Method and device for generating solid electrolyte interfacial film

Abstract

The invention discloses a method and device for generating a solid electrolyte interface film, and the method comprises the steps: executing a periodic processing flow on a battery monomer under the condition that a negative electrode interface of the battery monomer starts a film forming reaction until the film forming reaction of the battery monomer is finished, and obtaining the battery monomer with the negative electrode interface having the solid electrolyte interface film; wherein the periodic processing flow comprises multiple times of periodic processing, each time of periodic processing comprises a charging process and a standing process, and each standing process is executed based on the previous standing process. Based on the scheme, the quality and the performance of the solid electrolyte interface film can be effectively improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method and device for generating a solid electrolyte interface film. Background Art

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, are widely used in mobile electronic devices, electric vehicles, and energy storage systems. During the manufacturing process of lithium-ion batteries, the formation of the solid electrolyte interface (SEI) film has a significant impact on battery performance. It not only determines the battery's initial coulombic efficiency but also directly affects its safety and service life.

[0003] Among the current SEI film formation methods, the SEI film formation process is usually optimized by controlling the charging current or adding film-forming additives. However, most of these methods remain at the parameter adjustment level, and the film-forming effect is limited, making it difficult to significantly improve the SEI film quality. Summary of the Invention

[0004] The embodiments of the present application provide a method and apparatus for generating a solid electrolyte interface film, which can effectively improve the quality and performance of the solid electrolyte interface film.

[0005] The technical solution of the embodiment of the present application is implemented as follows: In a first aspect, an embodiment of the present application provides a method for forming a solid electrolyte interface film, the method comprising: When a film-forming reaction begins at the negative electrode interface of the battery cell, a periodic treatment process is performed on the battery cell until the film-forming reaction of the battery cell is completed, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; The periodic processing flow includes multiple periodic processings, each periodic processing includes a charging process and a rest process, and each rest process is executed based on the previous rest process.

[0006] In this embodiment, by starting a periodic processing flow when the film-forming reaction begins at the negative electrode interface of the battery cell, alternating charging and rest processes are performed on the battery cell, and each rest process is performed based on the previous rest process, that is, the execution of the rest process in the next periodic processing can be determined based on the current rest process, thereby continuing the process until the film-forming reaction is completed, thereby ensuring that the formation process of the solid electrolyte interface film is controllable and sufficient, improving the quality of the solid electrolyte interface film, and improving the battery life.

[0007] In some embodiments of the present application, a periodic processing process is performed on a battery cell, including: During the execution of the current cycle processing, obtaining voltage change data of the battery cell during the current static process; wherein the voltage change data is used to determine the relationship between the voltage change of the battery cell and time; the current static process is the static process in the current cycle processing; executing a next rest process in the next cycle processing according to the voltage change data; The first rest process in the first periodic process after the next periodic process is executed based on the voltage change data of the next rest process until the periodic process flow is completed.

[0008] In this embodiment, by collecting and analyzing the voltage change data of the static process in each cycle, the static process in the subsequent cycle processing is executed, and dynamic decision-making of the static process in each cycle is realized, so that each cycle processing is conducive to the formation of the solid electrolyte interface film, thereby improving the stability and efficiency of the film formation process, reducing the accumulation of side reactants, and optimizing the structure of the solid electrolyte interface film.

[0009] In some embodiments of the present application, executing a next rest process in a next cycle of processing according to the voltage change data includes: Performing mathematical transformation on the time variable of the voltage change data to obtain transformed voltage change data; Perform linear fitting on the converted voltage change data to determine the current equilibrium voltage; First target information is determined based on the current equilibrium voltage, and a next rest process is performed according to the first target information.

[0010] In this embodiment, by mathematically transforming the time variable of the voltage change curve to obtain the converted voltage change data, and performing linear fitting on the converted voltage change data, the equilibrium voltage reflecting the internal state of the battery is extracted, and a reasonable static strategy is determined based on this to obtain the first target information. Subsequently, the static process in the next cycle processing will be executed according to the first target information, which can make the distribution of additives and by-products more uniform, enhance the concentration drive effect, and further improve the density and uniformity of the solid electrolyte interface membrane.

[0011] In some embodiments of the present application, determining the first target information based on the current equilibrium voltage includes: Get the current initial voltage of the battery cell at the beginning of the current rest process; Determine the current internal resistance information based on the difference between the current initial voltage and the current equilibrium voltage, as well as the current charging current; The ratio of the current static time to the current internal resistance information is determined as the first target information; wherein the current static time is the duration of the current static process.

[0012] In this embodiment, the internal resistance information is calculated based on the voltage difference between the current initial voltage and the current equilibrium voltage and the charging current, and is linked to the standing time. The ratio of the current standing time to the current internal resistance information is determined as the first target information to obtain a scientific standing reference basis, making each round of standing process more accurate, helping to promote the stable formation of the solid electrolyte interface film, and reducing the problem of uneven film layer caused by too short or too long standing.

[0013] In some embodiments of the present application, performing the next static process according to the first target information includes: During the execution of the next static process, the duration and real-time voltage data of the next static process are obtained; determining second target information based on the real-time voltage data and the duration; When the second target information is equal to the first target information, the next rest process is stopped.

[0014] In this embodiment, the voltage and duration of the static process are monitored in real time, and the second target information is calculated using the real-time voltage data and duration. The termination condition is dynamically determined based on the second target information, that is, whether the second target information is equal to the first target information, so as to accurately control the operation of each stage, avoid the adverse effects of excessive static or premature termination, and ensure that the optimal conditions for the formation of the solid electrolyte interface film are maintained.

[0015] In some embodiments of the present application, the method further comprises: According to the preset time constraint strategy, the charging time of the charging process and the rest time of the rest process in each cycle processing are constrained; Among them, the preset time constraint strategy is used to constrain the charging time to be greater than or equal to the first preset time, the static time to be greater than or equal to the charging time, and the product of the charging time and the charging rate of the charging process to be less than or equal to the first preset power.

