CN108614221B - Evaluation method for lithium ion battery formation process - Google Patents
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Abstract
The invention relates to an evaluation method for a lithium ion battery formation process. The method comprises the steps of detecting the primary pressure drop after formation and aging processes, detecting the secondary pressure drop after volume grading and aging processes, and comparing the difference value of the primary pressure drop and the secondary pressure drop. The evaluation method respectively carries out aging acceleration tests on the batteries after formation and capacity grading, and judges the activation effects of different formation procedures through comparison of the difference value of the primary pressure drop and the secondary pressure drop. The SEI film formed in the good formation process has the characteristics of compactness, uniformity, small solubility in electrolyte, good thermal stability and chemical stability, can prevent the electrode material from reacting with the electrolyte, reduces side reactions and reduces the self-discharge rate, and accordingly, the invention evaluates the formation effect of the lithium ion battery through the pressure drop generated by an aging acceleration test, and is very suitable for lithium ion battery manufacturers to quickly and accurately screen the appropriate formation process.
Description
Technical Field
The invention belongs to the field of formation of lithium ion batteries, and particularly relates to an evaluation method for a formation process of a lithium ion battery.
Background
The lithium ion battery is used as an efficient energy storage element, has the advantages of high energy density, long cycle life, good rate capability and safety performance and the like, and is widely applied to the fields of electronic equipment, communication equipment, medical equipment, new energy automobiles and the like at present.
Formation is an important process in the production process of lithium ion batteries, and a passivation layer, namely a solid electrolyte interface film (SEI) is formed on the surface of a negative electrode during formation, and the quality of the SEI directly influences the cycle life, stability, self-discharge property, safety and other electrochemical properties of the batteries. Formation is the first charge and discharge process of the lithium ion battery, for example, patent application with publication number CN106684426A discloses a formation method of a soft package lithium ion battery, which comprises pre-charging the soft package lithium ion battery with a current of 0.01C-0.05C to a low current to a cut-off voltage of 3.0V; then, charging the battery by adopting a current of 0.1-1.0C at a constant current until the cut-off voltage is 3.6V; then charging with 0.5C-3.0C current constant current and constant voltage until the cut-off voltage is 4.2V and the cut-off current is 0.01C-1.0C.
The formation process of the lithium ion battery is diversified, and the complexity of the formation process is increased by selecting parameters such as charging current, heating and pressurizing modes and the like. How to evaluate the advantages and disadvantages of different formation processes is of great significance to enable battery manufacturers to quickly screen appropriate formation processes. At present, the formation effect of the battery is evaluated by adopting a lithium ion battery cycle test method, and the method has long time consumption and poor practicability.
Disclosure of Invention
The invention aims to provide an evaluation method for a lithium ion battery formation process, so as to solve the problems of long time consumption and poor practicability of the conventional evaluation method.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for evaluating a formation process of a lithium ion battery comprises the following steps:
1) after the battery is formed, the detection voltage is U1(ii) a Then aging the battery, and detecting the voltage to be U after aging2Recording the first voltage drop DeltaU1＝U1-U2；
2) Carrying out a cycle test on the battery subjected to the aging treatment in the step 1), wherein the detection voltage is U3Then aging the batteries after capacity grading, wherein the detection voltage is U after aging4Recording the secondary voltage drop DeltaU2＝U3-U4；
3) Calculating the difference between the first pressure drop and the second pressure drop, delta U ═ delta U1-ΔU2Comparing the delta U values of different formation procedures, wherein if the delta U is less than or equal to 0, the formation procedure does not achieve the activation effect; if Δ U > 0, the formation step is said to have an activating effect, and the greater the Δ U value, the better the formation effect in the formation step.
The invention provides an evaluation method of formation processes of lithium ion batteries, which is used for respectively carrying out aging acceleration tests on the formed batteries and the batteries with different capacities, and judging the activation effects of different formation processes by comparing the difference value of the primary pressure drop and the secondary pressure drop. The SEI film formed in the good formation process has the characteristics of compactness, uniformity, small solubility in electrolyte, good thermal stability and chemical stability, can prevent the electrode material from reacting with the electrolyte, reduces side reactions and reduces the self-discharge rate, and accordingly, the invention evaluates the formation effect of the lithium ion battery through the pressure drop generated by an aging acceleration test, and is very suitable for lithium ion battery manufacturers to quickly and accurately screen the appropriate formation process.
In the step 1), the aging treatment is carried out for 24-48h at 35-55 ℃.
In the step 2), the cycle test is to discharge and charge circularly, and the cycle times are 2-4 times. Preferably, the discharge and charge rates are both 1C during cycling. In the cycle, the charge is made to the cut-off voltage of the chemical conversion process.
In the step 2), the aging treatment of the battery after capacity grading is carried out for 24-48h at 35-55 ℃.
