Surface-modified silicon negative electrode plate, preparation method thereof and lithium ion battery

Abstract

The invention provides a surface-modified silicon negative pole piece, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries, a functional coating is formed on the surface of the silicon negative pole piece, the functional coating comprises lithium sulfide and a solid electrolyte and is formed by laminating and compounding a lithium sulfide layer and a solid electrolyte layer, the surface modification of the silicon negative electrode plate is realized, the wettability of the electrolyte on the interface of the electrode plate can be improved, the use amount of the electrolyte is reduced, the formation of the interface SEI can be optimized, the volume expansion of the electrode plate is relieved, and the technical effects of effectively relieving the defects of the silicon negative electrode and fully improving the cycle performance of a battery cell are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a surface-modified silicon negative electrode sheet and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] With the development of the automobile industry, the demand for high energy density in power batteries is becoming more and more obvious. Although lithium metal as a negative electrode can meet the requirements of car companies, its safety performance worries manufacturers. Therefore, silicon negative electrode, as a material with high discharge capacity and low discharge potential, has become the most popular negative electrode material for lithium-ion batteries.

[0003] However, the silicon negative electrode will produce a huge volume expansion effect during the cycle, which will cause the active material to fall off during the cycle, resulting in loss of electrical contact and ultimately reducing the cycle life of the silicon negative electrode.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] One of the purposes of the present invention is to provide a surface-modified silicon negative electrode pole piece, which can effectively alleviate the defects of the silicon negative electrode itself and fully improve the cycle performance of the battery cell.

[0006] The second object of the present invention is to provide a method for preparing a surface-modified silicon negative electrode sheet, which has a simple process, high efficiency, high success rate and is suitable for industrial production.

[0007] A third object of the present invention is to provide a lithium ion battery with a long cycle life.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted: In a first aspect, a surface-modified silicon negative electrode plate comprises a silicon negative electrode plate and a functional coating on its surface; The functional coating comprises lithium sulfide and a solid electrolyte; The functional coating is formed by laminating and compounding a lithium sulfide layer and a solid electrolyte layer; The lithium sulfide layer in the functional coating is adhered to the surface of the silicon negative electrode plate; The loading amount of lithium sulfide on the surface of the electrode is 0.01 mg / cm 2 ~0.3mg / cm 2 .

[0009] Furthermore, the solid electrolyte is Li 1+x A x B 2-x(PO4)3, wherein x is between 0.01 and 0.5, A is selected from at least one of Al, Y, Ga, Cr, In, Fe, Se and La, and B is selected from at least one of Ti, Ge, Ta, Zr, Sn, Fe, V, Hf and their derivatives.

[0010] Furthermore, the thickness of the solid electrolyte layer is 0.5 μm to 3 μm.

[0011] In a second aspect, a method for preparing a surface-modified silicon negative electrode sheet as described in any one of the above items comprises the following steps: Firstly, a lithium sulfide solution is applied to a silicon negative electrode plate to form a coating to obtain a lithium sulfide modified electrode plate, and then a solid electrolyte membrane is transferred to the lithium sulfide modified electrode plate to obtain the surface-modified silicon negative electrode plate.

[0012] Furthermore, the solvent used in the lithium sulfide solution includes at least one of an alcohol solvent and an ammonium salt solution; Preferably, the alcohol solvent includes at least one of methanol and ethanol; Preferably, the solute salt of the ammonium salt solution includes at least one of NH4FSI, tetraethylammonium nitrate, ammonium fluoride and ammonium tetrafluoroborate; Preferably, the solvent of the ammonium salt solution includes at least one of sulfone compounds, amide compounds, nitrile compounds, ester compounds and ether compounds.

[0013] Furthermore, the method for preparing the solid electrolyte membrane comprises the following steps: The solid electrolyte and the binder are mixed and dissolved and then coated on a substrate to form a stability film, and the stability film is dried to obtain the solid electrolyte membrane.

[0014] Further, the binder includes at least one of a water-based binder and an oil-based binder; Preferably, the aqueous binder comprises at least one of polyacrylic acid, lithium polyacrylate, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, sodium carboxymethyl cellulose and styrene-butadiene rubber; Preferably, the oily binder includes at least one of poly(diene fluoride) and poly(diene fluoride-co-hexafluoropropylene).

[0015] Furthermore, the solid electrolyte membrane is transferred by a double roller machine; Preferably, the double roller machine performs transfer at a pressure of 0.01 MPa to 1 MPa and a temperature of 40° C. to 100° C.

