Method for manufacturing electrode plates for secondary batteries

Abstract

To suppress variation in performance of a completed battery even when an active material used as an electrode material has variation in specific surface area.SOLUTION: A method for manufacturing an electrode plate of a secondary battery comprises: a design specific surface area determination step of determining a design specific surface area S1 [m2 / g], which is the design median value of negative electrode active material particles in a completed battery; a specific surface area change measurement step of measuring the amount of change in the specific surface area S2 [m2 / g] from before a coating step after the completion of a pressing step; a powder specific surface area measurement step of measuring the powder specific surface area S3 [m2 / g] of an active material before undergoing the mixing step; and a specific surface area change setting step of obtaining the target change X [m2 / g] in the specific surface area in the mixing step from X=S1-S2-S3 (Equation 1) when the target change in the specific surface area in the mixing step is denoted as X, and adjusting the change amount V of the specific surface area by a load L per unit time in the mixing step on the basis of the target change X.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrode plate for a secondary battery, and more particularly to a method for manufacturing an electrode plate for a secondary battery with little variation in specific surface area. [Background technology]

[0002] The electrode plate of a secondary battery contains an active material in an electrode composite layer that is responsible for the main reaction of the battery. To fix this active material to a substrate that serves as a current collector, such as a metal foil, a binder consisting of a binding agent and a viscosity modifier is mixed in. The active material, binder, and solvent are then mixed and kneaded to form a paste. The paste thus kneaded is then applied to the substrate in a coating process. After coating, the substrate is dried to remove the solvent, and the solids are fixed to the substrate, forming a composite layer. This composite layer is then pressed to a uniform thickness in a pressing process.

[0003] In such electrode plates, the reaction rate varies depending on the specific surface area of ​​the active material responsible for the main reaction, so a large specific surface area is desirable. However, during kneading, the specific surface area can decrease due to factors such as the adhesion of resin binders to the surfaces of the active material particles, which can lead to a decrease in battery performance. In particular, when negative electrode plates are produced using the same manufacturing method for active materials with different specific surface areas, there is a problem of variations in the performance of the completed batteries.

[0004] Therefore, the invention described in Patent Document 1 discloses that the BET (specific surface area measured by the BET method) of the negative electrode plate can be controlled by the press density. Furthermore, the invention described in Patent Document 2 discloses that the amount of binder adhering to the active material is controlled by the kneading time, thereby adjusting the BET.

[0005] With these inventions, it is possible to control the BET of the electrode plate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 1998-116604 [Patent Document 2] Japanese Patent Application Publication No. 2013-206737 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the invention described in Patent Document 1 has a problem in that not only the BET but also the press density and the thickness of the electrode plate change. Furthermore, in the invention described in Patent Document 2, although the BET of the electrode plate can be controlled by adjusting the kneading time, changing the kneading time each time during the secondary battery manufacturing process affects the takt time of the manufacturing line, which causes a problem of deteriorating manufacturing efficiency.

[0008] The problem to be solved by the method for manufacturing an electrode plate for a secondary battery of the present invention is to suppress the variation in performance of the completed battery even when there is variation in the specific surface area of ​​the active material that becomes the electrode material. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the method for manufacturing an electrode plate for a secondary battery of the present invention includes a kneading step of kneading a plurality of electrode materials including an active material in a kneader to produce an electrode mixture paste used for manufacturing an electrode plate for a secondary battery, a coating step of coating the electrode mixture paste onto a current collector, and a pressing step of pressing the electrode plate coated with the electrode mixture paste, and the method for manufacturing an electrode plate for a secondary battery includes a design specific surface area S1 [m 2 / g], and the specific surface area change S2 [m 2 / g] of the powder specific surface area S3 [m 2When the target change in specific surface area in the kneading step is X, the target change in specific surface area X [m 2 / g] and adjusts the load L per unit time in the kneading step based on the target change X, thereby adjusting the change V in the specific surface area.

[0010] The step of setting the amount of change in specific surface area may be such that the load L is changed by changing the kneading resistance of a kneader in the kneading step, thereby adjusting the amount of change V in specific surface area. Alternatively, the relationship between the load L in the kneading process and the change in specific surface area in the kneading process may be measured in advance, and the load L may be adjusted based on the measurement results so that the change in specific surface area V in the kneading process is the target.

[0011] Furthermore, the step of setting the amount of change in specific surface area may adjust the load L in the kneading process based on the power consumption [Wh] per unit time of the kneader. Furthermore, the step of setting the specific surface area change amount may adjust the load L depending on the value of the solid content rate NV in the kneading step.

[0012] The solid content rate NV may be adjusted by changing the amount of the solvent that is the material of the electrode mixture paste. In addition, the step of setting the specific surface area change may involve changing the active material to be used as the electrode material to an active material having a different specific surface area. Furthermore, the load L may be adjusted by changing the shape and gap of the rotating members of the kneading machine to change the kneading resistance. Furthermore, the load L may be adjusted by changing the rotation speed of the kneading machine to change the kneading resistance.

