Secondary electrolyte injection method and alkali metal ion battery thereof

Abstract

The application discloses a secondary electrolyte injection method and an alkali metal ion battery thereof, and the secondary electrolyte injection method comprises the following steps: injecting a first electrolyte into a semi-finished product battery cell and sealing, aging, standing and forming, wherein the first electrolyte comprises an electrolyte salt, a non-aqueous solvent and a basic additive; continuously injecting a second electrolyte, and obtaining an alkali metal secondary battery after secondary sealing and capacity distribution; the second electrolyte comprises the first electrolyte, a first additive and a second additive; the first additive is lithium fluorosulfonate or sodium fluorosulfonate, and the second additive is at least one of a fluorine-containing pyridine compound shown in the following formula (I) or a fluorine-containing imidazole compound shown in the following formula (II), and the specific structure is referred to the description. Through the secondary injection of the first additive and the second additive, the high-temperature cycle performance, the high-temperature storage performance and the low-temperature cycle performance of the battery can be improved, the rate discharge performance of the battery is improved, and the power of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of electrolytes, and particularly to a secondary electrolyte injection method and its alkali metal ion battery. Background Technology

[0002] Alkali metal ion batteries, due to their high energy density, high-voltage operating platform, and environmental friendliness, have expanded from traditional small electronic devices to electric vehicles, energy storage, power tools, aerospace, and other fields. This has led to greater demands on the comprehensive performance of alkali metal ion batteries in more complex external environments, such as high and low temperatures. Currently, pure electric vehicles (EVs) and hybrid electric vehicles (HEVs) require batteries with a temperature range of -30 to 70°C; the requirements for battery temperature range are even more stringent in the military and aerospace fields, requiring an operating temperature range of -50 to 80°C. Although the lithium-ion battery field is developing rapidly, it still cannot achieve high performance within this temperature range. Therefore, research into developing wide-temperature lithium-ion batteries that combine high-temperature and low-temperature performance is urgently needed. The electrolyte, as a crucial component of the lithium-ion battery system, acts as a bridge connecting the positive and negative electrodes, playing a role in lithium ion transport and is closely related to high and low temperature performance and battery cycle life. Introducing small amounts of additives into the electrolyte can significantly improve the high and low temperature cycle performance of the battery.

[0003] Patents CN 106882820A and CN 112234252A disclose that lithium fluorosulfonate exhibits excellent high and low temperature performance when used as an electrolyte additive, especially under low temperature conditions, it has good low-temperature discharge performance and low-temperature cycling performance. However, patent CN117895085A and Ma Guohua et al. (Study on the interfacial electrochemical behavior of lithium bis(fluorosulfonyl)imide electrolyte and aluminum positive current collector, Diss. Huazhong University of Science and Technology, 2017.) point out that the fluorosulfonic acid produced by the dissociation of fluorosulfonate compounds is highly corrosive. Even when the addition amount is 50 ppm, it will corrode the aluminum foil, causing aluminum ions to dissolve in the electrolyte. It can even undergo a reduction reaction during cycling, deposit on the surface of the negative electrode, destroy the negative electrode SEI film, increase parasitic side reactions, and lead to the degradation of the battery's high and low temperature cycling performance, as well as poor long-term cycling performance.

[0004] Therefore, it is both necessary and urgent to propose a method to effectively inhibit the corrosion of aluminum current collectors by fluorosulfonates and improve the high and low temperature performance of batteries. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a secondary electrolyte injection method containing fluorosulfonate electrolyte. By using a combination of fluoropyridine compounds and / or fluoroimidazole compounds with fluorosulfonates and simultaneously performing secondary electrolyte injection, this method not only inhibits the corrosion of the positive electrode current collector by fluorosulfonates and improves the high and low temperature performance of the battery, but also modifies the interfacial film on the electrode surface, enhancing the long-term cycle stability of the battery. Furthermore, it unexpectedly improves the high-rate discharge performance of the battery, increasing its power output.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for secondary electrolyte injection, the method comprising:

[0008] The first electrolyte is injected into the semi-finished battery cell and then sealed, aged, left to stand and formed. The first electrolyte contains electrolyte salts, non-aqueous solvents and basic additives.

