An electrolyte additive composition, an electrolyte, and a lithium-ion battery containing the electrolyte

Abstract

The present invention discloses an electrolyte additive composition, an electrolyte, and a lithium-ion battery containing the electrolyte. The additive composition includes: a cyclic sulfate additive and a triazine additive represented by the following formula (I). The additive composition of the present invention can inhibit the increase in acidity during long-term storage of the electrolyte, and at the same time can improve the high-temperature performance and low-temperature performance of the lithium-ion battery using the electrolyte.

Description

Technical Field

[0001] The present invention relates to the field of electrolytes, in particular to electrolytes for lithium-ion batteries, and particularly to an additive composition containing cyclic sulfate esters and triazine additives, an electrolyte containing the additive composition, and a lithium-ion battery containing the electrolyte. Background Art

[0002] The electrolyte plays a crucial role in the battery. The electrolyte is in direct contact with internal components such as the positive electrode, negative electrode, and separator of the battery, significantly affecting the electrochemical performance of the battery. In particular, additives in the electrolyte, such as vinylene carbonate, ethylene sulfate, 1,3-propane sultone, etc., generally have a usage amount within 10% of the total amount of the electrolyte, but have a certain modifying effect on both the positive and negative electrode interfaces, effectively inhibiting side reactions of the positive and negative electrode materials, solvents, and main lithium salts, and improving the electrochemical performance of the battery such as high-temperature storage, cycling, and rate performance.

[0003] Patent CN1411092A of TDK Corporation discloses a cyclic sulfate ester compound. This additive can form a dense and well-permeable modification film on the surface of battery negative electrode materials such as graphite, reduce the battery impedance, and reduce side reactions during battery use or storage, thereby improving the electrochemical performance of the battery such as room-temperature cycling, low-temperature discharge, and rate cycling. However, it is prone to hydrolysis reaction with trace water in the electrolyte during storage, resulting in problems such as increased acidity of the electrolyte, increased side reactions, and discoloration, and this problem intensifies as the acidity of the electrolyte increases, ultimately leading to the failure of the additive and the attenuation of battery performance.

[0004] Currently, industrial use of a cold storage at -20 to 0 °C is usually adopted to alleviate the problems of acidity increase and failure of cyclic sulfate ester compounds during storage and transportation. However, this method cannot fundamentally solve the problem of acidity increase in the electrolyte, and there is also the problem of significantly increasing storage and transportation costs.

[0005] Solving this problem by using water and acid removal additives is a method that has been frequently mentioned to inhibit the growth of acidity inside the electrolyte and improve the electrochemical performance of the battery. Among them, the most studied is to utilize the characteristics that silicon-oxygen bonds or silicon-nitrogen bonds are prone to hydrolysis or acidolysis. Patents CN111525192A, CN111900470A, CN112625062A, CN112635833A, and CN112886064A all disclose the use of additives containing at least one characteristic structure of silicon-oxygen bonds and silicon-nitrogen bonds, and utilize this characteristic structure to play the role of acid and water removal. However, when substances containing these two structures react with hydrofluoric acid, fluorosilane will be formed. This substance has a low boiling point, is easy to vaporize, and has a low solubility in the electrolyte, which will exacerbate the gas generation problem of the battery during high-temperature storage and high-temperature cycling, and thus affect the electrochemical performance of the battery; when substances containing these two structures react with water, silanol will be formed. This substance is prone to self-condensation to form disiloxane and generate water. Therefore, the long-term water removal performance of this type of substance is not good.

[0006] Therefore, it is crucial to propose an additive or additive composition that can stably inhibit the growth of electrolyte acidity in the long term and does not have side effects on the high-temperature performance of the battery. Summary of the Invention

[0007] To solve the above technical problems, the present invention proposes an additive composition for inhibiting the growth of electrolyte acidity, an electrolyte containing the additive composition, and a lithium-ion battery containing the electrolyte, which can simultaneously improve the high-temperature performance and low-temperature performance of the battery.

