JP2021180083A - New polymer binder composition for negative electrode of secondary battery - Google Patents

Abstract

To provide a new binder material to make a secondary battery with stable high capacity and excellent charge/discharge cycle.SOLUTION: There is provided a polymer binder composition for a negative electrode of a secondary battery containing a compound represented by the following formula (I) and a polyacid. In the formula, R1 and R2 are any substituents selected from a group consisting of a hydrogen atom, a saturated hydrocarbon chain having 1 to 12 carbon atoms, and a cyclic hydrocarbon having 6 to 10 carbon atoms; and n represents an integer from 10 to 500.SELECTED DRAWING: None

Description

The present invention relates to a novel polymer binder composition for a negative electrode of a secondary battery.

Chemical batteries that generate electricity by the chemical reaction of substances are roughly classified into single-use type primary batteries, secondary batteries that can be repeatedly charged and discharged, and fuel cells. Of these, two that can be repeatedly charged and discharged. Sub-batteries are used for various purposes such as mobile devices and emergency storage batteries. Here, the secondary battery may be referred to as a storage battery or a rechargeable battery.

Conventionally, nickel-cadmium secondary batteries have been used for a long time, but small, lightweight and high-power nickel-lithium secondary batteries (hereinafter sometimes referred to as "lithium-ion batteries") have been developed and mobile phones. , Became the mainstream of power sources for laptop computers and the like. In nickel ion batteries, "lithium cobalt oxide" is generally used as a positive electrode material, graphite is generally used as a negative electrode material, and an organic type is generally used as an electrolytic solution. Discharge and charge are realized by the movement of lithium ions (cations) contained in lithium nickel cobalt oxide.
Lithium-ion batteries have many advantages such as high voltage and energy density, no memory effect, and compact packaging, so they are currently the mainstream as general-purpose secondary batteries. Occupies the seat of.

Among the members that make up secondary batteries, members such as positive electrodes, negative electrodes, and electrolytes have always been in the limelight, and active basic research has been carried out. On the other hand, polyvinylidene fluoride (hereinafter, may be abbreviated as "PVDF") has been widely used as a binder for a lithium ion secondary battery (FIG. 1) for a long time, but in recent years, a new binder has been used. Although the number of papers is increasing, it cannot be said that it has been fully examined.
In addition, cross-linked polyacrylic acid binders for high-capacity silicon-based negative electrodes for next-generation lithium-ion batteries are known (Organic Square 55, 2016).

In addition, graphite has been used for many years as the active material for the negative electrode for conventional commercial lithium-ion secondary batteries, but the discharge capacity has been limited to about ^{300 mAhg -1 at the highest. On the other hand, it is known that the theoretical capacity of silicon is about 10 times (4200 mAhg -1} ) larger than that of graphite, which is currently mainly used as a negative electrode active material, and it is expected that the graphite negative electrode will be replaced with a silicon negative electrode. Has been done. As such a technique, a technique utilizing a binder such as polyacrylic acid has been proposed (see Non-Patent Document 1; hereinafter referred to as "conventional technique 1").

Further, in a lithium ion battery, it is known that a binder plays a role of "adhering an electrode active material". In the negative electrode, the binder binds a carbon material or other active material to a copper foil or other metal foil which is a current collector. As such a binder, vinylidene fluoride resin has been used for a long time. It is known that the binder plays an important role in the formation of the coating film (Solid Electrolyte Interphase, hereinafter sometimes referred to as "SEI") on the surface of the negative electrode. As a binder for the silicon negative electrode, a conjugated polymer is used. It has also been reported to be used (see Non-Patent Document 2; hereinafter referred to as "conventional technique 2").

Review article: DOI: 10.1039 / c7cs00858a S. G Pa111aik, R. Vedarajan, N. Matswni, J. Mater. Chem. A, 5, 17909-17919 (2017)

The prior art 1 provides a chemical structure of a polymer binder that is a candidate for improving the defects of a conventional binder (PVDF, etc.) caused by a volume change (300%) during lithium conversion and delithiumization of a silicon negative electrode. It was introduced in detail. However, no solution has been provided for the following points, which have been a problem when silicon is used as a negative electrode material.

The first problem is that pure silicon has low conductivity and cannot be used as a battery material. For this reason, it has also been proposed to dope silicon monoxide, silicon dioxide, or silicon in order to impart conductivity to the material as an impurity semiconductor (n or p-type). To compensate for the low conductivity of silicon, carbon-based materials are mainly used as conductive aids.

Since the battery volume is defined by the standard, increasing the amount of the conductive auxiliary agent directly leads to the decrease in the amount of the active material, which leads to a decrease in the battery capacity. In order to avoid this problem, there is a problem that the conductive auxiliary agent must be attached to all the silicon particles and the distance between the conductive auxiliary agents must be made as small as possible to construct a structure in which they come into contact with each other. At present, no system has been found that industrially provides a stable and high-capacity charge / discharge cycle, and industrially, 10-20 wt% silicon is added to graphite to achieve 400-500 mAhg-l. It is still in the stage of doing.

