Lithium ion battery negative plate containing silicon-carbon coating and lithium ion battery

Abstract

The invention discloses a silicon-carbon coating-containing lithium ion battery negative electrode plate and a lithium ion battery, the negative electrode plate comprises a metal current collector, first silicon-containing negative electrode active layers are coated on the nightside and the sunny side of the metal current collector, and second graphite negative electrode active layers are coated on the surfaces of the first silicon-containing negative electrode active layers; the material of the first silicon-containing negative electrode active layer comprises negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene and a binder; the mass ratio of the negative electrode graphite to the silicon oxide to the SWCNT to the conductive carbon black to the graphene to CMC to SBR is (96.8-97.8): (0.03-0.08): (0.001-0.006): (0.3-1): (0.001-0.005): (0.8-1.6): (1-2); the second graphite negative electrode active layer comprises negative electrode graphite, conductive carbon black and a binder, and the mass ratio of the negative electrode graphite to the conductive carbon black to the CMC to the SBR is (96.8-97.8): (0.3-1): (0.8-1.6): (1-2). The composite material has the characteristics of low volume expansion rate, high cycling stability and excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of ion batteries, and in particular to a lithium ion battery negative electrode sheet containing a silicon-carbon coating and a lithium ion battery. Background Art

[0002] With the development of the new energy industry, lithium-ion batteries have higher and higher requirements for energy density. How to make full use of its space within a limited volume to obtain a larger capacity while ensuring its rate performance and cycle performance has become the focus and difficulty of the industry's development. At present, commercial lithium-ion batteries mainly use graphite carbon materials as negative electrode active materials, but due to the low specific capacity of carbon negative electrode materials (372mah / g), it is difficult to meet the high power and high capacity requirements of lithium-ion batteries.

[0003] Compared with graphite negative electrode, silicon-carbon negative electrode has the characteristics of high theoretical specific capacity (theoretical capacity can be as high as 4200mah / g), and has advantages in energy density. However, silicon-carbon negative electrode material has the characteristics of large volume effect change: when charging, lithium ions embedded in silicon crystals will cause serious expansion (expansion rate can reach 300%, while carbon material is only 16%); when discharging, lithium ions will escape from silicon crystals and cause material contraction. This continuous charging and discharging process will lead to repeated generation of SEI film. As the cycle progresses, the volume collapses and pulverizes severely, resulting in low initial coulomb efficiency and affecting the cycle performance of the battery, which directly limits its promotion and application. Summary of the invention

[0004] The purpose of the present invention is to provide a lithium ion battery negative electrode sheet containing silicon-carbon coating and a lithium ion battery, which have the characteristics of low volume expansion rate, high cycle stability and excellent electrochemical performance.

[0005] The present invention can be implemented by the following technical solutions:

[0006] The present invention discloses a lithium-ion battery negative electrode sheet containing silicon-carbon coating, comprising a metal current collector, characterized in that: the negative surface and the positive surface of the metal current collector are coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer;

[0007] The materials of the first silicon-containing negative electrode active layer include negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the mass ratio of negative electrode graphite: silicon oxide: SWCNT: conductive carbon black: graphene: CMC: SBR is 96.8-97.8: 0.03-0.08: 0.001-0.006: 0.3-1: 0.001-0.005: 0.8-1.6: 1-2;

[0008] The materials of the second graphite negative electrode active layer include negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 96.8-97.8: 0.3-1: 0.8-1.6: 1-2.

[0009] Furthermore, in the first silicon-containing negative electrode active layer, the silicon-carbon composite slurry is prepared by the following method:

[0010] S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 20-40 Hz, rotating at 20-40 Hz, stirring for 25-35 min, and mixing them evenly to obtain mother dispersion;

[0011] S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 20-40 Hz, rotating at 20-40 Hz, stirring for 25-35 min, and mixing them evenly to obtain a silicon-containing dispersion;

[0012] S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

[0013] Further, in the second graphite negative electrode active layer, the graphite negative electrode slurry is prepared by the following method:

[0014] S20, preparation of graphite composite material: mixing and stirring negative electrode graphite, CMC and conductive carbon black, revolving at 20-40 Hz, rotating at 0 Hz, and stirring for 25-35 min to uniformly mix and obtain a composite material;

[0015] S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 20-40 Hz, rotating at 0 Hz, stirring for 70-90 min, and mixing them evenly to obtain mother dispersion;

[0016] S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

[0017] Furthermore, the negative electrode sheet is prepared by the following method:

[0018] S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector.

