CN116706279A - Preparation method and application of lithium ion battery cell - Google Patents
Preparation method and application of lithium ion battery cell Download PDFInfo
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- CN116706279A CN116706279A CN202211116789.8A CN202211116789A CN116706279A CN 116706279 A CN116706279 A CN 116706279A CN 202211116789 A CN202211116789 A CN 202211116789A CN 116706279 A CN116706279 A CN 116706279A
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- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 834
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 738
- 238000002360 preparation method Methods 0.000 title abstract description 62
- 229910000103 lithium hydride Inorganic materials 0.000 claims abstract description 209
- 238000000034 method Methods 0.000 claims abstract description 164
- 238000000354 decomposition reaction Methods 0.000 claims abstract description 117
- 238000007599 discharging Methods 0.000 claims abstract description 91
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 219
- 238000007600 charging Methods 0.000 claims description 171
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 134
- 239000007789 gas Substances 0.000 claims description 116
- 230000015572 biosynthetic process Effects 0.000 claims description 85
- 230000008569 process Effects 0.000 claims description 77
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 67
- 239000001569 carbon dioxide Substances 0.000 claims description 53
- 229910052739 hydrogen Inorganic materials 0.000 claims description 30
- 239000001257 hydrogen Substances 0.000 claims description 30
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 23
- 238000003487 electrochemical reaction Methods 0.000 claims description 16
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 12
- 238000005520 cutting process Methods 0.000 claims description 10
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 10
- 150000002431 hydrogen Chemical class 0.000 claims description 9
- 238000004817 gas chromatography Methods 0.000 claims description 8
- 239000007784 solid electrolyte Substances 0.000 claims description 7
- 238000000691 measurement method Methods 0.000 claims description 3
- 239000000523 sample Substances 0.000 claims 1
- SIAPCJWMELPYOE-UHFFFAOYSA-N lithium hydride Chemical compound [LiH] SIAPCJWMELPYOE-UHFFFAOYSA-N 0.000 abstract 3
- 230000002829 reductive effect Effects 0.000 description 40
- 239000000306 component Substances 0.000 description 30
- 238000010277 constant-current charging Methods 0.000 description 26
- 238000004519 manufacturing process Methods 0.000 description 20
- 238000006243 chemical reaction Methods 0.000 description 19
- 238000000605 extraction Methods 0.000 description 19
- 230000000694 effects Effects 0.000 description 18
- 238000010438 heat treatment Methods 0.000 description 17
- 229910052744 lithium Inorganic materials 0.000 description 17
- 150000001335 aliphatic alkanes Chemical class 0.000 description 14
- 238000004806 packaging method and process Methods 0.000 description 14
- 238000013461 design Methods 0.000 description 9
- 239000003792 electrolyte Substances 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- 230000002411 adverse Effects 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- 238000005086 pumping Methods 0.000 description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 6
- 229910002804 graphite Inorganic materials 0.000 description 6
- 239000010439 graphite Substances 0.000 description 6
- 239000007773 negative electrode material Substances 0.000 description 6
- 238000003860 storage Methods 0.000 description 6
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 5
- 238000001514 detection method Methods 0.000 description 4
- 238000009830 intercalation Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 230000004044 response Effects 0.000 description 4
- 230000032683 aging Effects 0.000 description 3
- 238000004590 computer program Methods 0.000 description 3
- 238000010280 constant potential charging Methods 0.000 description 3
- 238000004880 explosion Methods 0.000 description 3
- 230000002441 reversible effect Effects 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 238000005538 encapsulation Methods 0.000 description 2
- 230000005484 gravity Effects 0.000 description 2
- 230000002687 intercalation Effects 0.000 description 2
- 229910003002 lithium salt Inorganic materials 0.000 description 2
- 159000000002 lithium salts Chemical class 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 238000007086 side reaction Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- 230000003044 adaptive effect Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000000740 bleeding effect Effects 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000008358 core component Substances 0.000 description 1
- 238000013500 data storage Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000037427 ion transport Effects 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- -1 lithium alkoxide Chemical class 0.000 description 1
- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Chemical compound [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 description 1
- 229910021450 lithium metal oxide Inorganic materials 0.000 description 1
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 1
- 229910001947 lithium oxide Inorganic materials 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 238000010517 secondary reaction Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000009966 trimming 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
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/44—Methods for charging or discharging
-
- 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
-
- 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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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Secondary Cells (AREA)
- Materials Engineering (AREA)
Abstract
The application provides a preparation method and application of a lithium ion battery cell, wherein the method comprises the following steps: discharging the first lithium ion battery cell to a target voltage to obtain a discharged first lithium ion battery cell, wherein the first lithium ion battery cell is charged for the first time, the first lithium ion battery cell comprises lithium hydride, and the target voltage meets the following conditions: the target voltage is less than the decomposition voltage of the lithium hydride under discharge conditions; and preparing a finished battery cell based on the discharged first lithium ion battery cell. The method can reduce the content of LiH in the prepared finished battery cell and improve the thermal stability and reliability of the finished battery cell.
Description
Technical Field
The application relates to the field of batteries, in particular to a preparation method and application of a lithium ion battery core.
Background
The lithium ion battery has the characteristics of high charge and discharge speed, good safety, high energy density and the like, and is the preferred battery of the power battery.
The lithium ion battery core is used as a core component of the lithium ion battery, and the quality of the lithium ion battery core directly influences the quality of the lithium ion battery. In the charge and discharge process of the lithium ion battery, the lithium ion battery core generates gas, and the more the content of the generated gas is, the more serious the problems of heating and expansion of the lithium ion battery core are, so that the aging of the lithium ion battery is accelerated.
Therefore, how to provide a method for preparing a lithium ion battery cell, which can solve the problem of gas production of the lithium ion battery cell during charge and discharge after the lithium ion battery cell is put into use, and is an important research subject in the technical field.
Disclosure of Invention
The application provides a preparation method and application of a lithium ion battery cell, and the method can reduce the content of LiH in the prepared lithium ion battery cell, thereby improving the problem of gas production of the lithium ion battery cell during charging and discharging after the lithium ion battery cell is put into use and improving the thermal stability, safety and reliability of the lithium ion battery cell.
In a first aspect, the present application provides a method for preparing a lithium ion battery cell, the method comprising: discharging the first lithium ion battery cell to a target voltage to obtain a discharged first lithium ion battery cell, wherein the first lithium ion battery cell is charged for the first time, the first lithium ion battery cell comprises lithium hydride, and the target voltage meets the following conditions: the target voltage is less than the decomposition voltage of the lithium hydride under discharge conditions; and preparing a finished battery cell based on the discharged first lithium ion battery cell, wherein the electric quantity of the finished battery cell meets the basic working electric quantity.
It can be understood that the finished battery cell is a finished product of the first lithium ion battery cell, and the finished battery cell can also be understood as a lithium ion battery cell which can be normally charged and discharged after being connected with an external circuit.
Illustratively, the finished cell meeting the basic power requirement refers to the finished cell meeting a shipment power condition, e.g., the shipment power condition is that the power of the finished cell is greater than or equal to 50% of the capacitance (other suitable values may be used, depending on the particular requirement).
In the present application, the first lithium ion battery cell may be a lithium ion battery cell after the first charging is completed, and is a battery cell to be shipped after at least one charging, for example, the first lithium ion battery cell may be a lithium ion battery cell after formation, or after capacity division.
According to the preparation method of the lithium ion battery core, in the process of discharging the first lithium ion battery core, lithium hydride (LiH) in the lithium ion battery core is subjected to electrochemical decomposition, so that the content of LiH generated in the preparation process of the first lithium ion battery core and remained in the first lithium ion battery core can be reduced, the gas yield of a finished battery core prepared based on the first lithium ion battery core during charging and discharging after the finished battery core is put into use is reduced, the problems of heating, expanding and accelerated aging of the battery core due to too much content of hydrogen generated by decomposing the LiH of the finished battery core after the finished battery core is put into use are solved, and the thermal stability, safety and reliability of the finished battery core are improved.
In one possible implementation, the target voltage further satisfies the following condition: the target voltage is smaller than the over-discharge protection voltage of the first lithium ion battery cell and is greater than or equal to the discharge termination voltage of the first lithium ion battery cell.
It can be appreciated that the above target voltage also satisfies the following condition: the target voltage is smaller than the over-discharge protection voltage of the first lithium ion battery core and larger than or equal to the discharge termination voltage of the first lithium ion battery core, which means that the target voltage is smaller than the decomposition voltage, smaller than the over-discharge protection voltage and larger than or equal to the discharge termination voltage.
Experimental measurement shows that the content of LiH in the lithium ion battery core with the residual electric quantity of 100% is ten times as high as that in the lithium ion battery core with the residual electric quantity of 0%, so that the target voltage is set to be smaller than the over-discharge protection voltage of the lithium ion battery core and larger than or equal to the discharge termination voltage of the lithium ion battery core, on one hand, a large amount of LiH in the first lithium ion battery core can be subjected to electrochemical decomposition under the over-discharge condition, the content of LiH in a finished battery core after the use is reduced, and the thermal stability and reliability of the finished battery core are improved; on the other hand, the first lithium ion battery core is ensured not to discharge to be lower than the discharge termination voltage, so that the effect of protecting the internal structure of the first lithium ion battery core can be achieved, and the quality of a Solid Electrolyte Interface (SEI) film except for LiH in a finished battery core can be ensured by ensuring that LiH is electrochemically decomposed to reduce the content of LiH in the finished battery core and improve the stability and reliability of the finished battery core.
In one possible implementation, the target voltage further satisfies the following condition: the target voltage is greater than or equal to a cutoff voltage at which the lithium hydride is completely decomposed under discharge conditions.
Therefore, when the first lithium ion battery cell is discharged to a target voltage, the target voltage is smaller than the decomposition voltage of lithium hydride and is larger than or equal to the cutoff voltage for complete decomposition of lithium hydride, for example, the target voltage is the cutoff voltage, liH in the first lithium ion battery cell is completely decomposed or almost completely decomposed in the discharging process, the content of LiH in the finished battery cell after being put into use is greatly reduced, and the thermal stability and reliability of the finished battery cell are greatly improved.
In one possible implementation manner, when the cut-off voltage of the lithium hydride in complete decomposition under the discharge condition is greater than the discharge end voltage of the first lithium ion cell, the decomposition voltage takes on the value of the cut-off voltage.
Therefore, while the LiH in the first lithium ion battery cell is decomposed in a large amount, other components except the LiH in the SEI film are not destroyed, and the quality of the finished battery cell is improved.
In one possible implementation, before the discharging the first lithium ion cell to the target voltage, the method further includes: the first lithium ion battery cell is charged for the first time based on the full voltage or the capacitance of the first lithium ion battery cell, the first lithium ion battery cell after the first charging is completed is obtained, and in the process of the first charging, the first lithium ion battery cell generates a solid electrolyte interface SEI film, and the SEI film comprises the lithium hydride; the preparing a finished product cell based on the discharged first lithium ion cell comprises the following steps: and charging the discharged first lithium ion battery cell based on the full voltage or capacitance of the first lithium ion battery cell so as to obtain the finished battery cell, wherein the electric quantity of the finished battery cell meets the basic working electric quantity.
It is understood that the capacitance of the first lithium ion battery cell may refer to a designed capacitance of the first lithium ion battery cell, and a theoretical value of the capacitance, and as for an actual value of the capacitance of the first lithium ion battery cell, the actual value of the capacitance of the first lithium ion battery cell may be obtained in the step of capacity division.
For example, charging the discharged first lithium ion battery cell based on the full voltage of the first lithium ion battery cell may be: and carrying out constant-current charging on the discharged first lithium ion battery cell, and charging to a first voltage threshold value, wherein the first voltage threshold value is smaller than or equal to the full-charge voltage of the first lithium ion battery cell. For example, the full voltage is 4.0, and the discharged first lithium ion cell is charged to 3.8 volts with a current level of 1.0C.
Illustratively, charging the discharged first lithium-ion battery cell based on the capacitance of the first lithium-ion battery cell may be: and carrying out constant-current charging on the discharged first lithium ion battery cell until the electric quantity of the first lithium ion battery cell meets a first electric quantity threshold value, wherein the first electric quantity threshold value is greater than or equal to 50% of the electric capacity (50% SOC) of the first lithium ion battery cell.
In one possible implementation manner, the first lithium ion battery cell contains carbon dioxide gas, in the process of discharging the first lithium ion battery cell to the target voltage, the lithium hydride is electrochemically decomposed to generate lithium ions, and in the process of charging the discharged first lithium ion battery cell based on the full voltage, the carbon dioxide and the lithium ions are electrochemically reacted under the charging condition to generate lithium carbonate.
In this way, during the charging process, the carbon dioxide gas and lithium ions electrochemically react under the charging conditions to produce lithium carbonate (Li) 2 CO 3 ) The Li is 2 CO 3 Lithium alkyl carbonate (ROCO 2 Li) belonging to SEI film, to generate the Li 2 CO 3 The SEI film quality is improved, so that the thermal stability and reliability of the finished battery cell can be further improved.
In one possible implementation, the first lithium ion battery cell contains carbon dioxide gas, and before the charging of the discharged first lithium ion battery cell based on the full voltage or capacitance of the first lithium ion battery cell, the method further includes: and extracting gas in the first lithium ion battery cell, wherein the gas comprises the carbon dioxide.