[0009] The second electrolyte is injected, and after secondary sealing and capacity testing, an alkali metal ion battery is obtained. The second electrolyte contains the first electrolyte, a first additive, and a second additive. The first additive is lithium fluorosulfonate or sodium fluorosulfonate, and the second additive is selected from at least one of the structures shown in formula (I) or (II) below:

[0010]

[0011] In the formula, R1, R2, R3, R4, R5, and R6 are independently selected from hydrogen, halogen, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 haloalkyl, C2-C5 alkenyl, C2-C5 alkynyl, C3-C8 cycloalkenyl, cyano, or isocyanate group. Preferably, R1, R2, R3, R4, R5, and R6 are independently selected from hydrogen, fluorine, methyl, ethyl, methoxy, ethoxy, trifluoromethyl, or vinyl.

[0012] More preferably, the second additive is selected from at least one of the compounds shown in the following structures:

[0013]

[0014]

[0015] When the first additive of this invention is used alone, although fluorosulfonate compounds have excellent high and low temperature performance, the fluorosulfonic acid produced by their dissociation is highly corrosive to the electrodes, increasing parasitic side reactions in the electrolyte and causing a rapid decline in the battery's cycle performance in the later stages. The second additive, when used alone, has dehydration and acid-suppressing effects; theoretically, its combination with the first additive should improve the battery's high and low temperature performance and cycle performance. However, when the first and second additives were added to the electrolyte simultaneously (in a single injection), the high and low temperature performance and long cycle performance did not improve; instead, the battery's power performance and low-temperature performance deteriorated.

[0016] Further research in this invention has revealed that by using a two-stage electrolyte injection method, first injecting a first electrolyte into the cell, and then injecting a second electrolyte containing both a first additive and a second additive, the interfacial film on the electrode surface can be selectively modified during battery cycling, eliminating the corrosive effects of fluorosulfonic acid on the electrodes and improving the battery's low-temperature and high-temperature performance. It can also effectively remove HF generated by parasitic side reactions during cycling, improving the battery's long-term cycle stability and exhibiting excellent high-rate discharge performance. The reason for this is that when the first and second additives are added to the electrolyte simultaneously (in a single injection), although the second additive can complex with the first additive, its own impedance is relatively high, significantly increasing the initial electrolyte / electrolyte interfacial impedance and deteriorating its high-temperature and low-temperature performance as well as its long-term cycle performance. Only when the first and second additives are added to the electrolyte through a two-stage injection method can the electrode / electrolyte interfacial composition be significantly modulated, significantly improving battery interfacial stability and thus enhancing the battery's high-temperature and low-temperature cycle performance. In addition, the addition of the first and second additives to the electrolyte through a secondary injection method can significantly reduce the initial electrode / electrolyte interfacial impedance, improve the polarization phenomenon during battery discharge, thereby enhancing the battery's rate discharge performance and improving battery power output.

[0017] The second electrolyte of this invention is based on the first electrolyte with the addition of a first additive and a second additive. Different ratios of the first electrolyte and the second electrolyte, as well as different amounts of the first additive and the second additive, will have different effects on the application effect.

[0018] Preferably, in the secondary electrolyte injection method of the present invention, the mass ratio of the first electrolyte to the second electrolyte is (50-95):(5-50). More preferably, the mass ratio of the first electrolyte to the second electrolyte is (80-90):10-20.

[0019] In the second electrolyte, the first additive accounts for 2 to 20 wt% of the total mass of the second electrolyte, and the second additive accounts for 1 to 10 wt% of the total mass of the second electrolyte. More preferably, the first additive accounts for 2 to 8 wt% of the total mass of the second electrolyte, and the second additive accounts for 1 to 3 wt% of the total mass of the second electrolyte.

[0020] In the first electrolyte, the electrolyte salt accounts for 5 to 30 wt% of the total mass of the first electrolyte, preferably 10 to 18 wt%.

[0021] When the alkali metal ion battery is a lithium-ion battery, the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, lithium bistrifluoromethanesulfonylimide, lithium bisoxalateborate, and lithium difluorooxalateborate, preferably lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide.

[0022] When the alkali metal ion battery is a sodium ion battery, the electrolyte salt is selected from at least one of sodium hexafluorophosphate, sodium difluorosulfonamide, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonamide) or sodium di(oxalateborate), preferably sodium hexafluorophosphate and / or sodium difluorosulfonamide.

[0023] The non-aqueous solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butene carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, fluoroethylene carbonate, difluoroethylene carbonate, methyl difluoroethyl carbonate, and methyl trifluoroethyl carbonate, and its amount accounts for 60-80 wt% of the total mass of the first electrolyte.

