ANOMALYSIS DETECTION METHOD, ANOMALYSIS DETECTION DEVICE, ELECTRICITY STORAGE DEVICE, AND COMPUTER PROGRAM

Abstract

This abnormality detection method detects an abnormality in a battery pack having a plurality of power storage elements with an abnormality detection device. Each of the plurality of power storage elements includes lithium iron phosphate and a lithium transition metal oxide, which is capable of occluding and releasing lithium ions in a higher potential range than the lithium iron phosphate, as a positive electrode active material, and the ratio of the charge electricity quantity based on the total amount of the lithium transition metal oxide to the charge electricity quantity based on the total amount of the positive electrode active material in the charge / discharge range in which the power storage element is used is 5% or more. The abnormality detection device acquires the voltage of each of the plurality of power storage elements in the vicinity of the charging end point in the charge / discharge range in which the power storage element is used, and uses the acquired voltage of the plurality of power storage elements to detect an abnormality of the battery pack.

Description

[Technical field]

[0001] The present technology relates to an abnormality detection method, an abnormality detection device, a power storage device, and a computer program for detecting an abnormality in a battery pack. [Background technology]

[0002] In recent years, energy storage elements such as lithium-ion secondary batteries have been used in a wide range of fields, including as power sources for portable terminals such as notebook personal computers and smartphones, renewable energy storage systems, and power sources for IoT devices. They are also being actively developed as power sources for next-generation clean energy automobiles, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] Lithium-ion secondary batteries use lithium transition metal composite oxides, such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, as their positive electrode active material.

[0004] Lithium iron phosphate, which contains iron, an abundant and inexpensive resource, as a constituent element, has also been used as a positive electrode active material instead of cobalt or the like (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-12613 A Summary of the Invention [Problem to be solved by the invention]

[0006] When a battery pack is constructed using energy storage elements that use lithium iron phosphate as the positive electrode active material (so-called LFP batteries), the change in voltage during charging and discharging is small, making it difficult to estimate the state of the battery pack based on the change in voltage.

[0007] An object of the present disclosure is to provide an abnormality detection method and the like that can suitably detect an abnormality in a battery pack. [Means for solving the problem]

[0008] An anomaly detection method according to one aspect of the present disclosure detects an anomaly in a battery pack having a plurality of storage elements by an anomaly detection device. Each of the plurality of storage elements contains, as a positive electrode active material, lithium iron phosphate and a lithium transition metal oxide capable of an insertion / extraction reaction of lithium ions in a potential range higher than that of the lithium iron phosphate, and a ratio of a charge amount of electricity based on the total amount of the lithium transition metal oxide to a charge amount of electricity based on the total amount of the positive electrode active material in a charge / discharge range in which the storage elements are used is 5% or more. The anomaly detection device obtains voltages of the plurality of storage elements near a charge end point in a charge / discharge range in which the storage elements are used, and detects an anomaly in the battery pack by using the obtained voltages of the plurality of storage elements. Effect of the Invention

[0009] According to the present disclosure, an abnormality in a battery pack can be suitably detected. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of a power storage device according to a first embodiment. [Diagram 2] FIG. 13 is a perspective view showing another example of the power storage device. [Diagram 3] FIG. 3 is an exploded perspective view of the electricity storage device of FIG. 2. [Figure 4] FIG. 2 is a block diagram of an anomaly detection device, etc. [Diagram 5] 1 is a charge / discharge curve showing the relationship between SOC and voltage for a mixed positive electrode active material of lithium iron phosphate and a non-ferrous lithium compound. [Figure 6] 13 is a flowchart illustrating an example of an abnormality detection process procedure. [Figure 7] 10 is a flowchart illustrating an example of an abnormality detection process procedure in the second embodiment. [Figure 8] 13 is a flowchart illustrating an example of an abnormality detection process procedure in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The abnormality detection method detects an abnormality in a battery pack having a plurality of storage elements by an abnormality detection device. Each of the plurality of storage elements contains, as a positive electrode active material, lithium iron phosphate and a lithium transition metal oxide capable of a lithium ion insertion / extraction reaction in a potential range higher than that of the lithium iron phosphate, and a ratio of a charged electric quantity based on the total amount of the lithium transition metal oxide to a charged electric quantity based on the total amount of the positive electrode active material in a charge / discharge range in which the storage elements are used is 5% or more. The abnormality detection device obtains voltages of the plurality of storage elements near a charge end point in a charge / discharge range in which the storage elements are used, and detects an abnormality in the battery pack using the obtained voltages of the plurality of storage elements.

[0012] In this specification, "abnormality in the battery pack" includes cases where an internal short circuit occurs in some of the multiple storage elements that make up the battery pack, cases where the capacity degradation of some of the storage elements is more advanced than that of the other storage elements beyond an allowable range, cases where the state of charge (SOC) of some of the storage elements deviates from that of the other storage elements beyond an allowable range, etc. "Abnormality in the battery pack" includes cases where an abnormality occurs in only some of the multiple storage elements that make up the battery pack. The term "voltage" refers to the potential difference between the positive electrode potential and the negative electrode potential when a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are combined to form an electricity storage element. "Potential" refers to the potential difference (V vs Li) between the positive electrode and the negative electrode alone relative to the Li reference electrode (standard electrode). + / Li). The term "charged electric quantity" refers to a value calculated by multiplying the mass (g) of the positive electrode active material in the electricity storage element by its theoretical capacity (Ah / g).

[0013] According to the above configuration, the battery pack includes an electric storage element in which lithium iron phosphate and a lithium transition metal oxide capable of performing an insertion / extraction reaction of lithium ions in a potential range higher than that of lithium iron phosphate are mixed as a positive electrode active material. Since this electric storage element contains lithium iron phosphate as a positive electrode active material, it has a plateau region in which the voltage hardly changes over a wide range in the charge / discharge characteristics. Due to the configuration in which lithium iron phosphate and lithium transition metal oxide are mixed, a region is formed near the end point of charge in which there is a voltage change (a gradient that enables state estimation) based on the insertion / extraction reaction of lithium ions in the lithium transition metal oxide. In this region, the voltage change during charging / discharging can be detected to estimate the state of the electric storage element. By acquiring the voltage of each of the multiple electric storage elements in this region, the state of each electric storage element can be accurately estimated, and an abnormality in the battery pack can be suitably detected based on the state difference between the electric storage elements.