According to the evaluation method for the lithium ion battery formation process, the aging treatment and the capacity grading treatment are carried out under the optimized process parameters, the formation effect of the battery can be simply and intuitively reflected, the evaluation method is simple, and the evaluation time is shortened.
Drawings
FIG. 1 is a process flow diagram of the evaluation method of the formation process of the lithium ion battery according to the present invention;
fig. 2 shows a comparison of cycle performance of lithium ion batteries using different formation processes in the test examples.
Detailed Description
The following examples are provided to further illustrate the practice of the invention.
Example 1
The method for evaluating the formation process of the lithium ion battery of the embodiment adopts the following steps as shown in fig. 1:
1) after the formation of the lithium ion battery is finished, the voltage of the lithium ion battery is detected to be U1Then aging the lithium ion battery for 24 hours at 45 ℃ and detecting the voltage to be U2Recording the first voltage drop DeltaU1＝U1-U2；
2) Circularly discharging and charging the aged battery in the step 1) at a multiplying power of 1C/1C, wherein the number of cycles is two, the battery is charged to the cut-off voltage of a formation process, and then a specific voltage value is detected and recorded as U3(ii) a Aging the battery after cyclic discharge and charge at 45 deg.C for 24 hr, and detecting voltage as U4Recording the secondary voltage drop DeltaU2＝U3-U4；
3) Calculating the difference between the first pressure drop and the second pressure drop, delta U ═ delta U1-ΔU2When Δ U > 0 and Δ U value are larger, the chemical conversion effect in the chemical conversion step is better when Δ U values in different chemical conversion steps are compared.
Example 2
The method for evaluating the formation process of the lithium ion battery of the embodiment adopts the following steps as shown in fig. 1:
1) after the formation of the lithium ion battery is finished, the voltage of the lithium ion battery is detected to be U1Aging the lithium ion battery for 48h at 35 ℃ and detecting the voltage to be U2Recording the first voltage drop DeltaU1＝U1-U2；
2) Circularly discharging and charging the aged battery in the step 1) at a multiplying power of 1C/1C, wherein the number of cycles is two, the battery is charged to the cut-off voltage of a formation process, and then a specific voltage value is detected and recorded as U3(ii) a Aging the battery after cyclic discharge and charge at 35 deg.C for 48h, and detecting voltage as U4Recording the secondary voltage drop DeltaU2＝U3-U4；
3) Calculating the difference between the first pressure drop and the second pressure drop, delta U ═ delta U1-ΔU2When Δ U > 0 and Δ U value are larger, the chemical conversion effect in the chemical conversion step is better when Δ U values in different chemical conversion steps are compared.
Example 3
The method for evaluating the formation process of the lithium ion battery of the embodiment adopts the following steps as shown in fig. 1:
1) after the formation of the lithium ion battery is finished, the voltage of the lithium ion battery is detected to be U1Aging the lithium ion battery at 55 ℃ for 24h, and detecting the voltage to be U2Recording the first voltage drop DeltaU1＝U1-U2；
2) Circularly discharging and charging the aged battery in the step 1) at a multiplying power of 1C/1C, wherein the number of cycles is two, the battery is charged to the cut-off voltage of a formation process, and then a specific voltage value is detected and recorded as U3(ii) a Aging the battery after cyclic discharge and charge at 55 deg.C for 24h, and detecting voltage as U4Recording the secondary voltage drop DeltaU2＝U3-U4；
3) Calculating the difference between the first pressure drop and the second pressure drop, delta U ═ delta U1-ΔU2When Δ U > 0 and Δ U value are larger, the chemical conversion effect in the chemical conversion step is better when Δ U values in different chemical conversion steps are compared.
Test examples
The present test example will describe the practical application of the method of the present invention in evaluating the formation process of a lithium ion battery, taking the method of example 1 as an example.
And (3) respectively adopting a formation process 1 and a formation process 2 to carry out formation treatment on the ternary lithium ion battery with the model of 10Ah soft package, and recording the pressure drop data of the formation process 1 and the formation process 2. The formation step 1 is specifically shown in table 1.
TABLE 1 working procedure of formation procedure 1
The formation step 2 is specifically shown in table 2.
TABLE 2 working procedure of formation Process 2
The pressure drop data of different formation procedures were measured, and the specific results are shown in tables 3 and 4.
