CN108614221A - A kind of evaluation method of lithium ion battery formation process - Google Patents

Abstract

The present invention relates to a kind of evaluation methods of lithium ion battery formation process.This method includes the pressure drop for the first time after detection chemical conversion, ageing process, and the secondary voltage drop after detection partial volume, ageing process compares the difference step of pressure drop for the first time and secondary voltage drop.The evaluation method carries out aging accelerated test respectively to the battery after chemical conversion and partial volume, by the comparison of pressure drop for the first time and secondary voltage drop difference, judges the activation effect of different formation process.The SEI films that good formation process is formed have the characteristics that fine and close, uniform, solubility is small in the electrolytic solution, thermal stability and chemical stability are good, it can prevent electrode material and electrolyte from reacting, it reduces side reaction and reduces self-discharge rate, correspondingly, the pressure drop size that the present invention is generated by aging accelerated test evaluates the formation effect of lithium ion battery, is highly suitable for lithium ion battery manufacturer and fast and accurately screens suitable formation process.

Description

A method for evaluating the formation process of lithium-ion batteries

technical field

The invention belongs to the field of formation of lithium-ion batteries, and in particular relates to an evaluation method for the formation process of lithium-ion batteries.

Background technique

As a high-efficiency energy storage element, lithium-ion batteries have the advantages of high energy density, long cycle life, long cycle life, good rate performance and safety performance, and have been widely used in electronic equipment, communication equipment, medical equipment and new energy vehicles. field.

Formation is an important process in the production process of lithium-ion batteries. During formation, a passivation layer is formed on the surface of the negative electrode, that is, a solid electrolyte interface film (SEI film). The quality of the SEI film directly affects the cycle life, stability, and Electrochemical properties such as self-discharge and safety. Formation is the first charge and discharge process of lithium-ion batteries. For example, the patent application with publication number CN106684426A discloses a method for the formation of soft-pack lithium-ion batteries. Carry out small current pre-charging to the cut-off voltage of 3.0V; then use 0.1C-1.0C current constant current charge to cut-off voltage 3.6V; then use 0.5C-3.0C current constant current and constant voltage charge to cut-off voltage 4.2V , cut-off current 0.01C-1.0C.

The formation process of lithium-ion batteries is diverse, and the selection of parameters such as charging current, heating and pressure method also increases the complexity of the formation process. How to evaluate the advantages and disadvantages of different formation processes is of great significance for battery manufacturers to quickly screen suitable formation processes. At present, the lithium-ion battery cycle test method is mostly used to evaluate the formation effect of the battery. This method takes a long time and has poor practicability.

Contents of the invention

The purpose of the present invention is to provide an evaluation method for the formation process of lithium-ion batteries, thereby solving the problems of long time consumption and poor practicability of the existing evaluation methods.

To achieve the above object, the technical solution adopted in the present invention is:

A kind of evaluation method of lithium-ion battery forming process, comprises the following steps:

1) After the battery completes the formation process, the detection voltage is U ₁ ; then the battery is subjected to aging treatment, and the detection voltage after aging treatment is U ₂ , and the first voltage drop ΔU ₁ = U ₁ -U ₂ is recorded;

2) Carry out a cycle test on the battery after the aging treatment in step 1), the detection voltage is U ₃ , then perform aging treatment on the battery after the aging treatment, the detection voltage after the aging treatment is U ₄ , record the secondary voltage drop ΔU ₂ =U ₃ -U ₄ ;

3) Calculate the difference between the first pressure drop and the second pressure drop ΔU=ΔU ₁ -ΔU ₂ , and compare the ΔU values of different formation processes. If ΔU≤0, it indicates that the activation effect has not been achieved in the formation process; if ΔU>0, it indicates that the formation The process achieves the activation effect, and the larger the ΔU value, the better the chemical conversion effect of the chemical conversion process.

