阅读说明：本技术 电解液、电化学装置和电子装置 (Electrolyte solution, electrochemical device, and electronic device ) 是由 张亚菲 于 2020-12-21 设计创作，主要内容包括：本申请提供了电解液、电化学装置和电子装置。电解液包括含氟锂盐和二氰胺锂,含氟锂盐包括氟磺酰(三氟甲基磺酰)亚胺锂。本申请的实施例通过对电解液进行改进,使锂盐包括氟磺酰(三氟甲基磺酰)亚胺锂和二氰胺锂,有利于增强负极的固体电解质界面(SEI)膜的稳定性,从而提升电化学装置的循环性能,并且基本不影响电解液的动力学性能。(The application provides an electrolyte, an electrochemical device and an electronic device. The electrolyte comprises fluorine-containing lithium salt and lithium dicyanamide, and the fluorine-containing lithium salt comprises lithium fluorosulfonyl (trifluoromethylsulfonyl) imide. The embodiment of the application improves the electrolyte, so that the lithium salt comprises lithium fluorosulfonyl (trifluoromethyl sulfonyl) imide and lithium dicyanamide, which is beneficial to enhancing the stability of a Solid Electrolyte Interface (SEI) film of a negative electrode, thereby improving the cycle performance of an electrochemical device and basically not influencing the dynamic performance of the electrolyte.)

1. An electrolyte comprising a lithium salt, wherein the lithium salt comprises a fluorine-containing lithium salt comprising lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and lithium dicyanamide.

2. The electrolyte of claim 1, wherein the molar content of the fluorine-containing lithium salt and the lithium dicyandiamide in the electrolyte is 0.9 to 3.0mol/L in total.

3. The electrolyte of claim 1, wherein the fluorine-containing lithium salt is present in the electrolyte in a molar amount of 0.8 to 2.0 mol/L; and/or

The molar content of the lithium dicyandiamide in the electrolyte is 0.1mol/L to 1.1 mol/L.

4. The electrolyte of claim 1, wherein the molar content of the lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte is from 1.5 to 2.0 mol/L.

5. The electrolyte of claim 1, wherein the lithium salt comprising fluorine further comprises lithium hexafluorophosphate.

6. The electrolyte according to claim 5, wherein a molar content of the lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte is equal to or greater than a molar content of the lithium hexafluorophosphate in the electrolyte.

7. The electrolyte of claim 1, wherein the electrolyte further comprises fluoroethylene carbonate.

8. An electrochemical device, comprising:

a positive electrode sheet comprising a positive active material;

a negative electrode sheet comprising a negative active material;

the isolating film is arranged between the positive pole piece and the negative pole piece;

an electrolyte;

wherein the electrolyte is the electrolyte according to claims 1 to 7.

9. The electrochemical device of claim 8, wherein the negative active material comprises at least one of lithium metal or a silicon-based material comprising at least one of silicon, a silicon oxy compound, a silicon carbon compound, or a silicon alloy.

10. The electrochemical device according to claim 9,

the mass content of a silicon element in the silicon-based material is more than or equal to 10%, and the molar content of the lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte is 0.8mol/L to 2.0 mol/L; or

The mass content of silicon element in the silicon-based material is more than or equal to 40%, and the molar content of the fluorine sulfonyl (trifluoromethyl sulfonyl) imide lithium in the electrolyte is 1.1mol/L to 2.0 mol/L.

11. An electronic device comprising the electrochemical device according to any one of claims 8 to 10.

Technical Field

The present application relates to the field of electrochemical energy storage, and more particularly to electrolytes, electrochemical devices, and electronic devices.

Background

As electrochemical devices (e.g., lithium ion batteries) are developed and advanced, higher and higher demands are made on their cycle performance. Although the current techniques for improving electrochemical devices are capable of improving the cycle performance of electrochemical devices to some extent, they are not satisfactory, and further improvements are expected.

Disclosure of Invention

Embodiments of the present application provide an electrolyte comprising a lithium salt, the lithium salt comprising a fluorine-containing lithium salt comprising lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and lithium dicyanamide.

