Method for judging optimal aging time and infiltration degree of manganese-based battery cell

Abstract

The invention relates to the technical field of battery testing, and discloses a method for judging the optimal aging time and infiltration degree of a manganese-based battery cell. The method for judging the optimal aging time of the base cell comprises the following steps: fully charging a plurality of cells of the same kind, the aging time of the cells of the same kind being different, and the aging time being distributed within an interval of 2-50 hours; obtaining the Mn dissolution amount of the battery cell: disassembling each fully charged battery cell, and measuring the Mn content, namely the dissolution amount, in the negative electrode active material; establishing a curve by using the measured Mn content and the corresponding aging time; the increase position of the growth rate of the Mn content in the curve is an inflection point, the time point corresponding to the inflection point is x, and any time range within (x-2)-(x + 6) h is the optimal aging time range. The testing process of the method is not affected by the outside, accuracy is high, and time is short.

Description

Technical Field

[0001] The present invention relates to the technical field of battery testing, and in particular to a method for determining the optimal aging time and infiltration degree of a manganese-based battery cell. Background Art

[0002] Currently, methods for judging the aging time of manganese-based material battery cells include the fluorescence method, which adds a fluorescent agent to the electrolyte and then observes the fluorescence intensity to judge the infiltration effect, but the results are highly subjective and have large errors; and the method of continuously performing EIS scanning on the battery cells during the aging process, using the change in Rs ohmic impedance for judgment, but this method requires continuous detection, which is time-consuming and labor-intensive, and the EIS test results are easily affected by the external environment and prone to fluctuations; there is also a method of judging the aging infiltration effect by testing the Li content of the negative electrode sheet after aging through ICP testing. The principle of this method is to feedback the degree of infiltration by detecting the Li element component in the electrolyte, but the electrolyte after disassembly is volatile and thus affects the results. In addition, there will be floating liquid between the electrode core layers during the disassembly process, which will also affect the test results; there is also a method of judging whether the infiltration is sufficient by measuring the voltage of the battery cell after formation, but the voltage test is easily affected by external factors such as external temperature, test leads, electromagnetic noise, etc., and some byproducts in the battery cell aging process will affect the internal resistance of the battery cell, thereby affecting the voltage measurement accuracy.

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

[0004] The purpose of the present invention is to provide a method for determining the optimal aging time and the degree of infiltration of manganese-based battery cells, aiming to improve at least one of the problems mentioned in the background art.

[0005] The present invention is achieved in that:

[0006] In a first aspect, the present invention provides a method for determining the optimal aging time of a manganese-based battery cell, comprising:

[0007] Take multiple cells of the same type and fully charge them. The aging time of the cells is different and ranges from 2 to 50 hours.

[0008] Obtain the amount of Mn dissolved from the battery cell: disassemble each fully charged battery cell, take the negative electrode sheet and place it in a humid environment to oxidize the negative electrode sheet until the yellow interface completely turns black. Scrape off the active material in the middle area of the oxidized negative electrode sheet and measure the Mn content in the scraped active material, i.e. the dissolved amount.

[0009] A curve was established using the measured Mn content and the corresponding aging time;

[0010] As time goes by, the curve includes the first stage, the second stage and the third stage in sequence, and the manganese dissolution growth rates are the first growth rate, the second growth rate and the third growth rate in sequence, among which the first growth rate and the third growth rate are greater than the second growth rate. The junction of the second stage and the third stage is the inflection point, and the time point corresponding to the inflection point is x. Any time range within (x-2) to (x+6) h is the optimal aging time range.

[0011] In an optional embodiment, the manganese-based battery cell refers to a battery cell using a manganese-based material as a positive electrode active material, and the manganese-based material is selected from at least one of lithium manganese iron phosphate, lithium manganate and nickel-cobalt-manganese ternary material.

[0012] In an optional embodiment, the full charging method is to charge according to a formation charging process.

[0013] In an optional embodiment, the charging method of the formation charging process includes: setting the current to 0.1-1C, the temperature to 35-55° C., and the charging cut-off voltage to 4-4.2V for charging.

[0014] In an optional embodiment, the humid environment is a non-sealed environment with a humidity of 10-30% RH.

[0015] In an optional embodiment, the negative electrode sheet is placed in a humid environment and the time required for the negative electrode sheet to be oxidized until the yellow interface completely changes to black is 2 to 4 days.

