Method and device for measuring solid-phase diffusion coefficient of battery

Abstract

The invention provides a determination method and a determination device for a solid phase diffusion coefficient of a battery. The determination method and the determination device solve the technical problem that a determination mode for determining the solid phase diffusion coefficient of the battery in the prior art is relatively long in time consumption. According to the method for measuring the solid-phase diffusion coefficient of the battery, the battery is subjected to constant-current charging and discharging by adopting the preset charging rate, then charging and discharging are stopped for the preset discontinuous duration, and then constant-current charging and discharging and charging and discharging stopping for the preset discontinuous duration are repeated until the battery is charged to the limit high voltage and discharged to the limit low voltage. Therefore, a curve of the solid-phase diffusion coefficient changing along with the charge state in the charging process and a curve of the solid-phase diffusion coefficient changing along with the charge state in the discharging process can be obtained. Compared with a method for calculating the solid-phase diffusion coefficient by adopting a GI TT method, the time for measuring the solid-phase diffusion coefficient of the battery is greatly shortened, and the measuring efficiency of the solid-phase diffusion coefficient of the battery is further improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method and device for measuring the solid-phase diffusion coefficient of a battery. Background Art

[0002] Lithium-ion batteries have been applied and commercialized in handheld devices, electronic products, hybrid vehicles and other fields due to their high energy density and good cycle performance. However, the key development processes of batteries, such as design, testing, safety, failure and life, are time-consuming and complex. Therefore, electrochemical simulation of lithium-ion battery systems can quickly measure electrolyte-related parameters (such as ionic conductivity, ion diffusion coefficient, etc.) and kinetic parameters (such as exchange current density, charge transfer coefficient, diffusion coefficient, etc.).

[0003] The diffusion coefficient is an essential kinetic parameter in the operation of lithium-ion batteries. The diffusion process involves both solid-phase and liquid-phase diffusion of lithium ions. The solid-phase diffusion coefficient reflects the diffusion rate of lithium ions within the electrode material, while the liquid-phase diffusion coefficient reflects the migration rate of lithium ions in the electrolyte.

[0004] In existing technology, the solid-state diffusion coefficient is derived from Fick's second law, with the most commonly used method being the constant current intermittent titration (GITT). However, GITT measures electrode process kinetics by applying a current pulse, then performing a long relaxation cycle until the open-circuit voltage (OCP) is reached. This cycle is then repeated until the battery is fully charged. The solid-state diffusion coefficient is related to the relaxation time, and the relaxation time required for GITT is relatively long. Therefore, CITT is more time-consuming to determine the solid-state diffusion coefficient. Summary of the Invention

[0005] In order to solve the above technical problems, the present application is proposed. The embodiments of the present application provide a method for determining the solid-phase diffusion coefficient of a battery and a measuring device. The present application provides a method for determining the solid-phase diffusion coefficient of a battery, by using a preset charging rate to perform constant current charging and discharging on the battery, then stopping charging and discharging for a preset interval length, and then repeating constant current charging and discharging, stopping charging and discharging for a preset interval length, until the battery is charged to the limit high voltage, and discharged to the limit low voltage using the same method, so that the curve of the solid-phase diffusion coefficient changing with the state of charge during the charging process, and the curve of the solid-phase diffusion coefficient changing with the state of charge during the discharge process can be obtained. Compared with the calculation of the solid-phase diffusion coefficient using the GITT method, which usually takes several days, the time for determining the solid-phase diffusion coefficient of the battery in the present application is greatly reduced, further improving the efficiency of determining the solid-phase diffusion coefficient of the battery.

[0006] As a first aspect of the present application, the present application provides a method for determining the solid-phase diffusion coefficient of a battery, comprising: performing multiple constant current charging stages on a test battery at a preset charging rate to a preset voltage upper limit, and multiple constant current discharging stages to a preset voltage lower limit, so as to respectively obtain a first relationship curve between the battery voltage and the charging time during the charging process and a second relationship curve between the battery voltage and the charging time during the discharging process; wherein the charging time of each charging stage is the preset charging time, a stop charging stage is set between two adjacent charging stages, charging is stopped in the stop charging stage, and the stop charging time is the preset intermittent charging time, the preset intermittent charging time is 10 to 30s, and the preset charging time is less than or equal to 30min; each discharge The discharge duration of each stage is a preset discharge duration, and an intermittent discharge stage is set between two adjacent discharge stages. Discharging is stopped in the intermittent discharge stage, and the discharge stop duration is the preset intermittent discharge duration, the preset intermittent discharge duration is 10 to 30 seconds, and the preset discharge duration is less than or equal to 30 minutes; the solid-phase diffusion coefficient of the battery corresponding to each charging stage is determined according to the first relationship curve, and the curve of the solid-phase diffusion coefficient change with the state of charge of the battery during the charging process is determined according to the solid-phase diffusion coefficient corresponding to each charging stage; the solid-phase diffusion coefficient of the battery corresponding to each discharge stage is determined according to the second relationship curve, and the curve of the solid-phase diffusion coefficient change with the state of charge of the battery during the discharge process is determined according to the solid-phase diffusion coefficient corresponding to each discharge stage.

[0007] In one embodiment of the present application, the solid-phase diffusion coefficient of the battery corresponding to each charging stage is determined according to the first relationship curve, including: determining the open circuit voltage change rate and the electrode potential change rate corresponding to each charging stage according to the first relationship curve; substituting the open circuit voltage change rate and the electrode potential change rate into the lithium ion diffusion formula for calculation to obtain the solid-phase diffusion coefficient of the corresponding charging stage.

[0008] In one embodiment of the present application, the open circuit voltage change rate and the electrode potential change rate corresponding to each charging stage are determined based on the first relationship curve, including: fitting the first curve segment corresponding to the charging stage into a first straight line segment, and determining that the slope of the first straight line segment is the open circuit voltage change rate of the corresponding charging stage; fitting the battery voltage and the charging stop time of the intermittent charging stage corresponding to the charging stage into a second straight line segment, and determining the electrode potential change rate corresponding to the charging stage.

