JP2018067463A - Method for manufacturing negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a negative electrode by use of a negative electrode active material, ceramic particles, and a thickener, by which a negative electrode capable of achieving the effect of enhancement in battery cycle characteristic can be manufactured readily.SOLUTION: A method for manufacturing a negative electrode comprises: the step S101 of coating a negative electrode current collector with a negative electrode paste including a negative electrode active material, ceramic particles, and a thickener; and the step S102 of drying the coated negative electrode paste to form a negative electrode active material layer. The thickener comprises a low molecular gelatinizer consisting of a peptide lipid compound. In the negative electrode paste, the low molecular gelatinizer is included at 0.5-10 mass% to a total solid content of the negative electrode paste. In the negative electrode paste, the ceramic particles are included at 3-20 mass% to the total solid content of the negative electrode paste.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a negative electrode.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries (lithium secondary batteries) are lighter and have higher energy density than existing batteries. It is used as a power source. In particular, lithium-ion secondary batteries that are lightweight and provide high energy density will become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is expected to do.

  A negative electrode used for a lithium ion secondary battery typically has a configuration in which a negative electrode active material layer is provided on a negative electrode current collector. The negative electrode active material layer typically includes a negative electrode active material such as a carbon material. The negative electrode active material is a material capable of reversibly occluding and releasing lithium ions that are charge carriers. A negative electrode used in a lithium ion secondary battery is typically manufactured by applying a mixed paste containing a negative electrode active material on one side or both sides of a negative electrode current collector, drying, and then pressing (rolling) the negative electrode current collector. . According to such a manufacturing method, the negative electrode active material can be filled and arranged at a high density.

  However, there are gaps between the negative electrode active materials. Therefore, in Patent Document 1, it is proposed to mix ceramic particles with a paste for producing a negative electrode active material layer and arrange the ceramic particles in a gap existing between the negative electrode active material layers. Patent Document 1 describes that this improves the mechanical strength of the negative electrode and improves the cycle characteristics.

Japanese Patent Laid-Open No. 10-255807

  When preparing the negative electrode paste, in order to improve the dispersibility of the negative electrode active material and adjust the viscosity of the negative electrode paste, it is generally performed to add a thickener such as carboxymethylcellulose. However, according to the study by the present inventors, when a general thickener such as carboxymethylcellulose is used for the negative electrode active material and the negative electrode paste containing ceramic particles, the mechanical strength of the negative electrode due to the ceramic particles is It has been found that the improvement effect cannot be obtained, and it is difficult to obtain the effect of improving the cycle characteristics of the battery.

  Accordingly, an object of the present invention is to provide a method for producing a negative electrode using a negative electrode active material, ceramic particles, and a thickener, and capable of easily producing a negative electrode that provides an effect of improving battery cycle characteristics. There is to do.

The method for producing a negative electrode disclosed herein includes a step of applying a negative electrode paste containing a negative electrode active material, ceramic particles, and a thickener on a negative electrode current collector, and drying the coated negative electrode paste. And forming a negative electrode active material layer. The thickener includes a low molecular gelling agent composed of a lipid peptide compound. In the negative electrode paste, the low-molecular gelling agent is contained in an amount of 0.5 to 10% by mass with respect to the total solid content of the negative electrode paste. In the negative electrode paste, the ceramic particles are contained in an amount of 3 to 20% by mass with respect to the total solid content of the negative electrode paste.
According to such a configuration, by using a low molecular gelling agent composed of a lipid peptide compound as a thickening agent, the thickening agent is temporarily reduced in molecular weight due to shearing force during kneading of the negative electrode paste. And the viscosity of the negative electrode paste can be reduced. Therefore, since the negative electrode paste has a low viscosity, the thickener and the ceramic particles move to the gaps between the negative electrode active materials generated by removing the solvent during drying, and the ceramic particles are sufficiently placed in the gaps between the negative electrode active materials. Can be arranged. Then, the solid skeleton of the negative electrode active material layer can be constructed by self-organizing the low molecular weight gelling agent into a polymer fiber by the completion of drying. For this reason, the negative electrode which gives the cycling characteristics improvement effect of a battery can be manufactured easily.

