Cyclic carbonate-sulfate compound and its application, non-aqueous electrolyte, secondary battery

Abstract

To overcome the problems of insufficient high-temperature performance and safety performance existing in existing high-voltage lithium-ion batteries, the present invention provides a cyclic carbonate-sulfate compound and its application, a non-aqueous electrolyte, and a secondary battery. The cyclic carbonate-sulfate compound includes the compound shown in Chemical Formula 1, and the specific rotation α of the cyclic carbonate-sulfate compound is -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g); Chemical Formula 1. When the cyclic carbonate-sulfate compound provided by the present invention is used as an electrolyte additive, the formed solid electrolyte membrane is smoother and more orderly, and thus has higher high-temperature stability, especially the film layer stability under thermal shock conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a cyclic carbonate-sulfate compound and its application, a non-aqueous electrolyte, and a secondary battery. Background Art

[0002] Lithium-ion batteries have been widely used in the fields of 3C digital products such as mobile phones and laptop computers, as well as new energy vehicles due to their advantages such as high working voltage, wide working temperature range, large energy density and power density, no memory effect, and long cycle life. In recent years, with the continuous development of the thinning of 3C digital products, the battery industry has higher and higher requirements for the high energy density of lithium-ion batteries. At the same time, considering the user side, good safety performance has become a basic requirement for batteries.

[0003] As the battery voltage gradually increases, the structural stability of the positive electrode material will deteriorate, and the transition metal in the positive electrode is prone to disproportionation reaction, dissolve in the electrolyte in the form of ions, causing damage to the positive electrode structure, and is prone to thermal runaway risk under high temperature and high pressure. Moreover, the dissolved metal ions migrate to the negative electrode interface, exchange ions with lithium in the negative electrode, occupy the lithium insertion position in the negative electrode, resulting in a decrease in the lithium storage capacity of the negative electrode and deterioration of the battery performance. Specifically, it is manifested as: the battery generates gas, the internal resistance increases rapidly, and the capacity drops sharply. The gas generation of the battery will cause an increase in the internal pressure, and further may develop into dangerous situations such as explosion and combustion of the battery. The above situation is particularly obvious when the battery is under high temperature conditions.

[0004] There is a class of polycyclic carbonate sulfate compounds. When used as an electrolyte additive, it can participate in film formation on the surfaces of the positive and negative electrodes during the battery formation stage. The formed solid electrolyte film has a certain improvement in the stability of battery materials, but there is still a large room for improvement in its improvement effect on the battery at high temperature. The inventor's research found that the spatial structure of the polycyclic carbonate sulfate compound has a certain influence on its battery performance improvement effect. However, there are significant technical obstacles in determining the influence of the spatial structure of the polycyclic carbonate sulfate compound on the battery performance. The main reason is that in the preparation method of the existing polycyclic carbonate sulfate compound, there is a situation where the chiral structure of the intermediate is unstable, and different stereoisomers are easily generated during the reaction process. Moreover, there are multiple chiral carbons in the polycyclic carbonate sulfate compound, and there are many types of stereoisomers. When there are many types of stereoisomers, chiral separation becomes difficult, and further research on the property differences of polycyclic carbonate sulfate compounds with different chiral structures is difficult. Summary of the Invention

[0005] In view of the problems of insufficient high-temperature performance and safety performance in existing high-voltage lithium-ion batteries, the present invention provides a cyclic carbonate-sulfate compound and its application, a non-aqueous electrolyte, and a secondary battery.

[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0007] On the one hand, the present invention provides a cyclic carbonate-sulfate compound, the cyclic carbonate-sulfate compound includes the compound shown in Chemical Formula 1, and the specific rotation α of the cyclic carbonate-sulfate compound is -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g);

[0008] .

[0009] Optionally, the compound shown in Chemical Formula 1 includes a characteristic structure compound, the characteristic structure compound is selected from the compound shown in Structural Formula 2 and / or the compound shown in Structural Formula 3, and in the compound shown in Chemical Formula 1, the content of the characteristic structure compound is ≥99wt%;

[0010] .

[0011] Optionally, the characteristic structure compound is selected from the compound shown in Structural Formula 2.

[0012] Optionally, the characteristic structure compound is selected from the compound shown in Structural Formula 3.

[0013] Optionally, the test conditions for the specific rotation α are: wavelength is 589nm, temperature is 20 degrees Celsius, solvent is acetonitrile, tube length is 100mm, and the concentration of the cyclic carbonate-sulfate compound is 0.126g / mL.

[0014] Optionally, the cyclic carbonate-sulfate compound satisfies at least one of the following conditions:

[0015] (Ⅰ) In the cyclic carbonate-sulfate compound, the content of the compound shown in Chemical Formula 1 is ≥99wt%;

[0016] (Ⅱ) The compound shown in Chemical Formula 1 further includes stereoisomeric impurities other than the characteristic structure compound, and the content of stereoisomeric impurities in the compound shown in Chemical Formula 1 is ≤1wt%;

[0017] (Ⅲ) The content of chlorine element in the cyclic carbonate-sulfate compound is ≤100ppm.

[0018] Optionally, the cyclic carbonate - sulfate compound further includes organic impurities, the mass content of the organic impurities ≤ 1 wt%, and the organic impurities include one or more of the following compounds:

[0019] .

[0020] On the other hand, the present invention provides the use of the cyclic carbonate - sulfate compound as described above as an electrolyte additive.

[0021] On the other hand, the present invention provides a non - aqueous electrolyte, which includes a non - aqueous organic solvent, an electrolyte salt, and an additive, and the additive includes the cyclic carbonate - sulfate compound as described above.

[0022] Optionally, based on the total mass of the non - aqueous electrolyte being 100%, the mass percentage content of the cyclic carbonate - sulfate compound is 0.01% - 5%.

[0023] On the other hand, the present invention provides a secondary battery, which includes the non - aqueous electrolyte as described above.

[0024] According to the cyclic carbonate-sulfate compound provided by the present invention, in order to improve the film-forming quality of the additive during the first charge and discharge process of the battery, the inventors found in previous studies that polycyclic sulfates with a carbonate backbone in the middle and sulfate rings on both sides (as shown in Chemical Formula 1) are beneficial to form the spatial structure of the solid electrolyte film on the positive and negative electrodes, and it has been reported in the previously applied patents. Based on further research, the inventors found that there are various chiral configurations in the compound shown in Chemical Formula 1, and there are certain differences in the film-forming properties among different chiral configurations of the compound shown in Chemical Formula 1, and there is also interference among them, which further affects the orderliness of the solid electrolyte film on the positive and negative electrodes. Through the purification and testing of different chiral configurations of the compound shown in Chemical Formula 1, it is found that the chiral configuration with an asymmetric structure of the compound shown in Chemical Formula 1 has a certain randomness during film formation because the chemical environments of the sulfate esters on both sides are different, resulting in the newly formed thin film not being able to cover the active sites in the most compact manner, causing more active sites to be exposed in the formed thin film, and the positive and negative electrode materials still not being effectively protected, and being broken down under continuous electrochemical action or continuous elevated heat shock, resulting in the cycle failure or thermal shock damage of the battery. When the content of the characteristic structure compounds shown in Structural Formula 2 and / or Structural Formula 3 in the compound shown in Chemical Formula 1 is relatively high, the formed solid electrolyte film is denser and more uniform, and its stability under high temperature conditions is improved, and the impedance is reduced. It is speculated that it is the control of the film-forming process brought by its axial symmetry. After the characteristic structure compound with axial symmetry coordinates with lithium ions, under the action of the electric field, an electrochemical reaction occurs at the electrode active sites to generate the corresponding inorganic salt-organic complex. At the same time, due to the axial symmetry of this type of molecule, when the lithium ion-additive complex film formed on the electrode plate forms a film again, the complexing properties of the two sulfate esters with lithium ions are similar. Therefore, after complexation, the spatial structure, the spatial conformation of the molecular complex, and the influence of the surrounding solvent molecules on its resistance tend to be similar, and at the same time, it will be guided by the already formed SEI or CEI film, so it can form a relatively regular and more ductile organic-inorganic composite film in the same or similar way, effectively covering most of the active sites and preventing them from further reacting electrochemically with other active components in the electrolyte or migrating to the counter electrode with the positive and negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the nuclear magnetic test hydrogen spectrum (1HNMR) of the carbonate polyol provided in Preparation Example 1 of the present invention, deuterated reagent: deuterated DMSO (in the figure, the abscissa f1(ppm) represents the chemical shift, and the ordinate represents the absorption peak intensity, the same below).

