Cell formation method

Abstract

Provided in the present application is a cell formation method, comprising the following steps: dividing cells into a control sample cell and a cell to be tested; subjecting the control sample cell to electrolyte filling and standing, then performing formation with an injection port being in an open state, and on the basis of the amount of gas generated during the formation process of the control sample cell and the charging SOC of the control sample cell, constructing a gas production curve of formation; dividing the obtained curve into three consecutive segments, wherein the cumulative amount of gas generated during the formation process corresponding to a first segment of the curve accounts for 1% of the total gas amount of the formation process, the cumulative amount of gas generated during the formation process corresponding to a third segment of said curve accounts for 1% of the total gas amount of the formation process, the charging SOC of the cell corresponding to a connection point between the first segment of said curve and a second segment of said curve is taken as a gas production initial SOC, and the charging SOC of the cell corresponding to a connection point between the second segment of said curve and the third segment of said curve is taken as a gas production cutoff SOC; and on the basis of the gas production charging SOC and the gas production cutoff SOC, performing formation on the cell to be tested that has been subjected to electrolyte filling and standing.

Description

A battery cell formation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410002369.X, filed on January 2, 2024, entitled “A method for forming a battery cell,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a formation method for a battery cell. Background Art

[0004] Battery cells are widely used in electronic devices such as mobile phones, laptop computers, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and power tools.

[0005] During the production of battery cells, they must be formed. This process is the first charge of the battery, activating the internal positive and negative electrode materials. The formation process plays a key role in the performance of the battery cells, and improving the efficiency of formation is a pressing issue.

[0006] Summary of the Invention

[0007] The present invention provides a method for forming a battery cell, comprising the following steps:

[0008] Dividing the battery cells into control sample battery cells and battery cells to be tested;

[0009] Taking a control sample battery cell after injection and standing, and performing formation with the injection port open, and constructing a formation gas production curve based on the gas production during the formation process of the control sample battery cell and the charging SOC of the control sample battery cell;

[0010] The obtained formation gas production curve is divided into three consecutive segments, the cumulative gas production of the formation process corresponding to the first segment of the curve accounts for 1% of the total gas production of the formation process, and the cumulative gas production of the formation process corresponding to the third segment of the curve accounts for 1% of the total gas production of the formation process. The charging SOC of the battery cell corresponding to the connection point of the first segment of the curve and the second segment of the curve is used as the gas production initial SOC, and the charging SOC of the battery cell corresponding to the connection point of the second segment of the curve and the third segment of the curve is used as the gas production cut-off SOC;

[0011] After injection and resting, the battery cells to be tested are formed. The formation process includes three stages:

[0012] In the first stage, the liquid injection port of the battery cell is closed, and the battery cell is charged with a constant current I1 until the charging SOC of the battery cell does not exceed the initial SOC of gas production;

[0013] In the second stage, the liquid injection port of the battery cell is in an open state, and the battery cell is charged until the charging SOC of the battery cell is not lower than the gas production cut-off SOC;

[0014] In the third stage, the battery cell injection port is closed, and the battery cell is charged until the battery cell reaches the charging cut-off voltage.

[0015] In the embodiment of the present application, a control sample battery cell is formed using the same formation process as that of the battery cell to be tested to obtain a formation gas production curve of the battery cell. According to the formation gas production curve, the charging SOC corresponding to the start time and the stop time of gas production in the formation process of the battery cell to be tested can be intuitively obtained. These two charging SOCs are used as the basis for judging whether to open and close the liquid injection port during the formation process. When the charging SOC reaches the initial gas production SOC, the liquid injection port is opened for open formation. When the charging SOC reaches the gas production cut-off SOC, the liquid injection port is closed for closed formation. The opening / closing operation of the liquid injection port is completed in a timely and accurate manner without relying on an external gas production detection device, thereby simplifying the formation process.

[0016] In some embodiments of the present application, the second stage includes: the liquid injection port of the battery cell is in an open state, the battery cell is charged to a first state with a constant current of current I2, and then charged with a constant voltage of voltage U1 until the charging SOC of the battery cell is not lower than the gas production cut-off SOC.

[0017] In some embodiments of the present application, the third stage includes: the liquid injection port of the battery cell is in a closed state, and the battery cell is charged at a constant voltage of voltage U1 to a charging cut-off voltage.

[0018] In some embodiments of the present application, the current I2 is 0.3C to 0.5C.

[0019] In some embodiments of the present application, the voltage U1 is 2.5V to 3.7V.

[0020] In some embodiments of the present application, the first state is when the charging SOC of the battery cell reaches 30% SOC to 45% SOC.

[0021] In some embodiments of the present application, the second stage includes: the liquid injection port of the battery cell is in an open state, and the battery cell is charged with a constant current I3 until the charging SOC of the battery cell is not lower than the gas production cut-off SOC.

[0022] In some embodiments of the present application, the third stage includes: the liquid injection port of the battery cell is in a closed state, the battery cell is charged to the second state with a constant current of current I3, and then charged to the charging cut-off voltage with a constant voltage of voltage U2.

