Negative electrode sheet and battery

Abstract

The present application relates to the field of batteries, in particular to a negative electrode sheet and a battery comprising the same. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating layer on at least one side surface of the negative electrode current collector, the negative electrode active coating layer comprising a negative electrode active material and a conductive agent, the negative electrode active material comprising a silicon-based material, and the conductive agent comprising a conductive material having a two-dimensional layered structure, the conductive material having a two-dimensional layered structure having an interlayer spacing D and a peeling energy N, and satisfying 0.4≤D / N≤10. The negative electrode sheet of the present application comprises a conductive agent having a two-dimensional layered structure and a silicon-based material, and can significantly improve the energy density and cycle life of the battery.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a negative electrode sheet and a battery comprising the negative electrode sheet. Background Art

[0002] The rapid development of portable electronics and electric vehicles has led to an increasing demand for high energy density and long lifespan in lithium-ion batteries. Conventional graphite anode materials are no longer able to meet these high-performance requirements, prompting researchers to search for novel anode materials. Silicon-based anode materials, with their high theoretical specific capacity, low discharge plateau, and environmentally friendly properties, are considered one of the most promising anode materials for next-generation lithium-ion batteries.

[0003] However, silicon-based negative electrode materials undergo huge volume expansion during the charge and discharge process, leading to electrode pulverization; in addition, the low conductivity and slow Li+ diffusion kinetics of silicon-based negative electrode materials may lead to huge local mechanical stress, causing the silicon-based negative electrode materials to fall off from the current collector and lose electrical contact, thereby leading to an increase in cracks.

[0004] Therefore, it is necessary to find ways to improve the above-mentioned problems of silicon-based negative electrode materials and invent a battery with both high energy density and long service life. Summary of the Invention

[0005] The present invention aims to overcome the aforementioned problems of the prior art and provides a negative electrode sheet and a battery comprising the same. The negative electrode sheet of the present invention comprises a conductive agent with a two-dimensional layered structure and a silicon-based material, which can significantly improve the cycle life and energy density of the battery.

[0006] A first aspect of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active coating on at least one side of the negative electrode current collector, wherein the negative electrode active coating comprises a negative electrode active material and a conductive agent, wherein the negative electrode active material comprises a silicon-based material, and the conductive agent comprises a conductive material having a two-dimensional layered structure, wherein the interlayer spacing of the conductive material having the two-dimensional layered structure is D, and the stripping energy of the conductive material having the two-dimensional layered structure is N, satisfying 0.4≤D / N≤10.

[0007] A second aspect of the present invention provides a battery, comprising the negative electrode sheet according to the first aspect of the present invention.

[0008] A third aspect of the present invention provides a battery, comprising an electrolyte and a negative electrode sheet, wherein the electrolyte comprises lithium hexafluorophosphate, the negative electrode sheet comprises a silicon-based material, and the content of lithium hexafluorophosphate in the electrolyte x1, the mass m2 of the silicon-based material in the negative electrode sheet, and the capacity C of the battery satisfy: 0.1≤a≤0.2, 0.4≤b≤0.8.

[0009] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0010] (1) The negative electrode sheet of the present invention comprises a silicon-based material and a conductive agent having a two-dimensional layered structure, which can significantly improve the conductivity and lithium ion diffusion rate, thereby increasing the energy density of the battery;

[0011] (2) The negative electrode sheet of the present invention comprises a silicon-based material and a conductive agent having a two-dimensional layered structure. The two-dimensional layered structure of the conductive agent provides a confined space, which can inhibit the volume expansion of the silicon-based material during the charge and discharge process, reduce electrode breakage and the loss of electrical contact between the silicon-based material and the current collector, thereby improving the cycle life of the battery.

[0012] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. 1 is a schematic cross-sectional view of a negative electrode sheet in an embodiment of the present invention.

[0014] Figure 2 Shown is a schematic diagram of the structure of the conductive agent in the negative electrode sheet of the present invention.

[0015] Figure 3 Shown is the XRD diffraction pattern of the negative electrode sheet in one example of the present invention.

[0016] Figure 4 Shown are SEM images of the negative electrode sheets in Examples 1-3 and Comparative Example 1 (before cycling).

[0017] Figure 5 Shown are SEM images of the negative electrode sheets of the batteries in Examples 1-3 and Comparative Example 1 after 500 cycles.

[0018] Figure 6 Shown are the thermogravimetric curves of the negative electrode sheets in Examples 1-3. DETAILED DESCRIPTION

[0019] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0020] The first aspect of the present invention provides a negative electrode sheet, which may include a negative electrode current collector and a negative electrode active coating on at least one side of the negative electrode current collector. Figure 1 The figure shows a cross-sectional schematic diagram of a negative electrode sheet in an embodiment of the present invention, wherein Figure 1 (a) The negative electrode active coating is set on one side; Figure 1 (b) and Figure 1 (c) is the case where the negative electrode active coating is installed on both sides. Figure 1 In (a), the negative electrode sheet includes a negative electrode current collector 1 and a negative electrode active coating 2 on one side of the negative electrode current collector 1; Figure 1 (b) and Figure 1 In (c), the negative electrode sheet includes a negative electrode current collector 1 and a negative electrode active coating 2 on both sides of the negative electrode current collector 1.

[0021] The negative electrode active coating may include a negative electrode active material and a conductive agent, the negative electrode active material may include a silicon-based material, the conductive agent may include a conductive material having a two-dimensional layered structure, the interlayer spacing of the conductive material having a two-dimensional layered structure is D (in nm), and the stripping energy of the conductive material having a two-dimensional layered structure is N (in eV / unit cel), satisfying 0.4≤D / N≤10 (in unit cel·nm / eV), for example, D / N is equal to 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0022] At present, in order to improve the energy density of lithium-ion batteries, the most commonly used means is to use silicon-based materials with higher theoretical specific capacity as negative electrode materials. However, silicon-based materials will produce a large volume expansion during the charge and discharge cycle, resulting in the problem of structural rupture of the silicon-based material itself and the problem of silicon-based materials falling off from the current collector, thereby reducing the cycle life and safety of the battery; In addition, the conductivity of the silicon-based material itself is poorer than that of the carbon material, which is not conducive to the effective release of the battery capacity (especially under high rate conditions). The inventors of the present invention have found that when a conductive material with a two-dimensional layered structure is used as a conductive agent, the conductive agent with the two-dimensional layered structure has good conductivity, mechanical strength and a stable layered structure, which can significantly improve the conductivity of the silicon-based material, and its two-dimensional layered structure has a confining effect, which can inhibit the volume expansion of the silicon-based material to a certain extent, thereby improving the structural stability of the silicon-based material; and when the interlayer spacing and / or peeling energy of the two-dimensional layered structure of the conductive agent is within a specific range, it can further inhibit the volume expansion of the silicon-based material without affecting the conductive performance and stability. The inventors of the present invention further discovered that when the interlayer spacing and exfoliation energy of the two-dimensional layered structure of the conductive agent satisfy a specific relationship, the volume expansion of the silicon material can be further suppressed. The reason may be that: when the ratio of the two is small (for example, less than 0.4), no space can be provided for the silicon-based material, thereby reducing the amount of active sites; and when the ratio of the two is large (for example, greater than 10), the limiting effect on the volume expansion of the silicon-based material is small.

