Estimation device, power storage module, estimation method, and computer program

Abstract

This estimating device estimates a state of charge of an electricity storage element provided with a negative electrode including a negative electrode active material containing Si. The estimating device is provided with a control unit which, on the basis of a charge / discharge history of the electricity storage element, determines whether to execute a first estimating method for estimating the state of charge of the electricity storage element using a relationship between the state of charge and the voltage of the electricity storage element.

Description

[Technical Field]

[0001] The present invention relates to an estimation device, an energy storage module, an estimation method, and a computer program for estimating the state of charge of an energy storage element. [Background technology]

[0002] Energy storage devices such as lithium-ion secondary batteries are used to store electrical energy and supply it as a power source when needed. Energy storage devices are used in a wide range of fields, including portable devices, power supply units, transportation equipment including automobiles and railways, and industrial equipment including aerospace and construction equipment.

[0003] Energy storage devices are required to have a high capacity depending on their applications. To address this issue, lithium-ion secondary batteries have been proposed that use, as the negative electrode active material, a Si-based material that has a theoretical capacity far greater than that of commonly used carbon materials such as graphite (see, for example, Patent Document 1).

[0004] When using an energy storage device, it is important to accurately estimate the state of charge of the device. One known method for estimating the state of charge of an energy storage device is the OCV method (voltage reference), which determines the state of charge based on the one-to-one correlation (SOC-OCV curve) between the state of charge (SOC) and open circuit voltage (OCV) of the energy storage device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-57767 Summary of the Invention [Problem to be solved by the invention]

[0006] When targeting energy storage elements that contain Si-based materials as the negative electrode active material, unlike energy storage elements that contain general carbon-based materials, there is a problem in that if the same method as for energy storage elements that contain carbon-based materials is used, the accuracy of estimating the state of charge of the energy storage element will decrease.

[0007] An object of the present disclosure is to provide an estimation device and the like that improves the accuracy of estimating the state of charge of an energy storage element that includes a negative electrode that includes a negative electrode active material containing Si. [Means for solving the problem]

[0008] An estimation device according to one aspect of the present disclosure estimates the state of charge of an energy storage device including a negative electrode containing a negative electrode active material containing Si. The estimation device includes a control unit that determines whether to execute a first estimation method for estimating the state of charge of the energy storage device using a relationship between the state of charge and the voltage of the energy storage device, based on a charge / discharge history of the energy storage device. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to improve the accuracy of estimating the state of charge of an energy storage device including a negative electrode that includes a negative electrode active material containing Si. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram illustrating a configuration example of a power storage device on which an estimation device according to a first embodiment is mounted. [Figure 2] FIG. 2 is a block diagram of an estimation device. [Figure 3] 1 is a graph showing the relationship between the number of cycles and the capacity retention rate in a Si-Gr mixed battery for each voltage range. [Figure 4] 1 is a graph showing the correlation between discharge capacity and voltage for each cycle in a Si-Gr mixed battery. [Figure 5] 1 is a graph showing the relationship between the number of cycles and the capacity retention rate in a Si-based battery for each voltage range. [Figure 6]1 is a graph showing the correlation between discharge capacity and voltage for each cycle in a Si-based battery. [Figure 7] 1 is a graph showing the relationship between the number of cycles and the capacity retention rate for a single positive electrode and a single negative electrode. [Figure 8] 10 is a flowchart illustrating an example of an estimation process procedure. [Figure 9] 1 is a graph showing the correlation between discharge capacity and voltage before and after deep discharge in a Si-based battery. DETAILED DESCRIPTION OF THE INVENTION

[0011] The estimation device estimates the state of charge of an energy storage device having a negative electrode including a negative electrode active material containing Si. The estimation device includes a control unit that determines whether to execute a first estimation method for estimating the state of charge of the energy storage device using a relationship between the state of charge and voltage of the energy storage device, based on a charge / discharge history of the energy storage device.

[0012] The control unit of the estimation device determines whether to execute a first estimation method based on the charge / discharge history of the storage element. The first estimation method may be a technique for estimating the state of charge based on the voltage of the storage element using the relationship (SOC-OCV curve) between the state of charge (SOC) and the voltage (OCV: Open Circuit Voltage) of the storage element.

[0013] The present inventors have found that in an energy storage device having a negative electrode containing a negative electrode active material containing Si, when the device is charged and discharged under specific conditions (for example, within a specific voltage range), a transient potential change occurs in the negative electrode. The transient potential change is a phenomenon in which charging and discharging under specific conditions changes the charge and discharge characteristics of the energy storage device, resulting in a temporary decrease in the capacity (capacity retention rate) of the energy storage device.

[0014] The inventors have found that even if the voltage of a storage element is the same, if the charge / discharge history is different, the state of charge corresponding to the voltage may be different, and further, if the voltage range in the charge / discharge of the storage element is different, the state of charge may be different. That is, the inventors have found that when estimating the state of charge of a storage element, it is necessary to take into account the voltage path information (voltage range) through which the storage element is used. According to the inventors' investigations, transient potential changes are eliminated by performing deep discharge.

[0015] According to the above configuration, the control unit determines whether to execute the first estimation method based on the charge / discharge history, that is, taking into account the voltage range, and therefore the accuracy of the estimation is good.

