Battery secondary liquid injection formation method and battery

Abstract

The invention relates to a battery secondary liquid injection formation method and a battery, and the battery secondary liquid injection method comprises the following steps: S1, providing a first electrolyte, carrying out primary liquid injection on the battery, and standing to obtain a primary liquid injection battery; the first electrolyte does not contain electrolyte salt; s2, providing a second electrolyte, carrying out secondary electrolyte injection on the battery after standing, and standing after vacuum sealing to complete a secondary electrolyte injection process; the second electrolyte comprises fluorobenzene and electrolyte salt; s3, formation is carried out; the liquid injection amount of the first liquid injection is m1, the liquid injection amount of the second liquid injection is m2, and m1 / m2 is larger than or equal to 0.1 and smaller than or equal to 1.5. According to the invention, the electrolyte is prepared into the first electrolyte free of electrolyte salt and the second electrolyte containing fluorobenzene and electrolyte salt in advance, secondary electrolyte injection is carried out, and by controlling the injection amount of the two times of electrolyte injection, not only can the overall infiltration time of the electrolyte injection process be obviously reduced, but also the cycle stability of the battery at normal temperature and high temperature can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a battery secondary liquid injection formation method and a battery. Background Art

[0002] Lithium-ion batteries have been widely used in electric vehicles, laptops, and energy storage due to their high energy density, long cycle life, and environmental friendliness. In the production process of lithium-ion batteries, the static process after injection is to fully infiltrate the electrode with the injected electrolyte. The quality of the infiltration plays a vital role in the SEI film formation and battery performance of the battery. In the actual production process, the battery after injection is usually placed in an environment of 25°C and 45°C successively, and the diffusion of the electrolyte inside the battery is used to achieve the infiltration of the core. In order to maintain sufficient infiltration, the total static time usually requires 16-24h. Longer static time increases energy consumption and reduces battery production efficiency. Therefore, it is urgent to develop such a low-energy and short-time infiltration method.

[0003] The methods for improving wetting reported so far mainly involve applying energy or mechanical force externally, including: (1) reciprocatingly squeezing the injected cell, utilizing the deformation of the core during the squeezing process to allow the electrolyte to penetrate the interior faster; (2) flipping the injected cell, utilizing the centrifugal force generated by the instrument and the gravity of the electrolyte to accelerate the entry of the electrolyte into the core; (3) evacuating the injected cell to a negative pressure or even a vacuum to extract the gas from the pores inside the battery and the core, allowing the electrolyte to enter the pores smoothly; and (4) ultrasonically treating the injected cell, utilizing the cavitation effect of ultrasound on the electrolyte to accelerate the wetting rate.

[0004] However, the above improvement methods all require additional equipment to process the battery cells, and the improvement effect is limited. Based on this, it is urgent to develop a convenient, fast-infiltration and improved-infiltration liquid injection method to improve battery production efficiency, reduce production costs, and further optimize battery performance. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a battery secondary liquid injection formation method and a battery. The present invention performs secondary liquid injection by pre-preparing the electrolyte into a first electrolyte without electrolyte salt and a second electrolyte containing fluorobenzene and electrolyte salt, and controls the injection amount of the two injections. This can not only significantly reduce the overall wetting time of the injection process, but also effectively improve the cycle stability of the battery at normal temperature and high temperature.

[0006] The present invention provides the following technical solutions:

[0007] The first aspect of the present invention provides a secondary liquid injection formation method for a battery, comprising the following steps:

[0008] S1, providing a first electrolyte, injecting the battery for the first time and leaving it to stand, to obtain a single-injection battery; the first electrolyte does not contain an electrolyte salt;

[0009] S2, providing a second electrolyte, injecting the primary injection battery for a second time, vacuum sealing and then standing to complete the secondary injection process; the second electrolyte comprises fluorobenzene and electrolyte salt;

[0010] S3, performing chemical formation;

[0011] The injection volume of the first injection is m1, and the injection volume of the second injection is m2, satisfying 0.1≤m1 / m2≤1.5.

[0012] Furthermore, 0.5≤m1 / m2≤1, for example, m1 / m2 is 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., including but not limited to the ratios listed above.

