Electrolyte for lithium ion battery and preparation method thereof

Abstract

The present application belongs to the technical field of lithium ion battery, and particularly relates to an electrolyte for lithium ion battery, which is composed of the following raw materials in parts by weight: ionic liquid 35-45 parts, emulsifier 3-5 parts, polypropylene 25-35 parts, gellan gum 8-12 parts, cyclodextrin 6-8 parts, lithium salt 4-8 parts, solvent 100-200 parts, and polyethylene glycol 3-5 parts. The electrolyte of the present application forms microcapsule type micro-particles with high lithium ion conductivity, which not only has excellent lithium ion conductivity, but also does not have the phenomenon of liquid leakage in the use process, and is safe and reliable; effectively improves the compatibility between the electrolyte film and the electrode material, improves the liquid retention rate and the conductivity, and reduces the internal resistance of the battery, thereby improving the safety and cycle performance of the lithium ion battery.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries have become increasingly important energy storage devices and are widely used in the fields of smart phones, electric vehicles, electric bicycles and aerospace. A lithium ion battery is usually composed of electrodes, electrolytes and separators, etc. The electrolyte, as an important part of the battery, is responsible for ion transmission between electrodes, and determines the electrochemical performance and safety performance of the battery. The electrolyte of a lithium ion battery is mainly divided into liquid, solid and gel states. At present, the commercialized electrolyte of a lithium ion battery is mainly an organic liquid electrolyte. During use, liquid leakage or short circuit may occur, and even the electrolyte may cause the battery to catch fire or explode, bringing serious safety hazards. At present, the all-solid-state electrolyte cannot meet the requirements of practical application due to low room temperature conductivity and other defects. In recent years, a kind of liquid ionic compound-ion liquid has appeared, which basically meets the principles of "green chemistry" proposed by American scientist Anastas. The ion liquid is a liquid composed of ions. It is a molten salt in a liquid state at room temperature, and has the advantages of not easy to volatilize, high temperature resistance, not easy to burn, large heat melting, wide electrochemical window and the like. Generally, ionic compounds are in a solid state at room temperature, while the ion liquid has large and asymmetric volume of anions and cations, so the steric hindrance is large. Therefore, the anions and cations cannot rely on electrostatic force to make their internal microstructure tightly packed, reducing the interaction between ions and the lattice energy, so that the melting and boiling points are reduced. Therefore, the ion liquid can be in a liquid state at room temperature. The ion liquid has some advantages that other chemicals cannot match, such as a wide electrochemical window (generally 4-6V), almost no vapor pressure, a wide temperature range of thermal stability (most of them are in a liquid state within 300℃), high chemical stability, not easy to volatilize, not easy to burn, large heat melting and the like. Due to the above advantages, the research on ion liquid as electrolyte has gradually become a research hotspot. However, the effect of the electrolyte prepared by using the ion liquid on the optimization of the flame retardant performance of the battery is limited. At present, the improvement of the flame retardant performance of the electrolyte is mainly realized by adding flame retardant additives to the electrolyte. The addition of the flame retardant additives changes the organic electrode liquid from flammable to difficult to burn or even flame-retardant, thereby enhancing the safety performance and use stability of the electrolyte and reducing the risk of combustion or explosion of the electrolyte during use. However, the addition of the flame retardant additives reduces the ionic conductivity of the electrolyte and the compatibility with the electrode material, resulting in an increase in the internal resistance of the battery, and further affecting the capacity development of the battery and the cycle service life of the battery. SUMMARY

[0003] The electrolyte for lithium ion battery and the preparation method thereof are provided to improve the ion conductivity of electrolyte, further improve the compatibility with electrode material, reduce the increase of battery internal resistance, and improve the safety and cycle performance of the battery.