[0016] In the estimation device, the control unit may determine whether to execute the first estimation method depending on an estimation result regarding a transient potential change of the negative electrode.

[0017] According to the above configuration, the control unit determines whether to execute the first estimation method based on the estimation result regarding the transient potential change of the negative electrode of the storage element. As described above, when a transient potential change of the negative electrode occurs, the state of charge corresponding to the voltage may be different. By including the estimation result regarding the transient potential change of the negative electrode as a determination factor, the timing to execute the first estimation method is appropriately determined, and a decrease in the estimation accuracy by the first estimation method is suppressed.

[0018] In the estimation device, the control unit may determine to execute the first estimation method when the voltage of the storage element is within a voltage threshold range that does not cause a transient potential change of the negative electrode according to the Si content in the negative electrode active material.

[0019] According to the above configuration, the control unit determines whether the voltage is within a range in which a transient potential change does not occur at the negative electrode based on the charge / discharge history and the negative electrode composition, and if the voltage is within the range in which a transient potential change does not occur, executes the first estimation method. If the voltage is within the range in which a transient potential change occurs, there is a high possibility that the state of charge cannot be determined uniquely by the voltage. By executing the first estimation method only when the voltage is within the range in which a transient potential change does not occur, a decrease in estimation accuracy is suppressed.

[0020] In the estimation device, the control unit may determine to execute the first estimation method when the storage element is discharged beyond a deep discharge threshold corresponding to the Si content in the negative electrode active material. In this specification, the deep discharge threshold is a voltage value that is predetermined depending on the Si content in the negative electrode active material of the storage element, and means a voltage value that is slightly higher than the lowest voltage value (e.g., the discharge end voltage) in the dischargeable voltage range.

[0021] According to the above configuration, the control unit executes the first estimation method when the storage element is discharged beyond the deep discharge threshold. The transient potential change is eliminated by discharging beyond the deep discharge threshold (deep discharge). When the voltage of the storage element is equal to or lower than the deep discharge threshold, the first estimation method can be executed to accurately estimate the state of charge.

[0022] In the estimation device, a state-of-charge-voltage profile showing the relationship between the state of charge and voltage of the storage element has a first region whose shape changes due to a transient potential change of the negative electrode and a second region whose shape does not change, and the control unit may estimate the state of charge using the state-of-charge-voltage profile of the second region.

[0023] The state-of-charge-voltage profile showing the relationship between the state of charge and voltage of the energy storage element has a first region whose shape changes due to a transient potential change of the negative electrode, and a second region whose shape does not change. According to the above configuration, the control unit uses the state-of-charge-voltage profile of the second region whose shape does not change, i.e., which is not affected by the transient potential change, and therefore the accuracy of estimation by the first estimation method is good.

[0024] In the estimation device, when the control unit determines not to execute the first estimation method, the control unit may execute a second estimation method that estimates the state of charge of the storage element using an integrated value of the current flowing into and / or out of the storage element.

[0025] According to the above configuration, when the control unit does not execute the first estimation method, i.e., when it is estimated that a transient potential change of the negative electrode has occurred, it executes the second estimation method, which estimates the state of charge of the storage element using an integrated value of the current flowing into and / or out of the storage element. The second estimation method is an estimation method that is not affected by the presence or absence of a transient potential change of the negative electrode. The control unit improves the accuracy of estimating the state of charge by selectively executing the first estimation method or the second estimation method as appropriate depending on the state of the transient potential change of the negative electrode.

[0026] The power storage module includes a power storage element and the above-described estimation device.

[0027] The estimation method estimates the state of charge of an energy storage device having a negative electrode containing a negative electrode active material containing Si, and determines whether to execute a first estimation method for estimating the state of charge of the energy storage device using a relationship between the state of charge and voltage of the energy storage device, based on a charge / discharge history of the energy storage device.

[0028] The computer program causes a computer that estimates the state of charge of a storage element having a negative electrode that includes a negative electrode active material containing Si to execute a process of determining whether to execute a first estimation method that estimates the state of charge of the storage element using the relationship between the state of charge and voltage of the storage element based on the charge / discharge history of the storage element.

[0029] Hereinafter, the present disclosure will be specifically described with reference to the drawings showing embodiments thereof.

[0030] (First embodiment) 1 is a schematic diagram showing a configuration example of an energy storage device 100 equipped with an estimation device 1 according to a first embodiment. The energy storage device 100 includes the estimation device 1, a plurality of energy storage elements 2, and a holder 3 that houses or holds the estimation device 1 and the energy storage elements 2.

[0031] The estimation device 1 is a flat circuit board that estimates the state of charge of the storage elements 2. The estimation device 1 is placed on the upper surfaces of the multiple storage elements 2. The estimation device 1 is connected to the multiple storage elements 2, acquires measurement data including the voltage and current of the storage elements 2, and estimates the state of charge of each storage element 2 based on the acquired measurement data. In the following, the SOC of the power storage element is estimated as the state of charge, but alternatively, the amount of power that can be discharged may be estimated as the state of charge.

