Parametric characterization method and device for abnormal changes in lithium-ion battery performance during charging and discharging

Abstract

The invention discloses a parameterized characterization method and device for abnormal performance changes of lithium-ion batteries during charging and discharging. The method comprises: obtaining a relaxation time distribution curve by analyzing an electrochemical impedance spectrum of a lithium-ion battery based on a relaxation time distribution method; determining the number of impedance links based on the number of peaks of the relaxation time distribution curve, and establishing a corresponding equivalent impedance model; obtaining characteristic parameters of the relaxation time distribution curve and the equivalent impedance model at a predetermined SOC point; obtaining a characteristic parameter set related to abnormal performance changes of the lithium-ion battery by comparing and analyzing characteristic parameter changes between different SOC points; and realizing parameterized characterization of abnormal performance changes of the lithium-ion battery at the SOC point based on a unified characterization of the change rate of each parameter in the characteristic parameter set. The invention can effectively identify abnormal changes in the battery performance decay process and has strong adaptability to different working conditions.

Description

Technical Field

[0001] The invention relates to a parameterized characterization method and device for abnormal changes in lithium-ion battery performance during charging and discharging, and belongs to the technical field of battery safety management. Background Art

[0002] The number of electric vehicles in my country is increasing year by year, and the large-scale application of electric vehicles has promoted the vigorous development of power batteries. During the use of power batteries, it is inevitable to charge and discharge the batteries. However, during the charging and discharging process of power batteries, performance degradation is inevitable, which brings operational safety challenges to electric vehicle power batteries.

[0003] During the normal battery performance decay process, the battery capacity decays approximately steadily with the number of cycles. However, through a large number of conventional cycle aging tests on ternary lithium-ion batteries, it was found that the battery has abnormal performance changes during the charging and discharging process. Most batteries begin to decay rapidly when the capacity retention rate is above 90%, and the battery volume expands significantly, which poses a huge hidden danger to the safe operation of the battery system. In severe cases, the battery material is dislocated, the diaphragm is twisted, and an internal short circuit is caused, which leads to fire and explosion of the battery system.

[0004] The core problem of abnormal performance changes of lithium-ion batteries during charging and discharging is that the mechanism of abnormal performance changes of batteries and the characterization of related physical parameters are unclear. In order to solve this problem, this application proposes a parameterized characterization method and device for abnormal performance changes of lithium-ion batteries during charging and discharging. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art, provide a parameterized characterization method and device for abnormal changes in lithium-ion battery performance during charging and discharging, establish relaxation time distribution curve and impedance model parameters as characteristic parameters for characterizing abnormal changes in battery performance, provide a parameterized characterization method for abnormal changes in battery performance, and achieve accurate characterization of abnormal changes in lithium-ion battery performance under different working conditions.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0007] In a first aspect, the present invention provides a parameterized characterization method for abnormal changes in performance of a lithium-ion battery during charging, comprising:

[0008] The relaxation time distribution curve is obtained by analyzing the electrochemical impedance spectrum of the lithium-ion battery based on the relaxation time distribution method;

[0009] Determine the number of impedance links based on the peak number of the relaxation time distribution curve, and establish a corresponding equivalent impedance model;

[0010] Obtaining characteristic parameters of the relaxation time distribution curve and the equivalent impedance model at a predetermined SOC point;

[0011] By comparing and analyzing the characteristic parameter changes between different SOC points, a characteristic parameter set related to abnormal changes in lithium-ion battery performance is obtained;

[0012] Based on the unified characterization of the change rate of each parameter in the characteristic parameter set, the parametric characterization of abnormal changes in lithium-ion battery performance under SOC points is achieved.

[0013] Optionally, the relaxation time distribution curve obtained by analyzing the electrochemical impedance spectrum of the lithium-ion battery based on the relaxation time distribution method includes:

[0014] Construct an expression for the electrochemical impedance of a lithium-ion battery:

[0015]

[0016] Among them, R o is the ohmic impedance of the lithium-ion battery, γ(lnτ) is the relaxation time distribution curve function, τ is the relaxation time, j is the imaginary number sign, and w is the angular frequency;

[0017] The expression of electrochemical impedance of lithium-ion battery Z DRT Discretize the expression:

[0018]

[0019]

[0020] Where μ is the shape factor, τ n is the central relaxation time of the nth impedance link, N is the number of impedance links, x n is the parameter;

[0021] Based on the electrochemical impedance spectroscopy of lithium-ion batteries DRT The obtained electrochemical impedance spectrum of the lithium-ion battery is fitted to minimize the sum of squares of its errors and determine the relaxation time distribution curve function γ(lnτ).