[0004] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0005] The electrolyte for lithium ion battery is composed of the following raw materials by weight:

[0006] 35-45 parts of ionic liquid, 3-5 parts of emulsifier, 25-35 parts of polypropylene, 8-12 parts of gellan gum, 6-8 parts of cyclodextrin, 4-8 parts of lithium salt, 100-200 parts of solvent, and 3-5 parts of polyethylene glycol;

[0007] The ionic liquid is one of 1-ethyl-2-methylpyrazole tetrafluoroborate, 1-methyl-3-ethyl imidazole dicyano imine, N-methyl-N-propyl pyrrole trifluoromethane sulfonamide, and N, N-dimethyl-N-ethyl-N-2-methoxy ethyl ammonium tetrafluoroborate.

[0008] The emulsifier is one of alkyl phenol polyoxyethylene ether formaldehyde, aralkyl phenol polyoxyethylene ether formaldehyde, and polyoxyethylene polyoxypropylene block copolymer.

[0009] In a preferred example, the lithium salt is one of LiPF6, LiBF4, and LiB(C2O4)2.

[0010] In a preferred example, the solvent is composed of DBP and DOP mixed at a volume ratio of 3:2.

[0011] Based on the overall inventive concept, another object of the present application is to provide the preparation method of the electrolyte for lithium ion battery, which comprises the following steps:

[0012] (1) Dissolve the polypropylene in the solvent, mix uniformly, then add the ionic liquid and the emulsifier, and slowly stir and disperse at a speed of 40-80 r / min for 20-30 min to form solution one;

[0013] (2) Mix the gellan gum, cyclodextrin, lithium salt, and polyethylene glycol uniformly at a temperature of 65-80℃ to prepare solution two;

[0014] (3) Under the ice water bath environment, drop solution one into solution two to obtain the particles with microcapsule structure, discharge, and dry;

[0015] (4) immerse the particles of microcapsule structure into 0.1% CaCl2 solution for 15 min, then transfer into 1.5% CaCl2 solution for 15 min, take out, wash the surface particles with distilled water and transfer into constant temperature vacuum drier, vacuum dry for 8-12 h to obtain electrolyte.

[0016] As preferred, the 0.1% CaCl2 solution and 1.5% CaCl2 solution are respectively adjusted to pH 4.5 with acetic acid.

[0017] As preferred, in step (3), the temperature of ice water bath environment is -10℃ to -30℃.

[0018] As preferred, in step (4), the temperature of vacuum drying is 55-65℃, and the vacuum degree is -0.05 to -0.1 MPa.

[0019] Compared with prior art, the present application forms microcapsule type micro particles with high lithium ion conductivity, which not only has excellent lithium ion conductivity, but also has no liquid leakage phenomenon in use, is safe and reliable, effectively improves the compatibility between electrolyte membrane and electrode material, improves the liquid retention rate and conductivity, and reduces the internal resistance of battery, thereby improving the safety and cycle performance of lithium ion battery. DETAILED DESCRIPTION

[0020] To make the object, technical scheme and advantages of the present application clearer and more apparent, the present application is further described in conjunction with specific embodiments, but the present application is not limited to these embodiments. It should be noted that, under the premise of no conflict, each embodiment described below or each technical feature can be combined with each other to form a new embodiment. In the present application, unless specified, all parts and percentages are mass units, and the equipment and raw materials used can be purchased from market or are common in the art. The methods in the following embodiments are conventional methods in the art, unless otherwise specified.

[0021] The terms "comprising", "including", "containing", or any other similar words used in this document are intended to cover non-exclusive inclusion. For example, the composition, step, method, article or device comprising the listed elements does not necessarily limit to only those elements, but can include other elements not explicitly listed or inherent to such composition, step, method, article or device.

[0022] When equivalent, concentration, or other value or parameter is expressed in a range or a preferred range or a series of ranges of upper preferred values and lower preferred values, it is to be understood that every range of values or preferred values between any of the upper and lower values, regardless of whether such range is expressly stated, is also contemplated. For example, a stated range of "1 to 5" should be interpreted to include not only the specifically recited ranges of "1 to 4," "1 to 3," "1 to 2," "1 to 2 and 4 to 5," "1 to 3 and 5," etc., but also the ranges of "2 to 5," "3 to 4," etc. When numerical ranges are expressed in this document, unless otherwise stated, the range is intended to include the end values and all integers and fractions within that range.