[0032] In FIG. 1 , the estimation device 1 is disposed near the top surface of the energy storage element 2. Alternatively, the location of the location may be near the side surface or bottom surface of the energy storage element 2. The estimation device 1 may be disposed outside the holder 3. The shape of the estimation device 1 is not limited to a flat plate. The estimation device 1 may include a cell monitoring unit (CMU) and a battery management unit (BMU) capable of communicating with the CMU. In addition to the CMU and / or BMU, the estimation device 1 may include a server device or an electronic control unit (ECU) that is located away from the energy storage element 2 and communicatively connected to the CMU or BMU. The location where the state of charge of the energy storage element 2 is estimated is not limited, and may be, for example, the BMU, the server device, or the ECU.

[0033] The energy storage element 2 is a battery cell such as a lithium ion secondary battery. The energy storage element 2 is electrically connected to form a battery pack and is used as a power source for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), as well as for industrial equipment such as aircraft, space equipment, and unmanned underwater vehicles, as well as for electronic devices and power storage.

[0034] 1 shows a single power storage module as the power storage device 100. Alternatively, the power storage device 100 may be a so-called high-voltage power supply, such as a power storage pack or power storage facility, that includes a plurality of power storage modules.

[0035] The energy storage element 2 includes a hollow rectangular parallelepiped container 21 and a pair of electrode terminals 22, 22 of opposite polarities provided on one side (terminal surface) of the container 21. Adjacent electrode terminals 22 of adjacent energy storage elements 2 are connected by a bus bar or the like (not shown), and the energy storage elements 2 are connected in series. The container 21 contains an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode, and an electrolyte (electrolytic solution).

[0036] The electrode assembly is constructed by stacking a sheet-shaped positive electrode and a sheet-shaped negative electrode with two sheet-shaped separators in between and winding them (vertical or horizontal). The separator is 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.

[0037] The positive electrode is an electrode plate in which a positive electrode active material layer is formed on the surface of a long strip-shaped positive electrode substrate made of, for example, aluminum, an aluminum alloy, or the like. The positive electrode active material layer contains a positive electrode active material. As the positive electrode active material used in the positive electrode active material layer, any known material can be used as long as it is a positive electrode active material capable of absorbing and releasing lithium ions. Examples of positive electrode active materials include transition metal oxides, transition metal sulfides, lithium-transition metal composite oxides, and lithium-containing polyanion metal composite compounds. The positive electrode active material layer may further contain a conductive additive, a binder, or the like.

[0038] The negative electrode is an electrode plate in which a negative electrode active material layer is formed on the surface of a long strip-shaped negative electrode substrate made of, for example, copper or a copper alloy. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes a Si (silicon)-based material. Examples of Si-based materials include simple Si, SiOx, and Si alloys, with SiOx being preferred. The negative electrode active material may be a Si-based material alone, or a mixture of a Si-based material and another material capable of absorbing and releasing lithium ions. Examples of other negative electrode active materials to be mixed with the Si-based material include carbon-based 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.

[0039] The electrolyte sealed in the container 21 can be the same as that used in conventional lithium-ion secondary batteries. For example, an electrolyte containing a supporting salt in an organic solvent can be used. As the organic solvent, for example, an aprotic solvent such as carbonates, esters, or ethers can be used. As the supporting salt, for example, a lithium salt such as LiPF6, LiBF4, or LiClO4 can be suitably used. The electrolyte may contain various additives such as a gas generating agent, a film-forming agent, a dispersant, or a thickener.

[0040] In FIG. 1, a prismatic lithium ion secondary battery having a wound electrode body has been described as an example of the energy storage element 2. Alternatively, the energy storage element 2 may be a cylindrical lithium ion battery. The energy storage element 2 may be a lithium ion battery having a stacked electrode body, or may be a laminated (pouch) lithium ion battery or the like. Furthermore, the energy storage element 2 may be an all-solid-state lithium ion battery using a solid electrolyte.

[0041] 2 is a block diagram of the estimation device 1. The estimation device 1 includes a control unit 10, a storage unit 11, an input unit 12, and an output unit 13.

[0042] The control unit 10 is an arithmetic circuit including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The CPU included in the control unit 10 executes various computer programs stored in the ROM and the storage unit 11, and controls the operation of each of the hardware components described above, thereby causing the entire device to function as the estimation device of the present disclosure. The control unit 10 may also include functions such as a timer that measures the elapsed time from when an instruction to start measurement is given until when an instruction to stop measurement is given, a counter that counts numbers, and a clock that outputs date and time information.

[0043] The memory unit 11 is a storage device such as a flash memory. Various computer programs and data are stored in the memory unit 11. The memory unit 11 stores an estimation program 111 for estimating the state of the energy storage element 2, charge / discharge history data 112, estimation data 113, voltage range data 114, and the like.

[0044] The estimation program 111 is provided, for example, by a non-transitory recording medium 1A on which a computer program is readably recorded. The recording medium 1A is a portable memory such as a CD-ROM, a USB memory, or an SD (Secure Digital) card. The control unit 10 reads a desired computer program from the recording medium 1A using a reading device (not shown) and stores the read computer program in the storage unit 11. Alternatively, the computer program may be provided by communication.