[0013] The secondary battery can be suitably implemented as a lithium ion secondary battery, and the electrode plate can be suitably implemented as a negative electrode plate. [Effects of the Invention]

[0014] The method of manufacturing an electrode plate for a secondary battery of the present invention can suppress variations in the performance of the completed battery even when there are variations in the specific surface area of ​​the active material that will be used as the electrode material. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of the appearance of a lithium ion secondary battery. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a wound electrode body. [Figure 3] 1 is a flowchart showing a manufacturing process of a negative electrode plate. [Figure 4] 10 is a flowchart showing a procedure for determining kneading conditions. [Figure 5] (a) A schematic diagram showing the coating process, (b) A schematic diagram showing the drying process, (c) A schematic diagram showing the pressing process, and (d) A schematic diagram showing the completed negative electrode plate. [Figure 6] 1 is a graph showing the change in specific surface area according to the prior art. [Figure 7] 1 is a graph showing the change in specific surface area in this embodiment. [Figure 8] (a) is a schematic diagram showing powdered negative electrode active material particles that are raw materials for a composite paste before raw materials are mixed, (b) is a schematic diagram showing negative electrode active material particles in the composite paste after raw materials are mixed, and (c) is a schematic diagram showing negative electrode active material particles in the composite paste after a kneading step. [Figure 9] FIG. 4 is a schematic diagram showing negative electrode active material particles after a kneading step. [Figure 10] 1 is a graph showing the relationship between the load L and the specific surface area in the kneading step. [Figure 11] 1 is a graph showing the relationship between the solid content NV and the specific surface area in the kneading step. DETAILED DESCRIPTION OF THE INVENTION

[0016] A method for manufacturing an electrode plate for a secondary battery according to the present invention will be described with reference to an embodiment of a method for manufacturing a negative electrode plate 2 of a lithium ion secondary battery 1 with reference to FIGS. <Principle of this embodiment> First, the principle of this embodiment will be described. In this embodiment, a lithium-ion secondary battery 1 is used as an example of a secondary battery, and a negative electrode plate 2 is used as an example of an electrode plate. Note that the present invention is broadly applicable to electrode plates of secondary batteries and is not limited by the description of this embodiment. As described in the explanation of the prior art, in the negative electrode plate 2 of a lithium-ion secondary battery 1, the negative electrode active material particles 22b, which are components of the negative electrode composite paste 22a, may have variations in specific surface area S. The specific surface area S of the active material is responsible for the main reaction of the secondary battery, and is therefore linked to battery performance. Therefore, by reducing the variation in the specific surface area S of the negative electrode plate 2, the variation in battery performance can also be reduced.

[0017] This embodiment is a method for manufacturing a negative electrode plate 2 that can suppress performance variations by appropriately managing the specific surface area S of the completed battery, even if there is variation in the specific surface area S of the raw material negative electrode active material particles 22b.

[0018] <Specific surface area S> Here, the specific surface area S [m 2 / g] is expressed as the area per unit mass. Specific surface area can be measured by adsorption, wet heat, reaction, etc., and adsorption methods include the BET method and the Langmuir method. In this embodiment, the widely used BET method (Berunauer Emmett and Teller's method, gas adsorption method) is used to determine the specific surface area of ​​a powder.

[0019] Specifically, for example, the negative electrode was cut into a strip measuring 1 cm x 20 cm, and this was used as the sample. The BET specific surface area measurement device used was a Quantasorb manufactured by Quanta Chrome, and nitrogen gas was used as the adsorption gas. A bulk solid cell was used as the sample cell, and the negative electrode sample was rolled up and placed inside this cell. Note that by using krypton as the adsorption gas, measurements can be made on even smaller samples.

[0020] <Control of Specific Surface Area in This Embodiment> The specific surface area of ​​the negative electrode composite layer 22 of the negative electrode plate 2 of the completed lithium-ion secondary battery 1 varies depending on the specific surface area S inherent to the negative electrode active material particles 22b that are the raw material, as well as the manufacturing process of the negative electrode plate 2. In particular, in the kneading process (FIG. 3, S4), the change in the specific surface area S varies depending on the kneading conditions.

[0021] <Changes in load L and specific surface area S per unit time in the kneading process (S4)> The present inventors have found that the change V in the specific surface area S can be appropriately adjusted by adjusting the load L per unit time in the kneading step (S4). Furthermore, they have found that the change in the specific surface area S in the kneading step (S4) depends on the load L in the kneading step (S4). In other words, the load L in the kneading step (S4) can be quantified by the power consumption [Wh] per unit time in the kneading step (S4), and by controlling the power consumption [Wh] per unit time, the change in the specific surface area S in the kneading step (S4) can be easily and appropriately controlled.

[0022] <Load L and solid content NV> The inventors also discovered that, in order to appropriately adjust the specific surface area S, the solid content NV of the negative electrode composite paste 22a significantly affects changes in the specific surface area S and that the solid content NV is strongly correlated with changes in the specific surface area S. Furthermore, they discovered that by measuring the relationship between the solid content NV and changes in the specific surface area S in advance and controlling the solid content NV, the specific surface area can be easily and appropriately adjusted. Here, the "solid content NV (Nonvolatile Content)" refers to the ratio of the mass of solids to the total mass of the negative electrode composite paste 22a. Specifically, it is measured using the method specified in "JIS K 5601_1_2 Paint Component Test Methods - Part 1 - Section 2: Heat Residue."

[0023] <Other conditions that affect the load L> The load L in the kneading step (S4) is not limited to the solid content NV, but also includes, for example, the size of the raw material negative electrode active material particles 22b. Other factors include the shape and clearance of the rotating parts (screws, rods, pads, blades) of the kneading machine (not shown). Furthermore, factors such as the rotation speed of the kneading machine also have an effect. By managing the power consumption per unit time [Wh] as an index of the load L that combines these factors, changes in the specific surface area S in the kneading step (S4) can be easily and appropriately managed.

[0024] <Configuration of lithium-ion secondary battery 1> First, a brief description will be given of the configuration of a lithium ion secondary battery 1, which corresponds to the secondary battery that is the premise of this embodiment.

