Electrolyte for high-voltage fast-charge alkali metal secondary battery and battery thereof

Abstract

The invention discloses an electrolyte for a high-voltage fast-charge alkali metal secondary battery and a battery thereof, the electrolyte comprises a main salt, a non-aqueous solvent and an additive, the main salt is selected from a main lithium salt or a main sodium salt, the additive at least comprises a first additive shown as a structural formula (I), the electrolyte also can comprise a sulfate compound as a second additive, a lithium / sodium salt additive as a third additive and other basic additives, and the specific structure is shown in the specification. Particularly, the electrolyte is stored for more than or equal to 12 hours at the temperature of-30 to 60 DEG C and then is injected. When the electrolyte is applied to the high-voltage fast-charge alkali metal secondary battery, not only can the high-temperature cycle performance be further improved, but also the high-temperature storage performance can be improved, the battery impedance can be reduced, the fast-charge performance can be improved, and both the fast-charge performance and the high-temperature performance under high voltage can be realized.

Description

Technical Field

[0001] The present invention relates to the field of electrolytes, and in particular to a low-impedance alkali metal secondary battery electrolyte having both fast charging and high temperature performance at high voltage and application thereof in lithium ion batteries or sodium ion batteries. Background Art

[0002] Alkali metal secondary batteries are considered to be the most promising new type of batteries in the fields of power, energy storage, digital, and communications, but their energy density needs to be further improved to meet market demand. In recent years, researchers have made great contributions to improving the upper voltage limit of cathode materials. However, for example, transition metal ions (especially Ni 3+ ) Due to its high oxidation activity, it will catalyze the decomposition reaction of the electrolyte, resulting in severe capacity decay of the battery. Therefore, the development of high-voltage alkali metal secondary batteries requires more stable electrolytes to avoid the violent decomposition of the solvent (mainly caused by the catalytic center on the surface of the positive electrode). At the same time, as people's requirements for fast charging are increasing, higher requirements are also placed on the fast charging performance of the electrolyte.

[0003] On the one hand, many researchers have devoted themselves to replacing carbonate solvents in traditional electrolytes with sulfones, ionic liquids, and nitriles, but most of them have high viscosity or are incompatible with graphite anodes. Therefore, this method is limited in applications that require both high voltage and fast charging.

[0004] On the other hand, by introducing low-impedance additives such as tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) phosphite (TMSPi), tris(trimethylsilyl) borate (TMSB), etc. to form a protective film on the positive electrode surface, although it can improve the stability of the positive electrode material and will not increase the negative electrode impedance and thus deteriorate the fast charging performance, but experiments show that when the working voltage of the positive electrode (NCM622) is ≥4.3V, the battery using this type of additive has the problem of high-temperature storage gas production and high-temperature cycle accelerated diving.

[0005] Patent KR100695109A discloses silanyl dicarboxylate compounds, which have the effect of improving the 1C charge and discharge rate cycle life at room temperature and inhibiting the growth of battery thickness during the cycle process, but the patent does not mention its fast charging performance under high voltage, let alone its possible defects in high temperature cycling and high temperature storage under high voltage fast charging system. The present invention has found through research that although the silanyl dicarboxylate compounds can improve the rate cycle life and inhibit the growth of battery thickness, once the charging voltage is increased or the charge and discharge rate is further increased, its cycle performance and storage performance are significantly reduced.

[0006] Therefore, how to achieve fast charging performance at high voltage while solving the problems of accelerated drop in high-temperature cycle performance and gas production during high-temperature storage, in order to obtain an electrolyte that achieves both high-voltage fast charging and high-temperature performance, is the current research direction of electrolytes. Summary of the invention

[0007] In order to solve the problems existing in the background technology, the present invention proposes an electrolyte for high-voltage fast-charging alkali metal secondary batteries, which can not only further improve the high-temperature cycle performance, but also improve the high-temperature storage performance, reduce battery impedance, and improve fast-charging performance, thereby achieving both fast-charging performance and high-temperature performance under high voltage.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] An electrolyte for a high-voltage fast-charge alkali metal secondary battery, comprising a main salt, a non-aqueous solvent and an additive, wherein the additive comprises at least:

[0010] The first additive is selected from the silane dicarboxylate compound represented by the following formula (I):

[0011]

[0012] In formula (I), R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from hydrogen, fluorine, C1-C6 alkyl, C1-C6 fluoroalkyl, C1-C6 alkoxy, or C1-C6 fluoroalkoxy; n is an integer of 0 to 4, and R7 and R8 in each repeating unit are selected from the same or different substituents;

[0013] Preferably, in formula (I), R1, R2, R3, R4, R5, R6, R7, R8 are independently selected from hydrogen, fluorine, C1-C4 alkyl, C1-C4 fluoroalkyl, C1-C4 alkoxy or C1-C4 fluoroalkoxy; n is selected from 0, 1 or 2.

[0014] Further preferably, in formula (I), R1, R2, R3, R4, R5, R6 are independently selected from methyl, ethyl, isopropyl, tert-butyl or fluoromethyl; R7 and R8 are independently selected from hydrogen, fluorine, methyl or fluoromethyl.

