Method and device for testing entropy heat coefficient of secondary battery

Abstract

This invention discloses a method and apparatus for testing the entropy-thermal coefficient of a secondary battery. The testing method includes: after performing constant-capacity formation treatment on the prepared secondary battery, measuring the open-circuit voltage (OCV) corresponding to different states of charge (SOC) under constant test temperature conditions to obtain one OCV data set corresponding to the test temperature; obtaining multiple OCV data sets when there are multiple test temperatures; determining the rate of change of OCV with test temperature based on the OCV data set corresponding to each test temperature; and determining the entropy-thermal coefficient based on the rate of change of OCV with test temperature. By changing the SOC to test different OCVs at a constant test temperature, side reactions occurring during the measurement process can be reduced, thereby improving the accuracy of OCV testing.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a method and apparatus for testing the entropy thermal coefficient of a secondary battery. Background Technology

[0002] The performance and safety of secondary batteries, such as lithium-ion batteries, are closely related to their thermal behavior. The entropy thermal coefficient is a key thermodynamic parameter that describes the reversible thermal effect generated by electrode materials in the electrochemical reaction process of secondary batteries. Accurate measurement of the entropy thermal coefficient can provide data for the state estimation and diagnosis of secondary batteries, battery health status assessment and life prediction, and realize the precise management of secondary batteries.

[0003] Therefore, improving the accuracy of entropy-heat coefficient measurement has become an urgent problem to be solved. Summary of the Invention

[0004] This invention provides a method and apparatus for testing the entropy-thermal coefficient of a secondary battery, which improves the accuracy of entropy-thermal coefficient measurement.

[0005] In a first aspect, embodiments of the present invention provide a method for testing the entropy thermal coefficient of a secondary battery, comprising: After the prepared secondary battery is subjected to constant-capacity formation treatment, the open-circuit voltage (OCV) corresponding to different states of charge (SOC) is measured under constant test temperature, and one OCV data set corresponding to the test temperature is obtained; when there are multiple test temperatures, multiple OCV data sets are obtained. Determine the rate of change of OCV with test temperature based on the OCV data set corresponding to each test temperature; The entropy coefficient is determined based on the rate of change of OCV with test temperature.

[0006] Secondly, embodiments of the present invention provide a testing apparatus for the entropy thermal coefficient of a secondary battery, comprising: Memory, used to store program instructions; The processor is used to call program instructions stored in memory and execute the test methods described in the first aspect above according to the obtained program.

[0007] Thirdly, embodiments of the present invention provide a computer storage medium storing executable instructions, which, when executed by a computer, cause the test method described in the first aspect above to be performed.

[0008] The beneficial effects of this invention are as follows: The present invention provides a method and apparatus for testing the entropy thermal coefficient of a secondary battery. Because the test temperature is kept constant during measurement, different OCVs are tested by changing the state of charge (SOC). If a lower test temperature is used, the OCVs under different SOCs are always obtained at this lower test temperature. This can reduce the side reactions that occur during the measurement process, thereby improving the accuracy of OCV testing. Attached Figure Description

[0009] Figure 1 This is a flowchart of a method for testing entropy heat coefficient provided in an embodiment of the present invention; Figure 2 The relationship curve between SOC and OCV corresponding to Embodiment 1 provided in this invention; Figure 3 The relationship curve between SOC and OCV corresponding to Embodiment 2 provided in this invention; Figure 4 The relationship curve between SOC and OCV corresponding to Embodiment 3 provided in this invention; Figure 5 The relationship curve between SOC and OCV corresponding to Embodiment 4 provided in this invention; Figure 6 The relationship curve between SOC and OCV corresponding to Embodiment 5 provided in this invention; Figure 7 The relationship curve between SOC and OCV corresponding to Embodiment 6 provided in this invention; Figure 8 The relationship curve between SOC and OCV corresponding to Embodiment 7 provided in this invention; Figure 9 The relationship curve between SOC and OCV corresponding to Embodiment 8 provided in this invention; Figure 10 The test results of the entropy heat coefficient of each embodiment provided in the embodiments of the present invention; Figure 11 The test results of the entropy heat coefficients of the various comparative examples provided in the embodiments of the present invention; Figure 12 The curve showing the relationship between SOC and OCV in Example 9 provided in this invention is shown. Detailed Implementation

[0010] The following detailed description, with reference to the accompanying drawings, outlines a method and apparatus for testing the entropy-thermal coefficient of a secondary battery according to an embodiment of the present invention. It should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0011] This invention provides a method for testing the entropy thermal coefficient of a secondary battery, such as... Figure 1 As shown, the test methods include: S101. After the prepared secondary battery is subjected to constant-capacity formation treatment, the open-circuit voltage (OCV) corresponding to different states of charge (SOC) is measured under constant test temperature to obtain one OCV data set corresponding to the test temperature; when there are multiple test temperatures, multiple OCV data sets are obtained. S102. Determine the rate of change of OCV with test temperature based on the OCV data set corresponding to each test temperature; S103. Determine the entropy coefficient based on the rate of change of OCV with test temperature.

