JP7521335B2 - DETECTION APPARATUS, DETECTION METHOD, AND COMPUTER PROGRAM - Google Patents

Description

The present invention relates to a detection device, a detection method, and a computer program.

In recent years, energy storage elements such as lithium-ion batteries have been used in a wide range of fields, including power sources for notebook personal computers, smartphones and other mobile devices, renewable energy storage systems, and power sources for IoT devices.

For example, a porous separator that is filled with electrolyte and allows ions to move is sandwiched between the positive and negative electrodes of a lithium-ion battery. The separator prevents the positive and negative electrodes from coming into contact with each other, and prevents a short circuit (internal short circuit) from occurring between the positive and negative electrodes (see, for example, Patent Document 1). When an internal short circuit occurs in any storage element, not just in lithium-ion batteries, heat is generated inside the battery, which can cause the battery to break down.

JP 2019-140100 A

Since an internal short circuit generates heat inside the battery, it is possible to detect an internal short circuit, for example, by measuring the temperature of the battery surface and detecting a rise in temperature on the battery surface. However, it takes a certain amount of time for the heat generated by an internal short circuit to be transferred to the battery surface, making it difficult to detect an internal short circuit in real time using this method.

The present invention was made in consideration of the above circumstances, and aims to provide a detection device, detection method, and computer program that can detect an internal short circuit at an early stage.

The detection device includes an electrode terminal and an electrode body having a conductive tab, and for an energy storage element in which the electrode body is connected to the electrode terminal via the conductive tab, an acquisition unit that acquires a sensor output from a temperature sensor that measures the temperature of the conductive tab, and a detection unit that detects an internal short circuit in the electrode body based on the acquired sensor output.

The detection method uses a computer to obtain a sensor output from a temperature sensor that measures the temperature of the conductive tab for an energy storage element that includes an electrode terminal and an electrode body having a conductive tab, the electrode body being connected to the electrode terminal via the conductive tab, and detects an internal short circuit in the electrode body based on the obtained sensor output.

The computer program causes the computer to execute a process for detecting an internal short circuit in an electrode body having an electrode terminal and a conductive tab, the process acquiring a sensor output from a temperature sensor that measures the temperature of the conductive tab for an energy storage element in which the electrode body is connected to the electrode terminal via the conductive tab, and the process detecting an internal short circuit in the electrode body based on the acquired sensor output.

This application makes it possible to estimate the resistance value of an internal short circuit, which was previously difficult to grasp, and therefore allows for early detection of an internal short circuit.

FIG. 2 is an external perspective view of the energy storage element. FIG. FIG. 2 is an exploded perspective view of an electrode body constituting an electricity storage element. FIG. FIG. 2 is a block diagram illustrating an internal configuration of a detection device. FIG. 2 is a circuit diagram showing an equivalent circuit of a storage element. 1 is a circuit diagram showing an equivalent circuit of an energy storage element in a state in which an internal short circuit has occurred. FIG. 11 is a circuit diagram showing an equivalent circuit of the combined energy storage elements. FIG. 2 is a schematic diagram showing a configuration example of a thermal circuit model in the first embodiment. 4 is a flowchart illustrating a procedure for detecting an internal short circuit in the first embodiment. FIG. 11 is a schematic diagram showing a configuration example of a thermal circuit model in the second embodiment. 13 is a flowchart illustrating a procedure for detecting an internal short circuit in the third embodiment. 13 is a flowchart illustrating a procedure for detecting an internal short circuit in the fourth embodiment. 13 is a flowchart illustrating a procedure for detecting an internal short circuit in the fifth embodiment. 10 is a flowchart illustrating a procedure for detecting a sign of an internal short circuit. A partial cross-sectional view of a storage element in embodiment 7. FIG. 2 is a perspective view showing an example of mounting a circuit breaker. 4 is a flowchart illustrating a procedure of a process executed by a control circuit. FIG. 2 is an external perspective view showing a laminate type energy storage element. FIG. 2 is an exploded perspective view showing a laminate type energy storage element.

The detection device comprises an electrode terminal and an electrode body having a conductive tab, and for an energy storage element in which the electrode body is connected to the electrode terminal via the conductive tab, an acquisition unit that acquires a sensor output from a temperature sensor that measures the temperature of the conductive tab, and a detection unit that detects an internal short circuit in the electrode body based on the acquired sensor output.
When an internal short circuit occurs in the energy storage element, the conductive tab heats up more quickly than the electrode assembly and the container that houses the electrode assembly. The detection device can detect the internal short circuit at an early stage by referring to the temperature of the conductive tab.

In the detection device, the detection unit may include an observer that estimates the short-circuit resistance of the internal short circuit based on the sensor output. With this configuration, the short-circuit resistance of the internal resistance that cannot be directly observed can be estimated through the state variables obtained from the observer.

In the detection device, the detection unit may estimate the short-circuit resistance of the internal resistor using a state estimation algorithm based on the sensor output and a thermal circuit model that simulates the thermal phenomenon of the storage element. With this configuration, the short-circuit resistance of the internal resistor that cannot be directly observed can be estimated using the state estimation algorithm.

In the detection device, the thermal circuit model may be a model that includes the electrode body, the conductive tab, and the short circuit portion as nodes, and includes the temperature and heat capacity at each node, as well as the thermal resistance between the nodes as parameters. With this configuration, it is possible to describe the thermal phenomenon in the energy storage element using a simple model.

In the detection device, the state estimation algorithm may include a procedure for determining the time transition of each state variable using a state equation that represents the time transition of state variables including the temperature and short-circuit resistance of each node, determining the likelihood of state estimation using an observation equation that describes the relationship between the state variables and observation quantities including the temperature observed by the temperature sensor, and updating the estimated value of the state variable according to the determined likelihood of state estimation. With this configuration, the short-circuit resistance of the internal resistance that cannot be directly observed can be estimated in a time series manner through the state variables that are successively updated.

In the detection device, the state estimation algorithm may include a particle filter, an ensemble Kalman filter, an extended Kalman filter, or an unscented Kalman filter. With this configuration, the state variables are successively updated using the particle filter, the ensemble Kalman filter, the extended Kalman filter, or the unscented Kalman filter, and the short-circuit resistance of an internal resistance that cannot be directly observed can be estimated in a time series manner.

The detection device may include an output unit that outputs the detection result by the detection unit. With this configuration, since the output unit that outputs the detection result is provided, it is possible to suggest, for example, stopping the use of the storage element or replacing it when an internal short circuit is detected.

In the detection device, the electrode body may be a laminated electrode body. With this configuration, the positive electrode plates (or negative electrode plates) of the storage elements are connected only via the conductive tab, so that if an internal short circuit occurs, the temperature of the conductive tab rises quickly. The detection device can detect an internal short circuit early on based on the sensor output from a temperature sensor that measures the temperature of the conductive tab.

The detection method uses a computer to obtain a sensor output from a temperature sensor that measures the temperature of an electrode terminal and an electrode body having a conductive tab, with the electrode body being connected to the electrode terminal via the conductive tab, and detects an internal short circuit in the electrode body based on the obtained sensor output for an energy storage element. According to this detection method, an internal short circuit can be detected early by referring to the temperature of the conductive tab.

The computer program causes a computer to execute a process for detecting an internal short circuit in an electric storage element that includes an electrode terminal and an electrode body having a conductive tab, the electrode body being connected to the electrode terminal via the conductive tab, by acquiring a sensor output from a temperature sensor that measures the temperature of the conductive tab and based on the acquired sensor output. According to this computer program, an internal short circuit can be detected early by referring to the temperature of the conductive tab.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
(Embodiment 1)
FIG. 1 is an external perspective view of the energy storage element 100, FIG. 2 is an exploded perspective view of the energy storage element 100, FIG. 3 is an exploded perspective view of an electrode body 200 constituting the energy storage element 100, and FIG. 4 is a partial cross-sectional view of the vicinity of the terminal. The energy storage element 100 is, for example, a lithium ion secondary battery. The energy storage element 100 stores power supplied from an external charging device and supplies the stored power to a predetermined load. The energy storage element 100 is used as a power source for automobiles (or mobile objects) such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), an aviation power source, a space power source, a power source for electronic devices, a power source for power storage, and the like.

The energy storage element 100 includes an electrode body 200 (see FIG. 2) housed in a container 110, and electrode terminals 310, 320 connected to an external charging device or load. One electrode terminal 310 is a positive electrode terminal, and the other electrode terminal 320 is a negative electrode terminal. The electrode body 200 is electrically connected to the electrode terminals 310, 320 via conductive tabs (a positive electrode tab 211 and a negative electrode tab 221, described below).

