JPWO2019194196A1 - Electrodes for secondary batteries, electrolyte layers for secondary batteries and secondary batteries - Google Patents

Abstract

The present invention includes an electrode current collector and an electrode mixture layer provided on the electrode current collector, and the electrode mixture layer contains an ionic liquid and an electrolyte salt, and the electrolyte salt comprises. Provided are an electrode for a secondary battery containing a first lithium salt which is an imide-based lithium salt and a second lithium salt different from the first lithium salt.

Description

The present invention relates to an electrode for a secondary battery, an electrolyte layer for a secondary battery, and a secondary battery.

In recent years, with the spread of portable electronic devices, electric vehicles, etc., high-performance secondary batteries are required. Among them, the lithium secondary battery has a high energy density, and is therefore attracting attention as a power source for electric vehicle batteries, power storage batteries, and the like. Specifically, lithium secondary batteries as batteries for electric vehicles include zero-emission electric vehicles that do not have an engine, hybrid electric vehicles that have both an engine and a secondary battery, and plug-in hybrids that charge directly from the power system. It is used in electric vehicles such as electric vehicles. Further, a lithium secondary battery as a power storage battery is used in a stationary power storage system or the like that supplies power stored in advance in an emergency when the power system is cut off.

Lithium secondary batteries with higher energy densities are required and are being developed for use in such a wide range of applications. In particular, lithium secondary batteries for electric vehicles are required to have high safety in addition to high input / output characteristics and high energy density, and therefore, more advanced technology for ensuring safety is required. ..

Conventionally, as a method of improving the safety of a lithium secondary battery, a method of making an electrolytic solution flame-retardant by adding a flame retardant, a method of using a flame-retardant ionic liquid as an electrolytic solution, and a method of using a polymer electrolyte or a gel electrolyte as the electrolytic solution. The method of changing to is known. For example, Patent Document 1 discloses a lithium ion secondary battery using an ionic liquid having a pyrrolidinium cation or the like.

Japanese Unexamined Patent Publication No. 2013-331918

Since the ionic liquid has the same ionic conductivity as the organic electrolyte used in the conventional lithium secondary battery, it is released by changing the organic electrolyte to the ionic liquid without deteriorating the battery performance. Burning of the electrolyte can be suppressed by reducing the amount of the electrolyte. However, even when an ionic liquid is used as the electrolytic solution, a higher performance lithium secondary battery, for example, a lithium secondary battery having high initial characteristics in which the initial discharge capacity (initial capacity) is as close as possible to the design capacity There is room for further improvement in order to obtain a lithium secondary battery having excellent charging characteristics, which can be charged to a predetermined voltage value when a secondary battery such as 1C charging is performed.

An object of the present invention is to provide an electrode for a secondary battery, an electrolyte layer for a secondary battery, and a secondary battery having excellent initial characteristics and charging characteristics, which can improve the initial characteristics and charging characteristics of the secondary battery. And.

The present invention comprises, as a first aspect, an electrode current collector and an electrode mixture layer provided on the electrode current collector, and the electrode mixture layer contains an ionic liquid and an electrolyte salt. However, an electrode for a secondary battery is provided, wherein the electrolyte salt contains a first lithium salt which is an imide-based lithium salt and a second lithium salt different from the first lithium salt.

The anion component of the first lithium salt preferably contains at least one selected from the group consisting of bis (fluorosulfonyl) imide anions and bis (trifluoromethanesulfonyl) imide anions.

The anion component of the second lithium salt preferably contains at least one selected from the group consisting of hexafluorophosphate anions and bisoxalate borate anions.

The content of the first lithium salt is preferably 50 parts by mass or more with respect to 100 parts by mass in total of the content of the first lithium salt and the content of the second lithium salt.

The ionic liquid preferably contains, as a cation component, at least one selected from the group consisting of a chain quaternary onium cation, a piperidinium cation, a pyrrolidinium cation, a pyridinium cation, and an imidazolium cation, and contains an anion component. As a result, it contains at least one kind of anionic component represented by the following general formula (1).
N (SO ₂ C _m F _{2 m + 1} ) (SO ₂ C _n F _{2n + 1} ) ⁻ (1)
[M and n each independently represent an integer of 0 to 5. ]

As a second aspect of the present invention, a second lithium salt containing an ionic liquid and an electrolyte salt, wherein the electrolyte salt is different from the first lithium salt which is an imide-based lithium salt and the first lithium salt. Provide an electrolyte layer for a secondary battery, including the above.

The present invention is a secondary battery including a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode as a third aspect, and at least one of the positive electrode and the negative electrode is the first described above. A secondary battery, which is an electrode according to the above embodiment, is provided.

The present invention is a secondary battery including a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode as a fourth aspect, and the electrolyte layer relates to the second aspect described above. Provided is a secondary battery which is an electrolyte layer.

A fifth aspect of the present invention is a secondary battery including a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the above-mentioned first. The present invention provides a secondary battery, which is an electrode according to the above-described embodiment, wherein the electrolyte layer is the electrolyte layer according to the second aspect described above.

According to the present invention, there is provided an electrode for a secondary battery, an electrolyte layer for a secondary battery, and a secondary battery having excellent initial characteristics and charging characteristics, which can improve the initial characteristics and charging characteristics of the secondary battery. Can be done.

It is a perspective view which shows the secondary battery which concerns on this embodiment. It is an exploded perspective view which shows one Embodiment of the electrode group in the secondary battery shown in FIG. It is an exploded perspective view which shows the electrode group of the secondary battery which concerns on 2nd Embodiment. (A) is a schematic cross-sectional view showing a battery member for a secondary battery according to one embodiment in the secondary battery shown in FIG. 3, and (b) is a schematic cross-sectional view showing another embodiment in the secondary battery shown in FIG. It is a schematic cross-sectional view which shows the battery member for the next 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.

Numerical values and their ranges herein are not intended to 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 described in another stepwise description. 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.

[First Embodiment]
FIG. 1 is a perspective view showing a secondary battery according to the first embodiment. As shown in FIG. 1, the secondary battery 1 includes an electrode group 2 composed of a positive electrode, a negative electrode, and an electrolyte layer (electrolyte layer for a secondary battery), and a bag-shaped battery outer body 3 accommodating the electrode group 2. It has. The positive electrode and the negative electrode are provided with a positive electrode current collecting tab 4 and a negative electrode current collecting tab 5, respectively. The positive electrode current collecting tab 4 and the negative electrode current collecting tab 5 project from the inside to the outside of the battery exterior 3 so that the positive electrode and the negative electrode can be electrically connected to the outside of the secondary battery 1, respectively.

The battery exterior 3 may be formed of, for example, a laminated film. The laminated film may be, for example, a laminated film in which a resin film such as polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, and stainless steel, and a sealant layer such as polypropylene are laminated in this order.

FIG. 2 is an exploded perspective view showing an embodiment of the electrode group 2 in the secondary battery 1 shown in FIG. As shown in FIG. 2, the electrode group 2A according to the present embodiment includes a positive electrode 6, an electrolyte layer 7, and a negative electrode 8 in this order. The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. The positive electrode current collector 9 is provided with a positive electrode current collector tab 4. The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 provided on the negative electrode current collector 11. The negative electrode current collector 11 is provided with a negative electrode current collector tab 5. Hereinafter, the positive electrode or the negative electrode may be referred to as an electrode (electrode for a secondary battery). That is, it can be said that the electrode includes an electrode current collector and an electrode mixture layer provided on the electrode current collector, and the electrode current collector is provided with an electrode current collector tab. ..

