Battery electrolyte and preparation method thereof, and battery

Abstract

The application provides a battery electrolyte, a preparation method thereof and a battery, and relates to the technical field of secondary battery materials.The battery electrolyte comprises a carbonic acid ester solvent, an electrolyte and an electrolyte additive, and the electrolyte additive is selected from squalene and / or squalane.A battery assembled based on the electrolyte can still exhibit high coulomb efficiency and good cycle stability at high voltage, can inhibit the adverse decomposition of the electrolyte, and the additive used is green and inexpensive.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery materials, and particularly relates to an electrolyte for a battery, a preparation method thereof, and a battery. Background Art

[0002] With the reserve crisis of fossil energy and the increasing deterioration of environmental conditions, the development of new energy has attracted more and more attention. The rapid development of electric vehicles and portable electronic products has made lithium-ion batteries a research hotspot. Both technological innovation and growing demand require modification and optimization of lithium-ion batteries. Among all the components constituting a battery, the positive electrode material has high cost and its discharge specific capacity is far lower than that of the negative electrode, which is a key factor restricting the further development of lithium-ion batteries. The optimization and improvement of positive electrode materials will greatly enhance the application prospects of lithium-ion batteries, and in particular, the increase in voltage can greatly improve the energy density of the battery. Among them, high-voltage positive electrode materials such as lithium-rich manganese-based positive electrode materials (xLi₂MnO₃·(1-x)LiMO₂, where M is a transition metal such as Mn, Ni, Co, 0<x<1) and lithium cobalt oxide exhibit high specific energy, low cost and good thermal stability, and have become a research hotspot of positive electrode materials. However, unfavorable decomposition of carbonate-based electrolytes easily occurs under high operating voltage, resulting in uneven accumulation of by-products on the electrode surface and consumption of active lithium ions and electrons. On the other hand, highly oxidized transition metal ions under high voltage easily absorb electrons from electrolyte components, leading to reduced valence state and irreversible phase transition.

[0003] Recently, people have begun to pay attention to the method of using electrolyte additives to form a protective layer on the positive electrode oxide, so as to form a uniform and stable positive electrode-electrolyte interface layer without hindering the interfacial charge transfer reaction. In addition, during the first charging process of the lithium-rich manganese base, the electrochemical activation of the superlattice component Li₂MnO₃ will inevitably release active oxygen, including oxygen (O₂) and superoxide radicals (O₂· — ), the superoxide radicals will react with the ethylene carbonate (EC) solvent in the electrolyte to generate gaseous products, such as CO and CO₂. Under high voltage, the degradation process of the positive electrode-electrolyte interface (such as surface O₂ loss, Li₂CO₃ decomposition and gas generation from the electrolyte, etc.) will lead to increased interface impedance and rapid deterioration of battery cycle performance. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an electrolyte for a battery, a preparation method thereof, and a battery.

[0005] The present invention solves its technical problems by adopting the following technical solutions.

[0006] A first aspect of the present invention provides an electrolyte for a battery, comprising a carbonate-based solvent, an electrolyte and an electrolyte additive, wherein the electrolyte additive is selected from squalene and / or squalane.

[0007] Furthermore, in a preferred embodiment of the present invention, the electrolyte additive has a mass fraction of 0.5% to 5% in the electrolyte.

[0008] Furthermore, in a preferred embodiment of the present invention, the carbonate solvent is selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and dimethyl carbonate.

[0009] Further, in a preferred embodiment of the present invention, the electrolyte is a lithium salt, which is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalateborate, lithium bis(oxalateborate), lithium difluorobis(oxalate)phosphate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, and lithium perchlorate.

[0010] Furthermore, in a preferred embodiment of the present invention, the concentration of the lithium salt in the battery electrolyte is 0.6 to 1.5 mol / L.

[0011] Furthermore, in a preferred embodiment of the present invention, the electrolyte additive further includes one or more of fullerene derivatives and 6-fluoropyridine-3-boronic acid.

[0012] Furthermore, in a preferred embodiment of the present invention, the ratio of the fullerene derivative to the 6-fluoropyridine-3-boronic acid is 1:3 to 6.