[0023] In some embodiments of the present application, the current I3 is 0.3C to 0.5C.

[0024] In some embodiments of the present application, the voltage U2 is 2.5V to 3.7V.

[0025] In some embodiments of the present application, the current I1 is 0.1C to 0.2C.

[0026] In some embodiments of the present application, the charging cut-off voltage is 3.7V to 4.5V.

[0027] In some embodiments of the present application, the battery cell is charged at a constant current of I1 until the charging SOC of the battery cell does not exceed the initial SOC of gas production, and then left to stand for 10s to 30s.

[0028] In some embodiments of the present application, the formation temperature of the formation process is 40°C to 55°C.

[0029] In some embodiments of the present application, the formation pressure of the formation process is -65KPa to -90KPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] FIG1 is a schematic flow chart of a battery cell formation method according to an embodiment of the present application.

[0032] FIG2 is a schematic structural diagram of a gas production detection device provided in an embodiment of the present application.

[0033] FIG3 is a graph showing a gas production curve obtained in an embodiment of the present application.

[0034] FIG4 is a picture of a fresh electrode interface obtained by disassembling a battery cell after formation in Example 1 of the present application.

[0035] FIG5 is a picture of the fresh electrode interface obtained by disassembling the battery cell after formation in Comparative Example 3 of the present application.

[0036] Explanation of the reference numerals: 1. control sample battery cell; 2. water storage bucket; 3. measuring cylinder; 4. exhaust pipe; 5. drain pipe. DETAILED DESCRIPTION

[0037] Below, with appropriate reference to the accompanying drawings, the embodiments of the sodium ion battery positive electrode material and its preparation method, the positive electrode sheet, the secondary battery and the electronic device of the present application are specifically disclosed in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0038] " range " disclosed in the application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range limited in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a particular parameter, it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the application, unless otherwise specified, the numerical range " ab " represents an abbreviation of any real number combination between a and b, characterized in that a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0040] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0041] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0042] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0043] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0044] Unless otherwise specified, the terms "connected" and "connection" in this application should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection, indirect connection through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0045] If not otherwise specified, in this application, the term "attach" refers to connection by adhesion, coating, etc.

[0046] Unless otherwise specified, in this application, the terms "first", "second", "third", "fourth", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0047] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be intercalated and extracted between the positive and negative electrodes of a battery cell, including but not limited to lithium ions, sodium ions, etc.

[0048] The term "plurality" used in this application refers to two or more (including two).

[0049] In the embodiments of the present application, battery cells may include lithium-ion secondary battery cells, lithium-ion primary battery cells, lithium-sulfur battery cells, sodium-lithium-ion battery cells, etc., and the embodiments of the present application do not limit this. Battery cells may be cylindrical, flat, rectangular, or other shapes, and the embodiments of the present application do not limit this. Battery cells are generally divided into three types based on the packaging method: cylindrical battery cells, prismatic battery cells, and soft-pack battery cells, and the embodiments of the present application do not limit this.

[0050] The battery referred to in the embodiments of this application refers to a single physical module that includes one or more battery cells to provide higher voltage and capacity. For example, the battery referred to in this application may include a battery module or a battery pack. A battery generally includes a casing that encloses one or more battery cells. The casing prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells.

[0051] A battery cell consists of a housing, an electrode assembly, and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. A battery cell primarily operates by allowing metal ions to migrate between the positive and negative electrode sheets through the electrolyte.

[0052] Formation is the process of using a certain charge and discharge method to activate the battery cell after injection to form the SEI film. The quality of the SEI film directly affects the battery cell's electrical properties such as cycle life, stability and self-discharge. During the battery cell formation process, the active material inside the battery cell is activated, the positive electrode material begins to release lithium ions, and the lithium ions begin to move in the system. After being solvated on the positive electrode surface, they pass through the diaphragm to reach the negative electrode surface. After the solvated lithium ions come into direct contact with the negative electrode and are embedded in the negative electrode material on the surface of the negative electrode, the electrolyte will undergo reduction and decomposition on the surface of the negative electrode material, generating byproduct gases while forming a solid electrolyte interface film (SEI film). These gases need to be discharged in a timely manner through the injection hole of the battery cell to ensure that the lithium ion channel is not blocked by bubbles and reduce the impact of battery interface abnormalities on battery performance.

[0053] On the other hand, the battery cell needs to be kept dry during the formation process, because excessive water in the battery cell will react with the electrolyte LiPF6 in the electrolyte to produce by-products such as POF3, LiF and HF. POF3 and LiF will be deposited on the surface of the SEI film, resulting in increased polarization, increased battery internal resistance, and abnormal battery interface; HF has a corrosive effect on the positive electrode material and the current collector, which will affect the reliability of the battery. Therefore, the humidity inside the battery cell needs to be controlled during the formation process.