[0014] The abnormality detection method may detect that an internal short circuit has occurred in at least one of the plurality of storage elements when a voltage difference between the plurality of storage elements during a lithium ion insertion reaction (during discharging) in the lithium transition metal oxide near the end point of charging is equal to or greater than a first threshold value. Since the charge / discharge characteristics have a slope near the end point of charge, the voltage difference between multiple storage elements discharging near the end point of charge can be used to detect the possibility of an internal short circuit occurring in a storage element that has a large voltage difference from other storage elements.

[0015] In the abnormality detection method, the first threshold value may be a value greater than an activation threshold value of a balancer that reduces a voltage difference between the plurality of storage elements during charging. By making the first threshold for detecting an internal short circuit larger than the balancer's activation threshold, the possibility of mistakenly determining that an internal short circuit has occurred in an energy storage element when in fact no internal short circuit has occurred can be reduced.

[0016] The abnormality detection method may include acquiring an integrated value of a current associated with an insertion or desorption reaction of lithium ions in the lithium transition metal oxide near the end of charge in the plurality of storage elements, and estimating a first degree of deterioration of each of the plurality of storage elements based on the acquired integrated value of the current. Since the charge / discharge characteristics have a gradient that enables state estimation near the end point of charge, the first deterioration degree of each of the multiple storage elements can be estimated based on the current integrated value in that region. For example, while acquiring (monitoring) the voltage of each storage element, the first deterioration degree of each storage element can be estimated based on the behavior when the storage element is discharged from a voltage equivalent to a nearly fully charged state until it reaches (drops) a voltage in the plateau region. A storage element 3 in which deterioration has progressed reaches a state in which the end point of charge is shifted to the left along the horizontal axis in FIG. 5, and reaches a voltage in the plateau region earlier than the other storage elements 3. Charging and discharging near the end point of charge makes it possible to efficiently detect an abnormality in the battery pack.

[0017] The abnormality detection method may detect an abnormality in the battery pack based on a comparison between a first deterioration level of one power storage element in the battery pack and a first deterioration level of another power storage element. For example, an abnormality in the battery pack can be suitably detected based on the difference in the first deterioration degree between the power storage elements.

[0018] The abnormality detection method may include estimating a second deterioration level of the plurality of power storage elements based on a usage history of the plurality of power storage elements, and comparing the first deterioration level and the second deterioration level of each of the plurality of power storage elements. By comparing and collating the first deterioration degree and the second deterioration degree obtained by different methods, the probability of the first deterioration degree and the second deterioration degree can be estimated. For example, when it is determined that the accuracy of the second deterioration degree estimated based on the usage history is low in comparison with the first deterioration degree estimated based on the charging and discharging near the end point of charging, it becomes possible to take measures such as correcting or updating the second deterioration degree based on the first deterioration degree.

[0019] In the abnormality detection method, the voltage of each of the plurality of storage elements may be acquired in a charge / discharge range of 3.2V or more. In conventional LFP batteries, the voltage in the plateau region is approximately 3.2 V, and the lithium ion insertion / extraction reaction occurs in this region. In conventional LFP batteries, the full charge voltage is set to approximately 3.4 V. The voltage change between 3.2 V and 3.4 V is very steep and is not due to the lithium ion insertion / extraction reaction. On the other hand, when the positive electrode active material contains a lithium transition metal oxide capable of the lithium ion insertion / extraction reaction in a voltage range higher than that of lithium iron phosphate, charging / discharging at 3.2 V or higher is also due to the lithium ion insertion / extraction reaction. By acquiring the voltage of each of the multiple storage elements in this charging / discharging range, the state of each storage element can be accurately estimated.

[0020] The abnormality detection device detects an abnormality in a battery pack having a plurality of storage elements. Each of the plurality of storage elements contains, as a positive electrode active material, lithium iron phosphate and a lithium transition metal oxide capable of undergoing a lithium ion insertion / extraction reaction in a potential range higher than that of the lithium iron phosphate, and a ratio of a charged electric quantity based on the total amount of the lithium transition metal oxide to a charged electric quantity based on the total amount of the positive electrode active material in a charge / discharge range in which the storage elements are used is 5% or more. The abnormality detection device includes an acquisition unit that acquires the voltages of the plurality of storage elements near a charge end point in a charge / discharge range in which the storage elements are used, and a detection unit that detects an abnormality in the battery pack using the voltages of the plurality of storage elements acquired by the acquisition unit.

[0021] The power storage device includes a battery pack having a plurality of power storage elements and the abnormality detection device described above.

[0022] The computer program causes a computer to detect an abnormality in a battery pack having a plurality of storage elements. Each of the plurality of storage elements contains, as a positive electrode active material, lithium iron phosphate and a lithium transition metal oxide capable of a lithium ion insertion / extraction reaction in a potential range higher than that of the lithium iron phosphate, and a ratio of a charging amount of electricity based on the total amount of the lithium transition metal oxide to a charging amount of electricity based on the total amount of the positive electrode active material in a charging / discharging range in which the storage elements are used is 5% or more. The computer program causes the computer to execute a process of acquiring voltages of the plurality of storage elements near a charging end point in a charging / discharging range in which the storage elements are used, and detecting an abnormality in the battery pack using the acquired voltages of the plurality of storage elements.

[0023] Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.

[0024] (First embodiment) FIG. 1 is a diagram showing an example of an energy storage device 1 according to a first embodiment. The energy storage device 1 includes an abnormality detection device 2, a battery pack 30 including a plurality of energy storage elements 3, and a holder 4 that houses or holds them. The plurality of energy storage elements 3 are connected to configure one battery pack 30. In the example of FIG. 1, one battery pack 30 is shown that is configured by connecting six energy storage elements 3 in series. Some of the energy storage elements 3 may be connected in parallel.

