Manufacturing method of secondary battery

Abstract

To improve the battery performance.SOLUTION: A secondary battery includes a positive electrode plate formed by applying a positive electrode composite material containing a positive electrode active material to a substrate that serves as a current collector. The BET specific surface area of the positive electrode active material that is the raw material of the positive electrode composite material is defined as the "powder BET", and the BET specific surface area of the positive electrode composite material in a state in which the positive electrode composite material applied to the substrate forms a positive electrode plate together with the substrate is defined as the "plate BET". Furthermore, the difference value obtained by subtracting the "powder BET" from the "plate BET" is defined as "ΔBET". During the manufacture of the secondary battery, this "ΔBET" is controlled to 0.3 square meters / gram or less.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a secondary battery. [Background technology]

[0002] Conventionally, for example, some secondary batteries such as lithium ion secondary batteries have their electrode plates formed by coating an electrode mixture containing an electrode active material on a substrate serving as a current collector. Furthermore, in such secondary batteries, the specific surface area of ​​the electrode active material contained in the electrode mixture has a large effect on the battery performance. For example, in Patent Documents 1 to 3, the specific surface area of ​​the electrode active material, which is a porous powder, is specified by a gas adsorption measurement method using the BET method, that is, the BET method. The battery performance is improved by controlling the BET specific surface area by the BET method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-238415 A [Patent Document 2] Patent Publication No. 2021-51880 [Patent Document 3] JP 2023-93555 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in applications requiring high levels of battery performance, such as electric vehicles, further improvements in performance are being sought on a daily basis, and therefore further improvements are being sought in the above-mentioned conventional technologies in order to meet the evolving requirements. [Means for solving the problem]

[0005] Various aspects of a method for producing a secondary battery that solves the above problems will be described. Aspect 1 is a method for manufacturing a secondary battery including a positive electrode plate formed by coating a substrate serving as a current collector with a positive electrode composite containing a positive electrode active material, in which a BET specific surface area of ​​the positive electrode active material serving as a raw material for the positive electrode composite is defined as a powder BET, a BET specific surface area of ​​the positive electrode composite in a state in which the coated positive electrode composite forms the positive electrode plate together with the substrate is defined as a plate BET, and a difference value obtained by subtracting the powder BET from the plate BET is defined as a ΔBET, and the ΔBET is controlled to be 0.3 square meters / gram or less.

[0006] That is, regardless of the values ​​of "powder BET" and "plate BET", excellent "overcharge resistance" can be ensured by keeping "ΔBET" at 0.3 m2 / gram or less. As for the "output characteristics", even if the value of "ΔBET" changes, there is no significant change in the relationship with "ΔBET". Therefore, with the above configuration, it is possible to achieve both excellent "output characteristics" and "overcharge resistance".

[0007] Aspect 2 is the method for producing a secondary battery according to Aspect 1, comprising the steps of: mixing raw materials for the positive electrode composite; kneading the mixed positive electrode composite; applying the kneaded positive electrode composite to the substrate; drying the applied positive electrode composite; and pressing the dried positive electrode composite, wherein the ΔBET is controlled by adjusting at least any of the steps.

[0008] According to the above-mentioned configuration, it is possible to manufacture a positive electrode plate for a secondary battery having excellent output characteristics and overcharge resistance. A third aspect of the present invention relates to the method for producing a secondary battery according to the second aspect, wherein the pressing pressure of the positive electrode mixture is adjusted.

[0009] That is, the higher the pressing pressure, the easier it is for the particles of the positive electrode active material contained in the positive electrode mixture to be crushed into smaller particles. In other words, the specific surface area increases, and the "plate BET" value increases. Therefore, by keeping the pressing pressure low, the "ΔBET" value can be kept low. This allows the "ΔBET" to be controlled with a simple configuration.

