CN116430257B - Method for representing electrical performance of lithium battery and application thereof - Google Patents
Method for representing electrical performance of lithium battery and application thereof Download PDFInfo
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- CN116430257B CN116430257B CN202310708687.3A CN202310708687A CN116430257B CN 116430257 B CN116430257 B CN 116430257B CN 202310708687 A CN202310708687 A CN 202310708687A CN 116430257 B CN116430257 B CN 116430257B
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- 238000000034 method Methods 0.000 title claims abstract description 49
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 29
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 29
- 238000012512 characterization method Methods 0.000 claims abstract description 88
- 238000012360 testing method Methods 0.000 claims abstract description 18
- 230000034964 establishment of cell polarity Effects 0.000 claims abstract description 13
- 238000002360 preparation method Methods 0.000 claims abstract description 10
- 238000012545 processing Methods 0.000 claims description 15
- 238000012937 correction Methods 0.000 claims description 12
- 238000007599 discharging Methods 0.000 claims description 12
- 238000011282 treatment Methods 0.000 claims description 6
- 230000010287 polarization Effects 0.000 abstract description 17
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 15
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 15
- 238000004519 manufacturing process Methods 0.000 abstract description 6
- 238000011284 combination treatment Methods 0.000 abstract description 2
- 239000000463 material Substances 0.000 description 9
- 230000009286 beneficial effect Effects 0.000 description 8
- 238000000576 coating method Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 6
- 239000011248 coating agent Substances 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- 239000006258 conductive agent Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 239000013543 active substance Substances 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000002347 injection Methods 0.000 description 3
- 239000007924 injection Substances 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 238000010606 normalization Methods 0.000 description 3
- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 239000006183 anode active material Substances 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 239000006182 cathode active material Substances 0.000 description 2
- 125000004122 cyclic group Chemical group 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- KFDQGLPGKXUTMZ-UHFFFAOYSA-N [Mn].[Co].[Ni] Chemical compound [Mn].[Co].[Ni] KFDQGLPGKXUTMZ-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 238000002484 cyclic voltammetry Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 229910021385 hard carbon Inorganic materials 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000002372 labelling Methods 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- DVATZODUVBMYHN-UHFFFAOYSA-K lithium;iron(2+);manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[Fe+2].[O-]P([O-])([O-])=O DVATZODUVBMYHN-UHFFFAOYSA-K 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000010295 mobile communication Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/387—Determining ampere-hour charge capacity or SoC
- G01R31/388—Determining ampere-hour charge capacity or SoC involving voltage measurements
-
- 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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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention relates to a method for representing the electrical performance of a lithium battery and application thereof, relating to the field of lithium ion batteries, and comprising the following steps: step 1: respectively testing to obtain a positive electrode voltage-specific capacity charge-discharge curve, a negative electrode voltage-specific capacity charge-discharge curve and a battery voltage-capacity representation charge-discharge curve; step 2: performing standardization and combination treatment to obtain a standardized charge-discharge curve of the voltage-capacity of the battery; step 3: obtaining beta and alpha, and dividing beta by alpha ratio by 1 to obtain relative offset coefficient lambda; step 4: obtaining U1 and U2, and subtracting to obtain U3; dividing U3 by the charge-discharge voltage interval value of the characterization battery to obtain U; step 5: the cell polarization value phi is equal to lambda plus U. The lithium battery electrical property characterization method can rapidly and simply judge the polarization degree and the electrical property of the lithium ion battery, and feed back important parameters in the preparation process section to optimize the manufacturing of the battery core.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a method for representing the electrical performance of a lithium battery and application thereof.
Background
Based on the advantages of light weight, high energy density, long service life and the like, the lithium ion battery is widely applied to the fields of mobile communication devices, electric vehicles, military electronic equipment, aerospace electronic systems and the like, and becomes one of important parts of novel renewable energy sources. Because the lithium ion battery needs to be subjected to different production process steps in the preparation process, such as homogenization, coating, rolling, die cutting, lamination, baking, liquid injection, formation, capacity division and the like, important parameters in different process steps have great influence on the performance of the finally prepared lithium ion battery, such as the density of anode and cathode coating surfaces in the coating process step, the density of anode and cathode pressure in the rolling process step, the liquid injection amount in the liquid injection process step and the like. At present, the methods for evaluating the electrical performance of the lithium ion battery mainly include testing means such as a multiplying power test, a cyclic test, an EIS test, a cyclic voltammetry curve and the like, but the characterization means all require longer testing time, such as the cyclic test and the multiplying power test, or require professional software to assist in processing test data, such as the EIS. In view of the above, the invention provides a method for representing the electrical performance of a lithium battery and application thereof.
Disclosure of Invention
The invention aims to provide a method for representing the electrical performance of a lithium battery and application thereof. The method aims to rapidly and simply judge the polarization degree and the electrical performance of the lithium ion battery, feed back important parameters in the preparation process section and optimize the manufacturing of the battery cell.
