CN114965889A - Method for testing high-rate long-cycle characteristics of graphite negative electrode material - Google Patents
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 69
- 239000010439 graphite Substances 0.000 title claims abstract description 69
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 69
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- 238000000034 method Methods 0.000 title claims abstract description 33
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- 239000010406 cathode material Substances 0.000 claims abstract description 36
- 239000000463 material Substances 0.000 claims abstract description 21
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- 239000002245 particle Substances 0.000 claims description 11
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- 239000006258 conductive agent Substances 0.000 claims description 8
- 239000010405 anode material Substances 0.000 claims description 7
- 238000006243 chemical reaction Methods 0.000 claims description 7
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- 238000010281 constant-current constant-voltage charging Methods 0.000 claims description 3
- 230000005611 electricity Effects 0.000 claims description 3
- 238000012544 monitoring process Methods 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
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 8
- 229910052744 lithium Inorganic materials 0.000 description 8
- 238000001035 drying Methods 0.000 description 4
- 239000002002 slurry Substances 0.000 description 4
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- 239000000084 colloidal system Substances 0.000 description 3
- 125000004122 cyclic group Chemical group 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000011889 copper foil Substances 0.000 description 2
- 230000002687 intercalation Effects 0.000 description 2
- 238000009830 intercalation Methods 0.000 description 2
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
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- 238000007796 conventional method Methods 0.000 description 1
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- 238000005520 cutting process Methods 0.000 description 1
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- 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
- 238000004146 energy storage Methods 0.000 description 1
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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 graphite cathode material high-rate long-cycle characteristic testing method consumes long time and affects the application period of a product, the graphite cathode material high-rate long-cycle characteristic testing method provided by the invention is simple and easy to implement, and whether the graphite cathode material is suitable for a long-cycle high-rate lithium ion battery can be judged only by testing basic parameters, the diffraction intensity of a crystal face and the electrochemical performance of the graphite cathode material, so that the influence on iterative updating of the product due to overlong verification time is greatly reduced, and the product application and material screening are easier.
Description
Technical Field
The invention belongs to the field of graphite cathode materials of lithium ion batteries, and relates to a performance test method for a graphite cathode material.
Background
With the development of lithium ion batteries, they are applied to various fields, in which applications in energy storage are widespread and the market is large. In the failure analysis of some lithium ion batteries, the positive electrode material still has the original capacity at the later cycle stage of the battery, and the capacity loss is more at 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 no lithium precipitation occurs at a rate of 2C or more, and the cycle 0.5C/0.5C 100% DOD is 6000 times or more.
At present, the testing of the high-rate long-cycle characteristics of the negative electrode material in the industry only remains long-term verification of the material, the material generally needs to be manufactured into a battery cell for verification, at least 1000 charge and discharge cycles need to be continuously performed, whether the material can be used can be known in a later prediction mode, furthermore, the performance of the material can be known only when the battery cell manufactured by the material is circulated to EOL (80% retention rate), the material selection time is greatly prolonged, and 4 months or more are less, namely 1 year or even 2 years. Long-term verification in the selection of the negative electrode material often misses the optimal product application period, and the corresponding product may face an lagging state.
Disclosure of Invention
The invention provides a method for testing the high-rate long-cycle characteristic of a graphite negative electrode material, which aims to solve the technical problems that the conventional method for testing the high-rate long-cycle characteristic of the graphite negative electrode material consumes long time and affects the application period of a product.
