JP7280211B2 - Method for measuring side reaction current value of secondary battery, method for estimating cell life of secondary battery, inspection method - Google Patents

Description

The present invention relates to a method for measuring the side reaction current value of a secondary battery, a method for estimating a cell life of a secondary battery , and a method for inspecting a cell of a secondary battery. The present invention relates to a method for measuring a side reaction current value, a method for estimating a cell life of a secondary battery, and an inspection method for more accurately estimating the life of a secondary battery .

As is well known, secondary batteries such as lithium-ion secondary batteries are used as power sources for portable electronic devices and as power sources for electric vehicles, hybrid vehicles, and the like.
A secondary battery deteriorates for various reasons, and a life estimation technology is indispensable for estimating in advance whether a secondary battery shipped as a product satisfies the life required by the user in the expected usage environment. .

Therefore, in the invention disclosed in Patent Document 1, as shown in FIG. 7, it is possible to estimate the life of the secondary battery by defining the deterioration rate of the entire battery by √ of the running distance based on the total running distance. It's becoming

JP 2007-195312 A

However, for example, the deterioration of a secondary battery mounted on a vehicle is affected not only by factors such as the travel distance of the vehicle, but also by factors such as the temperature of the operating environment and the state of the SOC of the secondary battery used.

In addition, there are various mechanisms of deterioration, such as deterioration/decomposition of positive and negative electrode active materials, film formation, electrolyte deterioration/consumption, deposition of lithium metal, generation of minute metals, and deterioration of separators.
In the invention described in Patent Document 1, there is a problem that the deterioration phenomenon that does not follow the √ of the travel distance is not taken into consideration.

Further, in Patent Document 1, since the deterioration of the entire battery is estimated, the deterioration of the positive electrode and the negative electrode constituting the secondary battery cannot be separately estimated. As a result, there is a problem that the accuracy of life estimation cannot be increased.

The present invention has been made in view of such circumstances, and its object is to estimate the deterioration rate of the positive electrode and the negative electrode that constitute the secondary battery separately, and to more accurately estimate the life of the secondary battery. It is an object of the present invention to provide a method for measuring a side reaction current value of a secondary battery, a method for estimating the life of the secondary battery, and a method for inspecting it, which can estimate the secondary battery and inspect whether or not it can be shipped based on the estimated value.

In order to solve the above problems, the method for measuring a side reaction current value of the present invention includes a storage step of storing a secondary battery under specific conditions, and a decrease in capacity of the battery full capacity before and after storage of the stored secondary battery. a step of measuring a battery capacity decrease amount of measuring the quantity Q _loss ; a step of measuring a self-discharge capacity of measuring the self-discharge capacity _QSD of the stored secondary battery before and after storage; and a step of measuring the side reaction current values of the positive electrode and the negative electrode under the specific conditions during storage from the QSD.

Further, in the storage step, it is preferable to set an arbitrary cell voltage V1 that does not exceed full charge and store at an arbitrary temperature T1 for an arbitrary storage period t1.
In the side reaction current value measurement step, the side reaction current _ISR(NE)0 of the negative electrode can be obtained by dividing the self-discharge capacity QSD by the storage period t1. In the step of measuring the side reaction current value, the side reaction current _ISR(NE)0 of the negative electrode is subtracted by the quotient obtained by dividing the amount of capacity decrease _Qloss by the storage period t1. The reaction current _ISR(PE)0 can be determined.

In the step of measuring the amount of decrease in battery capacity, it is also preferable to determine the amount of decrease in capacity Q _loss from the difference between the fully discharged battery capacity before and after storage and the fully charged battery capacity.
In the self-discharge amount measurement step, the self-discharge capacity QSD is obtained from the difference between the battery capacity from the fully discharged state before storage to an arbitrary cell voltage V1 and the remaining capacity until the fully discharged state after storage. preferable.

The fully discharged state may also be determined as the fully discharged state when the cell SOC is 0%. In addition, the fully discharged state may be determined when the cell voltage is 3.0V.
The secondary battery can be suitably applied to a lithium ion secondary battery.

In addition, by using these methods for measuring side reaction current values, a side reaction current value measurement step for obtaining the side reaction current values of the positive electrode and the negative electrode under specific conditions, and the side reaction current value measurement step obtained in advance. A deterioration amount calculation step of calculating the amount of deterioration of the positive electrode and the amount of deterioration of the negative electrode under the assumed use environment using the relationship between the side reaction current values of the positive electrode and the negative electrode and the time-lapse data of the use environment. and a life estimation step of estimating the life of the secondary battery based on the amount of deterioration.

In this method for estimating the life of a secondary battery, it is preferable that in the step of calculating the deterioration amount, the temporal data of the usage environment include any one of temperature, positive and negative electrode potentials, and accumulated deterioration amount.
Further, the life estimation step using such a secondary battery life estimation method, the estimated life of the secondary battery estimated by the above secondary battery life estimation method, and the preset expected life are compared. and passing the test if the estimated life span is equal to or longer than the expected life span.

According to the method for measuring the side reaction current value of the secondary battery, the method for estimating the lifetime, and the method for inspecting the secondary battery of the present invention, the deterioration rate of the positive electrode and the negative electrode constituting the secondary battery can be separately estimated, and the lifetime of the secondary battery can be estimated more accurately. , and can be implemented to check this.

1 is a block diagram showing the configuration of a life estimation device for a lithium-ion secondary battery according to the present embodiment; FIG. FIG. 2 is a perspective view showing an example of the configuration of each cell of the lithium ion secondary battery of the embodiment; 4 is a flow chart for measuring a side reaction current value according to the present embodiment; A list of input data in the shipping inspection method of the present embodiment. 4 is a flow chart of a shipping inspection method according to the present embodiment; The schematic diagram of the vehicle by which the lithium ion secondary battery of other embodiment is mounted. 4 is a flow chart showing the flow of processing related to life estimation in the prior art.

(First embodiment)
With reference to FIGS. 1 to 5, an embodiment in which a method for measuring a side reaction current value, a method for estimating a life span, and a method for inspecting a secondary battery according to the present invention is embodied using a lithium-ion secondary battery 1 for vehicle use as an example. will be described as an example.