The container 110 is composed of a rectangular parallelepiped container body 111 and a lid 112 that closes the opening of the container body 111. The container body 111 and the lid 112 are formed of a weldable metal such as stainless steel, aluminum, or an aluminum alloy. Alternatively, the container body 111 and the lid 112 may be formed of a resin. The container body 111 is sealed by the lid 112 after accommodating the electrode body 200 and the like. An electrolyte (not shown) is sealed inside the container 110. As the electrolyte, for example, an electrolyte containing a supporting salt in an organic solvent is used. As the organic solvent, for example, an aprotic solvent such as carbonates, esters, or ethers is used. As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , or LiClO ₄ is preferably used. The electrolyte may include various additives such as a gas generating agent, a film forming agent, a dispersant, and a thickener. The lid 112 may include an inlet for injecting an electrolyte into the container 110, a gas exhaust valve for exhausting gas from inside the container when the internal pressure of the container 110 increases, and the like.

The electrode terminals 310, 320 of the energy storage element 100 are attached to the lid 112 of the container 110 by crimping or the like. Specifically, the electrode terminals 310, 320 each have an axial portion (rivet portion) extending downward, and this axial portion is inserted into the through holes of the upper gasket 120, the lid 112, the lower gasket 130, and the current collector 140 and crimped. In this way, the electrode terminals 310, 320 are attached to the lid 112 of the container 110 together with the upper gasket 120, the lid 112, the lower gasket 130, and the current collector 140.

Here, the upper gasket 120 is a flat sealing member disposed between the lid 112 of the container 110 and the electrode terminals 310, 320. The lower gasket 130 is a sealing member disposed between the lid 112 of the container 110 and the current collector 140. The upper gasket 120 and the lower gasket 130 are formed from an insulating resin material such as polypropylene (PP), polyethylene (PE), polyphenylene sulfide resin (PPS), etc.

The current collector 140 is a rectangular flat conductive member that electrically connects the electrode terminals 310, 320 and the conductive tabs (positive electrode tab 211 and negative electrode tab 221) of the electrode body 200. The current collector 140 is formed of a material such as a metal, such as aluminum, an aluminum alloy, copper, or a copper alloy. The positive electrode side current collector 140 is connected to the electrode terminal 310 by crimping or the like, and is connected to the positive electrode tab 211 provided on the electrode body 200 by welding or the like. Similarly, the negative electrode side current collector 140 is connected to the electrode terminal 320 by crimping or the like, and is connected to the negative electrode tab 221 provided on the electrode body by welding or the like. Alternatively, the current collector 140 may be connected to the electrode terminals 310, 320 by a method such as welding or screw fastening, or may be connected to the positive electrode tab 211 and the negative electrode tab 221 by a method such as crimping or screw fastening.

The electrode body 200 is a laminate of a positive electrode plate 210, a negative electrode plate 220, and a separator 230. The electrode body 200 shown as an example in FIG. 3 is made up of a laminate in which a separator 230, a negative electrode plate 220, a separator 230, a positive electrode plate 210, ... are repeatedly laminated in this order.

The positive electrode plate 210 is composed of a substrate and a positive electrode active material layer formed on the substrate. The substrate of the positive electrode plate 210 is a current collector foil. The current collector foil is made of a known material such as nickel, iron, stainless steel, titanium, baked carbon, conductive polymer, conductive glass, or Al-Cd alloy. The positive electrode active material layer includes a positive electrode active material, a conductive assistant, and a binder. For the positive electrode active material, a material capable of absorbing and releasing lithium ions is used. As the positive electrode active material, polyanion compounds such as _LiMPO4 , _LiMSiO4 , _LiMBO3 (M is one or more transition metal elements selected from Fe, Ni, Mn, _Co , etc.), spinel-type _lithium manganese oxides such as _{LiMn2O4 and LiMn1.5Ni0.5O4 ,} and lithium transition metal oxides such as _LiMO2 (M is one or more transition metal elements selected from Fe, Ni, Mn, Co, etc., including lithium-excess composite oxides) are used. As the conductive assistant, for example, carbon black such as acetylene black (AB) and other carbon materials (graphite, etc.) are preferably used. As the binder, for example, a material such as polyvinylidene fluoride (PVDF) is used.

The positive electrode plate 210 has a positive electrode tab 211. The positive electrode tab 211 is a rectangular conductive tab that protrudes from one side of the positive electrode plate 210. The positive electrode tab 211 is formed integrally with the substrate (current collector foil). The positive electrode tabs 211 of each positive electrode plate 210 are bundled together to form a tab bundle.

The negative electrode plate 220 is composed of a substrate and a negative electrode active material layer formed on the substrate. The substrate of the negative electrode plate 220 is a current collector foil. The current collector foil is made of the same material as the current collector foil constituting the substrate of the positive electrode plate 210. The negative electrode active material layer includes a negative electrode active material, a conductive assistant, and a binder. The negative electrode active material is made of a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material include lithium metal, lithium alloys (lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and lithium metal-containing alloys such as Wood's alloy), alloys capable of absorbing and releasing lithium, carbon materials (e.g., graphite, difficult-to-graphitize carbon, easy-to-graphitize carbon, low-temperature fired carbon, amorphous carbon, etc.), silicon oxides, metal oxides, lithium metal oxides (Li ₄ Ti ₅ O ₁₂ , etc.), polyphosphate compounds, and compounds of transition metals such as Co ₃ O ₄ and Fe ₂ P, which are generally called conversion negative electrodes, and elements of Groups 14 to 16. The conductive assistant and binder are the same materials as the conductive assistant and binder constituting the positive electrode active material layer.

The negative electrode plate 220 has a negative electrode tab 221. The negative electrode tab 221 is a rectangular conductive tab that protrudes from one side of the negative electrode plate 220 at a position that does not overlap with the positive electrode tab 211. The negative electrode tab 221 is formed integrally with the substrate (current collector foil). The negative electrode tabs 221 of each negative electrode plate 220 are bundled together to form a tab bundle.

The separator 230 is a rectangular sheet having microporosity. For example, a woven fabric or nonwoven fabric insoluble in organic solvents, or a synthetic resin microporous film made of a polyolefin resin such as polyethylene, is used as the material for the separator 230. The separator 230 may be configured by laminating a plurality of microporous films having different materials, weight average molecular weights, porosities, etc., and may be configured such that these microporous films contain appropriate amounts of additives such as various plasticizers, antioxidants, and flame retardants, or may have inorganic oxides such as silica applied to one or both sides of these microporous films.

In the first embodiment, a lithium ion secondary battery having a laminated electrode body 200 has been described as the energy storage element 100. Alternatively, the energy storage element 100 may be a lithium ion secondary battery having a wound electrode body. The energy storage element 100 may be a cylindrical lithium ion battery or a laminated lithium ion battery. The energy storage element 100 may be an all-solid-state lithium ion battery using a solid electrolyte, or a metallic lithium secondary battery using metallic lithium as the negative electrode. Furthermore, the energy storage element 100 may be a battery other than a lithium ion secondary battery, such as a zinc-air battery, a sodium ion battery, or a lead battery, or a capacitor such as an electric double layer capacitor.

Not limited to the above-mentioned energy storage element 100, the positive and negative plates in the energy storage element are spaced apart so as not to come into contact with each other. As a result, short circuits (internal short circuits) between the positive and negative plates are avoided. In such energy storage elements, if a foreign object gets into the container or if the separator is damaged, insulation between the positive and negative plates can no longer be maintained, and an internal short circuit can occur. If an internal short circuit occurs in the energy storage element, heat is generated inside the battery, leading to battery failure.

Because an internal short circuit generates heat inside the battery, it is possible to detect an internal short circuit, for example, by measuring the temperature of the battery surface and detecting a rise in temperature on the battery surface. However, it takes a certain amount of time for the heat generated by an internal short circuit to be transferred to the battery surface, making it difficult to detect an internal short circuit in real time using this method. In addition, it is difficult to actually measure the resistance of an internal short circuit, and no technology existed to grasp the resistance of an internal short circuit.

