Method for nondestructive testing of lithium ion battery lithium precipitation and lithium precipitation back-embedding

Abstract

The invention provides a method for nondestructive detection of lithium precipitation of a lithium ion battery, and the method comprises the following steps: S001, placing a battery to be detected in a constant temperature box, connecting the constant temperature box to a test cabinet, and carrying out charging and discharging tests on the battery under different conditions; s002, recording changes of voltage and current along with time in the charging and discharging process of the battery, namely a U-t curve and an I-t curve; s003, according to the record, calculating to obtain an DMI-t curve of current change and time in the constant voltage stage; according to the lithium ion battery lithium precipitation detection method, whether lithium precipitation occurs in the battery or not is judged according to the current change in the constant-voltage charging stage of the battery, and the lithium precipitation detection method is simple, easy to implement and lossless and has good application value in the lithium ion battery lithium precipitation detection method.

Description

Technical Field

[0001] The present invention belongs to the field of battery manufacturing equipment, and particularly relates to a method for non-destructively detecting lithium deposition and lithium deposition back-insertion in lithium-ion batteries. Background Art

[0002] Due to its advantages such as high energy density and long cycle life, lithium-ion batteries have received increasing attention in the applications of electronic products and electric vehicles. If lithium deposition occurs during the cycling of lithium-ion batteries, it will have a greater impact on the cycle life and safety performance of lithium-ion batteries.

[0003] The traditional method for detecting lithium deposition in batteries is to disassemble the battery to be tested and observe whether lithium deposition appears on the surface of its negative electrode. This method causes the direct scrapping of the battery to be tested and may also cause certain safety problems. Therefore, the research on non-destructive detection of lithium deposition in batteries has always been a hot topic in the industry. The Chinese invention patent with the publication number CN112782582 applied for a method for detecting lithium deposition on the negative electrode of a lithium-ion battery, and judged whether the battery had lithium deposition by the plateau on the voltage curve during the rest period after lithium deposition in the battery, realizing non-destructive detection of lithium deposition.

[0004] However, in the actual testing process of the battery, its testing mechanism often includes a constant voltage charging stage, that is, when maintaining the battery voltage constant, the charging current gradually decreases until the set cut-off current is reached. Because lithium deposition back-insertion reaction also occurs in this stage, resulting in the weakening or disappearance of the voltage plateau of lithium deposition back-insertion in the battery during the subsequent rest period, it will be more difficult to judge whether the battery has lithium deposition.

[0005] Therefore, it is necessary to design a method for non-destructively detecting lithium deposition and lithium deposition back-insertion in lithium-ion batteries to solve the above-mentioned existing technical problems. Summary of the Invention

[0006] In view of the above problems, the present invention provides a method for non-destructively detecting lithium deposition in lithium-ion batteries, and the method includes:

[0007] S001. Place the battery to be tested in a constant temperature box, connect it to a test cabinet, and perform charge and discharge tests on the battery under different conditions;

[0008] S002. Record the changes of voltage and current with time during the charge and discharge of the battery, that is, the U~t curve and the I~t curve;

[0009] S003. According to the record, calculate the ▲I~t curve of the current change and time in the constant voltage stage;

[0010] S004. Judge the lithium deposition situation of the battery according to the ▲I~t curve.

[0011] In the above method, by calculating the ▲I~t curve, the lithium plating situation of the battery can be judged, so that the accuracy of detecting lithium plating can be greater than that of the conventional U~t and dU / dt methods, and it can judge the occurrence of lithium plating in the battery more accurately than the method where the negative electrode potential of the three-electrode battery is less than 0V. This method is simple, non-destructive, easy to operate, and more suitable for the actual test situation of the battery, so it has good application value.

[0012] In any implementation manner, in the S003, the current change and time ▲I~t curve in the constant voltage stage are calculated by the following formula: ▲I = I(t1) - I(t2), where t1 and t2 are respectively the first sampling time and the second sampling time adjacent to each other in the constant voltage section, and both t1 and t2 are less than or equal to 30 s.