In some embodiments, the molar content of the fluorine-containing lithium salt and the lithium dicyandiamide in the electrolyte is 0.9mol/L to 3.0mol/L in total. In some embodiments, the molar content of the fluorine-containing lithium salt in the electrolyte is 0.8mol/L to 2.0 mol/L. In some embodiments, the lithium salt comprising fluorine is lithium fluorosulfonyl (trifluoromethylsulfonyl) imide. In some embodiments, the molar content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte is 1.5 to 2.0 mol/L. In some embodiments, the molar content of lithium dicyanamide in the electrolyte ranges from 0.1mol/L to 1.1 mol/L.

In some embodiments, the lithium fluoride-containing salt further comprises lithium hexafluorophosphate. In some embodiments, the lithium fluoride-containing salt further comprises at least one of lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate, lithium bis-fluorosulfonylimide, or lithium bis-trifluoromethanesulfonylimide.

In some embodiments, the molar content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte is equal to or greater than the molar content of lithium hexafluorophosphate in the electrolyte.

In some embodiments, the electrolyte further comprises an additive comprising fluoroethylene carbonate. In some embodiments, the additive further comprises at least one of vinylene carbonate, 1, 3-propane sultone, vinyl sulfate, methylene methanedisulfonate, or lithium dioxalate borate.

Another embodiment of the present application provides an electrochemical device including: the positive pole piece comprises a positive active material; the negative pole piece comprises a negative active material; the isolating film is arranged between the positive pole piece and the negative pole piece; an electrolyte; wherein the electrolyte is any one of the above electrolytes.

In some embodiments, the negative active material includes at least one of lithium metal or a silicon-based material. In some embodiments, the silicon-based material comprises at least one of silicon, a silicon oxy compound, a silicon carbon compound, or a silicon alloy.

In some embodiments, the silicon element content in the silicon-based material is 10% by mass or more, and the molar content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is 0.8mol/L to 2.0 mol/L.

In some embodiments, the silicon element content in the silicon-based material is greater than or equal to 40% by mass, and the molar content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is 1.1mol/L to 2.0 mol/L.

Embodiments of the present application also provide an electronic device including the above electrochemical device.

The embodiment of the application improves the electrolyte, so that the lithium salt comprises fluorine sulfonyl (trifluoromethyl sulfonyl) imide lithium and dicyanamide lithium, and the stability of a Solid Electrolyte Interface (SEI) film of a negative electrode is enhanced, thereby improving the cycle performance of an electrochemical device and ensuring the better dynamic performance of the electrolyte.

Drawings

Fig. 1 shows a schematic view of an electrode assembly of an electrochemical device of an embodiment of the present application.

Detailed Description

The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.

One important means to improve the cycle performance of the electrochemical device is to enhance the stability of the negative electrode SEI film. At present, the stability of the SEI film of the negative electrode can be enhanced by adding fluoroethylene carbonate (FEC) into the electrolyte, but the FEC can be decomposed on the surface of the negative electrode to generate HF and H₂Especially when the lithium salt in the electrolyte is LiPF₆And has H₂In the presence of O, this reaction is accelerated. The generation of HF deteriorates a solid electrolyte interface (CEI) film of the positive electrode, reducing the cycle performance of the electrochemical device at high temperature. Therefore, the negative electrode film formation by increasing the electrolyteThe content of the additive FEC to enhance the SEI film has certain limitations.

Embodiments of the present application provide an electrolyte comprising a fluorine-containing lithium salt comprising lithium fluorosulfonyl (trifluoromethylsulfonyl) imide (LiFTFSI) and lithium dicyanamide (LiDCA). Anion FTFSI in lithium fluorosulfonyl (trifluoromethylsulfonyl) imide (LiTFSI)^-As follows:

anionic DCA in lithium dicyanamide (LiDCA)^-As follows:

in some embodiments, the lithium salt comprising fluorine is lithium fluorosulfonyl (trifluoromethylsulfonyl) imide (LiFTFSI).