[0054] In the current formation process, since the formation exhaust needs to be considered while controlling the humidity inside the battery cell, it is necessary to control the environment of the entire formation room in a dry state (generally controlling the relative humidity to ≤2%). This formation method has strict requirements on environmental conditions and high energy consumption. In order to improve the problem of high requirements on environmental humidity and high energy consumption in the current formation process, a formation method combining open exhaust and closed formation is proposed, that is, the liquid injection port is opened for exhaust during the gas production stage of the battery cell formation, and the liquid injection port is closed for closed formation during the non-gas production stage of the battery cell formation. This combination of open exhaust and closed formation can timely discharge the gas generated during the internal formation process of the battery. During the exhaust process, due to the high air pressure inside the battery, external water vapor is difficult to enter, which can reduce the reaction between water and electrolyte. Closing the port during the non-gas production stage of formation can also have the effect of sealing the internal environment of the battery to prevent water from entering.

[0055] Although the formation method that combines open formation and closed formation can reduce the requirements for the formation environment to a certain extent, the timing of opening and closing has not been deeply explored. The timing of opening or closing the liquid injection port has a great influence on the formation effect. If the liquid injection port is opened too early, there is no gas inside the battery to be discharged from the liquid injection port, and external gas will enter the battery and react with the electrolyte; if the liquid injection port is opened too late, too much gas will accumulate inside the battery, causing the battery to swell. Similarly, if the battery liquid injection port is closed too early, the gas inside the battery cannot be completely discharged, resulting in gas pressure. If the liquid injection port is closed too late, water vapor will enter the battery. In addition, in the related art, whether gas is produced during the formation process is usually judged by the gas production. After the battery formation starts to produce gas, the liquid injection port is opened for formation. When the gas production is detected, the liquid injection port is closed for closed formation. This detection method requires the installation of additional detection equipment and is not suitable for large-scale application and promotion.

[0056] In view of the problems existing in the relevant technology, the embodiment of the present application provides a battery cell formation method that opens first and then closes. This method combines the formation characteristics of the battery cell, determines the time nodes for opening and closing the liquid filling port through the charging SOC during the battery formation process, and then opens and closes the battery liquid filling port in time.

[0057] As shown in FIG1 , an embodiment of the present application provides a battery cell formation method, the method comprising the following steps:

[0058] S100, dividing the battery cells into control sample battery cells and battery cells to be tested;

[0059] During the battery cell formation process, cells of the same specifications exhibit identical formation characteristics. These identical specifications refer to cells with identical outer shell dimensions, electrode assemblies, electrolytes, and electrolyte injection volumes. Identical formation characteristics mean that, at the same formation moment, the cells exhibit identical gas production and charge SOC. Therefore, the battery cells are divided into control sample cells and test cells. By performing formation testing on the control sample cells, the formation characteristics of the test cells can be determined.

[0060] S200, taking a control sample battery cell after injection and rest, performing formation with the injection port open, and constructing a formation gas production curve based on the gas production during the formation of the control sample battery cell and the charging SOC of the control sample battery cell;

[0061] In the embodiments of the present application, SOC refers to the state of charge of the battery, which is the ratio of the current remaining charge of the battery to the rated charge. SOC can reflect the charging state of the battery cell during the formation process.

[0062] The gas production of the battery cell during the formation process will change regularly with the formation time, and the formation charging SOC will also change with the formation time. By detecting and recording the gas production and charging SOC of the control sample battery cell at different times during the formation process, a formation gas production curve showing the change of gas production with charging SOC can be constructed. According to the formation gas production curve, the corresponding gas production of the control sample battery cell at different charging SOCs can be intuitively obtained, and then the corresponding gas production of the battery cell to be tested at different charging SOCs can be obtained.

[0063] In the embodiment of the present application, the formation process of the control sample battery cell is the same as the formation process of the battery cell to be tested.

[0064] In the embodiments of the present application, the formation gas production curve can be a curve drawn with the charging SOC as the horizontal axis and the gas production as the vertical axis, or a curve drawn with the gas production as the horizontal axis and the charging SOC as the vertical axis. In the process of constructing the formation gas production curve, abnormal points can be eliminated. The gas production and charging SOC corresponding to multiple time points can be collected by a detection device.

[0065] In some embodiments, the gas production during the formation of the control sample battery cells can be detected by gas detection equipment such as a gas flow meter, a barometer, and a pressure sensor.

[0066] FIG2 shows an apparatus for detecting gas production at multiple formation moments using a water displacement method in one embodiment of the present application. As shown in FIG2 , the apparatus comprises a control sample battery cell, a water storage bucket, a graduated cylinder, an exhaust pipe, and a drain pipe. The battery sample is placed in the formation storage location, and an exhaust pipe is connected to the liquid injection port. The other end of the exhaust pipe is connected to the upper end of a water storage bottle filled with water and is not inserted into the water. The water storage bottle is filled with water to 90% of its volume. A drain pipe is connected to the water storage bottle, one end of the drain pipe is inserted into the bottom of the water, and the other end is connected to a graduated cylinder. The connections between the exhaust pipe and the liquid injection port, the exhaust pipe and the water storage bottle, and the drain pipe and the water storage bottle are all kept sealed to prevent air leakage. The above apparatus can convert the detection of gas production during the formation process into the detection of drainage volume. The drainage volume collected in the graduated cylinder is equivalent to the gas production corresponding to the battery cell formation process.

