Electrolyte based on hollow mesoporous silica microspheres and preparation method thereof

Abstract

The invention provides an electrolyte based on hollow mesoporous silica microspheres and a preparation method thereof. The preparation method of the electrolyte based on the hollow mesoporous silica microspheres comprises the following steps: immersing the hollow mesoporous silica microspheres with a lithium electrolyte. The electrolyte provided by the invention takes the hollow mesoporous silica microspheres as a coating material, and the lithium electrolyte is coated in the hollow mesoporous silica microspheres, so that the risk of battery short circuit spontaneous combustion caused by diaphragm puncture due to lithium dendrite growth is effectively solved; meanwhile, the electrolyte provided by the invention has better capacity retention capability in long-acting circulation.

Description

Technical Field

[0001] The present invention relates to the field of lithium electrolytes, and more particularly to a lithium electrolyte based on hollow mesoporous silica microspheres and a preparation method thereof. Background Art

[0002] As the anode material with the highest energy density in current batteries, lithium has extremely wide applications in energy storage, new energy vehicles and other fields. However, it is limited by electrolyte instability and dendrite formation, leading to serious safety issues. To this end, many manufacturers, especially battery suppliers for new energy vehicles, have adopted a variety of solutions. For example, BYD’s blade battery, published in patent CN220021192U, uses a special battery shape to solve the problem. Another example is Geely’s solution of hydrochloric acid ultrasonic treatment of the negative electrode published in patent CN118507717A. However, these solutions cannot prevent the formation of lithium dendrites.

[0003] To completely resolve the safety issues caused by lithium dendrites damaging the separator, the industry consensus is that developing related batteries is necessary. Existing technologies use carbon as a coating material or cubic sulfur as a separator to prepare electrolytes in an effort to completely resolve the lithium dendrite problem. Summary of the Invention

[0004] The first purpose of the present invention is to provide a method for preparing an electrolyte based on hollow mesoporous silica microspheres. The electrolyte obtained by this preparation method uses hollow mesoporous silica microspheres as a coating material. The lithium electrolyte is coated inside the hollow mesoporous silica microspheres. The high rigidity of the silica microspheres is used to prevent the growth of lithium ion dendrites, thereby shielding the risk of battery spontaneous combustion caused by dendrite penetration. The electrolyte is a highly available and safe semi-solid electrolyte.

[0005] The preparation method of the electrolyte based on hollow mesoporous silica microspheres comprises the following steps: immersing the hollow mesoporous silica microspheres in a lithium electrolyte.

[0006] TEM images clearly show that the lithium electrolyte prepared using the above preparation method is encapsulated within the mesoporous hollow silica microspheres. The electrolyte obtained by the present invention exhibits good long-term battery capacity retention, preferably maintaining a high cycle capacity retention rate for more than 2,000 cycles.

[0007] In a preferred embodiment of the present invention, the lithium electrolyte is a mixture of a lithium salt and DMC. The lithium salt can be one or more of LiPF6, LiBF4, LiBOB, and LiPO2F2. To further increase the fill level and achieve a higher capacity, the lithium salt is preferably LiPF6. In a preferred embodiment of the present invention, to further ensure low internal resistance and high initial capacity during long-term testing, the concentration of the lithium salt in DMC is 1 mol / L to 2 mol / L.

[0008] In a specific embodiment of the present invention, immersion is complete submersion, preferably with lithium electrolyte until it covers 1 cm to 1.5 cm above the silica powder. To further increase capacity, the immersion time is 40 to 48 hours. Applicants have found through time-parallel experiments that the quality of the filtrate remains virtually unchanged after 48 hours.

[0009] In a specific embodiment of the present invention, in order to further improve the immersion rate of the obtained electrolyte, the above-mentioned "immersion" process is preferably carried out under negative pressure conditions, for example, at 0.01 MPa to 0.05 MPa (actual pressure).

