JP2014160592A - Method for controlling secondary battery device and secondary battery device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling a secondary battery device, which improves the accuracy of calculation of an SOC of a secondary battery, and to provide a secondary battery device.SOLUTION: The secondary battery device includes: a battery pack BT including at least one nonaqueous electrolyte secondary battery 10 using lithium titanate as a negative electrode active material; an AC oscillation source SS for applying an AC voltage/current of a predetermined frequency to a main circuit connected between the battery pack BT and a load or a power supply; a monitoring circuit VTM for detecting a battery voltage of the nonaqueous electrolyte secondary battery 10; a current detection circuit 200 for detecting a current of the main circuit; and an SOC calculation unit 202 which receives values of the battery voltage and the current of the main circuit, calculates an impedance Z of the battery to the AC voltage/current outputted from the AC oscillation source SS on the basis of the received values, and calculates an SOC of the nonaqueous electrolyte secondary battery 10 on the basis of the calculated impedance Z.

Description

  FIELD Embodiments described herein relate generally to a secondary battery device control method and a secondary battery device.

  As a large-sized and large-capacity power source used for an electric vehicle (EV), a hybrid electric vehicle (HEV), an electric motorcycle, a forklift, etc., a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) having a high energy density Secondary batteries) are attracting attention. Non-aqueous electrolyte secondary batteries have been developed for increasing the size and capacity while taking into account the longer life and safety. As a large-capacity power supply, an assembled battery containing a large number of secondary batteries connected in series and in parallel has been developed in order to increase driving power.

  When the secondary battery is mounted on various devices, the secondary battery is controlled by calculating a state of charge (SOC) of the secondary battery. For example, in an electric vehicle, it is determined whether or not the vehicle can travel to a charging station based on the SOC of the secondary battery. Further, for example, in a hybrid vehicle, it is determined whether to charge at the next timing or to preserve the current state based on the SOC of the secondary battery. In addition, since the secondary battery has a short life due to overcharge and overdischarge, the charging and discharging operations are controlled by the SOC of the secondary battery.

JP 2012-90404 A

  In recent years, secondary batteries have been developed with a focus on life and quick charge characteristics. There are a plurality of options for the electrode material of the secondary battery, but the electrode potential of the secondary battery is kept substantially constant over a wide range of SOC by the electrode material. While this characteristic is good as the output capacity characteristic of the secondary battery, it is difficult to calculate the SOC based on the electrode voltage of the secondary battery.

  Embodiments of the present invention have been made in view of the above circumstances, and an object of the present invention is to provide a secondary battery device control method and a secondary battery device that improve the accuracy of the SOC calculation of the secondary battery. .

  According to the embodiment, the battery pack includes at least one non-aqueous electrolyte secondary battery using lithium titanate as a negative electrode active material, and a main circuit connected between the battery pack and a load or a power source has a predetermined value. An AC oscillation source for applying an AC voltage / current having a frequency; a monitoring circuit for detecting a battery voltage of the non-aqueous electrolyte secondary battery; a current detection circuit for detecting a current of the main circuit; the battery voltage; A value of the circuit current is received, the impedance of the battery with respect to the AC voltage / current output from the AC oscillation source is calculated based on the received value, and the non-aqueous electrolyte secondary battery is calculated based on the calculated impedance There is provided a secondary battery device comprising an SOC calculation unit that calculates the SOC.

FIG. 1 is a diagram schematically illustrating an example of a non-aqueous electrolyte secondary battery. FIG. 2 is a diagram illustrating an example of a partial cross-section of the sealed secondary battery. FIG. 3A is a diagram illustrating an example of a battery voltage characteristic with respect to the SOC of the nonaqueous electrolyte secondary battery and an example of an AC impedance characteristic of the battery with respect to the SOC. FIG. 3B is a diagram illustrating an example of a positive electrode potential and a negative electrode potential with respect to the SOC of the nonaqueous electrolyte secondary battery, and an example of an AC impedance characteristic of the negative electrode with respect to the SOC. FIG. 4 is a diagram schematically illustrating a configuration example of the secondary battery device according to the embodiment. FIG. 5 is a flowchart for explaining an example of the control method of the secondary battery device of the present embodiment.

A nonaqueous electrolyte secondary battery control method and a secondary battery device according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically illustrating an example of a non-aqueous electrolyte secondary battery. FIG. 2 is a diagram illustrating an example of a partial cross section of the nonaqueous electrolyte secondary battery.

