Electrolyte injection method for battery

Abstract

Disclosed in the present application is an electrolyte injection method for a battery. The electrolyte injection method comprises primary electrolyte injection and primary formation. The mass percent of an electrolyte injection amount of the primary electrolyte injection in a total electrolyte mass is higher than 82% and lower than 96%; the electrolyte injection amount of the primary electrolyte injection and the length-to-height ratio and length-to-width ratio of a housing satisfy: <formula 1>, wherein x represents the length-to-height ratio of the housing, y represents the length-to-width ratio of the housing, and z represents the mass percent of the electrolyte injection amount of the primary electrolyte injection in the total electrolyte mass.

Description

A battery injection method

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 14, 2023, with application number 202311191243.3. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a battery injection method. Background Art

[0003] Lithium-ion batteries are mainly composed of positive electrode, negative electrode and electrolyte. Although the electrolyte does not provide capacity, it is responsible for conducting Li between the positive and negative electrodes. + The electrolyte plays an important role, so the cycle life and rate performance of lithium-ion batteries are closely related to the characteristics of the electrolyte. Since the electrolyte will continuously undergo oxidation and reduction reactions at the positive and negative electrodes during the operation of the lithium-ion battery, too little electrolyte injection is not conducive to the cycle life of the lithium-ion battery. At the same time, if the amount of electrolyte is too little, some active materials will not be able to be infiltrated, which is not conducive to the full utilization of the battery capacity. However, too much electrolyte injection will also cause the energy density of the lithium-ion battery to decrease and the cost to increase.

[0004] The injection process is a key step in the production of lithium-ion batteries. It is usually difficult to inject all the electrolyte into the battery at once. The injection process is divided into two injections. It is important to confirm the amount of liquid to be injected each time. Too much liquid injection will increase the injection time and even cause liquid spraying in severe cases, affecting the injection efficiency and production capacity. Too little liquid injection will cause poor electrode wetting, resulting in excessive gas generation during the formation process and increased battery internal resistance, affecting battery performance. Therefore, the appropriate injection amount is particularly important for lithium batteries.

[0005] In the related art, the amount of liquid injected into ordinary lithium-ion batteries is determined based on the injection coefficient. Specifically, the battery model capacity is determined, and then the injection coefficient of the battery (2.5-4) is determined. Then, according to the formula injection coefficient = electrolyte density · theoretical injection volume / design capacity = (electrolyte density · (positive electrode plate pore size + negative electrode plate pore size + diaphragm pore size)) / design capacity, the total injection volume of the battery is determined. The injection volume of ordinary batteries is often 80%-90% of the total injection volume.

[0006] For batteries with special aspect ratios and / or special length-to-height ratios, due to the special size and structure, the electrolyte transmission path after injection is too long or the transmission surface is too wide. Once insufficient injection occurs, it often directly leads to insufficient wettability of the electrolyte, which in turn causes black spots to appear on the battery after formation. Technical issues

[0007] In related technologies, for batteries with special aspect ratios and / or special length-to-height ratios, due to the special size and structure of the batteries, the electrolyte transmission path after injection is too long or the transmission surface is too wide. Once insufficient injection occurs, it often directly leads to insufficient electrolyte wettability, which in turn causes black spots to appear on the battery after formation. For example, in order to free up the longitudinal space in the vehicle, the blade battery is designed with the battery tabs in the length / width direction of the battery instead of the height direction, thereby improving space utilization.

[0008] Based on the above, when the battery with the above-mentioned special aspect ratio and / or special height ratio continues to use the injection amount and method of ordinary lithium-ion batteries recorded in the background technology to inject liquid from the injection port, the battery transmission path is too long or the transmission surface is too wide, so that the electrolyte transmission path is forced to be elongated or widened. Once insufficient injection occurs, it often directly leads to insufficient wettability of the electrolyte, which in turn causes black spots to appear on the battery after formation. The main reason for the black spots is that when the electrolyte wettability is insufficient, concentration polarization is easily generated (the phenomenon that the electrode potential deviates from the equilibrium potential due to the different ion concentrations in the insufficiently wetted area and the normal area), which in turn causes the temperature of the insufficiently wetted area to rise and the black spots phenomenon occurs.