The negative electrode current collector 11 may be a metal such as aluminum, copper, nickel, or stainless steel, or an alloy thereof. Since the negative electrode current collector 11 is lightweight and has a high weight energy density, it is preferably aluminum or an alloy thereof. The negative electrode current collector 11 is preferably copper from the viewpoint of ease of processing into a thin film and cost. In addition to the above, the negative electrode current collector 11 may be made of any material as long as it does not cause changes such as dissolution and oxidation during use of the battery, and its shape, manufacturing method, etc. Not limited.

The thickness of the negative electrode current collector 11 may be 10 μm or more and 100 μm or less, preferably 10 μm or more and 50 μm or less from the viewpoint of reducing the volume of the entire negative electrode, and the negative electrode is wound with a small curvature when forming a battery. From the viewpoint of turning, it is more preferably 10 μm or more and 20 μm or less.

In one embodiment, the negative electrode mixture layer 12 contains an ionic liquid and an electrolyte salt.

The ionic liquid contained in the negative electrode mixture layer 12 contains the following anionic component and cation component. The ionic liquid in this embodiment is a substance that is liquid at −20 ° C. or higher.

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 general formula (1).
N (SO ₂ C _m F _{2 m + 1} ) (SO ₂ C _n F _{2n + 1} ) ⁻ (1)
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.

Anion component represented by formula (1) may, for ^{_{example, N (SO 2 C 4 F}} 9) 2 -, N (SO 2 F) 2 -, N (SO 2 CF 3) 2 - and N _(SO 2 C ₂ F _{5) 2} ^- a. _{The anionic component of the ionic liquid is more preferably N (SO 2} C ₄ F ₉ ) ₂ ⁻ , CF ₃ SO from the viewpoint of further improving the ionic conductivity and the charge / discharge characteristics with a relatively low viscosity. _It contains at least one selected from the group consisting of 2 O ⁻ , N (SO ₂ F) ₂ ⁻ , N (SO ₂ CF ₃ ) ₂ ⁻ , and N (SO ₂ C ₂ F ₅ ) ₂ ^{−, and is more preferable.} is _{N (SO 2 F)} 2 ^- containing.

In the following, the following abbreviations may be used.
[FSI] ⁻ : N (SO ₂ F) ₂ ⁻ , bis (fluorosulfonyl) imide anion [TFSI] ⁻ : N (SO ₂ CF ₃ ) ₂ ⁻ , bis (trifluoromethanesulfonyl) imide anion [BOB] ⁻ : B (O ₂ C ₂ O ₂ ) ₂ ⁻ , bisoxalate borate anion [f3C] ⁻ : C (SO ₂ F) ₃ ⁻ , tris (fluorosulfonyl) carbanion

The cation component of the ionic liquid contained in the negative electrode mixture layer 12 is preferably at least one selected from the group consisting of a chain quaternary onium cation, a piperidinium cation, a pyroridinium cation, a pyridinium cation, and an imidazolium cation. Is.

The chain quaternary onium cation is, for example, a compound represented by the following general formula (2).

［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。］

[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. ]

The piperidinium cation is, for example, a nitrogen-containing six-membered cyclic compound represented by the following general formula (3).

［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。］

[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. ]

The pyrrolidinium cation is, for example, a five-membered cyclic compound represented by the following general formula (4).

［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。］

[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. ]

The pyridinium cation is, for example, a compound represented by the following general formula (5).

［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。］

[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, where 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. ]

The imidazolium cation is, for example, a compound represented by the general formula (6).

［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。］

[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, where 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. ]

The ionic liquid contained in the negative electrode mixture layer 12 may contain any of the above-mentioned anion component and cation component, but preferably contains N (SO ₂ F) ₂ ⁻ as the anion component and is a cation component. Includes imidazolium cations and / or pyrrolidinium cations. Such ionic liquids include, for example, 1-ethyl-3-methylimidazolium bis (fluorosulfonyl) imide (EMI-FSI) and N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide (Py13-FSI). ).

The content of the ionic liquid contained in the negative electrode mixture layer 12 is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, based on the total amount of the negative electrode mixture layer. The content of the ionic liquid contained in the negative electrode mixture layer 12 is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, based on the total amount of the negative electrode mixture layer.

In one embodiment, the electrolyte salt contained in the negative electrode mixture layer 12 preferably contains a first lithium salt which is an imide-based lithium salt and a second lithium salt different from the first lithium salt.

The present inventors have clarified that when the first lithium salt and the second lithium salt are applied to the negative electrode mixture layer as the electrolyte salt, the initial characteristics and charging characteristics of the secondary battery can be improved. .. The present inventors speculate that the reason for obtaining such an effect is as follows. First, by applying the first lithium salt and the second lithium salt as electrolyte salts to the negative electrode mixture layer, a stable film is formed on the surface of the negative electrode. As a result, side reactions such as reduction decomposition of ionic liquids and lithium salts are suppressed, and the Coulomb efficiency is increased, which is presumed to improve the initial characteristics.

Further, in a conventional lithium secondary battery, when charging with a large current (for example, 1C), the reason why the charging is not completed is considered to be that a side reaction in which the cation component of the ionic liquid is inserted into the negative electrode proceeds. On the other hand, by applying the first lithium salt and the second lithium salt as the electrolyte salt to the negative electrode mixture layer, a good film is formed on the surface of the negative electrode, and the film inserts the cation component into the negative electrode. I presume that it will be suppressed.

The imide-based lithium salt as the first lithium salt is a lithium salt having an imide bond in the anionic component. Examples of the anion component having an imide bond include bis (fluorosulfonyl) imide anion ([FSI] ⁻ ), bis (trifluoromethanesulfonyl) imide anion ([TFSI] ⁻ ), and bis (pentafluoroethanesulfonyl) imide (N). _{(SO 2 C 2 F 5)} 2 -) and the like, among the anionic component is bis (fluorosulfonyl) imide anion and bis (trifluoromethanesulfonyl) comprise at least one selected from the group consisting of imide anion Is preferable.

The first lithium salt may be at least one selected from the group consisting of Li [FSI], Li [TFSI] and LiN (SO ₂ C ₂ F ₅ ) _{2, preferably Li [FSI], Li.} It is at least one selected from the group consisting of [TFSI].

The second lithium salt is not particularly limited as long as it is a lithium salt different from the first lithium salt. The anionic component of the second lithium salt, for example, halide ions ^{(I -, Cl -, Br} - , _{^{etc.), SCN -, BF 4 -}} , BF 3 (CF 3) -, BF 3 (C 2 F 5 _{^{) -, PF 6 -, ClO}} 4 -, SbF 6 -, B (C 6 H 5) 4 -, B (O 2 C 2 H 4) 2 -, C (SO 2 F) 3 -, C (SO 2 CF ₃ ) ₃ ⁻ , CF ₃ COO ⁻ , CF ₃ SO ₂ O ⁻ , C ₆ F ₅ SO ₂ O ⁻ , B (O ₂ C ₂ O ₂ ) ₂ ^−, etc. may be used. The anion component of the second lithium salt preferably comprises at least one selected from the group consisting of _{hexafluorophosphate anion (PF 6} ^{−) and bisoxalate borate anion (BOB).}

The second lithium salt is LiPF ₆ , LiBF ₄ , Li [f3C], Li [BOB], LiClO ₄ , LiBF ₃ (CF ₃ ), LiBF ₃ (C ₂ F ₅ ), LiBF ₃ (C ₃ F ₇ ). , LiBF ₃ (C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiCF ₃ SO ₂ O, LiCF ₃ COO, and LiRCOO (R is an alkyl group, phenyl group, or naphthyl group having 1 to 4 carbon atoms. It may be at least one selected from the group consisting of (.), And preferably at least one selected from the group consisting of _{LiPF 6 and Li [BOB].}

The negative electrode mixture layer 12 may further contain an electrolyte salt (other electrolyte salt) other than the above-mentioned first lithium salt and second lithium salt.

