Electrolyte, preparation method thereof and lithium ion battery
By using additives with isocyanate and nitrile substituents in lithium-ion batteries in synergy with sulfur heterocyclic compounds, the problem of poor compatibility between ternary cathode materials and electrolytes was solved, thereby improving the electrochemical performance and cycle stability of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI XUANYI NEW ENERGY DEV CO LTD
- Filing Date
- 2026-03-27
- Publication Date
- 2026-05-29
AI Technical Summary
In existing lithium-ion batteries, the poor compatibility between ternary cathode materials and electrolytes leads to poor battery cycle performance. Furthermore, electrolyte oxidation and decomposition, as well as HF attack on the CEI film, result in transition metal dissolution and increased battery impedance.
The first additive, which contains isocyanate and nitrile substituents, and the second additive, which contains sulfur heterocyclic compounds, work synergistically to form a stable interfacial film, inhibiting the oxidative decomposition of the electrolyte and the dissolution of transition metals, thereby improving electrochemical performance.
It improves the electrochemical performance of lithium-ion batteries, enhances the compatibility of ternary cathode materials, improves the cycle stability and high and low temperature performance of batteries, and reduces battery impedance.
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Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, and more specifically, to an electrolyte, a method for preparing the electrolyte, and a lithium-ion battery. Background Technology
[0002] Lithium-ion batteries are widely used in 3C digital products, power and energy storage applications due to their advantages such as high operating voltage, long cycle life, low self-discharge rate, environmental friendliness and no memory effect, making them the most widely used rechargeable batteries today.
[0003] In lithium-ion batteries, the electrolyte is a key component, responsible for the transfer of lithium ions between the positive and negative electrodes, and significantly impacts the battery's cycle life, fast charging, and high / low temperature performance. Lithium-ion battery electrolytes should meet the following conditions: (1) high ionic conductivity and high dielectric constant to ensure the solubility and migration rate of lithium ions in the electrolyte; (2) low melting point and high boiling point to ensure the operating temperature range of the lithium-ion battery; (3) a wide electrochemical stability window to form a good interfacial film; and (4) low cost and environmental friendliness. In practical applications, commercial electrolytes need to find a balance among these properties to meet the requirements of lithium-ion battery products.
[0004] With the increasing demand in the electric vehicle market, the demand for lithium-ion batteries is also growing, and the performance requirements for lithium-ion batteries are constantly improving. Lithium-ion battery electrolytes consist of lithium salts, solvents, and additives. Among these, electrolyte additives, used in small quantities but with significant effects, have been extensively studied. Additives can be categorized by function into film-forming additives, dehydration and acid removal additives, overcharge prevention additives, conductive additives, flame-retardant additives, etc. Some multifunctional additives possess two or more functions simultaneously.
[0005] Ternary cathodes are among the cathode materials with great development potential, but there are still many problems to be solved. For example, ternary materials have poor compatibility with electrolytes, and the high voltage plateau and surface active sites of ternary materials easily lead to the oxidative decomposition of the electrolyte. At the same time, HF in the electrolyte can attack the CEI and cause the dissolution of transition metals. The dissolved transition metals are deposited on the negative electrode, causing the battery impedance to increase, and ultimately deteriorating the cycle performance of ternary cathode batteries. Summary of the Invention
[0006] The main objective of this application is to provide an electrolyte, its preparation method, and a lithium-ion battery to solve the problem of poor compatibility between the electrolyte and ternary cathode material in the prior art, which leads to poor battery cycle performance.
[0007] To achieve the above objectives, according to one aspect of this application, an electrolyte is provided, comprising a lithium salt, a first additive, a second additive, and a solvent; wherein the first additive is a compound having isocyanate substituents and nitrile substituents in its molecular structure; and the second additive is a sulfur-containing heterocyclic compound.
[0008] Further, the first additive is a C5-C10 cyclic compound or a C3-C10 chain compound carrying isocyanate substituents and nitrile substituents, and in addition to isocyanate substituents and nitrile substituents, the hydrogen atoms at other carbon positions of the C5-C10 cyclic compound or the C3-C10 chain compound may optionally be substituted by the following groups: halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy.
[0009] Furthermore, the first additive is a six-membered ring compound carrying isocyanate substituents and nitrile substituents, and in addition to the isocyanate substituents and nitrile substituents, the other carbon hydrogen atoms of the six-membered ring compound may optionally be substituted by the following groups: halogen, substituted or unsubstituted C1~C6 alkyl, substituted or unsubstituted C1~C6 alkoxy.
