Formation method for improving cycling stability of silicon-containing soft package lithium ion battery

Abstract

The invention relates to a formation method for improving cycle stability of a silicon-containing soft package lithium ion battery, which comprises the following steps of: pre-forming batteries with specific water content, and determining formation process parameters of batch batteries through a differential tolerance curve (dQ / dV-V); the method comprises the following steps: carrying out hot-pressing formation on batch batteries according to set formation process parameters, picking out batteries with unqualified moisture through a formation cabinet, and then carrying out high-temperature and normal-temperature aging on formed battery cells with qualified moisture; the aged battery is placed in the hot-pressing formation cabinet again for two times of charging and discharging operation, so that the SEI film of the silicon-containing battery is repaired and recombined again, then the battery is subjected to subsequent preparation procedures such as air exhaust, secondary sealing and edge cutting, and a semi-finished product battery is obtained; and aging the semi-finished battery at normal temperature to obtain a finished battery. The SEI film of the obtained silicon-containing soft package lithium ion battery is uniform, stable and high in compactness, and the obtained silicon-containing soft package lithium ion battery is smooth in surface, high in hardness, good in cycling stability and high in consistency.

Description

Technical Field

[0001] The present invention relates to a formation method for a soft-pack lithium-ion battery, and particularly to a formation method for improving the cycle stability of a silicon-containing soft-pack lithium-ion battery. It is a technology that improves the cycle stability of a silicon-containing soft-pack lithium-ion battery by means of stepped charging pre-formation and two charge-discharge processes to repair the SEI film. Background Art

[0002] With the continuous increase in the demand for high-energy-density lithium-ion batteries, doping silicon into the graphite anode has become an inevitable trend. The theoretical capacity of the silicon anode is as high as 4200 mAh / g, and the lithium intercalation potential is higher than that of graphite, which can effectively solve the problems of low lithium intercalation potential and easy lithium precipitation of graphite. Although the silicon-carbon anode has a high specific capacity, the volume expansion of silicon in the anode during the alloying process with lithium is relatively large. The high expansion rate will continuously damage the solid electrolyte interface (SEI) film on the anode surface, resulting in continuous damage or repair of the SEI film during the charge-discharge process of the lithium-ion battery, causing consumption of the electrolyte and active lithium ions, and thus problems such as poor cycle stability and consistency of the battery. To solve the problem of cycle instability caused by the expansion of graphite and silicon-carbon, many solutions have been proposed in the industry, especially for the formation stage. Formation is an important process in the production of lithium-ion batteries. Formation forms an SEI film on the anode surface, and forming a uniform and stable SEI film can well adapt to the volume expansion caused by the insertion and extraction of lithium ions.

[0003] CN108258347B proposes three means of controlling the upper limit voltage of charging in stages, applying mechanical external pressure outside the battery, and applying negative pressure inside the battery to control the uniform change of the volume of the silicon-based anode during the charge-discharge process. Although it can solve the problem of wrinkles of the silicon-based anode in the lithium-ion soft-pack battery, the process uses multiple vacuum extractions, and part of the electrolyte will be extracted. On the one hand, it will cause the battery to lack liquid, and on the other hand, too much injection volume will cause waste of the electrolyte. Similarly, CN115425309A and CN115986218A also propose multiple exhaust-injection-formation or multiple exhaust-multiple injection-formation processes for the high-nickel ternary / silicon-carbon system. On the one hand, considering the large amount of gas generated during the formation stage of high-nickel ternary, the problem of battery exhaust is solved, and on the other hand, the problem of large electrolyte consumption of the silicon-carbon anode is solved. However, both methods also cause waste of the electrolyte, and multiple gas bag cutting and air extraction and injection are carried out, so the amount of aluminum-plastic film used for a single battery is greater than that in industrial-scale production, increasing the battery cost and not being suitable for industrial-scale production.

[0004] In order to generate a dense SEI film during formation and improve its cycling performance, the industry also adds a discharging process during formation. For example, CN108539305B adds a step of discharging process at 3.60V and 3.70V. However, for silicon-containing batteries, the silicon-carbon negative electrode reaches its maximum expansion value at full charge. The expansion process of silicon will cause the rupture, recombination, and re-repair of the SEI film, consuming electrolyte and lithium salt. Although CN112510265A has experienced a full charge-discharge process, it discharges to 50% - 70% SOC, followed by high-temperature hot pressing, and the formation ends. This method does not charge and repair the rupture of the SEI film caused by the expansion of the silicon-carbon negative electrode, and the SEI film will be re-repaired during the charging process after the second sealing, which will cause the consumption of electrolyte and will affect the cycling stability and consistency of the battery to a certain extent. CN116914291A discloses a method for determining the formation process by collecting data on the change in the state of charge SOC of a sample battery and the expansion rate P of its negative electrode sheet. After pre-charging treatment at room temperature and aging, high-temperature formation is carried out. This method takes into account the electrode expansion process, but due to the use of manual disassembly of the electrode sheet to measure the expansion of the negative electrode sheet, there are large test errors, etc., which will cause inaccuracies in the voltage range, etc.

[0005] In summary, for the formation method of silicon-containing soft-pack lithium-ion batteries at present, there are many disadvantages such as large consumption of aluminum-plastic film for single-cell batteries, large electrolyte injection volume, low liquid retention coefficient, complex process, unstable SEI film, poor cycling stability of the battery, poor battery consistency, and being not conducive to industrial promotion. Therefore, for silicon-containing lithium-ion batteries, especially soft-pack batteries at present, there is an urgent need for a formation method that is easy to promote industrially and convenient for various large and small enterprises to apply. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a formation method with reasonable design, short formation time, simple process, and easy to promote. The battery designed according to the method of the present invention has the advantages of less injection volume, high liquid retention coefficient, flat battery surface, good battery hardness, uniform, dense and not easily broken SEI film. At the same time, the obtained silicon-containing soft-pack lithium-ion battery has the advantages of high first efficiency, good cycling stability, good battery consistency, and excellent calendar life.

[0007] To achieve the above object, the technical solution disclosed by the present invention is as follows:

[0008] A formation method for improving the cycling stability of silicon-containing soft-pack lithium-ion batteries, comprising the following steps:

[0009] The first step: pre-formation of the sample battery:

[0010] (1) Take several batteries in mass production as sample batteries for baking. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked batteries, denoted as H1; the designed capacity of the battery is denoted as Q1; transfer the baked battery cores from the baking oven to a glove box for liquid injection; then, activate the batteries.

