An electrolyte additive combination, electrolyte, lithium battery and preparation method thereof

Abstract

The application provides an electrolyte additive combination, an electrolyte, a lithium battery and a preparation method thereof, and relates to the field of lithium ion batteries. The electrolyte additive in the electrolyte comprises lithium difluorophosphate, ethylene sulfate or a cyclic sulfate, a tri-furyl phosphite or an electron-rich aromatic heterocycle-containing phosphite, and a tetra-vinyl silane or a silane compound containing multiple vinyl groups; the tetra-vinyl silane participates in the formation of a negative electrode SEI film, preferentially forms a silane polymer with high lithium ion conductivity at a low voltage, inhibits electron tunneling and impedance growth, the tri-furyl phosphite plays a water-removing and acid-inhibiting function, and preferentially forms a film on the positive and negative electrodes to improve the high-temperature performance of the battery; further, the combination of the organic sulfate DTD and the inorganic lithium salt LiDFP can introduce Li2SO4 and ROSO2Li into the SEI film, the components of the additive synergize with each other, inhibit gas generation during the cycle process of the battery, simultaneously reduce impedance, and improve the rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more particularly to an electrolyte additive combination, an electrolyte, a lithium battery, and a method for preparing the same. Background Technology

[0002] With the increasing technological development and demands for mobile devices, the demand for lithium batteries as an energy source has increased dramatically. Among these lithium batteries, lithium-ion batteries, with their high energy density and high voltage, have been commercialized and are widely used.

[0003] Lithium metal oxides are used as the cathode active material in lithium-ion batteries, while crystalline carbon, amorphous carbon, or carbon composite materials are used as the anode active material. The active material is coated with a current collector of appropriate thickness and length, or the active material itself is coated in thin film form, and then wound or laminated together with a separator, which serves as an insulator, to prepare an electrode assembly. The electrode assembly is then placed in a container, and a battery is prepared by injecting an electrolyte solution.

[0004] During charging and discharging, lithium-ion batteries repeatedly undergo the process of lithium ions intercalating and deintercalating from the lithium metal oxide positive electrode to the graphite negative electrode. In this process, due to the high reactivity of lithium, it reacts with the carbon electrode to form Li₂CO₃, LiO, LiOH, etc., thereby forming a thin film on the surface of the negative electrode. This thin film is called a "solid electrolyte interface (SEI)" film.

[0005] The SEI film formed during the initial charging stage prevents lithium ions from reacting with the carbon anode or other substances during charging and discharging. Furthermore, the SEI film acts as an ion channel, allowing only lithium ions to pass through. This ion channel prevents the carbon anode structure from being damaged by high-molecular-weight organic solvents in the electrolyte solution forming co-intercalations with the carbon anode.

[0006] Therefore, to improve the cycle performance of lithium-ion batteries, a robust SEI film must be formed at the negative electrode. Once formed during the initial charging process, the SEI film prevents lithium ions from reacting with the negative electrode or other substances during subsequent charge-discharge cycles, and acts as an ion channel that allows lithium ions to pass solely between the electrolyte solution and the negative electrode.

[0007] However, lithium-ion battery products that currently use traditional electrolytes generally have the risk of gas generation and swelling under high-temperature cycling. The main reason for this is that the SEI film does not sufficiently block the electron tunneling effect. In particular, the electron blocking ability of the SEI film formed by traditional additives (such as VC and FEC) is insufficient, which is the root cause of the chain gas generation reaction. Once this reaction occurs in lithium-ion batteries, it is an irreversible process.