The other electrolyte salt may be at least one selected from the group consisting of sodium salt, calcium salt, and magnesium salt.

Sodium salts include NaPF ₆ , NaBF ₄ , Na [FSI], Na [TFSI], Na [f3C], Na [BOB], NaClO ₄ , NaBF ₃ (CF ₃ ), NaBF ₃ (C ₂ F ₅ ), NaBF. ₃ (C ₃ F ₇ ), NaBF ₃ (C ₄ F ₉ ), NaC (SO ₂ CF ₃ ) ₃ , NaCF ₃ SO ₂ O, NaCF ₃ COO, and NaRCOO (R is an alkyl group with 1 to 4 carbon atoms). , Phenyl group, or naphthyl group).

Calcium salts are Ca (PF ₆ ) ₂ , Ca (BF ₄ ) ₂ , Ca [FSI] ₂ , Ca [TFSI] ₂ , Ca [f3C] ₂ , Ca [BOB] ₂ , Ca (ClO ₄ ) ₂ , Ca. [BF ₃ (CF ₃ )] ₂ , Ca [BF ₃ (C ₂ F ₅ )] ₂ , Ca [BF ₃ (C ₃ F ₇ )] ₂ , Ca [BF ₃ (C ₄ F ₉ )] ₂ , Ca [C (SO ₂ CF ₃ ) ₃ ] ₂ , Ca (CF ₃ SO ₂ O) ₂ , Ca (CF ₃ COO) ₂ , and Ca (RCOO) ₂ (R is an alkyl group having 1 to 4 carbon atoms, phenyl. It may be at least one selected from the group consisting of a group or a naphthyl group).

Magnesium salts include Mg (PF ₆ ) ₂ , Mg (BF ₄ ) ₂ , Mg [FSI] ₂ , Mg [TFSI] ₂ , Mg [f3C] ₂ , Mg [BOB] ₂ , Na (ClO ₄ ) ₂ , Mg. [BF ₃ (CF ₃ )] ₂ , Mg [BF ₃ (C ₂ F ₅ )] ₂ , Mg [BF ₃ (C ₃ F ₇ )] ₂ , Mg [BF ₃ (C ₄ F ₉ )] ₂ , Mg [C (SO ₂ CF ₃ ) ₃ ] ₂ , Mg (CF ₃ SO ₃ ) ₂ , Mg (CF ₃ COO) ₂ , and Mg (RCOO) ₂ (R is an alkyl group or phenyl group having 1 to 4 carbon atoms. , Or a naphthyl group), which may be at least one selected from the group.

The electrolyte salt contained in the negative electrode mixture layer 12 may be dissolved in an ionic liquid and contained. The total content of the electrolyte salt and the ionic liquid contained in the negative electrode mixture layer 12 is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 10 based on the total amount of the negative electrode mixture layer. It is 5% by mass or more, preferably 30% by mass or less, more preferably 25% by mass or less, and further preferably 20% by mass or less.

The concentration of the electrolyte salt per unit volume of the ionic liquid contained in the negative electrode mixture layer 12 is preferably 0.5 mol / L or more, more preferably 0.7 mol / L or more, still more preferably, from the viewpoint of improving the discharge characteristics. Is 0.8 mol / L or more, preferably 3.0 mol / L or less, more preferably 2.8 mol / L or less, and further preferably 2.5 mol / L or less.

The content of the first lithium salt in the electrolyte salt is preferable with respect to a total of 100 parts by mass of the content of the first lithium salt and the content of the second lithium salt from the viewpoint of further improving the initial characteristics. Is 50 parts by mass or more, more preferably 70 parts by mass or more, still more preferably 90 parts by mass or more. The content of the first lithium salt is 99.5 parts by mass or less, or 99.0 parts by mass with respect to a total of 100 parts by mass of the content of the first lithium salt and the content of the second lithium salt. It may be:

The negative electrode mixture layer 12 may contain other components such as a negative electrode active material, a conductive material, and a binder.

As the negative electrode active material, a material commonly used in the field of energy devices can be used. Examples of the negative electrode active material include metallic lithium, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), lithium alloys or other metal compounds, carbon materials, metal complexes, organic polymer compounds and the like. Examples of carbon materials include natural graphite (scaly graphite), graphite such as artificial graphite (graphite), amorphous carbon, carbon fiber, and acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. Carbon black and the like. The negative electrode active material may be silicon, tin or a compound containing these elements (alloy with oxides, nitrides, other metals) from the viewpoint of obtaining a larger theoretical capacity (for example, 500 to 1500 Ah / kg). Good.

The content of the negative electrode active material contained in the negative electrode mixture layer 12 may be 60% by mass or more, 65% by mass or more, or 70% by mass or more based on the total amount of the negative electrode mixture layer. The content of the negative electrode active material may be 99% by mass or less, 95% by mass or less, or 90% by mass or less based on the total amount of the negative electrode mixture layer.

The conductive material is not particularly limited, but may be a carbon material such as graphite, acetylene black, carbon black, or carbon fiber. The conductive material may be a mixture of two or more of the above-mentioned carbon materials.

The content of the conductive material contained in the negative electrode mixture layer 12 may be 0.1% by mass or more, 1% by mass or more, or 3% by mass or more, and is 15% by mass or less, based on the total amount of the negative electrode mixture layer. It may be 10% by mass or less, or 8% by mass or less.

The binder is not particularly limited, but contains at least one selected from the group consisting of ethylene tetrafluoride, vinylidene fluoride, hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate, and methyl methacrylate as a monoma unit. It may be a polymer, a styrene-butadiene rubber, an isoprene rubber, a rubber such as acrylic rubber, or the like. The binder is preferably polyvinylidene fluoride, a copolima containing ethylene tetrafluoride and vinylidene fluoride as structural units, and a copolyma containing vinylidene fluoride and hexafluoropropylene as structural units.

The content of the binder may be 0.5% by mass or more, 1% by mass or more, or 3% by mass or more based on the total amount of the negative electrode mixture layer. The content of the binder may be 20% by mass or less, 15% by mass or less, or 10% by mass or less based on the total amount of the negative electrode mixture layer.

The negative electrode mixture layer 12 may further contain a polymer having a structural unit represented by the following general formula (A).

In the general formula (A), Y ⁻ represents a counter anion. Here, Y ^- as, for example, BF ₄ ^- (tetrafluoroborate anion), PF ₆ ^- (hexafluorophosphate anion), N _{(FSO 2) 2} ^- (bis (fluorosulfonyl) imide anion, [FSI] _{^{-), N (CF 3 SO}} 2) 2 - ( bis (trifluoromethanesulfonyl) imide _{^{anion, [TFSI] -), C}} (SO 2 F) 3 - ( tris (fluorosulfonyl) carbanions, [f3C] ^-) _{, B (C 2 O 4)} 2 - ( bis oxalate borate _{^{anion, [BOB] -), BF}} 3 (CF 3) -, BF 3 (C 2 F 5) -, BF 3 (C 3 F 7) ⁻ , BF ₃ (C ₄ F ₉ ) ⁻ , C (SO ₂ CF ₃ ) ₃ ⁻ , CF ₃ SO ₂ O ⁻ , CF ₃ COO ⁻ , RCOO ⁻ (R is an alkyl group having 1 to 4 carbon atoms, phenyl A group or a naphthyl group) and the like. Among them, Y ^- is preferably _{^{BF 4 -, PF 6 -,}} [FSI] -, [TFSI] - and [F3C] ^- at least one member selected from the group consisting of, more preferably [TFSI] ^- in is there.