[0009] In one embodiment of the present application, the measurement method also includes: calculating the internal resistance of the battery in the charging stage based on the second straight line segment of the intermittent charging stage corresponding to the charging stage and the preset charging rate of the charging stage; and drawing a curve of the change of the internal resistance of the battery with charging time based on the internal resistance of the battery corresponding to each charging stage.

[0010] In one embodiment of the present application, the solid-phase diffusion coefficient of the battery corresponding to each discharge stage is determined according to the second relationship curve, including: determining the open circuit voltage change rate and the electrode potential change rate corresponding to each discharge stage according to the second relationship curve; substituting the open circuit voltage change rate and the electrode potential change rate into the lithium ion diffusion formula for calculation to obtain the solid-phase diffusion coefficient of the corresponding discharge stage.

[0011] In one embodiment of the present application, the open circuit voltage change rate and the electrode potential change rate corresponding to each discharge stage are determined according to the second relationship curve, including: fitting the second curve segment corresponding to the discharge stage into a third straight line segment, and determining the slope of the third straight line segment as the open circuit voltage change rate of the corresponding discharge stage; fitting the battery voltage and the discharge stop time of the intermittent discharge stage corresponding to the discharge stage into a fourth straight line segment, and determining the electrode potential change rate corresponding to the discharge stage.

[0012] In one embodiment of the present application, the lithium ion diffusion formula is:

[0013]

[0014] Where D is the solid phase diffusion coefficient, V m is the molar volume of the electrode material; A is the contact area between the electrode and the electrolyte; is the open circuit voltage change rate, is the rate of change of electrode potential.

[0015] In one embodiment of the present application, the preset charging time is 5 to 10 minutes; and / or the preset discharging time is 5 to 10 minutes.

[0016] In one embodiment of the present application, before the test battery is subjected to multiple constant current charging stages to a preset voltage upper limit and multiple constant current discharging stages to a preset voltage lower limit at a preset charging rate, the measurement method further includes: determining the charging rate and discharge rate of the test battery based on the diameter and capacity of the electrode sheet of the test battery.

[0017] As a second aspect of the present application, the present application also provides a device for measuring the solid-phase diffusion coefficient of a battery, comprising: a charge and discharge controller, configured to perform multiple constant current charging stages on a test battery at a preset charging rate to a preset voltage upper limit, and multiple constant current discharge stages to a preset voltage lower limit, so as to respectively obtain a first relationship curve between the battery voltage and the charging time during the charging process and a second relationship curve between the battery voltage and the charging time during the discharge process; wherein the charging time of each charging stage is the preset charging time, a stop charging stage is set between two adjacent charging stages, charging is stopped during the stop charging stage, and the stop charging time is the preset intermittent charging time, the preset intermittent charging time is 10 to 30 seconds, and the preset charging time is less than or equal to 30 minutes; each discharge stage The discharge duration of each segment is a preset discharge duration, an intermittent discharge stage is set between two adjacent discharge stages, the discharging is stopped in the intermittent discharge stage, and the discharging is stopped for a preset intermittent discharge duration, the preset intermittent discharge duration is 10 to 30 seconds, and the preset discharge duration is less than or equal to 30 minutes; a diffusion coefficient curve determination unit is used to determine the solid-phase diffusion coefficient of the battery corresponding to each charging stage according to the first relationship curve, and determine the solid-phase diffusion coefficient change curve of the battery during the charging process according to the solid-phase diffusion coefficient corresponding to each charging stage; and determine the solid-phase diffusion coefficient of the battery corresponding to each discharge stage according to the second relationship curve, and determine the solid-phase diffusion coefficient change curve of the battery during the discharge process according to the solid-phase diffusion coefficient corresponding to each discharge stage.

[0018] The present application provides a method for determining the solid-phase diffusion coefficient of a battery, which performs constant-current charging on the battery using a preset charging rate, then stops charging for a preset interruption time, and then repeats constant-current charging, stopping charging for a preset interruption time, constant-current charging, stopping charging for a preset interruption time, constant-current charging, stopping charging for a preset interruption time... until the battery is fully charged. In this way, a first relationship curve between the battery voltage and the charging time during the charging process can be obtained by using multiple constant-current charging stages, and the solid-phase diffusion coefficient corresponding to each constant-current charging stage is determined based on the first relationship curve, and a curve of the solid-phase diffusion coefficient changing with the state of charge during the charging process is obtained. At the same time, during the discharge process of the battery, the battery is discharged at a constant current, and then the discharge is stopped for a preset intermittent time, and then the constant current discharge, the stop discharge for a preset intermittent time, the constant current discharge, the stop discharge for a preset intermittent time, the constant current discharge, the stop discharge for a preset intermittent time..., until the battery is discharged to the ultimate low voltage, so that a second relationship curve between the battery voltage and the discharge time during the discharge process can be obtained by using multiple constant current discharge stages, and the solid phase diffusion coefficient corresponding to each constant current discharge stage is determined according to the second relationship curve, and a curve of the solid phase diffusion coefficient changing with the state of charge during the discharge process is obtained. The constant current charging time is still the constant current discharge time (for example, it can be within 30 minutes), and the preset intermittent charging time and the preset intermittent discharge time are shorter (for example, 10 to 30 seconds). Therefore, the solid phase diffusion coefficient corresponding to each charging stage and the solid phase diffusion coefficient corresponding to each discharge stage can be calculated in a shorter time. Compared with the GITT method for calculating the solid-phase diffusion coefficient, which usually takes several days, the time for measuring the solid-phase diffusion coefficient of the battery in this application is greatly reduced, further improving the efficiency of measuring the solid-phase diffusion coefficient of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other purposes, features, and advantages of the present application will become more apparent through a more detailed description of the embodiments of the present application in conjunction with the accompanying drawings. The accompanying drawings are intended to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the drawings, the same reference numerals generally represent the same components or steps.

[0020] Figure 1 This is a corresponding relationship diagram between the open circuit voltage of a battery and the charging time during the battery charging process provided by an exemplary embodiment of the present application.

[0021] Figure 2 Shown is a flow chart of a method for determining the solid-phase diffusion coefficient of a battery provided by an exemplary embodiment of the present application.

[0022] Figure 3The figure shows a curve showing the change of the solid-phase diffusion coefficient with the state of charge during the battery charging process, which is measured using the method for measuring the solid-phase diffusion coefficient of the battery in the embodiment of the present application.