[0015] More preferably, the first additive is selected from at least one of the compounds shown in the following structures:

[0016]

[0017] The main salt is selected from a main lithium salt or a main sodium salt, and the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium tetrafluorooxalatephosphate, lithium trioxalatephosphate, or lithium difluorobis(oxalatophosphate); the main sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonylimide), sodium bis(trifluoromethylsulfonylimide), or sodium difluorophosphate, and the concentration of the main lithium salt or main sodium salt in the electrolyte is 0.1-3M;

[0018] Preferably, the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(fluorosulfonyl)imide; the main sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium bis(fluorosulfonyl)imide; and the concentration of the main lithium salt or the main sodium salt in the electrolyte is 0.5 to 2M.

[0019] The special feature of the present invention is that unlike conventional electrolytes that are injected and formed immediately after preparation to produce alkali metal secondary batteries, the electrolyte containing the first additive and the main salt of the present invention is stored at a temperature of -30 to 60°C for ≥12 hours before injection.

[0020] Preferably, the electrolyte is stored at a temperature of 20 to 45° C. for ≥24 hours before injection. More preferably, the electrolyte is stored at a temperature of 20 to 30° C. for ≥72 hours before injection. In a specific embodiment, the storage time of the electrolyte at a temperature of 20 to 30° C. is 0.5 to 7 days, and most preferably between 1 day and 3 days.

[0021] The present invention found in the research process that the content of the first additive and the main salt in the electrolyte changed after storage. The gas chromatography found that the content of the first additive decreased, and the ion chromatography found that the content of the main salt also decreased. At the same time, new substance peaks were detected. Therefore, the present invention infers that the first additive and the main salt reacted during the storage process to generate a new additive, which was generated in situ and was found through electrochemical performance testing to further improve the high-temperature cycle performance of the battery under high-voltage fast-charging conditions.

[0022] The reaction between the first additive and the main salt can be controlled if and only if the storage temperature and storage time of the electrolyte meet the aforementioned limitations. If the storage temperature is too low or the time is too short, the first additive and the main salt do not react completely, and the high-temperature cycle performance is reduced. If the storage temperature of the electrolyte containing the first additive and the main salt is too high or the storage time is too long, the side reactions in the electrolyte will be aggravated, the acidity will increase, and the battery performance will deteriorate.

[0023] Therefore, when the electrolyte contains additives other than the first additive, it is preferred that during the preparation of the electrolyte, the main salt and the first additive are mixed evenly and then stored at the aforementioned temperature and time for reaction, and then other additives (such as the second additive, the third additive and other basic additives, etc.) are further added after the reaction, and the mixture is mixed evenly before injection. Of course, the main salt, the first additive and other additives may also be added to the electrolyte to form a complete electrolyte, and then stored and reacted together.

[0024] The additives of the present invention also include:

[0025] The second additive is selected from the cyclic sulfate compounds represented by the following formula (II-A) or (II-B):

[0026]

[0027] Wherein G1, G2, G3, and G4 are independently selected from hydrogen, fluorine, methyl, or fluoromethyl, G5, G6, G7, and G8 are independently selected from a direct bond, methylene, or fluoromethylene, and M is selected from one of the following structures:

[0028] *-*

[0029] Among them, G9, G 10 is selected from methine, p is selected from an integer of 0-6, and q and r are independently selected from an integer of 1-4;

[0030] The third additive is selected from at least one of the inorganic salt additives having the structure represented by the following formula (III-1), (III-2) or (III-3):

[0031]

[0032] In formulas (III-1), (III-2) and (III-3), when the electrolyte is applied to a lithium ion secondary battery, X is Li; when the electrolyte is applied to a sodium ion secondary battery, X is Na.

[0033] Preferably, the second additive is selected from at least one of the compounds shown in the following structures:

[0034]

[0035] In order to simultaneously meet the requirements of reducing impedance, taking into account fast charging performance and high temperature cycle and high temperature storage performance, the addition amounts of the first additive, the second additive and the third additive account for a%, b% and c% of the total mass of the electrolyte respectively, and meet the following relationship:

[0036] 0.01≤a≤3, 0.01≤b≤2.5, 0.01≤c≤3; and,

[0037] 0.2≤a+b≤5, 0.05≤a / c≤10, 0.03≤(a+b) / c≤20

[0038] Preferably, the addition amounts of the first additive, the second additive and the third additive satisfy the following relationship:

[0039] 0.1≤a≤2, 0.2≤b≤2, 0.2≤c≤2; and,

[0040] 0.4≤a+b≤3, 0.1≤a / c≤4, 0.2≤(a+b) / c≤6

[0041] In the electrolyte of the present invention, the first additive and the main salt coexist to achieve a reaction between the two, which significantly improves the high-temperature cycle performance; further, by combining the first additive, the second additive and the third additive and adjusting the ratio of the three, the battery impedance can be significantly reduced, and the high-temperature storage performance, high-temperature cycle and fast-charge cycle performance can be improved. When the ratio of the three does not meet the above conditions, the above performance cannot be achieved.