[0011] (2) Place the fully activated sample batteries into a fixture forming device, heat up to 60 - 80 °C, and perform hot pressing formation in a stepped segmented manner. The formation process is as follows:

[0012] First stage: Apply a pressure P1 to the battery surface, charge at a constant current I1 until the voltage reaches U1, and the charging time is T1.

[0013] Second stage: Increase the pressure on the battery surface to P2, charge at a constant current I2 until the voltage reaches U2, and the charging time is T2; leave it standing for 5 min, and the pre - formation ends.

[0014] (3) Collect the charging capacity Q and the corresponding voltage V data of the sample batteries during the charging process. Import the voltage V and capacity Q data into the Origin plotting software. Use the voltage V as the X - axis and the capacity Q as the Y - axis. After software processing, plot the differential capacitance curve (dQ / dV - V) of the formation process; take the voltage values corresponding to the first reaction peak from its appearance to the end in the voltage range of 1.50 - 3.00 V of the differential capacitance curve (dQ / dV - V), denoted as V1 and V2 in sequence. This voltage range is the decomposition voltage range of water in the battery; similarly, observe the change of the dQ / dV - V peak in the voltage range of 3.00 - 4.50 V, and take the voltage values corresponding to the highest peak from its appearance to the end, denoted as V3 and V4 in sequence. This voltage range is the voltage range where lithium ions rapidly escape from the positive electrode and embed into the negative electrode.

[0015] Second step: Mass battery formation and aging:

[0016] (4) Bake the batteries in mass production. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked soft - pack batteries, denoted as H2; then transfer the baked battery cores from the baking oven to a glove box for liquid injection, and perform liquid injection and activation according to the process of the sample batteries.

[0017] (5) Place the fully activated sample batteries into a fixture forming device, heat up to 45 - 80 °C, and perform hot pressing formation in a stepped segmented manner. The formation process is as follows:

[0018] First stage: Apply a pressure P3 to the battery surface, charge at a constant current I3 until the voltage reaches U3, and the charging time is 15 - 30 min; let it stand for 5 min.

[0019] The second stage: The surface pressure of the battery increases to P4, and it is charged at a constant current I4 until the voltage reaches U4. The charging time is 10 - 60 minutes.

[0020] The third stage: The surface pressure of the battery increases to P5, and it is charged at a constant current and constant voltage until the voltage reaches U5, with a cut-off current of I6. The charging time is 30 - 120 minutes, and then it is left to stand for 5 minutes, marking the end of formation.

[0021] (6) After the battery formation is completed, use the formation cabinet to conduct a full inspection and screening of the end voltage after the first-stage battery charging. Batteries with a voltage lower than V2 are determined to be batteries with excessive moisture content, picked out and properly distinguished, and marked as Class B batteries; batteries with a voltage greater than or equal to V2 are batteries with qualified moisture content and are marked as Class A batteries.

[0022] (7) Subsequently, place the formed batteries in a high-temperature aging chamber for high-temperature aging, and after the high-temperature aging is completed, conduct normal-temperature aging.

[0023] The third step: The stage of re-repairing and re-organizing the SEI film;

[0024] (8) Place the aged Class A batteries in a fixture formation device for charge and discharge. First, set the hot-press formation temperature to 40 - 60 °C, and apply a pressure P6 on the battery surface. The specific process is as follows:

[0025] The first stage: Charge at a constant current and constant voltage with current I7 until the voltage reaches U6, with a cut-off current of I8. The charging time is 60 - 180 minutes; let it stand for 5 minutes.

[0026] The second stage: Discharge at a constant current I9 until the voltage reaches U7, with a time of 10 - 180 minutes; let it stand for 5 minutes.

[0027] The third stage: Charge at a constant current I 10 until the voltage reaches U8, with a time of 10 - 90 minutes; let it stand for 5 minutes.

[0028] The fourth stage: Discharge at a constant current I 11 until the voltage reaches U9, with a time of 10 - 90 minutes; let it stand for 5 minutes.

[0029] The fifth stage: Charge at a constant current and constant voltage with current I 12 until the voltage reaches U 10 , with a cut-off current of I 13 , with a time of 10 - 90 minutes; let it stand for 5 minutes.

[0030] (9) Conduct subsequent battery preparation processes such as air extraction, second sealing, and edge cutting on the batteries obtained in step (8) to obtain semi-finished batteries.

[0031] (10) Put the semi-finished battery obtained in step (9) into a normal-temperature aging chamber for aging. The aging temperature is 20 - 30 °C, and the aging time is 24 - 48 h, finally obtaining a finished battery.

[0032] Further, in step (1), the designed capacity Q1 of the battery is 0.5 - 10 Ah; the positive electrode is one or a mixture of any several of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate, and the single-sided surface density of the positive electrode is 140 - 250 g / m 2 ; the negative electrode is a silicon-carbon negative electrode, in which the content of nano-silicon is 1% - 15%;

[0033] The moisture content H1 of the sampled battery is 200 - 400 ppm; the content of the electrolyte additive fluoroethylene carbonate FEC is 5% - 20% (vol), and the content of vinylene carbonate VC is 1% - 10% (vol); the electrolyte injection coefficient is 2.1 - 3.6 g / Ah; the activation temperature is 40 - 65 °C, and the time is 12 - 48 h.

[0034] Further, in step (2), the surface pressure P1 of the battery = (10% - 40%) * P2, P2 = 1 - 8 MPa / PCS, the charging current I1 is 0.01 - 0.03 C, and the charging current I2 is 0.1 - 0.5 C; the charging voltage U1 is 3.0 - 3.30 V, and the charging voltage U2 is 4.20 - 4.50 V; the charging time T1 is 15 - 30 min, and the charging time T2 is 80 - 800 min.

[0035] Further, in step (3), V1 is 1.50 - 3.00 V, V2 is 1.50 - 3.00 V, V3 is 3.50 - 4.20 V, and V4 is 3.50 - 4.20 V.

[0036] Further, in step (4), the moisture content H2 of the battery is 100 - 150 ppm.