<Overview of First Embodiment>
As described in the conventional technology, a life estimation technology is indispensable for estimating whether the life required by the user is satisfied in the assumed usage environment at the time of production and shipment of automotive lithium-ion secondary batteries.

Therefore, in the life estimation method of the present embodiment, the present inventors measured the side reaction current value of the lithium ion secondary battery 1 as a premise in order to estimate the life of the lithium ion secondary battery 1 more accurately. 3), the side reaction current value, which serves as a reference under constant conditions, was obtained. Specifically, the lithium ion secondary battery 1 is stored under specific temperature, starting voltage, and duration conditions, and the changes in the positive electrode side reaction current value and the negative electrode side reaction current value specific to the lithium ion secondary battery 1 are separately measured. Found it. The change per unit time (h) is estimated from the change in the side reaction current value ISR _{(PE)0 of the} positive electrode and the side reaction current value _{ISR(NE)0 of} the negative electrode, and this is measured under predetermined storage conditions. It can be grasped as the rate of deterioration specific to the lithium ion secondary battery 1 .

On the other hand, the side reaction current value _ISR(PE)0 of the positive electrode and the side reaction current value _ISR(NE)0 of the negative electrode of the lithium ion secondary battery 1 are adjusted in advance under predetermined conditions by the environmental temperature T and the cell voltage V. Measure the relationship as a map of what kind of change there is in comparison with the case of saving.

In addition, in the lithium ion secondary battery 1 to be mounted on the vehicle, the environmental temperature T and the cell voltage V are set in advance from the start of use to the expected life tmax (set according to the warranty period, etc., for example, 10 years). The time-varying data TD and the time-varying data VD are created assuming how they change.

Then, the rate of deterioration inherent to the lithium ion secondary battery 1, the change in the usage environment such as the assumed environmental temperature T over time data TD and the cell voltage V over time data VD, and the deterioration in the usage environment Read impact. By integrating these, the side reaction current values of the positive electrode and the negative electrode are obtained, and the capacity reduction amount Q _loss of the lithium ion secondary battery 1 is calculated. From this, it is estimated how much deterioration is accumulated in the lithium ion secondary battery 1 at the time of life tmax assumed from the speed of deterioration inherent in the lithium ion secondary battery 1 and the speed of deterioration. I found out what I can do.

That is, the positive electrode side reaction current value I _{SR (PE) 0} and the negative electrode side reaction current value I _{SR (NE) 0} under predetermined conditions are corrected while considering the influence of the environmental temperature T and the cell voltage V. The deterioration from t0 to the assumed life tmax is calculated and integrated every predetermined time t2. From this, the state of deterioration at the assumed life tmax can be known.

Then, <user request>, which is the amount of capacity decrease set in advance by the user as a threshold, is compared with the amount of capacity decrease predicted at the time of life tmax of the lithium ion secondary battery 1, and the lithium ion secondary battery 1 is compared. Whether or not the battery 1 can be shipped as a product is inspected by determining whether or not the battery 1 has an electric capacity up to the life tmax.

<Lithium ion secondary battery 1>
Next, the lithium ion secondary battery 1 to be inspected will be described. A vehicle-mounted lithium ion secondary battery 1 is formed by combining a plurality of cells 1A as shown in FIG. The cell 1A includes an electrode body 14 in which a positive electrode sheet 15, a negative electrode sheet 16, and a separator 17 for separating them are wound in a case 12, and is filled with an electrolytic solution. The positive electrode contains an active material such as lithium cobalt oxide, and the negative electrode contains an active material such as graphite.

Deterioration of the lithium ion secondary battery 1 mounted on such a vehicle includes deterioration/decomposition of the positive and negative electrode active materials, formation of a film, deterioration/consumption of the electrolyte, precipitation of lithium metal, generation of fine metal, and separator deterioration. deterioration, etc. Therefore, in addition to factors such as the mileage of the vehicle, the temperature of the operating environment, the SOC state of the secondary battery used, and other history factors also contribute to deterioration.

<Lithium ion secondary battery life estimation device>
FIG. 1 is a block diagram showing the configuration of a life estimation device 2 for a lithium ion secondary battery 1. As shown in FIG. A life estimating device 2 for a lithium ion secondary battery 1 of this embodiment includes a well-known charging/discharging device 3 , cell voltage measuring device 4 , cell current measuring device 5 , thermometer 6 and heat retaining device 7 . It also has a control device 8 comprising a well-known computer having an interface for controlling them. The control device 8 has a CPU 81 and a memory 82 . The memory 82 includes RAM and ROM.

These functions as a life estimation device 2 for the lithium ion secondary battery 1 and as storage means for storing the lithium ion secondary battery 1 under specific conditions. It also functions as a battery capacity decrease amount measuring means for measuring the amount of decrease in capacity Q _loss of the stored lithium ion secondary battery 1 before and after storage at full capacity. It also functions as self-discharge amount measuring means for measuring the self-discharge capacity QSD of the stored lithium-ion secondary battery 1 before and after storage. Further, using the measured capacity decrease amount Q _loss and self-discharge capacity QSD, and the relationship between the side reaction rate and the usage environment obtained in advance, the deterioration amount of the positive electrode and the deterioration amount of the negative electrode under the assumed usage environment are calculated. It functions as a deterioration amount calculating means for calculating each. Then, it functions as life estimation means for estimating the life of the lithium ion secondary battery 1 based on the deterioration amount. Furthermore, it can be implemented as a shipping inspection device for lithium ion secondary batteries.

(Action of the first embodiment mode)
<Flowchart for measurement of side reaction current value>
Next, the measurement of the side reaction current value, which is the premise of the method for estimating the lifetime of the lithium ion secondary battery of the present embodiment, will be described with reference to the flowchart of FIG. By measuring the side reaction current value, individual differences in the deterioration rate of the lithium ion secondary battery 1 can be found.

