Battery performance analysis method

Abstract

The invention belongs to the technical field of battery testing, and discloses a battery performance analysis method which comprises the following steps: measuring initial parameters of a battery; the method comprises the following steps: connecting a first adjustable resistor and a second adjustable resistor outside a battery, connecting the second adjustable resistor with a negative pole of the battery and a shell of the battery, discharging the battery, and measuring the battery to obtain a first test parameter after a preset time period; keeping the resistance values of the first adjustable resistor and the second adjustable resistor unchanged, and measuring the first test parameter of the battery every preset time period to obtain a first test parameter table until the voltage of the battery reaches a final voltage; and calculating according to the initial parameter and the first test parameter to obtain a self-discharge rate, judging the aging degree of the shell, and evaluating the performance of the battery. According to the invention, the problems of low test efficiency, high test cost and unstable test environment condition in the self-discharge aging test of the battery are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery testing, and particularly relates to a battery performance analysis method. BACKGROUND

[0002] Lithium ion batteries are applied to electric vehicles, energy storage systems, consumer electronics and other fields. In actual storage and use, lithium ion batteries will have self-discharge phenomenon, that is, the voltage and capacity of the battery gradually decrease over time without external load. The size of the self-discharge rate directly affects the storage performance, safety and life of the battery, so the self-discharge characteristic is an important index in quality evaluation and factory inspection of lithium ion batteries. The existing self-discharge verification method is usually as follows: the battery is stored for a long time at full charge or a certain state of charge, and after a certain period, the remaining voltage and capacity of the battery are measured, and the self-discharge rate is calculated accordingly. This method has the disadvantages of long test period, low efficiency, and great influence of environmental conditions. For example, under different humidity or temperature conditions, the self-discharge rate of the battery will change significantly, resulting in poor repeatability of the test results. At the same time, long-term storage verification not only increases the detection cost, but also is not conducive to large-scale and rapid factory inspection. SUMMARY

[0003] The technical problem to be solved by the application is to provide a battery performance analysis method, which solves the problems of low test efficiency, high test cost and unstable test environment in battery self-discharge aging test.

[0004] The technical solution of the application is that the application provides a battery performance analysis method, which comprises the following steps:

[0005] Step 1: measuring initial parameters of the battery;

[0006] Step 2: connecting a first adjustable resistor and a second adjustable resistor outside the battery, connecting the first adjustable resistor to the positive pole of the battery and the shell of the battery respectively, connecting the second adjustable resistor to the negative pole of the battery and the shell of the battery respectively, discharging the battery, and measuring first test parameters of the battery after a preset time period;

[0007] Step 3: keeping the resistance values of the first adjustable resistor and the second adjustable resistor unchanged, repeating step 2, measuring the first test parameters of the battery every interval of the preset time period to obtain a first test parameter table, and stopping until the voltage of the battery reaches a terminal voltage;

[0008] Step 4: calculating a self-discharge rate according to the initial parameters and the first test parameters, judging the aging degree of the shell, and evaluating the performance of the battery.

[0009] Further, the initial parameters of the battery include initial positive electrode versus negative electrode voltage, initial positive electrode versus shell voltage, initial negative electrode versus shell voltage, initial positive electrode versus negative electrode resistance, initial positive electrode versus shell resistance, and initial negative electrode versus shell resistance.

[0010] Further, the method further comprises:

[0011] Step 5: adjusting the first adjustable resistance and the second adjustable resistance, discharging the battery, measuring second test parameters of the battery after the preset time period;

[0012] Step 6: keeping the resistance values of the first adjustable resistance and the second adjustable resistance unchanged, repeating step 5 to measure the second test parameters of the battery every interval of the preset time period to obtain a second test parameter table until the battery reaches a terminal voltage;

[0013] Step 7: calculating a self-discharge rate according to the initial parameters and the second test parameters, judging the shell aging degree, and evaluating the battery performance.

[0014] Further, the first test parameters and the second test parameters both include positive electrode versus negative electrode voltage, positive electrode versus shell voltage, negative electrode versus shell voltage, positive electrode versus negative electrode resistance, positive electrode versus shell resistance, and negative electrode versus shell resistance.

[0015] Further, in step 3, the battery voltage reaches the terminal voltage when the difference between the positive electrode versus negative electrode voltage measured in the current preset time period and the positive electrode versus negative electrode voltage measured in the previous preset time period is less than 0.001.

[0016] Further, in step 4, the self-discharge rate is calculated according to the initial parameters and the first test parameter table, which comprises:

[0017] calculating the difference between the positive electrode versus negative electrode voltage in the previous preset time period and the positive electrode versus negative electrode voltage in the current preset time period, and dividing the difference by the preset time to obtain the self-discharge rate in the current preset time period.

