JP2015008069A - Negative electrode and method of manufacturing negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode and a method of manufacturing the negative electrode capable of enhancing the filled density of a negative electrode active material layer by suppressing generation of spring back.SOLUTION: A negative electrode 24 includes a negative electrode active material layer 26 including a negative active material particle 26a on both surfaces of a metal foil 25 for the negative electrode. In the negative electrode 24, the negative electrode active material layer 26 includes: the negative electrode active material particle 26a; a binder 26b formed of styrene-butadiene rubber; and an additive agent 26c formed of zinc stearate or zinc palmitate.

Description

  The present invention relates to a negative electrode provided with a negative electrode active material layer containing negative electrode active material particles on a current collector, and a method for producing the negative electrode.

  Conventionally, lithium-ion secondary batteries and nickel-hydrogen secondary batteries are well known as power storage devices mounted on vehicles and the like. For example, in a lithium ion secondary battery, a positive electrode or negative electrode active material layer containing active material particles is formed on the surface of a metal foil (current collector). It is set as the structure accommodated in the case.

  In such a lithium ion secondary battery, as an example of the manufacturing process of the positive electrode and the negative electrode, the active material paste (active material mixture) applied to the metal foil is subjected to press working, and the active material particles in the active material layer The density (hereinafter referred to as packing density) is increased. However, when press working is performed, cracks may occur in the active material layer, or expansion (so-called spring back) may occur in the active material layer over time due to residual internal stress applied during press working. As a result, many voids are formed in the active material layer, the packing density in the active material layer is reduced, and the internal resistance of the active material layer is increased.

  Therefore, in order to suppress an increase in internal resistance of the active material layer, it has been proposed to add a higher fatty acid lithium salt as a lubricant to the active material paste (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-16567

  In order to improve the energy volume density of the power storage device, it has been further desired to suppress an increase in internal resistance of the active material layer. The addition of the lubricant to the active material paste described in Patent Document 1 facilitates the relative movement of the active material particles, and can suppress the occurrence of cracks and springback during press working. However, the suppression of spring back has room for further improvement because residual internal stress is generated for the purpose of increasing the packing density, that is, as long as press working is performed.

  An object of the present invention is to provide a negative electrode and a method for manufacturing the negative electrode that can suppress the occurrence of springback and increase the packing density of the negative electrode active material layer.

  In order to solve the above problem, the negative electrode according to claim 1 is a negative electrode comprising a current collector and a negative electrode active material layer containing negative electrode active material particles, wherein the negative electrode active material layer comprises at least The gist of the invention is to contain the negative electrode active material particles, a binder made of rubber, and an additive made of saturated fatty acid.

  According to this, since the additive consisting of saturated fatty acid has an action as a lubricant, in the negative electrode active material mixture part formed in the current collector, the additive enters between the negative electrode active material particles, The additive reduces the frictional resistance between the negative electrode active material particles. For this reason, when it press-processes, while negative electrode active material particle is closely packed, it can suppress that a negative electrode active material layer cracks.

  Furthermore, in combination with a binder made of rubber, when the negative electrode active material mixture part is heated to form the negative electrode active material layer, vulcanization of the binder is promoted by an additive made of saturated fatty acid, and the binder is intermolecular. Is promoted. As a result, the binding force by the binder is increased, so that the negative active material layer is prevented from expanding (spring back) over time due to the residual internal stress applied during the press working. As a result, voids are hardly formed in the negative electrode active material layer, and an increase in internal resistance of the negative electrode active material layer is suppressed.

Regarding the negative electrode, the rubber is preferably styrene butadiene rubber.
According to this, the vulcanization promoting action by the additive consisting of saturated fatty acid further promotes cross-linking between molecules in the styrene butadiene rubber, the binding force of the negative electrode active material particles by the binder made of rubber, and the current collector The binding force with the negative electrode active material particles can be increased.

In the negative electrode, the saturated fatty acid may be zinc palmitate.
According to this, vulcanization of the binder can be surely promoted by zinc palmitate.

In the negative electrode, the saturated fatty acid may be zinc stearate.
According to this, vulcanization of the binder can be surely promoted by zinc palmitate.

  The method for producing a negative electrode according to claim 5 is a method for producing a negative electrode comprising a current collector provided with a negative electrode active material layer containing negative electrode active material particles, wherein at least the negative electrode active material particles, rubbers And applying a negative electrode active material mixture containing an additive consisting of a saturated fatty acid to the current collector, and pressing the negative electrode active material mixture applied to the current collector. The gist is to include a pressing step to be applied and a heating step of heating the negative electrode active material mixture after the pressing step.