In order to solve the technical problems, the first object of the present invention is to provide a method for characterizing electrical performance of a lithium battery, comprising the following steps:
step 1: respectively testing the charge and discharge processes of the assembled positive half-cell and negative half-cell to obtain a positive voltage-specific capacity charge and discharge curve and a negative voltage-specific capacity charge and discharge curve; testing the charge and discharge process of the characterization battery to obtain a charge and discharge curve of the characterization battery voltage-capacity;
step 2: performing standardization processing on the positive electrode voltage-specific capacity charge-discharge curve to obtain a positive electrode voltage-specific capacity standardized charge-discharge curve, performing standardization processing on the negative electrode voltage-specific capacity charge-discharge curve to obtain a negative electrode voltage-specific capacity standardized charge-discharge curve, and performing combination processing on the positive electrode voltage-specific capacity standardized charge-discharge curve and the negative electrode voltage-specific capacity standardized charge-discharge curve to obtain a battery voltage-specific capacity standardized charge-discharge curve;
step 3: selecting an intersection point in the standardized charge-discharge curve of the battery voltage-capacity as a standardized origin A, dividing the capacity corresponding to the standardized origin A by the total capacity of the charge curve in the standardized charge-discharge curve of the battery voltage-capacity, and obtaining a standardized coefficient alpha; selecting an intersection point of the charge-discharge curves representing the voltage-capacity of the battery as a representation point B, dividing the capacity corresponding to the representation point B by the total charge capacity of the battery to obtain a representation coefficient beta; the ratio of the characterization coefficient beta divided by the standardized coefficient alpha is subtracted by 1, and the obtained value is a relative offset coefficient lambda;
step 4: multiplying the standardized coefficient alpha by the total charge capacity of the characterization battery to obtain a characterization standardized capacity C; in the charge-discharge curve representing the voltage-capacity of the battery, taking the representing standardized capacity C as an abscissa base point, making a vertical line with an X axis, enabling the vertical line to be intersected with the charge-discharge curve representing the voltage-capacity of the battery respectively, correspondingly obtaining a representing charge absolute voltage U1 and a representing discharge absolute voltage U2, and subtracting the representing charge absolute voltage U2 from the representing charge absolute voltage U1 to obtain an absolute offset voltage U3; dividing the absolute offset voltage U3 by the charge-discharge voltage interval value of the characterization battery to obtain a relative offset voltage U;
the charge and discharge voltage interval of the characterization battery is not fixed, the voltage interval in the standardized charge and discharge curve is only required to be ensured to be consistent with the charge and discharge interval of the characterization battery, and if the charge and discharge interval of the characterization battery is 2.75-4.2V, the standardized charge and discharge curve is also 2.75-4.2V; if the battery charge-discharge interval is 3-4V, the standardized charge-discharge curve only takes 3-4V data. The charge-discharge voltage interval of the characterization battery is determined according to a battery cell specification given by a manufacturer or according to GB/T31486;
step 5: and adding the relative offset coefficient lambda to the relative offset voltage U to obtain a battery cell polarization value phi representing the battery, and judging whether the electrical performance of the battery cell is good or not according to the magnitude of the battery cell polarization value phi, wherein the larger the battery cell polarization value phi is, the worse the electrical performance of the battery cell is represented.
For the following reasons: when the battery is being charged, lithium ions are extracted from the positive electrode at the moment, electrons are extracted along with the gradual migration of the electrolyte to the negative electrode, and electrons reach the negative electrode along with an external circuit at a higher speed, so that electrons of the negative electrode are accumulated, the lithium ions in the electrolyte are not migrated to the negative electrode, the potential of the original metal lithium to the metal lithium is 0V, but when the electrons are accumulated on the metal lithium, the potential of the metal lithium is possibly lower than 0V. Assuming that the potential of the negative electrode is-0.1V at this time, when the charge cut-off voltage is set to 4.2V in the external charge-discharge machine, the potential of the positive electrode is actually only 4.1V, and the true potential thereof does not reach the desired potential, which is a polarization phenomenon, that is, polarization causes a situation that the voltage of the battery tested in the external charge-discharge machine does not conform to the true potential of the material itself. In this case, the cut-off voltage of the battery charge needs to be higher to reach the desired actual potential, the charging curve moves upward to the left, and the greater the polarization, the more moves. Similarly, the discharge curve needs to be shifted downward and leftward.
