A lithium ion battery electrolyte and a lithium ion battery containing the electrolyte

Abstract

The application discloses a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. The electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the additive is a quaternary phosphonium salt P1B or a mixture containing the quaternary phosphonium salt P1B. The additive of the application can effectively improve the low-temperature performance, rate performance and cycle performance of the electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] Lithium-ion batteries have become the fastest-growing new type of high-energy storage battery due to their advantages such as high energy density and long cycle life. However, as the application fields of batteries become more and more extensive, people's requirements for batteries are also increasing.

[0003] Electrolyte is one of the core materials of lithium-ion batteries. It acts as a medium, transporting ions and conducting current between the positive and negative electrodes. As one of the most important raw materials for lithium-ion batteries, electrolyte has received increasing attention, with research mainly focusing on the use of various additives—specifically, research on additives that can effectively improve the electrochemical performance of lithium-ion batteries with small amounts. Electrolyte additives generally do not participate in the electrode reactions of lithium-ion batteries, but they can significantly and directionally improve various properties of the electrolyte, helping lithium-ion batteries achieve excellent characteristics such as high energy density, long cycle life, high rate performance, wide temperature range, and high safety. They are an indispensable component of lithium-ion battery electrolytes.

[0004] Currently, different types of electrolyte additives can be used to target and improve various battery performance characteristics. Existing mainstream additives can be categorized into different functional groups based on their functions. Therefore, developing new, stable, and multifunctional additives is crucial for improving battery rate cycling and high / low temperature performance. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte. The electrolyte provided by this invention improves the low-temperature performance and rate performance of lithium-ion batteries, while also improving the long-term cycle performance of lithium-ion batteries.

[0006] The first aspect of the present invention provides a lithium-ion battery electrolyte, the electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the additive is a quaternary phosphine salt P1B or a mixture comprising quaternary phosphine salt P1B.

[0007] Furthermore, the quaternary phosphine salt P1B has the following structural formula:

[0008]

[0009] Furthermore, the specific preparation process of the quaternary phosphine salt P1B is as follows:

[0010] At -50 to -20°C under a nitrogen atmosphere, PCl5 was slowly added to a tetrahydrofuran solution containing 1,1,3,3-tetramethylguanidine, refluxed, filtered to remove the precipitate, washed with water, dehydrated, evaporated under reduced pressure, and recrystallized to obtain compound P1A.

[0011] The obtained P1A was dissolved in water, and NaBF4 was added to react and a precipitate was obtained. The precipitate was stirred, filtered, washed, and recrystallized from methanol to obtain quaternary phosphine salt P1B.

[0012] Furthermore, the molar ratio of PCl5 to 1,1,3,3-tetramethylguanidine is 1:5 to 10.

[0013] Furthermore, the volume of the tetrahydrofuran solution is 2–5 mL / g based on the mass of 1,1,3,3-tetramethylguanidine.

[0014] Furthermore, the molar ratio of compound P1A to NaBF4 is 1:1 to 1.2.

[0015] Furthermore, the reflux, vacuum distillation, filtration, washing, recrystallization, and other operations can all be performed using conventional methods in the field, without any particular limitations.

[0016] Furthermore, in the lithium-ion battery electrolyte, based on the mass of the lithium-ion battery electrolyte, the content of the organic solvent is 60% to 90%, the content of the lithium salt is 5% to 40%, and the content of the additive is 0.1% to 5.0%.

[0017] Further, the organic solvent includes at least two of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), or propylene carbonate (PC), preferably at least two of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0018] Furthermore, the lithium salt is lithium hexafluorophosphate (LiPF6).

[0019] Furthermore, the concentration of the lithium salt is 0.5 mol / L to 3 mol / L.

[0020] Furthermore, the mixture comprising quaternary phosphine salt P1B is a mixture of quaternary phosphine salt P1B and additive A.