It is said that the prior art 2 provided as a binder a bisiminoacenaftenquinone (BIAN) -fluorene polymer having significantly improved electrochemical performance, cycling behavior and specific capacity at output as compared with a conventional electrode containing a PVDF binder. It is an excellent invention in terms of points. However, there is room for further improvement in order to solve the problem caused by the above-mentioned volume change of the silicon electrode.
The second problem is that the insertion / desorption of lithium ions causes the silicon particles to expand / contract, thus varying the volume of the electrode. Fluctuations in the volume of the electrodes occur even when a graphite-based negative electrode is used, but the degree of fluctuation is large when a silicon-based negative electrode is used, and by repeating charging and discharging, silicon particles are crushed and the conductive network of the negative electrode is used. There is a problem that the negative electrode is cut off or the negative electrode is peeled off from the current collector.

In order to solve these problems, new binder materials are required. In designing the film, the mixture with the electrode active material is good, the film forming ability on the current collector is high, the film with high adhesiveness can be formed, and the interfacial resistance with the electrode active material is low. It is necessary to consider that it is electrochemically stable and has various properties such as being able to assist in the formation of a good solid electrolyte interface (SEI).

Therefore, there has been a high social demand for a new binder material having the above-mentioned properties required for realizing a system that industrially provides a stable and high-capacity charge / discharge cycle.

The inventors of the present invention have conducted extensive research under the above circumstances, and as a new binder material, π-conjugated having a bisiminoacenaftecinone (hereinafter, abbreviated as "BIAN") structure. The present invention was completed by synthesizing a system polymer.
That is, one aspect of the present invention is a polymer binder composition for a negative electrode of a secondary battery containing a compound represented by the following formula (I) and a polyacid.

Here, in the above formula (I), R ₁ and R ₂ are any one selected from the group consisting of a hydrogen atom, a saturated hydrocarbon chain having 1 to 12 carbon atoms, and a cyclic hydrocarbon having 6 to 10 carbon atoms. It is a substituent, and n represents an integer of 10 to 500.

The compound represented by the formula (I) is preferably any compound selected from the group consisting of the compounds represented by the following formula (II).

In the above formula, R ₁ and R ₂ are any group selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a pentyl group, a hexyl group and a naphthyl group, and n is 10 Represents an integer of ~ 500.

Here, the compound represented by the formula (I) or (II) is preferably any compound selected from the group consisting of the compounds represented by the following formulas (III) to (VIII), and is preferably described below. In the compounds represented by the formulas (III) to (VIII), n represents an integer of 10 to 500.

The polyacid is preferably polyacrylic acid or phytic acid, and the polyacrylic acid is preferably a compound having a number average molecular weight of 3,000 to 500,000. The compound represented by any of the formulas (I) to (VIII) is preferably a polymer of a dihalide compound having a bisiminoasenaftequinone skeleton and a diethynylfluorene derivative. The number average molecular weight of these compounds is preferably 3,500 to 4,500.

In another aspect of the present invention, the above-mentioned polymer binder composition for a negative electrode of a secondary battery, a negative electrode active material, and a conductive material are dispersed and mixed in a solvent to prepare a slurry, and the slurry is used as a current collector. It is a negative electrode for a secondary battery manufactured by applying it on top and drying it.

Here, the negative electrode for a secondary battery is preferably a silicon negative electrode containing 20 to 80% by weight of silicon as a negative electrode active material and 10 to 25% by weight of acetylene black as a conductive material, and further contains graphite. Is preferable.

The silicon negative electrode preferably further contains the polymerized π-conjugated polymer and polyacrylic acid, and graphite: silicon: acetylene black: the polymerized π-conjugated polymer: polyacrylic acid = 28. It is preferable to contain ~ 32: 23 to 27: 18 to 22: 18 to 22: 1 to 9 (% by weight).

Yet another aspect of the present invention is a self-healing matrix formed in a negative electrode by preparing a slurry containing the above-mentioned polymer binder composition for a negative electrode of a secondary battery. Here, the self-healing matrix is preferably a compound having a hydrogen bond represented by the following formula (IX). As used herein, "self-healing" is defined as the ability of mechanically occurring structural damage to be repaired by reshaping the water-bound network.

Yet another aspect of the present invention is a secondary battery comprising the negative electrode described above. Here, it is preferable that the secondary battery includes a polymer binder composition for the negative electrode of the secondary battery in the negative electrode.