The lithium salt containing fluorine herein uses LiFTFSI, which is itself a fluorine-containing film-forming additive that can react at the surface of the negative electrode (e.g., with the silicon-based material of the negative active material or lithium metal) to help form a complete and robust SEI film. In addition, with LiPF₆In contrast, the concentration of the anionic charge of LiFTFSI is low, the electronegativity is strong, and the content of the inorganic component (e.g., LiF) of the formed SEI film is high. In addition, the dissociation capability of LiTFSI and lithium ions is strong, which is beneficial to the rapid film formation of an SEI film and can improve the ionic conductivity of the lithium ions in the electrolyte. Meanwhile, the LiDCA is dissolved in the electrolyte and has small influence on the viscosity of the electrolyte, so that the LiTFSI is matched with the LiDCA, the influence of the increase of the concentration of the lithium salt on the viscosity of the electrolyte can be effectively reduced, and the dynamic performance of the electrolyte is improved. In addition, by including LiFTFSI and LiDCA in the lithium salt, the stability of FEC in the electrolyte can be increased, and the damage of the CEI film caused by the generation of HF can be reduced, thereby improving the cycle performance of the electrochemical device.

In some embodiments, the molar content of the lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and the lithium dicyanamide in the electrolyte is 0.9mol/L to 3.0mol/L in total. If the molar content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and lithium dicyanamide is too high, for example, more than 3.0mol/L, the lithium salt concentration may be excessively high to precipitate, and the cost of the electrolyte may be increased. If the molar contents of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and lithium dicyanamide are too low, for example, less than 0.9mol/L, lithium replenishment of the electrochemical device at the latter stage of the cycle is not facilitated, and the conductivity of the electrolyte is lowered.

In some embodiments, the molar content of the lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte ranges from 0.8mol/L or more to less than 2.0 mol/L. If the molar content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide is too high, for example, greater than 2.0mol/L, the lithium salt concentration may be too high to precipitate and increase the cost of the electrolyte; in addition, as the viscosity of the lithium fluorosulfonyl (trifluoromethyl sulfonyl) imide solution is high, the lithium ion transmission rate is reduced and the dynamic performance of the electrolyte is reduced due to the high content of the lithium fluorosulfonyl (trifluoromethyl sulfonyl) imide solution. If the molar content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide is too low, for example, less than 0.8mol/L, the effect of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide on improving the stability of an SEI film is insignificant.

In some embodiments, the lithium fluoride-containing salt further comprises M, which comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate, lithium bis-fluorosulfonylimide, or lithium bis-trifluoromethanesulfonylimide. Therefore, the lithium salt of the electrolyte in the present application may include only lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and lithium dicyanamide, or may include the above-mentioned suitable fluorine-containing lithium salt.

In some embodiments, M comprises lithium hexafluorophosphate.

In some embodiments, the molar content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide, lithium dicyanamide, and M in the electrolyte is collectively 0.9 to 3.0 mol/L. If the molar contents of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide, lithium dicyanamide and M are too high, for example, more than 3.0mol/L, the lithium salt concentration may be excessively high to precipitate and the cost of the electrolyte may be increased. If the molar contents of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide, lithium dicyanamide and M are too low, for example, less than 0.9mol/L, lithium replenishment of the electrochemical device at the end of the cycle is not facilitated and the conductivity of the electrolyte may be reduced.

In some embodiments, the molar content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and M, i.e., lithium salt containing fluorine, in the electrolyte is 0.8mol/L to 2.0mol/L in total. If the molar content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and M in the electrolyte is too high, for example, greater than 2.0mol/L, the dynamic performance of the electrolyte is reduced due to the high viscosity of the solution of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and M, and the cost of the electrolyte is also increased. If the molar content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and M in the electrolyte is too low, for example, less than 0.8mol/L, the effect of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide on improving the stability of the SEI film is weak, and the molar content of the fluorine-containing lithium salt in the electrolyte needs to be maintained to form a stable SEI film on the surface of the negative electrode, that is, the molar content of the fluorine-containing lithium salt in the electrolyte needs to be ensured.

In some embodiments, the molar content of M in the electrolyte is less than or equal to the molar content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte. Namely, regarding the fluorine-containing lithium salt in the electrolyte, the ratio of the molar content of the lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte to the molar content of the fluorine-containing lithium salt in the electrolyte is 50% or more and less than 100%. If the molar content of M is too high, for example, higher than the molar content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide, the molar content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide is too low, so that the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide has a limited effect of improving the stability of the SEI film.

In some embodiments, the molar content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide in the electrolyte is equal to or greater than the molar content of lithium hexafluorophosphate in the electrolyte.

