Electrode for lithium ion secondary battery and method for producing electrode for lithium ion secondary battery

Abstract

The problem to be solved by the present invention is to provide an electrode for a lithium ion secondary battery and a method for manufacturing the same, which can enhance the adhesion of an electrode active material without increasing the amount of a binder and can obtain a preferred energy density of a lithium ion secondary battery. In order to solve the above problems, the present invention is an electrode for a lithium ion secondary battery, comprising an electrode active material, a dendrimer, and a binder, wherein the dendrimer is chemically bonded to the surface of the electrode active material, and the dendrimer is chemically bonded to the binder.

Description

Technical Field

[0001] The present invention relates to an electrode for a lithium ion secondary battery and a method for manufacturing the electrode for a lithium ion secondary battery. Background Art

[0002] In the past, lithium-ion secondary batteries were widely used. Electrodes for lithium-ion secondary batteries are formed by bonding electrode active material powders to a current collector using a binder. It is known that the electrodes of lithium-ion secondary batteries expand and contract with charging and discharging, thereby causing the capacity of the lithium-ion secondary battery to deteriorate. Therefore, a technology is known that suppresses the capacity degradation of lithium-ion secondary batteries caused by charging and discharging by adjusting the type and content of the binder (for example, refer to Patent Document 1).

[0003] [Prior art literature]

[0004] (Patent Document)

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-285966 Summary of the invention

[0006] [Problems to be solved by the invention]

[0007] There is a problem as described in Comparative Document 1, that is, only using an adhesive to bond the electrode active material, the bonding force of the adhesive will decrease with charging and discharging. Assuming that the amount of adhesive is increased, the bonding force can be enhanced and the expansion and contraction of the electrode can be suppressed. However, there are the following problems: the wettability of the electrolyte is reduced, and the electrode performance is reduced; and the impregnation of the electrolyte is reduced, and the aging time during electrode manufacturing is increased. In addition, there is also the following problem: due to the swelling of the electrode during electrolyte immersion, the density of the electrode active material is reduced, resulting in a decrease in the energy density of the lithium-ion secondary battery.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode for a lithium ion secondary battery and a method for manufacturing the same, which can enhance the bonding force of an electrode active material without increasing the amount of a binder and can obtain a preferred energy density of a lithium ion secondary battery.

[0009] [Technical means to solve the problem]

[0010] (1) The present invention relates to an electrode for a lithium ion secondary battery, comprising an electrode active material, a dendrimer, and a binder, wherein the dendrimer is chemically bonded to a surface of the electrode active material, and the dendrimer is chemically bonded to the binder.

[0011] According to the invention of (1), it is possible to provide an electrode for a lithium ion secondary battery which can enhance the bonding force of an electrode active material without increasing the amount of a binder and can obtain a preferred energy density of a lithium ion secondary battery.

[0012] (2) An electrode for a lithium-ion secondary battery according to (1), wherein the electrode active material is a negative electrode active material, the density of the negative electrode mixture layer after immersion in the electrolyte is at least 95% of the density of the negative electrode mixture layer before immersion in the electrolyte, and the negative electrode mixture layer comprises the electrode active material, the dendrimer, and the binder.

[0013] According to the invention of (2), it is possible to prevent the reduction in the density of the electrode active material of the electrode due to the immersion of the electrolyte. In addition, it is possible to ensure the minimum space inside the battery cell, which takes into account the deviation of the thickness and width of the electrode required for the design of the lithium-ion secondary battery. Therefore, the volume energy density of the lithium-ion secondary battery can be improved.

[0014] (3) The electrode for a lithium ion secondary battery according to (1) or (2), wherein the electrode active material is a negative electrode active material, and the amount of the dendrimer chemically bonded to the surface of the negative electrode active material is 0.1 to 1.0 parts by mass relative to 100 parts by mass of the negative electrode active material.

[0015] According to the invention of (3), the electrode for lithium ion secondary battery described in (2) can be obtained.

