JP6992690B2 - Secondary battery reaction distribution estimation method - Google Patents

Description

The present invention relates to a method for estimating the reaction distribution of a secondary battery.

Patent Document 1 proposes a technique for monitoring the charge rate of a secondary battery for the purpose of suppressing overcharge and overdischarge in the charge / discharge of the secondary battery. In Patent Document 1, the heat flux from the secondary battery to the outside is detected, and the calorific value of the secondary battery is calculated based on this detected value. Then, the open end voltage is calculated based on the charge / discharge current, the voltage between terminals, and the calorific value, and the charge rate of the secondary battery is estimated from the open end voltage.

Patent Document 2 proposes a technique for predicting the battery life based on the measured value of the heat flux by utilizing the fact that the change in the heat flux of the secondary battery correlates with the battery life.

Patent Document 3 discloses a technique for estimating a lithium ion concentration distribution caused by over-discharging or over-charging in a lithium ion secondary battery. In Patent Document 3, the heat generation distribution of the secondary battery is calculated based on the heat flow from the lithium ion secondary battery to the outside, and the lithium ion concentration distribution is estimated from this heat generation distribution.

Patent Document 4 discloses a method of measuring the resistance distribution of an electrode on which an electrode active material layer is formed on a current collector using a probe. The resistance distribution of the electrode is measured by electrically connecting the counter electrode in the probe and the electrode active material layer via the electrolytic solution.

Japanese Unexamined Patent Publication No. 2016-133413 Japanese Unexamined Patent Publication No. 2014-92428 Japanese Unexamined Patent Publication No. 2016-149917 Japanese Unexamined Patent Publication No. 2014-25850

Secondary batteries are used not only as power sources for mobile devices such as mobile phones and laptop computers, but also as power sources for electric vehicles and hybrid vehicles. If the electrochemical reaction inside the secondary battery is not uniform, the current distribution will be non-uniform, and some of the electrode active materials where the current will be concentrated will deteriorate, causing problems in durability and safety such as over-discharging and over-charging. There is a fear. Therefore, it is required to uniformly maintain the electrochemical reaction inside the secondary battery. However, in order to evaluate the reaction distribution inside the secondary battery, it is necessary to disassemble the secondary battery that has been repeatedly charged and discharged and analyze the electrode active material of each part, which is troublesome.

In Patent Document 1, the charge rate is estimated from the calorific value of the secondary battery during charging / discharging, but the reaction distribution cannot be estimated. Further, the scope of application is limited to a small laminated lithium-ion battery, and it cannot be applied to a large battery used as an assembled battery by connecting a plurality of secondary batteries mounted on an electric vehicle or the like in series. Further, also in Patent Document 2, it is not possible to estimate the reaction distribution or the current distribution.

In Patent Document 4, which measures the resistance distribution of the electrode, it is necessary to bring the probe into contact with the electrode active material layer, so that it is necessary to disassemble the secondary battery. Further, the method disclosed in Patent Document 4 cannot evaluate the change in resistance due to the change in the state of the electrolytic solution.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a technique capable of easily obtaining a reaction distribution of a secondary battery.

In the method for estimating the reaction distribution of a secondary battery according to one aspect of the present invention, the secondary battery is charged and discharged with at least two different current values, and the outside of the secondary battery is located at a plurality of locations on the surface of the secondary battery. The first step of measuring the heat flux toward the current and acquiring a plurality of measurement data at each of the plurality of locations, and the integration of the plurality of measurement data for each current value, and the integration value for each current value. The second step of calculating the average value of, the third step of calculating the first relational expression between the current value and the average value, and the fourth step of estimating the reaction distribution based on the first relational expression. Has.

In the method for estimating the reaction distribution of a secondary battery according to another aspect of the present invention, the secondary battery is charged and discharged under at least two different resistance level conditions of the secondary battery in the first step, and the first step is performed. Through the two steps and the third step, a plurality of first relational expressions under the respective resistance level conditions are acquired, and in the fourth step, the inclination of each of the plurality of first relational expressions and the average of the secondary battery are obtained. A step of calculating the second relational expression from the resistance value, a step of calculating the resistance ratio with respect to the average resistance value from the second relational expression at each of the plurality of places, and the resistance ratio and the above-mentioned at each of the plurality of places. It includes a step of estimating the reaction distribution from the average current value of the secondary battery.