According to the binder composition of the present invention, the π-conjugated polymer having a bisiminoacenaftecinone (BIAN) structure contained in the binder composition interacts with graphite, which is required as a binder, and dissolves in NMP. In terms of properties, interaction with the current collector, etc., it exerts a particularly advantageous effect over the conventional binder.

Also, by using the binder composition of the present invention, a self-healing matrix for protecting the negative electrode is provided. This matrix allows self-healing of conductive networks broken due to volume fluctuations in silicon electrodes.

FIG. 1 shows the three-dimensional structure (A) of poly (BIAN) -poly (acrylic acid), which is a hydrogen-bonded polymer as a binder, and poly (BIAN) (B) and polyacrylic acid (hereinafter referred to as polyacrylic acid), which are components of the polymer. , "PAA" may be abbreviated.) It is a figure which shows the structure of (C). FIG. 2 is a schematic diagram showing four possibilities as a metal electrode. It shows electrochemical lithium formation in the form of (I) surface plating with Li metal, (II) Li hypersaturation, (III) equilibrium alloy formation, and (IV) solid state amorphization of Li-metal alloy. FIG. 3 is a graph (Nyquist plot) showing the CV and EIS profiles of performing cells having a BP-copolymer (compound represented by the above chemical formula (III)) / PAA binder.

FIG. 4 is a graph showing the CV profile of an anode half cell containing a BP-copolymer / PAA as a binder. FIG. 5 is a graph showing the discharge amount of a graphite-silicon composite (cell 1) having poly (BIAN) -PAA as a binder. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material. FIG. 6 is a graph showing the profile comparison result 1 when only PAA is used as the binder and when the BIAN-PAA binder is used in cell 1. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material.

FIG. 7 is an electron microscope image (No. 1) showing the surface of the negative electrode before cycling ((A1) to (A3)) and after 335 cycling ((B1) to (B3)). FIG. 8 is an electron microscope image (No. 2) showing the surface of the negative electrode before cycling ((A1) to (A3)) and after 335 cycling ((B1) to (B3)). FIG. 9 is a graph (No. 1) showing the discharge amount of the graphite-silicon composite (cell 2) having poly (BIAN) -PAA as a binder. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material.

FIG. 10 shows the discharge amount (No. 2) of the electrode (cell 2) containing the graphite-silicon composite having poly (BIAN) -PAA as the binder. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material. FIG. 11 is an electron microscope image (No. 1) showing the surface of the negative electrode before cycling ((A1) to (A3)) and after 320 cycling ((B1) to (B3)) at position 1. FIG. 12 is an electron microscope image (No. 2) showing the surface of the negative electrode before cycling ((A1) to (A3)) and after 320 cycling ((B1) to (B3)) at position 1.

FIG. 13 is a chromatogram (No. 1) of FT-IR of the electrode material after applying the slurry of BP-copolymer and GSiBP_PAA on the copper foil. FIG. 14 is a chromatogram of FT-IR (No. 2) of the electrode material after the slurry of BP-copolymer and GSiBP_PAA is coated on the copper foil. FIG. 15 is a graph showing the EIS profile and CV of the anode half cell after fabrication. FIG. 16 is a CV profile of an anode half cell containing BP-copolymer / PAA as a binder.

FIG. 17 is a graph showing the discharge amount of the rGO-silicon composite electrode containing poly (BIAN) -PAA as a binder. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material. FIG. 18 is a graph showing the profiles of the PAA-only binder and the BIAN-PAA binder in the rGO-Si system. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material.

FIG. 19 is a diagram showing the EIS profile and CV profile of the anode half cell after fabrication.

FIG. 20 is a diagram showing the CV profile of an anode half cell containing a BP-copolymer / PAA binder. FIG. 21 is a graph showing the discharge amount of a graphite-silicon electrode containing BIAN-PAA and phytic acid as a binder. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material. FIG. 22 is a graph showing the comparison result of the profiles of the PAA-only binder and the BIAN-PAA binder in the case of the phytic acid system. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material.

FIG. 23 is a graph showing the results of evaluating the performance of a high silicon content cell containing BIAN-PAA as a binder. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material. FIG. 24 is a graph showing the results of evaluating the performance of a cell containing only silicon containing BIAN-PAA as a binder (without graphite). (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material. FIG. 25 is a graph showing the results of evaluating the performance of low BIAN-PAA binder content (15 wt%) cells. (A) is a normal discharge capacity, and (B) is a discharge capacity calculated based on the silicon content in the active anode material.

Hereinafter, the present invention will be described in more detail with reference to the drawings as necessary.
The present invention is a polymer binder composition for a negative electrode of a secondary battery containing a compound represented by the following formula (I) and a polyacid.