[0042] Specifically, in the electrolyte of the present invention, the sum of the contents of the first additive and the second additive is between 0.2 and 5, preferably between 0.4 and 3. Once the sum of the contents of the two is too small (such as less than 0.2), the high-temperature storage and high-temperature cycle performances will deteriorate; once the sum of the contents of the two is too large (such as greater than 5), the battery impedance will increase and the fast charging cycle performance will deteriorate.

[0043] In the electrolyte of the present invention, the ratio of the content of the first additive to that of the third additive is between 0.05 and 10, preferably between 0.1 and 4. Once the ratio of the content of the first additive to that of the third additive is too small (such as less than 0.05), the negative electrode film-forming effect is not significantly improved, and the high-temperature cycle performance is deteriorated; once the ratio of the content of the first additive to that of the third additive is too large (such as greater than 10), the negative electrode film is thicker, which will increase the battery impedance and deteriorate the fast charge cycle performance.

[0044] In the electrolyte of the present invention, the ratio of the sum of the contents of the first additive and the second additive to the third additive is between 0.03 and 20, preferably between 0.2 and 6. Once the ratio is too small (such as less than 0.03), the negative electrode film-forming effect is not significantly improved, and the high-temperature storage and high-temperature cycle performances are deteriorated; once the ratio is too large (such as greater than 20), the battery impedance will increase and the fast charging cycle performance will be deteriorated.

[0045] After meeting the specific content ratio relationship between the first additive, the second additive and the third additive, the respective amounts of the first additive, the second additive and the third additive must still meet the following requirements, namely:

[0046] 0.01≤a≤3, preferably 0.1≤a≤2. If the amount of the first additive added is too low (such as less than 0.01), the negative electrode film-forming effect is poor and the high-temperature cycle performance of the battery is reduced; if the amount of the first additive added is too high (such as higher than 3), the battery impedance increases and the fast-charge cycle performance deteriorates.

[0047] 0.01≤b≤2.5, preferably 0.2≤b≤2. If the amount of the second additive added is too low (such as less than 0.01), the negative electrode film-forming effect is poor and the high-temperature storage performance of the battery is reduced; if the amount of the second additive added is too high (such as higher than 2.5), the battery impedance increases and the fast-charge cycle performance is reduced.

[0048] 0.01≤c≤3, preferably 0.2≤c≤2. If the amount of the third additive added is too low (such as less than 0.01), the negative electrode film-forming effect is poor, the battery impedance increases, and the fast charge cycle performance decreases; if the amount of the third additive added is too high (such as higher than 3), the high temperature storage and high temperature cycle performance of the battery decreases.

[0049] The second additive of the present invention can participate in the formation of the interface film and improve stability, improve high-temperature storage performance, and inhibit gas production during high-temperature storage of the battery, but the combination of the first additive and the second additive alone will still increase the negative electrode interface impedance; the addition of the third additive can generate components with high ionic conductivity such as fluorophosphates on the electrode surface, improve the ion conductivity of the interface film layer, inhibit the decomposition of the electrolyte, reduce the content of inorganic lithium salts in the interface film, and thus reduce the battery impedance and improve the fast charge cycle performance. Therefore, when the first additive, the second additive, and the third additive meet the specific content ratio relationship, and the first additive, the second additive, and the third additive each meet the dosage regulations, the synergistic effect of the three additives can be exerted, and the SEI film formed can take into account the toughness of the organic film layer and the rigidity of the inorganic film layer, forming an effective ion-conducting structure, thereby simultaneously improving the stability of the battery's high-temperature cycle and high-temperature storage and the low impedance characteristics required for the fast charge cycle.

[0050] In the electrolyte of the present invention, the non-aqueous solvent is selected from at least one of C3-C6 carbonate or fluorinated carbonate compounds, C3-C8 carboxylic acid ester or fluorinated carboxylic acid ester compounds, sulfone compounds or ether compounds;

[0051] Specifically, the C3-C6 carbonate or fluorinated carbonate compound is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate or ethyl propyl carbonate;

[0052] The C3-C8 carboxylic acid ester or fluorocarboxylic acid ester compound is selected from at least one of γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate and propyl propionate;

[0053] The sulfone compound is selected from at least one of sulfolane, dimethyl sulfoxide, dimethyl sulfone or diethyl sulfone;

[0054] The ether compound is selected from at least one of triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether and dioxolane.

[0055] Further, the non-aqueous solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl 2,2-difluoroacetate, ethyl 2,2,2-trifluoroacetate, ethyl 2,2-difluoropropionate, and propyl 2,2-difluoropropionate.

[0056] In the actual electrolyte formulation application process, organic solvents are all complex multi-component systems, among which cyclic carbonates have high dielectric constants and can better dissolve the main salt to provide high conductivity; linear carbonates and carboxylates can effectively adjust the viscosity and liquid range of the electrolyte, and realize organic solvent systems with more suitable comprehensive performances through the mutual matching of different types of solvents. Therefore, the non-aqueous solvent of the present invention is preferably a composite solvent formed by cyclic carbonates (ethylene carbonate and / or propylene carbonate), linear carbonates (at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate) or linear carboxylates (at least one of methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, and propyl propionate) in a certain ratio.

