JPWO2019177055A1 - Lithium ion secondary battery - Google Patents

Abstract

An electrode including a positive electrode having a positive electrode mixture layer provided on the positive electrode current collector and the positive electrode current collector, an electrolyte layer, and a negative electrode having a negative electrode mixture layer provided on the negative electrode current collector and the negative electrode current collector. A group and an outer body accommodating the electrode group are provided, the electrode group contains an ionic conductive material containing a solvent and a lithium salt, and the total mass of the ionic conductive material per unit volume of the outer body is 0.12. ~ 0.35 g / cm ³ , the solvent contains a solvent having a vapor pressure of 200 Pa or less at 20 ° C., and the content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. is based on the total amount of the solvent. Disclosed as a lithium ion secondary battery, which is 85 mol% or more.

Description

The present invention relates to a lithium ion secondary battery.

In recent years, the development of lithium-ion secondary batteries has been actively promoted. In particular, the development of batteries used in electric vehicles is underway, and lithium ion secondary batteries are required to have even higher capacities.

On the other hand, in order to realize a high capacity of the lithium ion secondary battery, it is necessary to improve the safety inside the battery. In particular, it is required to ensure safety (safety at the time of overcharging) when the controller or the like causes an abnormality and the battery voltage becomes higher than the voltage normally used.

As a method for enhancing such safety, for example, a method of replacing the electrolytic solution used in the lithium ion secondary battery with a liquid having low volatility and flame retardancy from the conventional carbonate-based organic electrolytic solution can be mentioned. ..

For example, Patent Document 1 discloses an electrolyte for a lithium ion secondary battery, which comprises a glime mixture composed of methyl triglime and methyl tetraglime, and a glime complex composed of lithium ions.

Japanese Unexamined Patent Publication No. 2010-287481

However, according to the studies by the present inventors, even when a liquid having low volatility and flame retardancy is used as the electrolytic solution, the conventional lithium ion secondary battery has sufficient safety at the time of overcharging. However, it has been found that the discharge rate characteristics may be further deteriorated.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a lithium ion secondary battery which is excellent in safety at the time of overcharging and also excellent in discharge rate characteristics.

As a result of diligent studies by the present inventors, in a lithium ion secondary battery having a specific configuration, a solvent that is hard to volatilize is adopted as a solvent used for the ion conductive material, and the amount of the ion conductive material in the battery is adjusted. As a result, it was found that the above problems could be solved, and the present invention was completed.

One aspect of the present invention is a positive electrode having a positive electrode mixture layer provided on the positive electrode current collector and the positive electrode current collector, an electrolyte layer, and a negative electrode mixture provided on the negative electrode current collector and the negative electrode current collector. An electrode group having a negative electrode having a layer and an outer body accommodating the electrode group, and the electrode group contains an ionic conductive material containing a solvent and a lithium salt, and the ionic conductive material per unit volume of the outer body The total mass is 0.12 to 0.35 g / cm ³ , and the content of the solvent contains a solvent having a vapor pressure of 200 Pa or less at 20 ° C. and a vapor pressure of 200 Pa or less at 20 ° C. Provided is a lithium ion secondary battery having an amount of 85 mol% or more based on the total amount of the solvent.

According to the above-mentioned lithium ion secondary battery, not only the safety at the time of overcharging is excellent, but also the discharge rate characteristic is excellent. The reason why such an effect is obtained is not always clear, but the present inventors have a range of the amount of the ionic conductive material in the battery which is a sufficient range for charging and discharging, and a liquid when overcharged. I think this is because it is within the range where withering can occur. When the liquid withers, the internal resistance of the battery rises and the current can be cut off by itself. Due to the manifestation of such current cutoff characteristics, the lithium ion secondary battery can be excellent in safety even when overcharged.

The mass of the ionic conductive material per unit volume of the positive electrode mixture layer may be ^{0.05 to 0.50 g / cm 3.} The mass of the ionic conductive material per unit volume of the negative electrode mixture layer may be ^{0.05 to 0.50 g / cm 3.}

The solvent having a vapor pressure of 200 Pa or less at 20 ° C. may contain grime represented by the following general formula (1). It may also contain triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.
R ¹ O- (CH ₂ CH ₂ O) _m- R ² (1)
[In the formula (1), R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 3 to 6 carbon atoms. ]

According to the present invention, there is provided a lithium ion secondary battery which is excellent in safety at the time of overcharging and also excellent in discharge rate characteristics.

It is a schematic cross-sectional view which shows one Embodiment of a lithium ion secondary battery. It is an exploded view of the lithium ion secondary battery shown in FIG. It is a schematic cross-sectional view which shows the other embodiment of a lithium ion secondary battery.

Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including steps and the like) are not essential unless otherwise specified. The sizes of the components in each figure are conceptual, and the relative size relationships between the components are not limited to those shown in each figure.

The same applies to the numerical values and the range thereof in the present specification, and does not limit the present invention. The numerical range indicated by using "~" in the present specification indicates a range including the numerical values before and after "~" as the minimum value and the maximum value, respectively. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. Good. Further, in the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

In this specification, a lithium ion secondary battery will be described as an example of the secondary battery, but the technical idea of the present invention is that, in addition to the lithium ion secondary battery, a sodium ion secondary battery, a magnesium ion secondary battery, and the like. It can also be applied to aluminum ion secondary batteries and the like.

[Lithium-ion secondary battery]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a lithium ion secondary battery. The lithium ion secondary battery 100 includes a positive electrode 70 having a positive electrode mixture layer 40 provided on the positive electrode current collector 10 and the positive electrode current collector 10, an electrolyte layer 50, and a negative electrode current collector 20 and a negative electrode current collector 20. It includes an electrode group 85 having a negative electrode 80 having a negative electrode mixture layer 60 provided above, and an exterior body 30 accommodating the electrode group 85. FIG. 2 is an exploded view of the lithium ion secondary battery shown in FIG. The exterior body 30 has a volume S. The positive electrode mixture layer 40 has a volume V1 and the negative electrode mixture layer 60 has a volume V2.

