Charge and discharge cycle test method for high energy density lithium metal batteries for solar drones

Abstract

The present invention discloses a charge-discharge cycle test method for a high-energy-density lithium metal battery for a solar-powered drone, comprising the following steps: determining the charge-discharge test environment temperature, charge rate, and discharge rate, and confirming that the battery cell is in a discharged state; turning on the power of the charge-discharge test equipment and setting a battery cell charge-discharge cycle test program; placing the cell into a fixture; charging the cell at the charge rate, wherein the fixture continuously applies a first pressure during charging, the first pressure value gradually increasing from an initial pressure value as the charging time increases; allowing the cell to stand for a third time; discharging the cell at the discharge rate, wherein the fixture continuously applies a second pressure during discharge, the second pressure value gradually decreasing as the discharge time increases; allowing the cell to stand for a fourth time; and repeating the above charge-discharge process until the number of cycle tests reaches a certain number. The present invention can improve the efficiency of cycle testing of lithium metal battery packs, reduce testing costs, and also reduce the risk of fire and explosion of the battery pack during testing.

Description

Technical Field

[0001] The present invention relates to the field of solar-powered unmanned aerial vehicle (UAV) energy storage batteries, and more specifically, to a charge-discharge cycle testing method for a high-energy-density lithium metal battery for a solar-powered unmanned aerial vehicle (UAV). Background Art

[0002] With the development of science and technology, metal lithium batteries are increasingly being used in the field of solar drones. Soft-pack metal lithium battery cells are a new type of structure that is being developed and matched for solar drones. The metal lithium battery cells in this structure have high power output characteristics and high specific energy. The measured cycle life of metal lithium battery cells can reach 80 cycles, or even more than 100 cycles. However, when metal lithium battery cells are combined into a metal lithium battery pack, its cycle performance can only reach 30 cycles or less. The ordinary metal plywood clamping method for charge and discharge testing cannot detect this defect in the early stage before the cell groups or installation. After the cell groups or installation, after multiple charge and discharge cycles, the metal lithium battery may experience expansion tension that exceeds the combined clamping force. In this case, the lithium dendrites in the expanded space inside the metal lithium battery may pierce the diaphragm, causing a short circuit in the battery and a battery fire. At present, the charge and discharge test method of metal lithium battery combinations is mainly achieved by actually making prototypes for cycle testing. For example, after being compressed with a preload force of 0N to 50,000N, the pressure value is passively affected by the installation status of the test battery and presents uncontrolled changes during the subsequent test. The battery cycle life is predicted by passively detecting the relationship between cycle life and pressure. However, this method wastes resources, manpower and time for various types and forms of metal lithium battery cells and combinations, and also has the risk of expanding dangerous situations and the scope of impact after grouping. Summary of the Invention

[0003] The purpose of the present invention is to propose a charge and discharge cycle testing method for high-energy-density lithium metal batteries for solar drones, so as to improve the cycle testing efficiency of lithium metal battery packs, reduce testing costs, and also reduce the risk of battery pack fire and explosion during the test.

[0004] To achieve the above objectives, the present invention proposes a charge-discharge cycle testing method for a high-energy-density lithium metal battery for a solar drone, comprising:

[0005] S1: Determine the charge and discharge test environment temperature, charge rate, and discharge rate according to the type of the metal lithium battery cell to be tested, and confirm that the metal lithium battery cell to be tested is in a discharged state;

[0006] S2: Turn on the power of the charge and discharge test equipment, and set the metal lithium battery single charge and discharge cycle test program according to the charge rate and the discharge rate;

[0007] S3: placing the lithium metal battery cell to be tested into a fixture for charge and discharge cycle testing, and setting the initial pressure value and the fully charged pressure value applied by the fixture to the lithium metal battery cell;

[0008] S4: executing a charge-discharge cycle test program at the charge-discharge test environment temperature, charging the metal lithium battery cell at the charge rate for a first period of time, during which the fixture continuously applies a first pressure to the metal lithium battery cell, wherein the value of the first pressure gradually increases from the initial pressure value as the charging time increases;

[0009] S5: leaving the lithium metal battery cell at rest for a third period of time, waiting for the internal polarization of the cell cell to disappear, the charge state to be balanced, and the temperature to return to normal temperature;

[0010] S6: discharging the lithium metal battery cell at the discharge rate for a second period of time, during which the fixture continuously applies a second pressure to the lithium metal battery cell, and the value of the second pressure gradually decreases as the discharge time increases;

[0011] S7: leaving the lithium metal battery cell at rest for a fourth period of time, waiting for the internal polarization of the cell cell to disappear, the charge state to be balanced, and the temperature to return to normal temperature;

[0012] S8: Repeat S4 to S7 until the set number of cycle tests is reached and the test is completed.