Table 3 voltage drop data of lithium ion battery corresponding to formation process 1
| Numbering | U1，V | U2，V | ΔU1，V | U3，V | U4，V | ΔU2，V | (ΔU1-ΔU2)，V |
| 1 | 4.1773 | 4.1282 | 0.0491 | 4.1977 | 4.1676 | 0.0301 | 0.0190 |
| 2 | 4.1706 | 4.1257 | 0.0449 | 4.1963 | 4.1697 | 0.0266 | 0.0183 |
| 3 | 4.1787 | 4.1267 | 0.0520 | 4.1959 | 4.1677 | 0.0282 | 0.0238 |
| 4 | 4.1736 | 4.1222 | 0.0514 | 4.1957 | 4.1663 | 0.0294 | 0.0220 |
| 5 | 4.1767 | 4.1247 | 0.0520 | 4.1967 | 4.1676 | 0.0291 | 0.0229 |
| 6 | 4.1748 | 4.1217 | 0.0531 | 4.1956 | 4.1687 | 0.0269 | 0.0262 |
| 7 | 4.1787 | 4.1274 | 0.0513 | 4.193 | 4.1648 | 0.0282 | 0.0231 |
| 8 | 4.1737 | 4.1257 | 0.0480 | 4.1917 | 4.1646 | 0.0271 | 0.0209 |
| 9 | 4.1783 | 4.1288 | 0.0495 | 4.191 | 4.1684 | 0.0226 | 0.0269 |
| 10 | 4.1726 | 4.1262 | 0.0464 | 4.1916 | 4.1688 | 0.0228 | 0.0236 |
| 11 | 4.1737 | 4.1266 | 0.0471 | 4.1919 | 4.1648 | 0.0271 | 0.0200 |
| 12 | 4.1742 | 4.1288 | 0.0454 | 4.1924 | 4.1674 | 0.0250 | 0.0204 |
| 13 | 4.1729 | 4.1304 | 0.0425 | 4.1904 | 4.1698 | 0.0206 | 0.0219 |
| 14 | 4.1727 | 4.1279 | 0.0448 | 4.1902 | 4.1667 | 0.0235 | 0.0213 |
| 15 | 4.1714 | 4.1281 | 0.0433 | 4.1894 | 4.1691 | 0.0203 | 0.0230 |
Table 4 voltage drop data of lithium ion battery corresponding to formation process 2
According to the detection results, the difference value between the primary voltage drop and the secondary voltage drop of the formation process 1 is large, and the formation process 1 is proved to be a formation process more suitable for the type of lithium ion battery.
Further adopting a cycle test method to detect the validity of the evaluation result, specifically performing cycle test on the batteries processed in the formation process 1 and the formation process 2 respectively, wherein the cycle test flow comprises the following steps: charging to 4.2V at constant current and constant voltage of 1C, cutting off the current of 0.02C, then discharging to 2.75V at constant current of 1C, and circulating for 600 weeks; the results of the cycling tests are shown in FIG. 2.
As can be seen from fig. 2, the cycle performance of the lithium ion battery corresponding to the formation step 1 is significantly better than that of the formation step 2, indicating that the formation step 1 has a better activation effect than that of the formation step 2 for the lithium ion battery of the type.
Compared with a cycle test method, the method provided by the invention can simply and visually reflect the advantages and disadvantages of different formation procedures of the lithium ion battery, and shortens the evaluation time, thereby being beneficial to lithium ion battery manufacturers to quickly screen out appropriate formation processes.
Claims (6)
1. A method for evaluating a formation process of a lithium ion battery, comprising the steps of:
1) after the battery is formed, the detection voltage is U1(ii) a Then aging the battery, and detecting the voltage to be U after aging2Recording the first voltage drop DeltaU1＝U1-U2；
2) Carrying out a cycle test on the battery subjected to the aging treatment in the step 1), wherein the detection voltage is U3Then aging the batteries after capacity grading, wherein the detection voltage is U after aging4Recording the secondary voltage drop DeltaU2＝U3-U4；
3) Calculating the difference between the first pressure drop and the second pressure drop, delta U ═ delta U1-ΔU2Comparing the delta U values of different formation procedures, wherein if the delta U is less than or equal to 0, the formation procedure does not achieve the activation effect; if Δ U > 0, the formation step is said to have an activating effect, and the greater the Δ U value, the better the formation effect in the formation step.
2. The method for evaluating a formation process of a lithium ion battery according to claim 1, wherein the aging treatment in step 1) is performed at 35 to 55 ℃ for 24 to 48 hours.
3. The method for evaluating a formation process of a lithium ion battery according to claim 1, wherein in the step 2), the cycle test is a cycle of discharging and charging, and the number of cycles is 2 to 4.
4. The method of evaluating a formation process of a lithium ion battery according to claim 3, wherein the rate of discharge and charge is 1C during the cycle.
5. The method of evaluating a chemical conversion process of a lithium ion battery according to claim 3 or 4, wherein the battery is charged to a cut-off voltage of the chemical conversion process during the cycle.
6. The method for evaluating a formation process of a lithium ion battery according to claim 1, wherein the aging treatment of the battery after the capacity grading in the step 2) is performed at 35 to 55 ℃ for 24 to 48 hours.
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| CN113589179B (en) * | 2021-07-30 | 2022-04-29 | 江南大学 | Power battery formation process state estimation method based on convex spatial filtering |
| US11650253B2 (en) | 2021-07-30 | 2023-05-16 | Jiangnan University | State estimation method for power battery formation process based on convex space filtering |
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