CN116540137B - Secondary battery capacity diving identification method and system - Google Patents
Secondary battery capacity diving identification method and system Download PDFInfo
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- CN116540137B CN116540137B CN202310820082.3A CN202310820082A CN116540137B CN 116540137 B CN116540137 B CN 116540137B CN 202310820082 A CN202310820082 A CN 202310820082A CN 116540137 B CN116540137 B CN 116540137B
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- 238000004364 calculation method Methods 0.000 claims description 8
- 238000007781 pre-processing Methods 0.000 claims description 5
- 238000012502 risk assessment Methods 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 24
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- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 2
- 239000004698 Polyethylene Substances 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
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- 238000007599 discharging Methods 0.000 description 2
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- 229920002981 polyvinylidene fluoride Polymers 0.000 description 2
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- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 1
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- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical group [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
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- 239000012300 argon atmosphere Substances 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
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- 229910052744 lithium Inorganic materials 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
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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]
- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
-
- 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]
- G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables
-
- 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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- Secondary Cells (AREA)
Abstract
The application discloses a secondary battery capacity diving identification method and system. The identification method comprises the following steps: acquiring the charge-discharge cycle capacity retention rate epsilon of the secondary battery; acquiring slope values kappa of charge-discharge cycle capacity retention rate epsilon variation of an xth cycle according to a plurality of charge-discharge cycle capacity retention rate epsilon data of the xth cycle, wherein the number of the charge-discharge cycle capacity retention rates epsilon acquired in each cycle is n, and the slope values kappa=tan [ slope (n epsilon values) are 100% ] are 180/3.1415; the slope value kappa and the preset diving threshold lambda are combined max And comparing, and judging the capacity water jump condition of the secondary battery. The method is simple and easy to implement, and can quickly identify the capacity jump point, and the technology can be applied to the secondary battery and plays a good role in the secondary battery cycle test process.
Description
Technical Field
The application relates to the technical field of batteries, in particular to a secondary battery capacity jump recognition method and system.
Background
The secondary battery is widely applied to 3C portable electronic consumer products, electric automobiles and terminal energy storage equipment due to the advantages of high energy density, long service life, recoverability and the like. Wherein the service life of the secondary battery is a major concern for manufacturers and users.
At present, a great deal of time and energy are consumed to carry out cycle test in the research, inspection and manufacturing processes of the secondary battery, so that the service life of the battery is obtained.
Disclosure of Invention
The present inventors have found that in a cycle test process for predicting the service life of a secondary battery, the cycle test time can be shortened by rapidly predicting the capacity jump point in the cycle test process of the secondary battery. The capacity retention rate curve of the battery under the circulation condition steadily declines in a period of time, and the decline rate is rapidly increased after exceeding a certain critical point, namely the battery capacity is subject to the phenomenon of water jump, and the critical point of sudden change of the decline rate is the water jump point.
The embodiment of the application provides a secondary battery capacity jump recognition method and system, which can simply and rapidly predict the capacity jump point in the secondary battery charge and discharge cycle process.
In a first aspect, the present application provides a secondary battery capacity jump identification method, including:
acquiring the charge-discharge cycle capacity retention rate epsilon of the secondary battery;
acquiring slope values kappa of changes of the charge-discharge cycle capacity retention rates epsilon of the xth cycle according to a plurality of charge-discharge cycle capacity retention rate epsilon data of the xth cycle, wherein the number of the charge-discharge cycle capacity retention rates epsilon acquired in each cycle is n, and the slope values kappa are obtained by adopting a formula shown in a formula (1):
kappa = tan [ slope (n epsilon values) ×100% ] 180/3.1415 (1);
the slope value kappa and a preset diving threshold lambda are combined max Comparing; when kappa is less than or equal to lambda max Judging that the secondary battery does not jump, and continuously acquiring a slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon in the x+1st period; when kappa > lambda max And judging that the secondary battery capacity jumps.
In some exemplary embodiments, n satisfies: n is more than or equal to 5 and less than or equal to 20.
In some exemplary embodiments, the secondary battery capacity jump recognition method includes: each cycle acquires n consecutive charge-discharge cycle capacity retention rates epsilon to acquire the slope value kappa.