[0045] The charge / discharge history data 112, the estimation data 113, and the voltage range data 114 store information used in the process of estimating the SOC of the storage element 2. As will be described in detail later, when estimating the SOC, the control unit 10 selectively executes either a first estimation method using a state-of-charge-voltage profile (SOC-OCV curve) that indicates the relationship between the state of charge and voltage of the storage element 2, or a second estimation method using an integrated value of the charge / discharge current of the storage element 2. The control unit 10 determines whether to execute the first estimation method or the second estimation method based on the charge / discharge history of the storage element 2. More specifically, the control unit 10 determines whether to execute the first estimation method or the second estimation method based on the voltage range during charge / discharge of the storage element 2. The control unit 10 executes the first estimation method or the second estimation method using the above-mentioned data to estimate the SOC of the storage element 2.

[0046] The charge / discharge history data 112 stores information indicating the charge / discharge history (operation history) of the energy storage element 2. The charge / discharge history data 112 includes, for example, information indicating the period (usage period) during which the energy storage element 2 was charged or discharged, and information regarding the charge or discharge performed by the energy storage element 2 during the usage period. The information indicating the usage period of the energy storage element 2 includes information indicating the start and end points of charge or discharge, and the accumulated usage period during which the energy storage element 2 was used. The information regarding the charge or discharge performed by the energy storage element 2 includes information indicating the voltage, rate, temperature, etc. during charging or discharging performed by the energy storage element 2. The control unit 10 acquires detected values ​​such as the current value, voltage value, and temperature of the energy storage element 2, and stores information based on the acquired detected values ​​in the charge / discharge history data 112. In this way, a charge / discharge history including time-series data of the detected values ​​of the energy storage element 2 is accumulated.

[0047] The estimated data 113 stores an SOC-OCV curve corresponding to the energy storage element 2. The SOC-OCV curve may be updated at predetermined time intervals in consideration of deterioration of the energy storage element 2. The control unit 10 acquires the SOC-OCV curve in advance, for example, by communicating with an external device (not shown), and stores the acquired SOC-OCV curve in the estimated data 113.

[0048] The voltage range data 114 stores information about a voltage range in which the first estimation method can be implemented. The voltage range in which the first estimation method can be implemented is a voltage range in which a transient potential change, described below, does not occur. The voltage range data 114 may store, for example, upper and lower limit values ​​that define the voltage range. Alternatively, the voltage range data 114 may store information about a voltage range in which the first estimation method cannot be implemented, i.e., a voltage range in which a transient potential change, described below, occurs. The control unit 10 acquires a voltage range corresponding to the negative electrode composition of the energy storage element 2 in advance, for example, by communicating with an external device (not shown), and stores the acquired voltage range in the voltage range data 114. The voltage range data 114 may also store information about a deep discharge threshold and a second region of the SOC-OCV curve, which are factors used to determine whether to implement the first estimation method. The deep discharge threshold and the second region will be described in detail in other embodiments.

[0049] The input unit 12 has an interface for connecting the sensor 4. The input unit 12 may include an A / D converter that converts an analog signal received from the sensor 4 into a digital signal. The sensor 4 includes, for example, a current sensor and a voltage sensor. The current sensor is an existing sensor such as a current transformer or a Hall effect current sensor, and measures the current flowing into and / or flowing out of the energy storage element 2 in a time series. The voltage sensor is an existing voltage sensor that measures the voltage between the terminals of the energy storage element 2 in a time series. The input unit 12 receives a signal related to the current measured by the current sensor and a signal related to the voltage measured by the voltage sensor. The control unit 10 acquires current values ​​and voltage values ​​as needed through the input unit 12. The sensor 4 may further include a temperature sensor such as a thermocouple or a thermistor. The temperature sensor measures the temperature of the energy storage element 2 in a time series. The control unit 10 acquires temperature data of the energy storage element 2 or the energy storage device 100 measured by the temperature sensor as needed through the input unit 12.

[0050] The output unit 13 includes a connection interface for connecting the display device 5. An example of the display device 5 is a liquid crystal display device. When an estimation result regarding the state of charge of the energy storage element 2 is obtained, the control unit 10 outputs information based on the estimation result from the output unit 13 to the display device 5. The display device 5 displays the estimation result based on the information output from the output unit 13.

[0051] Alternatively, the output unit 13 may include a communication interface for communicating with an external device. The external device communicatively connected to the output unit 13 is a terminal device such as a personal computer or smartphone used by a user or administrator. When an estimation result regarding the state of charge of the storage element 2 is obtained, the control unit 10 transmits information based on the estimation result from the output unit 13 to the terminal device. The terminal device receives the information transmitted from the output unit 13 and displays the estimation result on its display based on the received information. The estimation device 1 may include a notification unit such as an LED lamp or a buzzer to notify the user of the estimation result of the state of charge of the storage element 2.

[0052] Here, the characteristics of the electricity storage element (hereinafter also referred to as battery) 2 having a negative electrode containing a negative electrode active material containing a Si-based material will be described in detail. As a result of extensive research, the present inventors have found that in a battery 2 having a negative electrode active material containing a Si-based material, a transient potential change occurs at the negative electrode when the battery is charged and discharged under specific conditions (for example, within a specific voltage range). The transient potential change is a phenomenon in which the charge and discharge characteristics of the battery 2 change when the battery is charged and discharged under specific conditions, resulting in a temporary decrease in the capacity of the battery 2 (capacity retention rate). In this specification, the capacity retention rate refers to the ratio of the battery capacity at a certain point in time to the initial battery capacity. This will be explained in detail below.

