JP2019067614A - Method of manufacturing negative electrode - Google Patents

Abstract

To provide a method of manufacturing a negative electrode plate having a good output retention.SOLUTION: The method of manufacturing a negative electrode includes, after laminating a composition containing amorphous carbon and a binder on a current collector to form an active material layer, heating the active material layer and setting a mass ratio of a binder in the active material layer to 1% by mass or less.SELECTED DRAWING: None

Description

  The present invention relates to a method of manufacturing a negative electrode of a storage element such as a lithium ion secondary battery.

  Conventionally, a method of manufacturing an electrode plate (electrode plate of a lithium ion secondary battery) having an electrode foil and a negative electrode active material layer formed on the electrode foil is known (for example, Patent Document 1).

  In the manufacturing method described in Patent Document 1, the negative electrode active material layer of the electrode plate is formed on the electrode foil and is formed on the first active material layer containing the first negative electrode active material, and on the first active material layer And a second active material layer including a second negative electrode active material having a higher potential for lithium ions than the first active material. In the manufacturing method described in Patent Document 1, a first active material layer forming step of applying a first paste containing a first negative electrode active material onto an electrode foil and drying it to form a first active material layer; A carbon compound layer forming step of forming a carbon compound layer composed of a carbon compound on the active material layer, and a second paste containing a second negative electrode active material on the carbon compound layer and dried, the second active material layer And a carbonizing step of carbonizing the carbon compound of the carbon compound layer after the second active material layer forming step of forming the second active material layer.

JP, 2014-078318, A

  Usually, when producing a negative electrode plate, a binder is added in order to ensure the binding property in the electrode plate. However, since the binder is an insulator, it increases the resistance of the negative electrode mixture layer. On the other hand, when the amount of binder is reduced, the viscosity of the slurry is insufficient, and it becomes difficult to form the mixture layer on the current collector foil. Thus, the present embodiment provides a method of manufacturing a negative electrode plate having a favorable output retention while securing a sufficient binder amount when forming the mixture layer on the current collector.

  In the method of manufacturing the negative electrode according to the present embodiment, after a composition containing amorphous carbon and a binder is laminated on a current collector to form an active material layer, the active material layer is heated to form the active material layer. The mass ratio of the binder is 1% by mass or less.

  According to the present embodiment, the retention of the output of the storage element can be improved.

FIG. 1 is a perspective view of a storage element according to the present embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG.

  Hereinafter, an embodiment of a storage element according to the present invention will be described with reference to FIGS. 1 and 2. The storage element includes a primary battery, a secondary battery, a capacitor and the like. In the present embodiment, a chargeable / dischargeable secondary battery will be described as an example of a storage element. In addition, the name of each component (each component) of this embodiment is in this embodiment, and may differ from the name of each component (each component) in background art.

  The storage element 1 of the present embodiment is a non-aqueous electrolyte secondary battery. More specifically, the storage element 1 is a lithium ion secondary battery utilizing electron transfer that occurs as lithium ion moves. This type of storage element 1 supplies electrical energy. The storage element 1 is used singly or in plurality.

  As shown in FIGS. 1 and 2, the storage element 1 is an electrode assembly 2 including a positive electrode and a negative electrode, a case 3 for housing the electrode assembly 2, and an external terminal 7 disposed outside the case 3 And an external terminal 7 electrically connected to the electrode body 2. In addition to the electrode body 2, the case 3, and the external terminal 7, the storage element 1 includes a current collecting member 5 and the like that electrically connect the electrode body 2 and the external terminal 7.

  The positive electrode (positive electrode plate) has a metal foil (current collector) and a positive electrode active material layer which is superimposed on the surface of the metal foil and contains active material particles. In the present embodiment, the positive electrode active material layers respectively overlap on both sides of the metal foil. The thickness of the positive electrode may be 40 μm or more and 300 μm or less.

  The metal foil is band-shaped. The metal foil of the positive electrode of the present embodiment is, for example, an aluminum foil. The positive electrode has a non-coated portion of the positive electrode active material layer (a portion where the positive electrode active material layer is not formed) at one end of the width direction which is the short direction of the band shape.

The positive electrode active material layer contains a particulate active material (active material particles), a particulate conductive assistant, and a binder. The thickness of the positive electrode active material layer (one layer) may be 12 μm or more and 142 μm or less. The coated amount of the positive electrode active material layer (one layer) may be 3 mg / cm ² or more and 30 mg / cm ² or less. The density (one layer) of the positive electrode active material layer may be 1.5 g / cm ³ or more and 3.5 g / cm ³ or less.