[0013] Furthermore, the mass percentage of electrolyte salt in the second electrolyte is 5%-75%, for example 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, etc., including but not limited to the mass percentages listed above.

[0014] Furthermore, the electrolyte salt is selected from one or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium acetate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium trifluoroacetate, lithium fluoroalkyl phosphate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium fluoride.

[0015] Furthermore, the mass percentage of fluorobenzene in the second electrolyte is 0.1%-10%, for example 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., including but not limited to the mass percentages listed above.

[0016] Furthermore, the first electrolyte and the second electrolyte both contain an organic carbonate solvent; the organic carbonate solvent is a cyclic carbonate solvent and / or a chain carbonate solvent; preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, and butylene carbonate, and the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0017] More preferably, the first electrolyte and the second electrolyte both contain at least one cyclic carbonate solvent and at least one chain carbonate solvent; the ratio of the cyclic carbonate solvent to the chain carbonate solvent in the first electrolyte and the second electrolyte is (1-2):(1-5), for example 1:1, 1:2, 1:3, 1:4, 1:5, 2:1, 2:3, 2:4, 2:5, etc., including but not limited to the ratios listed above.

[0018] Further, the first electrolyte and / or the second electrolyte further comprises an additive; the additive may be selected from one or more of vinylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sultone, methanedisulfonic acid methylene ester, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, adiponitrile, maleic anhydride, triallyl isocyanate and trimethylsilyl diethylamine.

[0019] Furthermore, in step S1, the battery is a fresh battery that has been homogenized, coated, rolled, slit, stacked / winded, bagged / cased, and baked, but has not yet been injected with liquid.

[0020] Furthermore, in step S1, the standing temperature is preferably 15-35°C, and the standing time is preferably 2-12h, for example, standing at 25°C for 2h, 4h, 6h, 8h, 10h or 12h.

[0021] Furthermore, in step S2, the vacuum degree of the vacuum seal is preferably lower than -70 KPa.

[0022] Furthermore, in step S2, the standing temperature is preferably 15-35°C, and the standing time is preferably 4-16h, for example, standing at 25°C for 4h, 6h, 8h, 10h, 12h, 14h or 16h.

[0023] Furthermore, step S1 and step S2 are performed under the condition of an ambient dew point of -80 to -20°C, more preferably -70 to -40°C.

[0024] Furthermore, in step S3, the chemical formation is a conventional chemical formation method.

[0025] A second aspect of the present invention provides a battery, which is prepared by the battery secondary liquid injection formation method described in the first aspect.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a secondary liquid injection formation method, in which an electrolyte is pre-formulated into a first electrolyte without electrolyte salt and a second electrolyte containing fluorobenzene and electrolyte salt, and secondary liquid injection is performed. By controlling the injection amount of the two injections, not only can the electrolyte quickly infiltrate the pole piece with low energy consumption, but also the battery prepared by the method shows excellent cycle stability at both room temperature and high temperature. DETAILED DESCRIPTION

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. The term "includes" or "comprising" described in the present invention means that it may include or contain other components in addition to the components described. The term "includes" or "comprising" described in the present invention may also be replaced by the closed form "for" or "consisting of..."

[0029] Since the quality of electrolyte wetting on the pole piece plays a crucial role in the SEI film formation and battery performance, in order to allow the injected electrolyte to fully infiltrate the pole piece, it is usually necessary to leave it for a long time after injection, which affects the production efficiency of the battery. Existing methods of improving the wetting effect of the electrolyte on the pole piece by applying external energy or mechanical force require additional equipment to process the battery cell, and the improvement effect is limited.

[0030] To solve the above problems, the embodiments of the present invention provide a secondary liquid injection formation method and a battery, comprising the following steps:

[0031] S1, providing a first electrolyte, injecting the battery for the first time and leaving it to stand, to obtain a single-injection battery; the first electrolyte does not contain an electrolyte salt;

[0032] S2, providing a second electrolyte, injecting the primary injection battery for a second time, vacuum sealing and then standing to complete the secondary injection process; the second electrolyte comprises fluorobenzene and electrolyte salt;

[0033] S3, performing chemical formation;

[0034] The injection volume of the first injection is m1, and the injection volume of the second injection is m2, satisfying 0.1≤m1 / m2≤1.5.