[0023] In one example, 1≤D / N≤4.5.

[0024] In the present invention, the interlayer spacing D of the conductive material having a two-dimensional layered structure can be obtained by a Monte Carlo (MC) simulation method, and the stripping energy N of the conductive material having a two-dimensional layered structure can be calculated by VASP software.

[0025] In the present invention, 0.2 nm ≤ D ≤ 1 nm, for example, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm or 1 nm.

[0026] In one example, 0.3 nm ≤ D ≤ 0.7 nm.

[0027] The inventors of the present invention have discovered that when D is within a specific range, the volume expansion of the silicon-based material can be further suppressed without affecting the conductive performance and stability.

[0028] In the present invention, 0.1 eV / unit cell ≤ N ≤ 0.8 eV / unit cell, for example, 0.1 eV / unit cell, 0.2 eV / unit cell, 0.3 eV / unit cell, 0.4 eV / unit cell, 0.5 eV / unit cell, 0.6 eV / unit cell, 0.7 eV / unit cell or 0.8 eV / unit cell.

[0029] In one example, 0.15 eV / unit cell ≤ N ≤ 0.3 eV / unit cell.

[0030] The inventors of the present invention have found that when N is within a specific range, the volume expansion of the silicon-based material can be further suppressed without affecting the electrical conductivity and stability.

[0031] In the present invention, the silicon-based material may include at least one of silicon, silicon carbide, silicon oxide (SiO

[0037] ,

[0036] , ,

[0035] , , , where 0 < x < 2) and silicon alloy.

[0032] In the present invention, the "silicon carbide" has its conventional meaning in the art, and generally, the "silicon carbide" refers to a composite material of silicon and carbon.

[0033] In one example, the silicon-based material includes nano-silicon.

[0034] In the present invention, the mass of the silicon-based material may account for 0.01% - 100% of the mass of the negative electrode active material, for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0035] Due to the large volume expansion of the silicon negative electrode, the prior art usually uses a small amount of silicon-based material in combination with a large amount of carbon-based material as the negative electrode active material, or uses the carbon-based material to modify the silicon-based material and then uses it as the negative electrode active material. The inventors of the present invention have found through extensive research that using a conductive material with a two-dimensional layered structure in combination with the silicon-based material can significantly suppress silicon expansion, thereby increasing the mass ratio of the silicon-based material in the negative electrode active material and improving the energy density of the battery.

[0036] In one example, the mass of the silicon-based material accounts for 95% - 100% of the mass of the negative electrode active material.

[0037] In the present invention, the mass of the conductive material having a two-dimensional layered structure may account for 0.01%-100% of the mass of the conductive agent, for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0038] In one example, the mass of the conductive material having a two-dimensional layered structure accounts for 95%-100% of the mass of the conductive agent.

[0039] The inventors of the present invention have discovered that when the mass of the conductive material having a two-dimensional layered structure accounts for a mass of the conductive agent within a specific range, the conductive performance can be improved and the volume expansion of the silicon-based material can be further suppressed.

[0040] In the present invention, the ratio of the mass of the silicon-based material to the mass of the conductive agent can be (0.1-10):1, for example, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1.

[0041] The inventors of the present invention have found that when the ratio of the mass of the silicon-based material to the mass of the conductive agent is within a specific range, a battery including the negative electrode sheet has a more excellent cycle life.

[0042] In one example, the ratio of the mass of the silicon-based material to the mass of the conductive agent is (0.5-3):1.

[0043] In one example, the ratio of the mass of the silicon-based material to the mass of the conductive agent is (0.8-1.4):1.

[0044] In the present invention, the negative electrode active coating layer may further include a binder, and the binder may include at least one of polyvinylidene fluoride, polyacrylic acid, and styrene-butadiene rubber.

[0045] In the present invention, based on the total weight of the negative electrode active coating, the content of the silicon-based material may be 8.19-90.45 wt % (e.g., 8.19, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 90.45 wt %), the content of the conductive agent may be 8.19-90.45 wt % (e.g., 90.45, 90, 80, 70, 60, 50, 40, 30, 20, 10 or 8.19 wt %), and the content of the binder may be 0.5-10 wt % (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 or 0.5 wt %).

[0046] In one example, based on the total weight of the negative electrode active coating, the content of the silicon-based material is 43.5-57.7 wt %, the content of the conductive agent is 41.3-54.5 wt %, and the content of the binder is 1-2 wt %.

[0047] In the present invention, the negative electrode current collector may include a negative electrode current collector commonly used in the art, such as copper foil.

[0048] The inventors of the present invention have discovered that when the thermal decomposition temperature of the negative electrode sheet is within a specific range, the negative electrode sheet is safe and stable. The reason may be that the conductive material with a two-dimensional layered structure used in the present invention will participate in the formation of the SEI film during the battery formation and cycling process, and through its own rigid structure (providing rigid support to the SEI film), thermal stability (high thermal failure temperature: 200°C-1600°C) and huge surface energy (the two-dimensional layered structure has a large bonding area with other components that form the SEI film and is firmly bonded), it increases the thermal stability of the SEI film, thereby improving the safety and stability of the negative electrode sheet.

[0049] In the present invention, the thermal decomposition temperature of the negative electrode sheet can be 200°C-1600°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C or 1600°C.

[0050] In the present invention, the thermal decomposition temperature of the negative electrode sheet can be tested by conventional methods in the art, for example, the following method can be used for testing: using a thermogravimeter with a heating rate of 10° C. / min.

[0051] In the present invention, the compaction density of the negative electrode sheet can be 0.6 g / cm 3 -1.7g / cm 3 , for example 0.6 g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm3 or 1.7 g / cm 3 .