Therefore, in the first embodiment, the detection device 10 described below performs a simulation with reference to the temperature of the conductive tab provided on the electrode body 200 of the energy storage element 100, and detects an internal short circuit in the energy storage element 100 based on the results of the simulation. For example, the detection device 10 estimates the short circuit resistance of the internal short circuit by simulation, and if the estimated short circuit resistance is less than a threshold value, it determines that an internal short circuit in the energy storage element 10 has been detected. Alternatively, the maximum temperature of the conductive tab may be obtained under various usage conditions (current value during charging or discharging, current flow time, etc.) that are expected in advance, and if the tab temperature during actual operation is higher than the previously obtained maximum temperature by a certain percentage or by a certain temperature or more, the detection device 10 may determine that an internal short circuit has been detected. Furthermore, the temperature of the conductive tab under various assumed usage conditions (such as the current value during charging or discharging and the duration of current flow) may be determined by experiment or simulation to clarify the relationship between the usage conditions and the tab temperature in advance, and if the tab temperature during actual operation is higher than the tab temperature under the corresponding usage conditions by a certain percentage or by a certain temperature, the detection device 10 may determine that an internal short circuit has been detected.

The configuration of the detection device 10 that executes the simulation will be described below.
FIG. 5 is a block diagram for explaining the internal configuration of the detection device 10. The detection device 10 is a dedicated or general-purpose computer including a calculation unit 11, a storage unit 12, an input unit 13, and an output unit 14. In the example of FIG. 5, the detection device 10 is provided outside the energy storage element 100. Specifically, the detection device 10 may be a battery management unit (BMU) that is provided outside the energy storage element 100, or may be a computer such as a server that is installed in a remote location. Alternatively, the detection device 10 may be built into the energy storage element 100.

The calculation unit 11 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 11 executes various computer programs stored in the ROM and the storage unit 12, and controls the operation of each of the above-mentioned hardware components, thereby causing the entire device to function as the detection device of the present application. Specifically, the calculation unit 11 estimates the short-circuit resistance in the energy storage element 100 using a state estimation algorithm based on the sensor output of the temperature sensor 250 that measures the temperature of the conductive tabs (positive electrode tab 211, negative electrode tab 221) and a thermal circuit model MD1 that simulates the thermal phenomenon of the energy storage element 100. The calculation unit 11 detects an internal short circuit in the energy storage element 100 based on the estimated short-circuit resistance.

The calculation unit 11 is not limited to the above configuration, and may be any processing circuit or calculation circuit equipped with multiple CPUs, a multi-core CPU, a GPU (Graphics Processing Unit), a microcomputer, a volatile or non-volatile memory, etc. The calculation unit 11 may also have functions such as a timer that measures the elapsed time from when an instruction to start measurement is given to when an instruction to end measurement is given, a counter that counts numbers, and a clock that outputs date and time information.

The memory unit 12 is a storage device such as a flash memory. Various computer programs and data are stored in the memory unit 12. The computer programs stored in the memory unit 12 include, for example, a state estimation program PG for causing the calculation unit 11 to execute calculations based on a state estimation algorithm. The data stored in the memory unit 12 include parameters used in the state estimation program PG, parameters used in a short-circuit equivalent circuit model and a thermal circuit model MD1 described below, and data temporarily generated by calculations by the calculation unit 11. The state estimation program PG is provided, for example, by a non-transient recording medium M on which the computer program is recorded in a readable manner. The recording medium M is a portable memory such as a CD-ROM, a USB memory, or an SD (Secure Digital) card. The calculation unit 11 reads a desired computer program from the recording medium M using a reading device not shown in the figure, and stores the read computer program in the memory unit 12. Alternatively, the computer program may be provided by communication.

The input unit 13 includes an interface for connecting the temperature sensor 250 and acquires the sensor output from the temperature sensor 250. The temperature sensor 250 is an existing sensor such as a thermocouple or a thermistor. The temperature sensor 250 is connected to one or more of the positive electrode tab 211 or the negative electrode tab 221 constituting the conductive tab. Alternatively, the temperature sensor 250 may be connected to the current collector 140 to which the conductive tab is joined. In the first embodiment, the number of the temperature sensors 250 is one. Alternatively, the number of the temperature sensors 250 may be multiple. The temperature sensor 250 may be connected to the input unit 13 by wire or wirelessly.

The output unit 14 has an interface for connecting an external device. One example of an external device is a display device 20 such as a liquid crystal display. Alternatively, the external device may be a terminal device (not shown) such as a computer or smartphone used by a user. The calculation unit 11 outputs the detection result of the internal short circuit to the external device from the output unit 14. The calculation unit 11 may output an estimated value of the short circuit resistance to the external device from the output unit 14 in addition to the detection result of the internal short circuit.

The detection device 10 may be equipped with an alarm unit such as an LED lamp or a buzzer to notify the user of the detection result of an internal short circuit.

The content of the calculation process executed by the detection device 10 will be described below.
In the first embodiment, an equivalent circuit of the energy storage element 100 is introduced to calculate the current during an internal short circuit. FIG. 6 is a circuit diagram showing the equivalent circuit of the energy storage element 100. In a typical laminated liquid type lithium ion battery, each layer is electrically connected in parallel. Therefore, the equivalent circuit of the energy storage element 100 is represented by, for example, a parallel circuit as shown in FIG. 6. The equivalent circuit shown in FIG. 6 represents a five-layer laminated battery. The number of layers is set appropriately depending on the number of positive electrode plates 210 and negative electrode plates provided in the electrode body 200 of the energy storage element 100.

Each layer of the energy storage element 100 is divided into a positive electrode tab 211, a battery section, and a negative electrode tab 221. The battery section includes a positive electrode plate 210, a separator 230, a negative electrode plate 220, an electrolyte, etc. In the equivalent circuit, the positive electrode tab 211 is represented as a positive electrode tab resistance (resistance value r _ptab ), and the negative electrode tab 221 is represented as a negative electrode tab resistance (resistance value r _ntab ). The battery section is represented by an equilibrium potential (voltage value E _eq ) and an internal resistance (resistance value r _e ). Here, the internal resistance of the battery section includes the ohmic resistance of the electrodes, the reaction resistance of the electrodes, and the ohmic resistance of the electrolyte.

In the equivalent circuit shown in FIG. 6, for simplification, each layer of the energy storage element 100 is divided into three parts: the positive electrode tab 211, the battery portion, and the negative electrode tab 221, but it may be divided into more fine parts. Also, in the equivalent circuit in FIG. 6, it is assumed that the external short-circuit layers are in the same state, but different states may be set for each external short-circuit layer.

Fig. 7 is a circuit diagram showing an equivalent circuit of the energy storage element 100 in a state where an internal short circuit has occurred. The equivalent circuit shown as an example in Fig. 7 shows an equivalent circuit in which the fifth layer is an internal short circuit layer and the first to fourth layers are external short circuit layers. The internal short circuit is represented by a short circuit resistor (resistance value _Rs ) connected in parallel to the battery portion. The same applies when an internal short circuit has occurred in the other layers.

In the equivalent circuit, each layer (1st to 4th layers) of the external short circuit layer can be regarded as the same, so each element of the external short circuit layer can be described by combining them. Fig. 8 is a circuit diagram showing an equivalent circuit of the storage element 100 after combining. The combined positive electrode tab resistance (r _ptab,ex ), combined internal resistance (r _e,ex ), and combined negative electrode tab resistance (r _ntab,ex ) in the external short circuit layer are described as in Equation 1.

where n represents the total number of layers. In this example, n=5. Since the layers are in parallel, the equilibrium potential is _Eeq .

The current flowing through the external short-circuit layer is I _ex , the current flowing through the internal short-circuit layer is I _in , and the current flowing through the short circuit portion is I _s . _{I ex} is the sum of the currents flowing through all the external short-circuit layers, and the current per layer is I _ex /(n-1). In the example of Fig. 8, the internal resistance of the battery in the internal short-circuit layer is denoted as r _e ,in to distinguish it from the internal resistance of the battery in the external short-circuit layer (r _e,ex ).

When the law of conservation of current is applied to the equivalent circuit shown in Figure 8, we obtain Equation 2.

When Kirchhoff's law is applied to a closed circuit consisting of the external short circuit layer, the tab portion of the internal short circuit layer, and the short circuit portion, we obtain Equation 3.

When Kirchhoff's law is applied to a closed circuit consisting of an internal short circuit layer and a short circuit, we obtain Equation 4.

By solving equations 2 to 4, the current I _in flowing through the internal short-circuit layer, the current I _ex flowing through the external short-circuit layer, and the current I _s flowing through the short circuit portion can be obtained as equations 5 to 7, respectively.

In Equations 5 to 7, all resistances other than the short-circuit resistance _Rs are known because they are determined by design values (material properties, shape). On the other hand, the short-circuit resistance _Rs cannot be determined by design, and cannot be measured.

