Method and apparatus for estimating the salt concentration of the electrolyte in a secondary battery

Abstract

To provide a technology that can estimate the salt concentration of the electrolyte in a secondary battery. [Solution] The method for estimating the salt concentration of the electrolyte of a secondary battery disclosed herein includes a capacity acquisition step S1 for acquiring the capacity of a secondary battery to be estimated, a discharge time acquisition step S2 for acquiring the discharge time when the secondary battery is discharged under predetermined conditions, and a salt concentration estimation step S3 for estimating the salt concentration of the electrolyte of the secondary battery based on the acquired capacity of the secondary battery, the acquired discharge time, and a table recording the relationship between the capacity of the secondary battery, the discharge time, and the salt concentration of the electrolyte of the secondary battery to be estimated.

Description

Technical Field

[0001] The present disclosure relates to a method for estimating the salt concentration of an electrolyte of a secondary battery and a salt concentration estimation device.

Background Art

[0002] For example, Japanese Patent Application Laid-Open No. 2018-073777 discloses a control system for a lithium-ion secondary battery including a detection device that detects the temperature, current, and voltage of the lithium-ion secondary battery, and a control device. In such a control system, it is described that the lithium-ion secondary battery is not used when the estimated value of the lithium precipitation amount is larger than a predetermined value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, according to the study of the present inventor, it has been found that the salt concentration of the electrolyte of a secondary battery can affect the deterioration resistance of the secondary battery to large current charge and discharge. Therefore, further development of a technique capable of estimating the salt concentration of the electrolyte of a secondary battery is required.

Means for Solving the Problems

[0005] The method for estimating the salt concentration of the electrolyte of a secondary battery disclosed herein includes a capacity acquisition step of acquiring the capacity of the secondary battery to be estimated. The salt concentration estimation method includes a discharge time acquisition step of acquiring the discharge time when the secondary battery is discharged under predetermined conditions. The salt concentration estimation method includes a salt concentration estimation step of estimating the salt concentration of the electrolyte of the secondary battery based on the acquired capacity of the secondary battery, the acquired discharge time, and a table recording the relationship between the capacity of the secondary battery, the discharge time, and the salt concentration of the electrolyte for the secondary battery to be estimated. According to this disclosure, a method for estimating the salt concentration of the electrolyte of a secondary battery can be provided.

[0006] The salt concentration estimation device for the electrolyte of a secondary battery disclosed herein is configured such that a capacity acquisition process for acquiring the capacity of the secondary battery to be estimated is performed by a computer. The salt concentration estimation device is configured such that a discharge time acquisition process for acquiring the discharge time when the secondary battery is discharged under predetermined conditions is performed by a computer. The salt concentration estimation device is configured such that a salt concentration estimation process for estimating the salt concentration of the electrolyte of the secondary battery is performed by a computer based on the acquired capacity of the secondary battery, the acquired discharge time, and a table recording the relationship between the capacity of the secondary battery, the discharge time, and the salt concentration of the electrolyte for the secondary battery to be estimated. According to this disclosure, it is possible to provide a device capable of estimating the salt concentration of the electrolyte of a secondary battery. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a flowchart showing a method for estimating the salt concentration of the electrolyte in a secondary battery according to one embodiment. [Figure 2] Figure 2 is a schematic diagram showing a device for estimating the salt concentration of the electrolyte of a secondary battery according to one embodiment. [Figure 3] Figure 3 is the first matrix diagram showing an example of a secondary battery capacity estimation map. [Figure 4] Figure 4 is a second matrix diagram showing an example of a secondary battery capacity estimation map. [Figure 5A] Figure 5A is the first graph showing the relationship between the time it takes for a secondary battery to reach a full charge capacity of 100% and the salt concentration. [Figure 5B] Figure 5B is a second graph showing the relationship between the time it takes for a secondary battery to reach a full charge capacity of 90% and the salt concentration. [Figure 5C] Figure 5C is the third graph showing the relationship between the time it takes for a secondary battery to reach 80% full charge capacity and the salt concentration. [Figure 6] Figure 6 is a matrix diagram showing an example of a map for estimating the salt concentration of the electrolyte in a secondary battery. [Figure 7] Figure 7 is a schematic diagram showing a device for estimating the salt concentration of the electrolyte of a secondary battery according to another embodiment. [Figure 8] Figure 8 is a flowchart showing a method for estimating the salt concentration of the electrolyte in a secondary battery according to another embodiment. [Modes for carrying out the invention]

[0008] Hereinafter, an embodiment of the technology disclosed herein will be described with reference to the drawings. Naturally, the embodiment described herein is not intended to limit the scope of this disclosure. Each drawing is a schematic diagram and does not necessarily faithfully reflect an actual implementation. Furthermore, components and parts that perform the same function are appropriately denoted by the same reference numerals, and redundant explanations are omitted as appropriate. Matters other than those specifically mentioned herein but necessary for implementing the technology disclosed herein (for example, the general configuration of a secondary battery not characteristic of this disclosure, or methods for measuring the capacity and discharge time of a secondary battery) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed herein and common technical knowledge in the relevant field. Furthermore, the notation "A~B" indicating a range in this specification means "A or greater and B or less." Also, the notation "A~B" encompasses the meanings of "greater than A" and "less than B."

[0009] In the following explanation, the method for estimating the salt concentration of the electrolyte in secondary battery 1 will be simply referred to as the "salt concentration estimation method." Similarly, the device for estimating the salt concentration of the electrolyte in secondary battery 1 will be simply referred to as the "salt concentration estimation device."

[0010] Here, Figure 1 is a flowchart illustrating a method for estimating the salt concentration of the electrolyte of a secondary battery 1 according to one embodiment. The method for estimating the salt concentration of the electrolyte of a secondary battery includes a capacity acquisition step S1, a discharge time acquisition step S2, and a salt concentration estimation step S3, as shown in Figure 1. Figure 2 is a schematic diagram showing a salt concentration estimation device 100. The salt concentration estimation device 100 includes a computer 10. This method for estimating the salt concentration of the electrolyte of a secondary battery is implemented by the computer 10.

