone, more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and even more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0033] The electrolyte may contain additives other than fluoroethylene carbonate. From the viewpoint of further improving the cycle characteristics, the additives other than fluoroethylene carbonate preferably further contain one or more selected from the group consisting of SEI film formation promoters such as vinylene carbonate (VC), chloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, and methyl propionate; and electrolyte stability enhancers such as dimethoxyethane, tetrahydrofuran, ethyl acetate, dimethyl sulfoxide, ethylene sulfide, triphenyl phosphate, fluorinated dimethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether, more preferably containing an SEI film formation promoter, and even more preferably containing vinylene carbonate.

[0034] In the lithium-ion secondary battery of the first embodiment, the content of additives other than fluoroethylene carbonate in the electrolyte is preferably 0.01% to 3.00% by volume, more preferably 0.05% to 2.00% by volume, even more preferably 0.10% to 1.00% by volume, and even more preferably 0.15% to 0.50% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume, from the viewpoint of further improving cycle characteristics.

[0035] In the lithium-ion secondary battery of the first embodiment, the electrolyte preferably includes an electrolyte. The electrolyte is preferably lithium hexafluoride phosphate (LiPF). ６ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorobis(oxalato) phosphate (LIDODFP), lithium difluorophosphate (LiPO ２ F ２ ), LiBF ４ LiCl, LiC ４ F ９ SO ３ and Li(CF ３ SO ２ ) ２It comprises one or more selected from the group consisting of N, and more preferably LiPF ６ LiBF ４ , comprising one or more selected from the group consisting of LiFSI and LiCl, more preferably LiPF ６ Includes.

[0036] In the lithium-ion secondary battery of the first embodiment, the concentration of the electrolyte in the electrolyte solution during the manufacturing of the lithium-ion secondary battery is preferably 0.001 mol / L or more and 5.0 mol / L or less, more preferably 0.01 mol / L or more and 5.0 mol / L or less, even more preferably 0.025 mol / L or more and 5.0 mol / L or less, even more preferably 0.05 mol / L or more and 5.0 mol / L or less, even more preferably 0.075 mol / L or more and 5.0 mol / L or less, even more preferably 0.1 mol / L or more and 2.5 mol / L or less, even more preferably 0.25 mol / L or more and 2.0 mol / L or less, even more preferably 0.5 mol / L or more and 1.5 mol / L or less, and even more preferably 0.75 mol / L or more and 1.25 mol / L or less, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and the cycle characteristics.

[0037] In the lithium-ion secondary battery of the first embodiment, the electrolyte content in the lithium-ion secondary battery is preferably 15 to 60 parts by mass, more preferably 20 to 55 parts by mass, even more preferably 25 to 50 parts by mass, and even more preferably 30 to 45 parts by mass, when the total of the negative electrode active material content and positive electrode active material content in the lithium-ion secondary battery is 100 parts by mass, from the viewpoint of further improving the cycle characteristics of the lithium-ion secondary battery.

[0038] [Second Embodiment] <Lithium-ion secondary battery> The lithium-ion secondary battery of the second embodiment is a lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1b) is 0.50 or more and 2.00 or less. Ratio [Volume %・g / m³] ２ ] = ((Content of the above fluoroethylene carbonate in the above electrolyte [volume %]) + (Content of the above sulfo-based compound in the above electrolyte [volume %])) / (Specific surface area of ​​the above Si-C composite particles by nitrogen adsorption BET method [m²] ２ / g]) ... (1b) Here, the content of fluoroethylene carbonate and the content of sulfo compounds in the electrolyte are values ​​when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume.

[0039] The lithium-ion secondary battery of the second embodiment can improve cycle characteristics by having the above configuration. The reason why the lithium-ion secondary battery of the second embodiment can improve cycle characteristics is not clear, but it is thought that when an electrolyte in which the ratio according to formula (1b) is within the above range is used, an SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode active material contained in the negative electrode active material layer, which can maintain its structure stably even after repeated charging and discharging.

[0040] In the lithium-ion secondary battery of the second embodiment, the ratio according to formula (1b) above is preferably 0.51 to 1.80, more preferably 0.52 to 1.60, even more preferably 0.53 to 1.50, even more preferably 0.54 to 1.40, and even more preferably 0.55 to 1.30, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and its cycle characteristics.

[0041] The configuration of the lithium-ion secondary battery of the second embodiment will be described with reference to the figures. Figure 1 is a schematic cross-sectional view showing an example of the lithium-ion secondary battery of this embodiment. In the second embodiment, the lithium-ion secondary battery 10 includes a positive electrode containing a positive electrode active material layer 1, a negative electrode containing a negative electrode active material layer 2, and an electrolyte. A separator 5 can be provided between the positive electrode and the negative electrode. Multiple pairs of positive and negative electrodes can be provided.

[0042] The lithium-ion secondary battery 10 has a positive electrode comprising a positive electrode current collector 3 and a positive electrode active material layer 1 containing a positive electrode active material provided thereon. The lithium-ion secondary battery 10 also has a negative electrode comprising a negative electrode current collector 4 and a negative electrode active material layer 2 containing a negative electrode active material provided thereon. The positive electrode and the negative electrode are stacked via a separator 5, for example, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. The electrode pair consisting of the positive electrode and the negative electrode is housed in a container formed by an outer casing 6 and an outer casing 7. A positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4. The positive electrode tab 9 and the negative electrode tab 8 are drawn out of the container. The injected electrolyte is sealed inside the container. The container may contain an electrode group in which multiple electrode pairs are stacked.

[0043] <Method for Manufacturing Lithium-Ion Secondary Batteries> In the second embodiment, lithium-ion secondary batteries can be manufactured according to known methods. For electrodes, for example, laminates or wound bodies can be used. For the outer casing, metal casings or aluminum laminate casings can be used as appropriate. The shape of the battery may be any shape such as laminate type, coin type, button type, sheet type, cylindrical type, prismatic type, or flat type, but laminate type batteries are preferred.

[0044] Next, we will explain lithium-ion secondary batteries by their constituent components.

[0045] [Electrolyte] In the lithium-ion secondary battery of the second embodiment, the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S).

[0046] In the lithium-ion secondary battery of the second embodiment, the content of fluoroethylene carbonate in the electrolyte is preferably 1.00% to 10.00% by volume, more preferably 1.10% to 9.50% by volume, even more preferably 1.20% to 9.00% by volume, even more preferably 1.30% to 8.50% by volume, even more preferably 1.40% to 8.00% by volume, even more preferably 1.50% to 7.50% by volume, even more preferably 1.60% to 7.00% by volume, even more preferably 1.70% to 6.50% by volume, and even more preferably 1.80% to 6.00% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume.

[0047] From the viewpoint of further improving the performance balance between reducing the amount of gas generated in lithium-ion secondary batteries and their cycle characteristics, the sulfo compounds preferably include one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone (PS), 1,3-propanesultone derivatives, ethylene sulfate (DTD), methylene methanedisulfonic acid ester (MMDS), ethylene disulfonic acid ester, propylene methanedisulfonic acid ester, vinyl sulfonic acid ester, sulfonic acid amide, methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, and biphenyldisulfonic acid, and more preferably include one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone (PS), methylene methanedisulfonic acid (MMDS), and ethylene sulfate (DTD). In the second embodiment, a sulfo-based compound is defined as a compound containing a functional group selected from the group consisting of a sulfo group, a sulfonic acid ester group, and a sulfonyl group (except for compounds containing lithium).

[0048] In the lithium-ion secondary battery of the second embodiment, the content of sulfo-based compounds in the electrolyte is preferably 1.00% to 5.00% by volume, more preferably 1.05% to 4.50% by volume, even more preferably 1.10% to 4.00% by volume, even more preferably 1.15% to 3.50% by volume, even more preferably 1.20% to 3.00% by volume, and even more preferably 1.30% to 2.50% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and the cycle characteristics.

[0049] The organic solvent (S) preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone, more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and even more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0050] The electrolyte may contain additives other than fluoroethylene carbonate. From the viewpoint of further improving the cycle characteristics, the additives other than fluoroethylene carbonate preferably further contain one or more selected from the group consisting of SEI film formation promoters such as vinylene carbonate (VC), chloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, and methyl propionate; and electrolyte stability enhancers such as dimethoxyethane, tetrahydrofuran, ethyl acetate, dimethyl sulfoxide, ethylene sulfide, triphenyl phosphate, fluorinated dimethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether, more preferably containing an SEI film formation promoter, and even more preferably containing vinylene carbonate.

[0051] In the lithium-ion secondary battery of the second embodiment, the content of additives other than fluoroethylene carbonate in the electrolyte is preferably 0.01% to 3.00% by volume, more preferably 0.05% to 2.00% by volume, even more preferably 0.10% to 1.00% by volume, and even more preferably 0.15% to 0.50% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume, from the viewpoint of further improving cycle characteristics.

[0052] In the lithium-ion secondary battery of the second embodiment, the electrolyte preferably includes an electrolyte. The electrolyte is preferably lithium hexafluoride phosphate (LiPF). ６ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorobis(oxalato) phosphate (LIDODFP), lithium difluorophosphate (LiPO ２ F ２ ), LiBF ４ LiCl, LiC ４ F ９ SO ３ and Li(CF ３ SO ２ ) ２It comprises one or more selected from the group consisting of N, and more preferably LiPF ６ LiBF ４ , comprising one or more selected from the group consisting of LiFSI and LiCl, more preferably LiPF ６ Includes.

[0053] In the lithium-ion secondary battery of the second embodiment, the concentration of the electrolyte in the electrolyte solution during the manufacturing of the lithium-ion secondary battery is preferably 0.001 mol / L or more and 5.0 mol / L or less, more preferably 0.01 mol / L or more and 5.0 mol / L or less, even more preferably 0.025 mol / L or more and 5.0 mol / L or less, even more preferably 0.05 mol / L or more and 5.0 mol / L or less, even more preferably 0.075 mol / L or more and 5.0 mol / L or less, even more preferably 0.1 mol / L or more and 2.5 mol / L or less, even more preferably 0.25 mol / L or more and 2.0 mol / L or less, even more preferably 0.5 mol / L or more and 1.5 mol / L or less, and even more preferably 0.75 mol / L or more and 1.25 mol / L or less, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and the cycle characteristics.

[0054] In the lithium-ion secondary battery of the second embodiment, the electrolyte content in the lithium-ion secondary battery is preferably 15 to 60 parts by mass, more preferably 20 to 55 parts by mass, even more preferably 25 to 50 parts by mass, and even more preferably 30 to 45 parts by mass, when the total of the negative electrode active material content and positive electrode active material content in the lithium-ion secondary battery is 100 parts by mass, from the viewpoint of further improving the cycle characteristics of the lithium-ion secondary battery.

[0055] [Third Embodiment] <Lithium-ion secondary battery> The lithium-ion secondary battery of the third embodiment is a lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, lithium fluorosulfate, and an organic solvent (S), wherein the content of fluoroethylene carbonate in the electrolyte is 1.50% by volume or more and 10.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is 100.0% by volume.

[0056] The lithium-ion secondary battery of the third embodiment can improve cycle characteristics by having the above configuration. The reason why the lithium-ion secondary battery of the third embodiment can improve cycle characteristics is not clear, but it is thought that when an electrolyte containing fluoroethylene carbonate and lithium fluorosulfate, and in which the fluoroethylene carbonate content is within the above range is used, an SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode active material contained in the negative electrode active material layer, which can maintain its structure stably even after repeated charging and discharging.

[0057] The configuration of the lithium-ion secondary battery of the third embodiment will be explained with reference to the figures. Figure 1 is a schematic cross-sectional view showing an example of the lithium-ion secondary battery of this embodiment. In the third embodiment, the lithium-ion secondary battery 10 includes a positive electrode containing a positive electrode active material layer 1, a negative electrode containing a negative electrode active material layer 2, and an electrolyte. A separator 5 can be provided between the positive electrode and the negative electrode. Multiple pairs of positive and negative electrodes can be provided.