[0016] In an optional embodiment, for single-sided density <20 mg / cm 2 Alternatively, for cells with a compaction density less than 2.4, the aging time is set to 4 to 24 hours, i.e., the aging time of multiple cells of the same type is different, and the aging time is distributed within the range of 2 to 24 hours.

[0017] In an optional embodiment, for single-sided density ≥ 20 mg / cm 2 Alternatively, for cells with a compaction density of ≥2.4, the aging time is set to be between 6 and 48 hours, i.e., the aging time of multiple cells of the same type is different, and the aging time is distributed within the range of 6 to 48 hours.

[0018] In an alternative embodiment, ICP is used to measure the manganese content in the active material.

[0019] In a second aspect, the present invention provides a method for determining the degree of wettability of a negative electrode of a manganese-based battery cell, comprising:

[0020] Obtaining a curve according to the determination method of any one of the aforementioned embodiments;

[0021] Take the same type of battery cell to be tested as the battery cell used to establish the curve, and measure the Mn dissolution amount of the battery cell to be tested according to the above method for obtaining the Mn dissolution amount of the battery cell;

[0022] The Mn dissolution amount of the battery cell to be tested is mapped to the curve. If the corresponding time is within the optimal aging time range, it indicates that the infiltration is sufficient and the aging time is appropriate; if the corresponding time does not reach the optimal aging time range, it indicates that the infiltration is insufficient and the aging time is too short; if the corresponding time exceeds the optimal aging time range, it indicates that the aging time is too long.

[0023] The present invention has the following beneficial effects:

[0024] The judgment method provided by the present invention determines whether the aging time is appropriate and whether the infiltration is sufficient by detecting the Mn content in the negative electrode active material after formation. Compared with the current testing method, the test results are not easily affected by the external environment, the method is more accurate, and does not require continuous detection of changes in a certain value, and the test time is short. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is the time-Mn dissolution relationship curve of Example 1;

[0027] Figure 2 This is the time-voltage relationship curve of Example 1;

[0028] Figure 3 This is the time-Mn dissolution relationship curve of Example 2;

[0029] Figure 4 This is the time-voltage relationship curve of Example 2. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0031] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0032] An embodiment of the present invention provides a method for determining the optimal aging time of a manganese-based battery cell, comprising:

[0033] Take multiple cells of the same type and fully charge them. The aging time of the cells is different and ranges from 2 to 50 hours.

[0034] Obtain the amount of Mn dissolved from the battery cell: disassemble each fully charged battery cell, take the negative electrode sheet and place it in a humid environment to oxidize the negative electrode sheet until the yellow interface completely turns black. Scrape off the active material in the middle area of the oxidized negative electrode sheet and measure the Mn content in the scraped active material, i.e. the dissolved amount.

[0035] A curve was established using the measured Mn content and the corresponding aging time;

[0036] As time goes by, the curve includes the first stage, the second stage and the third stage in sequence, and the manganese dissolution growth rates are the first growth rate, the second growth rate and the third growth rate in sequence, among which the first growth rate and the third growth rate are greater than the second growth rate. The junction of the second stage and the third stage is the inflection point, and the time point corresponding to the inflection point is x. Any time range within (x-2) to (x+6) h is the optimal aging time range.

[0037] Under high temperature conditions, the manganese element in the positive electrode manganese-based material is prone to dissolution, and enters the negative electrode side through the electrolyte path and then through the diaphragm. Therefore, the process of electrolyte infiltration of the positive and negative electrode sheets, that is, the process of diffusion of the dissolved manganese element, when the electrolyte infiltrates the electrode sheets, the diffusion path is fully expanded, resulting in a sudden increase in the manganese content of the negative electrode. Therefore, the judgment method provided by the present invention determines whether the aging time is appropriate by detecting the Mn content in the negative electrode active material after formation. Compared with the current test method, the test results are not easily affected by the external environment, the method is more accurate, and does not require continuous detection of changes in a certain value, and the test time is short.

[0038] It should be noted that if insufficiently oxidized negative electrode sheet powder is used for testing, the lithium embedded in the graphite can easily react with external moisture and burn, causing damage to the testing equipment. In addition, if unoxidized powder is used during the hanging process, the powder specific surface area will increase, and the frictional heat generated during the hanging process can easily cause a fire. Therefore, during the test, the negative electrode sheet needs to be placed in a humid environment to allow it to slowly oxidize before testing to avoid the above problems.

[0039] Optionally, the manganese-based battery cell refers to a battery cell using a manganese-based material as a positive electrode active material, and the manganese-based material is selected from at least one of lithium manganese iron phosphate, lithium manganese oxide and nickel-cobalt-manganese ternary materials.

