Method for removing formation gas of pre-lithiated lithium battery and application of method

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for removing formation gas of a pre-lithiated lithium battery and application of the method. The method comprises the following steps: S1, restraining a pre-lithiated lithium battery provided with an air bag on a formation cabinet, firstly carrying out low-frequency ultrasonic treatment, and then setting formation steps; s2, when the charging voltage reaches a gas production peak period range, processing by synchronously adopting an ultrasonic wave and pressure pulse alternate circulation mode, and enabling the charging current at the moment to be less than or equal to 0.1 C, and enabling the number of gas production peak periods to be more than one; and S3, after formation charging is finished, treatment is conducted in a high-frequency ultrasonic circulation mode, then air exhausting and vacuum secondary sealing are conducted on the air bag, and the air bag is removed. The key point of the invention lies in that by adopting a combined technology of low-frequency ultrasonic treatment before formation, ultrasonic and pressure pulse cooperative treatment in a gas production peak period and high-frequency ultrasonic treatment after formation, a cooperative and superposed exhaust effect is realized, and the battery is ensured to have good first-effect performance and cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a method for removing formation gas of pre-lithiated lithium batteries and application thereof. BACKGROUND

[0002] During the first charging process of a lithium ion battery, the electrolyte will undergo irreversible decomposition, and the solid-state electrolyte interface (SEI film) generated on the negative electrode surface will cause irreversible loss of active lithium, resulting in capacity loss of the battery, affecting the energy density and cycle life of the battery. Based on the pre-lithiation / lithium supplement strategy of supplementing additional active lithium, the loss of irreversible active lithium in the battery is compensated, which helps to realize the performance of high-capacity electrode energy density and improve the battery coulomb efficiency and cycle life performance. Among them, the positive electrode lithium supplement technology can directly add a positive electrode lithium supplement agent in the slurry preparation process of the positive electrode slurry, and the positive electrode lithium supplement agent decomposes and releases active lithium, thereby compensating for the irreversible loss of active lithium. However, the lithium battery pre-lithiated by the positive electrode lithium supplement agent is prone to produce a large amount of gas during the formation stage, for example, lithium-rich lithium iron oxide Li5FeO4 (LFO), when charged to 4.2V, 1 LFO molecule can release up to 4 lithium ions, and the specific capacity can reach 700mAh / g, and the reversible specific capacity is very small, which is an ideal positive electrode lithium supplement additive. It mainly exists in the 3.0~4.0V interval due to charging formation, and there are two stages of delithiation gas reaction: (1) Li5FeO4-2Li + -2e - →Li3FeO 3.5 +0.25O2; (2) Li3FeO 3.5 -2Li + -2e - →LiFeO2+0.75O2. A large amount of gas is generated in the lithium battery formation stage inside the battery, which cannot be discharged, causing the battery to swell, and the gas bubbles formed adhere to the negative electrode sheet, which is not conducive to the good adhesion of the positive and negative electrode sheets and the separator, and also causes the SEI film formed by the negative electrode sheet to be loose and uneven, which easily leads to lithium precipitation or local area not embedded with lithium. Most of the current lithium battery formation gas discharge methods have the problem of electrolyte discharge accompanying gas discharge during the gas discharge process, which reduces the amount of electrolyte in the battery, reduces the cycle performance of the battery, and has poor gas discharge effect, causes great damage to the internal structure of the battery, and reduces the quality and performance of the battery.

[0003] How to effectively improve the problems of poor adhesion of electrode sheets and separators and battery swelling caused by gas production during the formation process, overcome the defects of the existing formation gas discharge method, improve the quality of pre-lithiated lithium batteries, reduce the battery scrap rate, and thus ensure that the battery has good initial efficiency performance and cycle performance, is a technical problem that needs to be solved. SUMMARY

[0004] The present application aims to overcome the problems of electrolyte accompanying gas discharge and incomplete gas discharge, great damage to the internal structure of the battery, poor adhesion of the pole piece and the diaphragm, and the decline of the quality and performance of the battery caused by the existing formation gas discharge method, and provides a method for removing the formation gas of pre-lithiated lithium batteries, which effectively improves the formation gas discharge effect and avoids damage to the structure of the battery during the gas discharge process, ensuring that the battery has good initial efficiency and cycle performance.

[0005] In a first aspect, the present application provides a method for removing the formation gas of pre-lithiated lithium batteries.

[0006] Specifically, the method comprises the following steps: S1. The pre-lithiated lithium battery provided with an air bag is placed on the formation cabinet for restraint, low-frequency ultrasonic treatment is first performed at a preset face pressure I, and then a formation charging process is performed by setting the formation step; S2. During the formation charging process, when the charging voltage reaches the gas production peak period range, the pre-lithiated lithium battery is treated by synchronously using an ultrasonic wave and a pressure pulse alternating cycle mode, and the charging current I5 of the formation charging process is ≤0.1C during the treatment process, and the number of the gas production peak period is more than one. S3. After the formation charging is completed, high-frequency ultrasonic wave cycle mode is used for treatment at a preset face pressure II, then the air bag is pumped, and after the pumping is completed, vacuum two-sealing is performed and the air bag is removed.

[0007] In a preferred embodiment, the positive electrode material of the pre-lithiated lithium battery is lithium iron phosphate.

[0008] In a preferred embodiment, the pre-lithiated lithium battery is obtained by pre-lithiation using lithium iron oxide as a positive electrode lithium supplement.

[0009] In a preferred embodiment, the pre-lithiated battery is a square shell battery or a soft package battery.

[0010] In a preferred embodiment, in step S1, the preset face pressure I is 0.1-0.3 MPa.

[0011] In a preferred embodiment, in step S1, the frequency of the low-frequency ultrasonic wave is 10-20 kHz.

[0012] In a preferred embodiment, in step S1, the time of the low-frequency ultrasonic wave treatment is 10-15 min.

[0013] In a preferred embodiment, in step S1, the formation charging process comprises the following stages: when the charging voltage is ≤3.3V, the charging current I1≤0.1C; when the charging voltage is ≤3.65V, the charging current I2≤0.5C; when the charging voltage is ≤3.9V, the charging current I3≤0.1C; when the charging voltage is ≤4.15V, the charging current I4≤0.5C.