The positive electrode active material is a compound capable of inserting and extracting lithium ions. The positive electrode active material is, for example, a lithium metal oxide. Specifically, the positive electrode active material, for _example, Li p _MeO t (Me represents one or more transition metal) complex oxide represented by _{(Li p Co s O 2,} Li p Ni q O 2 _{, Li p Mn r O 4,} Li p Ni q Co s Mn r O 2 , etc.), _{or, Li p Me u (XO v} ) w (Me represents one or more transition metals, X is for example P , Si, B, and V) (Li _p Fe _u PO ₄ , Li _p Mn _u PO _{4 and the} like).

The positive electrode active material may be a lithium transition metal complex oxide represented by a chemical composition of Li _x Ni _a Mn _b Co _c M _d O _2-δ . However, 0 <x <1.2, 0.8 <a + b + c + d <1, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, and 0 ≦ d ≦ 1 and 0 ≦ δ ≦ 0.5, and M is at least one selected from the group consisting of B, Mg, Al, Ti, V, Zn, Y, Zr, Mo, and W.

In the present embodiment, the positive electrode active _{material, Li p Ni q Mn r Co} s O t chemical lithium represented by a composition transition metal composite oxides (provided that at 0 <p <1.2, 0.8 < q + r + s <1, 0 ≦ q ≦ 1, 0 ≦ r ≦ 1, 0 ≦ s ≦ 1, and 1.7 ≦ t ≦ 2.3). Note that 0 <q <1, 0 <r <1, and 0 <s <1.

  The binder used for the positive electrode active material layer is, for example, polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid Styrene butadiene rubber (SBR), carboxymethyl cellulose salt (CMC) and the like. The binder of the present embodiment is polyvinylidene fluoride.

  The conductive support agent of the positive electrode active material layer is a carbonaceous material. The carbonaceous material is, for example, ketjen black (registered trademark), acetylene black, graphite or the like. The positive electrode active material layer of the present embodiment has acetylene black as a conductive additive. The positive electrode active material layer may contain 1% by mass or more and 10% by mass or less of the conductive additive.

  The negative electrode (negative electrode plate) has a metal foil (current collector) and a negative electrode active material layer formed on the metal foil. In the present embodiment, the negative electrode active material layers are respectively superimposed on both sides of the metal foil. The metal foil is band-shaped. The metal foil of the negative electrode of the present embodiment is, for example, a copper foil. The negative electrode has a non-coated portion of the negative electrode active material layer (a portion where the negative electrode active material layer is not formed) at one end of the width direction which is the short direction of the band shape. The thickness of the negative electrode may be 40 μm or more and 300 μm or less.

  The negative electrode active material layer may include at least a particulate active material (active material particles) and may include a binder. The negative electrode active material layer is disposed to face the positive electrode through the separator. The width of the negative electrode active material layer is larger than the width of the positive electrode active material layer.

The thickness of the negative electrode active material layer (one layer) may be 16 μm or more and 146 μm or less. The coated amount (one layer) of the negative electrode active material layer may be 3 mg / 100 cm ² or more and 20 mg / 100 cm ² or less. The density (one layer) of the negative electrode active material layer may be 0.9 g / cm ³ or more and 2 g / cm ³ or less.

  In the preparation of the negative electrode plate, after a composition containing amorphous carbon and a binder is used as a current collector to form an active material layer, the mass ratio of the binder is 1% or less by heating the active material layer. I assume. Specifically, a composition (slurry) containing amorphous carbon and a binder is prepared, and applied or sprayed to a current collector to form an active material layer. At this time, the mass ratio of the binder in the composition is made larger than 1% with respect to the total mass of the amorphous carbon and the binder. By making the mass ratio of the binder larger than 1%, the viscosity of the slurry can be secured, so that the coating or spraying on the current collector is stable, and the formation of the active material layer is easy. Thereafter, the binder is carbonized by heating the active material layer, and the mass ratio of the binder is set to 1% or less with respect to the total mass of the amorphous carbon and the binder. By carbonizing the binder, retention of the output can be improved.

  The mass of the binder in the composition before heating the active material layer is preferably 2% or more, more preferably 3% or more, with respect to the total mass of the amorphous carbon and the binder. By setting the mass of the binder to 2% or more, the viscosity of the composition can be sufficiently secured. On the other hand, since the energy density decreases when the mass of the binder is large, the upper limit of the mass of the binder is preferably 10% with respect to the total mass of the amorphous carbon and the binder.

