Crystal form of lithium ion battery additive ethylene disulfate and preparation method thereof
By controlling the crystal form and preparation process of ethylene disulfate, the problems of impurity generation and poor stability in the existing technology have been solved, and the preparation of high-purity and stable ethylene disulfate has been achieved, improving battery performance and storage convenience.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-03-10
AI Technical Summary
Existing methods for preparing vinyl disulfate suffer from problems such as impurity generation, decreased purity, difficulty in controlling crystal form, and poor stability, leading to decreased battery performance and inconvenience in storage and transportation.
N,N'-thiodiimidazole was used as the sulfonating agent to prepare ethylene disulfate under alkaline catalytic conditions. Impurities were adsorbed by activated carbon and mercaptosilica gel, and microwave-vacuum drying technology was used to control the preparation of crystal form A and crystal form B, thereby reducing the moisture and impurity content.
A ethylene disulfate crystal form with uniform particle size distribution and high stability was obtained, which can be stably stored at room temperature for more than 2 years, reducing transportation and storage costs, improving battery capacity retention and ionic conductivity of SEI film, suppressing side reactions, and extending battery life.
Smart Images
Figure CN121627633A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a crystal form of a lithium ion battery additive, bisvinylene sulfate, and a preparation method thereof. BACKGROUND
[0002] Lithium secondary batteries are widely used as power sources for electronic devices such as mobile phones and notebook computers, or power sources for electric vehicles or electric power storage devices. In particular, in recent years, there has been a sharp increase in demand for high-capacity, high-power, and high-energy-density batteries that can be installed in hybrid or electric vehicles. Mainly composed of a positive electrode and a negative electrode, the positive electrode and the negative electrode contain a material capable of absorbing and desorbing lithium, and a non-aqueous electrolyte solution contains a lithium salt and a non-aqueous solvent. The electrolyte, as the main medium for lithium ion conduction in the battery system, has a great influence on the overall performance of the battery. One of the factors known to cause an increase in battery reexistence is the passivation film based on solvent decomposition products or inorganic salts formed on the surface of the negative electrode. It is generally known that, due to the presence of lithium metal in the negative electrode active material under charging conditions. The reduction decomposition reaction of the electrolyte occurs on the surface of the negative electrode. In the case of such a continuous reduction decomposition, the resistance of the battery increases, the charging and discharging efficiency decreases, and the energy density of the battery decreases. In addition, on the other hand, with respect to the positive electrode, it is also known that, as time passes, a deterioration reaction accumulates, the resistance continuously increases, and the battery performance is degraded. Compared to changing the battery structure design, improving the high-temperature, low-temperature, and long-cycle performance of the battery by adding a functional additive to the electrolyte is undoubtedly one of the most efficient ways to improve the overall performance of the battery at present.
[0003] Bisvinylene sulfate can be used as a lithium ion secondary battery electrolyte additive, and can form a more optimal SEI protective layer on the positive and negative electrode surfaces, avoiding the oxidative decomposition of the electrolyte under high pressure. The SEI film on the positive and negative electrode surfaces has high stability and high conductivity, and the cycle life of the battery is increased. In view of the excellent performance and application range of bisvinylene sulfate, it has very great application prospects. The structural formula of bisvinylene sulfate is shown as formula I: Formula I Although bisvinylene sulfate has excellent performance and great application potential, it has the essential defects of sulfate compounds, such as easy water absorption and hydrolysis in air, instability to heat, discoloration at room temperature, and the need for cold chain logistics at a storage temperature of 2-8℃, which brings many inconveniences to industrial production and transportation. Therefore, it is particularly important to prepare a sulfate additive that not only improves the performance of the battery but also has good thermal stability. In addition, there is still a need in the art to develop battery additives with better use effects to further improve the battery capacity retention rate, battery capacity recovery rate, delay the capacity decay of the battery, reduce the internal resistance of the battery, and improve the adjustment of the interface composition effect.
[0004] In addition, the existing preparation method of ethylene bisulfate in the prior art is as follows: Route 1: esterification reaction of erythritol, dimethyl carbonate and sulfuric chloride to obtain an intermediate product ethylene bisulfite, and then oxidation of the intermediate product in the presence of a catalyst (such as a ruthenium salt, a molecular sieve capable of catalyzing oxidation, etc.) using an oxidizing agent (such as hydrogen peroxide / sodium periodate / sodium hypochlorite / calcium hypochlorite, etc.) to obtain ethylene bisulfate, and the reaction equation is shown in the following figure: Route 2: erythritol, N,N'-sulfonyldiimidazole and solvent tetrahydrofuran are reacted at-10℃ to obtain an intermediate product ethylene bisulfite, and then the intermediate product is oxidized in the presence of a catalyst ruthenium trichloride using an oxidizing agent sodium periodate to obtain ethylene bisulfate, and the reaction equation is shown in the following figure: Route 2 is similar to Route 1, and Route 2 uses N,N'-sulfonyldiimidazole to prepare ethylene bisulfite, and then uses ruthenium trichloride and sodium periodate for oxidation, which has higher cost than Route 1 and is not suitable for industrial production. The existing technology is mainly based on Route 1, but Route 1 generates impurities such as chlorinated impurities and hydrolyzed impurities during preparation, resulting in a decrease in product purity and difficulty in controlling the crystal form. SUMMARY
[0005] In view of the problems existing in the prior art, the purpose of the present application is to provide a crystal form of lithium ion battery additive ethylene bisulfate and a preparation method thereof. The new crystal form provided by the present application has large particle size, is easy to remove water, can obtain a product with low water content, has high stability, and the crystal form is controllable, has low requirements for storage conditions, can be stored stably, saves transportation and production costs, can enhance the use effect of ethylene bisulfate as a battery additive, improves the battery capacity retention rate and the battery capacity recovery rate, is beneficial to delaying the capacity decay of the battery, better improves the composition of the electrode interface film, improves the ion conductivity and stability of the SEI film, inhibits the occurrence of side reactions, reduces the internal resistance of the battery, and has a better effect on adjusting the interface composition.
