CN114965889B - Method for testing high-rate long-cycle characteristics of graphite anode material - Google Patents
Method for testing high-rate long-cycle characteristics of graphite anode material Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 67
- 239000010439 graphite Substances 0.000 title claims abstract description 67
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 67
- 238000012360 testing method Methods 0.000 title claims abstract description 66
- 239000010405 anode material Substances 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 title claims abstract description 40
- 239000000463 material Substances 0.000 claims abstract description 21
- 239000010406 cathode material Substances 0.000 claims abstract description 14
- 239000013078 crystal Substances 0.000 claims abstract description 8
- 238000007600 charging Methods 0.000 claims description 52
- 239000007773 negative electrode material Substances 0.000 claims description 21
- 238000007599 discharging Methods 0.000 claims description 20
- 239000002245 particle Substances 0.000 claims description 11
- 238000004458 analytical method Methods 0.000 claims description 8
- 239000006258 conductive agent Substances 0.000 claims description 8
- 238000009826 distribution Methods 0.000 claims description 7
- 238000004364 calculation method Methods 0.000 claims description 6
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 239000011230 binding agent Substances 0.000 claims description 4
- 230000001186 cumulative effect Effects 0.000 claims description 4
- 238000002441 X-ray diffraction Methods 0.000 claims description 3
- 230000005611 electricity Effects 0.000 claims description 2
- 238000012544 monitoring process Methods 0.000 claims description 2
- 230000009466 transformation Effects 0.000 claims description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 8
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 8
- 238000012795 verification Methods 0.000 abstract description 6
- 238000012216 screening Methods 0.000 abstract description 2
- 238000007796 conventional method Methods 0.000 abstract 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 8
- 229910052744 lithium Inorganic materials 0.000 description 8
- 239000000047 product Substances 0.000 description 6
- 239000011248 coating agent Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 239000002002 slurry Substances 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- 239000000084 colloidal system Substances 0.000 description 3
- 239000011889 copper foil Substances 0.000 description 3
- 230000002687 intercalation Effects 0.000 description 3
- 238000009830 intercalation Methods 0.000 description 3
- 239000007774 positive electrode material Substances 0.000 description 3
- 238000005096 rolling process Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 238000010281 constant-current constant-voltage charging Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000011883 electrode binding agent Substances 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 239000007788 liquid Substances 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
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 210000003097 mucus Anatomy 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/378—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC] specially adapted for the type of battery or accumulator
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- 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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Abstract
The invention belongs to the field of graphite cathode materials of lithium ion batteries, and relates to a method for testing high-rate long-cycle characteristics of a graphite cathode material. In order to solve the technical problems that the conventional method for testing the high-rate long-cycle characteristics of the graphite anode material consumes long time and affects the application period of products, the method for testing the high-rate long-cycle characteristics of the graphite anode material is simple and easy to implement, and can judge whether the method is suitable for long-cycle high-rate lithium ion batteries or not only by testing basic parameters, diffraction intensity of crystal faces and electrochemical performance of the graphite anode material, so that the influence on iterative updating of products caused by overlong verification time is greatly reduced, and the application of the products and the screening of the materials are easier.
Description
Technical Field
The invention belongs to the field of graphite negative electrode materials of lithium ion batteries, and relates to a performance test method of a graphite negative electrode material.
Background
With the development of lithium ion batteries, they are applied to various fields, wherein the application in energy storage is common and the market is large. The energy storage application scene often has stricter requirements on high safety and high reliability of the battery core, the service life of the battery core is required to be as long as ten thousands times, in failure analysis of some lithium ion batteries, the positive electrode material is found to have the original capacity at the later period of battery cycle, and the capacity loss is more in the negative electrode, so that the test of the high-rate long-cycle characteristic of the negative electrode material is particularly important.
The high rate long cycle characteristic means that lithium precipitation does not occur at a rate of 2C or more and that the cycle of 0.5C/0.5C 100% DOD is 6000 times or more.
At present, the test of the high-rate long-cycle characteristic of the cathode material is only long-term verification of the material, the material generally needs to be manufactured into a battery cell for verification, and needs to be continuously subjected to charge and discharge cycles for at least 1000 times, whether the material can be used or not can be known in a prediction mode at the later stage, and even more, the performance of the material can be known when the battery cell manufactured into the material is circulated to EOL (80% retention rate), so that the material selection time is greatly prolonged, and the time for selecting the material is reduced by 4 months, 1 year or even 2 years. Long-term verification in the selection of the anode material often misses the optimal product application period, and the corresponding product may face a lagging state.