[0012] If different OCVs are tested by changing the test temperature under constant SOC conditions, the secondary battery needs to be continuously heated and cooled, causing it to undergo repeated high and low temperature cycles. Since higher test temperatures increase the likelihood of side reactions in the secondary battery, the measured OCV error becomes larger, resulting in less accurate OCV readings. This leads to significant errors in the data at each SOC, resulting in low accuracy of the obtained entropy coefficient. In this embodiment of the invention, because the test temperature is kept constant during measurement, different OCVs are tested by changing the SOC. If the test temperature is lower, the OCVs at different SOCs are always obtained at a lower test temperature, thus reducing side reactions during the measurement process and improving the accuracy of the OCV test.

[0013] I. The following is an introduction to secondary batteries.

[0014] In some embodiments, the secondary battery can be a negative electrode half-cell, thus obtaining the entropy thermal coefficient as the negative electrode's entropy thermal coefficient. Alternatively, the secondary battery can be a positive electrode half-cell, thus obtaining the entropy thermal coefficient as the positive electrode's entropy thermal coefficient. Therefore, in the embodiments of the present invention, the method for testing the entropy thermal coefficient is applicable not only to positive electrode half-cells but also to negative electrode half-cells.

[0015] In some embodiments, when the secondary battery is a negative electrode half-cell, the negative electrode half-cell includes: a negative electrode and an electrolyte, with the negative electrode immersed in the electrolyte. The area of ​​the negative electrode can be set to 30 cm². 2 ~60cm2 An excessively large negative electrode area increases the heat conduction time within the secondary battery, thus increasing the settling time and consequently leading to a longer testing time. Settling time refers to the time spent resting after a temperature change from one test temperature to another. Furthermore, an excessively large negative electrode area can cause temperature inconsistencies between different parts of the negative electrode and the ambient temperature of the secondary battery during heating and cooling processes. In this case, the measured OCV (Optical Value Capacity) will be a "mixed potential," increasing the error in the calculated entropy thermal coefficient. Conversely, an excessively small negative electrode area reduces the mass of the negative electrode active material, resulting in a lower capacity of the secondary battery. During testing, even minor disturbances can cause significant voltage fluctuations, which can mask voltage changes caused by temperature variations, reducing the signal-to-noise ratio of the data. Therefore, the negative electrode area is set to 30 cm². 2 ~60cm 2 The testing effect of entropy heat coefficient can be improved from the perspectives of testing time, testing accuracy, signal-to-noise ratio, etc.

[0016] The negative electrode active material includes carbon-based materials, which can include at least one of the following: artificial graphite, modified graphite, hard carbon, soft carbon, etc. In practice, the carbon-based material is not limited to these listed types; other materials capable of serving as negative electrode active materials can also be used, and this is not a limitation here. The functions of carbon-based materials include: enabling reversible and high-capacity storage of active ions such as lithium ions; efficiently conducting electrons; and providing a basis for the formation of a stable solid electrolyte interphase (SEI) film.

[0017] The negative electrode active material also includes silicon-based materials. These silicon-based materials can include at least one of the following: silicon-oxygen materials, silicon nanomaterials, and silicon alloys. In practice, the silicon-based material is not limited to those listed above; other materials capable of serving as negative electrode active materials can also be used, and this is not a limitation here. By adding silicon-based materials to the negative electrode active material, and combining carbon-based and silicon-based materials to form a silicon-carbon composite material, the capacity and capacity density of the secondary battery can be significantly improved.

[0018] Therefore, the testing methods provided in the embodiments of the present invention are applicable regardless of whether the negative electrode active material includes carbon-based materials and silicon-based materials, or includes carbon-based materials but not silicon-based materials.

[0019] The negative electrode includes a current collector and a negative electrode active layer. The negative electrode active layer is located on the surface of the current collector, and the aforementioned negative electrode active material is located in the negative electrode active layer. In addition to carbon-based and silicon-based materials, the negative electrode active layer also includes: a conductive agent, a dispersant, and a binder. The mass percentage of carbon-based and silicon-based materials in the negative electrode active layer is 90% to 95%, and the mass ratio of carbon-based and silicon-based materials is 5:95 to 95:5. The mass percentage of the conductive agent in the negative electrode active layer is 2.0% to 5.0%, the mass percentage of the dispersant in the negative electrode active layer is 1.0% to 2.0%, and the mass percentage of the binder in the negative electrode active layer is 2.0% to 3.0%.

[0020] The conductive agent may include at least one of the following: conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and graphyne. In specific implementations, the conductive agent is not limited to the above-listed types and may also be other materials that can be used as conductive agents, which is not limited here. The dispersant may include at least one of the following: sodium carboxymethyl cellulose, sodium alginate, and hydroxyethyl cellulose. In specific implementations, the dispersant is not limited to the above-listed types and may also be other materials that can be used as dispersants, which is not limited here. The binder may include at least one of the following: styrene-butadiene latex, polyacrylic acid, polyethylene oxide, polyvinyl alcohol, and polyimide. In specific implementations, the binder is not limited to the above-listed types and may also be other materials that can be used as binders, which is not limited here.