A test method for high-rate long-cycle characteristics of a graphite negative electrode material is characterized by comprising the following steps:
1) testing basic parameters of the graphite cathode material to perform particle size distribution test, and obtaining D50 and D10 values of the graphite cathode material; d50 represents a particle size at which the cumulative distribution of graphite negative electrode material particles is 50%, D10 represents a particle size at which the cumulative distribution of graphite negative electrode material particles is 10%;
performing tap density test to obtain tap density of the graphite cathode material;
carrying out a specific surface area test to obtain the specific surface area of the graphite negative electrode material;
carrying out X-ray diffraction to obtain the ratio OI of the graphite cathode material I004/I110; I004/I110 represents the ratio of the diffraction intensity I004 of the 004 crystal face of the graphite cathode material to the diffraction intensity I110 of the 110 crystal face;
the step 2) is carried out under the conditions 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) preparing the graphite cathode material into a button cell;
2.2) carrying out charge and discharge test on the button cell to obtain data of capacity A and voltage B, and drawing a charge and discharge V (B) -Q (A) curve, wherein B is voltage and A is capacity;
2.3) carrying out conversion calculation on the capacity data A during charging to obtain the capacity data A during charging i And data A n Ratio C of i ,C i ＝A i /A n ，A i For capacity data recorded at i-th time during charging, A n The capacity data recorded last time when charging, i ═ 1,2,3 … … n;
calculating (C) 2 -C 1 )/(B 2 -B 1 ) D1, obtained by analogy with (C) i+1 -C i )/(B i+1 -B i ) Value Di, B of i Is a and A i Corresponding voltage data when B i+1 ＝B i Only one of the data is reserved; accordingly, a charging B-D curve is drawn, wherein B is an x axis, and D is a Y axis;
2.4) carrying out conversion calculation on the capacity data A during discharge to obtain the capacity data A during discharge i And data A n Ratio C of i ,C i ＝A i /A n ，A i For the capacity data recorded at the i-th time during discharge, A n The capacity data recorded at the last time of the discharging process is i-1, 2,3 … … n;
calculating (C) 2 -C 1 )/(B 2 -B 1 ) D1, obtained by analogy with (C) i+1 -C i )/(B i+1 -B i ) Value Di of (B), when B i+1 When Bi is obtained, only one data is kept, and a discharge B-D curve is drawn, wherein B is an x axis, and D is a Y axis;
2.5) drawing the charging B-D curve and the discharging B-D curve in the same coordinate system to form a charging and discharging B-D curve; the wave crests on the charging and discharging B-D curves are named clockwise from left to right: the first peak was named F1, the second peak was named F2, the third peak was named F3, the fourth peak was named F4, the 5 th peak was named F5, and the sixth peak was named F6;
2.6) acquiring a corresponding value FX1 of F1 on an X axis, a corresponding value FX2 of F2 on the X axis and a corresponding value FX3 of F3 on the X axis according to a charging and discharging B-D curve;
step 2.7) is carried out under the conditions that FX1 is more than or equal to 3.3V, FX2 is more than or equal to 3.3V and less than or equal to 3.4V and FX3 is more than or equal to 3.4V and less than or equal to 3.45V;
2.7) obtaining a numerical value F3X of a difference FX34 of F3 and F4 on an X axis, a numerical value F2X of a difference FX25 of F2 and F5 on the X axis, and a numerical value F1X of a difference FX16 of F1 and F6 on 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) carrying out charging and discharging tests on the full-electric battery to obtain data of capacity A and voltage B during charging, obtaining a charging B-D curve of the full-electric battery by adopting the method in the step 2.3), and naming wave crests on the charging B-D curve of the full-electric battery from left to right: the first peak was designated F1, the second peak was designated F2, and the third peak was designated F3;
3.2) obtaining corresponding values FY2, FY3 and FY1 of the full batteries F2, F3 and F1 on a Y axis according to a charging B-D curve of the full batteries, and calculating FY2, FY3, 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 a value of L1 according to formula 1);
L1＝((a1+a2)*I1+b1*c1)*(f3x+f2x+f1x)-f6y (1)；
wherein a1 is a numerical value of D50, a2 is a numerical value of D10, I1 is a numerical value of ratio OI, b1 is a numerical value of specific surface area, c1 is a numerical value of tap density, f3x is a numerical value of FX34, f2x is a numerical value of FX25, f1x is a numerical value of FX16, and f6y is a calculated value of FY2: FY3: FY 1;
when L1 is less than or equal to 5.1, the negative electrode material has high-rate long-cycle characteristics.
