CN110707387A - Self-discharge screening method for lithium iron phosphate core - Google Patents
Self-discharge screening method for lithium iron phosphate core Download PDFInfo
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- CN110707387A CN110707387A CN201910862727.3A CN201910862727A CN110707387A CN 110707387 A CN110707387 A CN 110707387A CN 201910862727 A CN201910862727 A CN 201910862727A CN 110707387 A CN110707387 A CN 110707387A
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- Prior art keywords
- battery cell
- ocv
- iron phosphate
- self
- lithium iron
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical group [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 33
- 238000000034 method Methods 0.000 title claims abstract description 30
- 238000012216 screening Methods 0.000 title claims abstract description 27
- 238000012360 testing method Methods 0.000 claims abstract description 21
- 238000007599 discharging Methods 0.000 claims abstract description 10
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 6
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 6
- 230000002950 deficient Effects 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/44—Methods for charging or discharging
- H01M10/441—Methods for charging or discharging for several batteries or cells simultaneously or sequentially
-
- 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
Abstract
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium iron phosphate core self-discharge screening method, which comprises the following steps: discharging the capacity-divided battery cell to cut-off voltage; storing for a certain time T1, and testing the open-circuit voltage OCV1 of the battery cell; storing for a certain time T2, and testing the open-circuit voltage OCV2 of the battery cell; continuously discharging the battery cell to cut-off voltage, and testing the discharge capacity C of the battery cellResidue ofCalculating the voltage drop △ OCV (OCV 1-OCV 2) of the cell in the time T2, and if the cell simultaneously meets the conditions that the Avg (△ OCV) -3.8 stdev (△ OCV) is not less than △ OCV is not less than Avg (△ OCV) +3.8stdev (△ OCV) and the 0.05 multiplied by the nominal capacity is not more than CResidue of<And if the nominal capacity is 0.1 multiplied, the battery cell is judged to be qualified. The good cells screened by the method are stored for 60 days, 2mV is used as a voltage range difference, and the misjudgment rate is less than 0.05%.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a self-discharge screening method for lithium iron phosphate cores.
Background
Lithium ion batteries are increasingly widely used in products such as mobile phones and electric tools. Because the voltage and the capacity of the lithium ion battery are low, a plurality of lithium ion batteries are required to be connected in series when the lithium ion battery is applied to tools so as to meet the use requirements of the tools. This requires that the uniformity of these series connected cells be high.
In the production process of lithium batteries, two self-discharge screening methods are commonly used for lithium iron phosphate cores at present: conventional full charge storage and 0% SOC storage. The conventional full-electricity storage method comprises the steps of charging the formed battery cell to full electricity at constant current and constant voltage, testing the open-circuit voltage once again after storing for a period of time, recording the residual capacity once after discharging, and recording the recovery capacity once after capacity grading. The conventional 0% SOC method comprises the steps of discharging the formed battery cell to a lower limit voltage, testing the primary open-circuit voltage, storing for a period of time, testing the primary open-circuit voltage again, detecting the rebound voltage in a capacity-division mode, and selecting the self-discharge battery cell.
However, after the good cells obtained by screening with the above two screening methods are stored for a certain time, there still exists a certain proportion of defective cells, and this proportion is recorded as a false rate, and the false rate is usually 0.5% to 3%.
Therefore, finding a screening method for self-discharge of lithium iron phosphate cores, reducing misjudgment rate and improving shipment consistency is a problem that needs to be solved by technical personnel in the field.
Disclosure of Invention
One of the objects of the present invention is: the self-discharge screening method of the lithium iron phosphate battery cell is provided, and after the battery cell is stored for a period of time, the proportion of defective products is reduced to 0.05%.
In order to achieve the purpose, the invention adopts the following technical scheme:
a self-discharge screening method of lithium iron phosphate cores comprises the following steps:
discharging the capacity-divided battery cell to cut-off voltage;
step two, storing for a certain time T1, and testing the open circuit voltage OCV1 of the battery cell;
step three, storing for a certain time T2, and testing the open circuit voltage OCV2 of the battery cell;
step four, continuously discharging the battery cell to the cut-off voltage, and testing the discharge capacity C of the battery cellResidue of；
Step five, calculating the voltage drop △ OCV (OCV 1-OCV 2) of the battery cell in the time T2, and if the battery cell simultaneously meets the conditions that the Avg (△ OCV) -3.8 stdev (△ OCV) is not less than △ OCV is not less than Avg (△ OCV) +3.8stdev (△ OCV) and the 0.05 multiplied by the nominal capacity is not more than CResidue of<The stdev function is based on a sample estimation standard deviation function, the function and the formula which take the voltage drop △ OCV as variables are fitted through a large number of experiments, the self-discharge defective products of the lithium iron phosphate battery core are screened through the formula, and the misjudgment rate can be reduced to be below 0.05%.