[0021] The manufacturing process of the negative electrode half-cell includes: According to the preset ratio, carbon-based materials, silicon-based materials, conductive agents, dispersants, and binders are weighed and mixed evenly to obtain a negative electrode slurry; The negative electrode slurry is uniformly coated on the surface of a current collector, such as copper foil, and then dried to obtain the negative electrode. In addition to copper foil, other materials can also be used to make the current collector, and there are no restrictions here. The prepared negative electrode is assembled into a negative electrode half cell, and then allowed to stand after liquid injection. The negative electrode half-cell, after being left to stand, is subjected to formation and volume determination treatment at a constant temperature to construct a stable SEI film, and the baseline capacity is measured.

[0022] In some embodiments, when the secondary battery is a positive half-cell, the positive half-cell includes: a positive electrode and an electrolyte, with the positive electrode immersed in the electrolyte. The area of ​​the positive electrode can be set to 30 cm². 2 ~60cm 2An excessively large positive electrode area increases the heat conduction time within the secondary battery, leading to longer settling time and consequently, longer testing times. Furthermore, an excessively large positive electrode area causes temperature discrepancies between different parts of the positive electrode and the ambient temperature of the secondary battery during heating and cooling processes. This results in a "mixed potential" OCV (Optical Value Capacity) and increases the error in the calculated entropy thermal coefficient. Conversely, an excessively small positive electrode area reduces the mass of the positive electrode active material, decreasing the capacity of the secondary battery. During testing, even minor disturbances can cause significant voltage fluctuations, which can mask voltage changes caused by temperature variations, reducing the signal-to-noise ratio of the data. Therefore, a positive electrode area of ​​30 cm² is recommended. 2 ~60cm 2 The testing effect of entropy heat coefficient can be improved from the perspectives of testing time, testing accuracy, signal-to-noise ratio, etc.

[0023] In summary, if both the positive and negative electrodes are referred to as electrodes, then the area of ​​the negative electrode is 30 cm². 2 ~60cm 2 The positive electrode area is 30 cm². 2 ~60cm 2 This results in the electrode area of ​​the secondary battery being 30 cm². 2 ~60cm 2 .

[0024] The positive electrode active materials include ternary materials, lithium iron phosphate materials, lithium cobalt oxide, lithium manganese oxide, and lithium manganese iron phosphate. In practice, the positive electrode active material is not limited to these listed types; other materials that can serve as positive electrode active materials can also be used, and this is not a limitation here. The functions of the positive electrode material include: enabling reversible and high-capacity storage of active ions such as lithium ions; efficiently conducting electrons; and providing a basis for the formation of a stable cathode electrolyte interface (CEI) film.

[0025] The positive electrode includes a current collector and a positive electrode active layer. The positive electrode active layer is located on the surface of the current collector, and the aforementioned positive electrode active material is located in the positive electrode active layer. In addition to the positive electrode active material, the positive electrode active layer also includes: a conductive agent, a dispersant, and a binder. The mass percentage of the positive electrode active material in the positive electrode active layer is 95%~98%, the mass percentage of the conductive agent in the positive electrode active layer is 1.0%~2.0%, and the mass percentage of the binder in the positive electrode active layer is 1.0%~3.0%.

[0026] The conductive agent may include at least one of the following: conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and graphyne. In specific implementations, the conductive agent is not limited to the above-listed types and may also be other materials that can be used as conductive agents, which are not limited here. The binder may include at least one of the following: polyvinylidene fluoride, polyacrylic acid, and styrene-butadiene rubber. In specific implementations, the binder is not limited to the above-listed types and may also be other materials that can be used as binders, which are not limited here.

[0027] The manufacturing process of the positive half-cell includes: According to the preset ratio, weigh out the positive electrode active material, conductive agent and binder and mix them evenly to obtain the positive electrode slurry. The positive electrode slurry is uniformly coated onto the surface of a current collector, such as aluminum foil, and then dried to obtain the positive electrode. In addition to aluminum foil, other materials can also be used to make the current collector, and there are no restrictions here. The prepared positive electrode is assembled into a positive electrode half cell, and then allowed to stand after liquid injection. The positive electrode half-cell, after being left to stand, is subjected to formation and volume stabilization treatment at a constant temperature to construct a stable CEI film, and the baseline capacity is measured.

[0028] II. The implementation method of the above step S101 will be introduced below.

[0029] In some embodiments, measuring the OCV corresponding to different SOCs under constant test temperature conditions includes: under constant test temperature conditions, the SOC range is 0~100%, and the OCV corresponding to one SOC is tested at preset intervals; the preset values ​​are 5%~10%.

[0030] For example, taking a preset value of 10% and testing in descending order of SOC, after selecting a test temperature, the OCV is measured when the SOC is 100%. Then, the SOC is reduced to 90%, and the OCV is measured again. Next, the SOC is reduced to 80%, and the OCV is measured again, and so on, until the SOC is reduced to 0, and the OCV is measured again. This completes the OCV measurements for different SOCs at that test temperature. Since each SOC corresponds to one OCV, multiple SOCs correspond to multiple OCVs, thus the various OCVs corresponding to each test temperature can form an OCV data set.