First, prior to explaining this flowchart, the terms used in the explanation will be explained in advance.
"T1 (°C)" is an arbitrary storage temperature (eg, 50°C).

"t1(h)" is an arbitrary retention period (eg, 24 hours).
“V1 (V)” is a value obtained from a fully discharged cell voltage of 3.0 (V) (in this embodiment, the cell voltage in a completely discharged state with a cell SOC of 0% is referred to as a “lower limit voltage”). A voltage (for example, 3.8 (V)) arbitrarily set between 4.1 (V) (cell SOC 0 to 100%) is referred to as an “upper limit voltage” in the present embodiment. In this embodiment, it is used to measure self-discharge capacity and is also an arbitrary initial cell voltage for storage.

"Q1 (Ah)" is the battery before storage in which the battery capacity was measured from the lower limit voltage of 3.0 (V) to the fully charged cell voltage of 4.1 (V) (here, the voltage at 100% cell SOC). It is full.

“Q2 (Ah)” is the interval capacity before storage measured from the lower limit voltage 3.0 (V) to the upper limit voltage V1=3.8 (V).
"Q3 (Ah)" is the remaining capacity after storage after discharging from the upper limit voltage V1 to the lower limit voltage 3.0 (V).

"Q4 (Ah)" is the battery full capacity after storage measured from the lower limit voltage of 3.0 (V) to the full charge of 4.1 (V).
"QSD (Ah)" is the self-discharge capacity during the storage period obtained from the difference between the interval capacity Q2 before storage and the residual capacity Q3 after storage.

"Q _loss (Ah)" is the amount of decrease in capacity obtained from the difference between the full battery capacity Q1 before storage and the full battery capacity after storage.
"I _SR(NE)0 (A)" is the side reaction current (rate) of the negative electrode obtained by dividing the self-discharge capacity QSD (Ah)/storage period t1 (h).

“I _{SR (PE) 0} (A)” is the difference between the negative electrode side reaction current (rate) I _{SR (NE) 0} and the quotient of capacity decrease amount Q _loss (Ah)/storage period t1 (h) This is the obtained side reaction current (speed) of the positive electrode.

This embodiment is defined as above.
<Procedure of measurement flow chart of side reaction current value>
Next, using these definitions, the procedure for measuring the side reaction current value of the lithium ion secondary battery 1 will be described along the flowchart of FIG.

First, when the process of measuring the side reaction current value is started (START), the battery is charged from the lower limit voltage of 3.0 (V) at the cell SOC of 0% at the time of complete discharge to the full charge of 4.1 (V) at the cell SOC of 100%. to measure the battery full capacity Q1 (Ah) before storage (S1).

Next, by charging in the voltage section from the lower limit voltage 3.0 (V) to the upper limit voltage V1=3.8 (V), the section capacity Q2 (Ah) before storage is measured (S2).
Subsequently, the voltage is adjusted to the upper limit voltage V1=3.8 (V). Then, it is stored at an arbitrary temperature T1 (eg, 50° C.) for an arbitrary period of time t1 (eg, 24 hours) (S4). This procedure corresponds to the "storage step". Therefore, this storage is performed under constant conditions of the starting cell voltage, the storage temperature T1, and the storage period t1.

After storage, the battery is set to the upper limit voltage V1=3.8 (V), discharged to the lower limit voltage of 3.0 (V), and the residual capacity Q3 (Ah) after storage is measured (S5). Subsequently, the battery is fully charged from the lower limit voltage of 3.0 (V) to the cell SOC of 100%, and the battery full capacity Q4 (Ah) after storage is measured. In this case, the cell SOC is defined instead of the voltage. This is because after storage, the maximum voltage may be lower than before storage due to deterioration of the active material/electrolyte, formation of a film, etc., and thus the voltage may not be the same as before storage.

Then, the difference between the section capacity Q2 (Ah) before storage and the remaining capacity Q3 (Ah) after storage is obtained. Compared to the interval capacity Q2 before storage, the remaining capacity Q3 after storage has a decrease in capacity due to self-discharge. In other words, by obtaining these in the same voltage section, the self-discharge amount during the storage period t1 can be obtained. By this procedure, the self-discharge capacity QSD is calculated from the electrical capacity that decreased during the storage period t1 (S7). This procedure corresponds to the "step of measuring the amount of self-discharge".

Next, the negative electrode side reaction current (rate) _ISR(NE)0 (A) is calculated by dividing the self-discharge capacity QSD(Ah) by the storage period t1(h) (S8).
Also, the capacity reduction amount Q _loss (Ah) is calculated from the difference between the full battery capacity Q1 (Ah) before storage and the full battery capacity Q4 (Ah) after storage (S9).

Finally, from the difference between the side reaction current (rate) I _{SR (NE) 0} (A) of the negative electrode and the quotient (A) obtained by dividing the capacity decrease amount Q _loss (Ah) by the storage period t1 (h), the positive electrode _is calculated (S11).

As described above, the side reaction current (rate) _ISR(NE)0 (A) of the negative electrode and the side reaction current (rate) _ISR(PE)0 of the positive electrode of the lithium ion secondary battery in the predetermined storage interval of the present embodiment The measurement procedure of (A) ends (END).

By such a procedure, the positive electrode side reaction current (rate) I _{SR (PE) 0} ( A) and the side reaction current (rate) _ISR(NE)0 (A) of the negative electrode can be measured. That is, the speed of deterioration that serves as a reference is found.

<Delivery inspection method for lithium-ion secondary battery products>
Next, FIG. 5 shows an embodiment of a shipping inspection method for a product of the lithium ion secondary battery 1, which is performed using the procedure for measuring the side reaction current value of the lithium ion secondary battery 1 shown in FIG. Description will be made with reference to flowcharts.

First, prior to the description of FIG. 5, data and the like that are prerequisites for such processing of the lithium ion secondary battery 1 will be described with reference to FIG.
FIG. 4 shows data and the like used in the shipping inspection method for the lithium ion secondary battery 1 shown in FIG. The data to be input in the shipping inspection method for the product of the lithium ion secondary battery 1 are (i) temporal data of assumed use environment input, (ii) data of pre-obtained map input, and (iii) measured side reaction current. There is data for I _SR (A) and the like.