[0019] S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

[0020] Furthermore, the lithium-ion battery is prepared by the following method:

[0021] S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain positive electrode sheets and negative electrode sheets;

[0022] S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet;

[0023] S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery;

[0024] S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

[0025] Furthermore, the coating thickness of the first silicon-containing negative electrode active layer is 15 μm to 20 μm, and the double-sided surface density is 13 g / ㎡ to 18 g / ㎡.

[0026] Furthermore, the silicon oxide is silicon monoxide and / or silicon dioxide.

[0027] Furthermore, the SWCNT is a quasi-metallic nanotube and / or a pure metallic nanotube.

[0028] Furthermore, the graphene is powdered graphene and / or flake graphene.

[0029] Another aspect of the present invention is to protect a lithium-ion battery, which includes the negative electrode sheet.

[0030] The present invention provides a lithium ion battery negative electrode sheet containing a silicon-carbon coating and a lithium ion battery, which have the following beneficial effects:

[0031] The lithium ion battery negative electrode sheet of the present invention uses SWCNT and graphene to coat silicon oxide, improves the conductivity of silicon oxide, reduces the cycle expansion coefficient of silicon negative electrode materials, and increases the cycle life of lithium ion batteries. The structures of SWCNT and graphene are very stable, and the connections between the internal carbon atoms are very flexible. When an external force is applied, the carbon atom plane will bend and deform, so that the carbon atoms do not have to rearrange to adapt to the external force, thereby maintaining a stable structure, effectively alleviating the volume effect of silicon materials during charging and discharging, and maintaining a good three-dimensional structure and conductive network. At the same time, when the silicon-carbon coated composite negative electrode sheet is charged for the first time, the lithium ions in the positive electrode active material react with the second graphite negative electrode active layer on the outside of the composite negative electrode sheet to form a stable SEI film after being deintercalated, thereby reducing the reaction between the silicon-based active material of the inner first silicon-containing negative electrode active layer and the positive electrode active material, effectively avoiding a large amount of lithium ions being consumed by the silicon-based material, thereby achieving the effect of improving the energy density of the lithium battery and the first coulomb efficiency; at the same time, it can buffer the volume expansion of the inner silicon-based active material, thereby effectively solving the problem of the silicon-based active material easily falling off the current collector due to the volume expansion effect, thereby extending the cycle life of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic structural diagram of a negative electrode sheet of a lithium-ion battery containing a silicon-carbon coating according to the present invention;

[0033] Figure 2-3 The box plot fitting process and results of the first charging and discharging efficiency of different embodiments are shown;

[0034] Figure 4-5 Box plot fitting process and structure of energy density for different embodiments. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0036] like Figure 1As shown, the present invention discloses a negative electrode sheet of a lithium-ion battery containing a silicon-carbon coating, comprising a metal current collector, characterized in that: the negative side and the positive side of the metal current collector are coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer; the material of the first silicon-containing negative electrode active layer comprises negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the negative electrode graphite: silicon oxide: SWCNT: conductive carbon black : The mass ratio of graphene: CMC: SBR is 96.8-97.8: 0.03-0.08: 0.001-0.006: 0.3-1: 0.001-0.005: 0.8-1.6: 1-2; the materials of the second graphite negative electrode active layer include negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 96.8-97.8: 0.3-1: 0.8-1.6: 1-2.

[0037] Furthermore, in the first silicon-containing negative electrode active layer, the silicon-carbon composite slurry is prepared by the following method:

[0038] S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 20-40 Hz, rotating at 20-40 Hz, stirring for 25-35 min, and mixing them evenly to obtain mother dispersion;

[0039] S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 20-40 Hz, rotating at 20-40 Hz, stirring for 25-35 min, and mixing them evenly to obtain a silicon-containing dispersion;

[0040] S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

[0041] Further, in the second graphite negative electrode active layer, the graphite negative electrode slurry is prepared by the following method:

[0042] S20, preparation of graphite composite material: mixing and stirring negative electrode graphite, CMC and conductive carbon black, revolving at 20-40 Hz, rotating at 0 Hz, and stirring for 25-35 min to uniformly mix and obtain a composite material;

[0043] S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 20-40 Hz, rotating at 0 Hz, stirring for 70-90 min, and mixing them evenly to obtain mother dispersion;

[0044] S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

[0045] Furthermore, the negative electrode sheet is prepared by the following method:

[0046] S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector.