  The negative electrode active material is amorphous carbon (non-graphitizable carbon, graphitizable carbon). Specifically, the negative electrode active material is preferably non-graphitizable carbon. Since non-graphitizable carbon has small expansion and contraction of active material particles during charge and discharge, even if the amount of binder is reduced by heating the active material layer, the binding property can be maintained in the active material layer. And peeling of the active material layer can be prevented. On the other hand, graphite as active material particles has a larger volume change associated with charge and discharge than amorphous carbon. When the active material particles are graphite, when the amount of the binder is reduced, the binding property between the particles is reduced due to the volume change of the graphite, and the peeling of the active material layer occurs.

  The mass of amorphous carbon with respect to the mass of the negative electrode active material layer is preferably 90% or more. Further, the negative electrode active material layer may contain a negative electrode active material other than amorphous carbon to such an extent that it does not affect peeling of the active material layer.

Amorphous carbon is one having an average interplanar spacing d ₀₀₂ of (002) plane of 0.340 nm or more and 0.390 nm or less determined by wide-angle X-ray diffraction using CuKα radiation as a radiation source in the discharge state. is there. In addition, the non-graphitizable carbon is one in which the average interplanar spacing d ₀₀₂ is 0.360 nm or more and 0.390 nm or less.

  The median diameter of the negative electrode active material is preferably 5 μm or less. When the median diameter of the active material is 5 μm or less, the volume change of the active material due to charge and discharge becomes relatively small compared to the active material with a large median diameter, and the amount of binder is reduced by heating the active material layer Even if it is made to be, binding property can be maintained in an active material layer, and exfoliation of an active material layer can be prevented. The median diameter of the active material may be 2 μm or more. The median diameter (average particle diameter D50) of the active material particles is determined by measuring the particle size distribution as follows.

  The particle size frequency distribution is determined by measurement using a laser diffraction / scattering type particle size distribution measuring apparatus. The particle size frequency distribution is determined by the volume basis of the particles. The measurement conditions are described in detail in the examples. In addition, when measuring the particle size frequency distribution of the particle contained in the active material layer of the manufactured battery, for example, after charging the battery until it reaches 4.2 V at a 1.0 C rate, a constant voltage of 4.2 V is further applied. The battery is discharged for 3 hours at a constant current discharge to 2.0 V at a 1.0 C rate. Subsequently, a constant voltage discharge at 2.0 V for 5 hours is performed. Then, the battery is disassembled in a dry atmosphere. The active material layer is taken out, washed with dimethyl carbonate and dispersed, and then the active material is vacuum dried for 2 hours or more. Then, it measures using a particle size distribution measuring apparatus.

  The binder (organic binder) that may be contained in the negative electrode active material layer is the same as the binder used in the positive electrode active material layer. Styrene butadiene rubber (SBR) tends to be present between particles, and carboxymethyl cellulose salt (CMC) tends to be present all over the surface of active material particles. SBR or CMC is preferable as a binder in view of securing conductivity between particles after carbonization.

  The amount of binder in the negative electrode active material layer is determined by thermogravimetric (TG) measurement. Specifically, the binder in the negative electrode active material layer is measured by performing measurement under conditions of temperature (25 ° C. to 450 ° C.), heating rate (10 ° C./min.) And measurement atmosphere (nitrogen atmosphere). Content is measured. The binder content of 1% by mass or less is determined by the fact that the weight loss between 100 ° C. and 400 ° C. is within 1%, as a result of the above TG measurement.

  On the surface of the negative electrode active material particles, carbides obtained by carbonizing the binder are attached. The surface of the active material particles may be covered with a carbonized layer containing such carbides. It is presumed that the resistance in the negative electrode active material layer can be suppressed to a relatively low value by the presence of the conductive carbide having the surface on the surface of the negative electrode active material particles in addition to the reduction of the mass ratio of the binder. The binder carbide can be grasped by the existence of the interface between the carbide and the amorphous carbon by TEM observation or the like.

  The negative electrode active material layer may further have a conductive aid such as ketjen black (registered trademark) or acetylene black. The negative electrode active material layer of the present embodiment does not have a conductive support agent.