[0016] (4) In addition, the present invention relates to a method for manufacturing an electrode for a lithium-ion secondary battery, comprising: an electrode mixture layer forming step, forming an electrode mixture layer on a current collector, the electrode mixture layer comprising an electrode active material, a dendrimer, and a binder; a pressing step, forming an electrode by pressurizing the current collector formed with the electrode mixture layer at a first temperature; and a vacuum drying step, vacuum drying the electrode formed by the pressing step at a second temperature.

[0017] According to the invention of (4), it is possible to produce an electrode for a lithium ion secondary battery which can enhance the bonding force of an electrode active material without increasing the amount of a binder and can obtain a preferred energy density of a lithium ion secondary battery.

[0018] (5) The method for producing an electrode for a lithium ion secondary battery according to (4), wherein the first temperature and the second temperature are adjusted so that the density of the electrode mixture layer after immersion in the electrolyte is adjusted to be at least 95% of the density of the electrode mixture layer before immersion in the electrolyte.

[0019] According to the invention of (5), the electrode for lithium ion secondary battery described in (2) can be produced. DETAILED DESCRIPTION

[0020] Hereinafter, an embodiment of the present invention will be described. However, the content of the present invention is not limited to the description of the following embodiment.

[0021] <Lithium-ion secondary battery>

[0022] The lithium-ion secondary battery of this embodiment comprises: a positive electrode and a negative electrode as electrodes; a separator that electrically insulates the positive electrode and the negative electrode; an electrolyte; and an outer body that contains the above substances. Inside the outer body, the positive electrode and the negative electrode face each other in a manner of sandwiching the separator, and at least a portion of the separator is immersed in the electrolyte.

[0023] [Electrodes for lithium-ion secondary batteries]

[0024] The positive electrode has a positive electrode composite layer as an electrode composite layer formed on the positive electrode current collector, and the negative electrode has a negative electrode composite layer as an electrode composite layer formed on the negative electrode current collector. The electrode for lithium ion secondary battery of this embodiment can be applied to the positive electrode or the negative electrode. It is particularly preferred to be applied to the negative electrode having the following tendency: the volume changes greatly due to the insertion and separation of lithium ions during charging and discharging.

[0025] (Electrode mixture layer)

[0026] The positive electrode composite layer at least includes a positive electrode active material, a dendritic polymer, and a binder as an electrode active material. Similarly, the negative electrode composite layer at least includes a negative electrode active material, a dendritic polymer, and a binder as an electrode active material. In addition, the electrode composite layer may also include a conductive additive. In the electrode composite layer, countless particles of the electrode active material are arranged in an aggregated manner. Dendritic polymers are chemically bonded to the surface of the particles of the electrode active material. In addition, the dendritic polymer is chemically bonded to the binder. As a result, the bonding force between the electrode active materials can be increased without increasing the amount of the binder, the density of the electrode active materials can be maintained, and the expansion and contraction of the electrode can be reduced during charging and discharging.

[0027] The density of the electrode mixture layer after impregnation with the electrolyte is preferably more than 95% of the density of the electrode mixture layer before impregnation with the electrolyte. Thereby, the reduction in the density of the electrode active material of the electrode caused by the impregnation of the electrolyte can be prevented. In addition, the space inside the battery cell can be ensured to a minimum, and this space takes into account the deviation in the thickness and width of the electrode required for the design of the lithium-ion secondary battery. Therefore, the volume energy density of the lithium-ion secondary battery can be improved. From the above viewpoints, the density of the negative electrode mixture layer after impregnation with the electrolyte is preferably 1.4g / cm 3 above.

[0028] (Electrode Active Material)

[0029] Examples of the negative electrode active material include carbon powder (amorphous carbon), silicon dioxide (SiO x ), titanium composite oxide (Li 4 Ti 5 O 7 、TiO 2 , Nb 2 TiO 7 ), tin composite oxides, lithium alloys, metallic lithium, etc., and one or more of them can be used. As the aforementioned carbon powder, one or more of soft carbon (easy graphitization carbon), hard carbon (difficult graphitization carbon), and graphite can be used.