Through the technical scheme, when the high-rate long-cycle characteristic of the graphite cathode material is tested, whether the graphite cathode material has the high-rate long-cycle characteristic can be judged only by testing basic parameters of the graphite cathode material, the diffraction intensity of a crystal face and the charge-discharge characteristics of a button cell and a full-electric cell, and compared with the existing verification method, the testing time is greatly saved.
Optionally, in step 2.1), when the graphite negative electrode material is made into a button cell, the material ratio of the button cell is as follows according to the mass ratio: graphite anode material: conductive agent: 95% -98% of binder: 1% -2.5%: 1 to 2.5 percent.
Optionally, in step 2.1), when the graphite negative electrode material is made into a button cell, the material ratio of the button cell is as follows according to the mass ratio: graphite anode material: conductive agent: 98% of binder: 1%: 1 percent.
Optionally, the rate of charging and discharging 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 negative electrode material into full electricity in step 3) specifically comprises: and preparing the graphite cathode material into a 1-7Ah battery core, and matching the battery core with the anode-lithium iron phosphate to prepare the full-electric battery.
To a certain extent, the small battery cell 1-7Ah can basically eliminate the influence of thermodynamics on the battery performance and is closer to the characteristics of the material, so that the test accuracy can be improved through the technical scheme.
Optionally, during the charging and discharging test of the full-electric battery in the step 3.1), the battery core performs constant-current constant-voltage charging to a voltage of V1 at a multiplying power of n, the current is cut off at 0.05C, and the battery core performs multiplying power n discharging after a standing time of T1; wherein n is less than or equal to 0.5C, V1 is 2.5-3.65V, and T1 is more than or equal to 30 min.
Optionally, n in step 3.1) is 0.2C.
Optionally, in order to ensure the accuracy of the test result, the number of charging and discharging in step 3.1) is 3.
Optionally, in the step 3.1), during the charge and discharge test, the temperature of the battery cell made of the graphite negative electrode material is monitored, and when the temperature rise of the battery cell is less than or equal to 10 ℃, the data of the capacity a and the voltage B in the charge and discharge process is available data.
Compared with the prior art, the invention has the beneficial effects that:
the test method of the high-magnification long-cycle characteristic of the graphite cathode material is simple and easy to implement, only the basic parameters of graphite are required to be tested, in addition, the graphite cathode material is made into a button cell and a full-electric cell, the button cell is subjected to 1-3 times of charge-discharge tests, and the obtained capacitance voltage data is converted and a curve is drawn; carrying out 1-3 times of charge and discharge tests on the full-electric battery, converting the obtained capacitance voltage data and drawing a curve; the relevant data obtained through the test can judge whether the test is suitable for the long-cycle high-rate lithium ion battery, and compared with the existing charge-discharge cycle test mode which passes more than 1000 times, the method greatly reduces the influence on iterative update of the product due to overlong verification time, and makes the product application and material screening easier.
Drawings
FIG. 1 shows the curves V (B) -Q (A) for the charge of a button cell made of graphite-5.
FIG. 2 is a B-D curve of charge and discharge when graphite-5 is made into button cell.
FIG. 3 is a schematic diagram showing the name of the peak of the charge-discharge B-D curve when graphite-5 is made into button cell.
Detailed Description
The test samples are graphite-1, graphite-2, graphite-3, graphite-4 and graphite-5, and the method for testing the high-rate long-cycle characteristics of the graphite negative electrode material of the present invention is described below by taking graphite-5 as an example.