Disclosure of Invention
The invention provides a method for testing high-rate long-cycle characteristics of a graphite negative electrode material, which aims to solve the technical problems that the existing method for testing the high-rate long-cycle characteristics of the graphite negative electrode material is long in time consumption and affects the application period of products.
The method for testing the high-rate long-cycle characteristic of the graphite anode material is characterized by comprising the following steps of: 1) Performing particle size distribution test on the basic parameter test of the graphite anode material to obtain D50 and D10 values of the graphite anode material; d50 represents a particle diameter at which the cumulative distribution of the graphite anode material particles is 50%, and D10 represents a particle diameter at which the cumulative distribution of the graphite anode material particles is 10%;
performing tap density test to obtain the tap density of the graphite anode material;
Carrying out a specific surface area test to obtain the specific surface area of the graphite anode material;
Performing X-ray diffraction to obtain the ratio OI of the graphite anode material I004/I110; I004/I110 represents the ratio of the diffraction intensity I004 of the 004 crystal face to the diffraction intensity I110 of the 110 crystal face of the graphite cathode material;
step 2) is carried out under the condition that D50 is less than or equal to 17um and D10 is less than or equal to 8 um;
2) The graphite cathode material is made into button cell for analysis
2.1 Manufacturing a button cell from a graphite negative electrode material;
2.2 Charging and discharging test is carried out on the button cell to obtain data of capacity A and voltage B, and a charging and discharging V (B) -Q (A) curve is drawn, wherein B is voltage, and A is capacity;
2.3 The conversion calculation is carried out on the capacity data A during charging to obtain the ratio C i,Ci＝Ai/An,Ai of the capacity data A i and the data A n during charging as the capacity data recorded at the ith time during charging, A n is the capacity data recorded at the last time during charging, and i=1, 2 and 3 … … n;
Calculating a value D1 of (C 2-C1)/(B2-B1), and analogically obtaining a value Di of (C i+1-Ci)/(B i+1-Bi), wherein B i is voltage data corresponding to A i, and when B i+1＝Bi is performed, only one data is reserved; drawing a charging B-D curve according to the method, wherein B is an x-axis, and D is a Y-axis;
2.4 The transformation calculation is carried out on the capacity data A during discharge to obtain the ratio C i,Ci＝Ai/An,Ai of the capacity data A i and the data A n during discharge as the capacity data recorded at the ith time during discharge, A n is the capacity data recorded at the last time during discharge, i=1, 2,3 … … n;
calculating a value D1 of (C 2-C1)/(B2-B1), analogically obtaining a value Di of (C i+1-Ci)/(B i+1-B i), when B i+1 =Bi, only retaining one of the data, and drawing a discharge B-D curve, wherein B is an x-axis, and D is a Y-axis;
2.5 Drawing a charging B-D curve and a discharging B-D curve under the same coordinate system to form a charging and discharging B-D curve; the peaks on the charge-discharge B-D curves are named from left to right and clockwise: the first peak is named F1, the second peak is named F2, the third peak is named F3, the fourth peak is named F4, the 5 th peak is named F5, and the sixth peak is named F6;
2.6 According to the charge-discharge B-D curve, corresponding values FX1 and FX2 of F1 and F2 and corresponding value FX3 of F3 in the X axis are obtained;
step 2.7 is carried out under the conditions that FX1 is more than or equal to 3.2 and less than or equal to 3.3V, FX2 is more than or equal to 3.3 and less than or equal to 3.4V, FX3 is more than or equal to 3.4 and less than or equal to 3.45V;
2.7 A value F3X of the difference FX34 of F3, F4 in the X axis, a value F2X of the difference FX25 of F2, F5 in the X axis, a value F1X of the difference FX16 of F1, F6 in the X axis;
Step 3) is carried out under the conditions that f3x is less than or equal to 0.1V, f2x is less than or equal to 0.1V and f1x is less than or equal to 0.15V;
3) Preparing graphite cathode material into full-electric battery for analysis
3.1 Charging and discharging test is carried out on the all-electric battery to obtain data of capacity A and voltage B during charging, a charging B-D curve of the all-electric battery is obtained by adopting the method of the step 2.3), and peaks on the charging B-D curve of the all-electric battery are named from left to right: the first peak was designated as F1, the second peak was designated as F2, and the third peak was designated as F3;
3.2 According to the charging B-D curve of the full-electric battery, acquiring corresponding values FY2, FY3 and FY1 of the full-electric batteries F2, F3 and F1 on the Y axis, and calculating FY2, FY3 and FY1, wherein the data is F6Y;
step 4) is carried out under the condition that f6y is more than 0.5;
4) Comprehensive judgment
Calculating the value of L1 according to formula (1);
L1＝((a1+a2)*I1+b1*c1)*(f3x+f2x+f1x)-f6y(1)；
wherein a1 is the value of D50, a2 is the value of D10, I1 is the value of the ratio OI, b1 is the value of the specific surface area, c1 is the value of the tap density, f3x is the value of FX34, f2x is the value of FX25, f1x is the value of FX16, and f6y is the calculated value of FY 2:FY3:FY1;
When L1 is less than or equal to 5.1, the anode material has high-rate long-cycle characteristic.