[0010] Furthermore, the six-membered cyclic compound is a benzene ring.
[0011] Furthermore, the molecular structure of the first additive carries one isocyanate substituent and one nitrile substituent.
[0012] Furthermore, the isocyanate substituent and nitrile substituent are located at the para, meta, or ortho positions in the six-membered ring compound.
[0013] Furthermore, the first additive is selected from at least one of the compounds with the structures shown in Formulas 1 to 3;
[0014] ;
[0015] Among them, R1~R 12 Each is independently selected from any one of hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy.
[0016] Furthermore, the substituted C1-C6 alkyl groups are fluorinated C1-C6 alkyl groups.
[0017] Furthermore, R1~R 12 Each is independently selected from hydrogen.
[0018] Furthermore, the first additive is selected from at least one of compounds 1 to 9:
[0019] .
[0020] Furthermore, the first additive is selected from at least one of compound 1 to compound 3.
[0021] Furthermore, the second additive is a cyclic compound containing a sulfonate group or a cyclic compound containing a sulfate group.
[0022] Furthermore, the second additive is selected from at least one of vinyl sulfate, methylene disulfonate, 1,3-propane sulfonyl lactone, and propenyl-1,3-sulfonyl lactone.
[0023] Furthermore, the weight percentage of the first additive in the electrolyte is 0.05% to 2%.
[0024] Furthermore, the second additive has a weight percentage of 0.1% to 3% in the electrolyte.
[0025] Furthermore, the weight ratio of the first additive to the second additive is (0.1~3):1.
[0026] Furthermore, the first additive has a weight percentage of 0.5% to 1% in the electrolyte.
[0027] Furthermore, the second additive has a weight percentage of 0.5-1.5% in the electrolyte.
[0028] Furthermore, the weight ratio of the first additive to the second additive is (0.3~1):1.
[0029] Furthermore, the solvent is selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, methyl acetate, propyl propionate, and acetonitrile.
[0030] Further, the solvent is ethylene carbonate and methyl ethyl carbonate; more preferably, the weight ratio of ethylene carbonate to methyl ethyl carbonate is (0.3~2):1.
[0031] Furthermore, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate)borate, and lithium di(fluorooxalate)borate.
[0032] Furthermore, the lithium salt is lithium hexafluorophosphate and lithium difluorosulfonylimide.
[0033] Furthermore, the weight ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is (1~10):1.
[0034] Furthermore, the concentration of lithium salt in the electrolyte is 0.8~1.5 mol / L.
[0035] Furthermore, the positive electrode sheet includes a positive electrode active material; the positive electrode active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel manganese oxide.
[0036] According to a second aspect of this application, a method for preparing the above-mentioned electrolyte is provided, wherein lithium salt, a first additive, a second additive and a solvent are mixed to obtain an electrolyte.
[0037] According to a third aspect of this application, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte is the electrolyte described above or an electrolyte prepared by the preparation method described above.
[0038] Compared with the prior art, this application has the following beneficial effects:
[0039] This application provides an electrolyte comprising a first additive containing isocyanate and nitrile groups in its molecular structure. The isocyanate group contains a nitrogen atom with a lone pair of electrons, which can remove water and HF from the electrolyte, preventing HF from attacking the CEI and causing the dissolution of transition metals and the destruction of the material structure. At the same time, the isocyanate group has high electrochemical reactivity and can participate in the film-forming reaction on the positive and negative electrode surfaces to form a good interfacial film. The nitrile group has a very strong complexing force with the transition metal on the surface of the positive electrode material, and its coordination effect can form CEI before formation, inhibiting the oxidative decomposition of the electrolyte and the dissolution of transition metal elements from the positive electrode.
[0040] The electrolyte provided in this application also includes a second additive containing sulfur, including sulfonate ester groups or sulfate ester groups. Sulfonate ester or sulfate ester-based electrolyte additives have certain advantages such as reducing impedance, suppressing gas generation, and improving performance at room temperature and high temperature. However, some sulfur-based additives, such as vinyl sulfate (DTD) and methylene disulfonate (MMDS), are prone to generating acidic substances during cycling or storage, leading to electrolyte discoloration and battery performance degradation. The first additive in this application has dehydration and deacidification functions, which can inhibit the generation of acidic substances by the second additive. The synergistic effect of the two additives fully utilizes their respective functions while avoiding their respective shortcomings, resulting in excellent synergistic effects. This ensures good compatibility between the electrolyte and the ternary cathode material, improving the electrochemical performance of the lithium-ion battery. Detailed Implementation
[0041] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.
