Lithium hexafluorosilicate doped with metal ions, preparation method thereof, negative electrode sheet, preparation method thereof and lithium ion battery

Abstract

The present invention relates to a metal-ion-doped lithium hexafluorosilicate, a preparation method thereof, a negative electrode sheet, a preparation method thereof, and a lithium-ion battery. Among them, the chemical formula of the metal-ion-doped lithium hexafluorosilicate is Li<subgt;2-x< / subgt;A<subgt;x< / subgt>SiF<subgt;6< / subgt>, where A is a Group I metal and does not include Li, and x is 0.5 - 1.5. The negative electrode sheet includes a current collector, an active material layer attached to the surface of the current collector, and a SEI film made of the Li<subgt;2-x< / subgt>A<subgt;x< / subgt>SiF<subgt;6< / subgt> described above. The Li<subgt;2-x< / subgt>A<subgt;x< / subgt>SiF<subgt;6< / subgt> of the present invention has a large interlayer spacing and a rich pore structure. By using Li<subgt;2-x< / subgt>A<subgt;x< / subgt>SiF<subgt;6< / subgt> to pre-form a SEI film on the surface of the negative electrode sheet, during the cycling process, the rich pore structure and the larger interlayer spacing can better improve the desolvation ability of Li<supgt;+< / supgt>, accelerate the transport of Li<supgt;+< / supgt>, and induce uniform lithium deposition, and then generate a SEI film rich in inorganic substances between the SEI film and the active material layer, further inhibiting the formation of lithium dendrites, improving the cycling stability and service life of the lithium-ion battery, and significantly enhancing the stability and capacity of the negative electrode sheet during fast charging.

Description

Technical Field

[0001] The present invention relates to the technical field of ion batteries, and particularly to a metal ion-doped lithium hexafluorosilicate, a preparation method thereof, a negative electrode sheet, a preparation method thereof, and a lithium ion battery. Background Art

[0002] During the first charge and discharge process of a lithium ion battery, the electrode material reacts with the electrolyte at the solid-liquid interface to form a SEI film covering the surface of the electrode material. A stable SEI film can effectively prevent solvent molecules from damaging the electrode material and improve the cycle stability and service life of the lithium ion battery. Summary of the Invention

[0003] Based on this, in view of the above problems, it is necessary to provide a metal ion-doped lithium hexafluorosilicate, a preparation method thereof, a negative electrode sheet, a preparation method thereof, and a lithium ion battery. By using the metal ion-doped lithium hexafluorosilicate to pre-form a SEI film on the surface of the negative electrode sheet, the cycle stability and service life of the lithium ion battery can be effectively improved, and the fast charging ability of the lithium ion battery can also be improved.

[0004] A metal ion-doped lithium hexafluorosilicate, the chemical formula of the metal ion-doped lithium hexafluorosilicate is Li 2- x A x SiF6, where A is a Group I metal and does not include Li, and x is 0.5 - 1.5.

[0005] In one embodiment, A is selected from at least one of Na and K.

[0006] A preparation method of the metal ion-doped lithium hexafluorosilicate includes the following steps:

[0007] Placing Li2SiF6 and A2SiF6 in an organic solvent and obtaining Li 2-x A x SiF6 by a proton transfer reaction, where A is a Group I metal and x is 0.5 - 1.5.

[0008] In one embodiment, SiO2 and LiPF6 are placed in an organic solvent and Li2SiF6 is prepared by a proton transfer reaction.

[0009] In one embodiment, the morphology of the SiO2 is porous spherical.

[0010] A negative electrode sheet includes a current collector and an active material layer attached to the surface of the current collector, and a SEI film made of the Li 2-x A x SiF6 is also attached to the surface of the active material layer.

[0011] In one embodiment, the negative electrode active material in the active material layer is selected from graphite.

[0012] A method for preparing the negative electrode sheet includes the following steps:

[0013] Provide a prefabricated negative electrode sheet, which includes a current collector and an active material layer attached to the surface of the current collector;

[0014] Put Li 2-x A x SiF6 and a binder into an organic solvent to obtain a dispersion, and place the dispersion on the surface of the active material layer of the prefabricated negative electrode sheet, and obtain a negative electrode sheet after drying.