According to the technical scheme, when the high-rate long-cycle characteristic of the graphite anode material is tested, only the basic parameters and the diffraction intensity of crystal faces of the graphite anode material and the charge and discharge characteristics of the manufactured button cell and the full-electric cell are required to be tested, so that whether the graphite anode material has the high-rate long-cycle characteristic can be judged, and compared with the existing verification method, the testing time is greatly saved.
Optionally, in step 2.1), when the graphite anode material is made into a button cell, the weight ratio of the materials of the button cell is as follows: graphite negative electrode material: conductive agent: binder = 95% -98%:1% -2.5%:1% -2.5%.
Optionally, in step 2.1), when the graphite anode material is made into a button cell, the weight ratio of the materials of the button cell is as follows: graphite negative electrode material: conductive agent: binder = 98%:1%:1%.
Optionally, the charge-discharge rate of the button cell in step 2.2) is 0.1C.
Through the technical scheme, the button cell can fully show the basic characteristics of the material under the multiplying power of 0.1C, so that the result is more accurate and reliable.
Optionally, the method for making the graphite anode material into full electricity in the step 3) specifically comprises the following steps: and (3) preparing a graphite cathode material into a 1-7Ah battery cell, and matching the battery cell with the positive electrode-lithium iron phosphate to prepare the full-electric battery.
To a certain extent, the small battery cells 1-7Ah can basically exclude the influence of thermodynamics on the battery performance and are closer to the characteristics of the material, so that the accuracy of the test can be improved through the technical scheme.
Optionally, in the step 3.1) full-electric battery charging and discharging test, the battery core is charged to a voltage V1 at a constant current and constant voltage with a multiplying power m, the current is cut off by 0.05C, and the multiplying power m discharging is carried out after the rest time T1; wherein m is less than or equal to 0.5C, V1=2.5-3.65V, and T1 is more than or equal to 30min.
Alternatively, m=0.2c in step 3.1).
Optionally, in order to ensure accuracy of the test result, the number of charging and discharging in step 3.1) is 3.
Optionally, in step 3.1), when the charge and discharge test is performed, the temperature of the battery core made of the graphite anode material is monitored, and when the temperature rise of the battery core is less than or equal to 10 ℃, the data of the capacity A and the voltage B in the secondary charge and discharge process are available data.
Compared with the prior art, the invention has the beneficial effects that:
The method for testing the high-rate long-cycle characteristic of the graphite negative electrode material is simple and easy to operate, only needs to test basic parameters of graphite, and in addition, the graphite negative electrode material is made into a button cell and an all-electric cell, the button cell is subjected to 1-3 times of charge and discharge tests, and the obtained capacitance voltage data is transformed and a curve is drawn; performing charge and discharge test on the full-electric battery for 1-3 times, converting the obtained capacitance voltage data and drawing a curve; the related data obtained through the test can judge whether the test is suitable for the long-cycle high-multiplying power lithium ion battery, and compared with the existing charge-discharge cycle test mode which is used for more than 1000 times, the method greatly reduces the influence on iterative updating of the product caused by overlong verification time, and ensures that the product application and material screening are easier.
Drawings
FIG. 1 is a graph of the charge V (B) -Q (A) for graphite-5 as a button cell.
FIG. 2 is a charge-discharge B-D curve of graphite-5 when made into a button cell.
FIG. 3 is a schematic diagram showing the peak naming of the charge-discharge B-D curve of graphite-5 when made into a button cell.
