JP2012104239A - Lithium ion battery electricity storage amount estimation method, lithium ion battery electricity storage amount estimation program, lithium ion battery electricity storage amount correction method, and lithium ion battery electricity storage amount correction program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate the state of charge (SOC) of an olivine based lithium ion battery with high accuracy.SOLUTION: A method for estimating the electricity storage amount of an olivine based lithium ion battery comprises a charge resistance calculation step for calculating the charge resistance of the lithium ion battery when it is charged, a discharge resistance calculation step for calculating the discharge resistance of the lithium ion battery when it is discharged, a resistance ratio calculation step for calculating a resistance ratio of the charge resistance calculated in the charge resistance calculation step to the discharge resistance calculated in the discharge resistance calculation step, and an electricity storage amount estimation step in which, based on correlation information that an electricity storage amount of the lithium ion battery increases as does a resistance ratio derived by dividing the charge resistance by the discharge resistance, the electricity storage amount is estimated from the resistance ratio calculated in the resistance ratio calculation step.

Description

  The present invention relates to a storage amount estimation method for estimating a storage amount of a lithium ion battery having an olivine structure.

  A lithium ion battery is known as a chargeable / dischargeable secondary battery. The state of charge (hereinafter referred to as “SOC”) of the lithium-ion battery is determined by the vehicle running state (for example, start, normal running, acceleration, deceleration, etc.) and vehicle load (stop lamp, headlamp, wiper, electric Therefore, it is necessary to monitor the SOC while using the lithium ion battery. Here, as a method for estimating the charged amount, Patent Document 1 discloses a battery that is detected when a charge current integrated value and a discharge current integrated value match with reference to the time when the battery charge amount matches the control center SOC. An SOC calculation device is disclosed that estimates the open circuit voltage of a battery and calculates the SOC based on the inter-terminal voltage and charge / discharge current and the internal resistance value obtained in advance.

JP 2007-192726 A

However, in the case of a lithium ion battery including an olivine structure represented by the general formula: LIMPO ₄ (wherein M is a transition metal) as the positive electrode active material (hereinafter referred to as an olivine-based lithium ion battery), the SOC is determined from the open-circuit voltage. Is difficult to calculate. FIG. 8 is a graph showing the relationship between the open circuit voltage and the SOC of the ternary lithium ion battery and the olivine lithium ion battery. In the figure, the SOC is defined by a voltage range that is generally usable (2.5 to 4.1 V in the case of an olivine type lithium ion battery).

In the ternary lithium ion battery, the positive electrode has a layered structure made of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and the negative electrode is made of graphite. In the olivine-based lithium ion battery, the positive electrode is made of LiFePO ₄ having an olivine structure, and the negative electrode is made of graphite.

  Referring to the figure, in the case of a ternary lithium ion battery, it can be seen that there is a correlation between the open-circuit voltage and the SOC because the SOC increases when the open-circuit voltage increases. Note that the open-circuit voltage means a voltage value between the battery terminals in a state where the battery is not connected to the device (a state where no current flows). On the other hand, in the case of an olivine-based lithium ion battery, it is understood that there is almost no change in the open circuit voltage when the SOC is in the range of about 10 to 98%, and there is no correlation between the open circuit voltage and the SOC in this range. Therefore, in the case of an olivine-based lithium ion battery, it is difficult to estimate the SOC from the open-circuit voltage, so another estimation method needs to be used. Then, this invention aims at estimating SOC of an olivine type lithium ion battery accurately.

In order to solve the above-mentioned problems, a method for estimating the amount of charge of a lithium ion battery according to the present invention includes: (1) an olivine structure represented by a general formula: LIMPO ₄ (wherein M is a transition metal) in the positive electrode active material A method for estimating a storage amount of a lithium ion battery including a positive electrode body including a negative electrode body,
A charging resistance calculating step of calculating a charging resistance when charging the lithium ion battery;
A discharge resistance calculating step for calculating a discharge resistance when the lithium ion battery is discharged;
A resistance ratio calculating step for calculating a resistance ratio between the charging resistance calculated in the charging resistance calculating step and the discharging resistance calculated in the discharging resistance calculating step, and a resistance ratio obtained by dividing the charging resistance by the discharging resistance is increased. And a storage amount estimation step of estimating the storage amount from the resistance ratio calculated in the resistance ratio calculation step based on correlation information in which the storage amount of the lithium ion battery increases in response. And