[0015] In one embodiment, the concentration of Li 2-x A x SiF6 in the dispersion is 12mg / mL - 18mg / mL. Based on a prefabricated negative electrode sheet with a diameter of 12mm, the dosage of the dispersion is 5μL - 10μL.

[0016] A lithium-ion battery, characterized in that it includes the negative electrode sheet described above.

[0017] Compared with Li2SiF6, the present invention uses a Group I main group metal ion with a larger ionic radius to dope and replace part of Li + of Li 2-x A x SiF6 has a larger interlayer spacing and a richer pore structure. Using Li 2-x A x SiF6 to pre-form a SEI film on the surface of the negative electrode sheet. During the cycling process, the rich pore structure and the larger interlayer spacing can better improve the desolvation ability of Li + , accelerate the transport of Li + , and induce uniform lithium deposition, and then generate an inorganic-rich SEI film between the SEI film and the active material layer, further inhibiting the formation of lithium dendrites, improving the cycling stability and service life of the lithium-ion battery. At the same time, the double-layer SEI film significantly improves the stability and capacity of the negative electrode sheet during fast charging, providing strong support for the fast charging of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 Scanning electron micrograph of LiNaSiF6 prepared in Example 3 of the present invention;

[0020] Figure 2 XRD patterns of Li2SiF6 prepared in Comparative Example 2 and LiNaSiF6 prepared in Example 3 of the present invention. Detailed implementation manners

[0021] To facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments or examples and are not intended to limit the present invention. The optional range of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The any and all combinations include any two related listed items, any more related listed items, or the combination of all related listed items.

[0023] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0024] The inherent pore structure and gap size of Li2SiF6 limit its ability to improve the performance of the electrode sheet and cope with mechanical strain. Therefore, the present invention provides a metal ion-doped lithium hexafluorosilicate, and the chemical formula of the metal ion-doped lithium hexafluorosilicate is Li 2-x A x SiF6, wherein A is a metal in the first main group and does not include Li. Since the ionic radius of the metal ion A is greater than that of Li, thus, by doping and replacing part of Li in Li2SiF6 with the metal ion A + it is possible to widen the layer spacing and increase the pores, so that Li 2-x A xSiF6 has a larger interlayer spacing and a more abundant pore structure than Li2SiF6. Preferably, A is selected from at least one of Na and K.

[0025] Since the doping amount of metal ions has an obvious influence on its lattice spacing, x is controlled within the range of 0.5 - 1.5. For example, x is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, and further preferably 0.8 - 1.1.

[0026] The present invention also provides a preparation method of the metal ion-doped lithium hexafluorosilicate, comprising the following steps:

[0027] Put Li2SiF6 and A2SiF6 in an organic solvent, and obtain Li 2-x A x SiF6 by a proton transfer reaction, where A is a metal of the first main group and x is 0.5 - 1.5.

[0028] For the preparation method of the present invention, there is no requirement for the preparation method and source of Li2SiF6. Among them, SiO2 has a high specific surface area, good thermal conductivity and stability. After synthesizing Li2SiF6 with SiO2 and then doping with metal ion A, the obtained Li 2-x A x SiF6 can have a more abundant pore structure and a larger interlayer spacing. Therefore, the present invention preferably puts SiO2 and LiPF6 in an organic solvent and prepares Li2SiF6 by a proton transfer reaction, and then performs a proton transfer reaction between Li2SiF6 and A2SiF6 to prepare Li 2-x A x SiF6. Among them, the morphology of the SiO2 is further preferably porous spherical, having a more abundant pore structure and a larger specific surface area, with better effects. When SiO2 and LiPF6 are put in an organic solvent for a proton transfer reaction, LiPF6 is in excess to ensure that SiO2 reacts completely.