[0042] As mentioned in the background section, ternary cathode materials and electrolytes have poor compatibility. The high voltage plateau and surface active sites of ternary materials easily lead to the oxidative decomposition of the electrolyte. Simultaneously, HF in the electrolyte attacks the CEI and causes transition metal dissolution. The dissolved transition metals deposit on the negative electrode, increasing battery impedance and ultimately degrading the cycle performance of the ternary cathode battery. Therefore, this application designs an electrolyte that effectively complements ternary cathode materials.
[0043] According to one aspect of this application, an electrolyte is provided, comprising a lithium salt, a first additive, a second additive, and a solvent; wherein the first additive is a compound having isocyanate substituents and nitrile substituents in its molecular structure; and the second additive is a sulfur-containing heterocyclic compound.
[0044] This application provides an electrolyte comprising a first additive containing isocyanate and nitrile groups in its molecular structure. The isocyanate group contains a nitrogen atom with a lone pair of electrons, which can remove water and HF from the electrolyte, preventing HF from attacking the CEI film and causing the dissolution of the transition metal in the ternary cathode material and the destruction of the material structure. At the same time, the isocyanate group has high electrochemical reactivity and can participate in the film-forming reaction on the positive and negative electrode surfaces to form a good interfacial film. The nitrile group has a strong complexing force with the transition metal on the surface of the cathode material, and its coordination effect can form a CEI film before formation, inhibiting the oxidative decomposition of the electrolyte and the dissolution of the transition metal elements in the cathode. The electrolyte of this application also includes a second additive containing sulfur, including sulfonate groups or sulfate groups. Electrolyte additives containing sulfonate groups or sulfate groups have certain advantages such as reducing impedance, suppressing gas generation, and improving performance at room temperature and high temperature. However, additives such as vinyl sulfate (DTD) and methylene disulfonate (MMDS) are prone to generating acidic substances during cycling or storage, which leads to electrolyte discoloration and battery performance degradation. The first additive of this application has the function of removing water and acid, which can inhibit the generation of acidic substances by the second additive. The two additives work synergistically, giving full play to their respective functions and avoiding their respective disadvantages, resulting in excellent synergistic effect. This makes the electrolyte and ternary cathode material have good compatibility and improves the electrochemical performance of lithium-ion batteries.
[0045] To ensure the first additive effectively removes water and acid, protects the ternary cathode material, and avoids other adverse effects, a more suitable molecular structure is selected. In some embodiments, the first additive is a C5-C10 cyclic compound or a C3-C10 chain compound carrying isocyanate and nitrile substituents. In addition to the isocyanate and nitrile substituents, the hydrogen atoms at other carbon positions in the C5-C10 cyclic compound or the C3-C10 chain compound are optionally substituted with the following groups: halogens, substituted or unsubstituted C1-C6 alkyl groups, substituted or unsubstituted C1-C6 alkoxy groups. Further, the first additive is a six-membered ring compound carrying an isocyanate substituent and a nitrile substituent, and in addition to the isocyanate substituent and the nitrile substituent, the other carbon hydrogen atoms of the six-membered ring compound are optionally substituted with the following groups: halogen, substituted or unsubstituted C1~C6 alkyl, substituted or unsubstituted C1~C6 alkoxy; further still, the six-membered ring compound is a benzene ring; further still, the molecular structure of the first additive carries one isocyanate substituent and one nitrile substituent; further still, the isocyanate substituent and the nitrile substituent are located at the para, meta, or ortho positions of the benzene ring.
[0046] Specifically, the first additive may be selected from at least one of the compounds with the structures shown in Formulas 1 to 3;
[0047] ;
[0048] Among them, R1~R in equations 1 to 3 12 Each is independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy; optionally, R1-R 12 Each is independently selected from hydrogen; optionally, the halogen is fluorine or chlorine; for example, the substituted C1-C6 alkyl group is a fluorine-substituted C1-C6 alkyl group; the substituted C1-C6 alkoxy group is a fluorine-substituted C1-C6 alkoxy group; and for example, R1-R 12 Each is independently selected from fluorine-substituted C1-C3 alkyl groups, such as fluorine-substituted methyl groups.
