Method for optimizing initial pretightening force of soft package battery and application of method

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a method for optimizing the initial pre-tightening force of a soft package battery and application thereof, and the method comprises the following steps: respectively applying different first initial pre-tightening forces to the soft package battery, testing the pressure of the soft package battery in the charge-discharge cycle process, and determining the optimal initial pre-tightening force according to the pressure test result. By optimizing the initial pre-tightening force of the soft package battery, the increase of the interface impedance of the soft package battery in the long cycle process is reduced, the risk that the negative electrode is separated from the current collector due to the breakage of negative electrode particles is reduced, the cycle life of the soft package battery is prolonged, and the soft package battery is guided to exert better performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and specifically to a method for optimizing the initial preload of soft-pack batteries and its application. More specifically, it relates to a method for optimizing the initial preload of soft-pack batteries, a method for constructing an initial preload database for silicon-containing negative electrode soft-pack batteries, a method for extending the cycle life of soft-pack batteries, soft-pack batteries, and electrical devices. Background Art

[0002] With the rapid development of lithium batteries, especially high-energy-density lithium batteries, they have become increasingly popular with OEMs. Silicon-containing materials, due to their high specific capacity, low lithium insertion potential, and good compatibility with numerous existing cathode materials, have become a primary approach to increasing the energy density of lithium batteries through the use of silicon anode materials. While silicon anode materials possess these advantages, they also suffer from significant drawbacks. Silicon-containing anodes experience volume expansion during charge and discharge, and long cycles can lead to repeated rupture of the interfacial film, causing degradation in battery performance. This is particularly true for soft-pack batteries, where the aluminum-plastic film has less binding force on the battery.

[0003] Existing improvement methods primarily involve modifying silicon anode materials at the material level. These efforts include using nano-silicon, coating the silicon anode surface, optimizing the silicon anode binder, and optimizing the binder formulation to mitigate the problem of silicon anode material particle expansion. However, capacity degradation still persists over long battery cycles due to the inherent expansion and cracking of silicon anode material particles. Summary of the Invention

[0004] The present invention aims to at least partially address one of the technical problems in the related art. To this end, the present invention proposes a method for optimizing the initial preload force of soft-pack batteries and its application. By applying an appropriate initial preload force, the cycle life of the soft-pack batteries can be effectively extended.

[0005] In a first aspect, the present application provides a method for optimizing the preload force of a soft-pack battery. According to an embodiment of the present application, the method comprises: providing m soft-pack batteries; applying different first initial preload forces to each of the m soft-pack batteries using a fixture; then subjecting the m soft-pack batteries to a charge-discharge cycle; and simultaneously testing the pressure between the soft-pack battery and the fixture in real time during the charge-discharge cycle, and recording the maximum pressure L' of each soft-pack battery. max and minimum pressure L' min , the maximum pressure L' max The value is the smallest and the minimum pressure L' min The first initial preload force corresponding to the soft-pack battery with a value greater than 0 is the optimal initial preload force, and m is an integer from 2 to 100.

[0006] By optimizing the initial preload force of soft-pack batteries in this application, the growth of interfacial impedance of soft-pack batteries, especially soft-pack batteries whose negative electrode materials contain silicon-based materials, during long cycles is reduced, the risk of negative electrode separation from the current collector due to negative electrode particle breakage is reduced, the cycle life of soft-pack batteries is improved, and the soft-pack batteries are guided to perform better.

[0007] According to an embodiment of the present application, the soft-pack battery may be a soft-pack battery whose negative electrode material contains a silicon-based material, and the content of the silicon-based material may be 3% to 50%, specifically 3% to 45%, based on the total mass of the negative electrode material. Thus, by determining the optimal initial preload force and then applying the optimal initial preload force to the soft-pack battery, the volume expansion problem of the silicon-based negative electrode material can be effectively improved for soft-pack batteries whose negative electrode material contains a silicon-based material, thereby effectively extending the cycle life of the soft-pack battery.

[0008] According to the embodiments of the present application, the thickness of the soft-pack battery can be 4mm to 12mm, specifically 6mm to 10mm. Within the above thickness range, it is easy to prepare and can meet different usage scenarios and requirements, and has a wide range of applications.

[0009] According to the embodiment of the present application, according to the first initial preload force from small to large, the m soft-pack batteries are defined as the M1 soft-pack battery, the M2 soft-pack battery, ..., the M m Soft-pack battery; wherein, the first initial preload force of the M1 soft-pack battery can be 0.001MPa to 0.005MPa, specifically 0.002MPa to 0.004MPa. Thus, the test range is wider and the optimal initial preload force is determined more accurately.

[0010] In some embodiments, the Mth m The first initial preload force of the soft-pack battery can be 0.04MPa to 0.06MPa, specifically 0.045MPa to 0.055MPa. As a result, the test range covers higher pressure values, and the optimal initial preload force is determined more accurately.

[0011] In some embodiments, the Mth j The first initial preload and the Mth j-1 The difference in the first initial preload force of the soft-pack batteries can be 0.001 MPa to 0.03 MPa, specifically 0.003 MPa to 0.02 MPa, where j is an integer from 2 to m. The first initial preload forces of the m soft-pack batteries can be relatively evenly distributed between 0 and the maximum pressure value that the soft-pack battery outer packaging can withstand, which can more accurately determine the optimal initial preload force of the soft-pack batteries.

[0012] According to an embodiment of the present application, in this step, the charge and discharge cycles of m soft-pack batteries can be performed at a current of 0.33C, with a charge and discharge cut-off voltage of (3.6-4.35) V to 2.5 V. The above test conditions are more consistent with the actual operating conditions of soft-pack batteries and can more accurately determine the optimal initial preload force.