In the above formula (I), R ₁ and R ₂ are any substituent selected from the group consisting of a hydrogen atom, a saturated hydrocarbon chain having 1 to 12 carbon atoms, and a cyclic hydrocarbon having 6 to 10 carbon atoms. Yes, n represents an integer from 10 to 500.
The compound represented by the formula (I) is any compound selected from the group consisting of the compounds represented by the following formula (II), while having high performance when the negative electrode is manufactured. This is preferable because it is possible to prevent a decrease in capacity due to a change in the volume of the negative electrode.

In the above formula, R ₁ and R ₂ are any group selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a pentyl group, a hexyl group and a naphthyl group, and n is 10 Represents an integer of ~ 500.
Further, the compound represented by the formula (I) or (II) may be referred to as a compound represented by the following formulas (III) to (VIII) (hereinafter, "polymerized π-conjugated polymer"). It is preferable that any compound selected from the group consisting of ()) is used because it has high performance when a negative electrode is produced and can prevent a decrease in capacity due to a change in the volume of the negative electrode. In the compounds represented by the following formulas (III) to (VIII), n represents an integer of 10 to 500.

The polyacid is preferably polyacrylic acid or phytic acid because it can form effective hydrogen bonds, and the polyacrylic acid has a number average molecular weight of 3,000 to 500,000, which gives sufficient mechanical properties. Therefore, it is preferable.

The compound represented by any of the formulas (I) to (VIII) is preferably a polymer of a dihalide compound having a bisiminoasenaftequinone skeleton and a diethynylfluorene derivative. The number average molecular weight of the compound represented by any of the formulas (I) to (VIII) is preferably 3,500 to 4,500.

A slurry is prepared by dispersing and mixing the negative electrode polymer binder composition for the negative electrode of the secondary battery of the present invention, the negative electrode active material, and the conductive material in a solvent, and the slurry is applied onto the current collector. It can be dried to produce a negative electrode for a secondary battery. In order to obtain the desired viscosity of the slurry, methyl cellulose, carboxymethyl cellulose (CMC) and other thickeners can be appropriately added as long as the characteristics of the binder of the present invention are not impaired.

Examples of the solvent include N-methyl-2-pyrrolidone (hereinafter, may be abbreviated as “NMP”), N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, hexamethylsulfoxide, and hexamethylsulfoxide. , And organic solvents such as methyl ethyl ketone can be used alone or in admixture. Further, various dispersants, surfactants, stabilizers and the like may be added as needed.

Since the battery capacity per weight is much larger than that of graphite, the negative electrode active material is preferably a silicon-based compound. As used herein, the term "silicon-based negative electrode active material" refers to silicon and silicon compounds that react with lithium ions during charging and discharging. For example, metallurgical grade silicon (silicon produced by reducing silicon dioxide with carbon), industrial grade silicon (silicon obtained by subjecting the above metallurgical grade silicon to acid treatment or one-way solidification to reduce impurities), high. Examples thereof include pure crystalline silicon (silicon produced from silane obtained by reacting silicon, and various crystalline states such as single crystal, polycrystal, and amorphous are known).

Here, the negative electrode for the secondary battery is a silicon negative electrode containing 20 to 80% by weight of silicon, which is a negative electrode active material, and 10 to 25% by weight of acetylene black, which is a conductive material, to realize a high discharge capacity. It is preferable because it can be done. Further, it is preferable that the silicon negative electrode further contains graphite because the conductivity is improved.

It is preferable that the silicon negative electrode further contains the above-mentioned polymerized π-conjugated polymer and polyacrylic acid from the viewpoint of the conductivity of the negative electrode matrix and the durability based on the self-repairing ability. The silicon negative electrode is graphite: silicon: acetylene black: the polymerized π-conjugated polymer: polyacrylic acid, and 28 to 32:23 to 27:18 to 22:18 to 22: 1-9 ( It is preferable to include it in a ratio of (% by weight) because the conductivity of the negative electrode matrix and the durability based on the self-repairing ability are further improved.

The negative electrode containing the binder of the present invention can be prepared as follows. For example, graphite or reduced graphene (hereinafter, may be abbreviated as “rGO”), silicon in a desired ratio in an N-methyl-2-pyrrolidone (hereinafter, abbreviated as “NMP”) solvent. A composition containing nanopowder, the above-mentioned BIAN-p-phenylene copolymer binder, PAA binder, and acetylene black can be dispersed to form a slurry, which can be coated on a desired metal foil to prepare the slurry.

The ratio of each compound contained in the above composition is, for example, about 25 to about 35 wt% for graphite or rGO, about 10 to about 20 wt% for silicon nanopowder, and about 15 to about 15 to about 15 to about BIAN-p-phenylene copolymer binder. It can be 25 wt%, PAA binder about 2-7 wt%, acetylene black about 15-about 25 wt%. As the metal foil constituting the current collector, foils such as aluminum, copper, zinc, nickel, titanium and stainless steel can be used.

