Secondary battery manufacturing method

Abstract

To provide a manufacturing method of a secondary battery which can suppress an over charge of a secondary battery, and provide a secondary battery.SOLUTION: A manufacturing method of a secondary battery according to an embodiment of the present invention contains: a first step S1 of specifying a negative electrode potential high change SOC region as a SOC region of which a potential change amount of a negative electrode is large in an objective secondary battery; a second step S2 of calculating a detection voltage correspondence SOC that corresponds to an over charge detection voltage for detecting an over charge of the secondary battery in the objective secondary battery; a third step S3 of determining a mixture basis weight in which the detection voltage correspondence SOC becomes within the negative electrode potential high change SOC region on the basis of the specified negative electrode potential high change SOC region, the calculated detection voltage correspondence SOC, and the mixture basis weight that is a mixture weight per unit area of the negative electrode to the mixture weight per unit area of a positive electrode of the objective secondary battery; and a fourth step S4 of manufacturing an electrode in accordance with the determined mixture basis weight.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Secondary batteries have traditionally been used in vehicles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles. Overcharging of secondary batteries can occur, causing their State of Charge (SOC) to exceed 100%, which can accelerate battery degradation and lead to the risk of the secondary battery emitting smoke or catching fire. Therefore, it is important to quickly detect and prevent overcharging of secondary batteries.

[0003] In this regard, Patent Document 1 discloses a nonaqueous electrolyte battery that uses lithium titanate for the negative electrode and is designed so that the ratio of the potential change of the negative electrode to the potential change of the positive electrode is 1 or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-91039 Summary of the Invention [Problem to be solved by the invention]

[0005] However, like the nonaqueous electrolyte battery disclosed in Patent Document 1, secondary batteries in which the ratio of the potential change in the negative electrode to the potential change in the positive electrode is 1 or more are quite limited. For example, in secondary batteries that use graphite for the negative electrode and nickel-cobalt-manganese for the positive electrode, the ratio of the potential change in the negative electrode is smaller than that of the positive electrode, so the technical idea of ​​making the ratio of the potential change in the negative electrode to the potential change in the positive electrode 1 or more cannot be applied. As a result, there has been a problem in that overcharging cannot be suppressed in various secondary batteries.

[0006] The present invention has been made to solve such problems, and an object of the present invention is to provide a method for manufacturing a secondary battery that can suppress overcharging of the secondary battery, and the secondary battery. [Means for solving the problem]

[0007] A method for manufacturing a secondary battery according to one embodiment of the present invention includes the steps of: a first step of identifying a negative electrode potential large change SOC region, which is an SOC region in which the amount of potential change of the negative electrode is large, for a target secondary battery; a second step of calculating, for a target secondary battery, a detection voltage-corresponding SOC corresponding to an overcharge detection voltage for detecting overcharge of the secondary battery; a third step of determining a composite weight ratio at which the detection voltage-corresponding SOC falls within the negative electrode potential increase change SOC region, based on the identified negative electrode potential increase change SOC region, the calculated detection voltage-corresponding SOC, and a composite weight ratio, which is the ratio of the composite weight per unit area of ​​the negative electrode to the composite weight per unit area of ​​the positive electrode of the target secondary battery; and a fourth step of manufacturing an electrode in accordance with the determined composite weight ratio.

[0008] The negative electrode potential high change SOC region can be identified based on the difference between a first differential value obtained by differentiating the change in the electrical quantity of the positive electrode OCP (Open Circuit Potential) of the target secondary battery with respect to the change in the electrical potential, and a second differential value obtained by differentiating the change in the electrical quantity of the OCV (Open Circuit Voltage) of the target secondary battery with respect to the change in the electrical potential.

[0009] The detection voltage-corresponding SOC can be calculated based on the specific surface area of ​​the positive electrode active material, the ratio of lithium to metals other than lithium in the positive electrode active material, and the positive electrode density.

[0010] The weight ratio of the composite material determined in the third step can be any value between 0.58 and 0.66.