[0052] Currently, the method used in related technologies to alleviate the volume expansion of silicon-based materials generally involves reserving space, which reduces the compaction density of the negative electrode sheet, thereby reducing the structural strength of the negative electrode sheet. The inventors of the present invention have discovered that the use of the conductive agent with a two-dimensional layered structure of the present invention can limit the expansion of silicon-based materials without reducing the compaction density of the negative electrode sheet. The inventors of the present invention have further discovered that when the compaction density of the negative electrode sheet is within a specific range, the negative electrode sheet has a higher energy density and can store more energy at the same volume, making it suitable for miniaturized applications. It has a higher structural strength, which can improve the mechanical properties, drop resistance and durability of the battery. In addition, it can also improve the irreversible expansion of the silicon-based material volume, thereby increasing the service life of the battery.

[0053] As the charge and discharge cycles progress, the volume of silicon-based materials continues to expand, accompanied by the rupture of the solid electrolyte interface (SEI) on the surface of the silicon material. This unstable SEI is repeatedly formed and accompanied by the continuous consumption of electrolyte, resulting in low coulombic efficiency. The inventors of the present invention have discovered that specific conductive agents can help form a stable solid electrolyte interface (SEI) layer that is conducive to lithium ion transport, reduce electrolyte consumption, and thus improve the coulombic efficiency of the battery.

[0054] In the present invention, the conductive agent may include at least one of a two-dimensional transition metal sulfide, a two-dimensional nitride, and a layered double hydroxide.

[0055] In the present invention, the terms "two-dimensional transition metal sulfide", "two-dimensional nitride" and "layered double hydroxide" have the conventional meanings in the art. It is generally believed that the chemical formula of the term "two-dimensional transition metal sulfide" can be written as MX2, where M represents a transition metal element, such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn or Re, and X represents a chalcogen element, such as S, Se or Te. The term "two-dimensional nitride" refers to a binary two-dimensional compound formed by nitrogen and an element with a lower electronegativity than nitrogen. The term "layered double hydroxide" refers to a special type of layered material composed of several layers with positive charges and anions in between to balance the charges.

[0056] In the present invention, the two-dimensional transition metal sulfide may include at least one of MoS2, WS2, TiS2, NbSe2, MoSe2 and MnSe2.

[0057] In one example, the two-dimensional transition metal sulfide includes MoS2.

[0058] In the present invention, the two-dimensional nitride may include at least one of boron nitride, gallium nitride and carbon nitride.

[0059] In one example, the two-dimensional nitride includes boron nitride.

[0060] In the present invention, the layered double hydroxide may include at least one of CoMo-LDH, FeCo-LDH, MgMn-LDH, ZnAl-LDH, and MgAl-LDH.

[0061] In one example, the layered double hydroxide includes CoMo-LDH.

[0062] In the present invention, the conductive agent may include two-dimensional transition metal sulfides and layered double hydroxides.

[0063] In one example, the conductive agent includes MoS2 and CoMo-LDH.

[0064] <Two-dimensional transition metal sulfides>

[0065] In the present invention, when the conductive agent includes the two-dimensional transition metal sulfide, the thermal decomposition temperature of the negative electrode sheet can be 300°C-1600°C, for example, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C or 1600°C.

[0066] The inventors of the present invention have discovered that when the conductive agent includes the two-dimensional transition metal sulfide, the conductive agent has excellent conductivity, mechanical strength and a stable layered structure, which can not only enhance the conductivity of the silicon-based material, but also improve the inhibitory effect on the volume expansion of the silicon material, thereby improving the structural stability of the silicon material; the inventors of the present invention have further discovered that when the XRD diffraction pattern of the negative electrode sheet has specific characteristic peaks and / or peak intensity ratios, the negative electrode sheet has a stable structure and can further inhibit the volume expansion of the silicon material.

[0067] In the present invention, when the conductive agent includes the two-dimensional transition metal sulfide, the XRD diffraction pattern of the negative electrode sheet has at least two characteristic peaks at 30°-40° and one characteristic peak at 55°-65°. The two characteristic peaks at 30°-40° are the first characteristic peak and the second characteristic peak (in ascending order of 2θ), and the characteristic peak at 55°-65° is the third characteristic peak.

[0068] In one example, the peak intensity of the first characteristic peak is I1, the peak intensity of the second characteristic peak is I2, and the peak intensity of the third characteristic peak is I3, satisfying 1 < I1 / I2 < 5 and 1.5 < I1 / I3 < 15.

[0069] In the present invention, when the conductive agent includes the two-dimensional transition metal sulfide, the tap density of the negative electrode sheet can be 0.7 g / cm 3 -1.7 g / cm 3 , such as 0.7 g / cm 3 , 0.8 g / cm 3 , 0.9 g / cm 3 , 1 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 or 1.7 g / cm 3 .

[0070] In the present invention, the conductive agent may include MoS2. As Figure 2 (a) shows a schematic structural diagram of MoS2.

[0071] When the conductive agent includes MoS2, in the XRD diffraction pattern of the negative electrode sheet, there are at least characteristic peaks at 27°-30°, 34°-36°, 38°-40° and 58°-60°, and 1 < I1 / I2 < 5, and 1.5 < I1 / I3 < 15. As Figure 3 (a) shows the XRD diffraction pattern of the negative electrode sheet (the conductive agent includes MoS2) in an example of the present invention. It can be seen from the figure that there are characteristic peaks at 27°-30°, 34°-36°, 38°-40° and 58°-60°, and 1 < I1 / I2 < 5, and 1.5 < I1 / I3 < 15.

[0072] The shape of the conductive agent can be granular, and the granular shape is formed by the aggregation of a plurality of sheet-like bodies. The sheet diameter of the sheet-like body can be 100 nm - 10 μm (such as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm), and the sheet thickness of the sheet-like body can be 10 nm - 500 nm (such as 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm); as Figure 4 (a) shows an SEM image of a negative electrode sheet (the conductive agent is MoS2) in an example of the present invention. It can be seen from the figure that the conductive agent has a granular shape, and the particles are formed by agglomerating several flakes, which helps to improve the conductivity.