Detailed Description
The test samples are graphite-1, graphite-2, graphite-3, graphite-4 and graphite-5, respectively, and the method for testing the high-rate long-cycle characteristics of the graphite negative electrode material of the present invention will be described below by taking graphite-5 as an example.
The method for testing the high-rate long-cycle characteristic of graphite-5 comprises the following steps:
1) Basic parameter testing
Performing particle size distribution test to obtain D50 and D10 values of graphite-5;
performing a solid density test to obtain the tap density of graphite-5;
Carrying out a specific surface area test to obtain the specific surface area of graphite-5;
Performing X-ray diffraction to obtain the I004/I110 ratio OI of graphite-5; I004/I110 represents the ratio of the diffraction intensity I004 of the 004 crystal face to the diffraction intensity I110 of the 110 crystal face of the graphite cathode material;
2) Graphite-5 was fabricated into button cell for analysis
The buckling manufacturing method specifically comprises the following steps: according to the mass ratio, graphite-5: conductive agent: colloid = 97%:1.5%:1.5%. Graphite (9.7000 +/-0.0001) g, conductive agent (0.1500 g+/-0.0001) g and negative electrode binder (0.1500+/-0.0001) g to be measured are respectively weighed, placed in a beaker, and are primarily mixed uniformly by a spoon, then 15ml of fresh deionized water is added, and is uniformly mixed by stirring, 1-5ml of water is properly added, a magnetic stirrer is turned on, stirring is continued for 6 hours, and stirring of the bottom of the beaker by the spoon is stopped until the bottom of the beaker is thick and the mucus is uniform during stirring. The slurry is used for coating the copper foil, the coated material is placed in a blast drying oven for drying for 30min at 75 ℃ so that water in the product is fully volatilized, and then the copper foil is placed in a vacuum oven for vacuum drying for 2 hours at 120 ℃, taken out and placed in a dryer for cooling for 5min. Cooling, rolling, vacuum baking for 1 hr, punching into 13.0mm diameter disc with a punch, vacuum baking at 70deg.C for 1 hr, drying the membrane (base membrane 12 microns, ceramic layer 4 microns), spring sheet, gasket and buckling shell, transferring into glove box, and dripping enough electrolyte to obtain the final product.
The prepared button cell is charged and discharged at 0.1C between 0.005V and 2V, and the needed charge and discharge data are obtained after 2 times of circulation. According to the data of the capacity A and the voltage B obtained in the charging and discharging process, a charging and discharging V (B) -Q (A) curve is drawn, wherein B is voltage, A is capacity, and only a charging V (B) -Q (A) curve is shown in fig. 1.
And judging the rationality of the acquired data of the capacity A and the voltage B according to the drawn charge-discharge V (B) -Q (A) curve.
Under the condition that the data of the capacity A and the voltage B are reasonable, a charging B-D curve and a discharging B-D curve are respectively manufactured.
Charging B-D curve preparation: the conversion calculation is performed on the capacity data a during charging, so that the ratio C i,Ci＝Ai/An,Ai of the capacity data a i and the data a n during charging is the capacity data recorded at the ith time during charging, a n is the capacity data recorded at the last time during charging, and i=1, 2,3 … … n.
Calculating the value D1 of (C 2-C1)/(B2-B1), and analogically obtaining the value Di of (C i+1-Ci)/(B i+1-B i), and when B i+1＝B i, only retaining one data; the upper half of the charge-discharge B-D curve shown in FIG. 1, i.e., the charge B-D curve, is drawn accordingly, where B is the x-axis and D is the Y-axis.
Table 1 below is a list of capacity a i, voltage B i, and conversion data C i、Di obtained during charging of graphite-5.
Table 1 list of related data obtained by charging
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In Table 1, the data for C i shows six bits after the decimal point, and the actual D i is calculated based on the actual value of C i, e.g., the actual value of C i is 0.0008119629203.
And (3) manufacturing a discharge B-D curve: the capacity data a during discharge is converted and calculated to obtain the ratio C i,Ci＝Ai/An,Ai of the capacity data a i and the data a n during discharge as the capacity data recorded at the ith time during discharge, and a n as the capacity data recorded at the last time during discharge, i=1, 2,3 … … n.