[0029] Li 2-x A x In Li 2-x A x SiF6, A is further preferably at least one of Na and K. Therefore, A2SiF6 is preferably at least one of Na2SiF6 and K2SiF6. In addition, when performing a proton transfer reaction between Li2SiF6 and A2SiF6 to prepare Li

[0030] Prepare Li2SiF6 by proton transfer reaction of SiO2 and LiPF6 and prepare Li by proton transfer reaction of Li2SiF6 and A2SiF6 2-x A x In the steps of SiF6, the organic solvents used can all be selected from acetonitrile, etc., and there are no special requirements.

[0031] The present invention also provides a negative electrode sheet, including a current collector and an active material layer attached to the surface of the current collector, and an SEI film made of the Li 2-x A x SiF6 is attached to the surface of the active material layer. Among them, the active material layer is made of negative electrode active material, binder, conductive agent, etc. in proportion.

[0032] The present invention uses Li 2-x A x SiF6 pre - forms an SEI film on the surface of the negative electrode sheet. Thus, after the negative electrode sheet is assembled into a lithium - ion battery, during the cycling process, the rich pore structure and larger layer spacing of the pre - formed SEI film can better improve the + desolvation ability of Li + accelerate the transport of Li

[0033] and induce uniform lithium deposition to generate an SEI film rich in inorganic substances between the SEI film and the active material layer, further inhibiting the formation of lithium dendrites and improving the cycle stability and service life of the lithium - ion battery. At the same time, the induced SEI film rich in inorganic substances and the pre - formed SEI film form a double - layer SEI film, which significantly improves the stability and capacity of the negative electrode sheet during rapid charging, providing strong support for the rapid charging of lithium - ion batteries. 2-x A x Graphite negative electrode sheets dominate in lithium - ion battery negative electrode sheets due to their high energy density, low cost, and long cycle life. However, due to the layered structure of graphite itself and the solvation effect of lithium ions, the ion transport rate of graphite negative electrode sheets is slow, and the fast - charging ability of the entire lithium - ion battery is limited. And the induced SEI film rich in inorganic substances and the pre - formed SEI film in the present invention form a double - layer SEI film, which significantly improves the stability and capacity of the negative electrode sheet during rapid charging. Therefore, the negative electrode active material in the active material layer of the present invention is selected from graphite, and then Li

[0034] The present invention also provides a preparation method of the negative electrode sheet, including the following steps:

[0035] Provide a prefabricated negative electrode sheet, the prefabricated negative electrode sheet including a current collector and an active material layer attached to the surface of the current collector;

[0036] Put Li 2-x A x SiF6 and a binder into an organic solvent to obtain a dispersion liquid, place the dispersion liquid on the surface of the active material layer of the prefabricated negative electrode sheet, and obtain a negative electrode sheet after drying.

[0037] It can be understood that the prefabricated negative electrode sheet is the traditional negative electrode sheet, which is made by mixing components such as negative electrode active material, conductive agent and binder into a slurry, coating the slurry on the current collector, and obtaining it after drying and slicing. The present invention mainly uses Li 2-x A x SiF6 to pre-form a SEI film on the surface of the negative electrode sheet.

[0038] Optionally, in the step of putting Li 2-x A x SiF6 and a binder into an organic solvent to obtain a dispersion liquid, the organic solvent is selected from N,N-dimethylformamide (DMF), etc., the binder is selected from sodium carboxymethyl cellulose (CMC-Na), polyvinylidene fluoride (PVDF), etc., and the concentration of Li 2-x A x SiF6 in the dispersion liquid is preferably 12mg / mL - 18mg / mL. Based on a prefabricated negative electrode sheet with a diameter of 12mm, the dosage of the dispersion liquid is 5μL - 10μL. The way of placing the dispersion liquid on the surface of the active material layer of the prefabricated negative electrode sheet can be coating, dropping, etc.

[0039] The present invention also provides a lithium-ion battery, the lithium-ion battery using the above negative electrode sheet.

[0040] Hereinafter, the lithium hexafluorosilicate doped with metal ions, its preparation method, the negative electrode sheet and its preparation method, and the lithium-ion battery will be further described through the following specific examples.

