Formation process of lithium ion battery and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a formation process of a lithium ion battery and the lithium ion battery, and the formation process of the lithium ion battery comprises the following steps: S1, placing the lithium ion battery at a first temperature, carrying out first-stage constant-current charging by adopting a first current and a first voltage, and standing; s2, placing the lithium ion battery at a second temperature, carrying out second-stage constant-current charging by adopting a second current and a second voltage, and standing; s3, carrying out mechanical extrusion vacuumizing treatment on the lithium ion battery, and carrying out primary sealing on the treated battery; s4, placing the lithium ion battery at a third temperature, and carrying out third-stage constant-current charging by adopting a third current and a third voltage; and S5, carrying out ultrasonic vacuumizing on the lithium ion battery obtained in the step S4, and carrying out hot-pressing secondary sealing to obtain the formed lithium ion battery. According to the invention, the capacity retention ratio and the safety performance of the battery in a low-pressure environment are improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium - ion batteries, and particularly to a formation process of a lithium - ion battery and a lithium - ion battery. Background Art

[0002] Due to their high energy density, long cycle life, and environmental friendliness, lithium - ion batteries have been widely used in fields such as portable electronic devices, electric vehicles, and aerospace. However, in high - altitude areas or aerospace applications, the low - pressure environment poses additional challenges to the performance and safety of lithium - ion batteries. Research shows that the low - pressure environment accelerates the aging process of lithium - ion batteries. Under the air pressure conditions of 96 kPa, 60 kPa, and 30 kPa, the internal structure of the battery may change, affecting the diffusion of lithium ions and the stability of the battery interface.

[0003] Under low - pressure conditions, the gas generated during the battery formation process is not easily discharged, resulting in an increase in the internal pressure of the battery, which may cause the battery case to bulge, be scrapped, or even explode. In addition, the electrolyte is prone to crystallization, causing the air - extraction pipeline to be blocked, affecting the battery formation process. Existing battery formation equipment has many problems in a low - pressure environment. For example, the rate of the internal electrochemical reaction of the battery is high, the side reactions are few, the battery cycle performance is improved by about 1 time, but the difference in the internal resistance expands, resulting in worse temperature uniformity, and at the same time, the battery heat dissipation performance decreases, leading to a sharp deterioration of its thermal stability.

[0004] Therefore, it is necessary to provide a formation process for lithium - ion batteries to improve the safety performance and capacity retention rate of lithium - ion batteries under low pressure. Summary of the Invention

[0005] The purpose of the present invention is to provide a formation process for lithium - ion batteries to improve the safety performance and capacity retention rate of lithium - ion batteries under low pressure in view of the deficiencies of the prior art.

[0006] To achieve the above - mentioned purpose, the present invention adopts the following technical solutions: A formation process for a lithium - ion battery, comprising the following steps:

[0007] Step S1: Place the lithium - ion battery at a first temperature, and perform constant - current charging in the first stage with a first current and a first voltage, and then let it stand;

[0008] Step S2: Place the lithium - ion battery at a second temperature, and perform constant - current charging in the second stage with a second current and a second voltage, and then let it stand;

[0009] Step S3: Perform mechanical extrusion and vacuum - pumping treatment on the lithium - ion battery, and perform a primary sealing on the treated battery;

[0010] Step S4: Place the lithium-ion battery at the third temperature and perform constant current charging in the third stage with the third current and the third voltage.

[0011] Step S5: Subject the lithium-ion battery obtained in Step S4 to ultrasonic vacuum pumping and perform thermal pressing for secondary sealing to obtain the formed lithium-ion battery.

[0012] Preferably, the first temperature T 1 , the second temperature T 2 , and the third temperature T 3 satisfy the relationship: T 1 < T 2 < T 3 ;

[0013] The first current I 1 , the second current I 2 , and the third current I 3 satisfy the relationship: I 1 < I 2 < I 3 ;

[0014] The first voltage U 1 , the second voltage U 2 , and the third voltage U 3 satisfy the relationship: U 1 < U 2 < U 3 .

