An electrolyte and a battery

Abstract

The present invention provides an electrolyte and a battery. The electrolyte includes a lithium salt, an organic solvent, and an additive, and the functional groups of the additive include a silicon group, a fluorinated alkyl group, an amino group, and a sulfonate group. By adding an additive containing a silicon group, a fluorinated alkyl group, an amino group, and a sulfonate group to the electrolyte, the silicon group in the additive can inhibit the corrosion of the cathode material by moisture, HF, and residual alkali substances and the decomposition of the electrolyte; the fluorinated alkyl group can promote the formation of a stable SEI film and reduce the charge transfer resistance; the amino group can have a coordination effect with the high-valent metal ions of the cathode to form a complex, thereby reducing the oxidative decomposition of the electrolyte by the cathode material; the sulfonate group can participate in film formation, and the interfacial film formed by it can reduce the interfacial impedance, thereby improving the cycling performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to an electrolyte and a battery. Background Art

[0002] Lithium-ion batteries have advantages such as high energy density, no memory effect, long service life, clean and pollution-free, and are widely used in various fields, including mobile phones, laptop computers, new energy vehicles and other fields. However, with the expansion of the scope of human activities, higher requirements are put forward for the performance of lithium-ion batteries, especially the cycling performance.

[0003] As an important component of lithium-ion batteries, the electrolyte plays an irreplaceable role in the cycling performance of lithium-ion batteries. It is generally believed that the most economical and effective technical means to improve the cycling performance of lithium-ion batteries is to add additives to the electrolyte. The improvement effect of existing additives on the cycling performance of lithium-ion batteries still needs to be improved. Summary of the Invention

[0004] Embodiments of the present invention provide an electrolyte and a battery, which can improve the cycling performance of existing lithium-ion batteries.

[0005] In a first aspect, embodiments of the present invention provide an electrolyte, comprising a lithium salt, an organic solvent and an additive, and the functional groups of the additive include a silicon group, a fluoroalkyl group, an amino group and a sulfonate group.

[0006] In one embodiment, the additive is tris(dimethylamino)silyl trifluoromethanesulfonate; and / or

[0007] The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate, lithium difluorooxalate phosphate, lithium bis(oxalato)borate.

[0008] In one embodiment, the mass content of the lithium salt in the electrolyte is 10-15%; and / or

[0009] The mass content of the tris(dimethylamino)silyl trifluoromethanesulfonate in the electrolyte is 0.3-1.0%.

[0010] In one embodiment, the organic solvent includes dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate, and the mass ratio of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate is (30-50):(20-30):(20-30):(1-10).

[0011] In one embodiment, the electrolyte further includes a film-forming protective agent.

[0012] In one embodiment, the mass content of the film-forming protective agent in the electrolyte is 2-4%; and / or

[0013] The film-forming protective agent includes at least one of vinylene trithiocarbonate, ethylene sulfate, ethylene carbonate, vinylene carbonate, and fluoroethylene carbonate.

[0014] In one embodiment, the film-forming protective agent includes vinylene carbonate and ethylene sulfate.

[0015] In one embodiment, the mass ratio of vinylene carbonate to ethylene sulfate is (4-6):(1-2).

[0016] In a second aspect, an embodiment of the present invention provides a battery, including the above-mentioned electrolyte.

[0017] In one embodiment, the battery includes a positive electrode, and the chemical formula of the active material of the positive electrode is LiMn x Fe 1- x PO4, where 0 < x < 1.

[0018] Beneficial effects of the embodiments of the present invention:

[0019] In the embodiments of the present invention, by adding an additive containing a silicon group, a fluoroalkyl group, an amino group, and a sulfonate group to the electrolyte, the silicon group in the additive can remove moisture, HF, and residual alkali substances in the positive electrode material, thereby inhibiting the corrosion of the positive electrode material by moisture, HF, and residual alkali substances and the decomposition of the electrolyte; the fluoroalkyl group can increase the reduction potential of the electrolyte, thereby promoting the formation of a stable SEI film and reducing the charge transfer resistance; each nitrogen atom of the amino group has a pair of lone pairs of electrons, which can form a coordination bond with the high-valent metal atoms (such as iron ions and manganese ions) of the positive electrode, thereby forming a complex, and further reducing the oxidative decomposition of the electrolyte by the positive electrode material; the sulfonate group can participate in film formation, and the formed interfacial film can reduce the interfacial impedance, and further improve the cycle performance of the lithium-ion battery. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0021] Figure 1 It is the structural formula of tris(dimethylamino)silyl trifluoromethanesulfonate provided by the embodiment of the present invention. Detailed Embodiments

