Formation method and application of cylindrical battery

Abstract

The invention provides a formation method of a cylindrical battery, and relates to the technical field of batteries. The formation method comprises the following steps: performing primary liquid injection on the cylindrical battery, performing high-temperature standing on the cylindrical battery in an upright placement state and an inverted placement state in sequence after the primary liquid injection is finished, then performing negative pressure formation on the cylindrical battery, and in the negative pressure formation process, charging the cylindrical battery to 80-100% SOC and then discharging to 40-60% SOC, carrying out secondary liquid injection on the cylindrical battery subjected to negative pressure formation, and after the secondary liquid injection is finished, carrying out high-temperature standing on the cylindrical battery in an upright placement state and an inverted placement state again in sequence; according to the formation method, a mode of inversely placing the cylindrical battery in a high-temperature standing stage after primary liquid injection and a high-temperature standing stage after secondary liquid injection is combined with a charging and discharging mode of firstly charging to a high SOC and then discharging to a low SOC in a negative pressure formation process, so that the infiltration effect and the liquid saturation amount of the cylindrical battery are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a formation method and application of cylindrical batteries. Background Art

[0002] With the rapid development of new energy, various electrical devices are constantly being updated and iterated, from small electronic watches to large electric vehicles. At the same time, consumers' requirements for the service life and endurance of electronic devices and new energy vehicles are also getting higher and higher, and these performances are closely related to lithium-ion batteries. One of the key factors determining the life of lithium-ion batteries is the electrolyte. It can be said that its content basically determines the life of lithium batteries. Because it undertakes the function of lithium-ion transmission, the electrolyte will be continuously consumed during the use of lithium batteries. Once the liquid level is low, the transmission of lithium ions will be blocked, resulting in capacity loss and reduced endurance; further reduction of the liquid level may even lead to the battery being unable to be used and there is a safety risk of lithium precipitation.

[0003] Due to its structural characteristics, the all-pole-ear cylindrical battery has a relatively simple manufacturing method. At the same time, the battery has higher energy density and overcurrent capacity, so it has become the mainstream design method of cylindrical batteries. However, it has an obvious defect that it is difficult to inject liquid, the saturated liquid volume is low, and it is difficult for the electrode sheet to infiltrate liquid. This is caused by its structural characteristics: the cylindrical winding structure itself has a large binding force, making it difficult for the electrolyte to infiltrate. At the same time, in the all-pole-ear process, after the pole ear is flattened, it is more difficult for the positive and negative electrodes to infiltrate liquid at both ends, further resulting in a low saturated liquid volume of the battery and poor infiltration of the electrode sheet; poor infiltration of the electrode sheet will cause lithium precipitation in the battery, affecting the battery life and even bringing safety risks. Therefore, it is particularly important to find a method to improve the electrolyte infiltration effect and saturated liquid volume of cylindrical batteries.

[0004] The existing methods to improve the saturated liquid volume of the battery and electrolyte infiltration mostly optimize the electrolyte, such as adding some additives to optimize the surface tension and improve the infiltration effect. However, this method has limited effect and the manufacturing cost will also increase; the existing technology also optimizes the electrode sheet design and liquid injection method. By reducing the compaction of the positive and negative electrode sheets, increasing the pores, improving the infiltration effect of the electrode sheet, and then increasing the saturated liquid volume by multiple liquid injection methods. However, this method has limited effect and will sacrifice some battery performances.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] Aiming at the deficiencies and defects existing in the prior art, the present invention aims to provide a formation method and application for improving the electrolyte infiltration effect and saturated liquid volume of cylindrical batteries.

[0007] In order to achieve the above object, the following technical solutions are adopted:

[0008] The first object of the present invention is to provide a formation method of a cylindrical battery, including the following steps:

[0009] S1. Perform a first liquid injection on the cylindrical battery. After the first liquid injection is completed, place the cylindrical battery upright and then upside down for high-temperature standing.

[0010] S2. Subject the cylindrical battery after high-temperature standing to negative-pressure formation. During the negative-pressure formation process, first charge the cylindrical battery to 80%-100% SOC, and then discharge it to 40%-60% SOC.

[0011] S3. Perform a second liquid injection on the cylindrical battery after negative-pressure formation. After the second liquid injection is completed, place the cylindrical battery upright and then upside down for high-temperature standing again.

[0012] S4. Subject the cylindrical battery after high-temperature standing again to subsequent sealing and grading.

