Anode material, secondary battery and electronic device

Abstract

The present invention provides a negative electrode material, a secondary battery, and an electronic device. The secondary battery includes a negative electrode piece, the negative electrode piece including a negative electrode material, and the negative electrode material including a composite material, the composite material including elemental silicon and a carbon material. In the first cycle lithium desorption curve of the composite material, the ratio of the intensity of the main dQ / dV peak to the intensity of the minor dQ / dV peak is 1.15 to 1.65. When the composite material in the secondary battery satisfies the above characteristics, the secondary battery has a relatively high specific capacity and excellent cycle and expansion characteristics.

Description

[Technical Field]

[0001] This application claims priority based on a Chinese patent application filed with the China Patent Office on December 30, 2022, bearing application number 202211721043.X and entitled "Negative electrode material, secondary battery and electronic device," the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the field of electrochemical technology, and in particular to negative electrode materials, secondary batteries and electronic devices. [Background technology]

[0003] Secondary batteries such as lithium-ion batteries have been widely used in various aspects of modern life due to their advantages such as no memory effect, small volume, light weight, and environmental friendliness. In recent years, secondary batteries have been rapidly developed in the fields of new energy vehicles and large-scale energy storage.

[0004] However, in conventional negative electrode materials for commercially available secondary batteries, such as lithium-ion batteries, carbon-based materials such as graphite have relatively low capacities, resulting in relatively low energy densities. On the other hand, silicon-based materials tend to expand, degrading the cycle characteristics of secondary batteries. This severely limits their large-scale application in secondary batteries. Summary of the Invention

[0005] The present invention aims to provide a negative electrode material, a secondary battery, and an electronic device that allow a secondary battery to have a relatively high specific capacity and excellent cycle characteristics and expansion characteristics.

[0006] A first aspect of the present invention provides an anode material, the anode material comprising a composite material comprising elemental silicon and a carbon material, wherein the ratio of the intensity of the main dQ / dV peak to the intensity of the minor dQ / dV peak in a first-cycle lithium desorption curve of the composite is 1.15 to 1.65, the main dQ / dV peak being a characteristic peak located between 0.25 V and 0.3 V, and the minor dQ / dV peak being a characteristic peak located between 0.4 V and 0.45 V. When the composite material in the anode material provided by the present invention satisfies the above characteristics, the secondary battery maintains a relatively high specific capacity and exhibits significantly improved cycle and expansion characteristics.

[0007] In some embodiments of the present invention, the elemental silicon includes at least one of silicon nanoparticles and silicon submicron particles, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0008] In some embodiments of the present invention, when the mass percentage of the carbon material is a and the mass percentage of the elemental silicon is b, relative to the total mass of the composite material, a is 40 wt% to 90 wt%, and b is 10 wt% to 60 wt%. When the carbon material content a and the elemental silicon content b in the composite material are within the above ranges, this is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0009] In some embodiments of the present invention, when the mass percentage of the carbon material is a and the mass percentage of the elemental silicon is b, relative to the total mass of the composite material, a is 55 wt% to 70 wt%, and b is 30 wt% to 45 wt%. When the carbon material content a and the elemental silicon content b of the composite material are within the above ranges, this is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0010] In some embodiments of the present invention, the ratio of a to b is 1 to 3. When the ratio of a to b is within the above range, it is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0011] In some embodiments of the present invention, when the silicon content in region I of a cross section of the composite particle is c, the silicon content in region II is d, and the silicon content in region III is e, c, d, and e satisfy c>d>e, and region I is a region that is 0.5 μm to 1.5 μm away from the edge of the cross section along the radial direction of the cross section, region II is a region that is 2.5 μm to 3.5 μm away from the edge of the cross section along the radial direction of the cross section, and region III is a region that is 4.5 μm to 5.5 μm away from the edge of the cross section along the radial direction of the cross section, which is advantageous in improving the cycle characteristics and expansion characteristics of a secondary battery.

[0012] In some embodiments of the present invention, the particle size D of the composite material V 50 is 5 μm to 10 μm, and the particle diameter D of the composite material V Controlling the particle diameters Dv50 and Dv99 of the composite material within the above ranges is advantageous in improving the cycle characteristics and expansion characteristics of the secondary battery.

[0013] In some embodiments of the present invention, the specific surface area of ​​the composite material is 1 m 2 / g~50m 2 The composite material having a specific surface area in the above range is advantageous in improving the cycle characteristics and expansion characteristics of the secondary battery.

[0014] In some embodiments of the present invention, the X-ray diffraction spectrum of the composite material does not contain any silicon crystallization peak, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0015] In some embodiments of the present invention, in the Raman spectrum of the composite material, -1 Intensity of the peak at 521 cm -1 The ratio of the peak intensities at I 521 / I 480is 0.6 to 1, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0016] In some embodiments of the present invention, the mass percentage of the oxygen element in the composite material is 1 wt % to 5 wt % relative to the total mass of the composite material. When the content of the oxygen element in the composite material is within the above range, it is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0017] In some embodiments of the present invention, the composite material has an initial lithium desorption specific capacity of 500 mAh / g to 2500 mAh / g, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery when the composite material has an initial lithium desorption specific capacity in the above range.