[0025] FIG. 1 is a perspective view showing the outline of the configuration of a lithium-ion secondary battery 1 of this embodiment. As shown in FIG. 1, the lithium-ion secondary battery 1 is configured as a cell battery. The lithium-ion secondary battery 1 includes a rectangular parallelepiped battery case 11 with an opening on the upper side. An electrode assembly 12 is housed inside the battery case 11. An electrolyte 13 is filled into the battery case 11 through a liquid filling hole. The battery case 11 is made of a metal such as an aluminum alloy, and forms a battery container sealed with a lid. The lithium-ion secondary battery 1 also includes a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging power.

[0026] <Electrode body 12> 2 is a schematic diagram showing the configuration of a wound electrode assembly 12. The electrode assembly 12 is formed by winding a negative electrode plate 2, a positive electrode plate 3, and a separator 4 disposed therebetween in a flat shape. The negative electrode plate 2 has a negative electrode composite layer 22 formed on a negative electrode current collector 21 that serves as a substrate. A negative electrode connection portion 23 is provided at one end in a width direction W (winding axis direction) perpendicular to the winding direction (winding direction L) where the negative electrode composite layer 22 is not formed and the negative electrode current collector 21 is exposed.

[0027] The positive electrode plate 3 has a positive electrode composite layer 32 formed on a positive electrode current collector 31 serving as a base material. A positive electrode connection portion 33 is provided on the other end side (opposite to the negative electrode connection portion 23) in a width direction W (winding axis direction) perpendicular to the direction in which the positive electrode current collector 31 is wound (winding direction L).

[0028] <Negative electrode plate 2> The negative electrode plate 2 is constructed by forming a negative electrode composite layer 22 on both sides of a negative electrode current collector 21. In this embodiment, the negative electrode current collector 21 is made of Cu foil. The negative electrode current collector 21 serves as a base for the aggregate of the negative electrode composite layer 22, and also functions as a current collecting member that collects electricity from the negative electrode composite layer 22. The negative electrode plate 2 is constructed by applying a negative electrode composite paste 22a onto the metallic negative electrode current collector 21, thereby forming the negative electrode composite layer 22. In this embodiment, the negative electrode active material is a material capable of absorbing and releasing lithium ions, and a powdered carbon material made of graphite or the like is used.

[0029] The negative electrode plate 2 is produced, for example, by kneading a negative electrode active material, a solvent, and a binder, and then applying the kneaded negative electrode mixture to the negative electrode current collector 21 and drying it. Here, for example, water or NMP (N-methyl-2-pyrrolidone) solution can be used as the solvent, and for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. can be used as the binder.

[0030] <Positive electrode plate 3> A positive electrode plate is formed by forming a positive electrode composite layer on both sides of a positive electrode current collector (not shown). In this embodiment, the positive electrode current collector is made of Al foil or Al alloy foil. The positive electrode current collector serves as a base for the positive electrode composite layer and also functions as a current collecting member that collects electricity from the positive electrode composite layer.

[0031] The positive electrode plate 3 has a positive electrode composite layer formed on the surface of a positive electrode current collector. The positive electrode composite layer contains a positive electrode active material. The positive electrode active material is a material capable of absorbing and releasing lithium, and examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), and lithium nickel oxide (LiNiO2). Alternatively, a material in which LiCoO2, LiMn2O4, and LiNiO2 are mixed in any ratio may be used.

[0032] The positive electrode mixture layer also contains a conductive material, such as carbon black, such as acetylene black (AB) or ketjen black, or graphite.

[0033] The positive electrode plate 3 is produced, for example, by kneading a positive electrode active material, a conductive material, a solvent, and a binder, and then applying the kneaded positive electrode mixture to a positive electrode current collector and drying it. In this embodiment, only the negative electrode plate 2 is illustrated, but it goes without saying that the present invention can also be implemented in the positive electrode plate 3.

[0034] <Separator 4> The separator 4 is a nonwoven fabric made of, for example, polypropylene, for holding the electrolyte solution 13 between the negative electrode plate 2 and the positive electrode plate 3. Alternatively, the separator 4 may be a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or a lithium ion or ion conductive polymer electrolyte membrane, either singly or in combination. When the electrode assembly 12 is immersed in the electrolyte solution 13, the electrolyte solution 13 permeates the separator 4 from the edges toward the center.

[0035] <Electrolyte 13> The electrolyte solution 13 is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent may be ethylene carbonate (EC). Alternatively, the non-aqueous solvent may be one or more materials selected from the group consisting of propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. The supporting salt may be one or more lithium compounds (lithium salts) selected from LiPF, LiBF, LiClO, LiAsF, LiCF, SO, LiCF, SO, LiN(CF, SO), LiC(CF, SO), LiI, etc.

[0036] <Manufacturing process of negative electrode plate 2> 3 is a flowchart showing the manufacturing process of the negative electrode plate 2. Next, the manufacturing process of the negative electrode plate 2 of this embodiment will be described with reference to FIG. <Measurement of the relationship between load L and specific surface area S (S1)> Before determining the kneading conditions (S2), the relationship between the load L in the kneading step (S4) and the change ΔS in the specific surface area S in the kneading step (S4) is measured in advance. Based on the measurement results, the load L is adjusted so that the change V in the specific surface area S becomes the target in the kneading step (S4).