In general formula (A) viscosity average molecular weight of the polymer having the structural unit represented by Mv (g · ^{mol -1)} is not particularly limited, 1.0 × 10 ⁴ or more, or 1.0 × 10 ⁴ or more It may be there. The viscosity-average molecular weight of polymer, 5.0 × 10 ⁶ or less, or 1.0 × 10 may be ^6.

In the present specification, the "viscosity average molecular weight" can be evaluated by the viscosity method, which is a general measuring method, and is, for example, from the ultimate viscosity number [η] measured based on JIS K 7376-3: 1999. Can be calculated.

From the viewpoint of ionic conductivity, the polymer having the structural unit represented by the general formula (A) is preferably a polymer consisting only of the structural unit represented by the general formula (A), that is, a homopolyma.

The polymer having the structural unit represented by the general formula (A) may be a polymer represented by the following general formula (B).

In the general formula (B), n is 300 to 4000, and Z ⁻ represents a counter anion. As Z ⁻ , the same one as exemplified by ^{Y − can be used.}

n is 300 or more, 400 or more, or 500 or more. n is 4000 or less, 3500 or less, or 3000 or less. Further, n is 300 to 4000, 400 to 3500, or 500 to 3000.

The method for producing a polymer having a structural unit represented by the general formula (A) is not particularly limited, and for example, the production method described in Journal of Power Sources 2009, 188, 558-563 can be used.

The content of the polymer having the structural unit represented by the general formula (A) is not particularly limited, but is, for example, 0.5% by mass or more based on the total amount of the negative electrode mixture layer. The content of the polymer is, for example, 25% by mass or less based on the total amount of the negative electrode mixture layer.

The thickness of the negative electrode mixture layer 12 may be 10 μm or more, 15 μm or more, or 20 μm or more from the viewpoint of further improving the energy density. The thickness of the negative electrode mixture layer 12 may be 60 μm or less, 55 μm or less, or 50 μm or less. By setting the thickness of the negative electrode mixture layer to 50 μm or less, it is possible to suppress a decrease in charge / discharge characteristics due to variations in salt concentration in the vicinity of the surface of the negative electrode mixture layer 12 and in the vicinity of the surface of the negative electrode current collector 11.

The electrolyte layer 7 may contain an ionic liquid and an electrolyte salt. In one embodiment, the electrolyte layer 7 contains one or more types of polymers, oxide particles, a lithium salt, a sodium salt, and calcium. It preferably contains at least one electrolyte salt selected from the group consisting of salts and magnesium salts, and an ionic liquid.

One or more polymers preferably have a first structural unit selected from the group consisting of ethylene tetrafluoride and vinylidene fluoride.

One or more types of polymers preferably contain the first structural unit and a second structural unit selected from the group consisting of hexafluoropropylene, acrylic acid, maleic acid, ethyl methacrylate, and methyl methacrylate. It may be included. That is, the first structural unit and the second structural unit may be contained in one kind of polymer to form a copolymer, and each of them is contained in another polymer and has a first structural unit. And a second polymer having a second structural unit may constitute at least two kinds of polymers.

Specifically, the polymer may be polyethylene tetrafluoride, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, or the like.

The content of one or more types of polymers is preferably 3% by mass or more based on the total amount of the electrolyte layer. The polymer content is preferably 70% by mass or less, more preferably 60% by mass or less, based on the total amount of the electrolyte layer.

The oxide particles are, for example, inorganic oxide particles. The inorganic oxide is, for example, an inorganic oxide containing Li, Mg, Al, Si, Ca, Ti, Zr, La, Na, K, Ba, Sr, V, Nb, B, Ge and the like as constituent elements. Good. The oxide particles are preferably at least one selected from the group consisting of _{SiO 2} , Al ₂ O ₃ , AlOOH, MgO, CaO, ZrO ₂ , TiO ₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , and BaTIO _3. It is a particle. Since the oxide particles have polarity, the dissociation of the electrolyte in the electrolyte layer 7 can be promoted and the battery characteristics can be enhanced.

The oxide particles may be oxides of rare earth metals. Specifically, the oxide particles include scandium oxide, yttrium oxide, lanthanum oxide, cerium oxide, placeodymium oxide, neodymium oxide, samarium oxide, urobium oxide, gadolinium oxide, terbium oxide, displosium oxide, formium oxide, erbium oxide, and oxidation. It may be turium, yttrium oxide, lutetium oxide or the like.

The specific surface area of the oxide particles is ^{2 to} 400 m 2 / g, and may be 5 to 100 m ² / g, 10 to 80 m ² / g, or 15 to 60 m ² / g. When the specific surface area is ² to 400 m 2 / g, the secondary battery using the electrolyte composition containing such oxide particles tends to have excellent discharge characteristics. The specific surface area of the oxide particles means the specific surface area of the entire oxide particles including the primary particles and the secondary particles, and is measured by the BET method.

The average primary particle size of the oxide particles (average particle size of the primary particles) is preferably 0.005 μm (5 nm) or more, more preferably 0.01 μm (10 nm) or more, from the viewpoint of further improving the conductivity. Yes, more preferably 0.015 μm (15 nm) or more. The average primary particle size of the oxide particles is preferably 1 μm or less, more preferably 0.1 μm or less, and further preferably 0.05 μm or less from the viewpoint of thinning the electrolyte layer 7. The average primary particle size of the oxide particles can be measured by observing the oxide particles with a transmission electron microscope or the like.

The average particle size of the oxide particles is preferably 0.005 μm or more, more preferably 0.01 μm or more, and further preferably 0.03 μm or more. The average particle size of the oxide particles is preferably 5 μm or less, more preferably 3 μm or less, and further preferably 1 μm or less. The average particle size of the oxide particles is preferably 0.005 μm or more and 5 μm or less, 0.005 μm or more and 3 μm or less, 0.005 μm or more and 1 μm or less, 0.01 μm or more and 5 μm or less, 0.01 μm or more and 3 μm or less, 0.01 μm or more. It is 1 μm or less, 0.03 μm or more and 5 μm or less, 0.03 μm or more and 3 μm or less, or 0.03 μm or more and 1 μm or less.

The content of the oxide particles may be 5% by mass or more, 10% by mass or more, or 15% by mass or more based on the total amount of the electrolyte layer. The content of the oxide particles may be 60% by mass or less, 50% by mass or less, and 40% by mass or less based on the total amount of the electrolyte layer.

The ionic liquid may be the same as the ionic liquid that can be used for the negative electrode mixture layer 12 described above. The ionic liquid contained in the electrolyte layer 7 is preferably an ionic liquid containing N (SO ₂ CF ₃ ) ₂ ⁻ as an anionic component and containing a chain quaternary onium cation as a cation component. The ionic liquid contained in the electrolyte layer 7 is, for example, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide (DEME-TFSI), 1-ethyl-3-3. Methyl imidazolium bis (fluorosulfonyl) imide (EMI-FSI) and N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide (Py13-FSI).