Thereby, carbon dioxide gas and lithium ions (Li + ) Electrochemical reaction under charging condition to generate Li 2 CO 3 . It can be appreciated that for lithium ion cells, li + The more the content of (C), the better the activity of the lithium ion battery cell, the faster the charging speed and the higher the quality, thereby preventing the CO 2 Gas and Li + Electrochemical reaction to Li 2 CO 3 Can effectively reduce Li in the first lithium ion battery cell + And the activity of the final finished battery cell is improved.
In one possible implementation manner, the decomposition voltage is a discharge voltage that makes the content of hydrogen generated by a second lithium ion battery cell in a discharge process be greater than 0, the second lithium ion battery cell contains lithium hydride, and the second lithium ion battery cell does not contain hydrogen, and the second lithium ion battery cell has the same specification as the first lithium ion battery cell.
It can be understood that the second lithium ion battery cell refers to a lithium ion battery cell used for measuring the decomposition voltage of lithium hydride in an experiment, and the first lithium ion battery cell can be a lithium ion battery cell for preparing a finished battery cell by using the decomposition voltage of lithium hydride obtained by measuring the second lithium ion battery cell.
In order to maintain the uniqueness of the experimental variables, the second lithium ion battery cell and the first lithium ion battery cell belong to the lithium ion battery cell with the same specification, for example, the capacitance of the second lithium ion battery cell and the capacitance of the first lithium ion battery cell are consistent, so that the experimental result (namely, the measured decomposition voltage of LiH) can be more accurate.
The second lithium ion battery core does not contain hydrogen, namely the hydrogen component generated in the discharging process of the second lithium ion battery core does not exist H comprising the generation of water consumed by a second lithium ion cell during initial charging 2 Therefore, the decomposition voltage of lithium hydride obtained through experiments can be more accurate.
To further increase the uniqueness of the experimental variables, in other possible implementations, the charging parameters of the first lithium ion battery cell when the second lithium ion battery cell is first charged are also consistent with the charging parameters of the first lithium ion battery cell when the first lithium ion battery cell is first charged, where the charging parameters include: the accuracy of the experimental result is further improved by the pressure value and the temperature value applied by the formation equipment to the lithium ion battery core, the design of the charging steps, and the charging current and the charging cut-off condition of each charging step.
In one possible implementation manner, the cut-off voltage is a larger discharge voltage of at least two discharge voltages corresponding to a first state of a second lithium ion battery cell, the first state is a discharge state that a content of hydrogen generated by the second lithium ion battery cell in a discharge process is no longer increased, the second lithium ion battery cell contains the lithium hydride, the second lithium ion battery cell does not contain hydrogen, and the second lithium ion battery cell and the first lithium ion battery cell have the same specification.
In one possible implementation manner, the first lithium ion battery cell is configured with an air bag, and the preparing a finished battery cell based on the discharged first lithium ion battery cell includes: carrying out capacity division on the discharged first lithium ion battery cell to obtain a capacity-divided first lithium ion battery cell; and extracting the gas in the separated first lithium ion battery cell and the gas bag, and cutting off the gas bag to obtain the finished battery cell, wherein the electric quantity of the finished battery cell meets the basic working electric quantity.
Therefore, on one hand, after the formation and capacity division steps of the first lithium ion battery cell are completed, the gas bag is cut, so that the LiH is subjected to electrochemical decomposition to reduce the content of the LiH in the finished battery cell, and meanwhile, the gas (hydrogen generated by the decomposition of the LiH) generated in the preparation process of the finished battery cell is prevented from being contained in the gas bag, so that the gas is retained in the lithium ion battery cell to bring adverse effects to the lithium ion battery cell. In another aspect, the shipment electric quantity of the first lithium ion battery core can be controlled in the capacity-dividing step, but not in the formation step before capacity-dividing, so that the number of times of charging the first lithium ion battery core can be reduced, and the preparation process is simplified.
In a second aspect, the present application provides a method of determining the decomposition voltage of lithium hydride, the method comprising: obtaining a second lithium ion battery cell, wherein the second lithium ion battery cell contains lithium hydride and does not contain hydrogen; discharging the second lithium ion battery cell; and in the discharging process, acquiring a first voltage, wherein the first voltage is a discharging voltage corresponding to the second lithium ion battery cell when the volume of hydrogen generated during discharging is greater than 0, and the first voltage is used for representing the decomposition voltage of the lithium hydride.
It can be understood that the second lithium ion battery core does not contain hydrogen, that is, the hydrogen component generated by the second lithium ion battery core in the discharging process does not contain H generated by the consumption of water by the second lithium ion battery core in the first charging process 2 Therefore, the decomposition voltage of lithium hydride obtained through experiments can be more accurate.
For example, to improve the uniqueness of the experimental variable, the second lithium ion battery cell and the first lithium ion battery cell may be lithium ion battery cells belonging to the same specification (for example, the same capacitance), and the charging parameter when the second lithium ion battery cell is charged for the first time is also consistent with the charging parameter when the first lithium ion battery cell is charged for the first time.
The method for determining the decomposition voltage of lithium hydride can determine the decomposition voltage of LiH in the lithium ion battery core, and based on the decomposition voltage, the finished battery core is prepared, and the content of LiH in the finished battery core can be reduced, so that the gas yield of the finished battery core in charge and discharge after the finished battery core is put into use is reduced, the problems of heating, expansion and accelerated aging of the battery core caused by too much content of hydrogen generated by decomposition of LiH of the finished battery core after the finished battery core is put into use are solved, and the thermal stability and reliability of the finished battery core are improved.
In one possible implementation, the method further includes: and in the discharging process, acquiring a second voltage, wherein the second voltage is a larger discharging voltage of at least two discharging voltages corresponding to a first state of the second lithium ion battery core in the discharging process, the first state is a discharging state that the volume of hydrogen generated by the second lithium ion battery core in the discharging process is not increased any more, and the second voltage is used for representing a cut-off voltage of complete decomposition of lithium hydride in the second lithium ion battery core under a discharging condition.
The method for determining the decomposition voltage of the lithium hydride can also determine the cut-off voltage of the lithium ion battery cell for completely decomposing the LiH under the discharge condition, and based on the cut-off voltage, the content of the LiH in the finished battery cell can be greatly reduced, and the thermal stability and the reliability of the finished battery cell can be greatly improved.
In one possible implementation manner, the obtaining the second lithium ion battery cell includes: obtaining N groups of second lithium ion battery cores, wherein N is a positive integer greater than or equal to 3; the discharging the second lithium ion battery cell includes: discharging each group of second lithium ion battery cells of the N groups of second lithium ion battery cells respectively, and stopping discharging until N unequal discharging voltages are reached, wherein the discharging voltages are larger than 0, so as to obtain N groups of discharged second lithium ion battery cells; the step of obtaining the first voltage in the discharging process comprises the following steps: determining the volume of hydrogen in each set of discharged second lithium ion battery cells of the N sets of discharged second lithium ion battery cells based on a drainage method and a gas chromatography measurement method to obtain N volume; determining a first volume, the first volume being a minimum volume of the N volumes greater than 0; and setting a maximum voltage of at least one discharge voltage corresponding to the first volume as the first voltage.
For example, the difference between each two of the N unequal discharge voltages is 1.0 volt.
In one possible implementation, the acquiring the second voltage during the discharging includes: determining a second volume, wherein at least two groups of the second volume are contained in the N volume, and the second volume is the largest volume in the N volume; the maximum voltage of at least one of the discharge voltages corresponding to the second volume is taken as the second voltage.
In one possible implementation, the determining the first volume includes: determining the first volume in case the N volume comprises a volume greater than 0; the determining the second volume includes: determining the second volume in case the N volume comprises a volume greater than 0; the method further comprises the steps of: in the case where the N volume amounts are all 0, the maximum value of the N unequal discharge voltages is determined.
In one possible implementation manner, the acquiring N groups of second lithium ion battery cells includes: acquiring N groups of second lithium ion battery cores which are not subjected to primary charging, wherein each group of lithium ion battery cores which are not subjected to primary charging in the N groups of second lithium ion battery cores which are not subjected to primary charging at least comprises one second lithium ion battery core; charging each group of second lithium ion battery cells in the N groups of second lithium ion battery cells for the first time based on the full charge voltage of the second lithium ion battery cells to obtain N groups of charged second lithium ion battery cells, wherein the N groups of charged second lithium ion battery cells all contain lithium hydride; and extracting the gas in the N groups of charged second lithium ion batteries to obtain N groups of extracted second lithium ion batteries, and taking the N groups of extracted second lithium ion batteries as the N groups of second lithium ion batteries.
It will be appreciated that the method for preparing a lithium ion battery cell according to any one of the above first aspects of the present application and the method for determining the decomposition voltage of lithium hydride according to any one of the above second aspects of the present application may be performed in combination, and specific reference may be made to the relevant description in the specific embodiments (for example, the relevant description of fig. 3 in example 1).
In a third aspect, a lithium ion battery cell is made based on the method of the first aspect or any possible implementation of the first aspect.
In a fourth aspect, a lithium ion battery comprises a lithium ion cell, wherein the lithium ion cell is made based on the method of the first aspect or any possible implementation of the first aspect.
Illustratively, a lithium-ion battery includes a protection circuit (or control circuit) and a lithium-ion cell, the protection circuit (or control circuit) providing conductors for electrons to move during an electrochemical reaction for the lithium-ion cell, as well as providing circuit protection for charging and discharging of the lithium-ion battery.
In a fifth aspect, a formation device for a lithium ion battery cell, the formation device comprising one or more control circuits for controlling the formation device to perform the method of the first aspect or any possible implementation of the first aspect, the method of the second aspect or any possible implementation of the second aspect.
In the embodiment of the present application, the adjustable range of the voltage value (the adjustable range may be also understood as an upper limit and a lower limit), the adjustable range of the current value, the adjustable range of the pressure value, and the adjustable range of the temperature value in the control circuit in the formation device support the adjustment to the voltage, the current, the pressure, and the temperature required to be reached by the first lithium ion battery cell and/or the second lithium ion battery cell during the charging process and/or the discharging process.
It can be understood that the lithium ion battery core provided in the third aspect and the lithium ion battery provided in the fourth aspect are prepared based on the method provided in the present application, and the formation equipment of the lithium ion battery core provided in the fifth aspect is used for executing the method provided in the embodiment of the present application. Therefore, the advantages achieved by the method can be referred to as the advantages of the corresponding method, and will not be described herein.
Drawings
Fig. 1 is a schematic diagram of a component structure of an SEI film on a negative electrode side according to an embodiment of the present application;
fig. 2 is a schematic flow chart of a method for preparing other lithium ion battery cells according to an embodiment of the present application;
fig. 3 is a schematic flow chart of a method for preparing a lithium ion battery cell according to an embodiment of the present application;
Fig. 4 is a schematic flow chart of a specific implementation manner of a preparation method of a lithium ion battery cell according to an embodiment of the present application;
fig. 5 is a schematic flow chart of a method for determining the decomposition voltage of LiH in a lithium ion battery cell according to an embodiment of the present application;
fig. 6 is a schematic flow chart of a preparation method of a lithium ion battery cell according to an embodiment of the present application;
fig. 7 is a schematic flow chart of a preparation method of a lithium ion battery cell according to an embodiment of the present application;
fig. 8 is a schematic flow chart of a preparation method of a lithium ion battery cell according to an embodiment of the present application;
fig. 9 is a schematic flow chart of a preparation method of a lithium ion battery cell according to another embodiment of the present application;
fig. 10 is a schematic flow chart of a preparation method of a lithium ion battery cell according to an embodiment of the present application;
fig. 11 is a flowchart of a specific implementation manner of a method for determining a completely decomposed cutoff voltage of LiH in a lithium ion battery cell according to an embodiment of the present application;
fig. 12 is a flowchart of a specific implementation manner of a method for determining a completely decomposed cutoff voltage of LiH in a lithium ion battery cell according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described with reference to the accompanying drawings.
The terms first and second and the like in the description, the claims and the drawings of the present application are used for distinguishing between different objects and not for describing a particular sequential order. Furthermore, the terms "comprising," "including," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion. Such as a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to the list of steps or elements but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly understand that the embodiments described herein may be combined with other embodiments.
In the present application, "at least one (item)" means one or more, "a plurality" means two or more, "at least two (items)" means two or three and more, "and/or" for describing an association relationship of an association object, and three kinds of relationships may exist, for example, "a and/or B" may represent: only a, only B and both a and B are present, wherein a, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship. "at least one of (a) or a similar expression thereof means any combination of these items. For example, at least one (one) of a, b or c may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c".
The following describes the terminology involved in the present application.
(1) Lithium ion battery core
Generally, a lithium ion battery is mainly composed of a lithium ion battery cell and a protection circuit (protection board).
The lithium ion battery cell comprises a positive electrode material, a negative electrode material and electrolyte. The positive electrode material is typically lithium metal oxide (e.g., lithium cobaltate), the negative electrode material is typically graphite, and the electrolyte is typically composed of a lithium salt and an organic solvent as a carrier for lithium ion transport.