[0013] Further, on the basis of the above technical solution of the present invention, the liquid injection volume of the first liquid injection is 70-90 wt% of the total liquid injection volume of the cylindrical battery.

[0014] Further, on the basis of the above technical solution of the present invention, in step S1, the temperature of the high-temperature standing is 43-47 °C, and the total time of the high-temperature standing is 22-26 h.

[0015] Further, on the basis of the above technical solution of the present invention, in step S1, the time of high-temperature standing in the upright state is 10-14 h, and the time of high-temperature standing in the upside-down state is 8-16 h.

[0016] Further, on the basis of the above technical solution of the present invention, in step S2, the temperature of the negative-pressure formation is 43-47 °C, and the pressure of the negative-pressure formation is -30 to -55 kPa.

[0017] Further, on the basis of the above technical solution of the present invention, in step S2, the charging current of the negative-pressure formation is 0.05-0.33 C, and the discharging current of the negative-pressure formation is 0.2-0.5 C.

[0018] Further, on the basis of the above technical solution of the present invention, in step S3, the liquid injection volume of the second liquid injection is 10-30 wt% of the total liquid injection volume of the cylindrical battery.

[0019] Further, on the basis of the above technical solution of the present invention, in step S3, the temperature of the high-temperature standing again is 43-47 °C, and the total time of the high-temperature standing again is 22-26 h.

[0020] Further, on the basis of the above technical solution of the present invention, in step S3, the time for the second high-temperature static placement in the upright state is 10 - 14h, and the time for the second high-temperature static placement in the inverted state is 8 - 16h.

[0021] The second object of the present invention is to provide an application of the formation method of the above cylindrical battery in the production of lithium-ion batteries.

[0022] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0023] The present invention provides a formation method for a cylindrical battery. In this formation method, the cylindrical battery is first filled with liquid once. After the first liquid filling is completed, the cylindrical battery is successively placed in an upright state and an inverted state for high-temperature static placement, and then the cylindrical battery is subjected to negative-pressure formation. During the negative-pressure formation process, the cylindrical battery is first charged to 80% - 100% SOC and then discharged to 40% - 60% SOC; the cylindrical battery after negative-pressure formation is subjected to secondary liquid filling, and after the secondary liquid filling is completed, the cylindrical battery is successively placed in an upright state and an inverted state for secondary high-temperature static placement; by combining the method of placing the cylindrical battery in an inverted state during the high-temperature static placement stage after the first liquid filling and the secondary high-temperature static placement stage after the secondary liquid filling and the charge-discharge method of first charging to a high SOC and then discharging to a low SOC during the negative-pressure formation process, the infiltration effect and the saturated liquid volume of the cylindrical battery are effectively improved. Description of the Drawings

[0024] Figure 1 It is a process flow diagram of the formation method of the cylindrical battery under an embodiment provided by the present invention;

[0025] Figure 2 It is a diagram of the negative electrode interface of the cylindrical battery after grading using the formation method of Embodiment 1 of the present invention;

[0026] Figure 3 It is a diagram of the negative electrode interface of the cylindrical battery after 200 cycles using the formation method of Embodiment 1 of the present invention;

[0027] Figure 4 It is a diagram of the negative electrode interface of the cylindrical battery after grading using the formation method of Comparative Example 1 of the present invention;

[0028] Figure 5 It is a diagram of the negative electrode interface of the cylindrical battery after 200 cycles using the formation method of Comparative Example 1 of the present invention. Detailed Embodiments

[0029] To make the objectives, technical solutions and advantages of the present invention clearer, the following will, in conjunction with the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually according to conventional conditions.

[0030] In the ranges disclosed in the present invention, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0031] According to the first aspect of the present invention, there is provided a formation method for a cylindrical battery. The schematic process flow diagram is as Figure 1 shown and includes the following steps:

[0032] S1. Perform a first liquid injection on the cylindrical battery. After the first liquid injection is completed, place the cylindrical battery upright and then upside down for high-temperature standing.

[0033] S2. Subject the cylindrical battery after high-temperature standing to negative-pressure formation. During the negative-pressure formation process, first charge the cylindrical battery to 80%-100% SOC, and then discharge it to 40%-60% SOC.

[0034] S3. Perform a second liquid injection on the cylindrical battery after negative-pressure formation. After the second liquid injection is completed, place the cylindrical battery upright and then upside down for another high-temperature standing.