[0058] The lithium-ion secondary battery 10 has a positive electrode comprising a positive electrode current collector 3 and a positive electrode active material layer 1 containing a positive electrode active material provided thereon. The lithium-ion secondary battery 10 also has a negative electrode comprising a negative electrode current collector 4 and a negative electrode active material layer 2 containing a negative electrode active material provided thereon. The positive electrode and the negative electrode are stacked via a separator 5, for example, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. The electrode pair consisting of the positive electrode and the negative electrode is housed in a container formed by an outer casing 6 and an outer casing 7. A positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4. The positive electrode tab 9 and the negative electrode tab 8 are drawn out of the container. The injected electrolyte is sealed inside the container. The container may contain an electrode group in which multiple electrode pairs are stacked.

[0059] <Method for Manufacturing Lithium-Ion Secondary Batteries> In the third embodiment, lithium-ion secondary batteries can be manufactured according to known methods. For electrodes, for example, laminates or wound bodies can be used. For the outer casing, metal casings or aluminum laminate casings can be used as appropriate. The shape of the battery may be any shape such as laminate type, coin type, button type, sheet type, cylindrical type, prismatic type, or flat type, but laminate type batteries are preferred.

[0060] Next, we will explain lithium-ion secondary batteries by their constituent components.

[0061] [Electrolyte] In the lithium-ion secondary battery of the third embodiment, the electrolyte comprises fluoroethylene carbonate, lithium fluorosulfate, and an organic solvent (S).

[0062] In the lithium-ion secondary battery of the third embodiment, the content of fluoroethylene carbonate in the electrolyte is 1.50% by volume or more and 10.00% by volume or less, when the content of organic solvent (S) contained in the electrolyte is taken as 100% by volume. From the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and its cycle characteristics, it is preferably 1.55% by volume or more and 10.00% by volume or less, more preferably 1.60% by volume or more and 9.50% by volume or less, even more preferably 1.65% by volume or more and 9.00% by volume or less, even more preferably 1.68% by volume or more and 8.50% by volume or less, even more preferably 1.70% by volume or more and 8.00% by volume or less, even more preferably 1.73% by volume or more and 7.50% by volume or less, even more preferably 1.75% by volume or more and 7.00% by volume or less, even more preferably 1.78% by volume or more and 6.50% by volume or less, and even more preferably 1.80% by volume or more and 6.00% by volume or less.

[0063] In the lithium-ion secondary battery of the third embodiment, the content of lithium fluorosulfate in the electrolyte is preferably 0.10% to 1.00% by volume, more preferably 0.15% to 0.95% by volume, even more preferably 0.20% to 0.90% by volume, and even more preferably 0.25% to 0.85% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and the cycle characteristics.

[0064] In the lithium-ion secondary battery of the third embodiment, the volume ratio of the fluoroethylene carbonate content to the lithium fluorosulfate content in the electrolyte is preferably 2.0 to 15.0, more preferably 2.5 to 14.0, even more preferably 3.0 to 13.0, and even more preferably 3.5 to 12.0, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and its cycle characteristics.

[0065] In the lithium-ion secondary battery of the third embodiment, the electrolyte preferably further includes a sulfo-based compound other than lithium fluorosulfate, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and its cycle characteristics. From the viewpoint of further improving the balance between reducing the amount of gas generated in lithium-ion secondary batteries and their cycle characteristics, sulfo compounds other than lithium fluorosulfate preferably include one or more selected from the group consisting of 1,3-propanesultone (PS), 1,3-propanesultone derivatives, methylene methanedisulfonic acid ester (MMDS), ethylene sulfate (DTD), ethylene disulfonic acid ester, propylene methanedisulfonic acid ester, vinyl sulfonic acid ester, sulfonic acid amide, methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, and biphenyldisulfonic acid, and more preferably include one or more selected from the group consisting of 1,3-propanesultone (PS), methylene methanedisulfonic acid (MMDS), and ethylene sulfate (DTD). In the third embodiment, a sulfo-based compound is defined as a compound containing a functional group selected from the group consisting of a sulfo group, a sulfonic acid ester group, and a sulfonyl group (except for compounds containing lithium).

[0066] In the lithium-ion secondary battery of the third embodiment, the content of the sulfo-based compound other than lithium fluorosulfate in the electrolyte is preferably 0.10% to 5.00% by volume, more preferably 0.20% to 4.50% by volume, even more preferably 0.30% to 4.00% by volume, even more preferably 0.40% to 3.50% by volume, even more preferably 0.50% to 3.00% by volume, even more preferably 0.60% to 2.50% by volume, even more preferably 0.70% to 2.00% by volume, and even more preferably 0.80% to 1.50% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume.

[0067] The organic solvent (S) preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone, more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and even more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0068] The electrolyte may contain additives other than fluoroethylene carbonate. From the viewpoint of further improving the cycle characteristics, the additives other than fluoroethylene carbonate preferably further contain one or more selected from the group consisting of SEI film formation promoters such as vinylene carbonate (VC), chloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, and methyl propionate; and electrolyte stability enhancers such as dimethoxyethane, tetrahydrofuran, ethyl acetate, dimethyl sulfoxide, ethylene sulfide, triphenyl phosphate, fluorinated dimethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether, more preferably containing an SEI film formation promoter, and even more preferably containing vinylene carbonate.

[0069] In the lithium-ion secondary battery of the third embodiment, the content of additives other than fluoroethylene carbonate in the electrolyte is preferably 0.01% to 3.00% by volume, more preferably 0.05% to 2.00% by volume, even more preferably 0.10% to 1.00% by volume, and even more preferably 0.15% to 0.50% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume, from the viewpoint of further improving cycle characteristics.

[0070] In the lithium-ion secondary battery of the third embodiment, the electrolyte preferably includes an electrolyte. The electrolyte is preferably lithium hexafluoride phosphate (LiPF). ６ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorobis(oxalato) phosphate (LIDODFP), lithium difluorophosphate (LiPO ２ F ２ ), LiBF ４ LiCl, LiC ４ F ９ SO ３ and Li(CF ３ SO ２ ) ２ It comprises one or more selected from the group consisting of N, and more preferably LiPF ６ LiBF ４ , comprising one or more selected from the group consisting of LiFSI and LiCl, more preferably LiPF ６ Includes.

[0071] In the lithium-ion secondary battery of the third embodiment, the concentration of the electrolyte in the electrolyte solution during the manufacture of the lithium-ion secondary battery is preferably 0.001 mol / L or more and 5.0 mol / L or less, more preferably 0.01 mol / L or more and 5.0 mol / L or less, even more preferably 0.025 mol / L or more and 5.0 mol / L or less, even more preferably 0.05 mol / L or more and 5.0 mol / L or less, even more preferably 0.075 mol / L or more and 5.0 mol / L or less, even more preferably 0.1 mol / L or more and 2.5 mol / L or less, even more preferably 0.25 mol / L or more and 2.0 mol / L or less, even more preferably 0.5 mol / L or more and 1.5 mol / L or less, and even more preferably 0.75 mol / L or more and 1.25 mol / L or less, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and the cycle characteristics.

[0072] In the lithium-ion secondary battery of the third embodiment, the electrolyte content in the lithium-ion secondary battery is preferably 15 to 60 parts by mass, more preferably 20 to 55 parts by mass, even more preferably 25 to 50 parts by mass, and even more preferably 30 to 45 parts by mass, when the total of the negative electrode active material content and positive electrode active material content in the lithium-ion secondary battery is 100 parts by mass, from the viewpoint of further improving the cycle characteristics of the lithium-ion secondary battery.

[0073] [Fourth Embodiment] <Lithium-ion secondary battery> The lithium-ion secondary battery of the fourth embodiment is a lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the volume ratio of the fluoroethylene carbonate content to the sulfo-based compound content in the electrolyte is 1.05 or more and 5.00 or less.

[0074] The lithium-ion secondary battery of the fourth embodiment can improve cycle characteristics by having the above configuration. The reason why the lithium-ion secondary battery of the fourth embodiment can improve cycle characteristics is not clear, but it is thought that when an electrolyte is used in which the volume ratio of the fluoroethylene carbonate content to the sulfo-based compound content is within the above range, an SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode active material contained in the negative electrode active material layer, which can maintain its structure stably even after repeated charging and discharging.

[0075] In the lithium-ion secondary battery of the fourth embodiment, the volume ratio of the fluoroethylene carbonate content to the sulfo-based compound content is preferably 1.08 to 4.50, more preferably 1.10 to 4.00, even more preferably 1.13 to 3.50, and even more preferably 1.15 to 3.00, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and its cycle characteristics.

[0076] The configuration of the lithium-ion secondary battery of the fourth embodiment will be described with reference to the figures. Figure 1 is a schematic cross-sectional view showing an example of the lithium-ion secondary battery of this embodiment. In the fourth embodiment, the lithium-ion secondary battery 10 includes a positive electrode containing a positive electrode active material layer 1, a negative electrode containing a negative electrode active material layer 2, and an electrolyte. A separator 5 can be provided between the positive electrode and the negative electrode. Multiple pairs of positive and negative electrodes can be provided.

[0077] The lithium-ion secondary battery 10 has a positive electrode comprising a positive electrode current collector 3 and a positive electrode active material layer 1 containing a positive electrode active material provided thereon. The lithium-ion secondary battery 10 also has a negative electrode comprising a negative electrode current collector 4 and a negative electrode active material layer 2 containing a negative electrode active material provided thereon. The positive electrode and the negative electrode are stacked via a separator 5, for example, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. The electrode pair consisting of the positive electrode and the negative electrode is housed in a container formed by an outer casing 6 and an outer casing 7. A positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4. The positive electrode tab 9 and the negative electrode tab 8 are drawn out of the container. The injected electrolyte is sealed inside the container. The container may contain an electrode group in which multiple electrode pairs are stacked.

[0078] <Method for Manufacturing a Lithium-Ion Secondary Battery> In the fourth embodiment, the lithium-ion secondary battery can be manufactured according to known methods. For electrodes, for example, laminates or wound bodies can be used. For the outer casing, metal casings or aluminum laminate casings can be used as appropriate. The shape of the battery may be any shape such as laminate type, coin type, button type, sheet type, cylindrical type, prismatic type, or flat type, but laminate type batteries are preferred.

[0079] Next, we will explain lithium-ion secondary batteries by their constituent components.

[0080] [Electrolyte] In the lithium-ion secondary battery of the fourth embodiment, the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S).

[0081] In the lithium-ion secondary battery of the fourth embodiment, the content of fluoroethylene carbonate in the electrolyte is preferably 1.00% to 10.00% by volume, more preferably 1.10% to 9.50% by volume, even more preferably 1.20% to 9.00% by volume, even more preferably 1.30% to 8.50% by volume, even more preferably 1.40% to 8.00% by volume, even more preferably 1.50% to 7.50% by volume, even more preferably 1.60% to 7.00% by volume, even more preferably 1.70% to 6.50% by volume, and even more preferably 1.80% to 6.00% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume.

[0082] From the viewpoint of further improving the performance balance between reducing the amount of gas generated in lithium-ion secondary batteries and their cycle characteristics, the sulfo compounds preferably include one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone (PS), 1,3-propanesultone derivatives, methylene methanedisulfonic acid ester (MMDS), ethylene sulfate (DTD), ethylene disulfonic acid ester, propylene methanedisulfonic acid ester, vinyl sulfonic acid ester, sulfonic acid amide, methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, and biphenyldisulfonic acid, and more preferably include one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone (PS), methylene methanedisulfonic acid (MMDS), and ethylene sulfate (DTD). In the fourth embodiment, a sulfo-based compound is defined as a compound containing a functional group selected from the group consisting of a sulfo group, a sulfonic acid ester group, and a sulfonyl group (except for compounds containing lithium).