Calculating the value D1 of (C 2-C1)/(B2-B1), and so on to obtain the value Di of (C i+1-Ci)/(B i+1-B i), wherein B i is voltage data corresponding to A i, only one of the data is reserved when B i+1＝B i is performed, and a discharging B-D curve is drawn, wherein the discharging B-D curve is the lower half part of the charging and discharging B-D curve shown in fig. 2, B is an x axis, and D is a Y axis.
Drawing a charging B-D curve and a discharging B-D curve under the same coordinate system to form a charging B-D curve shown in figure 2; as shown in fig. 3, peaks on the charge-discharge B-D curve are named left to right and clockwise: the first peak was designated as F1, the second peak was designated as F2, the third peak was designated as F3, the fourth peak was designated as F4, the 5 th peak was designated as F5, and the sixth peak was designated as F6.
And according to the charge-discharge B-D curve, acquiring corresponding values FX1 and FX2 of F1 and F2 and corresponding value FX3 of F3 in the X axis.
Under the conditions that FX1 is more than or equal to 3.2 and less than or equal to 3.3V, FX2 is more than or equal to 3.3 and less than or equal to 3.4V, FX3 is more than or equal to 3.4 and less than or equal to 3.45V, the numerical value F3X of the difference value FX34 of F3 and F4 in the X axis, the numerical value F2X of the difference value FX25 of F2 and F5 in the X axis, and the numerical value F1X of the difference value FX16 of F1 and F6 in the X axis are obtained.
Under the conditions that f3x is less than or equal to 0.1V, f2x is less than or equal to 0.1V and f1x is less than or equal to 0.15V, the cathode material has stronger dynamic performance, and the step 3 is carried out.
3) Graphite-5 was prepared into an all-electric cell for analysis
The manufacturing method of the all-electric battery specifically comprises the following steps: the positive electrode material takes lithium iron phosphate material as a main material, and the mass ratio of the positive electrode material to the conductive agent and the colloid is 96 percent: 2%:2%, mixing into slurry, coating on a 12-micrometer current collector, wherein the coating surface density is 41.6mg/cm 2, the rolling thickness is 187 micrometers, and drying and cutting the pole piece into small pieces with 120mm and 62 mm. The mass ratio of graphite-5 to the conductive agent to the colloid is 97 percent: 1%:2, after being prepared into slurry, the slurry is coated on a copper foil with 6 microns, the coating surface density is 19.6mg/cm 2, the rolling thickness is 125 microns, a pole piece is dried and cut into small pieces with 125mm or 66mm, 18 layers of positive pole pieces, 19 layers of negative pole pieces and a diaphragm with the thickness of 16 microns are selected for lamination, a required battery cell is obtained, the required battery cell is packaged by an aluminum-plastic film with the thickness of 153 microns, and finally the required battery cell is obtained by liquid injection.
The required battery core is charged at constant current and constant voltage of 0.2C between 2.5V and 3.65V, the cut-off current is 0.05C, and the battery core is kept stand for 30min, and the constant current discharge is carried out at 0.2C; and (3) circularly performing charge and discharge, wherein the times are 3, selecting data, monitoring the temperature in the charge and discharge process, and selecting the charge and discharge data of the time as object data when the temperature rise of the battery cell is less than or equal to 10 ℃.
The charging B-D curve of the all-electric battery is obtained by adopting the same method as the manufacturing of the charging B-D curve of the button battery, and the peaks on the charging B-D curve of the all-electric battery are named from left to right: the first peak was designated as F1, the second peak was designated as F2, and the third peak was designated as F3.
According to the charging B-D curve of the full-electric battery, acquiring corresponding values FY2, FY3 and FY1 of the full-electric batteries F2, F3 and F1 on the Y axis, and calculating FY2, FY3 and FY1, wherein the data is F6Y;
The B-D charging curve of the lithium ion battery is the key of research when the battery is fully charged, F1, F2 and F3 respectively correspond to three lithium intercalation reactions of lithium ion intercalation graphite, and the strength and the speed of the reactions directly determine the multiplying power and the cycle performance of the material. And calculating the ratio of the obtained three peak values, wherein the values FY2, FY3 and FY1 corresponding to the axes F2, F3 and F1 are FY2, FY3 and FY1, the ratio FY231 (FY 2: FY3: FY 1) is more than 0.5, and the closer to 1, the stronger the dynamic performance and the stronger the multiplying power performance of the material are, and the better the reversibility of the contraction and expansion of the material is under the same multiplying power.
