CN117630692A - Simple and convenient test method for lithium ion battery core lithium precipitation - Google Patents
Simple and convenient test method for lithium ion battery core lithium precipitation Download PDFInfo
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- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 63
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 62
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 33
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 31
- 238000010998 test method Methods 0.000 title claims abstract description 17
- 238000001556 precipitation Methods 0.000 title claims description 24
- 238000012360 testing method Methods 0.000 claims abstract description 54
- 238000007600 charging Methods 0.000 claims abstract description 20
- 238000007599 discharging Methods 0.000 claims abstract description 20
- 230000003068 static effect Effects 0.000 claims abstract description 17
- 230000008859 change Effects 0.000 claims abstract description 12
- 238000000926 separation method Methods 0.000 claims abstract description 11
- 238000012544 monitoring process Methods 0.000 claims abstract description 7
- 238000000034 method Methods 0.000 claims description 25
- 230000000052 comparative effect Effects 0.000 claims description 18
- 239000000463 material Substances 0.000 claims description 11
- 125000004122 cyclic group Chemical group 0.000 claims description 9
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 6
- 230000008569 process Effects 0.000 claims description 6
- 239000011162 core material Substances 0.000 abstract description 66
- 238000001514 detection method Methods 0.000 description 19
- 230000007774 longterm Effects 0.000 description 7
- 238000012795 verification Methods 0.000 description 7
- 239000003792 electrolyte Substances 0.000 description 6
- 239000007773 negative electrode material Substances 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 230000002238 attenuated effect Effects 0.000 description 3
- 238000010280 constant potential charging Methods 0.000 description 3
- 238000010281 constant-current constant-voltage charging Methods 0.000 description 3
- 239000010439 graphite Substances 0.000 description 3
- 229910002804 graphite Inorganic materials 0.000 description 3
- 239000007774 positive electrode material Substances 0.000 description 3
- 230000007547 defect Effects 0.000 description 2
- 238000003487 electrochemical reaction Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000002161 passivation Methods 0.000 description 2
- 229910000572 Lithium Nickel Cobalt Manganese Oxide (NCM) Inorganic materials 0.000 description 1
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 description 1
- FBDMTTNVIIVBKI-UHFFFAOYSA-N [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] Chemical compound [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] FBDMTTNVIIVBKI-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 238000001612 separation test Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- General Physics & Mathematics (AREA)
- Secondary Cells (AREA)
Abstract
The invention relates to a simple and convenient test method for lithium ion battery cell lithium separation, which comprises the following steps: s1, charging or discharging a battery cell, and acquiring a cut-off voltage when the charging or discharging is finished; the battery cell comprises a battery cell to be tested and a comparison battery cell; s2, standing the charged or discharged battery cell for T hours, monitoring the voltage change of the battery cell during standing and the static voltage at the end of standing, acquiring rebound voltage from the cut-off voltage and the static voltage, and respectively drawing a voltage-time curve of the battery cell; and S3, judging whether the battery cell to be tested is out of lithium or not through comparison of rebound voltage and voltage-time curves of the battery cell to be tested and the comparison battery cell. The invention does not need to damage the battery core or use other special equipment, ensures the simplicity of working conditions and the accuracy of test results, is suitable for different lithium ion battery core material systems and different battery core shape designs, and can be well applied to the actual use scene of the battery core.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a simple testing method for lithium ion battery core lithium precipitation.
Background
The common lithium separation detection mode of the lithium ion battery comprises the methods of disassembly, three-electrode test, special equipment test, electrical property test and the like. Specifically, disassembling refers to that the situation of a pole piece is observed after the battery cell is disassembled, and if an off-white area appears on the surface of the negative pole piece, the battery cell is indicated to be subjected to lithium precipitation; the three-electrode test method is characterized in that a reference electrode is required to be introduced into a battery cell, and the voltage between the negative electrode of the battery cell and the reference electrode is measured so as to monitor the lithium-opposite potential of the negative electrode, and whether lithium precipitation occurs in the battery cell is judged; the special equipment detection comprises the modes of cell thickness detection, ultrasonic detection and the like, and the state of the cell is detected through some special equipment to indirectly judge whether the cell is subjected to lithium precipitation or not; the battery cell charging and discharging test device is directly used for monitoring the electrical property of the battery cell, the battery cell is tested under specific working conditions, and whether lithium precipitation occurs in the battery cell or not is judged according to charging and discharging data of the battery cell.