[0030] As the positive electrode active material, for example, lithium composite oxide (LiNi x Co y Mn z O 2 (x+y+z=l), LiNi x Co y Al z O 2 (x+y+z=l)), lithium iron phosphate (LiFePO 4 (LFP)) etc. The above may be used alone or in combination of two or more.

[0031] The electrode active material preferably has at least a portion of a hydroxyl group or a carboxyl group, thereby allowing the dendrimer to chemically bond to the surface of the electrode active material.

[0032] (Dendrimer)

[0033] Dendrimer is a general term for polymers having a branched structure. Examples of dendrimers include dendrons, dendrimers, and hyperbranched polymers.

[0034] Dendrons can be synthesized by common methods or commercial products can be used. Such commercial products can be obtained from Aldrich, for example. Specific examples of dendrons manufactured by Aldrich include: polyester-8-hydroxy-1-ethynyl bis-MPA dendron, third generation (Catalog No. 686646); polyester-16-hydroxy-1-ethynyl bis-MPA dendron, fourth generation (Catalog No. 686638); polyester-32-hydroxy-1-ethynyl bis-MPA dendron, fifth generation (Catalog No. 686611); polyester-8-hydroxy-1-carboxyl bis-MPA dendron, third generation (Catalog No. 686670); polyester-16-hydroxy-1-carboxyl bis-MPA dendron, fourth generation (Catalog No. 686662); polyester-32-hydroxy-1-carboxyl bis-MPA dendron, fifth generation (Catalog No. 686654).

[0035] Dendrimers can be synthesized using conventional methods or commercially available from Aldrich. Examples include: amino-terminated polyamidoamine dendrimers, ethylenediamine core, generation 0.0 (Catalog No. 412368); polyamidoamine dendrimers, ethylenediamine core, generation 1.0 (Catalog No. 412368); polyamidoamine dendrimers, ethylenediamine core, generation 2.0 (Catalog No. 412406); polyamidoamine dendrimers, ethylenediamine core, generation 3.0 (Catalog No. 412407); 422)); polyamidoamine dendrimer, ethylenediamine core, 4.0 generation (catalog number: 412446)); polyamidoamine dendrimer, ethylenediamine core, 5.0 generation (catalog number: 536709)); polyamidoamine dendrimer, ethylenediamine core, 6.0 generation (catalog number: 536717)); polyamidoamine dendrimer, ethylenediamine core, 7.0 generation (catalog number: 536725)), etc. In addition to the amino terminal, the dendrimers with hydroxyl terminal, carboxyl terminal, and trialkoxysilyl terminal can also be obtained.

[0036] In addition to being synthesized using conventional methods, hyperbranched polymers can also be obtained from commercial products from Aldrich, such as hyperbranched bis-MPA polyester-16-hydroxy, second generation (catalog number: 686603); hyperbranched bis-MPA polyester-32-hydroxy, third generation (catalog number: 686581); hyperbranched bis-MPA polyester-64-hydroxy, fourth generation (catalog number: 686573), etc.

[0037] The amount of the dendrimer chemically bonded to the surface of the electrode active material is preferably 0.1 to 1.0 parts by mass relative to 100 parts by mass of the electrode active material. In addition, it is more preferably 0.25 to 1.0 parts by mass. Thus, the swelling of the electrode can be suppressed without increasing the amount of the binder component in the electrode. Therefore, the energy density of the electrode and the lithium-ion secondary battery monomer can be increased.

[0038] The dendrimer preferably has a branched structure within a certain range and has a functional group capable of cross-linking reaction at the terminal. Thus, since the bonding force between the active materials is maintained and the branched structure of the appropriate molecular weight does not hinder the movement of lithium ions, a low-resistance battery cell can be made even if a high-density electrode body is formed in the battery cell. The following shows a preferred example of a dendrimer. The dendrimer shown below has the characteristics of being electrochemically stable and not easily decomposed in the battery.