[0016] In a third aspect, a lithium-ion battery comprises the surface-modified silicon negative electrode sheet as described in any one of the above items.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The surface-modified silicon negative electrode pole piece provided by the present invention realizes the surface modification of the pole piece through a specific functional coating, which can not only improve the electrolyte wettability of the pole piece interface and reduce the amount of electrolyte, but also optimize the interface SEI formation and alleviate the volume expansion of the pole piece; a lithium sulfide protective layer is formed on the surface of the silicon negative electrode, which can promote the uniform deposition / desorption of lithium ions at the negative electrode, while inhibiting the growth of lithium dendrites, avoiding the side reaction between the deposited lithium metal and the electrolyte, improving the cycle life, and avoiding the damage to the SEI caused by the volume expansion during the deposition / desorption of lithium ions; the formed LATP protective layer is helpful to improve the lithium ion conduction, and the protective layer has good mechanical stability, which helps to inhibit the volume expansion of the silicon negative electrode; the present invention combines the advantages of the two materials to achieve the technical effect of effectively alleviating the defects of the silicon negative electrode itself and fully improving the cycle performance of the battery cell.

[0018] The method for preparing the surface-modified silicon negative electrode sheet provided by the present invention is simple and efficient to operate, is compatible with existing lithium battery processes, and can be applied on a large scale.

[0019] The lithium ion battery provided by the invention has a long cycle life. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] According to a first aspect of the present invention, there is provided a surface-modified silicon negative electrode plate, comprising a silicon negative electrode plate and a functional coating on its surface; The functional coating includes lithium sulfide and a solid electrolyte; The functional coating is formed by laminating and compounding a lithium sulfide layer and a solid electrolyte layer; The lithium sulfide layer in the functional coating is adhered to the surface of the silicon negative electrode piece.

[0022] In the present invention, the loading amount of lithium sulfide on the surface of the electrode can be 0.01 mg / cm 2 ~0.3mg / cm 2 , a typical but non-limiting loading is, for example, 0.01 mg / cm 2 , 0.02mg / cm 2 , 0.03mg / cm 2 , 0.04mg / cm 2 , 0.05mg / cm 2, 0.06mg / cm 2 , 0.07mg / cm 2 , 0.08mg / cm 2 , 0.09mg / cm 2 , 0.1mg / cm 2 , 0.11mg / cm 2 , 0.12mg / cm 2 , 0.13mg / cm 2 , 0.14mg / cm 2 , 0.15mg / cm 2 , 0.16mg / cm 2 , 0.17mg / cm 2 , 0.18mg / cm 2 、0.19mg / cm 2 , 0.20mg / cm 2 , 0.21mg / cm 2 , 0.22mg / cm 2 , 0.23mg / cm 2 , 0.24mg / cm 2 , 0.25mg / cm 2 , 0.26mg / cm 2 , 0.27mg / cm 2 、0.28mg / cm 2 , 0.29mg / cm 2 , 0.3mg / cm 2 .

[0023] The surface-modified silicon negative electrode pole piece provided by the present invention realizes the surface modification of the pole piece through a specific functional coating, and a lithium sulfide protective layer is formed on the surface of the silicon negative electrode, which can promote the uniform deposition / desorption of lithium ions at the negative electrode, and at the same time inhibit the growth of lithium dendrites, avoid the side reaction between the deposited lithium metal and the electrolyte, and improve the cycle life, and can avoid the damage to SEI caused by the volume expansion during the deposition / desorption of lithium ions; the formed LATP protective layer is helpful to improve the lithium ion conduction, and the protective layer has good mechanical stability, which helps to inhibit the volume expansion of the silicon negative electrode, thereby achieving the technical effect of effectively alleviating the defects of the silicon negative electrode itself and fully improving the cycle performance of the battery cell.

[0024] It should be noted that the silicon negative electrode plate is a conventional silicon-containing negative electrode plate in the art, which contains an active substance, a conductive agent and a binder; wherein the active substance can be a mixture of silicon and non-silicon active materials, silicon active materials include but are not limited to at least one of pure silicon, silicon oxide and silicon carbon, and non-silicon active materials include but are not limited to at least one of graphite and hard carbon; the conductive agent includes but is not limited to at least one of nanotubes, graphene, conductive carbon black and carbon fiber; the binder includes but is not limited to at least one of polyacrylic acid, lithium polyacrylate, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, sodium carboxymethyl cellulose and styrene-butadiene rubber.