[0040] Specifically, the judgment method is:

[0041] S1. Prepare multiple cells for establishing curves

[0042] Take multiple cells of the same type and age them. The ageing times of these cells are different. The specific ageing conditions are as follows:

[0043] The aging temperature is set at 35-55°C; the aging time is for single-sided density <20mg / cm 2 For cells with compaction less than 2.4, the aging time is set within the range of 4 to 24 hours, for example, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, and 24 hours respectively; for cells with single-sided density ≥ 20 mg / cm 2 Alternatively, for cells with a compaction level ≥ 2.4, the aging time is set within the range of 6 to 48 hours, for example, 6 hours, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours, and 48 hours respectively.

[0044] S2. Obtain the manganese dissolution amount of multiple cells of the same type but with different aging times

[0045] After aging, the cells were subjected to formation charging process, with the current set to 0.1C~1C, the temperature set to 35~55℃, and the charge cut-off voltage set to 4~4.2V;

[0046] Each fully charged battery cell was disassembled, and the negative electrode sheet was placed in a humid environment to oxidize until the yellow interface of the negative electrode sheet completely turned black. The active material in the middle area of the oxidized negative electrode sheet was scraped off, and the Mn content in the scraped active material, i.e., the dissolution amount, was measured.

[0047] Optionally, the humid environment is an environment with a humidity of 10 to 30% RH.

[0048] Optionally, the time required for the negative electrode sheet to be oxidized until the yellow interface completely changes to black is 2 to 4 days.

[0049] Optionally, the method for scraping off the active material in the middle area of the oxidized negative electrode sheet is as follows: using a sheet cutter (area 15.2mm 2 ) Take the central area of the electrode and scrape the powder off the copper foil with a ceramic knife.

[0050] Alternatively, ICP can be used to detect the Mn content. ICP testing is not affected by external factors or subjective judgment and has high accuracy. The testing method is simple and rapid, and does not require continuous testing.

[0051] S3. Create a curve

[0052] A curve was established based on the measured Mn content of the negative electrode sheets of each battery cell and the corresponding aging time.

[0053] The curve shows that as the time value increases, manganese dissolution increases; from the curve direction, it includes three stages. According to the growth of time, the curve includes the first stage with a larger growth rate, the second stage with a flat growth rate area, and the third stage with an increased growth rate. The manganese content growth rates are the first growth rate, the second growth rate, and the third growth rate, respectively. Among them, the first growth rate and the third growth rate are greater than the second growth rate. The junction of the second and third stages is the inflection point. The time point corresponding to the inflection point is x. Any time range within (x-2) to (x+6) h is the optimal aging time range.

[0054] Specifically, the time range corresponding to the inflection point area is defined as follows: after drawing the curve, the graph shows that the inflection point is approximately 30 hours, then the optimal aging time can be any range within 28 to 36 hours, such as 28 to 30 hours, 28 to 33 hours, 28 to 36 hours, 30 to 33 hours, 30 to 36 hours, 33 to 36 hours or 35 to 36 hours, or any point value among 28 hours, 30 hours, 32 hours, 34 hours or 36 hours.

[0055] It should be noted that the more battery cells are used to establish the curve, the more accurate the curve will be, and the more accurate the optimal aging time range reflected by the curve will be. When the curve accuracy is higher, the inflection point value will be closer to the value that ensures the shortest aging time and complete infiltration.

[0056] An improved method for determining the wettability of a negative electrode of a manganese-based battery cell according to an embodiment of the present invention includes:

[0057] Obtaining a curve according to the judgment method provided by an embodiment of the present invention;

[0058] Take the same type of battery cell to be tested as the battery cell used to establish the curve, and measure the Mn dissolution amount of the battery cell to be tested according to the above method for obtaining the Mn dissolution amount of the battery cell;

[0059] The Mn dissolution amount of the battery cell to be tested is mapped to the curve. If the corresponding time is within the optimal aging time range, it indicates that the infiltration is sufficient and the aging time is appropriate; if the corresponding time does not reach the optimal aging time range, it indicates that the infiltration is insufficient and the aging time is too short; if the corresponding time exceeds the optimal aging time range, it indicates that the aging time is too long.

[0060] That is, the established curve can be used to measure the manganese dissolution amount of the same type of battery cell to be tested, and the dissolution amount can be mapped to the curve to determine whether the aging time of the battery cell to be tested is appropriate and whether the electrode infiltration is sufficient.