[0014] In a preferred embodiment, when the pre-lithiated lithium battery is a lithium battery obtained by pre-lithiation using lithium iron oxide as a positive electrode lithium supplement and lithium iron phosphate as a positive electrode material, the gas production peak period has two.

[0015] In a preferred embodiment, the first gas production peak period is 3.20-3.40V, and the second gas production peak period is 3.80-4.10V.

[0016] In a preferred embodiment, in step S2, when the charging voltage reaches the first gas production peak period, the processing time of the ultrasonic wave and pressure pulse alternating cycle mode I is 10-30min.

[0017] In a preferred embodiment, in step S2, in the ultrasonic wave and pressure pulse alternating cycle mode I, the frequency of the ultrasonic wave I is 30-45kHz, and the duration h1 of the ultrasonic wave I in a single cycle is 30-60s.

[0018] In a preferred embodiment, in step S2, in the ultrasonic wave and pressure pulse alternating cycle mode I, the surface pressure of the pressure pulse I is 0.7-0.9MPa, the pulse amplitude is ±0.2-0.35MPa, the pulse frequency is 0.5-2.0Hz, and the duration h2 of the pressure pulse I in a single cycle is 60-180s.

[0019] In a preferred embodiment, in step S2, when the charging voltage reaches the second gas production peak period, the processing time of the ultrasonic wave and pressure pulse alternating cycle mode II is 10-30min.

[0020] In a preferred embodiment, in step S2, in the ultrasonic wave and pressure pulse alternating cycle mode II, the frequency of the ultrasonic wave II is 30-45kHz, and the duration h3 of the ultrasonic wave II in a single cycle is 30-60s.

[0021] In a preferred embodiment, in step S2, in the ultrasonic wave and pressure pulse alternating cycle mode II, the surface pressure of the pressure pulse II is 0.7-0.9MPa, the pulse amplitude is ±0.4-0.6MPa, the pulse frequency is 0.5-2.0Hz, and the duration h4 of the pressure pulse II in a single cycle is 60-180s.

[0022] In a preferred embodiment, in step S3, the preset surface pressure II is 0.1-0.3 MPa.

[0023] In a preferred embodiment, in step S3, the processing time of the high-frequency ultrasonic wave cycle mode is 0.5-1.5 min.

[0024] In a preferred embodiment, in step S3, in a single cycle of the high-frequency ultrasonic wave cycle mode, the duration of the high-frequency ultrasonic wave h5 is 0.5-3.0 s, and the standing time h6 is 5-10 s.

[0025] In a preferred embodiment, in step S3, the frequency of the high-frequency ultrasonic wave is 90-110 kHz.

[0026] In a preferred embodiment, in step S1, before the pre-lithiated lithium battery is restrained on the formation cabinet, the pre-lithiated lithium battery is allowed to stand at 40-50°C for 12-32 h.

[0027] In a preferred embodiment, in step S2, after the pre-lithiated lithium battery is treated by the ultrasonic wave and pressure pulse alternating cycle mode, the process includes: suspending the formation charging, pumping the air bag, and then performing vacuum sealing after the pumping is completed, and then continuing the formation charging process.

[0028] In step S3, before the pre-lithiated lithium battery is treated by the high-frequency ultrasonic wave cycle mode, the process includes: allowing the pre-lithiated lithium battery after the formation charging to stand at 40-50°C for 12-32 h.

[0029] In a second aspect, the application provides an application of the above method for removing the formation gas of the pre-lithiated lithium battery in the manufacturing of lithium ion batteries.

[0030] Beneficial effects: the method for removing the formation gas of pre-lithiation lithium battery provided by the present application, the key is to realize the effect of discharging the formation gas by adopting the combination technology of low-frequency ultrasonic wave treatment before formation charging, ultrasonic wave and pressure pulse cooperative treatment during the gas production peak period and high-frequency ultrasonic wave treatment after the end of formation charging, which not only can efficiently discharge the formation gas and solve the problem of battery gas swelling, but also has little potential damage to the battery structure (such as pole piece, diaphragm, etc.) and SEI film, thereby ensuring that the battery has good initial efficiency performance and cycle performance. It is speculated that the reason may be that: the low-frequency ultrasonic wave treatment before formation charging can break the surface tension of the electrolyte, accelerate the infiltration of the pole piece pore and the diaphragm, reduce the un-infiltrated "dead zone", and enhance the permeability of the electrolyte; when the pre-lithiation lithium battery is treated by adopting the ultrasonic wave and pressure pulse alternating cycle mode during the gas production peak period, the ultrasonic wave has a cavitation effect on the formation battery, that is, when the cavitation bubbles generated by the ultrasonic wave in the liquid break, local high pressure and microjet flow can be generated, which promotes the gas to escape from the electrolyte or separate from the electrode surface, at the same time, the ultrasonic wave vibration can promote the combination or migration of the micro-bubbles to the exhaust port, and the pressure pulse has a directional driving force, which applies pulse pressure, can compress the gap between the pole pieces when the pressure is increased, promotes the gas to extrude from the pore, releases the elastic stress of the pole piece when the pressure is reduced, and forms a micron-level gap for the gas to escape, thereby accelerating the migration of the gas to the exhaust port and reducing the gas accumulation. As described above, the cavitation effect of the ultrasonic wave can disperse the micro-bubbles, and the pulse pressure provides a directional driving force, and the combination of the two has a synergistic gain effect: in the time dimension, after the ultrasonic wave breaks the bubbles, the pressure pulse pushes the gas to be quickly discharged, avoiding secondary aggregation; in the spatial dimension, the ultrasonic cavitation field covers the local area, and the pressure pulse realizes the global flow field driving, forming a coupling effect of "local crushing-global transportation"; the high-frequency ultrasonic wave treatment after the end of formation charging can be used for local fine treatment, further removing the residual gas in the pole piece pore. As described above, the method provided by the present application can significantly improve the exhaust efficiency and effect of the formation gas by adopting the combination technology of low-frequency ultrasonic wave treatment before formation charging, ultrasonic wave and pressure pulse cooperative treatment during the gas production peak period and high-frequency ultrasonic wave treatment after the end of formation charging, while effectively avoiding the potential damage of a single technology to the battery structure, and improving the infiltration and permeability of the electrolyte, thereby achieving a synergistic gain effect, and ensuring that the obtained lithium battery has good initial efficiency performance and cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the gas production trend chart of the LFO pre-lithiation soft package battery with a gas bag in example 1 during the formation charging process.