[0035] S4. Perform subsequent sealing and grading on the cylindrical battery after another high-temperature standing.

[0036] The present invention provides a formation method for a cylindrical battery. This method increases the electrolyte infiltration effect and significantly improves the saturated liquid volume by adding some methods at different stages of the subsequent processes of the battery. The specific methods are as follows:

[0037] In step S1, after the first liquid injection of the cylindrical battery, during the interval of high-temperature standing (resting), by reversing the battery at least once (for example, changing the battery from an upright placement state to an upside-down placement state), the electrolyte can flow quickly, the contact opportunity between the electrode plate and the electrolyte can be improved, and the liquid immersion effect can be improved.

[0038] In step S2, during the negative pressure formation stage, first charge to a high state of charge (SOC), and then discharge to a lower SOC. During this period, the wound core will have a process of expansion and contraction. Specifically, first charge to a high SOC. During this process, the wound core will expand, and each turn of the electrode in the battery cell will have a rapid adsorption effect on the electrolyte, enabling the inner electrode to fully absorb the electrolyte. Then discharge to a low SOC, and the wound core will contract, releasing the space between the wound core and the housing.

[0039] Since the space between the wound core and the housing is released when discharging to a low SOC during the negative pressure formation in step S2, in step S3, after secondary liquid injection and before battery sealing, more free electrolyte can be accommodated, improving the liquid saturation of the battery. At the same time, during the high-temperature standing (soaking) period after secondary liquid injection, perform at least one battery inversion (for example, change the battery from an upright placement state to an inverted placement state), so that the electrolyte deposited at the bottom can flow again, further increasing the contact with the electrode, thereby improving the wetting effect and liquid saturation of the electrode.

[0040] The present invention provides a formation method for improving the electrolyte wetting effect and liquid saturation of a cylindrical battery. By combining the method of inverting the placement of the cylindrical battery during the high-temperature standing process after the first liquid injection and during the high-temperature standing process after the second liquid injection, and the charge and discharge method of first charging to a high SOC and then discharging to a low SOC during the negative pressure formation process, the wetting effect and liquid saturation of the cylindrical battery can be effectively improved.

[0041] In addition, the present invention inverts the cylindrical battery during the high-temperature standing stage after liquid injection instead of during the formation stage. There are the following problems with inverting the battery cell during the formation stage: First, the formation process generally takes only a few hours, and the electrolyte may not flow sufficiently. Second, the formation process is generally negative pressure formation. Inverting the battery cell will cause most of the electrolyte to be sucked away by the negative pressure pipeline, resulting in insufficient electrolyte in the first injection, and too much electrolyte entering the pipeline may cause pipeline blockage or even pipeline corrosion. However, inverting the battery during the high-temperature soaking stage after the formation in the present invention will not have the above problems; at the same time, it will not cause any impact on the equipment, only adding a simple battery cell inversion action during the soaking period.

[0042] As an optional implementation of the technical solution of the present invention, in step S1, the liquid injection volume of the first liquid injection is 70-90 wt% of the total liquid injection volume of the cylindrical battery, such as 70 wt%, 75 wt%, 80 wt%, 85 wt% or 90 wt% etc. and the numerical range between any two points.

[0043] After the first liquid injection, high-temperature standing is carried out. As an optional implementation of the technical solution of the present invention, in step S1, the temperature of the high-temperature standing is 43-47°C, and the total time of the high-temperature standing is 22-26h. Typical but non-limiting standing temperatures are 43°C, 44°C, 45°C, 46°C, 47°C, etc. and the numerical range between any two points. Typical but non-limiting total high-temperature standing times are 22h, 23h, 24h, 26h, etc. and the numerical range between any two points.

[0044] The total time of the high-temperature standing is divided into the high-temperature standing time in the upright state of the cylindrical battery and the high-temperature standing time in the inverted state. As an optional implementation of the technical solution of the present invention, in step S1, the high-temperature standing time in the upright state is 10-14h (such as 10h, 12h, 13h, 14h, etc.), and the high-temperature standing time in the inverted state is 8-16h (such as 8h, 10h, 12h, 13h, 14h, 16h, etc.).

[0045] As a preferred implementation of the technical solution of the present invention, in step S1, after the first liquid injection, the cylindrical battery is subjected to high-temperature standing for 12±2h in the upright (normal) state, and then the cylindrical battery is inverted to continue high-temperature standing in the inverted (upside-down) state.