In some exemplary embodiments, obtaining the charge-discharge cycle capacity retention rate epsilon for the x+1th cycle comprises:
n charge-discharge cycle capacity retention rates epsilon are selected from any one of the charge-discharge cycle capacity retention rates epsilon after the first charge-discharge cycle capacity retention rate epsilon in the x-th cycle to obtain the slope value kappa for that cycle.
In some exemplary embodiments, X is less than a preset number of charge-discharge cycle lives X of the secondary battery max 。
In some exemplary embodiments, the preset diving threshold lambda max The method meets the following conditions: -15 ∈λ max ≤-5。
In some exemplary embodiments, the charge-discharge cycle capacity retention ε is obtained using the formula shown in equation (2):
ε=C m /C 0 *100% （2）
wherein C is m The capacity of the secondary battery for the mth charge-discharge cycle, m > 3; c (C) 0 The reference capacity is the capacity of the secondary battery of the ith charge-discharge cycle, and i is more than or equal to 1 and less than or equal to 5.
In some exemplary embodiments, the charge-discharge cycle capacity retention rate ε may satisfy: epsilon is more than 80 percent.
In a second aspect, the present application provides a secondary battery capacity jump recognition system, comprising:
a preprocessing device for acquiring the charge-discharge cycle capacity retention rate epsilon of the secondary battery;
the slope value characteristic calculation module is configured to obtain, according to a plurality of charge-discharge cycle capacity retention rate epsilon data of an xth cycle, slope values kappa of changes in the charge-discharge cycle capacity retention rate epsilon of the xth cycle, where the number of obtained charge-discharge cycle capacity retention rates epsilon is n, and the slope values kappa are obtained by using a formula shown in a formula (1):
kappa = tan [ slope (n epsilon values) ×100% ] 180/3.1415 (1);
a diving risk assessment module for comparing the slope value k with a preset diving threshold lambda max Comparing; when kappa is less than or equal to lambda max Judging that the secondary battery does not jump, and continuously acquiring a slope value kappa of the charge-discharge cycle capacity retention epsilon variation of the (x+1) th period by the slope value characteristic calculation module; when kappa > lambda max And judging that the secondary battery capacity jumps.
In some exemplary embodiments, the preprocessing device is further used for performing a charge-discharge cycle test on the secondary battery; the secondary battery capacity jump recognition system further includes:
diving control module for controlling when kappa > lambda max When the pretreatment device is in operation, the pretreatment device is controlled to stop acquiring the charge-discharge cycle capacity retention rate epsilon and stop the secondary treatmentAnd (5) testing the charge and discharge cycles of the battery.
The secondary battery capacity water jump identification method and system based on the embodiment of the application have at least the following beneficial effects:
the secondary battery capacity jump recognition method provided by the application can be used for recognizing the jump point parameter by analyzing the capacity retention rate curve and confirming the slope value of the capacity retention rate change. The water jump identification method can only utilize the existing capacity data in the circulating experiment to carry out water jump monitoring and early warning, and does not need to destructively disassemble the battery or measure other parameters; the method can rapidly calculate the capacity retention rate along with continuous charge-discharge cycle experiments, obtain the slope value of the capacity retention rate change in real time, and has strong dynamic property and real-time property. Reasonably setting a preset diving threshold lambda through big data analysis and statistics max The method is convenient for detecting the secondary battery diving in time, and improves the accuracy and timeliness of the secondary battery diving detection. The method for identifying the diving has stronger universality and portability, for example, in the using stage of the secondary battery, if the trend of the battery capacity changing along with the using time can be obtained, the method can also be applied to diving early warning in the using stage. After the secondary battery is circulated for a few times, whether the secondary battery jumps or not can be judged, the jump phenomenon can be judged at the initial stage of the circulation, the jump judgment reaction is timely, and delay is reduced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings described below are only some embodiments of the present application, and other drawings may be obtained according to these drawings to those skilled in the art.
Fig. 1 is a graph showing the number of charge and discharge cycles and the charge and discharge cycle capacity retention epsilon for a secondary battery sample of example 1 of the present application;
fig. 2 is a graph showing the number of charge and discharge cycles and the slope value κ of the secondary battery sample of example 1 of the present application;
fig. 3 is a graph showing the number of charge and discharge cycles and the charge and discharge cycle capacity retention epsilon for a secondary battery sample of example 2 of the present application;
fig. 4 is a graph showing the number of charge and discharge cycles and the slope value κ of the secondary battery sample of example 2 of the present application.