[0026] Figure 2 is the nuclear magnetic test carbon spectrum of the carbonate polyol provided in Preparation Example 1 of the present invention ( 13CNMR), deuterated reagent: deuterated DMSO;

[0027] Figure 3 is the hydrogen nuclear magnetic resonance spectrum of the cyclic carbonate-sulfate compound provided in Preparation Example 1 of the present invention ( 1 HNMR), deuterated reagent: deuterated acetonitrile;

[0028] Figure 4 is the carbon nuclear magnetic resonance spectrum of the cyclic carbonate-sulfate compound provided in Preparation Example 1 of the present invention ( 13 CNMR), deuterated reagent: deuterated acetonitrile;

[0029] Figure 5 is the hydrogen nuclear magnetic resonance spectrum of the cyclic carbonate-sulfate compound provided in Preparation Example 1 of the present invention ( 1 HNMR), deuterated reagent: deuterated DMSO;

[0030] Figure 6 is the carbon nuclear magnetic resonance spectrum of the cyclic carbonate-sulfate compound provided in Preparation Example 1 of the present invention ( 13 CNMR), deuterated reagent: deuterated DMSO;

[0031] Figure 7 is the crystal space structure diagram of the compound shown in Structural Formula 2 (Example 1);

[0032] Figure 8 is the ellipsoid diagram of the compound shown in Structural Formula 2 (Example 1);

[0033] Figure 9 is the comparison diagram of the powder diffraction and single crystal simulation diffraction of Structural Formula 2 (Example 1, in the figure, the vertical coordinate Intensity(a.u.) represents the relative intensity of the diffraction peak, the horizontal coordinate 2θ(degrees) represents the 2θ angle, and the upper right corner As synthesized represents the powder diffraction peak of the Structural Formula 2 sample, and Simulated represents the single crystal simulation diffraction peak of Structural Formula 2);

[0034] Figure 10 is the hydrogen nuclear magnetic resonance spectrum of the cyclic carbonate-sulfate compound provided in Preparation Example 3 of the present invention ( 1 HNMR), deuterated reagent: deuterated acetonitrile;

[0035] Figure 11 is the carbon nuclear magnetic resonance spectrum of the cyclic carbonate-sulfate compound provided in Preparation Example 3 of the present invention ( 13 CNMR), deuterated reagent: deuterated acetonitrile;

[0036] Figure 12 is the electron microscope observation diagram of the positive electrode sheet provided in Example 3 and Comparative Example 2 of the present invention. Detailed implementation mode

[0037] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] An embodiment of the present invention provides that the cyclic carbonate-sulfate compound includes the compound shown in Chemical Formula 1, and the specific rotation of the cyclic carbonate-sulfate compound α is -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g);

[0039] .

[0040] When the specific rotation of the cyclic carbonate-sulfate compound α is -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g), the molecular structure of its characteristic structure compound has higher symmetry, which is beneficial to forming a regular and stable solid electrolyte interface film on the surfaces of the positive and negative electrodes during the battery formation stage, thereby improving the electrochemical performance of the secondary battery.

[0041] In some embodiments, the compound shown in Chemical Formula 1 includes a characteristic structure compound, the characteristic structure compound is selected from the compound shown in Structural Formula 2 and / or the compound shown in Structural Formula 3, and in the compound shown in Chemical Formula 1, the content of the characteristic structure compound is ≥99wt%;

[0042] .

[0043] Since there are multiple chiral carbons in the compound shown in Chemical Formula 1, there are multiple chiral configurations in the compound shown in Chemical Formula 1, and there are large differences in the film-forming performance among different chiral configurations of the compound shown in Chemical Formula 1, and there is also interference among them, thereby affecting the orderliness of the solid electrolyte film on the surfaces of the positive and negative electrodes.

[0044] Through the purification and testing of different chiral configurations of the compound shown in Chemical Formula 1, it was found that for the chiral configuration of the non-axisymmetric structure of the compound shown in Chemical Formula 1, when forming a film, due to the certain randomness of the sulfate esters on both sides, the newly formed film cannot cover the active sites in the most compact manner, resulting in a relatively large number of exposed active sites in the formed film. The positive and negative electrode materials are still not effectively protected and may break down during the continuous electrochemical process or under continuous elevated heat shock, leading to the cycle failure or thermal shock damage of the battery. When the content of the characteristic structure compounds selected from the compounds shown in Structural Formula 2 and / or Structural Formula 3 in the compound shown in Chemical Formula 1 is relatively high, the formed solid electrolyte film is denser and more uniform, and its stability under high-temperature conditions is improved. It is speculated that this is due to the control of the film-forming process brought about by its axial symmetry. After the characteristic structure compound with axial symmetry coordinates with lithium ions, under the action of an electric field, an electrochemical reaction occurs at the electrode active sites to generate the corresponding inorganic salt-organic complex. At the same time, due to the axial symmetry of this type of molecule, when the lithium ion-additive complex that is about to form a film on the electrode plate forms a film again, since the complexing properties of the two sulfate esters with lithium ions are the same, the spatial structure, the spatial conformation of the molecular complex, and the influence of the surrounding solvent molecules on its resistance after complexation are the same. At the same time, it will be guided by the already formed SEI or CEI film, so it can form a relatively regular and more ductile organic-inorganic composite film in the same way, effectively covering most of the active sites and preventing them from further reacting electrochemically with other active components in the electrolyte or migrating to the counter electrode with the positive and negative electrode materials.

[0045] Among them, as measured Figure 7 and measured Figure 8 As shown, Structural Formula 2 has a two-fold rotational axis of symmetry (abbreviated as "axisymmetry"). The compound shown in Structural Formula 2 belongs to the monoclinic crystal system, characterized by no high-order symmetry axis, the b-axis being the unique axis, and there being no more than one two-fold symmetry axis and symmetry plane. The b-axis is orthogonal to both the a-axis and the c-axis, while the a-axis and the c-axis are inclined to each other, with the axial angles α = γ = 90°, β ≠ 90°, and the axial units a ≠ b ≠ c. And the space group of Structural Formula 2 is P21, and its symmetry elements include a two-fold rotation axis and a glide plane, that is, the symmetry operations of Structural Formula 2 include two-fold rotation around the b-axis and a glide plane perpendicular to the b-axis.

[0046] Structural Formula 3 has the same molecular formula as Structural Formula 2 and is a mirror image relationship in terms of the three-dimensional structure. Therefore, the compound shown in Structural Formula 3, as an additive, plays almost exactly the same role in the electrolyte as the compound shown in Structural Formula 2. The compounds shown in Structural Formula 2 and Structural Formula 3 can be distinguished by measuring the specific rotation.

[0047] In a preferred embodiment, the specific rotation of the cyclic carbonate-sulfate compound αis from -7.724°∙mL / (dm∙g) to +7.724°∙mL / (dm∙g).

[0048] In a more preferred embodiment, the specific rotation of the cyclic carbonate-sulfate compound α is from -7.525°∙mL / (dm∙g) to +7.525°∙mL / (dm∙g).

[0049] In a more preferred embodiment, the specific rotation of the cyclic carbonate-sulfate compound α is from -7.310°∙mL / (dm∙g) to +7.310°∙mL / (dm∙g).

[0050] In a preferred embodiment, in the compound shown in Formula 1, the content of the characteristic structure compound is ≥99 wt%.

[0051] When the content of the characteristic structure compound in the compound shown in Formula 1 is higher, it is more beneficial to improve the orderliness of the formed solid electrolyte membrane and avoid the influence of compounds of other isomers.

[0052] Compared with the mixture of the compound shown in Structural Formula 2 and the compound shown in Structural Formula 3, when the characteristic structure compound is selected from a single chiral configuration, it is more beneficial to improve the thermal shock resistance of the formed solid electrolyte membrane, indicating that the characteristic structure compound with a single chiral configuration is related to improving the orderliness of the solid electrolyte membrane.

[0053] In some embodiments, in the cyclic carbonate-sulfate compound, the content of the compound shown in Formula 1 is ≥99 wt%.

[0054] In some embodiments, the compound shown in Formula 1 further includes stereoisomer impurities other than the characteristic structure compound, and the content of stereoisomer impurities in the compound shown in Formula 1 is ≤1 wt%.

[0055] In a preferred embodiment, the content of stereoisomer impurities in the compound shown in Formula 1 is ≤0.5 wt%.

[0056] The sources of the stereoisomer impurities are mainly two aspects. On the one hand, it is the stereoisomer impurities contained in the preparation raw materials. For example, when D-mannitol is used as the initial raw material for the preparation of the compound shown in Structural Formula 2, among them, the sorbitol or other types of stereoisomers contained may be reflected in the final product of the synthesis reaction. On the other hand, it is generated during the preparation process. For example, the stereoconfiguration of some intermediates is unstable, resulting in phenomena such as chiral inversion, and stereoisomer impurities appear in the compound shown in Structural Formula 2 obtained by preparation.

[0057] By reducing the impurity content, it is beneficial to reduce the problem of insufficient densification of the solid electrolyte membrane caused by the presence of stereoisomers.

[0058] In some embodiments, the content of chlorine element in the cyclic carbonate-sulfate compound is ≤100 ppm.

