JP2008262768A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion battery which is improved in charge/discharge cycle characteristics and excellent in battery life characteristics. <P>SOLUTION: In an anode for a lithium ion secondary battery which is composed of an anode active substance mixture formed of a graphite material as a main composition and deposited on the metal foil of a current collector, (A) the porosity of the anode active substance layer as regulated in a formula (1) is 10% or higher and 60% or lower, and (B) a ratio of an amount of an electrolyte solution with respect to a pore volume (cm<SP>3</SP>) of the anode active substance layer is one time or larger and 30 times or smaller. The formula (1): porosity = (He substitute volume measured by a pycnometer - anode active substance volume)/(anode active substance volume) and the formula (2): porosity volume = He substitute volume measured by pycnometer - anode active substance volume. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery with improved charge / discharge characteristics.

  Non-aqueous electrolyte lithium ion secondary batteries using lithium-containing composite oxide for the positive electrode and carbon material or lithium metal for the negative electrode can realize high energy density, so as a power source for mobile phones, laptop computers, etc. Furthermore, it has attracted attention as a power source for hybrid vehicles because it can realize high input / output characteristics.

  In this lithium ion secondary battery, the negative electrode has a negative electrode active material layer mainly composed of a material capable of occluding and releasing lithium ions, for example, a graphite material, an amorphous carbon material, and an Si or Si compound material. In order to ensure conductivity in the material layer, for example, a conductivity imparting agent such as carbon black and a binder such as polyvinylidene fluoride (PVdF) are mixed in order to ensure adhesion between particles. A negative electrode active material mixture is applied onto a metal foil (for example, copper foil) as a current collector, dried, then compressed to a predetermined thickness by a press, combined with a positive electrode and a separator, a metal can, Alternatively, it is common to use a method of obtaining a lithium ion secondary battery by storing the battery case in an outer package such as a laminate film and impregnating with an electrolytic solution, and then sealing the battery outer package.

  In the negative electrode for lithium ion secondary batteries, for example, Patent Document 1 discloses the relationship between the pore volume and the void volume in the negative electrode mixture, and Patent Document 2 describes the relationship between the size of the electrode particles and the porosity. Reference 3 defines the porosity of the active material layer, and Patent Document 4 defines the porosity of the metal-graphite composite particles.

  However, in these Patent Documents 1 to 4 describing the prior art, there is no description about an appropriate amount of the electrolytic solution, and the deterioration of the charge / discharge cycle characteristics due to the excessive or insufficient amount of the electrolytic solution cannot be sufficiently suppressed.

Japanese Patent Laid-Open No. 10-50298 Japanese Patent Laid-Open No. 11-242955 JP 2006-210089 A JP 2006-269110 A

  The present invention has been made in view of the above problems, and by optimizing the relationship between the porosity of the negative electrode active material layer and the amount of the electrolyte, lithium having excellent battery life, particularly charge / discharge cycle characteristics. An object is to provide an ion secondary battery.

In order to solve the above problems, the lithium ion battery of the present invention has a negative electrode active material layer in which a negative electrode active material mixture mainly composed of a positive electrode, an electrolytic solution, and a graphite material is formed on a metal foil as a current collector. In a lithium ion secondary battery including a negative electrode, the negative electrode (A) has a porosity of the negative electrode active material layer defined by the following formula (1) of 10% or more and 60% or less, and ( B) The amount of the electrolytic solution with respect to the negative electrode active material layer is 1 to 35 times the pore volume (cm ³ ) of the negative electrode active material layer defined by the following formula (2).
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)

  Furthermore, it is preferable that the mixing ratio of the graphite material in the negative electrode active material layer is 85 mass (hereinafter referred to as wt)% or more.

Further, the lithium ion battery of the present invention includes a negative electrode having a negative electrode active material layer in which a negative electrode active material mixture mainly composed of a positive electrode, an electrolytic solution, and an amorphous carbon material is formed on a metal foil as a current collector. In the lithium ion secondary battery, the negative electrode (C) has a porosity of the negative electrode active material layer defined by the following formula (1) of 20% or more and 55% or less, and (D) The amount of the electrolytic solution with respect to the negative electrode active material layer is 1 to 15 times the pore volume (cm ³ ) of the negative electrode active material layer defined by the following formula (2).
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)

  Furthermore, it is preferable that the mixing ratio of the amorphous carbon material in the negative electrode active material layer is 80 wt% or more.