In the first step, the capacity grading is specifically that the battery cell is subjected to capacity grading at 0.5 ℃, and then stands for 5-15 min.
As an improvement of the lithium iron phosphate core self-discharge screening method, in the first step, the capacity-divided core is discharged to a cut-off voltage of specifically 0.1C to 2000 mV. The electric quantity stored in the battery cell can be discharged as soon as possible, so that the screened battery cells are all in an empty state.
As an improvement of the lithium iron phosphate core self-discharge screening method, in the second step, the storage time T1 is 2-4 days.
As an improvement of the lithium iron phosphate core self-discharge screening method according to the present invention, in the second step, the storage time T1 is 3 days.
As an improvement of the lithium iron phosphate core self-discharge screening method, in the third step, the storage time T2 is 6-10 days. The longer the storage time is, the more obvious the self-discharge phenomenon of the lithium iron phosphate battery cell can be realized, the storage time is set to 6-10 days, the self-discharge difference condition of the battery cell can be distinguished, the testing efficiency can be improved, and the online time of the battery cell is reduced.
As an improvement of the self-discharge screening method for the lithium iron phosphate battery cell, in step three, the storage time T2 is 8 days.
As an improvement of the lithium iron phosphate core self-discharge screening method, in the fourth step, the core continues to discharge until the cut-off voltage is specifically 0.5C to 2000 mV.
The beneficial effects of the invention include but are not limited to: the invention provides a self-discharge screening method of a lithium iron phosphate core, which screens self-discharge through voltage difference and residual capacity, summarizes a set of formulas suitable for self-discharge of the lithium iron phosphate core through a large number of experiments, and can accurately judge the self-discharge phenomenon of the lithium iron phosphate core by testing the voltage twice and the residual capacity of one-time discharge. Good products screened by the method are stored for 60 days, 2mV is used as a voltage range, and the proportion of the electric core outside the range is less than 0.05%.
Detailed Description
In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A self-discharge screening method of lithium iron phosphate cores comprises the following steps:
step one, dividing the capacity of a 5-section 18650 type lithium iron phosphate battery cell by 0.5 ℃, standing for 5-15 min, and discharging the divided battery cell to 2000mV by 0.1 ℃; the step can discharge the electric quantity stored in the battery cell as soon as possible, so that the screened battery cells are all in an empty state.
Step two, storing for 3 days at normal temperature, and testing the cell open circuit voltage OCV 1;
step three, storing for 8 days at normal temperature, and testing the cell open circuit voltage OCV 2; the longer the storage time is, the more obvious the self-discharge phenomenon of the lithium iron phosphate battery cell can be realized, the storage time is set to 6-10 days, the self-discharge difference condition of the battery cell can be distinguished, the testing efficiency can be improved, and the online time of the battery cell is reduced.
Step four, continuously discharging the battery cell to 2000mV at 0.5C, and testing the discharge capacity C of the battery cellResidue of；
Step five, calculating the voltage drop △ OCV (OCV 1-OCV 2) of the battery cell in the time T2, and if the battery cell simultaneously meets the conditions that the Avg (△ OCV) -3.8 stdev (△ OCV) is not less than △ OCV is not less than Avg (△ OCV) +3.8stdev (△ OCV) and the 0.05 multiplied by the nominal capacity is not more than CResidue of<And if the nominal capacity is 0.1, the standard capacity is judged to be qualified. The nominal capacity is 2400 mA/h.
The number of the recording battery cell is 1-5.
Example 2
The difference from the example 1 is that in the second step, the battery cell is stored for 2 days at normal temperature, and the open-circuit voltage OCV1 of the battery cell is tested.
The rest is the same as embodiment 1, and the description is omitted here.
The number of the recording battery cell is 6-10.