[0023] Example 1

[0024] An electrolyte for lithium ion battery, which is composed of the following raw materials by weight:

[0025] 40 parts of ionic liquid, 4 parts of emulsifier, 30 parts of polypropylene, 10 parts of gellan gum, 7 parts of cyclodextrin, 6 parts of LiPF6 lithium salt, 150 parts of solvent, 4 parts of polyethylene glycol;

[0026] The ionic liquid is N-methyl-N-propyl pyrrole trifluoromethane sulfonamide, the emulsifier is aralkyl phenol polyoxyethylene ether formaldehyde, and the solvent is composed of DBP and DOP mixed in a volume ratio of 3:2;

[0027] The preparation method of the electrolyte for lithium ion battery, which comprises the following steps:

[0028] (1) Dissolve polypropylene in a solvent, mix uniformly, then add ionic liquid and emulsifier, and slowly stir and disperse at a speed of 60 r / min for 25 min to form solution one;

[0029] (2) Mix gellan gum, cyclodextrin, lithium salt and polyethylene glycol uniformly at a temperature of 72°C to prepare solution two;

[0030] (3) Under the environment of ice water bath at -20°C, drop solution one into solution two to obtain particles with microcapsule structure, discharge, and dry;

[0031] (4) Soak the particles with microcapsule structure in 0.1% CaCl2 solution for 15 min, then transfer to 1.5% CaCl2 solution for 15 min, take out, wash the surface particles with distilled water, and transfer into a constant-temperature vacuum dryer, and vacuum dry for 8-12 h to obtain the electrolyte;

[0032] The 0.1% CaCl2 solution and the 1.5% CaCl2 solution are respectively adjusted to pH 4.5 by acetic acid; the temperature for vacuum drying is 55-65°C, and the vacuum degree is -0.05 to -0.1 MPa.

[0033] Example 2

[0034] An electrolyte for lithium ion battery, which is composed of the following raw materials by weight:

[0035] ion liquid 45 parts, emulsifier 3 parts, polypropylene 35 parts, gellan gum 8 parts, cyclodextrin 8 parts, LiBF4 lithium salt 4 parts, solvent 200 parts, polyethylene glycol 3 parts;

[0036] The ion liquid is 1-ethyl-2-methyl pyrazole tetrafluoroborate, the emulsifier is alkyl phenol polyoxyethylene ether formaldehyde, and the solvent is composed of DBP and DOP mixed in a volume ratio of 3:2;

[0037] The preparation method of the electrolyte for lithium ion battery, comprising the following steps:

[0038] (1) Dissolve polypropylene in the solvent, mix uniformly, then add ion liquid and emulsifier, and slowly stir and disperse at a speed of 80 r / min for 20 min to form solution one;

[0039] (2) Mix gellan gum, cyclodextrin, lithium salt and polyethylene glycol uniformly at a temperature of 80℃ to prepare solution two;

[0040] (3) Under the ice water bath environment at -30℃, drop solution one into solution two to obtain particles with microcapsule structure, discharge, and dry;

[0041] (4) Soak the particles with microcapsule structure in 0.1% CaCl2 solution for 15 min, then transfer to 1.5% CaCl2 solution for 15 min, take out, wash the surface particles with distilled water, and transfer into a constant temperature vacuum dryer, and vacuum dry for 8 h to obtain the electrolyte.

[0042] The 0.1% CaCl2 solution and the 1.5% CaCl2 solution are respectively adjusted to pH 4.5 by acetic acid; the temperature of vacuum drying is 65℃, and the vacuum degree is -0.05.

[0043] Example 3

[0044] An electrolyte for lithium ion battery, which is composed of the following raw materials by weight:

[0045] ion liquid 45 parts, emulsifier 3 parts, polypropylene 35 parts, gellan gum 8 parts, cyclodextrin 8 parts, LiBF4 lithium salt 4 parts, solvent 200 parts, polyethylene glycol 3 parts;

[0046] The ion liquid is N, N-dimethyl-N-ethyl-N-2-methoxyethyl ammonium tetrafluoroborate, the emulsifier is polyoxyethylene polyoxypropylene block copolymer, and the solvent is composed of DBP and DOP mixed at a volume ratio of 3:2.