[0018] A second aspect of the present invention provides a secondary battery comprising a positive electrode piece, a negative electrode piece, and an electrolyte, wherein the negative electrode piece comprises the negative electrode material according to any one of the above embodiments. Therefore, the secondary battery provided by the present invention has good cycle characteristics and expansion characteristics.

[0019] In some embodiments of the present invention, the secondary battery is subjected to 100 cycles of 1C charge, 0.5C discharge, and 0.025C cutoff at 25°C, and the mass percentage of oxygen in the composite material is 5 wt% to 15 wt% relative to the total mass of the composite material in the negative electrode piece. Controlling the oxygen content of the composite material in the negative electrode piece within the above range is advantageous for improving the cycle characteristics of the secondary battery.

[0020] A third aspect of the present invention provides an electronic device, including the secondary battery according to any one of the above embodiments, and therefore the electronic device provided by the present invention has good performance in use.

[0021] The beneficial effects of the present invention are as follows:

[0022] The present invention provides a negative electrode material, a secondary battery, and an electronic device, wherein the secondary battery includes a negative electrode piece, the negative electrode piece includes a negative electrode material, the negative electrode material includes a composite material, the composite material includes elemental silicon and a carbon material, and the ratio of the intensity of the main dQ / dV peak to the intensity of the minor dQ / dV peak in a first cycle lithium desorption curve of the composite material is 1.15 to 1.65. When the composite material in the secondary battery provided by the present invention satisfies the above characteristics, the secondary battery has a relatively high specific capacity and excellent cycle and expansion characteristics.

[0023] Of course, it is not necessary for all of the above advantages to be achieved simultaneously in practicing any one product or method of the present invention. [Brief explanation of the drawings]

[0024] In order to more clearly explain the embodiments of the present application and the technical solutions of the prior art, the following will briefly describe the drawings necessary for describing the embodiments and the prior art. Of course, the drawings described below are merely a part of the embodiments of the present invention, and those skilled in the art can obtain other embodiments based on these drawings. [Figure 1] FIG. 1 shows the first cycle charge-discharge curve of the composite material in Example 1. [Figure 2] FIG. 2 is a differential capacity curve of the composite material in Example 1 during lithium desorption in the first cycle. [Figure 3] FIG. 3 is a scanning electron microscope (SEM) image of a cross section of a composite particle in Example 1. [Figure 4] FIG. 4 is a schematic diagram of a region selection of a cross section of a composite particle in Example 1. [Figure 5] FIG. 5 is an X-ray diffraction spectrum of the composite material in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, the technical solutions in the embodiments of the present invention will be described in detail with reference to the drawings in the embodiments of the present invention. Of course, the described embodiments are only a part of the embodiments of the present invention, and are not all of the embodiments. Based on the embodiments of the present invention, all other embodiments that those skilled in the art can obtain based on the present invention fall within the protection scope of the present invention.

[0026] In the following, the present invention will be described using a lithium ion battery as an example of a secondary battery, but the secondary battery of the present invention is not limited to a lithium ion battery.

[0027] A first aspect of the present invention provides a negative electrode material, the negative electrode material comprising a composite material comprising elemental silicon and a carbon material, wherein a ratio of the intensity of a main dQ / dV peak to the intensity of a minor dQ / dV peak in a first cycle lithium desorption curve of the composite material is 1.15 to 1.65, the main dQ / dV peak being a characteristic peak located between 0.25 V and 0.3 V, and the minor dQ / dV peak being a characteristic peak located between 0.4 V and 0.45 V.

[0028] The inventors' research has led to the following findings. The first-cycle charge-discharge curve of a composite material is obtained by plotting the first-cycle charge-discharge specific capacity of the composite material as the abscissa and the voltage as the ordinate. For example, FIG. 1 shows the first-cycle charge-discharge curve of the composite material in Example 1. Furthermore, the first-cycle lithium desorption specific capacity Q of the composite material is first differentiated with respect to the voltage V and plotted against the voltage V to obtain a differential capacity curve. For example, FIG. 2 shows the differential capacity curve of the first-cycle lithium desorption of the composite material in Example 1. The differential capacity curve reflects the capacity contained in the composite material per unit voltage range. A relatively high capacity at a certain voltage platform means that a large capacity contribution occurs within a small voltage fluctuation range, and one characteristic peak appears on the curve. One characteristic peak represents one electrochemical reaction. The characteristic peak located between 0.25 V and 0.3 V corresponds to the desorption of amorphous Li. xThe characteristic peak at 0.4V to 0.45V represents the lithium desorption reaction of Si. 15 This shows the lithium desorption reaction of Si4. The stronger the intensity of the characteristic peak located at 0.4V to 0.45V, the more crystalline Li 15 Si4 increases, and crystalline Li 15 The rate of lithium desorption reaction of Si4 becomes relatively high, and further, the cycle characteristics and expansion characteristics of the composite material deteriorate. When the ratio of the intensity of the main dQ / dV peak to the intensity of the sub dQ / dV peak in the first cycle lithium desorption curve is 1.15 to 1.65, the secondary battery has a relatively high specific capacity and the cycle characteristics and expansion characteristics of the secondary battery are improved.