[0049] More specifically, the first additive may be selected from at least one of compounds 1 to 9;
[0050] ;
[0051] The nine specific compounds selected in this application contain isocyanate and nitrile groups, which can better remove water and HF from the electrolyte, prevent HF from attacking the CEI and causing the dissolution of transition metals in the ternary cathode material and the destruction of the material structure; at the same time, the isocyanate group has high electrochemical reactivity and can participate in the film-forming reaction on the positive and negative electrode surfaces to form a good interfacial film; the nitrile group has a very strong complexing force with the transition metal on the surface of the cathode material, and its coordination effect can form CEI before formation, inhibiting the oxidative decomposition of the electrolyte and the dissolution of transition metal elements in the cathode; preferably, at least one of compound 1 to compound 3 can be selected.
[0052] In some embodiments, the second additive is a cyclic compound containing a sulfonate group or a cyclic compound containing a sulfate group; specifically, the second additive is selected from at least one of vinyl sulfate, methylene disulfonate, 1,3-propane sulpholactone, and propenyl-1,3-sulfonate lactone. The sulfonate or sulfate group compounds selected in this application as the second additive can better reduce impedance, suppress gas generation, and improve performance at room temperature and high temperature. When additives such as vinyl sulfate (DTD) and methylene disulfonate (MMDS) generate acidic substances during circulation or storage, the matching first additive utilizes its dehydration and deacidification functions to better suppress the acidic substances generated by the second additive, thus ensuring good compatibility between the electrolyte and the ternary cathode material.
[0053] To fully utilize the first additive for dehydration, acid removal, and protection of the ternary cathode material, and to complement the second additive in suppressing side reactions, the amount of the first additive is strictly controlled. In some embodiments, the weight percentage of the first additive in the electrolyte is 0.05% to 2%; for example, any value or range between 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.25%, 1.5%, 1.8%, and 2%; or, for example, 0.5% to 1%; or, for example, 0.5% to 0.8%. Controlling the amount of the first additive within the above range allows the isocyanate and nitrile groups to fully participate in the formation of the SEI or CEI film, forming an effective protective film on the electrode surface without affecting lithium-ion transport performance. An appropriate amount of the first additive can also effectively remove moisture and HF, protect the transition metal, and suppress side reactions between the electrolyte and the cathode material. Furthermore, the amount of the first additive must be matched with the amount of the second additive to suppress other side reactions.
[0054] To further optimize the overall battery performance, a suitable amount of a second additive is added to the electrolyte. In some embodiments, the weight percentage of the second additive in the electrolyte is 0.1% to 3%; any value or a range between any two of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.25%, 1.5%, 1.8%, 2%, 2.5%, 2.5%, 2.8%, and 3%; for example, 0.5% to 1.5%, and more specifically, 0.8% to 1.2%. Simultaneously, the weight ratio of the first additive to the second additive is (0.1 to 3):1; for example, (0.3 to 1):1. Controlling the amount of the second additive within the above range balances its advantages of impedance reduction and degassing with its disadvantage of easy acid formation at high temperatures, thus matching the amount of the first additive. Controlling the amounts of both additives within the above range ensures that the first additive can eliminate the acid formation caused by the second additive, promote CEI film formation, and protect the ternary cathode material without causing other negative effects.
[0055] To improve battery cycle stability, high and low temperature performance, and safety, a suitable non-aqueous solvent, such as an ester solvent, is selected. In some embodiments, the solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate, ethyl methyl carbonate (EMC), dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, methyl acetate, propyl propionate, and acetonitrile. The weight ratio of EC to EMC is (0.3~2):1. For example, EC to EMC is any value from 0.3, 0.5, 0.8, 1.0, 1.5, 2, or any range between two values. In addition to promoting lithium salt dissolution, improving electrolyte fluidity, and accelerating battery charge and discharge speeds, the aforementioned ester solvents also contribute to the formation of stable solid electrolyte interfacial films, such as SEI films. Among them, EC is more conducive to the formation of stable SEI films, improving battery cycle performance and lifespan; EMC can improve electrolyte fluidity, thereby increasing lithium ion migration rate and accelerating battery charge and discharge speeds. When the two are mixed in the above proportions, the viscosity and dielectric constant in the electrolyte can be balanced, ensuring both lithium salt dissolution and electrolyte fluidity, thus improving the battery's fast charging performance and low-temperature performance.