[0067] At the start of formation, gases generated within the battery cell are discharged through the exhaust pipe into the water storage bottle. The increased pressure in the water storage bottle causes the water in the water storage bottle to be discharged through the drain pipe into the graduated cylinder. The volume of the discharged water is recorded in the graduated cylinder. The time when formation begins is recorded as the initial formation time. The time corresponding to each increase in the volume of water in the graduated cylinder by a preset volume is recorded as multiple times. The corresponding charge state of charge (SOC) at each time is recorded. A drainage volume-charge SOC curve is plotted to obtain the formation gas production curve.

[0068] In the above embodiment, the preset volume may include 1 mL, 2 mL, 3 mL, 5 mL, 8 mL, and 10 mL. Preferably, the preset volume may be 2 mL, 3 mL, or 5 mL. Selecting the above preset volume allows for obtaining a more accurate trend when constructing a formation gas production curve, resulting in a formation gas production curve that better matches the actual gas production state.

[0069] In the above embodiment, the exhaust volume can also be detected by recording the weight of the discharged water. The weight of the discharged water at multiple moments is continuously recorded using equipment such as a balance and an electronic scale. A drainage weight-charging SOC curve is drawn based on the drainage weight and the charging SOC at the corresponding moment, and a gas production curve can also be obtained.

[0070] S300, dividing the obtained formation gas production curve into three consecutive segments, wherein the cumulative gas production of the formation process corresponding to the first segment accounts for 1% of the total gas production of the formation process, and the cumulative gas production of the formation process corresponding to the third segment accounts for 1% of the total gas production of the formation process. The charging SOC of the battery cell corresponding to the connection point of the first and second segments is used as the gas production start SOC, and the charging SOC of the battery cell corresponding to the connection point of the second and third segments is used as the gas production cutoff SOC.

[0071] FIG3 shows a formation gas production curve in an embodiment of the present application. In the early stage of formation, the gas production inside the battery sample is relatively small. At this stage, the detection device is almost unable to detect gas. In the formation gas production curve with formation SOC as the horizontal coordinate and gas production as the vertical coordinate, the slope of the formation gas production curve is close to 0. As the formation time increases, the gas production continues to increase. During this process, the detection device can detect that gas is generated inside the battery cell, and as the formation time increases, the gas production continues to increase. At this stage, in the formation gas production curve with formation SOC as the horizontal coordinate and gas production as the vertical coordinate, the curve is presented as having a larger slope. As the formation time continues to increase, the gas production that the detection device can detect gradually decreases. At this stage, in the formation gas production curve with formation SOC as the horizontal coordinate and gas production as the vertical coordinate, the slope of the formation curve is presented as gradually decreasing. As the formation time increases further, the gas production continues to decrease until no gas is produced, and the detection device can hardly detect gas production. At this stage, in the formation gas production curve with the formation SOC as the horizontal axis and the gas production as the vertical axis, the slope of the formation gas production curve approaches 0.

[0072] The formation gas production curve is divided into three continuous segments. The first segment corresponds to the initial stage of the formation process. The cumulative gas production during this stage accounts for 1% of the total gas production during the formation process. It can be considered that almost no gas is produced during this stage, and this stage is classified as the non-gas production stage. The second segment corresponds to the intermediate stage of the formation process. During this stage, a large amount of gas is produced during the formation process, and the cumulative gas production accounts for 98% of the total gas production during the formation process. Almost all the gas during the formation process is produced during this stage, and this stage is classified as gas production. The third segment corresponds to the late stage of the formation process. The cumulative gas production during this process accounts for 1% of the total gas production during the formation process. It can be considered that almost no gas is produced during this stage, and this stage is classified as the non-gas production stage.

[0073] In the above embodiment, the formation gas production curve of the control sample battery cell is divided according to the gas production amount to obtain the initial gas production SOC and the gas production cut-off SOC, and the initial gas production SOC and the gas production cut-off SOC are used as the basis for judging whether gas is produced during the formation process of the battery cell to be tested. Specifically, the battery cell to be tested is formed with the liquid injection port closed until the charging SOC reaches the initial gas production SOC, the liquid injection port is opened for open formation, and the formation is continued until the charging SOC of the battery cell to be tested reaches the gas production cut-off SOC, and the liquid injection port is closed for closed formation. Therefore, the time nodes of opening and closing the liquid injection port are judged by the charging SOC during the formation process of the battery cell, and there is no need to set up an additional detection device for gas production detection, which can greatly simplify the formation process.