[0016] In this embodiment, by setting a preset time constraint strategy, the charging time, standing time and charging rate in each cycle processing are constrained, so that the energy input of each operation can be controlled, while ensuring sufficient time for the additive to diffuse to the graphite surface, which is conducive to the uniform growth of the solid electrolyte interface film and improves the film formation quality.

[0017] In some embodiments of the present application, the method further comprises: Detect the voltage of the battery cell; In response to the voltage of the battery cell reaching a first voltage, determining to start a film forming reaction; In response to the voltage of the battery cell reaching a second voltage, it is determined that the film forming reaction is completed; the first voltage is lower than the second voltage.

[0018] In this embodiment, the voltage of the battery cell can be detected, and the start of the film formation reaction can be determined using the real-time voltage of the battery cell, thereby achieving precise control of the solid electrolyte interface film formation process.

[0019] In a second aspect, an embodiment of the present application provides a device for generating a solid electrolyte interface film, comprising: a periodic treatment process module, configured to execute a periodic treatment process on the battery cell when a film-forming reaction begins at the negative electrode interface of the battery cell, until the film-forming reaction of the battery cell is completed, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; The periodic processing flow includes multiple periodic processings, each periodic processing includes a charging process and a rest process, and each rest process is executed based on the previous rest process.

[0020] In this embodiment, by starting a periodic processing flow when the film-forming reaction begins at the negative electrode interface of the battery cell, alternating charging and rest processes are performed on the battery cell, and each rest process is performed based on the previous rest process, that is, the execution of the rest process in the next periodic processing can be determined based on the current rest process, thereby continuing the process until the film-forming reaction is completed, thereby ensuring that the formation process of the solid electrolyte interface film is controllable and sufficient, improving the quality of the solid electrolyte interface film, and improving the battery life.

[0021] In some embodiments of the present application, the periodic processing flow module is also used to obtain the voltage change data of the battery cell during the current static process during the execution of the current periodic processing; and to execute the next static process in the next periodic processing based on the voltage change data; and to execute the first static process in the first periodic processing after the next periodic processing based on the voltage change data of the next static process, until the periodic processing flow is completed; wherein the voltage change data is used to determine the relationship between the voltage change of the battery cell and time; the current static process is the static process in the current periodic processing.

[0022] In this embodiment, by collecting and analyzing the voltage change data of the static process in each cycle, the static process in the subsequent cycle processing is executed, and dynamic decision-making of the static process in each cycle is realized, so that each cycle processing is conducive to the formation of the solid electrolyte interface film, thereby improving the stability and efficiency of the film formation process, reducing the accumulation of side reactants, and optimizing the structure of the solid electrolyte interface film.

[0023] In some embodiments of the present application, the periodic processing flow module is further used to perform mathematical conversion on the time variable of the voltage change data to obtain the converted voltage change data; and perform linear fitting processing on the converted voltage change data to determine the current equilibrium voltage; and determine the first target information based on the current equilibrium voltage, and execute the next static process according to the first target information.

[0024] In this embodiment, by mathematically transforming the time variable of the voltage change curve to obtain the converted voltage change data, and performing linear fitting on the converted voltage change data, the equilibrium voltage reflecting the internal state of the battery is extracted, and a reasonable static strategy is determined based on this to obtain the first target information. Subsequently, the static process in the next cycle processing will be executed according to the first target information, which can make the distribution of additives and by-products more uniform, enhance the concentration drive effect, and further improve the density and uniformity of the solid electrolyte interface membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiment below.The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present application.

[0026] Figure 1 Schematic diagram of film-forming reaction; Figure 2 A schematic diagram of the implementation process of the method for forming a solid electrolyte interface membrane proposed in an embodiment of the present application; Figure 3 A schematic diagram of voltage changes in the periodic processing flow proposed in an embodiment of the present application; Figure 4 Schematic diagram of voltage change during film formation process; Figure 5 A schematic diagram of voltage changes during the film forming process proposed in an embodiment of the present application; Figure 6 A schematic diagram of a differential capacitance curve proposed in an embodiment of the present application; Figure 7 A schematic diagram of a secondary differential capacitance curve proposed in an embodiment of the present application; Figure 8 A schematic diagram of the converted voltage change data proposed in an embodiment of the present application; Figure 9 This is a schematic diagram of performing linear fitting on the converted voltage change data proposed in an embodiment of the present application; Figure 10 A schematic diagram of voltage difference changes in the periodic processing flow proposed in an embodiment of the present application; Figure 11A schematic diagram of the internal resistance change of the periodic processing flow proposed in an embodiment of the present application; Figure 12 A schematic diagram of the test results of the charge-discharge cycle test proposed in an embodiment of the present application; Figure 13 This is a schematic diagram of the composition structure of the device for generating the solid electrolyte interface film proposed in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to explain the related applications and are not intended to limit the applications. It should also be noted that for ease of description, only the portions relevant to the related applications are shown in the drawings.

[0028] When charging for the first time, the negative electrode material of the lithium-ion battery will react with the electrolyte to form a SEI film. Figure 1 As shown in the figure, the positive electrode material of a lithium-ion battery is on the left, and the negative electrode material is on the right. During the first charge, a side reaction called SEI film formation occurs. When the electrolyte contains film-forming additives, the additives preferentially participate in the film-forming reaction, forming the SEI layer and other side reactants. The quality of the SEI film directly affects the battery's cycle performance and lifespan. However, current constant current formation strategies struggle to effectively control the uniformity and density of the SEI film, leading to problems such as uneven distribution of electrolyte additives and accumulation of byproducts, which in turn reduces the overall stability of the SEI film.