The test method of the graphite-5 high-magnification long-cycle characteristic comprises the following steps:
1) basic parameter testing
Carrying out particle size distribution test to obtain D50 and D10 values of graphite-5;
performing a tap density test to obtain the tap density of the graphite-5;
carrying out a specific surface area test to obtain the specific surface area of the graphite-5;
carrying out X-ray diffraction to obtain the ratio OI of I004/I110 of graphite-5; I004/I110 represents the ratio of the diffraction intensity I004 of the 004 crystal face of the graphite cathode material to the diffraction intensity I110 of the 110 crystal face;
2) graphite-5 was made into button cell for analysis
The electricity buckling manufacture method specifically comprises the following steps: according to the mass ratio, graphite-5: conductive agent: 97% of colloid: 1.5%: 1.5 percent. Weighing 9.7000 +/-0.0001 g of graphite to be detected, 0.1500 +/-0.0001 g of conductive agent and 0.1500 +/-0.0001 g of negative electrode binder in a beaker, initially mixing uniformly by using a spoon, adding 15ml of fresh deionized water, stirring uniformly, properly adding 1-5ml of water, starting a magnetic stirrer, continuously stirring for 6 hours, and stopping stirring the bottom of the beaker by using the spoon during stirring until the viscosity is proper and the mucus is uniform. The slurry is used to coat on a copper foil, the coated material is placed in an air-blast drying oven to be dried for 30min at 75 ℃ to ensure that water in the product is fully volatilized, then the product is placed in a vacuum drying oven to be dried for 2 h at 120 ℃, and then the product is taken out and placed in a dryer to be cooled for 5 min. And (3) cooling, rolling, drying in a vacuum oven for 1 hour in vacuum, punching into a wafer with the diameter of 13.0mm by using a punching machine, putting into the vacuum oven, baking for 1 hour at 70 ℃ in vacuum, drying the prepared diaphragm (the base film is 12 microns, and the ceramic layer is 4 microns) with the thickness of 16 microns, the spring piece, the gasket and the button cell shell, transferring into a glove box, and dropwise adding a sufficient amount of electrolyte to assemble the button cell.
The prepared button cell is charged and discharged at 0.1C between 0.005V and 2V, and the required charge and discharge data is obtained after 2 times of circulation. According to the data of the capacity A and the voltage B acquired in the charging and discharging processes, a charging and discharging V (B) -Q (A) curve is drawn, wherein B is the voltage, A is the capacity, and only the charging V (B) -Q (A) curve is shown in figure 1.
And judging the rationality of the acquired data of the capacity A and the voltage B according to the drawn charging and discharging 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 prepared.
B-D charging curve preparation: converting and calculating the capacity data A during charging to obtain the capacity data A during charging i And data A n Ratio C of i ,C i ＝A i /A n ，A i For capacity data recorded at i-th time during charging, A n The capacity data recorded last time at the time of charging is i1, 2,3 … … n.
Calculating (C) 2 -C 1 )/(B 2 -B 1 ) D1, and so on (C) i+1 -C i )/(B i+1 -B i ) Value Di of (B), when B i+1 ＝B i Only one of the data is reserved; accordingly, the upper half of the charging and discharging B-D curve shown in FIG. 1, i.e., the charging B-D curve, is plotted, wherein B is the x-axis and D is the Y-axis.
Table 1 below shows the capacity A obtained during the charging of graphite-5 i Voltage B i And transform data C i 、D i A list of (a).
Table 1 list of relevant data obtained by charging
Data in Table 1, C i Showing only six digits after the decimal point, actual D i Is calculated according to C i Calculated from the actual value of (e.g. C) i The actual value of (a) is 0.0008119629203.
Making a discharge B-D curve: performing conversion calculation on the capacity data A during discharge to obtain the capacity data A during discharge i And data A n Ratio C of i ,C i ＝A i /A n ，A i For the capacity data recorded at the i-th time during discharge, A n The capacity data recorded at the last time of the discharge process is i ═ 1,2,3 … … n.