[0047] The preparation method of the electrolyte for the lithium ion battery comprises the following steps:

[0048] (1) Dissolve polypropylene in a solvent, mix uniformly, then add ion liquid and emulsifier, and slowly stir and disperse at a speed of 40 r / min for 30 min to form solution I;

[0049] (2) Mix inositol, cyclodextrin, lithium salt and polyethylene glycol uniformly at a temperature of 65℃ to prepare solution II;

[0050] (3) Under the condition of ice water bath at-10℃, drop solution I into solution II to obtain particles with microcapsule structure, discharge, and dry;

[0051] (4) Soak the particles with microcapsule structure in 0.1% CaCl2 solution for 15 min, then transfer to 1.5% CaCl2 solution for 15 min, take out, wash the surface particles with distilled water, and transfer into a constant-temperature vacuum dryer, and vacuum dry for 12 h to obtain the electrolyte.

[0052] The 0.1% CaCl2 solution and the 1.5% CaCl2 solution are respectively adjusted to pH 4.5 by acetic acid, the temperature of vacuum drying is 55℃, and the vacuum degree is-0.1 MPa.

[0053] Test Example 1

[0054] The test method of conductivity is as follows: pour the electrolyte into a polytetrafluoroethylene mold, cut into a circle with a diameter of 1 cm, place between two stainless steel electrodes (SS), assemble into a SS / electrolyte film / SS simulated battery for detection. The test range is 1 MHz-0.01 Hz, and the alternating voltage amplitude is 10 mV; before testing, the device is heated at 60℃ for 2 h to ensure sufficient contact between the electrode and the electrolyte film. The obtained test data is simulated and analyzed by Ziew software, and the test results are shown in Table 1.

[0055] The test method of mechanical property is as follows: the tensile property of the electrolyte film is tested by using a Shimadzu AG-50kN device, and the test conditions are as follows: test temperature is 25℃, test rate is 1 N / min, sample width is 8 mm, and sample length is 60 mm. The test results are shown in Table 1.

[0056] Table 1: Test results of conductivity and mechanical property of electrolytes of Examples 1-3

[0057]

[0058]

[0059] Test Example 2

[0060] The electrolyte prepared in Examples 1-3 was assembled into LiFePO4 / Li button cells, and the charge-discharge performance was tested at 45℃ and a rate of 0.5C. The results are shown in Table 2.

[0061] Table 2. Results of cycle performance test of lithium ion battery of Examples

[0062]

[0063] As can be seen from the experimental data in Table 2, the capacity attenuation after 100 cycles is less when the electrolyte of the Examples is assembled into a button cell for charge-discharge performance test, indicating that the electrolyte prepared in the present application has a stable film structure, good compatibility with the positive and negative electrodes, and can react on the surface of the electrode during the charge-discharge process to form a flexible SEI film, thereby tightly bonding the electrolyte and the lithium battery electrode together, and significantly improving the compatibility between the electrolyte and the electrode material.

[0064] Test Example 3

[0065] The lithium ion battery electrolytes of Examples 1-3 were respectively configured with ethylene carbonate (EC) and diethyl carbonate (DEC) into an electrolyte with a concentration of 1.0 mol / L, and a lithium ion battery was prepared. The lithium ion battery was prepared using artificial graphite as the negative active material to make a negative electrode sheet, LiNi 0.75 Mn 0.25 O2 as the positive active material to make a positive electrode sheet, and a ceramic separator, to assemble a 5 Ah lithium ion battery. The ceramic separator used included a PE separator substrate and an alumina coating layer coated on the separator substrate, and the thickness of the alumina coating layer was 2.5 μm. The obtained lithium ion battery was subjected to safety tests of overcharge, short circuit, and needle puncture.

[0066] The lithium ion battery prepared above was subjected to overcharge test at 3C and 10V in a constant voltage and then a constant current in a fume hood at an ambient temperature of 20℃, and the test results are shown in Table 3.