  (2) In the configuration of (1), the correlation information exists individually for each of a plurality of temperature information of the lithium ion battery, and a temperature information acquisition step of acquiring information about the temperature of the lithium ion battery; A correlation information specifying step for specifying the correlation information corresponding to the temperature information acquired in the temperature information acquisition step, and the storage amount estimation step is based on the correlation information specified in the correlation information specifying step. The charged amount can be estimated from the resistance ratio calculated in the discharge resistance calculating step. According to the configuration of (2) above, it is possible to estimate the charged amount using more accurate correlation information corresponding to the temperature.

(3) In order to solve the above-mentioned problem, a storage capacity estimation program for a lithium ion battery according to the present invention is an olivine structure represented by a general formula: LIMPO ₄ (wherein M is a transition metal) in the positive electrode active material. A storage capacity estimation program for a lithium ion battery that causes a computer to execute a process for estimating a storage capacity of a lithium ion battery including a positive electrode body and a negative electrode body,
A charging resistance calculating step of calculating a charging resistance when charging the lithium ion battery;
A discharge resistance calculating step for calculating a discharge resistance when the lithium ion battery is discharged;
A resistance ratio calculating step for calculating a resistance ratio between the charging resistance calculated in the charging resistance calculating step and the discharging resistance calculated in the discharging resistance calculating step, and a resistance ratio obtained by dividing the charging resistance by the discharging resistance is increased. And a storage amount estimation step of estimating the storage amount from the resistance ratio calculated in the resistance ratio calculation step based on correlation information in which the storage amount of the lithium ion battery increases in response. And

  (4) In the configuration of (3) above, the correlation information exists individually for each of a plurality of temperature information of the lithium ion battery, and a temperature information acquisition step of acquiring information about the temperature of the lithium ion battery; A correlation information specifying step for specifying the correlation information corresponding to the temperature information acquired in the temperature information acquisition step, and the storage amount estimation step is based on the correlation information specified in the correlation information specifying step. The charged amount can be estimated from the resistance ratio calculated in the discharge resistance calculating step. According to the configuration of (4) above, it is possible to estimate the charged amount using more accurate correlation information according to the temperature.

  (5) integrating the first step of estimating the first charged amount stored in the lithium ion battery by the method described in (1) or (2) above and the charge / discharge amount of the lithium ion battery; To calculate the difference between the second step of estimating the second storage amount stored in the lithium ion battery and the first and second storage amounts estimated in the first and second steps. And when the difference is equal to or larger than a threshold value, a fourth step of reducing the charged amount of the lithium ion battery to a predetermined value or less by discharging, and the charged amount of the lithium ion battery to the predetermined value or less. In a reduced state, a fifth step of measuring the open-ended voltage of the lithium-ion battery, a sixth step of calculating a third charged amount of the lithium-ion battery from the open-ended voltage, Storage amount correction method for a lithium-ion battery, characterized in that it comprises a seventh step of correcting the second power storage amount in the third power storage amount. According to the configuration of (5) above, it is possible to accurately determine whether or not there is an error in the first charged amount by comparing the first and second charged amounts. Further, in the estimation method for estimating the storage amount by integrating the charge / discharge amount, even when an error in the reference storage amount increases due to accumulation, more accurate estimation information (third storage amount) is used. The reference charged amount can be corrected.

  (6) In the configuration of (5), the predetermined value can be set to 10%. According to the configuration of (6) above, it is possible to further increase the estimation accuracy of the third power storage amount.

(7) a first step of estimating a first power storage amount stored in the lithium ion battery by causing a computer to execute the program according to (3) or (4);
A second step of estimating a second amount of electricity stored in the lithium ion battery by integrating the amount of charge and discharge of the lithium ion battery; and the first and second steps estimated in the first and second steps A third step of calculating a difference between the second power storage amounts, a fourth step of reducing the power storage amount of the lithium ion battery to a predetermined value or less by discharging when the difference is equal to or greater than a threshold value; A fifth step of measuring an open-ended voltage of the lithium-ion battery in a state where the charged amount of the lithium-ion battery is reduced to the predetermined value or less; and a third charged amount of the lithium-ion battery from the open-ended voltage A sixth step of calculating, and a seventh step of correcting the second charged amount to the third charged amount; Lamb. According to the configuration of (7) above, it is possible to accurately determine whether or not there is an error in the first charged amount by comparing the first and second charged amounts. Further, in the estimation method for estimating the storage amount by integrating the charge / discharge amount, based on more accurate estimation information (third storage amount) even when an error in the reference storage amount increases due to accumulation. The reference charged amount can be corrected.