The electrode group 85 contains an ionic conductive material containing a solvent and a lithium salt. The total mass of the ionic conductive material (total mass of the ionic conductive material / volume S of the exterior body 30) per unit volume of the exterior body 30 is 0.12 to 0.35 g / cm ³ . The solvent contains a solvent having a vapor pressure of 200 Pa or less at 20 ° C., and the content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of substance of the solvent.

Electrode group [Positive electrode]
The positive electrode 70 has a positive electrode current collector 10 and a positive electrode mixture layer 40 provided on the positive electrode current collector 10. The positive electrode mixture layer 40 contains a positive electrode active material and an ionic conductive material. If necessary, the positive electrode mixture layer 40 may contain a positive electrode conductive material for imparting conductivity, a positive electrode binder for binding these, and the like.

<Positive current collector>
The positive electrode current collector 10 is not particularly limited, and a positive electrode current collector generally used in a secondary battery can be used. The positive electrode current collector 10 is preferably a low resistance conductor having heat resistance that can withstand heating during the secondary battery manufacturing process and the operating temperature of the secondary battery. Examples of such a positive electrode current collector 10 include a metal foil (thickness 10 to 100 μm), a perforated metal foil (thickness 10 to 100 μm, pore diameter 0.1 to 10 mm), an expanded metal, a foamed metal plate, and a glassy carbon plate. And so on. Examples of the metal type include aluminum, stainless steel, titanium, precious metals (for example, gold, silver, platinum) and the like.

<Positive electrode mixture layer>
The positive electrode mixture layer 40 is a positive electrode current collector obtained by first mixing a positive electrode active material, a positive electrode conductive material, a positive electrode binder, a dispersion medium, and the like with a positive electrode mixture slurry by a doctor blade method, a dipping method, a spray method, or the like. Apply to 10. Next, the dispersion medium of the positive electrode mixture slurry is dried, and the positive electrode active material layer is formed by pressure molding by a roll press. Next, the positive electrode mixture layer 40 can be produced by dropping the ionic conductive material onto the obtained positive electrode active material layer with a micropipette or the like. Further, by performing such a step a plurality of times, it is also possible to laminate the positive electrode mixture layer 40 on the positive electrode current collector 10.

(Positive electrode active material)
The positive electrode active material may be, for example, a lithium composite oxide containing a transition metal. Examples of the lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₃ MO ₈ (M = Fe, Co). , Ni, Cu, Zn), Li _1-x M _x Mn ₂ O ₄ (M = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca, x = 0.01 to 0.1), LiMn _2-x M _x O ₂ (M = Co, Ni, Fe, Cr, Zn, Ta, x = 0.01 to 0.2), LiCo _1-x M _x O ₂ (M = Ni, Fe, Mn) , X = 0.01 to 0.2), LiNi _1-x M _x O ₂ (M = Mn, Fe, Co, Al, Ga, Ca, Mg, x = 0.01 to 0.2), LiNi _{1 -x-y Mn x Co y O} 2 (x = 0.1~0.8, y = 0.1~0.8, x + y = 0.1~0.9), LiFeO 2, LiFePO 4, LiMnPO 4 And so on.

(Positive electrode conductive material)
Positive positive conductive materials are manufactured from acrylic fibers and fibers produced by carbonizing conductive fibers (for example, by-products such as vapor-grown carbon, carbon nanotubes, and pitch (by-products of petroleum, coal, coal tar, etc.)) at high temperatures. It may be carbon fiber, etc.). Further, the positive electrode conductive material preferably has a lower electrical resistivity than the positive electrode active material and is difficult to oxidize and dissolve at the positive electrode charge / discharge potential (usually 2.5 to 4.5 V). As such a material, for example, corrosion resistant metal (titanium, gold, etc.), carbides (SiC, WC, etc.), nitrides _{(Si 3} N 4, BN, etc.) and the like. Further, the positive electrode conductive material may be a carbon material having a high specific surface area (for example, carbon black, activated carbon, etc.).

(Positive binder)
Examples of the positive electrode binder include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF); and a mixture thereof.

(Dispersion medium)
Examples of the dispersion medium include water, 1-methyl-2-pyrrolidone and the like.

(Ion conductive material)
The ionic conductive material contains a solvent and a lithium salt. The solvent contains a solvent having a vapor pressure of 200 Pa or less at 20 ° C., and the content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of substance of the solvent.

Examples of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. include grime, an ionic liquid, and a cyclic carbonate represented by the following general formula (1).
R ¹ O- (CH ₂ CH ₂ O) _m- R ² (1)

In formula (1), R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 3 to 6 carbon atoms. The alkyl group as R ¹ and R ² may be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group and the like. Among these, the alkyl group is preferably a methyl group or an ethyl group.

Examples of the glyme include triethylene glycol dimethyl ether (triglyme, 20 ° C vapor pressure: 120 Pa), tetraethylene glycol dimethyl ether (tetraglyme, 20 ° C vapor pressure: 1 Pa), pentaethylene glycol dimethyl ether (pentaglyce), hexaethylene glycol dimethyl ether. (Hexaglyme) and the like. Pentagrime and hexagrim are similar in structure to tetraglime and have a higher molecular weight than tetraglime. From this, it is expected that the 20 ° C. vapor pressure of pentaglime and hexagrim is about the same as or lower than that of tetraglime. These may be used individually by 1 type or in combination of 2 or more type. Among these, grime is preferably triglime or tetraglime.

It is known that ionic liquids have almost no vapor pressure, unlike molecular liquids such as water and organic solvents, due to the strong electrostatic interaction between the constituent cations and anions. Therefore, the ionic liquid is expected to have a vapor pressure of 200 Pa or less at 20 ° C.