  As shown in FIGS. 1 and 2, the sealed secondary battery is configured as a thin nonaqueous electrolyte secondary battery 10 such as a lithium ion battery, for example. The secondary battery 10 includes a flat rectangular box-shaped outer container 12 and an electrode body 16 accommodated in the outer container 12 together with the nonaqueous electrolytic solution 14.

  For the non-aqueous electrolyte 14, carbonates such as propylene carbonate, ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate, lactones such as γ-butyrolactone, and other nitriles can be used. As the electrolyte, LiPF6 (lithium hexafluorophosphate) or LiBF4 (lithium tetrafluoroborate) can be used.

  In addition, electrolytes and electrolytes that can transport lithium ions, such as solid electrolytes, can be used.

  The outer container 12 includes a container body 12a having an open upper end, and a rectangular plate-like lid body 12b welded to the container body 12a to close the opening of the container body, and is formed airtight. The container main body 12a includes a bottom wall facing the opening, two main walls extending between the opening and the bottom wall and facing each other, and two side walls extending between the two main walls. The electrode body 16 is formed in a flat rectangular shape, for example, by winding a positive electrode plate and a negative electrode plate in a spiral shape with a separator interposed therebetween, and further compressing in a radial direction.

As the outer container 12, the current collector, and the conductive material, aluminum, aluminum alloy, or the like can be used.

In the present embodiment, a positive electrode active material using LiNi _0.33 Co _0.33 Mn _0.33 O ₂ as a positive electrode is further mixed with carbon black and PVdF (polyvinylidene fluoride) at a weight ratio of 100: 5: 5. What mixed and apply | coated both sides to the aluminum foil was used. Note that the positive electrode active material is not limited to the above materials. As the positive electrode active material, for example, LiMnO ₂ (lithium manganate), LiFePO ₄ (lithium iron phosphate), LiCoO ₂ (lithium cobaltate), LiNiO ₂ (lithium nickelate), or the like can be used.

  Further, as the negative electrode, a negative electrode active material using spinel type lithium titanate, further mixed with graphite and PVdF (polyvinylidene fluoride) at a weight ratio of 100: 5: 5, and coated on both sides of an aluminum foil is used. It was. Note that the negative electrode active material is not limited to the above materials.

The coating amount of each of the positive electrode and the negative electrode was 100 g / m ² , the positive electrode was coated with a width of approximately 5 cm and a length of approximately 100 cm, and the negative electrode was coated with a width of approximately 6 cm and a width of approximately 110 cm. The separator is made of, for example, polyethylene and has a thickness of 30 μm, a width of about 7 cm, and a length of about 200 cm.

  The positive electrode terminal 20p and the negative electrode terminal 20m are provided at both ends in the longitudinal direction of the lid body 12b and project from the lid body 12b. The positive electrode terminal 20p and the negative electrode terminal 20m are electrically connected to the positive electrode and the negative electrode of the electrode body 16, respectively.

  As shown in FIG. 2, the negative electrode terminal 20m extends through the lid 12b. Between the negative electrode terminal 20m and the lid 12b, a sealing material made of an insulating material such as synthetic resin or glass, for example, a gasket 18 is provided. The gasket 18 hermetically seals between the negative electrode terminal 20m and the outer container 12 and is electrically insulated.

  As shown in FIGS. 1 and 2, a liquid injection hole 34 for injecting the nonaqueous electrolyte solution 14 into the outer container 12 is formed in the lid 12 b and communicates with the outer container. The liquid injection hole 34 is formed in a circular shape, for example. The liquid injection hole 34 is sealed by a sealing plug (not shown) fixed to the lid body 12b. A pressure release valve 32 is disposed at the center of the lid 12b. In addition, you may comprise the pressure release valve 32 by the thin part which made the plate | board thickness of the cover body 12b partially thin, for example. When the internal pressure of the exterior container 12 increases above a certain level, the pressure release valve 32 is opened, and the internal pressure is lowered to prevent problems such as rupture of the exterior container.

  FIG. 3A is a diagram illustrating an example of a voltage with respect to the SOC of the secondary battery 10 and an example of an AC impedance with respect to the SOC. In FIG. 3A, the voltage characteristics of the secondary battery 10 are indicated by a solid line, and the AC impedance is indicated by a broken line.

  FIG. 3B is an example of potentials of the positive electrode and the negative electrode with respect to the lithium of the battery shown in FIG. 3A, and an AC impedance example of the positive electrode and the negative electrode.

