Detection device and detection method

Abstract

To acquire the more accurate SOC of a lithium ion secondary battery.SOLUTION: A detection device of the present disclosure detects the state of a lithium ion secondary battery, and the detection device comprises a control unit that applies AC current within a range of 100 kHz or more and 30 MHz or less to the lithium ion secondary battery, acquires a real part and / or an imaginary part of an AC impedance, and estimates the SOC from the acquired real part and / or the imaginary part of the AC impedance.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This specification discloses a detection device, a management device, and a detection method.

Background Art

[0002] Conventionally, as a method for estimating the State Of Charge (SOC) of a lithium secondary battery, for each of a plurality of charge rates of a lithium-ion secondary battery, the absolute value of the slope and the intercept of a straight line approximating the correlation between the imaginary component of the alternating current impedance at a specific frequency among a plurality of frequencies when performing alternating current impedance measurement and the charge rate, and the battery capacity of a second lithium-ion secondary battery to be the object of charge rate estimation are stored. When an alternating current having a specific frequency is applied to the second lithium-ion secondary battery, the alternating voltage generated between the second lithium-ion secondary batteries is measured, the alternating current impedance is calculated from the applied alternating current and the measured alternating voltage, the real component and the imaginary component of the calculated alternating current impedance are calculated, and the charge rate is estimated by a predetermined calculation (see, for example, Patent Document 1). In this detection method, it is stated that it is possible to estimate the charge rate of a lithium-ion secondary battery with high accuracy. Further, as an SOC estimation method, a plurality of first maps having different characteristics indicating the correspondence between the temperature and the internal resistance value of a lithium-ion secondary battery are used, and a plurality of first maps having different characteristics are switched based on the intercalation stage of graphite to estimate the internal resistance value (see, for example, Patent Document 2). In this estimation method, it is stated that a battery system capable of improving the estimation accuracy of SOC can be provided. Further, as a method for detecting the state of a lithium-ion secondary battery, the real part of the alternating current impedance at a frequency showing 10 times or more due to the skin effect with respect to the real part of the alternating current impedance of 1 kHz is obtained, and the precipitation of lithium and / or the presence of foreign metal inside the lithium-ion secondary battery is detected using the obtained real part of the alternating current impedance (see, for example, Patent Document 3). In this detection method, the state of a lithium-ion secondary battery such as the precipitation of lithium and / or the presence of foreign metal can be detected by a simpler method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above Patent Documents 1 and 2, there are effects on the state of the lithium-ion secondary battery, such as lithium precipitation and capacity degradation, and it has been required to further improve the estimation accuracy. Also, in Patent Documents 1 and 2, there were cases where accurate results could not be obtained unless measurements were taken during rest in order to remove the relaxation of the internal resistance for both voltage and impedance. For example, the battery voltage is the sum of the open-circuit voltage and the internal resistances with different time constants for various responses, and since the relaxation time of the resistance varies greatly depending on the degradation of the battery, there was a problem that it took time to measure in order to improve the accuracy. In addition, since the relaxation behavior of the internal resistance of the battery varies depending on the crystal structure of the graphite negative electrode, it was also difficult to attribute it only from the measured values under charge and discharge. In Patent Document 3, lithium precipitation and foreign metals can be detected, but the estimation of the state of charge has not been sufficiently studied.

[0005] The present disclosure has been made in view of such problems, and the main object thereof is to provide a novel detection device and detection method capable of obtaining a more accurate state of charge (SOC) of a lithium-ion secondary battery.

Means for Solving the Problems

[0006] As a result of intensive research to achieve the above object, the present inventors have found that the SOC can be estimated by paying attention to the high-frequency impedance that is less affected by the relaxation of the resistance of the lithium-ion secondary battery, and have completed the invention disclosed in this specification.

[0007] That is, the detection device disclosed in this specification is a detection device for detecting the state of a lithium-ion secondary battery, a control unit that applies an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, acquires the real part and / or imaginary part of the alternating impedance, and estimates the SOC from the acquired real part and / or imaginary part of the alternating impedance; and is provided with the above.

[0008] The detection method disclosed in this specification is a detection method for detecting the state of a lithium-ion secondary battery, including the steps of applying an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, acquiring the real part and / or imaginary part of the alternating impedance, and estimating the SOC from the acquired real part and / or imaginary part of the alternating impedance. and includes the above.

