JP2012129079A - Anode plate manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an anode plate which includes an anode active material layer which is uniform in the orientation of at least surface particles out of anode active material particles.SOLUTION: The manufacturing method of an anode plate 20, including a plate-like current collector plate 28 having a principal plane 28X, anode active material particles 22 whose magnetic field orientation by a magnetic field is changeable and an anode active material layer 21 formed on the principal plane, comprises a coating step in which an active material paste 21P having anode active material particles dispersed in a solvent AQ is applied to the principal plane of the current collector plate, an orientation step in which a magnetic field H is applied to a coated film PS consisting of the active material paste so that surface particles 22H located on at least a surface PSA, out of anode active material particles 22 in the coated film, will have their magnetic fields oriented, and a drying step in which, after the orientation step, the coated film is dried in a windless environment.

Description

  The present invention relates to a method for producing a negative electrode plate used for a lithium ion secondary battery.

In recent years, lithium-ion secondary batteries (hereinafter simply referred to as batteries) that can be charged and discharged have been used as power sources for driving portable electronic devices such as hybrid cars, notebook computers, and video camcorders.
With respect to such a battery, for example, in Patent Document 1, a paste (active material paste) in which graphite particles (negative electrode active material particles) are dispersed in a solvent is applied to a base sheet (current collector plate), and then in a magnetic field. For the lithium secondary battery in which the (002) surface of the graphite particles (negative electrode active material particles) is oriented perpendicularly to the sheet surface (main surface) of the base material sheet (current collector plate) and then the solvent is removed. A method for producing a negative electrode (negative electrode plate) is disclosed. Specifically, in the manufacturing method of Patent Document 1, a magnetic field is once applied to the applied paste (active material paste) to align the orientation of graphite particles (negative electrode active material particles), and then a heating furnace is used. The solvent is removed by drying.

JP 2003-197189 A

  However, in the negative electrode plate manufacturing method of Patent Document 1, when air is dried using a wind in a heating furnace, the negative electrode active material particles once oriented are physically moved by the wind, such as falling down, and after drying, In many cases, the orientation of the negative electrode active material particles is disturbed.

  This invention is made | formed in view of this problem, Comprising: The manufacturing method of a negative electrode plate provided with the negative electrode active material layer with which the orientation of at least surface particle | grains was uniform among negative electrode active material particles is provided.

  One embodiment of the present invention is a negative electrode including a plate-shaped current collector having a main surface, and a negative electrode active material layer including negative electrode active material particles that can be magnetically oriented by a magnetic field and formed on the main surface. A method for producing a plate, wherein an active material paste in which the negative electrode active material particles are dispersed in a solvent is applied onto the main surface of the current collector plate, and a coating film made of the active material paste. An orientation step of applying a magnetic field to magnetically orientate at least the surface particles located on the surface of the negative electrode active material particles in the coating film, and a drying step of drying the coating film without wind after the orientation step And a method for producing a negative electrode plate.

  By the way, according to the research of the inventors, in the drying process, the coating film is blown in comparison with a battery using a negative electrode plate formed by applying wind (hot air) to the coating film and drying the coating film. It has been found that a battery using a negative electrode plate which is formed by drying without applying can reduce its internal resistance. This is because the coating film can be dried without destroying the orientation of the surface particles of the coating film by not applying wind (hot air) when the coating film is dried. Thus, in the above-described method for producing a negative electrode plate, since the coating film is dried without wind in the drying step, a negative electrode plate capable of reducing the internal resistance of the battery can be produced.

Examples of negative electrode active material particles that can be magnetically oriented by a magnetic field include natural graphite such as flaky graphite, massive graphite, and earthy graphite, artificial graphite, and spherical graphite obtained by processing natural graphite or artificial graphite into a spherical shape. Examples thereof include particles having high crystal anisotropy, such as graphite particles, and a property that the orientation of the particles can be changed by the diamagnetic magnetic field orientation.
In the drying step, examples of the method of drying the coating include heating by using infrared rays, electromagnetic induction heating (IH), and a condenser dryer, and evaporating the solvent to dry the coating. The term “no wind” means that the air is not forcedly moved by a fan or the like such as hot air is applied to the coating film, and air movement by natural convection accompanying heating or the like is allowed.

  Furthermore, in the above-described method for manufacturing a negative electrode plate, the negative electrode active material particles may be a method for manufacturing a negative electrode plate that is flat graphite particles.