[0041] Comparative Example 1

[0042] Weigh 320mg of artificial graphite material, 40mg of conductive carbon black and 40mg of carboxymethyl cellulose, add an appropriate amount of deionized water and then ball mill for 2h using a planetary ball mill. Coat the ball milled slurry on a copper foil, and vacuum dry at 80°C for 12h and then cut into a graphite negative electrode sheet with a diameter of 12mm, and the loading is 2.5mg / cm 2 .

[0043] Comparative Example 2

[0044] Weigh 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder in a glove box. Subsequently, add 10 mL of acetonitrile solution and stir magnetically for 24 h to obtain a suspension of Li2SiF6 through a proton transfer reaction. Centrifuge the obtained suspension several times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dry it in the glove box to obtain Li2SiF6 powder.

[0045] Weigh 100 mg of PVDF powder, add 20 mL of DMF solution, and stir magnetically for a period of time to make it a homogeneous solution. Then disperse the Li2SiF6 material obtained by centrifugation above into the homogeneous solution and shake it to disperse evenly to obtain a dispersion liquid. Among them, the concentration of the Li2SiF6 material in the dispersion liquid is 15 mg / mL.

[0046] Pipette 10 μL of the above dispersion liquid and evenly drop it on the surface of the graphite negative electrode sheet of Comparative Example 1. Subsequently, dry it at 80 °C for 20 min to obtain a negative electrode sheet with a SEI film on its surface.

[0047] Comparative Example 3

[0048] Weigh 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder in a glove box. Subsequently, add 10 mL of acetonitrile solution and stir magnetically for 24 h to obtain a suspension of Li2SiF6 through a proton transfer reaction. Centrifuge the obtained suspension several times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dry it in the glove box to obtain Li2SiF6 powder.

[0049] Weigh 500 mg of the Li2SiF6 powder obtained above and 90 mg of Na2SiF6 and dissolve them in 10 mL of acetonitrile solution and stir magnetically for 24 h to obtain a suspension of Li 1.7 Na 0.3 SiF6 through a proton transfer reaction. Centrifuge the obtained suspension several times with acetonitrile in the glove box to obtain the Li 1.7 Na 0.3 SiF6 material.

[0050] Weigh 100 mg of PVDF powder, add 20 mL of DMF solution, and stir magnetically for a period of time to make it a homogeneous solution. Then disperse the Li 1.7 Na 0.3 SiF6 material obtained by centrifugation above into the homogeneous solution and shake it to disperse evenly to obtain a dispersion liquid. Among them, the concentration of the Li 1.7 Na 0.3 SiF6 material in the dispersion liquid is 16 mg / mL.

[0051] 10 μL of the above-mentioned dispersion was evenly drop-coated on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dried at 80 °C for 20 min to obtain a negative electrode sheet with an SEI film on its surface.

[0052] Comparative Example 4

[0053] In a glove box, 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder were weighed, and then 10 mL of acetonitrile solution was added. Magnetic stirring was carried out for 24 h to obtain a suspension of Li2SiF6 through a proton transfer reaction. The obtained suspension was centrifuged multiple times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dried in the glove box to obtain Li2SiF6 powder.

[0054] 500 mg of the obtained Li2SiF6 powder and 540 mg of Na2SiF6 were weighed and dissolved in 10 mL of acetonitrile solution, and magnetic stirring was carried out for 24 h to obtain a suspension of Li 0.2 Na 1.8 SiF6 through a proton transfer reaction. The obtained suspension was centrifuged multiple times with acetonitrile in the glove box to obtain Li 0.2 Na 1.8 SiF6 material.

[0055] 100 mg of PVDF powder was weighed and added to 20 mL of DMF solution. After magnetic stirring for a period of time to make it a homogeneous solution, the Li 0.2 Na 1.8 SiF6 material obtained by the above centrifugation was dispersed into the homogeneous solution and shaken to make it evenly dispersed to obtain a dispersion. Among them, the concentration of Li 0.2 Na 1.8 SiF6 material in the dispersion was 17 mg / mL.