[0059] The source of chlorine element is mainly due to chlorine-containing impurities carried in the reaction raw materials or solvents. The presence of chlorine element in the cyclic carbonate-sulfate compound has a great impact on its performance as an electrolyte additive. Although chlorine element is usually formed as a substituent in the impurities of the cyclic carbonate-sulfate compound, under electrochemical conditions, the chlorine-containing impurities are unstable and easily decompose to form free chlorine. The free chlorine in the non-aqueous electrolyte is likely to induce the corrosion of the positive electrode current collector and also easily cause the dissolution of transition metal ions in the positive electrode material. Therefore, it is necessary to control the content of chlorine element in the cyclic carbonate-sulfate compound to reduce the influence.

[0060] In some embodiments, the cyclic carbonate-sulfate compound further includes organic impurities, and the mass content of the organic impurities is ≤1%. The organic impurities include one or more of the following compounds:

[0061] 。

[0062] Among the organic impurities, there are impurities derived from unreacted raw materials, such as etc., or impurities caused by transesterification at other positions in step S1, such as etc. These are not conducive to the uniform film formation of the solid electrolyte membrane on the surfaces of the positive and negative electrodes, thus forming defects on the solid electrolyte membrane, resulting in problems such as uneven thickness of the solid electrolyte membrane. By controlling the purification conditions and reaction yield to reduce the content of the organic impurities, it is beneficial to reduce the defects on the solid electrolyte membrane, ensure the thermal shock resistance of the solid electrolyte membrane, and improve the battery safety performance.

[0063] Another embodiment of the present invention provides an application of the cyclic carbonate-sulfate compound as described above as an electrolyte additive.

[0064] Another embodiment of the present invention provides a preparation method of the cyclic carbonate-sulfate compound as described above, including the following operating steps:

[0065] S1. Mix and react a hexahydric alcohol, a basic catalyst, a carbonate, and a lower alcohol to obtain a carbonate polyhydric alcohol. The hexahydric alcohol includes the compound shown in structural formula 4 and / or the compound shown in structural formula 5. The carbonate polyhydric alcohol includes the compound shown in structural formula 6 and / or the compound shown in structural formula 7. The lower alcohol is a monohydric alcohol and / or a dihydric alcohol;

[0066] 。

[0067] S2. React the carbonate polyol with N,N'-sulfonyldiimidazole to obtain the compound shown in Chemical Formula 1.

[0068] The reaction route is as follows:

[0069] 。

[0070] In the preparation method provided by the present invention, the preparation method of step S1 has a certain similarity with Patent KR1020190116899. First, an ester exchange reaction is carried out between a carbonate and a hexahydric alcohol to prepare a carbonate polyol. Since the hexahydric alcohol has multiple hydroxyl groups, which are located on different carbons respectively, in this ester exchange reaction, the carbonate will undergo an ester exchange reaction with any hydroxyl group to obtain different types of reaction products, resulting in problems such as a decrease in the product yield and difficulty in subsequent purification. Therefore, a lower polyol is added in step S1 of this preparation method. When the lower polyol is present, it can greatly improve the reaction activity of the hydroxyl groups on the two middle carbons in this ester exchange reaction, while inhibiting the reaction activity of the hydroxyl groups on both sides of the hexahydric alcohol, thereby ensuring that the reaction product obtained is mainly a carbonate polyol, which can greatly improve the reaction yield and reduce the purification difficulty.

[0071] In the process of further preparing the compound shown in Chemical Formula 1 from the carbonate polyol, in the existing preparation method, there is a problem that the chiral structure of the intermediate is unstable and chiral inversion occurs. The chiral structure of the reaction intermediate is unstable, so that its chiral structure undergoes chiral inversion during the reaction to obtain different stereoisomers, which affects the chiral configuration purity of the final product. To solve this technical problem and ensure the consistency of the stereoconfiguration of the compound shown in Chemical Formula 1, the present invention uses N,N'-sulfonyldiimidazole to react with the carbonate polyol (Structural Formula 6 or 7) to obtain the target product; a non-protic solvent with a small dielectric constant is used to avoid the configuration inversion during the reaction that may be caused by a strongly polar solvent / protic solvent. Using N,N'-sulfonyldiimidazole has a larger steric hindrance, which is beneficial to maintaining the chiral configuration and can maintain the spatial configuration of the carbonate polyol (Structural Formula 6 or 7) to obtain the characteristic structure compound shown in Structural Formula 2 or Structural Formula 3. And the content of the characteristic structure compound shown in Structural Formula 2 and / or Structural Formula 3 obtained finally is ≥99 wt%.

[0072] In some embodiments, in step S1, the molar ratio of the carbonate to the hexahydric alcohol is 5:1 to 10:1.

[0073] The theoretical molar ratio of carbonate to hexahydric alcohol is 1:1. In this preparation method, adding an excessive amount of carbonate is beneficial to accelerating the reaction. However, the addition amount of the carbonate cannot be too high, as too much carbonate is likely to increase the substitution probability of hydroxyl groups at both side positions, resulting in impurities.

[0074] In some embodiments, in step S1, the molar ratio of lower alcohol to carbonate is 1:1 to 5:1.

[0075] The lower alcohol promotes the reaction activity of the hydroxyl group at the middle position of the hexahydric alcohol and inhibits the reaction activity of the hydroxyl groups at both side positions of the hexahydric alcohol in the transesterification reaction, thereby inhibiting side reactions. When the addition amount of the lower alcohol is too low, it is difficult to ensure the inhibitory effect on side reactions, resulting in reactions between hydroxyl groups at non-predetermined positions and carbonates, forming a large number of unnecessary by-products. However, since the lower alcohol itself is also a reaction product of carbonate and hexahydric alcohol, when the addition amount of the lower alcohol is too high, it will inhibit the forward progress of the reaction, leading to an extended reaction time and affecting production efficiency.

[0076] In step S1, adding a basic catalyst is beneficial to improving the reaction activity between the hexahydric alcohol and the carbonate.

[0077] In some embodiments, the basic catalyst includes one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, lithium carbonate, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium tert-butoxide, triethylamine, and pyridine.

[0078] In some embodiments, the added mass of the basic catalyst is 0.1% to 0.8% of the mass of the hexahydric alcohol.

[0079] When the addition amount of the basic catalyst is within the above range, it is beneficial to ensure the basic environment required for the reaction, while avoiding problems such as difficult subsequent purification and introduction of impurities caused by excessive addition.

[0080] In some embodiments, in step S1, the reaction temperature is 45 to 70 °C.

[0081] In specific embodiments, in step S1, the reaction temperature can be 45 °C, 48 °C, 50 °C, 52 °C, 55 °C, 58 °C, 60 °C, 62 °C, 65 °C, 68 °C, or 70 °C.

[0082] When the reaction temperature in step S1 is within the above range, it is beneficial to maintain a relatively high reaction rate for the reaction, while avoiding an increase in the reaction activity of the terminal hydroxyl groups of the hexahydric alcohol caused by too high a temperature, resulting in side reactions.

[0083] In some embodiments, in step S1, the reaction time is 2 to 24 h.

[0084] In a specific embodiment, in step S1, the reaction time can be 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h or 24 h.

[0085] The reaction time can be adjusted accordingly according to the actual reaction rate. If the reaction time is too short, the reaction yield will be affected and raw material waste will be caused; if the reaction time is too long, the production efficiency will be affected and there will be no special beneficial effect on the improvement of the yield.

[0086] In some embodiments, the carbonate includes one or more of cyclic carbonates and chain carbonates. The cyclic carbonate includes ethylene carbonate, and the chain carbonate includes one or more of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate and diphenyl carbonate.

[0087] In a preferred embodiment, the lower alcohol includes methanol.

[0088] In some embodiments, in step S1, after the reaction of the hexahydric alcohol, the basic catalyst, the carbonate and the lower alcohol, the reaction product is concentrated under reduced pressure to precipitate a solid. After separating the solid, recrystallization is carried out to obtain the carbonate polyol.

[0089] The operations of concentration under reduced pressure and recrystallization are beneficial to purify the carbonate polyol in the reaction product, avoid the reaction of unreacted raw materials, basic catalysts or by-products with N,N'-sulfonyldiimidazole in step S2, and reduce the generation of impurities and the consumption of N,N'-sulfonyldiimidazole.

[0090] In some embodiments, the temperature of concentration under reduced pressure is 25°C to 45°C.

[0091] In some embodiments, during the recrystallization process, methanol is added to dissolve the solid. The mass ratio of the methanol added for recrystallization to the carbonate polyol is 1:1 to 1:3; then ethyl acetate is slowly added dropwise, and the mass ratio of the methanol added for recrystallization to ethyl acetate is 1:5 to 1:9, preferably 1:6 to 1:8, to precipitate the carbonate polyol crystals.

[0092] In some embodiments, in step S2, the molar ratio of N,N'-sulfonyldiimidazole to the carbonate polyol is 2:1 to 5:1.

[0093] The preferred molar ratio is 2:1 to 3:1.