[0011] Here, computer 10 includes a storage device (such as memory) and an arithmetic unit (such as a CPU). Each process of computer 10 is embodied as a processing module executed by a predetermined program. Each function of computer 10 can be appropriately embodied through the cooperation of physical components and control based on calculation results performed in accordance with a predetermined program. Computer 10 may also be a collaborative system of multiple computers. For example, if computer 10 is connected to an external computer via a LAN cable or the internet, the processing of computer 10 may be performed in cooperation with such an external computer. For example, information or some of the information stored in computer 10 may be stored by an external computer, or processing or part of processing performed by computer 10 may be performed by an external computer.

[0012] <Salt concentration estimation device 100> The salt concentration estimation device 100 is a device for estimating the salt concentration of the electrolyte of the secondary battery 1. As shown in Figure 2, it comprises a capacity acquisition processing unit 20, a discharge time acquisition processing unit 21, and a salt concentration estimation processing unit 22. The capacity acquisition processing unit 20, the discharge time acquisition processing unit 21, and the salt concentration estimation processing unit 22 are each implemented in the computer 10.

[0013] As shown in Figure 2, in this embodiment, the secondary battery 1 is mounted on an electric vehicle. Here, the specific type of electric vehicle is not particularly limited, but examples include electric bicycles, electric motorcycles, electric automobiles, and trains. Examples of electric automobiles include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). Here, a salt concentration estimation device 100 related to the secondary battery 1 mounted on an electric vehicle is illustrated. The salt concentration estimation device 100 is not limited to electric vehicles and can also be used, for example, in electric ships.

[0014] Secondary battery 1 refers to a battery in which charging and discharging occur through the movement of charge carriers between a pair of electrodes (positive electrode and negative electrode) via an electrolyte (in this case, an electrolyte solution). Secondary battery 1 in this context is a non-aqueous electrolyte secondary battery. Examples of secondary battery 1 include lithium-ion secondary batteries, sodium-ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, etc. In this embodiment, secondary battery 1 is a lithium-ion secondary battery, but the type of secondary battery is not intended to be limited to lithium-ion secondary batteries.

[0015] Although detailed illustrations are omitted, the secondary battery 1 comprises a case, an electrode body housed in the case, and an electrolyte housed in the case. The shape of the case is not particularly limited and may be, for example, a flattened rectangular parallelepiped or a cylindrical shape. The electrode body includes, for example, a positive electrode (positive electrode sheet) as a positive electrode element, a negative electrode (negative electrode sheet) as a negative electrode element, and a separator placed between the positive electrode and the negative electrode. The type of electrode body is not particularly limited and may be, for example, a laminated electrode body or a wound electrode body.

[0016] The electrolytic solution contains, for example, a supporting salt and a non-aqueous solvent. The electrolytic solution is, for example, a non-aqueous electrolytic solution in which the supporting salt is dissolved in the non-aqueous solvent. As an example of the non-aqueous solvent, carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate can be mentioned. These may be included alone or in combination of two or more. As an example of the supporting salt, lithium salts such as LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI) can be mentioned. These may be included alone or in combination of two or more. Although not particularly limited, the concentration of the supporting salt can be, for example, 0.6 mol / L to 1.8 mol / L (preferably 0.7 mol / L to 1.5 mol / L). The electrolytic solution may contain various additives such as an oxalato complex, a film-forming agent such as vinylene carbonate (VC), a gas-generating agent such as biphenyl (BP) and cyclohexylbenzene (CHB); a thickening agent; etc. In this specification, the "salt concentration of the electrolytic solution of the secondary battery" means the concentration (for example, ion concentration) of the supporting salt in the electrolytic solution of the secondary battery. When two or more types of supporting salts are contained in the electrolytic solution, it means the total value of these concentrations. For example, in this embodiment, the salt concentration of the electrolytic solution of the secondary battery 1 means the concentration of the lithium salt (lithium ion concentration) in the electrolytic solution. Such a salt concentration can be measured, for example, by a commercially available ion measuring instrument. In the following description, "mol / L" may be simply denoted as "M".

[0017] (Capacity acquisition processing unit 20) The capacity acquisition processing unit 20 is configured to execute a process of acquiring the capacity of the secondary battery 1 to be estimated. The capacity acquisition processing unit 20 is configured to acquire the capacity of the secondary battery 1, for example, by a method of estimating the capacity of the secondary battery 1 from the number of years of use and the temperature history, or a method of estimating the capacity of the secondary battery 1 from the interval capacity during charging. The capacity acquisition processing unit 20 is preferably configured to be able to receive information such as the usage history, temperature history, and charging time from the secondary battery 1. The method of capacity acquisition embodied by the capacity acquisition processing unit 20 will be described in more detail later.

[0018] (Discharge time acquisition processing unit 21) The discharge time acquisition processing unit 21 is configured to execute a process of acquiring the discharge time when the secondary battery 1 is discharged under predetermined conditions. Specifically, the discharge time acquisition processing unit 21 is configured to acquire the discharge time when the secondary battery 1 is discharged under the discharge conditions described later. In the present embodiment, the discharge time acquisition processing unit 21 is configured to acquire the discharge time when the secondary battery 1 is discharged under predetermined conditions in the use of an electric vehicle. The discharge time acquisition processing unit 21 is configured to be able to receive information such as the discharge time from the secondary battery 1, for example.

[0019] (Salt concentration estimation processing unit 22) In the salt concentration estimation processing unit 22, based on the capacity of the secondary battery 1 obtained above, the discharge time obtained above, and a table (hereinafter also referred to as a "map") in which the relationship between the capacity and discharge time of the secondary battery 1 and the salt concentration of the electrolytic solution regarding the secondary battery 1 to be estimated is recorded, a process of estimating the salt concentration of the electrolytic solution of the secondary battery 1 is executed. Specifically, based on the capacity of the secondary battery 1 obtained by the capacity acquisition processing unit 20 and the discharge time of the secondary battery 1 obtained by the discharge time acquisition processing unit 21, a map as shown in FIG. 6 is referred to. And the corresponding salt concentration in the map is acquired as the salt concentration of the electrolytic solution of the secondary battery 1 at the time of measurement. In this way, the salt concentration estimation processing unit 22 can estimate the salt concentration of the electrolytic solution of the secondary battery 1.

[0020] In a preferred aspect, the discharge time acquisition processing unit 21 acquires the discharge time when the secondary battery 1 is discharged in a state where the SOC is at least 50%. Details will be described in the <Salt concentration estimation method> described later, but according to such a configuration, it becomes easier to acquire the discharge time.