[0011] The electrode manufactured in the fourth step has an overcharge detection voltage of 4.75 to 4.85 [V] and a specific surface area of ​​the positive electrode active material of 1.0 to 4.0 [cm 2 / g], the ratio of lithium to metals other than lithium in the positive electrode active material is 1.10 to 1.25, and the positive electrode density is 2.3 to 3.2 [g / cm 3 ] can be one of the following:

[0012] A secondary battery including a positive electrode and a negative electrode having a composite according to one embodiment of the present invention comprises: a ratio of the weight of the negative electrode composite material per unit area to the weight of the positive electrode composite material per unit area is 0.58 to 0.66; The overcharge detection voltage for detecting overcharge of the secondary battery is any one of 4.75 to 4.85 [V], The specific surface area of ​​the positive electrode active material is 1.0 to 4.0 cm 2 / g], The ratio of lithium to metals other than lithium in the positive electrode active material is 1.10 to 1.25, The positive electrode density is 2.3 to 3.2 [g / cm 3 ] can be one of the following: [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method for manufacturing a secondary battery that can prevent overcharging of the secondary battery, and the secondary battery. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a flowchart showing a method for manufacturing a secondary battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the trends of the differential value dQ / dV of the positive electrode OCP and the differential value dQ / dV of the OCV of a secondary battery according to one embodiment of the present invention. [Figure 3] FIG. 1 is a diagram showing the positive electrode OCP, negative electrode OCP, and OCV of two types of secondary batteries having different composite weight ratios. [Figure 4] FIG. 10 is a diagram showing an example of the results of multiple regression analysis based on an overcharge evaluation of a secondary battery. [Figure 5]FIG. 10 is a diagram showing negative electrode potential change SOC regions of secondary batteries having different composite weight ratios. [Figure 6] FIG. 10 is a diagram showing the relationship between the difference between the SOC corresponding to the detection voltage (SOCy) and the upper limit SOC (SOCx2) of other secondary batteries having different composite weight ratios, and the SOC corresponding to the detection voltage (SOCy). DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an exemplary embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a method for manufacturing a secondary battery according to one embodiment of the present invention. In step S1, an SOC region in which the amount of change in the negative electrode potential is large (hereinafter referred to as the "negative electrode large potential change SOC region") is identified for a target secondary battery. The negative electrode large potential change SOC region can be identified based on the difference in differential value dQ / dV obtained by differentiating the change in electric quantity dQ by the change in potential dV for each of the positive electrode OCP and OCV of the target secondary battery. The target secondary battery can use graphite as the negative electrode active material and nickel-cobalt-manganese or the like as the positive electrode active material.

[0016] 2 is a diagram showing the trends of the positive electrode OCP differential value dQ / dV and the OCV differential value dQ / dV of a secondary battery. The positive electrode OCP differential value dQ / dV corresponds to the first differential value. The OCV differential value dQ / dV corresponds to the second differential value.

[0017] As shown in FIG. 2, these differential values ​​dQ / dV have two peaks. In identifying the negative electrode potential high change SOC region, attention is focused on the high voltage peak. The range of SOC corresponding to the OCV and positive electrode OCP where there is a difference between the differential value dQ / dV of the positive electrode OCP and the differential value dQ / dV of the OCV (hereinafter referred to as the "differential value difference") near this peak corresponds to the negative electrode potential high change SOC region. The negative electrode potential high change SOC region is defined by a lower limit SOC and an upper limit SOC. As shown in FIG. 2, the OCV and positive electrode OCP where the differential value difference is large are located at the lower limit SOC (SOC x1 ) and the minimum value of the differential value dQ / dV corresponds to the upper limit SOC (SOC x2 ) corresponds to

[0018] When the differential value dQ / dV of a secondary battery having a composite weight ratio of 0.68, which is the ratio of the composite weight per unit area of ​​the negative electrode to the composite weight per unit area of ​​the positive electrode, was examined, it was found that the negative electrode potential high change SOC region of the secondary battery was in the range of 154 to 194%.