[0037] FIG. 10 is a graph showing the relationship between the change in load L in the kneading step (S4) and the change ΔS in the specific surface area S. The horizontal axis shows the power consumption [Wh] per unit time, which indicates the load L of the kneader in the kneading step (S4). The vertical axis shows the change ΔS in the specific surface area S at that time. ΔS0 is the change ΔS in the specific surface area S when the load L is the design value L0 [Wh]. X is the change ΔS when the load L is L0 [Wh]. The load Lmax is the upper limit load L, and the load Lmin is the lower limit load L.

[0038] 10, as the load L increases, the decrease in the change ΔS in the specific surface area S increases accordingly. For example, if it is desired to set the change ΔS in the specific surface area S to the target change X, then if the load L is set to load Lx, the change ΔS in the specific surface area will become the target change X.

[0039] Therefore, if the relationship shown in FIG. 10 is measured in advance for the negative electrode active material particles 22b of the secondary battery to be manufactured, it is possible to derive the target load Lx when the change ΔS in the specific surface area S is desired to be the target change X.

[0040] Therefore, in measuring (S1) the relationship between the load L and the amount of change ΔS in the specific surface area S in the kneading step (S4), the relationship between the change in the load L in the kneading step (S4) and the amount of change ΔS in the specific surface area S is measured as shown in Fig. 10. Then, this is stored in a storage device of the manufacturing device for lithium ion secondary batteries (not shown) so that it can be read out in the form of a map or conversion table.

[0041] <Determining the kneading conditions (S2)> Next, the kneading conditions are determined (S2). Here, based on the negative electrode active material particles 22b that will be the electrode material, the blending ratio of the negative electrode active material particles 22b, binder, thickener, other additives, and solvent is determined so as to achieve a predetermined solid content NV. Also, the kneading members of the kneader are selected, and the kneading time and kneading speed are set.

[0042] Details will be provided later. <Raw material blend (S3)> Negative electrode active material particles 22b, which are raw materials for negative electrode composite paste 22a, a binder, a thickener, other additives, and a solvent are mixed in the mixture determined in the step of determining the kneading conditions (S2).

[0043] <Kneading process (S4)> In the kneading step (S4), the raw materials mixed in the raw material mixing step (S3) are mixed in a kneader according to the mixing conditions determined in the mixing condition determination step (S2) to produce negative electrode composite paste 22a.

[0044] <Change in specific surface area in the kneading process (S4)> Here, Fig. 6 is a graph showing the change in specific surface area in the conventional method. As shown in Fig. 6, the specific surface area S3 of the powdered negative electrode active material particles 22b used as the raw material for the negative electrode composite paste 22a before the raw material blending step (S3) is reduced after the kneading step (S4). This means that even if the specific surface area S3 of the negative electrode active material particles 22b becomes S3', the change ΔS and the change ΔS' are equal if the kneading conditions are the same. Furthermore, the changes S2 and S2' in the specific surface area S after the coating step (S5), drying step (S6), and pressing step (S7) are also equal.

[0045] That is, S3-S3'=S1-S1', and the difference between the powder specific surface area S3 and the powder specific surface area S3' is not eliminated. <Effect of the kneading step (S4) of this embodiment> FIG. 8(a) is a schematic diagram showing powdered negative electrode active material particles 22b, which are the raw material for negative electrode composite paste 22a before raw material blending (S3). FIG. 8(b) is a schematic diagram showing negative electrode active material particles 22b of negative electrode composite paste 22a after raw material blending (S3). FIG. 8(c) is a schematic diagram showing negative electrode active material particles 22b of negative electrode composite paste 22a after kneading step (S4). As shown in FIG. 8(a), negative electrode active material particles 22b before raw material blending have nothing covering their surfaces, and therefore have their original specific surface area, i.e., powder specific surface area S3. Thereafter, as shown in FIG. 8(b), auxiliary materials such as binder 22c and solvent 22d are mixed in the raw material blending step (S3). Even at this stage, the particles still have their original specific surface area, i.e., powder specific surface area S3. Then, as shown in FIG. 8(c), when the procedure of the kneading step (S4) is completed, part of the binder 22c adheres to the surface of the negative electrode active material particles 22b, covering part of the surface of the negative electrode active material particles 22b.

[0046] 9 is a schematic diagram showing negative electrode active material particles 22b after the kneading step (S4). After the kneading step (S4), a portion of the binder 22c adheres to the surface of the negative electrode active material particles 22b, covering a portion of the surface of the negative electrode active material particles 22b. The specific surface area of ​​the portion of the negative electrode active material particle surface 22e covered with the binder 22c is reduced. Therefore, the powder specific surface area S3, which is the specific surface area S of the negative electrode active material particle surface 22e after the kneading step (S4), is reduced.

[0047] The mechanism explained using FIGS. 8 and 9 is one of the factors that cause a decrease in the specific surface area S, and other factors in kneading also cause changes in the surface shape of the active material, which in turn causes a change in the specific surface area. <Kneader load L> This decrease in the specific surface area S results from a larger load L in the kneading step (S4) when the amount of solvent 22d is relatively small and the solid content NV is high. That is, in the so-called "stiff kneading" where the amount of solvent 22d is relatively small, the amount of solvent 22d is small and the binder 22c and the like are strongly rubbed and adhere in large amounts to the surfaces of the negative electrode active material particles 22b. That is, the decrease in the specific surface area S is large. Conversely, when the amount of solvent 22d is large and the solid content NV is low, the load L in the kneading step (S4) is small. That is, the flow resistance is small and the force with which the binder 22c and the like are rubbed is reduced. As a result, less binder 22c adheres to the surfaces of the negative electrode active material particles 22b. That is, the decrease in the specific surface area S is small.