It is a flowchart which shows each process of the manufacturing method of the negative electrode which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the internal structure of the lithium ion secondary battery using the negative electrode obtained by the manufacturing method which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the winding electrode body of the lithium ion secondary battery using the negative electrode obtained by the manufacturing method which concerns on one Embodiment of this invention.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, the general configuration and manufacturing process of the negative electrode that does not characterize the present invention) It can be grasped as a design matter of those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Also, the dimensional relationships (length, width, thickness, etc.) in the figure do not reflect actual dimensional relationships.

In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor. Further, in the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as a charge carrier and is charged / discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes.
Hereinafter, the present invention will be described in detail with reference to one embodiment, but the present invention is not intended to be limited to such an embodiment.

  In FIG. 1, each process of the manufacturing method of the negative electrode which concerns on this embodiment is shown. The negative electrode manufacturing method according to the present embodiment includes a step (paste coating step) S101 of applying a negative electrode paste containing a negative electrode active material, ceramic particles, and a thickener on a negative electrode current collector, and the coating. And a step of drying the processed negative electrode paste to form a negative electrode active material layer (drying step) S102. The said thickener contains the low molecular gelling agent comprised from a lipid peptide compound. In the negative electrode paste, the low-molecular gelling agent is contained in an amount of 0.5 to 10% by mass with respect to the total solid content of the negative electrode paste. In the negative electrode paste, the ceramic particles are contained in an amount of 3 to 20% by mass with respect to the total solid content of the negative electrode paste.

  First, paste application process S101 is demonstrated. Paste coating process S101 can be implemented as follows, for example. First, a paste containing a negative electrode active material, ceramic particles, and a thickener is prepared. In this specification, “paste” refers to a mixture in which a part or all of the solid content is dispersed in a solvent, and includes so-called “slurry”, “ink”, and the like.

As a negative electrode active material, what is used for the conventional secondary battery can be used without particular limitation. For example, a carbon material having a graphite structure at least in part can be mentioned, and among these, carbon materials such as graphite, hard carbon, and soft carbon can be suitably used. The surface of the carbon material may be covered with an amorphous carbon film.
The average particle diameter of the negative electrode active material is not particularly limited, and may be approximately the same as that of a conventional secondary battery. The average particle diameter of the negative electrode active material is, for example, 50 μm or less, typically 20 μm or less, preferably 1 μm to 20 μm, more preferably 5 μm to 15 μm.
In the present specification, “average particle size” means, unless otherwise specified, a particle size (D50) at which the cumulative frequency is 50% by volume in the particle size distribution measured by the laser diffraction scattering method. Say.
The negative electrode active material is preferably contained in an amount exceeding 50% by mass in the total solid content of the negative electrode paste, more preferably 70% by mass to 96% by mass, and still more preferably 75% to 95% by mass.

As the ceramic particles, those not involved in the charge / discharge reaction are preferable, and examples thereof include alumina, boehmite, aluminum hydroxide and the like. These can be used alone or in combination of two or more. Since the ceramic particles are usually a material much harder than the negative electrode active material particles that are carbon materials, the mechanical strength, for example, the hardness of the negative electrode active material layer can be increased. As a result, the secondary battery using the negative electrode obtained by the manufacturing method of the present embodiment has excellent cycle characteristics (particularly high-rate cycle characteristics) because the compression deformation of the negative electrode active material layer is suppressed.
The average particle size of the ceramic particles is not particularly limited, but is preferably 1/5 or less of the average particle size of the negative electrode active material.

  In the negative electrode paste, the ceramic particles are contained in an amount of 3 to 20% by mass with respect to the total solid content of the negative electrode paste. When the content of the ceramic particles is less than 3% by mass, the effect of improving the mechanical strength of the negative electrode active material layer obtained by containing the ceramic particles, and thus the effect of improving the cycle characteristics of the battery cannot be sufficiently obtained. On the other hand, when the content of the ceramic particles exceeds 20% by mass, the ceramic particles are components that become resistors, so the proportion of the components that become resistors in the negative electrode active material layer increases, and the cycle characteristics of the battery deteriorate. Invite.

