Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention discloses a lithium ion battery electrolyte and a lithium ion battery, and belongs to the technical field of lithium ion battery materials. The electrolyte is composed of an organic solvent, a lithium salt and an additive, the additive is one or more selected from a structural formula I, and R1 and R2 are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl and substituted or unsubstituted C2-C6 unsaturated alkyl. The electrolyte additive disclosed by the invention can be adsorbed on the surface of a positive electrode material, optimizes the composition of an interfacial film and inhibits the electrolyte from being decomposed on the surface of a positive electrode, so that the structural stability of the interfacial film is improved, and the electrolyte disclosed by the invention can remarkably improve the cyclicity of a lithium ion battery under high voltage.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery materials, and in particular relates to a lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles, energy storage systems, mobile power supplies, smart homes, smart wearable devices and other fields due to their high energy density, long cycle life and environmental protection. With the advancement of technology and the growth of demand, lithium-ion batteries play an important role in promoting global clean energy and sustainable development. In order to meet the market demand for high energy density of lithium-ion batteries, the charging cut-off voltage of the battery is constantly increasing. However, as the charging voltage of the positive electrode material continues to increase, such as when it reaches above 4.4V, the oxidation reaction of the organic solvent of the electrolyte on the surface of the positive electrode material becomes more serious, resulting in an increase in the internal resistance of the lithium-ion battery and deterioration of the cycle performance; in addition, the dissolution problem of transition metal ions is also more prominent. The dissolved transition metal is reduced and deposited on the negative electrode side to destroy the SEI film, which will further deteriorate the battery performance.

[0003] Therefore, there is an urgent need to further optimize the electrolyte to solve the deficiencies of existing technical problems and adapt to high-voltage batteries. Summary of the invention

[0004] One of the purposes of the present invention is to provide a lithium ion battery electrolyte to solve the problem of oxidative decomposition in lithium ion electrolyte;

[0005] A second object of the present invention is to provide a lithium ion battery, which includes the lithium ion battery electrolyte, to solve the problem of poor cycle performance of existing lithium ion batteries.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] In a first aspect, a lithium ion battery electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the additive is selected from one or more compounds of formula I;

[0008]

[0009] Wherein, R1 and R2 are each independently selected from hydrogen (-H), halogen (-X, X=F, Cl, Br, I), substituted or unsubstituted C1~C6 alkyl, substituted or unsubstituted C2~C6 unsaturated hydrocarbon group.

[0010] Furthermore, the C1-C6 alkyl group is an alkyl group having 1 to 6 carbon atoms, and the alkyl group may be a chain alkyl group or a cyclic alkyl group; specifically, the C1-C6 alkyl group includes but is not limited to methyl, ethyl, propyl, butyl, pentyl, cyclopentyl or ethyl.

[0011] Furthermore, the C2-C6 unsaturated hydrocarbon group is an unsaturated hydrocarbon group having 1 to 6 carbon atoms, and the unsaturated hydrocarbon group may be a cyclic alkenyl group, a phenyl group, or a chain alkenyl group or a chain alkynyl group; specifically, the C2-C6 unsaturated hydrocarbon group includes but is not limited to vinyl or propenyl.

[0012] Furthermore, the substituted C1-C6 alkyl and substituted C2-C6 unsaturated hydrocarbon groups are specifically alkyl or unsaturated hydrocarbon groups in which one or more hydrogen atoms are replaced by other atoms or groups (referred to as substituents), and the substituents include halogen (-X, X=F, Cl, Br, I), hydroxyl (-OH), amino (-NH2), nitro (-NO2), alkoxy (-OR) or aryl; for example, a methyl group may be replaced by a fluorine atom to form a fluoromethyl group (-CH2F), or by an amino group to form an aminomethyl group (-CH2NH2);

[0013] The unsubstituted C1-C6 alkyl group and the unsubstituted C2-C6 unsaturated hydrocarbon group specifically refer to an alkyl group or an unsaturated hydrocarbon group in which no hydrogen atom is replaced by other atoms or groups.

[0014] Furthermore, the additive is selected from one or more of Compound A-1 to Compound A-6:

[0015]

[0016] Furthermore, in the lithium ion battery electrolyte, the amount of the additive added is 0.1wt% to 5.0wt% of the total mass of the electrolyte; specifically, the amount of the additive added is 0.1wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt% of the total mass of the electrolyte, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable; further, the amount of the additive added is 0.5wt% to 2.0wt% of the total mass of the electrolyte.

[0017] Further, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate and lithium hexafluoroarsenate.