The lithium ion battery of the present invention also includes a negative electrode having a negative electrode active material layer in which a positive electrode, an electrolyte, and a negative electrode active material mixture mainly composed of Si or Si compound material are formed on a metal foil as a current collector. In the lithium ion secondary battery, the negative electrode (E) has a porosity of the negative electrode active material layer defined by the following formula (1) of 15% or more and 70% or less, and (F) the negative electrode The amount of the electrolytic solution with respect to the active material layer is 1 to 40 times the pore volume (cm ³ ) of the negative electrode active material layer defined by the following formula (2).
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)

  Furthermore, it is preferable that the mixing ratio of Si or Si compound material in the negative electrode active material layer is 70 wt% or more.

  According to the present invention, for a negative electrode using various negative electrode active material materials, by optimizing the relationship between the porosity of each negative electrode active material layer and the amount of electrolytic solution, battery resistance due to lack of electrolytic solution is achieved. The increase in the battery life and the decrease in the charge / discharge cycle characteristics, the promotion of the electrolytic solution decomposition reaction by the excessive electrolyte, and the decrease in the charge / discharge cycle characteristics can be suppressed, and the battery life characteristics are improved.

(Battery configuration according to the present invention)
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the lithium ion secondary battery of the present invention.

  As shown in FIG. 1, a positive electrode active material layer 12 containing a positive electrode active material that can occlude and release lithium ions on the positive electrode current collector 11 and a negative electrode active material that occludes and releases lithium ions on the negative electrode current collector 14. A negative electrode active material layer 13 containing a substance is disposed and configured to face each other with an electrolyte solution 15 and a separator 16 including the electrolyte solution 15 interposed therebetween.

(Positive electrode)
Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _1.5 O ₄ , and LiFePO ₄ . The transition metal portion of these lithium-containing composite oxides may be substituted with other elements, or a mixture thereof. These positive electrode active materials, conductivity imparting agents composed of carbon black and the like, and binders composed of PVdF and the like were mixed with a dispersion medium such as N-methyl-2-pyrrolidone (NMP) capable of dissolving the binding agent. Then, the positive electrode active material layer 12 is formed by a method such as coating on a current collector such as an aluminum foil and drying the solvent.

(Negative electrode)
As the negative electrode active material, for example, a binder is dissolved together with a graphite material, an amorphous carbon material, a Si or Si compound material, a conductivity imparting agent made of carbon black, and a binder made of PVdF. The negative electrode active material layer 13 is formed by a method such as dispersion and kneading in a solvent such as NMP, which is applied onto a current collector such as a copper foil, and the solvent is dried. Here, the graphite material is a material whose true density is close to 2.2 g / cm ³ and whose crystal structure shows a staged stage structure change due to insertion and extraction of lithium ions accompanying charging and discharging. The material means a carbon material having a true density of about 1.5 to 2.0 g / cm ³ and having a crystal structure that does not show a stepwise stage structure change due to insertion and extraction of lithium ions accompanying charge and discharge.

  Whether the carbon material is a graphite material or an amorphous carbon material can be confirmed by measuring an X-ray diffraction spectrum. In the case of a graphite material, since it has a crystal structure, a clear (sharp) peak appears in the X-ray diffraction spectrum. In addition, when lithium ions are occluded, lithium is inserted between the carbon layers, so that the layers expand (lattice spacing increases), and the movement of the peak position and peak It can be detected as a change in shape.

  On the other hand, in the case of an amorphous carbon material, the X-ray diffraction spectrum is wide (or almost no spectrum is detected), and even when lithium ions are occluded, no clear peak shape change is shown. Therefore, it is possible to determine whether the material is a graphite material or an amorphous carbon material based on the difference in the shape of the peak in the spectrum.

The physical properties of the carbon material include graphite layer spacing (d ₀₀₂ ), crystallite size (La, Lc), specific surface area by nitrogen gas adsorption method, etc. It is preferable to use the peak change of the X-ray diffraction spectrum.

  Examples of the Si or Si compound material include Si-based materials such as crystalline Si, amorphous Si, and compounds of Si and Fe, Co, Ni, Cu, etc. A Si-carbon composite material coated with a carbon material or the like can also be used.