[0025] The abnormality detection device 2 is a flat circuit board disposed on the upper surface of the multiple storage elements 3, and estimates the state of each storage element 3 at a predetermined timing to detect an abnormality in the assembled battery 30. Specifically, the abnormality detection device 2 acquires measurement data including the voltage of the storage elements 3 and the current flowing through the storage elements 3, and estimates the state of each storage element 3 based on the acquired measurement data. The abnormality detection device 2 detects abnormalities in the storage elements 3 and the assembled battery 30 based on the state of each storage element 3.

[0026] In FIG. 1, the abnormality detection device 2 is disposed near the upper surface of the energy storage element 3. Alternatively, the location of the arrangement may be near the side surface of the energy storage element 3 or near the lower surface of the energy storage element 3. The shape of the abnormality detection device 2 is not limited to a flat plate. The abnormality detection device may include a cell monitoring unit (CMU) and a battery management unit (BMU) capable of communicating with the CMU. Only the CMU may be disposed near the multiple energy storage elements 3 as shown in FIG. 1, and the BMU may be disposed at a location remote from the energy storage elements 3. In addition to the CMU and / or BMU, the abnormality detection device 2 may include a server device or an electronic control unit (ECU) that is disposed at a location remote from the energy storage elements 3 and is communicatively connected to the CMU or BMU. The location where abnormality detection of the assembled battery is performed is not limited, and may be performed, for example, by the BMU, the server device, or the ECU.

[0027] The energy storage element 3 is a battery cell such as a lithium ion secondary battery. The energy storage element 3, in the form of a battery pack in which a plurality of the energy storage elements 3 are electrically connected, is applied to power sources for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power sources for electronic devices, power storage power sources, and the like.

[0028] 1 shows a single power storage module as the power storage device 1. Alternatively, the power storage device 1 may be a so-called high-voltage power supply, such as a power storage pack or power storage facility including a plurality of power storage modules.

[0029] 2 and 3 show another example of the power storage device 1, where Fig. 2 is a perspective view of the power storage device 1 and Fig. 3 is an exploded perspective view of the power storage device 1. The power storage device 1 is a so-called low-voltage power supply, such as a 12V power supply or a 48V power supply, that is suitably mounted on engine vehicles, EVs, HEVs, and PHEVs.

[0030] The energy storage device 1 has a rectangular parallelepiped storage case 4a that stores an abnormality detection device 2 and an assembled battery 30 consisting of a plurality of energy storage elements 3. The abnormality detection device 2 is a BMU. The energy storage elements 3 are lithium ion secondary batteries. The storage case 4a also stores a plurality of bus bars 5, a current sensor 7 (see FIG. 4), and the like. In FIGS. 2 and 3, the energy storage device 1 is a 12V power supply, and one assembled battery 30 consisting of four energy storage elements 3 connected in series is stored in the storage case 4a.

[0031] The storage case 4a is made of synthetic resin. The storage case 4a includes a case body 41, a lid portion 42 that closes the opening of the case body 41, a storage portion 43 provided on the outer surface of the lid portion 42, a cover 44 that covers the storage portion 43, an inner lid 45, and a partition plate 46. The inner lid 45 and the partition plate 46 do not necessarily have to be provided. The energy storage element 3 is inserted between the partition plates 46 of the case body 41.

[0032] A plurality of metal bus bars 5 are placed on inner lid 45. Inner lid 45 is disposed near the terminal surface on which terminals 32 of energy storage elements 3 are provided, and adjacent terminals 32 of adjacent energy storage elements 3 are connected by bus bars 5, so that the energy storage elements 3 are connected in series.

[0033] The storage section 43 is box-shaped and has a protruding section 43a that protrudes outward from the center of one long side surface in a plan view. A pair of external terminals 6, 6 made of metal such as a lead alloy and having different polarities are provided on both sides of the protruding section 43a on the lid section 42. The storage section 43 stores an abnormality detection device 2. The abnormality detection device 2 is connected to the energy storage elements 3 via a conductor (not shown). The abnormality detection device 2 manages the states of the multiple energy storage elements 3 and controls each section of the energy storage device 1.

[0034] The energy storage element 3 includes a hollow rectangular parallelepiped case 31 and a pair of terminals 32, 32 having opposite polarities provided on one side (terminal surface) of the case 31. The case 31 accommodates an electrode assembly 33 formed by stacking a positive electrode 33a, a separator 33b, and a negative electrode 33c, and an electrolyte (electrolytic solution) (not shown).

[0035] The electrode body 33 is constructed by stacking a sheet-shaped positive electrode 33a on which a positive electrode active material layer is formed and a sheet-shaped negative electrode 33c on which a negative electrode active material layer is formed, with two sheet-shaped separators 33b in between, and rolling them up (vertically or horizontally). The separators 33b are formed of a porous resin film. As the porous resin film, a porous resin film made of a resin such as polyethylene (PE) or polypropylene (PP) can be used.

[0036] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer may further include a conductive assistant, a binder, and the like. As the positive electrode active material, a mixed positive electrode active material including a first positive electrode active material as a main component and a second positive electrode active material is used. The first positive electrode active material and the second positive electrode active material are both capable of inserting and extracting lithium ions, and have different potential ranges in which the insertion and extraction reactions of lithium ions occur. The second positive electrode active material is capable of the insertion and extraction reaction of lithium ions in a higher potential range than the first positive electrode active material. The potential range associated with the insertion and extraction reaction of lithium ions will be described later.

[0037] The first positive electrode active material is lithium iron phosphate (LiFePO4) containing lithium and iron as constituent elements.