[0073] In the present invention, the sheet diameter and sheet thickness of the sheet can be obtained by testing conventional methods in the field, such as through SEM micrographs, taking any conductive agent particle, measuring the sheet diameter and sheet thickness of at least 50 sheets constituting the conductive agent particle, and taking the average value. When the cross-sectional shape of the sheet is a regular circle, the sheet diameter of the sheet is the diameter of the circle; when the cross-sectional shape of the sheet is an irregular circle, the sheet diameter of the sheet is the equivalent diameter of the diameter of a regular circle with the same area as the irregular circle. When the thickness of a sheet of the sheet is non-uniform, the sheet thickness is the average thickness of the sheet (for example, randomly taking 10 points on the edge of the sheet, measuring the thickness at these 10 points, and taking the average value).

[0074] The inventors of the present invention have discovered that when the sheet diameter and thickness of the sheet are within specific ranges, the volume expansion of the silicon-based material can be further improved.

[0075] In the present invention, when the conductive agent includes the two-dimensional transition metal sulfide, the median particle size Dv50 of the conductive agent can be 1μm-30μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm or 30μm.

[0076] The inventors of the present invention have found that when the median particle size Dv50 of the conductive agent is within a specific range, it is beneficial to improve the structural stability of the negative electrode sheet.

[0077] In the present invention, the median particle size Dv50 of the conductive agent can be measured by conventional methods in the art, for example, by using a laser particle size analyzer.

[0078] <Two-dimensional nitrides>

[0079] In the present invention, when the conductive agent includes a two-dimensional nitride, the thermal decomposition temperature of the negative electrode sheet can be 600°C-1200°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C.

[0080] The inventors of the present invention have found that when the conductive agent includes the two-dimensional nitride and when the XRD diffraction pattern of the negative electrode sheet has specific characteristic peaks and / or peak intensity ratios, the conductive agent has excellent conductivity, mechanical strength, and a stable layered structure. It can not only enhance the conductivity of the silicon-based material but also improve the inhibition of the volume expansion of the silicon material, thereby improving the structural stability of the silicon material.

[0081] In the present invention, when the conductive agent includes a two-dimensional nitride, in the XRD diffraction pattern of the negative electrode sheet, there are characteristic peaks at least in the range of 5° - 13° and 25° - 35°. The characteristic peak in the range of 5° - 13° is the fourth characteristic peak, and the characteristic peak in the range of 25° - 35° is the fifth characteristic peak.

[0082] In one example, the peak intensity of the fourth characteristic peak is I4, and the peak intensity of the fifth characteristic peak is I5, satisfying 2 < I5 / I4 < 6.

[0083] In the present invention, when the conductive agent includes a two-dimensional nitride, the tap density of the negative electrode sheet can be 0.6 g / cm 3 -1.7 g / cm 3 , for example, 0.6 g / cm 3 , 0.7 g / cm 3 , 0.8 g / cm 3 , 0.9 g / cm 3 , 1 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 or 1.7 g / cm 3 .

[0084] In the present invention, the conductive agent may include boron nitride. As Figure 2 (b) shows the structural schematic diagram of boron nitride. <-->g / cm When the conductive agent includes boron nitride, in the XRD diffraction pattern of the negative electrode sheet, there are characteristic peaks at least in the range of 9.5° - 11° and 27° - 30°, and 2 < I5 / I4 < 6. As Figure 3 (b) shows the XRD diffraction pattern of the negative electrode sheet (the conductive agent includes boron nitride) in an example of the present invention. It can be seen from the figure that there are characteristic peaks in the range of 9.5° - 11° and 27° - 30°, and 2 < I5 / I4 < 6.

[0086] <Layered double metal hydroxide>

[0087] In the present invention, when the conductive agent includes a layered double hydroxide, the thermal decomposition temperature of the negative electrode sheet may be 200°C-600°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C or 600°C.

[0088] The inventors of the present invention have discovered that when the conductive agent includes a layered double hydroxide and when the XRD diffraction pattern of the negative electrode sheet has specific characteristic peaks and / or peak intensity ratios, the conductive agent has excellent conductivity, mechanical strength and a stable layered structure, which can not only enhance the conductivity of the silicon-based material, but also improve the inhibitory effect on the volume expansion of the silicon material, thereby improving the structural stability of the silicon material.

[0089] In the present invention, when the conductive agent includes the layered double hydroxide, the XRD diffraction pattern of the negative electrode sheet has characteristic peaks at least at 8°-15° and 25°-40°. The characteristic peak at 8°-15° is the sixth characteristic peak, and the characteristic peak at 25°-40° is the seventh characteristic peak.

[0090] In one embodiment, the peak intensity of the sixth characteristic peak is I6, and the peak intensity of the seventh characteristic peak is I7, satisfying 5 <I7 / I6<15。

[0091] In the present invention, when the conductive agent includes the layered double hydroxide, the compaction density of the negative electrode sheet can be 0.8 g / cm 3 -1.7g / cm 3 , for example 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 or 1.7 g / cm 3 .

[0092] The inventors of the present invention have discovered that when the compaction density of the conductive agent is within a specific range, it is beneficial to suppress the volume expansion of the silicon-based material.

[0093] In the present invention, the conductive agent may include CoMo-LDH. Figure 2 (c) Schematic diagram of the structure of CoMo-LDH.

[0094] When the conductive agent includes CoMo-LDH, in the XRD diffraction pattern of the negative electrode sheet, there are at least characteristic peaks at 10°-13° and 27°-30°, and 5 < I7 / I6 < 15. As Figure 3 (c) shows the XRD diffraction pattern of the negative electrode sheet (the conductive agent includes CoMo-LDH) in an example of the present invention. It can be seen from the figure that there are characteristic peaks at 10°-13° and 27°-30°, and 5 < I7 / I6 < 15.

[0095] In the present invention, when the conductive agent includes the layered double metal hydroxide, the median particle size Dv50 of the conductive agent can be 100 nm - 1 μm, such as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm or 1 μm. The shape of the conductive agent can be an irregular polycrystalline aggregate; as Figure 4 (c) shows the SEM micrograph of the negative electrode sheet (the conductive agent is CoMo-LDH) in an example of the present invention. It can be seen from the figure that the conductive agent is an irregular polycrystalline aggregate.

[0096] The negative electrode sheet of the present invention includes a conductive agent with a two-dimensional layered structure and a silicon-based material. Compared with traditional carbon black, the conductive agent with a two-dimensional layered structure can significantly improve the conductivity and the lithium ion diffusion rate, promote the capacity release of the silicon-based material, thereby improving the energy density and rate performance of the battery; the groups on the surface of the conductive agent can help form a stable solid electrolyte interface (SEI) layer that is beneficial to lithium ion transport, reduce the consumption of the electrolyte, thereby improving the Coulomb efficiency of the battery; the two-dimensional layered structure can inhibit the volume expansion of the silicon-based material during charge and discharge, reduce electrode fragmentation and the loss of point contact between the silicon-based material and the current collector, thereby improving the cycle life of the battery.