[0056] To provide high conductivity and good solubility, a suitable electrolyte lithium salt is selected; in some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate. For example, the lithium salt is lithium hexafluorophosphate (LiPF6) and the lithium bis(fluorosulfonyl)imide (LiFSI); wherein, the weight ratio of LiPF6:LiFSI is (1 to 10):1, for example (5 to 9):1. Again, for example, the lithium salt concentration for formulating the electrolyte solution is 0.8 to 1.5 mol / L. Selecting lithium salts of the above types all have good solubility, have good stability within a suitable electrochemical window, and have high lithium ion conductivity; wherein using LiPF6:LiFSI in the above ratio for compounding not only can improve the overall conductivity of the electrolyte, but also helps to form stable and uniform SEI and CEI films, reduce the decomposition of the electrolyte solution, improve the battery cycle performance, and at the same time, also has high thermal stability, reducing side reactions and gas generation at high temperatures of the battery.
[0057] According to the second aspect of the present application, a method for preparing the above electrolyte solution is provided, by mixing a lithium salt, a first additive, a second additive, and a solvent to obtain the electrolyte solution.
[0058] According to the third aspect of the present application, a lithium ion battery is provided, which includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte solution; the electrolyte solution is the above electrolyte solution or the electrolyte solution prepared by the above preparation method; wherein the separator and the electrolyte solution are disposed between the positive electrode plate and the negative electrode plate.
[0059] In some embodiments, the positive electrode plate includes a positive electrode active material; the positive electrode active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel manganese oxide; wherein, the molecular formula of the lithium nickel cobalt manganese oxide positive electrode material is LiNi x Co y Mn z O2, wherein, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1.
[0060] In some embodiments, the ratio between the injection amount of the electrolyte solution and the capacity of the lithium ion battery is 2.5 to 3.5; wherein, the unit of the injection amount of the electrolyte solution is g, and the unit of the capacity of the lithium ion battery is Ah. The charging cut-off voltage of the lithium ion battery ≥ 4.2V. The above designed injection amount, battery capacity, and charging cut-off voltage of the lithium ion battery of the present application can achieve the best comprehensive performance of the battery.
[0061] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.
[0062] The compound raw materials used in the embodiments of this application are all prior art and commercially available, as follows:
[0063]
[0064] The abbreviations of the technical terms used in this application are explained below:
[0065] DTD: Vinyl sulfate; MMDS: Methylene disulfonate; PS: 1,3-propanesulfonyl lactone; PST: Propylene-1,3-sulfonyl lactone;
[0066] EC: Ethylene carbonate; EMC: Ethyl methyl carbonate;
[0067] LiPF6: Lithium hexafluorophosphate; LiFSI: Lithium difluorosulfonylimide.
[0068] Example 1
[0069] The lithium-ion electrolyte formulation is as follows: 0.5 wt% of the first additive (compound 1), 1 wt% of the second additive (DTD), 14 wt% of the lithium salt (LiPF6:LiFSI=12.5%:1.5%), and the balance is solvent (EC:EMC=3:7), totaling 100%; the concentration of lithium salt in the electrolyte is 1.1 mol / L; see Table 1 for details.
[0070] Example 2
[0071] The difference between Example 2 and Example 1 is that the second additive is replaced with MMDS; see Table 1 for details.
[0072] Example 3
[0073] The difference between Example 3 and Example 1 is that the second additive is replaced with PS; see Table 1 for details.
[0074] Example 4
[0075] Example 4 differs from Example 1 in that the second additive is replaced with PST; see Table 1 for details.
[0076] Example 5
[0077] Example 5 differs from Example 1 in that the first additive is replaced with compound 2; see Table 1 for details.
[0078] Example 6
[0079] Example 6 differs from Example 1 in that the first additive is replaced with compound 3; see Table 1 for details.
[0080] Example 7
[0081] Example 7 differs from Example 1 in that the first additive is replaced with compound 4; see Table 1 for details.
[0082] Example 8
[0083] Example 8 differs from Example 1 in that the first additive is replaced with compound 5; see Table 1 for details.
[0084] Example 9
[0085] Example 9 differs from Example 1 in that the first additive is replaced with compound 6; see Table 1 for details.
[0086] Example 10
[0087] Example 10 differs from Example 1 in that the first additive is replaced with compound 1 and compound 4 in a weight ratio of 1:1; the other steps are the same.
[0088] Example 11
[0089] Example 11 differs from Example 1 in that the first additive is replaced with compound 1 and compound 5 in a weight ratio of 1:1; the other steps are the same.