Therefore, the battery voltage-capacity standardized charge-discharge curve is obtained by carrying out standardization and combination treatment on the positive electrode voltage-specific capacity charge-discharge curve and the negative electrode voltage-specific capacity charge-discharge curve, wherein the battery voltage-capacity standardized charge-discharge curve is obtained after polarization influence is eliminated, an intersection point in the battery voltage-capacity standardized charge-discharge curve is selected as a standardized origin A, and the capacity corresponding to A is divided by the total capacity of the charge curve in the battery voltage-capacity standardized charge-discharge area curve to obtain a standardized coefficient alpha; selecting an intersection point of the charge-discharge curves representing the voltage-capacity of the battery as a representation point B, dividing the capacity corresponding to B by the total charge capacity of the representation battery to obtain a representation coefficient beta, and comparing a standardization coefficient alpha with the representation coefficient beta to judge the deviation degree of the representation point B relative to the standardization origin A so as to reflect the polarization of the standard battery; multiplying alpha by the total charge capacity of the characterization battery to obtain a characterization standardized capacity C, taking C as an abscissa base point in a charge-discharge curve of the characterization battery voltage-capacity, making a perpendicular line with an X axis, enabling the perpendicular line to intersect with the charge-discharge curve of the characterization battery voltage-capacity respectively, correspondingly obtaining a characterization charge absolute voltage U1 and a characterization discharge absolute voltage U2, and subtracting the characterization discharge absolute voltage U2 from the characterization charge absolute voltage U1 to obtain an absolute offset voltage U3; dividing the absolute offset voltage U3 by the charge-discharge voltage interval value of the characterization battery to obtain a relative offset voltage U, and finally subtracting the ratio of the characterization coefficient beta divided by the standardized coefficient alpha by 1 to obtain a relative offset coefficient lambda, wherein the value is the relative offset coefficient lambda, and the purpose is to obtain the voltage relative offset condition generated due to polarization; the alpha is obtained by dividing the intersection point A in the standardized curve by the total charge capacity of the standardized curve, so that the capacity obtained by multiplying the total charge capacity of the standardized curve by the alpha in the standardized curve is the abscissa of the intersection point A, and at the moment, the perpendicular line for the abscissa of the intersection point A is just coincided with the intersection point A, namely, the intersection point A is intersected with both the charge curve and the discharge curve, and no voltage difference exists; when alpha is multiplied by the total charge capacity of the characterization battery, voltage difference occurs due to polarization, and the larger the polarization is, the larger the voltage difference is, otherwise, the relative value of the voltage difference can be used as a method for judging the polarization; the battery cell polarization value phi of the characterization battery is equal to the relative offset coefficient lambda plus the relative offset voltage U, and the larger the battery cell polarization value phi of the characterization battery is, the worse the battery cell electrical performance of the characterization battery is.
The beneficial effects of the invention are as follows: aiming at the phenomenon that the research on new materials of the anode and the cathode of the lithium ion battery is more at present, but no good characterization method exists in the charge-discharge voltage range of the lithium ion battery made of the developed new materials, the lithium ion battery electrical property characterization method provided by the invention can rapidly and simply judge the polarization degree and the electrical property of the lithium ion battery, feed back important parameters in the preparation process section, and optimize the manufacturing of the battery core.
On the basis of the technical scheme, the invention can be improved as follows.
Further, in the step 1, the surface density of the positive electrode sheet in the assembled positive electrode half cell is not more than 100g/m 2 The surface density of the negative electrode plate in the assembled negative electrode half cell is not more than 50g/m 2 。
The active substances in the positive electrode plate in the positive half battery are required to be the same as the active substances (the types and the types of the active substances are the same) in the positive electrode plate of the tested characterization battery, and the negative electrode plate is also the same. For example, if the active material of the positive electrode sheet in the positive electrode half-cell is nickel-rich 811, then the active material of the positive electrode sheet in the cell is also nickel-rich 811 of the same type.
In addition, when the positive electrode plate and the negative electrode plate are prepared, the mass ratio of the conductive agent and the adhesive added during the preparation of the positive electrode plate is not lower than 5%, and the mass ratio of the conductive agent and the adhesive added during the preparation of the negative electrode plate is not lower than 5%; the material of the positive electrode plate is mainly lithium iron phosphate, lithium cobalt oxide, nickel cobalt manganese ternary, lithium manganate, lithium manganese iron phosphate or other common lithium battery positive electrode materials; the material of the negative electrode plate is mainly graphite, hard carbon, silicon carbon, lithium titanate, silicon or other common lithium battery negative electrode materials.
The beneficial effects of adopting the further scheme are as follows: by adopting the above surface density, the positive electrode and the negative electrode can reduce the polarization phenomenon of the positive electrode and the negative electrode in the charge-discharge curve of voltage-specific capacity, and improve the accuracy of the characterization of the invention.
Further, in the step 1, the multiplying power is not more than 0.05C when the positive half cell is charged and discharged and when the negative half cell is charged and discharged.
The beneficial effects of adopting the further scheme are as follows: when the positive and negative half batteries are charged and discharged, the invention adopts small current to charge and discharge, reduces or even eliminates polarization phenomenon of positive and negative voltage-specific capacity charge and discharge curves, and further optimizes the accuracy of the characterization of the invention.
In step 1, the charge-discharge curve of the positive electrode voltage-specific capacity is a charge-discharge curve of the second cycle of the charge-discharge cycle of the positive electrode half cell, and the charge-discharge curve of the negative electrode voltage-specific capacity is a charge-discharge curve of the second cycle of the charge-discharge cycle of the negative electrode half cell.
