Method for predicting high-temperature storage performance of battery

Abstract

The invention discloses a method for predicting the high-temperature storage performance of a battery. The method comprises the following steps: manufacturing a negative plate into a soft package symmetrical battery; measuring the open-circuit voltage of the soft package symmetrical battery; at least three different scanning speeds are selected, a CV curve of the soft package symmetrical battery is made, at each scanning speed, two current values corresponding to the open-circuit voltage are I1 and I2 respectively, and I is recorded as 0.5 * (I1-I2); the scanning speed and the corresponding I value are fitted to obtain an oblique line, the slope of the oblique line is electric double layer capacitance Cdl, and normalization processing is performed according to a formula C = Cdl / S or C = Cdl / m to obtain unit capacitance; testing the high-temperature full-power recovery rate of the soft package symmetrical battery with the known C value at the test temperature after N days; drawing a standard curve by using multiple groups of data; and preparing the negative plate to be measured into a symmetrical battery, and substituting the measured capacitance into the standard curve to obtain the full-charge recovery rate after N days. The method can quickly predict the high-temperature storage performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection, and in particular, to a method for predicting high-temperature storage performance of a battery. Background Art

[0002] Currently, if you want to understand the high-temperature storage performance of a battery, you can do it by, for example, fully charging the battery, leaving it at high temperature for a specific number of days, and measuring the full-charge storage recovery rate after the specific number of days. This method takes a long time to verify and is cumbersome to operate. If a prediction method for the high-temperature storage performance of a battery with a short detection cycle can be provided, it will undoubtedly improve the efficiency of battery quality testing.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The object of the present invention is to provide a method for predicting the high temperature storage performance of a battery.

[0005] The present invention is achieved in that: In a first aspect, the present invention provides a method for predicting high temperature storage performance of a battery, comprising: Step A: The negative electrode sheets are made into soft-pack symmetrical batteries in the form of alternating negative electrode sheets-separator-negative electrode sheets; Measure the open circuit voltage a of the soft-pack symmetrical battery; In the range of scanning speed 1~40mv / s, select at least 3 different scanning speeds to make the CV curve of the soft-pack symmetrical battery. The CV scanning interval is (ab)~(a+b), where b is 0.03~0.1; At each scanning speed, the two current values ​​corresponding to the open circuit voltage a are I 1 and I 2 , record △I=0.5*(I 1 -I 2 ); A slope is obtained by fitting at least 3 different scanning speeds and corresponding △I values. The slope of the slope is the double-layer capacitance Cdl. The unit capacitance is obtained by normalization according to the formula C=Cdl / S or C=Cdl / m, where S is the geometric area of ​​the electrode and m is the mass of the active layer on the electrode. Step B: Test the high temperature full charge recovery rate of soft-pack symmetrical batteries with known C value at the test temperature after N days; Step C: According to the operations of step A to step B, different batteries are manufactured, and multiple groups of full-charge storage recovery rate data after N days under different C values ​​are obtained, and the data are used to draw a standard curve; Step D: The negative electrode sheet used to prepare the target battery to be tested is made into a soft-pack symmetrical battery according to step A and its unit capacitance C is measured. The unit capacitance C is inserted into the standard curve to obtain the full charge recovery rate after N days.

[0006] In an optional embodiment, the scanning speed is 2-10 mv / s.

[0007] In an optional embodiment, before formally scanning to obtain the CV curve of the soft-pack symmetrical battery, the process further includes scanning the activated electrode at any value within the scanning speed range of 1 to 40 mv / s.

[0008] In an optional embodiment, at least 2 scans are performed at each scanning speed, and the scanning data of the last scan is taken to draw a curve.

[0009] In an alternative embodiment, the active material of the negative electrode sheet is graphite.

[0010] In an optional embodiment, the battery with the same type of negative electrode material to be tested is a lithium iron phosphate-graphite battery.

[0011] In an optional embodiment, the test temperature is 35-65°C.

[0012] In an alternative embodiment, b is 0.05.

[0013] The present invention has the following beneficial effects: For batteries with stable positive electrode performance, their high-temperature storage performance is mainly determined by the negative electrode sheet. Therefore, the high-temperature storage performance of the battery equipped with the negative electrode sheet can be inferred based on the properties of the negative electrode sheet.