(2) Preparation process of lithium ion battery cell
Generally, the preparation process of the lithium ion battery cell comprises the following three procedures: front stage process (stage sheet manufacture), middle stage process (cell synthesis), and back stage process (formation package).
The production objective of the former process is to complete the manufacture of the pole pieces (positive pole piece and negative pole piece).
The production goal of the middle process is to finish the manufacture of the battery cell, and the technical routes and production line equipment of the middle process of different types of lithium batteries are different. Illustratively, the middle-stage process mainly includes orderly assembling the separator, the electrolyte, and the pole piece made in the front-stage process.
The production goal of the back-end process is to complete the formation package. The main flow of the subsequent process is formation, and one or more of capacity division, detection and separation can be performed besides formation.
It can be understood that the functional structure of the lithium ion battery cell is already formed by stopping the process from the middle stage, and the meaning of the latter stage process is to activate the lithium ion battery cell. After the subsequent process is completed, the finished battery cell can be obtained.
The preparation method of the lithium ion battery cell is improved aiming at the subsequent process, and the lithium ion battery cell described by the application is a lithium ion battery cell with complete functional structure.
Specifically, the preparation method of the lithium ion battery cell provided by the application is suitable for the lithium ion battery cell after the middle-stage process and before the air bag of the lithium ion battery cell is cut off and packaged.
For example, after the middle process, the lithium ion battery core with complete functional structure is prepared into a finished battery core by adopting the preparation method of the lithium ion battery core provided by the application to continue the formation and capacity division steps, so as to obtain the finished battery core.
As can be appreciated, the finished cell refers to: the lithium ion battery cell which can be normally used (for example, normally discharged) after being connected with an external circuit can be also understood as a shipment battery cell. In the embodiment of the application, the finished battery cell may be a lithium ion battery formed in a later stage process, or the finished battery cell may be a lithium ion battery formed in a later stage process and subjected to capacity division.
(3) Formation into
The formation is a key step in the production of lithium ion batteries, and refers to the first charging process after the liquid injection of the lithium ion batteries, and the process can activate active substances in the batteries to activate the lithium batteries. Meanwhile, the lithium salt and the electrolyte undergo side reactions, a solid electrolyte interface (solid electrolyte interface, SEI) film is generated on the negative electrode side of the lithium battery, and in addition, the SEI film can prevent the side reactions from further happening, thereby reducing the loss of active lithium in the lithium battery.
(4) Solid electrolyte interface film (SEI film)
The SEI film has the characteristic of solid electrolyte, is an excellent conductor of lithium ions, and can freely insert and extract lithium ions through the SEI film to perform lithium extraction work (including that lithium ions in the positive electrode of a lithium ion battery cell can enter the surface of a graphite negative electrode through the SEI film and lithium-inserted graphite particles can be retransmitted to the positive electrode of the battery cell through the SEI film). Meanwhile, the SEI film is also a good electronic insulator, so that the probability of short circuit inside a lithium ion battery core can be effectively reduced, and self-discharge is improved. In addition, the SEI film can also effectively prevent the co-intercalation of solvent molecules, and avoid damage to electrode materials caused by the co-intercalation of the solvent molecules, so that the SEI film can greatly improve the cycle performance and the service life of the lithium ion battery core.
For example, referring to fig. 1, after the lithium ion battery cell is charged for the first time, the structural components of the SEI film generated on the negative electrode side are shown in fig. 1. The SEI film generally has a thickness of more than 20 nm and less than two hundred nm. The components of SEI are conventionally considered to comprise lithium carbonate (Li 2 CO 3 ) Lithium fluoride (LiF), lithium oxide (Li) 2 O), lithium hydroxide (LiOH), and the like, and lithium alkyl carbonate (ROCO) 2 Li), lithium alkoxide (ROLi), and the like.
In addition, experiments prove that the SEI film further comprises a lithium hydride (LiH) component. Illustratively, the water (D 2 O) isotope titration gas chromatography technique, it was confirmed that LiH was contained in the SEI in the graphite anode. Illustratively, in the formation step of the lithium ion cell, the lithium ion cell is charged for the first time, wherein water participates in the reaction to generate hydrogen (H 2 ) Lithium intercalation graphite negative electrode (Li) x C 6 ) Absorption of H 2 The reaction produced the LiH.
(5) Over-discharge protection voltage and discharge termination voltage
In a lithium ion battery, the over-discharge protection voltage refers to the lowest voltage of the protection plate for protecting the battery cell during discharge transition, and when the lithium ion battery cell is discharged to the over-discharge protection voltage, the protection plate cuts off a circuit so as to achieve the purpose of protecting the battery cell.
In the embodiment of the application, the discharge termination voltage refers to the voltage drop to the lowest working voltage value of the lithium ion battery core, which is not suitable for continuous discharge.
In the embodiment of the present application, the over-discharge protection voltage is greater than the discharge termination voltage, and the values of the over-discharge protection voltage and the discharge termination voltage are determined according to the design of specific requirement parameters, which is not limited herein. The over-discharge protection voltage is, for example, 3 volts and the discharge termination voltage is 2 volts.
The following describes in detail the advantages of the preparation method of the lithium ion battery cell provided in the embodiment of the application in combination with other preparation methods of lithium ion battery cells:
in some other preparation methods of lithium ion battery cells, in the formation step, as shown in fig. 2, after the lithium ion battery cells are placed in the formation equipment, the lithium ion battery cells are heated and pressurized (S201) based on the formation equipment, the lithium ion battery cells are charged until the residual electric quantity (SOC) is greater than or equal to 50% or less than or equal to 100% (S202), the lithium ion battery cells generate an SEI film, then the lithium ion battery cells are cooled and depressurized (S203) based on the formation equipment, the lithium ion battery cells are taken out from the formation equipment, and finally the lithium ion battery cells are subjected to air extraction and encapsulation to obtain finished battery cells (S204).
However, this method can cause LiH in the SEI film to be formed during the formation process, and after formation, liH remains in the finished battery cell of the lithium ion battery cell, and the thermal stability and reliability of the finished battery cell need to be improved.
Illustratively, in the formation step of the lithium ion cell (i.e., in S202), the lithium ion cell is charged for the first time, wherein water participates in the reaction to generate hydrogen (H 2 ) Lithium intercalation graphite negative electrode (Li) x C 6 ) Absorption of H 2 The reaction produced the LiH. The presence of LiH components leads to a decrease in thermal stability and deterioration in reliability of the battery cell/cell.
Illustratively, as shown in equation 1 below, it is generally believed that LiH decomposes under abusive conditions (e.g., superheated conditions) to form Li molecules and H 2 A molecule. In addition, during the use of the lithium ion battery, heat generation is unavoidable (for example, the lithium ion battery is applied in a terminal device, and the lithium ion battery inevitably generates heat when the terminal device is operated at high power), which clearly provides reaction conditions for decomposition of LiH in the lithium ion battery core, and the decomposition of LiH generates H 2 On the one hand, if H is generated 2 The lithium ion battery can not be consumed in a short time, so that the heating and expansion of the lithium ion battery core can be further increased, and the service life of the lithium ion battery is shortened; on the other hand, if the temperature rise of the lithium ion battery core is diffused to the whole equipment, the service life of other parts in the whole equipment is also adversely affected, and in addition, the user is also adversely experienced.
In view of the above, the application provides a preparation method of a lithium ion battery cell, which can reduce the content of LiH in the prepared finished battery cell and improve the thermal stability and reliability of the finished battery cell.
In the preparation method of the lithium ion battery core, in the formation step or after the formation step and the capacity division step, the first lithium ion battery core which is charged for the first time is discharged to the target voltage, the discharged first lithium ion battery core is obtained, the target voltage is smaller than the decomposition voltage of LiH under the discharge condition, and the finished battery core is prepared based on the discharged first lithium ion battery core.
According to the preparation method of the lithium ion battery cell, in the process of discharging the first lithium ion battery cell, liH in the lithium ion battery cell is subjected to electrochemical decomposition, so that the content of LiH in the discharged first lithium ion battery cell is reduced compared with that of the first lithium ion battery cell, namely the content of LiH in a finished battery cell prepared based on the first lithium ion battery cell is reduced. Therefore, after the finished battery cell is applied to a lithium ion battery and the lithium ion battery is put into use (for example, after being applied to complete equipment), the lithium ion battery cell can improve the condition that LiH is decomposed to generate H due to the overheat decomposition of LiH in the charging process 2 Or can improve the condition of reaching the electrochemical decomposition voltage of LiH in the discharge process to lead the decomposition of LiH to generate H 2 And, improving H generated by decomposition of the LiH 2 Safety caused by heating expansion of lithium ion battery and shortening service life of lithium ion battery, and improving H generated by decomposition of LiH 2 The temperature rise of the lithium ion battery is diffused to the whole equipment, the problem that the service lives of other parts in the whole equipment are adversely affected is solved, and the use experience of a user in using the whole equipment containing the lithium ion battery is improved. In conclusion, the method provided by the application can improve the thermal stability, safety and reliability of the lithium ion battery cell.
In addition, the lithium ion battery core prepared by the preparation method of the lithium ion battery core provided by the application has the advantages that the discharge voltage of over-discharged gas production is reduced, and H in the over-discharged gas production component is reduced 2 The content is also reduced, and the thermal stability and the reliability of the lithium ion battery cell can be improved. It can be understood that if two lithium ion cells of the same specification, in which the lithium ion cell having relatively low LiH content is referred to as cell a and the lithium ion cell having relatively high LiH content is referred to as cell B, the cell a and the cell B are discharged to the same overdischarge voltage (overdischarge voltage is also the discharge voltage having a voltage less than the overdischarge protection voltage), the gas yield of the cell a will be less than the gas yield of the cell B, that is, the cell a prepared by the preparation method of the lithium ion cell provided by the application can be discharged to a lower voltage than the cell B without generating gas, that is, the discharge voltage of the cell a for overdischarge gas generation is reduced, and the gas generation component H is overdischarged 2 The content is also reduced, and the thermal stability and the reliability are better.
Furthermore, the LiH in the first lithium ion battery cell is subjected to electrochemical decomposition under the discharge condition, and Li is generated + And hydrogen to obtain Li in the lithium ion battery cell after discharge + Is based on the increase of the content after dischargeThe better the activity, the faster the charging speed and the higher the quality of the finished battery cell prepared by the first lithium ion battery cell.
In another possible implementation manner, in the method for preparing a lithium ion battery cell provided by the present application, the first lithium ion battery cell contains CO 2 In the process of discharging the first lithium ion battery cell to the target voltage, the LiH in the target lithium ion is electrochemically decomposed to generate Li + And after the discharged first lithium ion battery cell is obtained, charging the discharged first lithium ion battery cell, wherein in the charging process, the CO 2 Gas and Li + Electrochemical reaction under charging conditions to lithium carbonate (Li) 2 CO 3 ) The Li is 2 CO 3 Belongs to an important component in SEI film, and generates the Li 2 CO 3 The SEI film quality is improved, and the thermal stability and reliability of the finished battery cell are further improved.
In another possible implementation manner, the method for preparing a lithium ion battery cell according to the present application further includes, before charging the discharged first lithium ion battery cell, adding a gas (including CO 2 Gas) is extracted, thereby preventing the CO during the process of charging the discharged first lithium ion battery cell 2 Gas and Li + Electrochemical reaction under charging condition to generate Li 2 CO 3 . It can be appreciated that for lithium ion cells, li + The more the content of (C), the better the activity of the lithium ion battery cell, the faster the charging speed and the higher the quality, thereby preventing the CO 2 Gas and Li + Electrochemical reaction to Li 2 CO 3 Can effectively reduce Li in the first lithium ion battery cell + And the activity of the final finished battery cell is improved.
In another possible implementation, the target voltage further satisfies the following condition: the target voltage is greater than or equal to the cutoff voltage of the LiH in the first lithium ion battery cell which is completely decomposed under the discharge condition. According to the preparation method of the lithium ion battery cell, liH in the first lithium ion battery cell is decomposed in a large amount in the process of discharging the first lithium ion battery cell, so that the content of LiH in a finished battery cell after being put into use is further reduced, and the thermal stability and reliability of the lithium ion battery cell are improved.
Illustratively, in one possible implementation, the target voltage also satisfies the following condition: and the target voltage is equal to the cut-off voltage of the LiH in the first lithium ion battery cell which is completely decomposed under the discharge condition, so that the LiH in the lithium ion battery cell is completely decomposed or almost completely decomposed in the process of discharging the first lithium ion battery cell, and the obtained first lithium ion battery cell after discharging does not contain or almost does not contain LiH, so that the thermal stability and the reliability of the lithium ion battery cell are greatly improved.
In another possible implementation, the target voltage satisfies the following condition: the target voltage is less than the over-discharge protection voltage of the first lithium ion battery cell and greater than or equal to the discharge termination voltage of the first lithium ion battery cell.