  In the electrode body 2 of the present embodiment, the positive electrode plate and the negative electrode plate configured as described above are stacked via a separator. Since the negative electrode plate of the present embodiment has a small amount of binder, the active material layer may be peeled off by an external force such as bending or bending of the negative electrode plate. Therefore, it is preferable to stack the negative electrode without bending or curving. That is, the electrode body includes a winding type in which a strip-like electrode plate and a separator are wound, and a lamination type in which the electrode plate and the separator are alternately laminated, but a lamination type electrode body is preferable.

  The separator is porous. The separator is, for example, a woven fabric, a non-woven fabric, or a porous membrane. Examples of the material of the separator include polymer compounds, glass, and ceramics. Examples of the polymer compound include at least one selected from the group consisting of polyacrylonitrile, polyamide, polyester such as polyethylene terephthalate, polyolefin such as polypropylene, polyethylene, polyimide, and cellulose.

The electrolyte is a non-aqueous electrolyte. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. The organic solvent is, for example, cyclic carbonates such as propylene carbonate and ethylene carbonate, linear carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrolyte salt is LiClO ₄ , LiBF ₄ , LiPF ₆ or the like. The electrolytic solution of this embodiment is a solution in which 0.5 mol / L or more and 1.5 mol / L or less of LiPF ₆ is dissolved in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed in a predetermined ratio. is there.

  Next, a method of manufacturing the storage element 1 of the above embodiment will be described.

  In the method of manufacturing the storage element 1, first, a composition containing an active material is applied to a metal foil to form an active material layer, and a positive electrode and a negative electrode are respectively produced. In addition, a commercially available separator is prepared or manufactured. Next, the positive electrode, the separator, and the negative electrode are stacked to form the electrode assembly 2. Furthermore, the electrode assembly 2 is placed in the case 3, and the storage element 1 is assembled by placing the electrolytic solution in the case 3.

  In the preparation of the positive electrode, for example, a positive electrode active material layer is formed by applying a composition containing active material particles, a binder, a conductive additive, and a solvent on both surfaces of a metal foil. A general method is adopted as a coating method for forming the positive electrode active material layer. The applied positive electrode active material layer is roll pressed at a predetermined pressure. By adjusting the pressing pressure, the thickness and density of the positive electrode active material layer can be adjusted.

In the preparation of the negative electrode, for example, a negative electrode active material layer is formed by applying a composition containing active material particles, a binder, and a solvent on both sides of a metal foil. A general method is adopted as the application method. For example, the solvent is volatilized from the applied composition by heating to 30 ° C. or more and 120 ° C. or less. Subsequently, roll pressing is performed at a predetermined pressure. The thickness and density of the negative electrode active material layer can be adjusted by adjusting the pressing pressure. Furthermore, it heats in inert gas, such as nitrogen, more than the temperature which a binder carbonizes (for example, 250 degreeC or more). Thereby, the binder is carbonized to make the content of the binder in the negative electrode active material layer 1% by mass or less. When a binder is a styrene butadiene rubber (SBR), it heats, for example to 250 degreeC or more and 450 degrees C or less, and carbonizes SBR. When the binder is a carboxymethylcellulose salt (CMC), the CMC is carbonized, for example, by heating to 100 ° C. or more and 250 ° C. or less.
By heating the binder to carbonize the binder so that the content of the binder is 1% by mass or less, the binder which is an insulator is reduced, and conductive carbides connect particulate amorphous carbon with each other. Will be placed in Thus, the retention of the output of the storage element can be improved.

  The electrode body 2 is formed by arranging and laminating a separator between the positive electrode plate and the negative electrode plate. Specifically, there is a method in which the positive electrode plate is accommodated in a bag-shaped separator and alternately stacked with the negative electrode plate, or a method in which the separator is made into a serpent shape and disposed between the positive electrode plate and the negative electrode plate.

  In assembling the storage element 1, the electrode body 2 is put in the case main body 31 of the case 3, the opening of the case main body 31 is closed by the cover plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case body 31 with the cover plate 32, the electrode body 2 is inserted into the case body 31, the positive electrode and one external terminal 7 are electrically connected, and the negative electrode and the other external terminal 7 are electrically connected. In the closed state, the opening of the case body 31 is closed by the cover plate 32. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 from the injection hole of the cover plate 32 of the case 3.