The lithium separation detection method has more limiting conditions and failure scenes, so that the lithium separation detection process cannot be well combined with the actual use process of the battery cell. The method for disassembling and observing needs to destroy the battery cell, and the disassembled battery cell cannot be used continuously. The three-electrode method requires structural modification of the battery cells, and the modified battery cells cannot be used for grouping and practical use. The special equipment is used for detection, so that extra cost is often required for purchasing, maintaining or renting the equipment, high requirements are provided for detection conditions, and the situation that the detection result is inaccurate due to the fact that various defects of the battery cell occur simultaneously can also occur. The battery cell can be subjected to nondestructive detection by using the charge-discharge testing device, and the device can also be applied to the actual use process of the battery cell. The existing common lithium separation test working conditions comprise long-cycle capacity comparison, coulomb efficiency comparison and other modes, the test methods need the battery cells to be kept full and fully charged, the actual working conditions are difficult to meet, the comparison is carried out by repeated cycle data, the test consumption time is long, the influence factors of the cycle capacity and the coulomb efficiency are not limited to lithium separation, and the test result is easy to produce misjudgment. In summary, in the lithium precipitation detection method commonly used at the present stage, the method capable of intuitively and accurately making the judgment often belongs to destructive tests or requires special detection conditions and equipment, and is not suitable for detecting the product battery cell under the condition of actual use; the existing charge and discharge test method can realize nondestructive test, has less requirements on conditions, but has the problems of complex test working condition, long consumption time, lower accuracy of test results and the like, and needs a simpler and more convenient test method with higher accuracy.
Disclosure of Invention
The invention aims to overcome the technical defects, and provides a simple and convenient test method for lithium ion battery cell lithium precipitation, which solves the technical problems of complex test working condition, long consumption time and lower accuracy of test results in the prior art.
In order to achieve the technical purpose, the technical scheme provided by the invention is as follows:
in a first aspect, the present invention provides a simple test method for lithium ion battery cell lithium separation, comprising the steps of: s1, charging or discharging a battery cell, and acquiring a cut-off voltage when the charging or discharging is finished; the battery cell comprises a battery cell to be tested and a comparison battery cell; s2, standing the charged or discharged battery cell for T hours, monitoring the voltage change of the battery cell during standing and the static voltage at the end of standing, acquiring rebound voltage from the cut-off voltage and the static voltage, and respectively drawing a voltage-time curve of the battery cell; and S3, judging whether the battery cell to be tested is out of lithium or not through comparison of rebound voltage and voltage-time curves of the battery cell to be tested and the comparison battery cell.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, by detecting and comparing the voltage changes of the battery core to be detected and the battery core to be compared (normal battery core), whether the battery core is separated from lithium is judged, the battery core is not required to be damaged or other special equipment is not required to be used, meanwhile, the simplicity of working conditions and the accuracy of test results are ensured, and the method is suitable for different lithium ion battery core material systems and different battery core shape designs, and can be well applied to actual use scenes of the battery core.
Drawings
FIG. 1 is a graph showing the comparison of the static voltage of the battery cell to be tested and the comparative battery cell of example 1 after discharging;
FIG. 2 is a graph of the result of cell disassembly verification in embodiment 1 of the present invention, wherein a-b are comparative cells and c-d are cells to be tested;
FIG. 3 is a graph showing the comparison of the static voltage after discharging the battery cell to be tested and the comparison battery cell according to example 2 of the present invention;
FIG. 4 is a graph of the result of cell disassembly verification in embodiment 2 of the present invention, wherein a-b are comparative cells and c-d are cells to be tested;
FIG. 5 is a graph showing the comparison of the static voltage after discharging the battery cell to be tested and the comparison battery cell according to example 3 of the present invention;
fig. 6 is a graph of the cell disassembly verification result in embodiment 3 of the present invention, wherein a-b are comparative cells and c-d are cells to be tested.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention provides a simple and convenient test method for lithium ion battery cell lithium precipitation based on charge and discharge test, which specifically comprises the following steps:
s1, charging or discharging a battery cell, and acquiring a cut-off voltage when the charging or discharging is finished; the battery cell comprises a battery cell to be tested and a comparison battery cell;
s2, standing the charged or discharged battery cell for T hours, monitoring voltage change data of the battery cell during standing and static voltage at the end of standing, acquiring rebound voltage by using cut-off voltage and static voltage, and drawing a voltage-time curve of the battery cell by using the voltage change data respectively;
and S3, judging whether the battery cell to be tested is out of lithium or not through comparison of rebound voltage and voltage-time curves of the battery cell to be tested and the comparison battery cell.