[0029] To address the aforementioned issues, the present invention provides a method for generating a solid electrolyte interface film. The device for generating the solid electrolyte interface film utilizes the concentration polarization drive principle by introducing a periodic treatment process during the SEI film formation phase to promote the uniform distribution of electrolyte additives on the surface of the graphite negative electrode and accelerate the diffusion of byproducts into the electrolyte phase, thereby reducing their interference with the SEI film structure. By detecting the voltage during each treatment cycle and determining whether film formation is complete based on the voltage, precise control of the SEI film formation process is achieved. Ultimately, while ensuring film quality, the service life and electrochemical performance of lithium-ion batteries are significantly improved.

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0031] An embodiment of the present application provides a method for forming a solid electrolyte interface film, such as Figure 2 As shown, the method for forming a solid electrolyte interface film may include the following steps: Step 101: When a film-forming reaction begins at the negative electrode interface of the battery cell, a periodic treatment process is performed on the battery cell until the film-forming reaction of the battery cell is completed, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; wherein the periodic treatment process includes multiple periodic treatments, each periodic treatment includes a charging process and a rest process, and each rest process is performed based on the previous rest process.

[0032] In an embodiment of the present application, a device for generating a solid electrolyte interface film can perform a periodic treatment process on the battery cell when a film-forming reaction begins at the negative electrode interface of the battery cell, until the film-forming reaction of the battery cell is completed, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; wherein the periodic treatment process includes multiple periodic treatments, each periodic treatment includes a charging process and a static process, and each static process is performed based on the previous static process.

[0033] In the embodiments of the present application, the charging process refers to the operation of applying a current of a certain rate to the battery cell, so that an electrochemical reaction occurs and continues inside the battery cell. The charging process can be achieved through operations such as constant current charging (CC) or constant voltage charging (CV); the static process refers to the operation of stopping charging the battery cell, so that the molecules inside the battery cell tend to equilibrium and promote the uniform distribution of additives on the surface of the negative electrode material; compared with the constant current charging method of the current formation technology, the periodic treatment process can more effectively control the film formation process, prevent the accumulation of by-products caused by local high concentrations, and thus reduce the adverse effects of by-product accumulation on the quality of the solid electrolyte interface film.

[0034] In some embodiments of the present application, a battery cell refers to a basic unit that can realize the mutual conversion between chemical energy and electrical energy, and can be used to make a battery module or battery pack to supply power to electrical devices.

[0035] For example, two bare cells, i.e., unpackaged wound or laminated electrode assemblies, are placed in parallel in a battery casing, the top cover is sealed by laser welding, and the electrolyte is injected after vacuum baking to remove moisture to form a battery cell to be formed; then, in the subsequent formation process, the solid electrolyte interface film generation method provided in the embodiment of the present application is used to generate a solid electrolyte interface film (SEI film) on the negative electrode surface of each bare cell, thereby activating the electrochemical properties of the battery cell; that is, the battery cell can be an independent electrochemical unit with a complete structure including a bare cell, a casing, an electrolyte, etc.

[0036] In some embodiments of the present application, when the battery cell enters the solid electrolyte interface film forming stage, the solid electrolyte interface film generating device can record and adjust the time of the static process in each cycle processing.

[0037] In some embodiments of the present application, when a solid electrolyte interface film generating device performs a periodic processing flow on a battery cell, it can obtain voltage change data of the battery cell during the current static process during the execution of the current periodic processing; wherein the voltage change data is used to determine the relationship between the voltage change of the battery cell and time; the current static process is the static process in the current periodic processing; the next static process in the next periodic processing is executed according to the voltage change data; the first static process in the first periodic processing after the next periodic processing is executed based on the voltage change data of the next static process, until the periodic processing flow is completed.

[0038] In the embodiments of the present application, the voltage change data can reflect the dynamic response during the electrochemical reaction inside the battery, especially the polarization phenomenon during the formation of the solid electrolyte interface film.

[0039] It can be understood that the first cycle processing refers to the next cycle processing after the next cycle processing is completed, and the first static process is the static process in the first cycle processing.

[0040] In some embodiments of the present application, when the solid electrolyte interface membrane generating device executes the next static process in the next cycle processing according to the voltage change data, it can perform mathematical conversion on the time variable of the voltage change data to obtain the converted voltage change data; perform linear fitting processing on the converted voltage change data to determine the current equilibrium voltage; determine the first target information based on the current equilibrium voltage, and execute the next static process according to the first target information.

[0041] In some embodiments of the present application, linear fitting processing is a mathematical method that performs regression analysis on voltage change data, removes noise interference, and constructs a straight line or smooth curve that is as close to the actual trend as possible, thereby more clearly revealing the trend of voltage change.

[0042] For example, Figure 3 As shown, in a certain cycle process, the charging process is performed first and then the rest process is performed. First, as the charging process is performed, the voltage will gradually increase, and then during the rest process, the voltage will gradually decrease.

[0043] In some embodiments of the present application, when mathematical transformation is performed on the time variable of the voltage change data, mathematical transformation may be performed on the time variable of the voltage change curve corresponding to the static process in the voltage change data.

[0044] For example, the voltage change curve of the static process in a certain cycle process is a curve of the mapping relationship between voltage (V) and time (T). The time variable T is mathematically converted to convert time into , so the converted voltage change data is voltage vs. time The curve between voltage and time The intercept of the curve is the final equilibrium voltage, that is, the current equilibrium voltage is obtained.

[0045] In some embodiments of the present application, executing the next static process according to the first target information mainly involves determining the end timing of the next static process based on the first target information.

[0046] In some embodiments of the present application, when determining the first target information based on the current equilibrium voltage, the solid electrolyte interface membrane generating device can obtain the current initial voltage of the battery cell at the beginning of the current static process; determine the current internal resistance information based on the difference between the current initial voltage and the current equilibrium voltage, and the current charging current; and then determine the ratio of the current static time to the current internal resistance information as the first target information; wherein the current static time is the duration of the current static process.

[0047] In some embodiments of the present application, the current initial voltage refers to the voltage of the battery cell measured at the beginning of the current rest process in the current cycle process. This voltage reflects the initial condition of the electrochemical state inside the battery cell at the beginning of the rest process.

