JP6858144B2 - Secondary battery and its manufacturing method - Google Patents

Description

The present invention relates to a secondary battery and a method for manufacturing the same.

In a non-aqueous electrolytic solution secondary battery such as a lithium ion secondary battery, a carbon material such as graphite has been conventionally used as a negative electrode active material. With such conventional secondary batteries, it is becoming increasingly difficult to meet the increasing demand for higher capacity in recent years, and studies on secondary batteries using higher capacity negative electrode active materials such as silicon are being considered. It is being advanced (see, for example, Patent Documents 1 and 2 below).

Patent Document 1 states that by using silicon as a negative electrode active material, a battery having a higher capacity than that using a carbon material can be obtained. Further, only a specific silicon complex is used as the negative electrode active material, and SiOx (0.3 ≦ x ≦ 1.6) is used for the silicon complex.
Use by mixing known negative electrode active materials such as particles made of silicon oxide represented by, natural graphite, artificial graphite, calcined organic compound such as phenol resin, powdered carbon substance such as coke, etc. Is described.

Further, Patent Document 1 describes polyvinylidene fluoride (PVDF) as a binder resin for binding an active material and a conductive auxiliary agent added to enhance the conductivity of an electrode to a current collector.
Examples thereof include fluorine-based polymers such as polytetrafluoroethylene (PTFE), rubbers such as styrene-butadiene rubber (SBR), and imide-based polymers such as polyimide.

Patent Document 2 aims to obtain a non-aqueous electrolyte secondary battery having excellent cycle characteristics, uses an active material containing a graphite material and silicon or a silicon compound as a negative electrode active material, and polyimide and polyvinylpyrrolidone as a negative electrode binder. A non-aqueous electrolyte secondary battery characterized by using the above is disclosed.

Japanese Unexamined Patent Publication No. 2013-234088 Japanese Unexamined Patent Publication No. 2012-160353

When silicon is used as the negative electrode active material, the expansion and contraction of the volume due to charging and discharging becomes larger than that of the conventional carbon material. Therefore, for example, in the non-aqueous secondary battery described in Patent Document 1, the silicon composite or a mixture of the silicon composite and a known negative electrode active material is used as the negative electrode active material, and the binder resin has a relatively strong binding force. When a weak PVDF, PTFE, SBR, or the like is used, the silicon composite may repeatedly expand and contract with the charging and discharging of the secondary battery and crack. When the silicon complex is cracked, the cycle characteristics of the secondary battery are deteriorated.

On the other hand, in the non-aqueous electrolyte secondary battery described in Patent Document 2, the cycle characteristics of the secondary battery are improved by using polyimide and polyvinylpyrrolidone having a relatively strong binding force as the negative electrode binder. However, in Patent Document 2, a negative electrode slurry prepared by dissolving a precursor of a polyimide resin in N-methyl-2-pyrrolidone (NMP) and further mixing polyvinylpyrrolidone, graphite and silicon is used as a negative electrode current collector. Apply on both sides of the copper foil,
After drying and rolling, it is heat-treated at 400 ° C. for 10 hours in an argon atmosphere to prepare a negative electrode. As described above, when the negative electrode current collector is exposed to a high temperature for a long time in the manufacturing process of the negative electrode, the strength of the negative electrode current collector is lowered or the weldability to a metal such as a current collector plate is lowered. ,
There is a risk of adversely affecting the subsequent manufacturing process of the secondary battery.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the cycle characteristics of a secondary battery without exposing the electrodes to high temperatures in the process of manufacturing the secondary battery.

In order to achieve the above object, the secondary battery of the present invention is a secondary battery provided with a negative electrode having a negative electrode foil and a negative electrode mixture layer, and the negative electrode mixture layer is composed of SiO-based active material particles. At least a part of the SiO-based active material particles containing a binder and the SiO-based active material particles is coated with a coating layer made of a resin material containing an imide bond imidized at a temperature higher than the heat resistant temperature of the binder. It is characterized by that.

According to the secondary battery of the present invention, the electrodes are not exposed to high temperatures in the manufacturing process of the secondary battery.
The cycle characteristics of the secondary battery can be improved.

The perspective view of the secondary battery which concerns on embodiment. The exploded perspective view which shows the internal structure of the secondary battery shown in FIG. The exploded perspective view of the electrode group shown in FIG. FIG. 3 is an enlarged cross-sectional view of the negative electrode shown in FIG. The flow chart which shows the manufacturing process of the negative electrode shown in FIG. The graph which shows the relationship between the number of cycles of the secondary battery and the capacity retention rate which concerns on Example. The graph which shows the relationship between the coverage of the silicon-based material of the secondary battery which concerns on Example, and the initial charge / discharge efficiency.

Hereinafter, the secondary battery and the method for manufacturing the secondary battery according to the embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view of the secondary battery 100 according to the first embodiment of the present invention. The secondary battery 100 of the present embodiment is, for example, a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

In the secondary battery 100 of the present embodiment, the negative electrode mixture layer provided with the negative electrode described later contains SiO-based active material particles as the negative electrode active material, and the SiO-based active material particles are higher than the heat-resistant temperature of the binder. The greatest feature is that at least a part of the coating layer is covered with a coating layer made of a resin material containing an imide bond that has been imidized at temperature. Hereinafter, the configuration of the secondary battery 100 of the present embodiment will be described in detail.