Detailed Description
The present application will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present application 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 application.
The present inventors have found that in a cycle test process for predicting the service life of a secondary battery, the cycle test time can be shortened by rapidly predicting the capacity jump point in the cycle test process of the secondary battery. The capacity retention rate curve of the battery under the circulation condition steadily declines in a period of time, and the decline rate is rapidly increased after exceeding a certain critical point, namely the battery capacity is subject to the phenomenon of water jump, and the critical point of sudden change of the decline rate is the water jump point. Based on the above, the embodiment of the application provides a secondary battery capacity diving identification method and system.
The secondary battery capacity water jump identification method of the embodiment of the application comprises the following steps:
s110: the charge-discharge cycle capacity retention rate epsilon of the secondary battery is obtained.
S120: acquiring slope values kappa of changes of the charge-discharge cycle capacity retention rates epsilon of the xth period according to the charge-discharge cycle capacity retention rate epsilon data of the xth period, wherein the number of the charge-discharge cycle capacity retention rates epsilon acquired in each period is n, and the slope values kappa are obtained by adopting a formula shown in a formula (1):
kappa=tan [ slope (n epsilon values) ×100% ] 180/3.1415 (1).
S130: the slope value kappa and the preset diving threshold lambda are combined max Comparing; when kappa is less than or equal to lambda max Judging that the secondary battery does not jump, and continuously acquiring a slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon of the (x+1) th period; when kappa > lambda max And judging that the secondary battery capacity jumps.
Wherein, the diving threshold lambda is preset max The method is obtained by carrying out big data analysis and statistics on the secondary battery circulating water jump data in advance. Preset diving threshold lambda max The method meets the following conditions: -15 ∈λ max Less than or equal to-5, e.g., lambda max Can be-15, -10, -8, -6, -5, etc.
The secondary battery capacity jump recognition method provided by the application can be used for recognizing the jump point parameter by analyzing the capacity retention rate curve and confirming the slope value of the capacity retention rate change.
The water jump identification method can only utilize the existing capacity data in the circulating experiment to carry out water jump monitoring and early warning, and does not need to destructively disassemble the battery or measure other parameters; the method can rapidly calculate the capacity retention rate along with continuous charge-discharge cycle experiments, obtain the slope value of the capacity retention rate change in real time, and has strong dynamic property and real-time property. Reasonably setting a preset diving threshold lambda through big data analysis and statistics max The method is convenient for detecting the secondary battery diving in time, and improves the accuracy and timeliness of the secondary battery diving detection. The method for identifying the diving has stronger universality and portability, for example, in the using stage of the secondary battery, if the trend of the battery capacity changing along with the using time can be obtained, the method can also be applied to diving early warning in the using stage. After the secondary battery is circulated for a few times, whether the secondary battery jumps or not can be judged, the jump phenomenon can be judged at the initial stage of the circulation, the jump judgment reaction is timely, and delay is reduced.
Optionally, in step S110, the method for testing the charge-discharge cycle capacity retention epsilon further includes:
step S111: and (3) standing for the first time, wherein the secondary battery is kept stand for a first time T1 in the environment of a first temperature q 1. Wherein q1 satisfies: 0 ℃ or less q1 or less than 55 ℃, for example, q1 may be 0 ℃, 15 ℃, 25 ℃, 30 ℃, 50 ℃ or the like; t1 satisfies: t1 is 10min less than or equal to 60min, for example, T1 can be 10min, 20min, 30min, 45min or 60min, etc.
Step S112: and (3) constant-current charging, namely, charging the secondary battery in the step (111) to a first rated voltage U1 by a first charging current c 1. Wherein, c1 satisfies: 0C < c1.ltoreq.2.0C, for example, C1 may be 0.1C, 0.5C, 1.0C, 1.5C, 2.0C or the like; u1 satisfies the following conditions: u1 is more than 0V and less than or equal to 4.5V.
Step S113: the constant voltage charging process changes the secondary battery of step S112 to constant voltage charging, and stops charging when the charging current is changed to the second charging current c2, and stands for a second time T2. Wherein, c2 satisfies: 0C < c2.ltoreq.0.08C, for example, C2 may be 0.01C, 0.03C, 0.05C, 0.06C or 0.08C, etc.; t2 satisfies: t2 is more than 0min and less than or equal to 30min, for example, T2 can be 10min, 15min, 20min, 25min or 30min, etc.
