JP2022026770A - Li PRECIPITATION SUPPRESSION CONTROL METHOD OF LITHIUM ION SECONDARY BATTERY, AND CONTROL APPARATUS OF THE LITHIUM ION SECONDARY BATTERY - Google Patents

Abstract

To achieve both of suppression of deposition and an effective use of a metalli lithium and of a lithium ion secondary battery.SOLUTION: A Li precipitation suppression control method of a lithium ion secondary battery, using a side reaction current, comprises: a voltage measurement step (S5) of measuring a cell voltage; an electric potential estimation step (S6) of estimating an electric potential of positive and negative electrodes from the cell voltage to be acquired; a cell temperature measurement step (S7) of acquiring a battery temperature; side reaction current estimation step (S8) of estimating a positive and negative electrode side reaction current value from the electric potential of the estimated positive and negative electrodes and the cell temperature; a negative electrode deterioration amount estimation step (S9) of estimating a negative electrode deterioration amount by integrating the estimated positive and negative electrode side reaction current value; and a charging current determination step (S10) of continuously determining an upper limit charging current permitted in the range where the Li precipitation is suppressed in accordance with the estimated negative electrode deterioration amount.SELECTED DRAWING: Figure 3

Description

The present invention relates to a Li precipitation suppression control method and a control device for a lithium ion secondary battery, and more particularly to a Li precipitation suppression control method and a control device for a lithium ion secondary battery using a side reaction current.

In general, a lithium ion secondary battery has a high energy density, and has a higher initial opening voltage and average operating voltage than other secondary batteries. Therefore, it is suitable for a power supply system for a hybrid vehicle that requires a large battery capacity and a high voltage. Further, the lithium ion secondary battery has an advantage that the charge / discharge efficiency is high because the coulomb efficiency is close to 100%, and therefore energy can be effectively used as compared with other secondary batteries.

However, the lithium-ion secondary battery is used in a usage mode (for example, charging at a high rate, charging from a high charging state (high SOC), continuing charging for a long time, charging at a low temperature (charging in a high resistance state)). Metallic lithium may be deposited on the surface of the negative electrode of the lithium ion secondary battery, and as a result, the lithium ion secondary battery may be deteriorated.

In an electric vehicle, the drive wheels connected to a battery-powered motor generator are braked by regenerative braking force. At this time, the electric power generated by the motor generator is recovered by charging the battery. However, if the battery is charged with the electric power obtained by regeneration exceeding the limit, the battery becomes overcharged and the precipitation of metallic lithium occurs. In order to prevent this, a battery charge control device that compares the battery voltage with the battery voltage limit and controls the battery charge so that the battery voltage does not exceed the battery voltage limit has been proposed.

In the invention described in Patent Document 1, charging of the secondary battery is controlled so that the charging current does not exceed the allowable current.

International Publication No. 2010/005079

However, in the invention described in Patent Document 1, since lithium precipitation is determined based on the voltage of the entire cell battery, it is said that the amount of capacity deterioration of the entire cell battery is large due to the deterioration of the positive electrode, which has little effect on lithium precipitation. There is a problem that the charging current is regulated even when the deterioration of the negative electrode is small.

Further, as shown in FIG. 15, when the charging is controlled so that the charging current does not exceed the allowable current set as the current at which the metal Li does not deposit on the negative electrode, it is determined in advance regardless of the usage mode of the vehicle. The user-set value of the allowable current is uniformly and statically set in the region 2. Therefore, there is also a problem that the charging performance is excessively limited even though the precipitation of metallic lithium can be suppressed even in the range of the region 1 during the period until the deterioration state assumed in advance is reached.

In order to solve the above problems, the present invention provides a Li precipitation suppression control method and apparatus for a lithium ion secondary battery, which can achieve both suppression of precipitation of metallic lithium in a lithium ion secondary battery and efficient utilization. To provide.

In order to solve the above problems, in the Li precipitation suppression control method of the lithium ion secondary battery of the present invention, the positive electrode open potential and the negative electrode open potential are estimated from the voltage measurement step of measuring the cell voltage and the acquired cell voltage. A side reaction that estimates the positive electrode side reaction current value and the negative electrode side reaction current value from the potential estimation step, the cell temperature measurement step for acquiring the cell temperature, and the estimated positive electrode open potential, negative electrode open potential, and cell temperature. A current estimation step, a negative electrode deterioration amount estimation step for estimating the negative electrode deterioration amount by integrating the estimated negative electrode side reaction current values, and a range in which Li precipitation is suppressed according to the estimated negative electrode deterioration amount are allowed. It is characterized by including a step of determining the charging current for determining the upper limit charging current.

In the step of determining the charging current, the upper limit charging current allowed within the range of suppressing Li precipitation is determined based on the map corresponding to the limit charging current that does not cause Li precipitation according to the amount of deterioration of the negative electrode. You may.

It is also preferable to further include a step of predicting the amount of capacity deterioration by estimating the amount of capacity deterioration from the estimated positive electrode side reaction current value and the negative electrode side reaction current value.
It is also possible to include a charging step that limits the charging current of the lithium ion secondary battery with the upper limit charging current allowed within the range of suppressing Li precipitation determined in the charging current determination step as a threshold value.

It is also preferable to update the threshold value every time the negative electrode deterioration amount is estimated in the negative electrode deterioration amount estimation step in the charging step.
In the step of calculating the amount of deterioration of the negative electrode, i ₀ is the exchange current density, α is the transfer coefficient, F is the Faraday constant, R is the gas constant, T is the absolute temperature, U _side is the film formation potential, and _UNE is the negative electrode open potential. When the _{UPE is set to the positive electrode open potential, the negative electrode side reaction current value iNE calculated} by the following equation (3) is calculated.

また、正極劣化量算出のステップにおいて、下記式（４）により正極副反応電流値ｉ_ＰＥを算出することも好ましい。

It is also preferable to calculate the positive electrode side reaction current value _iPE by the following equation (4) in the step of calculating the amount of deterioration of the positive electrode.

また、前記負極劣化量算出のステップにおいて、経過時間に応じて副反応電流値を減衰させた値を用いて負極劣化量を算出することも好ましい。

Further, in the step of calculating the negative electrode deterioration amount, it is also preferable to calculate the negative electrode deterioration amount by using the value obtained by attenuating the side reaction current value according to the elapsed time.

Further, before executing the method for controlling Li precipitation suppression of the lithium ion secondary battery, a storage step of storing the lithium ion secondary battery under specific conditions and a battery before and after the storage of the stored lithium ion secondary battery are further performed. The step of measuring the capacity reduction amount to measure the capacity reduction amount of the full capacity, the self-discharge capacity measurement step of measuring the self-discharge capacity before and after storage of the stored lithium ion secondary battery, and the capacity reduction amount and self-discharge. It is also preferable to include a step of acquiring deterioration characteristics including a step of obtaining a side reaction current value of the positive electrode and the negative electrode under the specific conditions at the time of storage from the capacity.

In the control device for the lithium ion secondary battery of the present invention, a voltage sensor for detecting the cell voltage of the lithium ion secondary battery, a temperature sensor for detecting the cell temperature of the lithium ion secondary battery, and a temperature sensor are used.
A control device for a lithium ion secondary battery including a computer having a CPU and a memory, wherein the computer suppresses Li precipitation of the lithium ion secondary battery according to any one of claims 1 to 8. It is characterized by configuring a control means for executing a control method.

In this case, the lithium ion secondary battery may be mounted on a vehicle, and the computer may be a computer mounted on the vehicle.

In the Li precipitation suppression control method and apparatus of the lithium ion secondary battery of the present invention, it is possible to achieve both suppression of precipitation of metallic lithium in the lithium ion secondary battery and efficient utilization.

The schematic diagram which shows an example of the structure of a lithium ion secondary battery. The schematic diagram schematically showing the whole structure of the vehicle equipped with the lithium ion secondary battery which concerns on this embodiment. The flowchart of the control method which suppresses Li precipitation of a lithium ion secondary battery using a side reaction current. The block diagram which shows the structure of the apparatus for acquiring the deterioration characteristic of a lithium ion secondary battery. A flowchart showing the procedure for acquiring deterioration characteristics. (A) A graph showing the positive electrode / negative electrode capacity before deterioration-OCP (Open circuit potential) characteristics (showing the relationship between the battery capacity and the open potential of the positive electrode / negative electrode at that time). (B) A graph showing OCP characteristics after deterioration. The graph which shows the SOC-OCP characteristic of the positive electrode and the negative electrode after deterioration of this embodiment. The flowchart which calculates the negative electrode deterioration amount Q integrated from the time t ₀ of this embodiment to a predetermined time t ₁ . Schematic diagram showing a model of film growth. An equation showing the relationship between the amount of film formed and the side reaction current value. A graph showing the attenuation rate of the current value with respect to the reciprocal of the coating amount. A table showing the relationship between the elapsed time, the amount of film formation, and the side reaction current value. The graph which compares the deterioration degree estimation result of the prior art and the deterioration degree estimation result of this embodiment. A graph showing a conceptual example of a negative electrode deterioration-Li precipitation allowable current map. The graph which shows the control of the conventional battery charge control device.

