JP6302322B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  A lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. And a positive electrode and a negative electrode, ie, an electrode, are comprised by mix | blending an electrode active material, and normally a conductive support agent and a binder are further mix | blended. Among them, the electrode active material is an important factor related to the capacity of the lithium ion secondary battery, and conventionally, graphite (graphite) is mainly used as the negative electrode active material.

  On the other hand, silicon attracts attention as a negative electrode active material that can realize a higher capacity lithium ion secondary battery. The theoretical capacity of the lithium ion secondary battery is, for example, 372 mAh / g when graphite is used as the negative electrode active material, and 4199 mAh / g when silicon is used.

  However, when a negative electrode is configured using silicon, it is known that the negative electrode expands and contracts in the process of inserting and extracting lithium ions during charge and discharge. In the negative electrode, four lithium ions can be occluded and released with respect to one silicon atom, and when the secondary battery operates, the negative electrode can expand and contract four times. Due to this expansion and contraction during charge / discharge, the negative electrode has a reduced current collecting property, and the discharge capacity is greatly reduced. As described above, the lithium ion secondary battery using silicon as the negative electrode active material has a problem that the capacity retention rate is low when charging and discharging are repeated.

On the other hand, a negative electrode using silicon oxide as a negative electrode active material is disclosed (see Patent Document 1). In a lithium ion secondary battery equipped with such a negative electrode, although it is possible to suppress a decrease in capacity retention rate when charging and discharging are repeatedly performed, lithium reacts irreversibly with silicon oxide in the initial charging step, and lithium silicate ( By-products such as Li ₄ SiO ₄ ) are produced, and this lithium cannot be involved in the discharge thereafter, resulting in a problem that the discharge capacity is reduced.

  As a method for solving such a decrease in discharge capacity, a method of forming a negative electrode by forming a silicon oxide film by a vacuum deposition method or a sputtering method has been disclosed (see Patent Document 2).

JP-A-6-325765 JP 2004-349237 A

  However, the technique disclosed in Patent Document 2 has a problem that the ratio of the discharge capacity at the first cycle to the rated capacity of the lithium ion secondary battery, that is, the so-called capacity expression rate is only about 80%, which is insufficient. there were.

  This invention is made | formed in view of the said situation, and makes it a subject to provide a lithium ion secondary battery with a high capacity | capacitance expression rate and a capacity | capacitance maintenance factor.

In order to solve the above problems, the present invention has a negative electrode active material layer formed using a negative electrode material comprising silicon oxide, a particulate conductive additive, a fibrous conductive additive and a binder, and lithium. Provided is a lithium ion secondary battery comprising a pre-doped negative electrode.
In the lithium ion secondary battery of the present invention, the particulate conductive additive is preferably carbon black, and the fibrous conductive additive is preferably a carbon nanotube.

  According to the present invention, a lithium ion secondary battery having a high capacity development rate and a high capacity maintenance rate is provided.

It is a front view which illustrates typically the principal part of the lithium ion secondary battery concerning the present invention. A The ¹ H-NMR data in Preparation Example 1, (a) is The ¹ H-NMR data of the boron trifluoride-diethyl ether complex for comparison, (b) the resulting lithium oxalate - boron trifluoride complex ¹ H-NMR data. A ¹⁹ F-NMR data in Preparation Example 1, (a) is ¹⁹ F-NMR data of the boron trifluoride-diethyl ether complex for comparison, (b) the resulting lithium oxalate - boron trifluoride complex ¹⁹ F-NMR data. It is IR data in manufacture example 1, (a) is IR data of the comparative lithium oxalate, (b) is IR data of the obtained lithium oxalate-boron trifluoride complex. It is the imaging data acquired with the scanning electron microscope (SEM) of the negative electrode active material layer in the negative electrode precursor obtained in Example 1. FIG.

<Lithium ion secondary battery>
The lithium ion secondary battery according to the present invention has a negative electrode active material layer formed using a negative electrode material in which silicon oxide, a particulate conductive auxiliary, a fibrous conductive auxiliary, and a binder are blended, and lithium Is provided with a pre-doped negative electrode.
This lithium ion secondary battery uses a particulate conductive aid and a fibrous conductive aid in combination, and further uses a negative electrode in which lithium is pre-doped, so that the capacity development rate and charge / discharge are repeated. Both the capacity retention rate is high and the charge / discharge characteristics are excellent.

In this specification, the “capacity development rate” in a lithium ion secondary battery means the ratio (%) of the discharge capacity at the first cycle to the rated capacity, and the expression “{[discharge capacity at the first cycle (mAh)”. ] / [Rated capacity (mAh)]} × 100 ”.
Further, in this specification, the “capacity maintenance ratio” in the lithium ion secondary battery is the ratio of the discharge capacity at a specific number of cycles to the discharge capacity of the first cycle (%) when the charge / discharge cycle is repeated. ) And is calculated by the formula “{[discharge capacity at a specific number of cycles (mAh)] / [discharge capacity at the first cycle (mAh)]} × 100)”. Here, the “specific number of cycles” is preferably 50 cycles or more.

[Negative electrode material]
In the present invention, the negative electrode material is formed by blending silicon oxide, a particulate conductive additive, a fibrous conductive additive and a binder, and the particulate conductive aid and the fibrous conductive assistant are added to silicon oxide. This is different from conventional negative electrode materials in that an agent is used in combination as an essential component.

(Silicon oxide)
_{Examples of the} silicon oxide include those represented by the general formula “SiO _z (wherein z is any number from 0.5 to 1.5)”. Here, when the silicon oxide is viewed in “SiO” units, this SiO is amorphous SiO, or around the Si of the nanocluster so that the molar ratio of Si: SiO ₂ is about 1: 1. This is a composite of Si and SiO _{2 in} which SiO ₂ exists. SiO ₂ is presumed to have a buffering action against the expansion and contraction of Si during charging and discharging.

The silicon oxide is preferably in the form of powder, more preferably in the form of particles, for example, the average particle diameter is preferably 30 μm or less, more preferably 20 μm or less, and 10 μm or less. Is particularly preferable, and most preferably 2.0 μm or less. Further, although depending on the blending ratio of silicon oxide and binder, the average particle diameter tends to be most preferable when it is 1.0 μm or less. By using such finely powdered silicon oxide, the effect of the combined use of the particulate conductive auxiliary and the fibrous conductive auxiliary can be obtained more remarkably.
The average particle diameter of silicon oxide is obtained, for example, by measuring the particle diameter of about 100 arbitrary silicon oxide particles using an electron microscope and calculating the average value.
For example, the average particle diameter of silicon oxide can be adjusted to a desired value by pulverizing by a known method using a ball mill or the like.

  In the negative electrode material, the ratio of the amount of silicon oxide to the total amount of silicon oxide, particulate conductive additive, fibrous conductive additive and binder is preferably 40 to 85% by mass, and is preferably 55 to 80%. More preferably, it is mass%. When the proportion of the compounding amount of silicon oxide is not less than the lower limit value, the lithium ion secondary battery has a further improved discharge capacity, and the proportion of the compounding amount of silicon oxide is not more than the upper limit value, so that the negative electrode It is easy to maintain a stable structure.

(Particulate conductive aid)
The particulate conductive aid is not particularly limited as long as it is in the form of particles functioning as a conductive aid, and preferred examples include carbon black such as acetylene black and ketjen black; graphite (graphite); fullerene and the like. It can be illustrated.

The particulate conductive auxiliary agent preferably has an average particle size of 10 to 100 nm, and more preferably 15 to 60 nm. Moreover, it is preferable that the particulate conductive auxiliary agent has a structure in which the particles are connected to each other, such as one in which each particle is connected in a daisy chain. By using the particulate conductive additive having such an average particle diameter or structure, the effect of the combined use with the fibrous conductive additive can be more remarkably obtained.
The average particle diameter of the particulate conductive auxiliary agent can be determined and adjusted by the same method as in the case of the average particle diameter of the silicon oxide.