[0031] Of course, this explanation uses a preset value of 10% as an example. In practice, the preset value can also be 5%, 6%, 7%, 8%, 9%, etc., which will not be listed here. Furthermore, when testing the OCV corresponding to each SOC at a certain test temperature, the tests can be conducted in order of SOC from high to low or in order of SOC from low to high; there are no restrictions here.

[0032] If the preset value is too small, the measurement time will be longer, leading to more side reactions during the measurement process and thus more inaccurate results for the entropy heat coefficient. If the preset value is too large, the data volume will be too small to reflect the true entropy heat coefficient, also resulting in inaccurate test results. When the preset value is between 5% and 10%, it ensures a sufficient amount of data to reflect the true entropy heat coefficient while avoiding the increased side reactions caused by longer measurement times, thereby improving the test results for the entropy heat coefficient.

[0033] In some embodiments, measuring the OCV corresponding to different SOCs under constant test temperature conditions includes: after measuring the OCV corresponding to one SOC under constant test temperature conditions, adjusting the current SOC to another SOC according to the load adjustment ratio, and testing the OCV corresponding to the other SOC; the load adjustment ratio is 0.01C~0.05C.

[0034] In other words, after measuring the OCV corresponding to each SOC, the SOC is adjusted to the next SOC according to the load adjustment ratio, such as adjusting from 90% SOC to 80% SOC. This allows the secondary battery to be controlled at different SOCs, thereby allowing the OCV to be measured at different SOCs.

[0035] The load adjustment ratio can be 0.01C, 0.02C, 0.03C, 0.04C, 0.05C, etc., which will not be listed here.

[0036] Furthermore, when adjusting the SOC, if the secondary battery needs to be charged, the charge adjustment rate corresponds to the charging rate, so the active ions, such as lithium ions, are in a lithium-intercalated state; if the secondary battery needs to be discharged, the charge adjustment rate corresponds to the discharge rate, so the active ions, such as lithium ions, are in a delithiated state.

[0037] Excessive charge adjustment leads to greater polarization in the secondary battery. Greater polarization results in more side reactions, causing inaccurate State of Charge (SOC) and consequently, inaccurate entropy coefficient (ECC) test results. Conversely, insufficient charge adjustment results in longer measurement times, allowing for continuous formation of SEI and CEI films. Thicker SEI and CEI films increase resistance to active ion insertion / extraction, consuming capacity and further reducing SOC accuracy, leading to inaccurate EOC test results. A charge adjustment rate of 0.01C to 0.05C achieves suitable polarization and allows for the formation of SEI and CEI films of appropriate thickness, thus improving the EOC test results.

[0038] In some embodiments, when there are multiple test temperatures, multiple OCV data sets are obtained, including: when there are multiple test temperatures, obtaining the OCV data set corresponding to each test temperature in ascending order. If the secondary battery first experiences a lower test temperature and then a higher test temperature, even if the later higher test temperature leads to more side reactions and thus affects the test results, the results measured at the lower test temperature in the early stage will be more accurate. Therefore, from an overall perspective, the test results of the entropy thermal coefficient can still be improved. Furthermore, starting with a lower test temperature and then increasing the test temperature can avoid the secondary battery repeatedly experiencing high temperatures, thereby avoiding serious side reactions in the secondary battery and thus avoiding affecting the accuracy of OCV measured at different SOCs.

[0039] Alternatively, when there are multiple test temperatures, multiple OCV data sets can be obtained. This includes obtaining the OCV data sets for each test temperature sequentially, either in descending order of the test temperatures or in a random order. In this case, even if the test temperature is initially higher and then lower, the OCV corresponding to different SOCs is measured under a constant test temperature. Therefore, regardless of where the lower test temperature is located, the OCV measured at the lower test temperature is relatively accurate, thus improving the test results for the entropy-heat coefficient.

[0040] In summary, if the OCV corresponding to different test temperatures is measured under constant SOC conditions, the test temperature will repeatedly cycle between high and low temperatures. This will lead to more side reactions. For example, taking a secondary battery as the negative electrode half-cell, when silicon and carbon are included in the negative electrode active material, side reactions occur between silicon and carbon and the electrolyte at 45°C. Therefore, repeated high and low temperature cycles will repeatedly place the battery at 45°C, exacerbating the side reactions between silicon and carbon and the electrolyte. This makes it difficult to adjust the SOC to an accurate value, and consequently, the measured OCV is also inaccurate. Therefore, the test results of the entropy thermal coefficient are inaccurate.

[0041] In this embodiment of the invention, the OCV corresponding to different SOCs is measured at a constant test temperature. The side reactions occurring when the test temperature is kept constant are significantly fewer than those occurring when the test temperature repeatedly cycles between high and low temperatures. Therefore, regardless of the stage at which the lower test temperature is located, the test results for the entropy-heat coefficient can be improved. Furthermore, if the lower test temperature is located in the initial stage, the occurrence of side reactions will be further reduced, resulting in higher accuracy when adjusting the SOC, and consequently, higher accuracy in the measured OCV, thereby further improving the test results for the entropy-heat coefficient.