  The negative electrode paste contains a solvent. As the solvent, an aqueous solvent is preferably used. The aqueous solvent refers to water or a mixed solvent mainly composed of water. Examples of the solvent other than water constituting the mixed solvent include organic solvents (eg, lower alcohol, lower ketone, and the like) that can be uniformly mixed with water. The aqueous solvent preferably contains 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more. Most preferably, the aqueous solvent is water.

  In this embodiment, a low molecular gelling agent composed of a lipid peptide compound is used as the thickener. The lipid peptide compound is a compound obtained by binding a fatty acid and a peptide through an amide bond, or a salt thereof. As the low molecular weight gelling agent, one type of lipid peptide compound may be used alone, or two or more types may be used in combination.

  The carbon number of the fatty acid (corresponding to the carbon number of the acyl group in formula (1) and formula (2) described later) is, for example, 10-30. In addition, carbon number here contains carbon of a carbonyl group (-CO-).

  The peptide has, for example, about 2 to 10 amino acid residues. The amino acid residue constituting the peptide may be a residue of two or more amino acids, or may be a residue of one amino acid. The amino acid can be selected from 20 types of amino acids, and examples thereof include glycine and histidine.

  When the number of amino acid residues constituting the peptide is 2 (when the peptide is a dipeptide), the lipid peptide compound is represented, for example, by the following formula (1). When the number of amino acid residues constituting the peptide is 3 (when the peptide is a tripeptide), the lipid peptide compound is represented, for example, by the following formula (2). As shown in the following formulas (1) and (2), the lipid peptide compound is composed of a hydrophobic lipid part (acyl group) and a hydrophilic peptide part.

In Formula (1) and Formula (2), R ₁ is, for example, a linear aliphatic group having about 9 to 29 carbon atoms (eg, an alkyl group). R _{2 to} R ₄ are each independently, for example, a group derived from any amino acid selected from all 20 amino acids, that is, R when the amino acid is represented by R—CH (CH ₂ ) COOH. The corresponding group (but hydrogen when the amino acid is glycine).

In addition, in the lipid peptide compound, in Formula (1) and Formula (2), one or more fatty acids are further bonded to the amino group of the peptide part (including the amino group of R _{2 to} R ₄ ) by an amidation reaction. It may be a compound.

  The molecular weight of the lipid peptide compound (one molecule) is, for example, about 50 to 1,000. Moreover, the low molecular weight gelling agent may usually contain an aggregate of a plurality of lipid peptide compounds, and the weight average molecular weight of the low molecular weight gelling agent is, for example, about 50 to 10,000. In addition, the weight average molecular weight of a low molecular gelling agent can be calculated | required by a gel permeation chromatography (GPC) measurement.

  The lipid peptide compound has a characteristic of forming a pseudo polymer fiber (supermolecular fiber) by self-assembly (self-organization) one-dimensionally in a solvent. For example, when a lipid peptide compound is introduced into an aqueous solvent, a plurality of lipid peptide molecules gather around the hydrophobic lipid part. In addition, between the plurality of lipid peptide molecules, the hydrogen of the peptide bond (—CONH—) of the peptide part forms a hydrogen bond. That is, a plurality of lipid peptide molecules form an intermolecular non-covalent bond. In this way, the lipid peptide compound forms a polymer fiber.

  Further, the formed polymer fiber is easily cut into a low molecular fiber or a lipid peptide molecule. This is because the polymer fibers are formed by hydrogen bonds having a weak binding force. As long as the low molecular fiber or lipid peptide molecule after cutting is in a solvent, it can self-assemble to re-form the polymer fiber.