  In the negative electrode active material layer described later, the particulate conductive auxiliary agent forms a structure in which fine particles such as nanoparticles are connected and increases the contact area between silicon oxide and the fibrous conductive auxiliary agent described later. It is presumed that it contributes to the improvement of sex.

  The particulate conductive auxiliary may be used singly or in combination of two or more. When two or more are used in combination, the combination and ratio are appropriately selected according to the purpose. That's fine.

  In the negative electrode material, the ratio of the amount of the particulate conductive additive to the total amount of silicon oxide, particulate conductive additive, fibrous conductive additive and binder is preferably 3 to 30% by mass, More preferably, it is 5-20 mass%. The proportion of the blending amount of the particulate conductive additive is more prominently obtained by using the particulate conductive additive, since the proportion of the blended conductive additive is equal to or greater than the lower limit. Is less than or equal to the above upper limit, the effect of the combined use with the fibrous conductive additive is more remarkably obtained.

(Fibrous conductive aid)
The fibrous conductive assistant is not particularly limited as long as it is a fibrous substance that functions as a conductive assistant, but preferred examples include carbon nanotubes and carbon nanohorns.

The fibrous conductive additive has an average fiber diameter of preferably 5 nm to 300 nm, and more preferably 10 nm to 150 nm. The fibrous conductive additive has an average fiber length of preferably 0.1 μm to 30 μm, and more preferably 0.5 μm to 20 μm. By using such a fibrous conductive additive, the effect of the combined use with the particulate conductive aid can be obtained more remarkably.
The average fiber diameter of the fibrous conductive assistant is obtained, for example, by measuring the fiber diameter of about 100 arbitrary fibrous conductive assistants using an electron microscope and calculating the average value. Similarly, the average fiber length of the fibrous conductive assistant is determined by measuring the fiber length of about 100 arbitrary fibrous conductive assistants using an electron microscope and calculating the average value.

  The fibrous conductive auxiliary agent contributes to the structural stabilization of the negative electrode active material layer by forming a network structure in the entire negative electrode active material layer, preferably in the negative electrode active material layer described later, and the negative electrode active material layer. It is presumed that a conductive network is formed therein and contributes to improvement of conductivity.

  The fibrous conductive assistant may be used alone or in combination of two or more. When two or more are used in combination, the combination and ratio are appropriately selected depending on the purpose. That's fine.

  In the negative electrode material, the ratio of the amount of fibrous conductive additive to the total amount of silicon oxide, particulate conductive auxiliary, fibrous conductive auxiliary and binder is preferably 1 to 25% by mass, It is more preferable that it is 2-15 mass%. The ratio of the blending amount of the fibrous conductive additive is more prominently obtained by using the fibrous conductive additive because the ratio of the blending amount of the fibrous conductive assistant is not less than the lower limit. Is less than or equal to the above upper limit value, the effect of the combined use with the particulate conductive additive is more remarkably obtained.

  In the negative electrode material, the mass ratio (mixing mass ratio) of the blending amount of “particulate conductive assistant: fibrous conductive assistant” is preferably 90:10 to 30:70, and 80:20 to 40: 60 is more preferable. When the blending mass ratio of the particulate conductive assistant and the fibrous conductive assistant is in such a range, the effect of the combined use of the particulate conductive assistant and the fibrous conductive assistant can be obtained more remarkably.

(binder)
The binder may be a known one, and preferable examples thereof include polyacrylic acid (PAA), lithium polyacrylate (PAALi), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF- Examples thereof include HFP), styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene glycol (PEG), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), and polyimide (PI).
The binder may be used alone or in combination of two or more. When two or more are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  In the negative electrode material, the ratio of the blending amount of the binder to the total blending amount of silicon oxide, particulate conductive auxiliary, fibrous conductive auxiliary and binder is preferably 3 to 30% by mass, and 5 to 20% by mass. % Is more preferable. When the proportion of the blending amount of the binder is equal to or higher than the lower limit value, the negative electrode structure is more stably maintained, and when the proportion of the blending amount of the binder is equal to or lower than the upper limit value, the discharge capacity is further improved. .

(Other ingredients)
The negative electrode material may be formed by further blending other components not corresponding to these in addition to silicon oxide, particulate conductive auxiliary, fibrous conductive auxiliary and binder.
The other components are not particularly limited and can be arbitrarily selected according to the purpose. As preferable components, the compounding components (silicon oxide, particulate conductive assistant, fibrous conductive assistant, binder) are dissolved or dispersed. Examples of the solvent used for the treatment are:
Such a negative electrode material further mixed with a solvent is preferably a liquid composition having fluidity at the time of use.

The said solvent can be arbitrarily selected according to the kind of said mixing | blending component, As a preferable thing, water and an organic solvent can be illustrated.
Preferred examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol and 2-propanol; linear or cyclic amides such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide (DMF); acetone And the like.
The solvents may be used alone or in combination of two or more, and when two or more are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  The amount of the solvent in the negative electrode material is not particularly limited, and may be adjusted as appropriate according to the purpose. For example, when a negative electrode material, which is a liquid composition containing a solvent, is applied and dried to form a negative electrode active material layer to be described later, the liquid composition has a viscosity suitable for coating. What is necessary is just to adjust the compounding quantity of a solvent. Specifically, in the negative electrode material, the blending of the solvent so that the ratio of the total amount of the blending components other than the solvent to the total amount of the blending components is preferably 5 to 60% by mass, more preferably 10 to 35% by mass. Adjust the amount.

  When a component other than the solvent (other solid component) is blended as the other component, the proportion of the blended amount of the other solid component with respect to the total amount of the blended component other than the solvent in the negative electrode material is 10% by mass. Or less, more preferably 5% by mass or less.

  The negative electrode material is particularly preferably one in which the particulate conductive auxiliary is carbon black and the fibrous conductive auxiliary is carbon nanotubes.

The said negative electrode material can be manufactured by mix | blending the said silicon oxide, a particulate-form conductive support agent, a fibrous conductive support agent, a binder, and another component as needed.
At the time of blending each component, it is preferable to add these components and thoroughly mix them by various means.
Each component may be mixed while sequentially adding them, or may be mixed after all components have been added, as long as the blended components are mixed uniformly.

  When the solvent is blended as the other component, the solvent is at least partially selected from the group consisting of the silicon oxide, the particulate conductive aid, the fibrous conductive aid, the binder, and other solid components. One or more of these components may be mixed in advance and blended as a solution or dispersion of these components. The total amount of the solvent used for preparing such a solution or dispersion may be sufficient.

The mixing method of each component is not specifically limited, For example, the well-known method using a stirring bar, a stirring blade, a ball mill, a stirrer, an ultrasonic disperser, an ultrasonic homogenizer, a self-revolving mixer etc. may be applied. A plurality of methods may be combined.
What is necessary is just to set suitably mixing conditions, such as mixing temperature and mixing time, according to various methods. Usually, the temperature during mixing is preferably 10 to 50 ° C, more preferably 15 to 35 ° C. Moreover, it is preferable that mixing time is 3 to 40 minutes, and it is more preferable that it is 5 to 20 minutes.

  The composition obtained by adding and mixing each component may be used as a negative electrode material as it is, or, for example, by removing a part of the blended solvent by distillation or the like, What was obtained by performing additional operations may be used as the negative electrode material.

[Negative electrode]
In the present invention, the negative electrode has a negative electrode active material layer formed using the negative electrode material and is pre-doped with lithium. For example, the negative electrode active material layer may be a current collector (negative electrode collector). Electric body) and is configured.
Such a negative electrode can be produced in the same manner as a known negative electrode except that the negative electrode material is used.