[0048] The amount of binder 22c adhering to the surface of the negative electrode active material particles 22b varies not only depending on the solid content NV but also on the negative electrode active material particles 22b themselves, which are the raw material. For example, the change in specific surface area S, ΔS, varies depending on the particle size of the negative electrode active material particles 22b. The change in specific surface area S, ΔS, also varies depending on the shape and clearance of the rotating parts (screws, rods, pads, blades) of the kneading machine, which changes the kneading resistance. Furthermore, the change in specific surface area S, ΔS, also varies depending on the kneading resistance, which is changed by changing the rotation speed of the kneading machine. These factors can be considered as the "load L" per unit time of the kneading machine.

[0049] The present inventors have found that the influence of these factors on the specific surface area S can be estimated from the load L of the kneading machine. According to experiments conducted by the present inventors, as shown in FIG. 10, it has been confirmed that when the load L of the kneading machine is changed, the change amount ΔS of the specific surface area S changes with a high correlation. For this reason, in this embodiment, the specific surface area S is controlled by controlling the load L. Furthermore, the present inventors have established a manufacturing method that can numerically grasp this load L as the power consumption [Wh] per unit time of the kneading machine. In other words, by controlling the power consumption [Wh] per unit time of the kneading machine, the load L can be controlled, and thereby the change in the specific surface area S can be controlled. <Coating process (S5)> Negative electrode composite paste 22a produced in the kneading step (S4) is applied by coater 5.

[0050] FIG. 5(a) is a schematic diagram showing the coating step (S5). In the coating step (S5), a negative electrode current collector 21, which is a long metal foil as shown in FIG. 5, is transported by a transport conveyor (not shown). A coater 5 is disposed opposite the transported negative electrode current collector 21 with a predetermined gap G therebetween. The coater 5 is configured as a die nozzle, and the negative electrode composite paste 22a produced in the kneading step (S4) is supplied to a die (not shown). A constant amount of the negative electrode composite paste 22a supplied to the die is ejected from a nozzle 51 onto the negative electrode current collector 21. With this configuration, a layer of the negative electrode composite paste 22a having a constant thickness D1 is formed on the negative electrode current collector 21, which is being transported at a constant speed.

[0051] <Drying process (S6)> 5(b) is a schematic diagram showing the drying step (S6). The layer of negative electrode composite paste 22a having a constant thickness D1 formed in the coating step (S5) is dried with drying equipment such as an infrared lamp. At this time, solvent 22d evaporates from layer of negative electrode composite paste 22a, causing the layer to harden. The layer of negative electrode composite paste 22a having a constant thickness D1 formed in the coating step (S5) becomes thinner, becoming negative electrode composite layer 22 having a thickness D2.

[0052] <Pressing process (S7)> FIG. 5(c) is a schematic diagram showing the pressing step (S7). As shown in FIG. 5(b), the layer of negative electrode composite paste 22a that has been dried and hardened in the drying step (S6) becomes negative electrode composite layer 22 with a thickness D2. This negative electrode composite layer 22 with thickness D2 is pressed in the pressing step (S7). Press 6 includes a pair of press rollers 61a, 61b that sandwich negative electrode plate 2. The pair of press rollers 61a, 61b have a gap G between them. Therefore, negative electrode composite layer 22 with thickness D2 is pressed as it passes through gap G between the pair of press rollers 61a, 61b, becoming negative electrode composite layer 22 with a thickness D3.

[0053] Fig. 5(d) is a schematic diagram showing the completed negative electrode plate. In the pressing step (S7), the surface of the completed negative electrode composite layer 22 shown in Fig. 5(d) is shaped flat to a thickness of D3, and dimensional accuracy is ensured.

[0054] 6, after the pressing step (S7), the specific surface area S increases compared to the specific surface area S before the pressing step (S7). This is thought to be because the pressing in the pressing step (S7) destroys the negative electrode active material particles 22b and peels off the sub-material covering part of the surface of the active material particles 22b, exposing new reaction surfaces, resulting in an increase in the specific surface area S.

[0055] <Cutting process (S8)> When the pressing step (S7) is completed, the negative electrode composite layer 22 of the negative electrode plate 2 is completed, and the peripheral portion is cut with a cutter to have a specified length and width, thereby completing the negative electrode plate 2 of the specified length and width.

[0056] <Assembling lithium-ion secondary batteries> Once the negative electrode plate 2 is completed using the above procedure, it is stacked with a positive electrode plate 3 and a separator 4, wound, and pressed, as shown in FIG. 2, to produce an electrode assembly 12. The electrode assembly 12, along with the lid of the battery case 11, is fitted with a positive electrode external terminal 14 and a negative electrode external terminal 15, and is then housed in the battery case 11 body as shown in FIG. 1. Note that the shapes of the positive electrode external terminal 14 and the negative electrode external terminal 15 are not limited to those shown in FIG. 1. The lid is then laser-welded to the battery case 11 body to seal it. After the interior is dried, electrolyte 13 is filled through the inlet of the lid. The cell battery is then completed through conditioning and inspection processes, including visual inspection, initial charging, aging, OCV inspection, internal resistance inspection, self-discharge inspection, and battery capacity measurement. The cell batteries are stacked to form an assembled battery, and several assembled batteries are housed in a battery pack, to which accessories are attached, to form an in-vehicle battery pack.

[0057] <Detailed procedure for determining mixing conditions (S2)> 4 is a flowchart showing the detailed procedure for determining the kneading conditions (S2). The procedure for determining the kneading conditions (S2) will be described in detail below with reference to FIG.

