JP2013164905A - Method for manufacturing negative electrode plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a negative electrode plate with a negative electrode paste that exhibits excellent filter penetrability and coating properties and requires only a short period of processing time (dispersion time).SOLUTION: A method for manufacturing a negative electrode plate 131 includes the steps of: making a negative electrode paste 60 by dispersing at least a portion of a negative electrode active material 20 and a first thickener 30 that exhibits a viscosity (mPa s) higher than or equal to 5000 and lower than or equal to 10000 in a 1 wt.% solution, in water 10, then adding and dispersing a second thickener 40 that exhibits a viscosity (mPa s) higher than or equal to 1000 and lower than 5000 in a 1 wt.% solution, and then adding and dispersing a binder 50; and forming a negative electrode active material layer 133 by applying the negative electrode paste 60 to negative electrode foil 132.

Description

  The present invention relates to a method for producing a negative electrode plate for a secondary battery, comprising a negative electrode foil and a negative electrode active material layer coated and formed thereon.

  2. Description of the Related Art Conventionally, as a negative electrode plate constituting a secondary battery, a negative electrode foil coated with a negative electrode active material layer is known. Such a negative electrode plate is prepared, for example, by preparing a negative electrode paste in which a negative electrode active material, a thickener, and a binder are dispersed in water, and applying the negative electrode paste to a negative electrode foil to form a negative electrode active material layer. Manufactured by the forming method.

  In Patent Document 1, as a method for preparing a negative electrode paste, first, a low-viscosity thickener having a viscosity of 10 wt% to 1800 mPa · s of a 1 wt% aqueous solution and a negative electrode active material are dispersed in the presence of water, and then further. It is disclosed that a 1 wt% aqueous solution having a viscosity of 3000 to 10000 mPa · s is added and dispersed, and then a binder is added to prepare a slurry-like coating composition (negative electrode paste). (See claim 1 of Patent Document 1).

JP 2009-099441 A

  However, in the method of Patent Document 1, when the negative electrode paste is passed through a filter or when the negative electrode paste is applied to the negative electrode foil, the viscosity increases rapidly when a shear force is applied to the negative electrode paste. Phenomenon), the filter permeability of the negative electrode paste may deteriorate, or the coating property may deteriorate. Further, the method of Patent Document 1 has a demerit that the processing time (dispersion time) of the negative electrode paste is long.

  The present invention has been made in view of the current situation, and provides a method for producing a negative electrode plate that can improve the filter permeability and coatability of the negative electrode paste and can reduce the processing time (dispersion time) of the negative electrode paste. The purpose is to provide.

  In one embodiment of the present invention for solving the above problems, at least a part of the negative electrode active material and a first thickener having a viscosity of 1 wt% aqueous solution of 5000 mPa · s to 10,000 mPa · s are dispersed in water, and then A negative electrode paste preparation step of preparing a negative electrode paste by further adding and dispersing a second thickener having a viscosity of 1 wt% aqueous solution of 1000 mPa · s or more and less than 5000 mPa · s, and then adding and dispersing a binder. And a negative electrode active material layer forming step of forming a negative electrode active material layer by coating the negative electrode paste on a negative electrode electrode foil.

According to this method for producing a negative electrode plate, the filter permeability and coating property of the negative electrode paste can be improved, and the processing time (dispersion time) of the negative electrode paste can be shortened.
The viscosity (mPa · s) of the 1 wt% aqueous solution of the first and second thickeners is a value measured with a BH viscometer.
Examples of the “negative electrode active material” include natural graphite such as spheroidized graphite, flaky graphite, massive graphite, and earthy graphite, and graphite (graphite) such as artificial graphite. Moreover, amorphous carbon (amorphous carbon) etc., such as low temperature baking coke and hard carbon, are mentioned.

Examples of the “first thickener” and “second thickener” include carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), and the like.
Examples of the “binder” include styrene / butadiene rubber (SBR), acrylonitrile / butadiene rubber (NBR), acrylic rubber, ethylene / propylene rubber (EPR), ethylene / butene rubber (EBR), and ethylene / propylene. -Diene rubber (EPDM) etc. are mentioned.