The current collector may be a known one, and preferable materials include those having conductivity such as copper (Cu), aluminum (Al), titanium (Ti), nickel (Ni), and stainless steel. it can.
Moreover, it is preferable that the said electrical power collector is a sheet form, and it is preferable that the thickness is 5-20 micrometers.

  Although the thickness of a negative electrode active material layer is not specifically limited, It is preferable that it is 5-100 micrometers, and it is more preferable that it is 10-60 micrometers.

The negative electrode active material layer may be formed on the current collector using the negative electrode material.
For example, when a liquid composition containing a solvent is used as the negative electrode material, the negative electrode active material layer can be formed by coating and drying the liquid composition.

  Examples of the coating method of the liquid composition include various coating methods such as a method using various coaters such as a bar coater, a gravure coater, a comma coater, and a lip coater; a doctor blade method; a dipping method.

  The liquid composition may be dried by a known method under normal pressure or reduced pressure. And it is preferable that drying temperature is 40-180 degreeC. When the drying temperature is equal to or higher than the lower limit value, drying can be performed in a short time, and when the drying temperature is equal to or lower than the upper limit value, the effect of suppressing the oxidation of the current collector is increased. The drying time may be appropriately adjusted according to the drying temperature, and can be, for example, 12 to 48 hours.

  The negative electrode active material layer may be formed directly on the current collector, or may be formed on another base material and then moved to the current collector, and may be crimped on the current collector. Good. And also when forming a negative electrode active material layer directly on a collector, you may make it crimp on a collector.

In the present invention, the negative electrode is further pre-doped with lithium, and at least the negative electrode active material layer is pre-doped with lithium.
The method for producing a negative electrode in which lithium is pre-doped is not particularly limited, but has a negative electrode active material layer, and is a negative electrode in which lithium is not pre-doped (hereinafter sometimes abbreviated as “negative electrode precursor”), preferably It is preferable that the negative electrode active material layer of the negative electrode precursor is brought into contact with an electrolytic solution, and the contact surface of the negative electrode precursor with the electrolytic solution is further brought into contact with metallic lithium. By applying such a method, lithium can be pre-doped more easily in a wide range in the negative electrode precursor. The electrolytic solution to be contacted is preferably the same as the electrolytic solution used when producing a lithium ion secondary battery using this negative electrode.
The metal lithium to be contacted is preferably in the form of a sheet (metal lithium foil).
Lithium pre-doping needs to be performed using metal lithium (Li) instead of lithium ions (Li ⁺ ).

The amount of lithium pre-doped on the negative electrode is preferably 1 to 4 times the molar amount, more preferably 2 to 4 times the molar amount of silicon dioxide (SiO ₂ ) in the negative electrode active material layer. The molar amount is preferably 3 to 4 times.

Since the negative electrode is pre-doped with lithium, it is presumed that this lithium reacts irreversibly with silicon dioxide in the negative electrode active material layer to generate lithium silicate (Li ₄ SiO ₄ ) in advance. . And the lithium ion secondary battery according to the present invention having such a negative electrode suppresses the reaction with the silicon oxide in the negative electrode active material layer even if lithium is occluded in the negative electrode in the initial charging step. It is presumed that the discharge during discharge is not hindered and the decrease in discharge capacity is suppressed. As will be described later, the lithium ion secondary battery according to the present invention has excellent charge / discharge characteristics.

  The lithium ion secondary battery according to the present invention is characterized by including the negative electrode, and can have the same configuration as a conventional lithium ion secondary battery except that the negative electrode is provided. A negative electrode, a positive electrode, and an electrolyte solution, a gel electrolyte, or a solid electrolyte are provided, and a separator may be provided between the negative electrode and the positive electrode as necessary.

[Positive electrode]
The positive electrode may be a known one, and a positive electrode active material layer formed using a positive electrode material in which a positive electrode active material, a binder and a solvent, and a conductive auxiliary agent are blended as necessary, Examples thereof include those provided on the positive electrode current collector. As the positive electrode, a commercially available product may be used.

  The binder, solvent and current collector in the positive electrode may all be the same as the binder, solvent and current collector in the negative electrode.

The conductive auxiliary in the positive electrode may be a known one, and preferable examples thereof include graphite (graphite); carbon black such as ketjen black and acetylene black; carbon nanotube; carbon nanohorn; graphene; fullerene.
The conductive auxiliary in the positive electrode may be used alone or in combination of two or more. When two or more are used in combination, the combination and ratio are appropriately selected according to the purpose. That's fine.

As the positive electrode active material, a lithium metal acid compound represented by the general formula “LiM _x O _y (wherein M is a metal; x and y are composition ratios of metal M and oxygen O)” Can be illustrated.
Examples of such a metal acid lithium compound include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and the like, and olivine iron phosphate having a similar composition. Lithium (LiFePO ₄ ) can also be used.
In the above general formula, M may be a plurality of types of the lithium metal acid compound. As such a metal acid lithium compound, the general formula “LiM ¹ _p M ² _q M ³ _r O _y (formula Where M ¹ , M ² and M ³ are different types of metals; p, q, r and y are the composition ratios of the metals M ¹ , M ² and M ³ and oxygen O). What is represented can be exemplified. Here, p + q + r = x.
Examples of such a metal acid lithium compound include LiNi _0.33 Mn _0.33 Co _0.33 O ₂ .
A positive electrode active material may be used individually by 1 type, may use 2 or more types together, and when using 2 or more types together, the combination and ratio may be suitably selected according to the objective.

  The ratio of the amount of each of the positive electrode active material, the binder, the solvent, and the conductive additive to the total amount of the compounding components in the positive electrode material is the ratio of the negative electrode active material and the binder to the total amount of the compounding components in the negative electrode material. , The solvent, and the proportion of each of the conductive additives can be the same.

  Although the thickness of a positive electrode active material layer is not specifically limited, It is preferable that it is 20-60 micrometers.

  The positive electrode active material layer can be formed by the same method as in the case of the negative electrode active material layer except that a positive electrode material is used instead of the negative electrode material.

[Electrolyte]
As the electrolytic solution, (A) lithium carboxylate, (B) boron trifluoride and / or boron trifluoride complex, and (C) an organic solvent (hereinafter referred to as “first electrolysis”). (It may be abbreviated as “liquid”).

  (A) Lithium carboxylic acid salt is an electrolyte, and an aliphatic carboxylic acid, an alicyclic carboxylic acid, and a fragrance as long as the carboxy group constitutes a lithium salt (—C (═O) —OLi). Any lithium salt of a group carboxylic acid may be used, and any lithium salt of a monovalent carboxylic acid and a polyvalent carboxylic acid may be used. And as for (A) carboxylic acid lithium salt, the number of the carboxy group which comprises lithium salt is not specifically limited. For example, when the number of carboxy groups is 2 or more, all the carboxy groups may constitute a lithium salt, or only some of the carboxy groups may constitute a lithium salt.

(A) Preferred lithium carboxylate is lithium formate (HCOOLi), lithium acetate (CH ₃ COOLi), lithium propionate (CH ₃ CH ₂ COOLi), lithium butyrate (CH ₃ (CH ₂ ) ₂ COOLi) , Lithium isobutyrate ((CH ₃ ) ₂ CHCOOLi), lithium valerate (CH ₃ (CH ₂ ) ₃ COOLi), lithium isovalerate ((CH ₃ ) ₂ CHCH ₂ COOLi), lithium caproate (CH ₃ (CH _{2) 4} COOLi) 1 monovalent lithium salts of carboxylic acids such as, lithium oxalate _((COOLi) 2), lithium malonate _(LiOOCCH 2 COOLi), lithium succinate _{((CH 2 COOLi) 2)} , lithium glutarate ( LiOOC (CH ₂ ) ₃ COOLi), adipine Lithium salt of a divalent carboxylic acid such as lithium acid ((CH ₂ CH ₂ COOLi) ₂ ); lithium salt of a monovalent carboxylic acid having a hydroxyl group such as lithium lactate (CH ₃ CH (OH) COOLi); lithium tartrate (( CH (OH) COOLi) ₂ ), lithium salt of a divalent carboxylic acid having a hydroxyl group such as lithium malate (LiOOCCH ₂ CH (OH) COOLi); lithium maleate (LiOOCCH = CHCOOLi, cis body), lithium fumarate ( Lithium salt of unsaturated divalent carboxylic acid such as LiOOCCH = CHCOOLi, trans isomer); lithium salt of trivalent carboxylic acid such as lithium citrate (LiOOCCH ₂ C (COOLi) (OH) CH ₂ COOLi) (3 having a hydroxyl group) Lithium salt of divalent carboxylic acid), and lithium formate Lithium acetate, lithium oxalate, and lithium succinate are more preferable, and lithium oxalate is particularly preferable.