[0056] 10 μL of the above-mentioned dispersion was evenly drop-coated on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dried at 80 °C for 20 min to obtain a negative electrode sheet with an SEI film on its surface.

[0057] Example 1

[0058] In a glove box, 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder were weighed, and then 10 mL of acetonitrile solution was added. Magnetic stirring was carried out for 24 h to obtain a suspension of Li2SiF6 through a proton transfer reaction. The obtained suspension was centrifuged multiple times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dried in the glove box to obtain Li2SiF6 powder.

[0059] Weigh 500 mg of the obtained Li2SiF6 powder and 150 mg of Na2SiF6, dissolve them in 10 mL of acetonitrile solution, and perform magnetic stirring for 24 h. Through a proton transfer reaction, a suspension of Li 1.5 Na 0.5 SiF6 is obtained. The obtained suspension is centrifuged multiple times with acetonitrile in a glove box to obtain Li 1.5 Na 0.5 SiF6 material.

[0060] Weigh 100 mg of PVDF powder, add it to 20 mL of DMF solution, and perform magnetic stirring for a period of time to make it a homogeneous solution. Then disperse the Li 1.5 Na 0.5 SiF6 material obtained by the above centrifugation into the homogeneous solution, and shake it to make it uniformly dispersed to obtain a dispersion liquid. Among them, the concentration of Li 1.5 Na 0.5 SiF6 material in the dispersion liquid is 15 mg / mL.

[0061] Pipette 10 μL of the above dispersion liquid and evenly drop it on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dry it at 80 °C for 20 min to obtain a negative electrode sheet with an SEI film on its surface.

[0062] Example 2

[0063] In a glove box, weigh 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder, then add 10 mL of acetonitrile solution, and perform magnetic stirring for 24 h. Through a proton transfer reaction, a suspension of Li2SiF6 is obtained. The obtained suspension is centrifuged multiple times with acetonitrile in a glove box to wash the residual LiPF6 in it, and then dried in the glove box to obtain Li2SiF6 powder.

[0064] Weigh 500 mg of the obtained Li2SiF6 powder and 180 mg of K2SiF6, dissolve them in 10 mL of acetonitrile solution, and perform magnetic stirring for 24 h. Through a proton transfer reaction, a suspension of Li 1.5 K 0.5 SiF6 is obtained. The obtained suspension is centrifuged multiple times with acetonitrile in a glove box to obtain Li 1.5 K 0.5 SiF6 material.

[0065] Weigh 100 mg of PVDF powder, add it to 20 mL of DMF solution, and perform magnetic stirring for a period of time to make it a homogeneous solution. Then disperse the Li 1.5 K 0.5 SiF6 material obtained by the above centrifugation into the homogeneous solution, and shake it to make it uniformly dispersed to obtain a dispersion liquid. Among them, the concentration of Li 1.5 K0.5 The concentration of the SiF6 material is 16 mg / mL.

[0066] 10 μL of the above-mentioned dispersion was evenly drop-coated on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dried at 80 °C for 20 min to obtain a negative electrode sheet with an SEI film on its surface.

[0067] Example 3

[0068] 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder were weighed in a glove box, and then 10 mL of acetonitrile solution was added, followed by magnetic stirring for 24 h. A suspension of Li2SiF6 was obtained through a proton transfer reaction. The obtained suspension was centrifuged multiple times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dried in the glove box to obtain Li2SiF6 powder.

[0069] 500 mg of the obtained Li2SiF6 powder and 300 mg of Na2SiF6 were weighed and dissolved in 10 mL of acetonitrile solution for magnetic stirring for 24 h. A suspension of LiNaSiF6 was obtained through a proton transfer reaction. The obtained suspension was centrifuged multiple times with acetonitrile in the glove box to obtain the LiNaSiF6 material as shown in Figure 1 As shown. At the same time, as shown in Figure 2 A is the XRD curve of the LiNaSiF6 material obtained in this example, and B is the XRD curve of the Li2SiF6 material obtained in Comparative Example 2. It can be seen from Figure 2 that for the LiNaSiF6 material obtained by Na ion doping, the peak shifts to the left, indicating that the lattice spacing of the material becomes larger and the doping is successful.