[0094] The theoretical reaction molar ratio of N,N'-sulfonyldiimidazole to the carbonate polyol is 2:1. By increasing the addition amount of N,N'-sulfonyldiimidazole, it is beneficial to ensure the full reaction of the carbonate polyol. At the same time, the solubility of N,N'-sulfonyldiimidazole is relatively good, and the excess N,N'-sulfonyldiimidazole can be directly separated by stirring and washing with a solvent, reducing the residue of impurities in the final product.

[0095] In some embodiments, the reaction in step S2 is carried out in an aprotic solvent with a dielectric constant less than 8.

[0096] The aprotic solvents with a dielectric constant less than 8 include, but are not limited to, one or more of ethyl acetate, methyl acetate, ethyl formate, chloroform, ether, dioxane, furan, dimethyl carbonate, diethyl carbonate, and n-heptane.

[0097] If a solvent with a large dielectric constant is used as the reaction solvent in step S2, the chiral configuration of the reaction product in step S2 will be unstable, and there is a probability that the configuration inversion will occur during the reaction. Therefore, by restricting the dielectric constant of the aprotic solvent, it is beneficial to maintain the stability of the chiral configuration during the reaction and obtain the compound shown in Formula 2 and / or the compound shown in Formula 3 with higher purity.

[0098] In some embodiments, aprotic solvents with a dielectric constant less than 4 are preferred, such as dioxane, furan, dimethyl carbonate, diethyl carbonate, n-heptane, etc.

[0099] It should be noted that the dielectric constant specifically refers to the dielectric constant of a substance at 25 °C.

[0100] In some embodiments, the mass ratio of the aprotic solvent to N,N'-thiobis(imidazole) ≥ 10:1;

[0101] Since the by-product of the reaction in step S2 is imidazole, and the dielectric constant of imidazole is greater than 8, there is a probability that the configuration inversion will occur during the reaction. Therefore, it is necessary to increase the amount of the aprotic solvent to achieve a dilution effect, reduce the influence of imidazole, and avoid chiral inversion.

[0102] In a preferred embodiment, the mass ratio of the aprotic solvent to N,N'-thiobis(imidazole) is 10:1 to 30:1.

[0103] In some embodiments, the reaction temperature in step S2 is 25 - 60 °C, and the reaction time is 1 - 12 h.

[0104] Under these reaction temperature and reaction time conditions, the forward progress of the reaction can be promoted, and at the same time, the occurrence of side reactions can be reduced.

[0105] In some embodiments, in step S2, after the reaction is completed, the reaction product is stirred and washed, then filtered under reduced pressure, and finally concentrated and dried to remove the unreacted N,N'-thiobis(imidazole) to obtain the target product.

[0106] Another embodiment of the present invention provides a non-aqueous electrolyte, including a non-aqueous organic solvent, an electrolyte salt, and an additive, and the additive includes the cyclic carbonate-sulfate compound as described above.

[0107] Due to the adoption of the cyclic carbonate-sulfate compound as described above, a uniform and dense solid electrolyte film can be formed on the surfaces of the positive and negative electrodes during the battery formation stage, which can avoid the continuous decomposition of the non-aqueous electrolyte during the battery cycling process. The thickness uniformity of this solid electrolyte film is high, has little influence on the insertion and extraction of lithium ions, and has a high ionic conduction efficiency. In particular, this solid electrolyte film has excellent high-temperature stability, thereby avoiding the problem of thermal runaway caused by the destruction of the positive electrode material structure under high-temperature conditions, while also improving the stability of the negative electrode and suppressing the growth of the negative electrode impedance, thus avoiding the accumulation of internal heat in the battery due to too large impedance and effectively improving the safety performance of the battery.

[0108] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the cyclic carbonate-sulfate compound is 0.01% - 5%.

[0109] In specific embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the cyclic carbonate-sulfate compound can be 0.01%, 0.05%, 0.05%, 0.1%, 0.12%, 0.15%, 0.3%, 0.5%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.7%, 1.9%, 2.1%, 2.2%, 2.4%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 4.2%, 4.4%, 4.7%, 4.9% or 5.0%.

[0110] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of cyclic sulfate compounds, sultone compounds, cyclic carbonate compounds, phosphate ester compounds, borate ester compounds, and nitrile compounds;

[0111] In a preferred embodiment, the cyclic sulfate compound is selected from at least one of ethylene sulfate, propylene sulfate, or vinyl methyl sulfate;

[0112] The sultone compound is selected from at least one of methylene bis(methanesulfonate), 1,3-propane sultone, 1,4-butane sultone, or 1,3-propene sultone;

[0113] The cyclic carbonate compound is selected from at least one of vinylene carbonate, fluoroethylene carbonate, or the compound shown in Structural Formula 6,

[0114] ;

[0115] In the said Structural Formula 8, R 21 , R 22 , R23 and R 24 and R 25 and R 26 are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

[0116] The phosphate compound is selected from at least one of tris(trimethylsilyl) phosphate and the compound shown in Structural Formula 9:

[0117] ;

[0118] In Structural Formula 9, R 31 and R 32 and R 32 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and at least one of R 31 and R 32 and R 33 is an unsaturated hydrocarbon group.

[0119] In a preferred embodiment, the unsaturated phosphate compound can be at least one of tris(trimethylsilyl) phosphate, triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyltrifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate, triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyltrifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate.

[0120] The borate compound is selected from tris(trimethylsilyl) borate;

[0121] The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile.

[0122] In other embodiments, the auxiliary additive may further include other additives that can improve the battery performance: for example, additives that enhance the battery safety performance, specifically flame retardant additives such as fluorophosphate and cyclophosphazene, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0123] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the auxiliary additive is 0.01% - 30%.

[0124] It should be noted that, unless otherwise specified, generally, the addition amount of any optional substance in the auxiliary additive in the non-aqueous electrolyte is 10% or less. Preferably, the addition amount is 0.1-5%, and more preferably, the addition amount is 0.1% to 2%. Specifically, the addition amount of any optional substance in the auxiliary additive can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%.

[0125] In some embodiments, when the auxiliary additive is selected from vinylene carbonate, based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the vinylene carbonate is 0.05% to 30%.

[0126] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass content of the non-aqueous organic solvent is 65% to 90%.

[0127] Specifically, based on the total mass of the non-aqueous electrolyte being 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, 90%.

[0128] In some embodiments, the non-aqueous organic solvent includes at least one of an ether solvent, a nitrile solvent, a carbonate solvent, a carboxylate solvent, and a sulfone solvent.

[0129] In some embodiments, the ether solvent includes cyclic ethers or linear ethers, preferably linear ethers having 3 to 10 carbon atoms and cyclic ethers having 3 to 6 carbon atoms. The cyclic ethers can specifically be, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the linear ethers can specifically be, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Since linear ethers have a high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. The ether compounds can be used alone or in combination of two or more in any combination and ratio. The addition amount of the ether compounds is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the high-compaction lithium-ion battery of the present invention. In a non-aqueous solvent with a volume ratio of 100%, it is generally 1% or more by volume, preferably 2% or more by volume, more preferably 3% or more by volume. Additionally, it is generally 30% or less by volume, preferably 25% or less by volume, more preferably 20% or less by volume.

[0130] In some embodiments, the nitrile solvent can specifically be, but is not limited to, at least one of acetonitrile, glutarodinitrile, and malononitrile.

[0131] In some embodiments, the carbonate solvents include cyclic carbonates or chain carbonates. The cyclic carbonates can specifically but not limited to be at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonates can specifically but not limited to be at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). There is no special limitation on the content of the cyclic carbonate, and it can be arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. However, when using a single type alone, the lower limit of its content is usually more than 3% by volume, preferably more than 5% by volume, relative to the total amount of the solvents of the non-aqueous electrolyte. By setting this range, it is possible to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and it is easy to make the high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery reach a good range. In addition, the upper limit is usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, which helps to improve the stability during high-temperature storage. There is no special limitation on the content of the chain carbonate. Relative to the total amount of the solvents of the non-aqueous electrolyte, it is usually 15% by volume or more, preferably 20% by volume or more, more preferably 25% by volume or more. In addition, it is usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less. By making the content of the chain carbonate within the above range, it is easy to make the viscosity of the non-aqueous electrolyte reach an appropriate range, inhibit the decrease of ionic conductivity, and further help to make the output characteristics of the non-aqueous electrolyte battery reach a good range. When using two or more chain carbonates in combination, it is only necessary to make the total amount of the chain carbonates meet the above range.

[0132] In some embodiments, it is also preferable to use chain carbonates having fluorine atoms (hereinafter simply referred to as "fluorinated chain carbonates"). The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms can be bonded to the same carbon or to different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc.