[0021] In one preferred embodiment, the discharge time acquisition processing unit 21 acquires the discharge time when the secondary battery 1 is discharged in a temperature environment where the average temperature is -10°C or lower. As will be explained in detail in the <Salt Concentration Estimation Method> section below, with this configuration, the salt concentration of the electrolyte can be suitably estimated even when, for example, the system cannot supply a large current.

[0022] The following describes the salt concentration estimation method implemented in the salt concentration estimation device 100. This description will include explanations of the salt concentration estimation device 100 as appropriate. It should be noted that the following description is not intended to limit the salt concentration estimation method disclosed herein to the following configuration. Each step described below can be performed in any order as long as the effects of the disclosed technology are obtained. Furthermore, additional steps may be added as needed, in addition to the steps described below.

[0023] <Method for estimating salt concentration> Figure 1 is a flowchart illustrating a method for estimating the salt concentration of the electrolyte in a secondary battery 1 according to one embodiment. As shown in Figure 1, the salt concentration estimation method according to this embodiment includes a capacity acquisition step S1, a discharge time acquisition step S2, and a salt concentration estimation step S3. In this embodiment, the salt concentration of the electrolyte in a secondary battery 1 mounted on an electric vehicle is to be estimated. Each step will be described below.

[0024] (Capacity acquisition process S1) In this process, the capacity of the secondary battery 1 to be estimated is obtained. Various methods can be used to obtain (estimate) the capacity of the secondary battery 1, for example, by estimating the capacity degradation rate. There are various methods for estimating the capacity of the secondary battery 1 and the capacity degradation rate, and an appropriate method can be adopted. An example of a method for obtaining the capacity of the secondary battery 1 is described below, but this is not intended to limit the methods for obtaining the capacity of the secondary battery 1 to what is described below.

[0025] One example of a method for obtaining the capacity of secondary battery 1 is to obtain it from the number of years of use and the temperature history of secondary battery 1. Specifically, first, a map is created in advance showing the relationship between the number of years of use of secondary battery 1, the temperature history of secondary battery 1, and the capacity of secondary battery 1. Here, Figure 3 is a first matrix diagram showing an example of a secondary battery 1 capacity estimation map. The map shown in Figure 3 is a preferred example of a map to be created in advance. Here, the number of years of use in Figure 3 may mean the number of years from the start of use of secondary battery 1 to the start of capacity measurement of secondary battery 1. Also, the temperature history of secondary battery 1 may mean, for example, the total time during which the temperature of secondary battery 1 was not within a predetermined temperature range within the number of years of use. Although not particularly limited, such a temperature range can be set to, for example, -30℃ to 60℃ (preferably -10℃ to 40℃). Here, the full charge capacity of secondary battery 1 is used as the capacity of secondary battery 1. Here, the full charge capacity of secondary battery 1 decreases over time with charging and discharging of secondary battery 1. The fully charged capacity of secondary battery 1 can refer to the battery capacity until secondary battery 1, which has been charged to its maximum charge capacity (SOC - States of Charge) of 100%, is completely discharged.

[0026] In this specification, "SOC" refers to the State of Charge. Specifically, SOC = 100% is defined as the charge state that is the upper limit of the operating voltage (i.e., the state in which the voltage does not rise even if charging continues). On the other hand, SOC = 0% is defined as the charge state that is the lower limit of the operating voltage (i.e., the state in which the voltage does not fall even if discharging continues). The specific means of measuring SOC can be any conventionally known measurement method without any particular limitations, and since this does not limit the technology disclosed herein, a detailed explanation is omitted.

[0027] For example, the map shown in Figure 3 shows the service life of secondary battery 1 in one-year increments, ranging from 1 to 10 years. It also shows the temperature history of secondary battery 1 in one-hour increments, ranging from 1 to 20 hours. The capacity of secondary battery 1 is shown as BC (Battery Capacity). The number in parentheses next to BC indicates (temperature history, service life). The map shown in Figure 3 can be created, for example, by preparing multiple secondary batteries 1 with different service lives and temperature histories and measuring their respective full charge capacities. Alternatively, it can be created through simulation based on past data without actually preparing multiple secondary batteries 1 with different service lives and temperature histories. Here, the full charge capacity of secondary battery 1 should be measured by a conventionally known method. The measurement conditions for the full charge capacity should be appropriately determined depending on the type and size of secondary battery 1. In this embodiment, the full charge capacity is expressed as a percentage (%). Specifically, this shows the percentage (%) of the fully charged capacity of secondary battery 1 at the time of measurement, with the fully charged capacity of secondary battery 1 when unused being set to 100%.

[0028] When acquiring the capacity of the secondary battery 1 as described above, the salt concentration estimation device 100 can operate as follows. Specifically, first, the capacity acquisition processing unit 20 of the salt concentration estimation device 100 acquires the number of years of use and the temperature history of the secondary battery 1 from the secondary battery 1 installed in the electric vehicle. Next, based on the number of years of use and temperature history acquired from the secondary battery 1, it refers to a pre-created capacity estimation map of the secondary battery 1 (see Figure 3). Then, it acquires the corresponding capacity in the capacity estimation map of the secondary battery 1 as the capacity of the secondary battery 1 at the time of measurement. In this way, the capacity of the secondary battery 1 can be acquired.

[0029] Another example of a method for obtaining the capacity of secondary battery 1 is to obtain it from the interval capacity during charging of secondary battery 1. Here, "interval capacity during charging of secondary battery" means the capacity of the secondary battery estimated from the time required to charge from a predetermined state of charge (SOC) to a predetermined SOC (hereinafter also referred to as "charging time") when charging with a predetermined current. Specifically, first, a map is created in advance for the capacity of secondary battery 1 and the charging time required when charging secondary battery 1 under predetermined charging conditions. The predetermined charging conditions refer to, for example, the SOC at the start of charging, the charging current, and the SOC at the end of charging. Here, Figure 4 is a second matrix diagram showing an example of a capacity estimation map for secondary battery 1. The map shown in Figure 4 is a preferred example of a map to be created in advance. It is preferable that the SOC at the start of charging, the charging current, and the SOC at the end of charging be appropriately set depending on the type of secondary battery 1 to be measured and the environment in which secondary battery 1 is placed. Here, the fully charged capacity of secondary battery 1 is used as the capacity of secondary battery 1.