[0006] The present application provides a new crystal form of lithium ion battery additive ethylene bisulfate, which is crystal form A and crystal form B, and the structural formula of the ethylene bisulfate is as follows: .
[0007] In the present application, the X-ray powder diffraction pattern of the crystal form A of the lithium ion battery additive ethylene bisulfate contains 2θ values of 21.0±0.2°, 23.8±0.2° and 24.6±0.2°.
[0008] The application provides a crystal form B of a lithium ion battery additive bithioethylene sulfate, which contains 2θ values of 12.2±0.2°, 18.0±0.2°, 24.4±0.2° and 36.9±0.2° in an X-ray powder diffraction pattern.
[0009] Bithioethylene sulfate (BiDTD) is an important sulfated compound and has the following structural formula: The code is HF02, BiDTD, and research shows that the addition of BiDTD in a ternary lithium battery can obviously inhibit the increase of impedance during high-temperature storage, and the improvement effect of BiDTD is better than that of DTD. This is because BiDTD helps to build a stable interface film, which can effectively inhibit the continuous decomposition of electrolyte. At the same time, the introduction of S heteroatoms can improve the ion conductivity of the SEI film and reduce the interface impedance, which will be beneficial to the improvement of the electrochemical comprehensive performance of the battery. Compared with DTD, BiDTD has better improvement effect on impedance, which is mainly because the double-ring structure of BiDTD increases the activity of the two tertiary carbon atoms shared therein, and the reduction potential is lower and more prone to participate in the reaction. At the same time, the content of the film-forming heteroatom is higher, the ion conductivity is better, and therefore the electrochemical performance is better. Research shows that BiDTD can generate a stable SEI film on the surface of the graphite negative electrode, inhibit solvent decomposition and reduce the impedance of the battery. At the same time, compared with DTD, BiDTD can greatly improve the high and low temperature performance of the battery, and exhibits more excellent electrochemical performance in the working temperature range of-20 to 60 DEG C. This shows that BiDTD has great potential for improving the application range of lithium ion batteries.
[0010] The application researches and finds that the crystal form of bithioethylene sulfate has a significant influence on the stability of the product, and the application also finds that the bithioethylene sulfate product prepared by the prior art has fine crystals and a greatly increased specific surface area. When contacting moisture, the instability of the product is greatly increased. During packaging, even if the operation of vacuumizing and replacing inert gas is increased, it is difficult to completely replace the moisture between the solids, and therefore low-temperature (2-8 DEG C) storage is required, which increases the difficulty of packaging and storage and shortens the shelf life.
[0011] The bithioethylene sulfate product (HF02, BiDTD) prepared by the prior art has a series of problems such as difficulty in removing water, poor stability, harsh storage temperature requirement, need for inert gas protection, short shelf life, difficulty in storage, high transportation cost and packaging cost and the like.
[0012] Research shows that the key factors affecting the stability of bithioethylene sulfate (HF02, BiDTD) can be summarized as the following five points: (1) Water residue and thermal sensitivity: The high water content caused by the water washing step in the product refining process, and its inherent thermal instability makes it prone to decomposition by conventional or high temperature dehydration methods, making it difficult to completely remove water.
[0013] (2) Crystal defects and mixing: The conventional crystallization process is prone to mixed crystal forms, and the crystal structure has defects, which makes its chemical stability, especially in high temperature and humidity conditions, far inferior to that of single crystal products.
[0014] (3) The influence of the whole process thermal history: The compound is sensitive to heat, not only the drying temperature, but also the whole process thermal history including reaction, crystallization, centrifugation, which will accumulate instability in the product and accelerate its decomposition during storage.
[0015] (4) Acid and base impurities catalysis: Trace amounts of acidic or basic impurities (including components from packaging materials) can act as efficient catalysts to induce and continuously accelerate the hydrolysis and ring-opening decomposition reactions of the compound.
[0016] (5) Metal ion synergistic catalysis: Trace amounts of transition metal ions (such as Fe 3+ , Cu 2+ ) are strong Lewis acids, which can produce a synergistic effect with trace amounts of water, significantly reducing the decomposition reaction energy barrier and sharply accelerating the decomposition.
[0017] The present application provides a crystal form A and a crystal form B of a double sulfate vinyl ester, which have compact crystal structures, small specific surface areas, and small water contact surface areas. Good crystalline morphology, and the elution of acid and base impurities and metal ions during post-processing, thereby making the product have higher stability, can be stored at room temperature (10-30℃) for more than 2 years, can avoid harsh storage conditions, and reduce storage, transportation, and use costs.
[0018] Preferably, the melting point of the crystal form A is 211-219℃, and the melting point of the crystal form B is 207-215℃. The particle size distribution of the two crystal forms has a narrow peak width, good crystalline morphology, uniform crystallization, and small specific surface area, and has better stability.