When an active material paste using flat graphite particles is used, the graphite particles are flat, so they are easily affected by wind, and the orientation of the graphite particles collapses during drying of the coating, causing the orientation to collapse. It is difficult to complete the drying of the coating film in a state where the orientation is uniform.
On the other hand, in the manufacturing method of the above-mentioned negative electrode plate, since the coating film is dried without wind, the coating film can be dried while maintaining its orientation while using flat graphite particles. Therefore, it is possible to form a negative electrode plate in which flat graphite particles are aligned with certainty.

  In addition, as flat graphite particle | grains, scaly graphite is mentioned, for example.

It is a perspective view of the battery concerning embodiment and a modification. It is a perspective view of the negative electrode plate concerning embodiment and a modification. It is a figure about the negative electrode active material particle used by embodiment and a deformation | transformation form, (a) is explanatory drawing showing the shape of typical particle | grains, (b) is explanatory drawing which shows the relationship between particle | grain outer periphery and a single layer ( FIG. 3B is a part B). It is explanatory drawing which shows the orientation state of the negative electrode active material particle in a negative electrode active material layer concerning embodiment and a deformation | transformation form. It is explanatory drawing of the application | coating process and orientation drying process concerning embodiment. It is explanatory drawing which concerns on embodiment and shows the orientation state of the negative electrode active material particle in the coating film in an orientation drying process. It is a graph which shows the relationship between the viscosity of an active material paste, and an electrode plate resistance value. It is a graph which shows the relationship between the viscosity of an active material paste, and the internal resistance value of a battery. It is explanatory drawing of the application | coating process and orientation drying process concerning a deformation | transformation form. It is explanatory drawing which shows the measurement principle of the gloss meter used for the manufacturing method of a deformation | transformation form. It is a graph which shows the relationship between the peak intensity ratio and glossiness about an uncompressed active material layer. It is a graph which shows the relationship between the glossiness about an uncompressed active material layer, and the internal resistance value of a battery.

(Embodiment)
Next, embodiments of the present invention will be described with reference to the drawings.
First, a battery 1 including the negative electrode plate 20 according to the present embodiment will be described with reference to FIG.
The battery 1 is a lithium ion secondary battery having a positive electrode plate 30 and a negative electrode plate 20. In addition, as shown in FIG. 1, the electrode body 10 and the electrolytic solution (not shown) are accommodated in a rectangular box-shaped battery case 80. Among these, the electrolytic solution is an organic electrolytic solution in which LiPF ₆ is added as a solute to a mixed organic solvent prepared by adjusting ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

  The battery case 80 of the battery 1 has a battery case body 81 and a sealing lid 82 both made of aluminum. A transparent insulating film (not shown) made of resin and bent in a box shape is interposed between the battery case 80 and the electrode body 10.

  Among these, the sealing lid 82 has a rectangular plate shape, closes the opening of the battery case body 81, and is welded to the battery case body 81. Of the positive electrode current collector 91 and the negative electrode current collector 92 connected to the electrode body 10, the positive electrode terminal portion 91 </ b> A and the negative electrode terminal portion 92 </ b> A located at the tips of the sealing lid 82 penetrate, respectively. 1 protrudes from the lid surface 82a facing upward. An insulating member 95 made of an insulating resin is interposed between the positive terminal portion 91A or the negative terminal portion 92A and the sealing lid 82 to insulate each other. Further, a rectangular plate-shaped safety valve 97 is also sealed on the sealing lid 82.

The electrode body 10 is formed by winding a belt-like positive electrode plate 30 and a negative electrode plate 20 into a flat shape via a belt-like separator (not shown) made of porous polyethylene. The positive electrode plate 30 and the negative electrode plate 20 of the electrode body 10 are respectively joined to a plate-like positive electrode current collector 91 or negative electrode current collector 92 bent in a crank shape.
Among the electrode bodies 10, a thin plate-like positive electrode plate 30 is a belt-like positive electrode current collector foil (not shown) made of aluminum, and a positive electrode active material layer (shown in the figure) formed on both main surfaces of the positive electrode current collector foil. Not). Among these, the positive electrode active material layer has positive electrode active material particles (not shown) made of LiNiCoMnO ₂ , a binder (not shown) made of PVDF, and a conductive agent (not shown) made of acetylene black. In this positive electrode active material layer, the weight ratio of the positive electrode active material particles, the conductive agent and the binder is positive electrode active material particles: conductive agent: binder = 90: 5: 5.