[0024] The basic additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, methanedisulfonate, vinylsilane, tris(trimethylsilane) phosphate, or tris(trimethylsilane) borate, and is used in an amount of 0.1 to 10.0 wt% of the total mass of the first electrolyte, preferably 0.5 to 5.0 wt%, more preferably 0.5 to 2.0 wt%.

[0025] The present invention also provides an alkali metal ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is obtained by injecting electrolyte using any of the above-described secondary injection methods.

[0026] When the alkali metal ion battery is a lithium-ion battery, the active material of the positive electrode is selected from lithium iron phosphate, manganese iron phosphate, lithium cobalt oxide, LiNi(1-xy)CoxMnyO2 (0≤x,y≤1), lithium titanate, nickel manganese spinel or lithium manganese oxide, and the active material of the negative electrode is selected from graphite, silicon carbide, silicon oxide materials, soft carbon, hard carbon or mesophase pitch carbide.

[0027] When the alkali metal ion battery is a sodium ion battery, the active material of the positive electrode is selected from sodium iron phosphate, sodium manganese phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium iron sulfate, sodium vanadium phosphate, sodium vanadium fluorophosphate, and NaMn. (1-x-y) Ni y M x O2 (0≤x, y≤1, M is Cu, Fe or Co), and the active material of the negative electrode is selected from hard carbon, carbon black, amorphous carbon, silicon carbide or silicon oxide materials.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This invention utilizes the combined use of a first additive and a second additive, along with a secondary liquid injection formation process, to achieve the water removal and acid suppression effects of the second additive, thereby improving the battery's high-temperature storage and high-temperature cycling performance. Simultaneously, during battery cycling, the electrode surface is selectively modified to form an interface film with uniformly distributed organic / inorganic components, improving the battery's low-temperature and high-temperature performance and broadening the operating temperature range of alkali metal ion batteries.

[0030] 2. By using the first additive and the second additive in combination with a secondary liquid injection formation process, this invention can regulate the electrode / electrolyte interface grouping, reduce the initial electrode / electrolyte interface impedance, reduce polarization during battery discharge, enhance the battery's rate discharge performance, and improve battery power output. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0032] Example 1

[0033] This embodiment provides a secondary electrolyte injection method for lithium-ion batteries, and the specific steps are as follows:

[0034] (1) Electrolyte preparation

[0035] In an argon-filled glove box (oxygen content <10ppm; moisture content <5ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2 were mixed thoroughly. Lithium hexafluorophosphate was added to the mixed solvent to dissolve it, preparing a 1.0M lithium hexafluorophosphate solution. Then, 1.5% vinylene carbonate (VC), 0.5% ethylene sulfate (DTD), and 1% fluoroethylene carbonate were added by mass to obtain the first electrolyte for battery filling.

[0036] A portion of the first electrolyte is taken, and lithium fluorosulfonate and second additive I-1 are introduced by internal addition to obtain the second electrolyte for battery injection, wherein lithium fluorosulfonate accounts for 2 wt% of the total mass of the second electrolyte, and the second additive accounts for 1 wt% of the total mass of the second electrolyte.

[0037] (2)Injection

[0038] The process involves injecting a first electrolyte into a semi-finished lithium-ion cell, followed by sealing, aging, settling, and formation. Then, a second electrolyte is injected, and after a second sealing and capacity testing, a lithium-ion secondary battery is obtained. The first electrolyte accounts for 80% of the total injected volume (by mass), and the second electrolyte accounts for 20% of the total injected volume (by mass).

[0039] Example 2

[0040] The operation of this embodiment is the same as that of embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 3 wt%, the content of the second additive I-1 is 1 wt%, and everything else remains the same.

[0041] Example 3

[0042] The operation of this embodiment is the same as that of embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 4 wt%, the content of the second additive I-1 is 1 wt%, and everything else remains the same.

[0043] Example 4

[0044] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-1 is 1 wt%, and everything else remains the same.

[0045] Example 5

[0046] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 6 wt%, the content of the second additive I-1 is 1 wt%, and everything else remains the same.

[0047] Example 6

[0048] The operation of this embodiment is the same as that of embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-1 is 2 wt%, and everything else remains the same.