[0038] The second positive electrode active material contains active material particles made of a lithium transition metal oxide (hereinafter also referred to as a non-ferrous lithium compound) that contains lithium and a transition metal element as constituent metal elements and has a higher potential for the lithium ion insertion / extraction reaction than the first positive electrode active material. Examples of the second positive electrode active material include manganese-based lithium composite oxides, cobalt-based lithium composite oxides, and nickel-based lithium composite oxides. These oxides are typically represented by the general formulas LiMnO2, LiCoO2, LiNiO2, and Li(Ni,Mn,Co)O2. The second positive electrode active material according to this embodiment does not exclude the inclusion of small amounts of other elements within a range that does not impair the effects of the present invention. The second positive electrode active material may form a solid solution.

[0039] The negative electrode active material layer includes a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, hard carbon, and soft carbon. The negative electrode active material layer may further include a binder, a thickener, and the like.

[0040] The electrolyte housed in the housing case 4a together with the electrode body 33 may be the same as that used in conventional lithium ion secondary batteries. For example, an electrolyte containing a supporting salt in an organic solvent may be used. For example, aprotic solvents such as carbonates, esters, and ethers are used as the organic solvent. For example, lithium salts such as LiPF6, LiBF4, and LiClO4 are preferably used as the supporting salt. The electrolyte may contain various additives such as a gas generating agent, a film forming agent, a dispersing agent, and a thickening agent.

[0041] 2 and 3, a rectangular lithium ion battery including a wound electrode body 33 has been described as an example of the energy storage element 3. Alternatively, the energy storage element 3 may be a cylindrical lithium ion battery. The energy storage element 3 may be a lithium ion battery including a stacked electrode body, or may be a laminated (pouch) lithium ion battery or the like. Furthermore, the energy storage element 3 may be an all-solid-state lithium ion battery using a solid electrolyte.

[0042] 4 is a block diagram of the abnormality detection device 2 etc. The power storage device 1 equipped with the abnormality detection device 2 is connected to a vehicle ECU 8 and a load 9 such as a starter motor for starting the engine and electrical equipment etc. The abnormality detection device 2 includes a calculation unit 21, a storage unit 22, a voltage measurement unit 23, an input unit 24, an output unit 25 etc.

[0043] The calculation unit 21 is a calculation circuit including a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), etc. The CPU included in the calculation unit 21 executes various computer programs stored in the ROM and the storage unit 22, and controls the operation of each of the above-mentioned hardware components, thereby causing the entire device to function as the anomaly detection device of the present disclosure. The calculation unit 21 may include functions such as a timer that measures the elapsed time from when a measurement start instruction is given to when a measurement end instruction is given, a counter that counts numbers, and a clock that outputs date and time information.

[0044] The storage unit 22 is a storage device such as a flash memory. Various computer programs and data are stored in the storage unit 22. The computer programs stored in the storage unit 22 include, for example, an abnormality detection program 221 for causing the calculation unit 21 to execute calculation related to abnormality detection of the power storage device 1.

[0045] The abnormality detection program 221 is provided, for example, by a non-transitory recording medium M on which a computer program is readably recorded. The recording medium M is a portable memory such as a CD-ROM, a USB memory, or a Secure Digital (SD) card. The calculation unit 21 reads a desired computer program from the recording medium M using a reading device (not shown), and stores the read computer program in the storage unit 22. Alternatively, the computer program may be provided by communication.

[0046] The storage unit 22 may store a table indicating the relationship between the voltage and the SOC of the storage element 3, which will be described later.

[0047] The voltage measurement unit 23 is connected to both ends of the storage elements 3 via voltage detection lines. The voltage measurement unit 23 measures the voltage value of each storage element 3 at a predetermined time interval to obtain the voltage of each storage element 3 and the total voltage of the assembled battery. The calculation unit 21 obtains the voltage value through the voltage measurement unit 23.

[0048] The input unit 24 includes an interface for connecting the current sensor 7. The input unit 24 receives a signal related to a current measured by the current sensor 7 at a predetermined time interval. The calculation unit 21 acquires a current value through the input unit 24.

[0049] A temperature sensor such as a thermocouple or a thermistor may further be connected to the input unit 24. The calculation unit 21 acquires, via the input unit 24, temperature data of the energy storage element 3 or the energy storage device 1 measured by the temperature sensor.

[0050] The output unit 25 may be a communication unit, or may include an interface for connecting an external device. An example of the external device is a display device (not shown) such as a liquid crystal display. Alternatively, the external device may be a terminal device (not shown) such as a computer or a smartphone used by a user. The calculation unit 21 outputs the abnormality detection result of the battery pack 30 from the output unit 25 to the external device.

[0051] The energy storage device 1 may include a balancer for reducing the voltage difference between the energy storage elements 3. The balancer is a circuit that includes a discharge load and a switch connected in parallel to each energy storage element, and flows a current through the discharge load to consume the amount of electricity in the energy storage elements. When the voltage value of any of the energy storage elements 3 is equal to or greater than a predetermined value (activation threshold), the calculation unit 21 activates the balancer of that energy storage element 3. When the balancer is activated and the switch is turned on, part of the current supplied from outside the energy storage elements 3 for charging flows into the balancer, and the amount of electricity is consumed.

[0052] The calculation unit 21 estimates the state of the storage element 3 based on the acquired current value, voltage value, temperature, etc., and detects an abnormality in the storage device 1.

[0053] Here, the charge / discharge characteristics of the energy storage element using the mixed positive electrode active material of this embodiment will be described in detail.

[0054] First, the charge / discharge characteristics when lithium iron phosphate and non-iron lithium compounds are used alone will be described. In the following, as the charge / discharge characteristics, a charge / discharge curve showing the relationship between the SOC and voltage of the energy storage element will be described. The charge / discharge curve is a graph showing SOC (%) on the horizontal axis and voltage (V) on the vertical axis.