[0009] If we continue to refer to the injection coefficient of ordinary lithium-ion batteries for this type of battery and then deduce the proportion of the single injection volume, we cannot obtain the single injection volume suitable for the battery. Therefore, these related parameters such as electrolyte density, positive electrode plate pore size, negative electrode plate pore size, diaphragm pore size, etc. are no longer applicable; in this regard, the present application creatively proposes to obtain the electrolyte injection volume for a single injection of the electrolyte by targeting the aspect ratio and length-to-width ratio of this type of battery, which can effectively improve the wettability of this type of battery, and when the ratio of the aspect ratio to the length-to-width ratio is too large, it will also affect the wettability of the battery. Technical Solutions

[0010] The present application provides a method for injecting electrolyte into a battery, wherein the battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, including:

[0011] The injection method includes one injection and one formation;

[0012] The mass percentage of the electrolyte injection amount of the first injection to the total electrolyte mass is greater than 82% and less than 96%, and the aspect ratio and length-to-width ratio of the electrolyte injection amount of the first injection to the shell satisfy the following formula:

[0013] Wherein, x represents the aspect ratio of the shell, y represents the aspect ratio of the shell, and z represents the mass percentage of the electrolyte injection amount of a single injection to the total electrolyte mass; the aspect ratio is greater than 3.0 and less than 6.0, and the aspect ratio is greater than 10.0 and less than 20.0. Beneficial effects

[0014] The beneficial effect of the present application is that the method provided in the present application can effectively improve the wettability of the electrode sheets in the battery.

[0015] The method provided in this application can make the battery form electrodes without any black spots after one injection.

[0016] The method provided in the present application can make the electrolyte gradually infiltrate from top to bottom during injection, thereby avoiding poor wettability on one side along the length direction of the battery cell.

[0017] The method provided in the present application can avoid poor contact between the pole pieces, the diaphragm, and the pole pieces due to the generation of gas between the pole pieces.

[0018] The method provided in the present application can first gradually form an SEI film during the charging process with a smaller current, and can gradually stabilize the formed SEI film layer during the secondary standing time. Then, in the secondary constant current charging process, because the charging current used in the secondary constant current charging is higher, not only can the side reactions be completely reacted, but more importantly, since the secondary constant current charging current is higher, the SEI film after the secondary standing can further form a denser SEI film. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic diagram of a battery structure provided in one embodiment of the present application;

[0020] Figure 2 is an impedance test diagram of different positive electrode sheet compaction densities.

[0021] Description of reference numerals:

[0022] 10. Outer shell; 11. Liquid filling port. Modes for Carrying Out the Invention

[0023] The present application provides a method for injecting electrolyte into a battery, wherein the battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, including:

[0024] The injection method includes one injection and one formation;

[0025] The mass percentage of the electrolyte injection amount of the first injection to the total electrolyte mass is greater than 82% and less than 96%, and the aspect ratio and length-to-width ratio of the electrolyte injection amount of the first injection to the shell satisfy the following formula:

[0026] Wherein, x represents the aspect ratio of the shell, y represents the aspect ratio of the shell, and z represents the mass percentage of the electrolyte injection amount of a single injection to the total electrolyte mass; the aspect ratio is greater than 3.0 and less than 6.0, and the aspect ratio is greater than 10.0 and less than 20.0.

[0027] It is worth noting that in this embodiment, when the shell is observed from the stacking direction of the multiple electrodes, it forms a rectangular shape with a long side and a short side, the long side refers to the length of the shell, the short side refers to the width of the shell, and the thickness in the direction perpendicular to the rectangular surface refers to the height of the shell.

[0028] Experiments have found that, especially in this type of battery, excessively high compaction density of the positive electrode sheet will lead to too low a porosity of the electrode sheet, hindering the transmission and diffusion of lithium ions in the electrolyte channel. Excessive compaction will increase rebound and increase side reactions at the interface, resulting in increased chemical resistance, reduced distance between active material contacts, and reduced physical resistance, causing actual changes in electrochemical impedance. As a result:

[0029] In a more preferred embodiment, the compaction density of the positive electrode sheet is 2.25 g / cm 3 Above and 2.65g / cm 3 Next, by limiting the compaction density of the positive electrode sheet, the wettability of the battery can be improved.