The beneficial effects of adopting the further scheme are as follows: the positive and negative half batteries have capacity loss when being charged and discharged for the first time, namely the first charge and discharge efficiency is generated, the first effect is short for the first time, along with the circulation, the structure of the material can be continuously damaged at a certain randomness, the original electric performance condition of the battery can not be accurately reflected, therefore, the second circle is adopted as a fitting curve, the complex influence of the first effect of the positive and negative half batteries due to the first circle circulation is eliminated, and meanwhile, the influence of the random damage of the material structure on the characterization result is avoided.
Further, in the step 1, the charge and discharge process of the characterization battery is tested according to GB/T31486 or the charge and discharge method specified by the characterization battery specification, so as to obtain the charge and discharge curve of the voltage-capacity of the characterization battery.
Further, in the step 2, the normalizing the charge-discharge curve of the positive electrode voltage-specific capacity and the charge-discharge curve of the negative electrode voltage-specific capacity includes the following specific steps:
step 2-1: dividing 1Ah by the specific charge capacity of the positive half cell to obtain a positive correction coefficient m 1 The method comprises the steps of carrying out a first treatment on the surface of the Multiplying the abscissa value of the charge-discharge curve of the positive electrode voltage-specific capacity by the positive electrode correction coefficient m 1 Obtaining a standardized charge-discharge curve of the voltage-capacity of the positive electrode;
step 2-2: dividing 1Ah by the discharge specific capacity of the negative half cell to obtain a negative correction coefficient m 2 The method comprises the steps of carrying out a first treatment on the surface of the Multiplying the abscissa value of the charge-discharge curve of the negative electrode voltage-specific capacity by the negative electrode correction coefficient m 2 And multiplying the N/P ratio of the characterization battery to obtain a standardized charge-discharge curve of the voltage-capacity of the negative electrode.
The N/P ratio (Positive/Positive) is the margin of Positive electrode capacity to Positive electrode capacity of the Positive electrode under the same conditions in the same stage, and there is another statement CB (cell Balance). N/p=gram capacity of anode active material×anode surface density×anode active material content ratio ≡ (gram capacity of cathode active material×anode surface density×cathode active material content ratio).
The beneficial effects of adopting the further scheme are as follows: in characterizing a battery, negative electrode capacity=positive electrode capacity×n/P, when N/p=1, negative electrode capacity=positive electrode capacity; when the charge-discharge curve test of the positive and negative half batteries is performed, the charge total capacity of the positive half battery=the discharge total capacity of the negative half battery cannot be ensured, and the abscissa of the positive half battery=the discharge total capacity of the negative half battery can be kept unchanged only when the charge total capacity of the positive half battery=the discharge total capacity of the negative half battery, and the ordinate is subtracted (the abscissa is the capacity and the ordinate is the voltage), so that the charge-discharge curve of the whole battery which can be compared with the characterization battery is obtained; the capacity of 1Ah is used as a standardized process to correct the positive electrode charge capacity to 1Ah and the negative electrode discharge capacity to 1Ah, thereby satisfying the requirements of steps 2-3 and 2-4.
Further, in the step 2-1, the specific charge capacity of the positive half-cell is a specific charge capacity when the positive half-cell is charged to a set cutoff voltage;
in the step 2-2, the specific discharge capacity of the negative half-cell is the specific discharge capacity of the negative half-cell when the negative half-cell is discharged to a set cut-off voltage.
The cut-off voltage is the termination voltage, and means that the voltage drops to the lowest working voltage value where the battery is not suitable to continue discharging when the battery discharges.
Further, in the step 2, the combination processing of the normalized charge-discharge curve of the positive electrode voltage-capacity and the normalized charge-discharge curve of the negative electrode voltage-capacity includes the following specific steps:
step 2-3: the abscissa value of the charging curve in the standardized charging and discharging curve of the positive electrode voltage-capacity is kept unchanged, and the ordinate value of the charging curve is correspondingly subtracted from the ordinate value of the discharging curve in the standardized charging and discharging curve of the negative electrode voltage-capacity to obtain a standardized charging curve of the battery;
step 2-4: maintaining the abscissa value of the discharge curve in the standardized charge-discharge curve of the positive electrode voltage-capacity unchanged, and correspondingly subtracting the ordinate value of the charge curve in the standardized charge-discharge curve of the negative electrode charge-discharge from the ordinate value of the discharge curve to obtain a standardized discharge curve of the battery;
step 2-5: and drawing the battery standardized charge curve and the battery standardized discharge curve in the same coordinate system to obtain the battery voltage-capacity standardized charge-discharge curve.
The beneficial effects of adopting the further scheme are as follows: the method is used for obtaining a full battery charge-discharge curve (standardized charge-discharge curve) which is electrodeless and has the same positive and negative poles as the characterization battery, and comparing the full battery charge-discharge curve with the charge-discharge curve of the characterization battery, so as to reflect the deviation degree of the characterization battery curve relative to the non-polarized full battery charge-discharge curve.