[0029] Specifically, the ratio of the intensity of the dQ / dV main peak to the intensity of the dQ / dV minor peak in the first cycle lithium desorption curve of the composite material may be 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, or a value within a range consisting of any two of the above values. Preferably, the ratio of the intensity of the dQ / dV main peak to the intensity of the dQ / dV minor peak in the first cycle lithium desorption curve of the composite material is 1.25 to 1.55. If the ratio of the intensity of the dQ / dV main peak to the intensity of the dQ / dV minor peak in the first cycle lithium desorption curve of the composite material is too low (e.g., less than 1.15), the crystalline Li 15 The rate of lithium desorption reaction of Si4 becomes relatively high, which affects the cycle and expansion characteristics of the composite. If the ratio of the intensity of the dQ / dV main peak to the intensity of the dQ / dV minor peak in the first cycle lithium desorption curve of the composite is too high (e.g., greater than 1.65), the amorphous Li xThe rate of lithium desorption reaction of Si becomes relatively high, which affects the capacity and energy density per gram of the composite material. By controlling the ratio of the intensity of the main dQ / dV peak to the intensity of the minor dQ / dV peak in the first cycle lithium desorption curve of the composite material within the above range, the secondary battery maintains a relatively high specific capacity and is also advantageous in improving the cycle characteristics and expansion characteristics of the secondary battery.

[0030] Overall, the composite material in the negative electrode material provided by the present invention contains elemental silicon and a carbon material, and in the first cycle lithium desorption curve of the composite material, the ratio of the intensity of the main dQ / dV peak to the intensity of the minor dQ / dV peak is 1.15 to 1.65, so that the resulting secondary battery has good cycle characteristics and expansion characteristics.

[0031] In some embodiments of the present invention, elemental silicon comprises at least one of silicon nanoparticles and silicon submicron particles.By selecting the above-mentioned type of elemental silicon, it is possible to reduce the crushing and powdering of silicon particles, and improve the transmission rate of active ions such as lithium ions, thereby improving the cycle characteristics and expansion characteristics of secondary batteries.For example, Figure 3 shows a scanning electron microscope (SEM) image of the cross section of the composite particle in Example 1.

[0032] In some embodiments of the present invention, when the mass percentage of the carbon material is a and the mass percentage of elemental silicon is b, relative to the total mass of the composite material, a is 40 wt% to 90 wt%, and b is 10 wt% to 60 wt%. Preferably, when the mass percentage of the carbon material is a and the mass percentage of elemental silicon is b, a is 55 wt% to 70 wt%, and b is 30 wt% to 45 wt%. Illustratively, a may be 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, or a value within a range consisting of any two of the above values, and b may be 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, or a value within a range consisting of any two of the above values. By controlling the values ​​of a and b within the above ranges, it is possible to achieve a balance between the capacity per gram of the composite material and its cycle characteristics and expansion characteristics.

[0033] In some embodiments of the present invention, the ratio of a to b is 1 to 3. Illustratively, the ratio of a to b may be 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3, or a value within a range consisting of any two of the above values. By controlling the ratio of a to b within the above range, the volume effect of the composite material can be reduced and the particle expansion coefficient can be suppressed, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0034] In some embodiments of the present invention, if the silicon content in Region I of a cross-section of a composite particle is c, the silicon content in Region II is d, and the silicon content in Region III is e, then c, d, and e satisfy the relationship c>d>e. Region I is a region 0.5 μm to 1.5 μm away from the edge of the cross-section along the radial direction of the cross-section, Region II is a region 2.5 μm to 3.5 μm away from the edge of the cross-section along the radial direction of the cross-section, and Region III is a region 4.5 μm to 5.5 μm away from the edge of the cross-section along the radial direction of the cross-section. For example, FIG. 4 shows a schematic diagram of region selection of a cross-section of a composite particle in Example 1. By controlling the silicon content c of region I, the silicon content d of region II, and the silicon content e of region III in the cross section of the composite particle so that they satisfy the above relationship, a certain silicon concentration gradient is formed in the composite material, which is advantageous for stress relaxation throughout the material, significantly reduces the expansion coefficient of the silicon material, and is advantageous for improving the cycle characteristics and expansion characteristics of secondary batteries.

[0035] In some embodiments of the present invention, the particle size D of the composite material V 50 is 5 μm to 10 μm, and the particle diameter D of the composite material V 99 is 15 μm to 25 μm. For example, particle diameter D V 50 may be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a value within a range consisting of any two of the above values, and the particle diameter D V and Dv50 and Dv99 may be 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, or a value within a range consisting of any two of the above values. Controlling the particle diameters Dv50 and Dv99 of the composite material within the above ranges can improve the dispersion uniformity of the slurry and improve the transmission of active ions, which is advantageous for improving the cycle characteristics and expansion characteristics of secondary batteries.

[0036] In the present invention, Dv50 refers to the particle size at which the cumulative volume from the small diameter side becomes 50% in the volume-based particle size distribution of the material, and Dv99 refers to the particle size at which the cumulative volume from the small diameter side becomes 99% in the volume-based particle size distribution of the material.