[0030] It should be noted that the electrolyte infiltration process can generally be divided into the following steps: 1. The electrolyte first enters from the injection port on the side of the shell; 2. The electrolyte diffuses along the electrode and diaphragm under the action of capillary pressure; 3. Since the electrolyte diffuses faster along the diaphragm, the electrolyte will diffuse more quickly from the diaphragm into the interior of the electrode. Therefore, the contact angle between the electrolyte and the electrode sheet, and the electrolyte and the diaphragm will affect the wettability between them. If the contact angle is not appropriate, it will lead to poor wettability or uneven wettability, which will cause black spots to appear during formation.

[0031] In this regard, in a more preferred embodiment, the contact angle between the electrolyte and the separator is greater than the contact angle between the electrolyte and the positive electrode plate.

[0032] In a more preferred embodiment, the contact angle between the electrolyte and the diaphragm is greater than 10° and less than 85°. Limiting the range of the contact angle between the electrolyte and the diaphragm can improve the wettability of the battery. Preferably, the contact angle between the electrolyte and the diaphragm is greater than 12° and less than 36°. More preferably, the contact angle between the electrolyte and the diaphragm is 21.1°.

[0033] In a more preferred embodiment, the contact angle between the electrolyte and the positive electrode sheet is greater than 10° and less than 80°. Preferably, the contact angle between the electrolyte and the positive electrode sheet is greater than 10° and less than 30°. Limiting the range of the contact angle between the electrolyte and the positive electrode sheet can improve the wettability of the battery. More preferably, the contact angle between the electrolyte and the positive electrode sheet is 18.4°.

[0034] In a more preferred embodiment, the injection direction is vertical injection, and the flow rate of the electrolyte during the vertical injection is greater than 2.3 L / min and less than 10.1 L / min. Preferably, the flow rate of the electrolyte during the injection is greater than 3.6 L / min and less than 7.2 L / min. More preferably, the flow rate of the electrolyte during the injection is 5.63 L / min.

[0035] When filling the battery cell, place it perpendicular to the ground with its length and the filling hole facing upward. Vertical filling allows the electrolyte to gradually seep from top to bottom, avoiding poor wettability on one side of the battery cell along its length.

[0036] It is important to note that when filling the battery, the battery cell should be placed with its length perpendicular to the ground and the filling hole facing upwards. The vertical direction here refers to the length direction.

[0037] In a more preferred embodiment, the pressure in the electrolyte chamber is greater than 0.1 MPa and less than 5 MPa. Preferably, the pressure in the electrolyte chamber is greater than 0.15 MPa and less than 1 MPa. More preferably, the pressure in the electrolyte chamber is 0.25 MPa.

[0038] In a more preferred embodiment, the water content of the electrolyte is less than 100 ppm, preferably, the water content of the electrolyte is 10 ppm; the hydrofluoric acid content of the electrolyte is less than 100 ppm, preferably, the hydrofluoric acid content of the electrolyte is 20 ppm; the density of the electrolyte is 0.8 g / cm 3 Above and 1.6g / cm 3 Preferably, the density of the electrolyte is 1.2 g / cm 3 ; and the conductivity of the electrolyte is greater than 6 mS / cm and less than 15 mS / cm at 25° C.

[0039] In a more preferred embodiment, the electrolyte comprises, by mass percentage, 70%-87% of a solvent, 10%-20% of a lithium source, and 3%-10% of a functional additive.

[0040] The solvent is selected from one or more of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC); preferably, the solvent is a mixture of high-viscosity and low-viscosity solvents, for example, the combination is ethylene carbonate (EC) + diethyl carbonate (DEC), ethylene carbonate (EC) + dimethyl carbonate (DMC), ethylene carbonate (EC) + dimethyl carbonate (DMC) + ethyl methyl carbonate (EMC), ethylene carbonate (EC) + dimethyl carbonate (DMC) + diethyl carbonate (DEC), etc., and the combination of ethylene carbonate (EC) + dimethyl carbonate (DMC) + diethyl carbonate (DEC) is preferred.

[0041] The lithium source is selected from one or more of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), and lithium bis(fluorosulfonyl)imide (LiFSI); preferably, the lithium source is lithium hexafluorophosphate (LiPF6).

[0042] The functional additives are selected from one or more of film-forming additives, high-temperature additives, low-temperature additives, overcharge protection additives, flame retardant additives, and rate-type additives; for example, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are selected, and vinylene carbonate (VC) is preferably added.

[0043] Of course, the electrolyte may also be a combination of other substances in the related art.