Generally, the charge-discharge voltage range of the standardized charge-discharge curve fitted by the charge-discharge curve of the positive half-cell and the charge-discharge curve of the negative half-cell is larger than the charge-discharge voltage range of the test characterization cell, for example, when the charge-discharge voltage range of the standardized charge-discharge curve is 2-4.3 v, the charge-discharge voltage range of the test characterization cell may be only 3-4.2 v (cut-off voltage), and the ordinate range value of the combined standardized charge-discharge curve only needs 3-4.2 v. Thus, further, the normalized charge-discharge curve of battery voltage-capacity employs the charge-discharge cutoff voltage characterizing the battery as an ordinate range value.
The beneficial effects of adopting the further scheme are as follows: the above ensures that alpha in the standardized curve can be compared with beta in the characterization cell, and if the selected voltage ranges are not consistent, no comparison can be made.
The second object of the present invention is to provide an application of the method for characterizing electrical performance of a lithium battery, wherein the method for characterizing electrical performance of a lithium battery is used for preparing a lithium battery.
The beneficial effects of adopting above-mentioned scheme are: in the preparation of the lithium battery, the method for representing the electrical performance of the lithium battery can be used for rapidly and simply judging the polarization degree and the electrical performance of the lithium battery, feeding back important parameters in a preparation process section and optimizing the manufacturing of the battery core.
Drawings
FIG. 1 is a charge-discharge graph of the positive electrode voltage-specific capacity of example 1 of the present invention;
fig. 2 is a charge-discharge graph of negative electrode voltage-specific capacity according to example 1 of the present invention;
FIG. 3 is a charge-discharge graph characterizing the voltage-capacity of the battery of example 1 of the present invention;
FIG. 4 is a standard charge-discharge curve of the positive electrode voltage-capacity of example 1 of the present invention;
FIG. 5 is a standard charge-discharge curve of the negative electrode voltage-capacity of example 1 of the present invention;
FIG. 6 is a diagram showing a normalized charge curve of the battery voltage-capacity obtained by the combination process in example 1 of the present invention;
FIG. 7 is a graph showing the normalized discharge curve of the battery voltage-capacity obtained by the combination process in example 1 of the present invention;
fig. 8 is a normalized charge-discharge curve of battery voltage-capacity according to example 1 of the present invention;
FIG. 9 is a schematic diagram of the operation of example 1 to obtain a representative charge absolute voltage U1 and a representative discharge absolute voltage U2;
fig. 10 is a charge-discharge graph representing the voltage-capacity of the battery according to comparative example 1 of the present invention;
FIG. 11 is a schematic diagram of the operation of comparative example 1 to obtain a representative charge absolute voltage U1 and a representative discharge absolute voltage U2;
fig. 12 is a schematic view of an assembled positive half cell of the present invention.
Detailed Description
The principles and features of the present invention are described below with examples given for the purpose of illustration only and are not intended to limit the scope of the invention.
Example 1: watch according to the inventionThe positive electrode surface density by the characterization method is 350g/m 2 Fast characterization of the soft pack battery of (a):
the method for representing the electrical performance of the lithium battery comprises the following steps:
step 1:
according to the mass ratio of 8:1:1 weighing the needed characterization soft package battery positive electrode material (ternary positive electrode), binder (PVDF) and conductive agent (SP), homogenizing, coating, baking, die cutting, assembling to obtain positive electrode half-cell (figure 12), and charging and discharging the prepared positive electrode half-cell at 0.05C, wherein the surface density is 50g/m 2 . The charge-discharge curve of the obtained positive electrode voltage-specific capacity is shown in figure 1;
according to the mass ratio of 8:1:1 weighing the required characterization soft package battery cathode material (silicon carbon), binder (LA 136D) and conductive agent (SP), homogenizing, coating, baking, die cutting, assembling to obtain a cathode half-cell, and charging and discharging the prepared cathode half-cell at 0.05C, wherein the surface density is 20g/m 2 . The charge-discharge curve of the obtained negative electrode voltage-specific capacity is shown in fig. 2;
optionally, the charge-discharge curve of the positive electrode voltage-specific capacity is a charge-discharge curve of the second cycle of the charge-discharge cycle of the positive electrode half-cell, and the charge-discharge curve of the negative electrode voltage-specific capacity is a charge-discharge curve of the second cycle of the charge-discharge cycle of the negative electrode half-cell. The positive and negative half batteries have capacity loss when being charged and discharged for the first time, namely the first charge and discharge efficiency is generated, namely the first effect is shortened, and the influence of the capacity loss can be almost eliminated in the subsequent charge and discharge, so that the second circle is adopted as a fitting curve, and the complex influence of the first effect of the positive and negative half batteries due to the first circle circulation is eliminated.
Performing charge and discharge test on the soft package battery to be characterized, wherein the charge multiplying power is 0.33C, the discharge multiplying power is 1C, and the charge and discharge voltage interval is 2.75V-4.2V; the resulting charge-discharge curve, which characterizes the voltage-capacity of the battery, is shown in fig. 3; optionally, the charge-discharge process of the characterization battery can be tested according to GB/T31486 or a charge-discharge method specified by the characterization battery specification, so as to obtain a charge-discharge curve of the voltage-capacity of the characterization battery.