The secondary battery 100 includes a flat box-shaped battery container 10 made of a metal material such as an aluminum alloy. The battery container 10 has an upper end surface 10a, a lower end surface 10b, and a wide side surface 1.
It is a flat rectangular parallelepiped housing having 0c and a narrow side surface 10d. The battery container 10 has a flat rectangular box-shaped battery can 11 having an open upper portion and a rectangular plate-shaped battery lid 12 that seals the upper portion of the battery can 11. The battery can 11 is formed in a bottomed square cylinder shape having a rectangular opening 11a at the top, for example, by deep drawing the metal material.

External terminals 20A and 20B of the positive electrode and the negative electrode are provided on the upper surface of the battery lid 12 outside the battery container 10 at both ends in the width direction of the battery container 10, that is, in the longitudinal direction of the battery lid 12. An insulating member 24 is arranged between the external terminals 20A and 20B and the battery lid 12, and the external terminal 20 is provided.
A and 20B are electrically insulated from the battery lid 12. The positive electrode external terminal 20A is made of, for example, aluminum or an aluminum alloy, and the negative electrode external terminal 20B is
For example, it is made of copper or copper alloy.

The external terminals 20A and 20B each include a conductive plate 21 and a bolt 22. The conductive plate 21 has a bolt 22 inserted from below to above through a through hole provided on the outside in the width direction of the battery container 10. The head of the bolt 22 is arranged between the insulating member 24 and the conductive plate 21.
It is electrically connected to the conductive plate 21. The conductive plate 21 has a connection terminal 23 inserted from below to above through a through hole provided inside the battery container 10 in the width direction. The tip of the connection terminal 23 is crimped on the upper surface of the conductive plate 21, plastically deformed so as to expand the diameter, and adheres to the conductive plate 21, so that the connection terminal 23 is electrically connected to the conductive plate 21 and is electrically connected to the conductive plate 21. It is electrically insulated from the lid 12.

A gas discharge valve 13 and a liquid injection port 14 are provided between the external terminals 20A and 20B of the positive electrode and the negative electrode of the battery lid 12. In the gas discharge valve 13, for example, the battery lid 12 is thinned to form a groove portion 1.
It is provided by forming 3a, and when the pressure inside the battery container 10 rises above a predetermined value, it cleaves and releases the gas inside, thereby lowering the pressure inside the battery container 10. The liquid injection port 14 is used for injecting an electrolytic solution into the battery container 10, and the liquid injection plug 15 is welded and sealed by laser welding, for example.

FIG. 2 is an exploded perspective view showing the internal structure of the secondary battery 100 shown in FIG. In FIG. 2, the battery can 11 is not shown. At both ends of the battery lid 12 in the longitudinal direction, on the lower surface of the battery lid 12 which is the inside of the battery container 10, a positive electrode and a negative electrode current collector plate 3 is provided via an insulating member (not shown).
0A and 30B are fixed. The positive electrode current collector plate 30A is made of, for example, aluminum or an aluminum alloy, and the negative electrode current collector plate 30B is made of, for example, copper or a copper alloy. The current collector plates 30A and 30B have a base portion 31 to which the base end portion of the connection terminal 23 is connected, and a terminal portion 32 extending from the base portion 31 toward the bottom surface 11b of the battery can 11, respectively.
have.

The connection terminal 23 connected to the base 31 of each of the current collector plates 30A and 30B is a battery container 1.
It extends outward from 0 and penetrates the battery lid 12. The connection terminal 23 is conductive with a through hole of an insulating member (not shown) arranged on the lower surface of the battery lid 12, a through hole of the battery lid 12, and a through hole of the insulating member 24 arranged on the upper surface of the battery lid 12. It penetrates through the through hole of the plate 21 and the tip portion is crimped on the upper surface of the conductive plate 21. As a result, the bases 31 of the current collector plates 30A and 30B are separated from each other.
It is electrically connected to the conductive plate 21 by the connection terminal 23, and is fixed substantially parallel to the lower surface of the battery lid 12 via an insulating member (not shown). The bases 31 and connection terminals 23 of the current collector plates 30A and 30B are electrically insulated from the battery lid 12 by an insulating member (not shown) arranged on the lower surface of the battery lid 12.

The terminal portions 32 of the positive electrode and negative electrode current collectors 30A and 30B form the bottom surface of the battery can 11 from both sides of the base 31 in the thickness direction of the battery container 10 along the wide side surface 11c of the maximum area of the battery can 11. It is formed in a plate shape extending toward 11b. The terminal portions 32 of the current collector plates 30A and 30B extend from the outer end of the base 31 in the winding axis D direction of the electrode group 40, which will be described later, and the current collector plate joint 41d at the end of the electrode group 40. , 42d, respectively. As a result, the positive electrode current collector plate 30A is arranged at one end of the electrode group 40 in the winding axis D direction and is electrically connected to the positive electrode 41 (see FIG. 3), and the negative electrode current collector plate 30B Is arranged at the other end of the electrode group 40 in the winding axis D direction and is electrically connected to the negative electrode 42 (see FIG. 3).