  The “negative electrode paste preparation step” can be performed, for example, with a medialess disperser such as a homogenizer, a planetary mixer, a jet mill, an ultrasonic disperser, a disperser (stirring blade), or an extrusion kneader. Alternatively, the negative electrode paste may be produced using media dispersion in which ceramic beads such as glass and zirconia are introduced into a dispersing machine such as a bead mill or a ball mill.

  In addition, as a method of “dispersing at least a part of the negative electrode active material and the first thickener in water”, (1) water is first put into a disperser or the like, and then the negative electrode active material and the first thickener are added thereto. (2) A method in which water is first added to a disperser, etc., a negative electrode active material is added thereto and stirred, and then a first thickener is added and dispersed. (3) Dispersion First, water is added to the machine, the first thickener is added and stirred, and then the negative electrode active material is added and dispersed. (4) The negative electrode active material and the first thickener are first added to the disperser. (5) A first thickener is first added to a disperser, etc., and water is added to this, followed by stirring, and then a negative electrode active material is added. Examples include a method of dispersing.

  Further, when only a part of the negative electrode active material is dispersed in water together with the first thickener, the remainder of the negative electrode active material can be added and dispersed after the second thickener is added. In addition, when the remainder of the negative electrode active material is added and dispersed after the binder is added, the adhesion function of the binder tends to be reduced due to the strong shearing force for dispersing the negative electrode active material. Therefore, the remainder of the negative electrode active material is preferably added and dispersed after adding the second thickener and before adding the adhesive.

  Furthermore, in the method for manufacturing the negative electrode plate, the weight ratio of the first thickener to the second thickener (first thickener / second thickener) in the negative electrode paste is 0. A method for producing a negative electrode plate of 4 to 2.5 is preferable.

  If the weight ratio of the first thickener and the second thickener in the negative electrode paste (first thickener / second thickener) is less than 0.4, dilatancy is likely to occur in the negative paste, The filter permeability and coating property of the negative electrode paste tend to deteriorate. On the other hand, when the weight ratio (first thickener / second thickener) is larger than 2.5, the dispersion time of the negative electrode paste tends to be long. On the other hand, since the weight ratio (first thickener / second thickener) is in the range of 0.4 to 2.5 in the negative electrode plate manufacturing method, the dilatancy of the negative electrode paste is effective. The filter permeability and coating property of the negative electrode paste can be made particularly good, and the dispersion time of the negative electrode paste can be made particularly short.

  In addition, it is preferable that the weight ratio of the whole thickener (total of a 1st thickener and a 2nd thickener) in solid content of a negative electrode paste shall be in the range of 0.5-2.0 wt%. The reason is that if this weight ratio is smaller than 0.5 wt%, dilatancy is likely to occur in the negative electrode paste, and the filter permeability and coating properties of the negative electrode paste are deteriorated. On the other hand, when the weight ratio is larger than 2.0 wt%, the IV resistance of the battery increases.

  Furthermore, in the method for manufacturing a negative electrode plate according to any one of the above, the negative electrode paste may be a method for manufacturing a negative electrode plate having a solid content concentration of 50 wt% or more.

  If the solid content concentration of the negative electrode paste is low, a large amount of heat is required to dry the negative electrode paste applied to the negative electrode foil, which requires a long drying time and a long drying furnace, resulting in high equipment costs. Become. Also, since the amount of negative electrode paste is larger than the amount of negative electrode active material required to form the negative electrode plate, the facilities necessary for the preparation and handling of the negative electrode paste, such as a disperser, a pump, and a tank, are increased in size. Cost increases. Therefore, it is preferable that the solid content concentration of the negative electrode paste is high, specifically 50 wt% or more.

  However, when a negative electrode paste having a high solid content concentration is prepared by the method of Patent Document 1 described above, dilatancy is particularly likely to occur in the negative electrode paste, and the filter permeability and coating properties of the negative electrode paste are particularly deteriorated. For this reason, in the method of Patent Document 1, it is difficult to highly solidify the negative electrode paste. On the other hand, if the negative electrode paste preparation process is performed as described above, even if the solid content concentration of the negative electrode paste is high, dilatancy of the negative electrode paste is prevented and the filter permeability and coating properties of the negative electrode paste are improved. The dispersion time of the negative electrode paste can be shortened. Therefore, when producing a negative electrode paste having a solid content concentration of 50 wt% or more, it is particularly effective to perform the above-described negative electrode paste production process.