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In the present invention, unless otherwise stated, the orientation terms such as "upper" and "lower" generally refer to the upper and lower in the actual use or working state of the device, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0023] The technical solutions of the present application are as follows:

[0024] In a first aspect, an electrolyte solution provided by an embodiment of the present application includes a lithium salt, an organic solvent, and an additive, and the functional groups of the additive include a silicon group, a fluoroalkyl group, an amino group, and a sulfonate group.

[0025] In the present application, by adding an additive to the electrolyte solution, the silicon group in the additive can remove moisture, HF, and residual alkali substances in the positive electrode material, thereby inhibiting the corrosion of the positive electrode material by moisture, HF, and residual alkali substances and the decomposition of the electrolyte solution; the fluoroalkyl group can increase the reduction potential of the electrolyte solution, thereby promoting the formation of a stable solid electrolyte interphase (SEI film for short) and reducing the charge transfer impedance; each nitrogen atom of the amino group has a pair of lone pairs of electrons, which can produce a coordination effect with the high-valent metal ions (such as iron ions and manganese ions) of the positive electrode, thereby forming a complex, and further reducing the oxidative decomposition of the electrolyte solution by the positive electrode material; the sulfonate group can participate in film formation, and the interface film formed by it can reduce the interface impedance, and further improve the cycle performance of the lithium-ion battery.

[0026] In some embodiments, the additive is tris(dimethylamino)silyl trifluoromethanesulfonate.

[0027] In the present application, by adding tris(dimethylamino)silyl trifluoromethanesulfonate to the electrolyte solution (the structural formula is as Figure 1 shown, and the molecular formula is C7H 18F3N3O3SSi, with a CAS number of 155166-32-8, has multiple functional groups including a silicon-based group, a fluoroalkyl group, an amino group, and a sulfonate group. Among them, the silicon-based group can remove moisture, HF, and residual alkali substances in the cathode material, thereby inhibiting the corrosion of the cathode material by moisture, HF, and residual alkali substances and the decomposition of the electrolyte; the fluoroalkyl group can increase the reduction potential of the electrolyte, thereby promoting the formation of a stable SEI film and reducing the charge transfer impedance; each of the nitrogen atoms of the three amino groups has a pair of lone pair electrons, which can coordinate with the high-valent metal ions (such as iron ions and manganese ions) of the cathode to form a complex, and further reduce the oxidative decomposition of the cathode material to the electrolyte; the sulfonate group can participate in film formation, and the interfacial film formed by it can reduce the interfacial impedance, thereby improving the cycle performance of the lithium-ion battery.

[0028] In some embodiments, the mass content of tris(dimethylamino)silyl trifluoromethanesulfonate in the electrolyte is 0.3 - 1.0%, for example, it can be 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, etc. Within this range, tris(dimethylamino)silyl trifluoromethanesulfonate can increase the DC impedance of the battery, thereby improving the cycle performance of the lithium-ion battery.

[0029] In some embodiments, the organic solvent includes dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate.

[0030] In some embodiments, the mass ratio of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate is (30 - 50):(20 - 30):(20 - 30):(1 - 10).

[0031] In some embodiments, the mass ratio of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate is 30:30:30:10.

[0032] In some embodiments, the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate, lithium difluorooxalate phosphate, and lithium bis(oxalato)borate.

[0033] In some embodiments, the mass content of the lithium salt in the electrolyte is 10 - 15%.

[0034] In some embodiments, the electrolyte further includes a film-forming protective agent.

[0035] In some embodiments, the mass content of the film-forming protective agent in the electrolyte is 2 - 4%.