[0083] In the lithium-ion secondary battery of the fourth embodiment, the content of sulfo-based compounds in the electrolyte is preferably 1.00% to 5.00% by volume, more preferably 1.05% to 4.50% by volume, even more preferably 1.10% to 4.00% by volume, even more preferably 1.15% to 3.50% by volume, even more preferably 1.20% to 3.00% by volume, and even more preferably 1.30% to 2.50% by volume, when the content of organic solvent (S) in the electrolyte is taken as 100% by volume, from the viewpoint of further improving the performance balance between reducing the amount of gas generated by the lithium-ion secondary battery and the cycle characteristics.

[0084] The organic solvent (S) preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone, more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and even more preferably comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0085] The electrolytic solution may contain additives other than fluoroethylene carbonate. From the viewpoint of further improving cycle characteristics, the additives other than fluoroethylene carbonate are preferably SEI film formation accelerators such as vinylene carbonate (VC), chloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, and methyl propionate; and one or more selected from the group consisting of electrolytic solution stability improvers such as dimethoxyethane, tetrahydrofuran, ethyl acetate, dimethyl sulfoxide, ethylene sulfide, triphenyl phosphate, fluorinated dimethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether. More preferably, the additives include an SEI film formation accelerator, and still more preferably, the additives include vinylene carbonate.

[0086] In the lithium ion secondary battery according to the fourth embodiment, the content of additives other than fluoroethylene carbonate in the electrolytic solution, from the viewpoint of further improving cycle characteristics, when the content of the organic solvent (S) contained in the electrolytic solution is 100% by volume, is preferably 0.01% by volume or more and 3.00% by volume or less, more preferably 0.05% by volume or more and 2.00% by volume or less, still more preferably 0.10% by volume or more and 1.00% by volume or less, and even more preferably 0.15% by volume or more and 0.50% by volume or less.

[0087] In the lithium ion secondary battery according to the fourth embodiment, the electrolytic solution preferably contains an electrolyte. The electrolyte is preferably lithium hexafluorophosphate (LiPF ６ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorobis(oxalato) phosphate (LiDODFP), lithium difluorophosphate (LiPO ２ F ２ ), LiBF ４ , LiCl, LiC ４ F ９ SO ３ and Li(CF ３ SO ２ ) ２comprises one or more selected from the group consisting of N, more preferably LiPF ６ , LiBF ４ , one or more selected from the group consisting of LiFSI and LiCl, and still more preferably LiPF ６ is included.

[0088] In the lithium ion secondary battery according to the fourth embodiment, the concentration of the electrolyte in the electrolytic solution at the time of producing the lithium ion secondary battery is preferably 0.001 mol / L or more and 5.0 mol / L or less, more preferably 0.01 mol / L or more and 5.0 mol / L or less, still more preferably 0.025 mol / L or more and 5.0 mol / L or less, still more preferably 0.05 mol / L or more and 5.0 mol / L or less, still more preferably 0.075 mol / L or more and 5.0 mol / L or less, still more preferably 0.1 mol / L or more and 2.5 mol / L or less, still more preferably 0.25 mol / L or more and 2.0 mol / L or less, still more preferably 0.5 mol / L or more and 1.5 mol / L or less, and still more preferably 0.75 mol / L or more and 1.25 mol / L or less, from the viewpoint of further improving the performance balance between reduction of gas generation amount and cycle characteristics of the lithium ion secondary battery.

[0089] In the lithium ion secondary battery according to the fourth embodiment, when the total content of the negative electrode active material and the positive electrode active material in the lithium ion secondary battery is 100 parts by mass, the content of the electrolytic solution in the lithium ion secondary battery is preferably 15 parts by mass or more and 60 parts by mass or less, more preferably 20 parts by mass or more and 55 parts by mass or less, still more preferably 25 parts by mass or more and 50 parts by mass or less, and still more preferably 30 parts by mass or more and 45 parts by mass or less, from the viewpoint of further improving the cycle characteristics of the lithium ion secondary battery.

[0090] [Description Common to the First to Fourth Embodiments] [Negative Electrode] The negative electrode of the present embodiment comprises a negative electrode active material layer. From the viewpoint of further improving the battery performance of the lithium ion secondary battery, the negative electrode of the present embodiment preferably comprises a negative electrode current collector and the negative electrode active material layer of the present embodiment.

[0091] In the lithium-ion secondary battery of this embodiment, the negative electrode active material contained in the negative electrode active material layer preferably has an SEI (Solid Electrolyte Interphase) film on at least a portion of its surface, and more preferably has an SEI film over the entire surface, from the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics. Generally, the SEI film is formed when the electrolyte decomposes on the surface of the negative electrode during initial charging and discharging. Specifically, the SEI film is a film formed on at least a portion of the surface of the negative electrode active material by the decomposition products of the electrolyte and its additives. The SEI film plays a role in inserting lithium ions into or detaching them from the negative electrode, while also reducing further decomposition of the electrolyte on the surface of the negative electrode.

[0092] For example, by the method of initial charging and discharging of a lithium-ion secondary battery described in the examples, an SEI film can be formed on at least a portion of the surface of the negative electrode (negative electrode active material). That is, when the lithium-ion secondary battery of this embodiment has an SEI film on at least a portion of the surface of the negative electrode active material contained in the negative electrode active material layer, it is a lithium-ion secondary battery after initial charging and discharging.

[0093] (Negative electrode active material layer) The negative electrode active material layer of this embodiment includes a negative electrode active material comprising graphite particles and Si-C composite particles containing silicon and carbon material, and preferably includes a negative electrode active material and a binder, and more preferably includes a negative electrode active material, a binder and a conductive additive, from the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics.

[0094] In this embodiment, the thickness of the negative electrode active material layer is preferably 10 μm to 500 μm, more preferably 15 μm to 300 μm, even more preferably 30 μm to 200 μm, and even more preferably 50 μm to 150 μm, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and its cycle characteristics.

[0095] In this embodiment, the density of the negative electrode active material layer is preferably 0.50 g / cm³, from the viewpoint of further improving the performance balance between reducing gas generation in the lithium-ion secondary battery and its cycle characteristics.３ 3.00g / cm or more ３ More preferably, 1.00 g / cm³ ３ 2.50g / cm or more ３ More preferably, 1.30 g / cm³ ３ 2.00g / cm or more ３ The following applies:

[0096] (Negative electrode active material) The negative electrode active material contained in the negative electrode active material layer of this embodiment includes graphite particles and Si-C composite particles containing silicon and carbon material.

[0097] In this embodiment, the ratio of Si-C composite particles to graphite particles in the negative electrode active material is preferably 0.01 to 1.00, more preferably 0.03 to 0.80, even more preferably 0.05 to 0.60, even more preferably 0.08 to 0.40, and even more preferably 0.10 to 0.20, from the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics.

[0098] In this embodiment, the content of the negative electrode active material in the negative electrode active material layer is preferably 50.0 parts by mass or more and 100.0 parts by mass or less, more preferably 75.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 85.0 parts by mass or more and 98.5 parts by mass or less, even more preferably 90.0 parts by mass or more and 98.0 parts by mass or less, and even more preferably 95.0 parts by mass or more and 97.5 parts by mass or less, when the total volume of the negative electrode active material layer is 100.0 parts by mass.

[0099] (Graphite particles) Median diameter D in the volume frequency particle size distribution of graphite particles in this embodiment as determined by laser diffraction scattering. ５０From the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics, the particle size is preferably 1.0 μm to 30.0 μm, more preferably 2.0 μm to 29.0 μm, even more preferably 3.0 μm to 28.0 μm, even more preferably 4.0 μm to 27.0 μm, even more preferably 5.0 μm to 26.0 μm, even more preferably 6.0 μm to 25.0 μm, even more preferably 7.0 μm to 24.0 μm, even more preferably 8.0 μm to 23.0 μm, and even more preferably 9.0 μm to 22.0 μm.

[0100] From the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics, the graphite particles preferably include graphite particles containing amorphous carbon on their surface, and more preferably include artificial graphite particles containing amorphous carbon on their surface.

[0101] From the viewpoint of further improving the balance between reducing gas generation and cycle characteristics, the content of graphite particles in the negative electrode active material of this embodiment is preferably 10 to 99 parts by mass, more preferably 20 to 98 parts by mass, even more preferably 30 to 97 parts by mass, even more preferably 40 to 96 parts by mass, even more preferably 50 to 95 parts by mass, even more preferably 60 to 94 parts by mass, even more preferably 70 to 93 parts by mass, and even more preferably 80 to 92 parts by mass, when the total content of graphite particles and Si-C composite particles is 100 parts by mass.

[0102] (Si-C composite particles containing silicon and carbon materials) In this embodiment, the Si-C composite particles containing silicon and carbon materials are preferably particles in which the carbon material includes a porous carbon material and silicon is present in at least a portion of the pores of the porous carbon material, from the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics. Hereinafter, the Si-C composite particles containing silicon and carbon materials may also be referred to as Si-C composite particles.

[0103] Porous carbon materials that constitute Si-C composite particles include, for example, activated carbon, aggregates of carbon fibers or carbon nanotubes, carbon obtained by heat treatment of resins or organic materials, and hard carbon. Porous carbon materials can be produced by known manufacturing methods such as activated carbon production methods or by heat treatment of polymers, but they can also be purchased commercially, and are not limited to these methods as long as silicon can be generated or incorporated into the pores of the porous carbon.

[0104] In this embodiment, the method for producing Si-C composite particles is not particularly limited, but for example, the following method can be employed. A porous carbon material is placed in a tubular furnace, and the inside of the tubular furnace is replaced with argon gas. Next, a mixed gas of silane gas containing 1 to 10 mol% silane gas and nitrogen gas is flowed into the tubular furnace at a flow rate of 250 to 1000 sccm, and the porous carbon material is treated under conditions of 450 to 550°C, 700 to 800 Torr, and 90 to 150 minutes to obtain a product. Next, the product is cooled to room temperature to obtain Si-C composite particles. More specifically, the method described in the examples can be used for producing Si-C composite particles.

[0105] From the viewpoint of further improving the balance between reducing gas generation and cycle characteristics, the true density of the Si-C composite particles is preferably 1.0 g / cm³. ３ 3.0g / cm or more ３ More preferably, 1.5 g / cm³ ３ 2.5g / cm or more ３ More preferably, 1.7 g / cm³ ３ 2.3g / cm or more ３ The following applies: The true density of Si-C composite particles can be controlled by appropriately adjusting the porous carbon material constituting the Si-C composite particles and the manufacturing method of the Si-C composite particles.

[0106] From the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics, the specific surface area of ​​Si-C composite particles obtained by nitrogen adsorption BET is preferably 1 m². ２ / g or more 20m ２ / g or less, more preferably 2m ２ / g or more 15m ２ / g or less, more preferably 3m ２ / g or more 10m ２ The specific surface area of ​​Si-C composite particles obtained by nitrogen adsorption BET can be controlled by appropriately adjusting the porous carbon material constituting the Si-C composite particles and the manufacturing method of the Si-C composite particles.

[0107] Median diameter D in volume frequency particle size distribution of Si-C composite particles by laser diffraction scattering method ５０ From the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics, the particle size is preferably 1.0 μm to 20.0 μm, more preferably 1.5 μm to 18.0 μm, even more preferably 2.0 μm to 15.0 μm, even more preferably 2.5 μm to 13.0 μm, and even more preferably 3.0 μm to 10.0 μm.

[0108] In this embodiment, the content of Si-C composite particles in the negative electrode active material is preferably 1 to 90 parts by mass, more preferably 2 to 80 parts by mass, even more preferably 3 to 70 parts by mass, even more preferably 4 to 60 parts by mass, even more preferably 5 to 50 parts by mass, even more preferably 6 to 40 parts by mass, even more preferably 7 to 30 parts by mass, and even more preferably 8 to 20 parts by mass, when the total content of graphite particles and Si-C composite particles is 100 parts by mass, from the viewpoint of further improving the performance balance between gas generation reduction and cycle characteristics.