[0042] In some embodiments, when there are three test temperatures, each test temperature is located at 20°C~30°C, 30°C~40°C, and 40°C~50°C, respectively. Further, each test temperature is 25°C, 35°C, and 45°C. Of course, these three test temperatures are not limited to 25°C, 35°C, and 45°C; they can also be other temperatures ranging from 20°C~30°C, 30°C~40°C, and 40°C~50°C, which is not limited here. Furthermore, the number of test temperatures is not limited to three; it can also be two, four, five, or other numbers, which is not limited here.

[0043] In some embodiments, when there are multiple test temperatures, multiple OCV data sets are obtained, including: after obtaining the OCV data set corresponding to one of the test temperatures, adjusting the current test temperature to the next test temperature, and subjecting the secondary battery to a static condition at the next test temperature; charging and discharging the secondary battery, using a reference capacity as the charge / discharge cutoff condition; the reference capacity is the product of the secondary battery's reference capacity and a first ratio; and under the condition that the next test temperature is constant, measuring the OCV corresponding to different SOCs to obtain the OCV data set corresponding to the next test temperature.

[0044] For example, taking three test temperatures as an example, after obtaining the OCV data set corresponding to the first test temperature, adjust to the second test temperature and let it stand for a period of time, then charge and discharge. Since the SOC has dropped to a relatively small value after the first test temperature test, it is necessary to increase the SOC to 100% at the second test temperature, so the secondary battery needs to be charged and discharged. After the charge and discharge is completed, the OCV data set corresponding to the second test temperature is measured. Then, adjust to the third test temperature and repeat the above steps until the OCV data set corresponding to the third test temperature is obtained.

[0045] The settling time during the static treatment is 1 to 5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc. The specific time can be set according to the actual situation, and will not be listed here. Furthermore, the settling time can be the same or different at different test temperatures.

[0046] Furthermore, the second percentage can be set to other values ​​such as 5%, 10%, 15%, 20%, etc., without any restrictions here.

[0047] Therefore, by allowing the secondary battery to stand at the corresponding test temperature, it can reach thermodynamic equilibrium, resulting in a more accurate OCV and thus improving the accuracy of the entropy coefficient.

[0048] In practice, after adjusting the current test temperature to the next test temperature, and before allowing the secondary battery to stand at the next test temperature, the secondary battery is subjected to a constant capacity treatment.

[0049] It should be noted that the implementation of steps S102 and S103 above can be any way that can be implemented in the art, and there is no limitation here.

[0050] III. The following describes a specific implementation using a negative electrode half-cell as an example.

[0051] Example 1: The fabrication process of the negative electrode half-cell includes: Step 1, weighing 190g of artificial graphite, 10g of silicon carbon, 11.11g of conductive carbon black, 4.44g of sodium carboxymethyl cellulose, and 6.66g of binder, and thoroughly mixing them to obtain a negative electrode slurry; Step 2, uniformly coating the negative electrode slurry onto both sides of a copper foil serving as a current collector, drying it, and controlling the double-sided areal density of the resulting electrode to be 50g / m². 2 Step 3: Cut into pieces with an area of ​​30cm² 2 The electrodes are assembled into a negative electrode half-cell, and 1g of electrolyte is injected and then left to stand; Step 4: Perform formation and volume determination treatment, and measure the reference capacity; wherein, the number of charge-discharge cycles is 3 cycles, and the volume determination rate is 0.1C.

[0052] The process of obtaining multiple OCV data sets includes: Step 1: For a negative electrode half-cell with 100% SOC (fully lithium-intercalated state), let it stand at 25°C for 2 hours and record the OCV; using 10% of the baseline capacity as the charging cutoff condition, charge at a charging rate of 0.01C and reduce the SOC to 90%, recording the OCV; repeat the above operation until the OCV at SOC is recorded; thus obtaining the OCV corresponding to each SOC at 25°C, these OCVs constitute one OCV data set corresponding to 25°C. Step 2: Repeat the volume adjustment process. For a negative electrode half-cell with 100% SOC (fully lithium-intercalated state), repeat the process of Step 1 above, except that the temperature is adjusted to 35°C, thus obtaining one OCV data set corresponding to 35°C. Step 3: Repeat the volume adjustment process. For a negative electrode half-cell with 100% SOC (fully lithium-intercalated state), continue to repeat the process of Step 1 above, except that the temperature is adjusted to 45°C, thus obtaining one OCV data set corresponding to 45°C. In this way, we can obtain OCV data sets corresponding to 25℃, 35℃ and 45℃ respectively.

[0053] Example 2: The difference between Example 2 and Example 1 is that the amount of artificial graphite in the negative electrode half cell is 100g and the amount of silicon carbon is 100g.

[0054] Example 3: The difference between Example 3 and Example 1 is that the amount of artificial graphite in the negative electrode half-cell is 10g and the amount of silicon-carbon is 190g.

[0055] Example 4: The difference between Example 4 and Example 3 includes that in the negative electrode half cell, the conductive carbon black is 4.21g, sodium carboxymethyl cellulose is 2.1g, and the binder is 4.2g.

[0056] Example 5: The difference between Example 5 and Example 4 includes: the areal density of both sides is 100 g / m³. 2 .