  The battery voltage shown in FIG. 3A is explained by the difference between the positive electrode potential and the negative electrode potential shown in FIG. 3B. Further, the AC impedance of the battery shown in FIG. 3A is represented by the sum of the impedances of the positive electrode and the negative electrode shown in FIG. 3B.

The battery voltage of the secondary battery 10 is low when the SOC is small, and is high when the SOC is large. In particular, since the negative electrode potential shown in FIG. 3B of the secondary battery 10 is kept substantially constant (approximately 1.55 V) over a wide range of SOC, the change in the battery voltage substantially depends on the change in the positive electrode potential. Become. At this time, when, for example, LiMn ₂ O ₄ is selected as the positive electrode of the secondary battery 10, the positive electrode potential is kept substantially constant (approximately 4.05 V) over a wide range of SOC. Therefore, since the range where the positive electrode potential and the negative electrode potential of the secondary battery 10 are almost constant is wide, it is difficult to determine the SOC based on the battery voltage of the secondary battery 10 in the SOC range where the voltage change is small. is there.

Note that the characteristics of the electrode potential with respect to the SOC of the secondary battery vary depending on the electrode material. For example, when LiMn ₂ O ₄ (lithium manganate) or LiFePO ₄ (lithium iron phosphate) is used as the positive electrode material, the SOC range in which the electrode potential becomes substantially constant is wide, and LiNiO ₂ (nickel acid) When lithium is used as the electrode material, the SOC range in which the electrode potential is substantially constant becomes relatively narrow, and LiCoO ₂ (lithium cobaltate) is intermediate between the two. Therefore, when LiMn ₂ O ₄ (lithium manganate) or LiFePO ₄ (lithium iron phosphate) is used as the positive electrode material, it is more difficult to determine the SOC based on the voltage of the secondary battery 10. Further, since the voltage of the secondary battery 10 at this time is an open circuit voltage, the voltage of the secondary battery 10 cannot be obtained when the secondary battery 10 is being charged or discharged, and the SOC is accurately calculated. Is difficult.

  In addition, a method for calculating the SOC by current integration and a method for calculating the SOC based on the resistance of the secondary battery 10 with respect to a DC voltage have been proposed. However, when calculating the SOC based on current integration, it is difficult to improve accuracy because it is necessary to consider the change in capacity due to deterioration of the secondary battery. When calculating the SOC based on the resistance of the secondary battery 10 with respect to the DC voltage, it is necessary to charge or discharge the secondary battery 10, so that the specification alone is difficult.

  On the other hand, as shown in FIG. 3B, the negative electrode of the secondary battery 10 has an AC impedance that decreases as the SOC increases from 0%, and increases again when the SOC approaches 100%. This AC impedance can be obtained, for example, by measuring the resistance value at a high frequency of 100 Hz to 10 kHz. This change in AC impedance is a phenomenon that occurs because the lithium titanate changes its electronic conductivity as the electronic structure changes as lithium is deinserted.

In comparison, as shown in FIG. 3B, the positive electrode of the secondary battery 10 has a smaller change in AC impedance due to the SOC than the negative electrode.

For this reason, as shown in FIG. 3A, since the impedance of the secondary battery 10 changes without being substantially constant with respect to the SOC, it is possible to determine the SOC based on this tendency. Furthermore, when a high frequency is applied to the secondary battery 10, it can be superimposed even when the secondary battery 10 is discharged or charged.

FIG. 4 is a diagram schematically illustrating a configuration example of the secondary battery device according to the embodiment.
The secondary battery device of the present embodiment includes an assembled battery BT, an assembled battery monitoring circuit VTM, a battery management unit (BMU: battery management unit) CTR, and an AC oscillation source SS.

  The assembled battery BT is configured by connecting a plurality of secondary batteries 10 in series and in parallel. The assembled battery BT is connected to a load or a power source via the switch S2. The switch S2 is provided in a main circuit that connects the assembled battery BT and a load or a power source.

  The assembled battery monitoring circuit VTM measures the battery voltage of each of the plurality of secondary batteries 10 and measures the temperature in the vicinity of the plurality of secondary batteries 10 at at least one location. The assembled battery monitoring circuit VTM includes communication means (not shown), and outputs values of the battery voltage and temperature measured via the communication means to the battery management unit CTR.