[0133] The carboxylic ester solvents include cyclic carboxylic esters and / or chain carbonates. Examples of the cyclic carboxylic esters can include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of the chain carbonates can include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0134] In some embodiments, the sulfone solvents include cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, they are usually compounds having 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms; in the case of chain sulfones, they are usually compounds having 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no special limitation on the addition amount of the sulfone solvents, and it can be arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. Relative to the total amount of the solvents in the non-aqueous electrolyte, the volume ratio is usually 0.3% or more, preferably 0.5% or more, more preferably 1% or more. Additionally, the volume ratio is usually 40% or less, preferably 35% or less, more preferably 30% or less. When two or more sulfone solvents are used in combination, the total amount of the sulfone solvents only needs to satisfy the above range. When the addition amount of the sulfone solvents is within the above range, it tends to obtain a non-aqueous electrolyte with excellent high-temperature storage stability.

[0135] In a preferred embodiment, the non-aqueous organic solvent includes a mixture of cyclic carbonates and chain carbonates.

[0136] In some embodiments, the electrolyte salt is selected from lithium salts, and the lithium salts include at least one of LiPF6, LiBOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium trioxalate phosphate, lithium lower aliphatic carboxylate having 4 or less carbon atoms, or lithium tetraphenylborate.

[0137] In some embodiments, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.1 mol / L to 4 mol / L. In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L or 2.5 mol / L.

[0138] In other embodiments, if the non-aqueous electrolyte is applied to a sodium-ion battery, the electrolyte can also select the corresponding sodium salt.

[0139] Another embodiment of the present invention provides a secondary battery, including the non-aqueous electrolyte as described above.

[0140] In some embodiments, the secondary battery is a lithium-ion battery.

[0141] In some embodiments, the positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material is selected from at least one of LiFe 1-x’ M’ x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z O2, where M’ is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, and 0 ≤ x’ < 1, 0 ≤ y’ ≤ 1, 0 ≤ y ≤ 1, 0 ≤ x ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1.

[0142] In a preferred embodiment, the positive electrode active material is selected from LiCoO2.

[0143] Among many cathode materials, LiCoO2 has the highest volumetric energy density and good rate performance. However, as the battery voltage gradually increases, LiCoO2 enters a higher delithiated state, the structural stability of the material deteriorates, Co in the cathode is prone to disproportionation reaction, dissolves in the electrolyte in the form of ions, causing damage to the cathode structure, and is prone to thermal runaway risk under high temperature and high pressure. When the cyclic carbonate-sulfate compound provided in this application is used in combination with LiCoO2, it can fully exert the improvement effect of the cyclic carbonate-sulfate compound on the crystal stability of the high-voltage cathode material, thereby obtaining a lithium-ion battery with both high volumetric energy density and high safety.

[0144] In some embodiments, the cathode material layer further includes a cathode binder and a cathode conductive agent, and the cathode active material, the cathode binder, and the cathode conductive agent are blended to obtain the cathode material layer.

[0145] The cathode binder includes at least one of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ether, copolymers of ethylene-tetrafluoroethylene, copolymers of vinylidene fluoride-tetrafluoroethylene, copolymers of vinylidene fluoride-trifluoroethylene, copolymers of vinylidene fluoride-trichloroethylene, copolymers of vinylidene fluoride-fluorinated ethylene, copolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0146] The cathode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0147] In some embodiments, the cathode current collector includes a metal material that can conduct electrons. Preferably, the cathode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the cathode current collector is selected from aluminum foil.

[0148] In some embodiments, the anode includes an anode material layer, the anode material layer includes an anode active material, and the anode active material includes at least one of a carbon-based anode, a silicon-based anode, a tin-based anode, and a lithium anode. Among them, the carbon-based anode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based anode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the tin-based anode may include tin, tin-carbon, tin-oxygen, tin metal compounds; the lithium anode may include metallic lithium or lithium alloys. The lithium alloy may specifically be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-indium alloy.

[0149] In a more preferred embodiment, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, graphene, and silicon-carbon composite materials.

[0150] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0151] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector includes a metal material capable of conducting electrons. Preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foils.

[0152] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0153] The negative electrode binder includes at least one of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene - butadiene rubber.

[0154] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0155] In some embodiments, the secondary battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0156] The separator can be an existing conventional separator, which can be a ceramic separator, a polymer separator, a non - woven fabric, an inorganic - organic composite separator, etc., including but not limited to single - layer PP (polypropylene), single - layer PE (polyethylene), double - layer PP / PE, double - layer PP / PP, and triple - layer PP / PE / PP separators.

[0157] The present invention will be further described below through examples.

[0158] Preparation Example 1

[0159] Preparation of cyclic carbonate - sulfate compound 1

[0160] ⑴. Put 20.0 g of D - mannitol (structural formula 4) and 40.0 mg of potassium carbonate (K₂CO₃) into a 500 - mL three - necked round - bottom flask, then add 60 mL of methanol, and heat up to 60 °C. While stirring, add 138.6 mL of dimethyl carbonate (DMC) dropwise over 30 minutes. After the addition of dimethyl carbonate is complete, heat to 66 °C and reflux with stirring for 3 hours for the reaction to produce the crude product of the compound shown in structural formula 6. Then, the solid obtained after concentration under reduced pressure is added to 40 mL of methanol. After complete dissolution, 200 mL of ethyl acetate (EA) is slowly added dropwise for recrystallization. The resulting crystals are filtered under reduced pressure to obtain 14.5 g of the target product. The target product is tested by proton nuclear magnetic resonance spectroscopy (¹H NMR) and carbon - 13 nuclear magnetic resonance spectroscopy (¹³C NMR), and the test results are as shown in Figure 1 and Figure 2 to determine that the structure is structural formula 6.

[0161] ⑵. Put 10.0 g of the compound shown in structural formula 6 and 20 g of N,N'-sulfonyldiimidazole into a 250 - mL three - necked round - bottom flask, then add 200 g of diethyl carbonate (dielectric constant 2.82, data source: Solvent Handbook), and heat up to 60 °C. The reaction time is 6 hours, and the reaction progress is monitored by thin - layer chromatography (TLC). After the reaction is completed, 20 mL of water is added for washing multiple times. Then, the solid obtained after concentration under reduced pressure is slurried with 20 mL of diethyl carbonate at a temperature controlled at 5 °C for 0.5 hours, followed by filtration under reduced pressure, concentration, and drying to obtain 11.5 g of cyclic carbonate - sulfate compound 1.

[0162] ⑶. The obtained cyclic carbonate - sulfate compound 1 is tested by liquid chromatography, and the mass content of the compound shown in chemical formula 1 in the cyclic carbonate - sulfate compound is 99%. The content of organic impurities is 1%. The chlorine content of the compound is tested by turbidimetry to be 100 ppm.

[0163] Meanwhile, the obtained cyclic carbonate - sulfate compound is dissolved in acetonitrile and injected for chromatographic testing by high - performance liquid chromatography (instrument: Agilent 1200 series high - performance liquid chromatography system, performed on a Waters ultra - high - performance convergence chromatography system, column temperature: 25 °C; flow rate: 1.0 mL / min). The single - configuration content of the compound shown in chemical formula 1 in cyclic carbonate - sulfate compound 1 is 99%. The ratio of stereoisomer impurities to the compound shown in chemical formula 1 is 1%.

[0164] Furthermore, the obtained cyclic carbonate - sulfate compound is tested by proton nuclear magnetic resonance spectroscopy (¹H NMR) and carbon - 13 nuclear magnetic resonance spectroscopy (¹³C NMR) using deuterated acetonitrile and deuterated DMSO respectively, and the test results are as shown in Figures 3 - 6 to determine that the structure is chemical formula 1; According to the carbon - 13 nuclear magnetic resonance spectrumFigure 4 With Figure 6 , except for the carbonyl carbon, there are only 3 kinds of chemically equivalent carbons instead of 6, and the obtained compound of Chemical Formula 1 belongs to a single configuration with axial symmetry.

[0165] Furthermore, single crystals of the cyclic carbonate-sulfate compound 1 were grown, and the single crystal was tested by single crystal X-ray diffraction (abbreviated as XRD). The test conditions were: T = 100.0(2) K, μ(GaKα) = 3.126 mm -1 , and the measured Figure 7 and the measured Figure 8 are as follows: The crystal belongs to the monoclinic system, space group: P21, crystal parameters: a = 9.0824(12) Å, b = 6.3730(8) Å, c = 10.1036(13) Å, β = 93.744(4)°, V = 583.57(13) Å 3 , Z = 2, and data processing was carried out to obtain Table 1 below.

[0166] Table 1 Crystal Structure Data Table

[0167]

[0168] As Figure 7 and Figure 8 shown, the compound shown in Structural Formula 2 belongs to the monoclinic system, characterized by no high-order symmetry axis, the b-axis is the unique axis, and there is no more than one secondary symmetry axis and symmetry plane. The b-axis is orthogonal to both the a-axis and the c-axis, while the a-axis and the c-axis are obliquely intersecting, the axial angles α = γ = 90°, β ≠ 90°, and the axial units a ≠ b ≠ c. And the space group of Structural Formula 2 is P21, and its symmetry elements include a two-fold rotation axis and a glide plane, that is, the symmetry operations of Structural Formula 2 include a two-fold rotation about the b-axis and a glide plane perpendicular to the b-axis. The single crystal spatial structure was determined to be Structural Formula 2.