  (A) Lithium carboxylate may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

(B) Boron trifluoride and boron trifluoride complex are those that undergo a complex formation reaction with (A) lithium carboxylate, and boron trifluoride complex is different from boron trifluoride (BF ₃ ). Coordinated to the component.

Preferred examples of the boron trifluoride complex include boron trifluoride dimethyl ether complex (BF ₃ .O (CH ₃ ) ₂ ), boron trifluoride diethyl ether complex (BF ₃ .O (C ₂ H ₅ ) ₂ ), three Boron fluoride di n-butyl ether complex (BF ₃ · O (C ₄ H ₉ ) ₂ ), boron trifluoride di tert-butyl ether complex (BF ₃ · O ((CH ₃ ) ₃ C) ₂ ), trifluoride Boron trifluoride alkyl ether complexes such as boron tert-butyl methyl ether complex (BF ₃ .O ((CH ₃ ) ₃ C) (CH ₃ )), boron trifluoride tetrahydrofuran complex (BF ₃ .OC ₄ H ₈ ) Boron trifluoride methanol complex (BF ₃ · HOCH ₃ ), boron trifluoride propanol complex (BF ₃ · HOC ₃ H ₇ ), boron trifluoride phenol A boron trifluoride alcohol complex such as a complex (BF ₃ .HOC ₆ H ₅ ) can be exemplified.
(B) As boron trifluoride and / or boron trifluoride complex, it is preferable to use the boron trifluoride complex from the viewpoint that it is easy to handle and the complex formation reaction proceeds more smoothly.

  (B) As boron trifluoride and / or a boron trifluoride complex, 1 type may be used independently and 2 or more types may be used together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  The blending amount of (B) boron trifluoride and / or boron trifluoride complex is not particularly limited, and (B) boron trifluoride and / or boron trifluoride complex or (A) lithium carboxylate type What is necessary is just to adjust suitably according to. Usually, the molar ratio of [(B) Boron trifluoride and / or boron trifluoride complex (mole number)] / [Mixed (A) moles of lithium atoms in carboxylic acid lithium salt] Is preferably 0.5 or more, and more preferably 0.7 or more. By setting it as such a range, the solubility of (A) lithium carboxylic acid salt with respect to the (C) organic solvent improves more. The upper limit of the molar ratio is not particularly limited as long as the effect of the present invention is not hindered, but is preferably 2.0, and more preferably 1.5.

(C) Although the organic solvent is not particularly limited, specific examples of preferable organic solvents include carbonate compounds such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, vinylene carbonate; γ-butyrolactone, etc. Lactone compounds; carboxylic acid ester compounds such as methyl formate, methyl acetate, and methyl propionate; ether compounds such as tetrahydrofuran and dimethoxyethane; nitrile compounds such as acetonitrile; and sulfone compounds such as sulfolane.
(C) An organic solvent may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

(C) The organic solvent is ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, vinylene carbonate, γ-butyrolactone, tetrahydrofuran, dimethoxyethane, methyl formate, methyl acetate, methyl propionate, acetonitrile and It is preferably at least one selected from the group consisting of sulfolane.
As the organic solvent (C) used in combination of two or more, those in which propylene carbonate and vinylene carbonate are blended, those in which propylene carbonate and ethylene carbonate are blended, and those in which ethylene carbonate and dimethyl carbonate are blended are preferable.

  The blending amount of the (C) organic solvent in the electrolytic solution is not particularly limited, and may be appropriately adjusted according to, for example, the type of the electrolyte. Usually, the blending amount may be adjusted so that the concentration of lithium atoms (Li) is preferably 0.2 to 3.0 mol / kg, more preferably 0.4 to 2.0 mol / kg. preferable.

Examples of the first electrolytic solution include a mixture of (E) a carboxylic acid lithium salt-boron trifluoride complex and (C) an organic solvent.
(E) As a carboxylic acid lithium salt-boron trifluoride complex, boron trifluoride (BF ₃ ) is coordinated to at least one carboxy group or lithium carboxy group in the carboxylic acid lithium salt. What was combined can be illustrated.
(E) As a carboxylic acid lithium salt which comprises a carboxylic acid lithium salt-boron trifluoride complex, the thing similar to (A) carboxylic acid lithium salt can be illustrated.

  The (E) carboxylic acid lithium salt-boron trifluoride complex contains, for example, (A) a lithium carboxylic acid salt, (B) boron trifluoride and / or boron trifluoride complex, and (C ′) a solvent. (A) a carboxylic acid lithium salt and (B) boron trifluoride and / or boron trifluoride complex are reacted (hereinafter abbreviated as “reaction process”), and the reaction after the reaction. A step of removing (C ′) solvent and (B) impurities derived from boron trifluoride and / or boron trifluoride complex from the liquid (hereinafter abbreviated as “removal step”). It can be manufactured by a manufacturing method. The (E) carboxylic acid lithium salt-boron trifluoride complex obtained by such a production method is such that (A) lithium carboxylic acid salt and (B) boron trifluoride and / or boron trifluoride complex are complexed. It has been formed by reaction.

  In this production method, (A) lithium carboxylate, (B) boron trifluoride and / or boron trifluoride complex are the same as described above. That is, (E) “lithium carboxylate” in the lithium carboxylate-boron trifluoride complex is the same as (A) the lithium carboxylate.

  (E) A lithium carboxylate-boron trifluoride complex may be used alone or in combination of two or more. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  The (C ′) solvent does not interfere with the complex formation reaction of (A) lithium carboxylic acid salt with (B) boron trifluoride and / or boron trifluoride complex in the reaction step, and can dissolve these. Although it will not specifically limit if it is a thing, An organic solvent is preferable and what can be distilled off under a normal pressure or pressure reduction is preferable.

  The boiling point of (C ′) solvent is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and particularly preferably 35 ° C. or higher. The boiling point of the (C ′) solvent is preferably 180 ° C. or lower, more preferably 150 ° C. or lower, and particularly preferably 120 ° C. or lower. (C ′) Since the boiling point of the solvent is not less than the lower limit, the reaction solution in the reaction step can be stirred at room temperature, so that the reaction step can be performed more easily. In addition, when the boiling point of the (C ′) solvent is not more than the above upper limit value, the (C ′) solvent can be more easily removed by distillation in the removing step.

(C ′) Preferred organic solvents in the solvent include chain carbonate compounds such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate (compounds having a carbonate ester bond in the chain structure); nitrile compounds such as acetonitrile; Cyclic ether compounds such as tetrahydrofuran (compounds having an ether bond in the cyclic structure); chain ether compounds such as diethyl ether and 1,2-dimethoxyethane (compounds having an ether bond in the chain structure); ethyl acetate, acetic acid Examples thereof include carboxylic acid ester compounds such as isopropyl.
Among these, as the organic solvent, a chain carbonate compound, a nitrile compound, and a cyclic ether compound are preferable.