[0049] Example 7

[0050] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-1 is 3 wt%, and everything else remains the same.

[0051] Example 8

[0052] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-2 is 2 wt%, and everything else remains the same.

[0053] Example 9

[0054] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-3 is 2 wt%, and everything else remains the same.

[0055] Example 10

[0056] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-4 is 2 wt%, and everything else remains the same.

[0057] Example 11

[0058] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-5 is 2 wt%, and everything else remains the same.

[0059] Example 12

[0060] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive I-7 is 2 wt%, and everything else remains the same.

[0061] Example 13

[0062] The operation of this embodiment is the same as that of Embodiment 1, except that the content of lithium fluorosulfonate in the second electrolyte is 5 wt%, the content of the second additive II-1 is 2 wt%, and everything else remains the same.

[0063] Example 14

[0064] The operation of this embodiment is the same as that of embodiment 1, except that the injection volume of the first electrolyte accounts for 70% of the total injection volume, and the injection volume of the second electrolyte accounts for 30% of the total injection volume, while all other aspects remain unchanged.

[0065] Example 15

[0066] The operation of this embodiment is the same as that of embodiment 1, except that the injection volume of the first electrolyte accounts for 90% of the total injection volume, and the injection volume of the second electrolyte accounts for 10% of the total injection volume, while all other aspects remain unchanged.

[0067] Comparative Example 1

[0068] The operation of this comparative example is the same as that of Example 1, except that only 5 wt% of lithium fluorosulfonate is added to the second electrolyte, while everything else remains the same.

[0069] Comparative Example 2

[0070] The operation of this comparative example is the same as that of Example 1, except that only 2 wt% of the second additive I-1 is added to the second electrolyte, while everything else remains the same.

[0071] Comparative Example 3

[0072] The operation of this comparative example is the same as that of Example 1, except that only 2 wt% of the second additive I-2 is added to the second electrolyte, while everything else remains the same.

[0073] Comparative Example 4

[0074] The operation of this comparative example is the same as that of Example 1, except that only 2 wt% of the second additive I-3 is added to the second electrolyte, while everything else remains the same.

[0075] Comparative Example 5

[0076] The operation of the comparative example is the same as in Example 6, except that 1.25 wt% of lithium fluorosulfonate is added to the first electrolyte, and only 2 wt% of I-1 is added to the second electrolyte, while everything else remains the same.

[0077] Comparative Example 6

[0078] The operation of the comparative example is the same as in Example 6, except that 0.5 wt% of I-1 is added to the first electrolyte, and only 5 wt% of lithium fluorosulfonate is added to the second electrolyte, while everything else remains unchanged.

[0079] Comparative Example 7

[0080] The operation of this comparative example is the same as that of Example 1, except that 2 wt% pyridine is used instead of 1 wt% second additive I-1 in the second electrolyte, and everything else remains the same.

[0081] Comparative Example 8

[0082] The operation of this embodiment is the same as that of embodiment 6, except that pyridine is used instead of the second additive I-1 in the second electrolyte, the amount added remains the same, and all other operations remain the same.

[0083] Comparative Example 9

[0084] The operation of this embodiment is the same as that of embodiment 1, except that the injection volume of the first electrolyte accounts for 40% of the total injection volume, and the injection volume of the second electrolyte accounts for 60% of the total injection volume, while all other aspects remain unchanged.

[0085] Comparative Example 10

[0086] The operation of this comparative example is the same as that of Example 1, except that only the second electrolyte is used for one injection.

[0087] Cyclic performance tests were conducted on the 1100mAh soft-pack lithium-ion batteries prepared in Examples 1-15 and Comparative Examples 1-10, specifically including:

[0088] (1) 45℃ high temperature cycle test: The lithium-ion battery is placed in a constant temperature oven at 45±1℃ and charged and discharged at 1C / 1C current for high temperature cycle. The discharge capacity is calculated every week. The cycle is stopped when the cycle reaches 800 cycles or the capacity retention rate is less than 80%. The capacity retention rate after the cycle is calculated.