[0055] For example, in the case of an LFP battery containing LiFePO4 as the positive electrode active material and graphite as the negative electrode active material, the voltage rises at the beginning of charging when the SOC is low, and then a plateau region where the voltage rises very slowly exists in a wide range of SOC 5% to 95%, and the voltage rises suddenly at the end of charging, resulting in an SOC-OCV (Open Circuit Voltage) curve. The voltage changes in a range of about 3.4V or less, and has a plateau region around 3.2V. This plateau voltage is the voltage at which the insertion reaction or desorption reaction of lithium ions occurs in LiFePO4. At the end of the plateau, the insertion reaction or desorption reaction of lithium ions is almost complete, and the voltage rise thereafter is not due to the insertion / desorption reaction of lithium ions and is very steep. Thus, when lithium iron phosphate is used alone, the voltage hardly changes over a wide range of SOC, and the range of SOC in which the voltage change can be detected is very narrow.

[0056] On the other hand, for example, the positive electrode active material is LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 In the case of a ternary battery containing O2(NCM111) and graphite as the negative electrode active material, the SOC-OCV curve shows that the voltage rises at the beginning of charging, and then steadily increases up to 100% SOC. The voltage changes in the range of approximately 3.4V to 4.1V. In this way, when a non-ferrous lithium compound is used alone, the charge / discharge curve has a slope over a wide range of SOC, making it easy to detect the change in voltage.

[0057] The present inventors have focused on the fact that the potential range and the degree of potential change in which the lithium ion insertion / extraction reaction can occur differ depending on the type of positive electrode active material. The present inventors have discovered that by mixing a non-ferrous lithium compound having a high potential in which the lithium ion insertion / extraction reaction can occur with a positive electrode active material mainly composed of lithium iron phosphate, the potential change due to two or more types of positive electrode active materials is reflected in the voltage change of the charge / discharge curve, and the state of the energy storage element 3 can be estimated using this voltage change, thereby making it possible to detect an abnormality in the battery pack 30.

[0058] FIG. 5 shows charge / discharge curves showing the relationship between SOC and voltage for a mixed positive electrode active material of lithium iron phosphate and a non-ferrous lithium compound. The horizontal axis is SOC (%), and the vertical axis is voltage (V). In FIG. 5, the solid line indicates the charge curve, and the dashed line indicates the discharge curve. Although not shown, the curve indicating OCV is located approximately halfway between the charge curve and the discharge curve. LiFePO4 and NCM111 were used as the positive electrode active material. Graphite was used as the negative electrode active material. The ratio of the charge electric quantity based on the total amount of LiFePO4 to the charge electric quantity based on the total amount of NCM111 is: For example, 90:10.

[0059] As shown in FIG. 5, when the mixed positive electrode active material is used, a rising region R1 where the voltage rises, a plateau region R2 where the voltage hardly changes, and a change region R3 where the voltage rises (changes) with a slope are formed in the charge / discharge curve. In the example of FIG. 5, the rising region R1 is formed in the range of SOC 0% to less than about 5%, the plateau region R2 is formed in the range of SOC about 5% to less than 90%, and the change region R3 is formed in the range of SOC 90% to 100%. The rising region R1 and the plateau region R2 are the range (SOC 0% to less than 90%) where lithium ions are inserted and removed in LiFePO4. The change region R3 is the range (SOC 90% to 100%) where lithium ions are inserted and removed in NCM111. In the example of FIG. 5, the change region R3 corresponds to the vicinity of the end point of charge.

[0060] The voltage change ranges in the rise region R1 and plateau region R2 correspond to the operating voltage range of an LFP battery (3.4V or less). The voltage change range in the change region R3 corresponds to the operating voltage range of a ternary battery (3.4V to 4.2V). The plateau region R2 is formed near a voltage of 3.2V. The change region R3, i.e., near the end of charge, may be in a charge / discharge range of 3.2V or higher.

[0061] In this embodiment, by mixing LiFePO4 and NCM111, the plateau end point of the plateau region is shifted toward a lower SOC than when LiFePO4 is used alone. This makes it possible to widen the range of the change region R3 formed near the end point of charge and to make the voltage rise in the change region R3 gentler. The range of the change region R3 and the slope of the voltage are appropriately set according to the mixture ratio of LiFePO4 and NCM111. By using the voltage change in the change region R3 near the end point of charge, the state of the storage element 3 can be accurately estimated based on the voltage, and an abnormality in the battery pack 30 can be suitably detected.

[0062] In this embodiment, the content of the non-ferrous lithium compound (second positive electrode active material) is preferably 5% or more of the charge amount based on the total amount of the non-ferrous lithium compound based on the charge amount based on the total amount of the positive electrode active material. The higher the content of the non-ferrous lithium compound, the more the voltage change can be detected in a wide SOC range. Therefore, the content of the non-ferrous lithium compound is more preferably 10% or more. Furthermore, when the content of the non-ferrous lithium compound is appropriate, the slope of the charge / discharge curve can be made appropriate and the predetermined safety of the energy storage element 3 can be ensured. Therefore, the content of the non-ferrous lithium compound can be less than 30%, more preferably less than 20%.

[0063] The abnormality detection device 2 detects an abnormality in the storage element 3 by measuring the voltage value of the storage element 3 in the above-mentioned change region R3. In this embodiment, an abnormality related to an internal short circuit of the storage element 3 is detected. The abnormality detection device 2 acquires the voltage value of each storage element 3 measured by the voltage measurement unit 23. The occurrence of an internal short circuit of each storage element 3 is detected by determining whether or not the difference between the acquired voltage values ​​of the storage elements 3 is equal to or greater than a first threshold value. The voltage value of a storage element 3 in which an internal short circuit has occurred is lower than the voltage value of a normal storage element 3. Therefore, the occurrence of an internal short circuit can be detected based on the voltage difference with other storage elements 3. Since the voltage value is acquired in the change region R3, the variation in the voltage value can be detected with high accuracy. From the viewpoint of being able to accurately and reliably detect an internal short circuit, the first threshold value is preferably 300 mV or less, and more preferably 50 mV or less and 20 mV or more.