[0035] In order to solve the problems that the current methods used to fully infiltrate the electrode with the electrolyte are time-consuming, energy-intensive, or complicated to operate and have poor infiltration effects, which affect the battery production efficiency and battery performance, the present invention provides a battery secondary liquid injection formation method, in which the electrolyte is pre-formulated into a first electrolyte containing no electrolyte salt and a second electrolyte containing fluorobenzene and electrolyte salt, and the first electrolyte containing no electrolyte salt has good wettability to the electrode, an appropriate amount of the first electrolyte is first injected to quickly pre-infiltrate the electrode, and then a certain amount of the second electrolyte is injected, and on the basis of the pre-infiltration and in the presence of fluorobenzene, the wettability of the second electrolyte containing electrolyte lithium salt to the electrode can be effectively improved, thereby promoting the rapid and sufficient infiltration of the electrode by the electrolyte.

[0036] More importantly, in the above-mentioned injection process, the injection amount of the first electrolyte and the second electrolyte needs to be controlled. Since electrolyte salt is a necessary component of the electrolyte, if the injection amount of the first electrolyte is too much, the concentration of the electrolyte salt in the injected second electrolyte is too high, which will significantly increase the viscosity of the second electrolyte, and increase the time for the electrolyte to fully infiltrate the electrode. At the same time, after the second electrolyte is added, the concentration difference of the liquid lithium salt inside the battery increases, resulting in the electrolyte inside the battery core cannot be well mixed within the set infiltration time, which in turn leads to an increase in the difference in electrolyte composition in various parts of the core in the formation stage, affecting the uniformity of SEI film formation, and then affecting the battery cycle performance; but the injection amount of the first electrolyte should not be too small. Too little first electrolyte cannot complete the pre-infiltration of the battery core within the set infiltration time, and too much second electrolyte containing electrolyte lithium salt required to be added will increase the standing time and energy consumption required for full infiltration, affecting the infiltration efficiency and effect. Therefore, in order to effectively improve the wetting efficiency of the electrolyte on the battery without affecting the uniformity of SEI film formation in the formation stage, so as to improve the battery production efficiency while ensuring the battery cycle performance, the first electrolyte injection volume m1 and the second electrolyte injection volume m2 need to be controlled in the range of 0.1-1.5, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, etc., more preferably in the range of 0.5-1, which can achieve sufficient wetting of the battery in a shorter time, and the battery prepared by the above method exhibits better cycle stability at both room temperature and high temperature.

[0037] In the present invention, the mass percentage of the electrolyte salt in the second electrolyte is preferably 5%-75%, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, etc., including but not limited to the mass percentages listed above. Preferably, the electrolyte salt can be selected from one or more of bistrifluoromethanesulfonyl imide lithium, bisfluorosulfonyl imide lithium, lithium acetate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium trifluoroacetate, lithium fluoroalkyl phosphate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium fluoride.

[0038] In the present invention, the mass percentage of fluorobenzene in the second electrolyte is preferably 0.1%-10%, for example 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., including but not limited to the mass percentages listed above.

[0039] In the present invention, the first electrolyte and the second electrolyte both contain an organic carbonate solvent; wherein the organic carbonate solvent is a cyclic carbonate solvent and / or a chain carbonate solvent; preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, and butylene carbonate, and the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0040] In some preferred embodiments of the present invention, the first electrolyte and the second electrolyte both contain at least one cyclic carbonate solvent and at least one chain carbonate solvent; more preferably, the ratio of the cyclic carbonate solvent to the chain carbonate solvent in the first electrolyte and the second electrolyte is (1-2):(1-5), for example 1:1, 1:2, 1:3, 1:4, 1:5, 2:1, 2:3, 2:4, 2:5, etc., including but not limited to the ratios listed above.

[0041] In the present invention, the first electrolyte and / or the second electrolyte further comprises an additive; the additive may be selected from one or more of vinylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sultone, methylene disulfonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, adiponitrile, maleic anhydride, triallyl isocyanate and trimethylsilyl diethylamine.