With reference to FIGS. 1 to 14, a Li precipitation suppression control method and a control device for a lithium ion secondary battery using the side reaction current of the present invention will be described by way of an embodiment.
<Outline of Embodiment>
The vehicle 10 of the present embodiment is, for example, a hybrid vehicle and exemplifies a vehicle that is charged by a regenerative brake or the like. Of course, as long as the vehicle 10 drives a motor generator with a lithium-ion secondary battery, not only a plug-in hybrid vehicle but also an electric vehicle and the like are targeted. The vehicle 10 is equipped with a lithium ion secondary battery 1, and the charging current of the lithium ion secondary battery 1 is controlled by an ECU (Electronic Control Unit) 100.

It is known that the precipitation of the lithium metal lowers the upper limit of the allowable charging current due to the deterioration of the lithium ion secondary battery 1. In particular, as the capacity of the negative electrode decreases, the upper limit value decreases.

Therefore, in the present embodiment, the negative electrode open potential _VNE0 and the positive electrode open potential _VPE0 at that time are accurately estimated from the measured cell voltage VB and the shift capacity ΔQ corresponding to the positive / negative electrode composition that changes at any time by the ECU 100. Based on the cell temperature TB in addition to the negative electrode open potential V _NE0 and the positive electrode open potential V _PE0 estimated accurately in this way, the side reaction current value i _NE at the negative electrode and the side reaction current value i _PE at the positive electrode are accurately calculated. .. Then, by integrating these, the negative electrode deterioration amount I _NE and the positive electrode deterioration amount I _PE are calculated based on the accumulation of the side reaction current value i _NE at the negative electrode and the side reaction current value i _PE at the positive electrode, respectively, and the positive and negative electrodes are calculated. The composition correspondence deviation capacity ΔQ is corrected. By repeating this process, the side reaction current value _iNE at the negative electrode and the side reaction current value _iPE at the positive electrode are estimated based on the negative electrode open potential _VNE0 and the positive electrode open potential _VPE0 . In other words, if the thickness of the SEI film (solid electrolyte interphase) of the negative electrode formed by the side reaction current value _iNE is accurately estimated, the deterioration of the negative electrode and the deterioration of the positive electrode can be distinguished and the deterioration of the negative electrode can be accurately estimated. You will be able to do it.

The decrease in the overall capacity of the lithium ion secondary battery 1 progresses due to the deterioration of the battery, but since the precipitation of metallic lithium mainly occurs at the negative electrode, the deterioration at the negative electrode is accurate in order to suppress the precipitation of metallic lithium. Need to be estimated. In the control method by the ECU 100, which is the Li precipitation suppression control device of the present embodiment, the charge current threshold value ICmax is set according to the change in the deterioration of the negative electrode estimated in this way. This "charging current threshold ICmax" can suppress the precipitation of metallic lithium in the negative electrode by experimentally setting the current value at the time of charging the lithium ion secondary battery 1 not to exceed this ICmax. It is a possible threshold. Then, by this charging current threshold ICmax, the upper limit of the high-rate charging current IC that causes the precipitation of metallic lithium is sequentially and dynamically limited to avoid the precipitation of metallic lithium. Therefore, the charging current IC is maximized within the range in which the precipitation of metallic lithium can always be suppressed, and the deterioration of the lithium ion secondary battery 1 is suppressed and the efficient use is achieved at the same time.

<Lithium-ion secondary battery 1>
FIG. 1 is a schematic diagram showing an example of the structure of the lithium ion secondary battery 1. The lithium ion secondary battery 1 includes an electrolyte (not shown) and a cell in which a positive electrode 3, a negative electrode 4, and a separator 5 are enclosed inside. Then, for example, a configuration in which a plurality of such cells are combined and packaged according to the application such as an in-vehicle power supply is common.

The positive electrode 3, the negative electrode 4, and the separator 5 have a sheet-like outer shape and are laminated. Further, by winding this laminated body, an electrode body 11 in which positive and negative electrodes and the separator 5 are alternately arranged in the radial direction is formed in a state where the separator 5 is sandwiched between the positive electrode 3 and the negative electrode 4. To. That is, two separators 5 are used to form the electrode body 11. Further, in many cases, the electrode body 11 has a flat outer shape by pressing the wound positive electrode 3, the negative electrode 4, and the separator 5 from the outside in the radial direction. The lithium ion secondary battery 1 is configured to accommodate such an electrode body 11 together with a non-aqueous electrolyte solution as an electrolyte, a non-aqueous electrolyte polymer, and the like in a case 12 constituting the outer shell of the cell 10. It has become.

Further, the positive electrode 3 and the negative electrode 4 are formed by, for example, applying a slurry containing an active material to the positive electrode current collector 13 and the negative electrode current collector 14 having a sheet-like outer shape, respectively. Specifically, for example, aluminum or the like is used for the positive electrode current collector 13, and lithium transition metal oxide is used as the positive electrode active material. Further, for example, copper or the like is used for the negative electrode current collector 14, and a carbon-based material is used for the negative electrode active material. Further, the case 12 of the lithium ion secondary battery 1 is provided with a positive electrode terminal 15 and a negative electrode terminal 16 projecting to the outside thereof. The lithium ion secondary battery 1 is configured such that the positive electrode current collector 13 and the negative electrode current collector 14 corresponding to the positive electrode terminal 15 and the negative electrode terminal 16 are electrically connected to the positive electrode terminal 15 and the negative electrode terminal 16, respectively. There is.

Lithium-ion secondary batteries are used in modes of use (for example, charging at a high rate, charging from a high charge state (high SOC), continuous charging for a long time, charging at a low temperature (charging in a high resistance state)). The absorption and diffusion at the negative electrode of the lithium ion secondary battery may not catch up with the supply of lithium ions, and metallic lithium may be deposited on the surface of the negative electrode of the lithium ion secondary battery.

Precipitation of metallic lithium causes a short circuit between the positive electrode 3 and the negative electrode 4 by penetrating the separator 5, and the self-discharge is large and the deterioration is remarkably accelerated. Further, once precipitated as metallic lithium, it does not return to lithium ions, so that deterioration due to a decrease in lithium ions progresses.

Therefore, it is necessary to suppress the precipitation of metallic lithium by controlling the charging current and the charging voltage.
<Overall configuration of vehicle 10 equipped with lithium-ion secondary battery 1>
Next, the vehicle 10 on which the lithium ion secondary battery 1 of the present embodiment is mounted will be briefly described.

FIG. 2 is a schematic diagram schematically showing the overall configuration of the vehicle 10 equipped with the lithium ion secondary battery 1 according to the embodiment. The vehicle 10 is a hybrid vehicle. The vehicle 10 includes a control device 18 for a lithium ion secondary battery 1, a PCU (Power Control Unit) 30, motor generators 41 and 42, an engine 50, a power split device 60, and a drive shaft 70. , The drive wheel 80 is provided.

The control device 18 of the lithium ion secondary battery includes the lithium ion secondary battery 1, the monitoring unit 20 that constantly monitors the cell voltage VB, the cell current IB, and the cell temperature TB of the lithium ion secondary battery 1, and these cells. It includes a memory 102 that stores a voltage VB, a cell current IB, and a cell temperature TB, and an ECU 100 having a CPU 101 that processes them.

<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 at the time of sudden acceleration. On the other hand, when the vehicle is braking or on a downward slope, the motor generator 42 operates as a generator to regenerate a large current and supply a large current to the lithium ion secondary battery 1.

In such an in-vehicle lithium ion secondary battery 1, the progress of deterioration may differ depending on the usage environment. For example, the environmental temperature changes from low temperature to high temperature and the cell temperature TB changes from low temperature to high temperature, high-rate charging / discharging is performed, and the charging / discharging status changes from low cell SOC to high cell SOC. This is the case.

<Lithium-ion secondary battery monitoring unit 20>
The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects the cell voltage VB. The current sensor 22 detects the current IB input / output to / from the lithium ion secondary battery 1. The temperature sensor 23 detects the cell temperature TB for each block. Each sensor outputs a signal indicating the detection result to the ECU 100. These cell voltage VB and cell current IB are stored as cell temperature TB and cell voltage VB at regular time intervals as the history of the lithium ion secondary battery 1.