  In addition, it is preferable that the solid content concentration of a negative electrode paste is 60 wt% or less. The reason is that if the solid content concentration is too high, dilatancy is likely to occur in the negative electrode paste, and the filter permeability and coating properties of the negative electrode paste are deteriorated.

  Furthermore, in the method for manufacturing a negative electrode plate according to any one of the above, the second thickener may be a negative electrode plate manufacturing method in which powder is added in advance without being dissolved in water.

  Thus, by adding the second thickener in the form of powder without dissolving it in water in advance, the man-hours and equipment for adjusting the aqueous solution of the second thickener in advance can be omitted.

  Furthermore, the negative electrode plate manufacturing method according to any one of the above, wherein the negative electrode plate is manufactured by using a homogenizer-type disperser.

  For example, when preparing a negative electrode paste using a planetary mixer or the like, it is necessary to go through a kneading process. At that time, the negative electrode active materials are rubbed with each other and the negative electrode active material is peeled off. Material may be altered. On the other hand, in this negative electrode plate manufacturing method, the negative electrode paste is prepared using a homogenizer-type disperser, so there is no need to perform a kneading step, and the negative electrode active material is prevented from being altered during the preparation of the negative electrode paste. it can.

  Furthermore, it is a manufacturing method of the negative electrode plate in any one of said, Comprising: The said 1st thickener and the said 2nd thickener are all good as the manufacturing method of the negative electrode plate which is carboxymethylcellulose.

  By using carboxymethyl cellulose (CMC) as the first thickener and the second thickener, the viscosity of the negative electrode paste can be easily adjusted to an appropriate viscosity, and the influence on the battery characteristics can be reduced.

  Furthermore, in any of the above methods for producing a negative electrode plate, the binder is preferably a method for producing a negative electrode plate made of styrene-butadiene rubber.

  By using styrene-butadiene rubber (SBR) as the binder, the peel strength of the negative electrode active material layer can be increased and the influence on the battery characteristics can be reduced.

It is a perspective view which shows the lithium ion secondary battery which concerns on embodiment. It is a longitudinal cross-sectional view which shows the lithium ion secondary battery which concerns on embodiment. It is an expanded view of an electrode body which concerns on embodiment and shows the state which mutually accumulated the positive electrode plate and the negative electrode plate through the separator. It is explanatory drawing which shows a negative electrode paste preparation process regarding the manufacturing method of the negative electrode plate which concerns on embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 show a lithium ion secondary battery 100 (hereinafter also simply referred to as a battery 100) according to the present embodiment. FIG. 3 shows a state where the wound electrode body 120 constituting the battery 100 is developed. In the following description, the thickness direction BH, the width direction CH, and the height direction DH of the battery 100 are defined as the directions shown in FIGS.

  The battery 100 is a square battery that is mounted on a vehicle such as a hybrid vehicle or an electric vehicle, or a battery-powered device such as a hammer drill. The battery 100 includes a rectangular parallelepiped battery case 110, a flat wound electrode body 120 accommodated in the battery case 110, a positive terminal 150 and a negative terminal 160 supported by the battery case 110, and the like. (See FIGS. 1 and 2). In addition, a non-aqueous electrolyte solution 117 is held in the battery case 110.

  Among these, the battery case 110 is made of metal (specifically, aluminum). The battery case 110 includes a box-shaped case main body member 111 opened only on the upper side, and a rectangular plate-shaped case cover member 113 welded in a form to close the opening 111h of the case main body member 111. (See FIGS. 1 and 2). The case lid member 113 is provided with a non-returnable safety valve 113v. Further, the case lid member 113 is provided with a liquid injection hole 113 h for the electrolytic solution 117, and is hermetically sealed with the sealing member 115.

  Further, in the case lid member 113, in the vicinity of both ends in the longitudinal direction (the width direction CH of the battery 100), a positive terminal (positive terminal member) 150 and a negative terminal that extend from the inside of the battery case 110 to the outside. (Negative electrode terminal member) 160 is fixed. Specifically, these terminals 150 and 160 are connected to the case lid via insulating members 155 and 165 made of resin together with bolts 153 and 163 for fastening connection terminals outside the battery, such as bus bars and crimp terminals. It is fixed to the member 113.