Example 3
The difference from the example 1 is that in the second step, the battery cell is stored for 4 days at normal temperature, and the open-circuit voltage OCV1 of the battery cell is tested.
The rest is the same as embodiment 1, and the description is omitted here.
The serial number of the recording battery cell is 11-15.
Example 4
The difference from the example 1 is that in the third step, the cell is stored at normal temperature for 6 days, and the cell open-circuit voltage OCV2 is tested.
The rest is the same as embodiment 1, and the description is omitted here.
The number of the recording battery core is 16-20.
Example 5
The difference from the example 1 is that in the third step, the battery cell is stored at normal temperature for 10 days, and the open-circuit voltage OCV2 of the battery cell is tested.
The rest is the same as embodiment 1, and the description is omitted here.
The number of the recording battery core is 21-25.
The number of the battery cell is 1-25 according toMethod for testing open-circuit voltages OCV1 and OCV2 and C in examples 1-5Residue ofJudging whether the formula is met, and if so, judging that the formula is qualified; if not, determining that the product is not qualified.
And storing the qualified battery cell for 60 days, and calculating the misjudgment rate by taking 2mV as the voltage range.
The test results are shown in Table 1.
TABLE 1
In conclusion, the self-discharge screening method for the lithium iron phosphate core screens the self-discharge through the voltage difference and the residual capacity, a set of formula suitable for the self-discharge of the lithium iron phosphate core is summarized through a large number of experiments, and the self-discharge phenomenon of the lithium iron phosphate core can be accurately judged by testing the voltage twice and the residual capacity of one-time discharge.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (8)
1. The self-discharge screening method of the lithium iron phosphate core is characterized by comprising the following steps of:
discharging the capacity-divided battery cell to cut-off voltage;
step two, storing for a certain time T1, and testing the open circuit voltage OCV1 of the battery cell;
step three, storing for a certain time T2, and testing the open circuit voltage OCV2 of the battery cell;
step four, continuously discharging the battery cell to the cut-off voltage, and testing the discharge capacity C of the battery cellResidue of；
Step five, calculating the voltage drop △ OCV (OCV 1-OCV 2) of the battery cell in the time T2, and if the battery cell simultaneously meets the conditions that the Avg (△ OCV) -3.8 stdev (△ OCV) is not less than △ OCV is not less than Avg (△ OCV) +3.8stdev (△ OCV) and the 0.05 multiplied by the nominal capacity is not more than CResidue of<And if the nominal capacity is 0.1 multiplied by the standard capacity, the battery cell is judged to be qualified.
2. The lithium iron phosphate battery cell self-discharge screening method according to claim 1, wherein in the first step, the capacity grading is specifically that the battery cell is subjected to capacity grading at 0.5C, and then is allowed to stand for 5-15 min.
3. The lithium iron phosphate battery cell self-discharge screening method according to claim 1, wherein in the step one, the battery cells after capacity grading are discharged to a cut-off voltage of 2000mV at 0.1C.
4. The lithium iron phosphate core self-discharge screening method according to claim 1, wherein in the second step, the storage time T1 is 2-4 days.
5. The lithium iron phosphate core self-discharge screening method according to claim 4, wherein in the second step, the storage time T1 is 3 days.
6. The lithium iron phosphate core self-discharge screening method according to claim 1, wherein in step three, the storage time T2 is 6-10 days.
7. The lithium iron phosphate battery cell self-discharge screening method according to claim 6, wherein in step three, the storage time T2 is 8 days.
8. The lithium iron phosphate battery cell self-discharge screening method according to claim 1, wherein in step four, the battery cells are continuously discharged until the cut-off voltage is specifically 0.5C to 2000 mV.
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| CN201910862727.3A CN110707387A (en) | 2019-09-12 | 2019-09-12 | Self-discharge screening method for lithium iron phosphate core |
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Cited By (2)
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| CN113361128A (en) * | 2021-06-24 | 2021-09-07 | 东莞塔菲尔新能源科技有限公司 | Abnormal battery cell screening method and system, computer equipment and storage medium |
| CN113533981A (en) * | 2021-07-30 | 2021-10-22 | 蜂巢能源科技有限公司 | Lithium ion battery self-discharge detection method and device and computer readable storage medium |
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Application publication date: 20200117 |