Effect of the Invention

[0009] The present disclosure can provide a novel detection device and a detection method for obtaining a more accurate state of charge (SOC) of a lithium-ion secondary battery. The reason why the present disclosure has such an effect is presumed as follows. For example, the SOC of a battery is determined by the amount of lithium ions in the positive electrode and the negative electrode. While the positive electrode mainly relies on the conductive material for electron conduction, the negative electrode has graphite as the active material responsible for electron conduction, and the electron conduction physical properties of the graphite negative electrode change according to the amount of lithium ions. Therefore, if the change in the dielectric relaxation associated with the change in the electron resistance of the graphite negative electrode and the change in the lithium amount of the positive and negative electrode materials can be measured, the SOC can be estimated with high sensitivity. On the other hand, the resistance below 1 kHz that has been conventionally used for measuring the impedance of a battery includes internal resistances such as reaction resistance, so it is greatly affected by capacity degradation and is not suitable for estimating the SOC. In the present disclosure, in the high-frequency region of 10 kHz, especially above 100 kHz, it becomes a region that does not include various internal resistances, and since the change in the electron resistance of the negative electrode is observed, it is presumed that a more accurate estimation of the SOC becomes possible.

Brief Description of the Drawings

[0010]

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Mode for Carrying Out the Invention

[0011] (Battery Management System 10) Embodiments of the detection device disclosed in this specification will be described below with reference to the drawings. FIG. 1 is a schematic explanatory diagram showing an example of the battery management system 10. The battery management system 10 is, for example, a system that executes the use management of a lithium-ion secondary battery (cell 30). This battery management system 10 includes a detection device 11 and a management device 20.

[0012] First, the cell 30 to be measured will be described. The cell 30 is configured as a lithium-ion secondary battery. The cell 30 may include, for example, a positive electrode, a negative electrode, and an ion conduction medium that is interposed between the positive electrode and the negative electrode and conducts carrier ions. The cell 30 may have a structure in which a positive electrode having a positive electrode composite material formed on both sides of a current collector and a negative electrode having a negative electrode composite material formed on both sides of the current collector are laminated, or may have a bipolar structure in which electrode bodies having a positive electrode composite material formed on one side of the current collector and a negative electrode composite material formed on the other side are laminated. The positive electrode may include, as a positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, etc. The positive electrode active material is, for example, a basic composition formula of Li (1-x) MnO 2 (0 < x < 1, etc., the same below) or Li(1-x) Mn 2 O 4 such as lithium manganese composite oxides having a basic composition formula of Li (1-x) CoO 2 such as lithium cobalt composite oxides having a basic composition formula of Li (1-x) NiO 2 such as lithium nickel composite oxides having a basic composition formula of Li (1-x) Ni a Co b Mn c O 2 (a + b + c = 1) such as lithium nickel cobalt manganese composite oxides can be used. Further, examples of the positive electrode active material include lithium iron phosphate. Note that the "basic composition formula" means that other elements may be included. The negative electrode may include a carbon material or a composite oxide containing lithium as the negative electrode active material. Examples of the negative electrode active material include lithium, lithium alloys, inorganic compounds such as tin compounds, carbon materials capable of occluding and releasing lithium ions, composite oxides containing a plurality of elements, and conductive polymers. Examples of the carbon material include cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among these, graphites such as artificial graphite and natural graphite are preferable. Examples of the composite oxide include lithium titanium composite oxides and lithium vanadium composite oxides. The ion conduction medium can be, for example, an electrolytic solution in which a supporting salt is dissolved. Examples of the supporting salt include LiPF 6 and LiBF 4Examples of such lithium salts include. Solvents for the electrolytic solution include, for example, carbonates, esters, ethers, nitriles, furans, sulfolanes, dioxolanes, etc., and these can be used alone or in combination. Specifically, examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, etc., and chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl - n - butyl carbonate, methyl - t - butyl carbonate, di - i - propyl carbonate, t - butyl - i - propyl carbonate, etc. Also, as the ion conduction medium, a solid ion - conductive polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder can be used. In this cell 30, a separator may be disposed between the positive electrode and the negative electrode. This separator may also serve as a solid electrolyte. The cell 30 may, for example, as shown in FIG. 1, include a positive electrode 31, a current - collecting terminal 32 connected to the positive electrode 31, a separator 34 interposed between the positive electrode 31 and the negative electrode 35, a negative electrode 35, a current - collecting terminal 36 connected to the negative electrode 35, and housing members 38, 39 for housing these components. Further, as a lithium - ion secondary battery, in addition to the current - collecting terminals 32, 36, a cell 30B in which a measurement terminal 33 connected to the positive electrode 31 of a single cell and a measurement terminal 37 connected to the negative electrode 35 are exposed to the outside may be used. In this cell 30B, while performing charge and discharge on an external device connected to the current - collecting terminals 32, 36, a measuring instrument can be connected to the measurement terminals 33, 37 to measure the AC impedance of the single - cell electrode.