  Next, the electrode body 120 will be described. The electrode body 120 is housed in the battery case 110 in a state where the electrode body 120 is laid down so that its axis (winding axis) is parallel to the width direction CH of the battery 100 (see FIG. 2). In this electrode body 120, a belt-like positive electrode plate 121 and a belt-like negative electrode plate 131 are overlapped with each other via two belt-like separators 141 and 141 made of a resin porous film (see FIG. 3). It is wound around and compressed into a flat shape.

  A part of the positive electrode plate 121 in the width direction protrudes from the separators 141 and 141 in a spiral shape to one side AC (in FIG. 2, left, upper in FIG. 3) in the axial direction. (Positive electrode terminal member) 150 is connected (welded). Further, a part of the negative electrode plate 131 in the width direction protrudes in a spiral shape from the separators 141 and 141 to the other side AD in the axial direction (in FIG. 2, right side, in FIG. 3, downward). The negative electrode terminal (negative electrode terminal member) 160 is connected (welded).

  Among these, the positive electrode plate 121 has a strip-shaped positive electrode foil 122 made of aluminum as a core material. A positive electrode active material layer (positive electrode mixture layer) 123 extending in a strip shape in the longitudinal direction EH (left and right direction in FIG. 3) is formed on a part of the other side AD in the width direction of both main surfaces of the positive electrode foil 122. , 123 are formed. These positive electrode active material layers 123 and 123 are formed of a positive electrode active material, a conductive agent, and a binder.

The negative electrode plate 131 has a strip-shaped negative electrode foil 132 made of copper as a core material. Negative electrode active material layers (negative electrode mixture layers) 133 and 133 extending in a strip shape in the longitudinal direction EH are respectively formed on a part of one side AC in the width direction of both main surfaces of the negative electrode foil 132.
These negative electrode active material layers 133 and 133 are formed of the negative electrode active material 20, thickeners (specifically, the first thickener 30 and the second thickener 40), and the binder 50. In this embodiment, amorphous coated graphite is used as the negative electrode active material 20, carboxymethyl cellulose (CMC), which will be described later as thickeners (first thickener 30 and second thickener 40), and styrene. Butadiene rubber (SBR) is used. Moreover, the mixing ratio of the negative electrode active material 20, the thickener (the total of the first thickener 30 and the second thickener 40) and the binder 50 is 98.3: 0.7: 1. 0. Moreover, the mixing ratio of the 1st thickener 30 and the 2nd thickener 40 in a thickener is 0.2: 0.5 by weight ratio.

The first thickener 30 is a high viscosity CMC in which the viscosity of a 1 wt% aqueous solution is 5000 mPa · s or more and 10,000 mPa · s or less. Specifically, it is CMC (Daiichi Kogyo Seiyaku: Serogen BSH-12) in which a value obtained by measuring a 1 wt% aqueous solution with a BH viscometer is within a range of 6000 to 8000 mPa.
The second thickener 40 is a low-viscosity CMC in which the viscosity of a 1 wt% aqueous solution is 1000 mPa · s or more and less than 5000 mPa · s. Specifically, it is CMC (Daiichi Kogyo Seiyaku: Serogen BSH-6) in which a value obtained by measuring a 1 wt% aqueous solution with a BH viscometer is within a range of 3000 to 4000 mPa.

Next, a method for manufacturing the negative electrode plate 131 and the battery 100 will be described.
First, a method for manufacturing the negative electrode plate 131 will be described. First, in the negative electrode paste preparation step, a negative electrode paste 60 is prepared in which the negative electrode active material 20, the first thickener 30, the second thickener 40, and the binder 50 are dispersed in water 10 (see FIG. 4). Specifically, water 10 is previously placed in a homogenizer type disperser. Then, the first thickener 30 is first added to the water 10 and stirred while operating the homogenizer type disperser. Thereafter, the negative electrode active material 20 is added thereto and stirred, and the first thickener 30 and the negative electrode active material 20 are dispersed in the water 10. Thereafter, the second thickener 40 is further introduced and dispersed. Thereafter, the binder 50 is charged and dispersed therein. In this way, the negative electrode paste 60 is produced.