[0023] Figure 4 The figure shows a curve showing the change of the solid-phase diffusion coefficient with the state of charge during the discharge process of the battery, which is measured using the method for measuring the solid-phase diffusion coefficient of the battery in the embodiment of the present application.

[0024] Figure 5 Shown is a flow chart of a method for measuring the solid-phase diffusion coefficient of a battery provided in another embodiment of the present application.

[0025] Figure 6 Shown is a curve showing the change of the internal resistance of a battery with the charging time, measured by a method for measuring the solid-phase diffusion coefficient of a battery provided in one embodiment of the present application.

[0026] Figure 7 Shown is a flow chart of a method for measuring the solid-phase diffusion coefficient of a battery provided in another embodiment of the present application.

[0027] Figure 8 Shown is a working block diagram of a device for measuring the solid-phase diffusion coefficient of a battery provided in one embodiment of the present application.

[0028] Figure 9 It is a structural diagram of an electronic device provided by an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0029] In the description of the present invention, the meaning of "multiple" is at least two, for example, two, three, etc., unless otherwise clearly and specifically limited. In the embodiment of the present invention, all directional indications (such as up, down, left, right, front, back, top, bottom ...) are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the steps or units listed, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, products or devices.

[0030] Additionally, references to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0031] Application Overview

[0032] Electrochemical simulation involves establishing a set of partial differential equations that describe the physical and chemical processes involved in the battery's charge and discharge processes. Finite element methods are then used to solve these partial differential equations to determine the battery's charge and discharge characteristics, as well as the temperature distribution and changes in its internal structure during charge and discharge. The partial differential equations involved in the electrochemical simulation model include multiple simulated physical property parameters related to the battery's materials and structure. Therefore, obtaining these simulated physical property parameters is crucial to the accuracy and effectiveness of the simulation results.

[0033] The solid-phase diffusion coefficient, as a kinetic parameter, needs to be obtained without destroying the battery structure. Currently, the solid-phase diffusion coefficient is mainly obtained through electrochemical methods, and the current electrochemical methods for obtaining the solid-phase diffusion coefficient are mainly:

[0034] The most commonly used galvanostatic intermittent titration (GITT) method, however, measures electrode process kinetics by applying a current pulse, then performing a pulse-current-relaxation cycle. After a long relaxation period, the open-circuit voltage (OCP) is reached; this cycle is repeated until the battery is fully charged. However, when determining the solid-phase diffusion coefficient using GITT, the relaxation time must be sufficiently long to ensure that the electrode potential remains constant. Therefore, GITT testing for solid-phase diffusion coefficient determination is time-consuming. For example, if each charging stage consists of 15 minutes of charging and 30 minutes of relaxation, for a total of 40 charging stages, the total charging time is approximately 40 hours.

[0035] During the research process, the applicant found that:

[0036] When the electrode system satisfies the following conditions: ① the electrode system is an isothermal adiabatic system; ② the electrode system has no volume change and phase change when current is applied; ③ the electrode response is completely controlled by the diffusion of ions inside the electrode; ④ the electronic conductivity of the electrode material is much greater than the ionic conductivity.

[0037] According to Fick's second law of one-dimensional diffusion, the electrochemical equation of lithium ion concentration versus time is given as formula 1:

[0038]

[0039] In formula (1), c(x, t) is the lithium ion concentration at a certain position and time in the electrode material, and D is the lithium ion solid phase diffusion coefficient;

[0040] The corresponding boundary conditions are:

[0041] C Li =C0 (0≤x≤L,t=0) Formula (2)

[0042]

[0043] In formula (2), formula (3) and formula (4), C Li is the lithium ion concentration in the electrode material, C0 is the initial lithium ion concentration in the bulk material; n is the number of moles of active ions transferred, n = 1 mol in lithium-ion batteries, F is the Faraday constant, I is the charge carried by each mole of electrons, the unit is C / mol, and its value is 96500 C / mol; D is the lithium ion solid phase diffusion coefficient, A is the contact area between the electrode and the electrolyte; L is the thickness of the electrode active material.

[0044] Wherein, formula (2) indicates that the lithium ion concentration at each thickness position of the lithium ion battery is equal to the initial lithium ion concentration. Formula (3) indicates that the total number of electrons transferred per unit time is equal to the flow rate reaching the electrode surface A (X = 0) during that time. Formula (4) indicates that under semi-infinite conditions, the lithium ion concentration at the far end of the electrode (X = L) remains unchanged.

[0045] The diffusion assumption occurs on the surface of the solid phase material. To ensure that this assumption holds, the applied current time t needs to be short and the relaxation time needs to be long enough. The solution of formula (1) at X = 0 is:

[0046]

[0047] In formula (5), C0 is the initial concentration of lithium ions in the bulk material, A is the contact area between the electrode and the electrolyte, and Z i is the number of transferred electrons, and L is the thickness of the electrode active material.

[0048] The applicant found that when t is much smaller than L 2 / D (at this time, t is the constant current charging time or constant current discharging time, that is, the preset charging time or the preset discharging time is less than or equal to 30 minutes), and t needs to be small enough to satisfy the linear relationship of dE / d√t (at this time, t is the preset intermittent charging time or the preset intermittent discharging time, which ranges from 10 to 30 seconds). The diffusion equation at the solid-liquid interface can be simplified to the following formula (5) using Laplace transform:

[0049]

[0050] In formula (6), C S (t) is the surface concentration of the solid-liquid interface at time t, D is the solid-phase diffusion coefficient of lithium ions, I is the charge carried by each mole of electrons, A is the contact area between the electrode and the electrolyte, and F is the Faraday constant;

[0051] The solid phase diffusion coefficient calculation formula used in the present invention is derived based on formula (6):

[0052]

[0053] In formula (7), V m is the molar volume of the electrode material; A is the contact area between the electrode and the electrolyte; Eoc is OCP (open circuit voltage), Δt I is the time of applying constant current during continuous OCP measurement, E is the electrode potential, and t is the current pause step time, that is, the time of stopping charging or stopping discharging;

