Electrolyte and use thereof

Abstract

The application provides an electrolyte and application thereof, the electrolyte comprises a base electrolyte and an additive; the base electrolyte comprises an organic solvent and a lithium salt; the additive comprises a carboxylic acid ester additive; the mass of the additive in the electrolyte is 0.1-4% of the mass of the base electrolyte.In the application, the electrolyte is added with the carboxylic acid ester additive with a specific content, which is beneficial to reducing the viscosity of the electrolyte and improving the wettability of the electrolyte; meanwhile, the electrolyte has high ionic conductivity, provides efficient transport power for high energy density batteries; and the electrolyte is good in adaptability to lithium ion batteries, so that the lithium ion batteries have high specific capacity and excellent cycle stability, and are beneficial to further developing lithium ion batteries with higher energy density.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte and application thereof. BACKGROUND

[0002] The infiltration process of a lithium ion battery refers to the diffusion and penetration process of electrolyte on the electrode in the battery. This process has an important influence on the performance and service life of the battery. Inhomogeneous infiltration will lead to uneven current density distribution and unstable electrolyte interface film (SEI) formed; meanwhile, incomplete infiltration will significantly affect the internal resistance of the battery, thereby directly affecting the battery performance such as rate, capacity development, cycle life, low-temperature performance, etc. In addition, insufficient infiltration will also lead to the occurrence of lithium precipitation, causing a series of safety problems. Therefore, how to improve the compaction density to increase the battery capacity while improving the problem of difficult electrolyte infiltration caused by high compaction density is a key technical challenge in developing high-energy-density lithium ion batteries.

[0003] The infiltration performance of the electrolyte is determined by the viscosity of the electrolyte. The viscosity of the electrolyte is determined by the electrolyte formula. Usually, the viscosity of the electrolyte is reduced and the wettability of the electrolyte is improved in the prior art by two aspects. On the one hand, the wettability of the electrolyte is improved by increasing the proportion of linear carbonate in the solvent to reduce the viscosity of the electrolyte; but the dielectric constant of linear carbonate is low, which cannot effectively dissociate lithium salt. On the other hand, the wettability of the electrolyte is improved by reducing the concentration of lithium salt in the electrolyte, but the low concentration of lithium salt will reduce the number of free Li + and cause insufficient ion dynamics.

[0004] Therefore, it is an urgent problem to be solved in the field to develop an electrolyte with low viscosity, good infiltration and high ionic conductivity, which can ensure that the lithium ion battery has excellent cycle stability and high capacity. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide an electrolyte and application thereof. The electrolyte solves the problem of insufficient wettability of the existing lithium ion battery electrolyte, which cannot meet the needs of high compaction electrode infiltration.

[0006] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides an electrolyte, which comprises a base electrolyte and an additive; the base electrolyte comprises an organic solvent and a lithium salt; the additive comprises a carboxylate additive; the mass of the additive is 0.1-4% of the mass of the base electrolyte.

[0008] In the present application, the electrolyte by adding a certain content of carboxylic acid ester additive, is conducive to reducing the viscosity of electrolyte, improve the electrolyte wettability; at the same time, the electrolyte has higher ionic conductivity, for high energy density battery provides efficient transport power; and the electrolyte is good with lithium ion battery adaptability, so that the lithium ion battery has high specific capacity and excellent cycle stability, is conducive to further development of higher energy density lithium ion battery.

[0009] In the present application, the mass of the additive is 0.1-4% of the mass of the base electrolyte, for example, it can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, etc.

[0010] In the present application, the mass percentage of the additive is too small, the wettability is not obviously improved; the mass percentage is too much, which will also cause the viscosity to increase, the capacity of the battery to decrease, the cycle stability to be poor, and the cost to increase.

[0011] Preferably, the carboxylic acid ester additive has the structure shown in formula I.

[0012]

[0013] wherein R1 is selected from linear alkyl with carbon atom number > 6, for example, the carbon atom number can be 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc.; R2 is selected from C1-C6 linear or branched alkyl, for example, it can be C1, C2, C3, C4, C5, C6 linear or branched alkyl.