[0018] Furthermore, in the lithium ion battery electrolyte, the concentration of lithium salt is 0.8 mol / L to 2 mol / L; specifically, the concentration of lithium salt includes but is not limited to 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, and 2.0 mol / L; further, the concentration of lithium salt in the lithium ion battery electrolyte is 0.8 to 1.2 mol / L.

[0019] Further, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, γ-butyrolactone, dioxolane, tetrahydrofuran, dimethyltrifluoroacetamide and dimethyl sulfoxide.

[0020] Furthermore, the lithium-ion battery electrolyte further comprises an auxiliary agent, and the auxiliary agent is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, propylene sulfite and 4-methyl vinyl sulfite;

[0021] And / or, the additive is added in an amount of 1wt% to 10wt% of the total mass of the electrolyte.

[0022] In a second aspect, a lithium ion battery comprises a positive electrode, a negative electrode, a separator and the above-mentioned lithium ion battery electrolyte.

[0023] Furthermore, the maximum charging voltage of the lithium-ion battery is 4.45V.

[0024] Furthermore, the positive electrode includes a positive electrode active material, and the positive electrode active material is one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, nickel cobalt aluminum lithium, lithium-rich layered oxide, and lithium nickel manganese oxide.

[0025] Furthermore, the negative electrode includes a negative electrode active material, and the negative electrode active material is a carbon negative electrode, a silicon negative electrode, a silicon-carbon negative electrode material, and a lithium metal negative electrode.

[0026] Furthermore, the lithium-ion battery can be assembled into a button battery, a soft-pack battery or a cylindrical battery.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention provides a lithium ion battery electrolyte, wherein a dibenzonitrile compound is selected and used as an electrolyte additive, and the electrolyte additive can be adsorbed on the surface of the positive electrode material, thereby forming a stable electrode-electrolyte interface film on the electrode surface, optimizing the composition of the interface film, reducing the surface activity of the positive electrode, thereby inhibiting the oxidative decomposition of the electrolyte on the positive electrode surface, improving the stability of the interface film structure, and improving the antioxidant properties of the electrolyte, which can effectively inhibit the side reactions in the battery and improve the cycle performance of the lithium ion battery at a high charging cut-off voltage. In addition, the preferred auxiliary agent in the present invention is used in combination with the additive to participate in the film formation of the electrolyte on the negative electrode of the battery, protect the negative electrode of the battery, inhibit the side reactions between the electrolyte and the negative electrode, improve the cycle performance, and achieve the effect of synergistically improving the life of the battery.

[0029] 2. The present invention also provides a lithium-ion battery, which has excellent cycle life and safety because it includes the lithium-ion battery electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the accompanying drawings.

[0031] Figure 1 This is a battery cycle performance diagram of the lithium ion battery (Application Example 2) prepared corresponding to Example 2 of the present invention after 300 cycles at 25° C.;

[0032] Figure 2 This is a battery cycle performance diagram of the lithium ion battery (comparative application example 1) prepared in accordance with comparative example 1 of the present invention after 300 cycles at 25°C;

[0033] Figure 3 This is a battery cycle performance diagram of the lithium ion battery (Comparative Application Example 2) prepared in accordance with Comparative Example 2 of the present invention after 300 cycles at 25°C. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] A lithium ion battery electrolyte is prepared by the following steps:

[0036] In a glove box filled with argon (O2 < 0.1ppm, H2O < 0.1ppm), lithium salt is added to an organic solvent to obtain a lithium salt solution with a concentration of 0.8mol / L to 2mol / L; an additive as shown in structural formula I is then added, and finally an auxiliary agent is added and mixed uniformly to obtain a lithium ion battery electrolyte, wherein the amount of the additive added is 0.1wt% to 5.0wt% of the total mass of the lithium ion battery electrolyte; the amount of the auxiliary agent added is 1wt% to 10wt% of the total mass of the lithium ion battery electrolyte.

[0037] In a specific embodiment, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate and lithium hexafluoroarsenate.

[0038] In a specific embodiment, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, γ-butyrolactone, dioxolane, tetrahydrofuran, dimethyltrifluoroacetamide and dimethyl sulfoxide.

[0039] In a specific embodiment, the electrolyte further includes an auxiliary agent, which is selected from one or more of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, propylene sulfite and 4-methyl vinyl sulfite.

[0040] Example 1

[0041] A lithium ion battery electrolyte is prepared by the following steps:

[0042] In a glove box filled with argon (O2<0.1ppm, H2O<0.1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and lithium hexafluorophosphate (LiPF6) is added thereto to obtain a lithium hexafluorophosphate solution with a concentration of 1.0 mol / L; compound A-1 is then added as an additive to the electrolyte; finally, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are added as auxiliary agents, mixed evenly, and a lithium ion electrolyte is obtained;

[0043] Among them, the addition amount of compound A-1 is 0.5wt% of the total mass of the electrolyte (that is, the mass fraction of compound A-1 in the electrolyte); the addition amount of VC is 1wt% of the total mass of the electrolyte, and the addition amount of FEC is 5wt% of the total mass of the electrolyte.