[0010] A fourth aspect of the present invention is the method for producing a secondary battery according to the second or third aspect, further comprising adjusting the density of the positive electrode mixture. That is, the smaller the particles of the positive electrode active material are contained, the higher the density of the positive electrode composite material is likely to be. In other words, the more particles with a large specific surface area are contained, the higher the value of the "plate BET". Furthermore, the density of the positive electrode composite material can be adjusted by changing the control parameters of the mixing process, the kneading process, and the drying process in addition to the pressing process. Therefore, according to the above configuration, the "ΔBET" can be controlled with a simple configuration.

[0011] Aspect 5 is the method for producing a secondary battery according to any one of Aspects 2 and 3, in which a plurality of types of the positive electrode active materials having different values ​​of ΔBET are mixed as raw materials for the positive electrode mixture. That is, by mixing a lot of electrode active material having a "ΔBET" larger than "0.3" (ΔBET>0.3) with a lot having a "ΔBET" smaller than "0.3" (ΔBET<0.3), the "ΔBET" after mixing can be controlled to "0.3" or less. Therefore, with the above-mentioned configuration, the "ΔBET" can be controlled with a simple configuration. Effect of the Invention

[0012] According to the present invention, it is possible to improve the battery performance. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view of a secondary battery. [Diagram 2] FIG. 2 is an exploded view of the electrode assembly. [Diagram 3]FIG. 3 is a side view of the secondary battery. [Figure 4] FIG. 4 is a flowchart showing the manufacturing process of an electrode sheet that becomes a plate of a secondary battery. [Diagram 5] FIG. 5 is a graph showing the relationship between "ΔBET" and the "overcharge tolerance" of a secondary battery. [Figure 6] FIG. 6 is a graph showing the relationship between "ΔBET" and the "output characteristics" of a secondary battery. [Figure 7] FIG. 7 is a table showing the test results of the secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a method for manufacturing a secondary battery will be described with reference to the drawings. (Lithium-ion secondary battery) 1, the secondary battery 1 includes an electrode assembly 10 in which a positive electrode 3, a negative electrode 4, and a separator 5 are integrated, and a case 20 that houses the electrode assembly 10. The secondary battery 1 of this embodiment has a configuration as a lithium ion secondary battery in which the electrode assembly 10 in the case 20 is impregnated with a non-aqueous electrolyte solution (not shown).

[0015] More specifically, in the secondary battery 1 of this embodiment, the positive electrode 3, the negative electrode 4, and the separator 5 are laminated with a sheet-like outer shape. Then, by winding up the laminate of the positive electrode 3, the negative electrode 4, and the separator 5, an electrode body 10 is formed in which the positive and negative electrodes and the separators 5 are alternately arranged in the radial direction with the separator 5 sandwiched between the positive electrode 3 and the negative electrode 4.

[0016] The case 20 of this embodiment includes a case body 21 having a flat, substantially rectangular box shape, and a lid member 22 that closes an open end 21x of the case body 21. The electrode body 10 of this embodiment has a flat outer shape that corresponds to the box shape of the case 20.

[0017] (Electrode sheet and electrode body) More specifically, as shown in FIG. 2, in the secondary battery 1 of this embodiment, the positive electrode 3 and the negative electrode 4 each have a configuration as an electrode sheet 35 including a current collector 31 having a sheet-like outer shape and an electrode mixture layer 32 laminated on this current collector 31.

[0018] Specifically, for the electrode sheet 35P for the positive electrode 3, an electrode mixture containing lithium transition metal oxide as a positive electrode active material, that is, a composite paste 37P as a positive electrode mixture, is applied to a substrate 36P made of aluminum or the like that constitutes the positive electrode current collector 31P. For the electrode sheet 35N for the negative electrode 4, an electrode mixture in the form of a slurry containing a carbon-based material that serves as a negative electrode active material, that is, a composite paste 37N as a negative electrode mixture, is applied to a substrate 36N made of copper or the like that constitutes the negative electrode current collector 31N. Furthermore, each of these composite pastes 37P and 37N contains a binder. In the secondary battery 1 of this embodiment, the composite pastes 37P and 37N are dried to form the corresponding positive electrode composite layer 32P and negative electrode composite layer 32N on the positive and negative electrode sheets 35P and 35N, respectively.