Calculate (C) 2 -C 1 )/(B 2 -B 1 ) D1, obtained by analogy with (C) i+1 -C i )/(B i+1 -B i ) Value Di, B of i Is a and A i Corresponding voltage data when B i+1 ＝B i When the discharge is performed, only one of the data is kept, and a discharge B-D curve is drawn to dischargeThe B-D curve is the lower half of the charge-discharge B-D curve shown in FIG. 2, where B is the x-axis and D is the Y-axis.
Drawing the charging B-D curve and the discharging B-D curve in the same coordinate system to form a charging and discharging B-D curve shown in figure 2; as shown in fig. 3, the peaks on the charging and discharging B-D curves are named from left to right clockwise: the first peak was named F1, the second peak was named F2, the third peak was named F3, the fourth peak was named F4, the 5 th peak was named F5, and the sixth peak was named F6.
According to the charging and discharging B-D curve, a value FX1 corresponding to F1 on an X axis, a value FX2 corresponding to F2 on the X axis and a value FX3 corresponding to F3 on the X axis are obtained.
Under the conditions that FX1 is not less than 3.3V and not less than 3.2, FX2 is not less than 3.4V and not less than 3.4, and FX3 is not less than 3.45V, the numerical value F3X of the difference FX34 of F3 and F4 on the X axis, the numerical value F2X of the difference FX25 of F2 and F5 on the X axis, and the numerical value F1X of the difference FX16 of F1 and F6 on 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 negative electrode material has stronger dynamic performance, and the step 3) is carried out.
3) Graphite-5 was fabricated into full-electric cells for analysis
The manufacturing method of the full-electric battery comprises the following steps: the positive electrode material takes a lithium iron phosphate material as a main material, and the mass ratio of the lithium iron phosphate material to the conductive agent and the colloid is 96%: 2%: 2 percent, mixed into slurry, and coated on a current collector with the thickness of 12 microns, and the coating surface density is 41.6mg/cm 2 The rolled thickness is 187 microns, and the pole pieces are dried and cut into small pieces of 120mm x 62 mm. The mass ratio of the graphite-5 to the conductive agent and the colloid is 97%: 1%: 2% of the resulting slurry, and then the resulting slurry was coated on a 6 μm copper foil to give a coating having a surface density of 19.6mg/cm 2 And rolling to 125 micrometers, drying and cutting the pole pieces into 125 mm-66 mm small pieces, stacking 18 layers of positive pole pieces, 19 layers of negative pole pieces and a diaphragm with the thickness of 16 micrometers to obtain a required battery core, packaging the required battery core by using an aluminum-plastic film with the thickness of 153 micrometers, and finally injecting liquid to obtain the required battery core.
The required battery cell is charged with constant current and constant voltage of 0.2C between 2.5V and 3.65V, the current is cut off at 0.05C, the battery cell is kept stand for 30min, and the battery cell is discharged with constant current at 0.2C; and (3) circularly performing charge and discharge, selecting data, monitoring the temperature in the charge and discharge process, and selecting the charge and discharge data as object data when the temperature rise of the battery cell is less than or equal to 10 ℃.
Acquiring a charging B-D curve of the full-electric battery by adopting the same method as the button battery charging B-D curve, and naming wave crests on the full-electric battery charging B-D curve from left to right: the first peak was designated F1, the second peak was designated F2, and the third peak was designated F3.
Obtaining corresponding values FY2, FY3 and FY1 of the full batteries F2, F3 and F1 on a Y axis according to a charging B-D curve of the full batteries, and calculating FY2, FY3, FY1, wherein the data is F6Y;
the B-D charging curve of the full-electric lithium ion battery is the key of research, F1, F2 and F3 respectively correspond to three lithium intercalation reactions generated by lithium ions intercalated into graphite, and the strength and the speed of the reactions directly determine the multiplying power and the cycle performance of the material. And (3) calculating the ratio of the obtained three peak values, wherein the ratio of the F2, F3 and F1Y axes corresponding to the values FY2, FY3 and FY1 is FY231(FY2: FY3: FY1) > 0.5, and the closer to 1, the stronger the dynamic performance and the stronger the rate capability of the material are, the better the reversibility of contraction and expansion of the material under the same rate is.