Step S114, discharging the secondary battery of step S113 to a first voltage V1 at a first discharging current c3, and standing for a third time T3. Wherein, c3 satisfies: 0C < c3.ltoreq.1.0C, for example, C3 may be 0.01C, 0.3C, 0.5C, 0.8C or 1.0C, etc.; t3 satisfies: t3 is more than 0min and less than or equal to 30min, for example, T3 can be 10min, 15min, 20min, 25min or 30min and the like; v1 satisfies: v is more than 2.5 and less than or equal to V1 and less than or equal to 3.0V.
Step S112 to step S114 are charge-discharge cycles, and each time the discharge capacity of the secondary battery after the third time T3 is obtained, the discharge capacity of the secondary battery in the charge-discharge cycle is obtained. The discharge capacity C of the secondary battery of the ith charge-discharge cycle is taken as a reference capacity C 0 I is an integer of 1 or more, preferably, i satisfies: i is more than or equal to 1 and less than or equal to 5. The charge/discharge cycle capacity retention rate epsilon of the secondary battery after the ith charge/discharge cycle selected from the plurality of charge/discharge cycle capacity retention rates epsilon of the xth cycle in step S120 and the plurality of charge/discharge cycle capacity retention rates epsilon of the xth+1th cycle in step S130. The discharge capacity of each charge-discharge cycle of the secondary battery after the ith charge-discharge cycle was designated as C m Charge-discharge cycle capacity retentionThe retention epsilon is obtained by adopting a formula shown in a formula (2):
ε=C m /C 0 *100% （2）。
in step S120, the number of charge-discharge cycle capacity retention rates epsilon acquired in each cycle may be equal or unequal, which is not limited in the present application, and may be specifically selected according to actual requirements. For example, n includes n1, n2, n3, and n1 > n2 > n3, and in the previous 1 to y1 charge-discharge cycles, the number of charge-discharge cycle capacity retention epsilon selected for each cycle is n1, in the previous y2 to y3 charge-discharge cycles, the number of charge-discharge cycle capacity retention epsilon selected for each cycle is n2, in the previous y3 to y4 charge-discharge cycles, the number of charge-discharge cycle capacity retention epsilon selected for each cycle is n3, so that in the case of high risk diving in the later cycle, the frequency of obtaining the slope value kappa is increased, so that the diving situation can be recognized more efficiently and sensitively.
The secondary battery of the application has preset charge-discharge cycle life times X max In the preset charge-discharge cycle life times X max The case where the secondary battery is capacity-jumped or no longer subjected to charge-discharge cycles, for example, no longer subjected to charge-discharge cycles, includes: after a limited number of charge and discharge cycles, the secondary battery does not have capacity jump, and the secondary battery satisfies the charge and discharge cycle number requirements. Optionally, 2.ltoreq.x < X max To preset the life times X of charge and discharge cycles max In this case, a plurality of charge-discharge cycle capacity retention rates ε can be selected for each cycle to obtain a slope value κ, and a slope value κ that changes in charge-discharge cycle capacity retention rate ε can be obtained for a plurality of cycles to more sensitively identify a diving situation.
Optionally, n satisfies: n is more than or equal to 5 and less than or equal to X max Preferably, n is more than or equal to 5 and less than or equal to 20, and n is controlled to be more than or equal to 5, so that the water jump condition of the secondary battery can be judged at the initial stage of circulation.
It will be appreciated that the secondary battery will undergo a number of charge and discharge cycles before the secondary battery is cycled, so that the secondary battery can be cycled. The secondary battery capacity jump recognition method includes: in each period, acquiring continuous n charge-discharge cycle capacity retention rates epsilon to acquire a slope value kappa; alternatively, n charge-discharge cycle capacity retention rates epsilon at intervals are obtained in each cycle to obtain a slope value kappa, for example, in one cycle, charge-discharge cycle capacity retention rate epsilon of a secondary battery of one charge-discharge cycle is obtained every time a charge-discharge cycle is performed at intervals.