[0039] The dendrimer preferably has 4 or more molecular ends in one molecule. In addition, it is preferred to have a specific functional group described later. By having a number of molecular ends within the above range, when the molecular end has a specific functional group, the contact probability of the specific functional group with the electrode active substance increases. Therefore, the amount of chemical bonding between the dendrimer and the electrode active substance is within an appropriate range, and the surface of the electrode active substance can be firmly chemically bonded to cover the surface of the electrode active substance. The dendrimer more preferably has 4 or more and 64 or less molecular ends. In addition, it is further preferred to have 8 or more hydroxyl groups and at least 1 carboxyl group as the above-mentioned specific functional group. Thus, for example, by dehydration condensation between the dendrimer and the electrode active substance, an ether bond is formed. In addition, any reaction can also be used to give the above-mentioned specific functional group to the terminal active group of the dendrimer exemplified above.

[0040] The number average molecular weight of the dendrimer is preferably 300 or more and 100,000 or less, and further preferably 800 or more and 10,000 or less. If the number average molecular weight is within the above range, the lithium ion insertion surface on the surface of the electrode active material particle can be fully covered, and the direct contact of the electrolyte on the lithium ion insertion surface can be suppressed, so that the durability of the electrode and the electrolyte can be improved. In addition, since the electrode mixture layer is covered with the dendrimer to a degree that does not hinder the movement of lithium ions, good lithium ion conductivity of the electrode mixture layer can be obtained.

[0041] (Adhesive)

[0042] The binder forms a chemical bond with the dendrimer. For example, the binder forms an ether bond with the dendrimer by dehydration condensation. The binder preferably has at least one of a hydroxyl group, a carboxyl group, a sulfonic acid group, a sulfinic acid group, a phosphoric acid group, and a phosphonic acid group.

[0043] As adhesives, cellulose polymers, fluorine resins, vinyl acetate copolymers, rubbers, etc. can be cited. Specifically, as adhesives when using solvent-based dispersion media, polyvinylidene fluoride (PVDF), polyimide (PI), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), etc. can be cited; as adhesives when using aqueous dispersion media, styrene-butadiene rubber (SBR), acrylic acid-modified SBR resin (SBR latex), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), hydroxypropyl methylcellulose (HPMC), tetrafluoroethylene monohexafluoropropylene copolymer (FEP), etc. can be cited. One of the above can be used, or two or more can be used in combination.

[0044] (Conductive additive)

[0045] Examples of the conductive auxiliary agent include carbon black such as acetylene black (AB) and Ketjen black (KB), carbon materials such as graphite powder, and conductive metal powders such as nickel powder. These may be used alone or in combination of two or more.

[0046] (Current Collector)

[0047] As materials for the positive electrode collector and the negative electrode collector, there can be listed: foils or plates of copper, aluminum, nickel, titanium, stainless steel; carbon sheets, carbon nanotube sheets, etc. The above materials can be used alone, or a metal foil composed of two or more materials can be used as needed. The thickness of the positive electrode collector and the negative electrode collector is not particularly limited, but for example, it can be set to a thickness in the range of 5 to 100 μm. From the viewpoint of improving structure and performance, the thickness of the positive electrode collector 2 and the negative electrode collector 5 is preferably set to a thickness in the range of 7 to 20 μm.

[0048] [Diaphragm]

[0049] The separator is not particularly limited, and examples thereof include porous resin sheets (films, nonwoven fabrics, etc.) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide.

[0050] [Electrolyte]

[0051] As the electrolyte, an electrolyte consisting of a non-aqueous solvent and an electrolyte can be used. The concentration of the electrolyte is preferably set in the range of 0.1 to 10 mol / L. An additive may also be added to the electrolyte, the additive comprising at least one compound selected from the group consisting of vinylene carbonate, fluoroethylene carbonate and propane sultone. Thus, by using an electrolyte to which a compound having reductive decomposition properties and easily forming an SEI film is added, the added compound is preferentially decomposed in the electrolyte and forms an SEI film on the negative electrode, thereby improving the durability of the electrolyte.

[0052] (Non-aqueous solvent)

[0053] The non-aqueous solvent is not particularly limited, and examples thereof include aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones. Specifically, examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile (AN), propionitrile, nitromethane, N,N-dimethylformamide (DMF), dimethyl sulfoxide, sulfolane, and γ-butyrolactone.

