An electrolyte and its preparation method and application

Abstract

The present invention belongs to the technical field of battery materials, and discloses an electrolyte and its preparation method and application. The electrolyte, based on 100 parts by weight of the electrolyte, comprises 0.6 - 1.8 mol / L of lithium salt, 0.5 - 40 parts of sulfonate ionic liquid, 0.1 - 0.8 parts of additive, and organic solvent; the additive is a fullerene metal endohedral complex. The fullerene metal endohedral complex has a special electronic structure and a symmetric spatial geometric feature. When the fullerene metal endohedral complex and the sulfonate ionic liquid are simultaneously added to the electrolyte, the fullerene metal endohedral complex can interact with the sulfonic acid group, enhancing the continuous and stable migration of lithium ions at the interface between the lithium cobaltate cathode and the electrolyte. Even when the charging voltage exceeds 4.2 V, it can still maintain the continuous and stable migration of lithium ions, greatly improving the cycle performance of the lithium cobaltate battery. It can also reduce the interfacial impedance of the negative electrode, which is also beneficial to improving the cycle performance of the lithium cobaltate battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to an electrolyte and its preparation method and application. Background Art

[0002] In the field of new energy, lithium-ion batteries are used more and more widely. A lithium-ion battery includes a positive electrode active material, a negative electrode active material, an electrolyte, and a separator. Commonly used positive electrode active materials include lithium iron phosphate and lithium cobaltate. Lithium cobaltate has the problem that its cycle performance deteriorates when the charging voltage is relatively high.

[0003] In the prior art, a common solution is to add some additives to the electrolyte to improve the cycle performance (cycle capacity retention rate) of lithium cobaltate batteries, thereby improving the service life. However, currently, the effect of improving the cycle capacity retention rate of lithium cobaltate batteries by improving the electrolyte is also mediocre. For example, the capacity retention rate after generally 100 cycles rarely exceeds 95%, and the service life of the battery still needs to be further improved.

[0004] Therefore, there is an urgent need to provide a new electrolyte to further improve the cycle performance of lithium cobaltate batteries. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above prior art. For this purpose, the present invention provides an electrolyte and its preparation method and application. The electrolyte is applied in a lithium cobaltate battery and has good cycle performance. Even when the charging voltage exceeds 4.2V, the lithium cobaltate battery still has good cycle performance.

[0006] The inventive concept of the present invention is as follows: The electrolyte of the present invention includes a lithium salt, an organic solvent, a sulfonate ionic liquid, and an additive, and the additive is a fullerene metal endohedral complex. The fullerene metal endohedral complex has a special electronic structure and a symmetric spatial geometric feature. When the fullerene metal endohedral complex and the sulfonate ionic liquid are added to the electrolyte simultaneously, the fullerene metal endohedral complex can interact with the sulfonic acid group, enhancing the continuous and stable migration of lithium ions at the interface between the lithium cobaltate positive electrode and the electrolyte. Even when the charging voltage exceeds 4.2V, it can still maintain the continuous and stable migration of lithium ions, greatly improving the cycle performance of the lithium cobaltate battery. It can also reduce the interfacial impedance of the negative electrode, which is also beneficial to improving the cycle performance of the lithium cobaltate battery.

[0007] The first aspect of the present invention provides an electrolyte.

[0008] Specifically, an electrolyte, based on 100 parts by weight of the electrolyte, includes 0.6 - 1.8 mol / L of a lithium salt, 0.5 - 50 parts of a sulfonate ionic liquid, 0.1 - 0.8 parts of an additive, and an organic solvent;

[0009] The additive is a metal-encapsulated fullerene.

[0010] Preferably, the metal-encapsulated fullerene is a fullerene encapsulating Sc element; more preferably, the metal-encapsulated fullerene is selected from Sc3N@C 80 、Sc3N@C 68 、Sc2@C 66 and at least one of them. When using Sc3N@C 80 、Sc3N@C 68 、Sc2@C 66 as the additive, electrons can interact among Sc, the fullerene carbon cage, the sulfonic acid group and lithium ions, which is beneficial to the stable migration of lithium ions during charge and discharge, thus improving the cycling performance of the lithium-ion battery.

[0011] Preferably, the sulfonate ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-butyl-3-methylimidazolium p-toluenesulfonate.

[0012] Preferably, the organic solvent is selected from at least one of ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl sulfoxide.

[0013] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0014] Preferably, the electrolyte further includes 1-butyl-3-methylimidazolium hexafluorophosphate. Introducing 1-butyl-3-methylimidazolium hexafluorophosphate, an ionic liquid containing a phosphate group, into the electrolyte to interact with the sulfonate ionic liquid and the metal-encapsulated fullerene further stabilizes the transfer function of lithium ions, thereby improving the cycling stability of the lithium-ion battery during charge and discharge.