[0057] In the actual electrolyte formula application process, the electrolyte formula is a complex multi-component system to obtain an alkali metal secondary battery with balanced and excellent comprehensive performance. Therefore, the additive of the present invention also includes a basic additive, and the basic additive is selected from fluoroethylene carbonate, vinylene carbonate, tris (trimethylsilyl) phosphate, 1,3-propylene sultone, lithium difluorophosphate, lithium bisfluorosulfonyl imide, succinic anhydride, adiponitrile, cyclohexylbenzene, lithium difluorophosphate bis oxalate, lithium difluoro oxalate borate, sodium difluoro oxalate borate, sodium difluorophosphate, sodium bisfluorosulfonyl imide, at least one of sodium difluorophosphate bis oxalate, and any one of the basic additives accounts for 0.1 to 5.0wt% of the total mass of the electrolyte, and the basic additive is different from the main salt.

[0058] In a specific embodiment, the basic additive adopts vinylene carbonate with a mass fraction of 0.1 to 2.0 wt% and lithium difluoro(oxalato)borate with a mass fraction of 0.1 to 2.0 wt%. Through the combined use of vinylene carbonate, lithium difluoro(oxalato)borate, and the first additive, the second additive, and the third additive, on the basis of improving the fast charge cycle, high-temperature storage, and high-temperature cycle performance of the lithium-ion battery, the cycle stability of the battery is further improved.

[0059] In a specific embodiment, the basic additive adopts a combination of vinylene carbonate with a mass fraction of 0.1 to 2.0 wt%, ethylene sulfate with a mass fraction of 0.1 to 3.0%, and lithium difluorophosphate with a mass fraction of 0.1 to 1.0%, which can further optimize the components of the positive and negative electrode - electrolyte interface film and improve the fast charge cycle performance of the battery.

[0060] The present invention also provides an alkali metal secondary battery, including a positive electrode, a negative electrode, and a separator, and the electrolyte described in any one of the above, and the electrolyte is stored at a temperature of -30 to 60 °C for ≥ 12 h and then injected.

[0061] Preferably, the electrolyte is stored at a temperature of 20 to 45 °C for ≥ 24 h and then injected. More preferably, the electrolyte is stored at a temperature of 20 to 30 °C for ≥ 72 h and then injected. In a specific embodiment, the storage time of the electrolyte at a temperature of 20 to 30 °C is 0.5 days to 7 days, and most preferably between 1 day and 3 days.

[0062] When the alkali metal secondary battery is a lithium-ion secondary battery, the active material of the positive electrode is selected from nickel cobalt manganese ternary materials, nickel cobalt aluminum ternary materials, lithium cobaltate materials, or lithium iron phosphate materials, and the active material of the negative electrode is selected from graphite, silicon carbon, silicon monoxide, silicon, tin, metallic lithium, or their composite materials;

[0063] When the alkali metal secondary battery is a sodium-ion secondary battery, the active material of the positive electrode is selected from NaMn (1-x-y) Ni y M x O2 (0 ≤ x, y ≤ 1, M is Cu, Fe, Co, sodium manganate, sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron phosphate, sodium manganese phosphate, sodium iron sulfate, Na x MnFe(CN)6 (0 < x ≤ 2) and at least one of them, and the active material of the negative electrode is selected from at least one of hard carbon, carbon black, amorphous carbon, graphite, SnS2, Na2Ti3O7, silicon-based materials, metal oxides, metal sulfides, or metallic sodium.

[0064] The working voltage of the alkali metal secondary battery is ≥4.3V, and the average charging rate at 0-100% SOC is ≥1C. In particular, under the action of the electrolyte of the present invention, when the working voltage of the alkali metal secondary battery is 4.3-4.6V and the average charging rate at 40-60% SOC is ≥1.5C, such as 1.5C, 2C, 3C, etc., the high-temperature cycle performance of the battery can still be improved, the high-temperature storage performance can be improved, and the fast-charging cycle performance is excellent, and the battery performance will not rapidly deteriorate with the increase of voltage and the increase of charging rate.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] 1. The present invention obtains the reaction additive by in-situ reaction through the storage of the first additive and the main salt, which is convenient to operate and low in cost, and can also significantly improve the high-temperature cycle performance of the battery and inhibit gas production during high-temperature storage.

[0067] 2. The present invention proposes the combined use of a silane dicarboxylate compound with a specific structure, a sulfate compound and an inorganic salt additive with a specific structure, and simultaneously regulates the distribution of the added contents of the three. Through the synergistic effect of the three additives, not only the battery impedance is reduced, but also the fast charging cycle performance under high voltage, high temperature storage performance and high temperature cycle performance can be taken into account. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Attached Figure 1 The anion component test result of the electrolyte in Example 1 of the present invention;

[0069] Attached Figure 2 The following are the test results of the anion components of the electrolyte of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0070] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0071] The electrolyte formula proposed in the present invention is particularly suitable for a high-voltage lithium-ion battery system using a nickel-cobalt-lithium-manganese oxide ternary material as a positive electrode, and in particular can maintain the stability of the battery system when a Ni7 positive electrode material is used. In other words, the electrolyte formula of the present invention can better demonstrate its advantages under the high-voltage conditions of a ternary lithium-ion battery. Therefore, the embodiments of the present invention carry out the preparation of the electrolyte, the manufacture of the battery, and the testing of its electrochemical performance on the premise of the basic electrolyte formula of the ternary lithium-ion battery system. Therefore, X in the third additive of the following embodiments and comparative examples is Na.