[0048] In some embodiments of the present application, the current charging current refers to the charging current corresponding to the charging process in the current periodic processing flow.

[0049] In some embodiments of the present application, when determining the current internal resistance information based on the difference between the current initial voltage and the current equilibrium voltage, and the current charging current, the ratio of the difference between the current initial voltage and the current equilibrium voltage to the current charging current can be determined as the current internal resistance information.

[0050] For example, assuming that the current process is the nth periodic process, the current initial voltage is expressed as , the current equilibrium voltage is expressed as , the current charging current is ; The difference between the current initial voltage and the current equilibrium voltage can be expressed as , the current internal resistance information can be expressed as .

[0051] In some embodiments of the present application, when the solid electrolyte interface film generating device performs the next static process according to the first target information, it can obtain the duration and real-time voltage data of the next static process during the execution of the next static process; then determine the second target information based on the real-time voltage data and the duration, and stop the next static process when the second target information is equal to the first target information.

[0052] In some embodiments of the present application, the real-time voltage data includes the initial voltage value of the battery cell measured at the beginning of the rest process in the next cycle processing, and also includes the voltage value at each time point in the real-time process of the subsequent rest process.

[0053] It can be understood that the duration of the next rest process represents the duration of the rest process up to the present in the process of executing the next rest process.

[0054] For example, assuming that the current process is the n-1th periodic processing flow, the first target information can be expressed as , and then when executing the next cycle processing, that is, the nth cycle processing, assuming that the nth charging process is executed first, and then the nth static process is started, the real-time voltage data and duration of the nth static process can be obtained, and the internal resistance value of the battery cell corresponding to the nth cycle processing can be calculated using the real-time voltage data and the charging current during the nth charging process , thereby using the internal resistance value and the duration of the current record Real-time calculation of second target information ,when When , the static process is stopped, and the nth periodic processing flow is completed.

[0055] In some embodiments of the present application, when the first target information is determined based on the current equilibrium voltage, the first target information may also be determined based on the difference between the current initial voltage and the current equilibrium voltage, and the current rest time.

[0056] For example, the current process is the n-1th periodic processing flow, and the voltage difference between the current initial voltage and the current equilibrium voltage can be expressed as , the current static time is expressed as , the ratio between the current static time and the voltage difference is determined as the first target information, then the first target information can be expressed as .

[0057] In some embodiments of the present application, when executing the next static process, when determining the second target information based on the real-time voltage data and the duration, the initial voltage value in the real-time voltage data and the voltage value at each time point in the real-time process of the static process can be directly used to calculate the real-time voltage difference, and the second target information can be calculated using the duration and the real-time voltage difference.

[0058] For example, assuming that the current process is the n-1th periodic processing flow, the first target information can be expressed as , and then when executing the next periodic processing flow, that is, the nth periodic processing flow, assuming that the nth charging process is executed first, and then the nth static process is started, the real-time voltage data of the nth static process can be obtained, and the real-time voltage data can be used to determine the real-time voltage difference , while recording the duration , thereby calculating the second target information in real time ,when When , the static process is stopped, and the nth periodic processing flow is completed.

[0059] In some embodiments of the present application, the solid electrolyte interface membrane generating device can also constrain the charging time of the charging process and the standing time of the standing process in each cycle processing according to a preset time constraint strategy; wherein, the preset time constraint strategy is used to constrain the charging time to be greater than or equal to a first preset time, the standing time to be greater than or equal to the charging time, and the product of the charging time and the charging rate of the charging process to be less than or equal to the first preset power.

[0060] In some embodiments of the present application, when the solid electrolyte interface film generating device performs the current cycle processing on the battery cell based on the current rest time, it can perform the current charging process on the battery cell based on the current charging time and the current charging rate; and then perform the current rest process on the battery cell based on the current rest time.

[0061] In some embodiments of the present application, the current charge rate refers to the ratio of the current used during the current cycle of charging to the rated capacity (Ah) of the battery. For example, charging at a current charge rate of 0.05C means charging at 5% of the rated capacity of the battery. The current charge duration refers to the duration of the continuous charging process at a specific charge rate.

[0062] Exemplarily, the first preset time is 1s, the first preset power can be 0.04%SOC, assuming that the current charging time is expressed as T1, the current standing time is expressed as T2, and the current charging rate is expressed as C1, then the relationship that needs to be satisfied between the current charging time and the current standing time can be expressed as: T2≥T1≥1s, and T1×C1≤0.04%SOC.

[0063] In some embodiments of the present application, the number of periodic processing included in the periodic processing flow can be determined based on the current charging duration, the current charging rate, and the second preset power.

[0064] For example, the second preset power is 8% SOC. Assuming that the current charging time is represented by T1, the current charging rate is represented by C1, and the number of times the periodic processing flow is executed is N, the method of determining the number of times the periodic processing flow is executed based on the current charging time, the current charging rate and the second preset power can be expressed as T1×C1×N≥8%SOC.

[0065] In some embodiments of the present application, the method for forming a solid electrolyte interface film may further include the following steps: Step 102: Detect the voltage of the battery cell.

[0066] In an embodiment of the present application, the device for generating the solid electrolyte interface film can detect the voltage of a battery cell.

[0067] In the embodiment of the present application, the voltage of the battery cell may be the voltage between the positive and negative electrodes of the battery cell.

[0068] In the embodiments of the present application, during each cycle processing, it is necessary to monitor the voltage of the battery cell in real time in order to accurately determine the formation status of the SEI film; the solid electrolyte interface film generating device can use the results of voltage detection to identify the starting and ending points of the film formation reaction.

[0069] Step 103 : In response to the voltage of the battery cell reaching a first voltage, determining to start a film forming reaction.

[0070] Step 104 : In response to the voltage of the battery cell reaching a second voltage, determining that the film forming reaction is finished.