  (C ') A solvent may be used individually by 1 type and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  In the removal step, as the impurities, (A) an excessive amount of (B) boron trifluoride and / or boron trifluoride complex remaining without reacting with the carboxylic acid lithium salt, and by-products generated therefrom More specifically, as the by-product, in the boron trifluoride complex which is the component (B), a component that was originally coordinated to boron trifluoride before the reaction can be exemplified. These impurities can be distilled off.

  (E) The 1st electrolyte solution using the lithium carboxylate-boron trifluoride complex is, for example, (A) lithium carboxylate and (B) boron trifluoride and / or boron trifluoride complex. Instead of blending, (E) by mixing a carboxylic acid lithium salt-boron trifluoride complex, (A) a carboxylic acid lithium salt, and (B) boron trifluoride and / or boron trifluoride complex. Can be obtained by the same method as the above-described first electrolytic solution. For example, the amount of (C) the organic solvent is not particularly limited, but the concentration of lithium atoms (Li) is preferably 0.2 to 3.0 mol / kg, more preferably 0.4 to 2.0 mol / kg. It is preferable to adjust the blending amount so as to be kg.

Further, as the electrolyte, lithium hexafluorophosphate as an electrolyte (LiPF _6), boron tetrafluoride lithium (LiBF _4), lithium bisfluorosulfonylimide (LiFSI), bis (trifluoromethanesulfonyl) imide (LiN (SO ₂ CF ₃ ) ₂ , LiTFSI) or other known lithium salt other than (A) carboxylic acid lithium salt dissolved in an organic solvent (hereinafter abbreviated as “second electrolyte solution”) There are also examples).

  The said electrolyte in a 2nd electrolyte solution may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

Examples of the organic solvent in the second electrolytic solution are the same as the organic solvent (C) in the first electrolytic solution.
The concentration of lithium atoms (Li) in the second electrolytic solution is the same as that in the first electrolytic solution.

The first and second electrolytic solutions are both the above-mentioned essential components ((A) lithium carboxylic acid salt, (B) boron trifluoride and / or boron trifluoride complex in the first electrolytic solution, (E In addition to (a) a carboxylic acid lithium salt-boron trifluoride complex, (C) an organic solvent; a lithium salt in the second electrolytic solution, an organic solvent), an optional component is blended within the range not impairing the effects of the present invention. It may be.
The arbitrary component may be appropriately selected according to the purpose and is not particularly limited.

  The 1st and 2nd electrolyte solution can be manufactured by mix | blending the said essential component and an arbitrary component as needed. The compounding method of each component is the same as the compounding method of each component at the time of manufacture of the said negative electrode material. However, the composition at the time of mixing is not particularly limited.

  In the present invention, the electrolytic solution contains (A) a carboxylic acid lithium salt and (B) a boron trifluoride and / or boron trifluoride complex, or (E) a carboxylic acid lithium salt-boron trifluoride complex. That is, the first electrolyte solution is preferable.

[Gel electrolyte]
As the gel electrolyte, (A) lithium carboxylate, (B) boron trifluoride and / or boron trifluoride complex, (C) an organic solvent, and (D) a matrix polymer are blended; E) A mixture of a lithium carboxylate-boron trifluoride complex, (C) an organic solvent, and (D) a matrix polymer can be exemplified, and if necessary, in the first and second electrolytic solutions An arbitrary component may be blended. Moreover, as said gel electrolyte, what further mix | blended (D) matrix polymer with the 1st electrolyte solution can be illustrated. Here, (A) carboxylic acid lithium salt, (B) boron trifluoride and / or boron trifluoride complex, (E) carboxylic acid lithium salt-boron trifluoride complex, and (C) organic solvent are any Is the same as in the first electrolyte solution.

The gel electrolyte may be molded into a desired shape using a mold.
In the gel electrolyte, components (electrolytic solution) other than (D) the matrix polymer are retained in the matrix polymer.

  The gel electrolyte may be one in which a part of the blended (C) organic solvent is removed by drying or the like, and an organic solvent (for dilution) different from the (C) organic solvent mainly remaining in the gel electrolyte at the time of production. Organic solvent) may be blended separately, and the organic solvent for dilution may be removed during the drying.

(D) A matrix polymer is not specifically limited, A well-known thing can be used suitably in the solid electrolyte field | area.
Preferred (D) matrix polymers include polyether polymers such as polyethylene oxide and polypropylene oxide (polymers having a polyether skeleton); polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polyfluoride. Fluorine-based polymers (polymers having fluorine atoms) such as vinylidene fluoride-hexafluoroacetone copolymer, polytetrafluoroethylene; poly (meth) methyl acrylate, poly (meth) ethyl acrylate, polyacrylamide, ethylene oxide units Examples include polyacrylic polymers such as polyacrylates (polymers having structural units derived from (meth) acrylates or acrylamides); polyacrylonitriles; polyphosphazenes; polysiloxanes Kill.

  (D) A matrix polymer may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  (D) The matrix polymer is polyethylene oxide, polypropylene oxide, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-hexafluoroacetone copolymer, polytetrafluoroethylene, It is preferably at least one selected from the group consisting of polyacrylonitrile, polyphosphazene and polysiloxane.

  In the gel electrolyte, the blending amount of the (D) matrix polymer is not particularly limited, and may be appropriately adjusted according to the type, but the ratio of the blending amount of the (D) matrix polymer to the total amount of blending components is 2-50. It is preferable that it is mass%. (D) When the blending amount of the matrix polymer is equal to or greater than the lower limit, the strength of the gel electrolyte is further improved, and (D) the blending amount of the matrix polymer is equal to or smaller than the upper limit, the lithium ion secondary battery Indicates better battery performance.

The organic solvent for dilution is preferably one that can sufficiently dissolve or disperse any of the components. Specifically, nitrile compounds such as acetonitrile; ether compounds such as tetrahydrofuran: amide compounds such as dimethylformamide It can be illustrated.
The organic solvent for dilution may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  The gel electrolyte is preferably one that does not exhibit fluidity in an environment of 40 ° C. or lower where a lithium ion secondary battery is normally used.

The blending method of each component at the time of manufacturing the gel electrolyte may be the same as in the case of the electrolytic solution.
The drying method for removing the diluting organic solvent is not particularly limited, and for example, a known method using a dry box, a vacuum desiccator, a vacuum dryer or the like may be applied.

[Solid electrolyte]
As the solid electrolyte, a composition obtained by blending (A) a lithium carboxylate, (B) boron trifluoride and / or boron trifluoride complex, an organic solvent for dilution, and (D) a matrix polymer. And (E) a composition obtained by blending a lithium carboxylate-boron trifluoride complex, an organic solvent for dilution, and (D) a matrix polymer, the organic solvent for dilution is removed by drying. And may be formed by blending arbitrary components in the first and second electrolytic solutions as necessary. Here, (A) carboxylic acid lithium salt, (B) boron trifluoride and / or boron trifluoride complex, (E) carboxylic acid lithium salt-boron trifluoride complex, and (C) organic solvent are any Are the same as those in the first electrolyte solution, and the organic solvent for dilution and (D) the matrix polymer are the same as those in the gel electrolyte.

  The solid electrolyte may be molded into a desired shape using a mold.

  In the solid electrolyte, the blending amount of the (D) matrix polymer is not particularly limited, and may be appropriately adjusted according to the type, but the ratio of the blending amount of the (D) matrix polymer to the total amount of blending components is 2 to 65. It is preferable that it is mass%. (D) When the blending amount of the matrix polymer is equal to or higher than the lower limit, the strength of the solid electrolyte (electrolyte membrane) is further improved, and (D) the blending amount of the matrix polymer is equal to or lower than the upper limit, Ion secondary batteries exhibit better battery performance.

The blending method of each component during the production of the solid electrolyte may be the same as in the case of the electrolytic solution.
The drying method for removing the diluting organic solvent may be the same as that for the gel electrolyte.

[Separator]
Although the material of the separator is not particularly limited, it can be exemplified by a microporous polymer film, a nonwoven fabric, glass fiber, and the like, and is preferably at least one selected from the group consisting of these materials.