[0013] The detection device 11 is a device that estimates the state of charge (SOC) of a lithium-ion secondary battery. The detection device 11 includes a control unit 12, a storage unit 13, a signal generator 14, a measurement unit 15, and a communication unit 16. The control unit 12 is configured as a processor centered around, for example, a CPU, and controls the entire device. The control unit 12 outputs signals to the storage unit 13, the signal generator 14, and the communication unit 16, and inputs signals from the storage unit 13, the measurement unit 15, and the communication unit 16. This control unit 12 estimates the SOC of the cell 30 using the information of the real part and / or the imaginary part of the AC impedance acquired from the measurement unit 15. The storage unit 13 is configured as a large-capacity storage device such as an HDD, for example, and stores information on measurement results and various programs for inspecting the cell 30. The signal generator 14 is a device that generates an alternating current in a predetermined frequency band of 10 kHz to 100 MHz, and applies the generated alternating current of the frequency to the cell 30 or extracts it from the cell 30. This predetermined frequency band is an alternating current in the range of 100 kHz or more and 30 MHz or less. This alternating current may be, for example, in the range of 1 MHz or more and 3 MHz or less, 8 MHz or more and 10 MHz or less, 100 kHz or more and 0.5 MHz or less, 3 MHz or more and 5 MHz or less, etc. The measurement unit 15 measures at least one of the voltage and current responses from the cell 30 corresponding to the signal output from the signal generator 14 to the cell 30. The control unit 12 can acquire the response from the measurement unit 15 and obtain the real part and the imaginary part of the AC impedance. The communication unit 16 is an interface for communicating with external devices. The communication unit 16 communicates with external devices, a locally connected management device 20, etc. via an external network 17 such as the Internet or a LAN.

[0014] The control unit 12 applies an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, or extracts it from the cell 30, acquires the real part and / or the imaginary part of the alternating impedance, and executes a process of estimating the SOC from the acquired real part and / or the imaginary part of the alternating impedance. This control unit 12 may estimate the SOC of the lithium-ion secondary battery using at least three frequencies of the real part of the alternating impedance, or may estimate the SOC of the lithium-ion secondary battery using at least three frequencies of the imaginary part of the alternating impedance. At this time, it is preferable that the control unit 12 performs an operation to eliminate the influence on the precipitation of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery, and estimates the SOC of the lithium-ion secondary battery. The control unit 12 may perform an operation to eliminate the influence of SOH and SOS using the map of the alternating impedance at three frequencies and the maps of State of Health (SOH) and State of Safety (SOS). SOH refers to the ratio of the fully charged capacity (Ah) at the time of degradation to the initial fully charged capacity (Ah) when the initial fully charged capacity (Ah) is set to 100%. SOS refers to the amount of precipitation of metallic lithium related to the safety of the cell. FIG. 2 is a flowchart showing an example of the SOC estimation processing routine using three frequencies. FIG. 3 is a relational diagram of the frequency and the real part of the impedance in degradation described in Patent Document 3, and illustrates a map of SOH. As shown in FIG. 2, this routine includes a step of measuring the alternating impedance at three frequencies in the above frequency range, a step of performing an operation to eliminate these influences using the maps of SOH and SOS, and a step of estimating the SOC with reference to the map. The case of measuring the alternating impedance of the cell 30 at three frequencies will be described. Let the differences from the initial states of the three frequencies of the cell 30 be ΔR(f) respectively, which are represented by Equations 1 to 3. Here, f1 and f2 may be frequencies that are particularly sensitive to SOS measurement and SOH measurement, respectively. Also, f3 is an arbitrary point. Further, Equation 1 is transformed into Equation 4, and when referring to the map, it becomes Equation 5. Also, Equation 2 is transformed into Equation 6, and when referring to the map, it becomes Equation 7. Substituting Equation 5 and Equation 7 into Equation 3, Equation 8 is obtained.Note that α to ζ are all algebraic expressions or functions that summarize the coefficients, and among them, ΔR(f) is the measured value at each frequency. By determining the SOC that satisfies the above equation with reference to the map, it becomes possible to estimate the SOC. The estimation of the SOC may be performed, for example, by obtaining the correspondence between the value of the AC impedance and the value of the SOC in advance, storing this as a map in the storage unit 13, and deriving the SOC from the map based on this correspondence when the value of the AC impedance is acquired.

