JP5668663B2 - Secondary battery inspection method and secondary battery manufacturing method - Google Patents

Description

  The present invention relates to a secondary battery inspection method and manufacturing method.

  In recent years, secondary batteries such as lithium ion batteries have been widely developed. For example, Patent Document 1 discloses a method for inspecting a lithium ion battery. In the inspection method of Patent Document 1, a voltage drop after a lithium ion battery is left for a predetermined time in an environment of 45 ° C. or higher is required.

  Patent Document 2 discloses a method for inspecting a short circuit of a nickel-hydrogen secondary battery. In the method of Patent Document 2, a short circuit inspection is performed while pressurizing the secondary battery.

Japanese Patent Laid-Open No. 2005-158643 JP 2001-236985 A

  Secondary batteries for automobiles are used in harsher environments. Therefore, it is necessary to perform the pre-shipment inspection of the secondary battery in various environments. For example, in order to start the engine at a low temperature, it is necessary to perform an inspection in a lower temperature environment. As a more specific example, assume that it is desired to confirm a 30% SOC (State of Charge) output at −30 ° C. In this case, the secondary battery is installed in an environment of −30 ° C., and the SOC 30% output is measured.

  However, since measurement in an environment of −30 ° C. is difficult from the viewpoint of cost and time, it is desirable to measure near room temperature. Therefore, it is desirable to perform a measurement having a high correlation with −30 ° C. and SOC 30% output near room temperature. When the measurement under the low temperature environment is replaced with the measurement under the room temperature environment, the inventors of the present application have found that there are the following problems.

  In a battery with a capacity ratio of 1.4 or less, there is a correlation even if only the temperature is changed without changing the SOC. That is, even in the same SOC, the correlation between the measurement under the low temperature environment and the measurement under the room temperature environment is high. However, in a battery having a large capacity ratio, there is no correlation between measurement in a room temperature environment and measurement in a low temperature environment.

  A secondary battery having a large capacity ratio has a large amount of negative electrode with respect to the positive electrode, and the ratio of the negative electrode resistance to the battery resistance becomes extremely small. The battery output under a low temperature environment is affected by the negative electrode Li ion acceptability. Therefore, when the measurement is performed in a room temperature environment, there is a problem that an accurate inspection cannot be performed without the contribution of the negative electrode being reflected.

  The present invention has been made in view of the above problems, and provides a secondary battery inspection method capable of accurately and easily inspecting a secondary battery, and a highly productive secondary battery manufacturing method. The purpose is to do.

  The inspection method according to the first aspect of the present invention includes a step of setting the SOC of a secondary battery having a capacity ratio of 1.5 or more to 3 to 15%, and an SOC of 3 in an environment of 10 to 30 ° C. Measuring the resistance of the secondary battery of ˜15%. Thereby, since a measurement with a high correlation with a low temperature environment can be performed without installing a secondary battery in a low temperature environment, it can test | inspect accurately and simply.

  The inspection method according to the second aspect of the present invention is characterized in that, in the step of setting the SOC, the SOC of the secondary battery is set to 4 to 10%. Thereby, measurement with higher correlation can be performed, and more accurate inspection can be performed.

  The inspection method according to the third aspect of the present invention is characterized in that the secondary battery is a lithium ion battery. Thereby, measurement with higher correlation can be performed, and more accurate inspection can be performed.

  The method for manufacturing a secondary battery according to the fourth aspect of the present invention uses a cell that is determined to be non-defective by the step of inspecting a cell of the secondary battery by the above-described inspection method, and the step of inspecting. A step of producing a secondary battery. Thereby, productivity can be improved.

  An inspection method according to a fifth aspect of the present invention includes a step of inspecting a cell of a secondary battery, a step of adjusting the SOC of a plurality of inspected cells, and the SOC adjusted by the above inspection method. Stacking a plurality of cells, producing a cell stack, and in a state where the SOC of the plurality of cells included in the cell stack is 50 to 90%, starting self-discharge of the cell stack, Measuring a voltage drop due to self-discharge of the cell stack. This makes it possible to detect a short-circuit cell in the cell stack with high accuracy.

