JP2015185279A - Binder resin, lithium ion secondary battery negative electrode using the binder resin, and lithium ion secondary battery - Google Patents

Abstract

【選択図】 なしProvided are a binder that maintains its performance even in a high-temperature environment, for example, at 60 ° C., a lithium ion secondary battery negative electrode that exhibits excellent characteristics, and a lithium ion secondary battery.
A binder mainly composed of a polyamide-imide resin represented by the following formula 1, a silicon powder or a mixture of the silicon powder, a negative electrode active material layer made of a conductive additive, and a current collector. A lithium ion secondary battery comprising a negative electrode for a lithium ion secondary battery.
[Chemical 1]

[Selection figure] None

Description

  The present invention relates to a binder resin optimal for a battery negative electrode, a lithium ion secondary battery negative electrode and a lithium ion secondary battery using the binder resin.

In recent years, with the spread of portable electronic devices such as notebook computers, smartphones, portable game devices, PDAs, etc., in order to reduce the weight of these devices and enable them to be used for a long time, Miniaturization and high energy density are required.
Particularly in recent years, the range of use of secondary batteries as power sources for vehicles such as electric bicycles, electric motorcycles, and electric vehicles has been expanded. Such a secondary battery used for a vehicle power source is required not only to have a high energy density but also to operate stably over a wide temperature range.

  Conventionally, nickel-cadmium batteries, nickel-hydrogen batteries and the like have been mainstream as large-capacity secondary batteries, but the use of lithium secondary batteries increases due to the demands for downsizing and higher energy density. There is a tendency. In the conventional lithium secondary battery, polyvinylidene fluoride (PVdF) is mainly used as a binder for the negative electrode.

  However, in an environment of 45 ° C. or higher, the polyvinylidene fluoride (PVdF) used for the binder of the lithium secondary battery swells, so that the electrode deteriorates and sufficient cycle life characteristics cannot be obtained.

  In order to improve durability at high temperatures, a method using a polyimide binder has been proposed (for example, Patent Document 1).

  In addition, as a negative electrode active material capable of increasing the energy density of a lithium secondary battery, many studies have been conducted on metals or metal oxides that can occlude lithium, such as silicon and tin. These active materials enable high energy density, but the expansion and contraction of the active materials accompanying reversible insertion / extraction of lithium ions is large. As described above, polyvinylidene fluoride (PVdF), which is a binder material of a conventional lithium secondary battery, cannot withstand the peeling from the current collector foil or the pulverization of the active material caused by the expansion and contraction, causing the electrode to collapse. Sufficient cycle life characteristics could not be obtained.

  In order to solve the above problems and improve cycle life characteristics, a method using a polyimide binder as a binder for a lithium secondary battery has been proposed. Furthermore, it has been proposed to use a water-soluble binder such as polyacrylic acid polymer or carboxymethylcellulose (for example, Patent Document 2).

JP 2013-89437 A JP 2000-348730 A

  However, polyimide is prepared by dissolving polyamic acid, which is a precursor of polyimide, in an organic solvent, and imidization is performed at the time of electrode preparation, so that high temperature treatment exceeding 300 ° C. is necessary, and in the state of the precursor There are problems such as unstable binder solution.

  In addition, polyacrylic acid polymers and water-soluble binders such as carboxymethylcellulose do not have problems such as high-temperature treatment during electrode preparation and unstable binder solution, but have insufficient cycle life characteristics.

  This invention is made | formed in view of said subject, Comprising: It aims at solving the said subject. For example, the following configuration is provided as a means for achieving the object.

As a means for solving the above-described problem, an embodiment of the present invention according to the present invention has the following configuration.
That is, it is a binder resin that binds a negative electrode active material mainly composed of polyamideimide represented by the following formula 1.

In addition, for example, the negative electrode is a lithium ion secondary battery negative electrode including a negative electrode active material layer made of the binder resin, an active material, and a conductive additive, and a current collector.
For example, the active material is silicon powder or a mixture of the silicon powder. Or
The active material is silicon powder, a mixture of silicon powder and artificial graphite, or a mixture of silicon powder and a conductive additive. Further, for example, the negative electrode active material layer and NMP are mixed to produce a slurry, and the slurry is applied to a current collector.
A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to any one of the above.