[0044] Embodiment 2 to Embodiment 8

[0045] The chemical structural formulas of the additives in the lithium-ion battery electrolytes provided in Examples 2 to 8 and their content ratios in the electrolytes are shown in Table 1, and their preparation methods are the same as in Example 1.

[0046] Comparative Example 1

[0047] A lithium ion battery electrolyte, which is different from Example 1 in that the additive (compound A-1) and auxiliary agent (VC, FEC) in Example 1 are not added, and the specific ratio is shown in Table 1. The other components and parameters are the same as those in Example 1.

[0048] Comparative Example 2

[0049] A lithium ion battery electrolyte, which is different from Example 1 in that the additive (Compound A-1) in Example 1 is not added. The specific proportions are shown in Table 1, and the remaining components and parameters are the same as those in Example 1.

[0050] Table 1

[0051] Lithium salt / concentration Organic solvents additive Additives Example 1 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 0.5wt%A-1 1wt%VC, 5wt%FEC Example 2 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 1.0wt%A-1 1wt%VC, 5wt%FEC Example 3 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 1.5wt%A-1 1wt%VC, 5wt%FEC Example 4 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 0.5wt%A-2 1wt%VC, 5wt%FEC Example 5 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 0.5wt%A-3 1wt%VC, 5wt%FEC Example 6 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 0.5wt%A-4 1wt%VC, 5wt%FEC Example 7 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 0.5wt%A-5 1wt%VC, 5wt%FEC Example 8 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 0.5wt%A-6 1wt%VC, 5wt%FEC Comparative Example 1 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 —— —— Comparative Example 2 <![CDATA[LiPF6(1.0M)]]> EC:EMC=3:7 —— 1wt%VC, 5wt%FEC

[0052] Application Example 1

[0053] A lithium ion battery is prepared by the following steps:

[0054] (1) Preparation of positive electrode sheet:

[0055] The active material lithium nickel cobalt manganese oxide (NCM), the conductive agent super conductive carbon (SP), and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in a solvent N-methyl-2-pyrrolidone at a mass ratio of 8:1:1, and then the obtained slurry is coated on the current collector carbon-coated foil, and the positive electrode sheet is obtained by slitting, die-cutting, and rolling;

[0056] (2) Preparation of negative electrode sheet:

[0057] The graphite negative electrode, the conductive agent super conductive carbon (SP), and the binder styrene butadiene rubber (SBR) are fully stirred and mixed in a solvent deionized water at a mass ratio of 8:1:1, and then the obtained slurry is coated on the current collector Cu foil, and the negative electrode sheet is obtained after slitting, rolling, and die cutting;

[0058] (3) Preparation of lithium-ion batteries:

[0059] The positive electrode sheet, the separator (the separator used is a polypropylene PP film coated with a nano-aluminum oxide coating, wherein the thickness of the PP film is 12 μm and the thickness of the nano-aluminum oxide coating is 4 μm), and the negative electrode sheet are stacked in sequence according to the process of stacked batteries to obtain a bare battery cell, and then the bare battery cell is pre-packaged in an aluminum-plastic film, and the lithium-ion battery electrolyte prepared in Example 1 is injected and then packaged to obtain a lithium-ion soft-pack battery.

[0060] Application Example 2 to Application Example 8

[0061] The lithium ion batteries provided in Application Examples 2 to 8 are different from those in Application Example 1 in that the electrolytes correspond to the lithium ion electrolytes in Examples 2 to 8, respectively, and the other preparation methods and parameters remain the same.

[0062] Comparative Application Example 1~Comparative Application Example 2

[0063] The lithium ion batteries provided in Comparative Application Examples 1 and 2 are different from those in Application Example 1 in that the electrolytes correspond to the lithium ion electrolytes in Comparative Examples 1 and 2, respectively, and the other preparation methods and parameters remain the same.