FIG. 1 is a front view schematically illustrating a main part of a lithium ion secondary battery according to the present invention.
In the lithium ion secondary battery 1 shown here, a sheet-like negative electrode 3 and a positive electrode 4 are laminated via a separator 2. The separator 2 may be composed of a single layer or may be composed of a plurality of layers in which two or more layers are laminated. In FIG. 1, the electrolytic solution is not shown. As a lithium ion secondary battery using a gel electrolyte or a solid electrolyte instead of the electrolytic solution, a battery provided with a gel electrolyte or a solid electrolyte instead of the separator 2 or a gel electrolyte or a solid electrolyte containing a separator can be exemplified.

Here, each of the negative electrode 3 and the positive electrode 4 is shown one by one. However, the repeating structure of the repeating unit is repeated so that the repeating unit is a laminated structure in which the negative electrode 3, the separator 2 and the positive electrode 4 are laminated in this order. A configuration in which a plurality of the laminated structures are repeatedly laminated with a separator 2 interposed therebetween may be employed.
In addition, the lithium ion secondary battery 1 shown here illustrates one embodiment of the present invention, and the lithium ion secondary battery according to the present invention is not limited to this.

What is necessary is just to manufacture the said lithium ion secondary battery according to a well-known method, for example in the glove box or a dry air atmosphere, using the said electrolyte solution, a gel electrolyte, or a solid electrolyte, an electrode, etc.
For example, in the case of a lithium ion secondary battery equipped with a gel electrolyte, a gel electrolyte heated to a liquid state is applied onto one or both of the negative electrode and the positive electrode, and then the gel electrolyte is used. It can manufacture easily by laminating | stacking the negative electrode and positive electrode which were equipped through the gel electrolyte so that these electrode surfaces may oppose, and interposing a separator between these electrode surfaces as needed. The liquid gel electrolyte can be coated on the electrode surface by a method using various coaters such as a bar coater.
Further, for example, in the case of a lithium ion secondary battery provided with an electrolytic solution, the gel electrolyte described above is used except that the electrolytic solution is placed in contact with the electrode surfaces of the negative electrode and the positive electrode instead of the gel electrolyte. It can be easily manufactured by the same method as the provided lithium ion secondary battery.

  The shape of the lithium ion secondary battery is not particularly limited, and can be adjusted to various shapes such as a cylindrical shape, a square shape, a coin shape, and a sheet shape.

  When a lithium ion secondary battery uses (A) lithium carboxylate and (B) boron trifluoride and / or boron trifluoride complex or (E) lithium carboxylate-boron trifluoride complex, An interfacial film containing lithium fluoride (LiF) (hereinafter abbreviated as “SEI”) is formed on the negative electrode surface during initial charging. This SEI prevents solvent molecules solvated with lithium ions from entering the negative electrode during charge and discharge, suppresses destruction of the negative electrode structure, and contributes to improvement of the cycle characteristics of the lithium ion secondary battery.

The lithium ion secondary battery according to the present invention has a high capacity development rate, preferably 83% or more, more preferably 87% or more.
In addition, the lithium ion secondary battery according to the present invention exhibits excellent cycle characteristics. For example, when the charge / discharge cycle is repeated, the capacity retention rate at 100 cycles is preferably 85% or more, more preferably 90% or more.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples.

(1) Used raw materials The raw materials used in this example are shown below.
-Conductive auxiliary agent acetylene black ("HS-100" manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size 48 nm)
Carbon nanotubes (“NT-7” manufactured by Hodogaya Chemical Co., Ltd., average fiber diameter of 65 nm, average fiber length of 6 μm or more)
Binder Styrene-butadiene resin (hereinafter abbreviated as “SBR”) (manufactured by JSR)
Polyimide (“DREAMBOND” manufactured by IST Corporation)
・ (A) Lithium carboxylate Lithium oxalate (Alfa)
・ (B) Boron trifluoride complex Boron trifluoride diethyl ether complex (BF ₃ · O (C ₂ H ₅ ) ₂ ) (manufactured by Aldrich)
(C) Organic solvent Ethylene carbonate (hereinafter abbreviated as “EC”) (Kishida Chemical Co., Ltd.)
Propylene carbonate (hereinafter abbreviated as “PC”) (manufactured by Kishida Chemical Co., Ltd.)
(C ′) Solvent Dimethyl carbonate (hereinafter abbreviated as “DMC”) (manufactured by Kishida Chemical Co., Ltd.)

<Production of (E) Organic Acid Lithium Salt-Boron Trifluoride Complex>
[Production Example 1] (Production of lithium oxalate-boron trifluoride complex)
Lithium oxalate (22.3 g, 223 mmol) was weighed into a round bottom flask and suspended in 200 mL DMC. To this, boron trifluoride diethyl ether complex (63.3 g, 446 mmol) was slowly added dropwise at 23 ° C. and then stirred at room temperature (23 ° C.) for 24 hours. The reaction solution became transparent and no insoluble matter was observed. It was confirmed that the solution was uniform. Subsequently, the solvent and impurities were distilled off from the reaction solution using a rotary evaporator. Thereafter, the precipitated white solid was dried at 50 ° C. to obtain a white powder of lithium oxalate-boron trifluoride complex ((COOLi) _2. (BF ₃ ) ₂ ) (yield 96.5). %).

About the obtained lithium oxalate-boron trifluoride complex, the structure was confirmed by NMR and IR. The obtained data are shown in FIGS. In FIG. 2, (a) is ¹ H-NMR data of a boron trifluoride diethyl ether complex (BF ₃ .O (C ₂ H ₅ ) ₂ ) for comparison, and (b) is the obtained lithium oxalate-3 It is ¹ H-NMR data of a boron fluoride complex ((COOLi) _2. (BF ₃ ) ₂ ). In FIG. 3, (a) is ¹⁹ F-NMR data of a boron trifluoride diethyl ether complex (BF ₃ .O (C ₂ H ₅ ) ₂ ) for comparison, and (b) is the obtained lithium oxalate. - a ¹⁹ F-NMR data of the boron trifluoride complex. In FIG. 4, (a) is IR data of comparative lithium oxalate, and (b) is IR data of the obtained lithium oxalate-boron trifluoride complex.

Methyl hydrogen (—CH ₃ ) and methylene hydrogen (—O—) derived from diethyl ether of boron trifluoride diethyl ether complex (BF ₃ .O (C ₂ H ₅ ) ₂ ) observed in FIG. The peak of CH ₂ —) is not observed in FIG. 2 (b), which means that the obtained lithium oxalate-boron trifluoride complex is added to impurities such as boron trifluoride diethyl ether complex and diethyl ether. Supported that it was not mixed.
In addition, since there is a difference in the chemical shift of fluorine observed in FIGS. 3A and 3B, it was confirmed that the coordination environment of boron trifluoride (BF ₃ ) is different from each other, It supported that the target product, lithium oxalate-boron trifluoride complex, was obtained. Further, since no impurity peak was observed in FIG. 3B and the boiling point of boron trifluoride simple substance (BF ₃ ) was −100 ° C., the remaining three in the reaction process was used. The boron fluoride diethyl ether complex was removed in the removal step, and it was considered that the boron trifluoride diethyl ether complex was not mixed in the obtained lithium oxalate-boron trifluoride complex.
4A and 4B, it is confirmed that the coordination environments of the carbonyl groups are different from each other. This is because the target product is lithium oxalate-boron trifluoride. It supported that the complex was obtained.
From the above, the target lithium oxalate-boron trifluoride complex was obtained, and it was confirmed that impurities such as boron trifluoride diethyl ether complex and diethyl ether were not mixed therein.

