Non-aqueous electrolyte and lithium ion battery thereof

Abstract

The application discloses a non-aqueous electrolyte and a lithium ion battery thereof. The non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, the non-aqueous organic solvent at least comprises a carboxylic acid ester solvent, and the additive comprises a compound A shown in a structural formula 1 and a compound B shown in a structural formula 2, wherein R is selected from halogen, a substituted or unsubstituted C1-C6 hydrocarbon group, and when substituted, the substituent is halogen. In the non-aqueous electrolyte, the compound A and the compound B are contained, a stable interface protection film can be constructed on the negative electrode surface, the reduction decomposition activity of the carboxylic acid ester solvent on the negative electrode interface is significantly reduced, and therefore, on the premise of taking into account the fast charging and low temperature performance, the high temperature storage stability of the lithium iron phosphate lithium ion battery is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a non-aqueous electrolyte and its lithium-ion battery. Background Technology

[0002] Lithium iron phosphate (LFP) cathode materials are widely used in power and energy storage batteries due to their high safety, long cycle life, and cost advantages. However, LFP has inherently low electronic / ionic conductivity, and its lithium-ion insertion / extraction kinetics deteriorate significantly at low temperatures, making its fast-charging capability and low-temperature discharge performance key bottlenecks restricting its further application. In traditional carbonate-based electrolytes, the high-viscosity solvent system is difficult to meet the ion transport requirements of LFP batteries under high-rate and low-temperature conditions.

[0003] In recent years, the introduction of low-viscosity carboxylic acid ester solvents has been considered an effective strategy to improve the low-temperature and fast-charging performance of LFP batteries. Carboxylic acid esters have low viscosity and high dielectric constant, which is beneficial for reducing the bulk impedance of the electrolyte and optimizing the Li... + Solvation structure. However, carboxylic acid ester molecules exhibit high reactivity at the negative electrode interface, especially under high-temperature storage conditions, where they are prone to continuous reductive decomposition. This leads to repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, resulting in irreversible lithium loss and increased internal resistance, ultimately manifesting as a sharp decline in battery capacity. Therefore, effectively suppressing interfacial side reactions at high temperatures while retaining the performance gains of carboxylic acid ester solvents for LFP batteries is a pressing technical challenge in current electrolyte development. Summary of the Invention

[0004] The purpose of this invention is to provide a non-aqueous electrolyte and its lithium-ion battery. The non-aqueous electrolyte contains additive compounds A and B, which can form a stable interface protective film on the negative electrode surface, significantly reducing the reductive decomposition activity of carboxylic acid ester solvents at the negative electrode interface. Thus, while taking into account both fast charging and low-temperature performance, it effectively improves the high-temperature storage stability of lithium iron phosphate lithium-ion batteries.

[0005] To achieve the above objectives, the present invention provides a non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent, and additives. The non-aqueous organic solvent includes at least a carboxylic acid ester solvent, and the additives include compound A shown in structural formula 1 and compound B shown in structural formula 2.

[0006] Structure 1 Structure 2 R is selected from halogenated, substituted or unsubstituted C1~C6 hydrocarbon groups. When substituted, the substituent is halogenated.

[0007] Compared with existing technologies, the non-aqueous electrolyte of the present invention contains additive compounds, namely compound A as shown in structural formula 1 and compound B as shown in structural formula 2. Compound A contains a sulfate ester functional group, which preferentially forms a lithium sulfite-containing component at the negative electrode interface. In the solid electrolyte interface layer, this component can significantly improve the interfacial resistance of lithium ions through the SEI, enhancing the battery's fast-charging performance. Simultaneously, compound B can form a polycyclic oligomer at the negative electrode interface. This oligomeric interfacial film component effectively reduces the reduction reaction of carboxylic esters at the negative electrode interface, improving the high-temperature stability of the carboxylic ester-based electrolyte, thereby improving the battery's high-temperature storage performance. Meanwhile, compounds A and B not only fully utilize their respective film-forming components as additives, but also compound A contains a nitrogen atom center. This electron-deficient component can better attract the electron-rich body brought by oxygen in compound B, allowing the two components to assist and promote each other's reaction during the formation stage. This achieves the function of directional regulation of the interface components, so that the interface components not only contain inorganic sulfide components to enhance the interfacial ion fast charging capability, but also inorganic oligomers to reduce the interfacial reactivity of carboxylic acid esters. As a result, the battery's high-temperature storage performance, room-temperature fast charging performance, and low-temperature performance are all improved.