[0022] Optionally, the unified characterization based on the change rate of each parameter in the characteristic parameter set includes:

[0023]

[0024] Among them, θ is the characteristic parameter of the battery after aging, θ0 is the characteristic parameter of the battery at the initial moment, and S is the operating condition, which includes the battery equivalent cycle number, equivalent throughput capacity, equivalent throughput energy and equivalent mileage.

[0025] In a second aspect, the present invention provides a parametric characterization device for abnormal changes in performance of a lithium-ion battery during charging, the device comprising:

[0026] A relaxation time distribution curve determination module is used to analyze the electrochemical impedance spectrum of the lithium-ion battery obtained based on the relaxation time distribution method to obtain a relaxation time distribution curve;

[0027] An equivalent impedance model determination module is used to determine the number of impedance links based on the peak number of the relaxation time distribution curve and establish a corresponding equivalent impedance model;

[0028] A characteristic parameter acquisition module is used to obtain characteristic parameters of a relaxation time distribution curve and an equivalent impedance model at a predetermined SOC point;

[0029] A characteristic parameter set acquisition module is used to obtain a characteristic parameter set related to abnormal changes in lithium-ion battery performance by comparing and analyzing changes in characteristic parameters between different SOC points;

[0030] The parameterized characterization module is used to uniformly characterize the change rate of each parameter in the characteristic parameter set, so as to realize the parameterized characterization of abnormal changes in the performance of lithium-ion batteries under the SOC point.

[0031] In a third aspect, the present invention provides a parameterized characterization system for abnormal changes in performance of a lithium-ion battery during charging, including a processor and a storage medium;

[0032] The storage medium is used to store instructions;

[0033] The processor is used to operate according to the instructions to execute the steps of any of the methods described above.

[0034] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that when the program is executed by a processor, the steps of any of the above-mentioned methods are implemented.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a parametric characterization method for abnormal changes in lithium-ion battery performance. By obtaining the relaxation time distribution (DRT) curve and impedance model parameters, the changes between different SOCs are compared and analyzed, and the lithium-ion batteries whose cycle times and health states are not in the same state are uniformly characterized in the form of change rate, effectively identifying the abnormal changes in the battery performance attenuation process. The method explains the mechanism of abnormal changes in battery performance and has strong adaptability to different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1It is a flow chart of a parameterized characterization method for abnormal changes in performance of a lithium-ion battery provided by an embodiment of the present invention;

[0038] Figure 2 is a schematic diagram of the electrochemical impedance spectrum of a lithium-ion battery provided by an embodiment of the present invention;

[0039] Figure 3 Schematic diagram of a relaxation time distribution curve of a lithium-ion battery provided by an embodiment of the present invention;

[0040] Figure 4 is a schematic diagram of an equivalent impedance model of a lithium-ion battery provided by an embodiment of the present invention;

[0041] Figure 5 It is a schematic diagram of a characterization result based on a unified characterization of the change rate of each parameter in a characteristic parameter set provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0043] Embodiment 1:

[0044] like Figure 1 As shown, an embodiment of the present invention provides a parameterized characterization method for abnormal changes in performance of a lithium-ion battery during charging, including:

[0045] The relaxation time distribution curve is obtained by analyzing the electrochemical impedance spectrum of the lithium-ion battery based on the relaxation time distribution method;

[0046] Determine the number of impedance links based on the peak number of the relaxation time distribution curve, and establish a corresponding equivalent impedance model;

[0047] Obtaining characteristic parameters of the relaxation time distribution curve and the equivalent impedance model at a predetermined SOC point;

[0048] By comparing and analyzing the characteristic parameter changes between different SOC points, a characteristic parameter set related to abnormal changes in lithium-ion battery performance is obtained;

[0049] Based on the unified characterization of the change rate of each parameter in the characteristic parameter set, the parametric characterization of abnormal changes in lithium-ion battery performance under SOC points is achieved.

[0050] Specifically, the electrochemical impedance spectroscopy of the lithium-ion battery is obtained by an impedance tester (EIS), such as Figure 2 As shown;

[0051] Based on the relaxation time distribution method, the electrochemical impedance spectrum of the lithium-ion battery is analyzed and obtained to obtain the relaxation time distribution curve, which specifically includes:

[0052] Construct an expression for the electrochemical impedance of a lithium-ion battery:

[0053]

[0054] Among them, R o is the ohmic impedance of the lithium-ion battery, γ(lnτ) is the relaxation time distribution curve function, τ is the relaxation time, j is the imaginary number sign, and w is the angular frequency;

[0055] The expression of electrochemical impedance of lithium-ion battery Z DRT Discretize the expression:

[0056]

[0057]

[0058] Where μ is the shape factor, τ n is the central relaxation time of the nth impedance link, N is the number of impedance links, x n is the parameter;

[0059] Based on the electrochemical impedance spectroscopy of lithium-ion batteries DRT Fit the obtained electrochemical impedance spectrum of lithium-ion battery to minimize the sum of squares of its errors and determine the relaxation time distribution curve function γ(lnτ), such as Figure 3 As shown in the figure, L1, L2 and L3 correspond to time positions respectively, and P1, P2 and P3 correspond to peaks of the curve respectively.