[0019] FIG. 3 shows an example of the positive electrode OCP, negative electrode OCP, and OCV of a secondary battery with a composite weight ratio of 0.809, and the positive electrode OCP, negative electrode OCP, and OCV of a secondary battery with a composite weight ratio of 0.688. As shown in FIG. 3, the negative electrode potential-increasing SOC region of a secondary battery with a low composite weight ratio is located on the lower SOC side compared to a secondary battery with a high composite weight ratio. Therefore, the negative electrode potential-increasing SOC region can be changed by changing the composite weight ratio. For example, changing the composite weight ratio from 0.809 to 0.688, i.e., decreasing the composite weight ratio, shifts the negative electrode potential-increasing SOC region toward the lower SOC side. In other words, the lower SOC limit and upper SOC limit become smaller. Note that increasing the composite weight ratio shifts the negative electrode potential-increasing SOC region toward the higher SOC side. In other words, the lower SOC limit and upper SOC limit become larger.

[0020] The degree of shift in the negative electrode potential-increasing SOC region depends on the degree of change in the composite weight ratio. For example, a 15% decrease in the composite weight ratio results in a 15% decrease in the upper and lower SOC limits. Similarly, a 3% decrease in the composite weight ratio results in a 3% decrease in the upper and lower SOC limits. Therefore, based on the finding that the negative electrode potential-increasing SOC region of a secondary battery with a composite weight ratio of 0.68 is 154 to 194%, the negative electrode potential-increasing SOC region of secondary batteries with other composite weight ratios can be derived. For example, as shown in Figure 5, the negative electrode potential-increasing SOC region of a secondary battery with a composite weight ratio of 0.58 (= 0.68 × 0.85) to 0.66 (= 0.68 × 0.97) can be derived to be 149 (= 154 × 0.97) to 169 (= 194 × 0.85)%.

[0021] In step S2, the SOC corresponding to the overcharge detection voltage for detecting overcharge of the target secondary battery (hereinafter referred to as "detection voltage corresponding SOC") is calculated. The detection voltage corresponding SOC can be calculated based on Equation 1.

number

[0022] Specifically, multiple secondary batteries with different design factors are prepared, each with a specific surface area of ​​the positive electrode active material, a Li / M ratio of the positive electrode active material, and a positive electrode density. These secondary batteries are subjected to an overcharge evaluation, and the SOC corresponding to the detection voltage of each secondary battery is calculated. Next, assuming that the relationship in Equation 1 holds, with the specific surface area of ​​the positive electrode active material, the Li / M ratio of the positive electrode active material, and the positive electrode density as explanatory factors and the SOC corresponding to the detection voltage as a target factor, multiple regression analysis is performed using the results of the overcharge evaluation of these secondary batteries to derive a1 to a3.

[0023] FIG. 4 is a diagram showing an example of the results of multiple regression analysis based on the overcharge evaluation of a secondary battery. In FIG. 4, the predicted value of SOC corresponding to the detection voltage and the actual measured value of SOC corresponding to the detection voltage are shown. The black dots in FIG. 4 indicate the relationship between the predicted value and the actual measured value of SOC corresponding to the detection voltage, and the dotted line represents this approximation line. As a result of the multiple regression analysis, the model formula is y=0.9985x, and the coefficient of determination R 2 was 0.8298. From these results, it was found that the SOC corresponding to the detection voltage can be predicted based on Equation 1 using the positive electrode Li / M ratio, the specific surface area of ​​the positive electrode active material, and the positive electrode density.

[0024] In the case of a secondary battery with a composite weight ratio of 0.58 to 0.66, if the overcharge detection voltage of the secondary battery is 4.75 to 4.85 [V], the positive electrode Li / M ratio is 1.10 to 1.25 and the positive electrode active material specific surface area is 1.0 to 4.0 [cm 2 / g], and the positive electrode density is 2.3 to 3.2 [g / cm 3 These values ​​are for the case where nickel cobalt manganese is used as the positive electrode active material.