[0074] S400: After injection and resting, the battery cells to be tested are formed. The formation process includes three stages:

[0075] In the first stage, the liquid injection port of the battery cell is closed, and the battery cell is charged with a constant current I1 until the charging SOC of the battery cell does not exceed the initial SOC of gas production;

[0076] In some embodiments, the current I1 is 0.1C to 0.2C. Charging currents within this range can preliminarily activate the active material and facilitate the formation of a stable SEI film. For example, the current I1 can be 0.10C, 0.11C, 0.12C, 0.13C, 0.14C, 0.15C, 0.16C, 0.17C, 0.18C, 0.19C, or 0.20C.

[0077] During the first stage, closed-cell formation is performed on the battery cells to reduce the ingress of moisture from the external environment. The charging SOC corresponding to the cutoff time of the first stage formation does not exceed the initial SOC for gas production. Preferably, the charging SOC corresponding to the cutoff time of the first stage formation is the initial SOC for gas production. After reaching the charging SOC corresponding to the cutoff time of the first stage formation, the liquid injection port is opened to proceed with the first stage formation.

[0078] In some embodiments, the charging SOC corresponding to the cut-off time of the first stage formation does not exceed the initial SOC of gas production and is not lower than the lower limit SOC, where the lower limit SOC = the initial SOC of gas production + 1% SOC.

[0079] When the charging SOC corresponding to the cut-off time of the first stage formation is lower than the lower limit SOC, the liquid filling port is opened earlier, the amount of gas discharged from the battery cell is less, the internal pressure is lower, and there is a risk of some moisture entering the battery cell.

[0080] In the second stage, the liquid injection port of the battery cell is in an open state, and the battery cell is charged until the charging SOC of the battery cell is not lower than the gas production cut-off SOC;

[0081] In the second stage, the battery cells undergo open-cell formation. Gases generated during the formation process are discharged through the liquid injection port. During the exhaust process, the internal pressure of the battery cells is higher than the external pressure, which can reduce moisture ingress. The charging SOC corresponding to the cutoff time of the second stage formation is not lower than the gas production cutoff SOC. Preferably, the charging SOC corresponding to the cutoff time of the second stage formation is the gas production cutoff SOC. After reaching the charging SOC corresponding to the cutoff time of the second stage formation, the liquid injection port is closed and the third stage formation is carried out.

[0082] In some embodiments, the charging SOC corresponding to the cut-off time of the second stage formation is not lower than the gas production cut-off SOC and does not exceed the upper limit SOC, where the upper limit SOC=the gas production cut-off SOC+5% SOC.

[0083] When the charging SOC corresponding to the cut-off time of the second stage formation exceeds the lower limit SOC, the liquid filling port is opened late, the gas discharge inside the battery cell is small, the internal pressure is small, and there is a risk of some moisture entering the battery cell.

[0084] In the third stage, the battery cell injection port is closed, and the battery cell is charged until the battery cell reaches the charging cut-off voltage.

[0085] In the third stage, the battery cells undergo closed-mouth formation. During this stage, almost no gas is generated during the formation process, and the liquid injection port is closed to reduce the entry of external moisture.

[0086] In some embodiments, the charge cut-off voltage may be 3.7 to 4.5 V. For example, the charge cut-off voltage may be 3.7 V, 3.8 V, 3.9 V, 4.0 V, 4.1 V, 4.2 V, 4.3 V, 4.4 V, or 4.5 V.

[0087] In the embodiment of the present application, a control sample battery cell is formed using the same formation process as that of the battery cell to be tested to obtain a formation gas production curve of the battery cell. According to the formation gas production curve, the charging SOC corresponding to the start time and the stop time of gas production in the formation process of the battery cell to be tested can be intuitively obtained. These two charging SOCs are used as the basis for judging whether to open and close the liquid injection port during the formation process. When the charging SOC reaches the initial gas production SOC, the liquid injection port is opened for open formation. When the charging SOC reaches the gas production cut-off SOC, the liquid injection port is closed for closed formation. The opening / closing operation of the liquid injection port is completed in a timely and accurate manner without relying on an external gas production detection device, thereby simplifying the formation process.

[0088] In the embodiment of the present application, the opening and closing operations of the liquid injection port can be performed by a liquid injection port opening and closing assembly, which can include a switch valve, a battery cell seal, etc. The opening and closing operations of the liquid injection port will not affect the internal formation process of the battery cell.

[0089] In some embodiments, the second stage includes constant current charging and constant voltage charging; and the third stage includes constant voltage charging.

[0090] Specifically, the second stage includes: the liquid injection port of the battery cell is in an open state, the battery cell is charged to a first state with a constant current of current I2, and then charged to a constant voltage of voltage U1 until the charging SOC of the battery cell is not lower than the gas production cut-off SOC;

[0091] The third stage includes: the liquid injection port of the battery cell is in a closed state, and the battery cell is charged at a constant voltage U1 to a charging cut-off voltage.