[0025] In a preferred embodiment, the solid electrolyte may be Li 1+x A x B 2-x (PO4)3, wherein x is between 0.01 and 0.5, A can be selected from at least one of Al, Y, Ga, Cr, In, Fe, Se and La, and B can be selected from at least one of Ti, Ge, Ta, Zr, Sn, Fe, V, Hf and their derivative materials.

[0026] In the present invention, the thickness of the solid electrolyte layer may be 0.5 μm to 3 μm, and typical but non-limiting thicknesses thereof are, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, and 3 μm.

[0027] In summary, with the coordinated cooperation of the specific components of the functional coating and its parameters, the surface-modified silicon negative electrode plate of the present invention can effectively alleviate the inherent defects of the silicon negative electrode, fully improve the cycle performance of the battery cell, and significantly improve the cycle life of the silicon negative electrode lithium-ion battery.

[0028] According to a second aspect of the present invention, there is provided a method for preparing a surface-modified silicon negative electrode sheet as described in any one of the above, comprising the following steps: First, a lithium sulfide solution is applied to a silicon negative electrode plate to form a coating to obtain a lithium sulfide modified electrode plate, and then a solid electrolyte membrane is transferred to the lithium sulfide modified electrode plate to obtain a surface-modified silicon negative electrode plate.

[0029] The method for preparing the surface-modified silicon negative electrode sheet provided by the present invention is simple and efficient to operate, is compatible with existing lithium battery processes, and can be applied on a large scale.

[0030] In a preferred embodiment, the solvent used in the lithium sulfide solution includes but is not limited to at least one of an alcohol solvent and an ammonium salt solution.

[0031] In the present invention, the alcohol solvent includes but is not limited to at least one of methanol and ethanol; the solute salt of the ammonium salt solution includes but is not limited to at least one of NH4FSI, tetraethylammonium nitrate, ammonium fluoride and ammonium tetrafluoroborate; the solvent of the ammonium salt solution includes but is not limited to at least one of sulfone compounds, amide compounds, nitrile compounds, ester compounds and ether compounds.

[0032] In a preferred embodiment, the solid electrolyte membrane may be a solid electrolyte release membrane, and the preparation method thereof comprises the following steps: The solid electrolyte and the binder are mixed and dissolved and then coated on the substrate to form a stability film, and the stability film is dried to obtain a solid electrolyte release film.

[0033] In the present invention, the solid electrolyte powder and the binder are first mixed in a solvent, stirred evenly, and then coated on a substrate to form a stable film, wherein the substrate can be PET or PP; after the coating is completed, the film is subjected to a high-temperature drying treatment at 100°C to remove the residual solvent in the film, thereby obtaining a solid electrolyte release film.

[0034] The present invention transfers the solid electrolyte via a release film, is simple to operate, and is easy to realize industrial production.

[0035] In the present invention, the solvent used when the solid electrolyte powder is mixed with the binder may be an aqueous solvent or an organic solvent, for example, at least one of deionized water, anhydrous ethanol, N,N-dimethylformamide and N-methyl-2-pyrrolidone (NMP), but is not limited thereto.

[0036] In a preferred embodiment, the binder mixed with the solid electrolyte powder can be at least one of an aqueous binder and an oily binder; wherein the aqueous binder includes but is not limited to at least one of polyacrylic acid, lithium polyacrylate, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, sodium carboxymethyl cellulose and styrene-butadiene rubber; the oily binder includes but is not limited to at least one of polydiethylene fluoride and poly(diethylene fluoride-co-hexafluoropropylene).

[0037] A typical method for preparing a surface-modified silicon negative electrode sheet comprises the following steps: (1) dispersing lithium sulfide powder in a solvent and stirring uniformly to obtain a lithium sulfide dispersion; (2) coating the lithium sulfide dispersion of step (1) onto the silicon negative electrode plate to form a coating, namely a lithium sulfide layer, to obtain a lithium sulfide-coated modified electrode plate; wherein the coating method may be at least one of brush coating, spray coating and roller coating; (3) drying the electrode sheet modified by the lithium sulfide coating in step (2); (4) mixing the solid electrolyte powder and the binder in a solvent and stirring them evenly to obtain a mixed solution; (5) applying the mixed solution of step (4) onto a substrate to form a stable film; wherein the coating method may be at least one of brushing, spraying and rolling; (6) drying the film of step (5) to remove residual solvent in the film to obtain a solid electrolyte release film; (7) The release film of step (6) is transferred to the electrode sheet after drying in step (3), thereby forming a solid electrolyte layer on the electrode sheet to obtain a silicon negative electrode sheet coated with a composite functional coating, i.e., a surface-modified silicon negative electrode sheet.