The electrode group 40 is fixed to the battery lid 12 via the current collector plates 30A and 30B and an insulating member (not shown) by being joined to the terminal portion 32. Further, the external terminals 20A and 20B, the insulating member 24, the insulating member (not shown) on the lower surface of the battery lid 12, the current collector plates 30A and 30B, and the electrode group 40 are assembled to the battery lid 12, so that the lid assembly can be formed. It is configured.

An insulating case 50 that covers the electrode group 40 is arranged between the battery can 11 and the electrode group 40.
The insulating case 50 includes a sheet-shaped sheet portion 51 and a case-shaped case portion 52. The insulating case 50 may be integrally molded. The insulating case 50 is made of, for example, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), tetrafluoroethylene (PFA), polyphenylene sulfide (PPS), or the like.

The sheet portion 51 has a width equivalent to the width of the electrode group 40 in the winding axis D direction, and the electrode group 40 has a width equivalent to that of the electrode group 40.
From the position facing the current collector plate joint 41d to which the terminal portion 32 of the positive electrode current collector plate 30A is connected, to the position facing the current collector plate joint 42d to which the terminal portion of the negative electrode current collector plate 30B is joined. Up to, it extends in the width direction of the battery container 10. Further, the sheet portion 51 extends from the vicinity of the battery lid 12 on the front side of the battery container 10 shown in FIG. 1 to the vicinity of the lower end surface 10b along the wide side surface 10c of the battery container 10, and is an electrode facing the bottom surface 10a of the battery container 10. It is folded back so as to cover the curved portion 40b of the group 40, and extends along the wide side surface 10c on the back side of the battery container 10 to the vicinity of the battery lid 12.

The case portions 52 are arranged at both ends of the electrode group 40 in the winding axis D direction, and are the current collector plates 30A, respectively.
, 30B is provided so as to cover the current collector plate joints 41d and 42d of the electrode group 40 to which the terminal 32 is joined. The case portion 52 has a rectangular parallelepiped box shape in which the inner surface in the winding axis D direction and the surface on the battery lid 12 side are open, and the terminal portions 32 of the current collector plates 30A and 30B are joined to the electrodes. Both ends of the group 40 in the winding axis D direction are covered over the entire height direction perpendicular to the lower end surface 10b of the battery container 10.

At the time of manufacturing the secondary battery 100, in the lid assembly composed of the members shown in FIG. 2, an insulating case 50 is arranged between the electrode group 40, the current collector plates 30A and 30B, and the battery can 11, and between them. The battery can 11 shown in FIG. 1 is electrically insulated from the curved portion 40b on the lower side of the electrode group 40.
It is inserted into the opening 11a of. In the electrode group 40, the narrow side surfaces 11d of the battery can 11 are located on both sides in the winding axis D direction, and the battery can 11 is substantially parallel to the bottom surface 11b and the wide side surface 11c of the battery can 11 in the winding axis D direction. It is housed inside.

As a result, in the electrode group 40, one curved portion 40b faces the battery lid 12, the other curved portion 40b faces the bottom surface 11b of the battery can 11, and the flat portion 40a faces the wide side surface 11c. Become. Then, in a state where the opening 11a of the battery can 11 is closed by the battery lid 12.
For example, by joining the entire circumference of the battery lid 12 to the opening 11a of the battery can 11 by laser welding, the battery container 10 composed of the battery can 11 and the battery lid 12 is formed.

After that, the non-aqueous electrolytic solution is injected into the battery container 10 through the liquid injection port 14 of the battery lid 12.
For example, the battery container 10 is sealed by joining and sealing the liquid injection plug 15 to the liquid injection port 14 by laser welding. Examples of the non-aqueous electrolytic solution to be injected into the battery container 10 include, for example.
_{A solution in which lithium hexafluorophosphate (LiPF 6} ) is dissolved at a concentration of 1 mol / liter can be used in a mixed solution in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 2.

FIG. 3 is an exploded perspective view of a part of the electrode group 40 shown in FIG. 2. The electrode group 40 is a wound electrode group formed by winding positive and negative electrodes 41 and 42 laminated with separators 43 and 44 around an axis parallel to the winding axis D to form a flat shape.

The electrode group 40 has a flat portion 40a and an upper and lower end surfaces 10a facing the wide side surface 10c of the battery container 10.
It is formed into a flat shape having a curved portion 40b facing 10b. The flat portion 40a is a portion in which the electrodes 41 and 42 and the separators 43 and 44 are flatly laminated, and the curved portion 40b
Is a portion in which the electrodes 41 and 42 and the separators 43 and 44 are laminated in a semi-cylindrical shape. The separators 43 and 44 insulate between the positive electrode 41 and the negative electrode 42, and the separator 44 is also wound around the outer periphery of the negative electrode 42 wound around the outermost circumference.