  (8) In the configuration of (7) above, the predetermined value can be set to 10%. According to the configuration of (8) above, it is possible to further increase the estimation accuracy of the third power storage amount.

  According to the configuration of (1) above, it is possible to improve the estimation accuracy of the charged amount of the olivine type lithium ion battery. According to the configuration of (3) above, it is possible to improve the estimation accuracy of the charged amount of the olivine type lithium ion battery.

It is a block diagram of the element in connection with a battery and charging / discharging control of a battery. It is the graph which showed each resistance ratio and SOC measurement result of an olivine type lithium ion battery and a ternary type lithium ion battery (battery temperature is 25 degreeC). It is the graph which showed each resistance ratio and SOC measurement result of an olivine type lithium ion battery and a ternary type lithium ion battery (battery temperature is 10 ° C.). It is the graph which showed each resistance ratio and SOC measurement result of an olivine type lithium ion battery and a ternary type lithium ion battery (battery temperature is −10 ° C.). It is an example of the data table which shows the correlation information of the resistance ratio and SOC of an olivine type lithium ion battery. 3 is a flowchart illustrating an SOC calculation method according to the first embodiment. 5 is a flowchart illustrating an SOC correction method according to a second embodiment. It is the graph which showed the relationship between the open end voltage and SOC of an olivine type lithium ion battery and a ternary type lithium ion battery.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of elements related to a battery and charge / discharge control of the battery. The battery 2 of this embodiment can be mounted on a hybrid vehicle or an electric vehicle.

  The battery 2 is connected to the booster circuit 102 via the system main relays 101A and 101B. Booster circuit 102 boosts the output voltage of battery 2 and outputs the boosted voltage to inverter 103. The inverter 103 converts the DC power from the booster circuit 102 into AC power and outputs the AC power to the motor / generator (three-phase AC motor) 104. The kinetic energy generated by the motor / generator 104 is used as energy for driving the vehicle 1.

  When the vehicle is braked, electric energy is generated by the motor / generator 104 and output to the inverter 103. The inverter 103 converts AC power from the motor / generator 104 into DC power and outputs the DC power to the booster circuit 102. The step-up circuit 102 steps down the output voltage of the inverter 103 and then outputs it to the battery 2 to charge the battery 2.

  The battery 2 includes a plurality of battery blocks 20A to 20Z. These battery blocks 20A to 20Z are electrically connected in series. The battery block 20A includes a plurality of unit cells 201A to 201E. These unit cells 201A to 201E are electrically connected in series. Since other battery blocks 20B to 20Z have the same configuration as battery block 20A, the description will not be repeated. A voltage detection sensor 105 is connected to each of the battery blocks 20A to 20Z, and each voltage detection sensor 105 outputs a block voltage of each of the battery blocks 20A to 20Z to the battery controller 106.

  A current detection sensor 107 is connected to the battery 2, and the current detection sensor 107 outputs information related to a current value flowing through the battery 2 to the battery controller 106. The memory 108 stores various calculation programs and the like for calculating the SOC described later. The battery controller 106 executes a calculation program stored in the memory 108.

  A temperature sensor 109 is provided in each of the unit cells 201A to 201Z. The temperature sensor 109 may be a thermistor element. The temperature information of each of the single cells 201 </ b> A to 201 </ b> Z output from the temperature sensor 109 is output to the battery controller 106.

The unit cell 201A is an olivine-type lithium ion battery including a positive electrode body including an olivine structure represented by a general formula: LIMPO ₄ (wherein M is a transition metal) as a positive electrode active material, and a negative electrode body. Here, the transition metal M in the olivine structure may be Fe, Mn, Co, or Ni.