[0015] Preferably, based on 100 parts by weight of the electrolyte, the electrolyte includes 0.6 - 1.2 mol / L of lithium salt, 2 - 30 parts of sulfonate ionic liquid, 0.2 - 0.5 parts of additive, and an organic solvent.

[0016] Preferably, based on 100 parts by weight of the electrolyte, the electrolyte includes 0.6 - 1.2 mol / L of lithium salt, 2 - 30 parts of sulfonate ionic liquid, 0.3 - 1.5 parts of 1-butyl-3-methylimidazolium hexafluorophosphate, 0.2 - 0.5 parts of additive, and an organic solvent.

[0017] The second aspect of the present invention provides a method for preparing an electrolyte.

[0018] Specifically, a method for preparing an electrolyte includes the following steps:

[0019] Mix each component to prepare the electrolyte solution.

[0020] Preferably, the method for preparing the electrolyte solution includes the following steps:

[0021] Mix a part of the organic solvent with the lithium salt, then add the sulfonate ionic liquid and the additive, stir, and then add the remaining organic solvent to prepare the electrolyte solution.

[0022] Preferably, when adding the additive, 1-butyl-3-methylimidazolium hexafluorophosphate is also added.

[0023] The third aspect of the present invention provides a lithium-ion battery.

[0024] Specifically, a lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the above-mentioned electrolyte solution.

[0025] Preferably, the positive electrode includes lithium cobaltate.

[0026] Preferably, the positive electrode is in a sheet shape.

[0027] Preferably, lithium cobaltate, acetylene black, and polyvinylidene fluoride are mixed in a weight ratio of 90:(2 - 5):(5 - 8), and pressed onto a metal foil to obtain a positive electrode sheet.

[0028] Preferably, the negative electrode is a lithium sheet.

[0029] Preferably, the separator is a PE (polyethylene) membrane or a PP (polypropylene) membrane.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The electrolyte solution of the present invention includes a specific amount of lithium salt, organic solvent, sulfonate ionic liquid, and additive, and the additive is a fullerene metal endohedral complex. The fullerene metal endohedral complex has a special electronic structure and a symmetric spatial geometric feature. When the fullerene metal endohedral complex and the sulfonate ionic liquid are added to the electrolyte solution at the same time, the fullerene metal endohedral complex can interact with the sulfonic acid group, enhancing the continuous and stable migration of lithium ions at the interface between the lithium cobaltate positive electrode and the electrolyte solution. Even when the charging voltage exceeds 4.2V, it can still maintain the continuous and stable migration of lithium ions, greatly improving the cycling performance of the lithium cobaltate battery. It can also reduce the interfacial impedance of the negative electrode, which is also beneficial to improving the cycling performance of the lithium cobaltate battery. Specific Embodiments

[0032] In order to make those skilled in the art more clearly understand the technical solutions of the present invention, the following examples are listed for illustration. It should be noted that the following examples do not limit the scope of protection required by the present invention.

[0033] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial channels or can be obtained by existing known methods.

[0034] An electrolyte, based on 100 parts by weight of the electrolyte, includes 0.6 - 1.8 mol / L of lithium salt, 0.5 - 50 parts of sulfonate ionic liquid, 0.1 - 0.8 parts of additive, and an organic solvent;

[0035] The additive is a fullerene metal endohedral complex.

[0036] The fullerene metal endohedral complex is a fullerene endohedral complex doped with Sc element; the fullerene metal endohedral complex is selected from at least one of Sc3N@C 80 、Sc3N@C 68 、Sc2@C 66 . When using Sc3N@C 80 、Sc3N@C 68 、Sc2@C 66 as the additive, electrons can interact between Sc, the fullerene carbon cage, the sulfonic acid group and lithium ions, which is beneficial to the stable migration of lithium ions during charge and discharge, thus improving the cycling performance of lithium-ion batteries.

[0037] The sulfonate ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-butyl-3-methylimidazolium p-toluenesulfonate.

[0038] The organic solvent is selected from at least one of ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl sulfoxide.

[0039] The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0040] The electrolyte further includes 1-butyl-3-methylimidazolium hexafluorophosphate. By further introducing 1-butyl-3-methylimidazolium hexafluorophosphate, an ionic liquid containing a phosphate group, into the electrolyte, it interacts with the sulfonate ionic liquid and the fullerene metal endohedral complex together, further stabilizing the transfer function of lithium ions, thus improving the cycling stability of lithium-ion battery charge and discharge.

[0041] An electrolyte, based on 100 parts by weight of the electrolyte, includes 0.6 - 1.2 mol / L of lithium salt, 2 - 30 parts of sulfonate ionic liquid, 0.2 - 0.5 parts of additive, and an organic solvent.