The positive electrode 41 has a positive electrode foil 41a, which is a positive electrode current collector, and a positive electrode mixture layer 41b made of a positive electrode active material mixture coated on both sides of the positive electrode foil 41a. One side of the positive electrode 41 in the width direction is
The positive electrode mixture layer 41b is not formed, and the positive electrode foil 41a is exposed as the foil exposed portion 41c.
In the positive electrode 41, the foil exposed portion 41c is arranged on the opposite side of the foil exposed portion 42c of the negative electrode 42 in the winding axis D direction, and is wound around the winding axis D.

For the positive electrode 41, for example, a positive electrode active material mixture obtained by adding a conductive material, a binder and a dispersion solvent to the positive electrode active material and kneading the positive electrode active material is applied to both sides of the positive electrode foil 41a except for one side in the width direction. It can be manufactured by drying, pressing and cutting. As the positive electrode foil 41a, for example, an aluminum foil having a thickness of about 20 μm can be used. The thickness of the positive electrode mixture layer 41b, which does not include the thickness of the positive electrode foil 41a, is, for example, about 90 μm.

As the material of the positive electrode active material mixture, for example, 100 parts by weight of lithium manganate (chemical formula LiMn ₂ O ₄ ) is used as the positive electrode active material, 10 parts by weight of scaly graphite is used as the conductive material, and 10 parts by weight is used as the binder. Polyvinylidene fluoride (hereinafter referred to as PVDF) and N-methylpyrrolidone (hereinafter referred to as NMP) can be used as the dispersion solvent.

The positive electrode active material is not limited to the above-mentioned lithium manganate, and for example, other lithium manganate having a spinel crystal structure, or a lithium manganese composite oxide partially substituted or doped with a metal element may be used. Further, as the positive electrode active material, lithium cobalt oxide or lithium titanate having a layered crystal structure, and a lithium-metal composite oxide obtained by substituting or doping a part of these with a metal element may be used.

The negative electrode 42 has a negative electrode foil 42a, which is a negative electrode current collector, and a negative electrode mixture layer 42b made of a negative electrode active material mixture coated on both sides of the negative electrode foil 42a. One side of the negative electrode 42 in the width direction is
The negative electrode mixture layer 42b is not formed, and the negative electrode foil 42a is exposed as the foil exposed portion 42c.
The negative electrode 42 has its foil exposed portion 42c arranged on the opposite side of the positive electrode 41 from the foil exposed portion 41c in the winding axis D direction, and is wound around the winding axis D.

FIG. 4 is a schematic enlarged cross-sectional view in which a part of the cross section of the negative electrode 42 shown in FIG. 3 is enlarged. The negative electrode mixture layer 42b is formed on both sides of the negative electrode foil 42a, but in FIG. 4, the negative electrode foil 4 is formed.
Only the negative electrode mixture layer 42b on one surface of 2a is shown, and the negative electrode mixture layer 42b on the other surface is not shown.

In the secondary battery 100 of the present embodiment, the negative electrode mixture layer 42b contains the SiO-based active material particles 1 and the binder 2 as the negative electrode active material, and the SiO-based active material particles 1 are the binder 2. The greatest feature is that at least a part of the coating layer 3 is covered with a coating layer 3 made of a resin material containing an imide bond imidized at a temperature higher than the heat resistant temperature. Further, in the present embodiment, the negative electrode mixture layer 42b contains carbon-based active material particles 4 such as natural graphite as the negative electrode active material.

The SiO-based active material particles 1 are, for example, silicon-based active materials represented by the chemical formula SiOx (where 0.8 <x <1.2), and are coarse-grained by, for example, a sieve having a sieve mesh size of 53 μm and a 270 mesh sieve. Is the removed particles. The entire or part of the surface of the SiO-based active material particles 1 is covered with the coating layer 3. The portion of the SiO-based active material particles 1 exposed from the coating layer 3 functions as a site responsible for receiving and discharging lithium (Li) ions during charging and discharging, and serves as an entrance / exit for storing and releasing Li ions.

The binder 2 is filled between the SiO-based active material particles 1 having the coating layer 3 and the carbon-based active material particles 4, and these are bound and held on the surface of the negative electrode foil 42a. The binder 2 is, for example,
It is composed of styrene-butadiene rubber (SBR) and contains, for example, carbon and scaly graphite as a conductive material. When the binder 2 is composed of SBR, it softens at a temperature of 100 ° C. or lower, so that the heat resistant temperature is 100 ° C. or lower. When the binder 2 is composed of PVDF, the melting point is, for example, 150 ° C. or higher and 180 ° C. or lower, so that the heat resistant temperature is 150 ° C. or lower. The heat-resistant temperature of the binder 2 is the upper limit of the temperature at which the binder 2 can maintain its function.