The positive electrode active material may include other oxides. The other oxide is a layered rock salt structure represented by LIMO ₂ (wherein M is a transition metal) or a spinel structure represented by LIM ₂ O ₄ (wherein M is a transition metal). May be. The transition metal M in the layered rock salt structure may be Ni, Mn, or Co. The transition metal M in the spinel structure may be Ni or Mn. The negative electrode active material may include a spinel structure represented by carbon or Li ₄ Ti ₅ O ₁₂ . The carbon may be graphite, soft carbon, or hard carbon.

  Here, the inventor of the present invention has characteristics that the olivine-based lithium ion battery is different from the ternary lithium-ion battery. Specifically, the olivine-based lithium ion battery is discharged with a charging resistance when the olivine-based lithium ion battery is charged. It was discovered that there is a proportional relationship between the ratio of the current discharge resistance (hereinafter also referred to as the resistance ratio) and the SOC. The characteristics of the olivine-based lithium ion battery will be described in detail with reference to FIGS.

  2 to 4 are graphs showing measurement results of each resistance ratio and SOC of the olivine lithium ion battery and the ternary lithium ion battery. Here, the charging resistance is obtained by dividing the voltage difference between the voltage before charging and the voltage after charging for a predetermined time by the current, and the predetermined time may be appropriately determined. In the present embodiment, the predetermined time is set to 10 seconds. The discharge resistance is obtained by dividing the voltage difference between the voltage before discharge and the voltage after discharge for a predetermined time by the current, and the predetermined time may be appropriately determined. In the present embodiment, the predetermined time is set to 10 seconds. The SOC was calculated from the accumulated current when the olivine lithium ion battery and the ternary lithium ion battery were charged and discharged, respectively. In the following description, a method for estimating the SOC from the current integration amount is referred to as a current integration method. Since the current integration method is a conventionally known method, detailed description thereof is omitted. An example of the current integration method is disclosed in Japanese Patent Laid-Open No. 2000-166105.

  This current integration method has a characteristic that the SOC estimation accuracy increases as the number of current integrations decreases, and the SOC estimation accuracy deteriorates due to accumulation of errors as the number of current integrations increases. Therefore, the SOC was measured by charging and discharging unused olivine lithium ion batteries and ternary lithium ion batteries. FIG. 2 corresponds to the case where the battery temperature of the olivine lithium ion battery and the ternary lithium ion battery is 25 ° C. FIG. 3 corresponds to the case where the battery temperature of the olivine lithium ion battery and the ternary lithium ion battery is 10 ° C. FIG. 4 corresponds to the case where the battery temperature of the olivine lithium ion battery and the ternary lithium ion battery is −10 ° C.

For the positive electrode of the olivine-based lithium ion battery, LiFePO ₄ having an olivine structure was used as the positive electrode active material, AB (acetylene black) was used as the conductive material, and PVDF (PolyVinylidene DiFluoride) was used as the binder. The ratio of LiFePO ₄ , AB (acetylene black) and PVDF (PolyVinylidene DiFluoride) was 87: 10: 3 in mass%.

For the negative electrode of the olivine-based lithium ion battery, graphite was used as the negative electrode active material, and PVDF (PolyVinylidene DiFluoride) was used as the binder. The ratio of graphite and PVDF (PolyVinylidene DiFluoride) was set to 95: 5 by mass%. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l in a mixed solution composed of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) was used. The ratio of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) was 3: 7 in mass%. As the separator, a three-layer separator composed of a PE (polyethylene) film, a PP (polypropylene) film, and a PE (polyethylene) film was used.

For the positive electrode of the ternary lithium ion battery, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ is used as the positive electrode active material, AB (acetylene black) is used as the conductive material, and PVDF is used as the binder. (PolyVinylidene DiFluoride) was used. The ratio of LiFePO ₄ , AB (acetylene black) and PVDF (PolyVinylidene DiFluoride) was 87: 10: 3 in mass%.

For the negative electrode of the ternary lithium ion battery, graphite was used as the negative electrode active material, and PVDF (PolyVinylidene DiFluoride) was used as the binder. The ratio of graphite and PVDF (PolyVinylidene DiFluoride) was set to 95: 5 by mass%. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l in a mixed solution composed of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) was used. The ratio of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) was 3: 7 in mass%. As the separator, a three-layer separator composed of a PE (polyethylene) film, a PP (polypropylene) film, and a PE (polyethylene) film was used.