[0013] Optionally, in step S4, the relationship between the value of the first pressure P1 and the charging time is:

[0014] P1=(P max -P min )×t1×C1+P min ;

[0015] Among them, P min is the initial pressure value, P max is the fully charged pressure value of the monomer, t1 is the charging time, C1 is the charging rate, and 0<t1≤1 / C1.

[0016] Optionally, in step S6, the relationship between the value of the second pressure P2 and the charging time is:

[0017] P2=P max -(P max -P min )×t2×C2;

[0018] Wherein, t2 is the charging time, C2 is the discharge rate, and 0<t2≤1 / C2.

[0019] Optionally, in step S1, the discharge state is an empty state in which the SOC of the metal lithium battery cell is 0; and the range of the charge and discharge test environment temperature is 20°C to 30°C.

[0020] Optionally, in step S2, the charging rate ranges from 0.05 to 1, and the discharging rate ranges from 0.05 to 10.

[0021] Optionally, in step S3, the initial pressure value ranges from 0.2 MPa to 0.3 MPa.

[0022] Optionally, in step S3 , the range of the fully charged cell pressure value is 3 MPa to 6 MPa.

[0023] Optionally, the third duration and the fourth duration range from 20 minutes to 40 minutes.

[0024] Optionally, the setting items of the charge and discharge cycle test program include: charge rate, charge time, rest time, discharge rate, discharge time, number of cycles, and test protection upper limit voltage, lower limit voltage and protection temperature.

[0025] Optionally, during the repeated execution of the cyclic test of S4-S7, the test data and appearance status of the single unit are observed in real time, and the test is stopped immediately if any abnormality is found.

[0026] The beneficial effects of the present invention are:

[0027] (1) The present invention adopts a method of continuous pressure application adapted to the corresponding battery type and working conditions combined with temperature control to perform charge and discharge tests, which can expose and eliminate potential internal short circuit hazards after grouping or installation in advance.

[0028] (2) The present invention adopts the expansion tension of the charging and discharging process combined with the adaptive continuous pressure of the charging and discharging rate conditions, which can not only simulate the actual use of metal lithium battery cells after being grouped, examine the battery's charge and discharge cycle performance and expose defects, but also avoid the unnecessary resource, manpower and time consumption of the existing means that must be used for group performance confirmation.

[0029] (3) Before charging, the present invention adjusts the initial pressure for pre-pressing, so that the state of the metal lithium single battery reaches stability before performing the charge and discharge test. Compared with the existing testing methods, it is safer, more accurate and reliable.

[0030] (4) The present invention uses the charge and discharge rate as one of the variables for continuous pressure regulation, and through a reasonable calculation method, it can efficiently achieve the purpose of the most practical pressure regulation.

[0031] The system of the present invention has other features and advantages that will be apparent from or will be described in detail in the accompanying drawings and subsequent detailed description incorporated herein, which together serve to explain the specific principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, in which like reference numerals generally represent like components.

[0033] Figure 1 A flowchart showing the steps of a charge and discharge cycle test method for a high energy density metal lithium battery for a solar drone according to the present invention is shown. DETAILED DESCRIPTION

[0034] The present invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention may be implemented in various forms and is not limited to the embodiments set forth herein. Rather, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0035] like Figure 1 As shown, a charge and discharge cycle testing method for a high specific energy metal lithium battery for a solar drone according to the present invention includes:

[0036] S1: Determine the charge and discharge test environment temperature, charge rate, and discharge rate according to the type of the metal lithium battery cell to be tested, and confirm that the metal lithium battery cell to be tested is in a discharged state;

[0037] In this step, the discharge state is the empty state of the metal lithium battery cell with a SOC of 0; the optional range of the charge and discharge test environment temperature is 20°C to 30°C, preferably 25°C.

[0038] This step confirms that the metal lithium battery cell is in a discharged state before testing, and determines the charge and discharge ambient temperature T and the charge rate (C1) and discharge rate (C2) according to the cell type.