<Cell voltage VB, cell current IB, cell temperature TB>
In the present embodiment, the cell voltage VB, the cell current IB, and so on are every Δt (for example, 0.1 seconds) from the start time t ₀ when the lithium ion secondary battery 1 is mounted on the vehicle 10 and during its operation. The cell temperature TB is measured and recorded, and deterioration is determined.

<ECU100>
The ECU (Electronic Control Unit) 100 provided with the memory 102 and the CPU 101 functions as a computer for control and functions as a control device for the lithium ion secondary battery of the present invention.

(Action of Embodiment)
<Control method for suppressing Li precipitation of lithium ion secondary battery using side reaction current>
FIG. 3 is a flowchart of a control method for suppressing Li precipitation of a lithium ion secondary battery using a side reaction current. In the present embodiment, the lithium ion secondary battery 1 and the vehicle 10 on which the lithium ion secondary battery 1 is mounted are controlled by the following procedure so as to suppress Li precipitation of the lithium ion secondary battery using a side reaction current.

<Battery deterioration characteristic acquisition (S1)>
First, before mounting the lithium ion secondary battery 1 on the vehicle 10, the initial state of the lithium ion secondary battery 1 mounted on the vehicle and the inherent characteristics of the deterioration rate are measured. By measuring the lithium-ion secondary battery 1 mounted on the vehicle in advance in this way, it is possible to accurately estimate the deterioration after the vehicle is mounted.

Here, the procedure for acquiring the deterioration characteristics will be described with reference to FIGS. 4 and 5. In order to accurately estimate the deterioration, the deterioration rate of the lithium ion secondary battery 1 mounted on the vehicle 10 which is the reference for the estimation, that is, the deterioration characteristics peculiar to the lithium ion secondary battery 1 are acquired in advance. It is important to keep it. Therefore, before the lithium ion secondary battery 1 is mounted on the vehicle, or the lithium ion secondary battery 1 mounted on the vehicle is removed from the vehicle and set in the device 200 for acquiring deterioration characteristics for measurement. Then, "preservation" is performed under a specific preset temperature, time, and charge / discharge conditions, and the rate of deterioration peculiar to the lithium ion secondary battery 1 is obtained from the difference between the measured values of the side reaction currents before and after that. Is measured separately for the positive electrode and the negative electrode. By correcting the measured side reaction current under the conditions expected in the future, the negative electrode deterioration amount I _NE [Ah] and the positive electrode deterioration amount I _PE [Ah] of the lithium ion secondary battery 1 can be accurately determined. It can be calculated in.

<Structure of device 200 for acquiring deterioration characteristics of lithium ion secondary battery>
FIG. 4 is a block diagram showing the configuration of the device 200 for acquiring the deterioration characteristics of the lithium ion secondary battery 1. The configuration of the device 200 for acquiring deterioration information of the lithium ion secondary battery 1 of the present embodiment includes a well-known charging / discharging device 203, a cell voltage measuring device 204, a cell current measuring device 205, a thermometer 206, and a heat retaining device 207. Further, a control device 208 including a well-known computer provided with an interface for controlling these is provided. The control device 208 includes a CPU 281 and a memory 282. The memory 282 includes a RAM and a ROM.

These function as a storage means for storing the lithium ion secondary battery 1 under specific conditions as a configuration of a device for acquiring deterioration characteristics of the lithium ion secondary battery 1. It also functions as a battery capacity reduction measuring means for measuring the capacity reduction amount Q _loss of the battery full capacity before and after storage of the stored lithium ion secondary battery 1. It also functions as a self-discharge amount measuring means for measuring the self-discharge capacity _QSD of the stored lithium ion secondary battery 1 before and after storage. In addition, using the measured capacity reduction Q _loss and self-discharge capacity Q _SD , and the relationship between the pre-acquired side reaction rate and the usage environment, the amount of deterioration of the positive electrode and the amount of deterioration of the negative electrode under the assumed usage environment Functions as a deterioration amount calculation means for calculating each of the above.

<Flow chart for acquiring deterioration characteristics>
FIG. 5 is a flowchart showing a procedure for acquiring deterioration characteristics. The procedure for acquiring deterioration characteristics will be described with reference to this flowchart.

Here, first, prior to the explanation of this flowchart, the terms used in the explanation will be described in advance.
“T1 [° C]” is an arbitrary storage temperature (for example, 50 ° C).

“T1 [h]” is an arbitrary storage period (for example, 24 hours).
"V1 [V]" is full from the voltage 3.0 [V] in which the cell voltage VB is completely discharged (in this embodiment, the cell voltage VB in the fully discharged state of the cell SOC 0% is referred to as "lower limit voltage"). A voltage (for example, 3.8 [V]) arbitrarily set between 4.1 [V] of charging (cell SOC 0 to 100%, referred to as "upper limit voltage" in this embodiment), and in this embodiment. , Called "reference voltage". In this embodiment, it is used as a reference voltage for measuring the self-discharge capacity and is also an arbitrary initial cell voltage VB for storage.

"Q1 [Ah]" is a battery in which the cell voltage VB is changed from the lower limit voltage 3.0 [V] to the upper limit voltage (fully charged cell voltage VB = 4.1 [V] (here, the voltage of the cell SOC 100%)). It is the full capacity of the pre-storing battery whose capacity has been measured.

It is the section capacity before storage measured at the reference voltage V1 = 3.8 [V] from the lower limit voltage 3.0 [V] of "Q2 [Ah]".
"Q3 [Ah]" is the remaining capacity after storage, which is discharged from the reference voltage V1 = 3.8 [V] to the lower limit voltage 3.0 [V] after storage.

"Q4 [Ah]" is the full capacity of the battery after storage measured from the lower limit voltage of 3.0 [V] to the upper limit voltage of 4.1 [V].
“ _QSD [Ah]” is the self-discharge capacity during the storage period obtained from the difference between the section capacity Q2 before storage and the remaining capacity Q3 after storage.

"Q _loss [Ah]" is a capacity decrease amount obtained from the difference between the battery full capacity before storage Q1 and the battery full capacity after storage.
“I _NE0 [A]” is a negative electrode side reaction current (velocity) determined by the self-discharge capacity _QSD [Ah] ÷ storage time t1 [h].

“I _PE0 [A]” is a positive electrode side reaction current obtained from the difference between the negative electrode side reaction current (velocity) _iNE0 and the quotient of the volume reduction amount Q _loss [Ah] ÷ storage time t1 [h]. Speed).

In this embodiment, it is defined as described above.
<Procedure of flowchart for acquiring deterioration characteristics>
Next, using these definitions, the procedure for acquiring the deterioration characteristics of the lithium ion secondary battery 1 will be described with reference to the flowchart of FIG.

First, when the process of acquiring deterioration characteristics is started (START), the battery is charged from the lower limit voltage 3.0 [V] of the cell SOC 0% at the time of complete discharge to the full charge of the upper limit voltage 4.1 [V] of the cell SOC 100%. The battery full capacity Q1 [Ah] before storage is measured (S101).

Next, the section capacity Q2 [Ah] before storage is measured by charging in the voltage section from the lower limit voltage 3.0 [V] to the reference voltage V1 = 3.8 [V] (S102).
Subsequently, while adjusting the voltage to the reference voltage V1 = 3.8 [V], it is stored at an arbitrary temperature T1 (for example, 50 ° C.) for an arbitrary time t1 (for example, 24 hours) (S104). This procedure corresponds to the "save step". Therefore, this storage is performed under the conditions that the start cell voltage, the storage temperature T1, and the storage time t1 are always constant.

After adjusting the voltage to the reference voltage V1 = 3.8 [V] before storage, the battery is discharged to the lower limit voltage 3.0 [V] after storage, and the remaining capacity Q3 [Ah] after storage is measured (S105). ). Subsequently, the battery is fully charged from the lower limit voltage of 3.0 [V] to the upper limit voltage of 4.1 [V], and the battery full capacity Q4 [Ah] after storage is measured (S106). In this case, it is specified by the voltage. This is because after storage, the full charge capacity is lower than before storage due to deterioration of the active material / electrolyte, formation of a film, and the like.

Then, the difference between the section capacity Q2 [Ah] before storage and the remaining capacity Q3 [Ah] after storage is obtained. Compared to the section capacity Q2 before storage, the remaining capacity Q3 after storage has a decrease in capacity due to self-discharge. The remaining capacity when the capacity charged from the lower limit voltage 3.0 [V] to the reference voltage V1 = 3.8 [V] is discharged to the lower limit voltage 3.0 [V] after storage is obtained. From this, the self-discharge amount of the storage time t1 can be obtained. By this procedure, the self-discharge capacity _QSD is calculated from the electric capacity reduced to the storage time t1 (S107). This procedure corresponds to the "step of self-discharge amount measurement".