[0037] Further, in step (5), the surface pressure P3 of the battery = (10% - 40%) * P5, P4 = (40% - 90%) * P5, P5 = 1 - 12 MPa / PCS, the charging current I3 is 0.01 - 0.03 C, the voltage U3 = V2 is 1.50 - 3.00 V, the charging current I4 is 0.1 - 0.5 C, U4 = V4 is 3.50 - 4.20 V, the charging current I5 is 0.3 - 1.0 C, the cut-off current I6 is 0.05 - 0.5 C, and the charging voltage U5 is 4.20 - 4.50 V.

[0038] Further, in step (6), V2 is 1.50 - 3.00 V.

[0039] Furthermore, in step (7), the aging temperature of high temperature aging is 40-60°C, and the aging time is 36-96h; the aging temperature of room temperature aging is 20-30°C, and the aging time is 12-36h.

[0040] Further, in step (8), the pressure P6 on the battery surface is 1-6 MPa / PCS; the current I7 is 0.6-1.5C, the charge cut-off current I8 is 0.05-0.2C, the voltage U6 is 4.20-4.50V, the discharge current I9 is 0.7-1.5C, the discharge cut-off voltage U7 is 2.50-4.20V, and the charge current I 10 1.0~2.0C, U8 is 4.20~4.50V; discharge current I 11 is 0.7~2.0C, the discharge cut-off voltage U9 is 2.45~4.20V; the charging current I 12 1.0~2.0C, charging cut-off current I 13 0.05~0.3C, charging voltage U 10 It is 3.8~4.30V.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] (1) The present invention preferentially performs pre-formation on sample batteries with specific water content, and performs differential capacitance (dQ / dV-V) analysis on the formed capacity and voltage curves. On the one hand, the decomposition voltage of water is determined, which provides data support for the subsequent selection of batteries with excessive water content in the formation stage of batch batteries. On the other hand, the method determines information such as the reaction voltage of lithium insertion / extraction of the positive and negative electrodes, providing a scientific guidance basis for determining the formation process, avoiding the drawback of using the same formation process for different battery systems in the prior art; at the same time, the present invention determines different formation processes according to different material systems, so that the positive and negative electrode SEI films are more uniform and dense, and the cycle stability is improved;

[0043] (2) The present invention adds a voltage screening process to the mass-produced batteries during the formation stage, the purpose of which is to select batteries with unqualified moisture content, thereby fundamentally avoiding the problem of excessive moisture content in the batteries due to insufficient baking, battery turnover from the baking room to the glove box, and battery retention inside the glove box. Therefore, after the battery formation is completed, the method is used to select and eliminate batteries with unqualified moisture content in advance, thereby ensuring the cycle stability, shipping quality and quality stability of the battery.

[0044] (3) After the battery ages, the present invention adds two charge-discharge processes for the re-repair and recombination of the SEI film. This process enables the silicon-carbon negative electrode to expand to its maximum value during the full-charge process, and repairs and recombines the SEI film during multiple charge-discharge processes. On the one hand, this process improves the uniformity and density of the SEI film of the silicon-containing negative electrode, and at the same time avoids the problem of electrolyte loss caused by the SEI repair and recombination after the second sealing. In addition, this process can also improve the liquid retention coefficient of the battery without increasing the liquid injection coefficient and the secondary liquid injection process, thereby reducing the loss of electrolyte and aluminum-plastic film per unit battery and lowering the production cost of the battery. Therefore, the silicon-containing soft-pack lithium-ion battery obtained by the method of this case has the advantages of less liquid injection volume, high liquid retention coefficient, flat battery surface, good battery hardness, uniform, dense and not easily broken SEI film, and good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0046] Figure 1 It is the determination of the differential capacitance curve (dQ / dV-V) of the battery with different moisture contents in Embodiment 1 of the present invention near 3.00V and V1, V2.

[0047] Figure 2 It is the determination of the differential capacitance curve (dQ / dV-V) of the battery during charging in Embodiment 1 of the present invention and V3, V4.

[0048] Figure 3 It is the determination of the differential capacitance curve (dQ / dV-V) of the battery with different moisture contents in Embodiment 2 of the present invention near 3.00V and V1, V2.

[0049] Figure 4 It is the determination of the differential capacitance curve (dQ / dV-V) of the battery during charging in Embodiment 2 of the present invention and V3, V4.

[0050] Figure 5 It is the determination of the differential capacitance curve (dQ / dV-V) of the battery with different moisture contents in Embodiment 3 of the present invention near 3.00V and V1, V2.

[0051] Figure 6 It is the determination of the differential capacitance curve (dQ / dV-V) of the battery during charging in Embodiment 3 of the present invention and V3, V4.

[0052] Figure 7It is a comparative diagram of the cycle performance of Example 1 and Comparative Example 1 at 1C / 1C-4.35 / 3.00@25℃. Detailed implementation manners

[0053] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0054] Here, the special term "embodiment", any embodiment described as "exemplary" does not have to be construed as superior to or better than other embodiments. For the performance index tests in the embodiments of the present application, unless otherwise specified, the conventional test methods in the art are adopted. It should be understood that the terms described in the present application are only used to describe specific embodiments and are not used to limit the content disclosed in the present application.

[0055] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as commonly understood by those of ordinary skill in the technical field to which the present application belongs; the test methods and technical means not specifically mentioned in the present application also refer to the experimental methods and technical means commonly adopted by those of ordinary skill in the art.

[0056] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "in", "on", "under", "rise", "fall", "vertical", "plane", "top", "bottom", "inside", "outside", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention.

[0057] In order to better illustrate the content of the present application, numerous specific details are given in the following specific embodiments. Those skilled in the art should understand that the present application can still be implemented without some specific details. In the embodiments, some methods, means, instruments, devices, etc. well-known to those skilled in the art are not described in detail in order to highlight the gist of the present application.

[0058] On the premise of no conflict, the technical features disclosed in the embodiments of the present application can be combined arbitrarily, and the obtained technical solutions belong to the content disclosed in the embodiments of the present application.

[0059] The present invention discloses a formation method for improving the cycle stability of a silicon-containing soft-pack lithium-ion battery.

[0060] To better understand the present invention, the following specific embodiments are used to further elaborate on the present invention. However, it should not be construed as a limitation of the present invention. For those skilled in the art, some non-essential improvements and adjustments made based on the above-mentioned invention content are also considered to fall within the protection scope of the present invention.