[0097] In the present invention, the conductive agent can be obtained by commercial purchase or by preparation. The present invention also provides a preparation method of the conductive agent. The preparation method can include at least one of high-temperature modification method, ball milling method, co-precipitation method, microwave synthesis method, chemical vapor deposition, wet chemical method and mechanical stripping method.

[0098] The present invention also provides a composite method of the conductive agent and the silicon-based material, which at least includes the following steps: mixing the conductive agent and the silicon-based material.

[0099] In the present invention, the mixing can include at least one of mechanical mixing, co-precipitation and hydrothermal method.

[0100] The second aspect of the present invention provides a battery, and the battery includes the negative electrode sheet of the first aspect of the present invention.

[0101] A third aspect of the present invention provides a battery, which may include an electrolyte and a negative electrode sheet, wherein the electrolyte may include lithium hexafluorophosphate, the mass content of lithium hexafluorophosphate in the electrolyte is x1 (unit %), the negative electrode sheet may include a silicon-based material, the mass m2 (unit g) of the silicon-based material in the negative electrode sheet and the capacity C (unit mAh) of the battery satisfy: 0.1≤a≤0.2 (e.g., 0.1, 0.15, or 0.2), 0.4≤b≤0.8 (e.g., 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or 0.8).

[0102] The inventors of the present invention found that when x1, m2 and C satisfy a specific relationship, a higher energy density and a lower volume expansion rate can be guaranteed. The reason may be that when the above relationship is satisfied, the electrical contact of the negative electrode sheet is better, and the mass content of lithium hexafluorophosphate is more moderate, the volume expansion inhibition effect of the silicon-based material is more significant, and there is no risk of lithium plating due to excessive polarization.

[0103] In one example, 0.12≤a≤0.18, 0.55≤b≤0.74.

[0104] In the above relational expressions of the present invention, each parameter is calculated using only its numerical part, and its unit part does not participate in the calculation.

[0105] In one embodiment, the negative electrode sheet further comprises the negative electrode sheet described in the first aspect of the present invention.

[0106] In the present invention, the electrolyte further includes an organic solvent, and the organic solvent may include at least one of ethylene carbonate, methyl ethyl carbonate, vinylene carbonate, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluorodimethyl carbonate, fluoroethyl methyl carbonate, ethylpropyl carbonate (EPC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC) and methylpropyl carbonate (MPC).

[0107] Components of the battery other than the negative electrode sheet and the electrolyte (such as the positive electrode sheet and the separator, etc.) can be conventionally selected in the art.

[0108] In one example, the battery further includes a positive electrode and a separator.

[0109] The positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer on at least one side of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material.

[0110] The positive electrode active material can be a conventional choice in the art. For example, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganeseate, lithium nickel cobalt aluminumate, lithium nickel cobalt manganese aluminumate, lithium manganate, lithium nickel manganeseate, lithium nickelate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium-rich manganese.

[0111] The battery can be assembled in accordance with conventional methods in the art.

[0112] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0113] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0114] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0115] Group I preparation examples are used to prepare two-dimensional transition metal sulfides

[0116] Preparation Example I1

[0117] The conductive agent MoS2 was prepared as follows:

[0118] 0.5g Na2MoO4 powder was dissolved in 110mL deionized water, stirred for 10min (30r / s), 0.4g CH3SNH2 powder was added, and stirring was continued for 20min; the uniformly stirred solution was poured into a 200mL stainless steel reactor and heated at 218°C for 18h; ultrasonically cleaned with deionized water and ethanol, centrifuged, and dried in a vacuum drying oven at 50°C for 24h to obtain black MoS2, wherein the MoS2 is granular in shape, and the granules are aggregated by several flakes, the flake diameter of the flakes is 500nm, the flake thickness is 15nm, and the median particle size Dv50 of MoS2 is 4μm.

[0119] Preparation Example I2

[0120] Prepare the conductive agent TiS2 by following the steps below:

[0121] Sponge titanium and sulfur powder are mixed in a molar ratio of 1:2.2, placed in a quartz tube, vacuum-sealed, and annealed at 660°C in a muffle furnace for 7 days. After cooling in the furnace, TiS2 is taken out to obtain TiS2, wherein the TiS2 is in the form of particles, which are aggregated by a number of flakes. The flake diameter of the flakes is 8 μm, the flake thickness is 500 nm, and the median particle size Dv50 of TiS2 is 20 μm.

[0122] Preparation Example I3

[0123] Prepare the conductive agent NbSe2 by following the steps below:

[0124] Nb powder (purity of 99%, average particle size of 200 mesh) and Se powder (purity of 99%, average particle size of 200 mesh) were mixed in a molar ratio of 1:2.2. The mixed powders were placed in a planetary ball mill using a solid phase synthesis method with a ball-to-material mass ratio of 10:1 (the ratio of the mass of zirconia ball milling beads to the sum of the mass of Nb powder and Se powder was 10:1). An appropriate amount of anhydrous ethanol (solid content of 40%) was added, and the mixture was vacuumed and Ar gas was introduced to prevent the powder from being oxidized. The mixture was then spun at a speed of 400 r / min. Grind for 10 hours; put the ball-milled powder into a stainless steel reactor, introduce Ar gas into the reactor to expel oxygen, put the reactor into a tubular furnace, heat it to 750℃ at a rate of 10℃ / min and keep it warm for 3 hours, cool it to room temperature with the furnace to obtain a dark green powder, grind it to obtain NbSe2, wherein the shape of NbSe2 is granular, and the granular shape is formed by the aggregation of several flakes, the flake diameter of the flake is 10μm, the flake thickness is 200nm, and the median particle size Dv50 of NbSe2 is 25μm.

[0125] Preparation Example I4

[0126] The conductive agent MoTe2 was prepared as follows:

[0127] Mo powder and Te powder are fully ground under argon in a molar ratio of 1:2.1, sealed in a quartz tube and transferred to a vacuum sealer for vacuum packaging, heated to 800°C in a tube furnace and kept warm for 2 days, and then quenched to room temperature to obtain polycrystalline MoTe2; TeBr4 is used as a transport agent and mixed with polycrystalline MoTe2 on one side of a quartz tube, and placed in a double-zone tube furnace, wherein the temperature of the low-temperature zone is set to 900°C, the temperature of the high-temperature zone is set to 1000°C, and the side containing the material is placed in the high-temperature zone. During the firing process, MoTe2 crystallizes in the low-temperature zone, and after keeping warm for 10 days, it is quenched at 900°C to obtain MoTe2, wherein the shape of MoTe2 is granular, and the granular shape is formed by the aggregation of several flakes, the flake diameter of the flake is 2μm, the flake thickness is 100nm, and the median particle size Dv50 of MoTe2 is 10μm.