<(i) Temporal data of assumed usage environment>
This temporal data indicates in what kind of environment the lithium ion secondary battery 1 is used from time t0 (at the time of shipment of the lithium ion secondary battery 1) to life tmax at time t2 (for example, 24 hours). It is temporal data assumed for each time (one day). The "lifetime tmax" is the period during which the lithium ion secondary battery 1 is assumed to have a predetermined performance and is used, in other words, the "lifetime" assumed as a product. (10 years). The contents are the cell voltage data estimated from the environmental temperature assumed from the region and season of use, and the cell voltage control assumed from the vehicle type and application.

As described above, the deterioration of the lithium-ion secondary battery cannot be accurately estimated based on the mileage alone, as in the past. Therefore, this temporal data reflects the effects of temperature and seasonal fluctuations in the area where the vehicle is used, the driving conditions of the user, etc., which cannot be determined simply from the mileage, in estimating the deterioration of the lithium ion secondary battery 1. This data is for The temporal data may be created based on past vehicle driving information or by assuming driving under severe conditions.

<(i)-1: Temporal data TD of environmental temperature T (every time t2)>
Both the deterioration rate of the positive electrode and the negative electrode change with temperature. Especially in lithium ion secondary batteries, the reaction rate increases at high temperatures, and the deterioration progresses remarkably. When the lithium ion secondary battery 1 is exposed to the scorching sun in a high-temperature region, the lithium-ion secondary battery 1 is significantly degraded, such as formation of a film. Also, when the temperature drops extremely in a cold region, deterioration of the lithium ion secondary battery 1 such as deposition of metallic lithium progresses. Such information on changes in the environmental temperature T due to extreme cold or extreme heat is an important factor for determining deterioration.

<(i)-2: Temporal data VD of cell voltage V (every time t2)>
Moreover, the deterioration rate of the positive electrode and the negative electrode changes depending on the cell voltage V. FIG. In a lithium-ion secondary battery, when the cell SOC is 0% or less (3.0 (V) or less in this embodiment) or the cell SOC is 100% or more (4.1 (V) or more in this embodiment), , the deterioration progresses remarkably. In addition, even if it is continuously placed in a cell SOC that is high on a daily basis, deterioration tends to progress. For this reason, information on the possibility of being placed at an extremely high cell voltage V or an extremely low cell voltage V depending on the application and vehicle type, such as commercial vehicles and private cars, passenger cars and trucks, is an important factor in determining deterioration. .

<(ii) Pre-acquisition map input>
Here, the following maps are created in advance.
As described above, the temporal data TD of the environmental temperature T in which the lithium ion secondary battery 1 is placed and the temporal data VD of the cell voltage V are important information for determining deterioration.

Next, it is necessary to know how much the environmental temperature T and the cell voltage V affect the deterioration of the lithium ion secondary battery 1 based on the temporal data TD and the temporal data VD. be. Therefore, depending on the environmental temperature T and the cell voltage V, the side reaction current (rate) _ISR(NE)0 of the negative electrode and the side reaction current (rate) _ISR(PE) of the positive electrode that serve as a reference when stored under predetermined conditions A map of the corrected values was created in advance to show how much it affects ₀ .

<(ii)-1: Environmental temperature-Negative electrode side reaction current (rate) _ISR(NE)0 >
<(ii)-2: Environmental temperature-positive side reaction current (rate) _ISR(PE)0 >
The side reaction current (rate) _ISR(NE)0 of the negative electrode and the side reaction current (rate) _ISR(PE)0 of the positive electrode, which are the criteria for determining the deterioration of the lithium ion secondary battery 1 to be inspected, are shown in FIG. 3, that is, the side reaction current (speed) at the storage temperature T1. However, according to the Arrhenius law, the rate of deterioration of the positive electrode and the negative electrode accelerates as the temperature rises, so the deterioration progresses and the side reaction current increases. In particular, lithium-ion secondary batteries deteriorate remarkably at high temperatures. In addition, lithium deposition and the like are likely to occur at extremely low temperatures. The effect differs between the positive electrode and the negative electrode due to the difference in their active materials. Therefore, even at the same predetermined time t2, the rate of deterioration varies greatly depending on the environmental temperature T during that time period. In addition, the influence is different between the positive electrode and the negative electrode.

Therefore, temperature-negative side reaction current (rate) _ISR(NE)0 and (ii)-2: temperature-positive side reaction current (rate) _ISR(PE)0 were prepared in advance as a map. . First, the side reaction current (rate) _ISR(NE)0 of the negative electrode and the side reaction current (rate) ISR _{(PE)0 of the} positive electrode are used as references. Then, using this map, the environmental temperature T in that time period is used as an argument, and the influence of the environmental temperature T is taken into account for each conversion. In this way, the positive electrode and the negative electrode are separated, and the corrected negative electrode side reaction current (rate) _ISR(NE)0 and positive electrode side reaction current (rate) _ISR(PE)0 are obtained.

<(ii)-3: negative electrode potential V _NE - negative electrode side reaction current (rate) I _SR(NE)0 >
<(ii)-4: positive electrode potential V _PE - positive electrode side reaction current (rate) I _{SR (PE)0} >
In this test, the side reaction current (rate) _ISR(NE)0 of the negative electrode and the side reaction current (rate) _ISR(PE)0 of the positive electrode are determined under a predetermined condition, that is, the upper limit voltage V1 at which storage starts (in the embodiment, , 3.8 (V)), the storage period t1, and the side reaction current (rate) at the storage temperature T1. However, the deterioration rate of the positive electrode and the negative electrode changes with the cell voltage V. In a lithium ion secondary battery, overdischarge at a cell SOC of 0% (3.0 (V) or less in this embodiment) or overcharge at a cell SOC of 100% or more (4.1 (V) or more in this embodiment) , the deterioration progresses remarkably. Degradation also progresses when the cell SOC is maintained at a high level all the time.