Further, as shown in FIG. 2, the negative electrode plate 20 is formed of a thin strip-shaped copper copper foil 28 (thickness: 10 μm), and two foil main surfaces 28X, 28X of the copper foil 28 disposed in a strip shape. And negative electrode active material layers 21 and 21.
Among these, the negative electrode active material layer 21 is composed of negative electrode active material particles 22 made of flaky graphite having an average particle diameter of 11 μm, a thickener 23 made of carboxymethyl cellulose (CMC), and a styrene butadiene rubber (SBR). A dressing 24 is included. In this negative electrode active material layer 21, the weight ratio of the negative electrode active material particles 22, the thickener 23 and the binder 24 was determined as follows: negative electrode active material particles 22: thickener 23: binder 24 = 98: 1: As 1.

Moreover, the negative electrode active material particles 22 made of scaly graphite are substantially flat, flat graphite particles as shown in FIG. This negative electrode active material particle 22 typically has two substantially tabular particle main surfaces 22f and 22f, and a particle outer peripheral edge 22s located at the outer peripheral edge of the particle main surface 22f.
The negative electrode active material particles 22 have a crystal structure in which a plurality of single layers CL extending in a plane direction parallel to the particle main surface 22f are stacked (see FIG. 3B). In addition, as shown in FIG.3 (b), the thickness direction DT between the two particle main surfaces 22f and 22f is the same as the direction where several single layer CL and CL laminate | stack. Further, in the negative electrode active material particles 22, lithium ions can be taken into and taken out from the interlayer (between planes) of the single layers CL through the outer peripheral edge 22s.

  Further, the negative electrode active material particles 22 have a diamagnetic magnetic field orientation capable of magnetic field orientation by a magnetic field. Specifically, when a strong magnetic field is applied to the negative electrode active material particles 22, the negative electrode active material particles 22 have a single-layer CL that forms the crystal structure of the negative electrode active material particles 22 (flaky graphite) with respect to the direction of the magnetic field. The layer plane (Baisal plane) is oriented in parallel. In other words, the negative electrode active material particles 22 are oriented so that the thickness direction DT thereof is orthogonal to the direction of the magnetic field.

  In addition, the state of the active material layer surface 21F among the negative electrode active material layers 21 in the negative electrode plate 20 of this embodiment is shown in FIG. FIG. 4 shows a plurality of surface particles 22 </ b> H that are exposed to the active material layer surface 21 </ b> F among the negative electrode active material particles 22. These surface particles 22H and 22H are respectively arranged in a direction in which the thickness direction DT of the surface particles 22H is parallel to the foil main surface 28X extending parallel to the paper surface of FIG.

Next, the manufacturing method of the battery 1 provided with the negative electrode plate 20 concerning this embodiment is demonstrated.
First, a method for manufacturing the negative electrode plate 20 will be described with reference to FIG. The manufacturing method of this negative electrode plate 20 applies the magnetic material to the coating process PS which consists of the application | coating process which apply | coats the active material paste 21P mentioned later on the foil main surface 28X of the copper foil 28, and the active material paste 21P. An orientation step of magnetically orienting the surface particles 22H in the PS, and a drying step of drying the coating film PS without wind after the orientation step are included.

  In these coating process, orientation process, and drying process, an apparatus 100 shown in FIG. 5 is used. The apparatus 100 includes an unwinding unit 101, a coater 110, a magnetic circuit including magnets 121 and 122, a dryer 130, a winding unit 102, and a plurality of auxiliary rollers 140 (see FIG. 5).

  Among these, the coater 110 is directed to the metal paste holding part 111 in which the active material paste 21P is stored inside, and the active material paste 21P held in the paste holding part 111 toward the foil main surface 28X of the copper foil 28. And a discharge port 112 that discharges continuously.

  Further, the magnetic circuit is disposed between the coater 110 and the dryer 130 described below. In this magnetic circuit, the first magnet 121 and the second magnet 122 are arranged across the surface PSA while facing the surface PSA of the coating film PS (copper foil 28). The first magnet 121 and the second magnet 122 can generate a magnetic field H between them from the first magnet 121 to the second magnet 122 (from the top to the bottom in FIG. 5). That is, the magnetic field H can be applied to the coating film PS positioned between them in a direction perpendicular to the coating film PS.