[0046] Generally, no action is taken during the high-temperature standing (shelving) of the battery cell after liquid injection. In fact, the electrolyte is basically deposited at the bottom of the battery cell and is in a static state, resulting in poor wetting of the electrode sheets in the upper and middle parts of the battery cell. However, adding the action of inverting the battery cell during the high-temperature standing can make the electrolyte at the bottom flow again, increasing the wetting effect of the wound core. At the same time, when the battery cell rotates into the next process, it will be in the upright state, and the electrolyte will flow again, which is equivalent to twice the wetting effect. Due to the increased wetting effect, the high-temperature shelving time can be appropriately reduced, thereby shortening the production cycle of the battery cell and improving production efficiency.

[0047] As an optional implementation of the technical solution of the present invention, in step S2, the temperature of the negative-pressure formation is 43-47°C, and the pressure of the negative-pressure formation is -30~-55kPa. Typical but non-limiting negative-pressure formation temperatures are 43°C, 44°C, 45°C, 46°C, 47°C, etc. and the numerical range between any two points. Typical but non-limiting negative-pressure formation pressures are -30kPa, -35kPa, -38kPa, -40kPa, -42kPa, -45kPa, -48kPa, -50kPa, -52kPa, -55kPa, etc. and the numerical range between any two points.

[0048] As an alternative embodiment of the technical solution of the present invention, in step S2, the charging current during negative-pressure formation is 0.05-0.33C, and the discharging current during negative-pressure formation is 0.2-0.5C. For example, during the charging process: charge at 0.05C for 30 min, charge at 0.1C for 45 min, charge at 0.2C for 45 min, and charge at a constant current of 0.33C until a specific SOC (80%-100% SOC); during the discharging process: discharge at 0.33C until a specific SOC (40%-60% SOC).

[0049] As an alternative embodiment of the technical solution of the present invention, in step S3, the liquid injection volume during secondary liquid injection is 10-30 wt% of the total liquid injection volume of the cylindrical battery, such as 10 wt%, 15 wt%, 20 wt%, 25 wt% or 30 wt%, etc., and the numerical range between any two points.

[0050] As an alternative embodiment of the technical solution of the present invention, in step S3, the temperature during the second high-temperature standing is 43-47°C, and the total time of the second high-temperature standing is 22-26 h. Typically but not limitedly, the temperature during the second high-temperature standing is 43°C, 44°C, 45°C, 46°C or 47°C, etc., and the numerical range between any two points; typically but not limitedly, the total time of the second high-temperature standing is 22 h, 23 h, 24 h or 26 h, etc., and the numerical range between any two points.

[0051] As an alternative embodiment of the technical solution of the present invention, in step S3, the time of the second high-temperature standing in the upright state is 10-14 h (such as 10 h, 12 h, 13 h or 14 h, etc.), and the time of the second high-temperature standing in the inverted state is 8-16 h (such as 8 h, 10 h, 12 h, 13 h, 14 h or 16 h, etc.).

[0052] As a preferred embodiment of the technical solution of the present invention, in step S3, after the secondary liquid injection, the cylindrical battery is placed upright for the second high-temperature standing for 12±2 h, and then the cylindrical battery is inverted to continue the second high-temperature standing in the inverted state.

[0053] Due to the above-mentioned upright and inverted states, the electrolyte will flow again, enhancing the wetting effect of the electrolyte, so that the high-temperature storage time can be appropriately reduced, the production cycle of the battery core can be shortened, and the production efficiency can be improved.

[0054] As a preferred embodiment of the technical solution of the present invention, the formation method of the cylindrical battery, the process flow schematic diagram is as Figure 1 shown, and includes the following steps:

[0055] S1. Subject the cylindrical battery to negative-pressure primary liquid injection. After the primary liquid injection is completed, let the cylindrical battery stand at a high temperature of 45 ± 2 °C for 24 ± 2 h. Specifically, let the cylindrical battery stand at a high temperature in the upright (normal) state for 12 ± 2 h, and then invert the cylindrical battery to continue standing at a high temperature in the inverted state until the high-temperature standing ends;

[0056] S2. Subject the cylindrical battery after high-temperature standing to negative-pressure formation (temperature: 45 ± 2 °C, pressure: -30 to -55 kPa). During the negative-pressure formation process, first charge the cylindrical battery to 80%-100% SOC, and then discharge it to 40%-60% SOC;

[0057] S3. Subject the cylindrical battery after negative-pressure formation to negative-pressure secondary liquid injection. After the secondary liquid injection is completed, let the cylindrical battery stand at a high temperature of 45 ± 2 °C again for 24 ± 2 h. Specifically, let the cylindrical battery stand at a high temperature in the upright (normal) state for 12 ± 2 h, and then invert the cylindrical battery to continue standing at a high temperature in the inverted state until the high-temperature standing ends;

[0058] S4. Subject the cylindrical battery after high-temperature standing again to subsequent sealing and grading.