[0054] (Electrolytes)

[0055] Examples of the electrolyte contained in the electrolytic solution include LiPF 6 , LiBF 4 、LiClO 4 、LiN(SO 2 CF 3 )、LiN(SO 2 C 2 F 5 ) 2 、LiCF 3 SO 3 ,LiC 4 F 9 SO 3 、LiC(SO 2 CF 3 ) 3 、LiF、LiCl、LiI、Li 2 S. Li 3 N.Li 3 P.Li 10 G 2 S 12 (LGPS), Li 3 PS 4 , Li 6 PS 5 Cl, Li 7 P 2 S 8 I. Li x PO y N z (x=2y+3z-5,LiPON)、Li 7 La 3 Zr 2 O 12 (LLZO), Li 3x La2 / 3-x TiO 3 (LLTO), Li 1+x Al x Ti 2-x (PO 4 ) 3 (0≤x≤l, LATP), Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP), Li 1+x+y AlxTi 2-x PcqI 3-y O 12 , Li 1+x+y Al x (Ti, Ge) 2-x PcqI 3-y O 12 , Li 4-2x Zn x GeO 4 (LISICON), etc. Among them, LiPF is preferably used. 6 , LiBF 4 , or a mixture thereof as the electrolyte.

[0056] As the electrolyte, in addition to the above, an electrolyte containing an ionic liquid or an electrolyte containing a copolymer containing an aliphatic chain such as polyethylene oxide (PEO) and polyvinylidene fluoride (PVDF) copolymer in the ionic liquid can also be listed. The electrolyte containing an ionic liquid can flexibly cover the surface of the electrode active material and can form a portion that contacts the surface of the electrode active material for ion movement.

[0057] <Method for producing an electrode for a lithium ion secondary battery>

[0058] The manufacturing method of the lithium-ion secondary battery of this embodiment comprises: an electrode mixture layer forming step, forming an electrode mixture layer on a collector, wherein the electrode mixture layer comprises an electrode active material, a dendrimer, and a binder; a pressing step, forming an electrode by pressurizing the collector formed with the electrode mixture layer at a first temperature; and a vacuum drying step, vacuum drying the electrode formed by the pressing step at a second temperature.

[0059] (Electrode Mixture Layer Formation Step)

[0060] The electrode mixture layer forming process may include, for example, a stirring process, stirring the mixture of the electrode active material and the dendrimer; a reduced pressure drying process, after the stirring process, drying the mixture under reduced pressure; an electrode slurry making process, after the reduced pressure drying process, mixing the mixture with a binder and dispersing it in a solvent to make an electrode slurry; and an electrode slurry coating process, coating the electrode slurry on the collector and drying it. The electrode mixture layer forming process is not limited to the above process as long as it can form the electrode mixture layer on the collector.

[0061] The reduced pressure drying step is, for example, a step in which the mixture of the electrode active material and the dendrimer is dried under reduced pressure at a predetermined temperature and time, so that the dendrimer is chemically bonded to the surface of the electrode active material. The temperature during the reduced pressure drying can be set to 100 to 200° C., preferably 120 to 150° C. The drying time is preferably 12 hours or more.

[0062] (Pressing process)

[0063] The pressing step is a step of forming an electrode by pressing the current collector having the electrode mixture layer formed thereon at a first temperature. The first temperature can be set, for example, to room temperature to 200° C., preferably 120° C. to 160° C. There is no particular limitation on the pressing method, and for example, a roll press, a hot press, etc. can be used.

[0064] (Vacuum drying process)

[0065] The vacuum drying process is a process of vacuum drying the electrode that has undergone the pressing process at a second temperature. Utilizing this process, chemical bonds are formed between the electrode active materials chemically bonded to the dendrimer, and between the dendrimer and the binder. The second temperature can be set, for example, to 120 to 200°C. The second temperature is preferably 120°C to 160°C. When the second temperature exceeds 200°C, it sometimes exceeds the heat resistance temperature of the binder, and the effect of suppressing the swelling of the electrode is reduced. When the second temperature is lower than 120°C, it takes time for the water generated by the dehydration reaction to be discharged from the electrode mixture layer having a pore structure, and therefore, the production efficiency is reduced. The vacuum condition of the vacuum drying process can be set, for example, to below -98kPa.