In the first embodiment, a thermal circuit model MD1 that simulates the thermal phenomenon of the energy storage element 100 is introduced to calculate the temperature during an internal short circuit. FIG. 9 is a schematic diagram showing an example of the configuration of the thermal circuit model MD1 in the first embodiment. The thermal circuit model MD1 is a model for simulating the thermal phenomenon of the energy storage element 100 by using the temperatures of a plurality of regions that divide the energy storage element 100 and the thermal resistance between the regions as parameters. The thermal circuit model MD1 illustrated in FIG. 9 divides the energy storage element 100 into seven regions (regions 1 to 7). Regions 1 to 7 correspond to the internal short circuit layer, the external short circuit layer, the positive electrode tab connected to the internal short circuit layer, the positive electrode tab connected to the external short circuit layer, the negative electrode tab connected to the internal short circuit layer, the negative electrode tab connected to the external short circuit layer, and the short circuit portion, respectively. In the thermal circuit model MD1, the temperatures of regions 1 to 7 are denoted as T ₁ to T ₇ , and the thermal resistance between regions i and j is denoted as R _ij (i, j = 1 to 7). For example, temperature T ₁ represents the temperature of the internal short circuit layer (battery temperature), temperature T ₂ represents the temperature of the external short circuit layer (battery temperature), and thermal resistance R ₁₂ represents the thermal resistance between the internal short circuit layer and the external short circuit layer. The temperatures of the other regions and the thermal resistance between the other regions are also as shown in FIG. 9.

From the thermal circuit model MD1 shown in FIG. 9, the heat conduction equation for temperatures T ₁ to T ₇ is expressed as in Equation 8.

Here, C _pi is the specific heat of region i, V _i is the volume of region i, and ρ _i is the density of region i. Q ₁ to Q ₇ represent heat generated by current flow (Joule heat and electrochemical reaction heat). For simplification, in the heat conduction equation shown in Equation 8, it is assumed that there is no heat release to the outside of the battery, and all heat generated by the short circuit current is used to increase the temperature of the battery. Alternatively, a heat conduction equation considering heat release to the outside of the battery may be used.

Equation 9 can be obtained by rearranging the terms in equation 8 and rewriting the time derivative on the left side as a difference. In equation 9, Δt represents the time step size of the calculation, and the superscripts k and k+1 represent the number of steps (time steps).

In the formula 9, by setting α _j =Δt/ρ _j C _pj V _j and rearranging, the formula 10 is obtained.

In the formula 10, the heat generation amounts Q ₁ ^k to Q ₇ ^k in each region are expressed as follows:

Here, the current I _in flowing through the internal short-circuit layer, the current I _ex flowing through the external short-circuit layer, and the current I _s flowing through the short circuit portion are described as in Equations 5 to 7, respectively. In Equations 5 to 7 and Equation 11, the only unknown parameter is the short-circuit resistance R _s . In order to clearly show that the heat amounts Q ₁ ^k to Q ₇ ^k are functions of the short-circuit resistance R _s , if we write Q _i ^k =Q _i ^k (R _s ), Equation 10 can be rewritten as follows:

In order to estimate the short-circuit resistance _Rs , the short-circuit resistance _Rs is added as a state quantity (=latent variable) to Expression 12. The detection device 10 has the calculation unit 11 function as an observer, and solves the eight state variables shown in Expression 13 using eight equations.

Also, a disturbance term may be added to perform state estimation while suppressing disturbances of the system and observation. Although the disturbance term is not essential, it may be preferable to add it in order to improve the progress of calculations. The equation with the disturbance term added is written as shown in Equation 14. In Equation 14, v _T1 ^k to v _T7 ^k , v _Rs ^k are disturbance terms.

Equation 14 can be rewritten as follows:

Here, x _k is a vector (state vector) having state quantities as elements, v _k is a vector (disturbance vector) having disturbance quantities as elements, and f represents a nonlinear differential equation shown in Equation 14.

In the first embodiment, the temperature sensor 250 is attached to the positive electrode tab 211. However, even if an internal short circuit occurs, it is not possible to know in which layer the internal short circuit has occurred. Therefore, even if an internal short circuit occurs, it is not possible to know whether the measurement value of the temperature sensor 250 represents the temperature of the positive electrode tab 211 connected to the internal short circuit layer or the temperature of the positive electrode tab 211 connected to the external short circuit layer. However, since the temperature rise of the tab of the external short circuit layer is more gradual than the temperature rise of the tab of the internal short circuit layer, a safety margin can be ensured by considering the measurement value of the temperature sensor 250 as the temperature of the positive electrode tab 211 connected to the external short circuit layer. In the following, it is assumed that the measurement value of the temperature sensor 250 is the temperature of the positive electrode tab 211 connected to the external short circuit layer.

The observation equation is expressed as in Equation 16.

Here, y _k is the observed value, c ^T is the observed vector, and w _k is the observed disturbance. Since the temperature T ₄ ^k of the positive electrode tab 211 connected to the external short circuit layer is the fourth component of x _k , c ^T is expressed as follows. The T on the right shoulder of c represents transposition.

In the observation equation above, we have assumed that there is only one observation. Alternatively, there may be multiple observations.

The detection device 10 according to the first embodiment utilizes a particle filter to sequentially calculate time updates of a time series model represented by the state equation of Expression 15 and the observation equation of Expression 16 to obtain the internal resistance _Rs . The detection device 10 detects an internal short circuit in the energy storage element 100 based on the obtained internal resistance _Rs .

The procedure for detecting an internal short circuit will now be described.
10 is a flowchart illustrating the procedure for detecting an internal short circuit in the embodiment 1. The calculation unit 11 of the detection device 10 provides an initial value of k=1 (step S101). The calculation unit 11 may provide the environmental temperature as the initial value of the temperature, and a provisional value set in advance as the initial value of the short circuit resistance.

Next, the calculation unit 11 generates N particles for each state variable (step S102), where N is usually a number between 10 ² and 10 ⁶ .

Next, the calculation unit 11 generates random numbers corresponding to v _k for i=1, 2, . . . , N (step S103).

The calculation unit 11 updates the particle states to the particle states at the next time step by performing calculations based on equation 18 for all N particles (step S104).

The calculation unit 11 acquires the sensor output of the temperature sensor 250 through the input unit 13 (step S105), and calculates particle weights _Pk ⁽ⁱ⁾ for all N particles based on the observation equation (step S106). The particle weight is the probability (likelihood) that the observation value _yk is observed when the state vector _xk of the particle i is obtained, and is described by the following equation.

The calculation unit 11 normalizes the particle weight P _k ⁽ⁱ⁾ calculated in step S106 based on the following equation (step S107).

The calculation unit 11 calculates a vector that is a weighted average of the particle weights and the state vector as an estimate by the particle filter (step S108). The calculation formula is as shown in Equation 21. This calculation provides an estimate of the temperature of each region and an estimate of the short-circuit resistance.

Next, the calculation unit 11 estimates the presence or absence of an internal short circuit in the energy storage element 100 based on the estimated value of the short circuit resistance. For example, the calculation unit 11 determines whether or not the estimated value of the short circuit resistance is less than a threshold value (step S109). The threshold value is set arbitrarily.

If the estimated value of the short-circuit resistance is not less than the threshold value (S109: NO), it is estimated that no internal short circuit has occurred in the energy storage element 100. If it is estimated that no internal short circuit has occurred, the calculation unit 11 resamples the particles (stratified sampling) for estimation of the next time step (step S110). The calculation unit 11 determines that the state vector x _k ⁽ⁱ⁾ at time step k is restored and sampled in proportion to p _k ⁽ⁱ⁾ , and determines the state vector at time step k+1. After resampling the particles, the calculation unit 11 returns the process to step S102.

If the estimated short-circuit resistance is less than the threshold value (S109: YES), it is estimated that an internal short circuit has occurred in the energy storage element 100. If it is estimated that an internal short circuit has occurred, the calculation unit 11 notifies the occurrence of an internal short circuit (step S111). For example, the calculation unit 11 generates text information indicating that an internal short circuit has occurred, and outputs the text information to the display device 20 from the output unit 14, thereby causing the display device 20 to display the text information. Alternatively, the calculation unit 11 may notify a terminal device (not shown) of the text information indicating that an internal short circuit has occurred from the output unit 14. The calculation unit 11 may also urge the user to stop using or replace the energy storage element 100, or may ask the user to decide whether to stop using or replace the energy storage element 100.

As described above, the detection device 10 in the first embodiment detects an internal short circuit in the energy storage element 100 based on the sensor output of the temperature sensor 250 that measures the temperature of the conductive tab. When an internal short circuit occurs in the energy storage element 100, the conductive tab heats up more quickly than the container 110 and the electrode body 200, and therefore the detection device 10 can detect the internal short circuit early by estimating the short circuit resistance based on the temperature of the conductive tab.