[0070] 100 mg of PVDF powder was weighed and added to 20 mL of DMF solution. After magnetic stirring for a period of time to make it a homogeneous solution, the LiNaSiF6 material obtained by the above centrifugation was dispersed into the homogeneous solution and shaken to make it evenly dispersed to obtain a dispersion. Among them, the concentration of the LiNaSiF6 material in the dispersion is 16 mg / mL.

[0071] 10 μL of the above-mentioned dispersion was evenly drop-coated on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dried at 80 °C for 20 min to obtain a negative electrode sheet with an SEI film on its surface.

[0072] Example 4

[0073] Weigh 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder in a glove box. Subsequently, add 10 mL of acetonitrile solution and stir magnetically for 24 h to obtain a suspension of Li2SiF6 through a proton transfer reaction. Centrifuge the obtained suspension multiple times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dry it in the glove box to obtain Li2SiF6 powder.

[0074] Weigh 500 mg of the above-obtained Li2SiF6 powder and 350 mg of K2SiF6, dissolve them in 10 mL of acetonitrile solution, and stir magnetically for 24 h to obtain a suspension of LiKSiF6 through a proton transfer reaction. Centrifuge the obtained suspension multiple times with acetonitrile in the glove box to obtain the LiKSiF6 material.

[0075] Weigh 100 mg of PVDF powder, add 20 mL of DMF solution, stir magnetically for a period of time to make it a homogeneous solution, and then disperse the above-obtained LiKSiF6 material obtained by centrifugation into the homogeneous solution and shake it to disperse evenly to obtain a dispersion. Among them, the concentration of the LiKSiF6 material in the dispersion is 16 mg / mL.

[0076] Pipette 10 μL of the above dispersion and evenly drop-coat it on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dry it at 80 °C for 20 min to obtain a negative electrode sheet with a SEI film on its surface.

[0077] Example 5

[0078] Weigh 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder in a glove box. Subsequently, add 10 mL of acetonitrile solution and stir magnetically for 24 h to obtain a suspension of Li2SiF6 through a proton transfer reaction. Centrifuge the obtained suspension multiple times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dry it in the glove box to obtain Li2SiF6 powder.

[0079] Weigh 500 mg of the above-obtained Li2SiF6 powder and 450 mg of Na2SiF6, dissolve them in 10 mL of acetonitrile solution, and stir magnetically for 24 h to obtain a suspension of Li 0.5 Na 1.5 SiF6. Centrifuge the obtained suspension multiple times with acetonitrile in the glove box to obtain Li 0.5 Na 1.5 SiF6 material.

[0080] Weigh 100 mg of PVDF powder, add 20 mL of DMF solution, stir magnetically for a period of time to make it a homogeneous solution, and then disperse the above-obtained Li 0.5 Na 1.5The SiF6 material is dispersed into a homogeneous solution and shaken to make it uniformly dispersed, obtaining a dispersion liquid. Among them, Li in the dispersion liquid 0.5 Na 1.5 The concentration of the SiF6 material is 17 mg / mL.

[0081] 10 μL of the above dispersion liquid is evenly pipetted and coated on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dried at 80 °C for 20 min to obtain a negative electrode sheet with an SEI film on its surface.

[0082] Example 6

[0083] In a glove box, 500 mg of porous spherical SiO2 powder and 1.5 g of LiPF6 powder are weighed, and then 10 mL of acetonitrile solution is added, and magnetic stirring is carried out for 24 h. A suspension of Li2SiF6 is obtained through a proton transfer reaction. The obtained suspension is centrifuged multiple times with acetonitrile in the glove box to wash the residual LiPF6 therein, and then dried in the glove box to obtain Li2SiF6 powder.