[0128] Group II preparation examples are used to prepare two-dimensional nitrides

[0129] Preparation Example III

[0130] Prepare the conductive agent boron nitride by following the steps below:

[0131] (1) establishing a static pressure of 300 kPa of NH3 gas, and ball milling amorphous boron powder (purity of 95%-97%) at room temperature (25°C) using a steel rotary ball mill with four hardened steel balls and a stainless steel tank for 150 hours, wherein the reaction gas during the ball milling process is anhydrous NH3;

[0132] (2) Annealing at 1200°C in a tube furnace for 5 hours under anhydrous NH3 gas at a flow rate of 500 mL / min-1000 mL / min.

[0133] Preparation Example II2

[0134] Prepare the conductive agent GaN by following the steps below:

[0135] (1) 4 g of Ga(OC2H5)3 powder was dissolved in 80 mL of anhydrous ethanol at room temperature, ultrasonicated for 5 min, and allowed to stand for 3 days for solubilization to obtain a transparent milky white gallium oxide gel for use;

[0136] (2) The gallium oxide gel obtained in step (1) was placed in the constant temperature zone of a tubular furnace and allowed to react in flowing ammonia gas for 20 minutes at a reaction temperature of 980° C. to obtain light yellow gallium nitride powder.

[0137] Preparation Example II3

[0138] Prepare the conductive agent carbon nitride by following the steps below:

[0139] Spread g-C3N4 flatly in a crucible, heat to 515°C at a rate of 5°C / min and keep warm for 5h to obtain white carbon nitride.

[0140] Group III Preparation Example for the Preparation of Layered Double Hydroxides

[0141] Preparation Example III1

[0142] The conductive agent CoMo-LDH was prepared by the following steps:

[0143] At room temperature (25°C), 1.66g CoC l2 6H2O and 12.3g (NH4)6Mo7O 246H2O was dispersed in 850 mL of water and stirred rapidly. A nitrogen-purged NaOH solution (0.045 M) was slowly added dropwise (at a rate of 2 mL / min) until the pH reached 9. The mixture was rapidly stirred at room temperature (25°C) for 12 hours. The product was isolated by centrifugation, washed three times with deionized water and three times with ethanol, and dried in an oven at 60°C for 12 hours. The median particle size Dv50 of the CoMo-LDH was 100 nm.

[0144] Preparation Example III2

[0145] The conductive agent MgMn-LDH was prepared by the following steps:

[0146] Solution 1 was prepared by dissolving 6.1 g of Mg(NO3)2·6H2O and 2.3 g of Mn(NO3)2 in 100 mL of deionized water, and solution 2 was prepared by dissolving 4 g of NaOH and 1 g of Na2CO3 in 100 mL of deionized water and then adding 0.8 mL of H2O2. Solution 1 and solution 2 were respectively placed in a constant pressure burette and dripped into a flask filled with distilled water, controlling the pH value between 9.0 and 10.0. After the dripping was completed, stirring was continued for 30 minutes. The mixture was crystallized in a 70°C oven for 48 hours, filtered, washed, and dried in a 70°C oven for 12 hours to obtain MgMn-LDH, wherein the median particle size Dv50 of MgMn-LDH was 150 nm.

[0147] Preparation Example III3

[0148] The conductive agent ZnAl-LDH was prepared by the following steps:

[0149] 8g ZnCl2 and 1.5g Al(NO3)3·9H2O were dissolved in 180mL deionized water and mixed thoroughly to obtain solution 1. 4g NaOH and 1g Na2CO3 were dissolved in 100mL deionized water and then 0.8mL H2O2 was added to obtain solution 2. Solution 1 and solution 2 were respectively placed in a constant pressure dropper and dripped into a flask filled with distilled water, controlling the pH value between 9.7 and 10.3. After the dripping was completed, stirring was continued for 30 minutes. The mixture was crystallized in a 70°C oven for 48 hours, filtered, washed, and dried in a 70°C oven for 12 hours to obtain ZnAl-LDH, wherein the median particle size Dv50 of ZnAl-LDH was 800nm.

[0150] Preparation Example III4

[0151] The conductive agent MgAl-LDH was prepared by the following steps:

[0152] 6 g of AlCl3·6H2O and 2.1 g of MgCl2·6H2O were dissolved in 160 mL of deionized water and mixed thoroughly to obtain solution 1. 4.1 g of NaOH and 1.2 g of Na2CO3 were dissolved in 100 mL of deionized water to obtain solution 2. Solution 1 and solution 2 were respectively placed in constant pressure droppers and dripped into a flask filled with distilled water, controlling the pH value between 9.9 and 10.5. Stirring was continued for 30 minutes after the dripping was completed. The mixture was crystallized in an 80°C oven for 48 hours, filtered, washed, and dried in an 80°C oven for 12 hours to obtain MgAl-LDH, wherein the median particle size Dv50 of MgAl-LDH was 170 nm.

[0153] Example

[0154] Prepare the battery as follows:

[0155] (1) Preparation of negative electrode sheet

[0156] The conductive agent prepared in Preparation Example I and the silicon-based material (wherein the median particle size Dv50 of the nano-silicon is 200 nm) are dispersed in acetone in a certain mass ratio and dried (or the conductive agent prepared in Group II or Group III and the nano-silicon are mechanically mixed); polyvinylidene fluoride (PVDF) is added, wherein the ratio of the mass of the polyvinylidene fluoride to the total mass of the conductive agent and the nano-silicon is 1.5:98.5, and deionized water is added to obtain a negative electrode active coating slurry with a solid content of 50 wt%; the above negative electrode active coating slurry is coated on a copper foil, dried, and roll-pressed to obtain a negative electrode sheet with a compaction density of 1.7 g / cm 3 ;

[0157] (2) Preparation of positive electrode sheet

[0158] Lithium cobalt oxide, PVDF and Super-P were mixed in a mass ratio of 97:1.5:1.5, and N-methylpyrrolidone was added, wherein the solid content was 55wt%, to obtain a positive electrode active coating slurry; the positive electrode active coating slurry was coated on aluminum foil, dried and rolled to obtain a positive electrode sheet with a compaction density of 4.1g / cm 3 ;

[0159] (3) Preparation of batteries

[0160] The negative electrode sheet prepared in step (1), the isolation film (polyethylene film), and the positive electrode sheet prepared in step (2) are wound and packaged to obtain a battery cell, into which an electrolyte is injected (the amount of lithium hexafluorophosphate added is shown in Table 1, and the organic solvent is a mixed solution of ethylene carbonate: diethyl carbonate: methyl ethyl carbonate: vinylidene carbonate in a mass ratio of 8:85:5:2), and the battery is formed, hot-pressed, and sealed to obtain a battery.