[0038] In a preferred embodiment, the solid electrolyte release film is transferred in a manner including but not limited to being transferred by a double roller machine.

[0039] In the present invention, the release film is transferred to the pole piece by a heated double roller machine, the operating pressure of which can be 0.01MPa~1MPa, and the operating temperature can be 40℃~100℃, which is more conducive to further improving the formation effect of the solid electrolyte layer on the pole piece.

[0040] According to a third aspect of the present invention, a lithium-ion battery is provided, comprising the surface-modified silicon negative electrode sheet as described above.

[0041] The lithium ion battery provided by the invention has a long cycle life.

[0042] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0043] Example 1 This embodiment provides a surface-modified silicon negative electrode plate, including a silicon negative electrode plate and a functional coating on its surface; the functional coating is formed by laminating and compounding a lithium sulfide layer and a solid electrolyte layer; Among them, the lithium sulfide layer in the functional coating is adhered to the surface of the silicon negative electrode plate.

[0044] The method for preparing the surface-modified silicon negative electrode sheet of this embodiment comprises the following steps: Preparation of silicon negative electrode sheet: (a) Graphite, nano-silicon, CMC, SBR and CNT were prepared into a slurry in a weight ratio of 80:16.72:0.40:0.88:2 by the following steps: Add CMC to deionized water and stir for 4 hours until CMC is completely stirred; Continue to add CNT to the above solution and stir for 30 min until the CNT is completely dispersed; Continue to add graphite powder (in two additions) and stir for 6 hours until the graphite powder is evenly dispersed; Continue to add nano-silicon particles and stir for 6 hours until the silicon particles are evenly dispersed; Finally, add SBR and stir for 2 h until it is evenly dispersed to obtain slurry; (b) coating the obtained slurry on a copper foil, drying it, and rolling it to obtain a silicon negative electrode sheet; Surface modification of silicon negative electrode: (1) dispersing lithium sulfide powder in anhydrous ethanol and mechanically stirring the mixture to obtain a lithium sulfide dispersion; (2) spraying the lithium sulfide dispersion of step (1) onto the silicon negative electrode plate, thereby forming a lithium sulfide layer on the plate, and obtaining a lithium sulfide-coated modified plate; (3) drying the modified electrode coated with lithium sulfide in step (2) at 40° C. for 2 h to ensure that the electrode is fully dried; (4) Mixing the solid electrolyte powder and the binder in a solvent, and mechanically stirring them to obtain a mixed solution; wherein the solid electrolyte is Li 1.3 Al 0.3 Ti 1.7 (PO4)3, the binder is PAA, and the solvent used is deionized water; (5) coating the mixed solution of step (4) onto a PP substrate to form a stable film with a thickness of 0.5 μm; (6) drying the film obtained in step (5) at 100° C. to remove residual solvent in the film, thereby obtaining a solid electrolyte release film; (7) The release film of step (6) is transferred to the electrode sheet dried in step (3) by rolling at 80°C and 0.05MPa, thereby forming a solid electrolyte layer on the electrode sheet to obtain a silicon negative electrode sheet coated with a composite functional coating, i.e., a surface-modified silicon negative electrode sheet, the lithium sulfide surface loading and the release film thickness of which are shown in Table 1.

[0045] Embodiment 2-10 Example 2-10 provides a surface-modified silicon negative electrode sheet, the lithium sulfide surface loading and release film thickness of which are shown in Table 1; The preparation method is similar to that of Example 1.

[0046] Table 1

[0047] Comparative Example 1 The difference from Example 1 is that in this comparative example, the surface of the silicon negative electrode sheet is not modified; The remaining steps and process parameters are the same as those in Example 1 to obtain a silicon negative electrode sheet.

[0048] Comparative Example 2 The difference from Example 1 is that in this comparative example, during the surface modification process of the silicon negative electrode sheet, the lithium sulfide solution is not sprayed onto the silicon negative electrode sheet, but only the solid electrolyte release film is used to modify the surface of the sheet; The remaining steps and process parameters are the same as those in Example 1 to obtain a modified silicon negative electrode sheet.

[0049] Comparative Example 3 The difference from Example 1 is that in this comparative example, during the surface modification process of the silicon negative electrode sheet, the surface of the sheet is modified only by spraying the lithium sulfide solution onto the silicon negative electrode sheet, and the surface modification is not performed using a solid electrolyte release film; The remaining steps and process parameters are the same as those in Example 1 to obtain a modified silicon negative electrode sheet.