The relationship between the porosity of the negative electrode active material layer and the amount of the electrolyte when a graphite material is used as the main component is (A) the porosity of the negative electrode active material layer defined by the following formula (1) is 10% or more. , 60% or less, and (B) the amount of the electrolyte with respect to the negative electrode active material layer is 1 to 35 times the pore volume (cm ³ ) of the negative electrode active material layer defined by the following formula (2) The following.
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)

  When the porosity of the negative electrode active material layer when the graphite material is used as the main agent is less than 10%, it is difficult for the electrolyte to penetrate into the negative electrode active material layer, the battery resistance increases, and the charge / discharge cycle characteristics decrease. Therefore, if it exceeds 60%, the reaction area with the electrolytic solution is increased, the decomposition reaction of the electrolytic solution is promoted, and the charge / discharge cycle characteristics are deteriorated. The more preferable porosity of the negative electrode active material layer when a graphite material is used as the main agent is 15% or more and 45% or less.

  In addition, when the amount of the electrolytic solution with respect to the negative electrode active material layer when the graphite material is used as the main agent is less than 1 times the pore volume of the negative electrode active material layer, the battery resistance increases due to the shortage of the electrolytic solution, and the charge / discharge cycle characteristics When the ratio exceeds 35 times, the decomposition reaction of the electrolytic solution due to the presence of the excessive electrolytic solution is promoted, and the charge / discharge cycle characteristics are deteriorated. The more preferable amount of the electrolyte solution with respect to the negative electrode active material layer when the graphite material is used as the main agent is 1.5 times or more and 20.0 times or less the pore volume of the negative electrode active material layer.

  Furthermore, when the active material mixing ratio is low, it is difficult to obtain a sufficient capacity as the negative electrode. Therefore, the graphite material mixing ratio in the active material layer when the graphite material is used as the main agent is preferably 85 wt% or more. 90 wt% or more is more preferable.

The relationship between the porosity of the negative electrode active material layer and the amount of the electrolyte when an amorphous carbon material is used as the main agent is (C) the porosity of the negative electrode active material layer defined by the following formula (1). 20% or more and 55% or less, and (D) the amount of the electrolyte solution with respect to the negative electrode active material layer is one or more times the pore volume (cm ³ ) of the negative electrode active material layer defined by the following formula (2) , 15 times or less.
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)

  When the porosity of the negative electrode active material layer when an amorphous carbon material is used as the main agent is less than 20%, the electrolyte is difficult to penetrate into the negative electrode active material layer, the battery resistance increases, and the charge / discharge cycle It is not preferable because the characteristics deteriorate, and if it exceeds 55%, the reaction area with the electrolytic solution increases, the decomposition reaction of the electrolytic solution is promoted, and the charge / discharge cycle characteristics deteriorate. A more preferable porosity of the negative electrode active material layer when an amorphous carbon material is used as a main agent is 25% or more and 45% or less.

  In addition, when the amount of the electrolytic solution with respect to the negative electrode active material layer when the amorphous carbon material is used as the main agent is less than 1 times the pore volume of the negative electrode active material layer, the battery resistance increases due to the shortage of the electrolytic solution, This is not preferable because the discharge cycle characteristics deteriorate, and if it exceeds 15 times, the decomposition reaction of the electrolyte due to the presence of an excess electrolyte is promoted, and the charge / discharge cycle characteristics deteriorate, which is not preferable. A more preferable amount of the electrolyte solution with respect to the negative electrode active material layer when an amorphous carbon material is used as the main agent is 1.5 times or more and 9.0 times or less of the pore volume of the negative electrode active material layer.

  Furthermore, when the active material mixing ratio is low, it is difficult to obtain a sufficient capacity as a negative electrode. Therefore, the amorphous carbon material mixing ratio in the active material layer when an amorphous carbon material is used as the main agent is obtained. Is preferably 80 wt% or more, more preferably 85 wt% or more.

The relationship between the porosity of the negative electrode active material layer and the amount of the electrolyte when Si or a Si compound material is used as the main agent is as follows: (E) The porosity of the negative electrode active material layer defined by the following formula (1) is 15% or more and 70% or less, and (F) the amount of the electrolyte solution with respect to the negative electrode active material layer is 1 or more times the pore volume (cm ³ ) of the negative electrode active material layer defined by the following formula (2) 40 times or less.
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)

  When the porosity of the negative electrode active material layer is less than 15% when Si or Si compound material is used as the main agent, the electrolyte does not easily penetrate into the negative electrode active material layer, the battery resistance increases, and the charge / discharge cycle It is not preferable because the characteristics deteriorate, and if it exceeds 70%, the reaction area with the electrolytic solution increases, the decomposition reaction of the electrolytic solution is promoted, and the charge / discharge cycle characteristics deteriorate. The more preferable porosity of the negative electrode active material layer when Si or Si compound material is used as the main agent is 20% or more and 50% or less.