[0161] Examples 1-13 were prepared according to the above method, except that the conductive agent, silicon-based material, the mass ratio of the conductive agent to the silicon-based material, and the mass content of lithium hexafluorophosphate in the electrolyte were changed, as shown in Table 1.

[0162] Table 1

[0163]

[0164]

[0165] Note: The silicon content of the "silicon oxide" in Examples 9a and 12a (median particle size Dv50 is 5 μm) is 50%; the silicon content of the "silicon carbon" in Examples 9b and 12b (median particle size Dv50 is 14 μm) is 22%.

[0166] Comparative Example 1

[0167] The method was carried out in accordance with Example 1, except that, in step (1), nano-silicon (median particle size Dv50 is 200 nm), conductive carbon black and polyvinylidene fluoride were mixed in a mass ratio of 97:1.5:1.5, and deionized water was added to obtain a negative electrode active coating slurry with a solid content of 50 wt %; the negative electrode active coating slurry was coated on a copper foil, dried and rolled to obtain a negative electrode sheet with a compaction density of 1.7 g / cm 3 .

[0168] Comparative Example 2

[0169] The method was carried out in accordance with Example 9a, except that, in step (1), silica (median particle size Dv50 was 5 μm), conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 97:1.5:1.5, and deionized water was added to obtain a negative electrode active coating slurry having a solid content of 50 wt %. The negative electrode active coating slurry was coated on a copper foil, dried, and rolled to obtain a negative electrode sheet having a compaction density of 1.7 g / cm 3 .

[0170] Comparative Example 3

[0171] The method was carried out in accordance with Example 9b, except that, in step (1), silicon carbon (median particle size Dv50 was 14 μm), conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 97:1.5:1.5, and deionized water was added to obtain a negative electrode active coating slurry having a solid content of 50 wt %. The negative electrode active coating slurry was coated on a copper foil, dried, and rolled to obtain a negative electrode sheet having a compaction density of 1.7 g / cm 3 .

[0172] Test Case

[0173] (1) Compacted electronic conductivity

[0174] The compacted electronic conductivity of the negative electrode sheets prepared in the Examples and Comparative Examples was tested as follows: the coating on the negative electrode sheets obtained in the Examples and Comparative Examples was scraped off, 0.1 g of the sample was pressed into a 10 mm diameter tablet using a tablet press, and carbon powder was clamped on both sides for an EIS (Electrochemical Impedance Test) (0.1 Hz to 106 Hz). The bulk resistance of the material at room temperature (25°C) was measured by impedance measurement.

[0175] The compacted electronic conductivity was calculated according to the following formula: σ = L / (R × S), where σ is the compacted electronic conductivity, L is the thickness, S is the area, and R is the bulk resistance. The results are recorded in Table 2.

[0176] (2) Scanning electron microscope (SEM) test

[0177] The batteries prepared in Examples 1-3 and Comparative Example 1 were cycled for 500 cycles at a rate of 4C, and the microstructure and morphology of the negative electrode sheets before and after the cycles were observed using a scanning electron microscope. Figure 4 The SEM images of the negative electrode sheets in Examples 1-3 and Comparative Example 1 (before cycling) are shown. Figure 4 (a) is Example 1, Figure 4 (b) is Example 2, Figure 4 (c) is Example 3, Figure 4 (d) is Comparative Example 1; Figure 5 The following are SEM images of the negative electrode sheets of the batteries in Examples 1-3 and Comparative Example 1 after 500 cycles: Figure 5 (a) is Example 1, Figure 5 (b) is Example 2, Figure 5 (c) is Example 3, Figure 5 (d) is comparative example 1. As can be seen from the figure, comparative example 1 is severely broken, indicating that the structure is damaged.

[0178] (3) Thermogravimetric analysis

[0179] The negative electrode sheets prepared in Examples 1-3 were subjected to thermogravimetric analysis. The specific test method is as follows: a thermogravimetric analyzer was used, wherein the test atmosphere was nitrogen and the heating rate was 10°C / min. The results are shown in FIG. Figure 6 As shown in the figure, it can be seen that in Example 1, the thermal decomposition temperature of the negative electrode sheet is 700℃-1200℃; in Example 2, the thermal decomposition temperature of the negative electrode sheet is 800℃-1100℃; in Example 3, the thermal decomposition temperature of the negative electrode sheet is 200℃-500℃.

[0180] (4) Capacity and capacity retention test

[0181] The batteries prepared in the examples and comparative examples were subjected to capacity tests and capacity retention rate tests. The test methods are as follows: the batteries were subjected to electrochemical charge and discharge performance tests. The battery was measured at 0.5Ag -1 Initial capacity under current density and capacity retention at 100th cycle, test voltage range 0.01V-3.0V, current density 0.5Ag -1 , the capacity retention rate at the 100th cycle was investigated, and the results are recorded in Table 2.

[0182] (5) XRD test

[0183] The negative electrode sheets prepared in Examples 1-3 were subjected to XRD testing. Figure 3 is the XRD pattern of the negative electrode sheet in Example 1-3, wherein Figure 3 (a) is Example 1. It can be seen from the figure that it has characteristic peaks at 27°-30°, 34°-36°, 38°-40° and 58°-60°. <I1 / I2<5,1.5<I1 / I3<15; Figure 3 (b) is Example 2. It can be seen from the figure that there are characteristic peaks at 9.5°-11° and 27°-30°. <I5 / I4<6; Figure 3 (c) is Example 3. It can be seen from the figure that there are characteristic peaks at 10°-13° and 27°-30°. <I7 / I6<15。

[0184] Table 2

[0185]

[0186]

[0187]

[0188] As can be seen from Table 2, the battery prepared with the negative electrode sheet of the present invention has significantly improved compacted electronic conductivity and capacity retention rate after 100 cycles compared with the comparative example.