Step 4) is carried out under the condition that f6y is more than 0.5);
4) comprehensive judgment
Calculating a value of L1 according to formula 1);
L1＝((a1+a2)*I1+b1*c1)*(f3x+f2x+f1x)-f6y(1)；
wherein a1 is a numerical value of D50, a2 is a numerical value of D10, I1 is a numerical value of ratio OI, b1 is a numerical value of specific surface area, c1 is a numerical value of tap density, f3x is a numerical value of FX34, f2x is a numerical value of FX25, f1x is a numerical value of FX16, and f6y is a calculated value of FY2: FY3: FY 1;
when L1 is less than or equal to 5.1, the negative electrode material has high-rate long-cycle characteristics.
The high-rate long cycle characteristics of graphite-1, graphite-2, graphite-3 and graphite-4 were measured according to the same test method, and the values of f3x, f2x, f1x, f6y, a1, a2, b1, c1 and L1 of the respective graphite negative electrode materials were obtained, as shown in table 2.
Table 2 test values of respective anode materials
| 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 |
Analysis from the results of the test: the comprehensive performance of graphite-3 is stronger than that of graphite-5, graphite-2, graphite-4 and graphite-1, and graphite-3 and graphite-5 are cathode materials suitable for large-magnification long-cycle.
In order to further prove the reasonability of the method, DCR tests under different SOC (state of charge), cycle tests under different multiplying powers and full-power disassembly tests after large-multiplying-power constant-current constant-voltage charging are carried out.
The cells made of graphite-1, graphite-2, graphite-3, graphite-4, and graphite-5 were charged, and DCR calculation was performed at different SOC (state of charge), and the obtained DCR test data are shown in table 3. From the data in table 3: at 50% SOC, the DC internal resistance of graphite-3 is the smallest, the comprehensive polarization of charging is the smallest, the charging polarization of graphite-1 is the largest, and lithium intercalation is more difficult.
Table 3 DCR test values of respective negative electrode materials
| SOC | Graphite-1/m omega | Graphite-2/m omega | Graphite-3/m omega | Graphite-4/m omega | 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 cells made of graphite-1, graphite-2, graphite-3, graphite-4 and graphite-5 were subjected to cycle testing at different magnifications, and the test data are shown in tables 4, 5 and 6.
TABLE 4 Cyclic test data for each negative electrode material at 1C/1C 100% DOD
| 1C/1C 100％DOD | Number of cycles | Voltage of discharge plateau |
| Graphite-1 | 1500 times 80 percent | 3.18 |
| Graphite-2 | 80 percent at 4000 times | 3.189 |
| Graphite-3 | 80 percent for 5000 times | 3.1975 |
| Graphite-4 | 3000 times 80% | 3.179 |
| Graphite-5 | 4500 times 80% | 3.19 |
1500 of the 1500 80% runs represented 80% of the initial capacity remaining after 1500 cycles.
TABLE 5 Cyclic test data for each negative electrode material at 1C/1C 100% DOD
| 0.5C/1C cycle 100% DOD | Number of cycles | Voltage of discharge plateau |
| Graphite-1 | 86% for 1500 times | 3.17 |
| Graphite-2 | 91% after 1500 times | 3.188 |
| Graphite-3 | 1500 times 93 percent | 3.1925 |
| Graphite-4 | 1500 times of 90 percent | 3.176 |
| Graphite-5 | 92 percent after 1500 times | 3.191 |
TABLE 6 Cyclic 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 larger the L1 value is, the less favorable the cycle is, and the smaller the L1 is, the better the cycle data with different magnification ratios is. It was also found that the discharge voltage plateau of graphite is also relevant for L1, the lower the L1 the higher the 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 cells were disassembled at full charge as shown in table 7.