As long as the temperature inside the battery can be accurately measured with almost no time lag, the installation position of the temperature sensor 250 is not limited to the conductive tab. For example, the temperature sensor 250 may be attached to the electrode terminals 310, 320 (more preferably, the rivet portion of the electrode terminals 310, 320). Alternatively, the temperature sensor 250 may be attached to the current collector 140 or a bus bar (not shown). Alternatively, the temperature sensor 250 may be attached to the outer surface of the container 110 that contains the electrode body 200. When the electrode body 200 is covered with an insulating bag and in contact with the inner surface of the container 110, the temperature of the container 110 rises quickly with the temperature rise of the electrode body 200. For this reason, an internal short circuit can be detected early by estimating the short circuit resistance based on the temperature of the container 110. In particular, when the electrode body 200 is in contact with the inner long side of the container 110 via the insulating bag, the temperature sensor 250 may be attached to the outer long side of the container 110.

The detection device 10 in the first embodiment estimates the short-circuit resistance using a particle filter. A particle filter is a filter method that targets state space models that have nonlinearity and non-Gaussianity, and can target more general state space models without assuming linearity or Gaussianity. In addition, the particle filter has a relatively simple algorithm and can be easily implemented in the detection device 10.

(Embodiment 2)
In the second embodiment, a configuration will be described in which a temperature sensor 250 is attached to a tab bundling section where a plurality of positive electrode tabs 211 (or a plurality of negative electrode tabs 221) are bundled, and an internal short circuit is detected based on the sensor output of this temperature sensor 250.

In the second embodiment, the temperature sensor 250 is attached to a tab bundling section where multiple positive electrode tabs 211 (or multiple negative electrode tabs 221) are bundled. In the second embodiment, it is assumed that the temperature of the tab of the internal short circuit layer is the same as the temperature of the tab of the external short circuit layer.

FIG. 11 is a schematic diagram showing a configuration example of a thermal circuit model MD2 in the second embodiment. The thermal circuit model MD2 is a model for simulating a thermal phenomenon of the energy storage element 100 by using the temperatures of a plurality of regions that divide the energy storage element 100 and the thermal resistance between the regions as parameters. The thermal circuit model MD2 shown in FIG. 11 divides the energy storage element 100 into five regions (regions 1 to 5). Regions 1 to 5 correspond to the internal short-circuit layer, the external short-circuit layer, the positive electrode tab, the negative electrode tab, and the short circuit portion, respectively. In the thermal circuit model MD2, the temperatures of regions 1 to 5 are represented as T ₁ to T ₅ , and the thermal resistance between region i and region j is represented as R _ij (i, j = 1 to 5). For example, temperature T ₁ represents the temperature of the internal short-circuit layer (battery temperature), temperature T ₂ represents the temperature of the external short-circuit layer (battery temperature), and thermal resistance R ₁₂ represents the thermal resistance between the internal short-circuit layer and the external short-circuit layer. The temperatures in the other regions and the thermal resistances between the other regions are also as shown in FIG.

From the thermal circuit model MD2 shown in FIG. 11, the heat conduction equation for temperatures T ₁ to T ₅ is expressed as in Equation 22.

Here, C _pi is the specific heat of region i, V _i is the volume of region i, and ρ _i is the density of region i. Q ₁ to Q ₅ represent heat generated by current flow (Joule heat and electrochemical reaction heat). For simplification, in the heat conduction equation shown in Equation 22, it is assumed that there is no heat release to the outside of the battery, and all heat generated by the short circuit current is used to increase the temperature of the battery. Alternatively, a heat conduction equation considering heat release to the outside of the battery may be used.

By rearranging the terms in Equation 22 and rewriting the time derivative on the left side as a difference, we obtain Equation 23. In Equation 23, Δt represents the time step size of the calculation, and the superscripts k and k+1 represent the number of steps (time steps).

In formula 23, by setting α _j =Δt/ρ _j C _pj V _j and rearranging, formula 24 is obtained.

In equation 24, the heat generation amounts Q ₁ ^k to Q ₅ ^k in each region are expressed as follows:

Here, the current I _in flowing through the internal short-circuit layer, the current I _ex flowing through the external short-circuit layer, and the current I _s flowing through the short circuit portion are written as in Equations 5 to 7, respectively, as described in the first embodiment. In Equations 5 to 7 and Equation 25, the only unknown parameter is the short-circuit resistance R _s . In order to clearly show that the heat amounts Q ₁ ^k to Q ₅ ^k are functions of the short-circuit resistance R _s , if Q _i ^k =Q _i ^k (R _s ) is written, Equation 24 can be rewritten as follows:

In order to estimate the short-circuit resistance _Rs , the short-circuit resistance _Rs is added as a state quantity (=latent variable) to Expression 26. The detection device 10 causes the calculation unit 11 to function as an observer, and solves the six state variables shown in Expression 27 using six equations.

Moreover, a disturbance term may be added to suppress disturbances in the system or observation. Although the disturbance term is not essential, it is preferable to add it in order to improve the progress of the calculation. The equation with the disturbance term added is written as shown in Equation 28. In Equation 28, v _T1 ^k to v _T5 ^k , v _Rs ^k are disturbance terms.

Number 28 can be rewritten as follows:

Here, x _k is a vector (state vector) having state quantities as elements, v _k is a vector (disturbance vector) having disturbance quantities as elements, and f represents a nonlinear differential equation shown in Equation 28.

In the observation, only a portion of the state quantities are observed. In the following, it is assumed that the measurement value of the temperature sensor 250 is the temperature of the bundling part where the positive electrode tabs 211 are bundled.

The observation equation is expressed as in equation 30.

Here, y _k is the observed value, c ^T is the observed vector, and w _k is the observed disturbance. Since the temperature T ₃ ^k of the binding portion of the positive electrode tab 211 is the third component of x _k , c ^T is expressed as follows. The T on the right shoulder of c represents transposition.

In the observation equation above, we have assumed that there is only one observation. Alternatively, there may be multiple observations.

As in the first embodiment, the detection device 10 uses a particle filter to sequentially calculate time updates of a time series model represented by the state equation of Expression 29 and the observation equation of Expression 30 to obtain the internal resistance _Rs . The detection device 10 detects an internal short circuit in the energy storage element 100 based on the obtained internal resistance _Rs .

As described above, in the second embodiment, the temperature sensor 250 is provided at the tab bundling section where multiple positive electrode tabs 211 (or multiple negative electrode tabs 221) are bundled, so that the temperature sensor 250 can be easily attached. In the second embodiment, the thermal circuit model MD2 is simplified and the number of parameters is reduced, making calculations easier.

(Embodiment 3)
In the third embodiment, a state estimation algorithm using an ensemble Kalman filter will be described. That is, the detection device 10 in the third embodiment uses the ensemble Kalman filter to sequentially calculate time updates of a time series model represented by the state equation of Expression 15 and the observation equation of Expression 16 to obtain the internal resistance _Rs . The detection device 10 detects an internal short circuit in the energy storage element 100 based on the obtained internal resistance _Rs .

12 is a flow chart for explaining the procedure for detecting an internal short circuit in the third embodiment. The calculation unit 11 of the detection device 10 provides an initial value of k=1 (step S121). The calculation unit 11 may provide the ambient temperature as the initial value of the temperature, and a provisional value set in advance as the initial value of the short circuit resistance. The variances of the disturbance term _vk in the state equation and the disturbance term _wk in the observation equation are respectively _Qk and _Rk .

Next, the calculation unit 11 generates N particles for each state variable (step S122), where N is usually a number between 10 ² and 10 ⁶ .

Next, the calculation unit 11 generates random numbers corresponding to _vk for i = 1, 2, ..., N (step S123). It is assumed that _vk follows a normal distribution and that the variance is known.

The calculation unit 11 updates the particle states to the particle states at the next time step by performing calculations based on equation 18 for all N particles (step S124).

The calculation unit 11 calculates the difference x _k ⁽ⁱ⁾ — bar between the state vector of each particle where i=1, 2, . . . , N and the average value of the state vectors of all the particles (step S125). x _k ⁽ⁱ⁾ — bar is expressed by Equation 33.

The calculation unit 11 calculates the covariance matrix P _k of the state quantity predicted values for all particles (step S126). The covariance matrix P _k is expressed by Equation 34.

The calculation unit 11 acquires the sensor output of the temperature sensor 250 through the input unit 13 (step S127). The acquired sensor output of the temperature sensor 250 gives the observed value y _k ⁱ of each particle at time step k.

