Method for accurately detecting self-discharge of lithium-ion battery

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically discloses a method for accurately detecting the self-discharge of lithium-ion batteries. The method at least includes: S01, charging or discharging the lithium-ion battery; S02, placing the lithium-ion battery in an environment of 35 to 60 °C for static treatment; S03, transferring the battery to an environment of 15 to 35 °C for static treatment; S04, detecting the battery voltage V1 and temperature T1 in S03; and converting V1 at this T1 temperature into T t voltage V at temperature t1 ; S05, applying pressure to the battery in S03 with a fixture and standing still in an environment of 15 °C to 35 °C; S06, detecting the voltage V2 and temperature T2 of the battery in S05; and converting V2 at this T2 into the above-mentioned T t voltage V t2 ; calculating the self-discharge rate of the lithium-ion battery after correcting the converted voltage. This method can effectively reduce the misjudgment of the battery by the traditional self-discharge test method and improve the test accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a method for accurately detecting the self-discharge of lithium-ion batteries. Background Art

[0002] Secondary lithium-ion batteries have many advantages such as high specific capacity, long charge and discharge life, no memory effect, and low environmental pollution. Since their commercialization in the early 1990s, they have quickly replaced nickel-cadmium and nickel-metal hydride batteries and are widely used in portable electrical appliances such as mobile phones, laptop computers, and video cameras. And there is a trend of developing towards new fields such as electric vehicles, aerospace, and energy storage power stations. However, lithium-ion batteries will experience self-discharge.

[0003] Generally, the self-discharge of lithium-ion batteries is considered to refer to the recoverable and non-recoverable loss of the battery's capacity caused by the oxidation-reduction reaction inside the battery when the battery is in a static state. This internal reaction is inevitable. Generally, the self-discharge of normal lithium-ion batteries is far from enough to affect people's use of terminal products such as mobile phones. However, when the internal separator of a lithium-ion battery is pierced by "protrusions" such as dust and electrode tab burrs or there is a risk of piercing, the self-discharge of the battery at this time will affect people's use of terminal products such as mobile phones and even pose a safety hazard. To avoid unsafe problems caused by the self-discharge of lithium-ion batteries, the self-discharge situation of lithium-ion batteries is generally detected / tested. The traditional self-discharge test method mainly involves leaving a lithium-ion battery that has been measured for capacity or voltage at a high temperature for a period of time, and then measuring the capacity or voltage of the battery again. The batteries with large self-discharge are selected by comparing the difference between the two capacities or voltages.

[0004] Since side reactions occur in lithium-ion batteries after charge and discharge and in high-temperature environments, and the side reaction rate at this time is greater than the side reaction rate when the battery is static in an environment such as a warehouse, the traditional test method cannot accurately select truly harmful self-discharge batteries.

[0005] Chinese Patent (Publication No. CN103513186A) discloses a method for testing the self-discharge of a lithium-ion battery. This testing method describes a method for determining the degree of self-discharge of a battery by means of magnetic field induction caused by the self-discharge current. Although this method is novel, it only detects the degree of self-discharge at a single point inside the battery at a single time point, and it is prone to missing detection and unable to detect the average self-discharge rate over a period of time. In addition, Chinese Patent (Publication No. CN103293481A) discloses a method for quickly detecting the self-discharge of a lithium-ion battery. This patent describes a method for calculating the self-discharge of a battery by measuring the voltage before and after 3 to 5 days at a high temperature. This method neither takes into account the voltage change caused by temperature nor involves the increase in self-discharge of the battery after charging and discharging or after being stored at a high temperature, which is prone to misjudgment. Therefore, it is necessary to find a new method for detecting the self-discharge of lithium-ion batteries. Summary of the Invention

[0006] The object of the present invention is to solve the problems of inaccurate detection of self-discharge and easy occurrence of misjudgment of self-discharge in existing lithium-ion batteries, and to provide a method for accurately detecting the self-discharge of lithium-ion batteries.

[0007] To achieve the above object of the invention, the embodiments of the present invention adopt the following technical solutions:

[0008] A method for accurately detecting the self-discharge of a lithium-ion battery, at least including the following steps:

[0009] Step S01. Charge or discharge the lithium-ion battery to make the voltage of the battery fall within the voltage range at the time of shipment of the battery.

[0010] Step S02. Place the battery processed in Step S01 in an environment of 35°C to 60°C and let it stand for 1 to 14 days.

[0011] Step S03. Transfer the battery processed in Step S02 to an environment of 15°C to 35°C and let it stand for 1 to 24 hours.

[0012] Step S04. Detect the voltage V1 and temperature T1 of the battery processed in Step S03; and convert the voltage at the T1 temperature to the voltage V at the T t temperature t1 ;

[0013] Step S05. Use a fixture to apply pressure to the battery processed in Step S03, and set the pressure value to 0.1 to 20 kg / cm 2 , and let it stand for 1 to 14 days in an environment of 15°C to 35°C.