[0010] In a preferred embodiment of the present invention, to obtain an electrolyte with a more suitable electrolyte soaking time and internal resistance, and a higher initial capacity, the pore diameter of the mesopores in the hollow mesoporous silica microspheres is 2-5 nm. The applicant has found that, in the solution of this application, an excessively large pore diameter reduces the electrolyte filling degree, resulting in a low initial capacity, while an excessively small pore diameter significantly increases the electrolyte soaking time and increases the internal resistance.

[0011] In a specific embodiment of the present invention, after the immersion is completed, the electrolyte of the present invention is obtained by filtration.

[0012] In a preferred embodiment of the present invention, the method for preparing the hollow mesoporous silica microspheres comprises the following steps: S1, mixing a surfactant, an organic medium, concentrated ammonia water, water and an alcohol, and reacting them at 35°C to 45°C for 0.5 to 1 hour to obtain a mixed solution; S2, adding the alcohol solution of silicate to the mixed solution of step S1, reacting at 35°C to 45°C, and collecting the solid after the reaction is completed; S3, mixing the solid from step S2 with an ethanol solution of concentrated hydrochloric acid, heating and stirring, filtering, and drying to obtain the product.

[0013] In a preferred embodiment of the present invention, carbon-containing silane and orthosilicate are used to prepare hollow mesoporous silica microspheres. The carbon-containing group is equivalent to modifying HMS during the preparation process, reducing a certain internal resistance and improving the wettability of the lithium salt solution therein.

[0014] In a preferred embodiment of the present invention, in step S1, the surfactant is one or more of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, and sodium lauroyl sarcosinate, preferably sodium dodecylbenzenesulfonate.

[0015] In a preferred embodiment of the present invention, in step S1, the organic medium can be benzene, cyclohexane, toluene, xylene, trimethylbenzene, cyclohexanone, tetrahydrofuran, acetone, pyridine, etc. In order to make the pore size of the obtained microspheres more uniform and the mesopore size more meet the infiltration requirements, the organic medium is preferably trimethylbenzene.

[0016] In a preferred embodiment of the present invention, in step S1, the mass ratio of surfactant, organic medium, concentrated ammonia water, water, and alcohol is 1: (1-5): (5-10): (100-120): (50-80). In the scheme of the present invention, the applicant has found through experiments that in this step, too little amount of surfactant will affect the number of pores in the obtained microspheres, thereby affecting the capacity of the obtained electrolyte and causing poor wetting. Excessive use of concentrated ammonia water will lead to the formation of flaky silica, thereby affecting the capacity of the obtained electrolyte. Too little use of concentrated ammonia water will cause the silane wall to be easily damaged and increase the production of amorphous silica. When the amount of water and alcohol used is within the above range, more uniform silica microspheres of the desired particle size can be effectively obtained.

[0017] In a specific embodiment of the present invention, the concentrated ammonia water is well known to those skilled in the art and is commercially available. The alcohol can be a conventional alcohol in the art, such as methanol, ethanol, etc.

[0018] In a preferred embodiment of the present invention, in step S2, the silicate comprises a first silicate and a second silicate. The first silicate is one or more of methyl silicate, ethyl silicate, vinyl silicate, propyl silicate, γ-chloropropyl silicate, and γ-aminopropyl silicate, preferably methyl silicate or γ-aminopropyl silicate, more preferably γ-aminopropyl silicate (even more preferably γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane), isopropyltrimethoxysilane, or isopropyltriethoxysilane. The second silicate is an orthosilicate, preferably methyl orthosilicate or ethyl orthosilicate. To further increase the capacity of the resulting electrolyte, the mass ratio of the first silicate to the second silicate is preferably 1:1 to 5.

[0019] In a preferred embodiment of the present invention, the mass ratio of the first silicate in step S2 to the surfactant in step S1 is (2-5):1.