[0021] Further, additive A comprises at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), 1,3-propanesulfonate lactone (1,3-PS), vinyl sulfate (DTD), N-methylpyrrole (MPL), 2-phenylimidazolium (PID), vinyl sulfite (ES), catechol carbonate (BO), and vinyl acetate (VA). Preferably, it comprises at least one of ethyleneene carbonate (VC), ethylene ethylene carbonate (VEC), vinyl sulfate (DTD), and vinyl sulfite (ES).

[0022] Further, the mixture of quaternary phosphine salt P1B and additive A, wherein quaternary phosphine salt P1B accounts for 0.1% to 2.0% of the total mass of the electrolyte; and additive A accounts for 0.5% to 3.0% of the total mass of the electrolyte.

[0023] The lithium-ion battery electrolyte of the present invention can be prepared using conventional methods in the art. For example, lithium salt can be slowly added to an organic solvent under an inert atmosphere, followed by the addition of additives, to obtain the lithium-ion battery electrolyte.

[0024] A second aspect of the present invention provides a lithium-ion battery using the above-mentioned lithium-ion battery electrolyte.

[0025] Furthermore, in the lithium-ion battery, the positive electrode (cathode) material is preferably a ternary nickel-cobalt-manganese alloy (such as NCM622) or lithium iron phosphate.

[0026] Furthermore, in the lithium-ion battery, the negative electrode (anode) material is preferably silicon-carbon or graphite.

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

[0028] 1. The inventors discovered through research that this invention uses quaternary phosphine salt P1B or a mixture including quaternary phosphine salt P1B as a novel electrolyte additive. Compared with other conventional electrolyte additives, it can effectively improve the low-temperature performance and rate performance of the electrolyte, and after battery formation, it can form a more stable SEI film on the electrode material surface, thus significantly improving cycle performance. Quaternary phosphine salt P1B is an unsaturated compound that is easily reduced at the negative electrode. Therefore, when added to the electrolyte and introduced into the battery, it is preferentially reduced at the negative electrode during formation, participating in the formation of the protective SEI film. The resulting film has good ion permeability and good electronic insulation, which is beneficial for lithium ions to enter and exit the negative electrode during charging and discharging. However, electrons on the negative electrode cannot contact solvent molecules, thus improving rate performance and also improving performance in storage, low-temperature discharge, and high-temperature charge and discharge.

[0029] 2. Further research by the inventors revealed that using quaternary phosphine salt P1B as a novel electrolyte additive results in a smaller dosage compared to conventional electrolyte additives. When the content of quaternary phosphine salt additive P1B is 1%, under the same conditions, the electrolyte discharge capacity retention rate at -20℃ is increased by 8%, and the 5C discharge rate performance is improved by 6%, demonstrating outstanding performance. Attached Figure Description

[0030] Figure 1 This is a comparison chart of the low-temperature performance of Examples 1-12 and Comparative Examples 1-3;

[0031] Figure 2 This is a comparison chart of the rate performance of Examples 1-12 and Comparative Examples 1-3. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and unless otherwise specified, % refers to percentages by mass.

[0033] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the embodiments.

[0034] Example 1

[0035] (1) Preparation of quaternary phosphine salt P1B

[0036] Under nitrogen protection at -30°C, 20.82 g (0.10 mol) of PCl5 was slowly added to 250 mL of a tetrahydrofuran solution containing 103.63 g (0.90 mol) of 1,1,3,3-tetramethylguanidine, followed by reflux for 4 hours. The precipitate was filtered off, the filtrate was washed with water, water was removed, the filtrate was evaporated under reduced pressure, and recrystallization was performed to give 41.75 g of compound P1A (80% yield). 1 H NMR (300MHz, CDCl3), δ (ppm): 2.82 (s, 48H, CH3). 13 C NMR (75MHz, CDCl3), δ (ppm): 157.82, 39.37.Elemental Anal. C 20 H 48 ClN 12 Theoretical values ​​(%) of elemental analysis: C, 45.92; H, 9.25; N, 32.13%. Actual measured values ​​(%) of elemental analysis: C, 46.03; H, 9.47; N, 32.25%. The theoretical values ​​and actual measured values ​​are consistent. The reaction process is shown in equation a.