  The dryer 130 is a known infrared dryer, and the atmosphere in the machine is configured to be replaced by natural convection. Using this dryer 130, the coating film PS made of the copper foil 28 and the active material paste 21P applied to the copper foil 28 is heated and dried without wind. Thereby, while moving the lower side (lower side in FIG. 5) of the dryer 130, the drying of the coating film PS applied to the copper foil 28 gradually proceeds and finishes passing through the dryer 130. When the coating film PS is completely dried, that is, all the water AQ in the coating film PS is evaporated.

First, an active material paste 21P in which the negative electrode active material particles 22, the thickener 23, and the binder 24 described above were dispersed in water AQ was prepared.
This active material paste 21P was produced as follows. First, the thickener 23 was dissolved in water AQ to make a 1% aqueous solution, the negative electrode active material particles 22 were added thereto, and the mixture was kneaded with a known biaxial planetary kneader. Then, water AQ and the binder 24 are added to this and further kneaded, and the weight ratio of the negative electrode active material particles 22, the thickener 23 and the binder 24 is determined as follows: An active material paste 21P was prepared in which the adsorbent 24 = 98: 1: 1, and the solid content of the negative electrode active material particles 22, the thickener 23, and the binder 24 was adjusted to 46%. This active material paste 21 </ b> P was put into the paste holding unit 111 of the coater 110 of the apparatus 100.

  In the coating process, the strip-shaped copper foil 28 wound around the unwinding portion 101 is moved in the longitudinal direction DA, and the active material paste 21P is applied on one foil main surface 28X of the copper foil 28 by the coater 110. . The coating speed is 5 m / min. The active material paste 21P applied to the copper foil 28 becomes a coating film PS on the foil main surface 28X, and proceeds to the orientation process described below.

  In the orientation step, a magnetic field is applied to the coating film PS using a magnetic circuit including a magnet (see FIG. 5). Specifically, using the first magnet 121 and the second magnet 122 forming a magnetic circuit, a magnetic field H is applied to the coating film PS positioned therebetween (magnetic flux density is 300 mT), and the negative electrode active material particles 22 are applied. Among these, at least the surface particles 22H located on the coating surface PSA are magnetically oriented. That is, the magnetic field orientation is performed so that the thickness direction DT is parallel to the foil main surface 28X of the copper foil 28, that is, the basal surface is orthogonal to the foil main surface 28X. In addition, FIG. 6 is explanatory drawing which shows the relationship between the negative electrode active material particle 22 and the surface particle 22H in the coating-film surface PSA of coating-film PS. In FIG. 6, the direction of the magnetic field H generated by the magnetic circuit is the direction from the front to the back with respect to the paper surface.

After the orientation step described above, a drying step is performed in which the coating film PS is dried without wind using the dryer 130 (see FIG. 5). That is, when hot air is applied to the surface particles 22H that have been magnetically aligned in the alignment step, the surface particles 22H may fall down, causing movement due to the wind hitting the coating film PS. While suppressing this, water AQ is evaporated from the coating film PS to dry the coating film PS. As a result, the uncompressed active material layer 21 </ b> B oriented in the direction in which the thickness direction DT of the surface particles 22 </ b> H is parallel to the foil main surface 28 </ b> X is completed.
Thereafter, the single-side supported copper foil 28K supporting the uncompressed active material layer 21B on the foil main surface 28X is temporarily wound around the winding portion 102.

Next, again using the apparatus 100, the active material paste 21P is applied to the other foil main surface 28X of the above-mentioned single-side supported copper foil 28K (copper foil 28), and the coating PS is applied on the foil main surface 28X. Form. And using the magnetic circuit (the 1st magnet 121, the 2nd magnet 122) mentioned above, the magnetic field H is applied to this coating film PS, the surface particle 22H of the coating film PS is magnetic-field-oriented, and drying machine after that The coating film PS is completely dried by 130 with no wind.
Thus, an active material laminate 20B before pressing in which the uncompressed active material layer 21B is laminated on both the foil main surfaces 28X and 28X of the copper foil 28 is produced.

  Thereafter, the active material laminate 20B is compressed by using a roll press (not shown), and the negative electrode active material layer 21 is disposed in a direction in which the thickness direction DT of the surface particles 22H is parallel to the foil main surface 28X. A negative electrode plate 20 was produced (see FIG. 2). At this time, the active material laminate 20B is compressed with a pressure that does not break the magnetic field orientation of the negative electrode active material particles 22 (surface particles 22H) of the uncompressed active material layer 21B. Thereby, the surface particles 22H of the negative electrode plate 20 are in a state in which the magnetic field orientation performed in the above-described orientation process is maintained.