  In the olivine-based lithium ion battery used in the experiments of FIGS. 2 to 4, Fe was used as the transition metal. However, as the resistance ratio increases, the correlation in which the storage amount of the olivine-based lithium ion battery increases is Since it is obtained by the two-layer cooperative reaction of the olivine structure, it is naturally obtained even when other transition metals are used.

Referring to FIG. 2, in the case of an olivine-based lithium ion battery at a battery temperature of 25 ° C., it was found that the SOC increases as the charge resistance / discharge resistance increases. When the axis indicating the SOC is the X axis and the axis indicating the charge resistance / discharge resistance is the Y axis, these relationships are:
y = 0.0046x + 0.8254.

In the case of the ternary lithium ion battery when the battery temperature is 25 ° C., it has been found that the SOC rapidly increases as the charge resistance / discharge resistance increases. These relationships are
It is expressed by a linear expression of y = 0.006x + 0.9719.

Referring to FIG. 3, it was found that in the case of an olivine-based lithium ion battery at a battery temperature of 10 ° C., the SOC increases as the charge resistance / discharge resistance increases. When the axis indicating the SOC is the X axis and the axis indicating the charge resistance / discharge resistance is the Y axis, these relationships are:
y = 0.0089x + 0.6316.

In the case of the ternary lithium ion battery when the battery temperature is 10 ° C., it has been found that the SOC rapidly decreases as the charge resistance / discharge resistance increases. These relationships are
y = −0.0014x + 1.0767.

Referring to FIG. 4, it was found that in the case of an olivine-based lithium ion battery when the battery temperature is −10 ° C., the SOC increases as the charge resistance / discharge resistance increases. When the axis indicating the SOC is the X axis and the axis indicating the charge resistance / discharge resistance is the Y axis, these relationships are:
It is expressed by a linear expression of y = 0.0005x + 0.9048.

In the case of a ternary lithium ion battery in which the battery temperature was controlled at −10 ° C., it was found that the SOC increased as the charge resistance / discharge resistance increased. These relationships are
y = 0.0034x + 0.8348 is represented by a linear expression.

  From these measurement results, it was found that in the case of an olivine-based lithium ion battery, the SOC tends to increase as the charge resistance / discharge resistance increases regardless of the battery temperature. In the case of a ternary lithium ion battery, it was found that the relationship between the charge resistance / discharge resistance and the SOC differs depending on the battery temperature, and the tendency is not constant.

  Therefore, the SOC of the olivine-based lithium ion battery can be accurately estimated by associating the primary expression indicating the relationship between the charge resistance / discharge resistance and the SOC with the battery temperature. That is, the SOC of the olivine-based lithium ion battery can be accurately estimated by storing a program for executing the calculation of the linear equation in the memory 108 for each temperature.

  As another method, the SOC of the olivine-based lithium ion battery is accurately estimated by storing in the memory 108 a data table in which the relationship between the charge resistance / discharge resistance and the SOC is associated with the battery temperature. Can do. FIG. 5 is an example of a data table, in which charge resistance / discharge resistance and corresponding SOC are grouped by the same No. By having such a data table for each temperature of the battery 2, the SOC can be estimated.

  Next, the SOC calculation method according to the present embodiment will be described in detail with reference to the flowchart of FIG. The battery controller 106 executes the flowchart of FIG. In step S101, the battery controller 106 proceeds to step S102 when charging of the battery 2 is started.

  In step S <b> 102, the battery controller 106 detects the block voltages of the battery blocks 20 </ b> A to 20 </ b> Z detected by the voltage detection sensors 105, the current values detected by the current detection sensors 107, and the single cells detected by the temperature sensors 109. The temperatures 201A to 201Z are sequentially stored in the memory 108. The battery controller 106 operates an internal timer (not shown).

  In step S103, the battery controller 106 determines whether or not the count time by the timer has reached 10 seconds. If the count time has reached 10 seconds, the process proceeds to step S104. In step S104, the battery controller 106 stops storing the block voltage, current value, and temperature in the memory 108, and stops the internal timer.