Step 2:
performing standardization processing on the positive electrode voltage-specific capacity charge-discharge curve to obtain a positive electrode voltage-specific capacity standardized charge-discharge curve, performing standardization processing on the negative electrode voltage-specific capacity charge-discharge curve to obtain a negative electrode voltage-specific capacity standardized charge-discharge curve, and performing combination processing on the positive electrode voltage-specific capacity standardized charge-discharge curve and the negative electrode voltage-specific capacity standardized charge-discharge curve to obtain a battery voltage-specific capacity standardized charge-discharge curve;
optionally, in the step 2, the normalizing the charge-discharge curve of the positive electrode voltage-specific capacity and the charge-discharge curve of the negative electrode voltage-specific capacity includes the following specific steps:
step 2-1: dividing 1Ah by the specific charge capacity of the positive half cell to obtain a positive correction coefficient m 1 The method comprises the steps of carrying out a first treatment on the surface of the Multiplying the abscissa values of the charge-discharge curve of the positive electrode voltage-specific capacity by a positive electrode correction coefficient m 1 Obtaining a standardized charge-discharge curve of the voltage-capacity of the positive electrode;
step 2-2: dividing 1Ah by the discharge specific capacity of the negative half cell to obtain a negative correction coefficient m 2 The method comprises the steps of carrying out a first treatment on the surface of the Multiplying the abscissa values of the charge-discharge curve of the negative electrode voltage-specific capacity by a negative electrode correction coefficient m 2 And multiplying the N/P ratio of the characterization battery to obtain a standardized charge-discharge curve of the voltage-capacity of the negative electrode.
Optionally, in the step 2-2, the specific discharge capacity of the negative half-cell is the specific capacity of the negative half-cell when the negative half-cell is discharged to the set cut-off voltage, and when the negative half-cell is discharged to 0V as shown in fig. 2, the specific capacity is 351mAh/g, the specific capacity is divided by 1Ah, and the ratio of 351mAh/g to 2.849g, and the abscissa of the charge-discharge curve of the negative voltage-specific capacity is multiplied by 2.849, and then multiplied by the N/P ratio, so as to obtain fig. 5.
Optionally, in the step 2, the combination processing of the standard charge-discharge curve of the positive electrode voltage-capacity and the standard charge-discharge curve of the negative electrode voltage-capacity includes the following specific steps:
step 2-3: the abscissa value of the charging curve in the standardized charging and discharging curve of the positive electrode voltage-capacity is kept unchanged, and the ordinate value of the charging curve is correspondingly subtracted from the ordinate value of the discharging curve in the standardized charging and discharging curve of the negative electrode voltage-capacity to obtain a standardized charging curve of the battery;
step 2-4: maintaining the abscissa value of the discharge curve in the standardized charge-discharge curve of the positive electrode voltage-capacity unchanged, and correspondingly subtracting the ordinate value of the charge curve in the standardized charge-discharge curve of the negative electrode voltage-capacity from the ordinate value of the discharge curve to obtain a standardized discharge curve of the battery;
step 2-5: and drawing the battery standardized charge curve and the battery standardized discharge curve in the same coordinate system to obtain the battery voltage-capacity standardized charge-discharge curve.
Optionally, the ordinate range of the standardized charge-discharge curve of the battery voltage-capacity adopts the charge-discharge cut-off voltage of the characterization battery as an ordinate range value. That is, the ordinate range of the standardized charge-discharge curve of the battery voltage-capacity is the same as the value of the ordinate range representing the charge-discharge cutoff voltage of the battery, and the same reference range is used.
The specific process of performing the standardization processing on the charge-discharge curve of the positive electrode voltage-specific capacity and the charge-discharge curve of the negative electrode voltage-specific capacity and the specific process of performing the combination processing on the standardization charge-discharge curve of the positive electrode voltage-specific capacity and the standardization charge-discharge curve of the negative electrode voltage-specific capacity may be referred to as "performing the standardization combination" on the measured charge-discharge curves of the positive electrode voltage-specific capacity, and when the N/P ratio of the soft-packed battery is 1, the obtained standardization charge-discharge curve of the positive electrode voltage-specific capacity is shown in fig. 4, the obtained standardization charge-discharge curve of the negative electrode voltage-specific capacity is shown in fig. 5, the battery standardization charge-discharge curve is shown in fig. 6, the battery standardization charge-discharge curve is shown in fig. 7, and the battery voltage-specific capacity standardization charge-discharge curve is shown in fig. 8;