Experimental measurement shows that the content of LiH in the lithium ion battery cell with the SOC of 100% is ten times as high as that in the lithium ion battery cell with the SOC of 0%, so that the target voltage is set to be smaller than the over-discharge protection voltage of the lithium ion battery cell and larger than or equal to the discharge termination voltage of the lithium ion battery cell, on one hand, a large amount of LiH in the first lithium ion battery cell can be subjected to electrochemical decomposition under the over-discharge condition, the content of LiH in a finished battery cell after the battery cell is put into use is reduced, and the thermal stability of the first lithium ion battery cell is improved; on the other hand, the first lithium ion battery core is ensured not to discharge to be lower than the discharge termination voltage, so that the function of protecting the internal functional structure of the first lithium ion battery core can be achieved, and other components in SEI are not damaged under the condition that LiH in the first lithium ion battery core is decomposed.
In one possible implementation manner, when the cut-off voltage is smaller than the discharge end voltage of the lithium ion battery cell, the target voltage may be smaller than or equal to the decomposition voltage of the lithium ion battery cell and larger than or equal to the discharge end voltage of the lithium ion battery cell.
Thus, in the case of decomposing LiH in the first lithium ion battery cell, other components in the SEI are not destroyed.
Example 1:
the following describes in detail the preparation method of the lithium ion battery cell provided by the application with reference to fig. 3. As shown in fig. 3, the method comprises the steps of:
s301, placing the first lithium ion battery cell in formation equipment, and heating and pressurizing the first lithium ion battery cell.
In the application, the first lithium ion battery cell refers to a lithium ion battery cell with complete functional structure, and the first lithium ion battery cell comprises a basic positive electrode level sheet, a basic negative electrode level sheet, an electrolyte and other functional structures.
It is understood that the formation device may provide the first lithium ion cell with an external circuit (charging circuit, discharging circuit) through which electrons in the first lithium ion cell are transferred between the positive electrode and the negative electrode, realizing a charging and discharging process of the first lithium ion cell, wherein during charging electrons may be moved from the positive electrode to the negative electrode through the external circuit, and during discharging electrons may be moved from the negative electrode to the positive electrode through the external circuit.
For example, after placing the first lithium ion cell in the formation device, the formation device may apply a first pressure to the first lithium ion cell and adjust the formation temperature to a first temperature. Wherein the first pressure is greater than or equal to 0.1 megapascals (MPa) and less than or equal to 5MPa, and the first temperature is greater than or equal to 25 degrees celsius (c) and less than or equal to 100 ℃. For example, the first pressure may be 1.5MPa, the first temperature may be 85 ℃, and other suitable values may be used according to specific designs and requirements, which is not limited herein.
For example, the first lithium ion battery cell is placed in a formation device, and specifically includes: the soft pack lithium ion cell (the first lithium ion cell) was placed in a clamping plate of a thermocompression forming apparatus, and a force of 1.5MPa was applied while heating to 85 ℃.
S302, the first lithium ion battery cell is charged for the first time, and the charged first lithium ion battery cell is obtained.
It can be appreciated that the first lithium ion cell is charged for the first time, i.e., a formation process in which the first lithium ion cell can form an SEI film containing lithium hydride on the negative electrode side, and with the generation of gas, the gas components include alkane, carbon dioxide (CO) 2 )、H 2 Etc.
In general, before the battery cell is subjected to air extraction and packaging to be a finished battery cell, an air bag is configured in the first lithium ion battery cell, and the air bag is contained in a packaging bag of the first lithium ion battery cell, for example, the material of the air bag can be an aluminum plastic film, and the material of the air bag is not limited herein. That is, in the formation step, the first lithium ion cell is provided with an air pocket, and the alkane and CO generated in the formation process 2 、H 2 The gas may be released (stored) in the gas bag.
For convenience of description herein, a state of charge (SOC) may be simply referred to as SOC.
Illustratively, the first charging of the first lithium-ion battery cell may be: and charging the first lithium ion battery cell for the first time based on the cut-off SOC. It is understood that the off SOC means that the charging is stopped when the remaining capacity of the first lithium ion battery cell is equal to the off SOC. For example, the first lithium ion battery cell is charged until the remaining electric power is equal to a first threshold (i.e., the cutoff SOC is the first threshold), which is greater than or equal to 50% and less than or equal to 100%. It is understood that for the amount of remaining charge of the lithium ion battery cell based on the theoretical design capacity, for example, 50% soc may be understood as 50% of the theoretical design capacity (total capacity) of the first lithium ion battery cell, before the actual capacity of the battery cell is determined without the capacity step.
For example, the first charging of the first lithium ion battery cell may be: and charging the first lithium ion battery cell for the first time based on the full voltage of the first lithium ion battery cell. For example, a first lithium ion battery cell is charged to a first voltage threshold that is less than or equal to a full charge voltage of the first lithium ion battery cell. For example, the full voltage of the lithium ion battery cell is 4.0V, and the first voltage threshold is greater than or equal to 3.8V and less than or equal to 4.0V. It can be understood that the full voltage of the battery cell and the SOC of the battery cell are only two different representations of the state of charge in the battery cell, the first lithium ion is charged for the first time, and the cutoff condition of the first charge can be determined based on the full voltage of the first lithium ion battery cell or based on the SOC of the battery cell, which is not limited herein.
Exemplary, the first charging based on the first lithium ion battery cell specifically includes: constant-current charging is carried out on the first lithium ion battery cell, wherein the current is greater than or equal to 0.01C and less than or equal to 5C; the first charge is turned off with a voltage, for example, when the charge voltage is equal to the first voltage threshold. Or the first charge is cut off by SOC, and the cut-off SOC is 50% or more and 100% or less.
Illustratively, first charging the first lithium-ion battery cell includes: and carrying out constant current charging on the first lithium ion battery cell in three steps, namely, first-step constant current charging, second-step constant current charging and third-step constant current charging.
The first step of constant current charging is used for pre-charging the first lithium ion battery, for example, the charging current of the first step of constant current charging can be greater than or equal to 0.1C and less than or equal to 0.2C, the first step of constant current charging can be stopped until the SOC of the first lithium ion battery core is greater than or equal to 3% and less than or equal to 20%,0.1C can also be read as 0.1 times of the product of the capacity of the first lithium ion battery core and the reciprocal of the hour, and C can be understood as the charging rate, and is used for representing the magnitude value of the current when the battery core is charged. For example, if the capacity of the first lithium ion cell is 1000 milliampere hours (mAh), then 0.1C is 100 milliampere hours (mA).
The second step of constant current charging may be understood as an adaptive phase of charging the first lithium ion battery cell with a larger current, for example, the charging current of the second step of constant current charging may be greater than or equal to 0.5C and less than or equal to 0.6C, and the second step of constant current charging may be stopped until the SOC of the first lithium ion battery cell is greater than or equal to 20% and less than or equal to 30%.
And thirdly, constant current charging is used for charging the first lithium ion battery cell with larger current. Illustratively, the charging current of the third-step constant current charging may be greater than or equal to 0.8C and less than or equal to 1C.
In one possible implementation manner, the SOC (target SOC) of the first lithium ion battery cell is recorded, and if in the third step of constant current charging, the SOC of the first lithium ion battery cell satisfies the condition of the target SOC before the charging voltage reaches 4.0V, the third step of constant current charging is stopped when the SOC of the first lithium ion battery cell reaches the target SOC.
In another possible implementation manner, the cut-off time of the third step of constant current charging is determined based on the current charging voltage, for example, if the current charging voltage is equal to the first voltage threshold, the charging is cut off, and the first lithium ion battery cell is obtained.
In another possible implementation manner, in the third step of constant current charging, after the charging voltage reaches the full-charge voltage of the first lithium ion battery cell, the charging of the first lithium ion battery cell is changed from the third step of constant current charging to the fourth step of constant voltage charging, where the constant voltage charging includes charging the first lithium ion battery cell with the full-charge voltage of the first lithium ion battery cell as a constant voltage, and stopping the charging after the charging current is reduced to 0.05C. The full charge voltage is 4.0V, the first lithium ion battery cell is charged by taking 4.0 as a constant charging voltage, and when the current is reduced to 0, the charging is stopped, so that the first lithium ion battery cell is obtained.
It will be appreciated that some of the above-described implementations for first charging the first lithium ion battery cell are merely examples, and that the first lithium ion battery cell may also be first charged by other suitable charging methods, which are not limited herein.
And S303, discharging the charged first lithium ion battery cell to a target voltage to obtain a discharged first lithium ion battery cell.
In the embodiment of the application, the target voltage is smaller than the decomposition voltage of the LiH under the charging condition, and the decomposition voltage refers to the voltage which can decompose the LiH in the first lithium ion battery cell after charging. The decomposition voltage may be a discharge voltage corresponding to a time point when LiH starts to decompose under the charging condition, and for example, the decomposition voltage may be an initial decomposition voltage or a maximum decomposition voltage of LiH; however, the decomposition voltage provided by the present application may be not only the initial decomposition voltage, but also any discharge voltage that can cause the LiH to undergo a decomposition reaction.
Exemplary, as shown in the following equation 2, in discharging the charged first lithium ion cell to the target voltage, liH in the negative electrode SEI film undergoes electrochemical decomposition to generate lithium ions (Li + ) Hydrogen (H) 2 ) And an electron (e) - ). Wherein H is 2 Can be released (stored) into the airbag.
In the embodiment of the present application, the target voltage may have the following two values (mode 1 and mode 2):
mode 1:
in one possible implementation, the target voltage may be determined based on an over-discharge protection voltage (over-discharge voltage) and/or a discharge termination voltage of the first lithium ion cell.
The target voltage is illustratively less than the overdischarge voltage of the first lithium ion cell and greater than or equal to the discharge termination voltage. For example, the overdischarge voltage of the lithium ion battery cell is generally 3.0V, and the discharge end voltage of the lithium ion battery cell is generally 2.0V, and the target voltage may have a value greater than or equal to 2.0V and less than or equal to 3.0V.
It should be noted that, determining the target voltage based on the overdischarge voltage of the first lithium ion battery cell is a reliable design made based on the experimental analysis result. By way of example, experimental measurements have found that as much as ten times the content of LiH in a 100% SOC lithium ion cell as in a 0% SOC lithium ion cell, it is reasonably speculated that LiH may be decomposed under discharge conditions, including over discharge conditions.
Therefore, the target voltage is set to be smaller than the over-discharge protection voltage of the first lithium ion battery cell and larger than or equal to the discharge termination voltage of the lithium ion battery cell, on one hand, a large amount of LiH (a large amount of LiH in LiH generated in the formation step of the lithium ion battery cell) can be subjected to electrochemical decomposition under the over-discharge condition, so that the content of LiH in a finished battery cell after being put into use is reduced, and the thermal stability and reliability of the first lithium ion battery cell are improved; on the other hand, the lithium ion battery core is ensured not to discharge to be lower than the discharge termination voltage, and the effect of protecting the lithium ion battery core structure can be achieved.
For example, assuming that the full voltage of the first lithium ion battery cell is equal to 4.0V, the over-discharge protection voltage is 3.0V, and the discharge cutoff voltage is 2.0V, an implementation manner of the preparation method of the lithium ion battery cell provided by the application may be as shown in fig. 4, and specifically includes: s401, heating and pressurizing the first lithium ion battery cell; s402, charging the first lithium ion battery to 3.8V-full voltage (or charging the first lithium ion battery core to 50-100% SOC); s403, discharging the first lithium ion battery cell to a certain voltage within 2.0V-3.0V, and decomposing LiH to generate Li + And H 2 The method comprises the steps of carrying out a first treatment on the surface of the S404, recharging the first lithium ion battery cell to 3.8V-full voltage (or charging the first lithium ion battery cell to 50% -100% SOC); s405, cooling and releasing pressure on the first lithium ion battery cell, and taking out the formed first lithium ion battery cell; s406, carrying out air extraction packaging on the first lithium ion battery cell to obtain a finished battery cell.
Mode 2:
in another possible implementation manner, if the decomposition voltage of LiH under the discharge condition is clear, the target voltage is smaller than the decomposition voltage of lithium hydride, and/or if the cutoff voltage of the LiH in the 'first lithium ion cell' obtained in the above step S302, which is completely decomposed under the charge condition, is clear, the target voltage is also greater than or equal to the cutoff voltage.
In the embodiment of the application, the decomposition voltage refers to the highest decomposition voltage that LiH can be electrochemically decomposed to generate lithium ions and hydrogen under the decomposition voltage, but does not represent the decomposition voltage. Illustratively, liH can be electrochemically decomposed under discharge conditions of 3V, 2.8V, and 2.6V, and then 3V, 2.8V, or 2.6V can be used as the decomposition voltage of LiH.
For example, if the highest decomposition voltage of LiH under the discharging condition is 3.3V, and the cutoff voltage of LiH in the 'first lithium ion battery cell' that is completely decomposed under the charging condition is 2.5V, the target voltage may have a value less than 3.3V and greater than or equal to 2.5V.
It can be understood that even if the cutoff voltage for completely decomposing the LiH can be clarified, the target voltage may be set to a specific value between less than the decomposition voltage and greater than the cutoff voltage, for example, the decomposition voltage is 3.3V, the cutoff voltage is 2.5V, and the target voltage may be 2.8V, so that a large amount of LiH is decomposed, and at the same time, irreversible or unpredictable damage of the cell caused by too low discharge voltage can be avoided.
In one possible implementation manner, an exemplary method for determining a decomposition voltage of LiH under a discharge condition according to an embodiment of the present application is described in detail with reference to fig. 5. As shown in fig. 5, the method includes:
s501, N groups of second lithium ion batteries are obtained, wherein the second lithium ion batteries contain lithium hydride, and the second lithium ion batteries do not contain hydrogen.