[0008] The object of the present invention is achieved by the following technical solutions:

[0009] An electrolyte additive composition, comprising:

[0010] At least one of the cyclic sulfate additives represented by the following formulas (Ⅱ), (Ⅲ), (Ⅳ), and (Ⅴ):

[0011]

[0012]

[0013] In the formulas, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 are independently selected from hydrogen, C1-C10 alkyl, C3-C10 cycloalkyl, C2-C10 alkenyl, C2-C10 alkynyl, C1-C10 alkoxy, phenyl, or phenoxy; n and m are independently selected from 0 or 1, X and Y are independently selected from hydrogen, C1-C6 alkyl, or halogen, and the hydrogen in R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 can optionally be substituted by halogen;

[0014] and a triazine additive represented by the following formula (I):

[0015]

[0016] In the formula, R13, R14, and R15 are independently selected from hydrogen, C1-C10 alkyl, C3-C10 cycloalkyl, C2-C10 alkenyl, C2-C10 alkynyl, or phenyl.

[0017] Preferably, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12 are independently selected from hydrogen, C1-C6 alkyl, C3-C6 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, C1-C6 alkoxy, phenyl, or phenoxy; X and Y are independently selected from hydrogen, C1-C3 alkyl, or halogen, and the hydrogen in R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12 may optionally be substituted by fluorine;

[0018] R13, R14, and R15 are independently selected from hydrogen, C1-C6 alkyl, C3-C6 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, or phenyl.

[0019] More preferably, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12 are independently selected from hydrogen, C1-C3 alkyl, C2-C3 alkenyl, C2-C3 alkynyl, or C1-C3 alkoxy; X and Y are independently selected from hydrogen, C1-C3 alkyl, or fluorine, and the hydrogen in R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12 may optionally be substituted by fluorine; R13, R14, and R15 are independently selected from hydrogen, C1-C3 alkyl, C2-C3 alkenyl, or C2-C3 alkynyl.

[0020] Even more preferably, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, R12 are independently selected from hydrogen, fluorine, methyl, ethyl, propyl, isopropyl, vinyl, allyl, propenyl, propargyl, propynyl, methoxy, or ethoxy; X and Y are independently selected from hydrogen, methyl, ethyl, propyl, or fluorine;

[0021] R13, R14, and R15 are independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, vinyl, ethynyl, allyl, propenyl, propargyl, or propynyl.

[0022] Most preferably, the cyclic sulfate additive is selected from at least one of the following structures:

[0023]

[0024]

[0025] The triazine additives are selected from at least one of the following structures:

[0026]

[0027]

[0028] When the additive composition of the present invention is used in combination, as long as the mass ratio of the cyclic sulfate additive to the triazine additive is not higher than 500:1 and not lower than 1:10, the purpose of inhibiting the increase in the acidity of the electrolyte can be achieved.

[0029] The present invention also provides a lithium-ion battery electrolyte, comprising: a main lithium salt, a non-aqueous solvent, and the additive composition described in any one of the above.

[0030] In the electrolyte formulation, by mass content, the addition amount of the cyclic sulfate additive is less than 5.0%, and the addition amount of the triazine additive is greater than 0.01%.

[0031] In order to form a SEI film with higher ionic conductivity on the surface of the negative electrode of the lithium-ion battery, the addition amount of the cyclic sulfate additive is 0.02% - 5.0%, and the addition amount of the triazine additive is 0.01% - 2.0%.

[0032] Preferably, the addition amount of the cyclic sulfate additive is 0.2% - 2.0%, and the addition amount of the second additive is 0.1% - 1.0%.

[0033] The main lithium salt of the present invention can be a commonly used main lithium salt in the electrolyte. As a preference, the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide, and the molar concentration in the electrolyte is 0.4 - 1.6 mol / L. More preferably, the main lithium salt is lithium hexafluorophosphate, and the molar concentration in the electrolyte is 0.6 - 1.2 mol / L.

[0034] The non-aqueous solvent of the present invention can be a commonly used solvent in the electrolyte. As a preference, the non-aqueous solvent is selected from at least one of C3 - C6 carbonates or fluorinated carbonate compounds, C3 - C8 carboxylate esters or fluorinated carboxylate esters, sulfone compounds, and ether compounds.