[0064] In the case where the energy storage device 1 includes a balancer, it is preferable that the first threshold value used for detecting an internal short circuit is larger than the second threshold value used for determining whether or not to operate the balancer. For example, when the abnormality detection device 2 determines that the difference in voltage value between the energy storage elements 3 is equal to or larger than the second threshold value during charging of the assembled battery 30, it outputs an operation instruction to the balancer. By operating the balancer of the energy storage element 3 having a higher voltage value than the other energy storage elements 3, the amount of electricity for the energy storage element 3 having the higher voltage value is adjusted, and the charging state between the energy storage elements 3 is equalized. By making the first threshold value larger than the second threshold value for operating the balancer, the occurrence of a voltage difference that is not eliminated by the operation of the balancer can be detected as an internal short circuit. The second threshold value can be, for example, 10 mV.

[0065] 6 is a flowchart showing an example of an abnormality detection process procedure. The calculation unit 21 of the abnormality detection device 2 executes the following processes at a predetermined timing according to the abnormality detection program 221.

[0066] During the discharging of each storage element 3 (during the insertion reaction of lithium ions into the positive electrode active material), the calculation unit 21 acquires a voltage value between the terminals of each storage element 3 through the voltage measurement unit 23 (step S11). When the abnormality detection device 2 is installed in a remote location, the calculation unit 21 receives the measurement data of the storage element 3 by communication via the output unit 25 (communication unit).

[0067] The calculation unit 21 judges whether the acquired voltage value is larger than a preset threshold value, and judges whether the acquired voltage value is within the change region R3 (near the end point of charging) (step S12). If it is determined that the voltage value is not within the change region R3 (step S12: NO), the calculation unit 21 ends the process. On the other hand, if it is determined that the voltage value is within the change region R3 (step S12: YES), the calculation unit 21 proceeds with the process and executes anomaly detection. The calculation unit 21 may execute anomaly detection if one or more of the acquired multiple voltage values ​​are within the change region R3.

[0068] The calculation unit 21 calculates a voltage difference indicating the difference between the minimum voltage value and the maximum voltage value (step S13) based on the acquired voltage values ​​of each storage element 3. The calculation unit 21 identifies the minimum voltage value and the maximum voltage value from among the acquired voltage values ​​of the multiple storage elements 3, and calculates the voltage difference by calculating the difference between the maximum voltage value and the minimum voltage value.

[0069] The calculation unit 21 determines whether or not an internal short circuit has occurred based on the calculated voltage difference (step S14). Specifically, the calculation unit 21 determines whether the calculated voltage difference is larger than a first threshold value set in advance, and determines whether or not the calculated voltage difference is equal to or larger than the first threshold value, thereby determining whether or not an internal short circuit has occurred.

[0070] When it is determined that no internal short circuit has occurred because the calculated voltage difference is less than the first threshold value (step S14: NO), the calculation unit 21 ends the process. The calculation unit 21 may output, via the output unit 25, information indicating that the battery pack 30 is normal.

[0071] If it is determined that an internal short circuit has occurred because the calculated voltage difference is equal to or greater than the first threshold value (step S14: YES), the calculation unit 21 outputs abnormality information indicating that an abnormality has been detected in the battery pack 30 through the output unit 25 (step S15), and ends the series of processes.

[0072] In the above process, the calculation unit 21 may determine the abnormality level indicating the degree of the abnormality as well as the presence or absence of an abnormality in the battery pack 30. The abnormality level is classified into a plurality of stages, for example, high, medium, and low. The calculation unit 21 determines the abnormality level based on the calculated voltage difference and a plurality of preset threshold values. The calculation unit 21 outputs abnormality information according to the abnormality level. When the abnormality level is medium or low, a warning message notifying the abnormality level or a message encouraging repair or replacement after a predetermined period of time has elapsed is output. When the abnormality level is high, the calculation unit 21 may cooperate with a device in which the battery pack 30 is mounted to forcibly display a highly urgent warning message on, for example, a display device of the vehicle, or may output a control signal for safely stopping the operation of the device.

[0073] According to this embodiment, in the battery pack 30 consisting of a plurality of storage elements 3, a positive electrode active material that is a mixture of lithium iron phosphate as a main component and a non-ferrous lithium compound is used, so that a change region R3 in which a voltage difference is easily detected can be formed near the end of charging. An internal short circuit can be accurately detected based on the voltage difference detected in this change region R3.

[0074] A charger for a 12V lead-acid battery mounted on a conventional vehicle performs constant voltage charging at 14.8V. When this charger is used for an energy storage device 1 including a battery pack 30 in which four energy storage elements 3 are connected in series, there is a risk of overcharging the energy storage elements 3 that use LiFePO4 alone as the positive electrode active material. By mixing LiFePO4 and NCM111, the voltage at which the battery is fully charged becomes higher, so that a charger for a 12V lead-acid battery can be suitably used.

[0075] In the present embodiment, an example has been described in which the calculation unit 21 of the anomaly detection device 2 executes each process in the process described in the flowchart of Fig. 6. Alternatively, the calculation unit 21 of the anomaly detection device 2 may execute the process in cooperation with an external device (not shown) by communicating with the external device (not shown) via the output unit 25 (communication unit). The processing entity that performs anomaly detection is not limited to the anomaly detection device 2.

[0076] Second embodiment In the second embodiment, an abnormality is detected regarding the degree of deterioration of the energy storage element 3. The following mainly describes the differences from the first embodiment, and the same reference numerals are used for the configurations common to the first embodiment, and detailed description thereof will be omitted.

[0077] The degree of deterioration may be the full charge capacity or the capacity maintenance rate of the storage element 3. The capacity maintenance rate is also called SOH (State of health) and is the ratio of the full charge capacity at the time of deterioration to the initial full charge capacity of the storage element 3. The abnormality detection device 2 estimates the degree of deterioration of each storage element 3 by performing charging and discharging in the change region R3 (near the end point of charging), and detects an abnormality in the battery pack 30 based on whether the degree of deterioration of some storage elements 3 is more advanced than that of other storage elements 3 beyond an allowable range.

[0078] 7 is a flowchart showing an example of an abnormality detection process procedure in the second embodiment. In charging and discharging each energy storage element 3, the calculation unit 21 of the abnormality detection device 2 executes the following process in accordance with the abnormality detection program 221. In the following, a process of estimating the capacity maintenance rate as the degree of deterioration will be described.