[0013] According to an embodiment of the present application, the method further includes: before applying the first preload force, placing the m soft-pack batteries in an optimal state of charge;

[0014] The optimal state of charge is determined by the following method:

[0015] Provide n soft-pack batteries with different states of charge;

[0016] The clamp is used to apply a second initial preload force to each of the n soft-pack batteries, and then the n soft-pack batteries are subjected to a charge-discharge cycle. During the charge-discharge cycle, the pressure between the n soft-pack batteries and the clamp is simultaneously tested in real time, and the maximum pressure L of each soft-pack battery is recorded. max and minimum pressure L min , the maximum pressure L max The value is the smallest and the minimum pressure L min The state of charge of the soft-pack battery with a value greater than 0 is the optimal state of charge;

[0017] Here, n is an integer from 2 to 100.

[0018] By predetermining the optimal state of charge and applying the optimal initial preload force to the soft-pack battery when it is in the optimal state of charge, the volume expansion problem of the soft-pack battery can be further improved, thereby effectively extending the cycle life of the soft-pack battery.

[0019] In some embodiments of the present application, according to the state of charge from low to high, the n soft-pack batteries are defined as the N1 soft-pack battery, the N2 soft-pack battery, ..., the N n wherein the state of charge of the N1th soft-pack battery may be 0% SOC to 5% SOC, specifically 2% SOC to 4% SOC. Thus, the soft-pack battery in a low state of charge can be effectively detected.

[0020] In some embodiments, the Nth n The state of charge of the soft-pack battery can be 95% SOC to 100% SOC, specifically 96% SOC to 98% SOC. Thus, the soft-pack battery at a high state of charge can be effectively detected.

[0021] In some embodiments, the difference between the state of charge of the Ni-th soft-pack battery and the state of charge of the Ni-1th soft-pack battery can be 1% SOC to 30% SOC, specifically 2% SOC to 20% SOC, where i is an integer from 2 to n. Thus, the states of charge of the n soft-pack batteries can be relatively evenly distributed between 0% SOC and 100% SOC, allowing for more accurate determination of the optimal state of charge of the soft-pack batteries.

[0022] According to an embodiment of the present application, the second initial preload is the minimum pressure that the clamp can apply. As an example, the second initial preload can be 0.001MPa~0.025MPa, specifically 0.002MPa~0.02MPa. Specifically, during the charging process of the soft-pack battery, the battery cell thickens due to the expansion of the negative electrode embedded with lithium. The clamp generally has a fixed gap. When the second initial preload is smaller, the maximum pressure of the soft-pack battery can be smaller when fully charged, because a larger pressure will cause the diaphragm to close the pores and the electrical performance impedance will increase. In order to maintain a longer cycle life, the initial preload needs to be as small as possible, which is conducive to improving the cycle life.

[0023] According to an embodiment of the present application, in this step, the n soft-pack batteries can also be charged and discharged at a current of 0.33C, with a charge and discharge cut-off voltage of (3.6-4.35) V to 2.5 V. The above test conditions are more in line with the actual operating conditions of soft-pack batteries and can more accurately determine the optimal initial preload force.

[0024] In the second aspect of the present application, a method for constructing an initial preload database for silicon-containing negative electrode soft-pack batteries is provided. According to an embodiment of the present application, the method includes: providing p silicon-containing negative electrode soft-pack batteries with different silicon contents; and using the method described in the first aspect of the present application to determine the optimal initial preload of the p silicon-containing negative electrode soft-pack batteries to form the database. This method can establish a connection between silicon content and optimal initial preload, guiding silicon-containing negative electrode soft-pack batteries to achieve better performance. Specifically, when applying silicon-containing negative electrode soft-pack batteries, the corresponding optimal initial preload can be found in the database based on the silicon content, providing theoretical guidance for battery development, saving R&D time and cost, and at the same time extending the cycle life of silicon-containing negative electrode soft-pack batteries.

[0025] It is understandable that the database may also include p optimal states of charge of the silicon-containing negative electrode soft-pack batteries, and the optimal states of charge and the optimal initial preload together constitute the database. Thus, a connection between silicon content, optimal state of charge, and optimal initial preload is established to guide silicon-containing negative electrode soft-pack batteries to achieve better performance. Specifically, when applying silicon-containing negative electrode soft-pack batteries, the corresponding optimal state of charge and optimal initial preload can be found in the database based on the silicon content, providing theoretical guidance for battery development, saving R&D time and costs, and further extending the cycle life of silicon-containing negative electrode soft-pack batteries.

[0026] The third aspect of the present application provides a method for extending the cycle life of a soft-pack battery. According to an embodiment of the present application, the method comprises: determining the optimal initial preload force of the soft-pack battery by the method for optimizing the preload force of the soft-pack battery according to the first aspect of the present application; and applying the optimal initial preload force to the soft-pack battery. As a result, the growth of the interfacial impedance of the soft-pack battery treated as above is effectively reduced during the long cycle, the risk of the negative electrode detaching from the current collector due to the crushing of the negative electrode particles is significantly reduced, the cycle life of the soft-pack battery is significantly extended, and the soft-pack battery can exert better comprehensive performance.

[0027] It is understood that the method may also include: determining the optimal state of charge and optimal initial preload of the soft-pack battery using the method for optimizing the preload of the soft-pack battery described in the first aspect of this application; adjusting the soft-pack battery to the optimal state of charge, and then applying the optimal initial preload to the soft-pack battery. As a result, the growth of the interfacial impedance of the soft-pack battery treated as described above during long-term cycling is further reduced, the risk of the negative electrode detaching from the current collector due to negative electrode particle breakage is further reduced, the cycle life of the soft-pack battery is further extended, and the soft-pack battery can further achieve better overall performance.

[0028] In a fourth aspect, the present application provides a soft-pack battery. According to an embodiment of the present application, the soft-pack battery is obtained by processing according to the method described in the third aspect of the present application. The soft-pack battery can achieve a longer cycle life and improved overall performance.