Anion component of the ionic liquid is not particularly ^{limited, Cl -, Br -, I} - halogen anions _{^{such, BF 4 -, N (SO}} 2 F) 2 - or the like of the inorganic _{anion, B} (C _{6 H} 5) _{^{4 -, CH 3 SO 2 O}} -, CF 3 SO 2 O -, N (SO 2 C 4 F 9) 2 -, N (SO 2 CF 3) 2 -, N (SO 2 C 2 F 5) 2 - It may be an organic anion such as. The anionic component of the ionic liquid preferably contains at least one of the anionic components represented by the following formula (A).
N (SO ₂ C _m F _{2 m + 1} ) (SO ₂ C _n F _{2n + 1} ) ^- (A)
[In the formula (A), m and n each independently represent an integer of 0 to 5. m and n may be the same or different from each other, and are preferably the same as each other. ]

The cation component of the ionic liquid is preferably at least one selected from the group consisting of chain quaternary onium cations, piperidinium cations, pyrrolidinium cations, pyridinium cations, and imidazolium cations.

［式（２）中、Ｒ^１〜Ｒ^４は、それぞれ独立に、炭素数が１〜２０の鎖状アルキル基、又はＲ−Ｏ−（ＣＨ_２）_ｎ−で表される鎖状アルコキシアルキル基（Ｒはメチル基又はエチル基を表し、ｎは１〜４の整数を表す。）を表し、Ｘは、窒素原子又はリン原子を表す。Ｒ^１〜Ｒ^４で表されるアルキル基の炭素数は、好ましくは１〜２０、より好ましくは１〜１０、更に好ましくは１〜５である。］The chain quaternary onium cation may be, for example, a compound represented by the following formula (2).

[In the formula (2), R ^{1 to} R ⁴ are independently chain alkyl groups having 1 to 20 carbon atoms or chain alkoxyalkyl groups represented by _{RO-O- (CH 2} ) _n-. (R represents a methyl group or an ethyl group, n represents an integer of 1 to 4), and X represents a nitrogen atom or a phosphorus atom. The ^{number of carbon atoms of the alkyl group represented by R 1 to} R ⁴ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5. ]

［式（３）中、Ｒ^５及びＲ^６は、それぞれ独立に、炭素数が１〜２０のアルキル基、又はＲ−Ｏ−（ＣＨ_２）_ｎ−で表されるアルコキシアルキル基（Ｒはメチル基又はエチル基を表し、ｎは１〜４の整数を表す。）を表す。Ｒ^５及びＲ^６で表されるアルキル基の炭素数は、好ましくは１〜２０、より好ましくは１〜１０、更に好ましくは１〜５である。］The piperidinium cation may be, for example, a nitrogen-containing six-membered cyclic compound represented by the following formula (3).

[In formula (3), R ⁵ and R ⁶ are independently alkyl groups having 1 to 20 carbon atoms or _{alkoxyalkyl groups represented by RO-O- (CH 2} ) _n- (R is methyl). It represents a group or an ethyl group, and n represents an integer of 1 to 4). The ^{number of carbon atoms of the alkyl group represented by R 5} and R ⁶ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5. ]

［式（４）中、Ｒ^７及びＲ^８は、それぞれ独立に、炭素数が１〜２０のアルキル基、又はＲ−Ｏ−（ＣＨ_２）_ｎ−で表されるアルコキシアルキル基（Ｒはメチル基又はエチル基を表し、ｎは１〜４の整数を表す。）を表す。Ｒ^７及びＲ^８で表されるアルキル基の炭素数は、好ましくは１〜２０、より好ましくは１〜１０、更に好ましくは１〜５である。］The pyrrolidinium cation may be, for example, a five-membered cyclic compound represented by the following formula (4).

[In formula (4), R ⁷ and R ⁸ are independently alkyl groups having 1 to 20 carbon atoms or _{alkoxyalkyl groups represented by RO-O- (CH 2} ) _n- (R is methyl). It represents a group or an ethyl group, and n represents an integer of 1 to 4). The ^{alkyl group represented by R 7} and R ⁸ has preferably 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, and further preferably 1 to 5 carbon atoms. ]

［式（５）中、Ｒ^９〜Ｒ^１３は、それぞれ独立に、炭素数が１〜２０のアルキル基、Ｒ−Ｏ−（ＣＨ_２）_ｎ−で表されるアルコキシアルキル基（Ｒはメチル基又はエチル基を表し、ｎは１〜４の整数を表す。）、又は水素原子を表す。Ｒ^９〜Ｒ^１３で表されるアルキル基の炭素数は、好ましくは１〜２０、より好ましくは１〜１０、更に好ましくは１〜５である。］The pyridinium cation may be, for example, a compound represented by the following formula (5).

[In formula (5), R ^{9 to} R ¹³ are independently alkyl groups having 1 to 20 carbon atoms and _{alkoxyalkyl groups represented by RO-O- (CH 2} ) _n- (R is a methyl group). Alternatively, it represents an ethyl group, and n represents an integer of 1 to 4), or a hydrogen atom. The ^{number of carbon atoms of the alkyl group represented by R 9 to} R ¹³ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5. ]

［式（６）中、Ｒ^１４〜Ｒ^１８は、それぞれ独立に、炭素数が１〜２０のアルキル基、Ｒ−Ｏ−（ＣＨ_２）_ｎ−で表されるアルコキシアルキル基（Ｒはメチル基又はエチル基を表し、ｎは１〜４の整数を表す。）、又は水素原子を表す。Ｒ^１４〜Ｒ^１８で表されるアルキル基の炭素数は、好ましくは１〜２０、より好ましくは１〜１０、更に好ましくは１〜５である。］The imidazolium cation may be, for example, a compound represented by the following formula (6).