[0014] Step S06. Detect the voltage V2 and temperature T2 of the battery after being processed by the above Step S05; and convert the voltage at the temperature T2 into the voltage V at the temperature T t at temperature t2 ;

[0015] After the above voltages are corrected respectively, the self-discharge rate of the battery is calculated according to the following calculation formula:

[0016]

[0017] The method for accurately detecting the self-discharge of a lithium-ion battery provided by the above embodiment of the present invention adopts a method of first aging at high temperature to eliminate side reactions, and then testing the self-discharge of the battery, eliminating the misjudgment of the self-discharge caused by reasons such as the recombination of the SEI film of the battery cell itself; and by aging with a normal-temperature fixture to flatten the battery to release in advance or accelerate the side reactions of the internally short-circuited battery, making it easier to distinguish between normal batteries and internally short-circuited batteries; by correcting the voltage, eliminating the self-discharge error caused by different temperatures during the two voltage tests, and finally improving the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 is a schematic diagram of the test process of the present invention;

[0020] Figure 2 is a histogram of the self-discharge rate test of Model A lithium-ion battery with a capacity of 2000 mAh provided in Embodiment 1 of the present invention;

[0021] Figure 3 is a histogram of the self-discharge rate test of Model B lithium-ion battery with a capacity of 3200 mAh provided in Embodiment 2 of the present invention;

[0022] Figure 4 is a histogram of the self-discharge rate test of Model C lithium-ion battery with a capacity of 4000 mAh provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following will further describe the present invention in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0024] An embodiment of the present invention provides a method for accurately detecting the self-discharge of a lithium-ion battery, which at least includes the following steps:

[0025] Step S01. Charge or discharge the lithium-ion battery so that the voltage of the battery falls within the voltage range when the battery is shipped.

[0026] Step S02. Place the battery processed in Step S01 in an environment of 35°C to 60°C and let it stand for 1 to 14 days.

[0027] Step S03. Transfer the battery processed in Step S02 to an environment of 15°C to 35°C and let it stand for 1 to 24 h.

[0028] Step S04. Detect the voltage V1 and temperature T1 of the battery processed in Step S03; and convert the voltage at the T1 temperature to the voltage V at the T t temperature. t1 ;

[0029] Step S05. Use a fixture to apply pressure to the battery processed in Step S03, and set the pressure value to 0.1 to 20 kg / cm 2 , and let it stand for 1 to 14 days in an environment of 15°C to 35°C.

[0030] Step S06. Detect the voltage V2 and temperature T2 of the battery processed in Step S05; and convert the voltage at the T2 temperature to the voltage V at the T t temperature. t2 ;

[0031] Then correct the measured voltage value.

[0032] Among them, in any embodiment, this detection method is applicable to lithium-ion batteries after pre-charging or grading. This is conducive to finding lithium-ion batteries with a large self-discharge rate or lithium-ion batteries with micro-shorts from the source, and then, according to the test results, selecting lithium-ion batteries with a low self-discharge rate and good performance for shipment.

[0033] In the above Step S01, when charging or discharging the lithium-ion battery, since lithium-ion batteries of different systems have different charge and discharge systems, the operation should be carried out according to the normal charge and discharge procedures of the lithium-ion battery of this system. After charging or discharging, the voltage value of the lithium-ion battery should be within the voltage range specified when the battery is shipped.

[0034] In Step S02, placing the lithium-ion battery at a higher temperature for a period of time is conducive to the occurrence of high-temperature aging. Through high-temperature aging, side reactions can be eliminated, and misjudgments of self-discharge caused by the recombination of the SEI film of the battery cell itself and other reasons can be eliminated.

[0035] Preferably, in step S02, the lithium-ion battery is placed in an environment with a temperature of 38°C to 45°C and only needs to be left standing for 3 to 7 days. The battery can achieve the effect of eliminating side reactions at 38°C to 45°C. It is known that for a normal battery during aging, the change rate of voltage is in a negative exponential law with the aging time. After three days at high temperature, the side reaction rate of the battery is already lower than the self-discharge caused by the battery defects. When the high-temperature time exceeds seven days and the high-temperature time is further increased, although there is a better effect, the increase in effect is not obvious, but the energy consumption generated during high temperature is increased and the shipping cycle is prolonged.

[0036] In step S03, the lithium-ion battery is placed in an environment with a temperature of 15°C to 35°C and left standing for 1 to 24 h to reduce the side reaction rate of the battery during high-temperature placement in step S02 and make it stable.