The coating layer 3 covers the entire surface or a part of the surface of the SiO-based active material particles 1.
It is firmly bound to the surface of the system active material particles 1. The coating layer 3 is, for example, polyimide (PI).
Alternatively, it can be composed of polyamide-imide (PAI). From the viewpoint of lowering the imidization temperature in the step of forming the coating layer 3, the coating layer 3 is preferably composed of PAI.

The average particle size of the carbon-based active material particles 4 is made larger than the average particle size of the SiO-based active material particles 1, for example. The ratio of the total weight of the carbon-based active material particles 4 to the total weight of the SiO-based active material particles 1 having the coating layer 3 is, for example, 95: 5. The carbon-based active material particles 4 are the coating layer 3
The binder 2 is bound to the surface.

Here, with reference to FIG. 5, the negative electrode 4 included in the manufacturing process of the secondary battery 100 of the present embodiment.
The manufacturing process of No. 2 will be described. FIG. 5A is a flow chart showing a manufacturing process of the negative electrode 42, and FIG. 5B is a flow chart showing details of the coating step S1 shown in FIG. 5A. The negative electrode 42 is manufactured through the coating step S1, the preparation step S2, and the coating drying step S3 shown in FIG. 5A.

The coating step S1 is a step of imidizing the precursor of the resin material to form a coating layer 3 made of the resin material containing an imide bond on at least a part of the surface of the SiO-based active material particles 1.
The coating step S1 includes a mixing step S11, a drying step S12, and a crushing step S13 shown in FIG. 5 (b).
It has a polymerization step S14, a crushing step S15, and a sorting step S16.

In the mixing step S11, first, SiOx having an average particle size of about 5 μm (however, 0.8 <x <1).
.. Approximately 5% of carbon is supported on the powder which is an aggregate of SiO-based active material particles 1 which are the particles of 2). Further, for example, a resin material such as PI or PAI is dissolved in a solvent such as NMP to prepare a solution of a precursor of the resin material. Then, these are put into a planetary mixer and mixed and stirred for about 20 minutes, for example. As a result, a mixture of the SiO-based active material particles 1 and the precursor of the resin material is obtained.

In the present embodiment, the total weight of the coating layer 3 formed by imidizing and polymerizing the precursor of the resin material is 1% or more and 5% or less of the total weight of the SiO-based active material particles 1. In addition, the weight of each material is adjusted.

In the drying step S12, the mixture obtained in the mixing step S11 is taken out from the planetary mixer, placed on a metal leaf such as aluminum, and dried in air at a temperature of about 80 ° C. for about 1 hour to evaporate the solvent. Let me. In addition, the dried mixture is placed in a vacuum, for example, about 100.
Allow to dry at a temperature of ° C. for about 2 hours to allow the solvent to evaporate completely. As a result, a lump containing the SiO-based active material particles 1 and the precursor of the resin material is obtained.

In the crushing step S13, the mass obtained in the drying step S12 is roughly crushed in, for example, a mortar and then crushed in a mill for 10 minutes or more until it becomes sandy, and the SiO-based active material particles 1 and the resin material are pulverized. Obtain a powder containing a precursor.

In the polymerization step S14, the precursor of the resin material is heated to a temperature of 250 ° C. or higher and 350 ° C. or lower together with the SiO-based active material particles 1 to be imidized. In the present embodiment, in the polymerization step,
The powder obtained in the pulverization step S13 is placed on a metal foil such as aluminum, for example, 3
The precursor of the resin material is polymerized and imidized by vacuum drying and heating at a temperature of 00 ° C. As a result, a resin material containing an imide bond such as PI or PAI is firmly bound to the surface of the SiO-based active material particles 1.

In the crushing step S15, a mass made of the SiO-based active material particles 1 obtained in the polymerization step S14 and a resin material containing an imide bond such as PI or PAI is cooled to room temperature, and then, for example, in a mortar and a mill. Crush for at least 5 minutes. This will cause at least part of the PI or PA
A powder of SiO-based active material particles 1 coated on a coating layer 3 made of a resin material containing an imide bond such as I is obtained.

In the sorting step S16, the powder obtained in the crushing step S15 is mixed with, for example, a mesh opening of 53 μm.
The coarse particles are removed by sieving with a 270 mesh to obtain a powder of SiO-based active material particles 1 having a particle size in a predetermined range and having at least a part of the surface coated on the coating layer 3. Based on the above, FIG. 5 (
The coating step S1 shown in a) is completed.

In the preparation step S2 shown in FIG. 5A, the SiO having the coating layer 3 obtained in the coating step S1
A slurry containing the active material particles 1 and the binder 2 is prepared. In this embodiment, the preparation step S2
In, as the negative electrode active material, a slurry containing not only the SiO-based active material particles 1 having the coating layer 3 but also the carbon-based active material particles 4 is prepared. Specifically, the total weight of the carbon-based active material particles 4 and
The ratio to the total weight of the SiO-based active material particles 1 having the coating layer 3 is, for example, 95: 5 to 95 :.
Mix up to 3 and dry mix with a planetary mixer.