[0032] Figure 2 is the real photo of the negative pole piece of the LFO pre-lithiation soft package battery after the completion of formation in examples 1-4 and comparative examples 1-4. DETAILED DESCRIPTION

[0033] The method for removing formation gas of pre-lithiated lithium battery provided by the application comprises the following steps: S1. The pre-lithiated lithium battery provided with a gas bag is constrained on a formation cabinet, low-frequency ultrasonic wave treatment is carried out under a preset surface pressure I, and then a formation charging process is carried out; S2. During the formation charging process, when the charging voltage reaches the range of a gas production peak period, the pre-lithiated lithium battery is treated by using an ultrasonic wave and a pressure pulse alternating cycle mode synchronously, and the charging current I5 of the formation charging process is less than or equal to 0.1C during the treatment process, and the number of the gas production peak period is more than one; S3. After the formation charging is completed, high-frequency ultrasonic wave cycle mode treatment is carried out under a preset surface pressure II, then the gas bag is pumped, and after the pumping is completed, vacuum secondary sealing is carried out and the gas bag is removed.

[0034] In the application, the positive electrode material, the lithium supplement and the negative electrode material of the pre-lithiated lithium battery are not specifically limited, the influence caused by different positive electrode materials and / or lithium supplements is mainly the difference in the range and number of the gas production peak period and the gas production amount during the formation charging process, at this time, the method provided by the application can still be used to remove the formation gas and complete the formation process of the battery. The positive electrode material of the pre-lithiated lithium battery is preferably lithium iron phosphate. The pre-lithiated lithium battery is preferably pre-lithiated by using lithium ferrite as a positive electrode lithium supplement. The packaging form of the pre-lithiated battery is not specifically limited in the application, which can be a square shell battery or a soft package battery.

[0035] In the application, in step S1, the preset surface pressure I is preferably 0.1-0.3 MPa, such as 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa or any value between them.

[0036] In the application, in step S1, the frequency of the low-frequency ultrasonic wave is preferably 10-20 kHz, such as 10 kHz, 12 kHz, 15 kHz, 18 kHz, 20 kHz or any value between them. The frequency of the low-frequency ultrasonic wave is controlled in the above preferred range, at this time, it is beneficial to the optimal cavitation effect of the ultrasonic wave, that is, the breaking of the cavitation bubbles produced by the ultrasonic wave can produce enough energy to destroy the surface tension of the electrolyte, further enhancing the permeability and wetting effect of the electrolyte.

[0037] In the present application, in step S1, the time of the low-frequency ultrasonic treatment is preferably 10-15 min, such as 10 min, 11 min, 12 min, 13 min, 14 min, 15 min or any value between them. Controlling the time of the low-frequency ultrasonic treatment in the above preferred range can help to avoid the situation that the ultrasonic time is too short (<10 min) to cover all the pole piece area, and the situation that the ultrasonic time is too long (>15 min) to cause electrolyte volatilization or separator damage due to cavitation accumulated heat, so as to better exert the cavitation effect of the low-frequency ultrasonic wave, and improve the electrolyte permeability and infiltration effect.

[0038] In the present application, in step S1, the formation charging process can include the following stages: when the charging voltage is ≤3.3 V, the charging current I1 is ≤0.1 C, when the charging voltage is ≤3.65 V, the charging current I2 is ≤0.5 C, when the charging voltage is ≤3.9 V, the charging current I3 is ≤0.1 C, and when the charging voltage is ≤4.15 V, the charging current I4 is ≤0.5 C. In addition, it should be noted that the process settings of the formation charging process of lithium batteries with different positive electrode materials can be adjusted adaptively. In the present application, "I1", "I2", "I3", "I4" and "I5" have no special meaning, and are only used to distinguish the charging currents in different stages for the purpose of description.

[0039] In the present application, when the pre-lithiated lithium battery is preferably a lithium battery obtained by pre-lithiating lithium iron phosphate (LFP) as a positive electrode material with lithium ferrite (LFO) as a positive electrode lithium supplement, the gas production peak period has two, one is mainly LFP gas production, and the other is mainly LFO gas production. Specifically, the first gas production peak period is preferably 3.20-3.40 V, such as 3.20 V, 3.25 V, 3.30 V, 3.35 V, 3.40 V or any value between them, and the second gas production peak period is preferably 3.80-4.10 V, such as 3.80 V, 3.85 V, 3.90 V, 3.95 V, 4.00 V, 4.05 V, 4.10 V or any value between them.

[0040] In the present application, in step S2, when the charging voltage reaches the first gas production peak period, the processing time of the ultrasonic wave and pressure pulse alternating cycle mode I is preferably 10-30 min, such as 10 min, 15 min, 20 min, 25 min, 30 min or any value between them.

[0041] Further, in the step S2, the frequency of the ultrasonic wave I in the ultrasonic wave and pressure pulse alternating circulation mode I is preferably 30-45 kHz, such as 30 kHz, 35 kHz, 40 kHz, 45 kHz or any value between them, which is beneficial to avoid the resonance frequency of the SEI film, so as to better play the role of the ultrasonic wave I in promoting the gas to escape from the electrolyte or to separate from the electrode surface while promoting the small bubbles to merge or migrate out, and to reduce the damage to the SEI film and other battery structures in the process. The duration h1 of the ultrasonic wave I in a single cycle is preferably 30-60 s, such as 30 s, 40 s, 50 s, 60 s or any value between them.