[0089] (2) 60℃ High-Temperature Storage Test: The lithium-ion battery was placed in a constant temperature environment of 25±1℃ and cycled at a charge / discharge current of 0.5C / 0.5C for one week. Then, it was charged at a constant current of 0.5C and charged at a constant voltage until the current dropped to 0.05C. The discharge capacity, internal resistance, and volume were recorded for the first week. The battery was then placed in a constant temperature oven at 60℃ for 28 days, followed by a charge / discharge cycle at room temperature of 0.5C / 0.5C for one week. The discharge capacity for the first week after high-temperature storage, the discharge capacity for the second week, and the volume after storage were recorded. The volume expansion rate, capacity retention rate, and capacity recovery rate of the battery after 60℃ high-temperature storage were calculated using the following formula:

[0090] Volume expansion rate = (Post-storage volume - Initial week 1 volume) / Initial week 1 volume * 100%

[0091] Capacity retention rate = (Charging capacity in the first week after high temperature rest / Initial discharge capacity in the first week) * 100%.

[0092] Capacity recovery rate = discharge capacity in the first week after high temperature settling / initial discharge capacity in the first week * 100%.

[0093] (3) -10℃ low temperature cycle test: The lithium-ion battery is placed in a constant temperature oven at -10±1℃ and charged and discharged at a current of 0.3C / 0.5C for low temperature cycle. The discharge capacity is calculated every week. The cycle is stopped when the capacity retention rate is less than 80% after 500 cycles. The capacity retention rate after the cycle is calculated.

[0094] (4) Rate discharge performance test: The lithium-ion battery was placed in a constant temperature oven at 25±1℃. First, it was cycled once with a charge / discharge current of 1C / 1C and the discharge capacity of the first week was recorded. Then, a high rate cycle performance test was performed with a charge / discharge current of 1C / 5C. The discharge capacity of each week was calculated. After 50 cycles or if the capacity retention rate was less than 80%, the cycle was stopped and the capacity retention rate after the cycle was calculated.

[0095] Capacity retention = Discharge capacity after high-rate cycling / Initial 1C discharge capacity * 100%

[0096] The test results are shown in Table 1:

[0097] Table 1. Performance test results of lithium-ion batteries

[0098]

[0099]

[0100] According to the test results in Table 1 above:

[0101] Comparing Examples 1-12 and Comparative Examples 1-4, it can be seen that simultaneously introducing lithium fluorosulfonate and fluorinated pyridine compounds or fluorinated imidazole compounds into the second electrolyte can not only improve the high-temperature cycling, high-temperature storage, and low-temperature cycling performance of the battery, but also improve the rate discharge performance of the battery and increase the battery power, compared to using lithium fluorosulfonate alone or using fluorinated pyridine compounds / fluorinated imidazole compounds alone.

[0102] Comparing Example 6 with Comparative Examples 5, 6, and 10, it can be seen that simultaneously introducing lithium fluorosulfonate and fluorinated pyridine / fluorinated imidazole compounds into the second electrolyte not only eliminates the disadvantage of high film-forming resistance of fluorinated pyridine additives, but also exerts its water removal and acid suppression effects, improving the high-temperature storage performance of the battery, and significantly improving the high-temperature and low-temperature cycling performance of the battery.

[0103] Comparing Example 6 and Comparative Example 8, it can be seen that when lithium fluorosulfonate and fluorinated pyridine compounds are introduced into the second electrolyte simultaneously, compared with the combination of lithium fluorosulfonate and non-fluorinated pyridine additives in the second electrolyte, only the synergistic effect of lithium fluorosulfonate and fluorinated pyridine additives can improve the high-temperature storage performance of the battery and improve the high-temperature cycle performance and low-temperature cycle performance of the battery.

[0104] Comparing Example 1 and Comparative Example 9, it can be seen that the electrolyte ratio of the first electrolyte to the second electrolyte is (8:2), which is different from the electrolyte ratio of (4:6). Only when the ratio of the first electrolyte to the second electrolyte is within a specific range can the electrolyte performance advantages be brought into play and the high-temperature cycle performance and low-temperature cycle performance of the battery be improved.

[0105] Example 15

[0106] This embodiment provides a secondary electrolyte injection method for sodium-ion batteries, and the specific steps are as follows:

[0107] (1) Electrolyte preparation

[0108] In an argon-filled glove box (oxygen content <10ppm; moisture content <5ppm), a solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2 was mixed thoroughly. Lithium hexafluorophosphate was added to the mixed solvent to dissolve it, preparing a 1.0M sodium hexafluorophosphate solution. Then, 1% by mass of fluoroethylene carbonate (FEC), 1% by mass of 1%, 3-propanesulfonate lactone (PS), and 1% by mass of 1%, 3-propenesulfonate lactone (PST) were added to obtain the first electrolyte for battery filling.