[0037]

[0038] 20.88 g (0.04 mol) of P1A was dissolved in 15 g of deionized water, and 4.39 g (0.04 mol) of NaBF4 was added. A precipitate was formed. The mixture was stirred for 1 h, filtered, washed with water, and recrystallized with methanol to obtain 21.2 g of compound P1B (yield 91%). 1 H NMR (300MHz, CDCl3), δ (ppm): 2.82 (s, 48H, CH3). 13 C NMR (75MHz, CDCl3), δ (ppm): 157.82, 39.37.Elemental Anal.C 20 H 48 BF4N 12 Theoretical values ​​(%) of elemental analysis: C, 41.82; H, 8.42; N, 29.26%. Actual measured values ​​(%) of elemental analysis: C, 41.13; H, 8.39; N, 29.30%. The theoretical values ​​and actual measured values ​​are consistent. The reaction process is shown in equation b.

[0039]

[0040] (2) Electrolyte preparation

[0041] The entire electrolyte preparation process was carried out in an argon atmosphere glove box (H2O < 0.5 ppm, O2 < 0.5 ppm), and included the following steps:

[0042] a. Under magnetic stirring conditions, weigh a certain mass of organic solvent (ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), with the mass ratio of EC:EMC:DEC being 30:20:33) and add it to a beaker for mixing. The magnetic stirring speed is 300 r / min.

[0043] b. Under magnetic stirring conditions, weigh a certain mass of LiPF6 (concentration of 1.2 mol / L) and add it to the beaker in a. After the LiPF6 is completely dissolved, continue stirring for 30 minutes until uniformly mixed. The magnetic stirring speed is 300 r / min.

[0044] c. Under magnetic stirring conditions, weigh a certain mass of P1B additive, add it to the beaker in b and mix to obtain an electrolyte. The magnetic stirring speed is 300 r / min.

[0045] d. Transfer the sample from beaker c to a clean aluminum bottle for later use.

[0046] In Example 1, the electrolyte contained additive P1B at 2% of its total mass, organic solvent at 83% of its total mass, and lithium salt at 15% of its total mass. The electrolyte composition is detailed in Table 2.

[0047] (3) Lithium-ion battery preparation

[0048] The positive electrode of the soft-pack lithium-ion battery is ternary NCM622, and the negative electrode is artificial graphite (D50 particle size 10-15 micrometers, specific surface area 1.5-2 m²). 2 / g), the cell is designed to have a capacity of 1Ah. The above-prepared electrolyte is injected at a mass of 3g per cell. After full immersion, the cells are subjected to formation, aging, and capacity testing.

[0049] Example 2

[0050] Lithium-ion batteries were prepared according to the method of Example 1. In Example 2, the electrolyte contained additive P1B at 1.0% of its total mass, organic solvent at 79% of its total mass, and lithium salt at 20% of its total mass. The electrolyte composition is detailed in Table 2.

[0051] Example 3

[0052] Lithium-ion batteries were prepared according to the method of Example 1. In Example 3, the electrolyte contained additive P1B at 0.5% of its total mass, organic solvent at 69.5% of its total mass, and lithium salt at 30% of its total mass. The electrolyte composition is detailed in Table 2.

[0053] Example 4

[0054] Lithium-ion batteries were prepared according to the method in Example 1.

[0055] The electrolyte preparation process is as follows:

[0056] The entire electrolyte preparation process was carried out in an argon atmosphere glove box (H2O < 0.5 ppm, O2 < 0.5 ppm), and included the following steps:

[0057] a. Under magnetic stirring conditions, weigh a certain mass of organic solvent (ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), with the mass ratio of EC:EMC:DEC being 30:20:30) and add it to a beaker for mixing. The magnetic stirring speed is 300 r / min.