TABLE 7 conditions of constant current and constant voltage charging of each negative electrode material under 2C condition, full-current disassembly of cell
| Interface (I) | |
| Graphite-1 | Severe lithium evolution at 100% interface |
| Graphite-2 | 50% interfacial lithium precipitation |
| Graphite-3 | Does not separate out lithium |
| Graphite-4 | 75% interfacial lithium precipitation |
| Graphite-5 | Does not separate out lithium |
As shown in table 7, when the interface of the cell was disassembled at a high rate, it was clearly seen that the L1 value was as low as possible and was best within 5.1 when the high rate exceeded 2C.
The test results of tables 3, 4, 5, 6 and 7 are consistent with the test results of the invention, which shows the accuracy of the test method of the invention.
Claims (9)
1. A test method for high-rate long-cycle characteristics of a graphite negative electrode material is characterized by comprising the following steps:
1) basic parameter test of graphite cathode material
Carrying out particle size distribution test to obtain D50 and D10 values of the graphite cathode material; d50 represents a particle diameter at which the cumulative distribution of graphite anode material particles is 50%, D10 represents a particle diameter at which the cumulative distribution of graphite anode material particles is 10%;
performing tap density test to obtain tap density of the graphite cathode material;
carrying out a specific surface area test to obtain the specific surface area of the graphite negative electrode material;
carrying out X-ray diffraction to obtain the ratio OI of the graphite cathode material I004/I110; I004/I110 represents the ratio of the diffraction intensity I004 of the 004 crystal face of the graphite cathode material to the diffraction intensity I110 of the 110 crystal face;
the step 2) is carried out under the conditions 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
1) Preparing a button cell from a graphite negative electrode material;
2) performing charge and discharge test on the button cell to obtain data of capacity A and voltage B, and drawing a charge and discharge V (B) -Q (A) curve, wherein B is voltage and A is capacity;
3) performing conversion calculation on the capacity data A during charging to obtain the ratio Ci of the capacity data Ai during charging to data An, wherein Ci = Ai/An, Ai is the capacity data recorded at the ith time during charging, An is the capacity data recorded at the last time during charging, and i =1,2,3 … … n;
calculating a value D1 of (C2-C1)/(B2-B1), and obtaining a value Di of (Ci + 1-Ci)/(B i +1-Bi) by analogy, wherein Bi is voltage data corresponding to Ai, and when B i +1= Bi, only one data is reserved; accordingly, a charging B-D curve is drawn, wherein B is an x axis, and D is a Y axis;
4) performing conversion calculation on the capacity data A during discharging to obtain the ratio Ci of the capacity data Ai during discharging to data An, wherein Ci = Ai/An, Ai is the capacity data recorded at the ith time during discharging, An is the capacity data recorded at the last time during discharging, and i =1,2,3 … … n;
calculating the value D1 of (C2-C1)/(B2-B1), obtaining the value Di of (Ci + 1-Ci)/(B i +1-B i) by analogy, and when B i +1= Bi, only retaining the data of one of the values and drawing a discharge B-D curve, wherein B is an x axis and D is a Y axis;
5) drawing the charging B-D curve and the discharging B-D curve in the same coordinate system to form a charging and discharging B-D curve; the wave crests on the charging and discharging B-D curves are named clockwise from left to right: the first peak was named F1, the second peak was named F2, the third peak was named F3, the fourth peak was named F4, the 5 th peak was named F5, and the sixth peak was named F6;
6) acquiring a corresponding value FX1 of F1 on an X axis, a corresponding value FX2 of F2 on the X axis and a corresponding value FX3 of F3 on the X axis according to a charging and discharging B-D curve;
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 3.3V and less than or equal to 3.4V and FX3 is more than or equal to 3.4 and less than or equal to 3.45V;
7) acquiring a numerical value F3X of a difference FX34 of F3 and F4 on an X axis, a numerical value F2X of a difference FX25 of F2 and F5 on the X axis, and a numerical value F1X of a difference FX16 of F1 and F6 on 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) the graphite cathode material is made into a full-electric battery for analysis