[0044] In a more preferred embodiment, the primary formation temperature is between 25°C and 55°C, and the vacuum level is between -150 kPa and -20 kPa. More preferably, the primary formation temperature is between 40°C and 50°C, especially 45°C. More preferably, the vacuum level is between -75 kPa and -60 kPa, especially -70 kPa.

[0045] Too low or too high a formation temperature, when the wettability of the injected electrolyte is insufficient, can easily lead to black spots on the interface formation. It should be noted that during the formation, this application specifically uses negative pressure to promptly discharge the gas generated by the formation, so as to avoid poor contact between the electrode, the diaphragm, and the electrode due to the generation of gas between the electrode pieces, thereby causing the formation of black spots.

[0046] In a more preferred embodiment, the one-step formation comprises the following steps:

[0047] One rest; one constant current charge; two rests; two constant current charges; three rests.

[0048] The current of the secondary constant current charging is greater than that of the primary constant current charging, and the time of the secondary constant current charging is less than that of the primary constant current charging.

[0049] Experiments have found that a low-current pre-charge method helps to form a stable SEI film during the formation process. However, long-term low-current charging will increase the impedance of the formed SEI film, thereby affecting the rate discharge performance of the lithium-ion battery. The long process time affects production efficiency. Therefore:

[0050] In a more preferred embodiment, the current of the secondary constant current charging is 8-16 times the current of the primary constant current charging.

[0051] In a more preferred embodiment, the charging current of the constant current charging is greater than 0.01C and less than 0.1C. Preferably, the charging current of the constant current charging is 0.025C.

[0052] In a more preferred embodiment, the charging current of the secondary constant current charging is greater than 0.05C and less than 0.5C. Preferably, the charging current of the secondary constant current charging is 0.3C.

[0053] In a more preferred embodiment, the charging current of the constant current charging is greater than 0.01C and less than 0.1C.

[0054] In a more preferred embodiment, the charging current of the secondary constant current charging is greater than 0.05C and less than 0.5C.

[0055] In a more preferred embodiment, the time for the first constant current charging is 50-360 minutes, preferably, the time for the first constant current charging is 150 minutes; the time for the second constant current charging is 30-360 minutes, preferably, the time for the second constant current charging is 89 minutes.

[0056] In a more preferred embodiment, the first standing time is 5-60 minutes, preferably, the first standing time is 10 minutes; the second standing time is 10-120 minutes, preferably, the second standing time is 45 minutes; the third standing time is 10-120 minutes, preferably, the third standing time is 10 minutes.

[0057] It is worth noting that the present application specifically adopts a two-stage interval constant current charging method, and the current of the secondary constant current charging is 8-16 times that of the primary constant current charging current. Based on the above constant current charging method, compared with the conventional one-stage constant current charging, it first gradually forms an SEI film during the charging process with a smaller current, and can gradually stabilize the formed SEI film layer during the secondary standing time. In the secondary constant current charging process, because the charging current used in the secondary constant current charging is higher, not only can the side reaction be completely reacted, but more importantly, because the secondary constant current charging current is higher, the SEI film after the secondary standing can further form a denser SEI film.

[0058] Comparative Example 1

[0059] The battery has an aspect ratio of 6 and a height ratio of 3.6, with a single injection volume accounting for 82.5%. Specifically, a battery with a length of 340.6mm, a width of 56.7mm, and a height of 94.6mm is produced. Graphite is used as the negative electrode material for the negative electrode sheet, lithium iron phosphate is used as the positive electrode material for the positive electrode sheet, a PE-based film is used for the separator, and the positive electrode is compacted to 2.47g / cm 3 . The positive electrode-diaphragm-negative electrode stack is used to form a core package and assembled into a battery. After that, the electrolyte is injected once, and the electrolyte uses 32% ethylene carbonate (EC) + 48% dimethyl carbonate (DMC) + 15% lithium hexafluorophosphate (LiPF6) + 5% vinylene carbonate (VC). The injection volume is 445.5g (total injection volume 540g), the flow rate during injection is 5.63L / min, the contact angle between the electrolyte and the diaphragm is 21.1°, and the contact angle between the electrolyte and the positive electrode is 18.4°. Let it stand for 10 minutes, then form it at 45°C and -75KPa. The charging current of the first constant current charge is 4.125A, the second stand is 45 minutes, the charging current of the second constant current charge is 49.5A, and the three stand times are 10 minutes. After the end, weld the sealing nails, fully charge and disassemble the battery, and analyze the electrode interface.