  According to this, since the additive has an action as a lubricant, in the negative electrode active material mixture part formed on the current collector after the coating step, the additive enters between the negative electrode active material particles, The additive reduces the frictional resistance between the negative electrode active material particles. For this reason, when it press-processes, while negative electrode active material particle is closely filled, generation | occurrence | production of a crack is suppressed.

  Further, in the heating step, the vulcanization of the rubber binder is promoted by the additive, and the bonding between the binder molecules is promoted. As a result, the binding force of the negative electrode active material particles by the binder and the binding force between the current collector and the negative electrode active material particles are increased, and the negative active material layer expands over time due to the residual internal stress applied during the press working. Doing (spring back) is suppressed.

  In addition, about the manufacturing method of a negative electrode, a heating process is a drying process for removing a solvent from a negative electrode active material mixture, for example, It is preferable that the heating temperature in the said heating process is 80-120 degreeC.

  According to this, by setting the heating temperature to less than 120 ° C., it is possible to make the influence of heat difficult to other materials contained in the negative electrode active material mixture, and for vulcanization such as styrene butadiene rubber. Even when a binder having an optimum temperature on the higher temperature side is used, vulcanization can be accelerated by the vulcanization promoting action of the additive.

  According to the present invention, it is possible to suppress the occurrence of springback and increase the packing density of the negative electrode active material layer.

The perspective view which shows a secondary battery. The disassembled perspective view which shows the component of an electrode assembly. (A) is a schematic diagram which shows an application | coating process, a predrying process, and a press process, (b) is a schematic diagram which shows a drying process. The schematic diagram which shows the cross section of a negative electrode.

Hereinafter, an embodiment embodying a negative electrode and a manufacturing method thereof will be described with reference to FIGS.
First, a secondary battery as a power storage device including a negative electrode will be described.

  As shown in FIG. 1, in the secondary battery 10, the case 11 contains an electrode assembly 14 and an electrolytic solution. The case 11 includes a bottomed rectangular parallelepiped main body member 12 and a rectangular flat plate-shaped lid member 13. The main body member 12 has an electrode assembly 14 and an electrolytic solution accommodating portion therein, and an insertion port communicating with the accommodating portion is opened. The lid member 13 closes the insertion port. Both the main body member 12 and the lid member 13 constituting the case 11 are made of metal (for example, stainless steel or aluminum). In addition, the secondary battery 10 of the present embodiment is a square battery whose appearance is a square, and is a lithium ion battery.

  A positive electrode terminal 14 a and a negative electrode terminal 14 b for taking out electricity from the electrode assembly 14 are electrically connected to the electrode assembly 14. The positive electrode terminal 14a and the negative electrode terminal 14b protrude out of the case 11 through the lid member 13, and the positive electrode terminal 14a and the negative electrode terminal 14b have ring-shaped insulating rings 13b for insulation from the case 11, respectively. It is attached.

  As shown in FIG. 2, the electrode assembly 14 includes a plurality of positive electrodes 21 and a plurality of negative electrodes 24 that are alternately stacked via separators 27. The positive electrode 21 has a rectangular positive electrode metal foil (aluminum foil in the present embodiment) 22 and a rectangular positive electrode active material layer 23 provided on both surfaces (surfaces) of the positive electrode metal foil 22. . The positive electrode 21 has a positive electrode-side uncoated portion 22d along which the positive electrode active material is not provided. And in the positive electrode 21, the positive electrode current collection tab 31 is provided in the state which protrudes in a part of one side of the positive electrode side uncoated part 22d.

  The negative electrode 24 is a rectangular negative electrode active material provided on both surfaces of a rectangular negative electrode metal foil (copper foil in this embodiment) 25 as a sheet-like current collector and the negative electrode metal foil 25. And a material layer 26.

  The negative electrode 24 has a negative electrode-side uncoated portion 25d along which the negative electrode active material is not provided. And in the negative electrode 24, the negative electrode current collection tab 32 protrudes in a part of one side of the negative electrode side uncoated part 25d.

  As shown in FIG. 4, the negative electrode active material layers 26 formed on both surfaces of the negative electrode metal foil 25 include negative electrode active material particles 26a, a binder 26b made of rubber, an additive 26c, and a conductive additive. Note that the conductive auxiliary agent is dispersed in the binder 26b. And in the formation area of the negative electrode active material layer 26 in the metal foil 25 for negative electrodes, each surface 25c in both surfaces of the metal foil 25 for negative electrodes is a flat surface, The negative electrode active material particle 26a, the binder 26b, and addition to the surface 25c Agent 26c is present. That is, the negative electrode active material particles 26 a are not embedded in the surface 25 c of the negative electrode metal foil 25.