[0042] In the present invention, in step S1, the standing temperature is preferably 15-35° C., and the standing time is preferably 2-12 h, for example, standing at 25° C. for 2 h, 4 h, 6 h, 8 h, 10 h or 12 h.

[0043] In the present invention, in step S2, the vacuum degree of vacuum sealing is preferably lower than -70KP; the standing temperature after vacuum sealing is preferably 15-35°C, and the standing time is preferably 4-16h, for example, standing at 25°C for 4h, 6h, 8h, 10h, 12h, 14h or 16h, etc.

[0044] In the present invention, step S1 and step S2 are performed under the condition of an ambient dew point of -80 to -20°C, more preferably -70 to -40°C, to control the ambient humidity during the injection process.

[0045] In the present invention, in step S3, conventional chemical formation methods can be used for chemical formation.

[0046] The embodiments of the present invention also provide a battery, which is prepared by the above-mentioned battery secondary liquid injection formation method, and the battery exhibits excellent cycle stability both at room temperature and high temperature.

[0047] In the present invention, the battery may be a cylindrical lithium-ion battery, a soft-pack lithium-ion battery or an aluminum-shell lithium-ion battery, or may be other secondary batteries.

[0048] In the present invention, the positive electrode active material and the negative electrode active material used in the battery are not limited, wherein the positive electrode active material can be selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium cobalt oxide, and the negative electrode active material can be selected from one or more of lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase carbon balls, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, and spinel structured Li-Al alloys.

[0049] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0050] Example 1

[0051] This embodiment relates to a secondary liquid injection formation method and the preparation of a lithium ion battery, which are specifically as follows:

[0052] 1. Preparation of lithium-ion batteries:

[0053] The positive electrode active material lithium iron phosphate, the conductive agent SP, and the binder polyvinylidene fluoride are fully stirred and mixed in a proper amount of N-methylpyrrolidone solvent according to a weight ratio of 96.7:1.5:1.8 to form a uniform positive electrode slurry; the slurry is coated on the positive electrode current collector Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0054] The negative electrode active material artificial graphite, the conductive agent SP, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in a proper amount of deionized water solvent according to a weight ratio of 95.7:1:1.5:1.8 to form a uniform negative electrode slurry; the slurry is coated on the negative electrode current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet.

[0055] Stack the positive electrode sheet, separator and negative electrode sheet in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, then wind them up and place them in the outer packaging foil. After the battery cell is baked, the electrolyte injection and infiltration process can be carried out when the moisture content of the positive and negative electrodes is less than 200ppm.

[0056] 2. Secondary liquid injection

[0057] Preparation of electrolyte:

[0058] First electrolyte: In an argon atmosphere glove box with a water content of less than 10ppm, ethylene carbonate and ethyl methyl carbonate are uniformly mixed in a weight ratio of 3:7, and then additives are added, wherein the concentrations of vinylene carbonate and vinyl sulfate are 1% and 2%, respectively. Before injection, the water content of the electrolyte is tested to ensure that the water content is less than 50ppm and the hydrofluoric acid content is less than 100ppm;

[0059] Second electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate and ethyl methyl carbonate were uniformly mixed in a weight ratio of 3:7, and 18.7% of LiPF was added. 6 Stir evenly, add 0.5% by mass of fluorobenzene, and finally add additives, in which the mass fractions of vinylene carbonate and vinyl sulfate are 1% and 2% respectively. Test the moisture content of the electrolyte before injection to ensure that the moisture content is less than 50ppm and the hydrofluoric acid content is less than 100ppm.

[0060] Second injection:

[0061] Transfer the baked battery and the first and second electrolytes required for injection to an environment with a temperature control of 25±3℃ and a dew point below -50℃. First, perform a first injection, inject 3g of the first electrolyte into the battery, and let it stand at room temperature for 6 hours; then perform a second injection, inject 9g of the second electrolyte into the battery, vacuum heat seal the opening, and let it stand at 25±3℃ for 8 hours, completing the battery electrolyte injection and infiltration process. The total injection coefficient is 4g / Ah, the total injection volume is 12g, and LiPF 6 The mass proportion in the total electrolyte (first electrolyte + second electrolyte) is 14%.