[0013] In this implementation manner, through the above formula, the current change and time ▲I~t curve in the constant voltage stage can be effectively calculated, so as to prepare for subsequent judgment of the lithium plating situation of the battery.

[0014] In any implementation manner, in the S004, the judgment of whether the lithium-ion battery has lithium plating includes:

[0015] If a current characteristic peak appears in the ▲I~t curve, the battery has lithium plating; if no current characteristic peak appears in the ▲I~t curve, the battery has no lithium plating.

[0016] In this implementation manner, through the ▲I~t curve, it can be seen whether a current characteristic peak appears, so as to prepare for whether the battery has lithium plating.

[0017] In any implementation manner, in the S001, the mechanism of the charge and discharge test includes a constant voltage charging stage.

[0018] In this implementation manner, the change of the current in the constant voltage section with time is applied. At this time, the voltage is a fixed value and does not change with time, and the test effect is more prominent.

[0019] In any implementation manner, the cut-off current I of the constant voltage charging stage satisfies I ≤ 0.05C.

[0020] In this implementation manner, the cut-off current I ≤ 0.05C makes the test effect better.

[0021] In any implementation manner, in the S001, the charge and discharge conditions include a rate test, a high and low temperature test, and a cycle test.

[0022] In this implementation manner, the rate test, the high and low temperature test, and the cycle test make the test data more comprehensive and the test accuracy higher.

[0023] In any implementation manner, in the S001, the operating temperature of the constant temperature box is -20°C - 55°C.

[0024] In this embodiment, the operating temperature is -20°C to 55°C, which better corresponds to the actual operating environment of the battery.

[0025] On the other hand, the present invention also provides a method for non-destructively detecting lithium deposition and lithium back-insertion in a lithium-ion battery. The lithium back-insertion method is implemented based on the above lithium deposition method. Among them, the lithium back-insertion method includes: judging the lithium deposition and lithium back-insertion capacity Q of the battery according to the I-t curve.

[0026] In the above manner, adding the judgment process of the lithium deposition and lithium back-insertion capacity Q can be used as a judgment basis for detecting the formation and back-insertion of lithium dendrites in a lithium-ion battery.

[0027] In any embodiment, the lithium deposition and lithium back-insertion capacity Q is the area of the region of the current characteristic peak on the I-t curve. The lithium deposition and lithium back-insertion capacity Q is obtained through the absolute integral area, that is, Q (mAh) = ▲i * t, where ▲i is the magnitude of the current that changes along the changing trend of the original current curve, and t is the time.

[0028] In this embodiment, the lithium deposition and lithium back-insertion capacity Q is quickly and effectively calculated through the absolute integral area.

[0029] The beneficial effects of the present invention are as follows:

[0030] The present invention discloses a method for non-destructively detecting lithium deposition and lithium back-insertion in a lithium-ion battery. This method is simple, non-destructive, easy to operate, and more suitable for the actual testing of batteries. Therefore, it has good application value.

[0031] Other features and advantages of the present invention will be described in the following specification. Moreover, some of them will become obvious from the specification, or can be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures pointed out in the specification, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 Shows a flowchart of a method for non-destructively detecting lithium deposition in a lithium-ion battery according to an embodiment of the present invention

[0034] Figure 2 Shows a schematic diagram corresponding to the change of voltage and current with time during constant current and constant voltage charging of a non-lithium-deposited battery according to the present invention;

[0035] Figure 3Shows the curves of the change of ▲I~t during the constant voltage charging stage of the battery at different rates according to the embodiments of the present invention;

[0036] Figure 4 Shows the curves of the change of I~t during the constant voltage charging stage of the battery at different rates according to the embodiments of the present invention;

[0037] Figure 5 Shows the curves of voltage U~t and voltage differential dU / dt~t during the shelf period after the constant voltage charging stage at different rates according to the embodiments of the present invention;

[0038] Figure 6 Shows the curves of the change of ▲I~t during the constant voltage charging stage of the battery with different number of cycles according to the embodiments of the present invention;

[0039] Figure 7 Shows the curves of the change of I~t during the constant voltage charging stage of the battery with different number of cycles according to the embodiments of the present invention;

[0040] Figure 8 Shows the curves of voltage U~t and voltage differential dU / dt~t during the shelf period after constant voltage charging with different number of cycles according to the embodiments of the present invention.