[0061] Example 1

[0062] A formation method for improving the cycle stability of silicon-containing soft-pack lithium-ion batteries, comprising the following steps:

[0063] The first step: Pre-formation of sample batteries:

[0064] (1) Take several batteries in mass production as sample batteries for baking. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked batteries, and the moisture content is 250 ppm; transfer the baked battery cores from the baking oven to a glove box for liquid injection; subsequently, activate the batteries, with the activation temperature being 45 °C and the time being 36 h; where the designed capacity of the battery is 3.45 Ah, the positive electrode is lithium nickel cobalt manganese oxide NCM111, the single-sided surface density of the positive electrode is 197 g / m 2 , the content of nano-silicon in the silicon-carbon negative electrode is 3%, the content of the electrolyte additive FEC is 5 vol%, and the content of VC is 1.5 vol%; the liquid injection coefficient of the electrolyte is 2.4 g / Ah;

[0065] (2) Put the fully activated sample batteries into a fixture formation device, heat up to 75 °C, and perform hot pressing formation in a stepped segmented manner. The formation process is as follows:

[0066] The first stage: Apply a pressure of 3 MPa to the battery surface, and perform constant current charging at a current of 0.01C (34.5 mA) until the voltage reaches 3.00 V, and the charging time is 30 min;

[0067] The second stage: Increase the pressure on the battery surface to 7 MPa, and perform constant current charging at a current of 0.1C (345 mA) until the voltage reaches 4.20 V, and the charging time is 700 min; leave it for 5 min, and the pre-formation ends;

[0068] (3) Collect the charging capacity Q and the corresponding voltage V data of the sample batteries during the charging process, import the voltage V and capacity Q data into the Origin plotting software, use the voltage V as the X-axis and the capacity Q as the Y-axis, and after software processing, plot the differential capacitance curve (dQ / dV-V) of the formation process; take the voltage values corresponding to the first reaction peak from the appearance to the end in the voltage range of 1.50 - 3.00 V of the differential capacitance curve (dQ / dV-V), and record them as V1 and V2 in sequence. This voltage range is the decomposition voltage range of water in the battery, such as Figure 1As described above, V1 = 2.00V and V2 = 2.23V; similarly, observe the change of dQ / dV-V peak in the voltage range of 3.00 to 4.35V, and take the voltage values corresponding to the highest peak from its appearance to the end, denoted as V3 and V4 in sequence. This voltage range is the voltage range where lithium ions rapidly escape from the positive electrode and embed into the negative electrode, as Figure 2 described above, V3 = 3.55V and V4 = 3.70V;

[0069] Step 2: Bulk battery formation and aging:

[0070] (4) Bake the batteries produced in batch. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked soft-pack batteries, and its moisture content is 100 ppm; then transfer them into a glove box for liquid injection, and perform liquid injection and activation according to the process of the sample battery;

[0071] (5) Put the fully activated sample batteries into a fixture formation device, heat up to 75°C, and perform thermal pressing formation in a stepped segmented manner. The formation process is as follows:

[0072] First stage: Apply a pressure of 3 MPa to the battery surface, and charge at a constant current of 0.01C (34.5 mA) until the voltage reaches 2.20V. The charging time is 15 min; let it stand for 5 min;

[0073] Second stage: Increase the pressure on the battery surface to 5 MPa, and charge at a constant current of 0.2C (690 mA) until the voltage reaches 3.70V. The charging time is 30 min;

[0074] Third stage: Increase the pressure on the battery surface to 10 MPa, and charge at a constant current and constant voltage of 0.5C (1725 mA) until the voltage reaches 4.15V, with a cut-off current of 0.02C (69 mA). The charging time is 70 min, and let it stand for 5 min to end the formation;

[0075] (6) After the battery formation is completed, use the formation cabinet to conduct a full inspection and screening of the end voltage after the first-stage battery charging. For the batteries with a voltage lower than 2.23V, they are batteries with excessive moisture content, pick them out and make distinctions, and mark them as Class B batteries; for the batteries with a voltage greater than or equal to 2.23V, they are batteries with qualified moisture content, and mark them as Class A batteries;

[0076] (7) Then put the formed batteries into a high-temperature aging chamber for high-temperature aging. The aging temperature is 45°C and the aging time is 36 h; after the high-temperature aging is completed, conduct normal-temperature aging. The aging temperature is 25°C and the aging time is 12 h;

[0077] Step 3: The stage of re-repairing and re-organizing the SEI film;

[0078] (8) Place the aged Class A batteries into the fixture formation equipment for charge and discharge. First, set the hot pressing formation temperature to 45 °C and the pressure applied to the battery surface to 5 MPa. The specific process is as follows:

[0079] The first stage: Constant current and constant voltage charge at a current of 1C (3450 mA) until the voltage reaches 4.25 V, with a cut-off current of 0.2C (690 mA). The charging time is 60 min; stand still for 5 min;

[0080] The second stage: Constant current discharge at a current of 1.50C (5175 mA) until the voltage reaches 2.50 V. The time is 60 min; stand still for 5 min;

[0081] The third stage: Constant current charge at a current of 1.0C (3450 mA) until the voltage reaches 4.25 V. The time is 60 min; stand still for 5 min;

[0082] The fourth stage: Constant current discharge at a current of 1.0C (3450 mA) until the voltage reaches 2.50 V. The time is 60 min; stand still for 5 min;

[0083] The fifth stage: Constant current and constant voltage charge at a current of 1.2C (4140 mA) until the voltage reaches 4.10 V, with a cut-off current of 0.2C (690 mA). The time is 90 min; stand still for 5 min;

[0084] (9) Perform subsequent battery preparation processes such as air extraction, secondary sealing, and edge cutting on the batteries obtained in step (8) to obtain semi-finished batteries;

[0085] (10) Place the semi-finished batteries obtained in step (9) into a normal temperature aging chamber for normal temperature aging. The aging temperature is 25 °C and the aging time is 24 h to finally obtain finished batteries.