[0019] Furthermore, in the secondary battery 1 of this embodiment, the positive and negative electrode sheets 35P, 35N are each shaped into a belt-like shape. The electrode body 10 of this embodiment has a configuration as a wound body in which the positive and negative electrode sheets 35P, 35N, which are stacked with the separator 5 sandwiched therebetween, are wound around a winding axis 10x extending in the width direction of the belt-like shape (the left-right direction in FIG. 2).

[0020] 2, the separator 5 and each electrode sheet 35 are wound in such a manner that the electrode sheet 35P constituting the positive electrode 3 is wound inward. However, this figure is one example showing the structure of the electrode body 10, and the separator 5 and each electrode sheet 35 may be wound in such a manner that the electrode sheet 35N constituting the negative electrode 4 is wound inward. This determines whether the electrode sheet 35 arranged on the outermost shell of the electrode body 10 is the electrode sheet 35P constituting the positive electrode 3 or the electrode sheet 35N constituting the negative electrode 4.

[0021] 1 to 3, the cover member 22 of the case 20 is provided with a positive electrode terminal 38P and a negative electrode terminal 38N that protrude to the outside of the case 20. Furthermore, each electrode sheet 35 has an uncoated portion 39 where the electrode mixture layer 32 is not formed on the current collector 31. The secondary battery 1 of this embodiment is configured such that, by utilizing these uncoated portions 39, the electrode sheet 35P constituting the positive electrode 3 and the positive electrode terminal 38P are electrically connected, and the electrode sheet 35N constituting the negative electrode 4 and the negative electrode terminal 38N are electrically connected.

[0022] Specifically, the electrode body 10 of this embodiment is housed in the case 20 with its winding axis 10x aligned along the longitudinal direction (left-right direction in FIG. 1) of the cover member 22, which is an elongated, generally rectangular plate. Furthermore, in this state, an uncoated portion 39P of an electrode sheet 35P constituting the positive electrode 3 is connected to a positive electrode terminal 38P via a connecting member 40P. Similarly, an uncoated portion 39N of an electrode sheet 35N constituting the negative electrode 4 is connected to a negative electrode terminal 38N via a connecting member 40N.

[0023] Furthermore, an electrolyte solution 45 is injected into the case 20. That is, the electrolyte solution 45 of the secondary battery 1 having a configuration as a lithium ion secondary battery is one in which a lithium salt serving as a supporting salt is dissolved in an organic solvent. Thus, the secondary battery 1 of this embodiment is configured such that the electrode body 10 sealed in the case 20 is impregnated with the electrolyte solution 45.

[0024] (Electrode sheet manufacturing process) 4, in the process of manufacturing the electrode sheet 35 forming the secondary battery 1 of this embodiment, first, the electrode active material, binder, thickener, etc., which are raw materials for the electrode mixture, are mixed (step 101). Then, the mixed electrode mixture is kneaded (step 102).

[0025] Next, the electrode mixture kneaded in step 102 is applied to the corresponding substrates 36P and 36N in the state of the above-mentioned composite pastes 37P and 37N (step 103, see FIG. 2). Next, the electrode mixture applied in step 103 is dried (step 104). In this embodiment, the application process in step 102 and the drying process in step 103 are continuously performed. Furthermore, in a state in which the electrode mixture applied on the substrate 36 forms the corresponding positive and negative electrodes, that is, the positive and negative electrodes, respectively, these are pressed to increase the adhesive strength of the electrode mixture to the substrate 36 (step 105). Then, in the secondary battery 1 of this embodiment, the electrode sheet 35 shaped into a foil extending in a strip shape as described above is manufactured through a cutting process (step 106) performed after the pressing process.