[In formula (6), R ^{14 to} R ¹⁸ are independently alkyl groups having 1 to 20 carbon atoms and _{alkoxyalkyl groups represented by RO-O- (CH 2} ) _n- (R is a methyl group). Alternatively, it represents an ethyl group, and n represents an integer of 1 to 4), or a hydrogen atom. The ^{number of carbon atoms of the alkyl group represented by R 14 to} R ¹⁸ is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 5. ]

Examples of the ionic liquid include N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium-bis (trifluoromethanesulfonyl) imide (DEME-TFSI), N, N-diethyl-N-methyl-. N- (2-methoxyethyl) ammonium-bis (fluorosulfonyl) imide (DEME-FSI), 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (EMI-TFSI), 1-ethyl-3 -Methylimidazolidium-bis (fluorosulfonyl) imide (EMI-FSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMI-TFSI), 1-butyl-3-methylimidazolium- Bis (fluorosulfonyl) imide (BMI-FSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13-TFSI), N-methyl-N-propylpiperidinium-bis (fluoro) Sulfonyl) imide (PP13-FSI), 1-methyl-1-propylpyrrolidium-bis (trifluoromethanesulfonyl) imide (PY13-TFSI), 1-methyl-1-propylpyrrolidium-bis (fluorosulfonyl) imide (PY13) -FSI) and the like. These may be used individually by 1 type or in combination of 2 or more type. Among these, the ionic liquid is preferably DEME-TFSI or EMI-FSI.

Examples of the cyclic carbonate include propylene carbonate (20 ° C. vapor pressure: 17 Pa), ethylene carbonate (20 ° C. vapor pressure: 21 Pa) and the like. These may be used individually by 1 type or in combination of 2 or more type. Among these, the cyclic carbonate is preferably propylene carbonate.

The content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of substance of the solvent. The content of the solvent may be 85-100 mol%, 90-100 mol% or 95-100 mol%, and may be composed only of the solvent (that is, 100 mol%). When the content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of substances of the solvent, the discharge rate characteristics are excellent.

The solvent may include a solvent having a vapor pressure of more than 200 Pa at 20 ° C. Such a solvent is not particularly limited, and a solvent usually used in a lithium ion secondary battery can be used. The content of the solvent may be 0 to 15 mol%, 0 to 10 mol%, or 0 to 5 mol% based on the total amount of substance of the solvent.

Examples of the lithium _{salt, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, lithium bis oxalate borate (LiBOB), lithium imide salt (e.g., lithium bis (Fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI)) and the like can be mentioned. These lithium salts may be used alone or in combination of two or more. Among these, the lithium salt is preferably LiTFSI.

The mass of the ionic conductive material per unit volume of the positive electrode mixture layer (mass of the ionic conductive material of the positive electrode mixture layer / volume V1 of the positive electrode mixture layer) may be ^{0.05 to 0.50 g / cm 3.} .. The mass of the ionic conductive material per unit volume of the positive electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ionic conductive material per unit volume of the positive electrode mixture layer is 0.05 g / cm ³ or more, the discharge rate characteristics tend to be superior, and when it is 0.50 g / cm ³ or less, it is overcharged. It tends to be better in safety.

[Negative electrode]
The negative electrode 80 has a negative electrode current collector 20 and a negative electrode mixture layer 60 provided on the negative electrode current collector 20. The negative electrode mixture layer 60 contains a negative electrode active material and an ionic conductive material. The negative electrode mixture layer 60 may contain a negative electrode conductive material for imparting conductivity, a negative electrode binder for binding these, and the like, if necessary.

<Negative electrode current collector>
The negative electrode current collector 20 is not particularly limited, and a negative electrode current collector generally used in a secondary battery can be used. Like the positive electrode current collector 10, the negative electrode current collector 20 is preferably a low resistance conductor having heat resistance that can withstand heating during the secondary battery manufacturing process and the operating temperature of the secondary battery. Examples of such a negative electrode current collector 20 include a metal foil (thickness 10 to 100 μm), a perforated metal foil (thickness 10 to 100 μm, a pore diameter 0.1 to 10 mm), an expanded metal, a foamed metal plate, and a glassy carbon plate. And so on. Examples of the metal type include aluminum, stainless steel, titanium, precious metals (for example, gold, silver, platinum) and the like.

<Negative electrode mixture layer>
The negative electrode mixture layer 60 is a negative electrode current collector obtained by first mixing a negative electrode active material, a negative electrode conductive material, a negative electrode binder, a dispersion medium, and the like with a negative electrode mixture slurry by a doctor blade method, a dipping method, a spray method, or the like. Apply to 20. Next, the dispersion medium of the negative electrode mixture slurry is dried, and the negative electrode active material layer is formed by pressure molding by a roll press. Next, the negative electrode mixture layer 60 can be produced by dropping the ionic conductive material onto the obtained negative electrode active material layer with a micropipette or the like. Further, by performing such a step a plurality of times, it is possible to laminate the negative electrode mixture layer 60 on the negative electrode current collector 20.

(Negative electrode active material)
Examples of the negative electrode active material include carbon-based materials (for example, graphite, graphitized carbon material, amorphous carbon material, etc.), conductive polymer materials (for example, polyacene, polyparaphenylene, polyaniline, polyacetylene, etc.), and the like. Examples thereof include lithium composite oxide (for example, lithium titanate: Li ₄ Ti ₅ O ₁₂ ), metallic lithium, and metals that alloy with lithium (for example, aluminum, silicon, tin, etc.).

(Negative electrode conductive material)
As the negative electrode conductive material, the same material as those exemplified for the positive electrode conductive material can be used.

(Negative electrode binder)
As the negative electrode binder, the same one as illustrated in the positive electrode binder can be used.

(Dispersion medium)
Examples of the dispersion medium include water, 1-methyl-2-pyrrolidone and the like.