[0015]

Number

[0016] The control unit 12 may estimate the SOC of the lithium-ion secondary battery using a frequency band with lower sensitivity to metal lithium precipitation and / or capacity degradation of the lithium-ion secondary battery. FIG. 4 is a flowchart showing an example of an SOC estimation processing routine using frequencies with low sensitivity to SOS and SOH. By using a frequency with lower sensitivity to SOH and SOS for the estimation of the SOC, it becomes possible to estimate the SOC with higher accuracy from the AC impedance. The frequencies shown as having no sensitivity to SOH and SOS in FIG. 4 are those of commercially available 18650 batteries, but it is expected that these frequencies with lower sensitivity to SOH and SOS will vary depending on the structure and materials of the battery, that is, the battery type. Therefore, this frequency may be appropriately selected according to the battery structure and battery materials.

[0017] The control unit 12 may correct the change in the AC impedance due to the precipitation of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery at the upper limit voltage and / or the lower limit voltage to estimate the SOC of the lithium-ion secondary battery. FIG. 5 is a flowchart showing an example of an SOC estimation processing routine for correcting based on the upper and lower limit voltages. In this routine, there are steps of adjusting to SOC = 100% by CCCV, measuring the impedance and performing SOC impedance relationship correction, measuring the temperature and impedance, estimating the SOC by referring to a MAP, determining whether SOC estimation is required again, and when SOC estimation is required again, repeating the temperature and impedance measurement steps. To correct the frequency shift due to SOS or SOH, for example, based on the impedance at a fixed upper limit voltage such as SOC = 100%, the SOC is estimated based on the difference therefrom. Alternatively, to correct the frequency shift due to SOS or SOH, for example, based on the impedance at a fixed lower limit voltage such as SOC = 0%, the SOC is estimated based on the difference therefrom. For example, in the profile of FIG. 8, based on the impedance at the timing when SOC = 100% is reached when the battery is charged and discharged, the SOC can be estimated from the change in impedance during subsequent discharge. At this time, the control unit 12 may perform temperature correction to estimate the SOC of the lithium-ion secondary battery. For temperature correction, for example, the correspondence relationship between the AC impedance and the SOC at different temperatures may be obtained, a map based on this may be created, and the map may be used.

[0018] Also, the impedance of these batteries can be measured under battery operation by using a calculation sensor from the attenuation waveform using the LC resonance shown in FIG. 7. That is, the control unit 12 may estimate the SOC of the lithium ion secondary battery from the AC impedance between the positive and negative electrodes of the lithium ion secondary battery, or may estimate the SOC of the lithium ion secondary battery from the AC impedance measured between two points of the positive electrode and / or between two points of the negative electrode of the lithium ion secondary battery. In this case, it is also possible to use the cell 30B provided with the measurement terminals shown in FIG. 1. In this SOC estimation method, since the influence of the precipitation of metallic lithium and capacity deterioration inside the cell can be further reduced and the SOC can be obtained, even during charge and discharge, a more accurate SOC can be estimated. At this time, by measuring the positive and negative electrodes themselves, the state of the cell can be grasped in more detail.