[0035] Furthermore, the C3 - C6 carbonates or fluorinated carbonate compounds are 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, fluorinated ethylene carbonate, and difluorinated ethylene carbonate;

[0036] The C3-C8 carboxylic acid ester or fluorinated carboxylic 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, propyl propionate, ethyl fluoroacetate, and (2,2-difluoroethyl) acetate;

[0037] The sulfone compound is selected from at least one of sulfolane, dimethyl sulfoxide, dimethyl sulfone, and diethyl sulfone;

[0038] The ether compound is selected from at least one of triglyme, tetraglyme, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0039] To improve the comprehensive performance of the battery, further, the electrolyte further includes a basic additive, and the basic additive is selected from at least one of sulfonic acid ester compounds, fluorinated carbonate compounds, unsaturated carbonate compounds, or fluorinated lithium salt compounds, and the dosage accounts for 0.1-5.0% of the total amount of the electrolyte. Among them:

[0040] The sulfonic acid ester compound is selected from at least one of 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and methylene methanedisulfonate;

[0041] The fluorinated carbonate compound is selected from at least one of ethyl fluorocarbonate, difluoroethylene carbonate, and propylene carbonate trifluoromethyl carbonate;

[0042] The unsaturated carbonate compound is selected from vinylene carbonate and / or vinyl ethylene carbonate;

[0043] The fluorinated lithium salt compound is different from the main lithium salt and is selected from at least one of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroxalate phosphate, lithium difluorobis(oxalate)phosphate, lithium difluorooxalate borate, and lithium trioxalate phosphate.

[0044] The present invention also provides an application of the electrolyte containing the additive composition described above in a lithium ion battery.

[0045] The present invention also provides a lithium ion battery, including a positive electrode, a negative electrode, a separator, and the lithium ion battery electrolyte described above.

[0046] In the present invention, a cyclic sulfate ester additive and a triazine additive are used in combination in an electrolyte. When there is proton hydrogen in the electrolyte, especially when hydrogen fluoride is present, the lone pair electrons on the N atom of the triazine additive can effectively capture the active proton hydrogen to form a tertiary amine cation as shown in the following formula (IA), thereby reducing the acidity of the electrolyte and solving the problem that the cyclic sulfate ester additive is easily decomposed by acid. When the acidity of the electrolyte is too high, this reaction can further proceed in the forward direction to form a more stable structure as shown in the following formula (IB). The reaction process is as follows:

[0047]

[0048] In particular, the effect of the triazine additive of the present invention in inhibiting the growth of the electrolyte acidity is not only reflected in the combination with the cyclic sulfate ester additive of the present invention. When the triazine additive is used in combination with other additives that are likely to cause the growth of the electrolyte acidity (such as borate compounds, phosphate compounds, phosphite compounds, etc.), it can also inhibit the growth of the electrolyte acidity.

[0049] Meanwhile, the above-mentioned triazine additive and its reaction product with acid contain unsaturated bonds, which are conducive to the occurrence of bond-opening and / or ring-opening reactions on the surface of the positive electrode of the lithium-ion battery to form a dense CEI film, which can significantly reduce the interfacial impedance of the positive electrode, is beneficial to the migration of lithium ions at the positive electrode interface, and the N atom not combined with proton hydrogen still has a lone pair of electrons, which can complex with the high-valent metal ions of the positive electrode, effectively reducing the oxidation activity of the positive electrode material to the electrolyte, thereby inhibiting the side reactions of the electrolyte, inhibiting gas generation, and improving the high-temperature storage performance and high-temperature cycling performance of the lithium-ion battery.

[0050] Generally speaking, the above-mentioned triazine additive is prone to undergo a reduction reaction at the negative electrode interface to form a SEI film with a relatively large impedance, which is not conducive to the migration of lithium ions on the surface of the negative electrode and will deteriorate the low-temperature performance of lithium ions. However, under the action of the triazine additive, the cyclic sulfate ester additive can stably exist during the long-term storage of the electrolyte. Therefore, during the first charging process of the battery, the cyclic sulfate ester additive can still maintain its reaction activity and preferentially form a stable, dense and well-permeable SEI film on the negative electrode prior to the triazine additive, effectively inhibiting the reduction decomposition of the triazine additive, thereby reducing the adverse effect of the triazine additive on the kinetics of the lithium intercalation process at the negative electrode.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] 1. The combination of the cyclic sulfate ester additive and the triazine additive of the present invention can not only inhibit the growth of acidity and discoloration during the long-term storage and transportation of the electrolyte, but also improve the high-temperature performance and low-temperature performance of the lithium-ion battery containing this electrolyte.

[0053] 2. Compared with using a single additive, the additive composition of the present invention has improved stability, good compatibility with common solvents and lithium salts, no reaction and no color change, and a high mutual solubility ratio.