The effect differs between the positive electrode and the negative electrode due to the difference in their active materials. Therefore, even at the same predetermined time t2, the rate of deterioration varies greatly depending on the cell voltage V in that time period. In addition, the influence is different between the positive electrode and the negative electrode. It is believed that the side reaction current (rate) _ISR(NE)0 of the negative electrode and the side reaction current (rate) _ISR(PE)0 of the positive electrode increase due to the formation of a coating such as an SEI coating. The formation of these films can be calculated by Tafel's formula. This can be calculated by separating the positive and negative electrodes. Thus, the negative electrode potential _VNE and the positive electrode potential _VPE are closely related to the film formation potential.

Therefore, negative electrode potential V _NE −negative side reaction current (rate) _ISR(NE)0 and (ii)-2: positive electrode potential V _PE −positive side reaction current (rate) _ISR(PE)0 I prepared the relationship as a map. 3, that is, the negative electrode side reaction current (rate) _ISR(NE)0 and the positive electrode side reaction current (rate) _ISR(PE)0 at the storage temperature T1. do. Then, using this map, the corrected negative electrode side reaction current (rate) I _{SR (NE) 0} and positive electrode side reaction current (rate) I _{SR (PE) 0} are corrected with the cell voltage V in that time period as an argument. are converted into positive and negative electrodes.

<(ii)-5: ∫ I _{SR (NE)} dt-I _{SR (NE) t} >
<(ii)-6: ∫I _{SR (PE)} dt-I _{SR (PE) t} >
In the lithium ion secondary battery 1, the side reaction current increases as deterioration accumulates, but the deterioration becomes a unique value depending on the history of the environmental temperature T, the cell voltage V, and the like. Therefore, here, the deterioration rate is derived by integrating the side reaction current having such a history for each time t and differentiating it. By doing so, it is a map for deriving the characteristic deterioration rate at time t2 of the lithium ion secondary battery 1 to be inspected having the history shown in the temporal data TD and the temporal data VD.

<(ii)-5: ∫ I _{SR (NE)} dt-I _{SR (NE) t} >
As described above, at each time t2, the negative electrode side reaction current _{ISR(NE) t derived from the history of the environment specific to the lithium ion secondary battery 1 is calculated from the negative electrode side reaction current ∫ISR(NE)dt.} lead. That is, it is a map for determining the rate of deterioration of the negative electrode specific to the lithium ion secondary battery 1 to be inspected. Based on the accumulated side reaction current ISR _{(NE)t of the} negative electrode obtained at time t2 from this map, the capacity reduction amount _Qloss is calculated every 2t.

<(ii)-6: ∫I _{SR (PE)} dt-I _{SR (PE) t} >
Similarly, every time t2, the positive electrode side reaction current I _SR(PE) t derived from the environmental history specific to the lithium ion secondary battery 1 is derived from the positive electrode side reaction current ∫I _{SR(PE) dt.} . That is, it is a map for determining the rate of deterioration of the positive electrode inherent to the lithium ion secondary battery 1 to be inspected. Based on the positive side reaction current _ISR(PE)t accumulated at time t2 obtained from this map, the capacity reduction amount _Qloss is calculated every 2t.

<(iii) Measured negative and positive side reaction currents (velocities) _ISR(NE)0 / _ISR(PE)0 >
Here, when the lithium-ion secondary battery 1 to be inspected is stored under specific conditions, the positive electrode side reaction current (rate) _ISR(PE)0 and the negative electrode side reaction current (rate) It is the result of measuring _ISR(NE)0 by the procedure shown in FIG. It is basic data that serves as an inspection standard unique to the lithium-ion secondary battery 1 to be inspected.

<(iii)-1: negative electrode side reaction current (rate)) _ISR(NE)0 >
It is the side reaction current of the negative electrode obtained by the procedure of FIG. 3, that is, the rate of deterioration of the negative electrode under the conditions of the initial cell SOC, the storage temperature T1, and the storage period t1, and is a reference value for this inspection method.

This inspection provides basic data for more accurate estimation of deterioration by correcting the reference value with reference to the temporal data TD and the temporal data VD.
<(iii)-2: positive electrode side reaction current (rate)) _ISR(PE)0 >
The side reaction current of the positive electrode obtained by the procedure of FIG. 3, that is, the rate of deterioration of the positive electrode under the conditions of the initial cell SOC, the storage temperature T1, and the storage period t1, is a reference value for this inspection method.

This inspection provides basic data for more accurate estimation of deterioration by correcting the reference value with reference to the temporal data TD and the temporal data VD.
<Embodiment flow chart of shipping inspection method>
Next, based on the side reaction current (rate) _{ISR (NE) 0} of the negative electrode and the side reaction current (rate) _{ISR (PE) 0} of the positive electrode obtained in FIG. An embodiment of the shipping inspection method using, etc. will be described with reference to the flow chart of FIG.

<Reading Time-lapse Data TD and Time-lapse Data VD>
First, from t0, the relevant environmental temperature T required for the processing at that time t2 stored for each time t2 is read from the temporal data TD, and the relevant cell voltage is read from the temporal data VD (S11). This reading is performed sequentially every time t2, first from t0 to time t2, then from the end of the previous time t2 to the next time t2, and the processing from S11 to S50 is repeated. .

<Calculation of negative electrode side reaction current (rate) _ISR(NE)t >
Here, first, the side reaction current (rate) _ISR(NE)t of the negative electrode corresponding to the degradation rate of the negative electrode is calculated (S25).

First, <negative electrode potential V _NE > is calculated from the cell voltage at the time t2 read from the temporal data VD (S20).
Next, <(iii)-1: negative electrode side reaction current (rate) _ISR(NE)0 > obtained by the procedure of FIG. 3, which serves as a reference, is read. In addition, map (ii)-1 <ambient temperature>-<negative side reaction current (rate) I _{SR (NE) 0} > and map (ii)-3 <negative electrode potential V _NE >-<<negative electrode side reaction current (rate) _ISR(NE)0 > is read out from negative electrode side reaction current (rate) _ISR(NE)0 > (S21).