The second lithium ion battery cell may be a lithium ion finished battery cell prepared by a preparation method of other lithium ion battery cells except the preparation method of the lithium ion battery cell provided by the application. For example, the second lithium ion battery cell may be a lithium ion battery cell obtained by performing formation by using a preparation method of other lithium ion battery cells and performing air extraction. For example, the second lithium ion battery cell may be a lithium ion battery cell formed by adopting other preparation methods of lithium ion battery cells, and subjected to capacity division and air extraction. The capacity division refers to analyzing capacity, and the capacity division step specifically includes that the formed battery cell is charged and discharged according to design standards so as to measure the actual capacitance of the battery cell.
Exemplary, the acquiring N groups of second lithium ion battery cells includes: acquiring N groups of second lithium ion battery cells, wherein the second lithium ion battery cells are not charged for the first time, and each group of lithium ion battery cells in the N groups of second lithium ion battery cells at least comprises one second lithium ion battery cell; performing first charging on each of the N groups of second lithium ion battery cells based on the full charge voltage of the second lithium ion battery cell (the charging manner of the first charging may refer to other related descriptions herein, for example, related descriptions in step S302) to obtain N groups of charged second lithium ion battery cells, where each of the N groups of charged second lithium ion battery cells includes lithium hydride; and extracting the gas in the N groups of charged second lithium ion batteries to obtain N groups of extracted second lithium ion batteries, and taking the N groups of extracted second lithium ion batteries as the N groups of second lithium ion batteries.
Illustratively, the second lithium ion battery cell may also be: and (3) pumping the first lithium ion battery cell obtained in the step S302 to obtain a pumped lithium ion battery cell.
In the embodiment of the application, the second lithium ion battery cell is an experimental battery cell for measuring the decomposition voltage and the cut-off voltage of complete decomposition of LiH, and the first lithium ion battery cell is a battery cell in the preparation process of practical application. That is, the above N groups of second lithium ion cells can be understood as experimental groups.
In one possible implementation manner, in order to maintain the uniqueness of the experimental variable, the second lithium ion battery cell and the first lithium ion battery cell belong to a lithium ion battery cell with the same specification, and a charging parameter of the first charging of the second lithium ion battery cell is consistent with a charging parameter of the first charging of the first lithium ion battery cell, where the charging parameter includes: the pressure value and the temperature value applied by the formation equipment to the lithium ion battery cell, the design of the charging steps, and the charging current and the charging cut-off condition of each charging step.
It is understood that the cut-off voltage corresponding to the complete decomposition of LiH is mainly related to the content of LiH contained in the cell, i.e. to the content of LiH generated in the formation step, which is mainly related to the specifications of the cell and to the charging parameters used in the formation process. Therefore, if the second lithium ion battery cell and the first lithium ion battery cell belong to the lithium ion battery cell with the same specification, and the charging parameter of the first charging of the second lithium ion battery cell is consistent with the charging parameter of the first charging of the first lithium ion battery cell, the value of the cut-off voltage obtained through experiments can be more accurate.
S502, discharging each group of second lithium ion battery cells of the N groups of second lithium ion battery cells respectively, and stopping discharging until different discharging voltages are reached, so that N groups of discharged second lithium ion battery cells are obtained.
In the embodiment of the present application, N is a positive integer greater than or equal to 3. The discharge voltages of the N groups of second lithium ion battery cells are gradually decreased, and the discharge voltages of the N groups of second lithium ion battery cells are all larger than or equal to preset voltage which is larger than 0V. For example, the minimum value of the preset voltage may also be determined based on the discharge end voltage of the second lithium ion battery cell, for example, the discharge end voltage of the second lithium ion battery cell is 2V, and the preset voltage is greater than 2V.
In one possible implementation, the discharge voltage is less than or equal to an over-discharge protection voltage of the lithium ion battery cell and less than or equal to a discharge termination voltage of the lithium ion battery cell.
For example, N has a value of 11, the over-discharge protection voltage of the lithium ion battery cell is 3.0V, the discharge termination voltage is 2.0V, and the discharge voltages corresponding to the second lithium ion battery cells of the 11 groups are 3.0V, 2.9V, 2.8V, 2.7V, 2.6V, 2.5V, 2.4V, 2.3V, 2.2V, 2.1V, and 2.0V in order.
It can be understood that the N groups of second lithium ion cells are respectively discharged to different discharge voltages, so as to clearly determine the change condition of LiH in the lithium ion cells after being discharged to different discharge voltages.
And S503, determining the volume of hydrogen in each set of discharged second lithium ion battery cells of the N sets of discharged second lithium ion battery cells based on a drainage method and a gas chromatography measurement method, and obtaining N volume quantities.
Illustratively, the gassing volume V of each set of discharged second lithium ion cells was measured using a drainage method. And measuring the gas generating components of each group of electric cells by Gas Chromatography (GC) to obtain the specific gravity A (H2) of H2 in the total gas generation.
Wherein, the gas production volume of H2 is: the product of the product gas volume V and the specific gravity a (H2), i.e. v×a (H2).
It can be appreciated that during the first charge of the lithium ion cell, the water in the electrolyte is consumed (almost completely consumed) to produce H 2 . In addition, generally, water in the electrolyte is consumed once during the first charge. And the second lithium ion battery cell does not contain H 2 In step S503, H is measured for the discharged second lithium ion battery cell 2 Does not contain H generated by water consumption during the first charging of the lithium ion battery cell 2 Therefore, the measurement data can be more accurate, and the value corresponding to the determined decomposition voltage of the lithium hydride is more accurate.
S504, a first volume is determined, which is a minimum volume among the N volumes that is greater than 0, and a maximum voltage among at least one discharge voltage corresponding to the first volume is taken as a first voltage.
In an embodiment of the application, the first voltage is used to represent the decomposition voltage of lithium hydride.
It is understood that the minimum volume is greater than 0, indicating that the discharge voltage of the experimental group corresponding to the minimum volume may be used to represent the decomposition voltage of lithium hydride. For example, the first voltage is used to represent the decomposition voltage of LiH, but it does not necessarily represent the first voltage as the initial decomposition voltage of LiH, and in an actual scenario, the initial decomposition voltage of LiH may be greater than or equal to the first voltage, which is not limited in the present application.
In one possible implementation manner, the method for determining the decomposition voltage of LiH under the discharge condition further includes:
s505, determining a second volume, wherein at least two groups of the second volume are contained in N volumes, and the second volume is the largest volume in the N volumes; the maximum voltage of the at least one discharge voltage corresponding to the second volume is taken as a second voltage. The second voltage is used to represent the cut-off voltage for complete decomposition of lithium hydride in the second lithium ion cell.
It can be understood that the discharge voltage corresponding to the volume amount of the hydrogen, that is, v×a (H2), starting to reach the stable maximum value is the cut-off voltage for completely decomposing the lithium hydride in the second lithium ion battery cell. Thereby making it
In one possible implementation manner, if the N volumes are all greater than 0 and equal, the initial decomposition voltage of LiH is greater than the maximum voltage of the discharge voltages corresponding to the N volumes, and the cutoff voltage of complete decomposition of LiH is also greater than the maximum voltage of the discharge voltages corresponding to the N volumes. In this case, the first voltage and the second voltage may be determined as the maximum voltage among the discharge voltages corresponding to the N volumes, for example, the 3.0V. Alternatively, another N experimental groups may be started again, and different discharge voltages may be reset to measure the decomposition voltage of LiH in the second lithium ion battery cell and the cutoff voltage of complete decomposition of LiH in the second lithium ion battery cell, which is not limited herein.
In the embodiment of the present application, based on the mode 2, the target voltage may be smaller than the decomposition voltage of LiH and greater than or equal to the cutoff voltage of the complete decomposition of LiH in the battery cell.
It will be appreciated that in some possible implementations, the above-mentioned modes 1 and 2 may also be implemented in combination, which is not limited herein.
For example, if the cutoff voltage (second voltage) of the LiH completely decomposed is smaller than the discharge end voltage of the battery cell, for example, the second voltage is smaller than the discharge end voltage by 2.0V, the decomposition voltage (first voltage) of the LiH is smaller than the over-discharge protection voltage, for example, the first voltage by 2.5V is smaller than the over-discharge protection voltage by 3.0V, the target voltage is greater than or equal to the discharge end voltage and is smaller than the first voltage.
In one possible implementation, the specific value of the target voltage is determined based on the second voltage and the discharge end voltage. For example, if the second voltage is less than or equal to the discharge end voltage, the target voltage takes on the value of the discharge end voltage; if the second voltage is greater than the discharge end voltage, the target voltage takes the value of the second voltage.
Therefore, under the condition that LiH in the first lithium ion battery core is decomposed, the first lithium ion battery core is not discharged to be lower than the discharge termination voltage, the effect of protecting the lithium ion battery core structure is achieved, and the lithium ion battery core structure can be understood as ensuring that LiH can be electrochemically decomposed and other SEI components are not damaged.
And S304, carrying out secondary charging on the discharged first lithium ion battery cell to obtain the second charged first lithium ion battery cell.
Illustratively, charging the discharged first lithium-ion battery cell includes: and charging the discharged first lithium ion battery cell until the residual electric quantity of the battery cell is equal to a first threshold value, wherein the first threshold value is more than or equal to 50% and less than or equal to 100%.
In one possible implementation, the discharged first lithium ion battery cell may be charged with a charging current greater than the charging current used in the stage corresponding to the first charging in step S302 at each stage of charging the discharged first lithium ion battery cell. For example, the charging current may be greater than or equal to 0.2C and less than or equal to 5C.
For example, the discharged first lithium ion battery cell may be charged in three stages. In the first stage, the battery cell is charged with a constant current with a smaller current (for example, 0.2C), and the charge cut-off state is that the SOC of the battery cell is more than or equal to 5%; in the second stage, the battery core is subjected to constant current charging by a larger current (for example, 5C), and the charging cut-off state is full-power voltage; and in the third stage, constant voltage charging is carried out on the battery cell, and when the charging current is about 0, the charging is stopped.
The specific manner of charging the discharged first lithium ion battery cell may also refer to the description of the first charging of the first lithium ion battery cell in step S302, which is not described in detail herein.
In the embodiment of the present application, in the process of charging the discharged first lithium ion battery cell in step S304, li generated in step S303 is represented by the following equation 3 + And e - Can be combined with CO under charging condition 2 Electrochemical reaction takes place on the negative electrode side to produce lithium carbonate (Li 2 CO 3 )。
In addition, referring to equation 4, for example, the corresponding equation after trimming of equation 3 may be as shown in equation 4 below. I.e. Li + And e - Can be combined with CO under charging condition 2 Electrochemical reaction on the negative electrode side to produce Li 2 CO 3 And carbon monoxide (CO) gas, wherein the generated CO may be released (stored) into the gas bag.
Illustratively, based on equation 2 above, during the process of discharging the first lithium ion cell to the target voltage in step S303, liH in the negative electrode SEI film is electrochemically decomposed to generate li+, H2, and e-. Wherein, under discharge conditions, the li+ can be transferred from the negative side to the positive side of the cell through the electrolyte, and e-can be transferred from the negative side to the positive side of the cell through the external circuit. While under the charging condition of step S304, the li+ and e-are transferred from the positive side to the negative side of the cell, and based on the charging condition, the li+ and e-electrochemically react with CO2 at the negative electrode to generate Li2CO3.
In another possible implementation manner, in the above step S303, li+ and e-in the negative electrode side are transferred to the positive electrode in large amounts under the discharge condition, and li+ and e-in the negative electrode exist in small amounts, and at this time, li+ and e-and CO2 may also be slowly chemically reacted on the negative electrode side and Li2CO3 is generated, which is not limited herein. However, under the discharge condition of step S303, the chemical reaction of li+ and e-and CO2 on the negative electrode side under the condition of not having the charge condition (which can be also understood as electrochemical reaction) is relatively slow, and the li+ and e-and CO2 react to form Li2CO3, mainly under the charge condition of step S304.
In the embodiment of the present application, the step S304 of secondary charging the discharged first lithium ion battery cell mainly has the following two purposes: 1) The lithium ion battery cell obtained after secondary charging can meet the basic electric quantity requirement of a finished battery cell (or can be understood as meeting the shipment state). 2) And the Li+ reacts with the e-and CO2 to generate Li2CO3, wherein the Li2CO3 belongs to lithium alkyl carbonate (ROCO 2 Li) in the SEI film, and the generation of the Li2CO3 is beneficial to improving the quality of the SEI film.
It should be noted that, since the first lithium ion battery cell after the above-mentioned discharge is charged for the first time, a complete SEI film is generated, and the SEI film may protect li+, for example, the generation of the SEI film may reduce the contact area between li+ and gas, and slow down (or inhibit) the reverse reaction between li+ and H2 during the secondary charging in step S304 to regenerate LiH. That is, even if li+ and H2 undergo a reverse reaction in step S304, the content of LiH generated by the reverse reaction is far lower than that of LiH decomposed electrochemically in step S303, so that the content of LiH in the final product cell finally prepared as a whole is reduced, thereby achieving the effect of improving the stability and reliability of the lithium ion cell.