[0029] In a fifth aspect, the present application provides an electrical device. According to an embodiment of the present application, the electrical device includes the soft-pack battery described in the fourth aspect of the present application. The electrical device can have a longer service life and exhibit better overall performance. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0031] In a first aspect, the present application provides a method for optimizing the initial preload force of a soft-pack battery. According to an embodiment of the present application, the method includes:

[0032] S10: Provide m soft-pack batteries.

[0033] S20: Using a fixture to apply different first initial preload forces to m soft-pack batteries, and then subjecting the m soft-pack batteries to a charge-discharge cycle. During the charge-discharge cycle, the pressure between the soft-pack battery and the fixture is simultaneously tested in real time, and the maximum pressure L' of each soft-pack battery is recorded. max and minimum pressure L' min , the maximum pressure L' max The value is the smallest and the minimum pressure L' min The first initial preload force corresponding to the soft-pack battery with a value greater than 0 is the optimal initial preload force, and m is an integer from 2 to 100.

[0034] It should be noted that the maximum pressure L' is selected max The value is minimum and the minimum pressure L' min The first initial preload corresponding to a soft-pack battery with a value greater than 0 is the optimal initial preload because: during the charging process of the soft-pack battery, active ions are released from the positive electrode and embedded in the negative electrode, causing the soft-pack battery to expand and gradually increase in thickness. Generally, when the state of charge of the soft-pack battery is 100% SOC, the thickness reaches its maximum value. At this time, the battery packaging needs to be able to withstand the stress caused by battery expansion to ensure the safe operation of the battery. In order to achieve higher energy density and avoid problems such as battery shaking and displacement, it is necessary to make full use of the battery space and try to achieve a higher group margin, that is, there should be no large gap between the bare cell and the battery outer packaging. The minimum pressure L' min A value greater than 0 indicates that the battery can occupy the entire space in the battery packaging after expansion, and the maximum pressure L' max The smallest value indicates that the pressure on the battery outer packaging after battery expansion is small, and the possibility of battery damage due to expansion pressure is minimal. That is, the battery outer packaging space is fully utilized, and the battery expansion will not cause excessive stress on the battery outer packaging. Therefore, the maximum pressure L' is selected max The value is minimum and the minimum pressure L' min The first initial preload force corresponding to the soft-pack battery with a value greater than 0 is the optimal initial preload force.

[0035] In this article, a soft-pack battery refers to a battery with a flexible composite film material (including but not limited to aluminum-plastic film, etc.) as its outer shell. The specific type of soft-pack battery is not particularly limited and can be flexibly selected according to actual use needs. As an example, a soft-pack battery can be a primary battery or a secondary battery; specifically, it can be a lithium-ion battery, a sodium-ion battery, a lithium metal battery, a sodium metal battery, etc.; depending on the different stacking methods of the electrode sheets, it can also be a laminated battery or a wound battery, which is not particularly limited in this application.

[0036] In some embodiments, the soft-pack battery may include a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and an outer packaging (usually a soft composite film material), wherein the separator is located between the positive electrode sheet and the negative electrode sheet; the electrolyte may be liquid, semi-solid (such as gel) or solid, and the liquid electrolyte can infiltrate the positive electrode sheet, the negative electrode sheet and the separator; and the semi-solid or solid electrolyte can be located between the positive electrode sheet and the negative electrode sheet; the outer packaging contains the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte.

[0037] Specifically, the positive electrode sheet may include a positive electrode current collector and a positive electrode material layer located on at least one side of the positive electrode current collector, and the positive electrode material layer generally includes a positive electrode material, a positive electrode binder, and a positive electrode conductor; while the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer located on at least one side of the negative electrode current collector, and the negative electrode material layer generally includes a negative electrode material, a negative electrode binder, and a negative electrode conductor.

[0038] It is understandable that soft-pack batteries will expand in volume during the charge and discharge cycle. For soft-pack batteries with large volume expansion, applying appropriate pre-tightening force can effectively improve their expansion phenomenon and increase the cycle life of the soft-pack batteries. Silicon-based negative electrode materials have higher capacity, but their more serious volume expansion problem has always been one of the challenges limiting their application. Through the method of optimizing the pre-tightening force of soft-pack batteries in this application, the optimal initial pre-tightening force of soft-pack batteries can be determined, which has a significant improvement effect on improving soft-pack batteries containing silicon-based materials as negative electrode materials.

[0039] Therefore, according to an embodiment of the present application, the soft-pack battery can be a soft-pack battery whose negative electrode material contains a silicon-based material, and based on the total mass of the negative electrode material, the content of the silicon-based material can be 3% to 50%, specifically 3% to 45%, more specifically 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. Therefore, by determining the optimal initial preload force and then applying the optimal initial preload force to the soft-pack battery, the volume expansion problem of the silicon-based negative electrode material can be effectively improved for the soft-pack battery whose negative electrode material contains a silicon-based material, thereby effectively extending the cycle life of the soft-pack battery.

[0040] Herein, silicon-based materials have the conventional meaning in the art, which refers to negative electrode materials containing silicon elements, including but not limited to silicon element, silicon-carbon materials, silicon-oxygen materials, silicon alloys, etc.

[0041] According to the embodiments of the present application, the thickness of the soft-pack battery is generally not particularly limited. As an example, the thickness of the soft-pack battery can be 4 mm to 12 mm, specifically 6 mm to 10 mm, and more specifically 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, etc. Within the above thickness range, it is easy to manufacture and can meet different usage scenarios and requirements, and has a wide range of uses.

[0042] It is understood that the m soft-pack batteries described herein may be soft-pack batteries with the same conditions, thereby making the determination of the optimal initial preload more accurate.

[0043] According to an embodiment of the present application, in the step of determining the optimal initial preload force, a smaller pressure value is preferably selected for the first initial preload force applied. In some embodiments, a smaller pressure value can be selected based on the range of pressure values that the clamp can apply, or an appropriate pressure value can be selected based on experience.