[0008] In existing technologies, when using electrolytes without electrolyte additives or containing electrolyte additives with inferior properties, the SEI film thickness increases by more than 300% after high-temperature cycling. The resulting SEI film, rich in organic matter, cannot completely block electron tunneling and has low ionic conductivity. Therefore, battery swelling caused by solvent chain reaction gas production is unavoidable, and the gas production rate increases exponentially with temperature. Furthermore, conventional electrolytes typically use EC as a solvent, which is highly prone to decomposition and gas production, accelerating battery expansion and significantly reducing the electrochemical stability of the electrolyte. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides an electrolyte additive combination, an electrolyte, a lithium battery, and a method for preparing the same. The electrolyte forms a robust SEI film with high ionic conductivity and low electronic conductivity at the negative electrode of the lithium-ion battery, effectively suppressing electrolyte decomposition and gas generation during high-temperature cycling. The electrolyte is a non-aqueous electrolyte comprising a non-aqueous organic solvent, an imide-based lithium salt, and electrolyte additives; the electrolyte additives include lithium difluorophosphate (LiDFP), vinyl sulfate (DTD), trifuranyl phosphite (FuP), and tetravinylsilane (TVS). The electrolyte of this application can form a robust SEI film, effectively blocking electron tunneling and reducing solvent decomposition and gas generation at the positive and negative electrode interfaces, thereby providing a lithium-ion battery with excellent high-temperature cycle life and low expansion rate.

[0010] In a first aspect, this application provides an electrolyte additive combination comprising lithium difluorophosphate, vinyl sulfate (DTD) or cyclic sulfate, trifuranyl phosphite (FuP) or phosphite containing an electron-rich aromatic heterocycle, and tetravinylsilane (TVS) or a silane compound containing multiple vinyl groups in a mass ratio of 0.1~5:0.1~3:0.5~5:0.1~4.

[0011] Furthermore, the mass ratio of lithium difluorophosphate, vinyl sulfate (DTD) or cyclic sulfate, trifuranyl phosphite (FuP) or phosphite containing an electron-rich aromatic heterocycle, and tetravinylsilane (TVS) or silane compound containing multiple vinyl groups is 0.5~2:0.5~1.5:1~3:0.5~2.

[0012] The core "synergistic effect" of the invention is based on the specific chemical reactions of LiDFP with DTD, FuP, TVS, etc. LiDFP decomposes to generate... LiF and phosphorus-oxygen-F species, these products together with sulfides generated by DTD constitute a specific "LiDFP-DTD composite interface phase".

[0013] Secondly, this application provides an electrolyte comprising a non-aqueous organic solvent, an imide-based lithium salt, and an electrolyte additive, wherein the concentration of the electrolyte additive in the electrolyte is 3-6 wt.%, and the electrolyte additive includes lithium difluorophosphate, vinyl sulfate or cyclic sulfate, trifuranyl phosphite or phosphite containing an electron-rich aromatic heterocycle, and tetravinylsilane or a silane compound containing multiple vinyl groups.

[0014] Furthermore, the concentration of lithium difluorophosphate is 0.1 to 5 wt%, the concentration of vinyl sulfate or cyclic sulfate is 0.1 to 3 wt%, the concentration of trifuranyl phosphite or phosphite containing electron-rich aromatic heterocycles is 0.5 to 5 wt%, and the concentration of tetravinylsilane or silane compound containing multiple vinyl groups is 0.1 to 4 wt%.

[0015] In this context, "multiple" in a silane compound with multiple vinyl groups refers to a compound containing two or more vinyl groups.

[0016] Ordinary alkyl phosphates (such as triethyl phosphite) can retain a certain acid removal capacity, but the alkyl chain has poor oxidative stability and may decompose under high pressure without forming a protective film, which will lead to a decrease in the high temperature and high voltage performance of the battery. TVS is replaced by monofunctional silane (vinyltrimethylsilane), which has reduced electrochemical reduction polymerization capacity and may be difficult to form a dense electron blocking layer with silane as the main chain.

[0017] Further, lithium difluorophosphate: 0.5~2 wt%, vinyl sulfate or cyclic sulfate 0.5~1.5 wt%, trifuranyl phosphite or phosphite containing electron-rich aromatic heterocycles 1~3 wt%, and tetravinylsilane or silane compound containing multiple vinyl groups 0.5~2 wt%.

[0018] Furthermore, the concentration of the lithium salt is 0.8-2 M / L; the lithium salt is at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0019] Furthermore, the non-aqueous organic solvent includes at least one of carbonates, carboxylic acid esters, and ether solvents.