[0036] In some embodiments, the film-forming protective agent includes at least one of vinylene trithiocarbonate, ethylene sulfate, ethylene carbonate, vinylene carbonate, and fluoroethylene carbonate.

[0037] In some embodiments, the film-forming protective agent includes vinylene carbonate and ethylene sulfate.

[0038] In this application, vinylene carbonate (VC) and ethylene sulfate (DTD) can improve the DC impedance of the battery and thus improve the cycling performance of the lithium-ion battery.

[0039] In some embodiments, the mass ratio of the vinylene carbonate (VC) to the ethylene sulfate (DTD) is (4 - 6):(1 - 2).

[0040] In a second aspect, an embodiment of this application provides a battery, including the above-mentioned electrolyte.

[0041] In some embodiments, the battery includes a positive electrode, and the chemical formula of the active material of the positive electrode is LiMn x Fe 1- x PO4, where 0 < x < 1. In this way, the active material of the positive electrode has a high potential and a stronger coordination effect with the amino group in the additive.

[0042] Example 1

[0043] An electrolyte and its preparation method include the following steps:

[0044] In a glove box filled with argon, LiPF6 is dissolved in a mixed solution of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC) with a mass ratio of 30:30:30:10. Then, vinylene carbonate (VC) and ethylene sulfate (DTD) are added. Finally, tris(dimethylamino)silyl trifluoromethanesulfonate is added. After stirring evenly, an electrolyte is obtained, where the mass content of LiPF6 is 12.5%, the mass content of VC is 3%, the mass content of DTD is 1%, and the mass content of tris(dimethylamino)silyl trifluoromethanesulfonate is 1%.

[0045] Example 2

[0046] This example is basically the same as Example 1, except that the mass content of tris(dimethylamino)silyl trifluoromethanesulfonate in this example is 0.3%.

[0047] Example 3

[0048] This example is basically the same as Example 1, except that the mass content of tris(dimethylamino)silyl trifluoromethanesulfonate in this example is 0.7%.

[0049] Example 4

[0050] This example is basically the same as Example 1, except that the mass content of tris(dimethylamino)silyl trifluoromethanesulfonate in this example is 0.5%.

[0051] Example 5

[0052] This example is basically the same as Example 1, except that LiPF6 is replaced by LiBF4 in this example.

[0053] Example 6

[0054] This example is basically the same as Example 1, except that LiPF6 is replaced by lithium bis(oxalato)borate (C4BLiO8) in this example.

[0055] Example 7

[0056] This example is basically the same as Example 1, except that the mass content of LiPF6 in this example is 10%.

[0057] Example 8

[0058] This example is basically the same as Example 1, except that the mass content of LiPF6 in this example is 15%.

[0059] Example 9

[0060] This example is basically the same as Example 1, except that the mass ratio of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate in this example is 40:25:25:5.

[0061] Example 10

[0062] This example is basically the same as Example 1, except that the mass ratio of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate in this example is 50:20:20:10.

[0063] Example 11

[0064] This example is basically the same as Example 2, except that vinylene sulfate (DTD) is not added in this example.

[0065] Example 12

[0066] This example is basically the same as Example 2, except that vinylene carbonate (VC) is not added in this example.

[0067] Example 13

[0068] This example is basically the same as Example 2, except that vinylene carbonate (VC) and divinyl sulfate (DTD) are not added in this example.

[0069] Example 14

[0070] This example is basically the same as Example 1, except that the mass content of tris(dimethylamino)silyl trifluoromethanesulfonate in this example is 2%.

[0071] Example 15

[0072] This example is basically the same as Example 1, except that the mass content of tris(dimethylamino)silyl trifluoromethanesulfonate in this example is 15%.

[0073] Comparative Example 1

[0074] This comparative example is basically the same as Example 13, except that tris(dimethylamino)silyl trifluoromethanesulfonate is not added in this comparative example.

[0075] Comparative Example 2

[0076] This comparative example is basically the same as Example 13, except that tris(dimethylamino)silyl trifluoromethanesulfonate is replaced with (trifluoromethyl)trimethylsilane in this comparative example.