[0015] Preferably, in Step S1, the first temperature is 20 - 25 °C, the first current is 0.15 - 0.2 C, and the first voltage is 3.1 V.

[0016] Preferably, in Step S2, the second temperature is 26 - 30 °C, the second current is 0.25 - 0.3 C, and the second voltage is 3.5 V.

[0017] Preferably, in Step S4, the third temperature is 31 - 35 °C, the third current is 0.4 - 0.45 C, and the third voltage is 4.2 V.

[0018] Preferably, in Step S3, the specific steps of the mechanical extrusion vacuum pumping include:

[0019] Step S1: Place the lithium-ion battery in a sealed bag to ensure there is no air inside the bag;

[0020] Step S2: Place the sealed bag in a vacuum chamber and start the vacuum pump;

[0021] Step S3: While maintaining the vacuum state, use a mechanical device to squeeze the battery;

[0022] Step S4: Turn off the vacuum pump, open the vacuum chamber, and take out the lithium-ion battery after the first sealing.

[0023] Preferably, in step S2, the pressure in the vacuum chamber drops to 1*(10 -4 -10 -3 ) Pa, and the holding time is 5 - 10 min;

[0024] And / or, in step S3, the pressure applied by the mechanical device is 0.1 - 0.5 MPa.

[0025] Preferably, in step S5, the specific steps of the ultrasonic vacuum hot pressing include:

[0026] Step S1: Place the lithium-ion battery in a sealed container containing an inert gas to ensure that there is no air in the sealed container;

[0027] Step S2: Start the vacuum pump, and start the ultrasonic generator while maintaining the vacuum state;

[0028] Step S3: Turn off the vacuum pump and the ultrasonic generator, open the container, take out the lithium-ion battery, and perform hot pressing for the second sealing.

[0029] Preferably, in step S2, the pressure in the sealed container drops to (1 - 1.2)*10 -4 Pa, the frequency of the ultrasonic generator is 80 - 100 kHz, the power is 80 - 100 W, and the processing time is 15 - 30 min;

[0030] And / or, in step S3, the temperature of the hot pressing is 180 - 200 °C, the time is 5 - 10 s, and the pressure is 0.5 - 1 MPa.

[0031] In addition, the present invention also provides a lithium-ion battery prepared by the formation process of the above lithium-ion battery.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: By combining the segmented formation technology with the two sealing technologies of mechanical extrusion vacuuming and ultrasonic vacuuming, the present invention improves the electrochemical performance and safety performance of the battery in a low-pressure environment. Among them, the segmented formation technology can form a dense SEI film and also make the battery generate gas more fully during the formation stage. By using the two sealing technologies of mechanical extrusion vacuuming and ultrasonic vacuuming again in the degassing process, it is ensured that there is no residual gas inside the lithium battery. Under low pressure, the battery is flat and has no bulging phenomenon, and the contact between the positive and negative electrode plates and the separator is more reliable, and the electrode plates will not move during charge and discharge, thereby improving the capacity retention rate of the lithium-ion battery under low pressure and also improving the safety performance of the lithium ions. Detailed Embodiments

[0033] To make the technical solutions and advantages of the present invention clearer, the following will, in conjunction with specific embodiments, clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0034] According to the first aspect of the present application, the present application provides a formation process for a lithium-ion battery, including the following steps:

[0035] Step S1: Place the lithium-ion battery at a first temperature, and perform constant current charging in the first stage using a first current and a first voltage, then let it stand;

[0036] Step S2: Place the lithium-ion battery at a second temperature, and perform constant current charging in the second stage using a second current and a second voltage, then let it stand;

[0037] Step S3: Subject the lithium-ion battery to mechanical extrusion and vacuum pumping treatment, and perform primary sealing on the treated battery;

[0038] Step S4: Place the lithium-ion battery at a third temperature, and perform constant current charging in the third stage using a third current and a third voltage;

[0039] Step S5: Subject the lithium-ion battery obtained in Step S4 to ultrasonic vacuum pumping, and perform thermal pressing for secondary sealing to obtain a formed lithium-ion battery.