  Therefore, when a low molecular gelling agent composed of a lipid peptide compound is used as a thickener, the lipid peptide compound is brought into a low molecular fiber or lipid peptide molecule state before the drying step S102 and dried. After step S102, the polymer fibers can be in a self-assembled polymer fiber state, whereby a large number of ceramic particles can be arranged in the gaps between the negative electrode active materials, and the strength of the negative electrode active material layer can be increased. Can be improved.

This will be described in detail. In the drying step S <b> 102, a space may be generated at the place where the solvent exists by removing the solvent. When a polymer thickener such as carboxymethylcellulose is used as in the prior art, the initial viscosity of the negative electrode paste is high, and the viscosity further increases as it dries. Therefore, in the drying step S102, the viscosity of the negative electrode paste becomes too high, and the polymer thickener and the ceramic particles cannot move, and the space generated by the removal of the solvent is removed by the polymer thickener and the ceramic particles. Can't fill. Therefore, in the negative electrode active material layer, the ceramic particles cannot be effectively arranged in the gaps between the negative electrode active materials, and the mechanical strength improvement effect of the negative electrode active material layer by the ceramic particles (and the battery cycle characteristic improvement effect) It is difficult to get enough.
On the other hand, it is conceivable to lower the viscosity of the negative electrode paste by using a low molecular thickener instead of the high molecular thickener. When the low molecular thickener is used, since the viscosity of the negative electrode paste is low, in the drying step S102, the low molecular thickener thickener moves to the space generated by the removal of the solvent. The particles also move (note that this movement occurs as a driving force by a capillary phenomenon in which the residual solvent moves into a narrow space (a gap between the negative electrode active materials) as the solvent decreases due to drying). As a result, the ceramic particles can be effectively arranged in the gaps between the negative electrode active materials. However, since the low molecular thickener has a short molecular chain and weak bonding force between the negative electrode active materials, it cannot build a strong skeleton in the negative electrode active material layer. As a result, the mechanical strength of the negative electrode active material layer is weakened.
However, according to the low molecular gelling agent composed of the lipid peptide compound, before the drying step S102, the lipid peptide compound is brought into a state of low molecular fiber or lipid peptide molecule, so that in the drying step S102, the solvent The low-molecular gelling agent moves to the space created by the removal of the solvent as the solvent moves due to capillary action, and the ceramic particles also move accordingly. As a result, the ceramic particles can be effectively arranged in the gaps between the negative electrode active materials. When drying is completed, the low-molecular gelling agent is in the state of polymer fibers due to self-organization, and the negative electrode active materials can be bonded with sufficient strength, and a strong skeleton is built in the negative electrode active material layer can do. Therefore, the effect of improving the mechanical strength of the negative electrode active material layer by the ceramic particles can be effectively obtained. And the secondary battery using the negative electrode obtained by the manufacturing method of this embodiment is excellent in cycle characteristics (particularly high rate cycle characteristics) because the compression deformation of the negative electrode active material layer is suppressed.

  In the negative electrode paste, the content of the low-molecular gelling agent is 0.5 to 10% by mass with respect to the total solid content of the negative electrode paste. If the content of the low molecular weight gelling agent is less than 0.5% by mass, the amount of the low molecular weight gelling agent that bonds between the negative electrode active materials becomes too small, and a sufficiently strong skeleton is constructed in the negative electrode active material layer. Can not do it. On the other hand, if it exceeds 10% by mass, the viscosity of the negative electrode paste becomes too high, the thickener and the ceramic particles cannot move, and the ceramic particles are sufficiently placed in the space generated by the removal of the solvent during drying. Can not be.

The negative electrode paste may contain a binder. Examples of the binder include styrene butadiene rubber (SBR) and modified products thereof, acrylonitrile butadiene rubber and modified products thereof, acrylic rubber and modified products thereof, and fluorine rubber. Of these, SBR is preferable.
The binder is preferably contained in an amount of 0.1% by mass to 8% by mass in the total solid content of the negative electrode paste, more preferably 0.2% by mass to 3% by mass, and still more preferably 0.3% by mass to 2% by mass is contained.