[0020] Thirdly, this application provides a lithium battery comprising the electrolyte described in this application.

[0021] Furthermore, the lithium battery exhibits the following high-temperature storage performance after 30 days at 60°C: capacity retention >87%, expansion rate <13%, and HF content <40 ppm; and high-temperature cycling performance after 500 cycles at 45°C (1C / 1C): cycle capacity retention >88%, DCR growth rate <128%, and HF content after cycling <40 ppm.

[0022] Fourthly, this application provides a method for preparing the lithium-ion battery described in this application.

[0023] Beneficial effects: 1. The electrolyte is composed of lithium salt, solvent, and additives, wherein the electrolyte additives are lithium difluorophosphate (LiDFP): 0.1%~5% (preferably 0.5%~2%), vinyl sulfate (DTD) or cyclic sulfate: 0.1%~3% (preferably 0.5%~1.5%), trifuranyl phosphite (FuP) or phosphite containing electron-rich aromatic heterocycles: 0.5%~5% (preferably 1%~3%), and tetravinylsilane (TVS) or silane compounds containing multiple vinyl groups: 0.1%~4% (preferably 0.5%~2%); the lithium salt is at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the non-aqueous organic solvent includes at least one of carbonates, carboxylic acid esters, and ether solvents.

[0024] Tetravinylsilane (TVS) can participate in the SEI film formation process of the negative electrode. Under low voltage, it preferentially forms silane polymers with high lithium-ion conductivity, significantly suppressing electron tunneling and impedance growth during high-temperature storage. Trifuranyl phosphite (FuP) plays a role in dehydration and acid suppression. Furthermore, the combination of organic sulfate DTD and inorganic lithium salt LiDFP can introduce [resources] into the SEI film, thus improving the high-temperature performance of the battery. and ,in, Its primary responsibility is to build a robust "shield" to suppress side reactions; while It acts as an efficient "bridge" to accelerate lithium-ion transport, and the two work together to improve the cycle life and rate performance of the battery; the properties of each component of the additive work together to form an SEI film that suppresses gas generation in the battery during cycling, while reducing impedance and improving rate performance.

[0025] 2. This application uses tetravinylsilane (TVS) and trifuranyl phosphite (FuP) as alternative electrolyte additives to PS (which have excellent film-forming properties but are carcinogenic). The addition of these additives introduces silane polymer components into the SEI film, significantly reducing the electron conductivity of the SEI film, thereby inhibiting the reaction of solvents such as EC and DMC in the electrolyte to generate a large amount of gas. The use of the electrolyte additive combination of this application in the electrolyte gives the electrolyte excellent film-forming properties and mechanical strength, and the formed SEI film can effectively block the electron tunneling effect, effectively remove the by-reaction product HF, and improve the high-temperature cycle life of the battery. Detailed Implementation

[0026] To make the technical solution of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. All operations are performed in an argon-protected glove box ( It was carried out in (< 0.1 ppm).

[0027] Example 1: A method for preparing a lithium battery, comprising the following preparation process:

[0028] (1) Preparation of electrolyte: The electrolyte is prepared by mixing according to the following mass ratio:

[0029] Solvents: 20 wt.% ethylene carbonate, 40 wt.% dimethyl carbonate, and 40 wt.% methyl ethyl carbonate.

[0030] Lithium salt: Lithium difluorosulfonylimide 1.2 M / L;

[0031] Additives: Lithium difluorophosphate: 1.0 wt.%, vinyl sulfate: 0.5 wt.%, trifuranyl phosphite: 2.0 wt.%, tetravinylsilane: 1.2 wt.%.

[0032] (2) Battery assembly and formation:

[0033] Positive electrode manufacturing: High-nickel ternary materials, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride are mixed in a mass ratio of 96.8:1:0.3:1.8. During the mixing process, N-methylpyrrolidone is used to prepare a positive electrode slurry with a solid content of 60%. The slurry is then coated onto an aluminum foil current collector, dried at 80~120℃, and then rolled and die-cut into the required positive electrode sheet.