The coating on the foil can be performed by a gravure method, a reverse roll method, a direct roll method, a doctor blade method, a knife method, an extrusion method or the like. It is preferable to adopt the doctor blade method because it can be applied in the form of a plate having a uniform thickness. In order to completely remove the NMP solvent from the homogeneous and consistent thickness electrode obtained by coating, this electrode is dried in vacuum, for example, at about 80 to about 95 ° C. for about 10 to 15 hours, and then. , For example, at about 70 to about 90 ° C., roll press to a desired thickness, for example, about 60 to about 90 μm. The electrode thus obtained is punched into a disk of a desired size using a punch, a separator is sandwiched between the electrode and a positive electrode prepared in advance, and the electrode is stored in a housing, and a coin for an electrochemical test is used. Make a mold battery.

Further, in the present invention, the negative electrode is prepared by preparing a polymer binder composition for a negative electrode of the secondary battery, dispersing the polymer binder composition in the above-mentioned solvent to form a slurry, and forming a negative electrode using this slurry. A self-healing matrix can be formed in it. Here, as the solvent, for example, NMP can be preferably used because the constituent components have good solubility and high dispersibility. Further, as the foil for coating the slurry, the above-mentioned foil can be used, but it is preferable to use a copper foil from the viewpoint of cost.

The self-healing matrix of the present invention is formed at the same time, for example, when forming the negative electrode containing the binder of the present invention prepared as described above. The self-repairing matrix is preferably a compound having a hydrogen bond represented by the following formula (IX) because it imparts conductivity based on the self-repairing ability and conductivity of the negative electrode matrix. By forming the self-healing matrix, it is possible to prevent the surface of the negative electrode from being roughened by the volume change of the negative electrode using silicon, and it is possible to improve the number of cycles of the cell including the negative electrode containing the binder of the present invention.

(Example 1) Fabrication of graphite-silicon composite anode half cell
The above half cell using N-paraphenylene-PAA (20wt% -5wt%) polymer as a binder was prepared as follows.
(1) Preparation of slurry An ultrafine powder of graphite (manufactured by Merck & Co., Ltd.) was used as the electrode active material. As a conductive additive, battery grade acetylene black with an average particle size of 40 nm (hereinafter, may be abbreviated as “AB”) was used. The composition for the negative electrode was prepared by a total weight of 100 g. The proportions of each component in this composition are 30 wt% graphite, 25 wt% silicon nanopowder (particle size less than 100 nm), 20 wt% BIAN-p-phenylene copolymer binder, and 5 wt% PAA binder. Acetylene black was set to 20 wt%.
A slurry was prepared by suspending 50 g of this composition in 100 mL of N-methyl-2-pyrrolidone (hereinafter, abbreviated as "NMP") solvent. A slurry having the composition shown in Table 1 below was also prepared in the same manner.

*1：還元型グラフェン *2：アセチレンブラック

* 1: Reduced graphene * 2: Acetylene black

(2) Preparation of Negative Electrode Next, the slurry was applied to one side of an electrolytic copper foil having a width of 220 mm and a thickness of 20 μm using a doctor blade so as to have a coating width of 200 mm and a coating thickness of 70 μm to prepare an electrode. ..
The electrodes were dried in vacuum at 90 ° C. for 12 hours to completely remove the NMP solvent. Further, the electrode was roll-pressed at 80 ° C. to a thickness of 70 μm and punched into a small disk (diameter 15 mm) to obtain the negative electrode of the present invention. This negative electrode was subjected to measurement immediately after production.

(3) Preparation of positive electrode Metallic lithium was used as the positive electrode. Then, a disk having the same size as the negative electrode was punched to prepare a positive electrode.

(4) Preparation of non-aqueous electrolytic solution In a glove box filled with argon gas, LiPF ₆ was dissolved in a mixed solution of ethylene carbonate: diethyl carbonate = 1: 1 (v / v) so as to be 1.0 M, and non-aqueous electrolyte solution was prepared. A water electrolyte was prepared.

(5) Preparation of Lithium Ion Secondary Battery (Coin Cell) For performance evaluation using the negative electrode, positive electrode, non-aqueous electrolyte, and separator of a 30 μm thick polypropylene microporous film prepared as described above. Coin-type lithium-ion secondary battery (non-aqueous electrolyte secondary battery) was manufactured.

(6) Calculation of charge amount in lithium-silicon alloy (6-1) In the case of electrochemically driven solid amorphous
The theoretical maximum capacity of silicon for Li ₂₁ Si ₅ ^{alloys has been reported to be 4200 mAhg -1} (P. Limthongkul et al. / Acta Materialia 51 (2003) 1103-1113 Huggins RA, Nix WD. Ionics 2000 See 6: 57.). It has also been confirmed that amorphization of lithium-silicon alloys in an electrochemical solid state is sufficiently possible at room temperature (reported by P. Limthongkul et al. In 2003).
Therefore, the charge amount of the electrode having the composition (Li / Si molar ratio) shown in Table 2 below was measured.