[0071] In an embodiment of the present application, the first voltage may be lower than the second voltage.

[0072] In an embodiment of the present application, the first voltage and the second voltage are specific voltage values ​​set according to the electrochemical behavior of the battery cell during the SEI film formation process, and are used to determine the starting and ending stages of the film formation reaction; wherein the first voltage represents the voltage at which the film formation reaction begins at the negative electrode interface, and the second voltage represents the voltage corresponding to the end of the film formation reaction.

[0073] In some embodiments of the present application, the first voltage may be 2V. When the voltage of the battery cell reaches 2V, it usually marks the beginning of the formation of the solid electrolyte interface film. The film-forming additives in the electrolyte begin to participate in the reaction and react preferentially on the negative electrode graphite surface, thereby promoting the initial formation of the solid electrolyte interface film.

[0074] In an embodiment of the present application, a solid electrolyte interface film generating device determines that the film-forming reaction is completed when it determines that the voltage of the battery cell reaches a second voltage during the process of detecting the voltage of the battery cell, and a battery cell having a solid electrolyte interface film at the negative electrode interface can be obtained; wherein the second voltage represents the voltage corresponding to the end of the film-forming reaction.

[0075] In some embodiments of the present application, the second voltage may be 2.7V.

[0076] It should be noted that the current chemical formation process adopts a one-step film formation method, that is, the battery is charged for the first time using a constant current, and the battery is directly charged to a certain target power. This operation starts before the film formation reaction and covers a long period of time after the film formation reaction is completed; for example, Figure 4 As shown, the relevant formation process uses a constant current method to directly charge the battery to a voltage of 3V, at which time the battery capacity is usually 15% SOC; there are also some methods that charge the battery directly to the shipping capacity, such as 50% SOC, the voltage value corresponding to this capacity is usually 3.3V; or charge the battery directly to 70% SOC, the voltage value corresponding to this capacity is usually 3.5V; and this application accurately identifies the voltage at which the film formation reaction starts and ends, and then performs multiple alternating charge and discharge operations for the process from the start to the end of the film formation reaction, such as Figure 5 As shown, due to the alternating charging and discharging, and the charging capacity is greater than the discharging capacity, the voltage shows a spiral increasing trend, which can help better form the SEI layer.

[0077] In some embodiments of the present application, the solid electrolyte interface film generating device can also perform differential operation processing on the differential capacitance curve data of the battery cell to obtain secondary differential capacitance curve data; wherein the differential capacitance curve data is data that characterizes the mapping relationship between differential capacitance and electrode potential; then, the first voltage and the second voltage are determined based on the positive peak and negative peak in the secondary differential capacitance curve relationship data; wherein the first voltage is less than or equal to the potential corresponding to the positive peak, and the second voltage is greater than or equal to the potential corresponding to the negative peak.

[0078] In the embodiment of the present application, the differential capacitance curve data can be a curve drawn by measuring the changing relationship between the electrode potential and the charge during the charging or discharging process of the battery. The differential capacitance curve can reflect the electrochemical reaction process occurring inside the battery; for example, Figure 6 As shown, in the differential capacitance curve, the ordinate can be the differential capacitance dQ / dV, which reflects the relationship between the rate of change of charge and the rate of change of voltage, and the abscissa can be the voltage. It can be seen that the reaction peak of the additive participating in the film-forming reaction appears between 2V and 2.5V; after performing differential operation on the differential capacitance curve data, the secondary differential capacitance curve data can be obtained, for example, Figure 7 As shown, two peak potentials can be obtained through the secondary differential capacitance curve data, including the voltage corresponding to the positive peak and the voltage corresponding to the negative peak. The first voltage V1 can be less than or equal to the voltage corresponding to the positive peak, and the second voltage V2 can be greater than or equal to the voltage corresponding to the negative peak.

[0079] In some embodiments of the present application, before the battery cell starts the film-forming reaction, that is, before the voltage of the battery cell reaches the first voltage, the battery cell can be charged first to make the voltage of the battery cell reach the first voltage. The charging method of the charging process is not limited in this application. For example, the voltage of the battery cell can be charged to the first voltage by constant current charging.

[0080] In some embodiments of the present application, after the voltage of the battery cell reaches the second voltage through multiple cycles of treatment, that is, after the battery cell has completed the formation of the solid electrolyte interface membrane, the battery cell can continue to be charged. The charging method of the charging process is not limited in this application. For example, the process can be completed by charging and standing. The process can be used to adjust the lithium insertion degree of the negative electrode graphite, that is, the battery SOC, and has a low impact on the solid electrolyte interface membrane.

[0081] The embodiment of the present application provides a method for generating a solid electrolyte interface film, wherein the solid electrolyte interface film generating device performs a periodic treatment process on the battery cell when a film-forming reaction begins at the negative electrode interface of the battery cell, until the film-forming reaction of the battery cell ends, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; wherein the periodic treatment process includes multiple periodic treatments, each periodic treatment includes a charging process and a resting process, and each resting process is performed based on the previous resting process. It can be seen that by starting the periodic treatment process when the film-forming reaction begins at the negative electrode interface of the battery cell, alternating charging and resting processes are performed on the battery cell, and each resting process is performed based on the previous resting process, that is, the execution of the resting process in the next periodic treatment can be determined based on the current resting process, thereby continuing the process until the film-forming reaction ends, thereby ensuring that the formation process of the solid electrolyte interface film is controllable and sufficient, improving the quality of the solid electrolyte interface film, and improving the battery life.

[0082] Based on the above embodiments, in another embodiment of the present application, illustratively, for the film-forming stage of SEI, by performing cyclic treatment multiple times, the additives are evenly distributed on the graphite surface, and the side reactants are transferred to the electrolyte liquid phase in a timely manner, thereby avoiding the side reactants from participating in the formation of the SEI film. This can not only effectively improve the quality of the SEI film, but also significantly extend the service life of the lithium-ion battery.