[0037] In some embodiments of the present invention, the specific surface area of ​​the composite material is 1 m 2 / g~50m 2 / g. For example, the specific surface area of ​​a composite material is 1 m 2 / g, 5m 2 / g, 10m 2 / g, 15m 2 / g, 20m 2 / g, 25m 2 / g, 30m 2 / g, 35m 2 / g, 40m 2 / g, 45m 2 / g, 50m 2 / g or a value within a range consisting of any two of the above values. By having the specific surface area of ​​the composite material within the above range, side reactions between the composite material and the electrolyte can be reduced, which is advantageous in improving the cycle characteristics and expansion characteristics of the secondary battery.

[0038] In some embodiments of the present invention, the X-ray diffraction spectrum of the composite material does not exhibit a silicon crystallization peak. That is, the silicon in the composite material is present in an amorphous form. For example, FIG. 5 shows the X-ray diffraction spectrum of the composite material in Example 1. If the silicon in the composite material satisfies the above requirements, it has a relatively large space within the silicon material, which can absorb the volume expansion that occurs when lithium ions are inserted into the silicon, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0039] In some embodiments of the present invention, the Raman spectrum of the composite material contains a peak at 480 cm -1 Intensity of the peak at 521 cm -1 The ratio of the peak intensities at I 521 / I 480 is 0.6 to 1. For example, 480 cm-1 Intensity of the peak at 521 cm -1 The ratio of the peak intensities at I 521 / I 480 may be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or a value within a range consisting of any two of the above values. -1 Intensity of the peak at 521 cm -1 The ratio of the peak intensities at I 521 / I 480 When the content of the amorphous silicon satisfies the above range, a higher amorphous silicon content is realized, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0040] In some embodiments of the present invention, the mass percentage of elemental oxygen in the composite material is 1 wt% to 5 wt% relative to the total mass of the composite material. For example, the mass percentage of elemental oxygen in the composite material may be 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or a value within a range consisting of any two of the above values. When the mass percentage of elemental oxygen in the composite material is within the above range, Li2O generated during the initial lithium ion insertion process functions as a buffer material, which is advantageous for improving the cycle characteristics and expansion characteristics of the secondary battery.

[0041] In some embodiments of the present invention, the initial lithium desorption specific capacity of the composite material is 500 mAh / g to 2500 mAh / g. For example, the initial lithium desorption specific capacity of the composite material may be 500 mAh / g, 750 mAh / g, 1000 mAh / g, 1250 mAh / g, 1500 mAh / g, 1750 mAh / g, 2000 mAh / g, 2250 mAh / g, 2500 mAh / g, or a value within a range consisting of any two of the above values. When the initial lithium desorption specific capacity of the composite material is within the above range, it is possible to achieve a balance between the development of capacity per gram of the composite material and its cycle characteristics and expansion characteristics.

[0042] In the present invention, the method for preparing a composite material is not particularly limited. For example, the method for preparing a composite material may include, but is not limited to, the steps of placing a porous carbon material in a reactor, passing a silicon-containing gas through the reactor, pyrolytically depositing the silicon-containing gas into elemental silicon within the pores of the carbon material, and then passing a carbon source gas through the reactor, pyrolytically depositing the carbon source gas into amorphous carbon to obtain a composite material. The silicon-containing gas may include, but is not limited to, at least one of monosilane, disilane, trisilane, tetrasilane, chlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane. The carbon source gas may include, but is not limited to, at least one of methane, acetylene, ethylene, ethane, propyne, propylene, propane, butyne, butene, and butane.

[0043] Typically, the ratio of the dQ / dV main peak intensity to the dQ / dV minor peak intensity in the first-cycle lithium desorption curve of a composite material can be controlled by changing the pyrolysis temperature, gas flow rate, and silicon-containing gas flow time. For example, increasing the pyrolysis temperature decreases the ratio, whereas decreasing the pyrolysis temperature increases the ratio. Increasing the gas flow rate decreases the ratio, whereas decreasing the gas flow rate increases the ratio. Extending the silicon-containing gas flow time decreases the ratio of the dQ / dV main peak intensity to the dQ / dV minor peak intensity, while shortening the silicon-containing gas flow time increases the ratio of the dQ / dV main peak intensity to the dQ / dV minor peak intensity. Engineers can adjust the silicon-containing gas or carbon source gas pyrolysis temperature, silicon-containing gas or carbon source gas flow rate, and silicon-containing gas or carbon source gas flow time as needed. For example, the silicon-containing gas or carbon source gas pyrolysis temperature can be 400°C to 800°C, the silicon-containing gas or carbon source gas flow rate can be 50 sccm to 500 sccm, the silicon-containing gas flow time can be 1 hour to 20 hours, and the carbon source gas flow time can be 1 hour to 20 hours.

[0044] A second aspect of the present invention provides a secondary battery comprising a positive electrode piece, a negative electrode piece, and an electrolyte, wherein the negative electrode piece comprises the negative electrode material according to any one of the above embodiments. Therefore, the secondary battery provided by the present invention has good cycle characteristics and expansion characteristics.