[0057] Example 6: The differences between Example 6 and Example 5 include: the electrolyte injection volume is 2g, and the area of ​​the cut electrode sheet is 60cm². 2 .

[0058] Example 7: The difference between Example 7 and Example 6 is that the number of charge-discharge cycles is 5.

[0059] Example 8: The difference between Example 8 and Example 7 is that at a certain temperature, OCV is measured starting from SOC of 0 until SOC reaches 100%, thus obtaining a set of OCV data at that temperature.

[0060] Comparative Example 1: The differences between Comparative Example 1 and Example 1 include: In the negative electrode half-cell, the amount of conductive carbon black is 25g, sodium carboxymethyl cellulose is 12.5g, and binder is 12.5g; at 100% SOC (fully lithium-intercalated state), the OCV is recorded after standing at 25°C for 2 hours, the temperature is adjusted to 35°C and stood for 2 hours, and the OCV is recorded again after standing at 45°C for 2 hours; then the negative electrode half-cell is placed at 25°C and stood for 2 hours, with 10% of the reference capacity as the charging cutoff condition and a charging rate of 0.01C, and the SOC is reduced to 90%; the above steps at 100% SOC are repeated; until the SOC is 0, the OCV at three temperatures is recorded.

[0061] Comparative Example 2: The differences between Comparative Example 2 and Comparative Example 1 include: in the negative electrode half-cell, the amount of conductive carbon black is 2.048g, sodium carboxymethyl cellulose is 1.024g, and the amount of binder is 1.024g.

[0062] Comparative Example 3: The differences between Comparative Example 3 and Comparative Example 1 include: in the negative electrode half-cell, the amount of conductive carbon black is 11.11 g, sodium carboxymethyl cellulose is 4.44 g, and binder is 6.66 g; the double-sided areal density is 40 g / m³. 2 .

[0063] Comparative Example 4: The differences between Comparative Example 4 and Comparative Example 1 include: in the negative electrode half-cell, the amount of conductive carbon black is 11.11 g, sodium carboxymethyl cellulose is 4.44 g, and binder is 6.66 g; the double-sided areal density is 110 g / m³. 2 .

[0064] Comparative Example 5: The differences between Comparative Example 5 and Comparative Example 1 include: in the negative electrode half-cell, the amount of conductive carbon black is 11.11g, sodium carboxymethyl cellulose is 4.44g, and binder is 6.66g; the number of charge-discharge cycles is 1.

[0065] Comparative Example 6: The differences between Comparative Example 6 and Comparative Example 1 include: in the negative electrode half-cell, the conductive carbon black is 11.11g, sodium carboxymethyl cellulose is 4.44g, and binder is 6.66g; the constant capacity is 0.5C.

[0066] Comparative Example 7: The differences between Comparative Example 7 and Comparative Example 1 include: in the negative electrode half-cell, the amount of conductive carbon black is 11.11g, sodium carboxymethyl cellulose is 4.44g, and binder is 6.66g; the charging rate when adjusting the SOC is 0.1C.

[0067] Comparative Example 8: The differences between Comparative Example 8 and Comparative Example 1 include: in the negative electrode half-cell, the amount of conductive carbon black is 11.11g, sodium carboxymethyl cellulose is 4.44g, and binder is 6.66g; the OCV is measured in order of increasing SOC.

[0068] The test results are as follows: The relationship curves between SOC and OCV in each embodiment are as follows: Figures 2 to 9 As shown, Figure 2 Corresponding to Example 1, Figure 3 Corresponding to Example 2, Figure 4 Corresponding to Example 3, Figure 5 Corresponding to Example 4, Figure 6 Corresponding to Example 5, Figure 7 Corresponding to Example 6, Figure 8 Corresponding to Example 7, Figure 9 Corresponding to Example 8, the test results of the entropy heat coefficient of each example are as follows: Figure 10 As shown, the test results of the entropy heat coefficients for each comparative example are as follows: Figure 11 As shown, Figure 10 and Figure 11 In this context, dU / dT represents the entropy-heat coefficient. The capacity loss for each embodiment and comparative example is shown in Table 1 below. The capacity loss in Table 1 refers to the percentage of lost capacity in the total capacity.

[0069] Table 1

[0070] First, the results shown in Table 1 above show that the capacity loss of each embodiment fluctuates between 0.07 and 0.651, while the capacity loss of each comparative example fluctuates between 1.98 and 3.98. Compared with the comparative examples, the capacity loss of the embodiments is reduced by nearly 10 times. This is because measuring the OCV corresponding to different SOCs under constant test temperature conditions can reduce the occurrence of side reactions. The more side reactions occur, the greater the capacity loss, and vice versa. Therefore, reducing side reactions can reduce capacity loss.

[0071] Secondly, from Figures 2 to 9 The results shown indicate that the test results under various embodiments are quite similar, or the differences between the test results are very small. This suggests that, based on the test method and the constant test temperature, the changes in the parameters of the negative electrode half-cell have little impact on the relationship between SOC and OCV.