[0041] Figure 9 Shows the curves of voltage U~t and voltage differential dU / dt~t during the shelf period after charging at different rates (without constant voltage charging) according to the embodiments of the present invention;

[0042] Figure 10 Shows the curves of the change of the negative electrode voltage U~t during the constant voltage charging of the battery at different rates according to the embodiments of the present invention;

[0043] Figure 11 Shows the curves of the change of ▲I~t during the constant voltage charging stage of the battery at different rates according to the embodiments of the present invention;

[0044] Figure 12 Shows the curves of the change of I~t during the constant voltage charging stage of the battery at different rates according to the embodiments of the present invention; Detailed implementation manners

[0045] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] Such as Figure 1As shown, the present invention provides a method for non-destructively detecting lithium plating in a lithium-ion battery. The method includes:

[0047] S001. Place the battery under test in an incubator, connect it to a test cabinet, and perform charge-discharge tests on the battery under different conditions. Among them, the mechanism of the charge-discharge test includes a constant-voltage charging stage, and the charge-discharge conditions include rate tests, high and low temperature tests, and cycle tests, etc. The operating temperature of the incubator is -20°C - 55°C. Among them, as Figure 2 shown, it is a schematic diagram of the voltage and current changes during constant-current and constant-voltage charging of a lithium-plating-free battery.

[0048] S002. Record the changes of voltage and current with time during the charge-discharge process of the battery, that is, the U~t curve and the I~t curve.

[0049] S003. Calculate the ▲I~t curve of the current change and time during the constant-voltage stage. Among them, the ▲I~t curve of the current change and time during the constant-voltage stage is calculated by the following formula: ▲I = I(t1) - I(t2), where t1 and t2 are the first and second sampling times adjacent to each other during the constant-voltage stage respectively, and the sampling times t1 and t2 are both less than or equal to 30 s, preferably 1 s. In addition, the cut-off current I during the constant-voltage charging stage is ≤ 0.05C, preferably 0.05C.

[0050] S004. Judge the lithium plating situation of the battery according to the ▲I~t curve, including:

[0051] If a current characteristic peak appears in the ▲I~t curve of the lithium-ion battery, the battery has lithium plating;

[0052] If no current characteristic peak appears in the ▲I~t curve of the lithium-ion battery, the battery has no lithium plating.

[0053] On the other hand, the present invention also provides a method for non-destructively detecting the lithium plating re-insertion in a lithium-ion battery. The lithium plating re-insertion method is realized by the above-mentioned lithium plating method. Among them, the lithium plating re-insertion method includes:

[0054] S005. Judge the lithium plating re-insertion capacity Q of the battery according to the I~t curve. The lithium plating re-insertion capacity Q is the area of the region of the current characteristic peak on the I~t curve. The lithium plating re-insertion capacity Q is calculated by the following formula:

[0055] Q(mAh) = ▲i * t, where ▲i is the magnitude of the current changing along the original current curve trend, and t is the time, usually obtained by the absolute area of software integration.

[0056] The present invention will be described in detail below with reference to embodiments.

[0057] Embodiment 1

[0058] Non-destructive lithium plating detection during different rate charging of the battery

[0059] S001. Place six ternary batteries in a thermostat at 25°C, discharge them to 3V, and leave them standing for 20 min.