[0042] Further, in the step S2, the surface pressure of the pressure pulse I in the ultrasonic wave and pressure pulse alternating circulation mode I is preferably 0.7-0.9 MPa, such as 0.7 MPa, 0.75 MPa, 0.8 MPa, 0.85 MPa, 0.9 MPa or any value between them; the pulse amplitude is preferably ±0.2-0.35 MPa, such as ±0.2 MPa, ±0.25 MPa, ±0.3 MPa, ±0.35 MPa or any value between them; the pulse frequency is preferably 0.5-2.0 Hz, such as 0.5 Hz, 0.8 Hz, 1.0 Hz, 1.2 Hz, 1.5 Hz, 1.8 Hz, 2.0 Hz or any value between them, which is more beneficial to be compatible with the elastic recovery time of the pole piece (0.1-0.3 s) and to avoid stress hysteresis, thereby facilitating the discharge of gas. The duration h2 of the pressure pulse I in a single cycle is preferably 60-180 s, such as 60 s, 80 s, 100 s, 120 s, 140 s, 150 s, 180 s or any value between them.

[0043] In the present application, in the step S2, when the charging voltage reaches the second gas generation peak period, the processing time of the ultrasonic wave and pressure pulse alternating circulation mode II is preferably 10-30 min, such as 10 min, 15 min, 20 min, 25 min, 30 min or any value between them.

[0044] Further, in the step S2, the frequency of the ultrasonic wave I in the ultrasonic wave and pressure pulse alternating circulation mode I is preferably 30-45 kHz, such as 30 kHz, 35 kHz, 40 kHz, 45 kHz or any value between them, which is beneficial to avoid the resonance frequency of the SEI film, so as to better play the role of the ultrasonic wave I in promoting the gas to escape from the electrolyte or to separate from the electrode surface while promoting the small bubbles to merge or migrate out, and to reduce the damage to the SEI film and other battery structures in the process. The duration h1 of the ultrasonic wave I in a single cycle is preferably 30-60 s, such as 30 s, 40 s, 50 s, 60 s or any value between them.

[0045] Further, in step S2, the surface pressure of the pressure pulse II in the alternating cycle mode II of the ultrasonic wave and the pressure pulse is preferably 0.7-0.9 MPa, such as 0.7 MPa, 0.75 MPa, 0.8 MPa, 0.85 MPa, 0.9 MPa, or any value between them; the pulse amplitude is preferably ±0.4-0.6 MPa, such as ±0.4 MPa, ±0.45 MPa, ±0.5 MPa, ±0.55 MPa, ±0.6 MPa, or any value between them; the pulse frequency is preferably 0.5-2.0 Hz, such as 0.5 Hz, 0.8 Hz, 1.0 Hz, 1.2 Hz, 1.5 Hz, 1.8 Hz, 2.0 Hz, or any value between them, which is more conducive to compatibility with the elastic recovery time of the pole piece (0.1-0.3 s) to avoid stress hysteresis, thereby facilitating gas discharge. The duration h4 of the pressure pulse II in a single cycle is preferably 60-180 s. For soft pack batteries, the pressure pulse I and the pressure pulse II preferably have a square wave shape (sharp rise and fall), which is more suitable for soft pack batteries and is well compatible with the elastic recovery time of the pole piece (0.1-0.3 s) to avoid stress hysteresis, thereby promoting gas discharge. For prismatic batteries, the pressure pulse I and the pressure pulse II preferably have a trapezoidal wave shape (slow rise and fall), which can reduce mechanical impact and reduce damage and damage to the battery structure.

[0046] In the present application, in step S3, the preset surface pressure II is preferably 0.1-0.3 MPa, such as 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, or any value between them.

[0047] In the present application, in step S3, the processing time of the high-frequency ultrasonic wave cycle mode is preferably 0.5-1.5 min, 0.5 min, 0.75 min, 1.0 min, 1.25 min, 1.5 min, or any value between them.

[0048] In the present application, in step S3, in a single cycle of the high-frequency ultrasonic wave cycle mode, the duration h5 of the high-frequency ultrasonic wave is preferably 0.5-3 s, such as 0.5 s, 1.0 s, 1.5 s, 2.0 s, 2.5 s, 3.0 s, or any value between them; the standing time h6 is preferably 5-10 s, such as 5 s, 6 s, 7 s, 8 s, 9 s, 10 s, or any value between them.

[0049] In the present application, in step S3, the frequency of the high-frequency ultrasonic wave is preferably 90-110 kHz, such as 90 kHz, 95 kHz, 100 kHz, 105 kHz, 110 kHz, or any value between them.

[0050] In the present application, before the pre-lithiated lithium battery is restrained on the formation cabinet in step S1, the pre-lithiated lithium battery can also be placed at T1 temperature for t1 time, wherein T1 is preferably 40-50°C, such as 40°C, 42°C, 45°C, 48°C, 50°C or any value between them, and t1 is preferably 12-32h, such as 12h, 16h, 20h, 24h, 28h, 32h or any value between them.

[0051] In the present application, for the gas collected in the air bag, the air bag can be pumped out after the high-frequency ultrasonic cycle mode treatment in step S3, and the air bag can also be preferably pumped out after the ultrasonic and pressure pulse alternating cycle mode treatment in step S2, so as to discharge most of the gas, which is beneficial to further reduce the potential damage to the battery structure (such as the pole piece, the diaphragm, etc.) and the SEI film due to the existence of a large amount of gas in the subsequent formation of the battery. The latter step can be as follows: pause the formation charging, pump the air bag, and after the pumping is completed, vacuum and seal, and then continue the formation charging process.

[0052] In the present application, before the pre-lithiated lithium battery is treated by the high-frequency ultrasonic cycle mode in step S3, the pre-lithiated lithium battery after the formation charging is ended is placed at T2 temperature for t2 time, wherein T2 is preferably 40-50°C, such as 40°C, 42°C, 45°C, 48°C, 50°C or any value between them, and t2 is preferably 12-32h, such as 12h, 16h, 20h, 24h, 28h, 32h or any value between them.