[0169] Furthermore, the cyclic carbonate-sulfate compound 1 was tested by powder diffraction and compared with the simulated diffraction of single crystal X-ray, and Figure 9 was obtained, indicating that the spatial structure of the obtained cyclic carbonate-sulfate compound is consistent with its single crystal spatial configuration. The spatial structure of the cyclic carbonate-sulfate compound was determined to be Structural Formula 2.

[0170] Furthermore, the specific rotation of the cyclic carbonate-sulfate compound 1 was tested according to the following method:

[0171] Weigh 5 g of cyclic carbonate - sulfate compound 1 and completely dissolve it with acetonitrile (acetonitrile purity > 99%, water content < 1000 ppm) to prepare a solution with a concentration of cyclic carbonate - sulfate compound 1 of 0.126 g / mL. Test according to the "General Test Method for the Determination of the Specific Rotation Ability (Specific Rotation) of Chemical Reagents - GBT613 - 2007". Test conditions: wavelength 589 nm, temperature 20 °C, solvent acetonitrile, tube length 100 mm, concentration 0.126 g / mL. The measured specific rotation α = - 7.982 °∙mL / (dm∙g), abbreviated as specific rotation α = - 7.982.

[0172] In summary, for cyclic carbonate - sulfate compound 1, the mass content of the compound shown in Chemical Formula 1 is 99% (the mass ratio of the compound shown in Structural Formula 2 to the compound shown in Chemical Formula 1 is 99%, and the mass ratio of the stereoisomer impurity to the compound in Chemical Formula 1 is 1%). The mass content of organic impurities is 1%. The chlorine content of the compound tested by the turbidimetry method is 100 ppm.

[0173] Furthermore, it can be further purified and separated by recrystallization (natural crystallization from a mixed solvent of acetonitrile and ethyl acetate) or preparative separation by high - performance liquid chromatography with gradient elution, batch collection and concentration to obtain cyclic carbonate - sulfate compounds with different purities. Test the influence of the ratio of Structural Formula 2 on the specific rotation of the cyclic carbonate - sulfate compound to obtain Table 2.

[0174] Test conditions: wavelength 589 nm, temperature 20 °C, solvent acetonitrile, tube length 100 mm, concentration of cyclic carbonate - sulfate compound 0.126 g / mL.

[0175] Table 2

[0176]

[0177] Preparation Example 2

[0178] Preparation of cyclic carbonate - sulfate compound 2

[0179] By further purifying the cyclic carbonate - sulfate compound 1 obtained in Preparation Example 1, cyclic carbonate - sulfate compound 2 is obtained.

[0180] Cyclic carbonate - sulfate compound 2: The mass content of the compound shown in Chemical Formula 1 is 99.8% (the mass ratio of the compound shown in Structural Formula 2 to the compound shown in Chemical Formula 1 is 99.8%, and the mass ratio of the stereoisomer impurities to the compound shown in Chemical Formula 1 is 0.2%). The mass content of organic impurities is 0.2%. The chlorine content of the compound measured by turbidimetry is 10 ppm. The specific rotation is -7.311°∙mL / (dm∙g).

[0181] Specific rotation test conditions: wavelength 589 nm, temperature 20 °C, solvent acetonitrile, tube length 100 mm, concentration of cyclic carbonate - sulfate compound 0.126 g / mL.

[0182] Preparation Example 3

[0183] Preparation of cyclic carbonate - sulfate compound 3

[0184] It includes most of the operation steps in Preparation Example 1, and the differences are: using L - mannitol (Structural Formula 5) instead of D - mannitol (Structural Formula 4); testing NMR to obtain Figure 10 and Figure 11 .

[0185] In the obtained cyclic carbonate - sulfate compound 3: The content of Chemical Formula 1 is 99.6% (the ratio of Structural Formula 3 to the compound of Chemical Formula 1 is 99.4%, and the ratio of stereoisomer impurities to the compound of Chemical Formula 1 is 0.6%). The content of organic impurities is 0.4%. The chlorine content of the compound measured by turbidimetry is 100 ppm. The specific rotation is +7.546°∙mL / (dm∙g).

[0186] Test conditions: wavelength 589 nm, temperature 20 °C, solvent acetonitrile, tube length 100 mm, concentration of cyclic carbonate - sulfate compound 0.126 g / mL.

[0187] Preparation Example 4

[0188] Preparation of cyclic carbonate - sulfate compound 4

[0189] Among them, cyclic carbonate - sulfate compound 4 is obtained by completely dissolving cyclic carbonate - sulfate compound 1 and cyclic carbonate - sulfate compound 3 in acetonitrile respectively, mixing them according to the mass ratio of 1 / 1, and then concentrating under reduced pressure. The specific rotation is +0.021°∙mL / (dm∙g). Specific rotation test conditions: test temperature 20 °C, wavelength 589 nm, tube length 100 mm, solvent acetonitrile, concentration of cyclic carbonate - sulfate compound 0.126 g / mL.

[0190] Preparation Example 5

[0191] It includes most of the operations in Preparation Example 1, with the differences being as follows:

[0192] Acetonitrile (dielectric constant 37.5) was used to replace diethyl carbonate in Example 1.

[0193] The cyclic carbonate - sulfate compound 5 was obtained. The mass content of the compound shown by Chemical Formula 1 in the cyclic carbonate - sulfate compound 5 was 99% (the mass ratio of the compound shown by Structural Formula 2 to the compound shown by Chemical Formula 1 was 65%, and the mass ratio of the stereoisomer impurities to the compound shown by Chemical Formula 1 was 35%). The mass content of organic impurities was 1%. The chlorine content of the compound tested by the nephelometry method was 100 ppm. The specific rotation was -8.575°∙mL / (dm∙g).

[0194] Specific rotation test conditions: wavelength 589 nm, temperature 20 °C, solvent acetonitrile, tube length 100 mm, concentration of the cyclic carbonate - sulfate compound 0.126 g / mL.

[0195] Preparation Example 6

[0196] Preparation of the cyclic carbonate - sulfate compound 6

[0197] ⑴ 20.0 g of D - mannitol and 40.0 mg of potassium carbonate (K2CO3) were placed in a 500 - mL three - necked round - bottom flask, then 60 mL of methanol was added, and the temperature was heated to 60 °C. While stirring, 138.6 mL of dimethyl carbonate (DMC) was added dropwise over a period of 30 minutes. After the addition of dimethyl carbonate was complete, the temperature was heated to 66 °C, and the mixture was refluxed and stirred for 3 hours for the reaction to produce a crude product of the compound shown by Structural Formula 4. Then, the solid obtained after concentration under reduced pressure was added to 40 mL of methanol. After complete dissolution, 200 mL of ethyl acetate (EA) was slowly added dropwise for recrystallization. The resulting crystals were filtered under reduced pressure to obtain 14.6 g of Intermediate 1.

[0198] ⑵ 10.0 g of Intermediate 1 and 12 g of thionyl chloride were placed in a 250 - mL three - necked round - bottom flask, then 100 g of dichloromethane was added, and the temperature was heated to 60 °C. The reflux reaction time was 6 hours. The reaction was carried out under aeration, and the tail gas was absorbed until no gas was generated. Then, the solid obtained after concentration under reduced pressure was added to 20 mL of diethyl carbonate for pulping, the temperature was controlled at 5 °C, and the stirring time was 0.5 hour. After filtration under reduced pressure and concentration and drying, 11.5 g of Intermediate 2 was obtained.

[0199] (3) Put 10.0 g of intermediate 2 and 100 g of acetonitrile into a 250 mL three-necked round-bottom flask, and control the temperature at 10 - 15 °C. Dropwise add 10 g of 40% hydrogen peroxide, control the temperature during the dropping process to be less than 35 °C, and stir for 6 hours. Then filter under reduced pressure, concentrate and dry to obtain 8.23 g of cyclic carbonate-sulfate compound.

[0200] After testing, the content of the compound shown in Chemical Formula 1 in the cyclic carbonate-sulfate compound 6 is 99.7% (the ratio of the structural formula 2 / 3 to the compound of Chemical Formula 1 is <1%, and the mass ratio of the stereoisomer impurity to the compound shown in Chemical Formula 1 is 99%). The mass content of organic impurities is 0.3%. The chlorine content of the compound measured by the turbidimetry method is 100 ppm. The specific rotation is -9.731°∙mL / (dm∙g). Specific rotation test conditions: test temperature 20 °C, wavelength 589 nm, tube length 100 mm, solvent acetonitrile, concentration of carbonate-sulfate compound 0.126 g / mL.