  The AC oscillation source SS applies an AC voltage / current having a predetermined frequency to the main circuit of the assembled battery BT. The operation of the AC oscillation source SS is controlled by, for example, a control signal from the battery management unit CTR, and applies a high-frequency AC voltage / current of, for example, 100 Hz to 10 kHz to the main circuit. The AC voltage / current applied from the AC oscillation source SS is superimposed on the discharge voltage or the charging voltage of the assembled battery BT.

  The AC oscillation source SS and the main circuit are connected via a switch S1. The switch S1 is an electrically operated switch such as a contactor, for example, and performs a switching operation based on a control signal from the battery management unit CTR to switch an electrical connection between the AC oscillation source SS and the main circuit. Since the AC oscillation source SS is connected to the main circuit in parallel with the load or the power source, a direct current is applied to the AC oscillation source SS when the switch S1 is closed. For this reason, it is desirable to have a high breakdown voltage such as by inserting a capacitor so that the circuit of the AC oscillation source SS is not destroyed by the DC voltage.

  The battery management unit CTR includes a memory M, an MPU 100, a current detection unit 200, and an interface circuit (not shown) connected to communication means of the assembled battery monitoring circuit VTM.

  The memory M is, for example, an EEPROM (Electronically Erasable and Programmable Read Only Memory). For example, a program that defines the operation of the MPU 100 is recorded in the memory M.

  The battery management unit CTR is supplied with a power supply voltage and an external charger signal from an external power source (not shown) and an external charger (not shown) via a connector (not shown). Further, the battery management unit CTR transmits and receives signals to and from the host control means via communication means (not shown).

  The interface circuit of the battery management unit CTR receives data such as the voltage value of the secondary battery 10 and the temperature value of the assembled battery from the assembled battery monitoring circuit VTM via the connector. The assembled battery monitoring circuit VTM and the battery management unit CTR perform insulated communication because the ground potential is different.

  The interface circuit supplies data such as the voltage value of the secondary battery cell and the temperature value of the assembled battery to the MPU 100 by, for example, I2C communication. The assembled battery monitoring circuit VTM is supplied with a clock signal and other data signals from the interface circuit.

  A main circuit that connects the negative electrode terminal of the assembled battery BT and a load or a power source passes through the current detection unit 200. The current detection unit 200 detects a current flowing through the main circuit and outputs it to the MPU 100.

  The MPU 100 includes an SOC calculation unit 202 that calculates the SOC of the secondary battery 10. The MPU 100 displays the SOC calculated from the voltage and temperature values received via the interface circuit and the current value received from the current detection unit 200 as the upper level. Output to the control unit. The MPU 100 controls the operation of the assembled battery monitoring circuit VTM and the AC oscillation source SS according to the control signal received from the host controller.

  In FIG. 4, the SOC calculation unit 202 is built in the MPU 100. However, the SOC calculation unit 202 may be provided outside the MPU 100, and a frequency characteristic analyzer (FRA) connected to the outside of the battery management unit BMU. It may be.

  Hereinafter, an example of an operation for calculating the SOC of the secondary battery 10 in the SOC calculation unit 202 of the MPU 100 will be described.

  FIG. 5 is a flowchart for explaining an example of the control method of the secondary battery device of the present embodiment. In the secondary battery device of the present embodiment, the SOC of the secondary battery 10 is periodically calculated as follows.

  First, the SOC calculation unit 202 outputs a control signal to the switch S1 and the AC oscillation source SS, and superimposes an AC voltage / current of 100 Hz to 10 kH from the AC oscillation source SS to the main circuit (step ST1). At this time, the frequency of the AC voltage / current output from the AC oscillation source SS can be selected as long as the frequency can be separated from the DC component. However, the lower the frequency, the longer the time required for calculating the SOC. It is desirable to set appropriately considering the impedance characteristics of the electrode with respect to the time and frequency required for the calculation.

  Subsequently, the SOC calculation unit 202 receives the battery voltage of the secondary battery 10 and the current of the main circuit from the assembled battery monitoring circuit VTM and the current detection unit 200 (step ST2).

  The SOC calculation unit 202 calculates the variation of the received battery voltage and the superimposed AC voltage / current from the value of the current by Fourier transform or the like, and the battery voltage V and the AC voltage for the superimposed AC voltage / current. The battery impedance Z (= V / I) is calculated from the current I with respect to the current (step ST3).