  Further, in the negative electrode active material layer 26, the additive 26c enters between the negative electrode active material particles 26a, the negative electrode active material particles 26a come close to each other, and the negative electrode active material particles 26a are densely packed. . The adjacent negative electrode active material particles 26a are bound together by a binder 26b.

  As shown in FIG. 2, the positive electrode 21 and the negative electrode 24 are arranged such that the positive electrode current collecting tabs 31 are arranged in a line along the stacking direction, and the negative electrode current collecting tabs 32 are not overlapped with the positive electrode current collecting tabs 31. Are stacked in a row along the stacking direction. Each of the positive electrode current collecting tabs 31 is electrically connected to the positive electrode terminal 14a in a state of being collected (bundled) within a range from one end to the other end of the electrode assembly 14 in the stacking direction. Further, each negative electrode current collecting tab 32 is electrically connected to the negative electrode terminal 14b in a state of being collected (bundled) within a range from one end to the other end of the electrode assembly 14 in the stacking direction.

Next, a method for manufacturing the negative electrode 24 will be described.
First, the material of the negative electrode active material layer 26 will be described. The negative electrode active material layer 26 is formed by applying a negative electrode active material mixture to the negative electrode metal foil 25. The negative electrode active material mixture includes negative electrode active material particles 26a, a binder 26b, an additive 26c, and a conductive additive. In the present embodiment, in the negative electrode active material mixture, as the negative electrode active material particles 26a, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, an element compound that has an element that can be alloyed with lithium, Alternatively, a polymer material or the like can be used. Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, coke, graphite, glassy carbon, organic polymer compound fired body, carbon fiber, activated carbon, or carbon black. The organic polymer compound fired body is obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Elements that can be alloyed with lithium are Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn. , Pb, Sb, Bi.

Elemental compounds having elements that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , and CaSi. _2, a _{CrSi 2, Cu 5 Si, FeSi} 2, MnSi 2, NbSi 2, TaSi 2, Vsi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O or the like. Examples of the polymer material include polyacetylene and polypyrrole.

  A conductive additive is added to increase the conductivity of the negative electrode 24 as necessary. As the conductive additive, carbon black, graphite, acetylene black, vapor grown carbon fiber, etc., which are carbonaceous fine particles, can be used alone or in combination of two or more.

  The binder 26b serves to bind the negative electrode active material particles 26a to each other and to bind the negative electrode active material particles 26a and the conductive additive to the negative electrode metal foil 25. As the binder 26b, rubbers such as styrene butadiene rubber (SBR) and acrylic acid-modified SBR resin (SBR latex) that are accelerated together with saturated fatty acids to accelerate vulcanization are used.

  The additive 26c enhances the slidability of the negative electrode active material particles 26a in the negative electrode active material mixture and promotes vulcanization of the binder 26b made of rubber. As the additive 26c having an action of accelerating the vulcanization of the binder 26b made of rubber, zinc stearate and zinc palmitate can be used more than saturated fatty acids. In addition, as the saturated fatty acid, zinc ricinoleate and zinc laurate can be used. The additive 26c is preferably contained in the negative electrode active material mixture in an amount of 0.001 to 0.1% by weight, and more preferably 0.01 to 0.04% by weight. If the content of the additive 26c is less than 0.001% by weight, the additive 26c may not be dispersed throughout the negative electrode active material mixture, which is not preferable. On the other hand, when the content of the additive 26c exceeds 0.1% by weight, a part where the concentration of the additive 26c is partially increased is generated, and the additive 26c causes phase separation of the binder 26b, so that the binder 26b serves as a binder 26b. This is because the binding strength cannot be obtained, which is not preferable.

Next, the manufacturing method of the negative electrode 24 will be described together with the operation.
The manufacturing method of the negative electrode 24 includes a coating process, a pre-drying process, a pressing process, a drying process that is one of heating processes, and a punching process.