[0034] Negative electrode manufacturing: Graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are prepared in a mass ratio of 94.5:1:1.5:2 and mixed with deionized water as a solvent to form a slurry with a solid content of 51%. The slurry is then coated onto a copper foil current collector, dried at 80~120℃, and then rolled and die-cut to form the required positive electrode sheet.

[0035] Dry cell manufacturing: The positive and negative electrode sheets prepared above are stacked with ceramic-coated PE separators of corresponding size and thickness of 12 micrometers using a stacking machine to produce a core with a capacity of 4Ah; after welding the tabs, they are packaged with aluminum-plastic film, baked at 85℃ for 24 hours, then injected with liquid for packaging, left to stand, and then formed.

[0036] The formation process is as follows: 1) Charge the battery at 0.08A for 4 hours at 25℃, with a cutoff voltage of 3.6V; 2) Charge the battery at 0.8A for 1.1 hours; 3) Charge the battery at 0.8A with constant current and constant voltage until 4.2V, with a cutoff current of 0.2A; 4) Let the battery cell age in a 38℃ high-temperature chamber for 48 hours, then remove it, vent it, and reseal it; 5) Charge the battery at 0.8A with constant current and constant voltage until 3.65V, with a cutoff current of 0.2A; 6) Discharge the battery cell at 1.33A with constant current until 2.0V; 7) Continue to charge and discharge the battery cell at 1.33A within the range of 2.0V to 3.65V for 2 weeks.

[0037] After formation is completed, final sealing is performed to obtain the lithium-ion secondary battery of this embodiment.

[0038] Example 2, a method for preparing a lithium battery, comprising the following preparation process:

[0039] The example is essentially the same as in Example 1, except that the content of trifuranyl phosphite decreased from 2.0 wt.% to 0.5 wt.%, as detailed below:

[0040] (1) Preparation of electrolyte: The electrolyte is prepared by mixing according to the following mass ratio:

[0041] Solvents: 20 wt.% ethylene carbonate, 40 wt.% dimethyl carbonate, and 40 wt.% methyl ethyl carbonate;

[0042] Lithium salt: Lithium difluorosulfonylimide 1.2M / L;

[0043] Additives: Lithium difluorophosphate: 1.0 wt.%, vinyl sulfate: 0.5 wt.%, trifuranyl phosphite: 0.5 wt.%, tetravinylsilane: 1.2 wt.%.

[0044] Comparative Example 1: A method for preparing a lithium battery, comprising the following preparation process:

[0045] The additive is essentially the same as in Example 1, except that trifuranyl phosphite is not used; instead, vinylsilane is used in equal amounts to replace tetravinylsilane, as detailed below:

[0046] (1) Preparation of electrolyte: The electrolyte is prepared by mixing according to the following mass ratio:

[0047] Solvents: 20 wt.% ethylene carbonate, 40 wt.% dimethyl carbonate, and 40 wt.% methyl ethyl carbonate;

[0048] Lithium salt: Lithium difluorosulfonylimide 1.2M / L;

[0049] Additives: Lithium difluorophosphate: 1.0 wt.%, vinyl sulfate: 0.5 wt.%, tetravinylsilane: 1.2 wt.%.

[0050] Comparative Example 2: A method for preparing a lithium battery, comprising the following preparation process:

[0051] This is essentially the same as Example 1, except that tetravinylsilane is not used in the additive, as detailed below:

[0052] (1) Preparation of electrolyte: The electrolyte is prepared by mixing according to the following mass ratio:

[0053] Solvents: 20 wt.% ethylene carbonate, 40 wt.% dimethyl carbonate, and 40 wt.% methyl ethyl carbonate;

[0054] Lithium salt: Lithium difluorosulfonylimide 1.2M / L;

[0055] Additives: Lithium difluorophosphate: 1.0 wt.%, vinyl sulfate: 0.5 wt.%, trifuranyl phosphite: 2.0 wt.%.