[0086] Example 2

[0087] A formation method for improving the cycle stability of silicon-containing soft-pack lithium-ion batteries, comprising the following steps:

[0088] The first step: Pre-formation of sample batteries:

[0089] (1) Take several batteries in mass production as sample batteries for baking. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked batteries, and the moisture content is 350 ppm; Transfer the baked battery cores from the baking oven to the glove box for liquid injection; Subsequently, activate the batteries. The activation temperature is 55 °C and the time is 48 h; The designed capacity of the battery is 2 Ah, the positive electrode is a mixed positive electrode of lithium nickel cobalt manganese oxide and lithium manganese oxide, and the mass ratio is: NCM523:LMO = 60:40. The single-sided surface density of the positive electrode is 150 g / m 2, the content of nano-silicon in the silicon-carbon negative electrode is 1.5%, the content of the electrolyte additive FEC is 8.0 vol%, and the content of VC is 3.0 vol%; the electrolyte injection coefficient is 2.9 g / Ah;

[0090] (2) Put the fully activated sample battery into the fixture forming equipment, heat it up to 65 °C, and perform hot pressing formation in a stepped segmented manner. The formation process is as follows:

[0091] The first stage: Apply a pressure of 2 MPa to the battery surface, and perform constant current charging at a current of 0.02C (40 mA) until the voltage reaches 3.00 V, and the charging time is 30 min;

[0092] The second stage: Increase the pressure on the battery surface to 5 MPa, and perform constant current charging at a current of 0.2C (600 mA) until the voltage reaches 4.10 V, and the charging time is 120 min; Leave it for 5 min, and the pre-formation is completed;

[0093] (3) Collect the data of the charging capacity Q and the corresponding voltage V of the sample battery during the charging process, import the voltage V and capacity Q data into the Origin drawing software, use the voltage V as the X-axis and the capacity Q as the Y-axis, and after software processing, draw the differential capacitance curve (dQ / dV-V) of the formation process; Take the voltage values corresponding to the first reaction peak from the appearance to the end in the voltage range of 1.50 - 3.00 V of the differential capacitance curve (dQ / dV-V), and record them as V1 and V2 in sequence. This voltage range is the water decomposition voltage range of the battery. As Figure 3 described, V1 = 2.40 V, V2 = 2.80 V; Similarly, observe the change of the dQ / dV-V peak in the voltage range of 3.00 - 4.35 V, and take the voltage values corresponding to the highest peak from the appearance to the end, and record them as V3 and V4 in sequence. This voltage range is the voltage range where lithium ions rapidly escape from the positive electrode and embed into the negative electrode. As Figure 4 described, V3 = 3.70 V, V4 = 3.85 V;

[0094] The second step: Mass battery formation and aging:

[0095] (4) Bake the batch-produced batteries, and use a Karl Fischer moisture tester to measure the moisture content of the baked soft-pack batteries after baking. The moisture content is 150 ppm; Then transfer them into the glove box for liquid injection, and perform liquid injection and activation according to the process of the sample battery;

[0096] (5) Put the fully activated sample battery into the fixture forming equipment, heat it up to 65 °C, and perform hot pressing formation in a stepped segmented manner. The formation process is as follows:

[0097] The first stage: Apply a pressure of 2 MPa to the battery surface, charge at a constant current of 0.01 C (20 mA) until the voltage reaches 2.70 V, and the charging time is 30 min; let it stand for 5 min;

[0098] The second stage: Increase the pressure on the battery surface to 6 MPa, charge at a constant current of 0.1 C (200 mA) until the voltage reaches 3.85 V, and the charging time is 90 min;

[0099] The third stage: Increase the pressure on the battery surface to 9 MPa, charge at a constant current and constant voltage of 0.8 C (1600 mA) until the voltage reaches 4.10 V, the cut-off current is 0.02 C (69 mA), the charging time is 90 min, let it stand for 5 min, and the formation is completed;

[0100] (6) After the battery formation is completed, use the formation cabinet to conduct a full inspection and screening of the end voltage after the first-stage battery charging. For the batteries with a voltage lower than 2.80 V, they are batteries with excessive moisture content, pick them out and make distinctions, and mark them as Class B batteries; for the batteries with a voltage greater than or equal to 2.80 V, they are batteries with qualified moisture content, and mark them as Class A batteries;

[0101] (7) Then put the formed batteries into a high-temperature aging chamber for high-temperature aging. The aging temperature is 40 °C and the aging time is 72 h; after the high-temperature aging is completed, conduct normal-temperature aging. The aging temperature is 20 °C and the aging time is 24 h;

[0102] The third step: The stage of re-repairing and re-organizing the SEI film;

[0103] (8) Put the aged Class A batteries into the fixture formation equipment for charge and discharge. First, set the hot-press formation temperature to 40 °C, and the pressure applied to the battery surface is 4 MPa. The specific process is as follows:

[0104] The first stage: Charge at a constant current and constant voltage of 1 C (2000 mA) until the voltage reaches 4.20 V, the cut-off current is 0.3 C (600 mA), and the charging time is 60 min; let it stand for 5 min;

[0105] The second stage: Discharge at a constant current of 1.40 C (2800 mA) until the voltage reaches 2.55 V, and the time is 80 min; let it stand for 5 min;

[0106] The third stage: Charge at a constant current of 1.20 C (2400 mA) until the voltage reaches 4.10 V, and the time is 60 min; let it stand for 5 min;

[0107] The fourth stage: Discharge at a constant current of 1.50 C (3000 mA) until the voltage reaches 2.45 V, and the time is 60 min; let it stand for 5 min;

[0108] The fifth stage: Constant current and constant voltage charging is carried out at a current of 1.0C (2000 mA) until the voltage reaches 4.05 V, the cut-off current is 0.1C (200 mA), and the time is 100 min; Stand still for 5 min;

[0109] (9) Perform subsequent battery preparation processes such as degassing, second sealing, and trimming on the battery obtained in step (8) to obtain a semi-finished battery;

[0110] (10) Place the semi-finished battery obtained in step (9) into a normal temperature aging chamber for normal temperature aging. The aging temperature is 20 °C and the aging time is 36 h to finally obtain a finished battery.