[0053] A battery 2 using a mixture of 20% by mass of SiO and 80% by mass of Gr (hereinafter also referred to as an Si-Gr mixed battery) as the negative electrode active material was subjected to charge-discharge cycle tests within several voltage ranges defined by upper and lower limit voltage values ​​described below. Figure 3 is a graph showing the relationship between the number of cycles and the capacity retention rate for the Si-Gr mixed battery for each voltage range. The horizontal axis of Figure 3 represents the number of cycles, and the vertical axis represents the capacity retention rate (%). During the test, a capacity confirmation test was conducted after the 50th cycle, and then charge-discharge was repeated again up to 100 cycles.

[0054] A plurality of thresholds were set between the full charge voltage Ei and the discharge end voltage E0 of the battery 2, and charging and discharging were repeated within a plurality of voltage ranges with the full charge voltage Ei as the upper limit and these thresholds as the lower limit. In the example of Fig. 3, six voltage ranges were set: a first range from voltage E1 to voltage Ei, a second range from voltage E2 to voltage Ei, a third range from voltage E3 to voltage Ei, a fourth range from voltage E4 to voltage Ei, a fifth range from voltage E5 to voltage Ei, and a sixth range from voltage E6 to voltage Ei. However, E0 <E1<E2<E3<E4<E5<E6<Eiである。

[0055] As shown in Figure 3, in a specific voltage range, the capacity retention rate decreased significantly with increasing number of cycles. In the example of Figure 3, the capacity retention rate decreased significantly when repeated charge / discharge was performed in the fifth and fourth ranges. This decrease in the capacity retention rate was temporarily resolved by conducting a capacity confirmation test in which the battery was deeply discharged over the range from the full charge voltage Ei to the end-of-discharge voltage E0.

[0056] Figure 4 is a graph showing the discharge capacity-voltage correlation for a Si-Gr mixed battery for each cycle. The horizontal axis of Figure 4 represents discharge capacity (mAh), and the vertical axis represents voltage (V). Figure 4 shows the discharge characteristics of the battery during the cycle test in the fourth range described above: initial capacity confirmation, 1st cycle, 10th cycle, 20th cycle, 50th cycle, and capacity confirmation after the 50th cycle. The capacity confirmation after the 50th cycle refers to the capacity confirmation after deep discharge after the 50th cycle (when a transient potential change occurred). As can be seen from Figure 4, the curve shape (profile) changes significantly with increasing cycle count, and the end-of-discharge point appears to shift to the left along the horizontal axis. The curve shape remains almost unchanged in the voltage range above approximately 3.5 V, but changes significantly from voltages below approximately 3.5 V to the end of discharge. Furthermore, the curve shape during capacity confirmation after the 50th cycle approaches the curve shape during initial capacity confirmation, indicating that deep discharge eliminates the change in curve shape. The rated capacity when the capacity was checked after 50 cycles was almost unchanged from the initial capacity check, and the discharge capacity recovered after undergoing capacity check involving deep discharge.

[0057] For a battery 2 (hereinafter also referred to as a Si-based battery) with the composition of the negative electrode active material being SiO (the content of SiO in the negative electrode binder is 90% by mass), the same experiment as above was conducted. In the Si-based battery 2, five voltage ranges (the seventh range to the eleventh range) were set with the fully charged voltage Ei as the upper limit and five different voltage values (E7 to E11, where E7 < E8 < E9 < E10 < E11) as the lower limits. Charge-discharge cycle tests were conducted for these five voltage ranges. FIG. 5 is a graph showing the relationship between the number of cycles and the capacity retention rate for each voltage range in the Si-based battery. FIG. 6 is a graph showing the correlation between the discharge capacity and voltage in the Si-based battery for each cycle. FIG. 6 shows the discharge characteristics at the time of initial capacity confirmation, the first cycle, the tenth cycle, the fiftieth cycle, and the capacity confirmation after the fiftieth cycle in the eleventh range from voltage E11 to voltage Ei.

[0058] As shown in FIG. 5, in the Si-based battery 2 as well, in a specific voltage range, the capacity retention rate decreased significantly with an increase in the number of cycles. However, different from the Si-Gr hybrid battery 2, when restricted to a high voltage range (for example, the eleventh range and the tenth range), the decrease in the capacity retention rate was remarkable. As shown in FIG. 6, in the Si-based battery 2 as well, with an increase in the number of cycles, the change in the curve shape became large, and the discharge end point shifted left along the horizontal axis direction. The curve shapes at the time of capacity confirmation after the fiftieth cycle and at the time of initial capacity confirmation almost coincided, and the change in the curve shape was eliminated by performing deep discharge. However, different from the Si-Gr hybrid battery 2, the deviation of the curve shape occurred in the region including almost all voltages from the start to the end of discharge.

[0059] To separate the contributions of the single positive and negative electrodes to the transient potential change, analytical half-cells using lithium as the counter electrode were fabricated for each of the positive and negative electrodes, and the capacity retention was measured. Figure 7 is a graph showing the relationship between the number of cycles and the capacity retention for each of the single positive and negative electrodes. The horizontal axis of Figure 7 represents the number of cycles, and the vertical axis represents the capacity retention (%). The compositions of the single positive and negative electrodes and five voltage ranges were set to match the composition and voltage range (SOC range corresponding to the voltage) of the full cell of the Si-based battery 2 in the cycle test shown in Figure 5.