[0019] The management device 20 is a device that manages the cell 30 based on the information detected by the detection device 11. The management device 20 executes a process of managing the SOC state of the cell 30 by the management unit 21. The management unit 21 is configured as, for example, a microprocessor centered on a CPU and controls the entire device. This management device 20 manages, for example, the estimated value of the SOC of the cell 30 output from the detection device 11.

[0020] (Detection method) Next, the operation of the detection device 11 of the present embodiment configured in this way, particularly the detection method for detecting the state of the lithium-ion secondary battery executed by the detection device 11, will be described. This detection method includes applying an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, acquiring the real part and / or imaginary part of the alternating impedance, and estimating the SOC from the acquired real part and / or imaginary part of the alternating impedance. In this detection method, the same processing as the above-described detection device may be performed. In this step, the SOC of the lithium-ion secondary battery may be estimated using at least three frequencies of the real part of the alternating impedance or at least three frequencies of the imaginary part of the alternating impedance. Further, in this step, an operation for eliminating the influence related to the deposition of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery may be performed to estimate the SOC of the lithium-ion secondary battery. Further, in this step, the SOC of the lithium-ion secondary battery may be estimated using a frequency band with a lower sensitivity related to the deposition of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery. Further, in this step, the change in the alternating impedance due to the deposition of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery may be corrected with the upper limit voltage and / or the lower limit voltage to estimate the SOC of the lithium-ion secondary battery. Further, in this step, the SOC of the lithium-ion secondary battery may be estimated from the alternating impedance between the positive and negative electrodes of the lithium-ion secondary battery, or the SOC of the lithium-ion secondary battery may be estimated from the alternating impedance measured between two points of the positive electrode and / or between two points of the negative electrode of the lithium-ion secondary battery. Further, in this step, temperature correction may be performed to estimate the SOC of the lithium-ion secondary battery.

[0021] Here, the correspondence between the components of the present embodiment and the components of the present disclosure will be clarified. The cell 30 of the present embodiment corresponds to the lithium-ion secondary battery of the present disclosure, the detection device 11 corresponds to the detection device, and the control unit 12 corresponds to the control unit. Note that in the present embodiment, an example of the detection method of the present disclosure is also clarified by describing the operation of the detection device 11.

[0022] In the embodiment described above, a novel detection device and a detection method for obtaining a more accurate state of charge (SOC) of a lithium-ion secondary battery can be provided. The reason for such an effect is presumed as follows. For example, the SOC of a battery is determined by the amount of lithium ions in the positive electrode and the negative electrode. The positive electrode mainly relies on the conductive material for electron conduction, while the negative electrode relies on graphite as the active material for electron conduction, and the electron conduction physical properties of the graphite negative electrode change depending on the amount of lithium ions. Therefore, if the change in the dielectric relaxation associated with the change in the electron resistance of the graphite negative electrode and the change in the lithium amount of the positive and negative electrode materials can be measured, the SOC can be estimated with high sensitivity. On the other hand, the resistance below 1 kHz that has been conventionally used for impedance measurement of batteries includes internal resistances such as reaction resistance, so it is greatly affected by capacity degradation and is not suitable for SOC estimation. In the present disclosure, in the high-frequency region of 10 kHz, particularly above 100 kHz, it becomes a region that does not include various internal resistances, and it is presumed that more accurate SOC estimation is possible because the change in the electron resistance of the negative electrode is observed.

[0023] It should be noted that the present disclosure is not limited to the above-described embodiment, and it goes without saying that various aspects can be implemented as long as they belong to the technical scope of the present disclosure.