[0058] b. Under magnetic stirring conditions, weigh a certain mass of LiPF6 (concentration of 1.2 mol / L) and add it to the beaker in a. After the LiPF6 is completely dissolved, continue stirring for 30 minutes until uniformly mixed. The magnetic stirring speed is 300 r / min.

[0059] c. Under magnetic stirring conditions, weigh a certain mass of P1B additive, add it to the beaker in b and mix to obtain an electrolyte. The magnetic stirring speed is 300 r / min.

[0060] d. Under magnetic stirring conditions, weigh a certain mass of the additive vinylene carbonate (VC), add it to the beaker in c and mix to obtain the electrolyte. The magnetic stirring speed is 300 r / min.

[0061] e. Transfer the sample from beaker d to a clean aluminum bottle for later use.

[0062] In Example 4, the electrolyte contained 2% P1B by mass, 3% vinylene carbonate (VC) by mass, 80% organic solvent, and 15% lithium salt. The electrolyte composition is detailed in Table 2.

[0063] Example 5

[0064] Lithium-ion batteries were prepared according to the method of Example 1. In Example 5, the electrolyte contained additive P1B at 1% of the total electrolyte mass, additive vinylene carbonate (VC) at 1% of the total electrolyte mass, organic solvent at 78% of the total electrolyte mass, and lithium salt at 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0065] Example 6

[0066] Lithium-ion batteries were prepared according to the method of Example 1. In the electrolyte of Example 6, additive P1B accounted for 0.5% of the total electrolyte mass, additive vinylene carbonate (VC) accounted for 2% of the total electrolyte mass, organic solvent accounted for 67.5% of the total electrolyte mass, and lithium salt accounted for 30% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0067] Example 7

[0068] Lithium-ion batteries were prepared according to the method of Example 1. In the electrolyte of Example 7, additive P1B accounted for 0.5% of the total electrolyte mass, additive vinylene carbonate (VC) accounted for 1% of the total electrolyte mass, organic solvent accounted for 78.5% of the total electrolyte mass, and lithium salt accounted for 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0069] Example 8

[0070] Lithium-ion batteries were prepared according to the method of Example 1. In the electrolyte of Example 8, additive P1B accounted for 2% of the total electrolyte mass, additive vinylene carbonate (VC) accounted for 1% of the total electrolyte mass, organic solvent accounted for 77% of the total electrolyte mass, and lithium salt accounted for 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0071] Example 9

[0072] Lithium-ion batteries were prepared according to the method of Example 1. In the electrolyte of Example 9, additive P1B accounted for 2% of the total electrolyte mass, additive vinylene carbonate (VC) accounted for 1% of the total electrolyte mass, organic solvent accounted for 77% of the total electrolyte mass, and lithium salt accounted for 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0073] Example 10

[0074] Lithium-ion batteries were prepared according to the method of Example 1. In the electrolyte of Example 10, additive P1B accounted for 2% of the total electrolyte mass, additive ethylene ethylene carbonate (VEC) accounted for 1% of the total electrolyte mass, organic solvent accounted for 77% of the total electrolyte mass, and lithium salt accounted for 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0075] Example 11

[0076] Lithium-ion batteries were prepared according to the method of Example 1. In the electrolyte of Example 11, additive P1B accounted for 2% of the total electrolyte mass, additive ethylene sulfate (DTD) accounted for 1% of the total electrolyte mass, organic solvent accounted for 77% of the total electrolyte mass, and lithium salt accounted for 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0077] Example 12

[0078] Lithium-ion batteries were prepared according to the method of Example 1. In the electrolyte of Example 12, additive P1B accounted for 2% of the total electrolyte mass, additive vinyl sulfite (ES) accounted for 1% of the total electrolyte mass, organic solvent accounted for 77% of the total electrolyte mass, and lithium salt accounted for 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0079] Comparative Example 1

[0080] Lithium-ion batteries were prepared according to the method of Example 1. Compared with Example 1, in Comparative Example 1, no additive P1B was added to the electrolyte, the organic solvent accounted for 85% of the total mass of the electrolyte, and the lithium salt accounted for 15% of the total mass of the electrolyte. The electrolyte composition is detailed in Table 2.