Preferably, in step S1, the electric core is charged or discharged, which may be specifically selected according to the situation, and only the electric quantity of the electric core to be tested and the electric quantity of the electric core to be compared are guaranteed to be the same in percentage of the actual capacity. For example, if the electric quantity of the electric core is greater than or equal to 80% of the actual capacity of the electric core, discharging is performed until the electric quantity of the electric core to be tested is equal to or greater than the actual capacity of the electric core, and the electric quantity of the electric core to be tested and the electric quantity of the electric core to be compared are equal to each other in percentage of the actual capacity; if the electric quantity of the battery cell is smaller than or equal to 20% of the actual capacity of the battery cell, charging is carried out until the battery cell is full of electricity or the battery cell is in any percentage of the actual capacity, and the electric quantity of the battery cell to be tested and the electric quantity of the battery cell to be compared are ensured to be the same as the percentage of the actual capacity.
Still more preferably, in step S1, the battery cell is charged to a full charge state or discharged to an empty charge state.
Preferably, in step S1, the comparative cell is a cell having the same structure and composition as the cell to be tested, and the capacity fade of the comparative cell is less than 3% after the comparative cell is subjected to a cyclic test or used.
Preferably, in the charging or discharging process of step S1, the charging current or discharging current is N times of the corresponding actual capacity value of each battery cell, the range of N may be 0.1-0.5, and may also be adjusted according to different battery cell designs and material systems, where the value of N takes the lower limit of the range or takes a smaller value, which is favorable for improving the accuracy of the constant volume of the battery cell, and may indirectly ensure the accuracy of the subsequent test. In the invention, the charge and discharge current corresponds to the respective battery cell, for example, the charge and discharge current of the battery cell to be measured is determined according to N times of the actual capacity value of the battery cell to be measured, and only the same multiple N of the charge and discharge of the battery cell to be measured and the comparative battery cell is ensured.
Further preferably, the actual capacity of the battery cell is obtained by fixing the volume of the battery cell; the constant volume is that the charge and discharge testing device is used for carrying out charge and discharge circulation on the battery cell for 3 times, and the average value of the discharge capacity of 3 times is taken as the actual capacity of the battery cell; in the cyclic charge and discharge, the charge and discharge current is N which is the magnitude of the corresponding nominal capacity value of each battery cell 1 Multiple of N 1 The range of (2) can be 0.1-0.5, and can be adjusted according to different cell designs and material systems, wherein N is 1 The lower limit of the range or the smaller value is favorable for improving the accuracy of the constant volume of the battery cell, and the accuracy of the subsequent test can be indirectly ensured.
Preferably, in step S2, T is not less than 3 and is an integer.
Further preferably, the value range of T is 3-8, and the T can be adjusted according to different cell designs and material systems, the standing time needs to be enough to enable the voltage of the cell to be stable, the change trend of the lithium-separated cell to be detected is almost the same as that of the lithium-separated cell to be compared in a short time, and the lithium-separated cell are difficult to distinguish at the moment; too long standing time can result in too long overall test time, resulting in reduced practicality of the test method.
Preferably, in step S2, the rebound voltage is the absolute value of the difference between the cut-off voltage and the static voltage.