  It is preferable that the storage element 1 manufactured as described above be used in a state in which the electrode body 2 is subjected to a compressive force. Because the amount of binder in the negative electrode active material layer of the electrode body 2 is relatively small as described above, particles of the negative electrode active material are less likely to be bound to each other. However, even if the electrode body 2 expands or contracts due to repeated charging and discharging, the above-described compressive force tends to maintain the contact between the particles of the negative electrode active material. Therefore, even after charge and discharge are repeated, it is possible to suppress the decrease in output. Note that, for example, the plurality of storage elements are arranged in one direction in contact with each other, and the arrangement of each storage element at the outermost side in the direction is restricted, whereby the electrode body 2 of each storage element 1 receives a compressive force It becomes a state.

  The storage element of the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the scope of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment. In addition, some of the configuration of an embodiment can be deleted.

  Although the storage element 1 including the stacked electrode body 2 has been described in detail in the above embodiment, the storage element of the present invention may include a wound electrode body.

  Although the above embodiment describes the case where the storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, lithium ion secondary battery), the type and size (capacity) of the storage element 1 are arbitrary. is there. Moreover, although the said embodiment demonstrated the lithium ion secondary battery as an example of the electrical storage element 1, it is not limited to this. For example, the present invention is applicable to storage devices of various primary batteries, secondary batteries, and other capacitors such as electric double layer capacitors.

  The storage element 1 (for example, a battery) may be used for a storage device (a battery module when the storage element is a battery). The power storage device includes one or more power storage elements 1 described above. The power storage device usually includes at least two power storage elements 1 and a bus bar member electrically connecting the power storage elements 1 with each other. In this case, the technique of the present invention may be applied to at least one storage element.

  As shown below, a non-aqueous electrolyte secondary battery (lithium ion secondary battery) was produced.

Example 1
(1) Preparation of Positive Electrode N-methyl-2-pyrrolidone (NMP), a conductive additive (acetylene black), a binder (PVdF) as a solvent, and an active material (LiNi _1/3 Co _1/3 Mn _1/3 The composition for the positive electrode was prepared by mixing and kneading O ₂ ) particles. The blending amounts of the conductive additive, the binder, and the active material were 5% by mass, 5% by mass, and 90% by mass, respectively. The prepared composition for a positive electrode was applied to one surface of an aluminum foil so that the coating weight was 8.5 mg / cm ² . After drying, a roll press was performed. Thereafter, it was vacuum dried to remove water and the like. The thickness of the active material layer (one layer) after pressing was 50 μm.

(2) Preparation of Negative Electrode As the active material, particulate non-graphitizable carbon (d002 3.65 Å) having a median diameter of 4.8 μm was used. Moreover, SBR and CMC were used as a binder. The composition for the negative electrode was prepared by mixing and kneading water as a solvent, a binder, and an active material. The binder was blended so that SBR was 2.0% by mass and CMC was 1.0% by mass, and the active material was blended so as to be 97% by mass. The prepared composition for a negative electrode was applied to one side of a copper foil so that the basis weight after drying was 3.6 mg / cm ² . After evaporating the water, the binder was carbonized by heating at 400 ° C. to form an active material layer. The content of the binder in the active material layer was 0.1 mass% (less than 1 mass%) as a result of measurement according to the following method. A roll press was performed and vacuum drying was performed to remove moisture and the like. The thickness of the active material layer (one layer) was 68 μm.

(3) Separator (Separator base material)
A polyethylene microporous film with a thickness of 22 μm was used as a separator substrate.

(4) Preparation of Electrolytic Solution As an electrolytic solution, one prepared by the following method was used. A solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a volume ratio of 30/35/35 as a non-aqueous solvent is used to dissolve LiPF ₆ in this non-aqueous solvent so that the salt concentration is 1 mol / L. The electrolyte was prepared.

(5) Production of Battery Using Laminated Package Body The above positive electrode plate and the above negative electrode plate were laminated such that the active material layers of each other face each other. The said separator was arrange | positioned between the positive electrode plate and the negative electrode plate, and the electrode body was produced. Next, this electrode body was inserted into a bag-like laminate outer package having one side open, and the leads provided on the positive electrode plate and the negative electrode were arranged to protrude from the opening of the laminate package. The electrolyte was injected from the opening of the laminate outer package, and the opening was sealed to fabricate a battery.

<Measurement of Amount of Binder Contained in Negative Electrode Active Material Layer>
The binder content was measured under the measurement conditions of a temperature rising rate of 10 ° C./min and a nitrogen atmosphere using a TG-DTA measuring apparatus “manufactured by BRUKER (TGDTA2000SA)” as a measuring apparatus. In the TG curve, the value obtained by subtracting the mass loss at 100 ° C. from the mass loss at 400 ° C. was defined as the content of the binder.