Next, the self-discharge capacity _QSD [Ah] is divided by the storage time t1 [h], and the side reaction current value (film formation current) of the negative electrode corresponding to the growth rate of the film, that is, the deterioration rate is i _NE0 [A]. Is calculated (S108).

Further, the capacity decrease amount Q _loss [Ah] is calculated from the difference between the battery full capacity Q1 [Ah] before storage and the battery full capacity Q4 [Ah] after storage (S109).
Finally, from the difference between the negative electrode side reaction current value i _NE0 [A] and the quotient [A] obtained by dividing the capacity reduction amount Q _loss by the storage time t1 [h], the positive electrode side reaction current value i _PE0 [A]. ] Is calculated (S110).

As described above, the procedure for acquiring the deterioration identification for measuring the side reaction current value i _NE0 [A] of the negative electrode of the lithium ion secondary battery and the side reaction current value i _PE0 [A] of the positive electrode in the predetermined storage section of the present embodiment is completed. End (END).

By such a procedure, the side reaction current value i _PE0 [A] of the positive electrode under the conditions of the reference voltage V1 [V] for starting storage, the storage temperature T1 [° C], and the storage time t1 [h], and the negative electrode. The side reaction current value i _NE0 [A] can be measured. That is, the deterioration characteristics of the lithium ion secondary battery 1 are revealed. That is, the "deterioration characteristic" is data that serves as a reference for determining deterioration from the cell voltage BV and the cell temperature TB. This procedure may be performed for each cell, but if the lithium ion secondary battery 1 has the same configuration, sampling inspection is sufficient without 100% inspection.

The above is the procedure for acquiring the deterioration characteristics of the lithium ion secondary battery 1. The deterioration characteristics acquired by the above procedure are stored in the memory 102 of the ECU 100 when the lithium ion secondary battery 1 is mounted on the vehicle 10.

<Negative electrode deterioration-Acquisition of Li precipitation allowable current map (S2)>
Further, prior to the start of use of the battery, the charge current at the limit where Li precipitation does not occur according to the deterioration amount of the negative electrode, that is, the value [Ah] in which the side reaction current forming the SEI film of the negative electrode is integrated. Acquire a map obtained experimentally for IC [A].

FIG. 14 shows a conceptual example of this negative electrode deterioration-Li precipitation allowable current map 2. Here, the vertical axis represents the charging current IC [A], and the horizontal axis represents the negative electrode deterioration amount _IN [Ah]. The deterioration amount of the lithium ion secondary battery 1 at that time, that is, the integrated negative negative voltage sub Depending on the reaction current value [Ah], the graph of the charge current threshold ICmax shows how much A the charge current IC can tolerate. For example, when the negative electrode deterioration amount I _NE0 = 0 without deterioration, the ICmax is maximum and charging is possible with a high charging current IC. Deterioration of the negative electrode progresses with the use of the battery, and when it reaches NEC 1, the corresponding charge current threshold _ICmax becomes IC ₁ , and the chargeable current IC that can be charged is limited from the start of use. Further, deterioration progresses due to the use of the battery, and when it becomes NEC 2, the corresponding charge current threshold IC _max becomes IC ₂ , and the charge current IC that can be charged is further limited. In this way, when the deterioration of the negative electrode set to be usable by the user becomes I _{NE END} , the charging current IC becomes IC _END , and the lithium ion secondary battery 1 in the vehicle cannot perform a sufficient function. , The use of the battery is finished. In the present embodiment, the negative electrode deterioration amount IN is calculated every 0.1 seconds, for example, and continuously changes, and the corresponding charge current threshold _ICmax also continuously changes accordingly. The interval for determining the charge current threshold value ICmax can be arbitrarily determined. In FIG. 14, the graph is represented by a straight line, but of course, it may be a curve based on experimental values. The map may be of course in any format, and may be a tabular table or a conversion formula, but it is sufficient if the allowable charging current threshold ICmax can be immediately derived with the deterioration amount [Ah] of the negative electrode as an argument.

<Start of use of lithium ion secondary battery 1 (S3)>
The power of the vehicle 10 is turned on, and the operation of the lithium ion secondary battery 1 mounted on the vehicle is started (S3). When the use of the lithium ion secondary battery 1 is started, the negative electrode deterioration amount _INE , which is the negative electrode side reaction current value accumulated up to that point, and the positive electrode deterioration amount, which is the positive electrode side reaction current value accumulated up to that point, are started. I _PE and is read out. When starting for the first time, since there is no information on the deterioration of the lithium ion secondary battery 1, recording is started based on the deterioration characteristics acquired first. After that, each time it is used, the deterioration of the lithium ion secondary battery 1 is calculated by the ECU 100 and stored in the memory 102 by the procedure as shown in S4 to S14. When the operation of the vehicle is started, the data of this deterioration is read and integrated.

<Data collection (S5, S7)>
When the use of the lithium ion secondary battery is started, the cell voltage VB is measured by the voltage sensor 21 in the monitoring unit 20 of the vehicle 10 (S5). In parallel with this, the cell temperature TB, which is the battery temperature, is measured by the temperature sensor 23 (S7). The measured data is stored in the memory 102 of the ECU 100.

<Estimation of positive and negative electrode potential (S6)>
The negative electrode open potential V _NE and the positive electrode open potential V _PE are estimated based on the cell voltage VB measured in S5 (S6).

FIG. 6A is a graph showing the capacity-OCP (Open circuit potential) characteristics of the positive electrode / negative electrode before deterioration (showing the relationship between the battery capacity and the open potential of the positive electrode / negative electrode at that time). FIG. 6B is a graph showing the OCP characteristics after deterioration. The graph shown in FIG. 6A is a graph showing the characteristics of the battery before initial deterioration, which is specified from the composition of the electrodes and the like. If the cell voltage VB is known, the initial negative electrode open potential according to the capacities of the negative electrode and the positive electrode is known. _VNE0 and the initial positive electrode open potential _VPE0 are known. After that, in the lithium ion secondary battery 1, the negative electrode and the negative electrode deteriorate, respectively. Therefore, in the first round of the flowchart in the initial state of the battery, the relationship between the positive electrode open potential V _PE and the negative electrode open potential V _NE is as shown in FIG. 6A, but in the second and subsequent rounds, the relationship is sequential. Deterioration shift occurs and changes as shown in FIG. 7.

<Correction of estimation of positive and negative electrode potentials in S6 based on positive and negative electrode composition deviation capacitance ΔQ>
In the procedure (S6) for estimating the potentials of the positive and negative electrodes in the flowchart shown in FIG. 3, in the first round, the lithium ion secondary battery 1 is in a state of not being deteriorated, as shown in FIG. There is no deviation in the capacity of the negative electrode. However, the deterioration of the positive electrode and the negative electrode of the lithium ion secondary battery 1 is generally larger in the negative electrode, and as a result, the difference between the deterioration of the positive electrode and the deterioration of the negative electrode causes a deviation capacity ΔQ corresponding to the positive / negative electrode composition. Here, for convenience of explanation, first, the displacement of the capacitance of only the negative electrode will be described.

The graph shown in FIG. 6A is a graph showing the characteristics of the battery before initial deterioration, which is specified from the composition of the electrodes and the like. If the cell voltage VB is known, the negative electrode open potential _VNE0 and the positive electrode corresponding to the capacity of the negative electrode are known. The positive electrode open potential V _PE0 corresponding to the capacity of is found. As can be seen from FIG. 6A, the graph _{UPE of the positive electrode OCP and the graph UNE0 of} the negative electrode OCP have irregular curves. In particular, the negative electrode becomes a stepped graph due to the intercalation of lithium ions. Here, the cell voltage VB is the potential difference between the potential V _PE0 of the positive electrode and the potential V _NE0 of the negative electrode. Then, the cell voltage VB changes depending on the relative positional relationship between the graph _UPE0 of the positive electrode OCP and the graph _UNE0 of the negative electrode OCP shown in FIG. 6A and the capacity of the positive and negative electrodes. At this time, the deviation capacity ΔQ corresponding to the positive and negative electrode compositions does not occur.

Therefore, in the lithium ion secondary battery 1, the potential of the lithium ion secondary battery 1 is estimated by using the “shift capacity ΔQ corresponding to the positive / negative electrode composition”. The “positive electrode composition correspondence deviation capacity ΔQ” is the amount of fluctuation in the battery capacity due to the deviation in the correspondence between the local charge rate on the surface of the positive electrode active material and the local charge rate on the surface of the negative electrode active material from the initial state.