Preferably, step S3 specifically includes:
s301, obtaining rebound voltage DeltaV of the comparison battery core and rebound voltage DeltaV of the battery core to be tested 1 Determining a fluctuation range from DeltaV;
s302, judging whether voltage-time curves of the battery cell to be tested and the comparison battery cell are coincident or not:
if the voltage-time curves of the battery cell to be detected and the comparison battery cell coincide, judging that the battery cell to be detected does not deposit lithium;
if the voltage-time curves of the battery cell to be tested and the comparative battery cell cannot be overlapped, calculating DeltaV 1 Whether the magnitude exceeds the fluctuation range of DeltaV; if DeltaV 1 And judging that the lithium is separated from the battery cell to be tested if the size exceeds the fluctuation range of delta V, otherwise, judging that the lithium is not separated.
According to the judging conditions, the voltage-time curve can play a role in rapid judgment, and if the two curves are coincident, a conclusion can be directly obtained without continuous judgment; if the two curves do not coincide, then ΔV is combined 1 The fluctuation range of the size and the delta V is further judged, and the accuracy is effectively improved.
Further preferably, the fluctuation range is 99% -101% of the average magnitude of the comparative cell Δv.
As an improvement of the method, in the whole test process, an independent voltage detection device can be selected, so that the accuracy of voltage data and the consistency of test equipment are improved, and the voltage measurement error caused by the equipment is avoided.
As an improvement of the method, in the test method, the battery cells are measured under the same temperature and humidity, and the test equipment with the same model is used for the test equipment, so that the influence of different test conditions on the test result is avoided.
The invention has the main action mechanism and advantages that:
(1) After the battery cell stops charging or discharging, the polarization effect in the battery cell disappears, part of lithium ions can return to the positive electrode/negative electrode, so that the positive electrode potential and the negative electrode potential of the battery cell are restored, and the overall voltage of the battery cell rebounds. When lithium is separated out from the surface of the negative electrode, lithium metal can cover the surface of the negative electrode material to prevent lithium ions from being inserted into the negative electrode material, and when the lithium separation is serious, metal lithium which cannot participate in electrochemical reaction and is coated by a passivation film can be formed in the negative electrode area, and the metal lithium is called dead lithium. The passivation film on the dead lithium surface can further increase the impedance of the surface of the negative electrode and prevent lithium ions from being inserted and extracted in the negative electrode. Therefore, after the lithium-separating cell is charged, part of lithium ions form dead lithium and do not participate in electrochemical reaction in the cell, negative lithium ions are difficult to separate, so that lithium ions capable of returning to a positive electrode are less than those of a normal cell, and the voltage rebound amplitude is smaller than that of the normal cell. And the same is done when the discharge is finished, lithium ions which can return to the negative electrode in the lithium separation battery cell are fewer than those in the normal battery cell, and the voltage rebound amplitude is smaller than that in the normal battery cell.
(2) The method is applicable to all lithium ion battery material systems including lithium iron phosphate, ternary materials (such as lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate), lithium cobaltate and other material systems, is not limited by the types of materials, and judges whether the battery core is separated from lithium by detecting and comparing the voltage change of the battery core to be detected and the voltage change of a comparison battery core (normal battery core). The test method can be completed by using the battery cell charge and discharge test device, does not need to damage the battery cell or use other special equipment, ensures the simplicity of working conditions and the accuracy of test results, is suitable for different lithium ion battery cell material systems and different battery cell shape designs, and can be well applied to the actual use scene of the battery cell.
(3) Compared with the voltage comparison, the voltage change value is only related to the charge/discharge conditions, is not influenced by the electric quantity state of the battery cell, and has wider application scene.
The invention is further illustrated by the following specific examples.
Example 1:
judging whether the battery core which is subjected to long-term cyclic test generates lithium precipitation or not.
4 lithium ion cells of the same batch are taken. The two cells are subjected to long-term cyclic test or long-term use, so that the capacity is attenuated to be less than 80% of the initial capacity, and the cells are marked as a test sample 1 and a test sample 2 (to-be-tested cells); after the other two cells are tested or used, the capacity attenuation is less than 3%, the internal resistance of the cells is increased to be more than 1.2 times of the internal resistance of the conventional aged cells before testing, and the conventional aged cells are marked as a comparison sample 1 and a comparison sample 2 (the conventional aged cells are adopted only for better comparison and verification, other normal cells can be used, and the capacity attenuation is ensured to be less than 3%). The positive electrode active materials of the battery cells are lithium iron phosphate, the negative electrode active materials are graphite, and the electrolyte is conventional electrolyte of lithium ion battery cells.