[0045] In some embodiments of the present invention, a secondary battery is subjected to 100 cycles at 25°C, with a cycle process of 1C charge, 0.5C discharge, and 0.025C cutoff, and the mass percentage of oxygen in the composite material is 5 wt% to 15 wt% relative to the total mass of the composite material in the negative electrode piece. For example, the mass percentage of oxygen in the composite material may be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, or a value within a range consisting of any two of the above values. By controlling the mass percentage of oxygen in the composite material in the negative electrode piece after 100 cycles within the above range, structural deformation of the composite material during the charge and discharge process can be suppressed, which is advantageous for improving the cycle performance of the secondary battery.

[0046] The negative electrode piece of the present invention further comprises a binder. In the present invention, the binder is not particularly limited as long as it can achieve the objectives of the present invention. For example, the binder may comprise at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polystyrene butadiene copolymer (styrene butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethylcellulose, potassium carboxymethylcellulose, sodium hydroxymethylcellulose, and potassium hydroxymethylcellulose, but is not limited thereto. By selecting the above binder, the resulting negative electrode piece has good structural stability, which is advantageous for improving the cycle characteristics of the secondary battery.

[0047] The negative electrode piece of the present invention further comprises a conductive agent, and in the present invention, the conductive agent is not particularly limited as long as it can achieve the objectives of the present invention, for example, the conductive agent may comprise at least one of acetylene black, conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, etc. In the present invention, the mass ratio of the negative electrode material, conductive agent, and binder is not particularly limited, and those skilled in the art can select it as needed as long as it can achieve the objectives of the present invention.

[0048] The negative electrode piece of the present invention includes a negative electrode current collector. In the present invention, the negative electrode current collector is not particularly limited as long as the objectives of the present invention are achieved, and may include, for example, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (e.g., a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). In the present invention, the thickness of the negative electrode current collector is not particularly limited as long as the objectives of the present invention are achieved, and for example, the thickness of the negative electrode current collector is 6 μm to 12 μm. In the present invention, the thickness of the negative electrode piece is not particularly limited as long as the objectives of the present invention are achieved, and for example, the thickness of the negative electrode piece is 50 μm to 150 μm.

[0049] In the present invention, the secondary battery further includes a positive electrode piece, which includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The phrase "a positive electrode material layer provided on at least one surface of the positive electrode current collector" refers to the positive electrode material layer being provided on one surface of the positive electrode current collector in its thickness direction, or on both surfaces of the positive electrode current collector in its thickness direction. Here, the "surface" may refer to the entire area of ​​the positive electrode current collector or a portion of the area of ​​the positive electrode current collector, and is not particularly limited as long as the objectives of the present invention can be achieved. In the present invention, the positive electrode current collector is not particularly limited, and may include, for example, aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector), as long as the objectives of the present invention can be achieved. The positive electrode layer includes a positive electrode active material. The positive electrode active material is not particularly limited in the present invention, as long as it achieves the objectives of the present invention. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (e.g., common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO), lithium manganese oxide, lithium manganese iron phosphate, and lithium titanate. The positive electrode layer further includes a conductive agent and a binder. The conductive agent and binder are not particularly limited in the present invention, as long as they achieve the objectives of the present invention. For example, they may be at least one of the conductive agents and binders listed above. The mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode layer is not particularly limited in the present invention, and those skilled in the art can select them as needed, as long as they achieve the objectives of the present invention. In the present invention, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the object of the present invention can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 12 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm. In the present invention, there are no particular limitations on the thickness of the positive electrode pieces, as long as the object of the present invention can be achieved. For example, the thickness of the positive electrode pieces is 50 μm to 150 μm.

[0050] In the present invention, the secondary battery further includes a separator that separates the positive and negative electrode pieces to prevent short circuits within the secondary battery, allow free passage of electrolyte ions, and prevent interference with the electrochemical charge and discharge process. The separator is not particularly limited as long as it achieves the objectives of the present invention. For example, the separator material may include, but is not limited to, at least one of polyolefins (POs) primarily consisting of polyethylene (PE) and polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. The separator type may include at least one of woven film, nonwoven film, microporous film, composite film, rolled film, and spun film.

[0051] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a porous nonwoven fabric, film, or composite film, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer may be provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic material. For example, the inorganic layer may include inorganic particles and a binder. The inorganic particles are not particularly limited and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is not particularly limited and may be, for example, at least one of the binders described above. The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0052] In the present invention, the secondary battery further includes an electrolyte solution, which includes a lithium salt and a nonaqueous solvent. The lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate. In the present invention, the concentration of the lithium salt in the electrolyte solution is not particularly limited as long as the object of the present invention can be achieved. For example, the concentration of the lithium salt in the electrolyte solution may be 0.9 mol / L to 1.5 mol / L. Illustratively, the concentration of the lithium salt in the electrolyte solution may be 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L, or a value within a range consisting of any two of the above values. In the present invention, the non-aqueous solvent is not particularly limited as long as it can achieve the object of the present invention. For example, the non-aqueous solvent may include at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, and another organic solvent, but is not limited thereto. The carbonate compound may include at least one of a chain carbonate compound, a cyclic carbonate compound, and a fluorocarbonate compound, but is not limited thereto. The chain carbonate compound may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC), but is not limited thereto. The cyclic carbonate may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC), but is not limited thereto.The fluorocarbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate. The carboxylic acid ester compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, and hexanolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate.