On the other hand, a paste (illustrated) in which positive electrode active material particles (LiNiCoMnO ₂ , not illustrated) and a conductive agent (acetylene black, not illustrated) are charged and kneaded in a solvent in which a binder (PVDF, not illustrated) is dissolved. Coating) and drying were performed on both sides of a strip-shaped aluminum positive electrode current collector foil (not shown).
Then, the paste dried with the roll press which is not illustrated was compressed, and the positive electrode plate 30 which has a positive electrode active material layer (not shown) was produced.

  The electrode body 10 is formed by winding a separator (not shown) between the positive electrode plate 30 and the negative electrode plate 20 manufactured as described above. Further, the positive electrode current collecting member 91 and the negative electrode current collecting member 92 are welded to the positive electrode plate 30 and the negative electrode plate 20, respectively, inserted into the battery case main body 81, and after injecting an electrolyte solution (not shown), the battery case main body 81 with the sealing lid 82. Seal with welding. Thus, the battery 1 is completed (see FIG. 1).

By the way, the present inventors investigated the orientation of the negative electrode active material particles 22 in the negative electrode active material layer 21 (active material layer surface 21F) for the negative electrode plate 20 produced as described above.
Specifically, for the negative electrode active material layer 21 (flaky graphite) in the negative electrode plate 20, the negative electrode active material particles 22 are obtained using an X-ray diffraction method (X-rays are irradiated perpendicularly to the negative electrode active material layer 21). Among the crystal planes, the peak intensities I (110) and I (002) of the (110) plane and the (002) plane were measured. Then, a peak intensity ratio (= I (110) / I (002)) obtained by dividing the peak intensity I (110) by the peak intensity I (002) was calculated. It can be seen that the larger the peak intensity ratio (= I (110) / I (002)), the more the negative electrode active material particles 22 are aligned in the negative electrode active material layer 21. Specifically, as the peak intensity ratio is larger, the plane (basal plane: (002) plane) formed by the single layer CL of more negative electrode active material particles 22 is aligned and orthogonal to the foil main surface 28X. I understand.

Also, a comparative negative electrode plate C20, which is a comparative example of the negative electrode plate 20 described above, was prepared. This comparative negative electrode plate C20 is the same as the negative electrode plate 20 up to the application step and the alignment step described above, but differs from the negative electrode plate 20 in that the coating film PS is dried using hot air in the drying step. .
For this comparative negative electrode plate C20, similarly to the negative electrode plate 20, the peak intensities I (110) and I (002) were measured using the X-ray diffraction method, and the peak intensity ratio (= I (110) / I (002) ) Was calculated and compared with the peak intensity ratio of the negative electrode plate 20.

  The peak intensity ratio of the comparative negative electrode plate C20 in which the coating film PS was dried using hot air was 0.200. On the other hand, the peak intensity ratio of the negative electrode plate 20 was 0.228, which was slightly larger than that of the comparative negative electrode plate C20. From this, it can be seen that the negative electrode active material particles 22 are more oriented in the negative electrode plate 20 than in the comparative negative electrode plate C20. This is because the negative electrode plate 20 was dried without applying wind (hot air) when drying the coating film PS in the drying step, so that the orientation of the surface particles 22H in the coating film PS was not destroyed. This is because the negative electrode plate 20 was produced by drying the film PS.

Next, in order to evaluate the characteristics of the battery 1 using the above-described negative electrode plate 20, the inventors of the present invention used a sample battery T1 using the same positive electrode plate, negative electrode plate, separator, and electrolyte as those used for the battery 1. Prepared.
Specifically, the positive electrode plate 30 and the negative electrode plate 20 described above were each cut to a length of about 5 cm, and a separator was interposed between the positive electrode plate, the negative electrode plate, and the separator. A flat laminated electrode body was formed. In this electrode body, the surface particles of the negative electrode plate are oriented so that the thickness direction DT thereof is parallel to the foil main surface 28X.
The electrode body is sandwiched between two sheet-like laminate sheets obtained by coating an aluminum foil with a resin, and a part of the positive electrode plate (positive electrode lead part) and a part of the negative electrode plate (negative electrode lead part) are A laminate type sample battery T1 was manufactured by enclosing the electrolyte solution inside while extending outward.