From these data, the product of <negative electrode side reaction current (rate) _ISR(NE)t > at time t2 and <time t2> is calculated (S22). The product of S22 is integrated to calculate <∫I _SR(NE) dt> (S23). From the map (ii)-5<∫I _SR(NE) dt−I _SR(NE)t >, read out <I _SR(NE)t > (S24), and read <negative electrode side reaction current at time t2. (Speed) _ISR(NE)t > is calculated (S25).

<Calculation of positive electrode side reaction current (rate) _ISR(PE)t >
On the other hand, the side reaction current (rate) _ISR(PE)t of the positive electrode is calculated in parallel with the processing of S20-25 (S30-35). For this purpose, after inputting at arbitrary <every time t2> from <t0> to <tmax> (S11), (i)-2 <cell voltage data over time VD (every time t2)> cell voltage <Positive electrode potential V _PE > is calculated (S30).

Subsequently, <(iii)-2: positive electrode side reaction current (rate) _ISR(PE)0 > obtained by the procedure of FIG. 3, which serves as a reference, is read. In addition, the map (ii)-2 of <environmental temperature>-<positive side reaction current (rate) I _{SR (PE) 0} > and <positive electrode potential V _PE >-<positive side reaction current ( <Positive side reaction current (speed) I _SR(NE)0 > at time t2 is read out from the data of map (ii)-4 of speed) I _SR(PE)0 > (S31).

From these data, the <positive side reaction current (rate) I _{SR (NE) t} > read from map (ii)-2 and map (ii)-4 at time t2, and the <negative electrode Read the product of the side reaction current (rate) I _{SR (NE) t} > and <time t2>, and calculate the product of <positive electrode side reaction current (rate) I _{SR (PE) t} > and <time t2> ( S32). The product of S32 is integrated to calculate <∫I _SR(PE) dt> (S33). Read < _ISR(NE) t> from < _∫ISR(NE) dt-ISR(NE _)t > from map (ii)-6 < _∫ISR(PE) dt-ISR _(PE)t > (S34), <Positive side reaction current (rate) _ISR(PE)t > at time t2 is calculated (S35).

<Calculation of capacity decrease amount Q _loss >
The capacity reduction amount Q _loss is obtained by increasing or decreasing the negative electrode side reaction current I _{SR (NE) 0} and the positive electrode side reaction current I _{SR (NE) 0} depending on the environmental temperature T, the negative electrode potential V _NE and the positive electrode potential V _PE. increase or decrease due to , and the current increase due to accumulated degradation, respectively. Therefore, in the Q _loss calculation step (S40), these factors are integrated to calculate the capacity reduction amount Q _loss at that time.

First, the product of <negative electrode side reaction current (rate) I _{SR (NE)} > read in S22 and <time t2> is read, and <positive electrode side reaction current (rate) I _{SR (PE)} > and <time t2> are read. > is calculated (S32). Next, from the relationship < _ISR(PE)0 = _ISR(NE)0 - _Qloss /t1> in S10 of FIG. 3, _Qloss =t1( _ISR(NE)0 - _{ISR(PE) 0} ) is derived, replace t1 with t2 to obtain the capacity reduction amount Q _loss .

On the other hand, <negative electrode side reaction current (rate) _ISR(NE)t > obtained in S25 is input.
Further, from the <positive side reaction current (rate) ISR _(PE)t > obtained in S35, the <capacity reduction amount Q _loss > is input from the side reaction current value.

In S40, the value obtained in S32, the value obtained in S25, and the value obtained in S35 are integrated, and the capacity reduction amount Q _loss at <time t2> is obtained.
<Calculate ∫ Q _loss >
The Q _loss at the time t2 obtained in S40 is integrated by <∫Q _loss > (S50), and the process returns to S11 again, and the procedure of S11 to S50 is sequentially repeated every time t2 from t0 to tmax. Then, Q _loss is integrated every time t2 from t0 to tmax.

<∫Q _loss > obtained in this manner means the deterioration state after the life tmax of the lithium ion secondary battery 1 to be inspected, that is, after 10 years in the present embodiment.
<Repetition of processing every time t2 from t0 to tmax>
In S50, when the processing for time t2 is completed, it is determined whether the processing for each time t2 has completed up to the life tmax. Repeat process.

If the process has been completed up to tmax (S51: YES), the process is regarded as completed, and the value of the amount of capacity decrease <∫Q _loss > accumulated up to that point is acquired.
<Pass/fail judgment of inspection>
In this embodiment, the amount of capacity decrease <∫Q _loss > accumulated in the lithium ion secondary battery 1 at the life tmax when the processing from t0 to tmax is completed in S51, and in this embodiment, it is set in advance by the user based on the warranty period. Then, it is compared with <user request>, which is the amount of capacity decrease after 10 years (S52).

In the case of "∫Q _loss <user request" (S52: NO), the battery does not meet the standards for shipment, and it is determined that the battery fails the inspection and cannot be shipped (S53). In the case of "∫Q _loss <user request" (S52: YES), the performance of the battery has reached the standard for shipment, and it is determined that the battery has passed the inspection and can be shipped (S54).

This completes the implementation of the shipping inspection method.
According to this shipping inspection, in the shipment of the lithium ion secondary battery 1 as a product, only those that meet the shipping standard that the life tmax exceeds the warranty period are shipped, and it is expected that the product standard will not be met at the time of the life tmax. things are never shipped.

(Effect of the first embodiment)
The effects of the method for measuring the side reaction current value, the method for estimating the lifetime, and the method for inspecting the lithium ion secondary battery 1 of the present embodiment are listed below.

(1) The service life can be accurately estimated by taking into consideration not only the travel distance and usage time, but also many deterioration factors such as the environmental temperature T and the cell SOC.
(2) The life of the lithium-ion secondary battery 1 can be estimated more accurately because deterioration can be determined by dividing the positive electrode and the negative electrode into individual cells as well as evaluating the cell 1A as a whole.