[0047] S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

[0048] Furthermore, the lithium-ion battery is prepared by the following method:

[0049] S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain positive electrode sheets and negative electrode sheets;

[0050] S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet;

[0051] S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery;

[0052] S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

[0053] Furthermore, the coating thickness of the first silicon-containing negative electrode active layer is 15 μm to 20 μm, and the double-sided surface density is 13 g / ㎡ to 18 g / ㎡.

[0054] Furthermore, the silicon oxide is silicon monoxide and / or silicon dioxide.

[0055] Furthermore, the SWCNT is a quasi-metallic nanotube and / or a pure metallic nanotube.

[0056] Furthermore, the graphene is powdered graphene and / or flake graphene.

[0057] Example 1

[0058] The present embodiment relates to a negative electrode sheet of a lithium-ion battery containing a silicon-carbon coating, comprising a metal current collector, characterized in that: the negative side and the positive side of the metal current collector are coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer; wherein the material of the first silicon-containing negative electrode active layer comprises negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the mass ratio of negative electrode graphite: silicon oxide: SWCNT: conductive carbon black: graphene: CMC: SBR is 97.8: 0.05: 0.001: 1: 0.003: 0.8: 2; the material of the second graphite negative electrode active layer comprises negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 97.3: 0.3: 1.6: 1.5.

[0059] In this embodiment, further, the coating thickness of the first silicon-containing negative electrode active layer is 20 μm, and the double-sided surface density is 15 g / ㎡; the silicon oxide is silicon monoxide and silicon dioxide; the SWCNT is a quasi-metallic nanotube and a pure metallic nanotube; the graphene is powdered graphene and flaky graphene.

[0060] In the first silicon-containing negative electrode active layer of this embodiment, the silicon-carbon composite slurry is prepared by the following method:

[0061] S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 40 Hz and rotating at 30 Hz, stirring for 25 min to mix them evenly to obtain mother dispersion;

[0062] S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 40 Hz, rotating at 30 Hz, stirring for 25 min, and mixing the mixture evenly to obtain a silicon-containing dispersion;

[0063] S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

[0064] In the second graphite negative electrode active layer of this embodiment, the graphite negative electrode slurry is prepared by the following method:

[0065] S20, preparation of graphite composite material: negative electrode graphite, CMC, and conductive carbon black are mixed and stirred, and the mixture is rotated at 40 Hz and 0 Hz, and stirred for 30 min to obtain a composite material;

[0066] S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 40 Hz, rotating at 0 Hz, stirring for 80 min, and mixing them evenly to obtain mother dispersion;

[0067] S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

[0068] In this embodiment, the negative electrode sheet is prepared by the following method:

[0069] S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector.

[0070] S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

[0071] The lithium ion battery of this embodiment is prepared by the following method:

[0072] S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain positive electrode sheets and negative electrode sheets;

[0073] S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet;

[0074] S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery;

[0075] S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

[0076] Example 2

[0077] The present embodiment relates to a negative electrode sheet of a lithium-ion battery containing a silicon-carbon coating, comprising a metal current collector, characterized in that: the negative side and the positive side of the metal current collector are both coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer; wherein the material of the first silicon-containing negative electrode active layer comprises negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the mass ratio of negative electrode graphite: silicon oxide: SWCNT: conductive carbon black: graphene: CMC: SBR is 97.3: 0.03: 0.006: 0.6: 0.001: 1.6: 1.5; the material of the second graphite negative electrode active layer comprises negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 96.8: 1: 1.2: 1.

[0078] In this embodiment, further, the coating thickness of the first silicon-containing negative electrode active layer is 17 μm, and the double-sided surface density is 13 g / ㎡; the silicon oxide is silicon monoxide; the SWCNT is a pure metallic nanotube; and the graphene is powdered graphene.