[0111] Example 3

[0112] A formation method for improving the cycle stability of silicon-containing soft-pack lithium-ion batteries, comprising the following steps:

[0113] The first step: Pre-formation of sample batteries:

[0114] (1) Take several batteries in mass production as sample batteries for baking. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked batteries, and the moisture content is 300 ppm; Transfer the baked battery cores from the baking oven to a glove box for liquid injection; Subsequently, activate the batteries. The activation temperature is 50 °C and the time is 36 h; The designed capacity of the battery is 5 Ah, the positive electrode is lithium cobaltate, and the single-sided surface density of the positive electrode is 168 g / m 2 , the content of nano-silicon in the silicon-carbon negative electrode is 5.0%, the content of the electrolyte additive FEC is 12.0 vol%, and the content of VC is 3.8 vol%; The electrolyte injection coefficient is 2.5 g / Ah;

[0115] (2) Place the fully activated sample batteries into a fixture formation device, heat up to 80 °C, and perform hot pressing formation in a stepped segmented manner. The formation process is as follows:

[0116] The first stage: Apply a pressure of 3 MPa to the battery surface, and perform constant current charging at a current of 0.02C (100 mA) until the voltage reaches 3.00 V, and the charging time is 30 min;

[0117] The second stage: Increase the battery surface pressure to 7 MPa, and perform constant current charging at a current of 0.4C (2000 mA) until the voltage reaches 4.20 V, and the charging time is 120 min; Set aside for 5 min, and the pre-formation ends;

[0118] (3) Collect the charging capacity Q and the corresponding voltage V data of the sample battery during charging. Import the voltage V and capacity Q data into the Origin plotting software. Use the voltage V as the X-axis and the capacity Q as the Y-axis. After software processing, plot the differential capacitance curve (dQ / dV-V) during the formation process; Take the voltage values corresponding to the first reaction peak from its appearance to the end in the voltage range of 1.50 - 3.00V of the differential capacitance curve (dQ / dV-V), and record them as V1 and V2 in sequence. This voltage range is the water decomposition voltage range of the battery. As Figure 5 described, V1 = 2.00V, V2 = 2.45V; Similarly, observe the changes in the dQ / dV-V peak in the voltage range of 3.00 - 4.35V, and take the voltage values corresponding to the highest peak from its appearance to the end, and record them as V3 and V4 in sequence. This voltage range is the voltage range where lithium ions rapidly escape from the positive electrode and embed into the negative electrode. As Figure 6 described, V3 = 3.90V, V4 = 4.10V;

[0119] Step 2: Formation and aging of batch batteries:

[0120] (4) Bake the batch-produced batteries. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked soft-pack batteries, and its moisture content is 100 ppm; Then transfer them into the glove box for liquid injection, and perform liquid injection and activation according to the process of the sample battery.

[0121] (5) Put the fully activated sample battery into the fixture formation equipment, heat up to 80°C, and perform thermal pressing formation in a stepped segmented manner. The formation process is as follows:

[0122] First stage: Apply a pressure of 3 MPa to the battery surface, and charge at a constant current of 0.01C (50 mA) until the voltage reaches 2.45V. The charging time is 30 min; Let it stand for 5 min;

[0123] Second stage: Increase the battery surface pressure to 6 MPa, and charge at a constant current of 0.3C (1500 mA) until the voltage reaches 3.90V. The charging time is 90 min;

[0124] Third stage: Increase the battery surface pressure to 10 MPa, and charge at a constant current and constant voltage of 1.2C (6000 mA) until the voltage reaches 4.20V, with a cut-off current of 0.1C (500 mA). The charging time is 90 min, and let it stand for 5 min. The formation is completed;

[0125] (6) After the battery formation is completed, use the formation cabinet to conduct a full inspection and screening of the end voltage after the first-stage battery charging. For batteries with a voltage lower than 2.45V, they are batteries with excessive moisture content, pick them out and make distinctions, and mark them as Grade B batteries; for batteries with a voltage greater than or equal to 2.45V, they are batteries with qualified moisture content, and mark them as Grade A batteries;

[0126] (7) Subsequently, place the formed batteries into a high-temperature aging chamber for high-temperature aging. The aging temperature is 50°C and the aging time is 36h; after the high-temperature aging is completed, conduct normal-temperature aging. The aging temperature is 30°C and the aging time is 36h;

[0127] The third step: The stage of re-repairing and re-combining the SEI film;

[0128] (8) Place the aged Grade A batteries into the fixture formation equipment for charge and discharge. First, set the hot-press formation temperature to 60°C and the pressure applied to the battery surface to 4MPa. The specific process is as follows:

[0129] The first stage: Constant current and constant voltage charge at a current of 1C (5000mA) until the voltage reaches 4.45V, with a cut-off current of 0.1C (500mA), and the charging time is 60min; stand still for 5min;

[0130] The second stage: Constant current discharge at a current of 1.20C (6000mA) until the voltage reaches 2.50V, and the time is 90min; stand still for 5min;

[0131] The third stage: Constant current charge at a current of 1.20C (2400mA) until the voltage reaches 4.35V, and the time is 60min; stand still for 5min;

[0132] The fourth stage: Constant current discharge at a current of 1.0C (5000mA) until the voltage reaches 2.75V, and the time is 60min; stand still for 5min;

[0133] The fifth stage: Constant current and constant voltage charge at a current of 1.5C (7500mA) until the voltage reaches 4.10V, with a cut-off current of 0.05C (75mA), and the time is 100min; stand still for 5min;

[0134] (9) Conduct subsequent battery preparation processes such as air extraction, secondary sealing, and edge cutting on the batteries obtained in step (8) to obtain semi-finished batteries;

[0135] (10) Place the semi-finished batteries obtained in step (9) into a normal-temperature aging chamber for aging. The aging temperature is 30°C and the aging time is 24h to finally obtain finished batteries.

[0136] To further prove the beneficial effects of the present invention for a better understanding of the present invention, the following comparative examples are provided to further clarify the technical features disclosed in the present invention, but it should not be construed as a limitation of the present invention. For other improvements made by those skilled in the art based on the above-mentioned invention content without creative work, they are also considered to fall within the protection scope of the present invention.

[0137] Comparative Example 1

[0138] This Comparative Example 1 is compared with Example 1, and formation is carried out using the formation process used by conventional battery enterprises, including the following steps:

[0139] (1) Bake the batteries produced in batches. After baking, use a Karl Fischer moisture tester to test the moisture content of the baked batteries, and the moisture content is 200 ppm; then transfer the baked battery cores from the baking oven to a glove box for liquid injection; subsequently, the batteries are activated, the activation temperature is 45 °C, and the time is 36 h; where the designed capacity of the battery is 3.45 Ah, the positive electrode is lithium nickel cobalt manganese oxide NCM111, the single-sided surface density of the positive electrode is 197 g / m 2 , the content of nano-silicon in the silicon-carbon negative electrode is 3%, the content of the electrolyte additive FEC is 5 vol%, and the content of VC is 1.5 vol%; the liquid injection coefficient of the electrolyte is 2.4 g / Ah;

[0140] (2) Put the fully activated sample batteries into a fixture formation device, heat up to 75 °C, and perform hot pressing formation in a stepped segmented manner. The formation process is as follows:

[0141] The first stage: Apply a pressure of 3 MPa to the battery surface, and charge at a constant current of 0.01C (34.5 mA) until the voltage reaches 3.00 V, and the charging time is 10 min; let it stand for 5 min;

[0142] The second stage: Increase the pressure on the battery surface to 5 MPa, and charge at a constant current of 0.2C (690 mA) until the voltage reaches 3.70 V, and the charging time is 20 min;

[0143] The third stage: Increase the pressure on the battery surface to 10 MPa, and charge at a constant current and constant voltage of 0.5C (1725 mA) until the voltage reaches 4.15 V, the cut-off current is 0.02C (69 mA), the charging time is 70 min, let it stand for 5 min, and the formation ends;

[0144] (3) After the battery formation is completed, put the batteries into a high-temperature aging chamber for high-temperature aging, the aging temperature is 45 °C, and the aging time is 36 h; after the high-temperature aging is completed, perform normal-temperature aging, the aging temperature is 25 °C, and the aging time is 12 h;

[0145] (4) Subject the battery obtained in step (3) to subsequent battery preparation processes such as air extraction, secondary sealing, and edge trimming to obtain a semi-finished battery;

[0146] (5) Place the semi-finished battery obtained in step (4) in a normal temperature aging chamber for normal temperature aging. The aging temperature is 25°C and the aging time is 24 h to finally obtain a finished battery.

[0147] Comparative Example 2

[0148] This Comparative Example 2 is compared with Example 2, and formation is carried out using the formation process used by conventional battery enterprises, including the following steps:

[0149] (1) Bake the batteries produced in batches. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked batteries, and the moisture content is 150 ppm; Subsequently, transfer the baked battery cores from the baking oven to a glove box for liquid injection; Subsequently, the battery is activated, the activation temperature is 55°C, and the time is 48 h; Among them, the designed capacity of the battery is 2 Ah, the positive electrode is a mixed positive electrode of lithium nickel cobalt manganese oxide and lithium manganese oxide, and the mass ratio is: NCM523:LMO = 60:40, and the single-sided surface density of the positive electrode is 150 g / m 2 , the content of nano-silicon in the silicon-carbon negative electrode is 1.5%, the content of the electrolyte additive FEC is 8.0 vol%, and the content of VC is 3.0 vol%; The liquid injection coefficient of the electrolyte is 2.9 g / Ah;

[0150] (2) Place the fully activated battery in a fixture formation device, heat it up to 65°C, and perform hot press formation in a stepped segmented manner. The formation process is as follows:

[0151] First stage: Apply a pressure of 2 MPa to the battery surface, and charge at a constant current of 0.01C (20 mA) until the voltage reaches 2.70 V. The charging time is 30 min; Let it stand for 5 min;

[0152] Second stage: Increase the pressure on the battery surface to 6 MPa, and charge at a constant current of 0.1C (200 mA) until the voltage reaches 3.85 V. The charging time is 90 min;

[0153] Third stage: Increase the pressure on the battery surface to 9 MPa, and charge at a constant current and constant voltage of 0.8C (1600 mA) until the voltage reaches 4.10 V, and the cut-off current is 0.02C (69 mA). The charging time is 90 min, and let it stand for 5 min to end the formation;

[0154] (3) Subsequently, place the battery in a high-temperature aging chamber for high-temperature aging. The aging temperature is 40°C and the aging time is 72 h; After the high-temperature aging ends, perform normal-temperature aging. The aging temperature is 20°C and the aging time is 24 h;

[0155] (4) Perform subsequent battery preparation processes such as degassing, secondary sealing, and edge trimming on the battery obtained in step (3) to obtain a semi-finished battery;

[0156] (5) Place the semi-finished battery obtained in step (4) into a normal temperature aging chamber for normal temperature aging. The aging temperature is 20 °C and the aging time is 36 h to finally obtain a finished battery.

[0157] Table 1 Comparison of liquid retention coefficient and cycle performance between examples and comparative examples

[0158]

[0159] Based on the above analysis, it can be seen that the present invention can not only quickly and efficiently select water-abnormal battery cells during the production process of battery cells, avoiding waste of resources caused by abnormal battery cells in subsequent processes; at the same time, it also prevents abnormal battery cells from flowing into the client side, increasing after-sales costs. At the same time, by determining the formation process parameters of a batch of batteries through the differential capacitance curve (dQ / dV-V) of the battery charging curve, the optimal formation process plan can be determined according to different battery systems. At the same time, through two charge-discharge formation processes of the present invention, the SEI film of the silicon-containing soft-pack lithium-ion battery obtained is uniform, stable, and highly dense. The obtained silicon-containing soft-pack lithium-ion battery has a flat surface, high hardness, and good cycle stability.