[0109] Take a portion of the first electrolyte and introduce sodium fluorosulfonate and second additive I-1 internally to obtain the second electrolyte for battery injection, wherein sodium fluorosulfonate accounts for 2 wt% of the total mass of the second electrolyte and the second additive accounts for 1 wt% of the total mass of the second electrolyte.

[0110] (2)Injection

[0111] The first electrolyte is injected into the semi-finished sodium-ion battery cell, followed by sealing, aging, settling, and formation. Then, the second electrolyte is injected, and after a second sealing and capacity testing, a sodium-ion secondary battery is obtained. The first electrolyte accounts for 80% of the total injected electrolyte volume (mass), and the second electrolyte accounts for 20% of the total injected electrolyte volume (mass).

[0112] Example 16

[0113] The operation of this embodiment is the same as that of embodiment 15, except that the sodium fluorosulfonate content in the second electrolyte is 4 wt%, the content of the second additive I-1 is 1 wt%, and everything else remains the same.

[0114] Example 17

[0115] The operation of this embodiment is the same as that of embodiment 15, except that the sodium fluorosulfonate content in the second electrolyte is 4 wt%, the content of the second additive I-1 is 2 wt%, and everything else remains the same.

[0116] Example 18

[0117] The operation of this embodiment is the same as that of embodiment 15, except that the content of lithium fluorosulfonate in the second electrolyte is 4 wt%, the content of the second additive I-1 is 3 wt%, and everything else remains the same.

[0118] Example 19

[0119] The operation of this embodiment is the same as that of embodiment 15, except that the content of lithium fluorosulfonate in the second electrolyte is 4 wt%, the content of the second additive II-1 is 2 wt%, and everything else remains the same.

[0120] Example 20

[0121] The operation of this embodiment is the same as that of embodiment 15, except that the injection volume of the first electrolyte accounts for 70% of the total injection volume, and the injection volume of the second electrolyte accounts for 30% of the total injection volume, while all other aspects remain unchanged.

[0122] Example 21

[0123] The operation of this embodiment is the same as that of embodiment 15, except that the injection volume of the first electrolyte accounts for 90% of the total injection volume, and the injection volume of the second electrolyte accounts for 10% of the total injection volume, while all other aspects remain unchanged.

[0124] Comparative Example 11

[0125] The operation of this comparative example is the same as that of Example 15, except that only 4 wt% sodium fluorosulfonate is added to the second electrolyte, while everything else remains the same.

[0126] Comparative Example 12

[0127] The operation of this comparative example is the same as that of Example 15, except that only 2 wt% of the second additive I-1 is added to the second electrolyte, while everything else remains the same.

[0128] Comparative Example 13

[0129] The operation of this comparative example is the same as that of Example 15, except that only 2 wt% of the second additive II-1 is added to the second electrolyte, while everything else remains the same.

[0130] Comparative Example 14

[0131] The operation of the comparative example is the same as in Example 17, except that: 1 wt% sodium fluorosulfonate is added to the first electrolyte, and only 2 wt% I-1 is added to the second electrolyte, while everything else remains unchanged.

[0132] Comparative Example 15

[0133] The operation of the comparative example is the same as that of Example 17, except that 0.5 wt% of I-1 is added to the first electrolyte, and only 5 wt% of lithium fluorosulfonate is added to the second electrolyte, while everything else remains the same.

[0134] Comparative Example 16

[0135] The operation of this comparative example is the same as that of Example 15, except that 2 wt% pyridine is used instead of 1 wt% second additive I-1 in the second electrolyte, and everything else remains the same.

[0136] Comparative Example 17

[0137] The operation of this comparative example is the same as that of Example 17, except that: in the second electrolyte, pyridine is used instead of the second additive I-1, the amount added remains the same, and all other operations remain the same.

[0138] Comparative Example 18

[0139] The operation of this comparative example is the same as that of Example 15, except that the injection volume of the first electrolyte accounts for 40% of the total injection volume, and the injection volume of the second electrolyte accounts for 60% of the total injection volume, while all other aspects remain unchanged.

[0140] Comparative Example 19

[0141] The operation of this comparative example is the same as that of Example 15, except that only the second electrolyte is used for one injection.