[0060] Comparative Example 2

[0061] The battery has an aspect ratio of 9 and a height ratio of 3.6, with the primary injection volume accounting for 84%. Specifically, a battery with a length of 340.6mm, a width of 37.8mm, and a height of 94.6mm was produced. Graphite was used as the negative electrode material to make the negative electrode sheet, lithium iron phosphate was used as the positive electrode material to make the positive electrode sheet, a PE-based film was used as the separator, and the positive electrode was compacted to 2.47g / cm3. The positive electrode-separator-negative electrode stack was formed into a core package and assembled into a battery. Afterwards, a primary injection was performed, and the electrolyte used was 32% ethylene carbonate (EC) + 48% dimethyl carbonate (DMC) + 15% lithium hexafluorophosphate (LiPF6) + 5% vinylene carbonate (VC). The primary injection volume was 453.6g (total injection volume 540g), with a flow rate of 5.63L / min. The contact angle between the electrolyte and the separator was 21.1°, and the contact angle between the electrolyte and the positive electrode sheet was 18.4°. The battery was then placed in a static state for 10 minutes, followed by formation at 45°C and -75 kPa. The battery was charged at a constant current of 4.125 A, followed by a second static state of 45 minutes, a second constant current charge of 49.5 A, and a third static state of 10 minutes. After welding the sealing nails, the battery was fully charged and disassembled to analyze the electrode interface.

[0062] Example 1

[0063] The battery has an aspect ratio of 12 and a height ratio of 3.6, and the liquid injection volume accounts for 85.5%. Specifically, the battery is made with a length of 340.6mm, a width of 28.4mm, and a height of 94.6mm. The negative electrode sheet is made of graphite as the negative electrode material, the positive electrode sheet is made of lithium iron phosphate as the positive electrode material, the separator is made of PE-based film, and the positive electrode is compacted to 2.47g / cm 3 . The positive electrode-diaphragm-negative electrode stack is used to form a core package and assembled into a battery. After that, it is injected once, and the electrolyte uses 32% ethylene carbonate (EC) + 48% dimethyl carbonate (DMC) + 15% lithium hexafluorophosphate (LiPF6) + 5% vinylene carbonate (VC). The injection volume is 461.7g (total injection volume 540g), the flow rate during injection is 5.63L / min, the contact angle between the electrolyte and the diaphragm is 21.1°, and the contact angle between the electrolyte and the positive electrode is 18.4°. Let it stand for 10 minutes, then form it at 45°C and -75KPa. The charging current of the first constant current charge is 4.125A, the second standing time is 45 minutes, the charging current of the second constant current charge is 49.5A, and the three standing times are 10 minutes. After the end, weld the sealing nails, fully charge and disassemble the battery, and analyze the electrode interface.

[0064] Example 2

[0065] The battery has an aspect ratio of 15 and a height ratio of 3.6, and the liquid injection volume accounts for 87%. Specifically, the battery is made with a length of 340.6mm, a width of 22.7mm, and a height of 94.6mm. The negative electrode sheet is made of graphite as the negative electrode material, the positive electrode sheet is made of lithium iron phosphate as the positive electrode material, the separator is made of PE-based film, and the positive electrode is compacted to 2.47g / cm 3 . The positive electrode-diaphragm-negative electrode stack is used to form a core package and assembled into a battery. After that, the electrolyte is injected once, and the electrolyte uses 32% ethylene carbonate (EC) + 48% dimethyl carbonate (DMC) + 15% lithium hexafluorophosphate (LiPF6) + 5% vinylene carbonate (VC). The injection volume is 469.8g (total injection volume 540g), the flow rate during injection is 5.63L / min, the contact angle between the electrolyte and the diaphragm is 21.1°, and the contact angle between the electrolyte and the positive electrode is 18.4°. Let it stand for 10 minutes, then form it at 45°C and -75KPa. The charging current of the first constant current charge is 4.125A, the second standing time is 45 minutes, the charging current of the second constant current charge is 49.5A, and the three standing times are 10 minutes. After the completion, weld the sealing nails, fully charge and disassemble the battery, and analyze the electrode interface.