[0201] Examples 1 - 9, Comparative Examples 1 - 3

[0202] 1) Preparation of non-aqueous electrolyte

[0203] Mix ethylene carbonate (EC) and diethyl carbonate (DEC) evenly at a weight ratio of 30:70, add LiPF6 to 1.15 mol / L, and then add the above-prepared cyclic carbonate-sulfate compound and dissolve it in the above non-aqueous organic solvent to obtain a non-aqueous electrolyte. The selection of the cyclic carbonate-sulfate compound and its content in the non-aqueous electrolyte in each example and each comparative example are shown in Table 3, and the content is calculated as a percentage of the total mass of the non-aqueous electrolyte.

[0204] 2) Preparation of positive electrode plate

[0205] Disperse the positive electrode active material LiCoO2, conductive carbon black, and binder PVDF into the non-aqueous organic solvent NMP (N-methyl-2-pyrrolidone) and mix evenly to obtain a positive electrode slurry; coat the positive electrode slurry evenly on the positive electrode current collector aluminum foil, and after drying, rolling, and cutting, obtain a positive electrode plate. The weight ratio of the positive electrode active material, conductive carbon black, and binder PVDF is 95:3:2.

[0206] 3) Preparation of negative electrode plate

[0207] Disperse the negative electrode active material graphite, conductive agent, CMC, and SBR at a weight ratio of 95:2:1:2 in deionized water and stir to obtain a negative electrode slurry; coat the negative electrode slurry evenly on the negative electrode current collector copper foil, dry, roll, and cut to obtain a negative electrode plate.

[0208] 4) Preparation of lithium-ion battery

[0209] Using the lamination process, the positive electrode sheet, the separator membrane, and the negative electrode sheet are laminated in sequence, and then after processes such as top and side sealing and injection of non-aqueous electrolyte, a soft-pack battery is made.

[0210] 5) Formation

[0211] The formation is carried out according to the following steps: constant current charging at 0.05C for 180 min, constant current charging at 0.1C for 180 min, shaping and sealing after standing for 24 hr, and then further constant current charging at a current of 0.2C until the cut-off is 100% SOC. After standing at room temperature for 24 hr, constant current discharging is carried out at a current of 0.2C to 3.0V.

[0212] Performance test

[0213] I. The lithium-ion batteries prepared in Example 3 and Comparative Example 2 are disassembled in a glove box filled with argon, and the positive electrode sheets are obtained. The obtained positive electrode sheets are cut into test samples of 8 mm × 8 mm in size and soaked and cleaned with a low-boiling-point dimethyl carbonate (DMC) solvent for half an hour. After being completely dried, transmission electron microscope (TEM) imaging is carried out, and the test results are as Figure 12 shown. Among them, "Fresh" is the positive electrode sheet without formation and cycling, "Example 3" is the test result of Example 3; "Comparative Example 2" is the test result of Comparative Example 2. It can be seen from the test results that there is an obvious problem of uneven thickness of the solid electrolyte film on the positive electrode surface in Comparative Example 2. The thickness is relatively thick at some positions and relatively thin at some positions. The thicker positions will increase the battery impedance, and the thinner positions will have protection defects, thereby continuously consuming the electrolyte and resulting in a decrease in the battery cycle life. However, the thickness of the solid electrolyte film on the positive electrode surface in Example 3 is relatively uniform, and the thickness difference at each position is small, which can achieve a better protection effect on the positive electrode material; it shows that compared with the cyclic carbonate-sulfate compound 6 in Comparative Example 2, the solid electrolyte film obtained by forming the cyclic carbonate-sulfate compound 1 provided in Example 1 has higher density and uniformity, can be evenly distributed on the surface of the positive electrode material, and thus inhibits the continuous increase of the impedance on the positive electrode surface and avoids the continuous consumption of the electrolyte on the positive electrode surface during the battery cycle.

[0214] The positive electrode sheets of Example 3 and Comparative Example 2 are reassembled into batteries, and after 300 charge-discharge cycles, the positive electrode sheets are taken out for phase transition observation, and the results are as Figure 12 shown. It can be seen from Figure 12 that the positive electrode particles in Example 3 maintain a good layered structure, while in Comparative Example 2, a phase transition occurs, losing the crystal structure of the material itself and presenting a salt rock phase.

[0215] II. The following tests were conducted on the batteries obtained in Examples 1-9 and Comparative Examples 1-3:

[0216] 1. Thermal box safety performance test: The formed battery was charged at a constant current of 0.5C to 4.5V and then charged at a constant voltage until the current dropped to 0.03C, and then discharged at a constant current of 0.5C to 3.0V. The battery was cycled at room temperature of 25°C for 5 cycles according to this procedure, and the discharge capacity of the battery was calculated. If the deviation of the discharge capacity was within ±10 mAh / g, the battery was charged at a constant current of 0.5C to 4.5V and then charged at a constant voltage until the current dropped to 0.03C, which was taken as the fully charged state of the battery. The fully charged battery was placed in a GX-3020-BL40 thermal shock test chamber, and the thermal box worked according to the set procedure of "heating from 25°C to 130°C at 5°C / min and maintaining for 30 min", and at the same time, the temperature channel and voltage channel of the "data acquisition instrument" panel started to record real-time data. During the test, the surface temperature of the battery detected by the data acquisition instrument did not exceed 200°C, the voltage drop did not exceed 0.3V, and at the same time, the battery did not explode or catch fire, then the thermal box passed (OK), otherwise it was NG. Record the highest value of the battery tabular temperature and take the average value, with 10 batteries in each group.

[0217] 2. High-temperature cycle performance test: The formed battery was placed in an oven at a constant temperature of 45°C, charged at a constant current of 1C to 100% SOC, and then discharged at a constant current of 1C to 3.0V. Such cycles were carried out 500 times, and the discharge capacity of the first time and the last time were recorded.

[0218] Calculate the capacity retention rate of the high-temperature cycle according to the following formula:

[0219] Capacity retention rate = Discharge capacity of the last time / Discharge capacity of the first time × 100%.

[0220] Impedance growth rate = (Impedance of the last time - Impedance of the first time) / Impedance of the first time × 100%

[0221] 3. High-temperature storage performance test: The formed battery was charged at a constant current of 0.5C to 4.5V and then charged at a constant voltage until the current dropped to 0.03C, and then discharged at a constant current of 0.5C to 3.0V. The initial discharge capacity was recorded. Then it was charged at a constant current of 0.5C to 4.5V and then charged at a constant voltage until the current dropped to 0.03C. The initial volume of the battery was measured by the drainage method. Then it was stored at 60°C for 30 days. After the battery was cooled to room temperature, the volume after storage was tested, and the battery was discharged at a constant current of 0.5C to 3.0V to measure the retention capacity. The calculation formula is as follows:

[0222] Capacity retention rate (%) = Retention capacity / Initial discharge capacity × 100%;

[0223] Swelling rate (%) = (Volume after storage - Initial volume) / Initial volume × 100%;

[0224] The test results obtained are recorded in Table 3:

[0225] Table 3

[0226]

[0227] Comparing the test results of Examples 1-9 and Comparative Examples 1-3, it can be seen that compared with the cyclic carbonate-sulfate compounds 5 and cyclic carbonate-sulfate compounds 6 whose specific rotation exceeds the range of -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g), when using the cyclic carbonate-sulfate compounds 1-4 with specific rotation in the range of -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g) as electrolyte additives for lithium-ion batteries, the high-temperature cycling performance and high-temperature storage performance of lithium-ion batteries can be significantly improved. In particular, the improvement of the thermal shock resistance performance and the effect of suppressing impedance growth of lithium-ion batteries are particularly obvious, indicating that the compounds shown in Structural Formula 2 and the compounds shown in Structural Formula 3 with axial symmetry have an obvious beneficial effect on improving the film-forming quality during the formation of SEI or CEI films in battery formation.

[0228] Comparing the test results of Example 2 and Example 5, and Example 3 and Comparative Example 1, it can be known that the film-forming quality of the cyclic carbonate-sulfate compound is greatly affected by the purity of the single chiral configuration in the compound. When the purity of the compound shown in Structural Formula 2 in the cyclic carbonate-sulfate compound is at a relatively high level, the high-temperature performance and thermal shock resistance performance of lithium-ion batteries can be significantly improved, and the impedance of lithium-ion batteries can be reduced.

[0229] Comparing the test results of Examples 1, 2, 4 and Examples 7-9, it can be known that when the compound shown in Chemical Formula 1 mainly contains the compound shown in Structural Formula 2 and / or the compound shown in Structural Formula 3, and when the characteristic structure compound is selected from a single chiral configuration (the compound shown in Structural Formula 2 or the compound shown in Structural Formula 3), it is more beneficial to improve the thermal shock resistance performance of the formed solid electrolyte film, indicating that the characteristic structure compound with a single chiral configuration is related to improving the order of the solid electrolyte film.

[0230] Examples 10-18, Comparative Examples 4-6

[0231] 1) Preparation of non-aqueous electrolyte:

[0232] Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:DEC:EMC = 1:1:1, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. A cyclic carbonate-sulfate compound was further added as an additive. The selection of the cyclic carbonate-sulfate compound and its content in the non-aqueous electrolyte in each example and each comparative example are shown in Table 4, and the content is calculated as a percentage of the total mass of the non-aqueous electrolyte.