[0053] The present application will be described in detail below through specific examples. The examples are intended to explain the present application and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0054] Example 1 (1) The positive electrode material-lithium iron phosphate (LFP), the conductive agent-conductive carbon black, the binder-polyvinylidene fluoride (PVDF), and the lithium supplement-lithium-rich lithium iron phosphate (LFO) are uniformly mixed, coated, and die-cut in a ratio of 96:1:2:1 to form a positive electrode sheet; the artificial graphite, the conductive agent (SP), the binder-styrene butadiene rubber (SBR), and the thickening agent-sodium carboxymethyl cellulose (CMC) are uniformly mixed, coated, and die-cut in a ratio of 95.5:1:2:1.5 to form a negative electrode sheet, and the LFO pre-lithiated soft package battery with an air bag is prepared through the processes of lamination, shell filling, top side sealing, liquid injection, and pre-sealing, and is placed at 45°C for 24h.

[0055] (2) Put the LFO pre-lithiation soft package battery with air bag on the restraint of the formation cabinet, and apply 15 kHz low-frequency ultrasound at an initial preset surface pressure of 0.2 MPa for 10 min.

[0056] (3) Then, the LFO pre-lithiation soft package battery is restrained on the formation cabinet, and the formation process is as follows: constant current charging at 0.05C to 3.2V, constant current charging at 0.1C to 3.4V, constant current charging at 0.5C to 3.65V, constant current charging at 0.05C to 3.95V, and constant current charging at 0.1C to 4.1V; the surface pressure preset during the formation charging process is 0.8 MPa, and the formation temperature is 45°C.

[0057] (4) When the LFO pre-lithiation soft package battery is charged to 3.3V on the restraint of the formation cabinet, the low-frequency ultrasound and low-pressure pulse alternating cycle mode are started simultaneously, and the cycle lasts for 15 min, and the charging current I5≤0.1C during the cycle lasts for 15 min, wherein one cycle period is to apply 35 kHz low-frequency ultrasound first, and then to apply 0.8±0.3 MPa surface pressure and 1.5 Hz low-pressure pulse (0.5 MPa~1.1 MPa square wave) for 90 s after 30 s.

[0058] (5) When the LFO pre-lithiation soft package battery is charged to 3.85V on the restraint of the formation cabinet, the low-frequency ultrasound and high-pressure pulse alternating cycle mode are started simultaneously, and the cycle lasts for 15 min, and the charging current I5≤0.1C during the cycle lasts for 15 min, wherein one cycle period is to apply 35 kHz low-frequency ultrasound first, and then to apply 0.8±0.45 MPa surface pressure and 1.5 Hz high-pressure pulse (0.35 MPa~1.25 MPa square wave) for 90 s after 30 s.

[0059] (6) When the LFO pre-lithiation soft package battery is charged to 4.0V on the restraint of the formation cabinet, the formation is paused, the air bag is pumped, and the vacuum sealing is performed after the pumping is completed.

[0060] (7) The LFO pre-lithiation soft package battery after pumping is continued to be charged until the formation is completed.

[0061] (8) The LFO pre-lithiation soft package after the formation is completed is placed at 45°C for 24 h, and then is treated by short-time high-frequency ultrasound mode at low surface pressure of 0.2 MPa, and the cycle lasts for 1 min, wherein one cycle period is to apply 100 kHz high-frequency ultrasound first for 1.5 s, and then to be placed for 8 s after the ultrasound is stopped, and the cycle is ended, the air bag is punctured for vacuum resealing, and the air bag is cut off, and thus the formation and pumping processes of the LFO pre-lithiation soft package battery are completed.

[0062] Example 2 The method of removing pre-lithiation lithium battery formation gas was carried out according to the method of example 1, except that steps (4) and (5) were as follows: (4) When the LFO pre-lithiation soft package battery was restrained on the formation cabinet and the charging SOC reached 3.2V, the low-frequency ultrasonic wave and the low-pressure pulse were opened synchronously in the alternating cycle mode, and the cycle lasted for 10 min and the charging current I5≤0.1C during the cycle, wherein one cycle period was to apply 30 kHz low-frequency ultrasonic wave first, and then to apply 0.7±0.2 MPa face pressure and 2 Hz pulse frequency low-pressure pulse (0.5 MPa~0.9 MPa square wave) for 90 s after 30 s; (5) When the LFO pre-lithiation soft package battery was restrained on the formation cabinet and the charging SOC reached 3.8V, the low-frequency ultrasonic wave and the high-pressure pulse were opened synchronously in the alternating cycle mode, and the cycle lasted for 10 min and the charging current I5≤0.1C during the cycle, wherein one cycle period was to apply 30 kHz low-frequency ultrasonic wave first, and then to apply 0.7±0.4 MPa face pressure and 2 Hz pulse frequency high-pressure pulse (0.4 MPa~1.1 MPa square wave) for 90 s after 30 s; The remaining conditions were the same as those of example 1, and thus the formation and exhaust process of the LFO pre-lithiation soft package battery was completed.

[0063] Example 3 The method of removing pre-lithiation lithium battery formation gas was carried out according to the method of example 1, except that steps (4) and (5) were as follows: (4) When the LFO pre-lithiation soft package battery was restrained on the formation cabinet and the charging SOC reached 3.35V, the low-frequency ultrasonic wave and the low-pressure pulse were opened synchronously in the alternating cycle mode, and the cycle lasted for 10 min and the charging current I5≤0.1C during the cycle, wherein one cycle period was to apply 45 kHz low-frequency ultrasonic wave first, and then to apply 0.85±0.3 MPa face pressure and 0.5 Hz pulse frequency low-pressure pulse (0.55 MPa~11.5 MPa square wave) for 90 s after 30 s; (5) When the LFO pre-lithiation soft package battery was restrained on the formation cabinet and the charging SOC reached 3.95V, the low-frequency ultrasonic wave and the high-pressure pulse were opened synchronously in the alternating cycle mode, and the cycle lasted for 10 min and the charging current I5≤0.1C during the cycle, wherein one cycle period was to apply 45 kHz low-frequency ultrasonic wave first, and then to apply 0.85±0.6 MPa face pressure and 0.5 Hz pulse frequency high-pressure pulse (0.25 MPa~1.45 MPa square wave) for 90 s after 30 s; The remaining conditions were the same as those of example 1, and thus the formation and exhaust process of the LFO pre-lithiation soft package battery was completed.