(Ion conductive material)
The ionic conductive material may be the same as the above-mentioned ionic conductive material.

The mass of the ionic conductive material per unit volume of the negative electrode mixture layer (mass of the ionic conductive material of the negative electrode mixture layer / volume V2 of the negative electrode mixture layer) may be ^{0.05 to 0.50 g / cm 3.} .. The mass of the ionic conductive material per unit volume of the negative electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ionic conductive material per unit volume of the negative electrode mixture layer is 0.05 g / cm ³ or more, it tends to be superior to the discharge rate characteristics, and when it is 0.50 g / cm ³ or less, it is overcharged. Better in safety.

[Electrolyte layer]
The electrolyte layer 50 contains an electrolyte component and an electrolyte binder. The electrolyte layer 50 can be produced, for example, by adding and mixing an electrolyte binder to the electrolyte components. The electrolyte layer 50 can also be produced by preparing a solution obtained by mixing an electrolyte component and an electrolyte binder with a dispersion medium and distilling off the dispersion medium.

<Electrolyte component>
The electrolyte component is composed of inorganic particles and an ionic conductive material. That is, the electrolyte layer 50 contains an ionic conductive material. The ionic conductive material may be supported on inorganic particles. As the electrolyte component, for example, inorganic particles and an ionic conductive material are mixed at a specific volume ratio, and a dispersion medium such as methanol is added and mixed to prepare an electrolyte component slurry. Then, the slurry is dropped onto a petri dish and the dispersion medium is distilled off to obtain an electrolyte component.

(Inorganic particles)
From the viewpoint of electrochemical stability, the inorganic particles are preferably insulating particles and are insoluble in the above-mentioned solvent. Such inorganic particles may be, for example, silica (SiO ₂ ) particles, γ-alumina (Al ₂ O ₃ ) particles, ceria (CeO ₂ ) particles, or zirconia (ZrO ₂ ) particles. Further, the inorganic particles may be other known metal oxide particles.

The holding amount of the ionic conductive material is considered to be proportional to the specific surface area of the inorganic particles. The average particle size of the primary particles of the inorganic particles may be 1 nm to 10 μm. When the average particle size is 10 μm or less, the inorganic particles can hold a sufficient amount of the ionic conductive material, and tend to easily form an electrolyte layer. When the average particle size is 1 nm or more, the intersurface force between the particles becomes too large and it is possible to prevent the particles from agglutinating with each other, which tends to facilitate the formation of an electrolyte layer. The average particle size of the primary particles of the metal oxide particles may be 1 to 50 nm or 1 to 10 nm. The average particle size of the primary particles can be determined by using a known particle size distribution measuring device using a laser scattering method.

_{When SiO 2} particles (average particle size: 7 nm, zeta potential: about -20 mV) are used as the inorganic particles, a highly heat-resistant electrolyte layer tends to be obtained.

_{When γ-Al 2} O ₃ particles (average particle size: 5 nm, zeta potential: about -5 mV) are used as the inorganic particles, the number of charge / discharge cycles of the secondary battery tends to be extended. The reason why such an effect is exerted is not clear, but it is considered that the use of alumina particles having high reduction resistance can suppress the precipitation of lithium dendrite on the negative electrode side during the charge / discharge cycle.

_{When CeO 2} particles (zeta potential: about 30 mV) or ZrO ₂ particles (zeta potential: about 40 mV) are used as the inorganic particles, a highly ionic conductive electrolyte layer tends to be obtained. It is considered that when particles having a high zeta potential are used as the inorganic particles, the adsorption of the ionic conductive material on the particle surface is weakened, and the ionic conductive material can move relatively freely. As a result, it is predicted that lithium ions will easily move from the ionic conductive material and lithium ion conduction will be promoted.

As the inorganic particles, by using an inorganic substance having lithium ion conductivity, an electrolyte layer having more excellent ion conductivity tends to be obtained. Examples of such an inorganic substance include Li _{5 + X} La ₃ (Zr _X , A _2-X ) O ₁₂ (in the formula, A is Sc, Ti, C, Y, Nb, Hf, Ta, Al, Si, Ga. , Ge, Sn One or more elements selected from the group, 1.4 ≤ X ≤ 2), Li _{1 + Y} Al _Y Ti _2-Y (PO ₄ ) ₃ (0 ≤ Y ≤ 1), Li _3Z La _{2 / 3-Z} TiO ₃ (0 ≦ Z ≦ 2/3) and the like can be mentioned. They tend to have high ionic conductivity at room temperature and high electrochemical stability.

(Ion conductive material)
The ionic conductive material may be the same as the above-mentioned ionic conductive material.

<Electrolyte binder>
A fluorine-based resin is preferably used as the electrolyte binder. Examples of the fluorine-based resin include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). By using PVDF or PTFE, the adhesion between the electrolyte layer and the electrode current collector is improved, so that the battery performance tends to be improved.

Exterior The exterior 30 is a battery case capable of accommodating an electrode group 85 including a positive electrode 70, an electrolyte layer 50, and a negative electrode 80. The material of the exterior body is preferably one having corrosion resistance such as aluminum, stainless steel, and nickel-plated steel. The volume S of the exterior body can be appropriately set according to the size of the battery.

The total mass of the ionic conductive material (total mass of the ionic conductive material / volume S of the exterior body) per unit volume of the exterior body is 0.12 to 0.35 g / cm ³ . The total mass of the ionic conductive material per unit volume of the exterior body is 0.15 g / cm ³ or more, 0.18 g / cm ³ or more, 0.21 g / cm ³ or more, 0.24 g / cm ³ or more, 0.27 g. / Cm ³ or more, 0.34 g / cm ³ or less, 0.33 g / cm ³ or less, 0.32 g / cm ³ or less, 0.31 g / cm ³ or less, 0.30 g / cm ³ or less There may be. When the total mass of the ionic conductive material per unit volume of the exterior body is 0.12 g / cm ³ or more, the discharge rate characteristics are excellent, and the total mass of the ionic conductive material per unit volume of the exterior body is 0.35 g / cm. ^When it is 3 or less, the safety at the time of overcharging is excellent.