  The negative electrode paste may contain a thickener other than the low-molecular gelling agent within the range not impairing the effects of the present invention.

  The solid content concentration of the negative electrode paste is preferably 40% by mass to 80% by mass, and more preferably 45% by mass to 60% by mass. When the solid content concentration is within the above range, the drying efficiency of the negative electrode paste can be improved. Moreover, since handling of the negative electrode paste is facilitated and uniform coating is facilitated, a negative electrode active material layer having a uniform thickness can be easily formed.

  The negative electrode paste can be prepared by mixing a negative electrode active material, ceramic particles, a solvent, and a low-molecular gelling agent as a thickener using a known mixing device, kneading device, or the like. . At the time of mixing or kneading, a condition is selected in which shearing force is generated so that the lipid peptide compound constituting the low molecular gelling agent becomes a low molecular fiber or a lipid peptide molecule. For example, according to the type and amount of the lipid peptide compound, the rotational speed of the mixing device or the kneading device is adjusted so that the lipid peptide compound is in the state of a low molecular fiber or lipid peptide molecule.

Next, the prepared paste is applied onto the negative electrode current collector.
As the negative electrode current collector, like a conventional lithium ion secondary battery, a conductive member made of a metal with good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) is preferably used. Copper is preferred. The shape of the negative electrode current collector is not particularly limited because it may vary depending on the shape of the lithium ion secondary battery constructed using the obtained negative electrode, such as a rod shape, plate shape, sheet shape, foil shape, mesh shape, etc. Various forms may be used. Preferably, the negative electrode current collector is in the form of a sheet or foil. Although the thickness of a negative electrode collector is not specifically limited, When using a copper sheet or copper foil as a negative electrode collector, the thickness is 6 micrometers-30 micrometers, for example.

  The negative electrode paste can be applied to the negative electrode current collector according to a known method. For example, it can be carried out by applying the negative electrode paste onto the negative electrode current collector using a coating apparatus such as a gravure coater, comma coater, slit coater, die coater or the like. Note that the negative electrode active material layer may be formed only on one side of the negative electrode current collector, or may be formed on both sides, preferably on both sides. Therefore, the coating of the negative electrode paste is performed on one side or both sides of the negative electrode current collector, preferably on both sides.

  Next, the drying step S102 will be described. The step S102 can be performed according to a known method. For example, it can be performed by removing the solvent from the negative electrode current collector coated with the negative electrode paste using a drying apparatus such as a drying furnace. The drying temperature and drying time may be appropriately determined according to the type of solvent used, and are not particularly limited. The drying temperature is, for example, more than 70 ° C. and 200 ° C. or less (typically 110 ° C. to 150 ° C.). The drying time is, for example, 10 seconds to 240 seconds (typically 30 seconds to 180 seconds).

By appropriately pressing the negative electrode after drying, the thickness, basis weight, density, etc. of the negative electrode active material layer can be adjusted.
As described above, a negative electrode in which a negative electrode active material layer is formed on a negative electrode current collector can be obtained.

According to the method for manufacturing a negative electrode according to the present embodiment, it is possible to easily manufacture a negative electrode that gives an effect of improving battery cycle characteristics while using a negative electrode paste containing a negative electrode active material, ceramic particles, and a thickener. it can. When the negative electrode obtained by the manufacturing method according to the present embodiment is used for a secondary battery (particularly, a lithium ion secondary battery), the cycle characteristics (particularly, high rate cycle characteristics) are excellent.
Hereinafter, a configuration example of a lithium ion secondary battery manufactured using the negative electrode obtained by the manufacturing method according to the present embodiment will be described with reference to FIGS. 2 and 3. In addition, the secondary battery comprised using the negative electrode obtained by the manufacturing method which concerns on this embodiment is not restricted to the following examples.