[0042] An electrolyte, based on 100 parts by weight of the electrolyte, includes 0.6 - 1.2 mol / L of a lithium salt, 2 - 30 parts of a sulfonate ionic liquid, 0.3 - 1.5 parts of 1-butyl-3-methylimidazolium hexafluorophosphate, 0.2 - 0.5 parts of an additive, and an organic solvent.

[0043] A method for preparing an electrolyte, comprising the following steps:

[0044] Mix a part of the organic solvent with the lithium salt, then add the sulfonate ionic liquid and the additive, stir, and then add the remaining organic solvent to obtain the electrolyte.

[0045] When adding the additive, 1-butyl-3-methylimidazolium hexafluorophosphate is also added.

[0046] A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and the above-mentioned electrolyte.

[0047] The positive electrode includes lithium cobaltate.

[0048] The positive electrode is in a sheet shape.

[0049] Mix lithium cobaltate, acetylene black, and polyvinylidene fluoride in a weight ratio of 90:(2 - 5):(5 - 8), and press them onto a metal foil to obtain a positive electrode sheet.

[0050] The negative electrode is a lithium sheet.

[0051] The separator is a PE (polyethylene) film or a PP (polypropylene) film.

[0052] Example 1

[0053] A method for preparing an electrolyte, comprising the following steps:

[0054] Mix 60 parts of an organic solvent (30 parts of ethylene carbonate and 30 parts of fluoroethylene carbonate) with a lithium salt (lithium hexafluorophosphate) to obtain a mixture, the concentration of lithium hexafluorophosphate in the mixture is 1.2 mol / L, then add 20 parts of a sulfonate ionic liquid (1-ethyl-3-methylimidazolium trifluoromethanesulfonate) and 0.2 parts of an additive (Sc3N@C 80 ), stir for 30 minutes, and then add the remaining organic solvent until the total weight of the electrolyte is 100 parts to obtain the electrolyte.

[0055] A method for preparing a lithium-ion battery, comprising the following steps:

[0056] Mix lithium cobaltate (LiCoO2), conductive carbon black, and polyvinylidene fluoride in a weight ratio of 90:4:6, press them onto an aluminum foil to obtain a positive electrode sheet, use a lithium sheet as the negative electrode, a PP film as the separator, and assemble the above-mentioned electrolyte into a lithium-ion battery (the battery assembly process is a conventional process in the art).

[0057] Example 2

[0058] A method for preparing an electrolyte, comprising the following steps:

[0059] Mix 70 parts of an organic solvent (35 parts of dimethyl carbonate and 35 parts of ethyl methyl carbonate) with a lithium salt (lithium bis(fluorosulfonyl)imide) to obtain a mixture, wherein the concentration of lithium bis(fluorosulfonyl)imide in the mixture is 1.1 mol / L, then add 15 parts of a sulfonate ionic liquid (1-butyl-3-methylimidazolium p-toluenesulfonate) and 0.1 part of an additive (Sc3N@C 68 ), stir for 40 minutes, and then add the remaining organic solvent until the total weight of the electrolyte is 100 parts to obtain the electrolyte.

[0060] Example 3

[0061] A method for preparing an electrolyte, comprising the following steps:

[0062] Mix 55 parts of an organic solvent (40 parts of dimethyl carbonate and 15 parts of dimethyl sulfoxide) with a lithium salt (lithium bis(trifluoromethylsulfonyl)imide) to obtain a mixture, wherein the concentration of lithium bis(trifluoromethylsulfonyl)imide in the mixture is 1.6 mol / L, then add 25 parts of a sulfonate ionic liquid (1-butyl-3-methylimidazolium p-toluenesulfonate) and 0.1 part of an additive (Sc2@C66), stir for 50 minutes, and then add the remaining organic solvent until the total weight of the electrolyte is 100 parts to obtain the electrolyte.

[0063] Example 4

[0064] A method for preparing an electrolyte, comprising the following steps:

[0065] Mix 65 parts of an organic solvent (40 parts of dimethyl carbonate and 25 parts of diethyl carbonate) with a lithium salt (lithium hexafluorophosphate) to obtain a mixture, wherein the concentration of lithium hexafluorophosphate in the mixture is 1.3 mol / L, then add 20 parts of a sulfonate ionic liquid (1-butyl-3-methylimidazolium p-toluenesulfonate) and 0.4 part of an additive (Sc3N@C 80 ), stir for 40 minutes, and then add the remaining organic solvent until the total weight of the electrolyte is 100 parts to obtain the electrolyte.

[0066] Example 5

[0067] A method for preparing an electrolyte, comprising the following steps:

[0068] Mix 55 parts of organic solvents (30 parts of dimethyl carbonate and 25 parts of diethyl carbonate) with a lithium salt (lithium hexafluorophosphate) to obtain a mixture. The concentration of lithium hexafluorophosphate in the mixture is 1.3 mol / L. Then add 18 parts of sulfonate ionic liquid (1-ethyl-3-methylimidazolium trifluoromethanesulfonate) and 0.3 parts of additive (Sc3N@C 80 ), stir for 45 minutes, and then add the remaining organic solvents until the total weight of the electrolyte is 100 parts to prepare the electrolyte.