FIG. 6B is a graph showing the capacitance-OCP characteristics of the positive electrode and the negative electrode in consideration of the deterioration of only the negative electrode. The deviation capacity ΔQ corresponding to the positive and negative electrode composition in the negative electrode will be described with reference to FIG. 6 (b). As the deterioration progresses due to use from the state shown in FIG. 6 (a), the negative electrode deviation amount ΔQ _NE due to a side reaction in the negative electrode becomes large as shown in FIG. 6 (b). Therefore, the position of the point on the graph _UNE0 of the negative electrode OCP shifts from the initial position to the position of the point on the graph _UNE1 of the negative electrode OCP shown on the left side, and the deviation capacity ΔQ corresponding to the positive and negative electrode composition indicated by the arrow pointing to the left. Occurs.

Here, the cell voltage VB is the potential difference between the positive electrode open potential V _PE and the negative electrode open potential V _NE . Then, the cell voltage VB becomes, for example, a potential difference of <positive open potential V _PE0 -negative open potential V _NE1 > from the potential difference of <positive positive open potential V _PE0 -negative open potential V _NE0 >, as shown in FIG. 6 (a). , The potential difference becomes smaller. Then, there will be a difference in the correspondence between the detected cell voltage VB and the capacity.

Therefore, the capacity deterioration due to use is estimated from the formation of the SEI film using the Tafel equation or the like, and the deviation capacity ΔQ corresponding to the positive / negative electrode composition is calculated. The positive / negative electrode composition-corresponding deviation capacity ΔQ is integrated at any time, and the positive / negative electrode composition-corresponding deviation capacity ΔQ is referred to when the positive electrode open potential V _PE and the negative electrode open potential V _NE are calculated from the cell voltage VB, respectively.

Here, since it is assumed that there is no change in the positive electrode, the deviation capacity ΔQ corresponding to the positive / negative electrode composition is equal to the decrease in the negative electrode deviation amount ΔQ _NE due to the side reaction in the negative electrode.
<Characteristics of calculation of deviation capacity ΔQ corresponding to positive / negative electrode composition of this embodiment>
Next, the calculation of the deviation capacity ΔQ corresponding to the positive and negative electrode composition in consideration of the deterioration of the positive electrode will be described. Although it has been known in the past that a positive electrode causes a side reaction in the same manner as a negative electrode, it is not well known what kind of side reaction acts and how. Also, it was not easy to estimate future side reaction currents. Furthermore, the effect of adverse reactions on the positive electrode was thought to be small. Therefore, it can be said that there was an impediment to considering only the deterioration of the negative electrode and considering the displacement of the positive electrode, which merely complicates the processing. Therefore, as shown in FIG. 6 (b), a side reaction of the positive electrode was not considered by those skilled in the art.

However, the present inventor analyzes what kind of characteristics the lithium ion secondary battery 1 itself has, and then what kind of side reaction occurs on the positive electrode and how it works. We have clarified this and found that the influence is not small by experiments, which led to the present invention. It was also experimentally confirmed that the reaction rate of the side reaction can be defined by the Tafel equation for the positive electrode as well as the negative electrode.

<Calculation of deviation capacity ΔQ corresponding to positive / negative electrode composition of this embodiment>
FIG. 7 is a graph showing the SOC-OCP characteristics of the positive electrode and the negative electrode after deterioration of the present embodiment. According to the findings of the present inventor, in reality, as shown in FIG. 7, a positive electrode deviation amount ΔQ _PE due to a side reaction also occurs in the positive electrode. When the positive electrode deviation amount ΔQ _PE occurs, the position on the point UP _E0 on the graph of the positive electrode OCP shown in FIG. 6A shifts to the left position by the positive electrode deviation amount ΔQ _PE indicated by the arrow pointing to the left, and is on the graph. It becomes the point _UPE1 .

That is, the decrease in the cell voltage _VB is caused by both the increase in the negative electrode open potential VNE and the decrease in the positive electrode open potential _VPE . Conventionally, as shown in FIG. 6B, since the decrease in the cell voltage _VB is greatly affected by the negative electrode open potential VNE, only the negative electrode is referred to. In other words, the deviation capacity ΔQ corresponding to the positive / negative electrode composition was regarded as the negative electrode deviation amount ΔQ _NE . However, in the present embodiment, the decrease in the cell voltage _VB is caused by both the increase in the negative electrode open potential VNE and the decrease in the positive electrode open potential _VPE , and these are separately analyzed.

In the present embodiment, the cell voltage VB before the deviation occurs is the potential difference of <positive electrode open potential V _PE0 -negative electrode open potential V _NE0 > as shown in FIG. 6A, but when the deviation occurs, FIG. 7 As shown in the above, the potential difference is <positive electrode open potential V _PE1 -negative electrode open potential V _NE1 >.

In the present embodiment, as shown in FIG. 7, as a result of dividing the decrease in the cell voltage _VB into the increase in the negative electrode open potential VNE and the decrease in the positive electrode open potential _VPE , even if the cell voltage VB is the same voltage. The increase in the negative electrode open potential _VNE shown in FIG. 7 of the present embodiment is smaller than the increase in the negative electrode open potential _VNE shown in the prior art of FIG. 6 (b).

In other words, the deviation capacity ΔQ corresponding to the positive and negative electrode composition is expressed as (conventional negative electrode deviation amount ΔQ _NE )> (negative electrode deviation amount ΔQ _NE of the present embodiment). The deviation capacity corresponding to the conventional positive and negative electrode composition is smaller than the deviation capacity ΔQ.

Further, from the relationship of (conventional negative electrode deviation amount ΔQ _NE )> (negative electrode deviation amount ΔQ _NE of the present embodiment), the deviation due to the decrease in the negative electrode deviation amount ΔQ _NE due to the side reaction at the negative electrode and the positive electrode deviation due to the side reaction at the positive electrode. The deviation due to the decrease in the amount ΔQ _PE is offset and the ΔQ becomes smaller. That is, the relationship is (positive electrode deviation composition corresponding deviation capacity ΔQ) = (negative electrode deviation amount ΔQ _NE − positive electrode deviation amount ΔQ _PE ). Therefore, the deviation capacity ΔQ corresponding to the positive / negative electrode composition of the present embodiment is further smaller than the conventional deviation capacity ΔQ corresponding to the positive / negative electrode composition.

That is, the present inventor has found that, in the conventional method, even if the cell voltage VB is the same voltage, there is a possibility that the deviation capacity ΔQ corresponding to the positive / negative electrode composition can be largely estimated. In the present embodiment, the deterioration is accurately calculated for each of the negative electrode deviation amount ΔQ _NE and the positive electrode deviation amount ΔQ _PE . By using the positive and negative electrode composition-corresponding deviation capacity ΔQ derived from this, the cell voltage VB is correctly distributed to the positive electrode open potential V _PE and the negative electrode open potential V _NE , and the negative electrode deviation amount ΔQ _NE and the positive electrode deviation amount ΔQ _PE are further divided. Accurately calculate the deterioration of each. By repeating this, the deviation capacity ΔQ corresponding to the positive and negative electrode composition can always be estimated more accurately.

By such a procedure, the negative electrode open potential _VNE0 and the positive electrode open potential _VPE0 can be accurately estimated.
<Estimate the positive and negative side reaction current values (S8)
Here, returning to the flowchart of FIG. 3, the positive and negative electrode side reaction current values are estimated based on the negative electrode open potential _VNE and the positive electrode open potential _VPE estimated in S6 and the cell temperature TB which is the battery temperature acquired in S4. The step (S5) to be performed will be described.

<Calculation of negative electrode side reaction current value i _NE and positive electrode side reaction current value i _PE from negative electrode open potential V _NE and positive electrode open potential V _PE >
FIG. 8 is an example of a flowchart for calculating the positive / negative electrode composition-corresponding deviation capacity Δ integrated from the time t ₀ of the present embodiment to the predetermined time t ₁ .

<Start calculating the deviation capacity ΔQ (t ₀ to t ₁ ) corresponding to the positive and negative electrode composition (S81)>
Hereinafter, a specific procedure of “estimating the positive / negative electrode side reaction current value (S8)” in the flowchart of FIG. 3 will be described with reference to FIG. First, the calculation of the deviation capacity ΔQ (t ₀ to t ₁ ) corresponding to the positive and negative electrode compositions is started (S81). Here, the time t ₀ is the time when the estimation of the deterioration of the lithium ion secondary battery 1 is started. Further, the time t ₁ is the time when the estimation of the deterioration of the lithium ion secondary battery 1 is completed. Δt is the elapsed time from time t ₀ to time t ₁ . The time t ₂ is the measurement interval time. For example, 0.1 seconds.