The calculation unit 11 calculates the measurement error r _k ⁱ of the i-th particle at the time step k (step S128), where w _k is the observed disturbance. The measurement error r _k ⁱ is expressed by Equation 35.

The calculation unit 11 calculates the Kalman gain K _k at the time step k (step S129). The Kalman gain K _k is expressed by Equation 36.

The calculation unit 11 calculates an estimate x _k ⁽ⁱ⁾ _hat of the i-th particle (step S130). The estimate x _k ⁽ⁱ⁾ _hat is expressed by Equation 37. That is, the calculation unit 11 corrects the initial prediction value of Equation 32 using the observation error r _k ⁱ of Equation 35 and the Kalman gain K _k of Equation 36.

The calculation unit 11 calculates the average value x _k _hat of each particle (step S131). The average value x _k _hat of each particle represents a state vector estimate obtained by the ensemble Kalman filter, and is calculated by the following formula.

The estimated value (average value x _k _hat of each particle) obtained by Equation 38 includes an estimated value of the temperature of each region and an estimated value of the short-circuit resistance. The calculation unit 11 estimates the presence or absence of an internal short circuit in the energy storage element 100 based on the estimated value of the short-circuit resistance. For example, the calculation unit 11 determines whether or not the estimated value of the short-circuit resistance is less than a threshold value (step S132). The threshold value is set arbitrarily.

If the estimated short-circuit resistance is not less than the threshold value (S132: NO), it is estimated that no internal short circuit has occurred in the energy storage element 100. If it is estimated that no internal short circuit has occurred, the calculation unit 11 returns the process to step S122 and executes the calculation for the next time step.

If the estimated short-circuit resistance is less than the threshold value (S132: YES), it is estimated that an internal short circuit has occurred in the energy storage element 100. If it is estimated that an internal short circuit has occurred, the calculation unit 11 notifies the occurrence of an internal short circuit (step S133). For example, the calculation unit 11 generates text information indicating that an internal short circuit has occurred, and outputs the text information to the display device 20 from the output unit 14, thereby causing the display device 20 to display the text information. Alternatively, the calculation unit 11 may notify a terminal device (not shown) of the text information indicating that an internal short circuit has occurred from the output unit 14. The calculation unit 11 may also urge the user to stop using or replace the energy storage element 100, or may ask the user to decide whether to stop using or replace the energy storage element 100.

The detection device 10 in the third embodiment estimates the short-circuit resistance using an ensemble Kalman filter. The ensemble Kalman filter is a filter method targeted at state space models that have nonlinearity and non-Gaussianity, and can be used for more general state space models. The ensemble Kalman filter has a relatively simple algorithm and can be easily implemented in the detection device 10.

(Embodiment 4)
In the fourth embodiment, a state estimation algorithm using an extended Kalman filter will be described. That is, the detection device 10 in the fourth embodiment uses an extended Kalman filter to sequentially calculate time updates of a time series model represented by the state equation of Expression 15 and the observation equation of Expression 16 to obtain the internal resistance _Rs . The detection device 10 detects an internal short circuit in the energy storage element 100 based on the obtained internal resistance _Rs .

13 is a flow chart for explaining the procedure for detecting an internal short circuit in the fourth embodiment. The calculation unit 11 of the detection device 10 provides an initial value of k=1 (step S141). The calculation unit 11 may provide the ambient temperature as the initial value of the temperature, and a provisional value set in advance as the initial value of the short circuit resistance. The variances of the disturbance term _vk in the state equation and the disturbance term _wk in the observation equation are respectively _Qk and _Rk . An initial variance-covariance matrix P is assumed.

The calculator 11 calculates the prior state estimate x ⁻ _k+1 _hat by the following equation (step S142).

The calculation unit 11 derives the Jacobian matrix of the nonlinear transformation f by the following procedure (step S143). For example, for a three-component vector represented by equation 40, if the nonlinear transformation f is expressed as equation 41, the Jacobian is calculated by equation 42. The calculation unit 11 may derive the Jacobian in advance and store it in the storage unit 12.

The calculation unit 11 calculates the a priori error covariance matrix P ⁻ _k+1 by the following equation (step S144): Here, the state transition matrix A _k is expressed by equation 44.

The calculation unit 11 calculates the Kalman gain g _k (step S145). The Kalman gain g _k is expressed by Equation 45.

The calculation unit 11 acquires the sensor output of the temperature sensor 250 through the input unit 13 (step S146). The acquired sensor output of the temperature sensor 250 gives the observed value y _k at the time step k.

The calculator 11 calculates the a posteriori state estimate x _k+1 —hat and the a posteriori error covariance matrix P _k by the following equations (step S147).

The estimate (post-state estimate x _k+1 _hat) obtained by Equation 46 includes an estimate of the temperature of each region and an estimate of the short-circuit resistance. The calculation unit 11 estimates the presence or absence of an internal short circuit in the energy storage element 100 based on the estimate of the short-circuit resistance. For example, the calculation unit 11 determines whether the estimate of the short-circuit resistance is less than a threshold value (step S148). The threshold value is set arbitrarily.

If the estimated short-circuit resistance is not less than the threshold value (S148: NO), it is estimated that no internal short circuit has occurred in the energy storage element 100. If it is estimated that no internal short circuit has occurred, the calculation unit 11 returns the process to step S142 and executes the calculation for the next time step.

If the estimated short-circuit resistance is less than the threshold value (S148: YES), it is estimated that an internal short circuit has occurred in the energy storage element 100. If it is estimated that an internal short circuit has occurred, the calculation unit 11 notifies the occurrence of an internal short circuit (step S149). For example, the calculation unit 11 generates text information indicating that an internal short circuit has occurred, and outputs the text information to the display device 20 from the output unit 14, thereby causing the display device 20 to display the text information. Alternatively, the calculation unit 11 may notify a terminal device (not shown) of the text information indicating that an internal short circuit has occurred from the output unit 14. The calculation unit 11 may also urge the user to stop using or replace the energy storage element 100, or may ask the user to decide whether to stop using or replace the energy storage element 100.

The detection device 10 in the fourth embodiment estimates the short-circuit resistance using an extended Kalman filter. The extended Kalman filter is a method that enables the application of a Kalman filter by linearly approximating a nonlinear model near a representative value such as the average value. The extended Kalman filter has a small computational load and can be realized by an inexpensive device.

(Embodiment 5)
In the fifth embodiment, a state estimation algorithm using an unscented Kalman filter will be described. That is, the detection device 10 in the fifth embodiment uses the unscented Kalman filter to sequentially calculate time updates of a time series model represented by the state equation of Expression 15 and the observation equation of Expression 16, and obtains the internal resistance _Rs . The detection device 10 detects an internal short circuit in the energy storage element 100 based on the obtained internal resistance _Rs .

14 is a flow chart for explaining the procedure for detecting an internal short circuit in the fifth embodiment. The calculation unit 11 of the detection device 10 provides an initial value of k=1 (step S161). The calculation unit 11 may provide the ambient temperature as the initial value of the temperature, and a provisional value set in advance as the initial value of the short circuit resistance. The variances of the disturbance term _vk in the state equation and the disturbance term _wk in the observation equation are respectively _Qk and _Rk . An initial variance-covariance matrix P is assumed.

The calculation unit 11 generates calculation points called sigma points by using the estimated value x ⁻ _k obtained in a certain calculation step and the variance-covariance matrix P _k (step S162). If the (2n+1) generated sigma points are numbered as in Expression 47, the jth sigma point (j is an integer satisfying −n≦j≦n) is expressed as in Expression 48.

where sig(j) is a function that gives -1 when j<0, 0 when j=0, and +1 when 0<j. κ is a positive adjustment parameter.

The weight w _j of each sigma point is expressed as w _j =κ/2(n+κ) when j≠0, and as w ₀ =κ/(n+κ) when j=0.

The calculation unit 11 updates the states, prior state estimates, and prior error covariance matrix of all sigma points as follows (step S163).

Since the calculation unit 11 has updated the prior state estimate and the prior error covariance matrix, it recalculates the sigma point using the following formula (step S164).

The calculation unit 11 updates the observed sigma point according to the following formula (step S165).

The calculator 11 calculates the prior observation estimated value y ⁻ _k+1 _hat by the following equation (step S166).

The calculation unit 11 calculates the covariance matrix P ⁻ _yy,k+1 of the prior observation errors by the following equation (step S167).

The calculation unit 11 calculates the covariance matrix P ⁻ _xy,k+1 of the prior state and observation errors by the following equation (step S168).

The calculation unit 11 calculates the Kalman gain g _k by the following equation (step S169).