In step S130, acquiring the charge-discharge cycle capacity retention rate epsilon of the (x+1) -th cycle includes: from any one of the charge-discharge cycle capacity retention rates epsilon after the first charge-discharge cycle capacity retention rate epsilon in the xth cycle, n charge-discharge cycle capacity retention rates epsilon are selected to obtain a slope value kappa for the cycle. The number n of the charge-discharge cycle capacity retention rates epsilon of each cycle is 10, the xth cycle includes charge-discharge cycle capacity retention rates epsilon corresponding to 3-12 th charge-discharge cycles, and the (x+1) th cycle may include charge-discharge cycle capacity retention rates epsilon corresponding to 4-13 th charge-discharge cycles, charge-discharge cycle capacity retention rates epsilon corresponding to 5-14 charge-discharge cycles, or charge-discharge cycle capacity retention rates epsilon corresponding to 6-15 charge-discharge cycles.
The embodiment of the application also provides a secondary battery capacity jump recognition system which is used for carrying out the secondary battery capacity jump recognition method. The secondary battery capacity diving identification system comprises a preprocessing device, a slope value characteristic calculation module and a diving risk assessment module.
The pretreatment device is used for obtaining the charge-discharge cycle capacity retention rate epsilon of the secondary battery.
The slope value characteristic calculation module is used for obtaining the slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon of the xth cycle according to the data of the charge-discharge cycle capacity retention rates epsilon of the xth cycle, wherein X is smaller than the preset charge-discharge cycle life times X of the secondary battery max . The number of the charge-discharge cycle capacity retention rates epsilon obtained in each period is n, and the slope value kappa is obtained by adopting a formula shown in a formula (1):
kappa=tan [ slope (n epsilon values) ×100% ] 180/3.1415 (1).
The diving risk assessment module is used for comparing the slope value kappa with a preset diving threshold lambda max Comparing; when kappa is less than or equal to lambda max Judging that the secondary battery does not jump, and continuously acquiring a slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon of the (x+1) th period by a slope value characteristic calculation module; when kappa > lambda max And judging that the secondary battery capacity jumps.
The secondary battery capacity jump recognition system provided by the embodiment of the application can be used for recognizing the jump point parameter by analyzing the capacity retention rate curve and confirming the slope value of the capacity retention rate change.
The pretreatment device is also used for carrying out charge-discharge cycle test on the secondary battery, the pretreatment device, the slope value characteristic calculation module and the diving risk evaluation module can realize linkage, the charge-discharge cycle capacity retention rate epsilon is automatically obtained, the diving state of the secondary battery is identified according to the slope value kappa of the charge-discharge cycle capacity retention rate epsilon variation of each period, manual operation is not needed, and the diving identification efficiency is high.
The secondary battery capacity jump recognition system further comprises a jump control module for controlling the jump when k > lambda max And when the secondary battery is identified to have circulating water jump, the control pretreatment device stops acquiring the charge-discharge circulating capacity retention rate epsilon and stops the charge-discharge circulating test of the secondary battery, so that the charge-discharge circulating operation of the secondary battery is stopped in time, and energy is saved.
The types of the electrolyte, the positive electrode sheet, the negative electrode sheet and the separation film of the secondary battery are not particularly limited, and any electrolyte, positive electrode sheet, negative electrode sheet and separation film known in the art can be used as long as the purpose of the application can be achieved.
The secondary battery capacity jump recognition method of the present application is described below with reference to specific embodiments. The secondary battery of each embodiment of the present application was obtained using the following method for manufacturing a secondary battery.
(1) Preparation of positive plate
An aluminum foil is used as a positive current collector, and a layer of lithium cobalt oxide slurry is uniformly coated on the surface of the aluminum foilThe composition of the lithium cobaltate slurry was 97.8wt% LiCoO 2 (LCO), 0.8wt% polyvinylidene fluoride (PVDF) and 1.4wt% conductive carbon black, and then cold-pressing, to prepare a positive electrode sheet.
(2) Preparation of negative electrode sheet
A copper foil is used as a negative electrode current collector, a layer of graphite slurry is uniformly coated on the surface of the copper foil, the composition of the graphite slurry is a combination of 97.7wt% of artificial graphite, 1.3wt% of carboxymethyl cellulose (CMC) and 1.0wt% of Styrene Butadiene Rubber (SBR), and then cold pressing is carried out to prepare the negative electrode plate.
(3) Preparation of electrolyte
In the dry argon atmosphere, uniformly mixing Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) according to the volume ratio of 1:1:1 to obtain the organic solvent. LiPF is put into 6 Dissolving in the organic solvent, adding vinylene carbonate, and mixing to obtain electrolyte. Wherein based on the total mass of the electrolyte, the LiPF 6 The mass percent of the catalyst is 12.5%, the mass percent of the vinylene carbonate is 3%, and the mass percent of the organic solvent is 84.5%.