  As shown in FIG. 3A, the coating process, the pre-drying process, and the pressing process are performed by a coating / drying device 35. The coating / drying device 35 includes a supply mechanism 36 that supplies a long strip-like metal foil 25 for negative electrode. Moreover, the coating drying apparatus 35 apply | coats a negative electrode active material mixture on both surfaces of the metal foil 25 for negative electrodes, and the 1st coating part G1 and 2nd coating part G2 as a negative electrode active material mixture part. , A pre-drying mechanism 38 that dries each coating part G1, G2, and a press mechanism 39 that presses both the coated parts G1, G2 after drying.

  The supply mechanism 36 of the coating / drying apparatus 35 includes a supply roll 36a around which a long strip-shaped negative electrode metal foil 25 is wound in the longitudinal direction. The supply roll 36a is rotatably supported by a support mechanism. And the metal foil 25 for negative electrodes wound by the supply roll 36a is conveyed in the conveyance direction X. FIG. The coating mechanism 37 includes a first slit die 37 a, and a discharge port (not shown) of the first slit die 37 a is disposed below one surface of the negative electrode metal foil 25 below the negative electrode metal foil 25. Has been. The coating mechanism 37 includes a second slit die 37b, and an outlet (not shown) of the second slit die 37b is located above the negative electrode metal foil 25 on the other surface of the negative electrode metal foil 25. Opposed.

  In the coating process, the negative electrode active material mixture is continuously discharged from the discharge ports of the first and second slit dies 37a and 37b, and the negative electrode metal foil 25 fed from the supply roll 36a has negative electrodes on both surfaces. The active material mixture is continuously applied in the longitudinal direction of the metal foil 25 for negative electrode. Then, a layer of the first coating part G1 is formed on one surface of the negative electrode metal foil 25 by the negative electrode active material mixture, and the other surface of the negative electrode metal foil 25 is formed by the negative electrode active material mixture. A layer of two coating parts G2 is formed. And the electrode material 30 is formed by forming each coating part G1, G2 in the metal foil 25 for negative electrodes.

  The pre-drying mechanism 38 includes a dryer 38a that dries the coating parts G1 and G2 by heat from a heat source, and the pre-drying process is performed by the pre-drying mechanism 38. The press mechanism 39 includes rotating press rollers 63a and 63b.

  In the pressing step, pressing is performed by sandwiching and pressing the electrode material 30 with the press rollers 63a and 63b, and the coating portions G1 and G2 are compressed to a predetermined thickness, respectively. Thereafter, the pressed electrode material 30 is wound on a winding roll 39a.

  As shown in FIG. 3B, the drying process performed after the pressing process is performed by setting the electrode material 30 wound around the winding roll 39 a in the drying furnace 41. Then, in the drying process, the additive 26c is heated to remove the solvent remaining in each of the coating parts G1 and G2 and accelerate the vulcanization of the binder 26b. Combined.

  In addition, it is preferable that the heating temperature in a drying process is set to the temperature range of 80-120 degreeC. This is because if the heating temperature is less than 80 ° C., it becomes difficult to express the vulcanization promoting action of the binder 26b by the additive 26c, which is not preferable. On the other hand, if the heating temperature exceeds 120 ° C., the vulcanization promoting action of the binder 26b by the additive 26c can be expressed, but it is not preferable because the conductive auxiliary agent may be affected by heat. .

  In the drying step, the solvent remaining in both coating parts G1 and G2 is removed, and the binder 26b is cured, and the negative electrode active material particles 26a and the negative electrode active material particles 26a and the negative electrode metal are cured by the binder 26b. The foil 25 is bound to form the negative electrode active material layer 26. Thereafter, although not shown, the electrode material 30 is punched into the shape of the negative electrode 24 to manufacture the negative electrode 24.

According to the above embodiment, the following effects can be obtained.
(1) In the negative electrode 24, the negative electrode active material layer 26 contains an additive 26c made of a saturated fatty acid together with a rubber binder 26b. For this reason, in the manufacturing process of the negative electrode 24, in the drying process, the bonding between the molecules of the binder 26b is promoted by the vulcanization promoting action of the binder 26b by the additive 26c. As a result, the binding force of the negative electrode active material particles 26a by the binder 26b and the binding force between the negative electrode metal foil 25 and the negative electrode active material particles 26a are increased, and the negative electrode active material particles 26a are missing from the negative electrode active material layer 26. Can be suppressed. Further, since the binding force of the negative electrode active material particles 26a by the binder 26b is increased, the spring back caused by the residual internal stress applied during the press working is also suppressed. As a result, in the negative electrode active material layer 26, formation of a thin portion or a void is suppressed, and an increase in internal resistance is suppressed.