[0060] like Figure 4 As shown, the number of peaks is counted to determine the number of links of the equivalent impedance model (3 in this embodiment), and then the circuit description code of the equivalent circuit model is determined to be R o (Q SEI R SEI )(Q dl (R ct Q w )), and thus determine the equivalent impedance model:

[0061]

[0062]

[0063]

[0064]

[0065] Obtaining the characteristic parameters of the relaxation time distribution curve and the equivalent impedance model at a predetermined SOC point includes:

[0066] The set of characteristic parameters of the relaxation time distribution curve is:

[0067] θ DRT ={P i , τ i , P i -P j , τ i -τ j}(i, j < n and i ≠ j)

[0068] where n is the number of peaks of the relaxation time distribution curve, P i is the impedance intensity of the i-th peak, and τ i is the position of the i-th peak;

[0069] The set of characteristic parameters of the equivalent impedance model is:

[0070] θ Model ={R o , R SEI , R ct , Q SEI , Q dl , Q w , n w}

[0071] where R o , R SEI and R ct are the ohmic impedance, SEI film resistance, and charge transfer resistance of the battery, respectively. Since the arc in the EIS curve is not an ideal semi-circular trajectory, usually due to the inhomogeneity of the electrode / electrolyte interface, this phenomenon is generally called the "dispersion effect". Therefore, a constant phase element CPE with capacitive properties is introduced, and its equivalent element is represented by Q. Therefore, the capacitances of the SEI film and the double layer can be represented by Q SEI , Q dl . Since the low-frequency straight line can also be approximated as an arc with a very large radius, Q w can also be used to represent the solid-phase diffusion impedance. n w is the order of the constant phase angle element, which is an empirical constant and lacks an exact physical meaning. It is used as a correction for the capacitance when fitting the impedance spectrum.

[0072] The impedance characteristics of the battery are not only closely related to different frequency ranges but also strongly dependent on its SOC state. When the battery is at different SOC points, due to the different lithium intercalation states of its positive and negative electrode materials, the corresponding electrochemical impedance spectra are also different.

[0073] Whether it is a battery with abnormal performance changes or a battery with normal aging, the charge transfer process dominates the impedance spectrum, and the impedance of this process first decreases and then increases with the increase of SOC. The difference is that the proportion of the increase in the impedance of the charge transfer process of the battery with abnormal performance changes is significantly reduced compared with the battery with normal aging. Therefore, the characteristic parameters of the DRT curve at different SOC states and the equivalent impedance model parameters are extracted to characterize the abnormal changes in battery performance.

[0074] Based on the unified characterization of the change rate of each parameter in the characteristic parameter set, it includes:

[0075] Among them, θ is the characteristic parameter of the battery after aging, θ0 is the characteristic parameter of the battery at the initial moment, and S is the operating condition, which includes the battery equivalent cycle number, equivalent throughput capacity, equivalent throughput energy and equivalent mileage.

[0076] Under different working conditions, the abnormal changes in battery performance based on impedance characteristic parameters are characterized as follows: Figure 5 shown.

[0077] Embodiment 2:

[0078] The embodiment of the present invention provides a parametric characterization device for abnormal changes in performance of a lithium-ion battery during charging, the device comprising:

[0079] A relaxation time distribution curve determination module is used to analyze the electrochemical impedance spectrum of the lithium-ion battery obtained based on the relaxation time distribution method to obtain a relaxation time distribution curve;

[0080] An equivalent impedance model determination module is used to determine the number of impedance links based on the peak number of the relaxation time distribution curve and establish a corresponding equivalent impedance model;

[0081] A characteristic parameter acquisition module is used to obtain characteristic parameters of a relaxation time distribution curve and an equivalent impedance model at a predetermined SOC point;

[0082] A characteristic parameter set acquisition module is used to obtain a characteristic parameter set related to abnormal changes in lithium-ion battery performance by comparing and analyzing changes in characteristic parameters between different SOC points;

[0083] The parameterized characterization module is used to uniformly characterize the change rate of each parameter in the characteristic parameter set, so as to realize the parameterized characterization of abnormal changes in the performance of lithium-ion batteries under the SOC point.