[0109] (Binder in the negative electrode active material layer) The negative electrode active material layer of this embodiment preferably further includes a binder from the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics. The binder in the negative electrode active material layer of this embodiment preferably includes fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), polyvinyl fluoride (PVF), copolymers of polyvinylidene fluoride and hexafluoropropylene; polycarboxylic acid polymers such as poly(meth)acrylic acid; conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; styrene-butadiene rubber (SBR), butadiene rubber (BR), etc. It comprises one or more selected from the group consisting of synthetic rubbers such as loloprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethylcellulose (CMC), xanthan gum, guar gum, and pectin; more preferably, it comprises one or more selected from the group consisting of fluororesins, polycarboxylic acid polymers, and synthetic rubbers; even more preferably, it comprises one or more selected from the group consisting of PVDF, polycarboxylic acid polymers, and SBR; even more preferably, it comprises polycarboxylic acid polymers; and even more preferably, it comprises poly(meth)acrylic acid.

[0110] In this embodiment, the binder content in the negative electrode active material layer is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 2.0 parts by mass or more and 5.0 parts by mass or less, when the total volume of the negative electrode active material layer is 100.0 parts by mass, from the viewpoint of further improving the performance balance between the rapid charging characteristics and cycle characteristics of the lithium-ion secondary battery.

[0111] (Conductive additive in the negative electrode active material layer) The negative electrode active material layer of this embodiment preferably further includes a conductive additive from the viewpoint of further improving the performance balance between reducing gas generation and cycle characteristics. The conductive additive in the negative electrode active material layer of this embodiment preferably includes one or more selected from the group consisting of carbon fibers such as carbon nanofibers; carbon black such as acetylene black and Ketjen black; activated carbon; mesoporous carbon; fullerenes; and carbon materials such as carbon nanotubes (CNTs), more preferably includes carbon materials, more preferably includes carbon nanotubes, and even more preferably includes single-walled carbon nanotubes.

[0112] In this embodiment, the content of the conductive additive in the negative electrode active material layer is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, more preferably 0.03 parts by mass or more and 1.0 parts by mass or less, even more preferably 0.05 parts by mass or more and 0.5 parts by mass or less, and even more preferably 0.07 parts by mass or more and 0.3 parts by mass or less, when the total volume of the negative electrode active material layer is 100.0 parts by mass.

[0113] (Negative electrode current collector) The negative electrode current collector of this embodiment includes, for example, one or more materials selected from the group consisting of copper, stainless steel, nickel, titanium, and alloys thereof. The shape of the negative electrode current collector may be, for example, a foil, a flat plate, or a mesh. The thickness of the negative electrode current collector is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

[0114] [Method for Manufacturing the Negative Electrode] The method for manufacturing the negative electrode is not particularly limited, as it can be carried out in accordance with generally known methods. For example, the method described in the examples can be used for manufacturing the negative electrode.

[0115] [Positive Electrode] The positive electrode of this embodiment includes a positive electrode active material layer. From the viewpoint of further improving the battery performance of the lithium-ion secondary battery, the positive electrode of this embodiment preferably comprises a positive electrode current collector and the positive electrode active material layer of this embodiment.

[0116] (Positive electrode active material layer) The positive electrode active material layer of this embodiment preferably includes the positive electrode active material and binder of this embodiment, and more preferably includes the positive electrode active material, binder and conductive additive of this embodiment, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and the cycle characteristics.

[0117] In this embodiment, the thickness of the positive electrode active material layer is preferably 10 μm to 500 μm, more preferably 15 μm to 300 μm, even more preferably 30 μm to 200 μm, and even more preferably 50 μm to 150 μm, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and its cycle characteristics.

[0118] In this embodiment, the density of the positive electrode active material layer is preferably 1.0 g / cm³, from the viewpoint of further improving the performance balance between reducing gas generation in the lithium-ion secondary battery and its cycle characteristics. ３ 6.0g / cm or more ３ More preferably, 2.0 g / cm³ ３ 5.0g / cm or more ３ More preferably, 2.5 g / cm³ ３ 4.5g / cm or more ３ The following applies:

[0119] (Positive Electrode Active Material) The positive electrode active material of this embodiment preferably includes a material with high electronic conductivity, from the viewpoint of facilitating electron transport by being able to reversibly release or absorb lithium ions. From the viewpoint of high electronic conductivity, the positive electrode active material preferably includes one or more selected from the group consisting of lithium-transition metal composite oxides, transition metal sulfides, transition metal oxides, and olivine-type lithium phosphorus oxides. Examples of lithium-transition metal composite oxides include lithium-nickel-cobalt-manganese composite oxide, lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-manganese-nickel composite oxide, lithium-nickel-cobalt-aluminum composite oxide, etc. Examples of transition metal sulfides include TiS ２ FeS, MoS ２ Examples include MnO, V２ O ５ , V ６ O １３ , TiO ２ These are some examples. Among these, the positive electrode active material of this embodiment preferably contains a composite oxide of lithium and a transition metal, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and the cycle characteristics, more preferably contains one or more selected from the group consisting of lithium-nickel-cobalt-manganese composite oxide, lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-manganese-nickel composite oxide and lithium-nickel-cobalt-aluminum composite oxide, and even more preferably contains lithium-nickel-cobalt-manganese composite oxide.

[0120] In this embodiment, the content of the positive electrode active material in the positive electrode active material layer is preferably 50.0 parts by mass or more and 99.9 parts by mass or less, more preferably 75.0 parts by mass or more and 99.5 parts by mass or less, even more preferably 85.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 90.0 parts by mass or more and 98.5 parts by mass or less, and even more preferably 95.0 parts by mass or more and 98.0 parts by mass or less, when the total volume of the positive electrode active material layer is 100.0 parts by mass, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and the cycle characteristics.

[0121] (Binder in the positive electrode active material layer) The binder in the positive electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), polyvinyl fluoride (PVF), and copolymers of polyvinylidene fluoride and hexafluoropropylene; polycarboxylic acid polymers such as poly(meth)acrylic acid; conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile-butadiene rubber (NBR); and polysaccharides such as carboxymethylcellulose (CMC), xanthan gum, guar gum, and pectin.

[0122] Among these, the binder in the positive electrode active material layer of this embodiment preferably comprises one or more selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and the cycle characteristics, more preferably comprises one or more selected from the group consisting of PVDF, polycarboxylic acid polymer, and SBR, and even more preferably comprises PVDF.

[0123] In this embodiment, the binder content in the positive electrode active material layer is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and the cycle characteristics.

[0124] (Conductive additive in the positive electrode active material layer) The conductive additive in the positive electrode active material layer of this embodiment includes, for example, one or more selected from the group consisting of carbon fibers such as carbon nanofibers; carbon black such as acetylene black and Ketjen black; activated carbon; mesoporous carbon; fullerenes; and carbon nanotubes. Among these, the conductive additive in the positive electrode active material layer of this embodiment preferably includes carbon materials, more preferably carbon nanotubes, and even more preferably single-walled carbon nanotubes, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and the cycle characteristics.

[0125] In this embodiment, the content of the conductive additive in the positive electrode active material layer is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass, from the viewpoint of further improving the performance balance between reducing the amount of gas generated in the lithium-ion secondary battery and the cycle characteristics.

[0126] (Positive electrode current collector) The positive electrode current collector of this embodiment includes, for example, one or more materials selected from the group consisting of aluminum, stainless steel, nickel, titanium, and alloys thereof. The shape of the positive electrode current collector may be, for example, a foil, a flat plate, or a mesh. The thickness of the positive electrode current collector is not particularly limited, but for example, it is 1 μm or more and 50 μm or less.

[0127] [Method for Manufacturing the Positive Electrode] The method for manufacturing the positive electrode is not particularly limited, as it can be carried out in accordance with generally known methods. For example, the method described in the examples can be used for manufacturing the positive electrode.

[0128] [Other Components of the Lithium-Ion Secondary Battery] The lithium-ion secondary battery of this embodiment includes an electrolyte, a positive electrode, and a negative electrode, and preferably further includes a separator. The separator is not particularly limited as long as it can be used in a lithium-ion secondary battery, and generally known separators can be used.

[0129] [Separator] From the viewpoint of improving heat resistance and reducing thermal shrinkage of the separator, the separator preferably includes a substrate and a ceramic layer provided on at least one surface of the substrate. As the substrate, for example, polyethylene, polypropylene, or a porous polyolefin film laminated thereon can be used. The ceramic layer can be formed, for example, by coating a ceramic layer forming material onto the substrate and drying it. As the ceramic layer forming material, for example, an inorganic filler and binder dispersed or dissolved in any solvent can be used. The inorganic filler and binder are not particularly limited as long as they are known materials used in separators of lithium-ion secondary batteries.

[0130] <Characteristics of the Lithium-ion Secondary Battery> The characteristics of the lithium-ion secondary battery of this embodiment will be described below.

[0131] [Capacity retention rate R ４５ The capacity retention rate R at 45°C of the lithium-ion secondary battery of this embodiment according to the following (Method 1) ４５ The capacity retention rate R of the lithium-ion secondary battery of this embodiment is preferably 79.0% or more, more preferably 79.2% or more, even more preferably 79.4% or more, even more preferably 79.6% or more, even more preferably 79.8% or more, and even more preferably 80.0% or more. The upper limit may be, for example, 99.9% or less, 99.0% or less, 97.0% or less, 95.0% or less, 93.0% or less, 91.0% or less, 89.0% or less, or 88.0% or less. ４５ It may be 79.0% or more and 99.9% or less, 79.0% or more and 99.0% or less, 79.0% or more and 97.0% or less, 79.2% or more and 95.0% or less, 79.4% or more and 93.0% or less, 79.6% or more and 91.0% or less, 79.8% or more and 89.0% or less, or 80.0% or more and 88.0% or less.

[0132] (Method 1) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times have been performed. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge is measured. After that, the capacity retention rate R is calculated from the following formula (2). ４５ The following is calculated: Equation (2): The above capacity retention rate R ４５ = (Discharge capacity at the 500th discharge) / (Discharge capacity at the 1st discharge) × 100

[0133] (Charge / Discharge Cycle) The lithium-ion secondary battery is charged at 30mA until the upper voltage limit of 4.25V is reached. After the upper voltage limit of 4.25V is reached, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30mA until the lower voltage limit of 2.5V is reached.

[0134] [Gas generation amount] The gas generation amount of the lithium-ion secondary battery of this embodiment according to the following (Method 2) is preferably 0.40 cc / Ah or less, more preferably 0.35 cc / Ah or less, even more preferably 0.30 cc / Ah or less, even more preferably 0.25 cc / Ah or less, and even more preferably 0.20 cc / Ah or less. The lower limit may be, for example, greater than 0.00 cc / Ah, greater than or equal to 0.05 cc / Ah, or greater than or equal to 0.10 cc / Ah. Furthermore, the amount of gas generated by the lithium-ion secondary battery of this embodiment may be more than 0.00 cc / Ah and 0.40 cc / Ah or less, more than 0.00 cc / Ah and 0.35 cc / Ah or less, more than 0.00 cc / Ah and 0.30 cc / Ah or less, 0.05 cc / Ah or more and 0.25 cc / Ah or less, or 0.10 cc / Ah or more and 0.20 cc / Ah or less.

[0135] (Method 2) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the first time is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times have been reached. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the 500th time is measured, and then the volume of the lithium-ion secondary battery after the 500th charge-discharge is measured. After that, the amount of gas generated (cc / Ah) is calculated from the following formula (3). Formula (3): Amount of gas generated = {(Volume of the lithium-ion secondary battery after the 500th charge-discharge) - (Volume of the lithium-ion secondary battery before the first charge-discharge)} / [{(Discharge capacity of the first time) + (Discharge capacity of the 500th time)} / 2]

[0136] (Charge / Discharge Cycle) The lithium-ion secondary battery is charged at 30mA until the upper voltage limit of 4.25V is reached. After the upper voltage limit of 4.25V is reached, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30mA until the lower voltage limit of 2.5V is reached.

[0137] <Applications of Lithium-ion Secondary Batteries> The lithium-ion secondary battery of this embodiment has improved cycle characteristics and can therefore be used in a variety of applications. The lithium-ion secondary battery of this embodiment can be used, for example, in industrial, consumer, automotive, and residential applications, but is not limited to these.