[0079] In the first silicon-containing negative electrode active layer of this embodiment, the silicon-carbon composite slurry is prepared by the following method:

[0080] S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 30 Hz, rotating at 20 Hz, stirring for 35 min to mix them evenly to obtain mother dispersion;

[0081] S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 30 Hz, rotating at 20 Hz, stirring for 35 min, and mixing them evenly to obtain a silicon-containing dispersion;

[0082] S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

[0083] In the second graphite negative electrode active layer of this embodiment, the graphite negative electrode slurry is prepared by the following method:

[0084] S20, preparation of graphite composite material: negative electrode graphite, CMC, and conductive carbon black are mixed and stirred, and the mixture is rotated at 30 Hz and 0 Hz, and stirred for 25 min to obtain a composite material.

[0085] S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 30 Hz, rotating at 0 Hz, stirring for 70 min, and mixing them evenly to obtain mother dispersion;

[0086] S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

[0087] In this embodiment, the negative electrode sheet is prepared by the following method:

[0088] S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector.

[0089] S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

[0090] The lithium ion battery of this embodiment is prepared by the following method:

[0091] S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain positive electrode sheets and negative electrode sheets;

[0092] S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet;

[0093] S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery;

[0094] S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

[0095] Example 3

[0096] The present embodiment relates to a negative electrode sheet of a lithium-ion battery containing a silicon-carbon coating, comprising a metal current collector, characterized in that: the negative side and the positive side of the metal current collector are coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer; wherein the material of the first silicon-containing negative electrode active layer comprises negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the mass ratio of negative electrode graphite: silicon oxide: SWCNT: conductive carbon black: graphene: CMC: SBR is 96.8: 0.08: 0.003: 0.3: 0.005: 1.2: 1; the material of the second graphite negative electrode active layer comprises negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 97.8: 0.5: 0.8: 1-2.

[0097] In this embodiment, further, the coating thickness of the first silicon-containing negative electrode active layer is 15 μm, and the double-sided surface density is 18 g / ㎡; the silicon oxide is silicon monoxide and silicon dioxide; the SWCNT is a quasi-metallic nanotube and a pure metallic nanotube; the graphene is powdered graphene and flaky graphene.

[0098] In the first silicon-containing negative electrode active layer of this embodiment, the silicon-carbon composite slurry is prepared by the following method:

[0099] S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 20 Hz and rotating at 40 Hz, stirring for 30 min to mix them evenly to obtain mother dispersion;

[0100] S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 20 Hz, rotating at 40 Hz, stirring for 30 min to mix evenly to obtain silicon-containing dispersion;

[0101] S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

[0102] In the second graphite negative electrode active layer of this embodiment, the graphite negative electrode slurry is prepared by the following method:

[0103] S20, preparation of graphite composite material: negative electrode graphite, CMC, and conductive carbon black are mixed and stirred, and the mixture is rotated at 20 Hz and 0 Hz, and stirred for 35 min to obtain a composite material.

[0104] S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 20 Hz, rotating at 0 Hz, stirring for 90 min, and mixing them evenly to obtain mother dispersion;

[0105] S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

[0106] In this embodiment, the negative electrode sheet is prepared by the following method:

[0107] S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector.

[0108] S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

[0109] The lithium ion battery of this embodiment is prepared by the following method:

[0110] S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain positive electrode sheets and negative electrode sheets;

[0111] S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet;

[0112] S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery;

[0113] S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

[0114] Example 4

[0115] The present embodiment relates to a negative electrode sheet of a lithium-ion battery containing a silicon-carbon coating, comprising a metal current collector, characterized in that: the negative side and the positive side of the metal current collector are coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer; wherein the material of the first silicon-containing negative electrode active layer comprises negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the mass ratio of negative electrode graphite: silicon oxide: SWCNT: conductive carbon black: graphene: CMC: SBR is 97: 0.05: 0.004: 0.8: 0.004: 1.4: 1.3; the material of the second graphite negative electrode active layer comprises negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 97.2: 0.8: 1.3: 1.2.

[0116] In this embodiment, further, the coating thickness of the first silicon-containing negative electrode active layer is 16 μm, and the double-sided surface density is 17 g / ㎡; the silicon oxide is silicon monoxide and silicon dioxide; the SWCNT is a quasi-metallic nanotube and a pure metallic nanotube; the graphene is powdered graphene and flaky graphene.