[0066] By adjusting the first temperature in the pressing process and the second temperature in the vacuum drying process, the density of the electrode mixture layer after the electrolyte is impregnated can be adjusted to more than 95% of the density of the electrode mixture layer before the electrolyte is impregnated. The first temperature can be adjusted, for example, using a non-contact thermometer attached to a roller press. The second temperature can be adjusted using a thermometer such as a thermistor attached to a vacuum high temperature tank.

[0067] [Example]

[0068] Hereinafter, the content of the present invention will be described in more detail based on examples. The content of the present invention is not limited to the description of the following examples.

[0069] The negative electrode plate of Example 1 is prepared in the following order. First, 0.1 parts by mass of a dendron (polyester-32-hydroxy-1-carboxybis-MPA dendron, 5th generation) as a dendritic polymer is weighed relative to 100 parts by mass of graphite as an electrode active material, and stirred in an aqueous solution for 1 hour. Then, it is dried under reduced pressure at 150°C for 16 hours, thereby obtaining a negative electrode material having a dendritic polymer bonded to the surface of the electrode active material. In addition, it is believed that all the dendrons as the above-mentioned dendritic polymers are chemically bonded to the surface of the electrode active material. Next, carboxymethyl cellulose (CMC) and a conductive aid are mixed and dispersed using a planetary mixer. Then, the negative electrode material obtained as described above is mixed and dispersed again using a planetary mixer. Then, a dispersion solvent and styrene-butadiene rubber (SBR) are added for dispersion to prepare an electrode slurry. The electrode slurry is coated on a current collector made of Cu and dried.

[0070] The Cu current collector coated with the electrode slurry and dried was pressed using a roller press at room temperature. It was placed in a vacuum drying furnace, heated to a vacuum drying temperature of 120°C, and subjected to a condensation reaction at -98 kPa or below for 12 hours to produce the negative electrode plate of Example 1. For the electrodes of other Examples and Comparative Examples, the negative electrode plates of each Example and Comparative Example were produced in the same manner as Example 1, except that the dendrimer content, pressing temperature, and vacuum drying temperature were set as shown in Table 1.

[0071] [Composite material density retention rate]

[0072] The negative electrode plates of each embodiment and comparative example were punched into 16 mm ф holes to prepare test pieces. The film thickness at room temperature after vacuum drying was measured using a micrometer, and the weight was measured to calculate the density (g / cm 3 ). Then, 10 μL of a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC): EMC = 3:4:4 (volume ratio) was dripped onto the test piece, and a glass piece was placed to prevent the solvent from drying. After 30 minutes, the glass piece was removed and the excess solvent was removed by allowing it to seep into a wipe (Kimwipe). After visually confirming that the solvent had been removed, the film thickness of the test piece was measured with a micrometer, and the weight was measured and the density (g / cm) of the test piece after the solvent was dripped was calculated. 3 The ratio of the density of the test piece after the solvent was dripped to the density of the test piece before the solvent was dripped was defined as the composite material density retention rate (%). The results are shown in Table 1.

[0073] [Manufacturing of lithium-ion secondary batteries]

[0074] A lithium ion secondary battery was produced using the negative electrode plates of the examples and comparative examples.

[0075] (Production of positive electrode)

[0076] Conductive additive and polyvinylidene fluoride (PVDF) were mixed and dispersed in a rotary mixer, and then Li as the positive electrode active material was mixed. 1 Ni 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) and mixed using a planetary mixer. Then, N-methyl-N-pyrrolidone (NMP) was added to prepare an electrode slurry. The electrode slurry was coated on an Al current collector and dried, then pressed using a roller press and dried in a vacuum at 120°C to prepare a positive electrode plate. The prepared electrode plate was punched into 30 mm × 40 mm for use. The thickness of the positive electrode plate was set to 70 μm.