[0018] Further, in step 4, the self-discharge rate is calculated according to the initial parameters and the first test parameter table, which further comprises:

[0019] calculating the self-discharge rate in each time period to obtain a self-discharge rate table, and drawing a self-discharge rate curve according to the self-discharge rate table.

[0020] Further, in step 4, the self-discharge rate is calculated according to the initial parameters and the first test parameter table to evaluate the battery performance, specifically: if the self-discharge rate in all time periods is less than 2%, the battery meets the requirements, otherwise, the battery is not up to standard.

[0021] Further, the self-discharge rate is calculated according to the initial parameters and the first test parameters in step 4 to determine the aging of the shell; the step includes observing whether the positive shell resistance and the negative shell resistance in the first test parameter table change, if the positive shell resistance and the negative shell resistance change, it is determined that the battery shell has aging phenomenon; if there is no change, it is determined that the battery shell has no aging phenomenon.

[0022] Further, the first adjustable resistance and the second adjustable resistance are adjusted in step 5 to discharge the battery; the step includes:

[0023] The first adjustable resistance is adjusted to 1MΩ, 10kΩ and 1kΩ, the second adjustable resistance is adjusted to 1MΩ, 10kΩ and 1kΩ, the conductive rate under dry conditions, humidity 60% and humidity 90% is simulated, and the battery is discharged.

[0024] The beneficial effects of the present application are: the present application simulates the conductive conditions under different environments by connecting the first adjustable resistance and the second adjustable resistance outside the battery, accelerates the self-discharge process without long-term natural storage, and quickly obtains the self-discharge rate and performance parameters of the battery. By simulating the environmental conductive conditions of the resistance and measuring the multiple test parameters of the battery, a test parameter table is established in combination with the initial parameters to determine the aging degree of the battery negative material under different conductive conditions, without preparing a large number of samples for multi-environment, multi-period comparison, reducing the consumption of test samples. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 A first flowchart of a battery performance analysis method is provided for the embodiments of the present application;

[0027] Figure 2 A structural schematic diagram of a battery performance analysis device is provided for the present application;

[0028] Figure 3 A second flowchart of a battery performance analysis method is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application.

[0030] In the present application, the terms "first", "second", and the like are mainly used to distinguish different devices, elements or components (the specific types and structures can be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, the meaning of "a plurality of" is two or more.

[0031] The implementation of the present application will be described in detail below with reference to specific drawings:

[0032] Figure 1 A first flowchart of a battery performance analysis method is provided for the embodiments of the present application, as shown in Figure 1 The method comprises the following steps:

[0033] Step 1: measuring initial parameters of the battery;

[0034] Step 2: connecting a first adjustable resistor and a second adjustable resistor outside the battery, connecting the first adjustable resistor to the positive pole of the battery and the shell of the battery respectively, connecting the second adjustable resistor to the negative pole of the battery and the shell of the battery respectively, discharging the battery, measuring a first test parameter of the battery after a preset time period;

[0035] Step 3: keeping the resistance values of the first adjustable resistor and the second adjustable resistor unchanged, repeating step 2, measuring the first test parameter of the battery every interval of the preset time period to obtain a first test parameter table until the battery voltage reaches a terminal voltage;

[0036] Step 4: calculating a self-discharge rate according to the initial parameters and the first test parameters, judging the shell aging degree, and evaluating the battery performance.

[0037] In the step 1, the initial parameters of the battery which is not discharged are measured, and the initial parameters include initial positive pole to negative pole voltage, initial positive pole to shell voltage, initial negative pole to shell voltage, initial positive pole to negative pole resistance, initial positive pole to shell resistance, and initial negative pole to shell resistance.

[0038] Step 2 is specifically: placing the battery to be tested in the same test environment, adjusting the first adjustable resistor and the second adjustable resistor to the same analog resistance value, connecting the first adjustable resistor to the positive pole of the battery to be tested and the aluminum shell of the battery respectively, connecting the second adjustable resistor to the negative pole of the battery to be tested and the aluminum shell of the battery respectively, opening the switch to simulate discharging the battery, after a preset time period, disconnecting the switch and measuring the current first test parameter of the battery, the first test parameter including the positive pole to negative pole voltage U +― , the positive pole to shell voltage U +s , the negative pole to shell voltage U ―s , the positive pole to negative pole resistance R +― , the positive pole to shell resistance R +s , and the negative pole to shell resistance R ―s In this embodiment, the preset time period is one week.