[0092] In some embodiments, the current I2 is 0.3C to 0.5C. When the formation current is within this range, the active material can be fully activated, which is conducive to the formation of a stable SEI film. For example, the current I2 can be 0.30C, 0.31C, 0.32C, 0.33C, 0.34C, 0.35C, 0.36C, 0.37C, 0.38C, 0.39C, 0.40C, 0.41C, 0.42C, 0.43C, 0.44C, 0.45C, 0.46C, 0.47C, 0.48C, 0.49C, or 0.50C.

[0093] In some embodiments, the voltage U1 is 2.5 V to 3.7 V. For example, the voltage U1 may be 2.5 V, 2.6 V, 2.7 V, 2.8 V, 2.9 V, 3.0 V, 3.1 V, 3.2 V, 3.3 V, 3.4 V, or 3.5 V.

[0094] In some embodiments, the first state is when the battery cell charging SOC reaches 30% to 45% SOC.

[0095] In the above embodiment, the cut-off SOC for constant current charging of the battery cell with the current I2 is lower than the gas generation cut-off SOC.

[0096] In some embodiments, the second stage includes constant current charging; and the third stage includes constant current charging and constant voltage charging.

[0097] Specifically, the second stage includes: the liquid injection port of the battery cell is in an open state, and the battery cell is charged with a constant current I3 until the charging SOC of the battery cell is not lower than the gas production cut-off SOC;

[0098] The third stage includes: the liquid injection port of the battery cell is in a closed state, the battery cell is charged with a constant current I3 to a second state, and then charged with a constant voltage U2 to a charging cut-off voltage.

[0099] In some embodiments, the current I3 is 0.3C to 0.5C. When the formation current is within this range, the active material can be fully activated, which is conducive to the formation of a stable SEI film. For example, the current I3 can be 0.30C, 0.31C, 0.32C, 0.33C, 0.34C, 0.35C, 0.36C, 0.37C, 0.38C, 0.39C, 0.40C, 0.41C, 0.42C, 0.43C, 0.44C, 0.45C, 0.46C, 0.47C, 0.48C, 0.49C, or 0.50C.

[0100] In some embodiments, the voltage U2 is 2.5 V to 3.7 V. For example, the voltage U2 may be 2.5 V, 2.6 V, 2.7 V, 2.8 V, 2.9 V, 3.0 V, 3.1 V, 3.2 V, 3.3 V, 3.4 V, or 3.5 V.

[0101] In some embodiments, the second state is when the battery cell charging SOC reaches 30% to 45% SOC.

[0102] In the above embodiment, the cut-off SOC for constant-current charging of the battery cell with the current I3 is higher than the gas generation cut-off SOC.

[0103] In some embodiments, the cutoff SOC for constant current charging of the battery cell can be equal to the gas production cutoff SOC. In these embodiments, the second stage includes a constant current charging stage, and the third stage includes a constant voltage charging stage. The current of the constant current charging can be the same as I2 or I3, and the voltage of the constant voltage charging can be the same as U1 or U2, which are not listed separately here.

[0104] In some embodiments, the first stage further comprises a resting step.

[0105] Specifically, the first stage includes: charging the battery cell with a constant current I1 until the charging SOC of the battery cell does not exceed the gas generation initial SOC, and then standing for 10 to 30 seconds.

[0106] After the first stage of constant current charging, a rest treatment is performed to stabilize the active materials inside the battery cells and facilitate the formation of a stable SEI film. For example, the rest time can be 10s, 11s, 12s, 13s, 14s, 15s, 16s, 17s, 18s, 19s, 20s, 21s, 22s, 23s, 24s, 25s, 26s, 27s, 28s, 29s, or 30s.

[0107] In some embodiments, the formation temperature in the formation process is 40° C. to 55° C.

[0108] Controlling the formation temperature within the above range can ensure that the electrolyte inside the battery cell has an appropriate viscosity and ion diffusion rate during the formation process, which is beneficial to reducing polarization and improving the formation effect. For example, the formation temperature can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, and 55°C.

[0109] In some embodiments, the formation pressure of the formation process is -65 KPa to -90 KPa.

[0110] The formation pressure is controlled within the above range. By applying a certain negative pressure inside the battery, the electrolyte and active material are fully in contact, which is conducive to improving the formation efficiency. For example, the formation pressure can be -65kPa, -70kPa, -75kPa, -80kPa, -85kPa, or -90kPa.

[0111] Example

[0112] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0113] Example 1

[0114] The control sample battery cell and the battery cell under test are both 150Ah soft-pack lithium-ion batteries, with lithium iron phosphate as the anode active material, hard carbon as the cathode active material, and an electrolyte of 1 mol / L LiPF6 / EC+DMC (volume ratio 1:1). The formation method is as follows:

[0115] S10. Take the control sample battery cell after injection and rest, and perform formation with the injection port open. First, charge it at a constant current of 0.1C to 2% SOC, then charge it at a constant current of 0.3C to 30% SOC, and then charge it at a constant voltage of 3.2V to a charge cutoff voltage of 4.0V. The formation temperature is 45°C and the formation pressure is -70kPa.