[0014] The prediction method provided by the present invention measures the unit capacitance value of a soft-pack symmetrical battery made of a negative electrode sheet, measures its high-temperature full-charge recovery rate under the condition that the capacitance value is known, and can establish a standard curve based on multiple groups of double-layer capacitance values ​​and corresponding full-charge recovery rates. In practical applications, it is only necessary to make a soft-pack symmetrical battery with the same negative electrode sheet as the target battery to be tested, calculate the unit capacitance value of the symmetrical battery, and bring the capacitance value into the standard curve to obtain its full-charge recovery rate, which is very close to the full-charge recovery rate of an actual commercial battery. Therefore, the prediction method for the high-temperature storage performance of a battery provided by the present invention can be used to predict the high-temperature storage performance of a commercial battery. This method is faster than actually testing the high-temperature storage performance of a battery, and this test method can provide guidance for quality testing of commercial batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 It is a schematic diagram of the structure of a soft-pack symmetrical battery; Figure 2 CV curves at 5 scanning speeds in the embodiment; Figure 3 The relationship curve between △I and scanning speed in the embodiment; Figure 4 This is a standard curve diagram obtained in Example. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0018] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0019] An embodiment of the present invention provides a method for predicting high temperature storage performance of a battery, comprising: Step A: The negative electrode sheets are made into soft-pack symmetrical batteries in the form of alternating negative electrode sheets-separator-negative electrode sheets; Measure the open circuit voltage a of the soft-pack symmetrical battery; In the range of scanning speed 1~40mv / s, select at least 3 different scanning speeds to make the CV curve of the soft-pack symmetrical battery. The CV scanning interval is (ab)~(a+b), where b is 0.03~0.1; At each scanning speed, the two current values ​​corresponding to the open circuit voltage a are I 1 and I 2 , record △I=0.5*(I 1 -I 2 ); A slope is obtained by fitting at least 3 different scanning speeds and corresponding △I values. The slope of the slope is the double-layer capacitance Cdl. The unit capacitance is obtained by normalization according to the formula C=Cdl / S or C=Cdl / m, where S is the geometric area of ​​the electrode and m is the mass of the active layer on the electrode. Step B: Test the high temperature full charge recovery rate of soft-pack symmetrical batteries with known C value at the test temperature after N days; Step C: According to the operations of step A to step B, different batteries are manufactured, and multiple groups of full-charge storage recovery rate data after N days under different C values ​​are obtained, and the data are used to draw a standard curve; Step D: The negative electrode sheet used to prepare the target battery to be tested is made into a soft-pack symmetrical battery according to step A and its unit capacitance C is measured. The unit capacitance C is inserted into the standard curve to obtain the full charge recovery rate after N days.

[0020] Since the high temperature storage performance of most batteries is determined by the negative electrode sheet, it is only necessary to measure the high temperature performance of the negative electrode sheet to infer the high temperature performance of the battery equipped with the negative electrode sheet. The prediction method provided by the present invention measures the unit capacitance value of a soft-pack symmetrical battery made of a negative electrode sheet, measures its high temperature full charge recovery rate under the condition that the capacitance value is known, and a standard curve can be established based on multiple groups of double-layer capacitance values ​​and corresponding full charge recovery rates. In practical applications, it is only necessary to make a soft-pack symmetrical battery with the same negative electrode sheet as the target battery to be tested, calculate the unit capacitance value of the symmetrical battery, and bring the capacitance value into the standard curve to obtain its full charge recovery rate, which is very close to the full charge recovery rate of the actual commercial battery. Therefore, the prediction method of the high temperature storage performance of the battery provided by the present invention can be used to predict the high temperature storage performance of commercial batteries. This method is faster than actually detecting the high temperature storage performance of the battery, and the test method can provide guidance for the quality inspection of commercial batteries.

[0021] Preferably, before the formal scanning to obtain the CV curve of the soft-pack symmetrical battery, the scanning speed also includes scanning the activated electrode at any value in the range of 1 to 40 mv / s, such as 1 mv / s, 2 mv / s, 5 mv / s, 10 mv / s, 15 mv / s, 20 mv / s, 25 mv / s, 30 mv / s, 35 mv / s or 40 mv / s.

[0022] Optionally, the scanning speed is 2~10mv / s.

[0023] Preferably, in order to improve the accuracy, at least 2 scans are performed at each scanning speed, and the scanning data of the last scan is taken to draw a curve.

[0024] Optionally, the negative electrode material is graphite.

[0025] Optionally, the positive electrode active material of the target battery to be tested is lithium iron phosphate. Lithium iron phosphate is stable in nature, and the high temperature storage performance of the battery using it as the positive electrode active material is mainly determined by the negative electrode sheet.

[0026] Optionally, the test temperature is 35-65° C. (eg, 35° C., 40° C., 50° C., 60° C., or 65° C.) The prediction method provided by the present invention is mainly used to test high-temperature storage performance.

[0027] Optionally, b is 0.05.

[0028] Optionally, N is any value between 7 and 56, for example, 7, 14, 28 or 26.