[0054] 3. The mass ratio range of the additive composition of the present invention is wide, and within a certain ratio range, it can be adjusted according to the actual use requirements and battery types. The controllability in the actual production process is strong, and the industrialization value is great. Detailed implementation manners

[0055] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific implementation manners. Those skilled in the art should recognize that the present invention covers all alternative solutions, improvement solutions, and equivalent solutions that may be included within the scope of the claims.

[0056] I. Preparation of electrolyte

[0057] Preparation of the basic electrolyte: In a glove box filled with argon (moisture < 5 ppm, oxygen content < 10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed according to a mass ratio of EC:EMC:DEC = 3:5:2. Lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution until the molar concentration of LiPF6 was 1.2 mol / L to obtain the basic electrolyte.

[0058] Example 1

[0059] In the basic electrolyte, 2.0 wt% of compound A1 and 1.0 wt% of compound B6 were added to obtain the electrolyte of this example.

[0060] Example 2

[0061] In the basic electrolyte, 2.0 wt% of compound A1 and 0.2 wt% of compound B6 were added to obtain the electrolyte of this example.

[0062] Example 3

[0063] In the basic electrolyte, 0.2 wt% of compound A1 and 0.4 wt% of compound B6 were added to obtain the electrolyte of this example.

[0064] Example 4

[0065] In the basic electrolyte, 0.5 wt% of compound A1 and 1.0 wt% of compound B6 were added to obtain the electrolyte of this example.

[0066] Example 5

[0067] In the basic electrolyte, 1.0 wt% of compound A1 and 0.5 wt% of compound B6 were added to obtain the electrolyte of this example.

[0068] Example 6

[0069] In the basic electrolyte, 1.0 wt% of compound A1 and 0.1 wt% of compound B6 were added to obtain the electrolyte of this example.

[0070] Example 7

[0071] In the basic electrolyte, 0.05 wt% of compound A1 and 0.05 wt% of compound B6 were added to obtain the electrolyte of this example.

[0072] Example 8

[0073] In the basic electrolyte, 5.0 wt% of compound A1 and 2.0 wt% of compound B6 were added to obtain the electrolyte of this example.

[0074] Example 9

[0075] In the basic electrolyte, 1.0 wt% of compound A2 and 0.5 wt% of compound B6 were added to obtain the electrolyte of this example.

[0076] Example 10

[0077] In the basic electrolyte, 1.0 wt% of compound A1 and 0.5 wt% of compound B4 were added to obtain the electrolyte of this example.

[0078] Example 11

[0079] In the basic electrolyte, 1.0 wt% of compound A7 and 0.5 wt% of compound B3 were added to obtain the electrolyte of this example.

[0080] Example 12

[0081] In the basic electrolyte, 1.0 wt% of compound A10 and 0.5 wt% of compound B9 were added to obtain the electrolyte of this example.

[0082] Example 13

[0083] In the basic electrolyte, 1.0 wt% of compound A17 and 0.5 wt% of compound B1 were added to obtain the electrolyte of this example.

[0084] Example 14

[0085] In the basic electrolyte, 1.0 wt% of compound A19 and 0.5 wt% of compound B2 were added to obtain the electrolyte of this example.

[0086] Example 15

[0087] In the basic electrolyte, 1.0 wt% of Compound A24 and 0.5 wt% of Compound B11 were added to obtain the electrolyte of this example.

[0088] Comparative Example 1

[0089] In the basic electrolyte, only 1.0 wt% of Compound A1 was added to obtain the electrolyte of this comparative example.

[0090] Comparative Example 2

[0091] In the basic electrolyte, only 1.0 wt% of Compound B6 was added to obtain the electrolyte of this comparative example.

[0092] Comparative Example 3

[0093] In the basic electrolyte, 6.0 wt% of Compound A1 and 0.01 wt% of Compound B6 were added to obtain the electrolyte of this comparative example.

[0094] Comparative Example 4

[0095] In the basic electrolyte, 0.02 wt% of Compound A1 and 3.0 wt% of Compound B6 were added to obtain the electrolyte of this comparative example.

[0096] Comparative Example 5

[0097] In the basic electrolyte, only 1.0 wt% of Compound A2 was added to obtain the electrolyte of this comparative example.

[0098] Comparative Example 6

[0099] In the basic electrolyte, only 0.5 wt% of Compound B4 was added to obtain the electrolyte of this comparative example.