  In addition, the mixing ratio of the negative electrode active material 20, the first thickener 30, the second thickener 40, and the binder 50 is 98.3: 0.2: 0.5: by weight as described above. 1.0. Moreover, the mixing ratio of these solid content 20, 30, 40, 50 and water 10 is 54:46 by weight ratio. Therefore, the negative electrode paste 60 has a solid content concentration of 54 wt%.

  Next, a strip-shaped negative electrode foil 132 made of copper is prepared, and in the negative electrode active material layer forming step, the negative electrode paste 60 is applied to the negative electrode foil 132 to form the negative electrode active material layers 133 and 133. Specifically, the negative electrode paste 60 is applied to a part of one main surface in the width direction of the negative electrode foil 132 using a die coater. Then, this is dried with hot air to form the negative electrode active material layer 133. Similarly, the negative electrode paste 60 is applied to a part of the main surface on the opposite side of the negative electrode foil 132 in the width direction, and dried with hot air to form the negative electrode active material layer 133. Thereafter, the negative electrode active material layers 133 and 133 are compressed by a pressure roll to increase the density. Thus, the negative electrode plate 131 is formed.

  Separately, the positive electrode plate 121 is manufactured. That is, a strip-shaped positive electrode foil 122 made of aluminum is prepared. And the positive electrode paste containing a positive electrode active material, a electrically conductive agent, and a binder is apply | coated to a part of width direction of one main surface among this positive electrode electrode foil 122, It is made to dry with a hot air, The positive electrode active material layer 123 Form. Similarly, the positive electrode paste is applied to a part of the main surface on the opposite side of the positive electrode foil 122 in the width direction and dried with hot air to form the positive electrode active material layer 123. Thereafter, the positive electrode active material layers 123 and 123 are compressed by a pressure roll to increase the density. Thus, the positive electrode plate 121 is formed.

Next, two strip-shaped separators 141 and 141 are prepared, and the above-described positive electrode plate 121 and negative electrode plate 131 are overlapped with each other through the separators 141 and 141 (see FIG. 3). Turn. Thereafter, the electrode body 120 is formed by compressing it into a flat shape.
Separately, a case lid member 113, a positive electrode terminal member 150, a negative electrode terminal member 160, and bolts 153 and 163 are prepared, and these are set in a mold for injection molding. Then, the insulating members 155 and 165 are integrally formed by injection molding, and the positive terminal member (positive terminal) 150 and the negative terminal member (negative terminal) 160 are fixed to the case lid member 113.

Next, the positive electrode terminal 150 and the negative electrode terminal 160 are welded to the electrode body 120, respectively. Thereafter, the case body member 111 is prepared, the electrode body 120 is accommodated in the case body member 111, and the opening 111 h of the case body member 111 is closed with the case lid member 113. Then, the case main body member 111 and the case lid member 113 are welded.
Next, the electrolytic solution 117 is injected into the battery case 110 through the injection hole 113h, and the injection hole 113h is hermetically sealed with the sealing member 115. Thereafter, the battery 100 is subjected to initial charging, aging, and various inspections. Thus, the battery 100 is completed.

(Examples and Comparative Examples)
Subsequently, the result of the test conducted in order to verify the effect of the manufacturing method of the negative electrode plate 131 according to the embodiment will be described.
As Example 1, the negative electrode plate 131 was manufactured by the manufacturing method of the negative electrode plate 131 according to the embodiment. In this method of manufacturing the negative electrode plate 131, in the negative electrode paste manufacturing step, as described above, the first thickener 30 having a high viscosity is first added and dispersed, and then the second thickener 40 having a low viscosity is further added. Are distributed. The weight ratio of the entire thickener (first thickener 30 and second thickener 40) in the solid content of the negative electrode paste 60 is 0.7 wt%. The weight ratio of the first thickener 30 to the second thickener 40 (first thickener / second thickener) is 0.20 / 0.50 = 0.4.