[0029] Example Graphite, conductive agent (conductive carbon black), binder (SBR), and dispersant (CMC) are mixed in a ratio of 95:1:2:2 to prepare a slurry, and then coated, dried, and rolled to obtain a negative electrode sheet; The negative electrode sheet is cut into S = 11cm * 11cm, and a soft-pack symmetrical battery is made in the form of alternating negative electrode sheet-diaphragm-negative electrode sheet, such as Figure 1 As shown; The open circuit voltage of the soft-pack symmetrical battery was tested to be -0.05V; With -0.1V~0V as the scanning interval, first use 10mv / s to scan 4 cycles to activate the electrode, then make the CV curve of the symmetrical battery at scanning speeds of 10mv / s, 8mv / s, 6mv / s, 4mv / s and 2mv / s, respectively, scan 2 cycles at each speed, record the scan data of the last cycle, and record the curves at the 5 scanning speeds in Figure 2 middle; For each curve at the scanning speed, the current at the open circuit voltage is recorded as I1 and I2, where △I=0.5*(I 1 -I 2 ), different scanning speeds correspond to different △I, a total of five points; plot the scanning speed and △I, and establish the following Figure 3 The relationship shown in the figure is fitted to obtain the slope, that is, the double-layer capacitance 𝐶dl=0.8291 F, and the mass is normalized: the unit capacitance C=Cdl / m, the total mass of the electrode coating slurry m=21.54g, and the calculated C is 0.038 mF / mg; The battery was tested for full-charge storage recovery rate at 60°C for 7 days, 14 days, 28 days and 56 days. The recovery rate was calculated as follows: recovery rate = battery capacity after storage / battery capacity before storage. The battery capacity test method before and after storage remained the same.

[0030] The above are samples of soft-pack symmetrical batteries A, B and C. The only difference between A, B and C is the type of graphite.

[0031] The unit capacitance C values ​​were calculated to be 0.0234 mF / mg, 0.036 mF / mg, and 0.045 mF / mg, as well as the full-charge storage recovery rates at 7 days, 14 days, 28 days, and 56 days, respectively.

[0032] The unit capacitance C values ​​measured by soft-pack symmetrical batteries A, B and C and their corresponding full-charge storage recovery rates at 7 days, 14 days, 28 days and 56 days are plotted to obtain a standard curve as shown in Figure 4 shown.

[0033] Experiment 1: (1) Provide a battery No. 1 to be tested, which is a lithium iron phosphate / graphite battery with a capacity of 5.5 Ah; the active layer of the positive electrode sheet of the battery is composed of lithium iron phosphate, a binder (PVDF), and a conductive agent (conductive carbon black) in a mass ratio of 96:2:2; the active layer of the negative electrode sheet of the battery is composed of graphite, a dispersant (CMC), a conductive agent (conductive carbon black), and a binder (SBR) in a mass ratio of 94.6:1.4:2:2.

[0034] (2) Take a negative electrode sheet that is the same as the negative electrode sheet of the battery to be tested, and make the negative electrode sheet into 5 soft-pack symmetrical batteries. Measure the unit capacitance according to the method mentioned in the above content of this embodiment and take the average value C=0.03mF / mg. Substitute the C value into the above standard curve, and calculate that the full-charge storage recovery rates of 7 days, 14 days, 28 days and 56 days are 96.7%, 95.5%, 94.4% and 91.5% respectively.

[0035] (3) Take 5 No. 1 batteries to be tested and measure their full-charge storage recovery rates after 7 days, 14 days, 28 days and 56 days respectively. Take the average value of the measured values ​​of the 5 batteries, and the average values ​​of the full-charge storage recovery rates after 7 days, 14 days, 28 days and 56 days are 96.8%, 95.2%, 94% and 91% respectively.

[0036] The recovery rate predicted by the method provided by the present invention is compared with the recovery rate measured by the prior art. The error values ​​of the predicted recovery rates for 7 days, 14 days, 28 days and 56 days compared with the recovery rates measured by the prior art are 0.1%, 0.3%, 0.4% and 0.5%, respectively. The error values ​​are all less than 1%, indicating that the prediction method provided in this embodiment has better reliability.