  According to the present invention, a binder that is excellent in solution stability and does not require high temperature treatment at 300 ° C. or higher, and a lithium ion secondary battery negative electrode that is excellent in high temperature characteristics and cycle life characteristics and excellent in high energy density, A lithium ion secondary battery using the same can be provided.

FIG. 1 is a graph showing the cycle characteristics of each coin-type lithium ion secondary battery of Examples 1 and 2 and Comparative Example 1 according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an invention according to the present invention will be described in detail with reference to the drawings. Specifically, a binder according to this embodiment, a negative electrode for a lithium ion secondary battery using the binder, and a lithium ion secondary battery including the negative electrode will be described.
A binder according to an embodiment of the present invention according to the present invention is made of, for example, a polyamideimide resin represented by Formula 1 polymerized using trimellitic acid derivatives and diaminodiphenyl ether as raw materials. A binder made of this resin is soluble in an amide organic solvent, and N-methylpyrrolidone, which is a solvent generally used in conventional PVdF binders, can be used.

  A polyamide-imide resin similar to the polyamide-imide resin used in this embodiment is commercially available, for example, under the name “SOXR-O” from Nippon Kogyo Paper Industry Co., Ltd. Was used as. The inventor of the present application has newly found that this insulating substrate material exhibits an excellent function as a binder of a lithium ion secondary battery.

  This will be specifically described below. The negative electrode for a lithium ion secondary battery of the present embodiment is a slurry in which the above-mentioned polyamideimide resin is the main component and NMP, an active material, and a conductive additive are mixed, and this is applied to a current collector. Thereafter, it is obtained by drying. In preparing the slurry, an epoxy monomer can be added within a range of 25 parts by weight or less with respect to 100 parts by weight of the polyamideimide resin in order to obtain a higher binding force. When the added epoxy monomer is 25 parts by weight or more, the heat resistance of the negative electrode is impaired, which is not preferable.

  As the active material, a negative electrode active material used in this technical field can be used. For example, an active material containing a large capacity silicon atom, tin atom, or germanium atom as the negative electrode active material can be used.

  Examples of the negative electrode active material containing silicon atoms include (i) silicon fine particles, (ii) tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony or chromium. And an alloy with silicon, (iii) a compound of boron, nitrogen, oxygen or carbon and silicon, (iv) a compound having the compound of (iii) and the metal exemplified in (ii), and the like.

Examples of silicon alloys or compounds include SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi. ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _x (0 <x ≦ 2) or LiSiO.

  Examples of the negative electrode active material containing tin atoms include (i) alloys of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony or chromium and tin, ( ii) compounds of oxygen or carbon and tin, (iii) compounds having the metal exemplified in (i) in addition to the compounds of (ii).

Examples of tin alloys or compounds include SnO _W (0 <w ≦ 2), SnSiO ₃ , LiSnO, or Mg ₂ Sn.
Examples of the negative electrode active material containing germanium include germanium oxide, carbide, nitride, and carbonitride. The surface of these negative electrode active materials may be covered with a conductive material such as carbon or copper for the purpose of improving the conductivity.

  The average particle size of the active material is preferably 0.1 to 10 μm. The surface of the active material may be treated with a silane coupling agent or the like. As a method for making the particle size of the active material as described above, and a method for producing a uniform mixture with artificial graphite and a conductive additive, for example, a method by mechanical milling is preferable because it is simple and can reduce costs. .

  The current collector is not particularly limited as long as it is a material having electronic conductivity and capable of energizing the held negative electrode material. For example, there are metal materials such as silicon and / or silicon alloys, tin and alloys thereof, silicon-copper alloys, copper, nickel, stainless steel, and nickel-plated steel, and carbon materials such as carbon cloth and carbon paper. In this. From the viewpoint of high electrical conductivity and a general-purpose material, it is particularly preferable to employ copper as a current collector.

  Although there is no restriction | limiting in particular in the shape of an electrical power collector, A foil-like base material, a three-dimensional base material, etc. can be used. Further, the current collector may be subjected to primer treatment such as undercoating as long as the heat resistance is not impaired.

  Using the negative electrode for the lithium ion secondary battery of the present embodiment described above, the lithium ion secondary battery of the present embodiment can be obtained.