[0117] In the first silicon-containing negative electrode active layer of this embodiment, the silicon-carbon composite slurry is prepared by the following method:

[0118] S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 25 Hz and rotating at 35 Hz, stirring for 28 min to mix them evenly to obtain mother dispersion;

[0119] S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 25 Hz, rotating at 35 Hz, stirring for 27 min, and mixing the mixture evenly to obtain a silicon-containing dispersion;

[0120] S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

[0121] In the second graphite negative electrode active layer of this embodiment, the graphite negative electrode slurry is prepared by the following method:

[0122] S20, preparation of graphite composite material: negative electrode graphite, CMC and conductive carbon black are mixed and stirred, and the mixture is rotated at 25 Hz and 0 Hz, and stirred for 28 min to obtain a composite material.

[0123] S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 28 Hz, rotating at 0 Hz, stirring for 75 min, and mixing them evenly to obtain mother dispersion;

[0124] S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

[0125] In this embodiment, the negative electrode sheet is prepared by the following method:

[0126] S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector.

[0127] S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

[0128] The lithium ion battery of this embodiment is prepared by the following method:

[0129] S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain positive electrode sheets and negative electrode sheets;

[0130] S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet;

[0131] S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery;

[0132] S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

[0133] Example 5

[0134] The present embodiment relates to a negative electrode sheet of a lithium-ion battery containing a silicon-carbon coating, comprising a metal current collector, characterized in that: the negative side and the positive side of the metal current collector are coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer; wherein the material of the first silicon-containing negative electrode active layer comprises negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the mass ratio of negative electrode graphite: silicon oxide: SWCNT: conductive carbon black: graphene: CMC: SBR is 97.8:0.07:0.003:0.5:0.002:0.9:1.2; the material of the second graphite negative electrode active layer comprises negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 96.8:0.4:1.6:2.

[0135] In this embodiment, further, the coating thickness of the first silicon-containing negative electrode active layer is 18 μm, and the double-sided surface density is 14 g / ㎡; the silicon oxide is silicon monoxide and silicon dioxide; the SWCNT is a quasi-metallic nanotube and a pure metallic nanotube; the graphene is powdered graphene and flaky graphene.

[0136] In the first silicon-containing negative electrode active layer of this embodiment, the silicon-carbon composite slurry is prepared by the following method:

[0137] S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 40 Hz, rotating at 20 Hz, stirring for 35 min to mix them evenly to obtain mother dispersion;

[0138] S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 30 Hz, rotating at 30 Hz, stirring for 30 min to mix evenly to obtain silicon-containing dispersion;

[0139] S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

[0140] In the second graphite negative electrode active layer of this embodiment, the graphite negative electrode slurry is prepared by the following method:

[0141] S20, preparation of graphite composite material: negative electrode graphite, CMC, and conductive carbon black are mixed and stirred, and the mixture is rotated at 30 Hz and 0 Hz, and stirred for 25-35 min to obtain a composite material;

[0142] S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 30 Hz, rotating at 0 Hz, stirring for 70-90 min, and mixing the mixture evenly to obtain mother dispersion;

[0143] S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

[0144] In this embodiment, the negative electrode sheet is prepared by the following method:

[0145] S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector.

[0146] S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

[0147] The lithium ion battery of this embodiment is prepared by the following method:

[0148] S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain positive electrode sheets and negative electrode sheets;

[0149] S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet;

[0150] S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery;

[0151] S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

[0152] Application Example 1

[0153] A 496292H-5500mAh soft-pack polymer lithium-ion battery was prepared by the method of Example 1, and subsequent performance tests were performed.

[0154] Comparative Example 1

[0155] The main difference between Comparative Example 1 and Application Example 1 is that the first silicon-containing negative electrode active layer and the second graphite negative electrode active layer are not provided in the silicon-containing composite active material of the negative electrode sheet. Instead, a silicon-carbon composite graphite slurry obtained by mixing silicon oxide + graphite composite active materials in proportion is directly applied on the metal current collector to prepare a 496292H-5500mAh soft-pack polymer lithium-ion battery for subsequent performance testing.

[0156] Comparative Example 2

[0157] The main difference between Comparative Example 2 and Application Example 1 is that silicon oxide is not added to the active material of the negative electrode sheet, and its mass proportion is replaced by negative electrode graphite, and a 496292H-5500mAh soft-pack polymer lithium-ion battery is prepared for subsequent performance testing.