[0138] <Lithium-ion secondary battery module> The lithium-ion secondary battery module of this embodiment includes the lithium-ion secondary battery of this embodiment. Preferably, the lithium-ion secondary battery module of this embodiment includes two or more lithium-ion secondary batteries of this embodiment connected in series or in parallel. More preferably, the lithium-ion secondary battery module of this embodiment further includes a housing capable of housing two or more lithium-ion secondary batteries of this embodiment connected in series or in parallel. The lithium-ion secondary battery module of this embodiment more preferably further includes one or more selected from the group consisting of a protection circuit to protect the lithium-ion secondary battery from overcurrent, a balance circuit to equalize the voltage between the electrodes of the lithium-ion secondary battery, a controller to control the lithium-ion secondary battery, a cooler capable of cooling the lithium-ion secondary battery, and a heater capable of heating the lithium-ion secondary battery.

[0139] The lithium-ion secondary battery module of this embodiment can be used in a battery system comprising two or more electrically connected lithium-ion secondary battery modules and a battery control system. Examples of battery systems include battery packs, stationary battery systems, automotive power battery systems, automotive auxiliary battery systems, and emergency power supply battery systems.

[0140] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., that do not impair the effects of the present invention are included in the present invention.

[0141] Hereinafter, this embodiment will be described in detail with reference to examples and the like. However, this embodiment is not limited in any way to the descriptions in these examples. Hereinafter, the examples and comparative examples related to the first embodiment of the present invention are Examples 1a to 17a and Comparative Examples 1a to 5a, the examples and comparative examples related to the second embodiment of the present invention are Examples 1b to 17b and Comparative Examples 1b to 5b, the examples and comparative examples related to the third embodiment of the present invention are Examples 1c to 17c and Comparative Examples 1c to 5c, and the examples and comparative examples related to the fourth embodiment of the present invention are Examples 1d to 17d and Comparative Examples 1d to 5d.

[0142] The following graphite particles and Si-C composite particles were used as the negative electrode active material in each example and comparative example.

[0143] <Negative electrode active material> [Graphite particles] ・Graphite particle 1 (artificial graphite particles containing amorphous carbon on the surface, median diameter D) ５０ : 10.0 μm) Graphite particle 2 (artificial graphite particles containing amorphous carbon on the surface, median diameter D ５０ : 14.0 μm) Graphite particle 3 (artificial graphite particle containing amorphous carbon on the surface, median diameter D ５０ (20.0 μm)

[0144] [Si-C composite particles] ・Si-C composite particle 1 (median diameter D) ５０ :5.0μm, BET specific surface area: 6.0m ２ / g, Si ratio in Si-C composite particles: 44.0% by mass, true density: 1.9g / cm ３ , (particles prepared according to the following (fabrication of Si-C composite particle 1)) ・Si-C composite particle 2 (median diameter D ５０ :5.0μm, BET specific surface area: 6.0m ２ / g, Si ratio in Si-C composite particles: 44.0 mass%, true density: 2.1 g / cm³ ３ , (particles prepared according to the following (fabrication of Si-C composite particles 2)) ・Si-C composite particles 3 (median diameter D ５０ :9.0μm, BET specific surface area: 4.0m ２ / g, Si ratio in Si-C composite particles: 44.0% by mass, true density: 1.9g / cm ３, (particles prepared according to the following (fabrication of Si-C composite particle 3)) ・Si-C composite particle 4 (median diameter D ５０ :3.0μm, BET specific surface area: 8.0m ２ / g, Si ratio in Si-C composite particles: 44.0% by mass, true density: 1.9g / cm ３ , (particles prepared according to the following (fabrication of Si-C composite particles 4)) ・Si-C composite particle 5 (median diameter D ５０ :5.0μm, BET specific surface area: 6.0m ２ / g, Si ratio in Si-C composite particles: 46.0% by mass, true density: 1.9g / cm ３ (Particles prepared according to the following (Preparation of Si-C composite particles 5))

[0145] The Si ratio in each Si-C composite particle was measured in accordance with the ash content test method specified in JIS K2272:1998.

[0146] (Fabrication of Si-C composite particles 1) Porous carbon material 1 (median diameter D) ５０ A 5.0 μm (Si-C) particle was placed in a tubular furnace, and the furnace was purged with argon gas. Subsequently, a mixed gas of 2 mol% silane gas and 98 mol% nitrogen gas was flowed into the tubular furnace at a flow rate of 300 sccm, and the porous carbon material 1 was treated at 500°C, 760 Torr, and 120 minutes to obtain the product. Next, the product was cooled to room temperature to obtain Si-C composite particles 1. EDS mapping was performed on the cross-section of the obtained Si-C composite particles 1 using a scanning electron microscope (Hitachi High-Tech Corporation, SU3500), an energy-dispersive X-ray spectrometer (Oxford Instruments, Ultim Max 40), and image analysis software (Oxford Instruments, Aztec), selecting secondary electrons as the detection target, and performing EDS mapping for silicon and carbon under the conditions of an acceleration voltage of 3 kV, 20 mapping integrations, and a magnification of 3000x. EDS mapping results confirmed that the Si-C composite particle 1 contains silicon, and that silicon is present in at least a portion of the pores of the porous carbon material 1 within the Si-C composite particle 1.

[0147] (Preparation of Si-C composite particles 2) Except for the mixed gas conditions, which were set to a mixture of 2 mol% silane gas and 98 mol% nitrogen gas at a flow rate of 1000 sccm, Si-C composite particles 2 were obtained by processing under the same conditions as (preparation of Si-C composite particles 1). EDS mapping was also performed on the obtained Si-C composite particles 2 using an energy-dispersive X-ray analyzer. From the results of the EDS mapping, it was confirmed that Si-C composite particles 2 contain silicon and that silicon is present in at least a portion of the pores of the porous carbon material 1 in Si-C composite particles 2.

[0148] (Fabrication of Si-C composite particles 3) Porous carbon material 2 (median diameter D) instead of porous carbon material 1 ５０ Except for using a 9.0 μm particle, Si-C composite particle 3 was obtained by processing under the same conditions as in (fabrication of Si-C composite particle 1). The obtained Si-C composite particle 3 was also subjected to EDS mapping using an energy-dispersive X-ray analyzer. From the results of the EDS mapping, it was confirmed that Si-C composite particle 3 contains silicon and that silicon is present in at least a portion of the pores of the porous carbon material 2 in Si-C composite particle 3.

[0149] (Fabrication of Si-C composite particles 4) Porous carbon material 3 (median diameter D) instead of porous carbon material 1 ５０ Except for using a 3.0 μm particle, Si-C composite particle 4 was obtained by processing under the same conditions as in (fabrication of Si-C composite particle 1). The obtained Si-C composite particle 4 was also subjected to EDS mapping using an energy-dispersive X-ray analyzer. From the results of the EDS mapping, it was confirmed that the Si-C composite particle 4 contains silicon and that silicon is present in at least a portion of the pores of the porous carbon material 3 in the Si-C composite particle 4.

[0150] (Preparation of Si-C composite particles 5) Except for the mixed gas conditions, which were set to a mixture of 5 mol% silane gas and 95 mol% nitrogen gas at a flow rate of 300 sccm, Si-C composite particles 5 were obtained by processing under the same conditions as (preparation of Si-C composite particles 1). EDS mapping was also performed on the obtained Si-C composite particles 5 using an energy-dispersive X-ray analyzer. From the results of the EDS mapping, it was confirmed that the Si-C composite particles 5 contain silicon and that silicon is present in at least a portion of the pores of the porous carbon material 1 in the Si-C composite particles 5.

[0151] <Positive Electrode Active Material> The following positive electrode active material was used for each example and comparative example. • Positive electrode active material: Particles composed of a single crystal of lithium-nickel-cobalt-manganese composite oxide, with a molar ratio of nickel, cobalt, and manganese of nickel:cobalt:manganese = 90:5:5 (median diameter D ５０ (3.5 μm)

[0152] <Electrolyte> The following materials were used for the electrolyte in each example and comparative example: • Organic solvent 1: Ethylene carbonate (hereinafter also referred to as EC) • Organic solvent 2: Ethyl methyl carbonate (hereinafter also referred to as EMC) • Organic solvent 3: Propylene carbonate (hereinafter also referred to as PC) • Electrolyte: Lithium hexafluoride phosphate (LiPF) ６ ) • Additive 1: Vinylene carbonate (hereinafter also called VC) • Additive 2: Fluoroethylene carbonate (hereinafter also called FEC) • Sulfo compound 1: Lithium fluorosulfate (LiSO4) ３ F) • Sulfo compound 2: 1,3-propanesultone (hereinafter also referred to as PS) • Sulfo compound 3: Methylene methanedisulfonate (hereinafter also referred to as MMDS) • Sulfo compound 4: Ethylene sulfate (hereinafter also referred to as DTD)

[0153] <Separator> The following materials were used for the separators in each example and comparative example: • Separator: A 10 μm thick microporous polyethylene film with ceramic coating on both sides.

[0154] <Negative Electrode> In addition to the negative electrode active material described above, the following materials were used for the negative electrode in each example and comparative example: • Negative electrode current collector: Copper foil (thickness: 6 μm) • Binder: Polyacrylic acid (hereinafter also referred to as PAA) • Conductive additive: Single-walled carbon nanotube (hereinafter also referred to as CNT) • Solvent: Pure water

[0155] <Positive Electrode> In addition to the positive electrode active material, the following materials were used for the positive electrode: • Positive electrode current collector: Aluminum foil (thickness: 13 μm) • Binder: Polyvinylidene fluoride (hereinafter also referred to as PVDF) • Conductive additive: Single-walled carbon nanotube (hereinafter also referred to as CNT) • Solvent: N-methyl-2-pyrrolidone (hereinafter also referred to as NMP)

[0156] <Method for measuring the particle size of positive electrode active material and negative electrode active material> Using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, model number: SALD-2300), the volume-based median diameter D of the positive electrode active material and negative electrode active material is measured by laser diffraction scattering. ５０ The median diameter D of the positive electrode active material was measured. ５０ The positive electrode active material was suspended in a 0.1% by mass sodium hexametaphosphate aqueous solution as a dispersion medium, and measured after ultrasonic dispersion. The median diameter D of the negative electrode active material was also measured. ５０ The negative electrode active material was suspended in a dispersion medium (0.1% by mass sodium hexametaphosphate aqueous solution), ultrasonically dispersed, and then measured. Five measurements were taken, and the average value was taken as the median diameter D. ５０ That's what I decided.

[0157] [Examples and Comparative Examples Related to the First Embodiment] (Examples 1a to 17a, Comparative Examples 1a to 5a) <Preparation of Lithium-ion Secondary Batteries> Lithium-ion secondary batteries were prepared using the following steps. The following will be a detailed explanation of the steps. First, the electrolytes used in the lithium-ion secondary batteries of each example and comparative example were prepared using the following procedure. EC, EMC, and PC were mixed in the amounts shown in Table 1, with the total organic solvent being 100% by volume, to obtain an organic solvent. Lithium hexafluoride phosphate (LiPF) was added to the obtained organic solvent. ６The solvent was dissolved to a concentration of 1.0 mol / L. Then, VC, FEC, and each sulfo-based compound were dissolved to the concentrations shown in Table 1 when the total organic solvent was considered to be 100% by volume, and the electrolytes for each example and comparative example were prepared.

[0158] Next, the positive electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. A positive electrode slurry was prepared by dispersing the positive electrode active material, binder (PVDF), and conductive additive (CNT) in a solvent (NMP) in a ratio of positive electrode active material:PVDF:CNT = 97.5:1.5:1.0 (mass ratio). Then, the positive electrode slurry was applied to a 13 μm thick aluminum foil, which serves as the positive electrode current collector, with an initial charge capacity of 4.0 mAh / cm² per unit area. ２ The coating amount was applied to achieve the desired result. The coated cathode slurry was then dried to obtain a cathode laminate. Next, using a roll press, the density of the cathode active material layer was measured to be 3.5 g / cm³. ３ The positive electrode laminate was pressed with such pressure to produce positive electrodes (thickness of the positive electrode active material layer: 100 μm) for each example and each comparative example.