[0030] For example, Figure 4 is a map showing the charging of secondary battery 1, with a State of Charge (SOC) of 20% at the start of charging, a charging current of 5A, and a State of Charge (SOC) of 80% at the end of charging. In the map shown in Figure 4, the charging time of secondary battery 1 is shown in 1-minute increments, ranging from 1 minute to 60 minutes. The capacity of secondary battery 1 is shown as BC. The number in parentheses next to BC indicates the charging time. The map shown in Figure 4 can be created, for example, by preparing multiple secondary batteries 1 with different full charge capacities, charging them under predetermined charging conditions, and measuring the charging time for each. Alternatively, it may be created by simulation based on past data without actually preparing multiple secondary batteries 1 with different full charge capacities.

[0031] In estimating the capacity of the secondary battery 1, the salt concentration estimation device 100 can operate as follows. Specifically, first, the capacity acquisition processing unit 20 of the salt concentration estimation device 100 acquires the charging time from the secondary battery 1 mounted on the electric vehicle when charged under predetermined charging conditions. Next, based on the charging time acquired from the secondary battery 1, it refers to the capacity estimation map of the secondary battery 1 (see Figure 4). Then, the capacity acquisition processing unit 20 acquires the corresponding capacity in the capacity estimation map of the secondary battery 1 as the capacity of the secondary battery 1 at the time of measurement. In this way, the capacity acquisition processing unit 20 can acquire the capacity of the secondary battery 1.

[0032] (Discharge time acquisition step S2) In this process, the discharge time is obtained when the secondary battery 1 is discharged under predetermined conditions. In this process, the secondary battery 1 is discharged under predetermined conditions, and the time it takes to reach a predetermined voltage is obtained as the discharge time. In this embodiment, the discharge time is obtained when the secondary battery 1 is discharged under predetermined conditions during the use of an electric vehicle.

[0033] The discharge conditions of the secondary battery 1 are not particularly limited, as long as the effects of the technology disclosed herein can be obtained. Examples of discharge conditions for the secondary battery 1 include the average temperature and average current during discharge, the state of charge (SOC) at the start of discharge, and the voltage at the end of discharge. Here, "average temperature during discharge" may mean, for example, the average value when the temperature during discharge is randomly taken at 5 or more points (for example, 10 points). Similarly, "average current during discharge" may mean, for example, the average value when the current during discharge is randomly taken at 5 or more points (for example, 10 points).

[0034] While not particularly limited, the average temperature during the discharge described above is, for example, 30°C or lower, but may also be 25°C or lower, 20°C or lower, or even 10°C or lower. Here, for example, the higher the current discharge or the longer the discharge time, the more easily the salt on the electrode surface dries out, so the drop in the discharge voltage curve due to the decrease in salt concentration tends to be more pronounced. Also, the discharge voltage curve tends to drop when the diffusion resistance is high. For example, when high current discharge can be performed, the drop in the discharge voltage curve is easier to see, making it easier to obtain the discharge time. However, for example, if the system cannot supply a high current, the drop in the discharge voltage curve is difficult to see, and it may be difficult to obtain the discharge time. In response to this, the inventors' research has shown that salt diffusion is slower in low-temperature environments than in room-temperature environments, and the effect of the decrease in salt concentration on diffusion resistance is greater. That is, for example, even if the system cannot supply a high current, it has been found that if the same current is supplied, it is easier to obtain the discharge time when the discharge is performed in a low-temperature environment than in a room-temperature environment. Based on the above, the average temperature during the discharge time is preferably -10°C or lower, and more preferably -20°C or lower, from the viewpoint of making it easier to obtain the discharge time even when, for example, a large current cannot be flowed through the system. In other words, in the discharge time acquisition step S2, it is preferable to discharge the secondary battery 1 in a low-temperature environment where the average temperature is -10°C or lower and measure the discharge time. Furthermore, the lower limit of the average temperature during the discharge is, for example, -40°C or higher, and may also be -30°C or higher.

[0035] While not particularly limited, the average current during discharge is, for example, 50A or more. On the other hand, from the viewpoint of making it easier to obtain the discharge time, the average current during discharge is preferably 100A or more, and more preferably 200A or more or 300A or more. Furthermore, the upper limit of the average current during discharge is, for example, 500A or less, and may be 400A or less. In other words, in the discharge time acquisition step S2, it is preferable to discharge the secondary battery 1 so that the average current during discharge is at least 100A, and then measure the discharge time.

[0036] While not particularly limited, the State of Charge (SOC) at the start of discharge may be, for example, 30% or more, or 40% or more. The inventors' research has shown that, for example, when discharging from a low SOC, the lower limit current (in other words, the minimum usable voltage constrained in the cell or system) is easily reached due to the voltage drop caused by DC and reaction resistance. That is, it has been found that discharging from a low SOC makes it difficult to perform high-current discharge or long-duration discharge to the extent that salt diffusion resistance (or salt depletion) can be observed. Therefore, from the viewpoint of making it easier to obtain the discharge time, discharge from a high SOC is preferred. Specifically, from the viewpoint of making it easier to obtain the discharge time, the SOC at the start of discharge is preferably 50% or more, more preferably 60% or more, or 70% or more, and even more preferably 80% or more, or 90% or more (it may even be 100%). In other words, in the discharge time acquisition step S2, it is preferable to discharge the secondary battery 1 from a high SOC state where the SOC is at least 50%, and measure the discharge time.

[0037] While not particularly limited, the voltage at the end of discharge is, for example, 0.5V or higher, and may be 1V or higher or 1.5V or higher. On the other hand, from the viewpoint of making it easier to obtain the discharge time, the voltage at the end of discharge is preferably 2V or higher, and more preferably 2.5V or higher. Furthermore, the upper limit of the voltage at the end of discharge is, for example, 5V or lower, and may be 4V or lower or 3V or lower. In other words, in the discharge time acquisition step S2, it is preferable to discharge the secondary battery 1 so that the voltage at the end of discharge is at least 2V and to acquire the discharge time.