(3) Even if the user's usage status in the past is not known, the status can be accurately grasped based on the time-lapse data TD and the time-lapse data VD, and the future life can be estimated.
(4) Based on the individual characteristics of each lithium-ion secondary battery 1, it is possible to accurately predict the future lifespan of each lithium-ion secondary battery 1 by accurately grasping the individual characteristics and conditions of deterioration.

(5) According to this life estimation method, the reliability of the quality of the lithium ion secondary battery 1 as a product can be guaranteed.
(Second embodiment)
The first embodiment is an invention in which the life of a battery is determined before shipment at the time the battery is manufactured. However, even for a second-hand lithium-ion secondary battery 1 with a usage history, it is possible to similarly determine the speed of deterioration inherent to the lithium-ion secondary battery 1 and the deterioration of the battery until the remaining life. Needless to say. Here, the remaining life of a secondary battery with a usage history is called "remaining life". The prediction of the "remaining life" is different from the life judgment at the time of manufacture, and by referring to the usage history of the lithium ion secondary battery 1, the relationship between the environmental temperature and cell SOC of the lithium ion secondary battery 1 and deterioration Therefore, it is possible to accurately predict the inherent remaining life of the lithium ion secondary battery 1 when used in a similar environment.

The basic inspection method is common in the second embodiment. The difference from the first embodiment is that the temporal data TD and the temporal data VD are past actual measurement values based on the past usage history, and the temporal data TD and the temporal data VD of the remaining life in the future are based on past data. It differs in that it is assumed based on history.

<Overall Configuration of Vehicle Mounted with Secondary Battery>
Next, the usage history of this lithium ion secondary battery 1 can be collected in the vehicle in which it is mounted. Therefore, a vehicle 10 in which the lithium ion secondary battery 1 of this embodiment is mounted will be briefly described.

FIG. 6 is a diagram schematically showing the overall configuration of a vehicle 10 equipped with a lithium ion secondary battery 1 according to the second embodiment. A vehicle 10 shown in FIG. 6 is a hybrid vehicle. The vehicle 10 includes a lithium ion secondary battery control device 18, a PCU (Power Control Unit) 30, motor generators 41 and 42, an engine 50, a power split device 60, a drive shaft 70, A drive wheel 80 is provided. The control device 18 for the lithium ion secondary battery includes a monitoring unit 20 for monitoring the lithium ion secondary battery 1, the cell voltage BV, the current BI, and the environmental temperature BT of the lithium ion secondary battery 1, temporal data TD, and temporal data TD. and an ECU (Electronic Control Unit) 100 having a memory 102 for storing the VD.

<Motor Generator 42>
The motor generator 42 mainly operates as an electric motor, and drives the drive wheels 80 with a large current supplied from the lithium ion secondary battery 1 during rapid acceleration. On the other hand, during braking of the vehicle or on a downward slope, the motor generator 42 operates as a power generator to regenerate a large current and supply the lithium ion secondary battery 1 with a large current.

In such a lithium-ion secondary battery 1 for vehicle use, the environmental temperature T changes from low to high, high-rate charge/discharge is performed, and the charge/discharge conditions change from a low cell SOC to a high cell SOC. Also, the progress of deterioration may differ depending on the usage environment.

<Lithium ion secondary battery monitoring unit 20>
Monitoring unit 20 includes a voltage sensor 21 , a current sensor 22 and a temperature sensor 23 . A voltage sensor 21 detects a cell voltage VB. A current sensor 22 detects a current IB that is input to and output from the lithium ion secondary battery 1 . A temperature sensor 23 detects a temperature TB for each block. Each sensor outputs a signal indicating the detection result to ECU 100 . These temperature TB, cell voltage VB, and current IB are stored as environmental temperature T and cell voltage V for each time t2 as a history of the lithium ion secondary battery 1, with temporal data TD and temporal data VD.

<Temporal data TD and temporal data VD in the past usage history>
In the first embodiment, the side reaction current value is measured when the lithium ion secondary battery 1 is manufactured. , the side reaction current value is measured, and the remaining life from that point is estimated.

In this case, time-lapse data TD and time-lapse data VD are collected and stored every time t2 by the voltage sensor 21, the current sensor 22, and the temperature sensor 23 of the monitoring unit 20 of the lithium-ion secondary battery 1 mounted on the vehicle. Keep That is, the history of the usage conditions such as the environmental temperature T and the cell voltage V of the lithium ion secondary battery 1 indicates in what environment the lithium ion secondary battery 1 has been used. The past time-lapse data TD and time-lapse data VD are not necessarily required if the current side reaction current value of the lithium ion secondary battery 1 is measured.

<Remaining life time data TD, time data VD>
When this lithium ion secondary battery 1 is mounted in the same vehicle 10, in order to estimate the remaining life of this lithium ion secondary battery 1, the time data TD up to the life tmax and the time data VD are used as this By using the time-lapse data TD and the time-lapse data VD based on the past performance, it is possible to make an accurate prediction in a similar usage environment.

(Action of Second Embodiment)
The operation of the present embodiment is different in that the temporal data TD and temporal data VD in the past usage history are referred to as the temporal data TD and the temporal data VD, but the method of measuring the side reaction current value shown in FIG. It is the same method, and the shipment inspection method shown in FIG. 6 is also the same method.

However, although the result is not strictly a shipment, it can be used as a pass/fail judgment when reselling the vehicle equipped with the lithium ion secondary electrons as a used vehicle. is read as whether it can be resold or not.

(Effect of Second Embodiment)
In addition to the effects of the first embodiment, the second embodiment has the following effects.
(6) Future temporal data TD and temporal data VD to be used for remaining life prediction are stored in the vehicle based on actual measurement values of the past usage history, and by referring to this, a more accurate usage environment can be predicted. can do. As a result, the remaining life can be estimated more accurately.

(Modification) The present invention is not limited to the above embodiments, and can be implemented as follows.
The control device 18 for the lithium-ion secondary battery according to the present embodiment has been described with an example of a configuration mounted on an electric vehicle. An electric vehicle is typically a hybrid vehicle (including a plug-in hybrid vehicle), but is not limited to this. The lithium-ion secondary battery control device 18 according to the present embodiment can be applied to vehicles in general that generate power using electric power supplied from the lithium-ion secondary battery. Therefore, the electric vehicle may be an electric vehicle or a fuel cell vehicle.