<Measurement of median diameter of negative electrode active material particles>
The negative electrode was taken out of the battery once manufactured. The taken out negative electrode was immersed in 50 times or more mass of NMP, and pretreated by ultrasonic dispersion for 15 minutes. Furthermore, the metal foil was removed from the negative electrode, and in a state in which the negative electrode active material layer was immersed in NMP, ultrasonic dispersion treatment was performed for 15 minutes. Thereafter, a dispersion containing a measurement sample of active material particles was prepared. In the measurement of the particle size frequency distribution of the measurement sample, a laser diffraction type particle size distribution measurement apparatus ("SALD2300" manufactured by Shimadzu Corporation) as a measurement apparatus, and dedicated application software DMS ver. 2 was used. As a specific measurement method, a scattering type measurement mode is adopted, and a wet cell in which the dispersion circulates is placed in an ultrasonic environment for 2 minutes and then irradiated with a laser beam, and the scattered light distribution from the measurement sample I got Then, the scattered light distribution was approximated by a logarithmic normal distribution, and measurement was performed in a range in which the minimum was set to 0.021 μm and the maximum was set to 2000 μm in the particle size frequency distribution (horizontal axis, σ). The median diameter based on the volume of the active material particles was 4.8 μm.

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that non-graphitizable carbon having a median diameter of 7.5 μm was used as the negative electrode active material.

(Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that graphitizable carbon (d002 3.45 Å) having a median diameter of 5.0 μm was used as the negative electrode active material.

(Example 4)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the heating temperature of the negative electrode active material layer was set to 350 ° C.

(Example 5)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the heating temperature of the negative electrode active material layer was set to 300 ° C.

(Comparative example 1)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that graphite (d002 3.35 Å) having a median diameter of 5.5 μm was used as the negative electrode active material.

(Comparative example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode active material was not heated at 400 ° C.

<Calculation of regenerative output>
1. The battery was charged to 4.2 V at 25 ° C. with a constant current of 3.5 mA and further charged for a total of 3 hours at a constant voltage of 4.2 V. Thereafter, the initial discharge capacity was determined by discharging to a final voltage of 2.4 V at a constant current of 7.0 mA.
2. The battery was charged to a voltage corresponding to 85% of the initial discharge capacity at 25 ° C., and further charged for a total of 2 hours with the voltage.
3. After storing for 5 hours at -10 ° C, charge for 1 second each in the order of A1 (7.0 mA) → A2 (14.0 mA) → A3 (21.0 mA) at -10 ° C, and after charging with each charge current Voltage V1, V2 and V3 were measured.
4. The measured A1 to A3 were plotted on the X axis and V1 to V3 on the Y axis, and the slope was calculated by the least squares method. A current value at the intersection of the calculated inclination and Y = 4.2 V was calculated, and a value obtained by multiplying the current value at the intersection and 4.2 V was defined as a regenerative output.
<High temperature storage test>
After the regeneration output was calculated, the battery was charged again to a voltage at 85 ° C. corresponding to 85% of the initial discharge capacity, and further charged for a total of 2 hours with the voltage. Then, it stored in a 65 degreeC thermostat for 15 days. Next, after storing for 5 hours in a -10 degreeC thermostat, regeneration output was similarly calculated at -10 degreeC. A value obtained by dividing the regenerative output after storage at 65 ° C. for 15 days by the regenerative output before storage at 65 ° C. for 15 days was defined as a regenerative output retention rate.

  As understood from Table 1, in Examples 1 to 5, the retention ratio of the regenerative output at low temperature after high temperature storage was 80% or more, and showed good output retention. On the other hand, the retention of the output of Comparative Example 1 in which graphite was used as the negative electrode active material and Comparative Example 2 in which heating for carbonization was not performed was low.

1: Storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
3: Case 31: Case body 32: Lid plate,
5: Current collecting member,
7: External terminal.

Claims (3)

  After a composition containing amorphous carbon and a binder is laminated on a current collector to form an active material layer, the active material layer is heated, and the mass ratio of the binder in the active material layer is 1 mass The manufacturing method of the negative electrode made into% or less.   The method for producing a negative electrode according to claim 1, wherein the amorphous carbon is non-graphitizable carbon.   The manufacturing method of the negative electrode of Claim 1 or 2 whose median diameter of the said amorphous carbon is 5 micrometers or less.

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