[0084] Embodiment three:

[0085] An embodiment of the present invention provides a parameterized characterization system for abnormal changes in performance of a lithium-ion battery during charging, including a processor and a storage medium;

[0086] The storage medium is used to store instructions;

[0087] The processor is configured to operate according to the instructions to execute the steps according to any one of the above methods.

[0088] Embodiment 4:

[0089] An embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the program implements the steps of any of the above methods when executed by a processor.

[0090] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0091] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0092] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0093] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1The steps for the functions specified in one or more boxes.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A parametric characterization method for abnormal changes in lithium-ion battery performance, characterized in that: include: The relaxation time distribution curve is obtained by analyzing the electrochemical impedance spectrum of the lithium-ion battery based on the relaxation time distribution method; The number of impedance links is determined based on the peak number of the relaxation time distribution curve, and the corresponding equivalent impedance model is established; if the number of impedance links is 3, the circuit description code of the equivalent impedance model is R o (Q SEI R SEI )(Q dl (R ct Q w )) Determine the equivalent impedance model Z according to the circuit description code Model : In the formula, R o , R SEI , R ct All of them are resistances, representing the ohmic impedance, SEI film resistance and charge transfer resistance of lithium-ion batteries respectively; Q SEI , Q dl , Q w They are all constant phase elements CPE, representing the SEI film capacitance, double layer capacitance and solid phase diffusion impedance of lithium-ion batteries, j is the imaginary number symbol, w is the angular frequency, n SEI 、n dl 、n w Q SEI , Q dl , Q w The order of the constant phase element CPE; All are intermediate variables; Obtaining characteristic parameters of the relaxation time distribution curve and the equivalent impedance model at a predetermined SOC point; By comparing and analyzing the characteristic parameter changes between different SOC points, a characteristic parameter set related to abnormal changes in lithium-ion battery performance is obtained; Based on the unified characterization of the change rate of each parameter in the characteristic parameter set, the parametric characterization of abnormal changes in lithium-ion battery performance under SOC points is achieved.

2. A parameterized characterization method for abnormal changes in lithium-ion battery performance according to claim 1, characterized in that: The relaxation time distribution curve obtained by analyzing the electrochemical impedance spectrum of the lithium-ion battery based on the relaxation time distribution method includes: Construct an expression for the electrochemical impedance of a lithium-ion battery: Among them, R o is the ohmic impedance of the lithium-ion battery, γ(lnτ) is the relaxation time distribution curve function, τ is the relaxation time, j is the imaginary number sign, and w is the angular frequency; The expression of electrochemical impedance of lithium-ion battery Z DRT Discretize the expression: Where μ is the shape factor, τ n is the central relaxation time of the nth impedance link, N is the number of impedance links, x n is the parameter; Based on the electrochemical impedance spectroscopy of lithium-ion batteries DRT The obtained electrochemical impedance spectrum of the lithium-ion battery is fitted to minimize the sum of squares of its errors and determine the relaxation time distribution curve function γ(lnτ).

3. A parameterized characterization method for abnormal changes in lithium-ion battery performance according to claim 1, characterized in that: The unified characterization based on the change rate of each parameter in the characteristic parameter set includes: Among them, θ is the characteristic parameter of the battery after aging, θ0 is the characteristic parameter of the battery at the initial moment, and S is the operating condition, which includes the battery equivalent cycle number, equivalent throughput capacity, equivalent throughput energy and equivalent mileage.

4. A parametric characterization device for abnormal changes in lithium-ion battery performance, characterized in that: The device is used to perform the steps of the method according to any one of claims 1 to 3, and the device comprises: A relaxation time distribution curve determination module is used to analyze the electrochemical impedance spectrum of the lithium-ion battery obtained based on the relaxation time distribution method to obtain a relaxation time distribution curve; An equivalent impedance model determination module is used to determine the number of impedance links based on the peak number of the relaxation time distribution curve and establish a corresponding equivalent impedance model; A characteristic parameter acquisition module is used to obtain characteristic parameters of a relaxation time distribution curve and an equivalent impedance model at a predetermined SOC point; A characteristic parameter set acquisition module is used to obtain a characteristic parameter set related to abnormal changes in lithium-ion battery performance by comparing and analyzing changes in characteristic parameters between different SOC points; The parameterized characterization module is used to uniformly characterize the change rate of each parameter in the characteristic parameter set, so as to realize the parameterized characterization of abnormal changes in the performance of lithium-ion batteries under the SOC point.

5. A parameterized characterization system for abnormal changes in lithium-ion battery performance, characterized in that: including processor and storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1-3.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 3 are implemented.

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