Deterioration estimation method

Abstract

To provide a deterioration estimation method for estimating battery deterioration by a simple process.SOLUTION: A deterioration estimation method when an ultrasonic transducer is installed in a vehicle includes a step of measuring the initial load of a secondary battery, a measurement step of measuring the load of the secondary battery after use, a step of calculating the load increase of the secondary battery on the basis of the initial load and the load after use, and an estimation step of estimating the capacity maintenance rate from the calculated load increase.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a degradation estimation method. [Background technology]

[0002] Patent Document 1 discloses a technology for determining the state of health (SOH) of a lithium-ion battery by using an ultrasonic transducer to transmit ultrasonic waves to a battery such as a lithium-ion battery and receiving or measuring the ultrasonic waves that pass through the lithium-ion battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-524361 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned Patent Document 1, when an ultrasonic transducer is mounted on a vehicle, the storage space of the vehicle is reduced, and therefore, a technique for estimating battery deterioration in a simple manner has been desired.

[0005] The present disclosure has been made in view of the above, and aims to provide a degradation estimation method that can estimate battery degradation in a simple manner. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the objectives, the deterioration estimation method of the present disclosure includes a measurement step of measuring an initial load and a load after use of a secondary battery, a calculation step of calculating a load increase amount of the secondary battery based on the initial load and the load after use, and an estimation step of estimating a capacity retention rate from the load increase amount. [Effects of the Invention]

[0007] The present disclosure provides an advantage in that it is possible to estimate battery deterioration using a simple method. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a secondary battery according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a flowchart showing an outline of the method for estimating deterioration of a secondary battery according to the first embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram showing the relationship between the number of cycles and the capacity retention rate of a secondary battery based on a current cycle test. [Figure 4] FIG. 4 is a diagram showing the relationship between the number of cycles and the load N of the secondary battery based on the current cycle test. [Figure 5] FIG. 5 is a diagram showing the relationship between the load N and time under each condition. [Figure 6] FIG. 6 is a flowchart illustrating an outline of a method for estimating deterioration of a secondary battery according to the second embodiment of the present disclosure. [Figure 7] FIG. 7 is a diagram illustrating the thickness of an unconstrained cell in its initial state and in its used state. [Figure 8] FIG. 8 is a diagram showing the relationship between the number of cycles of a secondary battery and the increase in battery thickness based on a current cycle test. [Figure 9] FIG. 9 is a graph showing the relationship between the battery thickness and the capacity retention rate. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a method for estimating deterioration of a secondary battery according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially identical. Furthermore, the figures referenced in the following description merely show a schematic representation of the shape, size, and positional relationship to the extent that the contents of the present disclosure can be understood. In other words, the present disclosure is not limited to only the shape, size, and positional relationship exemplified in each figure.

[0010] (Embodiment 1) [Configuration of secondary battery] FIG. 1 is a schematic diagram of a secondary battery according to a first embodiment. The secondary battery 1 shown in FIG. 1 includes a plurality of cells 2 and end plates 3. The end plates 3 are provided on both ends of the cells 2 in the arrangement direction, and function as restraining devices that restrain the cells 2 from both ends. As a result, the end plates 3 restrain each of the cells 2, generating a load, and the secondary battery 1 functions as a battery pack. Here, the load refers to the surface pressure generated by the restraint by the end plates 3.

[0011] [Method for estimating deterioration of secondary batteries] Next, we will explain a method for estimating deterioration of the secondary battery 1. Fig. 2 is a flowchart showing an outline of the method for estimating deterioration of the secondary battery 1. Note that, in the following, it is assumed that the method is performed using a well-known measuring device capable of measuring the load of the secondary battery 1.

[0012] As shown in FIG. 2, first, the measurement device measures the initial load on the secondary battery 1 (step S101), and then measures the post-use load on the secondary battery 1 (step S102).

[0013] Next, the measuring device calculates the load increase amount of the secondary battery 1 based on the initial load and the load after use (step S103), and estimates the capacity maintenance rate from the load increase amount of the secondary battery 1 (step S104). After step S104, this process ends.

[0014] FIG. 3 is a diagram showing the relationship between the number of cycles and the capacity retention rate of the secondary battery 1 based on a current cycle test. FIG. 4 is a diagram showing the relationship between the number of cycles and the load N of the secondary battery 1 based on a current cycle test. FIG. 5 is a diagram showing the relationship between the load N and time under each condition. In FIG. 3, the horizontal axis indicates the number of cycles, and the vertical axis indicates the capacity retention rate. Curves L1, L2, and L3 in FIG. 3 show the relationship between the number of cycles and the capacity retention rate for each temperature. In FIG. 4, the horizontal axis indicates the number of cycles, and the vertical axis indicates the load N. Curve L4 in FIG. 4 shows the relationship between the number of cycles and the load N. Furthermore, in FIG. 5, the horizontal axis indicates time (sec) and the vertical axis indicates the load N. Furthermore, curve L5 shows the relationship between the load N and time.