The method for evaluating the formation process of lithium-ion batteries provided by the present invention is to conduct accelerated aging tests on the batteries after formation and capacity separation, and to judge the activation effects of different formation processes by comparing the difference between the first pressure drop and the second pressure drop. The SEI film formed by a good chemical formation process has the characteristics of compactness, uniformity, low solubility in the electrolyte, good thermal stability and chemical stability, which can prevent the reaction between the electrode material and the electrolyte, reduce side reactions and reduce self-discharge rate , Correspondingly, the present invention evaluates the formation effect of the lithium-ion battery by the pressure drop generated by the accelerated aging test, and is very suitable for lithium-ion battery manufacturers to quickly and accurately screen the appropriate formation process.

In step 1), the aging treatment is at 35-55° C. for 24-48 hours.

In step 2), the cycle test is to discharge and charge cyclically, and the number of cycles is 2-4 times. Preferably, during the cycle, the rate of discharge and charge are both 1C. During the cycle, it is charged to the cut-off voltage of the formation process.

In step 2), the aging treatment is at 35-55° C. for 24-48 hours.

The evaluation method of the lithium ion battery formation process of the present invention can simply and intuitively reflect the formation effect of the battery by performing aging treatment and volume separation treatment under the above-mentioned optimal process parameters. The evaluation method is simple and the evaluation time is shortened.

Description of drawings

Fig. 1 is the process flow diagram of the evaluation method of lithium-ion battery forming process of the present invention;

Figure 2 Comparison of cycle performance of lithium-ion batteries using different formation processes in the test example.

Detailed ways

The embodiments of the present invention will be further described below in conjunction with specific examples.

Example 1

The evaluation method of the lithium-ion battery formation process of the present embodiment, the process flow is shown in Figure 1, and the following steps are adopted:

1) After the lithium-ion battery is formed, its voltage is detected as U ₁ , then the lithium-ion battery is aged at 45°C for 24 hours, the detected voltage is U ₂ , and the first voltage drop ΔU ₁ = U ₁ -U ₂ is recorded;

2) The aging battery in step 1) is subjected to cyclic discharge and charge at a rate of 1C/1C, the number of cycles is two, and it is charged to the cut-off voltage of the formation process, and then the specific voltage value is detected and recorded as U ₃ ; then the cycle The voltage after discharge and charge is aged at 45°C for 24 hours, the detection voltage is U ₄ , and the secondary voltage drop ΔU ₂ = U ₃ -U ₄ is recorded;

3) Calculate the difference between the first pressure drop and the second pressure drop ΔU=ΔU ₁ -ΔU ₂ , and compare the ΔU values of different formation processes. If ΔU>0 and the larger the ΔU value, the better the formation effect of the formation process.

Example 2

The evaluation method of the lithium-ion battery formation process of the present embodiment, the process flow is shown in Figure 1, and the following steps are adopted:

1) After the lithium-ion battery is formed, its voltage is detected as U ₁ , then the lithium-ion battery is aged at 35°C for 48 hours, the detected voltage is U ₂ , and the first voltage drop ΔU ₁ = U ₁ -U ₂ is recorded;

2) The aging battery in step 1) is subjected to cyclic discharge and charge at a rate of 1C/1C, the number of cycles is two, and it is charged to the cut-off voltage of the formation process, and then the specific voltage value is detected and recorded as U ₃ ; then the cycle The voltage after discharge and charge is aged at 35°C for 48 hours, the detection voltage is U ₄ , and the secondary voltage drop ΔU ₂ = U ₃ -U ₄ is recorded;

3) Calculate the difference between the first pressure drop and the second pressure drop ΔU=ΔU ₁ -ΔU ₂ , and compare the ΔU values of different formation processes. If ΔU>0 and the larger the ΔU value, the better the formation effect of the formation process.

Example 3

The evaluation method of the lithium-ion battery formation process of the present embodiment, the process flow is shown in Figure 1, and the following steps are adopted:

1) After the lithium-ion battery is formed, its voltage is detected as U ₁ , then the lithium-ion battery is aged at 55°C for 24 hours, the detected voltage is U ₂ , and the first voltage drop ΔU ₁ = U ₁ -U ₂ is recorded;

2) The aging battery in step 1) is subjected to cyclic discharge and charge at a rate of 1C/1C, the number of cycles is two, and it is charged to the cut-off voltage of the formation process, and then the specific voltage value is detected and recorded as U ₃ ; then the cycle The voltage after discharge and charge is aged at 55°C for 24 hours, the detection voltage is U ₄ , and the secondary voltage drop ΔU ₂ = U ₃ -U ₄ is recorded;

3) Calculate the difference between the first pressure drop and the second pressure drop ΔU=ΔU ₁ -ΔU ₂ , and compare the ΔU values of different formation processes. If ΔU>0 and the larger the ΔU value, the better the formation effect of the formation process.