<Manufacture of lithium ion secondary batteries>
[Example 1] (Production of negative electrode material)
Silicon monoxide (SiO, average particle diameter 0.8 μm, 69 parts by mass), acetylene black (10 parts by mass), carbon nanotubes (6 parts by mass), lithium polyacrylate (50 mol% of all acid groups are lithium salts) In the following, 10 parts by mass (sometimes abbreviated as “PAALi”) and SBR (5 parts by mass) are placed in a reagent bottle, and distilled water is added thereto to adjust the concentration. This concentration adjusted using a mixer was mixed for 3 minutes at 2000 rpm. Next, this mixture was subjected to a dispersion treatment for 10 minutes using an ultrasonic homogenizer, and then this dispersion was again mixed for 3 minutes at 2000 rpm using a self-revolving mixer to obtain a negative electrode material. All the operations so far were performed at 25 ° C. Table 1 shows each compounding component at this time and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components.

(Manufacture of electrolyte)
As an organic solvent, a mixed solvent of EC and PC (EC: PC = 30: 70 (volume ratio)) is weighed into a sample bottle, and a lithium oxalate-boron trifluoride complex (1.82 g) is added thereto, An electrolyte solution was obtained by mixing at 23 ° C. so that the concentration of lithium atoms in the lithium oxalate-boron trifluoride complex was 1.0 mol / kg.

(Manufacture of negative electrode)
By applying the negative electrode material obtained on both sides of a 15 μm thick copper foil using a bar coater, drying it on a hot plate at 50 ° C., and then pressing at 1 kN using a roll press A negative electrode active material layer having a thickness of 25 μm was formed on a copper foil as a current collector to obtain a negative electrode precursor.

  FIG. 5 is imaging data obtained by a scanning electron microscope (SEM) of the negative electrode active material layer in the obtained negative electrode precursor. In FIG. 5, (a) is 10000 times the imaging data of the negative electrode active material layer, (b) is the enlarged imaging data of the circled region a1 in (a), and (c) is in (b). This is enlarged image data of the circled region b1. As is clear from FIGS. 5A to 5C, SiO (silicon oxide) is uniformly dispersed in the negative electrode active material layer, while carbon nanotubes (fibrous conductive assistants) are negative electrode active materials. In the material layer, a network structure was formed in the entire negative electrode active material layer. In addition, acetylene black (particulate conductive additive) formed a structure in which the nanoparticles were connected in the peripheral portion of SiO in the negative electrode active material layer, and increased the contact area between SiO and acetylene black.

On the negative electrode active material layer of the obtained negative electrode precursor, the electrolytic solution obtained above is dropped so that the dropping amount is 50 μL / cm ^2, and a 200 μm thick lithium foil is stacked on the dropping surface. And by leaving still in this state for 24 hours, the negative electrode precursor was pre-doped with lithium to obtain a negative electrode. This lithium foil was removed from the negative electrode after pre-doping.

(Manufacture of positive electrode)
Nickel, cobalt, lithium manganate (Ni: Co: Mn = 1: 1: 1, LiNMC) (93 parts by mass), polyvinylidene fluoride (PVDF) (3 parts by mass), carbon black ( 4 parts by mass) was mixed to prepare a positive electrode mixture, which was dispersed in N-methylpyrrolidone (NMP) to prepare a positive electrode material (slurry). Next, the positive electrode material was applied to both sides of an aluminum foil having a thickness of 15 μm using a bar coater, dried under reduced pressure at 100 ° C., 0.1 MPa for 10 hours, and then roll-pressed, whereby a current collector was obtained. A positive electrode active material layer having a thickness of 60 μm was formed on the aluminum foil to obtain a positive electrode.

(Manufacture of lithium ion secondary batteries)
The negative electrode and positive electrode obtained above were punched into a disk shape having a diameter of 16 mm. Further, a separator made of glass fiber was used as a separator, and this was punched into a disk shape having a diameter of 17 mm. These disc-shaped positive electrode, separator and negative electrode are laminated in this order in a battery container made of SUS (CR2032), and the separator, negative electrode and positive electrode are impregnated with the electrolytic solution obtained above. A coin-type cell was manufactured as a lithium ion secondary battery by placing a plate (thickness: 1.2 mm, diameter: 16 mm) and covering the plate.

[Example 2] (Production of negative electrode material)
Silicon monoxide (SiO, average particle size 0.8 μm, 69 parts by mass), acetylene black (10 parts by mass), carbon nanotubes (6 parts by mass), and polyimide (15 parts by mass) are put in a reagent bottle, and further here After NMP was added to adjust the concentration, this concentration adjusted using a self-revolving mixer was mixed at 2000 rpm for 3 minutes. Next, this mixture was subjected to a dispersion treatment for 10 minutes using an ultrasonic homogenizer, and then this dispersion was again mixed for 3 minutes at 2000 rpm using a self-revolving mixer to obtain a negative electrode material. All the operations so far were performed at 25 ° C. Table 1 shows each compounding component at this time and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components.

(Manufacture of electrolyte, negative electrode, positive electrode, and lithium ion secondary battery)
A negative electrode, a positive electrode, and a lithium ion secondary battery were manufactured in the same manner as in Example 1, except that an electrolytic solution was manufactured in the same manner as in Example 1, and the obtained negative electrode material was used.

[Comparative Example 1]
As shown in Table 1, a lithium ion secondary battery was manufactured in the same manner as in Example 1 except that lithium was not pre-doped with respect to the negative electrode precursor.

[Comparative Example 2]
As shown in Table 1, a lithium ion secondary battery was manufactured in the same manner as in Example 2 except that lithium was not pre-doped with respect to the negative electrode precursor.

[Comparative Example 3] (Production of negative electrode material)
Silicon monoxide (SiO, average particle size 0.8 μm, 75 parts by mass), acetylene black (10 parts by mass), PAALi (50 mol% of all acid groups are converted to lithium salt, 10 parts by mass), and SBR (5 parts by mass) was placed in a reagent bottle, and distilled water was further added thereto to adjust the concentration. Then, this concentration adjusted using a self-revolving mixer was mixed at 2000 rpm for 3 minutes. Next, this mixture was subjected to a dispersion treatment for 10 minutes using an ultrasonic homogenizer, and then this dispersion was again mixed for 3 minutes at 2000 rpm using a self-revolving mixer to obtain a negative electrode material. All the operations so far were performed at 25 ° C. Table 1 shows each compounding component at this time and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components. In Table 1, “-” means that the component is not blended.

(Manufacture of electrolyte, negative electrode, positive electrode, and lithium ion secondary battery)
A negative electrode, a positive electrode, and a lithium ion secondary battery were manufactured in the same manner as in Example 1, except that an electrolytic solution was manufactured in the same manner as in Example 1, and the obtained negative electrode material was used.

[Comparative Example 4] (Production of negative electrode material)
Silicon monoxide (SiO, average particle size 0.8 μm, 75 parts by mass), acetylene black (10 parts by mass), and polyimide (15 parts by mass) were placed in a reagent bottle, and NMP was further added thereto to adjust the concentration. Thereafter, this concentration-adjusted one using a self-revolving mixer was mixed at 2000 rpm for 3 minutes. Next, this mixture was subjected to a dispersion treatment for 10 minutes using an ultrasonic homogenizer, and then this dispersion was again mixed for 3 minutes at 2000 rpm using a self-revolving mixer to obtain a negative electrode material. All the operations so far were performed at 25 ° C. Table 1 shows each compounding component at this time and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components.

(Manufacture of electrolyte, negative electrode, positive electrode, and lithium ion secondary battery)
A negative electrode, a positive electrode, and a lithium ion secondary battery were manufactured in the same manner as in Example 1, except that an electrolytic solution was manufactured in the same manner as in Example 1, and the obtained negative electrode material was used.