[0077] Comparative Example 3

[0078] This comparative example is basically the same as Example 13, except that tris(dimethylamino)silyl trifluoromethanesulfonate is replaced with tris(dimethylamino)methylsilane in this comparative example.

[0079] Test Example:

[0080] Detection of DC impedance (DCR) of battery discharge: Inject the electrolyte samples prepared in the examples and comparative examples into the LiMn 0.4 Fe 0.6 PO4-based lithium-ion battery to test the DC internal resistance (DCR) at 25°C. After adjusting the state of charge (SOC) to 50% and leaving it standing for 1 h, record the terminal voltage as V0. Discharge at a constant current of 1.0C for 60 s, and the terminal voltage is V1. Discharge: DCR = (V0 - V1) / I, and calculate the DCR at 50% SOC, as shown in Table 1.

[0081] Charge and discharge cycle test of battery at 25°C and 45°C: Inject the electrolyte samples prepared in the examples and comparative examples into the LiMn 0.4 Fe 0.6In the PO4 lithium-ion battery, at 25 °C and 45 °C respectively, charge and discharge at 0.5C, the voltage range is 2.5 - 3.65V, and calculate the capacity retention rate: Capacity retention rate = discharge capacity after 1000 cycles / discharge capacity in the first cycle * 100%, as shown in Table 1.

[0082] Data table

[0083] Table 1 Test results of examples and comparative examples

[0084]

[0085]

[0086] As can be seen from Table 1, compared with Examples 11, 12, and 13, the lithium-ion battery of Example 1 has lower DC impedance and higher capacity retention rate. It can be seen that using vinylene carbonate (VC) and divinyl sulfite (DTD) as film-forming protectants can improve the cycling performance of the battery. Compared with Examples 14 and 15, the lithium-ion batteries of Examples 1 - 4 have lower DC impedance and higher capacity retention rate. It can be seen that the addition amount of tris(dimethylamino)silyl trifluoromethanesulfonate can affect the cycling performance of the battery. Compared with Comparative Example 1, the lithium-ion battery of the example has lower DC impedance and higher capacity retention rate. It can be seen that tris(dimethylamino)silyl trifluoromethanesulfonate can improve the cycling performance of the battery. Compared with Comparative Examples 2 and 3, the lithium-ion batteries of the examples have lower DC impedance and higher capacity retention rate. It can be seen that tris(dimethylamino)silyl trifluoromethanesulfonate can improve the cycling performance of the battery more than (trifluoromethyl)trimethylsilane and tris(dimethylamino)methylsilane.

[0087] The above has introduced the embodiments of the present invention in detail. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those skilled in the art, based on the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An electrolyte, characterized in that, It includes a lithium salt, an organic solvent and an additive. The additive is tris(dimethylamino)silyl trifluoromethanesulfonate, and the mass content of the additive in the electrolyte is 0.3 - 1.0%.

2. The electrolyte according to claim 1, wherein The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate, lithium difluorooxalate phosphate, lithium bis(oxalato)borate.

3. The electrolyte according to claim 1, wherein the mass content of the lithium salt in the electrolyte is 10 - 15%.

4. The electrolyte according to claim 2, characterized in that, The organic solvent includes dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate, and the mass ratio of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate is (30 - 50):(20 - 30):(20 - 30):(1 - 10).

5. The electrolyte according to claim 2, wherein The electrolyte further includes a film-forming protective agent.

6. The electrolyte according to claim 5, characterized in that, The mass content of the film-forming protective agent in the electrolyte is 2 - 4%; and / or the film-forming protective agent includes at least one of vinylene trithiocarbonate, vinyl sulfate, ethylene carbonate, vinylene carbonate, fluoroethylene carbonate.

7. The electrolyte according to claim 5, wherein The film-forming protective agent includes vinylene carbonate and vinyl sulfate.

8. The electrolyte according to claim 7, wherein The mass ratio of vinylene carbonate to vinyl sulfate is (4 - 6):(1 - 2).

9. A battery, characterized in that, It includes the electrolyte according to any one of claims 1 - 8.

10. The battery according to claim 9, characterized in that, The battery comprises a positive electrode, the chemical formula of the active material of the positive electrode is LiMn x Fe 1-x PO4, where 0<x<1.

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