[0020] In a specific embodiment of the present invention, the alcohol in the alcoholic silicate solution is preferably the alcohol corresponding to the silicate. For example, when the second silicate is methyl orthosilicate, the alcohol is preferably methanol, and when the second silicate is ethyl orthosilicate, the alcohol is preferably ethanol. In a preferred embodiment of the present invention, to further improve the capacity of the resulting electrolyte, the mass ratio of the second silicate to alcohol in the alcoholic silicate solution is (1-5):(1-25). In step S2, the reaction time is preferably 3-5 hours. In a preferred embodiment, to obtain more uniform microspheres, the addition rate is (1%-2%) / min, where the percentage refers to the volume ratio. That is, 1%-2% of the alcoholic silicate solution is added to the system per minute. This is not further described in the exemplary embodiments of the present invention. At this addition rate, the resulting microspheres are more uniformly dispersed and have a complete shape, resulting in a better capacity of the resulting electrolyte.

[0021] In a preferred embodiment of the present invention, in step S3, the volume ratio of concentrated hydrochloric acid to ethanol in the concentrated hydrochloric acid ethanol solution is 1:(50-150). Concentrated hydrochloric acid is well known to those skilled in the art and is commercially available. In step S3, the amount of concentrated hydrochloric acid ethanol solution used is sufficient to disperse the solid prepared in step S2, and this amount does not affect the properties of the resulting electrolyte.

[0022] In a preferred embodiment of the present invention, in step S3, in order to further ensure the electrolyte infiltration rate, increase the initial capacity of the electrolyte and have a suitable internal resistance, the solid of step S2 is mixed with an ethanol solution of concentrated hydrochloric acid and stirred at 80-100° C. for 18-30 hours.

[0023] In step S3, drying is performed to remove the residual gas and liquid in the hollow mesoporous silica microspheres. Drying is usually performed under negative pressure, such as 0.01MPa~0.05MPa (the reduced pressure value on the pressure pump is 0.05MPa~0.09MPa), and at 200~250°C to remove the residual gas and liquid in the hollow mesoporous silica microspheres.

[0024] The electrolyte obtained by the preparation method provided by the present invention comprises hollow mesoporous silica microspheres and lithium electrolyte; the lithium electrolyte is coated inside the pores of the hollow mesoporous silica microspheres.

[0025] That is, another object of the present invention is to provide an electrolyte based on hollow mesoporous silica microspheres obtained by the above preparation method.

[0026] Another object of the present invention is to provide an electrolyte based on hollow mesoporous silica microspheres, comprising hollow mesoporous silica microspheres and a lithium electrolyte; the lithium electrolyte is coated inside the pores of the hollow mesoporous silica microspheres.

[0027] The optimization of other parameters can be found in the above content and will not be described in detail here.

[0028] The electrolyte obtained by the preparation method provided by the present invention is a semi-solid electrolyte, which effectively reduces the risk of internal short circuit due to damage, and solves the risk of battery short circuit and spontaneous combustion caused by the growth of lithium dendrites and the puncture of the diaphragm. At the same time, the electrolyte provided by the present invention has higher cycle stability. At the same time, compared with other electrolytes in the prior art, the hollow mesoporous silica microspheres in the electrolyte provided by the present invention are also recyclable and have better capacity retention in long-term cycles (the capacity retention rate is above 85% after more than 2,000 cycles, which is far better than the prior art). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 SEM images of the hollow mesoporous silica microspheres (upper left) and the product (lower left) obtained in step 4) of Example 1, and the hollow mesoporous silica microspheres (upper right) and the product (lower right) obtained in step 5) of Example 2; Figure 2 The long-term cycle retention rate curve of the battery capacity of the electrolyte provided in the examples and comparative examples is shown. DETAILED DESCRIPTION