  In step S105, the battery controller 106 determines whether or not the battery 2 has started to be discharged. When discharging of the battery 2 is started, the process proceeds to step S106. In step S <b> 106, the battery controller 106 detects the block voltages of the battery blocks 20 </ b> A to 20 </ b> Z detected by the voltage detection sensors 105, the current values detected by the current detection sensors 107, and the single cells detected by the temperature sensors 109. The temperatures 201A to 201Z are sequentially stored in the memory 108. The battery controller 106 operates an internal timer (not shown).

  In step S107, the battery controller 106 determines whether or not the count time by the timer has reached 10 seconds. If the count time has reached 10 seconds, the process proceeds to step S108. In step S108, the battery controller 106 stops storing the block voltage, current value, and temperature in the memory 108, and stops the internal timer.

  In step S109, the battery controller 106 calculates an average temperature of each of the battery blocks 20A to 20Z based on the information stored in the memory 108. Specifically, the average temperature of the single cells 201A to 201E included in the battery block 20A is calculated and stored in the memory 108 as the average temperature of the battery block 20A. For the other battery blocks 20B to 20Z, the average temperature is calculated by the same method and stored in the memory 108. In addition, the battery controller 106 calculates a charging resistance and a discharging resistance based on information stored in the memory 108, and further calculates a resistance ratio obtained by dividing the charging resistance by the discharging resistance.

  In step S110, the battery controller 106 specifies correlation information corresponding to the average temperature stored in the memory 108 based on the average temperature calculated in step S109.

  In step S111, the battery controller 106 calculates the SOC based on the resistance ratio calculated in step S109 and the identified correlation information, and stores this in the memory 108. According to the above-described embodiment, the SOC of the olivine-based lithium ion battery can be accurately estimated.

(Embodiment 2)
The SOC of the olivine lithium ion battery calculated based on the estimation method of the first embodiment can be used as correction information for correcting the SOC calculated by the current integration method. As described above, the current integration method has a merit that the SOC estimation accuracy is very high when the number of current integrations is small. On the other hand, when the number of current integrations increases, the estimation accuracy decreases due to accumulation of errors. There is a demerit. Therefore, the battery controller 106 needs to reset the current integration once to eliminate the error.

  FIG. 7 is a flowchart showing a correction method for correcting the SOC calculated by the current integration method. A program for executing this flowchart is stored in the memory 108. The battery controller 106 may execute this program when the SOC calculation count by the current integration method reaches a predetermined number, or may execute it at a predetermined cycle.

  In step S201, the SOC is estimated from the charge resistance / discharge resistance based on the method of the first embodiment. The SOC estimated based on the method of Embodiment 1 is referred to as a first SOC. In step S202, the battery controller 106 estimates the SOC based on the current integration method. The SOC estimated based on the current integration method is referred to as a second SOC.

  In step S203, the battery controller 106 calculates a difference between the first SOC calculated in step S201 and the second SOC calculated in step S202, that is, ΔSOC. In step S204, the battery controller 106 compares ΔSOC with a threshold value, and determines whether ΔSOC is equal to or less than the threshold value. The threshold value may be set as appropriate based on performance data and the like from the viewpoint of maintaining the SOC estimation accuracy.

  If ΔSOC is greater than or equal to the threshold value in step S204, the process proceeds to step S205. Here, when ΔSOC is equal to or larger than the threshold value, an error in the SOC calculated by the current integration method is large. Therefore, in order to eliminate this error, it is necessary to reset the SOC that is the reference value of the current integration method once. . In step S205, the battery controller 106 determines whether or not the battery 2 is being charged. If the battery 2 is being charged in step S205, the process proceeds to step S206.

  In step S206, the battery controller 106 switches charging to discharging, and proceeds to step S207. If charging is not being performed in step S205, that is, if discharging is in progress, the process proceeds to step S207. Here, the reason for setting the battery 2 to discharge in step S205 and step S206 is as follows.

  Referring to FIG. 8, unlike the ternary lithium ion battery, the olivine-based lithium ion battery is difficult to grasp the correlation between the open-circuit voltage and the SOC, but the SOC is low (specifically, as the boundary value). 10%), the open circuit voltage increases as the SOC increases, as in the ternary lithium ion battery. For this reason, the SOC can be accurately estimated by measuring the open circuit voltage in a state where the olivine lithium ion battery is discharged and the SOC is once lowered. The SOC obtained by measuring the open-circuit voltage is referred to as a third SOC. By replacing the third SOC with the first SOC and using it as a reference value (initial value) in the current integration method, errors can be reduced.