[0019] The present application also provides a preparation method of the crystal form A, comprising the following steps: (1) mixing erythritol and a solvent, adding a base as a catalyst, then adding a 28-32% N,N'-sulfonyl diimidazole acetonitrile solution to the reaction system, controlling the reaction temperature not to exceed 15℃, after the addition is completed, incubating at 10-20℃ for 4-8 hours, after the reaction is completed, adding dilute hydrochloric acid to adjust the pH to 5-6, filtering, and drying to obtain a double sulfate vinyl ester crude product; the reaction equation is as follows: ; (2) The double vinyl sulfonate crude product obtained in step (1) is stirred to dissolve in a solvent, then activated carbon + mercapto silica gel is stirred to decolorize and adsorb heavy metal impurities in the product, filtered, and the filtrate is concentrated under reduced pressure, then cooled to below 20℃, and crystallized at this temperature for 1-2h, filtered, and dried to obtain crystal form A.
[0020] We found through a large number of studies on the process that using N,N'-sulfonyl diimidazole as a sulfonylation reagent and a base as a catalyst can directly perform sulfonate esterification to generate double vinyl sulfonate.
[0021] In step (1), the solvent is a mixed solvent of acetonitrile and water in a mass ratio of 10-10.5:1; the mass ratio of erythritol to the solvent is 1:5-10; the molar ratio of erythritol to N,N'-sulfonyl diimidazole is 1.0:2.1-3.0; the base is potassium carbonate, sodium carbonate, cesium carbonate, sodium hydroxide, or potassium hydroxide; the amount of the base used is that the molar ratio of erythritol to the base is 1:0.4-5.0; and the concentration of the dilute hydrochloric acid is 5-6%.
[0022] Preferably, step (2) is: the double vinyl sulfonate crude product is stirred to dissolve in 10-30 times the volume of a solvent, heated to 35-45℃, then stirred for 2h with activated carbon + mercapto silica gel to decolorize and adsorb heavy metal impurities in the product, filtered, the filtrate is concentrated under reduced pressure to 1 / 2 of the original solvent volume, cooled to below 20℃, and crystallized at this temperature for 1-2h, filtered, and dried to obtain crystal form A with a crystal form purity of ≥95%.
[0023] Preferably, in step (2), the solvent is one of the following solvents: dimethyl carbonate, diethyl carbonate, a mixed solvent of dimethyl carbonate and ethyl acetate in a mass ratio of 10:1-3, and a mixed solvent of diethyl carbonate and ethyl acetate in a mass ratio of 10:1-3.
[0024] More preferably, in step (2), the solvent is one of the following solvents: a mixed solvent of dimethyl carbonate and ethyl acetate in a mass ratio of 10:1-3, and a mixed solvent of diethyl carbonate and ethyl acetate in a mass ratio of 10:1-3. Through a large number of studies, we found that using the above solvents can obtain crystal form A with very high product purity and crystal form purity, and the yield of crystal form A prepared using the above mixed solvents is higher than that using single solvent dimethyl carbonate or diethyl carbonate.
[0025] In order to maintain the stability of the crystal form A, it is necessary to remove heavy metal impurities and remove moisture to obtain a product with as low heavy metal impurity content and moisture as possible. The present application first uses activated carbon + mercapto silica gel adsorption, decolorization and adsorption of heavy metal impurities in the product; finally, vacuum drying is adopted to dry the solvent of the product to obtain a crystal form A which can be stored stably. The holding time of crystallization is 1-2 h, and the product has better crystallization uniformity.
[0026] Preferably, in step (2), the amount of solvent used is 10-30 times the volume of the crude ethylene bisulfate, the temperature is raised to 35-45 DEG C, and the reduced pressure concentration is reduced to 1 / 2 of the original solvent volume; in step (2), the drying is vacuum drying, the temperature is 30-40 DEG C, and the drying time is 1-3 hours.
[0027] The above preparation method can obtain a crystal form A with very high product purity and crystal form purity, good stability, and a particle size distribution showing a unimodal normal distribution, and low water content after drying.
[0028] The present application also provides a preparation method of crystal form B, comprising the following steps: (1) mixing erythritol and a solvent, adding a base as a catalyst, and then adding a 28-32% N,N'-sulfonyl diimidazole acetonitrile solution dropwise into the reaction system, controlling the reaction temperature to be not more than 15 DEG C, after the dropwise addition is completed, keeping the reaction at 10-20 DEG C for 4-8 hours, after the reaction is completed, adding dilute hydrochloric acid to adjust the pH to 5-6, filtering, and drying to obtain a crude ethylene bisulfate; the reaction equation is as follows: ; (2) stirring and dissolving the crude ethylene bisulfate obtained in step (1) with a solvent acetonitrile, decolorizing and filtering with activated carbon + stirring with mercapto silica gel, simultaneously decolorizing and adsorbing heavy metal impurities in the product, reducing the pressure to concentrate to 4-5 times the volume of the ethylene bisulfate, then adding purified water dropwise, the dropwise addition time is 1-5 h, the volume of the dropwise added purified water is 4-15 times the volume of the ethylene bisulfate, after the dropwise addition is completed, keeping the reaction at 10-30 DEG C to crystallize, filtering, and drying to obtain crystal form B.
[0029] We have found through a large number of researches on the process that using N,N'-sulfonyl diimidazole as a sulfonylation reagent and a base as a catalyst can directly perform sulfation to generate ethylene bisulfate.
[0030] Preferably, step (2) is: stirring and dissolving the crude bisulfuric acid ethylene ester with 10-30 volumes of solvent acetonitrile, stirring with activated carbon and mercapto silica gel for 2-2.2 hours to remove color and adsorb heavy metal impurities in the product, filtering, concentrating the filtrate to 4-5 volumes of bisulfuric acid ethylene ester under reduced pressure, then adding purified water dropwise, the dropwise adding time is 1-5 hours, preferably 1-2 hours, the volume of the dropwise adding purified water is 4-15 volumes of bisulfuric acid ethylene ester, preferably 6-10 volumes, after the dropwise adding is completed, keeping at 10-30 DEG C for 1 hour, filtering, drying to obtain the crystal form B.