Test case

This test example takes the method of Example 1 as an example to illustrate the practical application of the method of the present invention in evaluating the formation process of lithium-ion batteries.

For the ternary lithium-ion battery with a model of 10Ah soft pack, the formation process 1 and formation process 2 were used to process the lithium-ion battery respectively, and the pressure drop data of formation process 1 and formation process 2 were recorded. The chemical conversion step 1 is specifically shown in Table 1.

Table 1 Workflow of chemical conversion step 1

The details of chemical conversion step 2 are shown in Table 2.

Table 2 Workflow of the formation step 2

The pressure drop data of different formation processes were detected, and the specific results are shown in Table 3 and Table 4.

Table 3 Pressure drop data of Li-ion battery corresponding to formation process 1

Numbering U ₁ , V U ₂ , V ΔU ₁ , V U ₃ , V U ₄ , V ΔU ₂ , V (ΔU ₁ -ΔU ₂ ), 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 Pressure drop data of Li-ion battery corresponding to formation process 2

From the above test results, the difference between the first pressure drop and the second pressure drop in the formation process 1 is relatively large, which proves that the formation process 1 is a more suitable formation process for this type of lithium-ion battery.

The validity of the above evaluation results is further tested by the cycle test method, specifically, the cycle test is carried out on the batteries after the formation process 1 and the formation process 2 respectively. The cycle test process is: 1C constant current and constant voltage charge to 4.2V, cut-off current 0.02 C, and then 1C constant current discharge to 2.75V, cycle 600 times; cycle test results are shown in Figure 2.

It can be seen from Figure 2 that the cycle performance of the lithium-ion battery corresponding to the formation process 1 is significantly better than that of the formation process 2, indicating that for this type of lithium-ion battery, the formation process 1 has a better activation effect than the formation process 2.

It can be concluded from the above test that, compared with the method of cycle test, the method of the present invention can simply and intuitively reflect the pros and cons of different formation processes of lithium-ion batteries, shorten the evaluation time, and thus help lithium-ion battery manufacturers to quickly screen out Appropriate chemical formation process.

Claims (6)

1. a kind of evaluation method of lithium ion battery formation process, which is characterized in that include the following steps：

1) after battery completes formation process, detection voltage is U₁；Then burin-in process is carried out to battery, electricity is detected after burin-in process Pressure is U₂, record pressure drop Δ U for the first time₁=U₁-U₂；

2) cyclic test is carried out to the battery after step 1) burin-in process, detection voltage is U₃, then the battery after partial volume is carried out Burin-in process, detection voltage is U after burin-in process₄, record secondary voltage drop Δ U₂=U₃-U₄；

3) the difference DELTA U=Δs U of pressure drop for the first time and secondary voltage drop is calculated₁-ΔU₂, the Δ U values of more different formation process, such as Δ U ≤ 0, illustrate that formation process does not reach activation effect；Such as Δ U ＞ 0, illustrate that formation process reaches activation effect, and Δ U values are got over Greatly, illustrate that the formation effect of the formation process is better.

2. the evaluation method of lithium ion battery formation process as described in claim 1, which is characterized in that described in step 1) Burin-in process is processing 24-48h at 35-55 DEG C.

3. the evaluation method of lithium ion battery formation process as described in claim 1, which is characterized in that described in step 2) Cyclic test is that cycle is discharged and charged, and the number of cycle is 2-4 times.

4. the evaluation method of lithium ion battery formation process as claimed in claim 3, which is characterized in that in cyclic process, put Electricity and the multiplying power of charging are 1C.

5. the evaluation method of lithium ion battery formation process as described in claim 3 or 4, which is characterized in that in cyclic process, Charge to the blanking voltage of formation process.

6. the evaluation method of lithium ion battery formation process as described in claim 1, which is characterized in that described in step 2) Burin-in process is processing 24-48h at 35-55 DEG C.