[0060] As shown in the upper panel of Figure 7, the capacity retention rate of the single positive electrode hardly decreased over any voltage range. On the other hand, as shown in the lower panel of Figure 7, the capacity retention rate of the single negative electrode significantly decreased with increasing cycle count within a specific voltage range. This confirmed that the transient potential change occurring in Si-based Battery 2 due to repeated charge-discharge cycles within a specific voltage range was caused by the negative electrode.

[0061] The mechanism by which transient potential changes occur in Battery 2, which has a negative electrode active material containing Si-based materials, has not yet been fully elucidated. x This is presumably due to the formation of a crystalline layer containing a Si alloy. In other words, Li ions are not absorbed homogeneously in the Si crystal, but are surrounded by Li ions. x It penetrates into the interior while forming a Si alloy. x The Si alloy has a plateau potential at which the charge / discharge potential hardly changes, and it is presumed that this plateau potential affects the change in the potential of the negative electrode when charge / discharge is repeated within a specific voltage range.

[0062] Although slight transient potential changes may occur at the positive electrode, these potential changes disappear with sufficient time between charges and discharges and are not dependent on the voltage range during discharge. The reaction of lithium ions at the positive electrode initially proceeds kinetically. The reaction rate varies depending on the reaction conditions (e.g., voltage range) during discharge, resulting in different degrees of potential change during the reaction, manifesting as a transient capacity change. However, with sufficient reaction time, the reaction proceeds thermodynamically after kinetic control, eventually converging to the energy of the product at the positive electrode, eliminating the potential change.

[0063] To summarize the above, in a battery 2 having a negative electrode active material containing a Si-based material, repeated charging and discharging within a specific voltage range changes the charge and discharge characteristics of the battery 2, resulting in a transient potential change that reduces the capacity of the battery 2. This transient potential change is resolved by discharging beyond a predetermined deep discharge threshold. The voltage range in which the transient potential change occurs varies depending on the content of Si-based material in the negative electrode active material (negative electrode composition). As described below, the estimation device 1 identifies a voltage range during charging and discharging of the battery 2, and if the voltage range is within which the transient potential change does not occur, it executes a first estimation method using the SOC-OCV curve. That is, if the voltage range is within which the transient potential change does not occur, it executes an SOC reset. If the voltage range is not within which the transient potential change does not occur, it executes a second estimation method using current integration. This makes it possible to accurately estimate the state of charge of a battery 2 having a negative electrode active material containing a Si-based material.

[0064] 8 is a flowchart showing an example of the estimation process procedure. The control unit 10 of the estimation device 1 executes the following process in accordance with the estimation program 111.

[0065] The control unit 10 of the estimation device 1 acquires the charge / discharge history by acquiring detected values ​​such as the current value, voltage value, and temperature of the battery 2 via the input unit 12 (step S11). When the estimation device 1 is installed in a remote location, the control unit 10 receives the detected values ​​of the storage element 2 by communication via the output unit 13. The control unit 10 stores the acquired charge / discharge history in the charge / discharge history data 112 of the memory unit 11.

[0066] The control unit 10 identifies a voltage range for use of the battery 2 based on the acquired charge / discharge history (step S12). The control unit 10 estimates whether a transient potential change occurs at the negative electrode based on the identified voltage range, and determines whether to execute the first estimation method (step S13). Specifically, the control unit 10 determines whether the voltage range in which the first estimation method can be executed matches the identified voltage range based on the information stored in the voltage range data 114. The control unit 10 determines whether to execute the first estimation method based on the determination result. The first estimation method is an OCV method (voltage reference) that determines the SOC based on an SOC-OCV curve. The voltage range in which the first estimation method can be executed is a voltage range in which no transient potential change occurs at the negative electrode.

[0067] If the charge / discharge history of battery 2 does not fall within a voltage range in which the first estimation method can be implemented, it is estimated that a transient potential change has occurred at the negative electrode of battery 2. In this case, the SOC-OCV curve is likely to be indeterminable, and the estimation accuracy of the first estimation method is likely to be reduced. On the other hand, if the charge / discharge history of battery 2 falls within a voltage range in which the first estimation method can be implemented, it is estimated that a transient potential change has not occurred at the negative electrode of battery 2. In this case, the SOC-OCV curve is likely to be indeterminable, and the SOC can be accurately estimated using the first estimation method.

[0068] If it is determined that the first estimation method should not be executed because the voltage range in which the first estimation method can be executed does not match the identified voltage range (step S13: NO), the control unit 10 executes a second estimation method to estimate the SOC (step S14). The second estimation method is a current integration method that determines the SOC using an integrated value of the current flowing through the battery 2.

[0069] As an arithmetic formula for the current integration method, for example, the following formula (1) may be used. SOC i =SOC i-1 +I i ×Δt i / Q×100…(1) SOC i This time's 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.

[0070] If it is determined that the first estimation method should be executed because the voltage range in which the first estimation method can be executed matches the identified voltage range (step S13: YES), the control unit 10 executes the first estimation method to estimate the SOC (step S15). Based on the SOC-OCV curve stored in the estimation data 113, the control unit 10 reads the SOC corresponding to the voltage value acquired in step S11 from the SOC-OCV curve.