And S305, taking the second charged first lithium ion battery cell out of the formation equipment to obtain the formed first lithium ion battery cell.
The reduction of the formation clamping plate in the formation equipment is 0, the formation temperature is reduced to the room temperature, and the second charged first lithium ion battery cell is taken out of the formation equipment to obtain the formed lithium ion battery cell.
S306, carrying out air extraction packaging on the first lithium ion battery cell after formation, and cutting off the air bag to obtain a finished battery cell.
It will be appreciated that the gas in the air bag prior to evacuation may include alkanes, CO 2 And H 2 Etc.
It can be understood that the above-mentioned air extraction packaging of the lithium ion battery cell after formation includes: and (3) extracting gas in the air bag and extracting gas contained in the lithium ion battery cell after the formation.
In another possible implementation manner, after the step S305 and before the step S306, the method for preparing a lithium ion battery cell further includes: and carrying out capacity division on the lithium ion battery core after the formation to obtain the lithium ion battery core after capacity division. And, above-mentioned carry on the encapsulation of bleeding to lithium ion battery cell after forming specifically includes: and carrying out air extraction packaging on the separated lithium ion battery cell. The capacity division refers to analysis capacity, specifically, the formed battery cell is charged and discharged according to design standards so as to measure the capacitance of the battery cell.
For example, the capacity of the lithium ion battery cell after the formation may be: charging the lithium ion battery cell to 100% SOC with a preset current, discharging the lithium ion battery cell to 0% SOC with the preset current, and charging the lithium ion battery cell to 50% SOC with the preset current again.
For example, the preset current is 0.5C, and the capacity division of the lithium ion battery cell after the formation specifically includes: the lithium ion cell is charged to 100% soc at a charge current of 0.5C and discharged to 0% soc at 0.5C and then charged to 50% soc at 0.5C under conditions of 25 ℃ or more and 45 ℃ or less, and the capacity of the lithium ion cell after formation is determined based on the required charge time for 100% soc to 0% soc and the required discharge time for 0% soc to 50% soc.
It can be appreciated that H is generated due to electrochemical decomposition of LiH in the first lithium ion cell under discharge conditions of target voltage 2 And during charging (including primary charging in S302 and secondary charging in S304) and discharging (including discharging operation in S303 and discharging operation in the above-described capacity-dividing operation) of the lithium ion battery cell, H is not eliminated 2 Other gases than (e.g. alkanes, CO 2 CO, etc.) are generated. If the gas exists in the internal structure of the lithium ion battery core, adverse effects such as potential expansion and heating are brought to the lithium ion battery core, and the gas bag arranged in the lithium ion battery core can temporarily store the gas, so that the potential expansion and heating problems are improved.
In view of this, the preparation method of lithium ion battery cells provided by the application does not dismantle the air bag before completing formation to obtain the lithium ion battery cells after formation or before completing capacity division to obtain the lithium ion battery cells after capacity division, but cuts the air bag after completing formation and capacity division steps, so that the lithium ion battery cells are electrochemically decomposed to reduce the content of the lithium ion battery cells, and meanwhile, the hydrogen generated by the decomposition of the lithium ion battery cells is prevented from bringing adverse effects to the internal structure of the lithium ion battery cells.
Example 2:
in another method for preparing a lithium ion battery cell provided by the present application, before the step S304 of secondary charging the discharged first lithium ion battery cell, the method further comprises the step of charging the gas (including CO 2 Gas) is extracted, thereby preventing the CO from being generated during the secondary charging of the discharged first lithium ion battery cell 2 Gas and Li + Electrochemical reaction under charging condition to generate Li 2 CO 3 。
Referring to fig. 6, another method for preparing a lithium ion battery cell according to the present application is described in detail, as shown in fig. 6, the method includes:
s601, placing the first lithium ion battery cell in formation equipment, and heating and pressurizing the first lithium ion battery cell.
In an embodiment of the present application, the first lithium ion battery cell is configured with an air pocket.
Reference is specifically made to the relevant description of step 301 in fig. 3, which is not described in detail here.
S602, the first lithium ion battery cell is charged for the first time, and the charged first lithium ion battery cell is obtained.
The first lithium ion cell is subjected to formation process, wherein the first lithium ion cell can generate SEI film on the negative electrode side, the SEI film contains LiH, and gas is generated in the process, and the gas comprises alkane and CO 2 、H 2 Etc., the generated gas may be released into the airbag.
Reference is specifically made to the description of step S302 in fig. 3, and details thereof will not be described here.
And S603, discharging the charged first lithium ion battery cell to a target voltage to obtain a discharged first lithium ion battery cell.
In the embodiment of the application, the target voltage is smaller than the decomposition voltage of LiH under the charging condition. The specific values refer to the description related to step S303 in fig. 3, and will not be described in detail herein.
Discharging the first lithium ion battery cell to a target voltage, wherein the purpose is to enable LiH in the SEI film to be subjected to electrochemical decomposition to generate Li + And H 2 . Wherein H is 2 Can be released into the air bag.
Therefore, the LiH in the first lithium ion battery cell is subjected to electrochemical decomposition in the discharging process, the content of LiH in the finished battery cell after being put into use is reduced, and the thermal stability and the reliability of the lithium ion battery cell are improved.
S604, pre-pumping and packaging the discharged first lithium ion battery cell, pumping out gas in the air bag and in the internal structure of the discharged first lithium ion battery cell, and obtaining the pumped first lithium ion battery cell.
It can be understood that the first lithium ion battery core after discharge is pre-pumped and packaged, and the alkane, CO2 and H stored in the air bag can be pumped out 2 Such gases, and gases that are extracted from the interior of the lithium ion cell structure, e.g., the hydrocarbons, CO2, H, that diffuse in the electrolyte and electrodes 2 And (3) waiting for gas.
Therefore, on one hand, the problem that the gas in the gas bag or the discharged lithium ion battery core is subjected to further electrochemical reaction or chemical reaction with the negative electrode active material of the lithium ion battery core in the subsequent preparation process to reduce the activity of the lithium ion battery core can be solved. Illustratively, CO can be reduced in the subsequent preparation process 2 With Li + Reaction to form Li 2 CO 3 Active lithium in the lithium ion cell is consumed. On the other hand, H in the subsequent preparation process can be avoided 2 With Li + LiH is generated by the secondary reaction, so that the content of LiH in the final prepared finished battery cell can be further reduced, and the thermal stability and reliability of the lithium ion battery cell are further improved.
And S605, carrying out secondary charging on the first lithium ion battery cell after air extraction to obtain the first lithium ion battery cell after secondary charging.
It can be understood that, in the embodiment of the present application, the purpose of the step S605 of recharging the first lithium ion battery cell after the air extraction is to make the lithium ion battery cell obtained after the recharging meet the basic electric quantity requirement of the finished battery cell (or can be understood as meeting the shipment status as well).
For the charging current used for secondary charging of the evacuated first lithium-ion battery cell, reference is made to the description related to step S304, and will not be described in detail herein.
In the embodiment of the present application, before the secondary charging of the first lithium ion battery cell and the extraction of the gas in the gas pocket in the first lithium ion battery cell and the gas in the first lithium ion battery cell, li generated in the step S603 is generated during the secondary charging of the extracted first lithium ion battery cell + And CO generated in the above step S602 2 Does not generate electrochemical reaction or chemical reaction, thereby effectively reducing Li in the first lithium ion battery cell + And the activity of the final finished battery cell is improved.
And S606, taking the second charged first lithium ion battery cell out of the formation equipment, carrying out air extraction packaging on the formed first lithium ion battery cell, and cutting off the air bag to obtain a finished product battery cell.
Reference is specifically made to the descriptions related to steps S305 to S306 in embodiment 2, and detailed description thereof will not be given here.
In another possible implementation manner, the steps S605 to S606 may be directly performed instead of the step S607 to S608 performed on the first lithium ion battery cell after the air extraction, where S607, the second charged first lithium ion battery cell is taken out from the formation device, and the capacity-dividing operation is performed on the first lithium ion battery cell after the air extraction, so as to obtain the capacity-divided lithium ion battery cell. And S608, carrying out air extraction packaging on the separated lithium ion battery cell, and cutting off the air bag to obtain a finished product battery cell.
It can be appreciated that H is generated due to electrochemical decomposition of LiH under discharge conditions of target voltage 2 If the gas exists in the internal structure of the lithium ion battery cell, the gas can have adverse effects on the lithium ion battery cell, such as potential expansion and heating. Discharging the lithium ion battery cell to a small value At a decomposition voltage of LiH and greater than or equal to a cutoff voltage of complete decomposition of LiH, and/or at a discharge cutoff voltage of lithium ion battery cell and greater than or equal to an overdischarge protection voltage of lithium ion battery cell, a large amount of LiH may be decomposed to generate a large amount of H 2 . In view of this, the present application is to execute the preparation method of the lithium ion battery cell provided by the present application on the lithium ion battery cell configured with the air bag, and it can also be understood that the preparation method of the lithium ion battery cell provided by the present application can be applied to the lithium ion battery cell obtained in the preparation process of the lithium ion battery cell without cutting the air bag.
In another possible implementation manner, the method for preparing a lithium ion battery cell according to the embodiment of the present application is also applicable to a lithium ion battery cell after formation and capacity division, that is, the steps S603 and S605 may be performed after the step S608, which is not limited herein.
Example 3:
by way of example, a specific implementation of the method for preparing a lithium ion battery cell according to embodiment 1 is described in detail below with reference to fig. 7.
As shown in fig. 7, the preparation method of the lithium ion battery cell specifically includes:
s701, placing the soft package lithium ion battery cell in a clamping plate of hot press forming equipment, applying 1.5MPa force, and simultaneously heating to 85 ℃.
In the embodiment of the application, the lithium ion battery core is not charged for the first time, and the lithium ion battery core is provided with an air bag.
S702, carrying out constant-current charging on the lithium ion battery cell in three steps, wherein the current of each step is respectively 0.2C, 0.6C and 1.0C, controlling the formation time of each step, and finally charging to 80% of SOC to stop charging.
It can be understood that the charging process in the step S702 is a formation process, and a good SEI film can be formed on the negative electrode of the lithium ion battery cell, during which gas components including alkane, CO2, H2, and the like are generated, and the gas components can be released into the air bag.
And S703, discharging the lithium ion battery core to 2.0V at 0.2C, so that the LiH component in the SEI film is subjected to electrochemical decomposition, and H2 is generated and released into the air bag.
In the embodiment of the application, the 2.0V is smaller than or equal to the over-discharge protection voltage of the lithium ion battery core and larger than or equal to the discharge cut-off voltage of the lithium ion battery core, or the 2.0V is smaller than or equal to the highest decomposition voltage of the LiH under the discharge condition and larger than or equal to the cut-off voltage of the LiH in the lithium ion battery core.
For example, the over-discharge protection voltage of the lithium ion battery cell is 3.0V, and the discharge cut-off voltage is 1.0V, that is, 2.0V of the above-mentioned discharging of the lithium ion battery cell to 2.0V at 0.2C is smaller than 3.0V and larger than 1.0V.
For example, the highest decomposition voltage of LiH under the discharge condition is 3.5V, and the cutoff voltage for completely decomposing LiH in the lithium ion cell is 2.0V, that is, the above-mentioned cutoff voltage for completely decomposing LiH by discharging the lithium ion cell to 2.0V at 0.2C is equal to 2.0V.
Thus, liH in the lithium ion cell undergoes electrochemical decomposition during discharge (Li generation) + And H 2 ) The LiH content in the finished battery cell after being put into use is reduced, and the thermal stability and reliability of the lithium ion battery cell are improved.
S704, recharging the lithium ion battery cell to 80% SOC at 1.0C.
During recharging of the lithium ion cell, CO in the air pocket or inside the lithium ion cell structure under charged conditions 2 Li capable of being attached to negative electrode side + Reaction to form Li 2 CO 3 The quality of the SEI film of the negative electrode in the lithium ion battery cell is improved.
In addition, the lithium ion battery cell is charged to 80% of SOC, so that the lithium ion battery cell can meet the basic shipment electric quantity of the finished battery cell.
And S705, reducing the pressure of the hot-press formation clamping plate to 0, reducing the temperature to room temperature, and taking out the lithium ion battery core to obtain the formed lithium ion battery core.
S706, carrying out air extraction packaging on the formed battery cell to obtain a finished battery cell.
The meanings of some terms related in embodiment 3 may refer to the relevant descriptions of other embodiments herein, and will not be described in detail herein.
Example 4:
by way of example, still another specific implementation of the preparation method of the lithium ion battery cell provided in the above embodiment 1 or embodiment 2 is described in detail below with reference to fig. 8.
As shown in fig. 8, the preparation method of the lithium ion battery cell specifically includes:
s801, placing the soft package lithium ion battery cell in a clamping plate of hot press forming equipment, applying 1.5MPa force, and heating to 85 ℃.
In the embodiment of the application, the lithium ion battery core is not charged for the first time, and the lithium ion battery core is provided with an air bag.
S802, carrying out constant-current charging on the lithium ion battery core in three steps, wherein the current of each step is respectively 0.2C, 0.6C and 1.0C, controlling the formation time of each step, and finally charging to 80% of SOC to stop charging.