[0050] Test example The pole pieces obtained in Examples 1-10 and Comparative Examples 1-3 were prepared into lithium ion secondary batteries for testing, which were recorded as Test Groups 1-10 and Comparative Test Groups 1-3, respectively. The test results are shown in Table 2.

[0051] The preparation steps of lithium-ion secondary batteries are as follows: The negative electrode sheet is rolled and cut to prepare a sheet with a sheet area length × width = 57 mm * 52 mm and a tab area length × width = 10 mm * 5 mm for standby use; The positive electrode ternary active material NMC811, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 90:5:5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 70wt%, and the mixture is stirred evenly; the slurry is evenly coated on an aluminum foil, and a pole piece with a specification of pole piece length × width = 55mm*50mm and pole ear piece length × width = 10mm*5mm is prepared by drying, rolling, and cutting, and the pole piece is set aside; After the negative electrode is encapsulated with a diaphragm, the positive electrode sheet and the negative electrode sheet are stacked to obtain a battery cell, the battery cell is placed in an aluminum-plastic film and then encapsulated, an electrolyte is injected, and then the sealing, standing, formation and exhaust processes are carried out in sequence to obtain a lithium-ion secondary battery.

[0052] Table 2

[0053] It can be seen from the data in Table 2 that the present invention can effectively alleviate the inherent defects of the silicon negative electrode by modifying the surface of the silicon negative electrode plate through a specific functional coating, thereby fully improving the cycle performance of the battery cell.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A surface-modified silicon negative electrode plate, characterized in that: Including silicon negative electrode plate and functional coating on its surface; The functional coating comprises lithium sulfide and a solid electrolyte; The functional coating is formed by laminating and compounding a lithium sulfide layer and a solid electrolyte layer; The lithium sulfide layer in the functional coating is adhered to the surface of the silicon negative electrode plate; The loading amount of lithium sulfide on the surface of the electrode is 0.01 mg / cm 2 ~0.3mg / cm 2 .

2. The surface-modified silicon negative electrode sheet according to claim 1, characterized in that: The solid electrolyte is Li 1+ x A x B 2-x (PO4)3, wherein x is between 0.01 and 0.5, A is selected from at least one of Al, Y, Ga, Cr, In, Fe, Se and La, and B is selected from at least one of Ti, Ge, Ta, Zr, Sn, Fe, V, Hf and their derivatives.

3. The surface-modified silicon negative electrode sheet according to claim 1 or 2, characterized in that: The thickness of the solid electrolyte layer is 0.5 μm to 3 μm.

4. A method for preparing a surface-modified silicon negative electrode sheet according to any one of claims 1 to 3, characterized in that: The following steps are involved: Firstly, a lithium sulfide solution is applied to a silicon negative electrode plate to form a coating to obtain a lithium sulfide modified plate, and then a solid electrolyte membrane is transferred to the lithium sulfide modified plate to obtain the surface-modified silicon negative electrode plate.

5. The preparation method according to claim 4, characterized in that: The solvent used in the lithium sulfide solution includes at least one of an alcohol solvent and an ammonium salt solution.

6. The preparation method according to claim 5, characterized in that: The alcohol solvent includes at least one of methanol and ethanol.

7. The preparation method according to claim 5, characterized in that: The solute salt of the ammonium salt solution includes at least one of NH4FSI, tetraethylammonium nitrate, ammonium fluoride and ammonium tetrafluoroborate.

8. The preparation method according to claim 7, characterized in that: The solvent of the ammonium salt solution includes at least one of sulfone compounds, amide compounds, nitrile compounds, ester compounds and ether compounds.

9. The preparation method according to claim 4, characterized in that: The method for preparing the solid electrolyte membrane comprises the following steps: The solid electrolyte and the binder are mixed and dissolved and then coated on a substrate to form a stability film, and the stability film is dried to obtain the solid electrolyte membrane.

10. The preparation method according to claim 9, characterized in that: The binder includes at least one of a water-based binder and an oil-based binder.

11. The preparation method according to claim 10, characterized in that: The aqueous binder includes at least one of polyacrylic acid, lithium polyacrylate, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, sodium carboxymethyl cellulose and styrene-butadiene rubber.

12. The preparation method according to claim 4, characterized in that: The solid electrolyte membrane is transferred by a double roller machine.

13. The preparation method according to claim 12, characterized in that: The double roller machine performs the transfer at a pressure of 0.01 MPa to 1 MPa and a temperature of 40° C. to 100° C.

14. A lithium ion battery, characterized in that: A surface-modified silicon negative electrode sheet comprising any one of claims 1 to 3.

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