[0058] <Step of inputting prerequisite kneading conditions (S21)> First, the design values ​​of the lithium-ion secondary battery 1 to be manufactured and the conditions for the kneading step (S4) are input. These conditions include the particle size of the raw material negative electrode active material particles 22b, in addition to the solid content NV, which affects the load L. The kneading machine can also be of any type, including those equipped with a stirring tank and rotating blades, or twin-screw kneaders using screws and rods. The shape and clearance of the rotating parts of the kneading machine (screws, rods, pads, and blades) are also kneading conditions. Furthermore, the rotational speed of the kneading machine also affects the load L per unit time, so it is also determined as a condition.

[0059] <Step of determining the design specific surface area (S22)> Next, in the step (S22) of determining the designed specific surface area, the “design specific surface area S1 [m 2 / g]" is determined.

[0060] <Step of measuring the change in specific surface area (S23)> In the step (S23) of measuring the change in specific surface area, the change S2 in specific surface area from before the coating step (S5) to after the completion of the pressing step (S7) is measured.

[0061] <Step of measuring powder specific surface area (S24)> In the powder specific surface area measurement step (S24), the powder specific surface area S3 of the raw material negative electrode active material particles 22b before the kneading step (S4) is measured.

[0062] <Step of calculating target change amount X (S25)> The target change in the specific surface area S in the kneading process (S4) is X [m 2 / g], powder specific surface area S3 + target change amount X + specific surface area change amount S2 from before the coating process (S5) to after the completion of the pressing process (S7) = design specific surface area S1 [m 2 / g]. Therefore, the target change amount X is calculated from this relationship.

[0063] The change amount X of the specific surface area S in the kneading step (S4) can be calculated from the following (Equation 1) as a target change amount X of the specific surface area in the kneading step. X=S1-S2-S3…(Formula 1) <Setting the amount of change in specific surface area (S26)> In the step of setting the specific surface area change amount V (S26), the specific surface area change amount V in the kneading step (S4) is set based on the target change amount X. In (Equation 1), the design specific surface area S1 [m 2 / g] and the specific surface area change S2 are known fixed values. The target change X, which is a variable, does not change even if the powder specific surface area S3 changes. 2 / g] is the value to be adjusted to match.

[0064] However, in an actual manufacturing process, there is a limit to the adjustment of the specific surface area S by adjusting the load L. In that case, the load L is adjusted to approach the target change amount X within the adjustable range. FIG. 11 is a graph showing the relationship between the change in solid content NV and the change ΔS in specific surface area S in the kneading step (S4). The horizontal axis of the graph is the change in solid content NV [%]. The vertical axis is the change ΔS in specific surface area S. ΔS0 is the change ΔS in specific surface area S at the design value. Here, the median value of solid content NV is NV0 = 58.6%, the upper limit is NVmax = 60.3%, and the lower limit is NVmin = 56.9%. This indicates that the change in specific surface area S is approximately ±0.2 [m 2 / g].

[0065] As shown in FIG. 7, the powder specific surface area S3 [m 2 / g], the negative electrode active material particles 22b actually used in production have a powder specific surface area S3' [m 2 / g]. In this case, the conventional method shown in Figure 6 requires a specific surface area S3 [m 2 / g] and the actual powder specific surface area S3´ [m 2 / g] is not improved even after the product is made, and the variation remains.

[0066] Therefore, the change in the specific surface area S in the kneading step (S4) is ΔS [m 2 / g] needs to be reduced. In other words, it is necessary to set it so that the load L is small. <Reading the relationship between the load L and the change in specific surface area ΔS (S27)> Next, in order to determine the kneading conditions, a graph showing the relationship between the load L and the amount of change ΔS in the specific surface area S in the kneading step (S4) shown in FIG. 10 is read out.

[0067] <Calculation of load L corresponding to change amount ΔS of specific surface area S (S28)> According to the graph shown in FIG. 10, in order to reduce the change in the specific surface area in the kneading step (S4) from the designed value ΔS to the change ΔS′, it is necessary to reduce the load L0 from the designed value to the load Lx.

[0068] <Determining the solid content NV to change the load L (S29)> If the relationship between the change in specific surface area ΔS and the solid content rate NV as shown in FIG. 11 is known, the solid content rate NV can be calculated directly from the change in specific surface area S ΔS. In this embodiment, the change in specific surface area S ΔS [m 2 In order to approach the solid content NV0 = 58.6 [%], which is the central value in the design, it is necessary to set NVx [%].

[0069] As a result of the above, the kneading conditions are determined to be the solid content rate NV [%] = NVx [%]. <Other mixing conditions> In this embodiment, the target change amount [m 2 / g]X, the solid content NV is set to NVx [%].

[0070] If the powder specific surface area [m 2 / g]S3′ is the designed powder specific surface area [m 2 / g]S3, the target change amount [m 2 / g]X, it is necessary to increase the load L. In such a case, the solid content NV is increased up to the upper limit of 60.3%.

[0071] Furthermore, the design specific surface area S1 [m 2 / g] to obtain the corrected specific surface area [m 2 / g], other factors are used to change the load L. For example, the particle size of the raw material negative electrode active material particles 22b can be considered. The type of kneader also varies, from one equipped with a stirring tank and rotating blades to a twin-screw kneader using screws and rods. The shape and clearance of the rotating parts of the kneader (screw, rod, pad, blade) also determine the kneading conditions. Furthermore, the rotation speed of the kneader also affects the load L per unit time, so it is determined accordingly. When changing these factors, the relationship between the change in load L and each factor is measured in advance. Alternatively, the relationship between the change in specific surface area S and each factor is measured in advance.