[0039] S2: Turn on the power of the charge and discharge test equipment, and set the metal lithium battery single charge and discharge cycle test program according to the charge rate and discharge rate;

[0040] Depending on the type of battery cell, the charge rate generally ranges from 0.05 to 1, and the discharge rate generally ranges from 0.05 to 10. The settings for the charge and discharge cycle test program include: charge rate (C1), charge duration, rest duration, discharge rate, discharge duration (C2), number of cycles, and test protection upper and lower voltage limits and protection temperature.

[0041] This step sets the test conditions in the single cell charge and discharge program based on the determined charge rate (C1) and discharge rate (C2) determined in step S1, and sets the charge and discharge time, interval rest time, etc., and sets the corresponding test protection conditions according to the parameter type of the metal lithium battery cell.

[0042] S3: Place the lithium metal battery cell to be tested into a fixture for charge and discharge cycle testing, and set the initial pressure value and the fully charged pressure value applied by the fixture to the lithium metal battery cell;

[0043] In this step, the initial pressure value ranges from 0.2 MPa to 0.3 MPa, and the pressure value of the fully charged cell ranges from 3 MPa to 6 MPa.

[0044] Place the lithium metal battery cell to be tested into the test fixture and set the fixture to apply the initial pressure (or the cell discharge pressure) P min And the single cell fully charged state pressure (maximum pressure) P max , P min The value is between 0.2MPa and 0.3MPa, and the maximum pressure P max In the range of 3Mpa ~ 6Mpa, it can be determined according to the type of metal lithium battery to be tested. After the setting is completed, adjust the fixture to apply the initial pressure P min , confirm that the fixture is clamping effectively and there is no possibility of loosening or sliding out, and the test preparation is complete.

[0045] S4: executing a charge-discharge cycle test program at a charge-discharge test environment temperature, charging the metal lithium battery cell at a charge rate for a first time period, during which the fixture continuously applies a first pressure to the metal lithium battery cell, wherein the value of the first pressure gradually increases from an initial pressure value as the charging time increases;

[0046] In this step, the relationship between the first pressure value P1 and the charging time is:

[0047] P1=(P max -P min )×t1×C1+P min ;

[0048] Among them, P min is the initial pressure value, P maxis the pressure value of the fully charged single cell, t1 is the charging time (in hours), C1 is the charging rate, 0<t1≤1 / C1.

[0049] Specifically, the charging process is prepared, and the clamp continuously applies pressure P1=(P max -P min )×t1×C1+P min , start the charge and discharge program, and first perform a charge test on the metal lithium battery cell at a charge rate of C1. The maximum value of the test time t1 must not be greater than 1 / C1.

[0050] S5: leaving the lithium metal battery cell at rest for a third period of time, waiting for the internal polarization of the cell cell to disappear, the charge state to be balanced, and the temperature to return to normal temperature (i.e., the test environment temperature);

[0051] In this step, the third duration ranges from 20 min to 40 min, preferably 30 min.

[0052] Specifically, the test enters the rest time t3 according to the set program. The setting value of t3 is determined by the type of metal lithium battery cell being tested to ensure that the polarization, charge state and temperature of the single cell do not affect the subsequent test state.

[0053] S6: discharging the lithium metal battery cell for a second period of time at a discharge rate, during which the fixture continuously applies a second pressure to the lithium metal battery cell, and the value of the second pressure gradually decreases as the discharge time increases;

[0054] In this step, the relationship between the second pressure value P2 and the charging time is:

[0055] P2=P max -(P max -P min )×t2×C2;

[0056] Wherein, t2 is the charging time (in hours), C2 is the discharge rate, and 0<t2≤1 / C2.

[0057] Specifically, the discharge process is prepared, and the clamp continuously applies pressure P=P during the discharge process. max -(P max -P min )×t2×C2, continue the charge and discharge procedure, and perform discharge test on the metal lithium battery cell at the discharge rate C2. The maximum value of the test time t2 must not be greater than 1 / C2.

[0058] S7: leaving the lithium metal battery cell at rest for a fourth period of time, waiting for the internal polarization of the cell cell to disappear, the charge state to be balanced, and the temperature to return to normal temperature;

[0059] In this step, the fourth time period ranges from 20 minutes to 40 minutes, preferably 30 minutes.