(6-2) Theoretical charge amount expected when the binder composition of the present invention is used The theoretical charge amount when the poly (BIAN) -PAA polymer binder of the present invention and the graphite / silicon composite are used is determined by graphite (6-2). It was calculated based on the theoretical charge of 372 mAhg ^-1 _{of LiC 6).} That is, since the Li ₁₅ Si ₄ alloy corresponds to 3569 mAhg ^-1 , the theoretical charge of the prepared electrode was 1423 mAhg ^-1 , that is, (0.333 × 3569) + (0.666 × 372). ..

(Example 2) Performance evaluation of executing cells (1) EIS profile using executing cells Cyclic voltammetry using the coin-type secondary battery (execution cell) produced in Example 1. (CV) and Electrochemical Impedance Spectroscopy (hereinafter, may be abbreviated as "EIS") profile were measured.

(VSP potentiostat (Bio-Logic Science Instruments)) was used to measure the EIS of the negative electrode / negative electrode symmetric model cell. The frequency range was 65 kHz to 10 mHz, the amplitude voltage was ± 5 mV, and the ambient temperature was 25 ° C. The results are shown in FIG.
As shown in FIG. 3, this measurement result showed a linear rise after drawing an arc on the Nyquist diagram both after mounting and after CV.

(2) CV profile using performing cells Then, by cyclic voltammetry test of a poly (BIAN) -PAA-based binder (binder of the present invention) for a silicon-graphite-based negative electrode, the electrochemical characteristics of the above binder Was evaluated. VSP potentiostats (Bio-Logic Science Instruments) were used for the cyclic voltammetry test. FIG. 4 shows a cyclic voltangram. Irreversible electrode decomposition was observed in cycle 1. Further, in cycles 2 to 4, a peak corresponding to delithiumization from graphite and a peak corresponding to delithiumization by dealloying Li + from silicon were observed.

(3) Measurement of discharge amount and Coulomb efficiency using performing cells Next, charge / discharge characterization including Coulomb efficiency was performed using Electrofield ABE 1024. The results are shown in FIG. 5 (A). As a result, in the graphite-silicon composite electrode containing the poly (BIAN) -PAA-based binder, the reversible capacitance after 335 cycles was 230 mAhg ^-1 . In addition, the Coulomb efficiency was almost constant at around 100%. From this, it was shown that when the negative electrode of the present invention was used, the amount of discharged electricity that could be effectively taken out was larger than the amount of electricity (Ah) required for charging. The reversible capacity after 335 cycles (FIG. 5 (B)) with respect to the amount of silicon as an active material was 470 mAhg ^-1 .

(Example 3) Performance evaluation using cells-1
(1) Measurement of discharge amount and coulomb efficiency
Using a cell containing a PAA-only binder as a control, the discharge capacity and the Coulomb efficiency of the cell containing the poly (BIAN) -PAA-based binder were measured. The measurement conditions were the same as in Example 2. The results are shown in FIG. 6 (A). Looking at the decrease in discharge capacity after 25 cycles, a clear difference was observed from the cells containing the above poly (BIAN) -PAA-based binder. In addition, the same tendency was shown in the amount of discharge with respect to the amount of silicon as an active material (FIG. 6 (B)).

(2) Changes in the electrode surface before and after cycling Fig. 7 shows changes in the electrode surface before and after cycling. Electron microscope images showing the state of the electrode surface of the three cells before cycling are shown as (A1) to (A3). The electron microscope images showing the state after 335 cycling used for the evaluation in (1) above are shown as (B1) to (B3). The magnification is 300 times for (A3) and (B3), 600 times for (A2) and (B2), and 2,000 times for (A1) and (B1), respectively.
The electrode surface (position 1) after cycling showed a large change due to the change in the capacitance of the electrode in the control as compared with the negative electrode (A1) and (B1) containing the binder of the present invention ((A2) in FIG. 7). ), (A3) and the same figure (B2), (B3)).

Further, for the other positions of the electrode surface, electron microscope images showing the states before and after cycling (before and after 335 cycling) were obtained as in FIG. 7 (see FIGS. 8 (A1) to 8 (B3)). .. These electron microscope images also showed the same results as in FIG. 7.

(Example 4) Performance evaluation using cells-2
(1) Measurement of discharge amount and Coulomb efficiency The same performance evaluation as in Example 3 was performed using another cell. The results are shown in FIG. For this cell, the reversible capacitance after 325 cycles was 510 mAhg ^-1 (FIG. 9 (A)). In addition, the reversible capacity with respect to the amount of silicon as an active material was 1122 mAhg ^-1 after 325 cycles (Fig. 9 (B)). In addition, FIG. 10 shows the results of comparing the control (cell containing a binder containing only PAA) and the cell containing the above poly (BIAN) -PAA-based binder. The same tendency as in Example 3 was shown.