step 3:
labeling "standardization original" according to FIG. 8Point a ", and dividing the capacity corresponding to the normalized origin a by the total charge capacity of the normalized charge-discharge curve, calculating a" normalized coefficient α ", wherein the capacity corresponding to the origin a is 0.4Ah, the total capacity is 0.95Ah,；
the "characterization point B" is labeled according to fig. 3, and the capacity corresponding to the characterization point B is divided by the total charge capacity of the characterization battery, calculating a "characterization coefficient β", wherein the characterization point B corresponds to a capacity of 3.8Ah, a total capacity of 9.6Ah,；
the value obtained by subtracting the ratio of the characterization coefficient beta divided by the normalization coefficient alpha from 1 is the relative offset coefficient lambda, in particular；
Step 4:
multiplying the standardized coefficient alpha by the total charge capacity of the characterization battery to obtain a characterization standardized capacity C; specifically, standard capacity is characterized；
In a charge-discharge curve of the battery voltage-capacity to be represented, taking 4.0416Ah as a reference, making a vertical line with an abscissa, and intersecting with the charge-discharge curve respectively to obtain a represented charge absolute voltage U1 and a represented discharge absolute voltage U2, as shown in fig. 9; then subtracting the characterization discharge absolute voltage U2 from the characterization charge absolute voltage U1 to obtain an absolute offset voltage U3; dividing the absolute offset voltage U3 by the charge-discharge voltage interval value of the characterization battery to obtain a relative offset voltage U, wherein the relative offset voltage U is specifically as follows:
absolute offset voltage；
Relative offset voltage；
Step 5: adding the relative offset coefficient lambda to the relative offset voltage U to obtain a cell polarization value phi representing the battery, in particular, the cell polarization value。
Comparative example 1: the positive electrode surface density is 470g/m by the characterization method 2 Fast characterization of the soft pack battery of (a):
the method for representing the electrical performance of the lithium battery comprises the following steps:
step 1: positive and negative half cells were prepared as described in steps 1 and 2 of example 1, and the same normalization coefficient α=0.421 was obtained;
performing charge and discharge test on the soft package battery to be characterized, wherein the charge multiplying power is 0.33C, the discharge multiplying power is 1C, and the charge and discharge voltage interval is 2.75V-4.2V; optionally, the charge-discharge process of the characterization battery can be tested according to GB/T31486 or a charge-discharge method specified by the characterization battery specification, so as to obtain a charge-discharge curve of the voltage-capacity of the characterization battery. The resulting charge-discharge curve is shown in fig. 10;
step 2: the "characterization point B" is labeled according to fig. 10, and the capacity corresponding to the characterization point B is divided by the total charge capacity of the characterization battery, calculating a "characterization coefficient β", wherein the characterization point B corresponds to a capacity of 3.9Ah, a total capacity of 12.281Ah,；
the value obtained by subtracting the ratio of the characterization coefficient beta divided by the normalization coefficient alpha from 1 is the relative offset coefficient lambda, in particular；
Step 3: multiplying the standardized coefficient alpha by the total charge capacity of the characterization battery to obtain a characterization standardized capacity C; tool withCharacterizing standard capacity in body；
In a charge-discharge curve of the battery voltage-capacity to be represented, taking 5.1703Ah as a reference, making a vertical line with an abscissa, and intersecting with the charge-discharge curve respectively to obtain a 'represented charge absolute voltage U1' and a 'represented discharge absolute voltage U2', as shown in FIG. 11; then subtracting the characterization discharge absolute voltage U2 from the characterization charge absolute voltage U1 to obtain an absolute offset voltage U3; dividing the absolute offset voltage U3 by the charge-discharge voltage interval value of the characterization battery to obtain a relative offset voltage U, wherein the relative offset voltage U is specifically as follows:
absolute offset voltage；
Relative offset voltage；
Step 4: adding the relative offset coefficient lambda to the relative offset voltage U to obtain a cell polarization value phi representing the battery, in particular, the cell polarization value。
Table 1 comparison of the results data of example 1 and comparative example 1
Comparing the cell polarization values of example 1 and comparative example 1, the polarization value of comparative example 1 is significantly larger, indicating that the positive electrode surface density is 470g/m 2 When the battery cell electrical property is obviously reduced, the positive electrode surface load in the subsequent coating working section is reduced, and the battery cell design is performed again.