[0053] The secondary battery of the present invention further includes a packaging bag for containing the positive electrode pieces, separator, negative electrode pieces, and electrolyte, as well as other components known in the art for secondary batteries, and the other components are not limited in the present invention. The packaging bag is not particularly limited in the present invention, and may be any packaging bag known in the art as long as it can achieve the object of the present invention.

[0054] The secondary battery of the present invention is not limited and may include any device that generates an electrochemical reaction. In some embodiments, the secondary battery may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0055] The process for preparing the secondary battery of the present invention is well known to those skilled in the art and is not particularly limited, and may include, for example, but is not limited to, stacking positive electrode pieces, separators, and negative electrode pieces in this order, and winding or folding the stack as necessary to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking positive electrode pieces, separators, and negative electrode pieces in this order, securing the four corners of the entire stack with adhesive tape to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, to prevent an increase in pressure inside the secondary battery and overcharging and discharging, an overcurrent protection element, lead plates, etc. may be provided in the packaging bag as necessary.

[0056] A third aspect of the present invention provides an electronic device, including the secondary battery according to any one of the above embodiments, and therefore the electronic device provided by the present invention has good performance in use.

[0057] The electronic device of the present invention is not particularly limited and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-based computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc, a walkie-talkie, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electrically assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household storage battery, and a lithium ion capacitor.

[0058] Example Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Measurements and evaluations are carried out as follows. Unless otherwise specified, "parts" and "%" are by mass.

[0059] Measurement methods and equipment Measurement of elemental silicon content The elemental silicon content in the composites can be measured using the characterization method of inductively coupled plasma (ICP).

[0060] Determination of silicon content in regions I, II, and III in the cross section of a composite particle A conductive adhesive was applied to a sample stage, and the composite powder samples of each example were evenly spread on the conductive adhesive. Unadhered powder was then blown off with an ear washing ball, followed by gold deposition and cross-sectioning of the powder sample particles using argon gas plasma. Scanning electron micrographs of the powder samples were taken using an energy dispersive X-ray spectroscopy (EDS) analyzer equipped with a Philips XL-30 field emission scanning electron microscope at an accelerating voltage of 10 kV and an emission current of 10 mA. Regions I, II, and III in the scanning electron micrographs were selected, and the silicon mass percentages of the particles were measured.

[0061] Specific capacitance measurement Negative electrode piece preparation process: The composite material of the present invention was used as the negative electrode active material, acetylene black as the conductive agent, and sodium alginate as the binder. The mass ratio of the negative electrode active material, acetylene black, and sodium alginate was 70:20:10. The negative electrode active material, acetylene black, and aqueous sodium alginate solution were thoroughly mixed to obtain a mixture slurry. The mixture slurry was then uniformly applied to copper foil and dried to obtain negative electrode pieces.

[0062] Preparation of positive electrode pieces: Super P was used as the conductive agent and PVDF as the binder, with the mass ratio of the positive electrode active material (LiFePO4), Super P, and PVDF being 70:20:10. The positive electrode active material, Super P, and 10 wt% PVDF solution were thoroughly mixed to obtain a mixture slurry, which was then uniformly applied to aluminum foil and dried to obtain positive electrode pieces.

[0063] A mixed solution containing 1 mol / L LiPF6 dissolved in ethylene carbonate / dimethyl carbonate (EC / DMC, volume ratio 1:1) and 5 vol% fluoroethylene carbonate (FEC) was used as the electrolyte, and Celgard 2400 was used as the separator. A button cell was assembled in a glove box using a lithium sheet as the counter electrode, and a button cell was assembled in a glove box using a piece of the positive electrode as the counter electrode.

[0064] Charge-discharge tests were performed on half-cells and whole cells using a LAND battery test system (LAND CT2001A). The half-cell test involved a constant current discharge of 0.1 C to 0.01 V over an operating voltage range of 0.01 V to 2 V, followed by a 5-minute hold, a further constant current discharge of 50 μA to 0.01 V, a 5-minute hold, and a 0.1 C constant current charge to 2.0 V. The initial charge capacity of the half-cell was recorded as the initial lithium desorption specific capacity. The whole-cell test involved a constant current charge of 0.1 C to 3.8 V over an operating voltage range of 2.4 V to 3.8 V, followed by a further constant voltage charge to a 50 μA cutoff at 3.8 V, a 5-minute hold, a 0.1 C constant current discharge to 2.4 V, and a 5-minute hold. The initial discharge capacity of the whole cell was recorded. The initial discharge specific capacity of the whole cell was calculated as the initial discharge capacity of the whole cell divided by the mass of the positive electrode active material.

[0065] Measurement of oxygen element content in composite material in negative electrode piece after 100 cycles After 100 cycles, the secondary battery was disassembled, and the negative electrode pieces were taken out. After air-drying them in a glove box, the powder was carefully scraped off with a knife, and finally the oxygen element content was measured using an Elementar elemental analyzer from Germany.