[0024] The present disclosure may be as shown in any of the following [1] to [9]. [1] A detection device for detecting the state of a lithium-ion secondary battery, a control unit that applies an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, obtains the real part and / or the imaginary part of the alternating impedance, and estimates the SOC from the obtained real part and / or the imaginary part of the alternating impedance; A detection device comprising the same. [2] The detection device according to [1], wherein the control unit estimates the SOC of the lithium-ion secondary battery using at least three frequencies of the real part of the alternating impedance. [3] The control unit performs an operation to eliminate the influence on the precipitation of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery, and estimates the SOC of the lithium-ion secondary battery, the detection device according to [1] or [2]. [4] The control unit estimates the SOC of the lithium-ion secondary battery using a frequency band with lower sensitivity to the precipitation of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery, the detection device according to any one of [1] to [3]. [5] The control unit estimates the SOC of the lithium-ion secondary battery by correcting the change in the AC impedance due to the precipitation of metallic lithium and / or the capacity degradation of the lithium-ion secondary battery with the upper limit voltage, the detection device according to any one of [1] to [4]. [6] The control unit estimates the SOC of the lithium-ion secondary battery from the AC impedance between the positive and negative electrodes of the lithium-ion secondary battery, the detection device according to any one of [1] to [5]. [7] The control unit estimates the SOC of the lithium-ion secondary battery from the AC impedance measured between two points on the positive electrode and / or between two points on the negative electrode of the lithium-ion secondary battery, the detection device according to any one of [1] to [6]. [8] The control unit performs temperature correction and estimates the SOC of the lithium-ion secondary battery, the detection device according to any one of [1] to [7]. [9] A detection method for detecting the state of a lithium-ion secondary battery, applying an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, obtaining the real part and / or the imaginary part of the AC impedance, and estimating the SOC from the obtained real part and / or the imaginary part of the AC impedance, A detection method including this.

Example

[0025] Hereinafter, an example in which the detection device and the detection method of the present disclosure are specifically studied will be described as an experimental example.

[0026] (Preparation of Test Battery: Battery Fabrication Example 1) As the positive electrode active material, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 was used. 92% by mass of the above positive electrode active material, 5% by mass of carbon black as a conductive material, and 3% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in a certain ratio, and an appropriate amount of N-methyl-2-pyrrolidone was added as a dispersant and dispersed to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of a 15-μm-thick aluminum foil current collector, dried, and then densified by roll pressing to obtain a positive electrode sheet. Note that the adhesion amount of the positive electrode active material was about 14 mg / cm 2 and about 20 mAh. As the negative electrode, a commercially available spherical graphite sheet with 1.5 mAh / cm 2 was used. The positive electrode and the negative electrode were cut to a predetermined length so that the positive electrode was about 10 mAh and the negative electrode was about 15 mAh. A microporous membrane separator made of polyethylene with a thickness of 20 μm was sandwiched between the fabricated positive electrode and negative electrode to fabricate a sheet-shaped electrode body. The electrode body was inserted into an aluminum laminate film, the electrolyte was impregnated into the aluminum laminate film, the laminate film was sealed by heat welding, fixed to a printed circuit board, and then constrained while applying a load with a restraining jig to obtain a laminated 10-mAh-class lithium-ion secondary battery.

[0027] (Activation + Capacity Confirmation) For the fabricated battery, after more than 1 hour had elapsed since the injection of the electrolyte, CCCV charge and discharge were performed at a charge and discharge rate of 0.1C with an upper limit voltage of 3.9V and a lower limit voltage of 3.0V at 20°C for 2 cycles to confirm activation and capacity. Next, after performing CCCV charging at 0.1C with an upper limit voltage of 3.9V, heat treatment was performed at 60°C for 6 hours to obtain an initial battery.

[0028] (SOC Adjustment) The fabricated battery was discharged at 0.1C at 20°C to obtain a battery with SOC = 0%.

[0029] (Battery Fabrication Example 2) The positive electrode current collector foil of the battery fabricated in Example 1 was made of a PET film, and current collector tabs were attached to both ends of the positive electrode. The positive electrode areal density was 7 mg / cm 2A battery was fabricated as Battery Fabrication Example 2 in the same manner as Battery Fabrication Example 1, except that the capacity was set to 10 mAh and the charge / discharge rate was set to 0.01C. This battery was adjusted to SOC = 0%.

[0030] (Battery Fabrication Example 3) The negative current collector foil of the battery fabricated in Battery Fabrication Example 1 was made of a PET film, and current collector tabs were attached to both ends of the negative electrode. The negative electrode coating weight was 3 mg / cm 2 A battery was fabricated as Battery Fabrication Example 3 in the same manner as Battery Fabrication Example 1, except that the capacity was set to 10 mAh and the charge / discharge rate was set to 0.01C. This battery was adjusted to SOC = 0%.

[0031] (Measurement Example 1: High-frequency Impedance Measurement) Using the batteries fabricated in the battery fabrication examples, impedance measurements of the batteries were performed. After adjusting the SOC to 0% and allowing the batteries to stand in an environment of 20°C for 1 hour or more, impedance measurements were taken 8 times using the two-port shunt-through method of a vector network analyzer from 100 kHz to 100 MHz to obtain the impedance.