[0039] Step 3 is specifically: keeping the resistance values of the first adjustable resistor and the second adjustable resistor unchanged, opening the switch to simulate discharging the battery again, after a preset time period, disconnecting the switch and measuring the current first test parameter of the battery, repeating step 2 until the battery voltage reaches the termination voltage, when the battery voltage reaches the termination voltage, the battery will not self-discharge, that is, the difference between the positive pole to negative pole voltage measured in the last cycle and the positive pole to negative pole voltage measured in the current cycle is less than 0.001, it is considered that the battery discharge has reached the termination voltage, and no further measurement is needed. Record the first test parameter measured in each cycle to obtain a first test parameter table.

[0040] Step 4 calculates the self-discharge rate of each cycle preset time period, the difference between the positive pole to negative pole voltage of the last cycle and the positive pole to negative pole voltage of the current cycle preset time period, the difference is divided by the preset time to obtain the self-discharge rate of the current preset time period, the self-discharge rate data obtained in each cycle is plotted into a self-discharge rate curve, and the self-discharge rate curve is observed, when the self-discharge rate in all time periods is less than 2%, it is considered that the battery meets the requirements, otherwise the battery is not up to standard.

[0041] Observe the first test parameter table to determine whether the shell has aged, specifically:

[0042] Observe whether the positive pole to shell voltage and the negative pole to shell voltage change, if only the positive pole to shell voltage gradually decreases, and the negative pole to shell voltage remains stable, it usually indicates that there may be an electrochemical leakage path formed between the positive pole of the battery and the shell, which may be caused by electrolyte penetration or corrosion of the shell near the positive pole, the shell on the positive pole side is aged or the local insulation performance decreases.

[0043] If only the negative electrode to the shell voltage gradually decreases, and the positive electrode to the shell voltage remains stable, it may be that the negative electrode material (such as lithium metal or graphite) has an electrochemical reaction with the shell or lithium dendrite growth contacts the shell, forming a leakage channel, and the insulation of the negative electrode side shell decreases or there is a potential short circuit risk.

[0044] If the positive electrode to the shell voltage and the negative electrode to the shell voltage decrease at the same time, it indicates that the insulation state of the entire shell deteriorates, which may be due to reasons such as moisture in the shell, high temperature aging, or electrolyte evaporation, causing multiple leakage paths to form inside the battery or the shell to be corroded as a whole, and the overall encapsulation or insulation state of the battery to decrease.

[0045] If the positive and negative electrode to the shell voltage fluctuates violently and is unstable, it may be caused by external factors such as poor test contact, electrode terminal oxidation, loose connection wire, etc. It may also indicate that the corrosion reaction inside the battery is in an unstable progress state, and whether there is an intermittent micro-short circuit or a dynamic bridge needs to be judged in combination with the internal resistance and leakage current changes.

[0046] If the resistance between the positive electrode and the negative electrode continues to rise, it usually indicates that the internal conductive path of the battery has deteriorated, and there may be: electrode material aging or structure collapse, leading to reduced conductivity; poor contact of electrode / tab weld or connection site; electrolyte drying or decomposition, reducing ion migration efficiency; lithium deposition or byproduct covering the electrode surface, forming a passivation layer; poor compaction of the pole piece, increasing the interface impedance.

[0047] If the resistance between the positive electrode and the negative electrode decreases significantly, there may be an internal short circuit trend, such as lithium dendrite piercing the separator causing a micro-short circuit; shell corrosion causing electrolyte to form a leakage path, thereby forming a "bypass conduction" phenomenon; or abnormal data caused by measurement error or test environment wiring change.

[0048] If the positive electrode to the shell resistance and the negative electrode to the shell resistance decrease, it indicates that there is a conduction path between the electrode and the shell, and the shell is electrochemically corroded; if the positive electrode to the shell resistance and the negative electrode to the shell resistance increase, it indicates that the test line contact is poor or the electrode terminal is oxidized, causing measurement error and requiring retesting; or the battery tab or shell surface is covered with corrosion products, causing the contact resistance to increase.

[0049] Figure 2 A structural schematic diagram of a battery performance analysis device provided by the present application is shown in Figure 2 As shown, the battery includes a shell 1 and a pole 2, and an adjustable resistor 3 is connected between the pole 2 and the shell 1, used to simulate the equivalent resistance between the pole 2 and the shell 1 stored in different environments.

[0050] Figure 3 A second flowchart of a battery performance analysis method provided by the present application is shown in Figure 2As shown, the battery performance analysis method provided by the embodiments of the present application further comprises:

[0051] Step 5: adjusting the first adjustable resistor and the second adjustable resistor, discharging the battery, and measuring a second test parameter of the battery after the preset time period;

[0052] Step 6: keeping the resistance values of the first adjustable resistor and the second adjustable resistor unchanged, repeating step 5 to measure the second test parameter of the battery every preset time period until the battery reaches a terminal voltage.