[0071] The control unit 10 outputs information based on the SOC estimation result to the display device 5 or the like (step S16), and ends the series of processes.

[0072] In the above-described process, the control unit 10 may estimate the SOC at each time a detection value is acquired from the input unit 12, or may store the detection values ​​for a certain period in the memory unit 11, and then sequentially read out the measurement data from the memory unit 11 to estimate the SOC at each time.

[0073] In the above description, the control unit 10 determines whether to execute the first estimation method based on whether the charge / discharge history of the battery 2 corresponds to a voltage range in which the first estimation method is feasible. Alternatively, the control unit 10 may determine whether to execute the first estimation method based on whether the charge / discharge history of the battery 2 corresponds to a voltage range in which the first estimation method is not feasible.

[0074] According to this embodiment, the state of charge of a battery 2 having a negative electrode active material containing a Si-based material can be accurately estimated based on the characteristics of the Si-based material. The estimation device 1 estimates the state of charge using a first estimation method using an SOC-OCV curve in a voltage range in which a transient potential change does not occur at the negative electrode. In a voltage range in which a transient potential change occurs at the negative electrode, the estimation device 1 calculates the state of charge using a second estimation method that performs current integration. The estimation device 1 reduces a decrease in the accuracy of estimating the state of charge by controlling the timing of executing the first estimation method depending on the result of estimating the occurrence state of a transient potential change at the negative electrode.

[0075] (Second embodiment) In the second embodiment, an example will be described in which the first estimation method is executed when the battery 2 is discharged beyond the deep discharge threshold. As described above, the transient potential change at the negative electrode of the storage element is eliminated by deep discharging. Deep discharging means discharging beyond the deep discharge threshold. The control unit 10 acquires information regarding the deep discharge threshold according to the composition of the battery 2 in advance and stores it in the estimation data 113.

[0076] 5, the control unit 10 of the estimation device 1 determines whether to execute the first estimation method based on whether discharge exceeding the deep discharge threshold has occurred in the battery 2. Specifically, the control unit 10 determines whether the voltage value acquired in step S11 is less than the deep discharge threshold based on the information stored in the voltage range data 114.

[0077] If the voltage value of the battery 2 is below the deep discharge threshold, i.e., if deep discharge has occurred, the control unit 10 determines to execute the first estimation method. Based on the SOC-OCV curve stored in the estimation data 113, the control unit 10 reads the SOC corresponding to the voltage value acquired in step S11 on the SOC-OCV curve.

[0078] If the voltage value of the battery 2 is equal to or greater than the deep discharge threshold, i.e., if deep discharging has not occurred, the control unit 10 determines not to execute the first estimation method.The control unit 10 executes the second estimation method and estimates the SOC by current integration.

[0079] According to this embodiment, the state of charge of battery 2 can be accurately estimated by using a deep discharge threshold determined according to the negative electrode composition and executing the first estimation method at the timing when it is estimated that the transient potential change has resolved.

[0080] (Third embodiment) In the third embodiment, an example in which a more detailed curve shape is taken into consideration in the first estimation method will be described. FIG. 9 is a graph showing the correlation between discharge capacity and voltage before and after deep discharge in a Si-based battery 2. The horizontal axis of FIG. 9 is discharge capacity, and the vertical axis is voltage (V). The discharge capacity is a value normalized by the discharge capacity corresponding to the discharge start voltage, and corresponds to the state of charge. In other words, the graph shown in FIG. 9 shows the state of charge-voltage profile of the Si-based battery. The estimation method of the third embodiment will be described using FIG. 9.

[0081] FIG. 9 shows the results of a capacity confirmation test after 100 cycles of cycle testing in the 11th range of voltages from E11 to Ei described in FIG. 5 using the same Si-based battery 2 as in the first embodiment. The dashed line in FIG. 9 shows the discharge curve obtained when the capacity was confirmed after 100 cycles without any residual discharge. That is, the dashed line in FIG. 9 shows the discharge curve obtained when the capacity was confirmed after the occurrence of a transient potential change and before deep discharge. The solid line in FIG. 9 shows the discharge curve obtained when the charge / discharge cycle was again performed over the entire voltage range from the full charge voltage to the end-of-discharge voltage after the capacity confirmation. That is, the solid line in FIG. 9 shows the discharge curve obtained when the capacity was confirmed after the occurrence of a transient potential change and after deep discharge.

[0082] As shown in FIG. 9 , the discharge curve before deep discharge has a first region where the curve shape changes (the deviation of the curve shape is large) compared to the discharge curve after deep discharge, and a second region where the curve shape hardly changes (the deviation of the curve shape is small). That is, the discharge curve when a transient potential change occurs has a first region where the curve shape changes due to the transient potential change and a second region where the curve shape hardly changes compared to the discharge curve when the transient potential change does not occur (is eliminated). In the example of FIG. 9 , the region from the start of discharge to a voltage of approximately 3.3 V or higher corresponds to the first region, and the region from a voltage less than approximately 3.3 V to the end-of-discharge voltage corresponds to the second region. When the voltage of the battery 2 is within the second region, the curve shape hardly changes due to the transient potential change, and therefore the voltage can be uniquely identified from the SOC-OCV curve. The control unit 10 of the estimation device 1 does not execute the first estimation method when the acquired voltage is within the first region, but executes the first estimation method when the acquired voltage is within the second region.