<Measurement of cell voltage VB and cell temperature TB (S82)>
Subsequently, the cell voltage VB of the lithium ion secondary battery 1 to be inspected measured in S7 and the cell temperature T of the cell are read (S82). The cell voltage VB and the cell temperature TB are measured by the voltage sensor 21 and the temperature sensor 23 (FIG. 1) of the monitoring unit 20 of the vehicle 10 on which the lithium ion secondary battery 1 is mounted.

<Calculation of negative electrode open potential _VNE (S83)>
Following the processing of S82, the negative electrode open potential VNE calculated from the cell voltage _VB is read in S6 (S83). In the first round of the flowchart, since the deviation capacity ΔQ = 0 corresponding to the positive and negative electrode compositions at time t ₀ , the cell voltage VB is set to the positive electrode open potential V _PE and the negative electrode open potential V _NE according to the graph of FIG. 6 (a). Can be sorted. From the second round onward, the changes are as shown in FIG.

<Negative side reaction current value _iNE calculation (S84)>
The negative electrode side reaction current value _iNE is calculated from the negative electrode open potential _VNE and the cell temperature TB (S84).

<Calculation of positive electrode open potential V _PE (S85)>
In parallel with the processing of S83, the positive electrode open potential _VPE is read from the cell voltage VB in the same procedure following the processing of S82 (S85).

<Positive side reaction current value _iPE calculation (S86)>
The positive electrode side reaction current value _iPE is calculated from the positive electrode open potential V _PE (S86).
<Calculation of deviation capacity ΔQ (t ₀ to t ₁ ) corresponding to the positive and negative electrode composition (S87)>
From the negative electrode deviation amount ΔQ _NE calculated in S84 and the positive electrode deviation amount ΔQ _PE calculated in S86, the positive and negative electrode composition-corresponding deviation capacity ΔQ (t ₀ to t ₁ ) = (negative electrode reaction current value i _NE -positive electrode reaction current value). i _PE ) × Δt is calculated. That is, the difference between the negative electrode side reaction current value _iNE and the positive electrode side reaction current value _iPE is multiplied by the elapsed time Δt to obtain the total capacity of the positive and negative electrode composition-corresponding deviation capacity ΔQ (t ₀ to t ₁ ) with the elapsed time Δt. Calculate (S87).

In this process, Δt is sequentially processed from time t0 to time t1. When this process is completed, the deviation capacity ΔQ (t ₀ to t ₁ ) corresponding to the positive and negative electrode composition is calculated in the next process. In this way, the deviation capacity ΔQ (t _n-1 to t _n ) corresponding to the positive and negative electrode compositions is calculated during the processing of t _n to t _{n + 1} . Therefore, as shown in FIG. 7, the cell voltage VB acquired in S82 divides the cell voltage VB into the positive electrode open potential V _PE and the negative electrode open potential V _NE according to the already calculated and accumulated deviation capacity ΔQ corresponding to the positive and negative electrode compositions. Can be done. By repeating this, the cell voltage _VB is accurately divided into the positive electrode open potential _VPE and the negative electrode open potential VNE according to the positive / negative electrode composition-corresponding shift capacity ΔQ calculated at that time, and as shown in FIG. By referring to the positive and negative electrode deviation capacity ΔQ, the processing in S83 and S85 can be performed accurately.

<Calculation of negative electrode side reaction current value i _NE and positive electrode side reaction current value i _PE >
Here, the negative electrode side reaction current value i _NE and the positive electrode side reaction current value i _PE are obtained as follows.

The negative electrode side reaction current value _iNE is the negative electrode side reaction current according to the following equation (1), where a _{NE is the exchange current density of the side reaction occurring on the negative electrode and b NE is} the overvoltage term of the side reaction occurring on the negative electrode. The value _iNE can be calculated.

また、正極副反応電流値ｉ_ＰＥは、ａ_ＰＥを正極上で起こる副反応の交換電流密度とし、ｂ_ＰＥを正極上で起こる副反応の過電圧項としたとき、下記式（２）により正極副反応電流値ｉ_ＰＥを算出することができる。

The positive electrode side reaction current value _{iPE is based on the following equation (2) when a PE is the exchange current density of the side reaction occurring on the positive electrode and b PE is the} overvoltage term of the side reaction occurring on the positive electrode. The reaction current value _iPE can be calculated.

なお、セル電池の副反応電流値は、電流密度に応じて算出される。これら式（１）及び式（２）から、負極副反応電流値ｉ_ＮＥと正極副反応電流値ｉ_ＰＥは、過電圧項ｂ_ＮＥの変化により指数関数的に増大することがわかる。

The side reaction current value of the cell battery is calculated according to the current density. From these equations (1) and (2), it can be seen that the negative electrode side reaction current value i _NE and the positive electrode side reaction current value i _PE increase exponentially with the change of the overvoltage term b _NE .

<How to determine the decrease in the amount of deterioration due to the side reaction current at the negative electrode>
Next, a method of specifically obtaining a decrease in the negative electrode side reaction current value _iNE and the positive electrode side reaction current value _iPE using the Tafel equation will be described.

Here, first, the negative electrode will be described. The negative electrode deterioration amount _iNE due to a side reaction can be obtained by using the Tafel equation.
That is, the amount of deterioration due to the side reaction in the negative electrode integrates the negative electrode side reaction current value _iNE between Δt. The negative electrode side reaction current value _iNE can be obtained by the following Tafel equation based on the cell voltage VB and the cell temperature TB.

<Calculation of negative electrode side reaction current value _iNE by Tafel equation>
In this embodiment, the negative electrode side reaction current value _iNE is obtained by the Tafel equation (formula (3)) shown below.

ここで、ｉ_０を交換電流密度、αを移動係数、Ｆをファラデー定数、Ｒを気体定数、Ｔを絶対温度、Ｕ_sideを被膜形成電位、Ｕ_ＮＥを負極開放電位とする。

Here, i ₀ is the exchange current density, α is the transfer coefficient, F is the Faraday constant, R is the gas constant, T is the absolute temperature, U _side is the film formation potential, and _UNE is the negative electrode open potential.

<Calculation of negative electrode deviation amount ΔQ _NE using Tafel equation>
For details on how to obtain the negative electrode side reaction current value _iNE by the Tafel equation (formula (3)), see paragraphs 0024 to 0081 of JP-A-2017-190979, in particular, the displacement capacity corresponding to the positive and negative electrode composition using the Tafel equation. Since the method for calculating ΔQ is disclosed in detail in paragraphs 0076 to 0081, detailed description thereof will be omitted here. Of course, the current density is converted into a side reaction current value as needed. The exchange current density i ₀ of the formula (3) becomes a substantially constant value because the formation rate of the SEI film becomes substantially constant when charging / discharging is repeated several times after the production of the lithium ion secondary battery 1 is completed. Therefore, a map corresponding to the cell temperature TB may be created in advance by a test or the like and read from this map.

The transfer coefficient α may be set to 0.5, for example, assuming that the charge / discharge efficiencies are the same. Further, the reduction decomposition of the electrolytic solution, which is the main factor of film formation, occurs continuously when the negative electrode open potential is 0.6 V to 1.0 V. Therefore, for example, the film formation potential Uside is set to 0.6 V, 0.8 V or 1. It may be set as 0.0V.

<Vaccine side reaction current value i _PE at positive electrode>
Conventionally, it has been considered that the deviation capacity ΔQ corresponding to the positive and negative electrode compositions is mainly affected by the formation of an SEI film (a side reaction) on the surface of the negative electrode. The coating formed on the negative electrode includes LiF, Li ₂ Co ₃ , etc. in addition to SEI, and the negative electrode side reaction current value _iNE was estimated by the above-mentioned Tafel equation.

The present inventor considered the same for the film formed by the positive electrode, made a hypothesis that it could be estimated by the Tafel equation, and found that this hypothesis was correct by experiments.

Therefore, also in the positive electrode, the positive electrode side reaction current value _iPE is calculated by the Tafel equation of the following equation (4) based on the cell voltage VB and the cell temperature TB.
Here, i ₀ is the exchange current density, α is the transfer coefficient, F is the Faraday constant, R is the gas constant, T is the absolute temperature, U _side is the film formation potential, and UP E is the _positive electrode open potential.

そして、この正極副反応電流値ｉ_ＰＥに基づいて、負極ずれ量ΔＱ_ＮＥを算出する。

Then, the negative electrode deviation amount _ΔQNE is calculated based on the positive electrode side reaction current value _iPE .