In some embodiments, the electrolyte further comprises an additive comprising at least one of fluoroethylene carbonate, vinylene carbonate, 1, 3-propane sultone, vinyl sulfate, methylene methanedisulfonate, or lithium dioxalate borate. In some embodiments, the additive is fluoroethylene carbonate. The fluoroethylene carbonate can enhance the stability of the negative electrode SEI film.

In some embodiments, the additive is fluoroethylene carbonate and lithium fluorosulfonyl (trifluoromethylsulfonyl) imide helps to increase the stability of fluoroethylene carbonate in the electrolyte.

In some embodiments, the electrolyte further includes a non-aqueous solvent, which may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), or a combination thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.

Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, or combinations thereof.

Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

Examples of other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.

As shown in fig. 1, a schematic view of an electrochemical device of the present application is provided. The electrochemical device comprises a positive pole piece 10, a negative pole piece 12, a separation film 11 arranged between the positive pole piece 10 and the negative pole piece 12, and electrolyte. In some embodiments, the electrolyte is the electrolyte described above. In some embodiments, the positive electrode tab 10 includes a positive active material. In some embodiments, the negative electrode tab 12 includes a negative active material.

In some embodiments, the negative electrode tab 12 may include a negative electrode current collector and a negative active material layer disposed on the negative electrode current collector. The anode active material layer may be disposed on one side or both sides of the anode current collector. In some embodiments, the negative electrode current collector may employ at least one of a copper foil, a nickel foil, or a carbon-based current collector. In some embodiments, the negative active material layer may include a negative active material. In some embodiments, the negative active material in the negative active material layer includes at least one of lithium metal or a silicon-based material. In some embodiments, the silicon-based material comprises at least one of silicon, a silicon oxy compound, a silicon carbon compound, or a silicon alloy.

In some embodiments, the silicon element content in the silicon-based material is 10% by mass or more, and the molar content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is 0.8mol/L to 2.0 mol/L. Silicon-based materials have a wide range of applications in electrochemical devices due to their large gram capacity. When the mass content of the silicon element in the silicon-based material is larger, the side reaction between some substances (for example, additive FEC) in the electrolyte and the silicon-based material is increased, so that the occurrence of the side reaction can be slowed down by adopting larger molar content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide (for example, more than 0.8 mol/L), and the stability of the negative SEI film is improved. However, too large a molar content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide is detrimental to the dynamic performance of the electrolyte.

In some embodiments, the silicon element content in the silicon-based material is greater than or equal to 40% by mass, and the molar content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is 1.1mol/L to 2.0 mol/L. As described above, when the mass content of the silicon element in the silicon-based material is increased, for example, from 10% or more to 40% or more, the molar content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide may be increased (for example, to 1.1mol/L or more) to slow down the occurrence of side reactions between the electrolyte and the silicon-based material, and to improve the stability of the negative electrode SEI film.

In some embodiments, a conductive agent and/or a binder may also be included in the negative active material layer. The conductive agent in the negative active material layer may include at least one of carbon black, acetylene black, ketjen black, flake graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. In some embodiments, the binder in the negative active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. It should be understood that the above disclosed materials are merely exemplary, and any other suitable materials may be employed for the anode active material layer. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode active material layer may be 80-99: 0.5-10: 0.5-10, it being understood that this is exemplary only and not limiting to the present application.

In some embodiments, the positive electrode tab 10 includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer may be located on one side or both sides of the positive electrode current collector. In some embodiments, the positive electrode current collector may be an aluminum foil, but other positive electrode current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 200 μm. In some embodiments, the positive electrode active material layer may be coated only on a partial area of the positive electrode collector. In some embodiments, the thickness of the positive electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and that other suitable thicknesses may be employed.

In some embodiments, the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive active material may include at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium nickel manganate, and the positive active material may be doped and/or coated. In some embodiments, the positive electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, a polyamide, polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, a polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the conductive agent in the positive electrode active material layer may include at least one of conductive carbon black, acetylene black, ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode active material layer may be 70-98: 1-15: 1 to 15. It should be understood that the above description is merely an example, and any other suitable material, thickness, and mass ratio may be employed for the positive electrode active material layer.

In some embodiments, the separator 11 comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 3 μm to 500 μm.