[0159] Next, the negative electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. Si-C composite particles and graphite particles were mixed in the mass ratio of Si-C composite particles to graphite particles shown in Table 1 to obtain the negative electrode active materials for each example and comparative example. The obtained negative electrode active materials, binder (PAA), and conductive additive (CNT) were dispersed in a solvent (pure water) in a mass ratio of negative electrode active material:PAA:CNT = 96.9:3.0:0.1 to prepare negative electrode slurries. Then, the negative electrode slurry was applied to a 6 μm thick copper foil, which serves as the negative electrode current collector, with an initial charge capacity of 4.3 mAh / cm² per unit area. ２ The material was applied in an amount that would result in the following. The applied negative electrode slurry was then dried to obtain a negative electrode laminate. Next, using a roll press, the density of the negative electrode active material layer was determined to be 1.65 g / cm³. ３The negative electrode laminate was pressed with a pressure such that the negative electrodes for each example and each comparative example were fabricated (thickness of the negative electrode active material layer for Examples 1a to 17a, Comparative Examples 1a to 2a and 4a to 5a: 100 μm; thickness of the negative electrode active material layer for Comparative Example 3a: 65 μm).

[0160] Next, lithium-ion secondary batteries for each example and comparative example were fabricated using the following procedure. One positive electrode coated on both sides and two negative electrodes coated on one side were placed facing each other with a separator between them, and the coated surfaces were stacked in the order of negative electrode, separator, positive electrode, separator, negative electrode. The resulting laminate was then wrapped in a laminate outer casing made by processing and molding a film mainly composed of aluminum. At this time, the aluminum foil and copper foil cut out for current collection were made to protrude from the laminate film. Subsequently, the side containing the protruding portion of the current-collecting foil and the other two sides were heat-sealed to create a laminate-type cell with only one side open. A predetermined amount of electrolyte prepared above was poured through the opening of the laminate-type cell. Then, the laminate-type cell was sealed under reduced pressure to fabricate a laminate-type lithium-ion secondary battery. Here, the amount of electrolyte injected was set so that when the total amount of positive electrode active material and negative electrode active material was 100 parts by mass, the amount of electrolyte was 30 parts by mass. Furthermore, the ratio of the total amount of fluoroethylene carbonate and sulfo-based compounds in the electrolyte to the amount of Si-C composite particles in the negative electrode active material was calculated using the following formula (1a). Here, the amount of fluoroethylene carbonate and sulfo-based compounds in the electrolyte is the value when the amount of organic solvent (S) contained in the electrolyte is set to 100% by volume, and the amount of Si-C composite particles in the negative electrode active material is the value when the total amount of negative electrode active material contained in the negative electrode active material layer is set to 100% by mass. Ratio [volume % / mass %] = ((amount of fluoroethylene carbonate in the electrolyte [volume %]) + (amount of sulfo-based compounds in the electrolyte [volume %])) / (amount of Si-C composite particles in the negative electrode active material [mass %]) ... (1a)

[0161] <Initial Charging and Discharging of Lithium-Ion Secondary Batteries> For each example of lithium-ion secondary battery, initial charging and discharging was performed under the following conditions to form an SEI film on the surface of the negative electrode active material, thereby obtaining the lithium-ion secondary battery after initial charging and discharging for each example. In the following, charging and discharging of the lithium-ion secondary battery was performed using a charge / discharge device in an environment of 25°C. Pre-charging was performed by charging each example of lithium-ion secondary battery to a battery voltage of 3.2V with a charging current of 0.05C, and then leaving it for 12 hours. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.05C. After reaching a battery voltage of 4.25V, constant voltage charging was performed until the current value decreased to 0.015C. Then, it was left for 10 minutes. After that, constant current discharge was performed to a battery voltage of 2.5V with a discharge current of 0.33C. After reaching a battery voltage of 2.5V, it was left for 10 minutes. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.33C. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, the charged lithium-ion secondary battery was stored for 48 hours in a 45°C environment while monitoring the battery voltage. After storage, the lithium-ion secondary battery was returned to a 25°C environment and constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, 10 minutes after the end of charging, constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After reaching 4.25V, constant voltage charging was performed until the current value dropped to 0.05C. Then, it was left standing for 10 minutes. After that, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V.

[0162] <Evaluation of Lithium-ion Secondary Battery Characteristics> The characteristics of lithium-ion secondary batteries obtained in each example and comparative example after initial charge and discharge were evaluated using the following method. The results are shown in Table 1.

[0163] [Gas Generation Amount] The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity for the first time was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the lithium-ion secondary batteries were charged and discharged according to the following (charge-discharge cycle), and the discharge capacity for the 500th time was measured for each, and then the volume of the lithium-ion secondary battery after the 500th charge-discharge was measured for each. After that, the gas generation amount (cc / Ah) was calculated for each from the following formula (3a). Formula (3a): Gas generation amount = {(Volume of lithium-ion secondary battery after 500 charge-discharge cycles) - (Volume of lithium-ion secondary battery before the first charge-discharge cycle)} / [{(Discharge capacity for the first time) + (Discharge capacity for the 500th time)} / 2] The volume of the lithium-ion secondary battery was measured using the Archimedes method. (Charge / Discharge Cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper voltage limit of 4.25 V was reached. After reaching the upper voltage limit of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then each lithium-ion secondary battery was discharged at a constant current of 30 mA until the lower voltage limit of 2.5 V was reached.

[0164] [Capacity retention rate R ４５ The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge was measured for each. After that, the capacity retention rate R was calculated from the following formula (2a).４５ The percentages (%) were calculated for each. Equation (2a): Volume retention rate R ４５ = (Discharge capacity at 500th cycle) / (Discharge capacity at 1st cycle) × 100 (Charge-discharge cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper limit voltage of 4.25 V was reached. After reaching the upper limit voltage of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then the lithium-ion secondary batteries were each discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V was reached.

[0165]

[0166] In each example where the ratio of the total content of fluoroethylene carbonate and sulfo compounds in the electrolyte to the content of Si-C composite particles in the negative electrode active material was within a specific numerical range, the cycle characteristics were improved compared to each comparative example that did not meet the above numerical range.

[0167] [Examples and Comparative Examples Related to the Second Embodiment] (Examples 1b to 17b, Comparative Examples 1b to 5b) <Preparation of Lithium-ion Secondary Batteries> Lithium-ion secondary batteries were prepared using the following steps. The following will be a detailed explanation divided into several steps. First, the electrolytes used in the lithium-ion secondary batteries of each example and comparative example were prepared using the following procedure. EC, EMC, and PC were mixed in the amounts shown in Table 2, with the total organic solvent being 100% by volume, to obtain an organic solvent. Lithium hexafluoride phosphate (LiPF) was added to the obtained organic solvent. ６ The solvent was dissolved to a concentration of 1.0 mol / L. Then, VC, FEC, and each sulfo-based compound were dissolved to the concentrations shown in Table 2 when the total organic solvent was considered to be 100% by volume, and the electrolytes for each example and each comparative example were prepared.

[0168] Next, the positive electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. A positive electrode slurry was prepared by dispersing the positive electrode active material, binder (PVDF), and conductive additive (CNT) in a solvent (NMP) in a ratio of positive electrode active material:PVDF:CNT = 97.5:1.5:1.0 (mass ratio). Then, the positive electrode slurry was applied to a 13 μm thick aluminum foil, which serves as the positive electrode current collector, with an initial charge capacity of 4.0 mAh / cm² per unit area. ２ The coating amount was applied to achieve the desired result. The coated cathode slurry was then dried to obtain a cathode laminate. Next, using a roll press, the density of the cathode active material layer was measured to be 3.5 g / cm³. ３ The positive electrode laminate was pressed with such pressure to produce positive electrodes (thickness of the positive electrode active material layer: 100 μm) for each example and each comparative example.

[0169] Next, the negative electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. Si-C composite particles and graphite particles were mixed in the mass ratio of Si-C composite particles to graphite particles shown in Table 2 to obtain the negative electrode active materials for each example and comparative example. The obtained negative electrode active materials, binder (PAA), and conductive additive (CNT) were dispersed in a solvent (pure water) in a mass ratio of negative electrode active material:PAA:CNT = 96.9:3.0:0.1 to prepare negative electrode slurries. Then, the negative electrode slurry was applied to a 6 μm thick copper foil, which serves as the negative electrode current collector, with an initial charge capacity of 4.3 mAh / cm² per unit area. ２ The material was applied in an amount that would result in the following. The applied negative electrode slurry was then dried to obtain a negative electrode laminate. Next, using a roll press, the density of the negative electrode active material layer was determined to be 1.65 g / cm³. ３ The negative electrode laminate was pressed with a pressure such that the negative electrodes for each example and each comparative example were fabricated (thickness of the negative electrode active material layer for Examples 1b to 17b, Comparative Examples 1b to 2b and 4b to 5b: 100 μm; thickness of the negative electrode active material layer for Comparative Example 3b: 65 μm).

[0170] Next, lithium-ion secondary batteries for each example and comparative example were fabricated using the following procedure. One positive electrode coated on both sides and two negative electrodes coated on one side were placed facing each other with a separator between them, and the coated surfaces were stacked in the order of negative electrode, separator, positive electrode, separator, negative electrode. The resulting laminate was then wrapped in a laminate outer casing made by processing and molding a film mainly composed of aluminum. At this time, the aluminum foil and copper foil cut out for current collection were made to protrude from the laminate film. Subsequently, the side containing the protruding portion of the current-collecting foil and the other two sides were heat-sealed to create a laminate-type cell with only one side open. A predetermined amount of electrolyte prepared above was poured through the opening of the laminate-type cell. Then, the laminate-type cell was sealed under reduced pressure to fabricate a laminate-type lithium-ion secondary battery. Here, the amount of electrolyte injected was set so that when the total amount of positive electrode active material and negative electrode active material was 100 parts by mass, the amount of electrolyte was 30 parts by mass. Furthermore, the ratio calculated from the specific surface area of ​​the Si-C composite particles by the nitrogen adsorption BET method, and the content of fluoroethylene carbonate and sulfo compounds was calculated using the following formula (1b). Here, the content of fluoroethylene carbonate and sulfo compounds in the electrolyte is the value when the content of organic solvent (S) contained in the electrolyte is set to 100 volume%. Ratio [volume%・g / m ２ ] = ((Content of the above fluoroethylene carbonate in the above electrolyte [volume %]) + (Content of the above sulfo-based compound in the above electrolyte [volume %])) / (Specific surface area of ​​the above Si-C composite particles by nitrogen adsorption BET method [m²] ２ / g])...(1b)

[0171] <Initial Charging and Discharging of Lithium-Ion Secondary Batteries> For each example of lithium-ion secondary battery, initial charging and discharging was performed under the following conditions to form an SEI film on the surface of the negative electrode active material, thereby obtaining the lithium-ion secondary battery after initial charging and discharging for each example. In the following, charging and discharging of the lithium-ion secondary battery was performed using a charge / discharge device in an environment of 25°C. Pre-charging was performed by charging each example of lithium-ion secondary battery to a battery voltage of 3.2V with a charging current of 0.05C, and then leaving it for 12 hours. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.05C. After reaching a battery voltage of 4.25V, constant voltage charging was performed until the current value decreased to 0.015C. Then, it was left for 10 minutes. After that, constant current discharge was performed to a battery voltage of 2.5V with a discharge current of 0.33C. After reaching a battery voltage of 2.5V, it was left for 10 minutes. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.33C. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, the charged lithium-ion secondary battery was stored for 48 hours in a 45°C environment while monitoring the battery voltage. After storage, the lithium-ion secondary battery was returned to a 25°C environment and constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, 10 minutes after the end of charging, constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After reaching 4.25V, constant voltage charging was performed until the current value dropped to 0.05C. Then, it was left standing for 10 minutes. After that, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V.