[0064] Example 4 The method of removing pre-lithiation lithium battery formation gas according to the method of Example 1 is carried out, except that steps (4) and (5) are as follows: (4) When the LFO pre-lithiation soft pack battery is restrained on the formation cabinet and the charging SOC reaches 3.3V, the low-frequency ultrasonic wave and the low-pressure pulse alternating cycle mode are started simultaneously, the cycle lasts for 15 min, and the charging current I5≤0.1C during the cycle lasts, wherein, a cycle period is to apply a low-frequency ultrasonic wave of 20 kHz first, and then apply a low-pressure pulse (0.2 MPa~0.8 MPa square wave) with a surface pressure of 0.5±0.3 MPa and a pulse frequency of 2 Hz for 90 s after 30 s; (5) When the LFO pre-lithiation soft pack battery is restrained on the formation cabinet and the charging SOC reaches 3.85V, the low-frequency ultrasonic wave and the high-pressure pulse alternating cycle mode are started simultaneously, the cycle lasts for 15 min, and the charging current I5≤0.1C during the cycle lasts, wherein, a cycle period is to apply a low-frequency ultrasonic wave of 20 kHz first, and then apply a high-pressure pulse (0.1 MPa~0.9 MPa square wave) with a surface pressure of 0.5±0.4 MPa and a pulse frequency of 2 Hz for 90 s after 30 s; The remaining conditions are the same as those of Example 1, and thus the formation and exhaust process of the LFO pre-lithiation soft pack battery is completed.

[0065] Example 5 The method of removing pre-lithiation lithium battery formation gas according to the method of Example 1 is carried out, except that step (2) is as follows: the LFO pre-lithiation soft pack battery with a gas bag is placed on the formation cabinet and restrained, and a low-frequency ultrasonic wave of 10 kHz is applied at an initial preset surface pressure of 0.2 MPa for a duration of 15 min; the remaining conditions are the same as those of Example 1, and thus the formation and exhaust process of the LFO pre-lithiation soft pack battery is completed.

[0066] Example 6 The method of removing pre-lithiation lithium battery formation gas according to the method of Example 5 is carried out, except that step (2) is as follows: the LFO pre-lithiation soft pack battery with a gas bag is placed on the formation cabinet and restrained, and a low-frequency ultrasonic wave of 20 kHz is applied at an initial preset surface pressure of 0.2 MPa for a duration of 10 min; the remaining conditions are the same as those of Example 1, and thus the formation and exhaust process of the LFO pre-lithiation soft pack battery is completed.

[0067] Example 7 The method of removing pre-lithiation lithium battery formation gas according to the method of Example 1 is carried out, except that steps (4) and (5) are as follows: (4) When the LFO pre-lithiated soft package battery is restrained on the formation cabinet and the SOC reaches 3.3V, the low-frequency ultrasonic wave and the low-pressure pulse are synchronously opened in the alternating cycle mode, the cycle lasts for 30 min, and the charging current I5≤0.1C during the cycle lasts for 30 min, wherein one cycle period is that the low-frequency ultrasonic wave of 35 kHz is applied first, and then the low-pressure pulse (0.5 MPa~1.1 MPa square wave) of 0.8±0.3 MPa and 1.5 Hz is applied after 60 s, and the cycle lasts for 180 s; (5) When the LFO pre-lithiated soft package battery is restrained on the formation cabinet and the SOC reaches 3.85V, the low-frequency ultrasonic wave and the high-pressure pulse are synchronously opened in the alternating cycle mode, the cycle lasts for 30 min, and the charging current I5≤0.1C during the cycle lasts for 30 min, wherein one cycle period is that the low-frequency ultrasonic wave of 35 kHz is applied first, and then the high-pressure pulse (0.35 MPa~1.25 MPa square wave) of 0.8±0.45 MPa and 1.5 Hz is applied after 60 s, and the cycle lasts for 180 s; The remaining conditions are the same as those in Example 1, and thus the formation and exhaust process of the LFO pre-lithiated soft package battery is completed.

[0068] Comparative Example 1 (1) The LFO pre-lithiated soft package battery with a gas bag is prepared according to the step (1) of Example 1, and is placed at 45℃ for 24 h.

[0069] (2) The LFO pre-lithiated soft package battery is placed on the formation cabinet for restraint, and the formation process is as follows: 0.05C constant current charging to 3.2V, 0.1C constant current charging to 3.4V, 0.5C constant current charging to 3.65V, 0.05C constant current charging to 3.95V, and 0.1C constant current charging to 4.1V; the surface pressure during the formation charging process is 0.8 MPa, and the formation temperature is 45℃.

[0070] (3) The LFO pre-lithiated soft package battery after the formation is placed at 45℃ for 24 h, then the gas bag is punctured for vacuum resealing, and the gas bag is cut off, and thus the formation and exhaust process of the LFO pre-lithiated soft package battery is completed.

[0071] Comparative Example 2 (1) The LFO pre-lithiated soft package battery with a gas bag is prepared according to the step (1) of Example 1, and is placed at 45℃ for 24 h.

[0072] (2) The LFO pre-lithiated soft package battery with a gas bag is placed on the formation cabinet for restraint, and the low-frequency ultrasonic wave of 15 kHz is applied under the initial preset surface pressure of 0.2 MPa, and the duration is 10 min.

[0073] (3) Then the LFO pre-lithiation soft package battery was placed on the formation cabinet and restrained, and the formation process was as follows: constant current charging to 3.2V at 0.05C, constant current charging to 3.4V at 0.1C, constant current charging to 3.65V at 0.5C, constant current charging to 3.95V at 0.05C, and constant current charging to 4.1V at 0.1C; the surface pressure during the formation charging process was 0.8MPa, and the formation temperature was 45℃.