Step 4) is carried out under the condition that f6y is more than 0.5;
4) Comprehensive judgment
Calculating the value of L1 according to formula 1);
L1＝((a1+a2)*I1+b1*c1)*(f3x+f2x+f1x)-f6y (1)；
wherein a1 is the value of D50, a2 is the value of D10, I1 is the value of the ratio OI, b1 is the value of the specific surface area, c1 is the value of the tap density, f3x is the value of FX34, f2x is the value of FX25, f1x is the value of FX16, and f6y is the calculated value of FY 2:FY3:FY1;
When L1 is less than or equal to 5.1, the anode material has high-rate long-cycle characteristic.
The high-rate long-cycle characteristics of graphite-1, graphite-2, graphite-3, and graphite-4 were tested in the same test method to obtain values of f3x, f2x, f1x, f6y, a1, a2, b1, c1, and L1 of each graphite negative electrode material, respectively, as shown in table 2.
Table 2 test values for each anode material
| f3x | f2x | f1x | f6y | a1 | a2 | b1 | c1 | L1 | |
| Graphite-1 | 0.1 | 0.13 | 0.12 | 0.325 | 18.6 | 9 | 1.52 | 1.17 | 8.9915 |
| Graphite-2 | 0.08 | 0.09 | 0.11 | 0.494 | 15.6 | 8.1 | 1.54 | 1.1 | 5.9523 |
| Graphite-3 | 0.06 | 0.09 | 0.11 | 0.519 | 12.4 | 5.8 | 1.66 | 1.16 | 3.7675 |
| Graphite-4 | 0.08 | 0.14 | 0.13 | 0.370 | 17.4 | 7.1 | 1.09 | 1.1 | 7.7675 |
| Graphite-5 | 0.06 | 0.09 | 0.11 | 0.612 | 15.6 | 7.6 | 1.5 | 1.11 | 4.6462 |
From the analysis of the results of the test: the comprehensive performance of the graphite-3 is stronger than that of the graphite-5, the graphite-2, the graphite-4 and the graphite-1, and the graphite-3 and the graphite-5 are cathode materials suitable for large-multiplying-power long-cycle.
In order to further prove the rationality of the method, DCR tests under different SOC (state of charge), cycle tests under different multiplying power and full-charge disassembly tests after high-multiplying power constant-current constant-voltage charging are carried out.
The DCR calculation was performed at different SOCs (states of charge) by charging the cells made of graphite-1, graphite-2, graphite-3, graphite-4, and graphite-5, and the obtained DCR test data are shown in table 3. From the data in table 3, it can be seen that: at 50% SOC, the direct current internal resistance of graphite-3 is minimum, the comprehensive polarization of charging is minimum, and the charging polarization of graphite-1 is maximum, so that lithium intercalation is more difficult.
TABLE 3 DCR test values for negative electrode materials
| SOC | Graphite-1/mΩ | Graphite-2/mΩ | Graphite-3/mΩ | Graphite-4/mΩ | Graphite-5/mΩ |
| 0.9 | 13.556 | 13.146 | 10.862 | 12.117 | 11.523 |
| 0.5 | 12.925 | 12.656 | 10.424 | 11.215 | 11.035 |
| 0.2 | 12.778 | 12.034 | 10.353 | 11.392 | 10.950 |
The battery cores made of graphite-1, graphite-2, graphite-3, graphite-4 and graphite-5 were subjected to cyclic tests at different multiplying powers, and the test data are shown in tables 4, 5 and 6.
TABLE 4 cycle test data at 1C/1C 100% DOD for each negative electrode material
| 1C/1C 100％DOD | Number of cycles | Discharge plateau voltage |
| Graphite-1 | 1500 Times 80% | 3.18 |
| Graphite-2 | 4000 Times 80% | 3.189 |
| Graphite-3 | 5000 Times 80% | 3.1975 |
| Graphite-4 | 3000 Times 80% | 3.179 |
| Graphite-5 | 4500 Times 80% | 3.19 |
1500 Out of 80% 1500 indicates that there is 80% of the initial capacity after 1500 cycles.
TABLE 5 cycle test data at 1C/1C 100% DOD for each negative electrode material
| 0.5C/1C cycle 100% DOD | Number of cycles | Discharge plateau voltage |
| Graphite-1 | 1500 Times 86% | 3.17 |
| Graphite-2 | 1500 Times 91% | 3.188 |
| Graphite-3 | 1500 Times 93% | 3.1925 |
| Graphite-4 | 1500 Times 90% | 3.176 |
| Graphite-5 | 1500 Times 92% | 3.191 |
TABLE 6 cycle test data for each negative electrode material at 2C/2C cycle 100% DOD
As can be seen from the data in tables 4, 5 and 6, the higher the L1 value, the more unfavorable the circulation, and the smaller the L1 value, the better. It was also found that the discharge voltage plateau of graphite was also related to L1, the lower L1 the higher its discharge plateau.