[0054] From formula (7), we can know that to calculate the solid phase diffusion coefficient, we only need to obtain (open circuit voltage change rate during charge and discharge), electrode potential change rate

[0055] Based on the above concept, an embodiment of the present invention provides a method for measuring the solid-phase diffusion coefficient of a battery, which is performed by using a preset charging rate (such as 0.01C, 0.02C, 0.05C, etc.) to charge the battery with a constant current, then stopping charging for a preset very short time, and then repeating constant current charging, stopping charging for a preset very short time, constant current charging, stopping charging for a preset very short time, constant current charging, stopping charging for a preset very short time... until the battery is fully charged. When charging the battery using this charging method, the corresponding relationship between the open circuit voltage of the battery and the charging time is shown in the figure below. Figure 1 According to the corresponding relationship between the open circuit voltage and charging time of the battery during the charging process, and according to the constant current charging time and the stop charging time of each stage of the battery: the change of the constant current charging open circuit voltage over time is calculated. (Open circuit voltage change rate during charge and discharge), stop charging and calculate the change of electrode potential over time corresponding to the length of time when charging is stopped When each stage (constant current charging time + stop charging time) is obtained as well as The solid-phase diffusion coefficient corresponding to each stage can be calculated. Due to the long constant current charging time (for example, less than 30 minutes) and the short charging stop time (for example, 10 to 30 seconds), the solid-phase diffusion coefficient corresponding to each charging stage can be calculated in a shorter time. Compared with the GITT method for calculating the solid-phase diffusion coefficient, which usually takes several days, the time for determining the solid-phase diffusion coefficient of the battery in this application is greatly reduced, further improving the efficiency of determining the solid-phase diffusion coefficient of the battery.

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0057] Exemplary Methods

[0058] As a first aspect of the present application, the present application provides a method for determining the solid-phase diffusion coefficient of a battery. Figure 1 FIG. 1 is a method for determining the solid phase diffusion coefficient of a battery provided by an embodiment of the present application, as shown in FIG. Figure 2 As shown, the method for determining the solid phase diffusion coefficient of a battery includes the following steps:

[0059] S1: performing a plurality of constant current charging stages to a preset upper voltage limit and a plurality of constant current discharging stages to a preset lower voltage limit on the test battery at a preset charging rate, so as to obtain a first relationship curve between the battery voltage and the charging time during the charging process and a second relationship curve between the battery voltage and the charging time during the discharging process;

[0060] Specifically, taking a lithium iron phosphate battery as an example, the preset upper voltage limit may be 3.75V and the preset lower voltage limit may be 2.0V.

[0061] Specifically, the battery is charged and discharged to a preset voltage upper limit (for example, until the battery is fully charged). The entire charging process is divided into multiple constant current charging stages, and the preset charging duration of each constant current charging stage can be less than or equal to 30 minutes. An intermittent charging stage is set between two adjacent constant current charging stages, and charging is stopped during the intermittent charging stage. The charging stop duration of the intermittent charging stage is the preset intermittent charging duration, which can be specifically 10 seconds to 30 seconds.

[0062] During the process of charging the battery in multiple constant current charging stages, there is a first relationship curve between the battery voltage and the charging time, such as Figure 1 shown.

[0063] Similarly, when the battery is charged and discharged to a preset voltage upper limit (for example, when the battery is fully charged), each discharge process includes multiple constant current discharge stages, and the preset discharge duration of each constant current discharge stage can be less than or equal to 30 minutes. There is an intermittent discharge stage between two adjacent constant current discharge stages, and the discharging is stopped in the intermittent discharge stage, and the discharging is stopped for a preset intermittent discharge duration, which can be 20S to 30S.

[0064] During the process of discharging the battery in multiple constant current discharge stages, a second relationship curve is formed between the battery voltage and the discharge time.

[0065] Optionally, the preset charging time is 5 to 10 minutes; and / or the preset discharging time is 5 to 10 minutes, so as to improve the test efficiency as much as possible without affecting the accuracy.

[0066] Optionally, the preset charge rate and the preset discharge rate can be 0.01C, 0.02C, 0.05C, 0.1C, 0.2C, 0.5C, etc., to reduce polarization, make the potential change closer to an even diffusion process, and make the potential change more obvious, thereby improving test accuracy.

[0067] Optionally, parameters such as the cell size, capacity, and voltage of the test battery directly affect the charge and discharge current of the test battery. Generally, larger battery sizes result in higher charge and discharge currents. Therefore, prior to S1, the measurement method further includes determining the charge rate and discharge rate of the test battery based on the diameter and capacity of the test battery's electrode sheet.

[0068] For example: For a 2032 button battery with a 12-16mm diameter disc, the capacity is generally around 38-4.2mAh. The smaller the current, the smaller the polarization. The charge rate and discharge rate are lower than 0.1C. Generally, a small current of 0.05C is used for constant current charging to the upper voltage limit and discharging to the lower voltage limit.

[0069] S2: determining the solid-phase diffusion coefficient of the battery corresponding to each charging stage according to the first relationship curve, and determining a curve of the solid-phase diffusion coefficient varying with the state of charge during the charging process according to the solid-phase diffusion coefficient corresponding to each charging stage;

[0070] Specifically, the solid-phase diffusion coefficient corresponding to each constant current charging stage during the battery charging process can be determined according to the first relationship curve. After the solid-phase diffusion coefficient corresponding to each constant current charging stage is determined, the curve of the solid-phase diffusion coefficient of the battery varying with the state of charge can be determined according to the solid-phase diffusion coefficient corresponding to each constant current charging stage, such as Figure 3 shown.

[0071] S3: determining the solid-phase diffusion coefficient of the battery corresponding to each discharge stage according to the second relationship curve, and determining a curve of the solid-phase diffusion coefficient varying with the state of charge during the discharge process according to the solid-phase diffusion coefficient corresponding to each constant-current discharge stage.

[0072] Specifically, the solid-phase diffusion coefficient corresponding to each constant-current discharge stage during the battery discharge process can be determined according to the second relationship curve. After determining the solid-phase diffusion coefficient corresponding to each constant-current discharge stage, the curve of the battery's solid-phase diffusion coefficient changing with the state of charge can be determined according to the solid-phase diffusion coefficient corresponding to each constant-current discharge stage, such as Figure 4 shown.