  In addition, when the amount of the electrolytic solution with respect to the negative electrode active material layer when Si or a Si compound material is used as the main agent is less than 1 times the pore volume of the negative electrode active material layer, the battery resistance increases due to the shortage of the electrolytic solution. Discharge cycle characteristics deteriorate, which is not preferable. Exceeding 40 times is not preferable because the decomposition reaction of the electrolyte due to the presence of excess electrolyte is promoted and charge / discharge cycle characteristics deteriorate. The more preferable amount of the electrolyte solution with respect to the negative electrode active material layer when Si or the Si compound material is used as the main agent is 2.0 times or more and 30.0 times or less the pore volume of the negative electrode active material layer.

  Furthermore, when the active material mixing ratio is low, it is difficult to obtain a sufficient capacity as the negative electrode. Therefore, the Si or Si compound material mixing ratio in the active material layer when Si or Si compound material is used as the main agent Is preferably 70 wt% or more, more preferably 80 wt% or more.

(Current collector)
Aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used as the positive electrode current collector 11, and copper, stainless steel, nickel, titanium, or an alloy thereof can be used as the negative electrode current collector 14. .

(Electrolyte)
As the electrolytic solution 15, an aprotic solvent in which an electrolyte is dissolved can be used. As a solvent for the electrolytic solution, cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), Aprotic organic solvents such as lactones such as γ-butyrolactone (GBL) can be used singly or in combination. Of these, PC, EC, GBL, DMC, DEC, EMC, etc. are preferably used alone or in combination, but are not limited thereto. Furthermore, for example, 1,3-propane sultone, vinylene carbonate, trioctyl phosphate, or the like can be used as an electrolytic solution additive.

In the case of a lithium ion secondary battery, a lithium salt is dissolved as an electrolyte in these organic solvents. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides, etc. . Further, a polymer electrolyte may be used instead of the electrolytic solution. The electrolyte concentration is, for example, 0.5 mol / L to 1.5 mol / L. If the concentration is too high, the density and viscosity increase, and if the concentration is too low, the electrical conductivity may decrease.

(Separator)
As the separator 16, a woven fabric, a nonwoven fabric, a porous film, or the like can be used. In particular, a polypropylene or polyethylene-based porous film is preferably used in terms of a thin film and a large area, film strength and film resistance.

  In the lithium ion secondary battery according to the present invention, a negative electrode and a positive electrode are laminated via a separator in a dry air or an inert gas atmosphere. After the impregnation, the battery outer package is sealed. There are no restrictions on the battery shape, and it can take the form of a positive electrode and negative electrode facing each other with a separator in between, a wound type, a laminated type, etc., and the cell can also be a coin type, laminate pack, square cell, cylinder Type cells can be used.

  Hereinafter, examples of the present invention will be described in detail with reference to FIG. 1, but the present invention is not limited to the following examples.

(Production of battery)
(Positive electrode)
A positive electrode active material and a conductivity-imparting agent were mixed and dispersed uniformly in NMP in which a binder was dissolved to prepare a slurry. LiMn ₂ O ₄ was used as the positive electrode active material, carbon black was used as the conductivity imparting agent, and PVdF was used as the binder. The slurry is applied on an aluminum metal foil having a thickness of 20 μm to be the positive electrode current collector 11, and then the positive electrode active material layer 12 is formed by evaporating NMP, followed by pressing, and a positive electrode having a porosity of 26.0%. A sheet was produced. The solid content ratio in the positive electrode active material layer was positive electrode active material: conductivity imparting agent: binder = 80: 10: 10 (wt%).

(Negative electrode)
A negative electrode active material and a conductivity-imparting agent were mixed and uniformly dispersed in NMP in which a binder was dissolved to prepare a slurry. The negative electrode active materials used in Examples 1 to 36 and Comparative Examples 1 to 27 are shown in Table 1. Carbon black was used as the conductivity-imparting agent, and PVdF was used as the binder. The slurry was applied on a copper foil having a thickness of 20 μm to be the negative electrode current collector 14, and NMP was evaporated to form the negative electrode active material layer 13, followed by pressing to prepare a negative electrode sheet. The mixing ratio of the negative electrode active material in the negative electrode active material layer is the value shown in Table 1, and the mixing ratio of the conductivity imparting agent and the binder is: conductivity imparting agent: binder = 1: 10 (wt%) did. Moreover, the porosity of the negative electrode active material layer described in Table 1 was calculated from the He substitution volume measured using a pentapicnometer manufactured by Yuasa Ionics Co., Ltd. of a negative electrode sheet having a predetermined shape.