[0066] Example 3

[0067] The differences are: the battery aspect ratio is 18, the length-to-height ratio is 3.6, and the single injection volume accounts for 88.5%. A battery with a length of 340.6 mm, a width of 18.6 mm, and a height of 94.6 mm is produced. The single injection volume is 469.8 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0068] Comparative Example 3

[0069] The differences are: the battery aspect ratio is 21, the length-to-height ratio is 3.6, and the single injection volume accounts for 90%. A battery with a length of 340.6 mm, a width of 16.2 mm, and a height of 94.6 mm is produced. The single injection volume is 486 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0070] Comparative Example 4

[0071] The differences are: the battery aspect ratio is 6, the length-to-height ratio is 4.5, and the single injection volume accounts for 85.5%. A battery with a length of 340.6 mm, a width of 56.7 mm, and a height of 75.7 mm is produced. The single injection volume is 461.7 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0072] Comparative Example 5

[0073] The differences are: the battery aspect ratio is 9, the length-to-height ratio is 4.5, and the single injection volume accounts for 87%. A battery with a length of 340.6 mm, a width of 37.8 mm, and a height of 75.7 mm is produced. The single injection volume is 469.8 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0074] Example 4

[0075] The differences are: the battery aspect ratio is 12, the length-to-height ratio is 4.5, and the single injection volume accounts for 88.5%. The battery is 340.6 mm long, 28.4 mm wide, and 75.7 mm high. The single injection volume is 477.9 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0076] Example 5

[0077] The differences are: the battery aspect ratio is 15, the length-to-height ratio is 4.5, and the single injection volume accounts for 90%. A battery with a length of 340.6 mm, a width of 22.7 mm, and a height of 75.7 mm is produced. The single injection volume is 486 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0078] Example 6

[0079] The differences are: the battery aspect ratio is 18, the length-to-height ratio is 4.5, and the single injection volume accounts for 91.5%. The battery is 340.6 mm long, 18.9 mm wide, and 75.7 mm high. The single injection volume is 494.1 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0080] Comparative Example 6

[0081] The differences are: the battery aspect ratio is 21, the length-to-height ratio is 4.5, and the single injection volume accounts for 93%. A battery with a length of 340.6 mm, a width of 16.2 mm, and a height of 75.7 mm is produced. The single injection volume is 502.2 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0082] Comparative Example 7

[0083] The differences are: the battery aspect ratio is 6, the length-to-height ratio is 5.4, and the single injection volume accounts for 88.5%. The battery is 340.6 mm long, 56.7 mm wide, and 63.1 mm high. The single injection volume is 477.9 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0084] Comparative Example 8

[0085] The differences are: the battery aspect ratio is 9, the length-to-height ratio is 5.4, and the single injection volume accounts for 90%. A battery with a length of 340.6 mm, a width of 37.8 mm, and a height of 63.1 mm is produced. The single injection volume is 486 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0086] Example 7

[0087] The differences are: the battery aspect ratio is 12, the length-to-height ratio is 5.4, and the single injection volume accounts for 91.5%. The battery is 340.6 mm long, 28.4 mm wide, and 63.1 mm high. The single injection volume is 494.1 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0088] Example 8

[0089] The differences are: the battery aspect ratio is 15, the length-to-height ratio is 5.4, and the single injection volume accounts for 93%. A battery with a length of 340.6 mm, a width of 22.7 mm, and a height of 63.1 mm is produced. The single injection volume is 502.2 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0090] Example 9

[0091] The differences are: the battery aspect ratio is 18, the length-to-height ratio is 5.4, and the single injection volume accounts for 94.5%. A battery with a length of 340.6 mm, a width of 18.9 mm, and a height of 63.1 mm is produced. The single injection volume is 510.3 g (total injection volume is 540 g). The remaining steps are the same as in Example 1.

[0092] Comparative Example 9

[0093] The differences are: the battery aspect ratio is 21, the length-to-height ratio is 5.4, and the single injection volume accounts for 96%. A battery with a length of 340.6 mm, a width of 16.2 mm, and a height of 63.1 mm is produced. The single injection volume is 518.4 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0094] Comparative Example 10

[0095] The differences are: the battery aspect ratio is 12, the length-to-height ratio is 2.7, and the single injection volume accounts for 82.5%. A battery with a length of 340.6 mm, a width of 28.4 mm, and a height of 126.1 mm is produced. The single injection volume is 445.5 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0096] Comparative Example 11

[0097] The differences are: the battery aspect ratio is 18, the length-to-height ratio is 2.7, and the single injection volume accounts for 85.5%. A battery with a length of 340.6 mm, a width of 18.9 mm, and a height of 126.1 mm is produced. The single injection volume is 461.7 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0098] Comparative Example 12

[0099] The differences are: the battery aspect ratio is 12, the length-to-height ratio is 6.3, and the single injection volume accounts for 94.5%. A battery with a length of 340.6 mm, a width of 28.4 mm, and a height of 54.1 mm was produced. The single injection volume was 510.3 g (total injection volume 540 g). All other aspects are consistent with Example 1.