[0059] It should be noted that the specific type of the cylindrical battery in the present invention is not limited, and it can be a conventional battery system in the art, such as lithium iron phosphate, lithium cobaltate, lithium manganate, lithium manganese iron phosphate, ternary material and other systems.

[0060] According to the second aspect of the present invention, an application of the formation method of the above cylindrical battery in the production of lithium-ion batteries is also provided.

[0061] The above formation method of the cylindrical battery can improve the service life of the battery, and at the same time improve the battery safety and avoid the generation of lithium plating in the battery. Therefore, it has good application prospects in the production of lithium-ion batteries.

[0062] The present invention will be further described in detail below with specific examples and comparative examples.

[0063] Example 1

[0064] This example provides a formation method for a cylindrical battery, including the following steps:

[0065] S1. Bake the cylindrical battery to be filled with liquid, and then perform the first liquid injection (the electrolyte composition: the solute is 1 mol / L LiFP6, and the solvents are ethylene carbonate EC and dimethyl carbonate DMC). The amount of the first liquid injection is 80% of the total liquid injection volume of the cylindrical battery. After the first liquid injection, place the cylindrical battery in a constant temperature chamber at 45 ± 2 °C for high-temperature standing. The high-temperature standing (soaking) time is 24 h. After 12 h during the high-temperature standing, reverse the positive and negative electrodes of the battery and continue to stand until the high-temperature standing ends;

[0066] S2. Perform high-temperature negative-pressure formation on the cylindrical battery after high-temperature standing. During the negative-pressure formation process, the temperature of the negative-pressure formation is 45 ± 2 °C, and the pressure of the negative-pressure formation is -45 kPa. First, charge the cylindrical battery to 100% SOC, and then discharge it to 50% SOC;

[0067] S3. Perform the second liquid injection on the cylindrical battery after negative-pressure formation. The amount of the second liquid injection is 20% of the total liquid injection volume of the cylindrical battery. After the second liquid injection, place the cylindrical battery in a constant temperature chamber at 45 ± 2 °C for another high-temperature standing. The time of the another high-temperature standing is 24 h. After 12 h during the another high-temperature standing, reverse the positive and negative electrodes of the battery and continue to stand until the another high-temperature standing ends;

[0068] S4. Seal, capacity test and off-line the cylindrical battery after the another high-temperature standing according to the normal process.

[0069] Among them, the preparation method of the cylindrical battery to be filled with liquid includes the following steps:

[0070] (a) Mix lithium iron phosphate, conductive agents (SP and CNT, mass ratio 1.5:0.5), binder (PVDF binder, specifically HSV900 and 5130 (mass ratio 1.5:0.5)), and solvent N-methylpyrrolidone evenly according to the mass ratio of 96:2:2:40 to obtain the positive electrode paste;

[0071] Coat the positive electrode paste evenly on the aluminum foil through a coater, then dry it in an oven to obtain the coated electrode sheet, and then obtain the positive electrode sheet through rolling and slitting;

[0072] (b) Mix graphite, conductive agent (SP), binder SBR (styrene-butadiene latex), thickener CMC (sodium carboxymethyl cellulose), and solvent deionized water evenly according to the mass ratio of 96.2:1:1.6:1.2:46 to obtain the negative electrode paste;

[0073] Coat the negative electrode paste evenly on the copper foil through a coater, then dry it in an oven to obtain the coated electrode sheet, and then obtain the negative electrode sheet through rolling and slitting;

[0074] (c) The positive electrode sheet, negative electrode sheet, and separator are wound to obtain a core, and then the tabs are flattened, the current collector plates are welded, and the periphery of the top cover is welded to obtain the cell to be filled with electrolyte.

[0075] Example 2

[0076] This example provides a formation method for a cylindrical battery. Except that in step S2, the cylindrical battery is first charged to 80% SOC and then discharged to 40% SOC, the other steps and process parameters are the same as those in Example 1.