  As the positive electrode of the secondary battery, materials similar to those used in conventional lithium ion secondary batteries such as oxides such as Mn, Co, Ni, and lithium salts such as iron phosphate can be used.

In addition, since the lithium ion secondary battery using the negative electrode of this embodiment needs to contain lithium ions, the electrolyte salt is preferably a lithium salt. The lithium salt is not particularly limited, and specific examples include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium trifluoromethanesulfonate. .
These lithium salts can be used singly or in combination of two or more. Since the above lithium salt has high electronegativity and is easily ionized, it has excellent charge / discharge cycle characteristics and can improve the charge / discharge capacity of the secondary battery.

  As the solvent for the electrolyte, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 繃 -butyrolactone, and the like can be used, and these solvents can be used singly or in combination of two or more. Furthermore, the electrolytic solution may further contain a film forming agent.

Specific examples of the film forming agent include vinylene carbonate, vinyl ethylene carbonate, vinyl ethyl carbonate, methyl phenyl carbonate, carbonate compounds such as fluoroethylene carbonate and difluoroethylene carbonate, alkene sulfides such as ethylene sulfide and propylene sulfide; 1,3- Examples thereof include sultone compounds such as propane sultone and 1,4-butane sultone; acid anhydrides such as maleic anhydride and succinic anhydride.
Moreover, the electrolyte used for the lithium secondary battery of the embodiment according to the present invention may be a solid electrolyte or an ionic liquid.

According to the lithium secondary battery having the above-described structure, it can function as a lithium secondary battery excellent in high temperature characteristics.
The structure of the lithium secondary battery of this embodiment is not particularly limited, but can be applied to existing battery forms and structures such as a stacked battery and a wound battery.

  Next, examples according to the present invention will be specifically described. However, the present invention is not limited to the examples described below, and can be applied as it is without departing from the scope of the present invention.

As described above, according to the present embodiment, a high temperature treatment exceeding 300 ° C. is not necessary at the time of electrode preparation, a binder having excellent solution stability, and high temperature characteristics and cycle life characteristics using the binder. And the lithium ion secondary battery negative electrode and lithium ion secondary battery which achieved high energy density can be provided.
Therefore, the lithium ion secondary battery according to the present embodiment has improved high-temperature durability compared to conventional lithium ion secondary batteries, can be reduced in cost in the manufacturing process, and can be used more widely. It becomes possible.

[Example 1]
Using a rotation / revolution mixer, an epoxy monomer (for example, for example, an NMP solution of a polyamideimide resin represented by the following formula 1 (for example, trade name SOXR-O, Mw = 140,000, manufactured by Nippon Kogyo Paper Industries Co., Ltd.) Nippon Steel & Sumitomo Chemical Co., Ltd., trade name Epototo) is added to a total solid content of 12% by weight to prepare a binder solution.

Silicon powder (for example, Nilaco, 350 mesh, purity: 99.9%) and artificial graphite (for example, TIMCAL, trade name KS-6) are weighed so that the weight ratio is 1: 1, For example, in the present embodiment, mechanical milling is performed for 5 hours at a rotational speed of 400 rpm in a centrifugal rotating ball mill S-100 manufactured by Retsch, thereby producing a negative electrode active material.
Next, acetylene black (for example, manufactured by Denki Kagaku Kogyo Co., Ltd.) is added as a negative electrode active material and a conductive auxiliary so that the weight ratio of the active material: conductive auxiliary: binder solution solids is 75: 9: 16, and N -Adjust the viscosity with methylpyrrolidone to make a slurry.

  This slurry is coated on a copper foil as a current collector by, for example, an applicator, preliminarily dried in an air atmosphere at 80 ° C. for 1 hour, pressed, and then finally dried in a vacuum atmosphere at 260 ° C. for 30 minutes. A negative electrode is prepared. As the positive electrode, for example, a lithium cobaltate positive electrode is used.

  In addition to the positive electrode and the negative electrode thus manufactured, a glass filter (for example, trade name GA-100, manufactured by ADVANTEC) as a separator, and ethylene carbonate and diethyl carbonate as an electrolytic solution are mixed at a volume ratio of 1: 1. A coin lithium ion secondary battery (CR2032) is manufactured based on a solution obtained by dissolving lithium hexafluorophosphate in a concentration of 1 mol / L in the solvent.