[0014] In the present application, long carbon chain carboxylic acid ester additive is preferred. In the molecular structure of the long carbon chain carboxylic acid ester additive, there is a van der Waals force between the electronegative center and the alpha-H of the carbonate solvent, which destroys the stable structure of the carbonate and makes the intermolecular force smaller, thereby causing the viscosity to decrease. At the same time, the long chain structure makes it difficult to form a large-scale network structure inside, and the nonpolar end of the long carbon chain carboxylic acid ester additive will be adsorbed on the surface of the solvent, further improving the wettability of the electrolyte.

[0015] Preferably, the carboxylic acid ester additive includes carboxylic acid ester additive A and carboxylic acid ester additive B, and the number of carbon atoms in the main chain of the carboxylic acid ester additive A is greater than that of the carboxylic acid ester additive B.

[0016] Preferably, the carboxylic acid ester additive A includes at least one of methyl decanoate, ethyl decanoate, methyl undecanoate, methyl laurate, ethyl laurate, methyl myristate, or ethyl myristate.

[0017] Preferably, the carboxylate additive B comprises at least one of methyl heptanoate, ethyl heptanoate, methyl octanoate, ethyl octanoate, methyl nonanoate or ethyl nonanoate.

[0018] Preferably, the mass ratio of the carboxylate additive A and the carboxylate additive B is (2-4):1, wherein the specific value in (2-4) can be 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, etc.

[0019] Preferably, the organic solvent comprises a cyclic carbonate and / or a chain carbonate, more preferably a cyclic carbonate.

[0020] Preferably, the cyclic carbonate comprises at least one of ethylene carbonate (EC), propylene carbonate (PC) or butylene carbonate (BC), more preferably propylene carbonate.

[0021] Preferably, the chain carbonate comprises at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) or methyl propyl carbonate (MPC).

[0022] Preferably, the concentration of the lithium salt in the base electrolyte is 0.1-2 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, etc.

[0023] Preferably, the lithium salt comprises an inorganic lithium salt and / or an organic lithium salt.

[0024] Preferably, the inorganic lithium salt comprises at least one of lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6) or lithium hexafluorophosphate (LiPF6).

[0025] Preferably, the organic lithium salt comprises at least one of lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(difluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0026] In the present application, the viscosity of the electrolyte is ≤9.6 mPa·s, preferably ≤9 mPa·s, more preferably ≤8.5 mPa·s, and particularly preferably 8 mPa·s at 25℃.

[0027] In the present application, the ionic conductivity of the electrolyte is ≥6.25 ms / cm at 25℃, preferably ≥6.5 ms / cm, more preferably ≥6.7 ms / cm, and particularly preferably ≥6.8 ms / cm.

[0028] In the present application, the preparation method of the electrolyte comprises: mixing and stirring the base electrolyte and the additive for ≥12h to completely dissolve, to obtain the electrolyte.

[0029] Preferably, the preparation method of the base electrolyte comprises uniformly mixing the organic solvent and the lithium salt to obtain the base electrolyte.

[0030] In the present application, before the addition of the additive, a step of using molecular sieves to remove water is further included; and the mixing is carried out in a high-purity argon glove box.

[0031] In a second aspect, the present application provides a lithium ion battery comprising the electrolyte of the first aspect.

[0032] In a third aspect, the present application provides a power device comprising the electrolyte of the first aspect or the lithium ion battery of the second aspect.

[0033] The numerical range of the present application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed, and for the sake of brevity and simplicity, the present application does not exhaustively list the specific point values included in the range.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] The electrolyte provided by the present application, by adding a specific content of carboxylic acid ester additive, is conducive to reducing the viscosity of the electrolyte and improving the wettability of the electrolyte; at the same time, the electrolyte has a high ionic conductivity, providing efficient transport power for high-energy-density batteries; and the electrolyte has good compatibility with lithium ion batteries, so that the lithium ion batteries have high specific capacity and excellent cycle stability, which is conducive to the further development of higher-energy-density lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The contact angle test result graph of the electrolyte provided for Examples 1-7 and Comparative Example 1 of the present application.