(1) The method comprises the steps of carrying out charge and discharge circulation on 4 electric cores for 3 times by using test equipment of the same model, wherein the charge and discharge current is 0.5 times of the value of the nominal capacity of the electric cores, the voltage range is 2.5-3.65V, the cut-off current of constant voltage charge is 0.05 times of the value of the nominal capacity of the electric cores, and the average value of 3 discharge capacity is the actual capacity of the electric cores; the battery core is taken as a lithium iron phosphate system battery core with the nominal capacity of 8Ah, the charge and discharge current is set to be 4A, and the constant voltage charge cut-off current is set to be 0.4A, and the same is true hereinafter.
(2) Constant-current constant-voltage charging is carried out on 4 electric cores, the current is 0.1 time of the actual capacity value in the step 1, and the constant-voltage charging cut-off current is 0.05 time of the actual capacity value in the step 1;
(3) Performing constant current discharge on the 4 electric cores, wherein the discharge cut-off voltage is 2V, the current is 0.1 time of the actual capacity value in the step 1, standing the electric cores for 3 hours after the discharge is finished, and monitoring the voltage change of the electric cores in the standing period and the static voltage at the end of the standing period;
(4) And (3) drawing a voltage-time curve by utilizing the voltage data in the step (3), wherein as shown in fig. 1, the curves of 2 comparison cells are found to be coincident, the rebound voltage at the end of standing is respectively 0.7675V, 0.76884V, the average value is 0.7680V, the fluctuation range of the rebound voltage is 0.7603V-0.7756V, the curves of 2 cells to be detected are not coincident with the curves of the comparison cells, the rebound voltage of the cells to be detected at the end of standing is 0.7331V and 0.7263V, the rebound voltage of the cells to be detected is 95.46% and 94.58% of the rebound voltage of the comparison cells, and the rebound voltage exceeds the fluctuation range, and the lithium is analyzed from the 2 cells to be detected. 4 cells are disassembled for verification, as shown in fig. 2, the lithium precipitation appears on the surface of the negative electrode of the cell to be tested (c-d in fig. 2), and the lithium precipitation does not appear on the surface of the comparative cell (a-b in fig. 2), so that the test result is correct.
Table 1 cell rebound voltage in example 1
Example 2:
judging whether the battery core which is subjected to long-term cyclic test generates lithium precipitation or not.
4 lithium ion cells of the same batch are taken. The two cells are subjected to long-term cyclic test, the capacity is attenuated to be less than 80% of the initial capacity, and the cells are marked as a test sample 1 and a test sample 2 (to-be-tested cells); after the other two cells are tested or used, the capacity decay is less than 3%, the internal resistance of the cells is increased by more than 1.2 times of the internal resistance of the conventional aged cells before testing, and the conventional aged cells are marked as a comparison sample 1 and a comparison sample 2. The positive electrode active materials of the battery cells are lithium iron phosphate, the negative electrode active materials are graphite, and the electrolyte is AB electrolyte for the lithium ion battery cells.