[0079] Charging and discharging are performed in the change region R3 for each storage element 3. During charging and discharging, the calculation unit 21 acquires a current value of the battery pack 30 through the input unit 24 at a predetermined interval (step S21). The calculation unit 21 also acquires a voltage value between the terminals of each storage element 3 through the voltage measurement unit 23 (step S22).

[0080] The calculation unit 21 obtains the charged or discharged amount of electricity of each storage element 3 in the change region R3 (near the end point of charging) based on the obtained current value and voltage value (step S23).

[0081] The calculation unit 21 estimates the first degree of deterioration (SOH) of each storage element 3 (step S24). For example, the first degree of deterioration of each storage element 3 can be estimated based on the behavior of the storage element 3 when it is discharged from a voltage corresponding to a fully charged state until it reaches (drops into) a voltage in a plateau region. A storage element 3 with advanced deterioration reaches a state in which the end point of charging is shifted to the left along the horizontal axis in FIG. 5, and reaches a voltage in the plateau region earlier than the other storage elements 3.

[0082] The calculation unit 21 compares the estimated first deterioration levels SOH of each storage element 3 (step S25) and determines whether or not the battery pack 30 is abnormal (step S26). Specifically, the calculation unit 21 identifies a maximum value and a minimum value from the acquired first deterioration levels SOH of the multiple storage elements 3, and calculates the difference between the maximum value and the minimum value. The calculation unit 21 determines whether or not an abnormality exists by judging whether or not the calculated difference between the maximum value and the minimum value is equal to or greater than a threshold value. If the difference between the maximum value and the minimum value is equal to or greater than the threshold value, it determines that an abnormality exists. If the difference between the maximum value and the minimum value is less than the threshold value, it determines that no abnormality exists.

[0083] When it is determined that the battery pack 30 is not abnormal (step S26: NO), the calculation unit 21 ends the process. The calculation unit 21 may output, via the output unit 25, information indicating that the battery pack 30 is normal.

[0084] When it is determined that the battery pack 30 is abnormal (step S26: YES), the calculation unit 21 outputs abnormality information indicating that an abnormality has been detected in the battery pack 30 via the output unit 25 (step S27), and ends the series of processes.

[0085] In the above, an abnormality is determined based on the difference between the maximum value and the minimum value. Alternatively, the calculation unit 21 may identify a reference first deterioration level (e.g., the maximum value or the minimum value) from the acquired first deterioration levels of each storage element 3, calculate the difference between the identified reference first deterioration level and the first deterioration levels of the other storage elements 3, and make a threshold determination. The abnormality detection may be performed by detecting a state difference between each storage element 3.

[0086] In the above, the capacity maintenance rate (degree of deterioration) is estimated as the state of the energy storage element 3. Alternatively, the calculation unit 21 may estimate the state of charge (SOC) as the state of the energy storage element 3. For example, the SOC is calculated using the following formula (1). SOC i =SOC i-1 +I i ×Δt i / Q×100…(1) SOC i This is the SOC, SOC i-1 is the previous SOC, I i is the current value, Δt i is the time interval and Q is the full charge capacity. An abnormality in the battery pack 30 may be detected when the SOC of some of the energy storage elements 3 deviates from that of the other energy storage elements 3 beyond an allowable range.

[0087] According to this embodiment, by acquiring an integrated value of the current in the change region R3, it is possible to suitably estimate the first deterioration level and detect an abnormality in the battery pack 30. When lithium iron phosphate is used alone, the plateau region with little voltage change is wide, and the deterioration level of the energy storage element 3 can be estimated substantially only by performing complete charging and discharging (performing so-called capacity confirmation). According to this embodiment, by using the voltage change in the change region R3, it is easy to determine the start and end of the change region R3, so that the deterioration level of the energy storage element 3 can be efficiently estimated by partial charging and discharging.

[0088] Third embodiment In the third embodiment, the degradation degree estimated by different methods is compared. In the following, the differences from the second embodiment are mainly described, and the same reference numerals are used for the configurations common to the first embodiment, and the detailed description thereof is omitted.

[0089] The calculation unit 21 estimates the accuracy of the second degree of deterioration by comparing the first degree of deterioration estimated from the integrated value of the current in the change region R3 with the second degree of deterioration obtained by a method different from the method for estimating the first degree of deterioration.

[0090] 8 is a flowchart showing an example of an anomaly detection process procedure in the third embodiment. The calculation unit 21 of the anomaly detection device 2 executes the following process at a predetermined timing according to the anomaly detection program 221. In the following, an example of estimating SOH as the first deterioration level and the second deterioration level will be described.

[0091] The calculation unit 21 estimates the second deterioration degree (step S31). The method of estimating the second deterioration degree is not particularly limited. The second deterioration degree may be sequentially calculated and stored by a mathematical model using actual measurement data of the usage history of the storage element 3, for example. The usage history data includes a current value, a voltage value, a temperature, and a usage time. The calculation unit 21 clearly distinguishes between current-on deterioration and non-current-on deterioration, calculates the respective deterioration degrees based on a root rule, and calculates the second deterioration degree by integrating these. The second deterioration degree is calculated for each of the first positive electrode active material and the second positive electrode active material.

[0092] The calculation unit 21 compares the first deterioration level with the second deterioration level related to the second positive electrode active material (step S32) and estimates the accuracy of the second deterioration level related to the second positive electrode active material (step S33). The accuracy may be estimated based on an error between the first deterioration level and the second deterioration level. For example, the calculation unit 21 determines that the accuracy is high when the error is less than a predetermined value, and that the accuracy is low when the error is equal to or greater than the predetermined value. Alternatively, the accuracy may be classified into three or more stages, or may be indicated by a numerical value.

[0093] The calculation unit 21 judges whether or not the estimation result of the second deterioration degree is abnormal based on the estimated accuracy (step S34). If it is judged that the estimation result of the second deterioration degree is not abnormal (step S34: NO), the calculation unit 21 ends the process. On the other hand, if it is judged that the estimation result of the second deterioration degree is abnormal (step S34: YES), the calculation unit 21 outputs abnormality information indicating that the estimation result of the second deterioration degree is abnormal (low accuracy) (step S35), and ends the series of processes.