  The inspection method according to a sixth aspect of the present invention is characterized in that self-discharge of the cell stack is started in a state where the SOC of the plurality of cells included in the cell stack is 55% to 65%. Is. Thereby, it becomes possible to detect the short-circuited cell in the cell stack with higher accuracy.

  The inspection method according to the sixth aspect of the present invention is to perform pass / fail determination according to the step of inspecting the cell stack by the above inspection method and the voltage drop due to self-discharge of the cell stack. Thereby, productivity can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, the inspection method of a secondary battery which can test | inspect a secondary battery correctly and simply and the manufacturing method of a secondary battery with high productivity can be provided.

It is a flowchart which shows the inspection method which concerns on this Embodiment. It is a graph which shows the correlation with -30 degreeC, SOC30% output, and 20 degreeC resistance when changing the capacity | capacitance ratio of a lithium ion battery. It is a graph which shows the relationship between 4 second resistance in 20 degreeC and SOC5%, and the output in -30 degreeC and SOC30%. It is a flowchart which shows the manufacturing method of the secondary battery which concerns on this Embodiment. It is a graph which shows the relationship between the self-discharge days and voltage when the amount of self-discharge is large. It is a graph which shows the relationship between the self-discharge days and voltage when the amount of self-discharge is small. It is a graph which shows the relationship between the start voltage of self-discharge, and a voltage change. It is a graph which shows the relationship between SOC of a battery, and negative electrode potential.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

Embodiment 1 FIG.
First, the inspection method according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a chart showing an inspection method. The inspection method of the present embodiment is an inspection method of a secondary battery such as a lithium ion battery. For example, a single cell of a lithium ion battery is inspected according to the flow shown in FIG. The inspection method according to the present embodiment is suitable for a secondary battery having a capacity ratio of 1.5 or more. The capacity ratio is the ratio of the negative electrode to the positive electrode, and the capacity ratio increases as the amount of the negative electrode increases.

  A cell of a lithium ion battery is prepared, and initial charge / discharge is performed on the cell (step S11). Here, a cell for a lithium ion battery is used. A cell of a lithium ion battery includes a positive electrode, a negative electrode, a non-aqueous electrolyte, a separator, and the like. In step S11, for example, the cell is charged and discharged, and a current is passed. As a result, the cell voltage becomes a predetermined value. Next, high temperature aging is performed on the cell. For example, after charging the cell until it reaches a high voltage, the cell is held at 60 ° C. for 20 hours. Thereby, it is possible to stabilize the cell and to cause initial deterioration. Moreover, when a metal foreign material mixes, a cell can be short-circuited.

  Next, the cell is self-discharged (step S13). For example, holding for 5 days in an environment of 20 ° C., the voltage drop due to self-discharge of the cell is measured. Then, pass / fail determination is performed based on the measured voltage drop amount. Even if the short-circuited cell is not energized, the amount of self-discharge increases, so the voltage decreases. Therefore, a cell whose voltage drop amount is larger than the threshold value is determined as a short-circuited cell. In this way, it can be determined whether or not the secondary battery is short-circuited. In addition, when the dispersion | variation by a manufacturing lot is large, you may change a threshold value for every manufacturing lot. Then, a shipping inspection is performed on the non-defective cell (step S14). In the shipping inspection process in step S14, the capacity, resistance, etc. of the secondary battery are measured.

  Hereinafter, the shipping inspection in step S14 will be described in detail. In the shipping inspection, resistance measurement is performed at 20 ° C. and 5% SOC instead of measuring -30 ° C. and SOC 30% output (W). For example, the standard required for starting an engine at a low temperature is −30 ° C., SOC 30% output (W), but the output measurement in a low temperature environment is replaced with a resistance measurement in a room temperature environment. Yes. The SOC to be measured is not limited to 5%, and the environmental temperature is not limited to 20 ° C. For example, resistance measurement is preferably performed at SOC 3% to 15% in a room temperature environment, and resistance measurement is more preferably performed at 4% to 10% SOC in a room temperature environment. Moreover, it is more preferable to measure at 10-30 degreeC. By doing in this way, it becomes possible to measure in a temperature environment that can be lowered by an air conditioner (air conditioner).