[0090] Example 12
[0091] Example 12 differs from Example 1 in that the first additive is replaced with compounds 7, 8 and 9 in a weight ratio of 1:1:1; the other steps are the same.
[0092] Example 13
[0093] The difference between Example 13 and Example 1 is that the amount of the first additive added is replaced with 0.05 wt%; see Table 1 for details.
[0094] Example 14
[0095] The difference between Example 14 and Example 1 is that the amount of the first additive added is replaced with 1 wt%; see Table 1 for details.
[0096] Example 15
[0097] The difference between Example 15 and Example 1 is that the amount of the first additive added is replaced with 2 wt%; see Table 1 for details.
[0098] Example 16
[0099] The difference between Example 16 and Example 1 is that the amount of the second additive added is replaced with 0.1 wt%; see Table 1 for details.
[0100] Example 17
[0101] The difference between Example 17 and Example 1 is that the amount of the second additive added is replaced with 0.5 wt%; see Table 1 for details.
[0102] Example 18
[0103] The difference between Example 18 and Example 1 is that the amount of the second additive added is replaced with 1.5 wt%; see Table 1 for details.
[0104] Example 19
[0105] The difference between Example 19 and Example 1 is that the amount of the second additive added is replaced with 3 wt%; see Table 1 for details.
[0106] Comparative Example 1
[0107] The difference between Comparative Example 1 and Example 1 is that the electrolyte does not contain 0.5 wt% of the first additive (compound 1), and the amount of the first additive is made up by the solvent, which is 85 wt%, for a total of 100%; see Table 1 for details.
[0108] Comparative Example 2
[0109] The difference between Comparative Example 2 and Example 2 is that the electrolyte does not contain 0.5 wt% of the first additive (compound 1), and the amount of the first additive is made up by the solvent, which is 85 wt%, for a total of 100%; see Table 1 for details.
[0110] Comparative Example 3
[0111] The difference between Comparative Example 3 and Example 3 is that the electrolyte does not contain 0.5 wt% of the first additive (compound 1), and the amount of the first additive is made up by the solvent, which is 85 wt%, for a total of 100%; see Table 1 for details.
[0112] Comparative Example 4
[0113] The difference between Comparative Example 4 and Example 4 is that the electrolyte does not contain 0.5 wt% of the first additive (compound 1), and the amount of the first additive is made up by the solvent, which is 85 wt%, for a total of 100%; see Table 1 for details.
[0114] Comparative Example 5
[0115] The difference between Comparative Example 5 and Example 1 is that the electrolyte does not contain 1 wt% of the second additive (DTD), and the amount of the second additive is made up by the solvent, which is 85.5 wt%, for a total of 100%; see Table 1 for details.
[0116] Comparative Example 6
[0117] The difference between Comparative Example 6 and Example 7 is that the electrolyte does not contain 1 wt% of the second additive (DTD), and the amount of the second additive is made up by the solvent, which is 85.5 wt%, for a total of 100%; see Table 1 for details.
[0118] Comparative Example 7
[0119] The difference between Comparative Example 7 and Example 8 is that the electrolyte does not contain 1 wt% of the second additive (DTD), and the amount of the second additive is made up by the solvent, which is 85.5 wt%, for a total of 100%; see Table 1 for details.
[0120] Comparative Example 8
[0121] The difference between Comparative Example 8 and Example 9 is that the electrolyte does not contain 1 wt% of the second additive (DTD), and the amount of the second additive is made up by the solvent, which is 85.5 wt%, for a total of 100%; see Table 1 for details.
[0122] Application Example 1
[0123] The non-aqueous electrolytes prepared in each embodiment and comparative example are used to prepare lithium-ion batteries. Specific methods include:
[0124] Step (1) Preparation of positive electrode:
[0125] LiNi cathode 0.8 Co 0.1 Mn 0.1 O2 powder, conductive carbon black, polyvinylidene fluoride (PVDF), and N,N-dimethylpyrrolidone (NMP) were mixed to prepare a uniform slurry. The slurry was uniformly coated onto aluminum foil and dried in a blower dryer at 70°C for 1 hour, then transferred to a vacuum drying oven and dried at 120°C for 12 hours to obtain LiNi. 0.8 Co 0.1 Mn 0.1 O2 positive electrode. In the dried electrode, LiNi... 0.8 Co 0.1 Mn 0.1 O2 accounts for 80% of the total coating, conductive carbon black accounts for 10%, and polyvinylidene fluoride accounts for 10%. The resulting electrode sheet is then cut into a 14mm diameter disc to serve as the positive electrode.