[0172] <Evaluation of Lithium-ion Secondary Battery Characteristics> The characteristics of lithium-ion secondary batteries obtained in each example and comparative example after initial charge and discharge were evaluated using the following method. The results are shown in Table 2.

[0173] [Gas Generation Amount] The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the lithium-ion secondary batteries were charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge was measured for each, and then the volume of the lithium-ion secondary battery after the 500th charge-discharge was measured for each. After that, the gas generation amount (cc / Ah) was calculated for each using the following formula (3b). Formula (3b): Gas generation amount = {(Volume of lithium-ion secondary battery after 500th charge-discharge) - (Volume of lithium-ion secondary battery before the first charge-discharge)} / [{(Discharge capacity after the first discharge) + (Discharge capacity after the 500th discharge)} / 2] The volume of the lithium-ion secondary battery was measured using the Archimedes method. (Charge / Discharge Cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper voltage limit of 4.25 V was reached. After reaching the upper voltage limit of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then each lithium-ion secondary battery was discharged at a constant current of 30 mA until the lower voltage limit of 2.5 V was reached.

[0174] [Capacity retention rate R ４５ The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge was measured for each. After that, the capacity retention rate R was calculated from the following formula (2b).４５ The percentages were calculated for each. Equation (2b): Capacity retention rate R ４５ = (Discharge capacity at 500th cycle) / (Discharge capacity at 1st cycle) × 100 (Charge-discharge cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper limit voltage of 4.25 V was reached. After reaching the upper limit voltage of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then the lithium-ion secondary batteries were each discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V was reached.

[0175]

[0176] In each example where the ratio calculated from the specific surface area of ​​Si-C composite particles by nitrogen adsorption BET method and the content of fluoroethylene carbonate and sulfo compounds was within a specific numerical range, the cycle characteristics were improved compared to each comparative example that did not meet the above numerical range.

[0177] [Examples and Comparative Examples Related to the Third Embodiment] (Examples 1c to 17c, Comparative Examples 1c to 5c) <Preparation of Lithium-ion Secondary Batteries> Lithium-ion secondary batteries were prepared using the following steps. The following will be a detailed explanation of the steps. First, the electrolytes used in the lithium-ion secondary batteries of each example and comparative example were prepared using the following procedure. EC, EMC, and PC were mixed in the amounts shown in Table 3, with the total organic solvent being 100% by volume, to obtain an organic solvent. Lithium hexafluoride phosphate (LiPF) was added to the obtained organic solvent. ６ The solvent was dissolved to a concentration of 1.0 mol / L. Then, VC, FEC, and each sulfo-based compound were dissolved to the concentrations shown in Table 3 when the total organic solvent was considered to be 100% by volume, and the electrolytes for each example and comparative example were prepared.

[0178] Next, the positive electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. A positive electrode slurry was prepared by dispersing the positive electrode active material, binder (PVDF), and conductive additive (CNT) in a solvent (NMP) in a ratio of positive electrode active material:PVDF:CNT = 97.5:1.5:1.0 (mass ratio). Then, the positive electrode slurry was applied to a 13 μm thick aluminum foil, which serves as the positive electrode current collector, with an initial charge capacity of 4.0 mAh / cm² per unit area. ２ The coating amount was applied to achieve the desired result. The coated cathode slurry was then dried to obtain a cathode laminate. Next, using a roll press, the density of the cathode active material layer was measured to be 3.5 g / cm³. ３ The positive electrode laminate was pressed with such pressure to produce positive electrodes (thickness of the positive electrode active material layer: 100 μm) for each example and each comparative example.

[0179] Next, the negative electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. Si-C composite particles and graphite particles were mixed in the mass ratio of Si-C composite particles to graphite particles shown in Table 3 to obtain the negative electrode active materials for each example and comparative example. The obtained negative electrode active materials, binder (PAA), and conductive additive (CNT) were dispersed in a solvent (pure water) in a mass ratio of negative electrode active material:PAA:CNT = 96.9:3.0:0.1 to prepare negative electrode slurries. Then, the negative electrode slurry was applied to a 6 μm thick copper foil, which serves as the negative electrode current collector, with an initial charge capacity of 4.3 mAh / cm² per unit area. ２ The material was applied in an amount that would result in the following. The applied negative electrode slurry was then dried to obtain a negative electrode laminate. Next, using a roll press, the density of the negative electrode active material layer was determined to be 1.65 g / cm³. ３ The negative electrode laminate was pressed with a pressure such that the negative electrodes for each example and each comparative example were fabricated (thickness of the negative electrode active material layer for Examples 1c to 17c, Comparative Examples 1c to 2c and 4c to 5c: 100 μm; thickness of the negative electrode active material layer for Comparative Example 3c: 65 μm).

[0180] Next, lithium-ion secondary batteries for each example and comparative example were fabricated using the following procedure. One positive electrode coated on both sides and two negative electrodes coated on one side were placed facing each other with a separator between them, and the coated surfaces were stacked in the order of negative electrode, separator, positive electrode, separator, negative electrode. The resulting laminate was then wrapped in a laminate outer casing made by processing and molding a film mainly composed of aluminum. At this time, the aluminum foil and copper foil cut out for current collection were made to protrude from the laminate film. Subsequently, the side containing the protruding portion of the current-collecting foil and the other two sides were heat-sealed to create a laminate-type cell with only one side open. A predetermined amount of electrolyte prepared above was poured through the opening of the laminate-type cell. Then, the laminate-type cell was sealed under reduced pressure to fabricate a laminate-type lithium-ion secondary battery. Here, the amount of electrolyte to be injected was such that when the total amount of positive electrode active material and negative electrode active material was 100 parts by mass, the amount of electrolyte was 30 parts by mass.

[0181] <Initial Charging and Discharging of Lithium-Ion Secondary Batteries> For each example of lithium-ion secondary battery, initial charging and discharging was performed under the following conditions to form an SEI film on the surface of the negative electrode active material, thereby obtaining the lithium-ion secondary battery after initial charging and discharging for each example. In the following, charging and discharging of the lithium-ion secondary battery was performed using a charge / discharge device in an environment of 25°C. Pre-charging was performed by charging each example of lithium-ion secondary battery to a battery voltage of 3.2V with a charging current of 0.05C, and then leaving it for 12 hours. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.05C. After reaching a battery voltage of 4.25V, constant voltage charging was performed until the current value decreased to 0.015C. Then, it was left for 10 minutes. After that, constant current discharge was performed to a battery voltage of 2.5V with a discharge current of 0.33C. After reaching a battery voltage of 2.5V, it was left for 10 minutes. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.33C. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, the charged lithium-ion secondary battery was stored for 48 hours in a 45°C environment while monitoring the battery voltage. After storage, the lithium-ion secondary battery was returned to a 25°C environment and constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, 10 minutes after the end of charging, constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After reaching 4.25V, constant voltage charging was performed until the current value dropped to 0.05C. Then, it was left standing for 10 minutes. After that, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V.

[0182] <Evaluation of Lithium-ion Secondary Battery Characteristics> The characteristics of lithium-ion secondary batteries obtained in each example and comparative example after initial charge and discharge were evaluated using the following method. The results are shown in Table 3.

[0183] [Gas Generation Amount] The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the lithium-ion secondary batteries were charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge was measured for each, and then the volume of the lithium-ion secondary battery after the 500th charge-discharge was measured for each. After that, the gas generation amount (cc / Ah) was calculated for each using the following formula (3c). Formula (3c): Gas generation amount = {(Volume of lithium-ion secondary battery after 500th charge-discharge) - (Volume of lithium-ion secondary battery before the first charge-discharge)} / [{(Discharge capacity after the first discharge) + (Discharge capacity after the 500th discharge)} / 2] The volume of the lithium-ion secondary battery was measured using the Archimedes method. (Charge / Discharge Cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper voltage limit of 4.25 V was reached. After reaching the upper voltage limit of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then each lithium-ion secondary battery was discharged at a constant current of 30 mA until the lower voltage limit of 2.5 V was reached.

[0184] [Capacity retention rate R ４５ The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times had occurred. Furthermore, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge was measured for each. After that, the capacity retention rate R was calculated from the following formula (2c).４５ The percentages (%) were calculated for each. Equation (2c): Volume retention rate R ４５ = (Discharge capacity at 500th cycle) / (Discharge capacity at 1st cycle) × 100 (Charge-discharge cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper limit voltage of 4.25 V was reached. After reaching the upper limit voltage of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then the lithium-ion secondary batteries were each discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V was reached.

[0185]

[0186] In each example where the electrolyte contained fluoroethylene carbonate and lithium fluorosulfate, and the fluoroethylene carbonate content in the electrolyte was within a specific numerical range, the cycle characteristics were improved compared to each comparative example that did not meet the above numerical range.

[0187] [Examples and Comparative Examples Related to the Fourth Embodiment] (Examples 1d to 17d, Comparative Examples 1d to 5d) <Preparation of Lithium-ion Secondary Batteries> Lithium-ion secondary batteries were prepared using the following steps. The following will be a detailed explanation of the steps. First, the electrolytes used in the lithium-ion secondary batteries of each example and comparative example were prepared using the following procedure. EC, EMC, and PC were mixed in the amounts shown in Table 4, with the total organic solvent being 100% by volume, to obtain an organic solvent. Lithium hexafluoride phosphate (LiPF) was added to the obtained organic solvent. ６ The solvent was dissolved to a concentration of 1.0 mol / L. Then, VC, FEC, and each sulfo-based compound were dissolved to the concentrations shown in Table 4 when the total organic solvent was considered to be 100% by volume, and the electrolytes for each example and comparative example were prepared.

[0188] Next, the positive electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. A positive electrode slurry was prepared by dispersing the positive electrode active material, binder (PVDF), and conductive additive (CNT) in a solvent (NMP) in a ratio of positive electrode active material:PVDF:CNT = 97.5:1.5:1.0 (mass ratio). Then, the positive electrode slurry was applied to a 13 μm thick aluminum foil, which serves as the positive electrode current collector, with an initial charge capacity of 4.0 mAh / cm² per unit area. ２ The coating amount was applied to achieve the desired result. The coated cathode slurry was then dried to obtain a cathode laminate. Next, using a roll press, the density of the cathode active material layer was measured to be 3.5 g / cm³. ３ The positive electrode laminate was pressed with such pressure to produce positive electrodes (thickness of the positive electrode active material layer: 100 μm) for each example and each comparative example.

[0189] Next, the negative electrodes for each example and comparative example of lithium-ion secondary batteries were prepared using the following procedure. Si-C composite particles and graphite particles were mixed in the mass ratio of Si-C composite particles to graphite particles shown in Table 4 to obtain the negative electrode active materials for each example and comparative example. The obtained negative electrode active materials, binder (PAA), and conductive additive (CNT) were dispersed in a solvent (pure water) in a mass ratio of negative electrode active material:PAA:CNT = 96.9:3.0:0.1 to prepare negative electrode slurries. Then, the negative electrode slurry was applied to a 6 μm thick copper foil, which serves as the negative electrode current collector, with an initial charge capacity of 4.3 mAh / cm² per unit area. ２ The material was applied in an amount that would result in the following. The applied negative electrode slurry was then dried to obtain a negative electrode laminate. Next, using a roll press, the density of the negative electrode active material layer was determined to be 1.65 g / cm³. ３ The negative electrode laminate was pressed with a pressure such that the negative electrodes for each example and each comparative example were fabricated (thickness of the negative electrode active material layer for Examples 1d to 17d, Comparative Examples 1d to 2d and 4d to 5d: 100 μm; thickness of the negative electrode active material layer for Comparative Example 3d: 65 μm).