[0061] Example 1

[0062] Take 27 newly assembled, unaged battery cells.

[0063] The positive electrode sheet of the battery cell is: copper foil as the current collector, the positive electrode active layer includes LMFP, PVDF, SP and dispersant, the mass ratio of which is 96%:1.8%:2%:0.2%, and the double-sided density is 37mg / cm 2 ;

[0064] The negative electrode sheet of the battery cell is: copper foil as the current collector, the negative electrode active layer includes graphite, SP, CMC, SBR, the mass ratio of which is 96%:2%:1.3%:0.7%, and the double-sided density is 20mg / cm 2 ;

[0065] The electrolyte is formulated in the following mass ratios: EC: 20%, DMC: 35%, EMC: 30%, and VC: 15%.

[0066] 24 of the above-mentioned multiple battery cells were divided into 8 groups, and the experiment was repeated with 3 battery cells in each group. The multiple groups of battery cells were aged for 6h, 12h, 18h, 24h, 30h, 36h, 42h, and 48h, respectively, and the aging temperature was 45°C.

[0067] After aging, charge at 0.5C at 40℃ and cut off at 4.2V.

[0068] The battery cell was disassembled and placed in a non-sealed humid environment at 20% RH for 4 days to completely oxidize the negative electrode sheet. 2 ) Take the central area of the electrode and scrape the powder from the copper foil with a ceramic knife for ICP testing to test the Mn content;

[0069] Take the average value of the Mn content measured in each group to draw the time-Mn dissolution relationship curve, such as Figure 1 shown.

[0070] from Figure 1 It can be seen that the first stage is approximately 0-18h, the second stage is approximately 18-30h, the third stage is approximately 30-48h, and the inflection point is approximately around 30h. The time range corresponding to the inflection point area is set to 30-36h, that is, the infiltration is sufficient when the aging time is 30-36h, which is the optimal infiltration time.

[0071] Take another 3 unaged cells and age them under the same conditions as above. During the aging process, use a multi-channel tester to measure the voltage of the cells at different aging time points and draw a time-voltage relationship curve, such as Figure 2 As shown. Figure 2It can be seen that at the beginning, the voltage rises sharply with the increase of time. After about 10 hours, the voltage tends to be stable in the range of 10 to 30 hours, which is basically consistent with the Mn dissolution result. After about 30 hours, the voltage drops significantly and rapidly with the increase of time, indicating that the battery cell is undergoing self-discharge process again due to sufficient infiltration.

[0072] Example 2

[0073] Take 27 newly assembled, unaged battery cells.

[0074] The positive electrode sheet of the battery cell is: copper foil as the current collector, the positive electrode active layer includes LFP, PVDF, SP, and dispersant, the mass ratio of which is 97%:1.8%:1%:0.2%, and the double-sided density is 38mg / cm 2 ;

[0075] The negative electrode sheet of the battery cell is: copper foil as the current collector, the negative electrode active layer includes graphite, SBR, SP, PAA, and CMC, with a mass ratio of 96.2%:1.3%:1.5%:0.5%:0.5%, and a double-sided density of 19 mg / cm 2 The electrolyte is formulated in the following mass ratios: EC: 20%; DMC: 40%, EMC: 25%, VC: 8%, FEC: 7%.

[0076] 24 of the above-mentioned multiple battery cells were divided into 8 groups, and the experiment was repeated with 3 battery cells in each group. The multiple groups of battery cells were aged for 6h, 12h, 18h, 24h, 30h, 36h, 42h, and 48h, respectively, and the aging temperature was 45°C.

[0077] After aging, charge at 0.5C at 40℃ and cut off at 4.2V.

[0078] The charged battery cell was disassembled and placed in a humid environment of 20% RH for 4 days to completely oxidize the negative electrode sheet. 2 ) Take the central area of the electrode and scrape the powder from the copper foil with a ceramic knife for ICP testing to test the Mn content;

[0079] Take the average value of the Mn content measured in each group to draw the time-Mn dissolution relationship curve, such as Figure 3 shown.

[0080] from Figure 1 It can be seen that the first stage is approximately 0-12h, the second stage is approximately 12-24h, the third stage is approximately 24-48h, the inflection point is approximately 24h, and the time range corresponding to the inflection point area is set to 24-30h, that is, the infiltration is sufficient when the aging time is 24-30h, which is the optimal infiltration time.