[0040] Among them, the lithium-ion battery adopts a segmented formation technology, which can form a dense SEI film and also allows the battery to generate gas more fully during the formation stage. In the degassing process, the two sealing technologies of mechanical extrusion vacuum pumping and ultrasonic vacuum pumping are reused to ensure that there is no residual gas inside the lithium battery. Under low pressure, the battery is flat and there is no bulging phenomenon, and the contact between the positive and negative electrode plates and the separator is more reliable. During charge and discharge, the electrode plates will not move, thereby improving the capacity retention rate of the lithium-ion battery under low pressure and also improving the safety performance of the lithium-ion battery.

[0041] In some embodiments, the standing time is 12 - 24h.

[0042] In some embodiments, the first temperature T 1 、the second temperature T 2 、the third temperature T 3 satisfy the relationship: T 1 <T 2 <T 3 ;

[0043] The first current I 1 、the second current I 2 、the third current I3 Satisfy the relationship: I 1 <I 2 <I 3 ;

[0044] The first voltage U 1 , the second voltage U 2 , the third voltage U 3 Satisfy the relationship: U 1 <U 2 <U 3 .

[0045] Among them, through the sectional formation technology, a dense SEI film can be formed, and the gas production of the battery during the formation stage is more sufficient.

[0046] In some embodiments, in step S1, the first temperature is 20 - 25 °C, for example, it can be 20 °C, 21 °C, 22 °C, 23 °C, 24 °C or 25 °C; the first current is 0.15 - 0.2 C, for example, it can be 0.15 C, 0.16 C, 0.17 C, 0.18 C, 0.19 C or 0.2 C; the first voltage is 3.1 V.

[0047] In some embodiments, in step S2, the second temperature is 26 - 30 °C, for example, it can be 26 °C, 27 °C, 28 °C, 29 °C or 30 °C; the second current is 0.25 - 0.3 C, for example, it can be 0.25 C, 0.26 C, 0.27 C, 0.28 C, 0.29 C or 0.3 C; the second voltage is 3.5 V.

[0048] In some embodiments, in step S4, the third temperature is 31 - 35 °C, for example, it can be 31 °C, 32 °C, 33 °C, 34 °C or 35 °C; the third current is 0.4 - 0.45 C, for example, it can be 0.4 C, 0.41 C, 0.42 C, 0.43 C, 0.44 C or 0.45 C; the third voltage is 4.2 V.

[0049] In some embodiments, in step S3, the specific steps of mechanical extrusion and vacuum pumping include:

[0050] Step S1: Put the obtained lithium ions into a sealed bag to ensure that there is no air in the bag;

[0051] Step S2: Put the sealed bag into a vacuum chamber and start the vacuum pump;

[0052] Step S3: Under the state of maintaining vacuum, use a mechanical device to extrude the battery;

[0053] Step S4: Turn off the vacuum pump, open the vacuum chamber, and take out the once-sealed lithium-ion battery.

[0054] In some embodiments, in step S2, the pressure drop in the vacuum chamber is 1×(10 -4 -10 -3 ) Pa, for example, it can be 1×10 -4 Pa or 1×10 -3 Pa;

[0055] And / or, in step S3, the pressure applied by the mechanical device is 0.1 - 0.5 MPa, for example, it can be 0.1 MPa, 0.2 MPa or 0.5 MPa, and the duration is 5 - 10 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min. If the pressure is too high, it will cause the internal battery cells to move and misalign, resulting in safety accidents. If the duration is too long, it will cause damage to the electrode sheets, affecting the electrical performance and safety performance of the battery; if the pressure and time are too small, it will not achieve the purpose of completely removing the gas.

[0056] In some embodiments, in step S5, the specific steps of ultrasonic vacuum hot pressing include:

[0057] Step S1: Place the lithium-ion battery in a sealed container containing an inert gas to ensure that there is no air in the sealed container;

[0058] Step S2: Start the vacuum pump, and start the ultrasonic generator while maintaining the vacuum state;

[0059] Step S3: Turn off the vacuum pump and the ultrasonic generator, open the container, take out the lithium-ion battery, and perform hot pressing for secondary sealing.