Then, for example, carboxymethyl cellulose (CMC) as a thickener is added to this mixture and stirred to adjust the viscosity to obtain a slurry having an appropriate viscosity. By adding, for example, styrene-butadiene rubber (SBR) as a binder to this slurry and kneading it, a slurry containing a negative electrode active material and a binder can be obtained. For CMC and SBR, for example, 2 parts by weight can be added to 98 parts by weight of the negative electrode active material. For example, ion-exchanged water can be used for adjusting the viscosity of the thickener, the dispersion solvent of the binder and the slurry.

In the coating / drying step S3 shown in FIG. 5A, the slurry obtained in the preparation step S2 is used as the negative electrode foil 4.
It is applied to both sides of 2a except for one side in the width direction, dried to melt or soften the binder, and then cooled to be pressed and cut. In the present embodiment, the drying temperature in the coating drying step S3 is lower than the temperature at which the precursor of the resin material of the coating layer 3 for coating the SiO-based active material particles 1 is polymerized in the coating step S1, for example, 120 ° C. or lower. , Preferably 100 ° C. or lower. As the negative electrode foil 42a, for example, a copper foil having a thickness of about 10 μm can be used.

As a result, as shown in FIG. 4, the binder 2 is sandwiched between the SiO-based active material particles 1 having the coating layer 3.
Is formed, and the negative electrode mixture layer 42b is formed on the surface of the negative electrode foil 42a. In the present embodiment, the layer of the binder 2 is also formed between the SiO-based active material particles 1 having the coating layer 3 and the carbon-based active material particles 4, and between the carbon-based active material particles 4. Negative electrode mixture layer 4 not including the thickness of the negative electrode foil 42a
The thickness of 2b is, for example, about 70 μm. From the above, the binder 2 between the particles of the negative electrode active material
A negative electrode 42 including the negative electrode mixture layer 42b containing the above can be manufactured.

In the present embodiment, the negative electrode active material contains both SiO-based active material particles 1 and carbon-based active material particles 4. However, only SiO-based active material particles 1 may be used as the negative electrode active material.
Further, the carbon-based active material particles 4 are not limited to the above-mentioned natural graphite capable of inserting and removing lithium ions, but are not limited to natural graphite, which is amorphous carbon, various artificial graphite materials, carbonaceous materials such as coke, Si, Sn, and the like. (For example, SiO, TiSi _2, etc.), or a composite material thereof may be used.
The particle shape of the negative electrode active material is also not particularly limited, and a particle shape such as scaly, spherical, fibrous or lumpy can be appropriately selected.

The binder used for the positive electrode and negative electrode mixture layers 41b and 42b is PVDF.
Not limited to SBR. As the binder described above, for example, polytetrafluoroethylene (
PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride,
A polymer such as an acrylic resin and a mixture thereof may be used.

Further, the shaft core when the positive electrode 41 and the negative electrode 42 are overlapped and wound with the separators 43 and 44 shown in FIG. 3 interposed therebetween is, for example, a positive electrode foil 41a, a negative electrode foil 42a, and separators 43 and 44.
A resin sheet having a higher bending rigidity than any of the above can be used.

In the winding axis D direction of the electrode group 40, the width of the negative electrode mixture layer 42b of the negative electrode 42 is the positive electrode 4
It is wider than the width of the positive electrode mixture layer 41b of 1. Further, negative electrodes 42 are wound around the innermost circumference and the outermost circumference of the electrode group 40. As a result, the positive electrode mixture layer 41b is sandwiched between the negative electrode mixture layers 42b from the innermost circumference to the outermost circumference of the electrode group 40.

The foil exposed portions 41c and 42c of the positive electrode 41 and the negative electrode 42 are bundled by the flat portion 40a of the electrode group 40, respectively, to form the above-mentioned current collector plate joint portions 41d and 42d (see FIG. 2). The current collector plate joints 41d and 42d of the positive electrode 41 and the negative electrode 42 are bonded to the terminal portions 32 of the positive electrode and negative electrode current collector plates 30A and 30B, for example, by ultrasonic welding or the like. As a result, on the positive electrode side and the negative electrode side, the external terminals 20A and 20B are electrically connected to the positive and negative electrodes 41 and 42 constituting the electrode group 40, respectively, via the current collector plates 30A and 30B, respectively.

In the winding axis D direction of the electrode group 40, the widths of the separators 43 and 44 are the negative electrode mixture layer 4.
Although wider than the width of 2b, the foil exposed portions 41c and 42c of the positive electrode 41 and the negative electrode 42 project outward in the width direction from the widthwise ends of the separators 43 and 44, respectively. Therefore,
The separators 43 and 44 do not hinder the welding of the exposed foil portions 41c and 42c in a bundle.

Hereinafter, the operation of the secondary battery 100 of the present embodiment and the method for manufacturing the secondary battery 100 will be described.