[0044] It is understood that battery preload refers to the predetermined force applied to the various battery components (such as cells, modules, and housings) during the battery assembly process to ensure a tight fit and structural stability between battery components. This preload can be derived from a variety of methods, including mechanical bolts, clamps, adhesives, or other fixing devices.

[0045] It is understood that in order to more accurately determine the optimal initial preload, the first initial preload of the m soft-pack batteries should be distributed as evenly as possible from lower pressure values to higher pressure values, and the greater the number of soft-pack batteries, the more accurate the result. It is understood that the highest pressure value should not exceed the maximum pressure value that the soft-pack battery outer packaging can withstand.

[0046] According to an embodiment of the present application, according to the first initial preload force from small to large, the m soft-pack batteries in the optimal state of charge are defined as the M1 soft-pack battery, the M2 soft-pack battery, ..., the M m Soft-pack battery; wherein, the first initial preload force of the M1 soft-pack battery may be 0.001MPa to 0.005MPa, specifically 0.002MPa to 0.004MPa, more specifically 0.001MPa, 0.002MPa, 0.003MPa, 0.004MPa, 0.005MPa, etc. Thus, the test range is wider and the optimal initial preload force is determined more accurately.

[0047] In some embodiments, the Mthm The first initial preload force of the soft-pack battery can be 0.04MPa to 0.06MPa, specifically 0.045MPa to 0.055MPa, more specifically 0.04MPa, 0.042MPa, 0.045MPa, 0.048MPa, 0.05MPa, 0.052MPa, 0.055MPa, 0.058MPa, 0.06MPa, etc. Therefore, the test range covers higher pressure values, and the optimal initial preload force is determined more accurately.

[0048] In some embodiments, the Mth j The first initial preload and the Mth j-1 The difference in the first initial preload force of the soft-pack battery can be 0.001 MPa to 0.03 MPa, specifically 0.003 MPa to 0.02 MPa, more specifically 0.001 MPa, 0.005 MPa, 0.01 MPa, 0.015 MPa, 0.02 MPa, 0.025 MPa, 0.03 MPa, etc., where j is an integer from 2 to m. The first initial preload forces of the m soft-pack batteries can be relatively evenly distributed between 0 and the maximum pressure value that the outer packaging of the soft-pack battery can withstand, which can more accurately determine the optimal initial preload force of the soft-pack battery.

[0049] According to an embodiment of the present application, in this step, a pressure sensor may be provided on the fixture, so that the pressure value between the soft-pack battery and the fixture can be monitored in real time during the charge and discharge cycle of the soft-pack battery.

[0050] According to the embodiments of the present application, the mode of charge and discharge cycle of m soft-pack batteries can be selected according to the positive and negative electrode materials of the battery. In some embodiments, the charge and discharge cycle of the soft-pack battery can be performed at a current of 0.33C, and the charge and discharge cut-off voltage is (3.6-4.35)V~2.5V. Specifically, the charging process is to charge the soft-pack battery with a current of 0.33C to a cut-off voltage of 3.6V~4.35V (the corresponding state is a fully charged state, i.e. 100% SOC), and the discharging process is to discharge the soft-pack battery with a current of 0.33C to a cut-off voltage of 2.5V (the corresponding state is an empty state, i.e. 0% SOC). The above test conditions are more in line with the actual use conditions of the soft-pack battery and can more accurately determine the optimal state of charge.

[0051] It should be noted that the charge and discharge cut-off voltage of the soft-pack battery during the charge and discharge cycle is generally related to the type of positive electrode material in the soft-pack battery. Soft-pack batteries using different positive electrode materials generally have different charge and discharge cut-off voltages during the charge and discharge cycle. Specifically, if the positive electrode material is an 8-series ternary positive electrode material, the charge and discharge cut-off voltage is 4.2V to 2.5V; if the positive electrode material is a 6-series ternary positive electrode material, the charge and discharge cut-off voltage is (4.3-4.35)V to 2.5V; if the positive electrode material is lithium iron phosphate and / or lithium manganese iron phosphate, the charge and discharge cut-off voltage is 3.6V to 2.5V. During the actual charge and discharge cycle, the corresponding charge and discharge cut-off voltage can be selected according to different positive electrode materials.

[0052] After completing a charge and discharge cycle, the maximum pressure L' of the soft pack battery can be recorded. max and minimum pressure L' min It can be understood that according to the volume expansion of the soft pack battery, the battery generally has a maximum pressure L' when fully charged. max , has the minimum pressure L' in the empty state min By comparing the maximum pressure L' corresponding to m soft-pack batteries max and minimum pressure L' min , maximum pressure L' max The value is the smallest and the minimum pressure L' min The first initial preload force corresponding to the soft-pack battery with a value greater than 0 is the optimal initial preload force.

[0053] For example, 7 soft-pack batteries with the first initial preload forces of 0.001 MPa, 0.004 MPa, 0.006 MPa, 0.008 MPa, 0.01 MPa, 0.02 MPa, and 0.04 MPa are tested, and 7 maximum pressures L' corresponding to the 7 soft-pack batteries are obtained. max and 7 minimum pressures L' min By comparison, the minimum pressure L' corresponding to the soft pack battery with the first initial preload of 0.02MPa min The value is greater than 0, and the maximum pressure L' max 7 maximum pressures L' recorded max The smallest value among them is 0.02MPa, which is the optimal initial preload force for the soft-pack battery. In the actual use of the soft-pack battery, applying the above optimal initial preload force to the soft-pack battery is more conducive to improving the cycle life of the soft-pack battery.

[0054] It is understood that before determining the optimal initial preload, a step of determining the optimal state of charge is also included. Specifically, a second initial preload can be applied to n soft-pack batteries at different states of charge, and then a charge-discharge cycle is performed on each of the n soft-pack batteries. The pressure value between the soft-pack battery and the fixture during the charge-discharge cycle is recorded in real time, and the maximum pressure L of the n soft-pack batteries at different states of charge is recorded. max and minimum pressure L min , maximum pressure L max The value is minimum and the minimum pressure L min The state of charge of the soft-pack battery with a value greater than 0 is the optimal state of charge.