  In the present embodiment, measurement is performed in a room temperature environment having a high correlation with measurement in a low temperature environment. The secondary battery is not installed in a low temperature environment, and measurement having a high correlation with the output in the low temperature environment can be performed. Thereby, manufacturing cost can be reduced and productivity can be improved. In particular, the engine can be reliably started in a low temperature environment for a secondary battery for a vehicle such as an automobile.

  FIG. 2 shows the correlation between -30 ° C., SOC 30% output and 20 ° C. 4-second resistance. In FIG. 2, the horizontal axis represents the capacity ratio, and the vertical axis represents the correlation between the output measurement in a low temperature environment and the resistance measurement in a room temperature environment. In FIG. 2, the correlation value between the output of −30 ° C., SOC 30% for 2 seconds and the reciprocal of the 4-second resistance at 20 ° C. is plotted. In the secondary battery according to the present embodiment, SOC 0% corresponds to the battery voltage 3.0V, and SOC 100% corresponds to the battery voltage 4.1V. Here, secondary battery cells having capacity ratios of 1.2, 1.4, 1.5, 1.6, 1.8, and 2.0 are prepared, and the correlation is measured. Further, the correlation is measured by setting the SOC to 1%, 3%, 5%, 10%, 15%, 20%, and 30%. When a SOC of 1%, 3%, 5%, 10%, 15%, 20%, and 30% is applied to a secondary battery cell having the above capacity ratio, a current of 20 A flows for 4 seconds. Measure the voltage. The resistance can be measured for 4 seconds by dividing the voltage by the current.

  As shown in FIG. 2, when the capacity ratio is 1.5 or more, it is understood that the correlation is low when the SOC is 1%, 20%, and 30%. For example, in the case of SOC 1%, the correlation is low regardless of the capacity ratio. When the capacity ratio is small, as shown by the dotted frame in FIG. 2, the correlation is high when the SOC is 20% and 30%, but the correlation is low when the capacity ratio is 1.5 or more. On the other hand, as shown by the solid line frame in FIG. 2, in the SOC 3%, 5%, 10%, and 15%, the correlation is high even when the capacity ratio is high. Thus, when the capacity ratio is 1.5 to 2.0, there is a correlation between the output at −30 ° C. and SOC 30% for 2 seconds and the resistance at 20 ° C., SOC 3%, 5%, 10% and 15% for 4 seconds. It is high.

  By measuring resistance at such a low SOC value, resistance measurement in a room temperature environment having a high correlation with output measurement in a low temperature environment becomes possible. A battery with a large capacity ratio has a large amount of negative electrode with respect to the positive electrode, and the ratio of the negative electrode resistance to the battery resistance is small. In particular, under the room temperature environment, the negative electrode contributes less to the battery resistance. On the other hand, in a low temperature environment, the negative electrode contributes to the battery resistance. Therefore, in a cell having a high capacity ratio, the contribution of the negative electrode to the battery resistance is increased by lowering the SOC. In this way, the increase in the negative electrode resistance contribution under the low temperature environment is compensated by reducing the SOC. Thereby, since a test | inspection can be performed correctly in a room temperature environment, a quality determination can be performed reliably. For example, the pass / fail judgment can be made by comparing the measured value of the resistance at 20 ° C. and SOC 5% for 4 seconds with a threshold value. Therefore, it is possible to reliably perform pass / fail determination.

  Hereinafter, some of the measurement results of various measurements performed by the inventors of the present application will be described. FIG. 3 is a graph showing measurement results of a lithium ion battery having a capacity ratio of 1.8. FIG. 3 shows the relationship between -30 ° C., SOC 30% output (W) and 4-second resistance at 20 ° C., SOC 5%. In FIG. 3, the measurement result when measuring with five batteries is shown. As shown in FIG. 3, when the reciprocal of the 4-second resistance at 20 ° C. and SOC 5% increases, the output (W) at −30 ° C. and SOC 30% also increases. The relationship between the -30 ° C, SOC 30% output (W) and the inverse of the 4-second resistance at 20 ° C, SOC 5% is almost linear. Therefore, the resistance measurement at 20 ° C. and SOC 5% has a high correlation with the output of −30 ° C. and SOC 30%. By making the SOC low and measuring the room temperature environment as a shipping inspection, it is not necessary to install the secondary battery in a low temperature environment. Thereby, while being able to shorten inspection time, it can test | inspect reliably. A secondary battery is manufactured using a cell determined to be a good product. By doing in this way, since the cell determined to be inferior goods can be decreased, the manufacturing cost of a secondary battery can be reduced.