  The lithium ion secondary battery 100 shown in FIG. 2 has a flat wound electrode body 20 and a nonaqueous electrolyte solution (not shown) accommodated in a flat rectangular battery case (that is, an exterior container) 30. This is a sealed lithium ion secondary battery 100 to be constructed. The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 set so as to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. Yes. In addition, the battery case 30 is provided with an inlet (not shown) for injecting a non-aqueous electrolyte. The positive terminal 42 is electrically connected to the positive current collector 42a. The negative electrode terminal 44 is electrically connected to the negative electrode current collector plate 44a. As the material of the battery case 30, for example, a light metal material having good thermal conductivity such as aluminum is used.

  As shown in FIGS. 2 and 3, the wound electrode body 20 has a positive electrode active material layer 54 formed along the longitudinal direction on one side or both sides (here, both sides) of an elongated positive electrode current collector 52. The positive electrode sheet 50 and the negative electrode sheet 60 in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62 are two long shapes. The separator sheet 70 is overlapped and wound in the longitudinal direction. The positive electrode active material layer non-forming portion 52a (that is, the positive electrode) formed so as to protrude outward from both ends in the winding axis direction of the wound electrode body 20 (referred to as the sheet width direction orthogonal to the longitudinal direction). The portion where the active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode active material layer non-formed portion 62a (that is, the portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed). ) Are joined with a positive current collector 42a and a negative current collector 44a, respectively.

Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil. Examples of the positive electrode active material included in the positive electrode active material layer 54 include lithium transition metal oxides (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O). ₄ , LiNi _0.5 Mn _1.5 O _{4 and the} like) and lithium transition metal phosphate compounds (eg, LiFePO _{4 and the} like). The positive electrode active material layer 54 can include components other than the active material, such as a conductive material and a binder. As the conductive material, for example, carbon black such as acetylene black (AB) and other (eg, graphite) carbon materials can be suitably used. As the binder, for example, polyvinylidene fluoride (PVdF) can be used.

  For the negative electrode sheet 60, a negative electrode obtained by the manufacturing method according to the above-described embodiment is used.

  Examples of the separator 70 include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat resistant layer (HRL) may be provided on the surface of the separator 70.

The non-aqueous electrolyte can be the same as that of a conventional lithium ion secondary battery, and typically, an organic solvent (non-aqueous solvent) containing a supporting salt can be used. As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, lactones and the like used in electrolytes of general lithium ion secondary batteries are used without particular limitation. Can do. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate. As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , or LiClO ₄ can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.
The non-aqueous electrolyte may contain various additives such as a gas generating agent, a film forming agent, a dispersing agent, and a thickener.

  The lithium ion secondary battery 100 configured as described above can be used for various applications. Suitable applications include driving power sources mounted on vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV).

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Preparation of Negative Electrodes A1-7 and Negative Electrodes B1-6>
Graphite having an average particle diameter of 10 μm as a negative electrode active material, ceramic particles, SBR as a binder, and a thickener, the mass ratio of these materials is graphite: ceramic particles: SBR: thickener = 99-xy: x: 0.5: y was charged into a kneader and kneaded while adjusting the viscosity with water to prepare a negative electrode paste (solid content concentration 50% by mass). In order to give a shearing force during kneading, the rotational speed was set to 50 rpm. However, the rotational speed was set to 20 rpm only when the negative electrode B1 was produced. Table 1 shows the type and amount of ceramic particles used (x in the above ratio), and the type and amount of thickener (y in the above ratio). The negative electrode paste is applied to both sides of a long copper foil (negative electrode current collector) having a thickness of 10 μm with a width of 105 mm, dried, and then pressed to a predetermined thickness. A negative electrode sheet having a layer was produced.

<Negative electrode paste viscosity measurement>
The viscosity of the negative electrode paste was measured using a B-type viscometer at a rotational speed of 20 rpm.

<Spring constant measurement>
50 pieces of the produced negative electrode were cut into 5 cm × 5 cm square and laminated to prepare a measurement sample. This sample was sandwiched between SUS plates, and a load was applied with an autograph precision universal testing machine. The spring constant was calculated as “spring constant = Δ load / Δ thickness displacement”. It can be said that the higher the spring constant, the higher the mechanical strength of the negative electrode active material layer.