[0060] In some embodiments, in step S2, the pressure drop in the sealed container is (1 - 1.2)×10 -4 Pa, for example, it can be 1×10 -4 Pa, 1.1×10 -4 Pa or 1.2×10 -4 Pa; the frequency of the ultrasonic generator is 80 - 100 kHz, for example, it can be 80 kHz, 85 kHz, 90 kHz, 95 kHz or 100 kHz; the power is 80 - 100 W, for example, it can be 80 W, 90 W or 100 W; the processing time is 15 - 30 min, for example, it can be 15 min, 20 min, 25 min or 30 min;

[0061] And / or, in step S3, the temperature of the hot pressing is 180 - 200 °C, for example, it can be 180 °C, 185 °C, 190 °C, 195 °C or 200 °C; the time is 5 - 10 s, for example, it can be 5 s, 6 s, 7 s, 8 s, 9 s or 10 s; the pressure is 0.5 - 1 MPa, for example, it can be 0.5 MPa, 0.8 MPa or 1.0 MPa. If the pressure is too high, the ultrasonic frequency is too high, the power is too high, or the time is too long, it will cause damage to the internal electrode sheets of the battery, affecting the electrical performance and safety performance of the battery; if each parameter is too small, the purpose of completely removing the gas cannot be achieved.

[0062] According to the second aspect of the present application, the present application provides a lithium-ion battery prepared by the formation process of the above lithium-ion battery.

[0063] In some embodiments, the lithium-ion battery includes a battery cell wound by a negative electrode sheet, a positive electrode sheet and a separator, an electrolyte, and a housing for encapsulating the battery cell and the electrolyte.

[0064] Among them, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be one or more combinations of compounds represented by, but not limited to, the chemical formula such as Li a Ni x Co y M z O 2-b N b (where 0.95 ≤ a ≤ 1.2, x > 0, y ≥ 0, z ≥ 0, and x + y + z = 1, 0 ≤ b ≤ 1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S), and the positive electrode active material can also be one or more combinations of, but not limited to, LiCoO 2 , LiNiO 2 , LiVO 2 , LiCrO 2 , LiMn 2 O 4 , LiCoMnO 4 , Li 2 NiMn 3 O 8 , LiNi 0.5 Mn 1.5 O 4 , LiCoPO 4 , LiMnPO 4 , LiFePO 4 , LiNiPO 4 , LiCoFSO 4 , CuS 2 , FeS 2, MoS 2 , NiS, TiS 2 or a combination of one or more of the above. The positive electrode active material can also be modified. The method for modifying the positive electrode active material should be known to those skilled in the art. For example, methods such as coating and doping can be used to modify the positive electrode active material, and the materials used for the modification treatment can be a combination of one or more of, but not limited to, Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive electrode current collector is usually a structure or part that collects current, and the positive electrode current collector can be various materials in the art suitable for use as the positive electrode current collector of a lithium-ion battery. For example, the positive electrode current collector can be, but not limited to, a metal foil, and more specifically, it can be, but not limited to, an aluminum foil, etc.

[0065] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material can be one or several of, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form an alloy with lithium. Among them, the graphite can be selected from one or several of artificial graphite, natural graphite, and modified graphite; the silicon-based materials can be selected from one or several of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; the tin-based materials can be selected from one or several of elemental tin, tin oxides, and tin alloys. The negative electrode current collector is usually a structure or part that collects current, and the negative electrode current collector can be various materials in the art suitable for use as the negative electrode current collector of a lithium-ion battery. For example, the negative electrode current collector can be, but not limited to, a metal foil, and more specifically, it can be, but not limited to, a copper foil, etc.

[0066] Example 1

[0067] Preparation of the positive electrode sheet:

[0068] Disperse 97.4% lithium nickel cobalt manganate, 0.8% conductive carbon, 0.8% carbon nanotubes, and 1.0% polyvinylidene fluoride evenly in N-methylpyrrolidone through a double planetary mixer, and uniformly coat it on a 9-μm aluminum foil on an extrusion coater. After drying, rolling to a certain thickness, and slitting to a certain width, a positive electrode sheet is obtained.