  (2) In the negative electrode 24, the negative electrode active material layer 26 contains an additive 26c, and the additive 26c has a function of a lubricant. Therefore, the additive 26c can reduce the frictional resistance between the negative electrode active material particles 26a. it can. For this reason, the negative electrode active material particles 26a are easily moved smoothly by the additive 26c. Therefore, when the coating parts G1 and G2 are pressed, the negative electrode active material particles 26a are densely filled. As a result, when the press working is performed, cracks in the negative electrode active material layer 26 are suppressed, and voids due to cracks are hardly formed in the negative electrode active material layer 26, and the internal resistance of the negative electrode active material layer 26 is reduced. The rise is suppressed.

  In addition, when the press working is performed, the negative electrode active material particles 26 a are suppressed from sinking into the surface 25 c of the negative electrode metal foil 25. Therefore, voids are hardly formed in the negative electrode active material layer 26, and an increase in internal resistance of the negative electrode active material layer 26 is suppressed.

  (3) The heating temperature in the drying step was set to 80 to 120 ° C. For this reason, the negative electrode active material particles 26a, the binder 26b, and the like can be hardly affected by heat. Note that the optimum temperature for vulcanization of SBR as the binder 26b is about 140 ° C., which is lower than the above temperature. However, the binder 26c does not prolong the heating time due to the vulcanization promoting action. 26b can be vulcanized.

  (4) As additive 26c, zinc stearate or zinc palmitate was used. For this reason, the vulcanization | cure acceleration | stimulation effect | action of the binder 26b by the additive 26c can be expressed reliably.

  (5) The manufacturing method of the negative electrode 24 includes the drying process of each coating part G1, G2. For this reason, the additive 26c contained in the negative electrode active material mixture is heated, and the vulcanization promoting action of the binder 26b by the additive 26c can be surely expressed.

  (6) Styrene butadiene rubber was used for the binder 26b. Further, zinc stearate or zinc palmitate was used as additive 26c. For this reason, the vulcanization of the styrene butadiene rubber can be surely promoted by zinc stearate or zinc palmitate, the binding force of the negative electrode active material particles 26a, and the negative electrode active material layer 26 and the negative electrode active material particles 26a. The binding force can be reliably increased.

In addition, you may change the said embodiment as follows.
(Circle) the metal foil 25 for negative electrodes used for the negative electrode 24 may be formed from different metals, such as nickel and stainless steel other than copper.

(Circle) you may change suitably the number of the positive electrode 21 which comprises the electrode assembly 14, and the negative electrode 24. FIG.
The electrode assembly 14 may be a wound-type electrode assembly in which the positive electrode 21 and the negative electrode 24 are formed in a band shape and wound with a band-shaped separator interposed therebetween.

The negative electrode 24 may be formed by applying a negative electrode active material mixture to one surface of the negative electrode metal foil 25.
A current collector is not limited to a metal foil as long as it can hold a negative electrode active material mixture. For example, a woven, net, or fibrous current collector may be used. Regardless of the shape of the current collector, the press working is an effective means for increasing the packing density of the negative electrode active material layer 26 in the manufacturing process, and in suppressing the spring back of the negative electrode active material layer 26 subjected to the press working. The present invention is effective.

  The power storage device may be embodied in a power storage device such as a nickel hydride secondary battery or an electric double layer capacitor.

  24 ... Negative electrode, 25 ... Metal foil for negative electrode as current collector, 26 ... Negative electrode active material layer, 26a ... Negative electrode active material particle, 26b ... Binder, 26c ... Additive.

Claims (6)

A negative electrode comprising a current collector and a negative electrode active material layer containing negative electrode active material particles,
The negative electrode active material layer includes at least the negative electrode active material particles, a binder made of rubber, and an additive made of a saturated fatty acid.   The negative electrode according to claim 1, wherein the rubber is styrene butadiene rubber.   The negative electrode according to claim 1, wherein the saturated fatty acid is zinc palmitate.   The negative electrode according to claim 1, wherein the saturated fatty acid is zinc stearate. A method for producing a negative electrode comprising a negative electrode active material layer containing negative electrode active material particles on a current collector,
An application step of coating the current collector with a negative electrode active material mixture containing at least the negative electrode active material particles, a binder made of rubber, and an additive made of saturated fatty acid;
A pressing step of pressing the negative electrode active material mixture coated on the current collector;
And a heating step of heating the negative electrode active material mixture after the pressing step.   The method for producing a negative electrode according to claim 5, wherein the heating temperature in the heating step is 80 to 120 ° C. 6.