The calculation unit 11 acquires the sensor output of the temperature sensor 250 through the input unit 13 (step S170). The acquired sensor output of the temperature sensor 250 gives the observed value y _k+1 at time step k+1.

The calculator 11 multiplies the difference between the observed value y _k+1 and the prior observed estimated value y ⁻ _k+1 _hat by the Kalman gain g _k to perform state estimation at time step k+1 (step S171).

The calculation unit 11 calculates the covariance matrix P _k+1 of the a posteriori observation errors by the following equation (step S172).

The posterior observation estimate (x _k+1 _hat) obtained by Equation 56 includes an estimate of the temperature of each region and an estimate of the short-circuit resistance. The calculation unit 11 estimates the presence or absence of an internal short circuit in the energy storage element 100 based on the estimate of the short-circuit resistance. For example, the calculation unit 11 determines whether the estimate of the short-circuit resistance is less than a threshold value (step S173). The threshold value is set arbitrarily.

If the estimated short-circuit resistance is not less than the threshold value (S173: NO), it is estimated that no internal short circuit has occurred in the energy storage element 100. If it is estimated that no internal short circuit has occurred, the calculation unit 11 returns the process to step S162 and executes the calculation for the next time step.

If the estimated short-circuit resistance is less than the threshold value (S173: YES), it is estimated that an internal short circuit has occurred in the energy storage element 100. If it is estimated that an internal short circuit has occurred, the calculation unit 11 notifies the occurrence of an internal short circuit (step S174). For example, the calculation unit 11 generates text information indicating that an internal short circuit has occurred, and outputs the text information to the display device 20 from the output unit 14, thereby causing the display device 20 to display the text information. Alternatively, the calculation unit 11 may notify a terminal device (not shown) of the text information indicating that an internal short circuit has occurred from the output unit 14. The calculation unit 11 may also urge the user to stop using or replace the energy storage element 100, or may ask the user to decide whether to stop using or replace the energy storage element 100.

The detection device 10 in the fifth embodiment estimates the short-circuit resistance using an unscented Kalman filter. The unscented Kalman filter sets multiple sample points called sigma points around the mean value and estimates the covariance matrix based on the statistical properties of these points. The unscented Kalman filter performs better than the extended Kalman filter in problems with strong nonlinearity.

(Embodiment 6)
In the sixth embodiment, a configuration will be described in which the detection device 10 detects a sign of an internal short circuit based on the short-circuit resistance _Rs .

15 is a flow chart for explaining the procedure for detecting a sign of an internal short circuit. The calculation unit 11 of the detection device 10 sequentially estimates the short circuit resistance _Rs in the energy storage element 100 using the same procedure as in the first to fifth embodiments (step S201).

The calculation unit 11 judges whether the estimated short-circuit resistance _Rs has decreased by a predetermined percentage from a reference value (step S202). The reference value is set to an average value of the short-circuit resistance _Rs in a state where no internal short circuit has occurred. The percentage set as the threshold is set appropriately. For example, if a sign of an internal short circuit is detected when the short-circuit resistance _Rs has decreased by 10% or more from the reference value, the threshold is set to 10%.

When the estimated short-circuit resistance R _s has not decreased by a predetermined percentage from the reference value (S202: NO), the calculation unit 11 returns the process to step S201 and continues estimating the short-circuit resistance R _s .

When the estimated short-circuit resistance R _s is lower than the reference value by a predetermined percentage (S202: YES), the calculation unit 11 estimates that a sign of an internal short circuit has occurred. When the calculation unit 11 determines that a sign of an internal short circuit has occurred, it notifies the user of the sign of an internal short circuit (step S203). For example, the calculation unit 11 generates text information indicating that a sign of an internal short circuit has been detected, and outputs the text information to the display device 20 from the output unit 14, thereby causing the display device 20 to display the text information. Alternatively, the calculation unit 11 may notify a terminal device (not shown) of the text information indicating that a sign of an internal short circuit has been detected from the output unit 14. In addition, the calculation unit 11 may urge the user to stop using or replace the energy storage element 100, or may ask the user to decide whether to stop using or replace the energy storage element 100.

In the sixth embodiment, the sign of an internal short circuit is detected by determining whether the estimated internal resistance _Rs has decreased by a predetermined percentage from the reference value. Alternatively, the calculation unit 11 may detect the sign of an internal short circuit based on the determination criterion of whether the estimated internal resistance _Rs has decreased a set number of times (e.g., five times).

In the first to sixth embodiments, the configuration is such that an internal short circuit, including a precursor, is detected based on the sensor output of the temperature sensor 250 that measures the temperature of the conductive tab. However, when a large current is output from the energy storage element 100, such as when a motor sports car is running or heavy machinery is used with a large torque, the conductive tab may reach a high temperature. In this case, the conductive tab reaches a high temperature, but this is within the range of normal use and is not an abnormality such as an internal short circuit. In order to distinguish between a case in which the conductive tab reaches a high temperature due to normal use and a case in which the conductive tab reaches a high temperature due to an internal short circuit, a heat transfer calculation based on the current flowing through the energy storage element 100 may be performed at the same time. The detection device 10 compares the temperature of the conductive tab measured by the temperature sensor 250 with the temperature of the conductive tab estimated from the current of the energy storage element 100, and if the two values are close, it can be determined that the temperature rise is not due to an internal short circuit but is due to normal use. On the other hand, if a temperature rise that cannot be caused by the current flowing through the energy storage element 100 is measured, the detection device 10 may determine that an internal short circuit may have occurred.

(Seventh embodiment)
In the seventh embodiment, a configuration is described in which, when an internal short circuit of the energy storage element 100 is detected, the current path between the electrode terminal 310 and the conductive tab (the positive electrode tab 211 or the negative electrode tab 221) is cut off.

The energy storage element 100 in embodiment 7 is equipped with a circuit breaker that cuts off the current path between the electrode terminal 310 and the conductive tab (positive electrode tab 211 or negative electrode tab 221) when an internal short circuit in the energy storage element 100 is detected by the detection device 10.

Figure 16 is a partial cross-sectional view of the energy storage element 100 in the seventh embodiment, and Figure 17 is a perspective view showing an example of the implementation of a circuit breaker. In addition to the configuration described in the first embodiment, the energy storage element 100 includes a control board 150, a control circuit 151, and a semiconductor switching element 152 (hereinafter referred to as FET 152). These are mounted, for example, in a space provided between the cover 112 of the energy storage element 100 and the current collector 140. In the seventh embodiment, the current collector 140 is divided into a first current collector 140a and a second current collector 140b. The first current collector 140a and the second current collector 140b are arranged with a gap provided between them. A positive electrode tab 211 is connected to the first current collector 140a, and a terminal electrode 310 is connected to the second current collector 140b.

The control board 150 is provided on the first current collector 140a and the second current collector 140b. The control board 150 is provided with rectangular cutouts 150a and 150b. The control circuit 151 is mounted on the control board 150. The FET 152 is mounted on the exposed surface of the first current collector 140a exposed from the cutout 150a.

The control circuit 151 acquires the detection result from the above-mentioned detection device 10, and turns on/off the FET 152 according to the acquired detection result. In the seventh embodiment, for convenience, the control circuit 151 and the detection device 10 are separate entities. Alternatively, the control circuit 151 and the detection device 10 may be integrated.

The FET 152 is, for example, a power MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor) for switching. The gate terminal 152G of the FET 152 is connected to the control circuit 151 via a printed wiring (not shown) formed on the control board 150. The drain terminal 152D is connected to the exposed surface of the first current collector 140a exposed from the notch 150a. The source terminal 152S is connected to the exposed surface of the second current collector 140b exposed from the notch 150b of the control board 150, across the gap between the first current collector 140a and the second current collector 140b.

The control circuit 151 can connect the drain terminal 152D and the source terminal 152S by applying a predetermined voltage (gate voltage) to the gate terminal 152G of the FET 152. As a result, the current path between the electrode terminal 310 and the positive electrode tab 211 is connected. On the other hand, the control circuit 151 can cut off the connection between the drain terminal 152D and the source terminal 152S by setting the gate voltage to zero. As a result, the current path between the electrode terminal 310 and the positive electrode tab 211 is cut off.

In the seventh embodiment, the FET 152 is disposed in the current path between the electrode terminal 310 and the positive electrode tab 211. Alternatively, the FET 152 may be disposed in the current path between the electrode terminal 320 and the negative electrode tab 221.

In the seventh embodiment, for the sake of simplicity, a configuration in which only one FET 152 is implemented has been described. Alternatively, the energy storage element 100 may further include an FET 152 in which the drain terminal 152D is connected to the second current collector 140b and the source terminal 152S is connected to the first current collector 140a.