[0060] S002. Charge the batteries at a constant current to 4.25V at different rates and then switch to constant voltage charging at 4.25V. The cut-off current for constant voltage charging is 0.05C. Leave them standing for 20 min. The charging rates for different batteries are 0.33C, 1C, 3C, 6C, and 9C.

[0061] S003. Record the changes in voltage and current over time during the charge and discharge processes of the batteries, with a sampling time of 1 s.

[0062] S004. Calculate the ▲I~t curves of the current changes and time during the constant voltage charging stage for different batteries:

[0063] S005. Judge the lithium plating situation of the batteries based on the ▲I~t curves:

[0064] S006. Judge the lithium plating back-insertion situation of the batteries based on the I~t curves:

[0065] As Figure 3 shown, it can be seen that when the charging rates of the batteries are 0.33C and 1C, there are no current characteristic peaks on the ▲I~t curves during the constant voltage stage. However, when the charging rate is 3C or higher, current characteristic peaks appear on the ▲I~t curves during the constant voltage stage, that is, the charging curve shows a peak envelope, as indicated by the arrows in the solid-line box in the figure. This phenomenon indicates that lithium plating occurs when the batteries are charged at rates of 3C / 6C / 9C, and as the rate increases, the area of the current characteristic peak becomes larger, indicating more severe lithium plating.

[0066] Based on the above judgment results, according to Figure 4 the area of the region of the lithium plating back-insertion current characteristic peak on the I~t curve, the lithium plating back-insertion capacity of each battery can be calculated, that is: Q1(3C)=2.563 mAh; Q2(6C)=17.922 mAh; Q3(9C)=46.934 mAh. (The calculation formula for converting the above capacity from A·s to mAh is: Q(mAh)=Q(A·s) / 3600*1000), where A is ampere and s is second.)

[0067] Based on the above results, since lithium plating back-insertion occurs during the constant voltage stage of the batteries, combined with Figure 5 ( Figure 5 the missing characteristic peak in Figure 9 is shown in

[0068] Example 2

[0069] Non-destructive Detection of Lithium Deposition during Battery Cycling

[0070] S001: Place the battery under test in an incubator at 25°C for cycling tests. The test steps are as follows: rest for 30 min, charge at a constant current of 1C to 3.65V, hold at 3.65V until the cut-off current of 0.05C, rest for 30 min, discharge at a constant current of 1C to 2V, repeat the above steps, and cycle 1500 times;

[0071] S002: Record the changes in battery voltage and current over time during cycling, with a sampling time of 30 s;

[0072] S003: Calculate the ▲I~t curve of the current change and time during the constant voltage charging stage of the battery at the 1st and 1500th cycles:

[0073] S004: Judge the lithium deposition situation of the battery according to the ▲I~t curve:

[0074] S005: Judge the lithium deposition situation of the battery according to the I~t curve:

[0075] From Figure 6 It can be seen that a current characteristic peak (marked by the solid line box in the figure) appears on the ▲I~t curve during the constant voltage stage when the battery cycles 1500 times, while no current characteristic peak appears on the ▲I~t curve during the constant voltage stage at the initial cycle (1st cycle) of the battery. This phenomenon indicates that lithium deposition occurs when the battery cycles to 1500 times, and there is no lithium deposition phenomenon in the fresh battery.

[0076] Based on the above judgment results, according to Figure 7 The area of the region of the lithium deposition back-insertion current characteristic peak on the I~t curve, the lithium deposition back-insertion capacity when the battery cycles 1500 times can be calculated, that is: Q = 1.211 mAh. (The calculation formula for converting the above capacity from A·s to mAh is: Q(mAh) = Q(A·s) / 3600*1000).

[0077] Based on the above results, since lithium deposition back-insertion occurs during the constant voltage section of the battery, combined with Figure 8 It can be seen that no characteristic peak of lithium deposition back-insertion appears on the rest voltage and the voltage differential curve after constant voltage charging at the 1500th cycle.