[0069] Preparation of the negative electrode sheet:

[0070] Disperse 97.7% graphite, 1.2% styrene-butadiene copolymer, and 1.1% lithium carboxymethyl cellulose evenly in deionized water through a double planetary mixer, and uniformly coat it on a 5-μm copper foil on an extrusion coater. After drying, rolling to a certain thickness, and slitting to a certain width, a negative electrode sheet is obtained.

[0071] Preparation of electrolyte:

[0072] Mix EC, PP, VC, DEC and PC evenly according to the following components and mass ratio to obtain an organic solution. Ethylene carbonate (EC): Propyl propionate (PP): Vinylene carbonate (VC): Diethyl carbonate (DEC): Propylene carbonate (PC) = 22:25:3:28:22; Add lithium salt LiPF 6 to the organic solution, and the mass ratio of the added lithium salt to the mass of the organic solution is 9.5:90.5; After mixing evenly, the electrolyte is obtained.

[0073] Preparation of secondary battery:

[0074] Weld the pole ears, apply glue, wind, cut, hot press, etc. to the positive electrode sheet, negative electrode sheet and separator with a certain width on a winding machine to obtain a bare battery cell. Take an aluminum plastic film with a suitable size for die cutting, and encapsulate the bare battery cell in the die-cut aluminum plastic film. The encapsulated battery cell is injected with the electrolyte prepared in the above steps and subjected to formation.

[0075] Formation process of lithium-ion battery:

[0076] Step S1: Place the lithium-ion battery at the first temperature (23 °C), and perform constant current charging in the first stage with the first current (0.15C) and the first voltage (3.1V), and let it stand for 12h;

[0077] Step S2: Place the lithium-ion battery at the second temperature (27 °C), and perform constant current charging in the second stage with the second current (0.25C) and the second voltage (3.5V), and let it stand for 12h;

[0078] Step S3: Put the battery cell into a sealed bag to ensure that there is no air in the bag; Put the sealed bag into a vacuum chamber and start the vacuum pump; Under the state of maintaining vacuum, use a mechanical device to squeeze the battery, and the pressure in the vacuum chamber drops to 1*10 -3 Pa, the squeezing pressure is 0.5MPa, and the maintenance time is 10min; Turn off the vacuum pump, open the vacuum chamber, and take out the lithium-ion battery after the first sealing.

[0079] Step S4: Place the lithium-ion battery at the third temperature (32 °C), and perform constant current charging in the third stage with the third current (0.4C) and the third voltage (4.2V);

[0080] Step S5: Put the lithium-ion battery obtained in Step S4 into a sealed container containing inert gas to ensure that there is no air in the sealed container; Start the vacuum pump, and the pressure in the sealed container drops to 1*10 -4While maintaining a vacuum state, start the ultrasonic generator with a frequency of 100 kHz, a power of 100 W, and a time of 30 min; turn off the vacuum pump and the ultrasonic generator, open the container, take out the lithium-ion battery, and perform hot pressing for secondary sealing at a hot pressing temperature of 200 °C, a pressure of 0.8 MPa, and a time of 10 s.

[0081] Example 2

[0082] The difference from Example 1 is only that in step S1, the first temperature is 25 °C; in step S2, the second temperature is 30 °C; in step S3, the pressure in the vacuum chamber drops to 1×10 -4 Pa, the extrusion pressure is 0.4 MPa, and the holding time is 8 min; in step S4, the third temperature is 35 °C; in step S5, the frequency of the ultrasonic generator is 80 kHz, the power is 80 W, the time is 20 min, the hot pressing temperature is 190 °C, the pressure is 0.5 MPa, and the time is 6 s.

[0083] The rest is the same as in Example 1 and will not be elaborated here.

[0084] Example 3

[0085] The difference from Example 1 is only that in step S3, the pressure is 0.1 MPa and the holding time is 10 min.

[0086] The rest is the same as in Example 1 and will not be elaborated here.

[0087] Example 4

[0088] The difference from Example 1 is only that the first current is 0.2 C, the second current is 0.3 C, and the third current is 0.45 C.

[0089] The rest is the same as in Example 1 and will not be elaborated here.