(2) Changes in the electrode surface before and after cycling The changes in the electrode surface before and after cycling are shown in FIGS. 11 and 12. In each of the drawings, electron microscope images showing the state of the electrode surface of the three cells before cycling are shown as (A1) to (A3). The electron microscope images showing the state after 320 cycling used for the evaluation in (1) above are shown as (B1) to (B3). The magnification of each image is the same as in FIG. It was observed that the surface of each of the electrode surfaces (position 1) and (position 2) after cycling changed significantly after cycling.

(3) FT-IR results of BP-copolymer and electrode material when slurry is applied on copper foil The BP-copolymer and electrode material when slurry is applied on copper foil in FIGS. 13 and 14. The result of FT-IR is shown. FIG. 13 shows the results of FT-IR of poly BIAN, and FIG. 14 shows the results of FT-IT of PAA. CN stretch was observed in Poly BIAN. In contrast, C = O stretch was observed in PAA.

(Example 5) Examination of binder composition-1
A half cell was prepared from a graphite-silicon composite (hereinafter sometimes referred to as "rGO-Si composite") containing a negative electrode containing a BIAN-paraphenylene-PAA (20wt% -5wt%) polymer as a binder, and its performance was evaluated. ..

(1) EIS profile measurement The negative electrode was prepared in the same manner as above except that rGO was used instead of graphite. FIG. 15 shows the results of measuring the EIS profile after fabrication and after CV under the same conditions as in Example 2. There was a large difference between the post-fabrication and post-CV profiles, showing an increase in interfacial resistance after cycling.

The CV profile was also measured under the same conditions as in Example 2. The results (cyclic voltangram) are shown in FIG. In cycle 1, irreversible electrode decomposition and partial electrode decomposition were observed. Also, in cycles 2-4, almost the same voltangram was obtained.

(2) Measurement of discharge capacity and coulombic efficiency The discharge capacity and coulombic efficiency were measured when the rGO-Si composite containing poly (BIAN) -PAA as a binder was used in the same manner as in Example 3. The results are shown in FIG. The discharge rate of the rGO-silicon composite electrode containing poly (BIAN) -PAA as a binder was 750 mAhg ^-1 after 330 cycles (Fig. 17 (A)). The amount of discharge relative to the amount of silicon as the active material ^{exceeded 1,500 mAhg -1} after 330 cycles (Fig. 17 (B)).

In addition, FIG. 18 shows the discharge capacity and the coulombic efficiency of the cell using the binder containing only PAA in the rGO-Si system and the cell using the binder containing BIAN-PAA. Cells with binders containing BIAN-PAA showed high discharge capacity.

(Example 6) Examination of binder composition-2
A half cell was prepared in the same manner as above except that a graphite-silicon composite containing a BIAN-paraphenylene-PAA (20wt% -5wt%) polymer and phytic acid was used as a negative electrode, and its performance was measured.

(1) EIS profile and CV
The EIS profile of the cell containing the BP-copolymer / PAA binder is shown in Figure 19. From this result, it was shown that the interfacial resistance was improved. The results of CV are shown in Fig. 20.

(2) Measurement of discharge capacity and Coulomb efficiency The discharge amount of the graphite-silicon electrode containing BIAN-PAA and phytic acid as a binder was measured under the same conditions as above. The discharge capacity after 400 cycles was 750 mAhg ^-1 . In addition, the discharge capacity with respect to the amount of silicon as an active material exceeded ^{1,600 mAhg -1 after 400 cycles.}

(3) Comparison of discharge capacity when PAA is used as a control A negative electrode using a binder containing only PAA was used as a control. The negative electrode containing poly (BIAN) and phytic acid showed a high discharge capacity (FIG. 21 (A)). The discharge capacity with respect to the amount of silicon as an active material is shown in FIG. 21 (B). This profile was similar to that shown in FIG. 21 (A).

(4) Examination of silicon content of negative electrode-1
The discharge capacity and Coulomb efficiency of the negative electrode containing 45 wt% Si, 10 wt% graphite, 25 wt% binder and 20 wt% acetylene black were measured in the same manner as above. The results are shown in FIGS. 22 (A) and 22 (B). The Coulomb efficiency was maintained at around 100%, and the discharge capacity was 500 mAhg ^-1 or more up to 300 cycles (Fig. 22 (A)). The discharge capacity with respect to the amount of silicon as an active material was also the same (Fig. (B)).