The content of the ionic liquid contained in the electrolyte layer 7 may be 10% by mass or more and 80% by mass or less based on the total amount of the electrolyte layer from the viewpoint of preferably producing the electrolyte layer 7.

The electrolyte salt contained in the electrolyte layer 7 is not particularly limited, and the first lithium salt and the first lithium salt, which are imide-based lithium salts, are the same as the electrolyte salt that can be used for the negative electrode mixture layer 12 described above. It may be a different second lithium salt and may be dissolved and contained in an ionic liquid. The electrolyte salt may be at least one selected from the group consisting of lithium salt, sodium salt, calcium salt, and magnesium salt. The type and content of the electrolyte salt contained in the electrolyte layer 7 may be the same as the electrolyte salt that can be used in the negative electrode mixture layer 12 described above.

The electrolyte salt contained in the electrolyte layer 7 is preferably one selected from the group consisting of an imide-based lithium salt, an imide-based sodium salt, an imide-based calcium salt, and an imide-based magnesium salt, but more preferably the above. A first lithium salt and a second lithium salt that can be used for the negative electrode mixture layer 12.

The imide-based lithium salt may be Li [TFSI], Li [FSI] or the like. The imide-based sodium salt may be Na [TFSI], Na [FSI] or the like. The imide-based calcium salt may be Ca [TFSI] ₂ , Ca [FSI] _2, or the like. The imide-based magnesium salt may be Mg [TFSI] ₂ , Mg [FSI] _2, or the like.

The total content of the electrolyte salt and the ionic liquid contained in the electrolyte layer 7 is preferably 10% by mass based on the total amount of the electrolyte layer from the viewpoint of further improving the conductivity and suppressing the decrease in the capacity of the secondary battery. The above is more preferably 25% by mass or more, and further preferably 40% by mass or more. The total content of the electrolyte salt and the ionic liquid is preferably 80% by mass or less based on the total amount of the electrolyte layer from the viewpoint of suppressing a decrease in the strength of the electrolyte layer.

The concentration of the electrolyte salt per unit volume of the ionic liquid contained in the electrolyte layer 7 is preferably 0.5 mol / L or more, more preferably 0.7 mol / L or more, still more preferably, from the viewpoint of further improving the charge / discharge characteristics. Is 0.8 mol / L or more, preferably 3.0 mol / L or less, more preferably 2.8 mol / L or less, and further preferably 2.5 mol / L or less.

The thickness of the electrolyte layer 7 is preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of increasing the strength and improving the safety. The thickness of the electrolyte layer 7 is preferably 200 μm or less, more preferably 150 μm or less, still more preferably 100 μm or less, from the viewpoint of further reducing the internal resistance of the secondary battery and further improving the large current characteristics.

In another embodiment, the electrolyte layer 7 can be formed from an electrolyte composition containing a solid electrolyte, an electrolyte salt, and a molten salt.

Examples of the solid electrolyte include polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte and the inorganic solid electrolyte are not particularly limited, and those used as the polymer electrolyte and the inorganic solid electrolyte for ordinary ion batteries can be used.

The polymer having the structural unit represented by the general formula (A) described above may have properties as a polymer electrolyte. Therefore, the polymer can be suitably used as a polymer electrolyte.

The inorganic solid electrolyte may be Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) or the like.

The electrolyte salt may be the same as the electrolyte salt that can be contained in the negative electrode mixture layer described above. As the molten salt, for example, the same one as the ionic liquid contained in the negative electrode mixture layer described above may be used, or a plastic crystal may be used.

If necessary, the electrolyte composition may further contain particles of oxides such as silica and alumina, or additives having a lithium salt dissociating ability such as fibers, borate esters and aluminate esters.

The positive electrode current collector 9 may be made of aluminum, stainless steel, titanium or the like. Specifically, the positive electrode current collector 9 may be, for example, an aluminum perforated foil having holes with a hole diameter of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like. In addition to the above, the positive electrode current collector 9 may be made of any material as long as it does not cause changes such as dissolution and oxidation during use of the battery, and its shape, manufacturing method, etc. Not limited.

The thickness of the positive electrode current collector 9 may be 10 μm or more and 100 μm or less, preferably 10 μm or more and 50 μm or less from the viewpoint of reducing the volume of the entire positive electrode, and the positive electrode is wound with a small curvature when forming a battery. From the viewpoint of turning, it is more preferably 10 μm or more and 20 μm or less.

In one embodiment, the positive electrode mixture layer 10 may contain a positive electrode active material.

The positive electrode active material may be a lithium transition metal compound such as a lithium transition metal oxide or a lithium transition metal phosphate. The lithium transition metal oxide may be, for example, lithium manganate, lithium nickel oxide, lithium cobalt oxide, or the like. The lithium transition metal oxide is a part of transition metals such as Mn, Ni, and Co contained in lithium manganate, lithium nickelate, lithium cobalt, etc., which is one or more other transition metals, or two or more other transition metals. It may be a lithium transition metal oxide substituted with a metal element (main group element) such as Mg or Al. That is, the lithium transition metal oxide may ^{be a compound represented by LiM 1} O ₂ or LiM ¹ O ₄ (M ¹ contains at least one transition metal). Specifically, the lithium transition metal oxides are Li (Co _1/3 Ni _1/3 Mn _1/3 ) O ₂ , LiNi _1/2 Mn _1/2 O ₂ , and LiNi _1/2 Mn _3/2 O. It may be _{4 mag.}

The lithium transition metal oxide is preferably a compound represented by the following formula (7) from the viewpoint of further improving the energy density.
Li _a Ni _b Co _c M ² _d O _{2 + e} (7)
[In the formula (7), M ² is at least one selected from the group consisting of Al, Mn, Mg and Ca, and a, b, c, d and e are 0.2 ≦ a ≦ 1. 2, 0.5 ≦ b ≦ 0.9, 0.1 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.2, −0.2 ≦ e ≦ 0.2, and b + c + d = 1. .. ]

Lithium transition metal phosphates are LiFePO ₄ , LiMnPO ₄ , LiMn _x M ³ _1-x PO ₄ (0.3 ≦ x ≦ 1, M ³ are Fe, Ni, Co, Ti, Cu, Zn, Mg and Zr. It may be at least one element selected from the group consisting of) and the like.

The positive electrode active material may be primary particles that have not been granulated, or secondary particles that have been granulated.

The particle size of the positive electrode active material is adjusted so as to be equal to or less than the thickness of the positive electrode mixture layer 10. When there are coarse particles having a particle size equal to or larger than the thickness of the positive electrode mixture layer 10 in the positive electrode active material, the coarse particles are removed in advance by sieving classification, wind flow classification, etc. A positive electrode active material having a diameter is selected.

The average particle size of the positive electrode active material is 0.1 μm or more, more preferably 1 μm or more. The average particle size of the positive electrode active material is preferably 30 μm or less, more preferably 25 μm or less. _{The average particle size of the positive electrode active material is the particle size (D 50} ) when the ratio (volume fraction) to the volume of the entire positive electrode active material is 50%. The average particle size (D ₅₀ ) of the positive electrode active material is measured by using a laser scattering type particle size measuring device (for example, Microtrac) to measure a suspension in which the positive electrode active material is suspended in water by a laser scattering method. You can get it.

The content of the positive electrode active material may be 70% by mass or more, 80% by mass or more, or 90% by mass or more based on the total amount of the positive electrode mixture layer. The content of the positive electrode active material may be 99% by mass or less based on the total amount of the positive electrode mixture layer.