[0081] Take another 3 unaged cells and age them under the same conditions as above. During the aging process, use a multi-channel tester to measure the voltage of the cells at different aging time points, take the average value of each group of voltages, and draw a time-voltage relationship curve, such as Figure 4 As shown. Figure 4 It can be seen that at the beginning, the voltage rises sharply with the increase of time. After reaching about 9 hours, the voltage tends to be stable in the range of 9 to 25 hours, which is basically consistent with the Mn dissolution result. Then, as time goes by, the voltage drops significantly and rapidly, indicating that the battery cell is undergoing self-discharge process again due to sufficient infiltration.

[0082] In the above embodiment, the feedback of whether the infiltration is sufficient by measuring the amount of Mn dissolved in the negative electrode sheet is basically consistent with the result of measuring the voltage of the battery cell, which shows the feasibility of the solution provided by the embodiment of the present invention.

[0083] In summary, the judgment method provided by the present invention determines whether the aging time is appropriate and whether the infiltration is sufficient by detecting the Mn content in the negative electrode active material after formation. Compared with the current test method, the test results are not easily affected by the external environment, the method is more accurate, and does not require continuous detection of changes in a certain value, and the test time is short.

[0084] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for determining the optimal aging time of a manganese-based battery cell, characterized in that: include: Fully charge multiple battery cells of the same type, wherein the battery cells have different aging times, and the aging times are distributed within a range of 2 to 50 hours; Obtaining the Mn dissolution amount of the battery cell: disassemble each fully charged battery cell, take the negative electrode sheet and place it in a humid environment to oxidize the negative electrode sheet until the yellow interface completely turns black. Scrape off the active material in the middle area of the oxidized negative electrode sheet, and measure the Mn content in the scraped active material, i.e. the dissolution amount; A curve was established using the measured Mn content and the corresponding aging time; As time increases, the curve includes a first stage, a second stage, and a third stage, and the manganese dissolution growth rates are a first growth rate, a second growth rate, and a third growth rate, respectively, wherein the first growth rate and the third growth rate are greater than the second growth rate, and the junction of the second stage and the third stage is an inflection point, and the time point corresponding to the inflection point is x, and any time range within (x-2) to (x+6) h is the optimal aging time range.

2. The judgment method according to claim 1, characterized in that: The manganese-based battery cell refers to a battery cell using a manganese-based material as a positive electrode active material, and the manganese-based material is selected from at least one of lithium manganese iron phosphate, lithium manganate and nickel-cobalt-manganese ternary material.

3. The judgment method according to claim 1, characterized in that: The method of fully charging is to charge according to the formation charging process.

4. The judgment method according to claim 3, characterized in that: The charging method of the formation charging process includes: setting the current to 0.1~1C, setting the temperature to 35~55℃, and setting the charging cut-off voltage to 4~4.2V.

5. The judgment method according to claim 1, characterized in that: The humid environment is a non-sealed environment with a humidity of 10-30% RH.

6. The judgment method according to claim 5, characterized in that: The negative electrode sheet is placed in a humid environment and oxidized until the yellow interface of the negative electrode sheet completely changes to black for 2 to 4 days.

7. The judgment method according to claim 1, characterized in that: For single-sided density <20mg / cm 2 Alternatively, for cells with a compaction density less than 2.4, the aging time is set to be within 4 to 24 hours, that is, the aging time of the multiple cells of the same type is different, and the aging time is distributed within the range of 2 to 24 hours.

8. The judgment method according to claim 1, characterized in that: For single-sided density ≥ 20 mg / cm 2 Alternatively, the battery cells with a compaction density of ≥2.4 are set to have an aging time of 6 to 48 hours, that is, the aging time of the multiple battery cells of the same type is different, and the aging time is distributed within the range of 6 to 48 hours.

9. The determination method according to any one of claims 1 to 8, characterized in that: ICP was used to measure the manganese content in the active material.

10. A method for determining the degree of wettability of a negative electrode of a manganese-based battery cell, characterized in that: include: Obtaining the curve according to the judgment method according to any one of claims 1 to 9; Take a cell to be tested that is the same type as the cell used to establish the curve, and measure the Mn dissolution amount of the cell to be tested according to the method for obtaining the Mn dissolution amount of the cell described above; The Mn dissolution amount of the battery cell to be tested is mapped to the curve. If the corresponding time is within the optimal aging time range, it indicates that the infiltration is sufficient and the aging time is appropriate; if the corresponding time does not reach the optimal aging time range, it indicates that the infiltration is insufficient and the aging time is too short; if the corresponding time exceeds the optimal aging time range, it indicates that the aging time is too long.

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