In Example 2, the weight ratio (first thickener / second thickener) was set to 0.10 / 0.60 = 0.17, and the rest was the same as in the embodiment (Example 1). A negative electrode plate was manufactured.
In Example 3, the weight ratio (first thickener / second thickener) was set to 0.35 / 0.35 = 1.0, and other than that, the same as in the embodiment (Example 1). A negative electrode plate was manufactured.
In Example 4, the weight ratio (first thickener / second thickener) was set to 0.50 / 0.20 = 2.5, and other than that, the same as in the embodiment (Example 1). A negative electrode plate was manufactured.

On the other hand, as Comparative Example 1, a negative electrode plate was manufactured using only the first thickener 30 as the thickener. In Comparative Example 1, the entire amount of the first thickener 30 was added before the negative electrode active material 20 was charged.
Further, as Comparative Example 2, instead of the second thickener 40, a low-viscosity thickener, specifically, a CMC (Daiichi Kogyo Seiyaku: Serogen WS, whose 1 wt% aqueous solution has a viscosity of 150 to 250 mPa · s). -CN) (labeled "low viscosity thickener" in Table 1). In addition, in the negative electrode paste preparation step, contrary to Examples 1 to 4, the low viscosity thickener is first added and dispersed, and then the high viscosity first thickener 30 is added and dispersed. A negative electrode paste was prepared.

Moreover, as Comparative Example 3, a negative electrode plate was manufactured using only the second thickener 40 as the thickener. In Comparative Example 2, the entire amount of the second thickener 40 was added before the negative electrode active material 20 was charged.
Further, as Comparative Example 4, in the negative electrode paste manufacturing step, contrary to Examples 1 to 4, first, the low-viscosity second thickener 40 is added and dispersed, and then the high-viscosity first thickener is added. 30 was added and dispersed to prepare a negative electrode paste.

  For Examples 1 to 4 and Comparative Examples 1 to 4, the processing time (dispersion time) (min) required to produce the negative electrode paste was measured. Specifically, the time required for the viscosity of the negative electrode paste to drop to 3000 mPa · s or less, which is a range where coating can be performed, was defined as the processing time (dispersion time). The viscosity of the negative electrode paste was measured using a rheometer (Anton Paar, shear rate 40 / s).

  Moreover, about each negative electrode paste which concerns on Examples 1-4 and Comparative Examples 1-4, the filter permeate | transmitted and investigated filter permeability | transmittance, respectively. The filter used was SFT50 (manufactured by Loki Techno Co.). The case where filter clogging did not occur was evaluated as “◯”, the case where filter clogging occurred slightly was evaluated as “Δ”, and the case where filter clogging occurred was evaluated as “x”.

Moreover, each negative electrode paste which concerns on Examples 1-4 and Comparative Examples 1-4 was applied to the negative electrode foil 132, and the number of the coating defects produced at that time was investigated, respectively. As for coating defects, the number of coating defects per unit length of the strip-shaped negative electrode plate was investigated using a die coater defect inspection machine.
These results are shown in Table 1.

  From Table 1, it can be seen that the processing time (dispersion time) of the negative electrode paste was as long as 97 minutes in Comparative Example 1, 58 minutes in Comparative Example 2, and 63 minutes in Comparative Example 4. In contrast, the dispersion time was as short as 7 minutes in Example 1, 6 minutes in Example 2, 14 minutes in Example 3, 34 minutes in Example 4, and 4 minutes in Comparative Example 3.

The reason why the dispersion time is shortened in Examples 1 to 4 is considered as follows. That is, in Examples 1 to 4, since the first thickener 30 having a high viscosity is added in the negative electrode paste preparation step, the first thickener having a high viscosity is formed on the surface of the negative electrode active material 20. 30 is preferentially adsorbed. On the other hand, since the second thickener 40 having a low viscosity added later is hardly adsorbed on the negative electrode active material 20 and exists in a state dissolved in the water 10 in the negative electrode paste, the viscosity of the negative electrode paste becomes too high. Absent. As a result, it is considered that the viscosity of the negative electrode paste could be sufficiently reduced by short-time dispersion.
In addition, the reason why the dispersion time was shortened in Comparative Example 3 was that only the second thickener having a low viscosity was used, so the viscosity of the negative electrode paste did not become too high, and the viscosity of the negative electrode paste was sufficient even with short-time dispersion. This is thought to be due to the reduction in

  On the other hand, the reason for the long dispersion time in Comparative Example 1 was that only the first thickener 30 having a high viscosity was used, so that it was not adsorbed on the negative electrode active material 20 and dissolved in water 10 in the negative electrode paste. There are many first thickeners 30. For this reason, it is considered that the viscosity of the negative electrode paste is increased, and it takes a long time to disperse the viscosity.