[0142] Cyclic performance tests were conducted on the sodium-ion batteries with a capacity of 1300 mAh prepared in Examples 15-21 and Comparative Examples 11-19, specifically including:

[0143] (1) 45℃ high temperature cycle test: The sodium-ion battery was placed in a constant temperature oven at 45±1℃ and subjected to high temperature cycle at a charge / discharge current of 1C / 1C. The discharge capacity was calculated per week. The cycle was stopped after 800 cycles or when the capacity retention rate was less than 80%. The capacity retention rate after the cycle was calculated.

[0144] (2) 60℃ High-Temperature Storage Test: The sodium-ion battery was placed in a constant temperature environment of 25±1℃ and cycled at a charge / discharge current of 0.5C / 0.5C for one week. Then, it was charged at a constant current of 0.5C and charged at a constant voltage until the current dropped to 0.05C. The discharge capacity, internal resistance, and volume were recorded for the first week. The battery was then placed in a constant temperature oven at 60℃ for 28 days, followed by a charge / discharge cycle at room temperature of 0.5C / 0.5C for one week. The discharge capacity for the first week after high-temperature storage, the discharge capacity for the second week, and the volume after storage were recorded. The volume expansion rate, capacity retention rate, and capacity recovery rate of the battery after 60℃ high-temperature storage were calculated using the following formula:

[0145] Volume expansion rate = (Post-storage volume - Initial week 1 volume) / Initial week 1 volume * 100%

[0146] Capacity retention rate = (Charging capacity in the first week after high temperature rest / Initial discharge capacity in the first week) * 100%.

[0147] Capacity recovery rate = discharge capacity in the first week after high temperature settling / initial discharge capacity in the first week * 100%.

[0148] (3) -10℃ low temperature cycle test: The sodium-ion battery is placed in a constant temperature oven at -10±1℃ and charged and discharged at a current of 0.3C / 0.5C for low temperature cycle. The discharge capacity is calculated every week. The cycle is stopped when the capacity retention rate is less than 80% after 500 cycles. The capacity retention rate after the cycle is calculated.

[0149] (4) Rate discharge performance test: The sodium-ion battery was placed in a constant temperature oven at 25±1℃. First, it was cycled once with a charge / discharge current of 1C / 1C and the discharge capacity of the first week was recorded. Then, a high rate cycle performance test was performed with a charge / discharge current of 1C / 5C. The discharge capacity of each week was calculated. The cycle was stopped after 50 cycles or when the capacity retention rate was less than 80%. The capacity retention rate after the cycle was calculated.

[0150] Capacity retention = Discharge capacity after high-rate cycling / Initial 1C discharge capacity * 100%

[0151] The test results are shown in Table 2:

[0152] Table 2 Sodium ion performance test results

[0153]

[0154]

[0155] According to the test results in Table 2 above:

[0156] Comparative Examples 15-19 and Comparative Examples 11-13 show that introducing sodium fluorosulfonate and fluorinated pyridine compounds or fluorinated imidazole compounds into the second electrolyte can improve the battery's high-temperature cycling, high-temperature storage, and low-temperature cycling performance, as well as its rate discharge performance and power, compared to using sodium fluorosulfonate or fluorinated pyridine compounds / fluorinated imidazole compounds alone.

[0157] Comparing Example 17 with Comparative Examples 14, 15, and 19, it can be seen that the simultaneous introduction of sodium fluorosulfonate and fluorinated pyridine / fluorinated imidazole compounds into the second electrolyte, compared with other introduction methods of sodium fluorosulfonate and fluorinated pyridine / fluorinated imidazole compounds into the first and second electrolytes, can not only eliminate the disadvantage of high film-forming resistance of fluorinated pyridine additives, but also exert its water removal and acid suppression effects, improve the high-temperature storage performance of the battery, and significantly improve the high-temperature and low-temperature cycling performance of the battery.

[0158] Comparing Example 17 and Comparative Example 17, it can be seen that when sodium fluorosulfonate and fluorinated pyridine compounds are introduced into the second electrolyte simultaneously, compared with the combination of sodium fluorosulfonate and non-fluorinated pyridine additives in the second electrolyte, only the synergistic effect of sodium fluorosulfonate and fluorinated pyridine additives can improve the high-temperature storage performance of the battery and improve the high-temperature cycle performance and low-temperature cycle performance of the battery.