(1) The same type of test equipment is used for carrying out charge and discharge circulation on 4 electric cores for 3 times, the charge and discharge current is 0.5 times of the value of the nominal capacity of the electric cores, the voltage range is 2.5-3.65V, the cut-off current of constant voltage charge is 0.05 times of the value of the nominal capacity of the electric cores, and the average value of the discharge capacity of 3 times is the actual capacity of the electric cores;
(2) Constant-current constant-voltage charging is carried out on 4 electric cores, the current is 0.1 time of the actual capacity value in the step 1, and the constant-voltage charging cut-off current is 0.05 time of the actual capacity value in the step 1;
(3) Performing constant current discharge on the 4 electric cores, wherein the discharge cut-off voltage is 2V, the current is 0.1 time of the actual capacity value in the step 1, standing the electric cores for 3 hours after the discharge is finished, and monitoring the voltage change of the electric cores in the standing period and the static voltage at the end of the standing period;
(4) And (3) drawing a voltage-time curve by utilizing the voltage data in the step (3), wherein as shown in fig. 3, the curves of 2 comparison cells are overlapped, the rebound voltage is respectively 0.8128V,0.8078V and the average value is 0.8103V when the battery is kept stand, the rebound voltage fluctuation range is 0.8022V-0.8184V, the curves of 2 cells to be tested are not overlapped with the curves of the comparison cells, the rebound voltage of the cells to be tested at the end of the standing is 0.7625V and 0.7712V, the rebound voltage amplitude of the comparison cells is 94.10 percent and 95.17 percent, and the rebound voltage exceeds the fluctuation range, so that the lithium is analyzed from the 2 cells to be tested. 4 cells are disassembled for verification, as shown in fig. 4, the lithium precipitation appears on the surface of the negative electrode of the cell to be tested (c-d in fig. 4), and the lithium precipitation does not appear on the surface of the comparative cell (a-b in fig. 4), so that the test result is correct.
Table 2 voltage after cell rest in example 2
Example 3:
judging whether the battery core which is subjected to long-term cyclic test generates lithium precipitation or not. 4 lithium ion cells of the same batch are taken. The two electric cores are subjected to long-term cyclic test, the capacity of the two electric cores is attenuated to be less than 80% of the initial capacity, and the two electric cores are marked as an experiment sample 1 and an experiment sample 2; after the other two cells are tested or used, the capacity decay is less than 3%, the internal resistance of the cells is increased by more than 1.2 times of the internal resistance of the conventional aged cells before testing, and the conventional aged cells are marked as a comparison sample 1 and a comparison sample 2. The positive electrode active material of the battery cell is lithium iron phosphate, the negative electrode active material is graphite, and the electrolyte is conventional lithium ion battery cell electrolyte.
(1) The same type of test equipment is used for carrying out charge and discharge circulation on 4 electric cores for 3 times, the charge and discharge current is 0.5 times of the value of the nominal capacity of the electric cores, the voltage range is 2.5-3.65V, the cut-off current of constant voltage charge is 0.05 times of the value of the nominal capacity of the electric cores, and the average value of the discharge capacity of 3 times is the actual capacity of the electric cores;
(2) Constant-current constant-voltage charging is carried out on 4 electric cores, the current is 0.1 time of the actual capacity value in the step 1, the constant-voltage charging cut-off current is 0.05 time of the actual capacity value in the step 1, the electric cores are kept stand for 3 hours after charging is finished, and the voltage change of the electric cores and the static voltage at the end of standing during the standing period are monitored;
(3) And (3) drawing a voltage-time curve by utilizing the voltage data in the step (2), wherein as shown in fig. 5, the curves of 2 comparison cells are overlapped, the rebound voltage at the end of standing is respectively 0.3083V,0.3015V, the average value is taken as 0.3049V, the rebound voltage fluctuation range is 0.3019V-0.3079V, the curves of 2 cells to be detected are not overlapped with the curves of the comparison cells, the rebound voltage of the cells to be detected at the end of standing is 0.1831V and 0.1623V, the rebound voltage of the cells to be detected is 60.05% and 53.23% of the voltage of the comparison cells, and the rebound voltage exceeds the fluctuation range, so that lithium is analyzed from the 2 cells to be detected. 4 cells are disassembled for verification, as shown in fig. 6, the lithium precipitation appears on the surface of the negative electrode of the cell to be tested (c-d in fig. 6), and the lithium precipitation does not appear on the surface of the comparative cell (a-b in fig. 6), so that the test result is correct.
Table 3 cell rebound voltage in example 3
Example 4
The only difference from example 3 is that: and (3) adjusting the charging cut-off condition in the step (2), wherein the charging cut-off condition is not limited to filling the battery cells, and the electric quantity of the battery cells to be tested and the electric quantity of the battery cells to be compared are ensured to be the same as the percentage of the actual capacity of the respective battery cells.
As a result, the test results were the same as those of example 3, and lithium analysis results of the cells to be tested and the comparative cells were distinguished. Therefore, the method can be used for lithium analysis detection of the battery cell in any electric quantity state of the battery cell.