[0056] Comparative Example 3: A method for preparing a lithium battery, comprising the following preparation process:

[0057] This is essentially the same as Example 1, except that lithium difluorophosphate and vinyl sulfate are not used in the additives, as detailed below:

[0058] (1) Preparation of electrolyte: The electrolyte is prepared by mixing according to the following mass ratio:

[0059] Solvents: 20 wt.% ethylene carbonate, 40 wt.% dimethyl carbonate, and 40 wt.% methyl ethyl carbonate;

[0060] Lithium salt: Lithium difluorosulfonylimide 1.2M / L;

[0061] Additives: Trifuranyl phosphite: 2.0 wt.%, Tetravinylsilane: 1.2 wt.%.

[0062] Comparative Example 4: A method for preparing a lithium battery, comprising the following preparation process:

[0063] The additives are essentially the same as in Example 1, except that lithium difluorophosphate, vinyl sulfate, trifuranyl phosphite, and tetravinylsilane are not used; instead, 2.7 wt.% vinylene carbonate is used, as detailed below:

[0064] (1) Preparation of electrolyte: The electrolyte is prepared by mixing according to the following mass ratio:

[0065] Solvents: 20 wt.% ethylene carbonate, 40 wt.% dimethyl carbonate, and 40 wt.% methyl ethyl carbonate;

[0066] Lithium salt: Lithium difluorosulfonylimide 1.2M / L;

[0067] Additive: Vinylene carbonate: 2.7 wt.%.

[0068] Performance testing:

[0069] The capacity retention of the assembled comparative and individual embodiment lithium batteries was tested after 500 cycles at 60°C.

[0070] The gas production of the assembled comparative and individual embodiment lithium batteries after cycling was tested.

[0071] The impedance growth rate of the assembled comparative and individual embodiment lithium batteries after cycling was tested.

[0072] (1) High temperature storage performance test: Store at 60℃ for 30 days and measure capacity retention rate and expansion rate.

[0073] Battery capacity retention rate (%) = (Discharge capacity after storage / Initial discharge capacity) * 100%

[0074] Expansion rate (%) = (Battery thickness after storage - Initial battery thickness) / Initial battery thickness * 100%

[0075] (2) High temperature storage performance test: Under 45℃ conditions, 500 cycles of 1C / 1C were performed to measure the cycle capacity retention rate and DCR growth rate.

[0076] Cycle capacity retention (%) = (500th discharge capacity / First discharge capacity) * 100%

[0077] DCR growth rate (%) = (DCR value after high-temperature cycling - initial DCR value) / initial DCR value * 100%

[0078] (3) Acidity of electrolyte after circulation

[0079] Table 1: High-temperature storage performance (stored at 60℃ for 30 days)

[0080]

[0081] Table 2: High-temperature cycling performance (45℃, 500 cycles at 1C / 1C)

[0082]

[0083] Key performance gap analysis

[0084] 1. Differences in high-temperature storage stability

[0085] Expansion rate: The expansion rate of Example 1 (8.5%) was only 36% of that of Comparative Example 4 (VC scheme, 23.5%), indicating that gas production was fundamentally suppressed. The absence of FuP (Comparative Example 1, 19.2%) or TVS (Comparative Example 2, 15.8%) both resulted in a doubling of the expansion rate, demonstrating that they play a key and complementary role in suppressing gas generation.

[0086] Capacity retention and acidity: Example 1 showed the highest capacity retention (92.5%) and the lowest HF content (<10ppm) after storage. Comparative Example 1 (lacking FuP) had an HF content as high as 85ppm and the lowest capacity retention (80.8%), directly demonstrating that the deacidification function of FuP is the decisive factor in maintaining long-term storage stability.

[0087] 2. High-temperature cycle life and impedance difference

[0088] Cyclic capacity retention: Example 1 (92.3%) was significantly higher than all comparative examples, and nearly 14 percentage points higher than the prior art (Comparative Example 4, 78.5%). DCR growth rate: Example 1 showed the best controlled DCR growth (85%). Comparison shows:

[0089] The absence of FuP (Comparative Example 1, 195%) resulted in the most dramatic increase in DCR, confirming the continuous corrosion of the interface by acidic substances; the absence of TVS (Comparative Example 2, 150%) also led to a significant increase in DCR, demonstrating the importance of the electron blocking layer in maintaining the stability of the interface impedance; the existing VC scheme (Comparative Example 4, 220%) had the worst DCR control capability.