[0072] All of these complex factors can be grasped as the mixer's power consumption per unit time [Wh]. <Example> A specific example of this embodiment will be described below.

[0073] Powder specific surface area S3[m 2 / g] is 3.8 [m 2 / g] of the negative electrode active material particles 22b, and the designed specific surface area S1 [m 2 / g] is 3.7 [m 2 / g]. 2 / g] variation is 3.8±0.4[m 2 / g].

[0074] <Conventional manufacturing method> 11, in the conventional manufacturing method, the solid content NV in the kneading step (S4) was fixed at 58.6% and was not changed, and as a result, the change ΔS in the specific surface area S in the kneading step (S4) was also constant.

[0075] Then, the designed specific surface area S1 [m 2 / g] is 3.7±0.4[m 2 / g](upper limit 4.1[m 2 / g], lower limit 3.3[m 2 / g]), and the powder specific surface area S3 [m 2 / g] variation is the same ±0.4 [m 2 / g].

[0076] <Manufacturing Method of the Example> In the manufacturing method of this example, the solid content ratio NV was adjusted in the kneading step (S4). Specifically, the solid content ratio NV of the upper limit sample of the negative electrode active material particles 22b was set to 56.9%, and the solid content ratio NV of the lower limit sample was set to 60.3%.

[0077] Then, as shown in FIG. 11, in the kneading step (S4), the change in the specific surface area V [m2 / g] is roughly ±0.2[m 2 / g]. This allows the design specific surface area S1 [m 2 / g] is 3.7±0.2[m 2 / g](upper limit 3.9[m 2 / g], lower limit 3.5[m 2 / g]).

[0078] That is, the upper limit of the powder specific surface area S3 [m 2 / g] is 3.8 + 0.4 [m 2 / g]=4.2[m 2 / g], the change in specific surface area V [m 2 / g] to -0.2 [m 2 / g].

[0079] Lower limit of powder specific surface area S3 [m 2 / g] is 3.8-0.4[m 2 / g]=3.4[m 2 / g], the change in specific surface area V [m 2 / g] to +0.2 [m 2 / g].

[0080] Therefore, the designed specific surface area S1 [m 2 / g] is 3.7±0.2[m 2 / g](upper limit 3.9[m 2 / g], lower limit 3.5[m 2 / g]) In other words, the powder specific surface area S3 [m 2 / g] variation ±0.4[m 2 / g] less than ±0.2[m 2 / g].

[0081] (Action of this embodiment) The method for manufacturing the negative electrode plate 2 of the lithium-ion secondary battery 1 according to this embodiment suppresses variations in the performance of the completed battery even when there is variation in the specific surface area S of the negative electrode active material particles 22b used as the electrode material. The load L [Wh] of the kneader can be changed by changing the solid content NV of the electrode material used to prepare the negative electrode composite paste 22a in the kneading step (S4). Changing the load L of the kneader can adjust the amount of change ΔS in the specific surface area S of the negative electrode composite paste 22a produced in the kneading step (S4). When the specific surface area S of the raw material negative electrode active material particles 22b is larger than the design value, the reduction in the specific surface area S in the kneading step (S4) is increased. Conversely, when the specific surface area S of the raw material negative electrode active material particles 22b is smaller than the design value, the reduction in the specific surface area S in the kneading step (S4) is reduced. This reduces the variation in the specific surface area S of the completed battery even when there is variation in the specific surface area S of the negative electrode active material particles 22b that serve as the electrode material. By reducing the variation in the specific surface area S of the completed battery, variation in the performance of the completed battery is reduced.

[0082] (Effects of this embodiment) (1) In the manufacturing method of the negative electrode plate 2 of the lithium ion secondary battery 1 of this embodiment, even if there is variation in the specific surface area S of the negative electrode active material particles 22b that serve as the electrode material, it is possible to suppress variation in the performance of the completed battery.

[0083] (2) In the method for manufacturing the negative electrode plate 2 of the lithium ion secondary battery 1 of this embodiment, the variation in the specific surface area S of the completed battery can be reduced, thereby reducing the variation in performance. (3) The variation in the specific surface area S of the completed battery can be suppressed by adjusting the change V in the specific surface area S in the kneading step (S4).

[0084] (4) The change V in the specific surface area S in the kneading step (S4) can be controlled by adjusting the load L per unit time of the kneader. (5) The load L per unit time of the kneader can be adjusted by, for example, adjusting the solid content NV of the electrode material.

[0085] (6) In addition, the load L per unit time of the kneader can be adjusted by changing the shape and clearance of the rotating parts (screw, rod, pad, blade) of the kneader to change the kneading resistance.

[0086] (7) Furthermore, the load L per unit time of the kneader can be adjusted by changing the rotation speed of the kneader to change the kneading resistance. (8) The load L can be managed as the power consumption [Wh] per unit time of the mixer. Therefore, not only the solid content NV but also other factors that affect the load L can be managed as the power consumption [Wh] per unit time of the mixer.

[0087] (9) By managing the load L as the power consumption [Wh] per unit time of the kneader, it becomes possible to numerically manage the specific surface area S. (10) In this embodiment, the design specific surface area S1 [m 2 The method further comprises a step (S22) of determining a design specific surface area, determining [(x / g)]. The method also comprises a step (S23) of measuring the change in specific surface area S2 from before the coating process to after the completion of the pressing process. The method further comprises a step (S24) of measuring the powder specific surface area S3 before the active material kneading process. When the target change in specific surface area in the kneading process is X, the target change in specific surface area X in the kneading process is calculated from X = S1 - S2 - S3 ... (Equation 1). This makes it possible to accurately calculate the target change in specific surface area X in the kneading process.