[0038] When measuring the discharge time of the secondary battery 1, the discharge time acquisition processing unit 21 of the salt concentration estimation device 100 acquires the discharge time from the secondary battery 1 mounted on the electric vehicle. Discharge under the predetermined conditions described above can be performed on an external load, for example. Examples of such external loads include resistors, fans, heaters, etc. Alternatively, the discharge time acquisition processing unit 21 can acquire data from the electric vehicle during operation when the above predetermined conditions are met as the discharge time. That is, the discharge time acquisition processing unit 21 can acquire data from the electric vehicle during operation when the above predetermined conditions are met as the discharge time.

[0039] (Salt concentration estimation process S3) In this process, the salt concentration of the electrolyte of secondary battery 1 is estimated based on the acquired capacity of secondary battery 1, the acquired discharge time, and a table that records the relationship between the capacity of secondary battery 1, the discharge time, and the salt concentration of the electrolyte of secondary battery 1. Specifically, a map is prepared in advance that records the relationship between the capacity of secondary battery 1, the discharge time of secondary battery 1, and the salt concentration of the electrolyte of secondary battery 1.

[0040] The above map can be created using, for example, a table (matrix) like the one shown below. Here, Figures 5A, 5B, and 5C are the first, second, and third graphs, respectively, showing the relationship between discharge time and salt concentration according to one embodiment. Figure 6 is a matrix diagram showing an example of a salt concentration estimation map for the electrolyte of secondary battery 1.

[0041] First, let's explain the graphs shown in Figures 5A, 5B, and 5C. The horizontal and vertical axes of each graph represent salt concentration and time to reach (discharge time), respectively. Each graph shows the values ​​when the full charge capacity is 100%, 90%, and 80%, respectively. Here, a full charge capacity of 100% for secondary battery 1 means that no capacity degradation has occurred in secondary battery 1. A full charge capacity of 90% for secondary battery 1 means that a 10% capacity degradation has occurred with use of secondary battery 1. And a full charge capacity of 80% for secondary battery 1 means that a 20% capacity degradation has occurred with use of secondary battery 1.

[0042] Next, we will explain the specific methods for obtaining each graph. Below, we will explain the method for obtaining the graph shown in Figure 5B as an example. Figures 5A, 5B, and 5C show graphs obtained when measurements were performed using a non-aqueous lithium-ion secondary battery (lithium nickel-cobalt manganese oxide-graphite, capacity: 4Ah) as secondary battery 1.

[0043] First, prepare multiple secondary batteries 1 with different salt concentrations in the electrolyte. While not particularly limited, from the viewpoint of obtaining a more accurate graph, it is preferable to prepare 3 or more secondary batteries 1 with different salt concentrations, more preferably 5 or more, and even more preferably 10 or more. From the viewpoint of cost, the upper limit of the number of secondary batteries 1 with different salt concentrations is preferably 20 or less, or 15 or less.

[0044] For example, in this embodiment, six secondary batteries 1 are prepared with electrolyte salt concentrations of 0.4M, 0.6M, ..., 1.4M. Next, the capacity degradation of the prepared secondary batteries 1 is accelerated by performing high-current charging and discharging. Here, the capacity degradation of the secondary batteries 1 is accelerated so that the full charge capacity becomes 90%. Subsequently, each secondary battery 1 with a full charge capacity of 90% is discharged under predetermined conditions. For example, in this embodiment, the discharge conditions are: average temperature during discharge: 25°C, average current during discharge: 300A, SOC at the start of discharge: 50%, voltage at the end of discharge: 2.5V. For each secondary battery 1, the discharge time when the voltage reaches 2.5V is obtained as the arrival time. Finally, each secondary battery 1 is disassembled and the salt concentration in the electrolyte of each is obtained. Then, by plotting the relationship between the arrival time and salt concentration obtained as described above, the graph shown in Figure 5B can be obtained. Note that the graphs shown in Figures 5A and 5C can also be obtained based on the method described above.

[0045] In the graphs of Figures 5A, 5B, and 5C, the time to reach the target voltage decreases as the vertical axis moves from top to bottom. Also, on the horizontal axis of each graph, the salt concentration decreases as the horizontal axis moves from left to right. As can be seen from each graph, as the salt concentration in the electrolyte decreases, the time to reach the target voltage (in this case, 2.5V) decreases. In addition, this time to reach the target voltage also decreases with a normal decrease in full charge capacity, but even with the same full charge capacity, the time to reach the target voltage decreases when the salt concentration decreases.

[0046] In this embodiment, in addition to the graphs in Figures 5A, 5B, and 5C, graphs for full charge capacities of 70%, 60%, 50%, 40%, 30%, 20%, and 10% are also obtained. Then, as shown in Figure 6, a map is created showing the relationship between the capacity of the secondary battery 1 (here, full charge capacity), the discharge time (time to reach), and the salt concentration of the electrolyte of the secondary battery 1. Here, in this map, the salt concentration of the electrolyte of the secondary battery 1 is shown as SC (Salt Concentration). The number in parentheses attached to SC indicates (time to reach, full charge capacity).

[0047] When estimating the salt concentration of the electrolyte of the secondary battery 1, the salt concentration estimation device 100 can operate as follows. Specifically, first, the salt concentration estimation processing unit 22 of the salt concentration estimation device 100 has a map (see Figure 6) prepared in advance that shows the relationship between the capacity of the secondary battery 1, the discharge time of the secondary battery 1, and the salt concentration of the electrolyte of the secondary battery 1. Then, based on the capacity of the secondary battery 1 obtained by the capacity acquisition processing unit 20 and the discharge time obtained by the discharge time acquisition processing unit 21, the map is referred to to obtain an estimated value of the salt concentration of the secondary battery 1. Note that Figure 6 is merely an example of the map used here. The map prepared here should be a predetermined table (matrix) in which the relationship between the capacity of the secondary battery 1, the discharge time, and the salt concentration of the electrolyte of the secondary battery 1 to be estimated is recorded.