According to the present invention, it is possible to provide a technique capable of easily obtaining a reaction distribution of a secondary battery.

It is a figure which shows the structure of the reaction distribution estimation apparatus of the secondary battery which concerns on embodiment. It is a figure which shows the sticking position of the heat flux sensor in a secondary battery. It is a figure explaining the process of attaching a heat conduction sheet to a secondary battery. It is a figure explaining the state which confined the secondary battery with a heat dissipation / restraint jig. It is a figure explaining the state which confined the secondary battery with a heat dissipation / restraint jig. It is a flow diagram explaining the reaction distribution estimation method of the secondary battery which concerns on embodiment. It is a figure which shows the relationship between the battery voltage by charge / discharge, and the heat flux. It is a figure which shows an example of the energization pattern for charging / discharging a secondary battery. It is a figure which shows an example of the measurement data of the heat flux of a secondary battery during charging and discharging. It is a figure which shows the integrated value of the measurement data measured by each of a plurality of heat flux sensors attached to a secondary battery, and the average value thereof. It is a figure which shows the relationship between the mean value of the heat flux integrated value, and the square of the mean current value. It is a figure explaining the current distribution estimation method of the secondary battery which concerns on embodiment. It is a flow figure explaining the reaction distribution estimation method of the secondary battery which concerns on other embodiment. It is a figure which shows the relationship between the mean value of the heat flux integrated value and the square of the mean current value at each evaluation temperature. It is a figure which shows the relationship between the inclination of the 1st relational expression, and the IV resistance value of a secondary battery. It is a figure which shows the relationship between the inclination of the 1st relational expression of an analysis area, and the inclination of the 1st relational expression of an analysis area.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Equivalent components in each figure are designated by the same reference numerals, and duplicate description is omitted.

Generally, a secondary battery has a plurality of stacked electrodes so that a separator is interposed between a positive electrode current collector and a negative electrode current collector. In the embodiment, a lithium ion secondary battery will be described as an example of the secondary battery.

The positive electrode current collector has a structure in which a positive electrode active material layer is formed on the surface of a current collector foil such as an aluminum foil. The positive electrode active material is a material that can occlude and release lithium, for example, lithium cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickel oxide (LiNiO ₂ ), and these are mixed in a predetermined ratio. Materials and the like can be used. The positive electrode active material layer may contain any binder, a conductive auxiliary agent, or the like. As the conductive material, for example, carbon black such as acetylene black (AB) or graphite (graphite) can be used. As the binder, polyvinylidene fluoride (PVDF) or the like can be used.

The negative electrode current collector has a structure in which a negative electrode active material layer is formed on the surface of a current collector foil such as a copper foil. The negative electrode active material is a material that can occlude and release lithium, and for example, graphite can be used. It may contain a negative electrode active material layer, any binder, a thickener, and the like. As the binder, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.

The electrolytic solution contains a lithium salt and a solvent, and a conventionally known material that can be used as an electrolytic solution for a lithium ion battery can be used. As the lithium salt, for example, lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluorophosphate (LiBF ₄ ) can be used. As the solvent, for example, cyclic esters (ethylene carbonate (EC) and the like) and chain esters (dimethyl carbonate (DMC) and the like) can be used.

The electrode body including the positive electrode current collector, the negative electrode current collector and the separator is housed in the battery case. The battery case has a rectangular box shape with an opening and is made of a metal material such as aluminum or steel. The opening of the battery case is closed by a rectangular plate-shaped sealing lid. The sealing lid is provided with a positive electrode terminal electrically connected to the positive electrode current collector and a negative electrode terminal electrically connected to the negative electrode current collector so as to protrude from the surface of the sealing lid.

In addition to the above-mentioned lithium ion battery, another secondary battery, for example, an all-solid-state battery may be used. In that case, as the electrolyte, a solid electrolyte is used instead of an electrolytic solution. The material of the solid electrolyte is not particularly limited as long as it is a conventionally known material that can be used as an electrolyte of an all-solid-state battery.