The positive electrode mixture layer 10 may further contain an ionic liquid, an electrolyte salt, a conductive material, a binder, and a polymer.

The types and contents of the ionic liquid, the electrolyte salt and the polymer contained in the positive electrode mixture layer 10 may be the same as the types and the contents of the ionic liquid and the electrolyte salt in the negative electrode mixture layer 12 described above.

The conductive material contained in the positive electrode mixture layer 10 is not particularly limited, but may be a carbon material such as graphite, acetylene black, carbon black, or carbon fiber. The conductive material may be a mixture of two or more of the above-mentioned carbon materials.

The content of the conductive material contained in the positive electrode mixture layer 10 may be 0.1% by mass or more, 1% by mass or more, or 3% by mass or more, and is 15% by mass or less, based on the total amount of the positive electrode mixture layer. It may be 10% by mass or less, or 8% by mass or less.

The positive electrode mixture layer 10 may further contain a binder similar to the binder that can be used for the negative electrode mixture layer 12 described above. The content of the binder contained in the positive electrode mixture layer 10 may be the same as the content of the binder in the negative electrode mixture layer 12 described above.

The thickness of the positive electrode mixture layer 10 may be 10 μm or more, 15 μm or more, or 20 μm or more from the viewpoint of further improving the energy density. The thickness of the positive electrode mixture layer 10 may be 100 μm or less, 80 μm or less, or 70 μm or less. By setting the thickness of the positive electrode mixture layer to 100 μm or less, it is possible to suppress a decrease in charge / discharge characteristics due to variations in salt concentration in the vicinity of the surface of the positive electrode mixture layer 10 and in the vicinity of the surface of the positive electrode current collector 9.

Subsequently, the method for manufacturing the secondary battery 1 described above will be described. The method for manufacturing the secondary battery 1 is the first step of forming the positive electrode mixture layer 10 on the positive electrode current collector 9 to obtain the positive electrode 6, and forming the negative electrode mixture layer 12 on the negative electrode current collector 11. It has a second step of obtaining the negative electrode 8 and a third step of providing an electrolyte layer 7 between the positive electrode 6 and the negative electrode 8.

In the first step, for the positive electrode 6, for example, the material used for the positive electrode mixture layer is dispersed in a dispersion medium to obtain a slurry-shaped positive electrode mixture, and then this positive electrode mixture is applied to the positive electrode current collector 9. It is obtained by volatilizing the dispersion medium. The dispersion medium is preferably an organic solvent such as N-methyl-2-pyrrolidone (NMP). The electrolyte salt contained in the positive electrode mixture layer 10 can be dissolved in an ionic liquid and then dispersed in a dispersion medium together with other materials.

The mixing ratio of the positive electrode active material, the conductive material, the binder, and the ionic liquid in which the electrolyte salt is dissolved in the positive electrode mixture layer 10 is, for example, the positive electrode active material: the conductive material: the binder: the ionic liquid in which the electrolyte salt is dissolved. = 69 to 82: 0.1 to 10: 5 to 12: 10 to 17 (mass ratio). However, it is not necessarily limited to this range.

In the second step, the negative electrode 8 is obtained in the same manner as the positive electrode 6 described above. That is, the material used for the negative electrode mixture layer 12 is dispersed in a dispersion medium to obtain a slurry-like negative electrode mixture, and then this negative electrode mixture is applied to the negative electrode current collector 11 and then the dispersion medium is volatilized. can get.

The mixing ratio of the negative electrode active material, the conductive material, the binder, and the ionic liquid in which the electrolyte salt is dissolved in the negative electrode mixture layer 12 is, for example, the negative electrode active material: the conductive material: the binder: the ionic liquid in which the electrolyte salt is dissolved. = 70 to 80: 0.1 to 10: 5 to 10: 10 to 17 (mass ratio). However, it is not necessarily limited to this range.

In the third step, in one embodiment, the electrolyte layer 7 is obtained by dispersing the material used for the electrolyte layer 7 in a dispersion medium to obtain a slurry-like electrolyte composition, and then applying this on a substrate. It is obtained as a sheet-like electrolyte layer (electrolyte sheet) by volatilizing the dispersion medium. The dispersion medium is preferably water, NMP, toluene or the like. In this case, in the third step, the secondary battery 1 is obtained by laminating the positive electrode 6, the electrolyte layer 7, and the negative electrode 8 by, for example, laminating. At this time, the electrolyte layer 7 is located on the positive electrode mixture layer 10 side of the positive electrode 6 and on the negative electrode mixture layer 12 side of the negative electrode 8, that is, the positive electrode current collector 9, the positive electrode mixture layer 10, and the electrolyte layer 7. , The negative electrode mixture layer 12 and the negative electrode current collector 11 are laminated in this order.

In the third step, in another embodiment, the electrolyte layer 7 is formed by coating on at least one of the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the negative electrode 8, preferably the positive electrode. It is formed by coating on both the positive electrode mixture layer 10 side of No. 6 and the negative electrode mixture layer 12 side of the negative electrode 8. In this case, for example, the secondary battery 1 can be obtained by laminating the negative electrode 8 provided with the electrolyte layer 7 and the positive electrode 6 provided with the electrolyte layer 7 so that the electrolyte layers 7 are in contact with each other.

In the method of forming the electrolyte layer 7 on the negative electrode mixture layer 12, for example, the material used for the electrolyte layer 7 is dispersed in a dispersion medium to obtain a slurry-like electrolyte composition, and then this electrolyte composition is used as a negative electrode mixture. This is a method of applying on the layer 12 using an applicator. The dispersion medium is preferably an organic solvent such as NMP.

The method of forming the electrolyte layer 7 on the positive electrode mixture layer 10 may be the same as the method of forming the electrolyte layer 7 on the negative electrode mixture layer 12.

[Second Embodiment]
Next, the secondary battery according to the second embodiment will be described. FIG. 3 is an exploded perspective view showing an electrode group of the secondary battery according to the second embodiment. As shown in FIG. 3, the difference between the secondary battery in the second embodiment and the secondary battery in the first embodiment is that the electrode group 2B includes the bipolar electrode 15. That is, the electrode group 2B includes a positive electrode 6, a first electrolyte layer 7, a bipolar electrode 15, a second electrolyte layer 7, and a negative electrode 8 in this order.

The bipolar electrode 15 includes a bipolar electrode current collector 16, a positive electrode mixture layer 10 provided on a surface (positive electrode surface) of the bipolar electrode current collector 16 on the negative electrode 8 side, and a positive electrode 6 side of the bipolar electrode current collector 16. The negative electrode mixture layer 12 provided on the surface (negative electrode surface) is provided. That is, since the bipolar electrode 15 has both a positive electrode function and a negative electrode function, the electrode group 2B in the second embodiment includes the bipolar electrode current collector 16 and the bipolar electrode in addition to the positive electrode 6 and the negative electrode 8. Another positive electrode having a positive electrode mixture layer 10 provided on the current collector 16 and another positive electrode including a bipolar electrode current collector 16 and a negative electrode mixture layer 12 provided on the bipolar electrode current collector 16. It can be seen that the negative electrode is included.