[0030] The following exemplary embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0031] Example 1 1) Mix 10 g of sodium dodecylbenzenesulfonate, 30 g of trimethylbenzene, 80 g of concentrated aqueous ammonia, 1000 g of water, and 500 g of ethanol, and heat at 35°C for 0.5 h to obtain a mixed solution; 2) Add an alcohol solution consisting of 20 g of γ-aminopropyltriethoxysilane, 40 g of ethyl orthosilicate, and 100 g of ethanol dropwise to the mixed solution at a rate of 2% / min. Stirring is continued for 4 h after the addition is complete. Filter and obtain a white substance. 3) The resulting white substance was placed in a concentrated hydrochloric acid-ethanol solution (1 g of 37% fuming concentrated hydrochloric acid, 80 g of ethanol), heated and stirred for 24 h, and then filtered to obtain a white solid; 4) Drying under negative pressure (actual pressure 0.01 MPa) at 200°C for 24 hours to remove gas and liquid to obtain a white powder; 5) Under negative pressure (actual pressure 0.01 MPa), submerge the obtained white powder in a 1 mol / L LiPF6 DMC solution (submerge until it covers 1 cm above the white powder), let it stand for 48 hours, and then filter to obtain the product, which is a white to light yellow powder.

[0032] in, Figure 1 The upper left image shows an SEM image of the white powder obtained in step 4) of this example, and the lower right image shows an SEM image of the product obtained in step 5) of this example. The image shows that the lithium electrolyte is encapsulated in the pores of the silica microspheres. The average particle size of the electrolyte obtained in this example (the material obtained in step 5) is 500 nm (the white powder obtained in step 4) and the product obtained in step 5) have the same average particle size value). The average pore size of the silica microspheres (the material obtained in step 4) is 3 nm. In the present invention, particle size is indicated by SEM, pore size (mesopore size) is determined by BET nitrogen adsorption and desorption testing, and the hollow structure is observed by TEM. The TEM image of the white powder obtained in step 4) of this example shows that the material has a hollow structure.

[0033] Example 2 1) Mix 10 g of sodium dodecylbenzenesulfonate, 50 g of cyclohexane, 50 g of concentrated aqueous ammonia, 1200 g of water, and 800 g of methanol, and heat at 35°C for 0.5 h to obtain a mixed solution; 2) Add an alcohol solution consisting of 20 g of isopropyltrimethoxysilane, 50 g of methyl orthosilicate, and 150 g of methanol dropwise to the mixed solution at a rate of 2% / min. Continue stirring for 4 h after the addition is complete. Filter to obtain a white substance. 3) The resulting white substance was placed in a concentrated hydrochloric acid-ethanol solution (1 g of 37% fuming concentrated hydrochloric acid and 80 g of ethanol), heated and stirred for 24 h, and then filtered to obtain a white solid. 4) Drying under negative pressure (actual pressure 0.01 MPa) at 200°C for 24 hours to remove gas and liquid to obtain a white powder; 5) Under negative pressure (actual pressure 0.01 MPa), submerge the obtained white powder with a LiPF6 DMC solution (submerge until it covers 1 cm above the white powder), let it stand for 48 hours, and then filter to obtain the product, which is a white to light yellow powder.

[0034] in, Figure 1 The upper right image shows an SEM image of the white powder obtained in step 4) of this example, and the lower right image shows an SEM image of the product obtained in step 5) of this example. The images show that the lithium electrolyte is encapsulated within the pores of the silica microspheres. The average particle size of the electrolyte obtained in this example (the material obtained in step 5) is 200 nm, and the average pore size of the silica microspheres (the material obtained in step 4) is 2 nm.

[0035] The electrolytes obtained in Example 1 and Example 2 were dispersed in nitrogen methyl pyrrolidone to form slurries, which were then covered on freshly polished aluminum foil and dried to form electrode sheets. The slurries were then assembled with the separator and electrode sheets to form a battery.

[0036] Comparative Example 1: A LiPF6 DMC solution was dispersed in NMP, covered on a freshly polished aluminum foil, and dried to form a positive electrode. This was then assembled with a separator and a lithium sheet to form a battery.