<Evaluation of charge / discharge characteristics of lithium ion secondary battery>
About the lithium ion secondary battery obtained by each said Example and comparative example, 0.2C constant current constant voltage charge was performed at 25 degreeC until the electric current value converged to 0.1C by setting the upper limit voltage to 4.2V. Thereafter, a constant current discharge of 0.2 C was performed up to 2.7 V. Subsequently, the charge / discharge current was set to 1C, and the charge / discharge cycle was repeated several times to several tens of times in the same manner to stabilize the state of the lithium ion secondary battery. Subsequently, the charge / discharge current was set to 1C, and the charge / discharge cycle was repeated in the same manner, and the capacity development rate ({[discharge capacity at the first cycle (mAh)] / [rated capacity (mAh)]} × 100) (% ), And capacity retention ratio at 100 cycles ({[discharge capacity at the 100th cycle (mAh)] / [discharge capacity at the first cycle (mAh)]} × 100) (%)). The results are shown in Table 2.

As is clear from the above results, the lithium ion secondary batteries of Examples 1 and 2 using a negative electrode in which a particulate conductive aid and a fibrous conductive aid are used in combination and lithium is pre-doped have different types of binders. Even if they were different, both the capacity development rate and the capacity maintenance rate at 100 cycles were sufficiently high, and the charge / discharge characteristics were excellent.
On the other hand, the lithium ion secondary batteries of Comparative Examples 1 and 2 using a negative electrode on which lithium was not pre-doped were particularly insufficient in capacity development rate regardless of the type of binder. In addition, the lithium ion secondary batteries of Comparative Examples 3 to 4 using the negative electrode not using the fibrous conductive additive were inadequate in capacity maintenance rate particularly at 100 cycles regardless of the type of binder. .

[Example 3]
<Production of silicon oxide particles with different average particle diameter (D50)>
Put 100g of silicon monoxide (D50 = 6μm, Osaka Titanium Technologies), 560g of φ1mm zirconia ball, 120g of 2-propanol in a special zirconia container, and pulverize silicon oxide using planetary ball mill (P-6: FRITSCH) Then, a 2-propanol dispersion of silicon monoxide particles having an average particle size (D50) (median size) of 1.5 μm was obtained.
The obtained dispersion was separated and collected by a centrifugal separator to obtain a wet cake (solid content 70%) of silicon monoxide particles (SiO, average particle size 1.5 μm).

  A negative electrode material was obtained in the same manner as in Example 1 using the silicon monoxide particles obtained above. All these operations were performed at 25 ° C. Table 3 shows each compounding component at this time and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components.

<Production and evaluation of lithium ion secondary battery>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the particle size of silicon monoxide was changed as described above. For the evaluation, in addition to the capacity maintenance rate at 100 cycles, the capacity maintenance rate at 200 cycles ({[discharge capacity at 200th cycle (mAh)] / [discharge capacity at 1st cycle (mAh)]} × 100) (%) was calculated. The results are shown in Table 4.

[Example 4]
The pulverization conditions of Example 3 were changed to obtain silicon monoxide particles having an average particle diameter (D50) of 0.9 μm. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 3 except that these particles were used. Table 3 shows each compounding component of the negative electrode material of Example 4 and the ratio (mass%) of each compounding component with respect to the total amount of the compounding components. The evaluation results are shown in Table 4.

[Example 5]
The pulverization conditions of Example 3 were changed to obtain silicon monoxide particles having an average particle diameter (D50) of 0.6 μm. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 3 except that these particles were used. Table 3 shows each compounding component of the negative electrode material of Example 5 and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components. The evaluation results are shown in Table 4.

[Example 6]
In the compounding of each component in the negative electrode material of Example 3, the amount of silicon monoxide particles was reduced to 65% by mass, and the amount of carbon nanotubes was increased to 10% by mass. An ion secondary battery was produced and evaluated. Table 3 shows each compounding component of the negative electrode material of Example 6 and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components. The evaluation results are shown in Table 4.

[Example 7]
In the blending of each component in the negative electrode material of Example 4, the amount of silicon monoxide particles was reduced to 65% by mass, and the amount of carbon nanotubes was increased to 10% by mass. An ion secondary battery was produced and evaluated. Table 3 shows each compounding component of the negative electrode material of Example 7 and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components. The evaluation results are shown in Table 4.

[Example 8]
In the blending of each component in the negative electrode material of Example 6, the blending amount of silicon monoxide particles was reduced to 62% by mass, the binder component PAALi was reduced to 6% by mass, while the SBR of the binder component was decreased to 12% by mass. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 6 except that the amount was increased. Table 3 shows each compounding component of the negative electrode material of Example 8 and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components. The evaluation results are shown in Table 4.

[Example 9]
In the blending of each component in the negative electrode material of Example 7, the blending amount of silicon monoxide particles was reduced to 62% by mass, the binder component PAALi was reduced to 6% by mass, while the SBR of the binder component was decreased to 12% by mass. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 7 except that the amount was increased. Table 3 shows each compounding component of the negative electrode material of Example 9 and the ratio (% by mass) of each compounding component with respect to the total amount of the compounding components. The evaluation results are shown in Table 4.

The above Example 3, Example 6, Example 8, and Example 9 are comparative examples.
In the above results, when Examples 3 to 5 were compared, in Examples 4 and 5 in which the average particle diameter of silicon monoxide particles was 1 μm or less, the capacity retention rate was particularly improved.
Further, when Examples 3 and 6 and Examples 4 and 7 having the same average particle diameter of silicon monoxide particles are compared with each other, the cycle characteristics are improved in Examples 6 and 7 in which the proportion of the fibrous conductive additive is increased. It was observed. One reason for this is that when the average particle diameter of the silicon oxide particles changes, the preferred ratio of the fibrous conductive aid for allowing the conductive network to function well changes.

Comparing Examples 6 to 9, when the average particle size is relatively large (Examples 6 and 8), the capacity retention rate can be increased by increasing the amount of binder (Example 8) accordingly. It was. On the other hand, when the average particle size was relatively small (Examples 7 and 9), the capacity retention rate was increased by the smaller amount of the binder (Example 7) accordingly.
Thus, the further improvement of the capacity retention rate was confirmed by adjusting the amount of the binder according to the average particle diameter (size) of the silicon oxide particles.
If considered normally, the ratio of the surface area to the total mass of the particle group becomes smaller as the average particle diameter of the silicon oxide particles becomes larger. However, this example showed the opposite result. That is, when the average particle size of the silicon oxide particles is large, it is preferable to increase the amount of the binder, and when the average particle size of the silicon oxide particles is small, it is preferable to decrease the amount of the binder. It was done.

  The present invention can be used in the field of lithium ion secondary batteries.

  DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 2 ... Separator, 3 ... Negative electrode, 4 ... Positive electrode

Claims (6)

It has a negative electrode active material layer formed using a negative electrode material in which silicon oxide, a particulate conductive additive, a fibrous conductive additive and a binder are blended, and includes a negative electrode in which lithium is pre-doped ,
The average particle diameter of the silicon oxide is 0.1 μm to 1.0 μm,
With respect to the total mass of the silicon oxide, the particulate conductive additive, the fibrous conductive additive and the binder,
The silicon oxide content is 65-80% by mass,
The content of the particulate conductive additive is 5 to 20% by mass,
Content of the said fibrous conductive support agent is 2-15 mass%,
Content of the said binder is 5-20 mass%, The lithium ion secondary battery characterized by the above-mentioned .   2. The lithium ion secondary battery according to claim 1, wherein the particulate conductive additive is carbon black and the fibrous conductive additive is a carbon nanotube. The lithium ion secondary battery according to claim 1, wherein the binder contains lithium polyacrylate. The lithium ion secondary battery according to claim 3, wherein the binder further contains styrene butadiene rubber. The lithium ion secondary battery according to any one of claims 1 to 4, wherein an average particle diameter of the particulate conductive auxiliary agent is 10 to 100 nm. The lithium ion secondary battery according to any one of claims 1 to 5, wherein an average fiber diameter of the fibrous conductive additive is 5 to 300 nm.