[0062] Formation:

[0063] The secondary-filled battery was transferred to a forming cabinet for a forming process. The forming fixture pressure was 0.3 MPa, the forming temperature was 45° C., and the forming process was completed by charging at a constant current of 150 mA for 4 hours.

[0064] The battery formed by the secondary liquid injection is subjected to shaping and other processes to complete the preparation of the lithium-ion battery.

[0065] Example 2

[0066] This embodiment relates to a secondary liquid injection formation method and preparation of a lithium ion battery. The only difference from the embodiment 1 is that: the injection amount of the first electrolyte in the primary injection is 4g, and the injection amount of the second electrolyte in the secondary injection is 8g; and the LiPF in the second electrolyte is 1. 6 The mass fraction of LiPF is 21%, 6 The mass proportion of the total electrolyte (first electrolyte + second electrolyte) is 14%. The remaining operations are the same to prepare the corresponding lithium ion battery.

[0067] Example 3

[0068] This embodiment relates to a secondary liquid injection formation method and preparation of a lithium ion battery. The only difference from the embodiment 1 is that: the injection amount of the first electrolyte in the primary injection is 5g, and the injection amount of the second electrolyte in the secondary injection is 7g; and the LiPF in the second electrolyte is 1. 6 The mass fraction of LiPF is 24%, 6 The mass proportion of the total electrolyte (first electrolyte + second electrolyte) is 14%. The remaining operations are the same to prepare the corresponding lithium ion battery.

[0069] Example 4

[0070] This embodiment relates to a secondary liquid injection formation method and preparation of a lithium ion battery. The only difference from the first embodiment is that the injection amount of the first electrolyte is 5.5g in the first injection, and the injection amount of the second electrolyte is 6.5g in the second injection; and the LiPF 6 The mass fraction of LiPF is 25.8%, 6 The mass proportion of the total electrolyte (first electrolyte + second electrolyte) is 14%. The remaining operations are the same to prepare the corresponding lithium ion battery.

[0071] Example 5

[0072] This embodiment relates to a secondary injection formation method and preparation of a lithium ion battery. The only difference from the first embodiment is that the injection amount of the first electrolyte is 6g in the first injection, and the injection amount of the second electrolyte is 6g in the second injection; and the LiPF in the second electrolyte is 6 The mass fraction of LiPF is 28%,6 The mass proportion of the total electrolyte (first electrolyte + second electrolyte) is 14%. The remaining operations are the same to prepare the corresponding lithium ion battery.

[0073] Example 6

[0074] This embodiment relates to a secondary injection formation method and preparation of a lithium ion battery. The only difference from the first embodiment is that the injection amount of the first electrolyte is 7g in the first injection, and the injection amount of the second electrolyte is 5g in the second injection; and the LiPF in the second electrolyte is 1. 6 The mass fraction of LiPF is 33.6%, 6 The mass proportion of the total electrolyte (first electrolyte + second electrolyte) is 14%. The remaining operations are the same to prepare the corresponding lithium ion battery.

[0075] Comparative Example 1

[0076] This comparative example relates to a secondary liquid injection formation method and the preparation of a lithium ion battery. The difference from Example 1 is that only one liquid injection is performed, and the LiPF in the electrolyte is 6 The mass fraction of is 14%, the injection amount is 12g, and the static time after injection is 14h. The rest operations are the same, and the corresponding lithium ion battery is prepared.

[0077] Comparative Example 2

[0078] This comparative example relates to a secondary liquid injection formation method and the preparation of a lithium ion battery. The difference from Example 1 is that only one liquid injection is performed, and the LiPF in the electrolyte is 6 The mass fraction of is 14%, the injection amount is 12g, and the total standing time after injection is 24h. The rest of the operations are the same, and the corresponding lithium-ion battery is prepared.

[0079] Comparative Example 3

[0080] This comparative example relates to a secondary liquid injection formation method and preparation of a lithium ion battery, and the difference from Example 3 is that: LiPF in the first electrolyte 6 The mass fraction of LiPF in the second electrolyte is 14%. 6 The mass fraction of is 14%. The rest of the operations are the same to prepare the corresponding lithium ion battery.