[0072] Again, from Figure 10 and Figure 11 The results shown indicate that, Figure 10 and Figure 11 The vertical axis in the figure represents the entropy-heat coefficient. Figure 11 In the comparison, regardless of the SOC value, the curves corresponding to each comparison sample fluctuate up and down, and the fluctuation range is large. The entropy thermal coefficients corresponding to two adjacent SOCs are significantly different. This is because changing the test temperature when the SOC is constant leads to more side reactions, which can easily cause overcharging and over-discharging of the negative electrode half-cell, resulting in large fluctuations in the entropy thermal coefficient.

[0073] exist Figure 10 Although the curves corresponding to each embodiment fluctuate, the fluctuation range is relatively small, especially when the SOC is 30%~90%, the fluctuation range is even smaller, and the entropy thermal coefficient is basically at a stable value. This is because changing the SOC when the test temperature is constant can reduce the occurrence of side reactions, so that the negative electrode half cell is in a good operating state, and the entropy thermal coefficient will be more stable, thus the obtained entropy thermal coefficient will be more accurate.

[0074] IV. The following describes a specific embodiment using a positive half-cell as an example.

[0075] Example 9: The fabrication process of the positive electrode half-cell includes: Step 1, weighing 200g of NCM, 2.04g of conductive carbon black, and 2.04g of binder, and mixing them thoroughly to obtain a positive electrode slurry; NCM is a lithium nickel cobalt manganese oxide used as the positive electrode active material; Step 2, uniformly coating the positive electrode slurry onto both sides of an aluminum foil used as a current collector, drying it, and controlling the double-sided areal density of the resulting electrode to be 100g / m². 2 Step 3: Cut into pieces with an area of ​​30cm² 2The electrodes are assembled into a positive half-cell, and 1g of electrolyte is injected and then left to stand. Step 4: Perform formation and volume determination treatment and measure the reference capacity. The charge and discharge cycle number is 3 cycles and the volume determination rate is 0.1C.

[0076] The process of obtaining multiple OCV data sets includes: Step 1: For a positive electrode half-cell with 100% SOC (fully delithiated state), let it stand at 25°C for 2 hours and record the OCV; using 10% of the baseline capacity as the discharge cutoff condition, discharge at a discharge rate of 0.01C to reduce the SOC to 90% and record the OCV; repeat the above operation until the OCV at SOC is recorded; thus obtaining the OCV corresponding to each SOC at 25°C, these OCVs constitute one OCV data set corresponding to 25°C. Step 2: Repeat the volume adjustment process. For a positive electrode half-cell with 100% SOC (fully delithiated state), repeat the process of Step 1 above, except that the temperature is adjusted to 35°C, thus obtaining one OCV data set corresponding to 35°C. Step 3: Repeat the volume adjustment process. For a positive electrode half-cell with 100% SOC (fully delithiated state), continue to repeat the process of Step 1 above, except that the temperature is adjusted to 45°C, thus obtaining one OCV data set corresponding to 45°C. In this way, we can obtain OCV data sets corresponding to 25℃, 35℃ and 45℃ respectively.

[0077] Comparative Example 9: The difference between Comparative Example 9 and Example 9 includes the following: The process of obtaining multiple OCV data sets includes: Step 1: For a positive electrode half-cell with 100% SOC (fully delithiated state), record the OCV after standing at 25°C for 2 hours; adjust the temperature to 35°C and stand for 2 hours to record the OCV; continue adjusting the temperature to 45°C and stand for 2 hours to record the OCV. Step 2: Then, place the positive electrode half-cell at 25°C and stand for 2 hours, using 10% of the baseline capacity as the discharge cutoff condition, and a discharge rate of 0.01C to discharge and reduce the SOC to 90%. Step 3: Repeat the OCV measurement operation at 25°C, 35°C, and 45°C until the OCV when the SOC is 0 is recorded; thus obtaining the OCV data sets corresponding to 25°C, 35°C, and 45°C respectively.

[0078] The test results are as follows: The capacity loss of Example 9 and Comparative Example 9 is shown in Table 2 below. The capacity loss in Table 2 refers to the percentage of lost capacity in the total capacity.

[0079] Table 2

[0080] The results shown in Table 2 above indicate that for the positive electrode half-cell, the capacity loss of Example 9 is 0.115, while that of Comparative Example 9 is 0.794. Compared with Comparative Example 9, the capacity loss of Example 9 is reduced by nearly 7 times. This is because measuring the OCV corresponding to different SOCs under constant test temperature conditions can reduce the occurrence of side reactions. The more side reactions occur, the greater the capacity loss, and vice versa. Therefore, reducing side reactions can reduce capacity loss.

[0081] The relationship curve between SOC and OCV in Example 9 is as follows: Figure 12 As shown, from Figure 12 The results shown indicate that the curves corresponding to different test temperatures are very close and overlap nearly 100%. This suggests that under constant test temperature conditions, fewer side reactions occur when measuring the OCV corresponding to different SOCs, thus weakening or eliminating the influence of test temperature on the relationship curve between SOC and OCV.