[0064] The performance of the lithium-ion batteries prepared in Example 1 to Example 8 and Comparative Example 1 to Comparative Example 2 was tested by the following method:

[0065] At room temperature (25°C), the lithium metal battery is charged and discharged once at 1.0C / 1.0C (the battery charging capacity is C0, the discharge capacity is C1), the upper limit voltage is 4.45V, and then charged and discharged at 1.0C / 1.0C for 300 cycles at room temperature (25°C) (the battery discharge capacity is C2), and the first coulombic efficiency and capacity retention rate are calculated;

[0066] First coulombic efficiency = (C1 / C0) × 100%

[0067] Capacity retention rate = (C2 / C1) × 100%

[0068] The test results are shown in Table 2:

[0069] Table 2

[0070] First coulombic efficiency Capacity retention rate after 300 cycles at room temperature Example 1 Application Example 1 83.0％ 82.1％ Example 2 Application Example 2 83.8％ 84.3％ Example 3 Application Example 3 82.6％ 81.7％ Example 4 Application Example 4 82.9％ 82.0％ Example 5 Application Example 5 82.4％ 81.5％ Example 6 Application Example 6 83.5％ 82.9％ Example 7 Application Example 7 83.2％ 82.3％ Example 8 Application Example 8 82.3％ 80.8％ Comparative Example 1 Comparative application example 1 79.0％ 2.1％ Comparative Example 2 Comparative Application Example 2 79.8％ 62.8％

[0071] The battery cycle performance of the lithium ion battery (Application Example 2) prepared in Example 2 after 300 cycles at 25°C is shown in the figure below: Figure 1 As shown; Comparative Example 1 corresponding to the prepared lithium ion battery (Comparative Application Example 1) at 25 ° C after 300 cycles of battery cycle performance diagram as shown Figure 2As shown; Comparative Example 2 corresponding to the prepared lithium ion battery (Comparative Application Example 2) at 25 ° C after 300 cycles of battery cycle performance diagram as shown Figure 3 shown.

[0072] From Table 2 and Figure 1 , Figure 2 and Figure 3 It can be seen that the electrolytes of Comparative Examples 1 to 2 do not add the electrolyte additives of the present invention, and the first coulombic efficiency and room temperature cycle performance of the corresponding batteries are not ideal, while the lithium ion batteries prepared by the electrolytes of all embodiments have good room temperature cycle performance, which shows that the electrolyte additives proposed by the present invention can optimize the composition of the interface film, form a stable and low-impedance interface film at the interface, and are conducive to improving the cycle performance of the lithium ion battery at high voltage; in addition, the combination of the auxiliary agent and the additive participates in the film formation of the electrolyte at the negative electrode of the battery, protects the negative electrode of the battery, inhibits the side reaction between the electrolyte and the negative electrode, improves the cycle performance, and further increases the life of the battery. From the comparison of the results of Examples 1 to 3, it can be seen that when the content of the additive is 1wt%, the cycle performance of the lithium ion battery is the best. The results show that there is an optimal content of the additive. Too high and too low will lead to a decrease in battery performance. Preferably, the content of the additive of the present invention is about 1wt%, including but not limited to 1.1wt%, 0.9wt%, etc.

[0073] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0074] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium ion battery electrolyte, characterized in that: It includes an organic solvent, a lithium salt, and an additive, wherein the additive is selected from one or more of the compounds of formula I; Wherein, R1 and R2 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 unsaturated hydrocarbon group.

2. A lithium ion battery electrolyte according to claim 1, characterized in that: The additive is selected from one or more of Compound A-1 to Compound A-6:

3. A lithium ion battery electrolyte according to claim 1, characterized in that: In the lithium ion battery electrolyte, the amount of the additive added is 0.1wt% to 5.0wt% of the total mass of the electrolyte.

4. A lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate and lithium hexafluoroarsenate.

5. A lithium ion battery electrolyte according to claim 1, characterized in that: In the lithium ion battery electrolyte, the concentration of lithium salt is 0.8 mol / L to 2 mol / L.

6. A lithium ion battery electrolyte according to claim 1, characterized in that: The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, γ-butyrolactone, dioxolane, tetrahydrofuran, dimethyltrifluoroacetamide and dimethyl sulfoxide.

7. A lithium ion battery electrolyte according to claim 1, characterized in that: The lithium-ion battery electrolyte further includes an auxiliary agent, which is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, propylene sulfite and 4-methyl vinyl sulfite; And / or, the amount of the additive added is 1wt% to 10wt% of the total mass of the lithium ion battery electrolyte.

8. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the lithium ion battery electrolyte according to any one of claims 1 to 7.

9. A lithium ion battery according to claim 8, characterized in that: The maximum charging voltage of the lithium-ion battery is 4.45V.

10. A lithium ion battery according to claim 8, characterized in that: The positive electrode includes a positive electrode active material, which is one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, nickel cobalt manganese oxide, nickel cobalt aluminum lithium, lithium-rich layered oxide, and lithium nickel manganese oxide; the negative electrode includes a negative electrode active material, which is a carbon negative electrode, a silicon negative electrode, a silicon-carbon negative electrode material, and a lithium metal negative electrode.

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