[0072] 1. Preparation of electrolyte

[0073] Preparation of basic electrolyte 1: In a glove box filled with argon (water content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 3:5:2 to form an organic solvent, and lithium hexafluorophosphate (LiPF6) is added until the concentration of lithium hexafluorophosphate added is 1 M based on the total amount of the electrolyte to obtain basic electrolyte 1.

[0074] Preparation of basic electrolyte 2: In a glove box filled with argon (water content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 3:5:2 to form an organic solvent, and lithium bis(fluorosulfonyl)imide (LiFSI) was added until the concentration of lithium bis(fluorosulfonyl)imide added was 1.2 M based on the total amount of the electrolyte to obtain basic electrolyte 2.

[0075] The first additive (Compound I-1) was added to the basic electrolyte 1, and the electrolyte storage experiment was carried out according to the data in Table 1 below:

[0076] Table 1 Electrolyte storage experiment 1

[0077]

[0078]

[0079] According to the electrolyte formula table 2 shown in the following table, the first additive, the second additive and the third additive are quantitatively added to the basic electrolyte 1; wherein, in Example 7.1 and Example 8-22, after the first additive is added to the basic electrolyte 1, the electrolyte is stored at 25°C for 2 days, and then the second additive and the third additive are added and mixed evenly to form an electrolyte; in Example 7.2 and Example 8.2, the first additive, the second additive and the third additive are added to the basic electrolyte 1, mixed evenly to form an electrolyte, and then stored at 25°C for 2 days.

[0080] Table 2 Electrolyte formula Table 1

[0081]

[0082]

[0083] Note 1: After the dosage of additives is adjusted, only the dosage of solvent in the basic electrolyte is adjusted, and the distribution ratio of each group in the solvent remains unchanged.

[0084] Note 2: The third additive is lithium salt.

[0085] The first additive is first added to the basic electrolyte 1 whose main salt is lithium hexafluorophosphate and the basic electrolyte 2 whose main salt is lithium bis(fluorosulfonyl)imide, respectively, and then stored according to the electrolyte storage requirements in Table 3 below, and then the second additive and the third additive are added and mixed evenly to obtain the electrolyte.

[0086] Table 3 Electrolyte storage experiment 2

[0087]

[0088]

[0089] In order to further improve the electrochemical performance of the battery, according to the electrolyte formula in Table 4 below, on the basis of the basic electrolyte 1, after adding the first additive, the electrolyte was stored at 25°C for 2 days, and then the second additive, the third additive, 0.2% by weight of vinyl carbonate (VC), and 1% by weight of vinyl sulfate (DTD) were added, and then lithium difluorophosphate (LiDFP), lithium bis(fluorosulfonyl)imide (LiFSI) and fluoroethylene carbonate (FEC) were further added and mixed to form an electrolyte:

[0090] Table 4 Electrolyte formula 2

[0091]

[0092] Note: After the dosage of additives is adjusted, only the dosage of solvent in the basic electrolyte is adjusted, and the distribution ratio of each group in the solvent remains unchanged.

[0093] 2. Battery production and performance testing

[0094] The lithium-ion battery electrolytes of the above-mentioned embodiments and comparative examples are respectively made into lithium-ion power batteries with a soft-pack capacity of 1000 mAh, wherein the lithium-ion power batteries include a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and battery auxiliary materials, wherein the positive electrode active material is lithium nickel cobalt manganese oxide, and the negative electrode active material is graphite.

[0095] The preparation process is as follows: the positive electrode sheet, separator and negative electrode sheet are wound together into a core, sealed with an aluminum-plastic film and then baked so that the electrode moisture meets the requirements. After baking, the battery cell is injected with electrolyte, and the finished soft-pack battery cell is obtained through standing, formation, aging, capacity separation and other processes.

[0096] The above lithium-ion batteries are tested for various performances, including:

[0097] ①Electrolyte anion composition test

[0098] The electrolytes prepared in Example 1 and Comparative Example 2 were diluted 100 times with deionized water to obtain clear and uniform solutions, and then analyzed and tested using an ion chromatograph.

[0099] Attached Figure 1 and Figure 2 The ion chromatograms of Example 1 and Comparative Example 2 are given respectively. Figure 1 , Figure 2 It can be seen that a new material peak appears at about 32 minutes after the storage reaction of the electrolyte containing the main salt and the first additive. It can be judged that the main salt and the first additive react in situ after the storage reaction to generate new additives.