* Further, the application of the method for estimating the life of a lithium-ion secondary battery according to the present embodiment is not limited to a vehicle, and may be a stationary one mounted on a building, for example.
〇 In this embodiment, the secondary battery is described as an example of a lithium ion secondary battery, but the secondary battery is not limited to a lithium ion secondary battery, and may be a nickel metal hydride secondary battery, or in the future. It does not exclude sodium ion secondary batteries, lithium air secondary batteries, etc.

〇 Since the inspection method of the secondary battery of this embodiment can be performed at any time, it can be used not only for inspection of whether the lithium ion secondary battery can be shipped at the time of manufacturing, but also for the lithium ion secondary collected from used vehicles. It can be done at the time of resale of the battery. In addition, of course, it can be used for other purposes simply to determine the deterioration of the secondary battery.

○ The flowcharts shown in FIGS. 3 and 5 are examples, and the order thereof can be changed, and steps can be added, deleted, or changed for implementation.
○ The list of input data in the shipping inspection method shown in FIG. 4 is an example, and the "assumed use environment input", "preliminary acquisition map input", etc. can be changed as appropriate.

○ It goes without saying that the present invention can be implemented as a device by adding, deleting or changing its configuration or changing its category by those skilled in the art as long as it does not depart from the scope of the claims.

DESCRIPTION OF SYMBOLS 1... Lithium ion secondary battery 1A... Cell 2... Life estimation apparatus of lithium ion secondary battery 3... Charge/discharge apparatus 4... Cell voltage measuring device 5... Cell current measuring device 6... Thermometer 7... Thermal insulation device 8... Control device 81 CPU
82...Memory 10...Vehicle 18...Control device 20...Monitoring unit 21...Voltage sensor 22...Current sensor 23...Temperature sensor 30...PCU
41, 42 Motor generator _ISR(NE)0 Negative side reaction current (speed)
I _{SR (PE) 0} ... side reaction current (rate) of the positive electrode
Q1: Full battery capacity before storage Q2: Interval capacity before storage Q3: Remaining capacity after storage Q4: Full battery capacity after storage.
QSD (Ah): Self-discharge capacity Q _loss (Ah) during storage period Capacity decrease amount T1 (°C) Storage temperature t0 (h) Start of use t1 (h) Storage period t2 (h) Hours (Processing unit of chronological data)
tmax (h) ... (assumed) life V1 (V) ... (initial voltage for storage) upper limit voltage

Claims (12)

a storage step of storing the secondary battery cell to be measured under specific conditions;
a step of measuring the amount of decrease in battery capacity for measuring the amount of decrease in capacity Q _loss of the battery full capacity before and after storage of the stored secondary battery cell ;
a self-discharge capacity measurement step of measuring the self-discharge capacity QSD of the stored secondary battery cell before and after storage;
a step of measuring side reaction current values for obtaining side reaction current values of the positive electrode and the negative electrode under specific conditions during storage from the capacity reduction amount Q _loss and the self-discharge capacity QSD. How to measure. The storing step includes:
2. The method for measuring a side reaction current value according to claim 1, wherein the cell voltage is set to an arbitrary cell voltage V1 not exceeding full charge, and stored at an arbitrary temperature T1 for an arbitrary storage period t1. The step of measuring the side reaction current value includes:
3. The method of measuring a side reaction current value according to claim 2, wherein the side reaction current _ISR(NE)0 of the negative electrode is obtained by dividing the self-discharge capacity QSD by the storage period t1. The step of measuring the side reaction current value includes:
The side reaction current I _{SR (PE) 0} of the positive electrode is obtained from the difference obtained by subtracting the quotient obtained by dividing the capacity decrease amount Q _loss by the storage period t1 from the side reaction current I _{SR (NE) 0} of the negative electrode. The method for measuring a side reaction current value according to claim 3 . The step of measuring the amount of decrease in battery capacity includes:
2. The method of measuring a side reaction current value according to claim 1, wherein the amount of decrease in capacity _Qloss is obtained from the difference in battery full capacity from a completely discharged state to a fully charged state before and after storage. The step of measuring the self-discharge capacity includes:
2. The method according to claim 1, wherein the self-discharge capacity QSD is obtained from the difference between the battery capacity from the fully discharged state before storage to an arbitrary cell voltage V1 and the remaining capacity from the fully discharged state after storage. Method for measuring side reaction current value. 7. The method of claim 5 or 6, wherein the fully discharged state is determined as a cell SOC of 0%. 7. The method of measuring a side reaction current value according to claim 5, wherein the fully discharged state is determined to be a cell voltage of 3.0V. The method for measuring a side reaction current value according to any one of claims 1 to 8, wherein the secondary battery is a lithium ion secondary battery. a step of measuring side reaction current values for obtaining side reaction current values of the positive electrode and the negative electrode under specific conditions using the method for measuring side reaction current values according to any one of claims 1 to 9;
Using the relationship between the side reaction current values of the positive electrode and the negative electrode obtained in advance by the step of measuring the side reaction current value and the temporal data of the usage environment, the deterioration amount of the positive electrode under the assumed usage environment and the negative electrode a step of calculating the amount of deterioration for calculating the amount of deterioration;
and a life estimation step of estimating the life of the secondary battery cell based on the deterioration amount. The step of calculating the amount of deterioration includes:
11. The method of estimating the life of a secondary battery cell according to claim 10, wherein the temporal data of the usage environment includes any one of environmental temperature, positive and negative potentials, and accumulated deterioration amount. A life estimation step using the life estimation method of a secondary battery cell according to claim 10 or claim 11;
The estimated lifetime of a secondary battery cell estimated by the method for estimating the lifetime of a secondary battery cell is compared with a preset expected lifetime, and if the estimated lifetime is equal to or greater than the expected lifetime, the battery is judged to have passed the test. A method for inspecting a cell of a secondary battery, comprising:

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