[Manufacturing method of lithium ion secondary battery]
The above-mentioned lithium ion secondary battery 100 includes a positive electrode 70 having a positive electrode mixture layer 40 provided on the positive electrode current collector 10 and the positive electrode current collector 10, an electrolyte layer 50, and a negative electrode current collector 20 and a negative electrode current collector. It can be manufactured by a manufacturing method including a step of producing an electrode group 85 including a negative electrode 80 having a negative electrode mixture layer 60 provided on the body 20 and a step of accommodating the electrode group 85 in the exterior body 30. ..

The positive electrode 70 includes, for example, a step of preparing a positive electrode precursor in which a positive electrode active material layer containing a positive electrode active material is provided on the positive electrode current collector 10, and a positive electrode mixture layer in which an ionic conductive material is added to the positive electrode active material layer. It can be manufactured by a manufacturing method including a step of forming 40.

The mass of the ionic conductive material per unit volume of the positive electrode mixture layer 40 (mass of the ionic conductive material of the positive electrode mixture layer / volume V1 of the positive electrode mixture layer) is 0.05 to 0.50 g / cm ^3. Good. The mass of the ionic conductive material per unit volume of the positive electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ionic conductive material per unit volume of the positive electrode mixture layer is 0.05 g / cm ³ or more, the discharge rate characteristics tend to be superior, and when it is 0.50 g / cm ³ or less, it is overcharged. It tends to be better in safety.

The electrolyte layer 50 can be manufactured by, for example, a manufacturing method including a step of adding and mixing an electrolyte binder to an electrolyte component and a step of forming the obtained mixture into a sheet.

The negative electrode 80 includes, for example, a step of preparing a negative electrode precursor in which a negative electrode active material layer containing a negative electrode active material is provided on the negative electrode current collector 20, and a negative electrode mixture layer in which an ionic conductive material is added to the negative electrode active material layer. It can be manufactured by a manufacturing method including a step of forming 60.

The mass of the ionic conductive material per unit volume of the negative electrode mixture layer 60 (mass of the ionic conductive material of the negative electrode mixture layer / volume V2 of the negative electrode mixture layer) is 0.05 to 0.50 g / cm ^3. Good. The mass of the ionic conductive material per unit volume of the negative electrode mixture layer may be 0.06 g / cm ³ or more, or 0.40 g / cm ³ or less. When the mass of the ionic conductive material per unit volume of the negative electrode mixture layer is 0.05 g / cm ³ or more, it tends to be superior to the discharge rate characteristics, and when it is 0.50 g / cm ³ or less, it is overcharged. Better in safety.

Next, the lithium ion secondary battery 100 can be obtained by accommodating the electrode group 85 including the obtained positive electrode 70, the electrolyte layer 50, and the negative electrode 80 in the exterior body 30. When the electrode group 85 is housed in the exterior body 30, even if the ionic conductive material is injected into the electrode group 85 and the total mass of the ionic conductive material per unit volume of the exterior body is adjusted to be within a predetermined range. Good. Since the injected ionic conductive material exists in the gap between the exterior body 30 and the electrode group 85, ions per unit volume of the positive electrode mixture layer 40 and the negative electrode mixture layer 60 before and after injection. It is inferred that the mass of the conductive material does not fluctuate.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the lithium ion secondary battery. The lithium ion secondary battery 200 includes a positive electrode current collector 10, a positive electrode mixture layer 40, an electrolyte layer 50, a negative electrode mixture layer 60, an interconnector 90, a positive electrode mixture layer 40, an electrolyte layer 50, and a negative electrode mixture layer 60. An electrode group 85 including an interconnector 90, a positive electrode mixture layer 40, an electrolyte layer 50, a negative electrode mixture layer 60, and a negative electrode current collector 20 in this order, and an exterior body 30 are provided. As shown in FIG. 3, it is considered that the lithium ion secondary battery 200 includes a plurality of combinations having the positive electrode mixture layer 40, the electrolyte layer 50, and the negative electrode mixture layer 60 in this order via the interconnector 90. be able to. Among the plurality of combinations, the outermost positive electrode mixture layer 40 is connected to the positive electrode current collector 10, and the outermost negative electrode mixture layer 60 is connected to the negative electrode current collector 20.

[Interconnector]
The interconnector 90 is required to have high electron conductivity, no ionic conductivity, and the surfaces in contact with the negative electrode mixture layer 60 and the positive electrode mixture layer 40 do not exhibit a redox reaction depending on their respective potentials. .. The interconnector 90 may be used as the positive electrode current collector 10 and the negative electrode current collector 20, and may be aluminum foil or SUS foil.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited thereto.

(Example 1)
<Preparation of ionic conductive material>
LiTFSI (lithium salt) and tetraglime (solvent (grime represented by the general formula (1)), vapor pressure at 20 ° C.: 1 Pa) are mixed at a molar ratio of 1: 1 and used in a glass bottle using a magnetic stirrer. Stirring was performed to prepare an ionic conductive material. The content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. was 100 mol%.

<Cathode preparation>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (positive electrode active material) 81.0 parts by mass, powdered carbon (positive electrode conductive material) 3.0 parts by mass and acetylene black (positive electrode conductive material) 6.0 Parts by weight were added to give a mixture. Separately, a solution prepared by dissolving 10.0 parts by mass of polyvinylidene fluoride (PVDF, positive electrode binder) in N-methyl-2-pyrrolidone (NMP, dispersion medium) was prepared, the above mixture was added thereto, and the viscosity was adjusted by NMP. While mixing with a planetary mixer, a positive mixture slurry was prepared. The positive electrode mixture slurry was uniformly and evenly applied to one side of a current collector (positive electrode current collector) made of SUS steel foil having a thickness of 12 μm with a coating machine. After coating, compression molding was performed by a roll press machine, pressure was applied at 5 MPa, and punching was performed to Φ10 mm to obtain a positive electrode precursor having a positive electrode active material layer. The mass of the positive electrode precursor per unit area was 15 mg / cm ² .