[0074] (4) When the LFO pre-lithiation soft package battery was restrained and charged on the formation cabinet and the SOC reached 4.0V, the formation was paused, the air bag was pumped, and the vacuum sealing was performed after the pumping was completed. (5) The LFO pre-lithiation soft package battery after pumping was continued to be charged until the formation was completed.

[0075] (6) The LFO pre-lithiation soft package after the formation was completed was placed at 45℃ for 24h, then the air bag was punctured for vacuum resealing, and the air bag was cut off, thus completing the formation and pumping of the LFO pre-lithiation soft package battery.

[0076] Comparative Example 3 (1) The LFO pre-lithiation soft package battery with an air bag was prepared according to the step (1) of the embodiment 1, and was placed at 45℃ for 24h.

[0077] (2) The LFO pre-lithiation soft package battery was placed on the formation cabinet and restrained, and the formation process was as follows: constant current charging to 3.2V at 0.05C, constant current charging to 3.4V at 0.1C, constant current charging to 3.65V at 0.5C, constant current charging to 3.95V at 0.05C, and constant current charging to 4.1V at 0.1C; the surface pressure during the formation charging process was 0.8MPa, and the formation temperature was 45℃.

[0078] (3) When the LFO pre-lithiation soft package battery was restrained and charged on the formation cabinet and the SOC reached 3.3V, the low-frequency ultrasonic wave and the low-pressure pulse were alternately cycled, and the cycle lasted for 15min, and the charging current I5≤0.1C during the cycle lasted for 15min, wherein one cycle period was to apply a low-frequency ultrasonic wave of 35kHz for 30s, then to apply a low-pressure pulse (0.5MPa~1.1MPa square wave) with a surface pressure of 0.8±0.3MPa and a pulse frequency of 1.5Hz for 90s.

[0079] (4) When the LFO pre-lithiated soft package battery is restrained to charge on the formation cabinet and the SOC reaches 3.85V, the low-frequency ultrasonic wave and the high-pressure pulse are synchronously started in the alternating cycle mode, the cycle lasts for 15 min, and the charging current I5≤0.1C during the cycle lasts, wherein, one cycle period parameter is to apply a low-frequency ultrasonic wave of 35 kHz, and then to apply a high-pressure pulse (0.35 MPa~1.25 MPa square wave) with a surface pressure of 0.8±0.45 MPa and a pulse frequency of 1.5 Hz after 30 s.

[0080] (5) When the LFO pre-lithiated soft package battery is restrained to charge on the formation cabinet and the SOC reaches 4.0V, the formation is suspended, the air bag is pumped, and the vacuum sealing is performed after the pumping is completed.

[0081] (6) The LFO pre-lithiated soft package battery after the pumping is continued to be charged until the formation is completed.

[0082] (7) The LFO pre-lithiated soft package after the formation is completed is placed at 45℃ for 24 h, then the air bag is punctured for vacuum resealing, and the air bag is cut off, thus the formation and the exhaust process of the LFO pre-lithiated soft package battery are completed.

[0083] Comparative Example 4 The formation gas of the pre-lithiated lithium battery is removed according to the method of Comparative Example 3, except that the charging current I5 in step (3) and step (4) is 0.5C, and the other conditions are the same as those in Comparative Example 3, thus the formation and the exhaust process of the LFO pre-lithiated soft package battery are completed.

[0084] Comparative Example 5 The formation gas of the pre-lithiated lithium battery is removed according to the method of Comparative Example 3, except that the step (2) of Comparative Example 1 is added between step (1) and step (2): the LFO pre-lithiated soft package battery with the air bag is placed on the formation cabinet and restrained, and the low-frequency ultrasonic wave of 15 kHz is applied at the initial preset surface pressure of 0.2 MPa, and the duration is 10 min; the other conditions are the same as those in Comparative Example 3, thus the formation and the exhaust process of the LFO pre-lithiated soft package battery are completed.

[0085] Comparative Example 6 The pre-lithiation lithium battery formation gas removal was carried out according to the method of Comparative Example 3, except that step (7) was: after the end of formation, the LFO pre-lithiation soft package was placed at 45°C for 24h, and then treated at a low surface pressure of 0.2 MPa using a short-time high-frequency ultrasonic mode, with a cycle lasting 1 min, wherein one cycle period was to first apply a high-frequency ultrasonic wave of 100 kHz for 1.5 s, and then stand for 8 s after the ultrasonic wave ended, after the cycle ended, the gas bag was punctured for vacuum two-sealing, and the gas bag was cut off; the remaining conditions were the same as those of Comparative Example 3, thus completing the formation and degassing process of the LFO pre-lithiation soft package battery.

[0086] Test Example 1 Take a container containing pure water, record the water level at this time, mark it as V0, and place the battery before formation in the container (make sure the pure water completely immerses the battery), mark the water level at this time as V1. Then place the battery formed to each voltage in the container, extract the pure water above the V1 water level, and measure the volume of the extracted pure water, which is the gas production volume value corresponding to the voltage, note that pure water needs to be supplemented to the water level V0 before each measurement. Figure 1 The soft package battery prepared in Example 1 was formed according to step (3) and the gas production trend graph obtained by the above method was tested.

[0087] Test Example 2 The LFO pre-lithiation soft package batteries obtained in the above examples and comparative examples were tested for performance according to the following method: (1) The state of the pole piece: fully charged and disassembled to observe the interface state of the negative pole piece, and observe whether there is bubble-shaped lithium precipitation & un-embedded area.

[0088] (2) First coulomb efficiency test: test the first coulomb efficiency at room temperature 25°C±2°C, the charging condition is consistent with the formation charging step, and the discharging condition is: constant current discharge to 2.5V at 0.1C, the cutoff current is 0.05C, record the first discharge capacity in the charging and discharging process and calculate the first coulomb efficiency (first coulomb efficiency=discharge capacity / charge capacity*100%).

[0089] (3) Cycle test: at room temperature 25°C±2°C, single cycle condition is: constant current charging to 3.65V at 1C, and then constant current discharging to 2.5V at 1C, calculate the capacity retention rate after 500 cycles.