  In order to increase the correlation with the output measurement under a low temperature environment, the SOC is preferably 3% to 15%, and more preferably 4 to 10%. Thus, by measuring the resistance value of SOC 3 to 15% in an environment of 10 ° C. to 30 ° C., it is possible to perform a measurement highly correlated with output measurement in a low temperature environment. Furthermore, measurement with higher correlation can be performed by measuring the resistance at SOC 4% to 10%. Therefore, the inspection time can be shortened and the inspection can be performed reliably. A secondary battery is manufactured using a cell determined to be a good product. By doing in this way, since the cell determined to be inferior goods can be decreased, the manufacturing cost of a secondary battery can be reduced.

Embodiment 2. FIG.
The inspection method according to this embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a secondary battery inspection method. First, the inspection process shown in the first embodiment is performed (step S21). That is, the cell inspection process in step S21 includes the initial charge / discharge process (step S11), the high temperature aging process (step S12), the cell self-discharge process (step S13), and the shipping inspection process (steps) shown in the first embodiment. S14). In step S21, a plurality of cells are inspected.

  Then, the stack process (step S23) is performed through the SOC adjustment process (step S22). In the SOC adjustment step of step S22, charging / discharging is performed so that the SOC of a plurality of cells falls within a certain range. The stack process S23 includes a stack restraint process and a stack self-discharge process. For example, a plurality of cells whose SOCs are adjusted in step S22 are prepared. And it restrains as the state which laminated | stacked the several cell. Thereby, a cell stack in which a plurality of cells are stacked is produced.

  Here, when a plurality of cells are stacked, the positive electrode and the negative electrode may be short-circuited. For example, metal foreign matter may be mixed between the positive and negative electrodes. In this case, when a load is applied in the stack restraining process, there is a possibility that the metal foreign matter breaks through the separator. Therefore, in this embodiment, after the stack restraining step, the cell stack is self-discharged to detect the presence or absence of a short circuit. That is, the cell stack is left for a certain period of time, and the voltage drop due to self-discharge is measured. If the voltage drop is larger than the threshold value, it is determined that the short circuit has occurred.

  However, even when a stack is manufactured using non-defective cells, there are cases where the self-discharge of the cells is large and small. For example, there is a variation in the magnitude of self-discharge depending on the production lot. When stacking a plurality of cells, cells of different production lots may be mixed and stacked. In this case, even when the non-defective cell determined as non-defective is used, the self-discharge amount varies. Therefore, in the present embodiment, in order to reduce the variation in the self-discharge amount, the SOC is adjusted in step S22 so that the SOC falls within a predetermined range. By carrying out like this, it can test | inspect more reliably.

  The reason for this will be described below. When the self-discharge of the non-defective cell is large, the relationship between the self-discharge days and the voltage is as shown in FIG. On the other hand, when the self-discharge of the non-defective cell is small, the relationship between the self-discharge days and the voltage is as shown in FIG. 5 and 6, the horizontal axis represents the number of days of self-discharge, and the vertical axis represents the voltage. FIG. 5 and FIG. 6 show how the voltages of the non-defective cells and the short-circuited cells are reduced. 5 and 6, the short-circuit resistance of the short-circuit cell is the same. As shown in FIGS. 5 and 6, the voltage gradually decreases as the number of days of self-discharge elapses.

  When the self-discharge of the non-defective cell is large, the ratio of the short circuit to the entire voltage is small. Therefore, it becomes difficult to detect a short circuit. On the other hand, when the self-discharge of the non-defective cell is small, the difference in voltage change between the non-defective cell and the short-circuit cell becomes large. Therefore, it becomes easy to detect a short circuit. That is, the smaller the self-discharge of the non-defective cell, the larger the (voltage drop due to short circuit) / (voltage drop of the non-defective cell), and thus the short-circuited cell is easier to detect. Therefore, if the self-discharge amount is measured under the condition that the self-discharge of the non-defective cell is small, the short-circuited cell can be easily detected.