[0100] Comparative Example 7

[0101] In the basic electrolyte, 1.0 wt% of Compound A2 and 0.5 wt% of hexamethyldisilazane (denoted as Compound C1) were added to obtain the electrolyte of this comparative example.

[0102] Comparative Example 8

[0103] In the basic electrolyte, 1.0 wt% of Compound A2 and 0.5 wt% of heptamethyldisilazane (denoted as Compound C2) were added to obtain the electrolyte of this comparative example.

[0104] Comparative Example 9

[0105] In the basic electrolyte, 1.0 wt% of compound A2 and 0.5 wt% of hexamethyldisiloxane (denoted as compound C3) were added to obtain the electrolyte of this comparative example.

[0106] Comparative Example 10

[0107] In the basic electrolyte, only 1.0 wt% of compound A7 was added to obtain the electrolyte of this comparative example.

[0108] Comparative Example 11

[0109] In the basic electrolyte, only 1.0 wt% of compound A10 was added to obtain the electrolyte of this comparative example.

[0110] Comparative Example 12

[0111] In the basic electrolyte, only 0.5 wt% of compound B3 was added to obtain the electrolyte of this comparative example.

[0112] Comparative Example 13

[0113] In the basic electrolyte, only 0.5 wt% of compound B9 was added to obtain the electrolyte of this comparative example.

[0114] Comparative Example 14

[0115] In the basic electrolyte, only 1.0 wt% of compound A17 was added to obtain the electrolyte of this comparative example.

[0116] Comparative Example 15

[0117] In the basic electrolyte, only 0.5 wt% of compound B1 was added to obtain the electrolyte of this comparative example.

[0118] Comparative Example 16

[0119] In the basic electrolyte, only 1.0 wt% of compound A19 was added to obtain the electrolyte of this comparative example.

[0120] Comparative Example 17

[0121] In the basic electrolyte, only 0.5 wt% of compound B2 was added to obtain the electrolyte of this comparative example.

[0122] Comparative Example 18

[0123] In the basic electrolyte, only 1.0 wt% of compound A24 was added to obtain the electrolyte of this comparative example.

[0124] Comparative Example 19

[0125] In the basic electrolyte, only 0.5 wt% of compound B11 was added to obtain the electrolyte of this comparative example.

[0126] II. Electrolyte Acidity Test

[0127] Take 20 g of the electrolytes of the above-mentioned examples and comparative examples in a conical flask, weigh and record as mass m, add 1 - 2 drops of neutral red methylene blue mixed indicator, titrate with triethylamine ultra-dry acetonitrile solution with a concentration of c, record the titration volume V of the standard solution, and calculate the electrolyte acidity according to the following formula:

[0128] Electrolyte acidity (ppm) = 20.006 * 1000 * V * c / m

[0129] Put the remaining electrolyte into a dried aluminum-plastic bottle, ensure it is sealed and then put it into an oven at 60 °C for three days. Then take out the electrolyte and measure the electrolyte acidity again according to the above method.

[0130] The test results are shown in Table 1 below:

[0131] Table 1 Test Results of Electrolyte Acidity

[0132]

[0133]

[0134] Comparing Example 5 and Comparative Example 1, it can be seen that the electrolyte additive composition containing sulfate ester additives and triazine additives can significantly inhibit the increase in acidity of the electrolyte during storage compared with the electrolyte using only sulfate ester additives. The same results can also be obtained by comparing Example 9 and Comparative Example 5, or Example 10 and Comparative Example 1, or Example 11 and Comparative Example 10, or Example 12 and Comparative Example 11, or Example 13 and Comparative Example 14, or Example 14 and Comparative Example 16, or Example 15 and Comparative Example 18.

[0135] Comparing Examples 1, 2, 6, 8 and Comparative Example 3, it can be seen that the addition amount of sulfate ester additives should be less than 5.0 wt%, the addition amount of triazine additives should be higher than 0.01 wt%, and the mass ratio of sulfate ester additives to triazine additives should not be higher than 500:1 to achieve the effect of inhibiting the increase in acidity of the electrolyte during storage.

[0136] Comparing Example 9 and Comparative Example 9, it can be seen that using triazine additives as water and acid removal additives can significantly inhibit the increase in acidity of the electrolyte during storage compared with the commonly used silicone oxide additives.