[0066] Measurement of thickness expansion rate of negative electrode piece The secondary batteries were disassembled before and after 100 cycles, and negative electrode pieces were obtained. The thickness of the electrode pieces was measured 12 times with a vernier caliper and the average value was calculated. If the thickness of the copper foil is a, the thickness of the electrode piece before 100 cycles is b, and the thickness of the electrode piece after 100 cycles is c, the thickness expansion coefficient k of the negative electrode piece after 100 cycles satisfies k = (cb) / (ba) × 100%.

[0067] Measurement of cycle capacity retention rate At 25°C, the half-cell was discharged at a constant current of 0.5C to 0.01V, allowed to stand for 5 minutes, discharged at a constant current of 50μA to 0.01V, allowed to stand for 5 minutes, charged at a constant current of 0.5C to 2.0V, allowed to stand for 5 minutes, and the discharge capacity at the first cycle was recorded. After that, 50 charge-discharge cycles were performed using the same steps, and the discharge capacity at the 50th cycle was recorded.

[0068] Half-cell 50-cycle capacity retention rate (%) = (discharge capacity at 50th cycle / discharge capacity at 1st cycle) × 100%.

[0069] In an environment of 25°C, the battery was charged at a constant current of 0.5C to 3.8V, then charged at a constant voltage of 3.8V to a 50μA cutoff, left to stand for 5 minutes, discharged at a constant current of 0.5C to 2.4V, left to stand for 5 minutes, and the discharge capacity at the first cycle was recorded. After that, the same charge-discharge cycle was repeated 100 times, and the discharge capacity at the 100th cycle was recorded.

[0070] 100-cycle capacity retention rate (%) of all batteries = (discharge capacity at 100th cycle / discharge capacity at 1st cycle) × 100%.

[0071] Example 1 <Preparation of composite material> 25 g of porous carbon material was placed in a reactor, and monosilane was passed through it at a flow rate of 200 sccm at 500°C for 10 hours. The monosilane was pyrolytically deposited into elemental silicon within the pores of the porous carbon material. Acetylene was then passed through it at a flow rate of 200 sccm at 500°C for 5 hours. The acetylene was pyrolytically deposited into amorphous carbon, yielding a composite material.

[0072] <Preparation of negative electrode pieces> The composite material of the present invention was used as the negative electrode active material, acetylene black as the conductive agent, and sodium alginate as the binder. The mass ratio of the negative electrode active material, acetylene black, and sodium alginate was 70:20:10. The negative electrode active material and acetylene black were thoroughly mixed according to the above ratio, and then ground to a uniform consistency. An aqueous sodium alginate solution was added according to the above ratio and stirred for 4 hours. The mixture slurry was then uniformly applied to copper foil, vacuum dried at 70°C for 12 hours, and punched out to obtain circular electrode pieces with a diameter of 10 mm. The loading amount of the negative electrode active material was 1.0 mg / cm. -2 It was decided.

[0073] <Preparation of positive electrode piece> Super P was used as the conductive agent and PVDF as the binder, with the mass ratio of the positive electrode active material (LiFePO4), Super P, and PVDF being 70:20:10. After thoroughly mixing the positive electrode active material and Super P according to the above ratio, the mixture was ground uniformly, and a 10 wt% PVDF solution was added according to the above ratio and stirred for 4 hours. The mixture slurry was then uniformly applied to aluminum foil, vacuum dried at 70°C for 12 hours, and punched out to obtain circular electrode pieces with a diameter of 10 mm. The loading amount of the positive electrode active material was 7.0 mg / cm. -2 It was decided.

[0074] <Preparation of electrolyte> In a glove box under a dry argon atmosphere, a mixed solution of ethylene carbonate / dimethyl carbonate (EC / DMC, volume ratio 1:1) containing 1 mol / L of LiPF6 and a mixed solution containing 5 vol% of fluoroethylene carbonate (FEC) were mixed uniformly to obtain an electrolyte solution.

[0075] <Preparation of separator> A porous polyethylene film (provided by Celgard) with a thickness of 20 μm was used.

[0076] <Preparation of lithium-ion batteries> A lithium sheet or a positive electrode piece was used as a counter electrode for the negative electrode piece, and a button-type half cell and a full cell were assembled in a glove box by placing the negative electrode piece, separator, and lithium sheet or positive electrode piece in this order.

[0077] Examples 2 to 8 <Preparation of composite material> was the same as in Example 1, except that the relevant preparation parameters were adjusted according to Table 1.

[0078] Comparative Examples 1 to 4 <Preparation of composite material> was the same as in Example 1, except that the relevant preparation parameters were adjusted according to Table 1.

[0079] Tables 1, 2 and 3 show the preparation parameters, powder property parameters and electrical property parameters of each example and comparative example.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] Referring to Tables 1, 2, and 3, as can be seen from Examples 1 to 8 and Comparative Examples 1 to 4, when the ratio of the intensity of the dQ / dV main peak to the intensity of the dQ / dV minor peak in the first-cycle lithium desorption curve of the composite material was too small (e.g., Comparative Examples 1 to 3), the lithium-ion battery had a relatively high specific capacity, but its cycle characteristics and expansion characteristics were clearly degraded. When the ratio of the intensity of the dQ / dV main peak to the intensity of the dQ / dV minor peak in the first-cycle lithium desorption curve of the composite material was too large (e.g., Comparative Example 4), the lithium-ion battery had relatively good cycle characteristics and expansion characteristics, but its specific capacity was clearly degraded. By controlling the ratio of the intensity of the dQ / dV main peak to the intensity of the dQ / dV minor peak in the first-cycle lithium desorption curve of the composite material within the range of the present invention, the lithium-ion battery can have a relatively high specific capacity and excellent cycle characteristics and expansion characteristics.