[0037] Comparative Example 2: 1μm lithium aluminum titanium phosphate particles were uniformly mixed with sucrose in a mass ratio of 10:1. The mixture was calcined at 650°C for 2 hours in a microwave sintering chamber with nitrogen as the shielding gas. After cooling, the mixture was dispersed in nitrogen-methyl pyrrolidone with a ternary positive electrode, polyvinylidene fluoride, and a carbon black conductive agent in a mass ratio of 5:90:3:2. The mixture was then covered on a freshly polished aluminum foil and dried to form a positive electrode sheet. The resulting mixture was then assembled with a separator and a lithium sheet to form a battery.

[0038] The discharge specific capacity and long-term cycle retention rate of the above-mentioned batteries were tested using cyclic voltammetry on an electrochemical workstation, referring to the standard GB / T 18287-2013.

[0039] The results are shown in Table 1 and Figure 2 , Figure 2 The long-term cycle retention rate curve of the battery capacity of the electrolyte provided in the examples and comparative examples is shown.

[0040] Table 1 sample Initial discharge specific capacity (mAh / g) Example 1 210.57 Example 2 222.75 Comparative Example 1 190.84 Comparative Example 2 220.94 From Table 1 and Figure 2 It can be seen that the electrolyte prepared by the present invention has a higher initial capacity and at the same time has a better capacity retention ability in long-term circulation.

[0041] Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an electrolyte based on hollow mesoporous silica microspheres, characterized in that: The steps include: The hollow mesoporous silica microspheres were immersed in lithium electrolyte.

2. The preparation method according to claim 1, characterized in that The lithium electrolyte is a mixture of lithium salt and DMC; the lithium salt is one or more of LiPF6, LiBF4, LiBOB, LiPO2F2, preferably LiPF6.

3. The preparation method according to claim 1, characterized in that The diameter of the mesopores in the hollow mesoporous silica microspheres is 2-5 nm.

4. The preparation method according to claim 1, characterized in that The preparation method of the hollow mesoporous silica microspheres comprises the following steps: S1, mixing a surfactant, an organic medium, concentrated ammonia water, water and an alcohol, and reacting them at 35°C to 45°C for 0.5 to 1 hour to obtain a mixed solution; S2, adding the alcohol solution of silicate to the mixed solution of step S1, reacting at 35°C to 45°C, and collecting the solid after the reaction is completed; S3, mixing the solid from step S2 with an ethanol solution of concentrated hydrochloric acid, heating and stirring, filtering, and drying to obtain the product.

5. The preparation method according to claim 4, characterized in that In step S1, The surfactant is one or more of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, and sodium lauroyl sarcosinate, preferably sodium dodecylbenzenesulfonate; And / or, the organic medium may be one or more of benzene, cyclohexane, toluene, xylene, trimethylbenzene, cyclohexanone, tetrahydrofuran, acetone, and pyridine, preferably trimethylbenzene.

6. The preparation method according to claim 4 or 5, characterized in that In step S1, the mass ratio of the surfactant, the organic medium, concentrated ammonia water, water and alcohol is 1: (1-5): (5-10): (100-120): (50-80).

7. The preparation method according to claim 4 or 5, characterized in that In step S2, the silicate includes a first silicate and a second silicate; the first silicate is one or more of methyl silicate, ethyl silicate, vinyl silicate, propyl silicate, γ-chloropropyl silicate and γ-aminopropyl silicate; the second silicate is an orthosilicate, preferably methyl orthosilicate or ethyl orthosilicate; the mass ratio of the first silicate to the second silicate is 1:(1~5).

8. The preparation method according to claim 7, characterized in that In step S2, the mass ratio of the first silicate to the surfactant in step S1 is (2-5):

1. 9 . The electrolyte based on hollow mesoporous silica microspheres obtained by the preparation method according to claim 1 .

10. An electrolyte based on hollow mesoporous silica microspheres, characterized in that: The invention comprises hollow mesoporous silica microspheres and lithium electrolyte; the lithium electrolyte is coated inside the pores of the hollow mesoporous silica microspheres.

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