[0060] Specifically, the test enters the rest time t4 according to the set program. The setting value of t4 is determined by the type of metal lithium battery cell being tested to ensure that the polarization, charge state and temperature of the single cell do not affect the subsequent test state.

[0061] S8: Repeat S4 to S7 until the set number of cycle tests is reached and the test is completed.

[0062] Specifically, the charge-discharge cycle test procedure is followed by the charge-discharge cycle from S4 to S7 until the set number of cycle tests is reached, completing the test. The number of cycles is determined by the type of lithium metal battery cell being tested and the project objectives used. During the cycle test, the cell test data and appearance are observed in real time. If any abnormality is found, the test is stopped immediately.

[0063] The advantages of the charge-discharge cycle testing method for metal lithium batteries of the present invention are:

[0064] (1) A method of continuous clamping and pressing adapted to the corresponding battery type and working conditions combined with ambient temperature control is used to expose and eliminate in advance the potential internal short circuit and excessive expansion of the metal lithium battery cells during use after grouping. This solves the technical problem that the existing single-cell charge and discharge cycle test of high-energy lithium-ion batteries for solar drones cannot simulate actual usage conditions.

[0065] (2) A method of actively and dynamically applying controllable pressure to different charge states is used to test the cycle life, thereby achieving the technical effect of replacing the combined battery cycle life test.

[0066] (3) The expansion tension during the charge and discharge process is combined with the adaptive continuous pressure of the charge and discharge rate conditions. This can not only simulate the actual use of metal lithium battery cells after being grouped, examine the battery's charge and discharge cycle performance and expose defects, but also avoid the unnecessary resource, manpower and time consumption of the existing means of grouping performance confirmation.

[0067] (4) The charge and discharge rate is used as one of the variables for continuous pressure regulation, and a reasonable calculation method can be used to efficiently achieve the purpose of pressure regulation that best fits the actual situation. Before charging, the present invention adjusts the initial pressure for pre-pressing, so that the state of the metal lithium single cell reaches a stable state before performing the charge and discharge test. Compared with the existing testing methods, it is safer, more accurate and reliable.

[0068] (5) A reasonable calculation and testing method was used to solve the technical problem of low efficiency in verifying the optimal combination of high-energy-density lithium-ion batteries for solar drones. This method solved the technical problem of the inability of charge and discharge cycle testing of high-energy-density metal lithium batteries for drones to simulate actual operating conditions, thereby improving the efficiency of testing the optimal combination of high-energy-density metal lithium batteries for drones.

[0069] The solution of the present invention is further explained below through a specific embodiment.

[0070] Example:

[0071] This embodiment provides a charge-discharge cycle testing method for a high-energy-density lithium metal battery for a solar drone, comprising the following steps:

[0072] Step 1: Select a high specific energy 13Ah lithium metal battery cell, set the charge rate to 0.2C, set the discharge rate to 0.2C, and control the charging and discharging ambient temperature at 25°C;

[0073] Step 2. Turn on the power of the charge and discharge test equipment and set the metal lithium battery single charge and discharge cycle test program: the battery single is first charged at 0.2C for 5 hours, left to stand for 0.5 hours, then discharged at 0.2C for 5 hours, and then left to stand for 0.5 hours. Repeat the above process 60 times. At the same time, set the protection upper limit voltage to 4.5V, the lower limit voltage to 2.7V, and the protection temperature to 60°C;

[0074] Step 3: Place the lithium metal battery cell to be tested into the test fixture. The initial pressure applied by the fixture is set to 0.3 MPa, and the pressure of the cell in a fully charged state is 3 MPa. Adjust the initial pressure of the fixture to 0.3 MPa, and confirm that the fixture is clamped effectively and there is no possibility of loosening or slipping. The test preparation is complete.

[0075] Step 4: The metal lithium battery cell is charged at 0.2C for 5 hours. During this period, the pressure applied by the fixture changes continuously with the charging time, following the relationship of pressure P = (3 MPa - 0.3 MPa) × t1 × 0.2 + 0.3 MPa. The maximum value of the charging time t1 does not exceed 1 / C1 = 5 hours.