[0031] Preferably, in step (1), the solvent is a mixed solvent of acetonitrile and water in a mass ratio of 10-10.5:1; the mass ratio of erythritol to the solvent is 1:5-10; the molar ratio of erythritol to N,N'-sulfonyldiimidazole is 1.0:2.1-3.0; the base is potassium carbonate, sodium carbonate, cesium carbonate, sodium hydroxide or potassium hydroxide; the amount of the base is: the molar ratio of erythritol to the base is 1:0.4-5.0; the concentration of the dilute hydrochloric acid is 5-6%; In step (2), the amount of solvent acetonitrile is 10-30 volumes of bisulfuric acid ethylene ester, the stirring time of activated carbon decolorization filtering and mercapto silica gel is 2-2.2 hours, and the crystallization keeping time is 1 hour; The drying is performed by a microwave-vacuum combined drying method, the microwave power is 50 W, the vacuum drying temperature is 30-40 DEG C, and the drying time is 1-3 hours. The microwave-vacuum drying can dry the solvent and moisture from the inside of the product, and the drying is more sufficient. If only microwave or only vacuum drying is used, the surface of the product may have reached the drying effect, but the internal moisture and solvent are still retained, so the product is unstable during storage and the storage period is shortened.
[0032] The above preparation method can obtain the crystal form B with very high purity and crystal form purity, good stability, unimodal normal distribution of particle size distribution, low water content after drying and high stability.
[0033] The crystal form A and the crystal form B prepared by the method can be packaged by a conventional method (the inner layer is a high-density polyethylene barrel, the outer layer is an aluminum foil bag, and the packaging is vacuum), can be stored stably, and has a long storage time.
[0034] In order to further improve the storage time and detect the sealing property of the packaging, color-changing silica gel can be added between the high-density polyethylene barrel and the vacuum aluminum foil bag. The addition of the color-changing silica gel can not only absorb a small amount of moisture in the packaging to ensure the stability and storage period of the product, but also can judge the stability of the product according to the color change degree of the color-changing silica gel when the packaging is damaged.
[0035] The application obtains products with higher purity, lower moisture content and lower impurity content by controlling the crystal form, and has better promotion effect on performance tests such as capacity retention rate, capacity recovery rate and internal resistance of the secondary battery.
[0036] Compared with the prior art, the application has the following advantages: (1) The crystal form of the lithium ion battery additive double sulfate ethylene provided by the application has a unimodal normal distribution of particle size distribution, can easily remove water during drying, can obtain products with low water content, has high stability, the crystal form is controllable, has low requirements on storage conditions, can be stably stored, and saves transportation cost and production cost.
[0037] (2) The crystal form provided by the application can enhance the use effect of double sulfate ethylene (BiDTD) as a battery additive, can improve the battery capacity retention rate and the battery capacity recovery rate, is beneficial to delaying the capacity decay of the battery, can better improve the composition of the electrode interface film, improve the ion conductivity and stability of the SEI film, inhibit the occurrence of side reactions, reduce the internal resistance of the battery, and has better effect on adjusting the interface composition.
[0038] (3) The application greatly improves the stability of double sulfate ethylene (BiDTD), can be stably stored, and reduces the harshness of the storage conditions. The prior art needs to be refrigerated at 2°C to 8°C, and absolutely avoids storage under high temperature conditions, such as above 20°C. Through the crystallization control of the product, the application can be stably stored at room temperature (10 to 30°C) for more than 2 years.
[0039] (4) The application controls the crystal form and simultaneously prepares products with better purity, has better promotion effect on performance tests such as capacity retention rate, capacity recovery rate and internal resistance of the secondary battery, and can greatly prolong the high-temperature service life of the secondary battery.
[0040] (5) The preparation method provided by the application can obtain crystal form A and crystal form B with high purity, high yield and high purity, low cost, and is suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS
[0041] Figure 1 is a powder diffraction spectrum of crystal form A; Figure 2 is a powder diffraction spectrum of crystal form B; Figure 3 is a microscope photo of crystal form A; Figure 4 is a microscope photo of crystal form B; Figure 5 is a liquid phase spectrum of crystal form A; Figure 6 is a DSC / TG spectrum of crystal form A; Figure 7 is a DSC / TG pattern of crystal form B; Figure 8 is a 1H NMR spectrum of the bis vinyl sulfonate crystal form A prepared in Example 1; Figure 9 is a capacity retention rate profile of the battery; Figure 10 is a capacity recovery rate profile of the battery; Figure 11 is a change in internal resistance profile of the battery; Figure 12 is a powder diffraction spectrum of the product prepared in Comparative Example 1. DETAILED DESCRIPTION
[0042] The present application is further described below by specific examples, which are only illustrative of the present application and do not limit the scope of the present application.