First, this sample battery T1 was charged (initial charge). Specifically, constant current charging was performed at 1 C until the voltage between the positive electrode plate and the negative electrode plate reached 4.1 V under a temperature environment of 25 ° C.
Thereafter, the internal resistance of the sample battery T1 was measured. Specifically, the sample battery T1 having an open-circuit voltage between the electrodes of 3.75 V was subjected to constant current discharges of 1/2, 1, 5, 10 C in a temperature environment of 25 ° C. The voltage when 10 seconds elapsed from the start of discharge was measured. Then, the voltage measured for each current value is plotted on a graph showing the voltage on the vertical axis and the value of constant current discharge on the horizontal axis, and the value of the internal resistance of the sample battery T1 is calculated from the slopes of the approximate straight lines at all points. Calculated.

On the other hand, a comparative battery C1, which is a comparative example of the sample battery T1, was prepared, and the battery characteristics of this battery were measured in the same manner as the sample battery T1.
However, the comparative battery C1 differs from the sample battery T1 in that the comparative negative electrode plate C20 described above, that is, the negative electrode plate prepared by drying the coating film PS using hot air after the alignment step is used.
The comparative battery C1 was first charged (initial charge) in the same manner as the sample battery T1, and then the internal resistance of the comparative battery C1 was measured in the same manner as the sample battery T1.

  The value of the internal resistance of the comparative battery C1 was 0.518Ω. On the other hand, the value of the internal resistance of the sample battery T1 was 0.496Ω, which was smaller than that of the comparative battery C1. As described above, in the negative electrode plate 20 of the sample battery T1, the thickness direction DT of more surface particles 22H is parallel to the foil main surface 28X of the copper foil 28 as compared with the comparative negative electrode plate C20 of the comparative battery C1. Oriented in the direction. For this reason, in the sample battery T1, as compared with the comparative battery C1, there are more surface particles 22H in which the outer peripheral edge 22s of the lithium ion is directed to the separator and the positive electrode plate 30. Thereby, the lithium ions that have moved from the positive electrode plate 30 can be easily taken into the surface particles 22H (negative electrode active material particles 22) through the outer peripheral edge 22s of the particles with the shortest moving distance as viewed from the positive electrode plate 30. . Thus, it is considered that the internal resistance of the sample battery T1 was made smaller than that of the comparative battery C1.

  As mentioned above, in the manufacturing method of the negative electrode plate 20 used for the battery 1 of this embodiment, since the coating film PS is dried without wind in the drying step, the negative electrode plate 20 capable of reducing the internal resistance of the battery 1 can be manufactured.

In addition, when the active material paste 21P using the flat negative electrode active material particles 22 is used, the negative electrode active material particles 22 (surface particles 22H) are flat, so that they are easily affected by wind and the coating film PS is being dried. It is difficult to complete the drying of the coating film PS in a state where the orientation of the negative electrode active material particles 22 (surface particles 22H) at the time of magnetic field orientation is aligned.
On the other hand, in the manufacturing method of the negative electrode plate 20 of this embodiment, since the coating film PS is dried without wind, the orientation is maintained while using the flat negative electrode active material particles 22 (surface particles 22H). Meanwhile, the coating film PS can be dried. Accordingly, it is possible to form the negative electrode plate 20 in which the orientations of the flat negative electrode active material particles 22 (surface particles 22H) are reliably aligned.

By the way, the present inventors prepared a plurality of pastes having different viscosities in order to investigate the relationship between the viscosity of the active material paste used for manufacturing the negative electrode plate and the resistance characteristics of the manufactured negative electrode plate. The viscosity of the paste was adjusted by changing the amount of water AQ. Moreover, about the viscosity of a paste, the measured value in 2 sec- ¹ of a well-known E-type viscosity meter is shown in Table 1.
A magnetic field is applied to the coating film to which each paste is applied in the above-described orientation step, and then a reference negative electrode plate is produced by hot air drying. This is cut into a flat plate of 2 cm × 2 cm to obtain a test piece. Two test pieces are overlapped, and when a load of 2000 N is applied in the overlapping direction, the resistance value between the two test pieces (hereinafter also referred to as electrode plate resistance value) is measured using a milliohm tester. It measured by the well-known 4 terminal method.
Table 1 shows the viscosity of each paste and the electrode plate resistance value of each negative electrode plate of the reference example using the paste.