[0015] As shown by curves L1 to L3 in Fig. 3 and curve L4 in Fig. 4, there is a correlation between the load increase and capacity retention rate that accompanies use of the secondary battery 1. For this reason, when the load increase amount is x and the capacity retention rate is y, the measurement device estimates the capacity retention rate y using the following correlation formula (1): y=-0.096239x+0.938002 ···(1) This allows the measuring device to estimate the capacity retention rate from the load increase amount of the secondary battery 1, i.e., to use a simple method to estimate the deterioration of the secondary battery 1. That is, the measuring device does not use current values ​​or voltage values ​​as in the prior art, and therefore can estimate the capacity retention rate without being affected by current or voltage sensor errors.

[0016] 5, the load of the secondary battery 1 varies depending on whether it is charged, discharged, at rest, or in a different SOC (State of Charge), so it is desirable to fix the load measurement conditions. That is, when estimating the capacity retention rate from the load increase of the secondary battery 1, the measurement device measures the initial load of the secondary battery 1 and the load after use under the same measurement conditions. It is preferable to measure the load when the secondary battery 1 is at rest after being fully charged.

[0017] According to the first embodiment described above, the initial load and the load after use on the secondary battery 1 are measured, the load increase amount of the secondary battery 1 is calculated based on the initial load and the load after use, and the capacity maintenance rate is estimated from the load increase amount of the secondary battery 1, so that the deterioration of the secondary battery 1 can be estimated in a simple manner.

[0018] (Embodiment 2) Next, a description will be given of a second embodiment. In the first embodiment, the initial load and the load after use of the secondary battery 1 are measured, but in the second embodiment, the capacity retention rate is estimated by measuring the initial thickness of the cells 2 in the secondary battery 1 and the thickness of the cells 2 after use. Therefore, a method for estimating deterioration of the secondary battery 1 according to the second embodiment will be described below.

[0019] 6 is a flowchart showing an outline of a method for estimating deterioration of a secondary battery 1 according to embodiment 2. Note that the method is performed using a known measuring device capable of measuring the thickness of cells 2 constituting the secondary battery 1.

[0020] As shown in Fig. 6, the measuring device first measures the initial thickness of each cell 2 constituting the secondary battery 1 (step S201), and then measures the thickness of each cell 2 constituting the secondary battery 1 after use (step S202). Fig. 7 is a diagram that schematically illustrates the thickness of each unconstrained cell 2 in its initial state and in its used state. As shown in Fig. 7, the measuring device measures the thickness D1 of each cell 2 in its initial state when not constrained by an end plate 3, and the thickness D2 of each cell 2 after use. In this case, the thickness of each cell 2 after use increases in the short-side direction as it is used.

[0021] Next, the measuring device calculates the increase in thickness of the cell 2 based on the initial thickness of the cell 2 and the thickness of the cell after use (step S203), and estimates the capacity maintenance rate from the increase in thickness of the cell 2 (step S204). After step S204, this process ends.

[0022] FIG. 8 is a diagram showing the relationship between the number of cycles and the increase in battery thickness of secondary battery 1 based on a current cycle test. FIG. 9 is a diagram showing the relationship between battery thickness and capacity retention rate. In FIG. 8, the horizontal axis represents the number of cycles, and the vertical axis represents the increase in battery thickness (mm). Furthermore, in FIG. 8, broken lines L10 to L12 show the relationship between the number of cycles and the increase in battery thickness for each temperature. Furthermore, in FIG. 9, the horizontal axis represents the increase in battery thickness (mm), and the vertical axis represents the capacity retention rate. Furthermore, in FIG. 9, straight line L13 shows the relationship between battery thickness and capacity retention rate.

[0023] As shown by the curves L1 to L3 in Fig. 3 and the broken lines L10 to L12 in Fig. 8, there is a correlation between the increase in thickness due to use of the secondary battery 1 and the capacity retention rate. Therefore, as shown by the straight line L13 in Fig. 9, when the increase in thickness is x and the capacity retention rate is y, the measuring device estimates the capacity retention rate y in the same way as with the correlation formula (1) described above. y=-0.096239x+0.938002 ···(1) As a result, the measuring device can estimate the capacity maintenance rate from the amount of increase in thickness of the secondary battery 1, that is, can estimate the deterioration of the secondary battery 1 in a simple manner.

[0024] According to the second embodiment described above, the increase in thickness of the cell 2 is calculated based on the initial thickness of the cell 2 and the thickness of the cell after use, and the capacity maintenance rate is estimated from the increase in thickness of the cell 2, so that the deterioration of the secondary battery 1 can be estimated in a simple manner.

[0025] (Other forms) Further advantages and modifications will readily occur to those skilled in the art. The invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

[0026] Although some of the embodiments of the present application have been described in detail above with reference to the drawings, these are merely examples, and the present invention can be implemented in other forms that have undergone various modifications and improvements based on the knowledge of those skilled in the art, including the aspects described in the disclosure of the present invention. [Explanation of symbols]

[0027] 1 Secondary battery 2 D cells 3 End Plate

Claims

[Claim 1] a measuring step of measuring an initial load and a load after use of the secondary battery; a calculation step of calculating a load increase amount of the secondary battery based on the initial load and the load after use; an estimation step of estimating a capacity maintenance rate from the load increase amount; Including, Deterioration estimation method.

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