[0090] Table 1

[0091] From the results of Table 1, compared with Comparative Examples 1-6, the method of Examples 1-7 of the present application is used to remove the formation gas of pre-lithiated lithium batteries, the bubble-shaped lithium precipitation & un-embedded area on the negative plate is less, the damage to the plate is small, thereby making the lithium battery have better first efficiency performance and cycle capacity retention rate.

[0092] Although the embodiments of the present application have been shown and described above, it should be understood by those skilled in the art that the above-mentioned embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application without departing from the principles and spirits of the present application.

Claims

1. A method of removing formation gas from prelithiated lithium batteries, characterized in that, The method comprises the following steps: S1. The pre-lithiated lithium battery provided with the air bag is placed on the formation cabinet and restrained, low-frequency ultrasonic treatment is carried out under a preset surface pressure I, and then a formation charging process is set to carry out the formation charging process; S2. In the formation charging process, when the charging voltage reaches the range of the gas generation peak period, the pre-lithiated lithium battery is treated by using the ultrasonic and pressure pulse alternating cycle mode synchronously, and the charging current I5 of the formation charging process is less than or equal to 0.1C during the treatment process, and the number of the gas generation peak period is more than one; S3. After the formation charging is completed, high-frequency ultrasonic treatment is carried out under a preset surface pressure II, then the air bag is pumped, vacuum two-sealing is carried out after the pumping is completed, and the air bag is removed.

2. The method of removing formation gas from prelithiated lithium batteries of claim 1, wherein, The positive electrode material of the pre-lithiated lithium battery is lithium iron phosphate; Preferably, the pre-lithiated lithium battery is pre-lithiated by using lithium iron oxide as a positive electrode lithium supplement agent; Preferably, the pre-lithiated battery is a square shell battery or a soft package battery.

3. The method of removing formation gas from prelithiated lithium batteries of claim 1 or 2, wherein, In step S1, the preset surface pressure I is 0.1-0.3 MPa; Preferably, the frequency of the low-frequency ultrasonic wave is 10-20 kHz; Preferably, the time of the low-frequency ultrasonic treatment is 10-15 min.

4. The method of removing formation gas from prelithiated lithium batteries of claim 1 or 2, wherein, In step S1, the formation charging process comprises the following stages: when the charging voltage is less than or equal to 3.3 V, the charging current I1 is less than or equal to 0.1C; when the charging voltage is less than or equal to 3.65 V, the charging current I2 is less than or equal to 0.5C; when the charging voltage is less than or equal to 3.9 V, the charging current I3 is less than or equal to 0.1C; and when the charging voltage is less than or equal to 4.15 V, the charging current I4 is less than or equal to 0.5C.

5. The method of removing formation gas from prelithiated lithium batteries of claim 1 or 2, wherein, When the pre-lithiated lithium battery is a lithium battery obtained by using lithium iron oxide as a positive electrode lithium supplement agent and lithium iron phosphate as a positive electrode material for pre-lithiation, the gas generation peak period has two; Preferably, the first gas generation peak period is 3.20-3.40 V, and the second gas generation peak period is 3.80-4.10 V.

6. The method of removing formation gas from prelithiated lithium batteries of claim 5, wherein, In step S2, when the charging voltage reaches the first gas generation peak period, the treatment time of the ultrasonic and pressure pulse alternating cycle mode I is 10-30 min; Preferably, in the ultrasonic and pressure pulse alternating cycle mode I, the frequency of the ultrasonic wave I is 30-45 kHz, the duration h1 of the ultrasonic wave I in a single cycle is 30-60 s; Preferably, in the ultrasonic and pressure pulse alternating cycle mode I, the surface pressure of the pressure pulse I is 0.7-0.9 MPa, the pulse amplitude is ±0.2-0.35 MPa, the pulse frequency is 0.5-2.0 Hz, and the duration h2 of the pressure pulse I in a single cycle is 60-180 s.

7. The method of removing formation gas from prelithiated lithium batteries of claim 5, wherein, In step S2, when the charging voltage reaches the second gas generation peak period, the treatment time of the ultrasonic and pressure pulse alternating cycle mode II is 10-30 min; Preferably, in the ultrasonic and pressure pulse alternating cycle mode II, the frequency of the ultrasonic wave II is 30-45 kHz, and the duration h3 of the ultrasonic wave II in a single cycle is 30-60 s; Preferably, in the ultrasonic and pressure pulse alternating cycle mode, the surface pressure of the pressure pulse II in mode II is 0.7-0.9 MPa, the pulse amplitude is ±0.4-0.6 MPa, the pulse frequency is 0.5-2.0 Hz, and the duration h4 of the pressure pulse II in a single cycle is 60-180 s.

8. The method of removing formation gas from prelithiated lithium batteries of claim 1 or 2, wherein, In step S3, the preset surface pressure II is 0.1-0.3 MPa; Preferably, the processing time of the high-frequency ultrasonic cycle mode is 0.5-1.5 min; Preferably, in the high-frequency ultrasonic cycle mode, the duration h5 of the high-frequency ultrasonic wave in a single cycle is 0.5-3.0 s, and the standing time h6 is 5-10 s. Preferably, the frequency of the high-frequency ultrasonic wave is 90-110 kHz.

9. The method of removing formation gas from prelithiated lithium batteries of claim 1 or 2, wherein, In step S1, the pre-lithiated lithium battery is placed in constraint before the formation cabinet, which includes: placing the pre-lithiated lithium battery in 40-50°C for 12-32 h; In step S2, after the pre-lithiated lithium battery is treated by the ultrasonic and pressure pulse alternating cycle mode, it includes: pausing the formation charging, pumping the air bag, and after pumping, vacuum sealing, and then continuing the formation charging process; In step S3, before the pre-lithiated lithium battery is treated by the high-frequency ultrasonic cycle mode, it includes: placing the pre-lithiated lithium battery after the formation charging is completed in 40-50°C for 12-32 h.

10. The application of the method for removing the formation gas of the pre-lithiated lithium battery in the manufacture of lithium ion batteries.

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