  In step S207, the battery controller 106 determines whether or not the first SOC has decreased to 10% or less. If the first SOC is higher than 10%, the process returns to step S206 and discharge is continued. If the first SOC has decreased to 10% or less, the process proceeds to step S208. In step S208, the battery controller 106 measures the open circuit voltage of the battery 2, and calculates the third SOC from the correlation between the open circuit voltage and the SOC in FIG. Here, a program for deriving a correlation between the open-circuit voltage and the SOC when the SOC is 10% or less is stored in the memory 108. The program may be a calculation program for calculating the SOC from a function expression obtained by formulating these correlations. The program may be a calculation program for calculating the SOC from a data table indicating these correlations.

  In step S209, the battery controller 106 rewrites the first SOC stored in the memory 108, that is, the SOC that is the reference for the current integration method, to the third SOC. Thereby, accurate estimation of SOC by the current integration method can be performed.

(Modification 1)
In the above-described embodiment, a plurality of correlation information of resistance ratio and SOC are prepared in association with individual temperature information. However, the present invention is not limited to this, and only one correlation information corresponding to a specific temperature is used. May be. In this case, one correlation information corresponding to a specific temperature is stored in the memory 108, and the SOC calculation program of the first embodiment or the SOC correction of the second embodiment is performed only when the temperature of the battery 2 reaches the specific temperature. The program may be executed. For example, when the temperature of the battery 2 illustrated in FIG. 2 is 25 ° C., the correlation information is stored in the memory 108, and the SOC calculation according to the first embodiment is performed when the temperature detected by the temperature sensor 109 reaches 25 ° C. The program or the SOC correction program of the second embodiment may be executed. In this case, the memory 108 does not need to store a plurality of the correlation information. The specific temperature may be a specific temperature range as described in Modification 2 below.

(Modification 2)
In the embodiment described above, the correlation information of the resistance ratio and the SOC corresponding to the measured temperature is stored in the memory 108, but the present invention is not limited to this, and the correlation information is stored for each predetermined temperature range. It may be stored in the memory 108. For example, the correlation information may be shared for 15 ° C. to 20 ° C. In this case, the correlation information stored in the memory 108 is reduced, and the cost can be reduced by using a low-capacity memory. The predetermined temperature may be 5 ° C. or 10 ° C.

(Modification 3)
In the above-described embodiment, data collection for calculating the charge resistance is performed first, and then data collection for calculating the discharge resistance is performed. However, the present invention is not limited to this, and these calculations are performed. The order may be reversed. Even when the calculation order is reversed, the effects of the first and second embodiments can be obtained.

(Modification 4)
In the second embodiment described above, the order may be reversed to step S201 and step S202. That is, after calculating the second SOC by the current integration method, the first SOC may be calculated from the resistance ratio and the correlation information. Even when the calculation order is reversed, the effects of the first and second embodiments can be obtained.

(Modification 5)
In the above-described embodiment, the resistance ratio is calculated by dividing the charging resistance by the discharge resistance. However, the present invention is not limited to this, and the resistance ratio may be obtained by dividing the discharging resistance by the charging resistance. In this case, the SOC of the olivine-based lithium ion battery decreases as the resistance ratio increases. Even if the resistance ratio is the reciprocal of the embodiment, the effects of the first and second embodiments can be obtained.

(Modification 6)
In the above-described embodiment, the resistance ratio is calculated from the block voltage. However, the present invention is not limited to this, and a voltage sensor is provided in each of the unit cells 201A to 201Z, and each unit cell 201A to 201Z has a resistance. A ratio may be calculated.