At the time of charging, lithium ions are released from the positive electrode active material of the positive electrode current collector, and the lithium ions are taken into the negative electrode active material of the negative electrode current collector via the electrolytic solution. At the time of discharge, lithium ions are released from the negative electrode active material of the negative electrode current collector, and the lithium ions are taken into the positive electrode active material of the positive electrode current collector via the electrolytic solution. A current collector is connected to the positive electrode current collector and the negative electrode current collector, respectively, and current is collected in the positive electrode terminal and the negative electrode terminal. Such a secondary battery can also be used for various purposes, particularly as a large drive battery mounted on a vehicle such as an electric vehicle or a hybrid vehicle. This secondary battery can also be used in the form of an assembled battery in which a plurality of batteries are connected in series and / or in parallel.

In such a secondary battery, there is a concern that the electrochemical reaction inside the secondary battery will be low at a location far from the current collector, and it is desired to easily obtain the reaction distribution of the secondary battery. .. As a result of diligent studies, the present inventor correlates between the square of the current value applied to charge and discharge the secondary battery and the heat flux (calorific value) measured during charging and discharging of the secondary battery. I found it to be related. By using this relationship, the in-plane current distribution can be evaluated without disassembling or analyzing the secondary battery, and the reaction distribution can be easily obtained.

The present invention relates to a method for estimating the reaction distribution of a secondary battery. In the reaction distribution estimation method according to the embodiment, the secondary battery is charged and discharged with at least two different current values, and the heat flux toward the outside of the secondary battery is measured at a plurality of points on the surface of the secondary battery. do. Then, the measurement data is integrated for each current value, the average value of the integrated values is calculated, and the relational expression between the current value and the average value is obtained. The reaction distribution is estimated by substituting the measured values of each of the multiple heat flux sensors into the relational expression.

FIG. 1 is a diagram showing a configuration of a reaction distribution estimation device for a secondary battery according to an embodiment. FIG. 2 shows the attachment position of the heat flux sensor 11 in the secondary battery W. As shown in FIGS. 1 and 2, the reaction distribution estimation device 10 includes a heat flux sensor 11, a constant temperature bath 12, a charging / discharging device 13, a heat flux logger 14, and a data analysis device 15.

The heat flux sensor 11 detects the heat flux from the secondary battery W to be evaluated toward the outside of the secondary battery W. Based on the measurement result by the heat flux sensor 11, the calorific value distribution due to charging / discharging of the secondary battery W can be measured. As shown in FIG. 2, the heat flux sensor 11 is attached to one of two surfaces perpendicular to the direction in which the electrodes are laminated on the outside of the battery case of the plate-shaped secondary battery W. .. That is, the surface to which the heat flux sensor 11 of the secondary battery W is attached is parallel to the electrode surface to be laminated.

In the embodiment, the heat flux sensor 11 is installed in each of the regions (1) to (9) in which one of the surfaces perpendicular to the stacking direction of the electrodes of the plate-shaped secondary battery W is divided into nine. As the heat flux sensor 11, for example, a sensor having a sensing unit provided only at the tip portion to be attached to the secondary battery W can be selected.

In order to measure the heat flux from the secondary battery W during charging and discharging with high sensitivity, both sides of the secondary battery W are sandwiched between rubber-like heat conductive sheets 16 as shown in FIG. The heat flux sensor 11 is sandwiched between the secondary battery W and the heat conductive sheet 16. Further, the secondary battery W sandwiched between the heat conductive sheets 16 is constrained by the heat dissipation / restraint jig 20. In order to stabilize the electrochemical reaction of the secondary battery W and the heat transfer state from the battery to the heat conductive sheet 16, the heat dissipation / restraint jig 20 restrains the secondary battery W with a constant surface pressure. The heat conductive sheet 16 promotes heat dissipation to the heat dissipation / restraint jig 20.