[0090] 3. Summary of Component Synergistic Effects

[0091] The core value of FuP: Without FuP (Comparative Example 1), it performed the worst in both tests (lowest storage capacity retention rate, highest cycle DCR growth), and its deacidification function cannot be replaced by other components.

[0092] The unique role of TVS: The absence of TVS (Comparative Example 2) significantly worsened both the expansion rate and the DCR growth rate, demonstrating that the polymer electron blocking layer formed by TVS makes a unique contribution to suppressing gas production and impedance growth.

[0093] Synergistic necessity: The performance of Comparative Example 3 (FuP+TVS only) was significantly inferior to that of Example 1, indicating that without LiDFP and DTD to provide the film-forming framework, FuP and TVS alone cannot build a stable interface, and there is a clear synergistic relationship among the four.

[0094] Dosage optimization: Example 2 (low FuP) showed performance between FuP deficiency and full FuP, demonstrating that FuP needs to reach a certain threshold (approximately 2.0%) to achieve the best results.

[0095] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. An electrolyte additive combination, characterized in that, It includes lithium difluorophosphate, vinyl sulfate or cyclic sulfate, trifuranyl phosphite or phosphite containing electron-rich aromatic heterocycles, and tetravinylsilane or silane compounds containing multiple vinyl groups in a mass ratio of 0.1~5:0.1~3:0.5~5:0.1~4.

2. The electrolyte additive combination according to claim 1, characterized in that, The mass ratio of lithium difluorophosphate, vinyl sulfate or cyclic sulfate, trifuranyl phosphite or phosphite containing an electron-rich aromatic heterocycle, and tetravinylsilane or silane compound containing multiple vinyl groups is 0.5~2:0.5~1.5:1~3:0.5~2.

3. An electrolyte, characterized in that, It comprises a non-aqueous organic solvent, an imide-based lithium salt, and an electrolyte additive, wherein the concentration of the electrolyte additive in the electrolyte is 3-6 wt.%, and the electrolyte additive includes lithium difluorophosphate, vinyl sulfate or cyclic sulfate, trifuranyl phosphite or phosphite containing electron-rich aromatic heterocycles, and tetravinylsilane or silane compounds containing multiple vinyl groups.

4. The electrolyte according to claim 3, characterized in that, The concentration of lithium difluorophosphate is 0.1-5 wt%, the concentration of vinyl sulfate or cyclic sulfate is 0.1-3 wt%, the concentration of trifuranyl phosphite or phosphite containing electron-rich aromatic heterocycles is 0.5-5 wt%, and the concentration of tetravinylsilane or silane compound containing multiple vinyl groups is 0.1-4 wt%.

5. The electrolyte according to claim 4, characterized in that, The lithium difluorophosphate comprises: 0.5-2 wt%, vinyl sulfate or cyclic sulfate 0.5-1.5 wt%, trifuranyl phosphite or phosphite containing electron-rich aromatic heterocycles 1-3 wt%, and tetravinylsilane or silane compound containing multiple vinyl groups 0.5-2 wt%.

6. The electrolyte according to any one of claims 3-5, characterized in that, The concentration of the lithium salt is 0.8-2 M / L; the lithium salt is at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

7. The electrolyte according to claim 6, characterized in that, The non-aqueous organic solvent includes at least one of carbonates, carboxylic acid esters, and ethers.

8. A lithium battery comprising the electrolyte as described in any one of claims 3-7.

9. A lithium battery according to claim 8, characterized in that, High-temperature storage performance at 60℃ for 30 days: capacity retention >87%, expansion rate <13%, HF content <40 ppm; High-temperature cycling performance at 45℃, 1C / 1C cycle 500 times: cycle capacity retention >88%, DCR growth rate <128%, HF content after cycling <40 ppm.

10. A method for preparing a lithium battery as described in claim 8 or 9.

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