[0055] Therefore, the above method of the present application also includes:

[0056] S30: Before applying the first preload, the m soft-pack batteries are placed in an optimal state of charge; the optimal state of charge is determined by the following method: providing n soft-pack batteries with different states of charge; applying a second initial preload to each of the n soft-pack batteries using the fixture, and then subjecting the n soft-pack batteries to a charge-discharge cycle; during the charge-discharge cycle, simultaneously and in real time testing the pressure between the n soft-pack batteries and the fixture, and recording the maximum pressure L of each soft-pack battery. max and minimum pressure L min , the maximum pressure L max The value is the smallest and the minimum pressure L min The state of charge corresponding to the soft-pack battery with a value greater than 0 is the optimal state of charge; where n is an integer from 2 to 100.

[0057] It should be noted that the maximum pressure L is selected max The value is the smallest and the minimum pressure L min The state of charge corresponding to the soft pack battery with a value greater than 0 is the optimal state of charge. The principle is the same as selecting the maximum pressure L' max The value is minimum and the minimum pressure L' min The first initial preload force corresponding to the soft-pack battery with a value greater than 0 is the optimal initial preload force, which will not be described in detail here.

[0058] In this step, the soft-pack battery can be the same as the softened battery used in the step for determining the optimal initial preload, and a detailed description thereof will not be given here. It is understood that the n soft-pack batteries with different states of charge described herein can be soft-pack batteries with all other conditions being identical, differing only in their states of charge. This allows for more accurate determination of the optimal state of charge.

[0059] As used herein, State of Charge (SOC) has a well-known meaning in the art and refers to the percentage of a battery's total capacity remaining at a given moment. It is an important parameter for measuring a battery's state of charge and is typically expressed as a percentage. SOC values range from 0% (fully discharged) to 100% (fully charged).

[0060] It can be understood that in order to more accurately determine the optimal state of charge, the state of charge of the n soft-pack batteries should be distributed from 0% SOC to 100% SOC as much as possible, and the more soft-pack batteries there are, the more accurate the result will be. However, taking into account factors such as actual operation execution, in some embodiments of the present application, according to the state of charge from low to high, the n soft-pack batteries are defined as the N1 soft-pack battery, the N2 soft-pack battery, ..., the N n Soft-pack battery; wherein the state of charge of the N1th soft-pack battery can be 0% SOC to 5% SOC, specifically 2% SOC to 4% SOC, more specifically 0% SOC, 1% SOC, 2% SOC, 3% SOC, 4% SOC, 5% SOC, etc. Thus, soft-pack batteries with low states of charge can be effectively detected.

[0061] In some embodiments, the Nth n The state of charge of the soft-pack battery can be 95% SOC to 100% SOC, specifically 96% SOC to 98% SOC, more specifically 95% SOC, 96% SOC, 97% SOC, 98% SOC, 99% SOC, 100% SOC, etc. Therefore, soft-pack batteries at high states of charge can be effectively detected.

[0062] In some embodiments, the difference between the state of charge of the Ni-th soft-pack battery and the state of charge of the Ni-1 soft-pack battery can be 1% SOC to 30% SOC, specifically 2% SOC to 20% SOC, and more specifically 1% SOC, 5% SOC, 10% SOC, 15% SOC, 20% SOC, 25% SOC, 30% SOC, etc., where i is an integer from 2 to n. Thus, the states of charge of the n soft-pack batteries can be relatively evenly distributed between 0% SOC and 100% SOC, allowing for more accurate determination of the optimal state of charge of the soft-pack batteries.

[0063] According to an embodiment of the present application, in the step of determining the optimal state of charge, a smaller pressure value is preferably selected for the second initial preload applied. In some embodiments, a smaller pressure value can be selected based on the range of pressure values that the clamp can apply, and a suitable pressure value can be selected based on experience. In some specific embodiments, the second initial preload is the minimum pressure that the clamp can apply, or the minimum value within the range of pressure values that the clamp can apply. For example, if the range of pressure values that the clamp can apply is 0.001 MPa to 5 MPa, the second initial preload is 0.001 MPa.

[0064] As an example, the second initial preload force may be 0.001MPa to 0.025MPa, specifically 0.002MPa to 0.02MPa, more specifically 0.001MPa, 0.005MPa, 0.01MPa, 0.015MPa, 0.02MPa, 0.025MPa, etc. Specifically, during the charging process of the soft-pack battery, the negative electrode expands due to lithium insertion, resulting in thickening of the battery cell. The fixture generally has a fixed gap. When the second initial preload force is smaller, the maximum pressure of the soft-pack battery can be smaller when fully charged. Because a larger pressure will cause the diaphragm to close and the electrical performance impedance to increase, in order to maintain a longer cycle life, the initial preload force needs to be as small as possible, thereby facilitating improved cycle life.

[0065] According to an embodiment of the present application, in this step, a pressure sensor may be provided on the fixture, so that the pressure value between the soft-pack battery and the fixture can be monitored in real time during the charge and discharge cycle of the soft-pack battery.

[0066] According to the embodiments of the present application, the mode of charge and discharge cycle of the soft-pack battery can be selected according to the positive and negative electrode materials of the battery. In some embodiments, the charge and discharge cycle of the soft-pack battery can be performed at a current of 0.33C, and the charge and discharge cut-off voltage is (3.6-4.35)V~2.5V. Specifically, the charging process is to charge the soft-pack battery with a current of 0.33C to a cut-off voltage of 4.2V (the corresponding state is a fully charged state, i.e., 100% SOC), and the discharging process is to discharge the soft-pack battery with a current of 0.33C to a cut-off voltage of 2.5V (the corresponding state is an empty state, i.e., 0% SOC). The above test conditions are more in line with the actual use conditions of the soft-pack battery and can more accurately determine the optimal state of charge.