(Electrolyte)
The electrolytic solution 15 was obtained by dissolving 1 mol / L LiPF ₆ as an electrolyte in EC: DEC = 40: 60 (vol%).

(Separator)
The separator 16 is made of polypropylene having a thickness of 25 μm and a porosity of 55%.

(Laminated battery assembly)
An aluminum laminate having a structure in which a positive electrode sheet and a negative electrode sheet are laminated via a separator, and a polypropylene resin (sealing layer, thickness 70 μm), polyethylene terephthalate (20 μm), aluminum (50 μm), and polyethylene terephthalate (20 μm) are laminated in this order. A laminate battery was manufactured by using two films and sandwiching the electrode laminate with the sealing layer facing each other, and heat-sealing the periphery of the laminate electrode. Before the last side was heat-sealed and sealed, the electrolyte solution was impregnated with the laminated electrode body. The amount of the electrolytic solution is shown in Table 1.

(Coin-type battery assembly)
The negative electrode sheet is punched into a circle, placed in one of the coin-shaped cases, the separator is placed on the negative electrode active material layer, impregnated with the electrolytic solution, Li is then placed on the separator, and the other coin-shaped case is inserted through the gasket. A coin-type battery was produced by caulking.

(Charge / discharge cycle test)
Using a laminate battery, at room temperature (25 ° C.), charging was performed at a constant current of 10 mA and a constant voltage for 5 hours to a final voltage of 4.3 V, and then the negative electrode active material was subjected to a constant current of 10 mA. In the case of a graphite material, the discharge rate is up to 3.0 V, and in the case where the negative electrode active material is an amorphous carbon material or Si, after discharging to a final voltage of 2.5 V, a charge rate of 1 C is used as a charge / discharge cycle test. At a discharge rate of 1 C, the end-of-charge voltage is 4.2 V. When the negative electrode active material is a graphite material, the end-of-discharge voltage is 3.0 V. When the negative electrode active material is an amorphous carbon material or Si, the discharge is stopped. The charge / discharge cycle test was performed under the condition of a final voltage of 2.5 V, and the capacity retention rate (%) = discharge capacity after 500 cycles / discharge capacity at the 10th cycle was calculated and shown in Table 1. “-” In Table 1 represents unmeasured.

(Negative electrode discharge capacity measurement)
In the negative electrode capacity measurement, a coin-type battery was used and charged at room temperature (25 ° C.) at a constant current and a constant voltage of 0.20 mA for 50 hours to a final voltage of 0.0 V, and then a current value of 0.20 mA. The discharge capacity was measured at a constant current of 2.5 V to a final voltage of 2.5 V, and the capacity was measured. “-” In Table 1 represents unmeasured.

(Effect of porosity of negative electrode active material layer and amount of electrolyte)
When Examples 1-11 are compared with Comparative Examples 1-8, the capacity retention rate of the charge / discharge cycle test is improved, and the porosity and the amount of electrolyte in the negative electrode active material layer when graphite material is used as the main agent (A) The porosity of the negative electrode active material layer is 10% or more and 60% or less, and (B) the amount of the electrolyte with respect to the negative electrode active material layer is 1 of the pore volume of the negative electrode active material layer. The porosity of the negative electrode active material layer is preferably 15% or more and 45% or less, and the amount of the electrolyte with respect to the negative electrode active material layer is more preferably It was confirmed that it was 1.5 times or more and 20.0 times or less of the pore volume.

  When Examples 13 to 23 and Comparative Examples 10 to 17 were compared, the capacity retention rate of the charge / discharge cycle test was improved, and the porosity of the negative electrode active material layer when an amorphous carbon material was used as the main agent The relationship between the amount of the electrolyte solution is that (C) the porosity of the negative electrode active material layer is 20% or more and 55% or less, and (D) the amount of the electrolyte solution with respect to the negative electrode active material layer is the porosity of the negative electrode active material layer The porosity of the negative electrode active material layer is more preferably 25% or more and 45% or less, and the amount of the electrolyte with respect to the negative electrode active material layer is more preferably negative electrode active material. It was confirmed that it was 1.5 times or more and 9.0 times or less of the pore volume of the material layer.