[0081] Comparative Example 2

[0082] Lithium-ion batteries were prepared according to the method of Example 1. In Comparative Example 2, the electrolyte contained P1B without additives, organic solvents accounted for 78% of the total electrolyte mass, vinylene carbonate (VC) accounted for 2% of the total electrolyte mass, and lithium salt accounted for 20% of the total electrolyte mass. The electrolyte composition is detailed in Table 2.

[0083] Comparative Example 3

[0084] Lithium-ion batteries were prepared according to the method of Example 1. Compared with Example 1, the additive in the electrolyte of Comparative Example 3 was replaced with an equal mass of P,P-dimethylpyrrolidone onium tetrafluoroborate. The electrolyte composition is detailed in Table 2.

[0085] Test case

[0086] -20℃ discharge capacity retention rate: The discharge capacity of a fully charged battery at 25℃ at -20℃ divided by the discharge capacity at 25℃.

[0087] The test results of the above embodiments and comparative examples are shown in Table 1.

[0088] Table 1

[0089]

[0090]

[0091] Table 2

[0092]

[0093] As can be seen from Tables 1 and 2, the low-temperature capacity retention rates of Examples 3 and 6 are relatively low. This may be because although the lithium salt concentration in the solutions of Examples 3 and 6 is high, the lithium ion concentration is low at low temperatures. This is because the lithium ion concentration in the electrolyte is not linearly related to the lithium salt concentration, but rather parabolic. The lithium ion concentration in the solvent depends on the strength of the dissociation and association of the lithium salt in the solvent. At low temperatures, lithium ions in Examples 3 and 6 are difficult to dissociate.

[0094] The embodiments described above are merely detailed descriptions of the technical solutions of the present invention, but the present invention is not limited to the above embodiments, that is, the present invention does not depend on the steps described in the above embodiments to be implemented. In summary, any improvements made to the present invention by those skilled in the art, including the substitution of the raw materials and additives described in the present invention, the selection of specific implementation methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the additive is a quaternary phosphine salt P1B or a mixture comprising quaternary phosphine salt P1B; the mixture comprising quaternary phosphine salt P1B is a mixture of quaternary phosphine salt P1B and additive A, wherein the quaternary phosphine salt P1B accounts for 0.1% to 2.0% of the total mass of the electrolyte, and the additive A accounts for 0.5% to 3.0% of the total mass of the electrolyte; the quaternary phosphine salt P1B has the following structural formula: ； Additive A includes at least one of fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, N-methylpyrrole, 2-phenylimidazole, vinyl sulfite, catechol carbonate, and vinyl acetate.

2. The electrolyte according to claim 1, characterized in that, In the lithium-ion battery electrolyte, based on the mass of the lithium-ion battery electrolyte, the content of the organic solvent is 60%~90%, the content of the lithium salt is 5%~40%, and the content of the additive is 0.1%~5.0%.

3. The electrolyte according to claim 1, characterized in that, The organic solvent includes at least two of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, or propylene carbonate.

4. The electrolyte according to claim 3, characterized in that, The organic solvent includes at least two of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

5. The electrolyte according to claim 1, characterized in that, The lithium salt is lithium hexafluorophosphate.

6. The electrolyte according to claim 1, characterized in that, The concentration of the lithium salt is 0.5 mol / L to 3 mol / L.

7. A lithium-ion battery, characterized in that, The lithium-ion battery electrolyte according to any one of claims 1-6 is used.

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