[0116] During the formation process, a gas flow meter is connected to the liquid injection port to monitor the gas production in real time. The gas flow meter is used to isolate the interior of the control sample battery cell from the outside world to prevent moisture from entering the control sample battery cell. A formation gas production curve is constructed based on the gas production during the formation process of the control sample battery cell and the charging SOC of the control sample battery cell, with the charging SOC as the horizontal axis and the gas production as the vertical axis.

[0117] S20, dividing the obtained formation gas production curve into three consecutive segments, wherein the cumulative gas production of the formation process corresponding to the first segment of the curve accounts for 1% of the total gas production of the formation process, and the cumulative gas production of the formation process corresponding to the third segment of the curve accounts for 1% of the total gas production of the formation process; the charging SOC of the battery cell corresponding to the connection point of the first segment of the curve and the second segment of the curve is used as the gas production initial SOC, and the charging SOC of the battery cell corresponding to the connection point of the second segment of the curve and the third segment of the curve is used as the gas production cut-off SOC; the gas production initial SOC is 3% SOC, and the gas production cut-off SOC is 20% SOC;

[0118] S30, taking the battery cell to be tested after injection and resting, and performing formation, which includes the following three consecutive stages:

[0119] Stage 1: The battery cell's injection port remains closed, and the battery is charged at a constant current of 0.1C to 2% SOC, then the injection port is opened.

[0120] The second stage: the battery cell's injection port remains open, and the battery is charged at a constant current of 0.3C to 22% SOC, and then the injection port is closed;

[0121] The third stage: the liquid injection port of the battery cell is kept closed, and the battery is charged at a constant current of 0.3C to 30% SOC, and then charged at a constant voltage of 3.2V to a charge cut-off voltage of 4.0V.

[0122] Examples 2 to 6

[0123] The method for constructing the formation gas production curve and the composition of the battery cell are the same as those in Example 1. The specific differences are detailed in Table 1.

[0124] Example 7

[0125] The models of the control sample battery cells and the battery cells to be tested are the same as those in Example 1, and the specific formation method is as follows:

[0126] S10. Take the control sample battery cell after injection and standing, and perform formation with the injection port open. First, charge it to 2% SOC at a constant current of 0.1C, let it stand for 10 seconds, then charge it to 30% SOC at a constant current of 0.3C, and then charge it to a charge cutoff voltage of 4.0V at a constant voltage of 3.2V. The formation temperature is 50°C and the formation pressure is -70KPa.

[0127] During the formation process, a gas flow meter is connected to the liquid injection port to monitor the gas production in real time. The gas flow meter is used to isolate the interior of the control sample battery cell from the outside world to prevent moisture from entering the control sample battery cell. A formation gas production curve is constructed based on the gas production during the formation process of the control sample battery cell and the charging SOC of the control sample battery cell, with the charging SOC as the horizontal axis and the gas production as the vertical axis.

[0128] S20, dividing the obtained formation gas production curve into three consecutive segments, wherein the cumulative gas production of the formation process corresponding to the first segment of the curve accounts for 1% of the total gas production of the formation process, and the cumulative gas production of the formation process corresponding to the third segment of the curve accounts for 1% of the total gas production of the formation process; the charging SOC of the battery cell corresponding to the connection point of the first segment of the curve and the second segment of the curve is used as the gas production initial SOC, and the charging SOC of the battery cell corresponding to the connection point of the second segment of the curve and the third segment of the curve is used as the gas production cut-off SOC; the gas production initial SOC is 3% SOC, and the gas production cut-off SOC is 20% SOC;

[0129] S30, taking the battery cell to be tested after injection and resting, and performing formation, which includes the following three consecutive stages:

[0130] Stage 1: The battery cell's injection port remains closed, and the battery is charged at a constant current of 0.1C to 2% SOC. After standing for 10 seconds, the injection port is opened.

[0131] The second stage: the battery cell's injection port remains open, and the battery is charged at a constant current of 0.3C to 21% SOC, and then the injection port is closed;

[0132] The third stage: the liquid injection port of the battery cell is kept closed, and the battery is charged at a constant current of 0.3C to 30% SOC, and then charged at a constant voltage of 3.2V to a charge cut-off voltage of 4.0V.

[0133] Comparative Examples 1-2

[0134] The method for constructing the formation gas production curve and the composition of the battery cell are the same as those in Example 1. The specific differences are detailed in Table 1.

[0135] Comparative Example 3

[0136] Using full-opening chemical formation, the specific methods include:

[0137] The battery cell to be tested after injection and standing was taken for formation. The injection port of the battery cell was kept open and charged at a constant current of 0.1C to 2% SOC, then at a constant current of 0.3C to 26% SOC. Continuing, it was charged at a constant current of 0.3C to 30% SOC, and then at a constant voltage of 3.2V to a charge cut-off voltage of 4.0V. The formation temperature was 50°C and the formation pressure was -70KPa.