[0013] The second invention provides a method for preparing a battery electrolyte as described in any one of the above claims, comprising: mixing the lithium salt and the carbonate solvent to prepare a basic electrolyte; adding the electrolyte additive to the basic electrolyte and mixing to obtain the battery electrolyte.

[0014] A third aspect of the present invention provides a lithium-ion battery, comprising: a positive electrode, a negative electrode, and an electrolyte for the battery as described in any one of the above.

[0015] Furthermore, in a preferred embodiment of the present invention, the positive electrode comprises a lithium cobalt oxide positive electrode material or a lithium-rich manganese-based positive electrode material.

[0016] The beneficial effects of the electrolyte for batteries and its preparation method, as well as the battery itself, according to embodiments of the present invention are:

[0017] This invention utilizes squalene-based electrolyte additives, which can react with oxygen free radicals generated during high-voltage charging of cathode materials, especially lithium-rich manganese-based cathode materials, reducing the release of harmful gases such as CO and CO2 during the first charging cycle. Furthermore, the squalene-based additives can form a stable and uniform cathode electrolyte interface layer on the cathode surface during cycling, exhibiting excellent cycle stability.

[0018] Furthermore, the electrolyte additives also include fullerene derivatives and 6-fluoropyridine-3-boronic acid. By introducing fullerene derivatives, 6-fluoropyridine-3-boronic acid, and squalene-based additives in combination, the formation of the spinel phase in the layered phase of the lithium-rich manganese-based cathode material can be slowed down, thus alleviating the voltage decay phenomenon. This further inhibits electrolyte decomposition and significantly improves electrolyte stability, especially effectively enhancing the cycle performance of lithium-rich manganese-based and lithium cobalt oxide cathode materials. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The first charge-discharge curves of lithium-ion batteries prepared according to the method of Example 8 are shown for the electrolyte of Example 1 and the electrolyte of Comparative Example 1 of the present invention, wherein the current density is 0.1C.

[0021] Figure 2 The image shows the cycle life of lithium-ion batteries prepared according to the method of Example 8 using the electrolyte of Example 1 and the electrolyte of Comparative Example 1. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The following provides a detailed description of the electrolyte for batteries, its preparation method, and the battery according to embodiments of the present invention.

[0024] This invention provides a battery electrolyte comprising a carbonate solvent, an electrolyte, and an electrolyte additive, wherein the electrolyte additive is a squalene additive selected from squalene and / or squalane.

[0025] Squalene compounds possess the ability to scavenge singlet oxygen and superoxide radicals. Their selection as additive components in battery electrolytes allows them to eliminate reactive oxygen species generated during high-voltage positive electrode charging and to form a stable positive electrode electrolyte interface layer, inhibiting undesirable electrolyte decomposition. Furthermore, squalene compounds are low-cost, widely available, and represent a green, pollution-free, and highly efficient electrolyte additive.

[0026] Specifically, the carbonate solvent is selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and dimethyl carbonate. Preferably, the carbonate solvent is obtained by compounding two or more components. By selecting a variety of carbonate solvents, the cycle performance of the battery can be further improved.

[0027] Specifically, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium bis(oxalate)borate, lithium difluorobis(oxalate)phosphate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, and lithium perchlorate. More preferably,

[0028] Furthermore, the concentration of lithium salt in the battery electrolyte is 0.6–1.5 mol / L. More specifically, the concentration of lithium salt in the battery electrolyte is 1 mol / L.

[0029] Further, the mass fraction of the electrolyte additive in the electrolyte is 0.5% to 5%. More preferably, the mass fraction of the electrolyte additive in the electrolyte is 0.5% to 1.5%.

[0030] Furthermore, in one embodiment, the electrolyte additive further includes one or more of fullerene derivatives and 6-fluoropyridine-3-boronic acid. More preferably, the electrolyte additive comprises fullerene derivatives, 6-fluoropyridine-3-boronic acid, and squalene additives in a mass ratio of 1:3 to 6:10 to 20.