[0032] (Measurement Examples 2 to 7) Batteries were fabricated and measured in the same manner as Measurement Example 1, except that the SOC of the batteries was adjusted to 16.6%, 33.3%, 50%, 66.6%, 83.3% and 100% respectively in the SOC adjustment process, and these were designated as Measurement Examples 2 to 7 respectively.

[0033] (Measurement Examples 8 to 10) Measurement Example 8 was the case where current collection was taken between the tabs at both ends of the positive electrode of the battery of Battery Fabrication Example 2, and impedance measurement was performed in the same manner as Measurement Example 1. Measurement Examples 9 to 10 were cases where batteries were fabricated and measured in the same manner as Measurement Example 1, except that the SOC of the battery of Measurement Example 8 was adjusted to 70% and 100% respectively in the SOC adjustment process.

[0034] (Measurement Examples 11 to 14) Power collection was taken between the tabs at both ends of the positive electrode of the battery in Battery Fabrication Example 3, and power collection was taken between the tabs at both ends of the negative electrode. The measurement in which impedance was measured in the same manner as in Measurement Example 1 was designated as Measurement Example 11. Measurement Examples 12 to 14 were respectively those in which batteries were fabricated and the same measurements were performed in the same manner as in Measurement Example 11, except that the SOC of the batteries was adjusted to 25%, 50%, and 80% respectively in the SOC adjustment process.

[0035] (Results and Discussion) A map of SOH and SOS is illustrated in FIG. 4. It was confirmed whether an SOC map could be obtained by eliminating the influence of this SOH and SOS. The battery described in Battery Fabrication Example 1 described above was fabricated, and the impedance of the battery was measured by the method of the battery measurement examples described above. FIG. 8 is a Bode diagram of the real part of the AC impedance at each SOC for Battery Fabrication Example 1. FIG. 9 is the measurement result of the real part of the impedance at three frequencies at each SOC, where FIG. 9A is the measurement result of the real part of the impedance at 100 kHz, FIG. 9B is the measurement result of the real part of the impedance at 1 MHz, and FIG. 9C is the measurement result of the real part of the impedance at 10 MHz. As shown in FIG. 8, a change was observed in the real part of the impedance from 100 kHz to 30 MHz with charging. In particular, the change in impedance was large near SOC = 0% during both charge and discharge, and the impedance changed almost linearly in other regions. The increase in impedance on the high-frequency side is presumed to reflect the increase in resistance due to the skin effect, and no change in resistance associated with SOC change was observed above 30 MHz. Therefore, it was presumed that it is preferable to observe the change in resistance at frequencies lower than 30 MHz. It was shown that the SOC can be estimated from the real part of the impedance by using this frequency range. From the results of FIGS. 8 to 10 described above, it was found that a higher-accuracy SOC can be obtained by the flowchart shown in FIG. 2. At this time, as shown in FIG. 3, it was found that an operation for eliminating these influences may be performed using the maps of SOH and SOS.

[0036] FIG. 10 is an explanatory diagram showing the frequency characteristics of the imaginary part of the AC impedance at each SOC. As shown in FIG. 10, in the verification of SOC estimation using the imaginary part of the impedance as in the real part, a change in the imaginary part of the impedance from 100 kHz to 1 MHz accompanying charging was observed. In particular, the change in impedance was large in the vicinity of SOC = 0% during both charging and discharging. No change in the imaginary part of the impedance was observed on the high-frequency side. Therefore, the change in the imaginary part is at a frequency lower than 1 MHz