A positive electrode having a positive electrode mixture layer was prepared by dropping the above-mentioned ionic conductive material onto the positive electrode active material layer of the obtained positive electrode precursor using a micropipette. At this time, the mass of the ionic conductive material per unit volume of the positive electrode mixture layer was adjusted to ^{0.3 g / cm 3.} The mass of the ionic conductive material dropped on the positive electrode active material layer was 0.0306 g, and the volume of the positive electrode mixture layer was 0.102 cm ³ . The volume of the positive electrode mixture layer was determined by measuring the thickness of the positive electrode mixture layer using a micrometer.

<Manufacturing of negative electrode>
A solution prepared by dissolving 10.0 parts by mass of PVDF (negative electrode binder) in NMP (dispersion medium) was added to 90.0 parts by mass of graphite (negative electrode active material), and mixed with a planetary mixer while adjusting the viscosity with NMP. A negative electrode mixture slurry was prepared. The negative electrode mixture slurry was uniformly and evenly applied to one side of a current collector (negative electrode current collector) made of SUS steel foil having a thickness of 12 μm with a coating machine. After coating, compression molding was performed by a roll press machine, pressure was applied at 5 MPa, and punching was performed to Φ10 mm to obtain a negative electrode precursor having a negative electrode active material layer. The mass of the negative electrode precursor per unit area was 6.8 mg / cm ² .

A negative electrode having a negative electrode mixture layer was prepared by dropping the above-mentioned ionic conductive material onto the negative electrode active material layer of the obtained negative electrode precursor using a micropipette. At this time, the mass of the ionic conductive material per unit volume of the negative electrode mixture layer was adjusted to ^{0.3 g / cm 3.} The mass of the ionic conductive material dropped on the negative electrode active material layer was 0.0225 g, and the volume of the negative electrode mixture layer was 0.075 cm ³ . The volume of the negative electrode mixture layer was determined by measuring the thickness of the negative electrode mixture layer using a micrometer.

<Preparation of sheet for electrolyte layer>
The above-mentioned ionic conductive material and SiO ₂ nanoparticles (inorganic particles) were mixed at a ratio of 62:38 on a volume basis, methanol was added thereto, and the mixture was stirred for 30 minutes. Then, the obtained electrolyte component slurry was spread on a petri dish, and methanol was distilled off to obtain a powdery electrolyte component. Polytetrafluoroethylene (PTFE, electrolyte binder) is added to this so as to have a thickness of 5% by mass, and after sufficiently mixing, the sheet is pressurized and stretched, and punched to Φ16 mm to obtain a sheet for an electrolyte layer having a thickness of about 30 μm. Obtained. The mass of the ionic conductive material in the electrolyte layer sheet was 0.0506 g.

<Battery production>
The prepared positive electrode, negative electrode, and electrolyte layer sheet are placed in a glove box filled with argon, and the negative electrode current collector, the negative electrode mixture layer, the electrolyte layer sheet, the positive electrode mixture layer, and the positive electrode current collector are used. They were stacked in order and housed in a 2032 size coin-type battery cell holder (exterior body, volume: 0.542 cm ^3). Next, the ion conductive material was injected into the coin-type battery cell holder using a micropipette, and the total mass of the ion conductive material per unit volume of the exterior body was adjusted to ^{0.29 g / cm 3.} The mass of the dropped ionic conductive material was 0.0535 g, and the total mass of the ionic conductive material was 0.1572 g. Then, the lithium ion secondary battery of Example 1 was produced by sealing with a caulking machine.

(Example 2)
As shown in Table 1, the lithium ion secondary battery of Example 2 was used in the same manner as in Example 1 except that the tetraglime was changed to DEME-TFSI (solvent (ionic liquid)) in the preparation of the ionic conductive material. Made.

(Example 3)
As shown in Table 1, in the preparation of the ionic conductive material, the lithium ion rechargeable battery of Example 3 was obtained in the same manner as in Example 1 except that the tetraglime was changed to propylene carbonate (cyclic carbonate, 20 ° C. vapor pressure: 17 Pa). The next battery was manufactured.

(Example 4)
As shown in Table 1, the lithium ion rechargeable battery of Example 4 was obtained in the same manner as in Example 1 except that the total mass of the ionic conductive material per unit volume of the exterior body ^{was adjusted to 0.35 g / cm 3.} The next battery was manufactured.

(Example 5)
As shown in Table 1, the lithium ion battery of Example 5 was adjusted in the same manner as in Example 1 except that the total mass of the ionic conductive material per unit volume of the exterior body ^{was adjusted to 0.23 g / cm 3.} The next battery was manufactured.

(Example 6)
As shown in Table 1, the mass of the ionic conductive material per unit volume of the positive electrode mixture layer and the negative electrode mixture layer is 0.27 g / cm ³ , and the total mass of the ionic conductive material per unit volume of the exterior body is 0.18 g. except that was adjusted to / cm ^3, the same procedure as in example 1 to prepare a lithium ion secondary battery of example 6.

(Example 7)
As shown in Table 1, the mass of the ionic conductive material per unit volume of the positive electrode mixture layer and the negative electrode mixture layer is 0.12 g / cm ³ , and the total mass of the ionic conductive material per unit volume of the exterior body is 0.12 g. except that was adjusted to / cm ^3, the same procedure as in example 1 to prepare a lithium ion secondary battery of example 7.