[0159] Comparing Example 15 and Comparative Example 18, it can be seen that the electrolyte ratio of the first electrolyte to the second electrolyte is (8:2). Compared with the electrolyte ratio of (4:6), the electrolyte ratio of the first electrolyte to the second electrolyte can only give full play to the performance advantages of the electrolyte and improve the high-temperature cycle performance and low-temperature cycle performance of the battery when it is within a specific ratio range.

Claims

1. A method for secondary electrolyte injection, the method comprising: The first electrolyte is injected into the semi-finished battery cell and then sealed, aged, left to stand and formed. The first electrolyte contains electrolyte salts, non-aqueous solvents and basic additives. The second electrolyte is injected, and after secondary sealing and capacity testing, an alkali metal ion battery is obtained. The second electrolyte contains the first electrolyte, a first additive, and a second additive. The first additive is lithium fluorosulfonate or sodium fluorosulfonate, and the second additive is selected from at least one of the structures shown in formula (I) or (II) below: In the formula, R1, R2, R3, R4, R5 and R6 are independently selected from hydrogen, halogen, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 haloalkyl, C2-C5 alkenyl, C2-C5 alkynyl, C3-C8 cycloalkenyl, cyano or isocyanate group.

2. The secondary electrolyte injection method according to claim 1, characterized in that: R1, R2, R3, R4, R5, and R6 are independently selected from hydrogen, fluorine, methyl, ethyl, methoxy, ethoxy, trifluoromethyl, or vinyl.

3. The secondary electrolyte injection method according to claim 2, characterized in that: The second additive is selected from at least one of the compounds shown in the following structures:

4. The secondary electrolyte injection method according to claim 1, characterized in that: The mass ratio of the first electrolyte to the second electrolyte is (50-95):(5-50).

5. The secondary electrolyte injection method according to claim 4, characterized in that: In the second electrolyte, the first additive accounts for 2 to 20 wt% of the total mass of the second electrolyte, and the second additive accounts for 1 to 10 wt% of the total mass of the second electrolyte.

6. The secondary electrolyte injection method according to claim 5, characterized in that: In the second electrolyte, the first additive accounts for 2 to 8 wt% of the total mass of the second electrolyte, and the second additive accounts for 1 to 3 wt% of the total mass of the second electrolyte.

7. The secondary electrolyte injection method according to claim 1, characterized in that: In the first electrolyte, The electrolyte salt accounts for 5-30 wt% of the total mass of the first electrolyte, preferably 10-18 wt%. When the alkali metal ion battery is a lithium-ion battery, the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), and lithium difluorooxalate-borate. When the alkali metal ion battery is a sodium-ion battery, the electrolyte salt is selected from at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, or sodium bis(oxalate-borate). The non-aqueous solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butene carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, fluoroethylene carbonate, difluoroethylene carbonate, methyl difluoroethyl carbonate, and methyl trifluoroethyl carbonate, and its amount accounts for 60-80 wt% of the total mass of the first electrolyte. The basic additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, methanedisulfonate, vinylsilane, tris(trimethylsilane) phosphate, or tris(trimethylsilane) borate, and is used in an amount of 0.1 to 10.0 wt% of the total mass of the first electrolyte, preferably 0.5 to 5.0 wt%.

8. An alkali metal ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: The electrolyte is obtained by injection using any one of the two-stage injection methods described in claims 1-7.

9. The alkali metal ion battery according to claim 8, characterized in that: When the alkali metal ion battery is a lithium-ion battery, the active material of the positive electrode is selected from lithium iron phosphate, manganese iron phosphate, lithium cobalt oxide, LiNi(1-xy)CoxMnyO2 (0≤x,y≤1), lithium titanate, nickel manganese spinel or lithium manganese oxide, and the active material of the negative electrode is selected from graphite, silicon carbide, silicon oxide materials, soft carbon, hard carbon or mesophase pitch carbide.

10. The alkali metal ion battery according to claim 8, characterized in that: When the alkali metal ion battery is a sodium-ion battery, the active material of the positive electrode is selected from sodium iron phosphate, sodium manganese phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium iron sulfate, sodium vanadium phosphate, sodium vanadium fluorophosphate, and NaMn. (1-x-y) Ni y M x O2 (0≤x, y≤1, M is Cu, Fe or Co), and the active material of the negative electrode is selected from hard carbon, carbon black, amorphous carbon, silicon carbide or silicon oxide materials.

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