[0137] III. Electrochemical Performance Test

[0138] The electrolytes of the above-mentioned examples and comparative examples were respectively made into soft-pack lithium-ion batteries with a capacity of 1500 mAh. The lithium-ion batteries include a positive electrode plate, a negative electrode plate, a separator, an electrolyte, and battery accessories. The positive active material is a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a lithium cobaltate material, or a lithium iron phosphate material. The negative active material is graphite, silicon, or metallic lithium material; among them, the positive active material is a ternary positive electrode LiNi 0.6 Co 0.2 Mn 0.2 O 2 , and the negative active material is high-capacity graphite. The preparation process is as follows: The positive electrode plate, the separator, and the negative electrode plate are wound together into a core, sealed with an aluminum-plastic film, and baked to make the electrode moisture meet the requirements. After baking, the electrolyte is injected into the battery cell. After standing, forming, grading, and aging processes, the finished soft-pack battery cell is obtained.

[0139] Performance tests were carried out on the prepared lithium-ion power batteries (soft-pack battery cells). The specific test items and methods are as follows:

[0140] (1) 60°C high-temperature storage test: Cycle at 0.5C / 0.5C at room temperature for 1 week, record the discharge capacity, internal resistance, and volume in the first week, then charge at a constant current of 0.5C to 4.20V and charge at a constant voltage until the current drops to 0.05C. Let it stand in a 60°C constant-temperature oven for 30 days, and then cycle at 0.5C / 0.5C at room temperature for 2 weeks. Record the discharge capacity in the first week after high-temperature standing, the discharge capacity in the second week, the internal resistance and volume after storage. Calculate the capacity retention rate, capacity recovery rate, internal resistance growth rate, and volume expansion rate of the battery after storage according to the following formula:

[0141] Capacity recovery rate = Discharge capacity in the first week after high-temperature standing / Discharge capacity in the first week * 100%.

[0142] Volume expansion rate = (Volume after storage - Volume in the first week) / Volume in the first week * 100%.

[0143] (2) 45°C high-temperature cycle test: The battery is cycled in an oven at 45 ± 1°C with a charge-discharge current of 1C / 1C, calculate the discharge capacity per week, cycle until 1000 weeks or the capacity retention rate is lower than 80%, stop cycling, and test the DCR value after the test is over. Calculate the capacity retention rate and DCR growth rate after cycling.

[0144] (3) Low-temperature performance test: Cycle at 0.5C / 0.5C at room temperature for 1 week, record the discharge capacity in the first week, then charge at a constant current of 0.5C to 4.20V and charge at a constant voltage until the current drops to 0.05C. Let it stand in a -20°C constant-temperature oven for 5h and discharge to 2.20V. Record the low-temperature discharge capacity. Calculate the low-temperature discharge capacity retention rate according to the following formula:

[0145] Capacity retention rate = Discharge capacity after low - temperature storage / Discharge capacity in the first week * 100%.

[0146] The test results are shown in Table 2 below:

[0147] Table 2 Test Results of Battery Electrochemical Performance

[0148]

[0149] Comparing Example 10 with Comparative Examples 1 and 6, it can be seen that the electrolyte additive composition using sulfate ester additives and triazine additives can ensure a higher capacity retention rate and a lower volume expansion rate during high - temperature storage, a higher capacity retention rate during high - temperature cycling, and a higher capacity recovery rate during low - temperature discharge, compared with the electrolyte using sulfate ester additives alone or triazine additives alone. The same results can be obtained by comparing Example 1 with Comparative Example 2, or Example 9 with Comparative Example 5, or Example 11 with Comparative Examples 10 and 12, or Example 12 with Comparative Examples 11 and 13, or Example 13 with Comparative Examples 14 and 15, or Example 14 with Comparative Examples 16 and 17, or Example 15 with Comparative Examples 18 and 19.

[0150] Comparing Examples 1, 3, 4, 7 with Comparative Example 4, it can be seen that the addition amount of sulfate ester additives should be higher than 0.02 wt%, the addition amount of triazine additives should be lower than 2.0 wt%, and the mass ratio of sulfate ester additives to triazine additives should be not less than 1:10 to achieve the effect of forming a SEI film with high ionic conductivity on the surface of the negative electrode of the lithium - ion battery, thereby ensuring both the high - temperature performance and low - temperature performance of the lithium - ion battery.