[0067] Table 3. Overcharge test results

[0068]

[0069]

[0070] The lithium ion batteries prepared above are subjected to 60℃ high temperature short circuit test and needle puncture test, respectively, and the results are shown in Table 4.

[0071] Table 4: Results of high temperature short circuit and needle puncture test

[0072]

[0073] The lithium ion battery prepared by using the electrolyte prepared by using the electrolyte of the application still has high safety and stability under overcharge, short circuit and needle puncture external conditions.

[0074] The above examples are only preferred embodiments of the application, and any simple modification, modification and alternative change made according to the technical essence of the application to the above examples are within the scope of the technical scheme of the application.

Claims

1. An electrolyte for lithium-ion batteries, characterized in that, Composed of the following raw materials in parts by weight: 35-45 parts ionic liquid, 3-5 parts emulsifier, 25-35 parts polypropylene, 8-12 parts gellan gum, 6-8 parts cyclodextrin, 4-8 parts lithium salt, 100-200 parts solvent, and 3-5 parts polyethylene glycol. The solvent is composed of DBP and DOP mixed in a volume ratio of 3:2; The ionic liquid is one of 1-ethyl-2-methylpyrazole tetrafluoroborate, 1-methyl-3-ethylimidazolium dicyanoimide, N-methyl-N-propylpyrrole trifluoromethanesulfonamide, and N,N-dimethyl-N-ethyl-N-2-methoxyethylammonium tetrafluoroborate. The emulsifier is one of alkylphenol polyoxyethylene ether formaldehyde, arylalkylphenol polyoxyethylene ether formaldehyde, and polyoxyethylene polyoxypropylene block copolymer. The method for preparing the electrolyte for lithium-ion batteries includes the following steps: (1) Dissolve polypropylene in a solvent, mix evenly, then add ionic liquid and emulsifier, and slowly stir and disperse at a speed of 40-80 r / min for 20-30 min to form solution one; (2) Mix gellan gum, cyclodextrin, lithium salt and polyethylene glycol at a temperature of 65-80°C to obtain solution two; (3) In an ice-water bath environment, add solution one drop to solution two to obtain particles with microcapsule structure, discharge the material and dry it; (4) Immerse the microcapsule structured particles in 0.1% CaCl2 solution for 15 min, then transfer them to 1.5% CaCl2 solution for 15 min, remove them, wash the surface particles with distilled water and transfer them to a constant temperature vacuum dryer for vacuum drying for 8-12 h to obtain electrolyte.

2. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The lithium salt is one of LiPF6, LiBF4, and LiB(C2O4)2.

3. A method for preparing an electrolyte for lithium-ion batteries as described in any one of claims 1 to 2, characterized in that, Includes the following steps: (1) Dissolve polypropylene in a solvent, mix evenly, then add ionic liquid and emulsifier, and slowly stir and disperse at a speed of 40-80 r / min for 20-30 min to form solution one; (2) Mix gellan gum, cyclodextrin, lithium salt and polyethylene glycol at a temperature of 65-80°C to obtain solution two; (3) In an ice-water bath environment, add solution one drop to solution two to obtain particles with microcapsule structure, discharge the material and dry it; (4) Immerse the microcapsule structured particles in 0.1% CaCl2 solution for 15 min, then transfer them to 1.5% CaCl2 solution for 15 min, remove them, wash the surface particles with distilled water and transfer them to a constant temperature vacuum dryer for vacuum drying for 8-12 h to obtain electrolyte.

4. The method for preparing an electrolyte for a lithium-ion battery according to claim 3, characterized in that, The 0.1% CaCl2 solution and the 1.5% CaCl2 solution were adjusted to pH 4.5 using acetic acid.

5. The method for preparing an electrolyte for a lithium-ion battery according to claim 3, characterized in that, Step (3): The temperature of the ice water bath environment is -10℃ to -30℃.

6. The method for preparing an electrolyte for a lithium-ion battery according to claim 3, characterized in that, Step (4): The vacuum drying temperature is 55-65℃ and the vacuum degree is -0.05--0.1MPa.

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