[0076] Step 5: Let the lithium metal battery cell stand for 0.5 hours according to the set program, waiting for the internal polarization of the cell to disappear, the charge state to balance, and the temperature to return to normal temperature;

[0077] Step 6: The lithium metal battery cell is discharged at 0.2C for 5 hours. During this period, the pressure applied by the fixture changes continuously with the charging time, following the relationship of pressure P = 3 MPa - (3 MPa - 0.3 MPa) × t2 × 0.2, and the maximum value of the discharge time t2 does not exceed 1 / C2 = 5 hours;

[0078] Step 7: Let the lithium metal battery cell stand for 0.5 hours according to the set program, waiting for the internal polarization of the cell to disappear, the charge state to balance, and the temperature to return to normal temperature;

[0079] Step 8. Repeat steps 4 to 7 and perform charge and discharge cycles 60 times according to the specified cycle test number. During this period, observe the test data and appearance of the single cell. If any abnormality is found, stop the test immediately.

[0080] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A charge-discharge cycle test method for a high-energy-density lithium metal battery for a solar drone, characterized in that: include: S1: Determine the charge and discharge test environment temperature, charge rate, and discharge rate according to the type of the metal lithium battery cell to be tested, and confirm that the metal lithium battery cell to be tested is in a discharged state; S2: Turn on the power of the charge and discharge test equipment, and set the metal lithium battery single charge and discharge cycle test program according to the charge rate and the discharge rate; S3: placing the lithium metal battery cell to be tested into a fixture for charge and discharge cycle testing, and setting the initial pressure value and the fully charged pressure value applied by the fixture to the lithium metal battery cell; S4: executing a charge-discharge cycle test program at the charge-discharge test environment temperature, charging the metal lithium battery cell at the charge rate for a first period of time, during which the fixture continuously applies a first pressure to the metal lithium battery cell, wherein the value of the first pressure gradually increases from the initial pressure value as the charging time increases; S5: leaving the lithium metal battery cell at rest for a third period of time, waiting for the internal polarization of the cell cell to disappear, the charge state to be balanced, and the temperature to return to normal temperature; S6: discharging the lithium metal battery cell at the discharge rate for a second period of time, during which the fixture continuously applies a second pressure to the lithium metal battery cell, and the value of the second pressure gradually decreases as the discharge time increases; S7: leaving the lithium metal battery cell at rest for a fourth period of time, waiting for the internal polarization of the cell cell to disappear, the charge state to be balanced, and the temperature to return to normal temperature; S8: Repeat S4 to S7 until the set number of cycle tests is reached and the test is completed.

2. The charge-discharge cycle testing method according to claim 1, characterized in that: In step S4, the relationship between the value of the first pressure P1 and the charging time is: P1=(P max -P min )×t1×C1+P min ; Among them, P min is the initial pressure value, P max is the fully charged pressure value of the monomer, t1 is the charging time, C1 is the charging rate, and 0<t1≤1 / C1.

3. The charge-discharge cycle testing method according to claim 2, characterized in that: In step S6, the relationship between the value of the second pressure P2 and the charging time is: P2=P max -(P max -P min )×t2×C2; Wherein, t2 is the charging time, C2 is the discharge rate, and 0<t2≤1 / C2.

4. The charge-discharge cycle testing method according to claim 1, wherein: In step S1, the discharge state is an empty state in which the SOC of the metal lithium battery cell is 0; and the range of the charge and discharge test environment temperature is 20°C to 30°C.

5. The charge-discharge cycle testing method according to claim 1, wherein: In step S2, the range of the charging rate is 0.05-1, and the range of the discharging rate is 0.05-10.

6. The charge-discharge cycle testing method according to claim 1, wherein: In step S3, the initial pressure value ranges from 0.2 MPa to 0.3 MPa.

7. The charge-discharge cycle testing method according to claim 1, characterized in that: In step S3 , the range of the fully charged cell pressure value is 3 MPa to 6 MPa.

8. The charge-discharge cycle testing method according to claim 1, wherein: The third duration and the fourth duration range from 20 minutes to 40 minutes.

9. The charge-discharge cycle testing method according to claim 1, wherein: The setting items of the charge and discharge cycle test program include: charge rate, charge time, rest time, discharge rate, discharge time, number of cycles, and test protection upper limit voltage, lower limit voltage and protection temperature.

10. The charge-discharge cycle testing method according to claim 1, characterized in that: During the repeated execution of the S4-S7 cycle test, the unit test data and appearance status are observed in real time. If any abnormality is found, the test is stopped immediately.

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