[0067] It should be noted that the charge and discharge cut-off voltage of the soft-pack battery during the charge and discharge cycle is generally related to the type of positive electrode material in the soft-pack battery. Soft-pack batteries using different positive electrode materials generally have different charge and discharge cut-off voltages during the charge and discharge cycle. Specifically, if the positive electrode material is an 8-series ternary positive electrode material, the charge and discharge cut-off voltage is 4.2V to 2.5V; if the positive electrode material is a 6-series ternary positive electrode material, the charge and discharge cut-off voltage is (4.3-4.35)V to 2.5V; if the positive electrode material is lithium iron phosphate and / or lithium manganese iron phosphate, the charge and discharge cut-off voltage is 3.6V to 2.5V. During the actual charge and discharge cycle, the corresponding charge and discharge cut-off voltage can be selected according to different positive electrode materials.

[0068] After completing a charge and discharge cycle, the maximum pressure L of the soft pack battery can be recorded. max and minimum pressure L min It can be understood that according to the volume expansion of the soft pack battery, the battery generally has a maximum pressure L when fully charged. max , has a minimum pressure L in the empty state min By comparing the maximum pressure L corresponding to n soft pack batteries max and minimum pressure L min , maximum pressure L max The value is the smallest and the minimum pressure L min The state of charge of the soft-pack battery with a value greater than 0 is the optimal state of charge.

[0069] For example, 10 soft-pack batteries with charge states of 3% SOC, 5% SOC, 7% SOC, 10% SOC, 30% SOC, 50% SOC, 70% SOC, 90% SOC, 95% SOC, and 97% SOC are tested, and 10 maximum pressures L corresponding to the 10 soft-pack batteries are obtained. max and 10 minimum pressure L min By comparison, the minimum pressure L corresponding to the soft pack battery of 30% SOC is min The value is greater than 0, and the maximum pressure L max Values recorded at 10 maximum pressures L max The smallest value is 30%, and 30% SOC is the optimal state of charge for the soft-pack battery. In the actual use of the soft-pack battery, applying an initial preload to the soft-pack battery when it is at the optimal state of charge is more conducive to improving the cycle life of the soft-pack battery.

[0070] Specifically, under the condition of initial preload, the expansion force of the soft pack battery will gradually increase with the increase of the number of cycles, so the life of the battery pack usually has a requirement for the expansion force of the soft pack battery. The value of the expansion force of the soft pack battery after each cycle is recorded as F N-cycle, where N refers to the number of cycles of the soft pack battery, which should meet F N-cycle <The maximum expansion force that the soft pack battery can withstand. The above-mentioned application can reduce F by adjusting the optimal initial preload force. N-cycle , so that the soft-pack battery can achieve a good cycle life and give full play to the performance of the soft-pack battery. Furthermore, through the optimization of the initial preload force of the soft-pack battery in this application, the growth of the interfacial impedance of the soft-pack battery, especially the soft-pack battery with silicon-based negative electrode materials, during long cycles is reduced, the risk of the negative electrode separating from the current collector due to the breakage of the negative electrode particles is reduced, the cycle life of the soft-pack battery is improved, and the soft-pack battery is guided to achieve better performance.

[0071] In the second aspect of the present application, a method for constructing an initial preload database for silicon-containing negative electrode soft-pack batteries is provided. According to an embodiment of the present application, the method includes: providing p silicon-containing negative electrode soft-pack batteries with different silicon contents; and using the method described in the first aspect of the present application to determine the optimal initial preload of the p silicon-containing negative electrode soft-pack batteries to form the database. This method can establish a connection between silicon content and optimal initial preload, guiding silicon-containing negative electrode soft-pack batteries to achieve better performance. Specifically, when applying silicon-containing negative electrode soft-pack batteries, the corresponding optimal initial preload can be found in the database based on the silicon content, providing theoretical guidance for battery development, saving R&D time and cost, and at the same time extending the cycle life of silicon-containing negative electrode soft-pack batteries.

[0072] It can be understood that the above silicon content refers to the mass percentage of the silicon-based material based on the total mass of the negative electrode material in the silicon-containing negative electrode soft-pack battery.

[0073] It is understandable that the database may also include p optimal states of charge of the silicon-containing negative electrode soft-pack batteries, and the optimal states of charge and the optimal initial preload together constitute the database. Thus, a connection between silicon content, optimal state of charge, and optimal initial preload is established to guide silicon-containing negative electrode soft-pack batteries to achieve better performance. Specifically, when applying silicon-containing negative electrode soft-pack batteries, the corresponding optimal state of charge and optimal initial preload can be found in the database based on the silicon content, providing theoretical guidance for battery development, saving R&D time and costs, and further extending the cycle life of silicon-containing negative electrode soft-pack batteries.

[0074] The third aspect of the present application provides a method for extending the cycle life of a soft-pack battery. According to an embodiment of the present application, the method comprises: determining the optimal initial preload force of the soft-pack battery by the method for optimizing the preload force of the soft-pack battery according to the first aspect of the present application; and applying the optimal initial preload force to the soft-pack battery. As a result, the growth of the interfacial impedance of the soft-pack battery treated as above is effectively reduced during the long cycle, the risk of the negative electrode detaching from the current collector due to the crushing of the negative electrode particles is significantly reduced, the cycle life of the soft-pack battery is significantly extended, and the soft-pack battery can exert better comprehensive performance.

[0075] It is understood that the method may also include: determining the optimal state of charge and optimal initial preload of the soft-pack battery using the method for optimizing the preload of the soft-pack battery described in the first aspect of this application; adjusting the soft-pack battery to the optimal state of charge, and then applying the optimal initial preload to the soft-pack battery. As a result, the growth of the interfacial impedance of the soft-pack battery treated as described above during long-term cycling is further reduced, the risk of the negative electrode detaching from the current collector due to negative electrode particle breakage is further reduced, the cycle life of the soft-pack battery is further extended, and the soft-pack battery can further achieve better overall performance.