It can be understood that the charging process in the step S802 is a formation process, and a good SEI film can be formed on the negative electrode of the lithium ion battery cell, during which gas components including alkane, CO2, H2, and the like are generated, and the gas components can be released into the air bag.
S803, discharging the lithium ion battery core to 2.0V at 0.2C, so that the LiH component in the SEI film is subjected to electrochemical decomposition, and H2 is generated and released into the air bag.
In the embodiment of the application, the 2.0V is smaller than or equal to the over-discharge protection voltage of the lithium ion battery core and larger than or equal to the discharge cut-off voltage of the lithium ion battery core, or the 2.0V is smaller than or equal to the highest decomposition voltage of the LiH under the discharge condition and larger than or equal to the cut-off voltage of the LiH in the lithium ion battery core.
For example, the over-discharge protection voltage of the lithium ion battery cell is 3.0V, and the discharge cut-off voltage is 1.0V, that is, 2.0V of the above-mentioned discharging of the lithium ion battery cell to 2.0V at 0.2C is smaller than 3.0V and larger than 1.0V.
For example, the highest decomposition voltage of LiH under the discharge condition is 3.5V, and the cutoff voltage for completely decomposing LiH in the lithium ion cell is 2.0V, that is, the above-mentioned cutoff voltage for completely decomposing LiH by discharging the lithium ion cell to 2.0V at 0.2C is equal to 2.0V.
Thus, liH in the lithium ion cell undergoes electrochemical decomposition during discharge (Li generation) + And H 2 ) The LiH content in the finished battery cell after being put into use is reduced, and the thermal stability and reliability of the lithium ion battery cell are improved.
S804, pre-pumping and packaging the lithium ion battery cell, pumping out gas in the gas bag, and not cutting off the gas bag of the lithium ion battery cell.
It can be understood that the lithium ion battery cell is pre-pumped and packaged, and the gas (including the alkane, CO2, H2 and the like) in the air bag is pumped, so that the gas can be prevented from further electrochemical reaction or chemical reaction with the negative electrode active material of the lithium ion battery cell in the subsequent preparation process.
Illustratively, CO can be reduced in the subsequent preparation process 2 With Li + Reaction to form Li 2 CO 3 Active lithium in the lithium ion cell is consumed. Illustratively, H can also be avoided during subsequent preparation 2 With Li + And reacting again to generate LiH. Therefore, the LiH can be decomposed, the thermal stability and the reliability of the lithium ion battery cell can be improved, and the activity of the lithium ion battery cell can be improved.
It can be understood that after the lithium ion battery cell is pre-pumped and packaged, the air bag of the lithium ion battery cell is not cut off, so that the air bag can store generated gas in the subsequent preparation process, and the risk of potential expansion and explosion of the lithium ion battery cell is avoided.
S805, recharging the lithium ion cell to 80% soc at 1.0C.
It can be appreciated that charging the lithium ion battery cell to 80% soc can cause the lithium ion battery cell to meet the basic shipment power of the finished battery cell.
S806, the pressure of the formation clamping plate is reduced to 0, the temperature is reduced to room temperature, and the lithium ion battery core is taken out, so that the lithium ion battery core after formation is obtained.
S807, carrying out air extraction packaging on the formed battery cell, and cutting off the air bag to obtain a finished battery cell.
The meanings of some terms related in embodiment 3 may refer to the relevant descriptions of other embodiments herein, and will not be described in detail herein.
Example 5:
by way of example, still another specific implementation of the method for preparing a lithium ion battery cell according to embodiment 2 is described in detail below with reference to fig. 9.
As shown in fig. 9, the preparation method of the lithium ion battery cell specifically includes:
s901, placing the soft package lithium ion battery cell in a clamping plate of hot press forming equipment, applying 1.5MPa force, and simultaneously heating to 85 ℃.
In the embodiment of the application, the lithium ion battery core is not charged for the first time, and the lithium ion battery core is provided with an air bag.
S902, carrying out constant-current charging on the lithium ion battery core in three steps, wherein the current of each step is respectively 0.2C, 0.6C and 1.0C, controlling the formation time of each step, and finally charging to 80% of SOC to stop charging.
It can be understood that the charging process in the step S902 is a formation process, and a good SEI film can be formed on the negative electrode of the lithium ion battery cell, during which gas components including alkane, CO2, H2, and the like are generated, and the gas components can be released into the air bag.
S903, discharging the lithium ion battery core to 2.0V at 0.2C, so that the LiH component in the SEI film is subjected to electrochemical decomposition, and H2 is generated and released into the air bag.
In the embodiment of the application, the 2.0V is smaller than or equal to the over-discharge protection voltage of the lithium ion battery core and larger than or equal to the discharge cut-off voltage of the lithium ion battery core, or the 2.0V is smaller than or equal to the highest decomposition voltage of the LiH under the discharge condition and larger than or equal to the cut-off voltage of the LiH in the lithium ion battery core.
For example, the over-discharge protection voltage of the lithium ion battery cell is 3.0V, and the discharge cut-off voltage is 1.0V, that is, 2.0V of the above-mentioned discharging of the lithium ion battery cell to 2.0V at 0.2C is smaller than 3.0V and larger than 1.0V.
For example, the highest decomposition voltage of LiH under the discharge condition is 3.5V, and the cutoff voltage for completely decomposing LiH in the lithium ion cell is 2.0V, that is, the above-mentioned cutoff voltage for completely decomposing LiH by discharging the lithium ion cell to 2.0V at 0.2C is equal to 2.0V.
Thus, liH in the lithium ion cell undergoes electrochemical decomposition during discharge (Li generation) + And H 2 ) The LiH content in the finished battery cell after being put into use is reduced, and the thermal stability and reliability of the lithium ion battery cell are improved.
S904, pre-pumping and packaging the lithium ion battery cell, pumping out gas in the gas bag, and not cutting off the gas bag of the lithium ion battery cell.
It can be understood that the lithium ion battery cell is pre-pumped and packaged, and the gas (including the alkane, CO2, H2 and the like) in the air bag is pumped, so that the gas can be prevented from further electrochemical reaction or chemical reaction with the negative electrode active material of the lithium ion battery cell in the subsequent preparation process.
Illustratively, CO can be reduced in the subsequent preparation process 2 With Li + Reaction to form Li 2 CO 3 Active lithium in the lithium ion cell is consumed. Illustratively, H can also be avoided during subsequent preparation 2 With Li + And reacting again to generate LiH. Therefore, the LiH can be decomposed, the thermal stability and the reliability of the lithium ion battery cell can be improved, and the activity of the lithium ion battery cell can be improved.
It can be understood that after the lithium ion battery cell is pre-pumped and packaged, the air bag of the lithium ion battery cell is not cut off, so that the air bag can store generated gas in the subsequent preparation process, and the risk of potential expansion and explosion of the lithium ion battery cell is avoided.
S905, the pressure of the formation clamping plate is reduced to 0, the temperature is reduced to room temperature, and the lithium ion battery core is taken out, so that the formed lithium ion battery core is obtained.
And S906, carrying out capacity division on the lithium ion battery cell after the formation to obtain a finished battery cell.
The capacity of the lithium ion battery core after the formation is divided, which comprises the following steps: charging the formed lithium ion battery cell to 100% SOC at 0.5C under the condition of 25-45 ℃, discharging the formed lithium ion battery cell to 0% SOC at 0.5C, and then charging the formed lithium ion battery cell to 50% SOC at 0.5C.
It can be understood that the control of the shipment electric quantity of the lithium ion battery core is completed in the capacity-dividing step, rather than in the formation step before capacity division, so that the number of times of charging the lithium ion battery core can be reduced, and the preparation process is simplified.
Example 6:
by way of example, still another specific implementation of the method for preparing a lithium ion battery cell according to embodiment 2 is described in detail below with reference to fig. 10.
As shown in fig. 10, the preparation method of the lithium ion battery cell specifically includes:
s1001, placing the soft package lithium ion battery cell in a clamping plate of hot press forming equipment, applying 1.5MPa force, and heating to 85 ℃.
In the embodiment of the application, the lithium ion battery core is not charged for the first time, and the lithium ion battery core is provided with an air bag.
S1002, constant-current charging is carried out on the lithium ion battery core in three steps, the current of each step is respectively 0.2C, 0.6C and 1.0C, the formation time of each step is controlled, and finally the lithium ion battery core is charged to 80% of SOC to stop charging.
It can be understood that the charging process in the step S1002 is a formation process, and a good SEI film can be formed on the negative electrode of the lithium ion battery cell, during which gas components including alkane, CO2, H2, and the like are generated, and the gas components can be released into the air bag.
S1003, the pressure of the formation clamping plate is reduced to 0, the temperature is reduced to room temperature, and the lithium ion battery core is taken out, so that the formed lithium ion battery core is obtained.
And S1004, carrying out capacity division on the lithium ion battery core after the formation to obtain the lithium ion battery core after capacity division.
The capacity of the lithium ion battery core after the formation is divided, which comprises the following steps: charging the formed lithium ion battery cell to 100% SOC at 0.5C under the condition of 25-45 ℃, discharging the formed lithium ion battery cell to 0% SOC at 0.5C, and then charging the formed lithium ion battery cell to 50% SOC at 0.5C.
S1005, discharging the separated lithium ion battery cell to 2.0V at 0.2C, so that the LiH component in the SEI film is subjected to electrochemical decomposition, and H2 is generated and released into the air bag.
In the embodiment of the application, the 2.0V is smaller than or equal to the over-discharge protection voltage of the lithium ion battery core and larger than or equal to the discharge cut-off voltage of the lithium ion battery core, or the 2.0V is smaller than or equal to the highest decomposition voltage of the LiH under the discharge condition and larger than or equal to the cut-off voltage of the LiH in the lithium ion battery core.
For example, the over-discharge protection voltage of the lithium ion battery cell is 3.0V, and the discharge cut-off voltage is 1.0V, that is, 2.0V of the above-mentioned discharging of the lithium ion battery cell to 2.0V at 0.2C is smaller than 3.0V and larger than 1.0V.
For example, the highest decomposition voltage of LiH under the discharge condition is 3.5V, and the cutoff voltage for completely decomposing LiH in the lithium ion cell is 2.0V, that is, the above-mentioned cutoff voltage for completely decomposing LiH by discharging the lithium ion cell to 2.0V at 0.2C is equal to 2.0V.
Thus, liH in the lithium ion cell undergoes electrochemical decomposition during discharge (Li generation) + And H 2 ) The LiH content in the finished battery cell after being put into use is reduced, and the thermal stability and reliability of the lithium ion battery cell are improved.
S1006, carrying out air extraction packaging on the lithium ion battery cell, extracting gas in the air bag, and cutting off the air bag of the lithium ion battery cell.
It can be understood that the lithium ion battery cell is pre-pumped and packaged, and the gas (including the alkane, CO2, H2 and the like) in the air bag is pumped, so that the gas can be prevented from further electrochemical reaction or chemical reaction with the negative electrode active material of the lithium ion battery cell in the subsequent preparation process.
Illustratively, CO can be reduced in the subsequent preparation process 2 With Li + Reaction to form Li 2 CO 3 Active lithium in the lithium ion cell is consumed. Illustratively, H can also be avoided during subsequent preparation 2 With Li + And reacting again to generate LiH. Therefore, the LiH can be decomposed, the thermal stability and the reliability of the lithium ion battery cell can be improved, and the activity of the lithium ion battery cell can be improved.
It can be understood that after the lithium ion battery cell is pre-pumped and packaged, the air bag of the lithium ion battery cell is not cut off, so that the air bag can store generated gas in the subsequent preparation process, and the risk of potential expansion and explosion of the lithium ion battery cell is avoided.
S1007, recharging the lithium ion battery cell to 80% SOC at 1.0C to obtain a finished battery cell.
It can be appreciated that charging the lithium ion battery cell to 80% soc can cause the lithium ion battery cell to meet the basic shipment power of the finished battery cell.
In the above examples 3, 4, 5, and 6, the lithium ion cell was discharged to 2.0V at 0.2C, so that the LiH component in the SEI film was electrochemically decomposed, and a discharge cut-off voltage of 2.0V, which generated release of H2 into the air pocket', was generated, and the decomposition voltage of LiH in the lithium ion cell was determined by the method shown in fig. 5.
Illustratively, in connection with fig. 11 and 12, a specific implementation of the method for determining the decomposition voltage of LiH in a lithium ion battery cell provided in fig. 5 according to the present application is described in detail, and as shown in fig. 11, the method includes:
s1101, placing the soft package lithium ion battery core in a clamping plate of hot press forming equipment, applying 1.5MPa force, and simultaneously heating to 85 ℃.
In the embodiment of the application, the lithium ion battery cell is not charged for the first time, the lithium ion battery cell is provided with an air bag, and the 11 groups of soft package lithium ion battery cells have the same specifications as the lithium ion battery cells in the embodiment 3, the embodiment 4, the embodiment 5 and the embodiment 6.
And S1102, carrying out primary charging on the lithium ion battery core, specifically, carrying out constant current charging in three steps in the charging process, wherein the current of each step is respectively 0.2C, 0.6C and 1.0C, controlling the formation time of each step, and finally, charging to 80% SOC to stop charging, thereby obtaining the formed lithium ion battery core.