[0026] (Electrode sheet manufacturing process and specific surface area of ​​electrode active material) In addition, the specific surface area of ​​the electrode active material used in the secondary battery 1 changes during the manufacturing process of the electrode sheet 35 that becomes the electrode plate. Specifically, the specific surface area of ​​the electrode active material becomes smaller by performing the kneading step (step 102) than before the raw materials are mixed (see FIG. 4, step 101). This is because the kneading step causes a binder to adhere to the electrode active material in the electrode mixture. Furthermore, the specific surface area of ​​the electrode active material in the electrode mixture applied to the substrate 36 becomes larger than before the drying step (step 104) by performing the drying step. This is because when the electrode mixture applied to the substrate 36 dries, the binder contained in the electrode mixture moves with the evaporation of the solvent. In other words, this is because the binder contained in the electrode mixture is detached from the electrode active material to which it is attached due to the occurrence of so-called migration. The specific surface area of ​​the electrode active material becomes larger than that before the pressing step (step 105) by crushing the electrode active material.

[0027] (Powder BET, Plate BET, and ΔBET) Here, the specific surface area of ​​a porous powder such as an electrode active material is measured, for example, by a gas adsorption measurement method using the BET method, that is, the BET method. The unit is "square meters / gram." The specific surface area measured by the BET method is called the "BET specific surface area." In this embodiment, the specific surface area of ​​the electrode active material is measured by the BET method using nitrogen as the adsorption gas.

[0028] Specifically, in the secondary battery 1 of this embodiment, the BET specific surface area of ​​the positive electrode active material that is the raw material of the positive electrode composite is measured as the "powder BET". In addition, the BET specific surface area of ​​the positive electrode composite in a state in which the positive electrode composite coated on the substrate 36P forms a positive electrode plate together with the substrate 36P is measured as the "plate BET". That is, the "powder BET" is a value measured before the blending process of step 101 in FIG. 4, and the "plate BET" is a value measured after the pressing process of step 105 in the same figure. Furthermore, in the secondary battery 1 of this embodiment, the difference value obtained by subtracting the "powder BET" from the "plate BET" is "ΔBET". The units of these "powder BET", "plate BET", and "ΔBET" are "square meters / gram". In addition, the secondary battery 1 of this embodiment is configured to improve the battery performance by controlling the "ΔBET".

[0029] That is, in the secondary battery 1, the "output characteristics" tend to improve when the specific surface area of ​​the positive electrode active material contained in the positive electrode composite is large. On the other hand, a small specific surface area of ​​the positive electrode active material is advantageous for improving the "overcharge resistance". However, by focusing on the above-mentioned "ΔBET", it is possible to change the relationship between the "overcharge resistance" and the specific surface area of ​​the positive electrode active material.

[0030] More specifically, when the relationship between "ΔBET" and "overcharge tolerance" is plotted on an orthogonal coordinate system (XY coordinate system) as shown in Figure 5, a change in the relationship between "ΔBET" and "overcharge tolerance" can be seen at the boundary of "ΔBET=0.3." Specifically, a decrease in the "overcharge tolerance" was confirmed in the region where "ΔBET" is greater than "0.3" (ΔBET>0.3).

[0031] On the other hand, when the relationship between "ΔBET" and "output characteristics" is plotted as shown in Figure 6, even if the value of "ΔBET" changes, there is no significant change in the relationship between "ΔBET" and "output characteristics".

[0032] In consideration of this, in the secondary battery 1 of this embodiment, the "ΔBET" of the positive electrode plate is controlled to "0.3 or less" (ΔBET≦0.3). Specifically, when manufacturing the electrode sheet 35P that becomes the positive electrode plate of the secondary battery 1, the "ΔBET" is controlled by adjusting at least one of the steps shown in FIG. 4. More specifically, for example, in the pressing step of step 105 in FIG. 4, the pressing pressure when compressing the positive electrode composite layer 32P together with the base material 36P in the thickness direction is adjusted. Note that the pressing pressure is synonymous with the pressing load. In addition, the density of the positive electrode composite is adjusted by changing the control parameters of the blending step of step 101, the kneading step of step 102, the drying step of step 104, and the like.

[0033] For each sample shown in Fig. 5 and Fig. 6, the variation range of "powder BET" is "1.88 to 2.8". Also, the variation range of "plate BET" is "1.92 to 3.12". The number of samples shown in Fig. 5 is "60", and the number of samples shown in Fig. 6 is "20".