The secondary battery 100 of the present embodiment is connected to, for example, the external terminals 20A and 20B of another secondary battery 100 by fastening a bus bar (not shown) to the bolts 22 of the external terminals 20A and 20B shown in FIG. , Used as an assembled battery. The secondary battery 100 has external terminals 20A and 20B.
The electric power supplied from the outside through the connection terminals 23 and the current collector plates 30A and 30 shown in FIG.
It accumulates in the electrode group 40 via B. Further, the electric power stored in the electrode group 40 is collected by the current collector plate 30A.
It is supplied to the outside from the external terminals 20A and 20B via the 30B and the connection terminal 23.

As the secondary battery 100 is charged and discharged, the SiO-based active material particles 1 and the carbon-based active material particles 4 contained in the negative electrode mixture layer 42b shown in FIG. 4 repeatedly expand and contract, but the SiO-based active material particles 1 The change in volume is larger than that of the carbon-based active material particles 4. Therefore, in the conventional secondary battery using PVDF, SBR, etc., which have a relatively weak binding force, as the binder resin, that is, the binder 2,
The SiO-based active material particles 1 may be cracked due to repeated expansion and contraction, and the cycle characteristics of the secondary battery may be deteriorated. Further, as a negative electrode binder, that is, as a binder 2, polyimide (
In a conventional secondary battery using PI) and polyvinylpyrrolidone (PVP), when the PI is imidized to form the binder 2, the negative electrode foil 42a is exposed to a high temperature and the strength and weldability are lowered. , There is a risk of adversely affecting the manufacturing process of the secondary battery 100.

On the other hand, in the secondary battery 100 of the present embodiment, the SiO-based active material particles 1 are formed of a coating layer 3 made of a resin material containing an imide bond imidized at a temperature higher than the heat resistant temperature of the binder 2. At least partly covered. As a result, the volume change of the SiO-based active material particles 1 during expansion and contraction can be reduced by the coating layer 3 made of a tough resin material having a higher binding force than the binder 2, or the SiO-based active material particles 1 can be reduced in volume. It is possible to suppress side reactions such as reduction decomposition of the electrolytic solution that occurs on the surface and suppress cracking of the SiO-based active material particles 1.

Further, the secondary battery 100 of the present embodiment has PI or PAI on the surface of the SiO-based active material particles 1 before the coating / drying step S3 of forming the binder 2 on the negative electrode foil 42a at the time of manufacturing the negative electrode 42.
It has a coating step S1 for forming a coating layer 3 made of a resin material containing an imide bond such as.
Further, the drying temperature in the coating drying step S3 is lower than the temperature at which the precursor of the resin material of the coating layer 3 is imidized and polymerized in the coating step S1. Therefore, the negative electrode foil 42
It is possible to avoid exposing a to the high temperature required for imidization polymerization.

Therefore, according to the secondary battery 100 of the present embodiment and the manufacturing method thereof, the cycle characteristics of the secondary battery 100 can be improved without exposing the negative electrode 42 to a high temperature in the manufacturing process.

When the resin material of the coating layer 3 is PAI, the temperature required for imidization polymerization is set to PI.
It contributes to the simplification of the manufacturing process of the secondary battery 100 and the reduction of the manufacturing cost. Further, when the binder 2 contains SBR, the flexibility of the binder 2 can be improved and the durability of the negative electrode mixture layer 42b can be improved. Further, since the negative electrode mixture layer 42b contains the carbon-based active material particles 4, the negative electrode mixture layer 42b contains only the SiO-based active material particles 1 as the negative electrode active material, as compared with the case where the negative electrode mixture layer 42b contains only the SiO-based active material particles 1. Expansion and contraction of

Further, in the coating step S1, the precursor of the resin material of the coating layer 3 is 2 together with the SiO-based active material particles 1.
It has a polymerization step S14 which is heated to a temperature of 50 ° C. or higher and 350 ° C. or lower to imidize. As a result, a tough coating layer 3 made of a resin material containing an imide bond such as PI or PAI firmly bonded to the surface of the SiO-based active material particles 1 can be formed.

Further, the coating step S1 includes a mixing step S11, a drying step S12, and a crushing step S13 before the polymerization step S14. As a result, in the polymerization step S14, the precursor of the resin material of the coating layer 3 which has been made into powder and the SiO-based active material particles 1 can be heated. Therefore, in the polymerization step S14, the coating layer 3 is more uniform and denser on the surface of the SiO-based active material particles 1 than in the case where the precursor of the resin material of the coating layer 3 and the SiO-based active material particles 1 are in the form of agglomerates. Can be formed.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and there are design changes and the like within a range that does not deviate from the gist of the present invention. Also, they are included in the present invention. For example, in the above-described embodiments and examples, an example in which the present invention is applied to a square secondary battery has been described, but the present invention is not limited to the square secondary battery, and for example, a cylindrical type, a laminated type, or the like, non-aqueous electrolysis. It can be applied to all negative electrodes of liquid secondary batteries.

[Example]
Hereinafter, examples of the secondary battery of the present invention and the method for manufacturing the same will be described.