[0077] Example 3

[0078] This example provides a formation method for a cylindrical battery. Except that in steps S1 and S3, the high-temperature standing time and the re-high-temperature standing time are both 26 h, the other steps and process parameters are the same as those in Example 1.

[0079] Comparative Example 1

[0080] This comparative example provides a method for injecting electrolyte and forming a cylindrical battery, including the following steps:

[0081] S1. The cylindrical battery to be filled with electrolyte is baked and then subjected to a first injection of electrolyte (electrolyte composition: the solute is 1 mol / L LiFP6, and the solvent is EC + DMC). The amount of the first injection is 80% of the total electrolyte injection amount of the cylindrical battery. After the first injection, the cylindrical battery is placed in a constant-temperature chamber at 45 ± 2 °C for high-temperature standing. The high-temperature standing time is 24 h, and the positive and negative electrodes of the battery are not reversed during the high-temperature standing.

[0082] S2. The cylindrical battery after high-temperature standing is subjected to high-temperature negative-pressure formation. During the negative-pressure formation, the temperature of the negative-pressure formation is 45 ± 2 °C, and the pressure of the negative-pressure formation is -45 kPa. The cylindrical battery is charged to 50% SOC.

[0083] S3. The cylindrical battery after negative-pressure formation is subjected to a second injection of electrolyte. The amount of the second injection is 20% of the total electrolyte injection amount of the cylindrical battery. After the second injection, the cylindrical battery is placed in a constant-temperature chamber at 45 ± 2 °C for re-high-temperature standing. The re-high-temperature standing time is 24 h, and the positive and negative electrodes of the battery are not reversed during the re-high-temperature standing.

[0084] S4. The cylindrical battery after re-high-temperature standing is sealed, capacity-divided, and taken off the production line according to the normal process.

[0085] Comparative Example 2

[0086] This comparative example provides a method for injecting electrolyte and forming a cylindrical battery. Except that the positive and negative electrodes of the battery are not reversed during the high-temperature standing period and the re-high-temperature standing period in steps S1 and S3, the other steps and process parameters are the same as those in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a method for injecting liquid and forming a cylindrical battery. Except that the positive and negative electrodes of the battery are not placed upside down during the second high-temperature static setting in step S3, the other steps and process parameters are the same as those in Example 1.

[0089] Comparative Example 4

[0090] This comparative example provides a method for injecting liquid and forming a cylindrical battery. Except that during the negative-pressure forming process in step S2, the cylindrical battery is charged to 50% SOC and no discharge treatment is performed, the other steps and process parameters are the same as those in Example 1.

[0091] In order to compare the technical effects of each example and comparative example, the following experimental examples are specially set up.

[0092] Experimental Example 1

[0093] (1) The saturated liquid content of the cylindrical batteries prepared in the examples and comparative examples was measured, and the specific results are shown in Table 1. Among them, the saturated liquid content of the cylindrical battery was calculated using the following formula:

[0094] m 饱 = m 分容后 - m 注液前 ;

[0095] In the formula, m 饱 is the saturated liquid content of the battery, with the unit of g;

[0096] m 分容后 is the mass of the battery after capacitance grading, with the unit of g;

[0097] m 注液前 is the weight of the battery before injecting liquid after baking, with the unit of g.

[0098] (2) The negative electrode interface conditions and electrolyte residue conditions of the cylindrical batteries prepared in the examples and comparative examples after being disassembled at different stages were measured, and the specific results are shown in Table 1 and Figures 2 - 5 as shown.

[0099] Battery disassembly: The batteries at different stages (after capacitance grading and after 200 cycles) were charged to 4.2V at a constant current and constant voltage of 0.5C, and the cut-off current was 0.05C; the batteries were disassembled in a low-humidity disassembly room, and the electrolyte residue conditions and negative electrode interface conditions were observed. Among them, the electrolyte residue amount was obtained by weighing the remaining free electrolyte in the housing during the disassembly process after the battery was capacitance graded.

[0100] Table 1

[0101]

[0102] As can be seen from the data in Table 1, the formation methods provided by the embodiments of the present invention can effectively improve the infiltration effect and the saturated liquid volume of the cylindrical battery, and improve the negative electrode interface condition.