[0190] Next, lithium-ion secondary batteries for each example and comparative example were fabricated using the following procedure. One positive electrode coated on both sides and two negative electrodes coated on one side were placed facing each other with a separator between them, and the coated surfaces were stacked in the order of negative electrode, separator, positive electrode, separator, negative electrode. The resulting laminate was then wrapped in a laminate outer casing made by processing and molding a film mainly composed of aluminum. At this time, the aluminum foil and copper foil cut out for current collection were made to protrude from the laminate film. Subsequently, the side containing the protruding portion of the current-collecting foil and the other two sides were heat-sealed to create a laminate-type cell with only one side open. A predetermined amount of electrolyte prepared above was poured through the opening of the laminate-type cell. Then, the laminate-type cell was sealed under reduced pressure to fabricate a laminate-type lithium-ion secondary battery. Here, the amount of electrolyte to be injected was such that when the total amount of positive electrode active material and negative electrode active material was 100 parts by mass, the amount of electrolyte was 30 parts by mass.

[0191] <Initial Charging and Discharging of Lithium-Ion Secondary Batteries> For each example of lithium-ion secondary battery, initial charging and discharging was performed under the following conditions to form an SEI film on the surface of the negative electrode active material, thereby obtaining the lithium-ion secondary battery after initial charging and discharging for each example. In the following, charging and discharging of the lithium-ion secondary battery was performed using a charge / discharge device in an environment of 25°C. Pre-charging was performed by charging each example of lithium-ion secondary battery to a battery voltage of 3.2V with a charging current of 0.05C, and then leaving it for 12 hours. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.05C. After reaching a battery voltage of 4.25V, constant voltage charging was performed until the current value decreased to 0.015C. Then, it was left for 10 minutes. After that, constant current discharge was performed to a battery voltage of 2.5V with a discharge current of 0.33C. After reaching a battery voltage of 2.5V, it was left for 10 minutes. Next, constant current charging was performed to a battery voltage of 4.25V with a charging current of 0.33C. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, the charged lithium-ion secondary battery was stored for 48 hours in a 45°C environment while monitoring the battery voltage. After storage, the lithium-ion secondary battery was returned to a 25°C environment and constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After the battery voltage reached 4.25V, constant voltage charging was performed until the current value decreased to 0.05C. Next, 10 minutes after the end of charging, constant current discharge was performed at a discharge current of 1C until the battery voltage reached 2.5V. Next, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V. After the battery voltage reached 2.5V, it was left for 10 minutes. Next, constant current charging was performed at a charging current of 0.33C until the battery voltage reached 4.25V. After reaching 4.25V, constant voltage charging was performed until the current value dropped to 0.05C. Then, it was left standing for 10 minutes. After that, constant current discharge was performed at a discharge current of 0.33C until the battery voltage reached 2.5V.

[0192] <Evaluation of Lithium-ion Secondary Battery Characteristics> The characteristics of lithium-ion secondary batteries obtained in each example and comparative example after initial charge and discharge were evaluated using the following method. The results are shown in Table 4.

[0193] [Gas Generation Amount] The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the lithium-ion secondary batteries were charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge was measured for each, and then the volume of the lithium-ion secondary battery after the 500th charge-discharge was measured for each. After that, the gas generation amount (cc / Ah) was calculated for each using the following formula (3d). Formula (3d): Gas generation amount = {(Volume of lithium-ion secondary battery after 500th charge-discharge) - (Volume of lithium-ion secondary battery before the first charge-discharge)} / [{(Discharge capacity after the first discharge) + (Discharge capacity after the 500th discharge)} / 2] The volume of the lithium-ion secondary battery was measured using the Archimedes method. (Charge / Discharge Cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper voltage limit of 4.25 V was reached. After reaching the upper voltage limit of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then each lithium-ion secondary battery was discharged at a constant current of 30 mA until the lower voltage limit of 2.5 V was reached.

[0194] [Capacity retention rate R ４５ The lithium-ion secondary batteries obtained in each example and comparative example were placed in a constant temperature bath at 45°C, and then charged and discharged according to the following (charge-discharge cycle), and the discharge capacity after the first discharge was measured for each. Next, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle) until a total of 499 times. Furthermore, the charging and discharging of the lithium-ion secondary batteries was repeated according to the following (charge-discharge cycle), and the discharge capacity after the 500th discharge was measured for each. After that, the capacity retention rate R was calculated from the following formula (2d).４５ The percentages were calculated for each. Equation (2d): Volume retention rate R ４５ = (Discharge capacity at 500th cycle) / (Discharge capacity at 1st cycle) × 100 (Charge-discharge cycle) The lithium-ion secondary batteries obtained in each example and comparative example were each charged at 30 mA until the upper limit voltage of 4.25 V was reached. After reaching the upper limit voltage of 4.25 V, the lithium-ion secondary batteries were each charged at a constant voltage until 2.5 hours had elapsed since the start of charging, and then the lithium-ion secondary batteries were each discharged at a constant current of 30 mA until the lower limit voltage of 2.5 V was reached.

[0195]

[0196] In each example where the volume ratio of fluoroethylene carbonate content to sulfo-based compound content was within a specific numerical range, the cycle characteristics were improved compared to each comparative example that did not meet the above numerical range.

[0197] This application claims priority based on Japanese Patent Applications No. 2025-057151, 2025-057152, 2025-057153, and 2025-057154, filed on 28 March 2025, and incorporates all of their disclosures herein.

[0198] 1. Positive electrode active material layer 2. Negative electrode active material layer 3. Positive electrode current collector 4. Negative electrode current collector 5. Separator 6. Outer casing 7. Outer casing 8. Negative electrode tab 9. Positive electrode tab 10. Lithium-ion secondary battery

Claims

1. A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1a) is 0.150 or more and 1.000 or less. Ratio [volume % / mass %] = ((Content of fluoroethylene carbonate in the electrolyte [volume %]) + (Content of sulfo-based compound in the electrolyte [volume %])) / (Content of Si-C composite particles in the negative electrode active material [mass %]) ... (1a) Here, the content of fluoroethylene carbonate and the content of sulfo-based compound in the electrolyte are values ​​when the content of the organic solvent (S) contained in the electrolyte is set to 100 volume %, and the content of Si-C composite particles in the negative electrode active material is value when the total amount of the negative electrode active material contained in the negative electrode active material layer is set to 100 mass %.

2. A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, and the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the ratio according to the following formula (1b) is 0.50 or more and 2.00 or less. Ratio [volume %・g / m³] ２ ] = ((Content of the fluoroethylene carbonate in the electrolyte [volume %]) + (Content of the sulfo-based compound in the electrolyte [volume %])) / (Specific surface area of ​​the Si-C composite particles by nitrogen adsorption BET method [m²] ２ / g]) ... (1b) Here, the content of fluoroethylene carbonate and the content of sulfo compounds in the electrolyte are values ​​when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume.

3. A lithium-ion secondary battery comprising a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, and an electrolyte, wherein the negative electrode active material contained in the negative electrode active material layer comprises graphite particles and Si-C composite particles containing silicon and carbon material, the electrolyte comprises fluoroethylene carbonate, a sulfo-based compound, and an organic solvent (S), and the volume ratio of the fluoroethylene carbonate content to the sulfo-based compound content in the electrolyte is 1.05 or more and 5.00 or less.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein the content of fluoroethylene carbonate in the electrolyte is 1.00% by volume or more and 10.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume.

5. The lithium-ion secondary battery according to any one of claims 1 to 4, wherein the sulfo-based compound comprises one or more selected from the group consisting of lithium fluorosulfate, 1,3-propanesultone, methylene methanedisulfonate, and ethylene sulfate.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, wherein the content of the sulfo-based compound in the electrolyte is 1.00% by volume or more and 5.00% by volume or less, when the content of the organic solvent (S) contained in the electrolyte is taken as 100% by volume.

7. The lithium-ion secondary battery according to any one of claims 1 to 6, wherein the content of the electrolyte in the lithium-ion secondary battery is 15 parts by mass or more and 60 parts by mass or less when the sum of the content of the negative electrode active material and the content of the positive electrode active material contained in the positive electrode active material layer is 100 parts by mass.

8. Median diameter D in the volume frequency particle size distribution of the graphite particles obtained by laser diffraction scattering method. ５０ A lithium-ion secondary battery according to any one of claims 1 to 7, wherein the particle size is 1.0 μm or more and 30.0 μm or less.

9. The lithium-ion secondary battery according to any one of claims 1 to 8, wherein the content of graphite particles in the negative electrode active material is 10 parts by mass or more and 99 parts by mass or less, when the total content of graphite particles and Si-C composite particles is 100 parts by mass.

10. The lithium-ion secondary battery according to any one of claims 1 to 9, wherein the carbon material in the Si-C composite particle includes a porous carbon material, and the silicon is present in at least a portion of the pores of the porous carbon material.

11. The specific surface area of ​​the Si-C composite particles obtained by the nitrogen adsorption BET method is 1 m². ２ / g or more 20m ２ A lithium-ion secondary battery according to any one of claims 1 to 10, wherein the value is less than or equal to / g.

12. Median diameter D in the volume frequency particle size distribution of the Si-C composite particles obtained by laser diffraction scattering method. ５０ A lithium-ion secondary battery according to any one of claims 1 to 11, wherein the particle size is 1.0 μm or more and 20.0 μm or less.

13. The lithium-ion secondary battery according to any one of claims 1 to 12, wherein the content of the Si-C composite particles in the negative electrode active material is 1 part by mass or more and 90 parts by mass or less, when the total content of the graphite particles and the Si-C composite particles is 100 parts by mass.

14. The lithium-ion secondary battery according to any one of claims 1 to 13, wherein the organic solvent (S) comprises one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyrolactone.

15. Volume retention rate R at 45°C according to the following (Method 1) ４５ However, the lithium-ion secondary battery according to any one of claims 1 to 14, wherein the concentration is 79.0% or more. (Method 1) The lithium ion secondary battery is placed in a constant temperature bath at 45° C., then the lithium ion secondary battery is charged and discharged by the following (charge-discharge cycle), and the first discharge capacity is measured. Then, the charge and discharge of the lithium ion secondary battery is repeated by the following (charge-discharge cycle) until the total number of times reaches 499. Further, the lithium ion secondary battery is charged and discharged by the following (charge-discharge cycle), and the 500th discharge capacity is measured. Thereafter, the capacity retention rate R is obtained from the following formula (2) ４５ is calculated. Formula (2): The capacity retention rate R ４５ = (the 500th discharge capacity) / (the first discharge capacity) × 100 (Charge-discharge cycle) The lithium ion secondary battery is charged at 30 mA until the voltage reaches an upper limit voltage of 4.25 V. After reaching the upper voltage limit of 4.25V, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30mA until it reaches the lower voltage limit of 2.5V.

16. A lithium-ion secondary battery according to any one of claims 1 to 15, wherein the amount of gas generated by the following method (Method 2) is 0.40 cc / Ah or less. (Method 2) The lithium-ion secondary battery is placed in a constant temperature bath at 45°C, and then the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the first time is measured. Next, the charging and discharging of the lithium-ion secondary battery is repeated according to the following (charge-discharge cycle) until a total of 499 times have been reached. Furthermore, the lithium-ion secondary battery is charged and discharged according to the following (charge-discharge cycle), and the discharge capacity of the 500th time is measured, and then the volume of the lithium-ion secondary battery after the 500th charge-discharge is measured. After that, the amount of gas generated (cc / Ah) is calculated from the following formula (3). Formula (3): Amount of gas generated = {(Volume of the lithium-ion secondary battery after the 500th charge-discharge) - (Volume of the lithium-ion secondary battery before the first charge-discharge)} / [{(Discharge capacity of the first time) + (Discharge capacity of the 500th time)} / 2] (Charge-discharge cycle) The lithium-ion secondary battery is charged at 30mA until the upper limit voltage of 4.25V is reached. After reaching the upper voltage limit of 4.25V, the lithium-ion secondary battery is charged at a constant voltage until 2.5 hours have elapsed since the start of charging, and then the lithium-ion secondary battery is discharged at a constant current of 30mA until it reaches the lower voltage limit of 2.5V.

17. A lithium-ion secondary battery module comprising a lithium-ion secondary battery according to any one of claims 1 to 16.

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