[0053] Step 7: calculating a self-discharge rate according to the initial parameter and the second test parameter, judging the aging degree of the shell, and evaluating the battery performance.

[0054] In step 5, the same battery to be tested as in step 1 is used, the first adjustable resistor and the second adjustable resistor are adjusted synchronously, the resistance values of the first adjustable resistor and the second adjustable resistor are made the same, the switch is turned on, and the second test parameter is measured after the preset time period. The second test parameter includes the positive electrode-to-negative electrode voltage, the positive electrode-to-shell voltage, the negative electrode-to-shell voltage, the positive electrode-to-negative electrode resistance, the positive electrode-to-shell resistance, and the negative electrode-to-shell resistance.

[0055] The adjustment mode of steps 6 and 7 is similar to that of steps 3 and 4, and will not be described here.

[0056] Meanwhile, three groups of batteries in the same initial state are connected to different simulation measurement resistors, and the measured experimental data are shown in the following tables. By connecting the battery poles and the aluminum shell with different resistance values (1MΩ, 10KΩ, and 1KΩ) under different humidity environments (30% dryness, 60% humidity, and 90% humidity), the self-discharge characteristics of the battery are measured. Table 1 shows the test parameters measured under the simulation humidity of 30%; Table 2 shows the test parameters measured under the simulation humidity of 60%; and Table 3 shows the test parameters measured under the simulation humidity of 90%.

[0057]

[0058] Table 1

[0059]

[0060] Table 2

[0061]

[0062] Table 3 By analyzing the above table, the voltage change trend, dry environment (1 MΩ): initial 3.35776 V → 3.33990 V after 189 days, down 0.53%, self-discharge is low; humidity 60% (10 KΩ): initial 3.35776 V → 3.34217 V after 189 days, down 0.46%, self-discharge is slightly higher than dry environment; humidity 90% (1 KΩ): initial 3.35776 V → 3.34082 V after 189 days, down 0.50%, self-discharge rate is close to dry environment, but initial fluctuation is larger.

[0063] Positive electrode to shell voltage, close to 0V (0.00012V→0.00029V) in dry environment, indicating that the shell has almost no leakage current with the positive electrode; positive-shell voltage significantly increases (0.00256V→

[0064] 0.00147V) when humidity is 90%, indicating that high humidity causes the shell to increase the leakage current.

[0065] Negative electrode to shell voltage, stable in dry environment (3.35766V→3.33854V), synchronous with positive-negative voltage; negative-shell voltage decreases faster (3.34552V→3.33327V) when humidity is 90%, indicating that the negative electrode is more sensitive to shell leakage.

[0066] Self-discharge rate, dry environment: rate is stable at 0.001%-0.094%, and tends to be 0 in later period, indicating good insulation performance; humidity 60%: initial rate is higher (0.1016%), and decreases to 0.0006% in later period; humidity 90%: initial fluctuation is large (0.0953%), and stabilizes at 0.0009% in later period, but still has a small leakage. Self-discharge rate is less than 2%, indicating that the battery performance is good.

[0067] Experimental data measured by the method show that the battery type causes the shell and the electrode to increase the leakage current under high humidity, especially the negative electrode to shell voltage decreases significantly. Self-discharge can be ignored in dry environment. The main path of self-discharge is electrode-shell, and the negative electrode to shell voltage decreases more significantly when humidity is 90%. Positive-shell leakage can be ignored, and the voltage is close to 0V.

[0068] By simulating the conductive conditions of different environmental humidities by external resistance, the leakage current path is forced to form, and the battery self-discharge process is accelerated. By combining voltage, resistance and other multi-parameter measurements, the battery self-discharge rate and the negative electrode aging degree are quickly calculated, replacing the traditional long-term static test, and quickly obtaining the self-discharge rate and performance parameters of the battery. By simulating the environmental conductive conditions by resistance and measuring multiple test parameters of the battery, and combining the initial parameters to establish a test parameter table, the aging degree of the negative electrode material of the battery under different conductive conditions is judged, without preparing a large number of samples for multi-environment, multi-period comparison, reducing the consumption of test samples.

[0069] It is apparent that the above-described embodiments are only preferred embodiments of the application and are used to illustrate the technical principles of the application. It is appreciated that those skilled in the art can make various modifications and changes to the embodiments without departing from the scope of the application. Therefore, the scope of the application should be subject to the appended claims.