In some embodiments, the release film surface may also compriseA porous layer disposed on at least one surface of the separation membrane, the porous layer comprising at least one of inorganic particles selected from alumina (Al) or a binder₂O₃) Silicon oxide (SiO)₂) Magnesium oxide (MgO), titanium oxide (TiO)₂) Hafnium oxide (HfO)₂) Tin oxide (SnO)₂) Cerium oxide (CeO)₂) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)₂) Yttrium oxide (Y)₂O₃) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator film have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the pole piece.

In some embodiments of the present application, the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly. In some embodiments, the electrochemical device is a lithium ion battery, but the application is not limited thereto.

In some embodiments of the present application, taking a lithium ion battery as an example, a positive electrode plate, a separator, and a negative electrode plate are sequentially wound or stacked to form an electrode assembly, and then the electrode assembly is packaged in, for example, an aluminum plastic film casing, and an electrolyte is injected into the casing, and then the electrode assembly is formed and packaged to obtain the lithium ion battery. And then, performing performance test on the prepared lithium ion battery.

Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure herein.

Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

In the following, some specific examples and comparative examples are listed to better illustrate the present application, wherein a lithium ion battery is taken as an example.

Example 1

Preparing a positive pole piece: preparing a positive electrode active material lithium cobaltate, a conductive agent conductive carbon black and a binder polyvinylidene fluoride according to a weight ratio of 96.5: 1.5: 2 in the solution of N-methylpyrrolidone (NMP) to form a positive electrode slurry. The aluminum foil is used as a positive current collector, and the positive slurry is coated on the positive current collector, wherein the coating weight is 17.2mg/cm²And drying, cold pressing and cutting to obtain the positive pole piece.

Preparing a negative pole piece: the cathode active material is a silicon oxide material (SiO)_x) And graphite with a capacity of 500 mAh/g. Mixing a negative electrode active material, polyacrylic acid, conductive carbon black and sodium carboxymethyl cellulose in a weight ratio of 92: 5: 2: 1 in deionized water to form cathode active material layer slurry, wherein the weight percentage of silicon in the silicon-based material is 10%. Coating the slurry of the negative active material layer on a negative current collector by using a copper foil with the thickness of 10 mu m as the negative current collector, wherein the coating weight is 6.27mg/cm²And drying until the water content of the negative pole piece is less than or equal to 300ppm to obtain a negative active material layer. And cutting to obtain the negative pole piece.

Preparing an isolating membrane: the isolating membrane adopts a polyethylene substrate (PE) with the thickness of 8 mu m, two sides of the isolating membrane are respectively coated with an alumina ceramic layer with the thickness of 2 mu m, and finally two sides of the isolating membrane coated with the ceramic layer are respectively coated with 2.5mg/cm²And (3) drying the polyvinylidene fluoride (PVDF).

Preparing an electrolyte: a lithium salt is mixed with a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): Propylene Carbonate (PC): Propyl Propionate (PP): Vinylene Carbonate (VC): 20: 30: 20: 28: 2, weight ratio) under an environment having a water content of less than 10ppm to form an electrolyte. See data in the table for specific ratios.

Preparing a lithium ion battery: and sequentially stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an outer packaging aluminum-plastic film, dehydrating at 80 ℃, injecting the electrolyte, packaging, and performing technological processes such as formation, degassing, edge cutting and the like to obtain the lithium ion battery.

In the remaining examples and comparative examples, parameters were changed in addition to the procedure of example 1, and specific changed parameters are shown in the following table.

The following describes a method of testing various parameters of the present application.

And (3) testing the cycle performance:

charging the lithium ion battery to 4.45V at a constant current of 0.5C in a constant temperature box with the temperature of 25 +/-2 ℃ or 45 +/-2 ℃, then charging to 0.05C at a constant voltage of 4.45V, standing for 15 minutes, discharging to 3.0V at a constant current of 0.5C, and standing for 5 minutes, wherein the process is a one-time charging and discharging cycle process. The capacity of the first discharge is taken as 100%, the charge-discharge cycle process is repeatedly carried out, and the number of cycle turns when the cycle capacity retention rate is 80% is recorded as an index for evaluating the cycle performance of the lithium ion battery.

Table 1 shows the respective parameters and evaluation results of examples 1 to 2 and comparative example 1.