[0048] As described above, in the salt concentration estimation method according to this embodiment, the salt concentration of the electrolyte of the secondary battery 1 can be estimated using the capacity of the secondary battery 1 calculated in the capacity acquisition step S1 and the discharge time measured in the discharge time acquisition step S2. As a result of the inventor's investigation, it was found that the discharge time when the secondary battery 1 is discharged under predetermined conditions differs for each capacity of the secondary battery 1. Focusing on this, the salt concentration of the electrolyte of the secondary battery 1 is estimated based on the acquired capacity of the secondary battery 1, the acquired discharge time, and a table that records the relationship between the capacity of the secondary battery 1, the discharge time, and the salt concentration of the electrolyte for the secondary battery 1 to be estimated, so that the salt concentration of the electrolyte can be estimated with high accuracy. In this way, by understanding the current salt concentration of the electrolyte of the secondary battery 1, it is possible to prevent the occurrence of various problems that may arise due to a decrease in the salt concentration of the electrolyte (for example, electrolyte freezing at low temperatures, decrease in input / output, decrease in degradation resistance to high-current charging and discharging, increase in estimation error of remaining driving distance, etc.), which are difficult to grasp from, for example, the estimation of the amount of Li deposition. Furthermore, such estimation of salt concentration can be performed, for example, by a salt concentration estimation device 100 equipped with a computer 10 having a capacity acquisition processing unit 20, a discharge time acquisition processing unit 21, and a salt concentration estimation processing unit 22.

[0049] Furthermore, in this embodiment, the secondary battery 1 is installed in an electric vehicle. In the discharge time acquisition step S2, the discharge time is acquired when the secondary battery 1 is discharged under predetermined conditions during use of the electric vehicle. Thus, according to the technology of this disclosure, for example, the salt concentration of the electrolyte of the secondary battery 1 can be estimated even when it is being used in an electric vehicle.

[0050] The embodiments of the technology disclosed herein (first embodiment) have been described above. However, the above description is illustrative and does not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated in the above description.

[0051] <Other Embodiments> For example, Figure 7 is a schematic diagram showing a salt concentration estimation device 200 for the electrolyte of a secondary battery 1 according to another embodiment (second embodiment). As shown in Figure 7, the salt concentration estimation device 200 according to the second embodiment includes a computer 110. The computer 110 includes a capacity acquisition processing unit 120, a discharge time acquisition processing unit 121, a salt concentration estimation processing unit 122, a determination processing unit 123, a notification processing unit 124, and a control processing unit 125. Note that the configurations of the capacity acquisition processing unit 120, the discharge time acquisition processing unit 121, and the salt concentration estimation processing unit 122 can be the same as those of the capacity acquisition processing unit 20, the discharge time acquisition processing unit 21, and the salt concentration estimation processing unit 22 described above, so a detailed explanation is omitted.

[0052] The determination processing unit 123 of the computer 110 determines whether the salt concentration of the electrolyte of the secondary battery 1, estimated by the salt concentration estimation processing unit 122, is below a predetermined salt concentration. The notification processing unit 124 notifies the user of the decrease in salt concentration when the determination processing unit 123 determines that the salt concentration of the electrolyte of the secondary battery 1 is below a predetermined salt concentration. The control processing unit 125 corrects the battery control values ​​(e.g., input / output values, etc.) of the secondary battery 1 to appropriate values ​​when the determination processing unit 123 determines that the salt concentration of the electrolyte of the secondary battery 1 is below a predetermined salt concentration. The salt concentration estimation method according to the second embodiment will now be described with reference to the salt concentration estimation device 200.

[0053] Here, Figure 8 is a flowchart showing a method for estimating the salt concentration of the electrolyte of a secondary battery 1 according to another embodiment (second embodiment). As shown in Figure 8, in the salt concentration estimation method according to the second embodiment, first, the salt concentration of the electrolyte of the secondary battery 1 is estimated (step S11). More specifically, a first capacity acquisition step, a first discharge time acquisition step, and a first salt concentration estimation step are performed. Here, in the first capacity acquisition step, the capacity of the secondary battery 1 to be estimated is acquired. In the first discharge time acquisition step, the discharge time when the secondary battery 1 is discharged under predetermined conditions is acquired. In the first salt concentration estimation step, the salt concentration of the electrolyte of the secondary battery 1 is estimated based on the acquired capacity of the secondary battery 1, the acquired discharge time, and a table that records the relationship between the capacity of the secondary battery 1, the discharge time, and the salt concentration of the electrolyte for the secondary battery 1 to be estimated.

[0054] In estimating the salt concentration, the salt concentration estimation device 200 operates the capacity acquisition processing unit 120, the discharge time acquisition processing unit 121, and the salt concentration estimation processing unit 122 to estimate the salt concentration of the electrolyte of the secondary battery 1. For details of the first capacity acquisition step, the first discharge time acquisition step, and the first salt concentration estimation step, please refer to the descriptions of the capacity acquisition step S1, the discharge time acquisition step S2, and the salt concentration estimation step S3 in the first embodiment described above.

[0055] Next, it is determined whether the salt concentration estimated in the first salt concentration estimation step is less than or equal to a predetermined salt concentration (here, X[M]) (step S12). That is, it is determined whether the salt concentration of the secondary battery 1 estimated in the first salt concentration estimation step is less than or equal to a predetermined salt concentration (first determination step).

[0056] In making such a determination, the determination processing unit 123 in the salt concentration estimation device 200 determines whether the salt concentration estimated by the salt concentration estimation processing unit 122 is less than or equal to a predetermined salt concentration. If the salt concentration estimated by the salt concentration estimation processing unit 122 is not less than or equal to the predetermined salt concentration (i.e., NO), the process ends. If the salt concentration estimated by the salt concentration estimation processing unit 122 is less than or equal to the predetermined concentration (i.e., YES), the process proceeds to step S13.

[0057] Next, the battery control value (in this case, the input / output value) of the secondary battery 1 is controlled (step S13). That is, when it is determined in the first determination step that the salt concentration of the secondary battery 1 is decreasing, the battery control value of the secondary battery 1 is controlled (control step). In this control, the control processing unit 125 in the salt concentration estimation device 200 controls the input / output value of the secondary battery 1. For example, by adjusting the input / output value of the secondary battery 1, the rate of decrease of salt in the electrolyte can be controlled.