[0037] Figure 2 The viscosity test result graph of the electrolyte provided for Examples 1-7 and Comparative Example 1 of the present application.

[0038] Figure 3 The ionic conductivity test result graph of the electrolyte provided for Examples 1-7 and Comparative Example 1 of the present application. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] Example 1

[0041] This embodiment provides an electrolyte comprising a base electrolyte and methyl decanoate; the base electrolyte comprises propylene carbonate and LiPF6; the concentration of LiPF6 in the base electrolyte is 1 mol / L; and the mass of the methyl decanoate is 0.1% of the mass of the base electrolyte.

[0042] This embodiment provides a method for preparing an electrolyte, specifically including the following steps:

[0043] First, methyl decanoate was dehydrated using molecular sieves. Then, lithium salt was weighed in a high-purity argon glove box and dissolved in PC at a molar concentration of 1 mol / L. The prescribed amount of methyl decanoate was then added to the solution, and the mixture was stirred with a magnetic stirrer for 12 hours until it was completely dissolved, thus obtaining the electrolyte.

[0044] Example 2

[0045] This embodiment provides an electrolyte that differs from Example 1 only in that the mass of the methyl decanoate is 0.2% of the mass of the base electrolyte, while the other components, amounts, and preparation methods are the same as in Example 1.

[0046] Example 3

[0047] This embodiment provides an electrolyte that differs from Example 1 only in that the mass of the methyl decanoate is 0.5% of the mass of the base electrolyte, while the other components, amounts, and preparation methods are the same as in Example 1.

[0048] Example 4

[0049] This embodiment provides an electrolyte that differs from Example 1 only in that the mass of the methyl decanoate is 1% of the mass of the base electrolyte, while the other components, amounts, and preparation methods are the same as in Example 1.

[0050] Example 5

[0051] This embodiment provides an electrolyte that differs from Example 1 only in that the mass of the methyl decanoate is 2% of the mass of the base electrolyte, while the other components, amounts, and preparation methods are the same as in Example 1.

[0052] Example 6

[0053] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 1 only in that the mass of the methyl decanoate in the electrolyte is 3% of the mass of the base electrolyte, and the other components, the dosages and the preparation method are the same as those in the embodiment 1.

[0054] Embodiment 7

[0055] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 1 only in that the mass of the methyl decanoate in the electrolyte is 4% of the mass of the base electrolyte, and the other components, the dosages and the preparation method are the same as those in the embodiment 1.

[0056] Embodiment 8

[0057] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the methyl decanoate is replaced by methyl acetate with the same mass, and the other components, the dosages and the preparation method are the same as those in the embodiment 5.

[0058] Embodiment 9

[0059] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the methyl decanoate is replaced by dodecanyl acetate with the same mass, and the other components, the dosages and the preparation method are the same as those in the embodiment 5.

[0060] Embodiment 10

[0061] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the total mass of the additives is unchanged, the methyl decanoate is replaced by methyl decanoate and methyl octanoate with a mass ratio of 2.5:1, and the other components, the dosages and the preparation method are the same as those in the embodiment 5.

[0062] Embodiment 11

[0063] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the total mass of the additives is unchanged, the methyl decanoate is replaced by methyl laurate and methyl nonanoate with a mass ratio of 3.5:1, and the other components, the dosages and the preparation method are the same as those in the embodiment 5.

[0064] Embodiment 12

[0065] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the total mass of the additives is unchanged, the methyl decanoate is replaced by methyl decanoate and methyl octanoate with a mass ratio of 1:1, and the other components, the dosages and the preparation method are the same as those in the embodiment 5.

[0066] Embodiment 13

[0067] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the total mass of the additive is unchanged, the methyl decanoate is replaced by methyl decanoate and methyl octanoate with a mass ratio of 5:1, and the other components, the amount and the preparation method are the same as those in the embodiment 5.

[0068] Embodiment 14

[0069] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the total mass of the additive is unchanged, the methyl decanoate is replaced by methyl decanoate and methyl octanoate with a mass ratio of 5:1, and the other components, the amount and the preparation method are the same as those in the embodiment 5.