[0088] (11) The method further includes a step of setting a specific surface area change amount V (S26) for adjusting the change amount V in the specific surface area by adjusting the load L per unit time in the kneading process based on the target change amount X. This allows the change amount V in the specific surface area to be set appropriately.

[0089] (12) This embodiment can be suitably implemented in the negative electrode plate 2 of a lithium ion secondary battery 1 as a secondary battery. (Another example) In the present embodiment, the present invention has been described using the lithium ion secondary battery 1 as an example, but it can also be applied to other secondary batteries.

[0090] Although the present embodiment has been described using the negative electrode plate 2 as an example, the present invention can also be applied to the positive electrode plate 3. In this embodiment, a thin-plate lithium-ion secondary battery 1 for vehicle use is illustrated, but the present invention can also be applied to cylindrical batteries. Furthermore, the present invention is not limited to vehicle use, but can also be applied to batteries for ships, aircraft, and even stationary use.

[0091] The numerical values ​​and ranges shown in FIGS. 7, 10, and 11 and in this embodiment are examples, and the present invention is not limited to these numerical values ​​and ranges. 1, 2, 5, 8, and 9 are schematic illustrations of this embodiment, but the present invention is not limited to these drawings.

[0092] The flowcharts shown in Figures 3 and 4 are examples, and those skilled in the art can add, delete, or modify the procedures, and change the order of the procedures. It goes without saying that those skilled in the art can add, delete, or modify the components of the present invention, and change the order of the components, without departing from the scope of the claims. [Explanation of symbols]

[0093] 1...Lithium-ion secondary battery (secondary battery) 2...Negative electrode plate (electrode plate) 3...Positive electrode plate (electrode plate) 4...Separator 5... Coating machine 6...Press machine 11...Battery case 12...Electrode body 13...Electrolyte 14...Positive external terminal 15...Negative external terminal 21...Negative electrode current collector 22...Negative electrode composite material layer 22a...Negative electrode mixture paste (electrode mixture paste) 22b...Negative electrode active material particles 22c...binder 22d...solvent 22e…Anode active material particle surface 23...Negative electrode connection part 51...Nozzle 61...Press roller S…Specific surface area [m 2 / g] S1...(Completed battery) Design specific surface area [m 2 / g] S1′, S1″…(Completed battery) corrected specific surface area [m 2 / g] S2: (During the coating and pressing processes) change in specific surface area [m 2 / g] S3: Powder specific surface area (m 2 / g] X... (in the kneading process) target change amount [m 2 / g] (Formula 1)…X=S1-S2-S3 L...Load per unit time in the kneading process L [Wh] Ls…Target load [Wh] V...Change in specific surface area (in the kneading process) [m 2 / g] ΔS, ΔS′, ΔS″: Change in specific surface area [m 2 / g]

Claims

1. a kneading step of kneading a plurality of electrode materials including active materials in a kneader to produce an electrode composite paste to be used in manufacturing an electrode plate of a secondary battery; a coating step of coating the electrode mixture paste onto a current collector; a pressing step of pressing the electrode plate coated with the electrode mixture paste, The designed specific surface area S, which is the designed median value of the active material in the completed battery １ [m ２ / g]; and The change in specific surface area S from before the coating process to after the completion of the pressing process ２ [m ２ / g]; The powder specific surface area S of the active material before the kneading process ３ [m ２ / g] powder specific surface area measurement step; When the target change in specific surface area in the kneading step is X, X=S １ -S ２ -S ３ ...From (Equation 1), the target change in specific surface area X [m ２ / g], The step of setting the specific surface area change amount adjusts the load L per unit time in the kneading step based on the target change amount X, thereby adjusting the change amount V of the specific surface area.

1. A method for manufacturing an electrode plate for a secondary battery, comprising:

2. 2. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the step of setting the change in specific surface area adjusts the change in specific surface area V by changing the load L by changing the kneading resistance of a kneading machine in the kneading process.

3. 3. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein a relationship between a load L in the kneading step and a change in specific surface area in the kneading step is measured in advance, and the load L is adjusted based on the measurement result so that a target change in specific surface area X in the kneading step is achieved.

4. The method for manufacturing an electrode plate for a secondary battery according to any one of claims 1 to 3, characterized in that the step of setting the amount of change in specific surface area adjusts the load L in the kneading process based on the power consumption [Wh] per unit time of the kneader.

5. 5. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the step of setting the change in specific surface area adjusts the load L depending on the value of the solid content NV in the kneading process.

6. 6. The method for manufacturing an electrode plate for a secondary battery according to claim 5, wherein the solid content rate NV is adjusted by changing the amount of a solvent that is a material of the electrode mixture paste.

7. The method for manufacturing an electrode plate for a secondary battery according to any one of claims 1 to 6, characterized in that, prior to the step of determining the designed specific surface area, the active material to be used as the electrode material is changed to an active material having a different specific surface area, thereby adjusting the powder specific surface area S 3 [m 2 / g] of the active material before the kneading step.

8. The method for manufacturing an electrode plate for a secondary battery according to any one of claims 1 to 7, characterized in that the load L is adjusted by changing the shape and gap of the rotating members of the kneading machine to change the kneading resistance.

9. 9. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the load L is adjusted by changing the rotation speed of a kneading machine to change the kneading resistance.

10. 10. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the secondary battery is a lithium ion secondary battery.

11. 11. The method for manufacturing an electrode plate for a secondary battery according to claim 1, wherein the electrode plate is a negative electrode plate.

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