[0058] Next, the salt concentration of the electrolyte in the secondary battery 1 after the input / output control described above is estimated (step S14). More specifically, a second capacity acquisition step, a second discharge time acquisition step, and a second salt concentration estimation step are performed. In the second capacity acquisition step, the capacity of the secondary battery 1 after the control described above that is to be estimated is acquired. In the second discharge time acquisition step, the discharge time when the secondary battery 1 after the control described above is discharged under predetermined conditions is acquired. In the second salt concentration estimation step, the salt concentration of the electrolyte in the secondary battery 1 after the control described above is estimated based on the acquired capacity of the secondary battery 1 after the control described above, the acquired discharge time after the control described above, and a table that records the relationship between the capacity of the secondary battery 1, the discharge time, and the salt concentration of the electrolyte in the secondary battery 1 that is to be estimated. Specifically, based on the capacity of the secondary battery 1 after control obtained above and the discharge time of the secondary battery 1 after control obtained above, the salt concentration of the electrolyte of the secondary battery 1 after control is estimated by referring to a pre-created table that shows the relationship between the capacity of the secondary battery 1, the discharge time of the secondary battery 1, and the salt concentration of the electrolyte of the secondary battery 1. In estimating the salt concentration, the capacity acquisition processing unit 120, the discharge time acquisition processing unit 121, and the salt concentration estimation processing unit 122 of the salt concentration estimation device 200 are activated to estimate the salt concentration of the electrolyte of the secondary battery 1 after control. For details of the second capacity acquisition step, the second discharge time acquisition step, and the second salt concentration estimation step, refer to the explanations of the capacity acquisition step S1, the discharge time acquisition step S2, and the salt concentration estimation step S3 in the first embodiment described above.

[0059] Next, it is determined whether the salt concentration estimated in the second salt concentration estimation step is less than or equal to a predetermined salt concentration (here, Y[M]) (step S15). That is, it is determined whether the salt concentration of the secondary battery 1 estimated in the second salt concentration estimation step is less than or equal to a predetermined salt concentration (second determination step). In making this determination, the determination processing unit 123 in the salt concentration estimation device 200 determines whether the salt concentration estimated by the salt concentration estimation processing unit 122 is less than or equal to a predetermined salt concentration. If the salt concentration estimated by the salt concentration estimation processing unit 122 is not less than or equal to a predetermined salt concentration (i.e., NO), the process ends. If the salt concentration estimated by the salt concentration estimation processing unit 122 is less than or equal to a predetermined concentration (i.e., YES), the process proceeds to step S16.

[0060] Finally, in the second determination step, if it is determined that the salt concentration of the electrolyte of the secondary battery 1 after the control has decreased, a warning is displayed to the user (step S16). That is, in the second determination step, if it is determined that the salt concentration of the electrolyte of the secondary battery 1 after the control has decreased to or below a predetermined salt concentration, the user is notified of the decrease in salt concentration (notification step). Such notification to the user can be carried out, for example, by a display or speaker provided by the electric vehicle. As shown in Figure 7, in this embodiment, the warning is displayed to the user by a display provided by the electric vehicle.

[0061] The predetermined salt concentration X[M] (also called the first salt concentration) in step S12 and the predetermined salt concentration Y[M] (also called the second salt concentration) in step S15 may be the same or different. On the other hand, from the viewpoint of more effectively preventing a decrease in the salt concentration in the electrolyte of the secondary battery 1, it is preferable that the second salt concentration be set higher than the first salt concentration. That is, it is preferable that the first salt concentration and the second salt concentration be set such that the relationship second salt concentration > first salt concentration is satisfied. The values ​​of X and Y are preferably determined appropriately depending on the type of secondary battery 1 and the environment in which the secondary battery 1 is placed.

[0062] With the above configuration, the salt concentration of the electrolyte in the secondary battery 1 can be estimated, and the user can be notified of a decrease in the salt concentration. This can, for example, encourage the electric vehicle to be brought in for maintenance. Furthermore, the decrease in salt concentration can be addressed by adjusting, for example, the input and output values ​​of the secondary battery 1.

[0063] The salt concentration estimation method according to the second embodiment described above includes a total of 10 steps, but is not limited thereto. The salt concentration estimation method disclosed herein may be configured to perform a total of 5 steps: the first capacity acquisition step, the first discharge time acquisition step, the first salt concentration estimation step, the first determination step, and the notification step. In this case, the computer of the salt concentration estimation device may include a capacity acquisition processing unit 120, a discharge time acquisition processing unit 121, a salt concentration estimation processing unit 122, a determination processing unit 123, and a notification processing unit 124. With such a configuration, the user can be notified of a decrease in the salt concentration of the electrolyte of the secondary battery 1 based on the estimation. This makes it possible to prevent various problems that may occur in the secondary battery 1 as described above.

[0064] Furthermore, the salt concentration estimation method according to the second embodiment performs a total of two determinations, the first determination step and the second determination step, but is not limited to this. In the salt concentration estimation method disclosed herein, if the salt concentration of the electrolyte of the secondary battery 1 after the control is less than or equal to a predetermined salt concentration in the second determination step, the control step may be performed again, and the capacity acquisition step, discharge time acquisition step, salt concentration estimation step, and determination step may be performed again. With such a configuration, the salt concentration of the secondary battery 1 can be adjusted with greater precision.

[0065] For example, the above embodiment describes a case where the secondary battery 1 is installed in an electric vehicle, but it is not limited to this. The salt concentration specifying device and salt concentration estimation method disclosed herein can also be used to estimate secondary batteries 1 located in facilities, for example.

[0066] For example, in the above embodiment, one secondary battery 1 is used as the target for estimation, but it is not limited to this. The salt concentration estimation device and salt concentration estimation method disclosed herein can also be used to estimate a battery pack (stack) comprising multiple secondary batteries 1. On the other hand, the former is more preferable from the viewpoint of estimating the salt concentration of the electrolyte of the secondary battery 1 with higher accuracy.

[0067] For example, in the above embodiment, the map shown in Figure 3 shows the years of use in increments of one year from 1 to 10 years, but is not limited to this. The range of years of use and the increments can be changed as appropriate. Also, for example, the map shown in Figure 4 shows the charging time in increments of one minute from 1 minute to 60 minutes, but is not limited to this. The range of charging time and the increments can be changed as appropriate. Furthermore, for example, the unit of temperature history can be "minutes" instead of "hours". And for example, the unit of charging time can be "hours" instead of "minutes". In the map shown in Figure 3, other conditions can also be added.