[0158] In order to verify the technical effect of the present invention, electrical performance tests were performed on Application Example 1, Comparative Example 1, and Application Example 2, and the test results are as follows:

[0159] Table 1 Performance test results

[0160]

[0161] The following conclusions were drawn from the battery performance tests of Application Example 1, Comparative Example 1 and Comparative Example 2:

[0162] 1. First efficiency:

[0163] By comparing the performance test results in Table 1, it can be concluded that the first efficiency of Application Example 1 is about 92-93%, and the first efficiency of Comparative Example 1 and Comparative Example 2 is about 88-89%. The first efficiency of the lithium-ion battery containing the silicon-carbon coated composite negative electrode sheet (Application Example 1) is higher than the lithium-ion battery containing the silicon-carbon but uncoated composite negative electrode sheet and the lithium-ion battery without the silicon-carbon negative electrode sheet (Comparative Example 1 and Comparative Example 2) (see the box line comparison of the first efficiency Figure 2-3 ). It is explained that in a lithium-ion battery in which a first silicon-carbon negative electrode active layer and a second graphite negative electrode active layer are arranged in the negative electrode sheet, lithium ions in the positive electrode active material are preferentially reacted with the second graphite negative electrode active layer to form a stable SEI film after being deintercalated during the first charge, so that in the subsequent charge and discharge process, the silicon-based active material of the silicon-carbon negative electrode active layer is effectively avoided from contacting and reacting with lithium ions, resulting in the SEI film being in a dynamic process of continuous fragmentation and repair, and continuously consuming the active lithium ions of the positive electrode material, thereby achieving the effect of improving the energy density and initial efficiency of the lithium battery.

[0164] 2. Energy density:

[0165] By comparing the performance test results in Table 1, it can be concluded that the energy density of Application Example 1 and Comparative Example 1 is about 765Wh / L-770Wh / L, and the energy density of Comparative Example 2 is about 755Wh / L-760Wh / L. The energy density of the lithium-ion battery containing the silicon-carbon coated composite negative electrode sheet and the lithium-ion battery containing the silicon-carbon but uncoated composite negative electrode sheet (Application Example 1 and Comparative Example 1) is higher than the lithium-ion battery without the silicon-carbon negative electrode sheet (Comparative Example 2) (box line comparison of energy density see Figure 4-5 ). This shows that adding silicon-carbon active materials to lithium ions, the silicon oxide material has a higher specific capacity (600mAh / g), which can be neutralized with the specific capacity of carbon negative electrode materials (372mAh / g), and can increase the content of positive electrode active materials in the limited volume space of the battery, which can greatly improve the capacity of the single cell and achieve the purpose of improving the energy density of lithium batteries.

[0166] 3. Cycle performance:

[0167] The conclusions of the battery charge and discharge cycle performance test cycle and volume change rate are compared through the performance test results in Table 1: the lithium ion battery containing the silicon-carbon coating composite negative electrode sheet and the lithium ion battery without the silicon-carbon negative electrode sheet (Application Example 1 and Comparative Example 2) are better than the lithium ion battery containing the silicon-carbon but without the coating composite negative electrode sheet (Comparative Example 1). It shows that in the lithium battery containing the silicon-carbon composite negative electrode sheet, the silicon-carbon active layer composite material is coated with silicon oxide by SWCNT and graphene, which can not only improve the conductivity of silicon oxide, but also effectively alleviate the large volume effect caused by the repeated generation of unstable SEI film by silicon-carbon materials during the charge and discharge process, effectively solve the problem that the silicon-based active material is easy to fall off from the current collector due to the volume expansion effect, and extend the cycle life of the lithium ion battery.

[0168] In summary, the silicon-carbon coating-containing composite negative electrode sheet and lithium-ion battery of the present invention have the characteristics of high initial efficiency, high energy density, small volume effect and good cycle performance.

[0169] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A lithium-ion battery negative electrode sheet containing a silicon-carbon coating, comprising a metal current collector, characterized in that: The negative side and the positive side of the metal current collector are both coated with a first silicon-containing negative electrode active layer, and the surface of the first silicon-containing negative electrode active material layer is coated with a second graphite negative electrode active layer; The materials of the first silicon-containing negative electrode active layer include negative electrode graphite, silicon oxide, SWCNT, conductive carbon black, graphene, and a binder, and the mass ratio of negative electrode graphite: silicon oxide: SWCNT: conductive carbon black: graphene: CMC: SBR is 96.8-97.8: 0.03-0.08: 0.001-0.006: 0.3-1: 0.001-0.005: 0.8-1.6: 1-2; The materials of the second graphite negative electrode active layer include negative electrode graphite, conductive carbon black, and a binder, and the mass ratio of negative electrode graphite: conductive carbon black: CMC: SBR is 96.8-97.8: 0.3-1: 0.8-1.6: 1-2.

2. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 1, characterized in that: In the first silicon-containing negative electrode active layer, the silicon-carbon composite slurry is prepared by the following method: S10, preparation of mother dispersion: dispersing SWCNT, graphene and conductive carbon black in CMC aqueous solution, revolving at 20-40 Hz, rotating at 20-40 Hz, stirring for 25-35 min, and mixing them evenly to obtain mother dispersion; S11, preparation of silicon-containing dispersion: adding silicon oxide to the dispersion obtained in S10, revolving at 20-40 Hz, rotating at 20-40 Hz, stirring for 25-35 min, and mixing them evenly to obtain a silicon-containing dispersion; S12, preparation of silicon-carbon composite slurry: evenly disperse the negative electrode graphite in the SBR aqueous solution, add the silicon-containing dispersion obtained in S11, adjust the viscosity, and mix them evenly to obtain the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer.

3. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 1, characterized in that: In the second graphite negative electrode active layer, the graphite negative electrode slurry is prepared by the following method: S20, preparation of graphite composite material: mixing and stirring negative electrode graphite, CMC and conductive carbon black, revolving at 20-40 Hz, rotating at 0 Hz, and stirring for 25-35 min to uniformly mix and obtain a composite material; S21, preparation of mother dispersion: adding deionized water to the composite material obtained in S20, revolving at 20-40 Hz, rotating at 0 Hz, stirring for 70-90 min, and mixing them evenly to obtain mother dispersion; S22. Preparation of graphite negative electrode slurry: adding the SBR aqueous solution to the mother dispersion obtained in S21, adjusting the viscosity thereof, and mixing them evenly to obtain the graphite negative electrode slurry of the second graphite negative electrode active layer.

4. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 1, characterized in that: The negative electrode sheet is prepared by the following method: S30, preparation of the pole piece of the first silicon-containing negative electrode active layer: coating the silicon-carbon composite slurry of the first silicon-containing negative electrode active layer obtained in S12 on the metal current collector according to the designed size, and baking it in a coating oven to obtain the first silicon-containing negative electrode active layer on the surface of the metal current collector. S31. Preparation of a composite electrode sheet for a second graphite negative electrode active layer: coating the graphite negative electrode slurry for the second graphite negative electrode active layer obtained in S22 on the electrode sheet surface of the first silicon-containing negative electrode active layer obtained in S30 according to the designed size, and baking in a coating oven to obtain a negative electrode sheet for the second graphite negative electrode active layer.

5. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 1, characterized in that: The lithium-ion battery is prepared by the following method: S40, electrode sheet production: coating the positive electrode and the negative electrode respectively and slitting them according to the designed size to obtain the positive electrode sheet and the negative electrode sheet; S50, winding assembly: taking the positive electrode sheet and the negative electrode sheet obtained in step S40 and winding them manually or by machine to obtain a bare cell with a separator separating the positive electrode sheet and the negative electrode sheet; S60, liquid injection and formation: placing the bare battery cell obtained in step S50 into a housing, injecting electrolyte, packaging, and then forming in a charge and discharge cabinet to obtain a lithium-ion battery; S70, secondary sealing and capacity division: after the gas generated by the lithium-ion battery formed by the liquid injection in step S60 is discharged, secondary sealing is performed in a charge and discharge cabinet to divide the capacity to obtain a lithium-ion battery that meets the capacity requirements.

6. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 1, characterized in that: The coating thickness of the first silicon-containing negative electrode active layer is 15 μm to 20 μm, and the double-sided surface density is 13 g / ㎡ to 18 g / ㎡.

7. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 6, characterized in that: The silicon oxide is silicon monoxide and / or silicon dioxide.

8. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 1, characterized in that: The SWCNT is a semi-metallic nanotube and / or a pure metallic nanotube.

9. The negative electrode sheet for lithium-ion battery containing silicon-carbon coating according to claim 8, characterized in that: The graphene is powdered graphene and / or flake graphene.

10. A lithium ion battery, characterized in that: The invention comprises the negative electrode sheet as described in any one of claims 1 to 9.

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