[0037] Experiment 2: (1) Provide a battery No. 2 to be tested, which is a lithium iron phosphate / graphite battery with a capacity of 20 Ah; the active layer of the positive electrode sheet of the battery consists of lithium iron phosphate, a conductive agent (conductive carbon black), a binder (PVDF), and a dispersant (CMC) in a mass ratio of 95.8:2:2:0.2; the active layer of the negative electrode sheet of the battery consists of graphite, a dispersant (CMC), a conductive agent (conductive carbon black), and a binder (SBR) in a mass ratio of 94.6:1.4:2:2. (2) Provide a battery No. 2 to be tested, take a negative electrode sheet that is the same as the negative electrode sheet of the battery to be tested, and make the negative electrode sheet into 5 soft-pack symmetrical batteries. According to the method mentioned in the above content of this embodiment, measure the unit capacitance C=0.042mF / mg, take the average value, and substitute the average value of C value into the above standard curve, and calculate that the full-charge storage recovery rates of 7 days, 14 days, 28 days and 56 days are 96.3%, 95%, 93.6% and 90.2% respectively.

[0038] (3) Take 5 No. 2 batteries to be tested and measure their full-charge storage recovery rates after 7 days, 14 days, 28 days and 56 days respectively. Take the average value of the measured values ​​of the 5 batteries, and the average values ​​of the full-charge storage recovery rates after 7 days, 14 days, 28 days and 56 days are 96.2%, 94.8%, 93.7% and 89.7% respectively.

[0039] The recovery rate predicted by the method provided by the present invention is compared with the recovery rate measured by the prior art. The error values ​​of the predicted recovery rates for 7 days, 14 days, 28 days and 56 days compared with the recovery rates measured by the prior art are 0.1%, 0.2%, 0.1%, 0.5% and , and the error values ​​are all less than 1%, indicating that the prediction method provided in this embodiment has better reliability.

[0040] In summary, the prediction method provided by the embodiment of the present invention measures the unit capacitance value of a soft-pack symmetrical battery made of a negative electrode sheet, and measures its high-temperature full-charge recovery rate under the condition that the capacitance value is known. A standard curve can be established based on the double-layer capacitance value and the corresponding full-charge recovery rate. In practical applications, it is only necessary to make a soft-pack symmetrical battery with the same negative electrode sheet as the target battery, calculate the unit capacitance value of the symmetrical battery, and bring the capacitance value into the standard curve to obtain its full-charge recovery rate, which is very close to the full-charge recovery rate of an actual commercial battery. Therefore, the prediction method for the high-temperature storage performance of a battery provided by the present invention can be used to predict the high-temperature storage performance of a commercial battery. This method is faster than actually detecting the high-temperature storage performance of the battery, and the test method can provide guidance for quality testing of commercial batteries.

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting high temperature storage performance of a battery, characterized in that: include: Step A: The negative electrode sheets are made into soft-pack symmetrical batteries in the form of alternating negative electrode sheets-separator-negative electrode sheets; Measuring the open circuit voltage a of the soft-pack symmetrical battery; In the range of scanning speed 1-40mv / s, at least 3 different scanning speeds are selected to make the CV curve of the soft-pack symmetrical battery, and the CV scanning interval is (ab)-(a+b), where b is 0.03-0.1; At each scanning speed, the two current values ​​corresponding to the open circuit voltage a are I1 and I2, respectively, where △I=0.5*(I1-I2); The at least three different scanning speeds and the corresponding ΔI values ​​are used to fit a slope, the slope of which is the double-layer capacitance Cdl, and the unit capacitance is obtained by normalization according to the formula C=Cdl / S or C=Cdl / m, where S is the geometric area of ​​the electrode and m is the mass of the active layer on the electrode; Step B: Testing the high temperature full charge recovery rate of the soft-pack symmetrical battery with a known C value at the test temperature after N days; Step C: According to the operations of step A to step B, different batteries are manufactured to obtain multiple groups of full-charge storage recovery rate data after N days at different C values, and the data are used to draw a standard curve; Step D: The negative electrode sheet used to prepare the target battery to be tested is made into a soft-pack symmetrical battery according to the method of step A and its unit capacitance C is measured. The unit capacitance C is inserted into the standard curve to obtain the full charge recovery rate after N days.

2. The prediction method according to claim 1, characterized in that: The scanning speed is 2~10mv / s.

3. The prediction method according to claim 1, characterized in that: Before formally scanning to obtain the CV curve of the soft-pack symmetrical battery, the method also includes scanning the activated electrode at any value within the scanning speed range of 1 to 40 mv / s.

4. The prediction method according to claim 1, characterized in that: At least 2 scans were performed at each scanning speed, and the scanning data of the last scan were taken to draw a curve.

5. The prediction method according to claim 1, characterized in that: The active material of the negative electrode sheet is graphite.

6. The prediction method according to any one of claims 1 to 5, characterized in that: The positive electrode active material of the target battery to be tested is lithium iron phosphate.

7. The prediction method according to claim 1, characterized in that: The test temperature is 35~65℃.

8. The prediction method according to claim 1, characterized in that: b is 0.05.

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