[Example 2]
Example except that the negative electrode active material was changed to silicon powder, acetylene black (for example, manufactured by Denki Kagaku Kogyo Co., Ltd.) and ketjen black (for example, manufactured by Lion Corp.), and the weight ratio was changed to 90: 5: 5. A coin-type lithium ion secondary battery (CR2032) is manufactured under the same conditions as in 1.

[Comparative Example 1]
As a binder solution, polyacrylic acid (for example, manufactured by SIGMA-ALDRICH, Mw = 700,000) and sodium carboxymethyl cellulose (for example, manufactured by SIGMA-ALDRICH, Mv = 450,000) are mixed at a volume ratio of 1: 1. A coin-type lithium ion secondary battery (CR2032) was produced under the same conditions as in Example 1 except that the mixture was used and distilled water was used to adjust the slurry viscosity.

(Battery performance test)
About the coin-type lithium ion secondary battery produced in Example 1, Example 2, and Comparative Example 1, a Nagano charge / discharge tester BTS-2003W was used, and a charge / discharge test was performed in an environment of 60 ° C., respectively. . The results are shown in FIG. FIG. 1 is a graph showing the cycle characteristics of each coin-type lithium ion secondary battery of Examples 1 and 2 and Comparative Example 1 according to the present invention. In FIG. 1, the vertical axis represents the discharge capacity (mAh / g), and the horizontal axis represents the number of cycles.

  As can be seen from the graph shown in FIG. 1, the lithium secondary battery of Comparative Example 1 in which the negative electrode binder is a mixture of polyacrylic acid and sodium carboxymethyl cellulose starts to decrease in battery capacity from about 10 cycles of charge and discharge, and is charged and discharged. The decrease is increased from 40 cycles, and the capacity is reduced by about 50% or more with respect to the initial capacity at 100 cycles. This is presumably because, in Comparative Example 1, when the silicon is charged and discharged at high temperature, the binder cannot withstand expansion and contraction due to the “insertion-desorption” of lithium ions, and the electrode collapses.

  On the other hand, the lithium secondary batteries of Example 1 and Example 2 have good charge / discharge cycle characteristics at a high temperature of 60 ° C., with almost no decrease in capacity even after 100 cycles of charge / discharge. I understand.

  As described above, according to this embodiment or example, by using the polyamideimide represented by the above formula 1 as a binder, not the precursor but the resin that has completed imidization is dissolved in the organic solvent. The binder solution is excellent in stability, and high temperature treatment at 300 ° C. or higher is not required at the time of electrode preparation. In addition, since the polyamideimide represented by the formula 1 has sufficient heat resistance and binding power, the negative electrode active material composed of silicon powder or a mixture of the silicon powder and a conductive auxiliary using this binder is used. A battery lithium ion secondary battery negative electrode having a material layer and a current collector, and a lithium ion secondary battery using the same are excellent in high temperature characteristics and cycle life characteristics and have high energy density. it can.

  ADVANTAGE OF THE INVENTION According to this invention, the high temperature durability, ie, the lithium ion secondary battery negative electrode excellent in cycling characteristics also at the time of high temperature can be provided. The lithium ion secondary battery of the present invention using this negative electrode is suitably used as a main power source for mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles and the like.

Claims (6)

Binder resin characterized by binding a negative electrode active material mainly composed of polyamideimide represented by the following formula 1.

  A lithium ion secondary battery negative electrode comprising a negative electrode active material layer comprising the binder resin according to claim 1, an active material, and a conductive additive, and a current collector. The lithium ion secondary battery negative electrode according to claim 2, wherein the active material is silicon powder or a mixture of the silicon powder. The lithium ion secondary battery negative electrode according to claim 2 or 3, wherein the active material is silicon powder, a mixture of silicon powder and artificial graphite, or a mixture of silicon powder and a conductive additive. 5. The negative electrode for a lithium ion secondary battery according to claim 2, wherein the negative electrode active material layer and NMP are mixed to prepare a slurry, and the slurry is applied to a current collector. . A lithium ion secondary battery comprising the lithium ion secondary battery negative electrode according to any one of claims 2 to 5.

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