[0031] Specifically, the fullerene derivative is selected from one or more of fluorinated fullerenes, hydroxylated fullerenes, and chlorinated fullerenes. Preferably, the fullerene derivative is a fluorinated fullerene.

[0032] By incorporating fullerene derivatives, 6-fluoropyridine-3-boronic acid, and squalene additives, a synergistic effect can be achieved, slowing down the formation of the spinel phase in the layered phase of lithium-rich manganese-based cathode materials and reducing voltage decay. Furthermore, the combination of these three components further inhibits electrolyte decomposition, resulting in higher electrolyte stability and significantly improving the cycle performance of lithium-rich manganese-based and lithium cobalt oxide cathode materials.

[0033] Embodiments of the present invention also provide a method for preparing the above-mentioned electrolyte for batteries, comprising:

[0034] Step S1: Mix the lithium salt and the carbonate solvent to prepare a basic electrolyte;

[0035] Step S2: Add the electrolyte additive to the base electrolyte and mix to obtain the battery electrolyte.

[0036] Embodiments of the present invention also provide a lithium-ion battery, comprising: a positive electrode, a negative electrode, and the above-described electrolyte for the battery.

[0037] Furthermore, in this lithium-ion battery, the positive electrode includes either lithium cobalt oxide or lithium-rich manganese-based positive electrode material. The chemical formula of the lithium-rich manganese-based positive electrode material is xLi₂MnO₃·(1-x)LiMO₂, where M represents nickel, cobalt, and manganese.

[0038] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0039] Example 1

[0040] This embodiment provides a battery electrolyte, including the following steps:

[0041] (a) Preparation of electrolyte for high-voltage lithium-ion batteries:

[0042] (1) Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a volume ratio of EC:DEC:EMC = 1:1:1, and purified by molecular sieve, calcium hydride, and lithium hydride to remove impurities and water, so as to obtain a mixed solvent.

[0043] (2) Dissolve lithium hexafluorophosphate with a concentration of 1.0 mol / L in the mixed solvent obtained in step (1), stir evenly, and obtain the basic electrolyte;

[0044] (3) Squalene is added to the basic electrolyte obtained in step (2) by adding 1% of the mass of the basic electrolyte to obtain the electrolyte for battery use.

[0045] Example 2

[0046] This embodiment provides a battery electrolyte, which differs from Embodiment 1 in that: step (3) is: squalane is added to the basic electrolyte obtained in step (2), and the amount added is 1% of the mass of the basic electrolyte, to obtain the battery electrolyte.

[0047] Example 3

[0048] This embodiment provides a battery electrolyte, which differs from Embodiment 1 in that: step (3) is: fluorinated fullerene, 6-fluoropyridine-3-boronic acid and squalene are added to the basic electrolyte obtained in step (2) in a mass ratio of 1:4:15, and the total amount added is 1% of the mass of the basic electrolyte, to obtain the battery electrolyte.

[0049] Example 4

[0050] This embodiment provides a battery electrolyte, which differs from Embodiment 1 in that: step (3) is: fluorinated fullerene and squalene with a mass ratio of 5:15 are added to the basic electrolyte obtained in step (2), and the total amount added is 1% of the mass of the basic electrolyte, to obtain the battery electrolyte.

[0051] Example 5

[0052] This embodiment provides a battery electrolyte, which differs from Embodiment 1 in that: step (2) is: dissolving lithium tetrafluoroborate with a concentration of 0.6 mol / L in the mixed solvent obtained in step (1), stirring evenly to obtain a basic electrolyte.

[0053] Example 6

[0054] This embodiment provides a battery electrolyte, which differs from Embodiment 1 in that: step (3) is: squalene is added to the basic electrolyte obtained in step (2), and the amount added is 0.5% of the mass of the basic electrolyte, to obtain the battery electrolyte.

[0055] Example 7

[0056] This embodiment provides a battery electrolyte, which differs from Embodiment 1 in that: step (3) is: squalene is added to the basic electrolyte obtained in step (2), and the amount added is 5% of the mass of the basic electrolyte, to obtain the battery electrolyte.