[0078] Comparative Example 1

[0079] Non-destructive Detection of Lithium Deposition during Different Charge Rates of the Battery

[0080] S001: Take another 5 ternary parallel sample batteries in Example 1 and place them in an incubator at 25°C, discharge to 3V, and rest for 20 min;

[0081] S002. Charge the batteries at a constant current at different rates until 4.25 V, and let them stand for 20 min. The charging rates of different batteries are 1C, 3C, 6C, and 9C;

[0082] S003. Record the changes in voltage and current over time during the charge and discharge processes of the batteries, with a sampling time of 1 s;

[0083] S004. Calculate the dU / dt~t curves of the voltage changes over time during the standing period after constant-current charging for different batteries:

[0084] S005. Judge the lithium plating situation of the batteries based on the dU / dt~t curves:

[0085] As Figure 9 shown, it can be seen that when the charging rates of the batteries are 1C and 3C, no obvious characteristic peaks of lithium plating back-insertion appear in the voltage and dU / dt~t curves during the standing period after charging. However, when the charging rates are 6C and 9C and above, obvious characteristic peaks of lithium plating back-insertion appear in the voltage and dU / dt~t curves during the standing period after charging (marked by the solid-line frames in the figure). Moreover, as the rate increases, the area of the voltage characteristic peak becomes larger. This phenomenon indicates that lithium plating occurs when the batteries are charged at a rate of 6C / 9C, but its detection accuracy is lower than that of the ▲I~t detection method in Example 1.

[0086] Comparative Example 2

[0087] S001. Take 4 ternary three-electrode batteries (the ternary battery is a full battery, and the ternary three-electrode battery implants a reference electrode in the full battery to monitor the electrode potential), place them in a constant-temperature oven at 25 °C, connect a multi-channel recorder, and monitor the voltages of the full battery, the positive reference, and the negative reference respectively;

[0088] S002. Discharge the batteries to 3 V, let them stand for 10 min, then charge them at a constant current at different rates until 4.25 V and then switch to constant-voltage charging at 4.25 V. The cut-off current for constant-voltage charging is 0.05C, and let them stand for 20 min. The charging rates of different batteries are 0.5C, 1C, 1.5C, and 2C;

[0089] S003. Record the voltage of the negative electrode and the changes in the voltage and current of the full battery over time during the charge and discharge processes of the batteries, with a sampling time of 1 s;

[0090] S004. Plot the curves of the voltage changes of the negative electrode during charging at different rates;

[0091] S005. Calculate the ▲I~t curves of the current changes over time during the constant-voltage charging stage for different batteries:

[0092] S006. Judge the lithium plating situation of the batteries based on the ▲I~t curves:

[0093] S007. Determine the lithium plating and intercalation conditions of the battery based on the I~t curve:

[0094] As Figure 10 shown, it can be seen that when the charging rate of the battery is 0.5C, the negative electrode voltage is greater than 0V, indicating that the battery does not have lithium plating. When the charging rate of the battery is 1C, the negative electrode voltage is less than 0V, but there is no obvious lithium plating platform. This phenomenon may be caused by lithium plating or battery polarization of the battery, indicating that there is a possibility of lithium plating in the battery. When the charging rates of the battery are 1.5C and 2C, obvious lithium plating platforms appear in the negative electrode voltage, marked by the solid line box in the figure. This phenomenon indicates that lithium plating occurs when the battery is charged at the rates of 1.5C / 2C, and as the rate increases, the lithium plating voltage platform of the negative electrode becomes longer, indicating that the lithium plating of the battery is more serious.

[0095] As Figure 11 shown, it can be seen that when the charging rate of the battery is only 0.5C, no current characteristic peak appears on the ▲I~t curve in its constant voltage stage. When the charging rates are 1C / 1.5C / 2C, current characteristic peaks appear on the ▲I~t curve in their constant voltage stages. Among them, the current characteristic peak at 1C is relatively weak, marked by an arrow. This phenomenon indicates that lithium plating occurs when the battery is charged at the rates of 1C / 1.5C / 2C, and as the rate increases, the area of the current characteristic peak becomes larger, indicating that the lithium plating of the battery is more serious.