FIGS. 4 and 5 show a state in which the secondary battery W is constrained by the heat dissipation / restraint jig 20. FIG. 4 is a side view of the secondary battery W, and FIG. 5 is a view of the secondary battery W seen from above where the electrode terminals are provided. As shown in FIGS. 4 and 5, a heat radiating plate 21 is provided so as to sandwich the both heat conductive sheets 16. The heat dissipation plate 21 is tightened by a nut screwed into the feed screw 22 so that a predetermined load is applied to the heat conduction sheet 16, the secondary battery W, and the heat flux sensor 11. This load is measured by the load cell 23.

Since the resistance value of the secondary battery W changes depending on the temperature, if there is temperature unevenness in the plane, the resistance will vary. Since the same voltage is applied between the positive electrode and the negative electrode, a large current flows in the portion where the resistance is small and the calorific value increases, and a small current flows in the portion where the resistance is large and the calorific value decreases. In order to prevent this in-plane variation in the amount of heat generated, the secondary battery W is arranged in the constant temperature bath 12 in a state of being constrained by the heat dissipation / restraint jig 20. The constant temperature bath 12 keeps the temperature of the secondary battery W at a predetermined temperature and suppresses variations in the in-plane resistance value of the secondary battery W.

A charging / discharging device 13 is connected to the positive electrode terminal and the negative electrode terminal of the secondary battery W. The charging / discharging device 13 charges / discharges the secondary battery W in a predetermined energization pattern described later. The heat flux logger 14 acquires and stores time-series measurement data of heat flux from a plurality of heat flux sensors 11, respectively. The data analysis device 15 estimates the reaction distribution based on a plurality of measurement data stored in the heat flux logger 14.

Here, a method for estimating the reaction distribution of the secondary battery according to the embodiment will be described with reference to FIGS. 6 to 12. FIG. 6 is a flow chart illustrating a method for estimating the reaction distribution of the secondary battery according to the embodiment. As shown in FIG. 6, first, a plurality of heat flux sensors 11 are attached to the surface of the secondary battery W (S1). As described above, in the embodiment, on the outside of the battery case of the secondary battery W, the heat flux sensor is formed in each of the regions (1) to (9) in which one of the surfaces perpendicular to the stacking direction of the electrodes is divided into nine. 11 is pasted.

Next, the secondary battery W to which the heat flux sensor 11 is attached is sandwiched between the heat conductive sheets 16, and the secondary battery W together with the heat conductive sheet 16 is restrained by the heat dissipation / restraining tool 20 (S2). On one surface of the secondary battery W, a heat conductive sheet 16 is attached so as to cover the surface of the secondary battery W from above the heat flux sensor 11. On the other side of the secondary battery W, the heat conductive sheet 16 is directly attached on the surface of the secondary battery W. Then, both heat conductive sheets 16 are sandwiched between the heat radiating plates 21, and the secondary battery W is restrained by the heat radiating / restraining jig 20 at a constant surface pressure.

After that, the secondary battery W in a state of being restrained by the heat radiation / restraint jig 20 is arranged in the constant temperature bath 12, and is left to stand until the temperature of the entire secondary battery W becomes a specified temperature (S3). As a result, the temperature in the electrode surface can be made uniform before the secondary battery W is energized. It is possible to confirm that the in-plane temperature of the secondary battery W is uniform because the measured values of the heat flux sensor 11 attached to the secondary battery W are substantially equal.

Since the resistance value of the secondary battery W changes depending on the voltage, it is necessary to adjust the voltage to an arbitrary voltage before measuring the heat flux during energization. Therefore, next, the voltage of the secondary battery W is adjusted to an arbitrary value by using the charging / discharging device 13 (S4). When the heat generated by the secondary battery W during charging / discharging is measured by the heat flux sensor 11, the relationship between the battery voltage and the heat flux shown in FIG. 7 can be obtained as an example. In FIG. 7, the horizontal axis represents the battery voltage (V) and the vertical axis represents the heat flux (W / m ² ). This is a heat generation (endothermic) profile due to charge / discharge. For example, the battery voltage shown by the alternate long and short dash line is selected so that the amount of heat generation (endothermic) due to energization is large and the sum of heat flux due to charge / discharge is small. As a result, it is possible to minimize the resistance change caused by the heat generation of the secondary battery W due to charging / discharging.