[0094] In the above-mentioned process, when it is determined that the accuracy of the second deterioration degree is low and the estimation result is abnormal, calculation unit 21 may update or reset the second deterioration degree related to the second positive electrode active material based on the first deterioration degree. After updating or resetting the second deterioration degree, calculation unit 21 may resume estimation of the second deterioration degree by using the updated second deterioration degree as a new reference value.

[0095] The calculation unit 21 may use the accuracy of the second deterioration degree for the second positive electrode active material to estimate the accuracy of the second deterioration degree for the first positive electrode active material. The calculation unit 21 may update or reset the second deterioration degree for the first positive electrode active material according to the accuracy of the second deterioration degree. The SOH derived from the second positive electrode active material obtained as the first deterioration degree does not strictly match the SOH derived from the first positive electrode active material. However, in a single storage element 3, the processing can be carried out assuming that these SOHs are almost the same. This makes it possible to obtain the accuracy of the second deterioration degree for the first positive electrode active material without comparing the first deterioration degree and the second deterioration degree of the first positive electrode active material.

[0096] According to this embodiment, the difference between the deterioration degrees obtained by two different methods is taken, and if there is a discrepancy between the two values, it can be determined that there is an abnormality. Since the second deterioration degree is an estimated value obtained based on the usage history, there is a concern that the estimation error will increase over time. By comparing and verifying with the first deterioration degree that is in line with the actual usage, the second deterioration degree can be appropriately updated (corrected).

[0097] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0098] 1. Energy storage device 2. Anomaly detection device 21 Arithmetic section 22 Memory section 23 Voltage measurement section 24 Input section 25 Output section 221 Anomaly Detection Program M Recording medium 3. Energy storage element 30 Battery pack 33a positive electrode

Claims

1. An abnormality detection method for detecting an abnormality in a battery pack having a plurality of storage elements by an abnormality detection device, comprising: Each of the plurality of storage elements is The positive electrode comprises, as a positive electrode active material, lithium iron phosphate and a lithium transition metal oxide capable of undergoing an insertion / extraction reaction of lithium ions in a potential range higher than that of the lithium iron phosphate, a ratio of a charging amount of electricity based on the total amount of the lithium transition metal oxide to a charging amount of electricity based on the total amount of the positive electrode active material in a charging / discharging range in which the storage element is used is 5% or more; The abnormality detection device includes: acquiring an integrated value of the voltage and current of each of the plurality of storage elements near a charge end point of a charge / discharge range in which the storage elements are used; An abnormality in the battery pack is detected using the acquired integrated values ​​of the voltages and currents of the plurality of storage elements. Anomaly detection methods.

2. When a voltage difference between the plurality of storage elements during an insertion reaction of lithium ions in the lithium transition metal oxide near the end point of charge is equal to or greater than a first threshold value, it is detected that an internal short circuit has occurred in at least one of the plurality of storage elements. The anomaly detection method according to claim 1 .

3. The first threshold value is a value greater than an activation threshold value of a balancer that reduces a voltage difference between the plurality of storage elements during charging. The anomaly detection method according to claim 2 .

4. An integrated value of a current associated with an insertion reaction or desorption reaction of lithium ions in the lithium transition metal oxide near the end of charge is obtained in the plurality of energy storage elements; A first deterioration degree of each of the plurality of storage elements is estimated based on the acquired integrated value of the current. The anomaly detection method according to any one of claims 1 to 3.

5. Detecting an abnormality in the battery pack based on a comparison between a first deterioration level of one of the power storage elements in the battery pack and a first deterioration level of another of the power storage elements. The anomaly detection method according to claim 4 .

6. estimating a second deterioration degree of the plurality of energy storage elements based on a usage history of the plurality of energy storage elements; The first deterioration level and the second deterioration level of each of the plurality of power storage elements are compared. The anomaly detection method according to claim 4 or 5.

7. The voltage of each of the plurality of storage elements is acquired in a charge / discharge range of 3.2 V or more. The anomaly detection method according to any one of claims 1 to 6.

8. An abnormality detection device that detects an abnormality in a battery pack having a plurality of storage elements, Each of the plurality of storage elements is The positive electrode comprises, as a positive electrode active material, lithium iron phosphate and a lithium transition metal oxide capable of undergoing an insertion / extraction reaction of lithium ions in a potential range higher than that of the lithium iron phosphate, a ratio of a charging amount of electricity based on the total amount of the lithium transition metal oxide to a charging amount of electricity based on the total amount of the positive electrode active material in a charging / discharging range in which the storage element is used is 5% or more; an acquisition unit that acquires an integrated value of a voltage and a current of each of the plurality of storage elements near a charge end point of a charge / discharge range in which the storage elements are used; a detection unit that detects an abnormality in the battery pack using the integrated values ​​of the voltages and currents of the plurality of power storage elements acquired by the acquisition unit. Anomaly detection device.

9. A battery pack having a plurality of storage elements and the abnormality detection device according to claim 8. Energy storage device.

10. A computer program for causing a computer to detect an abnormality in a battery pack having a plurality of storage elements, Each of the plurality of storage elements is The positive electrode comprises, as a positive electrode active material, lithium iron phosphate and a lithium transition metal oxide capable of undergoing an insertion / extraction reaction of lithium ions in a potential range higher than that of the lithium iron phosphate, a ratio of a charging amount of electricity based on the total amount of the lithium transition metal oxide to a charging amount of electricity based on the total amount of the positive electrode active material in a charging / discharging range in which the storage element is used is 5% or more; The computer includes: acquiring an integrated value of the voltage and current of each of the plurality of storage elements near a charge end point of a charge / discharge range in which the storage elements are used; An abnormality in the battery pack is detected using the acquired integrated values ​​of the voltages and currents of the plurality of storage elements. A computer program for executing a process.

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