[0008] As a preferred technical solution, R is selected from fluorine, substituted or unsubstituted C1-C6 alkyl groups, and when substituted, the substituent is fluorine.

[0009] As a preferred technical solution, compound A includes at least one of the following compounds: compound 1 and compound 2.

[0010] Compound 1 (CAS: 2627021-21-8) Compound 2 (CAS: 2627021-26-3).

[0011] As a preferred technical solution, the mass percentage of compound A in the non-aqueous electrolyte is 0.1% to 5.0%. Preferably, the mass percentage of compound A in the non-aqueous electrolyte is 0.5% to 3.0%. Specifically, the mass percentage of compound A in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.5%, 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0012] As a preferred technical solution, the mass percentage of compound B in the non-aqueous electrolyte is 0.1% to 5%. Preferably, the mass percentage of compound B in the non-aqueous electrolyte is 0.3% to 2.0%. Specifically, the mass percentage of compound B in the non-aqueous electrolyte can be, but is not limited to, 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0013] As a preferred technical solution, the mass percentage of the carboxylic acid ester solvent in the non-aqueous electrolyte is 10% to 50%. Preferably, the mass percentage of the carboxylic acid ester solvent in the non-aqueous electrolyte is 20% to 40%. As an example, the mass percentage of the carboxylic acid ester solvent in the non-aqueous electrolyte can be, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0014] As a preferred technical solution, the carboxylic acid ester solvent includes at least one of γ-butyrolactone (GBL), γ-valerolactone (GVL), δ-valerolactone (DVL), methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate (BAC), propyl propionate (PP), and butyl propionate (PRB).

[0015] As a preferred technical solution, the non-aqueous organic solvent also includes carbonate solvents, which include at least one of ethylene carbonate (EC), propylene carbonate (PCA), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and propylene carbonate (PC).

[0016] As a preferred technical solution, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalate-borate)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate-borate (LiDFOB), lithium difluorodioxalate-phosphate (LiDFBP), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0017] As a preferred technical solution, the mass percentage of lithium salt in the non-aqueous electrolyte is 6.5% to 15.5%. Specifically, the mass percentage of lithium salt in the non-aqueous electrolyte can be, but is not limited to, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 12.5%, 13.0%, 14.0%, 15.0%, and 15.5%.

[0018] Another aspect of the present invention provides a lithium-ion battery, comprising a positive electrode material, a negative electrode material, and the aforementioned non-aqueous electrolyte.

[0019] As a preferred technical solution, the cathode material of the present invention is lithium iron phosphate.

[0020] As a preferred technical solution, the anode material includes at least one of carbon-based anode, silicon-based anode, tin-based anode, and lithium anode. Specifically, carbon-based anodes may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; silicon-based anodes may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; tin-based anodes may include tin, tin-carbon, tin-oxygen, and tin metal compounds; lithium anodes may include metallic lithium or lithium alloys. Specifically, lithium alloys may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys. Detailed Implementation

[0021] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0022] It should be noted that compound B, represented by structural formula 2 of the present invention, can be prepared according to the following synthetic route:

[0023] For any other items in the examples and comparative examples where specific conditions are not specified, they can be carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained commercially.

[0024] Example 1 1.1 Preparation of non-aqueous electrolyte: In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), 18 g of diethyl carbonate (DEC), 28 g of propylene carbonate (PC), and 40 g of ethyl acetate (EA) were mixed thoroughly to obtain a mixed solvent, which was then used as an organic solvent. 1 g of compound 1 and 0.5 g of compound B were added to obtain a mixed solution. The mixed solution was sealed and packaged, then frozen in a freezer (-4°C) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), and mixed thoroughly to prepare a non-aqueous electrolyte.