In one embodiment, the bipolar electrode 15 can be seen as a battery member for a secondary battery including the bipolar electrode current collector 16 and the negative electrode mixture layer 12 provided on the bipolar electrode current collector 16. FIG. 4A is a schematic cross-sectional view showing a battery member for a secondary battery according to an embodiment. As shown in FIG. 4A, the battery member 17 includes a bipolar electrode current collector 16, a positive electrode mixture layer 10 provided on one surface of the bipolar electrode current collector 16, and a positive electrode mixture layer. A battery member including a negative electrode mixture layer 12 provided on the opposite side of the bipolar electrode current collector 16 on the 10.

In the bipolar electrode current collector 16, the positive electrode surface may be preferably made of a material having excellent oxidation resistance, and may be made of aluminum, stainless steel, titanium, or the like. The negative electrode surface of the bipolar electrode current collector 16 using graphite or an alloy as the negative electrode active material may be formed of a material that does not form an alloy with lithium, and specifically, stainless steel, nickel, iron, titanium, or the like. It may be formed. When dissimilar metals are used for the positive electrode surface and the negative electrode surface, the bipolar electrode current collector 16 may be a clad material in which dissimilar metal foils are laminated. However, when a negative electrode 8 that operates at a potential that does not form an alloy with lithium, such as lithium titanate, is used, the above-mentioned limitation is removed, and the negative electrode surface may be made of the same material as the positive electrode current collector 9. In that case, the bipolar electrode current collector 16 may be a single metal leaf. The bipolar electrode current collector 16 as a single metal foil may be an aluminum perforated foil having holes with a hole diameter of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like. In addition to the above, the bipolar electrode current collector 16 may be made of any material as long as it does not cause changes such as dissolution and oxidation during use of the battery, and its shape, manufacturing method, etc. Is not restricted.

The thickness of the bipolar electrode current collector 16 may be 10 μm or more and 100 μm or less, preferably 10 μm or more and 50 μm or less from the viewpoint of reducing the volume of the entire bipolar electrode, and is bipolar with a small curvature when forming a battery. From the viewpoint of winding the electrode, it is more preferably 10 μm or more and 20 μm or less.

The negative electrode mixture layer 12 in the battery member 17 may be made of the same material as the negative electrode mixture layer 12 in the first embodiment described above.

In another embodiment, it can be seen that the electrode group 2B includes a battery member including the first electrolyte layer 7, the bipolar electrode 15, and the second electrolyte layer 7 in this order. FIG. 4B is a schematic cross-sectional view showing a battery member for a secondary battery according to another embodiment. As shown in FIG. 4B, the battery member 18 includes a bipolar electrode current collector 16, a positive electrode mixture layer 10 provided on one surface of the bipolar electrode current collector 16, and a positive electrode mixture layer. A second electrolyte layer 7 provided on the opposite side of the bipolar electrode current collector 16 and a negative electrode mixture layer 12 provided on the other surface of the bipolar electrode current collector 16 and a negative electrode mixture layer. A first electrolyte layer 7 provided on the opposite side of the bipolar electrode current collector 16 on the 12 is provided.

The bipolar electrode current collector 16, the positive electrode mixture layer 10, and the negative electrode mixture layer 12 in the battery member 18 are the bipolar electrode current collector 16, the positive electrode mixture layer 10, and the negative electrode mixture layer 12 in the battery member 17 described above. It may be composed of the same material as.

The first electrolyte layer 7 and the second electrolyte layer 7 in the battery member 18 may be made of the same material as the electrolyte layer 7 in the first embodiment described above. The first electrolyte layer 7 and the second electrolyte layer 7 may be the same kind or different from each other, and are preferably the same kind to each other.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
[Preparation of electrodes]
<Cathode preparation>
Layered lithium-nickel-manganese-cobalt composite oxide (positive electrode active material) 78.5 parts by mass, acetylene black (conductive material, product name: HS-100, average particle size 48 nm, manufactured by Denka Co., Ltd.) 5 parts by mass, 2.5 parts by mass of a copolyma solution (solid content 12% by mass) of vinylidene fluoride and hexafluoropropylene and N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide (Py13-FSI) which is an ionic liquid. Lithium bis (fluorosulfonyl) imide (first lithium salt, Li [FSI]) and lithium hexafluorophosphate (second lithium salt, LiPF ₆ ) were dissolved as electrolyte salts in a 1: 1 mass ratio. An ionic liquid (concentration of electrolyte salt in the ionic liquid: 1.5 M) was mixed with 14 parts by mass to prepare a positive electrode mixture slurry. This positive electrode mixture slurry is applied onto a positive electrode current collector (aluminum foil with a thickness of 15 μm) at a coating amount of 125 g / m ² , and heated at 80 ° C. to dry, thereby resulting in a mixture density of 2.7 g / m. thereby forming a positive electrode mixture layer of cm ^3. This was cut into a width of 30 mm and a length of 45 mm to obtain a positive electrode plate, and as shown in FIG. 2, a positive electrode current collecting tab was attached to this positive electrode plate.

<Manufacturing of negative electrode>
Graphite 1 (negative electrode active material, manufactured by Hitachi Kasei Co., Ltd.) 78 parts by mass, graphite 2 (negative electrode active material, manufactured by Nippon Graphite Industry Co., Ltd.) 2.4 parts by mass, carbon fiber (conductive material, product name: VGCF-H, Showa Denko Co., Ltd.) 0.6 parts by mass, 5 parts by mass of copolyma solution of vinylidene fluoride and hexafluoropropylene (solid content 12% by mass), ionic liquid Py13-FSI as electrolyte salt Li [FSI] (No. 1 lithium salt) and LiPF ₆ (second lithium salt) dissolved in a 1: 1 mass ratio ionic liquid (electrolyte salt concentration in ionic liquid: 1.5M) 14 parts by mass are mixed and the negative electrode A mixture slurry was prepared. This negative electrode mixture slurry is applied onto a negative electrode current collector (copper foil with a thickness of 10 μm) at a coating amount of 60 g / m ² , heated at 80 ° C., and dried to obtain a mixture density of 1.8 g / m. A cm ³ negative electrode mixture layer was formed. This was cut into a width of 31 mm and a length of 46 mm to obtain a negative electrode plate, and as shown in FIG. 2, a negative electrode current collecting tab was attached to this negative electrode plate.

[Preparation of electrolyte sheet]
Copolima of vinylidene fluoride, which is the first structural unit, and hexafluoropropylene, which is the second structural unit (mass ratio of the content of the first structural unit to the content of the second structural unit = 95/5. Hereinafter, PVDF-HFP is also referred to as 21% by mass, SiO ₂ particles (average particle size 0.1 μm) which are oxide particles are 14% by mass, and Li [as an electrolyte salt is added to Py13-FSI which is an ionic liquid. FSI] (first lithium salt) and LiPF ₆ (second lithium salt) dissolved in a 1: 1 mass ratio to 65% by mass of an ionic liquid (concentration of electrolyte salt in the ionic liquid: 1.5M). Was dispersed in NMP, which is a dispersion medium, to prepare a slurry containing an electrolyte composition. The obtained slurry was applied to a base material made of polyethylene terephthalate and heated to volatilize the dispersion medium to obtain an electrolyte sheet. The thickness of the electrolyte layer in the obtained electrolyte sheet was 25 ± 2 μm.

[Preparation of electrode group]
The prepared positive electrode plate and the prepared negative electrode plate were opposed to each other via the prepared electrolyte sheet to prepare a laminated electrode group.

[Manufacturing of lithium-ion secondary battery]
As shown in FIG. 1, the electrode group was housed in a battery outer body made of an aluminum laminated film. The opening of the battery container was closed by taking out the positive electrode current collecting tab and the negative electrode current collecting tab to the outside inside the battery exterior, and the lithium ion secondary battery of Example 1 was produced. The aluminum laminate film is a laminate of polyethylene terephthalate (PET) film / aluminum foil / sealant layer (polypropylene or the like). The design capacity of the produced lithium ion secondary battery was 20 mAh.