[0043] Example 1 A crystal form A of a lithium ion battery additive bis vinyl sulfonate, the preparation method comprising the following steps: (1) 122 g (1.0 mol, 1.0 eq) of erythritol is added to a mixed solvent of acetonitrile and water (732 g of acetonitrile, 73.2 g of water), 56 g (1.0 mol, 1.0 eq) of potassium hydroxide is added, and then a 30% N,N'-sulfonyldiimidazole acetonitrile (435.6 g, 2.2 mol, 2.2 eq, acetonitrile 1016.4 g) solution is added dropwise to the reaction system, the reaction temperature is controlled to be not more than 15°C, after the dropwise addition is completed, the reaction is incubated at 10-20°C for 5 hours, after the reaction is completed, 5% dilute hydrochloric acid is added dropwise to adjust the pH to 5-6, filtered, and dried to obtain a crude bis vinyl sulfonate; the reaction equation is as follows: (2) The crude bis vinyl sulfonate obtained in step (1) is stirred to dissolve in 20 times the volume of solvent, heated to 40°C, and then stirred until dissolved, the solvent is a mixed solvent of dimethyl carbonate and ethyl acetate in a mass ratio of 10:2, then activated carbon + mercaptosilica gel is added and stirred for 2 h to decolorize and adsorb heavy metal impurities in the product, filtered, and the filtrate is concentrated under reduced pressure to 1 / 2 of the original solvent volume, cooled to below 20°C, and crystallized at this temperature, the crystallization incubation time is 1.5 h, filtered, and vacuum dried at a temperature of 35°C for 2 hours to obtain crystal form A with a crystal form purity of 99.99% and a yield of 97.3%.
[0044] The prepared crystal form A is tested: The powder diffraction spectrum of crystal form A is shown in Figure 1 , by Figure 1It can be seen that the X-ray powder diffraction pattern of crystal form A contains 2θ values of 21.087°, 23.858°, and 24.603°, indicating a very high crystal form purity. Microscopic photograph of crystal form A is shown below. Figure 3 The crystal form A prepared by the present invention has a good crystal morphology, and the crystal form is rod-shaped crystal with regular crystal structure and uniform texture.
[0045] The liquid phase spectrum of crystal form A is shown below. Figure 5 ,pass Figure 5 It can be seen that the crystal form A product prepared by this invention has high purity, with a liquid phase purity of over 99.99%; The DSC / TG spectrum of crystal form A is shown below. Figure 6 ,pass Figure 6 The melting point of crystal form A is 211.92~218.18℃, and the decomposition temperature is 236.70~240.81℃, indicating that crystal form A has a high melting point and decomposition temperature and is not easily decomposed.
[0046] The 1H NMR spectrum of crystal form A is shown in the figure. Figure 8 , 1H-NMR (600 MHz, acetone-d6) δ(ppm): 5.74-5.71(2H, m), 5.23-5.20 (2H, m), 5.05-5.02 (2H, m).
[0047] Example 2 A lithium-ion battery additive, ethylene disulfate crystal form B, is prepared by the following steps: (1) Add 122g (1.0mol, 1.0eq) of erythritol to a mixed solvent of acetonitrile / water (732g acetonitrile, 73.2g water), add 56g (1.0mol, 1.0eq) of potassium hydroxide, and then add dropwise a 30% N,N'-thiodiimidazole solution in acetonitrile (435.6g, 2.2mol, 2.2eq, 1016.4g acetonitrile) to the reaction system. Control the reaction temperature not to exceed 15℃. After the addition is complete, keep the reaction at 10~20℃ for 6 hours. After the reaction is complete, add 5% dilute hydrochloric acid to adjust the pH to 5~6, filter, and dry to obtain crude ethylene disulfate. The reaction equation is as follows: (2) The crude diethylene sulfate obtained in step (1) was stirred and dissolved in acetonitrile, which was 20 times the volume of solvent. The mixture was stirred with activated carbon and mercaptosilica for 2 hours to decolorize and adsorb heavy metal impurities. After filtration, the filtrate was concentrated under reduced pressure to 4.5 times the volume of diethylene sulfate. Purified water was added dropwise over 1.5 hours. The volume of purified water added was 8 times the weight of diethylene sulfate. After the addition was complete, the mixture was kept at 20°C for 1 hour. After filtration, the mixture was dried using a microwave-vacuum combined drying method. The microwave power was 50W, the vacuum drying temperature was 35°C, and the drying time was 2 hours. Crystal form B was obtained with a purity of 99.99% and a yield of 95.4%.
[0048] The prepared crystal form B was tested: The powder diffraction pattern of crystal form B is shown below. Figure 2 ,pass Figure 2 It can be seen that the X-ray powder diffraction pattern of crystal form B contains 2θ values of 12.256°, 18.070°, 24.481°, and 36.991°, indicating a very high crystal form purity.
[0049] Microscopic images of crystal form B are shown below. Figure 4 Crystal form B has a granular, fine crystal structure. Although it is not as regular as the rod-shaped crystals of crystal form A, the fine crystals aggregate to form small spherical particles, which can prevent water from entering the crystal interior to a certain extent and maintain the stability of the product.
[0050] The DSC / TG spectrum of crystal form B is shown below. Figure 7 ,pass Figure 7 The melting point of crystal form B is 207.53~214.65℃, and the decomposition temperature is 226.53~232.02℃, indicating that crystal form B has a high melting point and decomposition temperature and is not easily decomposed.
[0051] Example 3 The crystal form of a lithium-ion battery additive, ethylene disulfate, is basically the same as that in Example 1, except that the solvent is replaced with dimethyl carbonate.
[0052] Upon testing, the crystal form obtained in Example 3 was crystal form A, with a yield of 90.1%.
[0053] Example 4 The crystal form of a lithium-ion battery additive, ethylene disulfate, is basically the same as that in Example 1, except that the solvent is replaced with diethyl carbonate.
[0054] Upon testing, the crystal form obtained in Example 4 was crystal form A, with a yield of 93.2%.