[0076] In a fourth aspect, the present application provides a soft-pack battery. According to an embodiment of the present application, the soft-pack battery is obtained by processing according to the method described in the third aspect of the present application. The soft-pack battery can achieve a longer cycle life and improved overall performance.

[0077] According to the embodiments of this application, there are no specific restrictions on the specific type of soft-pack battery, and it can be flexibly selected according to actual use needs. As an example, the soft-pack battery can be a primary battery or a secondary battery; specifically, it can be a lithium-ion battery, a sodium-ion battery, a lithium metal battery, a sodium metal battery, etc.; depending on the stacking method of the electrode sheets, it can also be a laminated battery or a wound battery, which is not specifically limited in this application.

[0078] In a fifth aspect, the present application provides an electrical device. According to an embodiment of the present application, the electrical device includes the soft-pack battery described in the fourth aspect of the present application. The electrical device can have a longer service life and exhibit better overall performance.

[0079] According to an embodiment of the present application, the soft-pack battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0080] The embodiments of the present application are described in detail below.

[0081] Example 1

[0082] S1: Prepare soft pack batteries with silicon contents of 3%, 5%, 10%, 18%, 22%, 24%, 30%, 36%, and 45% as required; the thickness of the soft pack batteries is 8.5mm. Specifically, in the soft pack battery, the positive electrode uses 11μm aluminum foil as the current collector, and in the positive electrode sheet, NCM811 (i.e. LiNi 0.8 Co 0.1 Mn 0.1 O2), PVDF, conductive carbon black, and conductive carbon nanotubes in a mass ratio of 97:1.3:1.2:0.5. The separator uses a 9+3μm PE wet-process ceramic separator. The electrolyte solution includes a carbonate organic solvent (composed of EC:EMC:DEC=3:2:5) and a lithium salt (LPF6, 1.15mol / L), with the addition of 1wt% VC, 0.5wt% DTD, and 5wt% FEC. The negative electrode uses 11μm aluminum foil as the current collector. In the negative electrode sheet, the mass ratio of silicon-carbon active material, SBR, PAA, conductive carbon black, and conductive carbon nanotubes is 95:1.5:1.5:1:1.

[0083] S2: Select a soft-pack battery with a silicon content of 24%, and use a splint pressure sensor to apply an initial preload of 0.0025 MPa to the soft-pack battery when it is at 3% SOC, 5% SOC, 7% SOC, 10% SOC, 30% SOC, 50% SOC, 70% SOC, 90% SOC, 95% SOC, and 97% SOC, respectively. Then, charge and discharge the soft-pack battery at a current of 0.33C, and the charge and discharge cut-off voltage is 4.2~2.5V. Record the pressure data of the splint pressure sensor, and record the maximum and minimum pressures of the splint pressure sensor corresponding to the soft-pack battery in each SOC state. When the minimum pressure is greater than zero and the maximum pressure is the minimum, it is recorded as the optimal SOC.

[0084] S3: For the soft-pack battery with 24% silicon content, pressures of 0.001MPa, 0.004MPa, 0.006MPa, 0.008MPa, 0.01MPa, 0.02MPa, 0.032MPa, and 0.04MPa are applied respectively at the corresponding optimal SOC, and then the soft-pack is charged and discharged at a current of 0.33C. The charge and discharge cut-off voltage is 4.2~2.5V. The pressure data of the splint pressure sensor is recorded, and the maximum pressure and the lowest pressure of the pressure sensor corresponding to the soft-pack battery under different pressures are recorded. When the minimum pressure is greater than zero and the maximum pressure is the minimum, it is recorded as the optimal initial preload.

[0085] S4: Repeat steps S2 to S3 to determine the optimal state of charge and optimal initial preload for soft-pack batteries with silicon contents of 3%, 5%, 10%, 18%, 22%, 30%, 36%, and 45%, respectively.

[0086] Example 2:

[0087] The thickness of the soft pack battery is 4.5 mm, and the rest is the same as in Example 1.

[0088] Example 3:

[0089] The thickness of the soft-pack battery is 6.5 mm, and the rest is the same as in Example 1.

[0090] Example 4

[0091] The charge and discharge cut-off voltage is 2.7 to 4.2 V, and the rest is the same as in Example 1.

[0092] Example 5:

[0093] The charge and discharge current is 0.5C, the charge and discharge cut-off voltage is 2.7-4.2V, and the rest is the same as in Example 1.

[0094] Table 1

[0095]

[0096] According to the optimal state of charge and the optimal initial preload shown in Table 1, different initial preloads (including the optimal initial preload) are applied to soft-pack batteries with different silicon contents when they are in different states of charge (including the optimal state of charge), and then the performance of the soft-pack batteries is tested. The specific states of charge and initial preloads are shown in Table 2, where the silicon content of the soft-pack batteries is 24%.

[0097] Table 2

[0098]

[0099]

[0100] Performance testing:

[0101] Cycling performance test: The battery cell was initially preloaded according to Examples 1-5. The battery cell was placed in an environment of 25±2°C and charged to 4.2V at a constant current and constant voltage of 1C. The cell was then left to stand for 10 minutes and discharged to 2.5V at a constant current of 1C. The capacity retention rate was calculated after 500 cycles.

[0102] Internal resistance test: Set the initial preload force of the battery cell according to Examples 1-5, adjust the battery cell state to 50% SOC, and then discharge at 2C for 10s to calculate the internal resistance, which is the difference between the static terminal voltage and the discharge end voltage divided by the discharge current.

[0103] Storage performance test: The battery cells were initially preloaded according to Examples 1-5. The cells were charged to 4.2 V at 1C constant current and constant voltage at 25±2°C. They were then stored at 45°C for 7 days. The capacity retention rate was tested using a 1C discharge current. The cells were charged using a 1C current and the storage capacity recovery rate was recorded.