2 battery 20A-20Z battery block 201A-201Z single cell 105 voltage sensor 106 battery controller 107 current sensor 108 memory 109 temperature sensor

Claims (8)

A method for estimating a storage amount of a lithium ion battery including a positive electrode body including an olivine structure represented by a general formula: LIMPO ₄ (wherein M is a transition metal) as a positive electrode active material, and a negative electrode body,
A charging resistance calculating step of calculating a charging resistance when charging the lithium ion battery;
A discharge resistance calculating step for calculating a discharge resistance when the lithium ion battery is discharged;
A resistance ratio calculating step for calculating a resistance ratio between the charging resistance calculated in the charging resistance calculating step and the discharging resistance calculated in the discharging resistance calculating step;
Based on the correlation information in which the storage amount of the lithium-ion battery increases as the resistance ratio obtained by dividing the charging resistance by the discharge resistance increases, the storage amount from the resistance ratio calculated in the resistance ratio calculation step A method for estimating a storage amount of a lithium ion battery, comprising the step of estimating a storage amount. The correlation information exists individually for each of the plurality of temperature information of the lithium ion battery,
A temperature information acquisition step of acquiring information about the temperature of the lithium ion battery;
A correlation information specifying step for specifying the correlation information corresponding to the temperature information acquired in the temperature information acquisition step,
The power storage amount estimation step estimates the power storage amount from the resistance ratio calculated in the discharge resistance calculation step based on the correlation information specified in the correlation information specification step. The method for estimating the amount of charge of the lithium ion battery described The computer executes a process for estimating the amount of charge of a lithium ion battery including a positive electrode body including an olivine structure represented by the general formula: LIMPO ₄ (wherein M is a transition metal) and a negative electrode body in the positive electrode active material A storage amount estimation program for a lithium ion battery
A charging resistance calculating step of calculating a charging resistance when charging the lithium ion battery;
A discharge resistance calculating step for calculating a discharge resistance when the lithium ion battery is discharged;
A resistance ratio calculating step for calculating a resistance ratio between the charging resistance calculated in the charging resistance calculating step and the discharging resistance calculated in the discharging resistance calculating step;
Based on the correlation information in which the storage amount of the lithium-ion battery increases as the resistance ratio obtained by dividing the charging resistance by the discharge resistance increases, the storage amount from the resistance ratio calculated in the resistance ratio calculation step And a storage amount estimation step for estimating a storage amount of a lithium ion battery. The correlation information exists individually for each of the plurality of temperature information of the lithium ion battery,
A temperature information acquisition step of acquiring information about the temperature of the lithium ion battery;
A correlation information specifying step for specifying the correlation information corresponding to the temperature information acquired in the temperature information acquisition step,
The storage amount estimation step estimates the storage amount from the resistance ratio calculated in the discharge resistance calculation step based on the correlation information specified in the correlation information specification step. The storage amount estimation program of the lithium ion battery described. A first step of estimating a first power storage amount stored in the lithium ion battery by the method according to claim 1;
A second step of estimating a second amount of electricity stored in the lithium ion battery by integrating the amount of charge and discharge of the lithium ion battery;
A third step of calculating a difference between the first and second power storage amounts estimated in the first and second steps;
If the difference is greater than or equal to a threshold, a fourth step of reducing the stored amount of the lithium ion battery to a predetermined value or less by discharging; and
A fifth step of measuring an open end voltage of the lithium ion battery in a state where the charged amount of the lithium ion battery is reduced to the predetermined value or less;
A sixth step of calculating a third charged amount of the lithium ion battery from the open-circuit voltage;
And a seventh step of correcting the second charged amount to the third charged amount. A method for correcting the charged amount of a lithium ion battery, comprising:   6. The method for correcting a charged amount of a lithium ion battery according to claim 5, wherein the predetermined value is 10%. A first step of estimating a first power storage amount stored in the lithium ion battery by causing a computer to execute the program according to claim 3 or 4;
A second step of estimating a second amount of electricity stored in the lithium ion battery by integrating the amount of charge and discharge of the lithium ion battery;
A third step of calculating a difference between the first and second power storage amounts estimated in the first and second steps;
If the difference is greater than or equal to a threshold, a fourth step of reducing the stored amount of the lithium ion battery to a predetermined value or less by discharging; and
A fifth step of measuring an open end voltage of the lithium ion battery in a state where the charged amount of the lithium ion battery is reduced to the predetermined value or less;
A sixth step of calculating a third charged amount of the lithium ion battery from the open-circuit voltage;
And a seventh step of correcting the second storage amount to the third storage amount. A storage amount correction program for a lithium ion battery, comprising: The storage capacity correction program for a lithium ion battery according to claim 7, wherein the predetermined value is 10%.

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