[0070] Embodiment 15

[0071] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the total volume of the organic solvent is unchanged, the PC is replaced by a mixed solvent of PC and DMC with a volume ratio of 1:4, and the other components, the amount and the preparation method are the same as those in the embodiment 5.

[0072] Embodiment 16

[0073] The embodiment provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the total mass of the additive is unchanged, the methyl decanoate is replaced by methyl decanoate and methyl octanoate with a mass ratio of 5:1, and the other components, the amount and the preparation method are the same as those in the embodiment 5.

[0074] Comparative Example 1

[0075] The comparative example provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that no additive is added, and the other components, the amount and the preparation method are the same as those in the embodiment 5.

[0076] Comparative Example 2

[0077] The comparative example provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the methyl decanoate is replaced by cyclohexane with the same mass, and the other components, the amount and the preparation method are the same as those in the embodiment 5.

[0078] Comparative Example 3

[0079] The comparative example provides an electrolyte, which is different from the electrolyte in the embodiment 5 only in that the mass of the methyl decanoate is 5% of the mass of the base electrolyte, and the other components, the amount and the preparation method are the same as those in the embodiment 5.

[0080] Performance test

[0081] (1) Contact angle test: a contact angle measuring instrument was used for the test; the specific method included that 5 μL of the electrolyte provided by Examples 1 to 16 and Comparative Examples 1 to 3 was dropped on the surface of a polyethylene separator with a thickness of 25 μm at 25°C, and the wettability of the electrolyte was measured according to the size of the contact angle formed by the electrolyte droplet on the separator. The time point of the droplet contact angle measurement was 1 s after the droplet contacted the surface of the separator. In order to eliminate errors as much as possible, the value of the contact angle between each electrolyte and the separator was the average value of 8 parallel experiments.

[0082] The contact angle test results of the electrolytes provided by Examples 1 to 7 and Comparative Example 1 are shown in Table 1. Figure 1 The results show that after the addition of methyl decanoate, the contact angles between the electrolyte and the separator are reduced to varying degrees; when the mass percentage content of methyl decanoate in the electrolyte is 2% and 3%, the contact angle between the electrolyte and the separator is the smallest. It is shown that after the addition of methyl decanoate, the wettability of the electrolyte is obviously improved, and the carboxylic acid ester additive can effectively improve the wettability between the electrolyte and the separator.

[0083] (2) Viscosity: 100 mL of the electrolyte provided by Examples 1 to 16 and Comparative Examples 1 to 3 was taken into a beaker at a constant temperature (25±0.1°C), and the rotor of a rotary viscometer was immersed in the electrolyte to be measured to obtain the viscosity of the electrolyte at 25°C.

[0084] The specific test results of the viscosity of the electrolytes provided by Examples 1 to 7 and Comparative Example 1 are shown in Table 2. Figure 2 The results show that when the content of the carboxylic acid ester additive gradually increases, the viscosity of the electrolyte continuously decreases; when the content of the carboxylic acid ester additive increases to 4%, the viscosity is slightly higher than that of Examples 5 and 6, but is still significantly lower than the viscosity of the electrolyte provided by Comparative Example 1.

[0085] (3) Ionic conductivity: 5 mL of the electrolyte provided by Examples 1 to 16 and Comparative Examples 1 to 3 was taken into a polytetrafluoroethylene reagent bottle, and after the insertion of a conductivity electrode, it was placed in a constant temperature test box for testing. The specific test steps were as follows: at 25°C, the electrolyte was allowed to stand for 1 h, and then a conductivity meter was used for measurement to obtain the ionic conductivity value of the electrolyte at 25°C.

[0086] The test results of the ionic conductivity of the electrolytes provided by Examples 1 to 7 and Comparative Example 1 are shown in Table 3. Figure 3 The results show that as the content of the carboxylic acid ester additive gradually increases, the ionic conductivity of the electrolyte gradually increases; when the content of the carboxylic acid ester additive increases to 4%, the ionic conductivity is slightly lower than that of Examples 5 and 6, but is still significantly higher than the ionic conductivity of the electrolyte provided by Comparative Example 1.