[0083] In some embodiments of the present application, as mentioned above Figure 6 As shown, in the differential capacitance curve drawn under the current constant current charging formation strategy, a reaction peak in which the additive participates in the film-forming reaction appears between 2V and 2.5V. Based on this, the embodiment of the present application provides the following formation method that can be directly mass-produced. During the formation process, it includes performing multiple cycle treatments for the film-forming stage to generate a good solid electrolyte interface film on the negative electrode interface of the battery cell.

[0084] For example, in the current related formation strategy, after being left at rest for a certain period of time, the battery cell can be charged at a certain charging rate. After being charged for a certain period of time, it can be left at rest again (Rest) or charged to reach the shipping capacity. During this process, the SEI film of the battery cell has already been formed. The formation process of the present application may include: first, after the battery cell is left at rest for 30 seconds, the battery cell is charged at a charging rate of 0.05C until the voltage reaches V1, that is, the voltage at which the film formation reaction starts; then, after a short rest of 30 seconds, multiple cycles can be started. Treatment, each cycle treatment includes a charging process and a standing process, wherein the charging process is charged at a charging rate of 0.05C for T1s, and the standing time is T2s. Multiple cycle treatments are performed alternately and repeated, until the voltage reaches V2, that is, when the film-forming reaction ends, the SEI film is determined to be formed; then the graphite lithium insertion degree can be selectively adjusted, for example, after standing for 30s, it can be charged at a charging rate of 0.1C for 2 minutes, and then it can be stood for 30s, and then charged at a charging rate of 0.33C for 3 minutes, and then it can be stood for 30 seconds.

[0085] For example, in order to accurately identify V1 and V2, the differential capacitance curve can be recalculated to obtain a secondary differential capacitance curve, and then the positive peak and negative peak in the secondary differential capacitance curve are used to determine V1 and V2, where V1 ≤ the voltage corresponding to the positive peak, and V2 ≥ the voltage corresponding to the negative peak.

[0086] In some embodiments of the present application, the discharge rate D1≤charge rate C1≤0.1C; the charge rate and discharge rate in this embodiment may be 0.05C.

[0087] In some embodiments of the present application, for the setting of some parameters in the periodic processing flow, assuming that the current charging time is represented by T1, the current standing time is represented by T2, and the current charging rate is represented by C1, the relationship that needs to be satisfied between the current charging time and the current standing time can be expressed as: T2≥T1≥1s, and T1×C1≤0.04%SOC; in addition, assuming that the number of times the periodic processing is performed in the periodic processing flow is N, then N needs to satisfy T1×C1×N≥8%SOC.

[0088] It should be noted that the current related chemical processes are all one-step film forming methods, that is, the film forming process is completed in one step with a constant current, and its voltage curve is as mentioned above. Figure 4 As shown, it increases linearly; this scheme focuses on the film formation stage, and through the strategy of alternating charging and standing, the additive is distributed more evenly on the graphite surface of the negative electrode; due to the use of the alternating charging and standing strategy, its voltage shows a spiral increase trend, as shown Figure 5As shown, this can help to better form the SEI layer.

[0089] In some embodiments of the present application, since the film formation stage, as the degree of SEI film formation increases, the planned impedance will gradually increase, so a longer static time is required to make the additive evenly distributed on the graphite surface; therefore, in order to more accurately formulate the static time in each cycle treatment, a valid voltage data can be recorded every second during the execution of each cycle treatment, as described above Figure 3 As shown in the figure, during a certain cycle, as the charging process is executed, the voltage gradually increases, and as the static process is executed, the voltage gradually decreases; the static voltage curve in each cycle, that is, the time variable T of the voltage and time curve of each static process, can be mathematically converted to convert time T into ,like Figure 8 As shown, the voltage and time The curve between the time , and by comparing voltage and time The curve between the linear fitting, such as Figure 9 As shown, the intercept of the curve is the final equilibrium voltage Vt, that is, the current equilibrium voltage is obtained.

[0090] For example, assuming that the current process is the nth cycle, the current initial voltage is expressed as , the current equilibrium voltage is expressed as , the current charging current is ; The difference between the current initial voltage and the current equilibrium voltage can be expressed as , the current internal resistance information can be expressed as .

[0091] For example, Figure 10 As shown in Figure 2, as the number of pulses (i.e., the number of times the cycle is processed) increases, the voltage difference will change accordingly. At the same time, as shown in Figure 2 Figure 11 As shown in the figure, as the number of pulses increases, the internal resistance will also change; the greater the internal resistance, the longer the time required for each static process, and vice versa; the time of the static process needs to meet or ,in, Indicates the internal resistance value corresponding to the nth cycle processing, is the duration of the static process in the nth cycle processing, Indicates the internal resistance value of the corresponding process for the n-1 cycle processing. Indicates the duration of the static process in the n-1th cycle processing.

[0092] For example, for mass-produced battery cells, a fixed shipping power is generally required. Therefore, after film formation, there will be high-rate charging steps such as 0.1C and 0.33C. On the one hand, the SEI film can be repaired to a certain extent, but the repair effect is weak. On the other hand, it is also used to adjust the power of the lithium battery for shipment. For example, as shown in Table 1 below, after obtaining a battery cell with an SEI film, multiple cycle processes can be continued to charge the battery cell to the power or voltage required for shipment: Table 1

[0093] In some embodiments of the present application, in order to better form the SEI layer, slow charging can be performed directly after formation; for example, the voltage required for shipment is set to the maximum voltage Vmax, the Vmax of lithium iron phosphate (LFP) is 3.65V, and the Vmax of nickel cobalt manganese oxide (NCM) is 4.4V. The voltage of the battery cell can be directly charged to the above-mentioned maximum voltage through the charging process of the formation stage, or after charging to 100% SOC, 50% of the power can be discharged at a rate of 0.05~0.33C to achieve 50% of the power required for shipment; generally speaking, the shipment power is between 30%~80% SOC.