[0025] 1.2 Preparation of the positive electrode: Lithium iron phosphate (LiFePO4), conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) were mixed uniformly at a mass ratio of 96.5:1.5:1:1 to prepare a lithium-ion battery positive electrode slurry of a certain viscosity. This slurry was then coated onto aluminum foil used for current collectors, with a coating weight of 324 g / m². 2 After drying at 85℃, the material is cold-pressed; then it is trimmed, cut into pieces, and slit. After slitting, it is dried at 85℃ for 4 hours under vacuum conditions, and then the tabs are welded to produce a lithium-ion battery positive electrode sheet that meets the requirements.

[0026] 1.3 Preparation of the negative electrode: Artificial graphite was mixed with conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. After thorough mixing, the slurry was coated onto both sides of copper foil, dried, and rolled to obtain the negative electrode sheet, thus producing a lithium-ion battery negative electrode sheet that meets the requirements. 1.4 Preparation of Lithium-ion Batteries: The positive electrode, negative electrode, and separator prepared according to the above process are stacked to form a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm, and a length of 60 mm. The battery is then vacuum-baked at 75°C for 10 hours and injected with the aforementioned non-aqueous electrolyte. After standing for 24 hours, it undergoes formation and capacity testing to produce a lithium-ion battery with a capacity of 1000 mAh.

[0027] The non-aqueous electrolyte formulations of Examples 1-9 and Comparative Examples 1-5 are shown in Table 1. The lithium-ion battery preparation steps of Examples 2-9 and Comparative Examples 1-5 are the same as those of Example 1. Table 1 Formulations of non-aqueous electrolytes in the examples and comparative examples

[0028] The structure of compound C is shown in Table 1.

[0029] Compound C The lithium-ion batteries prepared in the examples and comparative examples were subjected to low-temperature discharge performance tests, high-temperature storage tests, and high-temperature cycling tests, respectively. The specific test conditions are as follows, and the performance test results are shown in Table 2.

[0030] Low-temperature discharge performance test of lithium-ion batteries Under normal temperature (25℃) conditions, a lithium-ion battery is subjected to a 0.5C / 0.5C charge and discharge cycle (discharge capacity denoted as C0), with an upper limit voltage of 3.65V. Then, the battery is charged to 3.65V under constant current and constant voltage conditions at 0.5C. The lithium-ion battery is then placed in a -20℃ low-temperature chamber for 4 hours and discharged at -20℃ at 0.5C (discharge capacity denoted as C1). The low-temperature discharge rate of the lithium-ion battery is calculated using the following formula: Low-temperature discharge rate = C1 / C0 × 100% High-temperature storage test of lithium-ion batteries Under normal temperature (25℃) conditions, a lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C0), with an upper limit voltage of 3.65V. The battery was then placed in a 60℃ oven for 30 days, removed, and placed in a 25℃ environment for a 0.3C discharge, with the discharge capacity recorded as C1. Finally, the lithium-ion battery was subjected to another 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C2). The capacity retention rate, capacity recovery rate, and thickness expansion rate of the lithium-ion battery were calculated using the following formulas: Capacity retention rate = C1 / C0 × 100% Capacity recovery rate = C2 / C0 × 100% Lithium-ion battery room temperature cycle test The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 8C until the voltage reached 3.65V, followed by constant voltage charging at 3.65V until the current reached 0.05C. Finally, it was discharged at a constant current of 8C until the voltage reached 2.3V. The first discharge capacity was recorded as C0. This constitutes one charge-discharge cycle. Then, 800 cycles of 8C / 8C charging and discharging were performed at 25°C, and the discharge capacity was recorded as C1.