[0068] For example, in the above embodiment, the fully charged capacity of the secondary battery 1 is calculated as a percentage (%), but the invention is not limited to this. In other embodiments, the fully charged capacity of the secondary battery 1 may be calculated as an actual numerical value (Ah). Also, for example, in the above embodiment, the fully charged capacity is measured as the capacity of the secondary battery 1, but the invention is not limited to this. The technology disclosed herein can also use the capacity measured under predetermined conditions as the capacity of the secondary battery 1.

[0069] For example, in the above embodiment, a map is created showing the relationship between the capacity of the secondary battery 1 (here, the full charge capacity), the discharge time (here, the time to reach the discharge), and the salt concentration, but it is not limited to this. The map may be created by adding other conditions in addition to these conditions.

[0070] As described above, specific embodiments of the technology disclosed herein include those described in the following sections.

[0071] Section 1: A capacity acquisition process to obtain the capacity of the secondary battery to be estimated, A discharge time acquisition step is to acquire the discharge time when the secondary battery is discharged under predetermined conditions, A salt concentration estimation step for estimating the salt concentration of the electrolyte of the secondary battery based on the acquired capacity of the secondary battery, the acquired discharge time, and a table recording the relationship between the capacity of the secondary battery, the discharge time, and the salt concentration of the electrolyte for the secondary battery to be estimated. A method for estimating the salt concentration of the electrolyte in a secondary battery, including [details omitted].

[0072] Section 2: The aforementioned secondary battery is installed in an electric vehicle. The method for estimating the salt concentration of the electrolyte of a secondary battery according to item 1, wherein the discharge time acquisition step acquires the discharge time when the secondary battery is discharged under predetermined conditions during use of the electric vehicle.

[0073] Section 3: The method for estimating the salt concentration of the electrolyte of a secondary battery according to item 1 or 2, wherein in the discharge time acquisition step, the secondary battery is discharged when the SOC is at least 50%, and the discharge time is acquired.

[0074] Section 4: The method for estimating the salt concentration of the electrolyte of a secondary battery according to any one of items 1 to 3, wherein the discharge time acquisition step involves discharging the secondary battery in a temperature environment with an average temperature of -10°C or lower and acquiring the discharge time.

[0075] Section 5: A capacity acquisition process to obtain the capacity of the secondary battery to be estimated, A discharge time acquisition process that acquires the discharge time when the secondary battery is discharged under predetermined conditions, A salt concentration estimation process that estimates the salt concentration of the electrolyte of the secondary battery based on the acquired capacity of the secondary battery, the acquired discharge time, and a table recording the relationship between the capacity of the secondary battery, the discharge time, and the salt concentration of the electrolyte for the secondary battery to be estimated. It is configured to be executed by a computer. A device for estimating the salt concentration of the electrolyte in a secondary battery.

[0076] Item 6: The aforementioned secondary battery is installed in an electric vehicle. The apparatus for estimating the salt concentration of the electrolyte of a secondary battery according to item 5, wherein the discharge time acquisition process acquires the discharge time when the secondary battery is discharged under predetermined conditions during use of the electric vehicle.

[0077] Section 7: The apparatus for estimating the salt concentration of the electrolyte of a secondary battery according to item 5 or 6, wherein the discharge time acquisition process acquires the discharge time when the secondary battery is discharged with a state of charge of at least 50%.

[0078] Section 8: The apparatus for estimating the salt concentration of the electrolyte of a secondary battery according to any one of items 5 to 7, wherein the discharge time acquisition process acquires the discharge time when the secondary battery is discharged in a temperature environment with an average temperature of -10°C or lower. [Explanation of symbols]

[0079] 1 Secondary battery 10,110 computers 20,120 Capacity acquisition processing unit 21,121 Discharge time acquisition processing unit 22,122 Salt concentration estimation processing unit 123 Determination Processing Unit 124 Notification Processing Unit 125 Control Processing Unit 100,200 Salt concentration estimation device

Claims

1. A capacity acquisition process to obtain the capacity of the secondary battery to be estimated, A discharge time acquisition step is to acquire the discharge time when the secondary battery is discharged under predetermined conditions, A salt concentration estimation step for estimating the salt concentration of the electrolyte of the secondary battery based on the acquired capacity of the secondary battery, the acquired discharge time, and a table recording the relationship between the capacity of the secondary battery, the discharge time, and the salt concentration of the electrolyte for the secondary battery to be estimated. A method for estimating the salt concentration of the electrolyte in a secondary battery, including [details omitted].

2. The aforementioned secondary battery is installed in an electric vehicle. The method for estimating the salt concentration of the electrolyte of a secondary battery according to claim 1, wherein the discharge time acquisition step acquires the discharge time when the secondary battery is discharged under predetermined conditions during use of the electric vehicle.

3. The method for estimating the salt concentration of the electrolyte of a secondary battery according to claim 1 or 2, wherein in the discharge time acquisition step, the secondary battery is discharged when the SOC is at least 50%, and the discharge time is acquired.

4. The method for estimating the salt concentration of the electrolyte of a secondary battery according to claim 1 or 2, wherein in the discharge time acquisition step, the secondary battery is discharged in a temperature environment with an average temperature of -10°C or lower, and the discharge time is acquired.

5. A capacity acquisition process to obtain the capacity of the secondary battery to be estimated, A discharge time acquisition process that acquires the discharge time when the secondary battery is discharged under predetermined conditions, A salt concentration estimation process that estimates the salt concentration of the electrolyte of the secondary battery based on the acquired capacity of the secondary battery, the acquired discharge time, and a table recording the relationship between the capacity of the secondary battery, the discharge time, and the salt concentration of the electrolyte for the secondary battery to be estimated. It is configured to be executed by a computer. A device for estimating the salt concentration of the electrolyte in a secondary battery.

6. The aforementioned secondary battery is installed in an electric vehicle. The apparatus for estimating the salt concentration of the electrolyte of a secondary battery according to claim 5, wherein the discharge time acquisition process acquires the discharge time when the secondary battery is discharged under predetermined conditions during use of the electric vehicle.

7. The apparatus for estimating the salt concentration of the electrolyte of a secondary battery according to claim 5 or 6, wherein the discharge time acquisition process acquires the discharge time when the secondary battery is discharged with a state of charge of at least 50%.

8. The apparatus for estimating the salt concentration of the electrolyte of a secondary battery according to claim 5 or 6, wherein the discharge time acquisition process acquires the discharge time when the secondary battery is discharged in a temperature environment with an average temperature of -10°C or lower.

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