[0025] In step S3, a composite weight ratio is determined based on the negative electrode potential change SOC region of the target secondary battery identified in step S1, the detection voltage-corresponding SOC of the target secondary battery calculated in step S2, and the composite weight ratio of the target secondary battery, such that the detection voltage-corresponding SOC falls within the negative electrode potential change SOC region. That is, a composite weight ratio is determined such that the lower limit SOC ≦ the detection voltage-corresponding SOC ≦ the upper limit SOC. If the detection voltage-corresponding SOC of the target secondary battery calculated in step S2 falls within the negative electrode potential change SOC region of the target secondary battery identified in step S1, the composite weight ratio of the target secondary battery is used as the desired composite weight ratio. On the other hand, if the detection voltage-corresponding SOC of the target secondary battery calculated in step S2 falls outside the negative electrode potential change SOC region of the target secondary battery identified in step S1, a composite weight ratio is determined such that the lower limit SOC ≦ the detection voltage-corresponding SOC after the change in the composite weight ratio ≦ the upper limit SOC.

[0026] For example, if the detection voltage-corresponding SOC of the target secondary battery calculated in step S2 is greater than the negative electrode potential-increasing SOC region of the target secondary battery identified in step S1, a composite weight ratio smaller than that of the target secondary battery is adopted. For example, if the overcharge detection voltage of the secondary battery is 4.75 to 4.85 V, the composite weight ratio may be set to any value between 0.58 and 0.66. The composite weight ratio of the secondary battery can be adjusted by increasing or decreasing the composite weight per unit area of ​​the positive electrode and / or the composite weight per unit area of ​​the negative electrode. When reducing the composite weight ratio of the secondary battery, the composite weight ratio of the secondary battery may be reduced by reducing the weight of the negative electrode composite. Alternatively, the composite weight ratio may be reduced by increasing the weight of the positive electrode composite. Furthermore, the composite weight ratio may be reduced by reducing the weight of the negative electrode composite and increasing the weight of the positive electrode composite.

[0027] Figure 6 shows the SOC (SOC) versus detection voltage for different secondary batteries with different composite weight ratios. y ) and upper SOC (SOC x2 ) and the difference in SOC corresponding to the detection voltage (SOC y 6 is a graph showing the relationship between the difference between the SOC corresponding to the detection voltage and the upper limit SOC (SOC y -SOC x2 ) is 0 or less, it means that the SOC corresponding to the detected voltage is equal to or less than the upper limit SOC.

[0028] As shown in Figure 6, the difference between the SOC corresponding to the detection voltage and the upper limit SOC for a secondary battery with a composite weight ratio of 0.809 is 0, which indicates that the SOC corresponding to the detection voltage and the upper limit SOC for this secondary battery are essentially the same. On the other hand, the difference between the SOC corresponding to the detection voltage and the upper limit SOC for a secondary battery with a composite weight ratio of 0.688 is -38%, which indicates that the SOC corresponding to the detection voltage for this secondary battery is 38% smaller than the upper limit SOC.

[0029] 6 also shows that for secondary batteries whose detection voltage-corresponding SOC is in a range below the upper limit SOC, the smaller the composite weight ratio, the smaller the detection voltage-corresponding SOC. Note that the degree of change in the negative electrode potential-high change SOC region due to changes in the composite weight ratio is greater than the degree of change in the detection voltage-corresponding SOC. Therefore, by adjusting the composite weight ratio, it is possible to manufacture an electrode in which the lower limit SOC ≦ the detection voltage-corresponding SOC after changing the composite weight ratio ≦ the upper limit SOC.

[0030] In step S4, an electrode is manufactured in accordance with the weight ratio of the composite material determined in step S3.

[0031] If the SOC corresponding to the detected voltage of the target secondary battery calculated in step S2 falls outside the negative electrode potential change SOC region of the target secondary battery identified in step S1, steps S1 and S2 are performed on the secondary battery whose composite weight ratio has been changed. This makes it possible to determine whether the SOC corresponding to the detected voltage of the secondary battery whose composite weight ratio has been changed falls within the negative electrode potential change SOC region of the secondary battery. Then, steps S1 to S4 are repeatedly performed until the SOC corresponding to the detected voltage of the secondary battery whose composite weight ratio has been changed falls within the negative electrode potential change SOC region of the secondary battery.