[0094] For example, considering the timeliness of the solution, in the actual production process, the lithium-ion battery cell after injection can be taken and subjected to high-temperature immersion at 45°C to 55°C for 20 to 30 hours. After the electrolyte fully infiltrates the positive and negative electrode sheets in the battery cell, the lithium-ion battery cell is charged and formed for the first time. The formation temperature is 45 to 55°C. By evacuating the lithium-ion battery cell and maintaining a negative pressure state throughout the process, the gas generated by the SEI film formation side reaction is promoted to be discharged in time. The formation process in an actual application scenario is shown in Table 2 below: Table 2

[0095] In some embodiments of the present application, as mentioned above Figure 5 As shown, due to multiple cyclic treatments, when the voltage reaches the second voltage, for example, 2.5V, the concentration of additives and side reactants in the SEI film formation process diffuses, resulting in a significant decrease in the voltage relaxation process. It can be seen that the present application stops operating when the voltage reaches the second voltage, and can also achieve the same formation improvement effect as stopping the formation when the voltage reaches 3.0V.

[0096] For example, to verify the SEI film between the method for forming the solid electrolyte interface film of the embodiment of the present application and the current related formation process, the battery cells obtained by the two methods can be cycled. The improved group is the strategy of the periodic treatment process of the present application, and the baseline group is the current constant current discharge formation process. The cycle strategy can be shown in Table 3 below: Table 3

[0097] For example, Figure 12 As shown, a charge-discharge cycle test at a rate of 1C at 45°C can be performed. It can be determined that compared to the current related constant current charging baseline group battery cells, the alternating charge and discharge strategy of the embodiment of the present application, that is, the battery cells obtained by the improved group for formation, have formed a better quality SEI layer. The performance of the SEI film is more stable during the cycle, so the corresponding capacity decay becomes slower. At the 50th cycle, the capacity retention rate of the baseline group is 95.9%, and that of the improved group is 96.2%, an increase of 0.3%. Compared with the current related methods of improving the SEI film quality through graphite improvement, such as low lithium consumption graphite, or through additive improvement, such as through high film quality additives, this application is the first in the industry to address the problem of uneven concentration of additives and side reactants during formation, and propose effective and low-cost improvement measures. In the experiment to verify the effect, the design, electrolyte, and additives of the baseline and improved group batteries are the same. The only difference is that this application adopts a method of performing a periodic treatment process during the film formation stage to produce a significant improvement in battery life.

[0098] The embodiment of the present application provides a method for generating a solid electrolyte interface film, wherein the device for generating the solid electrolyte interface film performs a periodic treatment process on the battery cell when a film-forming reaction begins at the negative electrode interface of the battery cell, until the film-forming reaction of the battery cell ends, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; wherein the periodic treatment process includes multiple periodic treatments, and each periodic treatment includes a charging process and a resting process. It can be seen that by starting the periodic treatment process when a film-forming reaction begins at the negative electrode interface of the battery cell, alternating charging and resting processes are performed on the battery cell, and each resting process is performed based on the previous resting process, that is, the execution of the resting process in the next periodic treatment can be determined based on the current resting process, thereby continuing the process until the film-forming reaction ends, thereby ensuring that the formation process of the solid electrolyte interface film is controllable and sufficient, improving the quality of the solid electrolyte interface film, and improving the battery life.

[0099] Based on the above embodiment, in another embodiment of the present application, a device for generating a solid electrolyte interface film is provided, such as Figure 13As shown, the solid electrolyte interface film generating device 1 may include a periodic processing module 11 and a voltage detection module 12 .

[0100] The periodic processing flow module 11 is used to execute a periodic processing flow on the battery cell when a film-forming reaction begins at the negative electrode interface of the battery cell, until the film-forming reaction of the battery cell is completed, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; wherein the periodic processing flow includes multiple periodic processings, each periodic processing includes a charging process and a rest process, and each rest process is executed based on the previous rest process.

[0101] In some embodiments of the present application, the periodic processing flow module 11 is also used to obtain voltage change data of the battery cell during the current static process during the execution of the current periodic processing; wherein the voltage change data is used to determine the relationship between the voltage change of the battery cell and time; the current static process is the static process in the current periodic processing; the next static process in the next periodic processing is executed according to the voltage change data; the first static process in the first periodic processing after the next periodic processing is executed based on the voltage change data of the next static process, until the periodic processing flow is completed.

[0102] In some embodiments of the present application, the periodic processing flow module 11 is further used to perform mathematical conversion on the time variable of the voltage change data to obtain the converted voltage change data; perform linear fitting processing on the converted voltage change data to determine the current equilibrium voltage; determine the first target information based on the current equilibrium voltage, and execute the next static process according to the first target information.

[0103] In some embodiments of the present application, the periodic processing flow module 11 is also used to obtain the current initial voltage of the battery cell at the beginning of the current rest process; determine the current internal resistance information based on the difference between the current initial voltage and the current equilibrium voltage, and the current charging current; and determine the ratio of the current rest time to the current internal resistance information as the first target information; wherein the current rest time is the duration of the current rest process.

[0104] In some embodiments of the present application, the periodic processing flow module 11 is also used to obtain the duration and real-time voltage data of the next static process during the execution of the next static process; determine the second target information based on the real-time voltage data and the duration; and stop the next static process when the second target information is equal to the first target information.

[0105] In some embodiments of the present application, the periodic processing flow module 11 is also used to constrain the charging time of the charging process and the rest time of the rest process in each periodic processing according to a preset time constraint strategy; wherein the preset time constraint strategy is used to constrain the charging time to be greater than or equal to a first preset time, the rest time to be greater than or equal to the charging time, and the product of the charging time and the charging rate of the charging process to be less than or equal to the first preset power.