[0034] As for "overcharge resistance", an evaluation test was carried out using a charge / discharge device while the secondary battery 1 for evaluation, which was made using each sample, was adjusted to a lower limit voltage and kept at a predetermined temperature. Specifically, the holding temperature was set to a range of 25°C to 60°C (e.g., 25°C). Furthermore, charging was performed at a constant current between 1C and 50C until the voltage of the secondary battery 1 reached an upper limit voltage (e.g., 5.0V) at which no abnormality due to overheating would occur. Then, the time required from a predetermined timing start voltage to the upper limit voltage was measured, and the measured value was used as an index value for "overcharge resistance".

[0035] That is, the measurement results of the charging test, that is, the longer the time required to reach the upper limit voltage during charging, the less likely abnormalities due to overheating will occur. In other words, this means that the overcharge resistance is excellent. In addition, in the graph of FIG. 5, the value of "overcharge resistance" shown on the vertical axis is based on the evaluation secondary battery 1 created using a sample with "ΔBET=0.3". And for each sample, the "time required to reach the upper limit voltage" is expressed as a "percentage (percentage)".

[0036] In addition, the so-called "discharge resistance" was measured as an index of the "output characteristics". Specifically, the evaluation secondary battery 1 prepared using each sample was held at a constant temperature in a thermostatic chamber and discharged at a constant current using a charge / discharge device. The holding temperature is set to a range of about -30°C to 60°C (for example, 25°C). Then, the resistance value when the battery is discharged at a constant current between 1C and 50C for a predetermined time (for example, 10 seconds) is calculated. In this case, the discharge may be performed until the "lower limit voltage of the secondary battery 1" is reached instead of the "predetermined time". That is, the smaller the value of the "discharge resistance" measured as described above, the smaller the overvoltage is, and the longer the time until the lower limit voltage is reached. In other words, it means that the output characteristics are excellent. In the graph of FIG. 6, the value of the "output characteristics" shown on the vertical axis is a value expressed as a percentage (percentage notation) based on the evaluation value based on the "discharge resistance" of each sample, using the evaluation secondary battery 1 prepared using the sample with "ΔBET=0.3" as a reference.

[0037] (action) That is, generally, the higher the pressing pressure, the easier it is to crush the particles of the positive electrode active material contained in the positive electrode composite into smaller particles. Furthermore, the smaller the particles of the positive electrode active material contained in the positive electrode composite, the easier it is to increase the density of the positive electrode composite. In other words, by making the above-mentioned adjustments, the "plate BET" of the state in which the positive electrode composite coated on the substrate 36P forms a positive electrode plate together with the substrate 36P changes. This makes it possible to control the "ΔBET" as described above.

[0038] Next, the effects of this embodiment will be described. (1) The secondary battery 1 includes an electrode sheet 35P as a positive electrode plate formed by applying a composite paste 37P containing a positive electrode active material to a substrate 36P as a current collector 31. The BET specific surface area of ​​the positive electrode active material that is the raw material of the positive electrode composite is defined as "powder BET", and the BET specific surface area of ​​the positive electrode composite in a state in which the positive electrode composite applied to the substrate 36P forms a positive electrode plate together with the substrate 36P is defined as "plate BET". Furthermore, the difference value obtained by subtracting the "powder BET" from the "plate BET" is defined as "ΔBET". During the manufacture of the secondary battery 1, this "ΔBET" is controlled to 0.3 square meters / gram or less.

[0039] That is, regardless of the values ​​of "powder BET" and "plate BET", excellent "overcharge resistance" can be ensured by keeping "ΔBET" at 0.3 m2 / gram or less. As for the "output characteristics", even if the value of "ΔBET" changes, there is no significant change in the relationship with "ΔBET". Therefore, according to the above configuration, it is possible to achieve both excellent output characteristics and overcharge resistance.