Similarly, the invention adjusts the discharge cut-off condition, is not limited to emptying the battery core, only controls the electric quantity of the battery core to be detected and the electric quantity of the comparison battery core to be the same as the percentage of the actual capacity of each battery core, and can also accurately perform lithium precipitation detection.
The method judges whether the battery cell is out of lithium or not in a static voltage detection mode, and is suitable for battery cells of any material system and any shape; the method can be used for lithium precipitation detection of the battery core in any electric quantity state of the battery core; the lithium separation detection is carried out on the battery cell without special conditions or special equipment; the lithium precipitation detection method does not damage the battery cell and does not influence the subsequent use of the battery cell; the method has the advantages of short time for detecting the lithium precipitation and small required data volume.
The above-described embodiments of the present invention do not limit the scope of the present invention. Any other corresponding changes and modifications made in accordance with the technical idea of the present invention shall be included in the scope of the claims of the present invention.
Claims (10)
1. A simple and convenient test method for lithium ion battery core lithium precipitation is characterized by comprising the following steps:
s1, charging or discharging a battery cell, and acquiring a cut-off voltage when the charging or discharging is finished; the battery cell comprises a battery cell to be tested and a comparison battery cell;
s2, standing the charged or discharged battery cell for T hours, monitoring the voltage change of the battery cell during standing and the static voltage at the end of standing, acquiring rebound voltage from the cut-off voltage and the static voltage, and respectively drawing a voltage-time curve of the battery cell;
and S3, judging whether the battery cell to be tested is out of lithium or not through comparison of rebound voltage and voltage-time curves of the battery cell to be tested and the comparison battery cell.
2. The method according to claim 1, wherein in step S1, the comparative cell is a cell having the same structure and composition as the cell to be tested, and the capacity fade of the comparative cell is less than 3%.
3. The simple and convenient test method for lithium ion battery cell lithium separation according to claim 1, wherein in the charging or discharging process of the step S1, the magnitude of the charging current or the discharging current is 0.1-0.5 times of the magnitude of the actual capacity of the battery cell; and when the charging or discharging is finished, the electric quantity of the battery cell to be tested and the electric quantity of the comparison battery cell occupy the same percentage of the actual capacity.
4. The simple and convenient test method for lithium ion battery cell lithium separation according to claim 3, wherein the actual capacity of the battery cell is obtained by fixing the volume of the battery cell; the constant volume is to circularly charge and discharge the battery cell for 3 times, and an average value of 3 discharge capacities is taken as the actual capacity of the battery cell; the current in the cyclic charge and discharge is 0.1-0.5 times of the nominal capacity value of the battery cell.
5. The method for testing lithium ion battery cell according to claim 1, wherein in step S2, T is an integer greater than or equal to 3.
6. The simple test method for lithium ion battery cell according to claim 1 or 5, wherein the value of T ranges from 3 to 8.
7. The method according to claim 1, wherein in step S2, the rebound voltage is the absolute value of the difference between the cut-off voltage and the static voltage.
8. The method for testing lithium ion battery cell according to claim 1, wherein step S3 specifically comprises:
s301, obtaining rebound voltage DeltaV of the comparison battery core and rebound voltage DeltaV of the battery core to be tested 1 Determining a fluctuation range from DeltaV;
s302, judging whether voltage-time curves of the battery cell to be tested and the comparison battery cell are coincident or not:
if the voltage-time curves of the battery cell to be detected and the comparison battery cell coincide, judging that the battery cell to be detected does not deposit lithium;
if the voltage-time curves of the battery cell to be tested and the comparative battery cell cannot be overlapped, calculating DeltaV 1 Whether the magnitude exceeds the fluctuation range of DeltaV; if DeltaV 1 And judging that the lithium is separated from the battery cell to be tested if the size exceeds the fluctuation range of delta V, otherwise, judging that the lithium is not separated.
9. The method for testing lithium ion battery cell according to claim 8, wherein the fluctuation range is 99% -101% of the average magnitude of the comparative battery cell Δv.
10. The method for testing lithium ion battery cell according to claim 1, wherein the material of the battery cell comprises lithium iron phosphate, ternary material or lithium cobaltate.
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