[0096] According to Figure 12 the area of the region of the lithium plating and intercalation current characteristic peak on the I~t curve in [], the lithium plating and intercalation capacities of the battery when charged at different rates can be calculated, that is: Q1(1C)=0.013mAh, Q2(1.5C)=0.035mAh, Q3(2C)=0.268mAh. (The calculation formula for converting the above capacities from A·s to mAh is: Q(mAh)=Q(A·s) / 3600*1000).

[0097] In summary, the method of detecting lithium plating of the battery by ▲I~t can more accurately judge the occurrence of lithium plating than the method of the negative electrode potential of the three-electrode battery, and can distinguish whether the negative electrode voltage of the battery is less than 0V due to lithium plating or polarization.

[0098] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to be equivalent change equivalent embodiments within the scope of the technical solution of the present invention. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for non-destructive testing of lithium ion battery lithium deposition, characterized in that: The method comprises: S001. Place the battery to be tested in a constant temperature box, connect it to the test cabinet, and perform charge and discharge tests on the battery under different conditions; S002. Record the changes of voltage and current over time during the battery charging and discharging process, i.e., the U~t curve and the I~t curve; S003. According to the records, the ▲I~t curve of the current change and time in the constant voltage stage is calculated; S004. Determine the lithium deposition situation of the battery based on the ▲I~t curve.

2. A method for nondestructive testing of lithium ion battery lithium deposition according to claim 1, characterized in that: In S003, the current change and time ▲I~t curve in the constant voltage stage is calculated by the following formula: ▲I=I(t1)-I(t2) Among them, t1 and t2 are respectively the first stepping time and the second stepping time adjacent to each other in the constant pressure section, and both t1 and t2 are less than or equal to 30s.

3. The method for nondestructive testing of lithium ion battery lithium deposition according to claim 1, characterized in that: In S004, the determination of whether the lithium-ion battery has lithium deposition includes: If the ▲I~t curve shows a current characteristic peak, the battery undergoes lithium deposition; If the ▲I~t curve does not show a current characteristic peak, then lithium deposition has not occurred in the battery.

4. The method for nondestructive testing of lithium ion battery lithium deposition according to claim 1, characterized in that: In S001, the mechanism of the charge and discharge test includes a constant voltage charging stage.

5. The method for nondestructive testing of lithium ion battery lithium deposition according to claim 4, characterized in that: The cut-off current I in the constant voltage charging stage is ≤0.05C.

6. A method for nondestructive testing of lithium ion battery lithium deposition according to any one of claims 1 to 5, characterized in that: In S001, the charge and discharge conditions include rate test, high and low temperature test and cycle test.

7. The method for nondestructive testing of lithium ion battery lithium deposition according to claim 3, characterized in that: In the above S001, the working temperature of the thermostat is -20°C to 55°C.

8. A method for non-destructive detection of lithium ion battery lithium deposition and reinsertion, characterized in that: The lithium precipitation and reinsertion method is implemented based on the lithium precipitation method according to any one of claims 1 to 7, wherein the lithium precipitation and reinsertion method comprises: The battery lithium deposition and reinsertion capacity Q is determined based on the I~t curve.

9. A method for nondestructive detection of lithium ion battery lithium deposition and reinsertion according to claim 8, characterized in that: The lithium deposition and reinsertion capacity Q is the area of ​​the current characteristic peak on the I~t curve.

10. The method for nondestructive detection of lithium ion battery lithium deposition and reinsertion according to claim 8, characterized in that: The lithium reinsertion capacity Q is obtained by the absolute integral area, that is, Q(mAh)=▲i*t, ▲i is the current magnitude that changes along the original current curve, and t is the time.

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