[0055] Comparative Example 1 A vinyl disulfate is prepared using the following existing process: (1) Put 122 g (1.0 mol, 1.0 eq) of erythritol into a solvent dimethyl carbonate 610 g, then add thionyl chloride (261.7 g, 2.2 mol, 2.2 eq), and heat to 30-40°C to cause esterification reaction. After the reaction is completed, concentrate to dryness to obtain an intermediate product bis-vinyl ethylene sulfate, then add dimethyl carbonate 610 g, stir to dissolve, then add a catalyst ruthenium trichloride hydrate (0.61 g, 0.5%), and use an oxidant sodium periodate to oxidize the intermediate product, to obtain a crude bis-vinyl ethylene sulfate product, and the reaction equation is shown in the following figure: (2) Stir the crude bis-vinyl ethylene sulfate product in 20 volume times of a solvent acetonitrile to dissolve, then stir to decolorize and adsorb metal impurities with activated carbon + mercapto silica gel, filter, and cool to below 20°C, and crystallize at this temperature for 1.5 h. Filter, and vacuum dry to obtain a bis-vinyl ethylene sulfate product, and the liquid phase purity is 99.80%.
[0056] The crude bis-vinyl ethylene sulfate product is prepared by using the existing route 1 in the step (1) of the comparative example, and is further refined to obtain a bis-vinyl ethylene sulfate product, and the product is tested. The powder diffraction spectrum is shown in Figure 12 , and it can be seen from Figure 12 that the X-ray powder diffraction pattern of the product prepared in Comparative Example 1 contains 2θ values of 12.788°, 17.321°, 18.732°, 19.161°, 22.177°, and the crystal form purity is 50.2%, and the crystal form purity is poor.
[0057] The melting point of the bis-vinyl ethylene sulfate product prepared in the comparative example is 201.21-215.43°C, which has a lower melting point, a lower decomposition temperature, and a longer melting range compared with the crystal forms A and B of the application, and the storage stability of the product is poor.
[0058] Performance test: I. Storage stability 1. The crystal forms A and B prepared in Examples 1-2 and the bis-vinyl ethylene sulfate prepared in Comparative Example 1 are tested, and the test results are shown in Table 1.
[0059] Table 1 Comparison of performance of products of the application and commercially available products Note: The execution standard is an internal standard of the enterprise.
[0060] 2, the crystal form A, the crystal form B prepared by example 1-2 and the double vinyl sulfonate prepared by comparative example 1 are respectively packaged by using conventional packaging, and the packaging forms are as follows: the inner layer is a high-density polyethylene barrel; the outer layer is an aluminum foil bag, and vacuum packaging.
[0061] After packaging, the accelerated stability test is carried out: the crystal form A, the crystal form B and the double vinyl sulfonate prepared by comparative example 1 packaged according to the above packaging are respectively subjected to accelerated test (temperature 40℃±2℃, humidity 75%RH±5%RH, time 6 months, sampling points 1 month, 2 months, 3 months, 6 months), and the results are shown in the following table.
[0062] Table 2: Accelerated stability test table of crystal form A Table 3: Accelerated stability test table of crystal form B Table 4: Accelerated stability of double vinyl sulfonate prepared by comparative example 1 From the above several tables, it can be seen that: (1) By controlling the crystallization conditions, water removal process and optimizing the drying process, the crystal forms A and B of double vinyl sulfonate are prepared, the product purity is better, the moisture is lower, and the product quality is better than that of the double vinyl sulfonate prepared by the existing process on the market.
[0063] (2) The different crystal forms obtained by crystallization control are also better than the products prepared by the existing process on the market, and the storage decomposition rates of the accelerated stability for 6 months are only 0.09%, 0.12%, which are much better than the double vinyl sulfonate prepared by the existing process on the market, and the storage stability is high. Through calculation, the storage time of the product at room temperature (10~30℃) can reach more than 2 years; it shows that the crystal form A and the crystal form B products obtained by controlling crystallization have good stability.
[0064] (3) We found that the crystal form A has more obvious advantages in storage, can be stably stored for 6 months, and the decomposition rate is only 0.09%; the crystal form B also has good storage stability, can be stably stored for 6 months, and the decomposition rate is 0.12%; we prepare different crystal forms by controlling the crystallization conditions, and different crystal forms have great difference in storage stability; there is a difference in stability between different crystal forms because the molecular packing mode and the interaction force are different, resulting in different Gibbs free energy. Under certain conditions, only one crystal form is thermodynamically stable (with the lowest free energy). Other crystal forms are metastable, and the crystal form A prepared by us has the best thermodynamic stability, is the optimal crystal form, and has the highest storage stability.
[0065] Secondary battery performance test Most of the time, the battery is in standby state, so the state change of the battery during storage is an important indicator of whether it can be put into the market. In order to speed up the experiment, high temperature storage is selected to accelerate the reaction, which can simulate the self-discharge effect and aging of the battery during daily storage.
[0066] Preparation of positive electrode sheet: The preparation method of the positive electrode sheet is as follows: the positive electrode active material lithium cobaltate (LiCoO2), polyvinylidene fluoride (PVDF), conductive additive (Super P) and carbon nanotube (CNT) are mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) is added as a solvent, and the mixture is stirred in a vacuum stirrer until a uniform and flowable positive electrode active paste is formed; then the paste is uniformly coated on both surfaces of the aluminum foil, and the coated aluminum foil is dried, rolled and cut to obtain the required positive electrode sheet.
[0067] Preparation of negative electrode sheet: The preparation method of the negative electrode sheet is as follows: the artificial graphite, silicon monoxide, sodium carboxymethyl cellulose, butadiene rubber, conductive carbon black and single-walled carbon nanotube are mixed in a mass ratio of 79.5:15:2.5:1.5:1:0.5, deionized water is added, and a uniform slurry is prepared by vacuum stirring. Then, the slurry is uniformly coated on both surfaces of the copper foil, first dried at room temperature, then completely dried at 80°C, and finally cold-pressed and cut to obtain the final negative electrode sheet.