The cells made of graphite-1, graphite-2, graphite-3, graphite-4 and graphite-5 were charged at constant current and constant voltage at 2C, and the case of full power disassembly of the cells is shown in table 7.
TABLE 7 constant current constant voltage charging of each negative electrode material under 2C conditions, full power disassembly of the cell
| Interface(s) | |
| Graphite-1 | 100% Interfacial severe lithium precipitation |
| Graphite-2 | 50% Interfacial lithium precipitation |
| Graphite-3 | Lithium is not separated out |
| Graphite-4 | 75% Interfacial lithium precipitation |
| Graphite-5 | Lithium is not separated out |
As shown in table 7, at a large rate, the interface of the fully charged disassembled cell clearly shows that the lower the L1 value, the better, and within 5.1, the larger the rate is beyond 2C.
The test results of tables 3, 4, 5,6, and 7 are consistent with the test results of the present invention, indicating the accuracy of the test methods of the present invention.
Claims (8)
1. The method for testing the high-rate long-cycle characteristic of the graphite anode material is characterized by comprising the following steps of:
【1】 Basic parameter test of graphite anode material
Performing a particle size distribution test to obtain a D50 value and a D10 value of the graphite anode material; d50 represents a particle diameter at which the cumulative distribution of the graphite anode material particles is 50%, and D10 represents a particle diameter at which the cumulative distribution of the graphite anode material particles is 10%;
performing tap density test to obtain the tap density of the graphite anode material;
Carrying out a specific surface area test to obtain the specific surface area of the graphite anode material;
Performing X-ray diffraction to obtain the ratio OI of the graphite anode material I004/I110; I004/I110 represents the ratio of the diffraction intensity I004 of the 004 crystal face to the diffraction intensity I110 of the 110 crystal face of the graphite cathode material;
Under the condition that D50 is less than or equal to 17um and D10 is less than or equal to 8um, performing a step (2);
【2】 The graphite cathode material is made into button cell for analysis
2.1 Manufacturing a button cell from a graphite negative electrode material;
2.2 Charging and discharging test is carried out on the button cell to obtain data of capacity A and voltage B, and a charging and discharging V (B) -Q (A) curve is drawn, wherein B is voltage, and A is capacity;
2.3 The conversion calculation is carried out on the capacity data A during charging to obtain the ratio C i,Ci＝Ai/An,Ai of the capacity data A i and the data A n during charging as the capacity data recorded at the ith time during charging, A n is the capacity data recorded at the last time during charging, and i=1, 2 and 3 … … n;
calculating a value D1 of (C 2-C1)/(B2-B1), and analogically obtaining a value Di of (C i+1-Ci)/(Bi+1-Bi), wherein B i is voltage data corresponding to A i, and when B i+1＝Bi is performed, only one data is reserved; drawing a charging B-D curve according to the method, wherein B is an x-axis, and D is a Y-axis;
2.4 The transformation calculation is carried out on the capacity data A during discharge to obtain the ratio C i,Ci＝Ai/An,Ai of the capacity data A i and the data A n during discharge as the capacity data recorded at the ith time during discharge, A n is the capacity data recorded at the last time during discharge, i=1, 2,3 … … n;
Calculating a value D1 of (C 2-C1)/(B2-B1), analogically obtaining a value Di of (C i+1-Ci)/(Bi+1-Bi), when B i+1 =Bi, only retaining one of the data, and drawing a discharge B-D curve, wherein B is an x-axis, and D is a Y-axis;
2.5 Drawing a charging B-D curve and a discharging B-D curve under the same coordinate system to form a charging and discharging B-D curve; the peaks on the charge-discharge B-D curves are named from left to right and clockwise: the first peak is named F1, the second peak is named F2, the third peak is named F3, the fourth peak is named F4, the 5 th peak is named F5, and the sixth peak is named F6;
2.6 According to the charge-discharge B-D curve, corresponding values FX1 and FX2 of F1 and F2 and corresponding value FX3 of F3 in the X axis are obtained;
step 2.7 is carried out under the conditions that FX1 is more than or equal to 3.2 and less than or equal to 3.3V, FX2 is more than or equal to 3.3 and less than or equal to 3.4V, FX3 is more than or equal to 3.4 and less than or equal to 3.45V;