[0082] The test results of the entropy-heat coefficient in Example 9 are as follows: Figure 10 As shown, the test results of the entropy heat coefficient of Comparative Example 9 are as follows: Figure 11 As shown; in Figure 11 In the comparison, regardless of the SOC value, the curve corresponding to Example 9 fluctuates significantly, with large amplitudes. The entropy-thermal coefficients corresponding to adjacent SOCs show substantial differences. This is because changing the test temperature at a constant SOC leads to more side reactions, easily causing overcharging and over-discharging of the positive electrode half-cell, resulting in larger fluctuations in the entropy-thermal coefficient. Figure 10 In Example 9, although the curve fluctuates, the fluctuation range is relatively small, especially when the SOC is 30%~90%, the fluctuation range is even smaller, and the entropy thermal coefficient is basically at a stable value. This is because changing the SOC when the test temperature is constant can reduce the occurrence of side reactions, so that the positive electrode half cell is in a good operating state, and the entropy thermal coefficient will be more stable, thus the entropy thermal coefficient obtained will be more accurate.

[0083] Based on the same inventive concept, this embodiment of the invention also provides a testing device for the entropy thermal coefficient of a secondary battery. The implementation principle of this testing device is basically similar to that of the testing method described above. Therefore, the specific implementation method of this testing device can be found in the relevant description in the aforementioned testing method, and repeated details will not be repeated.

[0084] Specifically, an embodiment of the present invention provides a testing device for the entropy thermal coefficient of a secondary battery, comprising: a memory for storing program instructions; and a processor for calling the program instructions stored in the memory and executing the testing method described above according to the obtained program.

[0085] Based on the same inventive concept, embodiments of the present invention also provide a computer storage medium storing executable instructions, which, when executed by a computer, cause the test method described above to be executed.

[0086] In summary, the technical solution provided by the embodiments of the present invention has the following advantages: the testing method is simple to operate, realizes charge-discharge linkage testing and entropy-thermal coefficient data acquisition and analysis under temperature control, and the obtained data is accurate, reliable, and highly consistent and repeatable. When using a half-cell system for testing, the interference of the positive electrode material in the full cell on the test results can be avoided. In addition, this method solves the capacity loss problem of high silicon-carbon content negative electrodes during the load adjustment process, and realizes precise adjustment of the target SOC; in particular, it overcomes the technical difficulty of measuring the entropy-thermal coefficient of single and mixed negative electrode materials, thus providing accurate data support for cell development and simulation.

[0087] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for testing the entropy thermal coefficient of a secondary battery, characterized in that, include: After the prepared secondary battery is subjected to constant-capacity formation treatment, the open-circuit voltage (OCV) corresponding to different states of charge (SOC) is measured under constant test temperature to obtain an OCV data set corresponding to the test temperature. When there are multiple test temperatures, multiple OCV data sets are obtained; Based on the OCV data set corresponding to each test temperature, determine the rate of change of the OCV with respect to the test temperature; The entropy coefficient is determined based on the rate of change of the OCV with the test temperature.

2. The test method as described in claim 1, characterized in that, Under constant test temperature, the OCV corresponding to different SOCs was measured, including: Under the condition of constant test temperature, the SOC ranges from 0 to 100%, and the OCV corresponding to the SOC is tested at preset intervals; the preset value is 5% to 10%.

3. The test method as described in claim 1, characterized in that, Under constant test temperature, the OCV corresponding to different SOCs was measured, including: Under the condition of constant test temperature, after measuring the OCV corresponding to one of the SOCs, the current SOC is adjusted to another SOC according to the load adjustment ratio, and the OCV corresponding to the other SOC is tested; the load adjustment ratio is 0.01C~0.05C.

4. The test method as described in claim 1, characterized in that, When there are multiple test temperatures, multiple sets of OCV data are obtained, including: When there are multiple test temperatures, the OCV data group corresponding to each test temperature is obtained sequentially in ascending order of the test temperatures.

5. The test method as described in claim 1, characterized in that, When there are three test temperatures, each test temperature is between 20℃ and 30℃, between 30℃ and 40℃, and between 40℃ and 50℃, respectively.

6. The test method as described in claim 1, characterized in that, When there are multiple test temperatures, multiple OCV data sets are obtained, including: After obtaining the OCV data set corresponding to one of the test temperatures, the current test temperature is adjusted to the next test temperature, and the secondary battery is subjected to a static treatment at the next test temperature. The secondary battery is charged and discharged, with a reference capacity as the charge / discharge cutoff condition; the reference capacity is the product of the secondary battery's reference capacity and a first ratio. Under the condition of constant test temperature, the OCV corresponding to different SOCs is measured to obtain the OCV data set corresponding to the next test temperature.

7. The test method as described in claim 1, characterized in that, The secondary battery is either a negative electrode half-cell or a positive electrode half-cell.

8. The test method according to any one of claims 1-7, characterized in that, The area of ​​the electrode in the secondary battery is 30 cm². 2 ~60cm 2 .

9. A testing device for the entropy thermal coefficient of a secondary battery, characterized in that, include: Memory, used to store program instructions; A processor is configured to invoke the program instructions stored in the memory and execute the test method as described in any one of claims 1-8 according to the obtained program.

10. A computer storage medium, characterized in that, The computer storage medium stores executable instructions, which, when executed by a computer, cause the test method as described in any one of claims 1-8 to be performed.

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