(4) Preparation of secondary battery
The positive pole piece and the negative pole piece are wound after being striped, and the positive pole piece and the negative pole piece are separated by a Polyethylene (PE) isolating film, so that the wound bare cell is prepared. The bare cell is subjected to top side sealing, code spraying, vacuum drying, electrolyte injection, high-temperature standing and formation and capacity, and the secondary battery can be obtained.
Example 1
(1) Method for cycle testing secondary battery
Placing the secondary battery in a constant temperature room, and standing for a first time T1 (30 min) in a first temperature q1 (25+/-3 ℃) environment; constant-current charging the secondary battery with a first charging current C1 (1.0C, 1.0C is the rated capacity of the secondary battery) to a voltage of a first rated voltage U1 (4.4V); charging the secondary battery at constant voltage, stopping charging when the charging current is changed to a second charging current C2 (0.05C), and standing for a second time T2 (10 min); the secondary battery was discharged to a first voltage V1 (3.0V) at a first discharge current C3 (0.5C), and left for a third time T3 (10 min). Thus, the charge-discharge cycle is repeated for one charge-discharge cycle, and the discharge capacity of the secondary battery per charge-discharge cycle is obtained.
(2) Method for acquiring charge-discharge cycle capacity retention epsilon
The discharge capacity C of the secondary battery with the 3 rd charge-discharge cycle as a reference 0 For example, the charge-discharge cycle capacity retention rate epsilon of the 4 th charge-discharge cycle=the discharge capacity/C of the 4 th charge-discharge cycle 0 *100, and the like, to obtain a charge-discharge cycle capacity retention rate epsilon and a secondary battery capacity retention rate curve of each charge-discharge cycle of the secondary battery.
(3) Slope value kappa acquisition method for charge-discharge cycle capacity retention epsilon variation
The gradient value kappa=tan [ slope (n epsilon values) 100% ] 180/3.1415, n is 10, namely, the charge-discharge cycle capacity retention epsilon of 10 secondary batteries is selected in each period, for example, the charge-discharge cycle capacity retention epsilon of the secondary batteries in the 3 rd to 12 th charge-discharge cycles is selected in the first period, and the gradient value kappa of the change of the charge-discharge cycle capacity retention epsilon in the first period is calculated; and selecting the charge-discharge cycle capacity retention rate epsilon of the secondary battery with 4-13 charge-discharge cycles in the second cycle, calculating to obtain a slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon in the second cycle, and the like to obtain the slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon in each cycle, and obtaining a slope value curve of the change of the capacity retention rate.
In this embodiment, a diving threshold lambda is preset max And (5) judging that the secondary battery is in a water jump phenomenon when the charge-discharge cycle capacity retention rate epsilon is lower than 80% in the process of the charge-discharge cycle test of the battery, and ending the charge-discharge cycle test.
1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8 total of 8 secondary battery samples were selected for testing. Fig. 1 is a graph of the number of charge and discharge cycles and the charge and discharge cycle capacity retention rate epsilon for 8 secondary battery samples, with the abscissa representing the number of charge and discharge cycles of the secondary battery and the ordinate representing the charge and discharge cycle capacity retention rate epsilon. Fig. 2 is a graph of the number of charge and discharge cycles of 8 secondary battery samples and the slope value κ, with the abscissa representing the number of charge and discharge cycles of the secondary battery and the ordinate representing the slope value κ of the change in the charge and discharge cycle capacity retention rate ε for each cycle.
If the secondary battery sample 1-3 shows that the secondary battery is in capacity-skip, according to fig. 1, if the secondary battery is judged to be in capacity-skip directly by the charge-discharge cycle capacity retention rate epsilon being lower than 80%, the secondary battery needs to be subjected to 130 charge-discharge cycles to recognize that the secondary battery is in capacity-skip. According to the embodiment of the application, according to fig. 2, when the slope value kappa is lower than-10, it is judged that the secondary battery generates capacity water jump and the charge and discharge cycle test is finished, then the secondary battery sample 1-3 secondary battery generating water jump only needs to perform charge and discharge cycles for about 110 times, the secondary battery generating capacity water jump and the charge and discharge cycle test is finished can be identified, the number of charge and discharge cycles can be reduced by 20 times, test resources are saved, and the secondary battery can be quickly identified to reach the water jump point. According to the slope value κ change curve of fig. 2, the slope values κ of the other batteries except 1-3 are higher than-10, indicating that the secondary battery cycle capacity retention rate is normal and no capacity jump occurs.