Moreover, the graph showing the relationship between the viscosity of each paste and the electrode plate resistance value of the negative electrode plate of Reference Examples 1-6 using this is shown in FIG.
According to this graph, when the viscosity of the active material paste is 4000 mPa · s or less, the electrode plate resistance can be suppressed to about 4 to 5 mΩ. On the other hand, when the viscosity of the active material paste exceeds 4000 mPa · s, it can be seen that the electrode plate resistance values all exceed 5.5 mΩ.

  When an active material paste having a viscosity exceeding 4000 mPa · s is used, even if a magnetic field H is applied to the coating film using a magnetic circuit in the above-described orientation step, surface particles 22H (negative electrode active material particles) 22) is difficult to move, so it is difficult to orient it. On the other hand, when an active material paste having a relatively low viscosity of 4000 mPa · s or less is used, the surface particles 22H can be magnetically aligned by applying a magnetic field H to the coating film in the alignment step. For this reason, the negative electrode plate manufactured using the active material paste having a viscosity of 4000 mPa · s or less has a uniform alignment as compared with the negative electrode plate using the active material paste exceeding 4000 mPa · s. Therefore, the negative electrode plate using the active material paste having a viscosity of 4000 mPa · s or less has a larger number of surface particles 22H facing the outer peripheral edge of the particle, which is a portion where lithium ions enter and exit, toward the separator and the positive electrode plate. It is thought that resistance became low. Thus, it can be seen that an active material paste having a viscosity of 4000 mPa · s or less is preferably used.

Further, the present inventors have evaluated the relationship between the viscosity of the active material paste and the internal resistance of the battery using the dried negative electrode plate after applying a magnetic field to the coating film using the active material paste. Several different pastes were prepared.
And about a battery provided with the negative electrode plate of the reference examples 1-6 using these pastes, it carries out charge (initial charge) first like the above-mentioned sample battery T1, and then like a sample battery T1, The internal resistance of each battery was measured.
The internal resistance values for each battery are also shown in Table 1.

Furthermore, the graph showing the relationship between the viscosity of each paste and the internal resistance value of a battery provided with a negative electrode plate using the paste is shown in FIG.
According to this graph, in the battery using the active material paste having a viscosity of 4000 mPa · s or less, all the internal resistance values are 0.52Ω or less. On the other hand, in the battery using the active material paste having a viscosity exceeding 4000 mPa · s, the internal resistance value exceeds 0.52Ω.
This is similar to the result of the electrode plate resistance value of the negative electrode plate described above (FIG. 7). In the battery using the active material paste having a viscosity exceeding 4000 mPa · s, the surface particles 22H (negative electrode active material particles 22) are magnetically aligned. It is difficult to let it. On the other hand, in a battery using an active material paste having a relatively low viscosity of 4000 mPa · s or less, the surface particles 22H are easily magnetically oriented. For this reason, the orientation of the surface particles 22H is uniform, and more surface particles 22H are directed to the separator or the positive electrode plate with the outer peripheral edge of the particles, which is the portion where lithium ions enter and exit, so that the internal resistance of the battery is reduced. Conceivable.

However, when the viscosity of the active material paste is extremely low, that is, 20 mPa · s or less, a part of the applied active material paste flows down from the main foil surface of the copper foil in the coating process, and on the main foil surface. A coating film cannot be formed properly.
Thus, it can be seen that the viscosity of the active material paste is preferably in the range of 20 mPa · s to 4000 mPa · s.

(Deformation)
Next, modifications of the manufacturing method according to the above-described embodiment will be described with reference to the drawings.
Note that the method for manufacturing a negative electrode plate according to this modified embodiment further includes a glossiness detection step for detecting the glossiness of the surface of the negative electrode active material layer after the drying step. It is different from the manufacturing method.
Therefore, the differences from the embodiment will be mainly described, and the description of the same parts as the embodiment will be omitted or simplified. In addition, the same effect is produced about the part similar to embodiment. In addition, the same contents are described with the same numbers.

Specifically, in the glossiness detection step, the glossiness of the uncompressed active material layer 21B that has been completely dried in the drying step is measured using the gloss meter 200 shown in FIG.
The gloss meter 200 includes a light source unit 210 that irradiates the uncompressed active material layer 21B with the irradiation light L1, and a light receiving unit 220 that receives the reflected light L2 from the uncompressed active material layer 21B. In the gloss meter 200, as shown in FIG. 10, the angle (measurement angle α) between the optical axes L1X and L2X of the light source unit 210 and the light receiving unit 220 and the direction of the perpendicular VL of the uncompressed active material layer 21B is set. , 85 degrees each.