[0070] It is noted that in the description of the specification, the description with reference to the terms "some embodiments", "other embodiments", and the like, means that the particular feature, structure, material or characteristic being described is included in at least one embodiment or example of the application. The illustrative appearances of the above-mentioned terms in the description are not necessarily referring to the same embodiment or example, and are not necessarily used in every embodiment or example. Furthermore, the particular features, structures, materials or characteristics can be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A battery performance analysis method, characterized in that: include: Step 1: Measure the initial parameters of the battery; Step 2: Connecting a first adjustable resistor and a second adjustable resistor outside the battery, connecting the first adjustable resistor to the positive electrode of the battery and the battery casing, respectively, and connecting the second adjustable resistor to the negative electrode of the battery and the battery casing, respectively, discharging the battery, and measuring the battery to obtain a first test parameter after a preset time period; Step 3: Keeping the resistance values ​​of the first adjustable resistor and the second adjustable resistor unchanged, repeating step 2, measuring the first test parameter of the battery at intervals of the preset time period to obtain a first test parameter table, until the battery voltage reaches the termination voltage; Step 4: Calculate the self-discharge rate based on the initial parameters and the first test parameters, determine the degree of shell aging, and evaluate battery performance.

2. The battery performance analysis method according to claim 1, wherein: The initial parameters of the battery include initial positive electrode to negative electrode voltage, initial positive electrode to shell voltage, initial negative electrode to shell voltage, initial positive electrode to negative electrode resistance, initial positive electrode to shell resistance and initial negative electrode to shell resistance.

3. The battery performance analysis method according to claim 1, wherein: The method further comprises: Step 5: adjusting the first adjustable resistor and the second adjustable resistor to discharge the battery, and measuring the battery to obtain a second test parameter after the preset time period; Step 6: Keeping the resistance values ​​of the first adjustable resistor and the second adjustable resistor unchanged, repeating step 5 at intervals of the preset time period, measuring the second test parameter of the battery to obtain a second test parameter table, until the battery reaches the termination voltage; Step 7 calculates the self-discharge rate based on the initial parameters and the second test parameters, determines the degree of shell aging, and evaluates battery performance.

4. The battery performance analysis method according to claim 3, wherein: The first test parameter and the second test parameter both include positive-to-negative voltage, positive-to-shell voltage, negative-to-shell voltage, positive-to-negative resistance, positive-to-shell resistance, and negative-to-shell resistance.

5. The battery performance analysis method according to claim 4, wherein: The battery voltage reaches the termination voltage in step 3, specifically: when the difference between the positive electrode to negative electrode voltage measured in the current preset time period and the positive electrode to negative electrode voltage measured in the previous preset time period is less than 0.001, the battery voltage reaches the termination voltage.

6. The battery performance analysis method according to claim 4, wherein: The self-discharge rate is calculated based on the initial parameters and the first test parameter table in step 4, including: The difference between the positive-to-negative voltage in the previous preset time period and the positive-to-negative voltage in the current preset time period is calculated, and the positive-to-negative voltage difference is divided by the preset time to obtain the self-discharge rate in the current preset time period.

7. The battery performance analysis method according to claim 6, wherein: The self-discharge rate is calculated according to the initial parameters and the first test parameter table in step 4; and further includes: The self-discharge rate in each time period is calculated to obtain a self-discharge rate table, and a self-discharge rate curve is drawn according to the self-discharge rate table.

8. The battery performance analysis method according to claim 7, wherein: In step 4, the self-discharge rate is calculated based on the initial parameters and the first test parameters to evaluate the battery performance. Specifically, if the self-discharge rate in all time periods is less than 2%, the battery meets the requirements; otherwise, the battery does not meet the requirements.

9. The battery performance analysis method according to claim 4, wherein: In step 4, the self-discharge rate is calculated according to the initial parameters and the first test parameters to determine the aging of the shell; the step includes: observing whether the positive electrode-to-shell resistance and the negative electrode-to-shell resistance in the first test parameter table change; if the positive electrode-to-shell resistance and the negative electrode-to-shell resistance change, it is determined that the battery shell has aged; if not, it is determined that the battery shell has not aged.

10. The battery performance analysis method according to claim 3, wherein: The step 5 of adjusting the first adjustable resistor and the second adjustable resistor to discharge the battery includes: The first adjustment resistor was adjusted to 1 MΩ, 10 kΩ, and 1 kΩ, and the second adjustment resistor was adjusted to 1 MΩ, 10 kΩ, and 1 kΩ. The conduction rates under dry conditions, 60% humidity, and 90% humidity were simulated to discharge the battery.

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