S1103, taking out the formed lithium ion battery cells, dividing the lithium ion battery cells into 11 groups, discharging each group of lithium ion battery cells at 0.2C, wherein the discharge cut-off voltage is one of voltage values of 2V to 3V, and the discharge cut-off voltages of each group of lithium ion battery cells are not equal.
I.e., 11 sets of lithium ion cells are discharged to 3.0V, 2.9V, 2.8V, 2.7V, 2.6V, 2.5V, 2.4V, 2.3V, 2.2V, 2.1V, and 2.0V, respectively.
Fig. 12 is another illustration of the embodiment of the present application, as shown in fig. 12, S1103 in fig. 11 may also be understood as S1201 in fig. 12.
And S1104, testing the gas generation volume V of each group of lithium ion battery cells by using a drainage method for each group of discharged lithium ion battery cells.
As shown in fig. 12, S1104 in fig. 11 may also be understood as S1202 in fig. 12.
S1105, measuring the gas generating components of each group of lithium ion battery cells by GC (gas chromatography) to obtain H 2 Wherein the proportion A (H 2 )。
As shown in fig. 12, S1105 in fig. 11 may also be understood as S1203 in fig. 12.
S1106, based on gas generation volume and H of each group of lithium ion battery cells 2 Determination of H in each set of lithium ion cells by product of ratios 2 Is the gas yield of (a), i.e. V.times.A (H) 2 ) Namely H in each group of lithium ion battery cells 2 And determining 11V x a (H) corresponding to 11 groups of lithium ion cells 2 ) The maximum discharge voltage of at least two discharge voltages corresponding to the stable maximum is the cut-off voltage of the lithium ion battery cell for completely decomposing LiH.
As shown in fig. 12, S1106 in fig. 11 can also be understood as S1204 in fig. 12.
It can be appreciated that since the lithium ion battery cell is once consumed after the first charge, only the LiH in the lithium ion battery cell is decomposed to generate H during the subsequent preparation process, i.e., the discharge process of step S1103 2 Thus, H 2 When the content of (C) reaches the stable maximum value, the LiH in the lithium ion battery cell is completely decomposed, H 2 The content of (2) does not continue to increase, i.e. the maximum discharge voltage of the corresponding at least two discharge voltages serves as the cut-off voltage for complete decomposition of LiH in the lithium ion cell.
Or, in other casesIn the implementation manner of (a), after step S1102 and before step S1103, the lithium ion battery cell after formation may be pumped first to pump out the gas (including alkane and CO) generated by the first charging of the lithium ion battery cell 2 、H 2 Etc.), after the evacuation, steps SS1103 to S1106 are performed again.
In the embodiment of the present application, the specifications of the lithium ion battery cell are the same as those of the lithium ion battery cell in embodiment 3, embodiment 4, embodiment 5, and embodiment 6, and the environmental conditions (including formation pressure, temperature, and charging current of each step) of the first charge of the lithium ion battery cell are the same as those of the lithium ion battery cell in embodiment 3, embodiment 4, embodiment 5, and embodiment 6, and the discharging current of the lithium ion battery cell after the first charge is completed is the same as that of the lithium ion battery cell in embodiment 3, embodiment 4, embodiment 5, and embodiment 6, so that the cutoff voltage of the lithium ion battery cell in the embodiment of the present application obtained by measuring the complete decomposition of LiH in the lithium ion battery cell in the embodiment 3, embodiment 4, embodiment 5, and embodiment 6 can be used to represent the cutoff voltage of the complete decomposition of LiH in the lithium ion battery cell in the embodiment 3, embodiment 4, embodiment 5, and embodiment 6, and the data has the authenticity and accuracy.
Exemplary, 11H corresponding to 11 lithium ion cells 2 Two or more than two equal gas production rates and H 2 Maximum H with maximum gas yield 2 And (3) generating gas, wherein the maximum voltage in at least two discharge voltages corresponding to the maximum gas generation is the cut-off voltage for complete decomposition of LiH.
For example, if 11H's correspond to 11 lithium ion cells 2 In the gas production, H 2 The maximum value of the gas production is Y, and the value of 3 gas production in 11 groups of gas production is Y, then H 2 The gas production amount is 3 discharge voltages of 3 groups of lithium ion battery cores corresponding to Y, and the maximum value of the 3 discharge voltages is the cut-off voltage for completely decomposing LiH. For example, the H 2 The discharge voltages corresponding to the 3 groups of lithium ion battery cells with the gas production rates of Y are 2.5V, 2.4V and 2.3V respectively, and the cut-off voltage of complete decomposition of LiH is 2.5V.
As used in the above embodiments, the term "when …" may be interpreted to mean "if …" or "after …" or "in response to determination …" or "in response to detection …" depending on the context. Similarly, the phrase "at the time of determination …" or "if detected (a stated condition or event)" may be interpreted to mean "if determined …" or "in response to determination …" or "at the time of detection (a stated condition or event)" or "in response to detection (a stated condition or event)" depending on the context.
In the above embodiments, it may be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented in software, may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When loaded and executed on a computer, produces a flow or function in accordance with embodiments of the present application, in whole or in part. The computer may be a general purpose computer, a special purpose computer, a computer network, or other programmable apparatus. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center by a wired (e.g., coaxial cable, fiber optic, digital subscriber line), or wireless (e.g., infrared, wireless, microwave, etc.). The computer readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server, data center, etc. that contains an integration of one or more available media. The usable medium may be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid state disk), etc.
Those of ordinary skill in the art will appreciate that implementing all or part of the above-described method embodiments may be accomplished by a computer program to instruct related hardware, the program may be stored in a computer readable storage medium, and the program may include the above-described method embodiments when executed. And the aforementioned storage medium includes: ROM or random access memory RAM, magnetic or optical disk, etc.
The above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the application.
Claims (19)
1. A method for preparing a lithium ion battery cell, the method comprising:
discharging the first lithium ion battery cell to a target voltage to obtain a discharged first lithium ion battery cell, wherein the first lithium ion battery cell is charged for the first time, the first lithium ion battery cell comprises lithium hydride, and the target voltage meets the following conditions: the target voltage is less than the decomposition voltage of the lithium hydride under discharge conditions;
And preparing a finished battery cell based on the discharged first lithium ion battery cell, wherein the electric quantity of the finished battery cell meets the basic working electric quantity.
2. The method of claim 1, wherein the target voltage further satisfies the following condition: the target voltage is smaller than the over-discharge protection voltage of the first lithium ion battery cell and is greater than or equal to the discharge termination voltage of the first lithium ion battery cell.
3. The method according to claim 1 or 2, characterized in that the target voltage also fulfils the following condition: the target voltage is greater than or equal to a cutoff voltage at which the lithium hydride is completely decomposed under discharge conditions.
4. The method of claim 2, wherein the decomposition voltage takes the value of the cutoff voltage when the cutoff voltage for complete decomposition of the lithium hydride under discharge conditions is greater than the discharge termination voltage of the first lithium ion cell.
5. The method of any one of claims 1 to 4, wherein prior to said discharging the first lithium ion cell to the target voltage, the method further comprises:
the first lithium ion battery cell is charged for the first time based on the full voltage or the capacitance of the first lithium ion battery cell, the first lithium ion battery cell after the first charging is completed is obtained, and in the process of the first charging, the first lithium ion battery cell generates a solid electrolyte interface SEI film, and the SEI film comprises the lithium hydride;
The preparing a finished product cell based on the discharged first lithium ion cell comprises the following steps:
and charging the discharged first lithium ion battery cell based on the full voltage or capacitance of the first lithium ion battery cell so as to obtain the finished battery cell.
6. The method of claim 5, wherein the first lithium ion cell contains carbon dioxide gas, wherein during discharging the first lithium ion cell to the target voltage, the lithium hydride is electrochemically decomposed to generate lithium ions,
and in the process of charging the discharged first lithium ion battery cell based on the full-charge voltage, the carbon dioxide and the lithium ions are subjected to electrochemical reaction under the charging condition to generate lithium carbonate.
7. The method of claim 5, wherein the first lithium ion cell contains carbon dioxide gas,
before the charging of the discharged first lithium ion battery cell based on the full voltage or capacitance of the first lithium ion battery cell, the method further comprises:
and extracting gas in the first lithium ion battery cell, wherein the gas comprises the carbon dioxide.
8. The method of any one of claims 1 to 7, wherein the decomposition voltage is a discharge voltage such that a second lithium ion cell generates hydrogen gas in an amount greater than 0 during discharge, the second lithium ion cell contains lithium hydride and the second lithium ion cell does not contain hydrogen gas, and the second lithium ion cell has the same specification as the first lithium ion cell.
9. The method according to claim 3 or 4, wherein the cut-off voltage is a larger discharge voltage of at least two discharge voltages corresponding to a first state of a second lithium ion battery cell, the first state is a discharge state in which a content of hydrogen generated by the second lithium ion battery cell in a discharge process is no longer increased, the second lithium ion battery cell contains the lithium hydride, and the second lithium ion battery cell does not contain hydrogen, and the second lithium ion battery cell has the same specification as the first lithium ion battery cell.
10. The method of any one of claims 1 to 4, wherein the first lithium-ion cell is configured with an air pocket, the preparing a finished cell based on the discharged first lithium-ion cell comprising:
Carrying out capacity division on the discharged first lithium ion battery cell to obtain a capacity-divided first lithium ion battery cell;
and extracting the gas in the separated first lithium ion battery cell and the gas bag, and cutting off the gas bag to obtain the finished battery cell.
11. A method of determining the decomposition voltage of lithium hydride, the method comprising:
obtaining a second lithium ion battery cell, wherein the second lithium ion battery cell contains lithium hydride and does not contain hydrogen;
discharging the second lithium ion battery cell;
and in the discharging process, acquiring a first voltage, wherein the first voltage is a discharging voltage corresponding to the second lithium ion battery cell when the volume of hydrogen generated during discharging is greater than 0, and the first voltage is used for representing the decomposition voltage of the lithium hydride.
12. The method of claim 11, wherein the method further comprises:
and in the discharging process, acquiring a second voltage, wherein the second voltage is a larger discharging voltage of at least two discharging voltages corresponding to a first state of the second lithium ion battery core in the discharging process, the first state is a discharging state that the volume of hydrogen generated by the second lithium ion battery core in the discharging process is not increased any more, and the second voltage is used for representing a cut-off voltage of complete decomposition of lithium hydride in the second lithium ion battery core under a discharging condition.
13. The method of claim 12, wherein the step of determining the position of the probe is performed,
the obtaining the second lithium ion battery cell includes:
obtaining N groups of second lithium ion battery cores, wherein N is a positive integer greater than or equal to 3;
the discharging the second lithium ion battery cell includes:
discharging each group of second lithium ion battery cells of the N groups of second lithium ion battery cells respectively, and stopping discharging until N unequal discharging voltages are reached, wherein the discharging voltages are larger than 0, so as to obtain N groups of discharged second lithium ion battery cells;
the step of obtaining the first voltage in the discharging process comprises the following steps:
determining the volume of hydrogen in each set of discharged second lithium ion battery cells of the N sets of discharged second lithium ion battery cells based on a drainage method and a gas chromatography measurement method to obtain N volume;
determining a first volume, the first volume being a minimum volume of the N volumes greater than 0;
and setting a maximum voltage of at least one discharge voltage corresponding to the first volume as the first voltage.
14. The method of claim 13, wherein said obtaining a second voltage during said discharging comprises:
Determining a second volume, wherein at least two groups of the second volume are contained in the N volume, and the second volume is the largest volume in the N volume;
the maximum voltage of at least one of the discharge voltages corresponding to the second volume is taken as the second voltage.
15. The method of claim 14, wherein the step of providing the first information comprises,
the determining the first volume includes:
determining the first volume in case the N volume comprises a volume greater than 0;
the determining the second volume includes:
determining the second volume in case the N volume comprises a volume greater than 0;
the method further comprises the steps of:
in the case where the N volume amounts are all 0, the maximum value of the N unequal discharge voltages is determined.
16. The method of any one of claims 13 to 15, wherein the obtaining N sets of second lithium ion cells comprises:
acquiring N groups of second lithium ion battery cores which are not subjected to primary charging, wherein each group of lithium ion battery cores which are not subjected to primary charging in the N groups of second lithium ion battery cores which are not subjected to primary charging at least comprises one second lithium ion battery core;
Charging each group of second lithium ion battery cells in the N groups of second lithium ion battery cells for the first time based on the full charge voltage of the second lithium ion battery cells to obtain N groups of charged second lithium ion battery cells, wherein the N groups of charged second lithium ion battery cells all contain lithium hydride;
and extracting the gas in the N groups of charged second lithium ion batteries to obtain N groups of extracted second lithium ion batteries, and taking the N groups of extracted second lithium ion batteries as the N groups of second lithium ion batteries.
17. A lithium-ion cell, characterized in that it is prepared on the basis of the method according to any one of claims 1 to 16.
18. A lithium ion battery comprising a lithium ion cell, wherein the lithium ion cell is prepared based on the method of any one of claims 1 to 16.
19. A formation device for lithium ion cells, characterized in that it comprises one or more control circuits for controlling the formation device to perform the method according to any one of claims 1 to 16.
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