[0100] ② Initial impedance test:

[0101] In the battery capacity division stage: at room temperature (25°C), charge at a constant current of 0.2C to the charge cut-off voltage (4.4V-4.45V), and charge at a constant voltage until the current drops to 0.05C; then discharge at a constant current of 0.2C to the discharge cut-off voltage (2.8V), and record the discharge capacity C1, which is the initial capacity of the battery;

[0102] Then charge at a constant current of 0.2C to the charging cut-off voltage (4.4V-4.45V), and charge at a constant voltage until the current drops to 0.05C; then discharge at a constant current of 0.2C until the capacity reaches 0.5*C1, i.e. 50% SOC state of charge, stand for 2 hours, and record the voltage U1;

[0103] Finally, discharge at a constant current of 4C for 30s, record the voltage U2, and calculate the initial impedance of the battery:

[0104] Initial impedance = (U1-U2) / 4*1000

[0105] ③Fast charging cycle performance test:

[0106] At 25°C, charge at a constant current of 2C or 4C to the charge cut-off voltage (4.4V-4.45V), then charge at a constant voltage until the current drops to 0.1C, then discharge at a constant current of 1C to the discharge cut-off voltage (2.8V), and repeat this cycle for a specific number of weeks. Record the discharge capacity C2 of the first week and the discharge capacity C3 of the last week. Calculate the capacity retention rate of the battery cycle as follows:

[0107] Fast charge cycle capacity retention rate = C3 / C2*100%

[0108] ④High temperature storage performance test

[0109] At room temperature (25°C), the battery was charged at a constant current of 1C to the charge cut-off voltage (4.4V-4.45V), and then charged at a constant voltage until the current dropped to 0.05C, and then placed in a 60°C constant temperature oven for 56 days. When the battery after storage cools to room temperature, the initial volume V1 and the volume after storage V2 are recorded; the battery is discharged at a constant current of 1C to the discharge cut-off voltage (2.8V), and the initial discharge capacity C4 and the discharge capacity C5 after storage are recorded; and the high-temperature storage volume expansion rate and capacity retention rate are calculated according to the following formula:

[0110] High temperature storage volume expansion rate = (V2 / V1-1)*100%

[0111] High temperature storage capacity retention rate = C5 / C4*100%

[0112] ⑤High temperature cycle performance test

[0113] At 45°C, charge at a constant current of 1C to the charge cut-off voltage (4.4V-4.45V), then charge at a constant voltage until the current drops to 0.1C, then discharge at a constant current of 1C to the discharge cut-off voltage (2.8V), and repeat this cycle for a specific number of weeks. Record the discharge capacity C6 of the first week and the discharge capacity C7 of the last week. Calculate the capacity retention rate of the battery cycle as follows:

[0114] High temperature cycle capacity retention rate = C7 / C6*100%

[0115] The specific test results are shown in Table 5, Table 6, Table 7, Table 8 and Table 9 below:

[0116] Table 5 Ni7 / / AG-2.8~4.4V electrochemical test results

[0117]

[0118] Table 6 Ni7 / / AG-2.8~4.4V electrochemical test results

[0119]

[0120]

[0121] Table 7 Ni7 / / AG-2.8~4.4V electrochemical test results

[0122]

[0123] Table 8 Ni7 / / AG-2.8~4.4V electrochemical test results

[0124]

[0125] Table 9 Ni7 / / AG-2.8~4.45V electrochemical test results

[0126]

[0127] By comparing Comparative Example 1, Example 1, Comparative Example 6 and Comparative Example 7, it can be seen that the use of the first additive alone can improve the high-temperature cycle performance, but will deteriorate the high-temperature storage performance; the use of the second additive alone can improve the high-temperature storage performance; the use of the third additive alone can reduce impedance and improve fast charging cycle performance.

[0128] By comparing Example 7.1 with Comparative Examples 8, 9 and 10, it can be seen that only when the first additive, the second additive and the third additive are used in combination can the initial impedance of the battery be reduced and the fast charging cycle performance, high temperature storage performance and high temperature cycle performance be improved at the same time. The combination of any two additives cannot achieve this effect.

[0129] By comparing Examples 7.1, 8.1, 9 to 12 and Comparative Examples 11, 12, 13 and 14, it can be seen that only when the first additive, the second additive and the third additive satisfy the relationship 0.2≤a+b≤5; 0.05≤a / c≤10; 0.03≤(a+b) / c≤20, can the effects of reducing the initial impedance of the battery and improving the fast charging cycle performance, high temperature storage performance and high temperature cycle performance be simultaneously achieved. If the sum of the contents of the first additive and the second additive is too small, the high-temperature storage and high-temperature cycle performances will deteriorate; if the sum of the two contents is too large, the battery impedance will increase and the fast charging cycle performance will deteriorate; if the ratio of the first additive to the third additive is too small, the negative electrode film formation effect will not be significantly improved, and the high-temperature cycle performance will deteriorate; if the ratio of the first additive to the third additive is too large, the negative electrode film formation will be thicker, which will increase the battery impedance and deteriorate the fast charging cycle performance; if the ratio of the sum of the contents of the first additive and the second additive to the third additive is too small, the negative electrode film formation effect will not be significantly improved, and the high-temperature storage and high-temperature cycle performances will deteriorate; if the ratio is too large, the battery impedance will increase and the fast charging cycle performance will deteriorate.