<Production of evaluation lithium-ion secondary battery>
A lithium ion secondary battery for evaluation was produced using the produced negative electrode.
Specifically, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (LNCM) having an average particle diameter of 5 μm as a positive electrode active material, acetylene black (AB) as a conductive material, and polyfluorination as a binder Vinylidene (PVdF) was charged into a kneader so that the mass ratio of these materials was LNCM: AB: PVdF = 92: 5: 3, and kneaded while adjusting the viscosity with N-methyl-2-pyrrolidone (NMP). Thus, a positive electrode paste (solid content concentration 50 mass%) was prepared. The positive electrode paste is applied to both sides of a 15 μm-thick long aluminum foil (positive electrode current collector) with a width of 100 mm, dried, and then pressed to a predetermined thickness, whereby a positive electrode active material is formed on both surfaces of the positive electrode current collector. A positive electrode sheet having a layer was produced.

  The positive electrode sheet and the negative electrode sheet produced above were laminated together with two separator sheets having a thickness of 24 μm (a porous sheet having a three-layer structure of PP / PE / PP), wound, and then pressed from the side surface direction. By flattening, a flat wound electrode body was produced. Next, a positive electrode terminal and a negative electrode terminal connected to the case lid were welded to the wound electrode body, and inserted into a rectangular battery case body having a liquid injection hole. The case lid and the battery case main body were welded and sealed.

Subsequently, a non-aqueous electrolyte was injected from the liquid injection hole of the battery case, and a sealing screw was tightened in the liquid injection hole to seal it airtight. The non-aqueous electrolyte includes a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 3: 3: 4 as a supporting salt. In which LiPF ₆ was dissolved at a concentration of 1.0 mol / L was used. The side surface of the battery case was restrained with a 500 kgf load with a SUS plate to obtain an evaluation lithium ion secondary battery (battery design capacity: 5 Ah).

<Measurement of battery resistance>
The prepared lithium ion secondary battery was adjusted to a SOC 60% charge state and then placed in an environmental atmosphere at 25 ° C. The battery resistance was calculated by discharging for 10 seconds at a current value of 20 C, measuring the voltage value 10 seconds after the start of discharge. This was defined as the initial battery resistance.

<High rate charge cycle test>
The lithium ion secondary battery whose battery resistance was measured was adjusted to a SOC 60% charge state and then placed in an environmental atmosphere at 25 ° C. Then, 2000 cycles of charging and discharging were performed with a constant current charge of 10 seconds at 30 C, a pause of 10 seconds, a constant current discharge of 300 seconds at 1 C, and a pause of 10 seconds as one cycle. The battery resistance after 2000 cycles was determined by the same method as described above. The rate of increase in resistance (%) was calculated from (battery resistance after 2000 cycles / initial battery resistance) × 100.