2.7 A value F3X of the difference FX34 of F3, F4 in the X axis, a value F2X of the difference FX25 of F2, F5 in the X axis, a value F1X of the difference FX16 of F1, F6 in the X axis;
Step [ 3 ] is performed under the conditions that f3x is less than or equal to 0.1V, f2x is less than or equal to 0.1V and f1x is less than or equal to 0.15V;
【3】 Preparing graphite cathode material into full-electric battery for analysis
3.1 Charging and discharging test is carried out on the all-electric battery to obtain data of capacity A and voltage B during charging, a charging B-D curve of the all-electric battery is obtained by adopting the method of the step 2.3), and peaks on the charging B-D curve of the all-electric battery are named from left to right: the first peak was designated as F1, the second peak was designated as F2, and the third peak was designated as F3;
3.2 According to the charging B-D curve of the full-electric battery, acquiring corresponding values FY2, FY3 and FY1 of the full-electric batteries F2, F3 and F1 on the Y axis, and calculating FY2, FY3 and FY1, wherein the data is F6Y;
under the condition that f6y is more than 0.5, performing a step [ 4 ];
【4】 Comprehensive judgment
Calculating the value of L1 according to formula (1);
L1＝((a1+a2)*I1+b1*c1)*(f3x+f2x+f1x)-f6y(1)；
wherein a1 is the value of D50, a2 is the value of D10, I1 is the value of the ratio OI, b1 is the value of the specific surface area, c1 is the value of the tap density, f3x is the value of FX34, f2x is the value of FX25, f1x is the value of FX16, and f6y is the calculated value of FY 2:FY3:FY1;
When L1 is less than or equal to 5.1, the anode material has high-rate long-cycle characteristic;
And 3.1) monitoring the temperature of a battery cell made of the graphite anode material when the charge and discharge test is carried out, and taking the data of the capacity A and the voltage B in the secondary charge and discharge process as available data when the temperature rise of the battery cell is less than or equal to 10 ℃.
2. The method for testing the high-rate long-cycle characteristics of the graphite anode material according to claim 1, wherein the method comprises the following steps:
step 2.1) when the graphite anode material is made into a button cell, the button cell comprises the following materials in percentage by mass: graphite negative electrode material: conductive agent: binder = 95% -98%:1% -2.5%:1% -2.5%.
3. The method for testing the high-rate long-cycle characteristics of the graphite anode material according to claim 2, wherein the method comprises the following steps:
Step 2.1) when the graphite anode material is made into a button cell, the button cell comprises the following materials in percentage by mass: graphite negative electrode material: conductive agent: binder = 98%:1%:1%.
4. The method for testing the high-rate long-cycle characteristics of the graphite anode material according to claim 1, wherein the method comprises the following steps:
The charge-discharge rate of the button cell in the step 2.2) was 0.1C.
5. The method for testing the high-rate long-cycle characteristics of the graphite anode material according to claim 4, wherein the method comprises the following steps:
The method for making the graphite anode material into full electricity in the step [ 3 ] comprises the following steps:
And (3) preparing a graphite cathode material into a 1-7Ah battery cell, and matching the battery cell with the positive electrode-lithium iron phosphate to prepare the full-electric battery.
6. The method for testing the high-rate long-cycle characteristics of the graphite anode material according to claim 5, wherein the method comprises the following steps:
Step 3.1), during the full-electric battery charge and discharge test, the battery core is charged to a voltage V1 at constant current and constant voltage with a multiplying power m, the current is cut off by 0.05C, and the multiplying power m is discharged after the rest time T1; wherein m is less than or equal to 0.5C, V1=2.5-3.65V, and T1 is more than or equal to 30min.
7. The method for testing the high-rate long-cycle characteristics of the graphite anode material according to claim 6, wherein the method comprises the following steps:
M=0.2c in step 3.1).
8. The method for testing high-rate long-cycle characteristics of an ink negative electrode material according to claim 7, characterized in that:
The number of charge and discharge times in step 3.1) was 3.
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