[0073] The present application provides a method for determining the solid-phase diffusion coefficient of a battery, which performs constant-current charging of the battery at a preset charging rate for a preset charging time, then stops charging for a preset intermittent charging time, and then repeats constant-current charging for a preset charging time, stops charging for a preset intermittent charging time, constant-current charging for a preset charging time, stops charging for a preset intermittent charging time, constant-current charging for a preset charging time, stops charging for a preset intermittent charging time, and so on, until the battery is fully charged. In this way, a first relationship curve between the battery voltage and the charging time during the charging process can be obtained by using multiple constant-current charging stages, and the solid-phase diffusion coefficient corresponding to each constant-current charging stage is determined based on the first relationship curve, and a curve of the solid-phase diffusion coefficient changing with the state of charge during the charging process is obtained. At the same time, during the discharge process of the battery, the battery is subjected to constant current discharge for a preset discharge time, and then the discharge is stopped for a preset intermittent discharge time, and then the constant current discharge is repeated for a preset discharge time, the stop discharge is set for a preset intermittent discharge time, the constant current discharge is repeated for a preset discharge time, the stop discharge is set for a preset intermittent discharge time, the constant current discharge is repeated for a preset discharge time, the stop discharge is set for a preset intermittent discharge time, the constant current discharge is repeated for a preset discharge time, the stop discharge is set for a preset intermittent discharge time, the constant current discharge is repeated for a preset discharge time, and the stop discharge is set for a preset intermittent discharge time... until the battery is discharged to the limit low voltage, so that a second relationship curve between the battery voltage and the discharge time during the discharge process can be obtained by using multiple constant current discharge stages, and the solid phase diffusion coefficient corresponding to each constant current discharge stage is determined according to the second relationship curve, and a curve of the solid phase diffusion coefficient changing with the state of charge during the discharge process is obtained. The preset charging time of the constant current charge is also the preset discharge time of the constant current discharge (for example, it can be within 30 minutes), and the preset intermittent charge time and the preset intermittent discharge time are shorter (for example, 10 to 30 seconds). Therefore, the solid phase diffusion coefficient corresponding to each charging stage and the solid phase diffusion coefficient corresponding to each discharge stage can be calculated in a shorter time. Compared with the GITT method for calculating the solid-phase diffusion coefficient, which usually takes several days, the time for measuring the solid-phase diffusion coefficient of the battery in this application is greatly reduced, further improving the efficiency of measuring the solid-phase diffusion coefficient of the battery.

[0074] In one embodiment of the present application, Figure 5S2 (determining the solid-phase diffusion coefficient of the battery corresponding to each charging stage according to the first relationship curve) specifically includes the following steps:

[0075] S21: Determine the open circuit voltage change rate and the electrode potential change rate corresponding to each charging stage according to the first relationship curve;

[0076] Specifically, according to the open circuit voltage change rate corresponding to each charging stage in the first relationship curve and the electrode potential change rate

[0077] Among them, the electrode potential change rate It is an indicator to measure how fast the electrode potential changes over time.

[0078] Optionally, S21 (determining the open circuit voltage change rate and the electrode potential change rate corresponding to each charging stage according to the first relationship curve) specifically includes the following steps:

[0079] S211: fitting a first curve segment corresponding to the charging stage into a first straight line segment, and determining that the slope of the first straight line segment is the open circuit voltage change rate of the corresponding charging stage;

[0080] Specifically, a straight line is fitted according to the first curve segment corresponding to each charging stage, and the slope of the straight line is determined to be the open circuit voltage change rate of the corresponding charging stage. Figure 1 The numerical points between 0-300s in .

[0081] S212: Fitting a second straight line segment according to the battery voltage and the charging stop duration in the intermittent charging phase corresponding to the charging phase to determine the electrode potential change rate corresponding to the charging phase.

[0082] Specifically, according to the second straight line segment of the intermittent charging stage corresponding to the charging stage, the electrode potential change rate corresponding to the corresponding charging stage is determined. The intermittent charging stage corresponding to the charging stage is the intermittent charging stage after the charging stage. Figure 1 The values shown are between 300 and 310 seconds. At this time, the slope of the second straight line segment is the rate of change of the electrode potential corresponding to the corresponding charging stage.

[0083] S22: Substitute the open circuit voltage change rate and the electrode potential change rate into the lithium ion diffusion formula for calculation to obtain the solid phase diffusion coefficient of the corresponding charging stage.

[0084] Specifically, the lithium ion diffusion formula is:

[0085]

[0086] Where D is the solid phase diffusion coefficient, Vm is the molar volume of the electrode material; A is the contact area between the electrode and the electrolyte; is the open circuit voltage change rate, is the rate of change of electrode potential.

[0087] Optionally, the determination method further comprises the following steps:

[0088] S5: Calculating the internal resistance of the battery in the charging phase according to the second straight line segment of the intermittent charging phase corresponding to the charging phase and the preset charging rate in the charging phase;

[0089] According to the kinetic formula of the diffusion process:

[0090]

[0091] Where R is the internal resistance of the battery, K is the diffusion resistance coefficient of the battery, and E I Where Δt is the potential before the current is interrupted, that is, the voltage before the current is interrupted; E(Δt) is the potential during or after the current is interrupted, that is, the voltage during or after the current is interrupted; and I is the charging current. By linearly fitting ΔE against Δt to obtain the intercept and slope, the internal resistance of the battery can be calculated based on the intercept of the second straight line segment.

[0092] In one embodiment, the intercept and slope of the second straight line segment can be determined using the least squares method based on the potential before the current interruption, the potential after the current interruption, and the preset intermittent charging duration. In another embodiment, the intercept and slope of the second straight line segment can be determined by fitting the potential before the current interruption, the potential during the current interruption, the intermittent charging duration during the current interruption, the potential before the current interruption, the potential after the current interruption, and the preset intermittent charging duration. That is, the second straight line segment is fitted based on the battery voltage during the intermittent charging stage and the charging stop duration. Solving the above formula, it can be obtained That is, the slope of the second straight line segment is the electrode potential change rate, and the intercept of the second straight line segment is -IR. Therefore, the battery internal resistance R can be determined by determining the charging current I.