[0084] Furthermore, as can be seen from Examples 1, 3, 4, 5, 6, and 7, by controlling the ratio of the intensity of the main dQ / dV peak to the intensity of the minor dQ / dV peak in the first cycle lithium desorption curve to be within the range of 1.25 to 1.55, it is advantageous to further balance the specific capacity, cycle characteristics, and expansion characteristics of the lithium ion battery, thereby improving the overall characteristics of the lithium ion battery.

[0085] The oxygen content of the composite material in the negative electrode pieces after cycling also affects the cycling performance of the lithium ion battery. As can be seen from Examples 1 to 7 and Example 8, controlling the oxygen content of the composite material in the negative electrode pieces after cycling within the range of the present invention is beneficial to further balance the specific capacity, cycling performance and expansion performance of the lithium ion battery, thereby improving the overall performance of the lithium ion battery.

[0086] D of composite materials V 50, D V 99, the specific surface area, the ratio of carbon material and elemental silicon generally affect the characteristics of lithium ion batteries. As can be seen from Examples 1 to 8, the D of the composite material V 50, D V 99, D V 50 / D V By controlling the ratio of the carbon material and elemental silicon within the range of the present invention, it is advantageous to obtain a lithium ion battery having excellent specific capacity, cycle characteristics, and expansion characteristics.

[0087] The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A negative electrode material, the negative electrode material comprises a composite material, the composite material comprising elemental silicon and a carbon material; In the first cycle lithium desorption curve of the composite material, the ratio of the intensity of the main dQ / dV peak to the intensity of the minor dQ / dV peak is 1.15 to 1.65; The dQ / dV main peak is a characteristic peak located between 0.25V and 0.3V, and the dQ / dV sub-peak is a characteristic peak located between 0.4V and 0.45V.

2. 10. The negative electrode material of claim 1, wherein the elemental silicon comprises at least one of silicon nanoparticles and silicon submicron particles.

3. 3. The negative electrode material according to claim 1, wherein a is a mass percentage of the carbon material and b is a mass percentage of the elemental silicon relative to the total mass of the composite material, and a is 40 wt% to 90 wt%, and b is 10 wt% to 60 wt%.

4. 4. The negative electrode material according to claim 1, wherein a is a mass percentage of the carbon material and b is a mass percentage of the elemental silicon relative to the total mass of the composite material, and a is 55 wt % to 70 wt %, and b is 30 wt % to 45 wt %.

5. 5. The negative electrode material according to claim 3, wherein the ratio of a to b is 1 to 3.

6. In a cross section of a particle of the composite material, when the silicon content of region I is c, the silicon content of region II is d, and the silicon content of region III is e, c, d, and e satisfy c>d>e; 6. The negative electrode material according to claim 1, wherein the region I is a region that is 0.5 μm to 1.5 μm away from the edge of the transverse cross section along the radial direction of the transverse cross section, the region II is a region that is 2.5 μm to 3.5 μm away from the edge of the transverse cross section along the radial direction of the transverse cross section, and the region III is a region that is 4.5 μm to 5.5 μm away from the edge of the transverse cross section along the radial direction of the transverse cross section.

7. The composite material comprises: (1) Particle diameter D of the composite material Ｖ 50 is 5 μm to 10 μm, and the particle diameter D of the composite material Ｖ 99 is 15 μm to 25 μm; (2) The specific surface area of ​​the composite material is 1 m ２ / g to 50m ２ / g, and (3) The X-ray diffraction spectrum of the composite material does not contain a silicon crystallization peak; (4) In the Raman spectrum of the composite material, －１ The intensity of the peak at 521 cm －１ The ratio of the intensities of the peaks at I ５２１ / I ４８０ is between 0.6 and 1, (5) The mass percentage of the oxygen element in the composite material is 1 wt% to 5 wt% with respect to the total mass of the composite material; (6) The initial lithium desorption specific capacity of the composite material is 500 mAh / g to 2500 mAh / g; The negative electrode material according to any one of claims 1 to 6, which satisfies at least one of the following conditions:

8. A secondary battery comprising a positive electrode piece, a negative electrode piece, and an electrolyte, A secondary battery, wherein the negative electrode piece comprises the negative electrode material according to any one of claims 1 to 7.

9. 9. The secondary battery according to claim 8, wherein the secondary battery is subjected to 100 cycles of 1 C charge, 0.5 C discharge, and 0.025 C cutoff at 25°C, and the mass percentage of the oxygen element in the composite material is 5 wt% to 15 wt% relative to the total mass of the composite material in the negative electrode piece.

10. An electronic device comprising the secondary battery according to claim 8 or 9.

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