  The reason why the dispersion time was long in Comparative Examples 2 and 4 is considered as follows. That is, in Comparative Examples 2 and 4, since the second thickener 40 having a low viscosity is first added in the negative electrode paste preparation step, the second thickening having a low viscosity is performed on the surface of the negative electrode active material 20. The agent 40 and the like are preferentially adsorbed. On the other hand, since the first thickener 30 having a high viscosity added later is hardly adsorbed by the negative electrode active material 20 and exists in a state dissolved in the water 10 in the negative electrode paste, the viscosity of the negative electrode paste increases. As a result, it is considered that it took a long dispersion time to lower the viscosity.

  Table 1 also shows that the negative electrode pastes according to Comparative Examples 2 to 4 had poor filter permeability (evaluation “x”). On the other hand, the negative electrode paste according to Example 2 has improved filter permeability (evaluation “Δ”) as compared with Comparative Examples 2 to 4. In Examples 1, 3, and 4, the filter permeability was further increased. It turns out that it was favorable (evaluation "(circle)").

  The reason why the filter permeability of the negative electrode pastes according to Comparative Examples 2 to 4 was poor was that a large amount of dilatancy was generated in the negative electrode paste when passing through the filter. On the other hand, only a little dilatancy was produced in the negative electrode paste according to Example 2, and almost no dilatancy was produced in Examples 1, 3, and 4, so that it was considered that the filter permeability was good.

  In addition, it is thought that dilatancy arises when negative electrode active materials mutually contact when a shearing force is applied to negative electrode paste. In Examples 1 to 4, as described above, in the negative electrode paste preparation step, the first thickener 30 having a high viscosity is added first, so that the surface of the negative electrode active material 20 has a high viscosity (molecular weight). Large) first thickener 30 is adsorbed. For this reason, it is considered that contact between the negative electrode active materials was prevented and dilatancy was hardly generated. On the other hand, in Comparative Examples 2 to 4, the second thickener 40 having a low viscosity (low molecular weight) or the like is adsorbed on the surface of the negative electrode active material 20. For this reason, it is considered that the frictional resistance when the negative electrode active materials are in contact with each other increases and dilatancy occurs.

  Further, it can be seen from Table 1 that there were many coating defects of 19 / m in Comparative Example 1 and 15 / m in Comparative Example 4. In contrast, 4 / m in Example 1, 3 / m in Example 2, 4 / m in Example 3, 6 / m in Example 4, 4 / m in Comparative Example 2, and comparison In Example 3, there were few coating defects as 1 piece / m.

  The reason why there were many coating defects in Comparative Examples 1 and 4 is considered as follows. That is, as described above, in Comparative Examples 1 and 4, the first thickener 30 having a high viscosity is not adsorbed by the negative electrode active material 20 but is present in the water 10 in the negative electrode paste. By the way, the first thickener 30 having a high viscosity is less soluble in the water 10 than the second thickener 40 having a low viscosity. It is easy to become. Since this spatter is swollen in water and its shape can be easily deformed, it may pass through a filter or the like. For this reason, when the negative electrode paste containing the spatter is applied to the negative electrode foil 132, it is considered that the portion of the spatter is greatly reduced in volume due to drying, resulting in a coating defect.

  As described above, in the method of manufacturing the negative electrode plate 131 according to the embodiment, the negative electrode active material 20 and the first thickener 30 having a high viscosity are dispersed in the water 10 and then the second thickening having a low viscosity is performed. The agent 40 is further added and dispersed, and then the binder 50 is added and dispersed to prepare the negative electrode paste 60. By doing in this way, while being able to make the filter permeability and coating property of the negative electrode paste 60 favorable, the processing time (dispersion time) of the negative electrode paste 60 can be shortened. In particular, in this embodiment, since the solid content concentration of the negative electrode paste 60 is 50 wt% or more (specifically, 54 wt%), dilatancy is prevented and the filter permeability and coating properties of the negative electrode paste 60 are improved. At the same time, the advantage of shortening the dispersion time of the negative electrode paste 60 is particularly great.