1) Carrying out charge and discharge tests on the full-electric battery to obtain data of capacity A and voltage B during charging, acquiring a charging B-D curve of the full-electric battery by adopting the method in the step 2.3), and naming wave crests on the charging B-D curve of the full-electric battery from left to right: the first peak was named F1, the second peak was named F2, and the third peak was named F3;
2) obtaining corresponding values FY2, FY3 and FY1 of the full batteries F2, F3 and F1 on a Y axis according to a charging B-D curve of the full batteries, and calculating FY2, FY3, 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 a value of L1 according to equation 1);
L1=（（a1+a2)*I1+b1*c1）*(f3x+f2x+f1x)-f6y （1） ；
wherein a1 is a numerical value of D50, a2 is a numerical value of D10, I1 is a numerical value of ratio OI, b1 is a numerical value of specific surface area, c1 is a numerical value of tap density, f3x is a numerical value of FX34, f2x is a numerical value of FX25, f1x is a numerical value of FX16, f6y is a calculated value of FY2: FY3: FY 1;
when L1 is less than or equal to 5.1, the negative electrode material has high-rate long-cycle characteristics.
2. The method for testing the high-rate long-cycle characteristics of the graphite negative electrode material according to claim 1, characterized in that:
step 2.1), when the graphite cathode material is prepared into the button cell, the button cell comprises the following materials in percentage by mass: graphite anode material: conductive agent: binder =95% -98%: 1% -2.5%: 1 to 2.5 percent.
3. The method for testing the high-rate long-cycle characteristics of the graphite negative electrode material according to claim 2, characterized in that:
step 2.1), when the graphite cathode material is prepared into the button cell, the button cell comprises the following materials in percentage by mass: graphite anode material: conductive agent: binder = 98%: 1%: 1 percent.
4. The method for testing the high-rate long-cycle characteristics of the graphite negative electrode material according to claim 1, characterized in that:
the multiplying power of the button cell in the step 2.2) for charging and discharging is 0.1C.
5. The method for testing the high-rate long-cycle characteristics of the graphite negative electrode material according to claim 4, wherein the method comprises the following steps:
the method for preparing the graphite cathode material into full electricity in the step 3) specifically comprises the following steps:
and preparing the graphite cathode material into a 1-7Ah battery core, and matching the battery core with the anode-lithium iron phosphate to prepare the full-electric battery.
6. The method for testing the high-rate long-cycle characteristics of the graphite negative electrode material according to claim 5, wherein the method comprises the following steps:
step 3.1) during the full-electric battery charging and discharging test, the battery cell carries out constant-current constant-voltage charging to a voltage V1 with a multiplying power n, the current is cut off to be 0.05C, and multiplying power n discharging is carried out after the standing time T1; wherein n is less than or equal to 0.5C, V1=2.5-3.65V, and T1 is more than or equal to 30 min.
7. The method for testing the high-rate long-cycle characteristics of the graphite negative electrode material according to claim 6, wherein the method comprises the following steps:
step 3.1) n = 0.2C.
8. The method for testing high-rate long cycle characteristics of an ink negative electrode material according to claim 7, characterized in that:
and 3.1) the charging and discharging times are 3 times.
9. The method for testing the high-rate long-cycle characteristics of the graphite negative electrode material according to claim 8, wherein the method comprises the following steps:
and 3.1) monitoring the temperature of the battery cell made of the graphite cathode material during the charge and discharge test, wherein the data of the capacity A and the voltage B in the charge and discharge process are available data when the temperature rise of the battery cell is less than or equal to 10 ℃.
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