[0151] Comparing Example 9 with Comparative Examples 7 and 8, it can be seen that the electrolyte additive composition using sulfate ester additives and triazine additives can not only significantly inhibit the increase in acidity of the electrolyte during storage, but also ensure a higher capacity retention rate and a lower volume expansion rate during high - temperature storage, a higher capacity retention rate during high - temperature cycling, and a higher capacity recovery rate during low - temperature discharge, compared with the electrolyte additive composition using sulfate ester additives and silazane additives.

Claims

1. An electrolyte additive composition, characterized in that: the additive composition comprises: at least one of cyclic sulfate esters additives represented by the following formulas (II), (III), (IV), and (V): In the formulas, R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 are independently selected from hydrogen, C1-C10 alkyl, C3-C10 cycloalkyl, C2-C10 alkenyl, C2-C10 alkynyl, C1-C10 alkoxy, phenyl, or phenoxy; n and m are independently selected from 0 or 1; X and Y are independently selected from hydrogen, C1-C6 alkyl, or halogen; and the hydrogen in R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 may optionally be substituted by halogen; and a triazine additive represented by the following formula (I): In the formula, R13, R14, and R15 are independently selected from hydrogen, C1-C10 alkyl, C3-C10 cycloalkyl, C2-C10 alkenyl, C2-C10 alkynyl, or phenyl.

2. The electrolyte additive composition according to claim 1, characterized in that: R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 are independently selected from hydrogen, C1-C6 alkyl, C3-C6 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, C1-C6 alkoxy, phenyl, or phenoxy; X and Y are independently selected from hydrogen, C1-C3 alkyl, or halogen; and the hydrogen in R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 may optionally be substituted by fluorine; R13, R14, and R15 are independently selected from hydrogen, C1-C6 alkyl, C3-C6 cycloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, or phenyl.

3. The electrolyte additive composition according to claim 2, characterized in that: R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11, and R12 are independently selected from hydrogen, fluorine, methyl, ethyl, propyl, isopropyl, vinyl, allyl, propenyl, propargyl, propynyl, methoxy, or ethoxy; X and Y are independently selected from hydrogen, methyl, ethyl, propyl, or fluorine; R13, R14, and R15 are independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, vinyl, ethynyl, allyl, propenyl, propargyl, or propynyl.

4. The electrolyte additive composition according to claim 3, characterized in that: the cyclic sulfate ester additive is selected from at least one of the following structures: the triazine additive is selected from at least one of the following structures:

5. The electrolyte additive composition according to any one of claims 1-4, characterized in that: the mass ratio of the cyclic sulfate ester additive to the triazine additive is not higher than 500:1 and not lower than 10:

1.

6. A lithium-ion battery electrolyte, comprising: a main lithium salt and a non-aqueous solvent, characterized in that the electrolyte further comprises the additive composition according to any one of claims 1-5.

7. The lithium-ion battery electrolyte according to claim 6, It is characterized in that: The addition amount of the cyclic sulfate ester additive is less than 5.0%, and the addition amount of the second additive is greater than 0.01%.

8. The lithium ion battery electrolyte according to claim 7, It is characterized in that: The addition amount of the cyclic sulfate ester additive is 0.02% - 5.0%, and the addition amount of the triazine additive is 0.01% - 2.0%.

9. The lithium ion battery electrolyte according to claim 6, It is characterized in that: The main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide, and the molar concentration in the electrolyte is 0.4 - 1.6 mol / L.

10. The lithium ion battery electrolyte according to claim 6, It is characterized in that: The non-aqueous solvent is selected from at least one of C3 - C6 carbonate or fluorinated carbonate compounds, C3 - C8 carboxylate or fluorinated carboxylate compounds, sulfone compounds, and ether compounds.

11. The lithium ion battery electrolyte according to any one of claims 6 - 10, It is characterized in that: The electrolyte further includes a basic additive, and the basic additive is selected from at least one of sulfonate compounds, fluorinated carbonate compounds, unsaturated carbonate compounds, or fluorinated lithium salt compounds, and the dosage accounts for 0.1% - 5.0% of the total amount of the electrolyte.

12. A lithium ion battery, comprising a positive electrode, a negative electrode, and a separator, It is characterized in that: The lithium ion battery further includes the lithium ion battery electrolyte according to any one of claims 6 - 10.

Images