[0138] Test section

[0139] The electrode interfaces of the battery cells after formation in each embodiment and comparative example were tested using the following method:

[0140] 1) Fresh electrode interface: Refill and fully charge the formed battery, then disassemble the battery, unfold the positive electrode sheet, obtain a fresh positive electrode interface, and observe whether there are any abnormalities such as black spots, lithium precipitation, and poor exhaust on the positive electrode interface;

[0141] 2) Electrode interface after 50 cycles: After the formed battery is recharged and the capacity is tested, it is cycled for 50 cycles and then fully charged. The battery is then disassembled and the positive electrode sheet is unfolded to obtain the positive electrode interface after 50 cycles of charge and discharge. The positive electrode interface is observed to see if there are any abnormalities such as black spots, lithium deposition, or poor exhaust.

[0142] The test results are shown in Table 2.

[0143] Table 2:

[0144] Figures 4 and 5 show photographs of the fresh positive electrode interfaces obtained after disassembly of the battery cells in Example 1 and Comparative Example 3, respectively. It can be seen that there are serious black spots on the positive electrode interface in Comparative Example 3. The presence of these black spots will lead to lithium precipitation during the cycle, damaging the battery positive electrode interface. In contrast, the electrode interface in Example 1 is good, with no black spots. It can be seen that the use of an open-first-closed formation process can effectively reduce the entry of external moisture into the battery cell, reduce the reaction between moisture and the interior of the battery cell, and reduce damage to the electrode interface.

[0145] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A formation method for a battery cell, comprising the following steps: Dividing the battery cell into a control sample battery cell and a battery cell to be tested; Taking the control sample battery cell after injection and standing, and performing formation with the injection port open, and constructing a formation gas generation curve based on the gas generation amount during the formation process of the control sample battery cell and the charging SOC of the control sample battery cell; Dividing the obtained formation gas generation curve into three consecutive segments. The cumulative gas generation amount during the formation process corresponding to the first segment curve accounts for 1% of the total gas generation amount during the formation process, and the cumulative gas generation amount during the formation process corresponding to the third segment curve accounts for 1% of the total gas generation amount during the formation process. Taking the charging SOC of the battery cell corresponding to the connection point between the first segment curve and the second segment curve as the initial gas generation SOC, and taking the charging SOC of the battery cell corresponding to the connection point between the second segment curve and the third segment curve as the cut-off gas generation SOC; Taking the battery cell to be tested after injection and standing for formation. The formation process includes three stages: The first stage, the injection port of the battery cell is in a closed state, and the battery cell is charged at a constant current of I1 until the charging SOC of the battery cell does not exceed the initial gas generation SOC; The second stage, the injection port of the battery cell is in an open state, and the battery cell is charged until the charging SOC of the battery cell is not lower than the cut-off gas generation SOC; The third stage, the injection port of the battery cell is in a closed state, and the battery cell is charged until the battery cell reaches the charging cut-off voltage.

2. The formation method of the battery cell according to claim 1, wherein, The second stage includes: the injection port of the battery cell is in an open state, and the battery cell is charged at a constant current of I2 to the first state, and then charged at a constant voltage of U1 until the charging SOC of the battery cell is not lower than the cut-off gas generation SOC.

3. The formation method of the battery cell according to claim 2, wherein, The third stage includes: the injection port of the battery cell is in a closed state, and the battery cell is charged at a constant voltage of U1 to the charging cut-off voltage.

4. The formation method for a battery cell according to claim 2 or 3, wherein, The current I2 is 0.3C to 0.5C; and / or The voltage U1 is 2.5V to 3.7V; and / or The first state is that the charging SOC of the battery cell reaches 30% SOC to 45% SOC.

5. The formation method of the battery cell according to claim 1, wherein, The second stage includes: the injection port of the battery cell is in an open state, and the battery cell is charged at a constant current of I3 until the charging SOC of the battery cell is not lower than the cut-off gas generation SOC.

6. The formation method of the battery cell according to claim 5, wherein, The third stage includes: the injection port of the battery cell is in a closed state, and the battery cell is charged at a constant current of I3 to the second state, and then charged at a constant voltage of U2 to the charging cut-off voltage.

7. The formation method for a battery cell according to claim 5 or 6, wherein, The current I3 is 0.3C to 0.5C; and / or The voltage U2 is 2.5V to 3.7V; and / or The second state is that the charging SOC of the battery cell reaches 30% SOC to 45% SOC.

8. The formation method of the battery cell according to any one of claims 1 to 7, wherein, The current I1 is 0.1C to 0.2C; and / or The charging cut-off voltage is 3.7V to 4.5V.

9. The formation method of the battery cell according to any one of claims 1 to 8, wherein, The first stage includes: charging the battery cell at a constant current of I1 until the charging SOC of the battery cell does not exceed the initial gas generation SOC, and then standing for 10s to 30s.

10. The formation method of the battery cell according to any one of claims 1 to 9, wherein, The formation temperature of the described formation process is 40°C to 55°C; and / or the formation pressure of the described formation process is -65 KPa to -90 KPa.

Images