Then, the secondary battery W is charged and discharged, and the heat flux of the energized secondary battery W is measured using a plurality of heat flux sensors 11 (S5). At this time, a predetermined energization pattern is applied by the charging / discharging device 13 while the temperature of the secondary battery W is kept constant in the constant temperature bath 12. FIG. 8 shows an example of an energization pattern for charging / discharging the secondary battery W. In the example shown in FIG. 8, the current −x (A) is applied for 10 seconds and the current + x (A) is applied for 10 seconds at a voltage of 3.5 (V), and n cycles are repeated. The time-series measurement data of the heat flux of the secondary battery W when this energization pattern is applied is acquired by each of the plurality of heat flux sensors 11.

The measurement of the heat flux of the secondary battery W of S5 is performed with at least two different current values. In the embodiment, the measurement of the heat flux of the secondary battery W is performed with three different current values. Here, condition 1 is 6.9A, condition 2 is 14.3A, and condition 3 is 21.6A. FIG. 9 shows the measurement data of the heat flux of the secondary battery W during charging / discharging. In FIG. 9, the solid line shows the measurement data of the condition 1, the broken line shows the measurement data of the condition 2, and the alternate long and short dash line shows the measurement data of the condition 3. In FIG. 9, the horizontal axis represents time (seconds) and the vertical axis represents heat flux (W / m ² ). The measurement data of one cycle in FIG. 9 shows the measurement data of the heat flux when one cycle of the energization pattern of FIG. 8 is applied. Such measurement data is acquired for each heat flux sensor 11 arranged in each region in the plane of the secondary battery W.

After that, after integrating a plurality of in-plane measurement data for each current value, the average value of the plurality of in-plane integrated values is calculated for each current value (S6). FIG. 10 shows the integrated value of the measurement data measured by each of the plurality of heat flux sensors 11 installed in each region (1) to (9) of the secondary battery W, and the average value thereof. By averaging the integrated values of a plurality of heat flux measurement data measured while applying the energization pattern of the above conditions 1 to 3, the average in-plane calorific value of the secondary battery W for each current value is acquired. Can be done.

Then, the relational expression between the square of the current value (Iave ² ) and the average value of the heat flux integrated value (ΣQave) is acquired (S7). This relational expression corresponds to the first relational expression described in the claims. When the relationship between the average value of the integrated heat flux and the square of the average current value flowing in the plane of the secondary battery W is graphed, the correlation as shown in FIG. 11 is obtained. From FIG. 11, the following relational expression (1) is obtained.
y = 31.218x + 130.74 ... (1)
The coefficient of determination at this time is R ² = 1, and it can be seen that there is a strong correlation between the square of the current value (Iave ² ) and the average value of the heat flux integrated value (ΣQave).

After that, the measured value of the heat flux by each heat flux sensor 11 is substituted into the above relational expression (1) (S8), and the in-plane current distribution of the secondary battery W is acquired (S9). Since the resistance in the electrode surface of the secondary battery W is uniform, the in-plane current distribution is estimated by substituting the individual measured values measured by the plurality of heat flux sensors 11 into the relational expression (1). be able to.

FIG. 12 is an enlarged view of the broken line portion of FIG. In FIG. 12, (1) shows the average value (in-plane heat flux average value) of the in-plane heat flux integrated value when the current value (average current) of the condition 3 is applied. In the example shown in FIG. 12, ◯ indicates the measured heat flux value (1) measured by the heat flux sensor 11 in the region of FIG. 2 (2), and ● indicates the measured value of heat flux in the region of FIG. 2 (8). The heat flux actual measurement value (2) measured by the heat flux sensor 11 is shown.