[0081] Comparative Example 4

[0082] This comparative example relates to a secondary liquid injection formation method and preparation of a lithium ion battery, and the only difference from Example 3 is that no fluorobenzene is added to the second electrolyte. The remaining operations are the same, and the corresponding lithium ion battery is prepared.

[0083] The injection parameters set in the process of preparing lithium-ion batteries in the above embodiments and comparative examples (a1 and a2 are the mass fractions of lithium salt in the first electrolyte and the second electrolyte, b1 and b2 are the mass fractions of fluorobenzene in the first electrolyte and the second electrolyte, m1 and m2 are the injection amounts of the first electrolyte and the second electrolyte, t1 and t2 are the standing time after the first injection and the second injection, respectively) are shown in Table 1 below:

[0084] Table 1

[0085]

[0086] Performance Testing

[0087] The cycle performance of the lithium ion batteries prepared in the above examples and comparative examples was tested as follows:

[0088] 1. Test method for 25℃ normal temperature cycle performance

[0089] Place the lithium-ion battery in a 25°C constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature; discharge it to 2.0V at a constant current of 1C and let it stand for 30 minutes; charge it to 3.65V at a constant current of 1C, and charge it at a constant voltage to a current of 0.05C; let it stand for 30 minutes; discharge it to 2.0V at 1C again. The capacity of this step is used as the benchmark and recorded as the discharge capacity of the first cycle. This step is repeated 500 times, and the discharge capacity of the 500th cycle is recorded. The capacity retention rate is calculated as follows: discharge capacity of the 500th cycle / discharge capacity of the first cycle × 100%.

[0090] 2. Test method for 45℃ high temperature cycle performance

[0091] Place the lithium-ion battery in a 45°C constant temperature box and let it stand for 60 minutes to allow the lithium-ion battery to reach a constant temperature; discharge it to 2.0V at a constant current of 1C and let it stand for 30 minutes; charge it to 3.65V at a constant current of 1C, and charge it at a constant voltage to a current of 0.05C; let it stand for 30 minutes; discharge it to 2.0V at 1C again. The capacity of this step is used as the benchmark and recorded as the discharge capacity of the first cycle. This step is repeated 500 times, and the discharge capacity of the 500th cycle is recorded. The capacity retention rate is calculated as follows: discharge capacity of the 500th cycle / discharge capacity of the first cycle × 100%.

[0092] The test results are shown in Table 2 below:

[0093] Table 2

[0094] Test Example 25℃ room temperature cycle performance (%) 45℃ high temperature cycle performance (%) Example 1 83.1 84.8 Example 2 88.7 86.4 Example 3 87.5 87.3 Example 4 91.2 88.1 Example 5 90.1 87.6 Example 6 87.1 86.3 Comparative Example 1 71.4 75.2 Comparative Example 2 88.4 86.1 Comparative Example 3 77.4 78.3 Comparative Example 4 81.9 82.1

[0095] It can be seen from Tables 1 and 2 that, compared with the lithium ion battery prepared by the single liquid injection formation method in Comparative Example 1, under the same liquid injection standing time, the lithium ion batteries prepared by the secondary liquid injection formation method in Examples 1-6 show better cycle stability at room temperature and high temperature; and Comparative Example 2 further increases the standing time from 14h to 24h on the basis of the single liquid injection formation method, and the cycle performance of the prepared lithium ion battery is significantly improved, which also shows that the secondary liquid injection method provided by the present invention is more conducive to the electrolyte to achieve full infiltration of the battery in a short time.