In the seventh embodiment, the configuration in which the energy storage element 100 includes an FET 152 as a circuit breaker that breaks the current path between the electrode terminal 310 and the conductive tab (positive electrode tab 211 or negative electrode tab 221) has been described. Alternatively, any circuit breaker may be used, such as a mechanical switch that is turned on/off by the control circuit 151, a switch using a bimetal that is deformed by heating by the control circuit 151, or a fuse that melts by heating by the control circuit 151. In addition, when the energy storage element 100 includes multiple electrode bodies 200, the control circuit 151 may break only the current path leading to the electrode body 200 in which an internal short circuit has occurred.

Figure 18 is a flowchart explaining the procedure of the process executed by the control circuit 151. The control circuit 151 obtains the detection result from the detection device 10 and determines whether or not an internal short circuit has occurred in the storage element 100 (step S301).

If the control circuit 151 determines that no internal short circuit has occurred in the storage element 100 (S301: NO), it maintains the on state of the FET 152 (step S302) and returns the process to step S301.

When the control circuit 151 determines that an internal short circuit has occurred in the storage element 100 (S301: YES), the control circuit 151 turns off the FET 152 to interrupt the current path between the electrode terminal 310 and the positive electrode tab 211 (step S303).

As described above, in embodiment 7, when an internal short circuit of the energy storage element 100 is detected by the detection device 10, the control circuit 151 cuts off the current path between the electrode terminal 310 and the conductive tab (positive electrode tab 211 or negative electrode tab 221), thereby preventing the energy storage element 100 from becoming too hot.

In the seventh embodiment, a configuration in which a current path is interrupted using a FET 152 has been described. Alternatively, a semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor), a thyristor, or a bipolar transistor may be used. Also, a bimetal may be used for the conductive tab, and the conductive tab may be distorted and cut off due to an increase in temperature. Furthermore, a configuration in which a current path is interrupted by removing the constraint of a mechanical spring may be used. Furthermore, a configuration in which a current path is interrupted by melting may be used.

In the seventh embodiment, when the detection device 10 detects an internal short circuit in the energy storage element 100, the control circuit 151 is configured to cut off the current path. Alternatively, when the detection device 10 detects a sign of an internal short circuit in the energy storage element 100, the control circuit 151 may cut off the current path. Since cutting off the current path may cause an operating device or a traveling vehicle to suddenly stop, the control circuit 151 may cut off the current path after confirming that the device or vehicle in which the energy storage element 100 is mounted has stopped.

The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the claims, not by the above meaning, and is intended to include all modifications within the meaning and scope of the claims.

For example, in the first to seventh embodiments, the detection method of an internal short circuit is described using the storage element 100 having the stacked electrode body 200 as an example, but the detection target for an internal short circuit may be a storage element having a wound electrode body. However, in the stacked electrode body 200, the positive electrode plates (or the negative electrode plates) are electrically connected to each other only through the positive electrode tab 211 (or the negative electrode tab 221), whereas in the wound electrode body, the positive electrode plates (or the negative electrode plates) are connected to each other not only through the tab but also through the winding part. Therefore, in the wound electrode body, even if the conductive tab is cut, the short circuit continues through the winding part. The effect of the present application is more effectively exerted in the storage element 100 having the stacked electrode body 200 than in the storage element having the wound electrode body.

The energy storage element in the embodiment may be a laminated type energy storage element. FIG. 19 is an external perspective view showing a laminated type energy storage element 500, and FIG. 20 is an exploded perspective view showing the laminated type energy storage element 500. The energy storage element 500 includes an exterior body 510 made of a laminate film, and a positive electrode lead terminal 520 and a negative electrode lead terminal 530 that protrude outward from both ends of the energy storage element 500 in the longitudinal direction. A power generation element 540 and an electrolyte (not shown) are stored inside the exterior body 1. The power generation element 540 shown as an example in FIG. 20 has a structure in which strip-shaped positive and negative electrodes are wound into an elongated cylindrical shape.

The exterior body 510 is formed into a cylindrical shape by stacking two laminate films facing each other and welding their ends. The welding parts at both ends of the energy storage element 500 are welded while sandwiching the positive electrode lead terminal 520 and the negative electrode lead terminal 530, respectively. The exterior body 510 has a laminate structure in which, for example, a PE (polyethylene) welding layer, a PET (polyethylene terephthalate) layer, an aluminum layer, a PET layer, and a PE layer are stacked in this order.

The positive electrode lead terminal 520 is joined to the positive electrode of the power generating element 540 inside the exterior body 510. The positive electrode lead terminal 520 is made of, for example, a clad material (laminate) in which an aluminum layer and a titanium layer are roll-bonded.

The negative electrode lead terminal 530 is joined to the negative electrode of the power generating element 540 inside the exterior body 510. The negative electrode lead terminal 530 is composed of a laminate including, for example, a copper layer and titanium layers provided on both sides of the copper layer.

In the above-described energy storage element 500, the temperature sensor 250 is attached to the positive electrode lead terminal 520 (or the negative electrode lead terminal). The detection device 10 acquires the sensor output of the temperature sensor 250 and detects an internal short circuit of the energy storage element 500 based on the acquired sensor output. The method of detecting an internal short circuit is the same as the detection method described in the first to sixth embodiments. As in the seventh embodiment, the energy storage element may be provided with a circuit breaker that interrupts the current path via the positive electrode lead terminal 520 (or the negative electrode lead terminal 530) when an internal short circuit of the energy storage element 500 is detected.

REFERENCE SIGNS LIST 10 Detection device 11 Calculation unit 12 Memory unit 13 Input unit 14 Output unit 100 Energy storage element 110 Container 150 Control board 151 Control circuit 152 Semiconductor switching element 200 Electrode body 210 Positive electrode plate 211 Positive electrode tab 220 Negative electrode plate 221 Negative electrode tab 250 Temperature sensor 230 Separator 310 Electrode terminal 320 Electrode terminal PG State estimation program MD1, MD2 Thermal circuit model

Claims (9)

an acquisition unit that acquires a sensor output from a temperature sensor that measures a temperature of an electrode terminal and an electrode body having a conductive tab, the electrode body being connected to the electrode terminal via the conductive tab, for an energy storage element;
A detection unit that detects an internal short circuit in the electrode body based on the acquired sensor output ,
The detection unit is a detection device including an observer that estimates a short-circuit resistance of the internal short circuit based on the sensor output . The detection device according to claim 1 , wherein the detection unit estimates the short-circuit resistance of the internal short circuit by using a state estimation algorithm based on the sensor output and a thermal circuit model that simulates a thermal phenomenon of the energy storage element. The detection device according to claim 2 , wherein the thermal circuit model includes the electrode body, the conductive tab, and the short circuit portion as nodes, and includes parameters including temperature and heat capacity at each node, and thermal resistance between the nodes. The state estimation algorithm comprises:
Using a state equation expressing the time transition of state variables including the temperature and short circuit resistance of each node, the time transition of each state variable is calculated;
calculating a likelihood of a state estimation using an observation equation describing a relationship between the state variables and an observation amount including an observation temperature by the temperature sensor;
The detection apparatus according to claim 3 , further comprising the step of updating the estimates of the state variables in accordance with the likelihood of the determined state estimate. The detection device according to claim 2 , wherein the state estimation algorithm comprises a particle filter, an ensemble Kalman filter, an extended Kalman filter, or an unscented Kalman filter. The detection device according to claim 1 , further comprising: an output unit that outputs a detection result by the detection unit. The detection device according to claim 1 , wherein the electrode body is a wound electrode body. The computer
a temperature sensor for measuring a temperature of an electric storage element including an electrode terminal and an electrode body having a conductive tab, the electrode body being connected to the electrode terminal via the conductive tab, the temperature sensor acquiring a sensor output from the temperature sensor measuring a temperature of the conductive tab;
A detection method for detecting an internal short circuit in the electrode assembly using an observer that estimates a short circuit resistance of the internal short circuit in the electrode assembly based on an acquired sensor output. On the computer,
a temperature sensor for measuring a temperature of an electric storage element including an electrode terminal and an electrode body having a conductive tab, the electrode body being connected to the electrode terminal via the conductive tab, the temperature sensor acquiring a sensor output from the temperature sensor measuring a temperature of the conductive tab;
A computer program for executing a process of detecting an internal short circuit in the electrode assembly using an observer that estimates a short circuit resistance of the internal short circuit in the electrode assembly based on the acquired sensor output.

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