[0068] Preparation of blank group electrolyte: The preparation method of the electrolyte is as follows: ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate are mixed in a mass ratio of 10:20:40:30 as organic solvent, then 1 mol / L lithium hexafluorophosphate is added to form a lithium salt basic system. Next, 5% of fluoroethylene carbonate and 2% of hexanitrile are introduced into the system as functional additives, all components are fully stirred and dissolved, and the moisture and free acid are detected to be qualified, then the target electrolyte is prepared.
[0069] Preparation of electrolyte with added crystal form A: 1% of crystal form A is added to the blank group electrolyte; Preparation of electrolyte with added crystal form B: 1% of crystal form B is added to the blank group electrolyte; Preparation of electrolyte with added commercial product: 1% of commercial product (the commercial product is the double vinyl sulfonate product prepared in Comparative Example 1) is added to the blank group electrolyte.
[0070] Preparation of secondary battery: The preparation of the secondary battery is as follows: firstly, the above positive plate, separator and negative plate are stacked in sequence and wound into an electric core; then the electric core is placed in an outer packaging aluminum foil, each group of electrolyte is injected, and then the processes of vacuum packaging, standing, formation, shaping and sorting are performed, and finally a battery with a working voltage range of 3.0V-4.45V is obtained.
[0071] After the battery is filled with electrolyte, the activation treatment is performed according to the conventional method. After sufficient activation, the initial rated discharge capacity C0 of the battery is detected, and after the battery is stored at 60℃ for 7 days, the remaining discharge capacity C1 of the battery is detected.
[0072] The capacity retention rate calculation formula is as follows: Capacity retention rate (%) = (C1 / C0) × 100% The capacity retention rate of each group of secondary batteries is shown in the following table: Figure 9 .
[0073] From Figure 9 It can be seen that after 7 days of storage, the capacity retention rates of the batteries added with crystal form A and crystal form B additives are 85.00% and 84.30% respectively, while the blank group is only 66.70%, and the capacity retention rate of the commercial product is 81.40%. This shows that during the storage process, the capacity retention rate of the battery added with double vinyl sulfite additive is much higher than that of the blank group, and the capacity retention rate of the battery with high purity crystal form A and crystal form B prepared by us is also higher than that of the commercial double vinyl sulfite product of 81.40%, which shows that the crystal form provided by the present application can enhance the use effect of double vinyl sulfite HF02, and the capacity retention rate of the battery of crystal form A is slightly higher than that of crystal form B.
[0074] The battery stored at 60℃ for 7 days is subjected to cycle test on a charge-discharge test cabinet, wherein the cycle test is carried out at room temperature of 25℃, and after 200 times of charge-discharge cycle at a current of 1C in the voltage range of 3.0V-4.45V, the remaining discharge capacity C2 of the battery is detected.
[0075] The capacity recovery rate is usually calculated by the following formula: Capacity retention rate (%) = (C2 / C0) × 100%.
[0076] The capacity recovery rate of each group of secondary batteries is shown in the following table: Figure 10 .
[0077] From Figure 10It can be seen that after 7 days of storage and recovery of charging and discharging, the capacity recovery rates of the batteries added with crystal form A and crystal form B additives are 98.80% and 98.30% respectively, while the capacity recovery rate of the blank group is only 94.70%, and the capacity recovery rate of the commercial product is 96.40%. This shows that during the storage process, the capacity recovery rate of the battery added with the double vinyl sulfonate additive is much higher than that of the blank group, and the capacity recovery rate of the battery added with the crystal form A and crystal form B prepared by the present application is also higher than 96.40% of the commercial product, which shows that the crystal form provided by the present application can enhance the use effect of the existing commercial double vinyl sulfonate product, and the capacity recovery rate of the crystal form A is slightly higher than that of the crystal form B. This shows that the crystal form provided by the present application is more conducive to delaying the capacity decay of the battery.
[0078] The direct current internal resistance (DCR) of the secondary battery is used to characterize the power performance of the battery. Generally, the smaller the internal resistance of the battery, the better the power performance of the battery. At 25℃, the secondary battery is charged at 1C constant current to 4.45V, then charged at 4.45V constant voltage to the cutoff current 0.05C, and then discharged at 1C constant current for 0.5h, and then rested for 30min, and the voltage V1 after resting was recorded. Then, discharge at 4C for 30s, and record the voltage V2 at the end of discharge.
[0079] The internal resistance of the battery is usually calculated by the following formula: The internal resistance (DCR) of the battery = (V1-V2) / I, I = the current corresponding to 4C rate.
[0080] The internal resistance change of the above-mentioned batteries after storage at 60℃ for 7 days is shown in Table 2. Figure 11 .
[0081] From Figure 11 It can be seen that after 7 days of storage at 60℃, the internal resistance change rates of the batteries added with crystal form A and crystal form B additives are 12.80% and 13.30% respectively, which are much better than 34.70% of the blank group, and also better than 16.40% of the commercial product; this shows that the crystal form provided by the present application can better improve the composition of the electrode interface film, improve the ion conductivity and stability of the SEI film, inhibit the occurrence of side reactions, and reduce the internal resistance of the battery, and the effect of crystal form A on adjusting the interface composition is better.
[0082] For the preparation method, performance, etc. of the crystal form of the given compound which are not listed in the examples, since they have similar effects to the crystal form of the compound listed in the examples, they are all applicable to the technical solution of the present application, so they will not be listed one by one here.
[0083] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications that can be thought of by those skilled in the art to the embodiments, or by combining part of the constituent elements of the embodiments, are also included in the scope of the present application without departing from the spirit of the present application.