[0096] In addition, it can be seen from Examples 1-6 that the ratio of the primary injection volume m1 to the secondary injection volume m2 in the secondary liquid injection formation method will affect the cycle performance of the battery. When the ratio of m1 / m2 is in the range of 0.33-1.4, as m1 / m2 increases, the cycle stability of the battery at room temperature and high temperature first increases and then decreases with the increase of the ratio. This is because if the value of m1 / m2 is too small, the amount of the first electrolyte injected is small, and the pre-infiltration of the battery core cannot be completed well within the set infiltration time, which then deteriorates the overall infiltration effect and affects the battery cycle performance; at the same time, if the value of m1 / m2 is too large, the lithium salt concentration in the second electrolyte is high, which will significantly increase the viscosity of the second electrolyte, and at the same time increase the concentration difference of the liquid lithium salt in the battery after the second electrolyte is added, resulting in the electrolyte inside the battery core cannot be well mixed within the set infiltration time, which then leads to an increase in the difference in the electrolyte composition of each part of the core in the formation stage, affecting the uniformity of SEI film formation, and thus affecting the battery cycle performance. Therefore, in order to effectively improve the wetting efficiency of the electrolyte to the battery without affecting the uniformity of the SEI film formation in the formation stage, so as to improve the battery production efficiency while ensuring the battery cycle performance, it is more preferred to control the ratio of m1 / m2 in the range of 0.5-1, so that the lithium-ion battery prepared by a short period of standing during the injection process has a capacity retention rate of more than 87.5% after 500 cycles at 25°C, and a capacity retention rate of more than 86.4% after 500 cycles at 45°C.

[0097] In addition, it can be seen from Example 3 and Comparative Example 3 that adding electrolyte salt to the first electrolyte will deteriorate the wettability of the first electrolyte to the battery within a predetermined time, thereby affecting the cycle performance of the battery. It can be seen from Example 3 and Comparative Example 4 that the addition of fluorobenzene to the second electrolyte can effectively improve the cycle stability of the lithium-ion battery at room temperature and high temperature, because fluorobenzene can effectively improve the electrolyte infiltration rate, especially the infiltration efficiency of the battery with a relatively high concentration of lithium salt electrolyte.

[0098] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A battery secondary liquid injection formation method, characterized in that: The following steps are involved: S1, providing a first electrolyte, injecting the battery for the first time and leaving it to stand, to obtain a single-injection battery; the first electrolyte does not contain an electrolyte salt; S2, providing a second electrolyte, injecting the primary injection battery for a second time, vacuum sealing and then standing to complete the secondary injection process; the second electrolyte comprises fluorobenzene and electrolyte salt; S3, performing chemical formation; The injection volume of the first injection is m1, and the injection volume of the second injection is m2, satisfying 0.1≤m1 / m2≤1.

5.

2. The battery secondary liquid injection formation method according to claim 1, characterized in that: 0.5≤m1 / m2≤1.

3. The battery secondary liquid injection formation method according to claim 1, characterized in that: The mass percentage of the electrolyte salt in the second electrolyte is 5%-75%; The electrolyte salt is selected from one or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium acetate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium trifluoroacetate, lithium fluoroalkyl phosphate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium fluoride.

4. The battery secondary liquid injection formation method according to claim 1, characterized in that: The mass percentage of fluorobenzene in the second electrolyte is 0.1%-10%.

5. The battery secondary liquid injection formation method according to claim 1, characterized in that: The first electrolyte and the second electrolyte both contain an organic carbonate solvent; the organic carbonate solvent is a cyclic carbonate solvent and / or a chain carbonate solvent; Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, and butylene carbonate, and the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; Preferably, the first electrolyte and the second electrolyte both contain at least one cyclic carbonate solvent and at least one chain carbonate solvent; the ratio of the cyclic carbonate solvent to the chain carbonate solvent in the first electrolyte and the second electrolyte is (1-2): (1-5).

6. The battery secondary liquid injection formation method according to claim 1, characterized in that: The first electrolyte and / or the second electrolyte further comprises an additive; The additive is selected from one or more of vinylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sultone, methylene methanedisulfonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, adiponitrile, maleic anhydride, triallyl isocyanate and trimethylsilyl diethylamine.

7. The battery secondary liquid injection formation method according to claim 1, characterized in that: In step S1, the standing temperature is 15-35° C., and the standing time is 2-12 hours.

8. The battery secondary liquid injection formation method according to claim 1, characterized in that: In step S2, the vacuum degree of the vacuum seal is lower than -70 KPa; The standing temperature is 15-35° C., and the standing time is 4-16 hours.

9. The battery secondary liquid injection formation method according to claim 1, characterized in that: Step S1 and step S2 are performed under the condition of an ambient dew point of -80 to -20°C.

10. A battery, characterized in that: The battery is prepared by the secondary liquid injection formation method according to any one of claims 1 to 9.

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