[0093] S6: Draw a curve showing the change of the battery's internal resistance over the charging time according to the internal resistance of the battery corresponding to each charging stage.

[0094] After the internal resistance corresponding to each charging stage is calculated, the internal resistance change curve of the battery during the charging and discharging process can be determined, such as Figure 6 shown.

[0095] In another embodiment of the present application, Figure 7 As shown, S3 (determining the solid-phase diffusion coefficient of the battery corresponding to each discharge stage according to the second relationship curve) further includes the following steps:

[0096] S31: determining the open circuit voltage change rate and the electrode potential change rate corresponding to each discharge stage according to the second relationship curve;

[0097] Specifically, according to the open circuit voltage change rate corresponding to each discharge stage in the second relationship curve and the electrode potential change rate

[0098] Among them, the electrode potential change rate It is an indicator to measure how fast the electrode potential changes over time.

[0099] S32: Substitute the open circuit voltage change rate and the electrode potential change rate into the lithium ion diffusion formula for calculation to obtain the solid phase diffusion coefficient of the corresponding discharge stage.

[0100] Specifically, the lithium ion diffusion formula is:

[0101]

[0102] Where D is the solid phase diffusion coefficient, V m is the molar volume of the electrode material; A is the contact area between the electrode and the electrolyte; is the open circuit voltage change rate, is the rate of change of electrode potential.

[0103] Optionally, S31 (determining the open circuit voltage change rate and the electrode potential change rate corresponding to each discharge stage according to the second relationship curve) specifically includes the following steps:

[0104] S311: fitting the second curve segment corresponding to the discharge stage into a third straight line segment, and determining that the slope of the third straight line segment is the open circuit voltage change rate of the corresponding discharge stage;

[0105] S312: Fitting a fourth straight line segment based on the battery voltage and the discontinuous discharge duration in the discharging phase corresponding to the discharging phase to determine the electrode potential change rate corresponding to the discharging phase. The specific method is as described above and will not be repeated here.

[0106] Exemplary devices

[0107] As a second aspect of the present application, the present application also provides a device for measuring the solid phase diffusion coefficient of a battery, such as Figure 8 As shown. The measuring device 100 includes:

[0108] The charge and discharge controller 101 is used to perform multiple constant current charging stages on the test battery at a preset charging rate to a preset voltage upper limit, and multiple constant current discharging stages to a preset voltage lower limit, so as to respectively obtain a first relationship curve between the battery voltage and the charging time during the charging process and a second relationship curve between the battery voltage and the charging time during the discharging process; wherein the charging duration of each charging stage is the preset charging duration, a stop charging stage is provided between two adjacent charging stages, charging is stopped during the stop charging stage, and the stop charging duration is the preset intermittent charging duration, the preset intermittent charging duration is 10 to 30 seconds, and the preset charging duration is less than or equal to 30 minutes; the discharge duration of each discharge stage is the preset discharge duration, an intermittent discharge stage is provided between two adjacent discharge stages, discharging is stopped during the intermittent discharge stage, and the stop discharge duration is the preset intermittent discharge duration, the preset intermittent discharge duration is 10 to 30 seconds, and the preset discharge duration is less than or equal to 30 minutes;

[0109] The diffusion coefficient curve determining unit 102 is used to determine the solid-phase diffusion coefficient of the battery corresponding to each charging stage according to the first relationship curve, and determine the curve of the solid-phase diffusion coefficient changing with the state of charge of the battery during the charging process according to the solid-phase diffusion coefficient corresponding to each charging stage; and determine the solid-phase diffusion coefficient of the battery corresponding to each discharging stage according to the second relationship curve, and determine the curve of the solid-phase diffusion coefficient changing with the state of charge of the battery during the discharging process according to the solid-phase diffusion coefficient corresponding to each discharging stage.

[0110] The measuring device provided in this application is used to perform the steps of the measuring method described above and has the corresponding effect of the measuring method. To avoid repetition, it will not be described here.

[0111] The method for obtaining the solid-phase diffusion coefficient of the present invention will be more specifically implemented below by showing specific embodiments.

[0112] Example 1:

[0113] This embodiment 1 provides a method for measuring the solid-phase diffusion coefficient of a battery, which specifically includes the following steps:

[0114] S101: Prepare a test battery and let it stand for 12 hours to allow the electrolyte to fully penetrate. Then, use a small current of 0.05C to perform constant current charging to the preset voltage upper limit of 3.75V of the test battery, and then discharge it to the preset voltage lower limit of 2.0V for activation:

[0115] The obtained electrode sheets were dried and assembled into a button cell in the order of battery shell, electrode sheet, separator, electrolyte, lithium sheet, spring, gasket, and battery shell. The shell size of the test battery was a 2032 button cell. The electrode sheet material was lithium iron phosphate. The electrolyte was lithium hexafluorophosphate.

[0116] The test battery in this embodiment may have a structural form of: a card-type battery, a soft-pack-type battery, a square-shell-type battery, a laminate-type battery, etc.

[0117] S102: The test battery is charged with a constant current of 0.1C for 10 minutes, and then the charging is interrupted for 30 seconds; during the constant current charging process, the changes in the voltage, current, capacity, etc. of the test battery with the charging time are recorded;

[0118] S103: Determine whether the battery voltage of the test battery is greater than 3.75V (a preset voltage upper limit corresponding to the test battery);

[0119] If the judgment result is yes, it means that the test battery is fully charged. After the test battery is fully charged, the test battery is discharged, that is, S104 is executed.

[0120] If the judgment result is no, it means that the test battery has not been fully charged, that is, the test battery is continuously charged with a constant current of 0.1C rate for 10 minutes, and then the charging is interrupted for 30 seconds, that is, S102 is executed.

[0121] That is, the test battery is repeatedly charged with a constant current for 10 minutes and then interrupted for 30 seconds until the test battery is fully charged (ie, the battery voltage of the test battery reaches 3.75V).

[0122] S104: The test battery is discharged at a constant current rate of 0.1C for 10 minutes, and then the charging is interrupted for 30 seconds. During the constant current discharge process, the changes in the voltage, current, and capacity of the test battery as a function of the charging time are recorded.