<Total capacity of deviation capacity ΔQ (t ₀ to t ₁ ) corresponding to positive and negative electrode composition>
Then, in S87 of the follow chart shown in FIG. 5, ΔQ (t0 to t1) = ( _iNE - _iPE ) from the negative electrode side reaction current value _iNE and the positive electrode side reaction current value _iPE calculated in this way. Calculate × Δt. That is, the difference between the negative electrode side reaction current value _iNE and the positive electrode side reaction current value _iPE is multiplied by the elapsed time Δt to obtain the total capacity of the positive and negative electrode composition-corresponding deviation capacity ΔQ (t ₀ to t ₁ ) with the elapsed time Δt. Calculate (S87). In addition, i _NE × Δt−i _PE × Δt = ΔQ _NE −ΔQ _PE = ΔQ (t ₀ to t ₁ ) may be set.

<Attenuation of the side reaction current value of the positive and negative electrodes according to the film growth>
In the Tafel equation, the influence of the thickness of the SEI coating on the current value is not taken into consideration. Therefore, in the calculation of ΔQ _PE and ΔQ _{NE, ΔQ PE and ΔQ NE are calculated} using the values obtained by attenuating the side reaction current values according to the amount of film formation at each elapsed time.

FIG. 9 is a schematic diagram showing a model of film growth. FIG. 10 is an equation showing the relationship between the film formation amount and the side reaction current value. FIG. 11 is a graph showing the attenuation rate of the current value with respect to the reciprocal of the coating amount. FIG. 12 is a table showing the relationship between the elapsed time, the amount of film formation, and the side reaction current value. FIG. 13 is a graph comparing the deterioration degree estimation result of the prior art and the deterioration degree estimation result of the present embodiment. With reference to FIGS. 9 to 13, the attenuation of the side reaction current values of the positive and negative electrodes according to the film growth will be described.

As shown in FIG. 10A, the time t ₀ immediately after the assembly of the lithium ion secondary battery 1 (before conditioning) is such that the current collector foil 1c and the mixture 1a are bonded to each other, and the SEI coating 1sei is formed. Not formed. Depending on use, at time t1, the SEI coating 1sei is formed as shown in FIG. ₁₀ (b). Further use is continued, and at time t2, the SEI coating 1sei grows thickly as shown in _FIG . 10 (c). This SEI coating 1sei becomes a resistance and obstructs the flow of current. The side reaction current value I depends on the thickness x. The side reaction current value I is proportional to 1 / x as shown in FIG. 11 (k is a coefficient). Then, when calculating ΔQ in (t ₁ to t ₂ ), it is attenuated due to the relationship between “1 / Σ subcurrent value × t / mAh” and “adverse reaction current value attenuation rate /%” shown in FIG. The ΔQ at (t ₁ to t ₂ ) is calculated using the side reaction current values at (t ₁ to t ₂ ).

As a result, as shown in FIG. 13, as the time elapses from t ₁ to t ₂ to t _n , the coating amount is cumulatively thickened, and the side reaction current value I is the reciprocal of the thickness x. It becomes smaller in proportion to.
In the present embodiment, since the attenuation of the side reaction current values of the positive and negative electrodes described above according to the film growth is taken into consideration, as shown in FIG. 14, the method of estimating the deterioration of the present embodiment is Tafel by the conventional technique. It is possible to estimate the deterioration closer to the actual deterioration than the deterioration estimation method using only the equation.

<Estimate the amount of negative electrode deterioration (S9)>
Here, returning to the flowchart of FIG. 3, the estimation of the amount of deterioration of the negative electrode (S9) will be described. The negative electrode deterioration amount is, that is, the negative electrode deviation amount ΔQ _NE , which is the sum of the adverse reaction current values _iNE of the negative electrode in that section calculated in S8.

<Determine the charge current threshold ICmax according to the amount of deterioration of the negative electrode (S10)>
Here, the charge current threshold ICmax estimated in the procedure of estimating the amount of negative electrode deterioration (S9) is determined from the map 2 (see FIG. 14) acquired in advance in the acquisition of the “negative electrode deterioration-Li precipitation allowable current map” (S2). (S10). The newly determined charge current threshold value ICmax is updated by overwriting the charge current threshold value ICmax stored in the memory 102 of the ECU 100 until then.

<Determining whether or not the charging current IC ≥ the charging current threshold IC max (S11)>
Subsequently, the charging current IC for the lithium ion secondary battery 1 is constantly monitored, and it is determined whether or not the charging current IC exceeds the charging current threshold ICmax with the charging current threshold ICmax determined in S10 as a reference value. .. If the charging current IC does not exceed the charging current threshold IC max (S11: NO), the charging current IC is not limited, and ΔQ obtained by integrating the negative electrode side reaction current value _iNE in that section calculated in S8 as it is. The _NE is stored (S14), and the next process is performed (S15: NO → S4).

On the other hand, when it is determined that the charging current IC exceeds the charging current threshold ICmax (S11: YES), the charging current IC applied to the lithium ion secondary battery 1 is suppressed to the charging current threshold ICmax by the limiter. (S12). Then, the ΔQ _NE obtained by integrating the negative electrode side reaction current value _iNE calculated in S8 is stored (S14), and the next process is performed (S15: NO → S4).

When the operation of the vehicle 10 is terminated by the driver of the vehicle 10 and the power is turned off and the use of the battery is terminated (S15: YES), the process is terminated.
(Effect of embodiment)
This embodiment has the following effects from the above configuration.

(1) In the Li precipitation suppression control method of the lithium ion secondary battery 1 using the side reaction current of the present embodiment, the lithium ion secondary battery 1 is charged within the range of the charging current IC in which metallic lithium does not precipitate at the negative electrode. , The precipitation of metallic lithium on the negative electrode can be effectively suppressed.

(2) Further, since the maximum charging current IC can be obtained within the range where metallic lithium does not precipitate, the battery performance can be maximized while suppressing the deterioration of the lithium ion secondary battery 1.

(3) Since the charging current threshold ICmax is continuously dynamically changed according to the deterioration state of the negative electrode, the performance is always maximized according to the deterioration state at that time while the deterioration due to the side reaction current progresses. It can be pulled out to the limit.

Conventionally, as shown in FIG. 15, the allowable charging current IC is fixedly limited, and further, not the negative electrode deterioration amount I _NE , which is closely related to the precipitation of metallic lithium, but only the capacity reduction amount of the entire battery. Therefore, the charging current IC was also statically limited at a constant current value regardless of the degree of deterioration of the negative electrode. Therefore, even when the capacity of the entire battery does not deteriorate, it is limited by looking at the margin. Therefore, the battery is charged in the range of the region 2 without applying the charging current IC in the portion of the region 1 shown in FIG. rice field. Furthermore, when the capacity of the entire battery drops to _ΔQ2 , even if the charging current IC is limited this time, the charging current IC becomes such that metallic lithium precipitates, which further accelerates the deterioration of the battery. It ends up.

On the other hand, in the present embodiment, as shown in FIG. 14, _paying attention to the negative electrode deterioration amount IN, the charge current IC allowed in the deteriorated state is calculated as the charge current threshold IC max, and the maximum current value in the range is calculated. Since it allows charging up to, it can be fully utilized within the permissible range regardless of whether the deterioration state is small or the deterioration state is large. Further, even at the end of the usage period, the deterioration is not promoted by sufficiently reducing the charge current threshold value ICmax.

(4) When using the lithium ion secondary battery 1, by acquiring the deterioration characteristics unique to the lithium ion secondary battery 1 in advance, the deterioration characteristics of the individual lithium ion secondary batteries 1 can be obtained when mounted on a vehicle. Precise control can be performed according to the situation. In the embodiment, a new vehicle is described as an example, but even in a used car or a used secondary battery, the side reaction current of the present embodiment can be obtained by acquiring the peculiar deterioration characteristics of the lithium ion secondary battery 1 in advance. The method for controlling Li precipitation suppression of the lithium ion secondary battery 1 used can be implemented.

(5) When the negative electrode open potential V _NE and the positive electrode open potential V _PE are estimated from the cell voltage VB, the positive electrode / negative electrode capacity-OCP (Open circuit potential) characteristics (battery capacity and opening of the positive electrode / negative electrode at that time). In the graph showing the relationship with the potential), the negative electrode open potential V _NE and the positive electrode open potential V _PE are estimated with reference to the positive / negative electrode composition-corresponding shift capacity ΔQ. Deterioration can be estimated accurately.

(6) Deterioration of the negative electrode of the lithium ion secondary battery 1 is determined based on the growth of the SEI coating based on the side reaction current value based on the Tafel equation. Therefore, since the growth of the SEI coating is estimated accurately by integrating the side reaction current values of the negative electrode, and the amount of capacitance deterioration of the negative electrode is accurately estimated from this data, the deterioration is theoretically accurate without actual measurement. Can be estimated.