TABLE 1

As can be seen from comparing examples 1 to 2 with comparative example 1, by using LiFTFSI and LiDCA as lithium salts, the number of cycles when the capacity retention rate of the lithium ion battery is 80% is increased, i.e., the cycle performance is better, compared to comparative example 1 without LiFTFSI and LiDCA. And when LiTFSI is partially substituted for LiPF₆And the circulation performance effect is better.

Table 2 shows the respective parameters and evaluation results of examples 3 to 5 and comparative examples 2 to 3.

TABLE 2

It can be seen by comparing comparative examples 2 to 3 and examples 3 to 5 that when lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and lithium dicyanamide are present as separate lithium salts, the cycle performance of the lithium ion battery is better when the molar contents of the lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and the lithium dicyanamide in the electrolyte are 0.9mol/L to 3.0mol/L in total, i.e., the cycle performance of examples 3 to 5 is better than that of comparative examples 2 to 3. Further, in examples 3 to 5, when the content range of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is 0.8mol/L or more, the cycle performance of the lithium ion battery is more excellent as the content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte increases.

Table 3 shows the respective parameters and evaluation results of examples 6 to 10.

TABLE 3

From examples 6 to 10, it is understood that the cycle performance of the lithium ion battery is excellent when the total content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide, the lithium dicyanamide and the lithium hexafluorophosphate in the electrolyte is 0.9mol/L to 3.0 mol/L. Further, when the total content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and lithium hexafluorophosphate in the electrolyte is 0.8mol/L to 2.0mol/L, the cycle performance of the lithium ion battery is relatively superior, and therefore, the cycle performance of the lithium ion batteries of examples 6 to 10 is slightly superior to that of the lithium ion battery of example 6. Further, when the content of lithium hexafluorophosphate in the electrolyte is less than or equal to the content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte (examples 7 to 10), the cycle performance of the lithium ion battery is relatively more excellent.

Table 4 shows the respective parameters and evaluation results of examples 11 to 15 and comparative examples 4 to 5.

TABLE 4

From comparative examples 4 to 5 and examples 11 to 15, it is understood that when lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and lithium dicyanamide are present as separate lithium salts, when the total content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide and lithium dicyanamide in the electrolyte is 0.9mol/L to 2.0mol/L, and the content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is in the range of 0.8mol/L or more (examples 11 to 15), the cycle performance of the lithium ion battery is superior to that of comparative examples 4 to 5 in which the content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is less than 0.8 mol/L. In addition, as the content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte increases, the cycle performance of the lithium ion battery tends to be improved. The addition of lithium dicyandiamide can reduce the viscosity of the electrolyte, and through the comparison of examples 11-15 and comparative examples 4-5, the high lithium salt concentration does not increase the viscosity of the electrolyte and affect the cycle performance.

Table 5 shows the respective parameters and evaluation results of examples 16 to 19 and comparative examples 6 to 7.

TABLE 5

It is understood from examples 16 to 19 and comparative examples 6 to 7 that when lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and lithium dicyanamide are present as separate lithium salts, the cycle performance of the lithium ion battery is more excellent when the total content of lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and lithium dicyanamide in the electrolyte is 0.9mol/L to 3.0 mol/L. Further, when the content range of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is 0.8mol/L or more (examples 16 to 19), the cycle performance of the lithium ion battery is more excellent than that of comparative examples 6 to 7 in which the content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is less than 0.8 mol/L. In addition, as the content of lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte increases, the cycle performance of the lithium ion battery tends to be improved. In addition, when the mass content of the silicon element in the silicon-based material is large (for example, 40% or more), the content of the lithium fluorosulfonyl (trifluoromethanesulfonyl) imide in the electrolyte is 1.1mol/L or more, and the cycle performance of the lithium ion battery is better.

As can be seen from comparative examples 5, 8, 13 and 14, when lithium fluorosulfonyl (trifluoromethylsulfonyl) imide and lithium dicyanamide are present as separate lithium salts, the molar concentration range of lithium dicyanamide is preferably 1.1mol/L or less, and when the molar concentration of lithium dicyanamide is further more than 1.1mol/L, the lithium ion battery cycle performance may deteriorate.

The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other combinations of features described above or equivalents thereof. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.