[0084] 500 mg of the obtained Li2SiF6 powder and 530 mg of K2SiF6 are weighed and dissolved in 10 mL of acetonitrile solution, and magnetic stirring is carried out for 24 h. A suspension of Li 0.5 K 1.5 SiF6 is obtained. The obtained suspension is centrifuged multiple times with acetonitrile in the glove box to obtain Li 0.5 K 1.5 SiF6 material.

[0085] 100 mg of PVDF powder is weighed and added to 20 mL of DMF solution, and magnetic stirring is carried out for a period of time to make it a homogeneous solution. Then the Li 0.5 K 1.5 SiF6 material obtained by the above centrifugation is dispersed into the homogeneous solution and shaken to make it uniformly dispersed, obtaining a dispersion liquid. Among them, Li in the dispersion liquid 0.5 K 1.5 The concentration of the SiF6 material is 17 mg / mL.

[0086] 10 μL of the above dispersion liquid is evenly pipetted and coated on the surface of the graphite negative electrode sheet of Comparative Example 1, and then dried at 80 °C for 20 min to obtain a negative electrode sheet with an SEI film on its surface.

[0087] The negative electrode sheets of the examples and comparative examples were used. Metallic lithium was used as the counter electrode and reference electrode. A PP separator was selected. The electrolyte used was a mixed solution of LiPF6 with a concentration of 1 mol / L and a volume ratio of 1:1 of diethyl carbonate and ethylene carbonate as the solvent. A button cell was assembled in a glove box under an argon atmosphere, and the obtained button cell was subjected to an electrochemical performance test at room temperature of 30 °C and a current density of 2C. The results are shown in Table 1.

[0088] Table 1

[0089]

[0090] As can be seen from Table 1, after doping with metal ion A and controlling the doping amount x within 0.5 - 1.5, the cycle stability, service life, and fast charging ability of the lithium-ion battery can be effectively improved. In addition, as can be seen from Table 1, after doping with Na ions and controlling the atomic ratio of Na ions to Li ions at about 1:1, the performance is the best. At a small current density of 0.2C, the initial efficiency can reach 92.12%, and at a relatively large current density of 2C, after 100 cycles, the specific capacity can still be maintained at 366.28 mAh g -1 and has excellent cycle stability and rate performance, as well as good fast charging performance.

[0091] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0092] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A method for preparing a negative electrode sheet, characterized in that: The following steps are involved: Providing a prefabricated negative electrode sheet, the prefabricated negative electrode sheet comprising a current collector and an active material layer attached to a surface of the current collector; SiO2 and LiPF6 are placed in an organic solvent and a proton transfer reaction is used to obtain Li2SiF6. Then Li2SiF6 and A2SiF6 are placed in an organic solvent and a proton transfer reaction is used to obtain Li 2-x A x SiF6, where A is the first main group metal, x is 0.8-1.1, and then Li 2-x A x SiF6 and a binder are placed in an organic solvent to obtain a dispersion, and the dispersion is placed on the surface of the active material layer of the prefabricated negative electrode sheet, and the negative electrode sheet is obtained after drying, wherein Li 2-x A x The concentration of SiF6 is 12 mg / mL-18 mg / mL, and based on the prefabricated negative electrode sheet with a diameter of 12 mm, the amount of the dispersion used is 5 μL-10 μL.

2. The method for preparing a negative electrode sheet according to claim 1, characterized in that: The SiO2 has a porous spherical shape.

3. The method for preparing a negative electrode sheet according to claim 1, characterized in that: The negative electrode active material in the active material layer is selected from graphite.

4. The method for preparing a negative electrode sheet according to claim 1, characterized in that: A is selected from at least one of Na and K.

5. A negative electrode sheet obtained by the preparation method according to any one of claims 1 to 4, characterized in that: The present invention comprises a current collector and an active material layer attached to the surface of the current collector, wherein the surface of the active material layer is also attached with a Li 2-x A x SEI film made of SiF6.

6. A lithium ion battery, characterized in that: Comprising the negative electrode sheet as claimed in claim 5.

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