From Table 1, in negative electrode B1 using a polymer thickener, the viscosity of the negative electrode paste was high, and the spring constant of the negative electrode (that is, the strength of the negative electrode active material layer) was low. Moreover, the resistance increase rate after the high-rate charge cycle test when it was set as the battery was high. This is because when the polymer thickener is used, the viscosity of the negative electrode paste is high, and the thickener and ceramic particles do not move into the space of the negative electrode active material layer generated by removing the solvent during drying. This is probably because ceramic particles were not sufficiently disposed in the gaps between the active materials.
In the negative electrode B2 using a polymer thickener, a high shearing force was applied to increase the number of rotations during kneading of the negative electrode paste, thereby cutting the polymer chain and reducing the molecular weight of the thickener. As a result, although the viscosity of the negative electrode paste was reduced, the spring constant of the negative electrode was hardly increased, and the resistance increase rate after the high-rate charge cycle test when the battery was made was high. This is because the viscosity of the negative electrode paste decreases due to the lower molecular weight of the thickener, and the thickener and ceramic particles move to the space of the negative electrode active material layer caused by the removal of the solvent during drying. This is probably because the skeleton of the negative electrode active material layer could not be strengthened because of the low molecular weight.
In contrast, the negative electrodes A1 to A7 had a very high spring constant (that is, the strength of the negative electrode active material layer), and the resistance increase rate after the high-rate charge cycle test when the battery was formed was low. This is because by using a low-molecular gelling agent composed of a lipid peptide compound as a thickener, the thickener can be temporarily reduced in molecular weight due to the shearing force during kneading of the negative electrode paste. This is probably because the viscosity of the paste was reduced. That is, since the negative electrode paste has a low viscosity, the thickener and the ceramic particles move to the space of the negative electrode active material layer generated by removing the solvent during drying, and the ceramic particles are sufficiently placed in the gaps between the negative electrode active materials. It is thought that it was because it was arranged. In addition to this, it is considered that the skeleton of the negative electrode active material layer could be strengthened by the low-molecular gelling agent self-organizing into a polymer fiber by the completion of drying.
In the negative electrode B3, the amount of ceramic particles added was 2% by mass, but the resistance increase rate after the high-rate charge cycle test when the battery was obtained was high. This is presumably because the additive amount of the ceramic particles was too small, and the adverse effect due to the portion where the spring constant in the negative electrode active material layer was not increased became significant.
In the negative electrode B4, the amount of ceramic particles added was set to 25% by mass. Although the spring constant of the negative electrode was high, the rate of increase in resistance after the high-rate charge cycle test when the battery was formed was high. This is presumably because the amount of ceramic particles other than those present between the negative electrode active materials that serve as resistors increases and the battery resistance increases.
In the negative electrode B5, the amount of the low-molecular gelling agent added was 0.3% by mass, but the increase in the spring constant of the negative electrode was small, and the resistance increase rate after the high-rate charge cycle test when the battery was made was high. This is presumably because the amount of the low-molecular gelling agent added was too small to sufficiently bond the negative electrode active materials, and a strong skeleton of the negative electrode active material layer could not be constructed.
In the negative electrode B6, the addition amount of the low-molecular gelling agent was 12% by mass, but the increase in the spring constant of the negative electrode was small, and the resistance increase rate after the high-rate charge cycle test when the battery was made was high. This is presumably because the amount of the low-molecular gelling agent added is too large, the viscosity of the negative electrode paste increases, and the same phenomenon as that of the negative electrode B1 occurs.

  From the above results, according to the method for manufacturing a negative electrode according to the present embodiment, it is easy to provide a negative electrode that can improve the cycle characteristics of a battery while using a negative electrode paste containing a negative electrode active material, ceramic particles, and a thickener. It can be seen that it can be manufactured. And when the negative electrode obtained by the manufacturing method concerning this embodiment is used for a secondary battery (especially lithium ion secondary battery), it will become what is excellent in cycling characteristics (especially high-rate cycling characteristics). I understand.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

20 wound electrode body 30 battery case 36 safety valve 42 positive electrode terminal 42a positive electrode current collector plate 44 negative electrode terminal 44a negative electrode current collector plate 50 positive electrode sheet (positive electrode)
52 Positive Current Collector 52a Positive Electrode Active Material Layer Non-Forming Portion 54 Positive Electrode Active Material Layer 60 Negative Electrode Sheet (Negative Electrode)
62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator sheet (separator)
100 Lithium ion secondary battery

Claims (1)

Applying a negative electrode paste containing a negative electrode active material, ceramic particles, and a thickener on the negative electrode current collector;
Drying the coated negative electrode paste to form a negative electrode active material layer;
A negative electrode manufacturing method comprising:
The thickener includes a low molecular gelling agent composed of a lipid peptide compound,
In the negative electrode paste, the low-molecular gelling agent is contained in an amount of 0.5 to 10% by mass with respect to the total solid content of the negative electrode paste,
In the negative electrode paste, the ceramic particles are contained in an amount of 3 to 20% by mass with respect to the total solid content of the negative electrode paste.
Manufacturing method of negative electrode.

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