[0040] (2) When manufacturing the electrode sheet 35P that will become the positive electrode plate, first, the electrode active material that will be the raw material of the electrode mixture is prepared (step 101), and the prepared electrode mixture is kneaded (step 102). Next, the kneaded electrode mixture is applied to the base material 36P in the form of a mixture paste 37N (step 103). Furthermore, the electrode mixture applied to the base material 36P is dried (step 104), and the dried electrode mixture is pressed (step 105). Then, by adjusting at least one of these steps, the "ΔBET" is controlled. This allows the manufacture of a positive electrode plate for the secondary battery 1 that is excellent in output characteristics and overcharge resistance.

[0041] (3) In the pressing process, the pressing pressure of the positive electrode composite is adjusted to control “ΔBET”. That is, the higher the pressing pressure, the easier it is for the particles of the positive electrode active material contained in the positive electrode mixture to be crushed into smaller particles. In other words, the specific surface area increases, and the "plate BET" value increases. Therefore, by keeping the pressing pressure low, the "ΔBET" value can be kept low. This allows the "ΔBET" to be controlled with a simple configuration.

[0042] (4) “ΔBET” is controlled by adjusting the density of the positive electrode mixture. That is, the smaller the particles of the positive electrode active material are contained, the higher the density of the positive electrode composite material is likely to be. In other words, the more particles with a large specific surface area are contained, the higher the value of the "plate BET". Furthermore, the density of the positive electrode composite material can be adjusted by changing the control parameters of the mixing process, the kneading process, and the drying process in addition to the pressing process. Therefore, according to the above configuration, the "ΔBET" can be controlled with a simple configuration.

[0043] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0044] In the above embodiment, the electrode active material having a variation range of "powder BET" of "1.88 to 2.8" and a variation range of "plate BET" of "1.92 to 3.12" was used as the raw material of the electrode composite. However, the present invention is not limited to this, and the "powder BET" and "plate BET" of the electrode active material may have any value. It is sufficient that "ΔBET" is "0.3" or less.

[0045] In the above embodiment, the adjustment of the pressing pressure in the pressing process (see FIG. 4, step 105) and the adjustment of the density of the positive electrode composite are exemplified as methods for controlling “ΔBET”. However, “ΔBET” may be controlled to 0.3 m2 / gram or less by other methods.

[0046] For example, a plurality of types of positive electrode active materials having different values ​​of "ΔBET" may be mixed as raw materials for the positive electrode composite. Specifically, in the mixing process, when there are a plurality of lots of electrode active materials to be raw materials for the electrode composite and the "ΔBET" of each lot is known, the electrode active materials from different lots are mixed in the mixing process. That is, an electrode active material from a lot having a "ΔBET" greater than "0.3" (ΔBET>0.3) is mixed with an electrode active material from a lot having a "ΔBET" smaller than "0.3" (ΔBET<0.3). Then, the "ΔBET" after the mixing may be controlled to be equal to or less than "0.3". Even if such a method is adopted, the same effect as that of the above embodiment can be obtained.

[0047] In the above embodiment, the electrode body 10 has a configuration as a wound body, but the positive and negative electrode sheets 35P, 35N stacked with the separator 5 sandwiched therebetween do not necessarily have to be wound. That is, the shape of the positive electrode plate is arbitrary. And, the secondary battery 1 to which this positive electrode plate is applied does not necessarily have to be a lithium ion secondary battery, and may be applied to other nonaqueous electrolyte secondary batteries.

[0048] The terminal shapes of the positive electrode terminal 38P and the negative electrode terminal 38N are not limited to the shapes shown in Fig. 1 and may be changed as desired. The shape of the case 20 that defines the outer shape of the secondary battery 1 is also not necessarily limited to a flat rectangular box shape and may be changed as desired, for example, to a cylindrical shape. EXAMPLES

[0049] Examples will be described below to more specifically explain the configuration and effects of the present invention, but the present invention is not limited to these examples. FIG. 7 is a table showing the results of the performance tests carried out on the secondary battery 1. As shown in FIG.