By substituting the heat flux measured value (1) into the relational expression (1), the in-plane current value (1) in the region (2) can be obtained. Similarly, by substituting the heat flux measured value (2) into the relational expression (1), the in-plane current value (2) in the region (8) can be obtained. By evaluating the current distribution generated in the electrode plane of the secondary battery W in this way, it is possible to estimate the reaction distribution without disassembling the secondary battery W. This reaction distribution estimation method can also be applied to large batteries mounted on vehicles such as electric vehicles and hybrid vehicles.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit. In the embodiment, the heat flux sensor 11 is provided on the surface of the secondary battery W, but instead of the heat flux sensor 11, a pair of temperature sensors can be installed inside and outside the battery case. The heat flux toward the outside of the secondary battery W can be measured from the temperature difference between the pair of temperature sensors, and the reaction distribution can be estimated in the same manner as described above. Further, the heat flux sensor 11 may be installed not only on the outside of the battery case but also on the inside.

In the above method, the in-plane current distribution is estimated from the measurement result of the heat generation distribution of the secondary battery W during energization by the heat flux sensor 11. At this time, it is necessary to make sure that there is no resistance unevenness in the electrode surface. However, when it is mounted on an actual vehicle, the restraint pressure and temperature become uneven, and resistance unevenness occurs. Therefore, as another embodiment, a method of evaluating the resistance distribution and the current distribution in the surface of the secondary battery W in a non-destructive manner even when resistance unevenness occurs in the electrode surface will be described below.

In the reaction distribution estimation method according to another embodiment, the secondary battery is charged and discharged with at least two different current values, and the heat flux toward the outside of the secondary battery is measured at a plurality of points on the surface of the secondary battery. Then, the first step of acquiring a plurality of measurement data of each of a plurality of locations, and the second step of integrating a plurality of measurement data for each current value and calculating the average value of the integrated values for each current value. It has a third step of calculating a first relational expression between a current value and an average value, and a fourth step of estimating a reaction distribution based on the first relational expression.

In the first step, the secondary battery is charged and discharged under at least two different resistance level conditions of the secondary battery, and after the second step and the third step, a plurality of first steps under the respective resistance level conditions are performed. 1 The relational expression is acquired. The fourth step is a step of calculating the second relational expression from the inclination of each of the plurality of first relational expressions and the average resistance value of the secondary battery, and the resistance to the average resistance value from the second relational expression at each of the plurality of locations. It includes a step of calculating the ratio and a step of estimating the reaction distribution from the resistance ratio of each of the plurality of locations and the average current value of the secondary battery. This makes it possible to evaluate the in-plane resistance distribution and reaction distribution in a non-destructive manner without disassembling the battery. It is also possible to evaluate changes in resistance due to changes in the state of the electrolytic solution.

In this embodiment, the reaction distribution estimation device 10 described with reference to FIGS. 1 to 5 can be used. A method for estimating the reaction distribution of the secondary battery according to another embodiment will be described with reference to FIGS. 13 to 16. FIG. 13 is a flow chart illustrating a method for estimating the reaction distribution of the secondary battery according to another embodiment. In FIG. 13, S11 to S17 are the same as S1 to S7 in FIG. 6, and duplicated description will be omitted.

In S15, the energization pattern applied by the charging / discharging device 13 can be the same as that in FIG. Further, also in the present embodiment, the heat flux of the secondary battery W is measured under three different current values (conditions 1, 2, and 3).

In this embodiment, an example in which the secondary battery W is charged and discharged under three temperature conditions of evaluation temperatures of 10 ° C., 25 ° C., and 45 ° C. will be described. The evaluation temperature is the temperature of the entire secondary battery W under evaluation. In S13, first, it is assumed that the temperature of the secondary battery W is set to 10 ° C. After the temperature of the secondary battery W reaches 10 ° C., the first relational expression when the evaluation temperature is 10 ° C. is acquired through S14 to S17.

After that, the evaluation temperature is changed from 10 ° C. to 25 ° C., and the resistance level of the secondary battery is changed (S18). Then, the process returns to S13, and the first relational expression when the evaluation temperature is 25 ° C. is acquired through S14 to S17. Similarly, by changing the evaluation temperature from 25 ° C. to 45 ° C. and repeating S13 to S17, the first relational expression when the evaluation temperature is 45 ° C. is obtained.