Example 2
The differences between this embodiment and embodiment 1 include:
in the cycle test method of the secondary battery, the first temperature q1 is 55±3 ℃.
Taking 8, namely selecting the charge-discharge cycle capacity retention rate epsilon of 8 secondary batteries in each period, for example, selecting the charge-discharge cycle capacity retention rate epsilon of the secondary batteries in the 3 rd to 10 th charge-discharge cycles in the first period, and calculating to obtain a slope value kappa of change of the charge-discharge cycle capacity retention rate epsilon in the first period; and selecting the charge-discharge cycle capacity retention rate epsilon of the secondary battery in the 4 th to 11 th charge-discharge cycles in the second cycle, calculating to obtain a slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon in the second cycle, and the like to obtain the slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon in each cycle, and obtaining a slope value curve of the change of the capacity retention rate.
This embodimentIn which a diving threshold lambda is preset max And (5) judging that the secondary battery is in a water jump phenomenon when the charge-discharge cycle capacity retention rate epsilon is lower than 80% in the process of the charge-discharge cycle test of the battery, and ending the charge-discharge cycle test.
A total of 2-1, 2-2, 2-3 secondary battery samples were selected for testing. Fig. 3 is a graph of the number of charge and discharge cycles and the charge and discharge cycle capacity retention rate epsilon for 3 samples of secondary batteries, with the abscissa representing the number of charge and discharge cycles of the secondary battery and the ordinate representing the charge and discharge cycle capacity retention rate epsilon. Fig. 4 is a graph of the number of charge and discharge cycles of 3 secondary battery samples and the slope value κ, with the abscissa representing the number of charge and discharge cycles of the secondary battery and the ordinate representing the slope value κ of the change in the charge and discharge cycle capacity retention rate ε for each cycle.
Among them, capacity jump occurred in all of the 3 secondary battery samples. Referring to fig. 3, if the secondary battery occurrence capacity skip is determined to be directly lower than 80% by the charge-discharge cycle capacity retention rate epsilon, the secondary battery occurrence capacity skip can be recognized by performing the charge-discharge cycle 100 times or more for all of the 3 secondary battery samples. According to the embodiment of the application, according to fig. 4, when the slope value kappa is lower than-10, the secondary battery is judged to generate capacity water jump and the charge-discharge cycle test is finished, then 3 secondary battery samples only need to be subjected to charge-discharge cycle for about 50 times, and the capacity water jump of each secondary battery can be identified and the charge-discharge cycle test is finished. The identification method provided by the embodiment of the application can be used for rapidly judging that the secondary battery generates capacity water jump, and the number of cycles can be reduced by half, so that the test resources are saved.
Specifically, taking the secondary battery sample 2-1 as an example, whether the preset water jump threshold lambda is reached by the slope value kappa max The determination method (i.e., the capacity skip inflection point) can determine that the secondary battery 2-1 has capacity skip at the 60 th charge/discharge cycle, and can end the charge/discharge cycle test. According to the charge-discharge cycle capacity retention epsilon<80% of the secondary battery 2-1 is judged to have capacity jump and the test is finished, and the conventional cycle cut-off mode is adopted, so that the secondary battery 2-1 needs to be charged and discharged until 99 th reaches the charge and discharge cycle capacity retention rate epsilon<80% can end the test. Thus, compared to ε<Determination method of 80% end test, this embodimentThe example of the determination method can perform the charge and discharge cycle of the secondary battery 2-1 39 times less, save the test resources, and effectively determine the capacity jump inflection point.
In addition, the secondary battery of the embodiment of the application does not need to carry out charge and discharge cycles for a plurality of times, the charge and discharge cycle capacity retention rate epsilon can be calculated after the secondary battery carries out charge and discharge cycles for a small number of times, and whether the secondary battery capacity jumps or not can be judged in the initial stage of the cycle.
In the description of the present application, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C.
The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the application.