[0189] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet includes a negative electrode collector and a negative electrode active coating on at least one side of the negative electrode collector, the negative electrode active coating includes a negative electrode active material and a conductive agent, the negative electrode active material includes a silicon-based material, the conductive agent includes a conductive material with a two-dimensional layered structure, the interlayer spacing of the conductive material with a two-dimensional layered structure is D, 0.2nm≤D≤1nm; the stripping energy of the conductive material with a two-dimensional layered structure is N, 0.1eV / unit cel≤N≤0.8eV / unit cel; D and N satisfy 0.4≤D / N≤10; the conductive material with a two-dimensional layered structure includes at least one of a two-dimensional transition metal sulfide, a two-dimensional nitride and a layered double metal hydroxide.

2. The negative electrode sheet according to claim 1, wherein: 1≤D / N≤4.5; and / or, 0.3 nm ≤ D ≤ 0.7 nm; and / or, 0.15eV / unit cel ≤ N ≤ 0.3eV / unit cel.

3. The negative electrode sheet according to claim 1 or 2, wherein: The mass of the silicon-based material accounts for 0.01%-100% of the mass of the negative electrode active material; And / or, the mass of the conductive material having a two-dimensional layered structure accounts for 0.01%-100% of the mass of the conductive agent; And / or, the mass ratio of the silicon-based material to the conductive agent is (0.1-10):1; And / or, the negative electrode active coating further includes a binder. Based on the total weight of the negative electrode active coating, the content of the silicon-based material is 8.19-90.45% by weight, the content of the conductive agent is 8.19-90.45% by weight, and the content of the binder is 0.5-10% by weight.

4. The negative electrode sheet according to claim 1, wherein: The mass of the silicon-based material accounts for 95%-100% of the mass of the negative electrode active material; And / or, the mass of the conductive material having a two-dimensional layered structure accounts for 95%-100% of the mass of the conductive agent; And / or, the mass ratio of the silicon-based material to the conductive agent is (0.8-1.4):

1.

5. The negative electrode sheet according to claim 1, wherein: The thermal decomposition temperature of the negative electrode sheet is 200°C-1600°C; And / or, the compaction density of the negative electrode sheet is 0.6 g / cm 3 -1.7g / cm 3 .

6. The negative electrode sheet according to claim 1, wherein: The two-dimensional transition metal sulfide includes at least one of MoS2, WS2, TiS2, NbSe2, MoSe2 and MnSe2; And / or, the two-dimensional nitride includes at least one of boron nitride, gallium nitride and carbon nitride; And / or, the layered double hydroxide stone includes at least one of CoMo-LDH, FeCo-LDH, MgMn-LDH, ZnAl-LDH and MgAl-LDH.

7. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes a two-dimensional transition metal sulfide; And / or, in the XRD diffraction pattern of the negative electrode sheet, there are at least two characteristic peaks at 30°-40° and one characteristic peak at 55°-65°.

8. The negative electrode sheet according to claim 7, wherein: The two characteristic peaks at 30°-40° are the first characteristic peak and the second characteristic peak, respectively. The characteristic peak at 55°-65° is the third characteristic peak. The peak intensity of the first characteristic peak is I1, the peak intensity of the second characteristic peak is I2, and the peak intensity of the third characteristic peak is I3. <I1 / I2<5,1.5<I1 / I3<15。 9. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes a two-dimensional transition metal sulfide, and the thermal decomposition temperature of the negative electrode sheet is 300° C.-1600° C.; And / or, the compaction density of the negative electrode sheet is 0.7 g / cm 3 -1.7g / cm 3 ; And / or, the median particle size Dv50 of the conductive agent is 1 μm-30 μm.

10. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes MoS2; And / or, the XRD diffraction pattern of the negative electrode sheet has characteristic peaks at least at 27°-30°, 34°-36°, 38°-40° and 58°-60°; And / or, the conductive material having a two-dimensional layered structure is in a granular shape, the granular shape is formed by aggregating a number of flakes, the flake diameter of the flake is 100 nm-10 μm, and the flake thickness of the flake is 10 nm-500 nm.

11. The negative electrode sheet according to claim 8, wherein: 1 <I1 / I2<5,1.5<I1 / I3<15。 12. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes a two-dimensional nitride; And / or, the XRD diffraction pattern of the negative electrode sheet has characteristic peaks at least at 5°-13° and 25°-35°.

13. The negative electrode sheet according to claim 12, wherein: The characteristic peak at 5°-13° is the fourth characteristic peak, the characteristic peak at 25°-35° is the fifth characteristic peak, the peak intensity of the fourth characteristic peak is I4, and the peak intensity of the fifth characteristic peak is I5, satisfying 2 <I5 / I4<6。 14. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes boron nitride; And / or, the XRD diffraction pattern of the negative electrode sheet has characteristic peaks at least at 9.5°-11° and 27°-30°.

15. The negative electrode sheet according to claim 13, wherein: 2 <I5 / I4<6。 16. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes a layered double metal hydroxide; And / or, the XRD diffraction pattern of the negative electrode sheet has characteristic peaks at least at 8°-15° and 25°-40°.

17. The negative electrode sheet according to claim 16, wherein: The characteristic peak at 8°-15° is the sixth characteristic peak, the characteristic peak at 25°-40° is the seventh characteristic peak, the peak intensity of the sixth characteristic peak is I6, and the peak intensity of the seventh characteristic peak is I7, satisfying 5 <I7 / I6<15。 18. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes a layered double metal hydroxide, and the thermal decomposition temperature of the negative electrode sheet is 200° C.-600° C.; And / or, the compaction density of the negative electrode sheet is 0.8 g / cm 3 -1.7g / cm 3 ; And / or, the median particle size Dv50 of the conductive agent is 100 nm-1 μm.

19. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes CoMo-LDH; And / or, the XRD diffraction pattern of the negative electrode sheet has characteristic peaks at least at 10°-13° and 27°-30°.

20. The negative electrode sheet according to claim 17, wherein: 5 <I7 / I6<15。 21. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes two-dimensional transition metal sulfides and layered double metal hydroxides.

22. The negative electrode sheet according to claim 1, wherein: The conductive material having a two-dimensional layered structure includes MoS2 and CoMo-LDH.

23. A battery, characterized in that: The battery comprises the negative electrode sheet according to any one of claims 1 to 22.

24. A battery according to claim 23, characterized in that in, The battery includes an electrolyte and a negative electrode sheet, and the electrolyte includes lithium hexafluorophosphate.

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