[0106] The voltage detection module 12 is used to detect the voltage of the battery cell during each charging process or static process, and in response to the voltage of the battery cell reaching a first voltage, determine the start of the film forming reaction; in response to the voltage of the battery cell reaching a second voltage, determine the end of the film forming reaction; the first voltage is less than the second voltage.

[0107] The embodiment of the present application provides a device for generating a solid electrolyte interface film, including a periodic processing flow module, which is used to perform a periodic processing flow on the battery cell when a film-forming reaction begins at the negative electrode interface of the battery cell, until the film-forming reaction of the battery cell is completed, thereby obtaining a battery cell having a solid electrolyte interface film at the negative electrode interface; wherein the periodic processing flow includes multiple periodic processings, each periodic processing includes a charging process and a static process, and each static process is performed based on the previous static process. It can be seen that by starting the periodic processing flow when the film-forming reaction begins at the negative electrode interface of the battery cell, alternating charging and static processes are performed on the battery cell, and each static process is performed based on the previous static process, that is, the execution of the static process in the next periodic processing can be determined based on the current static process, thereby continuing the process until the film-forming reaction is completed, thereby ensuring that the formation process of the solid electrolyte interface film is controllable and sufficient, improving the quality of the solid electrolyte interface film, and improving the battery life.

[0108] In addition, the functional modules in this embodiment may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated units may be implemented in the form of hardware or software functional modules.

[0109] If the integrated unit is implemented as a software functional module and not sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this embodiment, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) or a processor to execute all or part of the steps of the method of this embodiment. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0110] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of hardware embodiments, software embodiments, or embodiments combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage and optical storage) containing computer-usable program code.

[0111] The present application is described with reference to the implementation flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the flowchart. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0112] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which is implemented in the implementation flow diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0113] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process described in the flowchart. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0114] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A method for forming a solid electrolyte interface film, characterized in that: The method comprises: When a film-forming reaction begins at the negative electrode interface of a battery cell, performing a periodic treatment process on the battery cell until the film-forming reaction of the battery cell is completed, thereby obtaining the battery cell having a solid electrolyte interface film at the negative electrode interface; The periodic processing flow includes multiple periodic processings, each periodic processing includes a charging process and a rest process, and each rest process is executed based on the previous rest process.

2. The method for forming a solid electrolyte interface film according to claim 1, wherein: The periodic processing process for the battery cell includes: During the execution of the current cycle processing, obtaining voltage change data of the battery cell during the current static process; wherein the voltage change data is used to determine the relationship between the voltage change of the battery cell and time; the current static process is the static process in the current cycle processing; executing a next rest process in a next cycle processing according to the voltage change data; The first static process in the first periodic process after the next periodic process is executed based on the voltage change data of the next static process until the periodic process flow is completed.

3. The method for forming a solid electrolyte interface film according to claim 2, wherein: The step of executing a next static process in a next cycle processing according to the voltage change data includes: Performing mathematical conversion on the time variable of the voltage change data to obtain converted voltage change data; Perform linear fitting on the converted voltage change data to determine the current equilibrium voltage; First target information is determined based on the current equilibrium voltage, and the next rest process is performed according to the first target information.

4. The method for forming a solid electrolyte interface film according to claim 3, wherein: The determining first target information based on the current equilibrium voltage includes: Obtaining a current initial voltage of the battery cell when the current rest process begins; determining current internal resistance information according to a difference between the current initial voltage and the current equilibrium voltage, and a current charging current; The ratio of the current static time to the current internal resistance information is determined as the first target information; wherein the current static time is the duration of the current static process.

5. The method for forming a solid electrolyte interface film according to claim 4, wherein: The performing the next static process according to the first target information includes: During the execution of the next static process, obtaining the duration and real-time voltage data of the next static process; determining second target information based on the real-time voltage data and the duration; When the second target information is equal to the first target information, the next rest process is stopped.

6. The method for forming a solid electrolyte interface film according to any one of claims 1 to 5, characterized in that: The method further comprises: Constraining the charging time of the charging process and the resting time of the resting process in each of the cycle processing according to a preset time constraint strategy; Among them, the preset time constraint strategy is used to constrain the charging time to be greater than or equal to a first preset time, the static time to be greater than or equal to the charging time, and the product of the charging time and the charging rate of the charging process is less than or equal to a first preset power.

7. The method for forming a solid electrolyte interface film according to any one of claims 1 to 5, characterized in that: The method further comprises: detecting the voltage of the battery cell; In response to the voltage of the battery cell reaching a first voltage, determining to start a film forming reaction; In response to the voltage of the battery cell reaching a second voltage, it is determined that the film forming reaction is completed; the first voltage is less than the second voltage.

8. A device for forming a solid electrolyte interface film, characterized in that: include: a periodic treatment process module, configured to, when a film-forming reaction begins at the negative electrode interface of a battery cell, execute a periodic treatment process on the battery cell until the film-forming reaction of the battery cell is completed, thereby obtaining the battery cell having a solid electrolyte interface film at the negative electrode interface; The periodic processing flow includes multiple periodic processings, each periodic processing includes a charging process and a rest process, and each rest process is executed based on the previous rest process.

9. The solid electrolyte interface film forming device according to claim 8, characterized in that: The periodic processing flow module is also used to obtain the voltage change data of the battery cell during the current static process during the execution of the current periodic processing; and to execute the next static process in the next periodic processing based on the voltage change data; and to execute the first static process in the first periodic processing after the next periodic processing based on the voltage change data of the next static process, until the periodic processing flow is completed; wherein the voltage change data is used to determine the relationship between the voltage change of the battery cell and time; and the current static process is the static process in the current periodic processing.

10. The solid electrolyte interface film forming device according to claim 9, characterized in that: The periodic processing flow module is further configured to perform a mathematical conversion on the time variable of the voltage change data to obtain converted voltage change data; perform a linear fitting process on the converted voltage change data to determine a current equilibrium voltage; and determine first target information based on the current equilibrium voltage, and execute the next static process according to the first target information.

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