[0126] Step (2) Preparation of negative electrode:
[0127] Graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed to form a uniform slurry. The slurry was then uniformly coated onto copper foil and dried in a blower dryer at 70°C for 1 hour, followed by drying in a vacuum drying oven at 120°C for 12 hours to obtain the graphite anode material. In the dried electrode, graphite accounted for 80% of the total coating, conductive carbon black for 10%, sodium carboxymethyl cellulose for 5%, and styrene-butadiene rubber for 5%. The resulting electrode was then cut into 14mm diameter discs to serve as the anode.
[0128] Step (3) Electrolyte preparation:
[0129] According to the electrolyte formulations of each embodiment and comparative example, in an argon atmosphere glove box with both water and oxygen content less than 1 ppm, lithium salt is first dissolved in a mixed solvent, then the first additive and the second additive are added, and the mixture is stirred evenly to obtain the electrolyte.
[0130] Step (4) Lithium-ion battery preparation:
[0131] Using the positive and negative electrode materials from steps (1) and (2) above as working electrodes, CR2025 coin cells were assembled in an argon-atmospheric glove box. The assembly sequence was as follows: positive electrode shell, positive electrode sheet, 40 μL electrolyte, separator, 40 μL electrolyte, negative electrode sheet, gasket, spring sheet, negative electrode shell, and then sealed with a sealing machine. After assembly, the cells were allowed to stand for 12 hours for electrochemical performance testing.
[0132] Performance testing:
[0133] The battery performance of each embodiment and comparative example assembled in Use Case 1 was tested, and the test results are shown in Table 2.
[0134] (1) Room temperature cycling test:
[0135] At 25°C, the battery was charged to 4.3V with a current density of 0.1C and discharged to 2.7V with the same current density, and this cycle was repeated 3 times as the battery formation stage.
[0136] After the formation stage is completed, the battery is charged to 4.3V at 25°C with a current density of 1C, and then discharged to 2.7V with the same current density. This cycle is repeated 100 times as the battery's cycle stage.
[0137] (2) High-temperature cycling test:
[0138] At 45°C, the battery is charged to 4.3V with a current density of 0.1C and discharged to 2.7V with the same current density, and this cycle is repeated 3 times as the battery formation stage.
[0139] After the formation stage is completed, the battery is charged to 4.3V at 45°C with a current density of 1C, and then discharged to 2.7V with the same current density. This cycle is repeated 100 times as the battery's cycle stage.
[0140] The capacity retention rate after cycling is calculated as follows: Capacity retention rate = Discharge specific capacity in the 100th cycle of the cycling phase / Discharge specific capacity in the 1st cycle of the cycling phase.
[0141] Table 1
[0142]
[0143] Table 2
[0144]
[0145] Table 2 shows that, compared to Comparative Examples 1-8, Examples 1-19 all exhibited higher capacity retention at room temperature, indicating that the simultaneous addition of the first and second additives has a good synergistic effect, which is even more pronounced at high temperatures. This is because the DTD and MMDS in the second additive readily generate acidic substances at high temperatures. The first additive, containing isocyanate and nitrile groups, inhibits the decomposition and acid production of the second additive. Simultaneously, the nitrile groups of the first additive complex with the transition metal on the cathode surface, forming a good CEI. Therefore, the examples containing the first additive exhibit better cycle stability.
[0146] In Comparative Examples 1 to 4, no first additive was added to the electrolyte, only the second additive was added. Under high temperature conditions, the DTD and MMDS of the second additive easily produced acidic substances, which affected the electrochemical performance of the battery and significantly reduced the battery capacity retention rate.
[0147] In Comparative Examples 5 to 8, only the first additive was added to the electrolyte, without the second additive. The isocyanate groups of the first additive can remove water and HF from the electrolyte, preventing HF from attacking the CEI and causing the dissolution of transition metals and the destruction of the material structure. Simultaneously, the isocyanate groups have high electrochemical reactivity and can participate in the film-forming reaction on the positive and negative electrode surfaces, forming a good interfacial film. The nitrile groups have a strong complexing force with the transition metals on the surface of the positive electrode material, and their coordination effect can form CEI before formation, inhibiting the oxidative decomposition of the electrolyte and the dissolution of transition metal elements from the positive electrode. The second additive contains sulfur, which has certain advantages in reducing impedance, suppressing gas generation, and improving performance at room temperature and high temperature. When the second additive is absent, electrolyte impedance and gas generation will reduce battery performance.