[0083] The upper and lower limits of the first and second regions described above vary depending on the negative electrode composition (Si content in the negative electrode active material). For example, in the Si-Gr mixed battery 2 shown in FIG. 4 of the first embodiment, there is almost no deviation in the curve shape at voltages of about 3.6 V or higher, but the curve shape changes significantly at voltages below about 3.6 V. That is, in the Si-Gr mixed battery 2, the region including high voltages corresponds to the second region, and the region including low voltages corresponds to the first region. The control unit 10 previously acquires information regarding the upper and lower limits of the second region according to the composition of the battery 2 and stores it in the voltage range data 114.

[0084] 5, the control unit 10 of the estimation device 1 determines whether to execute the first estimation method by determining whether the voltage value acquired in step S11 is within the second region. Specifically, the control unit 10 determines whether the voltage value acquired in step S11 is within the range between the upper limit and lower limit of the second region, based on the information stored in the voltage range data 114.

[0085] If it is determined that the voltage value is within the second region, the control unit 10 determines to execute the first estimation method. Based on the SOC-OCV curve stored in the estimation data 113, the control unit 10 reads the SOC corresponding to the voltage value acquired in step S11 in the second region of the SOC-OCV curve.

[0086] If it is determined that the voltage value is not within the second range, the control unit 10 determines not to execute the first estimation method. The control unit 10 executes the second estimation method and estimates the SOC by current integration.

[0087] The control unit 10 may comprehensively determine whether to execute the first estimation method by determining whether the charge / discharge history of the battery 2 corresponds to a voltage range in which the first estimation method can be executed, in addition to determining whether the above-mentioned voltage value is within the second range.

[0088] According to this embodiment, the voltage at which the first estimation method can be performed is specified based on more detailed charge / discharge characteristics according to the negative electrode composition, thereby enabling the state of charge of the battery 2 to be estimated with high accuracy.

[0089] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The technical features described in each embodiment can be combined with each other, and the scope of the present invention is intended to include all modifications within the scope of the claims and the scope equivalent to the claims. [Explanation of symbols]

[0090] 100 Energy storage device (energy storage module) 2. Energy storage element 1 Estimation device 10 Control Unit 11 Storage section 12 Input section 13 Output section 111 Estimation Program 112 Charge and discharge history data 113 Estimated Data 114 Voltage Range Data

Claims

1. An estimation device for estimating a state of charge of an energy storage element including a negative electrode including a negative electrode active material containing Si, a control unit that determines whether to execute a first estimation method for estimating the state of charge of the storage element using a relationship between the state of charge and a voltage of the storage element based on a charge / discharge history of the storage element; The control unit determines whether to execute the first estimation method depending on the estimation result regarding the transient potential change of the negative electrode. Estimation device.

2. An estimation device for estimating the state of charge of a storage element having a negative electrode including a negative electrode active material containing Si, a control unit that determines whether to execute a first estimation method for estimating the state of charge of the storage element using a relationship between the state of charge and a voltage of the storage element based on a charge / discharge history of the storage element; The control unit determines to execute the first estimation method when the voltage of the energy storage element is within a voltage threshold range that does not cause a transient potential change of the negative electrode according to the Si content of the negative electrode active material. Estimation device.

3. An estimation device for estimating the state of charge of a storage element having a negative electrode including a negative electrode active material containing Si, a control unit that determines whether to execute a first estimation method for estimating the state of charge of the storage element using a relationship between the state of charge and a voltage of the storage element based on a charge / discharge history of the storage element; a state-of-charge-voltage profile showing the relationship between the state of charge and the voltage of the energy storage element has a first region in which the shape changes due to a transient potential change of the negative electrode, and a second region in which the shape does not change; The control unit estimates the state of charge using a state of charge-voltage profile of the second region. Estimation device.

4. The control unit determines to execute the first estimation method when the energy storage device is discharged beyond a deep discharge threshold corresponding to a Si content in the negative electrode active material. The estimation device according to any one of claims 1 to 3.

5. When the control unit determines not to execute the first estimation method, it executes a second estimation method for estimating the state of charge of the storage element using an integrated value of current flowing into and / or flowing out of the storage element. The estimation device according to any one of claims 1 to 4.

6. A storage element; The estimation device according to any one of claims 1 to 5, A storage module comprising:

7. A method for estimating the state of charge of a storage element having a negative electrode including a negative electrode active material containing Si, comprising: determining whether to execute a first estimation method for estimating the state of charge of the storage element using a relationship between the state of charge and the voltage of the storage element based on a charge / discharge history of the storage element; and determining whether to execute the first estimation method according to the estimation result regarding the transient potential change of the negative electrode. Estimation method.

8. A computer that estimates the state of charge of a storage element having a negative electrode including a negative electrode active material containing Si, determining whether to execute a first estimation method for estimating the state of charge of the storage element using a relationship between the state of charge and the voltage of the storage element based on a charge / discharge history of the storage element; and determining whether to execute the first estimation method according to the estimation result regarding the transient potential change of the negative electrode. A computer program for executing a process.

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