Claims (9)
1. A secondary battery capacity jump recognition method, characterized by comprising:
acquiring the charge-discharge cycle capacity retention rate epsilon of the secondary battery; the charge-discharge cycle capacity retention epsilon is obtained by adopting a formula shown in the formula I:
ε=C m /C 0 *100% of formula I;
wherein C is m The capacity of the secondary battery for the mth charge-discharge cycle, m > 3; c (C) 0 The reference capacity is the capacity of the secondary battery of the ith charge-discharge cycle, i is more than or equal to 1 and less than or equal to 5;
acquiring slope values kappa of changes of the charge-discharge cycle capacity retention rates epsilon of the xth period according to a plurality of charge-discharge cycle capacity retention rate epsilon data of the xth period, wherein the number of the charge-discharge cycle capacity retention rates epsilon acquired in each period is n, and the slope values kappa are obtained by adopting a formula shown in a formula II:
kappa = tan [ slope (n epsilon values) 100% ] formula ii 180/3.1415;
the slope value kappa and a preset diving threshold lambda are combined max Comparing; when kappa is less than or equal to lambda max Judging that the secondary battery does not jump, and continuously acquiring a slope value kappa of the change of the charge-discharge cycle capacity retention rate epsilon in the x+1st period; when kappa > lambda max And judging that the secondary battery capacity jumps.
2. The secondary battery capacity jump recognition method according to claim 1, wherein n satisfies: n is more than or equal to 5 and less than or equal to 20.
3. The secondary battery capacity jump recognition method according to claim 2, wherein the secondary battery capacity jump recognition method includes: each cycle acquires n consecutive charge-discharge cycle capacity retention rates epsilon to acquire the slope value kappa.
4. The secondary battery capacity-jump recognition method according to claim 3, wherein obtaining the charge-discharge cycle capacity retention rate epsilon of the x+1th cycle includes:
n charge-discharge cycle capacity retention rates epsilon are selected from any one of the charge-discharge cycle capacity retention rates epsilon after the first charge-discharge cycle capacity retention rate epsilon in the x-th cycle to obtain the slope value kappa for that cycle.
5. The secondary battery capacity jump recognition method according to claim 2, wherein X is smaller than a preset charge-discharge cycle life number X of the secondary battery max 。
6. The secondary battery capacity jump recognition method according to claim 1, wherein the preset jump threshold valueλ max The method meets the following conditions: -15 ∈λ max ≤-5。
7. The secondary battery capacity jump recognition method according to any one of claims 1 to 6, wherein the charge-discharge cycle capacity retention rate epsilon satisfies: epsilon is more than 80 percent.
8. A secondary battery capacity jump recognition system, comprising:
a preprocessing device for acquiring the charge-discharge cycle capacity retention rate epsilon of the secondary battery; the charge-discharge cycle capacity retention epsilon is obtained by adopting a formula shown in the formula I:
ε=C m /C 0 *100% of formula I;
wherein C is m The capacity of the secondary battery for the mth charge-discharge cycle, m > 3; c (C) 0 The reference capacity is the capacity of the secondary battery of the ith charge-discharge cycle, i is more than or equal to 1 and less than or equal to 5;
the slope value characteristic calculation module is used for obtaining slope values kappa of the change of the charge-discharge cycle capacity retention rate epsilon of the xth period according to the charge-discharge cycle capacity retention rate epsilon data of the xth period, the number of the obtained charge-discharge cycle capacity retention rates epsilon is n, and the slope values kappa are obtained by adopting a formula shown in a formula II:
kappa = tan [ slope (n epsilon values) 100% ] formula ii 180/3.1415;
a diving risk assessment module for comparing the slope value k with a preset diving threshold lambda max Comparing; when kappa is less than or equal to lambda max Judging that the secondary battery does not jump, and continuously acquiring a slope value kappa of the charge-discharge cycle capacity retention epsilon variation of the (x+1) th period by the slope value characteristic calculation module; when kappa > lambda max And judging that the secondary battery capacity jumps.
9. The secondary battery capacity jump recognition system according to claim 8, wherein the preprocessing means is further for performing a charge-discharge cycle test on the secondary battery; the secondary battery capacity jump recognition system further includes:
diving control module for controlling when kappa > lambda max And controlling the pretreatment device to stop acquiring the charge-discharge cycle capacity retention rate epsilon and stopping the charge-discharge cycle test of the secondary battery.
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