Furthermore, in this embodiment, the weight ratio (first thickener / second thickener) between the first thickener 30 and the second thickener 40 is in the range of 0.4 to 2.5. Therefore, dilatancy can be effectively prevented, the filter permeability and coating properties of the negative electrode paste 60 can be made particularly good, and the dispersion time of the negative electrode paste 60 can be made particularly short.
Moreover, in this embodiment, since the 2nd thickener 40 is added as powder without previously dissolving in water, the man-hour and equipment for adjusting the aqueous solution of the 2nd thickener 40 beforehand can be omitted.
Moreover, in this embodiment, since the negative electrode paste 60 is produced using a homogenizer type disperser, it is not necessary to perform a kneading step, and the negative electrode active material 20 can be prevented from being altered during the production of the negative electrode paste 60. .

  Moreover, in this embodiment, since CMC is used as the first thickener 30 and the second thickener 40, the viscosity of the negative electrode paste 60 can be easily adjusted to an appropriate viscosity, and the influence on the battery characteristics can be reduced. . In addition, since SBR is used as the binder, the peel strength of the negative electrode active material layer 133 can be increased and the influence on the battery characteristics can be reduced.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the first thickener 30 is first added to the water 10 and then the negative electrode active material 20 is added and dispersed. However, the negative electrode active material 20 and the first thickener 30 are dispersed in the water 10. The method is not limited to this. For example, the negative electrode active material 20 and the first thickener 30 may be simultaneously added to the water 10 and dispersed. Alternatively, the negative electrode active material 20 may be first added to the water 10 and stirred, and then the first thickener 30 may be added and dispersed.

  In the embodiment, the entire amount of the negative electrode active material 20 is dispersed in the water 10 together with the first thickener 30, but only a part of the negative electrode active material 20 is dispersed in the water 10 together with the first thickener 30. Also good. In this case, the remainder of the negative electrode active material 20 can be added and dispersed after the second thickener 40 is added.

10 water 20 negative electrode active material 30 first thickener 40 second thickener 50 binder 60 negative electrode paste 100 lithium ion secondary battery (battery)
120 Electrode body 121 Positive electrode plate 131 Negative electrode plate 132 Negative electrode electrode foil 133 Negative electrode active material layer 141 Separator

Claims (7)

At least a part of the negative electrode active material and a first thickener having a viscosity of 1 wt% aqueous solution of 5000 mPa · s to 5000 mPa · s are dispersed in water, and then the viscosity of 1 wt% aqueous solution is 1000 mPa · s to 5000 mPa · s. Less than the second thickener is further added and dispersed, and then the binder is added and dispersed to prepare a negative electrode paste preparation step,
A negative electrode active material layer forming step of coating the negative electrode paste on a negative electrode foil to form a negative electrode active material layer. It is a manufacturing method of the negative electrode plate according to claim 1,
The negative electrode paste has a weight ratio of the first thickener and the second thickener (first thickener / second thickener) of 0.4 to 2.5. . It is a manufacturing method of the negative electrode plate according to claim 1 or 2,
The said negative electrode paste is a manufacturing method of the negative electrode plate whose solid content concentration is 50 wt% or more. It is a manufacturing method of the negative electrode plate according to any one of claims 1 to 3,
The said 2nd thickener is a manufacturing method of the negative electrode plate which does not melt | dissolve in water previously but adds with powder. It is a manufacturing method of the negative electrode plate according to any one of claims 1 to 4,
A method for producing a negative electrode plate, wherein the negative electrode paste is prepared using a homogenizer type disperser. It is a manufacturing method of the negative electrode plate according to any one of claims 1 to 5,
Both the first thickener and the second thickener are carboxymethylcellulose manufacturing methods of a negative electrode plate. It is a manufacturing method of the negative electrode plate according to any one of claims 1 to 6,
The method for producing a negative electrode plate, wherein the binder is styrene-butadiene rubber.

Images