[0037] In any embodiment, for the battery voltage conversion in step S04. Since the voltage change rate of lithium-ion batteries in different systems varies with temperature. Therefore, when performing self-discharge detection, it is necessary to first test and statistically analyze the voltage change with temperature for lithium-ion batteries in each system to make a reference table. Since these are conventional tests, they are not described in detail in this invention patent text.

[0038] Specifically, those skilled in the art can make a table showing the change of battery voltage with temperature as shown in Table 1.

[0039] In Table 1, it shows the change rate of the voltage of lithium cobalt oxide battery with temperature. For example, when the battery voltage is 3.0V, at a temperature of 15 to 20°C, for every 1°C increase in temperature, the voltage decreases by 0.0008 mV.

[0040] Table 1 Change of Lithium Cobalt Oxide Battery Voltage with Temperature

[0041]

[0042]

[0043] In any embodiment, the pressing plate of the fixture in step S05 has stable performance and should meet the requirements of not deforming with temperature change and being acid and alkali resistant, etc. The plane where the pressing plate surface of the fixture is located should be parallel to the plane where the lithium-ion battery electrode plate is located to facilitate pressing on the electrode plate and achieve the side reaction of quickly or prematurely releasing the internal short circuit and micro short circuit of the lithium-ion battery, making it easier to distinguish between normal lithium-ion batteries and internally short-circuited lithium-ion batteries. It should be noted that when using the fixture to apply pressure to the lithium-ion battery, the battery should be placed upright.

[0044] Preferably, the pressure value of the pressing plate of the fixture is set to 1 to 8 kg / cm 2, in an environment of 15°C to 35°C, it only needs to be left standing for 3 to 7 days.

[0045] For a well-known battery, the rate of change of voltage during aging follows a negative exponential law. After the high-temperature step of S02, the rate of side reactions of the battery is already lower than the self-discharge rate caused by battery defects. The pressing plate pressure value of the fixture is set to 1 to 8 kg / cm 2 When it is, within three days at room temperature, the average self-discharge rate of the battery is lower than 1 / 2 of the self-discharge rate of the defective battery cell, and within seven days at room temperature, the average self-discharge rate of the battery is lower than 1 / 3 of the self-discharge rate of the defective battery cell. Within 3 to 7 days at room temperature, normal battery cells and abnormal battery cells can be clearly distinguished. Continuing to increase the fixture pressure or the aging time, although there is a better effect, the increase in the effect is not obvious, and the shipping cycle is extended.

[0046] In any embodiment, for the voltage conversion in step S06, it is the same as the voltage conversion method in step S03.

[0047] It should be noted that in the following formula (1) for calculating the self-discharge rate of the lithium-ion battery, V t1 and V t2 are both corrected average values. By performing multiple corrections, the misjudgment of self-discharge caused by different temperatures during the two tests can be eliminated as much as possible. The time difference between the two tests refers to the time difference between the test time in step S03 and the test time in step S06.

[0048]

[0049] The method for accurately detecting the self-discharge of a lithium-ion battery provided in the above embodiments of the present invention reduces the misjudgment of the battery by the traditional self-discharge test method and improves the test accuracy by first subjecting the battery to high-temperature aging to eliminate side reactions and then testing the self-discharge, applying pressure to the battery with a fixture at room temperature to accelerate the reaction rate of the internally short-circuited battery, and correcting the voltage difference caused by temperature.

[0050] To better illustrate the method for accurately detecting the self-discharge of a lithium-ion battery provided in the embodiments of the present invention, examples are given below for illustration.

[0051] Example 1

[0052] 1), Fabricate a batch of 9000 pcs of A-type lithium-ion batteries with a capacity of 2000 mAh according to the conventional lithium-ion battery manufacturing process. After pre-charging / grading the A-type lithium-ion batteries, charge them at a constant current of 1000 mA to 3.95 V, and then switch to constant voltage charging at 3.9 V, with a constant voltage cut-off current of 40 mA;

[0053] 2), Transfer the lithium-ion batteries in 1) to a high-temperature environment of 45°C and leave them standing for 3 days;

[0054] 3), Transfer the lithium-ion battery in step 2) to a normal temperature environment of 25°C. After standing for 24 hours, test the voltage and temperature of the battery, and convert the battery voltage measured at this test temperature to the battery voltage at 25°C;

[0055] 4), Use a fixture to apply pressure to the battery in step 3). The battery is placed with the plane of the battery electrode parallel to the fixture pressing plate, and the pressure is set at 2 kg / cm 2 , and stand in a normal temperature environment of 25°C for 3 days;

[0056] 5), Take out the battery after normal temperature aging in step 4) from the fixture, test the voltage and temperature of the battery, convert the battery voltage measured at this test temperature to the battery voltage at 25°C, calculate the self-discharge rate, and the self-discharge rate results are as shown in the appendix Figure 2 as follows.