[0160] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A formation method for improving the cycle stability of silicon-containing soft-pack lithium-ion batteries, characterized in that, It includes the following steps: The first step: Pre-forming of sample batteries: (1) Take several batteries in mass production as sample batteries for baking. After baking, use a Karl Fischer moisture tester to measure the moisture content of the baked batteries, denoted as H1; the designed capacity of the batteries is denoted as Q1; transfer the baked battery cores from the baking oven to a glove box for liquid injection; subsequently, activate the batteries. (2) Put the fully activated sample batteries into a fixture forming device, heat up to 60 - 80 °C, and perform hot pressing forming in a stepped segmented manner. The forming process is as follows: The first stage: Apply a pressure P1 to the battery surface, charge at a constant current I1 until the voltage reaches U1, and the charging time is T1. The second stage: Increase the pressure on the battery surface to P2, charge at a constant current I2 until the voltage reaches U2, and the charging time is T2; leave it for 5 minutes, and the pre-forming ends. (3) Collect the charging capacity Q and the corresponding voltage V data of the sample batteries during the charging process, import the voltage V and capacity Q data into Origin plotting software, use the voltage V as the X-axis and the capacity Q as the Y-axis, and after software processing, plot the differential capacitance curve (dQ / dV - V) of the forming process; take the voltage values corresponding to the first reaction peak in the voltage range of 1.50 - 3.00 V of the differential capacitance curve (dQ / dV - V) from the appearance to the end, denoted as V1 and V2 in sequence. This voltage range is the decomposition voltage range of water in the battery; similarly, observe the change of the dQ / dV - V peak in the voltage range of 3.00 - 4.50 V, and take the voltage values corresponding to the highest peak from the appearance to the end, denoted as V3 and V4 in sequence. This voltage range is the voltage range where lithium ions rapidly escape from the positive electrode and embed into the negative electrode. The second step: Mass battery forming and aging: (4) Bake the batteries in mass production, use a Karl Fischer moisture tester to measure the moisture content of the baked soft-pack batteries after baking, denoted as H2; then transfer the baked battery cores from the baking oven to a glove box for liquid injection, and perform liquid injection and activation according to the process of the sample batteries. (5) Put the fully activated sample batteries into a fixture forming device, heat up to 45 - 80 °C, and perform hot pressing forming in a stepped segmented manner. The forming process is as follows: The first stage: Apply a pressure P3 to the battery surface, charge at a constant current I3 until the voltage reaches U3, and the charging time is 15 - 30 minutes; let it stand for 5 minutes. The second stage: Increase the pressure on the battery surface to P4, charge at a constant current I4 until the voltage reaches U4, and the charging time is 10 - 60 minutes. The third stage: Increase the pressure on the battery surface to P5, charge at a constant current I5 and constant voltage until the voltage reaches U5, with a cut-off current I6, and the charging time is 30 - 120 minutes. Leave it for 5 minutes, and the forming ends. (6) After the battery forming is completed, use a forming cabinet to conduct a full inspection and screening of the end voltage after the first-stage battery charging. Determine the batteries with a voltage lower than V2 as batteries with excessive moisture content, pick them out and make distinctions, and mark them as Class B batteries; the batteries with a voltage greater than or equal to V2 are batteries with qualified moisture content, and mark them as Class A batteries. (7) Subsequently, the formed battery is placed in a high-temperature aging chamber for high-temperature aging. After the high-temperature aging is completed, normal-temperature aging is carried out; Step 3: The stage of SEI film re-repair and recombination; (8) The aged Class A batteries are placed in a fixture forming device for charge and discharge. First, the hot-pressing forming temperature is set to 40 - 60 °C, and the pressure P6 is applied to the battery surface. The specific process is as follows: The first stage: Constant current and constant voltage charging to voltage U6 with current I7, cut-off current I8, and the charging time is 60 - 180 min; Stand still for 5 min; The second stage: Constant current discharging to voltage U7 with current I9, and the time is 10 - 180 min; Stand still for 5 min; The third stage: with a current I 10 Constant current charging to a voltage U8 for a time of 10 to 90 minutes; standing still for 5 minutes; Fourth stage: with a current I 11 Constant current discharge to voltage U9 for 10 - 90 minutes; stand still for 5 minutes; Fifth stage: with a current I 12 Constant current and constant voltage charging to voltage U 10 , the cut-off current is I 13 , the time is 10 - 90 min; stand still for 5 min; (9) The batteries obtained in step (8) are subjected to subsequent battery preparation processes such as air extraction, second sealing, and edge cutting to obtain semi-finished batteries; (10) The semi-finished batteries obtained in step (9) are placed in a normal-temperature aging chamber for aging. The aging temperature is 20 - 30 °C, and the aging time is 24 - 48 h, and finally finished batteries are obtained.

2. The forming method according to claim 1, characterized in that In step (1), the designed capacity Q1 of the battery is 0.5 to 10 Ah; the positive electrode is one or any mixture of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate, and the single-sided surface density of the positive electrode is 140 to 250 g / m 2 ; the negative electrode is a silicon-carbon negative electrode, and the content of nano-silicon is 1% to 15%; The water content H1 of the sampled batteries is 200 - 400 ppm; the content of the electrolyte additive fluoroethylene carbonate FEC is 5% - 20% (vol), and the content of vinylene carbonate VC is 1% - 10% (vol); the electrolyte injection coefficient is 2.1 - 3.6 g / Ah; the activation temperature is 40 - 65 °C, and the time is 12 - 48 h.

3. The formation method according to claim 1, characterized in that, In step (2), the battery surface pressure P1 = (10% - 40%) * P2, P2 = 1 - 8 MPa / PCS, the charging current I1 is 0.01 - 0.03 C, and the charging current I2 is 0.1 - 0.5 C; the charging voltage U1 is 3.0 - 3.30 V, and the charging voltage U2 is 4.20 - 4.50 V; the charging time T1 is 15 - 30 min, and the charging time T2 is 80 - 800 min.

4. The formation method according to claim 1, characterized in that, In step (3), V1 is 1.50 - 3.00 V, V2 is 1.50 - 3.00 V, V3 is 3.50 - 4.20 V, and V4 is 3.50 - 4.20 V.

5. The formation method according to claim 1, wherein, In step (4), the water content H2 of the battery is 100 - 150 ppm.

6. The formation method according to claim 1, characterized in that, In step (5), the battery surface pressure P3 = (10% - 40%) * P5, P4 = (40% - 90%) * P5, P5 = 1 - 12 MPa / PCS, the charging current I3 is 0.01 - 0.03 C, the voltage U3 = V2 is 1.50 - 3.00 V, the charging current I4 is 0.1 - 0.5 C, U4 = V4 is 3.50 - 4.20 V, the charging current I5 is 0.3 - 1.0 C, the cut-off current I6 is 0.05 - 0.5 C, and the charging voltage U5 is 4.20 - 4.50 V.

7. The formation method according to claim 1, wherein In step (6), V2 is 1.50 - 3.00 V.

8. The formation method according to claim 1, characterized in that, In step (7), the aging temperature for high-temperature aging is 40 - 60 °C, and the aging time is 36 - 96 h; the aging temperature for normal-temperature aging is 20 - 30 °C, and the aging time is 12 - 36 h.

9. The formation method according to claim 1, wherein In step (8), the pressure P6 on the battery surface is 1 to 6 MPa / PCS; the current I7 is 0.6 to 1.5 C, the charging cut-off current I8 is 0.05 to 0.2 C, the voltage U6 is 4.20 to 4.50 V, the discharge current I9 is 0.7 to 1.5 C, the discharge cut-off voltage U7 is 2.50 to 4.20 V, and the charging current I 10 is 1.0 to 2.0 C, and U8 is 4.20 to 4.50 V; the discharge current I 11 is 0.7 to 2.0 C, and the discharge cut-off voltage U9 is 2.45 to 4.20 V; the charging current I 12 is 1.0 to 2.0 C, and the charging cut-off current I 13 is 0.05 to 0.3 C, and the charging voltage U 10 is 3.8 to 4.30 V.

Images