[0100] Comparative Example 13

[0101] The differences are: the battery aspect ratio is 18, the length-to-height ratio is 6.3, and the single injection volume accounts for 97.5%. A battery with a length of 340.6 mm, a width of 18.9 mm, and a height of 54.1 mm is produced. The single injection volume is 526.5 g (total injection volume is 540 g). All other aspects are consistent with Example 1.

[0102] Comparative Example 14

[0103] The difference is that in one formation, only one constant current charge is implemented, the charging current is 0.1C, and the standing time is 55 minutes. The rest is the same as in Example 1.

[0104] Comparative Example 15

[0105] The difference is that in one formation, only one constant current charge is implemented, the charging current is 0.1C, and the standing time is 8 hours. The rest is the same as in Example 1.

[0106] Comparative Example 16

[0107] The difference is that the resting temperature during the first resting is 45° C., and the rest is consistent with Example 1.

[0108] Comparative Example 17

[0109] The difference is that the compaction density of the positive electrode sheet is 2.7 g / cm3, and the rest is consistent with Example 1.

[0110] Comparative Example 18

[0111] The difference is that the compaction density of the positive electrode sheet is 2.2 g / cm3, and the rest is consistent with Example 1.

[0112] The battery is made of a housing 10, a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive and negative electrode sheets are cut to size and stacked together with the separator, placed in the housing, and the electrolyte is injected through the injection port 11 for formation.

[0113] After formation, the battery cell is disassembled to confirm the electrolyte infiltration at the electrode interface and whether there are black spots on the electrode interface. The specific cross-test results are shown in the following table.

[0114] Table 1 Test results of examples and comparative examples

[0115] Note: The more “+” there are, the worse the infiltration is and the more black spots are formed; “0” means the condition is good.

[0116] Comparative Examples 1-9 show that, since the electrolyte is injected from the injection port on one side, although the aspect ratios are 3.6, 4.5, and 5.4, respectively, their high aspect ratios, as shown in FIG1 , result in the electrolyte infiltration channel of the battery being too deep and narrow, making it difficult to fully infiltrate the battery cell at the end. If the aspect ratio is too low, the infiltration channel is too wide, making it difficult for the electrolyte flowing from the injection port to fully spread and infiltrate the battery cell, resulting in poor wettability and the formation of black spots.

[0117] According to Comparative Examples 10-13, although the aspect ratios are 12 and 18 respectively, due to the excessively high or low aspect ratios, the electrolyte infiltration channels formed by their cross sections are difficult to fully infiltrate the battery cells, thereby forming black spots.

[0118] According to Comparative Examples 14-15, it can be seen that when the battery cells are subjected to one formation after standing, compared with the two-stage constant current charging method used in the embodiment, the fixed current charging and the fixed current charging for a long time have insufficient standing time, resulting in insufficient reaction at the interface of the battery electrode, affecting the formation of the SEI film. Although the SEI film can be formed after sufficient standing, its density is relatively low, which affects the overall performance of the battery.

[0119] According to Comparative Example 16, although high temperature is used during a single standing state to facilitate electrolyte infiltration, it takes a long time. In order to achieve efficient and rapid liquid injection, the present application can be at room temperature during standing state, and a high temperature negative pressure condition is simultaneously applied during constant current charging, thereby effectively improving production efficiency and electrolyte infiltration, while reducing the generation of black spots.

[0120] This application also analyzes the wettability of the electrolyte based on the positive electrode compaction density, such as in Comparative Example 17: the positive electrode compaction density is 2.7g / cm 3 (High compaction density), Comparative Example 18: The compaction density of the positive electrode sheet is 2.2 g / cm 3 The battery (low compaction density) was subjected to EIS testing and wettability and black spot observation. Referring to Figure 2, it can be seen that high compaction produces high interface impedance (charge exchange impedance), indicating that its chemical resistance is higher and its physical resistance is lower. Its electrode porosity is lower, electrolyte infiltration is more difficult, and wettability is worse, which will lead to black spots on the interface. If the compaction density is too low, the electrolyte will easily flow out and it will be difficult to fully infiltrate.