  Subsequently, the SOC calculation unit 202 acquires the SOC corresponding to the calculated impedance Z based on a previously measured impedance table with respect to the SOC of the secondary battery 10 (step ST4). The impedance table of the secondary battery 10 with respect to the SOC may be stored in advance in the memory M, for example, or may be appropriately read from, for example, a memory connected to the secondary battery device.

  Here, the SOC calculation unit 202 determines whether or not the SOC corresponding to the calculated impedance Z is uniquely obtained (step ST5). That is, for example, when the characteristic of the impedance Z with respect to the SOC of the secondary battery 10 changes as shown in FIG. 3A, two SOC values may be obtained for one impedance Z value.

  Therefore, for example, when a plurality of SOC values are obtained for one impedance Z value, the battery voltage received from the assembled battery monitoring circuit VTM is used to determine which value is set (step ST6). For example, when there are two SOCs with respect to the impedance Z value, the SOC calculation unit 202 sets the SOC closer to the SOC obtained from the battery voltage value as the SOC of the secondary battery 10.

  The secondary battery 10 may be used in the SOC range except for the vicinity of complete discharge (SOC = 0%) and full charge (SOC = 100%). In this case, when the SOC for one impedance Z is always determined uniquely, step ST5 and step ST6 can be omitted.

  After obtaining the SOC for one impedance Z uniquely at step ST5 and obtaining one SOC at step ST6, the SOC computing unit 202 outputs the computed SOC to the host controller (step ST7). .

  As described above, the SOC of the secondary battery 10 can be obtained more accurately by calculating the SOC using the characteristics of the secondary battery 10. That is, according to the present embodiment, it is possible to provide a secondary battery device control method and a secondary battery device that improve the accuracy of the SOC calculation of the secondary battery.

  In the above embodiment, the secondary battery device has the AC oscillation source SS. However, when a high frequency voltage is applied as noise from the load or power source connected to the assembled battery BT, The AC oscillation source SS can also be omitted by calculating the impedance from the battery voltage and current for the component and calculating the SOC of the secondary battery 10 based on the calculated impedance. Even in that case, the same effect as the above-described embodiment can be obtained.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  BT ... Battery, VTM ... Battery monitoring circuit, CTR ... Battery management unit, SS ... AC oscillation source, S1 ... Switch, M ... Memory, 10 ... Secondary battery (nonaqueous electrolyte secondary battery), 14 ... Non Water electrolyte, 16 ... electrode body, 20p ... positive electrode terminal, 20m ... negative electrode terminal, 100 ... MPU, 200 ... current detection unit, 202 ... SOC calculation unit.

Claims (5)

An assembled battery including at least one non-aqueous electrolyte secondary battery using lithium titanate as a negative electrode active material;
An AC oscillation source for applying an AC voltage / current having a predetermined frequency to a main circuit connected between the assembled battery and a load or a power source;
A monitoring circuit for detecting a battery voltage of the non-aqueous electrolyte secondary battery;
A current detection circuit for detecting a current of the main circuit;
Receiving values of the battery voltage and the current of the main circuit, calculating the impedance of the battery with respect to the AC voltage / current output from the AC oscillation source based on the received value, and based on the calculated impedance A secondary battery device comprising: an SOC calculation unit that calculates the SOC of the nonaqueous electrolyte secondary battery.   2. The secondary battery according to claim 1, wherein the positive electrode of the non-aqueous electrolyte secondary battery uses at least one of lithium manganate, lithium iron phosphate, and lithium cobalt oxide as a positive electrode active material. apparatus.   The SOC calculation unit selects the SOC value of the non-aqueous electrolyte secondary battery using the battery voltage when the SOC value of the non-aqueous electrolyte secondary battery based on the calculated impedance is 2 or more. The secondary battery device according to claim 1. An alternating voltage / current having a predetermined frequency is applied to a main circuit connected between a battery pack and a battery pack including at least one non-aqueous electrolyte secondary battery using lithium titanate as a negative electrode active material;
While detecting the battery voltage of the non-aqueous electrolyte secondary battery, detecting the current of the main circuit,
Receiving the value of the battery voltage and the current of the main circuit, and calculating the impedance of the battery with respect to the AC voltage / current output from the AC oscillation source based on the received value;
A control method of a secondary battery device, wherein the SOC of the non-aqueous electrolyte secondary battery is calculated based on the calculated impedance.   The SOC value of the nonaqueous electrolyte secondary battery is selected using the battery voltage when the SOC value of the nonaqueous electrolyte secondary battery based on the calculated impedance is 2 or more. 4. The method for controlling a secondary battery device according to 4.

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