[0057] Example 2

[0058] 1), Manufacture a batch of 6291 pcs of B-type lithium-ion batteries with a capacity of 3200 mAh according to the conventional lithium-ion battery manufacturing process. After pre-charging / grading the B-type lithium-ion batteries, use a constant current of 1600 mA to charge them to 3.99 V, and then switch to constant voltage charging at 3.99 V. The constant voltage cut-off current is 64 mA;

[0059] 2), Transfer the lithium-ion batteries in step 1) to a high temperature environment of 45°C and stand for 7 days;

[0060] 3), Transfer the lithium-ion battery in step 2) to a normal temperature environment of 25°C. After standing for 24 hours, test the voltage and temperature of the battery, and convert the battery voltage measured at this test temperature to the battery voltage at 25°C;

[0061] 4), Use a fixture to apply pressure to the battery in step 3). The battery is placed with the plane of the battery electrode parallel to the fixture pressing plate, and the pressure is set at 4 kg / cm 2 , and stand in a normal temperature environment of 25°C for 3 days;

[0062] 5), Take out the battery after normal temperature aging in step 4) from the fixture, test the voltage and temperature of the battery, convert the battery voltage measured at this test temperature to the battery voltage at 25°C, calculate the self-discharge rate, and the self-discharge rate results are as shown in the appendix Figure 3 as follows.

[0063] Example 3

[0064] 1), Manufacture a batch of 10054 C-type lithium-ion batteries with a capacity of 4000 mAh according to the conventional lithium-ion battery manufacturing process. After pre-charging / grading the C-type lithium-ion batteries, charge them at a constant current of 2000 mA until 3.99 V, and then switch to constant voltage charging at 3.99 V with a constant voltage cut-off current of 80 mA;

[0065] 2), Transfer the lithium-ion batteries in 1) to a high-temperature environment of 45 °C and let them stand for 7 days;

[0066] 3), Move the lithium-ion batteries in 2) to a normal-temperature environment of 25 °C. After standing for 24 hours, test the voltage and temperature of the battery, and convert the battery voltage measured at this test temperature to the battery voltage at 25 °C;

[0067] 4), Use a fixture to apply pressure to the battery in 3). The battery is placed with the battery electrode plane parallel to the fixture pressing plate, and the pressure is set at 8 kg / cm 2 , and let it stand in a normal-temperature environment of 25 °C for 7 days;

[0068] 5), Take out the battery in 4) from the fixture after normal-temperature aging, test the voltage and temperature of the battery, convert the battery voltage measured at this test temperature to the battery voltage at 25 °C, calculate the self-discharge rate, and the self-discharge rate results are as attached Figure 4 shown.

[0069] As can be seen from Figures 2 to 4 , there are obvious differences between the abnormal cells with large self-discharge and the normal self-discharge cells.

[0070] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for accurately detecting the self-discharge of a lithium-ion battery, comprising at least the following steps: Step S01. Charge or discharge the lithium-ion battery to make the voltage of the battery fall within the voltage range at the time of the battery's shipment; Step S02. Place the battery processed in Step S01 in an environment of 35°C to 60°C and let it stand for 1 to 14 days; Step S03. Transfer the battery processed in Step S02 to an environment of 15°C to 35°C and let it stand for 1 to 24 h; Step S04. Detect the voltage V1 and temperature T1 of the battery after being processed by the said Step S03; and convert the voltage at the temperature T1 into the voltage V at temperature T t at temperature T t1 ; Step S05. Apply pressure to the battery processed in the said Step S03 with a fixture, and set the pressure value to 0.1 - 20 kg / cm 2 , and leave it standing for 1 - 14 days in an environment of 15°C - 35°C; Step S06. Detect the voltage V2 and temperature T2 of the battery after being processed by the said Step S05; and convert the voltage at the temperature T2 into the voltage V at the said T t temperature t2 ; The self-discharge rate of the battery is calculated according to the following formula:

2. The method for detecting the self-discharge of a lithium-ion battery according to claim 1, characterized in that: The method of applying pressure to the battery in Step S05 is: place the battery upright, and the pressing plate of the fixture is parallel to the plane where the battery electrode plate is located.

3. The method for detecting the self-discharge of a lithium-ion battery according to any one of claims 1-2, characterized in that: The pressure value in the step S05 is 1 to 8 kg / cm 2 , and it is left standing for 3 to 7 days.

4. The method for detecting the self-discharge of a lithium-ion battery according to any one of claims 1-2, characterized in that: In Step S02, the environment is 38°C to 45°C and it stands for 3 to 7 days.

5. The method for detecting the self-discharge of a lithium-ion battery according to claim 1, characterized in that: The V in the calculation formula (1) t1 and V t2 are both corrected average values.

6. The method for detecting the self-discharge of a lithium-ion battery according to any one of claims 1-2, characterized in that: In Step S01, the battery is a pre-charged or formation-tested lithium-ion battery.

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