[0104] The specific test results are shown in Table 3 below.

[0105] Table 3

[0106]

[0107]

[0108] As can be seen from the test results in Table 3 above, by designing an experimental system to study the effects of different initial states of charge (SOC) and their corresponding initial preloads, the results show that: under the same initial SOC conditions, as the initial preload increases, the internal resistance of the cell increases significantly, and the cumulative effect of impedance during the cycle is further aggravated, resulting in a decrease in capacity retention, and the charge retention rate in the storage stage is simultaneously reduced; under the same initial preload conditions, increasing the initial SOC will accelerate the cell cycle life decay, accompanied by a continuous increase in impedance. Mechanism analysis shows that when the cell is discharged for the first time under a high SOC state, the lack of external pressure constraints leads to poor contact at the electrode interface, which intensifies the interface side reactions and ultimately accelerates the capacity decay process through the impedance growth mechanism. In summary, the patent of this invention studies the mechanism of the influence of initial preload adjustment and the optimal initial state of charge (SOC) on the performance of silicon-containing system cells during the clamp cycle process, determines the optimal clamp force application parameters (including the force magnitude and the corresponding initial SOC state), and establishes the optimization principles, judgment criteria and implementation conditions for improving the cycle life of the cell.

[0109] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0110] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0111] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for optimizing the initial preload of a soft-pack battery, characterized in that: include: Provide m soft pack batteries; A clamp is used to apply different first initial preload forces to the m soft-pack batteries, and then the m soft-pack batteries are subjected to a charge-discharge cycle. During the charge-discharge cycle, the pressure between the m soft-pack batteries and the clamp is simultaneously tested in real time, and the maximum pressure L' of each soft-pack battery is recorded. max and minimum pressure L' min , the maximum pressure L' max The value is the smallest and the minimum pressure L' min The first initial preload force corresponding to the soft-pack battery with a value greater than 0 is the optimal initial preload force; Here, m is an integer from 2 to 100.

2. The method according to claim 1, characterized in that According to the first initial preload force from small to large, the m soft-pack batteries are defined as the M1 soft-pack battery, the M2 soft-pack battery, ..., the M m soft pack battery; The m soft-pack batteries meet at least one of the following conditions: The first initial preload force of the M1 soft-pack battery is 0.001 MPa to 0.005 MPa, preferably 0.002 MPa to 0.004 MPa; The Mth m The first initial preload force of the soft pack battery is 0.04 MPa to 0.06 MPa, preferably 0.045 MPa to 0.055 MPa; No. M j The first initial preload and the Mth j-1 The difference in the first initial preload force of the soft-pack battery is 0.001 MPa to 0.03 MPa, preferably 0.003 MPa to 0.02 MPa, wherein j is an integer from 2 to m.

3. The method according to claim 1 or 2, characterized in that include: Before applying the first initial preload force, the m soft-pack batteries are in an optimal state of charge; The optimal state of charge is determined by the following method: Provide n soft-pack batteries with different states of charge; The clamp is used to apply a second initial preload force to each of the n soft-pack batteries, and then the n soft-pack batteries are subjected to a charge-discharge cycle. During the charge-discharge cycle, the pressure between the n soft-pack batteries and the clamp is simultaneously tested in real time, and the maximum pressure L of each soft-pack battery is recorded. max and minimum pressure L min , the maximum pressure L max The value is the smallest and the minimum pressure L min The state of charge of the soft-pack battery with a value greater than 0 is the optimal state of charge; Here, n is an integer from 2 to 100.

4. The method according to claim 3, characterized in that According to the state of charge from low to high, the n soft-pack batteries are defined as the N1 soft-pack battery, the N2 soft-pack battery, ..., the N n Soft-pack batteries; n of the soft-pack batteries satisfy at least one of the following conditions: The state of charge of the N1-th soft-pack battery is 0% SOC to 5% SOC, preferably 2% SOC to 4% SOC; The Nth n The state of charge of the soft pack battery is 95% SOC to 100% SOC, preferably 96% SOC to 98% SOC; Nth i State of charge of soft pack batteries and Nth i-1 The difference in state of charge of the soft pack battery is 1% SOC to 30% SOC, preferably 2% SOC to 20% SOC, wherein i is an integer from 2 to n.

5. The method according to claim 3, characterized in that The second initial pre-tightening force is the minimum pressure that can be applied by the clamp. Preferably, the second initial pre-tightening force is 0.001 MPa to 0.025 MPa, and more preferably 0.002 MPa to 0.02 MPa.

6. The method according to claim 1, characterized in that The negative electrode material in the soft-pack battery contains a silicon-based material. Based on the total mass of the negative electrode material, the content of the silicon-based material is 3% to 50%, preferably 3% to 45%.

7. The method according to claim 1, characterized in that The soft pack battery is subjected to the charge and discharge cycle at a current of 0.33C, and the charge and discharge cut-off voltage is (3.6-4.35)V to 2.5V.

8. The method according to claim 1, characterized in that The thickness of the soft pack battery is 4 mm to 12 mm, preferably 6 mm to 10 mm.

9. A method for constructing an initial preload database for silicon-containing negative electrode soft-pack batteries, characterized in that: include: Providing p silicon-containing negative electrode soft-pack batteries with different silicon contents, where p is an integer from 2 to 100; The optimal initial preload force of p silicon-containing negative electrode soft-pack batteries is determined using the method according to any one of claims 1 to 8 to form the database.

10. A method for extending the cycle life of a soft pack battery, characterized in that: include: Determine the optimal initial preload force of the soft pack battery by the method according to any one of claims 1 to 8; Applying the optimal initial preload force to the soft pack battery.

11. A soft pack battery, characterized in that: It is obtained by processing using the method according to claim 10.

12. An electrical device, characterized in that: Including the soft pack battery according to claim 11.

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