[0090] Example 5

[0091] The difference from Example 1 is only that in step S5, the pressure in the sealed container drops to 1.2×10 -4 Pa, the treatment time of the ultrasonic wave is 15 min, the hot pressing temperature is 180 °C, the time is 5 s, and the pressure is 1 MPa.

[0092] The rest is the same as in Example 1 and will not be elaborated here.

[0093] Comparative Example 1

[0094] The difference from Example 1 is only that the formation process of the lithium-ion battery is different. In the formation process of this comparative example, the segmented formation technology is not adopted. The formation temperature is 25 °C, the current is 0.2 C, the voltage is 3.9 V, normal degassing is performed, and the vacuum degree is 1×10^-3 Pa, with a time of 3 s. After injecting the electrolyte, a primary sealing is performed. During the sealing, the vacuum degree is maintained at 60 KPa, and at the same time, the pressure holding time is 3 s. After formation, a secondary sealing is carried out. During the sealing, the vacuum degree is maintained at 60 KPa, and at the same time, the pressure holding time is 3 s.

[0095] The rest is the same as in Experimental Example 1 and will not be elaborated here.

[0096] Comparative Example 2

[0097] The difference from Example 1 is only in the formation process of the lithium-ion battery. In the lithium-ion formation process of this comparative example, the segmented formation technology is not adopted. The formation temperature is 45 °C, the current is 0.2 C, the voltage is 3.8 V, normal degassing is carried out, and the vacuum degree is 1*10^ -5 Pa, with a time of 3 s. After injecting the electrolyte, a primary sealing is performed. During the sealing, the vacuum degree is maintained at 50 KPa, and at the same time, the pressure holding time is 5 s. After formation, a secondary sealing is carried out. During the sealing, the vacuum degree is maintained at 50 KPa, and at the same time, the pressure holding time is 5 s.

[0098] The rest is the same as in Example 1 and will not be elaborated here.

[0099] Comparative Example 3

[0100] The difference from Example 1 is only in the formation process of the lithium-ion battery. In the lithium-ion formation process of this comparative example, the mechanical extrusion vacuum pumping technology is not adopted.

[0101] The rest is the same as in Example 1 and will not be elaborated here.

[0102] Comparative Example 4

[0103] The difference from Example 1 is only in the formation process of the lithium-ion battery. In the lithium-ion formation process of this comparative example, the ultrasonic vacuum pumping technology is not adopted.

[0104] The rest is the same as in Example 1 and will not be elaborated here.

[0105] Comparative Example 5

[0106] The difference from Example 1 is only in the formation process of the lithium-ion battery. In step S3 of this comparative example, the pressure in the vacuum chamber drops to 1*10 -2 Pa, and the maintenance time is 5 min. The pressure of the mechanical device extrusion is 0.8 MPa.

[0107] The rest is the same as in Example 1 and will not be elaborated here.

[0108] Comparative Example 6

[0109] The difference from Example 1 is only that the formation process of the lithium-ion battery is different. In this comparative example, in step S5, the frequency of the ultrasonic generator is 50 kHz, the power is 50 W, the treatment time is 10 min, the temperature of hot pressing is 180 °C, the time is 15 s, and the pressure is 0.04 MPa.

[0110] The rest is the same as in Example 1 and will not be elaborated here.

[0111] The batteries prepared in the examples and comparative examples were respectively subjected to the following performance tests:

[0112] (1) Capacity retention rate test: At 20 Kpa, charge at 0.5C to 4.2V, let it stand for 10 min, and then discharge at 0.5C to 3.0V. Repeat this cycle 10 times, and calculate the percentage of the discharge capacity to the rated capacity.

[0113] (2) Bulging test: Place the batteries at 50 kpa, 40 kpa, 20 kpa, and 10 kpa respectively for 5 min, and observe whether the batteries bulge.

[0114] Among them, the above performance test results are shown in Table 1 below.