(Comparative Example 1)
As shown in Table 1, the lithium ion rechargeable battery of Comparative Example 1 was obtained in the same manner as in Example 1 except that the total mass of the ionic conductive material per unit volume of the exterior body ^{was adjusted to 0.59 g / cm 3.} The next battery was manufactured.

(Comparative Example 2)
As shown in Table 1, the lithium ion rechargeable battery of Comparative Example 2 was obtained in the same manner as in Example 1 except that the total mass of the ionic conductive material per unit volume of the exterior body ^{was adjusted to 0.41 g / cm 3.} The next battery was manufactured.

(Comparative Example 3)
As shown in Table 1, the mass of the ionic conductive material per unit volume of the positive electrode mixture layer and the negative electrode mixture layer is 0.05 g / cm ³ , and the total mass of the ionic conductive material per unit volume of the exterior body is 0.09 g. except that was adjusted to / cm ^3, the same procedure as in example 1 to prepare a lithium ion secondary battery of Comparative example 3.

(Comparative Example 4)
As shown in Table 1, in the preparation of the ionic conductive material, Examples were made except that the tetraglime was changed to a mixed solution of tetraglime (80 mol%) and dimethyl carbonate (20 ° C. vapor pressure: 5300 Pa, 20 mol%). The lithium ion secondary battery of Comparative Example 4 was produced in the same manner as in 1.

<Evaluation of coin cell batteries>
(Evaluation of discharge rate characteristics)
The lithium ion secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4 were charged at 0.1 C using a 1480 potentiostat (manufactured by Solartron), and 1 at 100% SOC (Stage of Charge). After holding for a long time, discharge was performed at 0.1 C. The upper limit potential was 4.2 V, the lower limit potential was 2.7 V, and the discharge capacity at 0.1 C was measured. Then, after charging at 0.1C, it was held at 100% SOC for 1 hour and discharged at 0.5C to measure the discharge capacity at 0.5C. At this time, the value represented by the following formula was used as the discharge rate characteristic. The results are shown in Table 2.
Discharge rate characteristic (%) = [(Discharge capacity at 0.5C) / (Discharge capacity at 0.1C)] x 100

(Evaluation of overcharge characteristics)
After evaluating the 0.5C rate characteristic, the battery was further discharged at 0.1C and left for 1 hour. Then, it was charged at 0.1C, and the amount of voltage change 1 hour after reaching 5V was measured. The results are shown in Table 2. In this test, the higher the value, the higher the internal resistance of the battery (that is, it has good current cutoff characteristics), and it can be said that the safety is excellent.

The lithium ion secondary batteries of Examples 1 to 7 were excellent in safety at the time of overcharging and also excellent in discharge rate characteristics. On the other hand, the lithium ion secondary batteries of Comparative Examples 1 and 2 in which the total mass of the ionic conductive material per unit volume of the exterior body ^{exceeds 0.35 g / cm 3 are excellent in discharge rate characteristics, but are safe during overcharging.} Was not enough. Further, the total amount of substance content solvent of the solvent vapor pressure is less than 200Pa total weight of the ion conductive material of Comparative Example 3 and 20 ° C. less than 0.12 g / cm ³ per unit volume of the outer body The lithium ion secondary battery of Comparative Example 4, which is less than 85 mol% as a reference, is excellent in safety at the time of overcharging, but the discharge rate characteristic is not sufficient. From these results, it was confirmed that the lithium secondary battery of the present invention is excellent in safety at the time of overcharging and also in discharge rate characteristics.

The lithium ion secondary battery obtained in the present invention can be used as a power storage device by connecting to a cell controller or a control panel and protecting it with a housing. The lithium ion secondary battery according to the present invention can be charged and discharged at a higher current, and can further suppress a decrease in storage performance due to a cycle. Further, the power storage device using the lithium ion secondary battery can be arranged on the front surface or the bottom surface of the vehicle body as a power source for an automobile. Further, the power storage device can be used as an industrial power source for balancing the supply and demand of electric power.

10 ... Positive electrode current collector, 20 ... Negative electrode current collector, 30 ... Exterior body, 40 ... Positive electrode mixture layer, 50 ... Electrolyte layer, 60 ... Negative electrode mixture layer, 70 ... Positive electrode, 80 ... Negative electrode, 85 ... Electrode group , 90 ... interconnector, 100, 200 ... lithium ion secondary battery, S ... volume (exterior body), V1 ... volume (positive electrode mixture layer), V2 ... volume (negative electrode mixture layer).

Claims (5)

A positive electrode having a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, an electrolyte layer, and a negative electrode having a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector. Electrode group to be provided and
An exterior body accommodating the electrode group and
With
The electrode group contains an ionic conductive material containing a solvent and a lithium salt.
The total mass of the ionic conductive material per unit volume of the exterior body is 0.12 to 0.35 g / cm ³ .
The solvent contains a solvent having a vapor pressure of 200 Pa or less at 20 ° C.
A lithium ion secondary battery in which the content of the solvent having a vapor pressure of 200 Pa or less at 20 ° C. is 85 mol% or more based on the total amount of substances of the solvent. The lithium ion secondary battery according to claim 1, wherein the mass of the ion conductive material per unit volume of the positive electrode mixture layer is 0.05 to 0.50 g / cm ^3. The lithium ion secondary battery according to claim 1 or 2, wherein the mass of the ion conductive material per unit volume of the negative electrode mixture layer is 0.05 to 0.50 g / cm ^3. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the solvent having a vapor pressure of 200 Pa or less at 20 ° C. contains grime represented by the following general formula (1).
R ¹ O- (CH ₂ CH ₂ O) _m- R ² (1)
[In the formula (1), R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 3 to 6 carbon atoms. ] The lithium ion secondary battery according to any one of claims 1 to 3, wherein the solvent having a vapor pressure of 200 Pa or less at 20 ° C. contains triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

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