[0032] In the above-described embodiment, in the first step, the negative electrode potential-increasing SOC region of the target secondary battery is identified. In the second step, the detection voltage-corresponding SOC of the target secondary battery is calculated. In the third step, a composite material weight ratio is determined based on the identified negative electrode potential-increasing SOC region, the calculated detection voltage-corresponding SOC, and the composite material weight ratio of the target secondary battery, such that the detection voltage-corresponding SOC falls within the negative electrode potential-increasing SOC region. In the fourth step, an electrode is manufactured according to the determined composite material weight ratio.

[0033] In the negative electrode potential high change SOC region, where the negative electrode potential change is large, the OCV value increases rapidly as the secondary battery is charged. Therefore, by configuring the composite weight ratio of the secondary battery so that the detection voltage corresponding SOC is within the negative electrode potential high change SOC region, the OCV of the secondary battery quickly reaches the overcharge detection voltage. Therefore, compared to a configuration in which the OCV increases gradually as the secondary battery is charged, it is easier to detect that the OCV has reached the overcharge detection voltage, and overcharging of the secondary battery can be quickly suppressed.

[0034] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in other embodiments, a secondary battery may be manufactured in which the detection voltage corresponding SOC falls within the negative electrode potential-dependent SOC region by adjusting not only the composite weight ratio but also the specific surface area of ​​the positive electrode active material, the Li / M ratio of the positive electrode active material, and / or the positive electrode density shown in Equation 1 to adjust the detection voltage corresponding SOC.

[0035] In another embodiment, a secondary battery may be manufactured in which the detection voltage corresponding SOC falls within the negative electrode potential large change SOC region by adjusting the detection voltage corresponding SOC by changing the specific surface area of ​​the positive electrode active material, the Li / M ratio of the positive electrode active material, and / or the positive electrode density shown in Formula 1 without adjusting the composite weight ratio. [Explanation of symbols]

[0036] S1 First step S2 Second process S3 Third process S4 Fourth process

Claims

1. A first step of identifying a high negative electrode potential change SOC region, which is a SOC (State Of Charge) region in which the amount of potential change of the negative electrode is large, for a target secondary battery that uses graphite as a negative electrode active material and nickel-cobalt-manganese as a positive electrode active material; a second step of calculating, for the target secondary battery, a detection voltage corresponding SOC corresponding to an overcharge detection voltage for detecting overcharge of the secondary battery; a third step of determining a composite weight ratio that makes the detection voltage corresponding SOC fall within the negative electrode potential large change SOC region, based on the identified negative electrode potential large change SOC region, the calculated detection voltage corresponding SOC, and a composite weight ratio that is the ratio of the composite weight per unit area of ​​the negative electrode to the composite weight per unit area of ​​the positive electrode of the target secondary battery; a fourth step of manufacturing an electrode in accordance with the determined composite weight ratio; A method for manufacturing a secondary battery, comprising:

2. 2. The method for manufacturing a secondary battery according to claim 1, wherein the negative electrode potential large change SOC region is identified based on a difference between a first derivative value obtained by differentiating a change in an electrical quantity of a positive electrode OCP (Open Circuit Potential) of the target secondary battery with respect to a change in an electrical potential, and a second derivative value obtained by differentiating a change in an electrical quantity of an OCV (Open Circuit Voltage) of the target secondary battery with respect to a change in an electrical potential.

3. 3. The method for manufacturing a secondary battery according to claim 1, wherein the detection voltage-corresponding SOC is calculated based on a specific surface area of ​​a positive electrode active material, a ratio of lithium to metals other than lithium in the positive electrode active material, and a positive electrode density.

4. 4. The method for manufacturing a secondary battery according to claim 1, wherein the weight ratio of the composite material determined in the third step is any one of 0.58 to 0.

66.

5. 5. The method for producing a secondary battery according to claim 4, wherein the electrode produced in the fourth step has an overcharge detection voltage of 4.75 to 4.85 V, a specific surface area of ​​the positive electrode active material of 1.0 to 4.0 cm / g, a ratio of lithium to metals other than lithium in the positive electrode active material of 1.10 to 1.25, and a positive electrode density of 2.3 to 3.2 g / cm.

Images