[0115] Table 1

[0116]

[0117]

[0118] The lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-6 were subjected to the capacity retention rate test and the bulging test. From the data in Table 1 above, it can be seen that no bulging occurred in the examples even at 20 kpa, but bulging occurred in the comparative examples at 50 kpa. At 20 kpa, after 10 charge and discharge cycles, the capacity retention rate of the examples was above 99%, but the capacity retention rate of the comparative examples had dropped below 48%. And at a pressure of 20 kpa, the lithium-ion batteries in the comparative examples were severely deformed after charge and discharge, while the appearance of the lithium-ion batteries in the examples remained unchanged.

[0119] According to the disclosure and teaching of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions, or variations made by those skilled in the art based on the present invention all fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A formation process for a lithium ion battery, characterized in that: The following steps are involved: Step S1, placing the lithium-ion battery at a first temperature, using a first current and a first voltage to perform a first-stage constant current charging, and leaving it to stand; Step S2, placing the lithium-ion battery at a second temperature, using a second current and a second voltage to perform a second-stage constant current charging, and leaving it to stand; Step S3, subjecting the lithium-ion battery to a mechanical extrusion and vacuum treatment, and sealing the treated battery once; Step S4, placing the lithium-ion battery at a third temperature, and performing a third-stage constant current charging using a third current and a third voltage; Step S5, the lithium ion battery obtained in step S4 is subjected to ultrasonic vacuuming and hot pressing secondary sealing to obtain a formed lithium ion battery.

2. The formation process of a lithium ion battery according to claim 1, characterized in that: The first temperature T1, the second temperature T2, and the third temperature T3 satisfy the relationship: T1<T2<T3; The first current I1, the second current I2, and the third current I3 satisfy the relationship: I1<I2<I3; The first voltage U1 , the second voltage U2 , and the third voltage U3 satisfy the relationship: U1 < U2 < U3 .

3. The formation process of a lithium ion battery according to claim 2, characterized in that: In step S1, the first temperature is 20-25°C, the first current is 0.15-0.2C, and the first voltage is 3.1V.

4. The formation process of a lithium ion battery according to claim 2, characterized in that: In step S2, the second temperature is 26-30°C, the second current is 0.25-0.3C, and the second voltage is 3.5V.

5. The formation process of a lithium ion battery according to claim 2, characterized in that: In step S4, the third temperature is 31-35°C, the third current is 0.4-0.45°C, and the third voltage is 4.2V.

6. The formation process of a lithium ion battery according to claim 1, characterized in that: In step S3, the specific steps of mechanical extrusion vacuuming include: Step S1, put the battery cell into a sealed bag to ensure that there is no air in the bag; Step S2, placing the sealed bag into the vacuum chamber and starting the vacuum pump; Step S3, using a mechanical device to squeeze the battery while maintaining a vacuum; Step S4, turning off the vacuum pump, opening the vacuum chamber, and taking out the lithium-ion battery after the primary sealing.

7. The formation process of a lithium ion battery according to claim 6, characterized in that: In step S2, the pressure in the vacuum chamber is reduced to 1*(10 -4 -10 -3 )Pa, maintaining time is 5-10min; And / or, in step S3, the extrusion pressure of the mechanical device is 0.1-0.5 MPa.

8. The formation process of a lithium ion battery according to claim 1, characterized in that: In step S5, the specific steps of ultrasonic vacuum hot pressing include: Step S1, placing the lithium-ion battery in a sealed container containing an inert gas, and ensuring that there is no air in the sealed container; Step S2, start the vacuum pump, and start the ultrasonic generator while maintaining the vacuum state; Step S3, turning off the vacuum pump and the ultrasonic generator, opening the container, taking out the lithium-ion battery, and performing secondary hot pressing sealing.

9. The formation process of a lithium ion battery according to claim 8, characterized in that: In step S2, the pressure in the sealed container drops to (1-1.2)*10 -4 Pa, the frequency of the ultrasonic generator is 80-100kHz, the power is 80-100W, and the processing time is 15-30min; And / or, in step S3, the hot pressing temperature is 180-200°C, the time is 5-10s, and the pressure is 0.5-1MPa.

10. A lithium ion battery, characterized in that: The lithium ion battery is prepared by the formation process of the lithium ion battery according to any one of claims 1 to 9.

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