[0057] Example 8

[0058] This embodiment provides a lithium-ion battery, including the following steps:

[0059] (1) Preparation of the positive electrode: Lithium-rich manganese-based positive electrode material, acetylene black, and PVDF were mixed in a mass ratio of 8:1:1. An appropriate volume of N-methylpyrrolidone (NMP) was then added and stirred in a homogenizer for 15 minutes at a speed of 15000 r / min to form a stable and homogeneous positive electrode slurry. This slurry was coated onto aluminum foil using a scraper and dried in a 60℃ oven for 12 hours until the NMP had completely evaporated. The chemical formula of the lithium-rich manganese-based positive electrode material used is 0.5Li₂MnO₃·0.5LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0060] (2) Battery assembly: The prepared positive electrode sheet is punched into a circular electrode sheet of Φ10mm. In an argon atmosphere, with lithium metal as the negative electrode and a polypropylene microporous membrane of model Celgard 2320 as the separator, the electrolytes of the batteries prepared in Examples 1 to 8 are injected into the batteries respectively and assembled into batteries (CR2025) in sequence.

[0061] (3) The battery is completely sealed to obtain a lithium-ion battery.

[0062] Comparative Example 1

[0063] This comparative example provides a battery electrolyte, which is the basic electrolyte obtained in Example 1.

[0064] Comparative Example 2

[0065] This comparative example provides a battery electrolyte, which differs from Example 1 in that: step (3) involves adding fluorinated fullerene and 6-fluoropyridine-3-boronic acid in a 1:4 ratio to the basic electrolyte obtained in step (2), with the addition amount being 1% of the mass of the basic electrolyte, to obtain the battery electrolyte.

[0066] Test case

[0067] The lithium-ion battery obtained in Example 8 was used as the test group. The electrolyte was replaced with the electrolyte prepared in Comparative Examples 1 and 2 using the same method as described above, which served as the control group.

[0068] Charge-discharge cycle tests were performed on the Blue Electric Tester. The test conditions were: charge-discharge cycle at a rate of 1C, charging cut-off voltage set to 4.8V, and test temperature of 25℃ (the current density was 0.1C for the first three cycles to activate the circuit, and then 1C for the next cycle). The test results are shown in Table 1 below.

[0069] Table 1

[0070]

[0071] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A battery electrolyte, characterized in that, It includes carbonate solvents, electrolytes, and electrolyte additives, wherein the electrolyte additives are selected from fluorinated fullerenes, 6-fluoropyridine-3-boronic acid, and squalene.

2. The electrolyte for batteries according to claim 1, characterized in that, The electrolyte additive has a mass fraction of 0.5% to 5% in the electrolyte.

3. The electrolyte for batteries according to claim 1, characterized in that, The carbonate solvent is selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and dimethyl carbonate.

4. The electrolyte for batteries according to claim 1, characterized in that, The electrolyte is a lithium salt, which is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalateborate, lithium bis(oxalateborate), lithium difluorobis(oxalate)phosphate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, and lithium perchlorate.

5. The electrolyte for batteries according to claim 4, characterized in that, The concentration of the lithium salt in the battery electrolyte is 0.6~1.5 mol / L.

6. The electrolyte for batteries according to claim 1, characterized in that, The ratio of the fluorinated fullerene to the 6-fluoropyridine-3-boronic acid is 1:3~6.

7. A method for preparing a battery electrolyte as described in any one of claims 1 to 6, characterized in that, include: The lithium salt and the carbonate solvent are mixed to prepare a basic electrolyte; The fluorinated fullerene, 6-fluoropyridine-3-boronic acid and squalene are added to the base electrolyte and mixed to obtain the electrolyte for the battery.

8. A lithium-ion battery, characterized in that, include: Positive electrode, negative electrode, and electrolyte for battery as described in any one of claims 1 to 6 or electrolyte obtained by the preparation method described in claim 7.

9. The lithium-ion battery according to claim 8, characterized in that, The positive electrode includes lithium cobalt oxide positive electrode material or lithium-rich manganese-based positive electrode material.

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