  When Examples 25-35 and Comparative Examples 19-26 were compared, the capacity retention rate of the charge / discharge cycle test was improved, and the porosity of the negative electrode active material layer when Si or Si compound material was used as the main agent The relationship between the amount of the electrolyte solution is that (E) the porosity of the negative electrode active material layer is 15% or more and 70% or less, and (F) the amount of the electrolyte solution with respect to the negative electrode active material layer is the porosity of the negative electrode active material layer The porosity of the negative electrode active material layer is more preferably 20% or more and 50% or less, and the amount of the electrolyte solution with respect to the more preferable negative electrode active material layer is the negative electrode active material layer. It was confirmed that it was 2.0 times or more and 30.0 times or less the pore volume of the material layer.

(Effect of mixing ratio of negative electrode active material)
When Examples 1 and 12 were compared with Comparative Example 9, there was a tendency for the negative electrode discharge capacity to decrease as the negative electrode active material mixing ratio decreased, and sufficient negative electrode capacity was ensured when graphite material was used as the main agent. Therefore, it was confirmed that the preferable negative electrode active material mixing ratio was 85 wt% or more, more preferably 90 wt% or more.

  When Examples 13 and 24 were compared with Comparative Example 18, there was a tendency for the negative electrode discharge capacity to decrease as the negative electrode active material mixing ratio decreased, and the negative electrode capacity when using an amorphous material as the main agent was sufficient. It was confirmed that the preferable negative electrode active material mixing ratio for securing was 80 wt% or more, more preferably 85 wt% or more.

  When Examples 25 and 36 were compared with Comparative Example 27, there was a tendency for the negative electrode discharge capacity to decrease as the negative electrode active material mixing ratio decreased, and the negative electrode capacity when using Si or a Si compound material as the main agent was sufficient. It was confirmed that the preferable negative electrode active material mixing ratio for ensuring the thickness was 70 wt% or more, more preferably 80 wt% or more.

The schematic diagram which shows the structure of the lithium ion secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Positive electrode collector 12 Positive electrode active material layer 13 Negative electrode active material layer 14 Negative electrode collector 15 Electrolytic solution 16 Separator

Claims (6)

In a lithium ion secondary battery including a negative electrode having a negative electrode active material layer in which a negative electrode active material mixture mainly composed of a positive electrode, an electrolyte, and a graphite material is formed on a metal foil as a current collector, the negative electrode is ( A) The porosity of the negative electrode active material layer defined by the following formula (1) is 10% or more and 60% or less, and (B) the amount of the electrolyte solution with respect to the negative electrode active material layer is represented by the following formula ( A lithium ion secondary battery, which is 1 to 35 times the pore volume (cm ³ ) of the negative electrode active material layer defined in 2).
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)   The lithium ion secondary battery according to claim 1, wherein a mixing ratio of the graphite material in the negative electrode active material layer is 85% by mass or more. In a lithium ion secondary battery including a negative electrode having a negative electrode active material layer in which a negative electrode active material mixture mainly composed of a positive electrode, an electrolyte, and an amorphous carbon material is formed on a metal foil as a current collector, The negative electrode (C) has a porosity of the negative electrode active material layer defined by the following formula (1) of 20% or more and 55% or less, and (D) the amount of the electrolyte with respect to the negative electrode active material layer is A lithium ion secondary battery characterized by being 1 to 15 times the pore volume (cm ³ ) of the negative electrode active material layer defined by the following formula (2).
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)   The lithium ion secondary battery according to claim 3, wherein a mixing ratio of the amorphous carbon material in the negative electrode active material layer is 80% by mass or more. In the lithium ion secondary battery including a negative electrode having a negative electrode active material layer in which a positive electrode, an electrolytic solution, and a negative electrode active material mixture mainly composed of Si or Si compound material are formed on a metal foil as a current collector, the negative electrode (E) The porosity of the negative electrode active material layer defined by the following formula (1) is 15% or more and 70% or less, and (F) the amount of the electrolyte solution with respect to the negative electrode active material layer is A lithium ion secondary battery, which is 1 to 40 times the pore volume (cm ³ ) of the negative electrode active material layer defined by the formula (2).
Porosity = (He substitution volume measured by pycnometer−negative electrode active material layer volume) / negative electrode active material layer volume (1)
Pore volume = He substitution volume measured by pycnometer−negative electrode active material layer volume (2)   6. The lithium ion secondary battery according to claim 5, wherein a mixing ratio of Si or Si compound material in the negative electrode active material layer is 70% by mass or more.

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