  FIG. 7 shows the relationship between the self-discharge start voltage (SOC) and the voltage change. In FIG. 7, the horizontal axis represents the stack self-discharge start voltage (SOC), and the vertical axis represents the stack self-discharge voltage change. Here, the voltage change due to self-discharge when the stack is left for 5 days is shown. As shown in FIG. 7, the voltage change is small when the self-discharge start voltage is in the range of SOC 50% to 90%. Therefore, it is preferable to set the SOC at the start of self-discharge to 50% to 90%. If the SOC exceeds 90%, the battery activity increases and self-discharge increases. On the other hand, when the SOC is smaller than 50%, the potential gradient of the negative electrode is large and the self-discharge becomes large. For example, as shown in FIG. 8, when the SOC is 50% or less, the potential gradient of the negative electrode becomes small. That is, when the SOC is 50% or less, the change in the negative electrode potential with respect to the decrease in the SOC increases, and the self-discharge amount increases. In FIG. 8, the horizontal axis indicates the SOC, and the vertical axis indicates the potential of the negative electrode. In self-discharge, since the negative electrode contributes greatly, it is preferable to perform stack self-discharge measurement in a range where the potential change of the negative electrode is gentle.

  For the above reasons, it is preferable to start stack self-discharge at an SOC of 50% to 90%, and more preferably to start stack self-discharge at an SOC of 55% to 66%. Therefore, before the stack restraining step, the SOC of each cell is adjusted so that the SOC is 50% to 90% (step S22). Then, a plurality of cells with adjusted SOC are prepared and stacked. As a result, a cell stack in which the SOC of all the cells is 50% to 90% is manufactured. If all the cells are in the range of 50% to 90% SOC, all the cells may have the same SOC or different values.

  Then, the cell stack is held for a certain period without being energized, and the voltage drop due to the self-discharge of the cell stack is measured. Then, pass / fail determination is performed by comparing the voltage drop amount with a threshold value. By doing so, the cell stack can be inspected stably. Therefore, it is possible to reliably determine whether the cell stack is good or not, and it is possible to improve productivity. In step S22, the SOC is preferably adjusted to 50% to 90%, and more preferably adjusted to SOC 55% to 65%. By doing in this way, it can test | inspect more reliably.

  Inspection is performed by the inspection method according to the first and second embodiments. Then, the cells and cell stacks determined as defective products are excluded, and only the cells and cell stacks determined as non-defective products are attached to the automobile. Thus, productivity can be improved by manufacturing the secondary battery for motor vehicles. In the above description, the inspection and manufacturing method of the lithium ion battery has been described. However, the present embodiment can be applied to a nonaqueous electrolyte secondary battery other than the lithium battery.

S11 Initial charge / discharge process S12 High temperature aging process S13 Cell self-discharge process S14 Shipment inspection process S21 Cell inspection process S22 SOC adjustment process S23 Stack process

Claims (6)

A method of inspecting a secondary battery for inspecting a vehicle lithium ion battery having a non-aqueous electrolyte,
Setting the SOC of a secondary battery having a capacity ratio of 1.5 or more to 3 to 15%;
Measuring the resistance of the secondary battery having an SOC of 3 to 15% under an environment of 10 ° C to 30 ° C.   2. The inspection method according to claim 1, wherein in the step of setting the SOC, the SOC of the secondary battery is set to 4 to 10%. Inspecting a cell of a secondary battery by the inspection method according to claim 1 or 2 , and
A secondary battery manufacturing method using the cell determined to be a non-defective product by the inspecting step. Inspecting a cell of a secondary battery by the inspection method according to claim 1 or 2 , and
Adjusting the SOC of the inspected cells;
Stacking a plurality of cells with adjusted SOC to produce a cell stack;
Starting a self-discharge of the cell stack in a state where the SOC of the plurality of cells included in the cell stack is 50 to 90%, and measuring a voltage drop due to the self-discharge of the cell stack. Secondary battery inspection method. 5. The inspection method according to claim 4 , wherein self-discharge of the cell stack is started in a state where the SOC of the plurality of cells included in the cell stack is 55% to 65%. A step of inspecting a cell stack by the inspection method according to claim 4 or 5 ,
A method for manufacturing a secondary battery, which performs pass / fail determination according to a voltage drop due to self-discharge of the cell stack.

Images