[0077] The laminated body with the separator sandwiched between the negative electrode and the positive electrode prepared above was introduced into a container formed by heat-sealing an aluminum laminate for secondary batteries (manufactured by Dai Nippon Printing Co., Ltd.) into a bag shape, and an electrolyte was injected into each electrode interface, thereby preparing a lithium ion secondary battery. As the electrolyte, LiPF 6 The solution was dissolved in a solution in which ethylene carbonate, ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 30:30:40 to obtain a 1.2 mol / L solution. The following test was performed using the prepared lithium ion secondary battery.

[0078] [10s asst initial resistance measurement]

[0079] The following method is used to measure the 10s asst initial resistance of the lithium ion secondary battery of each embodiment and comparative example. First, the charge level (State of Charge, SOC) of the lithium ion secondary battery is adjusted to 50%. Then, the C rate is set to 0.5C for a 10-second pulse discharge, and the voltage during the 10-second discharge is measured. Then, the horizontal axis is set to the current value, the vertical axis is set to the voltage, and the voltage during the 10-second discharge is plotted relative to the current at 0.2C. Then, after standing for 5 minutes, supplementary charging is performed to restore the SOC to 50%, and then, it is placed for another 5 minutes. Then, the above operation is performed for each C rate of 1C, 1.5C, 2C, 2.5C, and 3C, and the voltage during the 10-second discharge is plotted relative to the current at each C rate. Then, the slope of the approximate straight line obtained from each plot is set to the 10s asst initial battery resistance of the lithium ion secondary battery. The results are shown in Table 1.

[0080] Table 1

[0081]

[0082] From the results in Table 1, it can be confirmed that the electrode for lithium ion secondary battery of each example has a higher composite density retention rate than the electrode for lithium ion secondary battery of the comparative example, and can prevent the density of the electrode active material of the electrode from decreasing.

Claims

1. An electrode for a lithium ion secondary battery, It contains electrode active material, dendrimer, and binder. The dendrimer is chemically bonded to the surface of the electrode active material. The dendrimer is chemically bonded to the binder. The aforementioned electrode active material is a negative electrode active material, The density of the negative electrode mixture layer after the electrolyte solution immersion is 95% or more of the density of the negative electrode mixture layer before the electrolyte solution immersion, and the negative electrode mixture layer includes the electrode active material, the dendrimer, and the binder. The dendrimer is a dendron having 8 or more hydroxyl groups and at least one carboxyl group at the molecular terminal.

2. The lithium ion secondary battery electrode according to claim 1, in, The aforementioned electrode active material is a negative electrode active material, The amount of the dendrimer chemically bonded to the surface of the negative electrode active material is 0.1 to 1.0 part by mass based on 100 parts by mass of the negative electrode active material.

3. A method for producing an electrode for a lithium ion secondary battery, comprising: An electrode mixture layer forming step is to form an electrode mixture layer on the current collector, wherein the electrode mixture layer comprises an electrode active material, a dendrimer, and a binder; a pressing step of forming an electrode by pressing the current collector having the electrode mixture layer formed thereon at a first temperature; and a vacuum drying step of vacuum drying the electrode formed by the pressing step at a second temperature, The aforementioned electrode active material is a negative electrode active material, The density of the negative electrode mixture layer after the electrolyte solution immersion is 95% or more of the density of the negative electrode mixture layer before the electrolyte solution immersion, and the negative electrode mixture layer includes the electrode active material, the dendrimer, and the binder. The dendrimer is a dendron having 8 or more hydroxyl groups and at least one carboxyl group at the molecular end. The dendrimer is chemically bonded to the surface of the electrode active material. The dendrimer is chemically bonded to the binder.

4. The method for producing an electrode for a lithium ion secondary battery according to claim 3, in, The first temperature and the second temperature are adjusted so that the density of the electrode mixture layer after the electrolyte solution immersion is adjusted to 95% or more of the density of the electrode mixture layer before the electrolyte solution immersion.

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