Claims

1. A method for injecting electrolyte into a battery, wherein the battery comprises a housing, a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein: The injection method includes one injection and one formation; The mass percentage of the electrolyte injection amount of the first injection to the total electrolyte mass is greater than 82% and less than 96%, and the aspect ratio and length-to-width ratio of the electrolyte injection amount of the first injection to the shell satisfy the following formula: Among them, x represents the aspect ratio of the shell, y represents the aspect ratio of the shell, and z represents the mass percentage of the electrolyte injection amount of a single injection to the total electrolyte mass; the aspect ratio is greater than 3.0 and less than 6.0; the aspect ratio is greater than 10.0 and less than 20.

0.

2. The battery injection method according to claim 1, wherein: The compaction density of the positive electrode sheet is 2.25 g / cm 3 Above and 2.65g / cm 3 the following.

3. The battery injection method according to claim 1, wherein: The contact angle between the electrolyte and the separator is greater than the contact angle between the electrolyte and the positive electrode plate.

4. The battery injection method according to claim 3, wherein: A contact angle between the electrolyte and the separator is greater than or equal to 10° and less than or equal to 85°.

5. The battery injection method according to claim 3, wherein: The contact angle between the electrolyte and the positive electrode sheet is greater than 10° and less than 80°.

6. The battery injection method according to claim 1, wherein: The injection direction of the primary injection is vertical injection, and the flow rate of the electrolyte during the vertical injection is greater than 2.3 L / min and less than 10.1 L / min.

7. The battery injection method according to claim 1, wherein: The pressure in the electrolyte chamber is greater than 0.1 MPa and less than 5 MPa.

8. The battery injection method according to claim 1, wherein: The water content of the electrolyte is less than 100 ppm; the hydrofluoric acid content of the electrolyte is less than 100 ppm; the density of the electrolyte is 0.8 g / cm 3 Above and 1.6g / cm 3 Below; at 25°C, the conductivity of the electrolyte is above 6mS / cm and below 15mS / cm.

9. The battery injection method according to claim 1, wherein: In terms of mass percentage, the electrolyte comprises: 70%-87% of a solvent, 10%-20% of a lithium source, and 3%-10% of a functional additive.

10. The battery injection method according to claim 9, wherein: The solvent is selected from one or more of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; the lithium source is selected from one or more of lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium bis(fluorosulfonyl)imide; the functional additive is selected from one or more of film-forming additives, high-temperature additives, low-temperature additives, overcharge protection additives, flame retardant additives, and rate-type additives.

11. The battery injection method according to claim 9, wherein: The solvent is selected from a mixed solvent of ethylene carbonate and diethyl carbonate, a mixed solvent of ethylene carbonate and dimethyl carbonate, a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate; the lithium source is lithium hexafluorophosphate; and the functional additive is selected from one or more of vinylene carbonate and fluoroethylene carbonate.

12. The battery injection method according to claim 1, wherein: The primary formation temperature is higher than 25° C. and lower than 55° C., and the vacuum degree is higher than -150 kPa and lower than -20 kPa.

13. The battery injection method according to claim 1, wherein: The one-step formation comprises the following steps: One rest; one constant current charge; two rests; two constant current charges; three rests.

14. The battery injection method according to claim 13, wherein: The current of the secondary constant current charging is greater than that of the primary constant current charging, and the time of the secondary constant current charging is less than that of the primary constant current charging.

15. The battery injection method according to claim 13, wherein: The current of the secondary constant current charging is 8-16 times of the current of the primary constant current charging.

16. The battery injection method according to claim 13, wherein: The charging current of the constant current charging is greater than 0.01C and less than 0.1C.

17. The battery injection method according to claim 13, wherein: The charging current of the secondary constant current charging is greater than 0.05C and less than 0.5C.

18. The battery injection method according to claim 13, wherein: The time of one constant current charging is 50-360min.

19. The battery injection method according to claim 13, wherein: The secondary constant current charging time is 30-360 minutes.

20. The battery injection method according to claim 13, wherein: The first standing time is 5-60 min; the second standing time is 10-120 min; and the third standing time is 10-120 min.

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