The negative electrodes of Examples 1 and 2 and Comparative Example 1 were manufactured based on the manufacturing method described in the above-described embodiment. In the negative electrodes of Examples 1 and 2, the total weight of PAI as the resin material of the coating layer was set to 3% and 5%, respectively, with respect to the total weight of the SiO-based active material particles. On the other hand, in the negative electrode of Comparative Example 1, the total weight of PAI as the resin material of the coating layer was set to 0% (without the coating layer) with respect to the total weight of the SiO-based active material particles. In the negative electrodes of Examples 1 and 2 and Comparative Example 1, the ratio of the total weight of the carbon-based active material particles to the total weight of the SiO-based active material particles having the coating layer is
It was 95: 3. These negative electrodes were superposed on the positive electrodes via separators to prepare small cells of Examples 1, 2 and 3, and the initial cycle characteristics were measured. The charging / discharging method of each small cell is as follows.

Charging: 0.5C constant current constant voltage charging, constant voltage value 4.2V, 0.01C termination Discharge: 0.5C constant current, 2.7V termination

In FIG. 6, the horizontal axis represents the number of charge / discharge cycles (cycle), and the vertical axis represents the capacity retention rate (%) of each cell. It is a graph which shows the relationship.

In FIG. 6, the measurement result of the small cell of Example 1 (PAI: 3%) is marked with a white triangle and a broken line, and the measurement result of the small cell of Example 2 (PAI: 5%) is marked with a white circle. And the solid line shows the measurement result of the small cell of Comparative Example 1 (PAI: 0%) by the black square mark and the alternate long and short dash line.
From the above results, the small cell using the SiO-based active material particles having the coating layers of Examples 1 and 2 has more cycle characteristics than the small cell using the SiO-based active material particles having no coating layer of Comparative Example 1. Was confirmed to improve.

Next, the negative electrodes of Examples 1 and 2 and Comparative Example 1 described above are manufactured, and the total weight of PAI (PAI coating amount) as the resin material of the coating layer is 1% with respect to the total weight of SiO-based active material particles.
The negative electrode of Example 3 was manufactured in the same manner. At each negative electrode, the ratio of the total weight of the carbon-based active material particles, the total weight of the SiO-based active material particles having the coating layer, and the total weight of the binder composed of the binder and the thickener is 95. The slurry was adjusted to be 3: 3: 2 and applied to the negative electrode foil. Using these negative electrodes, a half cell with metallic lithium as the counter electrode was prepared, and the initial charge / discharge efficiency of the negative electrode was measured. FIG. 7 shows a value obtained by dividing the discharge capacity when charging and discharging are performed under the following conditions by the charging capacity.

Charging: 0.5C constant current constant voltage charging, constant voltage value 0.01V vs Li metal, 0.01C termination Discharge: 0.5C constant current, 1.5V vs Li metal termination

FIG. 7 is a graph showing the relationship between the initial charge / discharge efficiency and the PAI coating amount, where the vertical axis represents the initial charge / discharge efficiency (%) and the horizontal axis represents the PAI coating amount (wt%). Example 1 (PAI coating amount: 3 wt)
%), Example 2 (PAI coverage: 5 wt%) and Example 3 (PAI coverage: 1 wt%)
And Comparative Example 1 (PAI coating amount: 0 wt%), it was confirmed that all the small cells of Examples 1 to 3 showed higher initial charge / discharge efficiency than the small cells of Comparative Example 1.

The initial charge / discharge efficiency of the small cell of each example is that of Example 3 (PAI coverage: 1 wt%).
The small cell of Example 2 (PAI coverage: 5 wt%) was the highest, and the small cell of Example 2 (PAI coverage: 5 wt%) was the lowest. That is, if the total weight of the coating layer is 1% or more and 5% or less of the total weight of the SiO-based active material particles, higher initial charge / discharge efficiency can be obtained as compared with the case without the coating layer, but the SiO-based activity can be obtained. It was confirmed that a higher initial charge / discharge efficiency can be obtained when the total weight of the material particles is 1% or more and 3% or less.

1 ... SiO-based active material particles, 2 ... Binder, 3 ... Coating layer, 4 ... Carbon-based active material particles, 42 ... Negative electrode, 42a ... Negative electrode foil, 42b ... Negative electrode mixture layer, 100 ... Secondary battery

Claims (1)

A method for manufacturing a secondary battery including a negative electrode having a negative electrode foil and a negative electrode mixture layer, and a current collector plate welded to the negative electrode foil.
The negative electrode mixture layer is formed between the SiO-based active material particles having a coating layer, the carbon-based active material particles, the conductive material, the SiO-based active material particles having the coating layer, and the carbon-based active material particles. Including filled binders
The binder is composed of a material different from that of the coating layer.
The carbon-based active material particles do not have the coating layer, and the binder is bound to the surface thereof.
The coating layer is constituted by Lee bromide-based resin material,
The binder is polyvinylidene fluoride, styrene butadiene rubber, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, rubber polysulfide, nitrocellulose, cyanoethylcellulose, latex, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride. , fluoride chloroprene, among acrylic resins, seen at least Tsuo含,
A method for producing a secondary battery , which comprises imidizing a precursor of a resin material at a temperature higher than the heat resistant temperature of the binder to form the coating layer made of the imide-based resin material .

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