<Example 2>
Same as in Example 1 except that 1-ethyl-3-methyl-imidazolium bis (fluorosulfonyl) imide (EMIFSI) was used as the ionic liquid in the preparation of the positive electrode, the negative electrode and the electrolyte sheet instead of Py13-FSI. A lithium ion secondary battery was produced by the above method.

<Example 3>
In the preparation of the positive electrode, the negative electrode and the electrolyte sheet, the lithium ion secondary battery was prepared by the same method as in Example 1 except that the first lithium salt and the second lithium salt were dissolved at a mass ratio of 99: 1. Made.

<Example 4>
Same as in Example 3 except that 1-ethyl-3-methyl-imidazolium bis (fluorosulfonyl) imide (EMIFSI) was used as the ionic liquid in the preparation of the positive electrode, the negative electrode and the electrolyte sheet instead of Py13-FSI. A lithium ion secondary battery was produced by the above method.

<Example 5>
The same as in Example 3 except that lithium bis (trifluoromethanesulfonyl) imide (Li [TFSI]) was used instead of Li [FSI] as the first lithium salt in the preparation of the positive electrode, the negative electrode and the electrolyte sheet. A lithium ion secondary battery was produced by the method.

<Example 6>
In the preparation of the positive electrode, the negative electrode and the electrolyte sheet, a lithium ion secondary battery was prepared by the same method as in Example 3 except that lithium bisoxalate boronate (LiBOB) was used instead of _{LiPF 6 as the second lithium salt.} Was produced.

<Example 7>
In the preparation of the positive electrode, the negative electrode and the electrolyte sheet, the lithium ion secondary battery was prepared by the same method as in Example 1 except that the first lithium salt and the second lithium salt were dissolved in a mass ratio of 3: 7. Made.

<Comparative example 1>
In the production of the negative electrode, a lithium ion secondary battery was produced by the same method as in Example 1 except that only the second lithium salt was used without using the first lithium salt.

<Comparative example 2>
In the production of the negative electrode, a lithium ion secondary battery was produced by the same method as in Example 1 except that only the first lithium salt was used without using the second lithium salt.

<Evaluation of lithium-ion secondary battery>
(Evaluation of initial characteristics)
Using a charging / discharging device (BATTERY TEST UNIT, manufactured by IEM Co., Ltd.), the lithium ion secondary batteries produced in Examples 1 to 7 and Comparative Examples 1 to 2 have a current value of 0.2 C and a charge termination voltage at 25 ° C. Constant current charging was performed at 4.2 V. After a 15-minute rest, constant current discharge was performed at a current value of 0.2 C and a discharge end voltage of 2.7 V. Charging and discharging were repeated three times under the above charging and discharging conditions, and the third discharging capacity (initial capacity) was measured. The initial characteristics of the lithium ion secondary battery were calculated from the following formula, and the initial characteristics were evaluated according to the following criteria. The evaluation results are shown in Table 1.
Initial characteristics (%) = (initial capacity / design capacity) x 100
A: Initial characteristics are 95% or more.
B: Initial characteristics are 90% or more and less than 95%.
C: Initial characteristics are 70% or more and less than 90%.
D: Initial characteristics are less than 70%.

(Evaluation of charging characteristics)
For the lithium ion secondary batteries produced in Examples 1 to 7 and Comparative Examples 1 and 2, charging and discharging were repeated three times under the same conditions as the charging and discharging conditions in the evaluation of the initial characteristics, and then the current value was 1C at 25 ° C. It was evaluated whether or not the battery was charged to a final charge voltage of 4.2 V by performing constant current charging. The evaluation results are shown in Table 1. In Table 1, the case where the battery is charged to 4.2 V is referred to as “A”, and the case where the battery is not charged to 4.2 V is referred to as “B”.

1 ... Secondary battery, 6 ... Positive electrode, 7 ... Electrolyte layer, 8 ... Negative electrode, 9 ... Positive electrode current collector, 10 ... Positive electrode mixture layer, 11 ... Negative electrode current collector, 12 ... Negative electrode mixture layer.

Claims (13)

An electrode current collector and an electrode mixture layer provided on the electrode current collector are provided.
The electrode mixture layer contains an ionic liquid and an electrolyte salt.
An electrode for a secondary battery, wherein the electrolyte salt contains a first lithium salt which is an imide-based lithium salt and a second lithium salt different from the first lithium salt. The electrode according to claim 1, wherein the anion component of the first lithium salt contains at least one selected from the group consisting of a bis (fluorosulfonyl) imide anion and a bis (trifluoromethanesulfonyl) imide anion. The electrode according to claim 1 or 2, wherein the anion component of the second lithium salt contains at least one selected from the group consisting of a hexafluorophosphate anion and a bisoxalate borate anion. Claim 1 that the content of the first lithium salt is 50 parts by mass or more with respect to a total of 100 parts by mass of the content of the first lithium salt and the content of the second lithium salt. The electrode according to any one of 3 to 3. The ionic liquid contains at least one selected from the group consisting of a chain quaternary onium cation, a piperidinium cation, a pyroridinium cation, a pyridinium cation, and an imidazolium cation as a cation component, and contains as an anion component. The electrode according to any one of claims 1 to 4, which contains at least one of an ionic components represented by the following general formula (1).
N (SO ₂ C _m F _{2 m + 1} ) (SO ₂ C _n F _{2n + 1} ) ⁻ (1)
[M and n each independently represent an integer of 0 to 5. ] For a secondary battery, which contains an ionic liquid and an electrolyte salt, wherein the electrolyte salt contains a first lithium salt which is an imide-based lithium salt and a second lithium salt different from the first lithium salt. Electrolyte layer. The electrolyte layer according to claim 6, wherein the anion component of the first lithium salt contains at least one selected from the group consisting of a bis (fluorosulfonyl) imide anion and a bis (trifluoromethanesulfonyl) imide anion. The electrolyte layer according to claim 6 or 7, wherein the anion component of the second lithium salt contains at least one selected from the group consisting of a hexafluorophosphate anion and a bisoxalate borate anion. 6. The content of the first lithium salt is 50 parts by mass or more with respect to 100 parts by mass in total of the content of the first lithium salt and the content of the second lithium salt. The electrolyte layer according to any one of 8 to 8. The ionic liquid contains at least one selected from the group consisting of a chain quaternary onium cation, a piperidinium cation, a pyroridinium cation, a pyridinium cation, and an imidazolium cation as a cation component, and contains as an anion component. The electrolyte layer according to any one of claims 6 to 9, which contains at least one of the anionic components represented by the following general formula (1).
N (SO ₂ C _m F _{2 m + 1} ) (SO ₂ C _n F _{2n + 1} ) ⁻ (1)
[M and n each independently represent an integer of 0 to 5. ] A secondary battery including a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode.
A secondary battery in which at least one of the positive electrode and the negative electrode is the electrode according to any one of claims 1 to 5. A secondary battery including a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode.
A secondary battery in which the electrolyte layer is the electrolyte layer according to any one of claims 6 to 10. A secondary battery including a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode.
At least one of the positive electrode and the negative electrode is the electrode according to any one of claims 1 to 5.
A secondary battery in which the electrolyte layer is the electrolyte layer according to any one of claims 6 to 10.

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