[0037] FIG. 11 shows the frequency characteristics of the imaginary part of the AC impedance of the positive electrode at each SOC according to Measurement Examples 8 to 10 of Battery Fabrication Example 2. FIG. 12 shows the frequency characteristics of the imaginary part of the AC impedance of the negative electrode at each SOC according to Measurement Examples 11 to 14 of Battery Fabrication Example 3. FIG. 13 shows the frequency characteristics of the real part of the AC impedance of the positive electrode at each SOC according to Measurement Examples 8 to 10 of Battery Fabrication Example 2. FIG. 14 shows the frequency characteristics of the real part of the AC impedance of the negative electrode at each SOC according to Measurement Examples 11 to 14 of Battery Fabrication Example 3. As shown in FIGS. 11 and 12, a change in the imaginary part of the impedance from 100 kHz to 100 MHz accompanying charging was observed between the two terminals within a single electrode. Also, in the positive electrode, the value of the imaginary part changed systematically corresponding to the SOC, and particularly from 100 kHz to 1 MHz, it was presumed that the imaginary part of the impedance decreased as the SOC increased, making it suitable for SOC measurement. These SOC dependencies were presumed to reflect the shift of the characteristic frequency of the dielectric relaxation accompanying the compositional change of the active material. Also, as shown in FIGS. 13 and 14, a change in the real part of the impedance from 100 kHz to 100 MHz accompanying charging was observed. In particular, during both charging and discharging, the change in impedance was large in the vicinity of SOC = 0% in the negative electrode, and the impedance changed almost linearly in other regions. Since the tendency of the change well matches the measurement example in Battery Fabrication Example 1, it was presumed that the measurement in the battery mainly reflects the impedance change of the negative electrode. Also, in the positive electrode, the change in impedance was large in the vicinity of SOC = 0%, and there was little change in other regions. These measurement results suggest that it is possible to estimate the SOC by taking out two upper terminals from the electrode and measuring the real part or the imaginary part of the impedance.

Industrial Applicability

[0038] The detection device and detection method disclosed in this specification can be used in the technical field of detecting the state of a lithium-ion secondary battery.

Explanation of Signs

[0039] 10 Battery management system, 11 Detection device, 12 Control unit, 13 Storage unit, 14 Signal generator, 15 Measurement unit, 16 Communication unit, 17 External network, 20 Management device, 21 Management unit, 30, 30B Cells, 31 Positive electrode, 32 Current collector terminal, 33 Measurement terminal, 34 Separator, 35 Negative electrode, 36 Current collector terminal, 37 Measurement terminal, 38, 39 Housing member.

Claims

1. A detection device for detecting the state of a lithium-ion secondary battery, comprising: a control unit that applies an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, acquires the real part and / or imaginary part of the alternating impedance, and estimates the SOC from the acquired real part and / or imaginary part of the alternating impedance; A detection device comprising the above.

2. The detection device according to claim 1, wherein the control unit estimates the SOC of the lithium-ion secondary battery using at least three frequencies of the real part of the alternating impedance or using at least three frequencies of the imaginary part of the alternating impedance.

3. The detection device according to claim 1 or 2, wherein the control unit performs an operation to eliminate the influence related to lithium metal precipitation and / or capacity deterioration of the lithium-ion secondary battery, and estimates the SOC of the lithium-ion secondary battery.

4. The detection device according to claim 1 or 2, wherein the control unit estimates the SOC of the lithium-ion secondary battery using a frequency band with lower sensitivity related to lithium metal precipitation and / or capacity deterioration of the lithium-ion secondary battery.

5. The detection device according to claim 1 or 2, wherein the control unit corrects the change in the alternating impedance due to lithium metal precipitation and / or capacity deterioration of the lithium-ion secondary battery with the upper limit voltage and / or the lower limit voltage, and estimates the SOC of the lithium-ion secondary battery.

6. The detection device according to claim 1 or 2, wherein the control unit estimates the SOC of the lithium-ion secondary battery from the alternating impedance between the positive and negative electrodes of the lithium-ion secondary battery.

7. The detection device according to claim 1 or 2, wherein the control unit estimates the SOC of the lithium-ion secondary battery from the alternating impedance measured between two points of the positive electrode of the lithium-ion secondary battery and / or between two points of the negative electrode of the lithium-ion secondary battery.

8. The detection device according to claim 1 or 2, wherein the control unit performs temperature correction and estimates the SOC of the lithium-ion secondary battery.

9. A detection method for detecting the state of a lithium-ion secondary battery, comprising: applying an alternating current in the range of 100 kHz or more and 30 MHz or less to the lithium-ion secondary battery, acquiring the real part and / or imaginary part of the alternating impedance, and estimating the SOC from the acquired real part and / or imaginary part of the alternating impedance; A detection method comprising the above steps.

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