[0103] Specifically, compared with Example 1, in Example 2, the charge-discharge SOC in the formation stage was appropriately adjusted, which had little impact on the saturated liquid volume and the negative electrode interface. This is mainly because charge and discharge can cause the winding core to expand and contract, achieving the effect of sufficient liquid absorption. At the same time, the expansion is limited. After charging to a certain extent, the winding core will not expand further, and there will be no obvious improvement in the liquid absorption effect. Compared with Example 1, in Example 3, the standing time was appropriately adjusted, which also had little impact on the saturated liquid volume and the negative electrode interface. This is because the liquid absorption capacity of the battery cell is limited. When it reaches a certain amount, increasing the standing time will have little impact on the saturated liquid volume and the negative electrode interface.

[0104] Compared with Example 1, in Comparative Example 1 and Comparative Example 2, the battery cells were not inverted during the high-temperature standing (shelf) process. The saturated liquid volume decreased significantly, and dark marks appeared on the negative electrode interface, and lithium deposition occurred after cycling, indicating that inverting during the standing process can significantly improve the liquid absorption effect. At the same time, by comparing Comparative Example 2 and Comparative Example 3, it can be found that inverting the battery cells during the high-temperature standing stage after the first liquid injection can significantly improve the liquid absorption effect, the saturated liquid volume increases significantly, and the electrode interface is better after formation, and no lithium deposition occurs after cycling, only dark marks appear.

[0105] In Comparative Example 4, only charging was performed during the negative-pressure formation process, and no discharging was performed. Its saturated liquid volume increased to a certain extent compared with Comparative Example 1, but there was still a significant decrease compared with Example 1. This also shows that the method of placing the cylindrical battery upside down during the high-temperature standing stage after the first liquid injection and the high-temperature standing stage after the second liquid injection, combined with the charge-discharge method of charging to a high SOC and then discharging to a low SOC during the negative-pressure formation process, can effectively improve the infiltration effect and the saturated liquid volume of the cylindrical battery.

[0106] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are within the scope of the claims of the present invention pending approval.

Claims

1. A formation method for a cylindrical battery, characterized in that, It includes the following steps: S1. Perform a primary liquid injection on the cylindrical battery. After the primary liquid injection is completed, place the cylindrical battery in an upright state and then an inverted state for high-temperature standing; S2. Subject the cylindrical battery after high-temperature standing to a negative-pressure formation. During the negative-pressure formation process, first charge the cylindrical battery to 80%-100% SOC, and then discharge it to 40%-60% SOC; S3. Perform a secondary liquid injection on the cylindrical battery after negative-pressure formation. After the secondary liquid injection is completed, place the cylindrical battery in an upright state and then an inverted state for high-temperature standing again; S4. Perform subsequent sealing and grading on the cylindrical battery after high-temperature standing again.

2. The formation method of the cylindrical battery according to claim 1, characterized in that, In step S1, the liquid injection volume of the primary liquid injection is 70-90 wt% of the total liquid injection volume of the cylindrical battery.

3. The formation method of the cylindrical battery according to claim 1, characterized in that, In step S1, the temperature of the high-temperature standing is 43-47 °C, and the total time of the high-temperature standing is 22-26 h.

4. The formation method of the cylindrical battery according to claim 3, characterized in that In step S1, the time of high-temperature standing in the upright state is 10-14 h, and the time of high-temperature standing in the inverted state is 8-16 h.

5. The formation method of the cylindrical battery according to claim 1, characterized in that, In step S2, the temperature of the negative-pressure formation is 43-47 °C, and the pressure of the negative-pressure formation is -30~-55 kPa.

6. The formation method of the cylindrical battery according to claim 1, wherein, In step S2, the charging current of the negative-pressure formation is 0.05-0.33 C, and the discharging current of the negative-pressure formation is 0.2-0.5 C.

7. The formation method of the cylindrical battery according to any one of claims 1-6, characterized in that, In step S3, the liquid injection volume of the secondary liquid injection is 10-30 wt% of the total liquid injection volume of the cylindrical battery.

8. The formation method of the cylindrical battery according to any one of claims 1-6, characterized in that, In step S3, the temperature of the high-temperature standing again is 43-47 °C, and the total time of the high-temperature standing again is 22-26 h.

9. The formation method of the cylindrical battery according to claim 8, wherein, In step S3, the time of high-temperature standing again in the upright state is 10-14 h, and the time of high-temperature standing again in the inverted state is 8-16 h.

10. Application of the formation method of the cylindrical battery according to any one of claims 1-9 in the production of lithium-ion batteries.

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