[0069] Example 6

[0070] Compared with Example 1, the difference in Example 6 is only that when adding the additive in Example 6, 1 part of 1-butyl-3-methylimidazolium hexafluorophosphate is also added, and the other components and procedures are the same as those in Example 1.

[0071] Comparative Example 1

[0072] Compared with Example 1, the difference in Comparative Example 1 is only that in Comparative Example 1, an equal amount of C 80 (CF3) 12 is used to replace Sc3N@C in Example 1 80 , and the other components and procedures are the same as those in Example 1. That is, in Comparative Example 1, an external substitution derivative of C 80 is used to replace the inclusion of C 80 .

[0073] Comparative Example 2

[0074] Compared with Example 1, the difference in Comparative Example 2 is only that in Comparative Example 2, an equal amount of C 60 is used to replace Sc3N@C in Example 1 80 , and the other components and procedures are the same as those in Example 1.

[0075] Comparative Example 3

[0076] Compared with Example 1, the difference in Comparative Example 3 is only that in Comparative Example 3, an equal amount of graphene oxide is used to replace Sc3N@C in Example 1 80 , and the other components and procedures are the same as those in Example 1.

[0077] Product effect test

[0078] The lithium-ion batteries prepared in the above Examples 1, 2, and 6 and Comparative Examples 1-3 were cycled at a rate of 0.5C for 100 cycles at a voltage of 3.0 - 4.3V at 20°C, and the capacity retention rate at the 100th cycle was recorded. The capacity retention rate after cycling (%) = discharge capacity ÷ first discharge capacity × 100%, and the results are shown in Table 1.

[0079] Table 1

[0080] Capacity retention rate after 100 cycles (%) Example 1 97.4 Example 2 97.2 Example 6 98.3 Comparative Example 1 85.6 Comparative Example 2 84.7 Comparative Example 3 81.3

[0081] As can be seen from Table 1, the cycling performance of the lithium-ion battery prepared in the embodiment of the present invention is significantly better than that of Comparative Examples 1-3. It can be seen therefrom that when the additive in the electrolyte of the present invention uses a fullerene inclusion, the prepared lithium-ion has the best cycling performance. From the results of Example 1 and Example 6, it can be seen that the addition of 1-butyl-3-methylimidazolium hexafluorophosphate in the electrolyte can further improve the cycling performance of lithium ions.

[0082] The lithium-ion battery prepared in Example 1 above was cycled 100 times at a rate of 0.5C at a voltage of 3.0-4.5V at 20°C, and the capacity retention rate of the 100th cycle was recorded, and the result was 97.1%. It can be seen therefrom that even when the charging voltage reaches 4.5V, the cycling performance of the lithium-ion battery of the present invention still remains good.

[0083] The effect data of the above other examples are similar to those of Example 1.

[0084] It should be noted that although the above embodiments have been described in this article, the protection scope of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, the changes and modifications made to the embodiments in this article, or the conventional substitutions made using the content of the specification of the present invention, are all included in the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, Based on 100 parts by weight of the electrolyte, it includes 0.6 - 1.8 mol / L of lithium salt, 0.5 - 50 parts of sulfonate ionic liquid, 0.1 - 0.8 parts of additive, and organic solvent; The additive is a metal-encapsulated fullerene; The fullerene metal endohedrons are selected from at least one of Sc3N@C 80 , Sc3N@C 68 , Sc2@C 66 ; The sulfonate ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-butyl-3-methylimidazolium p-toluenesulfonate; The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

2. The electrolyte according to claim 1, wherein The electrolyte further includes 1-butyl-3-methylimidazolium hexafluorophosphate.

3. The electrolyte according to claim 2, wherein, The electrolyte, based on 100 parts by weight of the electrolyte, includes 0.6 - 1.2 mol / L of lithium salt, 2 - 30 parts of sulfonate ionic liquid, 0.3 - 1.5 parts of 1-butyl-3-methylimidazolium hexafluorophosphate, 0.2 - 0.5 parts of additive, and organic solvent.

4. The preparation method of the electrolyte according to any one of claims 1-3, characterized in that, It includes the following steps: Mix each component to obtain the electrolyte.

5. The method for preparing the electrolyte according to claim 4, characterized in that, It includes the following steps: Mix part of the organic solvent with the lithium salt, then add the sulfonate ionic liquid and the additive, stir, and then add the remaining organic solvent to obtain the electrolyte.

6. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the electrolyte according to any one of claims 1 - 3.