[0130] By comparing Example 7.1 with Examples 13 to 22, it can be seen that compounds I-1, I-2, I-3, I-4, I-5, compounds II-1, II-2, II-3, II-4, II-5 and compounds III-1, III-2, III-3 all have the functions of the additives represented and can be used interchangeably.

[0131] Comparing Example 7.1 with Comparative Examples 15 and 16, the commonly used silane-containing additives in the industry (such as TMSP, TMSB, etc.) when the battery operating voltage is ≥4.3V, even if used in combination with sulfate compounds and inorganic salt additives, the battery still has the problem of degradation of high-temperature storage and high-temperature cycle performance. The combined use of the first additive, the second additive and the third additive can significantly improve the high-temperature storage performance and high-temperature performance, and can take into account both impedance and fast charge cycle performance.

[0132] Comparing Example 7.1, Example 7.2, Example 8.1 and Example 8.2, compared with adding the first, second and third additives to the basic electrolyte 1 and then storing the electrolyte, first adding the first additive to the basic electrolyte 1, then storing the electrolyte, and finally adding the second and third additives is more conducive to improving the overall performance of the battery.

[0133] Comparing Example 1, Example 4 and Example 5, when the electrolyte containing the first additive and the main salt is stored for the same number of days, the battery performance is equivalent at a temperature range of 20 to 30°C; comparing Example 1 and Example 2, the electrolyte containing the first additive and the main salt has the same storage temperature, and the storage time is increased (1 to 3 days), and the battery performance is equivalent; comparing Example 1 and Comparative Example 2, the high-temperature cycle performance will be degraded if the electrolyte containing the first additive and the main salt is stored for too short a time; comparing Example 1 and Comparative Example 3, the battery performance will be degraded if the electrolyte containing the first additive and the main salt is stored for too long a time; comparing Example 1 and Comparative Example 4, the high-temperature cycle performance of the battery will be degraded if the electrolyte containing the first additive and the main salt is stored at too low a temperature; comparing Comparative Example 1 and Comparative Example 5, the battery performance will be degraded if the electrolyte containing the first additive and the main salt is stored at too high a temperature, including increased impedance, degraded fast charge cycle, degraded high-temperature storage and high-temperature cycle performance.

[0134] Comprehensively comparing the data in Table 5 and Table 7, the battery performance is consistent when only the first additive is added to the basic electrolyte and when the first, second and third additives are added to the basic electrolyte in terms of electrolyte storage temperature and time.

[0135] By comparing Example 7.1, Examples 23 to 29, and Comparative Examples 17 to 24, it can be seen that by changing the type of the main salt, in the presence of the first additive, the second additive, and the third additive, the battery performance in terms of electrolyte storage temperature and time shows the same rule.

[0136] According to Tables 5 to 8 above, by comparing Example 1 and Examples 30 to 33, it can be seen that the first additive, the second additive and the third additive are further used in combination with vinyl sulfate, vinylene carbonate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide and fluoroethylene carbonate to further reduce the initial impedance and improve the battery fast charging cycle, high temperature storage and high temperature cycle performance.

[0137] According to Table 9 above, when the charging voltage is further increased to 4.45V and the charging rate is increased to 4C, the fast charging cycle, high temperature storage and high temperature cycle performance of the electrolytes of Examples 7.1 and 7.2 are slightly reduced compared to those at a charging voltage of 4.4V and a charging rate of 2C, but the fast charging cycle, high temperature storage and high temperature cycle performance of the electrolytes of Comparative Examples 2 and 17 are significantly reduced compared to those at a charging voltage of 4.4V and a charging rate of 2C.

Claims

1. An electrolyte for a high voltage fast charge alkali metal secondary battery, the electrolyte comprising a main salt, a non-aqueous solvent and an additive, characterized in that: The additives include at least: The first additive has a structure as shown in the following formula (I): In formula (I), R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from hydrogen, fluorine, C1-C6 alkyl, C1-C6 fluoroalkyl, C1-C6 alkoxy, or C1-C6 fluoroalkoxy; n is an integer of 0 to 4, and R7 and R8 in each repeating unit are selected from the same or different substituents; The main salt is selected from a main lithium salt or a main sodium salt, and the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium tetrafluorooxalatephosphate, lithium trioxalatephosphate, or lithium difluorobis(oxalatophosphate); the main sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonylimide), sodium bis(trifluoromethylsulfonylimide), or sodium difluorophosphate, and the concentration of the main lithium salt or main sodium salt in the electrolyte is 0.1-3M; The electrolyte is stored at a temperature of -30 to 60° C. for ≥12 hours before injection.

2. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 1, characterized in that: The electrolyte is stored at a temperature of 20 to 45° C. for ≥24 hours before injection.

3. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 1, characterized in that: In formula (I), R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from hydrogen, fluorine, C1-C4 alkyl, C1-C4 fluoroalkyl, C1-C4 alkoxy, or C1-C4 fluoroalkoxy; and n is selected from 0, 1, or 2.

4. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 3, characterized in that: In formula (I), R1, R2, R3, R4, R5, and R6 are independently selected from methyl, ethyl, isopropyl, tert-butyl, or fluoromethyl; and R7 and R8 are independently selected from hydrogen, fluorine, methyl, or fluoromethyl.

5. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 4, characterized in that: The first additive is selected from at least one of the compounds shown in the following structures:

6. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 1, characterized in that: The non-aqueous solvent is selected from at least one of C3-C6 carbonate or fluorinated carbonate compounds, C3-C8 carboxylic acid ester or fluorinated carboxylic acid ester compounds, sulfone compounds or ether compounds; The C3-C6 carbonate or fluorocarbonate compound is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate or ethyl propyl carbonate; the C3-C8 carboxylic acid ester or fluorocarboxylic acid ester compound is selected from at least one of γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate and propyl propionate; the sulfone compound is selected from at least one of cyclopentane sulfoxide, dimethyl sulfoxide, dimethyl sulfone or diethyl sulfone; the ether compound is selected from at least one of triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether and dioxolane.

7. The electrolyte for high voltage fast charge alkali metal secondary battery according to any one of claims 1 to 6, characterized in that: The additives also include: The second additive is selected from the cyclic sulfate compounds represented by the following formula (II-A) or (II-B): Wherein G1, G2, G3, and G4 are independently selected from hydrogen, fluorine, methyl, or fluoromethyl, G5, G6, G7, and G8 are independently selected from a direct bond, methylene, or fluoromethylene, and M is selected from one of the following structures: Among them, G9, G 10 is selected from methine, p is selected from an integer of 0-6, and q and r are independently selected from an integer of 1-4; The third additive is selected from at least one of the inorganic salt additives having the structure represented by the following formula (III-1), (III-2) or (III-3): In formulas (III-1), (III-2) and (III-3), when the electrolyte is applied to a lithium ion secondary battery, X is Li; when the electrolyte is applied to a sodium ion secondary battery, X is Na.

8. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 7, characterized in that: The second additive is selected from at least one of the compounds shown in the following structures:

9. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 7, characterized in that: The amounts of the first additive, the second additive and the third additive respectively account for a%, b% and c% of the total mass of the electrolyte, and meet the following relationship: 0.01≤a≤3, 0.01≤b≤2.5, 0.01≤c≤3; and, 0.2≤a+b≤5, 0.05≤a / c≤10, 0.03≤(a+b) / c≤20.

10. The electrolyte for high voltage fast charge alkali metal secondary battery according to claim 9, characterized in that: The amounts of the first additive, the second additive and the third additive satisfy the following relationship: 0.1≤a≤2, 0.2≤b≤2, 0.2≤c≤2; and, 0.4≤a+b≤3, 0.1≤a / c≤4, 0.2≤(a+b) / c≤6.

11. The electrolyte for high voltage fast charging alkali metal secondary battery according to any one of claims 1 to 10, characterized in that: The additives also include: A basic additive, wherein the basic additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, tris(trimethylsilyl) phosphate, 1,3-propylene sultone, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, succinic anhydride, adiponitrile, cyclohexylbenzene, lithium difluorobis(oxalate)phosphate, lithium difluorooxalatoborate, sodium difluorooxalatoborate, sodium difluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium difluorobis(oxalate)phosphate, and any one of the basic additives accounts for 0.1 to 5.0 wt% of the total mass of the electrolyte, and the basic additive is different from the main salt.

12. An alkali metal secondary battery comprising a positive electrode, a negative electrode and a separator, characterized in that: The alkali metal secondary battery is filled with the electrolyte according to any one of claims 1 to 11, and the electrolyte is stored at a temperature of -30 to 60° C. for ≥12 hours before being filled.

13. The alkali metal secondary battery according to claim 12, characterized in that: When the alkali metal secondary battery is a lithium ion secondary battery, the active material of the positive electrode is selected from nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium cobalt oxide material or lithium iron phosphate material, and the active material of the negative electrode is selected from graphite, silicon carbon, silicon dioxide, silicon, tin, metallic lithium or a composite material thereof; When the alkali metal secondary battery is a sodium ion secondary battery, the active material of the positive electrode is selected from NaMn (1-x-y) Ni y M x O2 (0 ≤ x, y ≤ 1, M is Cu, Fe, Co, sodium manganate, sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron phosphate, sodium manganese phosphate, sodium iron sulfate, Na x MnFe(CN)6 (0 < x ≤ 2), and the active material of the negative electrode is selected from at least one of hard carbon, carbon black, amorphous carbon, graphite, SnS2, Na2Ti3O7, silicon-based materials, metal oxides, metal sulfides, or metallic sodium.

14. The alkali metal secondary battery according to claim 13, characterized in that: The working voltage of the alkali metal secondary battery is ≥4.3V, and the average charging rate at 0-100% SOC is ≥1C.

15. The alkali metal secondary battery according to claim 14, characterized in that: The working voltage of the alkali metal secondary battery is 4.3-4.6V, and the average charging rate at 40-60% SOC is ≥1.5C.

Images