When the relationship between the average value of the integrated heat flux and the square of the average current value flowing in the plane of the secondary battery W is graphed, the correlation for each evaluation temperature as shown in FIG. 14 is obtained. The three first relational expressions can be calculated from FIG. As described above, in this embodiment, three first relational expressions are obtained under the temperature conditions of the evaluation temperatures of 10 ° C, 25 ° C, and 45 ° C. As shown in FIG. 14, the slope of the first relational expression is tilted A when the evaluation temperature is 10 ° C., the slope of the first relational expression is tilted B when the evaluation temperature is 25 ° C., and the first relation is tilted when the evaluation temperature is 45 ° C. Let the slope of the relational expression be the slope C.

Further, the slope of the first relational expression (the rate of increase of the average value of the battery heat flux integrated value with respect to the square of the average current value) has a correlation with the IV resistance of the secondary battery. In the present embodiment, the in-plane resistance distribution and the current distribution are derived by utilizing this relationship.

The IV resistance between the terminals of the secondary battery W is the average value of the resistance calculated by measuring the overvoltage during charging and discharging when a current is applied and dividing those values by the applied current value ( Average resistance value). Here, the IV resistance is calculated by dividing the amount of voltage drop (V) after 10 s of energization by the applied current value (A), but the time after energization can be arbitrarily changed.

When the relationship between the slope of the first relational expression and the IV resistance of the secondary battery W is graphed, the correlation shown in FIG. 15 is obtained. In S19, the second relational expression is calculated from the slopes A, B, C of each of the above-mentioned three first relational expressions and the average resistance value of the secondary battery W. From FIG. 15, the following second relational expression (2) is obtained.
y = 11.24x + 24.925 ... (2)
The coefficient of determination at this time is R ² = 0.9998, and it can be seen that there is a strong correlation between the slope of the first relational expression and the average resistance value of the secondary battery W.

Then, in S20, the in-plane current distribution is derived from the relationship between the second relational expression and the individual heat flux integrated value ΣQ. The measured values of the individual heat fluxes in the plane of the secondary battery W are affected by the current distribution due to the resistance distribution. If the resistance ratio to the in-plane average resistance value (IV resistance between terminals) is defined as z, a current of 1 / z times flows in a place where the resistance is z times higher according to Ohm's law. Utilizing this, the in-plane resistance distribution and current distribution can be derived from the second relational expression (2) and the measured value of heat flux.

Specifically, first, in each of the nine divided regions (1) to (9) (hereinafter referred to as an analysis area) to which the heat flux sensor 11 is attached, the resistance ratio to the average resistance value is calculated from the second relational expression. calculate. As described above, the relationship between the slope of the first relational expression of the in-plane average of the secondary battery W and the average resistance value is expressed as follows from the second relational expression (2).
(Slope of the first relational expression) = 11.24 × (average resistance value) + 24.925 ... (3)

It is considered that the same relationship holds in each of the analysis areas.
(Slope of the first relational expression in the analysis area) = 11.24 × (average resistance value in the analysis area) +24.925 ... (4)
Here, it is defined as (average resistance value in the analysis area) = (average resistance value) × z ... (5).

By substituting the equation (5) into the equation (4), the following equation is obtained.
(Slope of the first relational expression in the analysis area) = 11.24 × (average resistance value × z) +24.925 ... (6)

Here, the slope S of the apparent first relational expression in the analysis area is obtained. The apparent slope S of the first relational expression in the analysis area is calculated with the vertical axis as the mean value ΣQave of the heat flux integrated value and the horizontal axis as the square of the current value I between the terminals of the secondary battery W.

FIG. 16 shows the relationship between the slope of the first relational expression in the analysis area and the apparent slope of the first relational expression in the analysis area. According to Ohm's law, when the resistance of the analysis area is z times higher, the current distributed to the analysis area is 1 / z times, so in the definition of equation (5), the current actually flowing at that location is the inter-terminal current. It becomes 1 / z ² of.

Therefore, the slope of the first relational expression in the actual analysis area is z2 times ⁽ S × z2) the slope of the apparent ^first relational expression in the analysis area calculated by using the current value between terminals.
(Slope of the first relational expression in the analysis area) = (Slope of the first relational expression in the analysis area) × z ² ... (7)

Substituting equation (7) into equation (6),
(Slope of the first relational expression apparently in the analysis area) × z ² = 11.24 × (average resistance value × z) +24.925 ... (8)
Will be. To organize this,
(Slope of the first relational expression apparently in the analysis area) × z ² -11.24 × (average resistance value × z) -24.925 = 0 ... (9)
The quadratic equation of is obtained.