In summary, the method for characterizing the electrical performance of the lithium battery provided by the invention can rapidly and simply judge the polarization degree and the electrical performance of the lithium ion battery, feed back important parameters in a preparation process section and optimize the manufacturing of the battery core.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (8)
1. A method for characterizing the electrical performance of a lithium battery, comprising the steps of:
step 1: respectively testing the charge and discharge processes of the assembled positive half-cell and negative half-cell to obtain a positive voltage-specific capacity charge and discharge curve and a negative voltage-specific capacity charge and discharge curve; testing the charge and discharge process of the characterization battery to obtain a charge and discharge curve of the characterization battery voltage-capacity;
step 2: performing standardization processing on the positive electrode voltage-specific capacity charge-discharge curve to obtain a positive electrode voltage-capacity standardized charge-discharge curve, performing standardization processing on the negative electrode voltage-specific capacity charge-discharge curve to obtain a negative electrode voltage-capacity standardized charge-discharge curve, and performing combination processing on the positive electrode voltage-capacity standardized charge-discharge curve and the negative electrode voltage-capacity standardized charge-discharge curve to obtain a battery voltage-capacity standardized charge-discharge curve;
step 3: selecting an intersection point in the standardized charge-discharge curve of the battery voltage-capacity as a standardized origin A, dividing the capacity corresponding to the standardized origin A by the total capacity of the charge curve in the standardized charge-discharge curve of the battery voltage-capacity, and obtaining a standardized coefficient alpha; selecting an intersection point of the charge-discharge curves representing the voltage-capacity of the battery as a representation point B, dividing the capacity corresponding to the representation point B by the total charge capacity of the battery to obtain a representation coefficient beta; the ratio of the characterization coefficient beta divided by the standardized coefficient alpha is subtracted by 1, and the obtained value is a relative offset coefficient lambda;
step 4: multiplying the standardized coefficient alpha by the total charge capacity of the characterization battery to obtain a characterization standardized capacity C; in the charge-discharge curve representing the voltage-capacity of the battery, taking the representing standardized capacity C as an abscissa base point, making a vertical line with an X axis, enabling the vertical line to be intersected with the charge-discharge curve representing the voltage-capacity of the battery respectively, correspondingly obtaining a representing charge absolute voltage U1 and a representing discharge absolute voltage U2, and subtracting the representing charge absolute voltage U2 from the representing charge absolute voltage U1 to obtain an absolute offset voltage U3; dividing the absolute offset voltage U3 by the charge-discharge voltage interval value of the characterization battery to obtain a relative offset voltage U;
step 5: adding the relative offset coefficient lambda to the relative offset voltage U to obtain a battery cell polarization value phi representing the battery, wherein the larger the battery cell polarization value phi is, the worse the battery cell electrical performance is represented;
in the step 2, the standardized processing of the charge-discharge curve of the positive electrode voltage-specific capacity and the charge-discharge curve of the negative electrode voltage-specific capacity includes the following specific steps:
step 2-1: dividing 1Ah by the specific charge capacity of the positive half cell to obtain a positive correction coefficient m 1 The method comprises the steps of carrying out a first treatment on the surface of the Multiplying the abscissa value of the charge-discharge curve of the positive electrode voltage-specific capacity by the positive electrode correction coefficient m 1 Obtaining a standardized charge-discharge curve of the voltage-capacity of the positive electrode;
step 2-2: divided by 1AhThe discharge specific capacity of the negative half cell is used for obtaining a negative correction coefficient m 2 The method comprises the steps of carrying out a first treatment on the surface of the Multiplying the abscissa value of the charge-discharge curve of the negative electrode voltage-specific capacity by the negative electrode correction coefficient m 2 And multiplying the N/P ratio of the characterization battery to obtain a standardized charge-discharge curve of the voltage-capacity of the negative electrode.
2. The method according to claim 1, wherein in step 1, the surface density of the positive electrode sheet in the assembled positive electrode half cell is not more than 100g/m 2 The surface density of the negative electrode plate in the assembled negative electrode half cell is not more than 50g/m 2 。
3. The method according to claim 1, wherein in step 1, the multiplying power of the positive half-cell and the negative half-cell is not more than 0.05C when the positive half-cell is charged and discharged.
4. The method according to claim 1, wherein in the step 1, the charge-discharge curve of the positive electrode voltage-specific capacity is a charge-discharge curve of the second cycle of the charge-discharge cycle of the positive electrode half-cell, and the charge-discharge curve of the negative electrode voltage-specific capacity is a charge-discharge curve of the second cycle of the charge-discharge cycle of the negative electrode half-cell.
5. The method according to claim 1, wherein in the step 2-1, the specific charge capacity of the positive half-cell is the specific charge capacity of the positive half-cell when the positive half-cell is charged to a set cutoff voltage;
in the step 2-2, the specific discharge capacity of the negative half-cell is the specific discharge capacity of the negative half-cell when the negative half-cell is discharged to a set cut-off voltage.
6. The method for characterizing electrical performance of a lithium battery according to claim 1, wherein in the step 2, the combination of the normalized charge-discharge curve of the positive electrode voltage-capacity and the normalized charge-discharge curve of the negative electrode voltage-capacity comprises the following specific steps:
step 2-3: the abscissa value of the charging curve in the standardized charging and discharging curve of the positive electrode voltage-capacity is kept unchanged, and the ordinate value of the charging curve is correspondingly subtracted from the ordinate value of the discharging curve in the standardized charging and discharging curve of the negative electrode voltage-capacity to obtain a standardized charging curve of the battery;
step 2-4: maintaining the abscissa value of the discharge curve in the standardized charge-discharge curve of the positive electrode voltage-capacity unchanged, and correspondingly subtracting the ordinate value of the charge curve in the standardized charge-discharge curve of the negative electrode voltage-capacity from the ordinate value of the discharge curve to obtain a standardized discharge curve of the battery;
step 2-5: and drawing the battery standardized charge curve and the battery standardized discharge curve in the same coordinate system to obtain the battery voltage-capacity standardized charge-discharge curve.
7. The method of claim 6, wherein the ordinate range of the standardized charge-discharge curve of battery voltage-capacity uses the charge-discharge cutoff voltage of the characterization battery as an ordinate range value.
8. A method for preparing a lithium battery, characterized in that the method for characterizing electrical properties of a lithium battery according to any one of claims 1 to 7 is used in the preparation of a lithium battery.
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