By the way, the present inventors investigated the relationship between the glossiness of the uncompressed active material layer and the degree of orientation (peak intensity ratio) of the uncompressed active material layer using the gloss meter 200 described above.
Specifically, a plurality of pastes (reference examples) having different viscosities described above were used.
Each paste was applied, a magnetic field was applied to the coating film in the orientation process described above, and then the glossiness of the uncompressed active material layer produced by hot air drying was measured using a gloss meter 200.
The glossiness of each uncompressed active material layer using the paste is also shown in Table 1.

In addition, for the uncompressed active material layer, the peak intensities I (110) and I (002) of the (110) plane and the (002) plane of the negative electrode active material particles 22 were measured using an X-ray diffraction method. Then, the peak intensity ratio (= I (110) / I (002)) was calculated in the same manner as in the embodiment.
The peak intensity ratio of each uncompressed active material layer is also shown in Table 1.

A graph showing the correlation between the peak intensity ratio and the glossiness is shown in FIG.
According to this graph, it can be seen that the greater the peak intensity ratio measured by the X-ray diffraction method, the smaller the glossiness. As described above, as the peak intensity ratio (= I (110) / I (002)) is larger, the orientation of the negative electrode active material particles 22 is more uniform in the uncompressed active material layer. Therefore, it can be seen that the higher the degree of orientation of the surface particles 22H, the smaller the glossiness. This is because the negative electrode active material layer having a higher degree of orientation has fewer particles that face the flat surface that easily reflects light.

  Note that, as shown in the above-described embodiment, the negative electrode active material layer 21 is increased as the peak intensity ratio of the negative electrode active material layer 21 increases, that is, as the degree of orientation of the negative electrode active material particles 22 (surface particles 22H) increases. The value of the internal resistance of the used battery can be reduced. Therefore, it is considered that the battery using the negative electrode plate having a lower glossiness can lower its internal resistance.

  The relationship between the glossiness described in Table 1 and the internal resistance value is shown in the graph of FIG. From this graph, it can be confirmed that the battery using the negative electrode plate having a lower glossiness has a smaller internal resistance value.

  From the above, for example, instead of measuring the peak intensity ratio by the X-ray diffraction method or the like, the degree of orientation of the surface particles 22H can be easily detected by measuring the gloss using the gloss meter 200 described above. It can be seen that it can be managed. Further, for example, based on the glossiness detected in the glossiness detection step, a negative electrode plate in which the orientation of the surface particles 22H (negative electrode active material particles 22) is aligned, and a low-resistance battery can be reliably manufactured.

In the above, the present invention has been described with reference to the embodiments and modifications. However, the present invention is not limited to the above-described embodiments and the like, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof. Yes.
For example, in the embodiments and the like, a method for drying the coating film PS by evaporating the solvent by using infrared rays in the drying step has been shown. For example, in addition to infrared rays, electromagnetic induction heating (IH), condenser dryer It is good also as a method of heating using and drying a coating film. In the orientation step, a magnetic field is applied using a magnetic circuit including a magnet. However, for example, an electromagnet may be used.

20 Negative electrode plate 21 Negative electrode active material layer 21P Active material paste 22 Negative electrode active material particles (graphite particles)
22H surface particles (surface graphite particles)
28 Copper foil (current collector plate)
28X foil main surface (main surface of current collector)
AQ Water (solvent)
H Magnetic field PS Coating film PSA Coating surface (surface)

Claims (2)

A plate-like current collector having a main surface; and
A negative electrode active material layer comprising negative electrode active material particles capable of magnetic field orientation by a magnetic field and formed on the main surface, comprising:
An application step of applying an active material paste in which the negative electrode active material particles are dispersed in a solvent on the main surface of the current collector;
An orientation process in which a magnetic field is applied to the coating film made of the active material paste, and at least surface particles located on the surface of the negative electrode active material particles in the coating film are magnetically aligned,
After the said orientation process, the drying process which dries the said coating film in a windless manner, The manufacturing method of a negative electrode plate provided with. It is a manufacturing method of the negative electrode plate according to claim 1,
The negative electrode active material particles are
A method for producing a negative electrode plate which is flat graphite particles.

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