[0233] 2) Preparation of the positive electrode plate:

[0234] Mix the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black Super-P, and polyvinylidene fluoride (PVDF), and then disperse them in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode paste. Aluminum foil was used as the positive electrode current collector, and the paste was evenly coated on both sides of the aluminum foil. After drying, rolling, and vacuum drying, a positive electrode material layer was obtained, and an aluminum lead wire was welded with an ultrasonic welder to obtain a positive electrode plate.

[0235] 3) Preparation of the negative electrode plate:

[0236] Mix the negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) at a mass ratio of 94:1:2.5:2.5, and then disperse them in deionized water to obtain a negative electrode paste. The paste was coated on both sides of the copper foil. After drying, rolling, and vacuum drying, and a nickel lead wire was welded with an ultrasonic welder to obtain a negative electrode plate.

[0237] 4) Preparation of the battery cell:

[0238] A three-layer separator with a thickness of 20 μm was placed between the positive electrode plate and the negative electrode plate. The porosity of the separator is shown in Table 2. Then, the sandwich structure composed of the positive electrode plate, the negative electrode plate, and the separator was wound, and the wound body was flattened and placed in an aluminum foil packaging bag, and vacuum baked at 85 °C for 48 h to obtain a battery cell to be filled with electrolyte.

[0239] 5) Filling the electrolyte and formation of the battery cell:

[0240] In a glove box with the dew point controlled below -40 °C, the above-prepared non-aqueous electrolyte was injected into the battery cell, vacuum-sealed, and left standing for 24 h.

[0241] Then, the first charge is normalized as follows: constant current charging at 0.1C for 45 minutes, constant current charging at 0.2C for 30 minutes, constant current charging at 0.5C for 75 minutes, secondary vacuum sealing, and then further constant current charging at a current of 0.5C until 4.4V, followed by constant voltage charging until the current drops to 0.02C. After standing for 5 minutes, it is discharged at a constant current of 0.5C until 3.0V, obtaining a LiNi 0.5 Co 0.2 Mn 0.3 O2 / artificial graphite lithium-ion battery.

[0242] Performance Test

[0243] The following tests are conducted on the batteries obtained in Examples 10 to 18 and Comparative Examples 4 to 6:

[0244] 1. Thermal box safety performance test: The formed battery is charged at a constant current of 0.5C until 4.4V and then charged at a constant voltage until the current drops to 0.03C, and then discharged at a constant current of 0.5C until 3.0V. The battery is cycled 5 times at room temperature of 25°C according to this procedure, and the discharge capacity of the battery is calculated. If the deviation of the discharge capacity is within ±10 mAh / g, the battery is charged at a constant current of 0.5C until 4.4V and then charged at a constant voltage until the current drops to 0.03C, which is used as the fully charged state of the battery. The fully charged battery is placed in a GX-3020-BL40 thermal shock test chamber, and the thermal box operates according to the set procedure "heating from 25°C to 130°C at a rate of 5°C / min and maintaining for 30 minutes", and at the same time, the temperature channel and voltage channel of the "data acquisition instrument" panel start to record real-time data. During the test, the surface temperature of the battery detected by the data acquisition instrument does not exceed 200°C, the voltage drop does not exceed 0.3V, and at the same time, the battery does not explode or catch fire, then the thermal box passes (OK), otherwise it fails (NG). Record the highest value of the battery tabular temperature and take the average value, with 10 batteries in each group.

[0245] 2. High-temperature cycle performance test: The formed battery is placed in an oven at a constant temperature of 45°C, charged at a constant current of 1C until 100% SOC, and then discharged at a constant current of 1C until 3.0V. It is cycled 500 times in this way, and the first discharge capacity, the first impedance, the last impedance, and the last discharge capacity are recorded.

[0246] The capacity retention rate of the high-temperature cycle is calculated according to the following formula:

[0247] Capacity retention rate = last discharge capacity / first discharge capacity × 100%.

[0248] Impedance growth rate = (last impedance - first impedance) / first impedance × 100%.

[0249] 3. High-temperature storage performance test: The formed battery is charged at a constant current of 0.5C to 4.4V and then charged at a constant voltage until the current drops to 0.03C, and then discharged at a constant current of 0.5C to 3.0V. Record the initial discharge capacity. Then charge at a constant current of 0.5C to 4.4V and then charge at a constant voltage until the current drops to 0.03C. Use the drainage method to measure the initial volume of the battery. Then store it at 60°C for 30 d. After the battery cools to room temperature, measure the volume after storage. Discharge at a constant current of 0.5C to 3.0V to measure the retention capacity of the battery. The calculation formulas are as follows:

[0250] Retention rate of capacity (%) = Retention capacity / Initial discharge capacity × 100%;

[0251] Swelling rate (%) = (Volume after storage - Initial volume) / Initial volume × 100%;

[0252] The test results obtained are recorded in Table 4:

[0253] Table 4

[0254]

[0255] Comparing the test results of Examples 10 - 18 and Comparative Examples 4 - 6, it can be seen that compared with cyclic carbonate-sulfate compound 5 and cyclic carbonate-sulfate compound 6 whose specific rotation exceeds the range of -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g), when using cyclic carbonate-sulfate compounds 1 - 4 with specific rotation in the range of -7.982°∙mL / (dm∙g) to +7.982°∙mL / (dm∙g) as electrolyte additives for lithium-ion batteries, the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries can be significantly improved. In particular, the improvement of the thermal shock resistance performance and the effect of inhibiting impedance growth of lithium-ion batteries are particularly obvious. It shows that the compounds shown in Structural Formula 2 and Structural Formula 3 with axial symmetry have an obvious beneficial effect on improving the film-forming quality during the formation of SEI or CEI films during battery formation.

[0256] Comparing the test results of Example 11 and Example 14, and Example 12 and Comparative Example 4, it can be known that the film-forming quality of cyclic carbonate-sulfate compounds is greatly affected by the purity of the single chiral configuration in the compound. When the purity of the compound shown in Structural Formula 2 in the cyclic carbonate-sulfate compound is at a relatively high level, the high-temperature performance and thermal shock resistance performance of lithium-ion batteries can be significantly improved, and the impedance of lithium-ion batteries can be reduced.

[0257] Comparing the test results of Comparative Examples 10, 11, 13 and Examples 16 to 18, it can be seen that when the compound shown in Chemical Formula 1 mainly contains the compound shown in Structural Formula 2 and / or the compound shown in Structural Formula 3, and when the characteristic structure compound is selected from a single chiral configuration (the compound shown in Structural Formula 2 or the compound shown in Structural Formula 3), it is more conducive to improving the thermal shock resistance of the formed solid electrolyte membrane, indicating that the characteristic structure compound with a single chiral configuration is related to improving the orderliness of the solid electrolyte membrane.

[0258] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cyclic carbonate - sulfate compound, characterized in that, The cyclic carbonate-sulfate compound includes the compound shown in Chemical Formula 1, and in the cyclic carbonate-sulfate compound, the content of the compound shown in Chemical Formula 1 is ≥ 99 wt%; The specific rotation of the cyclic carbonate-sulfate compound α is -7.982°.mL / (dm·g) to -7.057°.mL / (dm·g); Chemical Formula 1 The compound shown in Chemical Formula 1 includes a characteristic structure compound, the characteristic structure compound is selected from the compounds shown in Structural Formula 2, and in the compound shown in Chemical Formula 1, the content of the characteristic structure compound is ≥ 99 wt%; 。 2. The cyclic carbonate-sulfate compound according to claim 1, wherein The specific rotation α was measured under the following conditions: wavelength 589 nm, temperature 20 °C, solvent acetonitrile, cell length 100 mm, concentration of the cyclic carbonate-sulfate compound 0.126 g / mL.

3. The cyclic carbonate-sulfate compound according to claim 1, characterized in that, The cyclic carbonate-sulfate compound satisfies the following conditions: In the cyclic carbonate-sulfate compound, the chlorine element content is ≤ 100 ppm.

4. The cyclic carbonate-sulfate compound according to claim 1, characterized in that, The cyclic carbonate-sulfate compound further includes organic impurities, the mass content of the organic impurities is ≤ 1 wt%, and the organic impurities include one or more of the following compounds: 。 5. Use of the cyclic carbonate-sulfate compound according to any one of claims 1 to 4 as an electrolyte additive.

6. A non-aqueous electrolyte, characterized in that, It includes a non-aqueous organic solvent, an electrolyte salt and an additive, and the additive includes the cyclic carbonate-sulfate compound according to any one of claims 1 to 4.

7. The non-aqueous electrolyte according to claim 6, characterized in that, Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the cyclic carbonate-sulfate compound is 0.01% - 5%.

8. A secondary battery, characterized in that, It includes the non-aqueous electrolyte according to claim 6 or 7.

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