[0123] S105: Determine whether the battery voltage of the test battery is less than 2.2V (the preset voltage lower limit corresponding to the test battery);

[0124] If the judgment result is yes, it means that the test battery is discharged completely.

[0125] If the judgment result is no, it means that the test battery has not been discharged completely, that is, the test battery is continuously discharged at a constant current rate of 0.1C for 10 minutes, and then charging is interrupted for 30 seconds, and S106 is executed.

[0126] That is, the test battery is repeatedly discharged at a constant current for 10 minutes and then the charging is interrupted for 30 seconds until the discharge of the test battery is complete (that is, the battery voltage of the test battery reaches 2.2V).

[0127] When charging the test battery, a first variation curve of the battery voltage over time is drawn according to the detected battery voltage, such as Figure 1 shown.

[0128] S106: fitting the first curve segment corresponding to the charging stage into a first straight line segment, and determining that the slope of the first straight line segment is the open circuit voltage change rate of the corresponding charging stage;

[0129] S107: Fitting a second straight line segment according to the battery voltage and the charging stop duration in the intermittent charging phase corresponding to the charging phase to determine the electrode potential change rate corresponding to the charging phase.

[0130] S108: Substituting the open circuit voltage change rate and the electrode potential change rate into the lithium ion diffusion formula for calculation to obtain the solid phase diffusion coefficient of the corresponding charging stage.

[0131] Specifically, the lithium ion diffusion formula is:

[0132]

[0133] Where D is the solid phase diffusion coefficient, V m is the molar volume of the electrode material; A is the contact area between the electrode and the electrolyte; is the open circuit voltage change rate, is the rate of change of electrode potential.

[0134] The solid phase diffusion coefficient corresponding to each charging stage can be calculated through S106, S107 and S108;

[0135] S109: Draw a curve of the solid-phase diffusion coefficient of the battery during the charging process as a function of the state of charge according to the solid-phase diffusion coefficient corresponding to each charging stage, such as Figure 3 shown.

[0136] S1091: Calculating the internal resistance of the battery in the charging phase according to the second straight line segment of the intermittent charging phase corresponding to the charging phase and the preset charging rate of the charging phase;

[0137] According to the kinetic formula of the diffusion process:

[0138]

[0139] Where R is the internal resistance of the battery, K is the diffusion resistance coefficient of the battery, and E I is the potential before the constant current time, and I is the charging current. The intercept and slope are obtained by linear fitting ΔE against Δt. That is, the internal resistance of the battery can be calculated based on the intercept of the second straight line segment.

[0140] S1092: Draw a curve of the battery's internal resistance versus charging time based on the battery's internal resistance corresponding to each charging stage, such as Figure 6 shown.

[0141] S1093: Fitting the second curve segment corresponding to the discharge stage into a third straight line segment, and determining that the slope of the third straight line segment is the open circuit voltage change rate of the corresponding discharge stage;

[0142] S1094: Fitting a fourth straight line segment according to the battery voltage and the discharging stop time in the intermittent discharging phase corresponding to the discharging phase to determine the electrode potential change rate corresponding to the discharging phase.

[0143] S1095: Substitute the open circuit voltage change rate and the electrode potential change rate into the lithium ion diffusion formula for calculation to obtain the solid phase diffusion coefficient of the corresponding discharge stage.

[0144] Specifically, the lithium ion diffusion formula is:

[0145]

[0146] Where D is the solid phase diffusion coefficient, V m is the molar volume of the electrode material; A is the contact area between the electrode and the electrolyte; is the open circuit voltage change rate, is the rate of change of electrode potential.

[0147] The solid phase diffusion coefficient corresponding to each discharge stage can be calculated through S1093, S1094 and S1095;

[0148] S1096: Draw a curve of the solid-phase diffusion coefficient of the battery changing with the state of charge during the discharge process based on the solid-phase diffusion coefficient corresponding to each discharge stage, such as Figure 4 shown.

[0149] Exemplary electronic devices

[0150] Figure 9 The figure shows a block diagram of an electronic device according to an embodiment of the present application.

[0151] like Figure 9 As shown, the electronic device 10 includes one or more processors 11 and a memory 12 .

[0152] The processor 11 may be a central processing unit (CPU) or other forms of processing units having data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device 10 to perform desired functions.

[0153] The memory 12 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory (cache), etc. The non-volatile memory may include, for example, read-only memory (ROM), a hard disk, a flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 11 may execute the program instructions to implement the method for determining the solid-phase diffusion coefficient of the battery of each embodiment of the present application described above and / or other desired functions. Various contents such as input signals, signal components, noise components, etc. may also be stored in the computer-readable storage medium.

[0154] In one example, the electronic device 10 may further include an input device 13 and an output device 14 , and these components are interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0155] When the electronic device 10 is a stand-alone device, the input device 13 may be a communication network connector, configured to receive collected input signals from the first device and the second device.

[0156] In addition, the input device 13 may also include, for example, a keyboard, a mouse, and the like.

[0157] The output device 14 can output various information to the outside, including determined distance information, direction information, etc. The output device 14 can include, for example, a display, a speaker, a printer, a communication network and a remote output device connected thereto, and the like.

[0158] Of course, to simplify, Figure 9 Only some of the components related to the present application in the electronic device 10 are shown, and components such as a bus, an input / output interface, etc. are omitted. In addition, the electronic device 10 may further include any other appropriate components according to specific application scenarios.