Claims
1. A crystalline form A of a lithium ion battery additive, ethylene bisulfate, characterized by: Its X-ray powder diffraction pattern contains 2θ values of: 21.0±0.2°, 23.8±0.2°, 24.6±0.2°, the structure of the double sulfate vinyl ester is as follows: 。 2. A process for preparing the crystalline Form A of claim 1, characterized in that: The method comprises the following steps: (1) erythritol and solvent are mixed, base is added as catalyst, 28-32% N,N'-sulfonyl imidazole acetonitrile solution is added dropwise into the reaction system, the reaction temperature is controlled to be not more than 15°C, after dropwise addition is completed, the reaction is kept at 10-20°C for 4-8 hours, after the reaction is completed, dilute hydrochloric acid is added dropwise to adjust pH to 5-6, filtration is carried out, and after drying, double sulfate vinyl ester crude product is obtained; the reaction equation is as follows: ； (2) the double sulfate vinyl ester crude product obtained in step (1) is stirred to be clear with a solvent, then activated carbon + mercapto silica gel is used for stirring, at the same time, heavy metal impurities in the product are removed by decolorization and adsorption, filtration is carried out, the filtrate is concentrated under reduced pressure, then cooling is carried out to be below 20°C, crystallization is carried out at the temperature, the crystallization time is 1-2 hours, filtration is carried out, and drying is carried out, to obtain crystal form A.
3. The preparation method of the crystal form A according to claim 2, characterized in that: in step (1), the solvent is a mixed solvent of acetonitrile and water with a mass ratio of 10-10.5:1; the mass ratio of erythritol to the solvent is 1:5-10; and the molar ratio of erythritol to N,N'-sulfonyl imidazole is 1.0:2.1-3.0; the base is potassium carbonate, sodium carbonate, cesium carbonate, sodium hydroxide or potassium hydroxide; the amount of the base is that the molar ratio of erythritol to the base is 1:0.4-5.0; the concentration of the dilute hydrochloric acid is 5-6%.
4. The method of claim 2, wherein the crystalline Form A is prepared by: in step (2), the solvent is one of the following solvents: dimethyl carbonate, diethyl carbonate, a mixed solvent of dimethyl carbonate and ethyl acetate with a mass ratio of 10:1-3, and a mixed solvent of diethyl carbonate and ethyl acetate with a mass ratio of 10:1-3.
5. A process for preparing the crystalline Form A of claim 3, characterized in that: in step (2), the solvent is one of the following solvents: dimethyl carbonate and ethyl acetate with a mass ratio of 10:1-3, and diethyl carbonate and ethyl acetate with a mass ratio of 10:1-3.
6. A process for preparing the crystalline Form A of claim 2, characterized in that: in step (2), the amount of the solvent is 10-30 times the volume of the double sulfate vinyl ester crude product, the temperature is raised to 35-45°C, and the concentration under reduced pressure is to 1 / 2 of the original solvent volume. in step (2), the drying is vacuum drying, the temperature is 30-40°C, and the drying time is 1-3 hours.
7. A crystalline form B of a lithium ion battery additive, ethylene bisulfate, characterized by: Its X-ray powder diffraction pattern contains 2θ values of: 21.0±0.2°, 23.8±0.2°, 24.6±0.2°, the structure of the double sulfate vinyl ester is as follows: 。 8. A process for preparing the crystalline Form B of claim 7, characterized in that: The method comprises the following steps: (1) erythritol and solvent are mixed, base is added as catalyst, 28-32% N,N'-sulfonyl imidazole acetonitrile solution is added dropwise into the reaction system, the reaction temperature is controlled to be not more than 15°C, after dropwise addition is completed, the reaction is kept at 10-20°C for 4-8 hours, after the reaction is completed, dilute hydrochloric acid is added dropwise to adjust pH to 5-6, filtration is carried out, and after drying, double sulfate vinyl ester crude product is obtained; the reaction equation is as follows: ； (2) The double vinyl sulfonate crude product obtained in step (1) is stirred and dissolved in solvent acetonitrile, activated carbon is used for decolorization and filtration, and thiol silica gel is used for stirring, decolorization and adsorption of heavy metal impurities in the product. After being concentrated under reduced pressure to 4-5 times the volume of the double vinyl sulfonate, purified water is added dropwise, the dropwise addition time is 1-5 h, the volume of the purified water added is 4-15 times the volume of the double vinyl sulfonate, and after the dropwise addition is completed, the product is kept at 10-30°C for crystallization, filtered, and dried to obtain crystal form B.
9. The preparation method of the crystal form B of claim 8, characterized in that: In step (1), the solvent is a mixed solvent of acetonitrile and water in a mass ratio of 10-10.5:1; the mass ratio of erythritol to the solvent is 1:5-10; the molar ratio of erythritol to N,N'-sulfonyldiimidazole is 1.0:2.1-3.0; the base is potassium carbonate, sodium carbonate, cesium carbonate, sodium hydroxide or potassium hydroxide; the amount of the base used is that the molar ratio of erythritol to the base is 1:0.4-5.0; and the concentration of the dilute hydrochloric acid is 5-6%; In step (2), the amount of solvent acetonitrile is 10-30 times the volume of the double vinyl sulfonate crude product, the stirring time of activated carbon decolorization and filtration + thiol silica gel is 2-2.2 h, and the crystallization keeping time is 1 h; The drying is performed by a microwave-vacuum combined drying method, the microwave power is 50 W, the vacuum drying temperature is 30-40°C, and the drying time is 1-3 hours.
10. The crystalline Form A of claim 1 or the crystalline Form B of claim 7, characterized by: The melting point of the crystal form A of claim 1 is 211-219°C, and the melting point of the crystal form B of claim 7 is 207-215°C.