By solving the following equation (10) obtained by this, the resistance ratio z with respect to the average resistance value can be derived.
az ² + bz + c = 0 ... (10)
a: Apparent slope of the first relational expression in the analysis area b: -1 x slope of the second relational expression x average resistance value c: -1 x intercept of the second relational expression

Then, the reaction distribution is estimated from the resistance ratio of each of the plurality of locations of the secondary battery W and the average current value of the secondary battery. Specifically, the current distribution can be derived by dividing the in-plane average current value of the secondary battery W by the value of the resistance ratio z obtained for each analysis area. Further, by multiplying the value of the resistance ratio z obtained for each analysis area by the IV resistance value (average resistance value), the resistance distribution in the W plane of the secondary battery can be derived.

As described above, in the other embodiment, the analysis method based on the current distribution in the electrode plane with respect to the correlation between the increase rate of the average value of the heat flux integrated value with respect to the square of the average current value and the average resistance value. Is used. As a result, the reaction distribution can be estimated from the heat flux actually measured by the heat flux sensor and the average resistance value and average current value of the secondary battery, and it is not necessary to disassemble the battery.

Further, even in the case where the resistance distribution is generated in the plane of the secondary battery, the error due to the influence of the in-plane resistance distribution does not occur, and the resistance distribution and the current distribution can be evaluated with high accuracy. This makes it possible to evaluate a secondary battery that simulates the state of being mounted on an actual vehicle. Furthermore, by applying this method, the resistance distribution caused by manufacturing caused by variations in the thickness of the electrodes can be evaluated without disassembling or analyzing the battery and without modifying the large battery. .. It is also possible to evaluate changes in resistance due to changes in the state of the electrolytic solution.

In the other embodiment described above, the evaluation temperature is shaken to shake the resistance level of the secondary battery, but the present invention is not limited to this. For example, it is possible to change the resistance level of the secondary battery by using the fact that the restraint pressure of the secondary battery, the SOC (State of charge), and the like depend on the resistance value of the secondary battery.

10 Reaction distribution estimation device 11 Heat flux sensor 12 Constant temperature bath 13 Charging / discharging device 14 Heat flux logger 15 Data analysis device 16 Heat conduction sheet 20 Heat dissipation / restraint jig 21 Heat dissipation plate 22 Feed screw 23 Load cell W Secondary battery

Claims (2)

The secondary battery is charged and discharged at at least two different current values, and the heat flux toward the outside of the secondary battery is measured at a plurality of points on the surface of the secondary battery, and a plurality of each of the plurality of points is measured. The first step to acquire the measurement data of
The second step of integrating the plurality of measurement data for each current value and calculating the average value of the integrated values for each current value.
The third step of calculating the first relational expression between the square of the current value and the average value, and
The fourth step of estimating the in-plane current distribution obtained by substituting the heat flux values measured at a plurality of points into the first relational expression and calculating the current value at each point as a reaction distribution.
Have,
A method for estimating the reaction distribution of a secondary battery. In the first step, the secondary battery is charged and discharged under at least two different temperature conditions of the secondary battery, and after the second step and the third step, a plurality of the first steps in each temperature condition are performed. 1 Get the relational expression,
The fourth step is
The second from the average resistance value calculated by dividing the slope of each of the plurality of first relational expressions and the value of the overvoltage during charging and discharging when a current is applied to the secondary battery by the applied current value . The process of calculating the relational expression and
A step of calculating the resistance ratio to the average resistance value from the second relational expression at each of the plurality of locations, and a step of calculating the resistance ratio to the average resistance value.
A step of estimating the in-plane current distribution obtained by dividing the average current value of the secondary battery by the value of the resistance ratio at each of the plurality of locations as a reaction distribution.
including,
The method for estimating the reaction distribution of a secondary battery according to claim 1.

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