[0159] The computer program product may be written in any combination of one or more programming languages to implement the program code for performing the operations of the embodiments of the present application, including object-oriented programming languages such as Java, C++, and conventional procedural programming languages such as "C" or similar programming languages. The program code may be executed entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0160] The computer-readable storage medium can adopt any combination of one or more readable media. The readable medium can be a readable signal medium or a readable storage medium. The readable storage medium can, for example, include but is not limited to a system, device or component of electricity, magnetism, light, electromagnetic, infrared, or semiconductor, or any combination thereof. More specific examples (non-exhaustive list) of readable storage media include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0161] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A method for measuring the solid-phase diffusion coefficient of a battery, characterized in that: include: The test battery is subjected to multiple constant current charging stages to a preset voltage upper limit and multiple constant current discharging stages to a preset voltage lower limit at a preset charging rate, so as to obtain a first relationship curve between the battery voltage and the charging time during the charging process and a second relationship curve between the battery voltage and the charging time during the discharging process, respectively; wherein, the charging duration of each charging stage is the preset charging duration, and an intermittent charging interruption is set between two adjacent charging stages. Charging is stopped in the intermittent charging stage, and the charging stop duration is the preset intermittent charging duration, the preset intermittent charging duration is 10 to 30 seconds, and the preset charging duration is less than or equal to 30 minutes; the discharge duration of each discharge stage is the preset discharge duration, and an intermittent discharge stage is set between two adjacent discharge stages. Discharging is stopped in the intermittent discharge stage, and the discharge stop duration is the preset intermittent discharge duration, the preset intermittent discharge duration is 10 to 30 seconds, and the preset discharge duration is less than or equal to 30 minutes; Determining the solid-phase diffusion coefficient of the battery corresponding to each charging stage according to the first relationship curve, and determining a curve of the solid-phase diffusion coefficient versus state of charge of the battery during the charging process according to the solid-phase diffusion coefficient corresponding to each charging stage; The solid-phase diffusion coefficient of the battery corresponding to each discharge stage is determined according to the second relationship curve, and the solid-phase diffusion coefficient versus state of charge curve of the battery during the discharge process is determined according to the solid-phase diffusion coefficient corresponding to each discharge stage.

2. The measuring method according to claim 1, wherein Determining the solid-phase diffusion coefficient of the battery corresponding to each charging stage according to the first relationship curve includes: Determining the open circuit voltage change rate and the electrode potential change rate corresponding to each charging stage according to the first relationship curve; The open circuit voltage change rate and the electrode potential change rate are substituted into the lithium ion diffusion formula for calculation to obtain the solid phase diffusion coefficient of the corresponding charging stage.

3. The measuring method according to claim 2, wherein Determining the open circuit voltage change rate and the electrode potential change rate corresponding to each charging stage according to the first relationship curve includes: Fitting a first curve segment corresponding to the charging stage into a first straight line segment, and determining that the slope of the first straight line segment is the open circuit voltage change rate of the corresponding charging stage; A second straight line segment is fitted according to the battery voltage and the charging stop duration in the intermittent charging stage corresponding to the charging stage, and the electrode potential change rate corresponding to the charging stage is determined.

4. The measuring method according to claim 3, wherein The determination method further comprises: Calculating the internal resistance of the battery in the charging stage according to the second straight line segment of the intermittent charging stage corresponding to the charging stage and the preset charging rate of the charging stage; and A curve showing the change of the battery's internal resistance over the charging time is drawn based on the internal resistance of the battery corresponding to each charging stage.

5. The measuring method according to claim 1, wherein Determining the solid-phase diffusion coefficient of the battery corresponding to each discharge stage according to the second relationship curve includes: Determining the open circuit voltage change rate and the electrode potential change rate corresponding to each discharge stage according to the second relationship curve; The open circuit voltage change rate and the electrode potential change rate are substituted into the lithium ion diffusion formula for calculation to obtain the solid phase diffusion coefficient of the corresponding discharge stage.

6. The measuring method according to claim 5, characterized in that Determining the open circuit voltage change rate and the electrode potential change rate corresponding to each discharge stage according to the second relationship curve includes: Fitting the second curve segment corresponding to the discharge stage into a third straight line segment, and determining the slope of the third straight line segment to be the open circuit voltage change rate of the corresponding discharge stage; A fourth straight line segment is fitted according to the battery voltage and the discharging stop time of the intermittent discharging stage corresponding to the discharging stage, and the electrode potential change rate corresponding to the discharging stage is determined.

7. The determination method according to any one of claims 2 to 6, characterized in that The lithium ion diffusion formula is: Where D is the solid phase diffusion coefficient, V m is the molar volume of the electrode material; A is the contact area between the electrode and the electrolyte; is the open circuit voltage change rate, is the rate of change of electrode potential.

8. The measuring method according to claim 1, wherein The preset charging time is 5 to 10 minutes; and / or The preset discharge time is 5 to 10 minutes.

9. The measuring method according to claim 1, wherein Before performing multiple constant current charging stages to a preset upper voltage limit and multiple constant current discharging stages to a preset lower voltage limit on the test battery at a preset charging rate, the measuring method further includes: The charge rate and discharge rate of the test battery are determined according to the diameter and capacity of the electrode sheet of the test battery.

10. A device for measuring the solid-phase diffusion coefficient of a battery, characterized in that: include: A charge and discharge controller, configured to perform multiple constant current charging stages on a test battery at a preset charging rate to a preset voltage upper limit, and multiple constant current discharging stages to a preset voltage lower limit, so as to respectively obtain a first relationship curve between the battery voltage and the charging time during the charging process and a second relationship curve between the battery voltage and the charging time during the discharging process; wherein the charging duration of each charging stage is the preset charging duration, an intermittent charging stage is provided between two adjacent charging stages, charging is stopped in the intermittent charging stage, and the duration of the charging stop is the preset intermittent charging duration, the preset intermittent charging duration is 10 to 30 seconds, and the preset charging duration is less than or equal to 30 minutes; the discharge duration of each discharge stage is the preset discharge duration, an intermittent discharge stage is provided between two adjacent discharge stages, discharging is stopped in the intermittent discharge stage, and the duration of the discharging stop is the preset intermittent discharge duration, the preset intermittent discharge duration is 10 to 30 seconds, and the preset discharge duration is less than or equal to 30 minutes; a diffusion coefficient curve determining unit, configured to determine the solid-phase diffusion coefficient of the battery corresponding to each charging stage according to the first relationship curve, and determine a curve of the solid-phase diffusion coefficient varying with the state of charge during the charging process of the battery according to the solid-phase diffusion coefficient corresponding to each charging stage; The solid-phase diffusion coefficient of the battery corresponding to each discharge stage is determined according to the second relationship curve, and the curve of the change of the solid-phase diffusion coefficient of the battery with the state of charge during the discharge process is determined according to the solid-phase diffusion coefficient corresponding to each discharge stage.

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