[0031] Capacity retention rate = C1 / C0 × 100% Table 2 Performance test results of lithium-ion batteries in the examples and comparative examples

[0032] As shown in Table 2, compared to Comparative Example 1, the lithium-ion batteries of Examples 1-9 of this invention exhibit superior overall high-temperature storage performance, low-temperature discharge performance, and room-temperature fast-charging performance. This may be because the non-aqueous electrolyte of this invention contains additive compounds, namely compound A shown in structural formula 1 and compound B shown in structural formula 2. Compound A contains a sulfate ester functional group, which preferentially forms a lithium sulfite-containing component at the negative electrode interface. In the solid electrolyte interface layer, this component can significantly improve the interfacial resistance of lithium ions through the SEI, enhancing the battery's fast-charging performance. Simultaneously, compound B can form a polycyclic oligomer at the negative electrode interface. This oligomeric interfacial film component effectively reduces the reduction reaction of carboxylic acid esters at the negative electrode interface, improving the high-temperature stability of the carboxylic acid ester-based electrolyte, thereby improving the battery's high-temperature storage performance. Meanwhile, compounds A and B not only fully utilize their respective film-forming components as additives, but also compound A contains N atomic centers. This electron-deficient component can better attract the electron-rich oxygen in compound B, allowing the two components to assist and promote each other's reactions during the formation stage. This achieves the function of directional regulation of the interface components, resulting in the presence of inorganic sulfide components to enhance the interfacial ion fast charging capability, as well as inorganic oligomers to reduce the interfacial reactivity of carboxylic acid esters. As a result, the battery's high-temperature storage performance, room-temperature fast charging performance, and low-temperature performance are all improved.

[0033] Further, as shown in Comparative Examples 2-5, the absence of either Compound A or Compound B prevents the simultaneous improvement of the overall performance of lithium-ion batteries in terms of high-temperature storage, room-temperature fast charging, and low-temperature performance. Comparative Example 6 shows that when Compound C replaces Compound B, the lack of an S-containing cyclic molecule in Compound C leads to a stronger binding affinity between Compound C and the fluorine atoms in Compound A. This prevents Compound C from reacting properly at the interface, hindering its interfacial film-forming ability and consequently impairing the control of the battery's high-temperature performance, resulting in reduced high-temperature cycling and storage performance.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A non-aqueous electrolyte, comprising a lithium salt, a non-aqueous organic solvent, and additives, characterized in that, The non-aqueous organic solvent includes at least carboxylic acid ester solvents, and the additive includes compound A shown in structural formula 1 and compound B shown in structural formula 2. Structure 1 Structure 2 R is selected from halogenated, substituted or unsubstituted C1~C6 hydrocarbon groups. When substituted, the substituent is halogenated.

2. The non-aqueous electrolyte according to claim 1, characterized in that, R is selected from fluorine, substituted or unsubstituted C1-C6 alkyl groups, and when substituted, the substituent is fluorine.

3. The non-aqueous electrolyte according to claim 1, characterized in that, Compound A includes at least one of the following compounds: compound 1 and compound 2. Compound 1 and Compound 2.

4. The non-aqueous electrolyte according to claim 1, characterized in that, The mass percentage of compound A in the non-aqueous electrolyte is 0.1% to 5.0%, and the mass percentage of compound B in the non-aqueous electrolyte is 0.1% to 5.0%.

5. The non-aqueous electrolyte according to claim 1, characterized in that, The carboxylic acid ester solvent accounts for 10% to 50% of the mass percentage in the non-aqueous electrolyte.

6. The non-aqueous electrolyte according to claim 1, characterized in that, The carboxylic acid ester solvents include at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent also includes carbonate solvents, which include at least one of ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate.

8. The non-aqueous electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), lithium difluorophosphate, lithium difluorooxalate-borate, lithium difluorodioxalate-phosphate, and lithium bis(oxalate-imide).

9. A lithium-ion battery, characterized in that, It includes positive electrode materials, negative electrode materials, and the non-aqueous electrolyte as described in any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that, The cathode material is lithium iron phosphate.

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