(5) Examination of silicon content of negative electrode-2
The discharge capacity and coulombic efficiency of the negative electrode containing 55 wt% Si, 25 wt% binder and 20 wt% acetylene black were measured in the same manner as above. The results are shown in FIGS. 23 (A) and 23 (B). The Coulomb efficiency was maintained at around 100%, and the discharge capacity was 400 mAhg ^-1 or more up to 120 cycles (Fig. 23 (A)). The discharge capacity with respect to the amount of silicon as an active material was also the same (Fig. (B)).

(6) Examination of silicon content of negative electrode-3
The discharge capacity and Coulomb efficiency of the negative electrode containing 40 wt% Si, 25 wt% graphite, 20 wt% acetylene black and 15 wt% binder were measured in the same manner as above. The results are shown in FIGS. 24 (A) and 24 (B). The Coulomb efficiency was maintained at around 100%, and the discharge capacity was 400 mAhg ^-1 or more up to 210 cycles (Fig. 24 (A)). The discharge capacity with respect to the amount of silicon as an active material was also the same (Fig. (B)).

(6) Negative electrode using a binder containing only BP-copolymer
The discharge capacity and Coulomb efficiency of the negative electrode using the binder containing only the BP-copolymer were measured in the same manner as above. The results are shown in FIGS. 25 (A) and 25 (B). The Coulomb efficiency was maintained at around 100%, and the discharge capacity was 1,000 mAhg ^-1 or more up to 200 cycles (Fig. 25 (A)). The discharge capacity with respect to the amount of silicon as an active material was also the same (Fig. (B)).

From the above, it was shown that by using the binder of the present invention, a negative electrode having a high discharge capacity and high Coulomb efficiency can be produced.

The present invention is useful in the field of secondary batteries.

Claims (15)

A polymer binder composition for a negative electrode of a secondary battery containing a compound represented by the following formula (I) and a polyacid.

In the above formula (I), R ₁ and R ₂ are any substituent selected from the group consisting of a hydrogen atom, a saturated hydrocarbon chain having 1 to 12 carbon atoms and a cyclic hydrocarbon having 6 to 10 carbon atoms. Yes, n represents an integer of 10 to 500. The negative electrode of the secondary battery according to claim 1, wherein the compound represented by the formula (I) is any compound selected from the group consisting of the compounds represented by the following formula (II). Polymer binder composition for.

In the above formula, R ₁ and R ₂ are any group selected from the group consisting of a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a pentyl group, a hexyl group and a naphthyl group, and n is 10 Represents an integer of ~ 500. Claim 1 is characterized in that the compound represented by the formula (I) or (II) is any compound selected from the group consisting of the compounds represented by the following formulas (III) to (VIII). Or the polymer binder composition for the negative electrode of the secondary battery according to 2.

In the compounds represented by the above formulas (III) to (VIII), n represents an integer of 10 to 500. The polymer binder composition for a negative electrode of a secondary battery according to any one of claims 1 to 3, wherein the polyacid is polyacrylic acid or phytic acid. The polymer binder composition for a negative electrode of a secondary battery according to claim 4, wherein the polyacrylic acid has a number average molecular weight of 3,000 to 500,000. The polymer binder composition for a negative electrode of a secondary battery according to claim 5, wherein the number average molecular weight of the compound represented by any of the formulas (I) to (VIII) is 3,500 to 4,500. thing. A slurry is prepared by dispersing and mixing the polymer binder composition for the negative electrode of the secondary battery according to any one of claims 1 to 6, the negative electrode active material, and the conductive material in a solvent, and the slurry is collected. A negative electrode for a secondary battery manufactured by applying it on the body and drying it. The seventh aspect of claim 7, wherein the negative electrode for a secondary battery is a silicon negative electrode containing 20 to 80% by weight of silicon as a negative electrode active material and 10 to 25% by weight of acetylene black as a conductive material. Negative electrode for secondary batteries. The negative electrode for a secondary battery according to claim 7, wherein the silicon negative electrode further contains graphite. The negative electrode for a secondary battery according to any one of claims 7 to 9, wherein the silicon negative electrode further contains the polymerized π-conjugated polymer and polyacrylic acid. The silicon negative electrode is graphite: silicon: acetylene black: the polymerized π-conjugated polymer: polyacrylic acid = 28 to 32: 23 to 27: 18 to 22: 18 to 22: 1 to 9 (% by weight). 10. The negative electrode for a secondary battery according to claim 10. A self-healing matrix formed in a negative electrode by preparing a slurry containing the polymer binder composition for a negative electrode of a secondary battery according to any one of claims 1 to 6. The self-repairing matrix according to claim 12, wherein the self-repairing matrix is a compound having a hydrogen bond represented by the following formula (IX).

A secondary battery comprising the negative electrode according to any one of claims 7 to 10. The secondary battery according to claim 14, wherein the secondary battery includes a polymer binder composition for the negative electrode of the secondary battery in the negative electrode.

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