(7) Further, the negative electrode side reaction current value _iNE decreases with the growth of the negative electrode SEI coating, but by reflecting the decrease of the negative electrode side reaction current value _iNE with the growth of the negative electrode SEI coating, it becomes more The deterioration of the negative electrode can be estimated accurately.

(8) From the cell voltage VB and the cell temperature TB based on the "deterioration characteristics peculiar to the lithium ion secondary battery" and the "negative electrode deterioration-Li precipitation allowable current map 2" stored in advance by the ECU 100 of the vehicle 10. It can be controlled only by data. Therefore, in the configuration of the vehicle 10, only by installing the program of the Li precipitation suppression control method of the present embodiment in the ECU 100, the control device 18 is combined with the Li precipitation suppression control device of the lithium ion secondary battery using the side reaction current. can do.

(9) Therefore, even in the existing vehicle 10, it has a simple structure and is easy to adapt, so that it can be easily mounted afterwards. Efficient control can be performed even with existing vehicles.
(Variation Example) The present invention is not limited to each of the above embodiments, and can be carried out as follows.

○ In the embodiment, an example of being mounted on a vehicle is shown, but the implementation is not necessarily limited to that mounted on an automobile, and does not exclude implementation on ships, railroads, aircraft, and even fixed type ones.
○ In the embodiment, the lithium ion secondary battery 1 as shown in FIG. 1 has been described as an example, but the lithium ion secondary battery 1 may have a cylindrical shape or a cubic shape. .. Further, the positive electrode and the negative electrode are not limited to those wound, and may be one in which a plurality of positive electrode plates and negative electrode plates are laminated.

○ FIG. 1 shows a single cell battery, but in the vehicle 10, the lithium ion secondary battery 1 is used as a stack by connecting the cell batteries as a unit, and is used as a stack. The Li precipitation suppression control method for the lithium ion secondary battery using the side reaction current is carried out independently for each cell battery, but the entire assembled battery may be controlled.

-In the embodiment of the embodiment, the mathematical formulas (1) to (4) shown in the equations 1 to 8 are examples of the processing, and the process is not limited as long as the charge current threshold value ICmax can be calculated. Regardless of the formula, all the data may be converted into a table or a map.

○ Regarding the control of the charging current IC, this may be converted into the charging voltage VC for control.
○ In the Li precipitation suppression control method for the lithium ion secondary battery of the present embodiment, the data obtained from this may be used to control the cell SOC and predict deterioration in charging, for example.

○ The control by the charge current threshold value ICmax may be provided with a certain margin for safety. Further, it may not be completely continuous, but may be changed stepwise or intermittently.
○ It goes without saying that the flowcharts illustrated in FIGS. 3, 5, and 8 are examples of processing, and the order can be changed, and steps can be added, deleted, or changed.

○ The graphs illustrated in FIGS. 6 (a) and 6 (b), FIG. 7, FIG. 11, FIG. 13, and FIG. 14 are conceptual examples and are not limited thereto. In addition, it is not always necessary to create a graph for implementation.

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

1 ... Lithium-ion secondary battery (secondary battery)
2 ... (Negative electrode deterioration-Li precipitation allowable current) Map 10 ... Vehicle 18 ... Control device 20 ... Monitoring unit 21 ... Voltage sensor 22 ... Current sensor 23 ... Temperature sensor 30 ... PCU
100 ... ECU
101 ... CPU
102 ... Memory 200 ... Device for acquiring deterioration characteristics VB ... Cell voltage IB ... Cell current TB ... Cell temperature IC ... Charging current ICmax ... Charging current threshold t ₀ ... Time (initial value)
t ₁ ... time Δt ... time (elapsed time)
ΔQ… Positive and negative electrode composition-corresponding displacement ΔQ _NE … Negative electrode displacement ΔQ _PE … Positive electrode displacement Q _loss … Capacity decrease in battery full capacity before and after storage Q _SD … Self-discharge capacity V _NE … (depending on the capacity of the negative electrode) Negative electrode open potential V _PE … (according to the capacity of the positive electrode) Positive electrode open potential V _NE0 … Negative electrode open potential according to the capacity of the negative electrode (initial value without deterioration)
V _PE0 : Positive electrode open potential according to the capacity of the positive electrode (initial value without deterioration)
I _NE ... Negative electrode deterioration amount [Ah]
I _PE ... Positive electrode deterioration amount [Ah]
i _NE ... Negative negative side reaction current value [A]
i _PE … Positive electrode side reaction current value [A]
i _NE0 ... Negative negative side reaction current value (acquired as deterioration characteristic) [A]
i _PE0 ... Positive electrode side reaction current value (acquired as deterioration characteristic) [A]

Claims (10)

The voltage measurement step to measure the cell voltage and
A step of potential estimation for estimating the positive electrode open potential and the negative electrode open potential from the acquired cell voltage, and
The cell temperature measurement step to acquire the cell temperature, and
A step of side reaction current estimation for estimating a positive electrode side reaction current value and a negative electrode side reaction current value from the estimated positive electrode open potential, negative electrode open potential, and cell temperature.
The step of estimating the negative electrode deterioration amount by integrating the estimated negative electrode side reaction current values and estimating the negative electrode deterioration amount, and
The Li precipitation suppression control of the lithium ion secondary battery is provided with a charging current determination step of determining the upper limit charge current allowed within the range in which Li precipitation is suppressed according to the estimated negative electrode deterioration amount. Method. In the charge current determination step, the upper limit charge current allowed within the range in which Li precipitation is suppressed is determined based on the map corresponding to the limit charge current that does not cause Li precipitation, depending on the amount of negative electrode deterioration. The method for controlling Li precipitation suppression of a lithium ion secondary battery according to claim 1. The lithium ion secondary according to claim 1 or 2, further comprising a step of predicting the amount of capacity deterioration for estimating the amount of capacity deterioration from the estimated positive electrode side reaction current value and the negative electrode side reaction current value. A method for controlling Li precipitation suppression of a battery. It is characterized by comprising a charging step of limiting the charging current of the lithium ion secondary battery with the upper limit charging current allowed in the range of suppressing Li precipitation determined in the charging current determination step as a threshold. The method for controlling Li precipitation suppression of a lithium ion secondary battery according to any one of claims 1 to 3. The Li precipitation suppression control method for a lithium ion secondary battery according to claim 4, wherein in the charging step, the threshold value is updated every time the negative electrode deterioration amount is estimated in the negative electrode deterioration amount estimation step. In the step of calculating the amount of deterioration of the negative electrode,
When i ₀ is the exchange current density, α is the transfer coefficient, F is the Faraday constant, R is the gas constant, T is the absolute temperature, U _side is the film formation potential, _UNE is the negative electrode open potential, and _UP E is the positive electrode open potential. ,
The following formula (3)

Calculate the negative electrode side reaction current value _iNE calculated by
In the step of calculating the amount of deterioration of the positive electrode,
The following formula (4)

The Li precipitation suppression control method for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the positive electrode side reaction current value _iPE is calculated by the above method. The lithium ion secondary battery according to claim 1 to 6, wherein in the step of calculating the negative electrode deterioration amount, the negative electrode deterioration amount is calculated using a value obtained by attenuated the side reaction current value according to the elapsed time. Li precipitation suppression control method. Before executing the Li precipitation suppression control method for the lithium ion secondary battery,
The storage step of storing the lithium-ion secondary battery under specific conditions,
The step of measuring the capacity reduction amount to measure the capacity reduction amount of the battery full capacity before and after the storage of the stored lithium ion secondary battery, and
The self-discharge capacity measurement step for measuring the self-discharge capacity of the stored lithium ion secondary battery before and after storage, and
Claims 1 to 7 include a step of acquiring deterioration characteristics including a step of obtaining a side reaction current value of a positive electrode and a negative electrode under a specific condition at the time of storage from the capacity decrease amount and the self-discharge capacity. The method for controlling Li precipitation suppression of a lithium ion secondary battery according to any one of the above. A voltage sensor that detects the cell voltage of a lithium-ion secondary battery,
A temperature sensor that detects the cell temperature of a lithium-ion secondary battery,
A control device for a lithium-ion secondary battery including a computer having a CPU and a memory.
The computer is a control device for a lithium ion secondary battery, which comprises a control means for executing the Li precipitation suppression control method for the lithium ion secondary battery according to any one of claims 1 to 8. The control device for a lithium ion secondary battery according to claim 9, wherein the lithium ion secondary battery is mounted on a vehicle, and the computer is a computer mounted on the vehicle.

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