[0087] (4) Electrochemical test: lithium metal was used as the counter electrode, 25 μm polyethylene separator was used as the separator, and the electrolyte was selected from the electrolytes provided in Examples 1-16 and Comparative Examples 1-3 (100 μL in volume). The CR2032 button cell was assembled and sealed in a glove box (LS800D, oxygen and water content ≤0.1 ppm). The assembled cell was allowed to stand at room temperature for 10 h, and then electrochemical test was performed.

[0088] The assembled cell was tested for charge-discharge cycle performance and rate performance by using a Wuhan Lan Electric CT2001A battery test system, and the test voltage range was set to 2.4-4.2 V (vs. Li + / Li); the temperature was 25°C.

[0089] The specific test results are shown in Table 1.

[0090] Table 1

[0091]

[0092] As shown in Table 1, the electrolyte provided in the present application, by adding a specific content of carboxylic acid ester additive, can not only effectively reduce the viscosity of the electrolyte and improve the wettability of the electrolyte, but also improve the capacity and cycle stability of the lithium ion battery. The lithium ion battery has a high specific capacity and capacity retention rate at different rates, and the performance is more obvious at a large rate of 5C. The battery comprising the electrolyte has an initial discharge capacity of ≥150 mAh at a rate of 0.2C, a first coulombic efficiency of ≥97.2%, an initial discharge capacity of ≥143 mAh at a rate of 1C, a cycle capacity retention rate of ≥81.3% after 500 cycles, an initial discharge capacity of ≥130 mAh at a rate of 2C, a cycle capacity retention rate of ≥75.4% after 200 cycles, an initial discharge capacity of ≥75 mAh at a rate of 5C, and a cycle capacity retention rate of ≥64.3% after 100 cycles, and even up to 90.6% or more.

[0093] The applicant declares that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed in the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a base electrolyte and additives; The basic electrolyte comprises an organic solvent and a lithium salt; The additives include carboxylic acid ester additives; The mass of the additive is 0.1-4% of the mass of the base electrolyte; The carboxylic acid ester additives include carboxylic acid ester additive A and carboxylic acid ester additive B, wherein the number of carbon atoms in the main chain of carboxylic acid ester additive A is greater than the number of carbon atoms in the main chain of carboxylic acid ester additive B; The mass ratio of the carboxylic acid ester additive A to the carboxylic acid ester additive B is (2~4):1; The carboxylic acid ester additive A includes at least one of methyl decanoate, ethyl decanoate, methyl undecanoate, methyl laurate, ethyl laurate, methyl myristate, or ethyl myristate. The carboxylic acid ester additive B includes at least one of methyl heptanoate, ethyl heptanoate, methyl octanoate, ethyl octanoate, methyl nonanoate, or ethyl nonanoate.

2. The electrolyte according to claim 1, characterized in that, The organic solvent includes cyclic carbonates and / or chain carbonates.

3. The electrolyte according to claim 2, characterized in that, The organic solvent is a cyclic carbonate.

4. The electrolyte according to claim 3, characterized in that, The cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, or butene carbonate.

5. The electrolyte according to claim 4, characterized in that, The cyclic carbonate is propylene carbonate.

6. The electrolyte according to claim 2, characterized in that, The chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or methyl propyl carbonate.

7. The electrolyte according to claim 1, characterized in that, The concentration of lithium salt in the basic electrolyte is 0.1~2 mol / L.

8. The electrolyte according to claim 1, characterized in that, The lithium salt includes inorganic lithium salts and / or organic lithium salts.

9. The electrolyte according to claim 8, characterized in that, The inorganic lithium salt includes at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, or lithium hexafluorophosphate.

10. The electrolyte according to claim 8, characterized in that, The organolithium salt includes at least one of lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(difluorosulfonyl)imide, or lithium bis(trifluoromethyl)sulfonyl)imide.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte according to any one of claims 1 to 10.

12. An electrical appliance, characterized in that, The electrical device includes the electrolyte according to any one of claims 1 to 10 or the lithium-ion battery according to claim 11.

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