[0050] More specifically, the "specimens 1" to "specimens 5" shown in the table in the figure have different values ​​for the BET specific surface area of ​​the positive electrode composite constituting the positive electrode plate, i.e., the three state values ​​shown in the above embodiment, namely, "powder BET", "plate BET", and "ΔBET". The unit of each of these values ​​is "square meters / gram" (omitted below).

[0051] Specifically, the "powder BET" values ​​of "specimen 1" and "specimen 5" are both "2.8", and the "powder BET" values ​​of "specimen 2" to "specimen 4" are "2.3". The "plate BET" values ​​of "specimen 1" and "specimen 5" are "3.1" and "2.9", respectively, and the "plate BET" values ​​of "specimen 2" to "specimen 4" are "2.8", "2.5", and "2.9", respectively, in that order. As a result, the "ΔBET" is "0.3" for "specimen 1", "0.5" for "specimen 2", "0.2" for "specimen 3", "0.6" for "specimen 4", and "0.1" for "specimen 5".

[0052] In this performance test, as in the above embodiment, the "time required to reach the upper limit voltage at which no abnormality occurs due to overheating during charging" was used as an index of "overcharge resistance", and the "discharge resistance" was used as an index of "output characteristics". In the table of Fig. 7, the "overcharge resistance" and "output characteristics" of each test specimen are shown in "percentage notation" based on "test specimen 1" with "ΔBET=0.3", which was the boundary value of the battery performance in the above embodiment.

[0053] That is, when compared with the standard "Test specimen 1" and "Test specimen 5," "Test specimen 5," which has the same "Powder BET" value as "Test specimen 1," also has an "output characteristic" of "100%." ​​And, since "Test specimen 5" has a "ΔBET" smaller than "0.3," it has a better "overcharge resistance" (104%) than the standard "Test specimen 1."

[0054] In addition, the "test specimens 2" to "test specimens 4", which have a smaller "powder BET" value than "test specimen 1", all have "output characteristic" values ​​of "93%", which are lower than "test specimen 1". However, when comparing the "overcharge resistance" of these "test specimens 2" to "test specimens 4", "test specimen 3", whose "ΔBET" is smaller than "0.3", has a better "overcharge resistance" than "test specimen 1". On the other hand, for "test specimens 4" and "test specimens 6", whose "ΔBET" is larger than "0.3", the "overcharge resistance" is lower than that of the standard "test specimen 1". From the above results, it was confirmed that it is preferable to control the "ΔBET" to 0.3 square meters / gram or less when manufacturing the positive plate. [Explanation of symbols]

[0055] 1…Secondary battery 31...Current collector 35P…Electrode sheet (positive electrode plate) 36P…Base material 37P…Composite paste (positive electrode composite)

Claims

1. A method for manufacturing a secondary battery having a positive electrode plate formed by coating a substrate serving as a current collector with a positive electrode mixture containing a positive electrode active material, comprising the steps of: The BET specific surface area of ​​the positive electrode active material that is a raw material of the positive electrode mixture is defined as powder BET, The BET specific surface area of ​​the positive electrode mixture in a state in which the applied positive electrode mixture forms the positive electrode plate together with the base material is defined as an electrode plate BET, A difference value obtained by subtracting the powder BET from the electrode plate BET is defined as ΔBET, A method for manufacturing a secondary battery, in which the ΔBET is controlled to 0.3 m 2 / g or less.

2. A step of mixing raw materials for the positive electrode mixture; kneading the prepared positive electrode mixture; applying the mixed positive electrode mixture to the substrate; drying the coated positive electrode mixture; and pressing the positive electrode mixture after the drying. The ΔBET is controlled by adjusting at least one of the steps. The method for producing the secondary battery according to claim 1 .

3. The method for producing a secondary battery according to claim 2 , wherein a pressing pressure of the positive electrode mixture is adjusted.

4. The method for producing a secondary battery according to claim 2 , wherein the density of the positive electrode mixture is adjusted.

5. The method for producing a secondary battery according to claim 2 , wherein a plurality of types of the positive electrode active materials having different values ​​of the ΔBET are mixed as raw materials for the positive electrode mixture.

Images