[0148] Therefore, by adding the first additive and the second additive simultaneously, the two additives work synergistically, giving full play to their respective functions while avoiding their respective shortcomings, resulting in excellent synergistic effects. This also ensures good compatibility between the electrolyte and the ternary cathode material, thereby improving the electrochemical performance of the lithium-ion battery.
[0149] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.
[0150] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. An electrolyte, characterized in that, The electrolyte comprises a lithium salt, a first additive, a second additive, and a solvent; wherein the first additive is a compound having isocyanate substituents and nitrile substituents in its molecular structure; and the second additive is a sulfur-containing heterocyclic compound.
2. The electrolyte according to claim 1, characterized in that, The first additive is a C5-C10 cyclic compound or a C3-C10 chain compound carrying the isocyanate substituent and the nitrile substituent, and in addition to the isocyanate substituent and the nitrile substituent, the hydrogen atoms at other carbon positions of the C5-C10 cyclic compound or the C3-C10 chain compound may optionally be substituted by the following groups: halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy; Preferably, the first additive is a six-membered cyclic compound carrying the isocyanate substituent and the nitrile substituent, and in addition to the isocyanate substituent and the nitrile substituent, the other carbon hydrogen atoms of the six-membered cyclic compound are optionally substituted with the following groups: halogen, substituted or unsubstituted C1~C6 alkyl, substituted or unsubstituted C1~C6 alkoxy. More preferably, the six-membered cyclic compound is a benzene ring; More preferably, the molecular structure of the first additive carries one isocyanate substituent and one nitrile substituent; More preferably, the isocyanate substituent and the nitrile substituent are located at the para, meta, or ortho positions of the six-membered cyclic compound.
3. The electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of the compounds with the structures shown in Formulas 1 to 3; ； Among them, R1~R 12 Each is independently selected from any one of hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy; Preferably, the substituted C1-C6 alkyl group is a fluorinated C1-C6 alkyl group; Preferably, R1~R 12 Each is independently selected from hydrogen.
4. The electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of compounds 1 to 9; ； Preferably, the first additive is selected from at least one of compound 1 to compound 3.
5. The electrolyte according to any one of claims 1 to 4, characterized in that, The second additive is a cyclic compound containing a sulfonate group or a cyclic compound containing a sulfate group; Preferably, the second additive is selected from at least one of vinyl sulfate, methylene disulfonate, 1,3-propane sulfonyl lactone, and propenyl-1,3-sulfonyl lactone.
6. The electrolyte according to any one of claims 1 to 5, characterized in that, The first additive has a weight percentage of 0.05% to 2% in the electrolyte; And / or, the second additive has a weight percentage of 0.1% to 3% in the electrolyte; And / or, the weight ratio of the first additive to the second additive is (0.1~3):
1.
7. The electrolyte according to any one of claims 1 to 5, characterized in that, The first additive has a weight percentage of 0.5% to 1% in the electrolyte; And / or, the second additive has a weight percentage of 0.5% to 1.5% in the electrolyte; And / or, the weight ratio of the first additive to the second additive is (0.3~1):
1.
8. The electrolyte according to any one of claims 1 to 7, characterized in that, The solvent is selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, methyl acetate, propyl propionate, and acetonitrile; preferably, the solvent is ethylene carbonate and methyl ethyl carbonate; more preferably, the weight ratio of ethylene carbonate to methyl ethyl carbonate is (0.3~2):
1. And / or, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate)borate, and lithium di(oxalate)borate; preferably, the lithium salt is the lithium hexafluorophosphate and the lithium bis(fluorosulfonyl)imide; more preferably, the weight ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is (1~10):1; And / or, the concentration of the lithium salt in the electrolyte is 0.8~1.5 mol / L.
9. A method for preparing an electrolyte according to any one of claims 1 to 8, characterized in that, The electrolyte is obtained by mixing lithium salt, first additive, second additive and solvent.
10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; characterized in that, The electrolyte is the electrolyte according to any one of claims 1 to 8 or the electrolyte prepared by the preparation method according to claim 9; Preferably, the positive electrode sheet includes a positive electrode active material; the positive electrode active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel manganese oxide.